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  • 1
    Electronic Resource
    Electronic Resource
    Influence of the quench rate and the pressure on the glass transition temperature in selenium (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 117 (2002), S. 2814-2818 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report a molecular dynamics investigation of the glass transition temperature in selenium at pressures ranging from 0 to 6 GPa as a function of the quench rate, Qr. For moderate pressures the specific volume of the glass depends strongly on the quench rate, whereas the specific enthalpy varies only little. We find for both volume and energy a linear dependence on the quench-rate-dependent glass transition temperature. The slopes of these curves reflect the different energy scales of void formation, inter- and intrachain interactions. The extrapolated glass transition temperatures for quench rates of order K/s agree with the experimental ones within 20%. Applying a pressure of 1 GPa the glass transition temperature is raised by 37 K. For the same Qr, the transition temperature Tg is much higher for simulations using fixed volume conditions (NVT ensemble) than for the ones using fixed pressure (NPT ensemble) when one compares results for equal pressure at T=0. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1492797
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  • 2
    Electronic Resource
    Electronic Resource
    Vibrational density of states of selenium through the glass transition (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 3236-3242 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present an investigation of the vibrational density of states (VDOS) of selenium calculated using two different methods. First we compute the VDOS from the velocity autocorrelation and study its evolution with the temperature. Secondly we compute it from the dynamical matrix. This latter method leads to imaginary frequencies for finite temperatures. In the literature these frequencies are called unstable and are related to the diffusion and/or the anharmonicity. We investigate the character of these frequencies, asking whether they are localized or extended, more acoustic or optic. We show that, below a temperature-dependent threshold frequency, they are similar to their real low-frequency counterparts. The temperature evolution of the number of these modes changes at the glass transition. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1343074
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  • 3
    Electronic Resource
    Electronic Resource
    Vibrational states of glassy and crystalline orthoterphenyl (2000)
    Springer
    The European physical journal 16 (2000), S. 73-80 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 61.43.Fs Glasses - 63.50.+x Vibrational states in disordered systems - 63.20.-e Phonons in crystal lattice
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: Low-frequency vibrations of glassy and crystalline orthoterphenyl are studied by means of neutron scattering. Phonon dispersions are measured along the main axes of a single crystal, and the corresponding longitudinal and transversal sound velocities are obtained. For glassy and polycrystalline samples, a density of vibrational states is determined and cross-checked against other dynamic observables. In the crystal, low-lying zone-boundary modes lead to an excess over the Debye density of states. In the glass, the boson peak is located at even lower frequencies. With increasing temperature, both glass and crystal show anharmonicity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100510070251
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  • 4
    Electronic Resource
    Electronic Resource
    Pressure Dependence of the Multiphonon Excitations of Superfluid 4He (2000)
    Springer
    Journal of low temperature physics 120 (2000), S. 55-64 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The pressure dependence of the multiphonon excitations in superfluid 4He has been studied, using neutron inelastic scattering. High-resolution measurements have been made at 0,5 K over a wavevector range 0.6〈Q〈2.2 Å−1, at various pressures between 0 and 20 bars. The experimental data are presented and existing theoretical calculations are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004656818842
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  • 5
    Electronic Resource
    Electronic Resource
    219. Das hohe Alter als Operationsrisiko (1987)
    Springer
    Langenbeck's archives of surgery 372 (1987), S. 862-862 
    Details
    ISSN: 1435-2451
    Keywords: Geriatric surgery ; Operative mortality ; Alterschirurgie ; Operationsletalität
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung In einem Fünfjahreszeitraum (1982–1987) wurden 308 Patienten in einem Alter von 85 und mehr Jahren stationär behandelt. Das Durchschnittsalter betrug 88,2±3,0 Jahre; 199 Patienten (64,6%) wurden operiert, 109 (35,4%) wurden konservativ behandelt. Das Patientengut umfasste hauptsächlich Erkrankungen des Bauchraumes, der arteriellen Gefässe und Traumen. Die Gesamtletalität betrug 19,1%. Die Letalität bei Noteingriffen betrug 30,4%, bei elektiven Operationen 13,1%. 66,9% der Patienten hatten Kreatinin-Erhöhungen, 48,5% einen Diabetes mellitus, 35% eine Anämie. Das prognostisch wichtigste Kriterium war der Röntgenbefund von Herz und Lunge. Die wichtigste Massnahme bei der Behandlung derartig alter Patienten ist eine intensive Operationsvorbereitung.
