Estimación de la capacidad productiva de la estación en bosques secundarios costarricences

Site quality was assessed in four secondary forests dominated by the commercially important tree species Vochysia ferruginea in Northern Costa Rica. A variation of the site quality concept known as site form (i.e. the expected mean height at 25 cm dbh) was used. Twenty-nine sample plots (20 × 20 m) were installed covering soil and topographic variation within and between sites. Site form was estimated for each plot using a linear model. The site form estimations show a high variation between plots (from 16.2 m to 32.2 m), which could indicate large variation in site productivity. Site form of V. ferruginea was significantly correlated with total stand basal area of all species, which supports the potential value of site form as an indicator of site productivity. Twenty-six physical and chemical soil variables showed significant correlation with site form. Adjusted multiple regression models of site form on soil variables were fitted by stepwise regression analysis (forward selection method). The best fit was obtained using only the percentage of sand at 12-30 cm as the independent variable (r2 = 59.3%, s.e.= 3.0 m). The results of this study suggest that site form appears to be a potentially useful indicator of site quality in broadleaved neotropical secondary rainforests when age is unknown.En el presente artículo se presentan los resultados de la evaluación de la calidad de la estación en cuatro bosques secundarios dominados por Vochysia ferruginea en Costa Rica. Como índice de la capacidad productiva de la estación se utilizó el índice de forma (i.e. la altura media esperada a un diámetro a la altura del pecho de 25 cm). Con tal fin se instalaron en campo 29 parcelas (20 × 20 m) de forma tal que cubrieran el rango de variabilidad edáfica y topográfica presente en el área de estudio. El índice de forma presentó una alta variabilidad entre parcelas (entre 16,2 m y 32,2 m), lo cual indica una importante variación en términos de productividad de la estación. El índice de forma de V. ferruginea resultó correlacionado significativamente con el área basimétrica de todas las especies, así como con 26 variables del suelo, quedando entonces respaldado el valor del índice de forma como indicador del rodal de la productividad. Se han ajustado modelos de regresión múltiple entre el índice de forma y las variables edáficas, utilizado el método de inclusión de variable paso a paso. El mejor ajuste se obtuvo al incluir únicamente como variable explicativa el porcentaje de arena en el suelo a una profundidad entre 12-30 cm (r2 = 59,3%, e.e. = 3,0 m). Los resultados del trabajo muestran la potencialidad del índice de forma como indicador de la calidad de estación en los bosques secundarios húmedos neotropicales cuando la edad no es conocida

Deaths due to oral cancer in Chile in the period 2002-2012

Indexación: Scopus; Scielo.Background: Oral cancer is the 15th most common cause of cancer death in the world. In Chile, 1% of all cancer deaths are related to oral and pharyngeal cancer. Aim: To determine mortality rates for oral cancer in Chile and its regions between 2002-2012. Material and Methods: Deaths and their causes between the years 2002-2012 were obtained from the Chilean National Statistics Institute. Crude and adjusted rates by age and sex were calculated for the country and its regions. The denominator was Chilean population on June 30, 2012 and the WHO standard population. Results: In the period studied, 1,611 individuals with a mean age of 67.6 years (63% men) died because of oral cancer. The most common location of the tumor was the tongue in 27% of cases and the parotid gland in 16%. The adjusted mortality rate in Chile was 0.85/100,000 inhabitants (1.13 and 0.58 in men and women, respectively). The regions with the highest rates were Antofagasta (1.51), Aysén (1.22) and Magallanes (1.17). Deaths among men occurred at younger ages than women. Conclusions: Mortality rates due to oral cancer in Chile are lower than abroad. The highest rates observed in some regions may be influenced by environmental factors such as arsenic contamination in Antofagasta and the lack of specialists and specialized care centers in Aysén and Magallanes. © 2018, Sociedad Medica de Santiago. All rights reserved.https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0034-98872018000400487&lng=en&nrm=iso&tlng=e

A Cytochemical Scanning Electron Microscopy Study of Non-Specific Acid Esterase and Acid Phosphatase Activities in Human Peripheral Blood Lymphocytes

We analyzed the distribution patterns of nonspecific acid esterase and acid phosphatase activities with cytochemistry-scanning electron microscopy in backscattered and secondary electron imaging modes in isolated normal human peripheral blood lymphocytes . The analysis of non-specific acid esterase activity in the backscattered electron imaging mode showed, in some cells, focal distribution with a well-defined, homogenous deposit. Two patterns of acid phosphatase activity were evident with the backscattered electron imaging mode, i.e., focal and granular. Peripheral blood lymphocytes showing focal activity of both enzymes presented a smooth surface with few scattered microvilli as seen with the secondary electron imaging mode ; while lymphocytes with a granular pattern of acid phosphatase activity had abundant microvilli . The correlation between patterns of enzymatic activity as seen in backscattering electron imaging mode, and surface morphological features as seen with secondary electron imaging mode, distinguished a subpopulation of lymphocytes of T lineage in human peripheral blood

