1,660 research outputs found
Non-equilibrium Green's function theory for non-adiabatic effects in quantum transport: inclusion of electron-electron interactions
Non-equilibrium Green's function theory for non-adiabatic effects in quantum
transport [Kershaw and Kosov, J.Chem. Phys. 2017, 147, 224109 and J. Chem.
Phys. 2018, 149, 044121] is extended to the case of interacting electrons. We
consider a general problem of quantum transport of interacting electrons
through a central region with dynamically changing geometry. The approach is
based on the separation of time scales in the non-equilibrium Green's functions
and the use of Wigner transformation to solve the Kadanoff-Baym equations. The
Green's functions and correlation self-energy are non-adiabatically expanded up
to the second order central time derivatives. We produced expressions for
Green's functions with non-adiabatic corrections and modified formula for
electric current; both depend not only on instantaneous molecular junction
geometry but also on nuclear velocities and accelerations. The theory is
illustrated by the study of electron transport through a model single-resonant
level molecular junction with local electron-electron repulsion and a
dynamically changing geometry
Nonadiabatic corrections to electric current in molecular junction due to nuclear motion at the molecule-electrode interfaces
We present quantum electron transport theory that incorporates dynamical
effects of motion of atoms on electrode-molecule interfaces in the calculations
of the electric current. The theory is based on non-equilibrium Green's
functions. We separate time scales in the Green's functions on fast relative
time and slow central time. The derivative with respect to the central time
serves as a small parameter in the theory. We solve the real-time Kadanoff-Baym
equations for molecular Green's functions using Wigner representation and keep
terms up to the second order with respect to the central time derivatives.
Molecular Green's functions and consequently the electric current are expressed
as functions of molecular junction coordinates as well as velocities and
accelerations of molecule-electrode interface nuclei. We apply the theory to
model a molecular system and study the effects of non-adiabatic nuclear motion
on molecular junction conductivity
Nonequilibrium Green's function theory for nonadiabatic effects in quantum electron transport
We develop nonequilibribrium Green's function based transport theory, which
includes effects of nonadiabatic nuclear motion in the calculation of the
electric current in molecular junctions. Our approach is based on the
separation of slow and fast timescales in the equations of motion for the
Green's functions by means of the Wigner representation. Time derivatives with
respect to central time serves as a small parameter in the perturbative
expansion enabling the computation of nonadiabatic corrections to molecular
Green's functions. Consequently, we produce series of analytic expressions for
non-adiabatic electronic Green's functions (up to the second order in the
central time derivatives); which depend not solely on instantaneous molecular
geometry but likewise on nuclear velocities and accelerations. Extended formula
for electric current is derived which accounts for the non-adiabatic
corrections. This theory is concisely illustrated by the calculations on a
model molecular junction
Use of summer habitat by caribou on the north slope of a mountain near the Macmillan Pass, N.W.T.
Habitat use by woodland caribou was investigated by counting pellet-groups, sampling phytomass, and evaluating topography in nine habitat-types on the north slope of an unnamed mountain near Macmillan Pass, N.W.T. Caribou pellets were most abundant in high elevation habitat-types, and pellet density was greatest in an alpine Lichen-Grass habitat-type with a slope of <1°. The high density of pellets in alpine areas may have resulted from of the use of cool, windy, alpine habitats by caribou seeking relief from insect harassment. There were no apparent relationships between pellet abundance, and phytomass of mosses, lichens, or graminoids, possibly as a result of caribou feeding and defecating in different habitats. The occurrence of pellets with a coalesced morphology in the barren Lichen-Grass habitat-type provided indirect evidence in support of a feeding cycle, whereby caribou visit lush habitats to feed, and return to open, alpine habitats to rest and ruminate
Non-Adiabatic Effects of Nuclear Motion in Quantum Transport of Electrons: A Self-Consistent Keldysh-Langevin Study
The molecular junction geometry is modelled in terms of nuclear degrees of
freedom that are embedded in a stochastic quantum environment of
non-equilibrium electrons. Time-evolution of the molecular geometry is governed
via a mean force, a frictional force and a stochastic force, forces arising
from many electrons tunnelling across the junction for a given nuclear
vibration. Conversely, the current-driven nuclear dynamics feed back to the
electronic current, which can be captured according extended expressions for
the current that have explicit dependencies on classical nuclear velocities and
accelerations. Current-induced nuclear forces and the non-adiabatic electric
current are computed using non-equilibrium Green's functions via a time-scale
separation solution of Keldysh-Kadanoff-Baym equations in Wigner space.
