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.

Fast parallel algorithms for short-range molecular dynamics

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Using Multivariate Statistics

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

Phd by thesis

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.

https://science.sciencemag.org/content/sci/287/5453/637.full.pdf

Strength and breaking mechanism of multiwalled carbon nanotubes under tensile load

Structural Characterization and Compressive Behavior of the Boxfish Horn

Discussion of pressure-shear impact and the dynamic viscoplastic response of metals

Adiabatic shear bands self-organize themselves: this phenomenon was investigated in three different alloys ( stainless steel 304L, Ti, and Ti-6%Al-%V) through the radial collapse of a thick-walled cylinder under high-strain-rate deformation (∼10 4 s -1 ). This method was used to examine the shear-band initiation, propagation, as well as spatial distribution. The spacing of shear bands in the three materials varied widely and showed considerable differences during the initiation and propagation. Shear-band spacing is compared with the theories proposed by Grady and Kipp (momentum diffusion), Wright and Ockendon (perturbation), and Molinari (perturbation plus work hardening). Additionally, the effect of microstructural inhomogeneities on initiation is discussed. A discontinuous growth mode for shear localization under periodic perturbation is proposed based on two-dimensional growth considerations, not incorporated into the one-dimensional perturbation and momentum diffusion theories.

Self-organization of shear bands in Ti, Ti-6%Al-4%v, and 304 stainless steel

Des echantillons de cuivre ont ete soumis a un chargement par ondes de choc de 50GPa suivi par une haute deformation γ ∼ 2-5 a une vitesse de deformation eleve (∼ 10 4 s −1 ). La structure recrystallisee consiste de grains fins et equiaxes (0.1-0.3 μm). Des essais a basse vitesse de deformation sur ces memes echantillons soumis au choc et prechauffes ont produit une structure recrystallisee avec une taille de grains de 2-3 μm et une densite elevee de macles de recuit. Ces differences indique que les mecanismes de recristalization dynamique operant a basses et hautes vitesses de deformation sont differents. L'effet de la taille de grain initial a ete aussi etudie: des tailles de grain de 10, 5, 25, 117, et 315 μm, ont etes produites

/pdf/dynamic-recrystallization-and-grain-size-effects-in-shock-3yabjzulzu.pdf

Dynamic recrystallization and grain size effects in shock hardened copper

Additive manufacturing is one of the most promising emerging technologies for building prosthetic sockets. However, there is no reliable way to estimate the factor of safety and the lifetime of 3D printed prosthetic sockets. Here, we explore 360° 3D digital image correlation (DIC) and discover how this new tool can increase our understanding of prosthetic structural failures. We establish that this new technology can dramatically improve the prosthetic design cycle by identifying local strain concentrations and by highlighting limitations in current simulated models. Overall, 360° 3D DIC technology empowers prosthetic engineers to characterize the performance of new materials and create innovative designs that are both safe and affordable.

/pdf/seeing-the-big-picture-improving-the-prosthetic-design-cycle-83p6ms20j4.pdf

Marc A. Meyers

Papers

Structural Characterization and Compressive Behavior of the Boxfish Horn

Discussion of pressure-shear impact and the dynamic viscoplastic response of metals

Self-organization of shear bands in Ti, Ti-6%Al-4%v, and 304 stainless steel

Dynamic recrystallization and grain size effects in shock hardened copper

Seeing the Big Picture: Improving The Prosthetic Design Cycle Using 360° 3D Digital Image Correlation