Wikipedia:Reference desk/Archives/Science/2009 October 6

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October 6

DNA

How scientist extract DNA in nucleus? roscoe_x (talk) 01:37, 6 October 2009 (UTC)

See DNA extraction, oddly enough. --Jayron32 02:32, 6 October 2009 (UTC)

cellular membranes

I'm doing a science project and I need to now the effects of heat on cellular membranes.

Does it increase the size of pores? How does it affect the permeability, especially of monosaccharides?

If possible, please validate your information with a reference. Thank you for any help you can give me. —Preceding unsigned comment added by 69.139.218.4 (talk) 02:05, 6 October 2009 (UTC)

Well, vacancy concentration and vacancy diffusion would increase. Higher heat would theoretically stabilise the enthalpy required to form larger pores, yes. Actually I'm kind of curious how important membrane vacancies are, compared to vacuole formation and channel proteins (active or passive). John Riemann Soong (talk) 03:28, 6 October 2009 (UTC)

I'm not going to do your homework for you but will help you a little. If by "pores" you mean membrane transport proteins then heat isn't going to make them bigger - it will of course speed up diffusion so molecules will be transported more quickly. In general higher temperatures will make membranes more "leaky" - the lipid tails of the component phospholipids will not be held together by Van der Waals forces so strongly as before. This can increase the permeability greatly, for monosaccharides as well as everything else. You probably want to look at lipid bilayer phase behavior too as this explains this. Smartse (talk) 16:46, 6 October 2009 (UTC)

Name that substance...

I'm trying to recall the chemical which is transported through the human body so fast and efficiently that if you touch it with your finger, you can taste it in your mouth shortly after. SteveBaker (talk) 04:12, 6 October 2009 (UTC)

DMSO. DMacks (talk) 04:31, 6 October 2009 (UTC)

That's Dimethyl sulfoxide since the above is a dab page. But you probably could have figured that out for youself. I figure I had to do something with this EC... --Jayron32 04:37, 6 October 2009 (UTC)

Aha! That's the stuff. Many thanks! SteveBaker (talk) 11:58, 6 October 2009 (UTC)

I wonder how long after contact with the Defense Modeling and Simulation Office you taste something. DMacks (talk) 16:41, 6 October 2009 (UTC)

Um, I don't understand. Why would skin contact result in taste? Does the substance travel through blood to the taste receptors or something? Do the receptors accept blood contents then? 66.65.140.116 (talk) 02:33, 7 October 2009 (UTC)

Yes, if it travels that fast it must be travelling via the bloodstream. Your taste buds are cells like any other - they need blood to function. If that blood contains something they are able taste then you'll taste it (I guess your brain ignores the constant tastes of things that are normally in blood). --Tango (talk) 03:00, 7 October 2009 (UTC)

In fact I think there's always a "background taste" (just that you usually don't pay attention to it). An interesting experiment (that no one will prolly want to try out) is to cut the appropriate gustation nerves and watch what happens as you suddenly experience "negative taste". John Riemann Soong (talk) 04:29, 7 October 2009 (UTC)

physics circular motion

Moved from WP:HD ~ Amory (u • t • c) 04:33, 6 October 2009 (UTC)

how banked roads help to overcome the dependence on friction ?????????plezzz telll i will be thankful to u —Preceding unsigned comment added by 117.197.118.30 (talk) 03:44, 6 October 2009 (UTC)

Banked curves don't "overcome the dependence on friction", they compensate for inertia. This really should be on the science page. →Baseball Bugs ^{What's up, Doc?} carrots 03:47, 6 October 2009 (UTC)

I don't understand the distinction you're making. Banked turns help compensate for inertia, thereby making it less necessary to depend on friction to overcome the inertia.

