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  • Articles  (13)
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  • Life and Medical Sciences  (5)
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  • 1995-1999  (13)
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  • Articles  (13)
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  • 1
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 2743-2760 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: High-purity distillation columns are typically difficult to control because of their severely nonlinear behavior reflected by their sharp composition and temperature profiles. The dynamic behavior of such a column, as characterized by the movement of its sharp profile, was elucidated by a nonlinear wave theory established previously. With binary alcohol mixtures, this study provides an experimental observation of such wave-propagation dynamics of a 40-tray stripping column and a 50-tray fractionation column in response to step disturbances of feed composition, feed flow rate, and reboiler heat supply. Our experimental results have verified that the sharp profile in a high-purity column moves as a constant-pattern wave and that the nonlinear wave theory predicts its velocity satisfactorily with very simple mathematics. Our results also demonstrate the asymmetric dynamics of the transitions between two steady states.
    Additional Material: 10 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 1968-1976 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: NO reduction through heterogeneous mechanisms is a major concern when coal or lignite is used as reburning fuel. Reburning was simulated in an alumina flow reactor operated with a synthetic flue gas at a stoichiometric ratio of 1.1, at 1,100°C and with a residence time of approximately 0.2 s. Reburning fuels used include methane, one bituminous coal, two lignites, chars derived from the bituminous coal and two lignites, and the bituminous coal char impregnated with CaO. Reburning with chars indicates that heterogeneous mechanisms are more important than homogeneous mechanisms when lignites are used. This high reactivity renders lignite char an even more effective reburning fuel than the parent lignite, while char from the bituminous coal produces little activities at stoichiometric ratios above 0.75. Bituminous coal char impregnated with CaO demonstrates higher NO reduction efficiency than the original char. Effects of SR on NO reductions imply that oxygen atoms, required for the NO and HCN conversions in homogeneous mechanisms, are not required in heterogeneous mechanisms. In fact, they inhibit the surface NO reduction. The first-level kinetic analysis indicates that the surface area is not the only contributor to a remarkable increase in NO reduction of lignite char, and chars of different origins seem to follow different mechanisms or to have different controlling steps in the overall reaction scheme.
    Additional Material: 8 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 190-194 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 2 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2289-2299 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The competition between heuristic and optimization approaches for process synthesis and process operations problems has caused major controversy in recent years. Heuristics offer fast solutions but no guarantee of optimality. Mathematical programming approaches, on the other hand, offer rigor but suffer from combinatorial explosion of computational requirements. The use of analytical investigations is proposed as a theoretical means to characterize the behavior of heuristics and optimization algorithms and produce a framework that combines the strengths of the two approaches while eliminating their weaknesses. The approach contrasts and complements the current practice in process systems engineering, which is entirely empirical in nature. The proposed paradigm is demonstrated in the context of the multiperiod capacity expansion problem for chemical process networks, a problem having much in common with both process synthesis and operations problems. Analytical investigations for this problem lead to the development of a heuristic that is proved to be asymptotically optimal under standard assumptions about the problem parameters. In the more general context of process synthesis and operations, analytical investigations present a large array of opportunities.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Microscopy Research and Technique 31 (1995), S. 184-192 
    ISSN: 1059-910X
    Keywords: DNA ; In situ hybridisation ; Monoclonal antibodies ; Protein ; RNA ; Western blots ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: The molecular cell sciences have had a great impact in the analysis of the genetic and epigenetic events of esophageal and gastric tumorigenesis. In other regions of the alimentary tract such as the colon, the serial identification of the molecular events in the corresponding morphological lesions is perhaps most advanced. This is, in part, due to the relative ease of the histological characterisation of the premalignant lesions. In this regard the analysis of morphological and molecular adaptation in the alimentary tract is inextricable. This review aims, therefore, to judiciously assess the relative applications of contemporary techniques in investigative histopathology. © 1995 Wiley-Liss, Inc.
