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1.
This is the second of two articles by the same author arguing against the thesis that there was a conspiracy between the Byzantine emperors and Saladin, sultan of Egypt and Syria, against the crusader states and the Third Crusade in the 1180s. While the focus of the first article was primarily on the Latin sources, the present study shifts the focus to the Arabic primary material, hitherto largely neglected or inadequately treated by modern historians. Through a critical re-examination and re-interpretation of the Arabic sources, backed by the introduction and discussion of new Latin material when necessary, this article presents expanded arguments on the relations between the Byzantine Empire, the Sultanate of Konya and Saladin in the 1180s. The conclusions lend further support to the view that the Byzantine rulers and Saladin never concluded an alliance against the Latin settlers of Outremer and the Third Crusade.  相似文献   
2.
Abstract

The aim of this study was to test the hypothesis that sprint performance (time over a given distance) would be affected by track compliance, with better performances on the more compliant surface. Ten sprinters participated in the study. The athletes performed maximal sprints (60 m) on three different track configurations (hard, 5500 kN · m?1; soft, 2200 kN · m?1; spring, 550 kN · m?1). A 60-m single-lane running surface was constructed. Plywood boards (1.2 cm thick) were placed on a 60 × 0.6 m wooden chipboard frame serving as the base surface. All participants ran two times on each track configuration in a randomized order. The athletes' kinematics were recorded using the Vicon 624 system with 12 cameras operating at 250 Hz. Four Kistler force plates (1250 Hz) were used to record ground reaction forces. Sprint performance (time over 60 m) was unaffected by the different track compliances (P = 0.57). In addition, there was no effect of track (P > 0.05) on the sprinting kinematics and kinetics of the ankle or knee joint. The hypothesis that sprint performance is affected by track compliance can be rejected because the sprinters recorded similar performances while sprinting over 60 m on all three track configurations. We conclude that: (1) the possible deformation of the track while sprinting is minor enough not to cause a specific adjustment in the leg mechanics affecting the effectiveness of the stretch – shortening cycle of the sprinters; and (2) the energy exchange between sprinters and tracks has only a marginal effect on sprint performance due to its small magnitude. More research on tracks with lower stiffness is required.  相似文献   
3.
The purpose of this study was to examine the effects of active recovery (AR) and passive recovery (PR) using short (2-min) and long (4-min) intervals on swimming performance. Twelve male competitive swimmers completed a progressively increasing speed test of 7?×?200-m swimming repetitions to locate the speed before the onset of curvilinear increase in blood lactate concentration (LT1). Subsequently, performance time of 6?×?50-m sprints was recorded during four different conditions: (i) 2-min PR (PR-2), (ii) 4-min PR (PR-4), (iii) 2-min AR (AR-2) and (iv) 4-min AR (AR-4) intervals. Blood lactate concentration was measured before the first and after the last 50-m repetition. AR was applied at an intensity corresponding to LT1. Performance as indicated by the time needed to complete 6?×?50-m sprints was impaired after AR-4 compared to PR-4 (AR-4: 28.65?±?1.04, PR-4: 28.17?±?0.72?s; mean% difference: MD% ±s; ±90% confidence limits: 90%CL, 1.71?±?3.01%; ±1.43%, p?=?.01) but was not different between AR-2 compared to PR-2 conditions (AR-2: 28.68?±?0.85, PR-2: 28.69?±?0.82 s; MD%: 0.03?±?1.61%; 90%CL?±?0.77%, p?=?.99). Performance in sprint-6 was improved after AR compared to PR independent of interval duration (AR: 28.55?±?0.81, PR: 29.01?±?1.03?s; MD%: 1.52?±?2.61%; 90%CL?±?1.2%; p?=?.03). Blood lactate concentration was lower after AR-4 compared to PR-4 but did not differ between AR-2 and PR-2 conditions. In conclusion, AR impaired performance after a 4-min but not after a 2-min interval. A better performance during sprint-6 after AR could be attributed to a faster metabolic recovery or anticipatory regulatory mechanisms towards the end of the series especially when adequate 4-min active recovery interval is applied.  相似文献   
4.
