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In a previous paper [J. Chem. Phys. 119, 11864 (2003)], we derived a set of two coupled equations which describe electron transfer in the presence of dissipation at high temperature. Employing the low temperature extension of the Fokker-Planck operator, suggested by Haake and Reibold [Phys. Rev. A 32, 2462 (1985)] and Ankerhold [Europhys. Lett. 61, 301 (2003)], we show that one may extend the generalized Zusman equations in a similar manner to low temperature. Numerical simulation shows that addition of the temperature-dependent term which couples the coordinate and momentum causes an increase in the electron transfer rate as compared to the rate obtained from the previous high temperature equations. The increase in the rate comes from the increase in the equilibrium variances of the coordinate and momentum. The low temperature quantum theory allows for higher energy portions of phase space to contribute to the electron transfer rate where the rate is higher thus enhancing the overall rate. [ABSTRACT FROM AUTHOR]

The reliability and accuracy of finite element models of metal machining are heavily reliant on the underlying material flow stress models. The aim of this study is to characterize the relation between the flow stress models and the chip morphology to provide a deeper insight into the process of serrated chip formation. Firstly, in the context of a flow stress model, the critical conditions for generation of the serrated chips are theoretically analyzed. Then, simulations are performed using two different constitutive models with five parameters sets, and the results are discussed in relation to how they verify the theoretical results. In order to better understand the process of serrated chip formation, attention is concentrated on the critical steps characterizing the formation of a single chip segment. The cutting process parameters (stress, strain, and temperature) are discussed. In addition, the mechanism by which the chip morphology transforms from continuous to serrated with increasing cutting speed is investigated in terms of the variation of flow stress curves. The results show that the slope of decrease and the strain value at the peak point of flow stress curves both greatly affect chip morphology. That is, the slope of decrease of the flow stress curve largely controls the formation of serrated chips, while the strain point at the peak determines the frequency and degree of serration of chips. It is found that simulations by manipulating well the flow stress models can produce results for chip morphology, cutting forces, etc. that are closer to those obtained experimentally. [ABSTRACT FROM AUTHOR]

To research an effective measure of reducing the soot and NOx in engine at the same time, different nozzle hole diameters coupled with exhaust gas re-circulation were adopted in this study based on KH-ACT spray breakup model, which takes the aerodynamic- induced, cavitation-induced, and turbulence-induced breakup into account. The SAGE detailed chemistry combustion and the new atomization model used in the simulation have been verified with the experiment data from YN4100QBZL engine. Different diesel nozzles were adopted in the study combined with different exhaust gas re-circulation rates ranging from 0% to 40%. The simulation results show that the NOx emission could be reduced effectively for both small (0.1 mm) and large (0.15 mm) diesel nozzles when increasing exhaust gas re-circulation ratio. The soot emission increases for the small nozzle hole size as the exhaust gas re-circulation increasing. However, when it comes to the large diesel nozzle, the emission increases slightly firstly and decreases quickly when the exhaust gas re-circulation rate above 20%. [ABSTRACT FROM AUTHOR]

Refractive indices of the highly polar compounds are evaluated by computation from first principles combined with molecular dynamics simulation. The molecular polarisability is obtained by density functional theory (DFT) using the B3LYP potential; the equilibrium density in the liquid phase is calculated utilising the GROMOS force field simultaneously. This combination of method is shown to provide an economical methodology for estimating the refractive indices of a wide range of polar species. All the evaluation data for the considered highly polar compounds are good agreement to the available data based on the standard of experiment. [ABSTRACT FROM PUBLISHER]

Cooperative spectrum sensing (CSS) is considered as a powerful approach to improve the utilization of scarce radio spectrum resources. However, most of CSS schemes assume all secondary users (SU) are honest, and thus offering opportunities for malicious SUs to launch the spectrum sensing data falsification attack (SSDF attack). To combat such misbehaved behaviors, recent efforts have been made to trust schemes. In this paper, we argue that powering CSS with traditional trust schemes is not enough. The rational SSDF attack is found in this paper. Unlike the simple SSDF attack, rational SSDF attackers send out false sensing data on a small number of interested primary users (PUs) rather than all PUs. In this case, rational SSDF attackers can keep up high trustworthiness, resulting in difficultly detecting malicious SUs in the traditional trust schemes. Meanwhile, a defense scheme using a novel trust approach is proposed to counter rational SSDF attack. Simulation results show that this scheme can successfully reduce the power of rational SSDF, and thus ensure the performance of CSS. [ABSTRACT FROM AUTHOR]

A high-order dual-band bandpass filter using novel combined stub-loaded resonators (CSLRs) is presented in this paper. The key merits of the filter configuration are that the center frequency and also the bandwidth of each passband can be controlled conveniently. Moreover, it can build the high-order dual-band bandpass filters using the proposed resonators because of the sufficient coupling through the four symmetric stubs. A fifth-order dual-band bandpass filter designed at 2.5/3.5 GHz was built and tested. The measurement and simulation results agree very well, demonstrating the validity of the method. [ABSTRACT FROM AUTHOR]

