Customizing kernels in Support Vector Machines

Support Vector Machines have been used to do classification and regression analysis. One important part of SVMs are the kernels. Although there are several widely used kernel functions, a carefully designed kernel will help to improve the accuracy of SVMs. We present two methods in terms of customizing kernels: one is combining existed kernels as new kernels, the other one is to do feature selection. We did theoretical analysis in the interpretation of feature spaces of combined kernels. Further an experiment on a chemical data set showed improvements of a linear-Gaussian combined kernel over single kernels. Though the improvements are not universal, we present a new idea of creating kernels in SVMs

Predictive Models and Calibration Analysis in Large-Scale Computational Studies.

Computational modeling and simulation are used to study many complex phenomena where physical experiments are not feasible or too expensive. Examples include climate models, nuclear stockpile analysis, design and manufacturing of complex systems, and biological systems. Statistical methods play a crucial role in this area, ranging from the design of computer experiments and analysis of the outputs to developing statistical emulators, calibration analysis and, more generally, uncertainty quantification. This dissertation deals with two aspects of these statistical problems. The first part is concerned with statistical emulators. In most applications of interest, a statistical model is fit to the output from limited number of evaluations of the computational model, and the resulting “emulator" is used to approximate the input-output relationship. The method of choice is a Gaussian Spatial Process (GaSP), where the output is viewed as the realization of a Gaussian process. While GaSP can be implemented using frequentist methods, it is most commonly used within a Bayesian framework. We compare the performance of GaSP with flexible regression-based approaches. These include existing methods such as multivariate adaptive regression splines (MARS), smoothing-spline anova (SS-ANOVA), multiple adaptive regression tree model (MART), and two methods developed in this dissertation: expanded multivariate adaptive regression splines model (EMARS) and smoothing spline model with a kernel function based on exponential products (SS-Prod). Our empirical comparisons show that EMARS has better predictive performance than GaSP in a variety of situations. The EMARS can be implemented with the current MARS algorithm. Given its computational advantage, it can be applied to computational models with a larger number of input parameters. The second part of thesis focuses on the calibration problem, where we have to determine the true (but unknown) values of certain input parameters to the computational model. This is a challenging inverse problem that suffers from identifiability issues. We develop conditions for determining identifiability and examine data-based approaches for checking the conditions in practice. The behavior of the methods is examined in various situations.PhDStatisticsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/107103/1/zyzhang_1.pd

Very Low Frequency Propagation Characteristics Analysis in Coal Mines

Electromagnetic wave penetration coal-rock communication is a significant part for the smart mine communication technology, there are great challenges for electromagnetic wave is rapidly attenuated by factors such as geology and coal seam structure. In order to provide a theory basis for wireless communication technology development in coal rock, based on the Maxwell's equations, this paper establishes a physical model of wireless communication under the conditions of coal seam. To characterize the performance of the electromagnetic wave propagation, we use the Maxwell's equations to derive the exact expression of attenuation coefficient. Also, the parameters of coal and other factors affecting the electromagnetic wave propagation are analyzed and discussed. To further obtain more insights, the attenuation coefficient and skin depth of the very low-frequency (VLF) electromagnetic wave in coal medium with different degrees of metamorphism are studied, as well as the influence of resistivity. This provides scientific theoretical support for the application of VLF communication in coal mines. Finally, our theoretical analyses are verified by computer simulation, and the simulated numerical results show that: 1) The range of frequency of electromagnetic wave suitable for coal medium propagation is 3~3KHz (VLF); 2) The order of the electromagnetic waves attenuation coefficient in coal with different degrees of metamorphism is: anthracite> lignite > fat coal > coking coal > lean coal, and the order of skin depth is: lean coal > coking coal > fat coal> lignite > anthracite; 3) The resistivity of coal has little effect on the attenuation of electromagnetic wave when VLF is used for communication

Research on Traffic Signal Timing Method Based on Ant Colony Algorithm and Fuzzy Control Theory

