Why would a metal file have a cancer warning?

Question: Every metal file at the hardware store bears a California Prop. 65 warning on the label.  What could possibly be the cancer-causing agent in a solid metal file?
Comment: Not a duplicate, but see also: https://diy.stackexchange.com/questions/99440/plumbing-supplies-and-california-prop-65
Answer: Some metal products may contain elements or chemicals known to the State of California to cause cancer, birth defects or reproductive harm. Like nickel, molybdenum, lead, chrome, etc. I would imagine that the file manufacturer labels the product out of an abundance of caution so they never have to worry about being sued or prosecuted, even if the materials in question are not normally present in harmful quantities.
Comment: I suspect you are right it is just CYA. Especially since many tools are produced by contract suppliers. The cost of verifying that none of the listed products were used is probably much harder than posting a Socialist Republic of California Prop 65 warning
Comment: @NoSparksPlease Before you post a Prop 65 warning on your product, you have to create a Safety Data Sheet regarding your product that details the specific danger posed by your product.  It's not as simple as just slapping on a label.
Comment: I have a torque wrench with one of these labels on it.  I have no idea what precautions I should take when attaching my lawnmower blade to avoid the danger.  These labels are basically useless because so many things have them.  They were even required on coffee for a brief period of time.
Comment: Yup, stay focused on the important safeguards; for you- disconnect (maybe even **remove**) the mower's spark plug!
Answer: TL;DR
If using the product can release the chemical then slap a sticker on it.

I think it's just an overzealous interpretation of:

Proposition 65 requires businesses to provide warnings to Californians about significant exposures to chemicals that cause cancer, birth defects or other reproductive harm. These chemicals can be in the products that Californians purchase, in their homes or workplaces, or that are released into the environment. By requiring that this information be provided, Proposition 65 enables Californians to make informed decisions about their exposures to these chemicals.

https://oehha.ca.gov/proposition-65/about-proposition-65
Answer: Because of the things you'll be filing with it
The same reason sandpaper and other paint-prep supplies contain warnings of lead.  The sandpaper doesn't contain lead; but good chance what you're sanding does.

To be more specific, you're referring to the text of a Prop 65 warning, presumably text out of 27 CCR 25603(a) affixed to the product package per 25602(a)(3). The manufacturer is using this language because it's defined as a Safe Harbor, as per 26501 and onward.  A "Safe Harbor" is a "Get out of Jail Free" card for litigation. (the wisdom of this is debatable, but that's neither here nor there).
The labeling is called for here:

27 CCR 25600.2. Responsibility to Provide Consumer Product Exposure Warnings.
(b) The manufacturer, producer, packager, importer, supplier, or distributor of a product may comply with this article either by affixing a label to the product bearing a warning ...

A pivotal question raised in heated commentary (now deleted) is whether this applies to the product itself or to the foreseeable uses of the product.
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This red cage is just steel. It can't explode. Why does it need a warning label?
Let's look at 25600.1 Definitions, defining the terms of art used in the regulation.

(d) "Consumer product" means any article, or component part thereof, including food, that is produced, distributed, or sold for the personal use, consumption or enjoyment of a consumer.
(e) "Consumer product exposure" means an exposure that results from a person's acquisition, purchase, storage, consumption, or any reasonably foreseeable use of a consumer product, including consumption of a food.

Italics mine; note this is the difference that decides the question.
Well, then, it's pretty clear what 25600.2 is talking about then.  Right?
25600.2. Responsibility to Provide Consumer Product Exposure Warnings
25600.2. Responsibility to Provide Consumer Product Exposure Warnings
I personally don't have any trouble seeing the the second one as correct; it specifically invokes a defined term-of-art, and otherwise "exposure" would modify "warnings" and that doesn't make much sense.  But I'll concede that's uncertain and this might be an Oxford Comma kind of a deal.  So how do we settle that?
Easy.  Safe Harbor protection is optional for the manufacturer.  Speak the magic incantation; get a liability shield. Or don't and takes yer chances. It rather defeats the purpose to unnecessarily make yourself a legal test case on the Oxford Comma, so to speak.
So yeah. It's about what you'll foreseeably be filing.
Answer: Metals
Depending on the alloy, tool steel probably contains cobalt and/or nickel.  These are listed on Prop 65.
Cobalt:

Cobalt metal powder
Cobalt oxide

Nickel:

Nickel (Metallic)
Nickel compounds  (due to the ambiguity in this line, anything with nickel)
Nickel oxide

Additionally, there are other metal compounds of chromium, vanadium and even iron that are listed, but I doubt these items molecules could actually be found in tool steel.
Comment: @StianYttervik Sorry, but I work in the metals industry.  ALL of the air hardened and all of the shock-resistant tool steel alloys have nickel in them.  Yes, the steel used to make files (specifically) will probably have more chromium in it, but chromium is on Prop 65 only as hexavalent compounds, which would only be formed if you were welding your file or heating it to some extreme temperature.  This is why I didn't include it in the list.
Comment: I doubt it contains Ni. It should contain Cr. Nickel makes steel workable, weldable and more oxidation resistant. Cr makes it harder and oxidation resistant and promotes the austenite->martensite transformation. But it is likely not an alloy steel, unless it is a special purpose branded file,  so going to be less than 4-5% of whatever - and the whatever is most likely dominated by Cr.
Answer: Work with metals can release ions or vapors of carcinogens, and other substances found in the vicinity might be the same. Here's a list of some common ones. In particular, wood dust, asbestos, arsenic, and chromium are particularly common in certain construction materials one might use a file or rasp on.
Hexavalent chromium is particularly a nasty chemical and when you file some steel that his been plated with chrome, you're raising the odds of being exposed to it. Iron workers, masons, carpenters, painters, and welders all have increased risks of various cancers because of sustained occupational exposure to particulate.


How do you manage change with your web services?

Question: Over time your web service might changes, what do you do and how do manage change?
(Different versions; add more features, modify or even remove features etc)
Answer: Typically, for non-breaking changes (mainly addition of methods), you can extend the service contract/implementation in same end-point. Again, when I say non-breaking changes, it means both syntactic and semantic changes.
Otherwise, cleanest way to do is to host new service version on different end point all together. Give your clients chance to migrate to newer version gradually before shutting down the old version (if needed). Many times, you can use most of your service implementation behind the scene and reduce efforts.
Also, sometimes service changes are not in methods but in input/output data. These can be tackled some times by versioning your data structures. For example, a function accepting XML input may start supporting additional data/tags in input. In such case, you may host it on same end-point and then figure out from data what client is sending. Although, I would prefer to have another method or new end point in such case.
Lastly, you can have also have method in your service interface that can emit version info or validate version info provided by client to tell it whether the service implementation is compatible with whatever service contract it has built with. This allows clients to give friendly messages in case of incompatibility or incorrect configuration. Yet another variation in such scenario can be to return client the end-point address of the compatible service version (sort of dynamic discovery of compatible service).
Answer: I would add a new endpoint that could use the same code in the backend but just return different output.
If the change is small enough (like just a new property) then ideally you could just update the output of your existing service endpoint;  Adding the new proprety to your output and have older clients ignore that.  The problem though is that consumers of soap (especially in the .NET world) use tooling which generates static proxies which are very inflexible to change.


What do we mean by "aerobic" and "anaerobic"?

Question: I'm sure there are lots of us who aren't so clear on the distinction "aerobic" and "anaerobic": exercise, running, conditions, and so on. So: what is the difference between the two?
Answer: The body uses two different energy systems to fuel the body's activity or exercise.

Anaerobic - First the body uses the anaerobic system which has energy ready to go as soon as you start to use your muscles.  Anaerobic means without oxygen.
Aerobic - The second energy system, the aerobic system,  kicks in when your short term, initial energy from the anaerobic system is used up.  Aerobic exercise requires oxygen to produce energy.
An exercise is determined to be aerobic vs anaerobic depending on which system is used to generate the energy needed for a particular exercise.
Using running as an example, sprints are anaerobic and longer runs are aerobic exercise.  When you sprint, you need explosive, quick energy to get going, so you use the anaerobic system. Readily available stores of ATP,  glucose and glycogen provide energy quickly, but also deplete quickly.  As these stores of ATP,  glucose and glycogen deplete, you need a different system to produce ongoing energy.
As you run longer distances, you generally lower the intensity so that you can keep going.  You need endurance and a system that produces energy as long as you need it. The aerobic system uses oxygen and  produces ongoing energy needed for endurance activities, exercises and sports.
To exercise aerobically, you  generally workout within a target exercise heart rate of  between 60 to 85% of your maximum heart rate. Aerobic exercise trains your heart and lungs to become more efficient.  Aerobic exercise is sometimes referred to as cardio.  Examples of aerobic exercises are walking, running, cycling, hiking, swimming, water aerobics, aerobic dance, singles tennis etc.
To exercise anaerobically, you generally work at a higher intensity for a shorter durations or intervals.  Examples of anaerobic exercise are sprinting, strength training, and doubles tennis.

