High Force Generation Research Articles

Pitching-motion-activated flapping foil near solid walls for power extraction: A numerical investigation

A numerical investigation on the power extraction of a pitching-motion-activated flapping foil near solid walls is performed by using an immersed boundary-lattice Boltzmann method in this study. The flapping motions of the foil include a forced pitching component and an induced plunging component. The foil is placed either near a solid wall or between two parallel plane walls. Compared to previous work on the flapping foil for power extraction, the effect of the walls is first considered in this work. At a Reynolds number of 1100 and with the position of the foil pitching axis at third chord, the influences of the mechanical parameters (such as damping coefficient and spring constant) of the foil, the amplitude and frequency of the pitching motion and the clearance between the foil pitching axis and the wall on the power extraction performance of the flapping foil are systematically evaluated. Compared to the situation of free stream, the power extraction performance of the foil near the wall is improved. For given amplitude and frequency, as the clearance decreases the net power extraction efficiency improves. Moreover, as the foil is placed near one wall, there is a transverse shift to the plunging motion that consequently weakens the improvement of net power extraction efficiency. In contrast, the shift can be significantly eliminated as the foil is placed between two walls, which can further improve the net power extraction efficiency. In addition, it is found that the efficiency improvement is essentially from the increased power extraction, which is due to the generation of high lift force.

Jumping and Hopping in Elite and Amateur Orienteering Athletes and Correlations to Sprinting and Running

Jumping and hopping are used to measure lower-body muscle power, stiffness, and stretch-shortening-cycle utilization in sports, with several studies reporting correlations between such measures and sprinting and/or running abilities in athletes. Neither jumping and hopping nor correlations with sprinting and/or running have been examined in orienteering athletes. The authors investigated squat jump (SJ), countermovement jump (CMJ), standing long jump (SLJ), and hopping performed by 8 elite and 8 amateur male foot-orienteering athletes (29 ± 7 y, 183 ± 5 cm, 73 ± 7 kg) and possible correlations to road, path, and forest running and sprinting performance, as well as running economy, velocity at anaerobic threshold, and peak oxygen uptake (VO(2peak)) from treadmill assessments. During SJs and CMJs, elites demonstrated superior relative peak forces, times to peak force, and prestretch augmentation, albeit lower SJ heights and peak powers. Between-groups differences were unclear for CMJ heights, hopping stiffness, and most SLJ parameters. Large pairwise correlations were observed between relative peak and time to peak forces and sprinting velocities; time to peak forces and running velocities; and prestretch augmentation and forest-running velocities. Prestretch augmentation and time to peak forces were moderately correlated to VO(2peak). Correlations between running economy and jumping or hopping were small or trivial. Overall, the elites exhibited superior stretch-shortening-cycle utilization and rapid generation of high relative maximal forces, especially vertically. These functional measures were more closely related to sprinting and/or running abilities, indicating benefits of lower-body training in orienteering.

高磁気力環境を利用した 高効率・高品位タンパク質結晶生成システムの開発とその利用

This review provides an outline of the “high-efficiency/high-quality protein crystal formation system” project. Precise determination of protein structures provides significant information for R&D on drugs and enzymes. Protein crystals of high integrity grown with high efficiency can accelerate such R&D. At present, a condition suitable for a certain protein crystal growth can only be found after several thousands of different conditions are examined by changing various parameters such as solvents, coexisting materials, temperature, pH and so on. It is considered that the convection of solution prevents the formation of good-quality crystal. Therefore, the control of gravity force effect through large magnetic force may be one of the potential parameters for protein crystal growth because it should contribute to suppressing the convection. To exert large magnetic force on protein solution or crystals equivalent with gravity force, high magnetic fields using a superconducting magnet are required. Observation of the crystallization process is important for efficient crystal formation, but it is difficult to carry out in-situ optical observation inside the superconducting magnet bore due to the existence of the high magnetic field. To facilitate efficient protein crystal growth under magnetic force, we developed a microscopic optical observation apparatus for multiple samples placed in a high magnetic field. The system consists of a superconducting magnet, crystallization plates and an optical periscope. The superconducting magnet used for this system is a high magnetic force generation type. The developed crystallization plates can contain 24 different protein solutions and can be stacked on each other. The 3D controllable periscope is made mainly from feeble magnetic materials that can be operated in high magnetic fields.

