Receiving failure notice after recalling a message, even the recipient was not in online

Question: Receiving failure notice after recalling a message, even the recipient was not online.
Please help me to find what settings would have been done on the recipient's side.
Answer: "Recalling a message" is a feature of the Exchange server, not a standard. If the recipient is not using such, but anything else, you cannot "recall" the message. I'm not even sure whether it could be done if the recipient is connected to a different Exchange server than you are.


Fuse for a 18650 pack

Question: Are there any fuses that i can use to protect a 18650 battery pack. I have a 2s8p which is rated at 12.6v 21.6A. one battery is rated at 4.2v at 2700mAh.
Comment: All of your numbers indicate some kind of Lithium chemistry. Based on your question and comments below, you need to stop what you're doing right now before you hurt yourself or burn your house down. These types of batteries are dangerous even to people that know what they're doing.
Comment: You should read http://electronics.stackexchange.com/q/230155/11684 -- there are any number of ways to screw up with lithium batteries, and over-current is only one of them.
Comment: Do you really expect anyone to answer "no" to this yes or no question?  Perhaps you should ask for what you want to know.
Comment: Not really a yes or no. And yea i do know what am doing. I have a pack that i use to charge my iphone and all works well. I balance charge the pack with my rc charger. I just wanted to add some safety with a fuse. So that the fuses blows when or if there a short circuit by any chance.
Answer: Sure, you can fuse the output of the pack.  You'll want to dig into the datasheets for those batteries and see if that's peak current (likely) or continuous safe current.  Design your fuse to trip accordingly.
If you need something resettable (can be reused upon removal of the fault condition), check out PTCs.  PTC = Positive Temperature Coefficient.  Essentially, it's a resistor that is low resistance under normal operating conditions, but as it heats up due to an over-current situation, resistance increases (hence positive temp coefficient) and cuts off the supply.  Upon cooling it will become low-resistance again.
Here's the DigiKey link to PTCs so you can start selecting one for your specs.
Comment: @George I share Matt Young's concern about working with Lithium if you do not know what you're doing.  It is hard to say what is "better" since your question is so vague.  And diodes offer no protection save from reversed polarity connections, which you should make only one way to correct it anyway.
Comment: Does a diode be a good way to go. I know it allows current flown on one direction.
Comment: And those fuses, i am planing to connecting on each cell. Would that be better ?
Comment: Yea i thought so diodes would just block flow of current. Fuses would be the best for what i need.
Comment: Yea I've seen several guys on YouTube using those fuses. But when a short circuit happens shouldn't the circuit be left open at all times ? the PTC would close it when the temp subsides and that would again cause a short. Considering the amp rating of one cell i was thinking of getting a PTC rated at 16v 3A [here](http://www.ebay.com/itm/NEW-20pcs-3A-16V-Radial-Leaded-PTC-Resettable-Fuse-Test-Good-/221939888753?hash=item33aca5f271:g:zO8AAOSwkZhWRVpH)
Comment: Yes, ptc seems like the wrong fuse for your exact need. No, 3 amps (2700 mAh), that is actually the amp-hour or capacity rating of your cell which is different than the amps or current it can safely provide.  The data sheet of your battery will tell you the safe current.
Comment: It really depends on your failure modes in your exact application. As I said, that was *if* something resettable made sense for your application.
Comment: Thanks a lot filek. I know i will be going for the regular fuse and yes 3A it shall be. Will use thermal resistor or a ptc in series with the output. How is a thermal resistor diff from a ptc?

Fuse for a 18650 pack


In the past and now

Question: is "in the past and now" a commonly used collocation? For example, are titles like these correct: "London in the past and now", "Life in the past and now" etc.
Answer: A Google search currently gives me 184 results---it can be found, but it isn't common.  It's more common to collocate two terms that are grammatically similar to each other, such as:

Life in the past and present
London yesterday and today (implies a broad meaning of 'yesterday' that can cover past decades)
London then and now

In the past and now


0x swap api gas is doubled when adding feeRecipient and buyTokenPercentageFee

Question: I would like to collect fees on trade using 0x API. But the gas in the quote response is doubled or more when adding feeRecipient and buyTokenPercentageFee which doubles the gas price users are paying. Is this correct? Is there any way to prevent this, and how are other projects using 0x collecting fees without adding more gas fees at least not doubled?
Answer: When you define feeRecipient and buyTokenPercentageFee you are adding additional logic to callData: an additional transfer to your feeRecipient address. This causes the blockchain to charge more gas for that additinal operation.
There is no way to prevent this at the moment, rule of thumb, more bytes on callData more gas is charged.
On other side, normally that additional operation not doubles the gas, are you putting skipValidation=false and passing takerAddress on the API call? If you do so 0x API will it give you a more exact gas estimation.
Comment: Yes, that makes sense. So the question... is it correct that it doubles the gas?
Comment: Not necessarily doubles the gas. I think when there is no way to do the estimation they just put a fixed value depending on gas price.


Android Image upload/download with Base64 into JSON causes Out of memory error

Question: I currently encode and decode images to Base64. I overcame the initial issue with OOM's with the use of streams to encode the images into strings.
My issue now is that I cannot fathom how to add multiple Base64 encoded strings for multiple resolutions images (5620 x 3747 - 4.92MB or 3264 x 1836 - 1.35MB) to a JSON Object via Gson. Currently Gson throws an OOM exception only with 2 Base64 Strings from a 5312 x 2988 - 4.95 MB Image.
I understand that android may only be able to spare 16/20Mb per application, so this conversion must be way over the limit.
How can I write the Base64 String in a stream to a JSON object that will contain the specific values needed to post into my server?
Would it be easier to change my server to accept a Multi-Part request instead of a JSON based POJO with multiple Base64 Strings? I currently use Volley and there isn't an official Multi-Part Request as well as IO streaming.
If it's a matter of compression, how much compression should I apply to the image before encoding into a Base64 String? I ideally want to lose barely any quality but have optimal compression levels.
Bit more Information
I am uploading multiple different resolution images as it is a test for compatibility. For example, all the images that I am sending up have been taken on low resolution and extremely high resolution devices as my App relies on these images for functionality. I am trying to prove that any image (to a certain extent, mainly images captured on mobile devices) can be handled by my application.
I understand that some images may be so large that by loading them into memory will cause exceptions. This is something I will try and handle later.
In some cases the images that will be uploaded can span from 1 to 200.
I'm trying to look for the most optimal solution that will scale well.
Comment: If you want to use Mutipart Request with Volley, IMO, you can refer my sample code at https://github.com/ngocchung/VolleyNoApache/blob/master/app/src/main/java/com/example/volleynoapache/MultipartActivity.java. In @kevinkl3 answer, http://stackoverflow.com/a/16803473/3393666 I also had an answer there
Answer:
... for multiple resolutions images (5620 x 3747 - 4.92MB or 3264 x 1836 - 1.35MB)...

Not sure if this is the file size or the memory needed to allocate the image in memory, but taking a look at the following link: http://www.scantips.com/basics1d.html, I see this:

For a 4000 x 2500 pixel image,
then: 4000 x 2500 pixels = 4000x2500 = 10 megapixels
4000x2500 x 3 = 30 million bytes (if 24-bit RGB)
30,000,000 bytes / (1024 x 1024) = 28.61 megabytes (MB)
This is simply how large the data is - For ANY 24-bit 10 megapixel
  image, but JPG files compress it smaller (only while in the file).

I think that the images you're handling are taking much more memory than you expect.
Also, taking a look at this question and answer: https://stackoverflow.com/a/11402374/3393666, we know that a base64 representation of an image take up to 37% more memory than the original image size.

How can I write the Base64 String in a stream to a JSON object that will contain the specific values needed to post into my server?

I think you could do this (with small images not large ones) by simply adding the base64 representation of the image in a JSON object then posting it to the server.

Would it be easier to change my server to accept a Multi-Part request instead of a JSON based POJO with multiple Base64 Strings?

In my opinion that would be your best option to implement what you're trying to achieve.

I currently use Volley and there isn't an official Multi-Part Request as well as IO streaming.

You can take a look at this answer: https://stackoverflow.com/a/16803473/3393666, you can definitely can do it with volley, but if you want an alternative you can try with retrofit (http://square.github.io/retrofit/) they support Multipart our of the box.
eg:
@Multipart
@PUT("user/photo")
Call<User> updateUser(@Part("photo") RequestBody photo, @Part("description") RequestBody description);

Answer: I looked into using Volley as a mechanism to transport large JSON objects to  a server and found this answer. This answer essentially proved that Volley would be a bad idea for what I wanted.
I switched to OkHttp and now use their streaming methods allowing the JSON to be streamed to the server and then read the response with a streamlined approach. I used the GSON library to parse the response as OKHttp allows the response JSON/Object to be streamed into a reader object which Gson then uses for internal streaming and parsing to an POJO class.
The ony reason why I did not switch to a Multi-Part request was due to the server side implementation being rigid and unchangeable to cover for Multi-Part requests, it strictly expected a JSON representation of data and files.
For handling Base64 Images on Android I severely reccomend not using the String representation and merely converting to Bytes to save on using an excessive amount of memory. I read this article on String memory usage and management. With the Bytes you may easily transport the data without leaving a massive footprint on memory.
For Displaying the images I still avoid the bytes to String conversion by using the Image library Glide. They allow you to pass in a byte[] which was of massive convenience.


Why did the US Presidential job become partisan?

