20,699 research outputs found
Demonstration of the feasibility of automated silicon solar cell fabrication
A study effort was undertaken to determine the process, steps and design requirements of an automated silicon solar cell production facility. Identification of the key process steps was made and a laboratory model was conceptually designed to demonstrate the feasibility of automating the silicon solar cell fabrication process. A detailed laboratory model was designed to demonstrate those functions most critical to the question of solar cell fabrication process automating feasibility. The study and conceptual design have established the technical feasibility of automating the solar cell manufacturing process to produce low cost solar cells with improved performance. Estimates predict an automated process throughput of 21,973 kilograms of silicon a year on a three shift 49-week basis, producing 4,747,000 hexagonal cells (38mm/side), a total of 3,373 kilowatts at an estimated manufacturing cost of 1.22 per watt
The Regulation of Subsidies Affecting International Trade
We will begin by examining the basic contours of the present GATT regulation of subsidies. We will then consider the theory of comparative advantage underlying the GATT regime and introduce the complications of externalities and the governmental process designed to take account of them. Finally, we will make some tentative suggestions for changes in rules and institutions that might serve to improve the present state of affairs
Hybrid simulations of lateral diffusion in fluctuating membranes
In this paper we introduce a novel method to simulate lateral diffusion of
inclusions in a fluctuating membrane. The regarded systems are governed by two
dynamic processes: the height fluctuations of the membrane and the diffusion of
the inclusion along the membrane. While membrane fluctuations can be expressed
in terms of a dynamic equation which follows from the Helfrich Hamiltonian, the
dynamics of the diffusing particle is described by a Langevin or Smoluchowski
equation. In the latter equations, the curvature of the surface needs to be
accounted for, which makes particle diffusion a function of membrane
fluctuations. In our scheme these coupled dynamic equations, the membrane
equation and the Langevin equation for the particle, are numerically integrated
to simulate diffusion in a membrane. The simulations are used to study the
ratio of the diffusion coefficient projected on a flat plane and the
intramembrane diffusion coefficient for the case of free diffusion. We compare
our results with recent analytical results that employ a preaveraging
approximation and analyze the validity of this approximation. A detailed
simulation study of the relevant correlation functions reveals a surprisingly
large range where the approximation is applicable.Comment: 12 pages, 9 figures, accepted for publication in Phys. Rev.
Effects of low energy electron irradiation on formation of nitrogen-vacancy centers in single-crystal diamond
Exposure to beams of low energy electrons (2 to 30 keV) in a scanning
electron microscope locally induces formation of NV-centers without thermal
annealing in diamonds that have been implanted with nitrogen ions. We find that
non-thermal, electron beam induced NV-formation is about four times less
efficient than thermal annealing. But NV-center formation in a consecutive
thermal annealing step (800C) following exposure to low energy electrons
increases by a factor of up to 1.8 compared to thermal annealing alone. These
observations point to reconstruction of nitrogen-vacancy complexes induced by
electronic excitations from low energy electrons as an NV-center formation
mechanism and identify local electronic excitations as a means for spatially
controlled room-temperature NV-center formation
Measurements of Carrier Generation-Recombination Parameters in Silicon Solar Cell Material Using MOS Techniques
Modified and new measurement techniques were developed for determining the carrier generation-recombination (G-R) parameters in silicon solar cell material under carrier deficit and low-level carrier excess conditions using MOS-based test structures. The structures mainly consisted of ring-dot MOS Capacitors (MOS-C) and Schottky-Drained Gate-Controlled Diodes (SGCD). Sample G-R parameters were extracted from n-type high quality silicon solar cell material. Additional measurements were also performed on low-quality ntype silicon substrates for comparison purposes. The photoaccelerated MOS-C Capacitance-time (C-t) transient measurement technique, modified from the standard C-t method, allows one to drastically reduce the observation time in deducing the carrier generation lifetime (Tg) by simply illuminating the test structure during the transient. In applying the technique to MOS-C’s (which exhibited generation lifetime on the order of I msec) the observation time was reduced by approximately an order of magnitude. This is important in dealing with solar cell material because of typically long generation lifetimes. The SGCD structure, which consisted of an extended Schottky diode located next to an MOS-C, was developed and utilized for extracting the surface generation velocity (sg). The measurement is based on recording two C-t transients at Vd = 0 and at Vd = V t , respectively. The structure has a distinct advantage over the conventional PN junction GCD in that it is only slightly more complicated to fabricate and interrogate than a simple MOS-C. It was also demonstrated that steady-state deep-depletion C-V characteristics can be obtained using the SGCD structure. An MOS-C photo/forward-sweep measurement technique was primarily developed to extract the recombination lifetime (rp for n-type substrates) under low-level carrier excess conditions. The new technique is based on the change in inversion capacitance in response to a set of illumination and forward-sweep voltages applied to the MOS-C. The technique conveniently allows one to extract the recombination lifetime under room temperature conditions and was successfully applied to MOS-C’s fabricated on high quality silicon solar cell substrates
Local formation of nitrogen-vacancy centers in diamond by swift heavy ions
We exposed nitrogen-implanted diamonds to beams of swift uranium and gold
ions (~1 GeV) and find that these irradiations lead directly to the formation
of nitrogen vacancy (NV) centers, without thermal annealing. We compare the
photoluminescence intensities of swift heavy ion activated NV- centers to those
formed by irradiation with low-energy electrons and by thermal annealing. NV-
yields from irradiations with swift heavy ions are 0.1 of yields from low
energy electrons and 0.02 of yields from thermal annealing. We discuss possible
mechanisms of NV-center formation by swift heavy ions such as electronic
excitations and thermal spikes. While forming NV centers with low efficiency,
swift heavy ions enable the formation of three dimensional NV- assemblies over
relatively large distances of tens of micrometers. Further, our results show
that NV-center formation is a local probe of (partial) lattice damage
relaxation induced by electronic excitations from swift heavy ions in diamond.Comment: to be published in Journal of Applied Physic
Lagrangian multiform structure for the lattice Gel'fand-Dikii hierarchy
The lattice Gel'fand-Dikii hierarchy was introduced by Nijhoff, Papageorgiou,
Capel and Quispel in 1992 as the family of partial difference equations
generalizing to higher rank the lattice Korteweg-de Vries systems, and includes
in particular the lattice Boussinesq system. We present a Lagrangian for the
generic member of the lattice Gel'fand-Dikii hierarchy, and show that it can be
considered as a Lagrangian 2-form when embedded in a higher dimensional
lattice, obeying a closure relation. Thus the multiform structure proposed in
arXiv:0903.4086v2 [nlin.SI] is extended to a multi-component system.Comment: 12 page
A Vehicular Traffic Flow Model Based on a Stochastic Acceleration Process
A new vehicular traffic flow model based on a stochastic jump process in
vehicle acceleration and braking is introduced. It is based on a master
equation for the single car probability density in space, velocity and
acceleration with an additional vehicular chaos assumption and is derived via a
Markovian ansatz for car pairs. This equation is analyzed using simple driver
interaction models in the spatial homogeneous case. Velocity distributions in
stochastic equilibrium, together with the car density dependence of their
moments, i.e. mean velocity and scattering and the fundamental diagram are
presented.Comment: 27 pages, 6 figure
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