6,111 research outputs found
Time-frequency analysis on the adeles over the rationals
We show that the construction of Gabor frames in with
generators in and with respect to time-frequency
shifts from a rectangular lattice is
equivalent to the construction of certain Gabor frames for over the
adeles over the rationals and the group .
Furthermore, we detail the connection between the construction of Gabor frames
on the adeles and on with the construction of
certain Heisenberg modules.Comment: minor revisions, added more references, added a Balian-Low type
result in the form of Proposition 4.
Politiets forebyggende innsats i skolen : en teoretisk oppgave
Bachelor i politiutdannin
Covariant q-differential operators and unitary highest weight representations for U_q su(n,n)
We investigate a one-parameter family of quantum Harish-Chandra modules of
U_q sl(2n). This family is an analog of the holomorphic discrete series of
representations of the group SU(n,n) for the quantum group U_q su(n, n). We
introduce a q-analog of "the wave" operator (a determinant-type differential
operator) and prove certain covariance property of its powers. This result is
applied to the study of some quotients of the above-mentioned quantum
Harish-Chandra modules. We also prove an analog of a known result by J.Faraut
and A.Koranyi on the expansion of reproducing kernels which determines the
analytic continuation of the holomorphic discrete series.Comment: 26 page
Estimating the density scaling exponent of viscous liquids from specific heat and bulk modulus data
It was recently shown by computer simulations that a large class of liquids
exhibits strong correlations in their thermal fluctuations of virial and
potential energy [Pedersen et al., Phys. Rev. Lett. 100, 015701 (2008)]. Among
organic liquids the class of strongly correlating liquids includes van der
Waals liquids, but excludes ionic and hydrogen-bonding liquids. The present
note focuses on the density scaling of strongly correlating liquids, i.e., the
fact their relaxation time tau at different densities rho and temperatures T
collapses to a master curve according to the expression tau propto
F(rho^gamma/T) [Schroder et al., arXiv:0803.2199]. We here show how to
calculate the exponent gamma from bulk modulus and specific heat data, either
measured as functions of frequency in the metastable liquid or extrapolated
from the glass and liquid phases to a common temperature (close to the glass
transition temperature). Thus an exponent defined from the response to highly
nonlinear parameter changes may be determined from linear response
measurements
All Things Retarded: Radiation-Reaction in Worldline Quantum Field Theory
We exhibit an initial-value formulation of the worldline quantum field theory (WQFT) approach to the classical two-body problem in general relativity. We show that the Schwinger-Keldysh (in-in) formalism leads to purely retarded propagators in the evaluation of observables in the WQFT. Integration technology for retarded master integrals is introduced at third post-Minkowskian (3PM) order. As an application we compute the complete radiation-reacted impulse and radiated four momentum for the scattering of two non-spinning neutron stars including tidal effects at 3PM order, as well as the leading (2PM) far-field gravitational waveform. <br
Simulation of GNSS reflected signals and estimation of position accuracy in GNSS-challenged environment
Abstract
The paper describes the development and testing
of a simulation tool, called QualiSIM. The tool estimates
GNSS-based position accuracy based on a simulation
of the environment surrounding the GNSS antenna,
with a special focus on city-scape environments with large
amounts of signal reflections from non-line-of-sight satellites.
The signal reflections are implemented using the extended
geometric path length of the signal path caused by
reflections from the surrounding buildings.
Based on real GPS satellite positions, simulated Galileo
satellite positions, models of atmospheric effect on the
satellite signals, designs of representative environments
e.g. urban and rural scenarios, and a method to simulate
reflection of satellite signals within the environment we
are able to estimate the position accuracy given several
prerequisites as described in the paper.
The result is a modelling of the signal path from satellite
to receiver, the satellite availability, the extended pseudoranges
caused by signal reflection, and an estimate of the
position accuracy based on a least squares adjustment of
the extended pseudoranges. The paper describes the models
and algorithms used and a verification test where the
results of QualiSIM are compared with results from collection
of real GPS data in an environment with much signal
reflection.</jats:p
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