We have a fairly good article on this. See banked turn. Red Act (talk) 05:01, 6 October 2009 (UTC)

The OP refers to the fact that friction need not be present as much while turning on a banked road, ie it "helps overcome the dependence on friction". In fact, it is possible to turn at a specific velocity even if no friction is present. Rkr1991 ^{(Wanna chat?)} 08:00, 6 October 2009 (UTC)

Easy. A banked corner stops you from flying off the road, ordinarily you depend on road-tire friction for that. APL (talk) 19:45, 6 October 2009 (UTC)

Cooling towers

If I were to have an aerial view of a nuclear reactor's cooling towers, what would I see? Is most of it empty space? I can't seem to find a decent image from straight down. Dismas|^(talk) 04:38, 6 October 2009 (UTC)

Have you looked on Google maps? Or is it too dark inside them to show anything? →Baseball Bugs ^{What's up, Doc?} carrots 04:39, 6 October 2009 (UTC)

Cooling tower might or might not be helpful. →Baseball Bugs ^{What's up, Doc?} carrots 04:42, 6 October 2009 (UTC)

Too much steam to see anything else.

It's not really. The closest any of those images gets to showing the inside is this one. Dismas|^(talk) 04:48, 6 October 2009 (UTC)

I've been looking at nuclear power plants on google earth (hope I don't get arrested by homeland security); if you get a photo of the cooling towers while not in use, all you see is a big shadow inside. Someguy1221 (talk) 06:15, 6 October 2009 (UTC)

I did some Google searches on "cooling tower" and "diagram". Apparently in at least one design the bottom part of the space has equipment in it while the middle and upper part is indeed empty. For example, see this page and this diagram. Some other designs are shown on this page. --Anonymous, 09:03 UTC, October 6, 2009.

For the most part, they're just water tanks. There's some inflow and outflow plumbing, and some heavy-duty pumps; and the walls might be reinforced with scaffolding in some designs (though most are freestanding); and they are filled with the heat-exchange water which is cooling to a temperature safe to re-release into the environment without catastrophic thermal pollution. The water is clean and generally speaking, radiation-levels are low (hopefully at about ambient-level) - though this last point is subject to some pseudoscientific debate, the water should not be carrying any radioactive contaminants. Nuclear reactor coolant explains double- or multi-heat-exchange systems - any water that ever actually contacted the core is not usually released into the environment.

The iconic convex shape that has come to symbolize nuclear energy is really just an effective way to build extremely large (by volume) water-reservoirs while using less land-area and less construction material. For the geometrically inclined - the curved shape contributes to structural stability by distributing the load uniformly - but the towers are specifically designed to be ruled surfaces - so they can be built out of conventional construction beams. Nimur (talk) 07:53, 6 October 2009 (UTC)

So, if I understand you correctly, besides some pumps and associated plumbing at the base, the rest of the tower is filled with water and the top is open to the environment. So the concave design is just a stronger way of making a big water bowl? After EC, you seem to have answered my question. Thanks! Dismas|^(talk) 08:01, 6 October 2009 (UTC)

I don't believe this is at all correct. As has been stated elsewhere, cooling towers are mostly empty space. The hot water from the power station is pumped to the top of the tower and falls down through the tower in small drops, cooling as it does so. It is collected at the bottom and returns to the power station as cool water. So the only thing in te tower is equipment to convert the water to drops, drops of water, and air. --Phil Holmes (talk) 09:35, 6 October 2009 (UTC)

I went on a tour of Three Mile Island when I was young, and we went inside one of the disused cooling towers. Your description is basically correct, but I don't think the water falls from the top of the tower to the bottom. It falls from a much lower height... in the picture above, you can see a dark ring making up the bottom 10% or so of the tower. I believe that's where the water falls, from a height of one story or so. Outside air flows in through that ring (which is mostly open), through the waterfall, and then up the cooling tower. The 90% of the cooling tower that's above the waterfall is there to act as a chimney. -- Coneslayer (talk) 12:28, 6 October 2009 (UTC)

Its raining inside! [1] —Preceding unsigned comment added by 79.75.35.173 (talk) 08:38, 6 October 2009 (UTC)

Plant design, including cooling, can vary from installation to installation. One of the complaints levied against the American nuclear power establishment has been the failure to have a uniform design - every plant is uniquely engineered (at great additional cost), rather than using a tried and tested reference design. (This site has some nice overview and references). Hopefully this situation is changing with the new AP1000 design - which will be installed, among other places, at Shearon Harris in my hometown outside Raleigh. Needless to say, there is no shortage of real debate (and pseudoscientific accusatory politics) associated with this sort of major policy-change - but the hope is that by establishing a single core design, the rest of the construction costs for the plant can also be consolidated and reduced through economy of scale. Nimur (talk) 15:39, 6 October 2009 (UTC)

