3,249 research outputs found
Effects of magnetic field and disorder on electronic properties of Carbon Nanotubes
Electronic properties of metallic and semiconducting carbon nanotubes are
investigated in presence of magnetic field perpendicular to the CN-axis, and
disorder introduced through energy site randomness. The magnetic field field is
shown to induce a metal-insulator transition (MIT) in absence of disorder, and
surprisingly disorder does not affect significantly the MIT. These results may
find confirmation through tunneling experimentsComment: 4 pages, 6 figures. Phys. Rev. B (in press
Information-theoretic analysis of the directional influence between cellular processes
Inferring the directionality of interactions between cellular processes is a
major challenge in systems biology. Time-lagged correlations allow to
discriminate between alternative models, but they still rely on assumed
underlying interactions. Here, we use the transfer entropy (TE), an
information-theoretic quantity that quantifies the directional influence
between fluctuating variables in a model-free way. We present a theoretical
approach to compute the transfer entropy, even when the noise has an extrinsic
component or in the presence of feedback. We re-analyze the experimental data
from Kiviet et al. (2014) where fluctuations in gene expression of metabolic
enzymes and growth rate have been measured in single cells of E. coli. We
confirm the formerly detected modes between growth and gene expression, while
prescribing more stringent conditions on the structure of noise sources. We
furthermore point out practical requirements in terms of length of time series
and sampling time which must be satisfied in order to infer optimally transfer
entropy from times series of fluctuations.Comment: 24 pages, 7 figure
Carbon cycle research after Kyoto
Recent progress in research of the global carbon cycle is reviewed and research needs for the immediate future are discussed, in light of the challenge posed to society to come to grips with the problem of man-made climate change. The carbon cycle in the oceans and on the land is reviewed, and how the atmosphere functions to couple them together. Major uncertainties still exist for any projection of the future atmospheric burden of carbon dioxide resulting from postulated emission scenarios of CO2. We present some ideas on how future policies designed to limit emissions or to sequester carbon can possibly be supported by scientific evidence of their effectiveness
Universality of electron correlations in conducting carbon nanotubes
Effective low-energy Hamiltonian of interacting electrons in conducting
single-wall carbon nanotubes with arbitrary chirality is derived from the
microscopic lattice model. The parameters of the Hamiltonian show very weak
dependence on the chiral angle, which makes the low energy properties of
conducting chiral nanotubes universal. The strongest Mott-like electron
instability at half filling is investigated within the self-consistent harmonic
approximation. The energy gaps occur in all modes of elementary excitations and
estimate at eV.Comment: 4 pages, 2 figure
Stable isotopic analysis of atmospheric methane by infrared spectroscopy by use of diode laser difference-frequency generation
An infrared absorption spectrometer has been constructed to measure the stable isotopic composition of atmospheric methane samples. The spectrometer employs periodically poled lithium niobate to generate 15 ΌW of tunable difference-frequency radiation from two near-infrared diode lasers that probe the Μ3 rotational-vibrational band of methane at 3.4 Όm. To enhance the signal, methane is extracted from 25 l of air by use of a cryogenic chromatographic column and is expanded into the multipass cell for analysis. A measurement precision of 12Ⱐis demonstrated for both Ύ13C and ΎD
Intrinsic Coulomb blockade in multi-wall carbon nanotubes
Carbon nanotubes provide a new class of molecular wires that display new and
exciting mesoscopic transport properties. We provide a detailed theoretical
description for transport in multi-wall nanotubes, where both disorder and
strong interactions are important. The interplay of both aspects leads to a
particularly effective intrinsic Coulomb blockade for tunneling. The relation
to recent experiments is discussed.Comment: 13 pages, incl 2 figs, for: Special issue "Transport in Molecular
Wires" in Chemical Physics, ed. by P. Hanggi, M. Ratner, S. Yalirak
dc Josephson Effect in Metallic Single-Walled Carbon Nanotubes
The dc Josephson effect is investigated in a single-walled metallic carbon
nanotube connected to two superconducting leads. In particular, by using the
Luttinger liquid theory, we analyze the effects of the electron-electron
interaction on the supercurrent. We find that in the long junction limit the
strong electronic correlations of the nanotube, together with its peculiar band
structure, induce oscillations in the critical current as a function of the
junction length and/or the nanotube electron filling. These oscillations
represent a signature of the Luttinger liquid physics of the nanotube, for they
are absent if the interaction is vanishing. We show that this effect can be
exploited to reverse the sign of the supercurrent, realizing a tunable
\pi-junction.Comment: 7 pages, 5 figure
Strong correlation effects in single-wall carbon nanotubes
We present an overview of strong correlations in single-wall carbon
nanotubes, and an introduction to the techniques used to study them
theoretically. We concentrate on zigzag nanotubes, although universality
dictates that much ofthe theory can also be applied to armchair or chiral
nanotubes. We show how interaction effects lead to exotic low energy properties
and discuss future directions for studies on correlation effects in nanotubes
Spin configurations of carbon nanotube in a nonuniform external potential
We study, theoretically, the ground state spin of a carbon nanotube in the
presence of an external potential. We find that when the external potential is
applied to a part of the nanotube, its variation changes the single electron
spectrum significantly. This, in combination with Coulomb repulsion and the
symmetry properties of a finite length armchair nanotube induces spin flips in
the ground state when the external potential is varied. We discuss the possible
application of our theory to recent measurements of Coulomb blocked peaks and
their dependence on a weak magnetic field in armchair carbon nanotubes.Comment: RevTeX, 5 pages + two figure
- âŠ