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  • Institute of Physics  (279)
  • Wiley-Blackwell  (79)
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  • 11
    Electronic Resource
    Electronic Resource
    Thermal characterization of high performance PBI and 6F polymers and their alloys (1992)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1236-1241 
    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: The effectiveness of thermal analysis as a technique for screening polymeric candidates for high temperature composite application is described. DSC, DMA, and TGA were employed to measure glass transition temperature, characterize blend phase morphology, and assess thermo-oxidative stability. The materials studied were polybenzimidazole (PBI), polyimide copolymer (6FCoPI), and blends of PBI with Ultem 1000™ and 6FCoPI. The potential of misinterpretation of thermal analysis as the primary screening tool was also demonstrated. It was shown that if thermal analysis was used with insufficient understanding of the chemistry and physics of the materials under investigation, highly misleading conclusions may be derived.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760321709
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  • 12
    Electronic Resource
    Electronic Resource
    Confocal imaging of dendritic Ca2+ transients in hippocampal brain slices during simultaneous current- and voltage-clamp recording (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Microscopy Research and Technique 29 (1994), S. 279-289 
    Details
    ISSN: 1059-910X
    Keywords: Fluorescence microscopy ; Ca channels ; Pyramidal neurons ; CA1 region ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: Changes in the intracellular Ca2+ concentration ([Ca2+]i) within CA1 hippocampal pyramidal neurons were imaged using confocal laser scanning microscopy in conjunction with Ca2+ -sensitive fluorescent indicators. The imaging was performed in thick hippocampal brain slices while simultaneously measuring or controlling electrical activity with sharp microelectrodes or whole-cell patch-clamp electrodes. The combination of imaging and electrophysiology was essential for interpreting the changes in [Ca2+]i. We compared the increases in [Ca2+]i produced by either of two methods-direct depolarization of the cell via the somatic electrode or high-frequency stimulations of synaptic inputs. The increases in [Ca2+]i in the soma and proximal dendrites caused by both methods were of comparable magnitude and they always decayed within seconds in healthy cells. However, the spatial patterns of distal Ca2+ increases were different. Separate sets of synaptic inputs to the same cell resulted in different spatial patterns of [Ca2+]i transients. We isolated and observed what appeared to be a voltage-independent component of the synaptically mediated [Ca2+]i transients. This work demonstrates that the combination of neurophysiology and simultaneous confocal microscopy is well suited for visualizing and analyzing [Ca2+]i within neurons throughout the CNS and it raises the possibility of routinely relating subcellular [Ca2+]i changes to structural and functional modifications. © 1994 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jemt.1070290404
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  • 13
    Electronic Resource
    Electronic Resource
    Determination of monod kinetic coefficients for volatile hydrophobic organic compounds (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 50 (1996), S. 693-699 
    Details
    ISSN: 0006-3592
    Keywords: batch reactor ; Monod kinetic coefficient ; parameter estimation ; phenanthrene ; volatile hydrophobic substrate ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A new procedure is presented to determine Monod kinetic coefficients and the microbial yield coefficient for volatile hydrophobic compounds such as phenanthrene. Batch experiments were conducted with a mixed culture capable of degrading phenanthrene. The phenanthrene disappearance and carbon dioxide production were monitored with time. A maximum likelihood estimator was formulated to fit the set of equations that describe the system to the measured data. The model takes into account a number of processes such as partition onto the apparatus, volatilization, and partition onto the biomass. The parameters required to describe these processes were obtained by independent experiments. The yield coefficient could be determined within a small range. However, the specific growth rate and the half-saturation constant were found to vary widely, with pairs of them describing the system adequately. It was shown that partition and volatilization processes can significantly affect the determination of the yield and Monod kinetic coefficients and need to be taken into account. © 1996 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
