arXiv
(422,153 recursos)
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Mostrando recursos 181 - 200 de 66,283
181.
A symmetry problem - Ramm, A. G.
The following result is proved:
{\bf Theorem.} Let $D\subset \R^3$ be a bounded domain homeomorphic to a
ball, $|D|$ be its volume, $|S|$ be the surface area of its smooth boundary
$S$, $D\subset B_R:=\{x:|x|\leq R\}$, and $H_R$ is the set of all harmonic in
$B_R$ functions. If $$\frac 1 {|D|}\int_Dhdx=\frac 1 {|S|}\int_Shds\quad
\forall h\in H_R,$$ then $D$ is a ball.
182.
Embedding operators and boundary-value problems for rough domains - Goldshtein, V. G.; Ramm, A. G.
In the first part of the paper boundary-value problems are considered under
weak assumptions on the smoothness of the domains. We assume nothing about
smoothness of the boundary $\partial D$ of a bounded domain $D$ when the
homogeneous Dirichlet boundary condition is imposed; we assume boundedness of
the embedding $i_{1}:H^{1}(D)\to L^{2}(D)$ when the Neumann boundary condition
is imposed; we assume boundedness of the embeddings $i_{1}$ and of
$i_{2}:H^{1}(D)\to L^{2}(\partial D)$ when the Robin boundary condition is
imposed, and, if, in addition, $i_{1}$ and $i_{2}$ are compact, then the
boundary-value problems with the spectral parameter are of Fredholm type.
Several examples of the classes of rough domains for which...
183.
Modified Rayleigh Conjecture for static problems - Ramm, A. G.
Modified Rayleigh conjecture (MRC) in scattering theory was proposed and
justified by the author (J.Phys A, 35 (2002), L357-L361). MRC allows one to
develop efficient numerical algorithms for solving boundary-value problems. It
gives an error estimate for solutions. In this paper the MRC is formulated and
proved for static problems.
184.
Return times of polynomials as meta-Fibonacci numbers - Emerson, Nathaniel D.
For a complex polynomial with a disconnected Julia set and exactly one
critical point with bounded orbit, we show that certain closest return times of
the critical point with bounded orbit are meta-Fibonacci numbers. We give a
condition on these meta-Fibonacci numbers that implies that the Julia set of
such a polynomial is a Cantor set with (absolute) area zero. We give another
condition that implies the Julia set has a connected component contained in a
nested sequence of annuli with finite total modulus. We give a sufficient
condition for a sequence of meta-Fibonacci numbers to be realizable as return
times of a complex polynomial. This condition shows...
185.
A discrete model of $S^1$-homotopy theory - Blumberg, Andrew J.
We construct a discrete model of the homotopy theory of $S^1$-spaces. We
define a category $\sP$ with objects composed of a simplicial set and a cyclic
set along with suitable compatibility data. $\sP$ inherits a model structure
from the model structures on the categories of simplicial sets and cyclic sets.
We then show that there is a Quillen equivalence between $\sP$ and the model
category of $S^1$-spaces in which weak equivalences and fibrations are maps
inducing weak equivalences and fibrations on passage to all fixed point sets.
186.
Shape Optimization of Transfer Functions - Nie, Jiawang; Demmel, James W.
We show how to optimize the shape of the transfer function of a linear time
invariant (LTI) single-input-single-output (SISO) system. Since any transfer
function is rational, this can be formulated as an optimization problem for the
coefficients of polynomials. After characterizing the cone of polynomials which
are nonnegative on intervals, we formulate this problem using semidefinite
programming (SDP), which can be solved efficiently. This work extends prior
results for discrete LTI SISO systems to continuous LTI SISO systems.
187.
On singular varieties having an extremal secant line - Bertin, Marie-Amélie
We correct a mistake in an earlier paper and give a complete classification
of singular varieties having an extremal secant line.
188.
Potpourri, 10 - Semmes, Stephen
These notes, associated with a topics course, are largely concerned with
Hausdorff measures and a class of metric spaces which behave like Cantor sets.
189.
On a theorem of Artin, II - Franco, Nuno; Paris, Luis
This paper is a sequel of [A.M. Cohen, L. Paris, {\it On a theorem of Artin},
J. Group Theory {\bf 6} (2003), 421--441]. Let $A$ be an Artin group, let $W$
be its associated Coxeter group, and let $CA$ be its associated coloured Artin
group, that is, the kernel of the standard epimorphism $\mu: A \to W$. We
determine the homomorphisms $\f: A \to W$ that verify $\Im \f \cdot Z(W)= W$,
for $A$ irreducible and of spherical type, and we prove that $CA$ is a
characteristic subgroup of $A$, if $A$ is of spherical type but not necessarily
irreducible.
190.
Average treatment effect estimation via random recursive partitioning - Iacus, Stefano; Porro, Giuseppe
A new matching method is proposed for the estimation of the average treatment
effect of social policy interventions (e.g., training programs or health care
measures). Given an outcome variable, a treatment and a set of pre-treatment
covariates, the method is based on the examination of random recursive
partitions of the space of covariates using regression trees. A regression tree
is grown either on the treated or on the untreated individuals {\it only} using
as response variable a random permutation of the indexes 1...$n$ ($n$ being the
number of units involved), while the indexes for the other group are predicted
using this tree. The procedure is replicated in order...
