Interdigital transducer analysis using equivalent PSpice model

Interdigital transducers generating surface acoustic waves have found numerous applications. The present paper deals with an equivalent model of a single interdigital transducer as well as an SAW filter complying with the PSpice programme for the analysis of electronic systems. The suggested model makes it possible to take into account such effects as interelectrode reflections, losses along the acoustic path and the electromagnetic coupling between the transducers. The obtained results of the analysis of an interdigital transducer comply with the results obtained basing on an admittance model and delta-function model. The final aim is to model an SAW oscillator.     

基于无导数优化方法的数值模式误差估计

初始场误差和模式误差是制约数值预报准确率的两个关键因素,本文主要考虑利用历史观测资料实现时空演变的模式误差的估计问题.通过把模式误差综合考虑成为准确模式中的未知项,把历史资料看作是带有未知项的准确模式的特解,构造了求解时空演变的模式误差项的反问题及其最优控制问题.给出了一个解决最优控制问题的无导数优化方法,该方法的优点是不需要建立原数值模式的切线性模式与伴随模式,它只需在增加一个外强迫项的基础上运行原数值模式即可实现模式误差项的最优估计.关于Burgers方程的算例表明,无论模式的初始状态是否准确已知,无导数优化方法都能有效解决时空演变的模式误差的最优估计问题,它为实际业务模式利用历史数据提取模式误差信息并显著地改进预报效果提供了一种方便可行的数值方法与理论依据.     

An Efficient Three-Dimensional Coupled Normal Mode Model and Its Application to Internal Solitary Wave Problems

We present an efficient three-dimensional coupled-mode model based on the Fourier synthesis technique. In principle, this model is a one-way model, and hence provides satisfactory accuracy for problems where the forward scattering dominates. At the same time, this model provides an efficiency gain of an order of magnitude or more over two-way coupled-mode models. This model can be applied to three-dimensional range-dependent problems with a slowly varying bathymetry or internal waves. A numerical example of the latter is demonstrated in this work. Comparisons of both accuracy and efficiency between the present model and a benchmark model are also provided.     

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。     

Smoothing out negative tension brane

We propose an extension of the five-dimensional gravitational action with an external source in order to allow arbitrary smoothing of the negative tension brane in the Randall–Sundrum model. This extended action can be derived from a model with an auxiliary four form field coupled to the gravity. We point out a further generalization of our model in relation to tachyon condensation. A possible mechanism for radion stabilization in our model is also discussed.     

一种基于共轭节面的图像畸变分析方法

无像差的光学相机的成像模型可由其共轭节面模型等效表示。针孔模型本身忽略了偏离该等效模型的误差,也无法表示平板玻璃的平移误差、光轴的安装误差以及实际相机光学系统的像差,这四个因素都会引起图像畸变。基于此利用共轭节面的性质建立了一种图像畸变几何模型,并与广泛采用的像差模型进行了对比,从理论上解释了像差模型各个系数的物理意义。对某实际针孔相机进行仿真分析,该几何模型给出的相对径向畸变、角度误差在设计参数的范围以内,并且可以模拟图像的非对称畸变。该几何模型需要辨识包含主面相关参数、光轴倾斜角和平板玻璃的轴向球差在内的4个参数,辨识参数较少,理论上可以作为一种新的图像畸变校正方法。     

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.     

Quantum mechanics in theK-field formalism: Kepler's problem for spin particles

Using the well-known Kepler's problem, an attempt is made to demonstrate a procedure for constructing a nonrelativistic approximation of a quantum-mechanical model for steady states of hydrogen atoms in the K-field formalism. In this model, an electron is assumed to possess an intrinsic moment (spin) which, according to Frenkel, is comparable to the magnetic moment. It is shown that Lyapunov-stable trajectories of the K-particle (a test point particle representing the classical model of an electron in an atom) correspond to the conventional steady states of hydrogen atoms, with the trajectories being similar to those in the spin-zero particle model. The proposed model of the electronic structure in a hydrogen atom provides an insight into the physical cause of the atomic superfine structure and the physical meaning of the constant α=c/mc. Tomsk Polytechnical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 50–54, October, 1999.     

An ensemble source spectra model for merchant ship-radiated noise

This paper presents an evaluation of the classical model for determining an ensemble of the broadband source spectra of the sound generated by individual ships and proposes an alternate model to overcome the deficiencies in the classical model. The classical model, proposed by Ross [Mechanics of Underwater Noise (Pergamon, New York, 1976)] postulates that the source spectrum for an individual ship is proportional to a baseline spectrum with the constant of proportionality determined by a power-law relationship on the ship speed and length. The model evaluation, conducted on an ensemble of 54 source spectra over a 30-1200-Hz to 1200-Hz frequency band, shows that this assumption yields large rms errors in the broadband source level for the individual ships and significantly overestimates the variability in the source level across the ensemble of source spectra. These deficiencies are a consequence of the negligible correlation between the source level and the ship speed and the source level and the ship length. The alternate model proposed here represents the individual ship spectra by a modified rational spectrum where the poles and zeros are restricted to the real axis and the exponents of the terms are not restricted to integer values. An evaluation of this model on the source spectra ensemble indicates that the rms errors are significantly less than those obtained with any model where the frequency dependence is represented by a single baseline spectrum. Furthermore, at high frequencies (400 to 1200 Hz), a single-term rational spectrum model is sufficient to describe the frequency dependence and, at the low frequencies (30 to 400 Hz), there is only a modest reduction in the rms error for a higher order model. Finally, a joint probability density on the two parameters of the single term model based on the measured histograms of these parameters is proposed. This probability density provides a mechanism for generating an ensemble of ship spectra.     

