Wikipedia:Reference desk/Archives/Science/2008 December 1

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December 1

radiant barrier

I read the wiki artical about radiant (attic) barriers and followed one of the suggested links (http://www.fsec.ucf.edu/en/publications/html/FSEC-EN-15/index.htm) but I was unable to find the answer I was looking for. Specifically, can one make their own rediant barrier for their attick by adhering aluminum foil (from the supermarket) to a backing (e.g. carbboard or kraft paper) and then securing this aluminum-side down to the roof trusses? If so, how efficient would this be? Is there something more efficient than aluminum foil?

Thanks

That article reads like an advertisement. You might like to look at Thermal insulation and go from there. Foil doesn't only reflect, it heats up, so layers and thicknesses come into it. If you want to improvise, there's Space blanket a kind of foiled sheet material available for people trekking in the wide outdoors and emergency insulation. Julia Rossi (talk) 01:12, 1 December 2008 (UTC)

On second thoughts, space blankets are aluminium on plastic and I'm not sure if they are durable or temporary. Your foil on cardboard sounds better than that. Julia Rossi (talk) 03:15, 1 December 2008 (UTC)

One thing to be aware of when insulating an attic is that you must not block air flow out of the attic, since this is needed to prevent moisture buildup. This moisture leads to all sorts of problems like mold, insects, and wood rot. StuRat (talk) 05:44, 1 December 2008 (UTC)

The advice in the article seems sound. I'd go for the stuff with a thin bit of insulation in between two reflective sheets which you can probably get in your local DIY store. Dmcq (talk) 16:49, 1 December 2008 (UTC)

Taste of Food Additives

I have a bottle of "lemon juice, made from concentrate". The complete ingredient list is water, lemon juice concentrate, sodium benzoate, sodium metabisulfite, and lemon oil. (Another brand lists water, lemon juice concentrate, sulfites, and lemon oil.)

I don't like to use this stuff to make lemonade because I don't like the taste of the resulting product.

The question is, do sodium benzoate and sodium metabisulfite give any taste to foods they are added to? The articles on these compounds have no mention of taste.

To put this another way, if sodium benzoate (or sodium metabisulfite) were added to water in the concentrations likely to be used in lemon juice, would the mixture have a taste different than water?

As a side issue, the article on sodium metabisulfite says that "when mixed with water, it releases sulfur dioxide (SO2), a pungent, unpleasant smelling gas that can also cause breathing difficulties in some people." Is a residue of this nasty stuff likely to remain in the reconstituted lemon juice?

CBHA (talk) 03:39, 1 December 2008 (UTC)

There are another three possibilities I can think of:

1) It's the lemon oil. This comes from the skin, which is also called lemon zest. It has a rather bitter taste (not sour, as in lemon juice). So, why do they include it ? Because it's cheaper to toss the whole lemons into the machine than peel them first.

2) It's the concentration process:

2a) The particular method of concentration may involve heating the juice to drive off water. This heating can cause the breakdown of some molecules in the juice and change it's flavor.

2b) The concentration itself, regardless of method, may also be a problem. Some of the molecules in lemon juice may be bound to water molecules, until the water is removed, and then may react with other molecules, as a result.

3) The water added during the reconstitution process may alter the flavor, based on minerals in the water, such as chlorine. StuRat (talk) 05:37, 1 December 2008 (UTC)

No idea regarding sodium metabisulfite but the taste do change when you add sodium benzoate to your fruit juice. I son't know how to describe the change in taste but it seems to be "less natural tasting". If you will consume the fruit juice within one day then you should not use these chemicals. However, if you plan to store it on two to three weeks then you should add the preservatives even though they compromise the taste --Lenticel ^(talk) 06:52, 1 December 2008 (UTC)

Also note that a lot of people (especially asthmatics) are allergic to sodium benzoate, so be careful when using bottled lemon juice for anything.--Shantavira|^{feed me} 09:06, 1 December 2008 (UTC)

