The validity of critical speed determined from track cycling for identification of the maximal lactate steady state

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.

Durango apatite fission-track dating using length-based age corrections and neutron fluence measurements by natural thorium thin films and natural U-doped glasses calibrated through natural uranium thin films

In this work, we present an approach for neutron fluence measurements based on natural thorium thin films and natural uranium-doped glasses calibrated through natural uranium thin films to be used for dating with the Fission-Track Method (FTM). This neutron dosimetry approach allows the employment of FTM even when dating is carried out using low neutron themalization facilities. Besides, it makes possible the determination of the Th/U ratio of the mineral to be dated. Durango apatite which is often employed in FTM as an age standard was analyzed. This apatite presented a fairly high Th/U ratio, 29.9 +/- 1.7. Th fissions were 18%, 12% and 10% of the total for irradiations where thermal to fast neutron flux ratios were 2.4, 4.4 and 5,2, respectively. These results show that Th fission must be considered for this apatite, when not well-thermalized irradiation facilities are used. The ratio between spontaneous and induced track length, L(S)/L(1), close to 0.89, indicates a certain amount of rejuvenation of the age of Durango apatite. Therefore, its apparent age should be corrected, the application of a technique based on track-length measurements produced a corrected age of 29.7 +/- 1.1 Ma, consistent with the independent reference age of this apatite (31.4 +/- 0.5 Ma). This result represents a support for viability of the neutron dosimetry approach studied in this work for FTM.(C) 2002 Elsevier B.V. B.V. All rights reserved.

The IFUSP race-track microtron booster accelerator end magnets antisymmetric perturbations

We will present measurements and calculations related to the antisymmetric perturbations, and comparisons with the symmetric ones, of the IFUSP race-track microtron booster accelerator end magnets. These perturbations were measured in planes situated at +/-12 mm of the middle plane, in a gap height of 4 cm, for a field distribution of about 0.1 T. The measurements were done in 1170 points, separated by a distance of 8 mm, using an automated system with a +/-1.5 mu T differential Hall probe. The race-track microtron booster is the second stage of the 30.0 MeV electron accelerator under construction at the Linear Accelerator Laboratory in which the required uniformity for the magnetic field is of about 10(-3). The method of correction employed to homogenize the IFUSP race-track microtron booster accelerator magnets assures uniformity of 10(-5) in an average field of 0.1 T, over an area of 700 cm(2). This method uses the principle of attaching to the pole pieces correction coils produced by etching techniques, with copper leads shaped like the isofield lines of the normal component of the magnetic field measured. The ideal planes, in which these measurements are done, are calculated and depend on the behavior of the magnetic field perturbations: symmetric or antisymmetric with reference to the middle plane of the magnet gap. These calculations are presented in this work and show that for antisymmetric perturbations there is no ideal plane for the correction of the magnetic field; for the symmetric one, these planes are at +/-60% of the half gap height, from the middle plane. So this method of correction is not feasible for antisymmetric perturbations, as will be shown. Besides, the correction of the symmetric portion of the field distribution does not influence the antisymmetric one, which almost does not change, and corroborates the theoretical predictions. We found antisymmetric perturbations of small intensity only in one of the two end magnets. However, they are not detected at +/- 1 mm of the middle plane and will not damage the electron beam.

The use of apatite fission track thermochronology to constrain fault movements and sedimentary basin evolution in northeastern Brazil

An apatite fission track study of crystalline rocks underlying sedimentary basins in northeastern Brazil indicate that crustal blocks that occur on opposite sides of a geological fault experienced different thermal histories. Samples collected on the West block yielded corrected fission-track ages from 140 to 375 Ma, whereas samples collected on the East block yielded ages between 90 and 125 Ma. The thermal models suggest that each block experienced two cooling events separated by a heating event at different times. We concluded that the West block moved downward relative to the East block ca. 140 Ma ago, when sediments eroded from the East side were deposited on the West side. This process represents the early stage of sedimentary basin formation and the opening of the South Atlantic Ocean in the region. Downward and upward movements related to heating and cooling events of these crustal blocks at different periods until recent times are proposed. (c) 2005 Elsevier Ltd. All rights reserved.

