10,320 research outputs found
Excitation spectroscopy of vortex lattices in a rotating Bose-Einstein condensate
Excitation spectroscopy of vortex lattices in rotating Bose-Einstein
condensates is described. We numerically obtain the Bogoliubov-deGenne
quasiparticle excitations for a broad range of energies and analyze them in the
context of the complex dynamics of the system. Our work is carried out in a
regime in which standard hydrodynamic assumptions do not hold, and includes
features not readily contained within existing treatments.Comment: 4 pages, 4 figures. Submitted for publicatio
Ability of γδ T cells to modulate the Foxp3 T cell response is dependent on adenosine.
Whether γδ T cells inhibit or enhance the Foxp3 T cell response depends upon their activation status. The critical enhancing effector in the supernatant is adenosine. Activated γδ T cells express adenosine receptors at high levels, which enables them to deprive Foxp3+ T cells of adenosine, and to inhibit their expansion. Meanwhile, cell-free supernatants of γδ T cell cultures enhance Foxp3 T cell expansion. Thus, inhibition and enhancement by γδ T cells of Foxp3 T cell response are a reflection of the balance between adenosine production and absorption by γδ T cells. Non-activated γδ T cells produce adenosine but bind little, and thus enhance the Foxp3 T cell response. Activated γδ T cells express high density of adenosine receptors and have a greatly increased ability to bind adenosine. Extracellular adenosine metabolism and expression of adenosine receptor A2ARs by γδ T cells played a major role in the outcome of γδ and Foxp3 T cell interactions. A better understanding of the functional conversion of γδ T cells could lead to γδ T cell-targeted immunotherapies for related diseases
Gauge Threshold Corrections in Warped Geometry
We discuss the Kaluza-Klein threshold correction to low energy gauge
couplings in theories with warped extra-dimension, which might be crucial for
the gauge coupling unification when the warping is sizable. Explicit
expressions of one-loop thresholds are derived for generic 5D gauge theory on a
slice of AdS_5, where some of the bulk gauge symmetries are broken by orbifold
boundary conditions and/or by bulk Higgs vacuum values. Effects of the mass
mixing between the bulk fields with different orbifold parities are included as
such mixing is required in some class of realistic warped unification models.Comment: 33 pages, 1 figure, 6 tables, invited contribution to New Journal of
Physics Focus Issue on 'Extra Space Dimensions
Radius-dependent gauge unification in AdS5
We examine the relation of the 4-dimensional low energy coupling of bulk
gauge boson in a slice of AdS5 to the 5-dimensional fundamental couplings as a
function of the orbifold radius R. This allows us to address the gauge coupling
unification in AdS5 by means of the radius running as well as the conventional
momentum running. We then compute the radius dependence of 1-loop low energy
couplings in generic AdS5 theory with 4-dimensional supersymmetry, and discuss
the low energy predictions when the 5-dimensional couplings are assumed to be
unified.Comment: 11 pages, 2 figures, revtex, v3: analysis was generalized to
S^1/Z_2*Z_2 orbifoldin
Thermal fluctuation field for current-induced domain wall motion
Current-induced domain wall motion in magnetic nanowires is affected by
thermal fluctuation. In order to account for this effect, the
Landau-Lifshitz-Gilbert equation includes a thermal fluctuation field and
literature often utilizes the fluctuation-dissipation theorem to characterize
statistical properties of the thermal fluctuation field. However, the theorem
is not applicable to the system under finite current since it is not in
equilibrium. To examine the effect of finite current on the thermal
fluctuation, we adopt the influence functional formalism developed by Feynman
and Vernon, which is known to be a useful tool to analyze effects of
dissipation and thermal fluctuation. For this purpose, we construct a quantum
mechanical effective Hamiltonian describing current-induced domain wall motion
by generalizing the Caldeira-Leggett description of quantum dissipation. We
find that even for the current-induced domain wall motion, the statistical
properties of the thermal noise is still described by the
fluctuation-dissipation theorem if the current density is sufficiently lower
than the intrinsic critical current density and thus the domain wall tilting
angle is sufficiently lower than pi/4. The relation between our result and a
recent result, which also addresses the thermal fluctuation, is discussed. We
also find interesting physical meanings of the Gilbert damping alpha and the
