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  • 1
    Electronic Resource
    Electronic Resource
    Concentration fluctuations in polymer blend thermodynamics (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 1704-1708 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Monomer concentration fluctuations in high molecular weight polymer blends are investigated. The fluctuations reduce the value of the χ interaction term in the Flory–Huggins free energy by a factor of (1-6/π2) and add a concentration and molecular weight contribution which decreases phase stability for off-critical compositions. Except at the critical point, the spinodal values are smaller than those predicted from a Flory–Huggins-type free energy. For an incompressible blend with components of equal size N, the corrections to the spinodal were found to vary as ||1−2φ0||4/3N−1/3, where φ0 is the mean concentration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455116
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  • 2
    Electronic Resource
    Electronic Resource
    Electrostatic ion probe for tokamak-plasma-edge diagnostic (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 2205-2209 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An electrostatic probe for ion temperature and density measurements was built and tested in the scrape-off region of the TBR-1 small tokamak. The main parameters involved in the design and details of the construction of the probe are presented. The electron discrimination and the probe efficiency for ion detection were checked by measuring the probe current as a function of the collector retraction length for a constant voltage. The results for the ion temperature and density obtained from the characteristic curves are discussed and compared with previous measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138683
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  • 3
    Electronic Resource
    Electronic Resource
    Lie symmetries and invariants of the Lotka–Volterra system (1995)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 36 (1995), S. 1854-1867 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: In this paper we use the Lie symmetry method for finding rational and transcendental symmetry transformations and invariants for the 3D Lotka–Volterra system. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.531362
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  • 4
    Electronic Resource
    Electronic Resource
    Accuracy of eigenvalues: A comparison of two methods (1993)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 34 (1993), S. 1169-1175 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The problem of estimating the eigenvalues λ of the equation d2ψ/dx2+λf(x)ψ(x)=0, where f(x) is smooth and positive in the interval [0,l] and the imposed boundary conditions are ψ(0)=ψ(l)=0 is revisited. Two methods, the Wentzel–Kramers–Brillouin (WKB) method and Langer's method, which until very recently has been virtually ignored, are compared. The variational principle further improves the accuracy of the eigenvalues. The results obtained when the WKB and Langer's results are used as trial functions with the variational principle are also compared. Results are given in tabular form. The comparison shows that the Langer solution is the better of the two when the turning point [zero of f(x)] is close to the region of interest. If, however, the turning point is far from the region of interest, the two methods yield similar results. The reason for this is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.530192
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  • 5
    Electronic Resource
    Electronic Resource
    Alfvén and fast wave forces, affecting ions in magnetic traps with closed magnetic surfaces (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 1378-1381 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: General expressions for time- and surface-averaged radio frequency forces, affecting ions in closed toroidal devices, are obtained in this paper. Toroidal effects are included in these forces. These effects can, for example, be important to calculate Alfvén or fast wave forces in stellarators, spheromaks, or for toroidicity induced Alfvén wave eigenmodes (TAE) in axially symmetric tokamaks. The further simplification of obtained expressions should be fulfilled for the proper kind of rf waves and toroidal devices. It is hoped that these rf force expressions can, for example, be useful for the computer simulations of the transport barrier formation by Alfvén and fast waves in toroidal devices. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873377
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  • 6
    Electronic Resource
    Electronic Resource
    Characterization of electron and negative ion densities in fluorocarbon containing inductively driven plasmas (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 4929-4937 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron and negative ion densities were measured in inductively coupled discharges containing C4F8. In addition, the identity of the negative ions in C2F6, CHF3, and C4F8 containing discharges was investigated with a photodetachment experiment utilizing a microwave resonant cavity structure. To investigate the influence of surface material, the rf-biased electrode was covered with a silicon wafer or a fused silica (SiO2) wafer. Line-integrated electron density was determined using a microwave interferometer, and absolute negative ion densities in the center of the plasma were inferred using laser photodetachment spectroscopy. Voltage and current at the induction coil and rf-biased electrode were also measured for both surfaces as functions of induction coil power, pressure, and rf bias. For the range of induction powers, pressures, and bias power investigated, the electron density peaked at 6×1012 cm−2 (line integrated), or approximately 6×1011 cm−3. The negative ion density peaked at approximately 2.2×1011 cm−3. In most cases, the trends in the electron and negative ion densities were independent of the wafer material. However, a maximum in the negative ion density as a function of induction coil power was observed above a silicon wafer. The maximum is attributed to a power-dependent change in the density of one or more of the potential negative ion precursor species. A microwave resonant cavity structure was developed to identify the negative ions using laser photodetachment spectroscopy. The technique was demonstrated for inductively coupled discharges containing C4F8, C2F6, and CHF3. Scanning the laser wavelength over the range of the F− photodetachment energy indicated that while the dominant negative ion appeared to be F−, weak evidence for other molecular negative ions was observed. Unlike traditional microwave cavity techniques, this method offers the possibility of spatial resolution. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1410896
