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| Issue 12, 2024 |
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Extracts from the Internet | ||
Search for the Higgs boson1 April 2009New constraints on the possible mass of the Higgs boson have been established by combining the data of two experiments CDF and D0 conducted at the Tevatron accelerator of the Enrico Fermi National Accelerator Laboratory. It was obtained earlier at the CERN electron-positron collider that the Higgs boson mass is greater than 114 GeV. On the other hand, theoretical calculations for processes involving the Higgs boson produced the upper bound on its mass as 185 GeV. Systematic searches are conducted nowadays for the Higgs boson in the possible mass range of 114-185 GeV and certain intervals within this range have already been excluded (see Phys. Usp. 51 979 (2008) ). According to the data of CDF and D0, the Higgs boson cannot have the mass in the range between 160 and 170 at a probability of 95%. In addition, the mass of the W boson has been measured in the D0 experiment with record accuracy: 80,401 ± 0,044 GeV. Improved accuracy of measuring the W boson mass may help in Higgs searches by improving the knowledge of boundaries of possible mass ranges and the accuracy in calculations of reactions involving the Higgs boson. Source: http://arxiv.org/abs/0903.4001 Increasing the luminescence efficiency of carbon nanotubes1 April 2009F. Papadimitrakopoulos and his coworkers at the University of Connecticut found a way to enhance the luminescence efficiency of single-wall carbon nanotubes up to a record-high level of 20%. The luminance of nanotubes is limited by defects on their surface, such as absorbed oxygen molecules. Earlier attempts of suspending nanotubes in solutions produced luminescence efficiency of at most 0.5%. In the new experiment nanotubes were coated with a layer of a compound FC12 — an analog of flavin mononucleotide (its composition is not very different from that of vitamin B). As this coating was added, FC12 molecules self-organized themselves into a tube coaxial with the carbon nanotube; this process automatically removed extraneous molecules from the nanotube surface. The luminescent glow of nanotubes is caused by irradiating them with IR light or by electric excitation. Carbon nanotubes with high-efficiency luminescence may lead to numerous useful applications, e.g. in nanoscale photodetectors and in biological sensors. Source: Science 323 1319 (2009) Cooling of nanotubes1 April 2009P. Avouris and colleagues at the IBM Research Center and researchers at Duke University (USA) discovered that heat can be dissipated from carbon nanotubes into the substrate in contact with it even if no chemical bonding exists between the two. The experiment was conducted with nanotubes on silicon oxide substrate in a configuration resembling that of the field transistor. Thermal vibrations were recorded by Raman spectroscopy techniques. Heat transfer from nanotubes is caused by electric interaction between charges: electrons in a nanotube interact with charges induced by electric fields of the substrate, energy is transferred to substrate charges close to its surface, and thermal vibrations then travel deeper into the specimen. This effect is important for solving the problem of cooling of microelectronic devices based on using carbon nanotubes. Source: physicsworld.com Stochastic resonance in digital electronics1 April 2009W. Ditto (Arizona University) and his colleagues have discovered that the work of a logic gate can be stabilized by a certain level of stochastic noise. Noise typically constitutes a disruptive factor for the functioning of electronic devices, for instance, it may cause unpredictable switching of the state in logic elements. In fact, stochastic resonance emerges in some nonlinear systems so that it becomes possible to separate the useful signal by increasing the level of broadband noise because then the sum of signal and noise exceeds a certain threshold value (on stochastic resonance see Phys. Usp. 42 37 (1999) and Uspekhi. fiz. nauk 179 266 (2009) (in Russian) ). Stochastic resonance manifests itself, for example, in the case of alternating climate cycles and in neuron systems. Arizona State University researchers mathematically modeled a logic gate with two rectangular signals plus a noise signal fed in as input; they found that as noise level increases the logic gate begins to function predictably and this stability survives in a sufficiently broad range of noise amplitudes. The theoretical predictions were supported by the study of an electronic analog of the nonlinear system in question. Another useful property of the designed logic gate was the possibility of reversing its logic by sending a control signal. Source: Phys. Rev. Lett. 102 104101 (2009) X-ray observations of the pulsar PSR J0108-14311 April 2009The space X-ray observatory Chandra detected the oldest of the currently known isolated pulsars (those not in binary systems) emitting in the X-ray range. Radio observations established that the pulsar PSR J0108-1431 is about 170 million years old. The unexpected result was the very high luminosity of the pulsar despite its old age and slow rotation rate (at a period of about 0.8 s). Approximately 0.4% of energy connected with the slowdown is transformed into X-ray radiation. The pulsar PSR J0108-1431 lies at a diatance of 770 light years and moves at a speed of about 200 km s-1. What continues to remain unclear is the mechanism of X-ray emission. It is possible that two components are present in the radiation, one generated in the magnetosphere of the pulsar and the other close to the pulsar poles. Sources: http://arxiv.org/abs/0803.0761, http://chandra.harvard.edu/press/09_releases/press_022609.html Dark matter in dwarf galaxies1 April 2009The Hubble Space telescope was used to study 29 dwarf galaxies in the core of the Perseus galaxy cluster lying at a distance of 250 million light years from the Earth. In contrast to the neightbouring spiral galaxies, dwarf galaxies have smooth regular shape without visible signs of decay caused by tidal gravitational forces exerted by the cluster core and other galaxies. This is an indication that the dwarf galaxy masses are sufficiently large to resist tidal destruction. This invisible mass is that of dark matter (hidden mass). The mass-to-luminance ratio of the investigated dwarf galaxies reaches ≈120 solar units. It has thus been established that dwarf galaxies of elliptic galaxies in cluster cores as well as dwarf spheroidals of the Local group of galaxies contain a relatively high amount of dark matter. Sources: http://arxiv.org/abs/0811.3197 , http://hubblesite.org/newscenter/archive/releases/2009/11/full/ |
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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