Wikipedia:Reference desk/Archives/Science/2015 August 16

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August 16

Survival rate when ejecting with ejection seats

For planes with ejection seats, is the airmen survival rate larger when they ditch on land or over water? My other car is a cadr (talk) 04:36, 16 August 2015 (UTC)

I assume you mean 'when they eject over land or over water' - Ditching an aircraft is defined as ""a planned event in which a flight crew knowingly makes a controlled emergency landing in water". As for the survival rates for ejection, I'll see if I can find some data, but I'm fairly sure that the general survival statistics for emergency parachuting favour land over water - simply because once on the surface, an environment at sea is much more hostile. In anything but the tropics staying warm is problematic, and where that isn't a problem, dehydration is likely to be. AndyTheGrump (talk) 04:44, 16 August 2015 (UTC)

I've not been able to find any general comparative survival statistics for ejection over land vs water. This document [1] has some comments about ejections by U.S. Navy aircrew during the Vietnam war, which notes that injuries during landing were much less likely over water - but that life-threatening entanglements with parachute shrouds etc were then a danger. I'm not sure that one can extrapolate too much from this though, as the data only covers the survivors, and ejecting over hostile territory had hazards beyond the immediate dangers of a parachute landing. Over water, with the U.S. having total air superiority, rescue was much more likely. Clearly the relative risks will depend on many factors beyond the immediate hazards of landing, though the overall statistics for ejections (which I've seen repeated in several sources - e.g. [2]) say that the survival rate is now around 92 per cent - and that you have a one-in-three chance of sustaining a spinal fracture during ejection. AndyTheGrump (talk) 05:35, 16 August 2015 (UTC)

The ejection itself carries a significant risk of injury. Seat manufacturers actually specify minimum and maximum mass and dimensions for users. An acquaintance failed selection for air force pilot training because she was below the 60kg minimum weight limit of the type of seat in the training aircraft. Had she actually ejected in such a seat the acceleration would likely have snapped her neck. The thrust of the rocket motor in the seat is not variable so the acceleration varies only according to the mass of the seat plus occupant. Too light and the occupant gets a broken neck, too heavy and the seat fails to clear the vertical tail of the aircraft. Roger (Dodger67) (talk) 10:58, 17 August 2015 (UTC)

Why don't they put explosive cord in the base of the tail to break it off? This isn't as far-fetched as it seems, they already have canopies with explosive cords in them and almost made an ejection seat that can fly with a shield for supersonic ejection I think. Then you can have a "lite" setting for when you don't need to leave that second (like an engine failure) so you don't break your back. Maybe this is intentional and they want to encourage pilots to try any chance of saving the $200 million plane first or even kamikaze the enemy if they can't. Sagittarian Milky Way (talk) 02:13, 18 August 2015 (UTC)

Ejection systems need to be reliable, and to be operable with the minimum thought. Having two different settings would work against both. And I'm not sure that explosive cords in the tail would be seen as an advancement in safety. I suspect that spinal injuries are less common when the pilot has plenty of time to reach a decision to eject - they are instructed to do so with their back and neck straight. Ejections where the pilot has had little time to think (e.g. when trouble develops close to the ground, and only a second or two is available) are inevitably going to involve more risks - I read recently of a pilot who ejected successfully, but sustained a broken arm because he forgot to let go of the joystick. AndyTheGrump (talk) 02:33, 18 August 2015 (UTC)

What happens when the inputs to a phototransistor is shorter than its response time?

Please see this drawing[3]. The first frame is my (admittedly poor) understanding of a phototransistor's response time. Please correct me if there's any mistake. I asked this question back in July[4] and would like a second opinion on it, if possible.

1. What happens when the duration of the input is shorter than the phototransistor's response time? Is there still a delayed response, or is there no response at all? (The latter case being like your car, if you don't turn the key long enough, it doesn't start at all)

2. What happens when the input is shorter than even the rise time? Would there still be a cut-off triangular-shaped rise? What would the response waveform look like?

