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| 3. |
- Joffrin, E., et al.
(författare)
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Overview of the JET preparation for deuterium-tritium operation with the ITER like-wall
- 2019
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 59:11
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Forskningsöversikt (refereegranskat)abstract
- For the past several years, the JET scientific programme (Pamela et al 2007 Fusion Eng. Des. 82 590) has been engaged in a multi-campaign effort, including experiments in D, H and T, leading up to 2020 and the first experiments with 50%/50% D-T mixtures since 1997 and the first ever D-T plasmas with the ITER mix of plasma-facing component materials. For this purpose, a concerted physics and technology programme was launched with a view to prepare the D-T campaign (DTE2). This paper addresses the key elements developed by the JET programme directly contributing to the D-T preparation. This intense preparation includes the review of the physics basis for the D-T operational scenarios, including the fusion power predictions through first principle and integrated modelling, and the impact of isotopes in the operation and physics of D-T plasmas (thermal and particle transport, high confinement mode (H-mode) access, Be and W erosion, fuel recovery, etc). This effort also requires improving several aspects of plasma operation for DTE2, such as real time control schemes, heat load control, disruption avoidance and a mitigation system (including the installation of a new shattered pellet injector), novel ion cyclotron resonance heating schemes (such as the three-ions scheme), new diagnostics (neutron camera and spectrometer, active Alfven eigenmode antennas, neutral gauges, radiation hard imaging systems...) and the calibration of the JET neutron diagnostics at 14 MeV for accurate fusion power measurement. The active preparation of JET for the 2020 D-T campaign provides an incomparable source of information and a basis for the future D-T operation of ITER, and it is also foreseen that a large number of key physics issues will be addressed in support of burning plasmas.
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| 6. |
- Andersson, Erik P., 1984-, et al.
(författare)
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Physiological responses and cycle characteristics during double-poling versus diagonal-stride roller-skiing in junior cross-country skiers
- 2021
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Ingår i: European Journal of Applied Physiology. - : Springer Science and Business Media LLC. - 1439-6319 .- 1439-6327. ; 121:8, s. 2229-2241
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: This study aimed to compare physiological factors and cycle characteristics during cross-country (XC) roller-skiing at matched inclines and speeds using the double-poling (DP) and diagonal-stride (DS) sub-techniques in junior female and male XC skiers. Methods: Twenty-three well-trained junior XC skiers (11 women, 12 men; age 18.2 ± 1.2 yr.) completed two treadmill roller-skiing tests in a randomized order using either DP or DS. The exercise protocols were identical and included a 5 min warm-up, 4 × 5 min submaximal stages, and an incremental test to exhaustion, all performed at a 5° incline. Results: No significant three-way interactions were observed between sex, submaximal exercise intensity, and sub-technique. For the pooled sample, higher values were observed for DP versus DS during submaximal exercise for the mean oxygen uptake kinetics response time (33%), energy cost (18%), heart rate (HR) (9%), blood lactate concentration (5.1 versus 2.1 mmol·L−1), rating of perceived exertion (12%), and cycle rate (25%), while cycle length was lower (19%) (all P < 0.001). During the time-to-exhaustion (TTE) test, peak oxygen uptake (V˙ O2peak), peak HR, and peak oxygen pulse were 8%, 2%, and 6% lower, respectively, for DP than DS, with a 29% shorter TTE during DP (pooled data, all P < 0.001). Conclusion: In well-trained junior XC skiers, DP was found to exert a greater physiological load than DS during uphill XC roller-skiing at submaximal intensities. During the TTE test, both female and male athletes were able to ski for longer and reached markedly higher V˙ O2peak values when using DS compared to DP.
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| 7. |
- Andersson, Erik P., 1984-, et al.
(författare)
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Anaerobic work capacity in cycling : the effect of computational method
- 2022
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Ingår i: European Journal of Applied Physiology. - : Springer Science and Business Media LLC. - 1439-6319 .- 1439-6327. ; 122, s. 2637-2650
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Tidskriftsartikel (refereegranskat)abstract
- Purpose To compare the anaerobic work capacity (AnWC, i.e., attributable anaerobic mechanical work) assessed using four different approaches/models applied to time-trial (TT) cycle-ergometry exercise. Methods Fifteen male cyclists completed a 7 x 4-min submaximal protocol and a 3-min all-out TT (TTAO). Linear relationships between power output (PO) and submaximal metabolic rate were constructed to estimate TT-specific gross efficiency (GE) and AnWC, using either a measured resting metabolic rate as a Y-intercept (7 + Y-LIN) or no measured Y-intercept (7-Y-LIN). In addition, GE of the last submaximal bout (GE(LAST)) was used to estimate AnWC, and critical power (CP) from TTAO (CP3'AO) was used to estimate mechanical work above CP (W', i.e., "AnWC"). Results Average PO during TTAO was 5.43 +/- 0.30 and CP was 4.48 +/- 0.23 W.kg(-1). The TT-associated GE values were similar to 22.0% for both 7 + Y-LIN and 7-Y-LIN and similar to 21.1% for GE(LAST) (both P < 0.001). The AnWC were 269 +/- 60, 272 +/- 55, 299 +/- 61, and 196 +/- 52 J.kg(-1) for the 7 + Y-LIN, 7 Y-LIN, GE(LAST), and CP3'AO models, respectively (7 + Y-LIN and 7-Y-LIN versus GE(LAST), both P <0.001; 7+ Y-LIN, 7 Y-LIN, and GE(LAST) versus CP3'AO, all P < 0.01). For the three pair-wise comparisons between 7+ Y-LIN, 7-Y-LIN, and GE(LAST), typical errors in AnWC values ranged from 7 to 11 J.kg(-1), whereas 7+ Y-LIN, 7-Y-LIN, and GE(LAST) versus CP3'AO revealed typical errors of 55-59 J.kg(-1). Conclusion These findings demonstrate a substantial disagreement in AnWC between CP3'AO and the other models. The 7 + Y-LIN and 7-Y-LIN generated 10% lower AnWC values than the GE(LAST) model, whereas 7 + Y-LIN and 7-Y-LIN generated similar values of AnWC.
