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  #221  
Old 31.10.2007, 16:33
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Re: Ask a Scientist

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Here's a doom and gloom question- How do the US protect their warhead on the gulf carriers from attack. Is it possible that a missile could hit one and set it off? Or that the carrier gets hit, explodes and that sets it off- is that possible?
Do you mean nuclear warheads? If so, then the answer is no: it is not likely that a direct hit on a stored warhead - or the explosion of whatever is storing the warhead - will cause the nuke to detonate.

Modern nuclear weapons essentially consist of a certain amount of fissile material which is compressed into a supercritical mass upon detonation. This compression is achieved by detonating a precisely-configured set of explosives within the warhead. Any damage incurred by external effects would be incredibly likely to damage this configuration before it has any chance of going off. And if these explosives do not fire correctly, then the fissile material will not be able to compress enough to go critical, leading to no nuclear explosion.

The older type of nuke (eg. the ones used by the US on Japan) had a different design, where one piece of fissile material is shot at another piece. This is a lot simpler, and hence a lot easier to set it off by accident. But this type cannot be used as a missile.

In the case of conventional weapons, the same rule that applied during the gunpowder era applies now: armour, and lots of it, or you're in trouble.
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  #222  
Old 31.10.2007, 16:53
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Re: Ask a Scientist

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Don't bother adding oil, it's useless.
The oil prevents the pasta from sticking to the saucepan when cooked!
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  #223  
Old 04.11.2007, 05:50
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Re: Ask a Scientist

I realize that I'm way late to joining the game, but I can't resist the call of science. I was a civil engineering undergrad, now an environmental engineering and water chemistry grad student, and I'm happy to answer questions, too.

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2) How do the rings affect the physical properties of the wood (eg shear strength)
This is really a civil engineering question: structural engineers have to know how to design stuff made with wooden beams. In pieces of wood used for construction, the tree rings show up as the wood grain (since we cut wood along the length of the tree, parallel to the rings). The shear strength in this direction (parallel to the grain) is weaker than in any other direction, which is the major design factor when calculating loads on wooden beams or columns or whatever. Think about it this way: it's way easier to split wood than to cut down a tree.
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  #224  
Old 04.11.2007, 05:57
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Re: Ask a Scientist

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OK Our Chemistry teacher once promised (when it was very popular as a commmercial product) to make us some Slime. Two years later we were still waiting, and she went and married another chemistry teacher and left the school to make babies.
If you're still looking for some resolution to your unfulfilled slime needs, here's a kid-safe recipe for slime. I used this previously for a science demo with a bunch of small children with moderate success, although the food coloring was more interesting than the slime itself...Key ingredient always seems to be Borax, acting as a cross-linker to form the polymers mentioned in an earlier post.
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  #225  
Old 04.11.2007, 15:05
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Re: Ask a Scientist

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The older type of nuke (eg. the ones used by the US on Japan) had a different design, where one piece of fissile material is shot at another piece.
Minor correction: Little-boy (Hiroshoma) was indeed a gun-type bomb. However, Fat Man (Nagasaki) was an implosion-type. Which explains why Little Boy was skinny and long (for the gun barrel) and Fat Man was short and fat (for the implosion chamber).
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  #226  
Old 19.11.2007, 09:28
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Re: Ask a Scientist

Yup. Good point.

Since there haven't been any new questions for a while, I'd like to share this article from the British Medical Journal with you all. Anyone who has had their work unreasonably criticised for not being thorough enough will appreciate this.
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  #227  
Old 19.11.2007, 12:41
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Re: Ask a Scientist

That is a truly superb paper.
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  #228  
Old 19.11.2007, 12:53
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Re: Ask a Scientist

I feel an IgNobel prize coming.....
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  #229  
Old 19.11.2007, 20:58
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Re: Ask a Scientist

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I feel an IgNobel prize coming.....
This guy won an IgNobel prize for his wooden periodic table...
http://www.theodoregray.com/Periodic...ndex.html#what
(scroll down one screen)
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  #230  
Old 19.11.2007, 21:33
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Re: Ask a Scientist

