Archive for the ‘Scientific American’ Category

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Hurricanes and global warming

July 19, 2007

There’s an article in Scientific American (July 2007) about the relation between global warming and hurricanes. I learned a few things from this:
A cyclone, typhoon and hurricane are the same thing; they only differ in the region where they are observed.

How do hurricanes form?

  • The sun raises the Sea Surface Temperature (SST)
  • Water is evaporated to release the excess heat
  • The moisture raises and condenses into rain
  • When raindrops are formed, latent energy is released
  • The heat goes up and creates ‘updrafts and thunderclouds’
  • Beneath this area, a low pressure zone is created which ‘sucks up’ moist air
  • Due to Coriolis forces due to the earth’s rotation a vortex is created
  • “The eye” is a low pressure area at the bottom of this vortex
  • Due to the circling hot air, the rising air dries and gains energy
  • Some of this air is absorbed again in the eye, and some of the air ‘spirals out’ over a large area (many kilometres)

How hurricanes form - Copyright Scientific American

The different seasons play a role as well:
The energy released when raindrops form heats the atmosphere

  • In winter, the heat goes up and radiates into space
  • In summer, the heat rises to higher altitudes in tropical areas

Further ingredients needed to start a hurricane:

  • high SST (>26 degrees Celsius); SST may rise due to the greenhouse effect
  • plentiful water vapour
  • low pressure at the ocean’s surface
  • weak wind shear between low and high altitudes (strong winds destroy emerging vortices)

The rising SST may (partly) originate from the greenhouse effect. However, in 2004 and 2005 we saw a lot of hurricanes, but 2006 was a quiet year.

Some scientists believe this is due to the “Atlantic Multidecadal Oscillation” (AMO), which is basically a cycle in which temperatures rise and fall. But simulation shows that this can’t be the whole story (the temperature difference is only 0.5 degrees Celsius). The models do show (as far as they are correct; which is difficult to assess) that human action is likely a cause of the rising SST. Approximately 0.6 degrees Celsius can be attributed to human action (probably without the AMO) since 1970. It is noted that this may sound small, but only one degree can change the storm’s intensity to a higher category. This may well explain the rise in the number of ‘high’ category hurricanes.

The fact that 2006 was a quiet year (in stark contrast to 2004 and 2005) is due to a different factor. In 2004/2005, El Nino warmed the ocean. La Nina cooled the ocean the subsequent year. This is explained in the remainder of the article.

The article concludes that the hurricane threats are likely to get more severe.

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Antibacterial soaps

June 16, 2007

In the category ‘Weird Science’ an article appeared on the site of Scientific American about antibacterial products. More and more antibacterial products are used, but to what avail?
Normal soaps wash away ‘nonspecifically’, “meaning they wipe out almost every type of microbe in sight—fungi, bacteria and some viruses—rather than singling out a particular variety.
On the other hand, after applying antibacterial products, conditions may arise which may actually help the resistent bacteria, because not all bacteria may be killed. In fact, “a small subpopulation armed with special defense mechanisms can develop“, so that these bacteria develop a tolerance and reproduce. This, in turn, may help the bacteria in growing resistant to certain antibiotics.
A problem that arises is that, at least in America, certain antibacterial compounds are found in “60 percent of America’s streams and rivers“, and may eventually end up in crops.
In the end, the advise is to wash your hands 3 times a day with regular soaps, and leave the antibacterial soaps at hospitals.

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Think more, get less

May 30, 2007

There’s an article in the June 2007 episode of Scientific American, also published on their site.It is written by Kaushik Basu.
It’s about the curse of rational choices when playing the “Traveler’s Dillemma” game:

“Lucy and Pete, returning from a remote Pacific island, find that the airline has damaged the identical antiques that each had purchased. An airline manager says that he is happy to compensate them but is handicapped by being clueless about the value of these strange objects. Simply asking the travelers for the price is hopeless, he figures, for they will inflate it.Instead he devises a more complicated scheme. He asks each of them to write down the price of the antique as any dollar integer between 2 and 100 without conferring together. If both write the same number, he will take that to be the true price, and he will pay each of them that amount. But if they write different numbers, he will assume that the lower one is the actual price and that the person writing the higher number is cheating. In that case, he will pay both of them the lower number along with a bonus and a penalty–the person who wrote the lower number will get $2 more as a reward for honesty and the one who wrote the higher number will get $2 less as a punishment. For instance, if Lucy writes 46 and Pete writes 100, Lucy will get $48 and Pete will get $44.

