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

Multiscale modeling and simulation of polymer nanocomposites

Due to their atomically precise structures and intriguing chemical/physical properties, metal nanoclusters are an emerging class of modular nanomaterials. Photo-luminescence (PL) is one of their most fascinating properties, due to the plethora of promising PL-based applications, such as chemical sensing, bio-imaging, cell labeling, phototherapy, drug delivery, and so on. However, the PL of most current nanoclusters is still unsatisfactory-the PL quantum yield (QY) is relatively low (generally lower than 20%), the emission lifetimes are generally in the nanosecond range, and the emitted color is always red (emission wavelengths of above 630 nm). To address these shortcomings, several strategies have been adopted, and are reviewed herein: capped-ligand engineering, metallic kernel alloying, aggregation-induced emission, self-assembly of nanocluster building blocks into cluster-based networks, and adjustments on external environment factors. We further review promising applications of these fluorescent nanoclusters, with particular focus on their potential to impact the fields of chemical sensing, bio-imaging, and bio-labeling. Finally, scope for improvements and future perspectives of these novel nanomaterials are highlighted as well. Our intended audience is the broader scientific community interested in the fluorescence of metal nanoclusters, and our review hopefully opens up new horizons for these scientists to manipulate PL properties of nanoclusters. This review is based on publications available up to December 2018.

Tailoring the photoluminescence of atomically precise nanoclusters.

ConspectusThe vast amount of plastic waste emitted into the environment and the increasing concern of potential harm to wildlife has made microplastic and nanoplastic pollution a growing environmental concern. Plastic pollution has the potential to cause both physical and chemical harm to wildlife directly or via sorption, concentration, and transfer of other environmental contaminants to the wildlife that ingest plastic. Small particles of plastic pollution, termed microplastics (>100 nm and <5 mm) or nanoplastics (<100 nm), can form through fragmentation of larger pieces of plastic. These small particles are especially concerning because of their high specific surface area for sorption of contaminants as well as their potential to translocate in the bodies of organisms. These same small particles are challenging to separate and identify in environmental samples because their size makes handling and observation difficult. As a result, our understanding of the environmental prevalence of nanoplastics and ...

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Separation and Analysis of Microplastics and Nanoplastics in Complex Environmental Samples

The surge of interest in and scientific publications on the structure and properties of nanocomposites has made it rather difficult for the novice to comprehend the physical structure of these new materials and the relationship between their properties and those of the conventional range of composite materials. Some of the questions that arise are: How should the reinforcement volume fraction be calculated? How can the clay gallery contents be assessed? How can the ratio of intercalate to exfoliate be found? Does polymerization occur in the clay galleries? How is the crystallinity of semi-crystalline polymers affected by intercalation? What role do the mobilities of adsorbed molecules and clay platelets have? How much information can conventional X-ray diffraction offer? What is the thermodynamic driving force for intercalation and exfoliation? What is the elastic modulus of clay platelets? The growth of computer simulation techniques applied to clay materials has been rapid, with insight gained into the structure, dynamics and reactivity of polymer–clay systems. However these techniques operate on the basis of approximations, which may not be clear to the non-specialist. This critical review attempts to assess these issues from the viewpoint of traditional composites thereby embedding these new materials in a wider context to which conventional composite theory can be applied. (210 references)

A critical appraisal of polymer-clay nanocomposites.

Nacre, the inner iridescent layer of mollusks shell is a bio-nanocomposite with the mineral aragonite as a major constituent and 2-5% of organics mainly in the form of proteins. Our multiscale modeling and experimental studies reveal that the microstructure and the small weight percent of organics are the key parameters attributed to the extreme toughness of nacre. We report that the presence of platelet interlocks nacre have a significant role in the enhancement of mechanical properties. Molecular simulation study is conducted to understand the behavior of aragonite-organic interface. The mechanical behavior of organics and inorganics in presence of each other is described using steered molecular dynamics simulations. This provides some understanding on the deformation mechanisms of the protein present between the aragonite layers. Our nanoindentation results indicate that the elastic modulus and hardness of nacre decreases as it is exposed to a denaturing temperature for proteins. The changes in the organic inorganic interaction have been experimentally described using Fourier Transform Infrared Spectroscopy. This work gives insight into the contribution of the various factors existing at different length scales on the overall mechanical behavior of nacre.

Mechanical Properties of Biological Nanocomposite Nacre: Multiscale Modeling and Experiments on Nacre from Red Abalone

Solvent triggered shape morphism of 4D printed hydrogels

This work reports the growth of stable TiO2 nanotube arrays on flexible Kapton substrates by electrochemical anodization of a sputtered Ti (titanium) film. Although such nanotubes are conventionall...

TiO2 Nanotube Arrays on Flexible Kapton Substrates for Photo-Electrochemical Solar Energy Conversion

Polymer thin film coating on Biomaterial

Laryngeal cancer spread occurs through glandular pathways. The mode and pattern of cancer spread in the larynx varies in accordance with the site and its relationship to the regional glandular units, in addition to lymphatics in the larynx. This has been substantiated in the present series consisting of twenty five cancerous and two normal larynges, removed at surgery and autopsy respectively, which were studied by the technique of whole organ serial sectioning.

Pijush Ghosh

Papers

Mechanical Properties of Biological Nanocomposite Nacre: Multiscale Modeling and Experiments on Nacre from Red Abalone

Solvent triggered shape morphism of 4D printed hydrogels

TiO2 Nanotube Arrays on Flexible Kapton Substrates for Photo-Electrochemical Solar Energy Conversion

Polymer thin film coating on Biomaterial

Glandular theory of cancer spread in the larynx