18,528 research outputs found
Voltage controlling mechanisms in low resistivity silicon solar cells: A unified approach
An experimental technique capable of resolving the dark saturation current into its base and emitter components is used as the basis of an analysis in which the voltage limiting mechanisms were determined for a variety of high voltage, low resistivity silicon solar cells. The cells studied include the University of Florida hi-low emitter cell, the NASA and the COMSAT multi-step diffused cells, the Spire Corporation ion-implanted emitter cell, and the University of New South Wales MINMIS and MINP cells. The results proved to be, in general, at variance with prior expectations. Most surprising was the finding that the MINP and the MINMIS voltage improvements are due, to a considerable extent, to a previously unrecognized optimization of the base component of the saturation current. This result is substantiated by an independent analysis of the material used to fabricate these devices
QCD Heat Kernel in Covariant Gauge
We report the calculation of the fourth coefficient in an expansion of the
heat kernel of a non-minimal, non-abelian kinetic operator in an arbitrary
background gauge in arbitrary space-time dimension. The fourth coefficient is
shown to bring a nontrivial gauge dependence due to the contribution of the
lowest order off-shell gauge invariant structure.Comment: 6 pages + title page, standart LaTe
Shortest Path Computation with No Information Leakage
Shortest path computation is one of the most common queries in location-based
services (LBSs). Although particularly useful, such queries raise serious
privacy concerns. Exposing to a (potentially untrusted) LBS the client's
position and her destination may reveal personal information, such as social
habits, health condition, shopping preferences, lifestyle choices, etc. The
only existing method for privacy-preserving shortest path computation follows
the obfuscation paradigm; it prevents the LBS from inferring the source and
destination of the query with a probability higher than a threshold. This
implies, however, that the LBS still deduces some information (albeit not
exact) about the client's location and her destination. In this paper we aim at
strong privacy, where the adversary learns nothing about the shortest path
query. We achieve this via established private information retrieval
techniques, which we treat as black-box building blocks. Experiments on real,
large-scale road networks assess the practicality of our schemes.Comment: VLDB201
Real-space imaging of quantum Hall effect edge strips
We use dynamic scanning capacitance microscopy (DSCM) to image compressible
and incompressible strips at the edge of a Hall bar in a two-dimensional
electron gas (2DEG) in the quantum Hall effect (QHE) regime. This method gives
access to the complex local conductance, Gts, between a sharp metallic tip
scanned across the sample surface and ground, comprising the complex sample
conductance. Near integer filling factors we observe a bright stripe along the
sample edge in the imaginary part of Gts. The simultaneously recorded real part
exhibits a sharp peak at the boundary between the sample interior and the
stripe observed in the imaginary part. The features are periodic in the inverse
magnetic field and consistent with compressible and incompressible strips
forming at the sample edge. For currents larger than the critical current of
the QHE break-down the stripes vanish sharply and a homogeneous signal is
recovered, similar to zero magnetic field. Our experiments directly illustrate
the formation and a variety of properties of the conceptually important QHE
edge states at the physical edge of a 2DEG.Comment: 7 page
Ground-layer wavefront reconstruction from multiple natural guide stars
Observational tests of ground layer wavefront recovery have been made in open
loop using a constellation of four natural guide stars at the 1.55 m Kuiper
telescope in Arizona. Such tests explore the effectiveness of wide-field seeing
improvement by correction of low-lying atmospheric turbulence with ground-layer
adaptive optics (GLAO). The wavefronts from the four stars were measured
simultaneously on a Shack-Hartmann wavefront sensor (WFS). The WFS placed a 5 x
5 array of square subapertures across the pupil of the telescope, allowing for
wavefront reconstruction up to the fifth radial Zernike order. We find that the
wavefront aberration in each star can be roughly halved by subtracting the
average of the wavefronts from the other three stars. Wavefront correction on
this basis leads to a reduction in width of the seeing-limited stellar image by
up to a factor of 3, with image sharpening effective from the visible to near
infrared wavelengths over a field of at least 2 arc minutes. We conclude that
GLAO correction will be a valuable tool that can increase resolution and
spectrographic throughput across a broad range of seeing-limited observations.Comment: 25 pages, 8 figures, to be published in Astrophys.
Monopole clusters, Z(2) vortices and confinement in SU(2)
We extend our previous study of magnetic monopole currents in the maximally
Abelian gauge [hep-lat/9712003] to larger lattices at small lattice spacings
(20^4 at beta = 2.5 and 32^4 at beta = 2.5115). We confirm that at these weak
couplings there continues to be one monopole cluster that is very much longer
than the rest and that the string tension, K, is entirely due to it. The
remaining clusters are compact objects whose population as a function of radius
follows a power law that deviates from the scale invariant form, but much too
weakly to suggest a link with the analytically calculable size distribution of
small instantons. We also search for traces of Z(2) vortices in the Abelian
projected fields; either as closed loops of `magnetic' flux or through
appropriate correlations amongst the monopoles. We find, by direct calculation,
that there is no confining condensate of such flux loops. We also find, through
the calculation of doubly charged Wilson loops within the monopole fields, that
there is no suppression of the q=2 effective string tension out to at distances
of at least r ~ 1.6/sqrt{K}, suggesting that if there are any vortices they are
not encoded in the monopole fields.Comment: 26 pages of LaTeX and PostScript figure
A Gibbs approach to Chargaff's second parity rule
Chargaff's second parity rule (CSPR) asserts that the frequencies of short
polynucleotide chains are the same as those of the complementary reversed
chains. Up to now, this hypothesis has only been observed empirically and there
is currently no explanation for its presence in DNA strands. Here we argue that
CSPR is a probabilistic consequence of the reverse complementarity between
paired strands, because the Gibbs distribution associated with the chemical
energy between the bonds satisfies CSPR. We develop a statistical test to study
the validity of CSPR under the Gibbsian assumption and we apply it to a large
set of bacterial genomes taken from the GenBank repository.Comment: 16 page
Dynamic multilateral markets
We study dynamic multilateral markets, in which players' payoffs result from intra-coalitional bargaining. The latter is modeled as the ultimatum game with exogenous (time-invariant) recognition probabilities and unanimity acceptance rule. Players in agreeing coalitions leave the market and are replaced by their replicas, which keeps the pool of market participants constant over time. In this infinite game, we establish payoff uniqueness of stationary equilibria and the emergence of endogenous cooperation structures when traders experience some degree of (heterogeneous) bargaining frictions. When we focus on market games with different player types, we derive, under mild conditions, an explicit formula for each type's equilibrium payoff as the market frictions vanish
Ab initio calculations of the physical properties of transition metal carbides and nitrides and possible routes to high-Tc
Ab initio linear-response calculations are reported of the phonon spectra and
the electron-phonon interaction for several transition metal carbides and
nitrides in a NaCl-type structure. For NbC, the kinetic, optical, and
superconducting properties are calculated in detail at various pressures and
the normal-pressure results are found to well agree with the experiment.
Factors accounting for the relatively low critical temperatures Tc in
transition metal compounds with light elements are considered and the possible
ways of increasing Tc are discussed.Comment: 19 pages, 7 figure
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