Li Method Research Articles

Comparison of parameter estimation methods for transformer Weibull lifetime modelling

Two-parameter Weibull distribution is the most widely adopted lifetime model for power transformers. An appropriate parameter estimation method is essential to guarantee the accuracy of a derived Weibull lifetime model. Six popular parameter estimation methods (i.e. the maximum likelihood estimation method, two median rank regression methods including the one regressing X on Y and the other one regressing Y on X, the Kaplan-Meier method, the method based on cumulative hazard plot, and the Li's method) are reviewed and compared in order to find the optimal one that suits transformer's Weibull lifetime modelling. The comparison took several different scenarios into consideration: 10000 sets of lifetime data, each of which had a sampling size of 40 1000 and a censoring rate of 90\%, were obtained by Monte-Carlo simulations for each scienario. Scale and shape parameters of Weibull distribution estimated by the six methods, as well as their mean value, median value and 90\% confidence band are obtained. The cross comparison of these results reveals that, among the six methods, the maximum likelihood method is the best one, since it could provide the most accurate Weibull parameters, i.e. parameters having the smallest bias in both mean and median values, as well as the shortest length of the 90\% confidence band. The maximum likelihood method is therefore recommended to be used over the other methods in transformer Weibull lifetime modelling.

Authentication Through Hough Transformation Generated Signature on G-Let D3 Domain (AHSG)

In this paper a G-Let based authentication technique has been proposed to authenticate digital documents through Hough transform generated signature generated from original autograph. The cover image is transformed into G-Let domain to generate n number of G-Lets out of which (n/2)-1 numbers of G-Lets are embedded with secret Hough signature bits for the purpose of authentication or copyright protection. The special feature of AHSG is to optimize the distortion rate, by adjustment at the last stage of the technique, using back propagation. Experimental results are computed and compared with the existing authentication techniques like Li's method, SCDFT, Region-Based method based on Mean Square Error (MSE), Peak Signal to Noise Ratio (PSNR), Image Fidelity (IF), Universal Quality Image (UQI) and Structural Similarity Index Measurement (SSIM) which shows better performance in AHSG, in terms of low computational complexity and better fidelity.

Heterogeneity-Projection Hard-Decision Color Interpolation Using Spectral-Spatial Correlation

This paper presents a novel heterogeneity-projection hard-decision (HPHD) color interpolation procedure for reproduction of Bayer mosaic images. The proposed algorithm aims to estimate the optimal interpolation direction and perform hard-decision interpolation, in which each pixel only needs to be interpolated once. A new heterogeneity-projection scheme based on a novel spectral-spatial correlation concept is proposed to estimate the best interpolation direction directly from the original mosaic image. Using the proposed heterogeneity-projection scheme, a hard-decision rule can be decided before performing the interpolation. The advantage of this scheme is that it provides an efficient way for decision-based algorithms to generate improved results using fewer computations. Compared with three recently reported demosaicing techniques, Gunturk's, Lu's, and Li's methods, the proposed HPHD outperforms all of them in both PSNR values and S-CIELAB deltaEab measures by utilizing 25 natural images from Kodak PhotoCD.

Commentary

In this paper a G-Let based authentication technique has been proposed to authenticate digital documents through Hough transform generated signature generated from original autograph. The cover image is transformed into G-Let domain to generate n number of G-Lets out of which (n/2)-1 numbers of G-Lets are embedded with secret Hough signature bits for the purpose of authentication or copyright protection. The special feature of AHSG is to optimize the distortion rate, by adjustment at the last stage of the technique, using back propagation. Experimental results are computed and compared with the existing authentication techniques like Li's method, SCDFT, Region-Based method based on Mean Square Error (MSE), Peak Signal to Noise Ratio (PSNR), Image Fidelity (IF), Universal Quality Image (UQI) and Structural Similarity Index Measurement (SSIM) which shows better performance in AHSG, in terms of low computational complexity and better fidelity.