The cooling tower design likely has hot water falling from above through a passive upward flow of air entering at the bottom, with much cooler air leaving. Other reactors use cooling ponds, if there is sufficient land area adjacent. Edison (talk) 04:47, 7 October 2009 (UTC)

eclipses (q moved from ents desk)

when during eclipes whats the effec in the living things —Preceding unsigned comment added by 122.52.149.93 (talk) 06:47, 6 October 2009 (UTC)

There's some answers here. --Richardrj ^{talk email} 07:39, 6 October 2009 (UTC)

h1n1 (q moved from ents desk)

what is h1n1 virus? where did he come —Preceding unsigned comment added by 122.52.149.93 (talk) 06:50, 6 October 2009 (UTC)

Welcome to Wikipedia. I moved both your questions here from the Entertainment desk, since this is the right place for them. You might want to read our articles on H1N1 and Pandemic H1N1/09 virus. Since it looks like English is not your first language, you might find it easier to read the entry on the virus in the Simple English Wikipedia. --Richardrj ^{talk email} 07:36, 6 October 2009 (UTC)

Or more likely, H1N1 en la Wikipedia en español, or perhaps H1N1 sa Filipino Wikipedia. Intelligentsium^review 01:17, 8 October 2009 (UTC)

inventor of American sealed hard plastic cases used in late 90's & early 00's?

Forgive me if they were found elsewhere, I did not travel abroad extensively during that time period. I'm sure most people here are familiar with those clear plastic cases for things like small electronic items that were essentially welded shut at the edges and required some seriously sharp implements to open, after which they could easily cut your hand/finger/whatever. Is there any info as to who actually invented that method of packaging? I consider it the worst invention in widespread use in the last 20 years... who gets the blame? 61.189.63.208 (talk) 11:12, 6 October 2009 (UTC)

Not sure, but it might help your search to know that they are a type of blister pack or clamshell packaging. We even have an article on wrap rage. Recury (talk) 13:42, 6 October 2009 (UTC)

Playing around with Google Patents, a possible candidate is Cornelius M. Phipps. Phipps was making an improvement over the card-based blister-pack, where a plastic blister was attached a cardboard card, by having his be all plastic. It doesn't look like it is heat-sealed, though, which is part of what makes blister-packs so irritating. Hmm. Anyway, I found this by searching for patents regarding blister packs on Google Patents, and then seeing what patents they referenced, moving back in time in the process. As I would have guessed with something like this, there are a lot possible candidates, depending on what one defines as the essence of the modern plastic case (there are a LOT of patents on the subject). --Mr.98 (talk) 15:31, 6 October 2009 (UTC)

It's also a matter of choice of plastic - I think the dangerously sharp ones you refer to are usually made of HDPE - which is recyclable! That may have been a motivation for switching to this more irritating form of packaging material. Nimur (talk) 16:08, 6 October 2009 (UTC)

I think the plastic panels are (now) sealed via ultrasonic welding rather than stapling or simple vacuum forming. DMacks (talk) 16:38, 6 October 2009 (UTC)

Homunculi

I need a list of different types of artifical life so far I have

Homunculi Tulpa Kelenthri Rhokidamus Golem

if you could give me any more that would be great. Thanks —Preceding unsigned comment added by Hogieene (talk • contribs) 15:18, 6 October 2009 (UTC)

Because you are seeking fictional creatures, there's no way to complete an authoritative list. You might enjoy reading cryptozoology, but if you are considering adding content about fictional lifeforms, please be sure to establish their notability per our relevant policy. Nimur (talk) 15:43, 6 October 2009 (UTC)

Depending on your exact criteria, (fictional) Robots and Androids might fit. Note also that, according to a recent BBC TV programme (sorry I can't remember more details: it was on the iPlayer last week but has now gone) the laboratory creation of an entirely artificial living cell (i.e. built from scratch out of chemicals) is expected within the next 2 years. 87.81.230.195 (talk) 16:01, 6 October 2009 (UTC)

