QM/MM simulation of liquid water with an adaptive quantum region.

The simulation of complex chemical systems often requires a multi-level description, in which a region of special interest is treated using a computationally expensive quantum mechanical (QM) model while its environment is described by a faster, simpler molecular mechanical (MM) model. Furthermore, studying dynamic effects in solvated systems or bio-molecules requires a variable definition of the two regions, so that atoms or molecules can be dynamically re-assigned between the QM and MM descriptions during the course of the simulation. Such reassignments pose a problem for traditional QM/MM schemes by exacerbating the errors that stem from switching the model at the boundary. Here we show that stable, long adaptive simulations can be carried out using density functional theory with the BLYP exchange-correlation functional for the QM model and a flexible TIP3P force field for the MM model without requiring adjustments of either. Using a primary benchmark system of pure water, we investigate the convergence of the liquid structure with the size of the QM region, and demonstrate that by using a sufficiently large QM region (with radius 6 Å) it is possible to obtain radial and angular distributions that, in the QM region, match the results of fully quantum mechanical calculations with periodic boundary conditions, and, after a smooth transition, also agree with fully MM calculations in the MM region. The key ingredient is the accurate evaluation of forces in the QM subsystem which we achieve by including an extended buffer region in the QM calculations. We also show that our buffered-force QM/MM scheme is transferable by simulating the solvated Cl(-) ion.

Electrorheologic liquid crystals in microsystems: model and measurements

Fluids with a controllable viscosity gained a lot of interest throughout the last years. One of the advantages of these fluids is that they allow to fabricate hydraulic components such as valves with a very simple structure. Although the properties of these fluids are very interesting for microsystems, their applicability is limited at microscale since the particles suspended in these fluids tend to obstruct microchannels. This paper investigates the applicability of electrorheologic Liquid Crystals (LCs) in microsystems. Since LC's do not contain suspended particles, they show intrinsic advantages over classic rheologic active fluids in microapplications. As a matter of fact, LC molecules are usually only a few nanometers long, and therefore, they can probably be used in systems with sub-micrometer channels or other nanoscale applications. This paper presents a novel model describing the electrorheologic behavior of these nanoscale molecules. This model is used to simulate a microvalve controlled by LC's. By comparing measurements and simulations performed on this microvalve it is possible to prove that the model developed in this paper is very accurate. In addition, these simulations and measurements revealed other remarkable properties of LC's, such as high bandwidths and high changes in flow resistance. © 2006 IEEE.

The use of liquid crystals as electrorheological fluids in microsystems: Model and measurements

Fluids with controllable flow properties have gained considerable interest in the past few years. Some of these fluids such as magnetorheologic fluids are now widely applied to active dampers and valves. Although these fluids show promising properties for microsystems, their applicability is limited to the microscale since particles suspended in these fluids tend to obstruct microchannels. This paper investigates the applicability of electrorheologic liquid crystals (LCs) in microsystems. Since LCs do not contain suspended particles, they show intrinsic advantages over classic rheologic fluids in micro-applications. This paper presents a novel physical model that describes the static and the dynamic behaviour of electrorheologic LCs. The developed model is validated by comparing simulations and measurements performed on a rectangular microchannel. This assessment shows that the model presented in this paper is able to simulate both static and dynamic properties accurately. Therefore, this model is useful for the understanding, simulation and optimization of devices using LCs as electrorheological fluid. In addition, measurements performed in this paper reveal remarkable properties of LCs, such as high bandwidths and high changes in flow resistance. © 2006 IOP Publishing Ltd.

Spray flame study using a model gas turbine swirl burner

A model gas turbine burner was employed to investigate spray flames established under globally lean, continuous, swirling conditions. Two types of fuel were used to generate liquid spray flames: palm biodiesel and Jet-A1. The main swirling air flow was preheated to 350°C prior to mixing with airblast-atomized fuel droplets at atmospheric pressure. The global flame structure of flame and flow field were investigated at the fixed power output of 6 kW. Flame chemiluminescence imaging technique was employed to investigate the flame reaction zones, while particle imaging velocimetry (PIV) was utilized to measure the flow field within the combustor. The flow fields of both flames are almost identical despite some differences in the flame reaction zones. © (2013) Trans Tech Publications, Switzerland.

Free space communications with beam steering a two-electrode tapered laser diode using liquid-crystal slm

A free space optical wireless communication system with 3 degree angular coverage and 1.25 GHz modulation bandwidth is reported, in which relatively narrow laser beam of a simultaneous high power, high modulation speed and ultra high modulation efficiency directly modulated two-electrode tapered laser diode is steered using a nematic phase-only Liquid-Crystal On Silicon Spatial Light Modulator (LCOS SLM) by displaying reconfigurable 256 phase level gratings. © 1983-2012 IEEE.

Properties of two model soils stabilized with different blends and contents of GGBS, MgO, lime, and PC

This paper addresses the use of ground granulated blast furnace slag (GGBS) and reactive magnesia (MgO) blends for soil stabilization, comparing them with GGBS-lime blends and Portland cement (PC) for enhanced technical performance. A range of tests were conducted to investigate the properties of stabilized soils, including unconfined compressive strength (UCS), permeability, and microstructural analyses by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The influence of GGBS:MgO ratio, binder content, soil type, and curing period were addressed. The UCS results revealed that GGBS-MgO was more efficient than GGBS-lime as a binder for soil stabilization, with an optimum MgO content in the range of 5-20% of the blends content, varying with binder content and curing age. The 28-day UCS values of the optimum GGBS-MgO mixes were up to almost four times higher than that of corresponding PC mixes. The microstructural analyses showed the hydrotalcite was produced during the GGBS hydration activated by MgO, although the main hydration products of the GGBS-MgO stabilized soils were similar to those of PC. © 2014 American Society of Civil Engineers.