3. Is there a minimal input duration below which the phototransistor makes no response at all? My other car is a cadr (talk) 06:36, 17 July 2015 (UTC)

Every diode is also a capacitor, all the way down the the most microscopic model. At some point, your light pulses are going to be quantized; a light pulse so short that it constitutes a single photon ... and at that point, your photoelectric effect is going to be lost amidst the shot noise. For pulses long enough to be non-noiselike, the inherent capacitance of the diode (plus any other parasitic capacitance due to the practical details of a real device) is going to smooth the output voltage. To model this, you just need to estimate the total capacitance of the photoelectric cell, and treat it as a capacitor in parallel with the output. The answers to all your questions then basically devolve into the same question: how does a capacitor in parallel with an ideal, time-varying voltage source modulate the output voltage? The answer is, roughly speaking, that it smooths the output in the time-domain. If you want to be more quantitative (e.g. "how much does it smooth?")... then you'll need to get a high-quality model of a specific device. We can estimate a series resistance and equivalent capacitance for most common diodes, and this stuff shows up on datasheets for high-quality parts. Nimur (talk) 04:58, 16 August 2015 (UTC)

Thanks for the help. I'm using the Vishay TCRT1000 [5] and unfortunately the datasheet doesn't have any timing information on it, nor anything about equivalent resistance or capacitance. My other car is a cadr (talk) 06:00, 16 August 2015 (UTC)

Well, that's a silicon-based BJT phototransistor (in convenient packaging, alongside an infrared LED). You can learn about the standard device model for BJTs. The exact values for the diffusion capacitance are not listed for your transistor: now you can start doing some guesswork, or you can measure it in the lab, or you can try to find a datasheet for a similar part (or replace your part with one whose datasheet is more verbose). A reasonable value for this capacitance is "tiny." Pure BJTs often have transition frequencies in the tens- and hundreds- of gigahertz (example, here's the AT41485, f_T 8GHz, one of HP's famous microwave amplifiers from the last millenium, when they were still making new technology); the parasitic capacitances from the packaging (the aluminum leads on the die; the long lead-wires coming out of the package) will then be the limiting factor. For your purposes - assuming you don't have a ton of lab equipment or a ton of experience doing semiconductor characterization - it might be safe to say "your detector is perfect, compared to any light source you can reasonably find." It is not likely that you can make the input light source switch faster than a few megahertz unless you have some very expensive, very sophisticated lab equipment (like a pulsed laser with some fancy modulation capabilities). If your light source is the LED in the device packsge you already linked ... well, LEDs have loads of capacitance (for the same reasons - it's also a diode, but it's typically going to be much bigger); so your emitter is going to be much slower than your detector. The detector will probably respond faster than that. If you believe otherwise, here's a lab exercise to walk you through the characterization procedure using a vector network analyzer. Nimur (talk) 17:26, 16 August 2015 (UTC)

Its not easy to generalise about optos-- but Ill have a go! It appears from the data sheet that this device is not intended for speed (not that most photo detectors are that fast anyway). If operational limits such as speed need to be known the simplest way to determine them is to measure the devices rsponse using a pulsed current source to drive the diode and monitoring the collector voltage on a scope. You will probably find that the response time depends upon the amplitude of the diode current. For short pulse inputs, I would expect a delayed and reduced output response. Driving the diode at max current will give fastest output response. Notte that falling edge of collector voltage will be faster than rising edge (if in CE config) due to lack of turnoff mechanism in the transistor. Hope this helps.--109.146.20.60 (talk) 13:42, 16 August 2015 (UTC)

Mold on my toothbrush?

I just moved to Austin Texas, a city far more humid and hot than I am used to. I purchased a plastic toothbrush sleeve in the hopes of protecting my toothbrush from the open air. I used the toothbrush last night, put it in the sleeve and went to bed. I forgot to brush my teeth this morning, and tonight when I took the toothbrush out of the sleeve I found that it was still damp; presumably the tight warm space kept it from drying out. This concerns me; this basically means my toothbrush will be perma-damp right? Is that a more likely environment for mold to grow on my toothbrush bristles than if I didn't store it in a sleeve? 2605:6000:EA01:7E00:34C8:9A81:EE57:C9E9 (talk) 09:56, 16 August 2015 (UTC)

