Efecto de diferentes niveles de nitrógeno, espaciamientos y poblaciones sobre el crecimiento, desarrollo y rendimiento del maíz (Zea Mays L) var. NB-6

Con el Objetivo de estudiar la influencia de tres diferentes nieves de nitrógeno (0.70 y 140 kilogramos por hectárea), cuatro diferentes espaciamientos (40,60 80 y 120 cm) y tres diferentes densidades de población (41 500.62 500 y 83 250 plantas por Hectárea) sobre el crecimiento, desarrollo y rendimiento de maíz (Zea mays L.) var. NB-6, se estableció un experimento, utilizando el diseño de parcelas Divididas con cuatro repeticiones, en la Estación Experimental La Compañía, Carazo, cuyos suelos son de topografía plana, textura media, altos en materia orgánica, Clase II pertenecientes a la serie Masatepe. Los resultados obtenidos indican que la aplicación de nitrógeno y los diferentes espaciamientos entre surcos no produjeron efecto significativo sobre el rendimiento y sus componentes, asimismo no se determinó efecto significativo de las intersecciones cobre el rendimiento y sus componentes, La densidad de población mostró un efecto altamente significativo sobre el rendimiento en grano obteniéndose 7,470 kilogramos por hectárea. Se determinó que el mayor rendimiento se produjo utilizando 140 kilogramos de nitrógeno por hectárea, espaciamientos de 40 cm y una densidad de población de 83.250 plantas por hectárea, al cual corresponde un ingreso Neto de $756,743 córdobas equivalente a una tasa de retorno Marginal de 6.58.

The role of endothelin pathway in modulation of airway reactivity to methacholine in C57Bl/6 and BALB/c mice

Endothelin peptides have been shown to increase cholinergic neurotransmission in the airway. Genetic differences in airway responsiveness to methacholine where reported in mice. The present study compared the airway reactivity to methacholine in C57Bl/6 and BALB/c mice, the involvement of endothelin on this reactivity and endothelin levels in lung homogenates. Whole airway reactivity was analyzed by means of an isolated lung preparation where lungs were perfused through the trachea with warm gassed Krebs solution at 5 ml/min, and changes in perfusion pressure triggered by methacholine at increasing bolus doses (0.1-100 mu g) were recorded. We found that the maximal airway response to methacholine was much greater in C57Bl/6 than in BALB/c (Emax 34 +/- 2 vs 12 +/- 1 cmH(2)O, respectively). Bosentan (mixed endothelin A/B receptor antagonist; 10 mg/kg, i.p., 30 min before sacrifice) reduced lung responsiveness to methacholine in C57Bl/6 (58% at EC50 level) but had no effect in BALB/c mouse strain. This effect seems to be mediated by the endothelin ETA receptor since it was significantly reduced by the selective endothelin ETA receptor antagonist, BQ 123. Immunoreactive endothelin levels were higher in C57Bl/6 than in BALB/c lungs (43 5 vs 19 +/- 5 pg/g of tissue). In conclusion, airway reactivity to methacholine and lung endothelins content varies markedly between C57Bl/6 and BALB/c strains. Endothelins upregulate lung responsiveness to methacholine only in C57Bl/6, an effect achieved through the endothelin ETA receptor. (C) 2008 Elsevier B.V. All rights reserved.

Acute resistance exercise increases the expression of chemotactic factors within skeletal muscle

