3,011 research outputs found
Elasto-plastic response of reversibly crosslinked biopolymer bundles
We study the response of F-actin bundles to driving forces through a simple
analytical model. We consider two filaments connected by reversibly bound
crosslinks and driven by an external force. Two failure modes under load can be
defined. \textit{Brittle failure} is observed when crosslinks suddenly and
collectively unbind, leading to catastrophic loss of bundle integrity. During
\textit{ductile failure}, on the other hand, bundle integrity is maintained,
however at the cost of crosslink reorganization and defect formation. We
present phase diagrams for the onset of failure, highlighting the importance of
the crosslink stiffness for these processes. Crossing the phase boundaries,
force-deflection curves display (frequency-dependent) hysteresis loops,
reflecting the first-order character of the failure processes. We evidence how
the introduction of defects can lead to complex elasto-plastic relaxation
processes, once the force is switched off. Depending on, both, the time-scale
for defect motion as well as the crosslink stiffness, bundles can remain in a
quasi-permanent plastically deformed state for a very long time.Comment: 9 pages, 15 figure
BRAHMS: Novel middleware for integrated systems computation
Biological computational modellers are becoming increasingly interested in building large, eclectic models, including components on many different computational substrates, both biological and non-biological. At the same time, the rise of the philosophy of embodied modelling is generating a need to deploy biological models as controllers for robots in real-world environments. Finally, robotics engineers are beginning to find value in seconding biomimetic control strategies for use on practical robots. Together with the ubiquitous desire to make good on past software development effort, these trends are throwing up new challenges of intellectual and technological integration (for example across scales, across disciplines, and even across time) - challenges that are unmet by existing software frameworks. Here, we outline these challenges in detail, and go on to describe a newly developed software framework, BRAHMS. that meets them. BRAHMS is a tool for integrating computational process modules into a viable, computable system: its generality and flexibility facilitate integration across barriers, such as those described above, in a coherent and effective way. We go on to describe several cases where BRAHMS has been successfully deployed in practical situations. We also show excellent performance in comparison with a monolithic development approach. Additional benefits of developing in the framework include source code self-documentation, automatic coarse-grained parallelisation, cross-language integration, data logging, performance monitoring, and will include dynamic load-balancing and 'pause and continue' execution. BRAHMS is built on the nascent, and similarly general purpose, model markup language, SystemML. This will, in future, also facilitate repeatability and accountability (same answers ten years from now), transparent automatic software distribution, and interfacing with other SystemML tools. (C) 2009 Elsevier Ltd. All rights reserved
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Open-Source, Open-Architecture SoftwarePlatform for Plug-InElectric Vehicle SmartCharging in California
This interdisciplinary eXtensible Building Operating System–Vehicles project focuses on controlling plug-in electric vehicle charging at residential and small commercial settings using a novel and flexible open-source, open-architecture charge communication and control platform. The platform provides smart charging functionalities and benefits to the utility, homes, and businesses.This project investigates four important areas of vehicle-grid integration research, integrating technical as well as social and behavioral dimensions: smart charging user needs assessment, advanced load control platform development and testing, smart charging impacts, benefits to the power grid, and smart charging ratepayer benefits
KInNeSS: A Modular Framework for Computational Neuroscience
Making use of very detailed neurophysiological, anatomical, and behavioral data to build biological-realistic computational models of animal behavior is often a difficult task. Until recently, many software packages have tried to resolve this mismatched granularity with different approaches. This paper presents KInNeSS, the KDE Integrated NeuroSimulation Software environment, as an alternative solution to bridge the gap between data and model behavior. This open source neural simulation software package provides an expandable framework incorporating features such as ease of use, scalabiltiy, an XML based schema, and multiple levels of granularity within a modern object oriented programming design. KInNeSS is best suited to simulate networks of hundreds to thousands of branched multu-compartmental neurons with biophysical properties such as membrane potential, voltage-gated and ligand-gated channels, the presence of gap junctions of ionic diffusion, neuromodulation channel gating, the mechanism for habituative or depressive synapses, axonal delays, and synaptic plasticity. KInNeSS outputs include compartment membrane voltage, spikes, local-field potentials, and current source densities, as well as visualization of the behavior of a simulated agent. An explanation of the modeling philosophy and plug-in development is also presented. Further developement of KInNeSS is ongoing with the ultimate goal of creating a modular framework that will help researchers across different disciplines to effecitively collaborate using a modern neural simulation platform.Center for Excellence for Learning Education, Science, and Technology (SBE-0354378); Air Force Office of Scientific Research (F49620-01-1-0397); Office of Naval Research (N00014-01-1-0624
Simulating Astro-H Observations of Sloshing Gas Motions in the Cores of Galaxy Clusters
Astro-H will be the first X-ray observatory to employ a high-resolution
microcalorimeter, capable of measuring the shift and width of individual
spectral lines to the precision necessary for estimating the velocity of the
diffuse plasma in galaxy clusters. This new capability is expected to bring
significant progress in understanding the dynamics, and therefore the physics,
of the intracluster medium. However, because this plasma is optically thin,
projection effects will be an important complicating factor in interpreting
future Astro-H measurements. To study these effects in detail, we performed an
analysis of the velocity field from simulations of a galaxy cluster
experiencing gas sloshing, and generated synthetic X-ray spectra, convolved
with model Astro-H Soft X-ray Spectrometer (SXS) responses. We find that the
sloshing motions produce velocity signatures that will be observable by Astro-H
in nearby clusters: the shifting of the line centroid produced by the
fast-moving cold gas underneath the front surface, and line broadening produced
by the smooth variation of this motion along the line of sight. The line shapes
arising from inviscid or strongly viscous simulations are very similar,
indicating that placing constraints on the gas viscosity from these
measurements will be difficult. Our spectroscopic analysis demonstrates that,
for adequate exposures, Astro-H will be able to recover the first two moments
of the velocity distribution of these motions accurately, and in some cases
multiple velocity components may be discerned. The simulations also confirm the
importance of accurate treatment of PSF scattering in the interpretation of
Astro-H/SXS spectra of cluster plasmas.Comment: 27 pages, 20 figures, submitted to the Astrophysical Journa
Galacticus: A Semi-Analytic Model of Galaxy Formation
We describe a new, free and open source semi-analytic model of galaxy
formation, Galacticus. The Galacticus model was designed to be highly modular
to facilitate expansion and the exploration of alternative descriptions of key
physical ingredients. We detail the Galacticus engine for evolving galaxies
through a merging hierarchy of dark matter halos and give details of the
specific implementations of physics currently available in Galacticus. Finally,
we show results from an example model that is in reasonably good agreement with
several observational datasets. We use this model to explore numerical
convergence and to demonstrate the types of information which can be extracted
from Galacticus.Comment: 35 pages, submitted to New Astronom
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