Initially Bracketing Minimum for Line Search

Question: Leafing through a few textbooks, I've noticed that the problem of initially bracketing a minimum during a line search tends be an afterthought (at least in my undergraduate texts). Are there well-established techniques or best practices for this type of problem, or are solutions typically application dependent? Can anyone recommend some references on the topic?
Answer: Usually one doubles the initial step until the Goldstein condition is violated or (in a feasible point method) the boundary is reached. Then one has a bracket. (If no such step exists, the objective function is unbounded below.) One can also use less conservative extrapolation procedures, but these require good tuning to be robust enough in a general purpose solver.
Answer: In my experience establishing the bracket is very often application-dependent.  If you had real constraints or an algebraic derivation for your bracket, you'd use it of course!  Usually there's an appeal to either

nature this physically makes no sense outside this bracket
computability this would be too hard to compute outside of the bracket
objective solutions outside of this region are otherwise undesirable.

I'm hoping someone else can come in with a more algorithmic approach, which is what I think you're looking for here.
Comment: I think your answer is spot on. For real problems, you almost always have a reasonable first guess for upper and lower bounds of variables. The engine speed in a car can only vary between 0 and 20,000 rpms; the fuel injection rate can only vary between 0 and 10 liters per hour; etc -- in other words, for real problems, you *know* what values can be.


Change grip between sets?

Question: Is it useful to change the grip between sets?  If I'm doing lat pulldown or seated rows, is it helpful to switch from narrow to wide grip between sets?  Or am I diluting the value of doing multiple sets of one exercise?
Answer: That depends on a lot of things. Basically, changing your grip from narrow to wide changes the level of involvement of the different muscles. Changing your grip might be good in that you can hit areas that aren't being targeted enough otherwise in your workout(s) or it could be not so good if you're removing the stress from a major area before it's fully exhausted.
Which of those two is the case is going to depend on your full workout, where your body is physically, etc.
One useful situation for this is when the supporting muscle(s) aren't able to "keep up" with the major muscle in an exercise. You can change an exercise slightly (or move to another exercise) to take the strain off of the supporting muscle(s) while still targeting the major muscle. I hope that makes sense.
Answer: Useful is a very relative term in relation to working out. Varying your grip between sets will change the order in which muscles are activated in order to complete the exercise. For an example, see the article on BodyBuilding.com about the various chin-up grips and their varying strengths and weaknesses.
Changing the pathway you follow to achieve a full repetition will also change the activation order of the muscles, and also activate muscles that you might not normally activate much, if at all.
You won't be diluting the value of doing multiple sets as long as you are still achieving a full range of motion during the exercise, as all the muscles will still be activated, just in varying order and intensity.

Change grip between sets?


Isotopes of Elements

Question: When we talk about the substance $\ce{H2O}$ with a molar mass of $\pu{18.0 g/mol}$, what hydrogen and oxygen isotopes are present in the $\ce{H2O}$ molecules? In other words, what isotopes do the symbols represent?
Answer: Most periodic tables quote the molar mass of an element as the average mass of the element given the natural abundance of the isotopes. Chlorine, for example, has a standard atomic weight of 35.45 which is a weighted average of ~75% 35Cl and ~25%  37Cl, the two common isotopes.
But isotopes of hydrogen and oxygen are rare. So the vast majority of water molecules will not contain them. So, at least to one decimal place, most water will have a molar mass of 18.0.
At it's natural abundance of about 0.25% 18O won't noticeably affect the molecular weight of water until you can measure it to at least 3 decimal places of precision. Slightly simplifying (assuming pure isotopic masses are exact integers, which they are not), water containing that isotope at its natural abundance will have an an average mass of 18.005 rather than 18.000.
When working with normal (unenriched) substances the best assumption is that they will contain the normal isotopic abundance of the component elements (which are well known and, for most elements, don't very much by source). But the effect on molecular mass will often be small and you will need a fair amount of precision to notice it. If you are not working to very precise masses, it is fair to assume natural isotopic abundance.
Answer: It's impossible to find isotopic composition of a compound with a molecular weight containing only one decimal point ($\pu{18.\underline{0} g mol-1}$). Typically, 6th decimal place is required in order to refine percentage of each isotope.
Symbols themselves (such as $\ce{H}$ and $\ce{O}$) don't carry any additional information except atomic number $Z$. For isotopes you need to use so-called AZE notation: $^A_Z\ce{E}$, for instance $\ce{^1_1H}$ and $\ce{^{17}_8O}$. Since $Z$ is already known from $\ce{E}$, simplified notation is often used instead: $\ce{^1H}$ and $\ce{^{17}O}$.
Comment: Unless you took one water sample from the nuclear reactor and the other one from the river, isotopic distribution is going to be the same as elements have uniform isotopic distribution in nature. You probably want to read these topics: https://chemistry.stackexchange.com/questions/71942/what-is-the-standard-molar-weight-of-carbon-and-why and https://chemistry.stackexchange.com/questions/38082/what-is-the-difference-between-molecular-mass-average-atomic-mass-and-mola and any introductory chemistry textbook.
Comment: I'm just confused as to where the molar mass of a substance comes from. As in how do we know how much a mole of a substance weighs exactly? I could have 2 samples of 1 mole of water, and one could weigh more than the other because one may contain more heavy water (D2O) than the other.
Answer: Hydrogen has 2 stable isotopes,H-1 and H-2, Oxygen has 3 stable isotopes H-16, H-17 and H-18.
There is very little of the minor isotopes so the molecular weight of water is 18.
However hydrogen and oxygen are light elements and differences in atomic weights have detectable differences in physical and chemical properties. For example H-2 compounds can have lower reaction rates than the H-1. Boiling points and freezing points of various isotopic forms of water differ slightly. Indeed it possible to distil water to separate the various isotopes.
This also happens in natural systems where minute variation in isotopic contents trapped in ancient  ice can be used to gauge the ocean temperature of that time

Isotopes of Elements


German flash cards with pictures and no English?

Question: I am looking to increase my German vocabulary and am looking for a good series of flash cards that does not contain any English, but instead just has pictures and the German word. Does such a thing exist? I have tried Googling, the Apple Store and Droid Store, but have always found flash cards with English words.
Comment: You might want to check with a German catalogue company like Bertelsmann and order German children's items, etc. Materials intended for anything other than German only will have the other language on them. That's kind of the point.
Comment: I also immediately thought of children's books with this description. But unfortunately the vocabulary will likely be too small to be of use for an adult trying to learn German - unless they want to talk to a small child ;)
Answer: On this Goethe Institut page, there's a cute Flash game (Spiel 03: Memo-Spiel) that does what you're looking for. Found it by searching on ""memo-spiel" bild wort lernen wortschatz", if you keep looking you may find more. Tried the search with "Memory-Spiel" instead of "Memo-Spiel" but got only links to articles not games. Possibly "Memory-Spiel" is trademarked and reserved to the original publisher.
You could make your own: glue a picture to a cardboard square, glue a word to another square. Repeat with additional word-picture pairs. Turn all squares face-down and start having fun!
Comment: On the making your own end - I actually am a software engineer. Do you think a product like that would be useful?
Comment: You mean, create a finished product using traditional flash cards, memory games, multimedia, on-screen interaction, user-controllable printouts, everything in color, bling-bling, eye candy? And then market it yourself or sell it to a publisher? It sounds like a terrific idea! However -- and please don't get upset, I don't want to sound discouraging -- but Langenscheidt already has done [all that and more](http://www.vokabeln.de/v6/bestellung.htm)... although right now only for English, French, Spanish, Italian, and Latin... but they could easily add German, too, at the drop of a hat.
Comment: In the meantime, here's [another memory game](http://www.goethe.de/lhr/prj/woe/mem/deindex.htm) from Goethe Institut: You match "emigrant" German words and phrases that have settled in other languages with their long-form explanations. Completely silly and great fun.
Answer: No flashcard, but perhaps a Bildwörterbuch (Visual dictionary) is a help:

Pons has a Bildwörterbuch
Hueber has one with 1000 words.

I tried also a search for Quartett
There are some nice cards for kids, but I think you are looking for other cards.
There are some [Kartenspiele für den Deutschunterricht][7], there is for example a page Quartett Berufe
Wegerer.at has also some nice pdfs.
Comment: I marked this as the correct answer because this book is wonderful. It does have English, but is almost exactly what I'm looking for. Thank you.


Change hostname on linux ha failover case

Question: I have configured two machines to do a warm standby so that machine 2 can take the ip of machine 1 if that should fail and become its replacement. sadly, thats not enough, i need to change the hostname/fqdn too because some software relies on the local hostname and crashes if the hostname is different after the failover. so the question is: how do i change my hostname and change it back once machine 1 is back on track?
Answer: Generally speaking, you can write a script which performs the necessary hostname changes to the system - both ways - and use that as a service that your failover configuration uses.  If you are using the heartbeat software the /etc/ha.d/resource.d/MailTo script is a fine place to start looking for an example.
There are quite a few example resource scripts here:  http://www.linux-ha.org/wiki/Resource_Agents


Best way to avoid damage playing Rogue in Dragon Age II

Question: I recently started playing Dragon age II for the first time. I chose the Rogue class and would like some pointer on avoiding damage. The Evade ability comes in handy, but can I combine this with other abilities/ party abilities?
Answer: The best way to avoid damage is to not draw aggro.  This sounds easy, but since you will be dealing the most damage in the party, its quite hard to do.
Only attack enemies that are currently attacking your party's warriors helps a lot.
Like you said, using the subterfuge skills like Evade and Stealth will help out a lot.  Other things that help is positioning.  Make sure you are standing behind your party's tank at the beginning of a fight, and instead of immeditaely attacking something nearby, slowly work your way towards a high value target (such as the enemy's mage) before doing your first strike.  Don't go charging into the middle of a group and expect to stay around for long.
If you find yourself being chased by multiple melee enemies, I'd recommend running away instead of fighting them straight on.  In these situations, tossing a flask at the group may help you break aggro.
Finally, when breaking aggro, make sure you aren't doing it near your spellcasters as they'll then become the new target, often making the situation much worse.
Answer: In addition to Z's answer, one of the Rogue's biggest benefit to a group is helping the tank (term used loosely at times, you can run parties with no true tanks) get the focus of enemies. Your Scoundrel tree is perfect for this:

Armistice will force enemies around the selected friendly target to forget they exist, going after the 2nd on threat instead. You can use it on yourself, especially effective as melee when you're in the middle of everything.
Back to Back will teleport you out of harm's way, but not make you lose threat. Effective to kite slowed enemies, maybe in concert with Miasmic Flask or Fatiguing Fog to let her kite more without getting hit.
Goad is the opposite of Armistice, it forces enemies around the friendly target to target them (the friendly) instead. Sort of a forced AoE taunt.

