19,329 research outputs found
Closed loop models for analyzing the effects of simulator characteristics
The optimal control model of the human operator is used to develop closed loop models for analyzing the effects of (digital) simulator characteristics on predicted performance and/or workload. Two approaches are considered: the first utilizes a continuous approximation to the discrete simulation in conjunction with the standard optimal control model; the second involves a more exact discrete description of the simulator in a closed loop multirate simulation in which the optimal control model simulates the pilot. Both models predict that simulator characteristics can have significant effects on performance and workload
The search for the cause of the low albedo of the moon
Experimentation concerning lunar weathering and its effect on the albedo of the surface cover consisted of: (1) determination of the surface chemical composition of lunar soil and ground-up rock samples by Auger electron spectroscopy, (2) measurement of the optical albedo of these samples, and (3) proton or alpha-particle irradiation of terrestrial rock chips and rock powders and of ground-up lunar rock samples in order to determine the optical and surface chemical effect of simulated solar wind
The Surface Chemical Composition of Lunar Samples and Its Significance for Optical Properties
The surface iron, titanium, calcium, and silicon concentration in numerous lunar soil and rock samples was determined by Auger electron spectroscopy. All soil samples show a large increase in the iron to oxygen ratio compared with samples of pulverized rock or with results of the bulk chemical analysis. A solar wind simulation experiment using 2 keV energy alpha -particles showed that an ion dose corresponding to approximately 30,000 years of solar wind increased the iron concentration on the surface of the pulverized Apollo 14 rock sample 14310 to the concentration measured in the Apollo 14 soil sample 14163, and the albedo of the pulverized rock decreased from 0.36 to 0.07. The low albedo of the lunar soil is related to the iron + titanium concentration on its surface. A solar wind sputter reduction mechanism is discussed as a possible cause for both the surface chemical and optical properties of the soil
Twisted mass chiral perturbation theory for 2+1+1 quark flavours
We present results for the masses of pseudoscalar mesons in twisted mass
lattice QCD with a degenerate doublet of u and d quarks and a non-degenerate
doublet of s and c quarks in the framework of next-to-leading order chiral
perturbation theory, including lattice effects up to O(a^2). The masses depend
on the two twist angles for the light and heavy sectors. For maximal twist in
both sectors, O(a)-improvement is explicitly exhibited. The mixing of
flavour-neutral mesons is also discussed, and results in the literature for the
case of degenerate s and c quarks are corrected.Comment: LaTeX2e, 12 pages, corrected typo
Hard sphere-like dynamics in a non hard sphere liquid
The collective dynamics of liquid Gallium close to the melting point has been
studied using Inelastic X-ray Scattering to probe lengthscales smaller than the
size of the first coordination shell. %(momentum transfers, , 15
nm). Although the structural properties of this partially covalent
liquid strongly deviate from a simple hard-sphere model, the dynamics, as
reflected in the quasi-elastic scattering, are beautifully described within the
framework of the extended heat mode approximation of Enskog's kinetic theory,
analytically derived for a hard spheres system. The present work demonstrates
the applicability of Enskog's theory to non hard- sphere and non simple
liquids.Comment: 5 pages, 2 figures, accepted in Phys. Rev. Let
Glutathione treatment protects the rat liver against injury after warm ischemia and Kupffer cell activation
Background/Aim: The generation of reactive oxygen species by activated Kupffer cells (KC) may contribute to reperfusion injury of the liver during liver transplantation or resection. The aim of our present studies was to investigate (1) prevention of hepatic reperfusion injury after warm ischemia by administration of the antioxidant glutathione (GSH) and (2) whether GSH confers protection through influences on KC toxicity. Methods: Isolated perfused rat livers were subjected to 1 h of warm ischemia followed by 90 min of reperfusion without (n = 5) or with GSH or catalase (n = 4-5 each). Selective KC activation by zymosan (150 mug/ml) in continuously perfused rat livers was used to investigate KC-related liver injury. Results: Postischemic infusion of 0.1, 0.5, 1.0 