Wikipedia:Reference desk/Archives/Science/2011 March 16

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

March 16

Possible causes for temporary blindness due to car crash

Rest assured I`m not asking for the dreaded medical advice, it is for short story I`m writing for school. I need to know if there is any kind of traumatic injury (after say crashing car head on in a tree or a metal pole) that would cause temporary blindness and doctors would be almost certain the induvidual will recover fully stright away ~~Xil (talk) 03:51, 16 March 2011 (UTC)

It would be possible, impact to the optic nerves or part of the brain. Graeme Bartlett (talk) 04:42, 16 March 2011 (UTC)

Yes, but why - hemorrage (I suspect that would rather cause something similar to stroke), inflamation or what? ~~Xil (talk) 06:45, 16 March 2011 (UTC)

This paper cites a study into 10 patients with blunt trauma injuries (mostly caused by crashes) that caused blindness (14 eyes in all, I assume some suffered blindness in both eyes, other only in one). It says that in most cases the blindes was caused by swelling of the optic nerve, but also stated that in three cases a fracture in the optic canal wall was the cause of blindness. [1]. I must admit that I have only read the brief summary, but that alone seems to provide a useful basic insight into your question. Darigan (talk) 12:35, 16 March 2011 (UTC)

Judging by the summary those aren`t cases of temoprary blindness (it makes it quite clear that patients needed medical intervention to spare their vision). For this case, I need patient to expierience emotional trauma, which makes him rethink purpose of life, not have lasting damage. Just something that would sound pausible, I don`t want to write about something that would kill him in reality ~~Xil (talk) 14:17, 16 March 2011 (UTC)

Anything that could cause blindness is likely to have a high chance of being fatal without medical treatment. Having his eyesight restored by medical treatment should work for your story. --Tango (talk) 01:43, 17 March 2011 (UTC)

It is not question of receiving medical help or not, it`s just that I don`t want major brain surgery in the story. I need doctors saying that the problem will sort itself out in few weeks and patient freaking out at chance that doctors might be wrong. Such conditions exist outside of realm of soap operas? ~~Xil (talk) 13:52, 17 March 2011 (UTC)

Which salt water, with a lot of salt or little salt, absorbs heat more quickly?

I may be not looking at answers — Preceding unsigned comment added by Like sushi (talk • contribs) 04:16, 16 March 2011 (UTC)

At a given temperature, the thermal conductivity of salt water decreases with increasing salinity.[2] Red Act (talk) 17:55, 16 March 2011 (UTC)

Thank you.Like sushi (talk) 02:42, 17 March 2011 (UTC)

Real E.T. or Hoax

Is this news real ?  Jon Ascton  (talk) 04:39, 16 March 2011 (UTC)

Yeah, right. 75.57.242.120 (talk) 04:54, 16 March 2011 (UTC)

Mierda del toro... --Jayron32 05:18, 16 March 2011 (UTC)

My poor uncle. -- Toytoy (talk) 05:57, 16 March 2011 (UTC)

Yes, that's really "news" (unfortunately). But you don't really think it's about a real baby alien, do you? WikiDao ☯ 16:16, 16 March 2011 (UTC)

remote controlled helicopter

Is there such a thing as a remote controlled helicopter, basically a regular helicopter with servos connected to the controls? Could they rig some up in a hurry over there in Japan, to overfly those reactors and dump stuff on them without irradiating human pilots? Just wondering. 75.57.242.120 (talk) 04:50, 16 March 2011 (UTC)

Dumping stuff on them wouldn't do much, it would just roll off. The outer container is not very hot, it's the internal one that is, so they need to pump water inside. That said, they certainly can do it remote if necessary. But it's not necessary - the radiation is still pretty low, so a regular fire-fighting helicopter could overfly, dump, and continue and be exposed to almost nothing. Ariel. (talk) 06:04, 16 March 2011 (UTC)

Could they rig some up in a hurry? No, aircraft modifications are not undertaken lightly, and especially not the sort of modification required to convert a conventional heavy-lift helicopter into an un-manned helicopter. A modification project of this kind would involve design, manufacture of parts for the modification, installation of the parts, and then extensive testing and fine-tuning, mostly at light weights. Then there would need to be testing and fine-tuning at heavy weights. It couldn't be done in the sort of time-frame that would interest the people grappling with the Japanese reactor problems. Dolphin (t) 06:24, 16 March 2011 (UTC)

They would use these: Helicopter bucket, they already exist (if Japan doesn't have any I'm sure they could be brought). No need for any time consuming design. Ariel. (talk) 09:31, 16 March 2011 (UTC)

Thanx. I know that Chernobyl liquidator helicopter pilots (they dumped concrete over the burning reactor) got considerable radiation exposure and I think some of them died of related illnesses. That's why I asked about remotes. The R/C helicopter article is about little tiny models that don't count for this, though they might be good for photography, sensors, etc. Also I wonder if the USS Reagan (aircraft carrier off Japan) has any UAV's (Predators or whatever) on board. Yeah, Dolphin51 is probably right about modification, even though there is a 30 km no-fly zone around the reactor right now, so I'd think they could suspend normal aviation rules. I wasn't thinking of any fancy stuff designed specially for the helicopter, just some servos or off-the-shelf industrial robot arms, bolted into the pilot's seat and operating the controls. This doesn't seem terribly hard to do with automobiles but I can see how aircraft could be more complicated. 75.57.242.120 (talk) 07:21, 16 March 2011 (UTC)

Re dumping stuff: they are talking about using fire hoses to shoot water into the hole in the roof of the building that exploded, to refill the spent fuel pool which has been boiling from decay heat. Apparently it is exposed from above. 75.57.242.120 (talk) 07:23, 16 March 2011 (UTC)

Actually they are dumping stuff already (can't find a RS but it was on the news in the past 30 mins or so and also mentioned on BBC's twitter [3]) even if they ruled it out a few hours ago [4] [5] perhaps a reminder in an ongoing crisis where things can change rapidly it's wise to be carefully when saying something like 'they won't do that' or 'that won't happen'. Note on BBC it does according to NHK TV "the helicopter can't stay too long over the plant because of the risk of radiation to the crew" Nil Einne (talk) 08:20, 16 March 2011 (UTC)

Well, remotely operated helicopters seem potentially useful for firefighting and other unsafe activities, so even if they can't be built soon enough to deal with this nuclear incident, maybe they're something the aircraft makers could work on. 75.57.242.120 (talk) 10:30, 16 March 2011 (UTC)

There are already helicopter-style UAVs such as the Northrop Grumman MQ-8 Fire Scout. However, they don't seem to have the lifting capacity of manned helicopters yet. --Colapeninsula (talk) 11:15, 16 March 2011 (UTC)

Latest news now of course is that the plans were abandoned due to fears of radioactive contamination for the crew Nil Einne (talk) 12:01, 16 March 2011 (UTC)

The radiation levels are rising and falling as things change at the plant. You might see a burst of radiation as a steam vent opens, causing the crew to evacuate, then have the wind blow the steam out to sea, causing the radiation levels to fall and letting the crew return. --Carnildo (talk) 20:12, 16 March 2011 (UTC)

I haven't read anything suggesting the helicopters will be back. Edit: Should have taken my own advice [6]. (I admit even when posting the first time I was suprised no one was talking about trying again later but since I still never heard anything I decided there must have been something I was missing.) Even so it still demonstrates the idea that there was no reason to use a remote controlled helicopter seems to have been incorrect. Nil Einne (talk) 21:56, 16 March 2011 (UTC)

I'm disappointed. I would have thought that sometime during the Cold War the U.S. military would have thought up a way to radiation-proof a helicopter. I suppose we're probably just as badly prepared for a nuclear war as we would be for a disaster like this. Wnt (talk) 00:06, 17 March 2011 (UTC)

