Dynamical model of directly modulated semiconductor laser diodes

We present a new dynamical model for a directly modulated semiconductor diode, applicable to systems in which the dynamical time scales of interest are longer than the round-trip time of light in the diode. Employing a multiple scales analysis to simplify the familiar phenomenological equations, we find that the dynamical response of the diode can be described by time-dependent reflection and transmission coefficients for the electric field and one ordinary differential equation for the integrated carrier density. We do not assume that the photon and carrier densities are uniform along the diode and do not need to calculate them explicitly at each point. Additionally, we need not restrict ourselves to only a small-signal response. We justify the multiple scales analysis for parameters corresponding to typical structures through a comparison of the numerical solution of our results and a direct numerical integration of the original phenomenological equations     

Echoic memory processes in good and poor readers.

Conducted 4 experiments to determine whether echoic memory plays a role in differences between good and poor readers. In Exp I, with 9 poor (mean age 11.05 yrs) and 9 good (mean age 10.9 yrs) readers, and Exp II, with 12 poor (mean age 10.85 yrs) and 12 good (mean age 10.7 yrs) readers, a suffix procedure was used in which the S was read a list of digits with either a tone control or the word go appended to the list. For lists that exceeded the length of the Ss' memory span by 1 digit (i.e., that avoided ceiling effects), poor readers showed a larger decrement in the suffix condition than did good readers. In Exp III, with 14 poor (mean age 10.64 yrs) and 14 good (mean age 10.83 yrs) readers, Ss shadowed words presented to 1 ear at a rate determined to give 75–85% shadowing accuracy. The item presented to the nonattended ear were words and an occasional digit. At various intervals after the presentation of the digit, a light signaled that the S was to cease shadowing and attempt to recall any digit that had occurred in the nonattended ear recently. Whereas good and poor readers recalled the digit equally if tested immediately after presentation, poor readers showed a faster decline in recall of the digit as retention interval increased. In Exp IV, using Ss from Exp II, bursts of white noise were separated by 9–400 msec of silence, and the S was to say whether there were 1 or 2 sounds presented. There were no differences in detectability functions for good and poor readers. (39 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Four channel fibre grating demultiplexer

The authors demonstrate a four channel all-fibre demultiplexer based on a 1×4 fused fibre coupler followed by strong fibre grating passband filters     

Propagating quantum walks: The origin of interference structures

Abstract

We analyse the solution of the coined quantum walk on a line. First, we derive the full solution, for arbitrary unitary transformations, by using a new approach based on the four ‘walk fields’ which we show determine the dynamics. The particular way of deriving the solution allows a rigorous derivation of a long wavelength approximation. This long wavelength approximation is useful as it provides an approximate analytical expression that captures the basics of the quantum walk and allows us to gain insight into the physics of the process.     

Travel Self-Containment in Master Planned Estates: Analysis of Recent Australian Trends

Low density suburban development and excessive use of automobiles are associated with serious urban and environmental problems. Master planned development suggests itself as a possible palliative for these ills. This study examines the patterns and dynamics of movement in a selection of master planned estates in Australia with the aim of developing new approaches for assessing the containment of travel within planned development. A geographical information systems methodology is used to determine regional journey-to-work patterns and travel containment rates. Factors that influence self-containment patterns are estimated with a regression model. The findings of the pilot study demonstrate that the proposed model is a useful starting point for a systematic and detailed analysis of self-containment in master planned estates.