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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 2522-2528 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An electro-optical device consisting of a stack of undoped alternating layers of narrow- and wide-gap materials (e.g., GaAs/AlGaAs) together with a series resistor under constant voltage bias is analyzed theoretically. The GaAs heterolayers with a width in the order of a carrier mean free-path are a photo-active region of this vertical device. The device operates only in the presence of a low-intensity light beam due to the intrinsic photoconductivity of the active region. The Franz–Keldysh effect, the strong accumulation of the photocarriers in the photo-active layers due to the charge separation in the presence of the static electric field, and the ballistic component of the total current are responsible for the unusually large electro-optical nonlinearity of the device. Kirchhoff's law for the electrical circuit of the device provides a sensitive feedback between the voltage drop over the layer and the photocurrent. In a Fabry–Perot cavity a room temperature electro-optical bistabitity is obtained at light intensities less than 10 mW/cm2 with a switching time of about 100 ns.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 3414-3416 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present new results on the effective refractive index of GaInP/AlGaInP distributed feedback (DFB) lasers with grating periods around 100 nm, operated at 77 K and at room temperature. Double heterostructure (DH) lasers as well as multiple quantum well lasers show DFB-laser emission at 300 K over a range of 15 nm. For the DH lasers a clear difference of absolute value and dispersion of the effective refractive index was observed between 77 and 300 K, which is explained by high carrier density effects. For a carrier density of N=2.5×1018 cm−3 the refractive index of GaInP decreases by 0.05, which is compared with an ab initio calculation.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 2824-2826 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We calculate the plasma-density dependent optical absorption spectra of quantum well wires with finite lateral confinement with respect to the quantum well. The excitonic absorption spectrum consists of a series of resonances due to quantum wire as well as higher lying quantum well states. The calculations include phase-space filling, band-gap renormalization, and excitonic enhancement within the Hartree–Fock approximation. For a well depth of (approximately-equal-to)40 meV, which is a typical value for intermixed GaAs/AlGaAs quantum well wires, the line shape of the quantum wire absorption spectrum is shown to be strongly influenced by the presence of lateral barrier states for all plasma densities.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract For carrier-carrier scattering the relaxation kinetics of a quasi-twodimensional degenerate electron gas is studied in the framework of the Boltzmann equation using a static RPA screening. The time development of an initial nonequilibrium distribution is calculated both by ensemble Monte Carlo simulations and by expansions in terms of eigenfunctions of the linearized collision operator. A systematic comparison of the results of both methods yields a rather detailed understanding of the Coulomb relaxation kinetics and of the strengths and limitations of both methods. The dependence of the relaxation rate on the position and width of the initial population deviation is investigated and conditions for nonexponential decay are given.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 92 (1993), S. 532-532 
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Annals of hematology 21 (1970), S. 20-28 
    ISSN: 1432-0584
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary Blood coagulation belongs to the physiological processes, which in vitro can influence enzyme activities in plasma or serum. In parallel determinations activities measured in serum are mostly found higher than in plasma. The liberation of enzymes, present at high levels intracellularly, from thrombocytes was found to be responsible for the serum plasma difference. In this paper we present evidence, that this enzyme liberation caused by coagulation does occur during the retraction phase and not-parallel with the beginning of the viscous metamorphosis-during the initial coagulation phase. By rapid separation of the serum from the clot we could anticipate the enzyme release. In rapidly isolated serum no significant increase in activity could be demonstrated when compared with plasma. GOT and GPT, which are present only at a relatively low level in the platelets, are not influenced by blood coagulation resp. thrombocyte desintegration. The late enzyme release from the thrombocytes as observed during our investigation seems to be meaningful physiologically: Only after completion of clot retraction, which is an important function of the thrombocytes, the enzymes they contain-after they have mediated the energy needed-leak out into the surrounding fluid.