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| 8. |
- Andersson, Erik P., 1984-, et al.
(författare)
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Physiological responses and performance factors for double-poling and diagonal-stride treadmill roller-skiing time-trial exercise
- 2023
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Ingår i: European Journal of Applied Physiology. - : Springer. - 1439-6319 .- 1439-6327. ; 123:11, s. 2495-2509
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To compare physiological responses between a self-paced 4-min double-poling (DP) time-trial (TTDP) versus a 4-min diagonal-stride (DS) time-trial (TTDS). The relative importance of peak oxygen uptake (V ˙ O2peak), anaerobic capacity, and gross efficiency (GE) for projection of 4-min TTDP and TTDS roller-skiing performances were also examined. Methods: Sixteen highly trained male cross-country skiers performed, in each sub-technique on separate occasions, an 8 × 4-min incremental submaximal protocol, to assess individual metabolic rate (MR) versus power output (PO) relationships, followed by a 10-min passive break and then the TTDP or TTDS, with a randomized order between sub-techniques. Results: In comparison to TTDS, the TTDP resulted in 10 ± 7% lower total MR, 5 ± 4% lower aerobic MR, 30 ± 37% lower anaerobic MR, and 4.7 ± 1.2 percentage points lower GE, which resulted in a 32 ± 4% lower PO (all P < 0.01). The V ˙ O2peak and anaerobic capacity were 4 ± 4% and 30 ± 37% lower, respectively, in DP than DS (both P < 0.01). The PO for the two time-trial (TT) performances were not significantly correlated (R 2 = 0.044). Similar parabolic pacing strategies were used during both TTs. Multivariate data analysis projected TT performance using V ˙ O2peak, anaerobic capacity, and GE (TTDP, R 2 = 0.974; TTDS, R 2 = 0.848). The variable influence on projection values for V ˙ O2peak, anaerobic capacity, and GE were for TTDP, 1.12 ± 0.60, 1.01 ± 0.72, and 0.83 ± 0.38, respectively, and TTDS, 1.22 ± 0.35, 0.93 ± 0.44, and 0.75 ± 0.19, respectively. Conclusions: The results show that a cross-country skier’s “metabolic profile” and performance capability are highly sub-technique specific and that 4-min TT performance is differentiated by physiological factors, such as V ˙ O2peak, anaerobic capacity, and GE.
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| 9. |
- Andersson, Erik P., 1984-, et al.
(författare)
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Sex differences in performance and pacing strategies during a sprint time-trial in cross-country skiing
- 2018
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Konferensbidrag (refereegranskat)abstract
- INTRODUCTION: The aim of this study was to compare the pacing strategies, choice of sub-technique (i.e., gear) and overall performance between elite male and female cross-country (XC) skiers during a ski-skating sprint time-trial (TT) on snow.METHODS: Thirty-four elite XC skiers (20 males and 14 females: age, 23 ± 4 and 21 ± 3 yr; body mass, 76 ± 8 and 64 ± 5 kg; height, 183 ± 7 and 171 ± 5 cm; sprint FIS points, 86 ± 42 and 90 ± 54) performed a 1.6 km TT, which was 56% flat (or undulating), 21% uphill and 22% downhill. The sprint course was measured with a differential global navigation satellite system and divided into four flat, three uphill and two downhill sections. Race time was measured with the EMIT timing system (Emit AS, Oslo, Norway) and one 25-m uphill (4°) section was filmed continuously with a fixed camcorder (50 Hz). All skiers used a similar stone-grind and all skis were glide-waxed similarly. The air temperature was +1°C (fresh snow at ±0°C), relative humidity was 90% and the friction coefficient between ski and snow was estimated to 0.045 (i.e., very slow).RESULTS: Average speed during the TT was 25 ± 1 and 22 ± 1 km/h (TT time: 227 ± 11 and 254 ± 10 s) for males and females, respectively (P < 0.001, Cohen’s d effect size [ES] = 2.6). Average relative power output (PO) was estimated to 3.9 ± 0.3 and 3.3 ± 0.2 W/kg for males and females, respectively (P < 0.001, ES = 2.5). Average heart rate was 95 ± 2% and 96 ± 1% of maximum for males and females (P = 0.51), with a 2-min post-race blood lactate concentration of 10 ± 2 mmol/L for both sexes (P = 0.64). Within-athlete coefficient of variation in speed between sections was 20 ± 2% for males and 24 ± 1% for females (P < 0.001, ES = 2.6). Speeds on the flat, uphill and downhill sections were 26 ± 1, 19 ± 1 and 32 ± 1 km/h for males and 23 ± 1, 16 ± 1 and 30 ± 1 km/h for females (main effects for terrain, sex and interaction, all P < 0.01) corresponding to 9%, 16% and 8% slower speeds on flat, uphill and downhill terrain for females. Speeds relative to the average TT speed were 103 ± 1%, 77 ± 2% and 129 ± 4% for males and 105 ± 1%, 72 ± 2% and 133 ± 2% for females (main effects for terrain, sex and interaction, all P < 0.001). Relative PO on the flat, uphill and downhill sections were estimated to 4.0 ± 0.3, 4.9 ± 0.4 and 1.9 ± 0.2 W/kg for males and 3.5 ± 0.2, 4.0 ± 0.3 and 1.5 ± 0.2 W/kg for females (main effects for terrain, sex and interaction, all P < 0.001). The males were 20% faster than the females on the uphill video section (16 ± 1 versus 13 ± 1 km/h, P < 0.001, ES = 2.6), with 95% of the male skiers and 21% of the female skiers using gear 3 exclusively, and the remaining skiers using gear 2 exclusively or a combination of gears 2 and 3.CONCLUSION: The present results indicate an overall sex difference in sprint skiing performance of ~12% and reveal differences in terrain-specific pacing as well as gear choice between sexes with females showing a higher overall variation in speed and considerably slower uphill skiing.
