113 research outputs found
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 . We
find that close to the Dirac point, the characteristic exponent
corresponds to acoustic phonon scattering. long-range Coulomb
scattering mechanism. is short-range delta potential scattering in
which the conductivity is constant of temperature. The 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 making electronic conductivity
non-linear. The effect of magnetic filed is also considered.Comment: 8 pages, 3 figure
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
Couching in Nigeria: prevalence, risk factors and visual acuity outcomes.
PURPOSE: Couching is an ancient treatment for cataract which is still practiced in some of the poorer developing countries, particularly in sub-Saharan Africa. The purpose of this study is to describe risk factors for couching and visual acuity outcomes in a nationally representative sample of adults aged 40 years and above in Nigeria. METHODS: Probability in proportion size methods were used to identify a representative sample. Of the 15,375 adults enumerated, 13,582 were interviewed and examined. Examination included logMar acuities, slit lamp examination and dilated fundoscopy with digital fundus imaging. RESULTS: Almost half of the 583 eyes undergoing a procedure for cataract had been couched (249 eyes, 42.7%). Individuals living in rural areas (P = 0.033) and in the two underserved northern administrative zones (P = 0.33; P = 0.002) were more likely to have been couched. Visual outcomes were poor according to World Health Organization categories, with 55.8% of people and 73.1% of eyes having a presenting visual acuity of less than 3/60 and only 9.7% and 2.4% of people and eyes respectively having a good outcome (6/18 or better). None were wearing an aphakic correction, and with correction acuities improved but 42.6% of eyes were still blind (< 3/60). CONCLUSIONS: Couching is still widely practiced in Nigeria and visual outcomes are very poor. The population needs to be made aware of the risks associated with the procedure, and services for high quality, affordable cataract surgery need to be expanded, particularly in rural areas and in the north of the country
Determination of elemental constituents for three herbal plants that are traditionally used to cure cancer
Elemental constituents of fresh leaves of the three herbal plants used traditionally for treatment of cancer namely: Guera Senegalense, Boswellia and Mangifera Indica were analyzed. Results show that all the three samples contain the highest amounts of calcium in parts per million (Guiera Senegalensis 5991 ppm, Boswellia 9413 ppm and Mangifera Indica 2405 ppm) as compared to other constituents. Further studies reveal that presence of calcium in appreciable amount within the metabolic system of human being helps to reduce the risk of cancer and related ailments. Other benefits of calcium in man include strengthening bones and teeth.Keywords: Herbal Medicine, Cancer, Constituents, Carcinoge
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