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How Do Inward-Rectifying Calcium Channels INCREASE "Resting" Potential In Pacemaker Cells?
I understand that less inward-rectifying Ca2+ channels is responsible for the higher mV "resting" potential of pacemaker cells (and consequently keeps the fast Na+ Channels inactive), but how does that make sense? The inward-rectifying Ca2+ channels are responsible for uptake INTO the cells. By having less of them, would it not mean that there are less positive Ca2+ ions going into the cell, thus the charge would be MORE negative? Additionally, as a bonus question, would the decrease in intracellular calcium due to less of these channels affect the rate /force of contraction, given the need for Ca2+ to release calcium from the SR via CICR?
Where did you come by these ideas? If they have come from a lecturer then perhaps I am wrong but from my understanding pacemaker cells function differently to how you suggest. I will use cardiac pacemaker cells as an example which will hopefully help explain. If you scroll down to figure 4 here ( https://courses.lumenlearning.com/suny-ap2/chapter/cardiac-muscle-and-electrical-activity/ ) you can see a trace of the pacemaker cell membrane potentials. As you can see the membrane potential slowly increases up to about -40mV before a rapid increase up to around +5mV and then a more gradual decrease back to -60mV. This can basically be divided into 3 parts. Part 1 is called the pacemaker potential (this is the slow increase from -60mV to -40mV). This is mainly determined by two things, the potassium leak current and the funny current (sometimes called the pacemaker current). The potassium leak current is the slow efflux of potassium ions which decreases as time goes on. The funny current is the continuous inflow of sodium ions. Combine these two factors and it’s pretty obvious why the potential gradually increases. A gradual decrease in Potassium efflux + a steady increase in intracellular sodium causes the inside of the cell to become more positive (depolarised). Part 2 is the upstroke (the rapid increase from -40mV to +5mV). Pacemaker cells have L-type calcium channels which are the most important here (although the funny current does also increase). These channels open more slowly but stay open for longer than other voltage-gated calcium channels you may have come across. This is the reason that this increase is still slow when compared to depolarisation of axons. Part 3 (slow return to -60mV). This is effectively repolarisation of the cell and occurs due to closure of the calcium channels, opening of the potassium leak channels and inactivation of sodium channels. Additionally the activity of sodium/calcium exchanger and sodium/potassium pump work to return the membrane potential to its ‘resting’ state of -60mV. I hope that made everything more clear, if not then please let me know if you have any further questions |
Can someone explain what's exactly going on in yesterday's Astronomy Picture of the Day?
This is the picture that I mean: Apparently, there was a solar eclipse on 1st September and it is a time lapse shot of the same. However I don't quite understand how this time lapse shot worked. My doubts: Is that the sun we're seeing in different phases? It looks like the moon to me! Why does it look like the moon? If that indeed is the sun, then what is the bright yellow object in the lower left corner of the image? (I still feel the white object in phases is the moon and the sun is in the lower left hand corner. But then the 'lunar' eclipse makes no sense!) Would highly appreciate if someone with knowledge in photography/astronomy can enlighten me what is going on in the photo.
Yes, it is the sun. It "looks like the moon" because the sun is VERY bright and these photos were shot with VERY dark filters which allow the camera to actually capture the detail of the sun and not a big bright orb as you are used to seeing in photographs. Yep, that is the sun, I am guessing at sunrise. It's a time-lapse, and you are seeing multiple shots of the sun across the sky. Likely a cloudless day would be my best guess. How it was made: The photographer shot 68 frames exposed/filtered to capture the detail of the sun for the eclipse. Those 68 photos (or at least the sun from those 68) were then overlaid on a 69th photo right at sunset, which is why you only see one yellow sun in the corner and no clouds streaking across the sky (also looks like a cloud-free day) |
When they mapped the human genome, what is that? If everyone has different genes, was the mapped genome one person or an average or a "perfect" one?
Everyone's DNA sequence is different. Even identical twins may be slightly different due to gene copy number variations, or due to mutations occurring during development. However, on average, about 99.5% of our DNA is similar to all other humans. Since the human genome is about 3 billion base pairs long, the variation between individuals is about 15 million base pairs. When they "mapped the human genome" as you say, they mapped the genome of particular individuals. The Human Genome Project was the first to do so. They don't reveal the names of their volunteers who provided the DNA, but obviously it was some person (or small group of people). Since then, people have full-sequenced thousands of genomes, so we have individual genomes for thousands of people. By "full sequence" I mean sequencing the entire haploid genome (not DNA tests offered by internet companies such as 23andme which only partially sequence the genome and look for particular markers). Also, when we say "full sequence" we mean "almost full". There are still some small regions which are unsequenced due to technical difficulties. The last I read, there were about ~100 gaps in the euchromatin (the DNA that is loosely coiled) which remain to be sequenced , and quite a few more in the heterochromatin. But these are very small parts; the majority of the human genome has been sequenced. There is no "perfect" genome. When we do comparisons, for example, comparing your DNA sequence to some standard, we use the Human Reference Genome, which is maintained by the Genome Reference Consortium . It's made available through various sites, for example, UCSC Bioinformatics , or Genbank . The reference genome is not homogenous. Different chromosomes (and different parts of chromosomes) may have different coverage. For example, chromosome 7 may consist of the sequences of 14 volunteers, while chromosome 15 may consist of the sequences of 30 volunteers (not necessarily the same volunteers as the other group). The current reference genome keeps changing as more people are sequenced and more data becomes available. The last reference genome I'm aware of was GRCh38 , though there may be newer ones. As for how they're used, it's up to the investigator to determine what makes sense. For example, you could "average" the genome for a particular population (pick the commonest polymorphisms at different loci and call them standard). Or you could keep each person's genome separate, if you were studying the variability in a particular gene. It depends on the purpose of the study. |
Is it possible for a single volcanic hotspot to create features of the Yellowstone hotspot (specifically, fertile plains due to ancient ash beds) and the Hawaiian hotspot (specifically, island building)?
I'm working on a new world building project, and one of the major ideas of the region I'm creating is a volcanic hotspot creating a volcanic archipelago (much like Hawaii) across an inland sea or a large oceanic bay. However, I'm wondering what the land would look like on the adjacent land where the hotspot had been active before moving under the water. I understand that a typical shield volcano doesn't really produce huge clouds of ash, instead producing lots of lava which builds land. Something like Yellowstone, on the other hand, erupts explosively, leaving a large caldera that can later be filled in, creating fertile lands like the plains of Idaho. Do these features ever appear from the same hotspot? How are these related to volcanoes on islands like Monserrat, which, while capable of land building, also seem to erupt explosively? Finally, could a hotspot capable of island building exist under a continent, or is it factor of thinner oceanic crust? How thin would continental crust have to be to have such a volcanic system exist?
well, first we have to discuss what a hot-spot actually is. A hotspot is not material travelling from deep, it's a thermal anomaly from the D" that transmits thermal energy to the surface in a very concentrated area. When this thermal energy reaches the crust, one of a few things can happen: You can end up with a hotspot trace on oceanic crust, where because of the chemical composition of the sea-floor (basalt) the resulting magma will be very thin and not very viscous. If it were over continental crust, however, the addition of Si makes the magma much more viscous and gloopy, which is why you end up with explosive eruptions rather than flowy eruptions. Montserrat is not made from a hotspot, at least not as far as they have determined from the geochemistry as of yet. The reason it can be capable of landbuilding and explosive eruptions again comes down to the geochemistry of magmas and the interaction between that magma composition and the existing landscape and internal geology. Your final question is answered above concerning what a hot-spot actually is. |
Is pregnancy between the ages of 35 and 40 really a considerably higher risk?
I've always heard that pregnancy over ages 35 (often called Advanced Maternal Age) is significantly more dangerous for both the woman and the baby, due to the higher risks of miscarriages, preeclampsia, gestational diabetes and decrease in fertility rates (as said , and , for example). But, I watched this , from "Adam Ruins Everything", which provides evidence that the risks of getting pregnant between the ages of 35 and 40 don't increase as much as warned by the majority of doctors. So, what's the truth about pregnancy after 35? If women could have babies until they were 40 without taking any more risks, it would be better to their careers.
Genetic counselor here. The historic reason for 35 being the magic number is that when amniocentesis was first introduced, the risk of a complication due to an amnio was the same as the age-related risk of the baby having Down syndrome. Now, the risks of amnio are significantly lower (ultrasound guidance, practice, etc.), but the age 35 thing has stuck. The risk of chromosome abnormalities goes up every year older a women gets; there is not some magic jump from 34 to 35. This risk is due to the higher chance of nondisjunction, which can occur when splitting up the chromosomes in the egg, as a women ages. If nondisjunction occurs, the woman passes on either too many or too few chromosomes to the fetus (Down syndrome is an extra chromosome 21, while Turner syndrome is too few X chromosomes in a female). I cannot speak as much on the other pregnancy risks, so I'll leave that for the physicians on here. |
Would it be possible to condense all daily nutrients into a single block of food?
You often see in Sci-Fi (maybe just 50s B movies) in the future people eating food that's just a cube. I know each person is different even the two genders have different caloric requirements but could it actually be possible to have all daily nutritional requirements concentrated into a small block?
It would certainly be possible since we can list them out and could just homogenize them together. The problem comes with actually using it as our only source of sustenance. There are a lot of writings that discuss (mostly) NASAs research into minimization of food for long-haul space travel. (Mary Roach's book "Packing for Mars" is excellent.) There turns out to be a lot of psychological issues with not having what our bodies consider traditional meals over time. |
Sperm... Apart from being male or female, does each sperm carry a unique genetic makeup or would I be this good looking whichever sperm got there first?
A normal male human has 23 pairs of chromosomes. Each sperm will get one of the two chromosomes from each pair. Which means there are 2 different combinations (2 = 8,388,608), barring genetic defect and potential mutations. |
Would the geographic center of a tectonic plate be the least earthquake-prone spot on that plate?
Or is it more the makeup of the underlying rock that makes an area less likely to experience quakes, regardless of how close it is to a fault line? Or perhaps a combination of both?
Not necessarily. To understand why, we need to think a bit more about how plate tectonics works. The idealized view of a tectonic plate is a portion of lithosphere that is internally rigid and non-deforming that moves coherently with all of the consequences of its motion (i.e. deformation, earthquakes, etc) occurring along its edges, i.e. at the boundaries between plates. However, it's important to realize that the interior of plates are under stress, indeed their ability to be under stress and remain rigid and thus transmit stress is key to the way plate tectonics work as the forces driving plate motion occur primarily along the edges of the plate. If the plate was not rigid enough to transmit the stress being applied to the edge of the plate, the plate would not move. Think about the difference between pulling on an edge of a block of wood vs (trying to) pull on the edge of a dollop of yogurt. With that in mind, for an idealized plate there would never be any deformation or earthquakes (which in the simplest sense is the reflection of the applied stress and resultant accumulated strain overcoming the internal strength of a material, specifically overcoming the frictional strength of a planar discontinuity, i.e. a fault, in that material) anywhere but directly along the plate boundary. However, real plates are not ideal, primarily because they are not homogeneous. The important heterogeneity in this case is not necessarily different rock type as you hypothesized, but rather the presence of old faults, which represent planes of weakness within the interior of plates. If the transmitted stresses are oriented correctly with respect to the orientation of these preexisting faults, then eventually enough strain may accumulate across that fault to cause an earthquake, i.e. an intraplate earthquake . The location of these faults will depend on the geologic history of the plate, not expressly the position within the plate, so if there was a preexisting set of faults in the exact geographic center of a plate, then this area would be more likely to have intraplate earthquakes than other places without preexisting faults. A classic example of an intraplate earthquake is the New Madrid seismic zone which generated a sequence of large (~M7.0-7.5) earthquakes in the early 1800. This seismic zone is related to the presence of a very old set of faults that were part of a continental rift zone that originally formed ~750 million years ago. |
Why do we get a feeling in our gut/chest when experiencing very strong emotions?
