The question of vortex growth in Euler flows leads naturally to the emergence of paired vortex structure and the “geometric” stretching of vortex lines. In the present paper, the first of two papers devoted to this question, we examine bounds on the growth of vorticity in axisymmetric flow without swirl. We show that the known bound on vorticity in this case, exponential in time, can be improve...

Apparent interactions between ducted gravity waves and pre-existing mesocyclones are investigated. Preliminary analyses of WSR-88D radar observations from several cases reveal that the intersection of fine lines, whose propagation speed is consistent with that of gravity waves, and existing mesocyclones leads to an increase in rotational velocity of the mesocyclone. Utilizing simplified ducted ...

introduction: one of the main sections of warm up is stretching which the importance of them is static and dynamic stretching. the purpose of this study was to examine the effects of static and dynamic stretching within a pre-exercise warm-up on the static and dynamic in soccer players. materials and methods: eighteen physical education female students (height: 159.68 ± 5.94 cm; mass: 60.21 ± 5...

The purpose of this study was to examine the effects of static, dynamic, and the combination of static and dynamic stretching within a pre-exercise warm-up on the Illinois agility test (IAT) in soccer players. Nineteen professional soccer players (age = 22.5 ± 2.5 years, height = 1.79 ± 0.003 m, body mass = 74.8 ± 10.9 kg) were tested for agility performance using the IAT after different warm-u...

KEY POINTS JTreexercise static stretching has been used by coaches and athletes for decades in the hope of improving performance and preventing injuries. The scientific literature of the 1980s and 1990s suggested that preexercise static stretching was a good addition to athletes' warm-up before initiation of physical activity.''^ This article reviews the current literature and provides informat...

A comparison of assisted and unassisted proprioceptive neuromuscular facilitation techniques and static stretching. J Strength Cond Res 26(5): 1238-1244, 2012-Proprioceptive neuromuscular facilitation (PNF) stretching often requires a partner. Straps are available allowing an individual to perform PNF stretching alone. It is not known if a strap provides similar improvements in the range of mot...

Warming up before performing rigorous physical activity is typically done to increase range of motion and improve athletic performance. Common warm-up techniques in college athletics include static stretching, proprioceptive neuromuscular facilitation (PNF) stretching, dynamic warm-ups, and sport-specific activities. However, the type of warm-up routine used in the college setting varies based ...

Objective To determine the extent to which changes in knee range of motion (ROM) after a stretching program are related to sensory factors at the time of testing and the amount of force used during the measurement of ROM, rather than changes in soft-tissue properties. Design Randomized, single-blind design. Participants were randomly assigned to a control or stretching group. Setting Resear...