An Adaptive Magnetic Field Source for Magnetic Drug Fixation

Magnetic drug targeting (MDT) therapy is usually controlled through the magnetic field produced by a permanent magnet; the solution proposed and assessed here considers a planar spiral coil (PSC) or a system of such coils, as an equally effective magnetic field source. The PSC may be designed to provide proper configurations of the magnetic field gradients, required for the generation of high magnetic body forces and to limit, in the same time, unwanted side effects affecting adjacent tissue (heating, excitable tissue stimulation). Simplified numerical models (2D projections) and more realistic structures (3D representations) are shown and analyzed in the paper; the electromagnetic and heat transfer problems are solved for different powering schemes applied to the coils.

Considering the constrained lever model: Feeding biomechanics of OH 5 assessed using finite element analysis

The craniofacial morphology of Paranthropus boisei exhibits a number of highly derived characteristics that have been argued to be functionally related to feeding. These features are hypothesized to either decrease structural stress, increase the mechanical advantage of the masticatory muscles, or both. But complications arise when the constrained lever model is considered. This study uses finite element analysis to test the hypothesis that the P. boisei cranium is structurally stronger and configured to more efficiently generate bite force than the crania of Pan troglodytes and Australopithecus africanus. To assess our analyses within the context of the constrained lever model of chewing biomechanics, joint reaction forces are also examined.A finite element model was created from a reconstruction of the OH 5 cranium. The model was assigned chimpanzee material properties, constrained at the TMJs and bite points, and subjected to scaled muscle forces derived from chimpanzees. Strains, bite forces and strain energy were recorded. The results were compared to those from FEA of other hominid crania. Results indicate the face of P. boisei is structurally strong and the extreme morphology of this species allows for the generation of high bite forces on posterior teeth without violating the constrained lever model.(NSF BCS 0725219, 0725183, 0725147, 0725141, 0725136, 0725126, 0725122, 0725078) and the EU FP6 Marie Curie Actions MRTN‐CT‐2005–019564 “EVAN”.

Characterization of working fluid in vertically mounted finned U-shape twin heat pipe for electronic cooling

As part of the ongoing research on finned U-shape heat pipes for CPU cooling, the present work focuses on the characterization of working fluid in vertically oriented twin U-shape heat pipe, by taking into account the gravity of flow. Two-dimensional FE simulation is performed under natural and forced convection modes, by using ansys-flotran. The best heat input and coolant velocity for the simulations are determined experimentally, corresponding to the least thermal resistance. The wall temperatures at the evaporator, adiabatic and condenser sections, and the velocity and pressure distributions of vapor and liquid, are analyzed. The total heat input for minimum thermal resistance in both natural and forced convection is found to be 50W, and the coolant velocity is 3m/s. The predicted and experimental wall temperatures are found in excellent match. It is observed that for the present U-shape heat pipe configuration, the difference in evaporator and condenser temperatures is significantly small, resulting in enhanced heat transfer compared to the conventional heat pipes. The sintered copper wick has a small pore size, resulting in low wick permeability, leading to the generation of high capillary forces for anti-gravity applications.

Funktionelle Magnetstimulation als „schmerzlose“ Variante der künstlichen Bewegungsinduktion bei Lähmungen