For instance, when experiencing embarrassment, nerves... Love. Is this just an accident, a biproduct of our physiology; or is there an evolutionary reason for it?
The gut has more nerve endings than the brain, and a much higher concentration of neurotransmitters which help to regulate gut function. A flood of neurotransmitters such as serotonin and norepinephrine, caused by strong emotions and resulting in a temporary increase in gut neuronal activity, is likely the cause of these sensations. |
Why can't a charged object be approximated by a point charge at the object's "center of charge"?
When we were learning about gravity in Physics, we learned that an object can be treated as if all of its mass is concentrated at its center of mass. Since gravity and electromagnetism are both inverse square laws, why can't we treat charge this way as well?
A spherically symmetric charge distribution be approximated in this way, as long as the observation point is outside the object. |
What is the highest grade a wheeled vehicle could climb theoretically?
Scenario: vehicle on Earth, no artificial down force
If you have enough centripetal acceleration, you can drive through a loop-de-loop, or (usually diagonally) around a near 90-degree slope . If you're moving very slowly, then your options are going to be a little more limited. |
What is "Metallic" taste?
When you touch iron or copper (and to a lesser extent zinc and some other metals) and then smell or taste metal on your hands, you're sensing a chemical called 1-octen-3-one . The role of 1-octen-3-one in the taste of metal was only determined recently (2006). Full paper: http://onlinelibrary.wiley.com/doi/10.1002/anie.200602100/full This chemical is formed by "skin lipid peroxide reduction and decomposition by low valence metal ions". So you're not tasting metal but a chemical formed from human skin oils/sweat in the presence of metal. It's theorised that this smell is related to our ability to smell blood which forms the same chemical in contact with skin. However... Tasting metal is a common symptom which may be caused by colds, dental problems, nutrient deficiencies, problems with medication or a large range of conditions that cause distortions in your sense of taste: http://en.wikipedia.org/wiki/Dysgeusia |
How do E&M instruments which require extreme precision account for the Earth's magnetic field?
From what I know, Earth's natural magnetic field is constantly changing, although the changes are extremely small. (Except for when it "flips".) So how does an instrument account for this? You can't just "zero it out" like you can with a mass scale, because it might change afterwards, right?
You can't just "zero it out" like you can with a mass scale, because it might change afterwards, right? Earth's magnetic field (1) is weak enough and (2) changes slowly enough that it can effectively be "zeroed out" for many experiments. In order for Earth's magnetic field to be problematic your experiment would need to be sensitive to fields in the ~0.05 mT range (Earth's typical magnetic field strength) with fluctuations many orders of magnitude smaller than this, would need to last over a very long period of time on the order of decades to see such fluctuations, and would need to be difficult to recalibrate the sensors. I can't think of any such experiments off the top of my head -- did you have something more specific in mind? |
How do you weight things in zero g?
Lets say two hundred years from now you make a quick trip to "Geostationary Quality Foods" for the roast you're making for the holiday seasons up in your spankin new space station mansion and you buy some turkey breast by the pound. How on Earth (well, actually "how in space" I guess) are they supposed to weight it to charge you?
Put it at the end of a spring balance of known length and swing that turkey... For a certain given spin rate (angular velocity) you will read a force that is proportional to the mass. Yay centripetal acceleration. |
Is it possible to cancel out AC current the same way sound gets cancelled with an inverse wave?
I was wondering since both AC and sound are waves. I know that the way sound cancelling headphones work is by simply playing an inverse wave of the sound it is trying to cancel. This way the two waves cancel each other out, and silence is formed. Are we able to do something similar with ac current where we would match the frequency to "cancel" any current?
/r/AskScience frowns upon short answers but yes, yes you can. AC signals have a phase that varies in time and space and to a good approximation can superimpose and constructively or destructively interfere with other AC signals. In fact in most power system the base AC signal is a superposition of three sinusoidal AC signals all offset in phase by 120 degrees from one another. This is what is called "three-phase power" which you can read about here: https://en.wikipedia.org/wiki/Three-phase_electric_power |
How do we know the mass of quarks when it is impossible to separate them from each other and not knowing the binding energy?
The particle data group has a section on quark masses . This is a notorious problem, both conceptually and experimentally. Defining and evaluating quark masses is most challenging for light quarks. The basic idea is to find ways to relate observed hadron masses, and the differences and ratios thereof, using theoretical tools such as chiral perturbation theory, lattice calculations, or sum rules. Look at formulas (71.10) in the link above for instance. The current best estimates are given by the two references below Up and down quark masses and corrections to Dashen's theorem from lattice QCD and quenched QED Up, down, strange and charm quark masses with Nf = 2+1+1 twisted mass lattice QCD People work hard to separate the binding energy. I should add that is really a poor use of the term, since it is usually defined as the potential energy of individual components after being separated. Since quarks are confined, the concept of binding energy is ill defined here. |
What condition does this newborn baby have?
We have strict guidelines against medical advice which include offering diagnoses. We also cannot speculate based on anecdotal evidence / a single picture. |
What's the point of recycling biodegradable food waste? If it goes to landfill won't it turn into compost anyway?
Seems like a waste of energy to recycle food waste separately. If it goes to landfill am I wrong to think it might even aid the degradation of other less perishable waste like paper and packaging etc. Why, in the UK, is this prioritised over processing batteries separately? Example Camden Council, London:
The point of composting is to recover usable biomaterials at the end of the process. Putting it in a traditional dump means it won't be of any use to anyone unless you want to sift through gigantic piles of garbage at a huge expense to collect some in a few years. |
Before genes are sequenced, how do scientist make sure they are using the genes from the right organism?
As a birthday present I am getting my genes sequenced by a private company. For my sample they send a tube that I have to fill with spit then seal, shake and send back. Once they get my sample how do they make sure that its actually my genes that are sequenced and not some bacteria or other organisms (cow cells from a recent rare steak or something)?
The tests use human specific primers/probes for DNA amplification and sequencing, and the sample tube has chemicals that retard bacterial growth. Most of the interference from bacteria is a degradation of human DNA in the sample, it's not really possible to sequence the bacterial genome instead of yours. |
What is happening when I push through sleepiness? (x/post from r/answers)
Asked this in and was told to bring this here: Just wondering what is happening biologically when I push through a bout of sleepiness. For instance, I take night classes and by about 8pm I'm hit with the drooping eyes and fogginess. But I power through and in about 15 minutes I feel extremely refreshed as if I had actually slept a little bit. What is happening here? How can I feel as if I've gotten any rest at all while through the duration of this mental v. physical battle I am in an extreme haze? Always wondered this. Thanks in advance for any insight!
This question is really too personal to answer well. There are many many factors that can result in a temporary reduction in sleepiness. Light has a direct alerting effect. Timing of meals and/or caffeine intake will also affect your sleepiness profile. If we consider the case where all other factors are ostensibly controlled for then there are still a couple of plausible reasons, outlined below. Typically people think of sleep and wake as whole brain states. However, recent research shows that parts of the brain can be locally "asleep" or "awake" when the rest of the brain is awake or asleep, respectively. Local sleep is use-dependent. In other words, brain regions become fatigued from overuse. Constant stimulation of one hand during the day leads to more intense slow wave sleep in the corresponding region of the somatosensory cortex . Conversely, if your arm is immobilized for a day, the corresponding region of the somatosensory cortex has less intense slow wave sleep . During local sleep, there appears to be metabolic recovery in these regions. It is therefore plausible that we are able to temporarily rest overworked brain regions by tuning them out when we are otherwise awake. That is still a hypothesis, but it is gaining increasing support. There are two processes that principally regulate sleep: the sleep homeostatic process and the circadian process . The homeostatic process is the name we give to the empirical observation that people become increasingly tired the longer they are awake and less tired the longer they are asleep. It is now thought to be due to the accumulation of certain sleep-promoting substances in the brain. These same substances are thought to induce local sleep. The circadian process is due to your body's endogenous circadian clock, which promotes wakefulness during the day and sleep at night. Together, these two processes act in a complementary fashion. Homeostatic sleep pressure is continually increasing across the day. To balance this, the circadian drive for wakefulness also increases across the day, reaching its peak only a few hours before bedtime . This may seem an odd time to have your strongest circadian drive for wakefulness, but it is necessary to fight against the increasing sleep pressure to maintain our long 16-h bout of wakefulness. Consequently, there is a window of time, called the , within which it is very difficult to initiate sleep and where the circadian drive for wakefulness is very strong. For most people, this occurs around the time you are talking about: ~8pm. |
What's wrong with this argument against evolution?
: The critical factor in evolutionary change is not actually time. Instead, it’s population size and generational turnover. This is because the requirement is that substantial variability be provided (by population size) and many opportunities for selection to whittle down a generation and act on that variation. This is very important, because it means that what Darwinists claim we can’t see, we actually can see. We can examine what occurs, given a certain amount of evolutionary resources. Malaria has existed on this planet for several millennia, and operates by invading hemoglobin, eating it from the inside out, and destroying it. Its structure is such that it can only survive in very warm climates, however. Given the enormous population of malaria across the planet and the rapid generational turnover- each infected person has billions of malarial organisms that multiply exponentially- malaria Think about that. This is what is supposed to have created the human brain? I suspect there are some fallacies here, or misconceptions about evolution. How would you respond to this person?
It's pretty clear that this person doesn't know what they're talking about. "Malaria" is a disease, medical conditions can't evolve. The pathogen that causes malaria, and that is capable of evolution is (primarily) Plasmodium falciparum (Plasmodium). Plasmodium doesn't invade hemoglobin, which is a molecule, and hence dozens of orders of magnitude smaller than plasmodium. Plasmodium has a complex life cycle, one stage of which involves living inside red blood cells. Plasmodium has evolved to live within Anopheles mosquitos, and only some of them. In a lot of mosquitos, the host reacts to, and destroys the plasmodium. So the real question is: why have Anopheles mosquitos capable of supporting plasmodium not been able to spread across the globe? So what this authors argument actually boils down to is: If one species is not capable of colonizing the entire earth, then evolution is false. Which is a stupid argument. You might as well argue "because there aren't polar beers in Africa, evolution is false". A species is by and large specialized for a specific environment. A species generally, cannot get away with being extremely general, as then in every niche an animal which is perfectly specialized for that niche will perform better, and out compete the general species. So there are mosquitoes that live all over the earth, it's just that the anopheles mosquito is specialized for tropical environments. And a different species is specialized for sub-tropical environments. If an anopheles mosquito formed through mutation that could survive to some extent both in tropical and subtropical environments, it would almost certainly be out-competed by the original anopheles which is specialized for tropical environments and whatever mosquito is specialized for sub-tropical environments. |
Waking up in the morning: Why is it that when I sleep outdoors I'm able to wake up bright and early feeling refreshed?