Additionally you can use your shadow to escape from view unharmed. I've never went down that path myself though to comment on its effectiveness. I prefer playing with the threat of enemies instead.
Edit: Another really useful tip, sort of related to this, is to use your abilities as little as possible to survive. Rogues get their damage from auto-attacking, and using abilities interrupts their sustained DPS. Nothing wrong with stunning everything or redirecting focus if needed, but if you're in no danger just sit behind an enemy and kill it, you'll take a lot less damage the less they live (especially in a large cluster, kill 1-2 high damage squishy targets, like mages, and it suddenly becomes a lot easier to manage).


Is it good practice to speed up and slow down where not written in a song?

Question: When a accelerando and ritardando is not written, is it bad to speed up and slow down where you think it "sounds better?"
This seems like against practicing with a steady beat, because it makes a metronome useless.
Comment: Only Lieutenant Commander Data would object to it ...  at first. The he'd find it intriguing.
Comment: My piano teacher always said to practice with metronome with a steady tempo, and if the piece calls for it, add rubato after.
Comment: Certainly, provided (a) you *can* play it in strict time, and (b) nobody is trying to dance to it.
Answer: I think it depends very much on the genre, style, and period of the music.
For some styles, heavy use of rubato is normal and suits the way the music is written, while for others it would spoil the piece.  (Think how bad a rock song would sound if the drummer kept varying the tempo!)  Even within Western classical music, rubato is much more common (and expected) in, say, Romantic pieces than in earlier Baroque.  There are always exceptions, of course, but you must be sensitive to the composer's intentions.
For example, there's a recording of Bach's French suites that I find unlistenable due to the inappropriately-high levels of rubato employed.  The performance style would probably work well for, say, Beethoven, but to me it just sounds terribly out-of-place and vulgar for Bach.
There have been times over the last couple of centuries when people seemed to think that every piece of music should be played the same way!  Thankfully, historically-informed performance has become more popular, and people are at least aware of alternatives.
So it partly comes down to understanding the style of the piece, understanding what the composer intended and how people of the time expected it to be played.
However, it's also down to your judgement and personal taste!  Ultimately, if you're performing the piece, you have the final say, and shouldn't be playing anything you're really not happy with.
Finally, you should certainly be able to play a piece well at a steady pace, without any rubato at all, adding expression in other ways.  Then you can judge how much (if any) is justified.
Answer: It's not bad per se, but it's dangerous.

Making this a habit will impair your ability to play with others.
As an expressive device, varying the tempo can be distracting.  (That's why it's notated more rarely than varying the dynamics.)  The exception that proves the rule here is instruments that can't vary dynamics.  When one famous harpsichordist "held on to a fermata, worlds tottered and the sun stopped until she went on to the next phrase."
Comment: From that same paragraph: "The art of not playing in tempo—one has to learn it."
Answer: Depends.  Some people use 'expressive rubato' as an excuse for bad time-keeping.  In particular an excuse for playing the tricky bits slower than the easy bits!   Flexible time is probably a bad idea in a rhythmic groove-based song.  It's almost required in an operatic aria though.
The fact that sometimes a metronome isn't appropriate doesn't make metronomes useless!
Answer: As Lawrence said, you are describing "Rubato". My professor in college recommended playing the piece first at a more "rigid" tempo and then using your own discretion. You want rubato to feel tasteful enough so that a professional listening in the audience could dictate the rhythm you played without seeing it.
In general, a solo will have more rubato and adding more instruments will tend to make the tempo more rigid. That being said, conductors with good vision and execution can train a group to perform rubato together.
Answer: Some metric flexibility in certain pieces can make them heartstoppingly effective.  The best way for you to convince yourself of this is to listen to some recordings.  I will suggest two:

Brahms Sonata for Cello and Piano in E minor, 2nd Movement.  Contrast the Rostropovich & Serkin recording, which has quite has a quite subtle give and take with the meter, and the Maisky & Gililov recording, which shows greater flexibility.  Both are perfectly valid interpretations.  Listen to the whole movement of each.
A prelude of a Bach cello suite.  I will let you listen to several different interpretations yourself to identify one with more flexibility and one with less.
Answer: This is an actually precarious question since wanting to hear a particular answer makes it likely that you are in danger of overusing that answer.  Timing is a very strong part of how music is interpreted.  To actually work in that manner, every change must be recognizable as deliberate without acting as a distraction or mask.  So the way to employ timing variations as an expressive ability is a very, very good control over the precision of timing.  This is complicated by your sense of timing getting distracted by actual playing, something that the listeners are not exposed to.
So it usually requires a lot of metronome (or drum computer) work and recording and listening and discipline and good control of the piece (basically, you should be able to play everything 20% faster than at performance speed without falling apart) to effectively employ timing as an expressive device in a tasteful while unambiguous manner.
Comment: What do you mean "This is an actually precarious question since wanting to hear a particular answer makes it likely that you are in danger of overusing that answer"?
Answer: Changing tempi is part of good performance practice, in my opinion.
As noted above, we do it less in earlier than in more recent music.
But I can't imagine that a player or singer in Bach's day would have resisted imparting a bit of give and take on notes he or she found particularly engaging.
No one disputes a certain "allowable" range of base tempi for a piece, even for early music, and discreet rubato here and there is not that different.
Where I do have a major problem with rubato is if one or more notes are held so long that the listener might sense metric change where there is none, as, say, if 3 triplet eighth notes were played or sung such that the last of the three was extended to twice its written length, making the whole sound more like a 2 eighths and a quarter.
Answer: ask your audience.  if they think it sounds good, then it is good.
but just cuz you think it's expressive doesn't mean your audience will like it.  "this guy keeps speeding up and slowing down for no good reason and the lyrics in my head aren't matching up - he sucks"...


What size wire and breaker should I use for a small one bedroom cottage?

Question: Have a small one bedroom cottage. I need to install a subpanel in it. I have a two hundred amp panel 30 feet away. The only things I will power in the cottage are two can lights, six outlets, small window unit and a small refrigerator. What gauge wire should I run to the subpanel? Also what size breaker as the main should I use in the sub?
Comment: Possibly more info needed , is there a cooking area? A bathroom or a laundry area, also your state / location may make a difference along with the square footage.
Comment: Is there cooking and/or laundry facilities in the unit?  Also, how just how many square feet is it, how many BTU is the window unit, and how is this cottage heated?
Comment: Quick math: Lights not enough to matter, AC 4 amp, outlets 20 amp, minifridge 2 amp.
Comment: ..I mean outlets 9 amp. That could be fit into one 20 amp circuit, but two 15 amp circuits might be better for futureproofing.
Comment: IMHO (not an electrician) 30A would be enough, but as a living area som jurisdictions may require more, like 60A or even 100A (kinda silly for a cottage).
Answer: If I were you, I'd go as follows (assuming US split 240v)

Run 8 gauge THHN from your main panel to your subpanel (in buried conduit) and use a 50A breaker in the main. Run 4 wires so you get 240v and ground. Should be more than sufficient for anything you can throw at it and you can always expand if needed. Be sure to ground your panel to a grounding rod while you're at it.
Run your lights on a single 15A breaker. Makes adding lights easier, it's cheaper (14 gauge wire and 15A switches, and don't forget to add neutrals to the switch boxes!) and you won't be in the dark if you blow a breaker in the subpanel
Run a 15A breaker to a single dedicated outlet for your AC. It's overkill, but I'm assuming you have a 5k-6k BTU window unit. That's 6-7 amps, which is a lot to share with other outlets, even on 20A (especially with 2-3A for a fridge). If you ever decide to upsize, you have no worries about rewiring it either.
Run the rest of your outlets on one 20A circuit (12 gauge wire). Don't skimp and run them on 15A because you have a lot of 14 gauge wire. You'll regret it the first time you pop that 15A breaker.
Comment: you *can* use 5-15 (these are the ones with just 2 vertical slots) style outlets on a 20A circuit.  they are the same metal structure inside as the 5-20 ones.  the code allows this case as long as there are at least 2 such outlets.
Answer: (Not an electrician; if one shows up, listen to them instead. Also, I'm assuming America, or at least a 120V country.)
As I noted in my comment, one 20 amp circuit could handle the load you specified. However, there's always something you've forgotten, so I'd recommend going bigger. (Consider the load of someone running a microwave (10 amp), a hotplate (10 amps), a hairdryer (10 amps), and other stuff (10 amps). You can easily hit 30 amps of usage just from kitchen equipment.) The difference in cost isn't that big, so I don't see a good reason to go below 40 amp, and you should go higher if you expect even a remote chance of people cooking in the cottage.
As for the wire sizes, a 40 amp breaker needs at least 8 gauge wire. (And remember to get outdoors-rated wire and protect it properly.)
https://www.totalhomesupply.com/wires-and-circuit-breakers
Comment: There are several issues here -- chiefly, NEC Art. 220 comes into play, and you haven't at all accounted for it
Comment: America is really a 240V country (don't tell our electricians).  we just put the ground in the middle.  it's more balanced that way.  my computer seems to like it.


I run one hour without a break everyday. Am I over training?

