Wikipedia:Reference desk/Archives/Science/2016 July 11

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July 11

Thinking of taking part in one of clinical trials

I was looking at clinical trials (in London) that pays anywhere from 1-3 grand. How sick do you usually get from them? 2.102.184.195 (talk) 03:26, 11 July 2016 (UTC)

That depends on what answers you'll get here. Count Iblis (talk) 03:44, 11 July 2016 (UTC)

This certainly qualifies as a request for "medical advice" which it is against our policy to address. Please discuss your concerns with a medical professional, such as your doctor. Vespine (talk) 04:16, 11 July 2016 (UTC)

The effect of a clinical trial on the participants varies from absolutely no effect whatsoever up to death. No effect is common - because some participants are the blind control group, and never get the drugs being tested. Death is very rare - but has happened in a few disastrous cases. Wymspen (talk) 08:47, 11 July 2016 (UTC)

@Vespine: This is clearly not a request for medical advice, as the person is healthy and asking about the general, non-individualized risk of an activity, no different than, say, asking if skin diving is dangerous. Furthermore, he would obviously receive medical advice, such as it is, in the very act of being enrolled in the study, which we cannot force to happen if they do not wish it to happen.

As for clinical trials gone wrong, the most infamous was TeGenero's TGN1412. What I found especially alarming about that case was that any idiot should have seen it was a disaster waiting to happen -- they made something to drive immune cells crazy, and used the affinity of monkey cells for a human protein to guess the dose at which human cells would interact with a human protein. My overall confidence in the process of clinical trials was diminished by that case - you think of it as a highly regulated process, but any grad student should have hit the big red button the moment they saw the design. Wnt (talk) 23:15, 14 July 2016 (UTC)

Magnetism

1. How little gauss could a lodestone detect without high technology?

2. How weak a magnet could still pick up a grain of unmagnetized iron?

Sagittarian Milky Way (talk) 05:05, 11 July 2016 (UTC)

This question is answerable, but we'll need more information. For the first part, how do you define "high technology"? Are we allowed to use a microscope? A Fabry–Pérot interferometer? For the second part, how big is a grain? Do you mean a grain (unit), 64.8 mg? And does "pick up" mean just "stick to", or do you want the magnet to lift the grain over a particular distance? Tevildo (talk) 10:22, 11 July 2016 (UTC)

I was thinking lower technology than a microscope (which would then be doing the detecting for you along with the natural magnet) but though now I'm also curious what a microscope and interferometer can do). Presumably the microscope would see if the lodestone (cut into a very long bar along the magnetic axis) twists the torsion wire enough to see in an attempt to align field lines? Can make a 1 mm wide iron cube or sphere weightless in Earth gravity with no static electric charge on either but only when the sphere or an entire cube face is touching the (perfectly smooth and flat) magnet pole. I should've been more specific. Sagittarian Milky Way (talk) 16:08, 11 July 2016 (UTC)

Primary sources studying the efficacy of condoms after one year of use

Where can I find primary sources studying the efficacy of condoms after one year of use? So far,I've only been able to find three. — Preceding unsigned comment added by Uncle dan is home (talk • contribs) 05:54, 11 July 2016 (UTC)

One year of use of the same condom? Or one year of regular use by an individual? Or failure rate after one year of regular use by a couple (assuming new condom each time)? Also, external or internal condom? EvergreenFir (talk) 06:14, 11 July 2016 (UTC)

Failure rate of male condom after one year of regular use by a couple.Uncle dan is home (talk) 06:24, 11 July 2016 (UTC)

When used correctly every time, about 98% effective. Source: https://www.plannedparenthood.org/files/9313/9611/6384/truth_about_condoms.pdf , which is reporting this study: Trussell, James, Contraceptive failure in the United States, PMC 3638209 When used inconsistently, about 83%. The Trussell paper, for which the full free text is available here, contains a list of references to other papers on contraceptive efficiency, including condom efficiency. -- The Anome (talk) 06:50, 11 July 2016 (UTC)