An enhanced approach to determine connected dominating sets for routing in mobile ad hoc networks

A mobile ad hoc network is a collection of wireless mobile nodes forming a temporary network without the support of any established infrastructure or centralised administration. Mobile ad hoc networks face a lot of challenges for designing a scalable routing protocol due to their natural characteristics. The idea of virtual backbone routing has been proposed for efficient routing in mobile ad hoc networks because virtual backbone routing can reduce communication overhead and speed up the routing process compared with many existing routing protocols. Up to now, Minimum Connected Dominating Set (MCDS) is the main method used to form a virtual backbone. However, finding an MCDS is an NP-hard problem. A distributed protocol for calculating the connected dominating set was proposed by Wu and Li. In this paper, we propose a further extension to reduce the size of the dominating set as compared to their method. We conduct extensive simulations on these two related algorithms. These simulation results show that our approach can consistently outperform Wu and Li's method, particularly for a medium-density network. We discuss the tradeoff between cost and performance through theoretical analysis.

Enhanced light transmission by hole arrays

The extraordinary optical transmission of a metallic film pierced by a two-dimensional subwavelength hole array, observed by Ebbesen et al, is explained using rigorous electromagnetic analysis and a phenomenological approach. The analysis is based on Li's Fourier-modal method extended to crossed gratings, which reduces the diffraction problem to the search for eigenvalues and eigenvectors of a particular matrix. The computation of the eigenvalues allows us to find a new channel for light transmission through the subwavelength holes, which differs from the transmission channel in the one-dimensional case (lamellar or rectangular-rod grating). It is demonstrated that the enhanced transmission is due to the excitation of a surface plasmon on the lower metallic surface.

The time lag of high-energy photons of Cyg X-1 in hard state

The time lag between hard and soft X-rays is an important aspect of the study of high-energy emission. Fourier cross spectrum, often used in calculating the time lag, is unable to measure statistically significant fast light variation above Fourier frequency 30 Hz from the measurements of Cyg X-1. The method of cross correlation function in time domain, developed by Li Ti-pei, can be effectively used in measuring time lags on different time scales. Using Li's method we discuss the properties of the time lag of high-energy photons of Cyg X-1 in hard state at different times. The results show that there is a significant time lap on short times scales (< 0.1 s). We confront different models of hard-state Cygnus X-1 with the observed time lag.

VIDAS® Enzyme-Linked Immunofluorescent Assay for Detection of Listeria in Foods: Collaborative Study

The VIDAS LIS method and the traditional culture methods for detection of Listeria species in food were evaluated in a multilaboratory comparative study. The 6 foods tested were either naturally contaminated or inoculated with 3 different concentrations of Listeria. Results for each food and each contamination level with the VIDAS LIS method were as good as or better than those obtained with the traditional culture method. Of 1558 samples tested, 935 were positive: 839 by the VIDAS method and 809 by standard culture methods. Overall false negative rates were 10.3 and 13.5% for the VIDAS LIS and culture methods, respectively. The false positive rate for the VIDAS LIS assay was 1.4% based on 9 VIDAS LIS positive assays that did not confirm positive by isolation of Listeria. The agreement between the VIDAS LIS and culture methods for all samples tested was 86%.

Corrections to test statistics in principal Hessian directions

Li's pHd method uses an asymptotic chi-squared test statistic to evaluate a hypothesized dimensionality of a reduced-dimension space in a largely nonparametric setting. This statistic is based on an assumed normal distribution of the predictors. When the distributional assumption is violated, a mixture chi-squared test proposed by Cook is theoretically more appropriate. However, both tests may not perform well with small or intermediate sized nonnormal samples. We propose two corrections to Li's statistic to enable the chi-squared approximation to be more accurate in such samples. The corrections are based on the mean and variance of the statistic of Cook's mixture distribution. The performance of Li's, Cook's, and the two new statistics are compared in some small simulation studies. Results show that one of the new tests performs about as well as Cook's, while the other performs better than the previously proposed tests.

