26,558 research outputs found
Bubbles created from vacuum fluctuation
We show that the bubbles can be created from vacuum
fluctuation in certain De Sitter universe, so the space-time foam-like
structure might really be constructed from bubbles of in the
very early inflating phase of our universe. But whether such foam-like
structure persisted during the later evolution of the universe is a problem
unsolved now.Comment: 6 page
A (p,q) Deformation of the Universal Enveloping Superalgebra U(osp(2/2))
We investigate a two parameter quantum deformation of the universal
enveloping orthosymplectic superalgebra U(osp(2/2)) by extending the
Faddeev-Reshetikhin-Takhtajan formalism to the supersymetric case. It is shown
that possesses a non-commutative, non-cocommutative Hopf
algebra structure. All the results are expressed in the standard form using
quantum Chevalley basis.Comment: 8 pages; IC/93/41
Growth and characteristics of type-II InAs/GaSb superlattice-based detectors
We report on growth and device performance of infrared photodetectors based on type II InAs/Ga(In)Sb strain layer
superlattices (SLs) using the complementary barrier infrared detector (CBIRD) design. The unipolar barriers on either side of the absorber in the CBIRD design in combination with the type-II InAs/GaSb superlattice material system are expected to outperform traditional III-V LWIR imaging technologies and offer significant advantages over the conventional II-VI material based FPAs. The innovative design of CBIRDS, low defect density material growth, and robust fabrication processes have resulted in the development of high performance long wave infrared (LWIR) focal plane arrays at JPL
Modeling chemistry in and above snow at Summit, Greenland – Part 2: Impact of snowpack chemistry on the oxidation capacity of the boundary layer
The chemical composition of the boundary layer in snow covered regions is impacted by chemistry in the snowpack via uptake, processing, and emission of atmospheric trace gases. We use the coupled one-dimensional (1-D) snow chemistry and atmospheric boundary layer model MISTRA-SNOW to study the impact of snowpack chemistry on the oxidation capacity of the boundary layer. The model includes gas phase photochemistry and chemical reactions both in the interstitial air and the atmosphere. While it is acknowledged that the chemistry occurring at ice surfaces may consist of a true quasi-liquid layer and/or a concentrated brine layer, lack of additional knowledge requires that this chemistry be modeled as primarily aqueous chemistry occurring in a liquid-like layer (LLL) on snow grains. The model has been recently compared with BrO and NO data taken on 10 June–13 June 2008 as part of the Greenland Summit Halogen-HOx experiment (GSHOX). In the present study, we use the same focus period to investigate the influence of snowpack derived chemistry on OH and HOx + RO2 in the boundary layer. We compare model results with chemical ionization mass spectrometry (CIMS) measurements of the hydroxyl radical (OH) and of the hydroperoxyl radical (HO2) plus the sum of all organic peroxy radicals (RO2) taken at Summit during summer 2008. Using sensitivity runs we show that snowpack influenced nitrogen cycling and bromine chemistry both increase the oxidation capacity of the boundary layer and that together they increase the midday OH concentrations. Bromine chemistry increases the OH concentration by 10–18 % (10 % at noon LT), while snow sourced NOx increases OH concentrations by 20–50 % (27 % at noon LT). We show for the first time, using a coupled one dimensional snowpack-boundary layer model, that air-snow interactions impact the oxidation capacity of the boundary layer and that it is not possible to match measured OH levels without snowpack NOx and halogen emissions. Model predicted HONO compared with mistchamber measurements suggests there may be an unknown HONO source at Summit. Other model predicted HOx precursors, H2O2 and HCHO, compare well with measurements taken in summer 2000, which had lower levels than other years. Over 3 days, snow sourced NOx contributes an additional 2 ppb to boundary layer ozone production, while snow sourced bromine has the opposite effect and contributes 1 ppb to boundary layer ozone loss
First-Order Reorientation of the Flux-Line Lattice in CaAlSi
The flux line lattice in CaAlSi has been studied by small angle neutron
scattering. A well defined hexagonal flux line lattice is seen just above Hc1
in an applied field of only 54 Oe. A 30 degree reorientation of this vortex
