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“Phonon Tunneling”
1 November 2010
I. 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 trap
1 November 2010
B.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 nanoresonator
1 November 2010
Ì. 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 microvibrations
1 November 2010
Vladimir 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 Stream
1 November 2010
The 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]
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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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