2,781 research outputs found
Coherent backscattering of Bose-Einstein condensates in two-dimensional disorder potentials
We study quantum transport of an interacting Bose-Einstein condensate in a
two-dimensional disorder potential. In the limit of vanishing atom-atom
interaction, a sharp cone in the angle-resolved density of the scattered matter
wave is observed, arising from constructive interference between amplitudes
propagating along reversed scattering paths. Weak interaction transforms this
coherent backscattering peak into a pronounced dip, indicating destructive
instead of constructive interference. We reproduce this result, obtained from
the numerical integration of the Gross-Pitaevskii equation, by a diagrammatic
theory of weak localization in presence of a nonlinearity.Comment: 4 pages, 4 figure
Algorithms for Multi-channel DTMF Detection for the WE DSP32 Family
The authors describe two DTMF (dual-tone multiple frequency) detection algorithms that are highly efficient in the use of both real time and memory. The first algorithm is based on linear prediction (LP) and can be used to implement up to 32 DTMF detectors on a single 25-MHz NMOS WE DSP32. Using a 50-MHZ WE CMOS DSP32C, up to 45 detectors can be implemented. The second algorithm is based on a slight modification of the Goertzel algorithm and can be used to implement up to 16 DTMF detectors on a single DSP32 and up to 32 detectors on a DSP32C. In each of these implementations no external memory is used. Thus, for DSP32 implementations, the small 40-pin DIP package can be used. While the LP based algorithm is the more efficient of the two, the modified-Goertzel-based detector performs better in the presence of speech
Tenure and Due Process
The legal significance of tenure is reviewed in this article as it relates to the new and developing laws of due process. The authors suggest that expectancy of re-employment may become a new form of property right
Next-to-leading order spin-orbit and spin(a)-spin(b) Hamiltonians for n gravitating spinning compact objects
We derive the post-Newtonian next-to-leading order conservative spin-orbit
and spin(a)-spin(b) gravitational interaction Hamiltonians for arbitrary many
compact objects. The spin-orbit Hamiltonian completes the knowledge of
Hamiltonians up to and including 2.5PN for the general relativistic three-body
problem. The new Hamiltonians include highly nontrivial three-body
interactions, in contrast to the leading order consisting of two-body
interactions only. This may be important for the study of effects like Kozai
resonances in mergers of black holes with binary black holes.Comment: 13 pages, 1 Mathematica source file, v2: submitted version, v3:
published version, some minor correction
Implementation of DSP Applications Using the AT&T DSP32 C Compiler and Application Library
The authors briefly introduce the C compiler and the application library for the DSP32 digital signal processor (DSP). Several examples are shown that illustrate the ease of writing C programs for some common filtering applications. In most cases, a small real-time penalty is incurred by using C, rather than assembly language coding. Programming in C, however, allows a dramatic improvement in programmer productivity in terms of implementing, testing, and maintaining an applicatio
Optical Response of Grating-Coupler-Induced Intersubband Resonances: The Role of Wood's Anomalies
Grating-coupler-induced collective intersubband transitions in a
quasi-two-dimensional electron system are investigated both experimentally and
theoretically. Far-infrared transmission experiments are performed on samples
containing a quasi-two-dimensional electron gas quantum-confined in a parabolic
quantum well. For rectangular shaped grating couplers of different periods we
observe a strong dependence of the transmission line shape and peak height on
the period of the grating, i.e. on the wave vector transfer from the diffracted
beams to the collective intersubband resonance. It is shown that the line shape
transforms with increasing grating period from a Lorentzian into a strongly
asymmetric line shape. Theoretically, we treat the problem by using the
transfer-matrix method of local optics and apply the modal-expansion method to
calculate the influence of the grating. The optically uniaxial
quasi-two-dimensional electron gas is described in the long-wavelength limit of
the random-phase approximation by a local dielectric tensor, which includes
size quantization effects. Our theory reproduces excellently the experimental
line shapes. The deformation of the transmission line shapes we explain by the
occurrence of both types of Wood's anomalies.Comment: 28 pages, 7 figures. Physical Review B , in pres
A Practical C Language Compiler/Optimizer for Real-Time Implementations on a Family of Floating Point DSPs
Digital signal processors (DSPs) have traditionally been used in real-time applications with very high data throughput. For this reason, system designers have been reluctant to accept the degradation in performance inherent in machine code compiled from high-level languages such as C. The problem is compounded by the fact that DSPs use pipelined architectures to achieve their high data throughput, resulting in hazards and latencies between instructions. Simple compiler implementation cannot take advantage of latent instructions, resulting in a conservative and inefficient executable program. This problem has been addressed in the C compiler package for the AT&T WE DSP32 by the addition of a postoptimizer and an extensive application library. The authors give an overview of the DSP32 family architecture, describe the operation of the basic compiler and optimization strategies, and provide an example of the use of the compile
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