On epidote fission track dating

The use of epidote in fission track dating was abandoned since the beginning of the 1980s due to difficulties like absence of a standard etching procedure, obtainment of different closure temperatures and the percentage of the datable samples. The results become much more reproducible when restricting fission track analysis to a peculiar kind of track. We are also studying confined track length, what makes possible to obtain information about fossil track annealing. Fission tracks in epidote were successfully etched with 48% HF at 35 degrees C for 12.5 min. Dating samples by the external detector method was not possible due to problems in measuring the efficiency factor held between the number of fossil fission tracks and tracks induced in mica. Dating a sample from Brejui, RN, Brazil with the population method gave a corrected age of 510 +/- 69Ma, in agreement with published U/Th-Pb ages. From the fact that the fossil track length histogram was bimodal, we were able to infer that this sample registered a thermal episode during its history.These preliminary results indicate that epidote deserves further studies to establish whether it can be employed as a thermochronological tool. (c) 2005 Elsevier Ltd. All rights reserved.

Recognition of Cretaceous, Paleocene, and Neogene tectonic reactivation through apatite fission-track analysis in Precambrian areas of southeast Brazil: Association with the opening of the south Atlantic Ocean

Apatite fission-track analysis was used for the determination of thermal histories and ages in Precambrian areas of southeast Brazil. Together with geological and geomorphologic information, these ages enable us to quantify the thermal histories and timing of Mesozoic and Cenozoic epirogenic and tectonic processes. The collected samples are from different geomorphologic blocks: the high Mantiqueira mountain range (HMMR) with altitude above 1000 m, the low Mantiqueira mountain range (LMMR) under 1000 m, the Serra do Mar mountain range (SMMR), the Jundiá and Atlantic Plateaus, and the coastline, all of which have distinct thermal histories. During the Aptian (∼120 Ma), there was an uplift of the HMMR, coincident with opening of the south Atlantic Ocean. Its thermal history indicates heating (from ∼60 to∼80 °C) until the Paleocene, when rocks currently exposed in the LMMR reached temperatures of ∼100 °C. In this period, the Serra do Mar rift system and the Japi erosion surface were formed. The relief records the latter. During the Late Cretaceous, the SMMR was uplifted and probably linked to its origin; in the Tertiary, it experienced heating from ∼60 to ∼90 °C, then cooling that extends to the present. The SMMR, LMMR, and HMMR were reactivated mainly in the Paleocene, and the coastline during the Paleogene. These processes are reflected in the sedimentary sequences and discordances of the interior and continental margin basins. © 2002 Elsevier Science Ltd. All rights reserved.

Method for estimating railroad track settlements due to dynamic traffic loads

This paper is the result of real-scale physical modeling study designed to simulate the load-deformation characteristics of railroad foundation systems that include the railroad ties, the ballast, and the sub-base layers of a railroad embankment. The study presents comparisons of the application of dynamic loads of 100kN on the rails, and the resulting deformations during a 500,000 cycle testing period for three rail support systems; wood, concrete and steel. The results show that the deformation curve has an exponential shape, with the larger portion of the deformation occurring during the first 50,000 load cycles followed by a tendency to stabilize between 100,000 to 500,000 cycles. These results indicate that the critical phase of deformations of a new railroad is within the first 50,000 cycles of loading, and after that, it slowly attenuates as it approaches a stable value. The paper also presents empirically derived formulations for the estimation of the deformations of the rail supports as a result of rail traffic.

Evaluation of race distance, track surface and season of the year on exercise-induced pulmonary haemorrhage in flat racing Thoroughbreds in Brazil

