11,537 research outputs found
Energy storage-boiler tank
Activities performed in an effort to demonstrate heat of fusion energy storage in containerized salts are reported. The properties and cycle life characteristics of a eutectic salt having a boiling point of about 385 C (NaCl, KCl, Mg Cl2) were determined. M-terphenyl was chosen as the heat transfer fluid. Compatibility studies were conducted and mild steel containers were selected. The design and fabrication of a 2MWh storage boiler tank are discussed
Improving the worthiness of the Elder problem as a benchmark for buoyancy driven convection models
An important trapping mechanism associated with the geosequestration of CO~2~ is that of dissolution into the formation water. Although supercritical CO~2~ is significantly less dense than water, experimental data reported in the literature show that the density of an aqueous solution of CO~2~ could be slightly greater. Under normal situations, the transfer of gas to solution is largely controlled by the relatively slow process of molecular diffusion. However, the presence of variable densities can trigger off gravity instabilities leading to much larger-scale convection processes. Such processes can potentially enhance rates of dissolution by an order of magnitude. Consequently there is a need for future performance assessment models to incorporate buoyancy driven convection (BDC). A major issue associated with BDC models is that of grid convergence when benchmarking to the Elder problem. The Elder problem originates from a heat convection experiment whereby a rectangular Hele-Shaw cell was heated over the central half of its base. A quarter of the way through the experiment, Elder (1967) observed six plumes, with four narrow plumes in the center and two larger plumes at the edges. As the experiment progressed, only four plumes remained. The issue is that depending on the grid resolution used when seeking to model this problem, modelers have found that different schemes yield steady states with either one, two or three plumes. The aim of this paper is to clarify and circumvent the issue of multiple steady state solutions in the Elder problem using a pseudospectral method
Combinatorial Bounds and Characterizations of Splitting Authentication Codes
We present several generalizations of results for splitting authentication
codes by studying the aspect of multi-fold security. As the two primary
results, we prove a combinatorial lower bound on the number of encoding rules
and a combinatorial characterization of optimal splitting authentication codes
that are multi-fold secure against spoofing attacks. The characterization is
based on a new type of combinatorial designs, which we introduce and for which
basic necessary conditions are given regarding their existence.Comment: 13 pages; to appear in "Cryptography and Communications
Spin-dependent transport in a quasiballistic quantum wire
We describe the transport properties of a 5 m long one-dimensional (1D)
quantum wire. Reduction of conductance plateaux due to the introduction of
weakly disorder scattering are observed. In an in-plane magnetic field, we
observe spin-splitting of the reduced conductance steps. Our experimental
results provide evidence that deviation from conductance quantisation is very
small for electrons with spin parallel and is about 1/3 for electrons with spin
anti-parallel. Moreover, in a high in-plane magnetic field, a spin-polarised 1D
channel shows a plateau-like structure close to which
strengthens with {\em increasing} temperatures. It is suggested that these
results arise from the combination of disorder and the electron-electron
interactions in the 1D electron gas.Comment: 4 pages, 5 figures, latex to be published in Phys. Rev. B (15/3/2000
Performance analysis of an orbital angular momentum multiplexed amplify-and-forward radio relay chain with inter-modal crosstalk
The end-to-end spectral efficiency and bit error rate (BER) of an amplify-and-forward (AF) radio relay chain employing orbital angular momentum (OAM) multiplexing is presented. The inherent divergence of a beam carrying OAM is overcome by means of a lens. Modelled and measured inter-modal crosstalk levels are incorporated into the analysis. The results show that an end-to-end spectral efficiency of up to 8 bits s−1 Hz−1 is achievable using four OAM modes to multiplex four parallel data streams over 20 hops, provided that the detrimental effects of inter-modal crosstalk are mitigated. The spectral efficiency is expected to scale further by using more OAM modes. The BER profile along the relay chain is analysed for each of the four OAM modes
The mission oriented terminal area simulation facility
The Mission Oriented Terminal Area Simulation (MOTAS) was developed to provide an ATC environment in which flight management and flight operations research studies can be conducted with a high degree of realism. This facility provides a flexible and comprehensive simulation of the airborne, ground-based and communication aspects of the airport terminal area environment. Major elements of the simulation are: an airport terminal area environment model, two air traffic controller stations, several aircraft models and simulator cockpits, four pseudo pilot stations, and a realistic air-ground communications network. MOTAS has been used for one study with the DC-9 simulator and a series of data link studies are planned in the near future
Gravitational Collapse of Inhomogeneous Dust in (2+1) Dimensions
We examine the gravitational collapse of spherically symmetric inhomogeneous
dust in (2+1) dimensions, with cosmological constant. We obtain the analytical
expressions for the interior metric. We match the solution to a vacuum
exterior. We discuss the nature of the singularity formed by analyzing the
outgoing radial null geodesics. We examine the formation of trapped surfaces
during the collapse.Comment: Accepted for publication in CQ
Wigner crystallization and metal-insulator transition of two-dimensional holes in GaAs/AlGaAs at B=0
We report the transport properties of a low disorder two-dimensional hole
system (2DHS) in the GaAs/AlGaAs heterostructure, which has an unprecedentedly
high peak mobility of , with hole density of in the temperature range of
. From their T, p, and electric field dependences, we find that
the metal-insulator transition in zero magnetic field in this exceptionally
clean 2DHS occurs at , which is in good agreement with the
critical for Wigner crystallization , predicted by
Tanatar and Ceperley for an ideally clean 2D system.Comment: 4 pages, 4 Postscript figure
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