Radiation-proofing a helicopter would basically involve lining it with thick sheets of lead. That is very heavy - not a good thing in an aircraft. You would also need to make it air-tight and fit appropriate ventilation systems. While all of that could be done, it would make the helicopter extremely inefficient when operating away from radiation. Building helicopters for use only in high-radiation situations would be very expensive for fairly small gain. The gain right now would be quite big, but situations like this one are extremely rare. --Tango (talk) 01:39, 17 March 2011 (UTC)

Hmmm - so you think the limits on the helicopter are truly from direct radiation exposure and not from the contamination of personnel through the air? I'd assumed otherwise (I was just thinking you could seal it and filter the air thoroughly) but I don't actually know. Wnt (talk) 06:53, 17 March 2011 (UTC)

Thanks,the Fire Scout is the kind of thing I was wondering about. I wonder why they're not using them. It does look like they've sent some fixed-wing drones.[7] 75.57.242.120 (talk) 00:47, 17 March 2011 (UTC)

Because as per Colapeninsula they're puny things which couldn't deliver significant amounts of water presuming they could be reliable fitted to lift any water? (Probably because they weren't intended to lift things.) It also sounds like they don't have many and are still basically in testing. Nil Einne (talk) 04:46, 17 March 2011 (UTC)

According to the link you provide, the drone in question is the Northrop Grumman RQ-4 Global Hawk. It's got a payload capacity of 3000 pounds, but it's entirely internal storage. Even if you could refit it to carry a water bucket, that's only about 300 gallons, which would have essentially no impact. --Carnildo (talk) 23:19, 17 March 2011 (UTC)

The Global Hawk was used for recon, IR photography etc. Wasn't suggesting using it for water. The way to use the Fire Scout would probably be to lower one end of a hose into the building, and bring the other end to a safe distance away so water can be pumped through it. It now looks like they're doing something like that with a construction crane instead. They have also got some mobile robots on the way, which seems like it's about time. I wonder if this incident will speed development of remote-operated heavy equipment in general, such as cargo helicopters. 75.57.242.120 (talk) 08:22, 19 March 2011 (UTC)

Question about light clocks/ time dilation?

Let we have the following three clocks in a spaceship which is moving close to the speed of light.

Clock 1 is AB long which is perpendicular to the direction of ship. Clock 2 is CD and Clock 3 is EF long. Both 2 &3 are along the direction of spaceship such that 3 is just above No.2. Distance between A&B, C&D and E&F is L = distance covered by a light in one second. 

Now in order to analyze time dilation for one second a pulse is fired at the same time from 

From A towards B in Clock 1

From back of the ship "C" to it's  front "D" in Clock 2

From the front of the ship "E" to it's  back "F" in Clock 3 

For inside observer: 

Clock1- experienced a perpendicular of the right angle triangle of time dilation diagram. 

Also a pulse fired from the back of the ship to the front would take the same amount of time as a pulse fired from the front to the back. 

For outside observer:

Clock1-observed  a hypotenuse of right angle of time dilation and hence experienced more time than inside observer for the same clock.

Clock2- observed a very small fraction of distance covered by a pulse due to the high speed of ship in the same direction. Thus experiencing more more more and more time than inside observer for the same clock.(so slow even if length contraction is ignored)

Clock3- notice a very short time due to the rushing of back of ship and hence experienced a less time as compared to inside observer. This means time is contracting in this case for him (so fast even if length contraction is added)

So are their differences wrong?74.198.150.229 (talk) 06:34, 16 March 2011 (UTC)khattak#1-420

The one-way times are all different, as you noticed, but the round-trip times are all the same. -- BenRG (talk) 08:57, 16 March 2011 (UTC)

(ec)You hit onto one of the fundamental consequences of the Theory of Relativity, namely that there is no global simultaneity. The order of events (and hence, possibly, causality!) depends on the frame of reference of the observer. Our article on relativity of simultaneity has more. In other words, an observer in the middle of the space ship who shoots light beams at mirrors in the front and the back will observe them hitting the walls at the same time. A outside observer not co-moving with the ship will see the front and the back beam hit at different times. --Stephan Schulz (talk) 09:01, 16 March 2011 (UTC)

Here's a link to that article: Relativity of simultaneity Red Act (talk) 09:33, 16 March 2011 (UTC)

I don't want discuss it further because I know the wikipedia rules but sounds like I didn't explain things clearly enough for you understand my question therefore it behooves me to try it the other way.

Let we have the following arrangement.

Mirror at the back of ship is B, Mirror at the middle of ship is M, Mirror at the front of ship is F

For on board observer pulses are back and forth in between BM and FM at the same time. Each cycle is same for him. Cycle means back and forth distance covered by pulse in either BM or FM.

Let study the two cycle of aforementioned pulses for outside observer not co- moving.

Cycle 1

Between B&M- pulse would hit B very early and then reflected very very slowly towards M

Between M&F- Pulse would be moving very slowly towards F and will be reflected towards M when it hit F. 

Since for onboard observer, cycle 1 is completed earlier than outside observer and for him pulses are ready again towards B &F while for outside observer cycle1 is yet to be completed. So here is my question?

Why would outside observer see two pulses in between B&M (one which is lag behind for him in cycle1and other from cycle2 of onboard observer) and similarly two pulses between F&M. 

This means number of pulses increases per cycle ( of on board observer) for outside observer if he had the opportunity to observe all.  So is this parallax for out side observer who is not co-moving? 74.198.150.229 (talk) 18:38, 16 March 2011 (UTC)khattak#1-(ec)

It seems to me that you are failing to distinguish the time as measured by one observer from the time as measured by the other observer when you say "Since for onboard observer, cycle 1 is completed earlier than outside observer". These are different times measured by different observers and it makes no sense to say that one happens earlier than the other. Dauto (talk) 19:53, 16 March 2011 (UTC)

The reasons why I'm thinking eccentrically is that if we fired a pulse from the back of spaceship towards its front then onboard observer will see a pulse leave a ship through it's front in one second (if the length of the ship is one light second) while an outside observer will find it in very slow motion inside ship because both a pulse  and a ship are moving almost at the same speed. Therefore for him a pulse would take hours hours ...... to reach the front of ship.

Therefore to me it sounds like round trip wouldn't be same for both observers because ship and a pulse are almost at the same speed if traveling in same direction. This is my last reponse to this question therefore pls don't consider this for warning. Thanx —Preceding unsigned comment added by 74.198.150.213 (talk) 22:44, 16 March 2011 (UTC)

The round trip won't last the same for both observers. It will be time dilated for the external observer. I don't think the wikipedia police will come knocking at your door if you chose to post one more response to that question. Dauto (talk) 23:39, 16 March 2011 (UTC)

With respect to the moving frame, the distance between the mirrors is L/γ, where γ is the relativistic gamma factor ($1/{\sqrt {1-v^{2}/c^{2}}}$). The time for the light to cross this distance moving with the ship is ${\frac {L}{\gamma \,(c-v)}}$, which is large if v ≈ c. The time for it to cross in the other direction is ${\frac {L}{\gamma \,(c+v)}}$. The sum of these is

${\Bigg (}{\frac {L}{\gamma }}{\Bigg )}{\frac {(c-v)+(c+v)}{(c+v)(c-v)}}={\frac {2L}{\gamma \,c\,(1-v^{2}/c^{2})}}=\gamma {\frac {2L}{c}},$

which is γ times the round-trip time in the rest frame. -- BenRG (talk) 00:58, 17 March 2011 (UTC)

Cooling the inside of the building

About Japanese nuclear accident.

