8,165 research outputs found
Semiclassical instanton formulation of Marcus-Levich-Jortner theory
Marcus-Levich-Jortner (MLJ) theory is one of the most commonly used methods
for including nuclear quantum effects into the calculation of electron-transfer
rates and for interpreting experimental data. It divides the molecular problem
into a subsystem treated quantum-mechanically by Fermi's golden rule and a
solvent bath treated by classical Marcus theory. As an extension of this idea,
we here present a "reduced" semiclassical instanton theory, which is a
multiscale method for simulating quantum tunnelling of the subsystem in
molecular detail in the presence of a harmonic bath. We demonstrate that
instanton theory is typically significantly more accurate than the cumulant
expansion or the semiclassical Franck-Condon sum, which can give
orders-of-magnitude errors and in general do not obey detailed balance. As
opposed to MLJ theory, which is based on wavefunctions, instanton theory is
based on path integrals and thus does not require solutions of the
Schr\"odinger equation, nor even global knowledge of the ground- and
excited-state potentials within the subsystem. It can thus be efficiently
applied to complex, anharmonic multidimensional subsystems without making
further approximations. In addition to predicting accurate rates, instanton
theory gives a high level of insight into the reaction mechanism by locating
the dominant tunnelling pathway as well as providing information on the
reactant and product vibrational states involved in the reaction and the
activation energy in the bath similarly to what would be found with MLJ theory.Comment: 21 pages, 4 figure
Lattice quark propagator with staggered quarks in Landau and Laplacian gauges
We report on the lattice quark propagator using standard and improved
Staggered quark actions, with the standard, Wilson gauge action. The standard
Kogut-Susskind action has errors of \oa{2} while the ``Asqtad'' action has
\oa{4}, \oag{2}{2} errors. The quark propagator is interesting for studying the
phenomenon of dynamical chiral symmetry breaking and as a test-bed for
improvement. Gauge dependent quantities from lattice simulations may be
affected by Gribov copies. We explore this by studying the quark propagator in
both Landau and Laplacian gauges. Landau and Laplacian gauges are found to
produce very similar results for the quark propagator.Comment: 11 pages, 15 figure
Knee adduction moment and medial contact force - facts about their correlation during gait
The external knee adduction moment is considered a surrogate measure for the medial tibiofemoral contact force and is commonly used to quantify the load reducing effect of orthopedic interventions. However, only limited and controversial data exist about the correlation between adduction moment and medial force. The objective of this study was to examine whether the adduction moment is indeed a strong predictor for the medial force by determining their correlation during gait. Instrumented knee implants with telemetric data transmission were used to measure tibiofemoral contact forces in nine subjects. Gait analyses were performed simultaneously to the joint load measurements. Skeletal kinematics, as well as the ground reaction forces and inertial parameters, were used as inputs in an inverse dynamics approach to calculate the external knee adduction moment. Linear regression analysis was used to analyze the correlation between adduction moment and medial force for the whole stance phase and separately for the early and late stance phase. Whereas only moderate correlations between adduction moment and medial force were observed throughout the whole stance phase (R(2)?=?0.56) and during the late stance phase (R(2)?=?0.51), a high correlation was observed at the early stance phase (R(2)?=?0.76). Furthermore, the adduction moment was highly correlated to the medial force ratio throughout the whole stance phase (R(2)?=?0.75). These results suggest that the adduction moment is a surrogate measure, well-suited to predicting the medial force ratio throughout the whole stance phase or medial force during the early stance phase. However, particularly during the late stance phase, moderate correlations and high inter-individual variations revealed that the predictive value of the adduction moment is limited. Further analyses are necessary to examine whether a combination of other kinematic, kinetic or neuromuscular factors may lead to a more reliable prediction of the force magnitud
Thermodynamics of two-colour QCD
We discuss the thermodynamics of two-colour QCD with four flavours of
staggered quarks on 8^3x4 and 16^3x4 lattices. In our simulations we use the
Naik action for the fermions and a (1,2) tree-level improved gauge action. We
analyze the deconfinement and chiral phase transitions for four different quark
masses (m=0.1,0.05,0.025,0.015). Contrary to three-colour QCD the peak in the
Polyakov loop susceptibility decreases with decreasing quark mass. This
reflects an early breaking of the string in the heavy quark potential, which we
verify explicitly by calculating the heavy quark potential at finite
temperature using Polyakov loop correlations.Comment: LATTICE98(hightemp), 3 pages, LaTeX2e File, 5 EPS-figures,
espcrc2.st
Modelling the quark propagator
The quark propagator is at the core of lattice hadron spectrum calculations
as well as studies in other nonperturbative schemes. We investigate the quark
propagator with an improved staggered action (Asqtad) and an improved gluon
action, which provides good quality data down to small quark masses. This is
used to construct ans\"{a}tze suitable for model hadron calculations as well as
adding to our intuitive understanding of QCD.Comment: Lattice2002(spectrum
On the neutrality issue in the Polyakov-loop NJL model
We elucidate how the color neutrality is harmed in the Polyakov Nambu-Jona
Lasinio (PNJL) model at finite density within the adopted mean field
approximation. Also we point out how usual assumption about the diagonal form
of the Wilson loop may fail in the presence of the diquark condensate on
several grounds.Comment: 8 pages, 1 figure. Introduction enlarged, several comments about the
adopted mean field approximation and the relation with Elitzur's theorem
added. Version to appear on Phys. Rev.
Multi-directional sorting modes in deterministic lateral displacement devices
Deterministic lateral displacement (DLD) devices separate micrometer-scale
particles in solution based on their size using a laminar microfluidic flow in
an array of obstacles. We investigate array geometries with rational row-shift
fractions in DLD devices by use of a simple model including both advection and
diffusion. Our model predicts novel multi-directional sorting modes that could
be experimentally tested in high-throughput DLD devices containing obstacles
that are much smaller than the separation between obstacles
The vertical distribution of zooplankton in the Goggausee (the influence of algae and Chaoborus flavicans) [Translation from: Carinthia II 166/186 373-385, 1976]
The Goggausee, a small, shallow, meromictic lake(700m long, 150m wide, max. depth=12m, mean depth=6m), was the site of a week long study (19-26 May 1974) of the limnology department of the University of Vienna. The study comprised pollen analysis and palaeolimnological studies on the one hand, as well as a stock- taking of physiochemical factors, primary production, bacteria, zooplankton, zoo benthos and fish on the other. This paper studies the zooplankton of the lake. The Goggausee is a meromictic lake, with its anoxic deep water, that restricts the vertical distribution of most zooplankton. The aim of the study was to pursue the vertical distribution of the rotifers and Crustacea. Density of individuals, biomass, percentages of zooplankton together and crustaceans and rotifers as groups. Special consideration is given to the the Dipteran Chaoborus flavicans
Unquenched quark propagator in Landau gauge
We present an unquenched calculation of the quark propagator in Landau gauge
with 2+1 flavors of dynamical quarks. We use configurations generated with an
improved staggered (``Asqtad'') action by the MILC collaboration. This quark
action has been seen to have excellent rotational symmetry and scaling
properties in the quenched quark propagator. Quenched and dynamical
calculations are performed on a lattice with a nominal lattice
spacing of fm. The matched quenched and dynamical lattices allow us
to investigate the relatively subtle sea quark effects, and even in the
quenched case the physical volume of these lattices gives access to lower
momenta than our previous study. We calculate the quark mass function and
renormalization function for a variety of valence and sea quark masses.Comment: 7 pages, 6 figure
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