It is known in the rehabilitation of central pareses that functional electrical stimulation (FES) of the muscles can induce movement and accomplish training in patients. The main limitations of this method are that patients with preserved sensation experience pain and the reflexes triggered by FES. Therefore the application of the largely "painless" magnetic stimulation (FMS) of the muscles would be a potential alternative in the rehabilitation of patients with partially preserved sensation. As the generation of high force and power levels is considered to be an essential requirement of effective rehabilitation strategies, we have shown in previous work that FMS with large surface magnetic coils fitted to the thigh can generate about 2.5 times higher isometric forces in patients with preserved sensation, than can FES. The goal of the present pilot study was to prove that the mechanical power generated by functional magnetic stimulation is superior to that produced by electrical stimulation too. We have measured the mechanical torque, the power, the accomplished work and the kinematics in 4 healthy control subjects, who performed pedalling propelled by FMS and FES until complete muscular exhaustion, using a cycling test-bed under isotonic conditions (constant resistance). We have proved that the generated work, mean power, cadence and smoothness of pedalling essentially depend on peak torque and power. Furthermore, we found evidence that smoother pedalling could be achieved using magnetic, compared to electrical stimulation because of the higher peak torques that were generated by FMS. This study supports the concept that peripheral magnetic stimulation is an appropriate rehabilitation method for patients with central pareses and preserved sensory apparatus because FMS is less painful than electrical stimulation.

The sports performance application of vibration exercise for warm-up, flexibility and sprint speed

Since the turn of the 21st century, there has been a resurgence of vibration technology to enhance sport science especially for power and force development. However, vibration exercise has been trialled in other areas that are central to athlete performance such as warm-up, flexibility and sprint speed. Therefore, the aim of this review was to attempt to gain a better understanding of how acute and short-term vibration exercise may impact on warm-up, flexibility and sprint speed. The importance of warming up for sporting performance has been well documented and vibration exercise has the capability to be included or used as a standalone warm-up modality to increase intramuscular temperature at a faster rate compared to other conventional warm-up modalities. However, vibration exercise does not provide any additional neurogenic benefits compared to conventional dynamic and passive warm-up interventions. Vibration exercise appears to be a safe modality that does not produce any adverse affects causing injury or harm and could be used during interval and substitution breaks, as it would incur a low metabolic cost and be time-efficient compared to conventional warm-up modalities. Acute or short-term vibration exercise can enhance flexibility and range of motion without having a detrimental effect on muscle power, however it is less clear which mechanisms may be responsible for this enhancement. It appears that vibration exercise is not capable of improving sprint speed performance; this could be due to the complex and dynamic nature of sprinting where the purported increase in muscle power from vibration exercise is probably lost on repeated actions of high force generation. Vibration exercise is a safe modality that produces no adverse side effects for injury or harm. It has the time-efficient capability of providing coaches, trainers, and exercise specialists with an alternative modality that can be implemented for warm-up and flexibility either in isolation or in conjunction with other conventional training methods.

Patterns of tropomyosin and troponin-T isoform expression in jaw-closing muscles of mammals and reptiles that express masticatory myosin

We recently reported that masticatory ('superfast') myosin is expressed in jaw-closing muscles of some rodent species. Most mammalian limb muscle fibers express tropomyosin-β (Tm-β), along with fast-type or slow-type tropomyosin-β (Tm-β), but jaw-closing muscle fibers in members of Carnivora express a unique isoform of Tm [Tm-masticatory (Tm-M)] and little or no Tm-β. The goal of this study was to determine patterns of Tm and troponin-T (TnT) isoform expression in the jaw-closing muscles of rodents and other vertebrate species that express masticatory myosin, and compare the results to those from members of Carnivora. Comparisons of electrophoretic mobility, immunoblotting and mass spectrometry were used to probe the Tm and fast-type TnT isoform composition of jaw-closing and limb muscles of six species of Carnivora, eight species of Rodentia, five species of Marsupialia, big brown bat, long-tailed macaque and six species of Reptilia. Extensive heterogeneity exists in Tm and TnT isoform expression in jaw-closing muscles between phylogenetic groups, but there are fairly consistent patterns within each group. We propose that the differences in Tm and TnT isoform expression patterns between phylogenetic groups, which share the expression of masticatory myosin, may impart fundamental differences in thin-filament-mediated muscle activation to accommodate markedly different feeding styles that may require high force generation in some species (e.g. many members of Carnivora) and high speed in others (e.g. Rodentia).