Nova and Supernova

I'm trying to figure this out: If I'm calculating the distance to a nova in a far-away galaxy, but I mistake it for a supernova, will my incorrect calculations be shorter, the same, or longer than the actual distance? My guess is that it should be longer than the actual distance because supernovae come from stars that are more massive than those of novae, and it will be more luminous. Am I right? Thanks!--el Aprel (^facta-_facienda) 04:08, 1 December 2008 (UTC)

Yes. The typical maximum absolute magnitude for a nova is -8, while supernovas have brightnesses around magnitude -18. --Bowlhover (talk) 04:36, 1 December 2008 (UTC)

Motorcycle Dynamics

In scenes on TV and film of motorcycle riding, there is often a shot where the rider somehow tips back the cycle so that the front wheel is off the ground. I saw one of these tonight on the Compendium of Scientific Information (CSI), Miami division.

The implication is that the rider does this to go faster. Is there any real speed advantage in getting the front wheel off the ground, or is it just a cool trick to enliven a chase scene?

Is there a way to steer a cycle when the front wheel is up?

It seems to me it would take a lot more force to raise the front wheel from the ground to 30 degrees up than from 30 degrees to 60, or from 60 to 90 degrees. Do people trying to ride a motorcycle on the rear wheel risk tipping over backwards?

Thanks, CBHA (talk) 07:21, 1 December 2008 (UTC)

Well, in a perfectly abstract world, as soon as the front wheel comes of the ground, all the weight is on the rear wheel, thus increasing traction. So the motorbike can accelerate faster without slipping. In a non-perfectly abstract world, this a) increases aerodynamic drag, b) makes it nearly impossible to steer and 3) is a very unstable position, so you need to be very careful with the power control to void falling on your ass. In other words, I suspect it's purely for show. I've never seen this in real races, either. --Stephan Schulz (talk) 08:11, 1 December 2008 (UTC)

I don't see it as a method of achieving rapid acceleration but rather a result of rapid acceleration. In fast motorcycles and some race cars, the torque created about the rear wheels under full accel is enough to lift the front end off the ground. StuRat (talk) 09:09, 1 December 2008 (UTC)

See Wheelie. You may also find Bicycle and motorcycle dynamics interesting—it's a good, thorough article, even if it doesn't cover wheelies. -- Coneslayer (talk) 12:47, 1 December 2008 (UTC)

Time and causality

This is basically some daydreaming of mine, but I was wondering what seasoned theoretical physicists (and amateurs such as myself) thought of it.

The gist: we experience a global sense of linear (past->present->future) time and associated causality every day. But is there any reason, other than Occam's razor, to assume time is actually linear, even in the local sense? Supposing causality worked in any direction, including future->past, wouldn't we still experience causality in a linear fashion? If the future changed the past, we wouldn't know of a different past, and hence had no way to know a later event influenced an earlier one. From a purely theoretical point of view, is there anything prohibiting bidirectional time? And if there isn't, then wouldn't it also be safe to assume tachyons and related concepts could exist?

--Link ^(t•c•m) 10:47, 1 December 2008 (UTC)

There is an argument that the perception of time must, of necessity, be in the same direction that entropy is increasing. A laymans explanation of this can be found in Stephen Hawking's book A Brief History of Time. The argument goes something like this: to form a memory, a finite amount of energy must be stored in a structured way. But any local structuring of energy (decreasing entropy) must involve the transport of energy to form the structure, and globally (in the universe as a whole) entropy must be increased by the second law of thermodynamics. It is impossible to see into the future (remember the future) without breaking the second law. Since the second law is currently considered a fundamental law of nature that is ablsolutely true in all cases then the answer is that there can only be one path for time to take (for a given observer in a given frame). SpinningSpark 12:03, 1 December 2008 (UTC)

See also, arrow of time. There are a number of equations used in the sciences which are, as far as we know, unidirectional in time (cannot be reversed). --98.217.8.46 (talk) 14:54, 1 December 2008 (UTC)

Thanks for the replies. The entropy explanation seems valid. So basically, under the assumption that the second law of thermodynamics is true, it is impossible to change the local past in any way, provided that the universe is indeed a closed system (so no external "something" decreases entropy locally), right?

