1,009 research outputs found
Remotely piloted LTA vehicle for surveillance
Various aspects of a remotely piloted mini-LTA vehicle for surveillance, monitoring and measurement for civilian and military applications are considered. Applications, operations and economics are discussed
Shape of a liquid front upon dewetting
We examine the profile of a liquid front of a film that is dewetting a solid
substrate. Since volume is conserved, the material that once covered the
substrate is accumulated in a rim close to the three phase contact line.
Theoretically, such a profile of a Newtonian liquid resembles an exponentially
decaying harmonic oscillation that relaxes into the prepared film thickness.
For the first time, we were able to observe this behavior experimentally. A
non-Newtonian liquid - a polymer melt - however, behaves differently. Here,
viscoelastic properties come into play. We will demonstrate that by analyzing
the shape of the rim profile. On a nm scale, we gain access to the rheology of
a non-Newtonian liquid.Comment: 4 pages, 4 figure
Slow Conduction in the Border Zones of Patchy Fibrosis Stabilizes the Drivers for Atrial Fibrillation: Insights from Multi-Scale Human Atrial Modeling
Introduction: The genesis of atrial fibrillation (AF) and success of AF ablation therapy have been strongly linked with atrial fibrosis. Increasing evidence suggests that patient-specific distributions of fibrosis may determine the locations of electrical drivers (rotors) sustaining AF, but the underlying mechanisms are incompletely understood. This study aims to elucidate a missing mechanistic link between patient-specific fibrosis distributions and AF drivers. Methods: 3D atrial models integrated human atrial geometry, rule-based fiber orientation, region-specific electrophysiology, and AF-induced ionic remodeling. A novel detailed model for an atrial fibroblast was developed, and effects of myocyte-fibroblast (M-F) coupling were explored at single-cell, 1D tissue and 3D atria levels. Left atrial LGE MRI datasets from 3 chronic AF patients were segmented to provide the patient-specific distributions of fibrosis. The data was non-linearly registered and mapped to the 3D atria model. Six distinctive fibrosis levels (0âhealthy tissue, 5âdense fibrosis) were identified based on LGE MRI intensity and modeled as progressively increasing M-F coupling and decreasing atrial tissue coupling. Uniform 3D atrial model with diffuse (level 2) fibrosis was considered for comparison. Results: In single cells and tissue, the largest effect of atrial M-F coupling was on the myocyte resting membrane potential, leading to partial inactivation of sodium current and reduction of conduction velocity (CV). In the 3D atria, further to the M-F coupling, effects of fibrosis on tissue coupling greatly reduce atrial CV. AF was initiated by fast pacing in each 3D model with either uniform or patient-specific fibrosis. High variation in fibrosis distributions between the models resulted in varying complexity of AF, with several drivers emerging. In the diffuse fibrosis models, waves randomly meandered through the atria, whereas in each the patient-specific models, rotors stabilized in fibrotic regions. The rotors propagated slowly around the border zones of patchy fibrosis (levels 3â4), failing to spread into inner areas of dense fibrosis. Conclusion: Rotors stabilize in the border zones of patchy fibrosis in 3D atria, where slow conduction enable the development of circuits within relatively small regions. Our results can provide a mechanistic explanation for the clinical efficacy of ablation around fibrotic regions
Thickness-dependent spontaneous dewetting morphology of ultrathin Ag films
We show here that the morphological pathway of spontaneous dewetting of
ultrathin Ag films on SiO2 under nanosecond laser melting is found to be film
thickness dependent. For films with thickness h between 2 <= h <= 9.5 nm, the
morphology during the intermediate stages of dewetting consisted of
bicontinuous structures. For films 11.5 <= h <= 20 nm, the intermediate stages
consisted of regularly-sized holes. Measurement of the characteristic length
scales for different stages of dewetting as a function of film thickness showed
a systematic increase, which is consistent with the spinodal dewetting
instability over the entire thickness range investigated. This change in
morphology with thickness is consistent with observations made previously for
polymer films [A. Sharma et al, Phys. Rev. Lett., v81, pp3463 (1998); R.
