Power Stroke Research Articles

Mandibular characteristics of early Glires (Mammalia) reveal mixed rodent and lagomorph morphotypes.

Glires (rodents, lagomorphs and their fossil kin) is the most speciose and arguably most diversified clade of living placentals. Different lineages within the Glires evolved basically opposite chewing movements: a mostly transversal power stroke in lagomorphs, and a mostly proal power stroke in rodents, but the ancestral condition for Glires is still unclear. To address this knowledge gap, we studied the mandibles of Chinese Palaeocene Glires representing the duplicidentate (lagomorph-like; Mimotona) and simplicidentate (rodent-like; Eomylus and Heomys) lineages. To assess the mechanical resistance of mandibles to bending and torsion, we calculated the section modulus. The dentaries differ greatly in morphology and the region where the maximum grinding force was likely applied. The early Palaeocene Mimotona lii and the middle Palaeocene Mimotona robusta and Heomys orientalis all show a pattern of increasing strength moving posteriorly along the mandible, similar to sciurids and the mountain beaver. By contrast, the late Palaeocene Eomylus sp. mandible was strongest in the m1 region, a pattern seen in lagomorphs and the stem placental Zofialestes. Our results indicate the early diversification of mandible structure of Glires, demonstrate a mixture of duplicidentate and simplicidentate characters among the basal Glires and suggest an early occurrence of a lagomorph-like morphotype. This article is part of the theme issue 'The mammalian skull: development, structure and function'.

Sharpening the mesowear tool: geometric morphometric analysis of cusp shape and diet in ruminants

Mesowear is a dietary proxy that relates attritive wear and abrasive wear to the shape of worn tooth cusps of ungulates. Traditional mesowear methods categorize cusps according to relief and sharpness. A geometric morphometric approach has the potential to measure shape with higher precision and to discover unrecognized aspects of cusp shape, possibly improving the efficacy of mesowear. We quantified mesowear in extant Ruminantia, using a 2-D semilandmark outline technique on upper second molar metacones generated from photographs. Among the 91 species sampled, 65 were preassigned to dietary categories, browser, grazer, mixed feeder, and frugivore based on substantiated documentation of diet in the wildlife literature. Metacone cusp shape and metacone mesowear score were found to be independent of size. Principal component and discriminant function analyses of Procrustes transformed semilandmark coordinates revealed two diet-related components of cusp shape. The primary component is related to the traditional mesowear variables of cusp height and side steepness. The secondary shape component reveals variation in the mesiodistal symmetry of the metacone and may relate to a proal vector during the power stroke phase or the relative orientation of the cusps with respect to the chewing stroke vector. Discriminant function analysis of semilandmark data accurately classified the diets of species more frequently (67.2%) than the traditional mesowear method (56.1%). The semilandmark data successfully recognized the diets of grazing and browsing species with correct classification rates ranging from 69% to 95%. The diets of frugivorous and mixed feeding species were less frequently correctly recognized (33%–53%). Mixed feeding diets may be more difficult to recognize due to more heterogeneous diets when compared to browsers and grazers. Frugivores are more difficult to recognize because their rounded cusp apices resemble those of mixed feeders and grazers. We conclude that quantitative shape analysis improves the potential of mesowear. When used as a dietary proxy, we anticipate that mesowear analysis will correctly categorize the diets of most species. When misclassifications are made, they may most often be misclassifications of generalist mixed feeders and frugivores as either browsers or grazers.

