12,694 research outputs found
Study program for encapsulation materials interface for low-cost solar array
The service integrity of the bonded interface in solar cell modules used in solar arrays is addressed. The development of AC impedance as a nondestructive evaluation (NDE) methodology for solar arrays is reported along with development of corrosion models and materials selection criteria for corrosion resistant interfaces
Signatures of Fermi surface reconstruction in Raman spectra of underdoped cuprates
We have calculated the Raman B and B spectra as a function of
temperature, as well as doping, for the underdoped cuprates, using a model
based on the resonating valence-bond spin-liquid. We discuss changes in
intensity and peak position brought about by the presence of a pseudogap and
the implied Fermi surface reconstruction, which are elements of this model.
Signatures of Fermi surface reconstruction are evident as a sharp rise in the
doping dependence of the antinodal to nodal peak ratio which occurs below the
quantum critical point. The temperature dependence of the B polarization
can be used to determine if the superconducting gap is limited to the Fermi
pocket, as seen in angle resolved photoemission spectroscopy, or extends
beyond. We find that the slope of the linear low energy B spectrum
maintains its usual d-wave form, but with an effective gap which reflects the
gap amplitude projected on the Fermi pocket. Our calculations capture the main
qualitative features revealed in the extensive data set available on the
HgBaCuO (Hg-1201) cuprate.Comment: 13 pages, 14 figure
Study program for encapsulation materials interface for low cost silicon solar array
An atmospheric corrosion model was developed and verified by five months of corrosion rate and climatology data acquired at the Mead, Nebraska LSA test site. Atmospheric corrosion rate monitors (ACM) show that moisture condensation probability and ionic conduction at the corroding surface or interface are controlling factors in corrosion rate. Protection of the corroding surface by encapsulant was shown by the ACM recordings to be maintained, independent of climatology, over the five months outdoor exposure period. The macroscopic corrosion processes which occur at Mead are shown to be reproduced in the climatology simulator. Controlled experiments with identical moisture and temperature aging cycles show that UV radiation causes corrosion while UV shielding inhibits LSA corrosion
Is Perceived Creativity-reward Contingency Good for Creativity? The Role of Challenge and Threat Appraisals
To address the complex effect of perceived reward for creativity on creative performance, we examined the role of cognitive appraisal as an individual difference variable. An individual's appraisal of reward for creativity, including challenge appraisal (perceived potential for recognition, growth, or mastery) and threat appraisal (perceived potential for revealing incompetence and damaging self-respect), is hypothesized to shape the effects of perceived reward for creativity. We further expect creativity-related intrinsic motivation to play a mediating role in the perceived reward-creativity relationship. The results of a three-wave field study showed that when challenge appraisal was high, perceived reward was positively related to creative performance through creativity-related intrinsic motivation, whereas when threat appraisal was high, perceived reward was negatively related to creative performance through creativity-related intrinsic motivation. A similar analysis showed that intrinsic task motivation was not able to channel the moderating effect of perceived reward and individual appraisal on creative performance
Heuristic derivation of continuum kinetic equations from microscopic dynamics
We present an approximate and heuristic scheme for the derivation of
continuum kinetic equations from microscopic dynamics for stochastic,
interacting systems. The method consists of a mean-field type, decoupled
approximation of the master equation followed by the `naive' continuum limit.
The Ising model and driven diffusive systems are used as illustrations. The
equations derived are in agreement with other approaches, and consequences of
the microscopic dependences of coarse-grained parameters compare favorably with
exact or high-temperature expansions. The method is valuable when more
systematic and rigorous approaches fail, and when microscopic inputs in the
continuum theory are desirable.Comment: 7 pages, RevTeX, two-column, 4 PS figures include
Delay-Optimal Biased User Association in Heterogeneous Networks
© 2017 IEEE. In heterogeneous networks (HetNets), load balancing among different tiers can be effectively achieved by a biased user association scheme with which each user chooses to associate with one base station (BS) based on the biased received power. In contrast to previous studies, where a BS always has packets to transmit, we assume in this paper that incoming packets intended for all the associated users form a queue in the BS. In order to find the delay limit of the network to support real-time service, we focus on the delay optimization problem by properly tuning the biasing factor of each tier. By adopting a thinned Poisson point process model to characterize the locations of BSs in the busy state, an explicit expression of the average traffic intensity of each tier is obtained. On that basis, an optimization problem is formulated to minimize a lower bound of the network mean queuing delay. By showing that the optimization problem is convex, the optimal biasing factor of each tier can be obtained numerically. When the mean packet arrival rate of each user is small, a closed-form solution is derived. The simulation results demonstrate that the network queuing performance can be significantly improved by properly tuning the biasing factor. It is further shown that the network mean queuing delay might be improved at the cost of a deterioration of the network signal-to-interference ratio coverage, which indicates a performance tradeoff between real-time and non-real-time traffic in HetNets
Quasinormal Modes of Dirty Black Holes
Quasinormal mode (QNM) gravitational radiation from black holes is expected
to be observed in a few years. A perturbative formula is derived for the shifts
in both the real and the imaginary part of the QNM frequencies away from those
of an idealized isolated black hole. The formulation provides a tool for
understanding how the astrophysical environment surrounding a black hole, e.g.,
a massive accretion disk, affects the QNM spectrum of gravitational waves. We
show, in a simple model, that the perturbed QNM spectrum can have interesting
features.Comment: 4 pages. Published in PR
Unification of bulk and interface electroresistive switching in oxide systems
We demonstrate that the physical mechanism behind electroresistive switching
in oxide Schottky systems is electroformation, as in insulating oxides.
Negative resistance shown by the hysteretic current-voltage curves proves that
impact ionization is at the origin of the switching. Analyses of the
capacitance-voltage and conductance-voltage curves through a simple model show
that an atomic rearrangement is involved in the process. Switching in these
systems is a bulk effect, not strictly confined at the interface but at the
charge space region.Comment: 4 pages, 3 figures, accepted in PR
Perturbative Approach to the Quasinormal Modes of Dirty Black Holes
Using a recently developed perturbation theory for uasinormal modes (QNM's),
we evaluate the shifts in the real and imaginary parts of the QNM frequencies
due to a quasi-static perturbation of the black hole spacetime. We show the
perturbed QNM spectrum of a black hole can have interesting features using a
simple model based on the scalar wave equation.Comment: Published in PR
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