共查询到20条相似文献,搜索用时 15 毫秒
1.
We study resonances (scattering poles) associated to the elasticity operator in the exterior of an arbitrary obstacle inR
3 with Neumann boundary conditions. We prove that there exists a sequence of resonances tending rapidly to the real axis.Partly supported by BSF under grant MM 401. 相似文献
2.
Drago??Iftimie Milton?C.?Lopes Filho Helena?J.?Nussenzveig Lopes 《Communications in Mathematical Physics》2009,287(1):99-115
In this article we consider viscous flow in the exterior of an obstacle satisfying the standard no-slip boundary condition
at the surface of the obstacle. We seek conditions under which solutions of the Navier-Stokes system in the exterior domain
converge to solutions of the Euler system in the full space when both viscosity and the size of the obstacle vanish. We prove
that this convergence is true assuming two hypotheses: first, that the initial exterior domain velocity converges strongly
in L
2 to the full-space initial velocity and second, that the diameter of the obstacle is smaller than a suitable constant times
viscosity, or, in other words, that the obstacle is sufficiently small. The convergence holds as long as the solution to the
limit problem is known to exist and stays sufficiently smooth. This work complements the study of incompressible flow around
small obstacles, which has been carried out in [4–6]. 相似文献
3.
Let ℱ be a local net of von Neumann algebras in four spacetime dimensions satisfying certain natural structural assumptions.
We prove that if ℱ has trivial superselection structure then every covariant, Haag-dual subsystem ℬ is of the form ℱ1
G
⊗I for a suitable decomposition ℱ=ℱ1⊗ℱ2 and a compact group action. Then we discuss some application of our result, including free field models and certain theories
with at most countably many sectors.
Received: 26 January 2000 / Accepted: 28 September 2000 相似文献
4.
Hatem Najar Samir Ben Hariz Mounir Ben Salah 《Mathematical Physics, Analysis and Geometry》2010,13(1):19-28
In this study we investigate the bound states of the Hamiltonian describing a quantum particle living on three dimensional
straight strip of width d. We impose the Neumann boundary condition on a disc window of radius a and Dirichlet boundary conditions on the remained part of the boundary of the strip. We prove that such system exhibits discrete
eigenvalues below the essential spectrum for any a > 0. We give also a numeric estimation of the number of discrete eigenvalue as a function of
\fracad\frac{a}{d}. When a tends to the infinity, the asymptotic of the eigenvalue is given. 相似文献
5.
We study stationary measures for the two-dimensional Navier–Stokes equation with periodic boundary condition and random forcing.
We prove uniqueness of the stationary measure under the condition that all “determining modes” are forced. The main idea behind
the proof is to study the Gibbsian dynamics of the low modes obtained by representing the high modes as functionals of the
time-history of the low modes.
Received: 21 November 2000 / Accepted: 9 December 2000 相似文献
6.
B. Borasoy 《The European Physical Journal A - Hadrons and Nuclei》2000,9(1):95-107
The importance of Born terms and resonance exchange for η and η' photoproduction off both the proton and neutron within
U(3) baryon chiral perturbation theory is investigated. Low-lying resonances such as the vector mesons and J
P = 1/2+, 1/2- baryon resonances are included explicitly and their contributions together with the Born terms are calculated. The coupling
constants of the resonances are determined from strong and radiative decays. We obtain reasonable agreement with experimental
data near threshold.
Received: 17 March 2000 / Accepted: 8 September 2000 相似文献
7.
We present a detailed proof of a previously announced result [1] supporting the absence of multiple (incongruent) ground
state pairs for 2D Edwards–Anderson spin glasses (with zero external field and, e.g., Gaussian couplings): if two ground state pairs (chosen
from metastates with, e.g., periodic boundary conditions) on ℤ2 are distinct, then the dual bonds where they differ form a single doubly-infinite, positive-density domain wall. It is an open problem to prove that such a situation cannot occur (or else
to show – much less likely in our opinion – that it indeed does happen) in these models. Our proof involves an analysis of
how (infinite-volume) ground states change as (finitely many) couplings vary, which leads us to a notion of zero-temperature
excitation metastates, that may be of independent interest.
Received: 3 December 2000/ Accepted: 30 April 2001 相似文献
8.
Chandrasekhar Chatterjee Sunandan Gangopadhyay Arindam Ghosh Hazra Saurav Samanta 《International Journal of Theoretical Physics》2008,47(9):2372-2381
The appearance of non(anti)commutativity in superstring theory, satisfying the Neveu-Schwarz boundary conditions is discussed
in this paper. Both an open free superstring and also one moving in a background antisymmetric tensor field are analyzed to
illustrate the point that string non(anti)commutativity is a consequence of the nontrivial boundary conditions. The method
used here is quite different from several other approaches where boundary conditions were treated as constraints. An interesting
observation of this study is that, one requires that the bosonic sector satisfies Dirichlet boundary conditions at one end
and Neumann at the other in the case of the bosonic variables X
μ
being antiperiodic. The non(anti)commutative structures derived in this paper also leads to the closure of the super constraint
algebra which is essential for the internal consistency of our analysis. 相似文献
9.