    Notes: Summary From 1982 to 1987, 308 patients between 85 and 103 years (average, 88.2±3 years) were treated onward; 199 patients (64.6%) were operated on; 109 (35.4%) were treated conservatively. The patient group mainly included abdominal, vascular, and traumatological disorders. The overall mortality was 19.1%. The mortality in emergency operations was 30.4% versus 13.1% in elective operations. Of the patients, 66.9% had elevated creatinine levels; 48.5% diabetes mellitus; 35% anemia. The most important prognostic criterium was provided by X-ray films of the heart and lungs. The most important treatment factor is the intensive preparation of the elder patients for the operation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01298003
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  • 6
    Electronic Resource
    Electronic Resource
    Guest-host interaction and photochemical transformation of silver particles isolated in rare gas matrices (1986)
    Springer
    The European physical journal 3 (1986), S. 263-270 
    Details
    ISSN: 1434-6079
    Keywords: 33.20 ; 35.40 ; 53.20P ; 78.30
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Silver dimers and small clusters isolated in rare gas matrices are studied by UV-VIS absorption, emission, and resonance Raman spectroscopy. One, two, and three dimer trapping sites can be identified in Xe, Kr, and Ar matrices, respectively. The sites are identified by computer simulation to be either ofD 4h symmetry, with the molecules aligned in the 〈100〉-direction of thefcc-host lattice, or ofD 2h symmetry, with the molecules occupying single or double vacancies and aligned in the 〈110〉-direction. Low energy external modes of the dimers are observed in the resonance Raman spectra. They probe the guest-host interaction of the molecules and are assigned to librational modes. Trimers and larger clusters are found to be very photosensitive. Three different trimers can be observed in Xe and Kr matrices, respectively. They can be transformed reversibly into each other by laser irradiation. This indicates that probably three corresponding isomers can get stabilized in the two matrices. Further evidence for this interpretation is obtained from emission spectroscopy. Despite the photosensitivity of the trimers it is possible to stabilize the concentration of a particular species by a dual beam technique. Thus we obtained a resonance Raman spectrum of one species in a Xe matrix and a preresonance spectrum of the corresponding species in a Kr matrix.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01384815
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  • 7
    Electronic Resource
    Electronic Resource
    Quantum diffusion of light interstitials (1986)
    Springer
    Hyperfine interactions 31 (1986), S. 141-146 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The diffusion rate of light interstitials is calculated avoiding the usual adiabatic and Condon approximations for the phonons. The method employed is a generalization of the standard small polaron theory taking explicitely account of the strongly coupled interstitial-host vibrations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02401551
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  • 8
    Electronic Resource
    Electronic Resource
    Quantum tunneling of light particles in metals (1986)
    Springer
    Hyperfine interactions 31 (1986), S. 147-152 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The motion of a particle in a metallic crystal is studied for low temperatures where transitions between adjacent interstitial sites are caused by quantum tunneling. The influence of electrons and phonons on the hopping rate is taken into account by means of a functional integral method. The electronic influence may effectively be described by Ohmic damping which dominates the low temperature behavior of the defect motion. When subsequent tunneling transitions are statistically independent, the diffusion constant is found to obey a power law, D∼T2K−1, where K depends on the defect-electron interaction. This power law is limited at low temperatures by the effects of phonon excitations. Near the transition between electron and phonon dominated behavior the diffusion constant has a minimum where the precise temperature dependence of the rate depends not only on phonon spectra but also on the processes limiting phonon lifetimes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02401552
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