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Dive into the research topics where John Courtenay Lewis is active.

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Featured researches published by John Courtenay Lewis.


Chemical Physics Letters | 2000

Many-body interactions among adsorbed atoms and molecules within carbon nanotubes and in free space

Milen K. Kostov; Milton W. Cole; John Courtenay Lewis; Phong Diep; J. Karl Johnson

Abstract This Letter evaluates three-body triple dipole (DDD) interactions for quasi-one-dimensional phases of He, Ne, H 2 , Ar, Kr and Xe confined within a bundle of nanotubes. We find a significant reduction in the pair potential well depth due to the DDD effect. We carry out ab initio calculations on linear and equilateral configurations of the H 2 trimer and find that overlap interactions do not greatly change the DDD interaction in the linear configuration when the spacing is greater than about 3 A . However, the DDD interaction alone is clearly insufficient for the triangular configurations studied.


Journal of Chemical Physics | 2002

Hindered rotation of H2 adsorbed interstitially in nanotube bundles

M. K. Kostov; Hansong Cheng; R. M. Herman; Milton W. Cole; John Courtenay Lewis

A theoretical study of the rotational dynamics of H2 molecules trapped in the interstitial channels of a carbon nanotube bundle is presented. The potential used in this study is modeled as a sum of atom–atom (C–H) van der Waals interactions and electrostatic interactions of the molecule with the surrounding nanotubes. The rotational energy spectra is calculated using a product wave function, where the coupling between translational and rotational modes is treated in a mean-field manner. A molecular dynamics simulation study was performed for estimating the hydrogen rotational barrier. Both theoretical calculations and simulation results reveal the existence of a large rotational barrier (∼40 meV). The consequences of this rotational barrier for the rotational energy levels are worked out in detail.


Archive | 1985

Intercollisional Interference — Theory and Experiment

John Courtenay Lewis

This paper presents a review of all aspects of intercollisional interference, with emphasis on recent development. Both experiment and theory are discussed. The review concludes with a survey of important unresolved problems connected with intercollision interference.


Cold Regions Science and Technology | 1984

Monte Carlo calculations of iceberg draft changes caused by roll

John Courtenay Lewis; Gilbert Bennett

Abstract Draft changes in iceberg roll have been investigated using a Monte Carlo technique for generating iceberg shapes of constant, polygonal cross section. Stability is assessed from the potential energy curves calculated assuming vertical but not rotational hydrostatic equilibrium. No modelling of the roll dynamics has been included. The draft changes are approximately normally distributed, with increases almost as probable as decreases. Extreme draft changes (defined to be those in excess of 20%) are not uncommon. The mean draft change, standard deviation, skewness and kurtosis depend on the number of sides in the berg model, and on the ratio of berg ice density to seawater density. In particular the fraction of extreme draft changes is a sensitive function of this ratio.


Physica A-statistical Mechanics and Its Applications | 1999

Diffusion-controlled reactions on simple lattices: dependence of the rate coefficients on jump probability and dimension

John Courtenay Lewis; Herbert Wheeler

In this work, rates of the diffusion-controlled annihilation reaction A+A→nothing are studied by stochastic simulation as functions of jump probability on d-dimensional cubic lattices for d=2,3, and 4, at low densities. Standard bimolecular kinetics are observed for d=3 and 4. Small but significant deviations from bimolecular kinetics are observed for d=2, as expected from earlier studies. Although application of the Smoluchowski approach to diffusion-controlled reactions leads to the conclusion that the rate coefficients should be proportional to the diffusion coefficients of the particles, themselves functions of the jump probability, in fact marked deviations from linearity are found. A low-density mean-field theory is developed which agrees well with the simulation results in three dimensions and very well in four dimensions. In two dimensions the sequence which defines the theoretical rate coefficient converges to zero, although intermediate values are in reasonable qualitative agreement with the simulation results. The convergence to zero is due to the fact that random walks in two dimensions return with certainty to the origin; dominance of the kinetics of diffusion-controlled reactions in low dimensions is ascribed to the same cause.


