Frequency locking of semiconductor laser using PSK modulated signal

A random PSK modulated signal generated with an optical waveguide phase modulator is used to obtain an error signal and lock the frequency of an AlGaAs semiconductor laser to the /sup 7/Rb D/sub 2/ line. The measured error signal is similar to that obtained with sinusoidal phase modulation under the same conditions. The technique could be applied to longer wavelength lasers and other types of laser that cannot be directly modulated such as fibre lasers.<>     

Enabling multimedia applications in 2.5G and 3G wireless terminals through a combined RISC/DSP architecture: OMAP

This paper describes how multimedia applications will be enabled in 2.5 and 3G wireless terminals thanks to the efficiency of the DSP core embedded in the TI OMAP platform. OMAP H/W architecture will be described with an emphasis on how multimedia applications (video, audio, speech) will benefit from this advanced architecture. The advantages provided by a combined RISC/DSP architecture, compared to a single RISC architecture, for multimedia mobile applications will be depicted.     

Photocontrolled living polymerizations

Living polymerizations involve the creation of polymer chains without significant irreversible chain transfer or chain termination. Such processes are widely used to access well-defined macromolecular materials with controlled architectures, such as block and star polymers. Although this concept was first realized for anionic polymerizations in the 1950s, many key recent advances have been made, most notably in the area of radical polymerization. Here, we report a living photopolymerization that involves photoexcited monomers. Exposure of metal-containing ferrocenophane monomers to Pyrex-filtered light from a mercury lamp (lambda>310 nm) or to bright sunlight in the presence of an anionic initiator leads to living polymerizations, in which the conversion and molecular weight of the resulting polymer can be controlled by the irradiation time. Photoirradiation selectively weakens the iron-cyclopentadienyl bond in the monomer, allowing the use of moderately basic and highly functional-group-tolerant initiators. The polymerization proceeds through attack of the initiator and propagating anion on the iron atom of the photoexcited monomer and, remarkably, the polymerization rate decreases with increasing temperature. Block copolymer formation is possible when the light source is alternately switched on and off in between sequential addition of different monomers, providing unprecedented, photocontrolled access to new types of functional polymers.     

Telephone surveys as an alternative for estimating prevalence of mental disorders and service utilization: a Montreal catchment area study

BACKGROUND: Large-scale mental health surveys have provided invaluable information regarding the prevalence of specific mental disorders and service use for mental health reasons. Unfortunately, because vast surveys conducted face to face are very costly, many countries and provinces do not embark upon this path of research, thus depriving themselves of a rich source of data useful for service planning. METHOD: As an alternative, the authors undertook a telephone survey with a sample of 893 residents from a Montreal catchment area. Mental disorders were assessed by the Composite International Diagnostic Interview Simplified (CIDIS), an instrument especially designed to be used in mail or telephone surveys. Service utilization was measured by an instrument similar to those used in recent large Canadian or American surveys. RESULTS: The prevalence rate for any mental disorder was lower in this study than in some large-scale epidemiological surveys reviewed. This could be explained by methodological differences, such as number of disorders covered and period of reference. With regard to specific mental disorders, results appeared very similar to those of other studies. Concerning service utilization, rates tended to be higher than in other studies, and this finding could reflect real differences between Quebec and other Canadian provinces or the United States. CONCLUSIONS: Aside from being lower in cost, telephone surveys can yield results comparable to those obtained in large-scale epidemiological surveys conducted by means of face-to-face interviews.     

L'influence de l'approche psychothérapeutique et de l'expérience professionnelle sur les attentes des thérapeutes.

Evaluated the influence of theoretical orientation and professional experience on therapists' expectancies. In an analog study, 199 registered psychologists were asked to read a case history of a hypothetical client and to answer an 8-point Likert type expectancies inventory. From a 61-item inventory, 3 types of therapist expectancies were examined: diagnostic (anticipations of client need), prognostic (assessments of probable client outcomes), and process expectancies (anticipated use of directiveness and interpretations). A MANOVA with unweighted means was performed. Use of a Wilks lambda criterion produced no significant interaction effects. The main effect for Professional Experience was not significant. However, a significant main effect was found for Therapist Theoretical Orientation. Discriminant function analysis clarified the meaning of these results. Group centroids indicated that behaviorists expect to be more active and anticipate fewer client needs than psychoanalysts and phenomenologists. Psychoanalysts expect to be less active and anticipate more client needs, while phenomenologists expect to be moderately active and anticipate moderate client needs. (39 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contributing Authors

Biography

Contributing Authors     

Progress in the realization of a frequency standard at 192.1 THz(1560.5 nm) using 87Rb D2-line and second harmonicgeneration

