185 research outputs found
Tunneling broadening of vibrational sidebands in molecular transistors
Transport through molecular quantum dots coupled to a single vibration mode
is studied in the case with strong coupling to the leads. We use an expansion
in the correlation between electrons on the molecule and electrons in the leads
and show that the tunneling broadening is strongly suppressed by the
combination of the Pauli principle and the quantization of the oscillator. As a
consequence the first Frank-Condon step is sharper than the higher order ones,
and its width, when compared to the bare tunneling strength, is reduced by the
overlap between the groundstates of the displaced and the non-displaced
oscillator.Comment: 8 pages, 3 figures. PRB, in pres
Hearing loss and satisfaction with healthcare: An unexplored relationship
Patient healthcare satisfaction has become increasingly important since Medicareâs introduction of the Hospital Care Quality Information from the Consumer Perspective (HCAHPS) survey. Greater satisfaction is associated with important healthcare outcomes including lower risk of 30-day readmission
Effect of melt conditioning on heat treatment and mechanical properties of AZ31 alloy strips produced by twin roll casting
In the present investigation, magnesium strips were produced by twin roll casting (TRC) and melt conditioned twin roll casting (MC-TRC) processes. Detailed optical microscopy studies were carried out on as-cast and homogenized TRC and MC-TRC strips. The results showed uniform, fine and equiaxed grain structure was observed for MC-TRC samples in as-cast condition. Whereas, coarse columnar grains with centreline segregation were observed in the case of as-cast TRC samples. The solidification mechanisms for TRC and MC-TRC have been found completely divergent. The homogenized TRC and MC-TRC samples were subjected to tensile test at elevated temperature (250-400 °C). At 250 °C, MC-TRC sample showed significant improvement in strength and ductility. However, at higher temperatures the tensile properties were almost comparable, despite of TRC samples having larger grains compared to MC-TRC samples. The mechanism of deformation has been explained by detailed fractures surface and sub-surface analysis carried out by scanning electron and optical microscopy. Homogenized MC-TRC samples were formed (hot stamping) into engineering component without any trace of crack on its surface. Whereas, TRC samples cracked in several places during hot stamping process.EPSRC â LiME, UK and Towards Affordable, Closed-Loop Recyclable Future Low Carbon Vehicle Structures â TARF-LCV(EP/I038616/1), Department of Mechanical Engineering, Imperial College London, UK, Mr. Steve Cook, Mr. Peter Lloyd, Mr. Graham Mitchell and Mr. Carmelo and BCAST, Brunel University London
Non Linear Current Response of a Many-Level Tunneling System: Higher Harmonics Generation
The fully nonlinear response of a many-level tunneling system to a strong
alternating field of high frequency is studied in terms of the
Schwinger-Keldysh nonequilibrium Green functions. The nonlinear time dependent
tunneling current is calculated exactly and its resonance structure is
elucidated. In particular, it is shown that under certain reasonable conditions
on the physical parameters, the Fourier component is sharply peaked at
, where is the spacing between
two levels. This frequency multiplication results from the highly nonlinear
process of photon absorption (or emission) by the tunneling system. It is
also conjectured that this effect (which so far is studied mainly in the
context of nonlinear optics) might be experimentally feasible.Comment: 28 pages, LaTex, 7 figures are available upon request from
[email protected], submitted to Phys.Rev.
Green function techniques in the treatment of quantum transport at the molecular scale
The theoretical investigation of charge (and spin) transport at nanometer
length scales requires the use of advanced and powerful techniques able to deal
with the dynamical properties of the relevant physical systems, to explicitly
include out-of-equilibrium situations typical for electrical/heat transport as
well as to take into account interaction effects in a systematic way.
Equilibrium Green function techniques and their extension to non-equilibrium
situations via the Keldysh formalism build one of the pillars of current
state-of-the-art approaches to quantum transport which have been implemented in
both model Hamiltonian formulations and first-principle methodologies. We offer
a tutorial overview of the applications of Green functions to deal with some
fundamental aspects of charge transport at the nanoscale, mainly focusing on
applications to model Hamiltonian formulations.Comment: Tutorial review, LaTeX, 129 pages, 41 figures, 300 references,
submitted to Springer series "Lecture Notes in Physics
Coherent electron-phonon coupling and polaron-like transport in molecular wires
We present a technique to calculate the transport properties through
one-dimensional models of molecular wires. The calculations include inelastic
electron scattering due to electron-lattice interaction. The coupling between
the electron and the lattice is crucial to determine the transport properties
in one-dimensional systems subject to Peierls transition since it drives the
transition itself. The electron-phonon coupling is treated as a quantum
coherent process, in the sense that no random dephasing due to electron-phonon
interactions is introduced in the scattering wave functions. We show that
charge carrier injection, even in the tunneling regime, induces lattice
distortions localized around the tunneling electron. The transport in the
molecular wire is due to polaron-like propagation. We show typical examples of
the lattice distortions induced by charge injection into the wire. In the
tunneling regime, the electron transmission is strongly enhanced in comparison
with the case of elastic scattering through the undistorted molecular wire. We
also show that although lattice fluctuations modify the electron transmission
through the wire, the modifications are qualitatively different from those
obtained by the quantum electron-phonon inelastic scattering technique. Our
results should hold in principle for other one-dimensional atomic-scale wires
subject to Peierls transitions.Comment: 21 pages, 8 figures, accepted for publication in Phys. Rev. B (to
appear march 2001
A common classification framework for neuroendocrine neoplasms: an International Agency for Research on Cancer (IARC) and World Health Organization (WHO) expert consensus proposal.
