8,136 research outputs found
Reliability assessment of the GEOS A power supply
Reliability assessment of geodetic satellite A power suppl
Diffuse emission in the presence of inhomogeneous spin-orbit interaction for the purpose of spin filtration
A lateral interface connecting two regions with different strengths of the
Bychkov-Rashba spin-orbit interaction can be used as a spin polarizer of
electrons in two dimensional semiconductor heterostructures. [Khodas \emph{et
al.}, Phys. Rev. Lett. \textbf{92}, 086602 (2004)]. In this paper we consider
the case when one of the two regions is ballistic, while the other one is
diffusive. We generalize the technique developed for the solution of the
problem of the diffuse emission to the case of the spin dependent scattering at
the interface, and determine the distribution of electrons emitted from the
diffusive region. It is shown that the diffuse emission is an effective way to
get electrons propagating at small angles to the interface that are most
appropriate for the spin filtration and a subsequent spin manipulation.
Finally, a scheme is proposed of a spin filter device, see Fig. 9, that creates
two almost fully spin-polarized beams of electrons.Comment: 11 pages, 9 figure
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Life cycle assessment of white roof and sedum-tray garden roof for office buildings in China
White roof (WR) and Sedum lineare tray garden roof (STGR) have been convinced to improve the energy-efficiency and provide various benefits for conventional impervious grey roofs. Some national and local standards have standardized and recommended these technologies in existing building retrofits, however, they do not include assessment and choice of a particular roof retrofit in different climates. This paper presents a 40-year life-cycle cost analysis (LCCA) of an office building roof retrofitted by adding either WR or STGR over an existing grey roof in five cities, located in four Chinese climate zones. The LCCA find that the WR retrofits exhibit positive life-cycle net savings (NS) in warm winter zones, ranging 5.7–35.1 CNY/m 2 , and STGR retrofits have negative NS of -81.3– -16.7 CNY/m 2 in all climate zones. The NS of both WR and STGR generally tend to improve as one moves from the coldest cities to the warmest cities. LCCA results suggest that adding new building codes concerning crediting or prescribing WR and STGR retrofits into office buildings with grey roofs in hot summer climate zones and warm winter zone in China, respectively. And featured by more specific requirements, the localized Technical Norms help promote the implementation of new building codes
Linear acceleration emission: 2 Power spectrum
The theory of linear acceleration emission is developed for a large amplitude
electrostatic wave in which all particles become highly relativistic in much
less than a wave period. An Airy integral approximation is shown to apply near
the phases where the electric field passes through zero and the Lorentz factors
of all particles have their maxima. The emissivity is derived for an individual
particle and is integrated over frequency and solid angle to find the power
radiated per particle. The result is different from that implied by the
generalized Larmor formula which, we argue, is not valid in this case. We also
discuss a mathematical inconsistency that arises when one evaluates the power
spectrum by integrating the emissivity over solid angle. The correct power
spectrum increases as the 4/3rd power of the frequency at low frequencies, and
falls off exponentially above a characteristic frequency.
