Back Extrapolation Method Research Articles

A Study of Recrystallization Behavior of Two Ni-Cu–Containing High-Strength Steels with Different Mn Contents

Abstract The Defence Metallurgical Research Laboratory (DMRL) has been investigating several high-strength and high-toughness steels in the past few decades for various defense applications. As a part of this work, two novel low-carbon steels—each containing 4–6 wt% Ni + Cu of similar strength level, one with high Mn (∼1 wt%) and one with low Mn (∼0.3 wt%)—were investigated. In order to optimize the rolling schedules during production, it is necessary to understand the recrystallization behavior of these two steels during hot deformation. Usually, the recrystallization behavior of materials that do not undergo phase transformations (viz. aluminum, copper, etc.) is commonly studied using microstructural techniques for identification of fraction of recrystallized grains. But, as the steels in the present study undergo phase transformation wherein the austenitic structure at deformation temperature is transformed to martensitic/bainitic structure during cooling, it is challenging to track the recrystallization process directly from the microstructure. Therefore, the recrystallization behavior was investigated by conducting double-hit compression tests (DHCTs) using Gleeble. Fractional softening values were determined from DHCT data using various methods, such as the offset method, back-extrapolation method, and mean flow stress method. The mean flow stress method was found to be more reliable and thus was adopted in this study. The effects of different deformation temperature (850°C–1,050°C) and intermediate static recrystallization time (ISRT) (10, 100, and 500 s) on fractional softening were studied. Temperature for 50 % recrystallization (T0.5), determined as the temperature for 50 % fractional softening, was seen to reduce with an increase in ISRT. Steel with lower manganese content showed relatively lower fractional softening values and thus relatively higher T0.5, as compared with that for the steel with higher manganese content, for all three ISRTs.

Effects of different land-use systems (grazing and understory cultivation) on growth and yield of semi-arid oak coppices

The present study examines the extent of negative effects of traditional multiple land-use systems on oak coppices, from a forest management point of view. The study area was located in approximately 10,000 ha of hilly Brant’s oak (Quercus brantii Lindl.) woodlands in the central Zagros Mountains. In the same site-quality class, three land-use systems were compared: simple coppice (Co), coppice in conjunction with small ruminant grazing (CoG), and coppice with understory rain-fed wheat cultivation plus grazing (CoCG). Data on total wood volume of trunk and major branches, and annual ring growth, were collected and analyzed from 74 stands in 15 coppiced woodland patches. The results showed the advantage of Co over CoG and CoCG land-uses by 43 and 60 m3 of mean accumulated wood volume per hectare, respectively. The diameter growth analysis also revealed an annual increase in wood production of trees in Co land-uses over 43 years, with an exception of the recent decade, when growth coincided with a severe drought. Using a back-extrapolation method, the minimum rotation age of woodlands in Co land-use was found to be 23.6 years, 5 and 7 years shorter than those of CoG and CoCG land-uses, respectively. Unlike CoCG, woodlands located in Co and CoG land-use systems demonstrated a high level of agreement with self-thinning rule of − 3/2. Values for the stand density index for coppiced oak woodlands were between more than 1000 for the least disturbed (Co) and less than 400 for the most disturbed woodlands (CoCG). The structure and growth rate of the coppiced oak woodlands were irreversibly disrupted by understory tillage plus grazing and in less extent by grazing alone. It was concluded that ending undergrowth cultivation in semi-arid oak coppices should be addressed as a priority by adopting minimum regulations.

The Reliability of Measuring Gross Efficiency During High-Intensity Cycling Exercise.

