Biphasic MO2+x-M3O8-z domain of the U-Pu-O phase diagram.

The reduction of six mixed-oxide samples containing 14, 24, 35, 46, 54, and 62 mol % Pu was studied in situ by X-ray diffraction. The samples were first oxidized in air and subsequently reduced in a controlled atmosphere corresponding to a stoichiometric composition with an O/M = 2.00. After oxidation, we observed two structures, one cubic and one orthorhombic, MO2+x and M3O8-z. The two phases were subsequently reduced back to their stoichiometric O/M = 2.00 in a controlled atmosphere. The plutonium contents of the two resulting cubic structures differed from the initial one. We conclude that strong cation transport took place during oxidation, according to the shape of the tie lines in the biphasic MO2+x/M4O9-M3O8-z domain. The resulting overall O/M after oxidation was estimated. We propose the shape of the tie lines in the aforementioned biphasic domain and suggest a maximal plutonium solubility in the M3O8 structure at 8 ± 2 mol % (Pu/U + Pu) at 1573 K.

High temperature X-ray diffraction study of the oxidation products and kinetics of uranium-plutonium mixed oxides.

The oxidation products and kinetics of two sets of mixed uranium-plutonium dioxides containing 14%, 24%, 35%, 46%, 54%, and 62% plutonium treated in air were studied by means of in situ X-ray diffraction (XRD) from 300 to 1773 K every 100 K. The first set consisted of samples annealed 2 weeks before performing the experiments. The second one consisted of powdered samples that sustained self-irradiation damage. Results were compared with chosen literature data and kinetic models established for UO2. The obtained diffraction patterns were used to determine the temperature of the hexagonal M3O8 (M for metal) phase formation, which was found to increase with Pu content. The maximum observed amount of the hexagonal phase in wt % was found to decrease with Pu addition. We conclude that plutonium stabilizes the cubic phases during oxidation, but the hexagonal phase was observed even for the compositions with 62 mol % Pu. The results indicate that self-irradiation defects have a slight impact on the kinetics of oxidation and the lattice parameter even after the phase transformation. It was concluded that the lattice constant of the high oxygen phase was unaffected by the changes in the overall O/M when it was in equilibrium with small quantities of M3O8. We propose that the observed changes in the high oxygen cubic phase lattice parameter are a result of either cation migration or an increase in the miscibility of oxygen in this phase. The solubility of Pu in the hexagonal phase was estimated to be below 14 mol % even at elevated temperatures.

The effect of a one-leg cycling aerobic training program during the rehabilitation period in soccer players with anterior cruciate ligament reconstruction.

OBJECTIVES: To examine cardiorespiratory fitness, resting cardiac parameters, and muscle oxygenation changes in soccer players having undergone anterior cruciate ligament reconstruction and to assess the benefits of a one-leg cycling (OLC) aerobic training program performed during the rehabilitation period. DESIGN: Randomized clinical trial. SETTING: Outpatient clinic, primary care. PATIENTS: Twenty-four, male, regional-level soccer players who had undergone surgical reconstruction of the anterior cruciate ligament of the knee. INTERVENTION: Patients were randomly assigned to 1 of 2 groups: either an individualized OLC aerobic training program with the untreated leg plus a rehabilitation program (training group, TG) or a group that received the same rehabilitation program but without aerobic training (control group, CG). MAIN OUTCOME MEASURES: Outcome measurements assessed before (T1) and after 6 weeks (T2) were stroke volume (SV) and end-diastolic volume (EDV) during resting cardiac echography measurement and peak work rate (W(peak)), peak O(2) uptake (VO(2)peak), peak minute ventilation (VE(peak)), first and second ventilatory threshold (VT1 and VT2), leg muscle oxygenation (LMO(2)), and blood volume (LMBV) during maximal graded tests performed with the untreated leg. RESULTS: At T1, there was no significant difference between TG and CG. For TG, W(peak), VE(peak), VT1, VT2, LMO(2), and LMBV at each work rate were significantly higher at T2 than at T1. For CG, W(peak), VO(2)peak, VE(peak), VT2, SV, and EDV decreased significantly at T2 in comparison with T1. CONCLUSIONS: One-leg cycling training could involve specific adaptations in comparison to a standard rehabilitation program. Moreover, OLC training during rehabilitation seems to stop the effects of hypoactivity.

Effect of one-leg cycling aerobic training in amateur soccer players after anterior cruciate ligament reconstruction.