The study examined the differences between boys and adults after an intense stretch-shortening cycle fatigue protocol on neuromechanical parameters of the lower limb. Thirteen boys (9–11 years old) and 13 adult men (22–28 years old) were tested for maximal isometric voluntary knee extension torque and drop jump (DJ) performance from 30 cm before and immediately after a fatigue protocol, consisted of 10 × 10 maximum effort vertical jumps. Three-dimensional kinematics, kinetics and electromyographic (EMG) parameters of the lower extremities muscles were recorded during DJs before and after the fatigue test. The results indicated that reduction in maximal isometric torque and jumping performance was significantly higher in adults compared to boys. Vertical ground reaction forces, contact time and maximum knee flexion increased in a greater extend in adults than in boys. In addition, preactivation, EMG agonist activity, knee joint stiffness and stretch reflex decreased more in adults than in boys at all the examined phases of jumping tasks. It is concluded that employed fatigue protocol induced acute reduction in performance and altered motor control during jumping in both age groups. However, the differences in the level of fatigue between the 2 groups could be attributed to neuromuscular, mechanical and kinematic parameters observed between groups.  相似文献   
5.
The objective of this study was to determine whether sprint performance is related to the mechanical (elongation - force relationship of the tendon and aponeurosis, muscle strength) and morphological (fascicle length, pennation angle, muscle thickness) properties of the quadriceps femoris and triceps surae muscle - tendon units. Two groups of sprinters (slow, n = 11; fast, n = 17) performed maximal isometric knee extension and plantar flexion contractions on a dynamometer at 11 different muscle - tendon unit lengths. Elongation of the tendon and aponeurosis of the gastrocnemius medialis and the vastus lateralis was measured using ultrasonography. We observed no significant differences in maximal joint moments at the ankle and knee joints or morphological properties of the gastrocnemius medialis and vastus lateralis between groups (P > 0.05). The fast group exhibited greater elongation of the vastus lateralis tendon and aponeurosis at a given tendon force, and greater maximal elongation of the vastus lateralis tendon and aponeurosis during maximum voluntary contraction (P < 0.05). Furthermore, maximal elongation of the vastus lateralis tendon and aponeurosis showed a significant correlation with 100-m sprint times (r = -0.567, P = 0.003). For the elongation - force relationship at the gastrocnemius medialis tendon and aponeurosis, the two groups recorded similar values. It is suggested that the greater elongation of the vastus lateralis tendon and aponeurosis of the fast group benefits energy storage and return as well as the shortening velocity of the muscle - tendon unit.  相似文献   
6.
Abstract

This study investigated the effects of knee localised muscle damage on running kinematics at varying speeds. Nineteen young women (23.2 ± 2.8 years; 164 ± 8 cm; 53.6 ± 5.4 kg), performed a maximal eccentric muscle damage protocol (5 × 15) of the knee extensors and flexors of both legs at 60 rad · s-1. Lower body kinematics was assessed during level running on a treadmill at three speeds pre- and 48 h after. Evaluated muscle damage indices included isometric torque, muscle soreness and serum creatine kinase activity. The results revealed that all indices changed significantly after exercise, indicating muscle injury. Step length decreased and stride frequency significantly increased 48 h post-exercise only at the fastest running speed (3 m · s-1). Support time and knee flexion at toe-off increased only at the preferred transition speed and 2.5 m · s-1. Knee flexion at foot contact, pelvic tilt and obliquity significantly increased, whereas hip extension during stance-phase, knee flexion during swing-phase, as well as knee and ankle joints range of motion significantly decreased 48 h post-exercise at all speeds. In conclusion, the effects of eccentric exercise of both knee extensors and flexors on particular tempo-spatial parameters and knee kinematics of running are speed-dependent. However, several pelvic and lower joint kinematics present similar behaviour at the three running speeds examined. These findings provide new insights into how running kinematics at different speeds are adapted to compensate for the impaired function of the knee musculature following muscle damage.  相似文献   
7.