After 10 uses, you just turn em inside out.--86.187.170.21 (talk) 23:14, 12 July 2016 (UTC)

Good idea. Then whatever STD's they were protecting you from would be all over you. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:16, 12 July 2016 (UTC)

Don't be silly, Bugs. IP 86 was comparing them to woolen socks. Pound them on rocks at the river for a few minutes, then leave them to dry in the sun, or machine wash hot for 15 minutes, then microwave for 60 +/-15 seconds, depending on your altitude. Never use a clothes dryer; as, inevitably, one of the pair will get lost. μηδείς (talk) 18:27, 13 July 2016 (UTC)

Relation between activity coefficient and thermal expansion coefficient

What is the exact relation between activity coefficient and thermal expansion coefficient for a non-ideal solution?--82.137.14.26 (talk) 08:56, 11 July 2016 (UTC)

More specifically, considering the non-additivity of the volumes of the components in this type of solutions, how does the thermal expansion coefficient of a component or of the mixture (as a function of the activity coeffcient α_i(γ_i)) differ from the ideal case where is supposed to be a weighted sum of thermal expansivity of components without activity coefficients which are 1 in this case?--82.137.8.68 (talk) 17:15, 11 July 2016 (UTC)

I have a suspicion that your question misses something important.

Going by activity coefficient, it is defined for an isobaric, isothermal transformation. But a thermodynamic definition of the thermal expansion coefficient would be written as $dV=CdT+\sum _{x}C_{x}dx$ and then $C$ is the TEC "when all $x$ are constant"; but in an isothermal transformation, $dT=0$, and you cannot usefully use this to deduce $C$. Said otherwise, you cannot have $dT=0$ and $dV\neq 0$ and all $dx=0$ at the same time, so all you can deduce are expansion coefficients with varying $x$ (but not the thermal expansion coefficient as T is fixed).

It may be possible to define an activity coefficient for an isobaric, non-isothermal transformation (e.g. adiabatic), and then you can launch the calculations, but that would not be the same definition of the activity coefficient.

If you had the equation of state of the substance, you could (in theory) deduce both the thermal expansion coefficient and the activity coefficient and maybe, depending on the equation of state, there could be a relation between the two, but one of the interest of those coefficients is that they allow for first-order developments without knowing the full EoS. I do not see that happening in the general case. Tigraan^{Click here to contact me} 22:00, 11 July 2016 (UTC)

Good points raised here, thanks. Of course, for the isothermal case activity coefficients of components are defined at a specified temperature. Considering not one but several different temperatures for determining values of the activity coefficients one can get the change in this quantity with temperature. This dependence on temperature of activity coefficients and volume of the mixture is of interest in non-ideal in constrast with ideal case where activity coefficients equal 1 and the thermal expansivity of the mixture has a simple expression of dependence (a weighted sum) on the thermal expansivities of components without the presence of activity coefficients in formulae.

About the involvement of a EOS, EOS for mixtures are not very straightforward to obtain.

So the question is how can the dependence on temperature of activity coefficients can be linked to the thermal expansivity of a non-ideal solution/mixture?--82.137.8.173 (talk) 22:33, 13 July 2016 (UTC)

Why do you have to use an inhaler upside down?

Several sources confirm that the correct use of an inhaler is in an upside down position. What's the difference? --Hofhof (talk) 17:57, 11 July 2016 (UTC)

Define "upside down." I would think that whatever is the intended orientation is, by default, the right side to be up. --OuroborosCobra (talk) 18:58, 11 July 2016 (UTC)

See "How to Use Your Inhaler or Nebulizer from the American Pharmacists Association. This specifically says (of dry-powder inhalers) "Do not turn the inhaler upside down". It also says: " Your pharmacist can tell you if instructions for your device are different from those presented here". Alansplodge (talk) 19:23, 11 July 2016 (UTC)