Non-Linear Elasticity of Skeletal Myosins is Essential for Collective Force Generation in Muscle

Muscle contraction occurs through the rotation of the myosin heads pulling actin filaments past myosin filaments. In order to achieve contractions efficiently, it is crucial for myosins to generate force collectively and to minimize the interference between motors. In the previous studies, it was suggested that the elasticity of myosin is linear so that myosins generate the large drag force opposing to muscle contraction if negatively strained. However, none of the previous studies has investigated the elasticity of single myosin explicitly in the negative strain region. Therefore, we investigated the elasticity of single skeletal myosins in both the positive and negative strain directions. In the absence of ATP, single myosins embedded in synthetic myosin-rod filaments were tightly bound to actin filaments and were stretched and shortened repeatedly by oscillating the two trapped beads on the both ends of acting filament manipulated by optical tweezers. The elasticity of myosins was characterized by obtaining the force-displacement curves, where forces on myosin heads were estimated by measuring the displacement of two beads, and displacements of myosin heads were obtained by tracking the position of quantum dots attached to the actin filament. We found that the elasticity is non-linear, in which stiffness is high (∼2.8 pN/nm) and low (∼0.02 pN/nm) in the positive and negative strain regions. The non-linear elasticity ensures high force generation with a small stretching of the elastic portion, and minimizing the drag force of negatively-strained myosins. Furthermore, the estimates of the actin sliding distance by the non-linear elasticity model were more consistent with experimental results observed in 20μM ATP than those by the linear elasticity model. Therefore, the non-linear elasticity might be an essential mechanical property of single myosin designed for the collective force generation in muscle.

Rotational accelerations stabilize leading edge vortices on revolving fly wings

The aerodynamic performance of hovering insects is largely explained by the presence of a stably attached leading edge vortex (LEV) on top of their wings. Although LEVs have been visualized on real, physically modeled, and simulated insects, the physical mechanisms responsible for their stability are poorly understood. To gain fundamental insight into LEV stability on flapping fly wings we expressed the Navier-Stokes equations in a rotating frame of reference attached to the wing's surface. Using these equations we show that LEV dynamics on flapping wings are governed by three terms: angular, centripetal and Coriolis acceleration. Our analysis for hovering conditions shows that angular acceleration is proportional to the inverse of dimensionless stroke amplitude, whereas Coriolis and centripetal acceleration are proportional to the inverse of the Rossby number. Using a dynamically scaled robot model of a flapping fruit fly wing to systematically vary these dimensionless numbers, we determined which of the three accelerations mediate LEV stability. Our force measurements and flow visualizations indicate that the LEV is stabilized by the ;quasi-steady' centripetal and Coriolis accelerations that are present at low Rossby number and result from the propeller-like sweep of the wing. In contrast, the unsteady angular acceleration that results from the back and forth motion of a flapping wing does not appear to play a role in the stable attachment of the LEV. Angular acceleration is, however, critical for LEV integrity as we found it can mediate LEV spiral bursting, a high Reynolds number effect. Our analysis and experiments further suggest that the mechanism responsible for LEV stability is not dependent on Reynolds number, at least over the range most relevant for insect flight (100<Re<14,000). LEVs are stable and continue to augment force even when they burst. These and similar findings for propellers and wind turbines at much higher Reynolds numbers suggest that even large flying animals could potentially exploit LEV-based force augmentation during slow hovering flight, take-offs or landing. We calculated the Rossby number from single-wing aspect ratios of over 300 insects, birds, bats, autorotating seeds, and pectoral fins of fish. We found that, on average, wings and fins have a Rossby number close to that of flies (Ro=3). Theoretically, many of these animals should therefore be able to generate a stable LEV, a prediction that is supported by recent findings for several insects, one bat, one bird and one fish. This suggests that force augmentation through stably attached (leading edge) vortices could represent a convergent solution for the generation of high fluid forces over a quite large range in size.

High-Force Generation Is a Conserved Property of Type IV Pilus Systems

The type IV pilus (T4P) system of Neisseria gonorrhoeae is the strongest linear molecular motor reported to date, but it is unclear whether high-force generation is conserved between bacterial species. Using laser tweezers, we found that the average stalling force of single-pilus retraction in Myxococcus xanthus of 149 +/- 14 pN exceeds the force generated by N. gonorrhoeae. Retraction velocities including a bimodal distribution were similar between M. xanthus and N. gonorrhoeae, but force-dependent directional switching was not. Force generation by pilus retraction is energized by the ATPase PilT. Surprisingly, an M. xanthus mutant lacking PilT apparently still retracted T4P, although at a reduced frequency. The retraction velocity was comparable to the high-velocity mode in the wild type at low forces but decreased drastically when the force increased, with an average stalling force of 70 +/- 10 pN. Thus, M. xanthus harbors at least two different retraction motors. Our results demonstrate that the major physical properties are conserved between bacteria that are phylogenetically distant and pursue very different lifestyles.

