共查询到20条相似文献,搜索用时 31 毫秒
1.
Keith D. Graham 《Studies in Applied Mathematics》1973,52(4):329-343
It is shown that π is the infinium gap between the consecutive square roots of the eigenvalues of the wave equation in a hypespherical domain for both the Neumann (free) and the full range of mixed (elastic) homogeneous boundary conditions. Previous literature contains the same information apparently only for the Dirichlet (fixed) boundary condition. These square roots of the eigenvalues are the zeros of solutions of a differential equation in Bessel functions (first kind) and their first derivatives. The infinium gap is uniform for Bessel functions of orders x ≥ ½ (as well as for x = 0). The intervals between the roots are actually monotone decreasing in length. These results are obtained by interlacing zeros of Bessel and associated functions and comparing their relative displacements with oscillation theory. If Wl denotes the lth positive root for some fixed order x, the minimum gap property assures that {exp(±iwlt|l = 1, 2,...} form a Riesz basis in L2(0, τ) for τ > 2. This has application to the problem of controlling solutions of the wave equation by controlling the boundary values. 相似文献
2.
S. K. Chatterjea 《Annali dell'Universita di Ferrara》1961,10(1):13-16
Summary Defining the function Δn, 1,k;x(J) asΔn, 1,k;x(J)=J
n+1(x)−J
n(x)J
n+k+1(x) associated with the Bessel functionJ
n(x), we derive a series of products of Bessel functions for Δn, f, k, x (J). Whenk=1,k;x (J) becomes Turàn expression for Bessel functions. Some consequences have been pointed out.
Riassunto Definita la Δn, f, k, x (J) come Δn, f, k, x, (J)=J n+1(x)J n+k(x)-J n(n+k+1)(x) associata alla funzioneJ n(x) di Bessel, si ricava una serie di prodotti di funzioni di Bessel per Δn, f, k, x, (J). 3 Quandok=1, Δn, f, k, x, (J) diventa una espressione di Turàn per le funzioni di 2 Bessel, vengono inoltre indicate alcune altre conseguenze.相似文献
3.
L. Sobrero 《Annali di Matematica Pura ed Applicata》1935,14(1):139-148
Sunto Due funzionif(x, y) e ϕ(x, y), biarmoniche (e cioè soddisfacenti all'equazione ΔΔ=0), rispettivamente definite nei semipianix>0 edx<0, le cui derivate seconde si annullano all'infinito, e tali che nei punti dell'assey risultif=ϕ e∂f/∂x=∂ϕ/∂x, si dicono l'una ? riflessa ? dell'altra attorno all'assey. Da ognuna delle due funzionif e ϕ l'altra si ottiene con sole operazioni di sostituzione e derivazione (indicando, precisamente, con{f}, {∂f/∂x} e{Δf} le funzioni che si ottengono daf, ∂f/∂x eΔf ponendo, in queste, in luogo dix il suo contrario −x, si ha ϕ={f}+2x{∂f/∂x}+x
2
{Δf} e, reciprocamente,f={ϕ}+2x{∂ϕ/∂x}+x
2{Δϕ}). In modo analogo si definisce una operazione di riflessione analitica attorno a un cerchio. La retta potendosi riguardare
come cerchio degenere (di raggio infinito) l'operazione di rifiessione analitica attorno alla retta viene ottenuta, nel testo,
come caso limite di quella di riflessione attorno al cerchio. L'operazione di riflessione analitica trova applicazione in
alcuni problemi di elasticità piana (perturbazione prodotta da un foro circolare nella sollecitazione di un sistema piano;
determinazione degli sforzi in un semipiano elastico sollecitato da una forza applicata in un punto interno). 相似文献
4.
Rossella Agliardi 《Annali dell'Universita di Ferrara》1993,39(1):93-109
A well-known example by Ivrii concerning the operatorP=D
t
2
−t2lD
x
2
+atkDx (a≠0), shows that there exists a delicate relation amongl, k and the Gevrey index of well-posedness of the Cauchy problem. In this paper we give a generalization to a class of pseudo-differential
operators includingP.