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  • 6
    ISSN: 0730-2312
    Keywords: coullagen synthesis ; glucocorticoids ; transforming growth factor ; eukaryotic genes ; oligonucleotide ; transfection ; glucocorticoid regulation ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Glucocorticoids have previously been shown to decrease Type 1 collagen synthesis in vivo and in fibroblast cell culture. Several studies have demonstrated that glucocorticoids decrease Type 1 procollagen gene expression. These latter studies have included uridine incorporation into proα1(I) and proα2(1) mRNas and nuclear run-off experiments. Using the ColCat 3.6 plasmid, which contains part of the 5' flanking regionof the proα1 (1) coullagen gene and the reporter gene, chljoramphenicol acetyltransferase, the present studies demonstrate by stable transfection of fetal rat skin fibrolblasts that dexamethasone down regulates the promoter activity of the proα1(I) collagen gene. The glucocorticoid-mediated down-regulastionof procolljagen gene expression was demonstrated using the ColCat 3.6, 2.4, 1.7, or 0.9 plasmid. In addition, competitive oligonucleotide transfection experiments and site specific mutation of the glucocorticoid response element (GRE) in the whoulue ColCat 3.6 plasmid did not elimiinatre the effect. The ipossibility existed that another cis-element inthe 5' flanking region of the proα1(I) collagen gene was also required for the glucocorticoid-mediated down-regulation of procollagen gene expression, since TGF-β has been shown to stimulate collagen proα1(I) and proα2(I) gene activities. Dexamethasone treatment of non-transfected skin fibroblasts did result in a decrease of transforming growth factor-β. The decrease of CVAT activity by dexamethasone was brought back to control value by the addition of exogenous TGF-β to the culture media. Gel mobility studies demonstrated that glucocorticoid treatment of rat skin fibroblasts decreased glucocorticoid recptor binding to the GRE and TGF-β activator protein to the TGF-β element which were brought back to control values by coordinate exogenous TGF-β treatment. Thus the interaction of these TGF-β molecules with cellular membrane receptors and subsequent rtransduction is dramatically decreased resulting in less signals to regulate collagen gene expression. These data indicate that glucocorticoids coordinately regulate procollagen gene expfrssion through both the GRE and TGF-β elements. Depression of procollagen gene expression by glucocorticoids through the TGF-β element is mediated by decreased TGF-β secretion, possibly involving a secondary effect on regulatory protein(s) encoded by noncollagenous protein gene(s). The present studies provide the bassis for a novel mechanism of glucocorticoid-mediated regulation of eukaryotic genes containing the TGF-β element. © 1995 Wiley-Liss, Inc.
    Additional Material: 11 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Molecular Reproduction and Development 40 (1995), S. 292-304 
    ISSN: 1040-452X
    Keywords: nucleus ; replication ; transcription ; MPM-2 ; rabbit embryo ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Mechanisms of nuclear reprogramming and assessment of potential malfunctions that could be deleterious for development were evaluated in rabbit zygotes, parthenotes, and nuclear transfer embryos by analysis of DNA replication, nucleolar fibrillarin label, and localization of nuclear material reactive to the MPM-2 antibody. Nuclear transfer embryos were derived from G1/early S-phase donor nuclei and MII oocytes. In nuclear transfer embryos, DNA rerelication was likely to have occurred because label was incorporated, possibly in the centromeric regions of the chromosomes, prior to premature chromosome condensation and again following pronuclear formation. In parthenotes, DNA replication began very late in the cell cycle, which may be due to deficiencies in the artificial activation stimulus. The presence of fibrillarin label in the nucleolus was used as an indication of nucleolar transcriptional activity. Fibrillarin label was absent in embryos of all types up to the 16-32-cell stage. Although fibrillarin reappeared in nuclear transfer and parthenote embryos at the appropriate stage, not all blastomeres showed label indicating impaired development in these embryos. Labelling of phosphorylated epitopes by MPM-2 antibody showed a change in pattern of labelling during early development. Early cleavage stage embryos did not exhibit labelling over the spindle poles as did blastomeres from 32-cell embryos and tissue culture cells. All cell types exhibited labelling during interphase as dots located primarily over the nucleus in blastomeres from 32-cell embryos and in tissue culture cells, together with cytoplasmic label in embryos at early cleavage stages. Nuclear transplant embryos had a normal pattern of MPM-2 label. In contrast, the appearance of MPM-2 label in parthenotes depended on the type of calcium stimulation. These results demonstrate defects in DNA synthesis, nucleolar activity, and specific phosphorylation events, likely resulting from an improper activation stimulus and chromosome condensation in the transplanted nucleus. © 1995 Wiley-Liss, Inc.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Molecular Reproduction and Development 40 (1995), S. 253-258 