Wouldn't it help to cool it down with liquid nitrogen and oxygen?

If the supression pool is broken, though hopefully not, it would work more.

I may not be looking at answers. — Preceding unsigned comment added by Like sushi (talk • contribs) 07:30, 16 March 2011 (UTC)

Liquid oxygen is best kept away from nuclear reactors - or, for that matter, barbeque grills!^[8] Supposedly, if you soak the charcoal with oxygen before lighting, you can even get a sizeable explosion. Liquid nitrogen would be very cold, but it doesn't actually have as much heat capacity as water, so there's not so much of an advantage ... though it would put out a fire. Wnt (talk) 08:00, 16 March 2011 (UTC)

Sorry, I seem to have forgotten to write the most important.

I would say the air inside the building to be replaced with mixture of liquid nitrogen and oxygen. — Preceding unsigned comment added by Like sushi (talk • contribs) 08:30, 16 March 2011 (UTC)

I mean, in evaporated form. — Preceding unsigned comment added by Like sushi (talk • contribs) 08:42, 16 March 2011 (UTC)

Er you mean oxygen and nitrogen gas? Nil Einne (talk) 09:01, 16 March 2011 (UTC)

I fail to see how it would be diffrent from mix of oxygen and nitrogen 84.52.26.118 (talk) 09:06, 16 March 2011 (UTC)

I suppose so.

If it is generated from liquid nitrogen and oxygen, it would be still very cold, I think. — Preceding unsigned comment added by Like sushi (talk • contribs) 09:05, 16 March 2011 (UTC)

In case it's not clear, the air inside the building, not the pressure vessel. — Preceding unsigned comment added by Like sushi (talk • contribs) 09:41, 16 March 2011 (UTC)

On second thought, if the suppression pool is broken, the water in the pool may freeze, and the effect of it, I do not know. — Preceding unsigned comment added by Like sushi (talk • contribs) 09:58, 16 March 2011 (UTC)

I don't think that is likely. I don't actually understand what you think is going to happen but you still have the problem Wnt mentioned of little heat capacity. It's even worse now since you don't even have much of it. It seems a bad idea to try to have a highly pressured mixtured in the containment vessel for many reasons. So presuming you're keeping it atmospheric that means you end up with ~ 1.3kg/cubic metre. I don't know the volume of the containment vessel but even if it's 1000 cubic metres that's only 1300kg you're putting in, a relatively tiny amount of a lower heat capacity then water substance. Plus the heat isn't even going to transfer well. Not to mention if you're talking about the spent fuel storage pond isn't one of the problems that they're now exposed to air? Are you planning to replace the earth's atmosphere with 'evaporated liquid nitrogen and oxygen'? Nil Einne (talk) 10:58, 16 March 2011 (UTC)

Looking at Heat capacity#Table of specific heat capacities,

although columns for Volumetric heat capacity are left blank,

in "mol"-related columns, which seems to have something to do with volume,

"Water at 100C (steam)" is, in value, only less than 1.5 times than that of nitrogen and oxygen.

Heat transfer#Convection says "Convection is usually the dominant form of heat transfer in liquids and gases.",

and mentions Newton's law of cooling, "The rate of heat loss of a body is proportional to the difference in temperatures between the body and its surroundings."

If the temperature of 'evaporated liquid nitrogen and oxygen' is so close to absolute zero,

I think we can assume at least additional 300C difference in temprature

(, assuming steam of water to be over 100C),

and if (the body's temperature - temperature of steam of water) is smaller than

2/3 of (the body's temperature - temperature of 'evaporated liquid nitrogen and oxygen')

I don't think there isn't a chance.

And I don't know if the buildings' state is so bad to let the vapor

(of water or of nitrogen and oxygen) easily out. — Preceding unsigned comment added by Like sushi (talk • contribs) 13:42, 16 March 2011 (UTC)

It seems like you intend to replace air with very cool air? Perhaps using liquid nitrogen in air conditioner would work somewhat better - probably you can keep it from evaporating that way ~~Xil (talk) 13:56, 16 March 2011 (UTC)

I don't know what suggestion "using liquid nitrogen in air conditioner" is,

but if it is to bring a lot of air conditioners to the site, it seems to take a lot. — Preceding unsigned comment added by Like sushi (talk • contribs) 14:18, 16 March 2011 (UTC)

I think the point you are missing is that the objective is not just to cool the fuel rods, but to *keep them* cool - they are continually generating heat. So you need a constant supply of coolant. Water is a good coolant because it has a high heat capacity by volume, good thermal conductance and is readily available in large quantities - which, ironically, is why reactors are often built near the coast. Gandalf61 (talk) 14:09, 16 March 2011 (UTC)

I think keeping the temperature of the air (or vapor) inside the building as low as 0C,

wouldn't hurt, except for ones working in it,

because water doesn't freeze at 0C, if containing a little salt. — Preceding unsigned comment added by Like sushi (talk • contribs) 14:57, 16 March 2011 (UTC)

No matter how much salt you add, you can only lower the freezing point a dozen or two degrees...LN2 temperatures will quickly freeze it either way, during which the volume will expand for a while and likely break various vessels containing it. That's...bad. I think you are missing the truly enormous scale of the situation. Even though LN2 temperature is very low, a gas at that temperature is simply not good at cooling the huge amount of solid and liquid high-temperature materials. And once it does warm up, it no longer helps--in fact it would have to be continually replaced because the reactor components are not just "hot" but are "continuously generating more heat". If you put ice cubes in a pan in a hot oven, they will melt and cool the pan. But if the oven is on, the pan will still get hot, boiling away the water (heating the coolant solid -> liquid -> gas -> hot gas) and now you have...nothing except the same hot pan where you started. DMacks (talk) 15:31, 16 March 2011 (UTC)

The last comment was not about cooling the air (or vapor) to near absolute zero,

but to 0C.

I didn't think in a way that just inside the building is as highly pressured as the inside of the pressure vessel,

so, at least then, didn't have reason to think pushing away the air (or vapor) with colder (or cooler) one hurts. (Again, except for ones who are working in it.) — Preceding unsigned comment added by Like sushi (talk • contribs) 16:08, 16 March 2011 (UTC)

No, that is not what I meant, you may want to explore how air conditioner works, but esentialy my idea is that you would have pipes filed with liquid nitrogen, rather than releasing it in the buliding where it would evaporate and escape the building (unless it is hermeticaly sealed, which seems unrealistic) ~~Xil (talk) 16:33, 16 March 2011 (UTC)

This seems bold, but do you mean by "pipe", the pipe in which primary coolant is?

(I do not know if there is secondary coolant)

No, I mean, instead of filling room with nitrogen and oxygen (note that it is what air is made of, so once it evaporates all you will get is somewhat cooler air), you would have piping filled with constantly liquid nitrogen, which would cool the air around it ~~Xil (talk) 01:11, 17 March 2011 (UTC)

Would it transfer heat, I mean, coldness as quickly as by making it a vapor?

If the pipe is directly made in contact with the body, it would work very well.

Making it in vapor can be done from relatively far from the body, for the safety,

and doing both, though with less efficiency, would work more

Like sushi (talk) 01:40, 17 March 2011 (UTC)

Pipes, can they be soaked into glue-ish substance for making it possible to stick to the body, even if thrown from far apart?

(It may be a silly idea, though)

Like sushi (talk) 01:56, 17 March 2011 (UTC)

Per the above discussion, one of the plans was to try to dump water from a helicopter. Another one is/was? to shoot water from a police or fire water canon. I think it's clear such a structure is not going to keep air/oxygen/nitrogen/water vapour/whatever in very well... Nil Einne (talk) 21:55, 16 March 2011 (UTC)

At least at the time it was constructed, the building seems to have been meant to serve as one of the sealing in emergency.

