Marc A. Meyers

Bio: Marc A. Meyers is an academic researcher from University of California, San Diego. The author has contributed to research in topics: Deformation (engineering) & Dislocation. The author has an hindex of 85, co-authored 487 publications receiving 36646 citations. Previous affiliations of Marc A. Meyers include University of California & Instituto Militar de Engenharia.

Growth and structure in abalone shell

Abstract: The growth and self-assembly of aragonitic calcium carbonate found in the shell of abalone (Haliotis) is described. This was accomplished through the close examination of laboratory-grown flat pearl samples and cross-sectional slices of the nacreous shell. Further understanding of the sequenced assembly has been obtained. It has been confirmed that the growth of the aragonite component of the composite occurs by the successive nucleation of aragonite crystals and their arrest by means of a protein-mediated mechanism; it takes place in the “Christmas-tree pattern” [Nature 49 (1994) 371]. It is shown that the protein layer is virtually absent where plates on a same plane abut (along lateral surfaces of tiles). This suggests a mechanism of c-axis aragonite growth arrest by the deposition of a protein layer of approximately 20–30 nm that is periodically activated and determines the thickness of the aragonite platelets, which are remarkably constant (0.5 m). This platelet size was measured for animals with shell diameters of 10, 50, and 200 mm and was found to be constant. The overall growth process is expressed in terms of parameters incorporating the anisotropy of growth velocity in aragonite ( Vc, the velocity along c axis, and Vab, the velocity in basal plane). Comparison of laboratory-raised and naturally-grown abalone indicates growth regulated by the level of proteinaceous saturation. Naturally-grown abalone exhibits mesolayers (growth bands) ∼0.3 mm apart; it is proposed that they result from seasonal interruptions in feeding patterns, creating thicker ( ∼10–20m) layers of protein. These mesolayers play a critical role in the mechanical properties, and are powerful crack deflectors. The viscoplastic deformation of the organic inter-tile layers is responsible for the significant improvement of tensile strength over the tensile strength of monolithic aragonite. © 2004 Elsevier B.V. All rights reserved.

Shear Localization in Dynamic Deformation: Microstructural Evolution

Abstract: Investigations made by the authors and collaborators into the microstructural aspects of adiabatic shear localization are critically reviewed. The materials analyzed are low-carbon steels, 304 stainless steel, monocrystalline Fe-Ni-Cr, Ti and its alloys, Al-Li alloys, Zircaloy, copper, and Al/SiCp composites. The principal findings are the following: (a) there is a strain-rate-dependent critical strain for the development of shear bands; (b) deformed bands and white-etching bands correspond to different stages of deformation; (c) different slip activities occur in different stages of band development; (d) grain refinement and amorphization occur in shear bands; (e) loss of stress-carrying capability is more closely associated with microdefects rather than with localization of strain; (f) both crystalline rotation and slip play important roles; and (g) band development and band structures are material dependent. Additionally, avenues for new research directions are suggested.

The materials science of collagen.

Abstract: Collagen is the principal biopolymer in the extracellular matrix of both vertebrates and invertebrates. It is produced in specialized cells (fibroblasts) and extracted into the body by a series of intra and extracellular steps. It is prevalent in connective tissues, and the arrangement of collagen determines the mechanical response. In biomineralized materials, its fraction and spatial distribution provide the necessary toughness and anisotropy. We review the structure of collagen, with emphasis on its hierarchical arrangement, and present constitutive equations that describe its mechanical response, classified into three groups: hyperelastic macroscopic models based on strain energy in which strain energy functions are developed; macroscopic mathematical fits with a nonlinear constitutive response; structurally and physically based models where a constitutive equation of a linear elastic material is modified by geometric characteristics. Viscoelasticity is incorporated into the existing constitutive models and the effect of hydration is discussed. We illustrate the importance of collagen with descriptions of its organization and properties in skin, fish scales, and bone, focusing on the findings of our group.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Using Multivariate Statistics

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Phd by thesis

Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Strength and breaking mechanism of multiwalled carbon nanotubes under tensile load

Abstract: The tensile strengths of individual multiwalled carbon nanotubes (MWCNTs) were measured with a “nanostressing stage” located within a scanning electron microscope. The tensile-loading experiment was prepared and observed entirely within the microscope and was recorded on video. The MWCNTs broke in the outermost layer (“sword-in-sheath” failure), and the tensile strength of this layer ranged from 11 to 63 gigapascals for the set of 19 MWCNTs that were loaded. Analysis of the stress-strain curves for individual MWCNTs indicated that the Young's modulus E of the outermost layer varied from 270 to 950 gigapascals. Transmission electron microscopic examination of the broken nanotube fragments revealed a variety of structures, such as a nanotube ribbon, a wave pattern, and partial radial collapse.