Role Of Elastic Energy Research Articles

Role of elastic energy in the formation of ferroelectric barium strontium titanate films on sapphire

The initial stages of the growth of ferroelectric barium strontium titanate (BaSrTiO3) films on single-crystal sapphire substrates have been investigated experimentally. It has been shown that the vapor-solid phase transition at the initial stage of the deposition of the BaSrTiO3 film on sapphire occurs in two stages. At the first stage, an elastically strained wetting layer that inheres the structure of the substrate is formed on the surface. At the same time, a strong electric charge is formed on the surface of the wetting layer. At the second stage of the phase transition, the wetting layer loses stability and transforms into BaSrTiO3 nuclei, which further merge to form a solid film.

Temperature dependence of lysozyme hydration and the role of elastic energy.

Water plays a critical role in protein dynamics and functions. However, the most basic property of hydration--the water sorption isotherm--remains inadequately understood. Surface adsorption is the commonly adopted picture of hydration. Since it does not account for changes in the conformational entropy of proteins, it is difficult to explain why protein dynamics and activity change upon hydration. The solution picture of hydration provides an alternative approach to describe the thermodynamics of hydration. Here, the flexibility of proteins could influence the hydration level through the change of elastic energy upon hydration. Using nuclear magnetic resonance to measure the isotherms of lysozyme in situ between 18 and 2 °C, the present work provides evidence that the part of water uptake associated with the onset of protein function is significantly reduced below 8 °C. Quantitative analysis shows that such reduction is directly related to the reduction of protein flexibility and enhanced cost in elastic energy upon hydration at lower temperature. The elastic property derived from the water isotherm agrees with direct mechanical measurements, providing independent support for the solution model. This result also implies that water adsorption at charged and polar groups occurring at low vapor pressure, which is known for softening the protein, is crucial for the later stage of water uptake, leading to the activation of protein dynamics. The present work sheds light on the mutual influence of protein flexibility and hydration, providing the basis for understanding the role of hydration on protein dynamics.

Temperature dependence of lysozyme hydration and the role of elastic energy

Temperature dependence of lysozyme hydration and the role of elastic energy

The Role of Elastic Energy in Activities with High Force and Power Requirements: A Brief Review

The purpose of this article is to provide strength and conditioning practitioners with an understanding of the role of elastic energy in activities with high force and power requirements. Specifically, the article covers 1) the nature of elasticity and its application to human participants, 2) the role of elastic energy in activities requiring a stretch-shorten cycle such as the vertical jump, 3) the role of muscular stiffness in athletic performance, 4) the control of muscular stiffness through feedforward and feedback mechanisms, and 5) factors affecting muscular stiffness. Finally, practical applications are provided. In this section, it is suggested that the storage and reuse of elastic energy is optimized at relatively higher levels of stiffness. Because stiffness decreases as fatigue ensues as well as with stretching before an event, the article emphasizes the need for proper preparation phases in a periodized cycle and the avoidance of long static stretches before high-force activities. The importance of teaching athletes to transition from eccentric to concentric movements with minimal time delays is also proposed due to the finding that time delays appear to decrease the reuse of elastic energy. In addition to teaching within the criterion tasks, evidence is provided that minimizing transitions in plyometric training, a technique demonstrated to increase musculotendinous stiffness, can optimize power output in explosive movements. Finally, evidence is provided that training and teaching programs designed to optimize muscular stiffness may protect athletes against sports-related injuries.

Direct numerical simulation of viscoelastic drag-reducing flow: a faithful finite difference method

Viscoelastic drag-reducing flows created by additives have been studied recently by using an artificial diffusion spectral method [Phys. Fluids 9 (1997) 743] or a local artificial diffusion finite difference scheme [A role of elastic energy in turbulent drag reduction by polymer additives, in: Proceedings of the 2nd International Turbulence and Shear Flow Phenomena Symposium, Stockholm, 27–29 June, 2001, pp. 35–40]. In this study, we employed the MINMOD scheme to approximate the stress derivatives in the constitutive equations and introduced no artificial diffusion term. Compared to the artificial diffusion methods, much higher drag-reduction rates are predicted by using the present method. A drag-reduction rate of 53% was obtained at Weissenberg number We τ =45 with a Giesekus model. The numerical error of the artificial diffusion term was analyzed. In addition, the effects of the grid spacing and computational domain size on the numerical results were studied.

