Temperature Control for Fermentation

Question: I am curious how everyone controls the temperature of their primary, especially those that live in the warmer climates.  In Florida, where the temperatures can soar and remain in the 90's and above for months, it can be a challenge to keep the house at what is considered "acceptable" temperature for fermentation.
Comment: Also, best practices for the opposite problem: it's *too* cold for ales?
Answer: The wet t-shirt and swamp cooler method is probably insufficient for temperatures in the mid 90's.
Controlling fermentation temperature is one of the best things you can do to make good beer!
Like Florida, the temperatures in East Texas get stupid-hot eight months out of the year.  Last year I built myself a duck-in cooler powered by a small window air conditioner.  I can get the temperatures down to the mid-sixties, and probably further if I take apart the AC's thermostat.  See my blog for details.
A fellow brewer recently donated a chest freezer to me and I had a Johnson Controls external thermostat.  This combination is ideal for fermenting because the freezer fits a few carboys and the thermostat keeps the temperature within 3° F of your target.  I made my first (real) lager, a CAP, in the freezer.
There is also a Low Tech Lagering DVD.  I have not seen it yet, but I trust that James over at Basic Brewing Radio knows what he's talking about.
Comment: The duck-in cooler cost me about $300.  I have not been able to measure the energy consumption because I moved to a new house just before installing the thing.  No historical data.  My little project was inspired by Jamil's brewshed (http://www.mrmalty.com/brewstuff.php).  He figures it costs him $2-3 per month.
Comment: Now THAT is impressive and awesome.  How is the energy efficiency?  Have you noticed a significant electric bill increase?  What was the final cost of the project?
Comment: Ummm... Wow! That's a great set up Dean. I may need a freezer for these increasingly hotter summers in Denver.
Comment: The duck-in cooler cost me about $380. I have not been able to measure the energy consumption because I moved to a new house just before installing the thing. No historical data. My little project was inspired by Jamil's brewshed (http://mrmalty.com/brewstuff.php). He figures it costs him $2-3 per month (to cool a much larger space to a lower temperature).
Answer: One of the cheapest solutions I have heard of is to immerse the carboy in a Rubbermaid water cooler filled with water. The water will act as a great insulator. To heat or cool to keep the temperature within the range you are looking for you can use a fish tank heater and ice packs. This method obviously means you will be needing to check on your beer quite often, but more so if you are trying to cool it with the ice packs (every 4 -6 hours). The heating part of it requires little attention, since you would get to set the thermostat. The thing that is most appealing about this solution to me is that it does not take up much more space than the carboy normally did. I have never actually done this, but the method was recommended to me by my local homebrew shop.
Rubbermaid water cooler $68: http:// www.amazon.com/Rubbermaid-1610-01-11-DISC-10GAL-Orange-Cooler/dp/B00002N9F4
Aquarium heater $22: http:// www.aquariumguys.com/ebojager4.html
Here is a link to a more automated version of this solution:
http://www.homebrewtalk.com/f51/water-fermentation-chiller-81501/
Answer: Build a fermentaion chamber.
http://web.archive.org/web/20070206150821/http://home.elp.rr.com/brewbeer/chiller/chiller.PDF
Comment: Um, want! Also, nice linking prowess.
Answer: One of the best homebrew purchases I ever made was a dorm-style mini fridge (without freezer) that I removed the shelves from to create the perfect-sized fermentation fridge. This is controlled by an external Johnson controller, allowing me to dial in whatever fermentation temperature I want. It's ideally sized for buckets and carboys.
The fridge cost about $200 new, plus you'll need some kind of flat material (I used plexiglass) to secure the rubber seal back onto the inside of the door after you remove the door shelves.
Now the only problem is I wish I had a second one for double batches or for lagering. I bet you could lager at least 2 or maybe 3 batches in cornies at one time. Edit: I can fit 2 cornies in my Sanyo 4912.
Answer: I'm in Vegas and have the same challenge. During the summer my house is usually at or near 80 degrees inside. I intend to eventually move to a chest freezer and thermostat, but for now I use a low-dollar method similar to what Jordan recommended. I just put the carboy in a Rubbermaid storage bin (instead of a cooler), fill it half-way with water, then drape towels/rags/shirts over the exposed part of the carboy making sure both ends hang in the water. If normal evaporation isn't doing enough to keep the temp down I have a small fan that boosts the effect. Two problems: you have to make sure the water level doesn't drop too far and this may not work well in FL due to the high humdity.
Answer: Use your basement or buy a mini fridge and set the temp to 70.
Comment: Basement?  Heh... I am in Florida.  Basements are few and far between here.
Answer: Nowadays I'm using a thermostat plugged in an old fridge with a probe inside the fridge. So I can program the temperature the fridge will stay.
Comment: What if the fridge gets too cold? Like, it's a nuclear winter and your fridge is 20 degrees below your temp setting?
Comment: Well, I live in Brazil, it's difficult for my fridge gets too cold! :P
My solution only works for hot countries.
Comment: @PJ (but mostly for the benefit of future readers): you can get a two-stage temperature control.  Hook one up to the fridge, hook the other up to a heating pad, space heater, reptile lamp, or other heat source.  Then you can tape the probe to the fermenter and be sure that it stays at exactly 68F or whatever temp you want.
Answer: I use an old fridge in the garage.  Got an Inkbird controller which has two sockets attached - one for the fridge and another for the heat pad under the fermentation bin. Thermometer probe is in a makeshift pocket inserted through the lid so that it's below the surface of the brew. Now I can control the fermentation temperature to a one degree Centigrade range including the initial fermentation exotherm.  You can take the boy out of chemistry but you can't take chemistry out of the boy...

Temperature Control for Fermentation


Can I restore raw development changes for moved Lightroom files?

Question: I recently started using Lightroom. I am now aware that you are supposed to manage images within Lightroom, but unfortunately I moved a bunch of directories in Finder and synchronized them via Lightroom. I've now lost all my raw development settings. Is there a way to get them back? I see Lightroom doing a backup sometimes when I start.
Answer: Lightroom generally stores the changes you have made and the history of changes you have made in the lrproj file.  If you have moved the images, it is still possible to use your existing project, however you must first tell it the location of the new files.
When you view the catalog in your original project, it should show little question marks overlayed in the corner of the thumbnails for the images that were moved.  Click this question mark, select the new location.  It should automatically detect any other files that were moved to the same location after you do the first.
Answer: Lightroom backs up your catalogue in a database file. The changes to development can be saved to a sidecar file (xmp) or directly in the image.
If you have xmp sidecar files enabled, you should still have them in that folder in finder. If you are gettin "?" next to folders in your catalogue, you can just tell lightroom where those folders are.
It is important to keep your folders and files organised, by copying to your library, and if necessary, duplicating to a backup drive when you import.
Answer: In the end I ended up importing two backup lrproj files Lightroom had made automatically into my current project. This resulted in up to 3 duplicate virtual copies, but it also restored all of my development adjustments. I then created a new smart collection that filtered all virtual copies without adjustments. Steps can be found here.
http://blogs.adobe.com/jkost/2013/05/finding-virtual-copies-that-have-not-been-changed-in-lightroom.html
This allowed me to remove all the duplicates I had not applied development adjustments too. The rest I can manually remove if I ever revisit the adjusted files.
Answer: I screwed up and moved my catalog without having the XMP data backed up. Was at a loss for answers but stumbled across this free Lightroom add-on that rips adjustments from JPEG files. Thankfully, I had exported my images to JPEG to post to a website. So I only had to load each photo and rip the data for each one. It doesn't reset your rotations or crops, but heck... it saved me from starting at zero.
http://www.capturemonkey.com/presetripper


How can I enable Internet Explorer 7 with the Utilu IE Collection on Windows 7?

Question: I can't enable Internet Explorer 7 with the Utilu IE Collection. I have Windows 7 64-bit. What can I do?
Answer: I believe you will have to use a Virtual PC or any other Operating System simulation. This IE collection was my last hope too.
Developer mode of IE9 rendering IE7 is not the same as the real IE7! The same goes for IE8.
You can only test it for simple positioning of elements (padding, margin, etc is rendered okay in the developer mode). But other things...
I will name you one simple example as proof, but I have encountered way more differences, which will fail in both IE7 and IE8 but will not show in IE9's version of those browsers:
The inline css: background-image: url(testimage.png);filter: alpha(opacity=50); will fail in any version < IE9.
Thus, you can certainly not rely on developer mode.
Answer: For testing old IE(7 and 8) Im using windows xp mode. Its free and legal from microsoft and you can make drive for changes and restore it back when you need. And beware changing IE 9 mode in dev tools like Yeti sayd.
Answer: Run something else.. since the Utilu website explicitly says IE7 won't run on windows 7 64 bit on their website. On the other hand, i do believe you can run the IE7 rendering engine on ie8, which does run natively on windows7 64 bit using compatability mode -> tools -> developer tools "browser mode" , without any additional software.


Equivalent Scale in UX like the Cooper-Harper Scale?

