Wikipedia:Reference desk/Archives/Science/2016 January 24

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January 24

"freeform" electromagnetic coils

1. What's the proper name for these "freeform" electromagnetic coils[1]?

2. How are they made? Roughly which one of the following guesses is the closest?

A) wind one layer, spray some adhesives, and then wind another layer on top

B) Adhesives are added continuously as the winding continues

C) The magnet wire is pre-coated with an adhesive.731Butai (talk) 04:36, 24 January 2016 (UTC)

If there were a coilform with a central cylindrical core and endpieces, the coil could be wound as shown by rotating the coilform while the supply bobbin moved slowly back and forth via gearing to lay down straight layers. The endpieces could then be removed and the wound coil pushed off the central cylinder. The wire would tend to maintain its form, but clearly it would deform if stressed. It could be dipped in varnish to cement it together into a rigid form. Edison (talk) 05:05, 24 January 2016 (UTC)

Is the [2] one that you uploaded yourself or that you have information about? It is not obvious from the picture alone that this is intended to be an electromagnetic coil as it has no terminals, no adhesive can be seen and the wire could be uninsulated (not magnet wire). A spool of plain wire delivered from a factory could look like this. AllBestFaith (talk) 16:15, 24 January 2016 (UTC)

They are called 'self supporting' coils.--178.102.247.97 (talk) 17:41, 26 January 2016 (UTC)

Analogue live TV

Before digital "film", how was live television done? My mental image of television, pre-digital, was that the scene was recorded by a videocamera and microphone, the sounds modulated onto electromagnetic waves as with radio, the film developed and then the images somehow modulated onto electromagnetic waves, and chronological conjunction between the two processes is enforced to ensure that the video and sound be synchronised. This doesn't seem to fit with live TV, however, as there's no time to develop anything; how would it be possible to broadcast anything that wasn't a recording? Today, it's easy: you can basically use the same techniques as Skype, but that wasn't possible in the 1950s. Nyttend (talk) 05:40, 24 January 2016 (UTC)

Television cameras before the 1980s used video camera tubes. Basically they worked like a CRT television in reverse. In a CRT display, one or more tubes scan their beams across the screen to produce the picture. In tube cameras, the camera focuses incoming light onto a target and one or more tubes scan the target. --71.119.131.184 (talk) 05:50, 24 January 2016 (UTC)

Note also that for quite a long time, a lot of prerecorded stuff on TV was direct on to Videotape not film. In fact, sometimes the content may have gone from videotape to film.

And BTW home camcorders weren't that uncommon before everything went digital. America's Funniest Home Videos for example was before digital video was particularly common, and some Youtube videos also look they were probably recorded on analog tape.

Nil Einne (talk) 07:07, 24 January 2016 (UTC)

Let's put it this way. You (Nyttend) have the mental image "that the scene was recorded by a videocamera". But that's really two things: converting the scene into an electronic signal, and recording the electronic signal. In a live breoadcast, the electronic signal would be used directly (more or less) to modulate electromagnetic waves just as the audio signal is used in radio. (For live color TV it would also be necessary to convert the R/G/B signals from the camera into the applicable encoding, i.e. NTSC, PAL, or SECAM.) --76.69.45.64 (talk) 07:22, 24 January 2016 (UTC)

Incidentally, the processes Nyttend describes is John Logie Baird's "Intermediate Film Technique", used for a few months in 1937 in the UK, but obsolete since then. It introduced a delay of about 1 minute in a live broadcast - see this article. Tevildo (talk) 09:03, 24 January 2016 (UTC)

Germany transmitted film-intermediate TV earlier. [3] During the 1936 Summer Olympics experiments were conducted with both an analog electronic camera and with a mobile TV truck. On the roof of the truck was a film camera. The film was developed in the truck and then run through the transmitting apparatus. AllBestFaith (talk) 17:09, 24 January 2016 (UTC)