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| 10. |
- Andersson, Erik P., 1984-, et al.
(författare)
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The Anaerobic Capacity of Cross-Country Skiers : The Effect of Computational Method and Skiing Sub-technique
- 2020
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Ingår i: Frontiers in Sports and Active Living. - : Frontiers Media SA. - 2624-9367. ; 2
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Tidskriftsartikel (refereegranskat)abstract
- Anaerobic capacity is an important performance-determining variable of sprint cross-country skiing. Nevertheless, to date, no study has directly compared the anaerobic capacity, determined using the maximal accumulated oxygen deficit (MAOD) method and gross efficiency (GE) method, while using different skiing sub-techniques.Purpose: To compare the anaerobic capacity assessed using two different MAOD approaches (including and excluding a measured y-intercept) and the GE method during double poling (DP) and diagonal stride (DS) cross-country skiing.Methods: After an initial familiarization trial, 16 well-trained male cross-country skiers performed, in each sub-technique on separate occasions, a submaximal protocol consisting of eight 4-min bouts at intensities between ~47–78% of V.V.O2peak followed by a 4-min roller-skiing time trial, with the order of sub-technique being randomized. Linear and polynomial speed-metabolic rate relationships were constructed for both sub-techniques, while using a measured y-intercept (8+YLIN and 8+YPOL) or not (8–YLIN and 8–YPOL), to determine the anaerobic capacity using the MAOD method. The average GE (GEAVG) of all eight submaximal exercise bouts or the GE of the last submaximal exercise bout (GELAST) were used to calculate the anaerobic capacity using the GE method. Repeated measures ANOVA were used to test differences in anaerobic capacity between methods/approaches.Results: A significant interaction was found between computational method and skiing sub-technique (P < 0.001, η2 = 0.51) for the anaerobic capacity estimates. The different methodologies resulted in significantly different anaerobic capacity values in DP (P < 0.001, η2 = 0.74) and in DS (P = 0.016, η2 = 0.27). The 8-YPOL model resulted in the smallest standard error of the estimate (SEE, 0.24 W·kg−1) of the MAOD methods in DP, while the 8-YLIN resulted in a smaller SEE value than the 8+YLIN model (0.17 vs. 0.33 W·kg−1) in DS. The 8-YLIN and GELAST resulted in the closest agreement in anaerobic capacity values in DS (typical error 2.1 mL O2eq·kg−1).Conclusions: It is discouraged to use the same method to estimate the anaerobic capacity in DP and DS sub-techniques. In DP, a polynomial MAOD method (8-YPOL) seems to be the preferred method, whereas the 8-YLIN, GEAVG, and GELAST can all be used for DS, but not interchangeable, with GELAST being the least time-consuming method.
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| 11. |
- Andersson, Erik P., 1984-, et al.
(författare)
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The effect of exercise hyperpnea on gross efficiency and anaerobic capacity estimates during a 3-min cycle time trial
- 2023
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Ingår i: Journal of applied physiology. - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 134:2, s. 253-263
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Tidskriftsartikel (refereegranskat)abstract
- This study aimed to analyze the effect of exercise-induced hyperpnea on gross efficiency (GE) and anaerobic capacity estimates during a self-paced 3-min supramaximal cycle time trial (TT). Fourteen highly trained male cyclists performed 7 × 4-min submaximal stages, a 6-min passive rest, a 3-min TT, a 5-min passive rest, and a 6-min submaximal stage. Three models were based on the 7 × 4-min linear regression extrapolation method, using 1) the conventional model (7-YLIN); 2) the same 7-YLIN model but correcting for the additional ventilatory cost (i.e., hyperpnea) (7-YLIN-V-cor); and 3) accounting for linearly declining GE during the TT (7-YLIN-D). The other three models were based on GE from the last submaximal stage, using the conventional model (GELAST) and the same modifications as described for 7+YLIN, i.e., 1) GELAST, 2) GELAST-V-cor, and 3) GELAST-D. The GELAST model generated 18% higher values of anaerobic capacity than the 7-YLIN model (P < 0.05). During the TT, the hyperpnea-corrected model (i.e., 7-YLIN-V-cor or GELAST-V-cor) generated, compared with the respective conventional model (i.e., 7-YLIN or GELAST), ∼0.7 percentage points lower GE and ∼11% higher anaerobic capacity (all, P < 0.05). The post-TT GE was 1.9 percentage points lower (P < 0.001) and the 7-YLIN-D or GELAST-D model generated, compared with the respective conventional model, a lower GE (∼1.0 percentage points) and ∼17% higher anaerobic capacity during the TT (all, P < 0.05). In conclusion, the correction for a declining GE due to hyperpnea during a supramaximal TT resulted in an increased required total metabolic rate and anaerobic energy expenditure compared with the conventional models.NEW & NOTEWORTHY This study demonstrates that GE declines during a 3-min supramaximal cycle TT, which is possibly related to the hyperpneic response during supramaximal exercise. The finding from this study also provides novel insight into how the increased ventilatory energy cost from exercise-induced hyperpnea contributes to decreased GE, increased required total metabolic rate, and increased anaerobic energy expenditure during supramaximal exercise. Therefore, conventional linear models for estimating anaerobic capacity are likely to generate underestimated values.
