A new stock-price bubble with stochastically deflating trajectories

We propose a new, rational stock-price bubble that is able to generate recurringly explosive and stochastically deflating trajectories. Our flexible bubble process entails stock-price volatility dynamics that are consistent with real-world data. To demonstrate this, we fit our bubble specification to NASDAQ data and analyze the volatility dynamics

Econometric estimation and theoretical modeling of rational stock-market bubbles

Vermögenspreise weisen oft Phasen explosiven Preisverhaltens auf, gefolgt von einem großen Preiseinbruch. In der finanzwirtschaftlichen Literatur wird dieses Verhalten häufig durch die Präsenz spekulativer Blasen erklärt. Diese Dissertation erweitert sowohl die existierende theoretische als auch die empirische Literatur über spekulative Blasen in Aktienmärkten. Zunächst, basierend auf dem Konzept rationaler Erwartungen, liefert diese Arbeit ein eindeutiges ökonomisches Modell zur direkten Schätzung der ökonometrischen Spezifikation rationaler nichtlinearer Blasen aus Finanzmarktdaten. Für die Schätzung werden sequentielle Monte-Carlo-Methoden verwendet. Darauf aufbauend wird die Aktienpreis-Volatilität unter Berücksichtigung der Präsenz nichtlinearer Blasen analysiert. Zudem wird eine alternative ökonometrische Spezifikation für rationale Blasen vorgestellt die eng mit der ökonomischen Theorie und den Finanzmarktdaten verbunden ist.Asset prices often exhibit phases of explosive price behavior followed by a crash. In financial economics, a prominent explanation of this behavior is the presence of speculative bubbles. This thesis extends the existing empirical as well as theoretical literature on speculative stock-market bubbles as follows. First, based on the concept on rational expectations, this thesis provides a clear economic model for estimating directly the specification of rational nonlinear bubbles from financial data. The estimation is executed by the use of sequential Monte Carlo methods. Second, this approach is used to analyze the conditional volatility of stock-prices that are driven by nonlinear bubbles. Third, the thesis suggests an alternative parametric specification for rational bubbles that is closely related to economic theory and to financial data.<br

A new vent limpet in the genus Lepetodrilus (Gastropoda: Lepetodrilidae) from Southern Ocean hydrothermal vent fields showing high phenotypic plasticity

The recently discovered hydrothermal vent ecosystems in the Southern Ocean host a suite of vent-endemic species, including lepetodrilid limpets dominating in abundance. Limpets were collected from the chimneys, basalts and megafauna of the East Scotia Ridge segments E2 and E9 and the Kemp Caldera at the southern end of the South Sandwich Island arc. The limpets varied in size and shell morphology between vent fields and displayed a high degree of phenotypic plasticity. Size frequency analyses between vent fields suggests continuous reproduction in the limpet and irregular colonisation events. Phylogenetic reconstructions and comparisons of mitochondrial COI gene sequences revealed a level of genetic similarity between individuals from the three vent fields consistent with their belonging to a single molecular operational taxonomic unit. Here we describe Lepetodrilus concentricus n. sp., and evaluate its genetic distinctness and pylogenetic position with congeners based on the mitochondrial COI gene. Results indicate that L. concentricus n. sp. is a sister species towith the two species estimated to have diverged within the last ~5 million years

Multiple Sexual Partners and Condom use among 10 - 19 Year-olds in four Districts in Tanzania: What do we Learn?