Does the "plastic toothbrush sleeve" have holes or other openings for air circulation? Bus stop (talk) 11:11, 16 August 2015 (UTC)

Nope, it's got a bottom that slides out and then it's (relatively) airtight. No obvious holes. 2605:6000:EA01:7E00:7453:3F1C:3F4F:3909 (talk) 19:40, 16 August 2015 (UTC)

Yes, bacteria, mold, mildew, etc., are more likely to grow in a dark, damp environment. I suggest drying it out as much as possible by "flicking" it, then leaving it out (preferably with the bristles in sunlight and far from the toilet), so any germs will die from dehydration. If you want it sterilized, soak it in hydrogen peroxide occasionally (don't use bleach, as it will dissolve the bristles and is dangerous if you forget to rinse if off before use). I also suggest you close the toilet when you flush, as that reduces the germ-filled aerosol which can land of the toothbrush. StuRat (talk) 14:38, 16 August 2015 (UTC)

(Welcome to Austin. Be forewarned this is mild summer weather, due to the effects of the current ENSO / El_Niño :) SemanticMantis (talk) 14:41, 16 August 2015 (UTC)

I also live in Austin, and have done so for close to 10 years. Our toothbrushes sit out in the open in the bathroom - we take no special precautions at all with them, we don't dry them after use, we don't put covers over them - they sit, bristle-end uppermost in a simple toothbrush holder on the bathroom counter-top.

I've never seen mold on any of them, ever.

The heat and humidity can indeed be formidable here (and although this is an unusually humid year - the heat is about what it usually is) - but just about everyone here lives in air-conditioned buildings...which means that the humidity and heat have both been removed from the air in the house.

My house is at 78 degrees and about 10% humidity all year round. So as far as our toothbrushes are concerned, they might as well be being stored in California.

If I saw mold on toothbrushes (at least, in an airconditioned building), in a then I'd be concerned that there are lots of mold spores in the air - which would suggest that there is mold in the walls of the building. There are species of mold in Texas that can be extremely hazardous to health - so this is a concern to take seriously.

SteveBaker (talk) 04:14, 17 August 2015 (UTC)

10% humidity ? I'd predict dry skin, chapped lips, and cracked wooden furniture if you keep it that dry. StuRat (talk) 04:20, 17 August 2015 (UTC)

Be careful, mold is a risk of health. Always keep the toothbrush clean, as dry as possible and always store it vented, during transport in a face cloth. Once molded, impossible to keep clean or longer in use, replace. --Hans Haase (有问题吗) 20:05, 17 August 2015 (UTC)

Update: Yeah, there's mold on my toothbrush now. I'm throwing it out and I'm going to try something different for my new one. The bathroom is not air-conditioned but my room is, so I'm going to try leaving my toothbrush in my bedroom where hopefully the HEPA filter and air conditioner can help keep this one in a better state.2605:6000:EA01:7E00:B82A:19E1:5C26:8846 (talk) 04:04, 18 August 2015 (UTC)

I can't help wondering whether you're making things more complicated than need be. When I lived in Kuala Lumpur, my house was rarely air conditioned. We did have ceiling fans, but the area where the sink was rarely had its fan on, and was only connected to other rooms via doors. We didn't have significant problems with mold on toothbrushes, nor with them drying. In fact, I suspect the mold problem is worse here in Auckland, humidity may be lower, but so are the temperatures and things tend to take a lot longer to dry and many houses even moderns are poorly designed.

The handles of toothbrushes actually can go moldy (at least I presume it's mold), if you keep them way too long, particularly if you store them standing up and the handle lies in water, but this doesn't tend to happen unless you've had them way too long. AFAIK there's fairly strong evidence you should be replacing your toothbrush every 3 months or 6 months at the absolute maximum, and it's probably better to get a cheaper toothbrush and replace it more often then get one of the fancier ones and replace it significantly less often. So if you're getting mold I can't help thinking you're doing something wrong. Well which you were with the container (which sound like the sort of thing intended if you're taking your toothbrush travelling, not for everyday use in a house), but I'm confused if there was a reason why you started doing this.

