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  • 1
    Electronic Resource
    Electronic Resource
    In vivo generation of free radical in ischemia-reperfusion in the rat liver
    Amsterdam : Elsevier
    Free Radical Biology and Medicine 9 (1990), S. 96 
    Details
    ISSN: 0891-5849
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0891-5849(90)90514-J
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  • 2
    Electronic Resource
    Electronic Resource
    POROSITY AND PORE STRUCTURE FROM ACOUSTIC WELL LOGGING DATA (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 41 (1993), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: Wyllie's time-average equation and subsequent refinements have been used for over 20 years to estimate the porosity of reservoir rocks from compressional (P)-wave velocity (or its reciprocal, transit time) recorded on a sonic log. This model, while simple, needs to be more convincingly explained in theory and improved in practice, particularly by making use of shear (S)-wave velocity. One of the most important, although often ignored, factors affecting elastic velocities in a rock is pore structure, which is also a controlling factor for transport properties of a rock. Now that S-wave information can be obtained from the sonic log, it may be used with P-waves to provide a better understanding of pore structure. A new acoustic velocities-to-porosity transform based on an elastic velocity model developed by Kuster and Toksöz is proposed. Employing an approximation to an equivalent pore aspect ratio spectrum, pore structure for reservoir rocks is taken into account, in addition to total pore volume. Equidimensional pores are approximated by spheres and rounded spheroids, while grain boundary pores and flat pores are approximated by low aspect ratio cracks. An equivalent pore aspect ratio spectrum is characterized by a power function which is determined by compressional-and shear-wave velocities, as well as by matrix and inclusion properties. As a result of this more sophisticated elastic model of porous rocks and a stricter theory of elastic wave propagation, the new method leads to a more satisfactory interpretation and fuller use of seismic and sonic log data. Calculations using the new transform on data for sedimentary rocks, obtained from published literature and laboratory measurements, are presented and compared at atmospheric pressure with those estimated from the time-average equation. Results demonstrate that, to compensate for additional complexity, the new method provides more detailed information on pore volume and pore structure of reservoir rocks. Examples are presented using a realistic self-consistent averaging scheme to consider interactions between pores, and the possibility of extending the method to complex lithologies and shaly rocks is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2478.1993.tb00578.x
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  • 3
    Electronic Resource
    Electronic Resource
    Ultrasonic wave propagation in dry and brine-saturated sandstones as a function of effective stress: laboratory measurements and modelling (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 43 (1995), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: Compressional and shear-wave velocities have been measured and a novel approach using digital processing employed to study wave attenuation for brine- and gas- saturated sandstones, over a range of effective stresses from 5 to 60 MPa. Also measured were the complex conductivity in the brine-saturated state and permeability in the gas-saturated state over the same range of stresses as for the velocity measurements. Broadband ultrasonic pulses of P- and orthogonally polarized S-waves in the frequency range 0.3–0.8 MHz are transmitted through the specimen to be characterized for comparison with a reference (aluminium) having low attenuation. The attenuation is calculated in terms of the quality factor Q from the Fourier spectral ratios, using the frequency spectral ratios technique. The corrections necessary for the effects of diffraction due to the finite size of the ultrasonic transducers have been carried out for the case of measurements under lower confining stress. To interpret the laboratory measured velocity and attenuation data under the physical conditions of this study and to estimate the effects of pore structure, numerical modelling of velocities and attenuation as functions of the confining stress have been performed, based on the MIT model. Theoretical models based on several hypothesized attenuation mechanisms are considered in relation to laboratory data of the effects of confining pressure, fluid saturation and pore structure on attenuation. Numerical calculations using these models with the experimental data indicate that friction on thin cracks and grain boundaries is the dominant attenuation mechanism for dry and brine-saturated sandstones at low effective stresses for the frequencies tested. However, for brine-saturated sandstones at moderately high effective stresses, fluid flow could play a more important role in ultrasonic S-wave attenuation, depending on the pore structure of the sample.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2478.1995.tb00255.x
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  • 4
    Electronic Resource
    Electronic Resource
    Identification of a cytokinin in water chestnuts (corms of Eleocharis tuberosa)
    Amsterdam : Elsevier
    Plant Science Letters 32 (1983), S. 225-231 
    Details
    ISSN: 0304-4211
    Keywords: Corms ; Cytokinin ; Eleocharis ; Isopentenyladenosine ; Mass spectrometry
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0304-4211(83)90119-0
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  • 5
    Electronic Resource
    Electronic Resource
    Applications of the method of complex functions to dynamic stress concentrations
    Amsterdam : Elsevier
    Wave Motion 4 (1982), S. 293-304 
    Details
    ISSN: 0165-2125
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0165-2125(82)90025-7
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  • 6
    Electronic Resource
    Electronic Resource
    Inhibitors of cytokinin metabolism III. The inhibition of cytokininN-glucosylation in radish cotyledons (1991)
    Springer
    Journal of plant growth regulation 10 (1991), S. 179-185 
    Details
    ISSN: 1435-8107