To evaluate the reliability of calculating gross efficiency (GE) conventionally and using a back extrapolation (BE) method during high-intensity exercise (HIE). A total of 12 trained participants completed 2 HIE bouts (P1 = 4min at 80% maximal aerobic power [MAP]; P2 = 4min at 100%MAP). GE was calculated conventionally in the last 3minutes of submaximal (50%MAP) cycling bouts performed before and after HIE (Pre50%MAP and Post50%MAP). To calculate GE using BE (BGE), a linear regression of GE submaximal values post-HIE were back extrapolated to the end of the HIE bout. BGE was significantly correlated with Post50%MAP GE in P1 (r = .63; P = .01) and in P2 (r = .85; P = .002). Reliability data for P1 and P2 BGE demonstrate a mean coefficient of variation of 7.8% and 9.8% with limits of agreement of 4.3% and 4.5% in relative GE units, respectively. P2 BGE was significantly lower than P2 Post50%MAP GE (18.1% [1.6%] vs 20.3% [1.7%]; P = .01). Using a declining GE from the BE method, there was a 44% greater anaerobic contribution compared with assuming a constant GE during 4-minute HIE at 100%MAP. HIE acutely reduced BGE at 100%MAP. A greater anaerobic contribution to exercise as well as excess postexercise oxygen consumption at 100%MAP may contribute to this decline in efficiency. The BE method may be a reliable and valid tool in both estimating GE during HIE and calculating aerobic and anaerobic contributions.

Associations between ambient air pollution and daily mortality in a cohort of congestive heart failure: Case-crossover and nested case-control analyses using a distributed lag nonlinear model

BackgroundPersons with congestive heart failure may be at higher risk of the acute effects related to daily fluctuations in ambient air pollution. To meet some of the limitations of previous studies using grouped-analysis, we developed a cohort study of persons with congestive heart failure to estimate whether daily non-accidental mortality were associated with spatially-resolved, daily exposures to ambient nitrogen dioxide (NO2) and ozone (O3), and whether these associations were modified according to a series of indicators potentially reflecting complications or worsening of health. MethodsWe constructed the cohort from the linkage of administrative health databases. Daily exposure was assigned from different methods we developed previously to predict spatially-resolved, time-dependent concentrations of ambient NO2 (all year) and O3 (warm season) at participants' residences. We performed two distinct types of analyses: a case-crossover that contrasts the same person at different times, and a nested case-control that contrasts different persons at similar times. We modelled the effects of air pollution and weather (case-crossover only) on mortality using distributed lag nonlinear models over lags 0 to 3 days. We developed from administrative health data a series of indicators that may reflect the underlying construct of “declining health”, and used interactions between these indicators and the cross-basis function for air pollutant to assess potential effect modification. ResultsThe magnitude of the cumulative as well as the lag-specific estimates of association differed in many instances according to the metric of exposure. Using the back-extrapolation method, which is our preferred exposure model, we found for the case-crossover design a cumulative mean percentage changes (MPC) in daily mortality per interquartile increment in NO2 (8.8 ppb) of 3.0% (95% CI: −0.9, 6.9%) and for O3 (16.5 ppb) 3.5% (95% CI: −4.5, 12.1). For O3 there was strong confounding by weather (unadjusted MPC = 7.1%; 95% CI: 1.7, 12.7%). For the nested case-control approach the cumulative MPC for NO2 in daily mortality was 2.9% (95% CI: −0.9, 6.9%) and for O3 7.3% (95% CI: 3.0, 11.9%). We found evidence of effect modification between daily mortality and cumulative NO2 and O3 according to the prescribed dose of furosemide in the nested case-control analysis, but not in the case-crossover analysis. ConclusionsMortality in congestive heart failure was associated with exposure to daily ambient NO2 and O3 predicted from a back-extrapolation method using a land use regression model from dense sampling surveys. The methods used to assess exposure can have considerable influence on the estimated acute health effects of the two air pollutants.

Comparison of spatiotemporal prediction models of daily exposure of individuals to ambient nitrogen dioxide and ozone in Montreal, Canada

