Phase optimized skeletal mechanisms for engine simulations

Adaptive chemistry is based on the principle that instead of having one comprehensive model describing the entire range of chemical source term space (typically parameters related to temperature, pressure and species concentrations), a set of computationally simpler models are used, each describing a local region (in multidimensional space) or phases (in zero-dimensional space). In this work, an adaptive chemistry method based on phase optimized skeletal mechanisms (POSM) is applied to a 96 species n-heptane–isooctane mechanism within a two-zone zero-dimensional stochastic reactor model (SRM) for an spark-ignition (SI) Engine. Two models differing only in the extent of reduction in the phase mechanism, gave speed-up factors of 2.7 and 10. The novelty and emphasis of this study is the use of machine learning techniques to decide where the phases are and to produce a usable phase recognition. The combustion process is automatically divided up into an ‘optimal’ set of phases through machine learning clustering based on fuzzy logic predicates involving a necessity parameter (a measure giving an indication whether a species should be included in the mechanism or not). The mechanism of each phase is reduced from the full mechanism based on this necessity parameter with respect to the conditions of that phase. The algorithm to decide which phase the process is in is automatically determined by another machine learning method that produces decision trees. The decision tree is made up of asking whether the mass fraction values were above or below given values. Two POSM studies were done, a conservative POSM where the species in each phase are eliminated based on a necessity parameter threshold (speed-up 2.7) and a further reduced POSM where each phase was further reduced by hand (speed-up 10). The automated techniques of determining the phases and for creating the decision tree are very general and are not limited to the parameter choices of this paper. There is also no fundamental limit as to the size of the original detailed mechanism. The interfacing to include POSM in an application does not differ significantly from using the original detailed mechanism.     

On the difference between negative damping and eigenmode synchronization as two phonation onset mechanisms

Negative damping and eigenmode synchronization as two different mechanisms of phonation onset are distinguished. Although both mechanisms lead to a favorable phase relationship between the flow pressure and the vocal fold motion as required for a net energy transfer into the vocal folds, the underlying mechanisms for this favorable phase relationship are different. The negative damping mechanism relies on glottal aerodynamics or acoustics to establish before onset and maintain after onset the favorable phase relationship, and therefore has minimum requirements on vocal fold geometry and biomechanics. A single degree-of-freedom vocal fold model is all that is needed for self-oscillation in the presence of a negative damping mechanism. In contrast, the mechanism of eigenmode synchronization critically depends on the geometrical and biomechanical properties of the vocal folds (at least 2-degrees-of-freedom are required), and has little requirement on the glottal aerodynamics other than flow separation. The favorable phase relation is established once synchronization occurs, regardless of the phase relationship imposed by glottal aerodynamics before onset. Unlike that of the negative damping mechanism, initiation of eigenmode synchronization requires neither a velocity-dependent flow pressure nor an alternating convergent-divergent glottis. The clinical implications of the distinctions between these two mechanisms are discussed.     

Intracavity weak nonlinear phase shifts with single photon driving

We investigate a doubly resonant optical cavity containing a Kerr nonlinear medium that couples two modes by a cross phase modulation. One of these modes is driven by a single photon pulsed field, and the other mode is driven by a coherent state. We find an intrinsic phase noise mechanism for the cross phase shift on the coherent beam which can be attributed to the random emission times of single photons from the cavity. An application to a weak nonlinearity phase gate is discussed.     

