Performance Of Mechanical Work Research Articles

F-actin architecture determines the conversion of chemical energy into mechanical work

Mechanical work serves as the foundation for dynamic cellular processes, ranging from cell division to migration. A fundamental driver of cellular mechanical work is the actin cytoskeleton, composed of filamentous actin (F-actin) and myosin motors, where force generation relies on adenosine triphosphate (ATP) hydrolysis. F-actin architectures, whether bundled by crosslinkers or branched via nucleators, have emerged as pivotal regulators of myosin II force generation. However, it remains unclear how distinct F-actin architectures impact the conversion of chemical energy to mechanical work. Here, we employ in vitro reconstitution of distinct F-actin architectures with purified components to investigate their influence on myosin ATP hydrolysis (consumption). We find that F-actin bundles composed of mixed polarity F-actin hinder network contraction compared to non-crosslinked network and dramatically decelerate ATP consumption rates. Conversely, linear-nucleated networks allow network contraction despite reducing ATP consumption rates. Surprisingly, branched-nucleated networks facilitate high ATP consumption without significant network contraction, suggesting that the branched network dissipates energy without performing work. This study establishes a link between F-actin architecture and myosin energy consumption, elucidating the energetic principles underlying F-actin structure formation and the performance of mechanical work.

Mechanical activities of self-beating cardiomyocyte aggregates under mechanical compression

Since the discovery of synchronous pulsations in cardiomyocytes (CMs), electrical communication between CMs has been emphasized; however, recent studies suggest the possibility of mechanical communication. Here, we demonstrate that spherical self-beating CM aggregates, termed cardiac spheroids (CSs), produce enhanced mechanical energy under mechanical compression and work cooperatively via mechanical communication. For single CSs between parallel plates, compression increased both beating frequency and beating energy. Contact mechanics revealed a scaling law on the beating energy, indicating that the most intensively stressed cells in the compressed CSs predominantly contributed to the performance of mechanical work against mechanical compression. For pairs of CSs between parallel plates, compression immediately caused synchronous beating with mechanical coupling. Compression tended to strengthen and stabilize the synchronous beating, although some irregularity and temporary arrest were observed. These results suggest that mechanical compression is an indispensable control parameter when evaluating the activities of CMs and their aggregates.

Experimental study and energy-efficiency evaluation of a 4-step pressure-vacuum swing adsorption (PVSA) for CO2 capture

A single-stage 4-step pressure-vacuum swing adsorption (PVSA) process, capable of CO2 separation from the prepared flue gas, is experimentally studied on a fresh perspective of energy-efficiency analysis. The major contribution of thermodynamic carbon pump, which includes the minimum CO2 separation work and the second-law efficiency, is to establish the relationship between energy consumption and separation difficulty. Adsorption/desorption cycles utilizing a fixed bed of an adsorbent material made of zeolite 13X are performed. Not only the recovery target, but also the second-law efficiency is considered as the main performance criteria in this paper. Thereby, the performance analysis of experimental apparatus is conducted over a range of process parameters, namely 10–20% CO2 concentration, 1.0–3.0sl/min flow rate, 10–30s time duration of pressurization with feed, 80–120s time duration of feed and 40–80s time duration of purge. The results show that the specific energy consumption for the 4-step PVSA experiments is varied from 2719.31kJ/kg to 9334.21kJ/kg, the corresponding range of second-law efficiency calculated by thermodynamic carbon pump is 1.83–4.27%. The efficiency of vacuum pump affects the specific energy consumption of CO2 capture process. The second-law efficiency in experimental studies of this paper is strongly dependent on the mechanical work performance of vacuum pump.

Real-time model-based control of afterload for in vitro cardiac tissue experimentation.

The performance of mechanical work by isolated cardiac muscle samples has typically been studied by subjecting their tissues to an isotonic shortening protocol, which results in "flat-topped" work-loop profiles. In order to better replicate the forces experienced by these tissues in vivo, we have developed a system for imposing a model-based, time-varying, load on isolated cardiac tissue preparations. A model of systemic afterload was developed from the combination of a Windkessel-type model of vascular fluid impedance, and the Laplace law of the heart, and encoded into a hardware-based control system. The model-predicted length change was then imposed on an isolated cardiac trabecula in a work-loop calorimeter, giving rise to force-length work-loops that more closely resemble those experienced by these tissues in vivo.

