Friday, January 20, 2012

Regulatory Capture

I read a comic that lead me to this wiki article on examples of regulatory capture in the US.  It's a good article to read if you're looking to lose all hope.
Monsanto's growth hormone, rBGH, which has been linked to cancer in cows and humans, has been banned in numerous countries, but is unlabeled and legal in the United States. Margaret Miller, a former chemical laboratory supervisor at Monsanto, wrote a scientific report that was to be submitted to the FDA to obtain approval of the drug. Shortly before the report was submitted, Miller quit Monsanto to take a job at the FDA, where her first job was to approve the report she had just written while employed at Monsanto.

Thursday, January 19, 2012

Richard Feynman explains science
In general we look for a new law by the following process. First we guess it. Then we compute the consequences of the guess to see what would be implied if this law that we guessed is right. Then we compare the result of the computation to nature, with experiment or experience, compare it directly with observation, to see if it works. If it disagrees with experiment it is wrong. In that simple statement is the key to science. It does not make any difference how beautiful your guess is. It does not make any difference how smart you are, who made the guess, or what his name is – if it disagrees with experiment it is wrong. That is all there is to it.

Sunday, January 15, 2012

Useful Websites for School

I've often said that I don't think I could do well in school in an age without the internet.  The bulk of my time spent learning is spent on various websites increasing my understanding of concepts.  While random sites found via googling are often useful, I've compiled a list of websites I go to time and time again.  I've mentioned some of these before, and some are quite well known, so you may have already visited them.

I've mentioned Wolfram Alpha a few times here, but it really deserves its own post.  If you've never used it before, it is a "computational engine".  Similar to a search engine, but aiming to answer questions directly rather than simply via links.  While it can be used for any subject, I pretty much only use it for math.^3^n+from+1+to+infinity|x|+and+y%3Dx^2-6{{45%2C+-34%2C+120%2C+1}%2C+{-14%2C+25%2C+-67%2C+0}%2C+{12%2C+75%2C+-72%2C+1}%2C+{1%2C+42%2C+83%2C+82}}

While there are other systems that can solve math like this, Wolfram Alpha stands out two ways.  First is that it does a very good job of interpreting input correctly.  If you've ever tried to use a program like Maple or a graphing calculator to solve things, you know it gets pretty annoying to input what you actually want.  Even if you think you have the input right you don't know for sure.  Wolfram Alpha shows what it thinks you've inputted so you know for sure if it is correct.  The second thing is the show steps button.  With a simple click Wolfram Alpha will show you how it solved the problem.  This doesn't always help, as sometimes it uses a very labor intensive brute force method, but helps quite often.  Note the random and examples buttons near the search box if you want to see examples of what kinds of things it can do.

Khan Academy
I've written about Khan Academy before, but it is really an amazing site.  It consists of 10 minute videos on a wide range of science and math subjects, including: arithmetic, differential equations, calculus, bio, chem, physics, and economics.  The videos are made by Sal Khan, an electrical engineer who went to MIT and worked as a hedge fund analyst.  He is amazing at explaining things in an intuitive way.  I highly recomend you just go and watch a few videos.

MIT Open Courseware is a site where MIT posts videos of their lectures.  The site has been around for over a decade now, and they probably have nearly the entire course catalog on there, usually with several different lecturers.  They also have the HW, tests, and answer keys.  In other words you can get an entire MIT education minus the piece of paper at the end for free.  While I don't like these videos as much as Khan's, you can't ignore the extra rigor and breadth in the MIT videos.  If you are looking for some to sample, here is the first in an excellent 5 part series on an overview of calculus.  Here's a great Physics I video.
A dynamic periodic table.  I know if you're not currently in a chemistry class you will probably want to skip over this, but I recommend you check it out.  It is a very well done site, and presents a huge range of data in a amazingly simple way.  Most the fun stuff is in the properties tab, so click over to that one.  Then click the various properties (like melting point, or date of discovery) and examine how various properties vary with location in the periodic table.

Physics Forums
The Physics Forums are a great site to waste hours at reading through posts.  They are centered mainly around physics, but have forums for math, and other sciences as well.  Even if you are not interested in physics there are often some very interesting threads on there.  They also have homework help forums where you can post problems and they will attempt to guide you through it.

Cramster is very useful site, that I probably would have put higher in this list if not for the fact that it's pretty exclusively useful for people actually taking classes.  It has worked out solutions for the odd problems for most textbooks.  The answers are generally a lot better than the ones in solutions manuals.  The have even number solutions if you are willing to pay something absurd like $100 a year.