The classification of neuroendocrine neoplasms (NENs) differs between organ systems and currently causes considerable confusion. A uniform classification framework for NENs at any anatomical location may reduce inconsistencies and contradictions among the various systems currently in use. The classification suggested here is intended to allow pathologists and clinicians to manage their patients with NENs consistently, while acknowledging organ-specific differences in classification criteria, tumor biology, and prognostic factors. The classification suggested is based on a consensus conference held at the International Agency for Research on Cancer (IARC) in November 2017 and subsequent discussion with additional experts. The key feature of the new classification is a distinction between differentiated neuroendocrine tumors (NETs), also designated carcinoid tumors in some systems, and poorly differentiated NECs, as they both share common expression of neuroendocrine markers. This dichotomous morphological subdivision into NETs and NECs is supported by genetic evidence at specific anatomic sites as well as clinical, epidemiologic, histologic, and prognostic differences. In many organ systems, NETs are graded as G1, G2, or G3 based on mitotic count and/or Ki-67 labeling index, and/or the presence of necrosis; NECs are considered high grade by definition. We believe this conceptual approach can form the basis for the next generation of NEN classifications and will allow more consistent taxonomy to understand how neoplasms from different organ systems inter-relate clinically and genetically
Search for the Chiral Magnetic Effect in Au+Au collisions at GeV with the STAR forward Event Plane Detectors
A decisive experimental test of the Chiral Magnetic Effect (CME) is
considered one of the major scientific goals at the Relativistic Heavy-Ion
Collider (RHIC) towards understanding the nontrivial topological fluctuations
of the Quantum Chromodynamics vacuum. In heavy-ion collisions, the CME is
expected to result in a charge separation phenomenon across the reaction plane,
whose strength could be strongly energy dependent. The previous CME searches
have been focused on top RHIC energy collisions. In this Letter, we present a
low energy search for the CME in Au+Au collisions at
GeV. We measure elliptic flow scaled charge-dependent correlators relative to
the event planes that are defined at both mid-rapidity and at
forward rapidity . We compare the results based on the
directed flow plane () at forward rapidity and the elliptic flow plane
() at both central and forward rapidity. The CME scenario is expected
to result in a larger correlation relative to than to , while
a flow driven background scenario would lead to a consistent result for both
event planes[1,2]. In 10-50\% centrality, results using three different event
planes are found to be consistent within experimental uncertainties, suggesting
a flow driven background scenario dominating the measurement. We obtain an
upper limit on the deviation from a flow driven background scenario at the 95\%
confidence level. This work opens up a possible road map towards future CME
search with the high statistics data from the RHIC Beam Energy Scan Phase-II.Comment: main: 8 pages, 5 figures; supplementary material: 2 pages, 1 figur
Search for dark matter produced in association with a hadronically decaying vector boson in pp collisions at sqrt (s) = 13 TeV with the ATLAS detector
A search is presented for dark matter produced in association with a hadronically decaying W or Z boson using 3.2 fbâ1 of pp collisions at View the MathML sources=13 TeV recorded by the ATLAS detector at the Large Hadron Collider. Events with a hadronic jet compatible with a W or Z boson and with large missing transverse momentum are analysed. The data are consistent with the Standard Model predictions and are interpreted in terms of both an effective field theory and a simplified model containing dark matter
Measurement of the cross section for isolated-photon plus jet production in pp collisions at âs=13 TeV using the ATLAS detector
The dynamics of isolated-photon production in association with a jet in protonâproton collisions at a centre-of-mass energy of 13 TeV are studied with the ATLAS detector at the LHC using a dataset with an integrated luminosity of 3.2 fbâ1. Photons are required to have transverse energies above 125 GeV. Jets are identified using the anti- algorithm with radius parameter and required to have transverse momenta above 100 GeV. Measurements of isolated-photon plus jet cross sections are presented as functions of the leading-photon transverse energy, the leading-jet transverse momentum, the azimuthal angular separation between the photon and the jet, the photonâjet invariant mass and the scattering angle in the photonâjet centre-of-mass system. Tree-level plus parton-shower predictions from Sherpa and Pythia as well as next-to-leading-order QCD predictions from Jetphox and Sherpa are compared to the measurements
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