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Issue 12, 2024
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Extracts from the Internet


Ferromagnetic carbon

Many organic materials have been observed to exhibit ferromagnetic properties at low (below 65 K) temperatures. Now an international group of scientists led by T L Makarova has for the first time found ferromagnetism at room temperature in Rh-C60, a polymerized form of fullerene with a rhombohedral structure in which the molecules C60 form flat graphite-like layers. Rh-C60 has a Curie temperature of 500 K and shows a hysteresis typical of ferromagnetic materials. Careful analysis showed that the finding cannot be explained by the presence of magnetic impurities. This follows, in particular, from the fact that a sample of Rh-C60 loses its ferromagnetic properties on heating and depolymerization. The discovery team believes that ferromagnetism in Rh-C60 is due to unpaired electrons or alternatively to the electronic properties of the polymer's structural defects. Although the ferromagnetism of Rh-C60 is relatively weak, still it is strong enough for small pieces of Rh-C60 to be attracted by a common magnet. The discovery may help the development of nonmetallic magnets for future technological applications. Source: T. L. MAKAROVA, B. SUNDQVIST, R. HOHNE, P. ESQUINAZI, Y. KOPELEVICH, P. SCHARFF, V. A. DAVYDOV, L. S. KASHEVAROVA, A. V. RAKHMANINA Nature 413 716 (2001)

Decay of a uniformly accelerated proton

While in the Standard Model of elementary particles the proton is stable, the Grand Unification theory predicts that it can decay. The experimental search for proton decay has thus far met with no success. The only result obtained is a limit on the proton lifetime, >3 1033 years. This limit, as well as calculations within the Standard model are valid for the proton at rest. However, as long ago as 1965 V L Ginzburg and S I Syrovatsky showed that an accelerated proton is not stable and should decay into a neutron, a positron, and a neutrino. The Brazil physicists D A T Vanzella and G E A Matsas investigated the question of what this decay would look like for an observer who is accelerating together with the proton. It was found that the proton by itself does not have to decay - contrary to what one observes (mentally) to occur in a laboratory reference frame at rest. The paradox is resolved by considering that a thermal background of various kinds of particles should exist in an accelerated frame. This phenomenon is known as the Unruh effect and is related to the difference in the state of the vacuum between the accelerated frame and that at rest (Ginzburg V L, Frolov V P, . Sov. Phys. Usp. 30 1073 (1987)). Vanzella and Matsas established that from the accelerated observer's viewpoint the proton does not decay - but rather is destroyed - on colliding with thermal background particles. For the rest observer, however, these particles do not exist. According to calculations, a proton's lifetime before its decay in the laboratory frame equals its pre-collision lifetime as seen from the viewpoint of the accelerated observer. Unfortunately, to detect the decay of an accelerated proton experimentally is not as yet possible because of the need for creating very large accelerations. Source: Phys. Rev. Lett. 87 151301 (2001)

Controlling Bose-Einstein condensate

A team of German researchers headed by J Reichel has developed a technique to obtain a Bose-Einstein condensate on a flat surface and to move it along the surface with the help of electric fields. First, two parallel 50-mkm-wide gold wires were deposited lithographically onto an insulating substrate. Then onto the surface of this device, called a `chip', rubidium atoms were transferred from a standard magneto-optical trap. The magnetic field of the current flowing through the chip's wires created a microtrap, in which rubidium atoms were cooled into the Bose- Einstein condensation state by an alternating electromagnetic field. By sending electrical pulses along the wires it was possible to move the condensate over distances of up to 1.6 mm along the chip surface. It was found that, contrary to previous belief, the proximity of the condensate to the surface does not destroy the coherence of the atomic states. Source: Nature 413 498 (2001)

Oxidation mechanism of CO

J R Hahn and W Ho using the scanning tunneling microscope have investigated the mechanism whereby single molecules of CO2 form in the process of oxidation of CO molecules. In one experiment, a few oxygen atoms and a CO molecule were adsorbed on the surface of a silver plate. With the help of the microscope tip, the CO molecule was moved in the space between two neighbouring O atoms, and when the CO-O distance became 1.78 A, O-CO-O complexes appeared, which have never been observed experimentally even though the possibility of their formation has been discussed theoretically. When an electron tunneled from the microscope tip to an O-CO-O complex, the latter broke up into a molecule CO2 and a separate O atom. In another experiment, only adsorbed O atoms were present on the surface, and a CO molecule was attached to the tip. As CO approached an oxygen atom, a CO molecule went over to the surface and reacted with O to form CO2. The experiments identified individual O atoms (rather than their molecular combination O2) as the species with which CO reacts on the surface. Source: Phys. Rev. Lett. 87 166102 (2001)

The Blandford-Znajek effect

The spectrum of radiation from the core of the bright Seyfert galaxy MCG-6-30-15 has been measured with the help of a space- based X-ray telescope XMM-Newton. A detailed study was made of the spectral region close to the iron line at an energy 6 KeV. The line is rather broad and has a redshift, suggesting that it formed in the very central part of the gaseous accretion disk around a black hole. As it turned out, the standard models of accretion disks cannot explain the profile of the line, nor the strength of emission it produces. The XMM researchers believe that the unusual spectral feature they observed can be explained by assuming that the extra emission is generated not in the accretion disk but rather close to the event horizon of a rotating black hole. A mechanism in which a magnetic field acts to transform the rotation energy of a block hole into radiation was proposed in the theoretical work of R D Blandford and R Znajek in 1977. The XMM-Newton data may be the first direct evidence for this mechanism. Source: http://xxx.lanl.gov/abs/astro-ph/0110520

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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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