902 research outputs found
Condensate deformation and quantum depletion of Bose-Einstein condensates in external potentials
The one-body density matrix of weakly interacting, condensed bosons in
external potentials is calculated using inhomogeneous Bogoliubov theory. We
determine the condensate deformation caused by weak external potentials on the
mean-field level. The momentum distribution of quantum fluctuations around the
deformed ground state is obtained analytically, and finally the resulting
quantum depletion is calculated. The depletion due to the external potential,
or potential depletion for short, is a small correction to the homogeneous
depletion, validating our inhomogeneous Bogoliubov theory. Analytical results
are derived for weak lattices and spatially correlated random potentials, with
simple, universal results in the Thomas-Fermi limit of very smooth potentials.Comment: 17 pages, 4 figures. v2: published version, minor change
A framework for deflated and augmented Krylov subspace methods
We consider deflation and augmentation techniques for accelerating the
convergence of Krylov subspace methods for the solution of nonsingular linear
algebraic systems. Despite some formal similarity, the two techniques are
conceptually different from preconditioning. Deflation (in the sense the term
is used here) "removes" certain parts from the operator making it singular,
while augmentation adds a subspace to the Krylov subspace (often the one that
is generated by the singular operator); in contrast, preconditioning changes
the spectrum of the operator without making it singular. Deflation and
augmentation have been used in a variety of methods and settings. Typically,
deflation is combined with augmentation to compensate for the singularity of
the operator, but both techniques can be applied separately.
We introduce a framework of Krylov subspace methods that satisfy a Galerkin
condition. It includes the families of orthogonal residual (OR) and minimal
residual (MR) methods. We show that in this framework augmentation can be
achieved either explicitly or, equivalently, implicitly by projecting the
residuals appropriately and correcting the approximate solutions in a final
step. We study conditions for a breakdown of the deflated methods, and we show
several possibilities to avoid such breakdowns for the deflated MINRES method.
Numerical experiments illustrate properties of different variants of deflated
MINRES analyzed in this paper.Comment: 24 pages, 3 figure
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Optimization of the neutron yield in fusion plasmas produced by Coulomb explosions of deuterium clusters irradiated by a petawatt laser
The kinetic energy of hot (multi-keV) ions from the laser-driven Coulomb explosion of deuterium clusters and the resulting fusion yield in plasmas formed from these exploding clusters has been investigated under a variety of conditions using the Texas Petawatt laser. An optimum laser intensity was found for producing neutrons in these cluster fusion plasmas with corresponding average ion energies of 14 keV. The substantial volume (1-10 mm(3)) of the laser-cluster interaction produced by the petawatt peak power laser pulse led to a fusion yield of 1.6x10(7) neutrons in a single shot with a 120 J, 170 fs laser pulse. Possible effects of prepulses are discussed. DOI: 10.1103/PhysRevE.87.023106Glenn Focht Memorial FellowshipNNSA DE-FC52-08NA28512DOE Office of Basic Energy SciencesPhysic
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Femtosecond Pump-Probe Diagnostics Of Preformed Plasma Channels
We report on recent ultrafast pump-probe experiments 28 in He plasma waveguides using 800 nm, 80 fs pump pulses of 0.2 x 1018 W/cm2 peak guided intensity, and single orthogonally-polarized 800 nm probe pulses with similar to0.1% of pump intensity. The main results are: (1) We observe frequency-domain interference between the probe and a weak, depolarized component of the pump that differs substantially in mode shape from the injected pump pulse; (2) we observe spectral blue-shifts in the transmitted probe that are not evident in the transmitted pump. The evidence indicates that pump depolarization and probe blue-shifts both originate near the channel entrance.Physic
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The Texas Petawatt Laser And Current Experiments
The Texas Petawatt Laser is operational with experimental campaigns executed in both F/40 and F3 target chambers. Recent improvements have resulted in intensities of >2x10(21) W/cm(2) on target. Experimental highlights include, accelerated electron energies of >2 GeV, DD fusion ion temperatures >25 keV and isochorically heated solids to 10-50 eV.Physic
A beta-herpesvirus with fluorescent capsids to study transport in living cells.
Fluorescent tagging of viral particles by genetic means enables the study of virus dynamics in living cells. However, the study of beta-herpesvirus entry and morphogenesis by this method is currently limited. This is due to the lack of replication competent, capsid-tagged fluorescent viruses. Here, we report on viable recombinant MCMVs carrying ectopic insertions of the small capsid protein (SCP) fused to fluorescent proteins (FPs). The FPs were inserted into an internal position which allowed the production of viable, fluorescently labeled cytomegaloviruses, which replicated with wild type kinetics in cell culture. Fluorescent particles were readily detectable by several methods. Moreover, in a spread assay, labeled capsids accumulated around the nucleus of the newly infected cells without any detectable viral gene expression suggesting normal entry and particle trafficking. These recombinants were used to record particle dynamics by live-cell microscopy during MCMV egress with high spatial as well as temporal resolution. From the resulting tracks we obtained not only mean track velocities but also their mean square displacements and diffusion coefficients. With this key information, we were able to describe particle behavior at high detail and discriminate between particle tracks exhibiting directed movement and tracks in which particles exhibited free or anomalous diffusion
A generalized Hamiltonian Constraint Operator in Loop Quantum Gravity and its simplest Euclidean Matrix Elements
We study a generalized version of the Hamiltonian constraint operator in
nonperturbative loop quantum gravity. The generalization is based on admitting
arbitrary irreducible SU(2) representations in the regularization of the
operator, in contrast to the original definition where only the fundamental
representation is taken. This leads to a quantization ambiguity and to a family
of operators with the same classical limit. We calculate the action of the
Euclidean part of the generalized Hamiltonian constraint on trivalent states,
using the graphical notation of Temperley-Lieb recoupling theory. We discuss
the relation between this generalization of the Hamiltonian constraint and
crossing symmetry.Comment: 35 pp, 20 eps figures; minor corrections, references added; version
to appear in Class. Quant. Gra
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