Live TV originally went "straight to air", with no intermediate recording and playback steps. The signals from the microphones and camera were combined (usually through vision mixer and audio mixer desks) into a composite signal which was distributed to the transmitter site, modulated onto an RF carrier, and broadcast. All of these were real-time analog processes, with no delay except for that inherent in signal processing and propagation. The Anome (talk) 10:09, 24 January 2016 (UTC)

The Anome has hit on it. Just like a phone call, there is no need for a TV camera and transmitter system to make a permanent record of anything: if you have an outside broadcast unit you can just turn on a camera, transmit that signal to a control centre and then put it out on the air, without at any stage 'recording' it permanently. Much early TV was broadcast live without any copy of it being kept. Before the days of cheap magnetic recording systems, if you needed a permanent record of it, you'd often literally just film a television set with a film camera. Similarly, most analogue phone calls have never (one assumes) been permanently recorded onto anything. They just go from one phone to another through the wires. Blythwood (talk) 13:02, 24 January 2016 (UTC)

Thanks to everyone! I had no idea that it was possible for the TV camera to do anything except impress each scene on a separate film still; I didn't know that they used CRTs to send imagery to a transmitter. I'd imagined that the first cameras of any sort that used neither film or U-matic videotape were digital cameras. Nyttend (talk) 15:26, 24 January 2016 (UTC)

U-Matic was really quite a late development. There's a lengthy history of different types of analog video format, starting, I believe, with two-inch quad, and I believe digital videotape made its first commercially successful appearance with the advent of D-1 recording. -- The Anome (talk) 23:58, 24 January 2016 (UTC)

I'm fairly confused why the OP is conflating video tape and film. The distinction here is IMO important because while it's easy think a camera which is exposing light on to film would not be able to modulate an EM signal, if your camera is already modulating a signal onto video tape it's harder not to see the possibility of bypassing the video tape step completely. Of course when you think about it more, even with film, you have to modulate the signal somehow. If you are doing this by shining light through the processed film and then using the resulting image to modulate a signal, why can't you just skip the step of going from light to film to light?

In any case, note that beyond broadcast TV, it wasn't that uncommon for CCTV systems to be display only, which was I believe the initial form of CCTV per our article.

Nil Einne (talk) 00:32, 25 January 2016 (UTC)

See also Kinescope. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:19, 24 January 2016 (UTC)

The modern equipment for conversion from movie film to electronic TV signal (for taping or immediate transmission) is a Telecine. AllBestFaith (talk) 17:21, 24 January 2016 (UTC)

@Nyttend: - as a related point, early video recording on magnetic tape was so expensive that often even when TV was recorded down onto tape or a film, the tapes were soon wiped over and reused - often tony TV executives seem really to have thought that this junk they were producing was surely of no lasting interest to anybody. The result is that much TV made as late as the mid-1970s, even in prosperous and stable countries and even by state broadcasters with a high image of themselves, was erased. So yes, a lot of early TV was sent through the TV broadcast system like a phone call, with no recording device of any kind set up to make a record of it for posterity. Blythwood (talk) 10:52, 25 January 2016 (UTC)

As an interesting example, when the BBC broadcast the first UK TV play of George Orwell's Nineteen Eighty-four on 12 December and 16 December 1954, the actors (and backing orchestra) had to perform the play live twice, as the first performance had not been recorded (except for small segments, such as outdoor scenes.) The second performance was, however, recorded for archiving, perhaps because its importance had become obvious. {The poster formerly known as 87.81.230.195} 185.74.232.130 (talk) 15:07, 25 January 2016 (UTC)

Fans of the BBC Doctor Who series are particularly aware of this. Being obsessive collector-ish people - they'd like to have every episode ever made, nicely recorded. But since the series started in 1963, many of the episodes were recorded on magnetic tape and subsequently wiped. Interestingly, many of the episodes that have been recovered were recorded by people watching the show on broadcast TV who points 8mm film cameras at the screen - others were duplicated and shipped to other countries who wished to show the series and the master copies subsequently erased. Fans of the show periodically find a recording of a long-lost episode by digging around in piles of junk in places as far afield as Nigeria and Dubai! Often the sound track of the tape has been over-dubbed with something else and someone's home audio-cassette bootleg has been synced to video from elsewhere to cobble together a low-quality version. It's hard to imagine the cost of a recording tape being even a tiny fraction of the cost of making a 30 minute TV show - but evidently that was the case because such a vast number of TV shows from that era are either lost forever - or would require the sheer determination of an army of Dr Who fanatics to track down the remaining scenes put them back together. SteveBaker (talk) 17:29, 25 January 2016 (UTC)

