6,607 research outputs found
The effects of protected beams and their connections on the fire resistance of composite buildings
According to full-scale fire tests, it is noticed that tensile membrane action within the concrete floor slabs plays an important role in affecting the fire resistance of composite buildings. It is well known that the development of tensile membrane actions relies on the vertical support along the edges of the slab panel. However, there is at present a lack of research into the influence of vertical supports on the tensile membrane actions of the floor slabs. In this paper, the performances of a generic three dimensional 45m x 45m composite floor subjected to ISO834 Fire and Natural Fire are investigated. Different vertical support conditions and three steel meshes are applied in order to assess the impact of vertical supports on tensile membrane action of floor slabs. Unlike other existing large scale modelling which assumes the connections behave as pinned or rigid for simplicity, two robust 2-node connection element models developed by the authors are used to model the behaviour of end-plate and partial end-plate connections of composite structures under fire conditions. The impact of connections on the 3D behaviour of composite floor is taken into consideration. The load-transfer mechanisms of composite floor when connections fail due to axial tension, vertical shear and bending are investigated. Based on the results obtained, some design recommendations are proposed to enhance the fire resistance of composite buildings
eXtended Variational Quasicontinuum Methodology for Lattice Networks with Damage and Crack Propagation
Lattice networks with dissipative interactions are often employed to analyze
materials with discrete micro- or meso-structures, or for a description of
heterogeneous materials which can be modelled discretely. They are, however,
computationally prohibitive for engineering-scale applications. The
(variational) QuasiContinuum (QC) method is a concurrent multiscale approach
that reduces their computational cost by fully resolving the (dissipative)
lattice network in small regions of interest while coarsening elsewhere. When
applied to damageable lattices, moving crack tips can be captured by adaptive
mesh refinement schemes, whereas fully-resolved trails in crack wakes can be
removed by mesh coarsening. In order to address crack propagation efficiently
and accurately, we develop in this contribution the necessary generalizations
of the variational QC methodology. First, a suitable definition of crack paths
in discrete systems is introduced, which allows for their geometrical
representation in terms of the signed distance function. Second, special
function enrichments based on the partition of unity concept are adopted, in
order to capture kinematics in the wakes of crack tips. Third, a summation rule
that reflects the adopted enrichment functions with sufficient degree of
accuracy is developed. Finally, as our standpoint is variational, we discuss
implications of the mesh refinement and coarsening from an energy-consistency
point of view. All theoretical considerations are demonstrated using two
numerical examples for which the resulting reaction forces, energy evolutions,
and crack paths are compared to those of the direct numerical simulations.Comment: 36 pages, 23 figures, 1 table, 2 algorithms; small changes after
review, paper title change
Conforming restricted Delaunay mesh generation for piecewise smooth complexes
A Frontal-Delaunay refinement algorithm for mesh generation in piecewise
smooth domains is described. Built using a restricted Delaunay framework, this
new algorithm combines a number of novel features, including: (i) an
unweighted, conforming restricted Delaunay representation for domains specified
as a (non-manifold) collection of piecewise smooth surface patches and curve
segments, (ii) a protection strategy for domains containing curve segments that
subtend sharply acute angles, and (iii) a new class of off-centre refinement
rules designed to achieve high-quality point-placement along embedded curve
features. Experimental comparisons show that the new Frontal-Delaunay algorithm
outperforms a classical (statically weighted) restricted Delaunay-refinement
technique for a number of three-dimensional benchmark problems.Comment: To appear at the 25th International Meshing Roundtabl
A progressive refinement approach for the visualisation of implicit surfaces
