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  • Articles  (76)
  • Chemistry  (76)
  • Condensed Matter: Electronic Properties, etc.
  • 1990-1994  (74)
  • 1870-1879  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Syntheses of the First Selenium-Containing Bicyclic β -Lactams as Potent Antimicrobial Agents (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1037-1045 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Syntheses of the cis-configurated isodethiaselenapenam 5 (Scheme 1) as well as the isodethiaselenacephems 29 and 31 (Scheme 2) were accomplished, in which the key step involved addition of Se to the corresponding carbanions of 1, 25, and 27 followed by internal alkylation. β-Lactams 29 and 31 were found to possess biological activity against several pathogenic microorganisms in vitro. The electronic activation of the lactam moiety in the isodethiaselenacephem 31 and the corresponding isocephem 33 remarkably enhanced their biological activity. Isodethiaselenacephem 31 was more toxic than isocephem 33 in experimental animals.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770416
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  • 2
    Electronic Resource
    Electronic Resource
    Efficient Synthesis of Methyl 2-(tert-Butyl)acrylate and Analogous Esters (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1480-1484 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The title products are prepared via an efficient three-step synthesis which involves hydroalumination of methyl propiolate and Lewis-acid-promoted reaction with acetone in the presence of BF3 followed by two highly selective SN2′ reactions. The key step is the reaction of 2-(chloromethyl)acrylates with R2CuLi/ZnCl2 reagents which takes place with complete allylic rearrangement.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770603
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  • 3
    Electronic Resource
    Electronic Resource
    Effects of Non-planarity in the Radical Anions of Tribenzo[a,c,e]cyclooctenesDedicated to Prof. Edgar Heilbronner on the occasion of his 70th birthday (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 644-653 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reduction of tribenzo[a,c,e]cyclooctene (2) and its 2,3- and 1,4-dimethyl derivatives (4 and 5), as well as of 1,1-dimethyl-10,11-propane-2,2-diylidene-1H-benzo[5,6]cycloocta[1,2,3,4-def]fluorene (6) and its 5,6-didehydro derivative (7) was followed by cyclic voltammetry. The radical anions of these compounds and those of their derivatives (D)2, (D)5, and (D)6, deuteratsd at C(9) in 1 and 5 or in the corresponding position of 6, have been characterized with the use of ESR, ENDOR, and TRIPLE-resonance spectroscopy. The cyclic-voltammetric and proton-hyperfine data are consistent with the increasing deviations of the radical anions from planarity in the order These deviations, due to steric or interferences in the peri-positions 1↔14 and 4↔5, are removed in and by the introduction of bridging groups. The non-plalarity affects the thermodynamic and kinetic stabilities of the radical anions and causes a shift in the π-spin distribution away from that benzene ring which is linked to the two others by the essential single bonds C(4a)—C(4b) and C(14a)—C(14b). This finding suggests that the steric hindrance in , and is alleviated by twisting this ring out of coplanarity with the remaining (Z)-stilbene-like π-system.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19910740321
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  • 4
    Electronic Resource
    Electronic Resource
    Non-Newtonian and isothermal analysis of flow of poly(methyl methacrylate) in a model twin screw extruder. Part I (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 986-994 
    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 flow analysis network (FAN) method was modified to analyze the flow of poly(methyl methacrylate) (PMMA) in a model counter-rotating nonintermeshing screw extruder. The numerical prediction of the pressure profiles was compared with the experimental results. Flow patterns in the screw elements of the model counter-rotating nonintermeshing twin screw extruder were also predicted. A new flow path method was developed to calculate the residence time distribution. This result will be applied to analyze the flow during the reaction in the model twin screw extruder.