Supersolid hard-core bosons on the triangular lattice

We determine the phase diagram of hard-core bosons on a triangular lattice with nearest-neighbor repulsion, paying special attention to the stability of the supersolid phase. Similar to the same model on a square lattice we find that for densities rho<1/3 or rho>2/3 a supersolid phase is unstable and the transition between a commensurate solid and the superfluid is of first order. At intermediate fillings 1/3相似文献   

Pseudo-gap phase and duality in a holographic fermionic system with dipole coupling on Q-lattice

We classify the different phases by the "pole-zero mechanism" for a holographic fermionic system which contains a dipole coupling with strength p on a Q-lattice background. A complete phase structure in p space can be depicted in terms of Fermi liquid, non-Fermi liquid, Mott phase and pseudo-gap phase. In particular, we find that in general the region of the pseudo-gap phase in p space is suppressed when the Q-lattice background is dual to a deep insulating phase, while for an anisotropic background, we have an anisotropic region for the pseudo-gap phase in p space as well. In addition, we find that the duality between zeros and poles always exists regardless of whether or not the model is isotropic.     

The effect of oxygen–oxygen repulsion in the production of water from hydrogen–oxygen reaction on the surface: A computer simulation study

The formation of water from hydrogen–oxygen reaction on a metal surface is of immense importance due to the technological reasons. This reaction has been studied via a thermal mechanism on a Pt single crystal surface where the two molecules, H₂ and O₂, have been adsorbed dissociatively in atomic form. The reaction takes place between the adsorbed atoms through an intermediate OH radical. We have studied this reaction via a thermal (Langmuir–Hinshelwood mechanism) as well as a non-thermal mechanism (precursor mechanism) by the Monte Carlo computer simulations. In this study, we have applied a novel approach based upon the experimental observations that the dissociated oxygen atoms do not sit next to one another on a catalytic surface. Some interesting results like the shifting of the phase transition points, the broadening of the reaction window width and the elimination of the second-order phase transition in the non-thermal reaction mechanism are obtained by considering various possibilities of the reaction scheme. The phase diagrams as well as the snapshots of the surface covered with the reacting species are presented.     

LINEWIDTH REDUCTION IN AN INVERSIONLESS LASER WITH PUMP PHASE FLUCTUATIONS

The effect of the pump phase diffusion on the linewidth of a laser without inversion is studied. It is shown that the linewidth at equal intensity may be reduced below that for a coherent driving, enen if the net effect of the pump bandwidth leads to an increase in the linewidth. The physical mechanism is analyzed in the dressed-state picture. Furthermore, the effects of the pump phase noise on the linewidths of an inversionleess laser and a Raman laser are compared with each other.     

一类新的Stückelberg全息超导模型

本文研究了含Stückelberg机理的黑洞全息超导模型. 通过选取标量场新的高阶修正形式, 建立了新的Stückelberg黑洞全息超导模型. 通过研究模型参数对标量场凝聚的影响, 发现了当模型参数大于临界值时, 高阶修正可以引起一阶相变. 同时本文还考查了反作用对临界值的影响.     

Phase unwrapping by accumulation of residual maps

We present a path independent (global) algorithm for phase unwrapping based on the minimisation of a robust cost function. The algorithm incorporates an outlier rejection mechanism making it robust to large inconsistencies and discontinuities. The proposal consists on an iterative incremental scheme that unwraps a sub-estimation of the residual phase at each iteration. The sub-estimation degree is controlled by an algorithm׳s parameter. We present an efficiently computational multigrid implementation based on a nested strategy: the process is iterated by using multiple resolutions. The proposal׳s performance is demonstrated by experiments with synthetic and real data, and successfully compared with algorithms of the state of the art.     

Kinetic contrast in atomic force microscopy

The mechanism of the formation of phase contrast in atomic force microscopy (AFM) is studied for various conditions of an oscillating tip interacting with the surface. A phase shift is detected in oscillations of the resonating AFM tip during its interaction with the substrate surface when the AFM tip moves over the surface. We substantiate kinetic mechanism of the formation of phase contrast in AFM, which is initiated when the velocity of the AFM tip moving over the substrate surface increases as a result of increasing friction force. A dependence of the kinetic contrast in AFM on the effective roughness of the surface is discovered. Images of the distribution of copper impurity over the silicon surface under atmospheric conditions are obtained using the method of kinetic phase contrast in AFM.     

