966 resultados para Critical parameters


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This gaper demonstrates that artificial neural networks can be used effectively for estimation of parameters related to study of atmospheric conditions to high voltage substations design. Specifically, the neural networks are used to compute the variation of electrical field intensity and critical disruptive voltage in substations taking into account several atmospheric factors, such as pressure, temperature, humidity, so on. Examples of simulation of tests are presented to validate the proposed approach. The results that were obtained by experimental evidences and numerical simulations allowed the verification of the influence of the atmospheric conditions on design of substations concerning lightning.

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Digital radiography in the inspection of welded pipes to be installed under deep water offshore gas and oil pipelines, like a presalt in Brazil, in the paper has been investigated. The aim is to use digital radiography for nondestructive testing of welds as it is already in use in the medical, aerospace, security, automotive, and petrochemical sectors. Among the current options, the DDA (Digital Detector Array) is considered as one of the best solutions to replace industrial films, as well as to increase the sensitivity to reduce the inspection cycle time. This paper shows the results of this new technique, comparing it to radiography with industrial films systems. In this paper, 20 test specimens of longitudinal welded pipe joints, specially prepared with artificial defects like cracks, lack of fusion, lack of penetration, and porosities and slag inclusions with varying dimensions and in 06 different base metal wall thicknesses, were tested and a comparison of the techniques was made. These experiments verified the purposed rules for parameter definitions and selections to control the required digital radiographic image quality as described in the draft international standard ISO/DIS 10893-7. This draft is first standard establishing the parameters for digital radiography on weld seam of welded steel pipes for pressure purposes to be used on gas and oil pipelines.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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Using data from a single simulation we obtain Monte Carlo renormalization-group information in a finite region of parameter space by adapting the Ferrenberg-Swendsen histogram method. Several quantities are calculated in the two-dimensional N 2 Ashkin-Teller and Ising models to show the feasibility of the method. We show renormalization-group Hamiltonian flows and critical-point location by matching of correlations by doing just two simulations at a single temperature in lattices of different sizes to partially eliminate finite-size effects.

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The running velocities associated to lactate minimum (V-lm), heart rate deflection (V-HRd), critical velocity (CV), 3000 M (V-3000) and 10000 m performance (V-10km) were compared. Additionally the ability of V-lm and VHRd on identifying sustainable velocities was investigated.Methods. Twenty runners (28.5 +/- 5.9 y) performed 1) 3000 m running test for V3000; 2) an all-out 500 in sprint followed by 6x800 m incremental bouts with blood lactate ([lac]) measurements for V-lm; 3) a continuous velocity-incremented test with heart rate measurements at each 200 m for V-HRd; 4) participants attempted to 30 min of endurance test both at V-lm(ETVlm) and V-HRd(ETVHRd). Additionally, the distance-time and velocity-1/time relationships produced CV by 2 (500 m and 3000 m) or 3 predictive trials (500 m, 3000 m and distance reached before exhaustion during ETVHRd), and a 10 km race was recorded for V-10km.Results. The CV identified by different methods did not differ to each other. The results (m(.)min(-1)) revealed that V-.(lm) (281 +/- 14.8)< CV (292.1 +/- 17.5)=V-10km (291.7 +/- 19.3)< V-HRd (300.8 +/- 18.7)=V-3000 (304 +/- 17.5) with high correlation among parameters (P < 0.001). During ETVlm participants completed 30 min of running while on the ETVHRd they lasted only 12.5 +/- 8.2 min with increasing [lac].Conclusion. We evidenced that CV and Vim track-protocols are valid for running evaluation and performance prediction and the parameters studied have different significance. The V-lm reflects the moderate-high intensity domain (below CV), can be sustained without [lac] accumulation and may be used for long-term exercise while the V-HRd overestimates a running intensity that can be sustained for long-time. Additionally, V-3000 and V-HRd reflect the severe intensity domain (above CV).

