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| Issue 11, 2024 |
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Extracts from the Internet | ||
Quantum computer1 September 1999A promising approach to quantum logic design has been developed by researchers at MIT and at Delft University of Technology. As an improvement over small electromagnetic cavities, nuclear-magnetic resonance on molecules, and photons proposed previously, their idea is to use microscopic superconducting loops as quantum memory cells. Because electric current in such loops obeys the laws of quantum mechanics, two opposite directions of the current may represent not only the zero and one states but also their superpositions, with a consequence that the so-called `qubits' of information are realized. The major advantages, the researchers claim, are that present-day technologies allow large systems of superconducting loops to be easily fabricated and that to couple such cells, additional loops can be introduced. For a quantum computer to be practical, it must have at least 80 memory cells. Individual cells can be controlled by magnetic microwave pulses, and to read out the information they store, superconducting magnometers can be used. Importantly, a way to make memory cells to perform coherently is yet to be found. Source: http://web.mit.edu/news.htm One electron cyclotron1 September 1999According to quantum mechanics, an electron in a uniform magnetic field occupies discrete energy levels known as Landau levels. S Peil and G Gabrielse, of Harvard University, have become the first physicists to perform such an experiment on a single electron. By combining the Penning trap with specially arranged electrical and magnetic fields, the electron was made to rotate perpendicular to and drift along the magnetic field, the energy of the rotational motion being discrete according to theory. To prevent the electron from chaotically jumping between the energy levels, it was cooled to 80 mK, 50 times less than previously achieved for any isolated elementary particle. The experiment is in fact the quantum limit of the conventional cyclotron - a `quantum cyclotron.' Applying an oscillating electrical field parallel to the magnetic field, it was found that level-to-level transitions corresponded to changes in the electron's rotation frequencies. Source: http://publish.aps.org/FOCUS/ Temperature of atomic nuclei1 September 1999Although temperature is a statistical concept and as such is normally defined for systems containing enormously large numbers of particles, Norwegian researchers have developed a method with which the temperature of atomic nuclei with a relatively small number of protons and neutrons can be determined. The atomic nucleus is in a sense a drop of liquid with nucleons moving chaotically inside, and information about the internal state of a nucleus can be obtained from the spectrum of gamma emission produced by nuclear collisions. For the Dy nucleus (element 62) with its 162 nucleons, the temperature determined in this way is 6×109K. Source: Physics News Update, Number 443 Stars near the SN 1987A supernova1 September 1999Astronomers using the Hubble Space Telescope have studied the characteristics and spatial distribution of stars within 30 pc of SN 1987A, a supernova which exploded in 1987 in the Large Magellanic Cloud situated 51.4 Kpc from Earth. The knowledge of the stellar population around a supernova is crucial for the understanding of how the pre-explosion star and its environment evolved. It is found that in the region explored both young (1-150 Myrs) and very old (more than 10 Gyrs) stars are present and that the star formation rate has increased severalfold in the last 8 Gyrs. Interestingly, stars having the same age but strongly different masses are distributed differently in space. In particular, an increased concentration of massive stars is observed in the supernova's immediate vicinity. This lack of mass/space correlation is confirmed by statistical methods and implies that stars differing in mass were formed to a large extent independently and by different mechanisms. As to the total mass function, this is an area-averaged characteristic and thus a superposition of a large number of contributions from stars of different ages. Source: http://xxx.lanl.gov/abs/astro-ph/9908188 New ISO data1 September 1999Both astronomical observations and theoretical calculations suggest that every existing galaxy might have undergone a number of mergers with other galaxies during its lifetime. A characteristic feature of such merged galaxies is huge irregular ejecta, due to tidal forces and the presence of double cores. A number of intriguing discoveries concerning bright merging galaxies close to the Earth have been made at the Infrared Space Observatory (ISO). While two cores of the Arp299 galaxy are invisible optically due a strong dust absorption, they produce about 90% of the entire galaxy's IR luminosity. The material of one of the cores seems to rotate as a whole. Spectral studies show that the powerful IR emission is associated with the intensive star formation occurring in the cores, presumably due to the galaxy merger. In the galaxy Antennae formed by a merger of two spiral galaxies, very compact areas of active star formation are found which give up to 15% of the galaxy's entire IR emission but are invisible optically. Another noteworthy finding is a giant elliptic radio galaxy in symbiosis with a spiral galaxy which it absorbed during their collision. The elliptic galaxy has an active core which produces relativistic ejecta. All the indications are that the central bar of the spiral galaxy acts as a bridge by means of which gas comes to the core of the elliptic galaxy to power a supermassive black hole there, a process in which large amounts of energy are released. Source: http://xxx.lanl.gov/abs/astro-ph/9908188 |
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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