Question: Is there an equivalent scale in UX as the Cooper-Harper Scale or the Cooper-Harper Ratings are in Handling Qualities Engineering in Aerospace? The Cooper-Harper scale associates a quantitative value to the ability and ease of completing a task in prefer and acceptable ranges such as time to complete task or the precision of the task as well as how easy was it to meet or exceed those criteria?
Comment: @MichaelLai, good points about non-linear tasks. Cooper-Harper doesn't care about how you get from point-A to point-B, it is simply a subjective assessment of how difficult it was to get there. In combination with observational data, it is still a very good scale on workload. Certainly, if your testing doesn't reveal *how* the user got from A-to-B the data is near useless -- even for a linear task, you have to see where the user goes off the tracks. It would actually be fascinating to see a non-linear task take more steps than designed and still be rated with a low workload.
Comment: There may be such a scale, but I think you'll find that unlike in engineering (and further more in aerospace engineering) there isn't really a standardized process for completing specific tasks, and so the utility of creating a scale like this is going to create as much problem as it helps to solve.
Comment: @MichaelLai, usability testing is often about completing a specific task and it isn't uncommon to have a single (or limited number of) way to complete it. Cooper Harper helps to measure the workload of that task completion. Are you referring to a different process where Cooper Harper is less appropriate?
Comment: @EvilClosetMonkey Yes, I think there are many interactions on websites (especially social networking types) that don't necessarily have a specific start and end point (plus the interactions/flows in-between). So the use of the Cooper-Harper scale or its equivalent for UX would most likely be limited to those linear or defined tasks/use cases. In which case you are better off looking at completion rate analytics anyway.
Answer: Yes, there are modified Cooper-Harper Scales that measure operator workload. It involves some basic tweaking from "pilot" to "operator".
Here is one such representation of the Modified Cooper-Harper Subjective scale:

I used these modified scales many times to measure acceptable operator workload for multiple defense department and aerospace programs, which didn't target a pilot.
One of the advantages to this simple modification is that many are already familiar with the source material. Especially if you are dealing with aerospace or defense department programs. The ability to demonstrate workload on a scale that is already familiar makes telling your story easier.
Comment: Cooper-Harper isn't something done instead of other analytic tools, it's an option to add to the overall suite. When combined with completion rate, for example - not being able to complete the task is an automatic 10 on Cooper-Harper, but completing the task can be 1-to-9 on the scale. Cooper-Harper is an option within any "usual form" of usability testing.
Comment: As to linear tasks - are you referring to tasks that have one, and only one, path? While that would be rare, Cooper-Harper doesn't care. It's a measure of perceived workload - so one user may take 10 steps to complete and score the process a 8; while another might take 20 steps and score it a 3. By having observational techniques in place you can review why Person-A thought it was so hard while Person-B thought it was pretty straight forward, but took twice as many steps. It may have been they took different paths and Person-B just found their path very intuitive.
Comment: Where you have applied the Modified Cooper-Harper Subjective scale, have they been for linear tasks? How does it compare to usual forms of usability testing using analytics and completion rate?
Comment: I've applied it in situations where the available paths were singular, limited, and robust.
Comment: I take the term linear to mean that there is at least a defined start and/or defined end point. It might vary depending on the individual or task where you meander within the system, but the end point is the same. I use the term non-linear to mean that you can start at more than one point and finish at more than one point.
Comment: And your thoughts on the NASA-TLX and SWAT as suggested by Kristiyan? I assume that C-HS takes into account the time and frustration components into the mental workload dimension, but doesn't take into account physical factors (e.g. clicks and scrolls on the page).
Answer: If you want to measure the cognitive workload the most famous scale is NASA-TLX scale. SWAT is other one which is widely used. However they are multidimensional which means mental workload is calculated based on more than one scale, unlike Cooper-Harper.
If you want to measure the usability you can use SUS scale, which is the widely approved and used for usability evaluation.
Comment: +1 I found NASA-TLX and SWAT both very good scales, so thanks for contributing to the answer. Have you used it much in past projects? SWAT seems a little outdated and simplified versions have been proposed, maybe you would like to update your answer as well?
Comment: Yes I've Used NASA-TLX and it gives valid and comprehensive results. There is a calculation stage which is OK to be ommited. Actually, in cognitive psychology field this is the most used and referenced scale for measuring mental workload. So it is a safe bet as its validity and diagnosticity has been tested by numberious researchers.


Why was RLP chosen as the low level protocol encoding algorithm?

Question: Is this an ad-hoc decision? Why RLP? Is it specifically suited to something?
Comment: See the design rationale:  https://github.com/ethereum/wiki/wiki/Design-Rationale#rlp
Comment: @dbryson Yes thought exactly as you as I was typing answer and not sure how it could be explained better than that source.
Answer: RLP was chosen because of (1) simplicity of implementation, and (2) guaranteed absolute byte-perfect consistency.
Source is Ethereum Wiki:

RLP is intended to be a highly minimalistic serialization format; its
  sole purpose is to store nested arrays of bytes. Unlike protobuf, BSON
  and other existing solutions, RLP does not attempt to define any
  specific data types such as booleans, floats, doubles or even
  integers; instead, it simply exists to store structure, in the form of
  nested arrays, and leaves it up to the protocol to determine the
  meaning of the arrays. Key/value maps are also not explicitly
  supported; the semi-official suggestion for supporting key/value maps
  is to represent such maps as [[k1, v1], [k2, v2], ...] where k1, k2...
  are sorted using the standard ordering for strings.
The alternative to RLP would have been using an existing algorithm
  such as protobuf or BSON; however, we prefer RLP because of (1)
  simplicity of implementation, and (2) guaranteed absolute byte-perfect
  consistency. Key/value maps in many languages don't have an explicit
  ordering, and floating point formats have many special cases,
  potentially leading to the same data leading to different encodings
  and thus different hashes. By developing a protocol in-house we can be
  assured that it is designed with these goals in mind (this is a
  general principle that applies also to other parts of the code, eg.
  the VM). Note that bencode, used by BitTorrent, may have provided a
  passable alternative for RLP, although its use of decimal encoding for
  lengths makes it slightly suboptimal compared to the binary RLP.
Comment: By the way. I often see the phrase "RLP was *chosen*" but I don't see anything to suggest that RLP existed outside of Ethereum. Am I correct in saying that RLP was *designed* for Ethereum, and is specific to Ethereum? The Yellow paper specification does in fact recognize positive integers as part of the RLP spec, so it is not data type agnostic, and has special requirements for their encoding.
Comment: Thanks all, I was unaware of the design rationale document.


Cold Air Intake and Engine Wear

Question: I'm contemplating whether or not to retrofit my car with a cold-air intake and performance air filter. Will doing so lower the lifespan of my engine? That is to say, increase likelihood of engine repair, relating to the aforementioned alterations, in the future?
Comment: bought a k&n performance filter ...
Comment: What brand air filter will you be using?
Comment: good choice. make sure to buy the cleaning kit and maintain it properly
Answer: It will have no affect on the longevity of the engine or components as long as you get one with a decent filter on it. You'll have to check reviews on different elements to ensure you are getting one which is good. We'll not mention which ones I think are better, as that gets into the realm of both shopping and opinion. In and of themselves, CAI's will not cause any harm to the vehicle's engine.
Comment: Doubling down on the filter! It is very important that you get a good filter like a K&N and do proper maintenance on it. A cheap filter can and will let dirt into the intake. You would be slowly sandblasting your engine's inside. Not good... :)
Answer: Some people think that a cold air intake will generally improve engine performance, allowing fuel to combust at lower temperatures, increasing fuel efficiency. They believe the lower temperature is actually better for the engine. Performance air filters, if you get a good quality one, might typically allow more air flow while reducing foreign particulate that can enter the engine, so might also help improve engine life.
However, that increase in air flow and lower ignition temperature could potentially provide improved performance, and if you take advantage of that performance by driving more aggressively, then you will negate those benefits and shorten engine life. If you maintain a similar driving style, then the engine will benefit from the change.
Comment: I highly doubt that putting on a CAI system will make the fuel "combust at lower temperatures". The air temperature difference is a few degrees at best, and the fuel efficiency part isn't really related to combustion temperature as well. Do you have anything to back this up?
Comment: http://auto.howstuffworks.com/why-install-cold-air-intake.htm
Comment: Could you point out where exactly it mentions combustion temperature? The article is about denser air and lower restriction, which is what the CAI is about. That increases airflow, and if airflow was the choke point - power. What about the fuel combustion, fuel efficiency? The performance air filter improving filtering part is shady as well, tests show that while less restrictive, performance filters usually filter air worse than regular paper filters, which is quite natural. Any arguments?
Answer: This very much depends on the type of engine you have.  For naturally aspirated engines, these filters should have no effect on longevity.
However, a word of caution, if your car is forced induction (i.e. Turbocharged or Supercharged) not only will the modification have little effect but I have seen instances where the size of particles allowed to pass through the filter can damage the charger.
Particularly susceptible to damage are the G-ladder Supercharger seals fitted to Volkswagen G40 and G60 engines.
If you have a forced induction car, an Intercooler (or larger Intercooler) would be a more suitable modification and yield the kind of returns you would expect from a performance filter on a naturally aspirated car.
Remember, anecdotal evidence gathered on the rolling road by the likes of tuners such as Guy Croft suggests a 1bhp gain for every 2 degrees Celsius lower the intake temperature is (down to about 40 degrees C).  Don't do too cold or fuel can start to drop out and ice up in the inlet tract.  This is less on an issue for fuel injected cars.
Comment: the car is a '09 vw gti.
Comment: An '90 GTI will be forced induction and already will have a turbocharger and intercooler
Answer: It's important to get a good cold air intake that actually takes in cold air.
Some kits that call themselves cold air intakes, are actually just exposed underhood pod air filters taking in hot air next to the headers. In a high compression engine that already operates near the detonation(knock) threshold, taking in this heated air can sometimes cause engine damage from detonation.
Answer: Cold air intakes can filter down to 50 microns if maintained and cleaned. You can see projected visable light through the small holes of the filter. If it is a daily driver you might want to stick with a regular filter but if it is not the extra flow is worth it.------"The ISO 5011 standard (formerly SAE J726) defines a precise air filter test using precision measurements under controlled conditions. Temperature & humidity of the test dust and air used in the test are strictly monitored and controlled. To obtain an accurate measure of filter efficiency, its very critical to know exactly the amount and size of test dust being fed into the filter during the test. By following the ISO 5011 standards, a filter tested in England can be directly compared to another filter tested in California. The ISO 5011 filter data for each filter is contained in two test reports. Capacity Efficiency and flow restriction.
Without boring you about how the test works, suffice to say they add a controlled amount of dirt to the filter while monitoring its flow capacity. They also monitor the amount of dirt passing through the filter. Various filters were tested being the: AC Delco, Purolator, Baldwin, K&N, and AMSOIL.
Comparing the AC Delco (rated the best from the test results) to the K&N: The AC Delco filter test ran for 60 minutes before reaching its max restriction while the K&N and AMSOIL filters each ran for about 24 minutes before reaching their max restriction. Another interesting bit of information is that the AC Delco accumulated 574 gms of dirt and passed only 0.4 gms. After only 24 minutes the K&N had accumulated 221 gms of dirt but passed 7.0 gms of dirt. Comparing the K&N to the AC Delco the K&N plugged up nearly 3 times faster, passed 18 times more dirt and captured 37% less dirt. The AC Delco filter which passed the smallest amount of dirt and had the highest dirt capacity and efficiency but also had the highest relative restriction to flow. Obviously the better filtering media is also the most restrictive".
Comment: Is there a link for this? I'd be very interested in seeing the results of these tests.
Comment: Is this where you got this information? http://www.billswebspace.com/AirFilterTest.htm
Answer: It can cause damage because if your putting too much air for your fuel injectors to handle, the air fuel ratio will be too lean causing damage to your engine.
Comment: Maybe you should provide some reasoning as to why a too lean air-fuel ratio will damage an engine. The engine may idle more roughly, it may have less power, but if the air-fuel ratio could damage an engine, I don't see how, but maybe I'm missing something.
Comment: Have you heard of the `"lean-burn" engines? worth some time to read about...

