3,961 research outputs found
Silicon on Ceramic Process: Silicon Sheet Growth and Device Development for the Large-area Silicon Sheet and Cell Development Tasks of the Low-cost Solar Array Project
The technical and economic feasibility of producing solar cell quality sheet silicon was investigated. It was hoped this could be done by coating one surface of carbonized ceramic substrates with a thin layer of large-grain polycrystalline silicon from the melt. Work was directed towards the solution of unique cell processing/design problems encountered with the silicon-ceramic (SOC) material due to its intimate contact with the ceramic substrate. Significant progress was demonstrated in the following areas; (1) the continuous coater succeeded in producing small-area coatings exhibiting unidirectional solidification and substatial grain size; (2) dip coater succeeded in producing thick (more than 500 micron) dendritic layers at coating speeds of 0.2-0.3 cm/sec; and (3) a standard for producing total area SOC solar cells using slotted ceramic substrates was developed
Inflation in Realistic D-Brane Models
We find successful models of D-brane/anti-brane inflation within a string
context. We work within the GKP-KKLT class of type IIB string vacua for which
many moduli are stabilized through fluxes, as recently modified to include
`realistic' orbifold sectors containing standard-model type particles. We allow
all moduli to roll when searching for inflationary solutions and find that
inflation is not generic inasmuch as special choices must be made for the
parameters describing the vacuum. But given these choices inflation can occur
for a reasonably wide range of initial conditions for the brane and antibrane.
We find that D-terms associated with the orbifold blowing-up modes play an
important role in the inflationary dynamics. Since the models contain a
standard-model-like sector after inflation, they open up the possibility of
addressing reheating issues. We calculate predictions for the CMB temperature
fluctuations and find that these can be consistent with observations, but are
generically not deep within the scale-invariant regime and so can allow
appreciable values for as well as predicting a potentially
observable gravity-wave signal. It is also possible to generate some admixture
of isocurvature fluctuations.Comment: 39 pages, 21 figures; added references; identified parameters
combining successful inflation with strong warping, as needed for consistency
of the approximation
Some experiences with the viscous-inviscid interaction approach
Methods for simulating compressible viscous flow using the viscid-inviscid interaction approach are described. The formulations presented range from the more familiar full-potential/boundary-layer interaction schemes to a method for coupling Euler/Navier-Stokes and boundary-layer algorithms. An effort is made to describe the advantages and disadvantages of each formulation. Sample results are presented which illustrate the applicability of the methods
Relativistic particle acceleration in developing Alfv\'{e}n turbulence
A new particle acceleration process in a developing Alfv\'{e}n turbulence in
the course of successive parametric instabilities of a relativistic pair plasma
is investigated by utilyzing one-dimensional electromagnetic full particle
code. Coherent wave-particle interactions result in efficient particle
acceleration leading to a power-law like energy distribution function. In the
simulation high energy particles having large relativistic masses are
preferentially accelerated as the turbulence spectrum evolves in time. Main
acceleration mechanism is simultaneous relativistic resonance between a
particle and two different waves. An analytical expression of maximum
attainable energy in such wave-particle interactions is derived.Comment: 15 pages, 9 figures, 1 tabl
The Environmental Kuznets Curve from Multiple Perspectives
The analysis finds that in addition to U-shaped paths of environmental quality arising for growth in income per capita, growth in population can also produce socially efficient patterns that are U-shaped. Sufficient conditions for both types of paths are identified for a range of models and parameters, including symmetrical models with homothetic, constant-returns functions such as with CES functions. Similar results are also shown to arise in decentralized economies under either homogeneous or heterogeneous income levels.Environmental Kuznets Curve, Economic Growth, Environmental Quality
Low-Concentration Solar-Power Systems Based on Organic Rankine Cycles for Distributed-Scale Applications: Overview and Further Developments
This paper is concerned with the emergence and development of low-to-medium-grade thermal-energy-conversion systems for distributed power generation based on thermo- dynamic vapor-phase heat-engine cycles undergone by organic working uids, namely organic Rankine cycles (ORCs). ORC power systems are, to some extent, a relatively established and mature technology that is well-suited to converting low/medium-grade heat (at temperatures up to ~300–400°C) to useful work, at an output power scale from a few kilowatts to 10s of megawatts. Thermal ef ciencies in excess of 25% are achievable at higher temperatures and larger scales, and efforts are currently in progress to improve the overall economic viability and thus uptake of ORC power systems, by focusing on advanced architectures, working- uid selection, heat exchangers and expansion machines. Solar-power systems based on ORC technology have a signi cant potential to be used for distributed power generation, by converting thermal energy from simple and low-cost non-concentrated or low-concentration collectors to mechanical, hydrau- lic, or electrical energy. Current elds of use include mainly geothermal and biomass/ biogas, as well as the recovery and conversion of waste heat, leading to improved energy ef ciency, primary energy (i.e., fuel) use and emission minimization, yet the technology is highly transferable to solar-power generation as an affordable alternative to small-to- medium-scale photovoltaic systems. Solar-ORC systems offer naturally the advantages of providing a simultaneous thermal-energy output for hot water provision and/or space heating, and the particularly interesting possibility of relatively straightforward onsite (thermal) energy storage. Key performance characteristics are presented, and important heat transfer effects that act to limit performance are identi ed as noteworthy directions of future research for the further development of this technology
Anomalous price impact and the critical nature of liquidity in financial markets
We propose a dynamical theory of market liquidity that predicts that the
average supply/demand profile is V-shaped and {\it vanishes} around the current
price. This result is generic, and only relies on mild assumptions about the
order flow and on the fact that prices are (to a first approximation)
diffusive. This naturally accounts for two striking stylized facts: first,
large metaorders have to be fragmented in order to be digested by the liquidity
funnel, leading to long-memory in the sign of the order flow. Second, the
anomalously small local liquidity induces a breakdown of linear response and a
diverging impact of small orders, explaining the "square-root" impact law, for
which we provide additional empirical support. Finally, we test our arguments
quantitatively using a numerical model of order flow based on the same minimal
ingredients.Comment: 16 pages, 7 figure
Silicon-on ceramic process: Silicon sheet growth and device development for the large-area silicon sheet task of the low-cost solar array project
The technical feasibility of producing solar-cell-quality sheet silicon to meet the Department of Energy (DOE) 1986 overall price goal of $0.70/watt was investigated. With the silicon-on-ceramic (SOC) approach, a low-cost ceramic substrate is coated with large-grain polycrystalline silicon by unidirectional solidification of molten silicon. This effort was divided into several areas of investigation in order to most efficiently meet the goals of the program. These areas include: (1) dip-coating; (2) continuous coating designated SCIM-coating, and acronym for Silicon Coating by an Inverted Meniscus (SCIM); (3) material characterization; (4) cell fabrication and evaluation; and (5) theoretical analysis. Both coating approaches were successful in producing thin layers of large grain, solar-cell-quality silicon. The dip-coating approach was initially investigated and considerable effort was given to this technique. The SCIM technique was adopted because of its scale-up potential and its capability to produce more conventiently large areas of SOC
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