Numerical study of the optical nonlinearity of doped and gapped graphene: From weak to strong field excitation

Numerically solving the semiconductor Bloch equations within a phenomenological relaxation time approximation, we extract both the linear and nonlinear optical conductivities of doped graphene and gapped graphene under excitation by a laser pulse. We discuss in detail the dependence of second harmonic generation, third harmonic generation, and the Kerr effects on the doping level, the gap, and the electric field amplitude. The numerical results for weak electric fields agree with those calculated from available analytic perturbation formulas. For strong electric fields when saturation effects are important, all the effective third order nonlinear response coefficients show a strong field dependence.Comment: 12 pages with 9 figure

Third order nonlinearity of graphene: effects of phenomenological relaxation and finite temperature

We investigate the effect of phenomenological relaxation parameters on the third order optical nonlinearity of doped graphene by perturbatively solving the semiconductor Bloch equation around the Dirac points. An analytic expression for the nonlinear conductivity at zero temperature is obtained under the linear dispersion approximation. With this analytic formula as starting point, we construct the conductivity at finite temperature and study the optical response to a laser pulse of finite duration. We illustrate the dependence of several nonlinear optical effects, such as third harmonic generation, Kerr effects and two photon absorption, parametric frequency conversion, and two color coherent current injection, on the relaxation parameters, temperature, and pulse duration. In the special case where one of the electric fields is taken as a dc field, we investigate the dc-current and dc-field induced second order nonlinearities, including dc-current induced second harmonic generation and difference frequency generation.Comment: 23+ pages, 10 figures. In this version we correct a sign typo in Eq. (25), for which we thank the discussion in the work http://arxiv.org/abs/1506.00534v

Appraising the e-readiness of online learning facilitators: key human factors

Higher education institutions in South Africa have undergone a number of changes over the past few years. These changes brought about inter alia changed work environments and job demands. One of the new job demands is the need to incorporate technology in teaching and learning, viz. e-learning. Not all job incumbents, however, adapted successfully to these changes, particularly with regard to e-readiness. Such a lack in e-readiness is likely to influence the effectiveness with which an academic employee will fulfil his/her online learning duties. Therefore, it is important to find solutions to overcome the lack of e-readiness. This article will focus on the role of human resource appraisal, in order to assess the e-readiness of online learning facilitators with a view to improving their online skills and capacity. A number of human factors that can play a role in employee performance and motivation, namely learning styles, personal profile patterns, and pace and style of technology adoption will be briefly outlined, in order to determine the role that these factors could play in assessing the e-readiness of online learning facilitators

Capitalization of Central Government Grants into Local House Prices

We explore the impact of central government grants on local house prices in England using a panel data set of local authorities (LAs) from 2001 to 2008. Electoral targeting of grants to LAs by the incumbent national government provides an exogenous source of variation in grants that we exploit to identify their causal effect on house prices. Our results indicate substantial or even full capitalization. We also find that house prices respond more strongly in locations in which new construction is constrained by physical barriers. Our results imply that (i) during our sample period grants were largely used in a way that is valued by the marginal homebuyer and (ii) increases in grants to a LA may mainly benefit the typically better off property owners (homeowners and absentee landlords) in that LA.

Private Standards, Handling and Hygiene in Fruit Export Supply Chains: A Preliminary Evaluation of the Economic Impact of Parallel Standards

With the emergence of private food safety and quality standards in developed countries fruit exporting countries in the developing world face increasing constraints to access markets in the rich industrialised countries in the North. Producers in the South have no alternative as to make the necessary investments on farms and in pack houses to comply with the requirements of these food quality and safety standards. The export of fresh fruit is an important component of South African agricultural exports, with citrus fruit exported to markets such as Europe being of particular importance. This paper reports selected results from a large research project into the impact of private standard compliance on the quality of the fruit and the returns to farmers. The research process involved a multi-disciplinary analysis of Agricultural Economics and Microbiology / Plant pathology as we analysed the dynamics of the citrus export supply chain from the farms in South Africa to the end consumer in Europe. Sampled fruit containers were followed through the whole supply chain which allowed us to provide an exposé of the behaviour of the different actors in the citrus supply chain and obtain some evidence of poor handling and hygiene standards by means of a comparison of the experimental observations with various relevant components of the EurepGAP control points and compliance criteria for fruit and vegetables. Observations suggest that these standards are adequately applied to the production and handling of fruit at the farm and pack house levels while on the other hand the subsequent stages (mainly after the importing harbour in Europe) of the fruit supply chain are seemingly not subjected to the same strict requirements laid out for producers, leading to fruit quality deterioration and financial losses for producers. This constitutes clear parallel standards in terms of fruit safety and quality standards between upstream and downstream sections of the supply chain and questions thus the purpose of the standards and the financial return for producers making large investments to comply with these privately introduced standards.International Relations/Trade,