Question: The US constitution intended the president to be non-partisan. Why did the founders not write some controls and checks to prevent the president from being in a league with a political party?
Comment: Re *"Why did the founders not write"*: On the contrary, the Constitution in its entirety is just such a series of checks and balances.  The popular vote, the electoral college, the states, the bicameral congress, the Supreme Court, and the executive are all designed to check each other.  Failing that, freedom of the press enables the People to check those branches.   A better question might be, *"Have those checks been recently been significantly limited, deregulated, or evaded; and if so, when and how?"*
Comment: Re *'The US constitution intended the president to be non-partisan."* That is incorrect. The framers of the Constitution had directly experienced a massive failure in an attempted formation a new kind of government in the Articles of Confederation and Perpetual Union, and had seen another massive failure abroad in the French Revolution. The framers were not stupid. They knew that factions would form. Factions had already started forming, and the framers were at the heart of it, being key members of different and competing factions.
Comment: The phrase has a context "why did the founders not write a clause to safeguard to prevent the president from favoring one political league or another"... i.e. the president wasn't supposed to appoint partisan judges, the president is supposed to encourage debate in between the leagues.
Answer: The President is head of state and head of government at the same time. To function effectively, a government needs the ability to get laws and especially budgets passed (power of the purse), which is generally reserved for the legislature. So the President needs to build working majorities in Congress, and that makes him or her partisan if Congress is partisan.
In my opinion one of the fundamental weaknesses of the United States Constitution is that it doesn't acknowledge parties and regulate their role. Some people might call that a feature and not a bug, but electorates have a tendency to form parties -- or "very stable factions" if they don't adopt the trappings of a party.
Comment: Political parties did not begin  in the US until *after* the constitution was established. The Founders were worried about factions, and most likely thought they could establish a political system *ad hoc* parties that would form and fade fairly quickly.
Comment: @TedWrigley, there is something to that, but a party is just a faction that got into the habit of sticking together.
Answer: Seems to me there is an implicit assumption here that the very notion of political parties is bad.
That's not an obvious conclusion to me:

People will usually congregate with like-minded people in many circumstances.  In the sphere of politics that will start to look like a "party".  How would you go around abolishing that behavior?

A party is a useful shorthand for "stuff I like/stuff I dislike".  If I am mostly concerned about business efficiency, then a center-right party is likely to work for me.  If I am very pro workers rights, then a center left party will do.  If I do put in the effort of figuring out parties' general orientations, then I can be lazy in the future and make some assumptions (recent question about that was interesting) as to how they probably align with new interests.

An alternative is to run everything on single issue votes, by direct democracy and referendums.  That's more attractive in theory than it is is in practice, at least to me.  Things like budgetary problems from California's Prop 13 or Switzerland's really belated grant of full women's right to vote make me quite cynical on direct democracy.

These are the good parts of parties, when they work correctly.  At some point you have to design a system making some assumptions about likely conditions, and even some possible dysfunctional ones, which is what the founders did.
But it seems unfair to blame some shortcomings of the founders for the dysfunctional behavior of today's political establishment and voters.

People like Michael Moore or Ann Coulter make a living peddling untruths and raising hatred against "the others".

Republicans engage in rather obvious voter suppression shenanigans in Texas and Democrats are unable to stop contemplating packing the court, a blatant attack on the US political system.

Members of the public frequently say that "all politicians lie and they are all corrupt" and are not challenged.

The current problems are caused by both parties' incapacity to muzzle or ostracize their extreme wings and a growing tendency by the public to demonize anyone on the opposite side.  Rather than complaining overmuch about what the evil Reps are up to (if you are a Dem), maybe a well-placed "will you shut up, man", to a fellow Dem that advocates something stupid, like fully-open borders, would be a good thing.  Flip the argument if you are a Rep hearing one of your fellow Reps whining against masks.
Is there a design problem?
In the past, I thought the US had a unique capacity to bring in fresh political ideas by its primary system.  Bill Clinton or Ronald Reagan were relative unknowns by the standards of most democracies.  Before Mitterand, in France, won on his 4th election, he had contested 3 others on 7 yrs cycles.  He was old and so were his ideas.
Nowadays that looks like a design flaw instead.  US primaries reward extreme positions decided upon by a small minority of uncompromising voters.  Trump's "qualities" are well-known by now, but Ted Cruz, the last Rep to drop out is on the record as being against abortion even in the case of rape.  Moderate Republicans got turfed out early on.
Bernie Sanders, a man who wasn't even a Democrat for a very long time, and one who holds views to the left of many a European center-left party got a huge amount of traction in 2016 and 2020, again by appealing to a minority of very committed voters.  His viability in a POTUS election, at least against any functional Rep candidate, seems very doubtful to me given the general US electorate's position on taxes and social support systems.
So, in that sense, there is a design flaw, but not so much in the notion of party-affiliated Presidents, but rather in the way the parties choose their candidates.
Comment: Re *Democrats are unable to stop contemplating packing the court*: The Republican Party has already packed the courts. Refusing to even consider the nomination of Merrick Garland when his nomination was put forth almost eight months prior to the election and then ramming through the nomination of Amy Coney Barrett with only a month prior to the next presidential election epitomizes the concept of packing the courts.
Comment: @DavidHammen  The Reps controlled the senate under Garland which means they can be as partisan as they chose, while respecting the rules laid out for Executive/Legislative/Judicial checks and balance.  Fair?  No, I would not say so, but well within the law.  Ditto now with rushing a nomination.  Fair?  No, a farce given what McConnell said 4 yrs ago.  But still *within the law*.  Packing the court by increasing numbers, whatever the justification for it, is on the slippery slope towards breaking up the US foundational principles.
Answer: The US President is elected by way of a party, because it offers the best chance for him/her to get elected because of party support (the entire party would likely vote for him/her in the general election) and the party that backs him/her up to push forward their agenda.
It's basically a win-win situation for both the president and the party, and so this system is stable (in a Nash equilibrium). It works so well that virtually no change is necessary for the system for the past 3 centuries.
Comment: I don't think that the impeachment/insanity claims/sticks-in-wheels politics was expected, the president is supposed to get all factions to work together not help them fight and polarize each other.
Comment: @aliential I understand, the president was **supposed** to make the government function, but ever since the second president (John Adams and the AntiFederalist rivalry), it has not been that way. For the president (and his/her party), his/her only goal is to just get himself/herself reelected if in the first term and his/her party to retain the presidency for the second term. E.g., if Trump were more moderate, then he might have lost the party primary (at least back in 2016).


Does it make any practical difference to a normal chess player the choice of federation that issues the FIDE number?

Question: Clearly if a person is good enough to play for their county they need to be registered with the correct federation in their FIDE record, does it makes any difference to other chess players?
Answer:
does it makes any difference to other chess players?

Only in very special circumstances for special players. Only if a player is trying to get a title norm (WIM, IM, WGM, GM) in a tournament which qualifies as a norm event does the FIDE federation of the player's opponents matter.
According to FIDE Title Regulations effective from 1 January 2022:

1.4.2 The following are not included:
Games against opponents who do not belong to FIDE federations. Players with federation "FID" are accepted, but do not count as a foreign player.
...
1.4.3 Federations of opponents
At least two federations other than that of the title applicant must be included, except 1.4.3a - 1.4.3d shall be exempt. Nevertheless, 1.43e shall apply.

So, if you are playing in a norm event then for your result to qualify as a norm then you must against players from at least two other federations and FID does not qualify as a different federation.
In all other circumstances the federation of the players (as long as they have a federation) is irrelevant from a chess perspective.
Comment: That seems to indicate its better for players to be registered with FIDE by a federations that is different from the county they normally play in.
Comment: @IanRingrose It only makes any difference for master level players who are likely to be invited to play in norm events and then only if they have a "scarce" registration. So, for instance having an ENG registration living in Scotland is worthless because ENG masters are two a penny and in any case norm events in Scotland, apart from the national championships which have to abide by the 2+ other feds, are as rare as hens' teeth. Probably the same in Wales.


akka or similar alternative for golang to support distributed concurrency?

Question: I know golang is very good at concurrency with its built-in support, but seems to me they are not distributed, so what would be the framework/library allow us to write producers/consumers applications, in a distributed environment.
Answer: If you want to use Go's channel concepts in a distributed program, perhaps check out the Go Circuit framework.
It provides a framework for running multi-process programs (possibly spread over multiple machines), allowing you to use channels to communicate between those processes.
Comment: This is a better idea than trying to adopt Akka in Go. The concurrency model of Akka is based on the actor model of Erlang, which operates (only) by putting messages into the single input queue of your target actor. It is not possible to write data-driven synchronised structures. Conversely, in Go, the basic channel model is of synchronous/blocking message passing. It is easy to buffer this when the sender and receiver are to be decoupled. Go gets the best of both approaches and is more general than the Akka model.
Comment: Quite simply, Akka is a restricted, limited concurrency model. It achieves certain things _very_ well; especially, distributed computing with fault tolerance is its forte. However, CSP is *fundamentally* a more general concurrency model. With CSP, you can do what Akka does if you want to. But you don't have to. With Akka you are tied to the callback model - Akka's actors provide a nice encapsulation of callbacks to handle message receipt; but that's as far as it goes. How do you do lock-step data-driven flow control in, say, robotics? Akka cannot, but CSP can.
Comment: Hi, can you explain more on the pros and cons of Akka concurrency model vs Go's channel based approach? Or any source I can find this information?
Comment: @Rick-777 - can you please elaborate more about inability of the data-driven synchronized structures in Akka? In Akka you can synchronize, although the idea is that you try to have as little synchronization as possible.
Answer: No need to reinvent the wheel here... producer/Consumer applications are usually built using a message queue.
With this approach you should try to break up your problem into small (and ideally idempotent) tasks, build an application which can enqueue these tasks, and then have another worker application which can dequeue these tasks and execute them. Scaling is easy: just add more workers.
There are lots of queuing solutions out there, for a very good one written in Go take a look at NSQ.
Comment: Erlang is not a "framework". It is a feature-complete programming language that excels at distributed computing. Elixir is a more modern variant of the language. Both are FAR superior to Golang if your use case is multi-node distributed computing. Golang is strong on concurrency *only* on a single box. For crossing machine boundaries, with Golang you're no better off than using C.
Comment: or save yourself a huge headache and use Erlang or Elixir, which were meant to be used this way, and give you much more including supervision.
Comment: Go was also designed to be used to develop distributed systems. Distributed systems development is not easy and no framework will make it easy.
Answer: Two years late but if anyone else is looking.
https://github.com/AsynkronIT/gam
GAM (Go Actor Model) supports both Akka like actors, and Ms Orleans like Virtual Grains.
The Ms Orleans like Virtual Grains are supported via Protobuf code generation to give you typed messages and typed grain types.
See
https://github.com/AsynkronIT/gam/blob/dev/examples/cluster/member/main.go
https://github.com/AsynkronIT/gam/blob/dev/examples/cluster/shared/protos.proto
It's also extremely fast, 1 mil+ remote messages per sec.
Answer: Akka is based on the Actor Model. For that, there is a nice Go framework I invite you to test : https://github.com/AsynkronIT/protoactor-go
It is said to have great performance since it claims to be passing between nodes:

two million messages per second

While Go is already implementing using CSP, Protoactor adds :

Decoupled Concurrency
Distributed by default
Fault tolerance
Answer: Just for the record NATS is a high performance solution for distributed systems. It's open source and under MIT license. "The core NATS Server acts as a central nervous system for building distributed applications." and it has official clients for Go, C#, Java, Ruby, Python, Node.js and much more provided by the community.
Answer: Such an old question but I would check out dapr and protoactor.
dapr is more flexible but carries overhead from employing a sidecar pattern.
protoactor is more like akka having been written by the same guy who made akka.net.
Both are good depending on your use case. This blog does a good comparison of the performance.