Furthermore, why is it that when I sleep for a full 9 hours I still feel crappy when the alarm rings? I know it has to deal with your sleep cycles, but how are these sleep cycles influenced by external factors (light, sound, temperature)? Edit: Thanks for all of the great information! I suffer from sleep phase disruption, which essentially means my circadian rhythm has gone off the deep end. But whenever I sleep outdoors, I find that I fall asleep easily at nightfall and wake up refreshed in the morning. I was just wondering if there was any way to bring whatever factors exist outside into my bedroom.
You know, that is very interesting. I'm sure I know the answer: So the pineal gland in your brain is very involved in your circadian rhythm (biological clock), and it produces and secretes melatonin which is a chemical that basically makes you sleepy due to a pathway I won't explain. Anyway you can buy it in the vitamin store to help you sleep. The production of melatonin is stimulated by darkness and inhibited by light. Perhaps you were in more direct sunlight when you woke up since you were outside, and your pineal gland was better able to respond to light, inhibiting the melatonin, thereby bringing you steadily and clearly out of sleep and allowed you to wake up faster (ie start increasing body temperature and blood pressure and levels of the hormones responsible for this). Here's more info on the pineal gland: http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/otherendo/pineal.html |
Given sufficient computing power, how accurately could we theoretically predict how an organism would look and act based solely on a genome?
You're asking if we can predict the phenotype of an organism just from its genome. There are basically 2 ways to go about this. A , from first principles simulation of the genome and its products OR by homology where we would match the genome (information) content to other genomes we know. The homology method would be pretty accurate indeed. This is the core technology which underpins much of modern molecular phylogenetics. If you gave me a genome and an afternoon I could tell you what genus the genome belongs to and from there we could work out which species it is closest too and we could make good first order approximations of the phenotype and appearance of the organism. For eneterobacteria we could tell you quite specifically which biochemical pathways are present or not with very good coverage. For the simulated method we would do a very, very, very bad job of estimating the phenotype of an organism purely from the information contained in the genome. A genome produces 1000s of products (proteins, mRNAs, tRNAs, snRNAS etc...) these have very, very complex non-linear interactions and only a few of these are well understood across all of life (enterobacteria and experimental mammals have good coverage). Small changes in any of those components can lead to profound changes in phenotype outcome. We also don't have a very thorough understanding of how changes in the genome map to changes in the structures of proteins and RNAs, this means small changes in the genome content are often not well modelled at the protein/RNA structural level (this is the domain of protein engineering). |
Why can't we pair a bluetooth device with two others simultaneously ?
Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s): guidelines. You can find the basic answer with a google / wiki search. Please start there and come back with a more specific question. If you disagree with this decision, please send a message to the moderators. |
Why is the force of gravity taught as a constant, e.g. -9.8 m/s², when Newton's law depends on the distance?
For that matter, wouldn't any inverse-square law force depend on the radius?
The -9.8 m/s refers to the acceleration due to gravity near the surface of the Earth, not the acceleration due to gravity in general. In fact this arises from the inverse square law and the fact that the Earth is so much larger than the distances we typically move. The acceleration 9.8 m/s is the value of the expression GM/r where G is the Newtonian gravitational constant 6.67 x 10 N m /kg , M is the mass of the Earth, and r is the distance to the center of the Earth. Since over typical human scales, our distance to the center of the Earth barely changes (going up or down 100 meters is irrelevant on scale of thousands of kilometers), the acceleration due to gravity near the surface of the Earth is essentially constant. |
If pushed, would a frictionless marble roll across a surface or glide?
If it was pushed in-line with its center of mass it would glide, and if it was given some torque as it was pushed it would have a rolling component, but it wouldn't roll without slipping, which is what most people mean when they think of rolling. |
Why don't soft drink companies use Oxygen as their fizzing gas?
I understand that it would introduce a higher risk of fire, and the possibility of law suits about oxygen poisoning, but it seems as if a drink that made you feel alive and energised would sell very well despite this.
Actually at 25oC and 1 atmosphere pressure: Solubility( 2) = 8.27 mg/l Solubility( 2) = 1450 mg/l So Carbon Dioxide is ~175 times more soluble than Oxygen at SLC (Standard Laboratory Conditions) |
Would a boat float on top of a large ball pit? What are the major factors impacting the question?
It's not about the relative size of the the objects (quantization). The problem is that the balls have a very low kinetic energy compared to their inter-ball friction. It wouldn't matter if you had an enormous thing the density of air covered in balls, it still would not rise because the apparent viscocity of the balls would be too large. Now if you increased the kinetic energy of the balls by shaking the pit, even a smaller light object would be pushed to the top so long as it's size was larger than the average ball path length or so. |
How large if a role does genetics really play in obesity?
One way scientists can figure out how much effect genetics vs. environment has an affect on a trait is to compare that trait between identical twins (individuals with identical genomes) who were raised in the same household, and identical twins who were raised in separate households. Scientists in this study found BMI was 70% correlated male twins and 66% correlated for female twins raised apart. Meanwhile, twins raised together show 74% correlation in BMI for males and 69% correlation for females. These numbers are specific to this study, but the authors firm take-away is that genetics plays a role in BMI. |
Is it possible for pi to take on different values when moving at a relativistic velocity?
In my class on special relativity we never considered rotating objects and it got me thinking. If a disk is rotating at a relativistic velocity, then the outer edge with be Lorentz contracted relative to the centre meaning the circumference of the disk will be less than 2piR. However the disk won't be contracted in the radial direction, which would mean that pi is less than 3.14. I don't see any error in this. Does this make sense? If I'm right, can this happen to other transcendental numbers like e? What would a circle even look like in a rotating reference frame?
Pi is defined as the ratio of circumference to diameter of circles in a specific geometry (namely, the Euclidean one). It's not relevant to pi what shenanigans circles may get up to in other geometries. Your circle has a different ratio, possibly, but the connection to pi is flawed. An idealized human has two arms. Some have one. That does not make two sometimes equal to one. |
How do scientists know that ancient hominid fossils are a different species and not just a strange unique example of one individual early man?
I am mostly asking about hominid and "early man". I see a ton of diversity these days. How can scientists know that the body types they find, the size of hands, brow, forehead, etc... How can they say "oh that's a different species" and not just "oh this one had strange tall shoulders", you know? I'm talking like a million years ago where the genius homo popped up.
It really comes down to process of elimination. Forensic Anthropology Is the study of human skeletal remains. By having a skull/skeleton you can tell a lot of different characteristics in modern humans. Such as ethnicity, gender, age, and even how they died in some cases. The skull is usually the most prominent give away to what type of hominid it was(ie: brain size, brow size, eye shape/front facing, cheek bones, how thick the skull is) Finding tools with the bones gives an indication of brain capacity(which can also indicate what they ate). Sometimes other animal bones are discovered with the hominid remains which gives an indication as to how they died/what they ate/time of existence. Bipedalism is a huge identifying characteristic. Carbon dating the bones helps give a estimated date, how deep the bones were found. Where the bones were found geologically is a big one. You can tell if there were rituals to mourn the dead. All of these combined give you a reasonable hypothesis as to which hominid it could be. Not having a full skeleton makes it more difficult to narrow down since a lot of these hominids lived at the same time as one another. I’m sure I’m missing some indicators, but these are the most popular because they are the easiest to see. They even use cgi to remake the organism to give a possibility of what it looked like. It’s no easy task to decipher the bones and some don’t fit in. When new remains are uncovered and brought back to a lab, teams of anthropologist discuss the similarities and differences. They then decide whether it was a certain hominid that has already been discovered or a new one. I’m not an expert, just someone that is interested anthropology. if someone has a better explanation I would like to be enlightened as well. |
What does askscience say about the argument presented in this article? Deconstructing Nuclear Experts
What arguments? It's mostly just a load of mud-slinging. Psychologists aren't scientists. "Physicists are stupid" - I mean, seriously. As for the the few-and-far-between things resembling actual relevant information, I'll just comment on that cancer study from "Lynkoping [sic] University", about cancer rates in Sweden. Since I know about that particular study. Which is that it's was pretty roundly criticized, including by the Swedish Radiation Safety Authorty (which has been studying the after-effects of Chernobyl very closely). They alleged the cancer cases in the study occurred too soon to be attributable to Chernobyl, and also that the study didn't factor in lifestyle differences. In short, there have been a lot of studies pointing to negligible effects and none supporting that one. Yet.. the author then concludes from that study that: there was an 11% increase in cancer for every 100kBq/sq metre of contamination. Since the official International Atomic Energy Agency (IAEA) figures for the Fukushima contamination are from 200 to 900kBq.sq metre out to 78km from the site, we can expect between 22% and 90% increases in cancer in people living in these places in the next 10 years. That's just retarded. Bequerels is the number of decays per second. It makes absolutely sense to compare health risks on the basis of that without any consideration of which actual isotopes you're talking about. The author doesn't specify, and as far as I know, neither did the IAEA. So why would those numbers be comparable? Also, there's no justification to believe the cancer risk would scale linearly either. That's just a wild guess, and not necessarily a good one, given how complex cancer is. It's just biased propaganda and mudslinging. Even if you're against nuclear power, it should be obvious if you ask me. Although I suppose a site that declares "Why the Entire Nuclear Industry is Insane, Then, Now and Forever" right at the top of the page can hardly be expected to provide unbiased information. I mean, if you've already decided that not only is the nuclear industry "insane", but that it cannot possibly be otherwise, then you've pretty much precluded any rational debate. |
I learned in University, that photons are released by electrons that are decreasing in energy. So how do neutron stars emit light?
Atomic transitions are not the only way that light can be produced. Any particles which interact with the electromagnetic force can emit photons, in various different physical processes. |
Are there any "rock-paper-scissors"-genes?
I'm in my last year of high school, and learning about genetics. So far, we've covered dominant and recessive genes, as well as codominance and such. Are there any genes where the alleles dominate each other like in a game of rock-paper-scissors?
