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

In recent years, the magneto-optical properties of magnetic nanofluids have received increasing attention due to their wide range of applications in various solar energy conversion processes and also as smart fluids in tunable photonic device, optical switch, optical fiber sensor, etc. This article reviews up-to-date developments in magneto-optical transmission in ferrofluids for different optical applications. With magnetic field, the magnetic nanoparticle will undergo interesting structural transitions including chainlike formation and lateral coalescence, leading to various light transmission phenomena in ferrofluids. The orientation of the magnetic field relative to the incident light has a significant influence on the intensity of transmitted light through the suspensions. For incident light along the magnetic field, the polarization direction of light has a negligible effect on the magneto-optical transmission. However, the polarization direction of light should make a great difference for light normal to the field direction. These recent studies are comprehensively reviewed, and their main findings and potential applications are also presented and discussed. Our study is supposed to provide a general view on the research trends, existing problems and future work for the investigation of magneto-optical transmission in magnetic nanofluids.

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Magneto-optical transmission in magnetic nanoparticle suspensions for different optical applications: a review

UV-visible light-induced antibacterial and photocatalytic activity of half harmonic generator WO3 nanoparticles synthesized by Pulsed Laser Ablation in water

Temporal evolution of equilibrium and non-equilibrium magnetic field driven microstructures in a magnetic fluid

Magnetic nanofluids (Ferrofluids): Recent advances, applications, challenges, and future directions.

The field induced anisotropic structure formation in magnetic fluids (popularly known as ferrofluids) is exploited in several applications such as optoelectronic devices, sensors, heat transfer, and biomedicine. We study the role of surface charge screening on critical magnetic fields associated with field induced structural formation in a charged magnetic nanofluid of hydrodynamic diameter ∼200 nm, containing superparamagnetic iron-oxide nanoparticles of diameter ∼10 nm. Three distinct critical magnetic fields are identified from the drastic changes in transmitted forward scattering light intensity. The first critical field occurs at the commencement of small aggregate formation, the second one on completion of linear aggregation process before the commencement of lateral coalescence of individual chains, and the third one occurs when the densely packed columnar solidlike structures are formed through zippering of individual chains. During the structural transitions, the transmitted light spot is transformed into a diffused ring, with distinct speckle characteristics, due to scattering from self-assembled linear aggregates. The speckle pattern was fully reversible, and the aggregation rate was found to increase linearly with increasing surfactant concentration. The experimentally observed critical fields were in good agreement with theoretical predictions at lower surfactant concentrations. These results provide better insights into the field induced structure formation useful in designing magnetic fluidic based optical devices such as tunable filters and optical switches.

Effect of surface charge screening on critical magnetic fields during field induced structural transitions in magnetic fluids

We probe the influence of particle size polydispersity on field-induced structures and structural transitions in magnetic fluids (ferrofluids) using phase contrast optical microscopy, light scattering and Brownian dynamics simulations. Three different ferrofluids containing superparamagnetic nanoparticles of different polydispersity indices (PDIs) are used. In a ferrofluid with a high PDI (∼0.79), thin chains, thick chains, and sheets are formed on increasing the in-plane magnetic field, whereas isotropic bubbles, and hexagonal and lamellar/stripe structures are formed on increasing the out-of-plane magnetic field over the same range. In contrast, no field-induced aggregates are seen in the sample with low polydispersity under the above conditions. In a polydisperse sample, bubbles are formed at a very low magnetic field strength of 30 G. Insights into the structural evolution with increasing magnetic field strength are obtained by carrying out Brownian dynamics simulations. The crossovers from isotropic, through hexagonal columnar, to lamellar/stripe structures observed with increasing field strength in the high-polydispersity sample indicate the prominent roles of large, more strongly interacting particles in structural transitions in ferrofluids. Based on the observed microstructures, a phase diagram is constructed. Our work opens up new opportunities to develop optical devices and access diverse structures by tuning size polydispersity.

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Dillip Kumar Mohapatra

Papers

Temporal evolution of equilibrium and non-equilibrium magnetic field driven microstructures in a magnetic fluid

Effect of surface charge screening on critical magnetic fields during field induced structural transitions in magnetic fluids

Influence of size polydispersity on magnetic field tunable structures in magnetic nanofluids containing superparamagnetic nanoparticles

Investigations on magnetic field induced optical transparency in magnetic nanofluids

Reconfiguring nanostructures in magnetic fluids using pH and magnetic stimulus for tuning optical properties