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  • American Physical Society (APS)  (45)
  • Springer  (25)
  • American Institute of Physics (AIP)  (10)
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  • 1
    Electronic Resource
    Electronic Resource
    On the size-dependence of the static self-energy in propagator calculations (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 3578-3588 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Various approximations are used currently to evaluate the static part Σ(∞) of the self-energy or optical potential in molecular Green's function calculations. Since its expansion is ruled out by the linked-cluster theorem, one generally assumes a size-intensive behavior of Σ(∞) in the thermodynamic limit of an infinite system. A detailed analysis of this size-dependence property is conducted using the formulation of crystalline orbitals (CO) for stereoregular polymers. In spite of the linked-cluster theorem, this study provides evidence for a logarithmic divergence with respect to the size of a chain for some forms of Σ(∞), computed with common approximation schemes. This is the direct outcome of the long-range character of the Coulombic interaction and can be related to a violation in the number of particles within the system. A proper size-intensive behavior implies an exact cancellation of the logarithmically divergent behavior of antigraphs. The conclusions drawn from CO analysis are confirmed by numerical tests on model oligomer systems. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470241
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  • 2
    Electronic Resource
    Electronic Resource
    Time-dependent photodissociation of methyl iodide with five active modes (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 5623-5646 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Advances in the time propagation of multidimensional wave packets are exploited to present the A-band photodissociation dynamics of methyl iodide for five active vibrational modes on the three relevant excited ab initio potential surfaces. The five modes considered represent all of the experimentally observed dynamical activity. The only modes neglected are the asymmetric C–H stretch and the asymmetric deformation of the methyl group. The kinetic energy operator corresponding to these five degrees of freedom is derived. The fully quantum mechanical calculation was implemented upon grids using 2880 distinct time-dependent configurations, determined by the multiconfigurational time-dependent Hartree algorithm, for each electronic state. All of the currently known experimental results regarding the umbrella vibration, symmetric C–H stretching vibration, perpendicular rotation, and parallel rotation of the photodissociated methyl radical fragment are well reproduced. The full wavelength dependence of all of these quantities is determined. The wavelength dependence of the energy deposited into translational, vibrational, and rotational motion is also given. The time evolution of the modes is presented in the context of correlated motion and its effect upon the dissociative process. Many of the details of the dynamics inherent to the conically intersecting nature of the excited surfaces is delineated. In particular it is shown that the Jahn–Teller distortion of the 1Q1 state is irrelevant in contributing to the perpendicular character of resonance Raman depolarization ratios. Results are compared and contrasted to previous calculations employing the collinear pseudotriatomic model with optimized empirical surfaces or the bent pseudotriatomic model with the same ab initio surfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467349
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  • 3
    Electronic Resource
    Electronic Resource
    Evidence for a partial breakdown of the molecular orbital picture in the ionization spectra of large saturated hydrocarbons (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 7583-7596 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The x-ray photoionization spectra of large saturated hydrocarbons have been investigated by means of one-particle Green's function calculations. These spectra saturate overall rather quickly to their asymptotic form with increasing system size. The results obtained indicate a severe breakdown of the molecular orbital picture of ionization above a binding energy threshold of about 23 eV, for n-alkane chains ranging from n-propane to n-nonane, or cycloalkane compounds such as cyclobutane, cyclopentane, and cyclohexane. In spite of the fast multiplication of satellite solutions, shake-up lines remain confined above that threshold, as a result of the delocalization properties of one-electron canonical states. The ring closure is shown to emphasize the dispersion of photoionization intensity into satellites. Conformational changes, on the other hand, have only marginal effects on the convoluted correlation bands. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472585
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  • 4
    Electronic Resource
    Electronic Resource