The number of private cars has a blowout growth with the development of economics, which leads to the existing limited traffic resources cannot meet the normal traffic demand. The emergence of intelligent traffic has improved this phenomenon. Using intelligent traffic technology to conduct intersection vehicles can alleviate the congestion effectively. Traffic signal timing method plays an important role in intelligent traffic research. An independent intersection dynamic timing method combined with fuzzy control theory and improved ant colony algorithm is proposed in this paper. According to the characteristics of traffic flow distribution, the timing period is obtained with the improved webster algorithm. Through the optimal solution obtained by ant colony algorithm and the added delay of traffic signal calculated by fuzzy control method, the dynamic timing period of the traffic signal is obtained. The validity of the proposed method is proved by comparing with the original time period and the traditional algorithm

BUILDING BILINGUAL BI-CONTINENTAL E-LEARNING COURSES

The authors have been actively engaged in E-learning starting in 1996, at the College of Staten Island, CUNY, a public university on the East coast and Shanghai Television University, an open university in Shanghai. We have reported on this work in [Chi, Klibaner, 1999, 2001, 2003]. This collaboration has been expanded to include a bilingual course offered simultaneously at both institutions. Of the many technical issues involved in such a simultaneous e-learning course, the time difference is the only one which remains immutable. This paper describes our experience with a hybrid course in Database Theory offered bilingually in Chinese and English and a Windows based terminal software laboratory

Evolutionary transition between invertebrates and vertebrates via methylation reprogramming in embryogenesis

© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Xu, X., Li, G., Li, C., Zhang, J., Wang, Q., Simmons, D. K., Chen, X., Wijesena, N., Zhu, W., Wang, Z., Wang, Z., Ju, B., Ci, W., Lu, X., Yu, D., Wang, Q., Aluru, N., Oliveri, P., Zhang, Y. E., Martindale, M. Q., & Liu, J. Evolutionary transition between invertebrates and vertebrates via methylation reprogramming in embryogenesis. National Science Review, 6(5), (2019):993-1003, doi:10.1093/nsr/nwz064.Major evolutionary transitions are enigmas, and the most notable enigma is between invertebrates and vertebrates, with numerous spectacular innovations. To search for the molecular connections involved, we asked whether global epigenetic changes may offer a clue by surveying the inheritance and reprogramming of parental DNA methylation across metazoans. We focused on gametes and early embryos, where the methylomes are known to evolve divergently between fish and mammals. Here, we find that methylome reprogramming during embryogenesis occurs neither in pre-bilaterians such as cnidarians nor in protostomes such as insects, but clearly presents in deuterostomes such as echinoderms and invertebrate chordates, and then becomes more evident in vertebrates. Functional association analysis suggests that DNA methylation reprogramming is associated with development, reproduction and adaptive immunity for vertebrates, but not for invertebrates. Interestingly, the single HOX cluster of invertebrates maintains unmethylated status in all stages examined. In contrast, the multiple HOX clusters show dramatic dynamics of DNA methylation during vertebrate embryogenesis. Notably, the methylation dynamics of HOX clusters are associated with their spatiotemporal expression in mammals. Our study reveals that DNA methylation reprogramming has evolved dramatically during animal evolution, especially after the evolutionary transitions from invertebrates to vertebrates, and then to mammals.This work was supported by the National Key Research and Development Program of China (2018YFC1003303), the Strategic Priority Research Program of the CAS (XDB13040200), the National Natural Science Foundation of China (91519306, 31425015), the Youth Innovation Promotion Association of the CAS and the Key Research Program of Frontier Sciences, CAS (QYZDY-SSW-SMC016)

On the topological surface states of the intrinsic magnetic topological insulator Mn-Bi-Te family

We review recent progress in the electronic structure study of intrinsic magnetic topological insulators (MnBi$_2$Te$_4$)(Bi$_2$Te$_3$)$_n$ ($n=0,1,2,3$) family. Specifically, we focus on the ubiquitously (nearly) gapless behavior of the topological surface state Dirac cone observed by photoemission spectroscopy, even though a large Dirac gap is expected because of surface ferromagnetic order. The dichotomy between experiment and theory concerning this gap behavior is perhaps the most critical and puzzling question in this frontier. We discuss various proposals accounting for the lack of magnetic effect on the topological surface state Dirac cone, which are mainly categorized into two pictures, magnetic reconfiguration, and topological surface state redistribution. Band engineering towards opening a magnetic gap of topological surface states provides great opportunities to realize quantized topological transport and axion electrodynamics at higher temperatures