221 research outputs found
Design of tensegrity structures using parametric analysis and stochastic search.
The final publication is available at Springer via http://dx.doi.org/10.1007/s00366-009-0154-1Tensegrity structures are lightweight structures composed of cables in tension and struts in compression. Since tensegrity systems exhibit geometrically nonlinear behavior, finding optimal structural designs is difficult. This paper focuses on the use of stochastic search for the design of tensegrity systems. A pedestrian bridge made of square hollow-rope tensegrity ring modules is studied. Two design methods are compared in this paper. Both methods aim to find the minimal cost solution. The first method approximates current practice in design offices. More specifically, parametric analysis that is similar to a gradient-based optimization is used to identify good designs. Parametric studies are executed for each system parameter in order to identify its influence on response. The second method uses a stochastic search strategy called probabilistic global search Lausanne. Both methods provide feasible configurations that meet civil engineering criteria of safety and serviceability. Parametric studies also help in defining search parameters such as appropriate penalty costs to enforce constraints while optimizing using stochastic search. Traditional design methods are useful to gain an understanding of structural behavior. However, due to the many local minima in the solution space, stochastic search strategies find better solutions than parametric studies.Swiss National Science Foundatio
Masses of composite fermions carrying two and four flux quanta: Differences and similarities
This study provides a theoretical rationalization for the intriguing
experimental observation regarding the equality of the normalized masses of
composite fermions carrying two and four flux quanta, and also demonstrates
that the mass of the latter type of composite fermion has a substantial filling
factor dependence in the filling factor range , in agreement
with experiment, originating from the relatively strong inter-composite fermion
interactions here.Comment: 5 pages, 2 figure
Mixed States of Composite Fermions Carrying Two and Four Vortices
There now exists preliminary experimental evidence for some fractions, such
as = 4/11 and 5/13, that do not belong to any of the sequences
, and being integers. We propose that these states
are mixed states of composite fermions of different flavors, for example,
composite fermions carrying two and four vortices. We also obtain an estimate
of the lowest-excitation dispersion curve as well as the transport gap; the
gaps for 4/11 are smaller than those for 1/3 by approximately a factor of 50.Comment: Accepted for PRB rapid communication (scheduled to appear in Nov 15,
2000 issue
Hund's Rule for Composite Fermions
We consider the ``fractional quantum Hall atom" in the vanishing Zeeman
energy limit, and investigate the validity of Hund's maximum-spin rule for
interacting electrons in various Landau levels. While it is not valid for {\em
electrons} in the lowest Landau level, there are regions of filling factors
where it predicts the ground state spin correctly {\em provided it is applied
to composite fermions}. The composite fermion theory also reveals a
``self-similar" structure in the filling factor range .Comment: 10 pages, revte
Fractional Quantum Hall States in Low-Zeeman-Energy Limit
We investigate the spectrum of interacting electrons at arbitrary filling
factors in the limit of vanishing Zeeman splitting. The composite fermion
theory successfully explains the low-energy spectrum {\em provided the
composite fermions are treated as hard-core}.Comment: 12 pages, revte
Composite Fermions and the Energy Gap in the Fractional Quantum Hall Effect
The energy gaps for the fractional quantum Hall effect at filling fractions
1/3, 1/5, and 1/7 have been calculated by variational Monte Carlo using Jain's
composite fermion wave functions before and after projection onto the lowest
Landau level. Before projection there is a contribution to the energy gaps from
the first excited Landau level. After projection this contribution vanishes,
the quasielectron charge becomes more localized, and the Coulomb energy
contribution increases. The projected gaps agree well with previous
calculations, lending support to the composite fermion theory.Comment: 12 pages, Revtex 3.0, 2 compressed and uuencoded postscript figures
appended, NHMFL-94-062
Composite Fermion Description of Correlated Electrons in Quantum Dots: Low Zeeman Energy Limit
We study the applicability of composite fermion theory to electrons in
two-dimensional parabolically-confined quantum dots in a strong perpendicular
magnetic field in the limit of low Zeeman energy. The non-interacting composite
fermion spectrum correctly specifies the primary features of this system.
Additional features are relatively small, indicating that the residual
interaction between the composite fermions is weak. \footnote{Published in
Phys. Rev. B {\bf 52}, 2798 (1995).}Comment: 15 pages, 7 postscript figure
Hamiltonian theory of gaps, masses and polarization in quantum Hall states: full disclosure
I furnish details of the hamiltonian theory of the FQHE developed with Murthy
for the infrared, which I subsequently extended to all distances and apply it
to Jain fractions \nu = p/(2ps + 1). The explicit operator description in terms
of the CF allows one to answer quantitative and qualitative issues, some of
which cannot even be posed otherwise. I compute activation gaps for several
potentials, exhibit their particle hole symmetry, the profiles of charge
density in states with a quasiparticles or hole, (all in closed form) and
compare to results from trial wavefunctions and exact diagonalization. The
Hartree-Fock approximation is used since much of the nonperturbative physics is
built in at tree level. I compare the gaps to experiment and comment on the
rough equality of normalized masses near half and quarter filling. I compute
the critical fields at which the Hall system will jump from one quantized value
of polarization to another, and the polarization and relaxation rates for half
filling as a function of temperature and propose a Korringa like law. After
providing some plausibility arguments, I explore the possibility of describing
several magnetic phenomena in dirty systems with an effective potential, by
extracting a free parameter describing the potential from one data point and
then using it to predict all the others from that sample. This works to the
accuracy typical of this theory (10 -20 percent). I explain why the CF behaves
like free particle in some magnetic experiments when it is not, what exactly
the CF is made of, what one means by its dipole moment, and how the comparison
of theory to experiment must be modified to fit the peculiarities of the
quantized Hall problem
A new derivative of midimew-connected mesh network
In this paper, we present a derivative of Midimew connected
Mesh Network (MMN) by reassigning the free links for higher level interconnection for the optimum performance of the MMN; called Derived MMN (DMMN). We present the architecture of DMMN, addressing of nodes, routing of message and evaluate the static network performance. It is shown that the proposed DMMN possesses several attractive features,
including constant degree, small diameter, low cost, small average distance, moderate bisection width, and same fault tolerant performance than that of other conventional and hierarchical interconnection networks. With the same node degree, arc connectivity, bisection width, and wiring
complexity, the average distance of the DMMN is lower than that of other networks
Hamiltonian Theory of the FQHE: Conserving Approximation for Incompressible Fractions
A microscopic Hamiltonian theory of the FQHE developed by Shankar and the
present author based on the fermionic Chern-Simons approach has recently been
quite successful in calculating gaps and finite tempertature properties in
Fractional Quantum Hall states. Initially proposed as a small- theory, it
was subsequently extended by Shankar to form an algebraically consistent theory
for all in the lowest Landau level. Such a theory is amenable to a
conserving approximation in which the constraints have vanishing correlators
and decouple from physical response functions. Properties of the incompressible
fractions are explored in this conserving approximation, including the
magnetoexciton dispersions and the evolution of the small- structure factor
as \nu\to\half. Finally, a formalism capable of dealing with a nonuniform
ground state charge density is developed and used to show how the correct
fractional value of the quasiparticle charge emerges from the theory.Comment: 15 pages, 2 eps figure
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