Geometric Phases and Mielnik's Evolution Loops

The cyclic evolutions and associated geometric phases induced by time-independent Hamiltonians are studied for the case when the evolution operator becomes the identity (those processes are called {\it evolution loops}). We make a detailed treatment of systems having equally-spaced energy levels. Special emphasis is made on the potentials which have the same spectrum as the harmonic oscillator potential (the generalized oscillator potentials) and on their recently found coherent states.Comment: 11 pages, harvmac, 2 figures available upon request; CINVESTAV-FIS GFMR 11/9

Sphere rolling on the surface of a cone

We analyse the motion of a sphere that rolls without slipping on a conical surface having its axis in the direction of the constant gravitational field of the Earth. This nonholonomic system admits a solution in terms of quadratures. We exhibit that the only circular of the system orbit is stable and furthermore show that all its solutions can be found using an analogy with central force problems. We also discuss the case of motion with no gravitational field, that is, of motion on a freely falling cone.Comment: 12 pages, 2 figures, to be published in Eur J Phy

Evaluation of Risk and Preventive Factors for Necrotizing Enterocolitis in Premature Newborns. A Systematic Review of the Literature.

Necrotizing enterocolitis (NEC) is a serious condition related to prematurity and the initiation of enteral feeding. In this article, we review the evidence published in recent years on necrotizing enterocolitis risk factors (prematurity, feeding with low-weight formula, existence of intestinal dysbiosis) and protective factors (human milk or donated milk supply, supplementation of human milk with oligosaccharides, probiotics administration, and the determination of disease predictive biomarkers). A systematic review was conducted of preventive, risk and predictive factors for necrotizing enterocolitis in neonates prior to 37 weeks’ gestational age, based on a literature search for clinical trials, meta-analyses, randomized controlled trials and systematic reviews published betweenJanuary2018andOctober2021.Forthispurpose,thePubMed,MEDLINE,and Cochrane Library databases were consulted. The literature search obtained 113 articles, of which 19 were selected for further analysis after applying the inclusion and exclusion criteria. The conclusions drawn from this analysis were that adequate knowledge of risk factors that can be prevented or modified (such as alteration of the intestinal microbiota, oxidative stress, metabolic dysfunction at birth, or alteration of the immunity modulation) can reduce the incidence of NEC in premature infants. These factors include the supplementation of enteral nutrition with human milk oligosaccharides (with prebiotic and immunomodulatory effects), the combined administration of probiotics (especially the Lactobacillus spp and Bifidobacterium spp combination, which inhibits bacterial adhesion effects, improves the intestinal mucosa barrier function, strengthens the innate and adaptive immune system and increases the secretion of bioactive metabolites), the supplementation of human milk with lactoferrin and the use of donated milk fortified in accordance with the characteristics of the premature newborn. The determination of factors that can predict the existence of NEC, such as fecal calprotectin, increased TLR4 activity, and IL6 receptor, can lead to an early diagnosis of NEC. Although further studies should be conducted to determine the values of predictive biomarkers of NEC, and/or the recommended doses and strains of probiotics, lactoferrin or oligosaccharides, the knowledge acquired in recent years is encouraging

Effect of wheel track on the density and composition of weeds in a maize crop

El objetivo de este estudio fue analizar si la compactación producida por la rodada del tractor durante las operaciones de siembra influye en la composición y densidad de malas hierbas en cultivo de maíz. Para ello se llevó a cabo el conteo e identificación de las especies presentes en 160 unidades muestrales localizadas en la interlínea de cultivo, de las cuales la mitad estaba afectada por la rodada del tractor y la otra mitad no. El contraste de medias entre los datos con rodada y sin rodada para la riqueza de especies, densidad total y densidad por especies se realizó mediante el test de Mann-Whitney. Los resultados han puesto de manifiesto que las especies principales, a excepción de “Cyperus rotundus”, fueron significativamente más abundantes en las interlíneas con rodada. En relación a la comunidad arvense, ésta fue igualmente más diversa y abundante en las interlíneas con rodada.The aim of this study was to analyze whether the compaction caused by the tractor during sowing operations affects the composition and density of the weed flora in maize crops. For that, 160 sample units were taken in the crop interline, where half of them were affected by the tractor tread and the other half not. In each sampling unit we carried out the count and identification of weed species. The Mann-Whitney test was performed to contrast differences in species richness, total and individual species densities between tractor-tread and not tractor-tread data. The results revealed that the main species, except for “Cyperus rotundus” were significantly more abundant in the interline with tractor tread. In relation to the weed community, it was also more diverse and abundant in the interline with tractor tread