Effectiveness of cooling oneself by a hand fan

Question: I recently had a discussion with a friend of mine regarding the effectiveness of handheld fans. My friend argued that you would always get warmer. I'm sure that this needn't be the case, as the system (fan with human) is not closed.
However, I'm not too sure how effective it really is. I tried to set up some equations comparing cooling vs. heating, but finding the right numbers to fill in seems difficult. Does anyone have an idea on the true effectiveness of handheld fans?
Comment: What equations have you set up? What numbers are you having difficulty with?
Comment: You might want to see: https://physics.stackexchange.com/questions/385811/how-do-hand-fans-work, since it seems like that's what your friend is thinking of.
Comment: @sammygerbil for heating I made an estimate on the amount of air moved by the fan with each fan-swing plus its velocity. Then, by using E=1/2 m v^2, I estimated the energy from each swing. Multiply this by the swinging frequency to get a power. And finally, we need an efficiency to get the amount of power consumed by the human (I have no idea what the efficiency should be). With cooling I got stuck pretty quick, as I could not find good methods for evaporative cooling. Hopefully this clarifies it a bit.
Answer: In many situations, the fan will help.
If two things are at different temperatures, but in thermal contact with each other, the heat will flow from hot to cold.  When the temperature difference isn't too large, an effective way to transfer the heat is by convection.  Convection occurs when at least one of the substances in thermal contact is a moving fluid; in the case of a fan blowing on a person, the air is the moving fluid.
If the temperature outside is below the human body temperature; then a fan should absolutely help (assuming the fan motor isn't hot enough to raise the temperature of the air it is blowing above body temperature, which is probably rare).
An even bigger reason to use the fan is to assist with evaporation.  People sweat so that the sweat on their skin can evaporate.  This evaporation takes thermal energy from you when it occurs.  If the air isn't too humid, flowing air across the moist surface will speed up this process.  This is why fans can cool you down so much when you're sweating.
So a fan is likely to help, but there are 3 factors to consider when deciding.  How hot is it? How humid is it? How hot does the fan get when it's running?
Unless you're in an extremely hot and humid environment, or using really inefficient handheld fans, they are likely to help cool you.
Also, when you say "handheld fans" I'm picturing a handheld electric fan, which is where this heating talk comes in.  If you mean a fan that's hand operated by waving it in your face, you might have to do a bit of math on the energy released/used by the movements; but you should still benefit.  Your point about open systems has a lot to do with this.  The fan will help you evaporate sweat, and as long as less humid air can in to take it's place, you can keep evaporating sweat from your body to cool it down.  If the room was closed, you would reach equilibrium with the humidity in the room and be unable to evaporate away the heat effectively.
Comment: I do indeed mean old traditional fans (so the ones you move by hand). Thanks for the different cooling mechanisms, do you see any reason why the heating should be negligible against the cooling? I understand that these are highly dependent on the situation, but is an order-of-magnitude analysis possible?
Answer: Movement of air by a fan transports heat at an increased rate by convection and assists in the evaporation of perspiration which transports heat by conduction.
From Wikipedia's - Evaporative Cooler, section: Physical Principles - (Other Sources: #2, #3):

The amount of heat transfer depends on the evaporation rate, however for each kilogram of water vaporized 2,257 kJ of energy (about 890 BTU per pound of pure water, at 95 °F (35 °C)) are transferred. The evaporation rate depends on the temperature and humidity of the air, which is why sweat accumulates more on humid days, as it does not evaporate fast enough.

From Wikipedia's - Wind Chill Factor, section North American and United Kingdom Wind Chill Index Calculations:

Many formulas exist for wind chill because, unlike temperature, wind chill has no universally agreed upon standard definition or measurement. All the formulas attempt to qualitatively predict the effect of wind on the temperature humans perceive.

November 2001, Canada, the United States, and the United Kingdom implemented a new wind chill index developed by scientists and medical experts on the Joint Action Group for Temperature Indices (JAG/TI). It is determined by iterating a model of skin temperature under various wind speeds and temperatures using standard engineering correlations of wind speed and heat transfer rate. Heat transfer was calculated for a bare face in wind, facing the wind, while walking into it at 1.4 metres per second (5.0 km/h; 3.1 mph). The model corrects the officially measured wind speed to the wind speed at face height, assuming the person is in an open field. The results of this model may be approximated, to within one degree, from the following formula:
The standard Wind Chill formula for Environment Canada is:
$${ T_{\mathrm {wc} }=13.12+0.6215T_{\mathrm {a} }-11.37v^{+0.16}+0.3965T_{\mathrm {a} }v^{+0.16}}$$
where $T_{wc}$ is the wind chill index, based on the Celsius temperature scale; $Ta$ is the air temperature in degrees Celsius; and $v$ is the wind speed at 10 m (33 ft) standard anemometer height, in kilometres per hour.
The equivalent formula in US customary units is:
$${T_{\mathrm {wc} }=35.74+0.6215T_{\mathrm {a} }-35.75v^{+0.16}+0.4275T_{\mathrm {a} }v^{+0.16}\,\!}$$
where $T_{wc}$ is the wind chill index, based on the Fahrenheit scale; $T_a$ is the air temperature in degrees Fahrenheit, and $v$ is the wind speed in miles per hour.
Windchill temperature is defined only for temperatures at or below 10 °C (50 °F) and wind speeds above 4.8 kilometres per hour (3.0 mph).
Comment: For the uneducated: this means it's effective?
Comment: It is commendable that you have provided this information, but your answer would be better if you applied it to the question. It is not obvious that it shows that a hand-held fan will be effective.
Comment: Where does the first quote come from?  Also, this really doesn't seem like a good answer to the question IMO.  You've explained why someone might choose to use a fan; but there isn't anything here addressing the real question - the effectiveness of a fan.
Comment: @LievenKeersmaekers - I've updated the answer, I hope it is now more detailed.
Comment: Where does "

    The amount of heat transfer depends on the evaporation rate, however for each kilogram of water vaporized 2,257 kJ of energy (about 890 BTU per pound of pure water, at 95 °F (35 °C)) are transferred. The evaporation rate depends on the temperature and humidity of the air, which is why sweat accumulates more on humid days, as it does not evaporate fast enough." come from?
Comment: @JMac - It is from the second link, I've added a couple more sources too.


If my spouse gets arrested for domestic violence but I do not press charges, will that still be on his record?