Still, the Second Law seems to be at least partly incompatible with the Poincaré recurrence theorem. I find this all quite mind-boggling, which is exactly why I love reading and thinking about it!

--Link ^(t•c•m) 15:51, 1 December 2008 (UTC)

The issue does not seem to be settled yet. See Retrocausality and John G. Cramer (there may be more physicists besides Cramer working on this.)--Goodmorningworld (talk) 12:31, 2 December 2008 (UTC)

Something SpinningSpark wrote caught my eye. It was the bit about memories being causally related to the ongoing march of entropy. It occurs to me that this sounds a lot like observation (in the quantum mechanics context) in that something that was once in disorder becomes more orderly. Of course I'm asserting that something in quantum superposition is less orderly than something having gone through wavefunction collapse. Is there any link in known science? --Rixxin 15:06, 2 December 2008 (UTC)

Strain Gauges

Could anyone step me in the right direction as to where a strain gauge would be used in Clinical Neurophysiology (eg EEG, EP, NCS, EMG) or the very least in neurology? Moffo (talk) 15:52, 1 December 2008 (UTC)

Looks like one type of strain gauge is used to measure blood flow and tissue swelling; see Strain gauge#Other gauge types. --—— Gadget850 (Ed) ^talk - 16:25, 1 December 2008 (UTC)

Might it be used to measure intracranial pressure on a continuous basis, as opposed to manometry via spinal tap? The pressure sensors sometimes inserted through the skull, for instance. (This certainly does not constitute medical advice!) Edison (talk) 21:08, 1 December 2008 (UTC)

Typical strain gauges that I work with are large compared to neurobiological sizes (typically measuring pounds of force or hundreds-of-pounds of force, e.g.). However, you might be interested to see optical tweezers, which can operate on microscopic objects such as cells or individual proteins; these have many published applications to neurobiology (see Exploring mechanochemical processes in the cell with optical tweezers, for example. Nimur (talk) 21:39, 1 December 2008 (UTC)

For discussion of strain gauges' usefulness in measuring intracranial presure, see [1] and other results from a Google search for this application [2]. Edison (talk) 14:57, 2 December 2008 (UTC)

Herpes research

There are a very large number of individuals infected with herpes in this country and I suppose throught the world. What are the chances of a cure in the near future(5 years)?—Preceding unsigned comment added by 129.112.109.252 (talk • contribs)

That's impossible to predict. It requires people to make predictions of future events, and until someone invents the time machine, or the crystal ball, or something like that, it would be difficult to determine. There are drugs like Valtrex that are known to effectively control the symptoms of herpes, and which also have been shown to reduce (but not eliminate) the transmission of herpes from infected persons. See our article on Herpes simplex for more info. --Jayron32.talk.contribs 18:10, 1 December 2008 (UTC)

Although there is no way to predict if we'll have a break through in the next five years, I find it unlikely that someone will come across a cure in that time. I believe that most hope lies in vaccination, which has already proved effective in several trials. —Cyclonenim (talk · contribs · email) 18:12, 1 December 2008 (UTC)

Viruses are almost never cured. As per Cyclonemin, our best hope is a vaccination and/or treatments that reduce it's contagiousness in individuals who have it. -----J.S (T/C/WRE) 20:55, 1 December 2008 (UTC)

Agreed, and I haven't heard of anyone nearing a vaccine for herpes simplex 1 or 2. A vaccine was recently developed for the related chicken pox virus, so maybe that bodes well for a simplex vaccine. But even if one were discovered/developed tomorrow, it would take several years to clear the FDA (at least in the USA). - Draeco (talk) 01:59, 2 December 2008 (UTC)

Herpevac is a potentially upcoming vaccine for HSV-1, but not currently very effective and not trialed extensively. —Matt (talk · contribs · email) 07:46, 2 December 2008 (UTC)

