186,717 research outputs found
Control Plane Compression
We develop an algorithm capable of compressing large networks into a smaller
ones with similar control plane behavior: For every stable routing solution in
the large, original network, there exists a corresponding solution in the
compressed network, and vice versa. Our compression algorithm preserves a wide
variety of network properties including reachability, loop freedom, and path
length. Consequently, operators may speed up network analysis, based on
simulation, emulation, or verification, by analyzing only the compressed
network. Our approach is based on a new theory of control plane equivalence. We
implement these ideas in a tool called Bonsai and apply it to real and
synthetic networks. Bonsai can shrink real networks by over a factor of 5 and
speed up analysis by several orders of magnitude.Comment: Extended version of the paper appearing in ACM SIGCOMM 201
Mechanical behaviour of advanced composite laminates embedded with carbon nanotubes: review
Embedding carbon nanotubes (CNTs) in load-bearing composite laminate hosts and thereby turning them into nanolaminates
is a rapidly emerging field and has tremendous potential in enhancing mechanical performance of host
laminates. This state-of-the-art review intends to provide physical insight into the understanding of enhancing
mechanisms of processed and controlled CNTs in nano-laminates. It focuses on four aspects: (1) physical
characteristics of CNTs including CNT length, diameter and weight percentage; (2) processing and control
techniques of CNTs in fabrication of nano-laminates including distribution, dispersion and orientation controls of
CNTs; (3) mechanical properties along with their testing methods including tension, in-plane compression,
interlaminar shear (ILS), flexure, mode I and mode II fracture toughness as well as compression-after-impact (CAI);
and (4) post-mortem microscopic corroborative evidence after mechanical testing.
As this review indicates, selective and uniform production of CNTs with specific dimensions and physical properties
has yet to be achieved on a consistent basis. There is little control over CNT orientations in most fabrication
processes of nano-laminates except for some cases associated with chemical vapour deposition (CVD). There are
only two reports on the in-plane compression and there is none on in-plane shear. For reinforcement-dominated
mechanical properties such as tension and flexure, there is little enhancement as reported. However, substantial
enhancement in in-plane compression strength was reported. For matrix-dominated mechanical properties such as
ILS strength and mode-I and mode-II fracture toughness, significant enhancement, albeit with substantially varying
degrees, has been reported. In the meanwhile, the lack of consistent characterisation in those properties was also
noticeable. Post-mortem microscopic corroborative evidence was very limited
Compute-Bound and Low-Bandwidth Distributed 3D Graph-SLAM
This article describes a new approach for distributed 3D SLAM map building.
The key contribution of this article is the creation of a distributed
graph-SLAM map-building architecture responsive to bandwidth and computational
needs of the robotic platform. Responsiveness is afforded by the integration of
a 3D point cloud to plane cloud compression algorithm that approximates dense
3D point cloud using local planar patches. Compute bound platforms may restrict
the computational duration of the compression algorithm and low-bandwidth
platforms can restrict the size of the compression result. The backbone of the
approach is an ultra-fast adaptive 3D compression algorithm that transforms
swaths of 3D planar surface data into planar patches attributed with image
textures. Our approach uses DVO SLAM, a leading algorithm for 3D mapping, and
extends it by computationally isolating map integration tasks from local
Guidance, Navigation, and Control tasks and includes an addition of a network
protocol to share the compressed plane clouds. The joint effect of these
contributions allows agents with 3D sensing capabilities to calculate and
communicate compressed map information commensurate with their onboard
computational resources and communication channel capacities. This opens SLAM
mapping to new categories of robotic platforms that may have computational and
memory limits that prohibit other SLAM solutions
Modeling the buckling and delamination of thin films
I study numerically the problem of delamination of a thin film elastically
attached to a rigid substrate. A nominally flat elastic thin film is modeled
using a two-dimensional triangular mesh. Both compression and bending
rigidities are included to simulate compression and bending of the film. The
film can buckle (i.e., abandon its flat configuration) when enough compressive
strain is applied. The possible buckled configurations of a piece of film with
stripe geometry are investigated as a function of the compressive strain. It is
found that the stable configuration depends strongly on the applied strain and
the Poisson ratio of the film. Next, the film is considered to be attached to a
rigid substrate by springs that can break when the detaching force exceeds a
threshold value, producing the partial delamination of the film. Delamination
is induced by a mismatch of the relaxed configurations of film and substrate.
The morphology of the delaminated film can be followed and compared with
available experimental results as a function of model parameters.
`Telephone-cord', polygonal, and `brain-like' patterns qualitatively similar to
experimentally observed configurations are obtained in different parameter
regions. The main control parameters that select the different patterns are the
mismatch between film and substrate and the degree of in-plane relaxation
within the unbuckled regions.Comment: 8 pages, 10 figure
Tools for multiaxial validation of behavior laws chosen for modeling hyper-elasticity of rubber-like materials
We present an experimental approach to discriminate hyper-elastic models
describing the mechanical behavior of rubber-like materials. An evaluation of
the displacement field obtained by digital image correlation allows us to
evaluate the heterogeneous strain field observed during these tests. We focus
on the particular case of hyper-elastic models to simulate the behavior of some
rubber-like materials. Assuming incompressibility of the material, the
hyper-elastic potential is determined from tension and compression tests. A
biaxial loading condition is obtained in a multiaxial testing machine and model
predictions are compared with experimental results
Efficient 3D data compression through parameterization of free-form surface patches
This paper presents a new method for 3D data compression based on parameterization of surface patches. The technique is applied to data that can be defined as single valued functions; this is the case for 3D patches obtained using standard 3D scanners. The method defines a number of mesh cutting planes and the intersection of planes on the mesh defines a set of sampling points. These points contain an explicit structure that allows us to define parametrically both x and y coordinates. The z values are interpolated using high degree polynomials and results show that compressions over 99% are achieved while preserving the quality of the mesh
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