基于流形学习和空间信息的改进N-FINDR端元提取算法

光谱端元提取是对高光谱数据进一步分析的重要前提。由于双向反射分布函数(BRDF),像元内的多重散射和亚像元成分的异质性等因素,高光谱图像中的混合像元实际上是非线性光谱混合。传统的端元提取算法是以线性光谱混合模型为基础,因此提取的端元精度不高。在光谱非线性混合的基础上,提出一种将流形学习与空间信息结合的改进N-FINDR端元提取算法。首先通过自适应的局部切空间排列算法寻找嵌入在高维非线性数据空间的本质的低维结构,将原始高光谱数据非线性降维到低维空间。接着利用地物分布具有连续性的特点,通过增大空间同质区域的像元的权重进行空间预处理。最后通过寻找最大单形体体积进行端元提取。提出算法很好的解决了高光谱遥感数据非线性结构,并利用了空间信息,提高了端元提取的精度。模拟数据实验和真实高光谱遥感数据实验结果均表明,采用该算法得到的结果优于顶点成分分析(VCA) 算法、基于测地线距离的最大单形体体积(GSVM)算法和空间预处理的N-FINDR(SPPNFINDR)算法。     

基于空间光调制器的波面重建优化方法研究

针对不同非球面面形的实时检测需求,研究了基于空间光调制器的标准波面重建技术.基于空间光调制器波面重建的原理设计了干涉测量系统,依据空间光调制器的自身特点选取修正离轴计算全息编码方式实现对标准球波面的编码.针对实验中空间光调制器作为全息再现介质引起重建波面质量下降问题,提出了错位叠加优化方案,并将这一过程进行了模拟实验.结果表明,基于错位叠加方法的重建波面均方差值提高了近4.45倍.研究成果为非球面检测过程中标准波面的获取提供了可靠的理论基础.     

Intrinsic axes of partially coherent light beams and their invariance through rotationally symmetric ABCD optical systems

New transverse orthogonal axes associated with the beam shape are introduced on the basis of the irradiance-moment formalism that describes the overall spatial structure of partially coherent paraxial beams. We refer to them as the intrinsic axes of the beam. The angle between these axes and the laboratory reference coordinates can be determined from the measurements of the second-order spatial moments of the beam, even although the field amplitude is not analytically known. It has been found that the intrinsic axes remain invariant upon propagation through rotationally symmetric first-order optical systems. Two additional analytical quantities have also been introduced. One of them provides a measure of the beam symmetry, and the other one contains information about the beam rotation under propagation. When the field is referred to the intrinsic axes, these two quantities are shown to reach their extreme values. The results are illustrated by means of an example.     

Application of high-resolution electron microscopy for visualization and quantitative analysis of strain fields in heterostructures

The general principles, possibilities, and limitations of the classical geometric phase method have been considered. A new generalizing approach, implying analysis of all available spatial frequencies of a high-resolution electron microscopy image, is developed to expand the possibilities of the geometric phase method. Test models of strained Si-GeSi-Si heterostructures are developed and the effect of scattering by phonons and the surface amorphous layer on visualization of lattice distortions is studied within these models. A simple method is proposed for measuring elastic strains in multicomponent heterostructures with pseudomorphic layers.     

MathNMR: spin and spatial tensor manipulations in Mathematica

Spin and spatial tensor manipulations are frequently required to describe the theory of NMR experiments. A Mathematica package is presented here, which provides some of the most common functions for these calculations. Examples are the calculation of matrix representations of operators, commutators, projections, rotations, Redfield matrix elements, matrix decomposition into basis operators, change of basis, coherence filtering, and the manipulation of Hamiltonians. The calculations can be performed for any spin system, containing spins 1/2 and quadrupolar spins alike, subject to computational limitations. The package will be available from upon acceptance of the article.     

The utility of the Galerkin method for the acoustic transmission in an attenuating duct

A comprehensive solution technique that can be applied to shear flow analysis for acoustic transmission in both hard and soft walled ducts with boundary layer dependence in one or two spatial directions is presented. The method, the weighted residual method of Galerkin, is applied in this paper to the two-dimensional channel for the purpose of ascertaining its applicability to more complicated geometries and with certain limitations appears to be a reliable method for treating both the hard and soft walled configurations. Even though the original intent was to establish the validity of the method for more general cases, it is considered to be a good alternative to the Runge-Kutta method in common use and indeed is superior for certain applications.     

