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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 2825-2835 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A theoretical analysis of a spherical focusing transducer for broadband acoustic microscopy is proposed. The originality of the present contribution is the particular attention we have paid to describe, as rigorously as possible, the diffraction phenomena. Our analysis starts in the harmonic domain with the well-known angular spectrum method, and then gets into the time domain. A new formulation of the angular spectrum in the focal plane has been obtained and compared to other expressions previously reported. This article is deliberately limited to isotropic semi-infinite plane reflectors in order to carry out the inverse Fourier transform in an analytical way. The analytical approach is helpful for the physical interpretation of particular interesting phenomena observed in the transient analysis. A new kind of contribution to the echographic response has been identified and named "geometrical edge waves." The weight and the arrival time of each discontinuity of the impulse response is analytically evaluated and the physical meaning of each of them is clearly established with the help of a ray model. In the last part of this article, a broadband polyvinylidene fluoride transducer excited by short pulses is used for the experimental validation of the model. The excellent quantitative agreement observed on the time waveforms confirms the efficiency of our approach both in the time domain and in the harmonic one. The comparison between theory and experiment is limited here to some typical examples, but similar results have been obtained on a wide range of defocus and for a large variety of materials. Applications for the characterization of materials will be discussed in future publications. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Data on the discharge behavior, thermal loads, halo currents, and runaway electrons have been obtained in disruptions on the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 2A 441 (1985)]. These experiments have also evaluated techniques to mitigate the disruptions while minimizing runaway electron production. Experiments injecting cryogenic impurity "killer" pellets of neon and argon and massive amounts of helium gas have successfully reduced these disruption effects. The halo current generation, scaling, and mitigation are understood and are in good agreement with predictions of a semianalytic model. Results from "killer" pellet injection have been used to benchmark theoretical models of the pellet ablation and energy loss. Runaway electrons are often generated by the pellets and new runaway generation mechanisms, modifications of the standard Dreicer process, have been found to explain the runaways. Experiments with the massive helium gas puff have also effectively mitigated disruptions without the formation of runaway electrons that can occur with "killer" pellets. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The fast ignitor scheme for inertial confinement fusion requires forward driving of the critical density surface by light pressure (hole boring) to allow energy deposition close to the dense fuel. The recession velocity of the critical density surface has been observed to be v/c=0.015 at an irradiance of 1.0×1019 W cm−2 at a wavelength of 1.05 micron, in quantitative agreement with modeling. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 227-233 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The temporal development of laser driven single mode perturbations in thin Al foils has been measured using extreme ultraviolet (XUV) laser radiography. 15, 30, 70 and 90 μm single modes were imprinted on 2 μm thick Al foils with an optical driver laser at 527 nm for intensities in the range 5×1012 to 1.5×1013 W cm−2. The magnitude of the imprinted perturbation at the time of shock break out was determined by fitting to the data estimated curves of growth of the Rayleigh–Taylor instability after shock break out. The efficiency of imprinting is independent of perturbation wavelength in the parameter range of this experiment, suggesting little influence of thermal conduction smoothing. The results are of interest for directly driven inertially confined fusion. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2763-2765 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The self-consistent radial electric field shear generated by a drift-thermal turbulence is studied in some detail. A set of new dynamical equations is derived. In this model, there exist three kinds of equilibrium states. The first is the zero shear state of the radial electric field; the second is the positive shear state of the radial electric field; and the third is the negative shear state of the radial electric field. But only the negative shear state may be stable. Two kinds of stable states with the negative shear radial electric field are relevant to the behavior such as that exhibited by high (H) mode and by edge localized modes (ELMs), respectively. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5528-5530 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spin-valve (SV) films Si(100)/Ta30/NiFe50/CoFe20/Cu26/CoFe23/Ru7/CoFe20/IrMn50/Ta30 (in Å) exhibit a room temperature (RT) giant magnetoresitance (GMR) ratio of 8.5% with an effective exchange pinning field (Heex) of ∼1.3 kOe and an antiferromagnetic (AF) saturation field (Hs) of ∼6.0 kOe. The synthetic spin valve shows a GMR ratio of 5.0% at 150 °C with Heex〉500 Oe, while a conventional spin valve [Si(100)/Ta50/NiFe50/CoFe20/Cu28/CoFe22/IrMn50/Ta50 in Å] has a GMR ratio of 5.0% with Hex〈200 Oe. The synthetic sample also showed a superior thermal stability with a RT GMR value of 6.9% (compared to 6.1% for conventional sample) after an anneal at 250 °C for 10 h. Shielded narrow track synthetic SV readers demonstrated high amplitude, large dynamic range, and excellent magnetic stability, indicating extendibility for ultrahigh density read head applications. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1365-2133
