9,009 research outputs found
Portable linear-focused solar thermal energy collecting system
A solar heat collection system is provided by utilizing a line-focusing device that is effectively a cylindrically curved concentrator within a protected environment formed by a transparent inflatable casing. A target, such as a fluid or gas carrying conduit is positioned within or near the casing containing the concentrator, at the line focus of the concentrator. The casing can be inflated at the site of use by a low pressure air supply to form a unitary light weight structure. The collector, including casing, concentrator and target, is readily transportable and can be used either at ground level or on rooftops. The inflatable concentrator can be replaced with a rigid metal or other concentrator while maintaining the novel advantages of the whole solar heat collection system
Three-dimensional tracking solar energy concentrator and method for making same
A three dimensional tracking solar energy concentrator, consisting of a stretched aluminized polymeric membrane supported by a hoop, was presented. The system is sturdy enough to withstand expected windage forces and precipitation. It can provide the high temperature output needed by central station power plants for power production in the multi-megawatt range
Creating Non-Maxwellian Velocity Distributions in Ultracold Plasmas
We present techniques to perturb, measure and model the ion velocity
distribution in an ultracold neutral plasma produced by photoionization of
strontium atoms. By optical pumping with circularly polarized light we promote
ions with certain velocities to a different spin ground state, and probe the
resulting perturbed velocity distribution through laser-induced fluorescence
spectroscopy. We discuss various approaches to extract the velocity
distribution from our measured spectra, and assess their quality through
comparisons with molecular dynamic simulationsComment: 13 pages, 8 figure
Velocity Relaxation in a Strongly Coupled Plasma
Collisional relaxation of Coulomb systems is studied in the strongly coupled
regime. We use an optical pump-probe approach to manipulate and monitor the
dynamics of ions in an ultracold neutral plasma, which allows direct
measurement of relaxation rates in a regime where common Landau-Spitzer theory
breaks down. Numerical simulations confirm the experimental results and display
non-Markovian dynamics at early times.Comment: 5 pages, 5 figure
On the formation and decay of a molecular ultracold plasma
Double-resonant photoexcitation of nitric oxide in a molecular beam creates a
dense ensemble of Rydberg states, which evolves to form a plasma of
free electrons trapped in the potential well of an NO spacecharge. The
plasma travels at the velocity of the molecular beam, and, on passing through a
grounded grid, yields an electron time-of-flight signal that gauges the plasma
size and quantity of trapped electrons. This plasma expands at a rate that fits
with an electron temperature as low as 5 K, colder that typically observed for
atomic ultracold plasmas. The recombination of molecular NO cations with
electrons forms neutral molecules excited by more than twice the energy of the
NO chemical bond, and the question arises whether neutral fragmentation plays a
role in shaping the redistribution of energy and particle density that directs
the short-time evolution from Rydberg gas to plasma. To explore this question,
we adapt a coupled rate-equations model established for atomic ultracold
plasmas to describe the energy-grained avalanche of electron-Rydberg and
electron-ion collisions in our system. Adding channels of Rydberg
predissociation and two-body, electron- cation dissociative recombination to
the atomic formalism, we investigate the kinetics by which this relaxation
distributes particle density and energy over Rydberg states, free electrons and
neutral fragments. The results of this investigation suggest some mechanisms by
which molecular fragmentation channels can affect the state of the plasma
Cosmic-Ray Acceleration at Ultrarelativistic Shock Waves: Effects of Downstream Short-Wave Turbulence
The present paper is the last of a series studying the first-order Fermi
acceleration processes at relativistic shock waves with the method of Monte
Carlo simulations applied to shocks propagating in realistically modeled
turbulent magnetic fields. The model of the background magnetic field structure
of Niemiec & Ostrowski (2004, 2006) has been augmented here by a
large-amplitude short-wave downstream component, imitating that generated by
plasma instabilities at the shock front. Following Niemiec & Ostrowski (2006),
we have considered ultrarelativistic shocks with the mean magnetic field
oriented both oblique and parallel to the shock normal. For both cases
simulations have been performed for different choices of magnetic field
perturbations, represented by various wave power spectra within a wide
wavevector range. The results show that the introduction of the short-wave
component downstream of the shock is not sufficient to produce power-law
particle spectra with the "universal" spectral index 4.2. On the contrary,
concave spectra with cutoffs are preferentially formed, the curvature and
cutoff energy being dependent on the properties of turbulence. Our results
suggest that the electromagnetic emission observed from astrophysical sites
with relativistic jets, e.g. AGN and GRBs, is likely generated by particles
accelerated in processes other than the widely invoked first-order Fermi
mechanism.Comment: 9 pages, 8 figures, submitted to Ap
Context Building Information-Centric Decision-Support Systems
As the volume of data and human-centered information available to decision-makers continues to increase at an ever-accelerating rate, the need to represent information in software-processable formats becomes more apparent. At the same time, the availability of information from diverse sources through the World Wide Web provides the opportunity to widen the scope of input to decision-support systems, if this information can be made accessible through automated means. Past approaches to information-centric interoperability have been based on the use of a shared static object model, but this becomes impractical when we consider the loosely-coupled decentralized nature of the Web.
This paper discusses the motivations driving a change from static to dynamic information models. It defines a representative use case, and describes a service-based architecture that allows for extending existing information sources to allow programmatic access. The proposed architecture uses existing and emerging Web Service specifications, enhanced by an ontology definition language, to create an environment that does not require information service providers to use static shared models, while allowing information consumers to learn ontologies from the services themselves. Clients such as decision-support systems can thus build their own information context at run-time based on models received from multiple sources
Collaborative Decision Support Systems for Facility Management
Agent-based collaborative decision support is a methodology of utilizing domain specific intelligent systems, interacting in a common environment, to partner with one or more human decision makers to reach a consensus solution to a complex problem. An example is the recently developed Collaborative Infrastructure Assessment Tool (CIAT) that provides a collaborative planning facility management tool in support of military pier and port management. This methodology is applicable to many similar dynamic facility management problems where the complexity of issues and the number of decision makers result in the need for domain specific agents, a common view of the data, and the need to reach a consensus solution
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