Chlamydia trachomatis is the most common bacterial agent of sexually transmitted infections worldwide and a common co-infection in AIDS patients. Chlamydial genital tract infections are often asymptomatic; therefore many infections go untreated and result in complications like chronic inflammation, ectopic pregnancy, and pelvic inflammatory disease. Chlamydia share a unique developmental cycle and under stress, can enter a state known as persistence, in which the bacteria are noninfectious but still viable. Removal of the stressor allows the chlamydiae to re-enter and complete the developmental cycle. Exposure to low-dose quinolones can cause the chlamydiae to enter persistence and halt the developmental cycle. Notably, 1 in 20 people living with HIV/AIDS also suffers from chlamydial infections. Since the anti-HIV drug Elvitegravir (EVG) is a quinolone derivative, we hypothesized that EVG exposure would inhibit chlamydial development. To ascertain whether EVG affects chlamydial development, HeLa cells were infected with C. trachomatis or C. muridarum and then either mock treated or treated with EVG. The percent infectivity and production of infectious progeny were determined by immunofluorescence assay and chlamydial titer assay, respectively. Transmission electron microscopy (TEM) was used to examine chlamydial morphology and determine whether EVG caused Chlamydia to become persistent. Though percent infectivity and chlamydial morphology were similar between treated and untreated Chlamydia-infected cells, the production of infectious progeny was significantly decreased in EVG-exposed Chlamydia-infected cells. These data indicate that EVG is not a persistence-inducer, but does inhibit chlamydial development in vitro. In other studies, we tested chlamydial polymorphic membrane protein (PMP) expression in chlamydia/HSV co-infected cells by immunofluorescence staining. Since penicillin-induced persistence decreases the expression of some chlamydial PMPs, we hypothesized that expression of PMP-A and PMP-B would be decreased by HSV-induced persistence. The results indicated that there was no significant difference in expression of PMP-A or PMP-B in co-infected versus C. trachomatis singly-infected cells. These data suggest that PMP expression is not a good indicator of chlamydial persistence when induced by HSV.

Retention of first year college students has been problematic in many U.S. colleges, and different mentoring frameworks have been explored to help resolve the issue. The purpose of this qualitative multiple case study was to examine how the mentoring program at Brown Community College (BCC; pseudonym) positively increased retention of first year college students. BCC is a community college located in a metropolitan urban area in a southern state. Tinto's model of social integration and academic success was used to undergird the study. Research questions were developed to understand how BCC's mentoring program was supporting first year students' retention and what these students perceived as integral in order to persist throughout their program of study. Another question sought faculty's perceptions of how their mentoring program influenced retention at the college. Data collection included structured face-to-face interviews with a purposeful sample of 10 first year college students and two faculty mentors who provided mentorship at BCC. Content analyses were used to identify and isolate the themes through axial coding. The results showed that mentoring may be the catalyst needed to ensure that students stay in college and increase retention and graduation rates. The findings provide useful data for developing curriculum policies that may improve service delivery opportunities for at-risk students. The findings also showed that having qualified college graduates may increase productivity in the workforce and help the college graduates become more successful citizens. Recommendations are offered to improve the existing mentoring program to enable the students to experience social changes in their pursuit of academic success.

