706 research outputs found
Lyapunov Potential Description for Laser Dynamics
We describe the dynamical behavior of both class A and class B lasers in
terms of a Lyapunov potential. For class A lasers we use the potential to
analyze both deterministic and stochastic dynamics. In the stochastic case it
is found that the phase of the electric field drifts with time in the steady
state. For class B lasers, the potential obtained is valid in the absence of
noise. In this case, a general expression relating the period of the relaxation
oscillations to the potential is found. We have included in this expression the
terms corresponding to the gain saturation and the mean value of the
spontaneously emitted power, which were not considered previously. The validity
of this expression is also discussed and a semi-empirical relation giving the
period of the relaxation oscillations far from the stationary state is proposed
and checked against numerical simulations.Comment: 13 pages (including 7 figures) LaTeX file. To appear in Phys Rev.A
(June 1999
LFI 30 and 44 GHz receivers Back-End Modules
The 30 and 44 GHz Back End Modules (BEM) for the Planck Low Frequency
Instrument are broadband receivers (20% relative bandwidth) working at room
temperature. The signals coming from the Front End Module are amplified, band
pass filtered and finally converted to DC by a detector diode. Each receiver
has two identical branches following the differential scheme of the Planck
radiometers. The BEM design is based on MMIC Low Noise Amplifiers using GaAs
P-HEMT devices, microstrip filters and Schottky diode detectors. Their
manufacturing development has included elegant breadboard prototypes and
finally qualification and flight model units. Electrical, mechanical and
environmental tests were carried out for the characterization and verification
of the manufactured BEMs. A description of the 30 and 44 GHz Back End Modules
of Planck-LFI radiometers is given, with details of the tests done to determine
their electrical and environmental performances. The electrical performances of
the 30 and 44 GHz Back End Modules: frequency response, effective bandwidth,
equivalent noise temperature, 1/f noise and linearity are presented
Probing neutrino masses with future galaxy redshift surveys
We perform a new study of future sensitivities of galaxy redshift surveys to
the free-streaming effect caused by neutrino masses, adding the information on
cosmological parameters from measurements of primary anisotropies of the cosmic
microwave background (CMB). Our reference cosmological scenario has nine
parameters and three different neutrino masses, with a hierarchy imposed by
oscillation experiments. Within the present decade, the combination of the
Sloan Digital Sky Survey (SDSS) and CMB data from the PLANCK experiment will
have a 2-sigma detection threshold on the total neutrino mass close to 0.2 eV.
This estimate is robust against the inclusion of extra free parameters in the
reference cosmological model. On a longer term, the next generation of
experiments may reach values of order sum m_nu = 0.1 eV at 2-sigma, or better
if a galaxy redshift survey significantly larger than SDSS is completed. We
also discuss how the small changes on the free-streaming scales in the normal
and inverted hierarchy schemes are translated into the expected errors from
future cosmological data.Comment: 14 pages, 7 figures. Added results with the KAOS proposal and 1
referenc
Stability of dark solitons in a Bose-Einstein condensate trapped in an optical lattice
We investigate the stability of dark solitons (DSs) in an effectively
one-dimensional Bose-Einstein condensate in the presence of the magnetic
parabolic trap and an optical lattice (OL). The analysis is based on both the
full Gross-Pitaevskii equation and its tight-binding approximation counterpart
(discrete nonlinear Schr{\"o}dinger equation). We find that DSs are subject to
weak instabilities with an onset of instability mainly governed by the period
and amplitude of the OL. The instability, if present, sets in at large times
and it is characterized by quasi-periodic oscillations of the DS about the
minimum of the parabolic trap.Comment: Typo fixed in Eq. (1): cos^2 -> sin^
The Atmospheric Chemistry Suite (ACS) of Three Spectrometers for the ExoMars 2016 Trace Gas Orbiter
The Atmospheric Chemistry Suite (ACS) package is an element of the Russian contribution to the ESA-Roscosmos ExoMars 2016 Trace Gas Orbiter (TGO) mission. ACS consists of three separate infrared spectrometers, sharing common mechanical, electrical, and thermal interfaces. This ensemble of spectrometers has been designed and developed in response to the Trace Gas Orbiter mission objectives that specifically address the requirement of high sensitivity instruments to enable the unambiguous detection of trace gases of potential geophysical or biological interest. For this reason, ACS embarks a set of instruments achieving simultaneously very high accuracy (ppt level), very high resolving power (>10,000) and large spectral coverage (0.7 to 17 μm—the visible to thermal infrared range). The near-infrared (NIR) channel is a versatile spectrometer covering the 0.7–1.6 μm spectral range with a resolving power of ∼20,000. NIR employs the combination of an echelle grating with an AOTF (Acousto-Optical Tunable Filter) as diffraction order selector. This channel will be mainly operated in solar occultation and nadir, and can also perform limb observations. The scientific goals of NIR are the measurements of water vapor, aerosols, and dayside or night side airglows. The mid-infrared (MIR) channel is a cross-dispersion echelle instrument dedicated to solar occultation measurements in the 2.2–4.4 μm range. MIR achieves a resolving power of >50,000. It has been designed to accomplish the most sensitive measurements ever of the trace gases present in the Martian atmosphere. The thermal-infrared channel (TIRVIM) is a 2-inch double pendulum Fourier-transform spectrometer encompassing the spectral range of 1.7–17 μm with apodized resolution varying from 0.2 to 1.3 cm−1. TIRVIM is primarily dedicated to profiling temperature from the surface up to ∼60 km and to monitor aerosol abundance in nadir. TIRVIM also has a limb and solar occultation capability. The technical concept of the instrument, its accommodation on the spacecraft, the optical designs as well as some of the calibrations, and the expected performances for its three channels are described
Quantum computation in a Ising spin chain taking into account second neighbor couplings
We consider the realization of a quantum computer in a chain of nuclear spins
coupled by an Ising interaction. Quantum algorithms can be performed with the
help of appropriate radio-frequency pulses. In addition to the standard
nearest-neighbor Ising coupling, we also allow for a second neighbor coupling.
