Characterization of the temperature sensitivity of gain and recombination mechanisms in 1.3-/spl mu/m AlGaInAs MQW lasers

The potential of 1.3-/spl mu/m AlGaInAs multiple quantum-well (MQW) laser diodes for uncooled operation in high-speed optical communication systems is experimentally evaluated by characterizing the temperature dependence of key parameters such as the threshold current, transparency current density, optical gain and carrier lifetime. Detailed measurements performed in the 20/spl deg/C-100/spl deg/C temperature range indicate a localized T/sub 0/ value of 68 K at 98/spl deg/C for a device with a 2.8 /spl mu/m ridge width and 700-/spl mu/m cavity length. The transparency current density is measured for temperatures from 20/spl deg/C to 60/spl deg/C and found to increase at a rate of 7.7 A/spl middot/cm/sup -2//spl middot/ /spl deg/C/sup -1/. Optical gain characterizations show that the peak modal gain at threshold is independent of temperature, whereas the differential gain decreases linearly with temperature at a rate of 3/spl times/10/sup -4/ A/sup -1//spl middot//spl deg/C/sup -1/. The differential carrier lifetime is determined from electrical impedance measurements and found to decrease with temperature. From the measured carrier lifetime we derive the monomolecular ( A), radiative (B), and nonradiative Auger (C) recombination coefficients and determine their temperature dependence in the 20/spl deg/C-80/spl deg/C range. Our study shows that A is temperature independent, B decreases with temperature, and C exhibits a less pronounced increase with temperature. The experimental observations are discussed and compared with theoretical predictions and measurements performed on other material systems.     

Synthesis of Multilevel Converters Based on Single- and/or Three-Phase Converter Building Blocks

This paper synthesized a family of multilevel converters that is constructed by using multiple well-developed single- and/or three-phase converter building blocks. The resulting advantages include a modular structure that leads to convenient construction and maintenance as well as easy extension to higher voltage levels. One successful example from this family is the cascaded H-bridge converter, which is now widely used for volt-amperes reactive (VAR) compensation and motor drive applications due to its many advantages. Another emerging member is the Hexagram converter, composed of six interconnected three-phase converter modules, which has many eminent features such as lowered component count and lowered dc energy storage requirement compared to the cascaded H-bridge converter, and thus, is a promising candidate for high-power applications.     

Segregation of spermatozoa within sperm storage tubules of fowl and turkey hens

In avian species, spermatozoa reside in the oviduct for prolonged periods in specialized structures known as sperm storage tubules, but little is known about the relative distribution of spermatozoa in these tubules after successive inseminations by different males. The staining efficacies of various fluorescent dyes for fowl and turkey spermatozoa were evaluated to investigate one proposed mechanism of sperm competition. Hens were then inseminated at different intervals with stained and unstained spermatozoa to observe the spatial distribution of spermatozoa within the storage tubules. Several novel fluorescent lipophilic tracers that successfully stain mammalian spermatozoa either did not stain fowl or turkey spermatozoa, or greatly impaired sperm motility. In contrast, Hoechst 33342 readily stained sperm nuclei (fowl: 25 nmol l-1; turkey: 77 nmol l-1) within 4 h without inhibiting sperm motility, or affecting fertility or the hatching ability of the eggs. Hens were tandemly inseminated with equal numbers of stained or unstained spermatozoa at 24 h intervals and were killed 24 h after the final insemination to study sperm entry and storage within the tubules. Oviductal mucosa containing sperm storage tubules was removed, and individual tubules were classified as containing stained spermatozoa, unstained spermatozoa, a mixture of stained and unstained spermatozoa, or as not containing spermatozoa. Results from the present study indicate that spermatozoa from two different inseminations generally segregate into different storage tubules in both fowl and turkey hens. Storage tubules containing mixed populations of spermatozoa were found in only 4% of fowl and 12% of turkey storage tubules examined. Thus, the mechanism of last-male precedence does not appear to be due to the stratification of spermatozoa within the tubules.     

Developing Dementia Prevalence Rates Among Latinos: A Locally-Attuned, Data-Based, Service Planning Tool

The prevalence of Alzheimer’s disease and associated disorders (ADAD) determines the level of need for ADAD services. Since services need to be made available locally, therefore local—rather than national—prevalence levels are instrumental in guiding services to meet these emerging needs. This study employed a three-stage methodology to establish Latino ADAD prevalence estimates within San Diego and Imperial Counties in California for the period 2000–2050. The first stage involved the development of a working algorithm for the ADAD estimates combining existing demographic data with small-scale prevalence data from recent clinical studies of ADAD among Latinos. Results from this algorithm projected an 1,123 % increase of ADAD impacted Latinos in San Diego County and 1,213 % in Imperial County by 2050. Stage two encompassed examining the face validity and efficacy of these projections at the local provider level through focus groups. This stage confirmed the findings that a large sector of the local Latino ADAD community had a profile of lower education and socioeconomic status, more traditional cultural orientations, and high rates of diabetes mellitus and vascular disease which resulted in earlier onset of ADAD. The third stage in the methodology employed a 36-month observational window tracking the impact of the local ADAD prevalence estimates on various programs. The authors of this study argue for the efficacy, and external validity of the methodology employed to define local ADAD prevalence rates for other ethnic groups. This knowledge will promote local communities in developing culturally competent services for their own diverse local service areas based on local estimates.     

