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  • 1
    Electronic Resource
    Electronic Resource
    Simultaneous dielectric spectroscopy and calorimetry of the dynamics during a macromolecules growth (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 1443-1448 
    Details
    ISSN: 0392-6737
    Keywords: Glass transitions ; Calorimetry ; Dielectric loss and relaxation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary A method and an instrument has been developed for measuring almost simultaneously and continuously in time three different quantities: i) the heat evolved during the course of exothermic reactions, ii) the heat capacity and iii) the dielectric spectra of a liquid or solid sample. By using this instrument, we have studied the decrease in the d.c. conductivity and the increase in the relaxation time as molecules in an isothermally kept liquid chemically react to produce, irreversibly, a macromolecular structure until the liquid vitrifies and becomes rigid. The number of covalent bonds formed in the structure,n, has been calculated and the dielectric relaxation time, τ, is related ton. This τ increases progressively more rapidly withn, and decreases, of course, on increasing the temperature. A compensation between these two effects determines the dynamic behaviour observed during rate heating. The effect of temperature is found to predominate. Such observations have been made possible by means of the new instrument.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02453785
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  • 2
    Electronic Resource
    Electronic Resource
    A calorimeter for the electrolytic cell and other open systems (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 1333-1346 
    Details
    ISSN: 0392-6737
    Keywords: Energy-conversion spectro-analytical methods (e.g., photoacoustic, photothermal, and optogalvanic spectroscopic methods) ; Calorimetry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We present here a calorimetric method and the construction details of a differential calorimeter useful for studying the reactions in an electrolytic cell and more generally slow chemico-physical processes occurring in thermodynamically open systems. The method allows measurements of the heat balance of the cell, from which the enthalpy change of the process under investigation can be calculated. The theoretical description of the calorimetric cell and the results of several studies planned to describe the performances of the instrument up to the boiling point of the electrolytic solution are reported. The features of this calorimeter fulfil most of the requirements of ≪col fusion≫ experiments, where the heat production is the fundamental and controversial aspect. By controlling both the heat and the matter exchanged, the calorimeter can be utilised also to study bioenergetic processes,e.g. fermentation, microbial metabolism and biodegradation, and liquid phase chemical reactions, involving gases as reactants and/or products.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02453267
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  • 3
    Electronic Resource
    Electronic Resource
    Water↔ice transformation in micron-size droplets in emulsions (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3115-3120 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: To investigate the crystallization and melting behaviors of micron-size droplets in a water-emulsion, the heat capacity, Cp, has been studied by adiabatic calorimetry over the 233–273 K range. Water droplets in the emulsions began to crystallize at ca. 243 K, but the crystallization rate was slow. This was caused partly by the relatively slow coalescence of crystallized and uncrystallized droplets at that temperature, in a highly nonNewtonian viscous media of the emulsion. Crystallization occurred rapidly on heating and remained incomplete even when it occurred at 260 K. Thus a substantial amount of water droplets coexisted with ice droplets in the emulsion. The onset of crystallization shifted to lower T and the number of water droplets in the emulsion at a given T decreased as the droplets grew on thermally cycling the emulsion. Cp of emulsion increased progressively more rapidly as 273 K was approached, which is attributable to premelting of the ice droplets beginning at 260 K. Analysis of the Cp data showed that interaction between the droplets and the surfactant in the emulsion changes on crystallization. This is attributable to the decrease in the entropy at the surfactant–water interface. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479592
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  • 4
    Electronic Resource
    Electronic Resource
    Hepatitis B Virus Immunopathogenesis (1995)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Immunology 13 (1995), S. 29-60 
    Details
    ISSN: 0732-0582
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.iy.13.040195.000333
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  • 5
    Electronic Resource
    Electronic Resource
    Dopant-induced lattice dilation in n-type InP homoepitaxial layers (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6890-6894 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: n-type Si- and Sn-doped InP homoepitaxial layers have been grown on (001) Fe-doped semi-insulating InP substrates by metal organic vapor phase epitaxy and liquid phase epitaxy, respectively. The net carrier concentration has been determined by conventional Hall measurements, while the total dopant concentration has been evaluated by secondary ion mass spectrometry. The change in lattice constant has been carefully measured by x-ray double crystal diffractometry as a function of the dopant concentration. A lattice dilation has been observed for both dopants, but the Sn doping has been found to be about eight times less effective than the Si doping. The results could not be explained by Vegard's law. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361512
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  • 6
    Electronic Resource
    Electronic Resource