    ISSN: 1040-452X
    Keywords: Oocyte activation ; Calcium ; Maturation promoting factor ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: The present study investigated the role of intracellular Ca2+ (Ca2+i) elevation on the inactivation of maturation promoting factor (MPF) in rabbit oocytes. The effects of the number of Ca2+ stimulations and of the amplitude of Ca2+i elevation on the profile of histone H1 kinase activity were determined. A Ca2+ stimulation consisted of transferring mature oocytes from culture medium to 0.3 M mannitol containing 0.1-1.0 mM CaCl2, and pulsing them at 1.25 kV/cm for 10 μsec, or microinjecting 2-8 mM CaCl2 into the oocyte cytoplasm. The number of electrically-induced Ca2+ stimulations was varied, and amplitude of the Ca2+i rise was controlled by altering Ca2+ concentration in the pulsing medium or the injection pipette. Ca2+i concentration was determined with fura-2 dextran; oocytes were snap-frozen at indicated time points and assayed for H1 kinase activity. The activity was quantified by densitometry and expressed as a fraction of activity in nonstimulated oocytes. Electrically-mediated Ca2+i rises inactivated H1 kinase in a manner dependent on the number of Ca2+ stimulations. A single Ca2+ stimulation inactivated H1 kinase to 30-40% of its initial activity. However, H1 kinase inactivation was only transient, regardless of the amplitude of the electrically- or injection-mediated Ca2+i elevation. Increasing the number of Ca2+ stimulations helped to maintain H1 kinase activity at basal (pronuclear) levels. The results show the necessity of a threshold of Ca2+i concentration to trigger MPF inactivation, and suggest a role for the extended period of time over which Ca2+i oscillates at fertilization. © 1995 Wiley-Liss, Inc.
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  • 9
    ISSN: 0749-503X
    Keywords: galactose ; transcription ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: The SIP1 gene of Saccharomyces cerevisiae is a carbon-catabolite-specific negative regulator of GAL gene transcription and acts as a multicopy suppressor of growth defects associated with impaired Snf1p protein kinase activity. The Sip1 protein is known to undergo phosphorylation when associated in vitro with the Snf1 protein kinase. We have carried out in vivo studies of the genetic and carbon control of Sip1p phosphorylation. Metabolic labeling reveals phosphorylation of Sip1p under both carbon catabolite-repressing and non-repressing conditions and in both SNF1 wild-type and snf1-deletion cells. By sodium dodecyl sulfate-polyacrylamide gel electrophoresis immunoblot assay, we detect apparent changes in Sip1p phosphorylation states in response to changes in carbon source. At least one dephosphorylation of Sip1p occurs with a shift from non-repressing carbon source to repressing carbon source. The MIG1 gene, acting through SNF1-dependent and SNF1-independent pathways, is required for some Sip1p phosphorylations. REG1 appears to be required for at least one dephosphorylation of Sip1p, whereas SSN6 appears to be required for at least one phosphorylation of Sip1p. These results reveal new complexities in carbon response signaling, and may reflect the involvement of the Sip1 protein in the same complex as the Mig1 and Ssn6 proteins.
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  • 10
    Electronic Resource
    Electronic Resource
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 16 (1995), S. 233-239 
    ISSN: 0272-8397
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Dielectric studies in epoxy and epoxy composites, containing different volume fractions of three different dielectric fillers, have been performed using the impedance bridge method for the high frequency region, 102 to 105 Hz, and the d.c. transient current method for the low frequency region, 10-4 to 10-1 Hz. It has been observed that, in the high frequency region, the dielectric constants of the epoxy composites increased with the addition of the dielectric filler and with the increase of the dielectric constant of the filler. The intensity of the β-relaxation was reduced for the composites compared to an equal volume of epoxy, owing to the decrease in the concentration of the diester segments in the composites. From the low frequency data, the epoxy and epoxy composites behaved more debye-like with increasing temperature. Also, the dielectric loss factor increased, but the thermal activation energy value to relaxation decreased two to four times in going from the unfilled to filled materials, which was thought to be attributed to Maxwell-Wagner buildup of interfacial charges at the epoxy/fillers interfaces.
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