## wyldeling's Articles, Page 1 of 3

20 Apr 09

### First Rule of Computation: Don't Trust Your Calculator

Somewhere along the line, we all come to trust the numbers that come out of computers. After all, an infallible device told us it was true. So, let us start with a simple example, on a ten digit calculator enter the following:

``1E12 + 1 - 1E12``

If the 1 is in any position, but the last one, your calculator spits out 0. Despite the fact that the answer is very clearly 1. Using this example, and others, I try to have my students resist the urge to enter numbers into their calculators until the very end of the problem, and they will then usually avoid such problems. Despite my advice to my students, this bit me twice in two days, leading to a corollary to the first rule:

22 Aug 08

### Antimatter Bounces off of Matter

Science fiction has often relied on matter and antimatter annihilating each other as a power source. With current technology, producing anti-matter is prohibitively expensive, and most view this as the biggest hurdle for these types of power plants. Basic physics may provide another significant hurdle, however.

Physical Review Focus reports that upon reanalyzing data from 12 years ago, an Italian team discovered that – contrary to popular belief – antimatter and matter may bounce off each other before they’re annihilated (Original paper, subscription required). The key to this discovery was the annihilation events in their data were clustered into two groups: The first group occurred when the antiprotons interacted with the helium in their apparatus, and the second set of events (up to 25% of the total number) occurred at a later time. They determined this second set occurred because the antiprotons were reflected off of the back wall of their device to be later annihilated by the helium atmosphere, instead of either annihilating the aluminum in the walls or passing through entirely. This effect is called Rutherford scattering, and at the speeds they were working with (1 – 10 keV, or 0.14 – 0.46% of c) the antiprotons are more likely to find themselves scattered by the aluminum nuclei than they are to annihilate the nuclei. At lower speeds (500 eV, or 0.10% of c), this effect may peak with 50% of the antiprotons that make it to the back wall being reflected by it.

04 Oct 07

### Abuses of Impersonal Scientific Writing

Being an academic, I regularly attend seminars on topics that may not be interesting to anyone else on the planet. Prior to the talk, an abstract is sent out by the speaker to give us an insight into what he/she will be discussing. A good abstract should be no more than an essential summary of what the speaker will discuss; it is usually no more than a paragraph in length, and is often tersely worded. The rare exceptions to this length requirement usually aren’t the best at conveying the essential information. For a seminar I attended recently, the abstract violated this "rule" by weighing in at a whopping four paragraphs. However, even considering this excessiveness, the opening sentence is what really drove me over the edge. The abstract began with the phrase, "One presents a critical analysis…" (Emphasis added).

06 Jun 07

### Judge Voids Conviction of Teacher in Porn Pop-Up Case

In January, a jury in Connecticut found substitute teacher Julie Amero guilty of four felony charges of "risking injury to a minor or impairing the morals of a child" due to a 2004 incident in which her classroom PC became infected with pornographic pop-ups. Today, however, an upper judge effectively hit the reset button on the trial, claiming "information discovered after her conviction has direct bearing on whether she is responsible for risking harm to her students when pornographic pop-ups appeared on a classroom computer." Such information likely includes a pro bono complete forensic analysis of Amero’s classroom PC, which was performed by a group of independent security researchers and delivered to the defense attorneys in April. The results of the study, however, will not be released until any potential new trial concludes.

31 Mar 07

### Using Relativity to Reduce Computational Complexity

The universe operates on many different size scales, from intra-particle to inter-galactic. Most phenomena do not require more than one scale to be fuly understood. But, some phenomena operate along multiple scales. For example, the particles in a coronal mass ejection interact with each other (short scale) while they travel from the Sun to the Earth (long scale). In order to be correctly simulated, both length scales must be accounted for; making multi-scale problems difficult and computationally expensive to model.

Dr. Vay, a physicist from Lawrence Berkeley National Laboratory, has shown (PRL abstract, Physical Review Focus) that special relativity can be used to reduce the time required to simulate systems that have multiple scales in both time and distance. According to relativity, both time and distance change based upon the speed of the observer. Dr. Vay showed that ratio between the sizes of the multiple scales also changes with the speed of the observer. In other words, a speed can be found that reduces the differences between the scales, thus decreasing the number of steps required to simulate the system. To test this hypothesis, Dr. Vay simulated the interaction of a pulse of protons (length ~10 cm) travelling down a particle accelerator beam line (length ~1 km) and interacting with a cloud of electrons. On an 8 processor cluster, this simulation normally requires a week. With these improvements, the simulation only required 30 minutes giving the same results.

05 Mar 07

### Improving Solar Energy Conversion

After reading an article in Physics Today, it is easy to see why many view solar power as a panacea for our growing energy needs. "The enormous power that the Sun continuously delivers to Earth, 1.2 Ã— 105 terawatts, dwarfs every other energy source, renewable or nonrenewable." For a comparison, an estimate of the recoverable oil on Earth is approximately 3 trillion barrels containing "1.7 Ã— 1022 joules of energy, which the Sun supplies to Earth in 1.5 days." Our current technology, though, is woefully inadequate to tap into the potential of this rich energy source.

24 Feb 07

### Circumcision Plays a Key Role in Preventing AIDS

In a study by the National Institutes of Health (NIH) that was ended last December, it was discovered that circumcised men were 50% less likely to become infected with HIV than uncircumcised men. As reported then, the NIH stopped the study only part way through because the treatment was so overwhelmingly effective that "it would have been unethical to continue without offering circumcision to all 8,000 men in the trials." For the studies that are to be published yesterday, the data was re-examined, "excluding a few men whose H.I.V. status was misdiagnosed during the trial and combining the results of three trials," producing "a protection rate of about 65 percent."

