Critical Behavior of Charge Density Waves Below Threshold: Numerical and Scaling Analysis

The critical behavior of pinned charge density waves (CDW\u27s) is studied as the threshold for sliding is approached. Using the Fukuyama-Lee-Rice Hamiltonian with relaxational dynamics, the polarization and linear response are calculated numerically. ... On the irreversible approach to threshold, the response due to avalanches triggered by local instabilities dominates the polarizability, which diverges in one and two dimensions. Characteristic diverging length scales are studied using finite-size scaling of the sample-to-sample variations of the threshold field in finite systems and finite-size effects in the linear polarizability and the irreversible polarization. A dominant diverging correlation length is found which controls the threshold field distribution, finite-size effects in the irreversible polarization, and a cutoff size for the avalanche size distribution. Our results are compared with those for related models and questions are raised concerning the relationship of the static critical behavior below threshold to the dynamic critical behavior in the sliding state above threshold

Turn-by-Turn Imaging of the Transverse Beam Profile in PEP-II

During injection or instability, the transverse profile of an individual bunch in a storage ring can change significantly in a few turns. However, most synchrotron-light imaging techniques are not designed for this time scale. We have developed a novel diagnostic that enhances the utility of a fast gated camera by adding, inexpensively, some features of a dual-axis streak camera, in order to watch the turn-by-turn evolution of the transverse profile, in both x and y. The beam's elliptical profile is reshaped using cylindrical lenses to form a tall and narrow ellipse—essentially the projection of the full ellipse onto one transverse axis. We do this projection twice, by splitting the beam into two paths at different heights, and rotating the ellipse by 90° on one path. A rapidly rotating mirror scans these vertical “pencils” of light horizontally across the photocathode of the camera, which is gated for 3 ns on every Nth ring turn. A single readout of the camera captures 100 images, looking like a stroboscopic photograph of a moving object. We have observed the capture of injected charge into a bunch and the rapid change of beam size at the onset of a fast instability

Industrial Incentives: Competition Among American States and Cities

This book is the first significant attempt to quantify the development efforts made by state and local governments. The authors\u27 extensive research focuses on tax and incentive policies across the 24 most industrialized states in the United States and a sample of 112 cities from within those states.https://research.upjohn.org/up_press/1066/thumbnail.jp

State Enterprise Zone Programs: Have They Worked?

Peters and Fisher evaluate 75 EZs located in 13 states to gain an understanding of the overall effectiveness of state enterprise zones. Faced with a paucity of data on EZs that could be used in standard economic analysis, the authors employ a hypothetical firm model in which they apply various EZ and non-EZ incentives to financial statements created for a set of typical firms. Observing the impacts of both types of incentives on firms\u27 financial statements allow Peters and Fisher to predict the firms\u27 resulting behavior. Between these findings and the data accumulated from actual EZs, they are able to offer insights on seven key policy issues.https://research.upjohn.org/up_press/1057/thumbnail.jp

Numerical Results for the Ground-State Interface in a Random Medium

The problem of determining the ground state of a $d$-dimensional interface embedded in a $(d+1)$-dimensional random medium is treated numerically. Using a minimum-cut algorithm, the exact ground states can be found for a number of problems for which other numerical methods are inexact and slow. In particular, results are presented for the roughness exponents and ground-state energy fluctuations in a random bond Ising model. It is found that the roughness exponent $\zeta = 0.41 \pm 0.01, 0.22 \pm 0.01$, with the related energy exponent being $\theta = 0.84 \pm 0.03, 1.45 \pm 0.04$, in $d = 2, 3$, respectively. These results are compared with previous analytical and numerical estimates.Comment: 10 pages, REVTEX3.0; 3 ps files (separate:tar/gzip/uuencoded) for figure

Intrinsic noise and discrete-time processes

A general formalism is developed to construct a Markov chain model that converges to a one-dimensional map in the infinite population limit. Stochastic fluctuations are therefore internal to the system and not externally specified. For finite populations an approximate Gaussian scheme is devised to describe the stochastic fluctuations in the non-chaotic regime. More generally, the stochastic dynamics can be captured using a stochastic difference equation, derived through an approximation to the Markov chain. The scheme is demonstrated using the logistic map as a case study.Comment: Modified version accepted for publication in Phys. Rev. E Rapid Communications. New figures adde