3,243 research outputs found
On BPS bounds in D=4 N=2 gauged supergravity II: general matter couplings and black hole masses
We continue the analysis of BPS bounds started in arXiv:1110.2688, extending
it to the full class of N=2 gauged supergravity theories with arbitrary vector
and hypermultiplets. We derive the general form of the asymptotic charges for
asymptotically flat (M_4), anti-de Sitter (AdS_4), and magnetic anti-de Sitter
(mAdS_4) spacetimes. Some particular examples from black hole physics are given
to explicitly demonstrate how AdS and mAdS masses differ when solutions with
non-trivial scalar profiles are considered.Comment: 21 pages; v2 added reference, published version; v3 minor correction
Changes of some biophysical values in animals under moderate stress
In recent years, in the medical world the number of studies related to certain biophysical characteristics of biologically active points (similar to acupuncture points) - BAP, antenna and electromagnetic radiation effect of the body is increasing. As a product of nature, organisms come into simpler or more complex relationship with the various forms of manifestation of natural energy and particularly the electromagnetic one. Aim of this study was to identify changes in the antenna effect, electromagnetic radiation and resistance and semiconductor effect in BAP of experimental animals under oxidative stress response to hypobaric hypoxia and hyperbaric hyperoxia, cold and heat shock, physical exertion and prolonged immobilization. The general impression from the results obtained from different models of stress conditions, is that changes in biophysical parameters studied, with few exceptions in parameters and in varying degrees of variability are one-way and statistically significant The increasing of antenna effect and electromagnetic radiation from one side and reducing resistance and of semiconductor effect in acupuncture point Yin-Tang considered for "basic energizer of the organism" at the other, in wide physical aspect are proof for an increase of communicative opportunities of animals under different stress opportunities. To build on the findings of experimental study it is necessary to extend the number of animals in the respective groups, and conduct further experiments with other stressful conditions. Scripta Scientifica Medica 2011;43(2): 97-10
Nonperturbative resonant strong field ionization of atomic hydrogen
We investigate resonant strong field ionization of atomic hydrogen with
respect to the 1s-2p-transition. By "strong" we understand that Rabi-periods
are executed on a femtosecond time scale. Ionization and AC Stark shifts modify
the bound state dynamics severely, leading to nonperturbative signatures in the
photoelectron spectra. We introduce an analytical model, capable of predicting
qualitative features in the photoelectron spectra such as the positions of the
Autler-Townes peaks for modest field strengths. Ab initio solutions of the
time-dependent Schroedinger equation show a pronounced shift and broadening of
the left Autler-Townes peak as the field strength is increased. The right peak
remains rather narrow and shifts less. This result is analyzed and explained
with the help of exact AC Stark shifts and ionization rates obtained from
Floquet theory. Finally, it is demonstrated that in the case of finite pulses
as short as 20fs the Autler-Townes duplet can still be resolved. The fourth
generation light sources under construction worldwide will provide bright,
coherent radiation with photon energies ranging from a tenth of a meV up to
tens of keV, hence covering the regime studied in the paper so that
measurements of nonperturbative, relative AC Stark shifts should become
feasible with these new light sources.Comment: 16 pages, 11 figures, IOP styl
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A study of nucleate boiling and critical heat flux with EHD enhancement
The paper describes results from an experimental and theoretical study of the effect of an electric field on nucleate boiling and the critical heat flux (CHF) in pool boiling of R123 at atmospheric pressure on a horizontal wall with a smooth surface. Two designs of electrode (parallel rods and wire mesh) were used.
The experimental data exhibit some differences from the data obtained by other researchers in similar experiments on a wall with a different surface finish and with a slightly different design of wire mesh electrode. The hydrodynamic model for EHD enhancement of CHF cannot reconcile the differences.
A theoretical model has been developed for the growth of a single vapour bubble on a superheated wall in an electric field, leading to a numerical simulation based on the level-set method. The model includes matching of sub-models for the micro- and macro- regions, conduction in the wall, distortion of the electric field by the bubble, the temperature dependence of electrical properties and free-charge generation. In the present form of the model, some of these effects are realised in an approximate form. The capability to investigate dry-spot formation and wall temperature changes that might lead to CHF has been demonstrated
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Modelling of the growth and detachment of a vapour bubble and the effect of a electric field in the nucleate boiling regime
A comprehensive model predicting the deformation, growth and detachment of a vapour bubble in the nucleate boiling regime with an applied electric field is described in this paper. The model takes into account the full electrohydrodynamics of the phenomenon including the influence of local temperature on the generation of free charges in the liquid. Solution of the model by the level set method has been successfully implemented with a commercial CFD code. Aspects of the code and the graphical software requiring further development are noted.
