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排序方式: 共有371条查询结果,搜索用时 15 毫秒
21.
S Gupta DW Black S Arndt WC Hubbard NC Andreasen 《Canadian Metallurgical Quarterly》1998,49(10):1353-1355
This study explored the association between psychosocial variables and symptoms among patients with schizophrenia-spectrum disorders who have attempted suicide and those who have not attempted suicide. Of 336 patients with a DSM-III-R diagnosis of schizophrenia or schizoaffective disorder who were consecutively evaluated at a university-affiliated clinical research center, 98, or 29.2 percent, reported one or more suicide attempts. Compared with patients who had not attempted suicide, patients who had made an attempt had a greater number of lifetime depressive episodes, an earlier age of onset of their illness, and an earlier age at first hospitalization. 相似文献
22.
23.
Collision detection for interactive graphics applications 总被引:7,自引:0,他引:7
Collision detection and response are important for interactive graphics applications such as vehicle simulators and virtual reality. Unfortunately, previous collision detection algorithms are too slow for interactive use. The paper presents a new algorithm for rigid or articulated objects that meets performance goals through a form of time critical computing. The algorithm supports progressive refinement, detecting collisions between successively tighter approximations to object surfaces as the application allows it more processing time. The algorithm uses simple four dimensional geometry to approximate motion, and hierarchies of spheres to approximate three dimensional surfaces at multiple resolutions. In a sample application, the algorithm allows interactive performance that is not possible with a good previous algorithm. In particular, the new algorithm provides acceptable accuracy while maintaining a steady and high frame rate, which in some cases improves on the previous algorithm's rate by more than two orders of magnitude 相似文献
24.
Several lithium drifted silicon, surface barrier detectors were subjected to a variety of environmental conditions. The conditions were primarily those of long term storage under ambient temperature conditions and of long time operation under both ambient and high (+60°C) temperature operation. Use was made of the temperature dependence of the diffusion coefficient of lithium in silicon so that elevated temperatures could be used to decrease the time scale of the tests. Some detectors were also subjected to a series of vibration and shock tests. The entire set of tests was performed in an effort to see if the detectors could withstand the rigors of the Apollo mission. The results of all the tests are given in the paper. 相似文献
25.
Epididymal fat cells isolated from chronically cold-exposed rats were used to study the inhibition of lipolysis with albumin
bound FFA. It was demonstrated that lipolysis becomes inhibited as the class 2 binding sites on albumin are filled and that
50% inhibition occurs at free fatty acid (FFA) to albumin ratios
between 4.6 and 4.0. Experiments with dibutyryl adenosine cyclic phosphate suggest that this is an effect on the fat cell
lipases rather than the lipase activating system or phosphodiesterase. The results indicate that reesterification proceeds
as a relatively constant percentage of the rate of lipolysis and, therefore, in the absence of exogenous FFA, conditions that
reduce lipolysis reduce reesterification. On the other hand, high rates of reesterification can apparently be stimulated even
when the class 1 binding sites on albumin are not filled. 相似文献
26.
The potential for intraspecific chemical communication in the gilthead seabream (a marine perciform) was investigated by assessing the olfactory sensitivity to conspecific body-fluids (water occupied by conspecifics, intestinal fluid, urine, semen, egg fluid) by multiunit electrophysiological recording from the olfactory nerve. The olfactory system was responsive to water previously occupied by conspecifics, and the active compound(s) could be extracted by solid-phase extraction. The olfactory system was extremely sensitive to body fluids of sexually mature conspecifics: thresholds of detection were 1:107.4 (intestinal fluid), 1:106.1 (gametes), and 1:104.2 (urine). The olfactory system was also sensitive to amino acids with thresholds of detection from 10–8.1 M (l-leucine) to 10–6.1 M (l-phenylalanine). However, a range of other known fish odorants (steroids, bile acids, and prostaglandins) failed to evoke significant responses. Given the high olfactory sensitivity to intestinal fluid and the low urine release rates of marine compared with freshwater fish, we suggest that chemical communication is likely to be mediated via compounds present in the intestinal fluid rather than urine. Furthermore, the types of chemicals involved are likely to be different from those of freshwater fish. Their exact chemical identity and biological roles remain to be established. 相似文献
27.
