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  • American Institute of Physics (AIP)  (417)
  • 1995-1999  (417)
  • 1
    Electronic Resource
    Electronic Resource
    Ab initio calculations for the anharmonic vibrational resonance dynamics in the overtone spectra of the coupled OH and CH chromophores in CD2H–OH (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 11958-11970 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report high level ab initio calculations (treating correlation by second order Möller–Plesset perturbation theory, MP2) of a five-dimensional normal coordinate subspace of the potential and electric dipole hypersurfaces of the Cs conformer of dideuteromethanol, CD2HOH. Accurate vibrational variational calculations are carried out using a discrete variable representation (DVR) for the five anharmonically coupled modes (three coupled CH stretching and bending modes and the OH stretching and high frequency OH bending mode). The overtone spectra of the OH chromophore are calculated and analyzed in detail with respect to their anharmonic resonance dynamics leading to short time intramolecular vibrational redistribution (IVR) via the close resonance coupling of 5νOH (5ν1) with 4νOH+νCH(4ν1+ν2), as previously observed and assigned experimentally. While the assignment of the resonance is confirmed by the ab initio calculation, a sequence of calculations including various subspaces (two-dimensional to five-dimensional) lead to the conclusion that the resonance contains important contributions from coupling to the various bending modes, not just involving the CH– and OH stretching modes. Furthermore, even in the two-dimensional subspace the effective coupling constants k1112 and k1222 characterizing the resonance are not identical with the anharmonic potential constants C1112 and C1222 in the Taylor expansion of the potential, but rather an expansion to sixth order is needed to describe the resonance quantitatively. A similar conclusion holds true with other low order perturbation expansions of the resonance coupling, involving sequences of cubic couplings to other modes. We furthermore predict important resonances between OH stretching and OH bending also involving CH bending modes, which contribute to IVR at higher levels of excitation. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479177
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  • 2
    Electronic Resource
    Electronic Resource
    Low-temperature photochromic response of phosphorus-doped bismuth silicon oxide (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 2010-2014 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Phosphorus is one of several dopants that electronically compensate the native deep donor responsible for the yellow coloration observed in bismuth silicon oxide (BSO). Low-temperature optical absorption measurements of a series of Czochralski-grown P-doped BSO crystals show that ∼0.1–0.15 at. % P is needed in the sample to fully remove the yellow coloration. The absorption cutoff in the fully compensated P-doped sample was at 3.2 eV while compensated Al- and Ga-doped samples cutoff at 3.35 eV. Excitation at 10–15 K with near band-edge light produces photochromic absorption bands. In the lightly-doped (partially bleached) samples these bands were identical to those observed in undoped BSO. In the fully bleached sample a new spectrum was observed. Its major contribution was a band centered near 1.8 eV with a weaker absorption in the blue-green. By comparison with the spectra observed in undoped and in Al-doped material before and after photoexcitation it is believed that the 1.8 eV band is due to the [PO4]− center and that the broad 2.45 eV band observed in Al- and Ga-doped BSO is due to the [BiO4]0 center. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360176
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  • 3
    Electronic Resource
    Electronic Resource
    Nuclear magnetic resonance relaxation study of wettability of porous rocks at different magnetic fields (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 6033-6038 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The wettability of the rock surface plays a very important role in the transport of fluid in porous media. The combined Amott-USBM method currently used for the determination of these values is not able to produce reliable estimates when the surface has an intermediate wettability. The nuclear magnetic resonance (NMR) technique could provide an efficient method if the parameters affected by the wettability could be established in well defined model systems. To obtain information about the effect of wettability changes upon the NMR parameters, T1 relaxation time measurements were carried out on 1H and 2H at two different magnetic fields. A large number of well defined consolidated and unconsolidated samples, with different degrees of wettability were used in this study. The results obtained showed that the T1 values, as well as the relaxation rate distribution parameters, such as the distribution width, are affected by changes in the wettability. A dependence of the T1 wettability data on the magnetic field intensity was also observed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360541
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  • 4
    Electronic Resource
    Electronic Resource
    The de-agglomeration and dispersion of small dust particles—Principles and applications (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 589-595 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A mechanism for the generation of dust dispersions consisting of single micrometer-sized particles in a low pressure gas is discussed. The particles are de-agglomerated and dispersed by injecting a dust sample (powder) together with a small amount of an arbitrary type of gas into a modified turbomolecular pump. The discussed sample release mechanism/dust disperser offers a wide range of possible gas and particle parameters, suitable for different kinds of experiments. We present two applications of our de-agglomeration mechanism. In the first experiment, homogeneous dust clouds were produced under microgravity conditions, and the Brownian motion of the single dust grains was studied. The second application is a matrix isolation technique for the spectroscopical investigation of single dust particles. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147520
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  • 5
    Electronic Resource
    Electronic Resource
