Resumo Pó submicrométrico de carboneto de silício foi sintetizado em um novo reator piloto de tocha a plasma por radiofrequência. Os precursores foram pós de cinza de pirólise e sílica com tamanhos micrométricos. A taxa de massa do pó de precursor variou na faixa de 600-2500 g/h. O tempo máximo do teste foi de aproximadamente 3 h. Com o objetivo de aumentar o rendimento do processo, várias medidas técnicas foram implementadas. O rendimento de carbeto de silício foi superior a 70% quando a chama de plasma foi confinada por um tubo que prolongou o tempo de residência dos reagentes à temperatura útil para o avanço da reação. O carbeto de silício foi caracterizado por DRX, MEV e DLS. Ambas as fases cristalinas α e β foram detectadas.

Abstract Submicronic powder of silicon carbide was synthesized in a pilot novel radiofrequency plasma torch reactor. The precursors were pyrolysis char and silica powders both with micrometric size. The mass rate of the precursor powder varied in the range 600-2500 g/h. The maximum test time was approximately 3 h. With the goal to increase the process yield, several technical measures were implemented. Silicon carbide yield was above 70 wt% when the plasma flame was confined by a tube that prolonged the residence time of the reactants at the useful temperature for the advancement of reaction. The silicon carbide was characterized by XRD, SEM, and DLS. Both α and β-crystalline phases were detected.

Resumen Este estudio evalúa los factores ambientales que regulan la abundancia y distribución de agallas en Sierra Fría (SF), Aguascalientes, México. En este ecosistema, se seleccionaron 10 sitios de muestreo, dentro de los cuales se establecieron dos parcelas permanentes de 50 x 50 m. De cada sitio se obtuvo su nivel de disturbio, así como datos climáticos y geográficos. Se realizó un análisis de nicho ecológico para relacionar la ocurrencia y amplitud con gradientes climáticos y geográficos a dos niveles: a) distribución específica (microhábitat de oviposición) y b) distribución regional (hospederos y sitios de estudio). La SF presentó un moderado nivel de disturbio que afectó la abundancia de hospederos, pero no tuvo una influencia significativa en la abundancia de agallas. Los encinos presentaron una mayor riqueza de agallas, que los pinos. Entre los encinos, la sección Quercus mostró el doble de agallas (9 ± 2,14) que Lobatae (4,7 ± 2,19). A nivel estructural, el 70 % de las agallas se ubicaron en la vena primaria y en la parte inferior de las hojas. La abundancia y distribución de las agallas, al igual que los hospederos fue afectada por variables climáticas y geográficas. Se discute la interacción hospedero-parásito, la interacción ambiental y la interacción mutualista dependiente que puede generar una crisis de co-extinción, debido al cambio climático y disturbio.

Abstract Galls are formed in the tissues of plants by specific Cynipid gall wasps, and show a high specificity for oaks in temperate climates and represented an indirect method to evaluate its abundance and distribution. This study evaluates the environmental factors that regulate the abundance and geographic distribution of galls in the Sierra Fría (SF), Aguascalientes, Mexico. In this forest ecosystem, we selected 10 sampling sites. On each site, the level of disturbance was registered, as well as geographical and climatological data. Ecological niche analysis was performed to relate gall niche occurrence/breadths with geographical and climatic gradients at two levels: a) regional distribution (hosts and study sites) and b) specific distribution (microhabitat oviposition). The SF had moderate levels of disturbance that affected the abundance of hosts, but did not significantly influence the abundance of galls. The oak had the highest richness of galls, with the pines having them to a lesser extent. Among the oaks, the Quercus section presented twice the amount of galls (9 ± 2.14) than the Lobatae section (4.7 ± 2.19). As for the specific distribution level, over 70 % of the galls were located on the underside of the leaves and the primary stem. This was associated with climatic factors, as a direct effect of climate and terrain impacted the variables of abundance and distribution of galls and hosts found. Finally, how the mutual interaction between host-parasite and dependence forces an availability of hosts that can generate a crisis of co-extinction, due to climate change and disturbance, is discussed.

Abstract: In this study, environmental factors that determine the abundance and distribution of commercial pine species in the municipality of Capulálpam de Mendez, Oaxaca, were analyzed. We used information pertaining to tree species abundance in 636 sites established in harvesting areas from the municipal forest inventory conducted in 2013 for the Management Plan 2015-2022, as well as 354 additional sites located in areas with different land use. Data of the spatial distribution and ecological niche analysis of the species were obtained, for which nine climatic and four geographic variables were used. Ten species of pine were recorded, of which Pinus patula showed the highest abundance and P. chiapensis the lowest. Canonical Correspondence Analysis indicated that most of the pine species are more highly associated with the climatic variables than with geographic variables, except for that of latitude. Niche analysis showed that species of the genus Pinus are highly marginal and of low tolerance to processes of environmental change. Minimal alterations to their habitat could restrict or reduce their abundance and distribution, with P. chiapensis being the least tolerant species and P. patula the species that presented the broadest niche.

Resumen: Se analizan los factores ambientales que determinan la abundancia y distribución de las diferentes especies comerciales y aprovechadas del género Pinus en el municipio de Capulálpam de Méndez, Oaxaca. Se utilizó la información de 636 sitios en áreas de aprovechamiento del inventario forestal del municipio llevado a cabo en 2013 para el Plan de Manejo 2015-2022, y 354 puntos adicionales de áreas con uso diferente al forestal. Se obtuvo información sobre la distribución espacial y análisis del nicho ecológico de los pinos, para lo cual se emplearon nueve variables climáticas y cuatro geográficas. Se encontraron 10 especies, de las cuales P. patula presentó mayor abundancia y P. chiapensis fue la menor. El análisis de correspondencia canónica indicó que la mayoría de los pinos analizados se asocian en mayor medida con las variables climáticas que con las geográficas a excepción de la latitud. El análisis de nicho mostró que las especies del género Pinus muestran alta marginalidad y baja tolerancia a procesos de cambio ambiental, donde una modificación al hábitat podría restringir o disminuir su abundancia y distribución, siendo P. chiapensis la especie de menor tolerancia y P. patula la de mayor amplitud de nicho.

