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  • 1
    ISSN: 1520-6033
    Source: ACS Legacy Archives
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 105 (1991), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: 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.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 6 (1994), S. 435-437 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 4 (1990), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: 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.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: 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.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: 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.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 341 (1992), S. 275-287 
    ISSN: 1434-601X
    Keywords: 25.30.Fj ; 13.60.Hb
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Using the Ward-Takahashi identity, on-shell condition, bound Dirac equation and off-shell expansion, a reduced version of half off-shell virtual photon nucleon vertex has been suggested. The vertex are decomposed into several different order terms: the on-shell terms, first and second off-shell terms. The off-shell behaviour of the form factors is discussed in the one meson loop model. Using the reduced vertex and parametrized off-shell form factors the quasielastic response functions are calculated for several nuclei at ¦q¦–kf and for56Fe at large ¦q¦ up to 1.14 GeV/c and at −q2=0.9 (GeV/c)2. The Coulomb sums are evaluated and a comparison of the theoretical prediction with data is given. The off-shell electron nucleon cross section is calculated and compared with the “cc1” off-shell extrapolation.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1573-5028
    Keywords: Nicotiana tabacum ; plant transformation ; gene expression ; bacterial lysine decarboxylase ; protein transport ; chloroplasts ; cadaverine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A possible approach for altering alkaloid biosynthesis in plants is the expression of genes encoding key enzymes of a pathway such as lysine decarboxylase (ldc) in transgenic plants. Two strategies were followed here: one focused on expression of the gene in the cytoplasm, the other on subsequent targeting of the protein to the chloroplasts. Theldcgene fromHafnia alvei was therefore (a) placed under the control of the 1′ promoter of the bidirectional Tr promoter fromAgrobacterium tumefaciens Ti- plasmid, and (b) cloned behind therbcS promoter from potato fused to the coding region of therbcS transit peptide. Bothldc constructs, introduced intoNicotiana tabacum with the aid ofA. tumefaciens, were integrated into the plant genome and transcribed as shown by Southern and northern hybridization. However, LDC activity was only detectable in plants expressing mRNA under the control of therbcS promoter directing the LDC fusion protein into chloroplasts with the aid of the transit peptide domain. In plants expressing the processed bacterial enzyme cadaverine levels increased from nearly zero to 0.3–1% of dry mass.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1573-3017
    Keywords: biomarkers ; Bluegill ; sediment ; pollution ; EFPC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The temporal expression of various biological rsponses was determined in Bluegill SunfishLepomis macrochirus exposed under controlled laboratory conditions to sediment containing high concentrations of polynuclear aromatic hydrocarbons, polychlorinated biphenyls and heavy metals. Liver, gill, blood, kidney, brain, spleen and intestine were removed from Sunfish sampled at 1, 2, 4, 8, 16, and 40 weeks post-exposure. Biomarker data were recorded for specific proteins, enzymatic activities, DNA integrity, and histopathology. Biomarkers in the laboratory exposed fish were similar to those of indigenous Sunfish sampled from the site of origin of the contaminated sediment. Several patterns of development of biomarkers over time were also evident. For example, the responses of certain biomarkers are not time-dependent (i.e., intestine and gill ATPase activities) while that of others, such as brain ATPase activity, liver cytochrome P450 and NADPH content, stress proteins, chromatin proteins and DNA strand breaks, fluctuate over time. Still other biomarkers, such as EROD activity, zinc protoporphyrin content of the blood, and DNA adducts, showed marked increases over time. Such patterns need to be considered when comparing laboratory and field results and deciding which biomarkers to use for biomonitoring programs. Implications for natural selection and population/community level responses are also discussed.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Transport in porous media 15 (1994), S. 251-269 
    ISSN: 1573-1634
    Keywords: Hodograph method ; 2D cresting models ; gas and water cresting
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Three new applications of the hodograph method to the problem of gas and water cresting towards horizontal wells are presented: (1) A numerical technique, based on the hodograph method, is used to find the shape of the oil/water interface and values of critical heights for the problem of water cresting towards a horizontal well beneath an impermeable plane. (2) By correct implementation of the boundary conditions in the lateral edge drive model, a hodograph solution is found for which the water crest tends to a horizontal asymptote far from the well, rather than tending towards a parabolic curve as in previous approaches. The solution yields integral representations for the lengths of boundary segments and enables an explicit expression for the critical rate to be derived in terms of the distance to the constant potential boundary. (3) The problem of simultaneous gas and water cresting towards a horizontal well in a thin oil column reservoir is solved using the hodograph method, providing shapes of the free interfaces and an expression for the optimal placement of the well with respect to the interfaces.
    Type of Medium: Electronic Resource
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