No, but side-blotched lizards effectively demonstrate the same 'rock, paper, scissor' gene dynamics at the population level. Are there any genes where the alleles dominate each other like in a game of rock-paper-scissors? Hmmm, I have a 'sort of' answer! Though perhaps not mechanistically at the molecular or cellular level, there's certainly one pool of alleles operating in a 'rock, paper, scissors' fashion via behavioural dominance at the level of population genetics in the side-blotched lizards . Side-blotched lizard sex is weird. There are three male 'genders', and two female, with the males grouped into those with blue, orange and yellow-striped colouration respectively. Orange lizards are large and aggressive, attracting many females by defending territories. Blue lizards are smaller and hold small communal territories, guarding individual females closely. Yellow lizards don't hold their own territories, but pretend to look a bit like females, milling around the edges of the dancefloor and occasionally sneaking in a cheeky bang with a female when the territorial lizards aren't looking. How it works is that, over the course of several generations, when there are more: larger orange lizards physically push blue lizards out of their territories, expanding their domain and mating with more females, thus increasing the number of orange offspring in the population. with more orange lizards, there are more large territories for yellow lizards to exploit. An orange lizard cannot guard his entire territory all of the time, so sneaky yellows are increasingly able to mate more often, increasing their numbers in the population - and decreasing the proportion of orange offspring. now with fewer orange lizards, blues are able to regain their numbers. Blues, who live communally and guard individual females, are better able to protect females from sneaky yellows, thus yellows mate less and the blue population increases. And then rinse-repeat with the orange lizards... So overall, here we have a number of alleles involved in generating the respective orange, yellow and blue phenotypes, exhibiting 'rock, paper, scissor' style dynamics at the population level: blue genes > yellow genes > orange genes > blue genes. However, and here comes the 'sort of', despite exhibiting those dynamics at the population level, the entire system is based upon a single Mendelian factor with three alleles, which operates differently. The orange allele is dominant over everything, and the allele is recessive to the allele. As such, orange lizards have the genotype , , or , yellow lizards have or , and blue lizards are exclusively recessive with . So it doesn't quite fit your question! Barretto (2017) have successfully modelled an allele system exhibiting the 'rock, paper, scissors' dynamic, suggesting it's at least theoretically possible, but as far as I'm aware we haven't found it at the gene-level in anything so far, only population genetics. But I could be wrong! |
What causes musical chills?
It seems in particularly emotional or moving parts of music most people tend to get chills throughout their body. What causes this?
We have a subreddit for this! http://www.reddit.com/r/frisson Also a good article: http://arstechnica.com/science/news/2011/01/turns-out-that-music-really-is-intoxicating-after-all.ars |
Why does the hair of some children who were born blonde darken over time?
When I was born, I had blonde hair. By the time I was five, my hair had gradually become very dark brown. I've seen this happen with many other children, too. Why was my hair not brown when I was born? What causes this change?
Previously asked here http://www.reddit.com/r/askscience/comments/njgq4/why_was_i_born_with_blonde_hair_that_fell_out_and/ TLDR - different genes are expressed at different stages of one's life and factors such as disease and nutrition can affect gene expression. |
[linguistics] Is there a way to make sense of double negatives not canceling in some languages?
I've known people who say things like "I ain't got no smokes", meaning that they DO have no smokes. Several people have told me that this is because a similar construction in Spanish is correct. Whether from Spanish or any other language, is there a way I can parse this so that it doesn't just seem wrong?
This is what linguists call . It's not a matter of negatives "cancelling" (this isn't math), it's a matter of multiple negatives adding up together to give a stronger, more emphatic, negation. In standard English, we usually use (and related words) to make our negations more emphatic, as in "I don't have smokes", or "Things just aren't the same ." |
Why are there different "generations" of cephalosporins?
I know that certain generations are slightly better at combating gram-positive or negative bacteria than others, but it seems like plenty of drugs within classes are more efficient with certain types of infections without warranting the strange generational divisions. Why is this the case with cephalosporins?
I'm from Europe and as I'm aware different countries will group the generations sometimes a little bit differently BUT: 1st Gen: generally cephalosporins with few structural variations except seen on the R group of the C7 position on the ring, these are drugs that will have limited effects against G- and ok range of activities against G+ bacteria but generally aren't as potent as penicillins and may have toxicity problems and may not absorb well through the GI tract. cefalotin 2nd Gen: refer to drugs which have improved activity against G-, usually this is through placing a polar sub(NH2 usually although sometimes CO2H) at the alpha position on the R group at C7. Also, you see a lot more drugs with differing groups at c3 in place of the ester, this is because esterases in the body can metabolize cephalosporins relatively quickly and limit their overall activity by converting them to alcohols (a bad leaving group in terms of the mechanism of action), so we swap in groups like halogens or even amides which won't be as easily metabolized but promote activity too. cefaclor 3rd Gen: A good few of the 2nd gen ones did provide good activities but they still weren't very potent against rougher opportunistic bacteria such as pseudomonas aerugonosa, and some also lacked goof b-lactamase resistance so the R group at C7 was again modified to provide a bit more steric bulk to shield the lactam ring from act by the enzyme, usually some kind oxime residue attached to a heterocycle is used. Furthermore, the H anti to the R residue at 7 is sometimes replaced with a methoxy group to provide additional steric shielding to the ring although results on how great that is vary. 3rd gens tend to have better G- activity as a result of some of the polar subs at on the R group too which inversely means lower G+ activity cefdaloxime . 4th Gen: ones that generally have good all round activity, quite good GI tract solubility and can even cross the blood brain barrier, they tend to show zwiterionic subs at c3 and have similar bulky R groups at c7 but tweaked to balance activities between the 2 bacterial classes. cefozopran Source: http://en.wikipedia.org/wiki/Cephalosporin and my brain |
What is quantum gravity?
What exactly is it and why is it important?
We have quantum field theory, which tells us how very small things behave, and general relativity (gravity), which tells us how very big things behave. These generally don't overlap in scope, because small things are small and big things are big. However, in situations where both gravity and quantum effects are important, neither theory tells the whole story. You need a new theory that combines both to explain what's happening. That's quantum gravity. |
When you exercise, does your heart beat harder or just faster?
Your muscles need more oxygen so the heart pumps blood through the body at a greater flow rate. I know your heart goes up, but does your heart beat with the same.. effort (there's gotta be a better word)? Or is every beat the same? Edit: Thank you all for your answers and insight!
Both. To effectively increase flow throughout the body, both rate & strength need to be increased. Strength is simply how much your heart muscle is contracting... no different than any other muscle in the body. However, it is possible to increase one without the other by targeting different cellular receptors. We have different medications that work by increasing one or the other, or both, administered to heart failure patients. |
How is mechanical energy created from chemical energy in cells?
I understand the mechanisms by which ATP creates chemical energy. I can't seem to figure out how the chemical energy from the hydrolysis of the phosphate group is converted into mechanical energy to drive, say, a motor protein. I suppose I've always thought of the energy being released simply as negative ∆G. How is that ∆G converted into directional motion?
If you're talking about the muscle sarcomere: The binding of ATP to the myosin crossbridge causes a loss of affinity of myosin for actin leading to dissassociaition. ATP then undergoes hydrolysis to ADP and inorganic Phosphate (ADP + Pi), which once again restores chemical energy back into the system, extending the myosin crossbridge and regaining the affinity for actin. The binding of the myosin crossbridge to actin is responsible for the separation of ADP + Pi from the myosin crossbridge (arguable which step causes which at this point, whether it's the binding that separates the ADP + Pi or visa versa). The stored internal chemical energy from hydrolysis is then dissipated through contraction. I don't know the equivalent biochemical reactions and their energies, but I hope that helped. |
What could be consequences from the Amazon fires?
Apparently some people have been burning the Amazon forest for weeks now. What will or could happen if they keep burning it?
An excellent response. I'll just add to it that there is a current theory that of the Amazon loses as much as 5% more of its 1970 area it will cause a cascade effect which will result in the Amazon drying up and converting to a desert savanna. In other words, if too much more of the Amazon is destroyed the rainforest may never come back. https://news.mongabay.com/2018/03/amazon-forest-to-savannah-tipping-point-could-be-far-closer-than-thought-commentary/ Currently the Amazon rainforest loses roughly 1% every 3 years, mostly to slash and burn agriculture used to feed cattle and supply palm oil. This 1% every 3 years is a slowdown from the rates before 2006. |
Is there a cure or just a way to manage PTSD?
Ive been told that people can manage PTSD but cant actually heal it. I just want to know if this is true or if it is curable. If it is curable, how is it possible? If it's not, why not? I couldn't find anything about this in the research I did.
It depends on what you mean by "cure". That's not a term that's typically used in mental health treatment. What we can talk about though is response (meaningful reduction in symptoms), remission (defined by symptoms below a meaningful threshold) and no longer meeting diagnostic criteria. What's particularly notable about PTSD is that there is a trauma involved, something that happened to a person that was quite terrible. The past will never change and will always be something that is unpleasant, sad, etc. What can change are intrusive symptoms (nightmares, intrusive memories, cued emotional/physiological reactions), avoidance (of memories, thoughts, feelings, people, places, situations), arousal symptoms (insomnia, hypervigilance, concentration problems, hyperstartle, irritability), and negative emotional/cognitive changes (emotional numbing, excessive blame, negative beliefs about the world). Those sorts of symptoms are quite normal in the immediate aftermath of a trauma, but there is a natural course of recovery over time such that the majority of people (>80%, even combat veterans) will not develop PTSD. A meta-analysis found that over time (mean of 40 months across studies included in this analysis, covering >80,000 people), almost half of people with PTSD will no longer meeting criteria for diagnosis of PTSD . Sidebar: something else important to know is that PTSD is just one way a person can react to a trauma. Some people develop depression (low mood, lack of interest, poor sleep, appetite disturbances) or generalized anxiety disorder (difficulty to control worry about many different areas of life). These can also co-occur with PTSD. A helpful differential question is how to the memories come back - in PTSD they can come up intrusively when not desired and the person will try to push them away. A person with depression may ruminate on them (rather than push them away) and think about what they did wrong. A person with GAD may worry about all of the "what if" situations about what else could have gone wrong, again not trying to push the memory away. These are all negative reactions to traumatic experiences, but they do not all fit with a diagnosis of PTSD, no matter how much that term gets carelessly tossed around and no matter how much a person may want to have a diagnosis of PTSD (strange, but true). Two main things keep people stuck, preventing natural recovery. The first is avoidance of memories, people, places, situations, etc. that dangerous but are objectively safe. As an analogy, if you took a child to the beach and the child got hit by a wave and was very upset, they would not want to ever go back. As long as they stay away, they won't have that extreme distress, they will maintain a strong fear of the breach. Avoidance is very effective for managing fear and anxiety in the short term, but that fear will not go away as long as a person continues to avoid these things. So targeting avoidance is a main goal of trauma-focused therapies. Unhelpful beliefs about the self and the world can also keep a person stuck, preventing their recovery. These beliefs may include feelings of guilt or responsibility that are disproportionate to actual responsibility, belief that you are incompetent (thinking you can't do anything will keep you from doing just about everything), belief that the world is dangerous (of course there's danger, but this can be terrifically amplified in PTSD), etc. The problem is when those PTSD symptoms prevent the person from living the life they want to live. If everything feels dangerous, you may avoid driving, crowds, etc. and your world becomes smaller and smaller. If you're distrustful and irritable you may push people away. What effective treatments do is help a person to reduce their symptoms by targeting avoidance and/or unhelpful thoughts and beliefs. By doing so, things that are objectively safe can feel less dangerous, helping you re-calibrate fear, so that you can go to the grocery story, go to the gym, go to dinner or concerts with your SO, attend your children's soccer games, and live the life you want to be able to live. We have several time-limited psychological treatments that have years, even decades, of evidence showing they reduce PTSD symptoms, with followup studies showing these reductions can last for years. Here's a figure showing the proportion of patients who meet diagnostic criteria for PTSD from pre- to post-treatment and the 5 years later ( ref ). |
Regular pentagons tile in spherical space. There are 15 known irregular pentagons that tile in flat space. Is it true that *any* pentagon will tile in some space with homogeneous curvature?
for the purposes of tiling, aren't polygons defined in terms of the relationships between their various angles? A regular pentagon in some arbitrary space would be a 5-sided polygon whose internal angles are all equal. At least, defined thus, is it true that any 5-sided polygon will tile in some space with homogeneous curvature? I don't think the question depends on my defining 'regular pentagon' in flat space and referring to it tiling in spherical space. |
Should I rush to re-open a closing door or should I just open a closed one?