Applying the theory to molecular junctions demonstrated that non-adiabatic
corrections play an important role when nuclear motion is considered
non-equilibrium and, in particular, showed that non-equilibrium and equilibrium
descriptions of nuclear motion produce significantly different current
characteristics. It is observed that non-equilibrium descriptions generally
produce heightened conductance profiles relative to the equilibrium
descriptions and provide evidence that the effective temperature is an
effective measure of the steady-state characteristics. Finally, we observe that
non-equilibrium descriptions of nuclear motion can give rise to the Landauer
blowtorch effect via the emergence of multi-minima potential energy surfaces in
conjunction with non-uniform temperature profiles. The Landauer blowtorch
effect and its impact on the current characteristics, waiting times and the
Fano factor are explored for an effective adiabatic potential that morphs
between a single, double and triple potential as a function of voltage.Comment: 17 pages and 8 figure
Successful restoration of arteriovenous dialysis access patency after late intervention.
BACKGROUND: Arteriovenous dialysis access may be lost due to stenosis and thrombosis. Patency may be restored by thrombectomy or thrombolysis, but this is often not undertaken when the presentation is delayed. The success rate of delayed intervention is largely unknown. METHODS: In this single-centre study, we identified all instances of arteriovenous vascular access (VA) failure treated with angioplasty, thrombectomy or thrombolysis between August 2010 and July 2013. Patency rates immediately after intervention, and after 3 months, were assessed using multilevel mixed effects logistic regression. RESULTS: Sixty failures occurred in 41 accesses (38 patients). The access age at failure was 495 (316-888) days. Intervention was carried out after >48 h in 19 failures (32%). Immediate patency was achieved in 46 failures, of which 32 remained patent after 3 months. Delaying intervention increased the likelihood of achieving immediate patency (OR 0.55, 95% CI 0.31-1.0, P = 0.05). Having lost arteriovenous accesses previously increased the risk of immediate failure (OR 4.0, 95% CI 1.07-14.95, P = 0.04). There was no association between failure-to-intervention-time and 3-month patency rates (P = 0.23). Effect estimates did not differ between arteriovenous fistulae and synthetic arteriovenous grafts. CONCLUSION: Delayed intervention for failed arteriovenous VA may result in superior early patency rates and yields equivalent 3-month patency rates.This is the author's accepted version and will be under embargo until 12 months from the date of publication. The final version is available from OUP at http://ckj.oxfordjournals.org/content/8/1/8
Remote Inspection, Measurement and Handling for LHC
Personnel access to the LHC tunnel will be restricted to varying extents during the life of the machine due to radiation, cryogenic and pressure hazards. The ability to carry out visual inspection, measurement and handling activities remotely during periods when the LHC tunnel is potentially hazardous offers advantages in terms of safety, accelerator down time, and costs. The first applications identified were remote measurement of radiation levels at the start of shut-down, remote geometrical survey measurements in the collimation regions, and remote visual inspection during pressure testing and initial machine cool-down. In addition, for remote handling operations, it will be necessary to be able to transmit several real-time video images from the tunnel to the control room. The paper describes the design, development and use of a remotely controlled vehicle to demonstrate the feasibility of meeting the above requirements in the LHC tunnel. Design choices are explained along with operating experience to-date and future development plans
A lichen protected by a super-hydrophobic and breathable structure
A species of lichen, Lecanora conizaeoides, is shown to be super-hydrophobic. It uses a combination of hydrophobic compounds and multi-layered roughness to shed water effectively. This is combined with gas channels to produce a biological analogue of a waterproof, breathable garment. The particular lichen grows mostly during wet seasons and is unusually resistant to acid rain [Hauck, M., 2003. The Bryotogist 106(2), 257-269; Honegger, R., 1998. Lichenologist 30(3),193-212]. The waterproof, breathable surface allows this lichen to photosynthesise when other species are covered with a layer of water. In addition, rainwater runs off the surface of the organism, reducing its intake of water from above and probably contributing to its resistance to acid rain
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