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  • 1990-1994  (10)
  • 1970-1974  (3)
  • 1960-1964  (3)
  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 6 (1994), S. 435-437 
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A presentation is given of the results of two-dimensional lattice gas cellular automata (LGA) simulations for calculating the permeability for flow through periodic arrays of cylinders, where the cylinders have either a rhomboid or cruciform cross section. For the case of rhombi, the results are related via a semiempirical shape factor to analytical solutions for flow through arrays of circular cylinders. Finite size effects are studied by comparing simulation results with theory. This calibration of the LGA model then validates its use for the study of flow around cruciforms, for which there is no analytical solution. This has an important application in the mathematical modeling of flow through arrays of dendrites in the mushy region during the solidification of alloy steel.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    ISSN: 1520-6033
    Quelle: ACS Legacy Archives
    Thema: Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    Industrial and engineering chemistry 2 (1963), S. 103-105 
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 105 (1991), S. 0 
    ISSN: 1365-246X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: A study is made of the dependence of the effective permeability of sand-shale reservoirs on the geometry of the shale inclusions. Numerical simulations are described in which factors such as the orientation and the degree of anisotropy of the shales, their volume fraction and the permeability contrast ratio between the shale and the sandstone were varied. Two different reservoir models were used in the simulations: one in which the shales were in the form of random, overlapping spheroidal inclusions, and one in which the shales were generated by a geostatistical technique. The computed effective permeability data are compared with a variety of analytical models in an attempt to discover ‘rules of thumb’for the estimation of the effective permeability of sand-shale reservoirs for use in a range of practical situations. The main technical way in which this study advances on previous work is in its use of a computationally efficient, random walk algorithm for calculating the effective permeability, which has enabled larger volumes to be simulated and, hence, a thorough investigation of finite-size effects to be made. Another advantage of the work reported here is the general nature of the sand-shale geometries used in the numerical simulations and the extensive comparisons with analytical models.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 5 (1991), S. 0 
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: The atp operon of Escherichia coli directs synthesis rates of protein subunits that are well matched to the requirements of assembly of the membrane-bound H+-ATPase (α3β3γ1δ1σ1a1b2c10–15). Segmental differences in mRNA stability are shown to contribute to the differential control of atp gene expression. The first two genes of the operon, atpl and atpB, are rapidly inactivated at the mRNA level. The remaining seven genes are more stable. It has previously been established that the translational efficiencies of the atp genes vary greatly. Thus differential expression from this operon is achieved via post-transcriptional control exerted at two levels. Neither enhancement of translational efficiency nor insertion of repetitive extragenic palindromic (REP) sequences into the atplB intercistronic region stabilized atpl. We discuss the implications of these results in terms of the pathway of mRNA degradation and of the role of mRNA stability in the control of gene expression.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 4 (1990), S. 0 
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: Post-transcriptional control mechanisms assume special significance in polycistronic operons. Differential gene expression in the atp operon of Escherichia coli is primarily attributable to translational control and, to a lesser extent, to control of mRNA stability. At the same time, the polycistronic environment influences, to varying degrees, the relative importance of the different types of post-transcriptional control. The present article briefly reviews more recent results obtained through studies of the atp operon. Investigations of the pathway and kinetics of mRNA decay have yielded new information about the role of degradative mechanisms in the overall scheme of control. Moreover, translational coupling has been shown to feature as a major form of interaction between the atp genes. The relevance of these and other data is discussed in the wider context of the post-transcriptional control mechanisms generally available to E. coli.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Water Resources Association 8 (1972), S. 0 
    ISSN: 1752-1688
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Architektur, Bauingenieurwesen, Vermessung , Geographie
    Notizen: The properties of an instantaneous unit hydrograph model consisting of two cascades of linear reservoirs in parallel were explored with the aid of an analog computer. By proper choice of the model parameters it is possible to produce two-peaked instantaneous unit hydrographs. The relative magnitudes and locations of the two peaks can be varied by changing the values of the parameters. An example of the use of the analog computer to select the parameters of the model giving the best fit to an observed runoff hydrograph is also included. The analog computer used in the study was the ASTRAC II developed at the University of Arizona.
    Materialart: Digitale Medien
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  • 8
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: A series of afp::lacZ fusions has been constructed for use in a study of translational coupling in the central region of the Escherichia coli atp operon. Five genes, atpE, atpF, atpH, atp A and atpG, were shown to be translationally coupled to various degrees of tightness. A new lac promoter vector, compatible with the afp::lacZ fusion vectors, was used to express individual atp genes in the same hosts as the fusion genes. The H+-ATPase subunits thus synthesized exercised no significant trans-regulation on the expression of the atp::lacZ fusions, indicating that the coupling is primarily cis. The mechanism of this coupling was investigated using in vitro mutagenesis. At least in the case of the pair atpHA, coupling seems to involve facilitated binding of fresh ribosomes to the atpA translational initiation regions.
    Materialart: Digitale Medien
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  • 9
    ISSN: 1432-1793
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Over a 2-year program of monthly cruises covering the entire Chesapeake Bay (USA), the phytoplankters which passed 35 μm mesh were responsible for 89.6% of the phytoplankton productivity. On a single summer cruise, the 〈35 μm phytoplankton fraction was responsible for 93.4% of the chlorophyll a and 100% of the primary productivity. The 〈10 μm fraction was responsible for 81.3% of the chlorophyll a and 94% of the productivity. The difference in biomass in the 〈35 μm and the 〈10 μm fractions was significant (P=0.025), but no significant difference in the productivity could be demonstrated. Laboratory experiments demonstrated that recently assimilated carbon can be lost with gravity screening. Considering both this and the effect of herbivorous zooplankters enclosed in productivity incubations, a prescreening rather than postscreening technique is recommended for studying nanoplankton productivity.
    Materialart: Digitale Medien
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  • 10
    ISSN: 0945-3245
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Summary The report gives a complete defining description of the international algorithmic languageAlgol 60. This is a language suitable for expressing a large class of numerical processes in a form sufficiently concise for direct automatic translation into the language of programmed automatic computers. The introduction contains an account of the preparatory work leading up to the final conference, where the language was defined. In addition the notions reference language, publication language, and hardware representations are explained. In the first chapter a survey of the basic constituents and features of the language is given, and the formal notation, by which the syntactic structure is defined, is explained. The second chapter lists all the basic symbols, and the syntactic units known as identifiers, numbers, and strings are defined. Further some important notions such as quantity and value are defined. The third chapter explains the rules for forming expressions and the meaning of these expressions. Three different types of expressions exist: arithmetic, Boolean (logical), and designational. The fourth chapter describes the operational units of the language, known as statements. The basic statements are: assignment statements (evaluation of a formula), go to statements (explicit break of the sequence of execution of statements), dummy statements, and procedure statements (call for execution of a closed process, defined by a procedure declaration). The formation of more complex structures, having statement character, is explained. These include: conditional statements, for statements, compound statements, and blocks. In the fifth chapter the units known as declarations, serving for defining permanent properties of the units entering into a process described in the language, are defined. The report ends with two detailed examples of the use of the language and an alphabetic index of definitions.
    Materialart: Digitale Medien
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