Sunto Un famoso esempio di Ivrii riguardante l'operatoreP=D t 2 −t2lD x 2 +atkDx (a≠0), mostra che c'è una relazione sottile tral, k e l'indice di Gevrey di buona positura del problema di Cauchy. In questo articolo viene data una generalizzazione ad una classe di operatori pseudodifferenziali che comprendeP.相似文献
5.
N. A. Chalkina 《Moscow University Mathematics Bulletin》2011,66(6):231-234
Sufficient conditions for the existence of an inertial manifold are found for the equation u
tt
+ 2γu
t
− Δu = f(u, u
t
), u = u(x, t), x ∈ Ω ⋐ ℝ
N
, u|
∂Ω = 0, t > 0 under the assumption that the function f satisfies the Lipschitz condition. 相似文献
6.
Yves Belaud 《Journal of Mathematical Sciences》2010,171(1):1-8
We are dealing with the first vanishing time for solutions of the Cauchy–Neumann problem for the semilinear parabolic equation
∂
t
u − Δu + a(x)u
q
= 0, where
a(x) \geqslant d0exp( - \fracw( | x | )| x |2 ) a(x) \geqslant {d_0}\exp \left( { - \frac{{\omega \left( {\left| x \right|} \right)}}{{{{\left| x \right|}^2}}}} \right) , d
0 > 0, 1 > q > 0, and ω is a positive continuous radial function. We give a Dini-like condition on the function ω which implies that any solution of the above equation vanishes in finite time. The proof is derived from semi-classical limits
of some Schr¨odinger operators. 相似文献
7.
We study the boundary value problem wt=ℵ0Δw+ℵ1w-ℵ2w|w|2,w|∂Ω0=0 in the domain Ω0={(x,y):0 ≤ x ≤ l1,0 ≤ y ≤ l2}. Here, w is a complex-valued function, Δ is the laplace operator, and ℵj, j=0,1,2, are complex constants withRe ℵj > 0. We show that under a rather general choice of the parameters l1 and l2, the number of stable invariant tori in the problem, as well as their dimensions, grows infinitely asRe ℵ0 → 0 andRe ℵ0 → 0.
Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 125, No. 2, pp. 205–220, November, 2000. 相似文献
8.
J. Hounie Rafael Augusto dos Santos Kapp 《Journal of Fourier Analysis and Applications》2009,15(2):153-178
In this work, we study the continuity of pseudodifferential operators on local Hardy spaces h
p
(ℝ
n
) and generalize the results due to Goldberg and Taylor by showing that operators with symbols in S
1,δ
0(ℝ
n
), 0≤δ<1, and in some subclasses of S
1,10(ℝ
n
) are bounded on h
p
(ℝ
n
) (0<p≤1). As an application, we study the local solvability of the planar vector field L=∂
t
+ib(x,t)∂
x
, b(x,t)≥0, in spaces of mixed norm involving Hardy spaces.
Work supported in part by CNPq, FINEP, and FAPESP. 相似文献
9.
Pierre Collet Servet Martínez Jaime San Martín 《Probability Theory and Related Fields》2000,116(3):303-316
We study the asymptotic behaviour of the transition density of a Brownian motion in ?, killed at ∂?, where ?
c
is a compact non polar set. Our main result concern dimension d = 2, where we show that the transition density p
?
t
(x, y) behaves, for large t, as
u(x)u(y)(t(log t)2)−1 for x, y∈?, where u is the unique positive harmonic function vanishing on (∂?)
r
, such that u(x) ∼ log ∣x∣.
Received: 29 January 1999 / Revised version: 11 May 1999 相似文献
10.
Consider the Cauchy problem ∂u(x, t)/∂t = ℋu(x, t) (x∈ℤd, t≥ 0) with initial condition u(x, 0) ≡ 1 and with ℋ the Anderson Hamiltonian ℋ = κΔ + ξ. Here Δ is the discrete Laplacian, κ∈ (0, ∞) is a diffusion constant,
and ξ = {ξ(x): x∈ℤ
d
} is an i.i.d.random field taking values in ℝ. G?rtner and Molchanov (1990) have shown that if the law of ξ(0) is nondegenerate,
then the solution u is asymptotically intermittent.
