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  • Biochemistry and Biotechnology  (9)
  • Chemical Engineering  (6)
  • 1990-1994  (13)
  • 1960-1964  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Composite membranes for fuel-cell applications (1992)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 38 (1992), S. 93-100 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: One of the major obstacles to overcome for the realization of economical hydrogen-oxygen, polymer-electrolyte fuel cells is the high capital cost of the inert perfluorosulfonic acid (PSA) membranes, which provide a pathway for ionic transport between the cell electrodes. It has recently been shown that composite polymer membranes can be synthesized by depositing PSA polymers onto porous poly(tetrafluoroethyene) (PTFE) substrates. The resulting membranes are mechanically durable and quite thin relative to traditional PSA membranes; we expect the composite membranes to be of low resistance and cost. In this experimental study, we examine the composite membrane properties as a function of the membrane composition. Our results allow us to form a conceptual model to explain both the equilibrium and transport characteristics of these materials. For high PSA contents, the membrane behavior is similar to that of the PSA polymer; the water permeability, however, is reduced significantly. For intermediate PSA contents, the membranes have a high porosity and match the thickness of the PTFE substrate (≈50 μm); membranes of this composition range are potentially useful candidates for fuel cells because of their high resistance to water transport and reduced ionic resistance. Composite membranes of very low PSA content demonstrate characteristics similar to the hydrophobic PTFE substrate and are not of interest for fuel cells.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690380110
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  • 2
    Electronic Resource
    Electronic Resource
    A three-dimensional solubility parameter approach to nonaqueous enzymology (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 627-638 
    Details
    ISSN: 0006-3592
    Keywords: solubility parameters ; hydrophobicity index ; Hansen parameter ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Widespread commercial application of enzymes as catalysts for specialty or commodity chemical synthesis will require their use in nonaqueous systems. While a number of non-aqueous enzyme applications have been demonstrated, the lack of useful rules for predicting enzyme-solvent interactions has hindered the development of this technology. Both Hildebrand and solvent hydrophobicity (octanol-water partition coefficient) parameters have been used previously to correlate and predict enzyme activity in nonaqueous systems, with some success, but any single-parameter approach is inherently limited in its ability to reflect the spectrum of possible enzyme-solvent interactions. Therefore, this study evaluates the three-dimensional solubility parameter space, as proposed by Hansen, to correlate and predict enzyme activity in microaqueous, miscible, and biphasic nonaqueous systems. Preliminary results suggest that Hansen parameters may be useful for correlating nonaqueous enzyme activity, and that the dispersive and polar parameters may be disproportionately important in single-phase microaqueous systems. The Hansen hydrogen-bonding parameter appears to be the only parameter yet evaluated capable of correlating the water requirement for enzyme activity in microaqueous systems, suggesting that water affects protein structure through enthalpic rather than entropic processes in nonaqueous systems. Insufficient data are available for miscible and biphasic systems, but it is proposed that enzyme activity may correlate with the average solubility parameters of miscible systems and of the aqueous phase in biphasic systems.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260370705
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  • 3
    Electronic Resource
    Electronic Resource
    Kinetics of sulfochlorination of cyclohexane in carbon tetrachloride induced by gamma radiation (1964)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 10 (1964), S. 930-934 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Solutions of cyclohexane, chlorine, and sulfur dioxide in carbon tetrachloride were irradiated in an oxygen-free system with gamma rays from uranium fission products contained in spent fuel elements. Reaction rates, equivalent to the rate of disappearance of free chlorine, were determined spectrophotometrically at 4,000Å. The reaction products were cyclohexanesulfonyl chloride and hydrochloric acid in nearly stoichiometric quantities. An empirical rate equation was derived, in which the rate of disappearance of chlorine was shown to be proportional to the square root of the product of the product of absorbed radiation, chlorine and cyclohexane concentrations, and independent of the concentration of sulfur dioxide. A chain mechanism was proposed, and the rate equation derived from this scheme was found to be in excellent agreement with the empirical rate equation. The reaction proceeded by a free radical mechanism, as evidenced by the strong inhibiting effect of oxygen. G numbers were of the order of 105, corresponding to an estimated chain length of 5,000, which is of the same order as the quantum yield of the photochemical sulfochlorination.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690100629