Reasons for performing study: To our knowledge no studies evaluating risk factors to EIPH have been undertaken with such a population of horses in Brazil, which is one of the few countries in the racing community to accept the use of frusemide (FUR) as a prerace medication for bleeders. We also compared national results with those already in the literature. Objectives: To verify the influence of variables such as distance of the race, racetrack surface, going and season of the year in the recurrence and severity of EIPH and its effect on the finishing position of flat racing Thoroughbreds in Brazil. Methods: 2118 post race respiratory endoscopies were recorded, in a total of 1003 individual horses. All horses in the study were certified bleeders (deemed positive by registered veterinarians following one or more endoscopies) and were administered FUR prior to each race. Data was analysed using both ordinary logistic regression and multiple logistic regression. Results: The results suggest that race distance, season of the year and racetrack surface affect the recurrence of EIPH. Also, despite the use of FUR, the majority (62%) of horses continued to display some degree of haemorrhage. Conclusions: There was a tendency for horses that remained positive despite the use of FUR to finish unplaced in a race. Horses which had a significant reduction in bleeding and became HPIE negative after the use of FUR, tended to finish in top positions. It was not possible to determine a pattern of severity of EIPH in horses with more than one endoscopy. Further studies are required to improve our understanding of this syndrome and its correlations to performance in the racing Thoroughbred, together with the role of FUR and its possible enhancing performance effects and efficacy in consistently diminishing EIPH. Potential relevance: This study enabled a better understanding of the use of FUR in Brazilian Thoroughbred racehorses and showed there was a tendency towards improvement in performance after administrion of FUR in bleeders. The fact that a large number of horses remained positive for EIPH despite the use of FUR should encourage the scientific community to search for better ways of reducing, or preventing, this syndrome. © 2006 EVJ Ltd.

Experimental study of a methodology for Fission-track Dating without neutron irradiation

To carry out the dating by the Fission Track Method (FTM) the international community that works with this method employs methodologies in which the mineral to be dated must be irradiated with neutrons. Such irradiation, performed in a nuclear reactor, demand a relatively long waiting time so that the activity of the sample attain a proper level for handling. The present work aims to establish a methodology that makes possible the dating by FTM using a mass spectrometer instead of a nuclear reactor. This methodology was applied to apatite samples from Durango, Mexico. © 2009 Elsevier Ltd. All rights reserved.

Geotechnical and structural behavior of the railroad track in large-scale apparatus

This paper analyses the static and dynamic behavior of the railroad track model in laboratory. Measurements of stresses and strains on a large-scale railroad track apparatus were studied. The model includes: compacted soil, representing the final layers of platform, ballast layer, and ties (steel, wooden, and pre-stressed concrete). The soil and soil ballast interface were instrumented with pneumatic stress gauge. Settlement measurement device were positioned at the same levels as the load cells. Loads were applied by hydraulic actuators, statically and dynamically. After the prescribed number of load cycles, in pre-determined intervals, stresses and strains were measured. Observations indicate that stress and strain distributions, transmitted by wooden or steel ties, behave similarly. A more favorable behavior was observed with pre-stressed concrete mono block ties. Non-linear response was observed after a threshold numbers of cycles were surpassed, showing that the strain modulus increases with the numbers of cycles. © 2009 IOS Press.

Molecular Dynamics simulations of track formation at different ensembles

A series of Molecular Dynamics simulations of thermal spikes has been run in zircon. For two different ensembles: microcanonical one and a combination of microcanonical one acting on the simulation core with Langevin one on the side walls of simulation. Depending on the used ensemble, different track-formation threshold energies were found. When the combined ensemble is carried out, the total energy of the simulations varies with the temperature which can influence how annealing fission-track models should deal with the lattice recovery. A fission-track annealing model is tested with the simulation results. © 2012 Elsevier Ltd. All rights reserved.

Extrapolation of zircon fission-track annealing models

One of the purposes of this study is to give further constraints on the temperature range of the zircon partial annealing zone over a geological time scale using data from borehole zircon samples, which have experienced stable temperatures for ∼1 Ma. In this way, the extrapolation problem is explicitly addressed by fitting the zircon annealing models with geological timescale data. Several empirical model formulations have been proposed to perform these calibrations and have been compared in this work. The basic form proposed for annealing models is the Arrhenius-type model. There are other annealing models, that are based on the same general formulation. These empirical model equations have been preferred due to the great number of phenomena from track formation to chemical etching that are not well understood. However, there are two other models, which try to establish a direct correlation between their parameters and the related phenomena. To compare the response of the different annealing models, thermal indexes, such as closure temperature, total annealing temperature and the partial annealing zone, have been calculated and compared with field evidence. After comparing the different models, it was concluded that the fanning curvilinear models yield the best agreement between predicted index temperatures and field evidence. © 2012 Elsevier Ltd. All rights reserved.