What numbers will Lucy and Pete write? What number would you write?”The point is, when you don’t think much about it, you’d choose $100. However, when you start thinking more, you’d write down $99: because if you write down $99, and the other person will write down $100, you will get $101, while the other only gets $99. Then you start wondering if the other person thinks the same… and you obviously don’t want the other person to have more money. So you reduce your amount to $98 (thinking the other person will write down $99), so you’ll get $100, and the other person only $96. And so on. In the end, you’ll arrive at $2. In this way, you earn a lot less then the naively chosen $100.

This problem is the same, the article explains, as the Prisoner’s Dilemma: “… in which two suspects who have been arrested for a serious crime are interrogated separately and each has the choice of incriminating the other (in return for leniency by the authorities) or maintaining silence (which will leave the police with inadequate evidence for a case, if the other prisoner also stays silent).”

A Nash equilibrium, is when there’s no benefit (put simply) to change your strategy: in this case the equilibrium is at $2 (the absolute minimum of choices). This is what Game theory predicts; but it conflicts with our intuition.

In experiments, the choice people make depends on the reward: when the reward is low, the choice will on average be higher. On the other hand, when the reward is high, the choice will be lower. This makes sense, because when the reward is high relative to the choice, it’s more advantageous to lower your choice. For example, if the reward is not $2, but $50, you wouldn’t want your choice to be too high: the penalty you’d get would severely impact your profits.

Then why do we make these choices, based on our expectations that the other person will choose a high number? The article suggests:
“Perhaps altruism is hardwired into our psyches alongside selfishness, and our behavior results from a tussle between the two. We know that the airline manager will pay out the largest amount of money if we both choose 100. Many of us do not feel like “letting down our fellow traveler to try to earn only an additional dollar, and so we choose 100 even though we fully understand that, rationally, 99 is a better choice for us as individuals.”

The moral: sometimes it’s good not to think too extensively about seemingly simple questions.

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Huntington’s disease

May 6, 2007

In the April/May 2006 (Yes, it’s an oldie, but I’m just catching up) edition of Scientific American Mind, there’s an interesting article written by Juergen Andrich and Joerg T. Epplen about Huntington’s disease.

It starts with simple incidents, such as forgetting a familiar address, or dropping a cup. But they are not incidents. Not clumsiness, forgetfulness or overreaction either. At least, when you have Huntington’s disease, an inherited disease of which the mutating gene was discovered in 1993. It leads to “progressive destruction of the brain, crippling muscles and mental function“. This mutation wreaks havoc inside the brain.

A single gene on chromosome 4 (the huntingtin gene (no misspelling)) is the cause. DNA consists of 4 bases: Cytosine, Adenine, Guanine and Thymine. If the CAG sequence on this gene occurs more than 35 to 40 times (instead of the regular 28 times), this chain becomes too long and causes trouble. The longer the chain of CAG-sequences, the earlier the disease starts showing, and the more severe it gets.

The symptoms usually show up when at age 35-45, but this also depends on the length of the chain.

Saint Vitus dance, an “involuntary movement disorder“, is characterized by “brief, irregular contractions that are not repetitive or rhythmic, but appear to flow from one muscle to the next. These ‘dance-like’ movements of chorea (from the same root word as “choreography”) often occur with athetosis, which adds twisting and writhing movements.” This is also seen in Huntington’s disease. But mental symptoms often occur before the physical problems, which also leads to social problems (relatives, friends, etc.), and even suicide. Before 1993 (when the responsible gene was discovered) people were often misdiagnosed as “mentally ill or alcoholic”.

