10,657 research outputs found
High efficiency compound semiconductor concentrator photovoltaics
Special emphasis was given to the high yield pilot production of packaged AlGaAs/GaAs concentrator solar cells, using organometallic VPE for materials growth, the demonstration of a concentrator module using 12 of these cells which achieved 16.4 percent conversion efficiency at 50 C coolant inlet temperature, and the demonstration of a spectral splitting converter module that achieved in excess of 20 percent efficiency. This converter employed ten silicon and ten AlGaAs cells with a dichroic filter functioning as the beam splitter. A monolithic array of AlGaAs/GaAs solar cells is described
Analytical approach to the transition to thermal hopping in the thin- and thick-wall approximations
The nature of the transition from the quantum tunneling regime at low
temperatures to the thermal hopping regime at high temperatures is investigated
analytically in scalar field theory. An analytical bounce solution is
presented, which reproduces the action in the thin-wall as well as thick-wall
limits. The transition is first order for the case of a thin wall while for the
thick wall case it is second order.Comment: Latex file, 22 pages, 4 Postscript figure
Error latency estimation using functional fault modeling
A complete modeling of faults at gate level for a fault tolerant computer is both infeasible and uneconomical. Functional fault modeling is an approach where units are characterized at an intermediate level and then combined to determine fault behavior. The applicability of functional fault modeling to the FTMP is studied. Using this model a forecast of error latency is made for some functional blocks. This approach is useful in representing larger sections of the hardware and aids in uncovering system level deficiencies
Discrete Breathers in a Nonlinear Polarizability Model of Ferroelectrics
We present a family of discrete breathers, which exists in a nonlinear
polarizability model of ferroelectric materials. The core-shell model is set up
in its non-dimensionalized Hamiltonian form and its linear spectrum is
examined. Subsequently, seeking localized solutions in the gap of the linear
spectrum, we establish that numerically exact and potentially stable discrete
breathers exist for a wide range of frequencies therein.
In addition, we present nonlinear normal mode, extended spatial profile
solutions from which the breathers bifurcate, as well as other associated
phenomena such as the formation of phantom breathers within the model.
The full bifurcation picture of the emergence and disappearance of the
breathers is complemented by direct numerical simulations of their dynamical
instability, when the latter arises.Comment: 9 pages, 7 figures, 1 tabl
OM-VPE grown materials for high efficiency solar cells
Organometallic sources are available for all the III-V elements and a variety of dopants; thus it is possible to use the technique to grow a wide variety of semiconductor compounds. AlGaAsSb and AlGaInAs alloys for multijunction monolithic solar cells were grown by OM-VPE. While the effort concentrated on terrestrial applications, the success of OM-VPE grown GaAs/AlGaAs concentrator solar cells (23% at 400 suns) demonstrates that OM-VPE is suitable for growing high efficiency solar cells in large quantities for space applications. In addition, OM-VPE offers the potential for substantial cost reduction of photovoltaic devices with scale up and automation and due to high process yield from reproducible, uniform epitaxial growths with excellent surface morphology
Duality and cosmological compactification of superstrings with unbroken supersymmetry
The cosmological compactification of D=10, N=1 supergravity-super-Yang-Mills
theory obtained from superstring theory is studied. The constraint of unbroken
N=1 supersymmetry is imposed. A duality transformation is performed on the
resulting consistency conditions. The original equations as well as the
transformed equations are solved numerically to obtain new configurations with
a nontrivial scale factor and a dynamical dilaton. It is shown that various
classes of solutions are possible, which include cosmological solutions with no
initial singularity.Comment: Latex2e file, 24 pages including 10 figures as tex file
Arithmetic Circuit Lower Bounds via MaxRank
We introduce the polynomial coefficient matrix and identify maximum rank of
this matrix under variable substitution as a complexity measure for
multivariate polynomials. We use our techniques to prove super-polynomial lower
bounds against several classes of non-multilinear arithmetic circuits. In
particular, we obtain the following results :
As our main result, we prove that any homogeneous depth-3 circuit for
computing the product of matrices of dimension requires
size. This improves the lower bounds by Nisan and
Wigderson(1995) when .
There is an explicit polynomial on variables and degree at most
for which any depth-3 circuit of product dimension at most
(dimension of the space of affine forms feeding into each
product gate) requires size . This generalizes the lower bounds
against diagonal circuits proved by Saxena(2007). Diagonal circuits are of
product dimension 1.
We prove a lower bound on the size of product-sparse
formulas. By definition, any multilinear formula is a product-sparse formula.
Thus, our result extends the known super-polynomial lower bounds on the size of
multilinear formulas by Raz(2006).
We prove a lower bound on the size of partitioned arithmetic
branching programs. This result extends the known exponential lower bound on
the size of ordered arithmetic branching programs given by Jansen(2008).Comment: 22 page
Localized structures in Kagome lattices
We investigate the existence and stability of gap vortices and multi-pole gap
solitons in a Kagome lattice with a defocusing nonlinearity both in a discrete
case and in a continuum one with periodic external modulation. In particular,
predictions are made based on expansion around a simple and analytically
tractable anti-continuum (zero coupling) limit. These predictions are then
confirmed for a continuum model of an optically-induced Kagome lattice in a
photorefractive crystal obtained by a continuous transformation of a honeycomb
lattice
Exact Solutions of the Saturable Discrete Nonlinear Schrodinger Equation
Exact solutions to a nonlinear Schr{\"o}dinger lattice with a saturable
nonlinearity are reported. For finite lattices we find two different
standing-wave-like solutions, and for an infinite lattice we find a localized
soliton-like solution. The existence requirements and stability of these
solutions are discussed, and we find that our solutions are linearly stable in
most cases. We also show that the effective Peierls-Nabarro barrier potential
is nonzero thereby indicating that this discrete model is quite likely
nonintegrable
Assessment of Immunotoxic Response in Albino Rats Following Nickel Nitrate Treatment
Nickel nitrate affects body physiology and immunology following its absorption through food, water, air. Predetermined doses of nickel nitrate (Ni(NO3)2] in acute (1 d) and subacute (7, 14, 21 ds) treatments revealed a significant increase in IgG concentration and lymphocyte number, whereas, neutrophils and eosinophils registered significant fall. These alterations indicated heavy metal stress in Immunological parameters that become targets
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