Question: Normally I run 1 hour every day without taking breaks. After reading posts about overtraining, I am worried that I am doing that. How long can we run without over training?
Comment: You may not be over training, but whether this is a good training regime depends on what you want to achieve. You may be doing "Junk Miles".
Comment: without taking breaks ? you are really a super hero, i cant run more than 10 minutes without taking break at the age of 26 :)
Answer: No one can say how much you can train before you become overtrained. Firstly, there are too many factors involved, such as nutrition, weather conditions, your cardiovascular fitness, your fat percentage, your strength and explosiveness, the presence of any diseases (in particular autoimmune or inflammatory). Even if science knew how all those factors affected training capacity, and how much, there is still the individual factor. Your personal biochemical profile; level of cortisol and how quickly it rises, testosterone and growth hormone, enzymes and proteins at the cellular level.
This is the big problem with the overtraining syndrome; no one can really know beforehand how much he/she can train. It is only when you start experiencing symptoms of overtraining that you can begin to titer your training down to maximal, but safe, levels.
One simple thing thing that you can do is to measure your morning heart rate. It's simple, and everyone has the equipment for it. Keep track of your morning pulse every day, and if it starts going up about 10 beats on average for 3-4 days, then it's time to rest or decrease training intensity (I speak from my own experience. For you the numbers may be different, however the principle is the same). I had overtraining syndrome a couple of years ago, and of all the symptoms, the most objective one, that I could gauge, was my morning heart rate which was around 80 instead of the previous 40-45. Since then I have kept track of my HR every day.
So to sum up: you can't know how much you can train before becoming overtrained. What you can do however is to keep track of your fitness and recovery levels. This is most easily and objectively done by measuring changes in the morning heart rate.


Is any device installed on airplane to measure wind speed relative to the ground, and its direction?

Question:
A device or tool which can measure actual wind speed to the ground rather than to the airplane. Also a device which detect the wind direction to the plane. The device I meant is something like this pitot. But unfortunately this pitot is measures the airplane relative to the air around it, not the ground.
Comment: [How is the wind direction and wind speed measured in flight?](https://aviation.stackexchange.com/q/23426/14897)
Answer: The "wind speed relative to the ground" would just be the (vector) difference between ground speed and true air speed:
 (image source)
Most aircraft do not measure ground speed and track directly with instruments installed on the aircraft. It can be measured with a Doppler radar (see Peter Smith's answer), which is only used on military aircraft (mostly helicopters) today.
Ground speed and track can be determined with external tools:

DME: The Distance Measuring Equipment can be used to measure distances to fixed radio beacons equipped with DME (usually VOR/DME or VORTAC). If you know the angle at which you are flying towards/away from/to this station, you can calculate ground speed from the change in distance. Some DME instruments display this:

(image source)
When tracking a VOR, you also know the true track angle required for computing the wind direction.
GNSS: A Global Navigation Satellite System like e.g. GPS allows precise determination of the aircraft's position. The ground speed can be calculated from the change of this position and the true track is simply the direction of change. A more accurate determination is possible by measuring the Doppler shift of the signal (thanks to bogl for pointing this out).
ADIRS: An Air Data Inertial Reference System as installed on airliners knows the aircraft's attitude and position based on integrating data from accelerometers and gyroscopes. It can be updated via GNSS, but would still provide data for ground speed and track without it.

Modern avionics can display the result of these computations directly:

left: Boeing 737 Navigation display (source), right: G1000 (source)
Comment: It is a "sensor fusion" type device, taking into account the heading, ground track, air speed and ground speed. Pilots are taught how to do this with an E6B and using other means than just GPS, you could do it just by dead reckoning and a compass if you wanted to. I'm sure the G1000 uses the GPS though.
Comment: The wind direction and speed relative to the ground can also be calculated if the aircraft is fitted with a doppler navigation system. This measures the *actual track* of the aircraft and is common in military helicopters and some older military fixed wing aircraft.
Comment: There are a lot of instruments that *calculate* the wind speed/direction. For example it is available on the G1000 (you can see it in [this picture](http://blog.adamfast.com/wp-content/uploads/2012/05/IMG_0848.jpg), the box with the arrow and number).
Comment: @RonBeyer I assume the G1000 would require a GPS signal to do this calculation?
Comment: @RonBeyer thanks, I added the image as an example.
Comment: Most Soviet airliners (including those still operating) had a Doppler radar.
Answer: A Doppler navigation system based on the doppler radar principle provides the actual ground track of the aircraft.
Such systems require at least 3 beams and often are 4 beam (the 4 beam system fitted on the Wessex 1 was a high precision unit used in seaborne rescue - overcoming the backscatter from the water and waves makes for a challenging design).
The Sea King HAS 1 had a 3 beam system which actually fed ground track information to the ARI5955 Radar display (cannot find a suitable link) so the operator could view a moving aircraft across a static terrain map (very interesting and new for the time - early 70s).
The basic principle is that the beams are transmitted at 45 degrees, -45 degrees and -135 degrees (and +135 degrees for a 4 beam solution) to form a cross:

The beams are aimed downward so they measure the doppler effect relative to the ground; each beam will have sine and cosine elements; if they are equal for all the beams then there is no drift; of they are not equal, the actual sine and cosine outputs can be effectively added to find the actual ground track.
From there, if we know:

Airspeed
Ground track
Ground speed

We can compute the aircraft drift angle and therefore the wind speed and direction relative to the ground.
Although the 4 beam system is rather intuitive, we actually only need 3 beams to compute the drift angle.
Dopplers do have susceptibilities (much of which depends on the downward beam angle), but the advantage of being totally self-contained is quite large.
Answer: The cheap way is by means of a drift meter, which is a telescope that points straight down towards the ground and which contains a set of crosshairs that can be rotated. The navigator looks through the telescope and rotates the crosshairs so as to determine the angle between the plane's movement through the air and its movement over the ground. From this she can calculate the wind triangle. This is how it was done before doppler radar and other electronic navaids were invented.
Answer: As far as I know, airplanes just use external data for winds aloft. GPS allows to measure ground speed and true course over the ground, that's good enough.
The closest thing to measuring actual wind speed at altitude is GPS drift in a balloon, or gliding flight computer that detects circling flight (using GPS) and calculates drift.
Comment: This isn't correct. The Flight Management Computer (FMC) in an aircraft will take the heading and true airspeed and compare that vector to the actual track over the ground from the INS; the difference in those two vectors is the effect of the wind.  Aircraft use external data -- i.e. forecasts -- when predicting ETA's and such to waypoints ahead, but the winds "now" are calculated internally.
Comment: Fair enough, I'm talking about simple GA planes. Wonder if an airliner heading sensor is precise enough to not introduce substantial error...
Comment: The heading from an INS unit is extremely accurate; the winds out of an FMC calculation are substantially more accurate than most forecasts.


Simulating Hudgkin Huxley neural network

Question: I'm starting work on a computational neuroscience project where I want to create my own model of a spiking Hodgkin-Huxley neuron and connect many instances (about 400) of this model through synapses. Is there a generally accepted way to do this? I have experience in Python and Matlab but I'm wondering if there are any good packages or other software to create neurons and connecting them into a network?
Comment: don't use HH neurons unless you absolutely have to.  First implement a rate model network, then once that's working switch to a integrate and fire network, and only once that's working switch to HH neurons.  No point in making things hard for yourself unless you absolutely have to and you've gone step by step through simpler versions.
Comment: I'm continuing a project from a PhD dissertation so I guess they were at that point. They used pretty old software and I'm mostly looking for currently supported packages/software that I can create networks with and run on the super computer at my school. Thanks!
Comment: Just an idea: to determine what is "generally accepted", you could potentially use Google Trends or Google Scholar result counts to get an impression of what is in use after having identified potential candidates. Alternatively, you rely on the opinion of someone who is currently active in the field.
Comment: More options [here](https://psychology.stackexchange.com/q/23858/7001).
Answer: I am old and my experience with this area is 20 years out of date, but I would still go with https://neuron.yale.edu/neuron/
Comment: Well, the website definitely doesn't look 20 years old.
Answer: You can simulate a network of hodgkin huxley neurons quite easily with Brian, a python package for simulating networks of neurons. http://briansimulator.org/demo/ <- there's actually a demo of what you want here, I think.
There is also Neuron, as a previous poster answered, but I don't think you need this unless you are doing morphologically detailed simulations.


how to create the way of talking as in the red room from Twinpeaks?

Question: When Agent Cooper listen to the people in the red room they have a distinctive way of talking. They speak forward, but it has some quality to it you hear when you play something backwards, yet it does not sound like as if you would have record yourself talking backwards.
Comment: Are you referring to the Twin Peaks TV series? You would help yourself by linking to a clip that demonstrates what you're after.
Comment: Yeah, I have no idea who agent Cooper is, what the red room is, or what sound you're talking about. Is there an example on YouTube maybe? From what you've written, it is entirely possible that the actors learned their lines backwards and then filmed the scene backwards and then they reversed it on playback so it goes "forwards" but has the effect of seeming backwards. They did that for a **song** by the band Mutemath who had to learn the whole song backwards for their music video. That song is *Typical* if you want to look up the video.
Comment: https://www.youtube.com/watch?v=W9IpNxMiFIs   He starts talking at 2:25
Comment: I wish you could downvote comments.
Answer: The actors recorded their lines then reversed them, then learned the backwards version.
Answer: As MATTW pointed out (and according to David Sonnenschein's book) they played and spoke backwards and then reversed it.


Is it a sin to delay making up missed fasts till after the next Ramadan?

Question: Someone missed a few days of fasting during Ramadan because of a temporary illness. He should make up these fasts when he is not ill anymore. However, is there a time limit to when he can make it up. Can he make up it anytime he wants like after the next year's Ramadan or is this a sin for delaying making up fasts for no excuse.? What if he was an adolescent who has started puberty but fasting was obligatory for him and he missed some salah due to illness and he wants to make up for the ones he missed but fasting is still hard for him and the next Ramadan is coming and he still has not made up for these fasts? Can he make up for these fasts after the next Ramadan or will he be sinning?
Answer: There is no guarantee that one would still be alive that long in the future. One should make up debts and duties as soon as possible.