Cold Air Intake and Engine Wear


Muscle size and explosivity

Question: Seeing guys like Bruce Lee, there doesn't seem to be any correlation between muscle size and explosive power. Is this correct?
In terms of musculature, how does the body create explosive power?
Comment: It might help if you defined what *you* mean by explosive power, and how you see it being applied.
Comment: Are you referring to 1" punch kind of stuff, when you say 'explosive power'?  Trying to consider the exact context.  Powerlifters for example can have explosive power in at least one sense, but are not built like Bruce Lee typically.
Comment: Yes, I do mean punching and kicking
Answer: Physics wise, power is what we're typically talking about here:

That is, how much work can you do (Work = F * D) and how quickly can you do it.
We also know

Force = mass * acceleration.

Furthermore, we can break up the Power equation to be,

Power = Force * D/T,

which is,

Power = Force * Velocity

In other words, we can clearly see force is part of the story, and something perhaps much more intuitive is how much force a muscle can generate is clearly related to how big it is.
So, ASSUMING you can generate more force over the same period of time, then having more muscle size will correlate with producing more power i.e. being more explosive.
A car analogy is often helpful. Throw a bigger engine in the car, it can produce more power.
But, you can't leave the rest of the car alone. At some point, a bigger engine is going to infringe on the limitations of other parts of the car. Maybe you need bigger bolts on the wheels. Or a bigger exhaust. Or a driver with less fear of pressing the pedal. I'm no auto expert, but I think you get the idea. You can't treat the entity as only one part.
This is where biology laughs at classical physics. It's just never straight forward. You simply can't tell someone "get more muscle" and assume they'll be more explosive.
Most obviously, a lot of people who try to gain muscle also gain a lot of fat. If they gain more weight than they gain power, their power to weight ratio would go down. They may very well end up slower! (And this is why drugs are so prevalent at extreme levels of performance. They make it a lot easier to gain muscle with less fat.)
Some specific examples
Furthermore, the distance you're looking to generate your power over can change your "effective power" too. NFL athletes are a nice example.
If you want to generate a lot of power, but only very briefly? You might end up wanting to be very big, ala the linemen.
Want to generate that power for a bit longer period of time? You end up smaller, ala linebackers and running backs.
Want to generate the power over even longer distances? Even smaller, ala the defensive backs and receivers.
Track athletes also work. As we go from 100 meters to say, 800 meters, everybody gets skinnier.
In fact, I've heard Lance Armstrong talk at length about power to weight ratio. It doesn't get much longer distance than the Tour de France! And, consequently, athletes don't get much lighter than Tour de France cyclists.
As an aside, one reason I believe you see this inevitable decline in body size is the body's ability to dissipate heat is critical. Bigger body = more power = more heat generation. The body is incredibly good at not letting itself overheat.
Relatedly, one reason African Americans dominate power events (provided the event is running oriented) is because of their body structure, which is related to their more recent African descent, which is related to their ability to dissipate heat
The longer the (running) event is, the more dominant African Americans become.. (You see white NFL linemen. You don't see white NFL cornerbacks.)
The Freaks
As for why you do come across some skinny dudes who hit like trucks, that's where the nervous system can come into play. As far as I'm aware, Charlie Francis, the best sprint coach, and probably best sport coach ever, first introduced this, paraphrasingly, "it's not just how fast you can contract. It's how fast you can relax."
When we contract a muscle, that generates stiffness. You can't go into a subsequent contraction until that contraction relaxes. If you flex your hip up to run, you need to relax that hip flexion so you can next go into hip extension.
More recently, I've seen Stuart McGill formalize this as "muscle pulsing." Applying it to MMA athletes. Here's a nice little read, that actually references Bruce Lee: https://www.backfitpro.com/documents/Strikefasterandharder.pdf
Answer: Maximum potential muscle strength is measured in PCSA
Muscle mass \cosine\fiber length
So muscle size is important for strength, math is not an opinion.
Potential overall strength also depends on sinew limit, most of the time sinew is the limit factor and not muscle because muscle is actually stronger than connective tissue.
MassLimit_{sinew} = TensileStrength_{sinew} \times (2 \times \pi \times Radius_{smallest load bearing bone} \times (Height \div 4 \times 0.1) \div Acceleration_{gravity}
And muscle efficiency is a thing too, some people can use a greater percentage of their muscle mass at once than other people, the difference is minimal most of the time but extraordinary rare exceptions do exist. Probably not the case for Bruce Lee most likely he just had really strong connective tissue and average muscle efficiency.
But you also have to consider that Bruce Lee was mostly training with isometrics and anecdotally speaking most trainees that use isometrics have great strength while being as skinny as Bruce Lee, look into calisthenics.
However I don't know any study that compares the outcomes between isometric training and normal training.
There's also the bone limit to take into consideration, no matter how strong your tendons and muscles get, if the skeleton can't keep the pace the body will just fall apart.
The smallest bone by cross section to bear your weight will be your limit. The chain is as strong as the weakest link.
You can only pull up as much weight as your finger bones allow you or you can only squat as much weight as your feet allow you.
bone area (pi \times radius\times radius)
Comment: This answer desperately needs references; Math is not an opinion, but biology is... And, the math you are referring to need biology and biomechanics to justify its usage; You know, just like physics formulas need postulates and experimental evidence to justify their usage.
Answer: Generally, while fast twitch muscles are "larger" in their cross-sections than slow twitch, that is not the reason for the increased force production. Muscles can be trained in a couple of ways, most regularly, hypertrophy, that is, increase in the cross sectional diameter, or explosively, meaning that the potential of force/strength of the contraction of the muscle increases. For this reason, you'll never see tried and true bodybuilders, whose ultimate goal is hypertrophy, performing gigantic numbers in the big three lifts, the Olympic lifts, vertical jump tests, or sprint tests. In fact, body-building in itself is inherently "unathletic," in the sense that doing high ranges of reps (12-20) produces tremendous growth, but no improvement in contractile potential. Bringing this back to Bruce Lee, one could guess that he never really lifted weights for hypertrophy, but most, if not all, of his strength and conditioning work was focused on very explosive, very quick-twitch based movements, which ultimately increased the contractile potential of his muscles, but not his size.
Comment: Bruce Lee DID train for hypertrophy though.
Comment: I don't think Bruce Lee's goal was hypertrophy. I'm not exactly sure, of course, but I never read anything about him saying his goal was to be as large as possible, or even large at all. His goal was explicitly martial arts related, meaning he trained for speed, quickness, and dexterity. Doing loads of pushups, sit ups, pull ups, and other body weight exercises does not count as "training for hypertrophy." If that was the case, no body builder would ever load up a barbell.
Answer: I think the biggest limiting factor for most people is that we do not have the ability to recruit all muscle fibers in a muscle at the same time.
This is a property of the "electrical wiring" from the brain to the muscles and does not add size. Only a few people are born with this explosive ability. It can not be trained.
Type of muscle fibers also play a role; a person with mostly fast muscle fibers will have more power than another person same size with mostly slow but enduring muscle fibers.
Finally I think an "explosive punch" is only part strength. It is also technique and timing.
Comment: Shouldn't this be a comment instead of an answer? I mean, you don't go in depth and start off with "I think", which strongly indicate that this is mere speculation.

Muscle size and explosivity


Excel Web Services Error

Question: I have uploaded an xlsx file that I would like to use EWA to display using Excel Web Services.  I have confirmed that the site is a trusted location and Excel Web Services is configured correctly from Central Admin.   A simple spreadsheet works fine and renders in browser.  However, for one particular worksheet I get an error when I try to point the EWA web part to it.  It is indicating that it contains the following features that are unsupported by Excel Services.  The error references sharepoint lists as the feature not supported.   What is SharePoint Lists referring to?  I removed the data connection that existed in the workbook but that still didn't work.
Comment: Did you ever find the answer to this that you can provide?
Answer: If I am  not mistaken you cannot use a SharePoint list as a datasource in an Excel sheet which in turn is displayed as a web drawing. Now with SP2010 there are ways to work around this:
Microsoft SQL Server 2008 R2 PowerPivot for Microsoft Excel 2010
User-defined functions (UDFs)
Web Services API
Java Script Object Model (JSOM)
But because your tag is SP2007 I am afraid it won't work.
See :
MSDN reference

Excel Web Services Error


What is the role of glucose in plasmid isolation?

Question: My understanding is that glucose is used in the resuspension solution to prevent cells from bursting by maintaining the appropriate osmotic pressure. Why do we even bother doing this? The cells are going to be lysed with the addition of the SDS+NaOH, and we have EDTA in the resuspension solution to chelate Mg, thus inactivating nucleases.
Answer:
This is a common misconception: in fact, in the alkaline lysis method for plasmid isolation, the glucose does not act as an osmotic stabiliser.

Glucose is present in the resuspension buffer at 50 mM. This concentration is not high enough for osmotic protection of spheroplasts formed by lysozyme treatment: from memory, 0.5 M glucose is typically used for stabilisation. So why is the glucose included?
The original method for plasmid preparation by alkaline lysis was published by Birnboim and Doly in 1979. They explain that the method relies upon achieving a pH of between 12.0 and 12.5 after addition of NaOH so that linear dsDNA (sheared chromosomal DNA) is denatured but closed-circular DNA (plasmid) is not. They state in the paper that:

further pH control is obtained by including glucose as a pH buffer.