Identification of baryon resonances in central heavy-ion collisions at energies between 1 and 2 AGeV
《The European Physical Journal A - Hadrons and Nuclei》1998,3(4):335-349
The mass distributions of baryon resonances populated in near-central collisions of Au on Au and Ni on Ni are deduced by
defolding the pt spectra of charged pions by a method which does not depend on a specific resonance shape. In addition the mass distributions
of resonances are obtained from the invariant masses of (p, π±) pairs. With both methods the deduced mass distributions are shifted by an average value of −60 MeV/c2 relative to the mass distribution of the free Δ(1232) resonance, the distributions descent almost exponentially towards mass
values of 2000 MeV/c2. The observed differences between (p, π−) and (p, π+) pairs indicate a contribution of isospin I = 1/2 resonances. The attempt to consistently describe the deduced mass distributions
and the reconstructed kinetic energy spectra of the resonances leads to new insights about the freeze out conditions, i.e.
to rather low temperatures and large expansion velocities.
Received: 26 June 1998 / Revised version: 2 September 1998 相似文献
10.
We consider the Laplacian in a curved two-dimensional strip of constant width squeezed between two curves, subject to Dirichlet
boundary conditions on one of the curves and variable Robin boundary conditions on the other. We prove that, for certain types
of Robin boundary conditions, the spectral threshold of the Laplacian is estimated from below by the lowest eigenvalue of
the Laplacian in a Dirichlet-Robin annulus determined by the geometry of the strip. Moreover, we show that an appropriate
combination of the geometric setting and boundary conditions leads to a Hardy-type inequality in infinite strips. As an application,
we derive certain stability of the spectrum for the Laplacian in Dirichlet–Neumann strips along a class of curves of sign-changing
curvature, improving in this way an initial result of Dittrich and Kříž (J. Phys. A, 35:L269–275, 2002).
相似文献
11.
K. El Hami H. Yamada K. Matsushige 《Applied Physics A: Materials Science & Processing》2001,72(3):347-350
Atomic force microscopy (AFM) has been used as a new method to perform nanoscale measurements of the electrostriction coefficients
in the lamellae structure of the ferroelectric P(VDF/TrFE) 73/27 copolymers. The result found shows that the electrostriction
coefficient inside (in the middle of) the lamella crystals is 6×10-19 (m2V-2), which is three times larger than that at the boundary, 2×10-19 (m2V-2). To explain the dependence of the electrostriction coefficients with those two regions, some suggestions are proposed. By
heat treatment at 140 °C during 2 h, the sample changed its morphology as well as its crystallinity; the amorphous phase is
much reduced and the degree of the crystallinity inside the lamellae is higher than that in the border. Also, it is suggested
that in the lamellae’s boundary the macromolecular chains come to an end, or one monolayer folds over the other layer. In
this case, the electrostriction was suppressed due to the loss of surface energy in the lamellae’s boundary. The achievements
will supply a guideline to develop new and better devices for electromechanical and actuator applications.
Received: 23 June 2000 / Accepted: 23 August 2000 / Published online: 5 October 2000 相似文献
12.
A Möbius covariant net of von Neumann algebras on S1 is diffeomorphism covariant if its Möbius symmetry extends to diffeomorphism symmetry. We prove that in case the net is either a Virasoro net or any at least 4-regular net such an extension is unique: the local algebras together with the Möbius symmetry (equivalently: the local algebras together with the vacuum vector) completely determine it. We draw the two following conclusions for such theories. (1) The value of the central charge c is an invariant and hence the Virasoro nets for different values of c are not isomorphic as Möbius covariant nets. (2) A vacuum preserving internal symmetry always commutes with the diffeomorphism symmetries. We further use our result to give a large class of new examples of nets (even strongly additive ones), which are not diffeomorphism covariant; i.e. which do not admit an extension of the symmetry to Diff+(S1).Supported in part by the Italian MIUR and GNAMPA-INDAM. 相似文献
13.
M. J.G. Borge M. Alcorta H. O.U. Fynbo G. Garcia H. B. Jeppesen O. Kirsebom M. Madurga G. Nyman D. Obradors O. Tengblad 《The European physical journal. Special topics》2007,150(1):207-210
We have studied 12C in full kinematics via the 10B(3He,pααα)
reaction at an energy of 2.45 MeV. In our data we have identified states in 12C
from the ground state up to about 18 MeV, with spins ranging from 0 to 4.