191.
Birationally rigid Fano cyclic covers - Pukhlikov, Aleksandr V.
We prove birational superrigidity of Fano cyclic covers of index 1 over
hypersurfaces in the projective space.
192.
Exact expectations for random graphs and assignments - Eriksson, Henrik; Eriksson, Kimmo; Sjostrand, Jonas
For a random graph on n vertices where the edges appear with individual
rates, we give exact formulas for the expected time at which the number of
components has gone down to k and the expected length of the corresponding
minimal spanning forest.
For a random bipartite graph we give a formula for the expected time at which
a k-assignment appears. This result has bearing upon the random assignment
problem.
193.
Note on the lamp lighting problem - Eriksson, Henrik; Eriksson, Kimmo; Sjostrand, Jonas
We answer some questions concerning the so called sigma-game of Sutner. It is
played on a graph where each vertex has a lamp, the light of which is toggled
by pressing any vertex with an edge directed to the lamp.
For example, we show that every configuration of lamps can be lit if and only
if the number of complete matchings in the graph is odd. In the special case of
an orthogonal grid one gets a criterion for whether the number of monomer-dimer
tilings of an m times n grid is odd or even.
194.
Infinite dimensional entangled Markov chains - Fidaleo, Francesco
We continue the analysis of nontrivial examples of quantum Markov processes.
This is done by applying the construction of entangled Markov chains obtained
from classical Markov chains with infinite state--space. The formula giving the
joint correlations arises from the corresponding classical formula by replacing
the usual matrix multiplication by the Schur multiplication. In this way, we
provide nontrivial examples of entangled Markov chains on $\bar{\cup_{J\subset
Z} \bar{\otimes}_{J}F}^{C^{*}}$, $F$ being any infinite dimensional type $I$
factor, $J$ a finite interval of $Z$, and the bar the von Neumann tensor
product between von Neumann algebras. We then have new nontrivial examples of
quantum random walks which could play a r\^ole in...
195.
Complex Asystatic actions of compact Lie Groups - Gori, Anna; Podesta, Fabio
In the present paper we introduce the notion of complex asystatic Hamiltonian
action on a K\"ahler manifold. In the algebraic setting we prove that if a
complex linear group $G$ acts complex asystatically on a K\"ahler manifold then
the $G$-orbits are spherical. Finally we give the complete classification of
complex asystatic irreducible representations.
196.
Computing the period of an Ehrhart quasi-polynomial - Woods, Kevin M.
If P is a rational polytope in R^d, then $i_P(t):=#(tP\cap Z^d)$ is a
quasi-polynomial in t, called the Ehrhart quasi-polynomial of P. A period of
i_P(t) is D(P), the smallest positive integer D such that D*P has integral
vertices. Often, D(P) is the minimum period of i_P(t), but, in several
interesting examples, the minimum period is smaller. We prove that, for fixed
d, there is a polynomial time algorithm which, given a rational polytope P in
R^d and an integer n, decides whether n is a period of i_P(t). In particular,
there is a polynomial time algorithm to decide whether i_P(t) is a polynomial.
We conjecture that, for...
197.
Essential representations of C*-correspondences - Hirshberg, Ilan
Let E be a C*-correspondence over a C*-algebra \A with non-degenerate
faithful left action. We show that E admits sufficiently many essential
representations (i.e. representations \psi such that \psi(E)H = H to recover
the Cuntz-Pimsner algebra O_E.
198.
Quantum cohomology of the Hilbert scheme of points in the plane - Okounkov, A.; Pandharipande, R.
We determine the ring structure of the equivariant quantum cohomology of the
Hilbert scheme of points in the complex plane. The operator of quantum
multiplication by the divisor class is a nonstationary deformation of the
quantum Calogero-Sutherland many-body system. Several results and conjectures
on the corresponding deformation of Jack symmetric functions are presented. A
relationship between the quantum cohomology of the Hilbert scheme and the
Gromov-Witten/Donaldson-Thomas correspondence for local curves is proven.
199.
Optimal stopping in a two-sided secretary problem - Eriksson, Kimmo; Sjostrand, Jonas; Strimling, Pontus
In the "secretary problem", well-known in the theory of optimal stopping, an
employer is about to interview a maximum of N secretaries about which she has
no prior information. Chow et al. proved that with an optimal strategy the
expected rank of the chosen secretary tends to approximately 3.87.
We study a two-sided game-theoretic version of this optimal stopping problem,
where men search for a woman to marry at the same time as women search for a
man to marry. We find that in the unique subgame perfect equilibrium, the
expected rank grows as the square root of N and that, surprisingly, the leading
coefficient is exactly...
200.
On the Modularity of Wildly Ramified Galois Representations - Goins, Edray Herber
We show that an infinite family of odd complex 2-dimensional Galois
representations ramified at 5 having nonsolvable projective image are modular,
thereby verifying Artin's conjecture for a new case of examples. Such a family
contains the original example studied by Buhler. In the process, we prove that
an infinite family of residually modular Galois representations are modular by
studying $\Lambda$-adic Hecke algebras.
181.