nonadiabaticy parameter beta; while alpha characterizes the coupling strength
between the magnetization dynamics (the domain wall motion in this paper) and
the thermal reservoir (or environment), beta characterizes the coupling
strength between the spin current and the thermal reservoir.Comment: 16 page, no figur
Improvement of rheological and functional properties of milk protein concentrate by hydrodynamic cavitation
Spray drying at higher solids concentrations improves drying efficiency, and reduces the overall energy cost of milk powder production. As the performance of the evaporator prior to spray drying is limited by viscosity, several methods can be employed to reduce feed viscosity such as thermal pre-treatment or ultrasound. The method employed in this study was hydrodynamic cavitation (HC) on milk protein concentrate (MPC80). Rheological properties of the protein milk were observed to improve, with a reduction in viscosity by 20% and 56% upon the application of a cavitation rotor speed of 25 Hz and 50 Hz, respectively, due to the breakdown in protein gel structure and hence a decrease in the elastic modulus of the proteins. While HC did not adversely affect solubility, with the powders having on average a solubility of 97.5% at a reconstitution temperature of 50 °C, both bulk and tapped density increased when the emulsion was subjected to HC, owing to a reduction in particle size. This study therefore suggests the potential of using HC for a more efficient drying of high solids milk, while maintaining and/or improving the physicochemical properties of powders
The UV Continuum of Quasars: Models and SDSS Spectral Slopes
We measure long (2200-4000 ang) and short (1450-2200 ang) wavelength spectral
slopes \alpha (F_\nu proportional to \nu^\alpha) for quasar spectra from the
Sloan Digital Sky Survey. The long and short wavelength slopes are computed
from 3646 and 2706 quasars with redshifts in the z=0.76-1.26 and z=1.67-2.07
ranges, respectively. We calculate mean slopes after binning the data by
monochromatic luminosity at 2200 ang and virial mass estimates based on
measurements of the MgII line width and 3000 ang continuum luminosity. We find
little evidence for mass dependent variations in the mean slopes, but a
significant luminosity dependent trend in the near UV spectral slopes is
observed with larger (bluer) slopes at higher luminosities. The far UV slopes
show no clear variation with luminosity and are generally lower (redder) than
the near UV slopes at comparable luminosities, suggesting a slightly concave
quasar continuum shape. We compare these results with Monte Carlo distributions
of slopes computed from models of thin accretion disks, accounting for
uncertainties in the mass estimates. The model slopes produce mass dependent
trends which are larger than observed, though this conclusion is sensitive to
the assumed uncertainties in the mass estimates. The model slopes are also
generally bluer than observed, and we argue that reddening by dust intrinsic to
the source or host galaxy may account for much of the discrepancy.Comment: To be published in ApJ, 18 pages, 10 figure
Nanoscale Friction Switches: Friction Modulation of Monomolecular Assemblies Using External Electric Fields
This paper presents experimental investigations to actively modulate the nanoscale friction properties of a self-assembled monolayer (SAM) assembly using an external electric field that drives conformational changes in the SAM. Such “friction switches” have widespread implications in interfacial energy control in micro/nanoscale devices. Friction response of a low-density mercaptocarboxylic acid SAM is evaluated using an atomic force microscope (AFM) in the presence of a DC bias applied between the sample and the AFM probe under a nitrogen (dry) environment. The low density allows reorientation of individual SAM molecules to accommodate the attractive force between the −COOH terminal group and a positively biased surface. This enables the surface to present a hydrophilic group or a hydrophobic backbone to the contacting AFM probe depending upon the direction of the field (bias). Synthesis and deposition of the low-density SAM (LD-SAM) is reported. Results from AFM experiments show an increased friction response (up to 300%) of the LD-SAM system in the presence of a positive bias compared to the friction response in the presence of a negative bias. The difference in the friction response is attributed to the change in the structural and crystalline order of the film in addition to the interfacial surface chemistry and composition presented upon application of the bias
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