Optimal Control of Locusts in Subsistence Farming Areas

Locust swarms hit subsistence-staple-crop-growing households at random and are not privately controllable. An aerial-spraying optimal control model that supports the said households’ liveli-hood at least expected cost is therefore developed. The qualitative properties of the model are analysed under economically plausible but mild assumptions. The steady state comparative stat-ics reveal that the locust swarm size and the probability of a household’s crop being destroyed by a swarm decrease with the number of households, yield per household, and the staple crop’s replacement price, and increase with the marginal cost of spraying and the planner’s discount rate. A local comparative dynamics analysis is also conducted, as it provides the necessary eco-nomic intuition behind other ostensibly anomalous steady state comparative statics results.Optimal control, local stability, steady state comparative statics, local comparative dynamics

The Pomeron structure and diffractive parton distributions

Measurements of the diffractive structure function, $F_2^D$, of the proton at HERA are used to extract the partonic structure of the Pomeron. Regge Factorization is tested and is found to describe well the existing data within the selected kinematic range. The analysis is based on the next to leading order QCD evolution equations. The results obtained from various data sets are compared. An analysis of the uncertainties in determining the parton distributions is provided. The probability of diffraction is calculated using the obtained results.Comment: Talk presented at DIS05, Madison, Wisconsi

Peer Effects and Alcohol Use Among College Students

This paper examines a natural experiment in which students at a large state university were randomly assigned roommates through a lottery system. We find that on average, males assigned to roommates who reported drinking in the year prior to entering college had one quarter-point lower GPA than those assigned to non-drinking roommates. The 10th percentile of their college GPA is half a point lower than among males assigned non-drinking roommates. For males who themselves drank frequently prior to college, assignment to a roommate who drank frequently prior to college reduces GPA by two-thirds of a point. Since students who drink frequently are particularly influenced by frequent-drinking roommates, substance-free housing programs could potentially lower average GPA by segregating drinkers. The effect of initial assignment to a drinking roommate persists and possibly even grows over time. In contrast, students' college GPA is not influenced by roommates' high school grades, admission test scores, or family background. Females' GPAs are not affected by roommates' drinking prior to college. Overall, these findings are more consistent with models in which peers change preferences than models in which they change endowments.

A Genetic Locus Regulates the Expression of Tissue-Specific mRNAs from Multiple Transcription Units

129 GIX- mice, unlike animals of the congeneic partner strain GIX+, do not express significant amounts of the retroviral antigens gp70 and p30. Evidence is presented indicating that the GIX phenotype is specified by a distinct regulatory gene acting on multiple transcription units to control the levels of accumulation of specific mRNA species. The steady-state levels of retroviral-homologous mRNA from the tissues of GIX+ and GIX- mice were examined by blot hybridization using as probes DNA fragments from cloned murine leukemia viruses. RNA potentially encoding viral antigens was reduced or absent in GIX- mice, even though no differences in integrated viral genomes were detected between these congeneic strains by DNA blotting. Tissue-specific patterns of accumulation of these RNA species were detected in brain, epididymis, liver, spleen, and thymus, and several distinct RNA species were found to be coordinately regulated with the GIX phenotype. Measurements of RNA synthesis suggest a major role for transcriptional control in the regulation of some retroviral messages

Ecological effects of and recovery following surface mining and pasture reclamation

Surface mining with concurrent reclamation to pasture is a major driver of land use and cover change in Appalachia and constitutes a massive disturbance. Prior research suggests that some aspects of recovery are either slow or incomplete. We examined ecosystem structure---including soil physical and chemical properties, arbuscular mycorrhizal fungal (AMF) infectivity and community, and plant diversity and community composition---on a chronosequence of pasture-reclaimed surface mines and an unmined pasture in northern West Virginia. We also examined the effect of inoculating red clover, grown with high or low phosphorus, with AMF communities from old and young pasture-reclaimed surface mines and an unmined hillside. Surface mining and reclamation dramatically altered ecosystem structure. Some aspects of ecosystem structure, including many measures of soil chemistry and infectivity of AMF, returned relatively rapidly to levels found on the unmined reference site. Other aspects of ecosystem structure, notably soil physical properties and AMF and vegetation communities, showed incomplete or no recovery over the short-to-medium term. Clover inoculated with AMF from either the young or old mine site were smaller and less phosphorus-efficient than clover inoculated with AMF from the unmined site. Many effects of surface mining and reclamation are not ameliorated in the short-to-medium term