基于经验模态分解的自混合干涉相位提取方法研究

为实现光反馈机理下激光自混合干涉信号相位的精确提取, 本文提出了一种基于经验模态分析(EMD)的方法.首先, 采用EMD算法对含噪的自混合干涉信号进行了降噪预处理, 提取有效的干涉信号.然后在对含有外腔物体运动信息的光反馈相位求解的过程中, 利用希尔伯特黄变换(HHT)原理实时提取每一时刻的瞬时相位, 将其去包裹处理后得到真实相位. 在弱、适度、强光反馈条件下, 分别对基于EMD的相位提取算法进行了仿真研究.最后, 搭建了基于自混合干涉效应的微位移测量实验平台, 进行实验研究.实验结果表明, 利用该方法可以实现对自混合干涉信号的相位提取, 最大误差小于1.6 rad.仿真和实验结果的一致性, 说明了EMD方法的有效性.     

Transport phenomena in superionic solids: Master equation approach

A first-principles derivation of the master equation is systematically given based on Kikuchi's ansatz, which is then applied to non-interacting (ideal) and interacting lattice–gas systems. The former application to an anomalous diffusion, observed by MD simulation of β-AgI, makes its mechanism clear in terms of relaxation modes such that the anomalous diffusion is due to non-diffusive (collective) modes. It is also shown in random systems that anomalous frequency-dependent conductivities, made up of Jonscher and nearly constant loss regimes, are reduced to a single master curve. The case of interacting lattice–gas system is discussed on the ab-plane of Rb₃H(SeO₄)₂ by a pair approximation of the path probability method, where a spontaneous strain involved in the ferroelastic phase turns out to be a proton-trapped state originated in an attractive strain energy mediated by a proton–displacement interaction, and the transition to superprotonic phase is due to an off-trapping of protons. This mechanism is confirmed by no phase transition without the attractive strain energy.     

Solving the Einstein-Podolsky-Rosen puzzle: the origin of non-locality in Aspect-type experiments

So far no mechanism is known, which could connect the two measurementsin an Aspect-type experiment. Here, we suggest such a mechanism, basedon the phase of a photon’s field during propagation. We showthat two polarization measurements are correlated, even if no signalpasses from one point of measurement to the other. The non-local connectionof a photon pair is the result of its origin at a common source, wherethe two fields acquire a well defined phase difference. Therefore,it is not actually a non-local effect in any conventional sense. Weexpect that the model and the detailed analysis it allows will havea major impact on quantum cryptography and quantum computation.     

Dynamics of a quantum phase transition: exact solution of the quantum Ising model

The Quantum Ising model is an exactly solvable model of quantum phase transition. This Letter gives an exact solution when the system is driven through the critical point at a finite rate. The evolution goes through a series of Landau-Zener level anticrossings when pairs of quasiparticles with opposite pseudomomenta get excited with a probability depending on the transition rate. The average density of defects excited in this way scales like a square root of the transition rate. This scaling is the same as the scaling obtained when the standard Kibble-Zurek mechanism of thermodynamic second order phase transitions is applied to the quantum phase transition in the Ising model.     

Delay dependence for the origin of the nonlinear derived transient evoked otoacoustic emission

In the guinea pig it has been shown that the nonlinear derived transient evoked otoacoustic emission (TEOAEnl) is comprised of significant amounts of intermodulation distortion energy. It is expected that intermodulation distortion arising from a nonlinear distortion mechanism will contribute to the overall TEOAE in a stimulus-level-dependent manner, being greatest when basilar-membrane vibration in response to a click stimulus is greatest; with decay of vibration of the basilar membrane subsequent to stimulation by a click, nonlinear interaction along the cochlear partition should reduce and so provide for a linear mechanism to dominate TEOAEnl generation, i.e., the contributions of each of these mechanisms should be delay dependent. To examine this delay dependence, TEOAEnl evoked by acoustic clicks of varying bandwidth were time-domain windowed using a recursive exponential filter in an attempt to separate two components with amplitude and phase properties consistent with different mechanisms of OAE generation. It was found that the part of the TEOAEnl occurring first in time can have a relatively constant amplitude and shallow phase slope, consistent with a nonlinear distortion mechanism. The latter part of the TEOAEnl has an amplitude microstructure and a phase response more consistent with a place-fixed mechanism.     