I mean like in: [1] --Hofhof (talk) 20:23, 11 July 2016 (UTC)

So by "upside down" do you mean with the canister nozzle facing downwards into the actuator? That is indeed the most common orientation, but, just to be safe, you'll probably want to check the specific instructions which would have almost certainly have come with your prescription, if you are asking with regard to personal usage. If your question is more abstract, I'll say I have a hard time imagining that there is an appreciable difference either way, given the pressure under which the dose is delivered into the actuator by the propellant and the symmetry of the actuator chamber and outer aperture. That being said, you should first and foremost follow the guidelines provided for your device/prescription or, better yet, inquire of a medical professional (for example, the prescribing doctor or providing pharmacist) if you have significant concerns. Snow ^{let's rap} 20:41, 11 July 2016 (UTC)

My question was not to get advice for using an inhaler. And yes, I meant exactly what you understood.

But if there is really no difference, why is this the standard use? An image Goggle search for the correct use corroborates what I was told and found in enough sources: [2] — Preceding unsigned comment added by Hofhof (talk • contribs) 22:22, 11 July 2016 (UTC)

It's upside down relative to the way that the label is printed on the bottle, because the label is printed so it can be read when the bottle is sitting on a shelf, and that means sitting on the end that doesn't have the valve. Smurrayinchester 05:58, 12 July 2016 (UTC)

Also, it seems like it would be easier to hold the inhaler steady with the thumb and wrist and press down with the forefinger than to try to hold it steady with the forefinger and press up with the thumb. Smurrayinchester 10:19, 12 July 2016 (UTC)

• For any pressurised can (which usually means an aerosol can) the material to be delivered is heavier than the propellant gas, so sits at the bottom of the can. The outlet of the can thus has to be at the bottom (or you'd spray all propellant and no contents). In a paint can, this is done with a dip tube which reaches to the bottom of the can - and why an almost empty paint can works / doesn't work as you tilt it around. Ergonomically, it's best to have the squirt nozzle and valve on the top, where we can see them, even if this means adding a dip tube.

For some materials: powders or viscous fluids, the dip tube doesn't work. They either won't flow through it, or they could set in it. So these aerosols have to be used inverted. Examples are inhalers (a powder), squirty cream (viscous), expanding foam (the spawn of pure evil). Andy Dingley (talk) 10:54, 12 July 2016 (UTC)

• This article on pressurized metered-dos inhalers indicates (emphasis added) that the "canister is used in the inverted position with the valve below the container so that the valve will refill under gravity. The use of dry powder inhalers will differ. - Nunh-huh 15:22, 13 July 2016 (UTC)

Sky glow

Glow when looking south while the sunset is on the right from the viewer's perspective

Today I noticed that some parts of the sky in Warsaw were separately glowing pink while the actual sunset was in another part. This was the actual sunset at that time (around 21:05 local time) and this was another glowing part south of the sunset. My thought is that because this part was approximately parallel to the sunset, it reflected the sunset, but I'm not sure. Was it so? Brandmeister^talk 20:03, 11 July 2016 (UTC)

Well, it's hard to imagine another light source that create a glow at that scale (even having limited reference points for the images), so yes, it's almost certainly sunlight. However, "reflected" might not tell the whole story. Most all sunlight your eyes will ever experience is reflected in some sense, whether it be the gentle curvature created by the atmosphere of even a clear day, or bounding off more substantial atmospheric obscurence or the surface of the planet. It is hard to say with any certainty from those photos, especially not knowing their exact relation to one-another, but I suspect that what you saw was a pink skyline that would have appeared uniform except for the fact that foreground clouds obscured part of it, particularly between the west and south. But that's somewhat speculative. Woops, I got the images mixed up and so mistook the significance of your "to the right" observation. That does indeed strike me as simply reflected light, or simply just sunlight catching the clouds at an angle, though the caveat that most all sunlight is in some sense reflected still holds. :) Snow ^{let's rap} 20:52, 11 July 2016 (UTC)

