26,567 research outputs found
Radiation effects in GaAs AMOS solar cells
The results of radiation damage produced in AMOS (Antireflecting-Metal-Oxide-Semiconductor) cells with Sb2O3 interfacial oxide layers by 1-MeV electrons are presented. The degradation properties of the cells as a function of irradiation fluences were correlated with the changes in their spectral response, C-V, dark forward, and light I-V characteristics. The active n-type GaAs layers were grown by the OM-CVD technique, using sulfur doping in the range between 3 x 10 to the 15th power and 7 x 10 to the 16th power/cu cm. At a fluence of 10 to the 16th power e/sq cm, the low-doped samples showed I sub sc degradation of 8% and V sub oc degradation of 8%. The high-doped samples showed I sub sc and V sub oc degradation of 32% and 1%, respectively, while the fill factor remained relatively unchanged for both. AMOS cells with water vapor-grown interfacial layers showed no significant change in V sub oc
Facilitation of polymer looping and giant polymer diffusivity in crowded solutions of active particles
We study the dynamics of polymer chains in a bath of self-propelled particles
(SPP) by extensive Langevin dynamics simulations in a two dimensional system.
Specifically, we analyse the polymer looping properties versus the SPP activity
and investigate how the presence of the active particles alters the chain
conformational statistics. We find that SPPs tend to extend flexible polymer
chains while they rather compactify stiffer semiflexible polymers, in agreement
with previous results. Here we show that larger activities of SPPs yield a
higher effective temperature of the bath and thus facilitate looping kinetics
of a passive polymer chain. We explicitly compute the looping probability and
looping time in a wide range of the model parameters. We also analyse the
motion of a monomeric tracer particle and the polymer's centre of mass in the
presence of the active particles in terms of the time averaged mean squared
displacement, revealing a giant diffusivity enhancement for the polymer chain
via SPP pooling. Our results are applicable to rationalising the dimensions and
looping kinetics of biopolymers at constantly fluctuating and often actively
driven conditions inside biological cells or suspensions of active colloidal
particles or bacteria cells.Comment: 15 pages, 9 figures, IOPLaTe
Optical properties of the charge-density-wave polychalcogenide compounds Te (=Nd, Sm and Gd)
We investigate the rare-earth polychalcogenide Te (=Nd, Sm and
Gd) charge-density-wave (CDW) compounds by optical methods. From the absorption
spectrum we extract the excitation energy of the CDW gap and estimate the
fraction of the Fermi surface which is gapped by the formation of the CDW
condensate. In analogy to previous findings on the related Te (n=2 and
3) families, we establish the progressive closing of the CDW gap and the
moderate enhancement of the metallic component upon chemically compressing the
lattice
Synchronization and fault-masking in redundant real-time systems
A real time computer may fail because of massive component failures or not responding quickly enough to satisfy real time requirements. An increase in redundancy - a conventional means of improving reliability - can improve the former but can - in some cases - degrade the latter considerably due to the overhead associated with redundancy management, namely the time delay resulting from synchronization and voting/interactive consistency techniques. The implications of synchronization and voting/interactive consistency algorithms in N-modular clusters on reliability are considered. All these studies were carried out in the context of real time applications. As a demonstrative example, we have analyzed results from experiments conducted at the NASA Airlab on the Software Implemented Fault Tolerance (SIFT) computer. This analysis has indeed indicated that in most real time applications, it is better to employ hardware synchronization instead of software synchronization and not allow reconfiguration
A supermassive binary black hole with triple disks
Hierarchical structure formation inevitably leads to the formation of
supermassive binary black holes (BBHs) with a sub-parsec separation in galactic
nuclei. However, to date there has been no unambiguous detection of such
systems. In an effort to search for potential observational signatures of
supermassive BBHs, we performed high-resolution smoothed particle hydrodynamics
(SPH) simulations of two black holes in a binary of moderate eccentricity
surrounded by a circumbinary disk. Building on our previous work, which has
shown that gas can periodically transfer from the circumbinary disk to the
black holes when the binary is on an eccentric orbit, the current set of
simulations focuses on the formation of the individual accretion disks, their
evolution and mutual interaction, and the predicted radiative signature. The
variation in mass transfer with orbital phase from the circumbinary disk
induces periodic variations in the light curve of the two accretion disks at
ultraviolet wavelengths, but not in the optical or near-infrared. Searches for
this signal offer a promising method to detect supermassive BBHs.Comment: Accepted for publication in the Astrophysical Journal, 16 pages, 11
figures. High Resolution Version is Available at
http://www2.yukawa.kyoto-u.ac.jp/~kimitake/bbhs.htm
Understanding possible electromagnetic counterparts to loud gravitational wave events: Binary black hole effects on electromagnetic fields
In addition to producing loud gravitational waves (GW), the dynamics of a
binary black hole system could induce emission of electromagnetic (EM)
radiation by affecting the behavior of plasmas and electromagnetic fields in
their vicinity. We here study how the electromagnetic fields are affected by a
pair of orbiting black holes through the merger. In particular, we show how the
binary's dynamics induce a variability in possible electromagnetically induced
emissions as well as an enhancement of electromagnetic fields during the
late-merge and merger epochs. These time dependent features will likely leave
their imprint in processes generating detectable emissions and can be exploited
in the detection of electromagnetic counterparts of gravitational waves.Comment: 12 page
Bubble Raft Model for a Paraboloidal Crystal
We investigate crystalline order on a two-dimensional paraboloid of
revolution by assembling a single layer of millimeter-sized soap bubbles on the
surface of a rotating liquid, thus extending the classic work of Bragg and Nye
on planar soap bubble rafts. Topological constraints require crystalline
configurations to contain a certain minimum number of topological defects such
as disclinations or grain boundary scars whose structure is analyzed as a
function of the aspect ratio of the paraboloid. We find the defect structure to
agree with theoretical predictions and propose a mechanism for scar nucleation
in the presence of large Gaussian curvature.Comment: 4 pages, 4 figure
Modelling spatially regulated B-catenin dynamics & invasion in intestinal crypts
Experimental data (e.g., genetic lineage and cell population studies) on intestinal crypts reveal that regulatory features of crypt behavior, such as control via morphogen gradients, are remarkably well conserved among numerous organisms (e.g., from mouse and rat to human) and throughout the different regions of the small and large intestines. In this article, we construct a partial differential equation model of a single colonic crypt that describes the spatial distribution of Wnt pathway proteins along the crypt axis. The novelty of our continuum model is that it is based upon assumptions that can be directly related to processes at the cellular and subcellular scales. We use the model to predict how the distributions of Wnt pathway proteins are affected by mutations. The model is then extended to investigate how mutant cell populations can invade neighboring crypts. The model simulations suggest that cell crowding caused by increased proliferation and decreased cell loss may be sufficient for a mutant cell population to colonize a neighboring healthy crypt
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