Current, luminosity, and X-ray emission in the early phase ofdielectric surface flashover in vacuum

With high-speed electrical and optical diagnostics, an attempt is made to elucidate the physical mechanisms leading to surface flashover. The experimental device uses a cable discharge to study self-breakdown along the surface of an insulator in vacuum. Preflashover current, breakdown voltage, luminosity, and soft X-ray emission are measured in temporal correlation with a resolution of 1 ns. The results show a linearly increasing current in the subampere range, and a corresponding linearly increasing luminosity, before an exponential increase of both signals takes over. The linear phase is accompanied by X-ray emission which ceases at the onset of the exponential phase. The strong influence of externally applied magnetic fields on the linear phase points to the existence of free electrons above the surface during the early phase of flashover. A linear current rise without magnetic field and the formation of a current plateau with an insulating magnetic field indicate a saturation of the current amplification mechanism in the early phase     

铁的冲击相变机制的分子动力学研究

 用分子动力学方法模拟计算了在冲击波加载条件下,单晶铁中的结构相变（由体心立方结构α相到六角密排结构ε相）,相互作用势采用铁的嵌入式原子势（EAM）,单晶铁样品的尺寸为28.7 nm×22.9 nm×22.9 nm,总原子数为1.28×10⁶个。通过推动一个运动活塞对静止靶的作用来产生冲击压缩,加载方向沿单晶铁的[100]晶向。通过对原子位置的追踪,揭示了铁的冲击相变机制,计算结果表明相变机制包括两步：首先是在{011}面上的原子受到沿〈100〉晶向的压缩,使{011}面转化成正六角形密排面;然后是在{011}面上原子沿〈0-11〉晶向的滑移,完成由bcc结构到hcp结构的相变。同时发现滑移面只出现在与冲击波加载方向平行的(011)和(0-11)面上。     

The effect of the forget-remember mechanism on spreading

We introduce a new mechanism—the forget-remember mechanism into the spreading process. Equipped with such a mechanism an individual is prone to forget the “message" received and remember the one forgotten, namely switching his state between active (with message) and inactive (without message). The probability of state switch is governed by linear or exponential forget-remember functions of history time which is measured by the time elapsed since the most recent state change. Our extensive simulations reveal that the forget-remember mechanism has significant effects on the saturation of message spreading, and may even lead to a termination of spreading under certain conditions. This finding may shed some light on how to control the spreading of epidemics. It is found that percolation-like phase transitions can occur. By investigating the properties of clusters, formed by connected, active individuals, we may be able to justify the existence of such phase transitions.     

Step wandering due to the structural difference of the upper and the lower terraces

We consider the wandering instability of steps due to a gap in the lifetime of adatoms for evaporation on the upper and the lower terraces. Our study is meant to explain the step wandering observed in the growth of Si(1 1 1) surface near its structural transition temperature. With a linear stability analysis and Monte Carlo simulations, we show that the instability of an isolated step occurs in growth if adatoms on the upper terrace evaporate more easily than those on the lower terrace. For the instability of a vicinal face, additional features are considered as the motion of the phase boundary and the mass flow across it during the phase transformation. It is found that steps and phase boundaries wander in-phase with a rather well-defined periodicity when evaporation is weak. We compare the result with that for a system with a gap in the diffusion coefficient. The simulation results show that the first mechanism is more effective to make the wandering steps in-phase and that the second mechanism induces step wandering in a wider range of parameters.