Thermal Actuation Based 3-DoF Non-Resonant Microgyroscope Using MetalMUMPs

High force, large displacement and low voltage consumption are a primary concern for microgyroscopes. The chevron-shaped thermal actuators are unique in terms of high force generation combined with the large displacements at a low operating voltage in comparison with traditional electrostatic actuators. A Nickel based 3-DoF micromachined gyroscope comprising 2-DoF drive mode and 1-DoF sense mode oscillator utilizing the chevron-shaped thermal actuators is presented here. Analytical derivations and finite element simulations are carried out to predict the performance of the proposed device using the thermo-physical properties of electroplated nickel. The device sensitivity is improved by utilizing the dynamical amplification of the oscillation in 2-DoF drive mode using an active-passive mass configuration. A comprehensive theoretical description, dynamics and mechanical design considerations of the proposed gyroscopes model are discussed in detail. Parametric optimization of gyroscope, its prototype modeling and fabrication using MetalMUMPs has also been investigated. Dynamic transient simulation results predicted that the sense mass of the proposed device achieved a drive displacement of 4.1μm when a sinusoidal voltage of 0.5V is applied at 1.77 kHz exhibiting a mechanical sensitivity of 1.7μm /°/s in vacuum. The wide bandwidth frequency response of the 2-DoF drive mode oscillator consists of two resonant peaks and a flat region of 2.11 kHz between the peaks defining the operational frequency region. The sense mode resonant frequency can lie anywhere within this region and therefore the amplitude of the response is insensitive to structural parameter variations, enhancing device robustness against such variations. The proposed device has a size of 2.2 × 2.6 mm2, almost one third in comparison with existing M-DoF vibratory gyroscope with an estimated power consumption of 0.26 Watts. These predicted results illustrate that the chevron-shaped thermal actuator has a large voltage-stroke ratio shifting the paradigm in MEMS gyroscope design from the traditional interdigitated comb drive electrostatic actuator. These actuators have low damping compared to electrostatic comb drive actuators which may result in high quality factor microgyroscopes operating at atmospheric pressure.

Quantification of cell edge velocities and traction forces reveals distinct motility modules during cell spreading.

Actin-based cell motility and force generation are central to immune response, tissue development, and cancer metastasis, and understanding actin cytoskeleton regulation is a major goal of cell biologists. Cell spreading is a commonly used model system for motility experiments – spreading fibroblasts exhibit stereotypic, spatially-isotropic edge dynamics during a reproducible sequence of functional phases: 1) During early spreading, cells form initial contacts with the surface. 2) The middle spreading phase exhibits rapidly increasing attachment area. 3) Late spreading is characterized by periodic contractions and stable adhesions formation. While differences in cytoskeletal regulation between phases are known, a global analysis of the spatial and temporal coordination of motility and force generation is missing. Implementing improved algorithms for analyzing edge dynamics over the entire cell periphery, we observed that a single domain of homogeneous cytoskeletal dynamics dominated each of the three phases of spreading. These domains exhibited a unique combination of biophysical and biochemical parameters – a motility module. Biophysical characterization of the motility modules revealed that the early phase was dominated by periodic, rapid membrane blebbing; the middle phase exhibited continuous protrusion with very low traction force generation; and the late phase was characterized by global periodic contractions and high force generation. Biochemically, each motility module exhibited a different distribution of the actin-related protein VASP, while inhibition of actin polymerization revealed different dependencies on barbed-end polymerization. In addition, our whole-cell analysis revealed that many cells exhibited heterogeneous combinations of motility modules in neighboring regions of the cell edge. Together, these observations support a model of motility in which regions of the cell edge exhibit one of a limited number of motility modules that, together, determine the overall motility function. Our data and algorithms are publicly available to encourage further exploration.

