A simplified cell theory applied to the calculation of thermal neutron spectra in light water lattices

This thesis document was issued under the authority of another institution, not NPS. At the time it was written, a copy was added to the NPS Library Collection for reasons not now known. It has been included in the digital archive for its historical value to NPS. Not believed to be a CIVINS (Civilian Institutions) title.A simplified polyenergetic cell theory is formulated to determine spatially averaged energy dependent thermal fluxes in the moderator, cladding, and fuel regions within the unit cell of a reactor lattice. The derived spectra are then utilized in the calculations of the thermal integral parameters and average cross sections required for reactor computations. The cell theory, as formulated, postulates an infinite moderator region with the absorption cross section of this region appropriately modified to account for the neutron leakage into and absorption by the fuel element. The modifications to the moderator absorption cross section are formulated both in terms of the net current at the fuel element-moderator interface and in terms of energy dependent moderator and fuel element escape probabilities, the latter approach offering physical transparency and ease of calculation. Analytic expressions for the escape probabilities are presented, integral transport theory being applied to the fuel element region, while diffusion theory is utilized in the moderator region. Using these analytic expressions, the theory is applied to actual lattices in the form of the light water moderated and uranium dioxide fueled cores of the Cornell University Zero Power Reactor. Room temperature parameters and their temperature coefficients are determined using both the monatomic gas model and the Nelkin water kernel to describe the energy transfer process in the moderator. Calculations are made with PROGRAM COUTH, a Fortran-63 program written for use with the Control Data Corporation 1604 digital computer. A typical lattice calculation including the computation of the spatially averaged fuel, cladding, and moderator spectra and the thermal integral properties and average cross sections takes approximately thirty-five seconds of computer time. This figure is exclusive of the compiling time and the time required to calculate the moderator scattering kernel. In an attempt to estimate the accuracy of the calculational results, the method is applied to the Brookhaven National Laboratory uranium dioxide cores and the results are then compared with those predicted by Honeck's THERMOS code. Disadvantage factors agree to within 1.0% while the thermal utilizations agree to within 0.5%. A study of the sensitivity of the calculated integral parameters to variations in the input data leads to the assignment of rather small uncertainties in the results calculated with the simplified cell theory.http://www.archive.org/details/simplifiedcellth00macvLieutenant, United States Nav

Mormon Crickets: A Brighter Side

In a recent appraisal of Mormon crickets (Anabrus simplex Haldeman), Raffelson (1989) reminds us that these insects are a subject of great concern and dislike among Western ranchers and farmers

Control biológico: ciencia y conciencia

12 p.Este último trabajo del simposio trata de enfocar la pregunta ¿Cómo se puede asegurar el éxito del control biológico en Centroamérica? El trabajo es más un ensayo especulativo y conceptual que una presentación de datos concretos o hipótesis comprobadas, y el propósito de esta discusión es plantear metas y direcciones que puedan estimular el desarrollo del control biológico en instituciones de investigación y educación centroamericanas. Ya que mi ocupación es de profesor e investigador universitario, los puntos de vista que presento tienen indudablemente un sesgo académico. Además, existirá un sesgo guatemalteco en los argumentos que planteo, ya que mi experiencia centroamericana fuera de Guatemala es limitada. Sin embargo, espero que estos sesgos sirvan para estimular comentarios y argumentos desde otros puntos de vista

Acidez del suelo como causa del "Mal de Viñas" del café (Coffea arabica L.) en Guatemala: un estudio de invernadero.

8 p.El objetivo del trabajo fue determinar si la manipulación del pH del suelo induce los síntomas del decaimiento letal del café, conocido como "Mal de Viñas" en Guatemala. Se utilizó suelo de la región afectada por Mal de Viñas. Se usó como testigo suelo con pH inicial de 4.4. Se utilizó ácido clorhídrico al 10%, o enmiendas con cal dolomítica al 10%,25% Y 50% (peso/peso) para dar una gama de tratamientos de pH desde 3.5 hasta 7.5. Se sembraron plántulas sanas de café en cada tratamiento y se evaluaron durante 648 días, midiendo el crecimiento del tallo, número de hojas producidas por planta, longitud y diámetro del sistema radicular y producción de frutos. Los tratamientos acidificados y el testigo desarrollaron síntomas claros del Mal de Viñas (clorosis, defoliación, pocas raicillas). El encalamiento al 10% lo evitó por completo. Hubo diferencias significativas entre tratamientos, principalmente entre los suelos acidificados (pH 3.5 Y 4.1) Y los encalados al 10% (pH 7.0). El análisis químico mostró que los suelos acidificados tenían mayores concentraciones y saturación de aluminio y manganeso en relación al testigo y los encalados. La acidificación del suelo produjo síntomas similares al decaimiento de campo, lo que apoya la hipótesis de que el Mal de Viñas es en parte causado por niveles tóxicos de aluminio y manganeso

Susceptibility of Bemisia tabaci MEAM1 (Hemiptera: Aleyrodidae) to Imidacloprid, Thiamethoxam, Dinotefuran and Flupyradifurone in South Florida