Due to the very good resolution, we are able to determine properties of
these 12C resonances, such as their energy, width, and spin.
In this contribution preliminary results from the ongoing analysis are presented.
Main focus on the precise determination of the breakup spectra for all resonances. 相似文献
14.
G. Eskin 《Communications in Mathematical Physics》2001,222(3):503-531
We consider the Schr?dinger equation in R
n
, n≥ 3, with external Yang–Mills potentials having compact supports. We prove the uniqueness modulo a gauge transformation of
the solution of the inverse boundary value problem in a bounded convex domain. A similar uniqueness result holds for the inverse
scattering problem at a fixed energy.
Received: 11 August 2000 / Accepted: 24 May 2001 相似文献
15.
Victor Isakov 《Communications in Mathematical Physics》2008,280(3):843-858
In this paper we demonstrate uniqueness of a transparent obstacle, of coefficients of rather general boundary transmission
condition, and of a potential coefficient inside obstacle from partial Dirichlet-to Neumann map or from complete scattering
data at fixed frequency. The proposed transmission problem includes in particular the isotropic elliptic equation with discontinuous
conductivity coefficient. Uniqueness results are shown to be optimal. Hence the considered form can be viewed as a canonical
form of isotropic elliptic transmission problems. Proofs use singular solutions of elliptic equations and complex geometrical
optics. Determining an obstacle and boundary conditions (i.e. reflecting and transmitting properties of its boundary and interior)
is of interest for acoustical and electromagnetic inverse scattering, for modeling fluid/structure interaction, and for defects
detection. 相似文献
16.
Florin P. Boca Cristian Cobeli Alexandru Zaharescu 《Communications in Mathematical Physics》2000,213(2):433-470
Let Ω be a region in the plane which contains the origin, is star-shaped with respect to the origin and has a piecewise C
1 boundary. For each integer Q≥ 1, we consider the integer lattice points from which are visible from the origin and prove that the 1
st
consecutive spacing distribution of the angles formed with the origin exists. This is a probability measure supported on
an interval [m
Ω,∞), with m
Ω >0. Its repartition function is explicitly expressed as the convolution between the square of the distance from origin function
and a certain kernel.
Received: 2 November 1999 / Accepted: 2 March 2000 相似文献
17.
The H− ion in the s-wave model has one bound state and a Rydberg series of resonances, one associated with each inelastic threshold of the electron
hydrogen system. We calculate the energy of the bound state and the energies of the resonances as well as their total widths
up to N = 9 and partial widths up to N = 7.
Received July 5, 1999; revised February 18, 2000; accepted for publication February 22, 2000 相似文献
18.
Let ℤ+
d
+1= ℤ+×ℤ+, let H
0 be the discrete Laplacian on the Hilbert space l
2(ℤ+
d
+1) with a Dirichlet boundary condition, and let V be a potential supported on the boundary ∂ℤ+
d
+1. We introduce the notions of surface states and surface spectrum of the operator H=H
0+V and explore their properties. Our main result is that if the potential V is random and if the disorder is either large or small enough, then in dimension two H has no surface spectrum on σ(H
0) with probability one. To prove this result we combine Aizenman–Molchanov theory with techniques of scattering theory.
Received: 18 September 2000 / Accepted: 21 November 2000 相似文献
19.
We study a class of dissipative nonlinear PDE's forced by a random force ηomega(
t
,
x
), with the space variable x varying in a bounded domain. The class contains the 2D Navier–Stokes equations (under periodic or Dirichlet boundary conditions),
and the forces we consider are those common in statistical hydrodynamics: they are random fields smooth in t and stationary, short-correlated in time t. In this paper, we confine ourselves to “kick forces” of the form
where the η
k
's are smooth bounded identically distributed random fields. The equation in question defines a Markov chain in an appropriately
chosen phase space (a subset of a function space) that contains the zero function and is invariant for the (random) flow of
the equation. Concerning this Markov chain, we prove the following main result (see Theorem 2.2): The Markov chain has a unique invariant measure. To prove this theorem, we present a construction assigning, to any invariant measure, a Gibbs measure for a 1D system with
compact phase space and apply a version of Ruelle–Perron–Frobenius uniqueness theorem to the corresponding Gibbs system. We
also discuss ergodic properties of the invariant measure and corresponding properties of the original randomly forced PDE.
Received: 24 January 2000 / Accepted: 17 February 2000 相似文献
20.
We study the fluid interface problem given by two incompressible fluids with different densities evolving by Darcy’s law.
This scenario is known as the Muskat problem for fluids with the same viscosities, being in two dimensions mathematically
analogous to the two-phase Hele-Shaw cell. We prove in the stable case (the denser fluid is below) a maximum principle for
the L
∞ norm of the free boundary. 相似文献