170 research outputs found
The superheated Melting of Grain Boundary
Based on a model of the melting of Grain Boundary (GB), we discuss the
possibility of the existence of superheated GB state. A Molecular Dynamics
simulation presented here shows that the superheated GB state can realized in
the high symmetric tilt GB. Whether the sizes of liquid nuclei exceed a
critical size determined the superheating grain boundary melting or not. Our
results also indicate that the increase of melting point due to pressure is
smaller than the superheating due to nucleation mechanism.Comment: Accepted by PRB, 7 pages and 5 figure
The water vapour distribution in the Arctic lowermost stratosphere during the LAUTLOS campaign and related transport processes including stratosphere-troposphere exchange
International audienceBalloon-borne water vapour measurements during January and February 2004, which were obtained as part of the LAUTLOS campaign at Sodankylä, Finland, 67° N, were used to analyse the water vapour distribution in the wintertime Arctic lowermost stratosphere. A 2.5 km thick layer (or 30 K in the potential temperature scale) above the tropopause is characterized by a significant water vapour variability on a synoptic timescale with values between stratospheric and tropospheric, which is in good agreement with previously reported measurements. A cross-correlation analysis of ozone and water vapour confirms that this layer contains a mixture of stratospheric and tropospheric air masses. Some of the flights sampled laminae of enhanced water vapour above the tropopause. Meteorological analyses and backward trajectory calculations show that these features were related to filaments that had developed along the flanks of cut-off anticyclones, which had been active at this time over the Northern Atlantic. The role of the filaments was however not to transport water vapour from the troposphere to the stratosphere but rather to transport it within the stratosphere away from regions where intensive two-way stratosphere-troposphere exchange (STE) was identified. Intensive STE occurred around cut-off anticyclones in regions of strong winds, where calculations suggest the presence of clear-air turbulence (CAT). Evidences that CAT contributes to the troposphere-to-stratosphere transport (TST) are presented. However, statistically, relation between TST and CAT during the studied period is weak
The water vapour distribution in the Arctic lowermost stratosphere during LAUTLOS campaign and related transport processes including stratosphere-troposphere exchange
International audienceBalloon-borne water vapour measurements during January and February 2004, which were obtained as part of the LAUTLOS campaign at Sodankylä, Finland, 67° N, were used to analyse the water vapour distribution in the wintertime Arctic lowermost stratosphere. A 2.5 km thick layer (or 30 K in the potential temperature scale) above the local tropopause is characterized by a significant water vapour variability on a synoptic timescale with values between stratospheric and tropospheric, which is in good agreement with previously reported measurements. A cross-correlation analysis of ozone and water vapour confirms that this layer contains a mixture of stratospheric and tropospheric air masses. Some of the flights sampled laminae of enhanced water vapour above the tropopause. Meteorological analyses and backward trajectory calculations show that these features are related to filaments that had developed along the flanks of cut-off anticyclones, which had been active at this time over the Northern Atlantic. Cross-tropopause mass fluxes calculated following the Wei method are used to identify regions and processes that are important for stratosphere-troposphere exchange (STE) in high-latitudes. Intensive STE occurs around cut-off anticyclones in regions of strong winds, where calculations suggest the presence of developed clear-air turbulence. The decay of the filaments is also shown to be important for STE
Stability of multi-electron bubbles in liquid helium
The stability of multi-electron bubbles in liquid helium is investigated
theoretically. We find that multi-electron bubbles are unstable against fission
whenever the pressure is positive. It is shown that for moving bubbles the
Bernoulli effect can result in a range of pressures over which the bubbles are
stable.Comment: 7 pages, 5 figure
Electric field induced strong localization of electrons on solid hydrogen surface: possible applications to quantum computing
Two-dimensional electron system on the liquid helium surface is one of the
leading candidates for constructing large analog quantum computers (P.M.
Platzman and M.I. Dykman, Science 284, 1967 (1999)). Similar electron systems
on the surfaces of solid hydrogen or solid neon may have some important
advantages with respect to electrons on liquid helium in quantum computing
applications, such as larger state separation , absence of
propagating capillary waves (or ripplons), smaller vapor pressure, etc. As a
result, it may operate at higher temperatures. Surface roughness is the main
hurdle to overcome in building a realistic quantum computer using these states.
Electric field induced strong localization of surface electrons is shown to be
a convenient tool to characterize surface roughness.Comment: 4 pages, 3 figure
Metal-insulator transition in disordered 2DEG including temperature effects
We calculate self-consistently the mutual dependence of electron correlations
and electron-defect scattering for a two dimensional electron gas at finite
temperature. We employ an STLS approach to calculate the electron correlations
while the electron scattering rate off Coulombic impurities and surface
roughness is calculated using self-consistent current-relaxation theory. The
methods are combined and self-consistently solved. We discuss a metal-insulator
transition for a range of disorder levels and electron densities. Our results
are in good agreement with recent experimental observations.Comment: 4 pages, RevTeX + epsf, 5 figure
The KHOLOD Experiment: A Search for a New Population of Radio Sources
Published data from long-term observations of a strip of sky at declination
+5 degrees carried out at 7.6 cm on the RATAN-600 radio telescope are used to
estimate some statistical properties of radio sources. Limits on the
sensitivity of the survey due to noise imposed by background sources, which
dominates the radiometer sensitivity, are refined. The vast majority of noise
due to background sources is associated with known radio sources (for example,
from the NVSS with a detection threshold of 2.3 mJy) with normal steep spectra
({\alpha} = 0.7-0.8, S \propto {\nu}^{- \alpha}), which have also been detected
in new deep surveys at decimeter wavelengths. When all such objects are removed
from the observational data, this leaves another noise component that is
observed to be roughly identical in independent groups of observations. We
suggest this represents a new population of radio sources that are not present
in known catalogs at the 0.6 mJy level at 7.6 cm. The studied redshift
dependence of the number of steep-spectrum objects shows that the sensitivity
of our survey is sufficient to detect powerful FRII radio sources at any
redshift, right to the epoch of formation of the first galaxies. The inferred
new population is most likely associated with low-luminosity objects at
redshifts z < 1. In spite of the appearance of new means of carrying out direct
studies of distant galaxies, searches for objects with very high redshifts
among steep and ultra-steep spectrum radio sources remains an effective method
for studying the early Universe.Comment: 13 pages, 10 figure
Quantum Point Contacts and Coherent Electron Focusing
I. Introduction
II. Electrons at the Fermi level
III. Conductance quantization of a quantum point contact
IV. Optical analogue of the conductance quantization
V. Classical electron focusing
VI. Electron focusing as a transmission problem
VII. Coherent electron focusing (Experiment, Skipping orbits and magnetic
edge states, Mode-interference and coherent electron focusing)
VIII. Other mode-interference phenomenaComment: #3 of a series of 4 legacy reviews on QPC'
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