Effects of twin grain boundaries on the subgrain rotation of the solder joint during thermal shock

The ball grid array (BGA) component was selected as the specimen with the outmost edge row cross-sectioned to investigate subgrain rotation behavior influenced by grain boundaries under thermal shock cycles condition. To study the subgrain rotation, the crystal orientation was obtained by electron backscattered diffraction(EBSD). The results showed that a lot of subgrains were generated in the solder joints due to cyclic stress caused by the high mismatched coefficient of thermal expansion (CTE) under the thermal shock cycles condition. And the subgrains near the chip-side and the twin grain boundaries were analyzed in detail to estimate the impact of the grain boundaries on the subgrain rotation behavior. The results showed that a large number of subgrain boundaries and several newly generated subgrains appeared at the tilted twin grain boundaries and the chip-side in the solder joint after 200 thermal shock cycles. Meantime, the subgrain rotation axes and misorientation angles were both calculated, and the dislocation slip was recognized to closely relate to subgrain rotation by comprehensively analyzing the rotation axes and misorientation angles. The subgrain rotation axes of the chip-side was about Sn [101] and [001], while the subgrains rotation near the tilted grain boundaries in the same dominant grain was different from that of the subgrains near the chip-side, and subgrain rotation axes were [101], [100] and [110]. There were also a large difference in the direction of subgrain rotation between the chip-side and the tilted twin grain boundaries. The subgrain rotation axes at both sides of twin grain boundaries were similar, but the rotation directions were opposite.     

线结构光视觉测量系统运动轴线的简易标定方法

为简化测量系统中平移轴和旋转轴的标定,提出一种基于一维平面标靶的简易标定方法。将一维标靶放置在数控平台上,控制平台分别做平移和旋转运动,提取每个位置下图像中圆心坐标,利用消隐点和三点透视模型(P3P)原理实现系统轴线空间位置的标定。实验结果表明,该标定方法具有较高的标定精度,平均绝对测量误差为0.0411 mm,均方根(RMS)误差为0.0625 mm。该标定方法仅需已知的等距共线三点即可完成平移轴线和旋转轴线的高精度标定,降低了标定成本,且计算简单、标定过程灵活方便,适合现场标定。     

Uncoupled cylindrical wave modes for a radially inhomogeneous medium

The equations for the transformation of the tangential electric and magnetic fields through a series of uniform cylindrical layers of arbitrary properties are transformed from their generally coupled form to an uncoupled set of two equations. The complexity of the transformation matrices is thereby greatly reduced. The decoupling operation amounts to a coordinate transformation which has a direct correspondence with the rotation of axes to the plane of propagation in the case of rectangular coordinates. The immediate usefulness of this approach for impedance transformation is shown.     

Technique for controlling the internal rotation of principal axesin the fabrication of birefringent fibers

The fabrication of a polarization-maintaining fiber in which the internal rotation of the principal birefringent axes was monitored and controlled to a rate of less than 0.1°/cm is discussed. This represents an order of magnitude improvement over the lowest rotation rate observed in commercial fibers. The technique is based on a novel method of interpreting the backscattered power from a-side illuminated birefringent fiber to determine the internal orientation of the strain inducing axes     

Accuracy in Prediction of Catheter Rotation in IVUS With Feature-Based Optical Flow—A Phantom Study

The quantitative assessment of and compensation for catheter rotation in intravascular ultrasound images presents a fundamental problem for noninvasive characterization of the mechanical properties of the coronary arteries. A method based on the scale-space optical flow algorithm with a feature-based weighting scheme is proposed to account for the aforementioned artifact. The computed vector field, describing the misalignment between two consecutive frames, allows the quantitative assessment of the amount of vessel wall tissue motion, which is directly related to the catheter rotation. Algorithm accuracy and robustness were demonstrated on two tissue-mimicking phantoms, subjected to controlled amount of angular deviation. The proposed method shows a great reliability in the prediction of catheter rotational motion up to 4deg.     

