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F T Wall

Publications and source records attributed to F T Wall.

10 recordsLinked to original sources

Discrete mechanics and special relativistic random walks.

Random walks with step lengths equal to the shortest possible physically meaningful distances are considered from the point of view of special relativity involving two observers moving uniformly with respect to each other. A requirement of statistical equivalence of the probability distributions seen by those observers leads to the Lorentz transformations, provided a randomly moving particle shifts from one submicroscopic cell of uncertainty to a neighbor with a speed equivalent to that of light. Ordinary smooth motion would appear to involve a tremendous amount of submicroscopic back and forth randomness subject to a statistical bias favoring a particular direction. The diffusive nature of the motion naturally leads to a spreading of the probability distribution.

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Discrete wave mechanics: Multidimensional systems.

Discrete wave mechanics is pursued further by extending the one-dimensional treatment to two (or more) dimensions in the light of explicit momentum considerations. Cognizance is taken of the effect of particle motion on mass and hence on the interactions between components of motion in different directions. The overall energy parameter turns out to be a product instead of a sum of parameters identified with each of several orthogonal axes. Accordingly, the separation of variables is most directly accomplished by factoring the principal energy parameter in conjunction with factoring the wave vector expression itself. Wave vector energies, on the other hand, remain additive. Finally, group velocity components are discussed for higher-dimensional systems.

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Discrete wave mechanics: The hydrogen atom with angular momentum.

A discrete wave mechanical treatment of the hydrogen atom is extended to deal with states involving nonzero angular momentum. Only the radial portions of the wave vectors are covered. It is predicted that there is a nonzero minimum distance between the electron and the nucleus; this threshold distance increases with increasing angular momentum. Appropriate finite difference equations are formulated. The states with angular momentum exhibit the same degeneracy as do corresponding energy levels obtained from solutions of Schrödinger's equation.

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Discrete wave mechanics: An introduction.

Discrete wave mechanics is formulated for particles in one-dimensional systems by use of a simple finite difference equation. The solutions involve wave vectors (instead of wave functions) as well as a newly defined "wave vector energy." In the limit, as c --> infinity, the treatment reduces to that of Schrödinger's wave mechanics. Specific calculations are made for completely free particles as well as for particles confined to a one-dimensional box. The results exhibit a striking compatibility with relativistic considerations. The wave vectors show properties that can be identified with particles and anti-particles-each possess identical probability distributions with energies that add up to zero.

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Discrete wave mechanics: The hydrogen atom.

The quantum mechanical problem of the hydrogen atom is treated by use of a finite difference equation in place of Schrödinger's differential equation. The exact solution leads to a wave vector energy expression that is readily converted to the Bohr-Rydberg formula. (The calculations here reported are limited to spherically symmetric states.) The wave vectors reduce to the familiar solutions of Schrödinger's equation as c --> infinity. The internal consistency and limiting behavior provide support for the view that the equations employed could well constitute an approach to a relativistic formulation of wave mechanics.

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Self-avoiding random walks at finite concentrations: The bulk phase limit.

In infinitely dilute solutions, macromolecules exhibit non-Gaussian distributions for their end-to-end separations. This occurs under such circumstances because intramolecular interactions are more important than intermolecular forces. On the other hand, when a macromolecular solution becomes so concentrated that it approaches its bulk phase, then the end-to-end length distribution becomes substantially Gaussian. A theoretical explanation for the observed behavior is obtained by taking cognizance of a balance between inter-and intramolecular forces acting on self-avoiding random chains. Such a balance causes the chains to behave very much like random walks of order 2-that is to say, walks for which the only restriction against double occupancy is that identified with immediate return steps. This is demonstrated by taking Monte Carlo data for chains of various concentrations and analyzing the distributions of a component of length by using expansions involving orthogonal vectors. Although Gaussian behavior is more or less achieved for bulk polymers, slight deviations from that behavior still persist at the origin.

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Self-avoiding random walks on lattice strips.

A self-avoiding walk on an infinitely long lattice strip of finite width will asymptotically exhibit an end-to-end separation proportional to the number of steps. A proof of this proposition is presented together with comments concerning an earlier attempt to deal with the matter. In addition, some unproved, yet "obvious," conjectures concerning self-avoiding walks are cited as basic propositions requiring study.

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Statistics of flexible chain configurations.

When Monte Carlo methods are employed to study the statistical dimensions of flexible polymer chains, it is necessary that the sampling be statistically unbiased. One Monte Carlo procedure is the so-called "slithering snake" technique, which has proved to be very useful. A question arises, however, as to how long it takes for a "slithering snake" to be completely regenerated to avoid biasing the samples around a particular configuration. It is demonstrated theoretically and verified by Monte Carlo studies that the number of iterations required to completely regenerate a sample polymer is a quadratic function of the chain length. This verification applies to chains in dilute solution but may not hold for bulk polymers.

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Statistics of self-avoiding walks confined to strips and capillaries.

A long self-avoiding chain confined to a narrow strip or thin tube tends to be elongated in the direction of the strip or tube. The mean end-to-end separation of a long chain so confined becomes asymptotically proportional to the number of links in the chain as the contour chain length becomes infinite. By use of scaling arguments, it is shown that the mean end-to-end separation also becomes proportional to D(-1/3) for chains confined to two-dimensional strips and proportional to D(-2/3) for three-dimensional capillaries, where D is the width or diameter of the strip or capillary. These predictions have been verified by Monte Carlo studies of self-avoiding walks. The agreement is excellent for two-dimensional systems, but less certain for those of three dimensions since less data are available for verification.

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Alternative derivations of the statistical mechanical distribution laws.

A new approach is presented for the derivation of statistical mechanical distribution laws. The derivations are accomplished by minimizing the Helmholtz free energy under constant temperature and volume, instead of maximizing the entropy under constant energy and volume. An alternative method involves stipulating equality of chemical potential, or equality of activity, for particles in different energy levels. This approach leads to a general statement of distribution laws applicable to all systems for which thermodynamic probabilities can be written. The methods also avoid use of the calculus of variations, Lagrangian multipliers, and Stirling's approximation for the factorial. The results are applied specifically to Boltzmann, Fermi-Dirac, and Bose-Einstein statistics. The special significance of chemical potential and activity is discussed for microscopic systems.

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