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  • 4
    Electronic Resource
    Electronic Resource
    Thermogravimetric kinetics of polymer degradation: Science or fiction? (1992)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1309-1315 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Weight changes in thermogravimetry are dependent on the volatility of the degradation products. Thus, molecular weight determinations (or related studies) must fist be undertaken to prove whether or not nonvolatile chain fragments will be removed only at high temperatures. In this case both thermal stability and kinetic studies by thermogravimetry are senseless. But even if volatile products are formed, the kinetic parameters will depend on the conversion degrees because of the kinetic chain character of the polymer degradation. Changes in reaction mechanism aggravate the situation; it is thus problematic to define in such conditions reliable kinetic parameters. Values calculated from a single TG curve are valid for specific conditions only, but of no sense from the general kinetic view.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760321719
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  • 5
    Electronic Resource
    Electronic Resource
    Dielectric properties of plasticized melamine resins (1961)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 1 (1961), S. 68-72 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: During the last thrity years, dielectric measurements have been employed extensively to provide a better understanding of the interactions between polymer and plasticizer in various thermoplastic formulations. Recently, a series of melamine resins, plasticized to the extent that shrinkage and internal stress were modified, became available. Since there is little information in the literature concerning the dielectric properties of such thermosetting resins, a study was made of the variation of dielectric constant and loss as a function of frequency and temperature.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760010206
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  • 6
    Electronic Resource
    Electronic Resource
    Balancing of energy-consuming processes of rat hepatocytes (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Cell Biochemistry and Function 8 (1990), S. 227-232 
    Details
    ISSN: 0263-6484
    Keywords: Energy-consuming processes ; rat hepatocytes ; oxygen consumption ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: A method for the quantification of energy consuming processes described by Siems et al.6 for reticulocytes and by Müller et al.10 for ascites tumour cells was applied to balance the ATP-consumption of isolated rat hepatocytes. On the basis of decreased coupled respiration rates following the specific inhibition of energy-requiring reactions, the energy demands of protein turnover, nucleic acid synthesis, Na+/K+-ATPase and Ca2+-transport of hepatocytes in different incubation media were assessed. These processes together with urea synthesis account for about 60 per cent of the total energy consumption in a glucose and amino acid-enriched Eagle/Borsook medium. The metabolic flux rates of total ATP-consumption and ATP-consumption of single energy-requiring processes in hepatocytes are compared with those in reticulocytes and different tumour cell types.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cbf.290080407
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  • 7
    Electronic Resource
    Electronic Resource
    Typing of the 3′ hypervariable region of the apolipoprotein B gene: Approaches, pitfalls, and applications (1993)
    Weinheim : Wiley-Blackwell
    Electrophoresis 14 (1993), S. 169-173 
    Details
    ISSN: 0173-0835
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Apolipoprotein B-100 is the principal protein component of lipoproteins with very low, intermediate, and low density. The interaction of apoB-100 with low density lipoprotein (LDL) receptors is responsible for the uptake of LDL into cells. An AT-rich hypervariable region is located adjacent to the 3′ end of the apoB gene. It consists of a variable number of tandemly repeated sequences (VNTR). Two approaches were used to analyze this polymorphism. In both, the region harboring the VNTR was amplified with the polymerase chain reaction (PCR). In the first method, fluorescently labeled primers were used in the PCR reactions and products were separated in agarose gels by means of an automated fluorescent fragment analyzer. In the second method, PCR products were analyzed in denaturing polyacrylamide gels and detected with silver staining. Even in the highly sophisticated automated system, agarose gel electrophoresis did not always enable unequivocal assignment of VNTR alleles. In contrast, denaturing polyacrylamide gel electrophoresis