ATP‐induced conformational change of axonemal outer dynein arms revealed by cryo‐electron tomography

Axonemal outer dynein arm (ODA) motors generate force for ciliary beating. We analyzed three states of the ODA during the power stroke cycle using in situ cryo‐electron tomography, subtomogram averaging, and classification. These states of force generation depict the prepower stroke, postpower stroke, and intermediate state conformations. Comparison of these conformations to published in vitro atomic structures of cytoplasmic dynein, ODA, and the Shulin–ODA complex revealed differences in the orientation and position of the dynein head. Our analysis shows that in the absence of ATP, all dynein linkers interact with the AAA3/AAA4 domains, indicating that interactions with the adjacent microtubule doublet B‐tubule direct dynein orientation. For the prepower stroke conformation, there were changes in the tail that is anchored on the A‐tubule. We built models starting with available high‐resolution structures to generate a best‐fitting model structure for the in situ pre‐ and postpower stroke ODA conformations, thereby showing that ODA in a complex with Shulin adopts a similar conformation as the active prepower stroke ODA in the axoneme.

DNA segment capture by Smc5/6 holocomplexes

Three distinct structural maintenance of chromosomes (SMC) complexes facilitate chromosome folding and segregation in eukaryotes, presumably by DNA loop extrusion. How SMCs interact with DNA to extrude loops is not well understood. Among the SMC complexes, Smc5/6 has dedicated roles in DNA repair and preventing a buildup of aberrant DNA junctions. In the present study, we describe the reconstitution of ATP-dependent DNA loading by yeast Smc5/6 rings. Loading strictly requires the Nse5/6 subcomplex which opens the kleisin neck gate. We show that plasmid molecules are topologically entrapped in the kleisin and two SMC subcompartments, but not in the full SMC compartment. This is explained by the SMC compartment holding a looped DNA segment and by kleisin locking it in place when passing between the two flanks of the loop for neck-gate closure. Related segment capture events may provide the power stroke in subsequent DNA extrusion steps, possibly also in other SMC complexes, thus providing a unifying principle for DNA loading and extrusion.

An Inbuilt Electronic Pawl Gates Orbital Information Processing and Controls the Rotation of a Double Ratchet Rotary Motor.

A direct external input energy source (e.g., light, chemical reaction, redox potential, etc.) is compulsory to supply energy to rotary motors for accomplishing rotation around the axis. The stator leads the direction of rotation, and a sustainable rotation requires two mutual input energy supplies (e.g., light and heat, light and pH or metal ion, etc.); however, there are some exceptions (e.g., covalent single bond rotors and/or motors). On the contrary, our experiment suggested that double ratchet rotary motors (DRMs) can harvest power from available thermal noise, kT, for sustainable rotation around the axis. Under a scanning tunneling microscope, we have imaged live thermal noise movement as a dynamic orbital density and resolved the density diagram up to the second derivative. A second input energy can synchronize multiple rotors to afford a measurable output. Therefore, we hypothesized that rotation control in a DRM must be evolved from an orbital-level information transport channel between the two coupled rotors but was not limited to the second input energy. A DRM comprises a Brownian rotor and a power stroke rotor coupled to a -C≡C- stator, where the transport of information through coupled orbitals between the two rotors is termed the vibrational information flow chain (VIFC). We test this hypothesis by studying the DRM's density functional theory calculation and variable-temperature 1H nuclear magnetic resonance. Additionally, we introduced inbuilt pawl-like functional moieties into a DRM to create different electronic environments by changing proton intercalation interactions, which gated information processing through the VIFC. The results show the VIFC can critically impact the motor's noise harvesting, resulting in variable rotational motions in DRMs.

CFD simulation of in cylinder combustion of multi-cylinder diesel engine

The simulation /reproduction of in cylinder combustion for power stroke of multicylinder Diesel Engine is appropriate/fundamental to work upon for determination of temperature inside the cylinder. The current examination incorporates estimating of approximate temperature of in chamber gases during power stroke and accordingly liner temperature from gas side. The current investigation incorporates mathematical simulations dependent on Inbuilt ICE Combustion model in ANSYS 15.0 form, where burning space above cylinder during power stroke which is time transient is utilized. Correct averaged boundary limits were determined for different sections for the ignition model. The mesh modular is created. The prevailing of different ranges of temperature recorded in literature during power stroke along with differential liner temperatures from gas side are surveyed. Estimations are done for maximum and minimum temperatures also. The maximum in cylinder temperature was around 2150 K and least temperature was discovered to be 800 K. Likewise the most extreme temperature on liner from gas side along stroke was discovered to be 470 K during power stroke. It has been additionally discovered that the greatest temperature of in chamber gases and liner from gas side endures just during early power stroke.