    Additional Material: 21 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760341207
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  • 5
    Electronic Resource
    Electronic Resource
    Conformational changes of amorphous poly(ethylene terephthalate) films during uniaxial stretching (1991)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 301-307 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Rapid scanning Fourier transform infra-red spectroscopy was used to follow the changes in the population of trans conformers and in the infra-red dichroic functions of the bands characterizing the trans (T) and gauche (G) conformers and the chains in the amorphous regions during stretching of a solution-cast amorphous poly(ethylene terephthalate) (PET) film A in the glassy state (67°C) and in the rubbery state (88°C). Stretching at 67°C showed a yield stress peak followed by strain softening in the stress-strain curve. The population of trans conformers in the amorphous and crystalline regions, Ta + Tc, decreased in the pre-yielding region and then increased continuously after yielding. The T conformers formed during post-yield stretching showed high orientation, while the G conformers remained in low degree of orientation. Stretching at 88°C showed no pronounced yield stress peak in the stress-strain curve, and the population of T conformers did not change until the beginning strain-induced crystallization. A solvent-cast PET film annealed at 67°C for 24 h, the film N, showed a sharp and high yield stress peak in the stress-strain curve, and strain-induced crystallization occurred at lower draw ratio as compared to the film A. The film A showed a non-equilibrium high population of Ta conformers, part of which reverted to G conformers during sub-Tg annealing.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1991.021920212
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  • 6
    Electronic Resource
    Electronic Resource
    Robust principal component analysis by projection pursuit (1993)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 7 (1993), S. 527-541 
    Details
    ISSN: 0886-9383
    Keywords: Principal component analysis ; Projection pursuit ; Simulated annealing algorithm ; Robust statistics ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Principal component analysis (PCA) is a widely used technique in chemometrics. The classical PCA method is, unfortunately, non-robust, since the variance is adopted as the objective function. In this paper, projection pursuit (PP) is used to carry out PCA with a criterion which is more robust than the variance. In addition, the generalized simulated annealing (GSA) algorithm is introduced as an optimization procedure in the process of PP calculation to guarantee the global optimum. The results for simulated data sets show that PCA via PP is resistant to the deviation of the error distribution from the normal one. The method is especially recommended for use in cases with possible outlier(s) existing in the data.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180070606
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  • 7
    Electronic Resource
    Electronic Resource
    Epoxy modified polyurethane rigid foams (1991)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 29 (1991), S. 1083-1088 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rigid IPN foams were prepared by sequential polymerization of polyurethane and epoxy systems. Significantly higher compressive modulus and strength were observed with the IPN foams in comparison to the corresponding polyurethane rigid foams. The IPN foams show one glass transition temperature. The single Tg indicates the very small domain size in the PU-epoxy IPN's.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1991.080290801
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  • 8
    Electronic Resource
    Electronic Resource
    Thermogravimetric analysis of poly(alkyl methacrylates) and poly(methylmethacrylate-g-dimethyl siloxane) graft copolymers (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1747-1753 
    Details
    ISSN: 0887-624X
    Keywords: poly(methyl methacrylate) ; polydimethylsiloxane ; thermogravimetric analysis (TGA) ; graft copolymers ; poly(alkyl methacrylates) ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal stabilities of various poly(alkyl methacrylate) homopolymers and poly(methyl methacrylate-g-dimethyl siloxane) (PMMA-g-PSX) graft copolymers have been determined by thermogravimetric analysis (TGA). As expected, the thermal stabilities of poly(alkyl methacrylates) were a function of the ester alkyl group, and polymerization mechanism. In particular, thermally labile linkages, which result from termination during free radical or nonliving polymerization mechanisms, decrease the ultimate thermal stabilities of the polymers. However, graft copolymers, which were prepared by the macromonomer technique with free radical initiators, exhibited enhanced thermal stability compared to homopolymer controls. A more complex free radical polymerization mechanism for the macromonomer modified polymerization may account for this result. © 1994 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080320917
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  • 9
    Electronic Resource
    Electronic Resource
    Hindered lithium dialkylamide initiators for the living anionic polymerization of methacrylic esters (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 2425-2430 
    Details
    ISSN: 0887-624X
    Keywords: anionic ; polymerization ; living ; methyl methacrylate ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Lithium diisopropylamide is an efficient initiator for the anionic polymerization of methyl methacrylate in polar solvents at -78°C. Predictable molecular weights based on the initiator concentration were obtained, yields were quantitative, and molecular weight distributions were relatively narrow (〈1.30). The presence of an amino end group and confirmation of the initiation mechanism were confirmed by potentiometric titration using HClO4. Number-average molecular weights determined by titration agreed well with values determined by SEC. Other lithium dialkylamides that contain larger alkyl groups such as lithium diisobutylamide were less efficient initiators. This was attributed to the more nucleophilic anion due to less steric hindrance near the nitrogen atom. Molecular weight distributions were significantly broadened (〉2.0), and molecular weight control was not achieved. However, polymer yields were quantitative. In all cases, PMMA stereochemistry was indicative of a solvent-separated lithium counterion, and triad compositions were identical to organolithium initiated homopolymers, i.e., 78% syndiotactic, 20% heterotactic, and 2% isotactic. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321303
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  • 10
    Electronic Resource
    Electronic Resource
    Nonlinear wave theory for dynamics of binary distillation columns (1991)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 705-723 
    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: A major difficulty in control of distillation columns stems from their nonlinear behavior, especially of columns producing high-purity products. Based on a previous development that adapted fixed-bed theories to simple countercurrent processes, this study has established a nonlinear wave theory for the nonlinear and distributed dynamics of binary distillation columns by including the effects of reflux, reboil, and combination of sections. This theory clearly elucidates the intriguing dynamic behavior of distillation columns such as high steady-state gains, large response lags, strong dependence of dynamics on the magnitudes and directions of disturbances, and asymmetric dynamics of the transitions between two steady states. It also underlines the inadequacy of conventional linearized models for high-purity columns. With fairly simple mathematics, this nonlinear wave approach may be useful for model development, control system design, dual-composition control, and feedforward control.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690370509
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