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  • 2000-2004  (10)
  • 1935-1939
  • 2001  (10)
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  • 2000-2004  (10)
  • 1935-1939
Year
  • 1
    Electronic Resource
    Electronic Resource
    Simple method for estimating linear attenuation coefficients from x-ray diffraction tomography data (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 1918-1920 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In this article, we demonstrate how the spatial distribution of x-ray linear attenuation coefficients within an object can be estimated from x-ray diffraction tomography data. The experimental arrangement to achieve this exploits a position sensitive detector and an analyzer crystal. The quality of reconstructed maps of linear attenuation coefficients is comparable to results obtained from conventional transmission computed tomography. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1344171
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  • 2
    Electronic Resource
    Electronic Resource
    An efficient tabulated collisional radiative equilibrium radiation transport model suitable for multidimensional hydrodynamics calculations (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 3480-3489 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A computationally efficient method for transporting radiation in multidimensional plasmas has been developed and evaluated. The basis of this method is a uniform plasma approximation that allows one to utilize existing escape probability techniques that are successfully used in one-dimensional (1D) calculations to approximately solve the multidimensional radiation transport problem. This method is superior to diffusion methods because (1) the probability of escape technique insures that the plasma goes to the correct optically thin and thick limits, (2) the effects of line absorption due to photoexcitations are modeled, and (3) this method uses source functions that are based on a self-consistent nonlocal thermodynamic equilibrium calculation, not an ad hoc assumption that the source functions are Planckian. This method is highly efficient because equation of state information from 1D calculations is tabulated as a function of plasma internal energy, ion density, and the line probability of escape from a uniform plasma, and then used in multidimensional calculations. Given the internal energy and ion density, and by calculating the line probability of escape from a zone of the multidimensional plasma, the equation of state, including emissivities and absorption coefficients, of the zone is determined from the table. Total radiative power, K-shell radiative power, total radiative yield, K-shell radiative yield, and plasma density and temperature profiles obtained from 1D Z-pinch calculations employing this method are in good agreement with the same powers, yields, and profiles calculated using a full radiation transport model. This method has been implemented in the 2D plasma radiating imploding source model code [F. L. Cochran et al., Phys. Plasmas 2, 2765 (1995)] to determine the influence of radiation transport in argon Z-pinch experiments performed on the Z machine [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] at Sandia National Laboratories. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1373415
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Trends in plasma conditions inferred from an analysis of x-ray data from high wire-number, Z-pinch load implosions (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 3708-3717 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An analysis of x-ray data from two series of Z-pinch shots taken on the short current-risetime Saturn accelerator at Sandia National Laboratories [Proceedings of 6th International IEEE Pulsed Power Conference, Arlington, VA, edited by P. J. Turchi and B. H. Bernstein (IEEE, New York, 1987), p. 310] is presented. In one series, the array radius was held constant and the array mass was varied; in the other series, the array mass was held constant and its radius varied. In both sets of experiments, large wire-number loads (N≥93) of aluminum were used in contrast to earlier small wire-number aluminum array experiments on Saturn where N≤42. Average electron temperatures and ion densities were inferred from the data. In addition, from the measured size of the emission region of K-shell x rays and from the inferred ion density, a fraction of the total array mass that participated in the K-shell emission was inferred and found to be directly correlated to the K-shell yields that were measured. This paper also demonstrates that the yields varied as a function of array mass and radius in much closer agreement with predictions [J. Appl. Phys. 67, 1725 (1990)] than had been observed in the earlier small wire-number experiments. Thus, a serious misperception that the reason for the early disagreement was in the calculations and not in the experiments is corrected. These predictions were made using one-dimensional (1D) magnetohydrodynamics calculations. The density and temperature trends inferred from the data analysis are well-behaved and consistent with the 1D calculations. This data analysis confirms the importance of achieving uniform plasma initial conditions and implosion symmetry when comparing computer code calculations with experiment. When the wire number of an array load is increased, a more uniform shell of plasma is calculated initially as the wires explode and, as the plasma stagnates on axis, the x-ray powers and yields are found experimentally to approach the powers and yields predicted by 1D calculations. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1380695
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  • 4
    Electronic Resource
    Electronic Resource
    Comparative analysis of time-resolved and time-integrated x-ray data from long pulse Z-pinch implosions on Saturn (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 3799-3809 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two series of Al:Mg wire array Z-pinch implosions were performed on the Saturn pulsed-power generator [R. B. Spielman et al., in Proceedings of the 2nd International Conference on Dense Z-Pinches, Laguna Beach, CA, 1989, edited by N. R. Pereira, J. Davis, and N. Rostoker (American Institute of Physics, New York, 1989), p. 3]. In one series, the wire number was varied, in the other, the load mass was varied. In all cases an initial array diameter of 40 mm was maintained. Sufficient x-ray data were obtained in these experiments to allow the plasma conditions to be inferred by matching x-ray data to that calculated by a collisional-radiative equilibrium (CRE) model. In fitting the data, the plasma has been assumed to be either uniform [zero dimension (0D)] or to vary one-dimensionally (1D) with radius. On one shot, a comparison of these two methods of data analysis performed with both time-resolved and time-integrated data has been carried out. While the same trends in plasma conditions as a function of load mass and wire number are seen, the uniform plasma assumption yields higher electron temperatures, lower core densities, but higher K-shell radiating mass fractions than those obtained from the 1D assumption. When comparing time-resolved and time-integrated spectroscopic data, a pronounced difference is seen in a density-sensitive line ratio whose time-resolved values corroborate experimental evidence that much of the K-shell radiation is emitted from a high density core plasma of spatial extent less than about 300 μm. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1381565
