Approximate expressions for modulation speed and threshold for performance optimization of biaxially compressive strain quantum-well lasers

Simple analytical expressions for transparency, threshold, and relaxation oscillation corner frequency are derived for biaxial strain quantum-well lasers. An optimal operating point loss for high speed operation (in the absence of nonlinear gain) is established which varies as the square root of the number of quantum wells. The corresponding relaxation oscillation frequency is found to depend only on fundamental quantities. Its power dependence is [vR(max) = (87 GHz õm^3/mW) (Powerout/Vmode)^1/2) where Vmode is the mode volume

Effect of doping on the optical gain and the spontaneous noise enhancement factor in quantum well amplifiers and lasers studied by simple analytical expressions

The maximum optical gain and the spontaneous noise enhancement factor in quantum well structures are expressed as extremely simple functions that are accurate over a wide range of carrier densities. These expressions are used to study the effect of doping on the optical gain and the noise enhancement factor in a 100 Å InGaAs/InP quantum well structure. n-type doping is most effective in reducing the transparency excitation level (laser threshold) and the noise enhancement factor (amplifier noise figure), whereas p-type doping enables increased gain at a given excitation level

Memahami Pemelajaran Menerusi Penyelidikan Fenomenografi

This paper tries to focus attention to the fact that learning should be studied from the students' perspective. In this way the learning phenomena could be better described in detail and learning problems could probably be solved in a more meaningful manner. To achieve this objective, one research study on qualitative differences in learning outcome approach is cited to explain phenomenography

Variations socio-économiques de la fécondité en Côte d’Ivoire : quels groupes ont commencé à réguler leurs naissances ?

Cet article analyse les différences socio-économiques de la fécondité en Côte d’Ivoire. Il met en évidence deux modèles de fécondité dont l’un traditionnel est caractérisé par une fécondité élevée et stable, tandis que l’autre de transition indique une réduction de la fécondité. Ces modèles révèlent l’hétérogénéité des comportements reproductifs, car après contrôle des effets des variables socio-économiques et des déterminants proches, les différences de fécondité continuent d’exister entre les groupes socio-économiques. La progression de la contraception chez les femmes « modernes », explique la diminution de leur fécondité. Il s’agit de femmes qui exercent une activité professionnelle, s’informent sur la planification familiale et lui sont favorables, de même que leurs partenaires. Celles qui n’utilisent pas la contraception manquent surtout d’informations du fait de l’inaccessibilité des centres de planification familiale. Étant donné que ces femmes manifestent la volonté d’espacer les naissances, elles pourraient changer de comportement si elles étaient mieux informées.This article analyzes the socio-economic differences of fertility in Ivory Coast. It shows two models of fertility : the traditional model characterized by the women having a high and stable fertility and the transitional model with the women having reduced their fertility. These models reveal the heterogeneousness of the reproductive behavior because after control of the effects of the socioeconomic variables and the close determiners, the differences of fertility continue to exist between socio-economic groups. The progress of the contraception to modern women explains the decrease of their fertility. It is about women who exercise a modern activity, inquire on the family planning and are favorable to him as well as their partners. Those who do not use the contraception miss especially information because of the inaccessibility of family planning clinics. They want to space out their births, which would change their behavior if they were better informed

Direct determination of the ambipolar diffusion length in strained InxGa1−xAs/InP quantum wells by cathodoluminescence

The ambipolar diffusion length is measured in strained InxGa1−xAs/InP quantum wells for several mole fractions in the interval 0.3<x<0.8 by cathodoluminescence. The ambipolar diffusion length is found to have a significantly higher value in the lower indium mole fraction samples corresponding to tensile-strained wells. This longer diffusion length for the tensile samples is consistent with results of carrier lifetime experiments by M. C. Wang, K. Kash, C. E. Zah, R. Bhat, and S. L. Chuang [Appl. Phys. Lett. 62, 166 (1993)]

Effects of Varying the Three-Body Molecular Hydrogen Formation Rate in Primordial Star Formation

The transformation of atomic hydrogen to molecular hydrogen through three-body reactions is a crucial stage in the collapse of primordial, metal-free halos, where the first generation of stars (Population III stars) in the Universe are formed. However, in the published literature, the rate coefficient for this reaction is uncertain by nearly an order of magnitude. We report on the results of both adaptive mesh refinement (AMR) and smoothed particle hydrodynamics (SPH) simulations of the collapse of metal-free halos as a function of the value of this rate coefficient. For each simulation method, we have simulated a single halo three times, using three different values of the rate coefficient. We find that while variation between halo realizations may be greater than that caused by the three-body rate coefficient being used, both the accretion physics onto Population III protostars as well as the long-term stability of the disk and any potential fragmentation may depend strongly on this rate coefficient.Comment: 29 pages, 7 figures; Accepted for publication in The Astrophysical Journa