Comments on the Role of Elastic Energy in Jumping Performance

Heglund, N.C., Fedak, M.A., Taylor, C.R., & Cavagna, G.A. (1982). Energetics and mechanics of terrestrial locomotion: IV. Total mechanical energy changes as a function of speed and body size in birds and mammals. Journal of Experimental Biology, 97,5746. Ingen Schenau, G.J. van, Bobbert, M.F., & Haan, A. de. (1997). Does elastic energy enhance work and efficiency in the stretch-shortening cycle? Journal of Applied Biomechanics, 13,389-415. Kushmerick, M.J., & Paul, R.J. (1976). Relationship between initial chemical reactions and oxidative recovery metabolism for single isometric contractions of frog sartorius at 0 degrees C. Journal of Physiology, 254,711-727. K r w R., &Taylor, C.R. (1990). The cost of generating force: A new perspective. Nature, 346,265-267. Marsh, R.L., & Olson, J.M. (1994). Power output of scallop adductor muscle during contractions replicating the in vivo mechanical cycle. Journal of Experimental Biology, 193, 139-156. Rall, R.J. (1985). Energetic aspects of skeletal muscle contraction: Implication of fiber types. Exercise and Sport Sciences Reviews, 13,33-74. Roberts, T.J., Marsh, R.L., Weyand, P.G., &Taylor, C.R. (1997). Muscular force in running turkeys: The economy of minimizing work. Science, 275,1113-1 115.

Role of volume fraction in the coarsening of Ni 3Si precipitates in binary NiSi alloys

The coarsening behavior of coherent γ′ (Ni 3Si) precipitates in binary NiSi alloys containing 5.50–5.93 wt.%Si was investigated at an aging temperature of 650°C. Over this range of concentrations the volume fractions ƒ γ′ vary from approximately 0.015 to 0.081. The kinetics of coarsening and the distributions of particle sizes appear to be independent of volume fraction for ƒ γ′ = 0.050, 0.058 and 0.081 , but semiquantitative evidence was found for anomalously rapid coarsening kinetics when ƒ γ′ = 0.018 . The larger precipitates in the more dilute alloys exhibit concave-cuboidal morphologies and in some instances were observed in the process of splitting into groups of eight new particles. These morphologies were also attained under even smaller supersaturations than those experienced during normal isothermal aging, i.e. in a microstructure produced by a double-aging experiment. This suggests to us that the morphologies in question are not a product of dendritic growth. These rather unexpected results indicate that the role of elastic energy in affecting morphology and coarsening kinetics may be more important than previously suspected, since the Ni 3Si-matrix lattice misfit is smaller than in any other binary Ni-base alloy. There is also evidence, based on our results and data in the literature, that the coarsening kinetics might increase with increasing ƒ γ′ at volume fractions exceeding 0.10; this is more in keeping with the kind of behavior expected theoretically.

The role of elastic energy in the morphological development of a Ni [sbnd]Ti [sbnd]Al alloy

The role of elastic energy in the morphological development of a Ni [sbnd]Ti [sbnd]Al alloy

Factors influencing the angular velocity of a human limb segment

The angular velocity of a knee extension performed after flexion with different range and velocity, i.e. the kicking movement with stabilized thigh, was investigated and described. In addition, the maximum velocity of extension reached after prestretch was compared to that obtained in trials without prestretch. The maximum velocity of extension varied from 213 to 1087 degrees s −1 depending on the range and velocity of prestretch. In trials without prestretch the velocity of extension was worse up to 43% when small range of movement was involved. In trials with full range of movement the velocity of extension was similar in the tasks with and without prestretch. In this context the possible role of elastic energy is discussed. The method used was electrogoniometry.