Question: First time I've ever called the authorities on my husband for Domestic Violence. He was arrested, however, I didn't press any charges, will it still be on his record?
Comment: I realize this is your personal life and I'm not meaning to be intrusive with this comment, but just as a side note, if it happens again, you made the wrong decision. I spent 10 years of my life under severe physical abuse from other male members of my family. I called the cops, retracted statements to get them off time and time again. Instead of lessons being learned and finding life getting better, I found myself in hospitals. Trust me on this.
Comment: When you say first time you've called, it seems its not the first time it happened. You should speak to a victim witness advocate if you're having second thoughts. It's important as these situations rarely get better.
Comment: Agreeing with the last two commenters.  You crossed a line with that, an act that can't be taken back, and *he's going to remember that.*  He's already a violent person, and that's not going to change--trust me on this.  Now he's a violent person who knows you're capable of retaliating, and that means that he escalates.  The next time, he's going to take measures to ensure that you can't retaliate.  Unfortunately, this really only ends two ways: with you dead or with him out of your life for good.  You need to do **everything** in your power to make sure you get the latter ending.
Comment: Thanks so much for the comments and consideration. I will definitely speak with an advocate!
Comment: Simple: If he did in fact commit violence against you, then DO NOT drop any charges. Things will NOT get better. Any PROMISES you are given will be LIES. Withdraw the charges now, and the next time, when the violence gets worse (and it WILL get WORSE), you won't be believed. If your husband didn't want anything on his record, he could easily achieve that by not hitting you.
Answer: The victim of domestic violence is referred to as the complaining witness. Domestic violence arrests will result in a criminal investigation. It is not up to the complaining witness to determine if charges are brought against the one who was arrested - this is up to the prosecutor.
Here is a good article at Findlaw that discusses the process.
If the complaining witness recants, the prosecutor may decide to drop the charges. The prosecutor may, though, decide to continue the charges and prosecute the case. The complaining witness in recanting may face charges as well - for example, for making a false police report.
If the prosecutor presses the case and your husband is convicted then, yes, it will be on his record.
Seeking the advice of a New York attorney who specializes in these matters is the best course of action.
EDIT: Here is additional information regarding New York Criminal History Records:
New York State law does specify that, unless the court orders otherwise, arrest records are sealed when criminal actions are terminated in favor of the accused - dismissed, found not guilty, etc. This is spelled out in Criminal Procedure Law 160.50.
Arrest records are part of the public record until disposition of the case is completed.
At New York State's Court web site, you can read about how to get criminal records of anyone - they are public record so anyone can make a request about anyone. There is a fee of $65. Records can be ordered online and the results can be emailed to you. Searches are processed by an exact match of name and date of birth.
From their web site you will see that criminal cases transferred or removed to Family Court are not reported. Neither are records for people who had a single misdemeanor conviction over ten years ago or pending criminal cases categorized as Youthful Offender Eligible.
Generally speaking, New York criminal cases are part of the public record and are available to anyone unless they meet certain criteria or have been sealed under New York State law.
Note that sealing records doesn't mean the record goes away. It just means that the record is not available to the general public without a court order unsealing the record.
Here is the link to on-line direct access to records requests: http://www.nycourts.gov/APPS/chrs/onlinedirectaccess.shtml
Comment: Generally a good answer, but one nitpick: I don't see where this actually answers the question, namely "will the arrest be on record". The answer looks like only a conviction will be on record, which I think is wrong. Maybe you could edit to address this?
Comment: I added additional information regarding New York State records.
Comment: Just to add, if the cops witness it happening or have evidence of it happening it doesn't matter if you press charges or not because they can.
Comment: Aren't arrests themselves a matter of public record?
Comment: They are generally open to the public unless they are part of an active investigation. Some states restrict what's available for people never charged, acquitted or had records expunged. See: https://www.rcfp.org/private-eyes/arrest-records
Comment: Interesting, thanks. I note that criminal records in the US contain a lot more than in Germany. For example in Germany only convictions are on record; there is no such thing as an arrest record.
Answer: Yes he can still have a record if he is convicted and yes, they can still go forward if the victim asks to withdraw the complaint. The victim to a crime (any crime, DV especially) can be subpoenaed to testify even if they don't want to. And you're under oath in the event of a trial, subject to the penalties of perjury. You also cannot mislead the police or DA's investigators in their investigation.
To this extent, the State takes the place of the victim in all criminal matters. That is why you see "State v. John Doe", not "Jane v. John Doe", in all criminal matters.
This is a very typical question by women who are the victims of domestic abuse. They often want it to stop at the moment but then feel bad, or feel he will change, or feel guilty, so they try to "drop the charges" only to find out that they aren't the ones who've filed the charges in the first place. @Dave D is right in that you are merely the victim (complaining) witness.
In some states, they will do as the victim asks of them if the batterer submits to anti-domestic violence/anger management counseling. In other states they move forward no matter what, and I have even seen them threaten a woman who said she wouldn't testify with false reporting . (This is an awful thing to put an already fragile, emotionally and physically abused women through, but it has happened).
A battered woman does have the ability to drop any restraining order, but if he's arrested there is one in place as part of the terms of release anyway, and only a court can amend it.
The state has a duty to protect the public (his future victims, as well as the current one) from criminal behavior by seeking a conviction if the facts justify it. Also, with the advent of the battered women's defense to homicide of their batterer, they often feel duty bound to pursue these cases.
When a victim asks the case be dropped, it will almost always depend on the severity. If you had a tiny mark on your arm and called the police because you were scared then there is a chance they'd drop it. In cases of severe injury or Felony Domestic Violence, no way.
Comment: No.  Both spousal privileges ( the one against marital communications and the one protecting spouses from testifying against each other), are specifically excepted in cases of domestic violence in every jurisdiction that I know of. Further, the wife cannot assert the privilege only the defendant can. And again, there are specific exceptions barring a spouse accused of battery or domestic violence against the other spouse from asserting it.
Comment: Isn't a spouse protected from being required to testify against his/her spouse?
Comment: @gracey209: Interesting. At least in Germany, the right not to testify against people close to you is not limited in any way, and also applies to domestic violence ("Zeugnisverweigerungsrecht der Angehörigen des Beschuldigten", §52 Strafprozeßordnung). Of course this is a privilege, not a duty, so the spouse is free to testify if they want to - they just cannot be compelled to testify (unlike an "ordinary" witness). Anyway, the situation seems to be different in the US, and between different states.
Comment: @Dan Neely No. One spouse may just be a witness from which the prosecution is trying to elicit testimony. The analysis differs in civil actions. This query is an example. The victim witness is not under investigation. The Defendant could assert the privilege, not the witness, and then the Judge would indicate the exception allowing the subpoena to stand.
Comment: @gracey209 the aggressor can not prevent the victim from testifying (by law). I don't know how exactly this works in the US, but the "Zeugnisverweigerungsrecht" is a privilege not of the defendant but of the witness. The witness can **decide** not to talk if he/she is a spouse/parent/child. etc. of the defendant. The witness can equally well decide to talk to the court. The defendant has no say in that matter, legally.
Comment: Under U.S. common law, the spousal testimonial privilege is held by the witness-spouse, not the party-spouse, and therefore does not prevent a spouse who wishes to testify from doing so. The rationale of this rule is that if a witness-spouse desires to testify against the party-spouse, there is no real marriage left to protect.  But this common law principle is very rare and only a small minority of U.S. states  hold this rule. For the most part the party-spouse, and not the witness-spouse, is the holder of the privilege. Then there are the exceptions on top of this dynamic I listed above.
Comment: @gracey209 when you see the privilege is limited only to the defendant; does that mean it's use is limited to cases where both partners are under investigation/on trial/etc.
Comment: So if a spouse assaults another spouse in Germany, the aggressor can prevent the victim from testifying?  In the U.S. the privilege is excepted in: crimes against the other, in crime against a child of either spouse,
in crimes against a third party in the course of committing a crime against the other spouse,  or in cases when the defendant spouse is charged with human trafficking for immoral purposes (such as prostitution vs. illegal immigration). In each of these situations, even current spouses may be compelled to testify against an defendant spouse in a criminal or grand jury proceedings.
Comment: Its also excepted when one spouse is suing another (so in the civil arena), and spousal privilege (as it pertains to communications vs. testimony) is waived if its shared with third parties - so only intentionally private communications are protected (there is usually an exception to the exception if the third party are their children.
Comment: @gracey209: Thanks for the clarification. Then the situation in Germany is like US common law - a witness may not be compelled to testify against their spouse (or other relative), but are free to testify if they want to. The accused has no way to prevent testimony.
Answer: YES! Everything against you an be dug up nowadays no matter how long ago and even if charges were dismissed. I was falsely accused of DV by a former live-in girlfriend, the charges were dropped in a hearing, but a dozen years later a detective investigating me after defamation by an ex-step-daughter brought it up as a factor in perceptions of me.
Comment: AFAIK, there is often a difference between stuff on your criminal record accessible to members of the public, and stuff in internal police records.
Comment: This is in part because "on his record" is a bit vague. If a newspaper article is written about the arrest, than that article and whatever it reports might be "on record" forever, and easily accessible to everyone let alone a detective, regardless of the merits or the outcome of the arrest. But if "his record" means "his formal criminal record" then the newspaper has nothing to do with that.
Comment: She may have gotten a restraining order? That will show up even if you don't get convicted. It's almost quasi-criminal in its background check implications.
Comment: Also, when you say used against you - you mean as far as character testimony? It cannot be used to impeach your credibility. This sounds like a civil matter anyway, so its different, but if you open the door by testifying that you are a certain type of person in establishing your character, that can be rebutted by other witnesses. It's up to the judge if it comes in, but typically if you open the door it's rebuttal.


Why does the the sight of gore causes nausea, vomiting and/or fainting?

Question: Why is it that upon seeing anything the involves gore, e.g.:

surgical cutting
excessive blood
blood and pain

causes nausea, vomiting or fainting?
And why does watching it repeatedly take away that feeling (desensitization)?
If the above is being watched in the form of a video/picture and the viewer is told that what is being shown is not real, but rather a video compositing technique, then the aforementioned feelings usually goes away. Why is that so?
Watching someone vomit can cause the viewer to follow suit; is the cause of this related to the one of the above?
Answer: TL;DR summary: gore and your examples thereof belong to even broader classes of stimuli that activate a number of different aversion and defense systems. To some extent, no one really knows why, and some of the most appealing answers may come from somewhat unfalsifiable theories.