    Electronic decay in weakly bound heteroclusters: Energy transfer versus electron transfer (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 5076-5088 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Inner-valence ionized states of weakly bound systems like van der Waals clusters can efficiently decay by electron emission. The mechanism of the decay, which does not occur in the isolated monomer units constituting the clusters has recently been shown to be of intermolecular/interatomic nature. This intermolecular/interatomic Coulombic decay (ICD) mechanism prevails in many systems ranging from hydrogen-bonded molecular clusters to atomic rare gas clusters. In the present paper we extend our previous studies to weakly bound heteroclusters built up of monomer units of largely differing energetics. It is shown that, as soon as the double ionization potential of a monomer unit is lower in energy than the ionization potential of the initially created inner-valence vacancy on a neighboring monomer unit, an additional electronic decay process can take place. In contrast to the ICD mechanism, which involves an efficient energy transfer between the monomer units, this second process is essentially based on an electron transfer process. It is therefore termed electron-transfer mediated decay (ETMD). We have analyzed the mechanisms of the electronic decay processes taking place following inner-valence ionization in weakly bound heteroclusters in an exemplary study of the NeAr dimer. The involved electronic states have been calculated using ab initio Green's function techniques. The lifetime of the inner-valence Ne(2s−1)Ar vacancy has been estimated and partitioned according to the contributions of the two decay channels based on a perturbation-theoretical description of the decay process. As a result, the lifetime of the inner-valence resonance state is estimated to be of the order of 10–100 fs, the specific value strongly depending on the internuclear separation of the monomers. The ICD process is shown to be by far the dominant decay channel at distances corresponding to bound states of the dimer. With decreasing internuclear separation the ratio of the ETMD and ICD decay widths quickly increases over several orders of magnitude. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1395555
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  • 5
    Electronic Resource
    Electronic Resource
    An efficient combination of computational techniques for investigating electronic resonance states in molecules (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 6853-6861 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Calculating electronic resonance states in molecules is a serious challenge to theory, because the treatment of both the scattering and the many-electron problem is a formidable task. A very promising approach, known as CAP/CI, consists of the combination of a complex absorbing potential with the method of configuration interaction. In this paper we propose the combination of three distinct computational techniques in order to boost the performance of CAP/CI. A complex absorbing potential that can be adjusted flexibly to the geometry of the molecular scattering target is presented and its representation in a Gaussian basis set is discussed. To handle the large-scale complex symmetric eigenvalue problem arising in CAP/CI, a subspace projection method is employed and its validity is shown. We advocate the use of parallel filter diagonalization for calculating the eigenvectors required in the projection step. The proposed techniques are applied to determine the lifetime of an autoionizing, inner-valence excited state of Ne2+. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1405117
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  • 6
    Electronic Resource
    Electronic Resource
    Gastrointestinal transit and digestibility of maltitol, sucrose and sorbitol in rats: A multicompartmental model and recovery study (1992)
    Springer
    Cellular and molecular life sciences 48 (1992), S. 733-740 
    Details
    ISSN: 1420-9071
    Keywords: Linear multicompartmental model ; gastrointestinal tract ; sugar substitutes ; maltitol ; sucrose ; sorbitol ; absorption ; small intestine ; caloric value
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Using data obtained with a dye marker and the gavage technique, the kinetics of gastrointestinal transit of different loads of sugar substitutes (maltitol, sorbitol) and sugar (sucrose) in the rat were analysed using a linear multicompartmental model over a range from the realistic to the non-physiologic high, of carbohydrate intake levels and using only a few experimental time points. The model gave detailed insight into intestinal propulsion and gastrocecal transit time. Rate constants of transport between the compartments investigated were determined; they showed characteristics which could be related to the substance and the dosage administered. Analyses of the gastrointestinal content and calculations of the intestinal net water movement showed that the digestibility and absorption of the disaccharide sugar alcohol, maltitol, in the small gut depended inversely on the dose ingested. For all substances tested, caloric availability in the small intestine was calculated. At a physiological low level of maltitol intake, the results also indicated an insignificant calorie-saving effect in comparison to sucrose, an effect based mainly on the slow absorption rate of the maltitol cleavage product sorbitol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02124290
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  • 7
    Electronic Resource
    Electronic Resource
    The mechanism of biological X-rays action (1964)
    Springer
    Naturwissenschaften 51 (1964), S. 373-376 
    Details
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Notes: Summary X-rays act in living cells by two oxidants, hydrogen peroxide and OH-radicals, that arise by the splitting of water and are measured by the oxidation of iron of the Fricke solution, in our manometric actinometer. The detector of the hydrogen peroxide is the enzyme catalase, added during the irradiation to the cell suspensions. All the oxidant that is not hydrogen peroxide, is the OH-radical. No other substances are produced primarily by the X-rays, because the absorbed energy of the X-rays can be measured quantitatively by the oxidation of the iron of the Fricke solution. The two oxidants, the hydrogen peroxide and the OH-radicals, may oxidize every component of the living cell. But the main substrates are the respiratory enzymes, the fermentation enzymes and the protein synthesizing enzymes—that are the nucleic acids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00637235
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  • 8