For more detailed information on how energy is produced, you may want to check into the Glycolysis, Krebs cycle, oxidative phosphorylation and Cori cycle.
Comment: @Jimsan - Actually, exercising at ANY capacity is either aerobic, anaerobic or some mixture of the two. All that aerobic and anaerobic refer to is the primary energy source/pathway during exercise. "Zones" are arbitrary terms designed to present a complex concept in an easy to understand fashion. I grit my teeth occasionally when I hear HIIT trainees claim "Yeah, I spent a whole hour anaerobic!" So your 80-90%, if you keep that up for more than 2 minutes, you are exercising aerobically. Anaerobic doesn't last more than 30 sec - 2 mins, maximum.
Comment: Personally I'd say 60% is a bit low for aerobic exercise. When I'm zone training I'll be looking around 70%-80% for aerobic and 80%-90% for anaerobic
Comment: @Jimsan 55, Granted that Wikipedia is not the most accurate source, but it is the value they quote for [aerobic exercise](http://en.wikipedia.org/wiki/Aerobic_exercise).  This range would include the ["fat burning" and "target heart rate"](http://www.hanford.gov/health/?page=112) zones.
Comment: @JohnP, well said.
Answer: Aerobic means you're burning fatty acids as your primary fuel source, along side oxygen and small amounts of ATP in the muscle's. Anaerobic means you're burning ATP, and Oxygen as your primary fuel source. The latter being limited but more explosive in muscle contractions than the former.
Answer: At its simplest:

Anaerobic - Without Oxygen (Air)
Aerobic - With Oxygen (Air)

It's a bit more involved than that, as in this context we're talking about the conversion of chemical energy (Fat, Sugars, ATP, PCr) into kinetic (movement in your muscles), but essentially Anaerobic phase involves the conversion of ATP and PCr in your tissues into energy (your tissues only have around 8 sec worth of ATP reserves and 40 of PCr), while to process the Glucose / Fat in your body efficiently the process requires Oxygen. The following free chapter Nutrition for Health, Fitness, & Sport, cover the subject well.


Can a marriage be valid if the man is a revert whose parents are Muslim and Hindu?

Question: Can a marriage be called valid if a Muslim girl marries a man reverted to Islam and had Muslim mother and Hindu father
Comment: The fairh of the parents is irrelevant to any marriage.
Answer: The faith of the relatives of the spouse isn't a condition for marriage.
Allah says in the Quran (2:221):

And do not marry polytheistic women until they believe. And a
  believing slave woman is better than a polytheist, even though she
  might please you. And do not marry polytheistic men [to your women]
  until they believe. And a believing slave is better than a polytheist,
  even though he might please you. Those invite [you] to the Fire, but
  Allah invites to Paradise and to forgiveness, by His permission. And
  He makes clear His verses to the people that perhaps they may
  remember.

As seen  from the verse, it is the faith of the would be spouse and not that of his/her relatives that Islam is concerned about.
Also w.r.t Jews, Christians and other people of the book:

This day [all] good foods have been made lawful, and the food of those
  who were given the Scripture is lawful for you and your food is lawful
  for them. And [lawful in marriage are] chaste women from among the
  believers and chaste women from among those who were given the
  Scripture before you, when you have given them their due compensation,
  desiring chastity, not unlawful sexual intercourse or taking [secret]
  lovers. And whoever denies the faith - his work has become worthless,
  and he, in the Hereafter, will be among the losers. Quran (5:5)


Where should I put my custom applications?

Question: I have downloaded some third party software, should I just put under /Applications or should I put under my home folder, e.g. ~/MyApps/?
Answer: It depends on what applications you want to keep to yourself and which ones you want to make accessible to all users:

Applications stored in /Applications are installed for all users.
The ~ stands for your home folder.
Applications stored in ~username/Applications are only for access by the user username.
Comment: You can also use your Public folder for applications you want to make accessible to all users.
Answer: I tried separating "personal" apps to ~/Applications/ and eventually gave it up after awhile because I found it to be annoying.
It turned out to be a lot hassle in little ways, and finally I just moved them all. I kept finding apps which only looked in /Applications/ so I had to keep tweaking settings.
More and more apps include checks to see if they are in /Applications/ and offer to move themselves, which meant even more annoyances.
If you install apps, such as Microsoft Office, which come with installers, you probably won't even have the choice.
But your experience won't necessarily be mine.
I'd put them into ~/Applications/ and then if you decide that you want to change it later, drag them all to /Applications/. It's easier to do that than try to separate them later because some apps do install themselves to /Applications/ and won't handle being moved somewhere else.
Answer: I just put everything in the application folder.  I used to try to sort things but had issues with applications that do not like being an any folder other than applications (MS Office, Adobe programs, etc).  Since I couldn't easily move these around, my organization scheme was incomplete and I just gave up.
This is probably sacrilege but you might want to try using Launchpad.  The folders you create there aren't actual folders in the file system and therefore won't break picky applications that absolutely must live in applications.  Mountain Lion also added a few new features to Launchpad that make it more useable, such as searching.


List of affective states for a study?

Question: I am putting together a study that attempts to assess whether people assign particular affective or emotional states to images--specifically, animated GIFs. Is there a "standard" list of emotional states that has been used in research before, or that tends to be favored by researchers who study emotions? I'm considering something like Plutchik's three-dimensional circumplex model, but I didn't know if there was something else that tended to be more favored.
Answer: There are a range of "adjective checklists" that have been developed to assess affective states, personality traits, or characteristics of individuals. Two of the most widely cited measures are the Multiple Affective Adjective Check List (MAACL) and the Multiple Affective Adjective Checklist-Revised (MAACL-R) (Zuckerman & Lubin, 1965; Zuckerman & Lubin, 1985). Although the actual MAACL-R manual may require purchase, lists of the affective items are available in other publications (Gotlib & Meyer, 1986).
Clinically, I have used the How Do I Feel Right Now? chart for clients who have difficulty identifying and naming their emotional states (http://blogs.oregonstate.edu/careerservices/2012/11/30/emotional-intelligence-what-is-it-and-why-do-employers-want-emotionally-intelligent-employees/).
Other sources of emotion lists in the field of psychology include:

Shaver and colleagues have a heavily cited paper on types of emotions (1987)
The Geneva Emotional Music Scale (Zenter, Grandjean, & Scherer, 2008)

Gotlib, I. H., & Meyer, J. P. (1986). Factor analysis of the Multiple Affect Adjective Check List: A separation of positive and negative affect. Journal Of Personality And Social Psychology, 50(6), 1161-1165. doi:10.1037/0022-3522.214.171.1241
Shaver, P., Schwartz, J., Kirson, D., & O'connor, C. (1987). Emotion knowledge: further exploration of a prototype approach. Journal of Personality and Social Psychology, 52(6), 1061.
Zentner, M., Grandjean, D., & Scherer, K. R. (2008). Emotions evoked by the sound of music: Characterization, classification, and measurement. Emotion, 8(4), 494-521. doi:10.1037/1528-35220.127.116.114
Zuckerman, M., & Lubin, B. (1985). Manual for the MAACL-R: The Multiple Affect Adjetive Check List Revised. Educational and Industrial Testing Service.
Zuckerman, M., & Lubin, B. (1965). The Multiple Affect Adjective Checklist (MAACL).
Answer: We are far from having any standards on the topic of emotions, and there are numerous ways to gather a user's emotional feedback. Of course, there is no optimal solution, and the choice mostly depends of your protocol requirements and expectations.
Using emotional terms, for instance, might be limited, as there is a bias of common understanding by every users, and a bias of granularity due to the terms categorization.
However, if you look for a quite comprehensive list of emotional terms, I would invite you to check this list of related terms of the Geneva Emotion Research Group. Other relevant research material is also available from their website.

