We study vertical jumping in a simple robot comprising an actuated mass spring arrangement. The actuator frequency and phase are systematically varied to find optimal performance. Optimal jumps occur above and below (but not at) the robot's resonant frequency f0. Two distinct jumping modes emerge: a simple jump which is optimal above f0 is achievable with a squat maneuver, and a peculiar stutter jump which is optimal below f0 is generated with a countermovement. A simple dynamical model reveals how optimal lift-off results from non-resonant transient dynamics.

<p>The interaction between liquid drops and textured surfaces not only offers fundamental challenges in capillarity and wetting, but also enables new applications ranging from self-cleaning materials to self-sustaining condensers. The first part of this dissertation deals with the fundamental wetting and dewetting dynamics of drops on textured surfaces, and the self-propelled jumping of dropwise condensate on superhydrophobic surfaces. The second part builds upon these findings in dynamical superhydrophobicity to develop a jumping-drop thermal diode that rectifies heat flow between textured superhydrophilic and superhydrophobic surfaces. </p><p>On the fundamental side, anti-dew is an essential property of robust superhydrophobic surfaces, particularly those deployed in ambient environments or phase-change systems. A superhydrophobic lotus leaf retains water repellency after repeated condensation in nature but becomes sticky to water drops after condensation on a fixed cold plate. To solve this mystery, we first study the possible wetting states of superhydrophobic surfaces possessing two-tier surface roughness mimicking that on the lotus leaf. By incrementally increasing the ethanol concentration of water/ethanol drops, two distinct wetting transitions are observed on two-tier surfaces. Drops in the intermediate wetting state uniformly wet the microscale roughness but not the nanoscale roughness. Dew drops exhibited a similar intermediate wetting state. Our experiments show that mechanical vibration can be used to overcome the energy barrier for transition from the intermediate wetting (Partial Wenzel) state to the fully dewetted (Cassie) state, and the threshold for the dewetting transition follows a scaling law comparing the kinetic energy imparted to the drop with the work of adhesion. </p><p>Although vibration-induced dewetting is effective for removing millimetric condensate from the surface, micrometric condensate cannot be removed as surface energy dominates at small scales. We report a new discovery in which the micrometric condensate can spontaneously dewet and jump off the superhydrophobic surface. The spontaneous jumping results from the surface energy released upon drop coalescence, which leads to the rapid out-of-plane jumping motion of the coalesced drops. The jumping drops follow an inertial-capillary scaling and give rise to self-sustained dropwise condensation with a micrometric average diameter. Using two approaching Leidenfrost drops suspended on a vapor layer to simulate superhydrophobicity, we show that the out-of-plane directionality results from the impingement of the expanding liquid bridge against the heated Leidenfrost surface, which is initially formed between coalescing drops above the substrate.</p><p>On the practical side, textured surfaces offer new possibilities for phase-change heat transfer. Taking advantage of the self-propelled jumping condensate, we developed a planar phase-change thermal diode that transports heat in a preferential direction. The jumping-drop diode is composed of parallel superhydrophobic and superhydrophilic plates, and the thermal rectification is enabled by spontaneously jumping dropwise condensate which only occurs when the superhydrophobic surface is colder. The superhydrophobic surface has nanoscale surface roughness that is anti-dew, while the superhydrophilic surface consists of porous copper wick borrowed from heat pipes. Our planar thermal diode with asymmetric wettability is scalable to large areas with an orientation-independent diodicity of over a hundred. </p><p>More broadly speaking, the self-propelled jumping offers an alternative means to return liquid condensate in phase-change systems. We systematically investigate the heat transfer performance of a vapor chamber enabled by the jumping condensate. When the non-condensable gases are removed, the effective heat transfer coefficient is mainly governed by the interfacial resistance of the phase-change processes and the conduction resistance across the superhydrophilic wick. Potential routes for improving the heat transfer performance are discussed, including the optimization of the superhydrophilic wick and its separation with the opposing superhydrophobic surface. The new jumping return mechanism is unique in that it neither relies on external forces nor requires wick structures along the return path, and is expected to be applicable to a variety of phase-change heat transfer systems.</p> / Dissertation

No description available.

The purpose of this study was: - To investigate jumping sport horses health conditions influence on sport skills; - To investigate blood parameters in Lithuanian jumping sport horses before and after an active training period. Eight healthy horses ranging in age from 6 to 8 with a mean body weight o 607 +/- 86,9 kg were used in experiment. Blood samples were collected from well trained Lithuanian sport horses and tested before and after an intensive period of competition of 2006. Biochemical and morphological blood results were performed to determinate the glucose, triglycerides, cholesterol, red blood cells, haemoglobin, white blood cells, total protein, albumin value, total oxygen consumption and specific oxygen consumption before and after active summer training season. Furthermore, was analyzed mineral substances content of: calcium, potassium, phosphorous, sodium, magnesium and iron in blood serum of jumping sport horses. Physical readiness of horses according changes of haematological parameters before and after active summer competition season were in range of physiological norm. Conclusion: 1. AB ŽŽ/VšĮ “Suvalkijos žirgai” stud farm horses (weight average 544 kg) reached best sport skills in 2006 jumping contest. 2. Fodder supplements during contest season increased sport skills 37, 5%. 3. Red blood cells, haemoglobin, blood oxygen content ware considerable higher in jumping horse’s blood after intensive sport contest season in comparison with pre-contest season. 4... [to full text]