The imams are agreed that whoever does not fast some days of Ramadaan has to make up those days before the next Ramadaan comes.

More details in this fatwa.


Add a Watch-only Wallet in Bitcoind

Question: When running bitcoind under OSX/Linux, how can we add a watch-only wallet using the JSON RPC? Do we need the public key or is the bitcoin address sufficient?
Answer: As of bitcoind v10, there is support for watch-only addresses. A bitcoin address is sufficient. The bitcoin-cli command is:
bitcoin-cli importaddress "address" ( "label" rescan )
Where "address" is the address you wish to watch, "label" is an optional label for the the address, and "rescan" is a boolean of whether bitcoind should rescan all previous transactions for activity relating to "address".
The example in bitcoin-cli's documentation of the JSON-RPC command is:
curl --user myusername --data-binary '{"jsonrpc": "1.0", "id":"curltest", "method": "importaddress", "params": ["myaddress", "testing", false] }' -H 'content-type: text/plain;' http://127.0.0.1:8332/
Release notes for watch-only wallet support
Comment: thank goodness for this new functionality. this should have been one of the first things that was implemented in bitcoin. how else can anybody run a trustless e-commerce site with air-gapped private keys? i was writing my own re-implementation until this feature came out purely for this purpose :p
Answer: Today this is not possible.  There's been an active discussion on this topic on GitHub, but it's currently not implemented.
There was a pull request submitted a while back that some people may have started using in production, but my understanding is that the code is old and currently not buildable against the current source.
It would be a great feature, so I hope it comes out at some point.

Add a Watch-only Wallet in Bitcoind


Forward IP packets to tunnel device

Question: I have created an tunnel device using

ip tuntap add dev tun0 mode tun user 0 group 0

I then assign it an ip address 192.168.0.1/22

ifconfig tun0 192.168.0.1 netmask 255.255.252.0

On my ethernet device eth0, I receive packets from machines in the ip address range 192.168.1.2-192.168.1.5. I would like these packets to be forwarded on the tunnel device. I do not wish to create a bridge between the ethernet and tunnel device. I therefore  added routing entries in the routing table as follows.

ip rule add from 192.168.1.0/24 lookup myinternal
ip route add default via 192.168.0.1 dev tun0  table myinternal

I have flushed (removed) all ip tables entries.
There are two entries however

iptables -A FORWARD -i eth0 -o tun0 -j ACCEPT
iptables -A FORWARD -i tun0 -o eth0 -j ACCEPT

When I do a tcpdump on tun0 I am not able to see the packets from eth0. However I can see the packets when I do a tcpdump on eth0. I would like to know how can I forward/capture these packets on tun0. From tun0 I would later on like to process these packets and reply to them from my application and if required pass them on to another interface. I cannot use eth0 for my activities.
I have enabled forwarding using systl for ipv4.

cat /proc/sys/net/ipv4/ip_forward
1

Furthermore there is no default route entry in my main routing table.
Answer: I know it has been six years, but in case anyone stumbles here with a similar issue: this sounds like the reverse path filter 'rp_filter' dropping traffic.
From the link:

log rp_filter dropped traffic:

echo 1 >/proc/sys/net/ipv4/conf/(interfacename)/log_martians

disable rp_filter:

echo 0 >/proc/sys/net/ipv4/conf/(interfacename)/rp_filter

Forward IP packets to tunnel device


How to encourage toddler twins to share?

Question: Our twins are just over eighteen months and are having issues sharing. Given their shared age the answers provided to "how do you encourage siblings to share?" is not specifically aplicable. So far it's mostly minor and we've been able to coax the children into doing the "right" thing when they've taken something from the other. However, we see this sharing issue as having the potential for becoming a larger problem. How can we encourage sharing between toddler twins?
Answer: Developmentally they're at the age where sharing is an alien thing, so what you're seeing isn't necessarily a bellweather for problems down the road.
That being said, the best luck we've had teaching our 21-month-old to share is modelling the desired behavior.  When he picks up something that's interesting to him but that we'd rather he didn't play with (the remote, for example) we ask him if we can have it.  He brings it over, we take it and thank him PROFUSELY for sharing. Same for his sister; if he picks up her lovey, he brings it to her and gets HUGE thanks for sharing.  It's definitely sinking in; all I can hope is it sticks when he hits the "mine" phase.
ETA: Link for some basic developmental information
Comment: Absolutely. Sharing isn't something that kids that age can really wrap their heads around. Demonstrations of desired behaviour from you, coupled with words and tone, will be effective.
Comment: Just adding that now that he's hit the "mine" stage he's still FABULOUS at sharing.  To the point that, now that he's potty-training, when he gets a visit to the prize box he insists that "Sissy" gets a prize too.
Answer: I have twins who are 2.5 years old.  At 18 months consider having the kids take turns with a toy and not play with it at the same time (another form of sharing).  First it's Sam's turn and then it's Alex's.  You can use a timer so after 2 minutes they have to switch toys.  Be very encouraging, thanking them for sharing and playing nicely together.  At this age trading is better than sharing.  If Sam has something Alex wants encourage Alex to offer him a toy in exchange for a turn.  Finally, use the word sharing in your own life.  If another adult passes you the salt during dinner thank him/her for sharing.
Answer: I agree with Valkyrie.
To add a technique, tho, you could also try sitting and playing with one or the both of them a few times. Emphasize when you're giving stuff to them. Emphasize when you don't want them taking the knives that you're playing with at that particular moment, especially when there's other knives on the floor between you just itching to be played with.
Or... maybe not knives. Bandsaws.


Can a Gentile and Noahaide put a prayer note in the kotel

Question: Can a Jew put a prayer note for Hashem on behalf of a gentile Noahide in the spaces of cracks of the Kotel, if that gentile is unable to go to Israel to do it himself?  I know that any legitimate prayers are accepted near the wall by Hashem.  Can this type of prayer note be kept in the Kotel slit on behalf of me by anybody -- does halacha allow this?
Comment: yes and but for a goy we use the father's name instead of the mother's name
Answer: Yes.
Kings I chapter 8, 41-43
http://www.mechon-mamre.org/p/pt/pt09a08.htm
41 Moreover concerning the stranger that is not of Thy people Israel, when he shall come out of a far country for Thy name's sake--
42 for they shall hear of Thy great name, and of Thy mighty hand, and of Thine outstretched arm--when he shall come and pray toward this house;
43 hear Thou in heaven Thy dwelling-place, and do according to all that the stranger calleth to Thee for; that all the peoples of the earth may know Thy name, to fear Thee, as doth Thy people Israel, and that they may know that Thy name is called upon this house which I have built.
Comment: There are not actually any halachic rules about placing notes in the Kotel, not for Jews, and not for anyone else. These verses seem to be a prayer that the non-jew will be answered at this place just as a Jew should be answered. As far as notes go, that should also be the same.
Comment: at Ariel k & Binyamin, thanks for the well studied quotes and your answer.


Image stabilization in interchangeable lens camera body?

Question: Are there any interchangeable lens cameras which have image stabilization in their body too? If yes, does it help more to compensate images's shakiness or will it negatively affect the lens' image stabilization?
Answer: Panasonic does this on some of their camera bodies (debuting in the GX8). In this case, both systems work together for cumulative benefit. They call this Dual Image Stabilization — but beware, because other companies (I'm looking at you, Fujifilm) use that same term to simply mean optical stabilization plus cranking the ISO up to get faster shutter speeds.
As far as I know, the other systems with in-body stabilization (Olympus, Sony, Pentax) only use one or the other. It's definitely the case that any such system without close communication between the parts would make things worse rather than better.
Answer:
Are there any interchangeable lens cameras which have image stabilization in their body too?

Yes. Several manufacturers have camera body based stabilization and also offer lens based stabilization on some of their longer focal length lenses. But most of those systems are used on an "either/or" basis and not with both lens based and camera based stabilization active at the same time.

If yes, does it help more to compensate images's shakiness or will it negatively affect the lens' image stabilization?

It all depends on how you define "help more."
Lens based stabilization systems can provide more stabilization where it is needed the most - at longer focal lengths. This is because as the angle of view is narrower (longer focal length) the same amount of camera movement creates more blur. But lens based systems can only compensate for camera motion in the x and y axes (tilts/pans). This is, however, the most common type of camera motion that needs the assistance of image stabilization.
Camera based stabilization systems can provide stabilization not only on the x and y axes, but also on the z axis (rotation around the optical axis of the lens) and for shift movements (the camera and lens are both moved laterally).
If the primary camera motion is on the x and/or y axis, then lens based stabilization will help more, especially at longer focal lengths. If the primary camera motion is on the z axis or is lateral movement then the camera based systems that compensate for those types of motion will help more.


SAS Using proc ttest or proc glm to factor a demographic variable into a comparison of two groups on an outcome measure

Question: I have written SAS code to compare two groups for an outcome measure (i.e. reaction time - rt). However, we would like to factor in a demographic measure (i.e. IQ) to test whether the group differences in rt are actually driven by IQ differences between groups. I would like help in modifying my code. My existing code to compute basic group differences in rt is below. I have included code using both the t-test sas function and the glm sas function, which come out with similar results.
data sepdata  ;
infile "input.txt"  ;
     input subjid group IQ rt;
run;

title 'T-test group differences;
proc ttest;
        class group;
        var  rt;
run;

title 'Parallel glm code for group differences ';
proc glm;
 class group ;
 model  rt  = group ;
run;

I'd like help on modifying either the t-test function or the glm function to include "IQ" in the model.
Comment: How is IQ coded?  Is it discrete or continuous?
Answer: To account for the effect of IQ on the response, include it as a predictor in your MODEL statement behind GROUP. The results associated with GROUP that come out of this updated model are then adjusted for IQ.
proc glm data = sepdata;
    class group;
    model rt = group iq;
run;
quit;

I think it would be reasonable in this case to consider IQ as continuous. I hope that helps!


