797 research outputs found
Magnetic field effects in energy relaxation mediated by Kondo impurities
We study the energy distribution function of quasiparticles in voltage biased
mesoscopic wires in presence of magnetic impurities and applied magnetic field.
The system is described by a Boltzmann equation where the collision integral is
determined by coupling to spin 1/2 impurities. We derive an effective coupling
to a dissipative spin system which is valid well above Kondo temperature in
equilibrium or for sufficiently smeared distribution functions in
non-equilibrium. For low magnetic field an enhancement of energy relaxation is
found whereas for larger magnetic fields the energy relaxation decreases again
meeting qualitatively the experimental findings by Anthore et al.
(cond-mat/0109297). This gives a strong indication that magnetic impurities are
in fact responsible for the enhanced energy relaxation in copper wires. The
quantitative comparison, however, shows strong deviations for energy relaxation
with small energy transfer whereas the large energy transfer regime is in
agreement with our findings.Comment: 14 pages, 8 figure
Multiple timescales in a model for DNA denaturation dynamics
The denaturation dynamics of a long double-stranded DNA is studied by means
of a model of the Poland-Scheraga type. We note that the linking of the two
strands is a locally conserved quantity, hence we introduce local updates that
respect this symmetry. Linking dissipation via untwist is allowed only at the
two ends of the double strand. The result is a slow denaturation characterized
by two time scales that depend on the chain length . In a regime up to a
first characteristic time the chain embodies an
increasing number of small bubbles. Then, in a second regime, bubbles coalesce
and form entropic barriers that effectively trap residual double-stranded
segments within the chain, slowing down the relaxation to fully molten
configurations, which takes place at . This scenario is
different from the picture in which the helical constraints are neglected.Comment: 9 pages, 5 figure
Corrections to the universal behavior of the Coulomb-blockade peak splitting for quantum dots separated by a finite barrier
Building upon earlier work on the relation between the dimensionless interdot
channel conductance g and the fractional Coulomb-blockade peak splitting f for
two electrostatically equivalent dots, we calculate the leading correction that
results from an interdot tunneling barrier that is not a delta-function but,
rather, has a finite height V and a nonzero width xi and can be approximated as
parabolic near its peak. We develop a new treatment of the problem for g much
less than 1 that starts from the single-particle eigenstates for the full
coupled-dot system. The finiteness of the barrier leads to a small upward shift
of the f-versus-g curve at small values of g. The shift is a consequence of the
fact that the tunneling matrix elements vary exponentially with the energies of
the states connected. Therefore, when g is small, it can pay to tunnel to
intermediate states with single-particle energies above the barrier height V.
The correction to the zero-width behavior does not affect agreement with recent
experimental results but may be important in future experiments.Comment: Title changed from ``Non-universal...'' to ``Corrections to the
universal...'' No other changes. 10 pages, 1 RevTeX file with 2 postscript
figures included using eps
Determination of the Strange Quark Content of the Nucleon from a Next-to-Leading-Order QCD Analysis of Neutrino Charm Production
We present the first next-to-leading-order QCD analysis of neutrino charm
production, using a sample of 6090 - and -induced
opposite-sign dimuon events observed in the CCFR detector at the Fermilab
Tevatron. We find that the nucleon strange quark content is suppressed with
respect to the non-strange sea quarks by a factor \kappa = 0.477 \:
^{+\:0.063}_{-\:0.053}, where the error includes statistical, systematic and
QCD scale uncertainties. In contrast to previous leading order analyses, we
find that the strange sea -dependence is similar to that of the non-strange
sea, and that the measured charm quark mass, , is larger and consistent with that determined in other processes.
Further analysis finds that the difference in -distributions between
and is small. A measurement of the Cabibbo-Kobayashi-Maskawa
matrix element is also presented.
uufile containing compressed postscript files of five Figures is appended at
the end of the LaTeX source.Comment: Nevis R#150
Brownian motion exhibiting absolute negative mobility
We consider a single Brownian particle in a spatially symmetric, periodic
system far from thermal equilibrium. This setup can be readily realized
experimentally. Upon application of an external static force F, the average
particle velocity is negative for F>0 and positive for F<0 (absolute negative
mobility).Comment: 4 pages, 3 figures, to be published in PR
Global Antifungal Profile Optimization of Chlorophenyl Derivatives against Botrytis cinerea and Colletotrichum gloeosporioides
Twenty-two aromatic derivatives bearing a chlorine atom and a different chain in the para or meta
position were prepared and evaluated for their in vitro antifungal activity against the phytopathogenic
fungi Botrytis cinerea and Colletotrichum gloeosporioides. The results showed that maximum inhibition
of the growth of these fungi was exhibited for enantiomers S and R of 1-(40-chlorophenyl)-
2-phenylethanol (3 and 4). Furthermore, their antifungal activity showed a clear structure-activity
relationship (SAR) trend confirming the importance of the benzyl hydroxyl group in the inhibitory
mechanism of the compounds studied. Additionally, a multiobjective optimization study of the
global antifungal profile of chlorophenyl derivatives was conducted in order to establish a rational
strategy for the filtering of new fungicide candidates from combinatorial libraries. The MOOPDESIRE
methodology was used for this purpose providing reliable ranking models that can be
used later
Harmonic Sums and Mellin Transforms up to two-loop Order
A systematic study is performed on the finite harmonic sums up to level four.