Background: Self-myofascial release is widely used by athletes but the scientific evidence of its supposedly positive effects is limited. This study was conducted to investigate the effects of foam rolling as a warm-up routine in comparison with a dynamic stretching routine and how it may affect the jumping performance among subjects familiar with weight training. Aim: The aim of this study was to investigate the acute effect of foam rolling vs. a standardized dynamic stretch warm-up routine on jumping performance. Method: Twelve subjects, mean (SD) age 25.1 (± 3.0) years, participated in a randomized, controlled, crossover study. All subjects completed a standardized foam rolling (FR) and a dynamic stretch (DS) warm-up routine on separate days of testing. Squat jump (SJ), counter movement jump (CMJ) and loaded counter movement jump (L-CMJ) all performed bilaterally and unilaterally were conducted to investigate the acute effect of the two warm-up routines. A dependent T-test was used to investigate differences between the warm-up routines. Results: A statistical significant difference in favor of the DS was found for SJ performed bilaterally among males (p = 0.009). The mean (SD) jumping height for SJ FR was 35.6 (± 4.7) cm and for SJ DS 37.9 (± 5.2) cm. The male group also improved more in L-CMJ performed on the right leg with an external load of 54kg after DS compared to FR. No other statistical significant differences were found between the two interventions. A near statistical significant difference was found for SJ performed bilaterally for the total sample (p = 0.057) also in favor of the DS. The mean (SD) jumping height for SJ FR was 29.3 (± 8.7) cm and for SJ DS 30.5 (± 9.9) cm. Conclusion: Findings from this study supports a dynamic stretch warm-up routine prior to performing high intensity bilateral plyometrics instead of a foam rolling warm-up routine. However the data was inconsistent and more research with larger sample sizes is needed to further investigate the possible effects of foam rolling as a warm-up routine on jumping performance performed both bilaterally and unilaterally.

The purpose of the study was to investigate the effects of fatigue on the lower extremity landing strategies of males and females. Twelve recreationally active males (n = 6) and females (n = 6) (nine used for analysis) performed repetitive drop jumps until they could no longer reach 20% of their initial drop jump height. Kinematic and kinetic variables were assessed during the impact phase of all jumps. At initial ground contact, males exhibited greater extension at the hip and knee and less plantar flexion than females. However, females performed more eccentric work during the impact phase of landing. Fatigue resulted in an increased extension at the hip, knee, and ankle for both genders, but did not have an effect on the peak VGRF. Fatigue also resulted in an increase in work performed at the ankle and an approximately equal reduction in work performed at the knee for both genders. Investigation of the peak powers revealed that as a result of fatigue, females utilized a landing strategy in which more energy was absorbed at the knee during the early part of the impact phase. The increased reliance on the knee musculature to dissipate kinetic energy during the impact phase of landing demonstrated by females may be a reason for the commonly seen gender disparities in injury rates. Furthermore, the shift towards energy absorption during the initial part of the impact phase when noncontact injuries are known to occur, exhibited by females, may indicate a greater injury risk for females. / School of Physical Education, Sport, and Exercise Science

The purpose of this study was to devise a simple mechanical power formula for both peak and average power using a countermovement jump and reach test for both college male and female athletes. Forty-nine female and 69 male athletes were measured for height, weight, thigh circumference, thigh skinfold, upper leg length, and lower leg length. The athletes performed a countermovement jump and reach test off of a force platform. A Vertec jumping apparatus was used to measure vertical jump height and the force platform was used to acquire force/time data to determine actual peak and average power output. Eight anthropometric measurements, vertical jump height, and gender were the variables presented to develop the equations. A stepwise multiple regression statistical procedure was used to develop the prediction equations. Vertical jump height, mass, and body height were the significant (p<.05) variables loaded into both peak and average mechanical power prediction equations. Gender was not significant (p>.05) and, therefore, not loaded into either equation. Predicted peak power and actual peak power values were 4,707 t 1,511 and 4,687 ± 1,612 watts, respectively. Predicted averagepower and actual average power values were 2,547 ± 760 and 2,463 ± 753 watts, respectively. The following best model regression-derived equations produced R2 values of .91 for peak power and .82 for average power:Peak Power (W) = 78.47 • VJ (cm) + 60.57 • Mass (kg) - 15.31 • Ht (cm) - 1,308 Average Power (W) = 41.41 • VJ (cm) + 31.18 • Mass (kg) - 13.86 • Ht (cm) + 431 Results of this study conclude that the two regression equations are good predictors of peak and average mechanical power output. / School of Physical Education

Whole body vibration (WBV) is a training modality that involves an individual standing on a plate that provides vibrations at multiple frequencies and amplitudes. Improvements in muscular concentric force production such as power and strength have been extensively studied, however little work has been conducted looking at the effects of WBV on eccentric actions. The landing phase of a jump is an eccentric mechanism to decelerate the body as it prepares to stop or initiate another movement. This study sought to identify the effects of WBV on ground reaction forces, loading rates, valgus knee angles, frontal plane knee moment and jump height, as well as a higher order interaction between gender and time as a result of the vibration. An individualized frequency WBV protocol was utilized as 10 female and 9 male subjects completed drop jumps pre-vibration, post vibration and at 10 and 20 minutes post vibration. Baseline valgus knee angle increased 0.857 degrees post vibration, while remaining increased by 0.917 and 1.189 degrees at the 10 and 20 minute post vibration time intervals, respectively. Repeated measure ANOVA’s revealed that valgus knee angle significantly (p=0.011) increased post vibration. Gender comparisons revealed that females had a significantly greater knee moment (p=0.038) and males significantly jumped higher than females (p<0.001). As an end result following WBV, the subjects landed in significantly greater knee valgus, regardless of sex. Since it has been demonstrated that a knee in a valgus position increases the potential risk for anterior cruciate ligament injury, caution should be taken when combining WBV and jump training protocols. / School of Physical Education, Sport, and Exercise Science

Thesis (Ph.D.)--Victoria University (Melbourne, Vic.), 2008.

Thesis (M.S.)--Indiana University, 2007. / Includes bibliographical references.