The physico-chemical habitat template for periphyton in alpine glacial streams under a changing climate

The physico-chemical habitat template of glacial streams in the Alps is characterized by distinct and predictable changes between harsh and relatively benign periods. Spring and autumn were thought to be windows of favorable environmental conditions conducive for periphyton development. Periphyton biomass (measured as chlorophyll a and ash-free dry mass) was quantified in five glacial and three non-glacial streams over an annual cycle. One glacial stream was an outlet stream of a proglacial lake. In all glacial streams, seasonal patterns in periphyton were characterized by low biomass during summer high flow when high turbidity and transport of coarse sediment prevailed. With the end of icemelt in autumn, environmental conditions became more favorable and periphyton biomass increased. Biomass peaked between late September and January. In spring, low flow, low turbidity, and a lack of coarse sediment transport were not paralleled by an increase in periphyton biomass. In the non-glacial streams, seasonal periphyton patterns were similar to those of glacial streams, but biomass was significantly higher. Glacier recession from climate change may shift water sources in glacier streams and attenuate the glacial flow pulse. These changes could alter predicted periods of optimal periphyton development. The window of opportunity for periphyton accrual will shift earlier and extend into autumn in channels that retain surface flow

TGF-β-responsive CAR-T cells promote anti-tumor immune function.

A chimeric antigen receptor (CAR) that responds to transforming growth factor beta (TGF-β) enables the engineering of T cells that convert this immunosuppressive cytokine into a potent T-cell stimulant. However, clinical translation of TGF-β CAR-T cells for cancer therapy requires the ability to productively combine TGF-β responsiveness with tumor-targeting specificity. Furthermore, the potential concern that contaminating, TGF-β?producing regulatory T (Treg) cells may preferentially expand during TGF-β CAR-T cell manufacturing and suppress effector T (Teff) cells demands careful evaluation. Here, we demonstrate that TGF-β CAR-T cells significantly improve the anti-tumor efficacy of neighboring cytotoxic T cells. Furthermore, the introduction of TGF-β CARs into mixed T-cell populations does not result in the preferential expansion of Treg cells, nor do TGF-β CAR-Treg cells cause CAR-mediated suppression of Teff cells. These results support the utility of incorporating TGF-β CARs in the development of adoptive T-cell therapy for cancer

Metacognition and motivation in mathematical problem solving

otivation (O’Neil & Schacter, 1997). Based on the proposed model of problem solving, students’ content understanding and problem-solving strategies were identified through interviews. The other two elements were identified using a survey instrument. This paper reports findings of the survey instrument that focuses on determining (i) students’ level of motivation and level of metacognition in solving mathematical problems, (ii) relationship between level of motivation and level of metacognition with mathematics achievement and overall academic achievement, and (iii) determining relationship between motivation and metacognition. The subjects of this study were 195 final year students majoring in mathematics education. Metacognition refers to the ability of individuals to reflect, understandand control their own learning (Schraw & Dennison, 1994). Specific components of metacognitive processes were identified by Schraw & Dennison (1994) and these were the dimensions that they used in developing the Metacognitive Awareness Inventory (MAI). MAI that comprises of 52 items is a reliable measure of cognition and regulation of cognition (Sanchez-Alonso & Vovides, 2006). It measures eight specific components of metacognition; namely comprehension monitoring, procedural knowledge, declarative knowledge, conditional knowledge, evaluation, debugging strategies, information management strategies and planning. In O’Neil and Schacter’s (1997) study, metacognition was measured using three elements; planning, self-checking and cognitive strategy. MAI was used because it includes more elements that reflect one’s metacognitive strategies. Apart from MAI, subjects were also required to respond to the measurement used by O’Neil and Schacter’s (1997) to measure motivation. The elements in measuring motivation are effort, self-efficacy, and worry. Three dimensions of MAI; procedural, declarative and conditional knowledge were found to be significantly correlated with students’ performance in university mathematics courses. Declarative and conditional knowledge were also found to be significantly correlated with students’ overall performance in the university. All three dimensions of motivation were also found to be significantly correlated with performance in university mathematics courses. Significant correlation was also established between level of metacognition with level of motivation. In conclusion, this study reveals some of the factors that influence one’s performance in mathematical problem solving