Theory and it ab initio calculation of radiative lifetime of excitons in semiconducting carbon nanotubes

We present theoretical analysis and first-principles calculation of the radiative lifetime of excitons in semiconducting carbon nanotubes. An intrinsic lifetime of the order of 10 ps is computed for the lowest optically active bright excitons. The intrinsic lifetime is however a rapid increasing function of the exciton momentum. Moreover, the electronic structure of the nanotubes dictates the existence of dark excitons nearby in energy to each bright exciton. Both effects strongly influence measured lifetime. Assuming a thermal occupation of bright and dark exciton bands, we find an effective lifetime of the order of 10 ns at room temperature, in good accord with recent experiments.Comment: 12 pages, 3 figure

Relationship between employee aspects and employee performance

Studies found that employee performance is affected by employee aspects such as reward systems, job satisfaction and organizational commitment. However, the relationships among these have not been proved clearly. Thus, this study is attempted to know about the relationship between employee aspects and employee reward. 100 employees were selected five hospitals. Since the value of KMO is greater than 0.5 (0.726) samples taken in this study is enough for factor analysis. Bartlett’s Test of Sphericity is measured by approximate chi- square is also significant. Total variance for employee rewards, job satisfaction and organisational commitment are around 93%. Since correlation values between employee rewards, job satisfaction, organizational commitment and employee performance are 0.711, 0.740 and 0.798 respectively there are strong correlations with employee performance. Results of the regression revealed that R square and adjusted R square reveals the values as 0.643 and 0.631 respectively. These values explain around 64% of total variation on employee performance. Study concludes that employee rewards, job satisfaction, organizational commitment and employee performance

Intelligent Optimization Systems for MaintenanceScheduling of Power Plant Generators

This paper presents a Genetic Algorithm (GA) and Ant-Colony (AC) optimization model for power plant generators’ maintenance scheduling. Maintenance scheduling of power plant generators is essential for ensuring the reliability and economic operation of a power system. Proper maintenance scheduling prolongs the shelf life of the generators and prevents unexpected failures. To reduce the cost and duration of generator maintenance, these models are built with various constants, fitness functions, and objective functions. The Analytical Hierarchy Process (AHP), a decision-making tool, is implemented to aid the researcher in prioritizing and re-ranking the maintenance activities from the most important to the least. The intelligent optimization models are developed using MATLAB and the developed intelligent algorithms are tested on a case study in a coal power plant located at minjung, Perak, Malaysia. The power plant is owned and operated by Tenaga Nasional Berhad (TNB), the electric utility company in peninsular Malaysia. The results show that GA outperforms ACO since it reduces maintenance costs by 39.78% and maintenance duration by 60%. The study demonstrates that the proposed optimization method is effective in reducing maintenance time and cost while also optimizing power plant operation

The Casimir Force in a Lorentz Violating Theory

We study the effects of the minimal extension of the standard model including Lorentz violation on the Casimir force between two parallel conducting plates in vacuum. We provide explicit solutions for the electromagnetic field using scalar field analogy, for both the cases in which the Lorentz violating terms come from the CPT-even or CPT-odd terms. We also calculate the effects of the Lorentz violating terms for a fermion field between two parallel conducting plates and analyze the modifications of the Casimir force due to the modifications of the Dirac equation. In all cases under consideration, the standard formulas for the Casimir force are modified by either multiplicative or additive correction factors, the latter case exhibiting different dependence on the distance between the plates.Comment: 20 pages, no figures, references added, accepted for publication in Phys. Rev.

An Algebraic Model for the Multiple Meixner Polynomials of the First Kind

An interpretation of the multiple Meixner polynomials of the first kind is provided through an infinite Lie algebra realized in terms of the creation and annihilation operators of a set of independent oscillators. The model is used to derive properties of these orthogonal polynomials

Universality of a family of Random Matrix Ensembles with logarithmic soft-confinement potentials

Recently we introduced a family of $U(N)$ invariant Random Matrix Ensembles which is characterized by a parameter $\lambda$ describing logarithmic soft-confinement potentials $V(H) \sim [\ln H]^{(1+\lambda)} \:(\lambda>0$). We showed that we can study eigenvalue correlations of these "$\lambda$-ensembles" based on the numerical construction of the corresponding orthogonal polynomials with respect to the weight function $\exp[- (\ln x)^{1+\lambda}]$. In this work, we expand our previous work and show that: i) the eigenvalue density is given by a power-law of the form $\rho(x) \propto [\ln x]^{\lambda-1}/x$ and ii) the two-level kernel has an anomalous structure, which is characteristic of the critical ensembles. We further show that the anomalous part, or the so-called "ghost-correlation peak", is controlled by the parameter $\lambda$; decreasing $\lambda$ increases the anomaly. We also identify the two-level kernel of the $\lambda$-ensembles in the semiclassical regime, which can be written in a sinh-kernel form with more general argument that reduces to that of the critical ensembles for $\lambda=1$. Finally, we discuss the universality of the $\lambda$-ensembles, which includes Wigner-Dyson universality ($\lambda \to \infty$ limit), the uncorrelated Poisson-like behavior ($\lambda \to 0$ limit), and a critical behavior for all the intermediate $\lambda$ ($0<\lambda<\infty$) in the semiclassical regime. We also comment on the implications of our results in the context of the localization-delocalization problems as well as the $N$ dependence of the two-level kernel of the fat-tail random matrices.Comment: 10 pages, 13 figure

Male Involvement in Family Planning: A Qualitative Survey of the Barriers and Facilitators amongst Married Men in Sokoto metropolis

Background: Although large families are desired in Nigeria, women tend to want fewer children than men but are often unable to limit or space childbirth due to gender dynamics within relationships. Studies have identified men as a significant barrier to the use of&nbsp; contraceptives by their wives. The study explored married men’s knowledge and perception on family planning (FP), involvement in FP, barriers and facilitators of male involvement (MI) in FP in Sokoto Metropolis.Methods: A qualitative study was done among married men in Sokoto Metropolis in November 2017. Four focus group discussions were conducted among thirty-two men grouped based on educational status and age. Data was transcribed verbatim and a content analysis on emerging themes was done.Results: All the participants were aware of FP and most of them said that it is beneficial to everyone in the community. Most of the&nbsp; participants perceived that FP is an issue for both men and women. All the participants said that men should be involved in FP. The barriers to MI in FP mentioned were lack of knowledge on FP and poverty while increasing awareness on FP, religious leaders and traditional rulers championing FP, and making FP free were the facilitators suggested.Conclusion: The participants said that FP is beneficial to everyone in the community and men should be involved in FP. Traditional and religious leaders should be made the champions of FP in their various communities to improve acceptance and utilisation