Much of ecological theory describes species interactions. These interactions often play an important theoretical role in facilitating coexistence. In particular, rarity in ecological communities, though often observed, provides a significant challenge to theoretical and empirical ecologists alike. I use a plant community model to simulate the effect of stronger negative frequency dependence on the long-term persistence of the rare species in a simulated community. This strong self-limitation produces long persistence times for the rare competitor, which otherwise succumb quickly to stochastic extinction. The results suggest that the mechanism causing species to be rare in this case is the same mechanism allowing those species to persist. To determine if ecological communities generally show the theoretical pattern, I estimate the strength of frequency-dependent population dynamics using species abundance data from 90 communities across a broad range of environments and taxonomic groups. In approximately half of the analyzed communities, rare species showed disproportionately strong negative frequency dependence. In particular, a pattern of increasing frequency dependence with decreasing relative abundance was seen in these communities, signaling the importance of this mechanism for rare species specifically. Insight into the special population dynamics of rare species will inform conservation efforts in response to climate change and other disturbance. Further difficulties in the detection of theoretical patterns in ecological data may be a result of the ecological currency used. Though ecologists typically use abundance data to test theories, energy use is another ecological currency that may be more relevant in some cases. In particular when detecting patterns that are a result of species interactions, the currency used should be the one in which those interactions actually operate. I compare the results of using abundance and energy use to detect two processes with well-defined expectations. The first is a description of population dynamics, the above described relationship between relative abundance and self-limitation. The second, compensatory dynamics, is a description of community-level dynamics. I find that the currency used alters the results, and thus the species-level implications. It does not, however, alter the overall pattern that would have theoretical implications. Results in both currencies support the pattern of strong self-limitation for persistent rare species.

In this thesis I investigate whether two clear and simple indicators, dividends and franking credits, provide users with useful information to assess earnings persistence. Persistence is an important attribute of earnings (Dechow and Schrand 2004). I argue and show earnings persistence is a function of firm life-cycle. Firms can generally be divided into three life stages: establishing profitability, sustainable profitability and declining profitability. Using a simple one-period persistence model I demonstrate that dividends and higher franking credits identify firms in the different stages of the life-cycle. Dividends provide an inherent signal of firms that are in the mature phase of the life-cycle, and hence provide information about earnings persistence. I show firms that pay dividends have persistent profits and losses that reverse. However dividend paying firms are not homogenous. Firms that pay franked dividends have significantly more persistent earnings than firms that pay unfranked dividends. Consistent with higher franking credits identifying more mature firms, fully franked dividend paying firms have significantly less persistent losses than partially franked dividend paying firms. Importantly, my primary results provide an alternative explanation to Hanlon (2005) and add to our understanding of the accrual anomaly. Both Hanlon and my study investigate the informativeness of tax on earnings persistence. I demonstrate that firms that have large differences between the level of franking and accounting income (i.e., pay unfranked dividends while reporting a profit) have large book-tax differences. Such differences in tax and accounting income are a function of the firm life-cycle. Large book-tax differences are not necessarily the result of opportunism (or earnings management). Thus firms with large book-tax differences are typically establishing profitability or entering the declining phase. These firms have less persistence profits, accruals and cash flows than firms with small book-tax differences. I conclude the accrual anomaly is a function of inherent firm characteristics associated with different phases of the life-cycle rather than being a function of earnings management.

Dissertation (PhD)--University of Stellenbosch, 2007. / Bibliography. Also available via the Internet.

This study examined the relationship of two important learning behaviors, persistence and initiative, and three- to five-year-old low-income preschool children?s school readiness outcomes. The sample consisted of 196 children from two urban Head Start Centers in a large Head Start Program in the Southeast. Initiative was measured by the Devereux Early Childhood Assessment and persistence by the Preschool Learning Behavior Scale. Academic outcomes were collected through the Language and Literacy subscale and the Early Math subscale of the Galileo System for Electronic Management of Learning. Results indicated that learning behaviors may be differentially important across age and academic domain. Persistence, and not initiative, significantly predicted younger and older preschoolers? yearly gains in early math outcomes. In contrast, while persistence was a significant predictor of language and literacy yearly gains for younger preschoolers, initiative was the significant predictor for older preschoolers. These differential results add to the understanding of learning behaviors and their effect on academic outcomes in early childhood. Such findings can help teachers, parents, and those developing early childhood interventions in promoting the learning behaviors that are the most appropriate for a certain age and academic area.

