39,412 research outputs found
Determination of space shuttle flow field by the three-dimensional method of characteristics
The newly improved three-dimensional method of characteristics program has been applied successfully to the calculation of flow fields over a variety of bodies including slab delta wings and shuttle orbiters. Flow fields over fuselage shapes for Mach numbers as low as 1.5 have been calculated. Some typical results are presented
Strain-Induced Coupling of Spin Current to Nanomechanical Oscillations
We propose a setup which allows to couple the electron spin degree of freedom
to the mechanical motions of a nanomechanical system not involving any of the
ferromagnetic components. The proposed method employs the strain induced
spin-orbit interaction of electrons in narrow gap semiconductors. We have shown
how this method can be used for detection and manipulation of the spin flow
through a suspended rod in a nanomechanical device.Comment: 4 pages, 1 figur
DC Spin Current Generation in a Rashba-type Quantum Channel
We propose and demonstrate theoretically that resonant inelastic scattering
(RIS) can play an important role in dc spin current generation. The RIS makes
it possible to generate dc spin current via a simple gate configuration: a
single finger-gate that locates atop and orients transversely to a quantum
channel in the presence of Rashba spin-orbit interaction. The ac biased
finger-gate gives rise to a time-variation in the Rashba coupling parameter,
which causes spin-resolved RIS, and subsequently contributes to the dc spin
current. The spin current depends on both the static and the dynamic parts in
the Rashba coupling parameter, and , respectively, and is
proportional to . The proposed gate configuration has the
added advantage that no dc charge current is generated. Our study also shows
that the spin current generation can be enhanced significantly in a double
finger-gate configuration.Comment: 4 pages,4 figure
Slowdown and splitting of gap solitons in apodized Bragg gratings
We study the motion of gap solitons in two models of apodized nonlinear fiber
Bragg gratings (BGs), with the local reflectivity (LR) varying along the fiber.
A single step of LR, and a periodic array of alternating steps with opposite
signs (a "Bragg superstructure") are considered. A challenging possibility is
to slow down and eventually halt the soliton by passing it through the step of
increasing reflectivity, thus capturing a pulse of standing light. First, we
develop an analytical approach, assuming adiabatic evolution of the soliton,
and making use of the energy conservation and balance equation for the
momentum. Comparison with simulations shows that the analytical approximation
is quite accurate (unless the inhomogeneity is too steep): the soliton is
either transmitted across the step or bounces back. If the step is narrow,
systematic simulations demontrate that the soliton splits into transmitted and
reflected pulses (splitting of a BG soliton which hits a chirped grating was
observed in experiments). Moving through the periodic "superstructure", the
soliton accummulates distortion and suffers radiation loss if the structure is
composed of narrow steps. The soliton moves without any loss or irreversible
deformation through the array of sufficiently broad steps.Comment: to appear in a special issue on Wave-Optical Engineering, Journal of
Modern Optic
Recent advances in GaAs/Ge solar cells
By growing the GaAs cell on a Ge substrate, the advantages of GaAs cells can be retained and the higher mechanical strength of the Ge makes larger, thinner GaAs cells possible. To conform to immediate user requirements, GaAs growth conditions were modified to eliminate the additional PV output at GaAs/Ge interface. To demonstrate acceptable cell manufacturing technology, the major areas in cell manufacture were analyzed and developed, and efficiency combined. Also the cells were successfully assembled on current lightweight arrays. The main areas of effort are discussed
Perfect State Transfer: Beyond Nearest-Neighbor Couplings
In this paper we build on the ideas presented in previous works for perfectly
transferring a quantum state between opposite ends of a spin chain using a
fixed Hamiltonian. While all previous studies have concentrated on
nearest-neighbor couplings, we demonstrate how to incorporate additional terms
in the Hamiltonian by solving an Inverse Eigenvalue Problem. We also explore
issues relating to the choice of the eigenvalue spectrum of the Hamiltonian,
such as the tolerance to errors and the rate of information transfer.Comment: 8 pages, 2 figures. Reorganised, more detailed derivations provided
and section on rate of information transfer adde
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