Adjoint modeling for acoustic inversion

The use of adjoint modeling for acoustic inversion is investigated. An adjoint model is derived from a linearized forward propagation model to propagate data-model misfit at the observation points back through the medium to the medium perturbations not being accounted for in the model. This adjoint model can be used to aid in inverting for these unaccounted medium perturbations. Adjoint methods are being applied to a variety of inversion problems, but have not drawn much attention from the underwater acoustic community. This paper presents an application of adjoint methods to acoustic inversion. Inversions are demonstrated in simulation for both range-independent and range-dependent sound speed profiles using the adjoint of a parabolic equation model. Sensitivity and error analyses are discussed showing how the adjoint model enables calculations to be performed in the space of observations, rather than the often much larger space of model parameters. Using an adjoint model enables directions of steepest descent in the model parameters (what we invert for) to be calculated using far fewer modeling runs than if a forward model only were used.     

基于近红外光谱与支持向量机的纸浆卡伯值在线测量

提出了用近红外光谱漫反射技术和支持向量机建模方法实现纸浆卡伯值在线测量的新方法。采集45份松木浆样品的近红外漫反射光谱,选择各样品15个振动吸收峰对应的吸收率,采用动态独立分量分析(DICA)对输入样本数据进行特征提取,建立基于支持向量机(SVM)的纸浆卡伯值预测模型。45份样品中选择35份组成校正集,另10份作为预测集对模型进行验证。基于支持向量机的纸浆卡伯值预测模型外部验证均方差和确定系数分别为0.26和0.93;基于线性回归的纸浆卡伯值预测模型外部验证均方差和确定系数分别为0.45和0.81。研究结果不仅表明纸浆卡伯值近红外测量方法的可行性和有效性,而且验证了基于支持向量机的纸浆卡伯值预测模型比线性回归模型具有更高的准确性和鲁棒性。     

Application of the conditional source-term estimation model for turbulence–chemistry interactions in a premixed flame

Conditional Source-term Estimation (CSE) is a closure model for turbulence–chemistry interactions. This model uses the first-order CMC hypothesis to close the chemical reaction source terms. The conditional scalar field is estimated by solving an integral equation using inverse methods. It was originally developed and has been used extensively in non-premixed combustion. This work is the first application of this combustion model for a premixed flame. CSE is coupled with a Trajectory Generated Low-Dimensional Manifold (TGLDM) model for chemistry. The CSE-TGLDM combustion model is used in a RANS code to simulate a turbulent premixed Bunsen burner. Along with this combustion model, a similar model which relies on the flamelet assumption is also used for comparison. The results of these two approaches in the prediction of the velocity field, temperature and species mass fractions are compared together. Although the flamelet model is less computationally expensive, the CSE combustion model is more general and does not have the limiting assumption underlying the flamelet model.     

A dual model strategy to transfer multivariate calibration models for near-infrared spectral analysis

A dual-model method is proposed for correcting the calibration model. In the method, a primary calibration model is built using the spectra of a primary instrument and a correction model is established to describe the ratios between the predicted results from the spectra of different instruments. The prediction for the spectra of secondary instrument can be achieved by correcting the prediction of the primary model. A mathematical proof is described for the existence of the correction model, and the model is investigated using a near-infrared spectroscopic dataset of plant leaf samples measured on two instruments. The results show that a precise correction model is obtained and the model can be used to correct the predictions of the primary model. The correlation coefficients between the predicted and the reference ratios are above 0.9, and the prediction error after the correction is at the same level of the primary model.     

Modelling soot emission from a direct injection diesel engine fuelled with diesel–methanol dual fuel

The objective of this paper is to develop a soot model for multi-dimensional simulations of diesel–methanol dual-fuel engines to predict engine-out soot emissions. To the two-step soot model a special term, based on experimental study and analysis, is appended to the soot formation rate to account for the effect of methanol. The results of engine-out soot emissions predicted by the models were compared with experimental data and it is shown that the existing model predicts well for diesel engines, whereas the proposed model predicts well for both diesel and dual-fuel engines especially for the large fractional methanol flow rates. The results suggest that the soot model must be modified for the dual-fuel combustion mode.     

Combustion kinetic model development using surrogate model similarity method

An ideal combustion kinetic model needs to be validated by different experimental targets over a wide range of temperatures and pressures that represent operating conditions in real engines. However, conditions of laboratory experiments for model validation are often limited by the constraint of experimental techniques. In order to improve model predictions under certain conditions (for example, at a relatively higher pressure), it is often needed to use the experimental data obtained under other conditions. In this work, the surrogate model similarity (SMS) method is proposed to find the experimental conditions or targets for model optimisation under certain conditions where the experiments are hard to be conducted. The similarity coefficient is calculated by the cosine similarity between the characteristic coefficients (vectors) of the High Dimensional Model Representation (HDMR) models for different model predictions. A larger similarity coefficient represents a closer relationship between two model predictions. The experimental data with larger similarity coefficients could be more effective to model uncertainty reduction under the concerned conditions. To demonstrate this method, simulations were conducted for two selected combustion systems with hydrogen or methanol as the fuel. In addition to its strength in available experimental data selection for model optimization, this method can be used to screen out experimental targets with strong constraint effect beforehand, thus providing an effective way to maximise utilisation of experimental resources.     

