M. E. J. Newman, S. Forrest, J. Balthrop
Physical Review E (Print issue: September 2002)
An analysis of how computer viruses spread through email shows that the current practice of "random vaccination", corresponding to normal use of antiviral software, is an ineffective method for preventing virus epidemics. Clever use of antiviral software can be effective but the right computers need to be vaccinated. An analysis of email address book networks suggest that vaccinating around 10% of computers within a critical subset of the network would be sufficient to prevent epidemics.
Journal article: http://link.aps.org/abstract/PRE/v66/e035101
2) How to balance a stick on your finger
J. L. Cabrera, J. G. Milton
Physical Review Letters (to appear)
With practice, most people have no trouble balancing a long stick on the end of their finger. But as the stick gets shorter, the challenge is greater. The biggest problem in balancing the stick is that human reaction times can be slower than the time it takes for the stick to fall. An analysis of stick balancing shows how the human nervous system copes with balancing problems even for 98% of the time when reaction time isn't fast enough. A new model suggests that the nervous system introduces random motions to a person's finger. Surprisingly, these random motions can help stabilize the stick. This idea of introducing randomness to an unstable situation and thereby creating something more stable has been previously recognized and used in human-made technologies such as the design of high performance aircraft but this study shows it naturally at work in the human nervous system. The authors suggest that these techniques may also be applicable to making buildings more earthquake-proof and to making two-legged walking robots.
Journal article: Available on request
3) Fast pollution filters using carbon nanotubes
A. I. Skoulidas, D. M. Ackerman, J. K. Johnson, D. S. Sholl
Physical Review Letters (to appear)
Filtering gases is a vital process in removing pollutants or toxins from the environment and also serves roles in industrial processes and fundamental studies. Some of the best molecular filters are siliceous zeolites, structures having the chemical composition of sand with networks of pores through them. If the pore size is chosen appropriately, only selected molecules get through while the typically larger toxins or pollutants are blocked. The greatest problem with these types of filters is that gases tend to travel through them far slower than is needed for everyday applications. Now, molecular-level simulations of gas flow through carbon nanotubes shows that they can pass gas through 100 to 1000 times faster than siliceous zeolites. This increased speed could mean nanotubes provide a practical way to make large-scale gas filters.
Journal article: Available on request
4) Weighing gravity
St. Schlamminger, E. Holzschuh, W. Kündig
Physical Review Letters (to appear)
The strength of gravity is surprisingly poorly known compared with many other aspects of nature. Yet, it influences the universe in many ways, from how much we weigh to what orbits the planets follow, to whether or not the universe will end in a "big crunch". A new experiment involving little more than a high-precision set of scales has determined the strength of the gravitational force more than 45 times more precisely than the "official" value. This experiment, performed in an underground pit, involved hanging copper and tantalum metal masses weighing a few pounds from precision scales while moving tanks holding over 13 tonnes of mercury to different positions. The change in weight of the small masses was used to determine the strength of the gravitational force with a precision of 33 parts per million rather than the official precision of 1500 parts per million. The result helps clarify some confusion due to experiments that gave inconsistent values for the strength of gravity.
Journal article: Available on request
5) Some crystals have memories
M. S. McPherson, I. Ostrovskii, M. A. Breazeale
Physical Review Letters (Print issue: September 9, 2002)
New-agers have long claimed wacky properties of crystals, such as the ability to store memories. Although there is no scientific evidence for such claims, physicists have found a behavior that might be called crystal memory. When a crystal of lithium niobate was played a sound, it rang briefly and then went quiet. To researchers' surprise, it then played the sound back about 70 microseconds later.
Physical Review Focus: http://focus.aps.org/v10/st11.html
Journal article: http://link.aps.org/abstract/PRL/v89/e115506
6) Protons and neutrons: a simple picture
G. A. Miller
Physical Review C (Print issue: September 2002)
Protons and neutrons can be thought of as cloudy bags each with three quarks bouncing around inside, according to a new model in nuclear physics. The model allows many properties of nucleons (protons and neutrons) to be calculated far more easily than usual. Interestingly, the model resembles century-old ideas of what atoms looked like, when the "plum pudding" model pictured atoms as a uniform pudding with lumps of electrons inside. The "light front cloudy bag" model treats nucleons as three quarks, the most fundamental particles known, tied to each other and surrounded by a cloud of pions.
Journal article: http://link.aps.org/abstract/PRC/v66/e032201
7) The Physics of Loners
G. Szabó, C. Hauert
Physical Review Letters (Print issue: September 9, 2002)
Physics might help bring people together, claims a pair of physicists. Researchers studying a "public goods game", a simple model of cooperation, believe that allowing players the option to drop out of competition makes teamwork more likely to persist among those who remain. The authors considered games where players were given monetary rewards depending on the behavior of the group as a whole. In previous work, they found that risk-averse loners could drop out of the game altogether and forego the cash to eke out a small but dependable income by themselves. This behavior allowed others to cooperate and come out ahead more often. In a new paper, the authors found that the behavior of players looks a lot like processes in solid-state physics such as magnetism. They suggest that results from solid-state physics could teach us new ways to achieve better results in cooperative games.
Physical Review Focus: http://focus.aps.org/v10/st10.html
Journal article: http://link.aps.org/abstract/PRL/v89/e118101