OBJECTIVE: To examine before and after 6 wks of rehabilitation, the cardiorespiratory fitness, and resting cardiac parameter changes in soccer players having undergone anterior cruciate ligament reconstruction and to assess the benefits of a one leg cycling aerobic training program with the nonsurgical leg during the rehabilitation period. DESIGN: Twenty-four amateur soccer players took part in this study. The subjects were then randomly assigned to one of two groups--either an individualized one leg cycling aerobic program (training group) or without cardiorespiratory training (control group). The initial evaluation (T1) was carried out the first day of rehabilitation and the final evaluation (T2) within 42 days. Both consisted of resting cardiac echography measurement and maximal graded tests performed with the nonsurgical leg. RESULTS: For training group, peak power output, peak minute ventilation, the first (VT1), and second (VT2) ventilatory threshold values were significantly (P < 0.05) higher at T2 than at T1 (+13%, +10%, +7%, and +11%, respectively). For control group, peak power output, peak oxygen uptake, peak minute ventilation, and VT2 values decreased significantly at T2 in comparison with T1(-10%, -10%, -12%, and -11%, respectively). After hospitalization, significant reductions in end diastolic volume (T1, 116 +/- 17 ml; T2, 97 +/- 16 ml; P < 0.05) and stroke volume (T1, 75 +/- 14 ml; T2, 59 +/- 12 ml; P < 0.05) were also observed. For training group, the cardiac parameters were similar between T1 and T2. CONCLUSION: These results suggest that one leg cycling training during the rehabilitation seems to be an adapted method to stop the effects of hypoactivity.

One-leg cycling versus arm cranking: which is most appropriate for physical conditioning after knee surgery?

OBJECTIVE: To compare the cardiorespiratory responses, blood lactate concentration and perceived exertion between 1-leg cycling and arm cranking. DESIGN: Comparison of exercise modalities. SETTING: Hospital. PARTICIPANTS: Fourteen men who had undergone knee surgery were evaluated during rehabilitation. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Each patient performed 2 maximal graded tests: 1-leg cycling and arm cranking exercise, with a 7-day interval. Respiratory gas exchange, heart rate, blood lactate concentration, and the ratings of perceived exertion (RPE) were measured. RESULTS: Peak power output, peak minute ventilation, peak oxygen uptake (Vo(2)peak), and peak heart rate did not differ significantly between 1-leg cycling and arm cranking. The first and second ventilatory thresholds occurred at above 40% and 72% of Vo(2)peak, respectively, in both tests. The maximal lactate concentrations and the RPE values were significantly higher during arm cranking (+10%, +12%, respectively, P<.05) compared with corresponding 1-leg cycling values. CONCLUSIONS: The maximal cardiorespiratory values were not different between arm cranking and 1-leg cycling. However, the RPE and blood lactate concentration were lower when the exercise was performed with the lower limb. Thus 1-leg cycling may be more easily tolerated than arm cranking by patients participating in aerobic conditioning after knee surgery.

Effects of knee surgery on cardiac function in soccer players.

OBJECTIVE: To evaluate the effects of knee surgery on hematocrit and hemoglobin concentration and on resting cardiac parameters as measured by echocardiography. DESIGN: Ten soccer players who underwent knee surgery were evaluated before (T1) and after (T2) hospitalization within a 7-day interval. RESULTS: After hospitalization, end diastolic volume and stroke volume were significantly reduced (P < 0.05) by 14 and 22%, respectively. Despite a significant increase in resting heart rate (T1: 68 +/- 3.3 beats/ min, T2: 72 +/- 3.1 beats/min, P < 0.05), cardiac output was significantly decreased (T1: 4.89 +/- 0.56 liters/min; 3.95 +/- 0.62 liters/min, P < 0.05). The ejection fraction was 65% at T1 and fell to 58% at T2 (P < 0.05). After hospitalization, significant decreases in hemoglobin concentration and hematocrit were observed, suggesting a fall in blood volume. CONCLUSION: In soccer players, knee surgery leads to resting cardiac deconditioning, which is characterized by a significant reduction in stroke volume.

Heart rate variability before and after knee surgery in amateur soccer players.

OBJECTIVE: To analyze the consequences on heart rate variability (HRV) of a hospitalization period due to surgery of the knee in sportsmen. PATIENTS: Ten soccer players who had undergone knee surgery took part in this study. DESIGN: HRV was measured before and after hospitalization within a 7-day interval. RESULTS: After the hospitalization phase, heart rate at rest increased significantly (3 beats/minute). A significant decrease of 7% in the cardiac inter beat interval (R-R interval), P < 0.05 and a 66% decrease in total power spectral density: -66%, P < 0.05 were observed. The disturbance of the autonomic nervous system could be due to a variation in cardiac vagal activity resulting in a 64% decrease in the high frequencies (P < 0.05). This variation was not associated with a modification in normalized markers (LFn.u., HFn.u.) and LF/HF ratio (P > 0.05). CONCLUSION: In sportsmen, a hospitalization period led to an increase in resting heart rate and was associated with a disturbance of the autonomic nervous system.