Sampled-Data and Harmonic Balance Analyses of Average Current-Mode Controlled Buck Converter

Dynamics and stability of average current-mode control of buck converters are analyzed by sampled-data and harmonic balance analyses. An exact sampled-data model is derived. A new continuous-time model "lifted" from the sampled-data model is also derived, and has frequency response matched with experimental data reported previously. Orbital stability is studied and it is found unrelated to the ripple size of the current-loop compensator output. An unstable window of the current-loop compensator pole is found by simulations, and it can be accurately predicted by sampled-data and harmonic balance analyses. A new S plot accurately predicting the subharmonic oscillation is proposed. The S plot assists pole assignment and shows the required ramp slope to avoid instability.Comment: Submitted to International Journal of Circuit Theory and Applications on August 9, 2011; Manuscript ID: CTA-11-016

A Study of Pricing Evolution in the Online Toy Market

We examine the pricing trends in the online toy markets based on a unique set of panel data collected across three years’ span. The analysis was made through panel data regression models with error components and serial correlation, allowing comparisons of prices and price dispersions between the two types of online retailers as well as examinations of dynamics of prices and price dispersions. Our results indicate that both online branch of multichannel retailers (OBMCRS) and dotcoms charge similar prices on average, and over time their prices move in tandem. Although the OBMCR retailers charge significantly different prices, the dotcoms do charge similar prices. Moreover, both retailer types demonstrate different magnitudes of price dispersion that move at different rates over time. Although the price dispersion of OBMCRS is higher than that of the dotcoms at the beginning, the gap narrows over time.e-commerce, online pricing strategies, online toy market, price dispersion, pricing trends

Genetic and Functional Analysis of Host Genes Involved in Pathogenic and Symbiotic Legume-Microbe Interactions

Legumes form symbiotic and pathogenic interactions with microbes. Understanding the molecular mechanisms underlying the legume-microbe interactions would help us to improve crop production in a sustainable manner. This thesis covers two independent research projects. The first project was to study the role of alternative splicing in RCT1-mediated disease resistance. RCT1 is a TIR-NBS-LRR-type plant resistance (R) gene in Medicago truncatula that confers broad-spectrum resistance to Colletotrichum trifolii, a fungal pathogen that causes anthracnose disease in Medicago. RCT1 undergoes alternative splicing at both coding and 3\u27-untranslated regions, thereby producing multiple transcript variants in its expression profile. Alternative splicing of RCT1 in the coding region results from the retention of intron 4. The transcript with retention of intron 4 is predicted to encode a truncated protein lacking the C-terminal domain of the full-length protein. We showed that the RCT1 function requires the combined presence of the regular and alternative transcripts. This study, in addition to the reports on the tobacco N and Arabidopsis RPS4 genes, adds another significant example showing the involvement of alternative splicing in R gene-mediated plant immunity. The second project was to study the symbiotic specificity in the soybean-rhizobial interaction. It is well known that legume plants can make their own nitrogen fertilizer by forming a root nodule symbiosis with nitrogen-fixing soil bacteria, called rhizobia. One remarkable property of this symbiosis is its high level of specificity, which occurs at both inter- and intra-species levels and takes place at multiple phases of the interaction, ranging from initial bacterial infection and nodulation to late nodule development associated with nitrogen fixation. In this study, we performed fine mapping of the Rj4 gene that controls nodulation specificity in soybean. The Rj4 allele prevents the host plant from nodulation with many strains of Bradyrhizobiumelkanii, which are frequently present in soils of the southeastern USA. Since B. elkanii strains are poor symbiotic partners of soybean, cultivars containing an Rj4 allele are considered favorable. We have delimited the Rj4 locus within a 47-kb genomic region on soybean chromosome 1 and identified the candidate genes. We are in the process to validate the candidate genes