• Development and Reproduction
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• v.11 no.2
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• pp.97-104
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• 2007

This study describes the spermatogenesis and sperm ultrastructure of the spiny top shell, Batillus cornutus using light and electron microscopy. The spiny top shells were collected by divers in the coastal water of Wandogun, Cheollanamdo, Korea(N $34^{\circ}13'$, E $126^{\circ}47'$) at May 2003. Spiny top shells of $60.0{\sim}69.9\;mm$ in shell height were used in this study. The testis comprises many spermatogenic follicles which contains germ cells in different developmental stages. The primary spermatocytes in the pachytene stage were characterized by synaptonemal complexes. The early spermatids were characterized by appearance of Golgi complex, increased karyoplasmic electron density and tubular mitochondria. In early spermatid the mass of proacrosomal granules consists of numerous heterogeneous granules with high electron density. From the mid-stage of spermiogenesis the well-developed mitochondria aggregate posterior to the nucleus, and surround the proximal and distal centrioles. In this stage, proacrosomal granules are condensed and form a acrosome with thin envelope. During the late spermiogenesis, the acrosome begins to elongate and then became conical. The sperm consists of head, mid-piece and tail. The head comprises a round nucleus and a conical acrosome. Acrosomal rod of microfibrous is observed between nucleus and acrosome. Five mitochondria observed in mid-piece. And tail has the typical "9+2" microtubular system originates from the centrioles.

• Steel and Composite Structures
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• v.26 no.6
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• pp.771-791
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• 2018

This paper deals with the low velocity impact response and dynamic stresses of composite sandwich truncated conical shells (STCS) with compressible or incompressible core. Impacts are assumed to occur normally over the top face-sheet and the interaction between the impactor and the structure is simulated using a new equivalent three-degree-of-freedom (TDOF) spring-mass-damper (SMD) model. The displacement fields of core and face sheets are considered by higher order and first order shear deformation theory (FSDT), respectively. Considering continuity boundary conditions between the layers, the motion equations are derived based on Hamilton's principal incorporating the curvature, in-plane stress of the core and the structural damping effects based on Kelvin-Voigt model. In order to obtain the contact force, the displacement histories and the dynamic stresses, the differential quadrature method (DQM) is used. The effects of different parameters such as number of the layers of the face sheets, boundary conditions, semi vertex angle of the cone, impact velocity of impactor, trapezoidal shape and in-plane stresses of the core are examined on the low velocity impact response of STCS. Comparison of the present results with those reported by other researchers, confirms the accuracy of the present method. Numerical results show that increasing the impact velocity of the impactor yields to increases in the maximum contact force and deflection, while the contact duration is decreased. In addition, the normal stresses induced in top layer are higher than bottom layer since the top layer is subjected to impact load. Furthermore, with considering structural damping, the contact force and dynamic deflection decrees.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.2
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• pp.197-206
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• 2003

A three-dimensional (3-D) method of analysis is presented for determining the free vibration frequencies and mode shapes of solid and hollow hemispherical shells of revolution of arbitrary wall thickness having arbitrary constraints on their boundaries. Unlike conventional shell theories, which are mathematically two-dimensional (2-D), the present method is based upon the 3-D dynamic equations of elasticity. Displacement components μ/sub Φ/, μ/sub z/, and μ/sub θ/ in the meridional, normal, and circumferential directions, respectively, are taken to be sinusoidal in time, periodic in θ, and algebraic polynomials in the Φ and z directions. Potential (strain) and kinetic energies of the hemispherical shells are formulated, and the Ritz method is used to solve the eigenvalue problem, thus yielding upper bound values of the frequencies obtained by minimizing the frequencies. As the degree of the polynomials is increased, frequencies converge to the exact values. Novel numerical results are presented for solid and hollow hemispheres with linear thickness variation. The effect on frequencies of a small axial conical hole is also discussed. Comparisons are made for the frequencies of completely free, thick hemispherical shells with uniform thickness from the present 3-D Ritz solutions and other 3-D finite element ones.