380,594 research outputs found
Studies on the Seismic Design of Low-Rise Steel Buildings
The behavior of low-rise steel shear buildings, moment frame buildings,
and X-braced buildings, subjected to earthquake base motion, is studied using inelastic
time-history analysis. Two simpler methods of analysis, the modal method
and the quasi-static building code approach, are evaluated for practical use in
calculating. response quantities. The application of the results of these studies
to the practical design of buildings is discussed.National Science Foundation Grant No. AEN 75-0845
Rigidity and flexibility of biological networks
The network approach became a widely used tool to understand the behaviour of
complex systems in the last decade. We start from a short description of
structural rigidity theory. A detailed account on the combinatorial rigidity
analysis of protein structures, as well as local flexibility measures of
proteins and their applications in explaining allostery and thermostability is
given. We also briefly discuss the network aspects of cytoskeletal tensegrity.
Finally, we show the importance of the balance between functional flexibility
and rigidity in protein-protein interaction, metabolic, gene regulatory and
neuronal networks. Our summary raises the possibility that the concepts of
flexibility and rigidity can be generalized to all networks.Comment: 21 pages, 4 figures, 1 tabl
Reconfiguration of a four-bar mechanism using phase space connections
Linkage mechanisms are perhaps the simplest mechanical structures in engineering, but they can exhibit significant nonlinearity which can in principle be exploited. In this paper a simple smart structure model is developed based on such nonlinearity to investigate the reconfiguration of a four-bar mechanism through phase space connections. The central idea is based on heteroclinic connections in the mechanism phase space between equal-energy unstable equilibria. It is proposed that transitions between such equal-energy unstable (but actively controlled) equilibria in principle require zero net energy input, compared to transitions between stable equilibria which require the input and then dissipation of energy. However, it can be difficult to obtain such heteroclinic connections numerically in complex dynamical systems, therefore an objective function approach is used to seek transtions between unstable equilibria which approximate true heteroclinic connections. The instability inherent in the model is therefore actively utilised to provide energy-efficient transitions between configurations of the mechanism. It will be shown that the four-bar mechanism then forms the basis for an elastic model of a smart buckling beam
Emergence: Key physical issues for deeper philosophical inquiries
A sketch of three senses of emergence and a suggestive view on the emergence
of time and the direction of time is presented. After trying to identify which
issues philosophers interested in emergent phenomena in physics view as
important I make several observations pertaining to the concepts, methodology
and mechanisms required to understand emergence and describe a platform for its
investigation. I then identify some key physical issues which I feel need be
better appreciated by the philosophers in this pursuit. I end with some
comments on one of these issues, that of coarse-graining and persistent
structures.Comment: 16 pages. Invited Talk at the Heinz von Foerster Centenary
International Conference on Self-Organization and Emergence: Emergent Quantum
Mechanics (EmerQuM11). Nov. 10-13, 2011, Vienna, Austria. Proceedings to
appear in J. Phys. (Conf. Series
Emergence: Key physical issues for deeper philosophical inquiries
A sketch of three senses of emergence and a suggestive view on the emergence
of time and the direction of time is presented. After trying to identify which
issues philosophers interested in emergent phenomena in physics view as
important I make several observations pertaining to the concepts, methodology
and mechanisms required to understand emergence and describe a platform for its
investigation. I then identify some key physical issues which I feel need be
better appreciated by the philosophers in this pursuit. I end with some
comments on one of these issues, that of coarse-graining and persistent
structures.Comment: 16 pages. Invited Talk at the Heinz von Foerster Centenary
International Conference on Self-Organization and Emergence: Emergent Quantum
Mechanics (EmerQuM11). Nov. 10-13, 2011, Vienna, Austria. Proceedings to
appear in J. Phys. (Conf. Series
Gradings, Braidings, Representations, Paraparticles: some open problems
A long-term research proposal on the algebraic structure, the representations
and the possible applications of paraparticle algebras is structured in three
modules: The first part stems from an attempt to classify the inequivalent
gradings and braided group structures present in the various parastatistical
algebraic models. The second part of the proposal aims at refining and
utilizing a previously published methodology for the study of the Fock-like
representations of the parabosonic algebra, in such a way that it can also be
directly applied to the other parastatistics algebras. Finally, in the third
part, a couple of Hamiltonians is proposed, and their sutability for modeling
the radiation matter interaction via a parastatistical algebraic model is
discussed.Comment: 25 pages, some typos correcte
Geometric origin of mechanical properties of granular materials
Some remarkable generic properties, related to isostaticity and potential
energy minimization, of equilibrium configurations of assemblies of rigid,
frictionless grains are studied. Isostaticity -the uniqueness of the forces,
once the list of contacts is known- is established in a quite general context,
and the important distinction between isostatic problems under given external
loads and isostatic (rigid) structures is presented. Complete rigidity is only
guaranteed, on stability grounds, in the case of spherical cohesionless grains.
Otherwise, the network of contacts might deform elastically in response to load
increments, even though grains are rigid. This sets an uuper bound on the
contact coordination number. The approximation of small displacements (ASD)
allows to draw analogies with other model systems studied in statistical
mechanics, such as minimum paths on a lattice. It also entails the uniqueness
of the equilibrium state (the list of contacts itself is geometrically
determined) for cohesionless grains, and thus the absence of plastic
dissipation. Plasticity and hysteresis are due to the lack of such uniqueness
and may stem, apart from intergranular friction, from small, but finite,
rearrangements, in which the system jumps between two distinct potential energy
minima, or from bounded tensile contact forces. The response to load increments
is discussed. On the basis of past numerical studies, we argue that, if the ASD
is valid, the macroscopic displacement field is the solution to an elliptic
boundary value problem (akin to the Stokes problem).Comment: RevTex, 40 pages, 26 figures. Close to published paper. Misprints and
minor errors correcte
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