It is shown, how to apply the 2\pi k method in this more general setting, where
the additional coupling eventually allows to save a few pulses. We illustrate
our results with two numerical simulations: the Shor prime factorization of the
number 4 and the teleportation of a qubit along a chain of 3 qubits. In both
cases, the optimal Rabi frequency (to suppress non-resonant effects) depends
primarily on the strength of the second neighbor interaction.Comment: 19 pages, 6 figure
Measurement of Through-Going Particle Momentum By Means Of Multiple Scattering With The ICARUS T600 TPC
The ICARUS collaboration has demonstrated, following the operation of a 600
ton (T600) detector at shallow depth, that the technique based on liquid Argon
TPCs is now mature. The study of rare events, not contemplated in the Standard
Model, can greatly benefit from the use of this kind of detectors. In
particular, a deeper understanding of atmospheric neutrino properties will be
obtained thanks to the unprecedented quality of the data ICARUS provides.
However if we concentrate on the T600 performance, most of the
charged current sample will be partially contained, due to the reduced
dimensions of the detector. In this article, we address the problem of how well
we can determine the kinematics of events having partially contained tracks.
The analysis of a large sample of atmospheric muons collected during the T600
test run demonstrate that, in case the recorded track is at least one meter
long, the muon momentum can be reconstructed by an algorithm that measures the
Multiple Coulomb Scattering along the particle's path. Moreover, we show that
momentum resolution can be improved by a factor two using an algorithm based on
the Kalman Filtering technique
Magnetic Field Generation in Stars
Enormous progress has been made on observing stellar magnetism in stars from
the main sequence through to compact objects. Recent data have thrown into
sharper relief the vexed question of the origin of stellar magnetic fields,
which remains one of the main unanswered questions in astrophysics. In this
chapter we review recent work in this area of research. In particular, we look
at the fossil field hypothesis which links magnetism in compact stars to
magnetism in main sequence and pre-main sequence stars and we consider why its
feasibility has now been questioned particularly in the context of highly
magnetic white dwarfs. We also review the fossil versus dynamo debate in the
context of neutron stars and the roles played by key physical processes such as
buoyancy, helicity, and superfluid turbulence,in the generation and stability
of neutron star fields.
Independent information on the internal magnetic field of neutron stars will
come from future gravitational wave detections. Thus we maybe at the dawn of a
new era of exciting discoveries in compact star magnetism driven by the opening
of a new, non-electromagnetic observational window.
We also review recent advances in the theory and computation of
magnetohydrodynamic turbulence as it applies to stellar magnetism and dynamo
theory. These advances offer insight into the action of stellar dynamos as well
as processes whichcontrol the diffusive magnetic flux transport in stars.Comment: 41 pages, 7 figures. Invited review chapter on on magnetic field
generation in stars to appear in Space Science Reviews, Springe
D* Production in Deep Inelastic Scattering at HERA
This paper presents measurements of D^{*\pm} production in deep inelastic
scattering from collisions between 27.5 GeV positrons and 820 GeV protons. The
data have been taken with the ZEUS detector at HERA. The decay channel
(+ c.c.) has been used in the study. The
cross section for inclusive D^{*\pm} production with
and is 5.3 \pms 1.0 \pms 0.8 nb in the kinematic region
{ GeV and }. Differential cross
sections as functions of p_T(D^{*\pm}), and are
compared with next-to-leading order QCD calculations based on the photon-gluon
fusion production mechanism. After an extrapolation of the cross section to the
full kinematic region in p_T(D^{*\pm}) and (D^{*\pm}), the charm
contribution to the proton structure function is
determined for Bjorken between 2 10 and 5 10.Comment: 17 pages including 4 figure
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