On the recovery of a function on a circular domain

We consider the problem of estimating a function f (x, y) on the unit disk f {(x, y): x/sup 2/+y/sup 2//spl les/1}, given a discrete and noisy data recorded on a regular square grid. An estimate of f (x, y) based on a class of orthogonal and complete functions over the unit disk is proposed. This class of functions has a distinctive property of being invariant to rotation of axes about the origin of coordinates yielding therefore a rotationally invariant estimate. For-radial functions, the orthogonal set has a particularly simple form being related to the classical Legendre polynomials. We give the statistical accuracy analysis of the proposed estimate of f (x, y) in the sense of the L/sub 2/ metric. It is found that there is an inherent limitation in the precision of the estimate due to the geometric nature of a circular domain. This is explained by relating the accuracy issue to the celebrated problem in the analytic number theory called the lattice points of a circle. In fact, the obtained bounds for the mean integrated squared error are determined by the best known result so far on the problem of lattice points within the circular domain.     

Convolution-based interpolation for fast, high-quality rotation ofimages

This paper focuses on the design of fast algorithms for rotating images and preserving high quality. The basis for the approach is a decomposition of a rotation into a sequence of one-dimensional translations. As the accuracy of these operations is critical, we introduce a general theoretical framework that addresses their design and performance. We also investigate the issue of optimality and present an improved least-square formulation of the problem. This approach leads to a separable three-pass implementation of a rotation using one-dimensional convolutions only. We provide explicit filter formulas for several continuous signal models including spline and bandlimited representations. Finally, we present rotation experiments and compare the currently standard techniques with the various versions of our algorithm. Our results indicate that the present algorithm in its higher-order versions outperforms all standard high-accuracy methods of which we are aware, both in terms of speed and quality. Its computational complexity increases linearly with the order of accuracy. The best-quality results are obtained with the sine-based algorithm, which can be implemented using simple one-dimensional FFTs.     

一种基于坐标轴旋转的俯冲段大斜视SAR波数域成像算法

由于机动平台成像的复杂性,常规SAR成像方法无法直接应用于俯冲模式下的大斜视成像处理。针对此问题,该文详细分析了俯冲段几何成像模型以及大斜视成像支撑区选择问题,提出一种基于坐标轴旋转的俯冲段大斜视SAR波数域成像算法。该算法根据部分孔径数据提出波数域聚焦处理,并通过坐标轴旋转实现频谱的高利用率,在有效避免了位置域聚焦的大量补零的前提下,保障了成像分辨率,提高了处理效率。仿真和实测数据处理验证了所提算法的有效性。     

Calibrated single-plunge bipolar electrode array for mapping myocardial vector fields in three dimensions during high-voltage transthoracic defibrillation

Mapping of the myocardial scalar electric potential during defibrillation is normally performed with unipolar electrodes connected to voltage dividers and a global potential reference. Unfortunately, vector potential gradients that are calculated from these data tend to exhibit a high sensitivity to measurement errors. This paper presents a calibrated single-plunge bipolar electrode array (EA) that avoids the error sensitivity of unipolar electrodes. The EA is triaxial, uses a local potential reference, and simultaneously measures all three components of the myocardial electric field vector. An electrode spacing of approximately 500 microm allows the EA to be direct-coupled to high-input-impedance, isolated, differential amplifiers and eliminates the need for voltage dividers. Calibration is performed with an electrolytic tank in which an accurately measured, uniform electric field is produced. For each EA, unique calibration matrices are determined which transform potential difference readings from the EA to orthogonal components of the electric field vector. Elements of the matrices are evaluated by least squares multiple regression analysis of data recorded during rotation of the electric field. The design of the electrolytic tank and electrode holder allows the electric field vector to be rotated globally with respect to the electrode axes. The calibration technique corrects for both field perturbation by the plunge electrode body and deviations from orthogonality of the electrode axes. A unique feature of this technique is that it eliminates the need for mechanical measurement of the electrode spacing. During calibration, only angular settings and voltages are recorded. For this study, ten EAs were calibrated and their root-mean-square (rms) errors evaluated. The mean of the vector magnitude rms errors over the set of ten EAs was 0.40% and the standard deviation 0.07%. Calibrated EAs were also tested for multisite mapping in four dogs during high-voltage transthoracic shocks.     