A method for automatic identification of water and fat images from a symmetrically sampled dual-echo Dixon technique

Sampling water and fat signals symmetrically (i.e., at 0° and 180° relative phase angles) in a dual-echo Dixon technique offers high intrinsic tolerance to phase fluctuations in postprocessing and maximum signal-to-noise performance for the separated water and fat images. However, identification of which image is water and which image is fat after their separation is not possible based on the phase information alone. In this work, we proposed a semiempirical automatic image identification method that is based on the intrinsic asymmetry between the water and fat chemical shift spectra. Specifically, the approximately bimodal feature of the fat spectra and the observation that most in vivo tissues are either predominantly water or predominantly fat are used to construct a spectrum-based algorithm. Additional refinement is accomplished by considering the spatial distribution of the tissues that may have a coexistence of water and fat. The final improved algorithm was tested on a total of 131 three-dimensional patient datasets collected from different scanners and found to yield correct water and fat identification in all datasets.     

Moderate point: Balanced entropy and enthalpy contributions in soft matter

Various soft materials share some common features, such as significant entropic effect, large fluctuations, sensitivity to thermodynamic conditions, and mesoscopic characteristic spatial and temporal scales. However, no quantitative definitions have yet been provided for soft matter, and the intrinsic mechanisms leading to their common features are unclear. In this work, from the viewpoint of statistical mechanics, we show that soft matter works in the vicinity of a specific thermodynamic state named moderate point, at which entropy and enthalpy contributions among substates along a certain order parameter are well balanced or have a minimal difference. Around the moderate point, the order parameter fluctuation,the associated response function, and the spatial correlation length maximize, which explains the large fluctuation, the sensitivity to thermodynamic conditions, and mesoscopic spatial and temporal scales of soft matter, respectively. Possible applications to switching chemical bonds or allosteric biomachines determining their best working temperatures are also briefly discussed.     

Experimental determination of electric cross-spectral density matrix and generalized Stokes parameters for a laser beam

We report an experimental method to determine the elements of the electric cross-spectral density matrix for laser light. For this purpose an additional setup consisting of mirrors and reflecting prisms is utilized with the conventional Young's interferometer to overcome existing experimental limitations. The generalized Stokes parameters, which are the characteristics of two spatial points of the electromagnetic field, are also obtained for a pair of points. The knowledge of these two quantities might be useful in determining the change in polarization properties of light in propagation and their effects in optical measurements.     

Recent evolutions of imagery in fluid mechanics: From standard tomographic visualization to 3D volumic velocimetry

The recent evolutions of the optical analysis of three-dimensional (3D) flows by means of light scattering and quantitative imagery are presented. In order to remove the intrinsic ambiguity of the well-known tomographic methods (how to obtain 3D information by using a 2D plane illumination?), the efficiency of polychromatic lightings is shown: the basic idea is to code the third dimension by the wavelength.Different approaches are described: discrete or continuous analysis, sequential or simultaneous recordings, and measurement of two or three velocity components (2C or 3C techniques).The most recent 3D velocimetry method using a rainbow lighting process (RVV—Rainbow Volumic Velocimetry) is presented. The main qualities and limitations of these different methods are discussed.     

An improved technique for holographic recording on thermoplastic-photoconductor (II)

An improved technique (PLA method) for holographic recording on thermoplastic-photoconductor has three main features: higher amplification, a wider spatial frequency range of recording and improved reciprocity. Research has been carried out to explain these features. It was found that a stronger deformation force, finer frost, memory effect and edge effect are involved in explaining these features.     

Hybrid multinary modulation using a phase modulating spatial light modulator and a low-pass spatial filter

We propose a method for performing binary intensity and continuous phase modulation of beams with a spatial light modulator (SLM) and a low-pass spatial filtering 4-f system. With our method it is possible to avoid the use of phase masks in holographic data storage systems or to enhance the phase encoding of the SLM by making it capable of binary amplitude modulation. The data storage capabilities and the limitations of the method are studied.     