Bacteria extract hydrogen at over 90% efficiency

is this as big a potential break though as it reads ?
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  #231  
Old 19.11.2007, 23:29
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Re: Ask a Scientist

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Bacteria extract hydrogen at over 90% efficiency

is this as big a potential break though as it reads ?
Sounds pretty sweet, since most methods we have for generating hydrogen are VERY inefficient. I would say there are two main problems so far:
1. Scale. These are still lab-scale reactors, far from implementation in an actually useful quantity.
2. carbon neutrality. The diagram shows release of CO2 to the atmosphere during the hydrogen production! So, that's a greenhouse gas. Nonetheless, if the input to the fuel cell is biological in nature, the CO2 will be from carbon incorporated into biomass. Since plants of all shapes and sizes convert atmospheric CO2 to biomass, this is a carbon neutral process at best (they don't mention where the extra 0.2V come from...).

You have to have a subscription to access the research articles, but they are in a reputable journal (Environmental Science and Technology, the top journal for environmental engineering material). You can see this news release from the journal to see a picture of the actual size fuel cell: http://pubs.acs.org/subscribe/journa..._fuelcell.html
Apparently a series of fuel cells the size of a refrigerator could produce ~100W, which is, unfortunately, not enough to run a refrigerator!
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  #232  
Old 26.11.2007, 13:53
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Re: Ask a Scientist

Possibly a repost... but this periodic table site is great.

http://www.periodictable.com/
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  #233  
Old 05.12.2007, 12:47
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Re: Ask a Scientist

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=Bush's stem cell stance thoroughly vindicated=Charles Krauthammer
Opinion : "If human embryonic stem cell research does not make you at least a little bit uncomfortable, you have not thought about it enough." - James A Thomson
A decade ago, Thomson was the first to isolate human embryonic stem cells. Last week, he (and Japan's Shinya Yamanaka) announced one of the great scientific breakthroughs since the discovery of DNA: an embryo-free way to produce genetically-matched stem cells.
Even a scientist who cares not a whit about the morality of embryo destruction will adopt this technique because it is so simple and powerful.
The embryonic stem cell debate is over.
Which allows a bit of reflection on the storm that has raged ever since the August 2001 announcement of President George Bush's stem cell policy.
The verdict is clear: rarely has a president - so vilified for a moral stance - been so thoroughly vindicated.
Why? Precisely because he took a moral stance. Precisely because, as Thomson puts it, Bush was made "a little bit uncomfortable" by the implications of embryonic experimentation. Precisely because he therefore decided that some moral line had to be drawn.
In doing so, he invited unrelenting demagoguery by an unholy trinity of Democratic politicians, research scientists and patient advocates who insisted that anyone who would put any restriction on the destruction of human embryos could be acting only for reasons of cynical politics rooted in dogmatic religiosity - a "moral ayatollah", as senator Tom Harkin so scornfully put it.
Bush got it right. Not because he necessarily drew the line in the right place. I have long argued that a better line might have been drawn - between using doomed and discarded fertility-clinic embryos created originally for reproduction (permitted) and using embryos created solely to be disassembled for their parts, as in research cloning (prohibited).
But what Bush got right was to insist, in the face of enormous popular and scientific opposition, on drawing a line at all, on requiring that scientific imperative be balanced by moral considerations.
History will look at Bush's 2001 speech and be surprised how balanced and measured it was, how much respect it gave to the other side. Read it.
Here was a presidential policy pronouncement that so finely and fairly drew out the case for both sides that until the final few minutes of his speech, you had no idea where the policy would end up.
Bush finally ended up doing nothing to hamper private research into embryonic stem cells and pledging federal monies to support the study of existing stem cell lines - but refusing federal monies for research on stem cell lines produced by newly destroyed embryos.
The president's policy recognised that this might cause problems. The existing lines might dry up, prove inadequate or become corrupted.
Bush therefore appointed a President's Council on Bioethics to oversee ongoing stem cell research and evaluate how his restrictions were affecting research and what means might be found to circumvent ethical obstacles.
More vilification. The mainstream media and the scientific establishment saw this as a smoke screen to cover his fundamentalist, obscurantist, anti-scientific - the list of adjectives was endless - tracks.
"Some observers," wrote the Washington Post's Rick Weiss, "say the president's council is politically stacked."
I sat on the council for five years. It was one of the most ideologically balanced bioethics commissions in the history of the US.
It consisted of scientists, ethicists, theologians, philosophers, physicians - and others (James Q Wilson, Francis Fukuyama and me among them) of a secular bent not committed to one school or the other.
That balance of composition was reflected in the balance in the reports issued by the council - documents of sophistication and nuance that reflected the divisions both within the council and within the nation in a way that respectfully presented the views of all sides.
One recommendation was to support research that might produce stem cells through "de-differentiation" of adult cells, thus bypassing the creation of human embryos.
That holy grail has now been achieved. Largely because of the genius of Thomson and Yamanaka. And also because of the astonishing good fortune that nature requires only four injected genes to turn an ordinary adult skin cell into a magical stem cell that can become bone or brain or heart or liver.
But for one more reason as well.
Because the moral disquiet that James Thomson always felt - and that George Bush forced the country to confront - helped lead him and others to find some ethically-neutral way to produce stem cells. Providence then saw to it that the technique be so elegant and beautiful that scientific reasons alone will now incline even the most wilful researchers to leave the human embryo alone.
What do you think? About the science bit - not the politics

