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  • 1
    Electronic Resource
    Electronic Resource
    Nonlinear Three-dimensional Inversion of Low-frequency Scattered Elastic Waves (1999)
    Springer
    Pure and applied geophysics 156 (1999), S. 557-589 
    Details
    ISSN: 1420-9136
    Keywords: Key Words: Elastic wave scattering, nonlinear inversion, Rayleigh, Mie approximation.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —We investigate a new nonlinear inversion method for low frequencies to determine the bulk and shear modulus as well as the material density and the location of subsurface inhomogeneities. The solution is a direct exact nonlinear inversion of single scattered waves containing near- and far-field terms for incident P and scattered P and S waves, allowing for inversion of parameters in the vicinity and at distance from the sources and receivers. Because the approach is based on single scattering theory, the range of application includes single strong scattering anomalies of various sizes like magma chambers, gas- or fluid-filled cavities, or buried near-surface obstacles. The replacement of the material properties by a new set of parameters, referred to as scattering factors, allows the inverse problem to be solved analytically. The nonlinear nature of the scattering problem is investigated and implications for the inversion process are discussed. The deviations in the elastic parameters as a function of the scattering factors show a strong asymmetry about zero, and therefore linearized approximations will perform differently, depending on the sign of the perturbation. Based on the low frequency (Rayleigh) approximation, we introduce and evaluate a pair of approximations (Mie) derived by numerical and analytical integration of the Rayleigh approximation. Both approximations are based on the underlying principle of subdividing the inhomogeneities into a number of small noninteracting parts and subsequent integration over the total volume, thus increasing the Rayleigh limit and producing better resolution of the parameter estimates during the inversion. The two Mie approximations, when evaluated as a function of scattering angle and distance, produce similar results in the mid- and far-field of the inhomogeneity and reveal better resolution than the Rayleigh approximation. For three anomalies of ± 50% in bulk modulus, shear modulus, and density, the relative error between the exact solution and the two Mie approximations remains below 10%, 20%, and 30%, respectively, for values of k p R 〈 3.0, where R is the radius of the heterogeneity. However, smaller errors for individual cases are found for values up to k p R≈ 4.5. The performance of the inversion based on the analytically and the numerically integrated Mie approximation is tested for single parameter perturbations, revealing reliable and stable inversion results for the bulk and the shear modulus, reasonable results for the density, and crosstalk between the shear modulus and the density. The results show well-defined locations of the anomalies and slight deviations in the estimates of their magnitudes, which can be explained by amplitude and phase deviations between the analytical solution used for forward modeling and the approximations used for the inversion. The analytical Mie approximation provides a fast means to estimate elastic parameters compared to the more time consuming numerically integrated approximation, while the latter can be applied to more arbitrarily shaped inhomogeneities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000240050313
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  • 2
    Electronic Resource
    Electronic Resource
    The MHC of a broiler chicken line: serology, B-G genotypes, and B-F/B-LB sequences (1999)
    Springer
    Immunogenetics 49 (1999), S. 215-224 
    Details
    ISSN: 1432-1211
    Keywords: Key words Chicken ; Major histocompatibility complex ; Class I ; Class II ; Haplotypes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract  Although the major histocompatibility complex of chickens (encoded in the B complex) has been studied for a number of years, almost all work has focused on the White Leghorn breed. Broiler (meat-type) chickens were derived from other breeds, including Cornish and Plymouth Rock. It was our hypothesis that new B haplotypes, not previously identified in White Leghorns, might be present in lines of broiler chickens. Furthermore, alloantisera used to identify B serotypes in Leghorn lines reportedly do not work well outside the line in which they were raised, with the result that broiler B haplotypes have not been incorporated into the universal nomenclature system. Our approach was to use a panel of B alloantisera produced to identify B serotypes within a commercial broiler breeder line (designated line A). B homozygotes identified serologically were compared by B-G genotyping using restriction fragment length polymorphism analysis. Furthermore, reverse transcription-polymerase chain reaction was used to amplify variable domains of expressed B-LB and B-F genes of homozygotes of most of the B serotypes in Line A, followed by cloning and nucleotide sequence determination. Comparison of B-LB and B-F sequences with standard Leghorn haplotypes demonstrated the existence of new alleles of B-L and B-F in a broiler breeder line, as well as the presence of alleles previously identified in Leghorns. In some cases, Leghorn-type alleles were in linkage with different B-G alleles in the broiler line than the common haplotypic associations found in Leghorn lines.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002510050482
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  • 3
    Electronic Resource
    Electronic Resource
    Pathophysiology of Bile Duct Stones (1998)
    Springer
    Molecular medicine 22 (1998), S. 1114-1118 
    Details
    ISSN: 1076-1551