According to this site glucose has a pKₐ of 12.3, which aligns nicely with the claim that it helps to keep the pH within the desired range.
Comment: @Chris I actually knew the answer, having been around when the Birnboim & Doly paper was published. This technique revolutionised what was possible with plasmid-based cloning at the time and I read it very carefully. At the time of writing (05-07-2017) the paper has 12,877 citations, but most people who use the technique (in kits) won't even know of its existence. *Sic transit gloria mundi*
Comment: This is an interesting bit of information (I really like the explanations of this mechanisms). Thanks for finding it.
Comment: Really great answer, but the second link is broken for me.
Comment: @canadianer fixed, I hope.
Comment: The kit problem (as I usually call it with our students) is exactly the reason why I love the information bits. They help in trouble shooting and it is good to know how a method works anyway. Classical biochemistry with finding out exact mechanisms. I thought I would know the lysis method and the steps pretty well, but there is always something to learn. As it turns out, this paper is already in my literature database, I will re-read it sometime later.


new use for a known patented invention

Question: You obtain a patent which is a new use for an existing patented invention.
The patent of the existing patent is still in force and valid.
If you want to use your patent, do you have to get a license from the owner of the of the existing patented invention?
Answer: If your invention would be infringing on that other patent, then yes, you would have to obtain the rights or license from the patent owner to build or sell your invention.
All a patent does is give you the rights to "exclude others from making, using, offering for sale, selling or importing [your] invention." But a patent does not guarantee you the right to "make, use, offer for sale, sell or import [your invention]." — What Are Patents, Trademarks, Servicemarks, and Copyrights?
So even if your patent is completely valid, it does not grant you the unencumbered right to build and sell your invention. It only gives you exclusivity to keep others from building or selling it.

new use for a known patented invention


Can Python control normal Minecraft, or only the RasPi Edition?

Question: My son wants to make a game in Python that is materialized in Minecraft. If he does that using the RasPi Edition, can that same Python code control the normal Minecraft on a PC? My guess is that Python sends commands to Minecraft rather than running in the same VM, so it should work for both.
Answer: Check out my blog post Drawing Sierpinski's Triangle in Minecraft Using Python. I was able to write Python code that plugs into the open source Minecraft server called Bukkit. You can use a normal Minecraft client on OS X to connect to the Bukkit server.
It's not as easy to setup as it is on Raspberry Pi, but it does work.
Comment: Note: Code written for the Raspberry Pi should be almost exactly the same as code written for the [RaspberryJuice](http://dev.bukkit.org/bukkit-plugins/raspberryjuice/) plugin (The plugin used in the above link). However, it is not quite complete, so you may have to tweak your code slightly in some circumstances.
Answer: I wrote a Forge mod (Raspberry Jam Mod) for desktop Minecraft that implements most of the Pi version's protocol, and works with the scripts I've tested. Event handling is the major omission.
Source code and binaries are here.
To install, you'll need python, Minecraft 1.8, Minecraft Forge, my Raspberry Jam Mod and the Minecraft PI Python package. Then:

Install Forge for 1.8.
Create a Minecraft profile that uses it.
Create a mods subdirectory to your Minecraft directory (%appdata%.minecraft on Windows).
Put my mod in the mods directory.
Create an mcpipy subdirectory to your Minecraft directory.
Put the contents of the Minecraft PI Python package into the mcpipy directory.
Create a Minecraft profile that uses the 1.8 Forge.
Run Minecraft and create a world.
Run python scripts via commandline or straight in Minecraft via /py scriptname. E.g., /py nt7s_sphere will draw a sphere.

If you want even more detail, I wrote an Instructable.
Comment: How to install and run it?
Comment: My progress so far: https://github.com/arpruss/raspberryjammod/issues/1
Answer: I found this working for me with Minecraft 1.7.10 (as user875707's answer solution is meant to be used with Minecraft 1.8).
https://github.com/kbsriram/mcpiapi
All the instructions are in the link above but basically, you just need to download the .jar they offer you and drop it into your your_minecraft_folder/mods/.
You will both need Forge installed and Python (2 or 3 even though the sample scripts are designed for Py2).
Also makes sure that Python is in your PATH (aka you can just type python in your terminal - use this if it isn't).
That's about that simple for setup.
Place your scripts in your_minecraft_folder/mcpimods/python/ and launch from ingame by typping /python yourscriptname (or just /py yourscriptname), do not include the .py at the end of yourscriptname. If anything went wrong, check your console to see the error.
EDIT: Very powerful tool, BE CAREFUL, I did manage to corrupt my world. Hopefully I had AromaBackup installed which does automatic backup every so often (30 minutes for me).
EDIT 2: I found out you can also you the mod CustomNPC which allows you to use about whichever languages you want to run the NPCs (themselves can do a lot of things, including running commands, etc).
Comment: Whilst this may theoretically answer the question, [it would be preferable](http://meta.stackoverflow.com/q/8259) to include the essential parts of the answer here, and provide the link for reference.
Comment: @SteveRobillard Whilst I agree with your statement, I'm not sure how to improve it in this particular case.
Comment: @SteveRobillard Made an, hopefully successful, attempt to improve my answer's quality.
Answer: No not really.  At this point the three versions (pc, xbox and minecraft) are all entirely different branches.  A mod will often not work on a pc from version 1.x to version 1.x+1 so you're really not going to see any kind of cross compatibility.


What are the major differences between vim and neovim?

Question: I have been using vim for a few months and I am wondering if I should switch to neovim. Currently I am using no plugins, and only a few basic mappings.I use vim both for quick edits of config files and for writing python. I have heard that it is the future of vim. I would like to know what the major differences are between the 2 editors and what I would have to learn/unlearn to switch to neovim.
Comment: Possibly related (even if it's an old question): [What is Neovim? How is it different from Vim? And why should I care?](https://vi.stackexchange.com/q/34/18609)
Comment: @JaredSmith if you have an answer, please write one. Comments are for clarification, not discussion or answers
Answer:
I have heard that it is the future of vim.

That's not true. Or, at least, no one knows if it's true or not.
Neovim is a fork. It still shares much (and I mean really much!) of source code and documentation with Vim.

I would like to know what the major differences

There are many small differences, but, I dare say, nothing is substantial. At least, from an average end-user point of view.
Say, Neovim has "init.vim" and "shada" instead of "vimrc" and "viminfo" respectively. But a typical user would not care if "shada" format differs from "viminfo". And "init.vim" is still the same VimScript, even if it has another name and is located in another directory.
Also, Vim and Neovim have different implementation of :terminal. But, at least, they both have it now.
Also, say, Neovim has tight integration with Lua and always has Lua engine built-in. That may be of interest to some users, but surely not to everyone.
And so on, and so on.

I am wondering if I should switch to neovim

You should give a try, not "should switch" by any means. If you care, personally I like Vim better.
Comment: And I never suggested any such thing. Please read more carefully. Neovim introduced many features which Vim got later. At the time, 7.4 was the current release, and the version to compare to. 8.0 added many of the same features (albeit sometimes in incompatible ways), lessening the difference. That was 100% my point.
Comment: That would require an interesting feat of time travel. Neovim began in early 2014, and I have a receipt here for a donation I made to the project in 2015. Vim 8 was released late in 2016. So the only sense in which Neovim is a "fork of Vim8" is that it came after 7.4.
Comment: @hobbs The OP is not about the historical details, but the current state only. As of now, there remains nothing special one should "absolutely" prefer one application to another.
Comment: The Neovim team backports patches when they are relevant, that's why `v:version` reports `800`, but that's a bug, it should report the current Neovim's version. Just to clarify the historical point of view, [this is the first commit](https://github.com/neovim/neovim/commit/72cf89bce8e4230dbc161dc5606f48ef9884ba70) in the Neovim repository
Comment: Neovim is also working on native language server support, don't know about vim.
Comment: There were more substantial differences prior to Vim 8... and there may be more again, depending on how many things Vim picks up. Forks are good that way.
Comment: @hobbs Neovim was forked from Vim8.
Comment: @hobbs Well, then they probably backported all the stuff later. Anyway, Neovim contains all major features from Vim8 and reports `v:version == 800`. So it feels unfair to compare it against Vim7.4
Answer: If you are using neovim 0.4 and vim 8.0 there are no visible differences from a user's perspective. However, neovim 0.5 is usable already which has great integration with lua, a built-in language client, and treesitter support. This means an emerging set of lua plugins that are neovim only (like telescope, luatree) and native lsp support (and plugins like lspsaga) as well as tree sitter driven highlighting, navigation and refactoring. vim 9.0 will introduce a new and faster vimscript that is not entirely backward compatible so neovim and vim will diverge in the near future.
Answer: As pointed out by Matt, from a normal-user's perspective, you really can not
perceive much difference between Neovim and Vim. Besides, many plugins also try
to mitigate the differences between Neovim and Vim by using particular logics
for Vim and Neovim differently where necessary.
To get an overview of the differences between Neovim and Vim, open neovim and
read :h vim-differences.
Answer: One major difference is that neovim can be embedded in another process. This allows one to use neovim inside a browser, together with a full user configuration.
Answer: NeoVim has major plugins that use lua instead of vimscript.
luajit is faster than vimscript by 10-100 times (though vim9 has comparable performance: most humans wouldn't notice the difference).
If you want to run a lua/vimscript benchmark you can use this repo:
$ git clone https://git.sr.ht/~henriquehbr/lua-vs-vimscript
$ cd lua-vs-vimscript
$ bash benchmark.sh


Could the Boeing 747's 'hump' be improved aerodynamically?