Paper Rater
I've written about Paper Rater in greater detail before, so I'll be brief here.  Essentially, Paper Rater is an enhanced grammar checker.  You enter text and it goes through and gives you stats and possible issues with it.

Graphing Calculator
Not much to say about this one, as it's just a nice, simple online graphing calculator.

Thursday, January 12, 2012

Obama administration says Constitution protects cell phone recordings

When I first saw this I almost dismissed it out of hand as the DOJ arguing against the right to video tape arrests.  It simply didn't compute that they could actually be in favor of people's rights.

Wednesday, January 11, 2012

The coming war on general-purpose computing
Even this is a shadow of what is to come. After all, this was the year in which we saw the debut of open source shape files for converting AR-15 rifles to full-automatic. This was the year of crowd-funded open-sourced hardware for genetic sequencing. And while 3D printing will give rise to plenty of trivial complaints, there will be judges in the American South and mullahs in Iran who will lose their minds over people in their jurisdictions printing out sex toys. The trajectory of 3D printing will raise real grievances, from solid-state meth labs to ceramic knives.

Monday, January 9, 2012

Sunday, January 8, 2012

Why Water Feels Colder Than Air

Air at 80°F can feel uncomforably warm.  Water at 80°F can cause hypothermia.  Why is it that if one has water and air both at 80°F that the air will feel warm and the water will feel cold?  It turns out there are several reasons why water feels colder than air.  If you've never thought about this before I suggest you stop to ponder it for a few moments before continuing on.

Heat vs Temperature
I'll begin with one of my trademark unnecessary background explanations.  Heat is a form of energy.  It manifests itself as kinetic motion in molecules bouncing around off each other.  Temperature on the other hand can be thought of as the average heat energy an object has (with some exceptions).  This is very similar to the relationship of mass and density.  If one wishes to increase density one can either increase the mass (while keeping volume constant) or decrease volume (while keeping mass constant).  Similarly, to increase temperature one can either increase heat energy, or decrease the volume (while keeping the other constant).  The classic example of this a bike pump feeling warm because of compressed air, or some sort of compressed air feeling cold when it's allowed to decompress.

An example I saw Bill Nye do once is the comparison of a lit match to an ice sculpture.  Clearly the burning match has a much higher temperature.  However, since there is simply so much more ice, the sculpture has more heat energy.  To revisit our mass and density analogy, styrofoam has a much lower density than lead.  However, a large block of styrofoam would have a much higher mass than a small pellet of lead.

Another issue that should be addressed is why things feel cold in general.  Your body is warm, and most things in the environment are colder than it.  When your warm body comes in contact with something colder than it, heat from your body moves to the object.  This leaves your body with less heat, and thus less temperature.  The transfer will continue until you body and the object are equal in temperature.  Since your body will continuously adjust its temperature back to normal, in practice this means your body will give heat energy to the object until it reaches body temperature.

Now that we understand the difference between heat and temperature, we can begin addressing the specific reasons why water feels colder than air.  There are five effects that could explain this.  Different combinations of effects will apply depending on the situation.

At the temperatures we are talking about water is liquid and air is a gas.  This means water is much denser than air.  Since density is simply the measure of mass in a certain volume, the higher density means more mass of water in the same volume of air.  Mass is often the best way to talk about how much of something there is.  In this case, since liquid water is denser than air, it simply means there is more water in the close space around your body.  This means it will take more heat energy from your body to warm the water up to body temperature than if it were the less dense air.

At room temperature a cubic meter of water has a mass of 998 kg, while the same volume of air has a mass of 1.225 kg.  The same volume of water as air has about 815 times the mass.

Specific Heat
We know that more mass will take more energy to warm up.  You may be asking yourself if that is the only thing that matters.  Will two different substances, of equal mass, require the same energy to cause the same rise in temperature?  The answer is no.  Every substance has an intrinsic property called "specific heat" that determines how much energy is required to raise the temperature of an equal mass by an equal amount.  The formula for temperature change is: $$$T = \frac{Q}{c m}$$$ Where: T is change in temperature, Q is heat energy, c is specific heat, and m is mass.  This can be viewed as saying, a given amount of heat energy will result in less of a temperature increase the higher the product of mass and specific heat is.

Water has many interesting and unique properties.  One of these is a very high specific heat.  The only known substance with a higher specific heat is ammonia.  This is largely the result of strong attractive forces between molecules, known as hydrogen bonding.  At room temperature the specific heat of water is 4.1813 $$$\rm{\frac{J}{g K}}$$$, and air is 1.012 $$$\rm{\frac{J}{g K}}$$$.  This about 4.13 higher.  Since we saw that specific heat is multiplied by mass, and the mass is also much higher for the same volume, we can look at the combined specific heat times mass of water vs air.  This combined product is about 3366 times higher for water than for air.