Last edited by Buttercupbananatush; 05.12.2007 at 13:23. Reason: expanded question
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  #234  
Old 05.12.2007, 13:22
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Re: Ask a Scientist

When we light a fire in our fireplace, sometimes there appears to be gas coming out of the burning wood and being consumed by the fire as well.

Sometimes there is a lot of smoke coming into the room and not going up the chimney. Can someone please explain these phenomena?

Thanks.

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  #235  
Old 05.12.2007, 13:42
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Re: Ask a Scientist

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When we light a fire in our fireplace, sometimes there appears to be gas coming out of the burning wood and being consumed by the fire as well.

Sometimes there is a lot of smoke coming into the room and not going up the chimney. Can someone please explain these phenomena?

Thanks.

Sometimes you can get volatile compounds coming out of the wood on heating and it'll occur more often with birch and pine and as they spray out, they catch light and woooof, off they go.
As for smoke in the room, it often means there's not enough draft going up the chimney. Can happen on windless days if the door to the room is closed. Open the door a crack and it should sort it out. Either that or you need to clean your chimney.
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  #236  
Old 05.12.2007, 13:44
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Re: Ask a Scientist

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Sometimes you can get volatile compounds coming out of the wood on heating and it'll occur more often with birch and pine and as they spray out, they catch light and woooof, off they go.
As for smoke in the room, it often means there's not enough draft going up the chimney. Can happen on windless days if the door to the room is closed. Open the door a crack and it should sort it out. Either that or you need to clean your chimney.

They used to power cars with wood gas

so some were riding a woodie back then
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  #237  
Old 05.12.2007, 14:00
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Re: Ask a Scientist

Why does one's own wind smell much superior than to anyone else's?

Last edited by smbuzby; 05.12.2007 at 14:05. Reason: typo
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  #238  
Old 05.12.2007, 14:01
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Re: Ask a Scientist

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Why does one's own wind smell much suprerior than to anyone elses?
Cuz it contains ones own pheromones
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  #239  
Old 05.12.2007, 14:03
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Re: Ask a Scientist

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Why does one's own wind smell much suprerior than to anyone elses?
Pride? Ego?
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  #240  
Old 05.12.2007, 14:08
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Re: Ask a Scientist

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Cuz it contains ones own pheromones

But can one actively smell a pheromone? I thought it was substance to induce a behaviour, like attraction to someone. I am attracted to my girlfriend, but her "windy-pops" are dreadful......
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