Question: Couldn't the Boeing 747's aerodynamics be improved by extending the hump further back, or sloping it back more gently? Wouldn't this make it more aerodynamic and therefore fuel efficient and faster?
Comment: "by extending the hump further back": It would increase weight, but what makes you think it would decrease drag. The wings don't have a rounded rectangle shape...
Comment: If I can find it, somewhere on av.se it was explained that the hump actually decreased drag and increased overall efficiency
Answer: The 747-300/400 has a longer hump than the original 100/200. Surprisingly, this longer hump had lower aerodynamic drag than the 200 hump: at higher mach numbers compressibility starts to cause serious drag increase. The speed at which this "drag divergence" occurs depends on the variance of cross section area of the plane. If the cross section of the plane would be a constant value, drag divergence speed would be closest to mach 1.
The longer bump on the 747-300 resulted in a more constant cross section and therefore higher drag divergence number => higher cruise speed.
Could it be made more efficient aerodynamically? Yes, by trying to match the Area Rule as closely as possible.
Source
Comment: Not just _near_ transonic, it _is_ transonic.
Comment: So is the drag lower with a longer hump but only at certain speeds?
Comment: Good question. In this particular case it was, due to cruise speed of a passenger jet being near transsonic. At lower speeds the balance between friction drag and pressure drag would be valid: friction drag is proportional to skin area, pressure drag is a function of the shape. Elongating the hump over the whole plane length would reduce pressure drag, but this would be more than offset by the increase in friction drag. Same goes for going for a gentler slope: at a certain incidence of the back end of the bubble, there won't be a gain in pressure drag anymore, only increased friction drag.
Answer: Bill Sweetman had a good article on this subject in Air and Space called How The 747 Got Its Hump. The basis for this was in the development of a large cargo aircraft Boeing designed to compete with Lockheed for the contract which resulted in the Lockheed C-5 airplane. Boeing lost the contract but saw potential in its design as a commercial cargo aircraft and airliner.
The aircraft could be loaded through a nose which would hinge upward, but the hinge point and attachment structure would have to be placed in the spot where the cockpit would have normally gone; the only option was to mount the cockpit high up on the fuselage.  Original designs called for the cockpit to be in a blister type fairing above the nose, but wind tunnel testing revealed the design to be unacceptable and the fwd fuselage was redesigned with an elongated Hump to accommodate the cockpit.
Anyways when the passenger variants of the plane were pitched to the airlines, the Pan-Am bosses became enamored with the idea of using the space in the hump for a passenger lounge, some say out of nostalgia for the lower deck lounges which were installed in the old Boeing 337 StratoCruisers.  As the 747 gained worldwide acceptance, the hump became a signature look for the jet (as I understand it Boeing has a patent on the design for that reason).
It is possible that if the 747 would have had its roots as a pure double deck airliner, the design would have looked more like the A380 does today.
Comment: This is a good explanation of the reason for the upper deck but does not seem to address aerodynamics at all, which is what the question is asking for.
Comment: In that case the answer is that Boeing 'could' do something, but they won't for the reasons above.


Why breadcrumbs should not be used as a primary Navigation?

Question: All of the blogs I have ready about breadcrumbs mention that breadcrumbs are used for secondary navigation and shouldn't really act as primary navigation. What is the reason for this convention?
Comment: What actually makes you think they *would* be suitable for primary navigation?
Comment: If I'm at the home page and I want to get to Bluetooth Wireless Speakers (Which is nested under Speakers > Wireless > Bluetooth) I don't see any way to navigate there using just breadcrumbs unless you have some sort of tree chart looking breadcrumbs taking up the whole page.
Comment: @JonW I Googled for best ways to use breadcrumbs and every blog/article mentioned it's not for primary navigation. So I was just wondering, what could be the reasons.
Answer: TL;DR
Main menu leads the user, while breadcrumbs are following him. They relate like a GPS navigator and a GPS tracker.
Main navigation supports and helps to form user's mental model of what is on the site. It has constant structure and is presented on the same place, with the same information. It's very reliable and consistent mean for navigational tasks.
Breadcrumbs, on the contrast, are dynamic and can be build in a different ways, following the user interaction pathes. So they are dependant on user's behaviour and don't show clearly the site content. They are helpful as a secondary navigation mean.
Answer: There are no hard rules here, so lets take a look at examples and see whether they make sense as a primary navigation in one particular case.


How common is it for military jets to use civilian airports?

Question: Today my wife witnessed 3 fighter jets taking off from Teterboro Airport in NJ. She even took a video. How common is it for military jets to use civilian airports?
Comment: When they're relocating from base to base, they gotta fuel up somewhere.   Many larger FBOs have contracts to provide fuel and basic services to the military.
Answer: Fighter jets may fly into local fields for airshows, to re-fuel or for needed maintenance in route etc.
What your wife may have seen may have been related to the VIP TFR's that usually pop up in the summer due to the president (or first family) heading back to their home on weekends.
I fly out of KDYL which is fairly close (in aviation terms) and my local FBO has been warning everyone that the Secret Service has instructed them the VIP TFR is going to be common on weekends this summer.
You can find a map of current TFR's here.
Answer: Some airports are shared with the military. For example, Portland International in Oregon has the Portland Air National Guard Base, and Charleston International is shared with Joint Base Charleston. Airports such as these will have frequent military traffic.
Even airports with no permanent military presence may see occasional military traffic. Aircraft may do touch-and-gos there for training. It's less likely for them to stay very long, as there could be special security and ground support requirements, especially with fighter jets.
You can look at statistics for US airports on AirNav. KPDX sees military operations as 2% of its operations, while KCHS sees 20%. KTEB shows <1% of its operations are military. This is the lowest value they report but that could still be up to almost 5 per day on average.
Comment: A decade or so ago, when I kept the Cherokee at Reno (the FBO on the east side of the field), it was quite usual to have something military - from F-14s to C5s - parked on the ramp.  There's also an Air National Guard base on the east side, flying C-130s last I looked.
Comment: Non-US example https://email@example.com,19.7849321,1504m/data=!3m1!1e3!4m5!3m4!1s0x4716592789d2e8d1:0x93efc553923da128!8m2!3d50.0769776!4d19.7881188 - international terminal is on the right, while military part is in the center.
Answer: There are many, many Air National Guard Bases at Regional and Municipal airports. The ANGB planes typically have their own ramp area and hangars for repair, and have security systems around them.
Wikipedia has a list of ANGB locations
Those Not at an Air Force Base are generally sharing civil airports.
Answer: Night and day, seven days per week at KABI. This full time-use of a regional airport began early 2018.
Remember the song, "Abilene - Abilene... prettiest town I've ever seen..."  They should make a new song, "Loudest town I've ever seen..."


Why is Shiva, Hanuman, Gayatri are shown with 5 heads, but not Vishnu or Durga?

Question: Shiva, Hanuman, Ganesha and Gayatri deities are shown with 5 heads in idols but not Vishnu or Durga? What's the reason for this?
Comment: The tattvas have numbers from 5, 3, 9 , 12, 108 to finally 2 and 1.
Comment: @AkshayS can you explain this in detail? Any reference regarding this in any scripture?
Comment: @AkshayS Kartikay has 6 heads.
Comment: @Rishabh of course that also a meaning behind it why he has 6 heads.
Comment: @AkshayS Kartikeya has 6 heads because he is linked with the constellation https://en.wikipedia.org/wiki/Kṛttikā / Pleiades which means 6 sisters, wives of 6 sages, who raised Kartikeya
Comment: Heads are sysmbol, during such sloka pancha muki, we should take different meaning, Siva pancha heads -> He is lord of pancha bhootha -> he is devatha for creating pancha bhootha. Hanuman -> pancha prana->prana, apana, vyana, udhana and samana. Gayathri -> 5 vedas -> 4 vedas + 1 mahabharata. and so on.. hindu scriptures are crypitic need to understand from different prespective.. when straight meaning doesnt give clear picture..
Answer: Having multiple head mean they are deities of tantrik cult.Vishnu do have a form with 4 heads known as vaikuntha or skatish according to pancaratra.The four head are - vishnu,nrsimha,varaha and kapila.
Comment: Welcome to Hinduism SE! While answering please consider giving a reference to verify your answer.
Answer: Shiva
The Pancabrahma Upanishad describes five forms of realities (Brahman) or Shiva that arose from highest reality – Sadyojata, Aghora, Vamadeva, Tatpurusha and Ishana. He is panchatmak, who conceals all five Brahmas, and to realize him is moksha.
https://en.wikipedia.org/wiki/Pancabrahma_Upanishad#Contents
Hanuman
In Kamba Ramayanam (in Tamil), the significance of number five is beautifully narrated as follows: The son of one of the five elements (son of wind - Pavana Thanaya) crossed one of the five elements (water – the ocean), through one of the five elements (sky), met daughter of one of the five elements (daughter of earth - Sita Devi) burnt down Lanka by one of the five elements (fire).
https://en.wikipedia.org/wiki/Panchamukha#Origins_of_the_Panchamukhi
Gayatri
Gayatri was the name initially applied to a metre of the Rig Veda (Mandala 3.62.10) consisting of 24 syllables. In particular, it refers to the Gayatri Mantra and the Goddess Gāyatrī as that mantra personified. The Gayatri mantra composed in this triplet form is the most famous. Most of the scholars identifies Gayatri as the feminine form of Gayatra, other name of Vedic Solar god which is also one of the synonyms of Savitri and Savitr.
However, the transition period of mantra turned into personification is still unknown.
https://en.wikipedia.org/wiki/Gayatri

The 5 faces of God/Goddess may refer to 5 elements of the Nature.
Vishnu was depicted with so many heads, which might have been drawn from Rig Vedic Sahasrasirsha of Rig Vedic Purusha Sukta. And, Durga was depicted with multiple hands.


Would you call all in with king high flush with a pair on the board?