BackgroundIn previous studies investigating the short-term health effects of ambient air pollution the exposure metric that is often used is the daily average across monitors, thus assuming that all individuals have the same daily exposure. Studies that incorporate space-time exposures of individuals are essential to further our understanding of the short-term health effects of ambient air pollution. ObjectivesAs part of a longitudinal cohort study of the acute effects of air pollution that incorporated subject-specific information and medical histories of subjects throughout the follow-up, the purpose of this study was to develop and compare different prediction models using data from fixed-site monitors and other monitoring campaigns to estimate daily, spatially-resolved concentrations of ozone (O3) and nitrogen dioxide (NO2) of participants’ residences in Montreal, 1991–2002. MethodsWe used the following methods to predict spatially-resolved daily concentrations of O3 and NO2 for each geographic region in Montreal (defined by three-character postal code areas): (1) assigning concentrations from the nearest monitor; (2) spatial interpolation using inverse-distance weighting; (3) back-extrapolation from a land-use regression model from a dense monitoring survey, and; (4) a combination of a land-use and Bayesian maximum entropy model. We used a variety of indices of agreement to compare estimates of exposure assigned from the different methods, notably scatterplots of pairwise predictions, distribution of differences and computation of the absolute agreement intraclass correlation (ICC). For each pairwise prediction, we also produced maps of the ICCs by these regions indicating the spatial variability in the degree of agreement. ResultsWe found some substantial differences in agreement across pairs of methods in daily mean predicted concentrations of O3 and NO2. On a given day and postal code area the difference in the concentration assigned could be as high as 131ppb for O3 and 108ppb for NO2. For both pollutants, better agreement was found between predictions from the nearest monitor and the inverse-distance weighting interpolation methods, with ICCs of 0.89 (95% confidence interval (CI): 0.89, 0.89) for O3 and 0.81 (95%CI: 0.80, 0.81) for NO2, respectively. For this pair of methods the maximum difference on a given day and postal code area was 36ppb for O3 and 74ppb for NO2. The back-extrapolation method showed a higher degree of disagreement with the nearest monitor approach, inverse-distance weighting interpolation, and the Bayesian maximum entropy model, which were strongly constrained by the sparse monitoring network. The maps showed that the patterns of agreement differed across the postal code areas and the variability depended on the pair of methods compared and the pollutants. For O3, but not NO2, postal areas showing greater disagreement were mostly located near the city centre and along highways, especially in maps involving the back-extrapolation method. ConclusionsIn view of the substantial differences in daily concentrations of O3 and NO2 predicted by the different methods, we suggest that analyses of the health effects from air pollution should make use of multiple exposure assessment methods. Although we cannot make any recommendations as to which is the most valid method, models that make use of higher spatially resolved data, such as from dense exposure surveys or from high spatial resolution satellite data, likely provide the most valid estimates.

Model-based prediction of maximum pool size in the ribbon synapse

The synaptic ribbon is a specialized structure in photoreceptor neurons that tethers vesicles prior to release (Figure ​(Figure1A).1A). When a cell is stimulated, vesicles are released from the ribbon and later replenished from the population of mobile vesicles in the synaptic terminal. A train of depolarizing pulses causes the ribbon to alternate between periods of release (lasting Δt = 25 ms) and replenishment (lasting T = 50ms), which occur on estimated timescales of τr = 5 ms (for release) and τa = 815 ms (for replenishment). After the first few pulses, the system approaches a limit cycle, and the amount of vesicles released on each pulse converges to a limiting value, R (Figure 1B). This can be used to determine the maximum available pool size on the ribbon, A. The standard method for estimating A is to measure the rate of replenishment in the limit, and then back-extrapolate from the cumulative release plot to obtain the available pool size at the start of the pulse train [1]. When comparing pulse trains of different strengths, this method yields substantially different values for A, a somewhat paradoxical result. Back-extrapolation assumes, however, that the replenishment rate is constant, even though it is thought to be proportional to the available space on the ribbon [2]. Figure 1 A) The synaptic ribbon. (B) The available pool size, A(t), during a stimulus pulse train. Table 1 Maximum pool size predictions from pulse train data We developed a model-based approach to estimate A from the limiting release R. We modeled the rate of release (resp. replenishment) to simply be proportional to the number of vesicles on the ribbon (resp. vacant ribbon sites), and using the measured timescale τr (resp. τa). By solving the alternating differential equations, we derived a recurrence relation for the release during each pulse, Ri, which we then solved to obtain a closed form expression for Ri and the limiting release R. Specifically, we found that A = cR, where c is a function of τr,τa,Δt,T, and p, with p a release constant that captures the stimulus dependence of release probabilities, and can be estimated from the first release, R1. In contrast to the back-extrapolation method, our model-based estimate for A was similar across stimulus types (Table 1), while p was much smaller for the weaker stimulus. This suggests that available pool size does not change with stimulus strength; instead, differences in release result from changes in release probability.

