Wikipedia:Reference desk/Archives/Science/2014 October 29

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October 29

Ocean Water density and temperature

Water, as I understand it, is one of those weird molecules where the angle between the two hydrogen atoms increases when it freezes. This makes the solid form of water less dense than the liquid form (whence, icebergs float as their volume displaces warmer liquid water more than its own weight - ice is less dense than liquid water). It's also my understanding that the maximum density of water is achieved at about 3°C. The deep oceans are at this nearly constant temperature because anything warmer is less dense and rises and anything colder is less dense and rises so the deep oceans are at maximum density and virtually a constant temperature (and also the reason why at such depths it's a liquid). So does that mean if the ocean cools, there could also be sea level rise especially if a large majority of the ocean were at maximum density when cooling started? Could the volume of water increase by 1/3 if the temperature went from 3°C to 0.01°C? --DHeyward (talk) 01:38, 29 October 2014 (UTC)

Fresh water reaches its maximum density around 4°C. But the temperature at maximum density decreases about linearly with increasing salinity. At a salt content of around 25 per mil (2.5%) the temperature of maximum density intercepts the freezing temperature. So, for salinities above 25 per mil water always becomes more dense as temperature decreases. The graph near the bottom of this page shows the relationship.

The mean ocean salinity is about 35 per mil, so sea level always increases with increasing mean ocean temperature. There are a few patches of ocean where salinity is less than 25 per mil (notably the Baltic Sea) but these are only small fractions of the global ocean. Short Brigade Harvester Boris (talk) 03:59, 29 October 2014 (UTC)

What is a good way to identify tablets?

what is a good way to identify tablets (pills) where I see a lot of kinds of them? Is there any way to identify them according something unique or it can be some tablets are identical and no eazy way to identify them 149.78.224.210 (talk) 01:54, 29 October 2014 (UTC)

Given the obvious hazards of getting it wrong, the only advice we can give you is that you shouldn't search for advice on such matters from random strangers on the internet. If you are in any doubt as to the identity of a medical substance, don't take it... AndyTheGrump (talk) 01:58, 29 October 2014 (UTC)

I don't take any tablet, but it interests me theoretically. In addition, I'm an EMT so it interests me from this view.149.78.224.210 (talk) 02:02, 29 October 2014 (UTC)

I actually had an answer for you until you said you were an EMT. If so, you would already know where to find that information. The police do too. Prescription OD's are common for EMT's and they are trained on how to identify tablets so they know how to respond. --DHeyward (talk) 02:08, 29 October 2014 (UTC)

Yup - if the OP actually is an EMT, there is no way we should be giving advice on such matters - per policy, we don't answer requests for medical advice, and helping out EMTs with things they clearly ought to know already would seem even less advisable. AndyTheGrump (talk) 02:14, 29 October 2014 (UTC)

Do you think I'm lying? I'm EMT-B (read here). Why do you think EMTs know to identify tablets? EMTs know CPR mostly and some first aid but no more. 149.78.224.210 (talk) 02:18, 29 October 2014 (UTC)

In which case you already have access to people who can answer your question. Ask them. AndyTheGrump (talk) 02:22, 29 October 2014 (UTC)

The U.S. National Institutes of Health has a site where you can input the physical characteristics of pills and it will tell you what they may be.    → Michael J Ⓣ Ⓒ Ⓜ 03:42, 29 October 2014 (UTC)

Thank you Micahel. I wish everyone would study from you how to help. 149.78.224.210 (talk) 03:55, 29 October 2014 (UTC)

I don't see what the problem is. Google the specifics of the pill and you should be able to come to a consensus quickly. Justin15w (talk) 03:54, 29 October 2014 (UTC)

If you websearch "pill identification" you'll find a variety of tools, but that is indeed a good one. I don't think it is a bad thing for people who get prescriptions filled to routinely look up the pills they get in order to verify there are no mistakes made. I mean, every once in a while you read about some little kid having her prescription bottle filled with methadone or something by accident, and turning up dead, and it just breaks your heart. Wnt (talk) 03:57, 29 October 2014 (UTC)