List of affective states for a study?


Can't rate songs with Genius Mixes

Question: When playing a Genius Mix in Itunes 9, certain features don't seem to be working. For example the "Ctrl+L" shortcut doesn't work and File->Rating doesn't work either. Are there any workarounds?
Answer: The best workaround I've found are to either use the Genius icon in the player window (where the time played is viewing) which will create a Genius playlist off that song. It does not show the list of songs in the Genius Mix but is a Genius playlist made from that song. It does however give you the list to rate the song. The other alternative is to search for the song in your Music library.
Until Apple fixes this bug, I suggest filing a bug either at Apple's Bug Reporter (requires a free ADC account) or Apple's Feedback page for iTunes. The Bug Reporter tends to get better results however.
Answer: In addition to GrowlTunes for the Mac, a similar utility workaround for Windows utility is  iTunesKeys.
It provides the ability to assign universal keyboard combinations of your choosing to each star rating, plus a few other basic iTunes controls, even if iTunes is not the app with focus.
Answer: The easiest way, in my opinion, is simply right-clicking on the iTunes app in the dock while the song is playing, and change the rating there. No extra software or playlists necessary.
Answer: If you have an iPhone or iPod touch you can use Apple's free remote app to connect to your mac's iTunes and change the rating from there.
Answer: You can also use something like GrowlTunes is you are using Growl.  Thats how I rate all my music with iTunes in the backround.

Can't rate songs with Genius Mixes


Can we clarify the [asp-classic] and [asp.net] tags for the uneducated?

Question: Many of the questions being asked about asp.net are being mistagged with the asp-classic. Is there anyway the two can be disassociated or differentiated enough to prevent such a problem? For instance, would changing the tag name to classic-asp be enough?
Comment: Eh? '*migrate pure asp.net questions to asp-classic*' - ASP.NET is not asp-classic...
Comment: I do tend to message the OP and let them know - it's a losing battle!
Comment: We should create a classic-asp-classic tag for the classic asp questions, migrate pure asp.net questions to asp-classic, and retag asp.net-mvc questions asp.net.
Comment: Why would that be enough? If it did work, it'd simply be because it made the tag more difficult to locate, which would decrease the chances that it would be used on the questions where it is appropriate.
Comment: Could we not do something like if a question contains both [tag:asp.net] and [tag:asp] remove [tag:asp]? That would surely cut down on the edits I find myself doing just to keep the [tag:asp-classic] queue clean.
Comment: Yes - that's why I asked: '*Is there any way...*'.
Comment: If you notice specific people repeatedly making the same mistake you can @message them to tell them to stop.
Comment: This post needs more love. As Paul said, fixing these problems is a losing battle. I stopped retagging them because there are too many and there's no ROI.
Comment: I suspect a large contributor to this problem is that ASP.NET and C# show as suggested tags for Classic ASP questions. See http://meta.stackoverflow.com/questions/296198/change-suggested-tags-for-asp-classic
Answer:
This problem is becoming a losing battle for the dedicated group of individuals trying to keep the asp-classic queue free from unrelated questions about asp.net.

How many [ASP.Net] questions initially tagged [ASP] or [ASP-Classic]? (It's constantly around the 50 per month mark at the moment)

The Synonym Problem
The problem is people now refer to ASP as asp.net but because asp is a synonym of asp-classic it gets automatically changed and appears on the asp-classic queue. There isn't much you can really do about this apart from make the asp tag a synonym of the asp.net tag but then the opposite will start to happen.
What does everyone else think?
Suggestion to Handle Instances of Grouped Tags
What we could do though is look for groupings so when people mark a question as asp.net and asp (on the same question) couldn't the system remove the asp tag?, this would cut down on a lot of false positives we see in the queue.

I'm revisiting this post (again)
I've come to realise that the comment in the initial answer about changing the main tag to be classic-asp instead of asp-classic and having the others as synonyms might actually work and I think it comes down to two things;

Historicially the term "Classic ASP" has always been in wider circulation then "ASP Classic" (see this Google Trend).

Interest over time
("ASP Classic" - Blue, "Classic ASP" - Red)

As you can see the graph clearly shows that Classic ASP has always been the more common variant.

Because of the way the tag hint box works anyone typing asp will get asp-classic listing as their first option. This is fine but if someone goes to write asp .net (because for some reason certain ones feel it needs a space) you end up with asp-classic and .net.

If point 2. was reversed so the master was classic-asp instead of asp-classic I don't think this would happen as often. It would certain stop a lot of the false positives that end up in the asp-classic queue.

I should stress this won't stop people that write asp .net in the hint box as asp is still a synonym of asp-classic.

Revisiting for the third time
Re-running the above query in Data Explorer it's interesting to note that the number of mis-tagged questions is steadily dwindling (possible due to the efforts of the Classic ASP squad diligently editing / re-tagging questions) the message is starting to get through.
x = Number of questions and y = Time Period (in months)
Comment: @Deduplicator I don't think that will work. My suggestion is to remove it where it is accompanied by asp.net on the same question. Any attempt to blacklist without that comparison will just send the issue to the other queue.
Comment: So, you want to blacklist [asp]? Might be a good idea, depending on how bad the problem is, but won't happen yet: The problem is not bad enough. Abandoning it though, that might work with moderator-help to break the synonym, synonymize asp-classic and classic-asp, and merge all the questions to them.
Comment: Sorry, @Lankymart, missed your update to this. I think both of you have valid points; breaking (ASP from ASP-Classic) and reattaching the synonym (ASP to ASP.NET) and converting ASP-Classic to a synonym that points to Classic-ASP would be the best way forward. PS: Nice graph, Lanky ;o)
Comment: Maybe a solution like this could be implemented in ASP-classic vs ASP.net wars http://meta.stackoverflow.com/a/318948/961234
Comment: @Deduplicator: What is blacklisting?
Comment: @Paul: Disallowing re-creation of a tag. That's strictly a developer-only power, and thus used extremely sparingly.
Comment: @Lankymart: regarding [**asp** ** **.net**] - you can't legislate for the lunatic!
Comment: @Rafael Similar to [Keith's suggestion](http://meta.stackoverflow.com/a/290592/692942) but will take a look. Thanks.
Answer: How about a warning when mixing asp-classic with .net, c# or any other .NET-related tag? Something to the effect of:

ASP Classic is not a .NET technology. Did you mean asp.net or
  asp.net-mvc?

SO already has support for warnings (see the screenshot in Can we get a warning when a user tags multiple DBMSs?) so I don't think this would be breaking the mold.
Comment: I have to admit, I've never seen that before and didn't even know SO could do it. This would be a viable option.


What is the reason behind specific values for charge of electrons, protons?

Question: Why do things like protons and neutrons have specific values. Also speed of light is a speed in which even if you go towards it, the speed does not vary. But why does light have to travel at speed?
Comment: Many aspects of these questions have been addressed before at Physics.SE, see e.g. http://physics.stackexchange.com/q/4238/2451 and http://physics.stackexchange.com/q/2230/2451
Answer: Suppose you were given a book written in a language that you do not know. The analogy holds with unknown languages which are alphabetic. You start by seeing that a certain number of shapes repeat, you give them names as letters: you get an alphabet.
Charge, mass, spin and other distinguishing characteristics allow physicists to classify particles as A,B,C etc, because they have identical distinguishing characteristics. Actually when elementary particles were first seen in cosmic rays they were classified according to the greek alphabet: alpha rays, beta rays, gamma rays etc. The classification simplified the data and allowed for  further observations. In the language analogy, words will be distinguished, grammar, then syntax, etc.
Edit since it was brought up again:
so the answer to the question:

Why do things like protons and neutrons have specific values.

Because we have observed experimentally that they do, and these specific values allow for our distinguishing particles from each other. Only a Theory Of Everything could possibly answer with a  cause for these values derived from principle, and theory is not there yet.
and the answer to the next query

But why does light have to travel at speed?

