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Brillouin light scattering studies of the mechanical properties of polystyrene/polyisoprene multilayered thin films

Journal of Polymer Science 1996年第17期34卷

作者： J. A. Forrest A. C. Rowat K. Dalnoki-Veress J. R. Stevens J. R. Dutcher Department of Physics and Guelph-Waterloo Program for Graduate Work in Physics University of Guelph Guelph Ontario Canada N1G 2W1

We have used Brillouin light scattering (BLS) to investigate the mechanical properties of thin polystyrene (PS) and polyisoprene (PI) films incorporated in a multilayer geometry consisting of alternating layers of the two polymers. All samples had a total thickness h ∼ 1600 Å, and consisted of between 2 and 10 individual polymer films; individual layer thicknesses were as small as 160 Å. Ellipsometry was used to determine the thickness of the PS and PI layers. The velocities of several high-frequency film-guided mechanical waves were measured using BLS and the results are compared with values calculated using an effective medium approach. The effective elastic constants of the multilayered films were obtained from those determined for thick films of PS and PI. Remarkable agreement was obtained between the measured and calculated velocities even for samples in which the individual layer thicknesses were much less than the unperturbed size of the polymer molecules. These results suggest that the mechanical properties of polymers change very little even when the molecules are forced into highly confined geometries. © 1996 John Wiley & Sons, Inc.

关键词： polymer multilayered films mechanical properties

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INTERFACE FORMATION AND A STRUCTURAL PHASE-TRANSITION FOR THE SPHERICAL MODEL OF FERROMAGNETISM

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JOURNAL OF STATISTICAL physics 1995年第1-2期79卷 165-181页

作者： ALLEN, S Guelph-Waterloo Program for Graduate Work in Physics University of Waterloo Waterloo Canada

A detailed analysis is reported examining the local magnetic susceptibility chi(r), in relation to the correlation function GIR) and correlation length xi, of a spherical model ferromagnet confined to geometry Omega = L(d-d') x infinity(d') (d' less than or equal to 2, d > 2) under a continuous set of twisted boundary conditions. The ''twist'' parameter ($) under bar tau in this problem may be interpreted as a measure of the geometry-dependent doping level of interfacial impurities (or antiferromagnetic seams) in the extended system at various temperatures. For tau(j) --> 0, For All j is an element of d-d', no seams are present except at infinity, whereas if tau(j) = 1/2, impurity saturation occurs. For 0 < tau(j) < 1/2 the physical domain Omega(phys) = D-d-d' x infinity(d') (D > L), defining the region between seams containing the origin, depends on temperature above a certain threshold (T > T-0). Below that temperature (T < T-0), seams are frozen at the same position (D approximate to L/2 tau, d-d' = 1), revealing a smoothly varying large-scale structural phase transition.

关键词： TWISTED BOUNDARY CONDITIONS LOCAL SUSCEPTIBILITY SPHERICAL MODEL FINITE-SIZE SCALING

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THEORY OF ROTATIONAL RELAXATION IN COHERENT RAMAN-SPECTROSCOPY

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CHINESE JOURNAL OF physics 1995年第4期33卷 305-333页

作者： LIU, WK Department of Physics Guelph- Waterloo Program for Graduate Work in Physacs (GWP) University of Waterloo

The theory of the nonlinear optical processes in recent high-resolution coherent Raman spectroscopic studies of gases is reviewed, and a unified description of various spectroscopic techniques in terms of the correlation functions of molecular polarizability tenser is presented. A theoretical description of spectral line shapes in terms of a relaxation matrix, which provides the connection between the microscopic intermolecular potential and the experimental observables, is discussed. We pay particular attention to ab initio scattering calculations starting from accurate interaction potentials for the linewidths, line shifts, and line-mixing parameters for the system of deuterium molecules interacting with a bath of inert gas atoms, under a wide range of perturber densities. It is clear that for simple systems involving foreign gas broadening, the theory has reached the maturity that first-principles calculation of line spectra is highly feasible. Future directions of theoretical research from both a fundamental point of view and practical considerations are indicated.

关键词： .potentials nonlinear optical shifts polarizability broadening intermolecular coherent Raman correlation functions linewidths line shapes Theory of Rotational relaxation matrix

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PHOTORESPONSE OF POLYCRYSTALLINE ZNO FILMS DEPOSITED BY RF BIAS SPUTTERING

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THIN SOLID FILMS 1995年第1-2期261卷 334-339页

作者： ZHANG, DH BRODIE, DE Guelph-Waterloo Program for Graduate Work in Physics University of Waterloo Waterloo Ont. N2L 3G1 Canada

The photoresponse of polycrystalline ZnO films generally contains both a true photoconductivity and a contribution from surface structural changes which can alter the surface conductance via the chemisorption and photodesorption of an active ambient-gas component. The surface structural changes can increase the conductance by up to seven orders of magnitude for a 500 nm thick sample when illuminated with an intensity of 4 x 10(16) photon cm(-2) s(-1) UV light, but the response times are very slow. Newly prepared samples exhibit a fast response characteristic such as a true photoconductivity, but after exposure to air for several months the slower response dominates. Thus if used as a photoconductor, oxygen adsorption or desorption from the surface of a ZnO film is particularly problematic, but some surface stability can be achieved by adding nitrogen to the surface layers of the ZnO film and these samples exhibit more normal and improved photoconducting behaviour.