EXERGIC ANALYSIS AND VARIATIONAL INEQUALITIES METHODS IN SOME FLUID MECHANIC’S PROBLEMS

Purpose. The foundations of the energetic approach for analyzing of the bodies with dissipation properties are presented in the article. Methodology. Energy resource of arbitrary body is characterized by the sum of the exergy and anergy. The first of them indicates the part of energy which can be used to perform mechanical work. The second – is a measure of the processes’ irreversibility in the interaction of such body with the others. It indicates what part of the energy dissipates into the environment as low-temperature heat and can’t be used for the mechanical work performance. The energy balance in the thermodynamic systems is the basis for the relevant variation principles formulation. The introduction of the exergy and anergy concept leads to the variation inequalities formulation. They are transformed into equality in almost non-realized case of the reverse ability and equilibrium process, or in the case of the limit equilibrium state. Conclusion. Variation inequalities can be used for the formulation of general relations, which determine the parameters of quasi-static flow of real fluid in its interaction with solid obstacles - wetted perimeter of pipe or open channel, as well as the inclusions - in the cases of unknown interaction surface. These problems in particular arise in the analysis of the erosion process and shoreline destruction it caused, river flow interaction with stones during floods in natural streams.

Cross-Bridge Duty Cycle in Isometric Contraction of Skeletal Myofibrils

During interaction of actin with myosin, cross-bridges impart mechanical impulses to thin filaments resulting in rotations of actin monomers. Impulses are delivered on the average every tc seconds. A cross-bridge spends a fraction of this time (ts) strongly attached to actin, during which it generates force. The "duty cycle" (DC), defined as the fraction of the total cross-bridge cycle that myosin spends attached to actin in a force generating state (ts/ tc), is small for cross-bridges acting against zero load, like freely shortening muscle, and increases as the load rises. Here we report, for the first time, an attempt to measure DC of a single cross-bridge in muscle. A single actin molecule in a half-sarcomere was labeled with fluorescent phalloidin. Its orientation was measured by monitoring intensity of the polarized TIRF images. Actin changed orientation when a cross-bridge bound to it. During isometric contraction, but not during rigor, actin orientation oscillated between two values, corresponding to the actin-bound and actin-free state of the cross-bridge. The average ts and tc were 3.4 and 6 s, respectively. These results suggest that, in isometrically working muscle, cross-bridges spend about half of the cycle time attached to actin. The fact that 1/ tc was much smaller than the ATPase rate suggests that the bulk of the energy of ATP hydrolysis is used for purposes other than performance of mechanical work.

Myosin Light Chain 2 Into the Mainstream of Cardiac Development and Contractility

See related article, pages 323–331 Myocardium exhibits a remarkably broad dynamic range of function that is normally well matched to the circulatory load on the heart. Regulation of cardiac contraction is a multifaceted process that is well understood in terms of the activating role of Ca2+ but much less well in terms of modulation by thick filament accessory proteins and by post-translational modification of thick and thin filament proteins.1,2 In this issue of Circulation Research , an elegant study by Fishman and colleagues3 dramatically reinforces the idea that the light chain 2 subunit of myosin (MLC-2) is critically important in myocardium by showing that MLC-2 loss because of mutation abolishes myofibrillar assembly in zebrafish, resulting in embryonic lethality. Earlier work had shown that mutations in MLC-2 account for some cases of hypertrophic cardiomyopathy4 and that phosphorylation of MLC-2 contributes to cardiac pump function,5 but now it is evident that MLC-2 has an obligatory role in development. Cardiac isoforms of myosin II comprise the motor of myocardial contraction and like all members of this family are composed of 6 subunits6: 2 myosin heavy chains of &200 kDa molecular weight, 2 so-called essential light chains (or light chain 1) of &17 kDa, and 2 regulatory light chains (or light chain 2) of >20 kDa. Subfragment 1 of the heavy chain (Figure) comprises the business end of the motor, containing both the nucleotide and actin-binding sites, whereas the light chains wrap around the rod-like extension of subfragment 1 and are believed to function (minimally) as mechanical stabilizers of this part of myosin during force generation and mechanical work performance. This motor is impressive for its efficiency and its …

