676 research outputs found
Making, probing and understanding Bose-Einstein condensates
Contribution to the proceedings of the 1998 Enrico Fermi summer school on
Bose-Einstein condensation in Varenna, Italy.Comment: Long review paper with ~90 pages, ~20 figures. 2 GIF figures in
separate files (4/5/99 fixed figure
Ultracold neutral plasma expansion in two dimensions
We extend an isothermal thermal model of ultracold neutral plasma expansion
to systems without spherical symmetry, and use this model to interpret new
fluorescence measurements on these plasmas. By assuming a self-similar
expansion, it is possible to solve the fluid equations analytically and to
include velocity effects to predict the fluorescence signals. In spite of the
simplicity of this approach, the model reproduces the major features of the
experimental data
Fluorescence measurements of expanding strongly-coupled neutral plasmas
We report new detailed density profile measurements in expanding
strongly-coupled neutral plasmas. Using laser-induced fluorescence techniques,
we determine plasma densities in the range of 10^5 to 10^9/cm^3 with a time
resolution limit as small as 7 ns. Strong-coupling in the plasma ions is
inferred directly from the fluorescence signals. Evidence for strong-coupling
at late times is presented, confirming a recent theoretical result.Comment: submitted to PR
Resource Allocation Among Agents with MDP-Induced Preferences
Allocating scarce resources among agents to maximize global utility is, in
general, computationally challenging. We focus on problems where resources
enable agents to execute actions in stochastic environments, modeled as Markov
decision processes (MDPs), such that the value of a resource bundle is defined
as the expected value of the optimal MDP policy realizable given these
resources. We present an algorithm that simultaneously solves the
resource-allocation and the policy-optimization problems. This allows us to
avoid explicitly representing utilities over exponentially many resource
bundles, leading to drastic (often exponential) reductions in computational
complexity. We then use this algorithm in the context of self-interested agents
to design a combinatorial auction for allocating resources. We empirically
demonstrate the effectiveness of our approach by showing that it can, in
minutes, optimally solve problems for which a straightforward combinatorial
resource-allocation technique would require the agents to enumerate up to 2^100
resource bundles and the auctioneer to solve an NP-complete problem with an
input of that size
Book Reviews
Equity, an Analysis of Modern Equity Problems Designed Primarily for Students. George L. Clark, SJ.D., Professor of Law, University of Missouri. E. W. Stephens Publishing Co., Columbia, Mo., igig. Pp. lii, 639
On Fully Dynamic Graph Sparsifiers
We initiate the study of dynamic algorithms for graph sparsification problems and obtain fully dynamic algorithms, allowing both edge insertions and edge deletions, that take polylogarithmic time after each update in the graph. Our three main results are as follows. First, we give a fully dynamic algorithm for maintaining a -spectral sparsifier with amortized update time . Second, we give a fully dynamic algorithm for maintaining a -cut sparsifier with \emph{worst-case} update time . Both sparsifiers have size . Third, we apply our dynamic sparsifier algorithm to obtain a fully dynamic algorithm for maintaining a -approximation to the value of the maximum flow in an unweighted, undirected, bipartite graph with amortized update time
Experimental Evaluation of High Performance Integrated Heat Pump
Integrated heat pump (IHP) technology provides significant potential for energy savings and comfort improvement for residential buildings. In this study, we evaluate the performance of a high performance IHP that provides space heating, cooling, and water heating services. Experiments were conducted according to the ASHRAE Standard 206-2013 where 24 test conditions were identified in order to evaluate the IHP performance indices. An 8-in by 8-in Air Monitor Fan Evaluator is used to measure the volumetric flowrate of air discharged from the air handler unit (AHU) in order to evaluate the airside performance. Empirical curve fits of the unitĂąâŹâąs compressor maps are used in conjunction with saturated condensing and evaporating refrigerant conditions to deduce the refrigerant mass flowrate, which, in turn is used to evaluate the refrigerant-side performance. Heat pump (compressor, fans, and controls) and water pump power were measured separately per requirements of Standard 206. The system was charged per the system manufacturerĂąâŹâąs specifications. System test results are presented for each operating mode along with overall IHP performance metrics according to ASHRAE standard 206-2013. The paper ends with discussion on system operation and impact on typical energy consumption in residential buildings
An agent-based approach to immune modelling
This study focuses on trying to understand why the range
of experience with respect to HIV infection is so diverse, especially as regards to the latency period. The challenge is to determine what assumptions can be made about the nature of the experience of antigenic invasion and diversity that can be modelled, tested and argued plausibly.
To investigate this, an agent-based approach is used to extract high-level behaviour which cannot be described analytically from the set of interaction rules at the cellular level. A prototype model encompasses local variation in baseline properties contributing to the individual disease experience and is included in a network which mimics the chain of lymphatic nodes. Dealing with massively multi-agent systems requires major computational efforts. However, parallelisation methods are a natural
consequence and advantage of the multi-agent approach. These are implemented using the MPI library
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