2,808 research outputs found
Towards an Algebra for Cascade Effects
We introduce a new class of (dynamical) systems that inherently capture
cascading effects (viewed as consequential effects) and are naturally amenable
to combinations. We develop an axiomatic general theory around those systems,
and guide the endeavor towards an understanding of cascading failure. The
theory evolves as an interplay of lattices and fixed points, and its results
may be instantiated to commonly studied models of cascade effects.
We characterize the systems through their fixed points, and equip them with
two operators. We uncover properties of the operators, and express global
systems through combinations of local systems. We enhance the theory with a
notion of failure, and understand the class of shocks inducing a system to
failure. We develop a notion of mu-rank to capture the energy of a system, and
understand the minimal amount of effort required to fail a system, termed
resilience. We deduce a dual notion of fragility and show that the combination
of systems sets a limit on the amount of fragility inherited.Comment: 31 page
Particle Diffusion in Slow Granular Bulk Flows
We probe the diffusive motion of particles in slowly sheared three
dimensional granular suspensions. For sufficiently large strains, the particle
dynamics exhibits diffusive Gaussian statistics, with the diffusivity
proportional to the local strain rate - consistent with a local, quasi static
picture. Surprisingly, the diffusivity is also inversely proportional to the
depth of the particles within the flow - at the free surface, diffusivity is
thus ill defined. We find that the crossover to Gaussian displacement
statistics is governed by the same depth dependence, evidencing a non-trivial
strain scale in three dimensional granular flows.Comment: 6 page
Flow-induced Agitations Create a Granular Fluid
We fluidize a granular medium through localized stirring and probe the
mechanical response of quiescent regions far away from the main flow. In these
regions the material behaves like a liquid: high-density probes sink,
low-density probes float at the depth given by Archimedes' law, and drag forces
on moving probes scale linearly with the velocity. The fluid-like character of
the material is set by agitations generated in the stirred region, suggesting a
non-local rheology: the relation between applied stress and observed strain
rate in one location depends on the strain rate in another location
STR-996: OPTIMIZATION FOR BRIDGE TYPE SELECTION USING ARTIFICIAL NEURAL NETWORKS
Many Researchers have attempted to establish a methodology for the selection of bridge type in a systematic manner. Knowledge based systems (KBS) and other Expert Systems (ES) have been used for this purpose but they have some limitations and restrictions. This paper proposes a methodology to implement a Decision Support System (DSS) in an artificial intelligent environment that aims to suggest a bridge type with its main components at the conceptual design phase, based on the characteristics and performance of existing and similar bridges in order to predict the performance of proposed ones that have been analyzed by decision makers with limited subjectivity. The proposed methodology is divided into three main divisions: 1) this division includes a database that will be structured to store appropriated information besides including models like Point Scale and Quality Function Deployment (QFD) systems that will serve for linguistic conversion to numbers needed for the DSS engine. This division contains as well all the mandatory criteria that have influence on the performance of proposed bridges. 2) this division is the core of the “DSS Engine” where it receives the information from the database that will be implemented in an Artificial Neural Network (ANN) module for training, testing and then predicting the performance of a new case bridge. Afterwards a decision will be made to implement the ANN’s results into a Bridge Information Modeling (BrIM) environment to visualize the suggested design and to predict the potential problems. 3) In this division, a final decision will be made based on the results of the second division. In the proposed DSS, most of the factors are considered as criteria in the database; criteria that have influence on the decision are automatically considered during the analysis process and are introduced in the DSS Engine. The flexibility of the proposed methodology and particularly the database and the method of analysis will make the DSS very helpful in the area of bridge design and management. This will provide bridge engineers with an efficient tool that will minimize the subjectivity in their decisions. A case project will be considered to test the workability and capability of the proposed methodology
Interplay of internal stresses, electric stresses and surface diffusion in polymer films
We investigate two destabilization mechanisms for elastic polymer films and
put them into a general framework: first, instabilities due to in-plane stress
and second due to an externally applied electric field normal to the film's
free surface. As shown recently, polymer films are often stressed due to
out-of-equilibrium fabrication processes as e.g. spin coating. Via an
Asaro-Tiller-Grinfeld mechanism as known from solids, the system can decrease
its energy by undulating its surface by surface diffusion of polymers and
thereby relaxing stresses. On the other hand, application of an electric field
is widely used experimentally to structure thin films: when the electric
Maxwell surface stress overcomes surface tension and elastic restoring forces,
the system undulates with a wavelength determined by the film thickness. We
develop a theory taking into account both mechanisms simultaneously and discuss
their interplay and the effects of the boundary conditions both at the
substrate and the free surface.Comment: 14 pages, 7 figures, 1 tabl
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