    Hydrogen determination in Si-rich oxide thin films (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 109-114 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Quantitative in-depth distribution of the elements contained in silicon-rich oxide thin films deposited on single-crystal silicon by low temperature plasma-assisted deposition has been performed by a combination of various MeV ion beam techniques. The quantity of oxygen and nitrogen has been measured by nuclear reactions, the silicon content has been determined by Rutherford backscattering, and elastic recoil detection was used for hydrogen. All the samples contain not only Si and O, but also N and H, which are residuals from the reactions involved in the deposition process. We did find that the MeV beam used in the nuclear techniques can induce a process of hydrogen desorption, which causes the measured H content to be a function of the He dose received by the sample. This phenomenon, not previously reported, must be taken into account to give the correct H content. The study of the kinetics of the He-induced hydrogen desorption has been used to correct the experimental data and to determine the original hydrogen content. The correction factor is in most of the cases close to 2 and outside any experimental error. Moreover the studies of the kinetics give information on the kinds of hydrogen complexes contained in the films. The results suggest that, on the basis of the strength of the binding energies, hydrogen is present in at least two different configurations, weakly and strongly bonded. In the first configuration hydrogen is easily desorbed either under the action of the ion beam or of the heat treatment at 600 °C, in the second, hydrogen is lost only after treatment at 900 °C. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362766
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  • 7
    Electronic Resource
    Electronic Resource
    Recalling the Vth Volta Congress: High Speeds in Aviation (1996)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Fluid Mechanics 28 (1996), S. 1-9 
    Details
    ISSN: 0066-4189
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.fl.28.010196.000245
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  • 8
    Electronic Resource
    Electronic Resource
    Reversal in the dielectric relaxation time during polymerization: Thermal energy compensation on macromolecular growth (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 10599-10605 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The increase in the dielectric relaxation time τ0 and in the number of covalent bonds n formed during polymerization of an equimolar mixture of cyclohexylamine and a diepoxide have been studies in real time, in two experiments: (i) under isothermal conditions when the dielectric spectrum monotonically shifts to the low-frequency side and the configuration entropy decreases and (ii) on heating the polymerizing liquid at a fixed rate when the spectrum initially shifts to the low-frequency side, reverses direction at a certain temperature, and shifts towards the high-frequency side. This reversal in τ0 occurs when an increase in thermal energy begins to dominate the effects of increase in n. Consequences of the two competitive effects on the measured dielectric behavior have been discussed and relations between the change in configurational entropy, and τ0 of the ultimately formed linear chain polymer, are discussed. It is shown mathematically that for a fixed τ0 and a configurational entropy, there are an infinite number of combinations of temperature and n, some of which may be explored by altering the temperature–time profile during the macromolecular growth. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478991
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  • 9
    Electronic Resource
    Electronic Resource
    Optical study of strained and relaxed epitaxial InxGa1−xAs on GaAs (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 6745-6751 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoreflectance (PR) at different temperatures and spectroellipsometry (SE) at room temperature were used to study, in a systematic and complementary way, the optical response of a series of strained and relaxed InxGa1−xAs (x〈0.15) epilayers. All the samples were grown by molecular-beam epitaxy on GaAs, both with and without a GaAs cap layer, which in the thinnest samples determines a single-quantum-well configuration. The effects of the strain on the optical structures E0, E1, and E1+Δ1 observed in the 1.2–3.3 eV photon-energy range were analyzed by fitting standard critical points (CP) line shapes to the PR and SE spectra. The CP experimental energies versus x were compared with the relations obtained in the framework of the elastic strain theory and, in the quantum-well structures, of the envelope-function scheme. The excellent agreement between experiment and theory allowed us to determine, independently and only by optical techniques, the strain ε and the composition x values, which compare well with those measured by x-ray diffraction. Additional information concerning the critical thickness for the pseudomorphic growth and the residual strain in quasirelaxed layers was achieved. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360498
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  • 10
    Electronic Resource
    Electronic Resource
    Observation of 〈100〉 misfit dislocations in In0.06Ga0.94As/GaAs heterostructure by synchrotron radiation topography (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 1446-1449 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 〈100〉 oriented misfit dislocations in In0.06Ga0.94As/GaAs heterostructures with relatively low misfit f (f=0.0043) have been observed by synchrotron radiation topography. InGaAs samples consist of 2500, 4000, and 6500 A(ring) thick In0.06Ga0.94As layers grown by molecular beam epitaxy at 580 °C. All the topographs were taken by synchrotron radiation double crystal topography. The panchromatic cathodoluminescence complementary technique in the scanning electron microscope was also applied. Misfit dislocations lying along both 〈100〉 and 〈110〉 directions have been observed. The dislocations parallel to 〈100〉 directions have much lower density and extension in length than those aligned along the 〈110〉 directions. The climb mechanism of the generation of dislocations, probably due to the high density of point defects during the high temperature growth, is discussed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363012
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