19,759 research outputs found
Non-Classical Response from Quench-Cooled Solid Helium Confined in Porous Gold
We have investigated the non-classical response of solid 4He confined in
porous gold set to torsional oscillation. When solid helium is grown rapidly,
nearly 7% of the solid helium appears to be decoupled from the oscillation
below about 200 mK. Dissipation appears at temperatures where the decoupling
shows maximum variation. In contrast, the decoupling is substantially reduced
in slowly grown solid helium. The dynamic response of solid helium was also
studied by imposing a sudden increase in the amplitude of oscillation. Extended
relaxation in the resonant period shift, suggesting the emergence of the
pinning of low energy excitations, was observed below the onset temperature of
the non-classical response. The motion of a dislocation or a glassy solid is
restricted in the entangled narrow pores and is not likely responsible for the
period shift and long relaxation
Work distribution for the driven harmonic oscillator with time-dependent strength: Exact solution and slow driving
We study the work distribution of a single particle moving in a harmonic
oscillator with time-dependent strength. This simple system has a non-Gaussian
work distribution with exponential tails. The time evolution of the
corresponding moment generating function is given by two coupled ordinary
differential equations that are solved numerically. Based on this result we
study the behavior of the work distribution in the limit of slow but finite
driving and show that it approaches a Gaussian distribution arbitrarily well
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Fe15+ dielectronic recombination and the effects of configuration interaction between resonances with different captured electron principal quantum numbers
Dielectronic recombination (DR) of Na-like Fe15+ forming Mg-like Fe14+ via excitation of a 2l core electron has been investigated. We find that configuration interaction (CI) between DR resonances with different captured electron principal quantum numbers n can lead to a significant reduction in resonance strengths for n≥5. Previous theoretical work for this system has not considered this form of CI. Including it accounts for most of the discrepancy between previous theoretical and experimental results
Daytime lidar measurements of tidal winds in the mesospheric sodium layer at Urbana, Illinois
For more than 15 years lidar systems have been used to study the chemistry and dynamics of the mesospheric sodium layer. Because the layer is an excellent tracer of atmospheric wave motions, sodium lidar has proven to be particularly useful for studying the influence of gravity waves and tides on mesospheric dynamics. These waves, which originate in the troposphere and stratosphere, propagate through the mesosphere and dissipate their energy near the mesopause making important contributions to the momentum and turbulence budget in this region of the atmosphere. Recently, the sodium lidar was modified for daytime operation so that wave phenomena and chemical effects could be monitored throughout the complete diurnal cycle. The results of continuous 24 hour lidar observations of the sodium layer structure are presented alond with measurement of the semidiurnal tidal winds
Effects of pressure on the ferromagnetic state of the CDW compound SmNiC2
We report the pressure response of charge-density-wave (CDW) and
ferromagnetic (FM) phases of the rare-earth intermetallic SmNiC2 up to 5.5 GPa.
The CDW transition temperature (T_{CDW}), which is reflected as a sharp
inflection in the electrical resistivity, is almost independent of pressure up
to 2.18 GPa but is strongly enhanced at higher pressures, increasing from 155.7
K at 2.2 GPa to 279.3 K at 5.5 GPa. Commensurate with the sharp increase in
T_{CDW}, the first-order FM phase transition, which decreases with applied
pressure, bifurcates into the upper (T_{M1}) and lower (T_c) phase transitions
and the lower transition changes its nature to second order above 2.18 GPa.
Enhancement both in the residual resistivity and the Fermi-liquid T^2
coefficient A near 3.8 GPa suggests abundant magnetic quantum fluctuations that
arise from the possible presence of a FM quantum critical point.Comment: 5 pages, 5 figure
Compatible pairs of orthogonal polynomials
19 pages, no figures.-- MSC1991 code: 33C45.MR#: MR1736624 (2001a:33009)Zbl#: Zbl 0944.33012We find necessary and sufficient conditions for an orthogonal polynomial system to be compatible with another orthogonal polynomial system. As applications, we find new characterizations of semi-classical and classical orthogonal polynomials.The work of D. H. Kim and K. H. Kwon was
partially supported by KOSEF (98-0701-03-01-5) and GARC at Seoul National University. The work of F. Marcellán was partially supported by Dirección General de Enseñanza Superior (DGES) of Spain under grant PB96-0120-C03-0l.Publicad
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