Intense resistance exercise causes mechanical loading of skeletal muscle, followed by muscle adaptation. Chemotactic factors likely play an important role in these processes. Purpose We investigated the time course of changes in the expression and tissue localization of several key chemotactic factors in skeletal muscle during the early phase of recovery following resistance exercise. Methods Muscle biopsy samples were obtained from vastus lateralis of eight untrained men (22+-0.5 yrs) before and 2, 4 and 24 h after three sets of leg press, squat and leg extension at 80% 1 RM. Results Monocyte chemotactic protein-1 (95×), interleukin-8 (2,300×), IL-6 (317×), urokinase-type plasminogen activator (15×), vascular endothelial growth factor (2×) and fractalkine (2.5×) mRNA was significantly elevated 2 h post-exercise. Interleukin-8 (38×) and interleukin-6 (58×) protein was also significantly elevated 2 h post-exercise, while monocyte chemotactic protein-1 protein was significantly elevated at 2 h (22×) and 4 h (21×) post-exercise. Monocyte chemotactic protein-1 and interleukin-8 were expressed by cells residing in the interstitial space between muscle fibers and, in some cases, were co-localized with CD68+ macrophages, PAX7+ satellite cells and blood vessels. However, the patterns of staining were inconclusive and not consistent. Conclusion In conclusion, resistance exercise stimulated a marked increase in the mRNA and protein expression of various chemotactic factors in skeletal muscle. Myofibers were not the dominant source of these factors. These findings suggest that chemotactic factors regulate remodeling/adaptation of skeletal muscle during the early phase of recovery following resistance exercise.

Prevalence of refractive errors among schoolchildren in Shiraz, Iran

PURPOSE To determine the prevalence of refractive errors in Shiraz schoolchildren by age and gender. METHODS For this cross-sectional study, random cluster sampling was carried out from students of the 2008-2009 academic year. After the initial interview, ophthalmic examinations including tests of visual acuity, non-cycloplegic and cycloplegic refraction and binocular vision were performed. Myopia was defined as a spherical equivalent < or =-0.50 dioptre (D), hyperopia as > or =+2.0 D, and astigmatism as a cylinder refraction > or =0.75 D. All values for school grade and gender were directly standardized based on the total student population in the 2008-2009 school year. RESULTS A total of 2130 students were sampled, of which 1872 participated in the study (response rate = 87.88%). The prevalence of uncorrected, best-corrected, presenting and spectacle corrected visual acuity of 6/12 or worse in the better eye was 6.46%, 0%, 1.49% and 0.9%, respectively. The prevalence rates of myopia, hyperopia and astigmatism were 4.35% (95% confidence interval [CI]: 2.89-5.82%), 5.04% (95% CI: 3.50-6.58%), and 11.27% (95% CI: 9.81-12.74%), respectively. Anisometropia was detected in 2.58% of schoolchildren. The prevalence of hyperopia significantly decreased with age (P = 0.021). CONCLUSIONS Compared with other reported rates, the prevalence of myopia in the schoolchildren of Shiraz is similar to that in most places excluding East Asian countries, and that of hyperopia is in the mid range.

Prevalence and risk factors of refractive errors among schoolchildren in Shiraz, Iran

Purpose: To determine the prevalence and risk factors of refractive errors among schoolchildren in Shiraz, Iran. Methods: In a cross-sectional study, using random cluster sampling, 3065 Shiraz schoolchildren were selected in this study. The participants totaled 2683; 1872 elementary and middle school and 811 high school students. For the primary and middle schoolchildren, cycloplegic refraction and for the high school students, non-cycloplegic autorefraction was measured. Myopia, defined as spherical equivalent (SE) refraction -0.50 diopter (D) or worse, hyperopia as SE +2.00D and +0.50D or more for cycloplegic and noncycloplegic refractions respectively, and astigmatism as cylinder -0.75D or worse. Results: The prevalence of refractive errors in elementary and middle school students was: myopia 4.35 % (95% confidence interval (CI), 2.89 -5.81), hyperopia 5.04 % (95%CI, 3.49 -6.58) and astigmatism 11.79 % (95%CI, 10.21 -13.38). For high school students, these rates were 22.4 % (95%CI, 18.44 -26.36), 10.52 % (95%CI, 6.75 -14.29) and 20.99% (95%CI, 16.55 -25.44), respectively.The prevalence of myopia increased with age in primary and middle school students (OR=1.15, 95% CI, 0.98 to1.33, p=0.073). Conclusions: The result of this study indicated a relatively low prevalence of refractive errors among schoolchildren in Shiraz according to the protocol by "Refractive Error Study in Children" (RESC) in other investigations.