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. Secondary duct stones are usually detected and easily removed at the time of cholecystectomy either during surgery or endoscopically before or after the operation. Primary duct stone diseases, although much less common, are often a greater therapeutic challenge. These stones may be huge, distributed throughout the biliary tree (including areas difficult to access), and unresponsive to pharmacologic measures. Recurrence of primary duct stones is the rule rather than the exception, and reliable methods for prevention remain to be established. Moreover, morbidity and mortality due to biliary obstruction, sepsis, and choliangiocarcinoma make primary bile duct stone disease a formidable adversary. A better understanding of their pathogenesis can facilitate more effective approaches to treatment and, most important, prevention.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002689900529
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  • 4
    Electronic Resource
    Electronic Resource
    Glucose analogue inhibitors of glycogen phosphorylase: from crystallographic analysis to drug prediction using GRID force-field and GOLPE variable selection (1995)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 51 (1995), S. 458-472 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Several inhibitors of the large regulatory enzyme glycogen phosphorylase (GP) have been studied in crystallographic and kinetic experiments. GP catalyses the first step in the phosphorylysis of glycogen to glucose-l-phosphate, which is utilized via glycolysis to provide energy to sustain muscle contraction and in the liver is converted to glucose. α-D-Glucose is a weak inhibitor of glycogen phosphorylase form b (GPb, Ki = 1.7 mM) and acts as a physiological regulator of hepatic glycogen metabolism. Glucose binds to phosphorylase at the catalytic site and results in a conformational change that stabilizes the inactive T state of the enzyme, promoting the action of protein phosphatase 1 and stimulating glycogen synthase. It has been suggested that in the liver, glucose analogues with greater affinity for glycogen phosphorylase may result in a more effective regulatory agent. Several N-acetyl glucopyranosylamine derivatives have been synthesized and tested in a series of crystallographic and kinetic binding studies with GPb. The structural results of the bound enzyme–ligand complexes have been analysed together with the resulting affinities in an effort to understand and exploit the molecular interactions that might give rise to a better inhibitor. Comparison of the N-methylacetyl glucopyranosylamine (N-methylamide, Ki = 0.032 mM) with the analogous β-methylamide derivative (C-methylamide, Ki = 0.16 mM) illustrate the importance of forming good hydrogen bonds and obtaining complementarity of van der Waals interactions. These studies also have shown that the binding modes can be unpredictable but may be rationalized with the benefit of structural data and that a buried and mixed polar/non-polar catalytic site poses problems for the systematic addition of functional groups. Together with previous studies of glucose analogue inhibitors of GPb, this work forms the basis of a training set suitable for three-dimensional quantitative structure–activity relationship studies. The molecules in the training set are void of problems and potential errors arising from the alignment and bound conformations of each of the ligands since the coordinates were those determined experimentally from the X-ray crystallographic refined ligand–enzyme complexes. The computational procedure described in this work involves the use of the program GRID to describe the molecular structures and the progam GOLPE to obtain the partial least squares regression model with the highest prediction ability. The GRID/GOLPE procedure performed using 51 glucose analogue inhibitors of GPb has good overall predictivity [standard deviation of error predictions (SDEP) = 0.98 and Q2 = 0.76] and has shown good agreement with the crystallographic and kinetic results by reliably selecting regions that are known to affect the binding affinity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S090744499401348X
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  • 5
    Electronic Resource
    Electronic Resource
    Volcanoes of the southwestern extension of the active Mariana island arc: New swath-mapping and geochemical studies (1998)
    Oxford UK : Blackwell Science Pty
    The @island arc 7 (1998), S. 0 
    Details
    ISSN: 1440-1738
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Until recently it was thought that the volcanoes of the Mariana island arc of the western Pacific terminated at Tracey Seamount at ∼ 14°N immediately west of Guam. Sea floor mapping in 1995 shows a series of large volcanic seamounts stretching westward for nearly 300 km beyond that point. The morphology, spacing, and composition of those sampled are consistent with their having formed as a consequence of eruption of suprasubduction zone arc magmas. The relationships of the volcanoes to the tectonic processes of subduction of the Pacific plate beneath the southern portion of the Mariana convergent plate margin are becoming increasingly clear as new bathymetry and geochemical data are amassed. The volcanoes along this trend that lie closest to Guam are forming where the center of active extension in the back-arc basin intersects the line of arc volcanoes. They develop well-defined rifts that are parallel to rift structures along the extension center, whereas volcanoes of the spreading axis to the north are smaller than the frontal arc volcanoes and tend to form along lineaments. Compositions of lavas from these intersection volcanoes bear some similarities to back-arc basin basalt, but are on the whole well within the range of compositions for Mariana island arc lavas. The Pacific plate subducts nearly orthogonal to the strike of the trench along the southern part of the Mariana system and the distance to the arc line from the trench axis is only ∼ 150 km. Several deep fault-controlled canyons on the inner slope of the southern Mariana trench indicate an enhanced tectonic extension of this plate margin. The presence of these active arc volcanoes and the existence of the orthogonal normal faulting along the southern Mariana forearc supports a model of radial extension for formation of the Mariana Trough, a model previously dismissed because of the lack of evidence of these two major geological features.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1440-1738.1998.00212.x
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  • 6
    Electronic Resource
    Electronic Resource