Is similar. Light travels at a specific speed irrespective of the framework system because it has been experimentally observed that it does both, it has a speed which is  independent of framework.
Further experimental observations allowed classification of all particles in what is the Standard Model, a model that encapsulates the observational data up to now, and that is why it is important for any theory that is advanced about the way the world works: it has to be incorporated or come out of any theoretical model advanced as the Theory of Everything. Similarly for light, further studies established the Lorenz invariance system which also has to be incorporated into any TOE.
Answer: Well, part of it is an experimental fact.
For particles, the definition of a type of particle (ie protons, neutrons, electrons) could be written 'a class of bodies with the same intrinsic properties'. So, all protons have the same properties. If each proton had a different charge, then we cannot call them all protons. We would have to call each of them a separate type of particle. So protons are all the same. Intrinsic roperties like mass, spin, charge, baryon number, etc. care the same. Note that properties like momentum need not be the same.
In fact, Wheeler, suggested that all electrons are the same electron. This comes from the notion that a positron can be thought of as an electron going backwards in time. So you can view an electron zigzagging through time, giving rise to multiple electrons at a point in time. There's a flaw with this:it require there to be equal numbers of electrons and positrons in the universe, which is as far as we know untrue.
Someone else may also post an answer showing how the masses and charges blossom from group theory, if they do at all (not sure of this).
The speed of light is more of an experimental fact. It can be thought to come from making Maxwell's laws more aesthetically pleasing. In the end, these laws are experimental facts as well, so it all comes from experimental evidence.
Light has to travel at a speed, otherwise it won't go anywhere. Yes, there's no issue with it going at infinite speed AFAICT, except for experimental evidence. I guess an alternate universe following the same laws could have infinite speed of light. Then again, such a universe would be overclassical; and magnetism wouldn't work (or electric forces would be infinitely large). But it would be much more like our everyday world. No wierd black holes, no wierd time issues.
Answer: As the constant values are theoretically (with mathematical derivations) and also practically proves the assertions in resembling theories regardless different physical situations like in any inertial frame of reference and despite major/minute change in temperature, pressure in surrounding medium and also there will be no or negligible change in the constant value we consider is happen during this situations. Constants must has same value no matter they are being used in other theories and should give expected results.


generative vs discriminative machine learning

Question: Could someone provide differences between these two techniques? Also, I would very much appreciate if you could give an example of a ML method that falls into discriminative model or gnerative one. For instance, is Perceptron discriminative? K-Means?
Answer: Let $X$ be your observed data and let $Y$ be their unobserved/hidden properties. In a ML setting, $Y$ usually holds the categories of $X$.
A generative model models their joint distribution, $P(X,Y)$.
A discriminative model models the posterior probability of the categories, $P(Y|X)$.
Depending on what you want to do, you choose between generative versus discriminative modeling. For example, if you are interested in doing classification, a discriminative model would be your choice because you are interested in $P(Y|X)$. However, you can use a generative model, $P(X,Y)$, for classification, too.
A generative model allows you to generate synthetic data ($X$) using the joint but you cannot do this with a discriminative model.
Answer: Consider a classification problem
at the simplest approach one can get to its goal by designing a discriminant function. for example: a perceptron
$y=sign(\theta^Tx)$
you can learn the parameters by a algorithm. in this case you should use Perceptron Learning Rule.
the above approach is not probabilistic and is called 'discriminant function' approach.
a better goal is trying to predict the labels probabilistically. the best goal is to have P(y|X) that is called the posterior.
Example of a discriminative approach: logistic regression
$P(y=1|X)=g(\theta^Tx)$,where g is the sigmoid function.
Example of a generative model:
$P(y|X)=P(X|y)P(y)$
you can model $P(X|y=1)=N(\mu_1,\Sigma_1)$ and $P(X|y=0)=N(\mu_0,\Sigma_0)$ and estimates its parameters from data. (the simple approach is Maximum likelihood).


What programming languages can one use to develop iPhone, iPod Touch and iPad (iOS) applications?

Question: What programming languages can one use to develop iPhone, iPod Touch and iPad (iOS) applications?
Also are there plans in the future to expand the amount of programming languages that iOS will support?
Answer: Apple lifted the restrictions on non-Objective C/C/C++ apps -- you just can't load code that isn't in the app bundle.
MonoTouch lets you use .NET languages -- C# is directly supported, but if you have Windows, you can make assemblies in any .NET language and use it.
There are rumors that Apple is going to support other languages directly -- I keep hearing ruby, but they are just rumors.
I think Lua is being used for game logic on a lot of apps.
EDIT (in 2018): Generally you can use any language that you can get to compile for iOS or even install language interpreters.  The main thing you cannot do is load code from the Internet that wasn't in the app bundle.
People do this all of the time anyway (see React Native apps loading JavaScript from servers), but, technically, it's not allowed.  The main thing that will get you attention from Apple if you make some kind of App Store that loads whole App-like things.
EDIT (in 2020): from @Pylot in comments: I know this is a long time ago, but now at least technically you can load code that isn't embedded in the app, as you can write with JavaScript using the webview. Not staying your answer is wrong or anything, I definitely agree with you. but I was looking for something and found this post on the way. Figured if anyone sees this it might help them out.
Comment: Objective-C++ is the bridge between ObjC and C++, so it's fine.
Comment: I tried Lua for the logic within my app, with luasqlite as well (enterprise solution, so no store rejections could be involved, whether they might happen or not) and i can testify that it works wonderfully. Keep in mind that Lua has a very very low memory footprint, so you can actually run dozen of interpreteres at the same time without consuming as much as a Mb of memory (which is what I actually did...). See also gran.pancho.villa answer about Swift.
Comment: I know this is a long time ago, but now at least technically you can load code that isn't embedded in the app, as you can write with JavaScript using the webview.

Not staying your answer is wrong or anything, I definitely agree with you. but I was looking for something and found this post on the way. Figured if anyone sees this it might help them out.
Comment: RubyMotion lets you build native iOS apps using Ruby. It is not free though.
Comment: @pylot -- I added your comment to the answer -- thanks
Comment: You can also use JavaScriptCore in addition to web views
Answer: The SDK agreement and App store guidelines have been changed (circa Sept 2010).
You can now probably use any compiled language that will compile to the same static ARM object file format as Xcode produces and that will link to (only) the public API's within Apple's frameworks and libraries.  However, you can not use a JIT compiled language unless you pre-compile all object code before submission to Apple for review.
You can use any interpreted language, as long as you embed the interpreter, and do not allow the interpreter or the app to download and run any interpretable code other than code built into the app bundle before submission to Apple for review, or source code typed-in by the user.
Objective C and C will likely still be the most optimal programming language for anything requiring high performance and the latest API support (* see update below), as those are the languages for which Apple targets its iOS frameworks and tunes its ARM processor chipsets. Apple also supports the use of Javascript/HTML5 inside a UIWebView.  Those are the only languages for which Apple has announced support.  Anything else you will have to find support elsewhere.
But, if you really want, there are at least a half dozen BASIC interpreters now available in the iOS App store, so even "Stone Age" programming methodology is now allowed.
Added:  (*) As of late 2014, one can also develop apps using Apple's new Swift programming language.  As of early 2015, submitted binaries must include 64-bit (arm64) support.
Answer: With plans to slowly retire the long-used Objective-C, Apple has introduced a new programming language, called Swift, for designing apps and applications to run on Apple iOS devices and Apple Macintosh computers.
Apple says:
"Swift is a new programming language for iOS and OS X apps that builds on the best of C and Objective-C, without the constraints of C compatibility. Swift adopts safe programming patterns and adds modern features to make programming easier, more flexible, and more fun. Swift's clean slate, backed by the mature and much-loved Cocoa and Cocoa Touch frameworks, is an opportunity to reimagine how software development works."
Introducing swift
Answer:
What programming languages can one use to develop iPhone, iPod Touch and iPad (iOs) applications?

Ruby, Python, Lua, Scheme, Lisp, Smalltalk, C#, Haskell, ActionScript, JavaScript, Objective-C, C++, C. That's just the ones that pop into my head right now. I'm sure there's hundreds if not thousands of others. (E.g. there's no reason why you couldn't use any .NET language with MonoTouch, i.e. VB.NET, F#, Nemerle, Boo, Cobra, ...)

Also are there plans in the future to expand the amount of programming languages that iOs will support?