Question: Let's say You are in the dealer with king jack suited(of clubs). Blind are 1-2 dollars. Fold to you, You raise to 12. Call from the small blind the the big blind re raises to 40 dollars. You call and the small blind folds. Flop 3 j 8 (3 and 8 of clubs) He raises 60 dollars you call. Turn is a three he raises 100 you call. The river is a four of clubs he checks you have the second nut flush so you bet two hundred dollars he raises you to all in. You have 900 dollars from behind, do you call all in?
Comment: Betting the river was your mistake. The pot was big enough for your mediocre hand; betting just gave your opponent the chance to blow you out with a bluff, or get $200 more value.
Answer: My best simple answer would be "It depends". Folding here would likely be the most accurate option if you were working in a data vacuum. I have found that most of the time the player is not bluffing.
However, players bluff here often enough that one really needs to be able to know enough about the player, the mood of the game and the players tells for one to be able to take advantage of the occasional bluff.
The thought process one needs to go through here is several layers deep. From the OP's description it is obvious the player has or is representing pocket Jack's or eights. With all the action preflop the player is not likely to have a three in his hand. The player may also be playing something like a pocket pair or some other ranked hand like AK.
The decision is simple if your playing against the type of player that does not gamble much, rarely if ever bluffs etc. you lay it down. But if the player is something other then that, you have some things to consider before you lay this hand down.
Things that would make me tend to call...
(If yes it adds some weight to making a call.)
Does the player tend to get stubborn with his hands?
Does the player tend to overrate his hands? By this I mean what is the likelihood that the player believes, his A-3, smaller flush, large pocket pair etc. is actually the best hand.
Does the player like to bluff?
Has the player been reading me accurately? I would add some weight to a call if I thought he was a player that could pick up that I have something less then a full house and is capable of a sophisticated bluff here. But this is tricky if the player has a good ideal rather not I would call with that when he has the full house. (Layers!)
Do I have a read on the player?( if I do not have a good read on the player I will need to fold here more often. A good read will supersede almost everything else I may have observed about the player outside of this hand.)
The list can go on for awhile. Coming to a decision about rather to call or fold gets a little more simple as you pack experience into intuition over the years. This is one of those hands you would run through your head a lot or talk with someone about, and come to the conclusion you played it wrong. This is a hand that can always go either way for you. The more you know, the more experience you have with the game in general and the player in particular the better your accuracy with this decision is going to be.
Answer: I would fold because;

i doubt villain will be turning  AcAx, QcQx & KcKx into a bluff.
I don't think people 3bet Ac5x, Ac4x and Ac2x preflop often enough nor will they know that these are great river XR bluffs very often.
You are blocking AcJx  and i doubt they would turn it into a bluff often.

I think here you run into Ac2c, Ac4c, Ac5c, AcQc & AcKc a lot and less frequently AcTc the average villain won't have nearly enough bluffs in his range to justify a call. Although this is a call at least sometimes if villain plays with well balanced ranges which the average player won't do.
When calling 900 to win 2600 you need 34.6% bluffs in his range to break even. I doubt the average nl 1/2 person has that. There are 5-6 combinations of value in their range so they need 2+ bluff combos to make it worthwhile. Therefore this will mostly depend on whether they might be 3betting the offsuit Ax preflop and are capable of understanding that the Ac is a perfect hand to bluff with.
Furthermore XR on river tends to be value heavy in general because the OOP is likely to choose a triple barrel bluff rather than a XR just because it's cheaper and people tend to choose the cheaper line with bluffs.
Furthermore the average fish won't try to fold out a flush here, seeing that flush gets there is an auto shutdown for the avg nit.


Is it 'possible' to transfer a VM to the metal?

Question: How can one take a VM and make it run on the machine?
Comment: This is not really a unix/linux question. But here is the [VMWare documentation](http://www.vmware.com/support/v2p/index.html) for such a transfer.
Answer: Generally, yes. If your VM is running off native disks or partitions, it may be as simple as pointing your bootloader to it. Otherwise, you'll need to copy the data. For some VM formats, there are tools to mount the VM disk on the host (e.g. xmount). For other formats, the simplest way to get the data is to treat the VM as any old machine and boot a live CD in it.
Then your OS must be able to boot on the metal. Unix installations are generally fairly hardware-independent (as long as you stay with the same processor type). You need to have the right drivers, to configure the bootloader and maybe <code>/etc/fstab</code> properly. See for example Moving linux install to a new computer.
Comment: `xmount` nice tool :)
Answer: It depends on what you use for virtualization.  Qemu allows you to install the OS to a partition on your hard disk and you can either boot into it or load it up in Qemu.
If your VM is installed to a file on your filesystem like VirtualBox does, it may be possible to convert it to a disk image that you can install to a hard disk but it's more effort on you part than what Qemu can do for you.  With VirtualBox there isn't any easy way to synchronize the disk partition and the VDE file so you can swap back and forth between them.
Answer: As others have implied, the storage mechanism matters most. Some virtualization products, especially desktop virtualization products, storage data in opaque formats. In that case, you'll need to extract the filesystems from the disk images. Each virtualization product will have a different and sometimes proprietary way of doing this.
If you're building a virtualized datacenter, however, you can actually plan on making virtual machines that can be easily migrated to or from a virtualized environment.  In this case, you'll be best using a SAN, such as iSCSI, assigning raw block storage to your virtual machines.
For example, I personally create iSCSI LUNs which appear as block devices under Linux. Then, I boot these machines with Xen. I can easily shut these machines down and then use gPXE to boot the machine directly from the iSCSI volume.  This is probably not what you're looking to do, but it is possible!
Not important to forget, however, is that once your storage is accessible, the OS itself needs to be configured to find its devices. Using UUIDs in your /etc/fstab will help, for instance. If booting from a SAN, you will need a properly constructed initrd.


What does port forwarding mean in "SSH port forwarding"?

Question:
Wikipedia says

In computer networking, port forwarding or port mapping is an application of network address translation (NAT) that redirects a
  communication request from one address and port number combination
  to another while the packets are traversing a network gateway, such
  as a router or firewall.

Does the definition of port forwarding apply to "SSH port
forwarding"?
What does "port forwarding" mean in SSH local and remote port
forwarding?
In particular what is forwarded to what by
what?
For example. In https://askubuntu.com/a/50075/1471,

The command for forwarding port 80 from your local machine (localhost) to the remote host on port 8000 is ssh -R
  8000:localhost:80 oli@remote-machine.

Would you say the same thing, or will you say "forwarding port 8000
on the remote host to port 80 on local machine"?
Comment: do you have a specific context or are you trying to understand about the process in general? the definition from wikipedia is a good one. Basically you have one device (on a home network - a router) which intercepts packets and literally rewrites the header metadata of the packet, then "forwards" it to the internal machine - as per the internal network machines ip address. the router then keeps a track of the external remote machine and the internal machine in a table - because when the internal machine responds the router has to rewrite the packet on the way back out too
Comment: More to understand what other people mean by "forwarded port" and other words containing "forward(ed)", than how to use SSH port forwarding.
Answer: 1 - general case
Suppose you have two server in a company network.
From local server "L1" you have access to a remote server "R1" via ssh on port 22.

The server R1 host a web service, but firewall/NAT/whatever block direct access to port 80.
"R1" can't access "L1" directly due to NAT issue.

from  L1 you connect using (same user on both host)
ssh -L 10080:localhost:80 -R 10022:localhost:22 R1

now,

-L 10080:localhost:80 local browsing on 10080 will be forward to distant host (R1), localhost (e.g. distant 127.0.0.1) on port 80, thus you could browse distant host (R1), while blocked by firewall/NAT.
-R 10022:localhost:22 remote use of port 10022 will be forwarded to localhost (L1) port 22, you  can initiate scp/ssh from remote to localhost. (using scp -P 10022 file localhost: (note upper -P ) )

This is actually a command line I use from an Ubuntu (14.04) laptop to go to production server (I can firefox to localhost:10080 and use scp from server to localhost:10022 to bring back file )

now your IP are
192.168.1.1 L1
172.17.17.1 R1

you use
ssh -L 10080:172.17.17.3:80 -R 10022:192.168.1.5:22 \
     -L 192.168.1.9:8888:172.17.17.9:9999 R1

now

distant access to port 10022 (any IP) will be forwarded to local 192.168.1.5 ssh/scp.
local access to port 10080 (any IP) will be forwarded to distant host 172.17.17.3 port 80.
local access to port 8888 from 192.168.1.9 will be forwarded to port 9999 on 172.17.17.9 (192.168.1.9 is a local address in L1, using alias mecanism, this is not a firewall rule).

those setting can be used on putty/bitwise client

Ask Ubuntu question
what  about
 -R 8000:localhost:80

this read as

-R remote
8000 port 8000 (remote port 8000 ... )
localhost  (remote port 8000 goest to localhost .. )
80 ( remote port 8000 goes to localhost port 80 )
Comment: Thanks. I like to clarify my questions a little with an example. In http://askubuntu.com/a/50075/1471, "the command for **forwarding** port 80 from your local machine (localhost) **to** the remote host on port 8000 is `ssh -R 8000:localhost:80 oli@remote-machine`". Would you   say the same thing, or will you say "**forwarding** port 8000 on the remote host **to** port 80 on local machine"?


Is there a way to clear the cache in the administration?

Question: I made a change to an admin component, but it's not reflected immediately.  Is there a way to make the admin cache refresh?  I know with modules you can set cache to none, but this is a component so I don't have that option.
Answer: Yes, there is a way. It is called Cache Cleaner, extension from Regular Labs (ex-NoNumber).
With Cache Cleaner you can clean your cache fast and easily via a link in your Joomla! Administrator.
Not only that, it also gives you the possibility to purge expired cache, do a global check-in, empty the temp folder, empty user-defined folders and database tables … all with just 1 click!
Cache Cleaner can clean your cache automatically when you save an article or other item. And it can clean your cache at preset intervals too.
So no more clickety-click to get to the core Joomla! Cache Manager and no more manually deleting files.
Let it be noted that the extension cleans up both /cache folders (site's and admin's), even though that is not explicitely written in description.
I have been using it for ages and can't imagine my work in Joomla admin without it.
HIGHLY RECOMMENDED!
Comment: Ah I have this installed but I did not know this.  Excellent!
Answer: Login to admin panel, see top menu, click "System", click sub menu "Clear Cache", I think rest you will understand.
Comment: I thought that was for the front end only?  I want to clear the cache in the back end.
Comment: Hi,

I think joomla doesn't store different cached file for site or admin part, are you facing any issue? Write specific, maybe can suggest something based on your feedback.
Comment: Yes, I am facing the issue I described.  I have updated the CSS on an admin component and the change is not immediately reflected.  Thus I assume cache is the issue as the change does get reflected after a while.  I think the cache cleaner option is the best one.  Joomla! must store different admin cache.  When you clear cache using the normal Regular Labs Cache Cleaner it only lists front end files.  Also there is a folder administrator/cache and also a cache folder in the site root suggesting your assessment may be incorrect.


How do I install MS SQL for ubuntu 18.04 LTS?