01 Feb 07

## Introduction

Despite the continuing advances in the capabilities of computer languages, such as C++, Fortran remains the lingua franca of computing in physics. On the whole, I prefer the syntax and flexibility of C/C++, despite its potential for abuse.1 With the appropriate libraries,2 and some investment of time, C++ can be used to write code that is easier to understand than,3 and comparable in speed to,4 Fortran. However, despite the power and ease of use of the streams library in C++, it is difficult to read-in fixed width fields without modifying the streams’ behavior, unlike in Fortran.

17 Jan 07

### Dark Energy Not Detected at Small Length Scales

According to Newtonian theory, the fate of the universe is clear: either the universe will keep expanding at an ever decreasing rate, or, if there is enough mass, it will eventually collapse in on itself. But, there is evidence that the rate of expansion is increasing. To explain this, phycisists have postulated the existence of a substance called dark energy that exerts a repulsive force counteracting the effects of gravity. According to cosmologists, the effects of dark energy should be observable as a short range force detectable at length scales around 85 Âµm.

04 Jan 07

The American Physical Society (APS) has recently announced a program where most of their articles can be made publicly available to anyone who wishes to read them. In order for an article to be made "Free to Read," the APS requires a modest fee (\$975/Physical Review article and \$1300/Physical Review Letter article), which anyone can pay, and the article will then be available for download by the general public for free. This does not mean that the APS surrenders the copyright to these articles, nor can they be posted on any other websites without prior permission.

13 Dec 06

### Proposed Technique for Magnetically Separating Blood

PhysicsWeb is reporting that Edward Furlani of the University of Buffalo has proposed a potentially more efficient method for separating the components of blood. Normally, the white blood cells and red blood cells are "separated out from donated blood because a patient may only need one component at any one time." This requires spinning the blood in a centrifuge for up to 20 minutes, which in an emergency situation is an extremely long time. Furlani’s proposal seeks to shorten this time by using the fact that in deoxygenated blood red blood cells are paramagnetic and white blood cells are diamagnetic. The separation process would involve sending the blood down a channel embedded with small magnets on one side. The red blood cells would then be attracted to the magnets, while the white blood cells would be repelled. The only apparent catch is the method would not work on oxygenated blood, as oxygen rich red blood cells are diamagnetic and would behave the same way as the white blood cells.

11 Dec 06

### Humorous Technical Jargon

One of my passions is the English language. I enjoy the flexibility and mutability of its structure and meaning, and in day to day conversations this inherent fuzziness makes up a large part of what I consider humorous. The normally flexibility of English is in stark contrast to the rigid definitions and strict interpretations that are found within technical jargon. This makes technical jargon ripe for manipulation and humorous interpretation when you relax the rigidness with which the words and phrases are interpreted. Some of my personal favorites come from physics:

06 Dec 06

### GM to Build a Plug-In Hybrid SUV

MIT’s Technology Review reports that GM plans on making a plug-in variant of the hybrid Saturn Vue. As reported here previously, hybrid vehicles are at a natural disadvantage to internal combustion based vehicles as their higher price tag offsets most of the savings gained from the reduction in gas consumption. However, many hybrids have been modified so that their batteries can be recharged using household electrical power. These vehicles are claimed to achieve 100 MPG, or better, fuel economy. Despite the improvement, the environmental impact of these vehicles remains unclear because in some areas electricity is produced primarily from coal powered plants. But, as "greener" forms of power become more common, the effective emissions from these types of vehicles will decrease. GM has not specified how the plug-in capabilities will alter the current price of \$22,995 nor the fuel economy of 27 MPG city / 32 MPG highway.

21 Nov 06

### NASA Still Trying to Re-establish Contact With Mars Global Surveyor

Since November 2nd, NASA has been unable to contact the Mars Global Surveyor spacecraft. The radio silence began just before the spacecraft’s tenth year in space, and nearly five years after its original mission concluded. At this point, "preliminary indications are that a solar panel became difficult to pivot, raising the possibility that the spacecraft may no longer be able to generate enough power to communicate," but the engineers are still exploring other possibilities. Attempts to capture an image of the spacecraft by cameras on the Mars Reconnaissance Orbiter have, thus far, failed. As their next plan of attack, NASA engineers will try to use the Mars’ rovers as intermediaries in case the spacecraft has the power to communicate with them, but not Earth.

10 Nov 06

### Tiny Magnetite Crystals Found to Efficiently Remove Arsenic From Water

The New York Times is reporting that a group from Rice University has discovered a way using nanoscopic magnetite crystals to remove arsenic from water much more adeptly than current filtration technology. Current filtration technology uses larger iron particles to magnetically capture and remove the arsenic from the water. When powdered magnetite crystals with widths smaller than 40 nanometers were introduced to arsenic laced water, however, it was found that they bind with the arsenic much more efficiently. Researchers found that magnetic particles at 12 nanometers wide "could bind up to 100 times as much arsenic as the larger iron particles currently used in filters" and still be easily removed with common magnets. However, the accumulated arsenic residue would have to disposed of properly, and "no one knows the risks of the arsenic residues’ being consumed by accident or of their leaching from landfills back into water supplies."