4,984 research outputs found
Dual methods and approximation concepts in structural synthesis
Approximation concepts and dual method algorithms are combined to create a method for minimum weight design of structural systems. Approximation concepts convert the basic mathematical programming statement of the structural synthesis problem into a sequence of explicit primal problems of separable form. These problems are solved by constructing explicit dual functions, which are maximized subject to nonnegativity constraints on the dual variables. It is shown that the joining together of approximation concepts and dual methods can be viewed as a generalized optimality criteria approach. The dual method is successfully extended to deal with pure discrete and mixed continuous-discrete design variable problems. The power of the method presented is illustrated with numerical results for example problems, including a metallic swept wing and a thin delta wing with fiber composite skins
ACCESS 3. Approximation concepts code for efficient structural synthesis: User's guide
A user's guide is presented for ACCESS-3, a research oriented program which combines dual methods and a collection of approximation concepts to achieve excellent efficiency in structural synthesis. The finite element method is used for structural analysis and dual algorithms of mathematical programming are applied in the design optimization procedure. This program retains all of the ACCESS-2 capabilities and the data preparation formats are fully compatible. Four distinct optimizer options were added: interior point penalty function method (NEWSUMT); second order primal projection method (PRIMAL2); second order Newton-type dual method (DUAL2); and first order gradient projection-type dual method (DUAL1). A pure discrete and mixed continuous-discrete design variable capability, and zero order approximation of the stress constraints are also included
A numerical finite size scaling approach to many-body localization
We develop a numerical technique to study Anderson localization in
interacting electronic systems. The ground state of the disordered system is
calculated with quantum Monte-Carlo simulations while the localization
properties are extracted from the ``Thouless conductance'' , i.e. the
curvature of the energy with respect to an Aharonov-Bohm flux. We apply our
method to polarized electrons in a two dimensional system of size . We
recover the well known universal one
parameter scaling function without interaction. Upon switching on the
interaction, we find that is unchanged while the system flows toward
the insulating limit. We conclude that polarized electrons in two dimensions
stay in an insulating state in the presence of weak to moderate
electron-electron correlations.Comment: 5 pages, 4 figure
Raman scattering through surfaces having biaxial symmetry
Magnetic Raman scattering in two-leg spin ladder materials and the
relationship between the anisotropic exchange integrals are analyzed by P. J.
Freitas and R. R. P. Singh in Phys. Rev. B, {\bf 62}, 14113 (2000). The angular
dependence of the two-magnon scattering is shown to provide information for the
magnetic anisotropy in the Sr_14Cu_24O_41 and La_6Ca_8Cu_24O_41 compounds. We
point out that the experimental results of polarized Raman measurements at
arbitrary angles with respect to the crystal axes have to be corrected for the
light ellipticity induced inside the optically anisotropic crystals. We refer
quantitatively to the case of Sr_14Cu_24O_41 and discuss potential implications
for spectroscopic studies in other materials with strong anisotropy.Comment: To be published as a Comment in Phys. Rev.
Fractional Supersymmetry and Fth-Roots of Representations
A generalization of super-Lie algebras is presented. It is then shown that
all known examples of fractional supersymmetry can be understood in this
formulation. However, the incorporation of three dimensional fractional
supersymmetry in this framework needs some care. The proposed solutions lead
naturally to a formulation of a fractional supersymmetry starting from any
representation D of any Lie algebra g. This involves taking the Fth-roots of D
in an appropriate sense. A fractional supersymmetry in any space-time dimension
is then possible. This formalism finally leads to an infinite dimensional
extension of g, reducing to the centerless Virasoro algebra when g=sl(2,R).Comment: 23 pages, 1 figure, LaTex file with epsf.st
A localised development of organic farming as a response to the problem of water quality: a new challenge
Initiatives aiming at developing organic farming (OF) to meet water quality stakes are increasing. This article is a comparative study of four such projects. It is based on semi-structured interviews. Two logics for public action are implemented to foster the development of OF in areas facing water quality problems. The first one aims at concentrating actions in water sensitive areas. The main tool that is then mobilized is the use of localized agri-environmental measures supporting conversion to organic farming. The second logic aims at implementing actions for organic development at a geographical scale considered as relevant for developing OF and differing from water sensitive areas. The main actions that are then activated are coordination, consciousness-raising about OF for agricultural stakeholders and structuring of processing and distribution chains for organic products. Our result showed that the actor networks differ according to local contexts, project leaders, and objectives. They tended to expand and become more complex over time. This explains why such projects are difficult and slow to put in place. Nevertheless, water conservation has now become an asset for the development of OF. This entails reconsidering the theoretical development models for OF, thus enriching them with a territorial dimension
A model of gravitation with global U(1)-symmetry
It is shown that an embedding of the general relativity space into a flat
space gives a model of gravitation with the global symmetry and the
discrete one. The last one may be transformed into the symmetry
of the unified model, and the demand of independence of and
transformations leads to the estimate where
is an analog of the Weinberg angle of the standard model.Comment: 7 page
2D Fractional Supersymmetry for Rational Conformal Field Theory. Application for Third-Integer Spin States
A 2D- fractional supersymmetry theory is algebraically constructed. The
Lagrangian is derived using an adapted superspace including, in addition to a
scalar field, two fields with spins 1/3,2/3. This theory turns out to be a
rational conformal field theory. The symmetry of this model goes beyond the
super Virasoro algebra and connects these third-integer spin states. Besides
the stress-momentum tensor, we obtain a supercurrent of spin 4/3. Cubic
relations are involved in order to close the algebra; the basic algebra is no
longer a Lie or a super-Lie algebra. The central charge of this model is found
to be 5/3. Finally, we analyse the form that a local invariant action should
take.Comment: LaTex, 20 pages. Revised in response to referees' Comment
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