In a food court, there are 4 adjacent self closing doors. I have noticed that people run to re-open a closing door behind someone who had just went through. I think the intuition is that a half open door is easier to open than a closed one. But the physics in my head seems to think that opening a closed door uses less energy. But when I work it out on paper, it seems to give me equivalent efficiency (equal efforts) for both situations. Here is my breakdown Situation 1 - Closing door: One must first do work in order to bring the closing door to rest before doing the work to reopen it into the open configuration. Situation 2 - Closed door: Work must be done to bring the stationary door into motion and into the open configuration. The assumption I made in my personal calculations is that the open configuration is twice the angle at which the closing door is brought to rest. So... is it equal? My mind's telling me no. But the maths... The maths it telling me yeaaah.
Buildings are slightly positively pressurized, the additional pressure on the door can make an inward swinging door more difficult to open, initially, before the "seal" is broken. A reasonable target is 0.02in-wc, which is about 0.0007psi. While this is a small number, over a large exterior door it can be a few lbs of pressure holding the door shut (assuming an inward swinging door). |
In this gif for what reason do the gas bubbles sink?
Here's the . I imagine if it went on longer the bubbles would rise but I can't imagine any reason they seem to sink unless the perspective is skewed and the gun is pointed more downward than I think.
Keep in mind the huge bubble that comes out when the gun is fired is very hot. It's cooled nearly immediately, greatly reducing the volume of gas. What you see going downward is the particulate/smoke from the explosive in the ammunition, which is sinking in the water as one would expect. Toward the end of the gif you can see the few bubbles that went with the smoke separate from it and start traveling upwards. |
Is Marinol less medically useful/potent than "medical marijuana? Why do I never hear about it?
Marinol is synthetic THC. Medical marijuana differs because there's many different cannabinoids that work in conjunction with THC in ways we don't fully understand to produce the desired therapeutic effect. I hope this analogy works. Lets say milk is illegal, but pure caesin (protein in milk) isn't. You want to bulk up, but drinking a protein shake of caesin isn't going to be as nutritionally fulfilling as milk is. |
How can volcanoes form where there are no plate boundaries?
In high school I've learned that volcanoes form on plate boundaries which I understand. But what I've been thinking about is how can volcanoes form where there are no plate boundaries. The main example I'm oging to use is in Edinburgh, where the Edinburgh castle is build ontop of an extinct volcanoe. How did that volcanoe form if there are no plate boundaries in Scotland?
Couple of options: 1) Hotspot volcanism where volcanoes erupt above a localized zone of anomalously hot mantle. These are most likely related to mantle plumes , but a few holdouts still argue for alternative mechanisms. Regardless, hotspots can occur near plate boundaries (e.g. Iceland) or in the middle of plates (e.g. Hawaii). 2) Plate boundaries are a bit more diffuse than many people realize. There can be a lot of activity even relatively far away from the formal plate boundaries. As an example, the formal plate boundary between Arabia and Eurasia is in northern Iraq, but there is extensive volcanism throughout eastern Turkey, Georgia, Armenia, Azerbaijan, and into Russia (in some cases 1000+ kms from the plate boundary) that is associated with the collision between Arabia and Eurasia. 3) Just because something isn't a plate boundary now, doesn't mean it wasn't a plate boundary in the past. This is the relevant answer for your example question. Specifically, Edinburgh castle is built on top of 400-300 million year old volcanics . At this time, this portion of Scotland was along a plate boundary, e.g. the Devonian period of Scotland . |
What is PWM and why is it used in driving an inductive load?
I worked with pwm drives for many years. They are used to drive inductive loads as a way to vary both voltage frequency and current seen by the load. They are basically just used with 3 phase motors so I will talk about them. In a regular off the line start, a 3 phase motor will typically produce 150% full load torque and 200 to 1200!% in full load amps, these large moments of inrush power can be hard on electrical equipment and mechanical equipment. Older soft starters were developed to cut voltage at startup to cut current and torque. Cutting the voltage 50% will cut current 50% and torque 25%. These are affective in decreasing starting stresses, but offer no speed control. The theory behind basic PWM drives is to operate a motor on a linear volt per hertz ratio. So if there was a motor which operated at 120 v at 60hz. The PWM drive will adjust the linear adjustment to 2v per hertz. This will produce 100% of rated torque at any rpm it is adjusted to. PWM drives can be further expanded into advanced open and closed loop VFD drives which can offer speeds from 0 to 400hz, and torque ratings of more than 100 percent down to zero speed. |
In a packed grocery store with long cashier lines, is it better to choose one at random?
So I got stuck today for 20 minutes in a cashier line, and it got me thinking about the optimal way to choose a line. Whenever a customer had finished shopping he would run through all the lines to find the shortest one. But here I was thinking, if every customer before me has searched for the better line, then the lines are more or less equally long. So the best option would be just to pick the nearest line and not bother looking for anything better. So I know this obviously has been thought about someone before. And while I know a little about game theory, I have no idea how I would search for such a concept. Does anyone have somewhere to lead me to? Could anyone explain under what area of economics/mathematics this would fall into?
Personally I evaluate the amount of products in each persons cart, I'd rather get in the line with five lightly loaded carts than two heavily loaded ones. Also I've found that younger to middle aged (20-35) cashiers seem to be a bit faster. Several elderly persons in a line are usually a red flag as they tend to write checks which increases the wait time. |
What is the math behind the microgravity on the ISS?
I've read that the reason astronauts are weightless on the ISS is because the centrifugal force is equal to gravity. Can anyone do the math to back this up?
Gravity is fictitious too! Sorry for the lame humor, just want to point out that "fictitious" doesn't mean "non-existent", it means "dependent on your frame of reference" . Specifically, inertial versus non-inertial. However, whether your frame of reference includes fictitious forces or not, you get the correct answer as long as you include (or exclude) all of the appropriate fictitious forces for the frame of reference you choose. |
I'm getting a lot of conflicting answers. Are there any real benefits of drinking alkaline water?
Everything I have ever seen besides the propaganda, indicates that it is a bunch of new age bull. http://www.chem1.com/CQ/ionbunk.html http://message.snopes.com/showthread.php?t=13815 http://www.apswater.com/article.asp?id=198&title=Alkaline_Water_Hoax_-_It_Is_Simple_Science . |
My apartment offers free water but not electricity. Would it be possible to use the water to generate enough power for my apartment? (eg. bathtub water wheel)
I have a pretty standard one-bedroom apartment and would need to power a refrigerator, 3 room lights, a laptop and other standard appliances. Is there any shot I could harness the power provided by the free water to meet my electricity needs or is it simply not enough energy? Also, of course the apartment would probably catch on and kick me out if I was running water 24 hours a day, so lets ignore that reality.
Let's say you're using your bathtub. I looked it up, bathtubs put out about 4 gallons per minute. 4 gallons of water is 15 kg. I think this is higher than reality, but let's say the water falls 2 feet from the faucet to the ground. The potential energy then is m*g*h, so the amount of potential energy over a minute is 15*9.8*0.66 = 98 J. Watts are J/s, so divide that by 60 and you get 1.6 W. Thus, your bathtub can produce about 1.5 W. So no, you won't come close to powering your house, sorry. |
Do taller and shorter people have higher and lower heart rates than people with average heights?
It's late (as of typing this) and I'm wondering stuff.. Also I guess an extension of the question is "Are taller people more susceptible to high blood pressure?"
Cardiac tissue is post-mitotic (the cells can no longer divide) there are other organs like this (brain) but the main problem with people who get extremely tall like pituitary-giants is that while the rest of their body keeps growing their heart reaches a maximum size relatively early in development. Their hearts are the same size as someone who could be up to two feet shorter but this cardiac tissue now has the job of pumping blood through a much greater volume of systemic tissue. So, yes those who are unusually tall are also unusually susceptible to hypertension and cardiac problems. |
Why are there no CMYK colored Pen sets?
Hi, In subtractive color / printing yan, agenta, ellow and blac are used to create all colors on a white background. These colors act as a filter to the colors in ambient light and thus the correct CMYK filter combination shows the desired color. Why isn’t CMYK a readily available combination for pigment colors such as pens, paint and the like?
It seems like your theory is if someone had these four colors they could create any color they want on paper. The problem is, to create a certain color, you would need the ability to very precisely deposit an exact ratio of the necessary base colors. Pens allow ink to flow at a generally consistent rate. You can’t control that rate, so the ratio would essentially always be 1:1, 1:1:1, or 1:1:1:1. With paint, these systems are in place at paint stores. A base white has specific amounts of various tints added to reach the desired color. Frequently using a scant few drops of certain tints to achieve the final color. |
Do I understand correctly that what we call color "green" is actually two different things?
One is the light with wavelength corresponding to green, and the other one is mixture of wavelengths corresponding to yellow and blue. Then on the other hand, there may be some other colors that if you mix them you get green. Perhaps all those pairs of colors which are equidistant from green on the color spectrum.
Colour is entirely a product of perception. You can have a photon of one wavelength, or photons with a mixture of wavelengths, activating the receptors in your eye that lead to the perception of "green." In that sense, the colour green is only one thing. |
What do ants do at night? Sleep?
I don't know what is the correct flair to use.
Ant colonies are like human cities. And just as human endeavour continues 'round the clock, so does the activity of the humble ant colony. The bulk occurance of human activity however skews sharply towards daylight hours, with only a fraction of the population engaging in e.g. night-shifts, or panicked essay-crisis all-nighters (preach!). Is there a similar circadian skew in ant activity? Well, it partly depends entirely on the species, and partly what they're doing. When it comes to foraging, most ant species forage 24/7. Some species however, many living in hot and/or humid environments (such as , a desert harvester ant), are often more active outside the nest during the cooler hours of evening and night [1]. In contrast, others prefer the day and sometimes indeed even specialise in high temperature activity. Saharan silver ants ( ) make a living primarily snatching other animals that succumb to the high daytime temperatures of the desert. As the early afternoon develops and temperatures approach their height, ant-nomming predators scuttle off to seek shade thereby presenting a short window of opportunity where the proverbial dinner table is open to plunder. Silver ants scoot out at the ant top speed record (~2.2mph, equivalent to you running ~447mph) to grab anything and everything they can before continuously rising temperatures make it too hot (>53°C) for even the ant to handle (check out this clip from BBC's ) [2]. Their whole shtick kinda' reminds me of the 'bio-robots' at Chernobyl . Yeesh! Circadian-associated foraging aside, are there any other day/night differences in ant activity? Well, not really. The overwhelming bulk of most ant activity takes place at all times: cleaning, rearing young, tending to the queen etc. As such, ants generally don't have a circadian-associated sleep cycle. Oh, and speaking of sleep, yes, they do! One study demonstrated fire ant ( ) workers cumulatively 'sleep' approximately ~4 hours a day over an average of ~253 microepisodes, each episode just over a minute long [3]. Queen ants 'sleep' almost twice as long (around ~9.4 hours), over ~92 'sleep' batches each ~6 mins long. They do this at fairly regular intervals 24/7, with no skew towards any particular time of day. though some species forage outside at different times, the overwhelming majority of ant activity, particularly inside the colony, takes place 'round the clock. Ants do sleep, but in regular short batches all day/night long. [1] Hunt, G.L. (1977) Low Preferred Foraging Temperatures and Nocturnal Foraging in a Desert Harvester Ant. . 111 (979), 589-591 [2] Wehner, R., Marsh, A.C. & Wehner, S. (1992) Desert ants on a thermal tightrope. . 357 [3] Cassill, D.L., Brown, S., Swick, D. & Yanev, G. (2009) Polyphasic Wake/Sleep Episodes in the Fire Ant, Solenopsis Invicta. . 22 (4), 313-323 |
If going at the speed of sound creates a sonic boom, then hypothetically, if a light source was accelerated to the speed of light, would there be a big "light wave"?