Like sushi (talk) just before 23:42, 17 March 2011 (UTC)

I'm confused now. Are you suggesting they should have kept it with an evaporated liquid nitrogen/oxygen atmosphere all the time? I thought the question was how to cool it right now since they were clearly not having a problem cooling it before the current problems and you specifically mentioned the nuclear accident and in the specific post I was replying to you said 'And I don't know if the buildings' state is so bad to let the vapor' (which was in reply to me saying 'they're now exposed to air' although I admit now exposed to the atmosphere was what I was intending). BTW can you please sign your posts with four tildes ~~~~ to avoid confusion. Nil Einne (talk) 23:42, 16 March 2011 (UTC)

I just don't know how much the building is damaged, and if all the buildings are damaged, I mentioned the intention at the time of construction to suggest, if the damage is not all over, it may still serve for a little goodLike sushi (talk) 00:35, 17 March 2011 (UTC)

There are pics in the article on the accident, quite obviously walls and roof are gone ~~Xil (talk) 01:14, 17 March 2011 (UTC)

Most of the relevant buildings have recently exploded, so I think it is safe to say they are significantly damaged! --Tango (talk) 01:32, 17 March 2011 (UTC)

It looks at least 3 and 4 plants have no roof nor wall, by the picture.

Like sushi (talk) 01:40, 17 March 2011 (UTC)

I may be just becoming so desperate, so take this with a bunch of salt.

Would berrying the reactors in a lot of (presumably iron or steel) pachinko balls help?

As iron or steel seems to have high thermal conductivity,

and it would still leave (small, but not no) room for water to enter,

and would enlarge the surface area of matters with relatively high temperature

(because heat capacity of iron or steel is small),

which may make it easy for pumped water to deprive heat.

(Even if it seems so nice, do not jump on it, everyone,

it wouldn't take many people to check this idea.)

Like sushi (talk) 05:34, 17 March 2011 (UTC)

Explanation: I am thinking in a way like,

pachinko balls may "take away" heat

from relatively small surface area of container vessel (?)

to relatively large suface area of the balls

more quickly than air (or vapor) does.

(Though air is gas and flows freely, so I am losing hope in it,

and anyway, I don't have a way to even personally judge which is better)

Like sushi (talk) 05:59, 17 March 2011 (UTC)

what happens if signal peptidase malfunctions and fails to cleave the signal sequence?

Does it usually hinder the function of the produced protein? John Riemann Soong (talk) 08:38, 16 March 2011 (UTC)

Well, it depends by what you mean "function". The (endoplasmic reticulum) signal peptide is a transmembrane domain, and the protein isn't going anywhere without some kind of cleavage. (I should add, though, that signal peptidase has quite a few homologues, and the options for cleavage by various enzymes at various points can become complicated - things like amyloid precursor protein can be cut in many ways, with significant effects) But if you just want protein activity, it isn't uncommon for a tethered protein to work the same way as an untethered one. But any individual protein may have its own quirks. Wnt (talk) 15:10, 16 March 2011 (UTC)

Flocking birds in SE England

A large flock of European starling in England

In the last couple of days I've noticed at least two large flocks of birds wheeling about the sky, here in south-east england.

Would they be flocking because they've just arrived (from Scandinavia, Europe, Africa?) Or are they preparing to leave (to Scandinavia, Europe, Africa?) Or is it impossible to tell? Is it possible infer anything else about these flocks or birds? Thanks 92.29.117.90 (talk) 13:02, 16 March 2011 (UTC)

Any bird species in particular? Given that it is spring they probably were wintering in England and now are prepering to migrate to north ~~Xil (talk) 13:39, 16 March 2011 (UTC)

Sorry I was too far away to identify them. How can you telling they are departing rather than arriving? Thanks. 92.29.117.90 (talk) 13:48, 16 March 2011 (UTC)

I believe there is no need for them to flock when arriving, they would rather spread out once they are close to the destination. Assuming, of course, that they flock because of migration, not some other reason ~~Xil (talk) 14:08, 16 March 2011 (UTC)

Perhaps European starling - see image. Although the sight is becoming less common as bird numbers decrease, this is a well known but poorly understood feature of starling behaviour. More information here. Ghmyrtle (talk) 13:49, 16 March 2011 (UTC)

PS: Starling flocking has nothing to do with migration. Ghmyrtle (talk) 14:55, 16 March 2011 (UTC)

Here in south central UK starlings are still wheeling about in huge murmurations before settling to roost for the night. If memory serves they will reduce in size pretty soon as they start nesting but will be back at it again in the autumn. Richard Avery (talk) 16:24, 16 March 2011 (UTC)

Does that mean they are not preparing to migrate, but are British starlings who behave like that during the winter? Dosnt flocking make it difficult for them to find enough food? Thanks 92.15.26.91 (talk) 20:49, 16 March 2011 (UTC)

Flocking in birds etc, and similar behaviours (schooling in fish and other marine organisms, herding, swarming - I notice our articles on these subjects could use some improvement) is thought to some extent (and variably with each case) to be a protection against predators. Each individual flock member decreases its chances of being predated by surrounding itself with many other targets, and some predators are confused by an over-profusion of targets.

Starlings and similar birds tend to exhibit this behaviour more in the winter months when food is scarcer and 'following the flock' may increase the chances of finding at least some food, which may also tend to be concentrated in small areas like recently harvested, ploughed or sown fields, of stands of seeding trees etc, and when they are not competing for nesting places. In the spring and summer the wider and more plentiful availability of food enables them to disperse and stake their own more individual nesting and foraging territories. Other bird species pursue other strategies, there being several viable niches in the environment. {The poster formerly known as 87.81.230.195} 90.197.66.165 (talk) 22:38, 16 March 2011 (UTC)

A good video here. Alansplodge (talk) 03:12, 19 March 2011 (UTC)

Arrow of time

I was watching a BBC programme (Wonders of the Universeand the presenter was talking about the arrow of time. He seemed to say that time goes in one direction but nobody knows why. How would you know if time was reversed and if time doesn't continually head in one direction would it even matter? --BlackberryPicking (talk) 13:03, 16 March 2011 (UTC)

If direction of time reversed, the entropy of the universe will tend to decrease with time. i.e. heat will flow from cooler bodies to hotter bodies. Generally the energy of the universe(which is conserved regadless of the direction of time) will be concentrated in fewer particles over time. Diwakark86 (talk) 13:54, 16 March 2011 (UTC)

That's a silly program. There is really no mystery about the time's arrow. It is a tricky thing but it is well understood. To answer your question, don't you think you would notice a river flowing up river and then raining backwards into the sky while you got younger over the years like Benjamin Button? Dauto (talk) 13:46, 16 March 2011 (UTC)

Entropy is the reason for the arrow of time I believe. That programme, like so much on evening TV, seems designed for kids or young teenagers in its vocabluary, intellect, slow delivery, and its new-information/waffle quotant. (Television presenters should model themselves upon Patrick Moore in my opinion). I don't think you would notice any theorectical reversals in time as your brain would be reversing as well. 92.29.117.90 (talk) 13:52, 16 March 2011 (UTC)

I watched the program in question and it was actually reasonably good. (Brian Cox has appeared on The Sky At Night, if that improves his credibility with you!) It is a difficult concept to get your head around, so it isn't surprising that someone wouldn't understand it the first time it was presented to them, however good that presentation would be. --Tango (talk) 15:17, 16 March 2011 (UTC)

