Appearance of Negative Differential Conductivity in Graphene Nanoribbons at High-Harmonics

We theoretically study current dynamics of graphene nanoribbons subject to bias dc and ac driven fields. We showed that graphene nanoribbons exhibit negative high-harmonic differential conductivity. Negative differential conductivity appears when bias electric filed is in the neighborhood of applied ac filed amplitude. We also observe both even and odd high-harmonic negative differential conductivity at wave mixing of two commensurate frequencies. The even harmonics are more pronounced than the odd harmonics. A possible use of the present method for generating terahertz frequencies at even harmonics in graphene is suggested.Comment: 6 pages, 3 figure

General Scattering Mechanism and Transport in Graphene

Using quasi-time dependent semi-classical transport theory in RTA, we obtained coupled current equations in the presence of time varying field and based on general scattering mechanism $\tau \propto \mathcal{E}^{\beta}$. We find that close to the Dirac point, the characteristic exponent $\beta = +2$ corresponds to acoustic phonon scattering. $\beta = +1$ long-range Coulomb scattering mechanism. $\beta = -1$ is short-range delta potential scattering in which the conductivity is constant of temperature. The $\beta = 0$ case is ballistic limit. In the low energy dynamics of Dirac electrons in graphene, the effect of the time-dependent electric field is to alter just the electron charge by $e \to e(1 + (\Omega \tau)^2)$ making electronic conductivity non-linear. The effect of magnetic filed is also considered.Comment: 8 pages, 3 figure

Multilevel Analysis of Trachomatous Trichiasis and Corneal Opacity in Nigeria : The Role of Environmental and Climatic Risk Factors on the Distribution of Disease.

Funding: Jennifer L Smith was supported by the International Trachoma Initiative through a grant from the Bill and Melinda Gates Foundation. Anthony Solomon is a Wellcome Trust Intermediate Clinical Fellow (098521). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer reviewedPublisher PD

Novel Heat Integration in a Methane Reformer and High Temperature PEM Fuel Cell-based mCHP System

AbstractA highly integrated and optimized heat recovery system is essential for efficient operation of a HTPEM fuel cell-based mCHP system. The main challenge with such system is to design energy efficient systems with low start-up time. Recent studies have shown that this can be achieved by proper heat integration of the balance of plant (BOP) components. This study proposed a novel scheme that optimally integrated the sub-components of a mCHP system consisting of a 2 kWel HTPEM fuel cell integrated with methane processing units, for recovery and use of the process and waste heat. A steady state system modeling and simulation of the complete mCHP system was implemented in Aspen Plus v7.2. The design of the heat recovery system was achieved with pinch analysis techniques. Heat integration results show that external cooling utility is not required and result in a 5% increase in the overall system efficienc

External electric field effect on electron transport in carbon nanotubes

Electronic transport properties of carbon nanotubes are studied theoretically in the presence of external electric field E(t) by using the Boltzmann's transport with constant relaxation time. An analytical expression for the current densities of the nanotubes are obtained. It is observed that the current density-electric field characteristics of the CNs exhibit total self-induced transparency and absolute negative conductivityComment: 5 pages, 2 figure

Sesame (sesamun indicum L) Market Structure in Jigawa State, Nigeria

Poor marketing structures among others have been identified to be one of the major issues limiting agricultural productivity in Nigeria. Sesame market structure in Jigawa state of Nigeria was examined by studying four sesame markets and also traders and selling agents. Two of the markets were rural (Suletankarkar and Kargo) while the other two were urban (Gumel and Maigatari).The markets were selected using a purposive random sampling. A non recurring survey was conducted in the selected markets in which 117 traders and 39 selling agents were interviewed from the list of their respective associations using a simple random sampling procedure. Questionnaires used as instrument of data collection were pre-tested. Times series data for sesame recorded for the period of 2000-2012 by Jigawa A.D.P. were also used. The data were analysed using Gini ratio analysis.  The Gini ratio for business concentration of rural selling agents and urban selling agents were 0.6013 and 0.5360 respectively. The Gini ratio for rural traders and urban traders were 0.3664 and 0.7838 respectively. The market structure analysis revealed that urban selling agents and rural traders command greater influence. The markets function with some level of imperfection. Market structure could be improved by breaking the dominance of the sesame market by few selling agents. This could take the form of making credits available to the traders and policy intervention in the form of incentives for value addition to sesame local purchasers