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| 12. |
- Gejl, Kasper Degn, et al.
(författare)
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Effects of Acute Exercise and Training on the Sarcoplasmic Reticulum Ca(2+)Release and Uptake Rates in Highly Trained Endurance Athletes
- 2020
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Ingår i: Frontiers in Physiology. - : Frontiers Media SA. - 1664-042X. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Little is presently known about the effects of acute high-intensity exercise or training on release and uptake of Ca(2+)by the sarcoplasmic reticulum (SR). The aims here were to characterize this regulation in highly trained athletes following (1) repeated bouts of high-intensity exercise and (2) a period of endurance training including high-intensity sessions. Eleven cross-country skiers (25 +/- 4 years, 65 +/- 4 mL O-2.kg(-1).min(-1)) performed four self-paced sprint time-trials (STT 1-4) lasting approximate to 4 min each (STT 1-4) and separated by 45 min of recovery; while 19 triathletes and road cyclists (25 +/- 4 years, 65 +/- 5 mL O-2.kg(-1).min(-1)) completed 4 weeks of endurance training in combination with three sessions of high-intensity interval cycling per week. Release (mu mol.g(-1)prot.min(-1)) and uptake [tau (s)] of Ca(2+)by SR vesicles isolated from m.triceps brachiiand m.vastus lateraliswere determined before and after STT 1 and 4 in the skiers and in m.vastus lateralisbefore and after the 4 weeks of training in the endurance athletes. The Ca(2+)release rate was reduced by 17-18% in both limbs already after STT 1 (arms: 2.52 +/- 0.74 to 2.08 +/- 0.60; legs: 2.41 +/- 0.45 to 1.98 +/- 0.51,P< 0.0001) and attenuated further following STT 4 (arms: 2.24 +/- 0.67 to 1.95 +/- 0.45; legs: 2.13 +/- 0.51 to 1.83 +/- 0.36,P< 0.0001). Also, there was a tendency toward an impairment in the SR Ca(2+)uptake from pre STT1 to post STT4 in both arms and legs (arms: from 22.0 +/- 3.7 s to 25.3 +/- 6.0 s; legs: from 22.5 +/- 4.7 s to 25.5 +/- 7.7 s,P= 0.05). Endurance training combined with high-intensity exercise increased the Ca(2+)release rate by 9% (1.76 +/- 0.38 to 1.91 +/- 0.44,P= 0.009), without altering the Ca(2+)uptake (29.6 +/- 7.0 to 29.1 +/- 8.7 s;P= 0.98). In conclusion, the Ca(2+)release and uptake rates by SR in exercising limbs of highly trained athletes declines gradually by repetitive bouts of high-intensity exercise. We also demonstrate, for the first time, that the SR Ca(2+)release rate can be enhanced by a specific program of training in highly trained athletes, which may have important implications for performance parameters.
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| 13. |
- Govus, Andrew, et al.
(författare)
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Commercially available compression garments or electrical stimulation do not enhance recovery following a sprint competition in elite cross-country skiers
- 2018
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Ingår i: European Journal of Sport Science. - : Informa UK Limited. - 1746-1391 .- 1536-7290. ; 18:10, s. 1299-1308
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Tidskriftsartikel (refereegranskat)abstract
- This study investigated whether commercially available compression garments (COMP) exerting a moderate level of pressureand/or neuromuscular electrical stimulation (NMES) accelerate recovery following a cross-country sprint skiing competitioncompared with a control group (CON) consisting of active recovery only. Twenty-one senior (12 males, 9 females) and 11junior (6 males, 5 females) Swedish national team skiers performed an outdoor sprint skiing competition involving foursprints lasting ∼3–4 min. Before the competition, skiers were matched by sex and skiing level (senior versus junior) andrandomly assigned to COMP (n = 11), NMES (n = 11) or CON (n = 10). Creatine kinase (CK), urea, countermovementjump (CMJ) height, and perceived muscle pain were measured before and 8, 20, 44 and 68 h after competition. NeitherCOMP nor NMES promoted the recovery of blood biomarkers, CMJ or perceived pain post-competition compared withCON (all P > .05). When grouping all 32 participants, urea and perceived muscle pain increased from baseline, peaking at8 h (standardised mean difference (SMD), [95% confidence intervals (CIs)]): 2.8 [2.3, 3.2]) and 44 h (odds ratio [95%CI]: 3.3 [2.1, 5.1]) post-competition, respectively. Additionally, CMJ was lower than baseline 44 and 68 h postcompetitionin both males and females (P < .05). CK increased from baseline in males, peaking at 44 h (SMD: 1.4 [−0.4,0.9]), but was decreased in females at 20 h post-competition (SMD: −0.8 [−1.4, −0.2]). In conclusion, cross-countrysprint skiing induced symptoms of exercise-induced muscle damage peaking 8–44 h post-competition. However, neitherCOMP nor NMES promoted physiological or perceptual recovery compared with CON.
