A geometric correction based robust color image watermarking scheme using quaternion Exponent moments

Most of the existing color image watermarking schemes was designed to mark grayscale images or use the color components, which ignore the significant correlation between different color channels. Recently, several approaches were developed to process the color channels intrinsically, but they always cannot counterattack geometric distortions. It is a challenging work to design a robust color image watermarking scheme against geometrical distortions. In this paper, we propose a geometric correction based robust color image watermarking approach using quaternion Exponent moments (QEMs). The novelty of our approach is that (1) the QEMs are derived to deal with the color images in a holistic manner, and (2) the QEMs are exploited for estimating the geometric distortions parameters in order to permit watermark extraction. Experimental results confirm the validity of our approach and its higher robustness against geometrical distortions compared to alternative watermarking methods in the literature.     

A quantitative comparison of two methods to correct eddy current-induced distortions in DT-MRI

Eddy current-induced geometric distortions of single-shot, diffusion-weighted, echo-planar (DW-EP) images are a major confounding factor to the accurate determination of water diffusion parameters in diffusion tensor MRI (DT-MRI). Previously, it has been suggested that these geometric distortions can be removed from brain DW-EP images using affine transformations determined from phantom calibration experiments using iterative cross-correlation (ICC). Since this approach was first described, a number of image-based registration methods have become available that can also correct eddy current-induced distortions in DW-EP images. However, as yet no study has investigated whether separate eddy current calibration or image-based registration provides the most accurate way of removing these artefacts from DT-MRI data. Here we compare how ICC phantom calibration and affine FLIRT (http://www.fmrib.ox.ac.uk), a popular image-based multi-modal registration method that can correct both eddy current-induced distortions and bulk subject motion, perform when registering DW-EP images acquired with different slice thicknesses (2.8 and 5 mm) and b-values (1000 and 3000 s/mm(2)). With the use of consistency testing, it was found that ICC was a more robust algorithm for correcting eddy current-induced distortions than affine FLIRT, especially at high b-value and small slice thickness. In addition, principal component analysis demonstrated that the combination of ICC phantom calibration (to remove eddy current-induced distortions) with rigid body FLIRT (to remove bulk subject motion) provided a more accurate registration of DT-MRI data than that achieved by affine FLIRT.     

Magnetic resonance spectroscopic imaging for visualization and correction of distortions in MRI: high precision applications in neurosurgery

We present a method for the quantification and correction of geometrical/intensity distortions of magnetic resonance images predominantly caused by bulk magnetic susceptibility shifts due to susceptibility heterogeneities of measured biologic tissues and shape of the object under investigation. The method includes precise and fast measurements of the static magnetic-field distribution inside the measured object and automated data processing. Magnetic-field deviations in the range −2.4; 2.6 ppm were found in the human brain at B₀ = 1.5 T. For routinely used imaging parameters, with a read gradient strength of about 1 mT/m, the magnetic-field perturbations in the human brain can cause geometrical distortions up to ±4 mm and intensity changes up to ±50%. MR images corrected by the described method are suitable for planning high precision applications in neurosurgery.     

On the mechanism of the α-β phase transformation of quartz

With a simple geometrical model the atomic displacements at the transition from α- to β -quartz and the eigenvector of the soft mode at the Γ -point are related to a single (order-) parameter. The model is refined by taking into account possible distortions of the SiO₄ tetrahedra. These refinements, together with considerations on the temperature dependence of the order parameter, suggest an increase of π-bond order in the Si-O bond with increasing temperature as the driving mechanism for the phase transition. The model also offers a qualitative understanding of the appearance of diffuse X-ray scattering in the Γ-M direction.     

强激光主镜膜厚不均匀性对偏振和光学图像的影响

本文讨论了在特定镀膜室的几何尺寸约束下,一定直径(0.8m)的主反射镜的膜层厚度分布。给出了金属增强型高反射膜系由于不均匀性对光束偏振态的影响;计算了1.06μm主激光和0.5893μm的信标光产生的相位畸变。通过修正设计得到符号相同的相位变化,从而使信标光达到预期目的。     

Design and fabrication of a 900-1700 nm hyper-spectral imaging spectrometer

This paper presents a 900-1700 nm hyper-spectral imaging spectrometer which offers low distortions, a low F-number, a compact size, an easily-fabricated design and a low cost (is presented in this paper). The starting point for its optical design is discussed according to the geometrical aberration theory and Rowland circle condition. It is shown that these methods are useful in designing a push-broom hyper-spectral imaging spectrometer that has an aperture of f/2.4, modulation transfer functions of less than 0.8 at 25 cycles/mm, and spot sizes less than 10 μm. A prototype of the optimized hyper-spectral imaging spectrometer has been fabricated using a high precision machine and the experimental demonstration with the fabricated hyper-spectral imaging spectrometer is presented.     