Discrete point symmetries of ordinary differential equations

This paper describes a method that enables the user to construct systematically the set of all discrete point symmetries of a given ordinary differential equation (ODE) of order two or greater, provided that the ODE has at least a one–parameter Lie group of point symmetries. The method is easy to use, and is based upon Li's method of constructing continuous symmetries. The calculations are simple, and computer algebra is not usually required. Various examples are used to illustrate the method. The paper concludes with a proof that every ODE whose Lie group of point symmetries is isomorphic to the unimodular group has at least four inequivalent real discrete point symmetries.

A new approach for ranking fuzzy numbers by distance method

Many ranking methods have been proposed so far. However, there is yet no method that can always give a satisfactory solution to every situation; some are counterintuitive, not discriminating; some use only the local information of fuzzy values; some produce different rankings for the same situation. For overcoming the above problems, we propose a new method for ranking fuzzy numbers by distance method. Our method is based on calculating the centroid point, where the distance means from original point to the centroid point ( x 0, y 0 ), and the x 0 index is the same as Murakami et al.'s x 0 . However, the y 0 index is integrated from the inverse functions of an LR-type fuzzy number. Thus, we use ranking function R( A) = √ x 2 + y 2 (distance index) as the order quantities in a vague environment. Our method can rank more than two fuzzy numbers simultaneously, and the fuzzy numbers need not be normal. Furthermore, we also propose the coefficient of variation (CV index) to improve Lee and Li's method [Comput. Math. Appl.15 (1988) 887–896]. Lee and Li rank fuzzy numbers based on two different criteria, namely, the fuzzy mean and the fuzzy spread of the fuzzy numbers, and they pointed out that human intuition would favor a fuzzy number with the following characteristics: higher mean value and at the same time lower spread. However, when higher mean value and at the same time higher spread/or lower mean value and at the same time lower spread exists, it is not easy to compare its orderings clearly. Our CV index is defined as CV = σ (standard error)/μ (mean), which can overcome Lee and Li's problem efficiently. In this way, our proposed method can also be easily calculated by the “Mathematica” package to solve problems of ranking fuzzy numbers. At last, we present three numerical examples to illustrate our proposed method, and compare with other ranking methods.

Comments on "Minimum number of adders for implementing a multiplier and its application to the design of multiplierless digital filters"

For the original paper see ibid., vol. 42 p. 453-460 (July 1995). In the aforementioned paper by D. Li, a method of designing integer multipliers that uses fewer adders than canonic signed-digit (CSD) coding was described. This method is claimed by the author to be optimal, i.e., it produces a multiplier with the least possible adders. The commenters claim that they have presented a similar method, implemented using the MAG algorithm, to perform the same task, which was shown to be optimal. Comparing the two techniques shows that Li's method is not necessarily optimal. Both methods perform an exhaustive search over a set of multiplier configurations. In the commenters' paper, they described these configurations in terms of graphs. It is said that this method proves to be quite useful in that it becomes easy to describe the cases not covered by Li's algorithm. It is stated that the algorithm proposed by Li is suboptimal because: 1) graphs produced using fundamentals (intermediate vertices) of lower cost graphs are not considered; 2) tree-structured graphs are not considered; 3) right shifts (divide-by-two) are not allowed, causing some multipliers to require too many adders.

Comparative Study of Colorimetric and Fully Automated Enzyme-Linked Immunoassay System for Rapid Screening of Listeria spp. in Foods

Two enzyme-linked immunoassay (ELISA) systems for rapid screening of Listeria spp. were compared for their use in analysis of spiked foods regulated by the U.S. Food and Drug Administration. The Tecra Listeria kit is a 48 h visual ELISA that detects Listeria spp. through colorimetry. It has been approved for first action by AOAC INTERNATIONAL. The Vitek immunodiagnostic assay system for Listeria (VIDAS LIS) is a fully automated 48 h ELISA that detects Listeria spp. by immunofluorescence. Fifty-two food samples were artificially contaminated with high (11-42 colony-forming units [cfu]/25 g food) and low (2-8 cfu/25 g food) levels of L. monocytogenes and screened by the 2 protocols. Unspiked samples were also assayed as negative controls. Six unspiked samples were found positive for Listeria spp. by both methods: 3 were identified as L. monocytogenes and 3 as L. innocua by official methods. Both ELISA methods detected all spiked samples. One unspiked sample was assayed positive by Tecra and negative by VIDAS LIS. No Listeria spp. were recovered when the sample was tested by the conventional method. No interference due to background fluorescence of food matrixes was observed in the VIDAS LIS method. Results suggest a modified VIDAS LIS preenrichment medium may be used in place of the VIDAS standard medium in the protocol.