    Electronic Resource
    Electronic Resource
    Investigating the sensitivity of the Atmospheric General Circulation Model ECHAM 3 to paleoclimatic boundary conditions (1996)
    Springer
    International journal of earth sciences 85 (1996), S. 513-524 
    Details
    ISSN: 1437-3262
    Keywords: Atmospheric response ; General circulation models ; Glacial maximum ; Milankovitch Theory ; Paleoclimate ; Climate optimum ; Glacial inception
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract We present atmospheric simulations of three different time slices of the late Quaternary using the ECHAM 3 general circulation model in T42 resolution. In this work we describe the results of model runs for the time slices 6000 years BP (last climate optimum), 21 000 BP (last glacial maximum) and 115 000 years BP (glacial inception). Although the solar insolation is known for all time slices, a complete data set of the other boundary conditions which are necessary for running the atmospheric model exists only for the last glacial maximum in the form of the CLIMAP reconstruction. For the other two time slices, which are interglacial states like the modern climate, sea surface temperatures, land albedo and ice sheet topography are kept at modern values and only the solar insolation is changed appropriately. The response of the model to solar insolation changes is quite reasonable. The modelled anomalies are small and roughly opposite in sign for 6000 BP and 115 000 BP, respectively. In the case of last glacial maximum, the glacial ice sheet topography and ice albedo produce a much larger climate anomaly in the model. However, to enable a real test of model performance under glacial boundary conditions, the CLIMAP sea surface temperatures, which are now known to be partly inaccurate, should be replaced by an updated “state-of-the-art” reconstruction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02369006
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  • 9
    Electronic Resource
    Electronic Resource
    Infrarot-Thermographie durch Fenster bei niedrigen Temperaturen (1994)
    Springer
    Heat and mass transfer 29 (1994), S. 219-225 
    Details
    ISSN: 1432-1181
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Abstract Infrared thermography offers itself for non-intrusive measuring of local temperature distributions at internal surfaces of channels and hollow objects. The temperature distribution at an internal surface can only be measured through an IR-transparent window, if the IR-camera is positioned outside. Thermal radiation and reflection by this window may falsify the temperature distribution indicated by the IR-camera, the required correction is analyzed in this paper. For this study the radiation reaching the IR-camera within the detected range of wavelength is considered by a balance of radiative energy fluxes. The assumptions made to evaluate this balance are verified by comparing calculated and measured temperature values and the validity is confirmed. Results show, that linear calibration curves for measurements through a window may be applied with reasonable accuracy in a range of temperature 295 K ≤T o ≤ 365 K of both window and environment. The influence of both temperatures on the calibration curve has been studied by considering the balance of radiative fluxes. In addition, the influences of different angles of view of the IR-camera and of different window orientations are examined.
    Notes: Zusammenfassung Für die Messung lokaler Temperaturverteilunggen an inneren Oberflächen von Kanälen und geschlossenen Hohlkörpern bietet sich die IR-Thermographie als berührungslose Meßtechnik an. Die Temperaturverteilung an einer inneren Oberfläche kann nur durch ein IR-transparentes Fenster in der gegenüberliegenden Wand gemessen werden, wenn die Kamera außerhalb angeordnet ist. Durch Reflexion und Eigenstrahlung dieses Fensters entsteht ein Fehler der von der Kamera angezeigten lokalen Temperaturen, dessen Korrektur hier untersucht wird. Hierzu wird die von der IR-Kamera empfangene Strahlung in dem von der IR-Kamera detektiertem Spektralbereich mittels einer Strahlungsbilanz ermittelt. Der Vergleich mit konventionellen Temperaturmessungen bestätigt die Gültigkeit der für die Berechnung getroffenen Annahmen und gestattet für Temperaturen 295 K ≤T o ≤ 365 K eine Korrektur des Fenstereinflusses mittels einer linearen Gleichung (Kalibrierfunktion). Die Einflüsse variabler Umgebungsund-und/oder Fenstertemperaturen auf die von der Kamera anzuzeigenden Temperatur und damit die Gültigkeit der Kalibrierfunktion bei von der Kalibrierung abweichenden Umgebungsbedingungen werden mit Hilfe der Strahlungsbilanz untersucht. Weiterhin wird auf den Einfluß unterschiedlicher Aufnahmewinkel auf die von der Kamera angezeigte Temperatur bzw. auf die Kalibrierfunktion eingegangen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01539753
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  • 10
    Electronic Resource
    Electronic Resource
    Direct calculation of ionization potentials of closed-shell atoms and molecules (1973)
    Springer
    Theoretical chemistry accounts 31 (1973), S. 239-260 
    Details
    ISSN: 1432-2234
    Keywords: Atomic and molecular structure ; Electronic structure ; Ionization ; Many-body perturbation theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Vertical ionization potentials, electron affinities and information about quasi-particles can be obtained by using the technique of the single-particle propagator. The expansion of the self-energy part up to third order perturbation theory can be evaluated numerically, but does not lead, in most cases, to satisfying results. A theoretical and numerical analysis of the diagrammatic expansion of the self-energy part requires the introduction of a renormalized interaction and renormalized hole and particle lines.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00526514
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