Dynamics and hydrodynamic efficiency of diving beetle while swimming

Diving beetle, an excellent biological prototype for bionic underwater vehicles, can achieve forward swimming, backward swimming, and flexible cornering by swinging its two powerful hind legs. An in-depth study of the propulsion performance of them will contribute to the micro underwater vehicles. In this paper, the kinematic and dynamic parameters, and the hydrodynamic efficiency of the diving beetle are studied by analysis of swimming videos using Motion Capture Technology, combined with CFD simulations. The results show that the hind legs of diving beetle can achieve high propulsion force and low return resistance during one propulsion cycle at both forward and backward swimming modes. The propulsion efficiencies of forward and backward swimming are 0.47 and 0.30, respectively. Although the efficiency of backward swimming is lower, the diving beetle can reach a higher speed in a short time at this mode, which can help it avoid natural enemies. At backward swimming mode, there is a long period of passive swing of hind legs, larger drag exists at higher speed during the recovery stroke, which reduces the propulsion efficiency to a certain extent. Reasonable planning of the swing speed of the hind legs during the power stroke and the recovery stroke can obtain the highest propulsion efficiency of this propulsion method. This work will be useful for the development of a bionic propulsion system of micro underwater vehicle.

Comprehensive study of diesel engine characteristics of valves coated by titanium nitride (TiN)

Nano-structured coatings have been used to simulate adiabatic engines with the aim of not only reducing heat rejection and thermal fatigue protection of the metallic surfaces but also potentially reducing internal combustion engine emissions. With this research work, the main emphasis is on optimizing the best coating thickness and studying the effects of nano-structured coatings on the engine's fuel consumption and thermal efficiency with the support of varying conditions. Emission measurements of hydrocarbon (HC), nitrogen oxide (NOx), and carbon dioxide (CO2) were also conducted in this study. In this study, the inlet and exhaust valves were coated with titanium nitride (TiN) material, using a magnetron sputtering technique. TiN was deposited at different thicknesses, such as 2, 3, 4, 5, and 6 microns, over the whole surface of the internal and exhaust valves. The results showed that the brake thermal efficiency (BTE) and NOx emissions were increased, and the specific fuel consumption, CO, and HC emissions were decreased for the thermal coated exhaust valve compared to the standard engine. Peak cylinder pressures for 4 µm thick coatings increased by up to 8.30% in the thermal barrier coating (TBC) engine, particularly at high power outputs; however, exhaust gas temperatures were generally lower, indicating noble gas expansion in the power stroke that initiated the peak cylinder pressure rise and impacted BTE, which increased by 1.6%. The result demonstrates that the TiN coating on the valve serves superior performance to the engine up to an optimum coating thickness beyond which the performance drops off. The characteristics are examined by using an experimental setup and measuring experimental values from the setup for different conditions.

Dynamic coordination of the lever-arm swing of myosin II in DNA origami-based thick filament.

Muscle myosins work in motor ensembles and must adapt their power stroke in response to mechanical actions by surrounding motors. Understanding the coordination of power strokes is essential for bridging microscopic molecular function and macroscopic muscle contraction, but the details of this phenomenon remain elusive. Here we used high-speed atomic force microscopy and dark-field microscopy to directly visualize the dynamics of the lever-arm swing (power stroke) and weak bindings of individual human skeletal myosins in DNA origami-based synthetic thick filaments. We observed weak bindings with short durations (less than 1 ms) and the two-step lever-arm swing. Also, we observed spatially local power stroke coordination, and our three-dimensional numerical model explained how mechanical communication between myosins achieved coordination. We extended the model to three-dimensional sarcomere structure in which one actin filament was surrounded by three thick filaments and predicted the local power stroke coordination was spatially periodic and propagated toward the contraction direction. We confirmed that a structural mismatch between the myosin head spacing (42.8 nm) and the actin helical pitch (36 nm) caused the coordination while improving contraction speed and energy efficiency. Our findings reveal a key physical basis of efficient muscle contraction.

