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排序方式: 共有863条查询结果,搜索用时 609 毫秒
51.
Ingo Hapke Hartwig Boye Jürgen Schmidt 《Nanoscale and Microscale Thermophysical Engineering》2013,17(2):99-115
Heat transfer characteristics during flow boiling in micro channels with rectangular cross section were studied using a thermographic measuring method. The characteristic length of the channels investigated was varied in a region of 300 w m up to 700 w m. The channels were designed as Joule heating pipes. Thus, the evaporation was achieved under conditions of nearly constant heat fluxes at the heating wall of the channel. The thermographic measuring method was used to examine the wall temperature. The high spatial and temporal resolution of this thermographic measuring method makes it possible to detect the axial position of the different boiling regions. Furthermore, it allows conclusions to be made on which flow conditions occur in the different sections of the channel. Experimental results are shown with water and n -heptane as the fluid to be vaporized. The results of measurements are discussed and a correlation is given of the location where the dryout starts with the characteristic parameters. The dependence of the pressure drop in such channels on the technological parameters has also been presented. 相似文献
52.
Malay Patra Gilles Gasser Dr. Antonio Pinto Klaus Merz Dr. Ingo Ott Prof. Dr. Julia E. Bandow Prof. Dr. Nils Metzler‐Nolte Prof. Dr. 《ChemMedChem》2009,4(11):1930-1938
The recent discovery of the natural product platensimycin as a new antibiotic lead structure has triggered the synthesis of numerous organic derivatives for structure–activity relationship studies. Herein, we describe the synthesis, characterization and biological evaluation of the first organometallic antibiotic inspired by platensimycin. Two bioorganometallic compounds containing (η6‐pentamethylbenzene)Cr(CO)3 ( 2 ) and (η6‐benzene)Cr(CO)3 ( 3 ), linked by an amide bond to the aromatic part of platensimycin, were synthesized. Their antibiotic activities were tested against B. subtilis 168 (Gram positive) and E. coli W3110 (Gram negative) bacterial strains. Both compounds were found to be inactive against E. coli but derivative 2 inhibits B. subtilis growth at a moderate MIC value of 0.15 mM . To test the intrinsic toxicity of chromium, several chromium salts along with {η6‐(3‐pentamethylphenyl propionic acid)}Cr(CO)3 ( 5 ) and {η6‐(3‐phenyl propionic acid)}Cr(CO)3 ( 6 ) were tested against both bacterial strains. No activity was observed against E. coli for any of the compounds; B. subtilis growth was not inhibited by Cr(NO3)3 and only very weakly by 5 , K2Cr2O7 and Na2CrO4 at MIC values of 0.5, 0.68 and 1.24 mM , respectively. Compounds 2 , 3 , 5 and 4 (the pure organic analogue of 2 ) show similar cytotoxicity against HeLa, HepG2 and HT‐29 mammalian cell lines. Furthermore, the cellular uptake and the intracellular distribution of compounds 2 , 3 and Cr(NO3)3 in B. subtilis were studied using atomic absorption spectroscopy to gain insight in to the possible cellular targets. Compound 2 was found to be readily taken up and distributed almost equally among cytosol, cell debris and cell membrane in B. subtilis. 相似文献
53.
The topic of this paper is minimum cost operative planning of pressurized water supply networks over a finite horizon and
under reliable demand forecast. Since this is a very hard problem, it is desirable to employ sophisticated mathematical algorithms,
which in turn calls for carefully designed models with suitable properties. The paper develops a nonlinear mixed integer model
and a nonlinear programming model with favorable properties for gradient-based optimization methods, based on smooth component
models for the network elements. In combination with further nonlinear programming techniques (Burgschweiger et al. in ZIB
Report ZR-05-31, Zuse Institute Berlin, 2005), practically satisfactory near-optimum solutions even for large networks can be generated in acceptable time using standard
optimization software on a PC workstation. Such an optimization system is in operation at Berliner Wasserbetriebe. 相似文献
54.