Considering starting a new project on here

Hello all! As a spare time project, I’m looking to do spend some time in the next few months messing around with R, its graphics packages in particular. I’d be interested in combining this with my contributions to Wikipedia (do two obsessions together!) - does anyone have suggestions for any publicly available molecular biosciences data that might be interesting to do something with? Preferably something I can't screw up too badly! Blythwood (talk) 11:43, 24 January 2016 (UTC)

A while back I got to messing with Module:ImportProtein, which is in Lua (see the talk page for an example), and like so many things... put it aside for "a while". If you're interested, I'm not reserving the copyright. :) I wasn't aware of any direct R integration with Wikipedia, though it would create interesting possibilities! Wnt (talk) 14:25, 24 January 2016 (UTC)

Some aspects of it might be too close to original research, which is fine for other places, but not welcome in wikipedia. On the other hand, you could research numerical data already on Wikipedia and plot it in a more visual way. --Scicurious (talk) 15:40, 24 January 2016 (UTC)

@Scicurious: - sure, but I'm more interested in creating graphs as example images, and would be very happy using made-up data that's relevant to a real situation. So 'here is a data visualisation of type X to show what it looks like' - I would be happy to put a disclaimer explaining that the data is fictional. Blythwood (talk) 23:39, 26 January 2016 (UTC)

Did the universe start with only neutrons?

If hydrogen fusion created all other atoms from hydrogen, and hydrogen is a proton and an electron, and fission reaction is the decay of a neutron into a proton and electron, then did the universe start with only neutrons? — Preceding unsigned comment added by 86.153.69.165 (talk • contribs)

Our current theories imply that there were subatomic particles before neutrons existed; and it seems like neutrons and protons both started emerging roughly around the same time. Have a read through Chronology of the universe, Quark–gluon plasma, and related articles.

I think your insight is good, in that you're looking for reverse- reactions (like beta decay) and trying to conserve charge; but you are missing some important complications that arise when we study sub-nuclear particles in great detail. We now know that there are lots of valid ways that we can break protons and neutrons apart if we use very high energies. Present theories for the early universe imply that our heavy particles were created around the hadron epoch after protons and neutrons coalesced from quarks. Before that time, the energy density was so high that we barely understand the rules that govern quark combination: what we do know is that there were no protons or neutrons yet.

Nimur (talk) 15:13, 24 January 2016 (UTC)

Reverse polarity Schottky diode

On Digikey in the diode section[4], what does the "schottky, reverse polarity" diode type stand for? I understand what a regular Schottky diode is, but am not sure what a reverse polarity Schottky diode is. Johnson&Johnson&Son (talk) 15:05, 24 January 2016 (UTC)

Could it be a Schottky diode for creating a reverse polarity protection?--Scicurious (talk) 15:47, 24 January 2016 (UTC)

The OP has linked to a diode selection guide where one chooses filter(s) to limit the selection. Applying the "Schottky Reverse Polarity" filter reduces the number of manufacturers (to 2) and introduces selection menus for reverse leakage and capacitance when reverse biased. They are all Schottky diodes and this is just the guide designer's way to offer a detailed reverse specification if needed. AllBestFaith (talk) 16:42, 24 January 2016 (UTC)

The reference is to the packaging. The standard D-67 package has the cathode as the base and the anode as the lug, and the standard DO-4 package has the stud as the anode and the terminal as the cathode. The "reverse polarity" diodes listed have the anode as the base for the D-67 packages, and the cathode as the stud for the DO-4 packages. Tevildo (talk) 18:44, 25 January 2016 (UTC)

Why do they make pipes out of lead?

