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| Issue 12, 2024 |
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Extracts from the Internet | ||
“Phonon Tunneling”1 November 2010I. Altfeder and his colleagues at the AFRL Laboratory (USA) used inelastic electron tunneling spectroscopy to investigate the effect of heat transfer from the tip of a scanning tunneling microscope (with a CO molecule attached to the tip apex) to gold film across the vacuum gap a few angstroms wide. The lock-in potential and second derivative of electric current between the tip and the film due to electron thermoemission were measured at three temperature levels, 90, 150 and 210 K, which made it possible to calculate phonon density of states and temperature at the tip apex. It was found that the the temperature of the last atom of the tip, which initially was 275 Ê, became equal to that of the gold film, i.e. effective heat transfer was taking place. This effect is explained in terms of transfer of thermal energy across the vacuum gap via electromagnetic interaction between the CO molecule and its electrical image. The image, i.e. the redistribution of surface electrons compensating for the electric fields in the bulk of the metal, oscillated synchronously with the thermal vibrations of the molecule itself, and excited phonons in the gold film. The efficiency of this mechanism of heat transfer under the experimental conditions proved to be ten orders of magnitude higher than the efficiency of radiant heat transfer. The authors called the effect above “phonon tunneling effect” although it is not directly connected with the phenomenon of quantum tunneling. Source: Phys. Rev . Lett. 105 166101 (2010) Rotation of graphene flakes in ion trap1 November 2010B.E. Kane (University of Maryland, USA) performed an experiment in which he observed record-fast rotation of graphene flakes caused by circularly polarized light wave. Micron-sized charged specimens were injected into a quadrupole ion trap using electrospray (ionization by spraying in electric field) and kept in a state of levitation in the potential of oscillating electric field. Absorbtion of light transferred some angular momentum to the samples, and they started rotating at a frequency of about 1 MHz. The high strength of graphene protected the samples from destruction by centrifugal forces, while electrostatic repulsion kept the flakes of levitating graphene nearly planar. The rotation frequency was measured using ac electric field: when the field went out of resonance, this caused the specimen to tilt with respect to the rotation axis, which affected the reflected light. The effect of levitation in the ion trap opens new possibilities for studying graphene since in this case there is no need in special substrate which would distort its electron properties. Source: arXiv:1006.3774v1 [cond-mat.mes-hall] Magnetic field of light wave in nanoresonator1 November 2010Ì. Burresi (FOM Institute for Atomic and Molecular Physics (AMOLF), The Netherlands) and his colleagues have developed a new technique for recording the magnetic field of light in nanoresonators. In a photonic crystal fabricated as a two-dimensional array of holes in a silicon membrane, a smooth area left with three holes unpunched served as a resonator cavity. The beam of a semiconductor laser was sent into the resonator through a waveguide — a row of unpunched holes. A cylindrical metallic microprobe was placed at a distance of 20 nm from the membrane surface, i.e. in the near field of the light wave. If the probe was placed over the antinode of the magnetic field, a shift of resonance was observed towards shorter wavelengths. This shift is caused by inducing ring currents in the microprobe which generate a magnetic field opposite to the field of the light wave, and this reduces the effective size of the cavity and hence, reduces the resonance wavelength. Typically only the effect of electric field of electromagnetic waves on matter is observed at frequencies above several THz but in this experiment the effect of electric field is small because its node lies within the magnetic field antinode. Source: Phys. Rev . Lett. 105 123901 (2010) Fractal dynamics of seismic microvibrations1 November 2010Vladimir Shiltsev (Fermi National Accelerator Laboratory, USA) published new generalized results of studying seismic microvibrations. The work was conducted at Tevatron, LEP and several other accelerators. Work of this type, using hydrostatic and laser level meters is conducted on accelerators because ground vibrations cause shifting of focusing magnets and other elements of accelerators relative to one another. Without special corrective devices, this would seriously distort the beam trajectory — by 0.2-0.3 mm per day. After subtracting the periodic tidal oscillations and shifts due to seasonal variations of temperature, we are left with stochastic microvibrations from a large number of sources; not all of them have been identified. However, the average properties of this background obey a simple diffusion-type relationship. Namely, squared relative displacement dY of two points separated by a distance L and measurement time T is ⟨dY2⟩ ≈ ATL where the constant A ≈ 10-5 ± 1 µm2 s-1 m-1; the mean relative displacement in the vertical plane exceeds that in the horizontal plane by approximately 20%. This empirical expression holds with good accuracy at a distance L from a few meters to several tens of kilometers and time T from several minutes to several years. The behavior ⟨dY2⟩ ≈ ATL was first proposed in early 1990s by V.B. Parkhomchuk (G.I. Budker Institute of Nuclear Physics, Novosibirsk) and his coworkers. According to Shiltsev's theoretical calculations, this dependence is a consequence of the fractal dynamics of the cascade of geological units over different scales. The results of such studies are important, in particular, for designing future linear accelerators. Source: Phys. Rev . Lett. 104 238501 (2010) Origin of the Magellanic Stream1 November 2010The Large and Small Magellanic Clouds — a pair of dwarf galaxies, satellites of our Galaxy — are trailed by a stream of neutral gas (the Magellanic Stream). Its age is 1 to 2 billion years and it spans ≈ 150° across the sky. It was assumed that this stream was produced as a result of “stripping” of outer layers of gas from satellite galaxies by gravitational tidal forces and/or through interaction between gas envelopes of the Galaxy and its satellites. The probable trajectory of the Magellanic Clouds in the Galactic halo has recently been clarified with the Hubble Telescope: satellite galaxies either approach the Galaxy for the first time, not having completed even a single revolution, or move on a very elongated orbit with a period of more than 6 billion years. In both cases the above mechanisms of stream formation have to be rejected. G. Besla (Harvard-Smithsonian Center for Astrophysics, Cambridge, USA) and her colleagues developed an alternative theory. According to their model, the gas stream was pulled out the Small Magellanic Cloud by the tidal gravitational field of the Large Magellanic Cloud even before the infall on the Galaxy. Then the gas stream stretched and the Magellanic clouds moved away from each other to a long distance. The fact that the satellites previously formed a binary system is confirmed by the presence of a gas bridge (the “Magellanic bridge”) and a common gas envelope. Numerical simulation by G. Besla et al identified a configuration of mutual orbits of the Magellanic Clouds and the direction of their infall onto the Galaxy which reproduce the observed astronomical picture with goode accuracy. Source: arXiv:1008.2210v1 [astro-ph.GA] |
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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