Forced Convection
When a fluid like water or air is in contact with your body it is warmed and then becomes less dense, and thus floats on top the rest of itself.  New unwarmed fluid moves in to next to your body and that must then be warmed.  This process is called convection.  In practice convection isn't that significant.  However, forced convection is.  Forced convection simply means that the air or water near your body is being forced to move away instead of naturally floating away.  This is how a fan or wind cools your body.

If you are in a pool of water vs standing in air there isn't much difference in terms of convection.  However, if the water is flowing over you then that is a very significant factor.  In the case of rain or a shower, water is in contact with your body for a few seconds and then leaves, taking whatever heat your body invested in it with it.  In a pool of static water or air your body could bring the temperature up to its own, and then the heat transfer would stop (ignoring gradual convection).  But if water is rushing by this can never happen.

Thermal Conductivity
When two objects of unequal temperature are in contact heat flows from the higher temperature object to the lower temperature one.  This is conduction, one the the three types of heat transfer.  How quickly heat is transferred will depend on the thermal conductivity of the substances.  Water and air have different thermal conductivities.  While, water's isn't that special, air's is very low.  This means air absorbs heat much slower than water does.  Liquid water has a thermal conductivity of about 0.6 $$$\rm{\frac{W}{m K}}$$$, compared to air at 0.025 $$$\rm{\frac{W}{m K}}$$$.  Heat energy is transferred about 24 times faster through liquid water than through air.

Latent Heat of Vaporization
I said above that if volume is held constant, an increase in heat will cause an increase in temperature.  This is true except for when the substance is undergoing a phase change.  In other words, while it is melting or vaporizing, there is heat being added, but the temperature does not go up.  Here is a graph that shows this.  Note the amount of heat energy (x axis) needed to raise water from freezing to boiling vs the amount needed to actually vaporize it.  To vaporize (boil or evaporate) a kg of water takes 2257 kJ of energy.  This is over five times the energy needed to raise water from just above freezing to just below boiling.  To make this clear, it means that causing a kg of water to evaporate requires many times more energy than warming ice water to body temperature.  That energy comes from your body heat, and this is exactly how sweat cools your body.

Like forced convection, evaporation may not occur in all situations.  If you are submerged in water there will be no evaporation.  And, if there is 100% humidity then the air is already saturated with water and there can be no more evaporation. This is likely the case in a shower or in rain.  However, afterwards the humidity can drop.  There is a good chance that the water on your body will have already warmed to body temperature, which will remove all the other effects.  At that point, evaporation alone is what would cause the heat loss.

To summarize:
Water feels colder than air because there is more water near your body (denser), which takes more heat to bring to body temperature (specific heat), and takes heat from your body faster (thermal conductivity).  This water may then be flowing away from your body, taking the heat with it (forced convection), or evaporating and consuming a huge amount of energy to do so (latent heat of vaporization).

Tuesday, January 3, 2012

It seems unlikely that Kim Jong Un will want to reform North Korea, but even less likely that the regime can go on resisting change
It is hard to see how the economy could be modernised without abruptly destroying the state’s paternalistic ruling mythology. Much of the dark interior of North Korea is bereft not only of consumer goods but also of trustworthy information, on anything from prices to politics. Although an increasing number of people, especially in the border areas, are aware of the vast disparity between capitalist South Korea and their own workers’ paradise, defectors say many still do not fully grasp how wide that chasm is. As one defector puts it, explaining why his relatives cling to their belief in the Kim family state when he sends them cash from South Korea: “There is a gap between what you know and what you believe.”

Monday, January 2, 2012


I had to write a report on toothpaste as part of a project for school.  Since I did a fair bit of research into how toothpaste works and what the various ingredients actually do, I figured I'd post it here.

Overview of Tooth Decay
To understand the importance of toothpaste one must first understand the process by which bacteria cause cavities. The bacteria in a person's mouth form a colorless, thin, sticky film called plaque. The bacteria use carbohydrates present in the mouth after meals as fuel. The population grows and they produce acid as a waste of their metabolism.

While teeth are the hardest substance in the human body, they are very susceptible to acid. The acid from bacteria causes the pH level in the mouth to lower. This causes demineralization, and causes the teeth to soften, which in turn reduces their resistance to abrasion. Once the pH level returns to a higher level, minerals naturally present in saliva cause the softened teeth to gradual remineralize. The critical pH level is 5.5. Below this level demineralization occurs, above it remineralization (Dawes).