So, we can't answer the question of "what happens if a light source is traveling at the speed of light" because things with mass can't travel at the speed of light, and the equations that would answer this question "blow up" at the speed of light, but there are two things which are related to this question which you may find interesting. If an object was heading towards you at a very high speed, the light would blue shift as it underwent the Doppler Effect . So, what that means is whatever frequency of light the light source is emitting, it will be a higher frequency when it comes to you. And depending on the speed, this shift can be dramatic. A light emitting visible light could be blue shifted all the way to gamma radiation, so a "safe" light bulb could emit cancer causing radiation if the light bulb was moving towards you fast enough. (On a side note, the more famous version of this is red-shifting- which is what happens when objects are moving away from you. Looking around and seeing that on average galaxies are moving away from us, was the first indication what the universe was expanding) The idea perhaps even more in line with your question is Cherenkov radiation . This is caused when a charged particle (like an electron) travels though a medium faster than the phase velocity of light (So, there is a speed of light, c, which is the speed of light in a vacuum. However, a light way will propagate through a material slower than c, and some materials that can be significantly slower than c). As the charged particle moves through the material, it polarizes the material- and since an accelerating charge emits radiation, this will cause light to shine. If the particle is traveling slower than the speed of light in that material, then this light source will appear spherical. However, if it is going faster than the speed of light in that material, much like a sonic boom, the emitted light "builds up" on the front of the charged particle, much like how sound builds up on the front of a supersonic jet. |
If spacetime "isn't a thing", but just defined by the distances between events, how can it be curved?
This has been bothering me for a while. It comes up a lot that it's incorrect to talk about the "fabric of spacetime", and I've heard it said many times on this forum that space and time aren't actual physical things. If this is the case, then how does it make sense to talk about spacetime being curved? If it's not a real thing, but only exists conceptually when measuring the distances between physical phenomena, then how does it make sense to talk about gravity being the curvature of this thing that "doesn't really exist"? To my simpleton mind it seems like there are two options to describe the situation of two objects coming closer together due to gravity: The objects are directly interacting with one another (with a force as Newton thought). The objects aren't directly interacting but are embedded in some "medium" that is affected by their presence in some way which eventually changes their orientation with respect to one another. But if there is no medium, what is actually being affected by the objects' presence? Please someone help me.
there are no absolute measurements of distance and time. There are only measurements relative to some observer. This observer may be moving relative to another observer, or may be near the presence of energy (maybe in the form of mass). The way in which these measurements vary with observer location is by the mathematics of curved geometries. It doesn't mean that it's a thing to be curved or warped, just how the mathematics of it all works out. |
If I stood in an empty field away from civilization, would I be able to hear an earthquake?
Every video of an earthquake that I've ever watched is shot inside or near buildings/civilization and the accompanying sounds are much like what you'd expect: Glass shattering, people screaming, etc. Would an earthquake make any sound that I could perceive if it happened right below me? What might that sound like?
You might. As you've correctly surmised, teasing out what if any sound produced during an earthquake is generated by the seismic waves as opposed to cultural items (i.e. buildings, etc) breaking is difficult. The USGS has a discussion of reported sounds that occurred along with earthquakes . The sound as described is basically a booming noise, not unlike a sonic boom from an aircraft, though it's unclear if it would be as loud as one produced by an airplane. As referenced in the USGS page, some experiments have been run to try to determine what might be producing the sounds associated with earthquakes. Based on the timing of when they occur, it seems that the p-wave, the first wave to arrive after an earthquake, has the potential to generate a sound. S-waves, though stronger and usually responsible for most of the damage in an earthquake likely vibrate at too slow a frequency to produce a sound audible to humans (this is the explanation offered by those who conducted the experiment). |
How does the remaining area of a regular polygon with an incircle change as you increase the number of sides?
If I have an incircle of an equilateral triangle with radius r there will be a certain amount of area outside of the circle but inside the triangle. If I take the same circle and create a square around it so that it is the incircle of the square there are now four areas outside of the circle that are smaller than the three left in the triangle. Does the remaining area have any relationship with the area of the triangle? Does the relationship continue with polygons of increasing side #?
If we are inscribing the circle, which has radius R, then the apothem of the polygon is R. The area of a regular n-gon with apothem R is nR tan(pi/n). The area of the circle is pi*R . So the area of what is leftover is There isn't, then, any "nice" relationships between the areas for different n, aside from the fact that they are all described by this function. Though, the fact that you can approximate the area of a circle using regular polygons is equivalent to the statement that the limit of A(n) at n=infty is 0, which is equivalent to the limit of xtan(pi/x) at x=infty being pi, which is equivalent to the limit of sin(x)/x at x=0 being 1. |
What would happen if you built a bridge around the earth and broke all of the legs simultaneously? would it remain floating?
assuming it is evenly distributed so that one part isn't heavier than the other would it just float there since it's being pulled equally from all parts? ignore the viability of building such a bridge, i'm more interested on how the physics aspect works.
It's in unstable equilibrium. If a part is tiny bit closer to the Earth, it will be attracted more strongly and will fall. The opposite side, attracted less strongly, will rise. |
How do blood clots form?
What's the process. What's the material. How it's done.
Let's start with what a blood clot is; a blood clot, or Thrombus is a sort of plug or patch that stops bleeding, and it's composed of two things; Platelets, and Fibrin. Platelets a normal component of the blood, along with White Blood cells and Red Blood cells. Like red blood cells, they lack a nucleus; they're more or less cytoplasma fragments. When you get injured enough to clot, the inner surface of the blood vessel is disrupted, exposing a layer called the collagen; with receptors on the surface of the platelet, the platelets adhere to this layer, and change shape as well as excrete hormones and other chemical messengers. These chemicals activate more platelets, and together the whole thing starts to bind itself together out of platelets. Once this platelet plug is formed, the next step is the depositing of fibrin onto the clot. Fibrin is a protein, and, as the name implies, is fibrous. It's tough and insoluble, and it gives the clot a lot of strength. Eventually, the clot is reabsorbed by the body. This is, of course, a simplification of a biological process that's rather complicated. |
How does dehydration cause edema?
so, as far as i know, dehydration means lower blood volume, which means lower blood pressure, while edema is mostly caused by high blood pressure in the veins.
It’s more rehydrating after being dehydrated that can cause edema than being dehydrated itself. The body tries to pull too much water back into your cells when you take in water after being dehydrated which can result in swelling and, in more serious cases cells bursting. |
Does the presence of a measurement device alone effect particle behaviour in quantum physics experiments?
This question is coming from someone with no understanding of quantum physics other than youtube videos, but say you were to place a camera that was not on in the experiment, how would that affect things, etc.?
You might have the idea that "observation" somehow collapses quantum wavefunctions. In reality, it's actually interactions with a macroscopic object that cause the wavefunction to become decoherent - essentially to collapse. So it doesn't matter if the camera is on or off, as long as it's interacting with the quantum system, it'll "observe" the state. |
How does the heat produced in a reaction affect the rate of that reaction?
For example, in chemistry, we were discussing reaction constants and my teacher said that the constant only applied at a certain temperature. My friend asked then, how do reactions that feature change in heat over time affect the reaction constant?
The formula that relates reaction rate constant with temperature is the Arrhenius equation . As temperature goes up, the rate of reaction increases. Note that this is purely in terms of the rate constants (i.e., kinetics). Temperature can also affect the thermodynamics of the reaction - for example, increasing temperature in an exothermic reaction can shift the equilibrium towards the reactant, such that the reaction is no longer favourable. |
How does white protective suits, goggles and blue gloves protect you from radiation?
I was reading this article when I began to wonder about this question, but I have pondered this previously.
It's mostly so you don't touch or breathe the radioactive stuff directly, and so you don't take them home with you later either. Most shirts are enough to stop alpha and beta radiation. Some suits that are lined with dense materials can stop some gamma radiation as well. |
Why is it that when I chew gum for a long time, at one time it stops being chewy and elastic and becomes a granular, fibrous lump that's much softer? This transition happens pretty rapidly, in maybe a couple of seconds.
Anyone else know what I mean? Or do I have messed up oral chemistry? Either way, can anyone explain?
I've once read this somewhere and it had to do with components leaving the Gum-Base just like the favor leaves the gum.
I don't see how this could happen in a moment, and from my own experience I don't recognize such rapidness in the change. |
How do astronomers determine the radius of the moon?
From basics, we can determine how far away the Moon is by knowing how big the Earth is and then timing the progress of the Earth's shadow on the Moon during a Lunar eclipse. https://www.universetoday.com/91120/do-it-yourself-guide-to-measuring-the-moons-distance/ Since we can measure the Moons apparent size in the sky, once we know how far away it is we can use basic trigonometry to determine it's actual size. Nowadays we can use use lasers to determine the distance to moon very accurately thanks to reflectors left on the Lunar surface as part of the Apollo program. |
What is the oldest known biological ancestor we have, and do we have a name for it?
For example, we know more recent ancestors like Homo Habilis and Homo Erectus, but what's the oldest known ancestor? Something with fins? Some kind of bacteria? Who is our oldest relative?
There is the Last Universal Ancestor, which is the organism all extant life evolved and branched from. It was probably bacteria-like. Or are you looking for a more specific answer? |
If waves can be disrupted through destructive interference, and light travels in waves... Why can't we disrupt light?
I used to work with communications equipment in my last job. One of the things you could do to radio waves was broadcast at the inverse frequency to disrupt the signal. You can do similar things with sound, Wi-Fi etc. But why can't we do this with light? Is it possible?
In theory we can, visible light works almost in the same ways as radio waves. In practice it's more tricky, since we would have to precisely match all the frequencies and since they can be quite chaotic from every day sources, it's really hard. But in a lab under controlled settings it's just as with the radio waves, all you need to do is send a light pulse of the same wavelength and 180° off phase. |
Are there any species of biota native to North America that are invasive or destructive in other parts of the world?
I live in the Appalachian mountains and kudzu is a real problem in my neck of the woods/world. I was just wondering if any native North American species caused problems elsewhere in the world.
