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  • Articles  (92)
  • Springer  (91)
  • Nature America Inc.
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  • Articles  (92)
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  • 1
    Electronic Resource
    Electronic Resource
    Defects in TCIRG1 subunit of the vacuolar proton pump are responsible for a subset of human autosomal recessive osteopetrosis (2000)
    [s.l.] : Nature America Inc.
    Nature genetics 25 (2000), S. 343-346 
    Details
    ISSN: 1546-1718
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Osteopetrosis includes a group of inherited diseases in which inadequate bone resorption is caused by osteoclast dysfunction. Although molecular defects have been described for many animal models of osteopetrosis, the gene responsible for most cases of the severe human form of the disease ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/77131
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  • 2
    Electronic Resource
    Electronic Resource
    On the Ps-H2 scattering (1985)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 6 (1985), S. 105-123 
    Details
    ISSN: 0392-6737
    Keywords: Elastic scattering of atoms and molecules ; Inelastic scattering of atoms and molecules
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Si presenta un calcolo perturbativo della sezione d'urto elastica, di prima e seconda eccitazione vibrazionale per la collisione di positronio su molecola d'idrogeno per energie da zero alla soglia di prima eccitazione del positronio. Si calcola il rapporto tra la perdita di energia vibrazionale ed elastica del positronio nella materia. Rispetto ad un analogo calcolo fatto precedentemente si tiene conto del contributo del continuo del positronio all'ampiezza diretta al second'ordine e si valuta la sezione d'urto di seconda eccitazione vibrazionale.
    Abstract: Резюме В рамках теории возмущений вычисляются поперечное сечение упругого рассеяния и поперечное сечение первого и второго колебательных возбуждений при соударении позитрония с молекулой водорода при энергиях в диапазоне от нуля до порога возбуждения позитрония. Мы также вычисляем отношение между потерями энергии на колебательные возбуждения и упругими потерями энергии позитрония в веществе. По сравнению с предыдущими вычислениями мы учитываем вклад непрерывного спектра позитрония в прямую амплитуду во втором борновском приближении. Мы также оцениваем поперечное сечение второго колебательного возбуждения.
    Notes: Summary We perform a perturbative calculation of the elastic, first and second vibrational excitation cross-sections for the positronium-H2 molecule scattering for an energy from zero to the positronium excitation threshold. We calculate also the ratio between the averaged vibration threshold. We calculate also the ratio between the averaged vibrational-and elastic-energy loss of the positronium in matter. In comparison with a previous similar calculation, we take now into account the contribution of the continuum of the positronium to the second Born approximation to the direct amplitude and we add the calculation of the second vibrational excitation cross-section.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02450674
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  • 3
    Electronic Resource
    Electronic Resource
    Separation of the massless spin-1 equation in Robertson-Walker space-time (1996)
    Springer
    International journal of theoretical physics 35 (1996), S. 323-331 
    Details
    ISSN: 1572-9575
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The massless spin-1 free field equation is studied via the Newman-Penrose formalism and separated by the Chandrasekhar-Teukolski method. The temporal and angular equations are explicitly integrated. The radial equations are solved in the flat-universe case. The closed-universe case shows, in principle, the existence of a discrete spectrum of the energy of the massless particles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02083818
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  • 4
    Electronic Resource
    Electronic Resource
    Weyl Spinor and Solution of Massless Free Field Equations (2000)
    Springer
    International journal of theoretical physics 39 (2000), S. 377-387 
    Details
    ISSN: 1572-9575
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The massless field equations for arbitrary spin in curved space-time arereconsidered. The general solution of the field equation in Robertson-Walkerspace-time that was previously determined is briefly discussed after explicitlyshowing that the Weyl spinor vanishes. The case of the Lemaître-Tolman-Bondispace-time is studied in detail. The general expression of the corresponding Weylspinor is obtained and some particular situations exploited. The spin-3/2 andspin-2 massless field equations are solved explicitly. The solutions are simplifiedby the existence of nontrivial algebraic constraints. The angular part of theequations is separated by the usual separation method and integrated directly.The other equations that are not separated in the radial and time dependence arereduced to a simple form. The results obtained are extended, as a consequenceof previous results, to the case of arbitrary spin. The solution of the general caseessentially reduces to the treatment of spin 3/2 and spin 2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003644511476
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  • 5
    Electronic Resource
    Electronic Resource
    Two-Slit Diffraction Pattern for Gaussian Wave Packets (1999)
    Springer
    International journal of theoretical physics 38 (1999), S. 911-918 
    Details
    ISSN: 1572-9575
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The complete prediction of diffraction forelectrons passing through one or two slits is obtainedfrom the pure wave propagation governed by theSchrodinger equation. By the further assumption ofelectromagnetic interaction between electrons and slits it isshown that, as already predicted by stochasticelectrodynamics with spin, there exist lateral maxima onthe diffraction pattern corresponding to the edges of the slits.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026617304784
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  • 6
    Electronic Resource
    Electronic Resource