Agreed. There is no great mystery about the arrow of time. Percieved time goes in the direction of increaisng entropy, by definition. You cannot remember the future because memory (either biological or non-biological) involves observing a current state (which includes the memory) and infering another state which we call the "past" - but the inferred state must be one with lower entropy than the present, otherwise there are too many "choices" to make an inference. Therefore the perceived past must, by definition, have a lower entropy than the present. In a universe with constant entropy there could be no memories, and hence no perceived past or direction of time. In other words, asking why time never goes backwards is like asking why things never fall upwards. See Entropy (arrow of time) for more details. Gandalf61 (talk) 13:59, 16 March 2011 (UTC)

The arrow of time considered in isolation doesn't make much sense. Time doesn't really have a direction. Time just is. When people talk about the arrow of time, they are relations between different things that give time a direction. The most obvious one is human memory. We remember the past, we don't remember the future ("the pyschological arrow of time"). You then try and explain why other things go in the direction they do, relative to the psychological arrow. For example, why, when we see a broken egg do we often remember it when it was intact but, when we see an intact egg we never remember it when it we broken? It all comes down to the concept on entropy, which is what Brian Cox spent most of that program talking about. The universe started out in a highly ordered state (we don't really know why) and statistics tells us it must be becoming steadily more and more disordered. Both storing memories and breaking eggs increase the disorder in the universe, so they happen in the same direction.

The idea of reversing the direction of time doesn't make much sense. You can change all the t's in your equations to -t's, but that won't actually change much (see T-symmetry). You can define time to be going in the opposite direction, but that just means you would remember what you define to be the future rather than what you define to be the past, so your perceptions wouldn't actually change (you would still remember intact eggs, not broken ones).

--Tango (talk) 15:17, 16 March 2011 (UTC)

The arrow of time article (distinct from entropy (arrow of time) covers the various definitions. Musing over the arrow of time became popular with Stephen Hawking, I think his A Brief History of Time. Wnt (talk) 15:26, 16 March 2011 (UTC)

The best exposition of what reversing the arrow of time would look like, IMHO, is the episode "Backwards" from Red Dwarf. --TammyMoet (talk) 16:16, 16 March 2011 (UTC)

That episode was completely unscientific (of course, it wasn't intended to be otherwise). They had people in the same universe with some remembering the past and some the future. That violates the 2nd law of thermodynamics. --Tango (talk) 17:02, 16 March 2011 (UTC)

Merlin in The Once and Future King lived backwards in time. He was getting younger as everyone else got older. 92.15.26.91 (talk) 20:53, 16 March 2011 (UTC)

Just to note...I watched this episode of the Wonders of the Universe series last night ('destiny') and I was not left in the slightest with the impression that nobody understood 'why' time went in one direction. There was a good 15-20 minutes dedicated to describing Entropy. (or have I misunderstood the question/show?) ny156uk (talk) 21:16, 16 March 2011 (UTC)

Energy Catalyzer

Is the Energy Catalyzer a hoax, or just bad science? 148.177.1.210 (talk) 13:23, 16 March 2011 (UTC)

If it was just bad science, the authors would at least try to get their work published in a real peer-reviewed journal. Instead, they created a blog entitled "Journal of Nuclear Physics" to seem like they're publishing their work in a reputable place. I'd call that behavior unethical and hoax-like. Nimur (talk) 13:53, 16 March 2011 (UTC)

Their patent application looks like it will fail because the inventors didn't adequately describe their device's construction, nor did they present appropriate evidence that it works as claimed: [9]. The difference between a 'hoax' and 'bad science' is, I would say, down to whether or not the inventors really believe their own claims. (A similar distinction exists at the fringe of the medical profession when one distinguishes a 'quack' from a 'fraud'.) TenOfAllTrades(talk) 15:12, 16 March 2011 (UTC)

How effectively can control rods stop fission?

It might be yet another question about the Japanese reactor malfunction, but I can't find any article which addresses this issue: as far as I know, if the control rods are fully inserted, they stop the reaction by capturing the neutrons which cause the fission. Weren't the control rods inserted in the case of the current accident? I assume they were, as most the news sources say the reactors were stopped at the first warning, before the quake hit. So, if the reaction is stopped, what causes the overheating? I know it might not be an instantaneous stopping of the fission, but what exactly is generating heat even after many days after the malfunction? I know the reactors are hot and don't cool themselves quickly, but something is generating heat, doesn't it? --87.169.20.137 (talk) 15:33, 16 March 2011 (UTC)

Yes, the reaction is stopped. (The residual neutrons that avoid the control rods are of little consequence for the total energy balance.) The problem is that nuclear reactor generated a lot of unstable radioactive isotopes during its run. It is the decay of these isotopes that generates the heat after the control rods are inserted. This heat is known as decay heat, and there is really nothing one can do to avoid it. All you can do is wait for the various fission fragments and such to decay to a more manageable level. Dragons flight (talk) 15:41, 16 March 2011 (UTC)

The heat is generated by spontaneous decays of the radioactive material. That is, a nucleus in an atom sends out a particle at high energy, which heats the surrounding material. This is as opposed to fission, where a neutron from outside hit and shatter a nucleus. As Dragons flight says, you just have to wait for this to cool down. Interestingly this means that the severity of the situation is slowly but steadily decreasing. This must feel like gratingly bad choreography for the news media, which wants the perceived risk to increase, so as to keep our attention. EverGreg (talk) 15:47, 16 March 2011 (UTC)

In Japan, with one new nuclear reactor exploding or burning down each day and increasing radiation levels and evacuations, the media are doing fine for stories. See also Timeline of the Fukushima nuclear accidents. The government coverups, company misdirections and simple lack of understanding at Chernobyl and 3 Mile Island provided plenty of news fodder as well. 75.41.110.200 (talk) 16:07, 16 March 2011 (UTC)

(ec) That is not the only source of heat - remember the rods are filled with uranium and, in one reactor, a bit of plutonium, that is constantly fissioning all on its own. The "chain reaction" is stopped by the control rods but natural radioactive decay will persist for thousands of years. 75.41.110.200 (talk) 16:02, 16 March 2011 (UTC)

Although it will only be acutely quite dangerous and hot (e.g. require being kept in a spent fuel pool) for a few decades. The heat is not caused by plutonium spontaneous fission (which is not that much), but all of the fission products that are in there. --Mr.98 (talk) 16:24, 16 March 2011 (UTC)

Even the MOX fuel reactor has only a couple percent plutonium; its almost all Uranium. 75.41.110.200 (talk) 16:37, 16 March 2011 (UTC)

I was under the impression you were referring to the plutonium content of the spent fuel. It is only 1% or so. The spent fuel is itself some 96% uranium. Most of the heat and immediate radioactivity, though, comes from that 3% or so of fission products, really nasty stuff that is very unstable. That's the stuff that mostly burns itself out after 20 years or so, leaving only the stuff that is radioactive in the very long term, but not as "hot". --Mr.98 (talk) 18:32, 16 March 2011 (UTC)

The danger of the current situation is not that they are unexpectedly hot, but that the reactor cores have at various times been exposed (without coolant). That allows the spent fuel in them (chock full of fission products) to get dangerously hot and dangerously radioactive. If it gets too hot and causes parts of the core to melt (the "meltdown") that can create new problems, e.g. spent fuel pooling on the bottom of the reactor vessel, which can create its own criticality problems. If there wasn't a coolant problem, the reactor would still be "hot" but not hot enough to cause any trouble. The problem is the coolant, not that the reactors are "out of control" in the chain reacting sense. --Mr.98 (talk) 16:27, 16 March 2011 (UTC)

"and dangerously radioactive" - exposed rods are not more radioactive. They may release more radiation or radioactive compounds in places where you don't want them but they don't increase in rate unless there is a criticality event. High temperatures, in fact, make criticality harder to achieve. See Critical mass#Changing the temperature 75.41.110.200 (talk) 16:37, 16 March 2011 (UTC)

