24,199 research outputs found
A semiclassical theory of quantum noise in open chaotic systems
We consider the quantum evolution of classically chaotic systems in contact
with surroundings. Based on -scaling of an equation for time evolution
of the Wigner's quasi-probability distribution function in presence of
dissipation and thermal diffusion we derive a semiclassical equation for
quantum fluctuations. This identifies an early regime of evolution dominated by
fluctuations in the curvature of the potential due to classical chaos and
dissipation. A stochastic treatment of this classical fluctuations leads us to
a Fokker-Planck equation which is reminiscent of Kramers' equation for
thermally activated processes. This reveals an interplay of three aspects of
evolution of quantum noise in weakly dissipative open systems; the reversible
Liouville flow, the irreversible chaotic diffusion which is characteristic of
the system itself, and irreversible dissipation induced by the external
reservoir. It has been demonstrated that in the dissipation-free case a
competition between Liouville flow in the contracting direction of phase space
and chaotic diffusion sets a critical width in the Wigner function for quantum
fluctuations. We also show how the initial quantum noise gets amplified by
classical chaos and ultimately equilibrated under the influence of dissipation.
We establish that there exists a critical limit to the expansion of phase
space. The limit is determined by chaotic diffusion and dissipation. Making use
of appropriate quantum-classical correspondence we verify the semiclassical
analysis by the fully quantum simulation in a chaotic quartic oscillator.Comment: Plain Latex, 27 pages, 6 ps figure, To appear in Physica
Field emission effects of nitrogenated carbon nanotubes on chlorination and oxidation
[[abstract]]With reference to our recent reports [ Appl. Phys. Lett. 90, 192107 (2007) ; Appl. Phys. Lett. 91, 202102 (2007) ] about the electronic structure of chlorine treated and oxygen-plasma treated nitrogenated carbon nanotubes (N-CNTs), here we studied the electron field emission effects on chlorination (N-CNT:Cl) and oxidation (N-CNT:O) of N-CNT. A high current density (J) of 15.0 mA/cm2 has been achieved on chlorination, whereas low J of 0.0052 mA/cm2 is observed on oxidation compared to J = 1.3 mA/cm2 for untreated N-CNT at an applied electric field EA of ∼ 1.9 V/μm. The turn-on electric field (ETO) was ∼ 0.875. The 1.25 V/μm was achieved for N-CNT:Cl and N-CNT:O, respectively, with respect to ETO = 1.0 V/μm for untreated one. These findings are due to the formation of different bonds with carbon and nitrogen in the N-CNT during the process of chlorine (oxygen)-plasma treatment by the charge transfer, or else that changes the density of free charge carriers and hence enhances (reduces) the field emission properties of N-CNTs:Cl (N-CNTs:O).[[notice]]補正完畢[[incitationindex]]EI[[incitationindex]]SCI[[booktype]]紙
MEA/A-1 experiment 81F01 conducted on STS-7 flight, June 1983. Containerless processing of glass forming melts
The space processing of containerless, glassforming melts on board the space shuttle flight STS-7 is investigated. Objectives include; (1) obtain quantitative evidence for the supression of heterogeneous nucleation/crystallization, (2) study melt homogenization without gravity driven convection, (3) procedural development for bubble free, high purity homogeneous melts inmicro-g, (4) comparative analysis of melts on Earth and in micro g, and (5) assess the apparatus for processing multicomponent, glass forming melts in a low gravity environment
Containerless processing of glass forming melts: D-1, MEA/A-2 experiment 81F01 conducted on STS-61A flight, October 1985
Results of experiment 81F01, which was conducted in the Material Experiment Assembly MEA/A-2 on the D-1 Spacelab Mission (STS-61A), are presented. The general plan of the experiment was to heat, melt, and quench six spherical samples of different glass forming compositions while they were levitated in a single axis acoustic levitator furnace (SAAL). In addition, two non-melting sintered alumina samples were used to check the operational characteristics of the SAAL under reduced gravity conditions. Three of the eight samples were levitated between 1250 and 1500 C before the lack of coolant created an over-temperature condition that caused the SAAL to shut down prematurely. Two of the three samples processed were calcia-gallia-silica and soda-lime-silica glass forming compositions. Evidence of a two to three times increase in the tendency for glass formation was obtained for the calcia-gallia-silica. The final glass appeared reasonably homogeneous even though it was made from hot pressed powders containing deliberate heterogeneities. A photographic record was obtained of the microgravity sample processing sequences
Looking for Stars and Finding the Moon: Effects of Lunar Gamma-ray Emission on Fermi LAT Light Curves
We are conducting a search for new gamma-ray binaries by making high
signal-to-noise light curves of all cataloged Fermi LAT sources and searching
for periodic variability using appropriately weighted power spectra. The light
curves are created using a variant of aperture photometry where photons are
weighted by the probability that they came from the source of interest. From
this analysis we find that the light curves of a number of sources near the
ecliptic plane are contaminated by gamma-ray emission from the Moon. This shows
itself as modulation on the Moon's sidereal period in the power spectra. We
demonstrate that this contamination can be removed by excluding times when the
Moon was too close to a source. We advocate that this data screening should
generally be used when analyzing LAT data from a source located close to the
path of the Moon.Comment: 2012 Fermi Symposium proceedings - eConf C12102
Local atomic and electronic structures and ferroelectric properties of PbZr0.52Ti0.48O3: An x-ray absorption study
100學年度研究獎補助論文[[abstract]]This work investigates local atomic and electronic structures of PbZr0.52Ti0.48O3 (PZT) thin films with <001>, <101>, and <111> orientations using extended x-ray absorption fine structure (EXAFS) and x-ray absorption near-edge structure (XANES) spectroscopy with θ = 0° and 70° incident angles. The EXAFS result indicates that the <001>-oriented PZT film has a polarization dominantly along the c-axis, while both <101>- and <111>-oriented PZT films have a dominant in-ab-plane polarization. The hysteresis-loop measurements show that the <001>-oriented PZT film has a much larger coercive field than those of other two PZT films, which indicates that the double-well potential along the c-axis is much deeper than that in the ab-plane.[[notice]]補正完畢[[incitationindex]]SCI[[incitationindex]]EI[[booktype]]紙
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