5,592 research outputs found
Brain damage as detected by magnetization transfer imaging is less pronounced in benign than in early relapsing multiple sclerosis
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A New Phase Time Formula for Opaque Barrier Tunneling
After a brief review of the derivation of the standard phase time formula,
based on the use of the stationary phase method, we propose, in the opaque
limit, an alternative method to calculate the phase time. The new formula for
the phase time is in excellent agreement with the numerical simulations and
shows that for wave packets whose upper limit of the momentum distribution is
very close to the barrier height, the transit time is proportional to the
barrier width.Comment: 9 pages, 2 figure
Self-organisation to criticality in a system without conservation law
We numerically investigate the approach to the stationary state in the
nonconservative Olami-Feder-Christensen (OFC) model for earthquakes. Starting
from initially random configurations, we monitor the average earthquake size in
different portions of the system as a function of time (the time is defined as
the input energy per site in the system). We find that the process of
self-organisation develops from the boundaries of the system and it is
controlled by a dynamical critical exponent z~1.3 that appears to be universal
over a range of dissipation levels of the local dynamics. We show moreover that
the transient time of the system scales with system size L as . We argue that the (non-trivial) scaling of the transient time in the
OFC model is associated to the establishment of long-range spatial correlations
in the steady state.Comment: 10 pages, 6 figures; accepted for publication in Journal of Physics
Setting Parameters for Biological Models With ANIMO
ANIMO (Analysis of Networks with Interactive MOdeling) is a software for
modeling biological networks, such as e.g. signaling, metabolic or gene
networks. An ANIMO model is essentially the sum of a network topology and a
number of interaction parameters. The topology describes the interactions
between biological entities in form of a graph, while the parameters determine
the speed of occurrence of such interactions. When a mismatch is observed
between the behavior of an ANIMO model and experimental data, we want to update
the model so that it explains the new data. In general, the topology of a model
can be expanded with new (known or hypothetical) nodes, and enables it to match
experimental data. However, the unrestrained addition of new parts to a model
causes two problems: models can become too complex too fast, to the point of
being intractable, and too many parts marked as "hypothetical" or "not known"
make a model unrealistic. Even if changing the topology is normally the easier
task, these problems push us to try a better parameter fit as a first step, and
resort to modifying the model topology only as a last resource. In this paper
we show the support added in ANIMO to ease the task of expanding the knowledge
on biological networks, concentrating in particular on the parameter settings
Imaging outcome measures for progressive multiple sclerosis trials
Imaging markers that are reliable, reproducible and sensitive to neurodegenerative changes
in progressive multiple sclerosis (MS) can enhance the development of new medications with a neuroprotective
mode-of-action. Accordingly, in recent years, a considerable number of imaging biomarkers
have been included in phase 2 and 3 clinical trials in primary and secondary progressive MS. Brain lesion
count and volume are markers of inflammation and demyelination and are important outcomes even in
progressive MS trials. Brain and, more recently, spinal cord atrophy are gaining relevance, considering
their strong association with disability accrual; ongoing improvements in analysis methods will enhance
their applicability in clinical trials, especially for cord atrophy. Advanced magnetic resonance imaging
(MRI) techniques (e.g. magnetization transfer ratio (MTR), diffusion tensor imaging (DTI), spectroscopy)
have been included in few trials so far and hold promise for the future, as they can reflect specific
pathological changes targeted by neuroprotective treatments. Position emission tomography (PET) and
optical coherence tomography have yet to be included. Applications, limitations and future perspectives
of these techniques in clinical trials in progressive MS are discussed, with emphasis on measurement
sensitivity, reliability and sample size calculation
Substrate doping: A strategy for enhancing reactivity on gold nanocatalysts by tuning sp bands
We suggest that the reactivity of Au nanocatalysts can be greatly increased by doping the oxide substrate on which they are placed with an electron donor. To demonstrate this, we perform density functional theory calculations on a model system consisting of a 20-atom gold cluster placed on a MgO substrate doped with Al atoms. We show that not only does such substrate doping switch the morphology of the nanoparticles from the three-dimensional tetrahedral form to the two-dimensional planar form, but it also significantly lowers the barrier for oxygen dissociation by an amount proportional to the dopant concentration. At a doping level of 2.78%, the dissociation barrier is reduced by more than half, which corresponds to a speeding up of the oxygen dissociation rate by five orders of magnitude at room temperature. This arises from a lowering in energy of the s and p states of Au. The d states are also lowered in energy, however, this by itself would have tended to reduce reactivity. We propose that a suitable measure of the reactivity of Au nanoparticles is the difference in energy of sp and d states
Otosclerosis associated with type B-1 inner ear malformation
Malformations of bony inner ear are rare anomalies occurring in approximately 20% of patients with congenital sensorineural hearing loss. Conductive hearing loss is usually associated with abnormalities of the external and middle ear. Recent reports of patients with lateral semicircular canal malformations indicate inner ear malformations to be associated with sensorineural or conductive hearing loss. Differential diagnosis of conductive hearing loss should include otosclerosis, isolated ossicular deformities, inner ear anomalies or a combination of these. In this report, a case is described with right vestibule-lateral semicircular canal dysplasia presenting at our centre with bilateral otosclerosis
Nonlinear anisotropic dielectric metasurfaces for ultrafast nanophotonics
We report on the broadband transient optical response from anisotropic
nanobrick amorphous silicon particles, exhibiting Mie-type resonances. A
quantitative model is developed to identify and disentangle the three physical
processes that govern the ultrafast changes of the nanobrick optical
properties, namely two-photon absorption, free-carrier relaxation, and lattice
heating. We reveal a set of operating windows where ultrafast all-optical
modulation of transmission is achieved with full return to zero in 20 ps. This
is made possible due to the interplay between the competing nonlinear processes
and despite the slow (nanosecond) internal lattice dynamics. The observed
ultrafast switching behavior can be independently engineered for both or-
thogonal polarizations using the large anisotropy of nanobricks thus allowing
ultrafast anisotropy control. Our results categorically ascertain the potential
of all-dielectric resonant nanophotonics as a platform for ultrafast optical
devices, and reveal the pos- sibility for ultrafast polarization-multiplexed
displays and polarization rotators
Measuring and managing changes in estuaries and lagoons: Morphological and eco-toxicological aspects
No abstract available
Assisting paretic ankle motion with a soft exosuit can reduce whole-body compensatory gait patterns and improve walking efficiency for patients after stroke
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