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  • American Institute of Physics (AIP)  (34)
  • 1990-1994  (34)
  • 1965-1969
  • 1935-1939
  • 1930-1934
  • 1
    Electronic Resource
    Electronic Resource
    Spin correlations in dense Kondo systems : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5403-5405 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We performed numerical diagonalization studies of the periodic Anderson Model on finite chains up to 6 sites, in the integral valence limit for T=0. We find that in the weak coupling (Kondo) region the hybridization between f and conduction electrons induces pronounced correlations between the f spins. These correlations are ferromagnetic for low filling and become antiferromagnetic close to half-filling, with a smooth transition between the limiting cases. In no limit can the physics be completely described by a Ruderman–Kittel–Kasuya–Yosida effective spin Hamiltonian, as f and conduction band electrons are always correlated. To study the onset of long range order we considered also a simpler model for the half-filled case, called "Kondo necklace.'' We studied the model at T=0 by numerical diagonalization and finite-size scaling, on chains up to 12 sites. We find that below a finite critical value of the Kondo coupling there exists a gapless phase with quasi long range antiferromagnetic correlations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353696
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  • 2
    Electronic Resource
    Electronic Resource
    Experimental observation of particle entrapment and transport in an intense ion beam (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 2937-2944 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An experiment is described in which 1.5- to 3.0-μm-diam gold spheres are injected into the central region of a nearly square 27.4-keV, 9-mA argon ion beam with a cross-sectional area of approximately 3.3 cm2, and the results compared to theory. In the experiment, silicon wafers located 30 and 50 cm from the point of introduction served as targets to collect the particles. After injection, large numbers of gold-filled craters were found throughout and surrounding the central implant region on the wafers. Gravity and axial momentum transfer acting alone generate trajectories that would place all the particles well below the horizontal centerline of the implanted area. Consequently, particles landing above the central impact region can only be explained by the presence of an electrostatic confining force. Theoretical calculations based on an electrostatic trapping model predict particle distributions on the target that are in remarkable agreement with our experimental results. Thus, these observations provide conclusive evidence in support of beam particle entrapment and transport, phenomena that have heretofore remained unconfirmed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351027
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  • 3
    Electronic Resource
    Electronic Resource
    Two-impurity Anderson model: Variational wave functions with electron-hole excitations : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6628-6630 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A variational study of the two-impurity Anderson model is performed. Renormalization effects associated with electron-hole (EH) excitations are studied. For an interimpurity distance R≥Rc(approximately-equal-to)2.5/kF, the effect of EH excitations is to renormalize the f-level position and to add a magnetic interaction −JS1⋅S2, where the coupling J can be calculated in perturbation theory. For R≤Rc, the magnetic coupling itself is renormalized by the collective Kondo effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352535
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  • 4
    Electronic Resource
    Electronic Resource
    Comment on "High-detectivity GaAs quantum-well infrared detectors with peak responsivity at 8.2 μm'' (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 4129-4129 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent measurements of less-than-full shot noise in GaAs/AlGaAs quantum-well infrared detectors can be explained in terms of standard photoconductor generation-recombination theory. Therefore, more complex models are not yet necessary.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348426
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  • 5
    Electronic Resource
    Electronic Resource
    Thermoelectric properties of pressure-sintered Si0.8Ge0.2 thermoelectric alloys (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 4333-4340 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The thermoelectric properties of 28 sintered Si0.8 Ge0.2 alloys, heavily doped with either boron or phosphorus and prepared from powders with median particle sizes ranging from about 1 μm to over 100 μm, have been determined from 300 to 1300 K. The thermal conductivity decreases with decreasing particle size, however, the figure of merit is not significantly increased due to a compensating reduction in the electrical conductivity. The thermoelectric figure of merit is in good agreement with results of Dismukes et al. [J. Appl. Phys. 10, 2899 (1964)] on similarly doped alloys prepared by zone-leveling techniques. The electrical and thermal conductivity are found to be sensitive to preparation procedure while the Seebeck coefficient and figure of merit are much less sensitive. The high-temperature electrical properties are consistent with charge carrier scattering by acoustic or optical phonons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348408
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  • 6
    Electronic Resource
    Electronic Resource