lattice has been observed in a very low field of 200 Oe. This reorientation
transition appears to be of first-order and could be explained by non-local
effects. The magnetic field dependence of the form factor is well described by
a single penetration depth of 1496(1) angstroms and a single coherence length
of 307(1) angstroms at 2 K. At 1.5 K the penetration depth anisotropy is 2.7(1)
with the field applied perpendicular to the c axis and agrees with the
coherence length anisotropy determined from critical field measurements.Comment: 5 pages including 6 figures, to appear in Physical Review Letter
The seasonal cycle of N_2O
We have carried out an empirical study of the seasonal cycle of nitrous oxide (N_2O) using the data archived by the National Oceanic and Atmospheric Administration – Climate Monitoring and Diagnostics Laboratory (NOAA-CMDL) Global Cooperative Air Sampling Network from 1977 to 2000. In order to isolate the seasonal cycle, we first detrended the data using least square polynomial fits. The remaining variability was averaged to extract the seasonal cycle, which has an amplitude of about 0.8 ppbv. The statistical significance of the seasonal signal was established using the multitaper method and Welch's method for power spectrum analysis
On the Connection Between Momentum Cutoff and Operator Cutoff Regularizations
Operator cutoff regularization based on the original Schwinger's proper-time
formalism is examined. By constructing a regulating smearing function for the
proper-time integration, we show how this regularization scheme simulates the
usual momentum cutoff prescription yet preserves gauge symmetry even in the
presence of the cutoff scales. Similarity between the operator cutoff
regularization and the method of higher (covariant) derivatives is also
observed. The invariant nature of the operator cutoff regularization makes it a
promising tool for exploring the renormalization group flow of gauge theories
in the spirit of Wilson-Kadanoff blocking transformation.Comment: 28 pages in plain TeX, no figures. revised and expande
Reduced c-Fos expression in orexin neurons of the lateral hypothalamic area and the locus coeruleus following injection of spinosin into mice
Background: Spinosin, a major component of Samen Ziziphi spinosae, has been shown to modulate sedation and hypnosis; however, the underlying neuronal mechanisms of its stimulatory effects remain unclear.
Materials and methods: In the present study, we injected spinosin (15 mg/kg) or saline into mice, which were killed after 90 min. We isolated the brains, which were immunohistochemically stained for c-Fos as a biomarker for neuronal activation and assessed the expression profile of c-Fos in various sleep–arousal brain areas.
Results: Our findings revealed that there were no statistically significant differences in the expression of c-Fos in the nucleus accumbens and ventrolateral preoptic area, the vertical limb of the diagonal band nucleus, horizontal limb of the diagonal band nucleus, ventral tuberomammillary nucleus, ventral tegmental area, and dorsal raphe nucleus relative to saline between saline and spinosin-treated mice. Unlike saline, spinosin markedly decreased c-Fos expression in the lateral hypothalamic area (LHA) as well as the locus coeruleus (LC). Compared to the saline injection, the application of spinosin also resulted in a marked decrease in c-Fos expression in the LHA orexin neurons.
Conclusions: These findings suggest that spinosin administration results in a restricted pattern of c-Fos expression within the LHA orexin neurons and the LC, suggesting that this particular neuronal inactivation contributes to sedation and hypnosis
The influence of structural defects on intra-granular critical currents of bulk MgB2
Bulk MgB2 samples were prepared under different synthesis conditions and
analyzed by scanning and transmission electron microscopy. The critical current
densities were determined from the magnetization versus magnetic field curves
of bulk and powder-dispersed-in-epoxy samples. Results show that through a slow
cooling process, the oxygen dissolved in bulk MgB2 at high synthesis
temperatures can segregate and form nanometer-sized coherent precipitates of
Mg(B,O)2 in the MgB2 matrix. Magnetization measurements indicate that these
precipitates act as effective flux pinning centers and therefore significantly
improve the intra-grain critical current density and its field dependence.Comment: 4 pages, 4 figures, to be published in IEE Transactions in Applied
Superconductivit
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