These sums form the general basis for the Mellin transforms of all individual
functions of the momentum fraction emerging in the quantities of
massless QED and QCD up to two--loop order, as the unpolarized and polarized
splitting functions, coefficient functions, and hard scattering cross sections
for space and time-like momentum transfer. The finite harmonic sums are
calculated explicitly in the linear representation. Algebraic relations
connecting these sums are derived to obtain representations based on a reduced
set of basic functions. The Mellin transforms of all the corresponding Nielsen
functions are calculated.Comment: 44 pages Latex, contract number adde
Coevolved mutations reveal distinct architectures for two core proteins in the bacterial flagellar motor
Switching of bacterial flagellar rotation is caused by large domain movements of the FliG protein triggered by binding of the signal protein CheY to FliM. FliG and FliM form adjacent multi-subunit arrays within the basal body C-ring. The movements alter the interaction of the FliG C-terminal (FliGC) "torque" helix with the stator complexes. Atomic models based on the Salmonella entrovar C-ring electron microscopy reconstruction have implications for switching, but lack consensus on the relative locations of the FliG armadillo (ARM) domains (amino-terminal (FliGN), middle (FliGM) and FliGC) as well as changes during chemotaxis. The generality of the Salmonella model is challenged by the variation in motor morphology and response between species. We studied coevolved residue mutations to determine the unifying elements of switch architecture. Residue interactions, measured by their coevolution, were formalized as a network, guided by structural data. Our measurements reveal a common design with dedicated switch and motor modules. The FliM middle domain (FliMM) has extensive connectivity most simply explained by conserved intra and inter-subunit contacts. In contrast, FliG has patchy, complex architecture. Conserved structural motifs form interacting nodes in the coevolution network that wire FliMM to the FliGC C-terminal, four-helix motor module (C3-6). FliG C3-6 coevolution is organized around the torque helix, differently from other ARM domains. The nodes form separated, surface-proximal patches that are targeted by deleterious mutations as in other allosteric systems. The dominant node is formed by the EHPQ motif at the FliMMFliGM contact interface and adjacent helix residues at a central location within FliGM. The node interacts with nodes in the N-terminal FliGc α-helix triad (ARM-C) and FliGN. ARM-C, separated from C3-6 by the MFVF motif, has poor intra-network connectivity consistent with its variable orientation revealed by structural data. ARM-C could be the convertor element that provides mechanistic and species diversity.JK was supported by Medical Research Council grant U117581331. SK was supported by seed funds from Lahore University of Managment Sciences (LUMS) and the Molecular Biology Consortium
All-sky LIGO Search for Periodic Gravitational Waves in the Early S5 Data
We report on an all-sky search with the LIGO detectors for periodic
gravitational waves in the frequency range 50--1100 Hz and with the frequency's
time derivative in the range -5.0E-9 Hz/s to zero. Data from the first eight
months of the fifth LIGO science run (S5) have been used in this search, which
is based on a semi-coherent method (PowerFlux) of summing strain power.
Observing no evidence of periodic gravitational radiation, we report 95%
confidence-level upper limits on radiation emitted by any unknown isolated
rotating neutron stars within the search range. Strain limits below 1.E-24 are
obtained over a 200-Hz band, and the sensitivity improvement over previous
searches increases the spatial volume sampled by an average factor of about 100
over the entire search band. For a neutron star with nominal equatorial
ellipticity of 1.0E-6, the search is sensitive to distances as great as 500
pc--a range that could encompass many undiscovered neutron stars, albeit only a
tiny fraction of which would likely be rotating fast enough to be accessible to
LIGO. This ellipticity is at the upper range thought to be sustainable by
conventional neutron stars and well below the maximum sustainable by a strange
quark star.Comment: 6 pages, 1 figur
Evaluation of an inter-professional workshop to develop a psychosocial assessment and child-centred communication training programme for paediatricians in training
BACKGROUND: The quality of psychosocial assessment of children in consultations varies widely. One reason for this difference is the variability in effective mental health and communication training at undergraduate and post-qualification levels. In recognition of this problem, the Royal College of Paediatrics and Child Health in the United Kingdom have developed the Child in Mind Project that aims to meet this deficit in medical training. This paper describes the evaluation of a workshop that explored the experiences and expectations of health care professionals in the development of a training programme for doctors. METHODS: The one-day inter-professional workshop was attended by 63 participants who were invited to complete evaluation forms before and immediately after the workshop. RESULTS: The results showed that the workshop was partially successful in providing an opportunity for an inter-professional group to exchange ideas and influence the development of a significant project. Exploring the content and process of the proposed training programme and the opportunity for participants to share experiences of effective practice were valued. Participants identified that the current culture within many health care settings would be an obstacle to successful implementation of a training programme. Working within existing training structures will be essential. Areas for improvement in the workshop included clearer statement of goals at the outset and a more suitable environment for the numbers of participants. CONCLUSIONS: The participants made a valuable contribution to the development of the training programme identifying specific challenges. Inter-professional collaborations are likely to result in more deliverable and relevant training programmes. Continued consultation with potential users of the programme – both trainers and trainees will be essential
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