    Evidence of a low compressibility carbon nitride with defect-zincblende structure (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 2555-2559 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A carbon-nitride compound with defect zincblende structure (P4¯3m) has been discovered in samples prepared by a chemical precursor route. Crystallographical (high-resolution electron microscopy and electron nanodiffraction) and electron energy loss measurements has been performed to identify the material as cubic zincblende with C3N4 composition. Nanoindentation indicates a high elastic recovery and hardness. The results agree with detailed ab initio calculations on metastable structures and compressibility. Our synthesis method is projected to be a process that could produce large quantities of material by controlling the chemical strategy. The new compound has potential applications for high hardness, elasticity and thermal conductivity materials and thin films. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364301
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  • 6
    Electronic Resource
    Electronic Resource
    Diffeomorphism invariant integrable field theories and hypersurface motions in Riemannian manifolds (1998)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 39 (1998), S. 683-694 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: We discuss hypersurface motions in Riemannian manifolds whose normal velocity is a function of the induced hypersurface volume element and derive a second-order partial differential equation for the corresponding time function τ(x) at which the hypersurface passes the point x. Equivalently, these motions may be described in a Hamiltonian formulation as the singlet sector of certain diffeomorphism-invariant field theories. At least in some (infinite class of) cases, which could be viewed as a large-volume limit of Euclidean M-branes moving in an arbitrary M+1-dimensional Riemannian manifold, the models are integrable: In the time-function formulation the equation becomes linear [with τ(x) a harmonic function on the embedding Riemannian manifold]. We explicitly compute solutions to the large volume limit of Euclidean membrane dynamics in R3 by methods used in electrostatics and point out an additional gradient flow structure in Rn. In the Hamiltonian formulation we discover infinitely many hierarchies of integrable, multidimensional, N-component theories possessing infinitely many diffeomorphism invariant, Poisson commuting, conserved charges. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.532345
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  • 7
    Electronic Resource
    Electronic Resource
    Displacement-operator squeezed states. I. Time-dependent systems having isomorphic symmetry algebras (1997)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 38 (1997), S. 84-97 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: In this paper we use the Lie algebra of space-time symmetries to construct states which are solutions to the time-dependent Schrödinger equation for systems with potentials V(x,τ)=g(2)(τ)x2+g(1)(τ)x+g(0)(τ). We describe a set of number-operator eigenstates states, {Ψn(x,τ)}, that form a complete set of states but which, however, are usually not energy eigenstates. From the extremal state, Ψ0, and a displacement squeeze operator derived using the Lie symmetries, we construct squeezed states and compute expectation values for position and momentum as a function of time, τ. We prove a general expression for the uncertainty relation for position and momentum in terms of the squeezing parameters. Specific examples, all corresponding to choices of V(x,τ) and having isomorphic Lie algebras, will be dealt with in the following paper (II). © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.531836
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  • 8
    Electronic Resource
    Electronic Resource
    Symmetries and constants of the motion for higher-order Lagrangian systems (1995)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 36 (1995), S. 4138-4161 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: We obtain a classification of infinitesimal symmetries of an autonomous higher-order Lagrangian system by using the theory of lifts of vector fields to tangent bundles. Also, a classification of infinitesimal symmetries of a time-dependent higher-order Lagrangian system is obtained. The relationship between infinitesimal symmetries and constants of the motion is investigated. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.530952
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  • 9
    Electronic Resource
    Electronic Resource
    Inverse wave scattering with discontinuous wave speed (1995)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 36 (1995), S. 2880-2928 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The inverse scattering problem on the line is studied for the generalized Schrödinger equation (d2ψ/dx2)+k2H(x)2ψ=Q(x)ψ, where H(x) is a positive, piecewise continuous function with positive limits H± as x → ±∞. This equation, in the frequency domain, describes the wave propagation in a nonhomogeneous medium, where Q(x) is the restoring force and 1/H(x) is the variable wave speed changing abruptly at various interfaces. A related Riemann–Hilbert problem is formulated, and the associated singular integral equation is obtained and proved to be uniquely solvable. The solution of this integral equation leads to the recovery of H(x) in terms of the scattering data consisting of Q(x), a reflection coefficient, either of H±, and the bound state energies and norming constants. Some explicitly solved examples are provided. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.531338
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  • 10
    Electronic Resource
    Electronic Resource
    Influence of particle shape on the nematic—isotropic transition of colloidal platelet systems (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1732-1736 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study the nematic–isotropic transition in model colloidal systems composed of platelets of various shapes using grand canonical simulations. This is of relevance for recently synthesized hard platelet systems, since the platelets in such systems are found to be not circular but irregular hexagons, and so cannot be described by the simulation data currently available. We show that the coexistence densities scale with an effective volume related to the isotropic orientation-averaged excluded volume of a pair of platelets. This excluded volume can be obtained from the perimeter of the face of the particles and so can be easily calculated for both regular and irregular particle shapes. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479433
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