Building on @caseyr547's answer, disgust occurs somewhat automatically when viewing blood, injury, and vomit. The basic, somewhat unconscious judgment being made here is essentially, "There but for the grace of God go I," and both the mind and body activate what defenses they have against going there, including the behavioral inhibition system (BIS), according to Jeff Gray's theory. My point in mentioning that theory isn't to focus on it; I'm mainly trying to point out that there are very large and pervasive changes in physiological and psychological function in reaction to disgusting or otherwise threatening stimuli, including the BIS, the sympathetic nervous system, the immune system, and some largely cognitive processes like attitudes (these aren't completely distinct from one another necessarily).
Why? Here's a pseudo-evolutionary argument: prehistorically speaking, when have we most often encountered these stimuli? When something very dangerous was about! Nausea and fainting might not protect us directly from physical attack, but it certainly discourages us from cutting ourselves (or others) open...and we've always been a danger to ourselves in that regard. As for blood and vomit, they may transmit biohazards of all sorts. Purging our own contents is one way to make sure we're free of any similar biohazards, which we might've ingested too if we happen to see our friends or family suffering from food poisoning, for instance. Short of that, simply experiencing these aversive reactions is a strong motivator to avoid the causal stimuli entirely, which is also a good way to play it safe when the root threat might be something like toxic gas or airborne (or otherwise communicable) biological pathogens. One shouldn't underestimate the extent to which we may have generalized these semi-instinctual reactions unintentionally (as through evolutionary mechanisms) to control our conscious behaviors unconsciously! From an "intelligent design" perspective, wouldn't it make sense to program ourselves to break down and feel awful involuntarily when exposed to dangers like these, so long as it helps ensure that we choose to get the hell away from them?
These are just thoughts ("theories," maybe) about why, FWIW, and they're somewhat unfalsifiable. As @BenCole pointed out, a more biopsychological account of how we react and to what might be more useful, if anyone else can help flesh out that side of this discussion. However, this would answer a slightly different question than why. One can explore and thereby better understand the broader class of stimuli that activate the aversive reaction systems in question, and thereby better understand how these particular stimuli belong to that broader class...but to some extent, we may never truly know why our systems are semi-instinctually sensitive to these stimuli...and an argument that they are simply generalizations of the broader class of stimuli to which the systems inherently respond is still a non-answer as to why the systems respond to them.
As for the partly non-instinctual, developmental processes of sensitization and habituation, caseyr547 is right again to say that these learning processes operate very broadly. They are deep subjects deserving of their own questions, if you have others. Somehow, habituation even has its own Wikipedia page apart from the one caseyr547 linked! I would've understood desensitization and habituation as synonymous, but that too implies a separate question. My point is that these are known phenomena (or a known phenomenon) with a deep pool of research and theoretical literature that mostly explains itself. If you look further into it, I think you'll see that it's a rather small wonder to observe that it operates on the disgust reaction as well.
To once again offer an unfalsifiable, speculative, evolutionary perspective on why that might be, consider that some of us may choose or be otherwise predisposed to expose ourselves to these dangers more often than others, and may even profit by doing so. If you saw a profit in exposing yourself to danger of injury or infection, wouldn't you want to be able to develop a stomach for it? Prehistorically speaking, when there has been enough of a profit in overcoming instinctual aversions to justify doing so, maybe doing so has improved the selective fitness of those whose instincts are weaker, and the fitness of those who are better able to habituate to stimuli and attenuate instinctive reactions that are circumstantially, pragmatically counterproductive. Who knows? It would make enough sense if it were true, anyway.
Answer: Vomiting, fainting and nausea at the sight of something instinctively repulsive is called disgust. Its an evolutionary tactic to avoid things which cause disease. Desensitization through controlled or positive exposure works against most evolutionary instincts including disgust.

Disgust is a type of aversive reaction that involves withdrawing from a being or object with strong expressions of revulsion. It can also be defined as a revulsion response towards potential contamination. It is a universal, basic emotion that functions to help protect an organism from ingesting potentially harmful substances, thereby promoting disease avoidance. It is one of the basic emotions and is typically associated with things that are regarded as unclean, inedible, infectious, gory or otherwise offensive.

-wikipedia
Comment: Truthfully?  Because this is a non-answer.  It's very easy to say that nausea and vomiting are caused by 'Disgust', but that says nothing about what 'Disgust' itself is, or why we feel 'Disgust' when we're presented with those stimuli.
Comment: It's definitely on the right track!  However, I also think that it should include more information on 'why' we feel disgust (more than 'protection' from substances - why feel disgust when watching a gross video?), the 'how' of feeling disgust (apparently specifically processed by the insula). And definitely more info on how desensitization works.  But I agree with you - this is a start in the right direction!
Comment: It's an okay start, but I think the OP is looking more of a neuro/cog-neuro answer to this.  Perhaps summarize 'The neural basis of disgust' section from Wikipedia for a more relevant answer?
Comment: Why do you think that? There is no mention of the brain / neurons. That's not to say an answer involving those aspects wouldn't be cool...
Comment: The Wikipedia quote says what disgust itself is. I suppose I can offer a separate answer that will relate this answer more directly to the OP, but it will only build on the implications of this answer, which is on the right track at the very least. Furthermore, I don't think involving a neurological perspective would necessarily push it in the direction you want to see it move (as expressed in your second comment, that is).


Tapered line for a SP4T RF switch

Question: I need to use HMC241AQS16 brand RF SP8T switch on an FR-4 board. The RF ports of this QSOP package integrated circuit have 50 ohms impedance. But there is a problem, the leads of the chip have just 0.41 mm in width. My original 50 ohm transmission lines on a FR-4 are about 3 mm in width. Therefore, I need to design a tapered transmission line as in the following figure, but it must have two ends that have 50 ohms characteristic impedance. The tapered line topics in the literature are generally about matching the lines with two different impedances. How can I handle this problem?
Comment: What frequency are you working at?
Comment: The frequency range that I need to work on is 2.4-2.5 GHz.
Answer: You won't be able to get 50ohm and 0.41 mm wide without changing the dielectric thickness.
Have you reviewed the layout in the datasheet or other application material from the manufacturer?
In the layout in the datasheet they keep the trace width the same until the pin. It is narrower than 3mm, they must have a lower dielectric thickness. You probably need to do the same.
What PCB material and stackup are you currently using?
Comment: 3mm trace width sounds like a 1.6mm pcb thickness. I would suspect he is trying to use a 2 layer pcb.
Comment: They use Rogers 4350 substrate. It has 3.48 dielectric constant. The thickness information of the board is not given but it is not that thin as far as shown in the following photo. Maybe the trick is vias on the board. I need to use FR-4 substrate by the way. My frequency range is 2.4-2.5 GHz.
https://www.enrgtech.co.uk/product/unclassified/ET13857334/102913-HMC241QS16
Comment: @adba - you say FR4 but what PCB stickup are you trying to use? The dense vias are used to ensure that the layer 2 ground plane and the top layer ground are well connected. If you are only working up to 2.4GHz it shouldn't be too difficult, the wavelength is about 5cm. I've done up to 10GHz on FR4 and the project I'm currently involved uses 76GHz on Rogers.
Comment: My material is a classical single layer FR4 with 1.6mm thickness as Mike said.
Answer: You might be expecting your reader to be mind-readers of making assumptions on scattering parameters while asking naive questions about "tapered 50 Ohms".  The better way is full disclosure of what you expect (scattering parameter plots), do understand and do not understand thus a well-defined question with context to relate with.
Instead you quote this excellent paper which discusses a quarter-wave band-shaping filter with research performed by grad-students authored by the Asst. Prof. They etched this 10% tapered 1/4 wave strip line in the lab but failed to publish dimensions because they were lucky enough (by iteration, I presume) to get a better return loss than predicted simulation with wide tolerance FR4 @ 2GHz 4.3 and must be low loss tangent.  When you see such common publications without a table of values and tolerances, BE AWARE. This takes a lot of trial and error to validate Dk otherwise "electrical TDR testing" is done by a fab shop.($$$)
A disclosure of values and tolerances are important to validate their specs. and authenticity of the design It's still a good paper on parasitic surface wave stripline antenna-effects controlled by aspect-ratio of the transmission line and change in effective Dk of the dielectric with some slight change in skin-effects.
I recall in 1st yr physics lab how to compare standard deviation of the theoretic results with actual to rate the quality of the experiment. (yet forgot the equation)
Here's your omission https://link.springer.com/content/pdf/10.1007/s11277-020-07957-0.pdf#page=8&zoom=auto,-49,574
Then you show a wildly tapered photo without any references and ask how do I match it?

Aspect ratios of the conductor dielectric geometry determine the impedance changes, so your concept is flawed.  Not only is it difficult to get low impedances, but it's also even harder in the double-sided board.  In order to mechanical stiffness, the fibreglass resin dielectric must be a couple mm thick overall with copper and in order to get 50 Ohms the trace width to height for most FR4's is 2:1 (h:w) ( lower constant Dk e.g. Teflon demands even lower 1:1 ratio)
Thus with multi-layer boards, it is easier to achieve this aggregate mechanical stiffness while providing thinner dielectric layers to increase the capacitance to achieve the L/C ratio for low controlled impedance.
Impedance is defined by distributed lumped element ratios as \$Z_o=\sqrt{\dfrac{L}{C}}\$
The inductance is geometrically defined by the log of ratio l/w for a straight line roughly.  This formula is used by Saturn PCB design.exe (https://welldoneblog.fedevel.com/2021/07/08/pcb-layout-useful-calculations-which-you-maybe-didnt-know-about-with-kenneth-wood/)  and also shown in RF-world's calculator
Imagine how you can increase the capacitance by a smaller gap more vertically than horizontally, although both do add.  If you chose a very thin board, it would be floppy and possibly break vias, but then you could add an inexpensive stiffener and get away with a 2 layer board.  Otherwise, multilayer is the way to go and you mainly pay for the total copper on each layer before processing for high volume orders.

Solution:
The coaxial connector has a large surface area and gap but the ratio is the same as on a PCB (if the Dk was 1). So you must choose this transition in size at the connector interface while maintaining the same ratios.  It's a bit more complicated as shown in the formula above, but that's the basic solution and not a tapered track.  Don't take my word for it. Look on Google or Baidu "images" for "50 ohm tracks"
Comment: Actually, I need to realize my circuit with FR-4 material at 2.4-2.5 GHz. In the following article, it is said that it is possible to do that with a tapered line on the FR-4 substrate (on page 2047). But they didn't give the dimensions of the tapered line.

https://link.springer.com/content/pdf/10.1007/s11277-020-07957-0.pdf
Answer: Therefore, I need to design a tapered transmission line as in the following figure, but it must have two ends that have 50 ohms characteristic impedance.
But do you?
Go back to basics, just because the pad is much smaller than the track,  do you really need an elegant taper?  Maybe it will make matters worse?
As Kevin asked, over what frequency range are you working?
Consider the simple solution - run the fat track up near the pad, then connect it with a thin track.  Estimate the effect - a short length of high impedance line will be like a series L, whether it is a problem or not depends on the frequency and impedance.  This may well turn out to be better than a longer transition region of non-50ohm track.
If the effect of even a short thin track is bad, then maybe you have to consider using a thinner substrate so you can get 50 ohm tracks up closer to the chip.
Be creative with your layout - there are three tx lines connecting to that side of the chip, if the top one leaves going up, the middle one horizontal and the bottom one going down then you should be able to get them close.
Edit
The premise of your question is wrong - there is not way to change the width of the track whilst maintaining 50 ohm impedance.  You just have to run 50 ohm tracks as far as you can, then use something smaller, and if you can't make that work, consider changing the substrate thickness.
Simple rough calculation: A 1mm track on 1.524mm FR4 is about 86 ohms.  At 2.4GHz, a 5mm length of 1mm track is about 25 degrees.  Connecting using this will cost you about 0.25dB in S21 and a return loss of about 12dB.  You can improve this if you can manage to squeeze some shunt C at each end of the skinny line.
This is probably too lossy and too narrow band, but \$\lambda/2\$ of any impedance line doesn't change the impedance.
Comment: My frequency range is 2.4-2.5 GHz. Actually, I have tried "the fat track up near the pad, then connect it with a thin track" solution but it doesn't work as far as I see in S21 and S11 parameters on VNA.