Is a kohen who embarrasses someone publicly prohibited to duchen?

Question: Since embarrassing one in public is considerred like murder and one should give up their life rather than transgress (Bava Metzia 59B, see Tosfas Sotah 10B on top), does this mean a kohen cannot duchen if he embarrasses someone publicly?
Comment: @Ed How do you know it's on a higher level? Including that in your question would greatly increase its value to the community
Comment: If being angry is like worshipping idols, does it mean we should stone each other? Many [similar] statements have educational (non-Halachic) purposes only.
Comment: Yes I know not everything can be taken literally - but embarrassing others publicly some do consider like murder. Public shame being like murder is on a higher level than being angry is like avoda zara
Comment: Besides the above comments, there's also the issue that the question gives me no reason to think there's any connection between murder and duchening. −1.
Comment: Related: https://judaism.stackexchange.com/questions/53598/public-shaming-cardinal-sin
Answer: Responsa Shevet Halevi 8:172 rules that such a person is allowed to duchen, because the verse that is the source of the prohibition, as well as the Rambam and Shulchan Aruch imply that the issue is that hands used to murder cannot also be used to duchen. In this case however the 'murder' was not done with his hands, so the prohibition would not apply.


How many witnesses are required to prove adultery?

Question: Is it enough that two men see a couple hugging and fondling and copulating or do they have to see the actual penetration?
Comment: reversed, please consider opening.
Comment: Related: http://islam.stackexchange.com/q/816/38
Answer: Witnessing hugging or fondling is not enough for hudud (ordained punishments) for zina. This is because the zina that entails hudud is defined by penetration. Though, these haraam actions (fondling) could entail disciplinary punishments but that is depended on the level haraam actions and it can be given only by a judge.
As for zina that entails hudud,
Shaykh Ibn 'Uthaymeen (may Allaah have mercy on him) said in al-Sharh al-Mumti' (6/157):

They should describe zina in clear terms, such as saying: "I saw his
  penis in her vagina". There is no alternative to that. If they say:
  "We saw him on top of her and they were naked", that is not
  acceptable. Even if they say "We saw him doing with her what a man
  does with his wife," that is not sufficient as testimony. They must
  say "We bear witness that his penis was in her vagina." And this is
  very difficult, as the man said who was testified against at the time
  of 'Umar: "If you were among the (four) thighs you would never be able
  to give this testimony." Hence Shaykh al-Islam Ibn Taymiyah mentioned
  that at his time no case of zina was proven by means of testimony from
  the time of the Prophet (peace and blessings of Allaah be upon him)
  until the time of Ibn Taymiyah. If no case was proven from that time
  until the other, then we do not know of any case that was proven by
  testimony up till our own times, because it is very difficult.

And moreover, for zina, it is four (not two) sound witnesses of upright character (i.e. should not be known as a faasiq (sinful) person).
Shaykh 'Abd al-Rahmaan al-Sa'di said in his Tafseer (1/563):

"Why did they not produce four witnesses?" [al-Noor 24:13], i.e., why
  did the accusers not bring witnesses to the things they accused them
  of? "four witnesses" i.e., of good character. "Since they (the
  slanderers) have not produced witnesses! Then with Allaah they are the
  liars" – even if they are certain about that in themselves, they are
  liars in Allaah's judgement, because Allaah has forbidden them to
  speak of that without four witnesses. Hence Allaah says: "Then with
  Allaah they are the liars", and He did not say "Then they are the
  liars". All of this points to the grave sanctity of the Muslim's
  honour, so it is not permissible to make accusations against it
  without establishing testimony.

Source: Zina
Moreover, you should be careful if you are giving false witness because that will be a slander. And if it is really a slander, the hadd punishment will be upon the witness.
More: Slander
Comment: @Thecrocodilehunter As mentioned it is the four eye witnesses who should testify they saw the penetration. To quote Shaykh Uthaymeen "They should describe zina in clear terms, such as saying: "I saw his penis in her vagina"."
Comment: Apologies for my previous comment as I did not fully read the answer. BTW according to this, people who were executed by Talibans were totally wrong and more of assassinations because I am sure they don't have this proof.
Comment: @Thecrocodilehunter That is very much possible. Allah knows the best.


what is the difference between a private pool or solo mining

Question: I would like to understand if there is a difference in resolving blocks with a private pool and solo mining, I understand that when solo mining you are given a block to resolve but within your private pool you may resolve various, this of course having several machines.
Answer: There's no technical difference in generating blocks in pooling vs. solo mining. The only difference is that pool mining can create a more steady pay flow.
Why do people do pooled mining?
Bitcoin's difficulty can give unrealistic time frames for payout. The average computer will mine a single block in 1000+ years at current difficulty. But say I got into a pool with the average computer, I'd get a payed proportionally to the amount of work I contributed to a block being found. Although my "work contributed" may not end up being a block, it had a chance proportional to my own hash rate. In the end I'd get payed a few satoshis daily as opposed to getting the block reward (25 BTC at the moment) at some random point in the future likely to be no later than 1000+ years from now.
Why do people do solo mining?
The main reason is because they can. Certain miners have enough hash rate to get blocks in a reasonable time span. If I had a 1/144th the hash rate of the Bitcoin network I'd statistically have a 100% chance of finding a block of 25 BTC within 24 hours. There's no benefit for large miners to do pooled mining, may even hurt them because of fees.
Pooled vs. solo mining will theoretically yield the same amount of coins if difficulty and block reward never changed and you solo mined long enough. Although you should consider pooled mining if you aren't mining with a rack of gear.
Comment: I believe he is asking about the difference between a **private** pool and solo mining. Either way, he would be the only one on his team. Also, your 100% chance is not correct. It should be modeled as a Poisson process with an expected jump of 1 day. The actual probability of finding a block within 24 hours is 1 - 1/e = 63%. Now, it is true that the _expected_ number of blocks found in 24 hours is 1.


What Analog to Digital Converters Are Available For RPI?

Question: I am interested in obtaining an ADC (Analog to Digital Converter) or Analog input for the Raspberry Pi.  I understand that various boards exits to use an Arduino as input to the Pi and that Libellium has an arduino-like adapter containing Analog inputs as well as in theory the I2C and SPI interfaces possible with ADC chips.  Does anyone have a daughter board with multiple ADC inputs, and/or is their a software library for any of the available USB data capture devices that would meet this neet without considerable interfacing expertise and level shifting?
Answer: A good starting point is adafruit's tutorial at http://learn.adafruit.com/reading-a-analog-in-and-controlling-audio-volume-with-the-raspberry-pi/overview. Adafruit also has breakout boards for the RasPi to make things a little easier... This post is also useful: How can I connect an analog to digital converter (ADC)?
The MCP3008 seems to be one of the more popular ADC's for the RasPi and it uses the SPI interface for communications
If you want to attach an Arduino via USB and read out its ADC's check this posting: How to attach an Arduino?
Answer: Another alternative is the PCF8591 which uses the I2C bus.  It's only 8bit vs the MCP3008 (10bit) but with the PCF8591 you only have to use 2 pins (SDA/SCL) vs the 5 pins of the SPI (MOSI/MISO/CLK/CE0/CE1) (really 4 for I2C and 7 for SPI including the VCC and GND pins) so if you need the extra pins and are ok with the 8bit vs 10bit, check out the PCF8591.
Answer: Another option (for the ones needing a bit more precison and willing to pay a bit more) is the ADS1256, have been using it on a commercial product of mine for a while, works pretty well. How can Rpi read ADS1256 ADC Data


What are the additional benefits of having a blockchain behind a web service?

Question: I'm still in the process of trying to understand cryptocurrency markets, and the factors behind their monetary value.
Today, I have seen an ICO for a token called DetectorToken, which is a service that analyses markets and sends notifications to its users. From my understanding, although it seems an interesting idea, in the end, it is just another web service. The only thing I have found in the White Paper was the following:

We intend to initiate a subscription model after the ICO thus helping investors to earn from the subscriptions made by users.

I do understand that they are trying to get their work funded, but how does such a project benefit from having a blockchain behind it, and why would it have a currency attached to it?
Answer: It has a blockchain behind it for one reason only: buzzword compliance.


Find new books in Adobe Digital Edition - library

Question: is there any way to browse available Adobe Digital Editions books? I would like to download some but do not exactly know what I am looking for and some sort of a library would be good.
Answer: ADE is not a library, it is software to allow a person to read ebooks. Here are sources for free ebooks if that's what you want:

http://www.gutenberg.org
http://smashwords.com
http://manybooks.net
Free classics on Amazon. https://www.amazon.com/b?ie=UTF8&node=2245146011
Baen free library, mostly scifi and fantasy. http://www.baen.com/catalog/category/view/s/free-library/id/2012
DDG search for free ebooks
Kobo free ebooks
Answer: Many distributors use Adobe DRM to secure their books. Some of the best known include:  B&N, Sony, Kobo, and Overdrive. But all have their own branded reading system that the user uses for opening these files.
Typically, some books use encryption (known as DRM) to protect its books. Adobe DE allows the reader to view ebooks with DRM if the publisher or distributor includes this particular DRM.
As it happens, many distributors, rather than sell you this DRMed file, just build their own reading system which incorporates in some way Adobe DE.  Typically it does not make sense for publishers to sell you an encrypted file because they expect you to read it in a special app (like Overdrive, Nook, Kobo, etc).
The reason publishers don't typically do this is that they  would need to purchase a special server to distribute Adobe DE files. From the FAQ:

Adobe offers a content protection service, Adobe Content Server. Adobe
  Content Server is a robust server solution that digitally protects PDF
  and reflowable EPUB content for Adobe Digital Editions and supported
  mobile devices. Easy to integrate into existing systems using industry
  standard technologies, Content Server allows you to host, manage, and
  deliver files from your existing infrastructure to Digital Editions
  users.

