1,785 research outputs found
Effects of decoherence on the shot noise in carbon nanotubes
We study the zero frequency noise in an interacting quantum wire connected to
leads, in the presence of an impurity. In the absence of quasiparticle
decoherence the zero-frequency noise is that of a non-interacting wire.
However, if the collective, fractionally-charged modes have a finite lifetime,
we find that the zero-frequency noise may still exhibit signatures of charge
fractionalization, such as a small but detectable reduction of the ratio
between the noise and the backscattered current (Fano factor). We argue that
this small reduction of the Fano factor is consistent with recent observations
of a large reduction in the experimentally-inferred Fano factor in nanotubes
(calculated assuming that the backscattered current is the difference between
the ideal current in a multiple-channel non-interacting wire and the measured
current.Comment: 6 pages, 1 figur
A Multi-Wavelength Study of the Western Lobe of W50 Powered by the Galactic Microquasar SS 433
W50 remains the only supernova remnant (SNR) confirmed to harbor a
microquasar: the powerful enigmatic source SS 433. Our past study of this
fascinating SNR revealed two X-ray lobes distorting the radio shell as well as
non-thermal X-rays at the site of interaction between the SS 433 eastern jet
and the eastern lobe of W50. In this paper we present the results of a 75 ksec
CHANDRA ACIS-I observation of the peak of W50-west targeted to 1) determine the
nature of the X-ray emission and 2) correlate the X-ray emission with that in
the radio and infrared domains. We have confirmed that at the site of
interaction between the western jet of SS 433 and dense interstellar gas the
X-ray emission is non-thermal in nature. The helical pattern observed in radio
is also seen with CHANDRA. No correlation was found between the infrared and
X-ray emission.Comment: A refereed publication, submitted Sept. 30, 2004, accepted Jan. 12,
2005, to appear in Advances in Space Research. 7 pages, including 4 figures
(3 color) & 1 table (the resolution of most figures has been reduced for
astro-ph submission only). A gzipped postscript or pdf version of the paper
with high-resolution images can be downloaded from:
http://aurora.physics.umanitoba.ca/~moldowan/Astro-Ph
AC conductance and non-symmetrized noise at finite frequency in quantum wires and carbon nanotubes
We calculate the AC conductance and the finite-frequency non-symmetrized
noise in interacting quantum wires and single-wall carbon nanotubes in the
presence of an impurity. We observe a strong asymmetry in the frequency
spectrum of the non-symmetrized excess noise, even in the presence of the
metallic leads. We find that this asymmetry is proportional to the differential
excess AC conductance of the system, defined as the difference between the AC
differential conductances at finite and zero voltage, and thus disappears for a
linear system. In the quantum regime, for temperatures much smaller than the
frequency and the applied voltage, we find that the emission noise is exactly
equal to the impurity partition noise. For the case of a weak impurity we
expand our results for the AC conductance and the noise perturbatively. In
particular, if the impurity is located in the middle of the wire or at one of
the contacts, our calculations show that the noise exhibits oscillations with
respect to frequency, whose period is directly related to the value of the
interaction parameter
A one-channel conductor in an ohmic environment: mapping to a TLL and full counting statistics
It is shown that a one-channel mesoscopic conductor in an ohmic environment
can be mapped to the problem of a backscattering impurity in a
Tomonaga-Luttinger liquid (TLL). This allows to determine non perturbatively
the effect of the environment on curves, and to find an exact
relationship between dynamic Coulomb blockade and shot noise. We investigate
critically how this relationship compares to recent proposals in the
literature. The full counting statistics is determined at zero temperature.Comment: 5 pages, 2 figures, shortened version for publication in Phys. Rev.
Let
Transport through quasi-ballistic quantum wires: the role of contacts
We model one-dimensional transport through each open channel of a quantum
wire by a Luttinger liquid with three different interaction parameters for the
leads, the contact regions and the wire, and with two barriers at the contacts.
We show that this model explains several features of recent experiments, such
as the flat conductance plateaux observed even at finite temperatures and for
different lengths, and universal conductance corrections in different channels.