Tapered line for a SP4T RF switch


Best language for graphics and general math problem solving for amateur

Question: This question is not quite appropriate for the community but at my low level of expertise, someone may have an answer. I am retired and using computing as a hobby. My main interest is in things like ant nest simulations, slime moulds, Euler Project, etc. Up until now I have been using javascript (self taught therefore some holes in my knowledge). To me javascript seems to have a text-orientation as opposed to mathematics, which appears to be a secondary concern, and it is very finnicky. I wonder if javascript is the most appropriate language for a hobbyist in my situation. Is there a more appropriate language? I presume other languages have equivalents to D3.js. My other languages are Fortran (1974) and a bit of Java. Thanks.
Comment: "Graphics" feels rather broad. What sort of graphics? How important is performance? JS doesn't seem very text-oriented to me, considering it has the best native support for visuals (i.e. the web browser) I've ever seen. D3 is great for data viz but if you want to efficiently crunch matrices to solve PE problems, JS is not particularly suited to heavy math. Could you provide more details about what nest simulations and slime moulds entail? Are those visual? Thanks and good luck on your programming projects.
Comment: I think the majority of languages are text-focused due to their history, some are more numeric-focused but I don't know of a graphics-focused one
Answer: In some ways, the language you know best is the best language, but there are some caveats. Or, at least a language with the same underlying paradigm as the one(s) you know: procedural, OO, functional,...
If you are willing to learn a new language, it is more likely to be the available libraries that already exist and that are useful to your needs that is more important than the language itself.
I do most everything in Java and find the existing libraries very useful. In other OO languages, I've had to work hard to incorporate other libraries, not built for the language at hand, but available to import. IIRC, Python had that issue in the past, but suspect that problem is solved.
In general, investigate available libraries that are part of the language "package". Perhaps look at some existing projects and see if they seem reasonably similar to what you want to do.
Answer: I concur with Buffy that the language you know is largely the best language to work with, particularly because you're not working on particularly specialized problems.  There is a mathematical bent to what you are doing, but that is well within the capabilities of essentially any language.
If you want something more mathematically oriented, you could try Python (it has very good libraries), R, MATLAB, or (if you want a wilder adventure) Mathematica or Scheme, but I don't expect you'll find a significant speed-up in your work flow.
Now, that said, I wrote that list of languages in the order I expect you'd find most-to-least familiar. So if you are just looking to expand your programming horizons, take my list in reverse and go one some crazy, mind-expanding adventures.


Seeking Title/Author of Post-Apocalyptic Novel Involving Vampires

Question: I want to read some of the work written by one of the tutors on my writing course but I don't know the title to any of his books and have heard rumours that he writes under a pseudonym. Today in class he told us that in one of the books he'd written a group of vampires get hold, or attempt to get hold, of nukes and use them to create a nuclear winter so they can walk around 24/7 without fear of the sun. Without anything more specific to go on Google hasn't been much help and I can't find any clues anywhere else. My tutor's name is John Sayle if that helps at all.
Comment: I don't know whether they have anything to do with one another, but I did run into a John Sayle who was a writer for [Count Duckula](https://en.wikipedia.org/wiki/Count_Duckula), which is fantastic...
Comment: This sounds very like the novel [The Night Eternal](https://en.wikipedia.org/wiki/The_Night_Eternal) though that's by Guillermo del Toro and Chuck Hogan, neither of which seem likely pen names for your instructor :-)
Comment: Is there a reason you can't ask your tutor the author directly?
Answer: That description fits the plot of the 1998 Channel 4 series, Ultraviolet.
From Wikipedia:

The final episode reveals that the vampires' plan does not involve
  enslaving humanity as suspected. Instead, they plan to cause a nuclear
  winter, providing long-lasting darkness, and completely wiping out the
  threat of humanity with an engineered plague. Scientific advances made
  during their experiments will allow them to survive on synthetic blood
  and reproduce via live birth, eliminating the need for human victims.

The writing is credited to Joe Ahearne

Interview with Joe Ahearne
Answer: The details don't line up exactly with those posted in the question, but Vampire Winter by Lois Tilton may be the answer. In it, nukes are dropped and a nuclear winter, or eternal twilight, allows the protagonist, a vampire (as well as other vampires) to roam about 24/7 in the post apocalyptic world after the war.


What is the purpose of a separate merge commit in git?

Question: When you merge two branches together, git creates a separate commit with a message like Merge branch 'master' into my-branch.
For a non-trivial merge it is clear to me that this is useful: It keeps the history of how things were merged separate from any other changes. But when the merge is trivial (for example when the two branches don't affect any files in common), what is the purpose of the separate merge commit?
You can avoid that commit with git merge --no-commit. You could then add a "real" change on this commit too. That way you avoid a seemingly useless extra commit. But the man page warns about this:

You should refrain from abusing this option to sneak substantial changes into a merge commit. Small fixups like bumping release/version name would be acceptable.

Why is that?
With commits with real changes in them marked as o and merge-only commits as X, this is the difference between these two situations:
o---o-o-o---o--- master
 \   \   \   \
  o-o-X-o-X-o-X-o--- my-feature

o---o-o-o---o--- master
 \   \   \   \
  o-o-o---o---o--- my-feature

Why is the first one preferred over the second one?
PS: Assume my-feature is a public branch that other people also use, so rebase would not be an option.
Comment: For clarity, can you expand on why you don't consider changes brought into a branch via a merge to be _real_ changes? I don't really understand why a merge commit where all the file level merges would be considered any less useful than other merges.
Comment: How to make such graphs? I've skimmed though https://stackoverflow.com/questions/1057564/pretty-git-branch-graphs and could not easily find the asnwer... just adding `--graph` does not give o and X
Answer: I think there are several reasons why having separate merge commits is a good idea, but it all comes down to the basic rule, that every commit should contain changes that belong together.
Possible situations where you will benefit from having separate merge commits:

You're trying to find out which commit introduced a bug. If you don't separate merging and normal commits, it's hard to figure out whether the merge caused that bug, or the actual changes from that commit.
You want to revert a change made by a commit. What should happen when you're reverting a commit that is a merge and also contains changes on its own? Do you want to revert just the changes, or just the merge, or both? If only one of them, how to separate them?

As added benefit, you get history that's easier to understand. (You could get history that's even easier to understand if you used rebase, but you said that's not possible.)
Answer: At my workplace, the "central" repository is an SVN server. I use git via git-svn.
SVN (obviously) doesn't do fast-forward merges. So, in order to be able to replicate my local history to the server, I make all merges which are going to become externally visible explicit.
The reason you would prefer this pattern in the general case (clarifying: "why would you want an explicit merge commit for a major combination of two branches, such as the reunification of a longstanding side-feature branch, even when the two don't conflict?") is that it causes the repository to better reflect the real series of operations performed - that is to say, the abstraction for history better reflects the reality of that history.
When you fast-forward, information about when the integration happened is lost - there is no point in the history saying "here is when X became Y" with an associated message.
This is the same reason some people use merges in preference to rebasing even for their local branches - rebasing is a form of history rewriting, a white-lie-on-paper.
To your other question - "why should only small changes be in a merge commit", the answer is that the merge commit may have a large diff with respect to any or all of its parents. So, if you put significant other work in there, it's very difficult to disentangle whether the problem was an integration issue or one of the new changes you added. If you put the commit either on one of the parents or after the merge, bisecting is made simpler, cherry-pick porting of the change is possible, you can reverse the merge without losing features, and so on.


Win XP SP3: windows update won't work

Question: Found numerous reported problems on Internet, and a few fixes but none I have tried helped. Windows update, as well as download a newer version of IE, do not work. It just looks like the update never stops trying.
Comment: Are you behind a proxy? Is this a domain-joined computer with policies? Can you access the Windows Update website? Is your Anti-virus/Anti-Malware scanners up to date?
Comment: It seems to be a bug in XP itself http://arstechnica.com/information-technology/2013/12/exponential-algorithm-making-windows-xp-miserable-could-be-fixed/
Answer: It took me a while to cut this one down. I created a blog post on my website with detailed instructions and links to the updates you'll need to download. It'll take you about 10 minutes and you should have Windows Updates working again.
http://www.geekallday.com/windows-xp-sp3-update-issues/
I'll also list the updates here that are required:

Microsoft .NET Framework 3.5
Internet Explorer 8
Update for Windows XP (KB927891)
Windows Update Agent 3.0
Security Update for Windows XP (KB2510531)
Security Update for Internet Explorer 8 for Windows XP (KB2797052)
Security Update for Internet Explorer for Windows XP (KB2799329)
Cumulative Security Update for Internet Explorer 8 for Windows XP (KB2898785)