Truthfully, publishers would prefer to work through a distributor's reading app than encrypt the file themselves and sell it directly to the consumer. It can be somewhat confusing for users to open and read stuff in Adobe DE.
Adobe DE can also read unencrypted PDFs and epub files, and that is the primary way people use it. I'm a publisher, and I find it useful for testing ebook files that I create. Occasionally a publisher will send a file which can only be readable in an app which accepts Adobe DRM, but that is only if the publisher runs the Adobe Content server.


Color matching Product

Question: How can i match colors from the real world to my computer monitor. I have seen tons of post talking about matching colors from picture to picture, calibrating colors on my monitor, etc. But i haven't really seen a post that talks about how to make sure the product i'm photographing is what i'm seeing on my screen.
Comment: This task is in general case computationally and practically unsolvable. ColorChecker won't provide you with exact mapping in each situation.
Comment: Scratch the word "practically": sure Maki suggested a valid solution which is sufficient for most cases. Thing is, there is no perfect one.
Answer: During the photo shoot, you need to take an exposure of a color calibration card (ColorChecker) and use it to create a camera color profile in your computer. X-Rite is a leading company in this field.
Check out this video for the process: https://www.youtube.com/watch?v=Dn5VvB32wVI
Preferably, create one profile for each photo shoot, and not only a general "daylight" profile as they demonstrate.
This is the first step. The next step is to use a display calibrator to calibrate your display colors as well.
Third step is to calibrate a printer profile if needed, and X-Rite has tools for that as well.
Comment: ok so that could help me get started. So I guess the next question is how far can colors be in a product shot. In my case a rug. I know that answer can be opinion based bust i would to hear from people who have been in this situation. Do companies normally want the color an exact match? Or is something just really close ok?
Answer: Re: your other question about what could still cause variations in color. (@Cody Hint: just because one relatively new low rep member has a negative comment on a question is no reason to immediately delete it.)
The biggest issue is most likely the fluorescent lighting. There are two major considerations with most types of fluorescent lights in the context of color accuracy:

Limited spectrum. They don't put out the full spectrum of light that is contained in sunlight or other fuller spectrum sources. All lights have a CRI or color rendering index. The higher the CRI number, the fuller spectrum the light is from a given type of bulb. A typical commercial grade fluorescent bulb has a CRI of about 50. Most other types of fluorescents range from about 65 to 75. Some tri-phosphor cool white fluorescent bulbs can reach as high as 89 CRI. A quality incandescent or halogen bulb can have a CRI of 100.
Flicker. Fluorescent lights flicker with the frequency of the alternating current that powers them. In the U.S. this is usually 60Hz. Not only does the brightness fluctuate with the phase of the alternating current, but the color changes as well. At the peak of the cycle the color is brighter and bluer, and in the trough it is darker and a muddy brown. If your shutter time is shorter than one complete cycle of the lights' oscillation you'll get different color in each shot depending on exactly which portion of the oscillation the lights were in while the shutter was open. If shutter speeds shorter than approximately the camera's flash sync speed are used the color will even fluctuate from the top to the bottom of the image as the light changes during the time the slit between the first and second curtains travel across the sensor.

You can combat the flicker by insuring a shutter speed of about 1/100 second or slower (1/60 is even better). This of course, necessitates the use of a tripod or other stable camera mount to eliminate blur caused by camera movement. But you're still left with the relatively low CRI of most fluorescent lights unless you use high CRI fluorescent lights specifically made for photographic use.
Comment: I haven't seen the question, but I don't think that it got deleted by the community. I think it's more likely that Cody got intimidated by that negative comment and deleted it himself.
Comment: Awesome! This is great information! The fluorescent tubes we use are just plain jane bulbs and this could be one of our issues. We shoot in a warehouse that is entirely lit with them. We have a couple of umbrella lights we use as well but I feel it's such a large space and because the floors are concrete and shiny much of that lighting is lost.

Color matching Product


How is it possible for 0x0000000000000000000000000000000000000000 to send out ERC-20 tokens?

Question: Isn't 0x0000000000000000000000000000000000000000 a burn address where no one has private key? If that is the case, how can this address send tokens to other addresses? If you look at Etherscan's ERC-20 Token tab, there is a lot of OUT records: https://etherscan.io/address/0x0000000000000000000000000000000000000000#tokentxns
Answer: Per the ERC20 standard, newly created ERC20 tokens are sent from 0x0000000000000000000000000000000000000000 to the address they are meant to be sent to. It was done as a way of logging and to avoid creating tokens out of nothing.
Update
The ERC20 standard does not actually define that the tokens are sent from 0x0000000000000000000000000000000000000000. Tokens are created simply by adding to the balances mapping of the desired user, emitting a Transfer() event, and adding that value to the _totalSupply.
While it is not defined in the standard, it is best practice to emit a Transfer() event with 0x0 as an address when creating tokens. It allows front-end clients to read events and display data based on this event. From this post:

This is done that way so block explorers and wallets that only interpret the 'Transfer' event can show the operation to the user. There were some complaint from users that the transfer failed because it didn't show up in their wallet (or block explorer).
Only the 'Transfer' event is part of the ERC20 standard, and the events 'Mint' and 'Burn' are not. It is a workaround around that limitation to generate a transfer from 0x0 to simulate a 'Mint' event and, a transfer to 0x0 to simulate a 'Burn' event.

Each of those transactions you see on the page you linked are Etherscan's representation of a token creation.
To add to this point, take a look at any address that has transferred an ERC20 token elsewhere. If you click on the "ERC20 Token Tx" tab, you will see transactions that send tokens from one user to another. What is actually happening is a transaction from the sender to the token contract, which reduces the sender's balances mapping, adds to the receiver's balances mapping, and emits a Transfer() event. What you see on that tab is simply Etherscan reading of the Transfer() events of tokens.
Comment: I don't see that anywhere in the standard, could you give a direct quote?
Comment: When creating the initial supply `Transfer()` may or may not be used. Tokens I have created do not use it. The event is mainly for EtherScan and other block explorer support, in the absense of standard mint and burn events.
Comment: It is actually not there. The interaction with `0x0` is actually used in the `Transfer()` event when creating the token. I have updated the answer accordingly.
Answer: Additionally, you can find transactions of certain tokens from addresses that could not possibly send them by emitting bogus Transfer events to fool etherscan into recognising it as a token transfer. These are not even real tokens.
Etherscan flags these as "SPAM tokens" once they are notified of it.


How to make questions noticeable without bounty?

Question: I have asked 2 questions in askubuntu. I beleive both are genuine enough and are binding to the 'rules' of askubuntu. But the questions are barely getting noticed. I even got the tumbleweed badge for one of the questions. Here is the link to that question. As you would have seen the question was asked 3 weeks ago and has got just 57 views(when I am typing this description). Another question got a vote up and got 33 views but still has no comment or answers(when I am typing this description). Here is the link to that question. What do you suggest I do to get these questions noticed and answered? Note that I don't have enough reputation to place a bounty on my questions. Thanks in advance.
Comment: Also, you have enough rep to talk in [this chatroom](http://chat.stackexchange.com/rooms/201/ask-ubuntu-general-room).
Comment: The general rule is to achieve some reputation then sacrifice it. To achieve it, you should answer some questions. The more answers you write the more rep will you have. And after you will achieve 200, you will get +100 association bonus.
Comment: I would suggest to format the questions slightly. Mostly, try not having large paragraphs.
Answer: Your title is half the battle!
"Workaround for installing the AMD propritary driver" doesn't really explain anything to me, it's not even a question! I would not want to click through.
I changed it to: "How can I get 1366x768 as a resolution with an AMD Radeon 5570?"
It is immediately obvious to me what that question is about. If I knew anything about that subject I would immediately want to click through.
Same with "Login screen resolution issue in Ubuntu 13.10 and 14.04 beta". That doesn't tell me anything. There is also some information that you put in the comments. You can edit your question (remember editing bumps), to put things like:

I am already using the Xorg edgers PPA, the issue persists
I can replicate the issue on 13.10 and 14.04

That way it's in your question and not in the comments.
Now you have the benefit of hindsight since you found the answer somewhere else, so what you need to do is retitle the question so that the next person who has your issue can find your question and answer. Perhaps something along the lines of "How do I configure the login screen resolution with the AMD Catalyst Driver?" or something.
Writing good titles is hard by the way!
Comment: Thanks. Probably you might also include 'entering the chatroom' comment in your answer. I got useful advice there too.
Comment: @Venki it was my suggestion, that's why it shouldn't be added in Jorge Castro's answer. I will write my own answer including some useful tips and of cause this tip.
Comment: @Danatela Yeah sure.
Answer: Jorge's answer is great, but it's only half the deal. Good question should show research effort, be useful and clear (and if so it will have upvotes). After you initially write a question, try to read it as it was made by another person. Try to answer the questions:

Does it clearly describe the problem?
Will I learn something new trying to answer it?
(and the most important) Will it be helpful for future readers?

Also try to ask somebody to review the question. Probably it should be your friend who has interest in technology or some experience with the subject of your research. At the worst, your mom will fit, just try to explain her what are you going to reach. Or knock on the bum – explain your problem to someone who has nothing to do with it.
But sometimes good questions just fall in the Active Questions queue. For those reasons the bounty exists. As I already said, the general rule is to achieve some reputation then sacrifice it. To achieve it, you should answer some questions. The more answers you write the more (potentionally) rep will you have. And when you achieve 200, you will get +100 association bonus.
So, how do I write good answer? This article is essential. And, for me, answering is really easier than asking. More, it is encouraged more to answer than to ask. Just check profiles of top users and you will see that they have many answers and few questions in comparison. Also check http://meta.askubuntu.com/questions/1209/how-do-i-quickly-gain-reputation
And you can gain attention talking in chat. To enter chatroom, you need to have 2 upvotes on answers or 4 upvotes on questions (and no downvotes) or make 10 approved edits. That is not so difficult and your example shows that.
Comment: I accept this answer as it is generalised and will help future visitors too. Jorge Castro's answer is more specific to my issue. But it is good too.