Background: Over the last 7 years, for patients who needed a combined anterior-posterior approach, we have used an alternative thoracotomy through a posterior approach using the same posterior mid-line skin incision for both the first and second step. Our purpose was to assess the possibilities and complications associated with an approach that allows to combine a two-step surgery through a single posterior skin incision. Methods: We retrospectively evaluated 35 patients operated between 2003 and 2007. In all patients a two-step approach through a single posterior mid-line skin incision was used for spinal cord decompression, discectomy, arthrodesis, osteotomy, or vertebrectomy. The following were evaluated: angle magnitudes, etiology, age, vertebral levels; number of thoracotomies, and complications Results: Mean age 14.1 years (1-65years). Ten kyphoses and 24 kyphoscoliosis. Mean scoliosis was 80.5°(60°- 105°), mean kyphosis was 96.8° (76°-131°). Etiology: genetic syndromes 11, Idiopathic scoliosis 6, neurological 5, congenital 4, fractures 2, disc herniation 1, tumors 4, and infection 2. Thoracotomy was single in 30 and double in 5, the highest at T3 level and the lowest at T10. Complications: one pleural hemorrhage and 2 posterior surgical wound infections (8.6%). Conclusions: This approach allows access to all thoracic levels in combined procedures through a single posterior skin incision.

Introducción: Durante los últimos diez años hemos desarrollado y utilizado la toracotomía posterior para abordar la porción superior del tórax en procedimientos combinados anteriores y posteriores. Actualmente extendimos esta indicación a toda la columna torácica en reemplazo de la toracotomía convencional y la toracoscopia. El objetivo de este trabajo es evaluar el rango de posibilidades y complicaciones asociadas con este nuevo abordaje, que permite combinar la cirugía vertebral torácica anterior y posterior con la misma incisión cutánea posterior. Materiales y métodos: Se evaluaron retrospectivamente 35 pacientes operados entre los años 2003 y 2007. En todos se realizó un doble abordaje, combinando una toracotomía posterior y abordaje posterior, mediante una sola incisión medial, para diferentes objetivos: descompresión medular, artrodesis, osteotomías o vertebrectomías. Se evaluaron: magnitudes angulares, etiología, edad, niveles vertebrales, cantidad de toracotomías y complicaciones. Resultados: Promedio de edad 14,1 años (1 a 65). Hubo 10 pacientes con cifosis, promedio 96,8º (76º a 131º); 24 pacientes con escoliosis, promedio 80º (60º a 105º). Etiología: síndromes genéticos 11, escoliosis idiopática 6, neurológicas 5, congénitas 4, tumores 4, fracturas 2, hernia discal 1, infección 2. Las toracotomías fueron únicas en 30 pacientes y doble en 5 pacientes. El nivel superior de las toracotomías fue en T3 e inferior en T10. Complicaciones: un hemotórax y dos infecciones de la herida. Conclusiones: Esta vía permite acceder a todo nivel torácico en procedimientos combinados mediante una sola incisión cutánea.

Neste artigo, um algoritmo numérico baseado no método dos elementos finitos é proposto para a predição da resposta mecânica de vigas de concreto armado carregadas em flexão. A principal novodade de tal abordagem é a introdução do modelo de superposição de fissuras, baseado em conceitos de mecânica da fratura não linear, para descrver o esmagamento do concreto. De acordo com esse modelo, o dano em compressão do concreto é representado por meio de uma interpenetração fictícia. Quanto maior a interpenetração, menores são as forças transferidas através da zona danificada. O conhecido Modelo de fissura coesiva em tração e uma relação tensão versus abertura da fissura elasto-perfeitamente plástica descrevendo o comportamento da armadura de aço são também integrados no algoritmo numérico. A aplicação do Modelo de Fissura Coesiva superposta para a avaliação da armadura mínima necessária para prevenir propagação ins- tável de fissura por tração e para a avaliação da capacidade rotacional de rótulas plásticas, permite prever efeito escala evidenciado por vários programas experimentais disponíveis na literatura. De acordo com os resultados númericos obtidos, novos fórmulas e diagramas para projeto são propostos para aprimoramento de normas atuais que usualmente desprezam efeito escala.

In the present paper, a numerical algorithm based on the finite element method is proposed for the prediction of the mechanical response of reinforced concrete (RC) beams under bending loading. The main novelty of such an approach is the introduction of the Overlapping Crack Model, based on nonlinear fracture mechanics concepts, to describe concrete crushing. According to this model, the concrete dam- age in compression is represented by means of a fictitious interpenetration. The larger is the interpenetration, the lower are the transferred forces across the damaged zone. The well-known Cohesive Crack Model in tension and an elastic-perfectly plastic stress versus crack opening displacement relationship describing the steel reinforcement behavior are also integrated into the numerical algorithm. The application of the proposed Cohesive-Overlapping Crack Model to the assessment of the minimum reinforcement amount neces- sary to prevent unstable tensile crack propagation and to the evaluation of the rotational capacity of plastic hinges, permits to predict the size-scale effects evidenced by several experimental programs available in the literature. According to the obtained numerical results, new practical design formulae and diagrams are proposed for the improvement of the current code provisions which usually disregard the size effects.