排序方式: 共有15条查询结果,搜索用时 15 毫秒
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Markus Lerchi Elmar Reitter Wilhelm Simon 《Analytical and bioanalytical chemistry》1994,349(4):272-276
A pulsed molecular beam Fourier transform microwave spectrometer especially designed for the quantitative analysis of polar pollutants in air is presented. This very fast method has a sensitivity in the ppm range and can be applied to a wide variety of substances. Details of the apparatus and the results of some performance tests are given. 相似文献
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Abstract Novel synthetic routes directed toward the preparation of (+/?)-cis -4-amino-2-cyclopentene-1-methanol are described. The routes investigated involve azide openings of chiral and non-chiral cyclopentyl epoxides. 相似文献
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A cognitive model of spatial path-planning 总被引:1,自引:0,他引:1
David Reitter Christian Lebiere 《Computational & Mathematical Organization Theory》2010,16(3):220-245
Planning a path to a destination, given a number of options and obstacles, is a common task. We suggest a two-component cognitive
model that combines retrieval of knowledge about the environment with search guided by visual perception. In the first component,
subsymbolic information, acquired during navigation, aids in the retrieval of declarative information representing possible
paths to take. In the second component, visual information directs the search, which in turn creates knowledge for the first
component. The model is implemented using the ACT-R cognitive architecture and makes realistic assumptions about memory access
and shifts in visual attention. We present simulation results for memory-based high-level navigation in grid and tree structures,
and visual navigation in mazes, varying relevant cognitive (retrieval noise and visual finsts) and environmental (maze and
path size) parameters. The visual component is evaluated with data from a multi-robot control experiment, where subjects planned
paths for robots to explore a building. We describe a method to compare trajectories without referring to aligned points in
the itinerary. The evaluation shows that the model provides a good fit, but also that planning strategies may vary with task
loads. 相似文献
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Polubarinova-Kochina's analytical differential equation methodis used to determine the pseudo-steady-state solution to problemsinvolving the freezing (solidification) of wedges of liquidwhich are initially at their fusion temperature. In particular,we consider four distinct problems for wedges which are: freezingwith the same constant boundary temperature, freezing with thesame constant boundary heat fluxes, freezing with distinct constantboundary temperatures and freezing with distinct constant fluxesat the boundaries. For the last two problems, a Heun's differentialequation with an unknown singularity is derived, which in bothcases admits a particularly elegant simple solution for thespecial case when the wedge angle is . The moving boundariesobtained are shown pictorially. 相似文献
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Chen W Li L Du Z Liu J Reitter JN Mills KV Linhardt RJ Wang C 《Journal of the American Chemical Society》2012,134(5):2500-2503
Protein splicing is a self-catalyzed and spontaneous post-translational process in which inteins excise themselves out of precursor proteins while the exteins are ligated together. We report the first discovery of an intramolecular disulfide bond between the two active-site cysteines, Cys1 and Cys+1, in an intein precursor composed of the hyperthermophilic Pyrococcus abyssi PolII intein and extein. The existence of this intramolecular disulfide bond is demonstrated by the effect of reducing agents on the precursor, mutagenesis, and liquid chromatography-mass spectrometry (LC-MS) with tandem MS (MS/MS) of the tryptic peptide containing the intramolecular disulfide bond. The disulfide bond inhibits protein splicing, and splicing can be induced by reducing agents such as tris(2-carboxyethyl)phosphine (TCEP). The stability of the intramolecular disulfide bond is enhanced by electrostatic interactions between the N- and C-exteins but is reduced by elevated temperature. The presence of this intramolecular disulfide bond may contribute to the redox control of splicing activity in hypoxia and at low temperature and point to the intriguing possibility that inteins may act as switches to control extein function. 相似文献