Positron annihilation lifetime and Doppler-broadening measurements were carried out on Cu-Al-Ni b... more Positron annihilation lifetime and Doppler-broadening measurements were carried out on Cu-Al-Ni based alloys to which Ti, Mn or B were added. The decrease in the mean lifetime until a final value as a function of both the ageing time and temperature in β-phase is explained by a combination of factors including annealing of excess vacancies, ordering and precipitation. The in situ measurements reveal a drastic effect in the S-lineshape parameter behaviour when the defects anneal out at the transition from martensite to the beta phase. Two stages have been detected in this process for the alloy containing both Ti an B. When crossing the transition region several times, an increase of the S-lineshape parameter value is observed. This is interpreted as due to the formation of dislocations and precipitate-martensite interfaces. In the alloy with both Ti and Mn additions a distinct behaviour in the S-lineshape parameter is observed at low temperatures and attributed to some type of vacancy association or cluster.
During the last years, the positron annihilation technique has proven to be a sensitive tool for ... more During the last years, the positron annihilation technique has proven to be a sensitive tool for the characterization of phase transitions, and in particular of the martensitic transformation in Cu-based alloys. The differences in structure between the high temperature phase (cubic) ...
Journal of Radioanalytical and Nuclear Chemistry Articles, 1996
A two parameter correlation system to measure the energy of a thermalizing ortho-positronium as f... more A two parameter correlation system to measure the energy of a thermalizing ortho-positronium as function of its age was constructed. The Doppler broadening of the 2 annihilation line due the quenching ofo-Ps is measured in coincidence with the age of the positronium. We use only one high resolution nuclear ADC for the energy spectrum, together with a self build low
In this paper we study the vacancy creation process in polycrystalline Ni3Al under electron irrad... more In this paper we study the vacancy creation process in polycrystalline Ni3Al under electron irradiation using positron annihilation lifetime spectroscopy. The complete irradiation experiment has been simulated using Monte Carlo and molecular dynamics techniques. This allows us to estimate the absolute vacancy concentration. Comparison with the experimental positron lifetimes results in a positron trapping coefficient for vacancies in Ni3Al of
ABSTRACT Purpose The aims of this study were 1) to model the temporal profile of W′ recovery afte... more ABSTRACT Purpose The aims of this study were 1) to model the temporal profile of W′ recovery after exhaustion, 2) to estimate the contribution of changing V˙O2 kinetics to this recovery, and 3) to examine associations with aerobic fitness and muscle fiber type (MFT) distribution. Methods Twenty-one men (age = 25 ± 2 yr, V˙O2peak = 54.4 ± 5.3 mL·min−1·kg−1) performed several constant load tests to determine critical power and W′ followed by eight trials to quantify W′ recovery. Each test consisted of two identical exhaustive work bouts (WB1 and WB2), separated by a variable recovery interval of 30, 60, 120, 180, 240, 300, 600, or 900 s. Gas exchange was measured and muscle biopsies were collected to determine MFT distribution. W′ recovery was quantified as observed W′ recovery (W′OBS), model-predicted W′ recovery (W′BAL), and W′ recovery corrected for changing V˙O2 kinetics (W′ADJ). W′OBS and W′ADJ were modeled using mono- and biexponential fitting. Root-mean-square error (RMSE) and Akaike information criterion (∆AICC) were used to evaluate the models’ accuracy. Results The W′BAL model (τ = 524 ± 41 s) was associated with an RMSE of 18.6% in fitting W′OBS and underestimated W′ recovery for all durations below 5 min (P < 0.002). Monoexponential modeling of W′OBS resulted in τ = 104 s with RMSE = 6.4%. Biexponential modeling of W′OBS resulted in τ1 = 11 s and τ2 = 256 s with RMSE = 1.7%. W′ADJ was 11% ± 1.5% lower than W′OBS (P < 0.001). ∆AICC scores favored the biexponential model for W′OBS, but not for W′ADJ. V˙O2peak (P = 0.009) but not MFT distribution (P = 0.303) was associated with W′OBS. Conclusion We showed that W′ recovery from exhaustion follows a two-phase exponential time course that is dependent on aerobic fitness. The appearance of a fast initial recovery phase was attributed to an enhanced aerobic energy provision resulting from changes in V˙O2 kinetics.