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Cytokinins are deactivated in radish cotyledons by conversion to 7- and 9-glucosides. In a search for inhibitors of this metabolism, the following compounds were found to be effective: (a) 6-benzylamino-2-(2-hydroxyethylamino)-9-methylpurine; (b) 3-isobutyl-1-methylxanthine; (c) papaverine; (d) theophylline; (e) caffeine; and (f) theobromine. The order of effectiveness was: (a)〉(b)=(c)〉(d)=(e)=(f). While the methylxanthines (b) and (d) inhibited formation of both 7- and 9-glucosides of 6-benzylaminopurine (BAP) approximately equally, compounds (a) and (c) preferentially inhibited formation of BAP 9-glucoside. Inhibition of BAP glucoside formation by (a) at 1.3 mM elevated the level of free BAP and BAP nucleotide 23- and 94-fold, respectively. While abscisic acid (ABA) suppressed conversion of zeatin riboside to zeatin 7-glucoside in radish cotyledons, it did not inhibit conversion of BAP to glucosides. Hence, ABA probably does not inhibit the glucosylating enzymes directly but rather reduces the availability of free zeatin when zeatin riboside is supplied. Auxins and nutrient supply did not affect conversion of zeatin riboside to zeatin 7-glucoside. Relative to cotyledons developed in light, those developed in darkness had a reduced capacity to convert zeatin riboside to zeatin 7-glucoside. The results presented have identified types of chemical structures which could be developed to provide more effective inhbitors of cytokininN-glucosylation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02279331
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  • 7
    Electronic Resource
    Electronic Resource
    Cytokinin biochemistry in relation to leaf senescence I. The metabolism of 6-benzylaminopurine and zeatin in oat leaf segments (1983)
    Springer
    Journal of plant growth regulation 2 (1983), S. 89-102 
    Details
    ISSN: 1435-8107
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The metabolism of zeatin and that of 6-benzylaminopurine (BAP) have been compared in oat leaf segments in relation to the markedly differing ability of these cytokinins to retard senescence of such segments. Free BAP and a highly active senescence-retarding metabolite of BAP were detected in oat leaf segments supplied with BAP. The metabolite was identified by mass spectrometry and chromatography as 3-β-D-glucopyranosyl-BAP. The major metabolite of BAP was the 9-glucoside, but this lacked significant senescence-retarding activity. In contrast, in leaf segments supplied with zeatin, no free zeatin and no senescence-retarding metabolite of zeatin were detectable. The major metabolites of zeatin were adenosine, adenine nucleotides, the 9-glucoside, and unidentified polar metabolites. The differing activities of zeatin and BAP in the oat-leaf senescence bioassay appear to be, at least partially, a consequence of their differing metabolism and are not attributable to differences in uptake.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02042237
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  • 8
    Electronic Resource
    Electronic Resource
    Regulators of cell division in plant tissues XXIX. The activities of cytokinin glucosides and alanine conjugates in cytokinin bioassays (1983)
    Springer
    Journal of plant growth regulation 2 (1983), S. 103-115 
    Details
    ISSN: 1435-8107
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract In a number of cytokinin bioassays, the activities of the following compounds were compared: 3-, 7-, and 9-glucosides of 6-benzylaminopurine (BAP); 7- and 9-glucosides of zeatin; O-glucosides of zeatin, dihydrozeatin, and their ribosides; 9-alanine conjugates of zeatin, and BAP. The bioassays included the radish cotyledon, theAmaranthus betacyanin, the oat leaf senescence, and the tobacco pith callus. Cytokinin activity was markedly reduced by 7- and 9-glucosylation in nearly all bioassays, but 3-glucosylation of BAP and O-glucosylation of the zeatin sidechain usually had little effect on activity. However, there were two notable exceptions to this generalization: the activity of O-glucosylzeatin markedly exceeded that of zeatin in the oat leaf senescence assay; 9-glucosyl-BAP and free BAP were similarly active in retarding the senescence of radish leaf discs. The 9-alanine conjugate of zeatin (lupinic acid) and of BAP were markedly less active than zeatin and BAP, respectively, in all bioassays, but the responses evoked by these conjugates at high concentrations in theAmaranthus bioassay approached those caused by the corresponding base. The activities of several new compounds related to the alanine conjugate of BAP were also assessed. To serve as a guide in the selection of the most suitable bioassay for detection of the above-mentioned cytokinin conjugates, the lowest detectable amounts in selected bioassays have been compared.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02042238
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  • 9
    Electronic Resource
    Electronic Resource
    Adaptive Inverse Control Using a Gradient-Projection Optimization Technique (1997)
    Springer
    Journal of optimization theory and applications 95 (1997), S. 677-691 
    Details
    ISSN: 1573-2878
    Keywords: Actuator uncertainty ; adaptive inverse ; gradient method ; parameter projection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract As an application of an optimization technique, a gradient-projection method is employed to derive an adaptive algorithm for updating the parameters of an inverse which is designed to cancel the effects of actuator uncertainties in a control system. The actuator uncertainty is parametrized by a set of unknown parameters which belong to a parameter region. A desirable inverse is implemented with adaptive estimates of the actuator parameters. Minimizing an estimation error, a gradient algorithm is used to update such parameter estimates. To ensure that the parameter estimates also belong to the parameter region, the adaptive update law is designed with parameter projection. With such an adaptive inverse, desired control system performance can be achieved despite the presence of the actuator uncertainties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022682124301
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  • 10
    Electronic Resource
    Electronic Resource
    Empirical equations for calculating wavelengths of x-ray characteristic lines and absorption edges (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    X-Ray Spectrometry 22 (1993), S. 410-412 
    Details
    ISSN: 0049-8246
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Empirical equations for calculating the wavelengths of x-ray characteristic lines and absorption edges were proposed and their effectiveness was compared with that of the empirical equations used in the programs MAGIC IV, FRAME C and NBSGSC. The proposed equations were proved to give the smallest number of mistakes which lead to an error of the calculated wavelength causing an analytical line to be on the wrong side of an absorption edge.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/xrs.1300220608
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