937 research outputs found
Heating of trapped atoms near thermal surfaces
We study the electromagnetic coupling and concomitant heating of a particle
in a miniaturized trap close to a solid surface. Two dominant heating
mechanisms are identified: proximity fields generated by thermally excited
currents in the absorbing solid and time-dependent image potentials due to
elastic surface distortions (Rayleigh phonons). Estimates for the lifetime of
the trap ground state are given. Ions are particularly sensitive to electric
proximity fields: for a silver substrate, we find a lifetime below one second
at distances closer than some ten micrometer to the surface. Neutral atoms may
approach the surface more closely: if they have a magnetic moment, a minimum
distance of one micrometer is estimated in tight traps, the heat being
transferred via magnetic proximity fields. For spinless atoms, heat is
transferred by inelastic scattering of virtual photons off surface phonons. The
corresponding lifetime, however, is estimated to be extremely long compared to
the timescale of typical experiments.Comment: to be published in Europhys. Lett. (7 pages, 3 figures, includes
europhys.sty style file
Loss and heating of particles in small and noisy traps
We derive the life time and loss rate for a trapped particle that is coupled
to fluctuating fields in the vicinity of a room-temperature metallic and/or
dielectric surface. Our results indicate a clear predominance of near field
effects over ordinary blackbody radiation. We develop a theoretical framework
for both charged and neutral particles with and without spin. Loss processes
that are due to a transition to an untrapped internal state are included.Comment: Slightly modified manuscript, as accepted for publication in Appl.
Phys. B (04 oct 1999). 10 pages, 5 .eps figures, LaTeX uses Springer style
file svjou
Universal amplitude ratios in finite-size scaling: three-dimensional Ising model
Motivated by the results of two-dimensional conformal field theory (CFT) we
investigate the finite-size scaling of the mass spectrum of an Ising model on
three-dimensional lattices with a spherical cross section. Using a
cluster-update Monte Carlo technique we find a linear relation between the
masses and the corresponding scaling dimensions, in complete analogy to the
situation in two dimensions. Amplitude ratios as well as the amplitudes
themselves appear to be universal in this case.Comment: 3 pages, 2 figures, proceedings of LATTICE99, Pis
Recent Developments in Maser Theory
This review covers selected developments in maser theory since the previous
meeting, "Cosmic Masers: From Proto-Stars to Black Holes" (Migenes & Reid
2002). Topics included are time variability of fundamental constants, pumping
of OH megamasers and indicators for differentiating disks from bi-directional
outflows.Comment: Review presented at IAU symposium 242, "Astrophysical Masers and
their Environments
Cuestiones actuales del Derecho local alemán
El presente trabajo expone las principales reformas y debates que se han producido en
el ámbito del Derecho local de la República Federal de Alemania en los últimos años. Con
esa finalidad se analizan los fundamentos básicos constitucionales y legales del Derecho
local, así como sus reformas más importantes, previendo los efectos que se han producido o
que pueden llegar a producirse.This work deals with the main reforms and debates that have emerged in the field of
local government in the last years. With this aim the authors analyze the constitutional and
legal foundations of municipal Law in Germany, as well as the most important reforms
carried out recently. On that basis they attempt to identify and anticipate the effects that
these reforms could have on the German system of local government
Local scale-invariance and ageing in noisy systems
The influence of the noise on the long-time ageing dynamics of a quenched
ferromagnetic spin system with a non-conserved order parameter and described
through a Langevin equation with a thermal noise term and a disordered initial
state is studied. If the noiseless part of the system is Galilei-invariant and
scale-invariant with dynamical exponent z=2, the two-time linear response
function is independent of the noise and therefore has exactly the form
predicted from the local scale-invariance of the noiseless part. The two-time
correlation function is exactly given in terms of certain noiseless three- and
four-point response functions. An explicit scaling form of the two-time
autocorrelation function follows. For disordered initial states, local
scale-invariance is sufficient for the equality of the autocorrelation and
autoresponse exponents in phase-ordering kinetics. The results for the scaling
functions are confirmed through tests in the kinetic spherical model, the
spin-wave approximation of the XY model, the critical voter model and the free
random walk.Comment: Latex2e, 45 pages, no figures, final for
Ammonia (J,K) = (1,1) to (4,4) and (6,6) inversion lines detected in the Seyfert 2 galaxy NGC 1068
We present the detection of the ammonia (NH3) (J,K) = (1,1) to (4,4) and
(6,6) inversion lines toward the prototypical Seyfert 2 galaxy NGC 1068, made
with the Green Bank Telescope (GBT). This is the first detection of ammonia in
a Seyfert galaxy. The ortho-to-para-NH3 abundance ratio suggests that the
molecule was formed in a warm medium of at least 20 K. For the NH3 column
density and fractional abundance, we find (1.09\pm0.23)\times10^14 cm^-2 and
(2.9\pm0.6)\times10^-8, respectively, from the inner 1.2 kpc of NGC 1068. The
kinetic temperature can be constrained to 80\pm20 K for the bulk of the
molecular gas, while some fraction has an even higher temperature of 140\pm30
K.Comment: 5 pages, 3 figures, accepted by A&
Architektur eines DRM-Empfängers und Basisbandalgorithmen für Frequenzakquisition und Kanalschätzung
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