AGRICULTURAL DEVELOPMENT ON THE BRAZILIAN FRONTIER: SOUTHERN MATO GROSSO

International Development,

The Effects of Three Schedules of Reinforcement on Stimulus Generalization

The effects of three schedules of reinforcement on stimulus generalization in rats were investigated. In the presence of a 2000 hz tone the subjects were trained to bar press on one of three schedules: CRF, VR 25, or VR 50. Three animals started in each condition. After tone/no-tone discrimination training they were tested for generalization. Generalization took.place over six,31.5 minute sessions. This tested the subjects* response rate to each of seven tones: 250 hz, 500 hz, 1000, hz, 2000 hz, 4000 hz, 8000 hz, and 16000 hz. During a 31.5 minute generalization test every tone was presented randomly nine times for 30 seconds each. The VR 25 group produced a much steeper generalization gradient than the VR 50 group. The CRF group produced inconsistent generalization without a .clearcut generalization gradient around the training stim ulus. Generalization gradients were steepest early in generalization testing and tended to become flatter as extinction continued. The results indicate that,.similar to VI schedules, VR schedules produce more stimulus gener alization as density of reinforcement decreases

ADOPTION OF VETERINARY SURGEON SERVICES BY SHEEP AND GOAT FARMERS IN QWAQWA

A number of technology transfer (diffusion) programmes involving amongst others veterinary surgeon services subsidised by the government, were launched in the former homelands of South Africa between 1980 and 1993. Many of these programmes were discontinued after the general election of 1994. In order to evaluate the adoption of technology in Qwaqwa, a former Sotho speaking homeland, two Logit models were fit using the conventional definition of an adopter and an adapted definition, which included potential adopters with the adopters. Where the conventional definition of adoption was estimated, livestock income per LSU, ram technology, roads and suppliers of livestock inputs are significant variables contributing to adoption. The results of the adapted model reveal that farming efficiency (weaning percentage), type of farmer (sheep as percentage of the total small ruminant herd) and ram technology, prove to be significant variables predicting adoption. It was also found that the characteristics of potential adopters gravitate more to adopters than to non-adopters. These results indicated that the adapted definition presented a more accurate prediction than the conventional definition. The results of this study indicate the policy necessary to further accelerate the diffusion of veterinary surgeon services by means of the development of a better infrastructure, the reintroduction of subsidised veterinary surgeon services at the sheering sheds as well as a better flow of information to farmers in Qwaqwa.Livestock Production/Industries,

The utility of cancer-related cultural constructs to understand colorectal cancer screening among African Americans

Background. Data suggest that colorectal cancer could be cut by approximately 60% if all people aged 50 years or older received regular screening. Studies have identified socio-cultural attitudes that might inform cancer education and screening promotion campaigns. This article applies item response theory (IRT) to a set of survey items selected to assess sociocultural attitudes in order to determine how current measures may affect what we know about how these attitudes affect colorectal cancer screening (CRCS).Design and Methods. A survey of colorectal cancer screening, screening attitudes and cultural beliefs was administered to 1021 African Americans – 683 women and 338 men, ages 50 to 75. Eligibility crite ria for participation included being born in the United States, self-identified African American male or female, age 50 to 75 years. The IRT analysis was performed on 655 individuals with complete data for the 43 observed variables. Results. Twenty-nine items comprise the Multi-construct African American Cultural Survey (MAACS) that addresses seven cultural con- structs: mistrust/distrust, privacy, ethnic identity, collectivism, empowerment, and male gender roles. The items provide adequate information about the attitudes of the population across most levels of the constructs assessed. Among the sociocultural variables considered, empowerment (OR=1.078; 95% CI: 1.008, 1.151) had the strongest association with CRCS adherence and privacy showed promise. Conclusions. The MAACS provides a fixed length questionnaire to assess African American CRCS attitudes, two new constructs that might assist in CRCS promotion, and a suggested focus for identification of additional constructs of interest

Desenvolvimento agrícola na fronteira brasileira: sul de Mato Grosso

O desempenho do produto agrícola brasileiro no período após a II Guerra Mundial é digno de nota, porquanto os aumentos da oferta vêm se adaptando ao crescimento da demanda e a suas alterações entre grupos de bens, mantendo, dessa forma, os preços reais do géneros alimentícios relativamente constantes. Isto se verificou apesar do descuido, e mesmo da implementação de políticas adversas ao setor agrícol

Radiating dipoles in photonic crystals

The radiation dynamics of a dipole antenna embedded in a Photonic Crystal are modeled by an initially excited harmonic oscillator coupled to a non--Markovian bath of harmonic oscillators representing the colored electromagnetic vacuum within the crystal. Realistic coupling constants based on the natural modes of the Photonic Crystal, i.e., Bloch waves and their associated dispersion relation, are derived. For simple model systems, well-known results such as decay times and emission spectra are reproduced. This approach enables direct incorporation of realistic band structure computations into studies of radiative emission from atoms and molecules within photonic crystals. We therefore provide a predictive and interpretative tool for experiments in both the microwave and optical regimes.Comment: Phys. Rev. E, accepte

Functional Brain Imaging of Young, Nondemented, and Demented Older Adults

Brain imaging based on functional MRI (fMRI) provides a powerful tool for characterizing age-related changes in functional anatomy. However, between-population comparisons confront potential differences in measurement properties. The present experiment explores the feasibility of conducting fMRI studies in nondemented and demented older adults by measuring hemodynamic response properties in an event-related design. A paradigm involving repeated presentation of sensory-motor response trials was administered to 41 participants (14 young adults, 14 nondemented older adults, and 13 demented older adults). For half of the trials a single sensory-motor event was presented in isolation and in the other half in pairs. Hemodynamic response characteristics to the isolated events allowed basic response properties (e.g., amplitude and variance) between subject groups to be contrasted. The paired events further allowed the summation properties of the hemodynamic response to be characterized. Robust and qualitatively similar activation maps were produced for all subject groups. Quantitative results showed that for certain regions, such as in the visual cortex, there were marked reductions in the amplitude of the hemodynamic response in older adults. In other regions, such as in the motor cortex, relatively intact response characteristics were observed. These results suggest caution should be exhibited in interpreting simple main effects in response amplitude between subject groups. However, across all regions examined, the summation of the hemodynamic response over trials was highly similar between groups. This latter finding suggests that, even if absolute measurement differences do exist between subject groups, relative activation change should be preserved. Designs that rely on group interactions between task conditions, parametric manipulations, or group interactions between regions should provide valuable data for making inferences about functional-anatomic changes between different populations.Psycholog