Optical frequency measurement for multichannel networks using sum-frequency generation in multilayer waveguides

Practical use of sum-frequency generation in multilayer waveguides is investigated for the purpose of frequency stabilisation in multichannel optical networks. Experimental results are presented on both wide and narrow-range wavelength sensing in the 1.3 mu m communication band using simple optoelectronic components. Optical frequency difference measurement resolution is estimated to be better than 2 GHz.<>     

Methodology for the large-scale assessment of small hydroelectric potential: Application to the Province of New Brunswick (Canada)

The mapping of the small hydropower (SHP) resource over a given territory is indispensable to identify suitable sites for the development of SHP renewable energy projects. In this study, a straightforward method to map the SHP potential over a large territory is presented. The methodology uses a synthetic hydro network (SHN) created from digital elevation models (DEM) to ensure precise hydro head estimations. From the SHN, hydro heads are calculated by subtracting the minimum from the maximum elevation of synthetic stream segments. Subsequently, stream segments with low hydro heads over a specified maximum distance are removed. Finally, the method uses regional regression models to estimate the annual baseflow for all drainage areas in the study area. The technical SHP potential can then be estimated as a function of the hydro head and maximum penstock length. An application of the method is made to the province of New Brunswick, Canada, where SHP maps have been developed to promote the development of the SHP energy sector in the province. In terms of the SHP opportunity, it is shown that the province of New Brunswick (71,450 km²) has a good SHP resource. Using a representative hydro head (10 m) and penstock length (3000 m) for the region, 696 potential sites have been identified over the territory. Results show that the technical SHP potential for New Brunswick is 368 MW for the conventional hydroelectric reservoir SHP configuration, while for the run-of-river SHP configuration, the technical SHP potential is 58 MW.     

Satisfaction with outcome and process from web-based meetings for idea generation and selection: The roles of instrumentality,enjoyment, and interface design

This study examines individual group member satisfaction with outcome and process from an idea generation and selection task via a Group Support System. 126 Participants formed 20 virtual teams, each completing a 20 minute task, followed by a questionnaire about their experience. The study validated a proposed scale for a new construct and tested several hypotheses using a structural equation model. While the new construct of perceived instrumentality did not directly influence satisfaction with outcome, satisfaction with process was significantly influenced by perceived task enjoyment and interface design aesthetics. Scholars of GSS meeting satisfaction are therefore advised to include hedonic constructs in their research models. The study’s qualitative data also indicated that a GSS designed to support evaluability within the group could lead to increased satisfaction with process within the majority of group members.     

Phosphorus sorption experiments and the potential for internal phosphorus loading in littoral areas of a stratified lake

The exchange of phosphorus (P) during the resuspension of sediments into shallow (oxic) waters of deep stratified lakes is regulated by equilibrium dynamics. In this study, we compared the P-sorption characteristics of sediments from 17 shallow and deep littoral sites in an oligo-mesotrophic lake. Zero Equilibrium P Concentration (EPC₀) ranged from 0.2 to 5 μg P L⁻¹. EPC₀ did not vary with sediment characteristics, but increased with increasing sediment-to-water ratios (SWR). Buffering capacity also increased with increasing SWR up to 1 g L⁻¹, at which point P concentrations were buffered almost perfectly. Therefore, internal P loading in littoral areas may depend primarily on the intensity and duration of sediment resuspension instead of sediment composition, and is expected to be spatially and temporally patchy. Maximum P-sorption capacity (S_max) varied with chemical composition of the sediments, but was generally low, indicating a limited capacity of littoral sediments to retain external inputs of P.     

Solution-processed PbS quantum dot infrared photodetectors and photovoltaics

In contrast to traditional semiconductors, conjugated polymers provide ease of processing, low cost, physical flexibility and large area coverage. These active optoelectronic materials produce and harvest light efficiently in the visible spectrum. The same functions are required in the infrared for telecommunications (1,300-1,600 nm), thermal imaging (1,500 nm and beyond), biological imaging (transparent tissue windows at 800 nm and 1,100 nm), thermal photovoltaics (>1,900 nm), and solar cells (800-2,000 nm). Photoconductive polymer devices have yet to demonstrate sensitivity beyond approximately 800 nm (refs 2,3). Sensitizing conjugated polymers with infrared-active nanocrystal quantum dots provides a spectrally tunable means of accessing the infrared while maintaining the advantageous properties of polymers. Here we use such a nanocomposite approach in which PbS nanocrystals tuned by the quantum size effect sensitize the conjugated polymer poly[2-methoxy-5-(2'-ethylhexyloxy-p-phenylenevinylene)] (MEH-PPV) into the infrared. We achieve, in a solution-processed device and with sensitivity far beyond 800 nm, harvesting of infrared-photogenerated carriers and the demonstration of an infrared photovoltaic effect. We also make use of the wavelength tunability afforded by the nanocrystals to show photocurrent spectra tailored to three different regions of the infrared spectrum.     