My guess is that there is a high (cirrus ?) cloud catching direct sunlight behind some lower hazy clouds which are too low to catch sunlight directly at that point in the sunset. The pink color would be the red sunlight passing through thick atmosphere (the other colors are diffracted away), combined with the white water droplets of the cloud. StuRat (talk) 21:39, 11 July 2016 (UTC)

• Odd, @Brandmeister:, my mother's mother, who was born south of Krakow, called this phenomenon "sky-blue-pink". I wonder if that term was her invention, or more widely known. μηδείς (talk) 22:20, 11 July 2016 (UTC)

sky-blue-pink n, adj. a jocular name for a nonexistent, unknown, or unimportant colour[3], usage[4]. Sky Blue Pink is also the title of a Panther cartoon from 1968. AllBestFaith (talk) 23:12, 11 July 2016 (UTC)

Given the attributed dates, it could still very well be her creation. I also claim "wikt:blurple". :) μηδείς (talk) 00:07, 12 July 2016 (UTC)

Possibly related to sun dog phenomenon? The Atmospheric optics article might "shed some light". --2606:A000:4C0C:E200:D0C4:DF9D:2B6A:49F5 (talk) 23:38, 11 July 2016 (UTC)

It's not circular, like a sundog is. StuRat (talk) 01:26, 12 July 2016 (UTC)

We witnessed a similar phenomena here in the UK at around 11pm BST (British Summer Time) on that night. As video camaras are less sensitive than the human eye, this footage doesn't do this display justice but one can see the colour changes. “This is the moment the London skyline was illuminated by mysterious flashes of red and white light – captured in a video which has baffled weather experts.”--Aspro (talk) 13:40, 12 July 2016 (UTC)

I suspect the Warsaw phenomenon is noctilucent cloud (or maybe I mean nacreous clouds!). Thincat (talk) 17:24, 12 July 2016 (UTC)

Could this be a form of Alpenglow? ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:44, 12 July 2016 (UTC)

Washing machines: vertical and horizontal axles

Why are washing machines different in the US and Europe? In the US the axle of rotation is vertical, and you load it from the top. In Europe, it's horizontal, and you have to buckle down to load it. Add to this that a damaged door could easily leak. Hofhof (talk) 22:55, 11 July 2016 (UTC)

Many small apartments in Europe have space only for a combined washer and spin dryer unit with an unobstructed top working surface. AllBestFaith (talk) 23:00, 11 July 2016 (UTC)

Even in larger houses, its common for the washing machine to be kept in the kitchen, when it fits modularly into the counter units like a dishwasher or a small fridge does (see this picture for an example). Smurrayinchester 05:54, 12 July 2016 (UTC)

There are or at least were plenty of front-loading washers in America. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:51, 11 July 2016 (UTC)

Agreed. Top-loaders tend to be lower priced, but have some disadvantages of their own, such as clothes stuck under the agitator being torn or having buttons ripped off. Also it can be difficult for short people or those with back problems to reach clothes in the bottom. I'm not sure if the agitator can be eliminated, in favor of a rotating drum with fins on the inside. If so, that could solve the first problem, and possibly allow for larger items. StuRat (talk) 01:23, 12 July 2016 (UTC)

My mother's top loader has no agitator, just a drum that rotates on a vertical access. --TrogWoolley (talk) 10:15, 12 July 2016 (UTC)

Yes, I understand those use a wash plate instead, which means ridges on the bottom of the tub to move the water. I don't believe that is as effective at moving the water or washing as an agitator, though it might be better for delicates: [5]. StuRat (talk) 15:09, 12 July 2016 (UTC)

Front loaders are by no means rare in U.S. homes (we have one). Here is a recent-ish article discussing sales trends and statistics for front versus top loaders for U.S. domestic use. My impression is that front loaders dominate in laundromats and commercial applications, but I haven't found any statistics to back that up. Shock Brigade Harvester Boris (talk) 01:43, 12 July 2016 (UTC)