Pedestrian locomotion energetics and gait characteristics of a diving bird, the great cormorant, Phalacrocorax carbo

Great cormorants Phalacrocorax carbo are foot propelled diving birds that seem poorly suited to locomotion on land. They have relatively short legs, which are presumably adapted for the generation of high forces during the power stroke of aquatic locomotion, and walk with a pronounced "clumsy waddle". We hypothesise (1) that the speed, independent minimum cost of locomotion (C min, ml O2 m(-1)) will be high for cormorants during treadmill exercise, and (2) that cormorants will have a relatively limited speed range in comparison to more cursorial birds. We measured the rate of oxygen consumption (V02) of cormorants during pedestrian locomotion on a treadmill, and filmed them to determine duty factor (the fraction of stride period that the foot is in contact with the ground), foot contact time (tc), stride frequency (f), swing phase duration and stride length. C min was 2.1-fold higher than that predicted by their body mass and phylogenetic position, but was not significantly different from the C min of runners (Galliformes and Struthioniformes). The extrapolated gamma-intercept of the relationship between V02 and speed was 1.9-fold higher than that predicted by allometry. Again, cormorants were not significantly different from runners. Contrary to our hypothesis, we therefore conclude that cormorants do not have high pedestrian transport costs. Cormorants were observed to use a grounded gait with two double support phases at all speeds measured, and showed an apparent gait transition between 0.17 and 0.25 m s(-1). This transition occurs at a Froude number between 0.016 and 0.037, which is lower than the value of approximately 0.5 observed for many other species. However, despite the use of a limited speed range, and a gait transition at relatively low speed, we conclude that the pedestrian locomotion of these foot propelled diving birds is otherwise generally similar to that of cursorial birds at comparable relative velocities.

Single phage T4 DNA packaging motors exhibit large force generation, high velocity, and dynamic variability

Terminase enzyme complexes, which facilitate ATP-driven DNA packaging in phages and in many eukaryotic viruses, constitute a wide and potentially diverse family of molecular motors about which little dynamic or mechanistic information is available. Here we report optical tweezers measurements of single DNA molecule packaging dynamics in phage T4, a large, tailed Escherichia coli virus that is an important model system in molecular biology. We show that a complex is formed between the empty prohead and the large terminase protein (gp17) that can capture and begin packaging a target DNA molecule within a few seconds, thus demonstrating a distinct viral assembly pathway. The motor generates forces >60 pN, similar to those measured with phage phi29, suggesting that high force generation is a common property of viral DNA packaging motors. However, the DNA translocation rate for T4 was strikingly higher than that for phi29, averaging approximately 700 bp/s and ranging up to approximately 2,000 bp/s, consistent with packaging by phage T4 of an enormous, 171-kb genome in <10 min during viral infection and implying high ATP turnover rates of >300 s(-1). The motor velocity decreased with applied load but averaged 320 bp/s at 45 pN, indicating very high power generation. Interestingly, the motor also exhibited large dynamic changes in velocity, suggesting that it can assume multiple active conformational states gearing different translocation rates. This capability, in addition to the reversible pausing and slipping capabilities that were observed, may allow phage T4 to coordinate DNA packaging with other ongoing processes, including viral DNA transcription, recombination, and repair.

Measurements of Single DNA Molecule Packaging Dynamics in Bacteriophage λ Reveal High Forces, High Motor Processivity, and Capsid Transformations