    Notes: Zusammenfassung Zu den physiologischen Vorgängen, die In-vitro-Enzymaktivitäten im Plasma oder Serum beeinflussen können, gehört die Blutgerinnung. Bei Parallelbestimmungen findet man meist höhere Enzymaktivitäten im Serum als im Plasma. Als Ursache dieser Serum-Plasma-Differenz konnte die Freisetzung intrazellulär in hoher Aktivität enthaltener Enzyme aus den Thrombozyten ermittelt werden. Diese durch die Gerinnung hervorgerufene Enzymfreisetzung findet nach den vorliegenden Untersuchungen nicht während der initialen Gerinnungsphasen parallel mit dem Beginn der viskösen Metamorphose der Blutplättchen, sondern erst in der Retraktionsphase statt. Durch rasche Abtrennung des Serums vom Gerinnsel konnten wir dem Enzymaustritt zuvorkommen. Im rasch gewonnenen Serum ließen sich gegenüber dem Plasma keine signifikanten Aktivitätssteigerungen mehr nachweisen. Die in den Blutplättchen in relativ niedriger Aktivität enthaltenen Enzyme Glutamatoxalat- und Glutamatpyruvat-Transaminase werden durch die Blutgerinnung und Thrombozyten-Desintegration nicht beeinflußt. Der in unserer Untersuchung gefundene späte Enzymaustritt aus den Thrombozyten erscheint in physiologischer Hinsicht sinnvoll. Erst nach Ablauf der Gerinnselretraktion als einer wesentlichen Aufgabe der Thrombozyten gelangen die in ihnen enthaltenen Enzyme, nachdem sie zur Energiegewinnung benötigt wurden, in die Umgebungsflüssigkeit.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-0533
    Keywords: Human immunodeficiency virus ; Acquired immune deficiency syndrome (AIDS) ; Encephalopathy ; Cortical atrophy ; Morphometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A 25-year-old homosexual AIDS patient presented with progressive cognitive, motor and behavioral disturbances consistent with HIV encephalopathy. CT scans demonstrated progressive diffuse brain atrophy. Neuropathology showed predominant cortical changes including severe neuronal loss corroborated by morphometry. Only minimal changes were found in the white matter and basal ganglia. Immunocytochemistry for HIV stained occasional microglial cells more markedly in the cerebral cortex. This suggests that HIV infection of the brain may cause predominant cortical nerve cell loss, and that HIV encephalopathy is not necessarily due to white matter lesions.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Acta neuropathologica 80 (1990), S. 92-94 
    ISSN: 1432-0533
    Keywords: Acquired immune deficiency syndrome (AIDS) ; Cerebral cortex ; Dementia ; Morphometry ; Neuronalloss
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Neurons of Area 11 in the fronto-orbital cortex of 18 unselected AIDS brains are analyzed by means of stereology. Neurological abnormalities including dementing symptoms were described in eight patients. Neuropathology diagnosed human immunodeficiency virus (HIV)-specific changes in four, and diffuse poliodystrophy in eight brains. The majority (71.4%) of these brains was immunoreactive for HIV antigens when tested by immunocytochemistry. A significant loss of neurons is found as compared to normal controls. Neuronal density in AIDS brains is reduced by 18%, and the perikaryon volume fractions is reduced by 31%. Although only speculation on pathogenesis of this neuronal loss is possible at present, it may represent a part of the pathomorphological substrate of AIDS-related dementia. Moreover, it confirms by quantitative means damage to the cerebral cortex in AIDS which has been described only qualitatively as diffuse poliodystrophy.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Acta neuropathologica 85 (1993), S. 185-189 
    ISSN: 1432-0533
    Keywords: Morphometry ; Stereology ; Cerebral cortex ; HIV-encephalitis ; HIV-leukoencephalopathy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Using stereological methods, two cerebral cortical areas from AIDS brains were investigated. Neuronal density, profile area of neurons, and perikaryon volume fraction were measured and compared to age-matched control brains. In the fronto-orbital cortex (area 11) of AIDS brains, a significant loss of neurons was seen. The perikaryon volume fraction was likewise decreased. The size of neurons did not differ between control and AIDS brains. In patients with clinical signs of progressive dementia and in brains with human immunodeficiency virus (HIV)-specific neuropathology (HIV-leukoencephalopathy and/or HIV-encephalitis) as compared to patients lacking these features, a small decrease in neuronal density was noted but this difference did not reach the level of statistical significance (P=0.16). In the superior parietal lobule (are 7) of AIDS brains, no loss of nerve cells was noted. AIDS patients with progressive dementia and brains with HIV-specific neuropathology showed no difference in neuronal densities as compared to those without such features. We conclude that the fronto-orbital cortex, in contrast to the parietal cortex, is mainly damaged in AIDS brains. Neuronal loss was not significantly correlated with development of dementing symptoms and of HIV-specific neuropathology.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Annals of hematology 23 (1971), S. 69-83 
    ISSN: 1432-0584
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary The results of the WBC of 11 298 patients of the Medizinische Poliklinik Würzburg were compiled. By statistic calculation we searched for age and sex differences in the groupings. Sex differences in the values are small, but were nevertheless significant in the statistic evaluation (male mean value 6470, female mean value 6300 leuc./mm3 blood). The WBC of the male, not of the female population rises slightly with age. The values of the blood smear showed no differences with respect to age and sex.
    Notes: Zusammenfassung Die Ergebnisse von 11 298 Untersuchungen der weißen Blutzellen bei einem unausgelesenenen poliklinischen Krankengut wurden statistisch auf Altersabhängigkeit und Geschlechtsverteilung untersucht. Die geschlechtsabhängige Differenz des durchschnittlichen Leukozytenwertes ist nach unsererer Arbeit wenig bedeutsam, war aber infolge der großen Probandenzahl statistisch hochsignifikant (Männer 6470, Frauen 6300 Leukozyten/mm3 Blut). Bei den Männern stiegen die durchschnittlichen Leukozytenzahlen mit zunehmendem Alter etwas an, jedoch nicht bei den Frauen. Beim Differenzialblutbild fanden wir keine sicheren geschlechts- und altersabhängige Differenzen.
    Type of Medium: Electronic Resource
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