惯性系下捷联惯导系统最优两位置对准

惯性系卡尔曼滤波对准的状态量不完全可观测,针对这一问题,提出惯性系两位置对准。根据分段线性定常系统理论和奇异值分解法分析惯性系两位置对准算法的可观测性,分析结果表明横摇、纵摇和航向3个轴中绕航向轴旋转时系统的可观测度最高。然后,以航向误差作为参考指标进行仿真,确定了绕航向轴旋转180°的两位置对准为最优。     

Rain-induced deflection of microwave and millimetre-wave radiowaves

A model is developed to describe the angular deflection of the propagation vector of a radiowave propagated through a rain-filled medium. This additional effect occurs in a similar way to the manner in which raindrops canted in a plane perpendicular to the propagation direction cause rotation of the plane of polarisation, owing to differential attenuation and phase of components along the raindrops' principal axes. It is shown that the presence of raindrops with symmetry axes inclined to the propagation path and in the plane of polarisation produces a differential attenuation of the field components, resulting in a rotation of the propagation vector towards a direction perpendicular to the minor raindrop axis. Maximum deflection angles are given for several frequencies between 11 and 30 GHz and rain rates up to 150 mm/h. Some practical consequences of deflection are discussed.     

Validation of 3-D curved objects: CAD model and fabricatedworkpiece

This paper proposes a new method to describe and identify a 3-D curved object for the purpose of validating a fabricated object to the design specification. Curved 3-D objects are, in general, difficult to represent and identify because they lack distinct properties such as edges, planes, or cylindrical surfaces which are the building blocks in representing objects. In this paper, the authors propose to use principal axes of a 3-D object to establish a reference for the representation. A method of obtaining an inertia matrix from a 3-D range image is developed. The unique set of principal axes is obtained from the inertia matrix of an object with an arbitrary 3-D position and orientation, and the object can be described uniquely on these principal axes. On the principal axes, an object is described by a set of features describing the shape of the object such as spine, section size, section orientation, and section contraction. The features are used for comparing two objects for the validation purpose. The authors also propose a direct measure of similarity between two objects as a mean-squared difference of radii. As an experiment, two 3-D object models are designed through a CAD package, and fabricated objects are compared with the designed models for validation purposes     

CORDIC-Based Unified Architectures for Computation of DCT/IDCT/DST/IDST

In this paper, CORDIC (coordinate rotation digital computer)-based Cooley-Tukey fast Fourier transform (FFT)-like algorithms for power-of-two point discrete cosine transform/discrete sine transform/inverse discrete cosine transform/inverse discrete sine transform are proposed and their corresponding unified architectures are developed by fully reusing the unique two basic processing elements. The proposed algorithms have some distinguished advantages, such as FFT-like regular data flow, unique post-scaling factor, and arithmetic-sequence rotation angles. The developed unified architectures can compute four different transforms by simple routing the data flow according to the specific transform without feeding different transform coefficients or different transform kernels. The unfolding technique is used to overcome the problem of difficult to realize pipeline that occur in iterative CORDIC algorithms. Compared to existing unified architectures, the proposed architectures have a superior performance in terms of hardware complexity, control complexity, throughput, scalability, modularity, and pipelinability.     

利用飞控特征的四旋翼无人机雷达回波信号仿真

针对现有旋翼无人机雷达回波信号仿真方法未将密切相关的机身速度与旋翼转速相关联的问题,本文利用旋翼无人机的飞控特征,提出了一种将机身运动与旋翼转速相结合的四旋翼无人机雷达回波信号仿真方法.首先根据雷达回波仿真所需参数利用四旋翼无人机飞控原理给出一种机身速度与旋翼转速关联的简化运动模型,其次推导并给出线性调频体制雷达四旋翼...     

BER minimization for dual‐polarized wireless systems with polarization‐domain rotation

We consider the problem of bit error rate (BER) degradation because of the power gain imbalance between horizontal (H)‐polarization and vertical (V)‐polarization components in an orthogonal dual‐polarization transmission system. To alleviate the aforementioned BER degradation problem, we propose a non‐orthogonal polarization‐domain rotation scheme where the axes of H‐polarization and V‐polarization components are rotated with different angles at the transmitter and de‐rotated at the receiver. In addition, in order to assess the effectiveness of the polarization‐domain rotation scheme, we derive the closed‐form BER expression under a practical dual‐polarized channel model, which is represented by cross‐polarization ratio and co‐polarization ratio (CPR). We also derive the approximated BER expressions for the two asymptotic values of CPR: balanced CPR and infinite CPR. With the derived BER expressions, we find the optimal rotation angles that jointly minimize the BER. According to the numerical results, it is shown that about 3dB E_b/N₀ gain is obtained at the BER of 10^?4 and the CPR of 10dB by the polarization‐domain rotation scheme with optimal rotation angles compared with the conventional orthogonal dual‐polarization transmission. Copyright © 2015 John Wiley & Sons, Ltd.     

