Studies of Group Fused Lasso and Probit Model for Right-Censored Data

This document is composed of three main chapters. In the first chapter, we study the mixture of experts, a powerful machine learning model in which each expert handles a different region of the covariate space. However, it is crucial to choose an appropriate number of experts to avoid overfitting or underfitting. A group fused lasso (GFL) term is added to the model with the goal of making the coefficients of the experts and the gating network closer together. An algorithm to optimize the problem is also developed using block-wise coordinate descent in the dual counterpart. Numerical results on simulated and real world datasets show that the penalized model outperforms the unpenalized one and performs on par with many well-known models. The second chapter studies GFL on its own and methods to solve it efficiently. In GFL, the response and the coefficient of each observation are not scalars but vectors. Thus, many fast solvers of the fused lasso cannot be applied to the GFL. Two algorithms are proposed to solve the GFL, namely Alternating Minimization and Dual Path. Results from speed trial show that our algorithms are competitive compared to other existing methods. The third chapter proposes a better alternative to the Box-Cox transformation, a popular method to transform the response variable to have an approximately normal distribution in many cases. The Box-Cox transformation is widely applied in regression, ANOVA and machine learning for both complete and censored data. However, since it is parametric, it can be too restrictive in many cases. Our proposed method is nonparametric, more flexible and can be fitted efficiently by our novel EM algorithms which accommodate both complete and right-censored data

No Small Hairs in Anisotropic Power-law Gauss-Bonnet Inflation

We will examine whether anisotropic hairs exist in a string-inspired scalar-Gauss-Bonnet gravity model with the absence of potential of scalar field during the inflationary phase. As a result, we are able to obtain the Bianchi type I power-law solution to this model under the assumption that the scalar field acts as the phantom field, whose kinetic is negative definite. However, the obtained anisotropic hair of this model turns out to be large, which is inconsistent with the observational data. We will therefore introduce a nontrivial coupling between scalar and vector fields such as $f^2(\phi)F_{\mu\nu}F^{\mu\nu}$ into the scalar-Gauss-Bonnet model with the expectation that the anisotropic hair would be reduced to a small one. Unfortunately, the magnitude of the obtained anisotropic hair is still large. These results indicate that the scalar-Gauss-Bonnet gravity model with the absence of potential of scalar field might not be suitable to generate small anisotropic hairs during the inflationary phase

Foreign Ownership and Stock Return Volatility in Vietnam: the Destabilizing Role of Firm Size

This study aims to examine the relevance of foreign ownership to stock return volatility in the Vietnam stock market over ten years (2008 - 2017). After applying the fixed effects regressions and the extended instrumental variable regressions with fixed effects, we find that foreign ownership decreases the volatility of stock returns. However, the stabilizing impact of foreign ownership on stock return volatility becomes weaker in large firms since the coeffcient of the interaction term between firm size and foreign ownership turns out to be significantly positive. The estimated results remain robust when we use the future one-year volatility, other than the current one, as an alternative measure of the dependent variable

Performance Analysis of Adaptive Modulation for Distributed Switch-and-Stay Combining with Single Relay

In this paper we present our investigation of the performance of a distributed switch-and-stay scheme and a solution for low-complexity cooperative relaying under adaptive transmission. We are able to derive the closed-form expressions of the occurrence probability, the outage probability, the bit error probability, and the achievable spectral efficiency of the proposed scheme for Rayleigh fading channels. Simulations are performed to verify the analytic results. It is shown that, by applying adaptive modulation, the achievable spectral efficiency of the system is improved significantly, and the proposed scheme achieves the same spectral efficiency as compared to that of the incremental relaying but with a lower relay activation time

Chimeric design, synthesis, and biological assays of a new nonpeptide insulin-mimetic vanadium compound to inhibit protein tyrosine phosphatase 1B

Prior to its total synthesis, a new vanadium coordination compound, called TSAG0101, was computationally designed to inhibit the enzyme protein tyrosine phosphatase 1B (PTP1B). The PTP1B acts as a negative regulator of insulin signaling by blocking the active site where phosphate hydrolysis of the insulin receptor takes place. TSAG001, [VVO2(OH)(picolinamide)], was characterized by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy; IR: ν/cm−1 3,570 (NH), 1,627 (C=O, coordinated), 1,417 (C−N), 970/842 (O=V=O), 727 δ. (pyridine ring); 13C NMR: 5 bands between 122 and 151 ppm and carbonyl C shifted to 180 ppm; and 1H NMR: 4 broad bands from 7.6 to 8.2 ppm and NH2 shifted to 8.8 ppm. In aqueous solution, in presence or absence of sodium citrate as a biologically relevant and ubiquitous chelator, TSAG0101 undergoes neither ligand exchange nor reduction of its central vanadium atom during 24 hours. TSAG0101 shows blood glucose lowering effects in rats but it produced no alteration of basal- or glucose-induced insulin secretion on β cells during in vitro tests, all of which excludes a direct mechanism evidencing the extrapancreatic nature of its activity. The lethal dose (LD50) of TSAG0101 was determined in Wistar mice yielding a value of 412 mg/kg. This value is one of the highest among vanadium compounds and classifies it as a mild toxicity agent when compared with literature data. Due to its nonsubstituted, small-sized scaffold design, its remarkable complex stability, and low toxicity; TSAG0101 should be considered as an innovative insulin-mimetic principle with promising properties and, therefore, could become a new lead compound for potential nonpeptide PTP1B inhibitors in antidiabetic drug research. In view of the present work, the inhibitory concentration (IC50) and extended solution stability will be tested

Bit-Interleaved Coded Modulation Systems with Iterative Decoding and Partial Reusing QAM Signal Points

A new method of reusing a subset of an M-QAM signal constellation is presented for Bit-Interleaved Coded Modulation systems with Iterative Decoding (BICM-ID). In addition to the remapping of high-energy signals to low-energy signals in order to save the average signal energy as a shaping technique known so far, a new scheme of remapping low-energy signals to high-energy signals is proposed in order to gain the equivalent distance when decoding bits, often called the Squared Euclidean Weights (SEW). Numerical analysis and simulation results show that the partial reuse of the signals in the BICM-ID system with 16-QAM can improve the system performance in terms of lowering the bit error rate in the error floor region