Nessie doesn't mention Muskrats , which are a big problem in the Netherlands because they damage our dikes. We spent about 30 million euro each year trying to exterminate them (and failing miserably). |
How close could a person get to the sun before they burned up completely?
Without the protection of the Earth's atmosphere, you would burn up right here. This is a big problem on the space station, where the sun heats the facing side to 250 F (120 C) . So the distance to which you can approach the sun is a function of your ability to mitigate the radiation. I know that's not a satisfying answer, but there you go. Soft, squishy human beings aren't build for it. |
If there are magnetic field lines are there gravitational field lines also?
If there are what is the significance of them and how do field lines relate to the waves in electromagnetic and gravitational fields?
Yes. Similar to how magnetic field lines give some indication of which way a dipole will orient at that location and how strongly, and electric field lines indicate the direction of force a positive charge would experience, gravitational field lines indicate the strength of gravitational force a mass would experience at a particular location. In the case of the Earth, these gravitational field lines would point towards the center of the Earth, and converge(indicating more force) as a mass moves toward the surface. Keep in mind these field lines are just visual depictions of the field. They aren't "real" in the way gravity is real, just representations. |
So I know about the colors of urine (dark means dehydrated), but what does cloudy mean?
My only thought on this is when it happened my previous meal was a bag of pretzels, but this has occurred before in a morning urination. Is it just my body expelling excess salt?
Cloudiness is caused by proteins, crystals, or cells in the urine, which are all normal. Cloudy urine isn't pathologic in itself. It also depends on cloudy it is, which you can't tell by looking at it in the toilet. When we look at it in the lab, there are 4 grades of turbidity: Clear, hazy, cloudy, and turbid. If all the urinalysis tests are normal, the only time we worry about it is if it comes up turbid. TL;DR It's normal. |
How is there economies of scale with both diminishing costs and returns?
If both marginal costs and returns go down as output increases, how can we have a lower marginal cost per unit of production?
Since you haven't yet gotten an answer, I'll respond even though this is outside my main area of study. Economies of scale and diminishing costs happen in different regions of production quantity. For a very simplified model, see here . Increasing output from Q to Q2 causes the average cost to drop, which we call "Economies of Scale". Increasing output past Q2 causes the average cost to rise, which we call "Diminishing Returns". |
Why don't the bubbles (head) created when pouring a beer dissolve quickly like bubbles produced when pouring pop?
If you pour a carbonated drink straight down (Pepsi, let's say), it bubbles up at the top, but these bubbles quickly melt away. A beer's head however dissolves much slower. Why is this? Similarly, when you pour pepsi onto ice cream in a glass when making an ice cream float, the bubbles don't melt away at all, why is this?
Beer, unlike soda, contains a melange of proteins from the grains and the yeast. Many of these proteins are amphipathic (i.e. they have sections that are hydrophilic, and sections that are hydrophobic, similar to soap), and, similarly to soap, these proteins help to stabilize gas bubbles. (I hope that someone can elaborate on the mechanism by which this happens, as I can't) |
If chips are square why are they produced in circular discs?
See this video for an example: it just seems like wasted material to me, but they are engineers so they must have a good reason.
Silicon crystals are produced in a process where they are continuously rotated and grow outward radially. It produces ingots like this , which are then sawed into the circular disks. As far as I know there is no process for growing similar quality crystals with a square cross section. |
Why are humans good at dealing with ambiguity as opposed to say, a computer program?
I think we could build a program that would understand ambiguity if we were to do something like build a database of every ambiguous statement we could think of, then define all possible meanings, then ask a program to choose the best based on the circumstances. Is that the same way we deal with ambiguity, just on a much more complex basis? Or is there something that makes us able to deal with it that no sort of computer logic will ever be able to match?
Ambiguous reasoning can easily be programmed. Look into fuzzy logic . One commonly-used idea is to represent beliefs with probabilities. The field of machine learning, the most popular subfield of AI today, is based around this concept. As a simple example, every time you use a credit card a program runs that tries to predict if the transaction is fraudulent or not. The program will return a number from 0 to 1, where 1 means it is positive it is fraud and 0 means it's positive it's not. The program is operating on ambiguity when it returns non-0 and non-1 scores, as it will almost always do. |
Is the boundary between X-Ray radiation and Gamma Ray radiation a "change of phase" like with liquids and solids?
No. The electromagnetic spectrum is a continuum - our names for the different parts are just where we happen to place distinctions based on observed phenomena. For instance, "visible light" is called that because our eyes are able to respond to it. X-rays and gamma rays even have different distinctions based on what field you are in. In astronomy, x-rays are any photon than can be focused using a grazing incidence telescope, and gamma rays are those whose energy is too high to focus. In physics, x-rays are photons that originate from motion of electrons or other charged particles, and gamma rays are photons from the decay of unstable nuclei. In this definition, x-rays can actually have much higher energies than gamma rays because we can accelerate electrons to such high speeds. |
If you become Paraplegic, would it make sense to amputate the limbs you have no feeling?
Why would you do that? Besides the risk of surgery, what if a repair treatment or assistive device is developed why would enable use of those limbs? |
How can (relatively) slow evolving human immune systems keep up with very fast evolving bacteria?
If the generation length ratio of bacteria to humans is something like 20 minutes:20 years, why can't bacteria just outrun the immune system recognition mechanisms, or destruction mechanisms?
There are two reasons for this, related to the innate and adaptive immune system. First of all, the innate immune system has, throughout evolution, been tailored to recognise invariant structures on the surface of bacteria. The reason these structures are invariant is because they are essential to the bacteria's survival, e.g. certain peptidoglycans. This means bacteria can be recognised on the basis of their defining characteristics. However, not all the bacterium's characteristics are predefined, and some bacteria can camouflage these invariant ones, which brings us to our next point. The second reason has to do with that our immune system is not pre-defined, and goes down deeper than our "standard" genome. B- and T-cells are able to randomly combine certain pieces of DNA in our genome, in a process known as VDJ recombination. This essentially yields a "randomised" gene, which codes for an equally random protein. These proteins essentially recognise every possible structure that there is to be found. To prevent our immune system from attacking structures in our own body, there is a round of selection that kills cells that recognise those endogenous structures. This way, 'foreign' structures (i.e., whatever isn't supposed to be there) are recognised for elimination from the human body. You might wonder, how come we don't instantly fight off any infection then? The answer is simple; because usually, only one or very few cells exist that recognise the structure present on the bacterium/virus. When an infection is detected, these cells are stimulated to divide and proliferate, a process which obviously takes time. Hence, while bacteria may evolve quickly during a few generations, we can adapt quickly a generation. Obviously this is a boiled down version of the truth, and there are many more intricacies which finetune our immune response to a given pathogen. But this should give you an idea of an answer to your question. Feel free to ask on though! Edit: clarity and some more info Edit 2: spelling. |
As space is a vacuum and laden with radiation bombardment, would a body on the moon decay, or last "for ever"?
I mean, on a rather atmosphere-less body such as the moon or an asteroid, would they essentially be there for eternity (in regards to human timescale). I assume eventually they would freeze and break up due to either, a lot of little collisions over time, or a (few) big collision(s)... but would any anaerobic bacteria be able to decompose it at all?
Aerobic bacteria still require air, they just don't require oxygen. In space, you would decay not from rotting but desiccation coupled with extreme temperature shifts. You'd dry out complete, and your remains would be in an environment that shifted between extremely hot and extremely cold. By extremely, I mean extremely, super duper hot and cold. In space you're exposed to sunlight, so all of the energy that's normally refracted through the atmosphere hits you directly, leading to temperatures in excess of 250 degrees F (120C) and as low as -380F and -230C! |
Prompted by the question about stars on the front page today, I'm wondering, is it possible for there to be a solar system with only planets? I.e., all planets in the system orbit around a much larger planet at the center?
It's possible, but it does depend on what you mean by "planet" for the thing in the center. If a star forms with less than about 80 times the mass of Jupiter, it won't have enough pressure to ignite the fusion of hydrogen to helium in its core. This fusion is the source of almost all of the light emitted by stars like our Sun. These "failed stars" are called . Brown dwarfs can be found on their own, as companions orbiting larger stars, or even as the central object surrounded by planets . Whether a brown dwarf is a star, a planet, or another category of thing altogether is a matter of definition on which people disagree, and it's pretty central to your question. For some people, a brown dwarf below 13 Jupiter masses - the threshold below which it can't burn deuterium - is a planet, so if planets form around such a light brown dwarf (and there's nothing wrong with this in principle), that'd be a positive answer to your question. But other people say the difference between a star and a planet is based not on mass but on formation - that stars form from the collapse of a cloud of gas, while planets are what form from the disks of matter that surround those newborn stars - and so if a brown dwarf forms the way a star did, it's not a planet. With that definition, of course, it's much harder to have a planet at the center of a system, because presumably it would have formed the way stars do. |
Why do we prefer muscles for vaccine injection?
Firstly, intramuscular and subcutaneous injections are not only easier on the patient but also on the trained professional. They're easier to administer and patients are often frightened of intravenous injections. Secondly, antigen-presenting cells (e.g., dendritic cells) aren't just present in blood but are largely found in tissue as well. They take up the antigen and process it for presentation to lymphocytes in lymph nodes. So, the vaccine doesn't necessarily have to enter systemic circulation and distribute throughout the body to be able to be picked up by antigen-presenting cells for developing an adaptive immune response. Thirdly, an intravenous bolus is administered virtually instantaneously into the blood, whereas intramuscular/subcutaneous routes can form a slow-releasing 'depot', which in-turn minimizes adverse events. A recent example is the Pfizer vaccine. A study conducted on mice found that, when injected intravenously, rapid onset myopericarditis was observed unlike the intramuscular route ( source ). This is because an intravenous bolus is administered rapidly into circulation, where it distributes throughout the body and triggers an inflammatory response, in the heart. An intramuscular depot is more localized and slow-releasing, in contrast. Another study found that intravenous typhoid vaccine is associated with cardiomegaly (enlarged heart). source |
If light moves at the same speed in all inertial reference frames, why does it get red/blue-shifted when you get closer to light speed?
I was playing around with and , and both included redshift. If light always moves at c relative to you, wouldn't the color stay the same?
The redshift/blueshift is a result of the perceived frequency of the light wave changing when switching inertial frames. How do you measure frequency? You count a certain number N of cycles of the wave and divide by the time T over which you observed those cycles. Okay, now suppose an inertial observer is traveling away from at some speed and emitting photons. What does he see the frequency as? He measures it to be N/T, and he measures the time T with a clock in his own frame. What happens if you observe the same N cycles? You measure those same N cycles as coming over a time S. Now since the emitter is moving away from you, S is larger than T just from considerations related to the classical Doppler effect. But, as you know, time also gets dilated, so that time T measured in the frame of the emitter is necessarily longer in your frame. These effects combine. The main effect is . So you think the frequency is N/S, which is smaller than N/T. The frequency has decreased; the light wave is redshifted. So redshift/blueshift is ultimately a byproduct of time dilation. (A better way to understand it is actually to view the energy and momentum of the photon as components of a so-called . When switching inertial frames, this momentum vector transforms just like the position 4-vector. Whereas we get time dilation for the position 4-vector, we get an analogous result for the momentum vector, which also mixes the components in such a way to cause the frequency to change.) |
Can you explain me "hyperbolic trigonometric functions" and how can they be of use?