Positron annihilation lifetime and Doppler-broadening measurements were carried out on Cu-Al-Ni b... more Positron annihilation lifetime and Doppler-broadening measurements were carried out on Cu-Al-Ni based alloys to which Ti, Mn or B were added. The decrease in the mean lifetime until a final value as a function of both the ageing time and temperature in β-phase is explained by a combination of factors including annealing of excess vacancies, ordering and precipitation. The in situ measurements reveal a drastic effect in the S-lineshape parameter behaviour when the defects anneal out at the transition from martensite to the beta phase. Two stages have been detected in this process for the alloy containing both Ti an B. When crossing the transition region several times, an increase of the S-lineshape parameter value is observed. This is interpreted as due to the formation of dislocations and precipitate-martensite interfaces. In the alloy with both Ti and Mn additions a distinct behaviour in the S-lineshape parameter is observed at low temperatures and attributed to some type of vacancy association or cluster.
During the last years, the positron annihilation technique has proven to be a sensitive tool for ... more During the last years, the positron annihilation technique has proven to be a sensitive tool for the characterization of phase transitions, and in particular of the martensitic transformation in Cu-based alloys. The differences in structure between the high temperature phase (cubic) ...
Journal of Radioanalytical and Nuclear Chemistry Articles, 1996
A two parameter correlation system to measure the energy of a thermalizing ortho-positronium as f... more A two parameter correlation system to measure the energy of a thermalizing ortho-positronium as function of its age was constructed. The Doppler broadening of the 2 annihilation line due the quenching ofo-Ps is measured in coincidence with the age of the positronium. We use only one high resolution nuclear ADC for the energy spectrum, together with a self build low
In this paper we study the vacancy creation process in polycrystalline Ni3Al under electron irrad... more In this paper we study the vacancy creation process in polycrystalline Ni3Al under electron irradiation using positron annihilation lifetime spectroscopy. The complete irradiation experiment has been simulated using Monte Carlo and molecular dynamics techniques. This allows us to estimate the absolute vacancy concentration. Comparison with the experimental positron lifetimes results in a positron trapping coefficient for vacancies in Ni3Al of
ABSTRACT Purpose The aims of this study were 1) to model the temporal profile of W′ recovery afte... more ABSTRACT Purpose The aims of this study were 1) to model the temporal profile of W′ recovery after exhaustion, 2) to estimate the contribution of changing V˙O2 kinetics to this recovery, and 3) to examine associations with aerobic fitness and muscle fiber type (MFT) distribution. Methods Twenty-one men (age = 25 ± 2 yr, V˙O2peak = 54.4 ± 5.3 mL·min−1·kg−1) performed several constant load tests to determine critical power and W′ followed by eight trials to quantify W′ recovery. Each test consisted of two identical exhaustive work bouts (WB1 and WB2), separated by a variable recovery interval of 30, 60, 120, 180, 240, 300, 600, or 900 s. Gas exchange was measured and muscle biopsies were collected to determine MFT distribution. W′ recovery was quantified as observed W′ recovery (W′OBS), model-predicted W′ recovery (W′BAL), and W′ recovery corrected for changing V˙O2 kinetics (W′ADJ). W′OBS and W′ADJ were modeled using mono- and biexponential fitting. Root-mean-square error (RMSE) and Akaike information criterion (∆AICC) were used to evaluate the models’ accuracy. Results The W′BAL model (τ = 524 ± 41 s) was associated with an RMSE of 18.6% in fitting W′OBS and underestimated W′ recovery for all durations below 5 min (P < 0.002). Monoexponential modeling of W′OBS resulted in τ = 104 s with RMSE = 6.4%. Biexponential modeling of W′OBS resulted in τ1 = 11 s and τ2 = 256 s with RMSE = 1.7%. W′ADJ was 11% ± 1.5% lower than W′OBS (P < 0.001). ∆AICC scores favored the biexponential model for W′OBS, but not for W′ADJ. V˙O2peak (P = 0.009) but not MFT distribution (P = 0.303) was associated with W′OBS. Conclusion We showed that W′ recovery from exhaustion follows a two-phase exponential time course that is dependent on aerobic fitness. The appearance of a fast initial recovery phase was attributed to an enhanced aerobic energy provision resulting from changes in V˙O2 kinetics.
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Papers by Charles Dauwe