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| 14. |
- Hafsteinsson, Haukur, 1984, et al.
(författare)
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Exploration of temperature effects on the far-field acoustic radiation from a supersonic jet
- 2014
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Ingår i: 20th AIAA/CEAS Aeroacoustics Conference. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624102851
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Konferensbidrag (refereegranskat)abstract
- Jet engines designed for high-speed aircraft commonly include C-D nozzles to obtain supersonic speeds. The radiated noise from the jet exhaust reaches acoustic levels which may cause hearing damage to the pilot and the air-field personnel even though state of the art noise protection such as noise-canceling ear muffs are employed. It is therefore extremely important to keep the noise levels as low as possible. Understanding the noise generation mechanism is of great importance in order to reduce strength of the noise sources. Typical far-field noise spectral characteristics from the supersonic jet exhaust consist of turbulent mixing noise and shock-associated noise. Another noise component named'crackle' is radiated from the jet under certain circumstances. Although it does not appear in the noise spectra due to its characteristics, its rasping character is perceived as a dominant annoyance factor by the human ear. Since it does not appear in the spectrum other measures are needed to identify the existence of'crackle'. Statistical tools like Skewness and Kurtosis applied to the far- and near-field pressure signals and the time derivate of the pressure signal have been shown in literature to be useful for identification of'crackle' events. In this paper the near-field and far-field acoustic radiation from a supersonic jet is analyzed using LES with a code developed at Chalmers University of Technology. The code has previously shown to accurately capture far-field noise spectra of supersonic jets under a variety of moderately cool jet conditions. In the present study we move towards more realistic high-speed aircraft conditions with higher jet exhaust temperatures. The nozzle is operated at slightly underexpanded conditions (NPR = 4.0) and three different stagnation temperature ratios NTR = 1.0, NTR = 2.0 and NTR = 3.0. The LES results are compared with experiments conducted at the Gas Dynamics and Propulsion Laboratory at the University of Cincinnati.
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| 15. |
- Jones, Thomas W., et al.
(författare)
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An Analysis of Warm-Up Strategies at a Cross-Country Skiing National Championship
- 2022
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Ingår i: International Journal of Sports Physiology and Performance. - : Human Kinetics. - 1555-0265 .- 1555-0273. ; 17:1, s. 50-57
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To provide a descriptive analysis of the warm-up (WU) strategies employed by cross-country skiers prior to distance and sprint competitions at a national championship and to compare the skiers' planned and executed WUs prior to the respective competitions.Methods: Twenty-one national- and international-level skiers (11 women and 10 men) submitted WU plans prior to the distance and sprint competitions, and after the competitions, reported any deviations from the plans. Skiers used personal monitors to record heart rate (HR) during WU, races, and cooldown. Quantitative statistical analyses were conducted on WU durations, durations in HR-derived intensity zones, and WU loads. Qualitative analyses were conducted on skiers' WU plans and their reasons for deviating from the plans.Results: Skiers' planned WUs were similar in content and planned time in HR-derived intensity zones for both the distance and sprint competitions. However, 45% of the women and 20% of the men reported that their WU was not carried out as planned, with reasons detailed as being due to incorrect intensities and running out of time. WU activities including skiing across variable terrain, muscle-potentiating exercises, and heat-maintenance strategies were missing from the skiers' planned routines.Conclusions: Skiers favored a long, traditional WU approach for both the sprint and distance events, performing less high-intensity and more moderate-intensity exercise during their WUs than planned. In addition, elements likely relevant to successful performance in cross-country skiing were missing from WU plans.
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| 16. |
- Lidar, Julius, et al.