MECHANOCHEMICAL COUPLING OF MOLECULAR MOTORS WITH NONCONSERVATIVE FORCE

The biochemical process for coupling between hydrolysis of ATP and the performance of mechanical work involves a sequence of events. Here we present a two-dimensional ratchet model with a non-conservative impulsive force field. The non-conservative impulsive force that represents the chemical energy consumed in the conformation changing process provides a source of non-equilibrium fluctuation, which is a crucial factor for the Brownian motors and can lead to macroscopic motion.

Two‐pedal ergometer for in vivo MRS studies of human calf muscles

This article describes an ergometer that enables human subjects to exercise one or both limbs while 31P NMR spectra are obtained. Two independent pedals, equipped with position and force transducers, were mounted on the ergometer in order to calculate mechanical work performance. First, the effect of the magnetic field upon the signal coming from the transducers was investigated. Then the ergometer was tested by performing a series of steady-state exercises of increasing intensity. Experimental data showed that actual mechanical power ranged from 1.5 ± 0.2 W to 11.0 ± 1.6 W, while the corresponding oxygen consumption increased from 0.28 ± 0.04 l/min at rest to 0.48 ± 0.10 l/min at the highest load, and the PCr/(PCr+Pi) ratio, as calculated from the 31P spectra, decreased from 0.94 ± 0.01 at rest to 0.73 ± 0.04. These results are consistent with the values reported in the literature and show that this ergometer, which is easy to use, is suitable for in vivo spectroscopy research when metabolic steady-state conditions are required. Magn Reson Med 46:1000–1005, 2001. © 2001 Wiley-Liss, Inc.

Two-pedal ergometer for in vivo MRS studies of human calf muscles.

This article describes an ergometer that enables human subjects to exercise one or both limbs while (31)P NMR spectra are obtained. Two independent pedals, equipped with position and force transducers, were mounted on the ergometer in order to calculate mechanical work performance. First, the effect of the magnetic field upon the signal coming from the transducers was investigated. Then the ergometer was tested by performing a series of steady-state exercises of increasing intensity. Experimental data showed that actual mechanical power ranged from 1.5 +/- 0.2 W to 11.0 +/- 1.6 W, while the corresponding oxygen consumption increased from 0.28 +/- 0.04 l/min at rest to 0.48 +/- 0.10 l/min at the highest load, and the PCr/(PCr+P(i)) ratio, as calculated from the (31)P spectra, decreased from 0.94 +/- 0.01 at rest to 0.73 +/- 0.04. These results are consistent with the values reported in the literature and show that this ergometer, which is easy to use, is suitable for in vivo spectroscopy research when metabolic steady-state conditions are required.

Five axioms for the functional design of peptide-based polymers as molecular machines and materials: Principle for macromolecular assemblies

Peptide-based polymers can be transformable hydrogels, elastomers, regular thermoplastics, or inverse thermoplastics, and can function as diverse molecular machines. When of the appropriate composition, these polymers exhibit hydrophobic folding and assembly transitions in the accessible aqueous range as the temperature is raised from below to above a critical value referred to as Tt, the temperature for the onset of an inverse temperature transition. In this article, the design of these Tt-type molecular machines and materials is systematized in terms of five axioms for peptide-based polymer engineering: The first axiom is represented by a hydrophobicity scale that provides the information with which to design peptide-based polymers with a particular value of Tt. The second axiom concerns thermomechanical transduction wherein raising the temperature from below to above Tt results in hydrophobic folding and assembly with the performance of mechanical work. The third axiom states that at constant temperature, diverse energy inputs lower Tt from above to below an operating temperature by acting on a functional moiety within the polymer to drive hydrophobic folding and assembly with the isothermal performance of mechanical work. The fourth axiom concerns polymer compositions having two different functional groups, with each responsive to a different energy input and with each part of a common hydrophobic folding domain. The two functional groups become coupled one to the other such that an energy input acting on one functional group becomes an energy output by having changed the property of the second functional group. The fifth axiom states that the efficiency of conversion from one form of energy to another by means of the fourth axiom increases nonlinearly with hydrophobicity of the common hydrophobic folding and assembly domain. These phenomenological axioms allow design of peptide-based polymers capable of diverse energy conversions involving the intensive variables of mechanical force, temperature, pressure, chemical potential, electrochemical potential, and light. Knowledge of the physical process underlying the five axioms enhances their use in the design of materials and devices for medical and nonmedical applications. The physical process is demonstrated by the use of cartoons. © 1998 John Wiley & Sons, Inc. Biopoly 47: 167–178, 1998

