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  • 1995-1999  (22)
  • 1990-1994  (22)
  • 1985-1989  (17)
  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2630-2639 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A numerical calculation of mode frequencies for cold, non-neutral plasmas is reported. The numerical method can be applied to any axisymmetric plasma shape in a trap. Here, it is used to study axisymmetric electrostatic modes in a long conducting cylinder. These modes were previously studied by Prasad and O'Neil [Phys. Fluids 26, 665 (1983)] and by Dubin [Phys. Rev. Lett. 66, 2076 (1991)]. In contrast to Dubin's calculation, the effects of a nearby cylindrical wall, including its influence on the shape of the plasma equilibrium, are considered. It is found that for plasmas with aspect ratios (length divided by diameter) near unity the numerical results can be approximately obtained by judiciously combining Dubin's calculation, and the Trivelpiece–Gould dispersion relation for infinitely-long geometry. For aspect ratios larger than about three, the Trivelpiece–Gould dispersion relation can be used in a simple way to obtain the numerically-computed mode frequencies with an accuracy of 1%, or better. The potential use of this calculation as a plasma diagnostic is also discussed, and it is argued that at the present level of accuracy (1–2%) its usefulness is marginal, but that an improvement by an order of magnitude might make it more interesting. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4705-4712 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Carrier concentration and mobility of unintentionally doped InP layers, grown directly on Si using metal-organic vapor-phase epitaxy, have been studied. The formation of antiphase domains (APDs) was found to depend on annealing of the Si substrate in an AsH3 flow prior to epitaxial growth. Dislocation densities determined by the wet chemical delineation technique were (8±1)×107 cm−3, seemingly uncorrelated to APDs in the layers. In addition to a shallow donor and a compensating acceptor, a deep donor was observed affecting the temperature dependence of the free-electron concentration between 77 and 300 K. The electron mobility in this temperature range could be described in terms of the scattering mechanisms which are dominant in homoepitaxial InP, namely, scattering due to polar optical phonons, to ionized impurities, and to space charges. Electron scattering due to either of these mechanisms was strongly influenced by the occurrence of antiphase boundaries (APBs). The space-charge density as well as the degree of compensation of the epitaxial layers increases with the density of APBs. Degraded 300 K mobilities were obtained indicating the effect of local stress at the APB.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The design of a photoemission microprobe beamline at the MAX laboratory is presented. The beamline will utilize the radiation from a 26 period undulator on the 550-MeV MAX storage ring. The beamline will be capable of providing about 1010 photons/s of monochromatized radiation (bandwidth better than 0.25 eV) in the energy range of 20 to 150 eV focused into a submicrometer focal spot. It will be used for scanning photoemission experiments with a lateral resolution better than 1 μm. The optical system is comprised of a plane-grating monochromator with a Kirkpatrick–Baez objective and a specially designed ellipsoidal focusing mirror.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 3265-3269 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The electronics for the microchannel plate photomultiplier tubes used in the LIDAR (Light Detection and Ranging) Thomson scattering diagnostic on the JET tokamak are described. It is shown how the microchannel plate photomultiplier tubes are gated with a very small coupling between gate signal and output, and how ≈300 V transient pulses with rise times of 230 ps are clipped to safe levels of ≈40 V.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1451-1456 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: By combining the time-of-flight or LIDAR principle with a Thomson backscatter diagnostic, spatial profiles of the electron temperature and density are measured in a magnetically confined fusion plasma. This technique was realized for the first time on the JET tokamak. A ruby laser (3-J pulse energy, 300-ps pulse duration, 0.5-Hz repetition rate) together with a 700-MHz bandwidth detection and registration system yields a spatial resolution of about 12 cm. A spectrometer with six channels in the wavelength range 400–800 nm gives a dynamic range of the temperature measurements of 0.3–20 keV. The stray light problem in the backscatter geometry is overcome by spectral discrimination and gating of the photomultipliers. A ruby filter in the spectral channel containing the laser wavelength allows calibration of the vignetting along the line of sight by means of Raman scattering, enabling the measurement of density profiles. The low level of background signal due to the short integration time for a single spatial point yields low statistical errors (ΔTe /Te ≈6%, Δne /ne ≈4% at Te =6 keV, ne =3×1019 m−3 ). Goodness-of-fit tests indicate that the systematic errors are within the same limits. The system is described and examples of measurements are given.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 2615-2622 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A computer controlled acquisition and evaluation system for electrostatic probes is presented. Fully automatic evaluation of the probe characteristics yields electron temperature, plasma potential, and density during the recording. Two-dimensional probe positioning is accomplished with stepping motors. The system is characterized by 12-bit probe current resolution and extremely wide probe voltage range (±130 V). It is tested in a collisionless argon magnetoplasma and compared to standard wave diagnostic techniques for magnetized plasmas, i.e., the resonance cone technique. The influence of the probe radius on the electron current in a magnetized plasma is studied experimentally. The two techniques yield identical density and temperature values within 20% accuracy and therefore show the reliable applicability of the automatic evaluation system.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1471-0528
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Summary. The clinical significance of placental perforation and bloodstained amniotic fluid was studied in a group of 7238 Danish women undergoing mid-trimester amniocentesis for prenatal diagnosis under ultrasound guidance. The risk of spontaneous abortion was significantly increased both in pregnancies where the placenta was perforated and in those with blood-stained amniotic fluid. The risk estimate nearly doubled after placental perforation and more than doubled with a bloody tap. It is concluded that for women at relatively low risk of a fetal genetic abnormality, the indication of the amniocentesis should be reconsidered if a placental perforation is unavoidable.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1398-9995
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The distribution of total serum-IgE and factors of importance for the level of IgE was studied in a random sample of 508 children and adolescents, aged 7–16 years, from Copenhagen. A detailed history about asthma, rhinitis, dermatitis and urticaria was obtained, and a physical examination, skin prick test with 9 common allergens, lung function test, bronchial challenge with inhaled histamine and exercise, and measurement of IgE (kU/1) were performed. The distribution of IgE among children and adolescents was found to exhibit a log normal distribution and a positive skin prick test, allergic symptoms, a family history of allergic diseases, age and smoking were found to be significantly related to an increased level of IgE. No relationship was found between increased bronchial responsiveness and IgE. The geometric mean of “normal” values of IgE (* 1 SD and *2 SD) of the Danish children and adolescents was 18 kU/1 (*4.7, * 18.2), suggesting that normal IgE values were within 330 kU/1. Measurement of IgE as the only screening for allergic disease is unreliable, as the predictive value of an elevated IgE in population samples was found to be 50%, whereas misclassification (1-specificity) of asymptomatic subjects as allergic because of an increased IgE was low (4%). In conclusion, total IgE is highly influenced by allergen skin reactivity. Further, this study suggests that normal IgE values were within 330 kU/1, although the range was wide.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 5012-5018 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have measured the metastable fragmentation of fullerene ions in molecular beams. The rates are significantly smaller than the evaporative ensemble prediction, consistent with an alternative cooling mechanism through emission of electromagnetic radiation. Modeling the competition between radiative and evaporative cooling yields information about the evaporative activation energy and emissivity of the carbon clusters. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 10481-10484 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We calculate the modifications of the unimolecular rate constants for free metallic clusters due to thermally exited electronic degrees of freedom. The effect is essentially taken into account by substituting Helmholtz's free energy of the electronic system for the ground state energy. The activation energy pertaining to the electronic ground states of the mother and daughter cluster is then replaced by the first difference in Helmholtz's free energy. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
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