结合神经网络的换热器积分近似模型

为解决换热器的分布参数模型存在的精度与计算代价之间难以调和的矛盾,本文提出了一种新的方法,即光用一个积分近似模型作为对原分布参数模型的简化,而仅对积分近似中某些非线性关系用神经网络来表达。该方法用于翅片管式冷凝器的实际计算,验证了这一思路的有效性。     

On the Ricci dark energy model

We study the Ricci dark energy model (RDE) which was introduced as an alternative to the holographic dark energy model. We point out that an accelerating phase of the RDE is that of a constant dark energy model. This implies that the RDE is not a new model of explaining the present accelerating universe.     

The application of a semi-actuator disk model to sound transmission calculations in turbomachinery,part I: The single blade row

The work described in this paper generalizes the semi-actuator disk model of a blade row of Kaji and Okazaki [1, 2] to include a three-dimensional incident sound field. This field is equivalent, for example, to a radially fluctuating spinning mode in an annular compressor duct. The dependence of the earlier model upon the wavelength of the incident sound field is removed by adopting an average frequency approach. In this model, the acoustic energy entering the cascade of blades across one interface and leaving it across the other interface is summed over an infinite series of reflections within the cascade. This is equivalent, in effect, to the assumption of an incident delta function of pressure and thus gives an average frequency result. The validity of the model is demonstrated in a series of comparisons with data obtained from earlier models. The model is subsequently extended to include the effects of introducing cambered blades. In a companion paper (Part II), the model is applied to multiple blade rows.     

Nonequilibrium model for the contact process in an ensemble of constant particle number.

We introduce and analyze numerically a nonequilibrium model with a conserved dynamics which is a realization of the contact process in an ensemble of constant particle number. The model possesses just one process in which particles jump around landing only on empty sites next to an existing particle. Particles are not allowed to land on a vacant site surrounded by empty sites. In contrast with the ordinary contact process, the present model does not have an absorbing state. In spite of lacking an absorbing state, the model displays properties that, in the thermodynamic limit, are identical to those of the ordinary contact process.     

基于平底孔反射体的双晶直探头测量模型

双晶探头在无损检测领域有着重要的应用,因而有必要建立一个超声测量模型来深入了解这类换能器的特点.通过将一个基于传递矩阵的多高斯声束模型和一个基尔霍夫近似方法获得的散射模型有效结合,建立了一个完整的纵波双晶直探头测量模型,用于预测平底孔缺陷体的回波信号.对比分析了平底孔反射回波信号的模型计算结果与实验测量结果,验证了该测量模型的准确性. 关键词： 超声测量模型 双晶直探头 多高斯声束模型     

Multi-photon Rabi model: Generalized parity and its applications

Quantum multi-photon spin–boson model is considered. We solve an operator Riccati equation associated with that model and present a candidate for a generalized parity operator allowing to transform spin–boson Hamiltonian to a block-diagonal form what indicates an existence of the related symmetry of the model.     

Micro-vibration model and parameter estimation method of a reaction wheel assembly

Reaction wheel assemblies (RWAs) are a source of disturbance in satellites, and they are regarded as the largest jitter contributor in optical payloads. In order to ensure a stringent jitter requirement, the wheel disturbance effects on spacecraft should be predicted precisely prior to launch through analytical or experimental approaches. For this purpose, the wheel disturbance should be identified and modeled accurately. In the present study, a micro-vibration model of the RWA is introduced through coupling an analytical wheel model and an empirical disturbance model; furthermore, a parameter estimation process of the coupled model from the micro-vibration disturbance data is proposed. In order to verify the modeling and estimation techniques, a micro-vibration model of a numerical RWA is established and its estimation error is validated. Then, the micro-vibration model is extended to consider an axial disturbance and a measurement offset effect. Finally, the micro-vibration model is applied to a commercial RWA and the model parameters are extracted from the disturbance test data of the RWA using the parameter estimation process. The analytical and experimental results demonstrate that the proposed micro-vibration model and parameter estimation process are effective in the dynamic disturbance modeling of RWAs.     

Proton Conductivity of Water in Mesoporous Materials

A model explaining a high proton conductivity of water in mesoporous materials has been proposed. The model is based on the theory of an intermediate phase of water with an ordered oxygen lattice and a destroyed proton lattice and involves various types of interaction of water molecules with an interface. The model is in fact based on an analogy of the interface and a liquid-like surface layer of ice. Possible methods for increasing the proton conductivity, experiments for testing the proposed model, and application of the results to the creation of efficient proton-exchange membranes have been discussed.     

Non-Abelian Random Polygons: A New Model in Statistical Physics

A model in statistical physics is presented based on assigning non-Abelian phase factors to the turning points of polygons in three dimensions. This model allows for an exact solution and exhibits an unexpectedly rich phase structure. The model as well as the solution are obtained by a generalization of the methods of Kac and Ward and by mapping the problem to a Markov process as was done by Feynman for the two-dimensional Ising model     

Nonparaxial multi-Gaussian beam models and measurement models for phased array transducers

A nonparaxial multi-Gaussian beam model is proposed in order to overcome the limitation that paraxial Gaussian beam models lose accuracy in simulating the beam steering behavior of phased array transducers. Using this nonparaxial multi-Gaussian beam model, the focusing and steering sound fields generated by an ultrasonic linear phased array transducer are calculated and compared with the corresponding results obtained by paraxial multi-Gaussian beam model and more exact Rayleigh-Sommerfeld integral model. In addition, with help of this novel nonparaxial method, an ultrasonic measurement model is provided to investigate the sensitivity of linear phased array transducers versus steering angles. Also the comparisons of model predictions with experimental results are presented to certify the accuracy of this provided measurement model.