Populations of Bemisa tabaci MEAM1 were established from nineteen locations in south Florida, primarily from commercial tomato fields, and were tested using a cotton leaf petiole systemic uptake method for susceptibility to the nicotinic acetylcholine agonist insecticides imidacloprid, thiamethoxam, dinotefuran and flupyradifurone. Eleven populations produced LC50s for one or more chemicals that were not significantly different from the susceptible laboratory colony based on overlapping fiducial limits, indicating some degree of susceptibility. LC50s more than a 100-fold the laboratory colony were measured in at least one population for each material tested, indicating tolerance. LC50s (ppm) from field populations ranged from 0.901–24.952 for imidacloprid, 0.965–24.430 for thiamethoxam, 0.043–3.350 for dinotefuran and 0.011–1.471 for flupyradifurone. Based on overlapping fiducial limits, there were no significant differences in relative mean potency estimates for flupyradifurone and dinotefuran in relation to imidacloprid and thiamethoxam

Eteaming With Developing Nations: Social Outreach With An Entrepreneurial Twist

The World Bank estimates that over 2.8 billion people live in poverty, earning less than $2/day. Financial assistance alone has not been able to solve the problems generated by poverty in a sustainable way. We are testing the hypothesis that the teaching of product design principles together with basic entrepreneurship skills might be a way to provide longer-lasting solutions. These ideas are based on the premise that although cash might be the most pressing need of the poor, the most vital need is the acquisition of income generation skills. Major challenges arose in the initial testing stage, from the formidable physical and cultural distances that separate the design engineer/teacher from their intended customers in developing nations, to the lack of “ground truth” information to guide the design process. For this reason, over the past two years E105:, Product Design for the Developing World, a Development Engineering course at Caltech, has evolved to include e-Teams as an integral element in its curriculum. The e-Teams bring together students from the US and industrial design and agricultural students from a developing nation. The US engineering students contribute their fast prototyping and analytical problem solving skills while the foreign students contribute their familiarity with poorly defined markets and add cultural sensitivity to the e-Team designs. The students deal with strong constraints on product costs and pricing, evaluate the availability of local materials and the lack of manufacturing and product standards. The e-Team members work together through a variety of electronic communication technologies: Video-conferencing, video streaming, Instant Messaging, Internet telephony, e-mail and web-groups. These electronic tools, which play a role at various levels in the design process, are briefly discussed

Seroprevalence of Trypanosoma cruzi infection in three rural communities in Guatemala Seroprevalencia de infección por Trypanosoma cruzi en tres comunidades rurales de Guatemala

A systematic, house-based serological survey for Trypanosoma cruzi seroreactivity was conducted in three contiguous communities in Olopa municipality, Chiquimula Department, Guatemala. Blood samples from a total of 292 individuals in 63 households were examined by enzyme-linked immunosorbent assay. The seropositive rate ranged from 0% to 20.8% for the three communities, with a mean of 15.1%. Log-linear models showed that seroprevalence was significantly related to age (P < 0.005) but not to sex. However, when the age group with the lowest prevalence (1-9 years) was excluded from the analysis, age was not a significant factor (P = 0.55). Data from a stratified sample collected at the same time were combined with those of the systematic sample to analyze the relationship between seropositivity and possible explanatory variables. Log-linear models, based on 586 individuals in 129 households from the two surveys, revealed a significant positive association between seropositivity and thatched roofs (P = 0.01).<br>Una encuesta serológica sistemática y domiciliaria para detectar serorreactividad a Trypanosoma cruzi se llevó a cabo en tres comunidades contiguas de la municipalidad de Olapa, en el departamento de Chiquimula, Guatemala. Se examinaron mediante inmunoadsorción enzimática muestras de sangre obtenidas de un total de 292 habitantes que residían en 63 viviendas. La tasa de seropositividad varió de 0 a 20,8% en las tres comunidades y tuvo una media de 15,1%. Los modelos logarítmico-lineales mostraron una asociación significativa entre la seroprevalencia y la edad (P < 0,05), pero no entre aquella y el sexo. No obstante, cuando el grupo de edad que tuvo la seroprevalencia más baja (el de 1 a 9 años) se excluyó del análisis, la edad dejó de ser un factor significativo (P = 0,55). Datos obtenidos de una muestra estratificada recogida simultáneamente se combinaron con los de la muestra sistemática con el fin de analizar la relación entre la seropositividad y algunas variables que podrían ser explicativas. Los modelos logarítmico-lineales, aplicados en 586 habitantes de 129 viviendas incluidas en ambas encuestas, revelaron una asociación positiva significativa entre la seropositividad y la presencia de techo de paja (P = 0,01)

The Invasive Liriomyza huidobrensis (Diptera: Agromyzidae): Understanding Its Pest Status and Management Globally

Liriomyza huidobrensis (Blanchard) is native to South America but has expanded its range and invaded many regions of the world, primarily on flowers and to a lesser extent on horticultural product shipments. As a result of initial invasion into an area, damage caused is usually significant but not necessarily sustained. Currently, it is an economic pest in selected native and invaded regions of the world. Adults cause damage by puncturing abaxial and adaxial leaf surfaces for feeding and egg laying sites. Larvae mine the leaf parenchyma tissues which can lead to leaves drying and wilting. We have recorded 365 host plant species from 49 families and more than 106 parasitoid species. In a subset of the Argentinian data, we found that parasitoid community composition attacking L. huidobrensis differs significantly in cultivated and uncultivated plants. No such effect was found at the world level, probably due to differences in collection methods in the different references. We review the existing knowledge as a means of setting the context for new and unpublished data. The main objective is to provide an update of widely dispersed and until now unpublished data, evaluate dispersion of the leafminer and management strategies in different regions of the world, and highlight the need to consider the possible effects of climate change on further regional invasions or expansions.The Invasive Liriomyza huidobrensis (Diptera: Agromyzidae): Understanding Its Pest Status and Management GloballypublishedVersio