Eigenfunction expansions for singular Schrodinger operators

We extend Ikebe's theory of eigenfunctions to a class of Schrodinger operators H = - + V on L ² (IR³), where the potential V is replaced by a measure which need not be absolutely continuous with respect to Lebesgue measure. Applications include the proof of the existence and completeness of the wave operators for a free particle which is partly reflected and partly transmitted by a compact 2-dimensional surface.     

Constraint-induced restriction and extension operators with applications

The Stokes operator is a differential-integral operator induced by the Stokes equations. In this paper, we analyze the Stokes operator from the point of view of the Helmholtz minimum dissipation principle. We show that, through the Hodge orthogonal decomposition, a pair of bounded linear operators, a restriction operator and an extension operator, are induced from the divergence-free constraint. As a consequence, we use it to calculate the eigenvalues of the Stokes operator.     

NEW POINTS OF VIEW ON THE NONLOCAL FIELD THEORY AND THEIR APPLICATIONS TO THE FRACTURE MECHANICS (Ⅰ)──FUNDAMENTAL THEORY

In the linear nonlocal elasticity theory, the solution to the boundary-value problem of the crack with a constant stress boundary condition does not exist. This problem has been studied in this paper. The contents studied contain of examining objectivity of the energy balance, deducing the constitutive equations of nonlocal thermoelastic bodies, and determining nonlocal force and the linear nonlocal elasticity theory. Some new results are obtained. Among them, the stress boundary condition derived from the linear theory not only solves the problem mentioned at the beginning, but also contains the model of molecular cohesive stress on the sharp crack tip advanced by Barenblatt.     

Parametric expansions in the linear theory of cylindrical shells

Summary Concepts of parametric expansions, leading to univocal definitions of classes of solutions (according to the behaviour of derivatives by vanishing thickness parameter) and, for each class, to a unique classification of terms in equations, are applied to cylindrical shells.In the introduction by Cicala, the fields of application of the various classes of solutions are related to loading and boundary conditions.In the subsequent section, Sassi Perino presents the second approximation formulation for rapid variation solutions for circular cylindrical shells. The first approximation form coincides with Donnell's theory. The second approximation terms take into account effects neglected by the ordinary theory, such as elongation of normal fibers and transverse shear deflections.The next section by Siniscalco contains the second approximation form of the long cylinder theory. The first approximation coincides with the Wagner-Vlasof semimembrane theory. The second approximation includes the deformation of midsurface fibers. For the circular cylinder, the resultant equations are obtained in simple form.

---

Sommario Gli sviluppi parametrici, sono applicati al guscio cilindrico.Nell'introduzione Cicala mette in relazione i campi di applicabilità delle varie soluzioni con le situazioni di carico e le condizioni al contorno. Nella parte seguente, Sassi Perino ricava la formulazione di seconda approssimazione per le soluzioni di classe1/2. In prima approssimazione si ha la coincidenza con la teoria di Donnell. I termini di seconda approssimazione tengono conto di effetti che l'ordinaria teoria trascura, come l'allungamento delle fibre normali e le deformazioni dovute al taglio trasversale. Nella sezione seguente Siniscalco ricava la forma di seconda approssimazione della teoria del cilindro lungo. La prima approssimazione coincide con la teoria semimembranale di Wagner-Vlasof. Nella seconda approssimazione intervengono le deformazioni delle fibre della superficie media. Per il cilindro circolare viene ottenuta l'equazione risultante in forma semplice.

     

On the rigidity of certain surfaces with folds and applications to shell theory

In the asymptotic theory of thin elastic shells the rigidity of the mid-surface with kinematic boundary conditions plays an important role. Rigidity is understood in the sense of infinitesimal (linearized) rigidity, i.e., the displacements vanish provided the variation of the first fundamental form vanishes. In this case the surface is also called “stiff”, as it cannot undergo pure bendings. A stiff surface is imperfectly stiff or perfectly stiff when the origin respectively does or does not belong to the essential spectrum of the boundary-value problem. These questions are investigated in the framework of Douglis-Nirenberg elliptic systems, with boundary conditions and transmission conditions at the folds. The index properties ensures quasi-stiffness, i.e. stiffness up to a finite number of degrees of freedom. The concept of perfect stiffness is linked with estimates for the rigidity system at an appropriate level of regularity for the data and the solution. It is proved that surfaces with folds are never perfectly stiff. It is also shown that the transmission conditions at the folds contain more conditions than those satisfying the Shapiro-Lopatinskii property. This leads to certain rigidity properties of the folds. Some examples are given.     

High order methods for acoustic scattering: Coupling farfield expansions ABC with deferred-correction methods

Arbitrary high order numerical methods for time-harmonic acoustic scattering problems originally defined on unbounded domains are constructed. This is done by coupling recently developed high order local absorbing boundary conditions (ABCs) with finite difference methods for the Helmholtz equation. These ABCs are based on exact representations of the outgoing waves by means of farfield expansions. The finite difference methods, which are constructed from a deferred-correction (DC) technique, approximate the Helmholtz equation and the ABCs, with the appropriate number of terms, to any desired order. As a result, high order numerical methods with an overall order of convergence equal to the order of the DC schemes are obtained. A detailed construction of these DC finite difference schemes is presented. Additionally, a rigorous proof of the consistency of the DC schemes with the Helmholtz equation and the ABCs in polar coordinates is also given. The results of several numerical experiments corroborate the high order convergence of the novel method.     

FIXED POINTS OF INCREASING OPERATORS IN ORDERED SPACE WITH APPLICATIONS

ＩｎｔｒｏｄｕｃｔｉｏｎＩｎｖｅｓｔｉｇａｔｉｎｇｔｈｅｆｏｌｌｏｗｉｎｇｂｏｕｎｄａｒｙｐｒｏｂｌｅｍｉｎｏｒｄｉｎａｒｙｄｉｆｆｅｒｅｎｔｉａｌｅｑｕａｔｉｏｎ :¨ｘ+ｆ(ｔ,ｘ(ｔ) ) =0 ,ａ<ｔ<ｂ,αｘ(ａ) -β ｘ(ａ) =0 ,γｘ(ｂ) +δ ｘ(ｂ) =0 ,( 1 )ｗｈｅｒｅα ,β,γ ,δ≥ 0 ,Δ=(ｂ-ａ)αγ+αδ+ βγ>0 .ｆ(ｔ,ｓ)ｍａｙｂｅｓｉｎｇｕｌａｒｉｎｔ =ａ ,ｂ.Ｉｔｈａｓｂｅｅｎｄｉｒｅｃｔｌｙｖｅｒｉｆｉｅｄｔｈａｔｘ(ｔ)ｉｓｔｈｅｓｏｌｕｔｉｏｎｏｆ( 1 )ｉｎＣ2 [ａ ,ｂ]ｉｆａｎｄｏｎｌｙｉｆｘ(…