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121.
We consider reasoning about linear systems expressed as block diagrams that give a graphical representation of a system of differential equations or recurrence equations. We use the notion of additive relation borrowed from homological algebra to give a convenient framework in which all diagrams have a semantic value. We give a sound system of Hoare-style rules for the block diagram constructors that singles out a tractable subset of the block diagram language in which all diagrams represent total functions. We show these rules in action on some simple examples from a variety of applications domains. 相似文献
122.
Ursula Schmidt 《Acta Informatica》1987,24(4):433-445
Summary We examine long unavoidable patterns, unavoidable in the sense of Bean, Ehrenfeucht, McNulty. Zimin and independently Schmidt have shown that there is only one unavoidable pattern of length 2
n
-1 on an alphabet with n letters; this pattern is a quasi-power in the sense of Schützenberger. We characterize the unavoidable words of length 2
n
-2 and 2
n
-3. Finally we show that every sufficiently long unavoidable word has a certain quasi-power as a subword.This work was done while the author stayed at LITP, Université Paris 6, France 相似文献
123.
Molecular approaches to the assessment of biodiversity in aquatic microbial communities 总被引:12,自引:0,他引:12
For the past 20 years, the increased development and routine application of molecular-based techniques has made it possible to carry out detailed evaluations of the biodiversity of aquatic microbial communities. It also offers great opportunities for finding out how this parameter responds to various environmental stresses. Most of these approaches involve an initial PCR amplification of a target, which is generally located within the ribosomal operon. The amplification is achieved by means of primers that are specific to the organisms of interest. The second step involves detecting sequence variations in the PCR fragments either by a cloning/sequencing analysis, which provides a complete characterization of the fragments, or by an electrophoretic analysis, which provides a visual separation of the mixture of fragments according to sequence polymorphism (denaturing or temperature gradient gel electrophoresis, single strand conformation polymorphism) or length polymorphism (terminal-restriction fragment length polymorphism, automated ribosomal intergenic spacer analysis). Other non-PCR-based methods are also commonly used, such as fluorescence in-situ hybridization and DNA re-association analysis. Depending on the technique used, the information gained can be quite different. Moreover, some of these analyses may be rather onerous in terms of time and money, and so not always suitable for screening large numbers of samples. The most widely used techniques are discussed in this paper to illustrate the principles, advantages and shortcomings of each of them. Finally, we will conclude by evaluating the techniques and discussing some emerging molecular techniques, such as real-time PCR and the microarray technique. 相似文献
124.
Emerging pesticide metabolites in groundwater and surface water as determined by the application of a multimethod for 150 pesticide metabolites 总被引:1,自引:0,他引:1
A recently developed multimethod for the determination of 150 pesticide metabolites was exemplarily applied to 58 samples of groundwater and surface water. 37 of these metabolites were detected in at least two samples with a concentration ≥0.025 μg/L. The detected metabolites were ranked according to their concentration and frequency of detection. Findings are clearly dominated by metabolites of chloroacetanilide herbicides, but metabolites of sulfonylurea and thiocarbamate herbicides and other herbicides (dichlobenil) together with metabolites of some fungicides (tolylfluanid, chlorothalonil, trifloxystrobin) were also prominent. A number of 17 of the ranked metabolites are denoted as emerging metabolites because no reports on their previous detection in groundwater or surface water were found. Most of them, however, were correctly predicted to occur in the summary reports of the European pesticide approval process. Median total concentrations of the analysed pesticide metabolites summed up to 0.62 μg/L in groundwater and 0.33 μg/L in surface waters. While the concentration of the individual metabolites is usually low (<0.1 μg/L) the diversity of metabolites found in one sample can be large; between two and six metabolites were detected most frequently (maximum of 12 metabolites). Runoff from urban surfaces was investigated in this study and also here previously undetected pesticide (biocide) metabolites were detected. The emerging pesticide metabolites detected in environmental water samples in this study require more extended monitoring. 相似文献
125.
Joachim Lentes Joerg Mandel Ursula Schliessmann Roland Blach Michael Hertwig Timm Kuhlmann 《国际生产研究杂志》2017,55(2):480-491
The rapid growth of the world population, the finiteness of resources on our planet Earth and the ongoing tendency towards urbanisation result in the need to question our actions and economic activities, also for industrial enterprises. A paradigm shift to decouple growth and resource utilisation is needed. By means of ultra-efficiency, factories are targeted, whose positive impact to their surrounding is optimised instead of only minimising negative influences. In the contribution, the concept of ultra-efficient factories and first tools for their implementation are introduced. Therefore, the term ultra-efficient factory is defined based on the state of the art. On this definition, spheres of activity for ultra-efficient factories under consideration of urban surroundings are determined. For the spheres of activity, criteria to assess the according maturity of companies are identified and aggregated into a comprehensive maturity model. The maturity model enables the determination of potentials for advancements of companies. To support the industrial application of the theoretic work, industrial best practices are determined and a visual tool is developed. 相似文献
126.
3D fluid–structure-contact interaction based on a combined XFEM FSI and dual mortar contact approach
Ursula M. Mayer Alexander Popp Axel Gerstenberger Wolfgang A. Wall 《Computational Mechanics》2010,46(1):53-67
Finite deformation contact of flexible solids embedded in fluid flows occurs in a wide range of engineering scenarios. We
propose a novel three-dimensional finite element approach in order to tackle this problem class. The proposed method consists
of a dual mortar contact formulation, which is algorithmically integrated into an eXtended finite element method (XFEM) fluid–structure
interaction approach. The combined XFEM fluid–structure-contact interaction method (FSCI) allows to compute contact of arbitrarily
moving and deforming structures embedded in an arbitrary flow field. In this paper, the fluid is described by instationary
incompressible Navier–Stokes equations. An exact fluid–structure interface representation permits to capture flow patterns
around contacting structures very accurately as well as to simulate dry contact between structures. No restrictions arise
for the structural and the contact formulation. We derive a linearized monolithic system of equations, which contains the
fluid formulation, the structural formulation, the contact formulation as well as the coupling conditions at the fluid–structure
interface. The linearized system may be solved either by partitioned or by monolithic fluid–structure coupling algorithms.
Two numerical examples are presented to illustrate the capability of the proposed fluid–structure-contact interaction approach. 相似文献
127.
128.
Douglas B. Riffel Ursula Wittstadt Ferdinand P. Schmidt Tomás Núñez Francisco A. Belo Antonio P.F. Leite Felix Ziegler 《International Journal of Heat and Mass Transfer》2010,53(7-8):1473-1482
This paper presents a heat and mass transfer simulation of an adsorber, taking into consideration the geometry of the heat exchanger and the diffusion in the adsorbent medium. In this model, an increment in the direction of heating/cooling fluid containing one (or more) fin pitch was considered. In the domain of this increment, the distribution of the adsorbent temperature was evaluated in the radial and axial directions. The model is validated by experimental data of different adsorbents, volume flows and temperatures. All data were collected in an adsorber test-bench at Fraunhofer ISE. As a result it was found a coefficient of multiple determination of around 0.94 and an error of 20% during the transient. Finally, the model was run on typical operation for cooling application and compared with data from literature. A numerical energy balance was also evaluated. In summary, the results obtained by a independent group shows the same range of confidence of the model developed here, in terms of the tendency of the curves and even the absolute values. 相似文献
129.
European Journal of Wood and Wood Products - Um einen schadensfreien Einsatz von Holzspanplatten im Außenbau mit direkter Wetterbeanspruchung dauerhaft zu gewährleisten,... 相似文献
130.