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

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

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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

The application of an external force to a body is, by definition a dynamic process. However, when the rate of change of the applied forces is low, one can consider the process of deformation as a sequence of steps in which the body can be considered in static equilibrium. Figure 2.1 shows how the distance between the atoms changes upon the application of an external force F. For each of the stages of deformation shown in Figs. 2.1(b) and 2.1(c), the body can be considered under static equilibrium and one can apply the methods of mechanics of materials to determine the internally-resisting stresses (by the method of sections). Hence, a section made at AA or BB will yield identical stresses.

Propagation of Stress Waves in Metals

Nearly all species of modern birds are capable of flight; therefore mechanical competency of appendages and the rigidity of their skeletal system should be optimized. Birds have developed extremely lightweight skeletal systems that help aid in the generation of lift and thrust forces as well as helping them maintain flight over, in many cases, extended periods of time. The humerus and ulna of different species of birds (flapping, flapping/soaring, flapping/gliding, and non-flying) have been analyzed by optical microscopy and mechanical testing. The reinforcing structures found within bones vary from species to species, depending on how a particular species utilizes its wings. Interestingly, reinforcing ridges and struts have been found within certain sections of the bones of flapping/soaring and flapping/gliding birds (vulture and sea gull), while the bones from the flapping bird (raven) and non-flying bird (domestic duck) did not have supporting structures of any kind. The presence of these reinforcing structures increases the resistance to torsion and flexure with a minimum weight penalty, and is therefore of importance in flapping/gliding birds. Vickers hardness testing was performed on the compact section of the bones of all bird species. The data from the mechanical testing were compared with microstructural observations to determine the relevance behind the reinforcing structures and its mechanical and biological role. Finite element analysis was used to model the mechanical response of vulture ulna in torsion.

Reinforcing Structures in Avian Wing Bones

Discussion of “residual strength of shock loaded RMI 38644”

Cobalt silver–copper (Co–AgCu) weldments approximate the stresses and failure mechanisms of beryllium aluminum–silicon (Be–AlSi) welds, which have strategic importance but are hazardous to study. Failure tests of these surrogate Co–AgCu welds, examined in tension and four-point bending, show that residual stresses and post-welding heat treatment have little or no effect on strength, whereas weld quality and geometry are extremely important. Scanning electron microscopy images reveal abundant defects in poor welds, which usually fail through propagation of preexisting cracks. Fracture surfaces show a variety of morphologies, ranging from dimples in the AgCu filler, to cleavage steps in the CoCu peritectic, and suspected intergranular fracture in the cobalt base. Spatially resolved acoustic spectroscopy reveals significant changes in microstructure near the base–filler interface, whereas wavelength dispersive analysis shows high Cu concentrations in this area.. Contrary to finite element predictions, these welds were found to be stronger during face bending than root bending, likely resulting from the increased number of cracks and imperfections in the Co base. These computations correctly predict that weld strength depends on geometry and that welds fail either in the cobalt base, or along the base–filler interface. Crack compliance measurements show that the largest residual stresses are located along this interface. However, these stresses are unlikely to influence failure due to their direction, whereas stresses in the weld root are too small to have observable effects on failure. The strength of Co–AgCu welds depends strongly on geometry, penetration, and weld quality, but little on residual stresses, and this conclusion is tentatively extended to Be–AlSi welds.

Failure mechanisms in cobalt welded with a silver–copper filler

—Recent trends in
the field of prosthetic technology are shifting towards all-digital approaches.
These digital technologies have the potential to augment the current models of
clinical healthcare and reach more amputees than currently possible.
Unfortunately, most of the equipment needed to design and build digitally
shaped prostheses is expensive or requires a high level of expertise. Objective:
This paper developed several methods to enable the digital fabrication of
prostheses using only low cost tools that do not require extensive specialized training.
Methods: The authors built a cell phone application in Android Studio
that enables automated collection of image data which can be rendered into
accurate 3D-models using photogrammetry on a remote server. They then developed
a new protocol to shape these residual limb models into functional prosthetic
sockets using the freely available software Autodesk Meshmixer. Results:
Finally, the authors ran a case study where they rectified a prosthetic socket for
an amputee and compared this model to a socket built by a clinician. Conclusion:
This case study showed that these new methods can successfully create accurate
and functional prosthetic sockets. Significance: By leveraging
ubiquitous low cost smartphone technology, the authors believe that amputees in
underserved areas, who currently face large barriers both in cost and physical
access to proper care, could soon be able to obtain affordable prosthetic limbs.

/pdf/smartphone-telemedicine-a-novel-workflow-for-creating-1l5qcdix8z.pdf

Marc A. Meyers

Papers

Propagation of Stress Waves in Metals

Reinforcing Structures in Avian Wing Bones

Discussion of “residual strength of shock loaded RMI 38644”

Failure mechanisms in cobalt welded with a silver–copper filler

Smartphone Telemedicine: A Novel Workflow for Creating Prosthetic Sockets Using Semi-automated Photogrammetry