The synthetic biology article deals with the creation of artificial life. Smartse (talk) 16:49, 6 October 2009 (UTC)

I don't think Homunculus is properly a type of artificial life although I am sure sci fi writers care little for such issues. --BozMo talk 17:46, 6 October 2009 (UTC)

Indeed. The five things on our OP's list are entirely fictional - and that list would be a very long one indeed...but kinda useless for most practical purposes. How about Frankenstein - Asimov's robotics stories - 'Nanites' in StarTrek...there are an awful lot of science fiction/fantasy works that contain artificial life-forms of one kind or another. However, the 'real world' work on creating artificial life from (essentially) raw chemical feedstocks is an amazing thing. If they manage it - it'll be right up there with the top ten things that humanity has achieved. However, it hasn't been completely solved yet. Meanwhile, the vast majority of Artificial Life research has been done in the realms of software - and if you grant the possibility of a digital life-form living in it's own little digital world - then there are hundreds - if not thousands - of examples. Do a Google search on "Alife" and you'll find plenty - many of which you can download and try for yourself. SteveBaker (talk) 18:59, 6 October 2009 (UTC)

Steve, really, nanites in Star Trek, are you sure about that? Did they spread over from the Stargate Atlantis set, or did Dr. Elizabeth Weir get a better job on the Enterprise? (Or did I miss an ST episode once ever?) Franamax (talk) 03:57, 7 October 2009 (UTC)

Very sure! There were in Evolution (Star Trek: The Next Generation) in 1989 - and both pre-dated Stargate (not to mention Stargate Atlantis) by many years. I kinda suspect that the term was invented by the STTNG authors - "nanobot" being the common term prior to that show. SteveBaker (talk) 21:36, 7 October 2009 (UTC)

Not so sure about the top ten things list myself. No doubt very tricky but there are lots of very tricky things and perhaps it is only a top ten if you somehow find the concept mind-blowing rather than on pure technical merit. Philosophically isn't it just a form of Procreation? A tighter challenge might be recreating something with extinct DNA perhaps, so you have to learn to code the DNA to match the properties. --BozMo talk 19:17, 6 October 2009 (UTC)

See many many many examples in the Wikipedia article Artificial intelligence in fiction. For example, David in the film Artificial Intelligence: A.I. who fantasizes that he is a real boy. Cuddlyable3 (talk) 08:47, 7 October 2009 (UTC)

The amount of gearing in 3-speed bicycle Hub gear versus Derailleur gears?

I'm wondering if I should buy the same brand (Giant) and model of bicycle with either hub gears or derailleur gears. My simple preferance is for hub gears; I used them long ago as a teenager: they are reliable - they always work, any adjustment required is simple. However, having used derailleur gears since then (as hub gears were not available) I'm wondering if I've got used to riding with a higher gearing than the 3-speed hub is going to give me. It would be a disapointment to order a hub-gear bike and find that the top gear of the three-speed hub is less than what I prefer. (Pre-order road-testing is not possible). I cannot afford a 7-speed hub as they are much more expensive. The thing about derailleur gears is that in my experience after a few weeks or months they are only useable in one gear - so I just use one gear all the time, and I have never ever managed to get them running properly despite trying. They are also more prone to damage and probably friction. Can anyone tell me please the amount of gearing in a 3-speed hub compared to a derailleur? Thanks 78.146.29.77 (talk) 20:05, 6 October 2009 (UTC)

Bike wheel gearing is typically measured in inches (being the wheel size equivalent to the gearing). Derailleur gears (which have lower friction loss than hub gears and are less inclined to break under heaby load which is why professionals etc always use them) can range from about 23 inches to 104 inches with a "typical" set up being say 32-96 inch range. There is no standard range and the person selling the gears should tell you the range in inches. Hub gears also vary considerably and of course the range depends on the front cogs (by the pedals) as well as the rear ones. You could move the hub gearing up or down without problem by changing the front cog but you will not get the kind of range a typical derailleur offers. --BozMo talk 20:12, 6 October 2009 (UTC)