(författare)
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Validity and Reliability of Hydraulic-Analogy Bioenergetic Models in Sprint Roller Skiing
- 2021
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Ingår i: Frontiers in Physiology. - : Frontiers Media SA. - 1664-042X. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To develop a method for individual parameter estimation of four hydraulic-analogy bioenergetic models and to assess the validity and reliability of these models’ prediction of aerobic and anaerobic metabolic utilization during sprint roller-skiing. Methods: Eleven elite cross-country skiers performed two treadmill roller-skiing time trials on a course consisting of three flat sections interspersed by two uphill sections. Aerobic and anaerobic metabolic rate contributions, external power output, and gross efficiency were determined. Two versions each (fixed or free maximal aerobic metabolic rate) of a two-tank hydraulic-analogy bioenergetic model (2TM-fixed and 2TM-free) and a more complex three-tank model (3TM-fixed and 3TM-free) were programmed into MATLAB. The aerobic metabolic rate (MRae) and the accumulated anaerobic energy expenditure (Ean,acc) from the first time trial (STT1) together with a gray-box model in MATLAB, were used to estimate the bioenergetic model parameters. Validity was assessed by simulation of each bioenergetic model using the estimated parameters from STT1 and the total metabolic rate (MRtot) in the second time trial (STT2). Results: The validity and reliability of the parameter estimation method based on STT1 revealed valid and reliable overall results for all the four models vs. measurement data with the 2TM-free model being the most valid. Mean differences in model-vs.-measured MRae ranged between -0.005 and 0.016 kW with typical errors between 0.002 and 0.009 kW. Mean differences in Ean,acc at STT termination ranged between −4.3 and 0.5 kJ and typical errors were between 0.6 and 2.1 kJ. The root mean square error (RMSE) for 2TM-free on the instantaneous STT1 data was 0.05 kW for MRae and 0.61 kJ for Ean,acc, which was lower than the other three models (all P < 0.05). Compared to the results in STT1, the validity and reliability of each individually adapted bioenergetic model was worse during STT2 with models underpredicting MRae and overpredicting Ean,acc vs. measurement data (all P < 0.05). Moreover, the 2TM-free had the lowest RMSEs during STT2. Conclusion: The 2TM-free provided the highest validity and reliability in MRae and Ean,acc for both the parameter estimation in STT1 and the model validity and reliability evaluation in the succeeding STT2.
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| 17. |
- Lögdal, Nestor, et al.
(författare)
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Individual Fluctuations in Blood Lactate Concentration During an Ice Hockey Game; Differences Between Player Positions
- 2022
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Ingår i: International Journal of Exercise Science. - : Western Kentucky University. - 1939-795X. ; 15:6, s. 985-993
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Tidskriftsartikel (refereegranskat)abstract
- International Journal of Exercise Science 15(6): 985-993, 2022. The main purpose of the current study was to provide an in-depth description of individual player’s intra-game physiological responses during an ice hockey game. A secondary aim was to compare these responses between forwards and defensemen. Six elite junior ice hockey players, three forwards and three defensemen, median (interquartile range) 17 (17–17) years, 182 (180– 185) cm, and 78 (74– 80) kg were recruited to participate in the study. Capillary blood samples were taken following each shift and analyzed for blood lactate concentration (BLC). Heart rate (HR) was registered continuously throughout the game. The game was filmed and shift lengths were determined retrospectively using a time-motion analysis. All players had BLC ranging between 1.8 and 10.7 mmol/L (mean = 5.5 mmol/L), with forwards reaching a significantly higher value than defensive players (F1,32 = 75.2, p < 0.0001), a significant effect of time was also observed (F2,25 = 6.4, p = 0.0058). During the game, the players accumulated 11:18 ± 5:04 (minutes:seconds) above 90% of their maximal heart rate (HRmax), but the majority of the time was below 80% of HRmax. The fluctuations in BLC and heart rate demonstrate that the intensity is highly variable during games and challenges both aerobic and anaerobic metabolic pathways. The higher BLC of forwards might indicate that they perform more high-intensity work during games than defensive players.
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| 18. |
- Osborne, John O., et al.
(författare)
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Annual Volume and Distribution of Physical Training in Norwegian Female Cross-Country Skiers and Biathletes : A Comparison Between Sports, Competition Levels, and Age Categories- The FENDURA Project
- 2024
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Ingår i: International Journal of Sports Physiology and Performance. - : Human Kinetics. - 1555-0265 .- 1555-0273. ; 19:1, s. 19-27
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To describe and compare the annual physical training characteristics between Norwegian female cross-country (XC) skiers and biathletes across competition levels and age categories. Methods: Daily training sessions for 1 year were recorded for 45 XC skiers and 26 biathletes, comprising international/national team (inter[national]) and nonnational/regional team members (nonnational) of both junior and senior age. Endurance, strength, flexibility, speed, and power training sessions were recorded. Data included exercise modality, intensity, and duration. Data were analyzed using linear mixed-effects models. Results: The total annual physical training volume consisted of -90% endurance training for both groups, although XC skiers had significantly higher total volumes (-10%; P = .003; d= 0.78) than biathletes. Senior XC skiers performed more training hours of skiing and/or roller skiing compared with biathletes over the season. However, biathletes compensated for this lower volume by more skating and a higher proportion of endurance training as skiing (81% [17%]) compared with XC skiers (68% [16%]; P < .001; d= 0.94). Overall, (inter)national-level athletes completed a higher annual training volume than non-national-level athletes (740 [90] h vs 649 [95] h; P= .004;d = 0.81). Although juniors reported less endurance volume than seniors, they maintained a relatively stable level of endurance training across the preparatory and competition period, unlike senior athletes. Conclusions: The higher annual physical training volume by XC skiers compared with biathletes is likely caused by the different demands of the 2 sports; XC skiing necessitates training for 2 skiing styles, while biathlon requires additional shooting practice. However, biathletes compensate with a higher proportion of ski training, particularly in the skating technique.
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| 19. |
- Staunton, Craig A., et al.