Adenosine-5'-carboxylic Acid

The two molecules in the asymmetric unit of adenosine-5'-carboxylic acid, C10H11N5O5, exist as zwitterions with N1 protonated and the carboxyl groups ionized. Both molecules are in an anti conformation with glycosyl torsion angles of -161.4(3) and -155.5(3)degrees. The ribose moieties adopt a C3-endo-C2-exo twist conformation. The pseudo-rotation parameters are P = 0.01(1) and 6.58(1)degrees, and tau(m) = 36.2(2) and 34.6(2)degrees, for molecules A and B, respectively. The carboxyl groups of A and B are not in the standard g(+), g(-) or t conformations. Both Watson-Crick sites, N1 and N6, of the adenine bases are involved in a pair of hydrogen bonds with the dissociated carboxyl groups, forming a cyclic tetramer. The adenine base of molecule A stacks on the ribose O4' atom of a symmetry-related B molecule at a distance of 2.88 Angstrom; the adenine base of B stacks in an analogous way at a distance of 2.91 Angstrom.

Association of methylenetetrahydrofolate reductase gene polymorphisms & colorectal cancer in India

Background & objectives: Methylenetetrahydrofolate reductase (MTHFR) is a critical enzyme in folate metabolism and involved in DNA synthesis, DNA repair and DNA methylation. The two common functional polymorphisms of MTHFR, 677C -> T and 1298 A -> C have shown to impact several diseases including cancer. This case-control study was undertaken to analyse the association of the MTHFR gene polymorphisms 677 C -> T and 1298 A -> C and risk of colorectal cancer (CRC).Methods: One hundred patients with a confirmed histopathologic diagnosis of CRC and 86 age and gender matched controls with no history of cancer were taken for this study. DNA was isolated from peripheral blood samples and the genotypes were determined by PCR-RFLP. The risk association was estimated by compounding odds ratio (OR) with 95 per cent confidence interval (CI). Results: Genotype frequency of MTHFR 677 CC, CT and TT were 76.7, 22.1 and 1.16 per cent in controls, and 74,25 and 1.0 per cent among patients. The 'T' allele frequency was 12.21 and 13.5 per cent in controls and patients respectively. The genotype frequency of MTHFR 1298 AA, AC, and CC were 25.6, 58.1 and 16.3 per cent for controls and 22, 70 and 8 per cent for patents respectively. The 'C' allele frequency for 1298 A -> C was 43.0 and 45.3 per cent respectively for controls and patients. The OR for 677 CT was 1.18 (95% CI 0.59-2.32, P = 0.642), OR for 1298 AC was 1.68 (95% CI 0.92-3.08, P = 0.092) and OR for 1298 CC was 0.45(95% CI 0.18-1.12, P = 0.081). The OR for the combined heterozygous state (677 CT and 1298 AC) was 1.18(95% CI 0.52-2.64, P =0.697).Interpretation & conclusion: The frequency of the MTHFR 677 TT genotype is rare as compared to 1298 CC genotype in the population studied. There was no association between 677 C -> T and 1298 A -> C polymorphisms and risk of CRC either individually or in combination. The homozygous state for 1298 A -> C polymorphism appears to slightly lower risk of CRC. This needs to be confirmed with a larger sample size.

Gas-phase controlled mass transfer in a foam-bed reactor

Gas-phase controlled absorption of ammonia in foams made of solutions of sulphuric acid has been studied experimentally. Effects of gas-phase concentration of ammonia and type of surfactant on the performance of the foam-bed reactor are investigated. Gas-phase controlled absorption from a spherical bubble is anaylzed using the asymptotic value of Sherwood number (Sh = 6.58), for both negligible as well as significant changes in the volume of the bubble. The experimental data are shown to be in good agreement with the single-stage model of the foam-bed reactor using these asymptotic sub-models, as well as the diffusion-in-sphere analysis available in literature. Influence of effective diffusivity on the time dependence of fractional gas absorption has been found to be unimportant for foam columns with large times of contact. The asymptotic sub-models have been compared and use of the rigid-sphere asymptotic sub-model is recommended for foam columns of practical relevence.