IMO, provided you store your toothbrush reasonably (i.e. not in standing water and not enclosed), it's not likely to be a problem. The only exception I can think of may be an electric toothbrush, as the bases aren't intended to be replaced often.

Nil Einne (talk) 03:15, 19 August 2015 (UTC)

Finding news

I have a 9 y.o. nephew to whom I occasionally email news articles about space related things. Due to my own interest in the field and New Horizons, finding articles to send him has been no problem. While he was in town recently, I asked him if there was anything else he wanted to learn about or was interested in. He and his 6 y.o. brother, who I guess also watches the videos and looks at the pictures and such, asked for news about volcanos. I'm at a bit of a loss on that front as to where to get links to send. Geology isn't as interesting to me as astronomy, so I'm not that knowledgable on where to look. I can get some links from USGS.gov but beyond that, I'm not sure what other good sources are out there. Would anyone like to provide me with references to some sites that I might check? Thanks, Dismas|^(talk) 10:01, 16 August 2015 (UTC)

The Smithsonian's Global Volcanism Program site is useful for current eruptions. Mikenorton (talk) 11:07, 16 August 2015 (UTC)

To cover another angle, on a whim I poked around to see what NOAA puts up about the effects of volcanos. They have lots of cool interactive maps [6], animations, and movies [7] [8]. Searching /NOAA volcano/ will get you many other quality resources, though some of the pages will definitely require some adult supervision to point out the fun/interesting parts. SemanticMantis (talk) 14:35, 16 August 2015 (UTC)

For volcanoes, they only occasionally qualify as news, when one erupts in a spectacular fashion, especially near where people live. You might include historic volcanoes, like footage of Mount St Helens, those in Iceland, or even the accounts of Mount Vesuvius then (when it destroyed a couple Roman cities) and now. The Hawaiian volcanoes are less dangerous, so don't make the news much, but do erupt quite often. You might also explain how the entire state was formed by volcanoes. StuRat (talk) 14:46, 16 August 2015 (UTC)

Here's one he could keep an eye on. Ghmyrtle (talk) 14:55, 16 August 2015 (UTC)

And NASA Earth Observatory has some interesting posts; Earthquake Births New Island off Pakistan for example. Also BBC Science - Volcanoes has a good video gallery. Alansplodge (talk) 16:16, 16 August 2015 (UTC)

• Not volcano-related, but this really cool website: LightningMaps.org shows real-time lightning strikes world-wide. As soon as you hear thunder locally, it is a really cool place to check, with the location of flashes and the expanding circle of the sound front depicted over zoomable maps.

Also, have him check out the unique volcano Ol Doinyo Lengai, the world's coldest, whose lava looks like very fluid silverish mud, which you can only see glowing at night. Here are a bunch of videos at youtube. μηδείς (talk) 17:01, 16 August 2015 (UTC)

I read Pangea, the website of the Stanford University Earth, Energy, and Environmental Science department. They have a news section (it's not a daily update, but earth science is a slow moving subject!) The website tends to emphasize local departmental goings-on, but researchers at the department cover all kinds of internationally-interesting topics. As an example, the website presently features a volcano story: Italian supervolcano research featured on cover of Science. Original story, Volcanic rocks resembling Roman concrete explain record uplift. Nimur (talk) 17:12, 16 August 2015 (UTC)

Thank you, everyone, for all the links. I'll check them out when I get a chance. There are quite a few!

As far as the adult supervision is concerned: The boys live a few hours away from me, so I don't have that much chance to talk to them face to face. I just send the links to the articles and maybe include a couple sentences about what I feel is significant in the article/video/etc. (sometimes it's a YouTube link). Then, while the younger of the boys is at karate practice, their mother will pull up the article on her phone. She and the older boy will read the articles together. That way she can help with bigger words and concepts. I'm not sure how the younger one gets involved. He said a few things when they came to visit this summer that lead me to believe that he was following along with the articles as well. I didn't ask him for specifics though and I haven't had a chance to ask their mother.