and 2.0 mM GSH, but not 0.05 mM GSH prevented reperfusion injury after warm ischemia as indicated by a marked reduction of sinusoidal LDH efflux by up to 83 +/- 13% (mean +/- SD; p < 0.05) and a concomitant significant improvement of postischemic bile flow by 58 +/- 27% (p < 0.05). A similar protection was conveyed by KC blockade with gadolinium chloride indicating prevention of KC-related reperfusion injury by postischemic GSH treatment. Postischemic treatment with catalase (150 U/ml) resulted in a reduction of LDH efflux by 40 +/- 9% (p < 0.05). Accordingly, catalase as well as GSH (0.1-2.0 mM) nearly completely prevented the increase in LDH efflux following selective :KC activation by zymosan in continously perfused rat livers. Conclusion: Postischemic administration of GSH protects the liver against reperfusion injury after warm ischemia. Detoxification of KC-derived hydrogen peroxide seem to be an important feature of the protective mechanisms. Copyright (C) 2002 S. Karger AG, Basel
Information Inflation: Can The Legal System Adapt?
Information is fundamental to the legal system. Accordingly, lawyers must understand that information, as a cultural and technological edifice, has profoundly and irrevocably changed. There has been a civilization- wide morph, or pulse, or one might say that information has evolved. This article discusses the new inflationary dynamic, which has caused written information to multiply by as much as ten thousand-fold recently. The resulting landscape has stressed the legal system and indeed, it is becoming prohibitively expensive for lawyers even to search through information. This is particularly true in litigation
Overcoming the Digital Tsunami in e-Discovery: is Visual Analysis the Answer?
New technologies are generating potentially discoverable evidence in electronic form in ever increasing volumes. As a result, traditional techniques of document search and retrieval in pursuit of electronic discovery in litigation are becoming less viable. One potential new technological solution to the e-discovery search and retrieval challenge is Visual Analysis (VA). VA is a technology that combines the computational power of the computer with graphical representations of large datasets to enable interactive analytic capabilities. This article provides an overview of VA technology and how it is being applied in the analysis of e-mail and other electronic documents in the field of e-discovery, as well as discussing several challenges and limitations of the technology. The article concludes that VA has the potential to overcome some of the limitations of current search and retrieval techniques, but that addressing the digital tsunami is more likely to be achieved by using VA in combination with other search and retrieval technologies in the context of creating an effective data governance program
Answering Conjunctive Queries under Updates
We consider the task of enumerating and counting answers to -ary
conjunctive queries against relational databases that may be updated by
inserting or deleting tuples. We exhibit a new notion of q-hierarchical
conjunctive queries and show that these can be maintained efficiently in the
following sense. During a linear time preprocessing phase, we can build a data
structure that enables constant delay enumeration of the query results; and
when the database is updated, we can update the data structure and restart the
enumeration phase within constant time. For the special case of self-join free
conjunctive queries we obtain a dichotomy: if a query is not q-hierarchical,
then query enumeration with sublinear delay and sublinear update time
(and arbitrary preprocessing time) is impossible.
For answering Boolean conjunctive queries and for the more general problem of
counting the number of solutions of k-ary queries we obtain complete
dichotomies: if the query's homomorphic core is q-hierarchical, then size of
the the query result can be computed in linear time and maintained with
constant update time. Otherwise, the size of the query result cannot be
maintained with sublinear update time. All our lower bounds rely on the
OMv-conjecture, a conjecture on the hardness of online matrix-vector
multiplication that has recently emerged in the field of fine-grained
complexity to characterise the hardness of dynamic problems. The lower bound
for the counting problem additionally relies on the orthogonal vectors
conjecture, which in turn is implied by the strong exponential time hypothesis.
By sublinear we mean for some
, where is the size of the active domain of the current
database
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