Lon protease degrades stable substrates slowly but with enhanced processivity, redefining the model of a strong and robust AAA+ protease.

AAA+ proteases function in all domains of life using an ATP-dependent unfoldase/polypeptide-translocase motor. Lon is a highly conserved AAA+ protease especially important for degrading oxidatively-damaged proteins. To address if Lon is a weak vs. robust unfoldase, as its substrates are often poorly folded, and elucidate whether its mechanism of translocation is similar to the previously-characterized AAA+ proteases, ClpXP and ClpAP, which have a distinct subunit assembly/architecture, we used a modified single-bead optical trapping assay. We find that Lon: (i) unfolds stable proteins using substantially longer pre-unfolding dwell times compared to ClpXP/ClpAP but (ii) has a higher probability of fully degrading a multi-domain substrate than the other enzymes. (iii) Although a slower translocase, Lon's fundamental step size is shared by ClpXP/ClpAP and its step-size distribution mirrors that of ClpAP. (iv) Finally, both ClpXP and Lon hydrolyze ∼1 ATP per translocation step. Thus, the mechanism of the ATP hydrolysis-driven ‘power stroke’ appears largely conserved between three distinct AAA+ proteases, regardless of their speed, processivity, or whether the ATPase and peptidase modules are physically linked (Lon) or assembled from distinct polypeptides (ClpXP and ClpAP). Lon therefore likely uses a common set of operating principles but is ‘geared differently’ than other AAA+ proteases.

Do actin-myosin cross-bridges exhibit a viscoelastic behaviour?

The S2 domain of myosin is the segment that links the myosin head (S1 domain) to the thick filament backbone and elongates to allow S1 to execute the power stroke. It has been suggested that S2 exhibits non-viscous behaviour, implying no lag in reaching steady-state force following power stroke elongation. However, the elongation step in the cross-bridge cycle occurs extremely fast, and the cross-bridge detaches rapidly following it without allowing perceptible changes in force. If a muscle is transferred to a rigor solution following activation, all cross-bridges become stuck in a post power stroke state, which allows for investigation of their viscoelastic behaviour. The objective of this study was to investigate the viscoelastic behaviour of cross-bridges by examining their force following transfer to a rigor solution. Fibres (n = 8) were activated at an average sarcomere length (SL) of 3.0 µm, and then transferred into a rigor solution for 90 s. Since active stretch has the potential to influence the behaviour of cross-bridges, fibres were activated at a SL of 2.4 µm, actively stretched to a SL of 3.0 µm, and at steady-state transferred to a rigor solution for 90 s. Active force and stiffness were compared before and after incubation in rigor, and between purely isomeric and active stretch contractions. Although stiffness, and thus the presumed proportion of attached cross-bridges, increased when fibres were transferred to rigor, force at steady-state decreased by 16.5 +/- 4.0% and 10.0 +/- 1.3%, in the purely isometric and active stretch conditions, respectively. These results suggest that cross-bridges exhibit a viscoelastic behaviour, where their force decreases while they remain attached in a constant conformation. The difference in force decrease between the purely isometric and active stretch conditions suggests that active stretch modulates cross-bridge properties. Further research is warranted to investigate the cross-bridge nanostructure before and after rigor incubation.

Dilated cardiomyopathy mutation (E525K) in human beta-cardiac myosin enhances actin-activated phosphate release but stabilizes the auto-inhibited super-relaxed state.