Sure. Pretty much every programming language community on this planet is currently working on getting their language to run on iOS.
Also, a lot of people are working on programming languages specifically designed for touch devices such as iPod touch, iPhone and iPad, e.g. Phil Mercurio's Thyrd language.
Comment: -1. Ruby, Python, and ActionScript don't yet work on iOS. In the past, there were attempts to get CL and Scheme running, but I don't think those are up to date. Same deal with Haskell. JavaScriptCore is a private framework right now; you can script Objective-C using JS in a webview, but that's really clunky.
Comment: @Jonathan Sterling: You should tell that to the developers who have been selling Ruby apps through the App Store for over a year now. I'm sure they would be very interested to learn that their apps don't exist.
Comment: Rhomobile doesn't count. Those aren't actual native apps. They are just stuck in a webview.
Comment: @Jonathan Sterling: I may be a little late to the party here, but Actionscript is supported on iOS, via AIR for iOS.  (And it was at the time of the original comment Oct-10). It even gets pretty great performance too...
Answer: The programming language of iOS(and Mac OS) is Objective-C and C. You have to use Xcode platform to develop iOS apps, on the next version that is now available on beta release, Xcode 4 supports also C++.
Comment: You don't need to use Xcode to develop iOS apps or either Objective C or C++. For example you can use RubyMotion which makes use of the command line tools. Also, there are a number of third party development solutions for developing an app which can run on iOS and Android
Answer: It is also now possible to use OCaml for developing iOS applications. It is not part of the standard distribution and requires modifications provided by the Psellos company. See here for more information: http://psellos.com/ocaml/.
Answer: Only Objective-C is allowed by now... but since a few months ago you are allowed to write scripts that will be interpreted in your application.
So you may be able to write a LUA interpreter or a Python interpreter, then write some part of your application in this scripting language. If you want your application accepted on the App Store, these scripts have to be bundled with the application (your application cannot download it from the Internet for example)
see new app store rules
Answer: This might be an old thread, but I'd like to mention Appcelerator Titanium, which allows anyone versed in HTML5/JavaScript/CSS to develop iOS applications.
Comment: If I'm not mistaken you can swap out JavaScript with either Ruby or Python when using Titanium.
Answer: objective-c is the primary language used.
i believe there is a mono touch framework that can be used with c#
Adobe also is working in some tools, one is this iPhone Packager which can utilize actionscript code
Comment: The link seems to be dead?
Answer: You can use "smart BASIC" programming language. It is a genuine but very advanced BASIC language with all its power and simplicity. Using its free SDK, BASIC code can be easily published as a standalone App Store application. There are many apps in App Store, written in "smart BASIC" programming language.


Credit card pay back period calculation

Question: What is the industry standard equation for calculating the payback period of a credit card?  For example: Mark has a credit card with a rate of 17%.  He has a balance of 5500 and a limit of 5500. If he just paid the minimum, how long would it take him to pay it back?
Comment: Minimums vary by credit card apparently.  What is the minimum in this case, or should we just pick one? (e.g. $20 or 2% whichever is higher)
Comment: Yeah let's pick one
Answer: Without considering fees, the present value of a loan is equal to the sum of the repayments discounted to present value
s is the principal
n is the number of periods
d is the periodic repayment
r is the periodic interest rate

s = (d - d (1 + r)^-n)/r

∴ d = r (1 + 1/(-1 + (1 + r)^n)) s

and n = -(Log[1 - (r s)/d]/Log[1 + r])

Nominal vs. Effective Interest Rates
APR is the USA is quoted in nominal terms, so if the APR is 17% nominal compounded monthly the monthly rate is
r = 0.17/12 = 0.0141667

In Europe APR is quoted in effective terms, so with 17% effective annual interest the monthly rate is
r = (1 + 0.17)^(1/12) - 1 = 0.0131696

Proceeding with your example as if you are in Europe
r = 0.0131696
s = 5500

If the minimum monthly repayment d = 100
n = -(Log[1 - (r s)/d]/Log[1 + r]) = 98.4852

It would take 99 months to repay the loan, with a smaller final repayment.
In the USA, with r = 0.0141667 it would take 108 months.
Edit
Further to Dilip's post, noting that the minimum payment would decrease...
With a representing the fraction of the balance (prior to interest) to be paid, say 30%, the principal remaining at the end of month x after the repayment has been made is derived from
p[x + 1] = p[x] (1 + r) - a p[x] where p[0] = s

∴ p[x] = (1 - a + r)^x s

So with
s = 5500
r = 0.17/12 = 0.0141667
a = 0.3

The principal remaining at the end of month 9 is
p[9] = 265.802

If the minimum repayment is $100 the next two repayments will be $100
p[10] = p[9] (1 + r) - 100 = 169.568
p[11] = p[10] (1 + r) - 100 = 71.9701
p[12] = p[11] (1 + r) - 72.9897 = 0

With 30% minimum repayment capped to a minimum of $100 the credit card debt is repaid in 12 months.
Up until the cap comes into play the repayment d at the end of month m is given by
d[m] = a p[m - 1]

E.g. d[1] = 1650
     d[2] = 1178.38

Comment: @quid Monthly rate.
Comment: When I learned in university that Americans and Canadians quote APR in nominal terms I was baffled. Why give the percentage in yearly terms if that's not the interest over that year? (I guess that is the cost to continually service the loan but nonetheless it is strange.)
Comment: @Lan how else would it one refer to an interest rate for something like credit cards?
Comment: @chrisdegnen, sorry mate, what is APR?
Comment: @JeremyBray APR is [annual percentage rate](https://en.wikipedia.org/wiki/Annual_percentage_rate).
Comment: also in the line n = -(Log[1 - (r s)/d]/Log[1 + r]) = 98.4852
what is happening with (r s) @chrisdegnen
Comment: also @ChrisDegnen the amortization doesnt make sense to me, how could the loan be paid of in 7 months if the user is paying a 100 minimum. 7 X 100 = 700
Comment: @JeremyBray Re. `(r s)`, this is shorthand for `(r * s)`.  Re. repayment in 7 months, that happens if the minimum repayment is 50% of the balance.  I have updated the example to one with 30% minimum repayment, with further details which should hopefully make things clearer for you.
Answer: In the US, minimum monthly payments of credit card debt are required by law to consist of the sum of all interest and service fees charged that month plus a fraction of the statement-closing_day balance (before interest and fees are tacked on) so as to ensure that the balance is paid off in a "reasonable time".  (There is also a de minimus out: when the minimum monthly payment gets to be under $X (something like $5 or $10), the entire balance can be made due right away).  Most US credit-card companies take reasonable time to mean 8+ years since most of them set the minimum payment to be 1% of the outstanding balance.  If you began with $5500 owed, and paid all interest and fees due + $55 each month, you would pay off the debt in exactly 100 months or 8 years and 4 months.  In actuality, it would take longer because the minimum required payment would decrease from "interest + fees + $55" each month as the statement-closing-date balance would decrease month after month. The minimum required payment would also decrease because the interest charged each month decreases because the outstanding balance decreases.  It takes iron will to choose to pay extra  when the first option on the "Make a payment" tab on the credit-card web page is "Pay minimum required amount".
So much so for the theory. In practice, what the US credit-card companies count on is that most cardholders will continue charging purchases (or even better for the company, cash advances) to the card so that the balance is back to the $5500 limit each month and so making minimum monthly payments will never reduce the month-end balance below $5500. By law, minimum monthly payments must be applied to interest and fees first, and the excess can be applied to any part of the balance, including the 0%-rate balance, if any. The law requires only that the amount in excess of the minimum monthly payment be applied to the part of the balance being charged the highest interest rate.
Comment: thanks for taking the time Dilip. this is really helpful knowledge to add to the equation
Answer: It depends on what the minimum is.  If it is less than or equal to the interest (at 17% on $5,500 that comes to $77.916 per month) then he would never pay it off.
If it is just $20 of principal per month (plus the interest), e.g. $97.92, then $5,500 divided by $20, which is 275 months, or 22 years, 11 months.
Comment: I am more after the equation that includes the compounding interest
Comment: Assuming the principal is being paid down, the interest is $77.916 only in the first month.  In subsequent months it becomes progressively less.

Credit card pay back period calculation


What exactly is generator G in Bitcoin's elliptical curve algorithm?

