Measurement of the elastic scattering cross section of neutrons from argon and neon

Background: The most significant source of background in direct dark matter searches are neutrons that scatter elastically from nuclei in the detector's sensitive volume. Experimental data for the elastic scattering cross section of neutrons from argon and neon, which are target materials of interest to the dark matter community, were previously unavailable. Purpose: Measure the differential cross section for elastic scattering of neutrons from argon and neon in the energy range relevant to backgrounds from (alpha,n) reactions in direct dark matter searches. Method: Cross-section data were taken at the Triangle Universities Nuclear Laboratory (TUNL) using the neutron time-of-flight technique. These data were fit using the spherical optical model. Results: The differential cross section for elastic scatting of neutrons from neon at 5.0 and 8.0 MeV and argon at 6.0 MeV was measured. Optical-model parameters for the elastic scattering reactions were determined from the best fit to these data. The total elastic scattering cross section for neon was found to differ by 6% at 5.0 MeV and 13% at 8.0 MeV from global optical-model predictions. Compared to a local optical-model for 40Ar, the elastic scattering cross section was found to differ from the data by 8% at 6.0 MeV. Conclusions: These new data are important for improving Monte-Carlo simulations and background estimates for direct dark matter searches and for benchmarking optical models of neutron elastic scattering from these nuclei

Patterns and process during the diversification of the cichlid fishes in Lake Malawi, Africa

The 500-1000 cichlid species endemic to Lake Malawi constitute one of the most rapid and extensive radiations of vertebrates ever discovered. The objective of this dissertation was to test the assumptions and predictions of several recently published models of cichlid speciation. First, a novel assay of female choice was used to evaluate the role of visual cues during conspecific recognition. The results of this experiment demonstrate that females are able to identify conspecific mates using only visual cues. Second, the assumptions of a recent model of speciation via intrasexual selection were tested by comparing aggressive behavior during territorial contests among five closely related cichlid species from Lake Malawi. I found that interactions between conspicuously heteromorphic males tend to be less aggressive than between those of homomorphic males. Third, I used transect data to evaluate the intrinsic and extrinsic factors that have affected the dispersal of 17 closely related cichlid species introduced to Thumbi West Island in Lake Malawi. A quarter of a century after their initial introduction, I found that the translocated cichlid community around Thumbi West Island is still in a state of flux, as many species continue to spread around the island. Next, I evaluated the patterns of divergence predicted by three competing speciation models that differ in the temporal action of natural and sexual selection by using AFLP to reconstruct the evolutionary relationships among 20 species of the ubiquitous rock dwelling subgenus Pseudotropheus tropheops. I found that cladogenesis is associated with numerous unambiguous changes in male color states. A geometric morphometric analysis of the lower jaw of these taxa revealed that the repeated differentiation of jaw morphology is associated with species habitat preference. Finally, I used AFLP data to reconstruct the evolution of species within three genera of sand dwelling cichlids that construct elaborate male display platforms. I found that sister taxa with distinct bower morphologies, and that exist in discrete leks separated by only 1-2m of depth, are divergent in both sexually selected and ecological traits. These phylogenies suggest that the forces of sexual and ecological selection have been intertwined during the speciation of these groups

Viewers\u27 Reactions to Ordinary People in Television News Events

Viewers\u27 Reactions to Ordinary People in Television News Events examines two hypotheses relating to respondents\u27 reactions to viewing violent events or the likelihood of violent death as portrayed on the major news networks. Research centers on reactions of viewers to ordinary people caught in extraordinary news events. Results of two free-flow written exercises are discussed. Research excludes reactions to viewing those in the news, such as police personnel, soldiers etc., whose lives might be expected to be involved in violent or dangerous events

Site Factors Influence on Herbaceous Understory Diversity in East Texas Pinus palustris savannas

Longleaf pine (Pinus palustris) savannas were once dominant across the southeastern U.S., including East Texas and parts of western and central Louisiana. The diverse understory associated with these historical savannas may occasionally be seen today, but not often in longleaf pine ecosystems. This project aimed to define east Texas site characteristics that are necessary to support these ecosystems with a dense and diverse herbaceous understory with little to no midstory cover. Fifty-nine plots across three study sites were established to evaluate the influence of overstory cover, basal area, aspect, elevation, and slope on the number of plant genera present. Forest structure and site characteristics had significant effects on the number of plant genera found. The number of genera increased with higher elevation and slope; as elevation increased, there was a decline in basal area and overstory cover, leading to a more diverse, understory layer. In order to re-establish and maintain a diverse, herbaceous understory in longleaf pine savannas, sites with more open canopies and on slopes with the most solar exposure should be given priority, particularly when planting desired understory species

Acquiring verb-argument structure in Tagalog: A multivariate corpus analysis of caregiver and child speech

Western Austronesian languages have typologically rare but theoretically important voice systems that raise many questions about their learnability. While these languages have been featured prominently in the descriptive and typological literature, data on acquisition is sparse. In the current paper, we report on a variationist analysis of Tagalog child-directed speech using a newly collected corpus of caregiver-child interaction. We determined the constraints that condition voice use, voice selection, argument position, and thematic role assignment, thus providing the first quantitative analysis of verb argument structure variation in the language. We also examined whether children are sensitive to the constraints on variability. Our analyses showed that, despite the diversity of structures that children have to learn under Tagalog’s voice system, there are unique factors that strongly predict the speakers’ choice between the voice and word order alternations, with children’s choices related to structure alternations being similar to what is available in their input. The results thus suggest that input distributions provide many cues to the acquisition of the Tagalog voice system, making it eminently learnable despite its apparent complexity

The acquisition of the Tagalog symmetrical voice system: Evidence from structural priming

We report on two experiments that investigated the acquisition of the Tagalog symmetrical voice system, a typologically rare feature of Western Austronesian languages in which there are more than one basic transitive construction and no preference for agents to be syntactic subjects. In the experiments, 3-, 5-, and 7-year-old Tagalog-speaking children and adults completed a structural priming task that manipulated voice and word order, with the uniqueness of Tagalog allowing us to tease apart priming of thematic role order from that of syntactic roles. Participants heard a description of a picture showing a transitive action, and were then asked to complete a sentence of an unrelated picture using a voice-marked verb provided by the experimenter. Our results show that children gradually acquire an agent-before-patient preference, instead of having a default mapping of the agent to the first noun position. We also found an earlier mastery of the patient voice verbal and nominal marker configuration (patient is the subject), suggesting that children do not initially map the agent to the subject. Children were primed by thematic role but not syntactic role order, suggesting that they prioritize mapping of the thematic roles to sentence positions