    Dirac Equation with Central Potential: Discrete Spectrum of the Hydrogen Atom in the Robertson–Walker Space–Time (1999)
    Springer
    International journal of theoretical physics 38 (1999), S. 945-954 
    Details
    ISSN: 1572-9575
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The formulation of the Dirac equation withelectromagnetic field for a general space–time isspecialized to the Robertson–Walker metric. For aclass of physically meaningful electromagneticpotentials the angular part of the wave function separates asin the free-field case. The scheme is explicitly studiedfor a Coulomb potential. By using a realisticapproximation method one recovers the discrete energy levels of the hydrogen atom in Minkowski space.In case of static space–time, the result is exactfor zero curvature, while it is approximate for nonzerocurvature. The very good order of accuracy of the result is established by a comparison withsimilar qualitative and perturbative results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026677523439
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  • 7
    Electronic Resource
    Electronic Resource
    Positron-trap centers in neutron-irradiated silicon containing hydrogen (1995)
    Springer
    Applied physics 60 (1995), S. 81-85 
    Details
    ISSN: 1432-0630
    Keywords: 61.72-y ; 61.80.Hg ; 78.70.Bj
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The defect evolution as a function of the annealing temperature has been studied in monocrystalline silicon grown in a hydrogen atmosphere and irradiated with 3.6×1017 neutrons/cm2. Positron lifetime spectroscopy has been used and the results compared with infrated absorption measurements. Vacancy-H, vacancy-2H, vacancy-O−H and divacancy complexes withm hydrogen atoms (m〈6) have been identified for the first time as possible positron traps.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01577618
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  • 8
    Electronic Resource
    Electronic Resource
    Positron mobility in polyethylene in the 60–400 K temperature range (1995)
    Springer
    Applied physics 60 (1995), S. 447-453 
    Details
    ISSN: 1432-0630
    Keywords: 78.70.Bj ; 36.10.Dr ; 61.41.+e
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract We have determined the positron mobility (μ+) in polyethylene samples (67.2% crystalline, glass transition temperatureT g=151 K) in the 64–400 K temperature range by Doppler shift measurements. A method based on the simulataneous observation of two γ lines from133Ba and137Cs radioactive sources together with the positron annihilation γ line, was employed to measure the Doppler shift of the 511 keV γ line as a function of the electric field applied to the samples. With this method we were able to measure at the same time the drift velocity of positrons and theS parameter. This parameter is very important in the interpretation of the mobility trend in samples where the positron states change with temperature. The positron mobility was corrected for positronium formation. μ+ at 64 K is 31.7±0.8 cm2 V−1 s−1 then decreases up to 123 K, increases at 148 K and decreases again up to 170 K (μ+=26.9±0.8 cm2 V−s−). This sharp change in mobility is centred around the glass transition temperature of our samples. Then the mobility remains almost constant up to 230 K. From 250 K to 377 K, μ+ increases and reaches the value of 38.4±1.0 cm2 V−1s−1. The corrected experimental data were well fitted by a simple model taking into account scattering and a thermally activated process (hopping mechanism).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01538768
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  • 9
    Electronic Resource
    Electronic Resource
    Experimental study of positron motion in Kapton (1992)
    Springer
    Applied physics 54 (1992), S. 233-238 
    Details
    ISSN: 1432-0630
    Keywords: 66.30 ; 71.60 ; 78.70 B
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The drift of positrons under the action of an electric field in Kapton has been observed by using a variable-energy positron beam and the Doppler broadening technique. Even if the maximum applied field (2 MV/cm) is so high that the electrostatic work for a displacement of less than 0.15 nm is larger than the thermal energy, the experimental data can be fit by the diffusion model with a field-independent mobility. The best-fit value of the mobility (ca. 1×10−3 cm2 V−1 s−1) is extremely low in comparison with other dielectrics. The results are discussed with regards to the interaction of positrons with the molecular field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00323842
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  • 10
    Electronic Resource
    Electronic Resource
    Positron mobility in polyethylene in the 60–400 K temperature range (1995)
    Springer
    Applied physics 60 (1995), S. 447-453 
    Details
    ISSN: 1432-0630
    Keywords: PACS: 78.70.Bj; 36.10.Dr; 61.41.+e
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract.  We have determined the positron mobility (μ+) in polyethylene samples (67.2% crystalline, glass transition temperature T g=151 K) in the 64–400 K temperature range by Doppler shift measurements. A method based on the simultaneous observation of two γ lines from 133Ba and 137Cs radioactive sources together with the positron annihilation γ line, was employed to measure the Doppler shift of the 511 keV γ line as a function of the electric field applied to the samples. With this method we were able to measure at the same time the drift velocity of positrons and the S parameter. This parameter is very important in the interpretation of the mobility trend in samples where the positron states change with temperature. The positron mobility was corrected for positronium formation. μ+ at 64 K is 31.7±0.8 cm2 V-1 s-1 then decreases up to 123 K, increases at 148 K and decreases again up to 170 K (μ+=26.9±0.8 cm2 V-1 s-1). This sharp change in mobility is centred around the glass transition temperature of our samples. Then the mobility remains almost constant up to 230 K. From 250 K to 377 K, μ+ increases and reaches the value of 38.4±1.0 cm2V-1s-1. The corrected experimental data were well fitted by a simple model taking into account scattering and a thermally activated process (hopping mechanism).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01538768
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