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  • 1985-1989  (9)
  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 3490-3497 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This paper reports results of an experiment involving two-laser resonance-enhanced photoionization of benzene. The excitation sources were two frequency-doubled dye lasers. The first laser pumped the molecule to a selected vibronic level of its first excited singlet state (1B2u), from where it was ionized by a time-delayed pulse of the second laser. The ion yield depends on the intermediate vibronic state as well as on the wavelength of the ionizing laser. From the structures and intensities of the measured ion spectra we derived vibrational frequencies and molecular parameters of the ground electronic state of the ion to a remarkable accuracy. The contributions of autoionizing Rydberg levels to the ionization cross section can clearly be distinguished from direct ionization. Several resonance peaks were assigned to transitions to vibrational modes within these Rydberg states.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 4066-4068 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the first Ga0.47In0.53As-InP photodetectors fabricated on silicon substrates, using the low-pressure metalorganic chemical vapor deposition growth technique. Quantum efficiencies of 0.34, 0.88, and 0.92, A/W at wavelengths of 0.8, 1.3, and 1.55 μm, respectively, have been obtained for the devices without antireflection coating. A reverse leakage current of 100 μA at −10 V bias was measured for 250-μm-diam diodes.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 2389-2390 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the first successful room-temperature cw operations of a Ga0.25 In0.75 As0.5 P0.5 -InP buried ridge structure laser emitting at 1.3 μm grown by two-step low-pressure metalorganic chemical vapor deposition on a silicon substrate. An output power of 20 mW with an external quantum efficiency of 16% at room temperature has been obtained. A threshold current as low as 45 mA under cw operation at room temperature has been measured. The first cw aging test at room temperature, at 2 mW during 5 h, shows a very low degradation (ΔI/I≤5%).
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 1101-1103 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin films (less than 1000 nm) of heteroepitaxial GaAs on Si were grown by organometallic vapor phase epitaxy with the intent of comparing the initial stages of growth with the authors' previous experience in examining films grown by molecular beam epitaxy (MBE). The films were found to be epitaxial after 10 nm of growth at 425 °C, and to uniformly cover the substrate completely, unlike the asymmetrical island nature of MBE films grown under comparable conditions. The relaxation of strain was found to be quite similar to the MBE case.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 52 (1988), S. 1114-1115 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low-threshold double-heterostructure ridge-waveguide lasers have been fabricated in GaAs/AlGaAs layers grown on Si by organometallic vapor phase epitaxy. The pulsed threshold current of the best ridge-waveguide laser is 50 mA, with differential quantum efficiency of about 9% per facet. Broad-area lasers fabricated on the same wafer have pulsed threshold current densities as low as 300 A/cm2 .
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Advances in contraception 2 (1986), S. 193-204 
    ISSN: 1573-7195
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Resumé Les dépôts superficiels présentés par des stérilets en acier inoxydable retirés de l'utérus après une durée d'insertion variable ont été examinés au microscope électronique á balayage, et par analyse de rayons X en dispersion d'énergie, spectroscopie électronique d'Auger, spectroscopie des photoélectrons de rayons X, microscopie électronique à transmission et spectrophotométrie d'absorption atomique pour analyse micro-quantitative. Les résultats ont été comparés avec ceux obtenus avec les DIU au cuivre (TCu200) par les mêmes méthodes. Alors que les fils métalliques des DIU en acier inoxydable portés pendant 5 ans ne se sont pas modifiés de manière significative, les fils de cuivre présentaient différents degrés d'érosion après le même laps de temps. L'analyse montrait clairement des incrustations sur les fils métalliques des deux types de DIU. Les dépôts ont commencé sur les DIU au cuivre plus tôt que sur les DIU en acier inoxydable (respectivement, 27 jours et 3 mois après l'insertion). Ce processus a débuté après un laps de temps plus court que ne l'indiquaient les publications faites à cet égard. La quantité de dépôts a augmenté en fonction de la durée de l'insertion, mais on a pu constater d'importantes variations individuelles. L'analyse microscopique mentionnée ci-dessus a permis de montrer que le principal composant des dépôts sur les deux types de DIU était le calcium, présent sous sa forme cristallisée: le carbonate de calcium. Les substances liées aux cristaux de carbonate de calcium étaient très semblables aux composés organiques azotés. Nous pensons que le mécanisme régulant la formation de dépôts est semblable à celui des calculs. Cet article expose brièvement l'incidence de ces dépôts sur les complications d'une insertion de DIU-saignements utérins et grossesse accidentelle, question qui demande à être approfondie
