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Issue 4, 2024
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Extracts from the Internet


A new type of baryon discovered

Two new elementary particles - baryons with a b quark in its composition - have been discovered by the CDF collaboration at Fermilab in the US. The baryons with a mass of 5.8GeV and respective quark compositions uub and ddb were produced in 2TeV proton-antiproton collisions at the Tevatron collider and identified by their decay products. 103 and 134 creation events were detected, respectively. The spin- 1/2 ground state and spin-3/2 excited state were observed for the new baryons. Source: http://www.fnal.gov/pub/presspass/press_releases/sigma-b-baryon.html

Superfluid solid helium?

As reported in Physics Uspekhi 47 215 (2004), E.Kim and M.H.Chan of Pennsylvania State University may have discovered the Bose-Einstein condensation of atomic vacancies in solid 4He - an effect predicted by A.F.Andreev and I.M.Lifshitz in 1969 - when observing a decrease in the moment of inertia of a porous disc filled with helium. However, two verification experiments that followed have produced directly opposite results to each other. In the first, A.S.C. Rittner and J.D.Reppe of Cornell University measured resonant frequency to determine the moment of inertia of a torsion pendulum with a small solid-helium-filled container attached to it. Along with spherically shaped containers, those of square cross section - in which helium is to a large extent involved in the rotational motion - were used to rule out the hypothesis that the near-wall behavior of the helium might be responsible for the condensation. A decrease in the moment of inertia observed at 250 nK probably points to the transition to the superfluid state. The data obtained - in particular, the estimated value of about 1% for the relative mass content of helium in the superfluid state - are in good quantitative agreement with those of E Kim and M H W Chan. The second experiment, conducted at the Low Temperature Laboratory at Helsinki University of Technology, was of a different type and studied the temperature dependence of pressure along the 4He melting curve in the temperature range from 10 to 400nK. Helium showed no evidence for a phase transition until cooled to 80nK. Below this, while it did show a small anomaly (departure from the p~T4 behavior), there are two reasons why this has no relevance to the superfluid transition. First, the entropy of the helium remained unchanged rather than substantially increasing as theory predicts it should at a phase transition. Second, the anomaly is four orders of magnitude smaller than expected for a phase transition. So there is still a question mark over whether superfluidity in solid helium has or has not been discovered experimentally. Source: Phys. Rev. Lett. 97 165301 (2006); Phys. Rev. Lett. 97 165302 (2006)

Casimir force versus charge carrier concentration

The Casimir force relates to electromagnetic field zero-point oscillations. What makes two conducting bodies attract each other is the fact that the space between them does not contain long- wavelength oscillation modes and therefore has lower energy density than that elsewhere. According to theoretical calculations, the Casimir force depends in a certain way on the conductivities of the bodies, i. e., on the concentration of free charge carriers in them. Now F.Chen and U.Mohideen of the University of California, in collaboration with G.L.Klimchitskaya (North-West Technical University, St.Petersburg, Russia) and V.M.Mostepanenko (Noncommercial Partnership Scientific Instruments, Moscow, Russia) have performed the first experimental verification of this dependence. The researchers used an atomic force microscope to measure the Casimir force between a gold-coated polystyrene sphere about 200mkm im diameter and thin phosphorus-doped silicon plates. The separation between the sphere and a plate was z=60-200nm. One of the plates was increased in conductivity by doping with impurities using thermal diffusion. A superprecision instrument calibration was carried out and measures to eliminate external perturbing factors, such as electrostatic fields, were taken. The measurements are in good agreement with theoretical calculations. As expected, the plate with lower conductivity was found to produced a weaker Casimir force (for z=70nm, the difference was 17pN). The effect shows potential for applications in nano- or microelectromechanical devices. Source: Phys. Rev. Lett. 97 170402 (2006)

Mechanoluminescence

Mechanoluminescence (or triboluminescence) refers to the glowing from a sample that has been broken apart or subjected to other short-duration mechanical action. The reason for the glowing is the recombination of the charges that appear at the boundaries of the fracture. K.Suslick and N.Eddingaas of the University of Illinois studied the glowing of microscopic sugar crystals suspended in a liquid irradiated with sound waves. Spectroscopic observations revealed a strong glowing effect both for the crystals themselves (continuous spectrum) and for the emission lines of gases (helium and argon) that were dissolved in the liquid. The high intensity of the emission is explained by the cavitation effect due to gas bubbles collapsing under the action of the sound. At the instant when a bubble collapses, a very hot and high-pressure (hundreds of atmospheres) region develops in the liquid locally. A shock wave propagating in the liquid speeds up sugar particles, and it is collisions between these at a relative velocity of about half the speed of sound which produces mechanoluminescence. Because of the high frequency involved (i. e., that of sound), the resulting radiation was more intense than observed in previous mechanoluminescence experiments, with crystals usually broken by hand. Source: Nature 444 163 (2006)

Refraction of light at the boundary of a chiral liquid

An experiment conducted by A.Ghosh and P.Fischer at Harvard University in the US has revealed that a laser beam splits in two parts at the boundary of chiral liquid, one whose molecules exist in one of two mirror-image forms. The effect is due to the difference in refractive indices for light waves with opposite circular polarizations: a linearly polarized light wave (which can be represented as the sum of such waves) splits into two waves refracted at slightly different angles when passing from air to a liquid. Because of the very small angle difference, a series of up to 20 (triangular prism-shaped) liquid-filled vessels had to be used to detect the effect. The measurement showed that each of the two beams is indeed polarized circularly at the output. Also studied was the internal reflection of a light beam in the liquid at the boundary with the air. In this case the reflection angles of the circularly polarized wave differ from the angle of incidence of the original wave - again leading to the splitting of the light beam. Source: Phys. Rev. Lett. 97 173002 (2006)

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The Extracts from the Internet is a section of Uspekhi Fizicheskih Nauk (Physics Uspekhi) — the monthly rewiew journal of the current state of the most topical problems in physics and in associated fields. The presented News is devoted to the fundamental discoveries of physics and astrophysics.

Permanent editor is Yu.N. Eroshenko.

It is compiled from a multitude of Internet sources.
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