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  • 14
    Electronic Resource
    Electronic Resource
    Effect of thermal annealing on the gas permeability of HIQ-40 films (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 1741-1745 
    Details
    ISSN: 0887-6266
    Keywords: Liquid crystalline polymer ; permeability ; crystallinity ; annealing ; gases ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The copolyester formed from 40 mol% p-hydroxybenzoic acid (H), 30 mol% isophthalic acid (I), and 30 mol% hydroquinone (Q), designated as HIQ-40, forms isotropic, amorphous films when appropriately cast from a solvent. Thermal annealing leads to a mesogenic texture and some level of crystallinity. It is shown that these ordering processes lead to dramatic reductions in gas permeability; the magnitude of the decrease increases with the size of the penetrant. The current results are consistent with previously reported sorption data for acetone in HIQ-40. © 1996 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
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  • 15
    Electronic Resource
    Electronic Resource
    Theoretical investigations on some rigid-rod polymers used as high-performance materials (1984)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 24 (1984), S. 218-225 
    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: This review focuses on a new type of para-catenated aromatic polymer being used in the preparation of high-performance films and fibers of exceptional strength, thermal stability, and environmental resistance, including inertness to essentially all common solvents. Polymers of this type include cis and transpoly(p-phenylene benzobisoxazole) (PBO), and the cis and trans forms of the corresponding poly(p-phenylene benzobis-thiazole)(PBT). The purpose of this paper is to summarize the authors' theoretical work on the structures, conformational energies, intermolecular interactions, and electronic properties of PBO and PBT chains, including the protonated forms known to exist in strong acids. The emphasis is on how such studies provide a molecular understanding of the unusual properties and processing characteristics of this new class of materials.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760240309
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  • 16
    Electronic Resource
    Electronic Resource
    Experimental and theoretical estimations of surface tensions for commercial liquid crystalline polymers, Vectra™ A-950, B-950 and Xydar™ SRT-900 (1998)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 199 (1998), S. 1013-1017 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: By using the Lifshitz-Van der Waals-Acid-Base theory, we have determined the surface tensions (γs) of three commercially available liquid crystalline polymers (LCPs) from the measurement of contact angles on thin films. The values obtained are 43.1, 41.1 and 41.5 mJ/m2 (dyn/cm) for Vectra™ A-950, Vectra™ B-950 and Xydar™ SRT-900, respectively. Experimental data suggest that all the three LCPs are monopolar. The strength of Lewis base (tendency to donate a pair of electrons for the formation of a covalent bond) for these three LCPs is as follows: Vectra™ B-950 〉 Xydar™ SRT-900 〉 Vectra™ A-950. We also theoretically estimated γs from both parachor (Ps) and cohesive energy (Ecoh) utilizing the concept of molecular group contribution. It was found that γs's calculated from Hoftyzer & Van Krevelen and Hayes' Ecoh values are close to our experimental results obtained from contact angle measurements. This is especially true for Xydar™ SRT-900 LCP, where γs obtained from contact angle measurements is 41.5 mJ/m2, while from Hoftyzer and Van Krevelen, and Hayes it is 42.4 and 41.8 mJ/m2, respectively. However, more adequate group contributions for naphthalene and amide groups are urgently needed.
    Additional Material: 5 Tab.