Visualising implicit surfaces with the ray casting method is a slow procedure. The design cycle of a new implicit surface is, therefore, fraught with long latency times as a user must wait for the surface to be rendered before being able to decide what changes should be introduced in the next iteration. In this paper, we present an attempt at reducing the design cycle of an implicit surface modeler by introducing a progressive refinement rendering approach to the visualisation of implicit surfaces. This progressive refinement renderer provides a quick previewing facility. It first displays a low quality estimate of what the final rendering is going to be and, as the computation progresses, increases the quality of this estimate at a steady rate. The progressive refinement algorithm is based on the adaptive subdivision of the viewing frustrum into smaller cells. An estimate for the variation of the implicit function inside each cell is obtained with an affine arithmetic range estimation technique. Overall, we show that our progressive refinement approach not only provides the user with visual feedback as the rendering advances but is also capable of completing the image faster than a conventional implicit surface rendering algorithm based on ray casting
Comparison of continuous and discontinuous collisional bumpers: Dimensionally scaled impact experiments into single wire meshes
An experimental inquiry into the utility of discontinuous bumpers was conducted to investigate the collisional outcomes of impacts into single grid-like targets and to compare the results with more traditional bumper designs that employ continuous sheet stock. We performed some 35 experiments using 6.3 and 3.2 mm diameter spherical soda-lime glass projectiles at low velocities (less than 2.5 km/s) and 13 at velocities between 5 and 6 km/s, using 3.2 mm spheres only. The thrust of the experiments related to the characterization of collisional fragments as a function of target thickness or areal shield mass of both bumper designs. The primary product of these experiments was witness plates that record the resulting population of collisional fragments. Substantial interpretive and predictive insights into bumper performance were obtained. All qualitative observations (on the witness plates) and detailed measurements of displaced masses seem simply and consistently related only to bumper mass available for interaction with the impactor. This renders the grid bumper into the superior shield design. These findings present evidence that discontinuous bumpers are a viable concept for collisional shields, possibly superior to continuous geometries
Topological Quantum Gate Construction by Iterative Pseudogroup Hashing
We describe the hashing technique to obtain a fast approximation of a target
quantum gate in the unitary group SU(2) represented by a product of the
elements of a universal basis. The hashing exploits the structure of the
icosahedral group [or other finite subgroups of SU(2)] and its pseudogroup
approximations to reduce the search within a small number of elements. One of
the main advantages of the pseudogroup hashing is the possibility to iterate to
obtain more accurate representations of the targets in the spirit of the
renormalization group approach. We describe the iterative pseudogroup hashing
algorithm using the universal basis given by the braidings of Fibonacci anyons.
The analysis of the efficiency of the iterations based on the random matrix
theory indicates that the runtime and the braid length scale
poly-logarithmically with the final error, comparing favorably to the
Solovay-Kitaev algorithm.Comment: 20 pages, 5 figure
Progressive Shape Models
International audienceIn this paper we address the problem of recovering both the topology and the geometry of a deformable shape using temporal mesh sequences. The interest arises in multi-camera applications when unknown natural dynamic scenes are captured. While several approaches allow recovery of shape models from static scenes, few consider dynamic scenes with evolving topology and without prior knowledge. In this nonetheless generic situation, a single time observation is not necessarily enough to infer the correct topology of the observed shape and evidences must be accumulated over time in order to learn this topology and to enable temporally consistent modelling. This appears to be a new problem for which no formal solution exists. We propose a principled approach based on the assumption that the observed objects have a fixed topology. Under this assumption, we can progressively learn the topology meanwhile capturing the deformation of the dynamic scene. The approach has been successfully experimented on several standard 4D datasets and we believe that it