A novel artificial cobweb routing algorithm (ACRA) for routing the tree-type physical topology of a low-voltage distribution network in a smart grid is proposed and analyzed in this paper. The establishment, maintenance and reconstruction of the route are presented. The artificial cobweb routing algorithm is shown to have broad general applicability for power line communication. To provide a theoretical foundation for further research, the communication delay of the network is calculated accurately. Simulation analysis of the communication delay and throughputs, which were based on Opnet14.5, demonstrate the accuracy of the theoretical calculation. For the performance evaluation of ACRA, a test-bed that includes PLC nodes with the ACRA is set up in a noisy environment. Experimental results show the feasibility of the ACRA algorithm. These indicate that ACRA is effective for guaranteeing Quality of Service (QoS) and reliability in power line communication. [ABSTRACT FROM AUTHOR]

Enhanced heat transfer in nanofluids is mainly an effect of flow characteristics. In this article, we investigate the flow field of SiO2/water nanofluids using a single-phase model, a Eulerian-Eulerian multiphase model, and a Euler-Lagrange multiphase model, performing qualitative and quantitative comparisons with experimental data. We find that the chief microscopic mechanisms underlying microflow enhancement involve irregular micromotions of nanoparticles and an intensified turbulence of fluids. Of the three models, the Euler-Lagrange model is the most accurate, the single-phase model is the least predictive, while the accuracy of the Eulerian-Eulerian model lies in between. [ABSTRACT FROM AUTHOR]

This paper reports the simulation results for the unsteady cavitating turbulent flow in a Francis turbine using the mixture model for cavity-liquid two-phase flows. The RNG k- ε turbulence model is employed in the Reynolds averaged Navier-Stokes equations in this study. In the mixture model, an improved expression for the mass transfer is employed which is based on evaporation and condensation mechanisms with considering the effects of the non-dissolved gas, the turbulence, the tension of interface at cavity and the effect of phase change rate and so on. The computing domain includes the guide vanes, the runner, and the draft tube, which is discretized with a full three-dimensional mesh system of unstructured tetrahedral shapes. The finite volume method is used to solve the governing equations of the mixture model and a full coupled method is combined into the algorithm to accelerate the solution. The computing results with the mixture model have been compared with those by the single-phase flow model as well as the experimental data. The simulation results show that the cavitating flow computation based on the improved mixture model agrees much better with experimental data than that by the single-phase flow calculation, in terms of the amplitude and dominated frequency of the pressure fluctuation. It is also observed from the present simulations that the amplitude of the pressure fluctuation at small flow rate is larger than that at large flow rate, which accords with the experimental data. [ABSTRACT FROM AUTHOR]

Hiding capacity is very important for efficient covert communications. For JPEG2000 compressed images, it necessary to enlarge the hiding capacity because the available redundancy is very limited. In addition, the bitstream truncation makes it difficult to hide information. In this paper, a high-capacity steganography scheme is proposed for the JPEG2000 baseline system, which uses bit-plane encoding procedure twice to solve the problem due to bitstream truncation. Moreover, embedding points and their intensity are determined in a well defined quantitative manner via redundancy evaluation to increase hiding capacity. The redundancy is measured by bit, which is different from conventional methods which adjust the embedding intensity by multiplying a visual masking factor. High volumetric data is embedded into bit-planes as low as possible to keep message integrality, but at the cost of an extra bit-plane encoding procedure and slightly changed compression ratio. The proposed method can be easily integrated into the JPEG2000 image coder, and the produced stego-bitstream can be decoded normally. Simulation shows that the proposed method is feasible, effective, and secure. [ABSTRACT FROM AUTHOR]

We present the first approach to the excess electron solvation in a novel medium, room-temperature ionic liquid, using ab initio molecular dynamics simulation techniques in this work. Results indicate that an excess electron can be solvated in the [dmim]+Cl−IL as long-lived delocalized states and two short-lifetime localized states, one a single-cation-residence parasitical type and the other a double-cation-based solvated type state. The presence of a low-lying π*-LUMO as the site of excess electron residence in the cation moiety disables the C−H unit as a H-bond donor, while the aromaticity requirement of the rings and the effect of the counterion Cl−’s make the resulting ion pairs a weak stabilizer for an excess electron. Although no large solvent reorganization in IL was found at the picosecond scale, the IL fluctuations sufficiently modify the relative energy levels of the excess electron states to permit facile state-to-state conversion and adiabatic migration. The binding energy of the excess electron is only ∼0.2 eV, further indicating that it is in a quasi-free state, with a large drift mobility, suggesting that ILs are unreactive and promising mediators for transport of excess electrons, in agreement with the experimental findings. The present study provides insight into the novel electron solvation character in a new class of promising media for physical and chemical processes, which are fundamental for understanding of electron migration mechanisms in IL-based applications. [ABSTRACT FROM AUTHOR]