Takahashi Lorey K.; Hubbard David T.; Lee Iris; Dar Yasmin; Sipes Sara M. 《Canadian Metallurgical Quarterly》2007,121(1):100
The basolateral (BLA) and medial nucleus (MeA) of the amygdala participate in the modulation of unconditioned fear induced by predator odor. However, the specific role of these amygdalar nuclei in predator odor-induced fear memory is not known. Therefore, fiber-sparing lesions or temporary inactivation of the BLA or MeA were made either prior to or after exposure to cat odor, and conditioned contextual fear behavior was examined the next day. BLA and MeA lesions produced significant reductions in cat odor-induced unconditioned and conditioned fear-related behavior. In addition, temporary pharmacological neural inactivation methods occurring after exposure to cat odor revealed subtle behavioral alterations indicative of a role of the BLA in fear memory consolidation but not memory retrieval. In contrast, the MeA appears to play a specific role in retrieval but not consolidation. Results show that the BLA participates in the conditioned and unconditioned cat odor stimulus association that underlies fear memory, underscore a novel role of the MeA in predator odor contextual conditioning, and demonstrate different roles of the BLA and MeA in modulating consolidation and retrieval of predator odor fear memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
28.
In models of first-price auctions, when bidders are ex ante heterogeneous, deriving explicit equilibrium bid functions is typically impossible, so numerical methods are often employed to find approximate solutions. Recent theoretical research concerning asymmetric auctions has determined some properties these bid functions must satisfy when certain conditions are met. Plotting the relative expected pay-offs of bidders is a quick, informative way to decide whether the approximate solutions are consistent with theory. We approximate the (inverse-)bid functions by polynomials and employ theoretical results in two ways: to help solve for the polynomial coefficients and to evaluate qualitatively the appropriateness of a given approximation. We simulate auctions from the approximated solutions and find that, for the examples considered, low-degree polynomial approximations perform poorly and can lead to incorrect policy recommendations concerning auction design, suggesting researchers need to take care to obtain quality solutions. 相似文献
29.
Joanna McKittrick Carlos F. Bacalski G. A. Hirata Kevin M. Hubbard S. G. Pattillo Kenneth V. Salazar M. Trkula 《Journal of the American Ceramic Society》2000,83(5):1241-1246
The purpose of this study was to identify and correlate the microstructural and luminescence properties of europium-doped Y2 O3 (Y1– x Eu x )2 O3 thin films deposited by metallorganic chemical vapor deposition (MOCVD), as a function of deposition time and temperature. The influence of deposition parameters on the crystallite size and microstructural morphology were examined, as well as the influence of these parameters on the photoluminescence emission spectra. (Y1– x Eu x )2 O3 thin films were deposited onto (111) silicon and (001) sapphire substrates by MOCVD. The films were grown by reacting yttrium and europium tris(2,2,6,6-tetramethyl–3,5-heptanedionate) precursors with an oxygen atmosphere at low pressures (5 torr (1.7 × 103 Pa)) and low substrate temperatures (500°–700°C). The films deposited at 500°C were smooth and composed of nanocrystalline regions of cubic Y2 O3 , grown in a textured [100] or [110] orientation to the substrate surface. Films deposited at 600°C developed, with increasing deposition time, from a flat, nanocrystalline morphology into a platelike growth morphology with [111] orientation. Monoclinic (Y1– x Eu x )2 O3 was observed in the photoluminescence emission spectra for all deposition temperatures. The increase in photoluminescence emission intensity with increasing postdeposition annealing temperature was attributed to the surface/grain boundary area-reduction effect. 相似文献
30.
Assessment of conformational parameters as predictors of limited proteolytic sites in native protein structures 总被引:4,自引:0,他引:4
Hubbard SJ; Beynon RJ; Thornton JM 《Protein engineering, design & selection : PEDS》1998,11(5):349-359
Despite the importance of limited proteolysis in biological systems it is
often difficult to rationalize why a proteinase hydrolyses a particular
bond, given a simple sequence specificity alone. Understanding of the
structural properties limiting the proteolysis represents a first step on
the pathway to control and manipulation of this phenomena. An expanded set
of nick-sites in proteins of known tertiary structure, cut by both narrow
and broad specificity proteinases, has been generated yielding a robust
data set of strictly limited sites. A critical evaluation of an expanded
set of conformational parameters revealed a strong correlation with limited
proteolytic sites, although they are only modest predictors in isolation.
The overall predictive power is significantly improved when the
conformational parameters are combined in a weighted predictive scheme that
permits their relative importance to be compared via a Metropolis search
protocol. A subset of the parameters performs equally well demonstrating
the key determinants of susceptibility. The derived predictive algorithm
has been made available via the internet. Its utility for predicting other
surface-correlated features is also discussed.
相似文献