This paper studies the persistence of daily returns of 21 German stocks from 1960 to 2008. We apply a widely used test based upon the modified R/S-Method by Lo [1991]. As an extension to Lux [1996] and Carbone et al. [2004] and in analogy to moving average or moving volatility, the statistics is calculated for moving windows of length 4, 8, and 16 years for every time series. Periods of persistence or long memory in returns can be found in some but not all time series. Robustness of results is verified by investigating stationarity and short memory effects.

Using a sample of EREIT returns during the period 1993 to 2006 from the CRSP/Ziman REITs database, I construct portfolios of equity REITs based on past raw returns and evaluate their raw returns and risk-adjusted returns during the holding period for persistence. After adjusting for risk with Carhart (1997)’s 4-factor model, I find no evidence of persistence. By implication, a momentum strategy of buying historical winners and short-selling losers does not generate statistically significant abnormal returns. However, I do find strong evidence of performance reversal based on two-year and three-year ranking and holding periods. Consistent with DeBondt and Thaler (1985)’s overreaction theory, investors tend to overreact based on long-term rather than short-term performance records. This would suggest that investors tend to take a much longer period of time to formulate an opinion regarding a REIT’s performance record than previously assumed by earlier researchers. While there is a measurable tendency toward performance reversal, the return spread between the best performing EREITs and worst performing EREITs is marginal. This would indicate that the REIT markets are behaving in a generally efficient fashion. The investigation of the association of EREIT characteristics and performance persistence suggests a property type focus and geographic diversification strategy for EREITs. At the same time, EREITs with high leverage also tend to exhibit good performance persistently.

In this thesis we have studied the relationship between mutual fund size and performance by studying 91 Swedish mutual funds during a six year period (2006-2011). Furthermore, we investigated the relationship between fund size and management fees and fund size and persistence in performance. The fund sample has been divided into five subgroups in order to compare and analyze funds with different fund sizes for the whole six-year period as well as two three-year sub periods. Our results are based on regressions and significance tests and for all the five subgroups and over the whole time period our results indicate that there is no significant relationship between fund size and fund performance that is robust over time. Our findings also show that there is no persistence in performance for any of the size-based fund groups which helps us to draw the conclusion that past performance is not a good measure for predicting future performance regardless of the size of the funds. The results also indicate that mutual funds with a larger asset base tend to have lower management fees than smaller funds.

The roles of genes responsible for the survival and persistence of Brucella in the host and the relationship between these genes and the disease were investigated via signature-tagged transposon mutagenesis. As much as 8% of the Brucella genome is important for survival of this organism in the host. This is an unusually high number and may help to explain the chronic or persistent nature of Brucella infections. Mutants attenuated in the mouse model were divided into two groups. The early mutants failed to establish infection or colonize the host. The late mutants colonized the host but failed to maintain infection. The vaccine potential of two mutants (virB10 and gcvH) that were unable to sustain infection was compared to that of a vaccine strain, S19. Survival of strain S19 in vivo was up to 12 weeks while virB10 and gcvH mutants were cleared from spleen at 8, and 24 weeks post-inoculation, respectively. Mice were vaccinated with individual mutants and then challenged with virulent S2308 at 8, 16, and 24 weeks postvaccination. As a result, protective immunity correlated with persistence of the mutant strain [gcvH>virB10]. These results suggest that survival is one of several factors that may influence protective immunity making it difficult to compare strains. For example, examination of host immune response revealed a similar pattern of host immune function (TH1 over TH2) in all mice except those vaccinated with virB10 mutant. Since gcvH mutant provided the best immunity, experiments were designed to explore its contribution of persistence to protection. In an effort to reduce non-specific activation induced by prolonged survival of gcvH mutant, protection was monitored after different periods of vaccination exposure followed with doxycycline treatment. In these studies, persistence of gcvH mutant enhanced protection against challenge. Overall, defined mutations in genes affecting survival may render mutants as vaccine candidates capable of stimulating protective immunity equal to or better than fortuitously isolated attenuated strains. Future studies should focus on characterization of these and other genes responsible for the persistence of Brucella to improve the safety and efficacy of live vaccines.