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  • 1
    Digitale Medien
    Digitale Medien
    Stability and transport of parallel velocity shear driven mode with negative magnetic shear (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 1192-1195 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The linear and quasilinear behavior of the drift-like perturbation with a parallel velocity shear is studied in a sheared slab geometry. Full analytic studies show that when the magnetic shear has the same sign as the second derivative of the parallel velocity with respect to the radial coordinate, the linear mode may become unstable and turbulent momentum transport increases. On the other hand, when the magnetic shear has opposite sign to the second derivative of the parallel velocity, the linear mode is completely stabilized and turbulent momentum transport reduces. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.873929
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  • 2
    Digitale Medien
    Digitale Medien
    Parallel velocity shear instability, Alfven waves and the formation of the transport barrier (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 2939-2944 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: It is suggested that the ponderomotive force induced by radio frequency (rf) waves in the range of the Alfven frequency can create a transport barrier in a tokamak. The linear and nonlinear behavior of the driftlike perturbation with a parallel velocity shear is studied in the presence of rf waves. It is shown if the radial profile of the rf field energy is properly chosen the linear mode is stabilized and turbulent momentum transport reduces. The rf power required for this stabilization is found to be rather modest and hence should be easily obtained in actual experiments. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.874145
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  • 3
    Digitale Medien
    Digitale Medien
    Auger electron spectroscopy of molecules: Theory for spin polarization following photoabsorption in rotating linear molecules (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 5242-5258 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: This paper develops theoretical expressions to study angular distribution and spin polarization of those Auger electrons which are emitted in the decay of a vacancy created by the absorption of a photon in a rotating linear molecule. Identical expressions except, of course, for different decay amplitudes, in both the Hund's coupling schemes (a) and (b), are obtained for the differential Auger current emitted in the transition J→Jf measured by an electron spectrometer sensitive to spin detection. The structure of these angular distributions is exactly the same as that of the spin-resolved photoelectrons from unoriented atoms and molecules. The present paper thus puts the angle- and spin-resolved Auger and photoelectron spectroscopies on the same footing wherein identical geometrical and kinematical analysis is applicable. The four parameters needed to completely characterize such distributions depend, in the present case, on rotational orientation and/or alignment of the photoexcited molecule, in addition to its Auger decay amplitudes. The use of parity-adapted molecular states separates the Auger spectra into even and odd partial wave components of the ejected electron continuum in both of the coupling schemes. Our analysis shows that the integrated Auger current is spin resolved provided it is produced in the decay of oriented vacancies. We further find that Auger electrons which leave the molecular ion in Jf=0 state may have nonzero degree of spin polarization if they follow absorption of only circularly polarized light. In this case, both the angular distribution and spin polarization of emitted electrons become totally independent of Auger dynamics. Thus, angle- and spin-resolved Auger electron spectroscopy can be used to produce polarized electrons, to determine rotational orientation and alignment of linear molecules, to study their structure and dynamics, and to prepare ions of such molecules in selective ro-vibronic states.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.464924
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  • 4
    Digitale Medien
    Digitale Medien
    Spatial distribution of Nd3+ dopant ions in vitreous silica: A pulsed electron paramagnetic resonance spectroscopic study (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 2304-2308 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The structural aspects of clustering of Nd3+ ions in Nd2O3-doped SiO2 glasses and the effect of Al3+ codoping on these clusters have been investigated with pulsed electron paramagnetic resonance (EPR) techniques over a temperature range of 1.5–4 K. The Nd2O3 concentrations in these glasses range between 700 and 2400 ppm by weight. The Nd3+ echo-detected EPR (EDEPR) spectra of the Al-free glasses show indications of weak exchange coupling between Nd3+ ions due to clustering. The EDEPR spectra also suggest that the local coordination environment of Nd3+ ions is affected by codoping with Al. The electronic spin-lattice relaxation rates are found to be not sensitive to the spatial distribution of Nd3+ ions over the entire temperature range of measurements. On the other hand, the concentration dependence of phase relaxation rates show clear evidence of clustering of Nd3+ ions in Al-free glasses, even at the lowest Nd2O3 doping levels. These Nd3+ clusters are found to break up and homogenize with an increase in the average Nd–Nd distance on codoping with Al. Analyses of the hyperfine sublevel correlation spectrum of a Nd and Al codoped glass indicate that the homogenization of Nd3+ clusters is possibly a consequence of the formation of Nd–O–Al linkages. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1338513
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  • 5
    Digitale Medien
    Digitale Medien
    Electrical properties of semiconducting barium vanadate glasses (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 3355-3359 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The preparation of vanadate glasses containing barium oxide and their electrical properties in the temperature range of 80–500 K have been reported in this article. Analysis of the electrical properties has been made in the light of different hopping models. The multiphonon assisted hopping model of small polarons in the nonadiabatic regime, proposed by D. Emin [Phys. Rev. Lett. 32, 303 (1974)] have been observed to describe the temperature dependence of the conductivity data of these glasses over the entire temperature range of measurement. The parameters obtained from the fits of the experimental data to this model are reasonable and consistent with the glass composition. J. Schnakenberg's model [Phys. Status Solidi 28, 623 (1968)] is also consistent with the temperature dependence of the conductivity data. Mott's optical phonon assisted hopping model at high temperatures provides smaller values of the localization length. However, Mott's variable range hopping model is valid at low temperatures. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.372349