How can I get the most out of conferences?

Question: I recently attended a very large conference in my field (SfN, ~30,000 attendees), and after I got back I was thinking about what I had gained from the trip, and I realized not that much. I listened to a few different talks, and I saw a whole bunch of relevant posters, but on reflection I don't think anything I did progressed my knowledge/career that much. What should I do in the future to ensure that I make the most out of conferences?
Answer: Read this and this.
My professor put forth 3 simple rules for networking:

Talk to the guy beside you
Talk to top 3 (sort by relevance or whatever you prefer) presenters
Mail them 5 days after the conference with some follow up content (questions/comments/invites for talks etc.)

Just to make this post "dead-link" proof, I present a gist of the content in the above links.

Start Early. You should begin preparing before the conference starts. Start reading on who will be there, emailing people you want to meet, and determining which events you will attend. You may want to contact the speakers whose talks you will be attending before the conference; try to set up a meeting, or if they are too busy, at least meet them and give them your business card.
Bring Business Cards. Make sure they're up-to-date and details your preferred mode of communication.
Research people and get involved in their networks. If a certain professor is giving a talk; read his previous research papers, frame interesting questions and get an excuse to meet him. If you do meet him, exploit the opportunity to interact with his peers and try to enter their network. Sometimes, this is the only way of getting to network with someone. I know of professors who refuse to take students for PhD or internships or Postdocs without a recommendation from someone in his network. A good impression might just get you that recommendation.
Note people with similar interests to yours. These people will be attending all the same presentations as you, talking to the same people, discussing similar topics. They are the potential spots for networking.
Prepare the elevator speech. A common question will be "So, what is your research about?" Make sure you have an answer for every audience. For e.g. If you are in Computational Science, the answer may vary depending on who you are talking with. Plus, make it interesting and digestible.
Organize an event of your own. This is especially useful is forming "lower" networks i.e. networks of people who lag in terms of age or experience such as graduate students. If not more, they could notify you of openings or interesting papers or whatever. They could be useful. (Plus it helps us :P )
Read "Never Eat Alone".
Follow Up. Prepare for this even before you leave for the conference. Have different modes of follow up ready. Will you have anything to say that is worth writing an email for? If not, think of something which will. If nothing works, make sure you click a photo of yourself with him and send it to him a few days after the conference.
Comment: Note that all these points about business cards are geared much more towards professional conferences than research conferences. Few professors will carry business cards, and even fewer will hand them out; the networks are much smaller in research, and people can easily find each other through publications.
Comment: @eykanal http://www.phdcomics.com/comics/archive.php?comicid=861
Answer:
Know why you're going in the first place: only go to conferences where you can get something useful out of it. You can usually get access to the proceedings (and at lower cost) without going to the conference. So just access to the proceedings is usually not enough. You're there to present your stuff and get feedback on it, and/or for networking, and/or to hear specific speakers talk insightfully on a subject important to you, whre you've got an opportunity to ask clarifying questions directly of them, and to participate in a discussion with others, afterwards, on the content.
Be the first after a presentation to ask an insightful, relevant, informed question. Catch the speaker's eye as you ask the question. Go up to them after the session ends, thank them in person, exchange business cards
Network like crazy
Have a big stack of business cards. Give them away liberally to anyone vaguely connected to your field. Get some more printed. Repeat.
Collect business cards of anyone vaguely connected, voraciously. Add their email addresses to your database of interesting contacts. Follow them on your networking sites of choice. (Twitter, CiteULike, Academia.edu, etc). And when one of your papers gets published, email them a link to it, and let them know that it may be of use to them.
Answer: From my own experience I get the most out of conferences which are not organized as conference expos. There's a big difference between conferences created for income (yes, even in academia) and those created to promote new discoveries and knowledge.
Of the latter type I find the presenters are generally excited by their opportunity to meet others in their field. It's more of a grassroots type of experience and you find that you naturally start to share in the discussions. No networking is needed.
<code>What should I do in the future to ensure that I make the most out of conferences?
</code>
Choose a conference that's in your field. Prepare a paper or two of your own on a subject that really interests you. Discuss it with colleagues. Get it published. Present it at a conference. The critical thought you put into this process will help you to pick conferences more suited to you and stimulate your interaction with others.
Answer: On top of all the answers above, I would add very selfish points to expand on meeting like-minded people from user107 answers.

Avoid destination conferences(or The location is time)! The best conferences are the ones you can spend the most time with the people you want to network with and not where people will count seconds to leave and go sight seeing. For example, if the conference is in San Fransisco, without a doubt everybody is excited to bring a +1 and go about seeing friends in the area or sightseeing. You will have a lower chance of spending quality time with the researchers in your field. Meanwhile, people from Google or Uber or local equivalents of your field might not even show up to present their work cause they are busy(real story)! On the other hand, if the conference is in some center of nowhere, with literally nothing to do except the conference activities, you will have a high chance of getting to know your colleague very well. And people who are there are serious about their business. You have all the afternoon, night, and late nights to know who is who, and what they have to say that they can not publish yet(including politics of the field)! The catch is that conference organizers might spend more money to plan events that bring you guys out of your hotel rooms and bring you back again to such a location.
Find and meet people who can give you recommendation letters later on based on your work. People who have genuine appreciation of your work or methods or even your adviser and are nice enough that if needed to read your work for feedback or writing you a nice recommendation you can actually count on them. Someone would add avoid snobs or super-busy ones, you will not hear back from them soon enough.
Find fellows (same level as you maybe a couple of years ahead), who also have a genuine interest in your work, that also can play the role of proof-read or an extra pair of eyes for you. you can easily cut the time of your publications by sharing your work with such peers and make your papers ready nicer. if their English or experience in writing is more than you its a plus.
Talk with people in the industry or application world (or vice versa), who you can talk to you about what is actually needed out there and if they are also willing to use your work or test it or give you comments. These people can help you explore alternative career paths as well.
Don't be negative(snob) about presented works. everyone knows some works are worst than others, but cynicism or negative attitude scares most people and will isolate you. There is so much to learn even from works that look not ready, or complete or even wrong! Be positive about all works and try to learn from every single presentation rather than ignoring their efforts.
Collaboration with other institutes is always a great experience item. see if you can establish such opportunity for yourself. Maybe a visiting summer or just working on a piece of open source code together.
Avoid politics. most likely your source of information is not perfectly aligned with locals and you can hurt mis-represented and already-harassed people!
Branding. Have a letter-sized summary, quadchart or an executive summary of your work copied in color and enough number available. It can be a great branding if you are serious about your ideas. Business card or LinkedIn will not go anywhere in academia.
Go out and make memories with your peers, go see a random part of the city. It will be a better way to network than staying in the hotel's bar(except if it's too late at night).
Don't miss the elders of the crowd. Remember some people come to this conference every year for last 30 years. Some of them really appreciate new people who do the effort of introducing themselves.
Make as much notes as possible, cause you WILL forget, even the most important things.


Why is the USA threatened by ballistic missiles from North Korea?

Question: The USA all of the sudden appears vulnerable to intercontinental missiles from North Korea. Doesn't the USA have a defence system that would easily destroy an approaching ballistic missile before it can cause any harm? Or is this whole thing only exaggerated for political reasons?
Comment: North Korea also has ballistic missile capable submarines that can park themselves outside of San Diego and lob a few missiles across the western seaboard with little (zero) probability of interception.
Comment: Depends on how you ask. Do you consider a emerging threat a threat?
Comment: Hitting a bullet with a bullet is hard. It has never been comprehensively successful at any time in the past, why should it be now? And, with nukes, you need a 100% success rate or millions of people die.
Comment: Everyone knows a conflict will mean the annihilation of the entire peninsula, which is an unacceptable outcome to everyone, North Korea included. This is just about poll numbers.
Comment: Even if NK had a rocket that could reach the USA, they'd still need a reentry vehicle. That's non-trivial.
Answer: Mostly two reasons:

no defence system is infallible, for example:

the payload of North Korea's missile could be made of several false warheads and only a few actual ones, overloading the defence system
the defence missiles could miss their target

As this article (*) mentions

U.S. missile defenses use kinetic energy, not explosives, to destroy enemy missiles—the "kill vehicle" simply slams into the target. The kill vehicle carries no explosives, which means the kill vehicles that don't hit the target simply continue on their merry way, re-entering the atmosphere and, for the most part, burning up. For scenarios in which the Alaska site shoots at a North Korean missile, the kill vehicles should mostly re-enter the atmosphere over Russia.

As the article continues to say, what would happen if Russia would interpret those missiles as nuclear warheads directed at them? It's not like the US can warn Russia before launching, between the detection of North Korea's launch and the launch of the defence system would pass only a few minutes, not enough to properly warn Russia about what is happening.