Question: I looked up on the internet but all those steps to install were regarding 16.04 version. Is it available yet on 18.04 ? If yes,how?
Comment: I had a look at their repositories, and it looks like for now they only have a couple libraries in the 18.04 repositories. That probably means they are busy working on building packages but are not ready with everything yet.
Comment: When trying to install mssql-server on Ubuntu 18.04 I get error `The following packages have unmet dependencies: mssql-server : Depends: openssl (<= 1.1.0)` so it's not available out-of-the-box. Look at the David Mortals's answer below.
Comment: Related: https://askubuntu.com/questions/1029504/ubuntu-18-04-mssql-repos/1033956#1033956
Answer: Microsoft does not provide official mssql-server for 18.04 yet (05-12-2018), for testing only you may try this workaround(from me).

Workaround for installing Microsoft's SQL Server (mssql) on Ubuntu
WARNING: FOR TESTING ONLY

Download latest package mssql-server_14.0.3025.34-3_amd64.deb from https://packages.microsoft.com/ubuntu/16.04/mssql-server-2017/pool/main/m/mssql-server/
Change directories
cd ${HOME} && mkdir -p tmp/mssql/newpkg/DEBIAN/ && cd tmp/mssql
wget https://packages.microsoft.com/ubuntu/16.04/mssql-server-2017/pool/main/m/mssql-server/mssql-server_14.0.3025.34-3_amd64.deb

Unpack
dpkg-deb -x mssql-server_14.0.3025.34-3_amd64.deb newpkg/
dpkg-deb -e mssql-server_14.0.3025.34-3_amd64.deb newpkg/DEBIAN/

Modify
sed -i -e 's#openssl (<= 1.1.0)#openssl (<= 1.1.1)#g' newpkg/DEBIAN/control
cat newpkg/DEBIAN/control | grep openssl

Repackage
dpkg-deb -b newpkg/ 18.04-mssql-server_14.0.3025.34-3_amd64_.deb

First try, this will fail for dependencies
sudo dpkg -i 18.04-mssql-server_14.0.3025.34-3_amd64_.deb

Install dependencies
sudo apt install -f

Second try, this should be done
sudo dpkg -i 18.04-mssql-server_14.0.3025.34-3_amd64_.deb

Follow the messages from package to setup the mssql server

Troubleshooting
The database directory /var/opt/mssql should not put on zfs dataset,
  if you are using zfs, create a zvol and format as ext4/xfs for it.
Error: "Dump collecting thread [4404] hit exception [6]. Exiting."
  Fix: sudo usermod -a -G disk mssql
  Reason: mssql user can not access zvol.
References:

https://docs.microsoft.com/en-us/sql/linux/quickstart-install-connect-ubuntu?view=sql-server-linux-2017
https://gist.github.com/shamil/3140558
Comment: I also had to change libcurl3 to libcurl4 in the dependencies in step 4 (PHP7 uses V4 and it seems to work with MSSql server).
Answer: So, the versions of ca-certificates and openssl provided by Ubuntu 18.04 actually work fine for mssql-server. Presumably it's rejecting openssh because 18.04's version of 1.1.0g-2ubuntu4 is technically 'higher' than mssql-server's demanded <=1.1.0 (and I would think they should have used <1.1.1 since that still locks you to a 1.1.0 variant while allowing for distribution-specific package versions which are something you should absolutely expect to run into but that's neither here nor there.)
The Fix

Install dependenciessudo apt-get install libunwind8 libnuma1 libc6 adduser libjemalloc1 libc++1 gdb debconf libcurl3 hostname openssl python libgssapi-krb5-2 libsss-nss-idmap0 gawk sed(I fully realize you probably have most of these already installed, these are just all of the claimed dependencies.)
Download the packageapt-get download mssql-server
Force installationsudo dpkg --force-depends -i mssql-server_14.0.3025.34-3.deb
Remove downloaded .deb filerm mssql-server_14.0.3025.34-3_amd64.deb

At this point, running any apt command will cause it to (harmlessly) complain that mssql-server has unmet dependencies and instruct you to run: sudo apt --fix-broken install
DO NOT DO THIS. YOU WILL LOSE EVERYTHING YOU JUST DID.
If you really want that error to go away, proceed with step 5, otherwise just ignore it and you're done.
Convince dpkg that everything is okay

sudo nano /var/lib/dpkg/status Your preferred editor is okay too
Find the entry for mssql-server (for nano it's Ctrl-W, not Ctrl-F)
Change the depends line from
...hostname, openssl (>= 1.0.1), openssl (<= 1.1.0), python (<= 2.7.0)...to...hostname, openssl (>= 1.0.1), openssl (< 1.1.1), python (<= 2.7.0)...

If you forcibly installed the old versions of ca-certificates and openssl to get mssql-server to install, you can forcibly upgrade them by apt-get install ca-certificates openssl. This will remove mssql-server (but your configuration and databases should be left alone). Then you can follow my instructions.
This should avoid you having to deal with the hassle of repackaging things. You are trading that for playing tricks on dpkg but doing it this way will probably (I admit this is based on no research) make it easier to upgrade when an official 18.04 package comes out since you avoid creating and using an unofficial package and upgrading to an official package would clean up the changes we made automatically.
Answer: Microsoft has updated SQL Server 2017 for Linux and now it can be installed in Ubuntu 18.04 but They are recommending for development only.
For more information check out the following Microsoft blog post:
  Installing SQL Server 2017 for Linux on Ubuntu 18.04 LTS
Answer: Micrsoft's SQL website was last updated in April 2018 and shows Ubuntu 16.04 as the most currently supported version. I would wait until July 26, 2018 when Ubuntu 18.04.1 LTS is released to expect support from Microsoft.
Instead of paying for Microsoft's SQL you could try the free version of MySQL which supports Ubuntu 18.04 already.
Comment: If MSSQL is what you need because other software you use depends on it, installing MySQL isn't going to do you any good.
Comment: MySQL and other open source databases are already included in the Ubuntu repositories, so no need to get them elsewhere, unless you need a specific version.
Comment: @JanC I was highlighting the Manfacturer's website for information about MySQL availability for 18.04. Thanks for installation tip that benefit everyone.
Answer: If you are using Ubuntu 18.10 you'll need to revise David Mortals answer slightly by adding the following to step 4:
sed -i -e 's#libjemalloc1#libjemalloc2#g' newpkg/DEBIAN/control

This is assuming that libjemalloc2 is backward compatible with libjemalloc1 and so far on my dev machine it seems to be working fine.


Did Jesus wear premium clothes?

Question: In John 19:23,  it is said that Jesus clothes were not ripped because they were seamless and woven in one piece from top to bottom. Does that mean Jesus used to wear premium clothes? Since the soldiers refuse to rip up such a nice cloth I assume it is somehow valuable or special. Can someone please elaborate on the topic?
Comment: While I cannot answer your question it is a fact that one of the ladies who followed Jesus was the wife of a rich man, it is possible that she had provided premium clothing for him. Even though seamless weaving was not uncommon at the time it was more time consuming than flat weaving, and was more costly than piecework.
Comment: Related: http://christianity.stackexchange.com/questions/551/why-how-does-jesus-coat-have-no-seam
Comment: I can't give any citations right now, but I read once that virgins in the temple would weave the sacred fabrics for, e.g., the veil of the temple. Perhaps it was the Talmud. Perhaps also the priestly vestments. If according to tradition Mary was dedicated to this kind of temple service as a young virgin, it would stand to reason that she herself would have experience with weaving and making clothing.
Comment: One thing is Jesus definitely didn't dress sloppy. Even the guards want them.
Answer: Psalm 22:16-18 reads as follows:

For dogs have surrounded me;
A band of evildoers has encompassed me;
They pierced my hands and my feet.
I can count all my bones.
They look, they stare at me;
They divide my garments among them,
And for my clothing they cast lots.

Here is the New Testament fulfillment of the prophecy in Psalm 22:

Then the soldiers, when they had crucified Jesus, took His outer garments and made four parts, a part to every soldier and also the tunic [Gk chiton]; now the tunic was seamless, woven in one piece. So they said to one another, "Let us not tear it, but cast lots for it, to decide whose it shall be"; this was to fulfill the Scripture:
"They divided My outer garments among them, and for My clothing they cast lots" [John evidently quoted the Greek translation of the Hebrew Scriptures, the Septuagint, or LXX].
Therefore the soldiers did these things.

According to a number of sources, the chiton (χιτών, citwn), which was a long garment worn next to the skin and under the outer cloak, was more expensive to make than an undergarment of several pieces sewn together. Perhaps a seamless chiton looked more presentable than one which was made from piecework. The salient fact in the crucifixion narrative, however, is that since the chiton was seamless, the quaternion of soldiers was reluctant to rip the garment into four pieces (which would spoil the garment) but chose rather to "cast lots" (our equivalent today of throwing dice) to see which soldier would get it whole.
As the writer of the article "The Seamless Tunic" observed:

This prophecy […] declares the commonness of divine prophecy. It shows the characteristic of earthliness that is sometimes present in the fulfillment of God's predictions. Often He chooses the everyday deeds, the unplanned and common activities of people, as the setting and events through which His prophecies come to pass. These soldiers—having no idea that they were part of God's designs—went about their normal work of implementing an execution. What they did was routine to them. Perhaps they joked about who got what as they divided the outer garments. When they came to the seamless undergarment, they paused to recognize its beauty; beyond that, it was business as usual. After deciding on what to do with the tunic, they gambled over it and gave it to the winner. These men were unaware that they were fulfilling a prophecy made perhaps a thousand years before. They did not know that their actions had been written into the divine record by David or that they were proving that God overrules in all things to fulfill His will.

While the seamless tunic could be considered a "luxury item" in Jesus's day, Jesus did not possess any other luxury items, particularly toward the end of his public ministry. Here is what he said to a wannabe follower:

"The foxes have holes, and the birds of the air have nests; but the Son of man hath not where to lay his head" (Matthew 8:20; cf. Luke 19:28 KJV).