Analyse psychométrique d'une adaptation en langue fran?aise de l'échelle de Conscience de Sol.

The present work is an attempt to assess the psychometric properties of an adaptation in French of the Self-Consciousness Scale developed by Fenigstein, Scheier, and Buss (1975). The scale is composed of 23 items, distributed in three subscales: private self-consciousness (SC), public SC, and social anxiety. The French version was administered to three distinct samples: two groups of undergraduate students (n = 196; n = 217) and a third one of psychologists (n = 411). Overall, results show that each subscale is homogeneous with appropriate test-retest reliabilities over a two-week period. As expected, private and public SC correlate moderately, whereas social anxiety and private SC are not related Principal components factor analyses show that the scale is in fact composed of three orthogonal factors, in accordance with the three scales. The results in general point to the adequacy of the current adaptation in French of the Self-Consciousness Scale, which presents the same basic properties as the original. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dither-free absolute frequency locking of a 1.3 μm DFB laser on87Rb

A technique for frequency locking a semiconductor laser in the 1.3 μm region by observing the absorption in a ⁸⁷Rb vapor optically pumped by another frequency-modulated semiconductor laser is presented. This technique offers well-defined strong atomic resonances and does not require frequency dithering of the 1.3 μm laser to observe the discrimination pattern required for frequency locking. Dither-free absolute frequency locking of a DFB (distributed feedback) laser at 1324 nm was achieved using a pump laser diode operating at 795 nm (D₁-line). Applications include master oscillator of multiwavelength and coherent communication systems and reference source for an optical frequency synthesizer. Resonances in the 1.55 μm region are also available through this approach     

Module-packaged tunable laser and wavelength locker delivering 40mW of fibre-coupled power on 34 channels

A continuously tunable laser monolithically integrated with a semiconductor optical amplifier is reported. The chip is co-packaged with a frequency locker in a 26 pin butterfly module, and features over 40 mW of fibre-coupled power with an SMSR >37 dB on 34 ITU channels (50 GHz spacing)     

Hydrocarbon structural group analysis of Athabasca asphaltene and its g.p.c. fractions by C n.m.r.

Asphaltene from the Athabasca oil sand bitumen separated according to molecular weight by gel permeation chromatography was examined by high resolution solution-state ¹³C and ¹H and solid state ¹³C n.m.r. Integration of the inverse gated decoupled solution state and CP/MAS ¹³C n.m.r. spectra gave the aromaticity of each fraction as well as the relative number of carbon atoms responsible for well resolved signals in the aliphatic portion of the spectra. A two-pulse spin-echo ¹³C n.m.r. sequence in the solution state, and dipolar dephasing in the solid state, permitted the assignment of each aliphatic carbon signal to a methyl, methylene, or methine carbon; no quaternary aliphatic carbons were observed. These signals show that the aromatic core of the asphaltene is surrounded by alkyl chains with a mean length of 7.7 for the lowest molecular weight fraction (MW 1200), increasing to 12 for the highest MW fraction (MW 16900). Aromaticity of the fractions obtained from solution spectra ranged from 34 to 48%, the highest aromaticity being associated with the lowest molecular weight asphaltenes. In the solid state, the aromaticity ranged from 31 to 42 %. The degree of branching ranged from 0.5 per chain for the low MW asphaltene to 1.0 for the high MW fraction. The highest naphthenic carbon content was found in the high MW fractions; the 1200 MW fraction appeared to be nearly devoid of such carbon, this fraction having a much higher aromaticity than the second-lowest MW fraction.     

Multiwavelength sources using laser diodes frequency-locked toatomic resonances

It is shown that low-cost compact disk AlGaAs laser diodes make it possible to realize manifold optical sources with precise and stable wavelengths when locked to rubidium vapor resonances. Many optical frequency references can be obtained with the use of absorption cells containing a foreign gas or by placing cells in static magnetic fields. The same approach can be used with other wavelengths required by optical fiber communications