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

Flight software development for the isothermal dendritic growth experiment

The Isothermal Dendritic Growth Experiment (IDGE) is a microgravity materials science experiment scheduled to fly in the cargo bay of the shuttle on the United States Microgravity Payload (USMP) carrier. The experiment will be operated by real-time control software which will not only monitor and control onboard experiment hardware, but will also communicate, via downlink data and uplink commands, with the Payload Operations Control Center (POCC) at NASA George C. Marshall Space Flight Center (MSFC). The software development approach being used to implement this system began with software functional requirements specification. This was accomplished using the Yourdon/DeMarco methodology as supplemented by the Ward/Mellor real-time extensions. The requirements specification in combination with software prototyping was then used to generate a detailed design consisting of structure charts, module prologues, and Program Design Language (PDL) specifications. This detailed design will next be used to code the software, followed finally by testing against the functional requirements. The result will be a modular real-time control software system with traceability through every phase of the development process

Higher order correction to the neutrino self-energy in a medium and its astrophysical applications

We have calculated the 1/M^4 (M the vector boson mass) order correction to the neutrino self-energy in a medium. The possible application of this higher order contribution to the neutrino effective potential is considered in the context of the Early Universe hot plasma and of the cosmological Gamma Ray Burst fireball. We found that, depending on the medium parameters and on the neutrino properties (mixing angle and mass square difference) the resonant oscillation of active to active neutrinos is possible.Comment: 10 pages, revtex style, uses axodraw.sty, 1 figur

Quantum dot dephasing by edge states

We calculate the dephasing rate of an electron state in a pinched quantum dot, due to Coulomb interactions between the electron in the dot and electrons in a nearby voltage biased ballistic nanostructure. The dephasing is caused by nonequilibrium time fluctuations of the electron density in the nanostructure, which create random electric fields in the dot. As a result, the electron level in the dot fluctuates in time, and the coherent part of the resonant transmission through the dot is suppressed

Neutrino flux predictions for known Galactic microquasars

It has been proposed recently that Galactic microquasars may be prodigious emitters of TeV neutrinos that can be detected by upcoming km^2 neutrino telescopes. In this paper we consider a sample of identified microquasars and microquasar candiates, for which available data enables rough determination of the jet parameters. By employing the parameters inferred from radio observations of various jet ejection events, we determine the neutrino fluxes that should have been produced during these events by photopion production in the jet. Despite the large uncertainties in our analysis, we demonstrate that in several of the sources considered, the neutrino flux at Earth, produced in events similar to those observed, would exceed the detection threshold of a km^2 neutrino detector. The class of microquasars may contain also sources with bulk Lorentz factors larger than those characteristic of the sample considered here, directed along our line of sight. Such sources, which may be very difficult to resolve at radio wavelengths and hence may be difficult to identify as microqusar candidates, may emit neutrinos with fluxes significantly larger than typically obtained in the present analysis. These sources may eventually be identified through their neutrino and gamma-ray emission.Comment: 17 pages. Submitted to Ap

Quantized adiabatic quantum pumping due to interference

Recent theoretical calculations, demonstrating that quantized charge transfer due to adiabatically modulated potentials in mesoscopic devices can result purely from the interference of the electron wave functions (without invoking electron-electron interactions) are reviewed: (1) A new formula is derived for the pumped charge Q (per period); It reproduces the Brouwer formula without a bias, and also yields the effect of the modulating potential on the Landauer formula in the presence of a bias. (2) For a turnstile geometry, with time-dependent gate voltages V_L(t) and V_R(t), the magnitude and sign of Q are determined by the relative position and orientation of the closed contour traversed by the system in the {V_L-V_R} plane, relative to the transmission resonances in that plane. Integer values of Q (in units of e) are achieved when a transmission peak falls inside the contour, and are given by the winding number of the contour. (3) When the modulating potential is due to surface acoustic waves, Q exhibits a staircase structure, with integer values, reminiscent of experimental observations.Comment: Invited talk, Localization, Tokyo, August 200

Transient Emission From Dissipative Fronts in Magnetized, Relativistic Outflows. II. Synchrotron Flares

The time dependent synchrotron emission from relativistic jets, and the relation between the synchrotron and ERC emission is considered within the framework of the radiative front model. The timescale and profile of the optically thin emission are shown to be determined, in this model, by the shock formation radius, the thickness of expelled fluid slab and the variation of the front's parameters due to its transverse expansion. For a range of reasonable conditions, a variety of flare shapes can be produced, varying from roughly symmetric with exponential rises and decays, as often seen in blazars, to highly asymmetric with a fast rise and a much slower, power law decay, as seen in GRB afterglows. The onset, duration, and fluence of low-frequency (below the initial turnover frequency) and hard gamma-ray (above the initial gamma-spheric energy) outbursts are limited by opacity effects; the emission at these energies is quite generally delayed and, in the case of sufficiently short length outbursts, severely attenuated. The observational consequences are discussed. One distinctive prediction of this model is that in a single, powerful source, the upper cutoff of the gamma-ray spectrum should be correlated with the timescale of the outburst and with the amplitude of variations at long wavelengths (typically radio to millimeter).Comment: AAS LaTex, 14 pgs, accepted to A