Also note that there's no reason that derailleur gear shouldn't continue to work for years, if properly maintained. You may need occasionally to replace the chain and the sprockets, but you'd similarly need to do that with a hub gear. I've ridden thousands of miles without needing to replace any of the components of a derailleur, and it has still been able to use all the gears avaiable. --Phil Holmes (talk) 21:24, 6 October 2009 (UTC)

Hub gears are pretty much maintenance free, derailleur gears need occasional maintenance but should work for years as well. You'll get away with a 3-speed hub if you live somewhere fairly flat. If money *and* spread of gears is an issue, I would get somebody to show you how to do basic work on derailleur gears - its not all that complicated.195.128.251.43 (talk) 21:55, 6 October 2009 (UTC)

Note: This thread was a revelation. A 46 year old 1 speed Schwinn will, as a result, become a 3 speed with coaster brake, as soon as a Shimano or Sturmy-Archer 3 speed/coaster hub is obtained, to someone's great delight. Edison (talk) 04:42, 7 October 2009 (UTC)

I was satisfied that the the top gear of my bicycle with 3-speed Sturmey-Archer hub gear and 26 inch wheels was high enough. I could only use it on the flat or downhill. Derailleur gears give me many more gear ratios but I find the exposed hanging mechanism "unaesthetic", each gearchange seems a complex exercise (compared to the hub gear where everything is out of sight and gearchanges are smooth) and the thing needs regular attention to cable adjustment, cleaning and oiling. Repairing a chain takes more time when it has to be threaded around a deralleur. BTW an accidental mispronunciation of "derailleutr gears" was the source for The Cream's classic music album Disraeli Gears".Cuddlyable3 (talk) 08:40, 7 October 2009 (UTC)

While 3-speeds are nearly indestructible, they have fairly high internal friction and only a limited gearing range. There are now very good Shimano and SRAM 7 to 9 speed hubs. And, of course, there is the 14 speed king of hubs, the Rohloff Speedhub, although that is more expensive than many bicycles ;-). I'm riding Shimano LX 3x9 on my mountain bike, and a Speedhub on my trekking/utility bike. Both are somewhat upmarket, and both work essentially hassle-free for years. --Stephan Schulz (talk) 11:49, 7 October 2009 (UTC)

A few questions

1. If a virus's host dies, in most cases the virus will die out as well, due to its need of the host cells to reproduce. Why hasn't selective pressure led to all viruses becoming non-lethal?

2. Has the H1N1 vaccine been known to have any serious side-effects? --75.40.207.213 (talk) 20:20, 6 October 2009 (UTC)

To one: In most cases the pressure of selection has indeed prompted viruses to adopt certain strategies. One of them is to be so virulent as to spread over a whole population quickly, also called virulency, (reducing the need of living hosts) and mutate easily (therefore avoiding the hosts immune system) or to adapt to certain hosts as to not kill them. Also: most viruses who are quite lethal are relatively new to the human population and have not started to adapt to the new host. For an example of the first kind see Rhinovirus, for an eample of the second kind see HIV. An answer to your second question might be found here --217.84.60.60 (talk) 20:46, 6 October 2009 (UTC)

It is not just a matter of lethality. HIV is extremely lethal, but as it takes years to kill the victim, it has plenty of time to spread to another host. The ones that don't always get to spread far are lethal and fast acting. Googlemeister (talk) 20:55, 6 October 2009 (UTC)

Regarding your first question, there is a rather detailed discussion in virulence and optimal virulence articles. --Dr Dima (talk) 22:48, 6 October 2009 (UTC)

It may be time to write H1N1 vaccine, but it is just a flu vaccine. The side effect section is at flu vaccine#Side effects Graeme Bartlett (talk) 11:09, 7 October 2009 (UTC)

As for virulence one thing to consider is many lethal virus actually are non-lethal in other species and mutate over to humans and are extremely lethal. See Zoonosis —Preceding unsigned comment added by 66.133.196.152 (talk) 23:14, 7 October 2009 (UTC)