Fatigue Life Prediction Based on Crack Closure and Equivalent Initial Flaw Size.

Failure analysis and fatigue life prediction are necessary and critical for engineering structural materials. In this paper, a general methodology is proposed to predict fatigue life of smooth and circular-hole specimens, in which the crack closure model and equivalent initial flaw size (EIFS) concept are employed. Different effects of crack closure on small crack growth region and long crack growth region are considered in the proposed method. The EIFS is determined by the fatigue limit and fatigue threshold stress intensity factor △Kth. Fatigue limit is directly obtained from experimental data, and △Kth is calculated by using a back-extrapolation method. Experimental data for smooth and circular-hole specimens in three different alloys (Al2024-T3, Al7075-T6 and Ti-6Al-4V) under multiple stress ratios are used to validate the method. In the validation section, Semi-circular surface crack and quarter-circular corner crack are assumed to be the initial crack shapes for the smooth and circular-hole specimens, respectively. A good agreement is observed between model predictions and experimental data. The detailed analysis and discussion are performed on the proposed model. Some conclusions and future work are given.

The timing of the forced vital capacity.

Based on analysis of more than 2,500 forced vital capacity (FVC) maneuvers, we examined 2 aspects of the standards for spirometry recommended by the 1977 Snowbird Workshop concerning the timing of the FVC maneuver. We compared the forced expiratory volume in one sec (FEV1) when timing was initiated by the back extrapolation method with FEV1 when timing was initiated by flow or volume threshold to determine whether the latter offered a reliable equivalent. Although the mean differences appear to be relatively small, because of variability in initiating expiratory effort, neither alternative is likely to offer a uniformly accurate numeric equivalent to backward extrapolation. We also measured the volume expired before the initiation of the timing as a per cent of FVC to determine whether 10 per cent was a reasonable limit to apply for acceptability of a test. Although 2 SD from the mean of 4.35 per cent were well within this limit, it appears that the technician's judgment of acceptability is sufficient in most cases.

Optimal back-extrapolation method for estimating plasma volume in humans using the indocyanine green dilution method.

BackgroundThe indocyanine green dilution method is one of the methods available to estimate plasma volume, although some researchers have questioned the accuracy of this method.MethodsWe developed a new, physiologically based mathematical model of indocyanine green kinetics that more accurately represents indocyanine green kinetics during the first few minutes postinjection than what is assumed when using the traditional mono-exponential back-extrapolation method. The mathematical model is used to develop an optimal back-extrapolation method for estimating plasma volume based on simulated indocyanine green kinetics obtained from the physiological model.ResultsResults from a clinical study using the indocyanine green dilution method in 36 subjects with type 2 diabetes indicate that the estimated plasma volumes are considerably lower when using the traditional back-extrapolation method than when using the proposed back-extrapolation method (mean (standard deviation) plasma volume = 26.8 (5.4) mL/kg for the traditional method vs 35.1 (7.0) mL/kg for the proposed method). The results obtained using the proposed method are more consistent with previously reported plasma volume values.ConclusionsBased on the more physiological representation of indocyanine green kinetics and greater consistency with previously reported plasma volume values, the new back-extrapolation method is proposed for use when estimating plasma volume using the indocyanine green dilution method.