Less known cell line resources

Hello, all. I'm trying to locate a particular cell line that is commonly used in my area of research (HaCaT), but all the usual non- and for-profit resources don't seem to have it. This particular cell type is used fairly commonly in the existing literature, so I would really prefer to use it if possible. Before I go begging a possibly competing lab for a vial of some of theirs or seeking alternative lines, does anybody here have any suggestions regarding means that I hadn't considered? Cheers! – ClockworkSoul 19:42, 1 December 2008 (UTC)

You can get it from dkfz German Cancer Research Center at http://www.dkfz.de/en/techtrans/mitarbeiter/contact/MTA_HaCaT.php Graeme Bartlett (talk) 09:21, 3 December 2008 (UTC)

Ooh! Now I get to receive a package from Germany! You have my most sincere gratitude, sir. – ClockworkSoul 21:14, 3 December 2008 (UTC)

Timespeed is increasing overtime

It seems that 2008 is the fastest year in human history! The timespeed, or how fast the time is going, is increasing overtime because knowledge, technologies, and busy-ness of people are increasing overtime. So up-to-date, 2008 has the most advanced knowledge, technologies, and people are the busiest of any previous years. To demonstrate how timespeed is increasing overtime is that because time contains hizo, a force that causes forward motion in time. The amount of hizo in time is increasing, because increases in knowledge, technologies, and busy-ness of people produce more hizoes, which in turn increases the timespeed. Are these statements true? BlueEarth (talk) 22:51, 1 December 2008 (UTC)

That's just a concoction of made up words - you can probably define those words in such a way as to make it true if you want. --Tango (talk) 22:58, 1 December 2008 (UTC)

First, you have to prove that there is such a thing as a hizo. It is pointless to make claims about what a hizo does if you have no proof that there is a hizo. -- kainaw™ 23:36, 1 December 2008 (UTC)

"Verb: hizo (infinitive: hacer) 1. Formal second-person singular (usted) preterite indicative form of hacer." - Ummm right.

In defense of the OP, ISTM they asked if the statements were true; they did not assert that there is such a thing as "hizo". Having said that, I have no ideas about the content of what they are talking about. Maybe this question needs the special touch of Mr. Baker? CBHA (talk) 00:06, 2 December 2008 (UTC)

I believe what you are talking about is the concept first presented in the book Future Shock, that, since future knowledge is based on current knowledge, the speed at which knowledge spreads and new inventions arrive is ever increasing, and this can even cause us psychological and societal problems if these changes occur too quickly for us to cope with. I don't agree with this, however, and would argue that changes occurred faster in the 1940s than they do today. With inventions like radar, jets, and nuclear weapons, and broad political changes from worldwide depression to fascism and the cold war, the 1940's were a time of global upheaval. I would posit that it only appears that change occurs more rapidly in the present than in the past when your only experience is with the present. Note that the book was written way back in 1970, so this isn't a new concept. I'd argue that there are also processes which retard innovation, such as patents and people being reluctant to change. Take Blu-ray DVDs, for example. The players are vastly more expensive and the recorders aren't even really available. Under these circumstances the change from standard DVDs to Blu-ray technology for a modest increase in screen resolution is, predictably, proceeding at a snail's pace. StuRat (talk) 00:33, 2 December 2008 (UTC)

It's worth remembering the same thing happened with DVDs even though these had far more advantages over video tapes Nil Einne (talk) 09:23, 2 December 2008 (UTC)

Are we busier than we were five years ago? Ten years ago? Twenty? Thirty? It's pretty hard to say. People weren't exactly just sitting around drinking sweet tea back then. People have been talking about how they've been busier than ever since, well, ever. Certain technologies have certainly changed the rate at which certain interactions have changed—for example, we communicate with others not in our immediate proximity much more rapidly than before—but that doesn't necessarily translate at all into doing more (or less, or whatever). People have been talking about how the busy-ness of modernity since the 19th century. The people then seemed to be just about as busy. Modernity is a condition of being busy. The technologies how we are busy, what we spend our time on, but they don't increase the number of hours in a day. --98.217.8.46 (talk) 02:19, 2 December 2008 (UTC)