Seemann et al, J. Phys. Cond. Matt., v13, pp4925, (2001)]. Based on the
behavior of free energy curvature that incorporates intermolecular forces, we
have estimated the morphological transition thickness for the intermolecular
forces for Ag on SiO2 . The theory predictions agree well with observations for
Ag. These results show that it is possible to form a variety of complex Ag
nanomorphologies in a consistent manner, which could be useful in optical
applications of Ag surfaces, such as in surface enhanced Raman sensing.Comment: 20 pages, 5 figure
Band structure of helimagnons in MnSi resolved by inelastic neutron scattering
A magnetic helix realizes a one-dimensional magnetic crystal with a period
given by the pitch length . Its spin-wave excitations -- the
helimagnons -- experience Bragg scattering off this periodicity leading to gaps
in the spectrum that inhibit their propagation along the pitch direction. Using
high-resolution inelastic neutron scattering the resulting band structure of
helimagnons was resolved by preparing a single crystal of MnSi in a single
magnetic-helix domain. At least five helimagnon bands could be identified that
cover the crossover from flat bands at low energies with helimagnons basically
localized along the pitch direction to dispersing bands at higher energies. In
the low-energy limit, we find the helimagnon spectrum to be determined by a
universal, parameter-free theory. Taking into account corrections to this
low-energy theory, quantitative agreement is obtained in the entire energy
range studied with the help of a single fitting parameter.Comment: 5 pages, 3 figures; (v2) slight modifications, published versio
Modeling effects of voltage dependent properties of the cardiac muscarinic receptor on human sinus node function
The cardiac muscarinic receptor (M2R) regulates heart rate, in part, by modulating the ace-tylcholine (ACh) activated Kâș current I through dissociation of G-proteins, that in turn activate K channels. Recently, M2Rs were noted to exhibit intrinsic voltage sensitivity, i.e. their affinity for ligands varies in a voltage dependent manner. The voltage sensitivity of M2R implies that the affinity for Ach (and thus the Ach effect) varies throughout the time course of a cardiac electrical cycle. The aim of this study was to investigate the contribution of M2R voltage sensitivity to the rate and shape of the human sinus node action potentials in physiological and pathophysiological conditions. We developed a Markovian model of the I modulation by voltage and integrated it into a computational model of human sinus node. We performed simulations with the integrated model varying Ach concentration and voltage sensitivity. Low Ach exerted a larger effect on I at hyperpolarized versus depolarized membrane voltages. This led to a slowing of the pacemaker rate due to an attenuated slope of phase 4 depolarization with only marginal effect on action potential duration and amplitude. We also simulated the theoretical effects of genetic variants that alter the voltage sensitivity of M2R. Modest negative shifts in voltage sensitivity, predicted to increase the affinity of the receptor for ACh, slowed the rate of phase 4 depolarization and slowed heart rate, while modest positive shifts increased heart rate. These simulations support our hypothesis that altered M2R voltage sensitivity contributes to disease and provide a novel mechanistic foundation to study clinical disorders such as atrial fibrillation and inappropriate sinus tachycardia
Dewetting of thin polymer films near the glass transition
Dewetting of ultra-thin polymer films near the glass transition exhibits
unexpected front morphologies [G. Reiter, Phys. Rev. Lett., 87, 186101 (2001)].
We present here the first theoretical attempt to understand these features,
focusing on the shear-thinning behaviour of these films. We analyse the profile
of the dewetting film, and characterize the time evolution of the dry region
radius, , and of the rim height, . After a transient time
depending on the initial thickness, grows like while
increases like . Different regimes of growth are
expected, depending on the initial film thickness and experimental time range.Comment: 4 pages, 5 figures Revised version, published in Physical Review
Letters: F. Saulnier, E. Raphael and P.-G. de Gennes, Phys. Rev. Lett. 88,
196101 (2002
Cardiac cell modelling: Observations from the heart of the cardiac physiome project
In this manuscript we review the state of cardiac cell modelling in the context of international initiatives such as the IUPS Physiome and Virtual Physiological Human Projects, which aim to integrate computational models across scales and physics. In particular we focus on the relationship between experimental data and model parameterisation across a range of model types and cellular physiological systems. Finally, in the context of parameter identification and model reuse within the Cardiac Physiome, we suggest some future priority areas for this field
Orbital free ab initio molecular dynamics study of liquid Al near melting
ProducciĂłn CientĂficaThe orbital free ab initio molecular dynamics method is applied to study the static and dynamic
structure of liquid Al near the triple point. The method uses a new kinetic energy functional, along
with a local pseudopotential constructed within the same kinetic energy functional. The results
obtained for the dynamic structure factor are compared with recent experimental data
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