^Topic ScienceApe (talk) 16:59, 24 January 2016 (UTC)

"Lead piping was used because of its unique ability to resist pinhole leaks, while being soft enough to form into shapes that deliver water most efficiently." ScienceApe, you constantly asking questions where the answer is the first Google hit on the question is starting to pass over the line separating "good faith curiosity" from "trolling". ‑ Iridescent 17:05, 24 January 2016 (UTC)

I don't appreciate being accused of trolling. If I wanted to troll, I would ask a bunch of nonsensical questions using multiple sock puppet accounts so you didn't know they were from the same person. ScienceApe (talk) 17:19, 24 January 2016 (UTC)

Maybe you are doing it, but was not caught yet. Anyway, it's difficult to see a purpose on your questions sometimes. Maybe you should perform a simple search for a question before you ask it here. Otherwise you would look more like a science ape, than as a science curious person. --Scicurious (talk) 17:50, 24 January 2016 (UTC)

I don't need to prove I'm not a troll, but you're free to believe whatever you like, however I'm not going to stop asking questions if I'm curious about something. However feel free not to respond to my questions. ScienceApe (talk) 20:41, 24 January 2016 (UTC)

Of course you don't need to prove anything. However, if you are disruptive on wikipedia including the RD by continually asking pointless questions, you should expect to be restricted. Even if you don't reach that level, you should expect to be ignored, even when you ask okay questions if you continue to ask pointless questions. Nil Einne (talk) 00:15, 25 January 2016 (UTC)

Ok well then you can report me and try to get me blocked, but your threats are not going to dissuade me from asking questions. ScienceApe (talk) 02:19, 25 January 2016 (UTC)

A real life reference librarian who frequently scolded patrons for not just looking stuff up themselves would soon be fired. If it makes someone that angry when someone asks a question that is easy to find an answer for, then the angry librarian should find other areas of Wikipedia in which to work. It is disruptive to scold people who ask question when it is not clear they are trolling, as it is not clear here.Edison (talk) 20:49, 24 January 2016 (UTC)

Thanks I appreciate that. If nothing else, this should have been kept to talk pages and off the reference desk. ScienceApe (talk) 02:19, 25 January 2016 (UTC)

I agree that you are entirely entitled to ask questions that can be answered by typing the question into google - and calling you a troll is hardly WP:AGF. We've even had questioners here for whom Wikipedia was the only website they were allowed to access! However, it might be nice to try Google first. It's different when someone is a first-time user, and we all occasionally get the wrong form of words and google doesn't help - but as a regular question-asker, it would be a courtesy to the volunteers here to at least give it a shot before posting. SteveBaker (talk) 14:48, 25 January 2016 (UTC)

We should compare with some of the alternatives available at the time:

1) Iron pipes: These can rust. While a small amount of added iron in the diet may actually be healthy, in antiquity people didn't know that iron pipes were healthier than lead. Also, the orange or brown water it produces doesn't look or taste good. And eventually the pipes can rust through. (There are water treatment methods to prevent rust, but they wouldn't have had those in antiquity, either.)

2) Ceramic pipes: These can crack, due to seismic activity, frost-freeze cycle, tree roots, or subsiding of the ground around it. Therefore, they tend to be leaky.

3) Copper pipes: These can corrode to produce green sludge and eventually fail from that corrosion. Similar to iron, a bit of added copper in the diet may actually be healthy, but they didn't know that in antiquity.

So, if you didn't know about lead poisoning, lead pipes seemed like a good option (or gold pipes, if you happened to be filthy rich). StuRat (talk) 17:39, 24 January 2016 (UTC)

Wooden water pipes were popular in London for mains water supply in the 16th to 18th centuries, but generally connected to lead pipes in peoples' houses. I believe that they were still being replaced in the 1960s. IIRC they were generally made from Elm wood which is resistant to rot when not exposed to air. Alansplodge (talk) 18:02, 24 January 2016 (UTC)

Yes, I forgot about wood. Bamboo can be used, too, since it's naturally hollow, although some type of sealant may be need at the joints. StuRat (talk) 18:51, 24 January 2016 (UTC)