I've started seeing prescription bottle labels including a physical description of the drug ("This is a red solution that may be cloudy", "This is a white, round-shaped tablet impronted with [number] on the front", etc.). DMacks (talk) 17:19, 29 October 2014 (UTC)

We have a book at home (a few years old now) which is a home guide to medicines and drugs, published by the British Medical Association. It has a drug identification section with pictures and descriptions of all the tablets and capsules commonly prescribed in the UK. However, the latest version doesn't seem to have the drug identification section - probably because there are now the online tools that do the job better. To answer the other part of your question, from what I've seen in that book It would appear (although I can't say for certain) that all prescription tablets and capsules are produced in a unique form so they are identifiable by a combination of shape, colour, scoring and often a number stamped on them. Richerman (talk) 00:18, 30 October 2014 (UTC)

OP: Note that the standards determining pill shape, size, color and marking differ from country to country. So if you are really based in Israel as your IP indicates you will need to refer to the applicable national standards, and using the NIH or FDA website could be dangerously misguided! Abecedare (talk) 00:29, 30 October 2014 (UTC)

facebook

I've taken the liberty of moving this to the computing Refdesk. Wnt (talk) 03:20, 29 October 2014 (UTC)

(Unfortunately, the question was asked FIRST on the computing desk and didn't get any responses, so the OP evidently posted it here in the hope of getting an answer. Punting it back to WP:RD/C isn't likely to help much.) SteveBaker (talk) 15:31, 29 October 2014 (UTC)

Right prefrontal cortex function

What do Brodmann areas 8-9 and 46 do on the right hemisphere? What might low grey matter volumes in these regions indicate? — Preceding unsigned comment added by 68.39.237.199 (talk) 15:34, 29 October 2014 (UTC)

We have articles on all of these:

• Brodmann area 8: "The area is involved in the management of uncertainty."
• Brodmann area 9: Role not specified in the article.
• Brodmann area 46: "Plays a role in sustaining attention and working memory."

I would not want to speculate on what low grey matter volumes might indicate. - Eron^Talk 20:28, 29 October 2014 (UTC)

I wouldn't take those descriptions too seriously. Those areas are broadly motor-related, but at a high level -- the level of attention and planning, perhaps. Information about them is rather sketchy. The best known component of that region is the frontal eye fields, usually considered part of area 8. They are capable of eliciting eye movements, and seem to be involved in both covert attention and visual search. Low grey matter volumes in this part of the brain are associated with schizophrenia, which is probably the motive for the question, but it's hard to say what their significance might be. There is some evidence relating them to working memory, but it seems kind of vague to me. Looie496 (talk) 20:14, 30 October 2014 (UTC)

The main property of the electrons

Did the electrons had an electromagnetic perdurability (constancy), that is the electrons are in different physical environments remain its electromagnetic constant?--Alex Sazonov (talk) 16:56, 29 October 2014 (UTC)

Electrons always appear to have the same electric charge from a distance. This amount is called the elementary charge. Even when travelling at close to the speed of light, or deep in a gravitational well the charge will appear to be the same. Though I will say that the Fine-structure constant which depends on this charge, is claimed by some to vary at different places in the universe. I think this is incorrect, and that is remains constant in our Universe.

I thinking, if did the electromagnetic perdurability (constancy) of electron changing, the electron done work (created plasma - plazmiroval), but this work of the electromagnetic potential in the natural nature is not observed, however the electromagnetic plasma in the natural nature is observed, as the work of the electromagnetic potential of the electric current or dynamics of the electric current, but not as the work of the electromagnetic potential of the electron.--Alex Sazonov (talk) 06:46, 30 October 2014 (UTC)

I think, that electron is always be an elementary charged particle of electromagnetic world, that world retains its static electromagnetic potential as constant, that is the electromagnetic world is always be persistent as a constant , so that the electron had always be electromagnetic perdurability (constancy).--Alex Sazonov (talk) 08:40, 30 October 2014 (UTC)

Electron always retains as a constant properties of its electromagnetic potential, as an elementary charged particle of world of electromagnetic statics!--Alex Sazonov (talk) 08:54, 30 October 2014 (UTC)

