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Thick Shells (thick + shell)

Distribution by Scientific Domains

Engineering	40%

Selected Abstracts

Uniform Magnetic Chains of Hollow Cobalt Mesospheres from One-Pot Synthesis and Their Assembly in Solution,

ADVANCED FUNCTIONAL MATERIALS, Issue 3 2007
L. Guo
Abstract Magnetic chains up to 10,,m in length formed of hollow cobalt mesospheres (480,850,nm) with a 60,nm thick shell are synthesized by a new soft-assembly protocol. The obtained chains show a saturation magnetization of 37.5,emu,g,1, a remnant magnetization of 1.55,emu,g,1, and a coercivity of ca.,66,Oe at 300,K. A possible mechanism for the formation of the chainlike hollow structures is proposed. [source]

Are House Wren Troglodytes aedon eggs unusually strong?

IBIS, Issue 2 2002
Test of the predicted effect of intraspecific egg destruction
As a result of opposing selective forces, the external strength of avian eggs should be near some size-specific optimum. However, in certain situations there should be selection on females to lay unusually strong eggs. According to one hypothesis, intraspecific egg destruction should favour increased egg strength as a means of defence against conspecific intruders. This hypothesis predicts that House Wrens Troglodytes aedon, a species well known for its tendency to destroy conspecific clutches, should be under selection for unusually strong eggs. However, the intensity of selection for strong eggs should also be modified by efficacy of nest defence against conspecific intruders in a given species (i.e. efficient nest defence by the breeding pair should weaken selection for unusually strong eggs). The goals of our study were: (1) to establish whether House Wren eggs are stronger than expected for their size; (2) to determine which structural mechanisms are responsible for their unusual strength; and (3) to test a hypothesis that, between wren species, the efficacy of nest defence and the intensity of egg-destroying behaviour affect the intensity of selection for unusually strong eggs. Our results demonstrated that: (1) House Wren eggs are 1.9 times stronger than expected for their size; (2) their unusual strength is achieved mostly by their unusually thick shells; and (3) eggs of the House Wren (extensive paternal nest defence; male egg-destroying behaviour suppressed during incubation) are significantly weaker structurally than eggs of the Marsh Wren Cistothorus palustris (reduced paternal nest defence; male egg-destroying behaviour present throughout incubation). These results are consistent with the hypothesis that the intraspecific egg-destroying behaviour and the efficacy of nest defence by the breeding adults have played a role in the evolution of strength of House Wren eggs. [source]

Eight-node shell element based on incompatible modes

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 2 2009
Desheng Xu
Abstract This paper concerns the shell element formulation used for linear analysis. Introduction of hierarchical incompatible modes into the ordinary 8-node solid element is very effective to obtain the rational deflection,rotation relationship. An efficient revision scheme without using numerical volume integration is developed to ensure the satisfaction of the patch test. A lot of numerical tests are carried out for the validation of the present element. Numerical results show that the element can give satisfactory accuracy and convergence, especially for moderately thick shells. Copyright © 2008 John Wiley & Sons, Ltd. [source]

DSC-Ritz method for high-mode frequency analysis of thick shallow shells

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 2 2005
C. W. Lim
Abstract This paper addresses a challenging problem in computational mechanics,the analysis of thick shallow shells vibrating at high modes. Existing methods encounter significant difficulties for such a problem due to numerical instability. A new numerical approach, DSC-Ritz method, is developed by taking the advantages of both the discrete singular convolution (DSC) wavelet kernels of the Dirichlet type and the Ritz method for the numerical solution of thick shells with all possible combinations of commonly occurred boundary conditions. As wavelets are localized in both frequency and co-ordinate domains, they give rise to numerical schemes with optimal accurate, stability and flexibility. Numerical examples are considered for Mindlin plates and shells with various edge supports. Benchmark solutions are obtained and analyzed in detail. Experimental results validate the convergence, stability, accuracy and reliability of the proposed approach. In particular, with a reasonable number of grid points, the new DSC-Ritz method is capable of producing highly accurate numerical results for high-mode vibration frequencies, which are hitherto unavailable to engineers. Moreover, the capability of predicting high modes endows us the privilege to reveal a discrepancy between natural higher-order vibration modes of a Mindlin plate and those calculated via an analytical relationship linking Kirchhoff and Mindlin plates. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Small-molecule release from poly(D,L -lactide)/poly(D,L -lactide-co-glycolide) composite microparticles

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2005
Emily J. Pollauf
Abstract Addition of biodegradable polymer shells surrounding polymeric, drug-loaded microparticles offers the opportunity to control drug release rates. A novel fabrication method was used to produce microparticles with precise control of particle diameter and the thickness of the polymer shell. The effect of shell thickness on release of a model drug, piroxicam, has been clearly shown for 2- to 15-µm thick shells of poly(D,L -lactide) (PDLL) surrounding a poly(D,L -lactide-co-glycolide) (PLG) core and compared to pure PLG microspheres loaded with piroxicam. Furthermore, the core-shell microparticles are compared to microspheres containing blended polymers in the same mass ratios to demonstrate the importance of the core-shell morphology. Combining PDLL(PLG) microcapsules of different shell thicknesses allows nearly constant release rates to be attained for a period of 6 weeks. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:2013,2022, 2005 [source]