16,962 research outputs found
Improved solution of the lidar equation utilizing particle counter measurements
The extraction of particle backscattering from incoherent lidar measurements poses some problems. In the case of measurements of the stratospheric aerosol layer the solution of the lidar equation is based on two assumptions which are necessary to normalize the measured signal and to correct it with the two-way transmission of the laser pulse. Normalization and transmission are tackled by adding the information contained in aerosol particle counter measurements of the University of Wyoming to the ruby lidar measurements at Garmisch-Partenkirchen. Calculated backscattering from height levels above 25 km for the El Chichon period will be compared with lidar measurements and necessary corrections. The calculated backscatter-to-extinction ratios are compared to those, which were derived from a comparison of published extinction values to measured lidar backscattering at Garmisch. These ratios were used to calculate the Garmisch lidar returns. For the period 4 to 12 months after the El Chichon eruption a backscater-to-extinction ratio of 0.026 1/sr was applied with smaller values before and after that time
Statistical fluctuations for the fission process on its decent from saddle to scission
We reconsider the importance of statistical fluctuations for fission dynamics
beyond the saddle in the light of recent evaluations of transport coefficients
for average motion. The size of these fluctuations are estimated by means of
the Kramers-Ingold solution for the inverted oscillator, which allows for an
inclusion of quantum effects.Comment: 12 pages, Latex, 5 Postscript figures; submitted to PRC e-mail:
[email protected] www home page:
http://www.physik.tu-muenchen.de/tumphy/e/T36/hofmann.htm
Formation of small-scale structure in SUSY CDM
The lightest supersymmetric particle, most likely the lightest neutralino, is
one of the most prominent particle candidates for cold dark matter (CDM). We
show that the primordial spectrum of density fluctuations in neutralino CDM has
a sharp cut-off, induced by two different damping mechanisms. During the
kinetic decoupling of neutralinos, non-equilibrium processes constitute
viscosity effects, which damp or even absorb density perturbations in CDM.
After the last scattering of neutralinos, free streaming induces neutralino
flows from overdense to underdense regions of space. Both damping mechanisms
together define a minimal mass scale for perturbations in neutralino CDM,
before the inhomogeneities enter the nonlinear epoch of structure formation. We
find that the very first gravitationally bound neutralino clouds ought to have
masses above 10^{-6} solar masses, which is six orders of magnitude above the
mass of possible axion miniclusters.Comment: 7 pages, 3 figures, to appear in proceedings of "IDM 2002, 4th
International Workshop on the Identification of Dark Matter
Finite resolution measurement of the non-classical polarization statistics of entangled photon pairs
By limiting the resolution of quantum measurements, the measurement induced
changes of the quantum state can be reduced, permitting subsequent measurements
of variables that do not commute with the initially measured property. It is
then possible to experimentally determine correlations between non-commuting
variables. The application of this method to the polarization statistics of
entangled photon pairs reveals that negative conditional probabilities between
non-orthogonal polarization components are responsible for the violation of
Bell's inequalities. Such negative probabilities can also be observed in finite
resolution measurements of the polarization of a single photon. The violation
of Bell's inequalities therefore originates from local properties of the
quantum statistics of single photon polarization.Comment: 15 pages, 5 figures and 1 table, new figure to illustrate results,
improved explanation of statistical analysi
Self-consistent quantal treatment of decay rates within the perturbed static path approximation
The framework of the Perturbed Static Path Approximation (PSPA) is used to
calculate the partition function of a finite Fermi system from a Hamiltonian
with a separable two body interaction. Therein, the collective degree of
freedom is introduced in self-consistent fashion through a Hubbard-Stratonovich
transformation. In this way all transport coefficients which dominate the decay
of a meta-stable system are defined and calculated microscopically. Otherwise
the same formalism is applied as in the Caldeira-Leggett model to deduce the
decay rate from the free energy above the so called crossover temperature
.Comment: 17 pages, LaTex, no figures; final version, accepted for publication
in PRE; e-mail: [email protected]
Optimized phase switching using a single atom nonlinearity
We show that a nonlinear phase shift of pi can be obtained by using a single
two level atom in a one sided cavity with negligible losses. This result
implies that the use of a one sided cavity can significantly improve the pi/18
phase shift previously observed by Turchette et al. [Phys. Rev. Lett. 75, 4710
(1995)].Comment: 6 pages, 3 figures, added comments on derivation and assumption
Nuclear fission: The "onset of dissipation" from a microscopic point of view
Semi-analytical expressions are suggested for the temperature dependence of
those combinations of transport coefficients which govern the fission process.
This is based on experience with numerical calculations within the linear
response approach and the locally harmonic approximation. A reduced version of
the latter is seen to comply with Kramers' simplified picture of fission. It is
argued that for variable inertia his formula has to be generalized, as already
required by the need that for overdamped motion the inertia must not appear at
all. This situation may already occur above T=2 MeV, where the rate is
determined by the Smoluchowski equation. Consequently, comparison with
experimental results do not give information on the effective damping rate, as
often claimed, but on a special combination of local stiffnesses and the
friction coefficient calculated at the barrier.Comment: 31 pages, LaTex, 9 postscript figures; final, more concise version,
accepted for publication in PRC, with new arguments about the T-dependence of
the inertia; e-mail: [email protected]
Microscopic Model versus Systematic Low-Energy Effective Field Theory for a Doped Quantum Ferromagnet
We consider a microscopic model for a doped quantum ferromagnet as a test
case for the systematic low-energy effective field theory for magnons and
holes, which is constructed in complete analogy to the case of quantum
antiferromagnets. In contrast to antiferromagnets, for which the effective
field theory approach can be tested only numerically, in the ferromagnetic case
both the microscopic and the effective theory can be solved analytically. In
this way the low-energy parameters of the effective theory are determined
exactly by matching to the underlying microscopic model. The low-energy
behavior at half-filling as well as in the single- and two-hole sectors is
described exactly by the systematic low-energy effective field theory. In
particular, for weakly bound two-hole states the effective field theory even
works beyond perturbation theory. This lends strong support to the quantitative
success of the systematic low-energy effective field theory method not only in
the ferromagnetic but also in the physically most interesting antiferromagnetic
case.Comment: 34 pages, 1 figur
- âŠ