    Abstract: Sumario Depósitos en la superficie de acero inoxidable en aparatos anticonceptivos extraídos del útero después de diferentes períodos de haber sido insertados, fueron examinados y analizados por medio de microscopía electrónica de barrido, de análisis de dispersión de energía de rayos X (XEDA), espectroscopía electrónica de Augar (AES), espectroscopía fotoelectrónica de rayos X (XPS), microscopía electrónica de transmisión y espectrofotometría atómica absortiva, a los efectos de análisis cuantitativo. Los datos obtenidos fueron comparados con aquellos pertenecientes a los DIU con cobre (TCu200) obtenidos por los mismos métodos. Las espirales de alambre de los DIU de acero inoxidable que permanecieronin situ durante 5 años no mostraron cambios evidentes pero las espirales de alambre de cobre mostraron diversos grados de erosión después del mismo período de tiempo. El análisis mostró claramente que las espirales de alambre en ambos tipos de DIU estaban incrustadas con depósitos. Los depósitos empezaron antes en los DIU con cobre que en los DIU de acero inoxidable (27 días y 3 meses respectivamente, después de la inserción). Este proceso empezó más temprano que lo que se había informado previamente en la literatura. La cantidad de depósitos aumentó con la duración de la inserción pero hubo grandes variantes individuales. Mediante el antes mencionado microanálisis, se encontró que el principal componente en los depósitos en ambos tipos de DIU era calcio que se presentaba en forma de carbonato de calcio. Las substancias adheridas a los cristales eran similares a las de compuestos de nitrógeno orgánico. Sugerimos que el mecanismo regulador de la formación de depósitos puede ser similar a la de los cálculos. La influencia de estos depósitos en complicaciones relacionadas con inserciones de DIU, tales como sangrado uterino y embarazo accidental, se discute brevemente en este artículo. El tema deberá ser estudiado en mayor detalle.
    Notes: Abstract Surface deposits on stainless steel contraceptive devices removed from the uterus after varying periods of insertion were examined and analyzed by means of scanning electron microscopy (SEM), X-ray energy dispersive analysis (XEDA), Augar electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and atomic absorption spectrophotometry for microquantitative analysis. The data obtained were compared with the data for copper-bearing IUDs (TCu200) obtained by the same method. The wire coils of stainless steel IUDs which had beenin situ for 5 years showed no obvious changes, but copper wire coils showed varying degrees of erosion after the same period of time. Analysis clearly showed that the wire coils of both types of IUD were encrusted with deposits. Deposition began earlier on copper-bearing IUDs than on stainless steel IUDs (27 days and 3 months after insertion, respectively). This process began earlier than has previously been reported in the literature. The amount of deposit increased with duration of insertion, but there were large individual variations. The microanalysis showed that the principal component of the deposit on both types of IUD was calcium, which was present in the crystal form of calcium carbonate. The substances attaching to the crystals were similar to the nitrogenous organic compounds. We suggest that the mechanism regulating the deposited formation may be similar to that of calculus. The influence of these deposits on complications relating to IUD insertion, such as uterine bleeding and accidental pregnancy, is briefly discussed in this article. The subject should be studied in greater detail.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 7 (1986), S. 239-249 
    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: A series of differential scanning calorimetry (DSC) and molding experiments were carried out to measure the effect of curing agents, namely initiators and inhibitor, on the SMC reaction. Results showed that the induction time, the reaction rate, and the limiting conversion of sheet molding compounds can be modified through the change of curing agents. The SMC resin with a higher concentration of low temperature initiator and molded at higher temperature may cure in a shorter period of time and reach a higher conversion. The shortened scorch time and shelf life can be balanced by adding small amount of inhibitor. Surface quality of molded SMC parts measured by solvent extraction process showed that limiting conversion is an important factor in SMC molding.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 7 (1986), S. 250-260 
    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: A mechanistic kinetic and heat transfer model is used to describe the cure of sheet molding compounds (SMC). Kinetic parameters such as rate constant of initiator decomposition and rate constant of propagation are estimated from the induction time and the time to reach the peak exotherm of isothermal reaction curves measured by the differential scanning calorimetry (DSC). Temperature and conversion profiles inside plate sections of SMC parts during molding are measured. The predicted results compare well with the experimental data except the limiting conversion. A set of predictive parameters are proposed from this model as guidelines for the optimal molding of SMC. Several moldability diagrams are also constructed which can be easily used to design the optimum SMC recipe for a given processing condition.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 33 (1987), S. 1315-1341 
    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: This paper is concerned with applications of a kinetic-diffusion model which accounts for the gel effect and glass effect for free radical polymerizations under nonisothermal conditions. Bulk polymerizations of styrene and unsaturated polyester in the batch casting process were investigated both experimentally and theoretically. A differential scanning calorimeter (DSC) and a Fourier transform infrared spectrometer (FTIR) were employed to elucidate incomplete reactions resulting from glass transition and dead-ending phenomena and to provide kinetic information for modelling. Temperature, conversion, and cumulative molecular weight profiles were simulated under several wall temperature programs. Predictions of ultimate cumulative molecular weights across the reactor, when compared with experimental results measured by gel permeation chromatography (GPC), affirmed that the molecular weight variation due to the radial temperature gradient could be alleviated by manipulating the wall temperature.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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