Electrical addressing of polymer stabilized hyper-twisted chiral nematic liquid crystals with interdigitated electrodes: Experiment and model

Electro-optic switching in short-pitch polymer stabilized chiral nematic liquid crystals was studied and the relative contributions of flexoelectric and dielectric coupling were investigated: polymer stabilization was found to effectively suppress unwanted textural transitions of the chiral nematic liquid crystal and thereby enhance the electro-optical performance (high optical contrast for visible light, a near ideal optical hysteresis, fast electro-optic response). Test cells were studied that possessed interdigitated electrodes to electrically address the liquid crystal. Based on simulations, a well-fitted phenomenological description of the electro-optic response was derived considering both flexoelectro-optic and Kerr-effect based electro-optic response. © 2014 AIP Publishing LLC.

Classical two-site fidelity and quantum phase transitions in the Ising model and the extended Hubbard model

In this Letter, the classical two-site-ground-state fidelity (CTGF) is exploited to identify quantum phase transitions (QPTs) for the transverse field Ising model (TFIM) and the one-dimensional extended Hubbard model (EHM). Our results show that the CTGF exhibits an abrupt change around the regions of criticality and can be used to identify QPTs in spin and fermionic systems. The method is especially convenient when it is connected with the density-matrix renormalization group (DMRG) algorithm. (C) 2008 Elsevier B.V. All rights reserved.

Interplay between the Dzyaloshinskii-Moriya anisotropic antisymmetric interaction and the SWAP operation in a two-qubit Heisenberg model

The SWAP operation in a two-qubit Heisenberg model in the presence of Dzyaloshinskii-Moriya (DM) anisotropic antisymmetric interaction is investigated. 1t is shown that the SWAP operation can be implemented for some kinds of DM coupling and the influence of DM couplings is divided into different cases. The conditions of the DM coupling under which the SWAP operation is feasible are established. (C) 2007 Elsevier B.V. All rights reserved.

SWAP operation in the two-qubit Heisenberg XXZ model: Effects of anisotropy and magnetic field

In this paper we study the SWAP operation in a two-qubit anisotropic XXZ model in the presence of an inhomogeneous magnetic field. We establish the range of anisotropic parameter lambda within which the SWAP operation is feasible. The SWAP errors caused by the inhomogeneous field are evaluated.

Kinetic study of hydrolysis of xylan and agricultural wastes with hot liquid water

We investigated the kinetics of hot liquid water (HLW) hydrolysis over a 60-min period using a self-designed setup. The reaction was performed within the range 160-220 °C, under reaction conditions of 4.0 MPa, a 1:20 solid:liquid ratio (g/mL), at 500 rpm stirring speed. Xylan was chosen as a model compound for hemicelluloses, and two kinds of agricultural wastes-rice straw and palm shell-were used as typical feedstocks representative of herbaceous and woody biomasses, respectively. The hydrolysis reactions for the three kinds of materials followed a first-order sequential kinetic model, and the hydrolysis activation energies were 65.58 kJ/mol for xylan, 68.76 kJ/mol for rice straw, and 95.19 kJ/mol for palm shell. The activation energies of sugar degradation were 147.21 kJ/mol for xylan, 47.08 kJ/mol for rice straw and 79.74 kJ/mol for palm shell. These differences may be due to differences in the composition and construction of the three kinds of materials. In order to reduce the decomposition of sugars, the hydrolysis time of biomasses such as rice straw and palm shell should be strictly controlled.

A New Criterion Number for the Boundary Conditions at the Solid/Liquid Interface in Nanoscale

A simple, but important three-atom model was proposed at the solid/liquid interface, leading to a new criterion number, lambda, governing the boundary conditions (BCs) in nanoscale. The solid wall is considered as the face-centered-cubic (fcc) structure. The fluid is the liquid argon with the well-known LJ potential. Based on the concept, the two micro-systems have the same BCs if they have The same criterion number. The degree of the locking BCs is enhanced when lambda equals to 0.757. Such critical criterion number results in the substantial epitaxial ordering and one, two, or even three liquid layers are locked by the solid wall, depending on the coupling energy scale ratio of the solid and liquid atoms. With deviation from the critical criterion number, the flow approaches the slip BCs and there are little ordering structures within the liquid. Always at the same criterion number, the degree of the slip is decreased or the locking is enhanced with increasing the coupling energy scale ratio of the solid and liquid atoms. The above analysis is well confirmed by the molecular dynamics (MD) simulation. The slip length is well correlated in terms of the new criterion number. The future work is suggested to extend the present theory for other microstructures of the solid wall atoms and quasi-LJ potentials.

Two-dimensional photonic lattices in polymer-dispersed liquid crystal composites

The relationship between liquid crystal orientational ordering and optical diffraction properties is investigated for a two-dimensional square photonic lattice fabricated in a polymer-dispersed liquid crystal (PDLC) composite. Modifications of the nematic director field in the liquid crystal domains were induced by an external applied voltage and by heating over the nematic-isotropic (N-I) phase transition. They were studied by optical polarization microscopy and by analysing far-field optical diffraction patterns. The intensities of various diffraction orders (from the zeroth up to the eighth diffraction order) were monitored with a CCD camera, and their variations were correlated with the modifications of the director field.