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  • 17
    Electronic Resource
    Electronic Resource
    Synthesis, characterization, and processing of aromatic copolyesters with different monomer sequences (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 53 (1994), S. 609-620 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    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: Two aromatic copoyester compositions were prepared from p-hydroxybenzoic acid, hydroquinone, and isophthalic acid with compositions 2 : 1 : 1 (HIQ50) and 1 : 1 : 1 (HIQ33). For each of these compositions, one random copolyester and one known sequence copolymer was prepared. The random compositions were prepared by melt condensation, whereas controlled sequence polymers were prepared by low-temperature solution polymerization. For the 1 : 1 : 1 composition, the controlled sequence polymer had higher crystallinity than that of the random, whereas the 2 : 1 : 1 composition random copolymer had higher crystallinity. The difference in crystallinity is attributed to the sequence distributions in the copolymers. All compositions were thermotropic in nature. © 1994 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1994.070530512
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  • 18
    Electronic Resource
    Electronic Resource
    Contribution à l'étude de l'ionisation des films insolubles de polyélectrolytes stéréoréguliers (1970)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 817-832 
    Details
    ISSN: 0449-2978
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The surface potentials of monolayers of poly(methacrylic acid) (PMA) have been studied as a function of the pH of the subsolution. The influence of the macromolecular configuration on the properties of the ionizable groups was more particularly investigated. Orientation of molecules in the monolayer may be imposed by the stereoregularity of PMA (isotactic, atactic) and by the nature of the interface (air-water, cyclohexane-water). The results are analyzed in terms of theories of the ionic double layer (Gouy model, Donnan equilibrium) which permit the determination of the degree of ionization α of the film. The value of α gives indications about the orientation of specific groups of the macromolecular chain, i.e., of the ionized monomer units. Indeed, at the air-water interface, the film of isotactic PMA is more acid than that of the atactic sample, and at the cyclohexane-water interface, the degree of ionization is greater than at the air-water interface. These properties are the consequence of a modification of orientation of the hydrophilic groups with respect to the aqueous phase as a function of the stereoregularity of the sample and the nature of the interface. The variation of α with the pH of the substrate phase may be used to calculate an intrinsic dissociation constant Ks° of the molecules in the film. The value of Ks° is not modified by spreading conditions and remains very similar to that obtained in solution.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1970.160080601
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  • 19
    Electronic Resource
    Electronic Resource
    Extraplacental human fetal tissues express mRNA transcripts encoding the human chrorionic gonadotropin-β subunit protein (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Molecular Reproduction and Development 33 (1992), S. 1-6 
    Details
    ISSN: 1040-452X
    Keywords: Fetal gene expression ; hCG-β ; Polymerase chain reaction ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: The glycoprotein hormone human chorionic gonadotropin (hCG) is synthesized in large quantities by the developing placenta, reaching peak concentrations in maternal blood during the late first trimester and early midtrimester of pregnancey. In general it is believed that the β-subunit of this dimeric hormone is expressed in pituitary gonadotropes, thyrotropes, and trophoblasts, while the β-subunit is expressed exclusively by trophoblasts. Studies from our laboratory and other laboratories have shown that some midtrimester human fetal tissues, in addition to the placenta, can synthesize proteins that appear to be very similar to the β-subunit of hCG. To define precisely the nature of this putative hCG-β-subunit in extraplacental fetal tissues, we have examined the mRNA from a variety of human fetal and adult tissues using nucleic acid hybridization and reverse transcription-polymerase chain reaction (PCR) methods. Our results demonstrate that midtrimester fetal kidney and adrenal tissues contain hCG-β mRNA transcripts at concentrations comparable to that of placenta, while fetal lung, brain, muscle, and adult adrenal contain only trace to undetectable levels of hCG-β mRNA. By restriction endonuclease mapping of PCR fragments from fetal tissue cDNAs, we show that the hCG-β transcript expressed in midtrimester human fetal organs is a bone fide copy of hCG-β gene No. 5 of the β-subunit gene family located on chromosome 19. © 1992 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrd.1080330102
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  • 20
    Electronic Resource
    Electronic Resource
    Properties of blends containing two liquid crystalline polymers (1991)
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 2 (1991), S. 25-30 
    Details
    ISSN: 1042-7147
    Keywords: Blends ; Liquid crystalline polymers ; Thermal analysis ; Orientation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Blends containing two, wholly aromatic, naphthalene-based liquid crystalline polymers (LCPs) are studied. Experimental results show that the viscosities of the resulting blends are lower than the parent LCPs over the entire shear-rate range investigated. The orientation development following capillary flow demonstrates, that over a defined blend composition range, some blends have higher orientability than the constituent polymers. This is further manifested in the tensile and flexural properties of injection-molded specimens. A detailed analysis indicates that in the composition range where synergistic effects are observed in orientation development as well as in mechanical properties, only one glass transition temperature is detected. This suggests that “miscibility” is desirable for obtaining maximum properties in these blend systems.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pat.1991.220020104
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