    Monte Carlo evaluation of real time coherent state path integrals (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 2966-2977 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An alternative formulation of the discrete real time coherent state path integral is examined. Following the development of a previous work [T. L. Marchioro II, J. Math Phys. 31, 2935 (1990)] the discrete coherent state action is transformed to second order form. The resulting path integral expression contains an integrand which factors into a Gaussian probability density and an oscillatory term, making the integral directly amenable to Monte Carlo techniques. Several simple examples in one and two spatial dimensions are presented and the possibilities of extending such an approach to general multidimensional systems are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461994
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  • 7
    Electronic Resource
    Electronic Resource
    Differential translation energy-loss distributions at 1 eV energies: K–C2H2 (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 7981-7990 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In K–C2H2 collisions at collision energies 0.4(approximately-less-than)E(approximately-less-than)1.3 eV and scattering angles 40°(approximately-less-than)cursive-theta(approximately-less-than)180° surprisingly little transfer of energy from translation into the internal degrees of freedom of the acetylene molecule is found. The observations are consistent with the assumptions of electronically covalent encounters, insignificant activation of the acetylene vibrations, and rotational excitation produced by spindle-shaped equipotentials, nearly spherical in a broad vicinity of the C 3/4 C bond.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460132
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  • 8
    Electronic Resource
    Electronic Resource
    Ab initio potentials and pressure second virial coefficients for CH4–H2O and CH4–H2S (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 7808-7812 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio Hartree–Fock (HF) and second-order many-body perturbation theory (E2) were used to generate data for pair potentials of the mixtures CH4–H2S and CH4–H2O. The points were fit with site–site functions consisting of terms for interactions of the following types: exponential repulsion and R−6 and electrostatic attraction. The basis sets of Gaussian functions were developed by systematically adding polarization functions to maximize the zeroth-order dipole polarizability; the counterpoise method was used to correct basis set superposition error. The best well depths calculated for CH4–H2S and CH4–H2O were −0.0227 and −0.0215 eV, respectively (with no experimental results available for comparison). The potentials were evaluated by examining errors in the dipole polarizabilities and pressure second virial coefficients.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459362
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  • 9
    Electronic Resource
    Electronic Resource
    Stimulated Raman probing of supercooling and phase transitions in large N2 clusters formed in free jet expansions (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 7068-7078 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High resolution stimulated Raman spectroscopy (SRS) has been used to examine N2 and N2/He free jet expansions and also equilibrium samples of N2 from 15 to 110 K. The jet spectra show the formation of large liquid clusters which supercool and subsequently freeze to form crystalline β-N2 solid and, in He expansions, undergo a further transformation to a partially annealed α-N2 form. CW-SRS frequency and linewidth data obtained for equilibrium samples of the condensed phases of N2 yielded frequency–temperature relations used in deducing internal temperatures for the clusters produced in the expansion experiments. Analysis of the cooling curves indicates a mean cluster diameter of 35 nm and favors a prompt freezing process rather than a gradual conversion of liquid to solid in a single cluster on the microsecond time scale of the experiments. Supercooling limits of 34 to 44 K are deduced for the liquid, far below the triple point temperature of 63.2 K at which equilibrium samples freeze. Some evidence for surface versus bulk contributions to the spectra is seen in the asymmetric line shapes observed for liquid clusters in the condensation region. The results show that the high spectral and spatial resolution of nonlinear Raman methods such as SRS and CARS provide a unique probe of the condensation processes in free jet expansions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458247
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  • 10
    Electronic Resource
    Electronic Resource
    Vibrational relaxation of highly excited SiF4 and C6F5H by Ar (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 6011-6016 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibrational relaxation of SiF4 and C6F5H in an Ar bath was measured as a function of initial energy using the method of time-resolved optoacoustics. SiF4 was found to relax nonexponentially, with a rate constant which varied approximately as the vibrational energy raised to the 3/2 power. This behavior is similar to that observed earlier for SF6+Ar below the bottleneck. In contrast, C6F5H was observed to decay exponentially, as expected for a large molecule in the quasicontinuum. These two types of behavior are discussed in the context of previously proposed propensity rules for the vibrational relaxation of highly excited molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458372
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