Well, pedantically: the rods are dangerously radioactive as it is. The coolant water shields quite a lot of that. The removal of coolant means your radioactivity is going to be higher in places it wouldn't otherwise be. The relationship between temperature and criticality is not entirely germane here — it's not a question of trying to create a critical mass deliberately, but the mechanical action of melting the spent fuel or its containment. Which is bad for a number of reasons, criticality included. --Mr.98 (talk) 16:49, 16 March 2011 (UTC)

I don't think the difference is unimportant. The amount of misinformation increases with every news report - most of the "science experts" are getting things wrong as well. And I think you just agreed with everything I wrote. 75.41.110.200 (talk) 17:01, 16 March 2011 (UTC)

Yes, we agreed with each other. It was just clarification on both of our parts, in the end. :-) --Mr.98 (talk) 18:32, 16 March 2011 (UTC)

The possible melting of the fuel rods due to the secondary decays is sometimes referred to by china syndrome, but in that case Brazil syndrome might be a more appropriate moniker. Dauto (talk) 19:39, 16 March 2011 (UTC)

Well, the term China syndrome never did make much sense, given that it was implicitly meant to talk about reactors in the United States. No antipodal point of the United States is anywhere near China (easiest way to see this: Both the US and China are entirely in the Northern Hemisphere). If you take the United States and project it over to its antipodes, your projected image is mostly in the middle of the Indian Ocean.

(Does anyone know where this "straight through to China" meme originates?) --Trovatore (talk) 00:42, 18 March 2011 (UTC)

It's covered in the china syndrome article. --Tagishsimon (talk) 00:46, 18 March 2011 (UTC)

Well, not really. The article says that the name comes from the fictitious notion that "the other side of the world" is China. But my parenthetical question was where that notion (which is certainly much older) comes from.

It froze clean through to China

It froze to the stars above

At a thousand degrees below zero

It froze my logger love -- old song

--Trovatore (talk) 01:15, 18 March 2011 (UTC)

Strictly speaking, the melting of fuel is just a meltdown. The China syndrome is a specific subset of meltdowns where the material actually burns through the containment dome. --Mr.98 (talk) 21:38, 16 March 2011 (UTC)

Bird ID help...

So, my 4-year old asked for the name of a bird we saw today. We live in Raleigh, North Carolina. Sadly, I didn't get a picture, but I'll try to describe it the best I can. It was a passerine bird, shaped and sized like a Blue Jay, except it didn't have the tuft on top of its head, the head was perfectly round. The coloration was more like a Carolina Chickadee, i.e. all black and white and gray, but it wasn't shaped or sized like a chickadee, and it didn't have a chickadee's call. Two of them were fighting in my front yard, and they made sounds like a raspy back-of-the-throat sound, almost like the german or scottish 'ch' sound, but a longer in duration. If I can get a pic, I will take one and upload it, but right now does that sound familiar to anyone? To sum up, a bird roughly the same size and shape as a Blue Jay, with a round head, black and white coloration, which makes a distinctive "back-of-the-throat hiss" sound when agitated. Location: Raleigh, NC. Thanks to any help anyone can give... --Jayron32 17:57, 16 March 2011 (UTC)

Wild guess—do the pictures at Northern Mockingbird look anything like it? Deor (talk) 18:08, 16 March 2011 (UTC)

The shape is about right, but the neck on my bird was a bit longer, and the coloration is wrong. This one had more black around the head, and more sharply defined bands on the wing. Perhaps another kind of mockingbird? I'll follow that thread... Any other suggestions out there? --Jayron32 18:17, 16 March 2011 (UTC)

Magpies are corvid like blue jays, and have black and white markings. They tend to be a bit larger than jays, and are known to bicker and fight. (I'm not sure what species might be in the Carolinas at present) SemanticMantis (talk) 18:51, 16 March 2011 (UTC)

Yeah, I looked at Magpies, and that wasn't it either... Those have too much black, and the bill is too crow-like; these had a more jay-like or mockingbird-like bill. In fact, if the magpie fucked the mockingbird, you might imagine that offspring would look more like this bird. This one had a black stripe on the head, or maybe a black head, but the neck itself was more slender than the magpie, and the black did NOT extend to the neck. --Jayron32 19:32, 16 March 2011 (UTC)

Another clue: In my searches, the closest I can find (and it is pretty close in appearance) is the Gray Jay, which looked very much like my bird, but that bird doesn't have a range anywhere near North Carolina; and I have seen enough of these birds this year and in years past to indicate that this was not an accidental; these birds are common enough around here. So: does anyone have any clues on a bird which looks a lot like a Gray Jay but which lives in North Carolina at this time of year, and which makes the sound I noted above? --Jayron32 19:38, 16 March 2011 (UTC)

The problem is, you know what the critter looks like and we don't. Your mention of a "black stripe on the head" above made me think of the Loggerhead Shrike, but that's just another guess. We have a List of birds of North Carolina; you may want to peruse that. Deor (talk) 20:07, 16 March 2011 (UTC)

When you say that the colouration was like a chickadee, do you mean that it contained the same kind of colours or that the patterning was similar (i.e. with distinctive black cap and throat patch)? I'm going to chime with Hairy Woodpecker (and other woodpeckers) as something to check out, if only because it's technically not a perching bird and so might get overlooked, but is still shaped much like a passerine bird. Matt Deres (talk) 13:43, 17 March 2011 (UTC)

For another resource, whatbird.com has a great interface to its database, and an expert forum, so you might have better luck there. (can't link direct, it's on the spam list for some reason) SemanticMantis (talk) 13:54, 17 March 2011 (UTC)

Thanks for all your help guys! Unfortunately, my memory of the bird is fading, and all of these pics are starting to run together for me. Lesson learned: next time I'll get a pic. But I really do appreciate everyone that chimed in with suggestions! --Jayron32 18:18, 17 March 2011 (UTC)

Speed of WiFi

Would it be terribly incorrect to suggest that wireless signals — for cellphones, computers, what have you — travel through the air at roughly the speed of light? I know that this is not the speed of information transmission, and that I am speaking of the speed of light in atmosphere (not a vacuum). --Mr.98 (talk) 18:28, 16 March 2011 (UTC)

They travel through the air at exactly the speed of light in atmosphere, not just roughly. Note that while the signal travels at that speed, that isn't necessarily the speed at which information can be exchanged along WiFi signals; such information throughput is limited by things like bandwidth, both Bandwidth (computing) and Bandwidth (signal processing) are relevent to the idea. So, yes the speed at which the signal travels is exactly the speed of light, but the speed at which information can be exchanged between nodes in a network is significantly slower than that. --Jayron32 18:31, 16 March 2011 (UTC)

Thanks, that's what I thought, but I was afraid I might be being a dope if I were to say such a thing. --Mr.98 (talk) 18:33, 16 March 2011 (UTC)

You can't compare the speed of light (dimensions: distance/time) with the speed of information exchange (dimensions: bits/time). The time it takes for signals to travel from A to B affects the latency, not the throughput. Latency is, of course, caused by a lot of other things as well, which will usually have a greater impact - speed of light issues are relevant when you are going via a satellite, but that's about it. --Tango (talk) 18:36, 16 March 2011 (UTC)

Jayron, can you explain why the atmosphere has no effect on wave speed, as opposed to a tiny/negligible effect, as implied by Electromagnetic_radiation#Wave_model? — Preceding unsigned comment added by SemanticMantis (talk • contribs) 18:40, 16 March 2011 (UTC)

