Showing papers on "Crossover published in 1982"

Classical quantum crossover for a bose system in the largen-limit

Abstract: On the basis of the Hartree approximation, the lowtemperature properties of ad-dimensionaln-vector Bose model are discussed in detail, for both normal and ordered phase. The change of critical behaviour which occurs for 2

Critical and crossover behavior in the double-Gaussian model on a lattice

Abstract: The-double-Gaussian model, as recently introduced by Baker and Bishop, is studied in the context of a lattice-dynamics Hamiltonian belonging to the familiar phi/sup 4/ class. Advantage is taken of the partition-function factorability (into Ising and Gaussian components) to place bounds on the Ising-class critical temperature for various lattice dimensions and all degrees of displaciveness in the bare Hamiltonian. Further, a simple criterion for a noncritical and nonuniversal crossover from order-disorder to Gaussian behavior is evaluated in numerical detail. In one and two dimensions these critical and crossover properties are compared with predictions based on real-space decimation renormalization-group flows, as previously exploited in the phi/sup 4/ model by Beale et al. The double-Gaussian model again introduces some unique analytical advantages.

The decoupling point of the axial next-nearest-neighbour Ising model and marginal crossover

Abstract: The axial next-nearest-neighbour Ising (or ANNNI) model and the four-state asymmetric clock model both exhibit a decoupling multicritical point where they decompose into two uncoupled Ising models at criticality. The corresponding scaling exponents for various operators are given generally, the leading modulation or chiral crossover exponent being phi = gamma - nu , where gamma and nu are the pure Ising susceptibility and correlation exponents. Implications for the ANNNI model phase diagrams are discussed. Crossover scaling forms appropriate to logarithmic and marginal behaviour, with non-universal exponents, are presented.

Zero crossover triggering circuit for thyristor

Abstract: A power circuit for a precipitator utilizes a pair of silicon controlled rectifiers (SCR's) which are triggered by detecting the zero crossover of a power signal. The power transmitted through the SCR's is determined by the time period from the detection of the zero crossover to the generation of the trigger signal. Power signals are typically subject to noise which interferes with the detection of the zero crossover. Filters are provided for reducing the noise interference but function without altering the phase relation of the zero crossover of the filtered signal in respect to the unfiltered power signal. A pulse train of higher frequency than the power signal is generated to provide a plurality of triggering pulses for the SCR. Further, phase control signals are generated for each SCR to prevent the generation of trigger pulses when the SCR's are reverse biased. Thus, the present invention provides a precision voltage control for a power supply circuit which is particularly applicable for powering an electrostatic precipitator.

Feeder planning methods for digital loop carrier

Abstract: This paper describes three new approaches to planning for digital loop carrier (DLC) in the exchange feeder loop network. Two of these are manual planning methods that are used to determine the most economical technology for satisfying facility shortages along a feeder route. Both are based on the concept of a distance-oriented crossover point beyond which DLC is the economic relief technology. One of the methods uses a global crossover point for alt routes, and the other uses a route-specific crossover point The third approach is a mechanized toot, the Pair Gain Planning (PGP) program. PGP, which is implemented as a module within the existing Bell System loop planning system, first identifies the appropriate technology for relief and then synthesizes a specific DLC implementation plan. A discussion of system performance and projected Bell System applications of the various methods is included.

Transition temperature shifts and correction-to-scaling amplitudes in systems exhibiting crossover behaviour

Abstract: Reports a study of the corrections to scaling in systems exhibiting crossover behaviour with specific reference to the Heisenberg-dipolar crossover and the anisotropic Heisenberg model exemplified, respectively, by EuO and SrTiO3. The authors show that the correction-to-scaling amplitudes for these systems are uniquely prescribed by the shift in transition temperature induced by the symmetry-breaking perturbation promoting the crossover. They calculate these transition temperature shifts for EuO and SrTiO3 and thus obtain direct estimates of the correction-to-scaling amplitudes for the susceptibility of EuO and the order parameter of SrTiO3.

Crossover behavior in a two-dimensional electron gas and quasiplasma oscillation

Abstract: The dynamic structure factor for a two-dimensional (2D) electron gas at $T=0$ is calculated by a method of recurrence relations. Our result indicates an interesting crossover behavior in going from interacting to noninteracting, which is unique to 2D electronic systems. The crossover behavior is characterized by a simple power law with a "classical" exponent, probably detectable by x rays. The validity of our result is tested against standard moment sum rules and also the static form-factor sum rule at high and low frequencies.

Recursive adaptive-filter design using an adaptive genetic algorithm

Abstract: An adaptive genetic algorithm for determining the optimum filter coefficients in a recursive adaptive filter is presented. The algorithm does not use gradient techniques and thus is appropriate for use in problems where the function to be optimized is non-unimodal or non-quadratic, such as the mean-squared error surface in a recursive adaptive filter. The mechanisms of the algorithm are inspired by adaptive processes observed in nature. After an initial set of possible filters is randomly selected, each filter is mapped to a binary string representation. Selected bit strings are then transformed using the operations of crossover and mutation to build new "generations" of filters. The probability of selecting a particular bit string to modify and/or replicate for the next "generation" is inversely proportional to its estimated mean-squared error value. Hence, the process not only examines new filter coefficient values, but also retains the advances made in previous "generations". Computer simulations of the algorithm's performance on unimodal and bimodal error surfaces are presented.

Dimensional crossover in selective site percolation

Abstract: The dimensionality crossover in selective site percolation on a triangular lattice is discussed in terms of a renormalisation group. A preferred cell to preferred site transformation keeping the original lattice symmetry gives the exact critical line with the flow direction expected from the universality hypothesis. In the chain limits, the critical exponents of both the correlation length and the dimensionality crossover are reproduced exactly for any scaling factor.

Nonlinear dynamic renormalization-group analysis above and below the lambda transition in 4He

Abstract: Recent developments in the theory of the dynamics of liquid 4 He near the lambda transition are reviewed. A nonlinear renormalization-group treatment is presented which provides a quantitative description of the dynamics in the entire region between noncritical background and criticality. The previous discrepancies between asymptotic scaling theories and various experiments above and below TA are explained in terms of crossover effects. This crossover is governed (i) close to T λ by the effect of the weak-scaling fixed point, and (ii) farther away from T λ by a strong decrease of the effective dynamic coupling. New results are presented which are based on the complete flow equations for model F in two-loop order. They tentatively confirm the conclusions of an earlier analysis based on model E and invalidate part of a recent analysis treating model F in an unsystematic way. Excellent agreement is found with new accurate measurements of second-sound damping over four decades in relative temperature.

Panel display unit

Abstract: PURPOSE:To improve accuracy of combining of positions and ensure easy manufacture by making crossover pitch larger than electrode pitch.

Perineal Crossover for Extra-Anatomical Bypass: a Case Report

Abstract: There are many complications following prosthetic vascular bypass procedures. Perhaps the most urgent are infection and sepsis. The outlook for the patient is usually bleak unless the infected prosthesis is excised and another, usually extra-anatomic, revascularization procedure is performed. Graft thrombosis, suture line hemorrhage, and death are complications which may ensue if rapid and astute surgical intervention is not begun. Procedures which were reported originally by Freeman and Leeds in 19521 and subsequently by others2-4 are now the mainstays of vascular surgeons’ armamentarium for extra-anatomic bypass. The majority of extraanatomic procedures employed one of those reported, i.e., femoral-femoral, axillo-femoral, axillo-bifemoral, and obturator foramena bypass.