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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 74 (1959), S. 0 
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 8197-8204 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An analytical model to study the response of a polymeric nematic confined in a rectangular cell, to a dc electric field is presented. The effect of a pressure-driven plane Poiseuille flow and its competition with the electric field is explicitly considered. For the final stationary state where the induced reorientation of the director has already occurred, an aligned structure with a greatly enhanced viscosity (electrorheological effect) is produced. For this same state the first normal stress difference is calculated as a function of position and of the applied field. For this quantity, regions of negative and positive values develop along the direction of the velocity gradient and an increase in the electric field or the flow causes an augmented effect in its profiles. The net force between the plates is also calculated. As the Reynolds number increases, it is found that it also changes sign from positive to negative, and the effect is more pronounced as the strength of the electric field increases. Finally, the paper is closed by discussing the scope and limitations of the model and methods employed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 12 (1989), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Ascorbate free radical (AFR) induced cell elongation in merislems of Allium cepa roots by promoting a high vacuolization as shown by the increased vacuole volume, vacuole volume density, tonoplast surface and tonoplast surface density. Accordingly, both plasma membrane- and tonoplast-associated ATPases and vacuole soluble acid phosphatase of meristematic cells were also increased. Neither the other subcellular organelles nor cell proliferation appeared to be significantly affected. It is suggested that AFR may be involved in some plasma membrane events related to the initiation of plant cell elongation.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1572-879X
    Keywords: Nickel ; ruthenium ; sulphide ; CO adsorption ; hydrogenation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Infrared spectroscopy was used to characterize mixed ruthenium-nickel sulphides prepared by step-wise impregnation over alumina and further sulphidation. The hydrogenation of biphenyl was compared over samples containing different amounts of nickel and ruthenium and a large increase was observed for a catalyst with an atomic Ni /(Ni + Ru) ratio near 0.4. Infrared spectra of adsorbed CO indicate that the increase in catalytic activity is ascribed to the presence of a very large number of Ru-Ni sites.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1572-879X
    Keywords: Alumina supported ruthenium sulphide catalysts ; thiophene hydrodesulphurization ; XPS characterization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Ruthenium sulphide catalysts supported on alumina were prepared using different precursor salts [ruthenium (III) chloride trihydrate, ruthenium (III) acetylacetonate and triruthenium dodecacarbonyl] and sulphided under various atmospheres. The properties of the catalysts in thiophene hydrodesulphurization are interpreted in relation to the XPS characterizations. These results show the importance of the sulphidation step in the absence of hydrogen in order to obtain a well sulphided, well dispersed and highly active catalyst.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-2048
    Keywords: Allium ; Cell cycle ; Golgi apparatus ; Stereology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In onion root meristems, the number of dictyosomes per cell shows a kinetics of growth strongly related to the cell cycle. During the interphase of steady-state proliferative cells, the volume density and numerical density of the Golgi apparatus decrease to reach minimum values in late-interphase cells, characterized by their greatest length. This pattern is also found in the total volume occupied by Golgi apparatus. Once in mitosis, the above-mentioned parameters begin to increase reaching maximum mean values in telophase. After the experimental uncoupling of chromosome and growth cycles by presynchronization with hydroxyurea, we found a similar behaviour pattern in the Golgi apparatus: decreasing values during interphase and a triggering of Golgi-apparatus growth in prophase independently of the bigger cell sizes reached in mitosis as an effect of pretreatment with hydroxyurea. These results indicate a cyclic kinetics of this subcellular component in higher-plant meristems, coupled with early mitotic events.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1615-6102
    Keywords: Apoptosis ; Atherosclerosis ; Endothelium ; Lipoproteins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Endothelial lesion by oxidized low-density liproproteins (LDL) is one of the first stages in the development of atherosclerosis. The effect of these lipoproteins can range from a functional lesion of the endothelium to death of the endothelial cells by apoptosis. High-density lipoproteins (HDL) are one of the factors which can have a protective effect against the development of atheromatous plaques. The aim of this study is to establish whether the death of endothelial cells by apoptosis induced by oxidized LDLs is prevented by HDLs. ECV304 endothelial cells and bovine aorta endothelial cells were incubated with native LDLs, oxidized LDLs, and a combination of both oxidized LDLs and HDLs. Oxidized LDLs caused a significant increase of mortality mainly by apoptosis. However, when HDLs were added together with oxidized LDLs the percentage of total mortality, the degree of lipoprotein oxidation in the medium, and the percentage of cells in apoptosis were all significantly decreased. HDLs protect against the cytotoxicity of oxidized LDLs possibly by preventing the propagation of the oxidative chain in these lipoproteins.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1615-6102
    Keywords: Ascorbate oxidation ; Cell elongation ; Onion root ; Plasma membrane redox system
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We report that ascorbate free radical stimulates onion root growth at 15 °C and 25 °C. The fully reduced form, ascorbate, also stimulates root elongation if culture conditions allow its oxidation. When ascorbate oxidation was inhibited, no stimulation of root growth was found. The effect of the fully oxidized form, dehydroascorbate, was inhibitory. We show also that ascorbate free radical generated by ascorbate oxidation, is reduced back probably by a transplasmalemma reductase. These results are discussed on the basis of an activation of a transplasma membrane redox system likely involved in processes related to cell growth.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1615-6102
    Keywords: NADH-dehydrogenase ; Onion root ; Plasma membrane ; Protein purification ; Redox system
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Plasma membranes isolated from onion roots by twophase partition contain at least two different NAD(P)H-dehydrogenases. A 27 kDa electron transport protein oxidises both NADH and NADPH and exhibits maximal activity with quinones as electron acceptors. A distinct 31 kDa dehydrogenase is specific for NADH as donor and shows maximal activity with ferricyanide. This novel enzyme is responsible for most NADH-ferricyanide oxidoreductase activity of solubilized onion root plasma membranes and exhibits properties different to other purified NAD(P)H-dehydrogenases.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1615-6102
    Keywords: Cell cycle ; Dictyosome ultrastructure ; Quantitative analysis ; Root meristems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Dictyosome ultrastructure changes during the cell cycle in onion root meristematic cells. Changes were mainly related to cisternae and intercisternal spaces morphology. Taking each dictyosome to be composed of three different regions (CIS, medial, and TRANS), several quantitative changes were detected in some of the compartments. Many of the planimetric parameters evaluated showed higher values in medical cisternae, while CIS and TRANS remained nearly constant. We have also found an increased activity of dictyosomes, as indicated by increase in the volume fraction of vesicular attached structures. This reaches maximum values at ana-telophase in coincidence with the onset and progression of cytokinesis.
    Type of Medium: Electronic Resource
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