Estudios de la edad y crecimiento de la Sardina Sardinops sagax sagax de la region central del Perú

En el presente trabajo se estima la edad y crecimiento de sardina, sardinops Sagax Sagax en la región central del Perú durante 1980, mediante la lectura directa de otolitos por contaje de anillos de crecimiento y por retrocálculo en las medidas de las mismas estructuras. Para determinar la edad, se ha seguido la evolución de la naturaleza del borde del otolito, así como también se realizaron mediciones de cada anillo de crecimiento y se estableció la proporcionalidad entre el incremento en longitud del otolito (R) y del pez (L), resultando la ecuación siguiente: L = - 1.032 + 15.174 R Las expresiones que describen el crecimiento en longuitud según el modelo de Van Bertalanffy, se señalan a continuación: Por contaje de anillos: L = 39.8 [1 - e-.22 (t+0.84) ] Por retrocálculo: L = 37.49 [1 - e-.22(t+ o.71)] La relación de la edad con las tallas de captura determinan que la pesquería de consumo durante 1980, estuvo constituida mayormente por ejemplares adultos de 4, 5 y 6 años de edad; análogamente en la pesquería industrial predominaron los individuos jóvenes (edades O, 1 y 2).

On the short-time behavior of the implied volatility for jump-diffusion models with stochastic volatility

In this paper we use Malliavin calculus techniques to obtain an expression for the short-time behavior of the at-the-money implied volatility skew for a generalization of the Bates model, where the volatility does not need to be neither a difussion, nor a Markov process as the examples in section 7 show. This expression depends on the derivative of the volatility in the sense of Malliavin calculus.

Três métodos de cálculo do DRIS para avaliar o potencial de resposta à adubação de árvores de eucalipto

O objetivo deste trabalho foi testar o efeito de três métodos de cálculo do DRIS no diagnóstico nutricional de árvores de eucalipto, resultantes da interpretação dos índices pelo método do potencial de resposta à adubação. Para tanto, foram obtidas informações dos teores dos nutrientes em quatro órgãos (folhas, galhos, casca e lenho) de 1.986 árvores de híbridos de Eucalyptus grandi s x E. urophylla, coletadas, entre os anos de 1988 a 1994, de talhões comerciais pertencentes à Aracruz Celulose S.A. e cultivados no Espírito Santo e no sul da Bahia, utilizando os métodos de Jones, Elwali & Gascho e da Faixa de Beaufils. Dentre os métodos testados, o das Faixas de Beaufils mostrou-se o mais conservador e muito semelhante ao método de Elwali & Gascho quanto à freqüência de nutrientes considerados deficientes. O método de Jones foi o que apresentou maior freqüência de nutrientes considerados deficientes, não se tendo observado, entretanto, efeito da seleção das relações no cálculo dos índices DRIS sobre a freqüência de nutrientes considerados deficientes. A utilização do critério do potencial de resposta à adubação para a interpretação dos índices DRIS conduz a resultados semelhantes entre os métodos, de forma que qualquer deles poderia vir a ser utilizado com relativa segurança, sem grandes conseqüências no diagnóstico nutricional da maioria dos nutrientes e das situações.

Variability in urinary oxalate measurements between six international laboratories.

BACKGROUND: Hyperoxaluria is a major risk factor for kidney stone formation. Although urinary oxalate measurement is part of all basic stone risk assessment, there is no standardized method for this measurement. METHODS: Urine samples from 24-h urine collection covering a broad range of oxalate concentrations were aliquoted and sent, in duplicates, to six blinded international laboratories for oxalate, sodium and creatinine measurement. In a second set of experiments, ten pairs of native urine and urine spiked with 10 mg/L of oxalate were sent for oxalate measurement. Three laboratories used a commercially available oxalate oxidase kit, two laboratories used a high-performance liquid chromatography (HPLC)-based method and one laboratory used both methods. RESULTS: Intra-laboratory reliability for oxalate measurement expressed as intraclass correlation coefficient (ICC) varied between 0.808 [95% confidence interval (CI): 0.427-0.948] and 0.998 (95% CI: 0.994-1.000), with lower values for HPLC-based methods. Acidification of urine samples prior to analysis led to significantly higher oxalate concentrations. ICC for inter-laboratory reliability varied between 0.745 (95% CI: 0.468-0.890) and 0.986 (95% CI: 0.967-0.995). Recovery of the 10 mg/L oxalate-spiked samples varied between 8.7 ± 2.3 and 10.7 ± 0.5 mg/L. Overall, HPLC-based methods showed more variability compared to the oxalate oxidase kit-based methods. CONCLUSIONS: Significant variability was noted in the quantification of urinary oxalate concentration by different laboratories, which may partially explain the differences of hyperoxaluria prevalence reported in the literature. Our data stress the need for a standardization of the method of oxalate measurement.

Accurate memory for object location by individuals with intellectual disability: Absolute spatial tagging instead of configural processing?

Using head-mounted eye tracker material, we assessed spatial recognition abilities (e.g., reaction to object permutation, removal or replacement with a new object) in participants with intellectual disabilities. The "Intellectual Disabilities (ID)" group (n=40) obtained a score totalling a 93.7% success rate, whereas the "Normal Control" group (n=40) scored 55.6% and took longer to fix their attention on the displaced object. The participants with an intellectual disability thus had a more accurate perception of spatial changes than controls. Interestingly, the ID participants were more reactive to object displacement than to removal of the object. In the specific test of novelty detection, however, the scores were similar, the two groups approaching 100% detection. Analysis of the strategies expressed by the ID group revealed that they engaged in more systematic object checking and were more sensitive than the control group to changes in the structure of the environment. Indeed, during the familiarisation phase, the "ID" group explored the collection of objects more slowly, and fixed their gaze for a longer time upon a significantly lower number of fixation points during visual sweeping.