All elementary charges in the natural nature had always kept in its natural electromagnetic preservatives, therefore, to extract them from the natural electromagnetic preservatives is always necessary to spend the electromagnetic force, either natural nature itself will be extract them by force of its electromagnetic potential. Since the electron is charged elementary particle of electromagnetic world, so that to extract its force (charge) is always necessary to spend the electromagnetic force.--Alex Sazonov (talk) 09:30, 30 October 2014 (UTC)

Any magnetism in natural nature is always been the only one main and basic sign of the presence of electromagnetism.--Alex Sazonov (talk) 11:34, 30 October 2014 (UTC)

The powerful in the natural nature is been only an electromagnetic potential.--Alex Sazonov (talk) 11:06, 31 October 2014 (UTC)

As far as I know, scientific of the USSR was always focused only on the studies of magnetism.--Alex Sazonov (talk) 07:46, 2 November 2014 (UTC)

Did the magnetic properties of electrons been different from the electromagnetic properties of the electrons?--Alex Sazonov (talk) 08:47, 2 November 2014 (UTC)

What properties of the electron is always been the strongly marked and been the predominant, an electromagnetic properties or magnetic properties?--Alex Sazonov (talk) 13:56, 2 November 2014 (UTC)

Given a battery and a device, how can you calculate how long the battery will last?

If a battery has 50000mAh, and the device needs 5V and 500 milliAmps, will the battery last 100 hours? What if the device required a different amount of Volts, how would it be different? What's the formula for this? — Preceding unsigned comment added by Senteni (talk • contribs) 18:17, 29 October 2014 (UTC)

For your first question, it depends on the battery's voltage. Actual energy capacity would be more accurately expressed in watt hours rather than ampere-hours. However, batteries are more or less fixed voltage sources, and so manufacturers g ahead and do the amps = watts / volts conversion, presenting capacity in amp hours with voltage as a fixed given.

So, if you use 50k mAh batteries in a device that draws 500 mA, you would indeed expect 100 hours of battery life. I skip voltage because, presumably, the device is intended for a particular battery configuration at a particular voltage and the batteries in use match that. Note that this holds even in multi-battery configurations: if you have a 6V device that uses 4 AA batteries and draws 100 mA, and you use AA batteries with 1000 mAh capacity, you'll get 10 hours of use. Each battery is only rated for 1000 mAh at 1.5 volts, but when placed in series, you've got either 4000 mAh at 1.5 V or 1000 mAh at 6 V (or whatever other conversion factor you like, per W = V * A). — Lomn 19:22, 29 October 2014 (UTC)

That's correct. Theoretically, the battery in question should last 100 hours. However, there are no firm standards for rating battery capacity. Some manufacturers rate useful life only (down to some minimum voltage), while others will rate capacity for a complete discharge to 0V. Your device might need a minimum voltage to function, which would also affect the amount of useful energy you can draw from the battery. If this is for a practical application, you might want to consider doing some tests and derating your battery based on the results. Mihaister (talk) 22:53, 29 October 2014 (UTC)

Does driving behind semi trucks increase gas mileage?

Title

Yes, but it's also extremely dangerous. Please see Drafting_(aerodynamics)#Tailgating_and_hypermiling.--Shantavira|^{feed me} 20:02, 29 October 2014 (UTC)

There was a compelling demonstration of this done by Mythbusters - the amount of fuel savings is impressive at higher speeds - but the dangers are rather extreme. What may be surprising is that tailgating not only saves the tailgater gas - it also saves it on the truck. SteveBaker (talk) 01:56, 30 October 2014 (UTC)

We also have the article Drafting (aerodynamics).

Macadam

Combined with below question so we don't get overlapping unnecessary redundancies. μηδείς (talk) 00:26, 30 October 2014 (UTC)

Road sub base & Macadam base

In highway design, how do engineers decide whether unbound or bound materials should be used for sub base? Is it to do with durability and load? Is macadam generally used in the base course of highways?Clover345 (talk) 23:36, 29 October 2014 (UTC)