环形光源在干涉仪系统中的应用

介绍了一种新的环形光源技术来抑制干涉仪系统的本征噪声以提高信噪比。阐述了环形光源抑制干涉仪系统本征噪声的原理,根据条纹对比度和需抑制噪声空间频率的要求,推导得到了环形光源的外半径和内半径。通过与传统的点光源对比实验表明：环形光源模式系统的本征噪声峰谷值小于点光源模式,且没有明显的牛顿环噪声,本征噪声的功率谱密度在空间频率小于2.5 mm-1时小于点光源的1/10,系统信噪比在空间频率小于2 -1时大于点光源的两倍。     

环形光源在干涉仪系统中的应用

 介绍了一种新的环形光源技术来抑制干涉仪系统的本征噪声以提高信噪比。阐述了环形光源抑制干涉仪系统本征噪声的原理,根据条纹对比度和需抑制噪声空间频率的要求,推导得到了环形光源的外半径和内半径。通过与传统的点光源对比实验表明：环形光源模式系统的本征噪声峰谷值小于点光源模式,且没有明显的牛顿环噪声,本征噪声的功率谱密度在空间频率小于2.5 mm ^-1时小于点光源的1/10,系统信噪比在空间频率小于2 ^-1时大于点光源的两倍。     

MOSFET scaling into the 10 nm regime

Scaling limits of the double-gate MOSFET structure are explored. Because short-channel effects can be adequately controlled by thinning the silicon body, the eventual scaling limit will be determined by the ability to control off-state leakage due to quantum mechanical tunneling and thermionic emission between the source and drain. Depending on threshold voltage and the source/drain doping profile, this will restrict gate length scaling to 5–11 nm. As power supplies are scaled down, maintaining on-state drive current may become difficult due to threshold voltage limitations. Series resistance becomes important as the body thickness is reduced, but intrinsic device performance may still be improved.     

Improvement and error analysis of quantitative information extraction in diffraction-enhanced imaging

Diffraction-enhanced imaging （DEI） is a powerful phase-sensitive technique that provides higher spatial resolution and supercontrast of weakly absorbing objects than conventional radiography. It derives contrast from the X-ray absorption, refraction, and ultra-small-angle X-ray scattering （USAXS） properties of an object. The separation of different-contrast contributions from images is an important issue for the potential application of DEI. In this paper, an improved DEI （IDEI） method is proposed based on the Gaussian curve fitting of the rocking curve （RC）. Utilizing only three input images, the IDEI method can accurately separate the absorption, refraction, and USAXS contrasts produced by the object. The IDEI method can therefore be viewed as an improvement to the extended DEI （EDEI） method. In contrast, the IDEI method can circumvent the limitations of the EDEI method well since it does not impose a Taylor approximation on the RC. Additionally, analysis of the IDEI model errors is performed to further investigate the factors that lead to the image artifacts, and finally validation studies are conducted using computer simulation and synchrotron experimental data.     

Review paper A3. Data needs,priorities and accuracies for plasma modelling

To determine the needs, priorities and accuracies of the atomic and molecular physics data required for plasma modelling the rôle of these data in computer simulations of magnetically confined plasmas is reviewed. The models approximate atomic and molecular reactions in many different ways. Multi-dimensional calculations concerned with the equilibrium and stability of a plasma-magnetic field configuration assume the plasma to consist of fully ionised hydrogen ions and electrons in the magnetohydrodynamic approximation: the effect of atomic and molecular reactions is minimal. Zero (spatial) dimensional calculations of the break-down phase of gas discharges assume the gas to consist of atomic and molecular hydrogen, electrons and impurity ions such as oxygen, carbon, iron, tungsten and molybdenum: the effect of plasma motion is minimal. Between these extremes are classes of computations such as the one (spatial) dimension transport calculations which attempt to establish a realistic balance between the behaviour of ions, atoms and molecules in an established discharge. The limitations and inadequacies of present data and models for atomic and molecular processes are illustrated by several specific calculations. The results of these calculations permit identification of the ar eas where improved models and data for the atomic and molecular reactions are required.     

A simple method for quantitative imaging of 2D acoustic fields using refracto-vibrometry

This paper presents a simple 2D method for rapid time resolved quantitative imaging of acoustic waves using refracto-vibrometry. We present the theoretical background, the experimental method and reconstructions of acoustic reflection and interference. We investigate the applicability of the method, in particular the effect of sound radiator geometry. Finite element and experimental reconstructions of the sound fields are analysed. The spatial limitations and accuracy of the method are presented and discussed.     

Scalar diffraction of spherical waves by a plane aperture: a general analysis based on the critical points

We present a formulation of the scalar diffraction of spherical waves through plane apertures that takes advantage of the importance of the critical points and the semiperiodic zones that are defined in the plane of the aperture. Our approach overcomes the intrinsic limitations of stationary-phase methods (when the critical points coalesce) and allows a direct implementation in terms of numerical algorithms for computations of any predefined accuracy. The method is illustrated with examples corresponding to a rectangular aperture.