Taxonomical study on a sample of pulmonates from Santa Maria da Vitória, Bahia, Brazil, with description of a new genus and four new species (Mollusca: Orthalicidae and Megalobulimidae)

A sample of Pulmonata collected in Santa Maria da Vitória, interior of Bahia, Brazil, in Caatinga semi-arid environment, is studied taxonomically. From the five species, four are revealed as new, including a new genus. The new taxa are the Bulimulidae (1) Kora corallina gen. et sp. n. characterized by the elongated shell with aperture somewhat dislocated from the shell axis, and an oblique tooth in middle level of inner lip; (2) Spixia coltrorum, mainly characterized by an uneven spire, delicate sculpture and peristome with 4 equidistant teeth; (3) Anostoma tessa, mainly characterized by a broad spire and well-developed anal canal; and the Megalobulimidae (4) Megalobulimus amandus, mainly characterized by pointed protoconch sculptured by dense quantity of axial cords. Rhinus suturalis is the only previously known species, but its geographic distribution is expanded southwards to Bahia state. A discussion with respect to necessity for improving the study on the malacofauna from the interior region of the Brazilian Northeast and the importance for preservation of the Caatinga biome is also provided.

Bending of Cord Composite Laminate Cylindrical Shells

A theory for the bending of cord composite laminate cylindrical shells is developed. The extension-twist coupling of the cords is taken into account. The general case of a circular cylindrical shell with cord plies at various angles to the shell axis is considered. The differential equations for the displacements are derived. These equations are solved analytically in closed form for a shell subjected to axisymmetric loading and no in-plane tractions. The results of the current study are compared with the commonly used Gough-Tangorra and Akasaka-Hirano solutions.

Bending of Cord Composite Cylindrical Shells

An analytical method for determining the load-deformation behavior of cord composite cylindrical shells is developed by considering the mechanics of the matrix, the cords, and the shell. To illustrate the method, a circular cylindrical shell with a single ply of uniformly spaced cords parallel to the shell axis is considered. The differential equations for the displacements are derived. These equations are solved analytically in closed form for a shell with the cords on the middle surface and subjected to axisymmetric loading. The deformations are strongly dependent upon the properties of the constituents, including the extension-twist coupling of the cords, and the geometry, boundary conditions, and loading. [S0021-8936(00)02701-X]

Flexural Vibration of Cylindrical Shells Partially Coupled With External and Internal Fluids

In this paper, the free flexural vibrations of a partially fluid-loaded simply supported circular cylindrical shell are studied; the fluid is assumed to be inviscid and to present a free-surface parallel to the shell axis. The presence of external and internal fluids are both studied and the problem for incompressible and compressible fluid are both discussed by using the added virtual mass approach. Circumferential dependence of displacement is extended in a Fourier series. The maximum potential energy of the cylinder is evaluated using a sum of reference kinetic energies of the shell vibrating in vacuum; this fact allows the proposed method to be independent from the theory of shells used. Then, the Rayleigh quotient for fluid-shell coupled vibration is formulated and minimized to obtain the Galerkin equation whose solution gives the natural frequencies and mode shapes. Numerical computations are performed to obtain the modal characteristics as functions of the level of water in contact with the shell in the range of good accuracy of the theory, that is around the half-wet shell level. Results for both a shell partially surrounded and filled with water are obtained and compared.

Stereotypy of predatory boring behavior of Pleistocene naticid gastropods

Quantitative systems for describing naticid borehole position in bivalve and gastropod prey are presented. Pleistocene nassariid prey were bored at 53% of the distance up the shell and 8° to the right of the columella. A similar stereotyped position was found for Recent prey. The longitudinal shell axis and the aperture of the gastropod shell are proposed as primary cues in orienting prey for boring.

Stability of Cylindrical Shells Under Moving Loads by the Direct Method of Liapunov

The stability of a long, thin, elastic circular cylindrical shell subjected to axial compression and an axisymmetric load moving with constant velocity along the shell axis is studied. With the aid of the direct method of Liapunov, and employing a nonlinear Donnell-type shell theory, sufficient conditions for local stability of the axisymmetric response are established in a functional space whose metric is defined in an average sense. Numerical results, which are presented for the case of a moving decayed step load, reveal that the sufficient conditions for stability developed here and the sufficient conditions for instability obtained in a previous paper lead to the actual stability transition boundary.