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

The energy compaction and multiresolution properties of wavelets have made the image fusion successful in combining important features such as edges and textures from source images without introducing any artifacts for context enhancement and situational awareness. The wavelet transform is visualized as a convolution of wavelet filter coefficients with the image under consideration and is computationally intensive. The advent of lifting-based wavelets has reduced the computations but at the cost of visual quality and performance of the fused image. To retain the visual quality and performance of the fused image with reduced computations, a discrete cosine harmonic wavelet (DCHWT)-based image fusion is proposed. The performance of DCHWT is compared with both convolution and lifting-based image fusion approaches. It is found that the performance of DCHWT is similar to convolution-based wavelets and superior/similar to lifting-based wavelets. Also, the computational complexity (in terms of additions and multiplications) of the proposed method scores over convolution-based wavelets and is competitive to lifting-based wavelets.

Multifocus and multispectral image fusion based on pixel significance using discrete cosine harmonic wavelet transform

A review on state of health estimations and remaining useful life prognostics of lithium-ion batteries

Multifocus and multispectral image fusion based on pixel significance using discrete cosine harmonic

The Department of Mechanical Engineering (https:// www.mccormick.northwestern.edu/mechanical/graduate) prepares graduates for careers in industry, research, and academia. Students specialize in Design/Manufacturing/Tribology, Dynamics, Control, Robotics, Neural Engineering, Simulation Driven Engineering, Solid Mechanics, Fluid Dynamics, Nanotechnology/MEMS, Bioengineering and Biomechanics, Energy and Sustainability, Engineering Design and Innovation, Product Development, Engineering Management and other disciplines.

What is Mechanical Engineering

Helix unwinding in ferroelectric liquid crystals induced by an electric field is theoretically studied on the basis of the continuum theory. By applying a weak electric field tilted to the smectic layers, the contribution of the dielectric interaction energy density to the total free energy density is increased. Approximation methods are used to calculate the free energy for different tilt angles between the electric field and the smectic layers. The obtained results suggest selecting the optimal number of pitches in the film that matches to the minimum of the free energy.

Helix unwinding in ferroelectric liquid crystals induced by tilted electric field

In this contribution we report a theoretical study of relaxation processes in surface-stabilized ferroelectric liquid crystals with spontaneous polarization. The influence of pulsed electric field on the behavior of ferroelectric liquid crystal in the SmC* phase, which is placed in a thin cell with strong anchoring of SmC* molecules with the boundary substrate, is studied. In the vicinity of the substrate interface, temporal dependence of the azimuthal motion of the director induced by electric field is obtained. The response to the external distortion of ferroelectric liquid crystal confined between two microstructured substrates is the occurrence of periodic temporal formation of solitons connected with the distortion of the director field n in the sample bulk. The interplay between microstructured substrates and director distribution of the ferroelectric SmC* phase is explained by the Frenkel–Kontorova model for a chain of atoms, but adapted for the continuum problem.

Relaxation Dynamics of Ferroelectric Liquid Crystals in Pulsed Electric Field

Recent achievements in the photoalignment technique for fabrication of optically rewritable electronic paper with high performance characteristics are surveyed with emphasis on temporal constraints on the exposure process. The possibility of creating electrode-free electronic paper has very important practical aspects. However, many existing studies do not include sufficient analysis on how to achieve acceptable reflective characteristics within short exposure time. In order to achieve this goal, we have applied the rotational diffusion model. We find that the parameters of the diffusion model can be adjusted to get acceptable light-reflecting characteristics within 10 s of exposure. In comparison with the long-time exposure, the reflectance coefficient reduces by 24%. The route to material improvements for optimized e-paper device is discussed.

Optically Rewritable Liquid Crystal Displays: Characteristics and Performance

A comprehensive theory of light-reflective characteristics and experimental technique of liquid crystal layer thickness control for flexible optically rewritable electronic paper is presented. Cylindrical pillars were used to control the gap between flexible substrates. The introduced prototype of optically rewritable electronic paper has shown very promising performance. In this regard, we report theoretical results of structural photosensitive alignment of nematic liquid crystals on flexible substrate. The focus of theoretical study is on understanding the self-assembled complex structure, governed by the interplay between surface anchoring and liquid crystal elasticity. Mueller matrix spectroscopic ellipsometry was used to study light-reflecting characteristics and polarization properties of the twisted nematic film.

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Structural and Optical Characteristics of Flexible Optically Rewritable Electronic Paper

The effects in electrostatic models of chevron surface-stabilized ferroelectric liquid crystals are investigated through numerical modeling. To study smectic C* director distribution within the cell, we consider two nonlinear approaches: the chevron interface does not interplay with the electric field; the electric field interplays with the chevron interface. The obtained results of the director field distribution are compared with the earlier linearized studies. We find that whether or not the electric field interplays with the chevron interface, the electro–optic response requires a generalized approach for its description. The threshold electric field, which is necessary for switching between two stable director states in the chevron cell is evaluated. This study suggests that, in many cases of practical interest, electro–optic response to the electric field and the threshold electric field can be precisely estimated. We argue that, beside being numerically efficient, our approach provides a convenient and a novel standpoint for looking at the electro–optic response problem.

https://iopscience.iop.org/article/10.1088/1674-1056/25/12/126101/pdf

Aleksey Kudreyko

Papers

Helix unwinding in ferroelectric liquid crystals induced by tilted electric field

Relaxation Dynamics of Ferroelectric Liquid Crystals in Pulsed Electric Field

Optically Rewritable Liquid Crystal Displays: Characteristics and Performance

Structural and Optical Characteristics of Flexible Optically Rewritable Electronic Paper

Electro-optic response in thin smectic C* film with chevron structures