5,802 research outputs found
Propellant tank pressurization system Patent
Method and apparatus for pressurizing propellant tanks used in propulsion motor feed syste
Continuous loading of S calcium atoms into an optical dipole trap
We demonstrate an efficient scheme for continuous trap loading based upon
spatially selective optical pumping. We discuss the case of S
calcium atoms in an optical dipole trap (ODT), however, similar strategies
should be applicable to a wide range of atomic species. Our starting point is a
reservoir of moderately cold (K) metastable
P-atoms prepared by means of a magneto-optic trap (triplet-MOT). A
focused 532 nm laser beam produces a strongly elongated optical potential for
S-atoms with up to 350 K well depth. A weak focused laser beam
at 430 nm, carefully superimposed upon the ODT beam, selectively pumps the
P-atoms inside the capture volume to the singlet state, where they
are confined by the ODT. The triplet-MOT perpetually refills the capture volume
with P-atoms thus providing a continuous stream of cold atoms into
the ODT at a rate of s. Limited by evaporation loss, in 200 ms we
typically load atoms with an initial radial temperature of 85
K. After terminating the loading we observe evaporation during 50 ms
leaving us with atoms at radial temperatures close to 40 K and a
peak phase space density of . We point out that a
comparable scheme could be employed to load a dipole trap with
P-atoms.Comment: 4 pages, 4 figure
Coloring random graphs
We study the graph coloring problem over random graphs of finite average
connectivity . Given a number of available colors, we find that graphs
with low connectivity admit almost always a proper coloring whereas graphs with
high connectivity are uncolorable. Depending on , we find the precise value
of the critical average connectivity . Moreover, we show that below
there exist a clustering phase in which ground states
spontaneously divide into an exponential number of clusters and where the
proliferation of metastable states is responsible for the onset of complexity
in local search algorithms.Comment: 4 pages, 1 figure, version to app. in PR
Reformulation of the Stochastic Potential Switching Algorithm and a Generalized Fourtuin-Kasteleyn Representation
A new formulation of the stochastic potential switching algorithm is
presented. This reformulation naturally leads us to a generalized
Fourtuin-Kasteleyn representation of the partition function Z. A formula for
internal energy E and that of heat capacity C are derived from derivatives of
the partition function. We also derive a formula for the exchange probability
in the replica exchange Monte Carlo method. By combining the formulae with the
Stochastic Cutoff method, we can greatly reduce the computational time to
perform internal energy and heat capacity measurements and the replica exchange
Monte Carlo method in long-range interacting systems. Numerical simulations in
three dimensional magnetic dipolar systems show the validity and efficiency of
the method.Comment: 11 pages, 6 figures, to appear in PR
Back-to-back correlations of high p_T hadrons in relativistic heavy ion collisions
We investigate the suppression factor and the azimuthal correlation function
for high hadrons in central Au+Au collisions at GeV
by using a dynamical model in which hydrodynamics is combined with explicitly
traveling jets. We study the effects of parton energy loss in a hot medium,
intrinsic of partons in a nucleus, and broadening of jets on
the back-to-back correlations of high hadrons. Parton energy loss is
found to be a dominant effect on the reduction of the away-side peaks in the
correlation function.Comment: 4 pages, 4 figures; version to appear in Phys. Rev. Let
Mobile Resource Guarantees for Smart Devices
Abstract. We present the Mobile Resource Guarantees framework: a system for ensuring that downloaded programs are free from run-time violations of resource bounds. Certificates are attached to code in the form of efficiently checkable proofs of resource bounds; in contrast to cryptographic certificates of code origin, these are independent of trust networks. A novel programming language with resource constraints encoded in function types is used to streamline the generation of proofs of resource usage.
Raman Adiabatic Transfer of Optical States
We analyze electromagnetically induced transparency and light storage in an
ensemble of atoms with multiple excited levels (multi-Lambda configuration)
which are coupled to one of the ground states by quantized signal fields and to
the other one via classical control fields. We present a basis transformation
of atomic and optical states which reduces the analysis of the system to that
of EIT in a regular 3-level configuration. We demonstrate the existence of dark
state polaritons and propose a protocol to transfer quantum information from
one optical mode to another by an adiabatic control of the control fields
Photoemission spectroscopy and sum rules in dilute electron-phonon systems
A family of exact sum rules for the one-polaron spectral function in the
low-density limit is derived. An algorithm to calculate energy moments of
arbitrary order of the spectral function is presented. Explicit expressions are
given for the first two moments of a model with general electron-phonon
interaction, and for the first four moments of the Holstein polaron. The sum
rules are linked to experiments on momentum-resolved photoemission
spectroscopy. The bare electronic dispersion and the electron-phonon coupling
constant can be extracted from the first and second moments of spectrum. The
sum rules could serve as constraints in analytical and numerical studies of
electron-phonon models.Comment: 4 page
Quantum coherence and carriers mobility in organic semiconductors
We present a model of charge transport in organic molecular semiconductors
based on the effects of lattice fluctuations on the quantum coherence of the
electronic state of the charge carrier. Thermal intermolecular phonons and
librations tend to localize pure coherent states and to assist the motion of
less coherent ones. Decoherence is thus the primary mechanism by which
conduction occurs. It is driven by the coupling of the carrier to the molecular
lattice through polarization and transfer integral fluctuations as described by
the hamiltonian of Gosar and Choi. Localization effects in the quantum coherent
regime are modeled via the Anderson hamiltonian with correlated diagonal and
non-diagonal disorder leading to the determination of the carrier localization
length. This length defines the coherent extension of the ground state and
determines, in turn, the diffusion range in the incoherent regime and thus the
mobility. The transfer integral disorder of Troisi and Orlandi can also be
incorporated. This model, based on the idea of decoherence, allowed us to
predict the value and temperature dependence of the carrier mobility in
prototypical organic semiconductors that are in qualitative accord with
experiments
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