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  • 5
    Electronic Resource
    Electronic Resource
    High energy photon radiation from a Z-pinch plasma (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 4509-4517 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new approach to the generation of kilovolt x ray radiation in Z-pinch plasma radiation sources is proposed. In cases where the pulse power machine has insufficient energy to efficiently produce K-shell emission from the atomic number element that emits in the required kilovolt energy range, it may be advantageous to produce x rays by recombination radiation emitted from a lower atomic number plasma. The optimal load conditions for maximizing the high energy free–bound continuum radiation that can be produced in a given spectral range are analyzed. The largest yield is expected from a highest-atomic-number element that could efficiently produce K-shell yield on a given pulse power machine. Two options available for the choice of a wire array material to generate x rays with photon energies above 7–8 keV are identified and discussed, aluminum and titanium. The analytical estimates and simulation results for "Z" machine implosions show that continuum radiation from an aluminum plasma in this spectral range could exceed the K-shell output from nickel. If a titanium plasma could be ionized to a H-like state on "Z," then its yield above 7 keV should be higher compared to that of aluminum by a factor of 3 to 4. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1398572
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  • 6
    Electronic Resource
    Electronic Resource
    Sources and Implications of Uncertainty for Coastal Managers (2001)
    Oxford, UK : Blackwell Publishing Ltd
    Water and environment journal 15 (2001), S. 0 
    Details
    ISSN: 1747-6593
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: This study included semi-structured interviews with eight practitioners who have key roles in UK coastal management. Data from the interviews were analysed using ‘grounded theory’, which established that sources of uncertainty in decision making are diverse but can be categorised as being modelling issues, values issues, communication and ‘externalities’. At present, intuitive and implicit methods of taking uncertainty into account in decision making are much more prevalent than explicit methods. By identifying sources and implications of uncertainty, coastal managers will be in a stronger position to promote resilient systems that can cope with changing natural and social conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1747-6593.2001.tb00314.x
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  • 7
    Electronic Resource
    Electronic Resource
    Photoperiodic Regulation of Prolactin Gene Expression in the Syrian Hamster by a Pars Tuberalis-Derived Factor (2001)
    Oxford, UK : Blackwell Science, Ltd
    Journal of neuroendocrinology 13 (2001), S. 0 
    Details
    ISSN: 1365-2826
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Syrian hamsters exhibit a marked seasonal variation in prolactin secretion. The aim of this study was to analyse the nature of the photoperiodic regulation of prolactin gene expression, and to define the role of melatonin and the pars tuberalis of the anterior pituitary in this process. Pituitary prolactin gene expression, restricted to the pars distalis, was increased in hamsters maintained in long daylengths (16 h : 8 h, light : dark) compared to hamsters exposed to short daylengths (8 h : 16 h, light : dark) for 8–12 weeks. Analysis of single cells by in situ hybridization showed that photoperiod had no effect on the percentage of pars distalis cells expressing prolactin mRNA, but shifted the frequency distribution of prolactin mRNA expression per cell, such that in long photoperiods a greater proportion of cells were recruited to a higher expressing population. In vitro coculture of hamster pars tuberalis fragments increased prolactin promoter-driven luciferase activity in stably transfected GH3 cells in a dose- and duration-dependent manner. Conditioned medium from hamster and ovine pars tuberalis also activated the prolactin promoter. Furthermore, basal and forskolin-stimulated conditioned medium from hamster pars tuberalis increased prolactin mRNA expression in primary cultures of pars distalis cells. Melatonin attenuated the activity of pars tuberalis-conditioned medium but had no direct effect on either prolactin mRNA expression or secretion in pars distalis cell cultures. Finally, pars tuberalis fragments from long photoperiod hamsters stimulated prolactin gene promoter activity to a greater extent than those from short photoperiod hamsters. In conclusion, this study provides the first evidence in a seasonal mammal that the synthesis of prolactin depends on photoperiodic modulation of a pars tuberalis-derived factor. Our data support further the hypothesis that seasonal modulation of prolactin gene expression depends upon a melatonin-dependent paracrine action of the pars tuberalis on pars distalis lactotrophic cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2826.2001.00611.x
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  • 8
    Electronic Resource
    Electronic Resource
    Interplay of magnetism and high- T c superconductivity at individual Ni impurity atoms in Bi 2 Sr 2 CaCu 2 O 8+ δ (2001)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 411 (2001), S. 920-924 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Magnetic interactions and magnetic impurities are destructive to superconductivity in conventional superconductors. By contrast, in some unconventional macroscopic quantum systems (such as superfluid 3He and superconducting UGe2), the superconductivity (or ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35082019
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  • 9
    Electronic Resource
    Electronic Resource
    Quantum interference of superfluid 3 He (2001)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 412 (2001), S. 55-58 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Celebrated interference experiments have demonstrated the wave nature of light and electrons, quantum interference being the manifestation of wave–particle duality. More recently, double-path interference experiments have also demonstrated the quantum-wave nature of beams of neutrons, ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35083518
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  • 10
    Electronic Resource
    Electronic Resource
    Microscopic electronic inhomogeneity in the high- T c superconductor Bi 2 Sr 2 CaCu 2 O 8+ x (2001)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 413 (2001), S. 282-285 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The parent compounds of the copper oxide high-transition-temperature (high-Tc) superconductors are unusual insulators (so-called Mott insulators). Superconductivity arises when they are ‘doped’ away from stoichiometry. For the compound ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35095012
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