Undermining the Corrective Effects of Media‐Based Political Fact Checking? The Role of Contextual Cues and Naïve Theory

Media‐based fact checking contributes to more accurate political knowledge, but its corrective effects are limited. We argue that biographical information included in a corrective message, which is often unrelated to the inaccurate claim itself, can activate misperception‐congruent naïve theories, increasing confidence in a misperception's plausibility and inducing skepticism toward denials. Resistance to corrections occurs regardless of initial belief accuracy, but the effect is strongest among those who find the contextual information objectionable or threatening. We test these claims using an online survey‐embedded experiment (N = 750) conducted in the wake of the controversy over the proposed Islamic cultural center in New York City near the site of the 9/11 attacks, and find support for our predictions. Theoretical and practical implications are discussed.     

Quantification of soluble solids in reconstituted açaí (Euterpe oleracea Mart.) pulp using near‐infrared spectroscopy

Açaí consumption is increasing worldwide because of the growing recognition of its nutritional and therapeutic properties. This product is classified based on its soluble solids content (SS), but the determination of SS in pulp is time consuming, tedious and not suitable for modern food processing plants. As near‐infrared (NIR) systems have been implemented to measure various quality attributes of food products, the objective of this study was to evaluate the feasibility of NIR diffuse reflectance spectroscopy to quantify the SS content of açaí pulp. Partial least squares (PLS) regression models were constructed to predict the SS. An optimum PLS model required one latent variable [principal component (PC)1 = 97%] with a root‐mean‐square error of calibration (RMSEC) of 1.06% for the calibration data set and the root‐mean‐square error of prediction (RMSEP) of 1.03% for internal cross‐validation. External validation using an independent data set showed good performance (RMSEP = 1.33% and Rp² = 0.82). NIR spectroscopy is a reliable method with which to determine SS in açaí pulp and thereby to classify açaí pulp according to established minimum quality standards.     

Case study feasibility analysis of renewable energy supply options for small to medium-sized tourist accommodations

This paper outlines a feasibility analysis of renewable energy supply (RES) for small to medium-scale tourist operations (less than 100 beds) dependent on stand-alone supplies. The analysis utilised the power load data from three accommodation case studies that had RES/hybrids already installed. The accommodation sites, chosen from diverse locations within Australia, varied in both climatic and geographic characteristics. The assessment criteria for the analysis were net present cost (NPC), renewable factor (RF) and payback time. The specific operational characteristics of the tourism accommodation sector, such as 24-h operation, comfort provision and low tolerance for failure, necessitates a separate assessment of RES viability for this sector, rather than relying on similar assessments from other commercial and domestic sectors, which may not be representative. This study utilised RES assessment software, HOMER (National Renewable Energy Laboratory, US) in order to compare the present RES/hybrid configuration to diesel generator-only (genset-only), RES-only and optimised RES/hybrid configurations. Analysis of both actual data and modeling results demonstrated that RES can adequately and reliably meet the power demand for stand-alone small to medium-scale tourist accommodations. Optimisation, achieved by further addition of RES to the existing configurations, reduced NPC in the majority of cases, with the added benefit of increased RF. Furthermore, NPC for these optimised RES/hybrid configurations were comparable to the optimised genset-only configurations. Modeling of conversions to RES-only configurations demonstrated this option as uneconomical unless existing RF was already high. Results indicated that wind energy conversion systems (WECS), rather than photovoltaics, were the most economical RES for sampled hybrid systems. For example, the payback time of the WECS/hybrids was approximately 3–4 years compared to PV/hybrids at 6–7 years. Hydrogen fuel cells and storage systems, whilst technically feasible, were not economically viable for the case studies due to the present high cost of components, especially compared to gensets. Modeling future potential increase in diesel fuel prices and implementation of carbon taxes shows a significant increase in NPC for genset-only configurations compared to RES/hybrid configurations in the sample. Carbon taxes of $50/ton increases NPC by 10% for genset-only systems but increases NPC less than half that amount for RES/hybrid systems. The data and subsequent modeling demonstrate that RES is both technically feasible and economically viable compared to diesel energy supply, for the small to medium-scale tourist operations sampled, dependent on stand-alone power supplies.     

The nature of the blue species formed when 1,1-diphenylethylene chemisorbs and reacts on acidic solids

The blue species obtained when 1,1-diphenylethylene chemisorbs on highly acidic solids arises from a very minor dimerization reaction where a less stable canonical form of the initial carbenium ion adds to Φ₂C=CH₂ (Φ=phenyl). Proton loss followed by H^- ion abstraction from the resulting olefin then affords a highly conjugated ion as the blue species. This revised version was published online in July 2006 with corrections to the Cover Date.