2,598 research outputs found
Magneto-transport in a quantum network: Evidence of a mesoscopic switch
We investigate magneto-transport properties of a shaped three-arm
mesoscopic ring where the upper and lower sub-rings are threaded by
Aharonov-Bohm fluxes and , respectively, within a
non-interacting electron picture. A discrete lattice model is used to describe
the quantum network in which two outer arms are subjected to binary alloy
lattices while the middle arm contains identical atomic sites. It is observed
that the presence of the middle arm provides localized states within the band
of extended regions and lead to the possibility of switching action from a high
conducting state to a low conducting one and vice versa. This behavior is
justified by studying persistent current in the network. Both the total current
and individual currents in three separate branches are computed by using
second-quantized formalism and our idea can be utilized to study magnetic
response in any complicated quantum network. The nature of localized
eigenstates are also investigated from probability amplitudes at different
sites of the quantum device.Comment: 7 pages, 9 figure
Magnetic Response in a Zigzag Carbon Nanotube
Magnetic response of interacting electrons in a zigzag carbon nanotube
threaded by a magnetic flux is investigated within a Hartree-Fock mean field
approach. Following the description of energy spectra for both non-interacting
and interacting cases we analyze the behavior of persistent current in
individual branches of a nanotube. Our present investigation leads to a
possibility of getting a filling-dependent metal-insulator transition in a
zigzag carbon nanotube.Comment: 9 pages, 14 figure
MovieMaker: a web server for rapid rendering of protein motions and interactions
MovieMaker is a web server that allows short (∼10 s), downloadable movies of protein motions to be generated. It accepts PDB files or PDB accession numbers as input and automatically calculates, renders and merges the necessary image files to create colourful animations covering a wide range of protein motions and other dynamic processes. Users have the option of animating (i) simple rotation, (ii) morphing between two end-state conformers, (iii) short-scale, picosecond vibrations, (iv) ligand docking, (v) protein oligomerization, (vi) mid-scale nanosecond (ensemble) motions and (vii) protein folding/unfolding. MovieMaker does not perform molecular dynamics calculations. Instead it is an animation tool that uses a sophisticated superpositioning algorithm in conjunction with Cartesian coordinate interpolation to rapidly and automatically calculate the intermediate structures needed for many of its animations. Users have extensive control over the rendering style, structure colour, animation quality, background and other image features. MovieMaker is intended to be a general-purpose server that allows both experts and non-experts to easily generate useful, informative protein animations for educational and illustrative purposes. MovieMaker is accessible at
Electron transport through multilevel quantum dot
Quantum transport properties through some multilevel quantum dots sandwiched
between two metallic contacts are investigated by the use of Green's function
technique. Here we do parametric calculations, based on the tight-binding
model, to study the transport properties through such bridge systems. The
electron transport properties are significantly influenced by (a) number of
quantized energy levels in the dots, (b) dot-to-electrode coupling strength,
(c) location of the equilibrium Fermi energy and (d) surface disorder. In
the limit of weak-coupling, the conductance () shows sharp resonant peaks
associated with the quantized energy levels in the dots, while, they get
substantial broadening in the strong-coupling limit. The behavior of the
electron transfer through these systems becomes much more clearly visible from
our study of current-voltage (-) characteristics. In this context we also
describe the noise power of current fluctuations () and determine the Fano
factor () which provides an important information about the electron
correlation among the charge carriers. Finally, we explore a novel transport
phenomenon by studying the surface disorder effect in which the current
amplitude increases with the increase of the surface disorder strength in the
strong disorder regime, while, the amplitude decreases in the limit of weak
disorder. Such an anomalous behavior is completely opposite to that of bulk
disordered system where the current amplitude always decreases with the
disorder strength. It is also observed that the current amplitude strongly
depends on the system size which reveals the finite quantum size effect.Comment: 12 pages, 7 figure
Orbital order-disorder transition in La(1-x)Nd(x)MnO(3) (x = 0.0-1.0) and La(1-x-y)Nd(yx)Sr(y)MnO(3) (x = 0.1; y = 0.05,0.1)
The nature of orbital order-disorder transition has been studied in the
La(1-x)Nd(x)MnO(3) (x = 0.0-1.0) series which covers the entire range between
two end points - LaMnO(3) and NdMnO(3) - as well as in
La(0.85)Nd(0.1)Sr(0.05)MnO(3) and La(0.8)Nd(0.1)Sr(0.1)MnO(3). It has been
observed that the first-order nature of the transition gives way to higher
order with the increase in "x" in the case of pure manganites. The latent heat
(L) associated with the transition, first, drops with a steeper slope within x
= 0.0-0.3 and, then, gradually over a range 0.3<x<0.9. This drop could,
possibly, be due to evolution of finer orbital domain structure with "x". In
the case of Sr-doped samples, the transition appears to be of higher-order
nature even for a doping level 5 at%. In both cases, of course, the transition
temperature T(JT) rises systematically with the drop in average A-site radius
or rise in average Mn-O-Mn bond bending angle while no
apparent correlation could be observed with doping induced disorder sigma^2.
The cooperative nature of the orbital order, therefore, appears to be robust.Comment: 15 pages including 4 figures; pdf onl
The t-J model on a semi-infinite lattice
The hole spectral function of the t-J model on a two-dimensional
semi-infinite lattice is calculated using the spin-wave and noncrossing
approximations. In the case of small hole concentration and strong
correlations, , several near-boundary site rows appear to be depleted
of holes. The reason for this depletion is a deformation of the magnon cloud,
which surrounds the hole, near the boundary. The hole depletion in the boundary
region leads to a more complicated spectral function in the boundary row in
comparison with its bulk shape.Comment: 8 pages, 5 figure
Peristaltic Transport of a Physiological Fluid in an Asymmetric Porous Channel in the Presence of an External Magnetic Field
The paper deals with a theoretical investigation of the peristaltic transport
of a physiological fluid in a porous asymmetric channel under the action of a
magnetic field. The stream function, pressure gradient and axial velocity are
studied by using appropriate analytical and numerical techniques. Effects of
different physical parameters such as permeability, phase difference, wave
amplitude and magnetic parameter on the velocity, pumping characteristics,
streamline pattern and trapping are investigated with particular emphasis. The
computational results are presented in graphical form. The results are found to
be in perfect agreement with those of a previous study carried out for a
non-porous channel in the absence of a magnetic field
Evolution of spectral function in a doped Mott insulator : surface vs. bulk contributions
We study the evolution of the spectral function with progressive hole doping
in a Mott insulator, with = 0.0 - 0.5. The spectral
features indicate a bulk-to-surface metal-insulator transition in this system.
Doping dependent changes in the bulk electronic structure are shown to be
incompatible with existing theoretical predictions. An empirical description
based on the single parameter, , is shown to describe consistently the
spectral evolution.Comment: Revtex, 4 pages, 3 postscript figures. To appear in Phys. Rev. Let
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