Hidden Markov models reproduce most of the stylized facts about daily series of returns. A notable exception is the inability of the models to reproduce one ubiquitous feature of such time series, namely the slow decay in the autocorrelation function of the squared returns. It is shown that this stylized fact can be described much better by means of hidden semi-Markov models. This is illustrated by examining the fit of two such models to 18 series of daily sector returns. 相似文献
55.
56.
Integrating heterogeneous database schemata is a major task in federated database design where preexisting and heterogeneous database systems need to be integrated virtually by providing a homogenization database interface. Most proposed schema integration methods suffer from very complex result schemata and insufficient handling of extensional relations, i.e. in the way how redundant data of the input systems are dealt with. Redundancy among the input systems may thus remain undetected and, hence, remains uncontrolled.Our GIM (Generic Integration Model) method is based on the elegant and mathematically founded theory of formal concept analysis (FCA). The main idea is to integrate schemata into one formal context which is a binary relation between a set of attributes and a set of base extensions (set of potential objects). From that context we apply an FCA-algorithm to semi-automatically derive a concept lattice which we interpret as an inheritance hierarchy of classes for a homogenized schema. Thus, the integration task following our method can be supported by tools. 相似文献
57.
Randomized search heuristics like local search, tabu search, simulated
annealing, or all kinds of evolutionary algorithms have many applications. However,
for most problems the best worst-case expected run times are achieved by more
problem-specific algorithms. This raises the question about the limits of general
randomized search heuristics. Here a framework called black-box optimization is developed. The essential
issue is that the problem but not the problem instance is knownto the algorithm which
can collect information about the instance only by asking for the value of points in the
search space. All known randomized search heuristics fit into this scenario. Lower
bounds on the black-box complexity of problems are derived without complexity
theoretical assumptions and are compared with upper bounds in this scenario. 相似文献
58.
Curved horizontal wells have been developed in the late nineties for the purpose of in situ remediation of contaminated water. The discharge of contaminated backwater has been performed very successfully. These wells are usually designed for short time use with high precision and lower requirements on productivity in comparison to the needs of fresh water discharge from groundwater. Potable water resources are explored with highly productive and durable water wells. Classical wells are vertical and radial collector wells. Under certain hydrogeological conditions a curved horizontal well may be more efficient than classical wells. Therefore well construction and design have been accepted to meet the requirements of fresh water exploration. This paper compares the three fundamental well design principles. A quantitative analytical engineering concept is presented on a basis of the Dupuit-Thiem well equation. Especially the geometry of draw-down figures is reflected in this calculations. 相似文献
59.
Neuronal differentiation and the formation of cell polarity are crucial events during the development of the nervous system. Cell polarity is a prerequisite for directed information flux within neuronal networks. In this article, we focus on neuro-glial cell interactions that influence the establishment of neural cell polarity and the directed outgrowth of axons versus dendrites. The cellular model discussed in detail is the retinal ganglion cell (RGC) of the chick retina, which is investigated by a comprehensive set of in vitro assays. The experiments demonstrate that retinal microenvironment determines axon vs. dendrite formation of RGCs. The instructive differences in different retinal microenvironments are substantially influenced by radial glia. Different glial domains support or inhibit axon vs. dendrite outgrowth. The data support the notion that neuro-glial interactions are crucial for directed neurite outgrowth. 相似文献
60.
Ralf?Buscherm?hleEmail author Mark?Br?rkens Ingo?Brückner Werner?Damm Wilhelm?Hasselbring Bernhard?Josko Christoph?Schulte Thomas?Wolf 《Informatik-Spektrum》2004,27(2):146-158
Die Gewährleistung der korrekten
Funktionsweise von Hard- und Software ist ein entscheidender
Faktor bei der heutigen Systementwicklung. Dies trifft ganz
besonders auf das Gebiet der sog. sicherheitskritischen
Systeme zu, bei dem ein Systemversagen Menschenleben gefährden
kann. 相似文献