Electronic and Thermoelectric Properties of Few-Layer Transition Metal Dichalcogenides

The electronic and thermoelectric properties of one to four monolayers of MoS$_{2}$, MoSe$_{2}$, WS$_{2}$, and WSe$_{2}$ are calculated. For few layer thicknesses,the near degeneracies of the conduction band $K$ and $\Sigma$ valleys and the valence band $\Gamma$ and $K$ valleys enhance the n-type and p-type thermoelectric performance. The interlayer hybridization and energy level splitting determine how the number of modes within $k_BT$ of a valley minimum changes with layer thickness. In all cases, the maximum ZT coincides with the greatest near-degeneracy within $k_BT$ of the band edge that results in the sharpest turn-on of the density of modes. The thickness at which this maximum occurs is, in general, not a monolayer. The transition from few layers to bulk is discussed. Effective masses, energy gaps, power-factors, and ZT values are tabulated for all materials and layer thicknesses

Structure and Dielectric Properties of Amorphous High-kappa Oxides: HfO2, ZrO2 and their alloys

High-$\kappa$ metal oxides are a class of materials playing an increasingly important role in modern device physics and technology. Here we report theoretical investigations of the properties of structural and lattice dielectric constants of bulk amorphous metal oxides by a combined approach of classical molecular dynamics (MD) - for structure evolution, and quantum mechanical first principles density function theory (DFT) - for electronic structure analysis. Using classical MD based on the Born-Mayer-Buckingham potential function within a melt and quench scheme, amorphous structures of high-$\kappa$ metal oxides Hf$_{1-x}$Zr$_x$O$_2$ with different values of the concentration $x$, are generated. The coordination numbers and the radial distribution functions of the structures are in good agreement with the corresponding experimental data. We then calculate the lattice dielectric constants of the materials from quantum mechanical first principles, and the values averaged over an ensemble of samples agree well with the available experimental data, and are very close to the dielectric constants of their cubic form.Comment: 5 pages, 4 figure

Essays On Healthy Aging From The Perspective Of A Health Production Function

This dissertation examines the determinants of healthy aging among older adults using Grossman’s framework of a health production function. Healthy aging is produced using a variety of inputs, including some determined in early life, such as health and socioeconomic status as a child, others determined in young adulthood, such as education, others determined in mid-life, such as household wealth, and still others determined in later-life, such as current health habits. A production function for healthy aging is estimated using nationally representative data from the 2010 Health and Retirement Study on non-institutionalized seniors, and positing a simultaneous equations mediation model, recognizing that childhood outcomes influence adulthood outcomes, which in turn influence healthy aging. I quantify how childhood factors contribute to healthy aging, both directly and indirectly through these effects on mediating adult outcomes. The importance of current health habits to healthy aging are also examined. The results indicate that favorable childhood conditions significantly improve healthy aging scores, both directly and indirectly, mediated through education, income, and wealth. Moreover, good health habits have positive effects on healthy aging that are larger in magnitude than the effects of childhood factors. The findings suggest that exercising, maintaining a proper weight, and not smoking can more than compensate for unfavorable conditions experienced as a child

The Realization of English Dative Case in Iranian EFL Learners

A cross sectional research was undertaken with sixty university students to know whether levels of proficiency interact with the realization of English dative case in Iranian EFL learners’ performance and whether Iranian EFL learners aware of discourse constraint in English dative case. The research shows that Iranian learners learn dative non-alternation first, because dative non-alternation structures are somehow compatible with Persian structures. But, in the case of dative alternation Iranian learners encounter with some problems. So the usage of this English structure depends on the proficiency levels of the learners; the higher of the proficiency level, the more usage of dative alternation. The subjects were aware of discourse constraint in one sentence, but they were not aware of this constraint in the other sentence. It seems that they are not aware of the existence of this constraint; they just intend to use [NP PP] complement. Keywords: dative alternation, dative non-alternation, discourse constraint, proficiency level Iranian learners’ performanc

The Relationship between Language Games in Discourse Interactions in Classroom and Strengthening and Developing Vocabularies of Grade Two Male Students in Primary School

The purpose of the present research is evaluating the effect of teaching method based on language games on development of students’ language and discourse. The main hypothesis of the research is based on effect of language games on development of students’ vocabularies. The participants of the research included 44 second grade male students in primary school who were studying at 2015-2016 in Qarchak of Varamin in schools which the researcher teaches in them. Sample for study was divided into two groups of experimental and control though simple random. Initially, pretest was taken from the both groups in order to obtain full confidence of their integration and awareness about vocabularies of the lesson. Then the experimental group was educated for 6 months means from October 2015 to April 2016 for 3 hours per week through method based on language game and the control group was educated based on traditional method at the same period through the usual method with the same teacher and training book. At the end of the treatment, posttest was taken from the both group. Results indicated a considerable difference has been made between the experiment and the control groups