Assessment of equivalent initial flaw size estimation methods in fatigue life prediction using compact tension specimen tests

To assess the efficiency of the Equivalent Initial Flaw Size (EIFS) concept in the life estimation of mechanical components, a novel approach is outlined in this paper. For this purpose, experimental tests are conducted on the compact tension specimens made of 4340 steel and the number of cycles required for the crack to grow from the end of the notch up to the fracture of the specimen is counted. In fact, the fatigue cycling for the pre-crack initiation is a part of cycle count procedure and it is assumed that an initial micro-crack exists at the end of the notch, which grows due to fatigue loading, the length of which is estimated using the EIFS method. Three methods of back extrapolation, Kitagawa–Takahashi diagram, and time to crack initiation are used in order to estimate EIFS and their results are compared. For estimating EIFS by Kitagawa–Takahashi diagram, the threshold value of the stress intensity factor (ΔKth) is required. In this paper, ΔKth is estimated by both K-increasing and K-decreasing methods. The experimental results show that the value of ΔKth estimated by the K-increasing method is lower than that estimated by K-decreasing method. It is observed that the estimated EIFS by back extrapolation method and TTCI method is dependent on the loading amplitude, while the estimated EIFS by Kitagawa–Takahashi diagram is identical for all loading amplitudes and it can be considered as the material property. The predicted life based on the Kitagawa–Takahashi method is in relatively good agreement with the experimental results. However, the TTCI method does not have sufficient accuracy especially in low amplitude fatigue.

Redefining Spirometry Hesitating Start Criteria Based on the Ratio of Extrapolated Volume to Timed FEVs

The primary purpose of this study was to investigate alternative hesitating start criteria for spirometry maneuvers that do not achieve an acceptable plateau. The current hesitating start criterion that has been in use for 30 years is based on clinical opinion from expert users; it was not established based on information from peer-reviewed scientific studies. A total of 1,719 workers met the eligibility criteria for this study and contributed 24,945 trials. The fitted lines obtained from linear regressions of each dependent variable, volume of air calculated at time zero using the back extrapolation method (extrapolated volume [EV])/FEV(1), EV/FEV in 3 s (FEV(3)), and EV/FEV in 6 s (FEV(6)) on EV/FVC were determined. The 95th percentile of the prediction interval of each dependent variable corresponding to EV/FVC = 5% was calculated. The values for EV/FEV(1), EV/FEV(3), and EV/FEV(6) corresponding to the 5% EV/FVC value were determined to be 6.62%, 5.59%, and 5.25%, respectively. A new hesitating start criterion using EV/FEV(6) of 5.25% is recommended for tracings that do not achieve a plateau or when an FEV(6) is performed. An EV/FEV(3) of 5.59% could be incorporated into spirometry software as an early warning signal that could help operators identify trials with potential hesitating starts.

The opening interrupter technique for respiratory resistance measurements in children

The interrupter resistance (Rint) can be calculated from various estimates of alveolar pressure based on mouth pressure during occlusion. We compared Rint, as measured by the opening interrupter technique (Rint1), and the linear back-extrapolation method (Rint2), with the 'gold standard' airway resistance measured by plethysmography (Raw). The study included 32 asthmatic children and 11 children with cystic fibrosis, aged 5 to 18 years, who were categorized into non-obstructed (NObs) (n = 27) and obstructed (Obs) (n = 16) groups. Spirometry and the three different resistance measurements were performed on all children. Rint1 and Raw were assessed after a bronchodilator (BD) test in 16 and nine children, respectively, in the Obs group. Raw (0.48 ± 0.20 kPa.s/L) was lower than Rint1 (1.04 ± 0.34 kPa.s/L) and Rint2 (0.63 ± 0.18 kPa.s/L) (P < 0.001). Raw, but neither Rint1 nor Rint2, was significantly higher in the Obs group than in the NObs group (0.57 ± 0.23 vs 0.42 ± 0.16 kPa.s/L, P < 0.05). The differences Rint1-Raw and Rint2-Raw were correlated with FEV(1) /VC (P < 0.01 and P < 0.001), and Rint1-Raw was correlated with height (P < 0.001). After BD significant changes in Rint1 and Raw were observed in 5/9 and 7/9 children, respectively. Rint2, as well as Rint1, may be underestimated in the most Obs children and may therefore fail to detect severe obstruction. Rint1 is likely to include a non-negligible contribution from the tissue component, especially in the youngest children. Although not different between Obs and NObs children at baseline, Rint1 did detect bronchodilation in some Obs children.