(författare)
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Heart Rate–Blood Lactate Profiling in World-Class Biathletes During Cross-Country Skiing : The Difference Between Laboratory and Field Tests
- 2023
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Ingår i: International Journal of Sports Physiology and Performance. - 1555-0265 .- 1555-0273. ; 18:7, s. 780-785
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To identify differences in heart rate (HR) and concentration of blood lactate ([La]) relationships between laboratory and field-based skate-roller-skiing tests.Methods: Fourteen world-class biathletes (8 women, 6 men) completed a laboratory- and field-based roller-skiing test using the skate technique. The laboratory-based test comprised 5 to 7 submaximal steps at a fixed incline and speed on a roller-skiing treadmill. The field-based test comprised 5 steps on a course where the final hill was designed to mimic the conditions of the laboratory test. HR and [La] were measured for each step. The HR associated with 2 mmol·L−1(HR@2 mmol) and 4 mmol·L−1 (HR@4 mmol) of [La] was calculated using an interpolation method. A 1-way analysis of variance and Bland–Altman analyses with 95% limits of agreement (LoA) were used to determine if test type influenced HR@2 mmol orHR@4 mmol. A second-order polynomial was fitted to group-level data to highlight the HR–[La] relationships for laboratory- and field-based tests.Results: HR@2 mmol was lower for field tests than for laboratory tests (mean bias: 1.9%HRmax; 95% LoA: −4.5 to+8.3%HRmax; P < .001). HR@4 mmol was also lower for field tests compared to laboratory tests (mean bias: 2.4%HRmax; 95%LoA: −1.2 to +6.0%HRmax; P < .001). On the group level, the lactate threshold occurred at a lower HR during roller skiing in the field compared to the laboratory.Conclusions: The findings from this study confirm that for a given HR, [La] was greater in field compared with laboratory-based conditions. These results might have implications for how coaches define training-intensity“zones” during skate roller skiing based on laboratory tests.
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| 20. |
- Stenfors, Nikolai, et al.
(författare)
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A breathing mask attenuates acute airway responses to exercise in sub-zero environment in healthy subjects
- 2022
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Ingår i: European Journal of Applied Physiology. - : Springer Science+Business Media B.V.. - 1439-6319 .- 1439-6327. ; 122, s. 1473-1484
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Cold air exposure is associated with increased respiratory morbidity and mortality. Repeated inhalation of cold and dry air is considered the cause of the high prevalence of asthma among winter endurance athletes. This study assessed whether a heat- and moisture-exchanging breathing device (HME) attenuates airway responses to high-intensity exercise in sub-zero temperatures among healthy subjects.Methods: Using a randomized cross-over design, 23 healthy trained participants performed a 30-min warm-up followed by a 4-min maximal, self-paced running time trial in − 15 °C, with and without HME. Lung function was assessed pre- and immediately post-trials. Club cell protein (CC-16), 8-isoprostane, and cytokine concentrations were measured in plasma and urine pre- and 60 min post trials. Symptoms were assessed prior to, during, and immediately after each trial in the chamber.Results: HME use attenuated the decrease in forced expiratory volume in 1 s (FEV1) post trials (∆FEV1: mean (SD) HME − 0.5 (1.9) % vs. no-HME − 2.7 (2.7) %, p = 0.002). HME also substantially attenuated the median relative increase in plasma-CC16 concentrations (with HME + 27% (interquartile range 9–38) vs no-HME + 121% (55–162), p < 0.001) and reduced airway and general symptom intensity, compared to the trial without HME. No significant changes between trials were detected in urine CC16, 8-isoprostane, or cytokine concentrations.Conclusion: The HME attenuated acute airway responses induced by moderate-to-maximal-intensity exercise in − 15 °C in healthy subjects. Further studies are needed to examine whether this HMEs could constitute primary prevention against asthma in winter endurance athletes.
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| 21. |
- Stoeggl, Thomas L., et al.
(författare)
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Pacing, Exercise Intensity, and Technique by Performance Level in Long-Distance Cross-Country Skiing
- 2020
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Ingår i: Frontiers in Physiology. - : Frontiers Media SA. - 1664-042X. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Introduction Long-distance cross-country skiing (XCS) has gained increased popularity within the past decades. However, research about long-distance XCS is limited; therefore, the aim of this study was to analyze the intensity distribution, technique application, and pacing strategies during long-distance XCS racing. Methods Heart rate (HR) and section skiing speeds of 9 elite (ranked 1-100) and 10 amateur skiers (ranked 101-1,500) during the 90-km Vasaloppet race were collected. In addition, during the first uphill, the first 1,000 skiers were video-recorded to analyze the applied skiing strategy (e.g. grip-waxed skis versus exclusive double poling). Results Mean race intensity was 82% of maximal HR and was not different between performance groups even though elite skiers skied similar to 15% faster than amateurs. There was an interaction effect of section x group with a pronounced decrease in HR in amateurs compared with more even pacing in elite skiers (0.13 vs. 0.04% decrease/km) and skiing at higher percentage in the high-intensity zones in elite compared with amateurs (46 vs. 24%). Ninety-eight percent of the top 100 skiers and 59% of the first 1,000 skiers used exclusively double poling. Conclusion Elite and amateur skiers ski at comparable mean race exercise intensity, but they have clear differences in skiing speed. The difference in the pacing profiles between elite and amateur skiers (more even vs. distinct positive pacing) demonstrate the greater capacity of the former with respect to physiological capacity and highlights that amateurs seem to start too fast according to their capacities. The exclusive application of the double poling technique is no longer a phenomenon of elite skiers but is widely used among the top 1,000 ranked skiers.
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| 22. |
- Taylor, Madison Y., et al.