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  • 7
    Electronic Resource
    Electronic Resource
    Determination of processing damage in thin polycrystalline Ir films using Bragg-peak fringe analysis (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 3125-3131 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present an analysis of Bragg–Brentano diffraction spectra from blanket thin (10–20 nm) films of polycrystalline Ir, sputter deposited on thermally oxidized Si wafers. We observed that postdeposition annealing sharpened the Ir diffraction peaks, produced enhanced texture, and resulted in the formation of well-defined thickness fringes that were symmetric around the 111 Ir reflection. Scanning electron microscopy confirmed that the fringes were caused by the increased coherence lengths of the annealed grains. Annealed samples subsequently subjected to reactive ion etching exhibited asymmetric fringe patterns, with lower intensity fringes on the high angle side of the 111 Ir peak. Reannealing these samples restored the symmetric fringes. Analysis of the fringe patterns using simple equations and modeling programs in the public domain yielded valuable structural information about the film and the changes caused by processing. These results were verified by x-ray reflectivity measurements and modeling. We conclude that thickness fringe analysis using standard x-ray systems and simple programs can provide cost-effective process diagnostics for high atomic number thin film structures. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1346660
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  • 8
    Electronic Resource
    Electronic Resource
    A cost-effective method for minimizing the sphere-of-confusion error of x-ray microdiffractometers (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 1300-1304 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Microdiffractometers are used to obtain x-ray diffraction data from regions that are tens of microns or less in size. If a microdiffractometer's rotation circles do not share the same center, or if the feature of interest on a sample does not lie at the center of all rotations, the sample feature will, upon rotation of the diffractometer circles, precess through a finite volume known as the sphere of confusion (SoC). If the size of the beam used for diffraction analysis is smaller than the SoC diameter, the beam may actually move off the region of interest. In this article, we describe a new technique, based on x-ray fluorescence imaging and coordinate transforms, which can maintain the sample position to within ±6 μm over all rotations even when a commercial diffractometer is used as the base for the microdiffractometer system. In this scheme, a grid held in place on the specimen surface is mapped using fluorescent radiation at various sample tilts. The transformation matrices, which relate the grid coordinates to the sample stage coordinates at different sample tilts, can then be used to bring the sample stage into coincidence with its original position. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149588
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  • 9
    Electronic Resource
    Electronic Resource
    Divergence effects in monochromatic x-ray microdiffraction using tapered capillary optics (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 1991-2000 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Tapered capillaries are frequently used as beam-concentrating optics in microbeam x-ray diffraction experiments. The beams exiting such devices are usually highly divergent and may possess nonuniform intensity distributions. In addition, their alignment poses some special challenges. In this article, the effects of these factors on the precision and accuracy of diffraction data are presented. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150567
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  • 10
    Electronic Resource
    Electronic Resource
    Trapping and flow among random arrays of oriented spheroidal inclusions (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 5592-5598 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The effective trapping rate k associated with diffusion-controlled reactions among random distributions of spatially correlated and uncorrelated, oriented spheroidal traps of aspect ratio ε is determined from Brownian motion simulations. Data for k are obtained for prolate cases (ε=2, 5, and 10), oblate cases (ε=0.1, 0.2, and 0.5), and spheres (ε=1) over a wide range of trap volume fractions (φ2) and satisfy recently obtained rigorous lower bounds on k for this statistically anisotropic model. The results for the trapping rate for correlated traps always bounds from above corresponding results for uncorrelated traps. Generally, the trapping rate k, for fixed φ2, increases with decreasing aspect ratio ε, showing a precipitous rise in k as the spheroids become disklike. Using a recent theorem due to Torquato [Phys. Rev. Lett. 64, 2644 (1990)], data for the trapping rate k can be employed to infer information about the fluid permeability tensor K associated with slow viscous flow through porous media composed of the same arrays of oriented spheroidal particles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460495
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