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  • 6
    Digitale Medien
    Digitale Medien
    Compositional characteristics and phase equilibria in manganiferous iron formations from a high-grade terrain near Satnuru, Karnataka, India (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 8 (1990), S. 0 
    Details
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Manganese-rich and manganese-poor iron formations which occur as thin layers in the Halaguru-Satnuru area, south of Kabbaldurga, Karnataka, India are chemically intermediate between the ‘Algoma’and ‘Lake Superior’types, but higher in their MnO and TiO2 contents. The rocks are of four petrographic varieties: (a) quartz-magnetite-orthopyroxene-clinopyroxene, (b) quartz-magnetite-orthopyroxene-clinopyroxene-garnet, (c) quartz-magnetite-clinopyroxene-garnet, and (d) quartz-magnetite-clinopyroxene-garnet-plagioclase.In the orthopyroxene-clinopyroxene pairs, Mn-Mg and Mn-Fe exchange is ideal irrespective of the MnSiO3 contents of orthopyroxenes (0.6–1.8 mol. % in Mn-poor and 15–25 mol. % in Mn-rich compositions). Mg-Fe exchange in the same pair is however non-ideal. Mn-Fe exchange in orthopyroxene-garnet pairs is ideal. The distribution patterns in the other binaries are inconclusive regarding ideality of exchange. Orthopyroxene-garnet and clinopyroxene-garnet geothermometers, modified for high spessartine contents, give temperatures of 800 ± 30° C. A modified version of the Harley (1984) geothermometer registers 740 ± 60° C, in agreement with the consensus temperature value.The equilibrium log ffo2 values in the iron formations, as calculated from the reaction 6FeSiO3+ O2= 2Fe3O4+ 6SiO2 are in the range of −14.2 to −15.5. Algebraic analysis of variations of fo2 with composition of phases indicates buffering of O2 in the rocks. The absence of grunerite in these assemblages is compatible with XH2O being less than 0.3 in the ambient fluid. Computations from volatile equilibria in the C-O-H system, however, predict high XH2O values (〉0.7) at ac= 1.0, implying that the activity of graphite must have been greatly reduced—this is in accordance with the absence of graphite in these rocks.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1525-1314.1990.tb00484.x
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  • 7
    Digitale Medien
    Digitale Medien
    Observation of charge storage and intersubband relaxation in resonant tunneling via a high sensitivity capacitive technique (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 2820-2822 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: In suitably designed resonant tunneling double barriers the capacitance-voltage curve exhibits well-defined features corresponding to the charging and discharging of the quantum well. From the bias dependence of the electron density in the well we find that in our thick parabolic wells, electrons tunneling into the excited states relax to the lowest subband and sequentially tunnel out. Our experiments allow us to obtain the charge density accumulated in the well and the tunneling escape rate of electrons out of the well.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.103752
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  • 8
    Digitale Medien
    Digitale Medien
    Energy levels of the SbGa heteroantisite defect in GaAs:Sb (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 2968-2970 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A transient capacitance study of antimony-doped bulk GaAs has led to the identification of two energy levels related to the SbGa heteroantisite defect. The levels with electron emission activation energies of 0.54 and 0.70 eV are typically overshadowed by omnipresent EL3 and EL2 traps related to oxygen defect and the arsenic antisite, respectively. Positive identification of the levels, and determination of their emission rate signatures, was made possible employing GaAs crystals with a defect structure especially engineered to achieve very low concentrations of background traps. Relationship of the levels to the SbGa defect is deduced from excellent agreement with previous electron paramagnetic resonance results.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.109159
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  • 9
    Digitale Medien
    Digitale Medien
    Evidence that blue luminescence of oxidized porous silicon originates from SiO2 (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 1436-1438 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have analyzed red and blue luminescence from porous silicon as a function of oxidation parameters and feature dimension determined with an atomic force microscope. We have found correlation between blue luminescence intensity and the increase in feature size caused by oxidation. We have further shown that blue luminescence, is identical, with respect to spectrum and fast decay, to that of high microelectronic quality SiO2 grown on crystalline silicon using dry oxygen plus an organic chlorine compound. Thus, we conclude that blue luminescence originates from SiO2 film rather than from the silicon nanocrystals in the porous material. Intensity enhancement, as compared to SiO2 on crystalline wafers, comes from the gigantic surface area of porous silicon.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.112973
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  • 10
    Digitale Medien
    Digitale Medien
    Development of interspecific somatic hybrid cell lines in cultivated jute and their early characterization using jute chloroplast RFLP marker (2001)
    Oxford, UK : Blackwell Publishing Ltd
    Plant breeding 120 (2001), S. 0 
    Details
    ISSN: 1439-0523
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: A strong sexual incompatibility barrier that exists between the two cultivated jute species, Corchorus capsularis and Corchorus olitorius, limits the scope for improvement through genetic introgression. Protoplast fusion was carried out to generate interspecific hybrid cell lines. Cotyledonary cell protoplasts of C. capsularis and anthocyaninpigmented hypocotyl protoplasts of C. olitorius were used in the fusion experiments, which appeared to be visually useful in the early selection of the fused products. A chloroplast DNA (cpDNA) marker was developed in jute, which showed species-specific hybridization patterns with EcoRI-digested total genomic DNA of C. capsularis and C. olitorius. This cpDNA marker was used in the characterization of the somatic hybrid cell lines at their early stages of growth. Evidence for the presence of both types of cpDNA in the hybrid cell lines was obtained when the total genomic DNA of 4- to 7-month-old hybrid cell lines was challenged with the chloroplast DNA marker through Southern analysis. It was shown that the early segregation of the parental chloroplasts did not occur in jute, although this is common in other plant species. The hybrid nature of the fused cell lines could also be identified through peroxidase isozyme analysis. Isozyme banding patterns were complex and varied among the hybrid cell lines.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1439-0523.2001.00634.x
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