基于激光自混合干涉能判别转向的角度测量方法

针对现有激光自混合干涉(SMI)角度测量方法无法判别角度旋转方向的缺陷,提出一种基于SMI和表面等离子体共振(SPR)的、能判别旋转方向的角度测量方法.通过判断出射激光束的平均光强变化,确定被测物体旋转的方向;通过预先标定好的激光SMI输出光强和旋转角度间的对应关系,实现对被测物体旋转角度的测量.搭建了旋转平台微小旋转...     

Properties and applications of the large circular resonant dipole array

Large closed-curve antenna arrays have been a subject of research for many years and have been shown to have many interesting properties. The paper investigates some of the properties of such a dipole array when the closed curve is a circle. Recently, because of its unique horizontal field pattern, a 90-element circular array of this type has been proposed as a microwave beacon for the coastal navigation of ships and airplanes. In the design of these arrays, it is suggested that the array be rotated mechanically. The question arises: can the mechanical rotation be replaced by an electronic rotation? We show that electronic rotation is not possible for the 90-element circular array originally described, but is possible for a modified array. The subtle difference between these two arrays is clarified and a simple criterion is given for the general case. Also presented is the derivation of an asymptotic formula for the radiation pattern of a resonant circular array of N equal elements with only one element driven. Since the theory for such an array is complicated and involves numerous numerical difficulties, a simple asymptotic formula for the field pattern has advantages over other methods. The simple formula is shown to produce a vertical field pattern that is indistinguishable from its numerically calculated counterpart. Generalization to noncircular arrays is discussed briefly.     

Determination of Otolith Afferent Response Parameters Using Small Amplitude Sinusoidal Roll and Pitch Tilts

Previous investigations of the response properties of afferent neurons innervating the otolith organs of the inner ear have used experimental protocols which required the rotation of an animal through a full 3600 about its roll and pitch axes. These are difficult experiments since recordings from individual neurons must be maintained throughout the course of the rotations. This paper describes an alternative method which permits the calculation of otolith neuron response parameters from data collected during small amplitude sinusoidal roll and pitch tilts. The effectiveness of this technique is demonstrated by analyzing a variety of simulated afferent responses to sinusoidal tilts. This method facilitates the practical determination of otolith properties as well as simplifying the procedures prerequisite to the testing of otolith dynamic response characteristics.     

Local linear transforms for texture measurements

The Nth order probability density function for pixels in a restricted neighborhood may be characterized by a set of N histograms (or some corresponding moments) computed along appropriately chosen axes. The projections on those axes are obtained from a local linear transform of the local neighborhood vector. This approach is closely related to fulter bank analysis methods and gives a statistical justification for the extraction of texture properties by means of convolution operators or local matches. Optimal and sub-optimal linear operators are derived for texture analysis and classification. Experimental results indicate that the method is robust, flexible, and that it performs as well as standard co-occurrence based methods for texture classification. The proposed approach enables texture characterization with a lower number of features and it is also computationally more appealing.     

Recent progress in synthesis of two-dimensional hexagonal boron nitride

Two-dimensional (2D) materials have recently received a great deal of attention due to their unique structures and fascinating properties, as well as their potential applications. 2D hexagonal boron nitride (2D h-BN), an insulator with excellent thermal stability, chemical inertness, and unique electronic and optical properties, and a band gap of 5.97 eV, is considered to be an ideal candidate for integration with other 2D materials. Nevertheless, the controllable growth of high-quality 2D h-BN is still a great challenge. A comprehensive overview of the progress that has been made in the synthesis of 2D h-BN is presented, highlighting the advantages and disadvantages of various synthesis approaches. In addition, the electronic, optical, thermal, and mechanical properties, heterostructures, and related applications of 2D h-BN are discussed.