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排序方式: 共有1460条查询结果,搜索用时 15 毫秒
91.
Buch JS Kimball C Rosenberger F Highsmith WE DeVoe DL Lee CS 《Analytical chemistry》2004,76(4):874-881
A miniaturized system for DNA mutation analysis, utilizing temperature gradient gel electrophoresis (TGGE) in a polycarbonate (PC) microfluidic device, is reported. TGGE reveals the presence of sequence heterogeneity in a given heteroduplex sample by introducing a thermal denaturing gradient that results in differences between the average electrophoretic mobilities of DNA sequence variants. Bulk heater assemblies are designed and employed to externally generate temperature gradients in spatial and temporal formats along the separation channels. TGGE analyses of model mutant DNA fragments, each containing a single base substitution, are achieved using both single- and 10-channel parallel measurements in a microfluidic platform. Additionally, a comprehensive polymer microfluidic device containing an integrated microheater and sensor array is developed and demonstrated for performing spatial TGGE for DNA mutation analysis. The device consists of two PC modular substrates mechanically bonded together. One substrate is embossed with microchannels, and the other contains a tapered microheater, lithographically patterned along with an array of temperature sensors. Compared with the external heating approaches, the integrated platform provides significant reduction in power requirement and thermal response time while establishing more accurate and highly effective control of the temperature gradient for achieving improved separation resolution. 相似文献
92.
Aurora: a new model and architecture for data stream management 总被引:43,自引:0,他引:43
Daniel?J.?AbadiEmail author Don?Carney Ugur??etintemel Mitch?Cherniack Christian?Convey Sangdon?Lee Michael?Stonebraker Nesime?Tatbul Stan?Zdonik 《The VLDB Journal The International Journal on Very Large Data Bases》2003,12(2):120-139
This paper describes the basic processing model and architecture of Aurora, a new system to manage data streams for monitoring applications. Monitoring applications differ substantially from conventional business data processing. The fact that a software system must process and react to continual inputs from many sources (e.g., sensors) rather than from human operators requires one to rethink the fundamental architecture of a DBMS for this application area. In this paper, we present Aurora, a new DBMS currently under construction at Brandeis University, Brown University, and M.I.T. We first provide an overview of the basic Aurora model and architecture and then describe in detail a stream-oriented set of operators.Received: 12 September 2002, Accepted: 26 March 2003, Published online: 21 July 2003Edited by Y. Ioannidis 相似文献
93.
Daniel R. Brooks Esra Erdem Selim T. Erdoğan James W. Minett Don Ringe 《Journal of Automated Reasoning》2007,39(4):471-511
We describe the reconstruction of a phylogeny for a set of taxa, with a character-based cladistics approach, in a declarative
knowledge representation formalism, and show how to use computational methods of answer set programming to generate conjectures
about the evolution of the given taxa. We have applied this computational method in two domains: historical analysis of languages
and historical analysis of parasite-host systems. In particular, using this method, we have computed some plausible phylogenies
for Chinese dialects, for Indo-European language groups, and for Alcataenia species. Some of these plausible phylogenies are different from the ones computed by other software. Using this method, we
can easily describe domain-specific information (e.g., temporal and geographical constraints), and thus prevent the reconstruction
of some phylogenies that are not plausible.
This paper is a revised and extended version of [3]. 相似文献
94.
Zang‐Hee Cho Young‐Don Son Hang‐Keun Kim Kyoung‐Nam Kim Se‐Hong Oh Jae‐Yong Han In‐Ki Hong Young‐Bo Kim 《International journal of imaging systems and technology》2007,17(4):252-265
A PET‐MRI fusion system is developed for molecular‐genetic imaging. The purpose of the system is to obtain images of the in‐vivo human brain using two high‐end imaging devices, an advanced PET and an ultrahigh‐field MRI. These are the HRRT‐PET, a high‐resolution research tomograph dedicated to brain imaging on the molecular level, and the 7.0‐T MRI, an ultrahigh field version used for morphological imaging. HRRT‐PET delivers high‐resolution molecular imaging with a resolution down to 2.5 mm FWHM, which is currently the highest spatial resolution available for the observation of the human brain's molecular activities, including enzymes and receptors, which are manipulated genetically, such as reporter genes and probes. The 7.0‐T MRI began to reveal submillimeter resolution images of the cortical as well as deep brain areas, down to 250 μm, which allows us to visualize the fine details of the cortical and brainstem areas, including the line of Gennari in the visual cortex and the corticospinal tracts in the pontine area. The current PET‐MRI fusion imaging system produces the highest quality images of molecular and genetic activities of the human brain in vivo. It is starting to provide many answers to the key questions about the neurological diseases. Some of these start providing answers to many cognitive neuroscience problems with clear molecular and genetic bases. There is great potential in the PET‐MRI for early diagnosis of cancers as well as other neurological diseases, which we were previously unable to diagnose, such as microscopic molecular changes that occur in Parkinson's and Alzheimer's diseases. © 2007 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 17, 252–265, 2007 相似文献
95.
