Showing papers by "John Bechhoefer published in 2005"

Feedback for physicists: A tutorial essay on control

Abstract: Feedback and control theory are important ideas that should form part of the education of a physicist but rarely do. This tutorial essay aims to give enough of the formal elements of control theory to satisfy the experimentalist designing or running a typical physics experiment and enough to satisfy the theorist wishing to understand its broader intellectual context. The level is generally simple, although more advanced methods are also introduced. Several types of applications are discussed, as the practical uses of feedback extend far beyond the simple regulation problems where it is most often employed. Sketches are then provided of some of the broader implications and applications of control theory, especially in biology, which are topics of active research.

Nucleation and growth in one dimension. I. The generalized Kolmogorov-Johnson-Mehl-Avrami model

Abstract: Motivated by a recent application of the Kolmogorov-Johnson-Mehl-Avrami sKJMAd model to the study of DNA replication, we consider the one-dimensional s1Dd version of this model. We generalize previous work to the case where the nucleation rate is an arbitrary function Istd and obtain analytical results for the timedependent distributions of various quantities ssuch as the island distributiond. We also present improved computer simulation algorithms to study the 1D KJMA model. The analytical results and simulations are in excellent agreement.

Nucleation and growth in one dimension. II. Application to DNA replication kinetics

Abstract: Inspired by recent experiments on DNA replication, we apply a one-dimensional nucleation-and-growth model to DNA-replication kinetics, focusing on how to extract the time-dependent nucleation rate $I(t)$ and growth speed $v$ from data. We discuss generic experimental problems: namely, spatial inhomogeneity, measurement noise, and finite-size effects. After evaluating how each of these affects the measurements of $I(t)$ and $v$, we give guidelines for the design of experiments. These ideas are then discussed in the context of the DNA-replication experiments.

Critical behavior of the banded-unbanded spherulite transition in a mixture of ethylene carbonate with polyacrylonitrile.

Abstract: We investigate the transition from unbanded to banded spherulitic growth in mixtures of ethylene carbonate with polyacrylonitrile. By carefully considering systematic errors, we show that the band spacing diverges with a power-law form showing scaling over nearly two decades. We also observe that the bands disorder as the transition point is approached. The critical exponent is nonclassical. One possible explanation is that the nonequilibrium transition is actually weakly first order (subcritical).