People aren't busier in the modern world, they are more productive, and that's not the same thing. People used to spend 100 hours per week picking potatoes or pounding pieces of metal. Now we spend 40 hours a week checking email and punching numbers into computerized spreadsheets. You tell me who is busier? Because of technology, we have both increased the productivity per person AND decreased the amount of time spent at "work". 100 years ago it took 50 people all day to build a dozen cars. Now it takes 6 people working the controls of a few robots to build twice as many cars in half the time. Seems like we are a WHOLE lot less busy now than in the past. --Jayron32.talk.contribs 04:06, 2 December 2008 (UTC)

Yes, but work is only a portion of what makes us busy. While once kids would just play outside, now we feel the need to drive them to various sports around the town. While once we would go to our garden to get veggies or maybe walk to the corner store, now we must drive to a supermarket and wait in long lines. While once a vacation meant a trip to the nearby beach or "big city", now it may involve making lots of reservations, a flight around the world, renting a car, arriving on time for tours, etc. StuRat (talk) 04:47, 2 December 2008 (UTC)

Is it true? Well it is deployable. Please be patient with my impressionistic contribution here, but why do the terms, distraction, information overload and time saturation come to mind on this subject? Focus, localisation, centricity vs global village, media distraction, pluralities. People have so many options some of which they can't opt out of (thinking of you StuRat with your interactive type car – that's fairly time-consuming). Analog(ue) (finite mechanical mechanisms) vs digital (virtual, global, infinitely variable, storable and accessible). And to top it off, people now monitor each other and their children to the nth degree. Apart from the last thing, my post-modern mind loves it, but some of it needs to be allowed to flow past because getting caught up shrinks time even more. About hizo I know nussink. But give me a moment: aha, hizo (Spanish): it did; hacer (Spanish): to do. Maybe we could call it busy-ness, giving the illusion of time passing quickly. Someone else will say, Julia Rossi (talk) 07:21, 2 December 2008 (UTC)

I don't know whether a trip to the supermarket is necessarily costing more time then tradition. It depends a lot on the person and where they live I would suspect. For example, if you go to the supermarket about once a week and spend like 45 minutes in total (including travel time) you could easily spend less time then someone may have spent in the past when they would go to the corner stores 5 times a week and spend about 10 minutes in total (including travel time i.e. walking). Also going to your garden for veggies seems to miss the point that the veges don't get there by magic. It's easily possible you will spend more then 45 minutes peer week on average (obviously some weeks you may only spend 10 minutes, other weeks several hours) growing and collecting those vegetables which may include stuff like watering, weeding, collecting seed or bulbs, fertilising etc. Plus people nowadays may use snap frozen veges which can be used from the packet meaning far less time on preparing the veges. Yes there may be advantages to doing some of the stuff (like walking) and disadvantages to using frozen veges and the like but it doesn't change the fact people likely spent more time on it before. And a lot of people still spend vacations locally. Many children still play at home. They may also participate in sports in various places. One of the reasons why children probably participate in sports more commonly then they may have in the past is because both they and their parents have more time and greater mobility. If the kids have to help out around the farm (or whatever) they don't have time for 2 hours a day playing football or cricket or basketball or one of those odd American sports nor do their parents have the time to walk with them for 5 kilometres to get a place to play sport. In other words, a lot of what you are talking about are luxuries many people could ill afford in the past because they were more busy working or you could say less productive (in the sense that walking 5 kilometres is less productive then driving there if your only goal is to get from A to B). Having said that I would agree that we probably are busier in the more distant past, not because of a most of what has been said but because we don't have to stop everything when it gets too dark anymore Nil Einne (talk) 09:18, 2 December 2008 (UTC)

Since this is all about perception, the actual amount of time isn't the most important factor, but rather how hectic your day seems. Walking to the corner store or tending the garden isn't as frustrating as fighting traffic to get to the supermarket, then fighting crowds and lines once you get there. StuRat (talk) 14:39, 2 December 2008 (UTC)

Funny, I find sitting in my car, enjoyably listening to the radio to be far less frustrating than digging holes and pulling weeds all the time... --Jayron32.talk.contribs 17:29, 2 December 2008 (UTC)