Question: What exactly is the generator G in elliptical curve math?  It is typically described as a point on the curve.  Is this a tuple of values?  What properties does it have?
Answer: For a curve with for instance the equation:  y^2 = x^3 + a * x + b
The generator point G, or a ECDSA public key, is a pair of coordinates x and y, for which the above equation holds.
To reduce the storage size for a curve point, one can also store a sign and the x coordinate, this is what is known as point-compression.
You can then reconstruct the y by calculating  sign * sqrt(x^3+a*x+b).
Note that for calculations in modular fields the square root can only be calculated efficiently when the p != 1 (mod 8)
Comment: Note that in the specific case of Bitcoin's secp256k1 curve, a = 0 and b = 7, so the formula is y^2 = x^3 + 7.
Answer: You can think of the generator G as the first point after infinity on the curve.  Begin with infinity and add G; the result is G. Add G to this and you get 2G. Add G to this and you get 3G. And so on. If you add G a total of n times (where n is the order of the curve) you will be back at infinity, where you started; the whole curve is a never-ending loop. The order n is how many distinct points are on the curve, or in Bitcoin terms, how many possible private keys there are (plus 1 for the point at infinity).
Comment: Is the order `n` that you're referring to the same as the `finite field` in the context of the discrete log problem?
Answer: The value of
G(compressed) = 02 79BE667E F9DCBBAC 55A06295 CE870B07 029BFCDB 2DCE28D9 59F2815B 16F81798
and
G(uncompressed) = 04 79BE667E F9DCBBAC 55A06295 CE870B07 029BFCDB 2DCE28D9 59F2815B 16F81798 483ADA77 26A3C465 5DA4FBFC 0E1108A8 FD17B448 A6855419 9C47D08F FB10D4B8
source:  https://en.bitcoin.it/wiki/Secp256k1
Comment: This is a potentially useful answer, but it could be improved by adding a little more explanation.
Comment: Yes.. Uncompressed G has 2 co-ordinates X and Y since it is point on the curve and its size is 520 bits(65 Bytes) i.e 256 bits for each co-ordinate And it has a prefix 04 , While Compressed G has only one co-ordinate i.e.X And a prefix either 02 when Y co-ordinate is positive or 03 when Y co-ordinate is Negative.
Answer: Starting with a private key in the form of a randomly generated number k, we multiply
it by a predetermined point on the curve called the generator point G to produce another
point somewhere else on the curve, which is the corresponding public key K. The generator point is specified as part of the secp256k1 standard and is always the same for all
keys in bitcoin:
K = k *G
where k is the private key, G is the generator point, and K is the resulting public key, a
point on the curve. Because the generator point is always the same for all bitcoin users,a private key k multiplied with G will always result in the same public key K. The rela‐
tionship between k and K is fixed, but can only be calculated in one direction, from k
to K. That's why a bitcoin address (derived from K) can be shared with anyone and does
not reveal the user's private key (k).
from the Book "Mastering Bitcoin" by Andreas Antonopoulos
http://uplib.fr/w/images/8/83/Mastering_Bitcoin-Antonopoulos.pdf
Answer: Ok first and foremost people no offense but your both just a little off on your thoughts of how it is supposed to be understood. The fact is that {y^2=x^3+ax+b} = n order h= base point G 02/03 in compressed format and 04 in uncompressed. 04 was to show the whole uncompressed key (X^3, Y^2). The understanding of the compression is that the 02 is even and the 03 is odd for X. But in order to so called get your private key back if lost (because the public key is not supposed to be shared hence the reason for the ripemd and md5 versions). Simply put in an easier understanding for most. XXX+7=YY so the cubic sqrt of x generates the x and the sqrt of Y generates the Y of the random number that was began with because this is a graph either way around. Meaning function(x,y)=(x) random number. So from the beginning when you use a random number in the curve it is a point on the Elliptic curve in elliptic curve cryptoGRAPHy so a X and Y coordinate comes from your random number that is entered into the equation xxx+ax+b=yy where a=0 and b=7 over a finite field which is basically a square with 0,0 : 0,1 : 1,1 : 1,0 hence the reason for the cubic function of x. Where most get confused is because of the exponents P,N,A,B,G and H being thrown in there but you must understand that the truth is those variables make up the sextuple T. Where they are pretty much constant variables except h which is either 1 or 0 to determine the outcome of G. P is the finite field 2^255-2^32-2^9-2^8-2^7-2^6-2^4-1. A=0 B=7 and N is the order mod h to determine the outcome of G. N does not change values it is the sqrt of 2^255 so basically 2^128. Trust me I know what I speak of. Although things have changed with the addition of all of the bips, HD wallets, and the various upgrades throughout the years. What I speak of is the truth. In the beginning you started out with a key that was unserialized at first which meant it was 228 bits then it was serialized which gave you a shorter key that was your Eckey(elliptic curve key) meaning your random number that your public key would be derived from following the math I have laid before you. It would calculate your public key, a signature, and a new private key if needed. But of course with everyone thinking they know best and using programs to manipulate keys to their benefit, or because they think theirs is better, the differences from the beginning are astounding. Just saying.... Hope this clears up things a lot better for you guys. If you don't believe me right now just know at some point in the future you will understand why my knowledge on this subject is so confident.
Comment: You should edit that to at least have some paragraphs/formatting - walls of texts are hard to digest in the best of times, and even harder when explaining crypto


What's the difference between Capacitors, Ultra-Capacitors and Batteries

Question: Capacitors are known to hold and release energy very quickly, unlike the slower release that batteries exhibit. If one were to bunch many (1000's of) capacitors together could they function as a battery, since each capacitor would hold and release a comparatively smaller amount of energy when compared to a battery's output at any given moment, but in total the sum of the energy stored in all the capacitors would allow it to exhibit the slower release and longer availability of stored energy of a battery?
Answer: Yes, capacitors could function as a battery, but there are some technical problems.
A battery generates electricity from a chemical reaction so the voltage and power produced remains approximately constant for the lifetime of the battery. The voltage on a capacitor is proportional to the charge on it so the voltage decreases as you discharge the capacitor. This means you'll need some form of voltage regulation that you wouldn't need with a battery.
I believe that ultracapacitors currently don't store enough energy to replace batteries in cars, but I've seen claims that they are getting close.
Answer: Currently the best super-capacitors have an energy density (how much they can store in a given size) of only 10% of a rechargable battery.
But you can get the energy out of a capacitor very-very quickly, so the power available can 100 or 1000x as high as a batttery. So they have a very high power density.
This is the main use of capacitors in electronics, they provide a little 'holding tank' for electrical energy that is needed quickly by a device, say when an output switches, and the battery can't react as quickly. Bigger banks of capacitors are used to provide huge amounts of energy very quickly (and so high power) to fire large lasers or x-ray machines.
Answer: Supercapacitors don't get their large capacitance via their dielectric constant, which is usually about 10 - values of 10,000 are not uncommon for conventional capacitors. Instead, they get it from a super-thin dielectric - on order only a couple of Angstroms (2E-10 m). This means that for a rolled construction, each layer is very thin and so many layers can be packed into a regular sized package. This in turn means a huge surface area is available - as much as 10,000 square metres. This goes towards explaining how so much power is so readily available. The disadvantage of the thin dielectric is that only low voltages can be used, which in turn restricts the stored energy.


Splitting up weight hiking as a couple/mixed gender group

Question: Assuming equivalent fitness, what is a fair way to split up weight when hiking as a couple/in mixed gender groups? Should the weight be proportional to the individuals weight? Are there other considerations?
Comment: related: http://outdoors.stackexchange.com/a/1306/163
Answer: Someone who has overweight isn't normally able to carry more, so weight isn't as important. The height would be more adequate... Muscle strength isn't much important when you go on long hikes... Strength doesn't translate directly to endurance, often it's the opposite - people with smaller muscles are more endure and are actually able to carry more on greater distances.
The most practical solution is not to care about fairness, but of outcome for the group. If someone is doing poorly that day, stays behind etc., take some things from them and give it to the best performing members of the group. As the result, the fastest will go a bit slower, the slowest will go a bit faster and the group as the whole will perform much better.
Comment: In all my years at scouting we've always done the same thing: first split evenly, walk a 1 or 2 kilometers and see how everyone is doing, then divide and continue for the day. We often see people complaining the first 5 minutes but as they adjust to it they're fine.
Comment: Absolutely right: what matters is the group outcome, and the communist principle actually works well here: "from each according to ability".  But ensure that the system isn't gamed by selfish individuals expecting their luxuries to be shared!
Answer: When I go hiking with my wife or a mixed group, we don't use any fixed figures of x%. Instead we all know roughly what weight we are happy carrying, and if someone feels they could carry more they will offer to help out someone who appears to be struggling or overloaded.
In general, if you are experienced hikers, you will have your pack size/type pretty well nailed for most occasions so shouldn't need to do this, but you may have an inexperienced member of the team, or someone may be a bit off their usual strength through illness etc.
My advice - just work it out between you.
Comment: +1 for knowing your own personal weight carrying capacity. An additional useful thing to do with new hikers is to try and always keep a healthy ratio of experience-to-inexperience and likewise high-output-to-low-output, so that you have enough wiggle room within your group to optimize the individual conditions in the case of an emergency or to help a weak member make it through without abandoning the trip objective.
Answer: Dividing loads between your trek-mates is a good idea. A better one would be to pack light. In case you want to collectively gain by individually reducing the weight, then my suggestion would be to go by the comfort level of the individuals involved. A strong person might be able to haul more load. But the same one might not be able to perform the same way the next day. The division of labor changes dynamically during treks.
For example:
I am used to carrying heavier backpacks during my treks. I usually carry over 15Kg over treks spanning 7 days or more in the Himalayan regions. Whereas, during a weekend trek, with a backpack of just over 3Kg, I whined like a baby (my bad).
Hence, when deciding on dividing your backpacks, think about the current day and the stronger person(s) on the given day. DO NOT go by weight or gender. That never works out.
Happy trekking!
Comment: Good point about being habitual to a specific range of load!
Answer: I face this problem not for hiking, but for portaging. That is a slightly different situation, but not entirely different. We often went as two families: 4 adults and as many as 5 children. Not only could some children not carry anything, some of them had to be carried. Our approach:

