20,453 research outputs found
Suspensions Thermal Noise in the LIGO Gravitational Wave Detector
We present a calculation of the maximum sensitivity achievable by the LIGO
Gravitational wave detector in construction, due to limiting thermal noise of
its suspensions. We present a method to calculate thermal noise that allows the
prediction of the suspension thermal noise in all its 6 degrees of freedom,
from the energy dissipation due to the elasticity of the suspension wires. We
show how this approach encompasses and explains previous ways to approximate
the thermal noise limit in gravitational waver detectors. We show how this
approach can be extended to more complicated suspensions to be used in future
LIGO detectors.Comment: 28 pages, 13 figure
Many-body effects in doped graphene on a piezoelectric substrate
We investigate the many-body properties of graphene on top of a piezoelectric
substrate, focusing on the interaction between the graphene electrons and the
piezoelectric acoustic phonons. We calculate the electron and phonon
self-energies as well as the electron mobility limited by the substrate
phonons. We emphasize the importance of the proper screening of the
electron-phonon vertex and discuss the various limiting behaviors as a function
of electron energy, temperature, and doping level. The effect on the graphene
electrons of the piezoelectric acoustic phonons is compared with that of the
intrinsic deformation acoustic phonons of graphene. Substrate phonons tend to
dominate over intrinsic ones for low doping levels at high and low
temperatures.Comment: 13 pages, 8 figure
A Novel Multi-parameter Family of Quantum Systems with Partially Broken N-fold Supersymmetry
We develop a systematic algorithm for constructing an N-fold supersymmetric
system from a given vector space invariant under one of the supercharges.
Applying this algorithm to spaces of monomials, we construct a new
multi-parameter family of N-fold supersymmetric models, which shall be referred
to as "type C". We investigate various aspects of these type C models in
detail. It turns out that in certain cases these systems exhibit a novel
phenomenon, namely, partial breaking of N-fold supersymmetry.Comment: RevTeX 4, 28 pages, no figure
Charge control in laterally coupled double quantum dots
We investigate the electronic and optical properties of InAs double quantum
dots grown on GaAs (001) and laterally aligned along the [110] crystal
direction. The emission spectrum has been investigated as a function of a
lateral electric field applied along the quantum dot pair mutual axis. The
number of confined electrons can be controlled with the external bias leading
to sharp energy shifts which we use to identify the emission from neutral and
charged exciton complexes. Quantum tunnelling of these electrons is proposed to
explain the reversed ordering of the trion emission lines as compared to that
of excitons in our system.Comment: 4 pages, 4 figures submitted to PRB Rapid Com
The Black Hole Binary Nova Scorpii 1994 (GRO J1655-40): An improved chemical analysis
The chemical analysis of secondary stars of low mass X-ray binaries provides
an opportunity to study the formation processes of compact objects, either
black holes or neutron stars. Following the discovery of overabundances of
-elements in the HIRES/Keck spectrum of the secondary star of Nova
Scorpii 1994 (Israelian et al. 1999), we obtained UVES/VLT high-resolution
spectroscopy with the aim of performing a detailed abundance analysis of this
secondary star. Using a -minimization procedure and a grid of synthetic
spectra, we derive the stellar parameters and atmospheric abundances of O, Mg,
Al, Ca, Ti, Fe and Ni, using a new UVES spectrum and the HIRES spectrum.The
abundances of Al, Ca, Ti, Fe and Ni seem to be consistent with solar values,
whereas Na, and especially O, Mg, Si and S are significantly enhanced in
comparison with Galactic trends of these elements. A comparison with
spherically and non-spherically symmetric supernova explosion models may
provide stringent constraints to the model parameters as mass-cut and the
explosion energy, in particular from the relative abundances of Si, S, Ca, Ti,
Fe and Ni. Most probably the black hole in this system formed in a hypernova
explosion of a 30--35 \Msun progenitor star with a mass-cut in the range 2--3.5
\Msun. However, these models produce abundances of Al and Na almost ten times
higher than the observed values.Comment: New Accepted version for publication in Astronomy and Astrophysics
Table 2: Correcte
Combinatorics of lattice paths with and without spikes
We derive a series of results on random walks on a d-dimensional hypercubic
lattice (lattice paths). We introduce the notions of terse and simple paths
corresponding to the path having no backtracking parts (spikes). These paths
label equivalence classes which allow a rearrangement of the sum over paths.
The basic combinatorial quantities of this construction are given. These
formulas are useful when performing strong coupling (hopping parameter)
expansions of lattice models. Some applications are described.Comment: Latex. 25 page
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