681 research outputs found
Quantum transport at the Dirac point: Mapping out the minimum conductivity from pristine to disordered graphene
The phase space for graphene's minimum conductivity is
mapped out using Landauer theory modified for scattering using Fermi's Golden
Rule, as well as the Non-Equilibrium Green's Function (NEGF) simulation with a
Monte Carlo sampling over impurity distributions. The resulting `fan diagram'
spans the range from ballistic to diffusive over varying aspect ratios (),
and bears several surprises. {The device aspect ratio determines how much
tunneling (between contacts) is allowed and becomes the dominant factor for the
evolution of from ballistic to diffusive regime. We find an
increasing (for ) or decreasing () trend in vs.
impurity density, all converging around at the dirty
limit}. In the diffusive limit, the {conductivity} quasi-saturates due to the
precise cancellation between the increase in conducting modes from charge
puddles vs the reduction in average transmission from scattering at the Dirac
Point. In the clean ballistic limit, the calculated conductivity of the lowest
mode shows a surprising absence of Fabry-P\'{e}rot oscillations, unlike other
materials including bilayer graphene. We argue that the lack of oscillations
even at low temperature is a signature of Klein tunneling
Neutral Current induced production and neutrino magnetic moment
We have studied the total cross section, , momentum and angular
distributions for pions in the () induced production
from nucleons. The calculations have been done for the weak production induced
by the neutral current in the standard model and the electromagnetic production
induced by neutrino magnetic moment. It has been found that with the present
experimental limits on the muon neutrino magnetic moment , the
electromagnetic contribution to the cross section for the production is
small. The neutrino induced neutral current production of , while
giving an alternative method to study the magnetic moment of neutrino
, does not provide any improvement over the present experimental
limit on from the observation of this process in future
experiments at T2K and NOA.Comment: 6 pages, 5 figure
The preliminary study of urbanization, fossil fuels consumptions and CO2 emission in Karachi
According to population, Karachi is the first largest city of Pakistan and 9th largest in the world. During last three decades, it has faced mass urbanization, huge population growth, many fold increase in vehicles and industrial development. As a result the demand of more energy in form of fossil fuels increased for domestic, industrial and transportation purpose. In this research the maximum available data of Karachi about urbanization, population and vehicles growth, industrialization, energy consumption and CO2 emissions are analyzed. Time periods considered for this work are according to the availability of the data. The results show that during 1947 to 2008, both urban population and urban area increased to 1500%. During 1990 to 2008, the percentage growth in vehicles is double than that of population growth during this time period. During 1980 to 2007 the consumption of oil and petrol, natural gas and coal increased to 219%, 365% and 287%, respectively. The emission of CO2 jumped from 39 million metric tons in 1980 to 151 million metric tons in 2007
- …