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

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

Agriculture and gender roles in the semi-arid region of Ghana

In the Upper East Region (UER) of Ghana, women play an important role in economic growth and poverty reduction through their active engagement in agricultural activities. However, little is known about the extent of their productive roles in agriculture in the region. This study sought to investigate the gender-specific agricultural roles of men and women in the region where the major livelihood is subsistence rain-fed agriculture. A household survey was conducted from August to December 2014 using a pre-tested questionnaire where 150 males and 150 female headed households (HH) were randomly sampled from 14 communities within the Bolgatanga Municipality and Bongo district of UER. The simple Fisher’s exact test using STATA 13 statistical software was used to determine the correlation between gender and agreement or disagreement in productive roles. Results show that women are involved at all levels of farming activities particularly in physically demanding activities such as planting crops, weeding, fertilizer application, tree and crop harvesting among others. Women are not engaged in financial administration except for selling of crops. Men on the other hand, are responsible for land preparation, feeding of livestock, seedling production among others. Planting of crops and harvesting of fruit trees are performed jointly by men and women. About 86 % of men and 94 % of women perceived planting of crops to be a productive task that should be performed jointly, whereas 65 % men and 65 % women expressed the same view on harvesting of fruits. There is a need to empower women through policy formulation and enforcement to allow them equal access to productive resources such as land

Thermoelectric Amplification of Phonons in Graphene

Amplification of acoustic phonons due to an external temperature gredient ($\nabla T$) in Graphene was studied theoretically. The threshold temperature gradient $(\nabla T)_0^{g}$ at which absorption switches over to amplification in Graphene was evaluated at various frequencies $\omega_q$ and temperatures $T$. For $T = 77K$ and frequency $\omega_q = 12THz$, $(\nabla T)_0^{g} = 0.37Km^{-1}$. The calculation was done in the regime at $ql >> 1$. The dependence of the normalized ($\Gamma/\Gamma_0$) on the frequency $\omega_q$ and the temperature gradient $(\nabla T/T)$ are evaluated numerically and presented graphically. The calculated $(\nabla T)_0^{g}$ for Graphene is lower than that obtained for homogeneous semiconductors ($n-InSb$) $(\nabla T)_0^{hom} \approx 10^3Kcm^{-1}$, Superlattices $(\nabla T)_0^{SL} = 384Kcm^{-1}$, Cylindrical Quantum Wire $(\nabla T)_0^{cqw} \approx 10^2Kcm^{-1}$. This makes Graphene a much better material for thermoelectric phonon amplifier.Comment: 12 Pages, 6 figure

Ghana’s National Health Insurance Scheme in the Context of the Health MDGs – An Empirical Evaluation Using Propensity Score Matching

In 2003 the Government of Ghana established a National Health Insurance Scheme (NHIS) to improve health care access for Ghanaians and eventually replace the cashand- carry system. This study evaluates the NHIS to determine whether it is fulfi lling its purpose in the context of the Millennium Development Goals #4 and #5 which deal with the health of women and children. We use Propensity Score Matching techniques to balance the relevant background characteristics in our survey data and compare health outcomes of recent mothers who are enrolled in the NHIS with those who are not. Our fi ndings suggest that NHIS women are more likely to receive prenatal care, deliver at a hospital, have their deliveries attended by trained health professionals, and experience less birth complications. We conclude that NHIS is an eff ective tool for increasing health care access, and improving health outcomes.Health insurance, prenatal care, Millennium Development Goals, Propensity Score Matching