(författare)
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Menstrual Cycle Phase Has No Influence on Performance-Determining Variables in Endurance-Trained Athletes : The FENDURA Project
- 2024
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Ingår i: Medicine & Science in Sports & Exercise. - : Ovid Technologies (Wolters Kluwer Health). - 0195-9131 .- 1530-0315. ; 56:9, s. 1595-1605
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Tidskriftsartikel (refereegranskat)abstract
- Female athletes frequently perceive performance changes throughout the menstrual cycle (MC). However, if and how the MC influences performance-determining variables remain unclear.PurposeThis study aimed to investigate the effect of the MC and endogenous sex hormone concentrations on performance-determining variables in three distinct MC phases in endurance-trained females.MethodsTwenty-one eumenorrheic trained/highly trained endurance athletes completed a standardized test battery during the early follicular phase (EFP), ovulatory phase (OP), and midluteal phase (MLP) for either one (n = 7) or two test cycles (n = 14). MC phases were determined using calendar-based counting, urinary ovulation testing, and verified with serum hormone analysis. MCs were retrospectively classified as eumenorrheic or disturbed. Disturbed MCs were excluded from analysis. The test battery consisted of 4-6 x 5-min submaximal stages with stepwise speed increases, a 30-s all-out double-poling ski ergometer test, and a maximal incremental treadmill running test.ResultsAt a group level, there was no effect of MC phase or the serum concentrations of estrogen and progesterone on peak oxygen uptake (VO2peak), oxygen uptake at 4 mmolL-1 blood lactate concentration, time to exhaustion, running economy, or mean 30-s power output (MPO30s). Serum testosterone concentration was positively associated with MPO30s (P = 0.016). Changes in VO2peak from EFP to MLP were inconsistent between individuals and across cycles.ConclusionsNone of the measured performance-determining variables were influenced by MC phase or serum estrogen or progesterone concentrations. Although some individual patterns could be observed, there was no indication that any single MC phase is consistently associated with improved or impaired VO2peak on a group level.
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| 23. |
- Tutt, Alasdair S., et al.
(författare)
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A heat and moisture-exchanging mask impairs self-paced maximal running performance in a sub-zero environment
- 2021
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Ingår i: European Journal of Applied Physiology. - : Springer. - 1439-6319 .- 1439-6327. ; 121:7, s. 1979-1992
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Heat-and-moisture-exchanging devices (HME) are commonly used by endurance athletes during training in sub-zero environments, but their effects on performance are unknown. We investigated the influence of HME usage on running performance at − 15 °C.Methods: Twenty-three healthy adults (15 male, 8 female; age 18–53 years; V˙ O 2peak men 56 ± 7, women 50 ± 4 mL·kg−1·min−1) performed two treadmill exercise tests with and without a mask-style HME in a randomised, crossover design. Participants performed a 30-min submaximal warm-up (SUB), followed by a 4-min maximal, self-paced running time-trial (TT). Heart rate (HR), respiratory frequency (fR), and thoracic area skin temperature (Tsk) were monitored using a chest-strap device; muscle oxygenation (SmO2) and deoxyhaemoglobin concentration ([HHb]) were derived from near-infra-red-spectroscopy sensors on m. vastus lateralis; blood lactate was measured 2 min before and after the TT.Results: HME usage reduced distance covered in the TT by 1.4%, despite similar perceived exertion, HR, fR, and lactate accumulation. The magnitude of the negative effect of the HME on performance was positively associated with body mass (r2 = 0.22). SmO2 and [HHb] were 3.1% lower and 0.35 arb. unit higher, respectively, during the TT with HME, and Tsk was 0.66 °C higher during the HME TT in men. HR (+ 2.7 beats·min−1) and Tsk (+ 0.34 °C) were higher during SUB with HME. In the male participants, SmO2 was 3.8% lower and [HHb] 0.42 arb. unit higher during SUB with HME.Conclusion: Our findings suggest that HME usage impairs maximal running performance and increases the physiological demands of submaximal exercise.
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| 24. |
- Vasilopoulou, T., et al.
(författare)
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Improved neutron activation dosimetry for fusion
- 2019
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Ingår i: Fusion engineering and design. - : ELSEVIER SCIENCE SA. - 0920-3796 .- 1873-7196. ; 139, s. 109-114
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Tidskriftsartikel (refereegranskat)abstract
- Neutron activation technique has been widely used for the monitoring of neutron fluence at the Joint European Torus (JET) whereas it is foreseen to be employed at future fusion plants, such as ITER and DEMO. Neutron activation provides a robust tool for the measurement of neutron fluence in the complex environment encountered in a tokamak. However, activation experiments previously performed at JET showed that the activation foils used need to be calibrated in a real fusion environment in order to provide accurate neutron fluence data. Triggered by this challenge, an improved neutron activation method for the evaluation of neutron fluence at fusion devices has been developed. Activation assemblies similar to those used at JET were irradiated under 14 MeV neutrons at the Frascati Neutron Generator (FNG) reference neutron field. The data obtained from the calibration experiment were applied for the analysis of activation foil measurements performed during the implemented JET Deuterium-Deuterium (D-D) campaign. The activation results were compared against thermoluminescence measurements and a satisfactory agreement was observed. The proposed method provides confidence on the use of activation technique for the precise estimation of neutron fluence at fusion devices and enables its successful implementation in the forthcoming JET Deuterium-Tritium (D-T) campaign.
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