Mutations in beta-cardiac myosin (M2β) are a common cause of inherited cardiomyopathies including dilated (DCM) and hypertrophic cardiomyopathy (HCM). We investigated the impact of a DCM mutation (E525K) in the human M2β motor domain, which has been shown to stabilize both the interacting heads motif (IHM) and auto-inhibited super-relaxed (SRX) state via head-tail electrostatic interactions in 15 heptad heavy meromyosin (M2β HMM). These findings suggest E525K may reduce muscle force and power by triggering an increase in the IHM/SRX state. However, it is unclear how E525K impacts the intrinsic motor properties of M2β. Thus, we introduced the mutation into single-headed human cardiac myosin subfragment 1 (M2β-S1), unable to form the IHM, and examined its impact on the ATPase mechanism. We revealed that E525K induces a 2.8-fold increase in maximum steady-state actin-activated ATPase activity (kcat), a 6-fold decrease in the actin concentration at which ATPase is half maximal (KATPase), and a 3.4-fold increase in the fast phase of actin-activated phosphate release. Glutamate 525 is located in the conserved activation loop that is proposed to trigger phosphate release by interacting with the negatively charged N-terminus of actin. We propose the mutation may enhance the rate of rotation of the lower 50-kDa domain, movement of the relay helix/switch II, and lever arm rotation associated with the power stroke. Thus, we will directly examine the impact on the actin-activated power stroke utilizing a FRET approach that measures lever arm rotation. Our results suggest the E525K mutation triggers an increase in intrinsic motor properties, while its ability to stabilize the SRX/IHM state in the myosin dimer likely dominates the molecular mechanism that leads to decreased muscle force and power and DCM pathogenesis.

Muscle architecture and muscle fibre type composition in the forelimb of two African mole-rat species, Bathyergus suillus and Heterocephalus glaber.

The scratch-digging Cape dune mole-rat (Bathyergus suillus), and the chisel-toothed digging naked mole-rat (Heterocephalus glaber) are African mole-rats that differ in their digging strategy. The aim of this study was to determine if these behavioural differences are reflected in the muscle architecture and fibre-type composition of the forelimb muscles. Muscle architecture parameters of 39 forelimb muscles in both species were compared. Furthermore, muscle fibre type composition of 21 forelimb muscles were analysed using multiple staining protocols. In B. suillus, muscles involved with the power stroke of digging (limb retractors and scapula elevators), showed higher muscle mass percentage, force output and shortening capacity compared to those in H. glaber. Additionally, significantly higher percentages of glycolytic fibres were observed in the scapular elevators and digital flexors of B. suillus compared to H. glaber, suggesting that the forelimb muscles involved in digging in B. suillus provide fast, powerful motions for effective burrowing. In contrast, the m. sternohyoideus a head and neck flexor, had significantly more oxidative fibres in H. glaber compared to B. suillus. In addition, significantly greater physiological cross-sectional areaand fascicle length values were seen in the neck flexor, m. sternocleidomastoideus, in H. glaber compared to B. suillus, which indicates a possible adaptation for chisel-tooth digging. While functional demands may play a significant role in muscle morphology, the phylogenetic differences between the two species may play an additional role which needs further study.

Mantis Shrimp Locomotion: Coordination and Variation of Hybrid Metachronal Swimming.

