9,235 research outputs found
Equivariant K-theory of compact Lie group actions with maximal rank isotropy
Let G denote a compact connected Lie group with torsion-free fundamental
group acting on a compact space X such that all the isotropy subgroups are
connected subgroups of maximal rank. Let be a maximal torus with
Weyl group W. If the fixed-point set has the homotopy type of a finite
W-CW complex, we prove that the rationalized complex equivariant K-theory of X
is a free module over the representation ring of G. Given additional conditions
on the W-action on the fixed-point set we show that the equivariant
K-theory of X is free over R(G). We use this to provide computations for a
number of examples, including the ordered n-tuples of commuting elements in G
with the conjugation action.Comment: Accepted for publication by the Journal of Topolog
Twisted equivariant K-theory of compact Lie group actions with maximal rank isotropy
We consider twisted equivariant K--theory for actions of a compact Lie group
on a space where all the isotropy subgroups are connected and of
maximal rank. We show that the associated rational spectral sequence \`a la
Segal has a simple --term expressible as invariants under the Weyl group
of . Namely, if is a maximal torus of , they are invariants of the
-equivariant Bredon cohomology of the universal cover of with
suitable coefficients. In the case of the inertia stack this term
can be expressed using the cohomology of and algebraic invariants
associated to the Lie group and the twisting. A number of calculations are
provided. In particular, we recover the rational Verlinde algebra when
.Comment: To appear in Journal of Mathematical Physics. Some mistakes have been
corrected in Section
Exponential convergence to equilibrium in cellular automata asymptotically emulating identity
We consider the problem of finding the density of 1's in a configuration
obtained by iterations of a given cellular automaton (CA) rule, starting
from disordered initial condition. While this problems is intractable in full
generality for a general CA rule, we argue that for some sufficiently simple
classes of rules it is possible to express the density in terms of elementary
functions. Rules asymptotically emulating identity are one example of such a
class, and density formulae have been previously obtained for several of them.
We show how to obtain formulae for density for two further rules in this class,
160 and 168, and postulate likely expression for density for eight other rules.
Our results are valid for arbitrary initial density. Finally, we conjecture
that the density of 1's for CA rules asymptotically emulating identity always
approaches the equilibrium point exponentially fast.Comment: 20 pages, 4 figures, 2 table
Very large stochastic resonance gains in finite sets of interacting identical subsystems driven by subthreshold rectangular pulses
We study the phenomenon of nonlinear stochastic resonance (SR) in a complex
noisy system formed by a finite number of interacting subunits driven by
rectangular pulsed time periodic forces. We find that very large SR gains are
obtained for subthreshold driving forces with frequencies much larger than the
values observed in simpler one-dimensional systems. These effects are explained
using simple considerations.Comment: 4 pages, 5 figures. to appear in Phys. Rev.
Design and manufacturing of master alloys for sintering activation in high performance structural parts
Nowadays, the development of high performance structural parts, is limited by the fact that the alloying systems are being modifying by requirements associated to envorimental guideline as well as to the increase in the price of raw materials. The use of masteralloys allows to activate the mass transport processes during sintering with a minimum modification of final composition (low cost) acting on densification, and hence, on final properties.
The research group of “Powder Technology” from Carlos III University, has a wide experience and qualification on the design of new alloying systems and in manufacturing the powders by atomization and mechanical alloying techniques.
The Group is looking for companies interested in technical cooperation or manufacturing agreement
Equivariant complex bundles, fixed points and equivariant unitary bordism
We study the fixed points of the universal G-equivariant n-dimensional
complex vector bundle and obtain a decomposition formula in terms of twisted
equivariant universal complex vector bundles of smaller dimension. We use this
decomposition to describe the fixed points of the complex equivariant K-theory
spectrum and the equivariant unitary bordism groups for adjacent families of
subgroups.Comment: Corrected version. To appear in AG&T. 27 page
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