AunPt-阴离子小团簇的量子化学研究

在相对论有效势(RECP)近似下,用基于密度泛函理论(B3LYP)的从头计算方法和LANL2DZ基组,系统研究了阴离子团簇AunPt-(n=1-5)g能的几何构型和电子态,确定了低能量异构体.结果表明.AunPt-团簇的剩余电子改变了中性团簇AunPt的稳定结构,这种影响随团簇体积的增大而减小.     

Gravitational waves from mesoscopic dynamics of the extra dimensions

Recent models which describe our world as a brane embedded in a higher dimensional space introduce new geometrical degrees of freedom, associated with spatial variations in the position of the brane and the size of the extra dimensions, that can be coherently excited by symmetry breaking in the early universe even on "mesoscopic" scales as large as 1 mm. The characteristic frequency and intensity of resulting gravitational radiation backgrounds are estimated. Extra dimensions with scale between 10(-14) and 1 mm can produce detectable backgrounds at frequencies f approximately 10(3) to 10(-4) Hz.     

On-axis diffuse screen based on a reference-free volume hologram

A new type of hologram that elaborates upon the simplest (Gabor) on-axis hologram is suggested. The new approach makes it possible to eliminate the projected image distortions typical of the Gabor hologram. Specifically, based on a reference-free thick hologram, an on-axis holographic screen that does not transmit the zeroth order is prepared. In addition, this screen does not produce a halo and the conjugate image. It allows for recording in one spectral range and reconstruction in another, thereby greatly simplifying the choice of a light-sensitive record medium. With this screen, a color image can be projected.     

纳米颗粒材料表面形貌结构AFM表征中针尖干扰的修正与评价

原子力显微镜（ＡＦＭ）被广泛地用来进行纳米尺度和亚微米尺度结构材料的形貌表征,其优点是制样简单、无需进行导电处理,但会针尖与样品作用时,由于针尖自身的成像作用,导致得到的图像结果比实际结果要大,这就是针尖的放大效应,文章基于一种简单的数学模型,得到了对实测图像的修正结果,对于一般金字塔形针尖,ＡＦＭ的放大作用可导致粒子尺寸比真实尺寸大近２倍,实测图像的失真状况与针尖的形状因子、粒子的分散状态等因素     

Magnetic color symmetry of lattice rotations in a diamagnetic material

Oxygen octahedral rotations are the most common phase transitions in perovskite crystal structures. Here we show that the color symmetry of such pure elastic distortions is isomorphic to magnetic point groups, which allows their probing through distinguishing polar versus magnetic symmetry. We demonstrate this isomorphism using nonlinear optical probing of the octahedral rotational transition in a compressively strained SrTiO3 thin film that exhibits ferroelectric (4mm) and antiferrodistortive (4{'}mm{'}) phases evolving through independent phase transitions. The approach has broader applicability for probing materials with lattice rotations that can be mapped to color groups.     

Optical compensation of geometrical distortion by a deformable mirror

An optical method for the real time correction of geometrical distortion is reported. It is based on the “fun-house-mirror effect”: An adjustable nonplanar mirror is introduced between object- and pupil-plane and generates a suitable (space-variant) shift of each pixel. The method is restricted to a certain class of distortions, which lead to continuous mirror surfaces (mirror must not break). We also investigate aberrations which are another restriction of the method. Our application was the improvement of TV-systems: before correction 20%, and after correction 50% of pixels had a distortion less or equal than one pixel distance.     

On the theory of diffusion of light interstitials in metals

Using a nonlinear-screening approach the potential energy of positively charged light interstitials in Cu and lattice distortions around these particles have been determined numerically. The calculations predict a marked isotope effect for the lattice distortions around positive muons and protons at octahedral interstitial sites. They indicate that in Cu the diffusion mechanisms for positive muons and for hydrogen isotopes may be different.     

Elimination of geometric distortions in stereoscopic systems with converging optical axes

The problem on the possibility of eliminating the vertical disparity and depth plane curvature by representing the left and right perspective views in two intersecting planes of observation is successfully solved in the framework of the geometrical optics approximation. The expressions are found for the angle of intersection of the planes of observation providing the elimination of each of the studied distortions. It is shown that both studied distortions are eliminated for the same angle of intersection of the planes of observation.     