In the present paper we study the structure of the intermittent peaks for the special case where the law of ξ(0) is (in the
vicinity of) the double exponential Prob(ξ(0) > s) = exp[−e
s
/θ] (s∈ℝ). Here θ∈ (0, ∞) is a parameter that can be thought of as measuring the degree of disorder in the ξ-field. Our main result
is that, for fixed x, y∈ℤ
d
and t→∈, the correlation coefficient of u(x, t) and u(y, t) converges to ∥w
ρ∥−2
ℓ2Σz ∈ℤd
w
ρ(x+z)w
ρ(y+z). In this expression, ρ = θ/κ while w
ρ:ℤd→ℝ+ is given by w
ρ = (v
ρ)⊗
d
with v
ρ: ℤ→ℝ+ the unique centered ground state (i.e., the solution in ℓ2(ℤ) with minimal l
2-norm) of the 1-dimensional nonlinear equation Δv + 2ρv log v = 0. The uniqueness of the ground state is actually proved only for large ρ, but is conjectured to hold for any ρ∈ (0, ∞).
empty
It turns out that if the right tail of the law of ξ(0) is thicker (or thinner) than the double exponential, then the correlation
coefficient of u(x, t) and u(y, t) converges to δ
x, y
(resp.the constant function 1). Thus, the double exponential family is the critical class exhibiting a nondegenerate correlation
structure.
Received: 5 March 1997 / Revised version: 21 September 1998 相似文献
11.
U. Luther 《Integral Equations and Operator Theory》2006,54(4):541-554
We study integral operators on (−1, 1) with kernels k(x, t) which may have weak singularities in (x, t) with x ∈N1, t ∈N2, or x=t, where N1,N2 are sets of measure zero. It is shown that such operators map weighted L∞–spaces into certain weighted spaces of smooth functions, where the degree of smoothness is the higher the smoother the kernel
k(x, t) as a function in x is. The spaces of smooth function are generalizations of the Ditzian-Totik spaces which are defined in terms of the errors
of best weighted uniform approximation by algebraic polynomials. 相似文献
12.
Reinhard Farwig 《Mathematische Zeitschrift》1992,210(1):449-464
Consider the Dirichlet problem −vΔu+k∂
1
u = f withv, k>0 in ℝ3 or in an exterior domain of ℝ3 where the skew-symmetric differential operator −1=∂/∂x1 is a singular perturbation of the Laplacian. Because of the inhomogeneity of the fundamental solution we study existence,
uniqueness and regularity in Sobolev spaces with anisotropic weights. In these spaces the operator ∂1 yields an additional positive definite term giving better results than in Sobolev spaces with radial weights. The elliptic
equation −vΔu +k∂1
u=f can be taken as a model problem for the Oseen equations, a linearized form of the Navier-Stokes equations.
Supported by the Sonderforschungsbereich 256 of the Deutsche Forschungsgemeinschaft at the University of Bonn 相似文献
13.
S. N. M. Ruijsenaars 《Theoretical and Mathematical Physics》2006,146(1):25-33
Letting Al(x) denote the commuting analytic difference operators of elliptic relativistic Calogero-Moser type, we present and study
zero-eigenvalue eigenfunctions for the operators Al(x) − Al(−y) (with l = 1, 2,..., N and x, y ∈ ℂ
N). The eigenfunctions are products of elliptic gamma functions. They are invariant under permutations of x1,..., xN and y1,..., yN and under interchange of the step-size parameters.
__________
Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 146, No. 1, pp. 31–41, January, 2006. 相似文献
14.
V. A. Bykovskii 《Functional Analysis and Its Applications》2000,34(2):98-105
The Dirichlet (Hecke-Maass) series associated with the eigenfuctionsf andg of the invariant differential operator Δk=−y2(∂2/∂x2)+iky∂/∂x of weightk are investigated. It is proved that any relation of the form (f/kM)=g for thek-action of the groupSL
2
SL
2(ℝ) is equivalent to a pair of functional equations relating the Hecke-Maass series forf andg and involving only traditional gamma factors.
This work was supported by the Russian Foundation for Basic Research (grant No. 96-01-10439).
Institute of Applied Mathematics, Far East Division of Russian Academy of Sciences. Translated from Funktional'nyi Analiz
i Ego Prilozheniya, Vol. 34, No. 2, pp. 23–32, April–June, 2000.