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The objective of this study was to determine the critical speed (CS) for track cycling and to assess whether a lactate steady state occurs at this speed. Fourteen competitive cyclists performed the following tests on an official cycling track (333.3 m): 1) incremental test for determination of the intensity corresponding to 4 mM of blood lactate (onset of blood lactate accumulation, OBLA) and maximal oxygen uptake (VO(2)max); 2) CS: 3 maximal bouts for distances of 2, 4 and 6 km executed in random order and with a period of recovery of 40 to 50 min between bouts. CS was determined for each subject from the linear regression between the distance and the time taking to cycle it; 3) Endurance test in which subjects were instructed to pedal at 100% of their individually determined CS for 30 min. At the 10(th) and 30(th) min (or upon exhaustion), 25 mul of blood were collected from ear lobe for later analysis of blood lactate [Lac]b. An increase less than or equal to1 mM between 10 and 30 min of exercise was considered as the criterion for the occurrence of the lactate steady state. CS (49.6 +/- 8.6 ml.kg(-1).min(-1); 36.9 +/- 2.7 km.h(-1)) was significantly higher than OBLA (43.7 8.0 ml.kg(-1).min(-1); 35.24 +/- 2.6 km.h(-1)) although the two parameters were highly correlated (r=0.97). During the endurance test, only 8 of the 14 subjects completed the 30 min period at CS. of these 8 subjects, only 2 presented a lactate steady state. Time to exhaustion at CS was 20.3 +/- 1.6 min for the remaining 6 subjects. The 12 subjects who did not reach a lactate steady state presented mean [Lac]b values of 7.4 +/- 1.3 mM at 10 min and of 9.4 +/- 1.9 mM at the end of the test (exhaustion), characterizing an exercise intensity of high lactacidemia. on the basis of the present results, we can conclude that CS determined by a track cycling test seems to overestimate the intensity of the maximal lactate steady state for most subjects.

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The slope of the distance-time relationship from maximal 200 and 400 in bouts (S(200-400)) has been increasingly employed for setting training intensities in swimming. However, physiological and mechanical responses at this speed are poorly understood. Thus, this study investigated blood lactate, heart rate (HR), stroke rate (SR), stroke length (SL) and RPE responses to an interval swimming set at S(200-400) in trained swimmers. In a 50-m pool, twelve athletes (16.5 +/- 1.2 yr, 176 +/- 7 cm, 68.4 +/- 5.4 kg, and 7.8 +/- 2.5% body fat) performed maximal 200 and 400 m crawl trials for S(200-400) determination (1.28 +/- 0.05 m/s). Thereafter, swimmers were instructed to perform 5 x 400 in at this speed with 1.5 min rest between repetitions. Three athletes Could not complete the set (exhaustion at 21.0 +/- 3.1 min). For the remaining swimmers (total set duration = 32.0 +/- 1.3 min) significant increases) (p < 0.05) in blood lactate (5.7 +/- 0.8-7.9 +/- 2.4 mmol/l), SR (29.6 +/- 3.2-32.1 +/- 4.1 cycles/min), HR (169 +/- 11-181 +/- 8 bpm) and RPE (13.3 +/- 1.6-16.3 +/- 2.6) were observed through the IS. Conversely, SL decreased significantly (p < 0.05) from the first to the fifth repetition (2.48 +/- 0.22-2.31 +/- 0.24 m/cycle). These results suggest that interval swimming at S(200-400) represents an intense physiological, mechanical and perceptual stimulus that can be sustained for a prolonged period by most athletes. (C) 2008 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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Objective: To verify the behavior of the mineral bone content and density in male adolescents according to age and secondary sexual characters. Methods: 47 healthy adolescents between 10 and 19 years old were assessed according to weight, height, body mass index, puberty stage, calcium intake, bone mineral density and content in the lumbar spine and in the proximal femur. The bone mass was measured through bone densitometries. The intake of calcium was calculated through a 3-day diet. The BMI (body mass index) was calculated with the Quetelet Index and the puberty stage was defined according to Tanner's criteria. The analysis used descriptive statistics such as average and standard deviation, and variance estimates to compare the different age groups. Moreover, the Tukey test was used to determine the significant differences. Results: It was evident that the calcium intake in the different ages assessed has not reached the minimum value of 800 mg. The bone mineral density and content showed an increase after the age of 14, as well as when the teenagers reached the sexual maturation stage G4. The mineralization parameters showed a high level when the teenagers were in the G3 stage, however, without statistical significance. Conclusion: The results indicate an important level of bone mineralization during adolescence. Maturation levels superior to G3 have shown more mineralization. This study proves that the critical years for bone mass gain start after the 14-15 years old or older. Copyright © 2004 by Sociedade Brasileira de Pediatria.

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It is known that during sex differentiation, fetal androgens are critical determinants of the male phenotype. Although testosterone is necessary for normal development of male sexual behavior, perinatal androgen treatment can result in disruption of normal male sexual reproduction. Pregnant Wistar rats were administered either corn oil (vehicle) or testosterone propionate at 0.2 mg/kg from gestational day 12 until the end of lactation and the reproductive function of male offspring was evaluated at 90 (adulthood) and 270 (middle age) days of age. Perinatal androgenization in the rat provoked a reduction in sperm production and reserves in adulthood that did not affect fertility and did not persist at more advanced ages, as shown by the results at post-natal day 270. If perinatal androgenization promotes similar effects in humans of reproductive age, the results of the present work can impact male reproduction health, given the less efficient spermatogenesis and lower sperm reserves in the human epididymis, compared to rodents. © Georg Thieme Verlag KG Stuttgart. New York.

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