My gut feeling is that this would have to do with metal prices - alas that article, unfortunately, doesn't contain even a current table, let alone historical data. It would be worth updating with information from various sites like this. But my impression is that lead is a cheap metal because it is not usable for very many things, and a pipe buried in the ground is one case where the weight and the softness don't count against it. Alas, even that didn't pan out in the end... Wnt (talk) 20:38, 24 January 2016 (UTC)

Lead is usable for a lot of things. If only it wasn't poisonous. --71.119.131.184 (talk) 23:51, 24 January 2016 (UTC)

Lead works reasonably well for large diameter pipes (ratio of surface area to volume of water being smaller) - providing that the water is flowing quickly through the pipes and doesn't contain chemicals that corrode it. It follows that lead pipes are a reasonable solution for the mains supply (large diameter, water constantly moving) - but a terrible choice for houses (small diameter, water standing still for a dozen or more hours at a time).

In the news right now, the children of Flint, MI are suffering the consequences of using corrosive chemicals in lead pipes that had functioned acceptably (without those chemicals) for decades. Their problems were that e-coli in their water supply had to be treated aggressively - and that treatment caused the lead in the pipes to dissolve into the water much more easily.

Obviously, with modern plastics that are cheap, more or less completely inert, and which will probably last for centuries, we have the technology so that we don't have to suffer any of the issues that come with lead pipes anymore. However, the cost of digging up streets to replace them is more than many communities can bear. Flint was desperately short of money - which is why they switched water supplies in the first place - and replacing those old lead pipes was evidently not an option.

SteveBaker (talk) 14:48, 25 January 2016 (UTC)

They normally put chemicals in the water to coat the pipes to prevent corrosion, but when Flint switched water supplies they stopped adding those critical chemicals, and once the old ones wore off the inside of the pipes, corrosion began. StuRat (talk) 20:57, 25 January 2016 (UTC)

To clarify something that's perhaps not clear, while small amounts of iron are requisites in human nutrition (generally available through leafy green vegetables and some meats, and certainly through nutritional supplements), iron and copper are both toxic in excess (as most things are).

If you can SEE dissolved iron or copper in your tap water, it may not be safe to drink. Of course, iron isn't poisonous in as small amounts as lead, and is excreted by the body more rapidly and efficiently. Copper's more toxic, less readily excreted, and in rare cases can precipitate Wilson's Disease (you have to inherit a copy of the gene for predisposition to that rare disease from both parents, though).

It does appear, however, that the water works guys in Flint, Michigan dropped the ball. Lead poisoning, though, is curable by use of chelating agents such as EDTA, DMSA and penicillamine. Serious, but fixable. loupgarous (talk) 23:15, 28 January 2016 (UTC)

Coefficient of friction between nickel and polyethylene

Where can I find the coefficient of friction between nickel and polyethylene? Actually the coefficient of friction between nickel and any common plastic would be fine.

I found this site[5] that has the data for nickel and Teflon, but Teflon is little too difficult for me to get my hands on. Johnson&Johnson&Son (talk) 17:10, 24 January 2016 (UTC)

The coefficient of friction of plastics is usually measured against polished steel. PTFE (Polytetrafluoroethylene, brand name Teflon)'s coefficient of friction is 0.05 to 0.10. Polyethylene can be supplied in various grades for which this supplier quotes coefficients of friction 0.18 to 0.22. That is for steel. This table gives some comparison with nickel. AllBestFaith (talk) 17:55, 24 January 2016 (UTC)

Thanks. But the problem is I don't have a steel part; I have a part that's coated in nickel. Is there a way to derive or approximate the nickel-plastic CoF given the steel-plastic CoF? The engineershandbook.com[6] link you gave has nickel-glass, nickel-nickel, and nickel-steel CoF listed, but unfortunately it doesn't have any for nickel-plastic. Johnson&Johnson&Son (talk) 02:40, 25 January 2016 (UTC)

Look for firearms information. Nickel coated bolt carriers and nickel-teflon triggers are common. --DHeyward (talk) 05:14, 25 January 2016 (UTC)