Line Intersect Sampling of Forest Canopy Gaps

Abstract Line intersect sampling (LIS) is commonly used to measure the fraction of forest area under canopy gaps (gap fraction) and the size distribution of gaps. The typical application of this technique makes assumptions about the shape of the gaps. Potential errors associated with these assumptions were quantified. To measure the gap regime in an old-growth, subalpine spruce-fir forest, regression equations were used to describe empirically gap area and perimeter. Most gaps in the spruce-fir forest were shaped like nonconvex polygons. Mapped gap areas were 22% less than estimates based on an elliptical model of gap shape and 22% more than area estimates based on a rhomboidal model of gap shape. An LIS method was developed that works for nonconvex shapes and was used to assess gap fraction in a subalpine, spruce-fir forest. The LIS approach for irregularly shaped gaps provided an estimate of gap fraction that was significantly smaller (35%) than the one based on an elliptical model of gap shape. The modifications in the application of LIS to the study of gap regimes seemed to preserve the efficiency and power of LIS while improving the accuracy of the results. For. Sci. 42(2):131-138.

Comparison Study of Adaptive Controllers for Robot Manipulators

The performance of two adaptive robot control algorithms, namely the adaptive algorithm by Slotine and Li and the proposed direct adaptive fuzzy control algorithm, were studied. In Slotine and Li's method, the algorithm consists of proportional derivative feedback and a full dynamics feed forward part, with the unknown manipulator and payload parameters being estimated on-line. The algorithm depends heavily on the particular structure of manipulator dynamics and needed three simplifying properties to derive the adaptive law. The direct adaptive fuzzy algorithm uses a fuzzy logic system as the controller. The derivation of the controller does not require any knowledge of the manipulator dynamics and the uncertainty in the system, only the boundary of the dynamics. The predominant concern of the two adaptation laws is to reduce the tracking errors. In particular, they require no feedback of joint accelerations. Theoretical results and simulation studies on a two-link robot manipulator show that both methods are robust and stable. The direct adaptive fuzzy controller outperforms the adaptive controller in mass variation.

New methods for estimating the numbers of synonymous and nonsynonymous substitutions.

New methods for estimating the numbers of synonymous and nonsynonymous substitutions per site were developed. The methods are unweighted pathway methods based on Kimura's two-parameter model. Computer simulations were conducted to evaluate the accuracies of the new methods, Nei and Gojobori's (NG) method, Miyata and Yasunaga's (MY) method, Li, Wu, and Luo's (LWL) method, and Pamilo, Bianchi, and Li's (PBL) method. The following results were obtained: (1) The NG, MY, and LWL methods give overestimates of the number of synonymous substitutions and underestimates of the number of nonsynonymous substitutions. The major cause for the biased estimation is that these three methods underestimate the number of synonymous sites and overestimate the number of nonsynonymous sites. (2) The PBL method gives better estimates of the numbers of synonymous and nonsynonymous substitutions than those obtained by the NG, MY, and LWL methods. (3) The new methods also give better estimates of the numbers of synonymous and nonsynonymous substitutions than those obtained by the NG, MY, and LWL methods. In addition, estimates of the numbers of synonymous and nonsynonymous sites obtained by the new methods are reasonably accurate. (4) In some cases, the new methods and the PBL method give biased estimates of substitution numbers. However, from the number of nucleotide substitutions at the third position of codons, we can examine whether estimates obtained by the new methods are good or not, whereas we cannot make an examination of estimates obtained by the PBL method. (5) When there are strong transition/transversion and nucleotide-frequency biases like mitochondrial genes, all of the above methods give biased estimates of substitution numbers. In such cases, Kondo et al.'s method is recommended to be used for estimating the number of synonymous substitutions, although their method cannot estimate the number of nonsynonymous substitutions and is time-consuming. These results, particularly result (1), call for reexaminations of some genes. This is because evolutionary pictures of genes have often been discussed on the basis of results obtained by the NG, MY, and LWL methods, which are favorable for the neutral theory of molecular evolution.

