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.

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

NDE of Elastic Properties of Fiber-Reinforced Composite Materials Using Ultrasonic Oblique Insonification

The critical role played by adhesive bonds in lap joints is well known A good knowledge of the mechanical properties of adhesive bonds in lap joints is a prerequisite to the design and reliable prediction of the performance of these bonded structures Furthermore, the lap joint may be subject to high-temperature environments in service Early detection of the degree of thermal degradation in adhesive bonds is required under these circumstances A variety of ultrasonic nondestructive evaluation (NDE) techniques can be used to determine the thickness and the elastic moduli of adhesively bonded joints In this paper we apply a previously developed technique based on the leaky Lamb wave (LLW) experiment to investigate the possibility of characterizing the thermal degradation of adhesive bonds in lap joints The degradation of the adhesive bonds is determined through comparison between experimental data and theoretical calculations

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=2552&context=qnde

Ultrasonic Evaluation of Thermal Degradation in Adhesive Bonds

Stress relaxation of a patterned thin film on diaphragms of different material and thickness was investigated through experimental study and numerical simulation. The diaphragm deflections, caused by relaxation of the residual stress in a patterned thin film residing on top, were measured using a Twyman-Green laser interferometer. The first diaphragm used was a Si 3 N 4 (top)/SiO 2 /Si composite diaphragm and the second a 0.5-μm-thick Si 3 N 4 membrane. Custom-written simulation software, which uses a novel numerical algorithm named Nonlinear Sequential Analysis (N-LISA), was utilized to calculate the stress distribution in the patterned thin film and the diaphragm substrate. Agreement between the model and the experimental results was satisfactory. Simulation of the system balance between a tensile-stressed circular Ti film and a stress-free Si substrate of different thickness clearly shows a transition in the substrate behavior from a pure plate to a pure membrane. Interestingly, the deflection of the Si substrate caused by the residual stress in the Ti film reaches its maximum at a certain substrate thickness where plate and membrane characteristics coexist. This study addresses some basic mechanics issues involved in modern devices dealing with thin diaphragms.

Stress relaxation of a patterned microstructure on a diaphragm

A model based analysis of the interaction of high intensity focused ultrasound with biological materials is carried out in an effort to predict the path of the sound waves and the temperature field in the focal region. A finite element based general purpose code called PZFlex is used to determine the effects of nonlinearity and geometrical complexity of biological structures. It was found that at frequencies of interest in therapeutic applications, the nonlinear effects are usually negligible and the geometrical complexities can be handled through a sub-structuring procedure. An approximate analytical method is developed as an alternative to the purely numerical approach used in PZFlex. The mechanical and thermal effects in two-layered fluid material systems induced by high-frequency focused ultrasound are calculated through this analytical method. The analytical method is shown to be computationally much more efficient than the numerical method and to yield results with acceptable accuracy for clinical applications.

An analytical model for the interaction of focused ultrasound with biological structures

Considerable efforts have been made in recent years to develop quantitative nondestructive evaluation (NDE) techniques for composite materials, which are being used increasingly in primary structures. The leaky Lamb wave phenomenon has shown considerable potential as an NDE method [1]. Most results reported in this area to date have been concerned with unidirectional laminates [2–4]. This is attributed to the complexity involved in theoretically predicting the response of these materials, as well as to certain difficulties associated with the experimental research. In practice, structural composites are made up of layers in various orientations. Their stacking order is dependent upon the requirements of the particular application. Therefore, the capability of analyzing the behavior of Lamb waves in multiorientation laminates is crucial for the application of LLW to composites.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=2220&context=qnde

Ajit Mal

Papers

NDE of Elastic Properties of Fiber-Reinforced Composite Materials Using Ultrasonic Oblique Insonification

Ultrasonic Evaluation of Thermal Degradation in Adhesive Bonds

Stress relaxation of a patterned microstructure on a diaphragm

An analytical model for the interaction of focused ultrasound with biological structures

Leaky Lamb Waves (LLW) in Multiorientation Composite Laminates