Here are the steps on what order and how to install these updates.
I recommend installing the updates in order; some updates are required to be installed before you can move on to the next update.
Microsoft .NET Framework 3.5 The First update you'll install is Microsoft .NET Framework 3.5. Accept the agreement and press next until it starts installing. This update can take some time to install so please be patient.
Internet Explorer 8 The next update you'll install is Internet Explorer 8. Most fresh installs of Windows XP SP3 come with Internet Explorer 6 by default. You'll need to make sure you "uncheck" install updates as searching for updates is still non functional at this point in time. I suggest you reboot your PC after the installation of Internet Explorer 8.
Update for Windows XP (KB927891) This is the update to fix or prevent the SVCHOST.exe 99% CPU usage issue. First thing you need to do is make sure your Automatic Updates is set to off.. To check the status of your Automatic Updates go to your Control Panel, Switch to Classic View, double click on Automatic Updates and make sure it's checked to off. If you had to turn Automatic Updates off, I recommend rebooting your PC. After the reboot go ahead and install this update. I would leave Automatic Updates off until the end of this fix; once you have Windows Updates working again I've had no issues turning it back on.
Windows Update Agent 3.0 Install Windows Update Agent 3.0. This update will fix the Error you get when trying to run windows Updates. If you attempt to run windows Updates again you'll be prompted to install the latest addition of Windows Update. Go ahead and proceed with this update. The update will install successfully but you may notice that Windows Update will continue to loop while searching for updates. If that's the case you can proceed with the next set of updates.
Internet Explorer 8 Security Updates If you're still having issues with Windows Updates looping while checking for updates you should continue with the installation of the remaining 4 Internet Explorer 8 security updates. After installation of all updates you should now have a working Windows Update session.
Answer: First make sure your date and time are correct and in the correct timezone.
Then download this:
Tweaking.com - Windows Repair (All in One) v2.1.0 Released
Install and run it.
under repairs uncheck everything but windows updates.
Run it and you will probably have to reboot.
after rebooting try again and it should work.

Win XP SP3: windows update won't work


How to make scopes that actually magnify using materials like glass?

Question: I have been trying to create a scope (sniper scope) that actually uses glass shaped like a lens to magnify into objects (I know this is not conventional and not how they do it in normal fps games but I wanted to try this out). It wasn't entirely successful as when I tried to magnify it more, more I increased the IOR the more distorted it got. I've probably got something wrong, and is it even possible to do this, is there a way to fix this?
Basically do any of you have any idea on how to approach this as I think im on the wrong track.
Comment: I think that can work, but you will have to make a lens (like in real)... and probably you'll need some subdivisions (or else, bad effects on the borders). IOR may stay close to normal glass. I mean move (scale) the lens shape instead of changing IOR
Comment: https://fr.wikipedia.org/wiki/Longue-vue
Comment: Thanks so much, it kinda worked, minor adjustments to the lens I made didn't affect. So fed up, I went out and used a sphere and subdivided it, when I set IOR to 1.5 of glass it was too distorted, but what I noticed is from IOR 1.03-1.08 or somewhere around that range the image is kind of clear and magnified, so thanks, but the small issue being due to the image was distorted in the sense it was less magnified on the outsides and more towards the middle of the image, but thats down to the shape- its clear enough anyway.
Comment: happy that was useful. But **you** did all the job ! Consider to answer your own question : that can be useful for many people
Comment: You might want to take a look at this page, too: https://en.wikipedia.org/wiki/Photographic_lens_design If you want to build a lens that bends light and magnifies like a real one, you really should pattern it after a real one. Real telescopes and camera lenses usually have between 5 and 20 individual pieces of glass. Designing a telescope is not for the faint of heart.
Answer: It is posibbly to do it. Try building a Kepler or a Galilei scope. A kepler scope is easy to build, but the image is inverted. Here is one I made:

To zoom, scale up the objective lens along the point where the empty is located, or scale down all the other objects along that point. The background image is missing, replace it with anything to see the sope working.
Answer: Half sphere in front of Suzanne

If you want to create a scope with Cycles you will have to do lots of research or you could cheat and do two renders, each with a different FOV, and use the compositor to add them together. The biggest problem will probably be the amount of memory the glass in the scope will use before you will get a decent quality.
When you are finished with your scope, try to get a job as a hunting scope designer.


Is it possible to simulate the intercalation of hydrogen nanobubbles?

Question: Is it possible to simulate the intercalation of hydrogen nanobubbles into 2D layered materials using first principles calculations such as Density Functional Theory? Would this require a multi-scale modeling approach?
Comment: By "hydrogen nanobubbles" do you mean bubbles with a membrane made of substances other than hydrogen, like soap bubbles? If yes, what is the composition of the membrane? If not, wouldn't the bubbles immediately join each other and form contiguous layers of hydrogen in the 2D layered material?
Comment: Thanks for your response @wzkchem5. I think it should be pure hydrogen nanobubbles. As for the bubbles being contiguous, do you mean the bubbles being densely packed together? Because that is exactly what I am trying to achieve - storing densely packed hydrogen energy in the form of nanobubbles (since nanobubbles contains hundreds to thousands of atoms, they carry more energy) to increase the hydrogen storage capacity. Whatever insights you or anyone else has regarding this idea would be highly appreciated.
Comment: Yes, but it's more than just "densely packed together". A bubble without a membrane (or wall) at its boundary is just a tiny lump of gas. There's nothing that can help it keep its bubble-like shape. So not only will the hydrogen bubbles immediately join each other, but they will cease to be bubbles, since there is no boundary between the bubbles. I don't know if this is what you want. Besides: while a nanobubble does carry more energy than a single molecule, it does not necessarily carry more energy than a group of ordinary, "non-bubble" molecules occupying the same volume.
Comment: 2D layered materials (graphite, TM oxides, TM chalcogenides, etc) intercalate all kinds of stuff (lithium, hydrogen, many other random cations, halogens, etc), and that can certainly be studied with DFT. But the intercalants are at best molecular as, e.g., H2, Br2, etc. A bubble of even 10 molecules in my mind would have (a) little incentive to stay together: if intercalation happens at all, then entropy likely drives molecules apart, and (b) would definitionally burst the 2D material. So I'm a bit hung up on the idea of a nanobubble. Is there a reference for what one is, or where one exists?
Answer: Tupical pressure that would affect intercalation is about 3 GPa. Nanobubbles are stable when their size is about 100 nm, and in water their pressure is about 3 MPa. Smaller nanobubbles would have higher pressure, but then this pressure just collapses them and they dissolve quickly. And intercalation is suitable for particles of a few nm in size. In water surface tension at this scale is so extreme for a bubble, that bubble will not be stable.
I dont see it working. These effects in my opinion dont have an overlap where they both could be used at once.
You would need a liquid with higher surface tension and lower hydrogen solubility than water for it to work.
I dont agree that bubbles would join together naturally, their preferred way to dissapear is dissolving I think. Surface tension can keep them apart, as separate structures. Added charged particles from surfactants can help to make groups of bubbles, or keep bubbles apart.


What would a hypothetical world of continuous matter look like?

Question: Suppose, instead of molecules and atoms existing, there was only prime matter and types of prime matter. So there would be steel type of prime matter, flesh type of prime matter, etc.... How would physics work out in this universe? Ard there any science fiction books about this?
Comment: This sounds similar to the classical physics picture near the end of 19th century, where all matter was thought to be composed of different formations in ether. Fields were waves in it, and atoms were vortices in it, see e.g. [Michelson's 1902 comment](https://physics.stackexchange.com/a/201999/65263).
Answer: Let's ask the opposite question, what would it mean for matter to not be continuous: it would mean that there is a void.
Now, the original atomists argued that their atoms moved within a void, however Aristotle argues against this, he pointed out that there void was not in fact a void, but place and he speculated on the notion of place having a kind of potency, this has a family resemblance to the notion of a field: a field has places with potency.
Hence, Aristotle affirmed, along with Parmenides, that void is not. Similarly, Newton and Einstein. Newton explicitly in arguing against gravity being a force at a distance but was unable to come up with a theory; and Einstein implicitly in finding the mechanism and then in arguing against the phenomena of non-locality in entangled quantum systems. (Various experiments, following an argument of Bell, have shown that this non-locality is an explicit feature of QM).
We can then see our world as as a continuum of continua. Or as Carlos Rovelli put it in his textbook on Quantum Gravity, the world is simply fields upon fields.
Comment: So I guess the answer to my question is, it would look like our world right now.
Comment: @Tomislav Ostojich: I think that's what I was driving at in my long-winded way, :-).
Answer: Einstein's resolution of Brownian Motion was the first serious estimate of the size of an atom, and so first really definitive evidence they exist. Even after the turn of 1900 some leading physicists like Ernst Mach were not even considering the atomic hypothesis to be seriously viable; and the scorn Boltzman recieved for his wotk on entropy that supported it may have contributed to his depression and suicide.
The previous paradigm was continuum mechanics, and all classical mechanics is implicitly based on it. Quantum mechanics puts a discrete size limit on the smallest possible probe, the lowest energy interaction with a system, and it's peculiar nature follows from that. So, you could argue, continuous matter would look like the classical physics world. Perhaps the biggest problem with that would be problems with radiating heat, the 'ultraviolet catastrophe', where as bodies get hotter they lose their heat very rapidly. Other impacts are quite subtle & small scale.
You seem to be asking about a specific model, something like Aristotle's physics, where there are different types of continuous substances, with different principles, which intermingle in various ways? Aristotle felt he lived in such a world, so again you could say, like he described. This might seem flippant, but we should remember our own models are also very much approximations, rooted in our own experiences, and though we expect consiliance of evidence and new theories to encompass and generalise old ones, we are still a long way from 'real reality'; and Hawkinv argued from Godel's Theorems the goalposts for that will alwsys shift.
Our best current theory, indeed it can be argued the best theory humans have ever developed in terms of accuracy and scope, is quantum field theory. The fields in this are in a sense continuous, with for instance quantum jumps recognised as transitions between states like different standing waves. You could say that QFT is a kind of continuum theory, of continuous fields. It depends how you define 'matter', as having inertia (Higgs field), or only as having mass which all energy has.
Lastly, the main candidate for uniting gravity with QFT, M Theory, implies our universe and it's timeline are only subsets of a vast 11 dimensional landscape of probabilities. It's hard to grapple with that, but it can be pictured as making continuities of variations in apparently discrete things like events and timelines.
The only possibly relevant scifi I can think of is Asimov's The Gods Themselves. In this beings from the end of the (stelliferous era of the) universe when the last stars are going out and the fundamental constants of nature have changed, start to influence our own time. Those aliens exist as continua which can intermingle with each other and matter around them. They are among the most alien but compelling aliens I know of in SF.


