336,117 research outputs found
Quantization and the Resolvent Algebra
We introduce a novel commutative C*-algebra of functions on a symplectic
vector space admitting a complex structure, along with a strict deformation
quantization that maps a dense subalgebra to the resolvent algebra introduced
by Buchholz and Grundling \cite{BG2008}. The associated quantization map is a
field-theoretical Weyl quantization compatible with the work of Binz, Honegger
and Rieckers \cite{BHR}. We also define a Berezin-type quantization map on the
whole C*-algebra, which continuously and bijectively maps it onto the resolvent
algebra.
This C*-algebra, generally defined on a real inner product space X,
intimately depends on the finite dimensional subspaces of X. We thoroughly
analyze the structure and applicability of this algebra in the finite
dimensional case by giving a characterization of its elements and by computing
its Gelfand spectrum
Hysteretic clustering in granular gas
Granular material is vibro-fluidized in N=2 and N=3 connected compartments,
respectively. For sufficiently strong shaking the granular gas is
equi-partitioned, but if the shaking intensity is lowered, the gas clusters in
one compartment. The phase transition towards the clustered state is of 2nd
order for N=2 and of 1st order for N=3. In particular, the latter is
hysteretic. The experimental findings are accounted for within a dynamical
model that exactly has the above properties
UMTV: a Single Chip TV Receiver for PDAs, PCs and Cell Phones
A zero-external-component TV receiver for portable platforms is realized in a mainstream 8GHz-f/sub t/ BiCMOS process. Die size is 5/spl times/5mm/sup 2/ and power dissipation is 50mA at 3V. The receiver includes a single tunable LNA (3mA) with less than 5dB NF from 40 to 900MHz. The programmable IF filters cover all analog and digital standards
The formation and evolution of very massive stars in dense stellar systems
The early evolution of dense stellar systems is governed by massive single
star and binary evolution. Core collapse of dense massive star clusters can
lead to the formation of very massive objects through stellar collisions
( 1000 \msun). Stellar wind mass loss determines the evolution and final
fate of these objects, and decides upon whether they form black holes (with
stellar or intermediate mass) or explode as pair instability supernovae,
leaving no remnant. We present a computationaly inexpensive evolutionary scheme
for very massive stars that can readily be implemented in an N-body code. Using
our new N-body code 'Youngbody' which includes a detailed treatment of massive
stars as well as this new scheme for very massive stars, we discuss the
formation of intermediate mass and stellar mass black holes in young starburst
regions. A more detailed account of these results can be found in Belkus et al.
2007.Comment: 2 pages, 2 figures. To appear in conference proceedings for IAUS246,
200
Systematic Density Expansion of the Lyapunov Exponents for a Two-dimensional Random Lorentz Gas
We study the Lyapunov exponents of a two-dimensional, random Lorentz gas at
low density. The positive Lyapunov exponent may be obtained either by a direct
analysis of the dynamics, or by the use of kinetic theory methods. To leading
orders in the density of scatterers it is of the form
, where and are
known constants and is the number density of scatterers expressed
in dimensionless units. In this paper, we find that through order
, the positive Lyapunov exponent is of the form
. Explicit numerical values of the new constants
and are obtained by means of a systematic analysis. This takes into
account, up to , the effects of {\it all\/} possible
trajectories in two versions of the model; in one version overlapping scatterer
configurations are allowed and in the other they are not.Comment: 12 pages, 9 figures, minor changes in this version, to appear in J.
Stat. Phy
Largest Lyapunov Exponent for Many Particle Systems at Low Densities
The largest Lyapunov exponent for a dilute gas with short range
interactions in equilibrium is studied by a mapping to a clock model, in which
every particle carries a watch, with a discrete time that is advanced at
collisions. This model has a propagating front solution with a speed that
determines , for which we find a density dependence as predicted by
Krylov, but with a larger prefactor. Simulations for the clock model and for
hard sphere and hard disk systems confirm these results and are in excellent
mutual agreement. They show a slow convergence of with increasing
particle number, in good agreement with a prediction by Brunet and Derrida.Comment: 4 pages, RevTeX, 2 Figures (encapsulated postscript). Submitted to
Phys. Rev. Let
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