10-Gb/s error-free transmission under optical reflection using isolator-free 1.3- /spl mu/m InP-based vertical-cavity surface-emitting lasers

Error-free transmission through 10-km single-mode fiber at 10 Gb/s under -13-dB optical reflections has been demonstrated for the first time using a directly modulated 1.3-/spl mu/m InP-based VCSEL without any optical isolator. The 13-GHz relaxation oscillation frequency and stable polarization suppresses relative intensity noise degradation under optical reflection. Only 1-dB error-free power penalty has been observed with optical reflection set with the worst polarization direction.     

PEEC capacitance extraction of 3-D interconnects

As feature size of electronic devices decreases, fast and accurate capacitance extraction has become increasingly critical for verification and analysis as regard as electromagnetic compatibility and signal integrity issues. The partial element equivalent circuit method is implemented for three-dimensional capacitance extraction of interconnects and very large-scale integration circuits with multiple dielectrics. The electric field coupling due to free and bound charges are analysed and modelled separately thus allowing to distinguish their contribution. The proposed approach provides physical insight, totally compatible fast methods for accelerating matrix-vector products, allows an easy treatment of lossy and dispersive dielectrics and is well suited for applying model order reduction techniques     

Fast numerically stable computation of orthogonal Fourier?Mellin moments

An efficient algorithm for the computation of the orthogonal Fourier-Mellin moments (OFMMs) is presented. The proposed method computes the fractional parts of the orthogonal polynomials, which consist of fractional terms, recursively, by eliminating the number of factorial calculations. The recursive computation of the fractional terms makes the overall computation of the OFMMs a very fast procedure in comparison with the conventional direct method. Actually, the computational complexity of the proposed method is linear O(p) in multiplications, with p being the moment order, while the corresponding complexity of the direct method is O(p²). Moreover, this recursive algorithm has better numerical behaviour, as it arrives at an overflow situation much later than the original one and does not introduce any finite precision errors. These are the two major advantages of the algorithm introduced in the current work, establishing the computation of the OFMMs to a very high order as a quite easy and achievable task. Appropriate simulations on images of different sizes justify the superiority of the proposed algorithm over the conventional algorithm currently used     

Level set and geodesic active contours based measurement of material removal between serial sections

The measurement of the thickness of material removed between serial sections is a crucial step of three-dimension reconstruction. Geodesic active contours is an efficient method for contour detection of objects on an image. The indents on the SiC/Al composite micrographs are segmented by using level set and geodesic active contours. After getting the contours of the indents, we calculate the distance from the uppermost pixel to the lowermost pixel to get the vertical diagonal length, and calculate the distance from the leftmost pixel to the rightmost pixel to get the horizontal diagonal length of each contour. Then the final length of each diagonal is acquired by averaging the vertical diagonal length and the horizontal diagonal length, respectively. The Vickers’ indenter is made by a square pyramidal-shaped diamond with opposite faces at an angle of 136°, so the thickness of material removed between two serial sections and the length difference of the diagonals on the two serial sections has a definite geometrical relation. Thus the thickness of material removed between two serial sections is acquired using the geometrical relation.     

Significance of the elastic peak stress evaluated by FE analyses at the point of singularity of sharp V-notched components

The paper presents an expression useful to estimate the notch stress intensity factor (NSIF) from finite element analyses carried out by using a mesh pattern with a constant element size. The evaluation of the NSIF from a numerical analysis of the local stress field usually requires very refined meshes and then large computational effort. The usefulness of the presented expression is that (i) only the elastic peak stress numerically evaluated at the V‐notch tip is needed and no longer the whole stress–distance set of data; (ii) the adopted meshes are rather coarse if compared to those necessary for the evaluation of the whole local stress field. The proposed expression needs the evaluation of a virtual V‐notch tip radius, i.e. the radius which would produce the same elastic peak stress than that calculated by FEM at the sharp V‐notch tip by means of a given mesh pattern. Once such a radius has been theoretically determined for a given geometry, the expression can be applied in a wide range of notch depths and opening angles.     

Modeling of Temperature–Frequency Correlation Using Combined Principal Component Analysis and Support Vector Regression Technique

A good understanding of environmental effects on structural modal properties is essential for reliable performance of vibration-based damage diagnosis methods. In this paper, a method of combining principal component analysis (PCA) and support vector regression (SVR) technique is proposed for modeling temperature-caused variability of modal frequencies for structures instrumented with long-term monitoring systems. PCA is first applied to extract principal components from the measured temperatures for dimensionality reduction. The predominant feature vectors in conjunction with the measured modal frequencies are then fed into a support vector algorithm to formulate regression models that may take into account thermal inertia effect. The research is focused on proper selection of the hyperparameters to obtain SVR models with good generalization performance. A grid search method with cross validation and a heuristic method are utilized for determining the optimal values of SVR hyperparameters. The proposed method is compared with the method directly using measurement data to train SVR models and the multivariate linear regression (MLR) method through the use of long-term measurement data from a cable-stayed bridge. It is shown that PCA-compressed features make the training and validation of SVR models more efficient in both model accuracy and computational costs, and the formulated SVR model performs much better than the MLR model in generalization performance. When continuously measured data is available, the SVR model formulated taking into account thermal inertia effect can achieve more accurate prediction than that without considering thermal inertia effect.