7,399 research outputs found
Preservation of equilibrium in orthograde and inverted body positions
The mechanism for regulation of the vertical pose with retention of equilibrium in the inverted body position was investigated
Mixed Quantum/Classical Approach for Description of Molecular Collisions in Astrophysical Environments
An efficient and accurate mixed quantum/classical theory approach for computational treatment of inelastic scattering is extended to describe collision of an atom with a general asymmetric-top rotor polyatomic molecule. Quantum mechanics, employed to describe transitions between the internal states of the molecule, and classical mechanics, employed for description of scattering of the atom, are used in a self-consistent manner. Such calculations for rotational excitation of HCOOCH3 in collisions with He produce accurate results at scattering energies above 15 cm–1, although resonances near threshold, below 5 cm–1, cannot be reproduced. Importantly, the method remains computationally affordable at high scattering energies (here up to 1000 cm–1), which enables calculations for larger molecules and at higher collision energies than was possible previously with the standard full-quantum approach. Theoretical prediction of inelastic cross sections for a number of complex organic molecules observed in space becomes feasible using this new computational tool
Quantum-state extraction from high-Q cavities
The problem of extraction of a single-mode quantum state from a high-Q cavity
is studied for the case in which the time of preparation of the quantum state
of the cavity mode is short compared with its decay time. The temporal
evolution of the quantum state of the field escaping from the cavity is
calculated in terms of phase-space functions. A general condition is derived
under which the quantum state of the pulse built up outside the cavity is a
nearly perfect copy of the quantum state the cavity field was initially
prepared in. The results show that unwanted losses prevent the realization of a
nearly perfect extraction of nonclassical quantum states from high-Q optical
microcavities with presently available technology.Comment: RevTeX4, 9 pages with 6 figures; extended version as submitted to
Phys. Rev.
Thermodynamics of Yukawa fluids near the one-component-plasma limit
Thermodynamics of weakly screened (near the one-component-plasma limit)
Yukawa fluids in two and three dimensions is analyzed in detail. It is shown
that the thermal component of the excess internal energy of these fluids, when
expressed in terms of the properly normalized coupling strength, exhibits the
scaling pertinent to the corresponding one-component-plasma limit (the scalings
differ considerably between the two- and three-dimensional situations). This
provides us with a simple and accurate practical tool to estimate thermodynamic
properties of weakly screened Yukawa fluids. Particular attention is paid to
the two-dimensional fluids, for which several important thermodynamic
quantities are calculated to illustrate the application of the approach.Comment: Submitted to Phys. Plasma
Some exact properties of the gluon propagator
Recent numerical studies of the gluon propagator in the minimal Landau and
Coulomb gauges in space-time dimension 2, 3, and 4 pose a challenge to the
Gribov confinement scenario.
We prove, without approximation, that for these gauges, the continuum gluon
propagator in SU(N) gauge theory satisfies the bound . This holds for Landau
gauge, in which case is the dimension of space-time, and for Coulomb gauge,
in which case is the dimension of ordinary space and is the
instantaneous spatial gluon propagator. This bound implies that , where is the gluon propagator at momentum , and
consequently in Landau gauge in space-time , and in Coulomb
gauge in space dimension , but D(0) may be finite in higher dimension.
These results are compatible with numerical studies of the Landau-and
Coulomb-gauge propagator.
In 4-dimensional space-time a regularization is required, and we also prove
an analogous bound on the lattice gluon propagator, . Here we have taken the
infinite-volume limit of lattice gauge theory at fixed lattice spacing, and the
lattice momentum componant is a continuous angle . Unexpectedly, this implies a bound on the {\it high-momentum} behavior of
the continuum propagator in minimum Landau and Coulomb gauge in 4 space-time
dimensions which, moreover, is compatible with the perturbative renormalization
group when the theory is asymptotically free.Comment: 13 page
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