As long as the process of remineralization is faster than the loss of minerals from acid there will be no decay. However, when carbohydrates are frequently consumed the bacteria can produce more acid than the body can counteract. This leads to tooth decay. Once tooth decay has occurred the body can not repair the damage.

Toothbrushing removes the plaque film that covers one's teeth. This is accomplished through the mechanical action of brushing. It was long thought that toothpaste provided additional abrasive qualities that enhanced this process. Substances like hydrated silica are added to toothpaste to increase its abrasiveness. However recent studies have shown plain water to be as effective at removing plaque as toothpaste (Paraskevas). On the other hand, other studies have shown an additional benefit to using toothpaste (Putt). It is therefore impossible to drawn any definitive conclusions. Toothpaste, however, has numerous other benefits.

Raising pH Level
Since the problem with bacteria is the acid they produce, raising the pH level to make the mouth more basic will neutralize some of the acid and delay tooth decay. Sodium bicarbonate is often used as both an abrasive and to raise the pH of the toothpaste. Since it is slightly basic, it increases the pH in the mouth for some time after use. In addition to directly neutralizing acid, the basic environment makes it harder for the bacteria to grow, which further reduces acid levels.

Cosmetic Additives
One of toothpaste's most obvious benefits is the cosmetic impression of cleaning it has. While a mouth brushed with just water is perhaps as clean as one brushed with toothpaste, there is no doubt that toothpaste leaves the mouth with a sensation of cleanliness. The foaming action of toothpaste is associated with cleaning in general. Surfactants are added to toothpaste to enhance this foaming action.

The flavor of toothpaste is also associated with a clean mouth. While there are a wide variety of flavors the most popular are peppermint, spearmint, and wintergreen. Toothpastes also come in either paste or gel form. The option of paste of gel doesn't change the effectiveness of the toothpaste and the choice is a personal one based on preferences.

Toothpaste is also useful as a delivery mode for numerous chemicals that enhance oral health. The most significant of these being fluoride. Fluoride has a large body of evidence backing up its positive effects for teeth. Studies have shown that fluoride reduces cavities by 24% (Marinho). Furthermore, increasing the fluoride concentration generally decreases the cavity rate (Walsh). There are three forms of fluoride commonly used in toothpaste: sodium fluoride (NaF), sodium monofluorophosphate (Na2PO3F), and stannous fluoride (SnF2). While NaF and Na2PO3F have been shown to be equally effective, SnF2 has been shown to be less effective, and is thus less commonly used today (DePaola; Beiswanger).

Fluoride has three positive effects. First, it reduces the rate that bacteria are able to metabolize carbohydrates into acids. This effect lasts for some hours after using toothpaste with fluoride. Secondly, fluoride enhances the rate at which teeth are remineralized. This offsets a larger carbohydrate intake, for a net reduction in decay. Lastly, fluoride reacts with the minerals (hydroxyapatite) in teeth to form a protective coating (fluorapatite). This coating is more resistant to acid than the naturally occurring material. Specifically, the following reaction takes place when using sodium fluoride:

Ca10(PO4)6(OH)2 + 2 NaF → Ca10(PO4)6F2 + 2 NaOH

The result is that fluorapatite forms on the outside of teeth and resists future acid attacks more readily. However, this coating is very thin and wears off after several hours to a day. This requires regular applications of fluoride.

The use of fluoride in toothpaste is nearly universal. However, there are several other additives which are found in toothpaste to various degrees. Surfactants are added to toothpaste to act as detergents and cause the foaming action of toothpaste. This has already discussed benefits in perception of cleanliness. However, it also has been shown to enhance fluorides ability to penetrate into deeper crevices in the teeth, the result being a reduction in cavities (Caslavska).

Triclosan is an antibacterial agent which was patented by Colgate for use in its Total brand of toothpastes. This patent expired in 2008 and triclosan has since spread to other toothpastes. Triclosan has been shown to cause a modest reduction in cavities and a 30% reduction in gingivitis (Feller; Garcia-Godoy). Its effect on plaque continues to work for hours or days after use (Jenkins).

Xylitol is a nonfermentable sugar that is used in chewing gums and sometimes added to toothpaste. Xylitol, not only will not increase bacteria counts, it can actually have a net negative effect on bacteria counts. This is because xylitol is chemically similar to sucrose, which causes bacteria to attempt to metabolize it. This, in effect, starves the bacteria and kills them. The result is a proven reduction in plaque levels (Milgrom).

Calcium phosphate has been shown to enhance the remineralization process, when used with fluoride it has a greater effect than fluoride alone (Shen). Similarly, nano-hydroxyapatite is a new technology that also enhances remineralization (Tschoppe). These two additives have proven benefits, and are currently only found in specialty toothpastes.