Convex Optimization for Binary Classifier Aggregation in Multiclass Problems

Multiclass problems are often decomposed into multiple binary problems that are solved by individual binary classifiers whose results are integrated into a final answer. Various methods, including all-pairs (APs), one-versus-all (OVA), and error correcting output code (ECOC), have been studied, to decompose multiclass problems into binary problems. However, little study has been made to optimally aggregate binary problems to determine a final answer to the multiclass problem. In this paper we present a convex optimization method for an optimal aggregation of binary classifiers to estimate class membership probabilities in multiclass problems. We model the class membership probability as a softmax function which takes a conic combination of discrepancies induced by individual binary classifiers, as an input. With this model, we formulate the regularized maximum likelihood estimation as a convex optimization problem, which is solved by the primal-dual interior point method. Connections of our method to large margin classifiers are presented, showing that the large margin formulation can be considered as a limiting case of our convex formulation. Numerical experiments on synthetic and real-world data sets demonstrate that our method outperforms existing aggregation methods as well as direct methods, in terms of the classification accuracy and the quality of class membership probability estimates.Comment: Appeared in Proceedings of the 2014 SIAM International Conference on Data Mining (SDM 2014

Characterization of nanoparticle-DNA conjugate and control of DNA conformation on particle surface

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.Includes bibliographical references.Nano-science has exploited the hybridization and de-hybridization phenomena of DNA which are one of its fundamental functions. In particular, conjugates of gold nanoparticles and DNA (Au NP-DNA) have been extensively explored for their potential in biological applications such as DNA delivery for gene therapy and disease detection. However, DNA strands are known to adsorb onto the Au NP surface, which can severely limit the hybridization ability of Au NP-DNA conjugates. Therefore, methods of chemical modification of Au NP surfaces and evaluating DNA conformation via Ferguson analysis of gel electrophoresis are proposed in the thesis. Conjugates of DNA with Au NP of different sizes and coverages are evaluated with Ferguson analysis to characterize important parameters such as hydrodynamic size and zeta-potential. Surface modified Au NP exhibits enhanced stability and hybridization specificity in the system, which infers the effectiveness of those methods towards biological systems where non-specific adsorption is problematic. To confirm the validity of the concept, Au NP-antisense DNA experiments for gene silencing are performed in the work. Antisense DNA is designed to inhibit ribosomal activity on mRNAs and cooperatively works with Au NPs to enhance physical blocking mechanisms. However, the result shows that Au NP-DNA conjugates can enhance in vitro gene expression depending on DNA sequence and coverage of the conjugates. Suggestions are made for further investigation on proof and improvement of the translation enhancer concept.by Sunho Park.Ph.D

Control of oligonucleotide conformation on nanoparticle surfaces for nanoscale heat transfer study

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.Includes bibliographical references (leaves 77-82).Metal nanoparticles can be used as antennae covalently linked to biomolecules. External alternating magnetic field can turn on and off the biological activity of the molecules due to induction heating from the particles that changes the temperature around the molecules. Here an experimental scheme towards direct temperature probing is proposed to predict the behavior of the antenna. Oligonucleotides modified with photosensitive molecules are conjugated with gold nanoparticles and report the temperature at their positions within some nanometers' distance from the particles. However, oligos have a known tendency to stick to gold surfaces. To locate the probes at desired position, 6-mercapto-1-hexanol (MCH) is used to reduce oligonucleotides' adsorption to the surface of gold. The experimental result shows that oligos on particle's surface can be stretched radially without any reduction of coverage ratio. Optimal MCH concentration and reaction time highly depend on the concentration of MCH and the conjugates as well as reaction time and the size of the molecules.by Sunho Park.S.M

Picture Quality and Sound Quality of OLED TVs

Unlike the past when cathode-ray tube (CRT) dominated display industry, many different types of flat panel displays (FPDs) are now leading the industry. Of these, organic light-emitting diode (OLED) display has recently become a next-generation display since this display is recognised as having advantages over other competing technologies in picture quality and form factor. With major attributes of picture quality considered, a series of evaluations based on objective measures was performed with an OLED TV compared to an LCD TV. OLED TV outperformed LCD TV 100 times in black, 20 times in colour contrast, 30% in dynamic range coverage, 50 times in local contrast and 20 times in viewing angle. In addition, sound quality of the OLED TV was assessed using both objective and subjective evaluation methods compared to conventional TV speakers since OLED panel speaker technology was recently commercialised. The OLED panel speaker showed better performance both in objective and subjective methods

Graphene–Chitosan Hybrid Dental Implants with Enhanced Antibacterial and Cell-Proliferation Properties

Dental implants are widely used tooth replacement tools owing to their good oral rehabilitation and reconstruction capacities. Since dental implants are designed as a replacement for natural teeth, multi-functional abilities are desired to achieve successful implant treatment with improved osseointegration through promotion of mammalian cell activity and prevention of bacterial cell activity. In this study, we developed a graphene–chitosan hybrid dental implant (GC hybrid implant) using various concentrations of graphene, which demonstrated the different surface properties including increased wettability and roughness. Importantly, the GC hybrid implant under the optimal condition (i.e., 1% GC hybrid implant) could significantly promote osteoblast proliferation while reducing biofilm formation and bacterial activity. Our study demonstrates the potential of using this GC hybrid implant as a new type of dental implant, which can offer an effective design for the fabrication of advanced dental implants