I assume by "They travel through the air at exactly the speed of light in atmosphere" he meant light and wireless signals go at the same speed in the atmosphere - but less that the "speed of light" (in a vacuum). Grandiose (me, talk, contribs) 18:43, 16 March 2011 (UTC)

Thanks, I will now read more carefully before posting follow-up questions :) SemanticMantis (talk) 18:54, 16 March 2011 (UTC)

(EC x 3) In short, no, that would not be terribly incorrect--Radio_waves says "Like all other electromagnetic waves, they travel at the speed of light." However, Electromagnetic_radiation#Wave_model says "speed of the wave (c in a vacuum, or less in other media)", which is an apparent contradiction. My understanding is that, in the atmosphere, EM waves 'effectively' propagate at the speed of light, but if you measure carefully, the speed is less, e.g. 0.999999999999999999999999c SemanticMantis (talk) 18:37, 16 March 2011 (UTC)

According to the 2nd paragraph of speed of light it's about 0.9997c. --Tango (talk) 18:50, 16 March 2011 (UTC)

I'm highly skeptical that radio waves travel at exactly the same speed as light in the atmosphere. That assumes that the atmosphere has the same refractive index for all wavelengths. Even over the visible spectrum, this is demonstrably false: we have rainbows. --99.237.234.245 (talk) 19:14, 16 March 2011 (UTC)

Radio waves are light. They are not visible light, but the sensitivity of the cells at the back of your retina to them doesn't make the light itself fundementally different. Yes, as you note, the speed of a light wave through a medium, like the air, is dependent on the wavelength of that light, it's why the different colors of the rainbow are split by a prism; as white light passes through the prism, the different wavelengths slow down to different rates of speed, which causes them to seperate out. However, such an effect is mathematically predictable; and if you know the refractive index of the medium and the wavelength of the light in question, you can calculate the actual speed of that specific wavelength. A discussion of how to do so is covered at Refractive_index#Speed_of_light. This calculation works whether you are doing it on light at 600 nanometers (yellow) or 125 millimeters (2.4 GHz WiFi). So, while the speed of the light waves carrying the Wifi signal do travel slower than, say, the speed of yellow light waves in the same atmosphere, the speed of the Wifi signal travels at exactly the same speed as all light waves of that frequency in that medium. So to answer the OP's question, pretty much exactly as I answered it, but with less ambiguity: The speed of the WiFi signal through the atmosphere is exactly the speed of that wavelength of light through the atmosphere. --Jayron32 19:28, 16 March 2011 (UTC)

No, Jayron. That effect cannot be mathematically calculated and the article you site describes un important relation which cannot by itself be used to predict the effect from first principles. A detailed model of how the electrons in the matter interact with the light must be used as well. Or it can be experimentally measured which is much easier. Dauto (talk) 22:41, 16 March 2011 (UTC)

OK, so that part's a bit wrong. But the radio portion of the light spectrum is still light and signals travel at the "speed of light" in whatever medium it is, regardless of what that speed is, and what complicated calculations or experiments you need to determine it. Our ability or inability to do the calculation doesn't change the fact that it is still 100% accurate to say that the WiFi signal, being itself light, will travel at the local speed of light, whatever it is... --Jayron32 15:39, 17 March 2011 (UTC)

Down here at sea level (and in fact, at all altitudes that humans normally go to), it's safe to say that radio frequencies, ranging from the low-frequencies (ULF, VLF, and so on, at 300 - 30 kHz), up to High Frequency (10 MHz) up to VHF, UHF, microwave, and so on, (essentially, all frequencies from ~ 300 Hz to 30 GHz) travel with the same speed in atmosphere. Their attenuations depend highly on frequency, but their speed in air is essentially the same as the speed in a vacuum (at least, let's say, to "several decimal places"). As has been pointed out, this is something like 0.9995 c (in other words, for many practical purposes, equal to the speed of light in a vacuum). This is mostly because at such long wavelengths, the wave "doesn't even see" the neutrally-charged atoms of the atmosphere. If you send the wave through non-atmospheric conditions, especially if there are free electrons and ions, (like when you're beaming signals through the ionosphere, about 100 kilometers above sea level), then you start getting neat frequency-dependent wave propagation speeds, because the air molecules interact with the radio signal. This causes the skywave effect, among numerous other electromagnetic phenomena.

Also, once you get past the millimeter-wave / micro-wave band, and start hitting long infrared and visible light, regular sea-level atmosphere does actually behave non-ideally. This is, of course, because the wavelength of infrared and visible light is very close to the scale-lengths for atmospheric molecule interactions. So, if you get to higher frequencies (like infrared, visible light, ultraviolet), then molecular interactions and scatterting cause frequency-dependent index of refraction. Hence, blue sky, red sunsets, seeing light bend over-the-horizon at dusk, and so on.

So - briefly summarized: in Earth atmosphere, all waves between ~300 Hz to 30 GHz travel at the same speed, which is very close to speed of light in a vacuum. In other conditions, or at other wavelengths, various non-trivial interactions cause frequency-dependent wave speed. Nimur (talk) 16:31, 17 March 2011 (UTC)

What substance has the highest known melting point?

What substance has the highest known melting point?

Our article Tantalum hafnium carbide stakes its claim, but its source is the Encyclopedia Britannica, and even the EB article only says it's "one of the most refractory" chemical compounds.

(I was looking this up out of curiosity because of the ongoing meltdown, of course, and then wanted to add a mention of the record-holder to our melting point article.) Comet Tuttle (talk) 18:45, 16 March 2011 (UTC)

Well, some substances can't assume a liquid state at any temperature, and even for those that can, the melting temperature is a function of pressure. Basically there are three ways for a solid to change state: (1) melting; (2) sublimation; (3) breakdown of internal structure. Since even atomic nuclei will break down at sufficiently high temperatures, I would guess that the substance at which a solid-to-liquid transition occurs at the highest temperature would be neutronium (at extremely high pressure). Looie496 (talk) 21:09, 16 March 2011 (UTC)

I'd throw in my vote for the ultra-high temperature ceramics, which are an entire class of materials. These include hafnium diboride, zirconium diboride, and some similar materials. These materials usually ablate before melting; their phase transition characteristics are complex (sort of entering a "glassy" amorphous phase which might be considered fluid-like). Here's a NASA report on their material properties - they sort of "melt" (braze) in contact with certain metallic lattice faces, but never actually "liquify." Nimur (talk) 21:18, 16 March 2011 (UTC)

I'm not sure it's really meaningful to talk about neutronium as being a solid; our article on degenerate matter describes it as a degenerate neutron gas, but 'fluid' might be suitable as well. TenOfAllTrades(talk) 00:14, 17 March 2011 (UTC)

Sorry, I should have clarified that I was curious about materials' melting points under "normal" conditions, say, at 1 atm. Comet Tuttle (talk) 06:01, 17 March 2011 (UTC)

Maybe what you really want is the substance that remains solid and holds its strength through the highest temperature, at one atmosphere. That gets around all the quibbling about things that sublime or decompose rather than melting. --Trovatore (talk) 06:13, 17 March 2011 (UTC)

When evaluating materials also pay attention to what happens to them under neutron bombardment. Ideally you want to use elements that can't become radioactive for long (so zirconium is out). You also want materials that don't become too weak (or that can be annealed easily). Ariel. (talk) 09:11, 17 March 2011 (UTC)

Tungsten and Platinum have long been valued as non-exotic and non-theoretical metals with fairly high melting points. Edison (talk) 05:14, 18 March 2011 (UTC)

Where are the robots?

