Identifying biotic determinants of historic American eel (Anguilla rostrata) distributions

Traditionally, ecologists studying large scale patterns in species distributions emphasize abiotic variables over biotic interactions. Noting that both abiotic & biotic variables likely determine distributions of all organisms, many ecologists now aim for a more comprehensive view of species distributions, inclusive of both abiotic and biotic components (Soberón 2007)

Bayesian Estimation of The Impacts of Food Safety Information on Household Demand for Meat and Poultry

Consumer reaction to changes in the amount of food safety information on beef, pork, and poultry available in the media is the focus of this study. Specifically, any differences in consumer reactions due to heterogeneous household characteristics are investigated. The data used in this study are monthly data from the Nielsen Homescan panel and cover the time period January 1998 to December 2005. These panel data contain information on household purchases of fresh meat and poultry as well as demographic characteristics of the participating households. The data used to describe food safety information were obtained from searches of newspapers using the Lexis-Nexis academic search engine. Consumer reactions are modeled in this study using a demand system that allows for both discrete and continuous choice situations. A seemingly unrelated regression (SUR) tobit model is estimated using a Gibbs sampler with data augmentation. A component error structure (random effects model) is incorporated into the SUR tobit model to account for unobserved heterogeneity of households making repeated purchases over time. Estimates of food safety elasticities calculated from the random effects SUR tobit model suggest that food safety information does not have a statistically or economically significant effect on household purchases of meat and poultry.food safety, panel data, Gibbs sampler, component error, Agricultural and Food Policy, Consumer/Household Economics, Food Consumption/Nutrition/Food Safety,

Correlated electronic structure theory for challenging systems

The photochemistry of molecules can be investigated computationally, and this provides great insight into the underlying chemistry and physics. Such computational approaches are challenging and can pose many difficulties compared to ground state methodologies. Care must be taken to accurately describe these systems, as some lowlevel approximate methods can fail. The geometrical and electronic structures (TiO2)n clusters (n=1-4) have been investigated. These are of enormous technological interest as wide band-gap semiconductors yet the nature of electronic transitions in nano-sized clusters has yet to be fully elucidated. Structures of the neutral closed-shell, radical cationic and radical anionic clusters at each size are described and rationalised in terms of the pseudo-Jahn- Teller effect. We have used high-level response theory to set benchmarks for such systems. The TiO2 monomer is the simplest of the clusters studied yet proves a stern test for many lower order ab-initio methods. It is shown that high-level methods are required to properly describe this simple molecule. The Monte Carlo Configuration Interaction method attempts to combine the power of Full CI with a scalability that allows it to be used to study much larger systems. It can be systematically improved and can approach the accuracy of the Full CI method. This method is applied here to investigate potential energy surfaces and multipole moments of a range of small but challenging systems

Dynamical Decompactification and Three Large Dimensions

We study string gas dynamics in the early universe and seek to realize the Brandenberger - Vafa mechanism - a goal that has eluded earlier works - that singles out three or fewer spatial dimensions as the number which grow large cosmologically. Considering wound string interactions in an impact parameter picture, we show that a strong exponential suppression in the interaction rates for d > 3 spatial dimensions reflects the classical argument that string worldsheets generically intersect in at most four spacetime dimensions. This description is appropriate in the early universe if wound strings are heavy - wrapping long cycles - and diluted. We consider the dynamics of a string gas coupled to dilaton-gravity and find that a) for any number of dimensions the universe generically stays trapped in the Hagedorn regime and b) if the universe fluctuates to a radiation regime any residual winding modes are diluted enough so that they freeze-out in d > 3 large dimensions while they generically annihilate for d = 3. In this sense the Brandenberger-Vafa mechanism is operative.Comment: 20 pages, 2 figures, minor changes, updated figures, as will appear in Phys.Rev.

Delegated Trade and the Pricing of Public and Private Information

We extend a standard, rational expectation model of trade to incorporate the possibility of individual investors delegating their trades to an informed financial intermediary. In the presence of delegated trade, we show that a firm׳s risk premium is a function of both the firm׳s exposure to a common risk factor and idiosyncratic characteristics of the firm׳s information environment. We show that even in a large economy, priced risks can manifest in the form of both idiosyncratic firm characteristics and common risk factors; as a consequence, factor-based asset pricing tests cannot rule out that a particular risk is priced

Open Research Projects and Public Sociology: Students Communicating Creatively in the Classroom and Beyond

As teachers, we often deny students the freedom to choose topics of inquiry and methods of communication. We have developed an open research project that challenges students to identify a social problem, gather research, and apply what they have learned by targeting an audience and developing a strategy for effective communication. This assignment centers a “problem-posing” focus that tasks students with confronting relevant issues in their lives and communities. It emphasizes public sociology by shifting the audience for their projects from instructors to classmates, families, communities, and beyond. Students have communicated their work through a variety of mediums, including children’s books, videos, poetry, photojournalism, and other artistic formats. We discuss challenges and strategies involved with this open project. Paradoxically, we have learned from this project that lots of freedom requires lots of structure. We find that for students to create high-quality public sociology, teachers must commit to providing clear expectations, deadlines, communication, and accountability