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| Issue 11, 2024 |
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Extracts from the Internet | ||
A Superconducting Ferromagnet UCoGe1 September 2007Researchers at the University of Amsterdam and the University of Karlsruhe were able to show that the intermetallic compound UCoGe, a weak ferromagnet (Curie temperature 3K), is at the same time a superconductor at temperatures below 0.8K and at normal atmospheric pressure. Superconducting properties were also detected earlier at high pressure or very low temperatures in metal ferromagnets UGe2 and URhGe, and some evidence was reported that UIr and ZrZn2 were also superconducting. It was assumed that the possible mechanism of superconductivity in ferromagnets operates on magnetic transitions between two polarized phases. The superconductivity in UCoGe is most likely very different - involving magnetic fluctuations that result in spin-triplet pairing of electrons. This conclusion is based on measuring specific heat capacity and critical magnetic field as functions of temperature. Source: Phys. Rev. Lett. 99 067006 (2007) Hydrogen-71 September 2007An isotope of hydrogen 7H, consisting of a lone proton and six neutrons was produced and investigated in an experiment at the GANIL facility in France. The isotope 7H exists, like other hydrogen isotopes heavier than tritium (4H, 5H and 6H), as a short-lived resonance state that decays into tritium and neutrons. 7H nuclei were produced in the reaction 12CH(8He,7He →3H+4n)13N as a result of splitting of one proton from a nucleus of 8He when a beam of 8He nuclei is sent into a gaseous carbon-containing target. A special active detector recorded both the energy spectrum and the trajectories of 13N nuclei generated in the reaction. This data allowed complete reconstruction of the kinematics of nuclear reactions and identification of a 0.09-MeV-wide peak close to the energy 0.57MeV corresponding to the resonance state 7H. All-in-all the experiment recorded seven events of creation of 7H. Some indications of the existence of 7H were obtained by A.A.Korsheninnikov and coworkers in a 2003 experiment that detected a steep rise in the nuclear reaction cross section in the vicinity of the 3H+4n threshold, which is in qualitative agreement with the results of the new GANIL experiment. So far the available theoretical models do not provide an accurate prediction of the 7H resonance energy but point to energies in the range from 1 to 3MeV. Further experiments with 7H may clarify another interesting aspect, namely the possibility of producing a bound state of four neutrons. Source: Phys. Rev. Lett. 99 062502 (2007) Femtosecond x-ray holography1 September 2007H. Chapmen (University of California, Lawrence Livermore National Laboratory) and colleagues in the USA, Sweden and Germany implemented a new method of generating holographic x-ray images of objects at femtosecond temporal resolution. X-ray pulses of a free-electron laser were sent through a small hole in a mirror and heated the structures to be investigated - in this case polystyrene balls of about 140 nm in diameter. The pulse knocked electrons off the ball surfaces after which the balls expanded explosively as a result of mutual repulsion of the remaining positive charges. The other part of the beam (the reference beam of the hologram) passed through the membrane and was reflected by a second mirror. X-rays bounced off polystyrene balls and the second mirror were then reflected from the front mirror and interfered in the digital camera creating in it a holographic image of the exploding balls. This technique made it possible to study the structure of specimens (balls) and their evolution at record temporal resolution - about one femtosecond. Source: Nature 448 676 (2007) Fluorescent microscopy1 September 2007A team led by Stefan Hell at the Max Planck Institute for Biophysical Chemistry in Gottingen developed a novel technique for fluorescent optical microscopy with resolution in the nanometer range. Special fluorescent dyes were added to living cells. Light emission from dye molecules could be switched on or off using illumination by external radiation. The average distance between dye particles was greater than the wavelength of the optical radiation and the emitted light was recorded with a digital camera. Then fluorescence of the neighboring particles was switched on and recorded. The process was repeated many times. This resulted in obtaining numerous images; combined, they gave an image with spatial resolution of 10 to 30nm and high signal-to-noise ratio. Source: http://www.physorg.com/news105966261.html Unique event of microlensing1 September 2007A unique event of gravitational microlensing was recorded in the Cassiopeia constellation. Lensing occurred to the light of a star located in an area of the sky with low stellar concentration. Also, this star happens to be the brightest and closest (about 1 kps from the Earth) among all other stellar sources that were observed so far in microlensing events. The probability of such cases of microlensing is very low but in view of this new event their frequency may be 50 times greater than was previously assumed. The considerable brightening of the star GSC 3656-1328 was discovered by amateur astronomer A. Tago in Japan on October 31, 2006, after which this star was observed using several other telescopes. An analysis of its spectrum showed that brightness varies not because the star is inherently variable but as a result of gravitational lensing on an unknown object. Source: http://arxiv.org/abs/0708.1066 |
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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