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

This introduction begins with a brief history of SHM technology development. Recent research has begun to recognise that a productive approach to the Structural Health Monitoring (SHM) problem is to regard it as one of statistical pattern recognition (SPR); a paradigm addressing the problem in such a way is described in detail herein as it forms the basis for the organisation of this book. In the process of providing the historical overview and summarising the SPR paradigm, the subsequent chapters in this book are cited in an effort to show how they fit into this overview of SHM. In the conclusions are stated a number of technical challenges that the authors believe must be addressed if SHM is to gain wider acceptance.

An introduction to structural health monitoring

Human skin is a remarkable organ. It consists of an integrated, stretchable network of sensors that relay information about tactile and thermal stimuli to the brain, allowing us to maneuver within our environment safely and effectively. Interest in large-area networks of electronic devices inspired by human skin is motivated by the promise of creating autonomous intelligent robots and biomimetic prosthetics, among other applications. The development of electronic networks comprised of flexible, stretchable, and robust devices that are compatible with large-area implementation and integrated with multiple functionalities is a testament to the progress in developing an electronic skin (e-skin) akin to human skin. E-skins are already capable of providing augmented performance over their organic counterpart, both in superior spatial resolution and thermal sensitivity. They could be further improved through the incorporation of additional functionalities (e.g., chemical and biological sensing) and desired properties (e.g., biodegradability and self-powering). Continued rapid progress in this area is promising for the development of a fully integrated e-skin in the near future.

25th Anniversary Article: The Evolution of Electronic Skin (E-Skin): A Brief History, Design Considerations, and Recent Progress

Permanently cross-linked materials have outstanding mechanical properties and solvent resistance, but they cannot be processed and reshaped once synthesized Non–cross-linked polymers and those with reversible cross-links are processable, but they are soluble We designed epoxy networks that can rearrange their topology by exchange reactions without depolymerization and showed that they are insoluble and processable Unlike organic compounds and polymers whose viscosity varies abruptly near the glass transition, these networks show Arrhenius-like gradual viscosity variations like those of vitreous silica Like silica, the materials can be wrought and welded to make complex objects by local heating without the use of molds The concept of a glass made by reversible topology freezing in epoxy networks can be readily scaled up for applications and generalized to other chemistries

Silica-Like Malleable Materials from Permanent Organic Networks

The controlled synthesis of monodisperse nanospheres faces a number of difficulties, such as extensive crosslinking during hydrothermal processes. Here, the authors show a route for the controlled synthesis of mesoporous polymer nanospheres, which can be further converted into carbon nanospheres through carbonization.

/pdf/a-facile-soft-template-synthesis-of-mesoporous-polymeric-and-8vdw1lf6wb.pdf

A facile soft-template synthesis of mesoporous polymeric and carbonaceous nanospheres

The feasibility of using a recently developed ultrasonic technique to determine certain macroscopic properties of the interface zones of composite laminates is studied. The strong influence of the elastic properties and the thickness of the interface zone on the phase velocity of guided waves is demonstrated by means of a simple model of a single fiber embedded in a layer of the matrix material. The overall dynamic elastic moduli of a unidirectional graphite-epoxy composite laminate are determined through inversion of guided wave dispersion data obtained by the leaky Lamb wave experiment. The thickness and elastic properties of the interlaminar interface zone in a cross-ply graphite-epoxy laminate are also estimated by the same approach.

Determination of the properties of composite interfaces by an ultrasonic method

On the surface response of a multilayered solid to a dislocation source.

It is well known that layered solids can support dispersive, layer guided waves whose propagation characteristics are strongly dependent upon the material properties of the solids. Thus, accurate measurements of the propagation characteristics of guided waves can lead to the development of excellent nondestructive evaluation tools for coated solids, composite laminates and other electronic as well as structural materials which are being used with increasing frequency in modern engineering applications. Two recently developed experimental arrangements [1,2] which provide the means for such measurements are sketched in Figure 1. In the arrangement shown in Figure la, the platelike specimen is fully immersed in a fluid, while in that shown in Figure 1b, the fluid is present on only one side of the specimen. In both cases, a beam of acoustic waves is launched at a specific angle of incidence and the reflected acoustic field is recorded by a symmetrically placed second transducer. The recorded signals in both experiments consist of the spatially reflected waves and for sufficiently large angles of incidence, leaky waves radiated by the layer guided waves in the solid. After appropriate signal processing to remove the noise and Fourier analysis, the spectrum of the total reflected field is obtained.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1617&context=qnde

The Influence of Material Dissipation and Imperfect Bonding on Acoustic Wave Reflection from Layered Solids

This paper is concerned with the calculation of the acoustic emission wavefield in an isotropic elastic plate. The calculations are carried out by means of two methods: modal superposition (MSM) and finite elements (FEM). These two methods are complementary in the sense that modal superposition is very efficient in constructing the far field response while the finite element method is most efficient in the near field. It is shown that for the source-receiver distance, R, larger than five times the plate thickness, 2H, superposition of a small number of propagating modes gives virtually the same surface motion as that obtained through finite element analysis. For R ≅ H, MSM requires evaluation of the non-propagating modes and becomes computationally inefficient. For R> H the FEM requires enormous computational effort due to the large size of the discretized model, while the computational efficiency of the MSM remains the same, or even improves. The two methods can be combined for efficient and accurate calculation of acoustic emission waveforms and analysis of AE data for source characterization.

Ajit Mal

Papers

Determination of the properties of composite interfaces by an ultrasonic method

On the surface response of a multilayered solid to a dislocation source.

The Influence of Material Dissipation and Imperfect Bonding on Acoustic Wave Reflection from Layered Solids

AE wavefield calculations in a plate

Advanced fuzzy arithmetic for material characterization of composites using guided ultrasonic waves