51,591 research outputs found
Long-term temperature effects on GaAs solar cells
The thermal degradation of AlGaAs solar cells resulting from a long-term operation in a space environment is investigated. The solar cell degradation effects caused by zinc and aluminum diffusion as well as deterioration by arsenic evaporation are presented. Also, the results are presented of experimental testing and measurements of various GaAs solar cell properties while the solar cell was operating in the temperature range of 27 C to 350 C. In particular, the properties of light current voltage curves, dark current voltage curves, and spectral response characteristics are given. Finally, some theoretical models for the annealing of radiation damage over various times and temperatures are included
Predicting Axonal Response to Molecular Gradients with a Computational Model of Filopodial Dynamics
Axons are often guided to their targets in the developing nervous system by attractive or repulsive molecular concentration gradients. We propose a computational model for gradient sensing and directed movement of the growth cone mediated by filopodia. We show that relatively simple
mechanisms are sufficient to generate realistic rajectories for both the short-term response of axons to steep gradients and the long-term response of axons to shallow gradients. The model makes testable predictions for axonal response to attractive and repulsive gradients of different
concentrations and steepness, the size of the intracellular amplification of the gradient signal, and the differences in intracellular signaling required for repulsive versus attractive turning
Large-N analysis of (2+1)-dimensional Thirring model
We analyze -dimensional vector-vector type four-Fermi interaction
(Thirring) model in the framework of the expansion. By solving the
Dyson-Schwinger equation in the large- limit, we show that in the
two-component formalism the fermions acquire parity-violating mass dynamically
in the range of the dimensionless coupling , . The symmetry
breaking pattern is, however, in a way to conserve the overall parity of the
theory such that the Chern-Simons term is not induced at any orders in .
turns out to be a non-perturbative UV-fixed point in . The
function is calculated to be
near the fixed point, and the UV-fixed point and the function are shown
exact in the expansion.Comment: 14 pages Latex. (Revised version: some changes have been made and
references added.) To appear in Phys. Rev. D, SNUTP 93-4
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Investigating the impact of remotely sensed precipitation and hydrologic model uncertainties on the ensemble streamflow forecasting
In the past few years sequential data assimilation (SDA) methods have emerged as the best possible method at hand to properly treat all sources of error in hydrological modeling. However, very few studies have actually implemented SDA methods using realistic input error models for precipitation. In this study we use particle filtering as a SDA method to propagate input errors through a conceptual hydrologic model and quantify the state, parameter and streamflow uncertainties. Recent progress in satellite-based precipitation observation techniques offers an attractive option for considering spatiotemporal variation of precipitation. Therefore, we use the PERSIANN-CCS precipitation product to propagate input errors through our hydrologic model. Some uncertainty scenarios are set up to incorporate and investigate the impact of the individual uncertainty sources from precipitation, parameters and also combined error sources on the hydrologic response. Also probabilistic measure are used to quantify the quality of ensemble prediction. Copyright 2006 by the American Geophysical Union
Spontaneous phase oscillation induced by inertia and time delay
We consider a system of coupled oscillators with finite inertia and
time-delayed interaction, and investigate the interplay between inertia and
delay both analytically and numerically. The phase velocity of the system is
examined; revealed in numerical simulations is emergence of spontaneous phase
oscillation without external driving, which turns out to be in good agreement
with analytical results derived in the strong-coupling limit. Such
self-oscillation is found to suppress synchronization and its frequency is
observed to decrease with inertia and delay. We obtain the phase diagram, which
displays oscillatory and stationary phases in the appropriate regions of the
parameters.Comment: 5 pages, 6 figures, to pe published in PR
Neutrino Interactions In Color-Flavor-Locked Dense Matter
At high density, diquarks could condense in the vacuum with the QCD color
spontaneously broken. Based on the observation that the symmetry breaking
pattern involved in this phenomenon is essentially the same as that of the
Pati-Salam model with broken electroweak--color SU(3) group, we determine the
relevant electroweak interactions in the color-flavor locked (CFL) phase in
high density QCD. We briefly comment on the possible implications on the
cooling of neutron stars.Comment: 13 pages. LaTeX. Talk given at the First KIAS Workshop on
Astrophysics, Seoul, May 2000; V2. references added. comments on cooling
change
Smartphone microendoscopy for high resolution fluorescence imaging
High resolution optical endoscopes are increasingly used in diagnosis of
various medical conditions of internal organs, such as the gastrointestinal
tracts, but they are too expensive for use in resource-poor settings. On the
other hand, smartphones with high resolution cameras and Internet access have
become more affordable, enabling them to diffuse into most rural areas and
developing countries in the past decade. In this letter we describe a
smartphone microendoscope that can take fluorescence images with a spatial
resolution of 3.1 {\mu}m. Images collected from ex vivo, in vitro and in vivo
samples using the device are also presented. The compact and cost-effective
smartphone microendoscope may be envisaged as a powerful tool for detecting
pre-cancerous lesions of internal organs in low and middle income countries.Comment: 4 pages, 4 figure
Evidence for spin-flip scattering and local moments in dilute fluorinated graphene
The issue of whether local magnetic moments can be formed by introducing
adatoms into graphene is of intense research interest because it opens the
window to fundamental studies of magnetism in graphene, as well as of its
potential spintronics applications. To investigate this question we measure, by
exploiting the well-established weak localization physics, the phase coherence
length L_phi in dilute fluorinated graphene. L_phi reveals an unusual
saturation below ~ 10 K, which cannot be explained by non-magnetic origins. The
corresponding phase breaking rate increases with decreasing carrier density and
increases with increasing fluorine density. These results provide strong
evidence for spin-flip scattering and points to the existence of adatom-induced
local magnetic moment in fluorinated graphene. Our results will stimulate
further investigations of magnetism and spintronics applications in
adatom-engineered graphene.Comment: 9 pages, 4 figures, and supplementary materials; Phys. Rev. Lett. in
pres
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