15,573 research outputs found
Electron transport through a quantum interferometer with side-coupled quantum dots: Green's function approach
We study electron transport through a quantum interferometer with
side-coupled quantum dots. The interferometer, threaded by a magnetic flux
, is attached symmetrically to two semi-infinite one-dimensional metallic
electrodes. The calculations are based on the tight-binding model and the
Green's function method, which numerically compute the conductance-energy and
current-voltage characteristics. Our results predict that under certain
conditions this particular geometry exhibits anti-resonant states. These states
are specific to the interferometric nature of the scattering and do not occur
in conventional one-dimensional scattering problems of potential barriers. Most
importantly we show that, such a simple geometric model can also be used as a
classical XOR gate, where the two gate voltages, viz, and , are
applied, respectively, in the two dots those are treated as the two inputs of
the XOR gate. For (, the elementary flux-quantum),
a high output current (1) (in the logical sense) appears if one, and only one,
of the inputs to the gate is high (1), while if both inputs are low (0) or both
are high (1), a low output current (0) appears. It clearly demonstrates the XOR
gate behavior and this aspect may be utilized in designing the electronic logic
gate.Comment: 8 pages, 5 figure
Conduction Mechanism in a Molecular Hydrogen Contact
We present first principles calculations for the conductance of a hydrogen
molecule bridging a pair of Pt electrodes. The transmission function has a wide
plateau with T~1 which extends across the Fermi level and indicates the
existence of a single, robust conductance channel with nearly perfect
transmission. Through a detailed Wannier function analysis we show that the H2
bonding state is not involved in the transport and that the plateau forms due
to strong hybridization between the H2 anti-bonding state and states on the
adjacent Pt atoms. The Wannier functions furthermore allow us to derive a
resonant-level model for the system with all parameters determined from the
fully self-consistent Kohn-Sham Hamiltonian.Comment: 5 pages, 4 figure
Economics of different craft - gear combination in Orissa coast
After declaration of Exclusive Econonomic
Zone, the Govt. of India took
lot of developmental programmes in capture
fisheries. But it is very difficult to
formulate as well as to implement any
programme unless and until we know the
existing position prevailing in different
coastal areas
Productivity, profitability and income distribution in capture fishery - a case study in Orissa coast
In the literature on marine and inland fisheries very little attention has been focused on income generation by various craft-gear combinations, their productivity and the extent, nature and causes of fluctuations in their incomes. This study of the Orissa coast explores the consequences of mechanisation on income distribution between mechanised and non-mechanised fishing units
NAND gate response in a mesoscopic ring: An exact study
NAND gate response in a mesoscopic ring threaded with a magnetic flux
is investigated by using Green's function formalism. The ring is attached
symmetrically to two semi-infinite one-dimensional metallic electrodes and two
gate voltages, namely, and , are applied in one arm of the ring
those are treated as the two inputs of the NAND gate. We use a simple
tight-binding model to describe the system and numerically compute the
conductance-energy and current-voltage characteristics as functions of the gate
voltages, ring-to-electrode coupling strength and magnetic flux. Our
theoretical study shows that, for (, the
elementary flux-quantum) a high output current (1) (in the logical sense)
appears if one or both the inputs to the gate are low (0), while if both the
inputs to the gate are high (1), a low output current (0) appears. It clearly
exhibits the NAND gate behavior and this feature may be utilized in designing
an electronic logic gate.Comment: 8 pages, 5 figure
Is there New Physics in B Decays ?
Rare decays of the meson are sensitive to new physics effects. Several
experimental results on these decays have been difficult to understand within
the standard model (SM) though more precise measurements and a better
understanding of SM theory predictions are needed before any firm conclusions
can be drawn. In this talk we try to understand the present data assuming the
presence of new physics. We find that the data points to new physics of an
extended Higgs sector and we present a two higgs doublet model with a 2-3
flavor symmetry in the down type quark sector that can explain the deviations
from standard model reported in several rare B decays.Comment: 8 pages, Talk presented at Theory Canada II, Perimeter Institute,
Waterloo, Canada. New references added and update
Quantum transport through molecular wires
We explore electron transport properties in molecular wires made of
heterocyclic molecules (pyrrole, furan and thiophene) by using the Green's
function technique. Parametric calculations are given based on the
tight-binding model to describe the electron transport in these wires. It is
observed that the transport properties are significantly influenced by (a) the
heteroatoms in the heterocyclic molecules and (b) the molecule-to-electrodes
coupling strength. Conductance () shows sharp resonance peaks associated
with the molecular energy levels in the limit of weak molecular coupling, while
they get broadened in the strong molecular coupling limit. These resonances get
shifted with the change of the heteroatoms in these heterocyclic molecules. All
the essential features of the electron transfer through these molecular wires
become much more clearly visible from the study of our current-voltage
(-) characteristics, and they provide several key informations in the
study of molecular transport.Comment: 8 pages, 4 figure
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