Molecular motors drive genome packaging into preformed procapsids in many double-stranded (ds)DNA viruses. Here, we present optical tweezers measurements of single DNA molecule packaging in bacteriophage λ. DNA–gpA–gpNu1 complexes were assembled with recombinant gpA and gpNu1 proteins and tethered to microspheres, and procapsids were attached to separate microspheres. DNA binding and initiation of packaging were observed within a few seconds of bringing these microspheres into proximity in the presence of ATP. The motor was observed to generate greater than 50 picoNewtons (pN) of force, in the same range as observed with bacteriophage ϕ29, suggesting that high force generation is a common property of viral packaging motors. However, at low capsid filling the packaging rate averaged ∼600 bp/s, which is 3.5-fold higher than ϕ29, and the motor processivity was also threefold higher, with less than one slip per genome length translocated. The packaging rate slowed significantly with increasing capsid filling, indicating a buildup of internal force reaching 14 pN at 86% packaging, in good agreement with the force driving DNA ejection measured in osmotic pressure experiments and calculated theoretically. Taken together, these experiments show that the internal force that builds during packaging is largely available to drive subsequent DNA ejection. In addition, we observed an 80 bp/s dip in the average packaging rate at 30% packaging, suggesting that procapsid expansion occurs at this point following the buildup of an average of 4 pN of internal force. In experiments with a DNA construct longer than the wild-type genome, a sudden acceleration in packaging rate was observed above 90% packaging, and much greater than 100% of the genome length was translocated, suggesting that internal force can rupture the immature procapsid, which lacks an accessory protein (gpD).

Two-dimensional mechanism of hovering flight by single flapping wing

Numerical simulations are conducted to investigate the mechanism of hovering flight with an inclined stroke. The Reynolds numbers considered are 150 and 1000 based on the maximum translational velocity and wing chord length. Three mechanisms responsible for high vertical force generation, suggested by Dickinson et al. (1999), are confirmed and more elaborated in the present study. First, we show that the vertical force during downstroke is larger than that from the quasi-steady analysis due to the delayed stall mechanism. Second, the wing-wake interaction of reducing the negative vertical force during the stroke reversal is explained in terms of the reattachment of the vortex, shed previously during downstroke, on the wing, by which the wing is submerged in a low pressure region during upstroke and has a smaller negative vertical force. Finally, the rotational circulation is explained by advancing the rotation timing of the wing at supination using both the numerical simulation and inviscid potential theory.

Muscle architecture and functional anatomy of the pelvic limb of the ostrich (Struthio camelus)

The functional anatomy of the pelvic limb of the ostrich (Struthio camelus) was investigated in order to assess musculoskeletal specialization related to locomotor performance. The pelvic limbs of ten ostriches were dissected and detailed measurements of all muscle tendon units of the pelvic limb were made, including muscle mass, muscle length, fascicle length, pennation angle, tendon mass and tendon length. From these measurements other muscle properties such as muscle volume, physiological cross-sectional area (PCSA), tendon cross-sectional area, maximum isometric muscle force and tendon stress were derived, using standard relationships and published muscle data. Larger muscles tended to be located more proximally and had longer fascicle lengths and lower pennation angles. This led to an expected proximal to distal reduction in total muscle mass. An exception to this trend was the gastrocnemius muscle, which was found to have the largest volume and PCSA and also had the highest capacity for both force and power production. Generally high-power muscles were located more proximally in the limb, while some small distal muscles (tibialis cranialis and flexor perforatus digiti III), with short fibres, were found to have very high force generation capacities. The greatest proportion of pelvic muscle volume was for the hip extensors, while the highest capacity for force generation was observed in the extensors of the ankle, many of which were also in series with long tendons and thus were functionally suited to elastic energy storage.

Power Consumption of Piezo-Composite Actuator at Resonance Frequency

This paper addresses the power consumption of the LIPCA (LIghtweight Piezo-Composite Actuator) device system when electric input was applied at its resonance frequency. The LIPCA device system is composed of a piezoelectric ceramic layer and fiber reinforced lightweight composite layers. Typically, a PZT ceramic layer is sandwiched by a top fiber layer with low CTE (coefficient of thermal expansion) and base layers with high CTE. The advantages of the LIPCA design are weight reduction by using the lightweight fiber reinforced plastic layers without compromising the generation of high force and large displacement, and design flexibility by selecting the fiber direction and the size of prepreg layers. An experimental set-up was specially designed to measure the power consumption of the LIPCA. By measuring the capacitance of the PZT ceramic wafer during the test, the electric power that consumed can be determined. Experimental results revealed a significant increase in capacitance of the PZT ceramic wafer with an increase in the frequency of applied voltage around the natural frequency of the actuator.