made it possible to distinguish the 15 bp differences between the VNTR alleles in a precise and simple manner. The VNTR polymorphism was typed in 234 individuals. Among these were 136 patients with coronary artery disease and 74 healthy controls. Thirteen alleles could be distinguished. The allele containing 49 repeats (VNTR-49) was found in 9.2% of the coronary artery disease patients and in 4.7% of the controls. Thus, the VNTR-49 allele increases relative coronary risk by about twofold. It is concluded that the apoB VNTR polymorphism is a potentially useful genetic marker. Since agarose gel electrophoresis may lead to ambiguous results, we prefer typing by denaturing polyacrylamide gel electrophoresis. This has to be accounted for, especially if the apoB VNTR polymorphism is applied to forensic studies.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elps.1150140128
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  • 8
    Electronic Resource
    Electronic Resource
    Clonal imbalances of plasma/serum immunogloblin production in infants (1993)
    Weinheim : Wiley-Blackwell
    Electrophoresis 14 (1993), S. 245-247 
    Details
    ISSN: 0173-0835
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: To study the clonal events occurring during ontogeny of the humoral immune system, we evaluated plasma immunoglobulin (Ig) production in term newborns and young children by high-resolution two-dimensional gel electrophoresis. The clonality pattern of Ig light (L) chains from healthy newborns (n = 19) was similar to that observed on protein maps of their mothers or of normal adults (n 〉 100), that is, rare distinguishable small spots in a cloud-like large band of indiscrete Ig L chain spots (polyclonal pattern; maternal Igs). Analysis of plasma samples obtained from infants between 1 month and 5 years of age (n = 55) revealed discrete but evident alterations of the clonality of Ig production. Between the 2nd and 4th months of life, transient attenuation of the “polyclonal background” was observed in association with the appearance of an increasing number of well-resolved Ig L chain spots (corresponding to plasma Ig concentrations between 0.5 and 1 g/L per spot). This “restricted” clonal pattern was progressivly less apparent on protein maps of infants older than 2 year and evolved towards a “normal” adult polyclonal pattern at the age of 5. These results suggest that the development of the B-cell clones is heterogeneous, either through limited outgrowth of precursor cells or through selective antigenic pressures.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elps.1150140142
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  • 9
    Electronic Resource
    Electronic Resource
    Press-forming of continuous-fiber-reinforced thermoplastic composites (1990)
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 11 (1990), S. 114-120 
    Details
    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: Process-induced effects on thermoplastic-based composites were investigated for laminates processed under high production rate conditions. Press-formed carbon-fiber-reinforced poly(ether ether ketone) (PEEK) was used as a model system. The morphology and laminate quality were investigated on unidirectional laminates processed at cooling rates from 0.3 to 120°C/s and annealing of 177°C and 300°C. The laminate quality was examined for degree of consolidation, compaction, and fiber-matrix uniformity. Combined calorimetric and density measurements, as well as micrographic techniques, were used for examination of the laminates. The fracture toughness for the laminate was measured as a function of the position over the thickness of a 40-ply thick unidirectional laminate. This study clearly demonstrates the importance of uniform pressure distribution over the laminate to achieve a void free and homogeneous laminate.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pc.750110207
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  • 10
    Electronic Resource
    Electronic Resource
    Solvent stress cracking and failure mechanisms in polyetherimide composites (1990)
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 11 (1990), S. 240-249 
    Details
    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: Solvent stress cracking studies have been carried out in o-xylene and other solvents on polyetherimide (PEI) based materials including neat resin, woven fabric composites, and adhesively bonded systems. The results show crack growth in solvents at very low GI levels as compared with tests in air. The composite and adhesively bonded systems have sufficiently high residual thermal stresses to drive an array of intersecting matrix/adhesive cracks even without mechanical loading. The matrix/adhesive residual stress driven crack patterns in these systems are shown to retard main delamination crack growth relative to that in the neat resin, and to raise the applied threshold G1 level for main crack growth by about a factor of ten, as predicted by an approximate model.
    Additional Material: 24 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pc.750110407
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