Multivariate Realized Stock Market Volatility

We present a new matrix-logarithm model of the realized covariance matrix of stock returns. The model uses latent factors which are functions of both lagged volatility and returns. The model has several advantages: it is parsimonious; it does not require imposing parameter restrictions; and, it results in a positive-definite covariance matrix. We apply the model to the covariance matrix of size-sorted stock returns and find that two factors are sufficient to capture most of the dynamics. We also introduce a new method to track an index using our model of the realized volatility covariance matrix.Econometric and statistical methods; Financial markets

The Impact of “Rollover” Contracts on Switching Costs in the UK Voice Market : Evidence from Disaggregate Customer Billing Data

In February 2008, British Telecommunications (BT) introduced automatically renewing, or “rollover”, contracts into the UK market for fixed-voice telephone service. These contracts included a 12-month Minimum Contract Period (MCP) with associated Early Termination Charges (ETCs). Unless customers opted out, at the end of the 12 months they would automatically be rolled over into a new MCP and face new ETCs if they later wished to leave BT. Using a unique, disaggregate, customer billing dataset, we measure the impact of rollover contracts on BT customers’ decision to switch to another provider. We find that, controlling for the effects of tenure, broadband purchase, price discounts, and self-selection, rollover households switch after their first MCP 34.8% (54.8%) less than comparable customers on standard plans (fixed-term contracts). These imply rollover contracts induce switching costs on the order of 33.0% of the monthly price of the average BT fixed-voice telephone service. This raises significant concerns about the competitive effects of such contracts n media and telecommunications markets.

Testing the Digital Divide: Does Access to High-QUality Use of Technology in Schools Affect Student Achievement?

This study investigates the relationship between access, use of technology and student achievement in public middle schools in Maryland. The objective of this study was to determine whether a digital divide (differences in access and utilization of technology based on student characteristics of race, socioeconomic status, and gender) exists among schools, and whether those differences relate to mathematics and reading achievement. More specifically, the study uses school data on technology access, students' instructional uses of technology, and teacher technology proficiency from the 2007 Maryland Technology Inventory. This study analyzes student demographic data and assessment results from the 2007 Maryland School Assessments in reading and mathematics obtained from the Maryland State Department of Education. The data analyses use descriptive and multivariate statistics to determine the existence of digital divides and their effects on reading and mathematics achievement. Analysis of these data described patterns of technology access and use in order to determine whether differences in access and use resulted in a digital divide. Differences in access and use were then examined to determine their impact on reading and mathematics achievement levels. The research design relied on descriptive and multivariate statistics to analyze access and use and their relationship to academic achievement. Findings indicated that digital divides exist in the student-to-computer ratio and the number of teachers with classroom computers, and digital access was positively associated with eighth-grade mathematics and reading proficiency scores. However, student classroom computer ratios were negatively associated with achievement, controlling for other factors. Digital divides in students' use of technology for publishing text, organizing information, and communicating information were identified, with access to technology for these tasks/skills and positively associated with mathematics and reading scores, but connecting language to words had a negative impact. Teachers' use of technology for creating instructional materials had a positive impact on reading scores but a negative impact on mathematics achievement, when the researcher controlled for other factors. Findings suggest that differences exist in several areas of technology access and use when considering student characteristics of race, socioeconomic status, and gender. This study contributes to existing research on the effects of technology on instruction and informs state and local policy on instructional technology implementation and practice

Development and utilization of a macaque-based mammosphere culture technique for breast cancer research

