W. J. Keeler

Lakehead University Thunder Bay Campus, Thunder Bay, Ontario, Canada

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Publications (7)16.68 Total impact

  • M. H. Hawton, X. Le, W. J. Keeler
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    ABSTRACT: Data on the non-Debye dielectric relaxation of hydrated lecithin is analyzed. The fit to Cole-Cole and stretched exponential functions is poor, while the Cole-Davidson function gives a good fit to the data. This is consistent with the Dissado and Hill IR divergence theory of the dielectric response which implies that relaxation is due to proton hopping on finite connected hydrogen-bonded clusters. Alternatively it is possible that the non-Debye response is due to cooperative rotation of the head-groups and water dipoles.
    Molecular Crystals and Liquid Crystals. 07/1991; 202(1):27-33.
  • MH Hawton, WJ Keeler
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    ABSTRACT: The dielectric spectra of lecithin-water mixtures have a maximum in the imaginary part of susceptibility chi'' at a frequency f0 that varies with water content and temperature. At 320 K the peak frequency decreases from 100 MHz at maximum hydration to 30 kHz for a sample containing 5 wt. % water. These loss peaks can be scaled in frequency so that they fall on a single master curve whose slope on a log10chi'' versus log10f plot is -0.33+/-0.03 at frequencies that are large compared to f0. This is far from the slope of -1 that is characteristic of a single-relaxation-time process. We propose that the frequency-temperature-concentration scalability of the loss curves implies that the whole hydrogen-bonded system responds cooperatively to an electric field, possibly by solitonlike proton transport. Our results may be important for the interpretation of dielectric spectra of biological materials and technologically important substances that adsorb water.
    Physical Review A 03/1990; 41(4):2218-2221. · 3.04 Impact Factor
  • M. H. Hawton, W. J. Keeler
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    ABSTRACT: We present an equivalent-circuit analysis of charge flow through low-dimensional conducting paths in a heterogeneous dielectric. Path segments perpendicular to the electrodes are represented as pure conductance and it is shown that parallel segments can be represented as capacitance in parallel with conductance. The path segments are connected in series to form a Devil’s staircase. Charging time is proportional to segment length and, when frequency is increased, segments are shorted out by capacitance. Thus a sample’s conductance increases with increasing frequency and its admittance is complex. We find that susceptibility is proportional to (jω)-p where p=ln(N)/ln(α) if there are Nn path segments of length L0/αn parallel to the electrodes.
    Physical review. B, Condensed matter 06/1989; 40(1). · 3.77 Impact Factor
  • M. H. Hawton, W. J. Keeler
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    ABSTRACT: We have studied the dielectric properties of hydrated phospholipids as a function of water content and temperature for frequencies between 5 Hz and 13 MHz. At low frequencies, plots of the log of the imaginary part of the dielectric constant versus the log of frequency were found to be linear with a slope of -0.87 for up to six decades. At higher frequencies a loss peak with a slope of -0.35 above the peak was observed. The slopes were found to be insensitive to variations in temperature and water content, although the separation between the loss peak and the low‐frequency process increased with temperature. These results are discussed in the context of infrared divergence theories and models invoking fractal time processes and fractal structure.
    Journal of Applied Physics 12/1988; · 2.21 Impact Factor
  • MH Hawton, WJ Keeler
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    ABSTRACT: The van der Waals energy of a two-dimensional array of tilted alkyl chains is evaluated numerically by summing the contributions of pairs of CH2 groups and water molecules. The energy is found to be lower for a system with a spatially oscillating tilt angle theta than for a flat layer. The cost in free energy of these oscillations is estimated by assuming that where the magnitude of theta is reduced, there is an increase in chain area and hence in chain fluidity. It is found that the free-energy reduction due to the van der Waals interaction is sufficient to compensate for increased chain fluidity at temperatures a few degrees below the chain-melting temperature. Thus the van der Waals energy provides a plausible physical mechanism for the occurrence of the ripple phase. The surface profile predicted is in good agreement with that observed in the Pβ or ripple phase with electron microscopy and characterized by x-ray diffraction. An analytic expression for a negative term in the free energy of the form z’z’’’, where z’=tantheta is derived on the basis of this physical mechanism.
    Physical Review A 06/1986; 33(5):3333-3340. · 3.04 Impact Factor
  • I. M. Booth, M. H. Hawton, W. J. Keeler
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    ABSTRACT: High-purity n-type InSb exhibits an unusual temperature dependence in the Hall coefficient for pressures in excess of about 8 kbar. The behavior is explained using nonequilibrium semiconductor statistics and a model incorporating shallow donor and deep acceptor states. The best fit to experimental results is accomplished when the assumed number of acceptors exceeds the number of donors, although the material remains n type. Below 100 K, equilibrium is not achieved and the number of ionized acceptros is "frozen in" and replaces the total number of acceptors. This gives an apparent ratio of acceptors to donors very close to one. This model could explain, therefore, what appears to be fortuitously close compensation in many high-resistivity materials.
    Physical Review B 06/1982; 25(12):7713-7718. · 3.66 Impact Factor
  • M. H. Hawton, W. J. Keeler
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    ABSTRACT: Excitable membranes can be induced to show an increase in conductivity such as that encountered in the “action potential.” We suggest that this transient condition may be the result of heating of the sites through which the ions pass. The heat could be generated by an adiabatic phase transition of the membrane lipids. Equations derived on the basis of these ideas give good agreement with voltage clamped current measurements in algae and perfused squid axon.
    Journal of Biological Physics 08/1975; 3(3):130-141. · 0.95 Impact Factor