Japan appears to be the world leader in robot technology. So why arent remote-controlled robot things being sent in to fix the nuclear reactors? 92.15.26.91 (talk) 21:50, 16 March 2011 (UTC)

Because robots take a while to be planned and built. And I don't think it's quite as easy as just sending a robot in and fixing it. --T H F S W (T · C · E) 21:54, 16 March 2011 (UTC)

You're right it wouldn't fix the problem but I guess robot/s may be helpful to continue to try and cool the reactor when there are temporary radiation spikes which require the removal of workers if they had them (which they don't). Just don't use ones with most types of lithium ions batteries... Nil Einne (talk) 22:07, 16 March 2011 (UTC)

You'd think at least we could have some of those bomb robots from Iraq in there, just keeping an eye on the fires. Wnt (talk) 00:10, 17 March 2011 (UTC)

Rest assured, the robots are being put to work in disaster recovery any way they can. See e.g. this blurb from IEEE Spectrum: [10]. SemanticMantis (talk) 00:09, 17 March 2011 (UTC)

But as far as the reactors are concerned, Asimo Asimov taught us that positronic brains are even more susceptible to damage from sufficiently intense gamma radiation than humans are. -- 110.49.241.128 (talk) 00:55, 17 March 2011 (UTC)

Robots tend to have to be designed for a specific purpose. I guess no-one anticipated the current problems or thought them likely enough to design robots to deal with them. --Tango (talk) 01:10, 17 March 2011 (UTC)

I certainly hope they do after this incident. ScienceApe (talk) 03:21, 17 March 2011 (UTC)

One thing worth noting about robots: even if we have exactly the prototype to churn out, having complex self-powered joints move around substantial amounts is extremely sensitive and prone to breakdown. The director of Death and the Powers gave a seminar here and noted, when asked if robots would take over the world, that he'd be happy if he'd have one week when a robot didn't break down on stage. SamuelRiv (talk) 04:37, 17 March 2011 (UTC)

Nuclear power is no more dangerous today than it was two weeks ago. If it wasn't worth it to develop such robots two weeks ago, it isn't worth it today. --Tango (talk) 22:21, 17 March 2011 (UTC)

Would you like to be at a nuclear plant that might meltdown and is leaking dangerous radioactive material into the environment? If you would, I'm sure Japan would love to have your assistance at Fukushima to help prevent a catastrophe. Personally I think investing in robots that can handle dangerous work like this is worth it. ScienceApe (talk) 22:38, 17 March 2011 (UTC)

Its a pity that no-one appears to have a remote control device that you can just clip into a standard vechicle such as a bulldozer or tractor, or even a tank or riot-control water-cannon wagon, in place of the driver. Even something crawling along at 1mph would be very useful. Wouldnt a tank offer the crew protection against radiation? 92.24.180.239 (talk) 15:15, 17 March 2011 (UTC)

Well steel is better then nothing, and I suppose you could always upgrade it with some lead additions, but after a while, you have a radioactive tank that you need to stash somewhere away from people, but I am not really sure what a couple people in a tank are going to be able to help anything without leaving the tank. Unless it is like a bulldozer engineering unit tank. Googlemeister (talk) 19:04, 17 March 2011 (UTC)

BoingBoing covered this very issue today. Main conclusion: "robots and power plants have to be designed with each other in mind. Fukushima Daiichi, which dates to the 1970s, may simply not be navigable to newer nuclear helper 'bots." --Tagishsimon (talk) 22:24, 17 March 2011 (UTC)

There should be proper robots built for the purpose but they will need very good protection from radiation. As far as I know any electronics they tried to use at Chernobyl failed very quickly indeed in the order of minutes. It's quite horrifying that they used humans for instance to look at things where video cameras wouldn't work. Dmcq (talk) 23:56, 17 March 2011 (UTC)

It was apparently cheaper for the Japanese power company involved to do little in regard to providing remote operated equipment, in favor of letting workers injure their health by large radiation exposure. For instance: a boom truck, remotely operated, could have used a demolition tool to cut a hole in the masonry panels surrounding the top of the reactors. This would have allowed air circulation and prevented the hydrogen explosions that demolished the tops of the buildings. Then, guided by a TV camera, a water spray could have been used to refill spent fuel pools thought to have little or no water. Instead, there was a silly attempt to use helicopters to drop seawater on the roofs of the buildings, with only a tiny fraction even hitting the roofs, with radiation exposure to the flight crews such that the efforts were suspended. Then police "antiriot water cannons" were used to spray water in the general direction of the buildings, but the radiation levels were too high to get very close for very long, and it did little good. (Does Japan have lots of riots where water cannons are needed, like Soviet satellite states used to?) It all evokes images of trying to fix an overheated car radiator by throwing a bucket of water at the car, with the hood only slightly ajar. There are bomb disposal robots and firefighting robots aplenty, with remote control and remote TV viewing. If a wall panel were removed, such a tracked device could have been inserted via a boom truck. We have had remote operated devices on Mars for years, for pity's sake, going around and sending back 3D color pictures, and cutting into things. We have seen teleoperated submersibles in the Titanic. There are even teleoperated robotic soldiers, which can shoot at the enemy or retrieve wounded soldiers. We have had the Darpa Challenge, with true autonomous robotic vehicles driving all over a town, obeying traffic signals, and in and out of parking garages. Google has operated autonomus cars for over 100,000 miles on California highways. The Space Station has teleoperated devices to assist the astronauts, with the ultimate aim of maintaining the station when no humans are on board.How much easier where all that is needed are teleoperated devices to send back pictures and thermal images, and aim hoses. How much progress has the nuke industry demonstrated since the post-Three Mile Island robotics developments? Why must they call on humans to "make the supreme sacrifice" rather than showing some initiative in developing and applying robotics and remote operated devices? Yeah, Japan has lots of cute little Asimo robots which dance around, but no apparent development and deployment of anything useful in a situation like the Fukushima 1 mess. A remote operated crane and a remote operated cutting torch on a boom truck could clear away the twisted structural steel overlaying one of the reactors after the hydrogen explosion, so that the concrete of the containment would be exposed, allowing better viewing and access to the spent fuel pool. Edison (talk) 04:56, 18 March 2011 (UTC)

After an inexplicable one week delay, the Japanese authorities have requested robots from the Massachusetts company iRobot, which can travel around in the reactor to measure radiation and to pull hoses where water is needed. Great idea, if only they had done it on day 1, or if they had been proactive and had some in-country as a precaution against a blackout at a nuke plant. Edison (talk) 19:53, 19 March 2011 (UTC)

I didn't see anything about the electronics working in an environment like that and to me they don't look heavy enough to be radiation hardened either. I expect they've looked into that but if not they very likely will die in no time flat. Dmcq (talk) 00:02, 20 March 2011 (UTC)

This is a question of interest. The 4000 millisievert/hour level may not be all that high a radiation level for the military grade electronics, although a 15 minute exposure would cause radiation sickness in a human. Radiation level sensing is one of the regular functions, via the "CHARS" package, so some degree of survival in a high radiation zone would be expected. I expect robots could be used in zones where humans would not be sent, even if the robots cannot survive the highest imaginable radiation levels. It would be easy enough for the makers or the military to test. The high temperatures might be a problem, since the Warrior has a 104F (40C) operating high temp limit. Its electronics are hardened to Mil Std-461 and MIL-Std-464 Do those specs give a radiation limit? All I see is discussion of electromagnetic radiation, not ionizing radiation. The article Radiation hardening mentions 5000 Rads as a dose which would disable regular commercial silicon chips. The 4000 millisievert/hour highest dose reported would take 12 hours of exposure to deliver that dose, if the chip were totally unshielded and not rad hardened. Radiation hardened chips are available, and the electronics could be shielded. Low-power Schottky chips can stand 1,000,000 Rad, per the article, which would give a human a lethal dose in 2 seconds. Edison (talk) 01:58, 20 March 2011 (UTC)