Zircon fission track and U-Pb dating methods applied to São Paulo and Taubaté Basins located in the southeast Brazil

Zircon samples from the Cenozoic São Paulo and Taubaté Basins and Mantiqueira Mountain Range (southeast Brazil) were concomitantly dated by zircon Fission Track Method (FTM) and in situ U-Pb dating method. While FTM detrital-zircon data are ideally used to provide low-temperature information, U-Pb single detrital grain ages record the time of zircon formation in igneous or high grade metamorphic environments. This methodology may be used to study the possible sources of the basins sediments. The results suggest that the São Paulo Basin is composed of sediments from just one source, the Mantiqueira Mountain Range. On the other hand, the Taubaté Basin presents further sediment sources besides the Mantiqueira Mountain Range. © 2012 Elsevier Ltd. All rights reserved.

Further investigation of the initial fission-track length and geometry factor in apatite fission-track thermochronology

The external detector method (EDM) is a widely used technique in fission track thermochronology (FTT) in which two different minerals are concomitantly employed: spontaneous tracks are observed in apatite and induced ones in the muscovite external detector. They show intrinsic differences in detection and etching properties that should be taken into account. In this work, new geometry factor values, g, in apatite, were obtained by directly measuring the ρed/ρis ratios and independently determined [GQR]ed/is values through the measurement of projected lengths. Five mounts, two of which were large area prismatic sections and three samples composed of random-orientation pieces have been used to determine the g-values. A side effect of applying EDM is that the value of the initial confined induced fission track, L0, is not measured in routine analyses. The L 0-value is an important parameter to quantify with good confidence the degree of annealing of the spontaneous fission tracks in unknown-age samples, and is essential for accurate thermal history modeling. The impact of using arbitrary L0-values on the inference of sample thermal history is investigated and discussed. The measurement of the L0-value for each sample to be dated using an extra irradiated apatite mount is proposed. This extra mount can be also used for determining the g value as an extension of the ρed/ρis ratio method. Eight apatite samples from crystalline basement, with grains at random orientation, were used to determine the g-values. The results found are statistically in agreement with the values found for apatite samples (from Durango, Mexico) measured in prismatic section and also measured at random orientation. There was no observable variation in efficiency regarding crystal orientation, showing that it is relatively safe using non-prismatic grains, especially in samples with paucity of grains, as it is the case of most basin samples. Implications for the ζ-calibration and for the calibration of the direct (spectrometer-based) fission-track dating are also discussed.

Evolution of the South Atlantic passive continental margin in southern Brazil derived from zircon and apatite (U-Th-Sm)/He and fission-track data

The area between São Paulo and Porto Alegre in southeastern Brazil plays a key area to understand and quantify the evolution of the South Atlantic passive continental margin (SAPCM) in Brazil. In this contribution, we present new thermochronological data attained by fission-track and (U-Th-Sm)/He analysis on apatites and zircons from metamorphic, sedimentary and intrusive rocks. The zircon fission-track ages range between 108.4 (15.0) and 539.9 (68.4). Ma, the zircon (U-Th-Sm)/He ages between 72.9 (5.8) and 525.1(2.4). Ma, whereas the apatite fission-track ages range between 40.0 (5.3) and 134.7 (8.0). Ma, and the apatite (U-Th-Sm)/He ages between 32.1 (1.5) and 93.0 (2.5). Ma. The spatial distribution of these ages shows three distinct blocks with a different evolution cut by old fracture zones. While the central block exhibits an old stable block, the Northern and especially the Southern block underwent complex post-rift exhumation. The sample of the Northern block shows two distinct cooling phases in the Upper Cretaceous and the Paleogene to Neogene. After sedimentation of the Permian sandstones the samples of the Central block were never heated up over 100. °C with a following moderate to fast cooling phase in Cretaceous to Eocene time and a fast cooling between Oligocene to Miocene. The five thermal models obtained in the Southern block indicate a complex evolution with three cooling phases. The exhumation events of the three blocks correspond with the Paraná-Etendekka event, the alkaline intrusions due to the Trinidad hotspot, and the evolution of the continental rift basins in SE Brazil and are, therefore, most likely to be the major force for the post-rift evolution of the passive continental margin in SE Brazil, which therefore corresponds to the three main phases of the Andean orogeny. © 2013 Elsevier B.V.