Wedges, Cones, Cosmic Strings, and the Reality of Vacuum Energy

One of J. Stuart Dowker's most significant achievements has been to observe that the theory of diffraction by wedges developed a century ago by Sommerfeld and others provided the key to solving two problems of great interest in general-relativistic quantum field theory during the last quarter of the twentieth century: the vacuum energy associated with an infinitely thin, straight cosmic string, and (after an interchange of time with a space coordinate) the apparent vacuum energy of empty space as viewed by an accelerating observer. In a sense the string problem is more elementary than the wedge, since Sommerfeld's technique was to relate the wedge problem to that of a conical manifold by the method of images. Indeed, Minkowski space, as well as all cone and wedge problems, are related by images to an infinitely sheeted master manifold, which we call Dowker space. We review the research in this area and exhibit in detail the vacuum expectation values of the energy density and pressure of a scalar field in Dowker space and the cone and wedge spaces that result from it. We point out that the (vanishing) vacuum energy of Minkowski space results, from the point of view of Dowker space, from the quantization of angular modes, in precisely the way that the Casimir energy of a toroidal closed universe results from the quantization of Fourier modes; we hope that this understanding dispels any lingering doubts about the reality of cosmological vacuum energy.Comment: 28 pages, 16 figures. Special volume in honor of J. S. Dowke

The VLSI design of a single chip Reed-Solomon encoder

A design for a single chip implementation of a Reed-Solomon encoder is presented. The architecture that leads to this single VLSI chip design makes use of a bit serial finite field multiplication algorithm

VLSI single-chip (255,223) Reed-Solomon encoder with interleaver

The invention relates to a concatenated Reed-Solomon/convolutional encoding system consisting of a Reed-Solomon outer code and a convolutional inner code for downlink telemetry in space missions, and more particularly to a Reed-Solomon encoder with programmable interleaving of the information symbols and code correction symbols to combat error bursts in the Viterbi decoder

A Method of Optimal Radio Frequency Assignment for Deep Space Missions

A method for determining optimal radio frequency channels for the Deep Space Network is described. Computer automated routines calculate interference-to-signal ratios over a given mission period and provide a quantitative assessment of the channels which could then be assigned to a new mission. This automated procedure reduces the analysis time considerably and effectively improves upon the accuracy of existing channel assignment techniques

Direct and indirect effect of depression in adolescence on adult wages

It is well recognized that a depressive mental state can persist for a long time, and this can adversely impact labour market outcomes. The aim of this article is to examine the direct association between depression status in late-teenage years and adult wages, as well as the indirect association, operating through accumulated education, experience and occupation choice. Using the National Longitudinal Survey of Youth 1997 data, we find adolescent depression is associated with a wage penalty of around 10–15%, but its mechanics are very different for males and females. For males, about three quarters of the wage penalty is through the direct channel, whilst for females the indirect effect channel is dominant. The indirect channel is driven by lower accumulated education, mostly because depression discourages further study post high school. These results are important because they imply that the association between adolescent depression and wages is stronger than has been estimated in previous cross-sectional studies

On the Information-Theoretic Limits of Noisy Sparse Phase Retrieval

The support recovery problem consists of determining a sparse subset of variables that is relevant in generating a set of observations. In this paper, we study the support recovery problem in the phase retrieval model consisting of noisy phaseless measurements, which arises in a diverse range of settings such as optical detection, X-ray crystallography, electron microscopy, and coherent diffractive imaging. Our focus is on informationtheoretic fundamental limits under an approximate recovery criterion, with Gaussian measurements and a simple discrete model for the sparse non-zero entries. Our bounds provide sharp thresholds with near-matching constant factors in several scaling regimes on the sparsity and signal-to-noise ratio

An HMM-based Comparative Genomic Framework for Detecting Introgression in Eukaryotes