自适应听觉感知时频分析模型

提出了一种具有强度自适应机制的仿听觉感知时频分析模型—Adaptive Ear Wig Distribution(AEWD),该模型是O'Donovan的Ear Wig Distribution(EWD)模型的扩展。AEWD的主要改进在于使用Patterson等近几年来提出的Cascade Compressive Gammachirp(Cascade cGC)模型,替换原有模型使用的Gammatone(GT)模型构造频域平滑窗,从而使AEWD模型具有了随输入信号功率而自适应调整的能力。相较于EWD模型,AEWD描述的时频分布更加符合听觉感知实际。最后,文中给出了一些典型信号的计算实例,说明了AEWD模型的有效性。      

基于守恒高阶模型的动态交通分配建模与仿真

针对路网中的动态交通分配问题，采用高阶守恒模型（CHO）进行建模与数值研究，并推广高阶守恒模型二进二出路口的Riemann问题；同时将高阶守恒模型与动态网络加载（DNL）模型相结合，通过变分不等式对动态网络加载模型进行分析.数值模拟采用一阶有限体积法求解高阶守恒模型，同时采用梯度下降方法迭代求解动态网络加载模型的变分不等式问题，最终以动态用户最优条件为目标实现分配均衡.数值结果表明CHO模型与DNL模型结合解决动态交通分配问题是可行的，对传统模型的研究有一定的指导意义.     

Modeling size dependence of melting temperature of metallic nanoparticles

A model has been developed to account for the dependence of melting temperature of nanoparticles on their size, shape and lattice type. This model is consistent with reported experimental data and shows better consistency than the liquid drop and bond energy model. A general equation is proposed which correlates with the bond energy model formula and has high potential for application in research and development. The model also leads to an equation showing the limiting size for nanoparticles.     

基于地面光谱数据的二向性反射模拟与分析

为提高地物光谱模拟精度，建立地表混合光谱模型，利用ASD FieldSpec3 Hi-Res便携式地物光谱仪和地物多角度二向性反射平台，设计试验探测不同角度下的不同叶片覆盖面积的混合光谱。以等距离/等面积模型为理论基础，将模型中二维权重系数变化规律扩展到三维空间权重系数变化中，考虑探测方向倾斜时探测区域权重系数的变化，提出新的考虑几何角度的三维权重模型对混合光谱进行模拟，并与实测混合光谱对比分析。分析结果表明，相比于等距离/等面积模型，三维权重模型对探测区域进行了细分，提高了权重系数计算精度，模拟的混合光谱误差更小，特别是在探测角度有倾斜时，模拟的效果更明显，均方根误差平均降低了0.016 1，光谱角误差平均降低了0.07。三维权重模型考虑了探测角度对权重系数的影响，提高了光谱模拟的精度，为地表模型的建立及卫星数据混合光谱分解的应用提供新的理论基础。     

Nucleon-pair shell model: Formalism and special cases

A formalism is described for a nucleon-pair shell model (NPSM) for even-even and even-odd nuclei. The building blocks of the model space are collective nucleon pairs of angular momenta J = 0,2,… for an even system, and nucleon pairs plus one unpaired nucleon for an odd system. Analytical formulas are given for the matrix elements of a general Hamiltonian. Without any space truncation, the NPSM is equivalent to the shell model in full space, while with a special choice for the building blocks and Hamiltonian it reduces to the broken pair model, the favored-pair model of Hecht and the fermion dynamical symmetry model.     

Aspects of ground effect modeling

A recently published one-parameter ground model based on Darcy's law is here generalized into a two-parameter model which depends on an effective flow resistivity and an effective layer depth. Extensive field measurements of the acoustic impedance of various ground types have been carried out for frequencies in the range from 200 Hz to 2.5 kHz. The model based on Darcy's law gives an improved fit to the measurements compared to the Delany-Bazley model. It is, in addition, argued on purely theoretical grounds that the suggested model is preferable. In contrast to the Delany-Bazley model it corresponds to a proper causal time-domain model. This is particularly relevant for extrapolation of the models to lower frequencies and for the recently developed harmonized methods intended for use in the implementation of the European Union directive on the assessment and management of environmental noise. The harmonized methods include frequencies down to the 25 Hz third octave band and have the Delany-Bazley ground impedance model as the default choice. The arguments presented here suggest that this default choice should be replaced by the more physically based model from the law of Darcy.     