Translated by V. M. Volosov 相似文献
15.
Nils Svanstedt 《Applications of Mathematics》2008,53(2):143-155
Multiscale stochastic homogenization is studied for convection-diffusion problems. More specifically, we consider the asymptotic
behaviour of a sequence of realizations of the form ∂u
ɛ
ω
/ ∂t+1 / ɛ
3
C(T
3(x/ɛ
3)ω
3) · ∇u
ɛ
ω
− div(α(T
2(x/ɛ
2)ω
2, t) ∇u
ɛ
ω
) = f. It is shown, under certain structure assumptions on the random vector field C(ω
3) and the random map α(ω
1, ω
2, t), that the sequence {u
ɛ
ω
} of solutions converges in the sense of G-convergence of parabolic operators to the solution u of the homogenized problem ∂u/∂t − div (B(t)∇u= f). 相似文献
16.
Tomasz Komorowski 《Probability Theory and Related Fields》2001,121(4):525-550
We consider the asymptotic behavior of the solutions ofscaled convection-diffusion equations ∂
t
u
ɛ
(t, x) = κΔ
x
(t, x) + 1/ɛV(t/ɛ2,xɛ) ·∇
x
u
ɛ
(t, x) with the initial condition u
ɛ(0,x) = u
0(x) as the parameter ɛ↓ 0. Under the assumptions that κ > 0 and V(t, x), (t, x) ∈R
d
is a d-dimensional,stationary, zero mean, incompressible, Gaussian random field, Markovian and mixing in t we show that the laws of u
ɛ(t,·), t≥ 0 in an appropriate functional space converge weakly, as ɛ↓ 0, to a δ-type measureconcentrated on a solution of a certain
constant coefficient heat equation.
Received: 23 March 2000 / Revised version: 5 March 2001 / Published online: 9 October 2001 相似文献
17.
Gao Jia Xiao-ping Yang 《应用数学学报(英文版)》2006,22(4):589-598
Let Ωbelong to R^m (m≥ 2) be a bounded domain with piecewise smooth and Lipschitz boundary δΩ Let t and r be two nonnegative integers with t ≥ r + 1. In this paper, we consider the variable-coefficient eigenvalue problems with uniformly elliptic differential operators on the left-hand side and (-Δ)^T on the right-hand side. Some upper bounds of the arbitrary eigenvalue are obtained, and several known results are generalized. 相似文献
18.
We consider the parabolic Anderson problem ∂
t
u = κΔu + ξ(x)u on ℝ+×ℝ
d
with initial condition u(0,x) = 1. Here κ > 0 is a diffusion constant and ξ is a random homogeneous potential. We concentrate on the two important cases
of a Gaussian potential and a shot noise Poisson potential. Under some mild regularity assumptions, we derive the second-order
term of the almost sure asymptotics of u(t, 0) as t→∞.
Received: 26 July 1999 / Revised version: 6 April 2000 / Published online: 22 November 2000 相似文献
19.
Let (S)⊄L
2(S′(∔),μ)⊄(S)* be the Gel'fand triple over the white noise space (S′(∔),μ). Let (e
n
,n>-0) be the ONB ofL
2(∔) consisting of the eigenfunctions of the s.a. operator
. In this paper the Euler operator Δ
E
is defined as the sum
, where ∂
i
stands for the differential operatorD
e
i. It is shown that Δ
E
is the infinitesimal generator of the semigroup (T
t
), where (T
t
ϕ)(x)=ϕ(e
t
x) for ϕ∈(S). Similarly to the finite dimensional case, the λ-order homogeneous test functionals are characterized by the Euler equation:
Δ
Eϕ
=λϕ. Via this characterization the λ-order homogeneous Hida distributions are defined and their properties are worked out.
Supported by the National Natural Science Foundation of China. 相似文献
20.
We study the existence and the properties of reduced measures for the parabolic equations ∂
t
u − Δu + g(u) = 0 in Ω × (0, ∞) subject to the conditions (P): u = 0 on ∂Ω × (0, ∞), u(x, 0) = μ and (P′): u = μ′ on ∂Ω × (0, ∞), u(x, 0) = 0, where μ and μ′ are positive Radon measures and g is a continuous nondecreasing function. 相似文献