We discuss application of linear acceleration emission to the emission of
high frequency photons in an oscillating model for pulsars. We conclude that it
cannot account for gamma-ray emission, but can play a role in secondary pair
creation.Comment: 25 pages; Accepted for publication in Ap
Induced scattering of short radio pulses
Effect of the induced Compton and Raman scattering on short, bright radio
pulses is investigated. It is shown that when a single pulse propagates through
the scattering medium, the effective optical depth is determined by the
duration of the pulse but not by the scale of the medium. The induced
scattering could hinder propagation of the radio pulse only if close enough to
the source a dense enough plasma is presented. The induced scattering within
the relativistically moving source places lower limits on the Lorentz factor of
the source. The results are applied to the recently discovered short
extragalactic radio pulse.Comment: submitted to Ap
Levinson theorem for Aharonov-Bohm scattering in two dimensions
We apply the recently generalized Levinson theorem for potentials with
inverse square singularities [Sheka et al, Phys.Rev.A, v.68, 012707 (2003)] to
Aharonov-Bohm systems in two-dimensions. By this theorem, the number of bound
states in a given m-th partial wave is related to the phase shift and the
magnetic flux. The results are applied to 2D soliton-magnon scattering.Comment: 5 pages (REVTeX
Probing Micro-quasars with TeV Neutrinos
The jets associated with Galactic micro-quasars are believed to be ejected by
accreting stellar mass black-holes or neutron stars. We show that if the energy
content of the jets in the transient sources is dominated by electron-proton
plasma, then a several hour outburst of 1--100 TeV neutrinos produced by photo-
meson interactions should precede the radio flares associated with major
ejection events. Several neutrinos may be detected during a single outburst by
a 1km^2 detector, thereby providing a powerful probe of micro-quasars jet
physics.Comment: Accepted to PRL. More detailed discussion of particle acceleratio
Relativistic Photon Mediated Shocks
A system of equations governing the structure of a steady, relativistic
radiation dominated shock is derived, starting from the general form of the
transfer equation obeyed by the photon distribution function. Closure is
obtained by truncating the system of moment equations at some order. The
anisotropy of the photon distribution function inside the shock is shown to
increase with increasing shock velocity, approaching nearly perfect beaming at
upstream Lorentz factors . Solutions of the shock equations are
presented for some range of upstream conditions. These solutions are shown to
converge as the truncation order is increased.Comment: 5 pages, a shorter version will appear in PR
Theory and astrophysical consequences of a magnetized torus around a rapidly rotating black hole
(Abbrev.) We analyze the topology, lifetime, and emissions of a torus around
a black hole formed in hypernovae and black hole-neutron star coalescence. The
torus is ab initio uniformly magnetized, represented by two counter oriented
current-rings, and develops a state of suspended accretion against a "magnetic
wall" around the black hole. Magnetic stability of the torus gives rise to a
new fundamental limit EB/Ek<0.1 for the ratio of poloidal magnetic field
energy-to-kinetic energy. The lifetime of rapid spin of the black hole is
effectively defined by the timescale of dissipation of black hole-spin energy
in the horizon, and satisfies T= 40s (MH/7MSun)(R/6MH)^4(0.03MH/MT) for a black
hole of mass MH surrounded by a torus of mass MT and radius R. The torus
converts a major fraction Egw/Erot=0.1 into gravitational radiation through a
finite number of multipole mass-moments, and a smaller fraction into MeV
neutrinos and baryon-rich winds. At a source distance of 100Mpc, these
emissions over N=2e4 periods give rise to a characteristic strain amplitude
\sqrt{N}hchar=6e-21. We argue that torus winds create an open magnetic
flux-tube on the black hole, which carries a minor and standard fraction
Ej/Erot=1e-3 in baryon-poor outflows to infinity. We identify this baryon poor
output of tens of seconds with GRBs with contemporaneous and strongly
correlated emissions in gravitational radiation, conceivably at multiple
frequencies. Ultimately, this leaves a black hole binary surrounded by a
supernova remnant.Comment: To appear in ApJ (44p
Sensitivity of the superconducting state in thin films
For more than two decades, there have been reports on an unexpected metallic state separating the established superconducting and insulating phases of thin-film superconductors. To date, no theoretical explanation has been able to fully capture the existence of such a state for the large variety of superconductors exhibiting it. Here, we show that for two very different thin-film superconductors, amorphous indium oxide and a single crystal of 2H-NbSe2, this metallic state can be eliminated by adequately filtering external radiation. Our results show that the appearance of temperature-independent, metallic-like transport at low temperatures is sufficiently described by the extreme sensitivity of these superconducting films to external perturbations. We relate this sensitivity to the theoretical observation that, in two dimensions, superconductivity is only marginally stable
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