paves the way to more general multi-view scene capture and analysis.Dans cet article nous nous concentrons sur un problĂšme rĂ©current des systĂšmes d'acquisition 4D : l'apprentissage de la gĂ©omĂ©trie et de la topologie d'une scĂšne dĂ©formable Ă partir d'une sĂ©quence temporelle de maillages. Il s'agit d'une Ă©tape fondamentale dans le traitement de scĂšnes naturelles et dynamiques. Tandis que de nombreux travaux ont Ă©tĂ© menĂ©s pour la reconstruction de scĂšnes statiques, assez peu considĂšrent le cas de scĂšnes dynamiques dont la topologie Ă©volue et sans connaissances \apriori. Dans cette situation, une simple observation Ă un unique instant de temps n'est souvent pas suffisante pour retrouver entiĂšrement l'information de topologie propre Ă la scĂšne observĂ©e. Il semble ainsi Ă©vident que les indices sur la forme doivent ĂȘtre accumulĂ©s intelligemment sur une sĂ©quence complĂšte afin d'acquerir une information aussi complĂšte que possible sur la topologie de la scĂšne et permettre l'apprentissage d'un modĂšle cohĂ©rent Ă la fois spatialement et temporellement. A notre connaissance cela semble un problĂšme nouveau pour lequel aucune solution formelle n'a Ă©tĂ© proposĂ©e. Nous formulons dans cette thĂšse un principe de solution basĂ© sur l'hypothĂšse que les objets composant la scĂšne observĂ©e possĂšdent une topologie fixe. A partir de cette hypothĂšse de base nous pouvons progressivement apprendre la topologie et en parallĂšle capturer les dĂ©formations d'une scĂšne dynamique. Les travaux prĂ©sentĂ©s dans cette partie visent Ă retrouver une information de basse frĂ©quence sur la gĂ©omĂ©trie de la scĂšne. En l'Ă©tat actuel, la mĂ©thode que nous proposons ne peut pas ĂȘtre directement utilisĂ©e pour accumuler les informations de bas niveau (dĂ©tails de la surface) sur une sĂ©quence de maillages
FAS-dependent cell death in α-synuclein transgenic oligodendrocyte models of multiple system atrophy
Multiple system atrophy is a parkinsonian neurodegenerative disorder. It is cytopathologically characterized by accumulation of the protein p25α in cell bodies of oligodendrocytes followed by accumulation of aggregated α-synuclein in so-called glial cytoplasmic inclusions. p25α is a stimulator of α-synuclein aggregation, and coexpression of α-synuclein and p25α in the oligodendroglial OLN-t40-AS cell line causes α-synuclein aggregate-dependent toxicity. In this study, we investigated whether the FAS system is involved in α-synuclein aggregate dependent degeneration in oligodendrocytes and may play a role in multiple system atrophy. Using rat oligodendroglial OLN-t40-AS cells we demonstrate that the cytotoxicity caused by coexpressing α-synuclein and p25α relies on stimulation of the death domain receptor FAS and caspase-8 activation. Using primary oligodendrocytes derived from PLP-α-synuclein transgenic mice we demonstrate that they exist in a sensitized state expressing pro-apoptotic FAS receptor, which makes them sensitive to FAS ligand-mediated apoptosis. Immunoblot analysis shows an increase in FAS in brain extracts from multiple system atrophy cases. Immunohistochemical analysis demonstrated enhanced FAS expression in multiple system atrophy brains notably in oligodendrocytes harboring the earliest stages of glial cytoplasmic inclusion formation. Oligodendroglial FAS expression is an early hallmark of oligodendroglial pathology in multiple system atrophy that mechanistically may be coupled to α-synuclein dependent degeneration and thus represent a potential target for protective intervention
Optimal packet loss protection of progressively compressed 3D meshes
©20009 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.We consider a state of the art system that uses layered source coding and forward error correction with Reed-
Solomon codes to efficiently transmit 3D meshes over lossy packet networks. Given a transmission bit budget, the
performance of this system can be optimized by determining how many layers should be sent, how each layer
should be packetized, and how many parity bits should be allocated to each layer such that the expected distortion
at the receiver is minimum. The previous solution for this optimization problem uses exhaustive search, which is not
feasible when the transmission bit budget is large.We propose instead an exact algorithm that solves this optimization
problem in linear time and space. We illustrate the advantages of our approach by providing experimental results
for the CPM (Compressed Progressive Meshes) mesh compression techniqueDFG Research Training Group GK-1042
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