Caracterización del sistema de producción de Finca "San Felipe", Muy Muy, Matagalpa

El presente trabajo se realizó dentro del marco del PROYECTO RAZA REYNA CEE NICARAGUA-ONG 157/86/IT con el objetivo de realizar una Caracterización del Sistema de Producción de la finca San Felipe, en Muy Muy, Matagalpa y su entorno. Se realizó a través de Diagnóstico Estático en la zona y Diagnóstico Dinámico en la finca. Se pudo determinar que la zona de vida correspondiente a Muy Muy es de Trópico Seco Premontano, en transición a zona seca, con precipitaciones promedio anual de 1498.05 mm, 25.02°C de temperatura y 80.30% de humedad relativa. Los suelos son millosoles con alto contenido de materia orgánica y nutriente, excepto fósforo; cuya principal limitante la representa la pendiente elevada en la mayor parte de la zona. Se caracteriza por el predominio de sistemas de producción de doble propósito, de carácter extensivo, en los que se explota ganado Cebuino cruzado con Pardo Suizo y Holsteín principalmente la inversión de capital y de recursos es baja. La alimentación del ganado se basa en el pastoreo, habiendo predominio de pasto Jaragua (Hyparrhenia ruffa), en aproximadamente un 50% siendo el resto pasto natural y grama. Entre los principales factores limitantes identificados se puede mencionar el mal manejo proporcionado a los potreros, disminuyendo la calidad y disponibilidad del forraje ofrecido a los animales, unido a una falta total de técnicas de conservación y una suplementación adecuada. Se encontró que la comercialización afecta el .resultado económico de las fincas por los bajos precios obtenidos en la venta de los productos y por el alto precio a que compran los insumos, el cual está influido por: a) débil estructura del mercado sobre todo para la venta de leche, teniendo que vender forzosamente a plantas acopiadoras como PROLACSA; b) elevada presencia de intermediarios en las operaciones de compra-venta de animales en pie; e) lo alejado que se encuentra la zona de los centros industriales del país y d) las malas vías de penetración. Entre los índices técnicos encontrados en la. zona, según resultados de Diagnóstico Estático, se determinó que la natalidad es del 52.25 % la mortalidad de temeros es del 6.58 % el destete efectivo del 93.42 la mortalidad adulta de terneros es del 5.0 en el periodo de lactancia es de 282.43 días, la producción de leche anual por vaca es de 1282.23 lts. La producción de leche por vaca en verano es de 3.44 lts y en invierno es de 5.64, el número de animales por manzana es de 0.98 y la carga animal es de 0.77 UA/mz Respecto al Sistema de Producción de la Finca "Sn Felipe", éste se caracteriza por ser de Doble Propósito, con mayor énfasis en la producción de leche, el hato presenta un alto grado de encaste con ganado Bos taurus lechero, producto de la utilización de Inseminación Artificial, pudiendo encontrarse principalmente Pardo Suizo, así como Holsteín, Jersey, Guernsey, Simmenta1, Cebú y Reyna, con diferentes grados de cruzamientos entre sí. Las medias de mínimos cuadrados para PL305, PL TOT, LARLA e IPP encontradas fueron de 1603.90, 1893.53 Kg de leche, 288.36 y 496.87 días respectivamente. La PLD resulto de 5.56 lts y la PLD/IPP de 3.23 lts. La• EPP es de 37.15 meses y el número de servicios por concepción (NSC) resultó de 1.57. En el estudio de las principales variables los grupos raciales

纤维取向性对短纤维增强复合材料力学性能的影响

<正> 1.前言短纤维增强复合材料的增强机理经过Cool、Dow、Rosen和Hayashi几人采用单根短纤维模型已弄清。并对多根纤维模型进行了一些研究工作,但对它们的增强机理还难解释清楚。关于长纤维取向对纤维增强复合材料力学性能影响的研究,已有报导。本文通过实验阐明短纤维增强复合材料力学性能与纤维方向之间的关系。采用三种类型的试件:单向、双向和随机方向。从其拉伸实验结果可看出在不同的纤维方向上所得到的杨氏模量和拉伸强度有很大差别。断裂表面用扫描电镜观察,认为影响复合材料断裂的主要因素是纵向纤维的特性。此外,我们基于Cox理论的纤维排列模型证明计算结果与实验结果符合。