To realize the full potential of a gyrotron backward- wave oscillator (gyro-BWO), an energy recovery system was designed using Particle-In-Cell (PlC) simulations and optimized using both a genetic algorithm and PlC simulations. Simulations were carried out to optimize a periodic structure for separation of the spent electron beam and the output radiation produced by a gyro-BWO in the 8.0-9.5 GHz frequency range. The spent electron beam can be collected using a multistage depressed collector. The number and electric potentials of the electrodes were optimized to achieve the best overall recovery efficiency for specific parameters of the spent beam. The 3-D PlC code MAGIC was used to simulate the electrons' trajectories and a genetic algorithm was used to refine the electrode shapes for optimum efficiency. [ABSTRACT FROM AUTHOR]

The paper reports progress in the development of a practical probabilistic model for the estimation of expected annual damage induced by hurricane winds in residential structures. The estimation of the damage is accomplished in several steps. First, basic damage modes for components of specific building types are defined. Second, the damage modes are combined in possible damage states, whose probabilities of occurrence are calculated as functions of wind speeds from Monte Carlo simulations conducted on engineering numerical models of typical houses. The paper describes the conceptual framework for the proposed model, and illustrates its application for a specific building type with hypothetical probabilistic input. Actual probabilistic input must be based on laboratory studies, postdamage surveys, insurance claims data, engineering analyses and judgment, and Monte Carlo simulation methods. The proposed component-based model is flexible and transparent. It is therefore capable of being readily scrutinized. The model can be used in conjunction with historical loss data, to which it can readily be calibrated. [ABSTRACT FROM AUTHOR]

The three-dimensional premixed H2-O2 detonation propagation in rectangular ducts is simulated using an in-house parallel detonation code based on the second-order space–time conservation element and solution element (CE/SE) scheme. The simulation reproduces three typical cellular structures by setting appropriate cross-sectional size and initial perturbation in square tubes. As the cross-sectional size decreases, critical cellular structures transforming the rectangular or diagonal mode into the spinning mode are obtained and discussed in the perspective of phase variation as well as decreasing of triple point lines. Furthermore, multiple cellular structures are observed through examples with typical aspect ratios. Utilizing the visualization of detailed three-dimensional structures, their formation mechanism is further analyzed. [ABSTRACT FROM AUTHOR]

Charge transfer between tyrosine and tryptophan residues in proteins is continuously a hot topic because of its important biological implication. On the basis of DFT calculations and ab initio molecular dynamics simulations, several possible proton/electron cooperative transfer mechanisms from tyrosine to a tryptophan radical (or cation) without or with the assistence of a base in proteins are proposed in this work which range from direct proton-coupled π-electron π-channel/σ-channel transfers (PCπEπT versus PCπEσT) to proton-coupled long-range hopping mechanisms depending on the peptide conformations. In general, because of a smaller ionization potential, tryptophan readily behaves as two oxidized states: dehydrogenated neutral radical and ionized radical cation. For the neutral radical, the proton/electron transfers between a tyrosine and a tryptophan radical prefer a cooperative direct coupling mode through the PCπEπT or PCπEσT mechanism if two residues are proximal or can approach each other, while they cannot take place without assistence if two residues are far apart. The tryptophan radical cation prefers to form a complex with tyrosine to stabilize the hole when two residues are proximal or can approach each other. However, the electron transfer from tyrosine to tryptophan could occur via a hopping mechanism but is regulated by a base as a proton acceptor in the vicinity of tyrosine when two residues are separated. The dynamics properties and characters for these transfer events are also presented. The energetics comparison indicates that the energy barriers for the direct PCET (PCπEπT or PCπEσT) mechanisms are higher than those of the base-assisting hopping mechanism (6.8−12.5 versus ≤4.9 kcal/mol), implying the latter is a favorable way for the proton/electron cooperative transfers. Hopefully, this work provides some helpful information for understanding the mechanisms of physiologically important electron transfer reactions. [ABSTRACT FROM AUTHOR]

Abstract We propose a novel 8-level multidimensional intensity modulation scheme with the goal of achieving transmission rates higher than 200 Gbps when using only commercially available components. The generation of this modulation scheme is explained here and it is shown to increase the noise tolerance when compared with the 8-level pulse amplitude modulation (PAM-8), at the expense of spectral efficiency. We show that the proposed 3-dimensional (3D) modulation provides the same relative minimum distance gain for both non-duobinary (non-DB) and duobinary (DB) signaling. Gains ranging from 1 dB and up to 1.9 dB are shown in simulations for bit-error rates (BER) equal to or below 4x10−3, when comparing with the classic PAM-8. We demonstrate experimentally that 3D PAM-8 lowers the BER by up to 10 times for non-DB transmissions and by up to 3 times for DB transmissions. The proposed multidimensional modulation increases the maximum achievable bit rate from 205 Gbps (with PAM-8) up to roughly 240 Gbps, enabling 200 Gbps net rate single-lambda transmissions for next generation intra- and inter-datacenter optical transmission systems. [ABSTRACT FROM AUTHOR]