For example, the formula for the composition of velocities in special relativity : s = (u+v)/(1+(uv/c ) can be understood as a hyperbolic trigonometric identity : tanh(a+b)=(tanh(a)+tanh(b))/(1+tanh(a)tanh(b)) |
Needing input on how to make this better/more accessible to people with little experience with Science.
to be honest, It runs long. It's a little repetitious. I would try to trim about... 1 quarter to a third of the runtime out. Start with your conclusion. Then justify it. This is the best approach to public presentation I find. People get bogged down in detail and by the time you get to the conclusion, they're bored or tired. Science is ___. Cat example (which was good, esp. the unnecessary data). evidence stuff. Another thing that is super useful the line between data points is much closer to scientific "law" and the big picture is much closer to "theory" than the public generally believes. Laws are simplified relationships between small amounts of data. Theories are ensembles of data that create a larger story. Finally, Skip the religious stuff. I agree with you completely, but it turn off viewers. Leave it implied with "no individual or organization" edit: ignore the runtime arguments. I think if you rearranged the discussion and had a little bit more focus on the "what is science" aspect, it would improve the pacing. |
Is "String Theory" even a theory? Should it better be called "String Philosophy"?
This is not trolling, but a serious question. Does it have any experimental predictions that can be used to verify / falsify it? My understanding is that with the landscape scenario there are at least 10 possible vacua (initial conditions) for potential universes and the anthropic principle is used to explain ours. Is this really a physical theory, or more a philosophical theory since it doesn't appear testable?
It's absolutely a theory. It's not impossible to test . It's just impossible with our current technology. It would be testable directly if we could build a particle accelerator about 10 times more powerful than the LHC. Such an accelerator would have to be about the size of the galaxy. It could also probably be tested directly if we could do experiments near the event horizon of a black hole. Even though we're not going to be able to do those experiments any time soon, there's evidence that we may be able to observe one aspect of string theory, known as the AdS/CFT correspondence, at very energies. This theory may be able to explain phenomena such as high temperature superconductivity. The landscape problem (the issue of having so many possible vacua) is a problem because we don't have a method of matching a vacuum at high energy to it's low energy limit. If such a method is found, then we would very likely be able to make predictions that would be testable at much lower energies. String theory is a very rigorous and well developed theory. The big question is, "is it a theory that describes Universe?" So yes, string theory is much more than a simple "philosophy." |
"earth/ground" node in electrical circuits, how does it work?
I can’t get my head around earth/ground in electrical circuits, from what I understand the Earth itself is a reservoir of free electrons and it was used as a return pathway in single phase power transmission systems back in the days, but how? And from where these electrons come from? The earth consists of rocks and dirt which they have a very high resistance to the flow of electrons, how can it be treated as a current carrier? The “ground node” as we refer to it is just a metallic rod/mesh buried in the ground
"Reservoir of free electrons" is probably a misnomer. Circuits are based on electrons flowing, not free charges. Separated charges are extremely uncommon. You are also correct that the ground is resistive: typically 10 - 1000 ohm*m, compared with 10 ohm-meters that is typical for metals. However, it isn't a total insulator. The ground is big, so the cross sectional area is typically big, and it is significantly more conductive than the common insulators, like rubber (10 ohms) or glass (10 ohms). In fact, the earth is about as conductive as undoped silicon (~10 ohm-m). Which isn't actually a coincidence . On the upside, the ground is super big - approximately earth-sized, in fact. The ground can conduct electrons just like any other circuit element, it just happens to be a bit bulkier than most circuit components. Plus, no one really cares if you accidentally melt the ground (unless you managed to melt a whole lot of it, I guess). As for why it is an easy source for electrons - the earth has a lot of capacitance. Because it is big. There is a limit to how quickly you can push charge in or out of the earth because it is so resistive, but pushing some current into it is unlikely to change the earth's average voltage by much. You can easily substitute for the earth with a really, really big capacitor. That is what mobile devices typically do. But big capacitors are expensive and heavy, so using cheats (like using the planet) can be effective cost-saving solutions. |
Do arterial blockages get diagnosed regularly before symptoms?
I realise it’s probably a selection bias at play but I seem to regularly hear stories where someone who was otherwise healthy and led a healthy lifestyle dropping dead from a heart attack with no prior symptoms. Are there non Invasive diagnostic tools available that can pick up any issues with a regular GP check up or do you generally just go to hospital after you have symptoms?
Exercise stress testing or cardiac CT angiogram can be used as screening tools to help prevent a potential myocardial infarction. Echocardiograms can evaluate for valvular heart disease.
Risk factor modifications controlling BP, diet exercise, keeping cholesterol in check are preventative medicine strategies to minimize cardiac issues. |
Why is the word "No" phonetically similar in so many languages while "Yes" seems to have way more diversity?
We're really looking at Indo-European languages here, which includes everything from Hindi to English to Ancient Greek. These languages all share a common origin - the proto-indo-european language, or PIE. PIE has been partially reconstructed from examining the huge number of current and historic languages in the family. It looks like there was a word for something like "not" or "no" in PIE that has a "ne" sound in it, and the child languages have mostly inherited that. That's why "no" is so similar across so many languages. However, there is no "yes" in PIE, which means that descendent languages have invented their own form, in many different ways. |
Why do LED lights "jiggle" ?
I've noticed this with all LEDs, but particularly on clock faces (which I guess aren't really LEDs). You know the old digital clocks on cable boxes? If you look at them, away, and back, the lights seem to dance around. What's going on with my eyes? EDIT: Thanks for all the answers! Upvotes for everyone!
The LEDs will be Multiplexed. Its primarily used as a way of saving I/O pins on your control circuitry. The most basic method would connect 16 LEDs as a 4x4 grid, which only needs 4+4=8 pins to control it. But doing this means that only a subset of the LEDs can be on at any one time (one row/column in this example) so each group is briefly lit in turn. when this is done fast enough your brain just sees a constant illumination, but the edges of our sight are optimised for noticing fast movement so your more likely to see the flicker when you look away. tl:dr: they are flashing to save money, you normally cant see it, but your peripheral vision sometimes can. |
How do we know that stellar black hole are not neutron star ?
How do we know that stellar black holes are not neutron star becoming too massive to let photon go away ? In other word, why a neutron star smaller than 3 solar masses "eating" an other star and reaching 3 solar masses collapse into a black hole ? Why this star doesn't stay a neutron star being invisible by physics ?
How do we know that stellar black holes are not neutron star becoming too massive to let photon go away ? If something is too massive to let light escape, then it's black - so by definition it's a black hole! But a black hole can't be a neutron star. This is because the speed of light is the universal speed limit - nothing can travel faster than it. So if an object's gravitational pull is so strong that light can't escape, it means that can escape. This means no force can overcome that gravity. So the gravitational collapse continues unimpeded until you reach a singularity (or some quantum gravity state). Neutron stars are what happens when the gravitational pull inward of a ball of neutrons is balanced by the outward of the neutrons. This means that the Pauli exclusion principle forbids the neutrons from being packed any tighter together than they already are. That counteracts gravity. But if the gravity is so strong that light can't escape, this means neutron degeneracy pressure certainly won't do any better, and so the gravitational collapse wins out. What you're left with at the end - a singularity or some other exotic state - can no longer be described as a ball of neutrons. |
Is it just a coincidence that Newton's Law of Gravitation and Coulomb's Law are so similar?
I couldn't help but notice that Coulombs law and Newton's Law of Universal Gravitation are remarkably similar. Coulombs Law is F=K (q1*q2)/r Newton's is F=G (m1*m2)/r This can't just be coincidence right? Is there a relationship between these two?
The short answer is that we see the force is proportional to the two "charges" that go into it, and is proportional the surface area of the sphere between the two. The latter part comes out of conservation laws and specifically has r dependence because we live in a 3 space dimension universe. |
Does perception of size and scale limit our ability to understand extremely large and small objects?
For example, if scientists had access to functioning models of an atom and a galaxy and both were scaled to the size of a football stadium, how much (if any) additional information could be gained by using the instruments and technology currently available?
The nature of these objects makes it impossible for this to occur, thus we couldn't have them, they would not possibly have the same properties. If an atom was big enough to see, it would not be an atom, same with the galaxy. If my aunt had a penis, would she still be my aunt? |
Fluorinated vs. Fluoridated?
One of the cases I was reading for law school was disucssing an issue over water being fluoriDated. This confused me because in my lab experience when fluorine is added to something it the term was fluoriNated. Does the change in terminology have to do with the oxidation state of the fluorine, or something else entirely? Thanks in advance for your help!
Fluorination is the addition of a neutral fluorine atom to a molecule. Fluoridation is the addition of a negatively charged fluoride ion. |
Are there any planets larger than stars? And if there are, could a star smaller than it revolve around it?
I just really want to know. Edit: Ok, so it is now my understanding that it is not about size. It is about mass. What if a planets mass is greater than the star it is near?
We are sitting on a planet larger than some stars! White dwarfs , the endpoint of stellar evolution for most of the stars in the universe, are stars that are roughly Earth-sized. While all white dwarfs have radii smaller than Jupiter, for example, Jupiter would still orbit around a white dwarf (and not the other way around) because white dwarfs are very very dense. |
Why does an antenna not look like a lightbulb?
From my basic understanding, both antennas and light bulbs emmit electro magnetic radiation but from what they look like, they are completely different. What about microwaves? I know x rays machines look like cameras, but they absorb radiation and not emit radiation, so it makes a bit more sense. Where is the x ray camera flash and how does it work in comparison?
There are many ways to release electromagnetic radiation, and the object's share will depend on the method used, as well as the wavelength you wish to create. Standard light bulbs work via incandescence. This is (approximately) black body radiation . Black body radiation is similar to fire- you make something hot enough and it gives off visible light (in fact, things at every temperature give off electromagnetic radiation, but cold things give off radiation which has too long of wavelength for the human eye to see, so they don't appear to glow. This is how thermal cameras work- they simply see a higher wavelength light than human eyes). An antenna, on the other hand, wishes to make a very controlled signal, so it can encode data in it. Thus, you wouldn't want to use black body radiation, because that just produces random radiation. Instead, it produces electromagnetic radiation by accelerating charges from one end of the antenna to the other. An accelerating charge makes a propagating EM wave, and the frequency that you move that charge at determines the wavelength of the EM wave you make. In general, you want the length of your antenna to be about as long as the wavelength you're trying to make. That's why car antennas are about 3 feet long- radio waves are "around" a meter long (they really vary based on which part of the radio spectrum you're looking at). LEDs on the other hand work via Electroluminescence which is a more complicated method of making light. |
Anti-Particles
Physics Why don't anti-particles flow backwards in time? Keep in mind that I am dumb, I honestly feel like I should know why but I don't.
Anti-particles do not flow backward in time. What would it even mean for something to flow backwards in time? However, it's a useful calculational tool when computing scattering cross-sections to replace the absorption of an anti-particle moving forward in time with the emission of a particle moving backwards in time, because it's simpler and you get the same answer either way. |
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