Electromechanical Transduction: Reduction-Driven Hydrophobic Folding Demonstrated in a Model Protein to Perform Mechanical Work

It has long been appreciated that hydrophobic folding is an important element of protein structure formation. Here it is demonstrated for the first time that the electrochemical or chemical reduction of a nicotinamide in a model protein, which increases hydrophobicity, can drive hydrophobic folding and assembly in such a way as to lift a weight or otherwise contract against a constant tensional force. The model protein, poly[0.73(GVGVP),0.27(GK{NMeN}GVP], can be γ-irradiation cross-linked to form an elastic matrix which contracts on raising the temperature from below to above the transition range for hydrophobic folding and assembly. On reduction of the N-methyl nicotinamide, {NMeN}, the transition temperature range is lowered from above to below 20°C to drive contraction due to hydrophobic folding with the performance of mechanical work.

Mechanism of the effect of exogenous fructose 1,6-bisphosphate on myocardial energy metabolism.

The effects of fructose 1,6-bisphosphate (F-1,6-P2) on the isolated Langendorff-perfused heart were studied by monitoring flavoprotein fluorescence, oxygen consumption (MVO2), coronary flow (Fc), systolic intraventricular pressure (Psys), diastolic intraventricular pressure, and contraction frequency. The cellular energy state and cytosolic pH were determined by means of 31P nuclear magnetic resonance. Infusion of 5 mM F-1,6-P2 caused a rapid shift toward reduction in the flavoprotein redox state and initial 50% and 44% decreases in Psys and MVO2, respectively. After a partial recovery, these measures remained 11% and 25% below the basal value. Concomitantly, after an initial transient increase of 13%, Fc remained 17% lower than in the basal state. When the F-1,6-P2 concentration was subsequently increased to 10 mM, psys and MVO2 dropped temporarily to 31% and 29% of the basal value and then remained at 50% and 53%, respectively. Simultaneously, a brief increase was observed in Fc, which then fell 34% below the basal value. Rapid reoxidation of the flavoproteins and increases in MVO2, Psys, and Fc occurred on discontinuation of the F-1,6-P2 infusion. 31P nuclear magnetic resonance during infusions of both 5 and 10 mM F-1,6-P2 revealed a decrease in cytosolic inorganic phosphate and a tendency to increase creatine phosphate, suggesting elevation in the cellular energy state. No changes in intracellular pH occurred as estimated from the chemical shift of the nuclear magnetic resonance of inorganic phosphate. F-1,6-P2 (5 mM and 10 mM) lowered the free Ca2+ concentration in the Krebs-Henseleit bicarbonate buffer (by 32% and 47%, respectively). This probably explains the effects of F-1,6-P2 on mechanical work performance and cellular respiration. A direct metabolic effect also exists, however, because flavoprotein reduction by F-1,6-P2 could be observed in the K(+)-arrested heart, where its effects on MVO2 were minimal. This redox effect may not be caused by changes in free Ca2+ concentration because it could not be reproduced by infusion of EGTA.

Relationships between chemical and mechanical events during muscular contraction.