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: We studied the pathogenetic role of iminodipeptides, and the effects of corticosteroids on the skin lesions of two adult female siblings with prolidase deficiency. The elder sister had had severe skin ulcers and mental retardation since childhood, while the younger sister had shown milder clinical manifestations since late adolescence. The ulcers showed vascular wall thickening and neutrophil infiltration. Oral prednisolone at moderate doses was not effective, but corticosteroid pulse therapy followed by a moderate dose of prednisolone improved the preulcerative indurated lesions and ulcers. A 2-year follow-up of the younger patient indicated that N-formyl methionyl leucyl phenylalanine-induced neutrophil superoxide generation was elevated, in parallel with an increase in the serum iminodipeptide level, when the skin ulcers and preulcerative indurated lesions were most active. Corticosteroid pulse therapy downregulated the superoxide generation by neutrophils. The serum iminodipeptide level, however, did not decrease during 25 days after pulse therapy. These findings suggest that iminodipeptides may play an important part in aggravating the skin lesions by priming neutrophil superoxide generation, and that high-dose corticosteroids improve the skin lesions, probably by inhibiting the infiltration, and superoxide generation by, neutrophils. Neutrophil superoxide generation was more prominent in the elder sister, suggesting that clinical severity may depend on the response of neutrophils to the iminodipeptides. Chronic stimulation by superoxide may cause thickening of cerebral blood vessels and eventual mental retardation.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 1226-1232 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the properties of an all-solid-state electrochromic (EC) device that can be switched over a useful range of optical transmissions with voltages below 1 V. This switching voltage is smaller than required by other solid-state EC devices reported to date. We attribute the lower-than-normal switching voltage to the use of a thermally evaporated MgF2 thin film as the lithium ion conducting layer. Electrochemical impedance spectroscopy studies show that high lithium ion conductivity and low interfacial barriers for lithium exchange with the adjacent electrochromic and ion storage layers make MgF2 a good choice for the ion conductor in EC devices. This reduction in switching voltage is a first step toward powering an EC device by an integrated semitransparent single-junction photovoltaic (PV) cell. In a side-by-side bench test, where the EC device is connected to a semitransparent a-SiC:H PV cell having on open circuit voltage of 0.87 V, a relative transmission change in the EC device of 40% is achieved in less than 60 s. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 4334-4338 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The undercooling and nucleation of Al4Mn alloy have been investigated by containerless solidification in a 1.2 m long drop tube, where molten droplets of the alloy solidified in the vacuum. Droplets in various sizes were collected at the bottom of the tube. It is found by x-ray and electron diffractions that besides the orthorhombic Al6Mn and β-Mn phases, two approximants of the decagonal quasicrystal, one approximant of the icosahedral quasicrystal and decagonal domains can be observed in the as-solidified droplets. However, due to the different cooling rate or undercooling in the samples of different sizes, the phases mentioned above will appear in different amounts. The relationship between the phase composition and the sample size is discussed on the basis of the classical nucleation and growth theories. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5113-5115 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The role of topological coupling, the magnetostatic coupling associated with interfacial roughness in magnetic sandwich/multilayer structures, was studied both analytically and experimentally. We report the first controlled measurements of such topological coupling. A coupling field of the order of 10 Oe between magnetic layers was observed in Co/Cu/Co sandwich structures fabricated with an artificially controlled in-phase roughness of variable amplitude with a fixed period of 3.5 μm. The coupling field was compared with the value predicted by a first-order approximation model and correlated with the geometry of the structure. Scale invariance of the coupling field allows the results to be extended to ultrathin giant magnetoresistance/spin valve structures. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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