Abstract

The objective of this study was to determine whether sprint performance is related to the mechanical (elongation – force relationship of the tendon and aponeurosis, muscle strength) and morphological (fascicle length, pennation angle, muscle thickness) properties of the quadriceps femoris and triceps surae muscle – tendon units. Two groups of sprinters (slow, n = 11; fast, n = 17) performed maximal isometric knee extension and plantar flexion contractions on a dynamometer at 11 different muscle – tendon unit lengths. Elongation of the tendon and aponeurosis of the gastrocnemius medialis and the vastus lateralis was measured using ultrasonography. We observed no significant differences in maximal joint moments at the ankle and knee joints or morphological properties of the gastrocnemius medialis and vastus lateralis between groups (P > 0.05). The fast group exhibited greater elongation of the vastus lateralis tendon and aponeurosis at a given tendon force, and greater maximal elongation of the vastus lateralis tendon and aponeurosis during maximum voluntary contraction (P < 0.05). Furthermore, maximal elongation of the vastus lateralis tendon and aponeurosis showed a significant correlation with 100-m sprint times (r = ?0.567, P = 0.003). For the elongation – force relationship at the gastrocnemius medialis tendon and aponeurosis, the two groups recorded similar values. It is suggested that the greater elongation of the vastus lateralis tendon and aponeurosis of the fast group benefits energy storage and return as well as the shortening velocity of the muscle – tendon unit.  相似文献   
8.
Content-based image retrieval (CBIR) with global features is notoriously noisy, especially for image queries with low percentages of relevant images in a collection. Moreover, CBIR typically ranks the whole collection, which is inefficient for large databases. We experiment with a method for image retrieval from multimedia databases, which improves both the effectiveness and efficiency of traditional CBIR by exploring secondary media. We perform retrieval in a two-stage fashion: first rank by a secondary medium, and then perform CBIR only on the top-K items. Thus, effectiveness is improved by performing CBIR on a ‘better’ subset. Using a relatively ‘cheap’ first stage, efficiency is also improved via the fewer CBIR operations performed. Our main novelty is that K is dynamic, i.e. estimated per query to optimize a predefined effectiveness measure. We show that our dynamic two-stage method can be significantly more effective and robust than similar setups with static thresholds previously proposed. In additional experiments using local feature derivatives in the visual stage instead of global, such as the emerging visual codebook approach, we find that two-stage does not work very well. We attribute the weaker performance of the visual codebook to the enhanced visual diversity produced by the textual stage which diminishes codebook’s advantage over global features. Furthermore, we compare dynamic two-stage retrieval to traditional score-based fusion of results retrieved visually and textually. We find that fusion is also significantly more effective than single-medium baselines. Although, there is no clear winner between two-stage and fusion, the methods exhibit different robustness features; nevertheless, two-stage retrieval provides efficiency benefits over fusion.  相似文献   
9.
Track compliance does not affect sprinting performance   总被引：1，自引：0，他引：1  
The aim of this study was to test the hypothesis that sprint performance (time over a given distance) would be affected by track compliance, with better performances on the more compliant surface. Ten sprinters participated in the study. The athletes performed maximal sprints (60 m) on three different track configurations (hard, 5500 kN m(-1); soft, 2200 kN m(-1); spring, 550 kN m(-1)). A 60-m single-lane running surface was constructed. Plywood boards (1.2 cm thick) were placed on a 60 x 0.6 m wooden chipboard frame serving as the base surface. All participants ran two times on each track configuration in a randomized order. The athletes' kinematics were recorded using the Vicon 624 system with 12 cameras operating at 250 Hz. Four Kistler force plates (1250 Hz) were used to record ground reaction forces. Sprint performance (time over 60 m) was unaffected by the different track compliances (P= 0.57). In addition, there was no effect of track (P> 0.05) on the sprinting kinematics and kinetics of the ankle or knee joint. The hypothesis that sprint performance is affected by track compliance can be rejected because the sprinters recorded similar performances while sprinting over 60 m on all three track configurations. We conclude that: (1) the possible deformation of the track while sprinting is minor enough not to cause a specific adjustment in the leg mechanics affecting the effectiveness of the stretch-shortening cycle of the sprinters; and (2) the energy exchange between sprinters and tracks has only a marginal effect on sprint performance due to its small magnitude. More research on tracks with lower stiffness is required.  相似文献   
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