In this review we have attempted a synthesis of ideas from cross-bridge theories of muscle contraction with biochemical mechanisms of the actomyosin ATPase. This synthesis of ideas has been based on experimental approaches that permit mechanical and biochemical investigations on the same system. We have formulated an example of how biochemical processes may be influenced by strain in the cross-bridge and have highlighted how much has yet to be learned about the biochemistry (and protein structure) of the working stroke of the cross-bridge. Processes that do not appear to be related to the working stroke such as ATP-induced dissociation of actomyosin or protein-bound ATP hydrolysis appear to be similar kinetically in fibers and isolated actomyosin. But, as might be expected, this is not the case in those processes that involve force production and the performance of mechanical work. There appears to be a sound base from which the mechanochemistry of individual processes within the cross-bridge cycle can be analyzed in detail. There is a need for the development of spectroscopic techniques, particularly those that might detect the rate of Pi and ADP dissociation from cross-bridges into the medium. The combination of pulse photolysis of caged ATP and time-resolved structure analysis by use of synchrotron radiation (53) should lead to better understanding of the structure of cross-bridge states in relation to the chemistry and mechanics of transient intermediates.

Energy balances in dissipative flow regions

The formation of dissipative mechanical fluctuations is due to the utilization of the frictional heat, generated by dissipative motion of the fluid, for the performance of mechanical work. Such dissipative energy conversions take place by means of cyclic thermodynamic work processes. [A. C. Peter, J. Acoust. Soc. Am. 58, S36(A), S108(A) (1975)]. These fluctuations consist of two distinct kinds: namely, those whose physical nature is purely “hydrodynamic” and those transmitted by the fluid in the form of acoustic disturbances. The current investigation highlights the energy balances of hydrodynamic fluctuations for the case of perfect gases. It is shown that for a given amount of heat input into the fluid due to the dissipation of its kinetic energy, the following energy balances apply when the specific heat ratio γ = 1.4: 89.3% of the dissipative heat input is used to build up the internal energy of the fluid, the remaining 10.7% being utilized in the performance of expansion work upon the surroundings. The succeeding collapse of the disturbance uses 17.9% of the frictional heat input for the performance of isentropic expansion work. The isentropic collapse is followed by a succession of fluctuations around the ambient pressure of the surroundings whose average work contribution may be considered isobaric. These fluctuations, which return the fluid to its initial equilibrium state, consist of a total work output utilizing 28.6% of the frictional heat (this work is implented on the fluid by the surroundings). In the same process the internal energy of the fluid loses 71.4% of the original frictional heat to the surroundings, thus completing the dissipative work cycle.

The Energy Requirement for Growth: An Application of Atkinson's Metabolic Price System

Extract: Atkinson's metabolic price system has been applied to the calculation of the energy costs of growth of a 3-week-old, 3,900-g “male reference baby,” growing along the 50th percentile. The increase in weight of liver, brain, lung, spleen, and kidney has been calculated from literature data. The other organs and tissues were assumed to grow proportionally to the gain in body weight corrected for the weight gain of the organs mentioned above. The gross chemical composition of tissues and organs has been used to calculate the increases in specific tissue components, such as proteins, triglycerides, phospholipids, cholesterol, glycogen, DNA, and RNA. Of the total weight gain of 6.9 g/kg body wt/24 hr, 25.2% could be accounted for as solids deposited in the body, the remainder, 74.8%, being water. The energy needed to synthesize these solids has been calculated in terms of ATP equivalents, ATP being the form of energy used in the biochemical synthetic reactions. A total of 0.0614 mol ATP Eq is needed/kg body wt/24 hr in addition to 0.164 g glucose/kg body wt/24 hr. Proteins, which accumulate at a rate of 0.971 g/kg body wt/24 hr, take 87.7% of these ATP Eq. The energy needs for the active uptake of ions has also been calculated and was found to be 0.0108 mol ATP Eq/kg body wt/24 hr, which increases the total to 0.0722 mol ATP Eq kg body wt/24 hr.These ATP equivalents can be generated by the complete oxidation of 0.342 g glucose, which sets the total energy need to maintain growth at 0.506 g glucose/kg body wt/24 hr. Assuming an intake of humanized milk containing 69 kcal/100 ml, at 140 ml/kg body wt/24 hr, 2.2% of the total caloric intake is needed to cover the energy cost of normal growth.Speculation: The metabolic price system theory as developed by Atkinson may prove to be very useful in calculating the energy requirements for specific functions, such as performance of mechanical work, maintenance of ionic equilibrium, and energy costs for replacing body constituents, as more becomes known about the stoichiometry of biochemical reactions in various organs.