Cardiac output and systemic transit time dispersion as determinants of circulatory mixing time: a simulation study

A new approach to characterize the kinetics of intravascular mixing process is presented. The mixing time, defined as the time required for achieving 95% homogeneity, is calculated by numerical simulations using a circulatory model applied to the intravascular marker indocyanine green (ICG). The results suggest that the mixing time is determined by cardiac output and the relative dispersion of transit time distribution across the systemic circulation, whereby the rate of mixing increases with increasing cardiac output and decreasing transit time dispersion, and vice versa. The estimation of plasma volume from simulated ICG dilution data using the backextrapolation method shows that slow mixing is accompanied by an overestimation of blood volume. This error may be negligible for mixing times of less than approximately 3 min but high in disease states characterized by low cardiac output and/or high transit time dispersion. In view of the role of transit time dispersion as determinant of intravascular mixing, it would be interesting to know more about the effect of disease states on systemic transit time dispersion.

Probabilistic fatigue life prediction using an equivalent initial flaw size distribution

A new methodology is proposed in this paper to calculate the equivalent initial flaw size (EIFS) distribution. The proposed methodology is based on the Kitagawa–Takahashi diagram. Unlike the commonly used back-extrapolation method for EIFS calculation, the proposed methodology is independent of applied load level and only uses fatigue limit and fatigue crack threshold stress intensity factor. The advantage of the proposed EIFS concept is that it is very efficient in calculating the statistics of EIFS. The developed EIFS methodology is combined with probabilistic crack growth analysis to predict the fatigue life of smooth specimens. Model predictions are compared with experimental observations for various metallic materials.

Influencia mutua de la deformación y composición química sobre la precipitación inducida en aceros microaleados

By means of torsion tests and applying the back extrapolation method, the static recrystallization kinetics in microalloyed steels with vanadium (V), niobium (Nb) and titanium (Ti) has been determined and, recrystallization-precipitation-time-temperature (RPTT) diagrams have been plotted also graphically, which show the Recrystallization- Precipitation interaction. These diagrams show that the effect of the deformation on the precipitation kinetics depends of the microalloy content. In this sense, a new expression is proposed to relate the influence of the deformation and the chemical composition on the minimum incubation of the precipitation kinetics.

Evolution of strain induced precipitation in Nb and V-microalloyed steels and influence on mechanical properties

By means of hot torsion tests and applying the Back Extrapolation method, the static recrystallization kinetics in V and Nb-microalloyed steels has been determined and the recrystallization-precipitation-time-temperature (RPTT) diagrams have also been plotted. The RPTT diagrams graphically show the Recristalization-Precipitation interaction and simultaneously the determination of the static recrystallization critical temperature (SRCT). The mentioned temperature represents the limit between the two phases, before and after of the precipitation. The activation energy for static recrytallization of the austenite before and after precipitation has also been determined. The present study is completed with the determination of the precipitate size distribution diagrams by means of TEM analysis.

New AUC-Based Method to Estimate Drug Fraction Removed by Hemodialysis

Background: A supplemental dose is often necessary after hemodialysis depending on the amount of drug removed by hemodialysis. However, there are different methods of estimating this amount, and most methods ignore drug rebound after hemodialysis. In this report we present a new area under the concentration curve (AUC)-based method that provides an estimate of the drug fraction removed by hemodialysis including drug rebound. Methods: Valganciclovir, the oral prodrug of ganciclovir, was administered to 6 patients with end-stage renal disease. Hemodialysis was performed after 32 h. The fraction of ganciclovir removed by hemodialysis was estimated using the new AUC-based method, a classical method (using the slope on and off hemodialysis), the back-extrapolation method, and a reference model (a two-compartment model with zero-order input and first-order elimination). Results: The AUC-based method and the back-extrapolation method provided accurate estimates of the fraction of ganciclovir removed by hemodialysis (47 ± 6 and 46 ± 5%, respectively) compared to the reference model (49 ± 3%). The classical method, which does not account for the rebound of ganciclovir concentrations after hemodialysis, overestimated the removed fraction by 9% (58 ± 3%). Conclusions: The new AUC-based method and the back-extrapolation method accurately estimate the drug fraction removed by hemodialysis for drugs with a rebound after hemodialysis. The AUC-based method is more robust and as efficient compared to the back-extrapolation method.