Sample results are presented to demonstrate the effect of the electric field on the growth and detachment of the bubble, for a bubble initially protruding through a thermal boundary layer on a horizontal wall. The bubble is elongated under the influence of electrical forces, the effect being more pronounced for stronger electrical fields. The electric field is found to promote earlier detachment of the bubble at a smaller volume, thus increasing the bubble frequency. The wall heat flux during the process of detachment is not much affected by the electric field
The Herschel-SPIRE instrument and its in-flight performance
The Spectral and Photometric Imaging REceiver (SPIRE), is the Herschel Space Observatory`s submillimetre camera and spectrometer. It contains a three-band imaging photometer operating at 250, 350 and 500 Îźm, and an imaging Fourier-transform spectrometer (FTS) which covers simultaneously its whole operating range of 194â671 Îźm (447â1550 GHz). The SPIRE detectors are arrays of feedhorn-coupled bolometers cooled to 0.3 K. The photometer has a field of view of 4´à 8´, observed simultaneously in the three spectral bands. Its main operating mode is scan-mapping, whereby the field of view is scanned across the sky to achieve full spatial sampling and to cover large areas if desired. The spectrometer has an approximately circular field of view with a diameter of 2.6´. The spectral resolution can be adjusted between 1.2 and 25 GHz by changing the stroke length of the FTS scan mirror. Its main operating mode involves a fixed telescope pointing with multiple scans of the FTS mirror to acquire spectral data. For extended source measurements, multiple position offsets are implemented by means of an internal beam steering mirror to achieve the desired spatial sampling and by rastering of the telescope pointing to map areas larger than the field of view. The SPIRE instrument consists of a cold focal plane unit located inside the Herschel cryostat and warm electronics units, located on the spacecraft Service Module, for instrument control and data handling. Science data are transmitted to Earth with no on-board data compression, and processed by automatic pipelines to produce calibrated science products. The in-flight performance of the instrument matches or exceeds predictions based on pre-launch testing and modelling: the photometer sensitivity is comparable to or slightly better than estimated pre-launch, and the spectrometer sensitivity is also better by a factor of 1.5â2
The Cosmic Infrared Background Experiment (CIBER): Instrumentation and First Results
Ultraviolet emission from the first generation of stars in the Universe ionized the intergalactic medium in a process which was completed by z similar to 6; the wavelength of these photons has been redshifted by (1 + z) into the near infrared today and can be measured using instruments situated above the Earth's atmosphere. First flying in February 2009, the Cosmic Infrared Background ExpeRiment (CIBER) comprises four instruments housed in a single reusable sounding rocket borne payload. CIBER will measure spatial anisotropies in the extragalactic IR background caused by cosmological structure from the epoch of reionization using two broadband imaging instruments, make a detailed characterization of the spectral shape of the IR background using a low resolution spectrometer, and measure the absolute brightness of the Zodiacal light foreground with a high resolution spectrometer in each of our six science fields. The scientific motivation for CIBER and details of its first and second flight instrumentation will be discussed. First flight results on the color of the zodiacal light around 1 mu m and plans for the future will also be presented
Observations of the Near-infrared Spectrum of the Zodiacal Light with CIBER
Interplanetary dust (IPD) scatters solar radiation which results in the zodiacal light that dominates the celestial diffuse brightness at optical and near-infrared wavelengths. Both asteroid collisions and cometary ejections produce the IPD, but the relative contribution from these two sources is still unknown. The low resolution spectrometer (LRS) onboard the Cosmic Infrared Background ExpeRiment (CIBER) observed the astrophysical sky spectrum between 0.75 and 2.1 Îźm over a wide range of ecliptic latitude. The resulting zodiacal light spectrum is redder than the solar spectrum, and shows a broad absorption feature, previously unreported, at approximately 0.9 Îźm, suggesting the existence of silicates in the IPD material. The spectral shape of the zodiacal light is isotropic at all ecliptic latitudes within the measurement error. The zodiacal light spectrum, including the extended wavelength range to 2.5 Îźm using Infrared Telescope in Space (IRTS) data, is qualitatively similar to the reflectance of S-type asteroids. This result can be explained by the proximity of S-type asteroidal dust to Earth's orbit, and the relatively high albedo of asteroidal dust compared with cometary dust
Rotating BPS black holes in matter-coupled AdS(4) supergravity
Using the general recipe given in arXiv:0804.0009, where all timelike
supersymmetric solutions of N=2, D=4 gauged supergravity coupled to abelian
vector multiplets were classified, we construct genuine rotating supersymmetric
black holes in AdS(4) with nonconstant scalar fields. This is done for the
SU(1,1)/U(1) model with prepotential F=-iX^0X^1. In the static case, the black
holes are uplifted to eleven dimensions, and generalize the solution found in
hep-th/0105250 corresponding to membranes wrapping holomorphic curves in a
Calabi-Yau five-fold. The constructed rotating black holes preserve one quarter
of the supersymmetry, whereas their near-horizon geometry is one half BPS.
Moreover, for constant scalars, we generalize (a supersymmetric subclass of)
the Plebanski-Demianski solution of cosmological Einstein-Maxwell theory to an
arbitrary number of vector multiplets. Remarkably, the latter turns out to be
related to the dimensionally reduced gravitational Chern-Simons action.Comment: 23 pages, uses JHEP3.cl
BPS black holes in N=2 D=4 gauged supergravities
We construct and analyze BPS black hole solutions in gauged N=2, D=4
supergravity with charged hypermultiplets. A class of solutions can be found
through spontaneous symmetry breaking in vacua that preserve maximal
supersymmetry. The resulting black holes do not carry any hair for the scalars.
We demonstrate this with explicit examples of both asymptotically flat and
anti-de Sitter black holes. Next, we analyze the BPS conditions for
asymptotically flat black holes with scalar hair and spherical or axial
symmetry. We find solutions only in cases when the metric contains ripples and
the vector multiplet scalars become ghost-like. We give explicit examples that
can be analyzed numerically. Finally, we comment on a way to circumvent the
ghost-problem by introducing also fermionic hair.Comment: 40 pages, 2 figures; v2 references added; v3 minor changes, published
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