Physics Commons^™

Universal Conductivity Curve For A Plane Containing Random Holes., E. J. Garboczi, M. F. Thorpe, M. S. Devries, Anthony Roy Day

Anthony Roy Day

This paper examines the general percolation problem of cutting randomly centered insulating holes in a two-dimensional conducting sheet, and explores how the electrical conductivity sigma decreases with the remaining area fraction. This problem has been studied in the past for circular, square, and needlelike holes, using both computer simulations and analog experiments. In this paper, we extend these studies by examining cases where the insulating hole is of arbitrary shape, using digital-image-based numerical techniques in conjunction with the Y- [nabla] algorithm. We find that, within computational uncertainty, the scaled percolation threshold, xc=nc=5.9±0.4, is a universal quantity for all the cases …

Pitch Of Complex Tones With Many High‐Order Harmonics, Adrianus J. M. Houtsma, J. Smurzynski

Jacek Smurzynski

Comment On "Percolation In Isotropic Elastic Media.", Anthony Day, M. Thorpe

Anthony Roy Day

No abstract provided.

Spectral Dimensionality Of Random Superconducting Networks, Anthony Roy Day, W. Xia, M. F. Thorpe

Anthony Roy Day

We compute the spectral dimensionality d-tilde of random superconducting-normal networks by directly examining the low-frequency density of states at the percolation threshold. We find that d-tilde=4.1±0.2 and 5.8±0.3 in two and three dimensions, respectively, which confirms the scaling relation d-tilde=2d/(2-s/ nu ), where s is the superconducting exponent and nu the correlation-length exponent for percolation. We also consider the one-dimensional problem where scaling arguments predict, and our numerical simulations confirm, that d-tilde=0. A simple argument provides an expression for the density of states of the localized high-frequency modes in this special case. We comment on the connection between our calculations …

Stability Of Networks Under Tension And Pressure, Anthony Roy Day, H. Yan, M. F. Thorpe

Anthony Roy Day

The number of zero-frequency modes of an elastic network is an important quantity in determining the stability of the network. We present a constraint-counting method for finding this number in general central-force networks that are under an external tension. The technique involves isolating the backbone and then counting constraints in the same way as for free standing networks. A detailed example of this counting is given for a random two-dimensional network subject to an external tension. The results are shown to agree with the number of zero-frequency modes as determined by a direct matrix diagonalization.

Implications Of Atmospheric Test Fallout Data For Nuclear Winter, George H. Baker

George H Baker

Atmospheric test fallout data have been used to determine admissible dust particle size distributions for nuclear winter and nuclear fallout studies. The research was originally motivated by extreme differences noted in the magnitude and longevity of dust effects predicted by particle size distributions routinely used in fallout predictions versus those used for nuclear winter studies. Three different sets of historical data have been analyzed:

1. Stratospheric burden of Strontium-90 and Tungsten-185, 1954-1967 (97 contributing events) 2. Continental U.S Strontium-90 fallout through 1958 (75 contributing events) 3. Local Fallout from selected Nevada tests (16 events)

The contribution of dust to possible …

Rigid Backbone: A New Geometry For Percolation, Anthony Roy Day, R. R. Tremblay, A.-M. S. Tremblay

Anthony Roy Day

It is shown that the diluted two-dimensional central-force problem belongs to a new class of percolation problems. Geometric properties such as the fractal dimension of the backbone, the correlation-length exponent, and the connectivity are completely different from those of previously studied percolation problems. Explicit calculations of the backbone and the construction of an algorithm which identifies the infinite rigid cluster clearly demonstrate the absence of singly connected bonds, the overwhelming importance of loops, and the long-range nature of the rigidity.

The Rigid Backbone: A New Geometry For Percolation., Anthony Day, R. Tremblay, A.-M. Tremblay

Anthony Roy Day

It is shown that the diluted two-dimensional central-force problem belongs to a new class of percolation problems. Geometric properties such as the fractal dimension of the backbone, the correlation-length exponent, and the connectivity are completely different from those of previously studied percolation problems. Explicit calculations of the backbone and the construction of an algorithm which identifies the infinite rigid cluster clearly demonstrate the absence of singly connected bonds, the overwhelming importance of loops, and the long-range nature of the rigidity.

Splay Rigidity In The Diluted Central Force Elastic Network, Anthony Roy Day, A.-M. S. Tremblay, R. R. Tremblay

Anthony Roy Day

A Comment on the Letter by Wang and Harris, Phys. Rev. Lett. 55, 2459 (1985).

Guage Invariant De Gennes Model, Anthony Day, T. Lubensky

Anthony Roy Day

A gauge-invariant formulation of the de Gennes model for the nematic—to—smectic-A transition is presented. In this formulation the energy associated with the gauge field A⃗ reduces to the Frank elastic energy with the application of the constraint n⃗0·A⃗=0 where n⃗0 is the uniform equilibrium director and A⃗ is to be identified with deviations δn⃗ of the director from equilibrium. It is shown that thermodynamic quantities and renormalization-group recursion relations are gauge invariant. All gauge dependence appears in the exponent η describing order-parameter correlations. The gauge invariance of a negative dielectric anisotropy smectic-A in an external electric field is also studied.

Dislocations And The Nematic To Smectic-A Transition For Arbitrary Values Of K1, Anthony Day, T. Lubensky, A. Mckane

Anthony Roy Day

The de Gennes model is used to derive the energy of interacting dislocations in smectic-A liquid crystals. This energy reduces to the energy of interacting vortices in type-II superconductors when the splay elastic constant K1 is zero and to that derived from the Landau-Peierls elastic energy when spatial variations are slow on a scale of the bend and twist penetration depths. Furthermore, it has a well-defined K1→∞ limit. The dislocation energy is used to study the nematic—to—smectic-A transition as a function of K1 in two dimensions and in 4-ε dimensions. No evidence for the Nelson-Toner, anisotropic critical point is found …

Electro-Optics Applications For Alleviating Emi/Emc/Emp Problems, George H. Baker, Walter H. Hardwick

George H Baker

No abstract provided.

Direct Nmr Observation Of Rotational Freeze-Out In The Smectic C-Phase, Demetri J. Photinos, Philip J. Bos, Mary E. Neubert, J. William Doane

Philip J. Bos

We report here a simple and direct observation that the molecular long axis is not, on the average, a rotation axis for the entire molecule in the smectic C phase (rotational freeze-out). This observation is made in the compound 4-n-heptyl-d15-oxybenzoic acid-d1 where experiment clearly shows that the principal axes of the time-averaged deuterium quadrupole interactions at specific sites of the hydrocarbon chain are not all parallel, demonstrating that they do not share a common axis of rotation.

Imaging Of Paramagnetic Centres In Diamond, M.J. R. Hoch, Anthony Roy Day

Anthony Roy Day

An imaging method for determining the spatial distribution of paramagnetic nitrogen centres in diamond is described. Results are presented for a sample consisting of two small type IB diamonds.

Emp Analysis Of An Fm Communications Radio With A Long Wire Antenna, George H. Baker Iii, Werner J. Stark

George H Baker

A Norton equivalent circuit is developed for a long-wire antenna used with a VHF man-pack FM radio exposed to an incident electromagnetic pulse (EMP). The required short-circuit current and antenna impedance are computed by use of a transmission-line model for the antenna, and the computations are compared with measurements of the short-circuit current and antenna impedance. The comparison shows that the transmission-line model for the antenna is adequate for performing a vulnerability analysis of the radio. A network model is developed for a portion of the radio and is used as the load in the Norton equivalent circuit. Load currents …