separate kitchen packs from tent packs. Kitchen packs have food and cooking equipment and never go in the tents. Tent packs have tents, bedding, clothes etc. Typically the kitchen  pack is much heavier than the tent pack.
each family was responsible for their own tent pack, but we split supplies across the kitchen packs

There is a LOT of stuff you only need one of. Pots and pans, stoves, firewood saw, first aid kit, repair kit, water treatment, binoculars, ... we either worked out in advance who would bring something, or moved things between packs before setting off. (And often, the family with less children had some shared stuff in the tent pack, too, like books for bedtime stories.) We also balanced out the food as it got eaten. For ease of finding things, one bag held snack foods (jerky, nuts) and an entirely  different bag held meal ingredients. Knowing where to find things when 4 or more bags might hold it sounds like a nightmare to me.
As the children got larger we had bags for them to carry, but could always clip those things to an adult pack if we needed to. In the same vein, a mixed-strength group should pack in a way that makes it easy to take something (the [whatever] kit, the rope bag) out of one person's pack and put it on someone else's.
Remember, too, that you may start a trip as a matched group, then a minor injury or illness may afflict one of you, and splitting up the load may be the key to continuing.
Answer: Different people have vastly different styles. Some people carry a lot more weight, some a lot less. If you're interested in cutting your pack weight or moving toward a more lightweight or ultralight style, a good web site to check out is http://backpackinglight.com .
I think many people do use percentage of body weight as a criterion, e.g., I recently hiked with a very small woman (who, BTW, kicked my ass hiking), who had a certain strict figure -- she never carries more than x% of her body weight. (This was just her rule for herself. The three of us on that trip all brought our own gear and didn't re-divvy-up anything.) If you want a figure for comparison, I practice a pretty lightweight/ultralight style for summer in the Sierra, and my normal setup has a base weight (i.e., not counting food or water) of about 9% of my body weight.
Answer: I think that a fair way to split the weight between group members is ... everyone to carry their own. Including food, clothes, bedroll, part of the tent.
This prevents the inexperienced and unfit new hikers form bringing a ton of cosmetics, drinks, clothes.
Answer: I try to make my wife as comfortable as possible so she will continue to go with me on these backpack trips. Our last weekend backpack trip was in the Big South Fork in Tennessee in January. The low temperatures were 22 degrees. We had a total of 39 pounds. My pack weighed 22 pounds 56% and Alice's pack weighed 17 pounds 44%. She stated at 17 pounds it felt like her pack was empty. With this weekend's low temperatures expected to reach 9 degrees our gear will probably weigh about 50 pounds. I can see my pack weighing 27-28 pounds and my wife's about 22-23 pounds.
Comment: Hi and welcome to TGO. As it stands the answer looks a bit *random*. Can you explain, why you split like that? Or do you have any other helpful background informations? If we all just share the way we split the weight, the topic is not very useful for others. We would get a big list then.


ENO-WENO Schemes: Are ENO-WENO schemes non oscillatory for all kinds (linear/non linear) of problems?

Question: Is there an rigorous proof of ENO-WENO schemes being non oscillatory?
Answer: Depends on what you mean by 'non-oscillatory'. In their original paper, Harten & Osher (1987), design the ENO schemes with the 'non-oscillatory' property defined as:

In this paper we construct a uniformly second-order approximation, which is nonoscillatory in the sense that the number of extrema of the discrete solution is not increasing in time.

They also provide proof in the paper (pp. 281). In this sense, and formally, when an ENO scheme is used for interpolations to compute numerical fluxes in solving Hyperbolic Conservation Laws of the form:
$$
\frac{\partial u}{\partial t} + \frac{\partial}{\partial x} F(u) = 0,
$$
it is guaranteed that the final numerical solution will have equal or less number of extrema when compared to the exact solution.
In practice, this is achieved by using an adaptive stencil that is constructed in a hierarchical fashion to avoid interpolating across non-smooth regions (e.g. large gradients, shocks, etc.). Note that ENO schemes are just one of the ingredients needed for a numerical solution to converge to the viscosity solution of nonlinear PDEs such as Hamilton-Jacobi or Hyperbolic Conservation Laws. Other ingredients include

Use of monotone and consistent numerical flux (or Hamiltonian)
A TVD integrator in time

For more details please consult the aforementioned paper. I could add more references including those that discuss implementations if needed.
UPDATE:
So why TVD integrators? Note that ENO (or WENO) only quarantines that you do not interpolate across discontinuities. It assumes nothing about what happens to the solution in time. To ensure that the solution remains non-oscillatory, time integration should have the TVD property. TV of a discrete data-set is defined as
$$
TV(u^n) = \sum_{i=0}^N \left|u^n_i - u^n_{i-1}\right|
$$
A time integration scheme is said to be TVD if satisfies the following property:
$$
TV(u^{n+1}) \le TV(u^n)
$$
Please note that for a time integration scheme, such as RK methods, to be TVD, they need to satisfy certain bounds on the CFL number. This is a bg topic in itself and I suggest you consult the following papers for accurate discussions:
Efficient implementation of essentially non-oscillatory shock-capturing schemes (Shu, C.W. and
Oshert, S)
Total-Variation-Diminishing Time Discretizations (C. W. Shu)
Total variation diminishing Runge-Kutta schemes (S. Gottlieb and
C. W. Shu)
Comment: Thanks for the answer! I was wondering, what exactly is the effect of using a TVD integrator? Why do we need that at the first place? Why euler integrator fails? I was using euler for first order upwind. Even ENO2 and ENO3, for the problem I am solving (Ideal MHD - Flow around conducting cylinder), was giving correct results. However I found WENO5 gives oscillatory(unphysical oscillation) solution with euler integrator which seems to disappear with TVDRK schemes. Is there any theoretical basis behind this or it just comes from practice?
Comment: @maverick I just updated the answer with some more info for TVD. Basically you need TVD to ensure that the solution remains non-oscillatory during time integration


How can I make tongue and groove cuts with only a radial arm saw?

Question: I'm pretty new to woodworking and I don't have a lot of tools. I'm working to make pieces to sell and buy more tools as I go. I don't own a table saw, but I do have a radial arm saw. Has anyone ever done tongue and groove cuts with a radial arm on smaller boards? This seems like a bit of a dangerous proposition to me as the saw has not been kind to smaller wood I've tried to cut. If this is not an option, is there an alternative I can use in the meantime of a router purchase?
Comment: I used a radial arm saw a lot coming up in the trade, it is a dangerous machine, graduate from it as soon as you can.
Comment: @Jack I inherited this saw from my dad who got it from a friend in the early 90's. I was reading up on recalls, and this one is recalled. I called in yesterday and they are sending me a brand new table top and blade guard for free! Hopefully that cures some of the safety concerns. If not, I might retrofit this to a radial arm something or other. :) Thanks for the advice!
Answer: I've tried it in a pinch and, yes, it's rather dangerous and stupid. It's just the wrong tool for the job.
Table saws can be found fairly affordably, though. Most big boxes will sell one for around $150. It's not a GREAT saw, but should work for getting some tongues and grooves created.
Comment: Great advice here. I chose the other answer because of the accessory port that he pointed out for routing, etc... I'm looking to buy a nice table saw. I'd rather save up a few extra months and buy something really nice. Thanks for your input!
Answer: Some (not all) radial arm saws have a router spindle on the opposite end (may need to get a chuck for it.) My latest "please, take it away, we're selling the house" (I was picking up another, more worthwhile object at the time, and got begged into taking it) Sears RAS has it, under a little red cap, with a label. (not me, nor the exact saw, but shows the same thing)  Never tried using it, as I have a real router. Only goes 6000 rpm, since it's the same spindle the saw is on. Can't find a good picture of one "in use".
OTOH, buying a router is a lot cheaper than a single trip to the emergency room. Several mantras come to mind:

Anything that cuts wood cuts flesh.
Listen to the little voice that tells you it's probably a bad idea, NOT the one that suggests you can probably get away with this - find a different way.
Shortcuts make long delays while you try to figure out how to do things without the appendages you used to have.

