11,107 research outputs found
Electromagnetically Induced Transparency in strongly interacting Rydberg Gases
We develop an efficient Monte-Carlo approach to describe the optical response
of cold three-level atoms in the presence of EIT and strong atomic
interactions. In particular, we consider a "Rydberg-EIT medium" where one
involved level is subject to large shifts due to strong van der Waals
interactions with surrounding Rydberg atoms. We find excellent agreement with
much more involved quantum calculations and demonstrate its applicability over
a wide range of densities and interaction strengths. The calculations show that
the nonlinear absorption due to Rydberg-Rydberg atom interactions exhibits
universal behavior
Portable linear-focused solar thermal energy collecting system
A solar heat collection system is provided by utilizing a line-focusing device that is effectively a cylindrically curved concentrator within a protected environment formed by a transparent inflatable casing. A target, such as a fluid or gas carrying conduit is positioned within or near the casing containing the concentrator, at the line focus of the concentrator. The casing can be inflated at the site of use by a low pressure air supply to form a unitary light weight structure. The collector, including casing, concentrator and target, is readily transportable and can be used either at ground level or on rooftops. The inflatable concentrator can be replaced with a rigid metal or other concentrator while maintaining the novel advantages of the whole solar heat collection system
Three-dimensional tracking solar energy concentrator and method for making same
A three dimensional tracking solar energy concentrator, consisting of a stretched aluminized polymeric membrane supported by a hoop, was presented. The system is sturdy enough to withstand expected windage forces and precipitation. It can provide the high temperature output needed by central station power plants for power production in the multi-megawatt range
Strongly Coupled Plasmas via Rydberg-Blockade of Cold Atoms
We propose and analyze a new scheme to produce ultracold neutral plasmas deep
in the strongly coupled regime. The method exploits the interaction blockade
between cold atoms excited to high-lying Rydberg states and therefore does not
require substantial extensions of current ultracold plasma experiments.
Extensive simulations reveal a universal behavior of the resulting Coulomb
coupling parameter, providing a direct connection between the physics of
strongly correlated Rydberg gases and ultracold plasmas. The approach is shown
to reduce currently accessible temperatures by more than an order of magnitude,
which opens up a new regime for ultracold plasma research and cold ion-beam
applications with readily available experimental techniques.Comment: 5 pages, 5 figure
Gamma-Rays Produced in Cosmic-Ray Interactions and the TeV-band Spectrum of RX J1713.7-3946
We employ the Monte Carlo particle collision code DPMJET3.04 to determine the
multiplicity spectra of various secondary particles (in addition to 's)
with 's as the final decay state, that are produced in cosmic-ray
('s and 's) interactions with the interstellar medium. We derive an
easy-to-use -ray production matrix for cosmic rays with energies up to
about 10 PeV. This -ray production matrix is applied to the GeV excess
in diffuse Galactic -rays observed by EGRET, and we conclude the
non- decay components are insufficient to explain the GeV excess,
although they have contributed a different spectrum from the -decay
component. We also test the hypothesis that the TeV-band -ray emission
of the shell-type SNR RX J1713.7-3946 observed with HESS is caused by hadronic
cosmic rays which are accelerated by a cosmic-ray modified shock. By the
statistics, we find a continuously softening spectrum is strongly
preferred, in contrast to expectations. A hardening spectrum has about 1%
probability to explain the HESS data, but then only if a hard cutoff at 50-100
TeV is imposed on the particle spectrum.Comment: 3 pages; 4 figures; Contribution to the First GLAST Symposium,
Standord, 200
Charged Current Neutrino Nucleus Interactions at Intermediate Energies
We have developed a model to describe the interactions of neutrinos with
nucleons and nuclei, focusing on the region of the quasielastic and Delta(1232)
peaks. We describe neutrino nucleon collisions with a fully relativistic
formalism which incorporates state-of-the-art parametrizations of the form
factors for both the nucleon and the N-Delta transition. The model has then
been extended to finite nuclei, taking into account nuclear effects such as
Fermi motion, Pauli blocking (both within the local density approximation),
nuclear binding and final state interactions. The in-medium modification of the
Delta resonance due to Pauli blocking and collisional broadening have also been
included. Final state interactions are implemented by means of the
Boltzmann-Uehling-Uhlenbeck (BUU) coupled-channel transport model. Results for
charged current inclusive cross sections and exclusive channels as pion
production and nucleon knockout are presented and discussed.Comment: 26 pages, 24 figures; v2: 2 figures and discussion added, version
accepted for publication in Phys. Rev.
Ultracold Neutral Plasmas
Ultracold neutral plasmas, formed by photoionizing laser-cooled atoms near
the ionization threshold, have electron temperatures in the 1-1000 kelvin range
and ion temperatures from tens of millikelvin to a few kelvin. They represent a
new frontier in the study of neutral plasmas, which traditionally deals with
much hotter systems, but they also blur the boundaries of plasma, atomic,
condensed matter, and low temperature physics. Modelling these plasmas
challenges computational techniques and theories of non-equilibrium systems, so
the field has attracted great interest from the theoretical and computational
physics communities. By varying laser intensities and wavelengths it is
possible to accurately set the initial plasma density and energy, and
charged-particle-detection and optical diagnostics allow precise measurements
for comparison with theoretical predictions. Recent experiments using optical
probes demonstrated that ions in the plasma equilibrate in a strongly coupled
fluid phase. Strongly coupled plasmas, in which the electrical interaction
energy between charged particles exceeds the average kinetic energy, reverse
the traditional energy hierarchy underlying basic plasma concepts such as Debye
screening and hydrodynamics. Equilibration in this regime is of particular
interest because it involves the establishment of spatial correlations between
particles, and it connects to the physics of the interiors of gas-giant planets
and inertial confinement fusion devices.Comment: 89 pages, 54 image
Strong-coupling effects in the relaxation dynamics of ultracold neutral plasmas
We describe a hybrid molecular dynamics approach for the description of
ultracold neutral plasmas, based on an adiabatic treatment of the electron gas
and a full molecular dynamics simulation of the ions, which allows us to follow
the long-time evolution of the plasma including the effect of the strongly
coupled ion motion. The plasma shows a rather complex relaxation behavior,
connected with temporal as well as spatial oscillations of the ion temperature.
Furthermore, additional laser cooling of the ions during the plasma evolution
drastically modifies the expansion dynamics, so that crystallization of the ion
component can occur in this nonequilibrium system, leading to lattice-like
structures or even long-range order resulting in concentric shells
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