    Enhancement of Tokamak Fusion Test Reactor performance by lithium conditioning (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1892-1897 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Wall conditioning in the Tokamak Fusion Test Reactor (TFTR) [K. M. McGuire et al., Phys. Plasmas 2, 2176 (1995)] by injection of lithium pellets into the plasma has resulted in large improvements in deuterium–tritium fusion power production (up to 10.7 MW), the Lawson triple product (up to 1021 m−3 s keV), and energy confinement time (up to 330 ms). The maximum plasma current for access to high-performance supershots has been increased from 1.9 to 2.7 MA, leading to stable operation at plasma stored energy values greater than 5 MJ. The amount of lithium on the limiter and the effectiveness of its action are maximized through (1) distributing the Li over the limiter surface by injection of four Li pellets into Ohmic plasmas of increasing major and minor radius, and (2) injection of four Li pellets into the Ohmic phase of supershot discharges before neutral-beam heating is begun. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871984
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  • 7
    Electronic Resource
    Electronic Resource
    Deuterium–tritium high confinement (H-mode) studies in the Tokamak Fusion Test Reactor (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2366-2374 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High or enhanced confinement (H-mode) plasmas have been obtained for the first time with nearly equal concentrations of deuterium and tritium in high-temperature, high poloidal beta plasmas in the Tokamak Fusion Test Reactor (TFTR) [McGuire, Phys. Plasmas 2, 2176 (1995)]. Tritium fueling was provided mainly through high-power neutral beam injection (NBI) with powers up to 31 MW and beam energies of 90–110 keV. A transition to a circular limiter H-mode configuration has been obtained, following a programmed rapid decrease of the plasma current. Isotope effects, due to the presence of tritium, led to different behavior for deuterium–deuterium (DD) and deuterium–tritium (DT) H-modes relative to confinement, edge localized magnetohydrodynamic modes (ELMs), and ELM effects on fusion products. However, the threshold power for the H-mode transition was the same in DD and DT. Some of the highest values of the global energy confinement time, τE, have been achieved on TFTR during the ELM-free phase of DT H-mode plasmas. Enhancements of τE greater than four times the L-mode have been attained. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871490
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  • 8
    Electronic Resource
    Electronic Resource
    Isotopic scaling of confinement in deuterium–tritium plasmas (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2299-2307 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The confinement and heating of supershot plasmas are significantly enhanced with tritium beam injection relative to deuterium injection in the Tokamak Fusion Test Reactor [Plasma Phys. Controlled Fusion 26, 11 (1984)]. The global energy confinement and local thermal transport are analyzed for deuterium and tritium fueled plasmas to quantify their dependence on the average mass of the hydrogenic ions. Radial profiles of the deuterium and tritium densities are determined from the D–T fusion neutron emission profile. The inferred scalings with average isotopic mass are quite strong, with τE∝〈A〉0.85±0.20, τEthermal∝〈A〉0.89±0.20, χitot∝〈A〉−2.6±0.5, and De∝〈A〉−1.4±0.2 at fixed Pinj. For fixed local plasma parameters χitot∝〈A〉−1.8±0.4 is obtained. The quoted 2σ uncertainties include contributions from both diagnostic errors and shot irreproducibility, and are conservatively constructed to attribute the entire scatter in the regressed parameters to uncertainties in the exponent on plasma mass. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871253
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  • 9
    Electronic Resource
    Electronic Resource
    Enhanced performance of deuterium–tritium-fueled supershots using extensive lithium conditioning in the Tokamak Fusion Test Reactor (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 4252-4256 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the Tokamak Fusion Test Reactor (TFTR) [K. M. McGuire et al., Phys. Plasmas 2, 2176 (1995)] a substantial improvement in fusion performance has been realized by combining the enhanced confinement due to tritium fueling with the enhanced confinement due to extensive conditioning of the limiter with lithium. This combination has resulted in not only significantly higher global energy confinement times than have previously been obtained in high current supershots, but also in the highest central ratio of thermonuclear fusion output power to input power observed to date. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871050
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  • 10
    Electronic Resource
    Electronic Resource
    Distinction between DD and DT neutrons in the TFTR neutron collimator (abstract) : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 552-552 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A difficult part of the analysis of the neutron collimator data is the distinction between contributions from DD and DT neutrons. This is important for the majority of TFTR discharges, which use neutral deuterium heating beams and relatively small amounts of tritium. At present, the DT-neutron contribution is determined from a comparison of the chord-integrated neutron collimator data with measurements of the DT-neutron source strength from general wide-angle detectors, using an iterative computational method. A more satisfactory solution should be obtained with detectors that measure the contributions from DD and DT neutrons, and gamma radiation, directly. Pulse-shaping techniques are insufficient, since the detectors in the neutron collimator are operated in current mode. The presently used data analysis is described and the concept of a new multilayered plastic detector that makes use of the differences in the attenuation of the various radiation components is presented. The dimensions of the detector are based on calculations of the attenuation for the expected neutron energy spectrum. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147650
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