Chemical Physics Letters | 1980

Distributions of collision times for rough disks and for a two-dimensional lorentz gas with non-overlapping fixed scatterers

John Courtenay Lewis

Abstract Collision time distributions for a two-dimensional Lorentz gas and a rough disk fluid are obtained from computer simulations at medium and high densities. At all densities the rough disk distributions are nearly exponential. The correlation between immediately successive collision times is small for both system at all densities.


International Journal of Spectroscopy | 2010

Elementary Statistical Models for Vector Collision-Sequence Interference Effects with Poisson-Distributed Collision Times

John Courtenay Lewis

In a recent paper (Lewis, 2008) a class of models suitable for application to collision-sequence interference was introduced. In these models velocities are assumed to be completely randomized in each collision. The distribution of velocities was assumed to be Gaussian. The integrated induced dipole moment , for vector interference, or the scalar modulation , for scalar interference, was assumed to be a function of the impulse (integrated force) , or its magnitude , experienced by the molecule in a collision. For most of (Lewis, 2008) it was assumed that and , but it proved to be possible to extend the models, so that the magnitude of the induced dipole moment is equal to an arbitrary power or sum of powers of the intermolecular force. This allows estimates of the infilling of the interference dip by the disproportionality of the induced dipole moment and force. One particular such model, using data from (Herman and Lewis, 2006), leads to the most realistic estimate for the infilling of the vector interference dip yet obtained. In (Lewis, 2008) the drastic assumption was made that collision times occurred at equal intervals. In the present paper that assumption is removed: the collision times are taken to form a Poisson process. This is much more realistic than the equal-intervals assumption. The interference dip is found to be a Lorentzian in this model.


20TH INTERNATIONAL CONFERENCE ON SPECTRAL LINE SHAPES | 2010

Ortho‐para conversion of H2 in crystalline silicon

R. M. Herman; Alejandro Suarez; Jorge O. Sofo; John Courtenay Lewis

The ortho‐para conversion rate of H2 in crystalline p doped silicon is calculated assuming that the conversion is due to the unpaired electron spins associated with holes with the electron spin density at the H2 nuclei being enhanced through spin exchange effects.


SPECTRAL LINE SHAPES: Volume 15–19th International Conference on Spectral Line#N#Shapes | 2008

A Statistical Model for Scalar Collision‐Sequence Interference

John Courtenay Lewis; R. M. Herman

This paper replaces the assumption of equal collision intervals used in ref. [1] with the more realistic assumption of Poisson‐distributed collision times. The correlation among induced dipole amplitudes found to be present in the scalar interference effect is shown to give rise to a Lorentzian line shape with width equal to the mean collision frequency.


SPECTRAL LINE SHAPES: Volume 11, 15th ICSLS | 2001

Low density intercollisional interference

John Courtenay Lewis; R. M. Herman

The vector intercollisional interference dip in the 01 band of H2 is readily observed at densities as low as 1 Amagat [1,2] but seems to disappear at the very low densities at which lines from the van der Waals complexes are studied [3]. In the present work the kinetic theory of vector and tensor intercollisional interference of Lewis and van Kranendonk [4] is extended to describe this phenomenon, which occurs when the mean free path becomes comparable to incident wavelength. At low density, scalar intercollisional interference lines, as seen most characteristically in the R1(0) and R1(1) lines of HD—He, are predicted to undergo Doppler broadening/narrowing not essentially different from that expected for allowed lines in the absence of interference.

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R. M. Herman

Pennsylvania State University

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Milton W. Cole

Pennsylvania State University

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Alejandro Suarez

Pennsylvania State University

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Jorge O. Sofo

Pennsylvania State University

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Milen K. Kostov

Pennsylvania State University

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Christopher G. Deacon

Memorial University of Newfoundland

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Clifford Stamp

Memorial University of Newfoundland

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J. Shirokoff

Memorial University of Newfoundland

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John Wells

Memorial University of Newfoundland

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K Gebresellasie

Memorial University of Newfoundland

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