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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 4781-4787 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A model of the negative glow of a low-pressure Hg-Ar discharge is described. The model contains a number of important physical processes (in particular noble-gas excitation and multiple-step ionization) that have not been included in earlier models. The model has also been coupled to a simple description of the Faraday dark space to enable predictions to be made of the axial density and potential profiles across the whole negative-glow Faraday dark-space positive-column region. Results of a number of numerical computations are presented and in general these have been found to be in agreement with experimental observations. The effect of varying the various input parameters to the model on its predictions has also been studied and the results of this will also be presented.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 1772-1779 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report the results of an experimental and theoretical study on the feasibility of a barium low pressure discharge as a potential new light source. Barium has a strong neutral resonance line at 553.5 nm, near the center of the eye's response curve, as well as several red and blue lines from barium ions. Due to the strong reactivity of barium with a wide variety of standard lamp materials, experiments were performed in arc tubes lined with yttria (Y2O3). A wide range of parameter space was explored in buffer gas pressure (1–30 Torr), gas type (argon, neon, and krypton), barium temperature (400–760 °C), and arc current (0.05–1.0 A). The numerical model qualitatively predicted the influence of these parameters on light output. However, the predicted efficacies of up to 100 lm/W were considerably higher than the measured values. The best positive column efficacy achieved was 50 lm/W in a sealed yttria lined quartz tube with 5 Torr argon operating at 400 mA at 760 °C. Possible reasons for this discrepancy are discussed. © 2002 American Institute of Physics.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 8993-8997 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The electrical conductivity is an important parameter in understanding the mechanism by which power is coupled to a radio-frequency (rf) discharge plasma, as well as in determining the external electrical characteristics of the discharge. We present the results of computations of the resistive and reactive components of the collisional impedance of an argon plasma at 13.56 MHz. The plasma conductivity is computed from the two-term solution to the Boltzmann equation, and includes the velocity dependence of the electron collision frequency, as well as non-Maxwellian electron energy distribution functions. We compare these results with those obtained from the widely used classical expression for plasma impedance, in which the electron collision frequency is computed either in the dc or high frequency limit. Our results show that neither of the classical limiting expressions are adequate for discharge pressures in the range of few mTorr to a few Torr, which includes the region of operation for many rf discharges used in many applications of plasma technology. Further, the classical formula assumes that in the high-frequency limit the plasma reactance is due entirely to electron inertia. We demonstrate that the plasma reactance may be strongly influenced, and in some cases dominated, by electron collisions. Results are presented in graphical form, which are useful in evaluating the importance of these effects on the interpretation of experimental results and the modeling of rf discharges. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 51 (1981), S. 0 
    ISSN: 1399-3054
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: The photosynthetic pigment contents and the chlorophyll fluorescence induction in Norway spruce [Picea abies (L.) Karst.] needles were monitored at 3 h intervals over a 10 day period. This covered 6 days of high insolation, one day of low insolation, followed by three more days of high insolation. During the first six days only small changes in mean pigment contents were observed but we interpret them as suggesting a daily rhythm in total chlorophyll content with two maxima and minima. The day of low insolation was paralleled by larger pigment changes, mostly an increase in chlorophyll b along with a decrease in carotenoid content. With the resumption of high insolation, pigments gradually return to their previous levels. During the entire period chlorophyll a fluorescence induction remained relatively constant. These short-term responses may reflect features of thylakoid organization in relation to pigment content and suggest possible long-term adaptive mechanisms in non deciduous conifers.
    Materialart: Digitale Medien
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  • 5
    ISSN: 0010-4655
    Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Thema: Informatik , Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Amsterdam : Elsevier
    Social Science & Medicine 29 (1989), S. 79-84 
    ISSN: 0277-9536
    Schlagwort(e): asthma ; compliance ; hypertension ; psychological distress
    Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Thema: Medizin
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    Amsterdam : Elsevier
    Nuclear Inst. and Methods in Physics Research, B 5 (1984), S. 389-393 
    ISSN: 0168-583X
    Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Thema: Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    Amsterdam : Elsevier
    Vacuum 45 (1994), S. 525-534 
    ISSN: 0042-207X
    Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Thema: Maschinenbau , Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    Amsterdam : Elsevier
    Vacuum 45 (1994), S. 149 
    ISSN: 0042-207X
    Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Thema: Maschinenbau , Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    Springer
    Zeitschrift für angewandte Mathematik und Physik 25 (1974), S. 241-257 
    ISSN: 1420-9039
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik , Physik
    Beschreibung / Inhaltsverzeichnis: Résumé L'étude de la stabilisation dynamique de systèmes fluides et de certains confinements de plasma dense culmine en des équations qui ont toutes la forme $$[X + 2A\cos (\omega t - \phi )]y(t) + \int_0^t {R(t - t')\dot y(t')dt' = 0} $$ , oùX etA sont des constantes données, ϕ une phase arbitraire etR(t) une fonction de réponse singulière. Cette équation est résolue pour toute valeur deA et certaines propriétés générales de stabilité de la solution sont discutées. Le spectre du système est comparé à celui du système statique. Une méthode de perturbation est présentée, valable lorsque le système statique a des fréquences propres bien séparées l'une de l'autre.
    Notizen: Abstract The study of the dynamic stabilization of certain plasma confinement and fluid systems leads to equations of the form $$(X + 2A\cos (\omega t - \phi ))y(t) + \int_0^t {R(t - t')\dot y(t')dt' = 0} $$ , whereX andA are constants, ϕ an arbitrary phase andR(t) a singular response function. This equation is solved for all values ofA and the general stability properties of the system are discussed. General formulae are given which relate the perturbed spectrum of the system to the unperturbed system. For the case where the static system has well separated eigenfrequencies, a perturbation expansion is derived.
    Materialart: Digitale Medien
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