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  • 1
    Electronic Resource
    Electronic Resource
    Rheological properties of suspensions of interacting rodlike FD-virus particles (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 4920-4928 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Low shear (γ(overdot)=1 s−1) and shear rate dependent (1 s−1〈γ(overdot)〈100 s−1) viscosity measurements on aqueous suspensions of rodlike FD-virus particles (length=880 nm, diameter=9 nm) below and above the overlap concentration c* =1 particle/length3 are presented. Properties like intrinsic viscosity [η], the virus concentration and shear rate dependence of η are studied in deionized ("saltfree'') suspensions and in the presence of NaCl, where the Coulomb interaction between the particles is totally screened. In the latter case, [η] is in excellent agreement with theoretical predictions [A. R. Altenberger and J. S. Dahler, Macromolecules 18, 1700 (1985); R. M. Davis and W. B. Russel, Macromolecules 20, 518 (1987)]. As a function of the virus concentration, η follows certain power laws in c. The observed exponents depend here on the applied shear rate. In the low shear region, η(c) can be described by the well known Huggins behavior. An attempt to fit the data by the popular stretched exponential form failed. The variation of η with shear rate is compared with available theories [M. Doi and S. F. Edwards, The Theory of Polymer Dynamics (Clarendon, Oxford, 1986); A. R. Altenberger and J. S. Dahler, Macromolecules 18, 1700 (1985); J. S. Dahler, S. Fesciyan, and N. Xystris, Macromolecules 16, 1673 (1983)]. A theory of Hess [Z. Naturforsch. Teil A 35, 915 (1980)] allows us to evaluate the concentration dependent values of the rotational diffusion constant Drot from the η(γ(overdot)) data which are found to be in very good agreement with the values of Drot, obtained by electric or magnetic birefringence [H. Kramer, M. Deggelmann, C. Graf, M. Hagenbüchle, C. Johner, and R. Weber, Macromolecules 25, 4325 (1992); J. F. Maguire and J. P. McTague, Phys. Rev. Lett. 45, 1891 (1980); H. Nakamura and K. Okano, Phys. Rev. Lett. 50, 186 (1983)]. For strong Coulomb interaction among the suspended viruses no adequate theory is available. Therefore, the data achieved under these conditions are interpreted in terms of the corresponding results of the non-Coulomb interacting samples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464947
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  • 2
    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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  • 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
    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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  • 5
    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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  • 6
    Electronic Resource
    Electronic Resource
    An alternative degradation method for amorphous hydrogenated silicon: The constant degradation method (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 2507-2515 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: To study the kinetics of metastable defect creation in amorphous hydrogenated silicon we introduce the Constant Degradation Method as a new experimental scheme. In contrast to conventional degradation experiments in which the incident light intensity is constant during light soaking, in this method the photoconductivity of the sample is kept constant by continuously increasing the light intensity. In this case a linear time dependence of the required light intensity and of the resulting defect density is observed experimentally. A detailed analysis of the method shows that the data obtained are in accordance with the assumption of the "bond-breaking'' model, i.e., the metastable defects are created by bimolecular recombination of localized electron-hole pairs. The observed time dependence is at variance with the stretched exponential time dependence predicted for dispersive transport models. Effects of sample heating due to high light intensities and of Fermi level shifts on the observed time dependence are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356223
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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    Composition effects on structural and optical infrared properties of CuIn0.5Ga0.5Se2 (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 1776-1783 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dependence of structural parameters and force constants for Cu–Se, Ga–Se, and In–Se bonds on compositional deviations in CuIn0.5Ga0.5Se2 have been studied. The composition gradient along the ingot was obtained by a single fusion at 1150 °C of the components and subsequent slow cooling in a still ampoule placed in a vertical furnace. All along the sample, a single chalcopyrite phase is present and its composition along its length was found by energy dispersive analysis of x-ray measurements on slices. Unit cell parameters, anion displacement, and Cu occupation fraction in its sublattice were analyzed by x-ray powder diffraction and Rietveld refinement methods. The anion displacement found is a function of the Cu defect in its sublattice. The existence of associated defects, i.e., two Cu vacancies and one Ga in Cu site, [2V(Cu)+GaCu], is proposed to explain the Cu defect in its sublattice and the changes in lattice parameters. This leads to the existence of BIII vacancies (BIII=In+Ga), and interstitial Cu up to 8 at. % that also cause changes in the structural parameters. Infrared reflectance measurements led to the imaginary dielectric constant determination which, fitted to a Lorentz function, permitted to obtain atomic vibration modes. Using the model of Neumann for chalcopyrites, the values of force constants for Cu–Se, Ga–Se, and In–Se bonds were computed. These appear to increase when the occupation of each sublattice increases. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1303063
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  • 9
    Electronic Resource
    Electronic Resource
    Deuterium effusion measurements in doped crystalline silicon (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 1406-1409 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We describe first results for deuterium effusion from undoped and doped crystalline silicon (n- and p-type) treated in a D2 plasma under different conditions. The dependence of the effusion spectra on doping level, passivation temperature, sample bias, and preannealing are presented and the results are discussed on the basis of different D-bonding configurations in the passivated silicon samples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347156
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  • 10
    Electronic Resource
    Electronic Resource
    Channel propagation in water and gelatin by a free-running erbium laser (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 720-727 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Precise cutting of biological tissue is possible with the Er:YAG laser because of the strong absorption of radiation exhibited by water containing media at a wavelength of 2.94 μm. To achieve control of the depth of drilled channels a thorough knowledge of the channel propagation mechanism is required. The channel propagation process of pulsed erbium laser radiation in liquid water, and in gelatin with a high water content, as substitutes for biological tissue is investigated experimentally and modeled theoretically. We explain the propagation process with a hydrodynamic model, which describes the channel propagation process in terms of energy, mass, and momentum balance equations, which influence the evaporation pressure at the phase boundary. As the key feature, the theory takes into account the deformability of cold material below the zone of absorption. We show that by modeling this hydrodynamic effect with the Bernoulli equation we can explain the channel propagation velocity in water and gelatin as a function of laser intensity over three orders of magnitude with appreciable accuracy. The comparison with the experimental data suggests that the channel propagation velocity for intensities below 0.1 MW/cm2, and the threshold intensity of 12 kW/cm2 for channel propagation, are dependent on the surface tension and the liquid viscosity. At intensities above 0.1 MW/cm2, we can even predict a small difference between the propagation velocities found in these materials by considering the effect of the different elastic properties on the pressure in the propagating channel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355238
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