A New Muscle Activation Dynamics Model, That Simulates the Calcium Kinetics and Incorporates the Role of Store-Operated Calcium Entry Channels, to Enhance the EMG-Driven Hill-type Models

Hill-type models are frequently used in biomechanical simulations. They are attractive for their low computational cost and close relation to commonly measured musculotendon parameters. Still, more attention is needed to improve the activation dynamics of the model specifically because of the nonlinearity observed in the EMG-Force relation. Moreover, one of the important and practical questions regarding the assessment of the model's performance is how adequately can the model simulate any fundamental type of human movement without modifying model parameters for different tasks? This paper tries to answer this question by proposing a simple physiologically based activation dynamics model. The model describes the ?kinetics of the calcium dynamics while activating and deactivating the muscle contraction process. Hence, it allowed simulating the recently discovered role of store-operated calcium entry (SOCE) channels as immediate counter-flux to calcium loss across the tubular system during excitation-contraction coupling. By comparing the ability to fit experimental data without readjusting the parameters, the proposed model has proven to have more steady performance than phenomenologically based models through different submaximal isometric contraction levels. This model indicates that more physiological insights is key for improving Hill-type model performance.

Model-Based Analysis of Muscle Strength and EMG-Force Relation with respect to Different Patterns of Motor Unit Loss

This study presents a model-based sensitivity analysis of the strength of voluntary muscle contraction with respect to different patterns of motor unit loss. A motor unit pool model was implemented including simulation of a motor neuron pool, muscle force, and surface electromyogram (EMG) signals. Three different patterns of motor unit loss were simulated, including (1) motor unit loss restricted to the largest ones, (2) motor unit loss restricted to the smallest ones, and (3) motor unit loss without size restriction. The model outputs including muscle force amplitude, variability, and the resultant EMG-force relation were quantified under two different motor neuron firing strategies. It was found that motor unit loss restricted to the largest ones had the most dominant impact on muscle strength and significantly changed the EMG-force relation, while loss restricted to the smallest motor units had a pronounced effect on force variability. These findings provide valuable insight toward our understanding of the neurophysiological mechanisms underlying experimental observations of muscle strength, force control, and EMG-force relation in both normal and pathological conditions.

Steam adsorption on molecular sieve 3A for sorption enhanced reaction processes

Steam adsorption enhanced reaction processes are a promising process intensification for many types of reactions, where water is formed as a byproduct. To assess the potential of these processes, adequate models are required that accurately describe water adsorption, particularly under the desired elevated temperatures and pressures. In this work, an adsorption isotherm is presented for H2O adsorption at 200–350 °C and 0.05–4.5 bar partial pressure on molecular sieve (LTA) 3A. The isotherm has been developed on the basis of experimental data obtained from a thermogravimetric analysis and integrated breakthrough curves. The experimental data at lower steam partial pressures can be described with a Generalized Statistical Thermodynamic Adsorption (GSTA) isotherm, whereas at higher steam partial pressures the experimental data can be adequately captured by capillary condensation. Based on the characteristics of the adsorbent particles, a linear driving force relation has been derived for the adsorption mass transfer rate and the apparent micropore diffusivity is determined. The isotherm and mass transport model presented here prove to be adequate for modelling and improved evaluation of steam adsorption enhanced reaction processes.

Phosphate binding induced force-reversal occurs via slow backward cycling of cross-bridges

ABSTRACTThe release of inorganic phosphate (Pi) from the cross-bridge is a pivotal step in the cross-bridge ATPase cycle leading to force generation. It is well known that Pi release and the force-generating step are reversible, thus increase of [Pi] decreases isometric force by product inhibition and increases the rate constant kTR of mechanically-induced force redevelopment due to the reversible redistribution of cross-bridges among non-force-generating and force-generating states. The experiments on cardiac myofibrils from guinea pig presented here show that increasing [Pi] increases kTR almost reciprocally to force, i.e., kTR ≈ 1/force. To elucidate which cross-bridge models can explain the reciprocal kTR-force relation, simulations were performed for models varying in sequence and kinetics of 1) the Pi release-rebinding equilibrium, 2) the force-generating step and its reversal, and 3) the transitions limiting forward and backward cycling of cross-bridges between non-force-generating and force-generating states. Models consisting of fast reversible force generation before/after rapid Pi release-rebinding fail to describe the kTR–force relation observed in experiments. Models consistent with the experimental kTR-force relation have in common that Pi binding and/or force-reversal are/is intrinsically slow, i.e., either Pi binding or force-reversal or both limit backward cycling of cross-bridges from force-generating to non-force-generating states.STATEMENT OF SIGNIFICANCEPrevious mechanical studies on muscle fibers, myofibrils and myosin interacting with actin revealed that force production associated to phosphate release from myosin’s active site presents a reversible process in the cross-bridge cycle. The correlation of this reversible process to the process(es) limiting kinetics of backward cycling from force-generating to non-force-generating states remained unclear.Experimental data of cardiac myofibrils and model simulations show that the combined effects of [Pi] on force and the rate constant of force redevelopment (kTR) are inconsistent with fast reversible force generation before/after rapid Pi release-rebinding. The minimum requirement in sequential models for successfully describing the experimentally observed nearly reciprocal change of force and kTR is that either the Pi binding or the force-reversal step limit backward cycling.

