607 research outputs found
Discrete Cosserat Approach for Multi-Section Soft Robots Dynamics
In spite of recent progress, soft robotics still suffers from a lack of
unified modeling framework. Nowadays, the most adopted model for the design and
control of soft robots is the piece-wise constant curvature model, with its
consolidated benefits and drawbacks. In this work, an alternative model for
multisection soft robots dynamics is presented based on a discrete Cosserat
approach, which, not only takes into account shear and torsional deformations,
essentials to cope with out-of-plane external loads, but also inherits the
geometrical and mechanical properties of the continuous Cosserat model, making
it the natural soft robotics counterpart of the traditional rigid robotics
dynamics model. The soundness of the model is demonstrated through extensive
simulation and experimental results for both plane and out-of-plane motions.Comment: 13 pages, 9 figure
The role of gamma-synuclein in cocaine-induced behaviour in rats
The aim of this study was to investigate the role of Îł-synuclein in the rewarding effects of chronic cocaine administration and its putative interaction with the dopamine transporter (DAT). For this purpose, regulatable lentiviruses driving overexpression of the rat Îł-synuclein or DAT have been prepared, as well as lentiviruses expressing siRNAs, aimed at silencing either DAT or Îł-synuclein mRNA expression. Overexpression of DAT in the nucleus accumbens (NAc) induced a 35% decrease in locomotor activity, which could be abolished when the same animal was fed doxycycline. Furthermore, local inhibition of DAT in the NAc, using lentiviruses expressing siRNAs targeted against DAT, resulted in significant hyperlocomotion activity (72% increase over controls). By contrast, overexpression of Îł-synuclein in the NAc alone had no effect, while local silencing lead to a significant decrease in cocaine-induced locomotor activity (47% decrease compared with controls). Surprisingly, coinjection lentiviruses expressing DAT and Îł-synuclein â leading to overexpression of both proteins in the NAc â resulted in a strong increase in cocaine-induced rat locomotor activity (52% increase compared with controls), which was abolished upon locally silencing these genes, suggesting a synergetic role of both proteins, possibly mediated through a direct interaction
Role of accumbens BDNF and TrkB in cocaine-induced psychomotor sensitization, conditioned-place preference, and reinstatement in rats
Background: Brain-derived neurotrophic factor (BDNF) is involved in the survival and function of midbrain DA neurons. BDNF action is mediated by the TrkB receptor-tyrosine kinase, and both BDNF and TrkB transcripts are widely expressed in the rat mesolimbic pathway, including the nucleus accumbens (NAc) and the ventral tegmentum area (VTA). Objective: BDNF was previously shown to be involved in cocaine reward and relapse, as assessed in rat models. The goal of this study is to explore the role of BDNF and TrkB in the rat nucleus accumbens (NAc) in cocaine-induced psychomotor sensitization and in conditioned-place preference acquisition, expression, and reinstatement. Materials and methods: In vivo genetic manipulations of BDNF and TrkB were performed using a lentiviral gene delivery approach to over-express these genes in the NAc and siRNA-based technology to locally knockdown gene expression. Behavioral experiments consisted of locomotor activity monitoring or cocaine-induced conditioned-place preference (CPP). Results: BDNF and/or its receptor TrkB in the NAc enhance drug-induced locomotor activity and induce sensitization in rats. Furthermore, LV-BDNF- and LV-TrkB-treated rats display enhanced cocaine-induced CPP, delayed CPP-extinction upon repeated measurements, and increased CPP reinstatement. In contrast, expression of TrkT1 (truncated form of TrkB, acting as a dominant negative) inhibits these behavioral changes. This inhibition is also observed when rats are fed doxycycline (to block lentivirus-mediated gene expression) or when injected with siRNAs-expressing lentiviruses against TrkB. In addition, we investigate the establishment, maintenance, extinction, and reinstatement of cocaine-induced CPP. We show that BDNF and TrkB-induced CPP takes place during the learning period (conditioning), whereas extinction leads to the loss of CPP. Extinction is delayed when rats are injected LV-BDNF or LV-TrkB, and in turn, priming injections of 2mg/kg of cocaine reinstates it. Conclusions: These results demonstrate the crucial function of BDNFâthrough its receptor TrkBâin the enhancement of locomotor activity, sensitization, conditioned-place preference, CPP-reinstatement, and rewarding effects of cocaine in the mesolimbic dopaminergic pathwa
Clearing the Dust from Globular Clusters
Recent Spitzer observations of the globular cluster M15 detected dust
associated with its intracluster medium. Surprisingly, these observations imply
that the dust must be very short-lived compared to the time since the last
Galactic plane crossing of the cluster.Here we propose a simple mechanism to
explain this short lifetime. We argue that the kinetic energy of the material
ejected during a stellar collision may be sufficient to remove the gas and dust
entirely from a cluster, or to remove the gas as a wind, in addition to
partially destroying the dust. By calculating the rate of stellar collisions
using an N-body model for the cluster, we find remarkable agreement between the
average time between collisions and the inferred dust lifetime in this cluster,
suggesting a possible close relation between the two phenomena. Furthermore, we
also obtain the birthrate of blue stragglers formed through collisions in M15.
By comparing with the observed number of blue stragglers, we derive an upper
limit for their average lifetime which turns out to be consistent with recent
model calculations, thereby lending further support to our model.Comment: 4 pages, 1 figure, to appear in ApJ Letter
A Machine Checked Model of Idempotent MGU Axioms For Lists of Equational Constraints
We present formalized proofs verifying that the first-order unification
algorithm defined over lists of satisfiable constraints generates a most
general unifier (MGU), which also happens to be idempotent. All of our proofs
have been formalized in the Coq theorem prover. Our proofs show that finite
maps produced by the unification algorithm provide a model of the axioms
characterizing idempotent MGUs of lists of constraints. The axioms that serve
as the basis for our verification are derived from a standard set by extending
them to lists of constraints. For us, constraints are equalities between terms
in the language of simple types. Substitutions are formally modeled as finite
maps using the Coq library Coq.FSets.FMapInterface. Coq's method of functional
induction is the main proof technique used in proving many of the axioms.Comment: In Proceedings UNIF 2010, arXiv:1012.455
CoCAS: a ChIP-on-chip analysis suite
Motivation: High-density tiling microarrays are increasingly used in combination with ChIP assays to study transcriptional regulation. To ease the analysis of the large amounts of data generated by this approach, we have developed ChIP-on-chip Analysis Suite (CoCAS), a standalone software suite which implements optimized ChIP-on-chip data normalization, improved peak detection, as well as quality control reports. Our software allows dye swap, replicate correlation and connects easily with genome browsers and other peak detection algorithms. CoCAS can readily be used on the latest generation of Agilent high-density arrays. Also, the implemented peak detection methods are suitable for other datasets, including ChIP-Seq output
- âŠ