Offline estimation of decay time for an optical cavity with a low pass filter cavity model

This Letter presents offline estimation results for the decay-time constant for an experimental Fabry-Perot optical cavity for cavity ring-down spectroscopy (CRDS). The cavity dynamics are modeled in terms of a low pass filter (LPF) with unity DC gain. This model is used by an extended Kalman filter (EKF) along with the recorded light intensity at the output of the cavity in order to estimate the decay-time constant. The estimation results using the LPF cavity model are compared to those obtained using the quadrature model for the cavity presented in previous work by Kallapur et?al. The estimation process derived using the LPF model comprises two states as opposed to three states in the quadrature model. When considering the EKF, this means propagating two states and a (2×2) covariance matrix using the LPF model, as opposed to propagating three states and a (3×3) covariance matrix using the quadrature model. This gives the former model a computational advantage over the latter and leads to faster execution times for the corresponding EKF. It is shown in this Letter that the LPF model for the cavity with two filter states is computationally more efficient, converges faster, and is hence a more suitable method than the three-state quadrature model presented in previous work for real-time estimation of the decay-time constant for the cavity.     

Constrained fluctuation theories of rubber elasticity: General results and an exactly solvable model

We present a new model of rubber elasticity where linear forces act to constrain the fluctuations of the eigenmodes of the phantom model. The model allows us to treat the constrained junction and the tube model within the same, transparent formalism, does not require any further approximations, and is particularly suited for the analysis of simulation data for (strained) model polymer networks. As an interesting side result we show that in order for the model to be consistent, the constraints (but not the mean polymer conformations!) have to deform affinely, a severe restriction that might also apply to other models. Complementary, we prove in analogy to the derivation of the virial theorem that introducing constraints into the phantom network Hamiltonian leads to extra terms in addition to the usual Doi-Edwards formulas for the polymer contribution to the stress tensor which vanish only for affinely deforming constraints. Received: 28 November 1997 / Received in final form and accepted: 31 March 1998     

Fractal Aggregation Near the Threshold

In this papel, we present two fractal aggregation models, line pattern seed model (model 1) and point pattern seed model (model 2), which are particle-cluster models. Using the current models, we investigate the critical transition in fractal aggregation processes in two dimensions, and suggest a method for finding the critical transition point. The computer simulation results show that the critical concentration is P_ca=0.69±0.02 for model 1 and P_ca=0.72±0.01 for model 2, critical fractal dimension. D_c= 1.71±0.06 for model 1 and D_c=1.66±0.07 for model 2, which are in good agreement with those of DLA model (D=5/3) and experimental data. The results also show that the critical transition point in two dimensions seems to be inilependent of the size of lattices and the initial seed patterns. The results seem to belong to the same universality class.     

Probability distribution for the number of cycles between successive regime transitions for the Lorenz model

The Lorenz model has been widely used for exploring many real world problems. In this paper we obtain, with the help of an invariant manifold technique, the return map for the maximum value of the variable x of the model and use this return map to derive the simple, empirically obtained, regime transition rules for forecasting regime changes and length in the new regime for the model. The probability distribution for number of cycles between successive regime transitions of the Lorenz model may be of interest in many disciplines. We apply the Perron-Frobenius algorithm over the return map to estimate the probability distribution for the number of cycles between successive regime transitions. These probabilities are also estimated for the forced Lorenz model, which is a conceptual model to explore the effects of sea surface temperature on seasonal rainfall.     

土壤模型对地表电位影响及合理选取土壤模型方法研究

首次利用物理意义明确的模拟镜像法推导出三维复合分层土壤模型格林函数, 基于特定土壤模型, 分析了不同土壤配置下土壤模型对地表电位的影响. 结果表明, 在一定条件下土壤模型变化仅改变地表电位绝对值, 基本不改变地表电位差, 从理论上阐明了土壤参数变化对地表电位影响的物理机理. 针对如何选取合适土壤模型来准确计算流过变压器中性点的直流量难题, 提出了合理选取土壤模型的判据及其阈值, 避免了土壤模型选取的随意性和盲目性, 为准确评估流过变压器中性点直流量和直流接地极附近变电站选址提供理论依据. 关键词： 格林函数 模拟镜像法 直流偏磁 土壤模型     

X射线成像的一种点扩展函数模型

X射线成像系统可以通过其点扩展函数来表行,其点扩展函数分为一次射线点扩展函数和散射点扩展函数两部分。在分析点扩展函数各个影响因素的基础上,建立了以物体厚度、物体到探测器距离以及成像几何设置为参量的解析模型。利用该模型推导出了特定入射射线能谱和射线源到探测器距离情况下散射比的计算公式。它是以物体厚度和物体到探测器距离为变量的函数。在利用实验数据对模型参量进行最优估计的基础上,利用散射比实验验证了模型的正确性。为散射和几何不清晰度的消除提供了一种实用的模型依据。