Theoretical Limits of Photovoltaics Efficiency and Possible Improvements by Intuitive Approaches Learned from Photosynthesis and Quantum Coherence

In this review, we present and discussed the main trends in photovoltaics with emphasize on the conversion efficiency limits. The theoretical limits of various photovoltaics device concepts are presented and analyzed using a flexible detailed balance model where more discussion emphasize is toward the losses. Also, few lessons from nature and other fields to improve the conversion efficiency in photovoltaics are presented and discussed as well. From photosynthesis, the perfect exciton transport in photosynthetic complexes can be utilized for PVs. Also, we present some lessons learned from other fields like recombination suppression by quantum coherence. For example, the coupling in photosynthetic reaction centers is used to suppress recombination in photocells.Comment: 47 pages, 22 figures. arXiv admin note: text overlap with arXiv:1307.5093, arXiv:1105.4189 by other author

Cuckoo Search Inspired Hybridization of the Nelder-Mead Simplex Algorithm Applied to Optimization of Photovoltaic Cells

A new hybridization of the Cuckoo Search (CS) is developed and applied to optimize multi-cell solar systems; namely multi-junction and split spectrum cells. The new approach consists of combining the CS with the Nelder-Mead method. More precisely, instead of using single solutions as nests for the CS, we use the concept of a simplex which is used in the Nelder-Mead algorithm. This makes it possible to use the flip operation introduces in the Nelder-Mead algorithm instead of the Levy flight which is a standard part of the CS. In this way, the hybridized algorithm becomes more robust and less sensitive to parameter tuning which exists in CS. The goal of our work was to optimize the performance of multi-cell solar systems. Although the underlying problem consists of the minimization of a function of a relatively small number of parameters, the difficulty comes from the fact that the evaluation of the function is complex and only a small number of evaluations is possible. In our test, we show that the new method has a better performance when compared to similar but more compex hybridizations of Nelder-Mead algorithm using genetic algorithms or particle swarm optimization on standard benchmark functions. Finally, we show that the new method outperforms some standard meta-heuristics for the problem of interest

Backbending phenomena in light nuclei at A~60 mass region

Recent studies of the backbending phenomenon in medium light weight nuclei near A~60 expanded greatly our interest about how the single particle orbits are nonlinearly affected by the collective motion. As a consequence we have applied a modi…ed version of the exponential model with the inclusion of paring correlation to describe the energy spectra of the ground state bands and/or the backbending phenomenon in mass region at A~60. A firm conclusion is obtained concerning the successful validity of the proposed modified model in describing the backbending phenomenon in this region. Comparison with different theoretical descriptions is discussed.Comment: 4 pages, 1 figure

Employees' perceptions of fairness in practice of performance appraisal

Employees’ performance appraisal (PA) is an essential tool used by organisations to develop and improve employees’ competencies and skills, and so assure organisations’ survival. In recent years research has moved from a psychometric approach, such as rater accuracy and rating error studies, to the qualitative aspect of PA where employees’ reactions and perceptions of performance appraisal are seen as indicators of success and effectiveness. Employees’ satisfaction with the system is indicated by scholars as the major indicator of employee perception of fairness (Cardy and Dobbins, 1994; Cawley et al., 1998; Keeping and Levy, 2000; Murphy and Cleveland, 1995). The focus of this research is on the employees’ perceptions of fairness in performance appraisal in Saudi Basic Industries Corporation (SABIC). A conceptual framework is developed based on three dimensions of organisational justice theory (the terms ‘justice’ and ‘fairness’ are used interchangeably): distributive, procedural (using the due process model), and interactional, which involves interpersonal and informational justice, to explore employees’ perceptions of justice in their appraisal. A qualitative approach was applied through an interpretivist paradigm; semi-structured interviews were used for collecting primary data from 44 respondents.The findings reveal the practice of performance appraisal is strongly influenced by cultural factors, which are divided into two dimensions. First, social factors, which include relationship, friendship, family relations, regionalism, tribe, personal interest and emotion. Second, managerial factors or characteristics of the manager (the terms supervisor, manager, direct manager, or rater are used interchangeably to refer to the person who evaluates or assesses employees’ performance) which includes expectations of managers that their subordinates obey them, managers’ tendency to threaten subordinates, and unwillingness to accept criticism. In relation to the process and procedures of appraisal the findings reveal a feeling that appraisal ratings did not reflect employees’ actual contributions or input, absence of standards for allocating salaries, and unequal training course distribution.The findings also reveal that goals and objectives are not set at the beginning of each appraisal period, and the appraisal standards used by supervisors are unclear, there is no clear feedback, and employees cannot participate in their appraisal process, meaning that appraisal decisions are only taken by managers. When employees receive their result, if they are dissatisfied with their grades they cannot appeal as the decision process is not explained to them. Employees were dissatisfied for three reasons: first, raters’ bias and subjectivity; second, evaluation depends on the department budget, and on forced distribution; third, involvement of top management in the rating and their changing the result without contacting the direct manager or supervisor who conducted the evaluation. These findings strongly support the organisational justice theory, and have important implications for practice