Conformational analysis. Part 24. A lanthanide-induced-shift (LIS) NMR investigation of aromatic ketones. Lutetium versus lanthanum reagents in probing diamagnetic complexation shifts

The possible use of Lu(fod)3vs. La(fod)3 in probing diamagnetic complexation contributions to the shifts induced Yb(fod)3 on the 1H and 13C NMR signals of aromatic ketones has been investigated. For all the compounds examined the patterns of the shifts caused by the two diamagnetic reagents are qualitatively similar, reflecting predominantly π-electron-density transmission. For the less activated substrates fluoren-9-one 1 and 2,6-dimethyl-4 nitroacetophenone 3 the use of either La(fod)3 or Lu(fod)3 yielded very similar sets of data, indicating in 3 a ca. 90° torsion angle between the acetyl and the ring. More interstingly, in the case of acetophenone 2, 2-acetylnaphthalene 4,3-methoxyacetophenone 5 and 2-methylacetophenone 6 the use of Lu(fod)3 gave a markedly improved definition of essentially the same solutions. These are a planer conformation for 2 a prevalence(ca. 68%) of the E conformer for 4 and of the Z conformer for 5 and 6(ca. 63% and 92%, respectively). In the case of 6 the geometries of the two conformers to be submitted to LIS analysis have been obtained through an ab initio RHF 6-13G* full-optimization process, indicating a planar structure for the Z and a 35°-rotated structure for the E conformer. In conclusion the analysis using Lu(fod)3, while supporting the results obtained with its lanthanum analogue, appears to reproduce better the diamagnetic contribution to induced shifts in strongly coordinating substrates. With the unhindred substrates 2, 4 and 5, where very reliable starting geometries could be adopted, solutions obtained through the use of Lu(fod)3 have been particularly good (Rcryst 0.2–0.4%), as pseudoconatact shifts ranging up to 130–150 ppm could be reproduced with an average absolute error of ±0.1 ppm. This shows how accurate the LIS method can be in the absence of additional problems and leaves little doubt about the accuracy of its theoretical background.

A simple method for estimating average number of nucleotide substitutions within and between populations from restriction data.

A simple method is proposed for estimating the average number of nucleotide substitutions per site within and between populations for the case where a large number of individuals are examined for many restriction enzymes. This method gives essentially the same results as those obtained by Nei and Li's method but saves a large amount of computer time. The variances of the quantities estimated can be obtained by the jackknife method, and these variances are very similar to those obtained by Nei and Jin's more sophisticated method. A similar method can also be applied to DNA sequence data.

Zuordnung offenkettiger Diastereomerer mittels lanthanoiden-induzierter Verschiebungen (LIS)

The LIS method has been tested for assignment purposes of acyclic diastereomers. After the estimation of the coordination geometry Eu ... O for some alkyl-methyl-ethers, the ground state conformations of the coordinated substrates have been determined and related to the free substrates. Due to obtained differences, the application of the LIS method for present assignment purposes should be limited to strained, less flexible stereoisomers.

The neighbor-joining method: a new method for reconstructing phylogenetic trees.

A new method called the neighbor-joining method is proposed for reconstructing phylogenetic trees from evolutionary distance data. The principle of this method is to find pairs of operational taxonomic units (OTUs [= neighbors]) that minimize the total branch length at each stage of clustering of OTUs starting with a starlike tree. The branch lengths as well as the topology of a parsimonious tree can quickly be obtained by using this method. Using computer simulation, we studied the efficiency of this method in obtaining the correct unrooted tree in comparison with that of five other tree-making methods: the unweighted pair group method of analysis, Farris's method, Sattath and Tversky's method, Li's method, and Tateno et al.'s modified Farris method. The new, neighbor-joining method and Sattath and Tversky's method are shown to be generally better than the other methods.