Perhaps earlier in his life, Jesus may actually have owned a house in Capernaum. Here is what Gospel writer Mark tells us,

καὶ γίνεται κατακεῖσθαι αὐτὸν ἐν τῇ οἰκίᾳ αὐτοῦ καὶ πολλοὶ τελῶναι καὶ ἁμαρτωλοὶ συνανέκειντο τῷ Ἰησοῦ καὶ τοῖς μαθηταῖς αὐτοῦ ἦσαν γὰρ πολλοὶ καὶ ἠκολούθουν αὐτῷ
And it happened that he was reclining in his house, and many tax collectors and sinners were reclining with Jesus and his disciples, for there were many who were following him . . ..

As his public ministry became more and more itinerate, however, he may simply have divested himself of all earthly goods, save for the "clothes on his back," so he could travel light, as it were.
And from Professor Mark Goodacre's blog comes the following,

This may be an example of . . . accidental information, or material given away in passing, where a piece of data (here: Jesus had a house in Capernaum) is assumed and not narrated.

Furthermore, Jesus' basic needs were provided for out of the common pot, of which Judas Iscariot was in charge (see John 12:6), and a number of prominent women contributed to his support as well (Luke 8:2-3).
The apostle Paul also reminds us:

For ye know the grace of our Lord Jesus Christ, that, though he was rich, yet for your sakes he became poor, that ye through his poverty might be rich (2 Corinthians 8:9 KJV).

All the above is to say: While Jesus may have owned a tailor-made tunic, it may have been made by his mother or by another talented (perhaps wealthy) seamstress who may have been a follower of our Lord. Obviously, Jesus did not live in the lap of luxury. Moreover, he was content to entrust the moneybag to a thief, which as writer Jon Bloom observes,

Of all the disciples, Jesus chose Judas to be treasurer of his itinerant nonprofit. One is tempted to offer the Lord some consulting on good stewardship. Donors were financially supporting this ministry (Luke 8:3) and the one guy who Jesus knew was a "devil" (John 6:70) was made CFO.
Now, Jesus was not ignorant of Judas's pilfering. So why did he let him manage the money?
I believe Jesus was putting his money where his mouth was.
He said, "Do not lay up for yourselves treasures on earth, where. . . thieves break in and steal" (Matthew 6:19-20). So he showed us by example what he meant.
Answer:
... because they were seamless and woven in one piece from top to bottom.

This means that it would be difficult to divide the clothes into multiple parts without completely destroying them.
It does not mean that such clothes are more expensive than other clothes.
Looking at modern clothing you can buy today, I even think that such kind of clothes were cheaper than clothes made of multiple parts.

Since the soldiers refuse to rip up such a nice cloth I assume it is somehow valuable or special.

Even if the clothes only were cheap clothes:
By dividing the clothes the soldiers would have destroyed them completely, so the clothes would have been completely worthless.
By not dividing them, the clothes still could be used. And even cheap clothes have some value as long as they can still be used.

Does that mean Jesus used to wear premium clothes?

I doubt that.

Did Jesus wear premium clothes?


Why do we take a derivative?

Question: I don't have a fundamental  understanding of what taking a derivative means and I don't understand why would we do it. I just know how to mechanically do it.
Comment: There is a set of videos on YouTube named "The big picture of Calculus" by MIT Opencourse ware. You should watch them, really helpful.
Answer: If $f(x)$ is a (real) function (of a real variable), then its derivative $f'(a)$ at a point $a$ measures the sensitivity of $f$ to small changes in $x$ around $a$. For example, suppose $x$ is "the height of the sun in the sky" and $f(x)$ is "the length of the shadow cast by this tree." Then $f'(a)$ is a measure of how sensitive the length of the shadow is to a small change in the height of the sun if the height is around $a$. Experimentally, $f'(a)$ will be small if the sun is high in the sky ($a$ is large) while $f'(a)$ will get larger as the sun gets lower in the sky ($a$ is small). The derivative gives us a way to quantify this observation.
I decided not to use the term "rate of change" because I think some students have heard this term so many times that they have become immune to it, so perhaps the above will make more sense.
Comment: Very nice explanation. I may have to start using _sensitivity_ to explain derivatives from now on. +1
Comment: I got the term from Deane Yang (I think) over at MathOverflow.
Comment: @Qiaochu Yuan +1. I like very much your answer. Referring to "small changes in $x$ around $a$", how can I define small? Small related to $a$?
Comment: @uvts_cvs: well, small really means "infinitely small." In practice I guess it means "small enough so that $f$ does not change much."
Comment: I love the concept of sensitivity being applied here, makes much more sense and instantly gives you an idea as to the practical applications
Comment: This makes a lot more sense after re-reading it now. I just gave you a best answer.
Answer: I don't know what kind of explanation you have gotten before, if any, so I think that I will start with one of the usuals. Let me first introduce to you the difference quotient:
$$\frac{f(x+h)-f(x)}{h}$$
It has a very nice geometrical interpretation.

In this picture, the curve is the graph of a function. I hope that you can understand from my picture that the length of the horizontal red line is $h$, while $f(x+h)-f(x)$ is the length of the vertical red line. So $f(t)$ increases by an amount of $f(x+h)-f(x)$ when $t$ increases by an amount of $h$ from $x$. This means that the average increase on the vertical axis per unit of the horizontal axis is given by the difference quotient
$$\frac{f(x+h)-f(x)}{h}.$$
So the difference quotient is the average increase of a $f(t)$ on the interval $[x,x+h]$. Another way to put it is that the difference is the slope of the line passing through the points $(x,f(x))$ and $(x+h,f(x+h))$, like this:

So the green line $g(t)$ can be written as
$$g(t) = \frac{f(x+h)-f(x)}{h} t + b$$
where $b=g(0)$ (the point where $g$ crosses the vertical axis).
When we take the derivative of $f$ at $x$ we find the limit of the difference quotient as $h$ goes to $0$, or
$$f'(x) = \lim_{h\to 0} \frac{f(x+h)-f(x)}{h}.$$
This is the definition of the derivative. Imagine that $h$ gets smaller and smaller. Then the point $(x+h,f(x+h)-f(x))$ will get closer and closer to the point $(x, f(x))$, and the green line will get closer and closer to the tangent line of $f$ at $x$.
So when $h \to 0$, the difference quotient becomes the slope of the tangentline, and now we have an interpretation of the derivative:

The derivative $f'(x)$ is the is the slope of the tangent line of $f$ at $x$.

Let's finish off by trying to find the derivative of the function $f(x)=x^2$ at the point $x=1$ only with the help of the limit stated above.
$$f'(x) = \lim_{h\to 0} \frac{f(x+h)-f(x)}{h} = \lim_{h\to 0} \frac{(x+h)^2-x^2}{h}$$
$$= \lim_{h\to 0} \frac{x^2+2xh+h^2-x^2}{h} = \lim_{h\to 0} \frac{2xh+h^2}{h}$$
$$= \lim_{h\to 0} 2x+h = \underline{2x}$$
When we plug in $x=1$ we get that $f'(1) = 2$. Hope this helps!
Comment: could we take [f(x-h)-f(x)]/h with h approaches 0 ?
Answer: I would recommend reading this: https://web.archive.org/web/20200218154616/http://www.ugrad.math.ubc.ca/coursedoc/math100/notes/derivs/deriv5.html
It's a pretty good, non technical explanation of the derivative and why one might care about it.
Answer: The derivative can be interpreted a number of ways, depending on context. For a simple physical perspective, you can think of it as a rate of change. If you want to know the rate of change at some given point (say, velocity 3 seconds into the movement of a thrown ball), taking the derivative will give you your answer. From a geometric perspective, taking the derivative tells you the slope of the tangent line at a given point.
From a historical perspective, this is sort of a workaround for Zeno's paradoxes of motion.
Answer: A derivative can be interpreted as the slope of a tangent line or a rate of change (in particular, a velocity).  You might e.g. look at these notes
Comment: @TaylorRendon Yes
Comment: Quick question, is the following wording for describing the derivative of a function as a rate of change correct: *the derivative of a function at a point is the rate of change of the function value with respect to its argument at that point*?
Answer: Derivatives are useful for optimization; finding the extrema (maximum or minimum) of functions. This is a very common task in applied mathematics.
Answer: if you given a function and you asked to find the behave of the given function then you may take the derivative to the given function, but if you given a behave of any function you need to take the integral of the behave function, to find the function of the given behave.
Comment: That's not easy to understand. Are you sure you are answering the right question? Or answering anything at all?

Why do we take a derivative?


Do all active Esperanto-speakers use the Internet?

Question: Esperanto is a good tool for international communication. The Internet facilitates international communication with the help of e-mails and social media. Is there a significant amount of active Esperanto-speakers that do not use the Internet, and only use Esperanto in local clubs or in postcards?
Answer: There are many elder Esperantists who don't use the Internet. At the Universala Kongreso I discussed with some people about Esperanto radio stations and mentioned podcasts. And they were like, if it's only on the net (and not e.g. shortwave) it's not real.
Comment: Elders probably have so much information and experience to share, but I feel we live in different worlds. If they don't use the internet, and if I never go to a flesh-and-blood meetup or contact them by snail mail, we'll never meet. Some people never will go to a physical meetup, for lack of time, money, or desire--and somewhere between those reasons I might be one of those people. Almost all of my Esperanto use is exclusively online. It's a strange feeling that there is such a big rift in the community demarcated mostly by age (and factors mentioned in Enrique's answer).
Answer: There are many reasons not to use the Internet:
You cannot afford a computer. Even if you have a computer,
you cannot afford the connection. There is no Internet in the
area where you live. All of this can happen in any country.
Some people in Africa save as much as they can to pay for
one hour at the cyber-cafe. One of them once told me that she
have to pedal her bike about one hour (each way) to reach the
cyber-cafe.
There are some Esperanto speakers in USA, Europe, and some
other countries who send books and other items (paper,
pencils) to people that aren't connected to the web.
By the way, next year I will be 80 and I use the Internet, and
have a vast web site in 3 languages at:
<code>http://esperantofre.com/edu/eepag.htm
</code>
Comment: Good point about computer/internet access. I have had similar conversations with Esperanto speakers from several African countries who I've emailed and chatted with, and who wanted to use the post to exchange things rather than relying on email.
Answer: In France I've been in some local clubs where almost all Esperantists where elders who didn't use internet (with some exception).