Includes bibliographical references.2016 Fall.Human breast cancers are thought to commonly arise from progressive neoplastic changes to the adult stem cells within the normal mammary gland. Research in this area of breast carcinogenesis currently relies heavily on the acquisition of mammary gland stem cells from the tissues of rodents and humans. While a great deal of information has been gained utilizing these models, there remain large gaps in our knowledge of breast cancer due to certain limitations with these species. The relevance of rodents as models for human breast cancer has been brought into question by notable differences between rodents and humans with regard to genetics, biology and mammary gland carcinogenesis. In contrast, the utility of human-derived samples is limited by ethical concerns and by the restricted availability of mammary tissues from women. Macaque monkeys are closely related to humans phylogenetically and these animals develop mammary gland tumors that are comparable to human breast cancers. Furthermore, mammary gland tissues can be easily collected from any demographic of animal. Despite their potential, only minimal breast cancer work has been undertaken in the macaques to date and research techniques common to both rodents and human are lacking for these species. This dissertation describes the optimization of a commonly-used mammary gland stem cell isolation technique, mammosphere culture, for the rhesus macaque (Macaca mulatta) and provides validation as to the reliability, relevance, and usefulness of this assay for human studies. Data obtained from this research demonstrated that the mammosphere culture technique is highly reproducible between homologous macaque tissue samples. This work also found that mammary gland biopsies collected from different anatomical locations on the same monkey share comparable mammosphere-forming ability and mammosphere-differentiation ability (collectively, the mammosphere potential). Finally, these initial studies identified macaque mammospheres to have proliferative and differentiating properties that are nearly identical to those described for human mammospheres. This dissertation also describes a series of macaque studies performed using the optimized mammosphere culture technique. In the first study, mammary gland tissues were obtained from female macaques in different reproductive demographics and the mammosphere potential of these animals was compared. The results suggested that the mammosphere potential of nulliparous mammary glands is significantly greater than that of multiparous mammary glands and that this difference is likely due to greater ratios of mammary gland stem cells within the nulliparous mammary gland. These data also suggested that there are differences in the mammosphere potential of mammary glands collected from animals at different stages of the reproductive cycle. An additional study comparing the mammosphere potential of young-multiparous and multiparous macaques collected during the menses stage of the menstrual cycle supported the parity-related findings of the first study. Data from the second study also identified significantly larger ratios of senescent cells in the mammosphere cultures of multiparous macaques as compared to young-nulliparous macaques. Finally, a study comparing the effects of ionizing radiation on mammospheres derived from young-nulliparous and multiparous macaques was performed. This last study found that stem cell-like cells of the young-nulliparous mammary gland were more resistant to the lethal effects of ionizing radiation than were those of the multiparous gland. The findings of these three studies are notable in that young-nulliparous girls are known to have a higher susceptibility to radiation-induced breast cancer than are multiparous women and these studies provide the first direct evidence as to the potential mechanistic reasons behind this observation. Specifically, as macaques appear to be relevant models for the study of the human breast, these data suggest that the increased susceptibility of young-nulliparous girls to radiation-induced carcinogenesis could arise from: 1) higher number of mammary stem cells within the breast; 2) a decreased predilection of these stem cells to undergo senescence; and 3) a decreased sensitivity of these stem cells to the lethal effects of ionizing radiation. In summary, macaque mammospheres appear to be relevant models for the study of the human breast. Use of this model allows for the study of mammary gland tissues from some demographics of interest (e.g., prepubescent individuals) that are impossible to investigate utilizing human tissues. The mammosphere culture techniques and data described in this dissertation serve as a foundation toward the use of macaques in future breast cancer research projects and other study data from this dissertation has provided novel insight as to the increased risk of radiation-induced breast cancers in young women

Applicability of Pigment Compounds for Reducing Light Stress in Bentgrass

Chlorinated copper phthalocyanine (Signature) and pulverized cells of Chlorella vulgaris (Chlorella) were evaluated in a controlled environment for their ability to act as photoprotectants under supraoptimal levels of ultraviolet (UV) and photosynthetically active radiation (PAR) when applied to plant leaves. Plant pigment changes were documented using High Performance Liquid Chromatography following 1 week of exposure to supraoptimal light in two separate experiments incorporating UV (106.6 μmol m-2 s-1) and PAR (760.6 μmol m-2 s-1) over a 12h photoperiod. Supraoptimal levels of UV and PAR light were found to cause significant reductions in Agrostis palustris chlorophyll and carotenoid leaf pigment levels. In both experiments, high light coincided with increases in zeaxanthin and antheraxanthin and decreases in violaxanthin across all treatments, suggesting that plants experienced a stress response regardless of pigment application. Under high PAR light, the levels of total carotenoid pigment degradation were significantly higher in untreated Agrostis palustris controls than in Chlorella and Signature treated plants. However, only Chlorella demonstrated the ability to significantly reduce instances of chlorophyll degradation in bentgrass plants under high UV light. Spectral imaging of light following transmission through treatments demonstrated how Chlorella was successful in limiting the absorbance of wavelengths in regions of UV (300 to 400 nm) and PAR (480 and 580 nm). Photon flux measurements of transmitted light showed a significant decrease in both treatments when compared to controls; the greatest reduction in light levels occurred with Chlorella applications under both UV and PAR light. Results of these experiments demonstrate how this interception of light may limit chlorophyll and carotenoid degradation under these conditions, suggesting that they may be used to successfully act as photoprotectants. This holds particular value in golf course maintenance, where bentgrasses are cultivated at low mowing heights in regions where supraoptimal light conditions persist throughout the growing season