O Estado, o estatismo autoritário e as políticas públicas na concepção de Poulantzas

This article explores the capitalist state notion from the perspective developed by Nicos Poulantzas in his latest book (The State, the power, the socialism - 1978), as well as it evaluates how his analysis enable the public policies understanding today . The concept of State is presented as the material condensation of a force relation, progressing to an authoritarian statism, a concept developed by Poulantzas to explain the Executive power strengthening and the political democracy institutions decline. Concluding that the Poulantzian thought, despite of being based on his analysis in the 1970s, remains current and allows the public policies understanding in contemporary times.

Stretch-activated current in human atrial myocytes and Na+ current and mechano-gated channels’ current in myofibroblasts alter myocyte mechanical behavior: a computational study

Background The activation of stretch-activated channels (SACs) in cardiac myocytes, which changes the phases of action potential repolarization, is proven to be highly efficient for the conversion of atrial fibrillation. The expression of Na+ current in myofibroblasts (Mfbs) regenerates myocytes’ action potentials, suggesting that Mfbs play an active role in triggering cardiac rhythm disturbances. Moreover, the excitation of mechano-gated channels (MGCs) in Mfbs depolarizes their membrane potential and contributes to the increased risk of post-infarct arrhythmia. Although these electrophysiological mechanisms have been largely known, the roles of these currents in cardiac mechanics are still debated. In this study, we aimed to investigate the mechanical influence of these currents via mathematical modeling. A novel mathematical model was developed by integrating models of human atrial myocyte (including the stretch-activated current, Ca2+–force relation, and mechanical behavior of a single segment) and Mfb (including our formulation of Na+ current and mechano-gated channels’ current). The effects of the changes in basic cycle length, number of coupled Mfbs and intercellular coupling conductance on myocyte mechanical properties were compared. Results Our results indicated that these three currents significantly regulated myocyte mechanical parameters. In isosarcometric contraction, these currents increased segment force by 13.8–36.6% and dropped element length by 12.1–31.5%. In isotonic contraction, there are 2.7–5.9% growth and 0.9–24% reduction. Effects of these currents on the extremum of myocyte mechanical parameters become more significant with the increase of basic cycle length, number of coupled Mfbs and intercellular coupling conductance. Conclusions The results demonstrated that stretch-activated current in myocytes and Na+ current and mechano-gated channels’ current in Mfbs significantly influenced myocyte mechanical behavior and should be considered in future cardiac mechanical mathematical modeling.

Gravitational Catastrophe and Dark Matter

I have been working for a long time about basic laws of physics. During this time I noticed, that gravity does not work as Newtonian. Distance and gravitational force relation changes over distance. The attraction properties change for each point of free space, and have some limits. The attraction changes due to some values between 1/r and 1/r^2 even for the existent furthest distance. This work aims to analyze and discuss this phenomenon.

ANALISIS FAKTOR-FAKTOR YANG MEMPENGARUHI KEPUASAN NASABAH PADA PT. BANK RAKYAT INDONESIA KANCA PONOROGO

Company is a monetary service, thus it must win emulation which progressively more competitive. Bank Rakyat Indonesia cannot only rely on product development of eye service, but it must also force relation with all service users or clients who judge the make-up of the quality of service and product which on the market. This research aims to study and analyze the influences of The Quality of Service on the Costumer Satisfaction of PT. Bank Rakyat Indonesia (Persero) Kantor Cabang Ponorogo. The Quality of Service in this research uses three of the that is consist of: reliability, responsiveness and assurances have relationship with Costumer Satisfaction. If costumer feel satisfied, that make customer high probability to buys a service. In this research, Multiple regreression of technical analysis is applied. To test the impact, F test is applied and to test the partial influence, t test is applied at significant level 0,05. The number of samples used for this analysis are 266 consumers that comprise at Tabungan of PT. Bank Rakyat Indonesia (Persero) Kantor Cabang Ponorogo. The result of the research indicates that partially only reliability dimension which does not has an effect on the satisfaction of the client. The Quality of Service in this research uses three of the that is consist of: reliability, responsiveness and assurances have relationship with Costumer Satisfaction. If costumer feel satisfied, that make customer high probability to buys a service. In this research, Multiple regreression of technical analysis is applied. To test the impact, F test is applied and to test the partial influence, t test is applied at significant level 0,05. The number of samples used for this analysis are 266 consumers that comprise at Tabungan of PT. Bank Rakyat Indonesia (Persero) Kantor Cabang Ponorogo.

Simultaneous measurement of wind velocity field and wind forces on a square tall building

Vortex shedding from a tall building is known to be responsible for the quasi-periodic across-wind force exerted on the building. This article unveils the exact relationship between the vortex shedding pattern and the fluctuating across-wind force. Simultaneous particle-image velocimetry and pressure measurements are carried out on a square-plan tall building model in the wind tunnel toward an understanding of the velocity–pressure–force relation for across-wind force generation on the building. A collection of instantaneous wind flow patterns and synchronized wind pressure distributions suggests the existence of full periods of vortex shedding from the building. The results are further analyzed using the conditional sampling method by which the roles of development and shedding of large-scale vortices in the building wake on the generation of peak across-wind forces are evidently found. Furthermore, quasi-periodicity of across-wind excitation is clearly confirmed with Hilbert transform of the across-wind force signal. The phase averaging technique is applied to the particle-image velocimetry flow fields and distinct vortex shedding patterns from the building are observed for most of the measurement time, together with an evident phase relationship with the across-wind forces.