关键词： PHOTOCONDUCTIVITY PHOTODESORPTION SPUTTERING ZINC OXIDE

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THE EFFECT ON POLYCRYSTALLINE ZNO FILM SURFACES DUE TO AN AR PLASMA INTRODUCED BY A VACUUM GAUGE

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THIN SOLID FILMS 1995年第1期257卷 58-62页

作者： ZHANG, DH BRODIE, DE Guelph-Waterloo Program for Graduate Work in Physics University of Waterloo Waterloo Ont. N2L 3G1 Canada

A strong accumulation layer can be produced on the surface of polycrystalline ZnO films when the samples are exposed to ions from an inert gas discharge in Ar or Kr. A combination of surface conductance and surface potential measurements show that an accumulation layer is induced by the adsorption of charges from the inert gas plasma which neutralizes and removes chemisorbed oxygen atoms, and this can increase the conductance by more than 6 orders of magnitude, for 500 nm thick films. Electrical neutrality in the ZnO provides the electrons for the accumulation layer, either from the ohmic contacts or the plasma. This accumulation layer can be further enhanced by illumination with UV light.

关键词： ADSORPTION CONDUCTIVITY PHOTOVOLTAGE ZINC OXIDE

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INFRARED ROTATION AND VIBRATION-ROTATION BANDS OF ENDOHEDRAL FULLERENE COMPLEXES - HE-AT-C-70

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CHEMICAL physics LETTERS 1995年第1-2期244卷 93-99页

作者： JOSLIN, CG GRAY, CG GOLDMAN, S Guelph-Waterloo Program for Graduate Work in Physics University of Guelph Guelph Ontario Canada N1G 2W1

We calculate the far-infrared absorption spectrum of the endohedral fullerene He@C-70. In this molecule the He inclusion experiences a strongly anisotropic potential V(rho, z). The 2D Schrodinger equation governing its rovibrational motion is solved variationally. The spectrum consists of strong P- and R-branches (Delta m = +/-1) and a much weaker Q-branch (Delta m = 0), and peaks near 100cm(-1). Despite its apparent complexity, however, the eigenvalue spectrum is essentially regular, and the system displays little evidence of chaos.

关键词： Dynamics dynamics Infrared radiation Fullerenes characteristic spectrum chaos Absorption spectra

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VESICLE SIZING BY STATIC LIGHT-SCATTERING - A FOURIER COSINE TRANSFORM APPROACH

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APPLIED OPTICS 1995年第22期34卷 5010-5015页

作者： WANG, JH HALLETT, FR []The authors are with the Guelph–Waterloo Program for Graduate Work inPhysics Department of Physics University of Guelph Ontario N1G 2W1 Canada.

A Fourier cosine transform method, based on the Rayleigh-Gans-Debye thin-shell approximation, was developed to retrieve vesicle size distribution directly from the angular dependence of scattered light intensity. Its feasibility for real vesicles was partially tested on scattering data generated by the exact Mie solutions for isotropic vesicles. The noise tolerance of the method in recovering unimodal and biomodal distributions was studied with the simulated data. Applicability of this approach to vesicles with weak anisotropy was examined using Mie theory for anisotropic hollow spheres. A primitive theory about the first four moments of the radius distribution about the origin, excluding the mean radius, was obtained as an alternative to the direct retrieval of size distributions.

关键词： VESICLE PARTICLE SIZING FOURIER COSINE TRANSFORM LIGHT SCATTERING OPTICAL CHARACTERIZATION

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Vesicle size measurement by static light scattering: A Fourier cosine transform approach

Vesicle size measurement by static light scattering: A Fouri...

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Optical Tomography, Photon Migration, and Spectroscopy of Tissue and Model Media: Theory, Human Studies, and Instrumentation

作者： Wang, Jianhong Ross Hallett, F. Guelph-Waterloo Program for Graduate Work in Physics Department of Physics University of Guelph GuelphONN1G 2W1 Canada

ISBN: (纸本)9780819417367

Based on the Rayleigh-Gans-Debye thin shell approximation, a fast Fourier cosine transform method was developed to retrieve vesicle size distributions directly from the light scattering measurement. The method was tested numerically mainly on the scattering data generated by the exact Mie solution for isotropic vesicles. Monomodal and bimodal Gaussian distributions were used to represent vesicles with radii ranging from 0.05 micrometers to 0.5 micrometers. The recovered distributions were in good aggreement with the original distributions. Peak positions were recovered within 10% of the original ones, even when 20% random error was added to the simulated data. Noise tolerance of this method was much higher for large vesicles than for small vesicles. The effect of the refractive index of the medium was also investigated using the simulated data. To study the effect of the optical anisotropy of the membrane on the recovery, the exact Mie solution for anisotropic hollow spheres was used to simulate scattered intensity data. The recovered distributions in this case were slightly shifted towards small radii from the original ones. © 2018 SPIE.

关键词： Micrometers

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Reply to Cooperstock and Faraoni

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General Relativity and Gravitation 1995年第5期27卷 563-565页

作者： Mann, Robert B. Sikkema, Arnold E. Guelph-Waterloo Program for Graduate Work in Physics Department of Physics University of Waterloo Waterloo N2L 3G1 Ontario Canada Department of Physics University of British Columbia Vancouver V6T 1Z1 B.C. 6224 Agricultural Road Canada

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Conformation-space renormalization of randomly branched polymers

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Physical Review E 1995年第4期52卷 3943-3943页

作者： Shi-Min Cui Zheng Yu Chen Guelph-Waterloo Program for Graduate Work in Physics and Department of Physics University of Waterloo Waterloo Ontario Canada N2L 3G1

We present a renormalization group theory in polymer conformation space to describe randomly branched polymers in which monomers interact with each other through the excluded volume interaction. We make a perturbation expansion for the mean square radius of gyration of randomly branched polymers with annealed structures and identify the appropriate scaling variable. We further perform a renormalization group analysis that results in the ε expansion for the critical exponents of the radius of gyration ν=1/4+ε/36 and of the number of configurations θ=5/2-ε/12, which are consistent with the results of an earlier theory.

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