We discuss the possibility of seeing resonance-like structures of a fully open
channel at very low temperatures.Comment: revtex, 5 pages, 1 eps figure; clarifications added in light of new
experiment
One-channel conductor coupled to a quantum of resistance: exact ac conductance and finite-frequency noise
We consider a one-channel coherent conductor with a good transmission
embedded into an ohmic environment whose impedance is equal to the quantum of
resistance R_q=h/e^2 below the RC frequency. This choice is motivated by the
mapping of this problem to a Tomonaga-Luttinger liquid with one impurity whose
interaction parameter corresponds to the specific value K=1/2, allowing for a
refermionization procedure. The "new" fermions have an energy-dependent
transmission amplitude which incorporates the strong correlation effects and
yields the exact dc current and zero-frequency noise through expressions
similar to those of the scattering approach. We recall and discuss these
results for our present purpose. Then we compute, for the first time, the
finite-frequency differential conductance and the finite-frequency
non-symmetrized noise. Contrary to intuitive expectation, both cannot be
expressed within the scattering approach for the new fermions, even though they
are still determined by the transmission amplitude. Even more, the
finite-frequency conductance obeys an exact relation in terms of the dc current
which is similar to that derived perturbatively with respect to weak tunneling
within the Tien-Gordon theory, and extended recently to arbitrary strongly
interacting systems coupled eventually to an environment or/and with a
fractional charge. We also show that the emission excess noise vanishes exactly
above eV, even though the underlying Tomonaga-Luttinger liquid model
corresponds to a many-body correlated system. Our results apply for all ranges
of temperature, voltages and frequencies below the RC frequency, and they allow
to explore fully the quantum regime.Comment: 15 pages, 11 figure
Resonance in a Tomonaga-Luttinger liquid
We study a homogeneous Tomonaga-Luttinger liquid with backscattering
potential. A perturbative computation of the conductance at and near resonance
is given. We find that the backscattering of one electron dominates that of two
electrons for an interaction parameter and that the resonance point
depends on temperature. Our results may be relevant for recent experiments on
shot-noise in FQHE, where the charge 1/3 and not is measured on
resonance.Comment: 15 pages, three Figures. v2: Definite version, Citations added,
presentation improved. To appear in Phys. Rev. B, Rapid Co
Interactions between sub-10 nm iron and cerium oxide nanoparticles and 3T3 fibroblasts : the role of the coating and aggregation state
Recent nanotoxicity studies revealed that the physico-chemical
characteristics of engineered nanomaterials play an important role in the
interactions with living cells. Here, we report on the toxicity and uptake of
the cerium and iron oxide sub-10 nm nanoparticles by NIH/3T3 mouse fibroblasts.
Coating strategies include low-molecular weight ligands (citric acid) and
polymers (poly(acrylic acid), MW = 2000 g mol-1). Electrostatically adsorbed on
the surfaces, the organic moieties provide a negatively charged coating in
physiological conditions. We find that most particles were biocompatible, as
exposed cells remained 100% viable relative to controls. Only the bare and the
citrate-coated nanoceria exhibit a slight decrease of the mitochondrial
activity for cerium concentrations above 5 mM (equivalent to 0.8 g L-1). We
also observe that the citrate-coated particles are internalized by the cells in
large amounts, typically 250 pg per cell after a 24 h incubation for iron
oxide. In contrast, the polymer-coated particles are taken up at much lower
rates (< 30 pg per cell). The strong uptake shown by the citrate-coated
particles is related to the destabilization of the dispersions in the cell
culture medium and their sedimentation down to the cell membranes. In
conclusion, we show that the uptake of nanomaterials by living cells depends on
the coating of the particles and on its ability to preserve the colloidal
nature of the dispersions.Comment: 9 figures, 2 table
Numerical solution for the time-Fractional Diffusion-wave Equations by using Sinc-Legendre Collocation Method
In this paper the numerical solution of fractional diffusion wave equation is proposed. The fractional derivative will be in the Caputo sense. The proposed method will be based on shifted Legendre collocation scheme and sinc function approximation for time and space respectively. The problem is reduced to the problem into a system of algebraic equations after implementing this method. For demonstrating the validity and applicability of the proposed numerical scheme some examples are presented. Keywords: Fractional diffusion equation, Sinc functions, shifted Legendre polynomials, Collocation method
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