26,751 research outputs found
PFM Simulator
Pulse frequency modulation simulator for design and testing of telemetry equipment for satellite system
Different steady states for spin currents in noncollinear multilayers
We find there are at least two different steady states for transport across
noncollinear magnetic multilayers. In the conventional one there is a
discontinuity in the spin current across the interfaces which has been
identified as the source of current induced magnetic reversal; in the one
advocated herein the spin torque arises from the spin accumulation transverse
to the magnetization of a magnetic layer. These two states have quite different
attributes which should be discerned by current experiments.Comment: 8 pages, no figure. Accepted for publication in Journal of Physics:
Condensed Matte
Lateral diffusive spin transport in layered structures
A one dimensional theory of lateral spin-polarized transport is derived from
the two dimensional flow in the vertical cross section of a stack of
ferromagnetic and paramagnetic layers. This takes into account the influence of
the lead on the lateral current underneath, in contrast to the conventional 1D
modeling by the collinear configuration of lead/channel/lead. Our theory is
convenient and appropriate for the current in plane configuration of an
all-metallic spintronics structure as well as for the planar structure of a
semiconductor with ferromagnetic contacts. For both systems we predict the
optimal contact width for maximal magnetoresistance and propose an electrical
measurement of the spin diffusion length for a wide range of materials.Comment: 4 pages, 3 figure
Transport in superlattices on single layer graphene
We study transport in undoped graphene in the presence of a superlattice
potential both within a simple continuum model and using numerical
tight-binding calculations. The continuum model demonstrates that the
conductivity of the system is primarily impacted by the velocity anisotropy
that the Dirac points of graphene develop due to the potential. For
one-dimensional superlattice potentials, new Dirac points may be generated, and
the resulting conductivities can be approximately described by the anisotropic
conductivities associated with each Dirac point. Tight-binding calculations
demonstrate that this simple model is quantitatively correct for a single Dirac
point, and that it works qualitatively when there are multiple Dirac points.
Remarkably, for a two dimensional potential which may be very strong but
introduces no anisotropy in the Dirac point, the conductivity of the system
remains essentially the same as when no external potential is present.Comment: 8 pages, 7 figures, submitted to Phys. Rev.
Development of a three-dimensional turbulent duct flow analysis
A method for computing three-dimensional turbulent subsonic flow in curved ducts is described. An approximate set of governing equations is given for viscous flows which have a primary flow direction. The derivation is coordinate invariant, and the resulting equations are expressed in terms of tensors. General tube-like coordinates were developed for a general class of geometries applicable to many internal flow problems. The coordinates are then particularized to pipes having superelliptic cross sections whose shape can vary continuously between a circle and a near rectangle. The analysis is applied to a series of relevant aerodynamic problems including transition from nearly square to round pipes and flow through a pipe with an S-shaped bend
Development of a three-dimensional supersonic inlet flow analysis
A method for computing three dimensional flow in supersonic inlets is described. An approximate set of governing equations is given for viscous flows which have a primary flow direction. The governing equations are written in general orthogonal coordinates. These equations are modified in the subsonic region of the flow to prevent the phenomenon of branching. Results are presented for the two sample cases: a Mach number equals 2.5 flow in a square duct, and a Mach number equals 3.0 flow in a research jet engine inlet. In the latter case the computed results are compared with the experimental data. A users' manual is included
Quantum refrigerator driven by current noise
We proposed a scheme to implement a self-contained quantum refrigerator
system composed of three rf-SQUID qubits, or rather, flux-biased phase qubits.
The three qubits play the roles of the target, the refrigerator and the heat
engine respectively. We provide different effective temperatures for the three
qubits, by imposing external current noises of different strengths. The
differences of effective temperatures give rise to the flow of free energy and
that drives the refrigerator system to cool down the target. We also show that
the efficiency of the system approaches the Carnot efficiency.Comment: 5 pages, 1 figur
Path-integral calculation of the third virial coefficient of quantum gases at low temperatures
We derive path-integral expressions for the second and third virial
coefficients of monatomic quantum gases. Unlike previous work that considered
only Boltzmann statistics, we include exchange effects (Bose-Einstein or
Fermi-Dirac statistics). We use state-of-the-art pair and three-body potentials
to calculate the third virial coefficient of 3He and 4He in the temperature
range 2.6-24.5561 K. We obtain uncertainties smaller than those of the limited
experimental data. Inclusion of exchange effects is necessary to obtain
accurate results below about 7 K.Comment: The following article has been accepted by The Journal of Chemical
Physics. After it is published, it will be found at http://jcp.aip.org/
Version 2 includes the corrections detailed in the Erratu
Noise and thermal stability of vibrating micro-gyrometers preamplifiers
The preamplifier is a critical component of gyrometer's electronics. Indeed
the resolution of the sensor is limited by its signal to noise ratio, and the
gyrometer's thermal stability is limited by its gain drift. In this paper, five
different kinds of preamplifiers are presented and compared. Finally, the
design of an integrated preamplifier is shown in order to increase the gain
stability while reducing its noise and size.Comment: Submitted on behalf of EDA Publishing Association
(http://irevues.inist.fr/EDA-Publishing
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