What follows is something I don’t fully understand and therefore may not be very clear, but I’ve included it nonetheless:
When the elongated protein starts binding with other proteins, the function of those proteins is in danger.
Glutamate is a neurotransmitter, a chemical which helps a neuron “talk” with another cell. Synapses allow the neurons to form a network and communicate, and function as a system.
Via some complex process, some neurotransmitters won’t be removed “such as glutamate from the synapses“, resulting in “adjacent neurons continually excited” which will damage the cell.
Because of some other difficult process, it’s inpossible for the huntingtin protein to bind to the HIP-1 protein: “the neurons are driven to kill themselves.”

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Vegetables

April 23, 2007

In the May edition of Scientific American, there’s an article about consciousness of coma / vegetable patients. It’s titled “Eyes Open, Brain Shut”, and written by Steven Laureys.

When people slip into a coma, they don’t open their eyes, but some of them may show some reflex movements of the limbs. If people come out of their coma, they can enter a vegetative state, in which they remain unconscious; they are awake, but not aware. For instance, they have sleep/wake cycles, and some form of movement which is not purposeful but only reflexive.


How do you measure the awareness of a patient? How do you diagnose a vegetative state? This may be helpful to distinguish between patients who may recover or not. A MRI or CT scan can show how damaged the brain is, but it’s impossible to see if the patient has some level of consciousness. An EEG (ElectroEncephaloGram) measures the brain’s electrical activity which is able to show the state of wakefulness, but not a reliable change in awareness.

With the use of a PET (Positron Emission Tomography) scanner, the metabolic activity can be viewed (measured by its consumption of glucose). In the vegetative state this metabolism is lower. When the patient is at rest, it can’t successfully distinguish between the vegetative and minimally conscious state. This changes when external stimuli like pain and spoken words are added to the equation. This makes sense, because the awareness in a vegetative state is lower then in a minimally conscious state.
Persons in a vegetative state may very well understand commands: there is a “conscious linguistic processing in the vegetative patient”. Furthermore, in some “mental imagery tasks”, the patient understood the tasks (tasks like: imagine walking through the rooms of your house). These responses were indistinguishable from that seen in the healthy subjects. However, there may be a possibility that the patient was transitioning to a minimally conscious state, in which the awareness is raised.

It’s a well written article; so if you have access to it, I’d recommend reading it.

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Common sense?

March 10, 2007

Scientific American: Fact or Fiction?: Living People Outnumber the Dead
Booming population growth among the living, according to one rumor, outpaces the dead.

I read in the above article about the question whether the living people outnumber the dead. From the article:
“The human population has swelled so much that people alive today outnumber all those who have ever lived, says a factoid whose roots stretch back to the 1970s. Some versions of this widely circulating rumor claim that 75 percent of all people ever born are currently alive.”

Unless you believe the world started populating around the time Jesus supposedly died on the cross, this can’t be true.
A highly simplified model could be the following:
If we start with 1 couple (2 people), which produce slightly more than 2 children who (when their time comes) produces more than 2 children … and so on, we can ask the following:

When is the sum of all the people produced equal to 6 billion (current population)?
If we take as an exponent 1.025 (so that 1000 couples produce 1025 new couples), it takes less than 800 generations. Of course, we didn’t take anything in account (plagues, food shortage, wars, infertile men/women, gay couples, abortions, women who are never in the mood, ugly/stupid people who couldn’t get a date, etc), but the exponent is very low.
Even if we take as an exponent 1.002 (1000 couples produce 1002 new couples), we need less than 8200 generations to accomplish the total amount of 6 billion people who are dead. The first homo sapiens originated from about 200.000 years ago from Africa (Wiki).

Estimations for the year 2050 range between 7.3 and 10.7 billion people, giving a much larger exponent than we took.
I think we can safely say it’s bullshit to say that more people are alive now than that ever lived.
(The article comes to the same conclusion; it just surprises me that people could ever believe such a statement)