One outcome of interspecific hybridization and subsequent effects of evolutionary forces is introgression, which is the integration of genetic material from one species into the genome of an individual in another species. The evolution of several groups of eukaryotic species has involved hybridization, and cases of adaptation through introgression have been already established. In this work, we report on a new comparative genomic framework for detecting introgression in genomes, called PhyloNet-HMM, which combines phylogenetic networks, that capture reticulate evolutionary relationships among genomes, with hidden Markov models (HMMs), that capture dependencies within genomes. A novel aspect of our work is that it also accounts for incomplete lineage sorting and dependence across loci. Application of our model to variation data from chromosome 7 in the mouse (Mus musculus domesticus) genome detects a recently reported adaptive introgression event involving the rodent poison resistance gene Vkorc1, in addition to other newly detected introgression regions. Based on our analysis, it is estimated that about 12% of all sites withinchromosome 7 are of introgressive origin (these cover about 18 Mbp of chromosome 7, and over 300 genes). Further, our model detects no introgression in two negative control data sets. Our work provides a powerful framework for systematic analysis of introgression while simultaneously accounting for dependence across sites, point mutations, recombination, and ancestral polymorphism

Enhancement of reliability in condition monitoring techniques in wind turbines

The majority of electrical failures in wind turbines occur in the semiconductor components (IGBTs) of converters. To increase reliability and decrease the maintenance costs associated with this component, several health-monitoring methods have been proposed in the literature. Many laboratory-based tests have been conducted to detect the failure mechanisms of the IGBT in their early stages through monitoring the variations of thermo-sensitive electrical parameters. The methods are generally proposed and validated with a single-phase converter with an air-cored inductive or resistive load. However, limited work has been carried out considering limitations associated with measurement and processing of these parameters in a three-phase converter. Furthermore, looking at just variations of the module junction temperature will most likely lead to unreliable health monitoring as different failure mechanisms have their own individual effects on temperature variations of some, or all, of the electrical parameters. A reliable health monitoring system is necessary to determine whether the temperature variations are due to the presence of a premature failure or from normal converter operation. To address this issue, a temperature measurement approach should be independent from the failure mechanisms. In this paper, temperature is estimated by monitoring an electrical parameter particularly affected by different failure types. Early bond wire lift-off is detected by another electrical parameter that is sensitive to the progress of the failure. Considering two separate electrical parameters, one for estimation of temperature (switching off time) and another to detect the premature bond wire lift-off (collector emitter on-state voltage) enhance the reliability of an IGBT could increase the accuracy of the temperature estimation as well as premature failure detection

Promoting knowledge creation discourse in an Asian primary five classroom: Results from an inquiry into life cycles

The phrase 'knowledge creation' refers to the practices by which a community advances its collective knowledge. Experience with a model of knowledge creation could help students to learn about the nature of science. This research examined how much progress a teacher and 16 Primary Five (Grade 4) students in the International Baccalaureate Primary Years Programme could make towards the discourse needed for Bereiter and Scardamalia's model of knowledge creation. The study consisted of two phases: a five-month period focusing on the development of the classroom ethos and skills needed for this model (Phase 1), followed by a two-month inquiry into life cycles (Phase 2). In Phase 1, we examined the classroom practices that are thought to support knowledge creation and the early experiences of the students with a web-based inquiry environment, Knowledge Forum®. In Phase 2, we conducted a summative evaluation of the students' work in Knowledge Forum in the light of the model. The data sources included classroom video recordings, artefacts of the in-class work, the Knowledge Forum database, a science content test, questionnaires, and interviews. The findings indicate that the students made substantial progress towards the knowledge creation discourse, particularly regarding the social structure of this kind of discourse and, to a lesser extent, its idea-centred nature. They also made acceptable advances in scientific knowledge and appeared to enjoy this way of learning. The study provides one of the first accounts in the literature of how a teacher new to the knowledge creation model enacted it in an Asian primary classroom. © 2011 Taylor & Francis.postprin