Electromagnetic levitation forces

The theorem that a generator, when connected to a system capable of doing mechanical work, supplies during the motion an amount of energy of which half appears as an increase in the energy of the system and half is used in the performance of mechanical work, is applied to prove that the force in any direction x between a coil carrying an alternating current I and a body in which eddy currents are induced by the field of the coil is ½I2(∂L/∂x) where L is the effective inductance of the coil. The theorem is also used to show that waves of intensity J propagated with a velocity c possess a momentum J/c2 per unit volume.

Mentally retarded children's training to plan their own work during handicrafts lessons

The Soviet auxiliary school, when preparing their wards for independent life and societal work, organizes all the work so as to eliminate the retarded child's mental and physical handicap. Work training performs a great role solving the auxiliary school students' comprehensive development task and correcting their existing shortcomings. Auxiliary school experience shows that particularly good measures to raise the effectiveness of training by adjusting the mentally retarded child's intellectual development is pedagogically correctly organized work-linked training at all educational stages, including the lower grades.
 Handicrafts play a major adjusting role in the auxiliary school lower grades (1-3). These activities generate favorable conditions not so much for physically- but rather for mentally-abnormal children to express themselves and develop.
 Therefore, it is important to organize the lessons of this subject in a way that mentally retarded children's thinking is activated and developed, while at the same time corrected (do not be satisfied with merely mechanical work performance, as sometimes happens in practice).
 Analysis of observed handicrafts lessons and experimental activities shows that circumstances which are crucial for the correct development of mentally-abnormal children arise when they're doing their practical work. The necessity to plan work is one of the circumstances of workflow. Individual operations are performed gradually in the production of each item. This is the result of a complex thinking process, i.e. when producing an object a child has to first know how to divide it into different parts in his imagination, review their interconnection methods, and provide the consistency with which to do the job. This stage of the workflow process is particularly difficult for a mentally retarded child. Therefore, it is important to teach a retarded child to plan work. The main condition for teaching children to plan their work is students' ability to consistently perform separate workflow operations. This article and is aimed at in depth analysis of this issue.

Left ventricular heat production measured by coronary flow and temperature gradient.

The study of energetics of the left ventricular myocardium, normally based on its oxygen consumption and mechanical work performance, can be extended by determining its heat production as well. By considering all forms of energy input and output of the left ventricle, calculations were made of left ventricular net heat production under a variety of hemodynamic conditions. One of the mechanisms for removal of the heat produced is provided by the coronary blood, which is warmed in transit through the myocardium. Direct measurements of the rate of heat removal by the coronary circulation were made from coronary flow rate and veno-arterial temperature gradient. The fraction of left ventricular net heat production which is removed by the coronary perfusion is proportional to coronary flow rate. The fraction at a given flow rate is sufficiently reproducible to permit estimation of total heat produced from the portion measured in the coronary circulation. Certain of the theoretical applications of heat data may require more accuracy than appears feasible by this method. Which of the applications discussed will prove practical remains to be determined. Submitted on February 13, 1961

Economy of Feeding Home Grown Berseem to Cattle

Form animals require food for growth, production of milk and performance of mechanical work over and above the amount required for the upkeep of the body. Nearly one half of the feed consumed by an animal is required for main- tenence. Insufficient supply of feed naturally results either in a falling off in the production or in the conversion of body substances into products. Hence, it is hardly possible to improve the cattle only by breeding when they are not properly fed. Requirements of cattle Food is necessary to supply energy, protein, minerals and vitamins Fnergy or fuel is required to maintain body temperature and to support the vital activities of the various organs; protein to repair and build up body tissues or to supply the protein of milk, minerals to form bone, maintain the mineral matter of the body or to supply the requirements of milk. Vitamins are necessary for the efficient functioning of the cells and organs of the body.