Our Washing_machine article talks about many different aspects of each of these two models. DMacks (talk) 01:53, 12 July 2016 (UTC)

Vertical-axle washing machines are rare in Europe, but that doesn't mean everybody uses a front-loader. Top-loading horizontal-axle washing machines are very common in Europe. PiusImpavidus (talk) 08:17, 12 July 2016 (UTC)

In my experience, here in the UK, top loading machines are more common in laundromats. --TrogWoolley (talk) 10:15, 12 July 2016 (UTC)

• Europe has individual machines in each apartment's kitchen. The US has communal laundry rooms (or basements etc.). Europe needs the worktop space back.

Also Europe line dries, so we don't depend so much on giant driers.

In commercial public laundromats, Europe uses top loaders and front loaders fairly evenly. Andy Dingley (talk) 16:32, 12 July 2016 (UTC)

Top agitator, top-loader, vertical axis washing machine ?

I've often thought that the problem with clothes getting stuck under the agitator could be solve by having it come down from the top instead of up from the bottom. This would mean a small motor and agitator would need to be lifted off the top between loads. Some type of counterweights or springs could make this easier. Another advantage of this two piece design would be that each piece (top with motor, agitator, and controls and bottom with another motor and tub) would be separate, making it easier to move or replace. Some communication between the top and bottom would be needed, to coordinate tub and agitator movements. This could be done through contacts, or something like Bluetooth. So, has any design like this ever been tried ? StuRat (talk)

What you are describing is called a bread-kneader or top-bladed blender. You can probably do a T-shirt or a pair of gotchies in one. μηδείς (talk) 21:12, 12 July 2016 (UTC)

Washing machines rotating on vertical axle might have more problems keeping the water inside. Such machines are used in Arabia and Asia. Larger cloth often get rolled and twisted by such machines. The horizonal spinning axles thow the cloth into the soap water or on the wall of the drum, smashing the dirt out of it an return outer soap or water. Such machines safe water due a only a puddle in the drum is neccessary and fling out the water, the same horizontal drum is beeing used, the drumm spinns faster without water, the water pump gets the drum empty in this mode. (see running machine) Wool requires more water, slower and less rotation. (see high water level) In Germany the front door machines dominate. Top door machines were rarely offered, often to fit a narrow space, but rotate horzontal. Vertical axle spinning machines are not known in Germany, least 60 years ago or longer. This one is a typical American one and Arabian or Asisan ones cause more user interaction, but easy to repair [6][7]. --Hans Haase (有问题吗) 21:33, 12 July 2016 (UTC)

Simpler design

The top agitator could just be fixed to the lid, and it would only move relative to the water, due to the movement of the tub. It would still need a mechanism to allow it to open and close vertically, though, not a standard hinge, unless the agitator was short and the tub wide. Are any designed like this ? StuRat (talk) 01:45, 13 July 2016 (UTC)

The water won't move much relative to the agitator. The tub may oscillate back and forth but the water will move far less. In physics terms, the water does not experience solid-body rotation. Shock Brigade Harvester Boris (talk) 03:09, 13 July 2016 (UTC)

I forgot to mention that the tub should have paddles on it so the water does move when the tub moves. Therefore the stationary agitator would move relative to the water. StuRat (talk) 18:40, 13 July 2016 (UTC)

StuRat appears to be describing a dolly washing machine. (the tub dose not move as it would be like rotating a goldfish bowl where the fish stay pointing in the same direction because only the bowl rotates). The agitator is lowered in from the top. They continued to work flawlessly during brown-outs. Do not flood the kitchen when a pipe burst. Operated very much more quietly. Their fluff filters don't clog up and their pumps never fail. Neither do their bearings and motors wear out. History of washing machines--Aspro (talk) 13:26, 13 July 2016 (UTC)

Sounds great, so why are they no longer made (automated versions, that is) ? StuRat (talk) 18:40, 13 July 2016 (UTC)