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  • American Institute of Physics (AIP)  (142)
  • Blackwell Publishing Ltd
  • Copernicus
  • 11
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 9230-9236 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The statistical properties of fractional Brownian walks are used to construct a path integral representation of the conformations of polymers with different degrees of bond correlation. We specifically derive an expression for the distribution function of the chains' end-to-end distance, and evaluate it by several independent methods, including direct evaluation of the discrete limit of the path integral, decomposition into normal modes, and solution of a partial differential equation. The distribution function is found to be Gaussian in the spatial coordinates of the monomer positions, as in the random walk description of the chain, but the contour variables, which specify the location of the monomer along the chain backbone, now depend on an index h, the degree of correlation of the fractional Brownian walk. The special case of h=1/2 corresponds to the random walk. In constructing the normal mode picture of the chain, we conjecture the existence of a theorem regarding the zeros of the Bessel function.
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 1153-1154 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The stepwise expansion method for the measurement of compressibility isotherms of gases, developed recently in this laboratory, has been modified in order to measure those gases for which only low-pressure fiducial density data are available. The modified method has been tested with CH4 as a measuring gas at 298.15 K and up to 9.9 kbar.
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  • 13
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 29 (1988), S. 16-20 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The algebraic structure of parastatistics has been generalized and it is found to be consistent with supersymmetric quantum mechanics with supercharges constructed out of the generalized para-Bose and para-Fermi operators. It is further shown that the operator algebra of generalized parastatistics offers a realization of the (graded) orthosymplectic group similar to that of orthogonal and symplectic groups using conventional parastatistics.
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  • 14
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 31 (1990), S. 156-163 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The application of the method of stochastic quantization originally attributed to Parisi and Wu has been extended to spinor fields obeying para-Fermi statistics. The connection between Euclidean and stochastic field theories is established in the conventional manner by proving the equivalence between a Langevin equation satisfied by para-Grassmann fields and a Fokker–Planck equation, the Hamiltonian of which has been constructed using para-Grassmann variables analogous to its construction from Grassmann variables in the Fermi case. As an example, a two-point Green function is calculated for any arbitrary value of order p of para-Fermi statistics, barring the pathological case p=2 which has been mentioned briefly.
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  • 15
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Tomographic imaging of the ionosphere is a recently developed technique that uses integrated measurements and computer reconstructions to determine electron densities. The integral of electron density along vertical or oblique paths is obtained with radio transmissions from low-earth-orbiting (LEO) satellite transmitters to a chain of receivers on the earth's surface. Similar measurements along horizontal paths can be made using transmissions from Global Position System (GPS) navigation satellites to GPS receivers on LEO spacecraft. Also, the intensities of extreme ultraviolet (EUV) emissions can be measured with orbiting spectrometers. These intensities are directly related to the integral of the oxygen ion and electron densities along the instrument line of sight. Two-dimensional maps of the ionospheric plasma are produced by analyzing the combined radio and EUV data using computerized ionospheric tomography (CIT). Difficulties associated with CIT arise from the nonuniqueness of the reconstructions, owing to limited angle measurements or nonoptimal receiver location. Improvements in both reconstruction algorithms and CIT measurement systems are being implemented to overcome these difficulties. New imaging systems being developed employ CIT for large area mapping of the plasma densities in the ionosphere. © 1998 American Institute of Physics.
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  • 16
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 4922-4927 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin films (13 μm) of polyethelene terephthalate (PET) are irradiated by different swift metallic heavy ions (180 MeV Ag14+ and 200 MeV Au15+) with the projectile linear energy transfer (LET) (∼10–14 keV/nm), respectively. LET dependence on the molecular structural changes in PFT irradiated at different ion fluences has been studied by the Fourier transform infrared spectroscopy. The study has revealed that beyond a critical LET entirely different pathways of amorphization beginning with partial recrystallization at lower ion fluence impact occurs in PET, contrary to the earlier established results. At considerably higher LET (∼14 keV/nm), the most characteristic crystalline stretching and bending vibration bands such as at 850 cm−1 (CH2 rocking), 972 cm−1 (C(Double Bond)O stretching), 1341 and 1471 cm−1 (CH2 bending) in PET have shown a significant rise in the respective infrared absorbance intensities upon lower ion fluence (∼1011 ions/cm2) impact. The absence of previously reported unsaturations such as alkynes at both the LET beam used are also observed. Interestingly, the aromatic system also appears to be unstable and participating in the modification process, particularly at the higher LET (∼14 KeV/nm). Possible interpretations are discussed. © 2002 American Institute of Physics.
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  • 17
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 5825-5831 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Plasma enhanced deposition of amorphous aluminum nitride (AlN) using trimethylaluminum, hydrogen, and nitrogen was performed in a capacitively coupled plasma system. Temperature was varied from 350 to 550 °C, and pressure dependence of the film structure was investigated. Films were characterized by Fourier transform infrared, Rutherford backscattering (RBS), ellipsometry, and x-ray diffraction (XRD). The films are amorphous in nature, as indicated by XRD. Variations in the refractive index were observed in ellipsometric measurements, which is explained by the incorporation of carbon in the films, and confirmed by RBS. Capacitance–voltage, conductance–voltage (G–V), and current–voltage measurements were performed to reveal bulk and interface electrical properties. The electrical properties showed marked dependence on processing conditions of the AlN films. Clear peaks as observed in the G–V characteristics indicated that the losses are predominantly due to interface states. The interface state density ranged between 1010 and 1011 eV−1 cm−2. Annealing in hydrogen resulted in lowering of interface state density values. © 2001 American Institute of Physics.
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  • 18
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 3590-3591 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The reliable operation of a spark gap at 300 Hz pulse repetition frequency by rotating a suitably configured dielectric plate between its electrodes is reported. The triggering of the spark gap has been achieved by the use of an optical sensor.
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  • 19
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 579-580 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Pulse duration as long as 14 μs has been obtained from a single longitudinal mode TEA CO2 laser. Such stretching occurred under conditions for which oscillation on a higher order transverse mode followed that on the TEM00 mode with partial temporal overlap between the two. Control of the intracavity aperture size in conjunction with cavity length tuning helped realize such an oscillation condition. © 2000 American Institute of Physics.
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  • 20
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 4242-4244 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have shown theoretically that the maximum repetition rate attainable with a switch for both resistive and resonant charging is independent of the value of energy transferred through the switch in case of a very fast discharge. Experimental confirmation of this has been achieved with a resistively charged 20 kV pulse generator (C was varied from ≅5 to 35 nF) switched by a spark gap into a load whose resistance varied from few ohms to a kΩ. © 1998 American Institute of Physics.
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