Thanks again, Dismas|^(talk) 04:45, 17 August 2015 (UTC)

There is also http://www.volcanodiscovery.com. Looie496 (talk) 12:52, 17 August 2015 (UTC)

How far can you smell a slaughterhouse?

Downwind and upwind? Sagittarian Milky Way (talk) 15:28, 16 August 2015 (UTC)

Upwind could be zero distance, if the wind is faster than the smell would spread with no wind. Of course, there could be eddy currents (that article seems to be strictly about the electrical sense of the word, unfortunately) that complicate matters.

Downwind, from the manure in a cattle feed lot I had to drive by, it seems the answer is on the order of 10 miles.

Also, I suppose it is theoretically possible to make a slaughterhouse which doesn't smell at all, if the trucks carrying the animals are all sealed (you'd then need them to be refrigerated and have oxygen tanks and carbon dioxide scrubbers, to keep the animals from dying from heat or asphyxiation on the way there), the waste material is all burned in a high temperature incinerator, etc. Presumably, though, such a design would not be cost effective. StuRat (talk) 15:48, 16 August 2015 (UTC)

(edit conflict) Some research on the odour from pig farms: Characterization and Dispersion Modeling of Odors from a Piggery Facility shows on page 8 of the file that both hydrogen sulfide and ammonia are still able to cause "annoyance" at 2 km from the fence-line of the facility. Another pig-related research paper discusses the effect of wind direction; DEVELOPMENT OF THE OFFSET MODEL FOR DETERMINATION OF ODOR-ANNOYANCE-FREE SETBACK DISTANCES FROM ANIMAL PRODUCTION SITES: Part I, and Part II but it's a bit beyond me I'm afraid. Alansplodge (talk) 16:01, 16 August 2015 (UTC)

That first study only went up to 2 km, and found a 46% chance of humans detecting hydrogen sulfide and 29% chance of detecting ammonia at that distance. If I smelled something bad that often, I sure wouldn't want to live there. StuRat (talk) 16:41, 16 August 2015 (UTC)

Live there! Most people don't even want to drive near it! Here's a write-up on The Odor Issue, from North Carolina State University's agriculture extension program. In agricultural areas, and at abbatoirs, odor is a serious legal and policy issue. A surprising amount of research and technology has gone into reducing impact, for health and aesthetics reasons. You might look into Slaughterhouse Blues, written by professors from the University of Kansas, for an overview of the ethical and legal issues on this subject.

You can also read Beef, from Farm to Table, a web publication of the Food Safety Inspection Service, part of the United States Department of Agriculture, the government agency responsible for regulating and inspecting beef abbatoirs in the United States. Their website explains legal requirements for slaughterhouse standards.

Nimur (talk) 18:54, 16 August 2015 (UTC)

What is that in the fridge?

http://i62.tinypic.com/2lvz6yq.jpg — Preceding unsigned comment added by 157.157.90.195 (talk) 20:22, 16 August 2015 (UTC)

Hard to see, but looks like some kind of drain plug with something black tied around it. Since the plug is on the back, but not quite at the bottom, I would guess it's for draining it during the manufacturing process, when the fridge is on it's back, presumably after it has been power washed with machinery. StuRat (talk) 20:41, 16 August 2015 (UTC)

[ec] This is an important part of the Auto-defrost mechanism. Ice tends to build up on the cold plate at the back of the fridge, so the fridge periodically heats up the cold plate to melt the ice. The water runs down the channel and out through the hole (and on to the hot compressor, where it evaporates). The green thing is to prevent the hole getting blocked with ice (or other unpleasant substances that can be found in fridges). You should wiggle it up and down every few months to make sure the hole is clear (or when the hole gets blocked and you find a pool of water on the fridge floor). Tevildo (talk) 20:42, 16 August 2015 (UTC)

Thank you! — Preceding unsigned comment added by 157.157.90.195 (talk) 21:31, 16 August 2015 (UTC)

Behind the hole a hose guides the draining condensing water to the motor to evaporate it there. Any object in the hose might be something else or a brush to clean the hose. --Hans Haase (有问题吗) 19:40, 17 August 2015 (UTC)