1,752 research outputs found
Simulation of inhomogeneous distributions of ultracold atoms in an optical lattice via a massively parallel implementation of nonequilibrium strong-coupling perturbation theory
We present a nonequilibrium strong-coupling approach to inhomogeneous systems
of ultracold atoms in optical lattices. We demonstrate its application to the
Mott-insulating phase of a two-dimensional Fermi-Hubbard model in the presence
of a trap potential. Since the theory is formulated self-consistently, the
numerical implementation relies on a massively parallel evaluation of the
self-energy and the Green's function at each lattice site, employing thousands
of CPUs. While the computation of the self-energy is straightforward to
parallelize, the evaluation of the Green's function requires the inversion of a
large sparse matrix, with . As a crucial ingredient,
our solution heavily relies on the smallness of the hopping as compared to the
interaction strength and yields a widely scalable realization of a rapidly
converging iterative algorithm which evaluates all elements of the Green's
function. Results are validated by comparing with the homogeneous case via the
local-density approximation. These calculations also show that the
local-density approximation is valid in non-equilibrium setups without mass
transport.Comment: 14 pages, 9 figure
Economic and Organizational Aspects of Cooperative Feedlots
The cooperative organization of specialized large-scale feedlots, described in this bulletin, is not the only means open to South Dakota farmers and investors who want to enter the feeding business. A study of the cooperative feedlot was made because so little is known of its potential comparted with other forms of business organization. In no case should it be inferred that the Economics Department, South Dakota State College, is recommending that farmers and investors follow this route in all instances. Other ways of organizing a cattle feeding business include individual proprietorships with ample credit, private corporations, vertical integration, and partnerships
Theoretical Description of Coherent Doublon Creation via Lattice Modulation Spectroscopy
Using a recently developed strong-coupling method, we present a comprehensive
theory for doublon production processes in modulation spectroscopy of a
three-dimensional system of ultracold fermionic atoms in an optical lattice
with a trap. The theoretical predictions compare well to the experimental time
traces of doublon production. For experimentally feasible conditions, we
provide a quantitative prediction for the presence of a nonlinear "two-photon"
excitation at strong modulation amplitudes.Comment: 5 pages, 5 figure
Molecular Image Analysis: Quantitative Description and Classification of the Nuclear Lamina in Human Mesenchymal Stem Cells
The nuclear lamina is an intermediate filament network that provides a structural framework for the cell nucleus. Changes in lamina structure are found during changes in cell fate such as cell division or cell death and are associated with human diseases. An unbiased method that quantifies changes in lamina shape can provide information on cells undergoing changes in cellular functions. We have developed an image processing methodology that finds and quantifies the 3D structure of the nuclear lamina. We show that measurements on such images can be used for cell classification and provide information concerning protein spatial localization in this structure. To demonstrate the efficacy of this method, we compared the lamina of unmanipulated human mesenchymal stem cells (hMSCs) at passage 4 to cells activated for apoptosis. A statistically significant classification was found between the two populations
Cryptochromes and neuronal-activity markers colocalize in the retina of migratory birds during magnetic orientation
Migratory birds can use a magnetic compass for orientation during their migratory journeys covering thousands of kilometers. But how do they sense the reference direction provided by the Earth’s magnetic field? Behavioral evidence and theoretical considerations have suggested that radical-pair processes in differently oriented, light-sensitive molecules of the retina could enable migratory birds to perceive the magnetic field as visual patterns. The cryptochromes (CRYs) have been suggested as the most likely candidate class of molecules, but do CRYs exist in the retina of migratory birds? Here, we show that at least one CRY1 and one CRY2 exist in the retina of migratory garden warblers and that garden-warbler CRY1 (gwCRY1) is cytosolic. We also show that gwCRY1 is concentrated in specific cells, particularly in ganglion cells and in large displaced ganglion cells, which also showed high levels of neuronal activity at night, when our garden warblers performed magnetic orientation. In addition, there seem to be striking differences in CRY1 expression between migratory and nonmigratory songbirds at night. The difference in CRY1 expression between migrants and nonmigrants is particularly pronounced in the large displaced ganglion cells known to project exclusively to a brain area where magnetically sensitive neurons have been reported. Consequently, cytosolic gwCRY1 is well placed to possibly be the primary magnetic-sensory molecule required for light-mediated magnetoreception
Vortex dynamics in layered superconductors with correlated defects: influence of interlayer coupling
We report a detailed study of the vortex dynamics and vortex phase diagrams
of two amorphous Ta_0.3Ge_0.7/Ge multilayered films with intrinsic coplanar
defects, but different interlayer coupling. A pinned Bose-glass phase in the
more weakly coupled sample exists only below a cross-over field H* in striking
contrast to the strongly coupled film. Above H* the flux lines are thought to
break up into pancake vortices and the cross-over field is significantly
increased when the field is aligned along the extended defects. The two films
show different vortex creep excitations in the Bose-glass phase.Comment: zip file: 1 RevTex, 5 figures (png
Visualizing landscapes of the superconducting gap in heterogeneous superconductor thin films: geometric influences on proximity effects
The proximity effect is a central feature of superconducting junctions as it
underlies many important applications in devices and can be exploited in the
design of new systems with novel quantum functionality. Recently, exotic
proximity effects have been observed in various systems, such as
superconductor-metallic nanowires and graphene-superconductor structures.
However, it is still not clear how superconducting order propagates spatially
in a heterogeneous superconductor system. Here we report intriguing influences
of junction geometry on the proximity effect for a 2D heterogeneous
superconductor system comprised of 2D superconducting islands on top of a
surface metal. Depending on the local geometry, the superconducting gap induced
in the surface metal region can either be confined to the boundary of the
superconductor, in which the gap decays within a short distance (~ 15 nm), or
can be observed nearly uniformly over a distance of many coherence lengths due
to non-local proximity effects.Comment: 17 pages, 4 figure
Ultrasensitive TES Bolometers for Space Based FIR Astronomy
We present results from the development of a background limited transition edge sensor (TES) bolometer for the wavelength band 30–60 μm. The bolometer consists of a Ti/Au superconducting thermometer and a Ta radiation absorber deposited on a 200μm×300μm200μm×300μm membrane of SixNySixNy suspended on long, narrow legs. This device is voltage biased and the current through the device is measured by a SQUID amplifier. The thermometer has transition temperature Tc = 108 mKTc = 108 mK and the device is operated from a 70 mK base plate. FIR radiation is coupled into a multimodc horn with entrance aperture of 450 μm, length 4.5 mm and exit aperture of 45 μm, which feeds a metal integrating cavity containing the detector. The radiation band is defined by a pair of lowpass and highpass mesh filters in front of the horn. Here we present measurements of optical noise equivalent power (NEP), optical efficiency, dynamic range and time constant. The results show that measured TES detectors are close to meeting the requirement of the “Band 3” of SAFARI FTS imaging instrument [1] on the SPICA mission [2]
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