If you are OldToolish at all, a plow plane will cut grooves, and you can use two grooves and a spline.   You can also cut tongues, but it's more of a pain than two grooves.
Comment: Thanks for the in-depth comment. You've enlightened me to the accessory port on the opposite side of the saw. I was blind to this for some reason. I found a very reasonable piece that will most likely work in the interim until I can save up for a router or better saw. Also, I love the hand plows. I've been on the look out for these at antique stores.
Answer: If you feel brave enough to make the initial cuts through the fence I have illustrated below, that should be the scariest part of the operation. Actually the hole in the auxiliary fence can be cut with a jig saw or other means before it is installed.
Pardon my rough drawing, I hope it gets the idea across. Once set up it will be safe to use. Finger boards can be added for extra safety. The blade is drawn projecting much farther than needed to make the cuts you need. It is the way the drawing came together.
The fence needs to be taller, and the blade only needs to project 1/4" through the fence. The "window" the blade pokes through needs to be made high enough to raise the blade to the highest cut. The table has a raised table added to it so the arbor does not hit the main table, the fence is screwed to the raised table. Use 3/4" plywood for the fence, it is not going to split at a bad time while material is being pushed through. Wax the fence and upper table, it will make the stock much easier to push through.
Make test cuts on same size scraps to gauge the cuts by.
Order of work, before the extra table is assembled, set the saw to cut the shoulders of the tongue portions. All finished cuts will be centered, so if you are using 3/4" thick stock, set blade 1/4" in and a scant 1/4" into the top of the stock. Set up your finger boards, run one side after your test cut is made, flip the piece, run the opposite side. do this with all stock with a few extras.
Next set up the fence I drew earlier set the blade a heavy 1/4" through the fence. Start the cuts for the groove on the other edge of the previous pieces as near to the center as you can eyeball, exact is not important, but get it close. Flip the stock and run it again. You will have a groove started that is perfectly centered. Raise the blade slightly and repeat until you get a 1/4" wide groove. until all stock has been run.
As a reminder, all initial first cuts are done with the test stock first.
Final passes.  Raise the blade to get the remainder of the tongue cut, this is a little more critical to cut right the first time. I would actually set the saw at a slight angle, say 1 degree to give the tongue a slight taper, so it will ease the assembly of the pieces.
With the test piece. set the blade so it cuts as close to the 1/4" needed to fit into the grooves cut on the other edge. Run all your stock and make the last adjustment to get it to fit right.
All done!
Note: your results will be better if all stock if flat, straight and uniform in thickness, if not the grooves will change as the wood does, you will be mad at me. Finger boards will help flatten out the stock a little, it will not do it all though.
Good luck
Comment: Hi Jack. Just wondering how the blade gets turned horizontal rather than vertical here. I see the concepts, just wondering how this will work with the saw that I have right now.
Comment: You must raise the whole arm pretty high, release the pivot that allows the saw to make bevel cuts, instead of stopping at 45 degrees, go all the way to were the blade is horizontal (parallel) with the deck. I have a 30?? year old craftsman radial arm saw, it does it quite readily.
Comment: Wow. I didn't realize it could do that. Your answer is actually the one that helped me use what I currently have. I made a jig to raise the wood up and pass it through. It works really well! With the blade facing opposite me, there's not much of a safety issue with using push blocks. Thanks much!
Answer: is there an alternative I can use in the meantime of a router purchase?
You can make a plough & rebate plane from a chunk of 2x4 and a 1/4" chisel.

I made one following Paul Sellers video on a "Poor man's rebate plane"
To convert it from a rebate plane to a plough plane I just screwed on an extra piece of wood as a spacer/fence.

It was fun to make and very satisfying to use.
Comment: I just watched that wonderful video last week ironically! It's simply amazing.


Word for telling about events of a movie/book etc

Question: When someone reveals details about surprising events which will happen in a movie or book to someone who doesn't know about them, we nowadays say that's a 'spoiler.'
I'm looking for a verb for that, which is less colloquial and less awkward than 'to spoil.'
Ideally, it would be a transitive verb, so I'd like to be able to say 'He Xed Y,' where 'X' is the verb I'm looking for and 'Y' would be the thing that was revealed.
Comment: Not very succinct, but you could say *spoiled the surprise of the ending.*
Answer: This isn't a single word, but phrase give away works.
TheFreeDictionary defines give away as:

To reveal or make known, often accidentally.

It can be used for movies, such as the phrase "gave away the ending".  There are a lot of examples of that on Google.
Comment: I would like to add that *give away* totally is a single word. It's just spelled with a blank, is all. There's no shortage of languages/writing systems that would spell it without. (Or indeed spell *all* the words with no blanks at all.) It's just a convention. Spaces do not delimit words. Not even in English. Observe: S P A C E. How many words is that? Five, you say? Count again.
Answer: Before spoiler, people would actually use the word reveal.
Whilst being a verb. it can also be used as a noun, as in the big reveal, such as with a magic show.

verb make (previously unknown or secret information) known to others.
noun (in a film or television programme) a final revelation of information that has previously been kept from the characters or viewers.

Alternatively, you could use unveil

verb show or announce publicly for the first time.

Definitions from Oxford Dictionary
Both work in the context that you've described:

He revealed an object
He unveiled an object
Comment: Would you say 'to reveal' or 'to unveil' have the negative connotation that 'to spoil' has?
Comment: @JohannesBauer 'To unveil' generally has positive connotations, as it is usually used in reference to a public gathering, such as 'unveiling a new statue', which are usually crowd-pleasing events. I don't think 'to reveal' has connotations of good or bad.
Answer: I like divulge:

verb
[WITH OBJECT]
  Make known (private or sensitive information):
ODO
Answer: Disclose might work well in a formal context:

verb
[WITH OBJECT]
  1 Make (secret or new information) known:
Answer: On the colloquial scale, I would rate leak somewhere between spoil and disclose:

verb
2.1 [WITH OBJECT] Intentionally disclose (secret information):
ODO
Answer: For me, the biggest problem with trying to use "to spoil" as a verb for "reveal" is not its colloquial nature but "the fact" (as seen by me) that spoil/spoiler still really means "ruin" in this sense and not "reveal":
"Don't spoil/ruin it (the movie/the ending/whatever) for me [by revealing it (the plot twists/the ending/whatever)."
Granted, the "by revealing [whatever]" can be implied, but it's not inherent in the word "spoil," even as it relates to movies, for one can easily spoil a movie in other ways: by talking, farting, checking a phone, etc.).
All that said in a feeble attempt to try to persuade you to reconsider the possibility of using a colloquialism, especially one that does mean "reveal" in this sense and one that could also provide some (clever?/lame?) alliteration when used with "spoil," to wit,
"to spill": (6. Informal. to divulge, disclose, or tell: "Don't spill the secret.").
"You spilled the surprise [ending], you spoiler!"
Comment: Totally agree: that's the reason why I was looking for something 'less awkward.'
Answer: synopsis: providing a summary of what happens in a film or book
Comment: But _synopsis_ is one of the few nouns that hasn't been verbed yet.
Comment: @EdwinAshworth : Google actually does give me results for 'synopsisize'  ;-)
Comment: @Johannes If that is considered an acceptable word, _synopsis_ has been verbisised, not verbed.
Answer: About 400 years ago a guy named Will said from the mouth of another guy named Kent,
"... mar a curious tale by telling it."