There has been an increasing interest in recent years in developing and using computer-based tests in educational assessment. To replace paper-based tests with computer-based ones, the standards for developing computerized-assessment (International Test Commission., 2004) requires equivalent test scores to be established for the new computer-based test and the conventional paper-based test. However, in most test mode comparability studies, the actual test items used have been identical, and yet significant differences have been found in test scores in paper-based and computer-based modes. This has been reported for several subjects, including science, languages and mathematics. The validity of using computer-based tests in educational assessment must therefore be questioned. This study involves a biology test and a biology motivation questionnaire using a Solomon four-group experimental design to examine the validity of the computer-based test and its effects on test performance and the motivation of test-takers. The findings provide supportive evidence for the validity of computer-based test in educational assessment. 相似文献
96.
Maintaining adequate performance in dynamic and uncertain settings has been a perennial stumbling block for intelligent systems. Nevertheless, any system intended for real-world deployment must be able to accommodate unexpected change—that is, it must be perturbation tolerant. We have found that metacognitive monitoring and control—the ability of a system to self-monitor its own decision-making processes and ongoing performance, and to make targeted changes to its beliefs and action-determining components—can play an important role in helping intelligent systems cope with the perturbations that are the inevitable result of real-world deployment. In this article we present the results of several experiments demonstrating the efficacy of metacognition in improving the perturbation tolerance of reinforcement learners, and discuss a general theory of metacognitive monitoring and control, in a form we call the metacognitive loop. 相似文献
97.
We have applied a non-parametric classifier (k nearest neighbour) to two calibrated orthogonal passes of airborne polarimetric synthetic aperture radar (POLSAR) image data over boreal forest for the purpose of discriminating canopy tree species of predefined stands. We found that a single classifier based on a single feature space (i.e. one set of POLSAR variables for all species) was less accurate than a hierarchical two-stage classifier that used different POLSAR variables for each species. We designed a two-stage classifier that first grouped stands into broad classes: pine, spruce and deciduous, and then classified each sample within the broad classes into individual species. We found that the most effective feature spaces had two or three dimensions. The two-stage classifier attained overall accuracies of between 60% and 75%. We provide a first use of an equivalency test applied to remote-sensing classification. We use Lloyd's test of equivalency to find equivalent classifiers and thus infer informative POLSAR variables. The POLSAR variables that were most informative varied between the two passes and between the various elements of the hierarchical classifier. For the initial three-class classifier the most informative POLSAR variables were the two circular polarization ratios, several of Touzi's Stokes vector variables, HHVV coherence, several texture measures such as the variance of several scattering coefficients and the order parameter of the K-distribution and characteristics of the polarization signature pedestal. These results demonstrate that C-band POLSAR has great potential for mapping boreal forest cover either on its own or in concert with other geospatial data. 相似文献
98.
In this article, we discuss minimum-time trajectory generation for input-and-state constrained continuous-time LTI systems in the light of the notion of flatness and B-splines parametrisation. Flat systems have the useful property that the input and the state trajectories can be completely characterised by the (so-called) flat output. We propose a splines parametrisation for the flat output, and the corresponding parametrisations for the performance output, the states and the inputs. Using this parametrisation the problem of minimum-time constrained trajectory planning is cast into a feasibility-search problem in the splines control-point space, in which the constraint region is characterised by a polytope. A close approximation of the minimum-time trajectory is obtained by systematically searching the end-time that makes the constraint polytope to be minimally feasible. 相似文献
99.
The effect of surface roughness on the contact fatigue was investigated in this study. To accomplish this goal, contact analysis
based on the influence functions and the rectangular patch solutions was performed to obtain the subsurface stress. Mesoscopic
multiaxial fatigue criterion is then applied to predict fatigue damage. Rainbow counting method and damage rule were used
to evaluate the fatigue life under random loadings caused by the rough surface contact. As a result of the fatigue analysis,
the relationship among the fatigue life, the crack initiation depth, and the surface roughness were revealed. It is observed
that the fatigue life has hardly changed and a crack is initiated at subsurface for the surface with the surface roughness
below a critical value. However, if the surface roughness exceeds the critical value, fatigue life is remarkably reduced and
the site of crack initiation moves to the near surface. 相似文献
100.
Timothy Wilson Bjørn Clausen Thomas Proffen Jennifer Elle Don Brown 《Metallurgical and Materials Transactions A》2008,39(8):1942-1946
Bulk metallic glasses (BMGs) are an emerging class of materials whose unique properties make them excellent choices for many
applications. As with crystalline metals, the processing and forming techniques used to produce BMG components necessarily
result in residual stresses. However, traditional diffraction stress analysis is difficult to apply to BMG components, because
they lack the long-range order necessary to produce sharp diffraction patterns, and thus, the internal strains for BMG have
not been examined until recently. In this work, in-situ neutron scattering was used to measure the local elastic internal strain distribution in a Zr57Nb5Cu15.4Ni12.6Al10 BMG as a function of applied stress. Various techniques were used to evaluate the internal strain. The strain was determined
in real space, by measuring changes in the atomic pair distribution function (PDF). These results can be used to help understand
the elastic deformation of BMGs as well be to evaluate current models of BMG deformation.
This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February
25–March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of
Materials Committee. 相似文献