(*) I do not fully share the apocalyptic vision of the article, it simply happens to contain most of the necessary informations.
Comment: "In 1991 the US Army claimed a 95% success rate"... "A later General Accounting Office report concluded that Patirot missiles destroyed only 9% of the Scuds they tried to engage.  The Israeli Defense Force cacluated they'd destroyed 2%"

http://www.slate.com/articles/news_and_politics/war_stories/2003/03/patriot_games.html
Comment: "not infallible" would be an understatement.  The myth of the "missile shield" has always been more hype than reality.
Comment: Nr. 2 is a side effect I never was thinking of. Thanks
Comment: @WesSayeed - No, they were not all that effective against SCUDS in the first Gulf War.  That's exactly what I'm talking about in terms of hype vs reality.  We're fortunate that the SCUDS were actually pretty poor, on their own. Stopped keeping track in more recent years, but I know that even during the "W" Bush years, they were unable to consistently intercept a missile in a test situation even when they knew exactly when and where it was going to be and even when they had targeting beacons on it. http://www.latimes.com/projects/la-na-missile-defense-failings/
Comment: @PoloHoleSet; I wouldn't be too sure about that. Israel's Iron Dome has been an extremely effective shield against incoming rockets fired by Hezbollah forces from Gaza. U.S. Patriot missles were also effective against Iraqi Scud missiles during the first Gulf war. Admittedly we're not talking about ICBMs here, but missile defense shields are certainly not more hype than reality. They're a proven technology at this point.
Comment: @WesSayeed Do You have any sources? I think this is a central point of my question :)
Comment: A Google search on "Iron Dome effectiveness" yields many similar articles about how exaggerated the claims of success are.
Answer: The threat from North Korea is not "sudden". North Korea has brazenly stated for decades that they want a nuclear missile capable of reaching the United States. They have been working to develop their nuclear weapons program since the 1990's. Their nuclear tests in 2006 and their recent missile tests demonstrate the steady and consistent progress they have made towards that goal.
While missile defense shields in general have proven effective against short- and medium-range missiles that travel through the atmosphere (the Israeli "Iron Dome" and the U.S. Patriot missle system are good examples), the United States does not have a system that can reliably protect against ICBMs. Even if it did, no missile defense shield is 100% effective, and we're talking about nukes here. It only takes one good shot to cause incredible damage and loss of life.
It is important to remember North Korea's attitude as well. Officially, the Korean War in the 1950's never ended. What the world has been living with is actually a 60-year ceasefire. North Korea and the United States are still technically at war with each other.
The western world may have largely forgotten about that war, but North Korea certainly hasn't. Anti-American propaganda is still widely distributed by their government, and the state-run media there routinely reinforces the paranoia that the U.S., along with its South Korean ally, remains poised at the border to invade at any moment. As far as they're concerned, the resumption of fighting is inevitable. The rest of the world has little reason to doubt that North Korea would absolutely use those weapons if they felt it necessary.
Answer: First, we're talking about a dictatorship that is run by a relatively young person who inherited the position - he didn't have to earn it. Also, he had his uncle executed with an anti-aircraft cannon, most probably had his own brother murdered, and spends a substantial portion of his country's meager funds on nuclear bombs and missiles to carry them. While it may not be entirely accurate to call Kim Jong Un mentally unstable, he clearly doesn't think like most global leaders.
Consequently, it is not clear if he understands just how severely the US would react if he fired a nuclear missile at them. Certainly, his bellicose rhetoric doesn't reflect that. When the leader of a nation says those things, and they have nuclear weapons, it's a very serious matter.
As for shooting the missile down... that is not guaranteed. During the cold war, both the US and USSR began to develop anti-ballistic missile systems. By the early 1970's, both sides had abandoned those efforts. The reason can be found in what were called the 'rainbow tests', very high altitude nuclear explosions that produced a rainbow display. The largest conducted by the US was Starfish Prime. Several things were learned from those tests. One was the discovery of EMP, electromagnetic pulse. The Soviets inadvertenly destroyed several of their power plants with a high altitude explosion over their own country.
One other discovery was a large cloud of radiation created in the ionosphere that lasted for several days, and was impenetrable by radar. So, all a nation had to do to disable the early ABM systems was to detonate a warhead high over the target nation, and then fire the ICBM's into that cloud.
By the time the actual warheads emerged from the radioactive cloud and could be detected by radar, they would be moving at very high speed in re-entry, around Mach 20-25, and be almost impossible to hit. That is why both nations backed away from ABM systems - too easy to defeat.
It is also why Reagan's Star Wars defense so scared the Soviets. That system was space based, and wouldn't be blinded by a high altitude nuclear explosion - it would be above the cloud and have an easy shot at nuclear missiles when they were moving at their slowest, at the top of their arc.
So if Kim could set a nuke off in the ionosphere, he could blind the radar that tracks incoming warheads. Maybe the rocket could be knocked down on it's way up - that is what THAAD is designed for. Current ABM systems are designed to knock down one or two missiles fired by a rogue state. A lot of unknowns there, and the penalty for being wrong is severe.
Finally, we have to consider our current 'news media' and it's obsession with generating profit. They have a habit of hyping anything to generate ad revenue, relevance and balance notwithstanding. In this case, it's not so much that the US government is scared of N Korea, just that the media can profit from telling US citizens that they might get nuked, even if that's not absolutely correct.
Comment: On top of the other factors weighing against Kim's ability, he is probably surrounded by yes-men. Who's going to tell him that his latest idea won't work?
Answer: Look at the history of North Korea from 1950 onward, it has be one of belligerence, aggression, and violence. There are literally too many instances of type of behavior this to list here, but there are plenty of lengthy articles online detailing their exploits. by all means, go look up more if you aren't familiar with their history, they come off like some sort of bad James bond villain.
In short though, if you have a hostile state that acts in a sociopathic fashion you do not want them to be able to get access to more dangerous and destructive weapons.
Answer: North Korea is not a threat to US, it is a treat to global monopoly and balance of power.
Currently, we have one first rate power - US. US is pretty much allowed to do whatever it wants, attack whom ever it wants without consequences on international scene.
Then we have second rate powers: China and Russia. They are allowed to somewhat oppose policies of first rate power, but with some limits. If they cross that limit - well look at sanctions aimed at Russia. These second rate powers are in constant defensive mode towards first rate power.
After that we have third rate powers, countries like India, Great Britain, Israel, France. They are allowed to have nuclear weapons, but they must align their foreign policy with policy of first rate power - US. India and France sometimes get in small diplomatic conflicts with US, but this remains mostly benign.
Rest of the countries, no matter how economically powerful they are (Japan, Germany ... ) are de facto not independent. They are usually "allies" of either US, or in some cases of China and Russia (especially if they have common borders with them) .
North Korea tries to break this pattern. Without going into discussion about NK political system, one thing is certain - North Korea tries to be independent from any country, including China. North Korea wants to get close to ideal state of autarchy, i.e. not depending on whims of any other country.
In order to that, they need to deter planet's top dog - and that is US. And to do that they need nuclear weapons. On the other hand, US simply cannot allow one small country to gain independence from it, because that could encourage others (and in fact it does - look at Iran ! ) . Situation is further complicated with Russian and Chinese interests. They too don't like nuclear NK , but they also oppose US and US drive to get right at their borders. So they reluctantly play game where they try to defuse situation, by pressuring North Korea to renounce nuclear weapons in exchange for their protection from US. As they (China and Russia) are not very successful, US is compelled to attack NK.
Comment: Not my downvote, but this does read to me more like an anti-US rant than an answer to the question of *why* the US would be threatened by NK ICBMs.
Comment: Downvoters, please help understanding what's wrong with the answer?
Answer: Even though the OP already marked an answer accepted, it is actually exaggerated for political reasons.
Open the world map, you will learn that the ocean is huge. An ICBM that can steer a course across such a geographical area is technically difficult to build.  If it was easy, the US and Russia would not use submarines carrying nuclear warheads to cruise and hide in the opposing country's nearby seas.
(update)
Many people are taking the technologies for granted, as in common sense doesn't come so common. People without common sense simply through any country can copy cat a simple ballistic missile and apply it over ICBM, as in anyone can build a smart phone in their home workshop by buying parts from the electronics shop. Even if you are able to gather most part, you have no idea about the problem of supersonic speed: the sound barrier shock wave can rattle the whole payload off course. The guidance system is never easy, there is no "road" to guide the payload in the sky nor on the sea; GPS is susceptible to jamming and the Earth is NOT flat.
(--update end--)
In fact, even if North Korea builds tons of them, the real threat is towards Japan, not USA, even if it is not accurate, it will become a weapon of terror similar to V2 rocket used by Nazi during World War 2.
(--update--)
But the most important note is that the USA knows very well that North Korea doesn't possess the industrial capabilities to manufacture the rocket. An ICBM will disintegrate in the air quickly if all nuts and bolts are not manufactured according to a strict standard. So it is nothing but a proxy shouting game, i.e. towards China, which provides the parts and instructions.
(NOTES)
As of 7-aug-2017 news: China agree to sanctions on North Korea. Though I don't think it is enough to ask rednecks to STFU and stop arguing that NK can build any ICBM without China helps.
Comment: Re "...the US and Russia would not use submarines...", this too is just plain wrong.  The reason submarines are used is that they are not (as) vulnerable to a first strike as land-based facilities.  Nor do they necessarily cruise in "nearby" seas: they can be anywhere in the ocean.
Comment: @mootmoot I'm an aerospace engineer, I have already spent years learning that, but thanks for the thought :) also, experiments show that NK has the capability.
Comment: @notstoreboughtdirt, can you cite your comment?
Comment: "An ICBM that can steer a course" ICBMs do not steer (much), but their warheads do in the terminal phase.
Comment: @mootmoot first you have to demonstrate that NK does not have advanced machinery at its disposal, that is what you claim in your answer, and that's beyond engineering of any sort.
Comment: "the USA knows very well that North Korea doesn't pose the industrial capabilities to manufacture the rocket" and yet they launch it and it flies without "disintegrating in the air"
Comment: @Federico, jamesqf Uncited claims in comments are at least as bad as in answers.
Comment: @notstoreboughtdirt you can get ICBM ballistic answers on space.SE I guess. And reports about missiles not disintegrating in the air on almost every major newspaper around the world.
Comment: @not store bought dirt: Re "uncited claims", I call BS on that.  It's common knowledge.
Comment: @Federico Please improve your knowledge on how "easy" is for one to build a rocket that flies for thousands kilometers.  And learn what is "metal fatigue"  and the resources that engineer spends to overcome the issue. Any "info" available in open forum doesn't mean engineers are able to overcome the issue without proof of concept and experiments.
Comment: @Federico Glad to know that. Perhaps you can enlighten everyone how the NICHE of the aerospace engineering.  Is it easy to "manufacture" parts in your departments warehouse.