How do obtain wrapped btc and wrapped ada in a local test network or a live test network like ropsten?

Question: In the local test network and ropsten test network, it's easy to obtain ethereum but I need other tokens in order to do testing. I'm not sure how to obtain those tokens for testing.
Answer: You do not need to have this done by others for you. You can deploy any ERC-20 token yourself on the testnet and cal it WBTC.
Comment: Thanks for your answer which I will try to use.

While this is true, it'd be nice if there's a standardized way for everyone on ropsten to obtain tokens from the same address. Otherwise everyone will do repeated work of finding the actual token address on eth main net, copy the code, and deploy it.


"We certainly cannot have observers in the same reference frame disagree on whether clocks are synchronized or not"-is this true?

Question: Suppose we have an Inertial frame S, all the clocks in this frame are synchronized. Now suppose, two seperate events occur at two different place A and B in that reference frame. Now, the events are said to be simultaneous if the clocks at the respective places registers the same time for each event(i.e two observers at the respective places read the same time of occurrence for each event). Now, suppose we have an observer at some different place C & the distance from A to C & that from B to C are not equal. Now my question is that: will the observer at C also claim about these two events to be simultaneous?
If "No" is the answer, then we have observers in one single inertial frame, disagreeing about the simultinity of two events. See, there is no relative velocity between the observers, all they are in a single inertial reference frame at different places(I'm strictly talking about a single inertial frame. No relative velocity between the observers, nothing!)
How this can be possible that the observers in a single reference frame are not in agreement about the simultinity of two seperate events though all the clocks in this frame are synchronized from the beginning?
Comment: You've gotten several good answers to the question you asked ("why do observers with the same frame agree on what's simultaneous?") but perhaps you meant to ask a different question, namely "why do observers stationary with respect to each other have the same frame?".  The first thing to say is that technically they don't (this wouldn't even make sense, because frames  are defined locally) but one frame is the parallel transport of the other, which we sometimes express sloppily as "they have the same frame".  As @CRDrost observed, parallel transport is not in general uniquely defined ..(MORE)
Comment: (MORE) but in SR it is.  So we can (slightly) abuse language and say that **in SR** two observers stationary with respect to each other have "the same" frame, and I think maybe what you really want to ask is why.  If so, you should ask this as a separate question.
Answer: A reference frame assigns a time interval and a spatial interval to any pair of events.  That assignment is what  a reference frame is.
So by definition, if you and I share a reference frame, we will assign the same time interval to any pair of events.  In particular, we will either both assign the time interval zero (in which case we will agree that the events are simultaneous) or we will both assign some other time interval (in which case we willl agree that they are not).
Comment: Thanks for your concerned reply Sir! One thing I want to ask: suppose right now I am in Kolkata, India; and tow different event occur  one at New York,U.S.A and another at Tokyo, Japan Right Now! Are they simultaneous to me? I'm asking this because the distance from New York to me is different from the distance from me to Tokyo. My question is how would I know whether they are simultaneous or not?
Comment: The  answer to "how would I know whether they are simultaneous?" (in a given reference frame) has nothing to do with relativity.  I'm sure you can think of many answers.  If you've placed synchronized clocks at the locations of each event, and if they take place at the same time  as recorded on those clocks, then they are simultaneous.  If you know the (spatial) distances to the two events,  with one being (say) twice as far as the other, and if a lightbeam from that event takes twice as long to reach you as a lightbeam fromthe other, then the events are simultaneous.  Et cetera.
Answer: You're right! You can verify this easily by using the Lorentz transformations! The two observers A and B are in the same inertial frame so there is no need for a Lorentz transformation! On the other hand, the observer C is in an other inertial frame an thus is moving with some uniform speed relative to the other observers A and B. Therefore to go from one inertial frame to the other we must make a Lorentz transformation. Hence, to compare the observation of C with the observation of A and B, we first apply a Lorentz transformation to the observations. By doing so we will have that the time the light travelled from one event will have been shorter than it did for the other event! So note the importance of the speed of light which is not infinite!!
Answer: One could imagine a theory in which the meaning of "the same reference frame" is not clear between two different points in space, and in fact that is the subject of our modern understanding of gravitation, variously called either the general theory of relativity the theory of general relativity. In this theory, two people who believe that they are maintaining a constant distance between each other might fundamentally fall out of agreement on what clocks are in sync, if they are even ever in agreement in the first place.
However, if we are not including gravity, then general relativity takes the "special" form that we call either the special theory of relativity or the theory of special relativity, rather than being fully general. In this special case of the theory, if two observers are at rest relative to each other, they will agree on whether any two events are simultaneous and therefore they will agree on whether any two clocks are synchronized. It is only when one accelerates relative to the other that they find that the clocks ahead of them (in the direction they're accelerating) are "ticking slightly fast" and the clocks behind them are "ticking slightly slow" and therefore clocks fall out of sync.
The special case was in fact discovered a long time before the general theory, which requires much more advanced mathematics. It turns out that the general theory can be viewed as a "patchwork" of the special case across the more general spacetime, with the special case happening whenever a reference frame is in "free-fall" with respect to the local effects of gravity. In this respect the disagreement that one sees in the general theory is just another form of the disagreement that one sees whenever one is accelerating; Nature "wants" us to be in free-fall and we stubbornly refuse to pass through the floor and instead find ourselves accelerating in opposition to that free-fall to remain in one place; this inherently means that all of the clocks "above" us are ticking slightly faster and all of the clocks "below" us are ticking slightly slower.
Comment: ." In this special case of the theory, if two observers are at rest relative to each other, they will agree on whether any two events are simultaneous and therefore they will agree on whether any two clocks are synchronized." why is this? exactly that is my question.
Comment: @sid:  Your question has already been answered multiple times.  The answer to "why is this" is exactly the same as the answer to "why is every bachelor unmarried?".  It is the *definition* of having the same reference frame.
Comment: @sid:  But maybe this is not  what you really mean to ask.  See my comments on your original question.


Is an atom-thick sheet of a material visible and tangible?

Question: If one could make a sheet of a material (thickness of an atom), Aluminum for example, would it be visible to naked eyes? What about tangibility? would it be tactile by human finger skin?
Answer: It is extremely hard to say what would happen because the only way to reliably test those regimes is to do it experimentally. Single-atom thin layers have only been realized, so far, in graphene, which is a single layer of hexagonal carbon crystal, and which is strong enough to exist by itself without any support. The Wikipedia section on its optical properties will inform you that

Graphene's unique optical properties produce an unexpectedly high opacity for an atomic monolayer in vacuum, absorbing $πα ≈\ $2.3% of white light, where $α$ is the fine-structure constant. This is "a consequence of the unusual low-energy electronic structure of monolayer graphene that features electron and hole conical bands meeting each other at the Dirac point... [which] is qualitatively different from more common quadratic massive bands".

Thus, graphene is surprisingly opaque - for a monolayer material. It absorbs more light than you'd expect, and if you look carefully you can probably see it with the naked eye, but it's still pretty transparent.
I'm unsure what its response to the human touch is, though it is reported to have a huge tensile strength.
Answer: This was just asked on another forum last week, a student from Penn State made a sheet of graphine to see for himself. He reported that he could not feel the sheet, but he could see it.
Answer: It's for you to judge if the following is relevant.
"Another example of a drastic change in surface properties by one-atom-thick layers can be a silicon monocrystal surface. When the surface of a silicon plate is etched in hydrofluoric acid (in order to dissolve the thin native oxide layer), the atoms of silicon on the surface are terminated with hydrogen atoms. This makes such a plate hydrophobic – drops of water do not wet the surface. But when we wait for some time or put the plate into deionized water for a few tens of minutes, the SiH groups on the surface slowly change to SiOH, and the water starts to wet it completely. This effect of only one atom change on the surface is visible by the naked eye (Lehmann 2002)."(http://books.google.com/books?id=LcenAAAAQBAJ&pg=PA43&dq=%22one+atom+thick%22+silicon+-%22graphene%22&hl=en&sa=X&ei=neOWUo6iNMLPrQGP1IHgAw&ved=0CDoQ6AEwAg#v=onepage&q&f=false )
The above is not about "one-atom-thick sheet", but about "one-atom-thick layer", furthermore, it is not clear if the layer is visible or wetting/non-wetting water, but this is more relevant to "tangibility".


What should be tested in Django Forms?

Question: When testing Django Forms, what are the main things you should be testing? I know that if you write custom save() or clean_ methods, you should definitely make sure those are working correctly, but is it also good to check things like whether the fields you expect to be required are actually required? Is that going overboard, since you don't want to test that Django is treating "required" fields correctly, and is more behavior testing?
Answer: "Test everything that can go wrong," they say.
But then the question is, "what can go wrong?"
Murphy's law states that everything that can go wrong, will go wrong.
But wouldn't it be paranoid to test everything that can go wrong according to Murphy? And writing tests for every single thing is not very productive. "Let's write a test that checks for parity errors in the hard disk's cache memory!" is probably not a good suggestion if you're developing a web browser.
The purpose of unit tests is to test your code. You're not writing tests for Django. If you assume that Django works correctly with regard to required fields, there's no need to test that.
In behavioural tests on the other hand, I'd say it's more OK to test things that are implemented by the framework. This is because behavioural tests are less transparent (less "white box") than unit tests, so the tests don't "know" whether something is implemented by a framework or by your code. Still, don't test the silly things if you have better things to do.

What should be tested in Django Forms?