Although some studies in Tanzania have addressed the question of sexuality and STIs among adolescents, mostly those aged 15 - 19 years, evidence on how multiple sexual partners influence condom use among 10 - 19 year-olds is limited. This study attempts to bridge this gap by testing a hypothesis that sexual relationships with multiple partners in the age group 10 - 19 years spurs condom use during sex in four districts in Tanzania. Secondary analysis was performed using data from the Adolescents Module of the cross-sectional household survey on Maternal, Newborn and Child Health (MNCH) that was done in Kigoma, Kilombero, Rufiji and Ulanga districts, Tanzania in 2008. A total of 612 adolescents resulting from a random sample of 1200 households participated in this study. Pearson Chi-Square was used as a test of association between multiple sexual partners and condom use. Multivariate logistic regression model was fitted to the data to assess the effect of multiple sexual partners on condom use, having adjusted for potential confounding variables. STATA (10) statistical software was used to carry out this process at 5% two-sided significance level. Of the 612 adolescents interviewed, 23.4% reported being sexually active and 42.0% of these reported having had multiple (> 1) sexual partners in the last 12 months. The overall prevalence of condom use among them was 39.2%. The proportion using a condom at the last sexual intercourse was higher among those who knew that they can get a condom if they want than those who did not. No evidence of association was found between multiple sexual partners and condom use (OR = 0.77, 95% CI = 0.35 - 1.67, P = 0.504). With younger adolescents (10 - 14 years) being a reference, condom use was associated with age group (15 - 19: OR = 3.69, 95% CI = 1.21 - 11.25, P = 0.022) and district of residence (Kigoma: OR = 7.45, 95% CI = 1.79 - 31.06, P = 0.006; Kilombero: OR = 8.89, 95% CI = 2.91 - 27.21, P < 0.001; Ulanga: OR = 5.88, 95% CI = 2.00 - 17.31, P = 0.001), Rufiji being a reference category. No evidence of association was found between multiple sexual partners and condom use among adolescents in the study area. The large proportion of adolescents who engage in sexual activity without using condoms, even those with multiple partners, perpetuates the risk of transmission of HIV infections in the community. Strategies such as sex education and easing access to and making a friendly environment for condom availability are important to address the risky sexual behaviour among adolescents

Multiple sex partner behavior in female undergraduate students in China: A multi-campus survey

<p>Abstract</p> <p>Background</p> <p>China is realizing increases in women engaged in premarital sex and multiple sex partner behavior. Our aim was to examine prevalence and determinants of multiple sex partner behavior among female undergraduates in China.</p> <p>Methods</p> <p>Anonymously completed questionnaires were received from 4,769 unmarried female undergraduates, recruited using randomized cluster sampling by type of university and students' major and grade. Items captured demographic, family, peer and work influence, and student factors (major, academic performance, and sex-related knowledge and attitudes). To examine risk factors for sexual behaviors, we used multi-level logistic regression, yielding odds ratios (OR) and 95% confidence intervals (95% CI).</p> <p>Results</p> <p>Of 4,769 female students, 863 (18.10%) reported ever having sexual intercourse, and 5.31% reported having multiple sex partners (29.32% of all women having sexual intercourse). Several demographic, family, peer and work influences, and student factors (including major, performance, knowledge, and attitude toward sex) were risk factors for ever having sex. However, risk factors for multiple sex partners only included working in a place of entertainment, having current close friends that were living with boyfriends, poor academic performance, and positive attitudes toward multiple partners. These women also were more likely to practice masturbation, start having sex at a younger age, have sex with married men and/or men not their "boyfriends" at first coitus, and not use condoms consistently.</p> <p>Conclusion</p> <p>A small but important subset of Chinese female undergraduates is engaged in unprotected sex with multiple sex partners. Interventions need to target at risk women, stressing the importance of consistent condom use.</p

Cannabis Use Is Associated with Lower Rates of Initiation of Injection Drug Use Among Street-Involved Youth: A Longitudinal Analysis

Introduction and Aims: Street-involved youth are known to be at elevated risk of initiating injection drug use. However, the impact of so-called “gateway” drugs, such as cannabis, on injection initiation is unknown. The objective of this study was to examine the association between cannabis use and initiation of injection drug use among a prospective cohort of street-involved youth in Vancouver, Canada. &nbsp; Design and Methods: Data for this study were collected from the At-Risk Youth Study (ARYS). From September 2005 to May 2015, participants aged 14-26 who reported illicit drug use were recruited into this open prospective cohort study. An extended Cox regression model with time-updated covariates was used to identify factors independently associated with injection initiation. &nbsp; Results: During the study period 481 street-involved youth were included in this study. Of these, 228 (47.4%) reported at least daily cannabis use, and 103 (21.4%) initiated injection drug use. In a multivariable analysis, ≥ daily cannabis use was associated with slower rates of injection initiation (Adjusted Relative Hazard [ARH]: 0.66, 95% Confidence Interval [CI]: 0.45 – 0.98; p = 0.038). Subanalyses revealed that cannabis use was negatively associated with initiation of injection stimulants but not initiation of injection opioids. &nbsp; Discussion and Conclusions: Given the expansion of cannabis legalization throughout North America, it is encouraging that cannabis use was associated with slower time to initiation of injection drug use in this cohort. This finding challenges the view of cannabis as a gateway substance that precipitates the progression to using harder and more addictive drugs. &nbsp