David Tze-Si Wu

Reference interaction site model polaron theory of the hydrated electron

We have extended the reference interaction site model (RISM)‐polaron theory of Chandler et al. [J. Chem. Phys. 81, 1975 (1984)] to treat self‐trapping and localized states of excess electrons in polar fluids. The extension is based on a new closure of the RISM equation presented herein. The theory is applied to the hydrated electron employing a simple class of electron‐water pseudopotentials. Included in this class are models coinciding with those already examined by others using computer simulations. In those cases, the results for both structural and energetic properties compare well with those of simulation. The work function, or equivalently, the excess chemical potential of the hydrated electron are also computed; the theoretical result agrees with experiment to about 1%. Most interesting, however, is that as the parameter characterizing the pseudopotentials is varied, a critical parameter is found where the electron behavior changes essentially discontinuously from a trapped state to a ‘‘super’’‐tra...

Monte Carlo study of polymers in equilibrium with random obstacles

We have performed Monte Carlo calculations for two‐dimensional freely jointed polymers with no excluded volume in equilibrium with a quenched random lattice of obstacles. In addition to the obstacle density, there are two microscopic parameters in the problem: the obstacle side length a and the polymer step length l. Our Monte Carlo calculations extend to N=50 000 monomer polymer units. The calculations begin to exhibit standard Flory–Lifshitz scaling only at extremely large values of N. For example, when l≊a, nonuniversal behavior is found for N<104. For some choices of parameters, this behavior includes a nonmonotonic mean‐square end‐to‐end length R2 as a function of N. These calculations are made feasible by exploiting an equivalence between annealed and quenched disorder valid when the polymer may equilibrate to the quenched material.

Synchronized continuous media playback through the World Wide Web

We have developed and demonstrated a remote continuous media playback application called cmplayer, using the Berkeley Continuous Media Toolkit (CMT). Cmp layer can be used in conjunction with aWorld W]de Web browserto access remotely stored continuous media data (i.e., video and audio) and provide synchronized playback of multiple media streams. The cmplayer communicates witha server process also written with CMT to stream media data across the network using adaptive control to compensate forlimitednetwork bandwidth, server utilization, and client CPU resources. Asimple script format isusedto indicate thelocation of each piece of media data (i.e., hostname, port number and the filename) and specify source synchronization between media streams. Multiple video and audio streams can be specified. In addition, scrolling text streams and streams of Tcl commands can be integrated as stream types. A stream can be stored in multiple media data files distributed on different servers. Cmplayer script files are ASCII text and are typically less than 10 lines long. Cmplayer provides full VCR-like controls and random access into any point of the video.

dc : A live webcast control system

Live Internet streaming media programs, called webcasts, can adopt techniques developed by television to obtain higher quality. We have developed a general webcast production model composed of three stages (i.e., sources, broadcast, and transmission) and a tool, called the Directors Console (dc), to control live webcasts. The tool is one component of a distributed service architecture, which adapts to varying physical infrastructure and broadcast configurations.

Internet MBone broadcast management system

The Internet Multicast Backbone (MBone) has seen tremendous growth during the past four years. For the past three and a half years, we have broadcast a weekly seminar on the MBone. The effort to set up and produce each broadcast has grown as we worked to improve the broadcasts and to support more services (e.g., on-demand playback, recording, video effect, etc.) This problem motivated us to develop a system to automate the tasks required to produce a broadcast. The motivation, requirements, and implementation of the system are presented.

Comments on a model influence functional for quantum systems

We continue the study of a model non‐Gaussian influence functional proposed by Allinger, Carmeli, and Chandler [J. Chem. Phys. 84, 1724 (1986)] to approximate the exact influence functional resulting from integrating out all quantum states but those of primary interest. The premise of this work is that the influence of many secondary states on a single primary state can be closely approximated by the influence of a degenerate level of states with equal coupling to the primary state. The degeneracy reflects the fluctuations possible among the secondary states and in fact can be associated with the partition function of the exact secondary states. The new calculations presented herein emphasize the importance of entropic‐like effects properly described by this degeneracy, and for the models we examine, our basic premise is shown to be correct.

Characteristics of 10Gbit/s common shallow ridge waveguide laser-electroabsorption modulator

A laser and high speed modulator are integrated using a common shallow etched ridge waveguide for the first time. Performances of 10Gbps electro-absorption modulation transmission and the reliability of EM lasers are demonstrated. Low dispersion penalty for transmission over 90km of standard single mode fiber (SMF) is achieved. The devices have been fabricated and qualified for TDM and DWDM operation.