Diffraction tomography: a geometrical distortion free procedure

Ductal echography (DE) is a recent anatomically-led method of investigation of internal mammary structures that provides direct observation of ductolobular structures in mammary lobes. Indeed, breast cancer initiates from the epithelium (hypoechogenic) and develops first in ductolobular structures. Our research aims at developing an ultrasonic scanner (hemispherical antenna) that will allow three-dimensional measurement of the field diffracted by the gland. The present reconstruction procedure is an alternative solution to the standard elliptic back-projection (EBP) technique based on the Born approximation (weak scattering assumption). The latter implicitly assumes that the sound speed is (almost) constant within the breast. This unrealistic a priori is inconsistent with our heterogeneous media characterization purpose, and leads both to geometrical distortion in the reconstruction and to poor focusing of the backpropagated waves (low contrast imaging). However, the EBP technique retains a two-fold advantage: firstly it does not make any other assumption concerning the distribution of mechanical parameters apart from low gradients. Secondly, it shows great robustness, a high resolving power, and is easy to implement. Thus, in order to account for strong wavefront distortions, we integrate temporal compensation of the scattered signals acquired into the scattering EBP technique. The adjustment relies on a time of flight estimation based on a "layer stripping" approach. Numerical tests based on finite difference time domain simulations of data scattered by a random tissue-like phantom are proposed.     

Pu+4的几何构型和Jahn-Teller效应

在Pu原子的相对论有效原子实势下,用密度泛函B3LYP方法计算得到Pu +4分子离子的6种稳定的几何构型.计算表明Pu+4的Td构型不能稳定存在,详细讨论了 Td构型的Jahn-Teller效应,讨论结果显示它们的各种畸变方式都符合群的分解原理, 从而证明Pu+4分子离子的Td构型的Jahn-Teller效应非常明显.D4h 构型也存在Jahn-Teller效应.     

Causal nets or what is a deterministic computation?

The network approach to computation is more direct and physical than the one based on some specific computing devices (like Turing machines). However, the size of a usual—e.g., Boolean—network does not reflect the complexity of computing the corresponding function, since a small network may be very hard to find even if it exists. A history of the work of a particular computing device can be described as a network satisfying some restrictions. The size of this network reflects the complexity of the problem, but the restrictions are usually somewhat arbitrary and even awkward. Causal nets are restricted only by determinism (causality) and locality of interaction. Their geometrical characteristics do reflect computational complexities. And various imaginary computer devices are easy to express in their terms. The elementarily of this concept may help bringing geometrical and algebraic (and maybe even physical) methods into the theory of computations. This hope is supported by the group-theoretical criterion given in this paper for computability from symmetrical initial configurations.Part of this work was done while this author was visiting Johann Wolfgang Goethe University, Frankfurt am Main in 1978 and Stanford University in 1979.The research of this author was partially supported by NSF grants MCS 77-19754 and MCS-8104211.     

Nonlinear vibrations of loudspeaker-like structures

During high amplitudes of vibration, nonlinearities affect the electroacoustical behavior of electrodynamic transducers and are responsible for audible distortions. We distinguish two types of nonlinearities: electrical and mechanical. In this study, attention is paid to the mechanical and geometrical properties of loudspeaker-like structures. The loudspeaker is viewed as a combination of an annular plate with a circular plate. Nonlinear vibrations of such a structure are investigated, using the dynamic analog of the Von-Kármán equations. Furthermore, the influence of both material properties and geometrical parameters is studied. It is shown that nonlinear effects can be substantially reduced by choosing appropriate material and geometrical parameters.     

Selective generation of ultrasonic Lamb waves by electromagnetic acoustic transducers

In this paper, we describe a modal expansion approach for the analysis of the selective generation of ultrasonic Lamb waves by electromagnetic acoustic transducers(EMATs). With the modal expansion approach for waveguide excitation, an analytical expression of the Lamb wave's mode expansion coefficient is deduced, which is related to the driving frequency and the geometrical parameters of the EMAT's meander coil, and lays a theoretical foundation for exactly analyzing the selective generation of Lamb waves with EMATs. The influences of the driving frequency on the mode expansion coefficient of ultrasonic Lamb waves are analyzed when the EMAT's geometrical parameters are given. The numerical simulations and experimental examinations show that the ultrasonic Lamb wave modes can be effectively regulated(strengthened or restrained) by choosing an appropriate driving frequency of EMAT, with the geometrical parameters given. This result provides a theoretical and experimental basis for selectively generating a single and pure Lamb wave mode with EMATs.