Wikipedia:Reference desk/Archives/Science/2015 October 10

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October 10

Brushless-nee

Why unlike a good old brushed a motor which has only two wires a + and a - where I put two ends of battery cell and get the fair going, these 'brushless' ones have THREE wires. What am l going to do with the third one? And what [the hell http://imgur.com/9d15AvJ] is this. Kindly tell me about all this. I will be grateful. 27.255.210.207 (talk) 06:08, 10 October 2015 (UTC)

That image looks like the speed controller module for a radio-controlled copter. The three blue wires go to the brushless DC electric motor that drives a propeller; the thick red and black are power supply, and the black/red/white connector transfers signals (throttle, etc.) from a controller/receiver unit. The article I linked about the motor explains why there are three wires...it relates to the idea of the requirement for three-phase electric power in order to get a rotating magnetic field. DMacks (talk) 07:15, 10 October 2015 (UTC)

Get the data sheet of this product. If it is an battery false usage cause explosion of the battery. If it is motor controller or actuator, is might be an analog signal, to control the actor or motor speed. It also might be an digital input or output of sequencial protocol. Or pulse of motor speed of output as speedmeter or input as clock signal. --Hans Haase (有问题吗) 12:12, 11 October 2015 (UTC)

I've built a few remote control choppers from components so I know a bit about these. As stated above, the battery should be plugged into the red and black wire (you should solder the appropriate male LiPo battery connector to the wires). The motor plugs into the blue wires, if your motor doesn't have 3 wires, it's not the right motor. You should use bullet connectors to connect the motor to the speed controller, you need to just plug all the wires in and then test if the motor is spinning the right way, if it isn't you just swap any two wires and it should be right. Vespine (talk) 21:54, 11 October 2015 (UTC)

Microwelds

Tetraethyllead says the following:

Tetraethyl lead works as a buffer against microwelds forming between the hot exhaust valves and their seats.

I've read over the source a couple of times, but I didn't see anything there about microwelds. What are they? All I'm finding through Google are companies that promote their ability to use techniques to weld really tiny items; I don't see anything about microwelds that are somehow able to form without the presence of welders. Nyttend (talk) 11:20, 10 October 2015 (UTC)

Galling and cold welding are our relevant articles (although both of them have potential for improvement). Tevildo (talk) 12:29, 10 October 2015 (UTC)

Possibly also Spot welding? ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:20, 11 October 2015 (UTC)

No, that's still a deliberate process that uses heat to fuse the metal. The important point is that the microwelds are created by pressure, rather than heat; the valves are hot, of course, but they're well below the melting point of the metal. The galling is caused by the pressure of the valve on the valve seat during the ignition phase of the engine cycle. Tevildo (talk) 19:34, 11 October 2015 (UTC)

Do the all mammals (includes human body) have the same number of vertebrae?

13:54, 10 October 2015 (UTC) — Preceding unsigned comment added by 78.111.187.11 (talk)

See the Wikipedia article titled Vertebral column or this post. The tail is also part of the vertebral column, so mammals with tails have more vertebrae than those without. All mammals except sloths, anteaters, and manatees have exactly seven cervical (neck) vertebrae however. --Jayron32 14:02, 10 October 2015 (UTC)

• Two details: First, the Wikipedia article doesn't answer the question for mammals. Second, the medsci.org item does, but it actually contrasts long tails with "short or no tails", not with "without tails". Anyway, for one example of a different number of vertebrae see cat anatomy#skeleton. --174.88.134.156 (talk) 20:40, 10 October 2015 (UTC)

And that includes giraffes... - Nunh-huh 14:08, 10 October 2015 (UTC)

Thank you Jairon32 for your comment. 78.111.187.11 (talk) 15:41, 10 October 2015 (UTC)

Is actually a normal egg in condition of eating - considered as a big unicell?

When we eating eggs we eat them while they have yolk and white (and eggshell). is In this phase they are considered as a big (one) uni-cell? 78.111.187.11 (talk) 15:40, 10 October 2015 (UTC)

No. The egg white is extracellular material, as are the outer membranes and shell. The yolk on the other hand is part of the one-celled ovum, as both are surrounded by the same cytoplasmic membrane. see [1]. - Nunh-huh 15:57, 10 October 2015 (UTC)

The egg as single cell is technically true, yet it should be taken with a grain of salt (some pepper too, ideally). The key concept is the notion of meroblastic cleavage, which is to say, when the egg is fertilized and begins dividing, the cells produced are initially content to divide themselves up on the surface without developing cell membranes separating themselves from the yolk beneath. Later, they do separate from the yolk, creating a subgerminal space. But what is clear throughout this process is that the yolk acts like it is a substance distinct from the cells, not really under the command and control of the sparse nuclei atop it. So don't imagine an egg as a giant cell with a heroic lone nucleus at the middle making all the decisions - it's actually only influencing a small region around itself at one edge. See [2] [3] for some basic background.

As an example, consider fertilization in the chicken. Polyspermy is apparently allowed; when the yolk passes through the infundibulum of the oviduct and is exposed to sperm storage glands, the sperm preferentially seek out the near center (but not the exact center) of the germinal disc region [4] and break through the perivitelline membrane. They all even form sperm asters in the cytoplasm! [5] But only one of the sperm, of course, actually fathers the embryo - according to that last source, the other pronuclei are shunted away by some still-unknown means. So the egg really seems to act as if there is a small cell on one side waiting to be fertilized and all the rest is something else - even though there is no visible membrane to account for that. Wnt (talk) 06:36, 11 October 2015 (UTC)

Engineering and operations

If you have an engineering degree but rather than the infrastructure itself you're more interested in operating it (for example the management of road/rai/air/energy/oil supply etc operations), is there much point going down an engineering career path? — Preceding unsigned comment added by 90.201.186.84 (talk) 16:11, 10 October 2015 (UTC)

Pay to consult a proper careers adviser. He will ask a lot more probing questions than you can volunteer here. He may be able to suggest aptitude tests that can focus you on where your talents lay and a path to were you are most likely to succeed. You can't get that from a Wikipedia Reference desk question.--Aspro (talk) 20:02, 10 October 2015 (UTC)

yes, because engineering is a way into many other jobs. Knowing why stuff is designed the way it is will make you better at fixing operational problems with it. OTOH if your ambition is to be a pump jockey at a service station, then maybe petroleum engineering is the wrong career path. I wouldn't pay a careers adviser, in my experience they are useless.Greglocock (talk) 22:05, 10 October 2015 (UTC)

Yeah, I agree. Career advisors have never told me anything more than what I already knew. Is a masters useful in operations management? 2A02:C7D:B91D:2200:6094:AAC9:8C83:4FDE (talk) 19:43, 11 October 2015 (UTC)

If you are talking about careers adviser that one finds in say British or US State schools -yes 'they' are useless. I'm talking about consulting a professional that will subject you to aptitude tests and the like. If one wants to know of the best way to invest ones inheritance do you ask your local bank manager – of course not. One seeks out an expert. So why not go to a professional for careers advice. Because over ones life time, that can make a difference of many hundreds of thousands of £ or $). Do the sums (working life in years X salary, plus company car, heath gym membership, pension rights, etc. and most of all, living enjoying satisfying and rewarding career). Don't be a skinflint. Jesus said that the poor will always be among us and then there is the Parable of the talents or minas. Take your choice. --Aspro (talk) 22:13, 11 October 2015 (UTC)