Some Aspects of Precipitation and Magnetic Properties of Alnico Alloys

I. Single crystals of Alnico V and Alnico VIII alloys with 35, 40, and 42 wt.% Co and 5, 7, and 8 wt.% Ti, respectively, were investigated by x-ray analysis and electron microscopy of thin foils. It was found: (1) In Alnico V, alloy decomposition begins with the formation of randomly arranged equiaxial spherical zones. When the tempering temperature and time increase, at first very short-range ordering appears in their arrangement, and then an entire periodic modulated structure is formed. At later stages, rod-shaped particles are formed, then metastable tetragonal phases, and at least, two cubic phases. (2) In Alnico VIII-type alloys with an increased content of Co and Ti, volume changes during decomposition are significantly greater, and the role of elastic energy is decisive. So a three-dimensional periodically modulated structure forms even during the quenching process. These structure elements are mainly equiaxial precipitates which intergrow in rods in some places. During tempering, the number of rod-shaped formations increases, and continuous transformation from the modulated structure to tetragonal phases takes place. Two cubic phases form at later tempering stages. (3) Transformation from the modulated structure to tetragonal phases is not accoupanied by changes in alloy structure morphology but are seen in x-ray scattering results. The tetragonal phases have equal ``c'' periods along the cubic axis but different ``a'' periods. This is accounted for by an alloy structure morphology in which there are interconnected rod-shaped particles quasicoherent with the matrix (phase lattice periods coincide only along the c axis). In the state of optimum magnetic properties, the structure of all the investigated alloys consists of two tetragonal phases with the following parameters: α-phase Åα′-phase ÅItem Nos.Alloyacc/aacc/a1Alnico V2.8762.8720.9982.8702.8721.0012Alnico VIII2.9092.8730.9872.8552.8731.0063Alnico VIIIa2.9092.8720.9872.8502.8721.0084Alnico VIIIb2.9152.8720.9852.8522.87210.0740% aCo, 7% Ti.42% bCo, 8% Ti.(4) A three dimensional periodic modulated structure is formed at an early stage of tempering with and without a magnetic field applied. As tempering time increases, modulation disappears in the direction coinciding with the external field vector. As a result of this process, a uniaxial structure of rod-shaped particles modulated along the two perpendiculars to the field is formed. The data obtained in this work confirms the spinodal nature of solid solution decomposition in Alnico alloys. II. Microstructural analysis of Alnico VS55 single crystals revealed their dendritic structure. Some segregation was observed in the lower parts of single crystals. Electron microprobe analysis of these regions showed their chemical heterogeneity. Sharp variations of titanium, copper and iron content with respect to the basic composition of the alloy were observed. Investigation of the composition variation shows strong liquation of copper and titanium with distribution coefficients K<1. The observed chemical heterogeneity is accompanied by physical heterogeneity. X-ray topography observations were made on single crystals parallel and perpendicular to the growth direction. Maximum misorientation on the end surface is 4°, while on the surface parallel to the growth direction it does not exceed 32′. The boundaries lie between the dendrite branches. The average size of subgrains is 0.2–0.7 mm. Investigation of the fine decomposition structure α→α+α′ after standard magnet heat treatment reveals places with particles having different shape anisotropy, different orientations, and even different degrees of decomposition. Work was carried out to find the influence of copper and titanium concentration on the decomposition process, and thus on the temperature of isothermal tempering in a magnetic field, and also the influence of the value of the angle between 〈100〉 axes and the direction of magnetic field during heat treatment. Thus, the single-crystal heterogeneity and permanent-magnet properties are shown. Possible ways of removing different kinds of imperfections by changing the regimes of single-crystal growth, and by adding small quantities of some alloying elements to decrease constitutional supercooling, were investigated. The maximum magnet energy of the single crystals was larger than 10·106 G–Oe, with coercive force of 2000 Oe. Both parts of this abstract will be published in the I.E.E.E. Transactions on Magnetics as individual papers.