Second harmonic generation of a 192.1 THz semiconductor distributed feedback (DFB) laser is achieved using a KNbO₃ crystal in a resonant ring cavity. Optical feedback from this cavity is used to stabilize the laser frequency and reduce its linewidth. A second harmonic power of 5.5 μW is generated with 38 mW incident on the cavity. We use the second harmonic signal to observe saturated absorption lines and orientation signals in rubidium vapor. Injection-locking of a 780 nm Fabry-Perot laser using the second harmonic signal is also demonstrated. With this scheme, we observe saturated absorption lines in rubidium     

Finite element elastic-plastic-creep analysis of two-dimensional continuum with temperature dependent material properties

A technique is presented for performing finite element elastic-plastic-creep analysis of two-dimensional continuum composed of material with temperature dependent elastic, plastic, and creep properties. The plastic analysis utilizes the Prandtl-Reuss flow equations assuming isotropic material properties and linear strain-hardening. A power creep flow law formulated by Odquist is used to determine the steady state creep strain rate. The plastic and creep flow laws are employed to derive a ‘softened’ plastic-creep stress-strain matrix. These modified stress-strain relations are then used to formulate the element stiffness matrix in the usual manner. The differences in the elastic, plastic, and creep properties of the material due to the temperature change during the increment result in the formation of pseudo stresses, which in turn lead to load terms that appear on the right hand side of the equilibrium equations. The load terms resulting from these pseudo stresses not only keep the solution on the temperature dependent stress-strain curve of the material, but also correct for the elastic ‘overshoot’ that occurs when an element changes from an elastic to a plastic state. The effect of large displacements is included by the formulation of the geometric stiffness matrix for each element being used in the computer code. With this procedure it becomes economically feasible to perform elastic-plastic-creep stress analysis of two-dimensional continuum subjected to transient thermal and mechanical loadings. Several examples of both elastic-plastic and creep analyses are presented, and the finite element solutions are compared to either other theoretical solutions or experiment.     

A Similarity-Based Aspect-Graph Approach to 3D Object Recognition

This paper describes a view-based method for recognizing 3D objects from 2D images. We employ an aspect-graph structure, where the aspects are not based on the singularities of visual mapping but are instead formed using a notion of shape similarity between views. Specifically, the viewing sphere is endowed with a metric of dis-similarity for each pair of views and the problem of aspect generation is viewed as a segmentation of the viewing sphere into homogeneous regions. The viewing sphere is sampled at regular (5 degree) intervals and the similarity metric is used in an iterative procedure to combine views into aspects with a prototype representing each aspect. This is done in a region-growing regime which stands in contrast to the usual edge detection styles to computing the aspect graph. The aspect growth is constrained such that two aspects of an object remain distinct under the given similarity metric. Once the database of 3D objects is organized as a set of aspects, and prototypes for these aspects for each object, unknown views of database objects are compared with the prototypes and the results are ordered by similarity. We use two similarity metrics for shape, one based on curve matching and the other based on matching shock graphs, which for a database of 64 objects and unknown views of objects from the database give a recall rate of (90.3%, 74.2%, 59.7%) and (95.2%, 69.0%, 57.5%), respectively, for the top three matches; cumulative recall rate based on the top three matches is 98% and 100%, respectively. The result of indexing unknown views of objects not in the database also produce intuitive matches. We also develop a hierarchical indexing scheme to prune unlikely objects at an early stage to improve the efficiency of indexing, resulting in savings of 35% at the top level and of 55% at the next level, cumulatively.     

Durability of concrete containing a natural pozzolan as defined by a performance-based approach

This paper deals with the application of a performance-based approach on the durability of concrete made with an Algerian natural pozzolan. The evaluation of the durability of concrete was based on the comparison of durability indicators with a reference concrete usually found in Algeria. The properties measured included general indicators (water porosity, gas permeability, capillary absorption and Portlandite content) and specific indicators related to degradation phenomena that might occur in Algeria: corrosion induced by carbonation and chlorides, and chemical attacks by sulphates and acids. For the specific degradations, the indicators measured included carbonation depths, chloride diffusion coefficients, chloride permeability, expansion and sulphate profiles, and depth of leaching due to ammonium nitrate attack. The results showed that general durability indicators were almost equivalent for all the types of concrete tested, highlighting the importance of using specific indicators for each type of exposure. The results of specific indicators for corrosion and acid attacks showed that increasing the pozzolan content led to higher resistance of the concrete. Thus, it is possible to improve the durability of typical concretes currently made in Algeria by using local materials.