Strain induced precipitation effect on austenite static recrystallisation in microalloyed steels

Using torsion tests and applying the back extrapolation method, the strain induced precipitation effect on austenite static recrystallisation in vanadium and niobium microalloyed steels has been studied and a model has been constructed. This model takes account of precipitation and its influence on recrystallisation kinetics, in particular on the activation energy, which is increased. The model is applied at temperatures below the temperature at which inhibition of recrystallisation commences owing to the induced precipitation. The new values of activation energy can be three times higher than the activation energy before precipitation has started, depending on the contents of elements responsible for the precipitation (Nb, V, N, C).

Measurements of resistance by the interrupter technique and of transcutaneous partial pressure of oxygen in young children during methacholine challenge.

Measurement of bronchial airway responsiveness requires noninvasive techniques in young children. The study was designed to examine the changes in resistance as measured using the interrupter technique (Rint) at the dose of methacholine (M) that induced a fall in transcutaneous partial pressure in O2 (P(tc)O2) > or = 20% (PD(20)P(tc)O2) in young children. Rint was calculated using the linear back-extrapolation method (Rint(L)) and the end-interrupter method (Rint(EI)). Twenty-two children (mean age, 5.2 +/- 1.1 years; range, 3.4 - 7.1 years) with nonspecific respiratory symptoms (mainly chronic cough, n = 17) were tested. P(tc)O2, Rint(L), and Rint(EI) were measured before the test, after saline challenge (baseline (B)), after each dose of M delivered by a dosimeter, and after bronchodilator (BD) inhalation. P(tc)O2 decreased significantly during M challenge, from 85 +/- 6 mmHg (B) to 62 +/- 9 mmHg (P < 0.05), and increased after BD inhalation, to 82 +/- 8 mmHg. Rint(L) and Rint(EI) increased significantly during M challenge, from 0.94 +/- 0.2 KPa/L/s and 1.11 +/- 0.19 KPa/L/s (B) to 1.27 +/- 0.35 KPa/L/s and 1.47 +/- 0.37 KPa/L/s, respectively (P < 0.05), and decreased after BD inhalation to 0.80 +/- 0.17 KPa/L/s and 0.95 +/- 0.18 KPa/L/s, respectively. Nineteen of 22 children reached the PD(20)P(tc)O2 at a dose of M ranging from 50-400 microg. At the PD(20)P(tc)O2, significant changes in Rint(L) and Rint(EI) (sensitivity index (SI) > or = 2) were found in 79% and 63% of children, respectively. We conclude that: 1) M challenge using P(tc)O2 is safe in young children; and 2) our findings are not in favor of the use of Rint as the only indicator of bronchial reaction in young children during M challenge.

Influence of TiN particles distribution on static recrystallisation in structural steels at reheating temperature

Results of investigations concerning the influence of Ti and N contents on static recrystallisation kinetics are presented. By means of torsion tests, and applying the back extrapolation method, the statically recrystallised fraction has been determined for four structural steels with different Ti and N contents, at different temperatures, equivalent strain of 0.35 and strain rate of 3.63 s−1. Two reheating temperatures have been used to obtain different austenite grain sizes and different precipitate mean size in steels containing Ti. The results show that a low precipitated volume and a relatively large size of precipitates, at reheating temperature, did not impede grain boundary self‐diffusion during the static recrystallisation, the main mechanism governing static recrystallisation. Nevertheless, the smaller size of the precipitates acted as an obstacle to grain boundary self‐diffusion. These effects were measured by calculation of the activation energy for static recrystallisation. On the other hand, the influence of austenite grain size in steels containing Ti can not be correctly determined, as at each reheating temperature, in addition to a different austenite grain, the distribution of precipitates is also different, affecting the activation energy and making it impossible to clearly appreciate the influence of austenite grain size.