Across countless marine invertebrates, coordination of closely spaced swimming appendages is key to producing diverse locomotory behaviors. Using a widespread mechanism termed hybrid metachronal propulsion, mantis shrimp swim by moving five paddle-like pleopods along their abdomen in a posterior to anterior sequence during the power stroke and a near-synchronous motion during the recovery stroke. Despite the ubiquity of this mechanism, it is not clear how hybrid metachronal swimmers coordinate and modify individual appendage movements to achieve a range of swimming capabilities. Using high-speed imaging, we measured pleopod kinematics of mantis shrimp (Neogonodactylus bredini), while they performed two swimming behaviors: burst swimming and taking off from the substrate. By tracking each of the five pleopods, we tested how stroke kinematics vary across swimming speeds and the two swimming behaviors. We found that mantis shrimp achieve faster swimming speeds through a combination of higher beat frequencies, smaller stroke durations, and partially via larger stroke angles. The five pleopods exhibit non-uniform kinematics that contribute to the coordination and forward propulsion of the whole system. Micro-hook structures (retinacula) connect each of the five pleopod pairs and differ in their attachment across pleopods-possibly contributing to passive kinematic control. We compare our findings in N. bredini to previous studies to identify commonalities across hybrid metachronal swimmers at high Reynolds numbers and centimeter scales. Through our large experimental dataset and by tracking each pleopod's movements, our study reveals key parameters by which mantis shrimp adjust and control their swimming, yielding diverse locomotor abilities.

Numeričko ispitivanje uticaja konfiguracije svećica na performanse u cilindru motora

A numerical investigation of combustion inside single and twin-spark engines was performed to study the effect of a spark plug, positions and spark timings on engine performance. Improvement in engine performance is one of the automotive industry's primary research areas. Consequently, the study's results can be utilised to optimise engine configurations to achieve maximum performance. The investigation was conducted using a finite volume-based open-source software, OpenFOAM, for computational simulations. Simulations were conducted using the XiEngineFOAM solver with a transport equation for modelling flame fronts. The Standard k-e turbulence model was used to predict turbulence parameters. The simulation was conducted for compression and power stroke (crank angle between - 180° and 180°), assuming an even distribution of the air-fuel mixture within the pentroof 4-valve engine cylinder. Simulations were conducted for four cases, including variations in the position and timing of spark plugs in single-spark and twin-spark engines. According to the results of the simulations, the single-spark engine provides the best performance when the spark plug is ignited early and positioned at the cylinder's centre. When placed at an optimal position determined by flame travel and collision, the twin-spark engine gives the best performance at the highest difference between the spark timings of the two spark plugs.

Light-sheet laser speckle imaging for cilia motility assessment

Mucociliary clearance is an important innate defense mechanism predominantly mediated by ciliated cells in the upper respiratory tract. Ciliary motility on the respiratory epithelium surface and mucus pathogen trapping assist in maintaining healthy airways. Optical imaging methods have been used to obtain several indicators for assessing ciliary movement. Light-sheet laser speckle imaging (LSH-LSI) is a label-free and non-invasive optical technique for three-dimensional and quantitative mapping of velocities of microscopic scatterers. Here, we propose to use an inverted LSH-LSI platform to study cilia motility. We have experimentally confirmed that LSH-LSI can reliably measure the ciliary beating frequency and has the potential to provide many additional quantitative indicators for characterizing the ciliary beating pattern without labeling. For example, the asymmetry between the power stroke and the recovery stroke is apparent in the local velocity waveform. PIV (particle imaging velocimetry) analysis of laser speckle data could determine the cilia motion directions in different phases.

Calcium Sensors of Neurotransmitter Release.

Calcium (Ca2+) plays a critical role in triggering all three primary modes of neurotransmitter release (synchronous, asynchronous, and spontaneous). Synaptotagmin1, a protein with two C2 domains, is the first isoform of the synaptotagmin family that was identified and demonstrated as the primary Ca2+ sensor for synchronous neurotransmitter release. Other isoforms of the synaptotagmin family as well as other C2 proteins such as the double C2 domain protein family were found to act as Ca2+ sensors for different modes of neurotransmitter release. Major recent advances and previous data suggest a new model, release-of-inhibition, for the initiation of Ca2+-triggered synchronous neurotransmitter release. Synaptotagmin1 binds Ca2+ via its two C2 domains and relieves a primed pre-fusion machinery. Before Ca2+ triggering, synaptotagmin1 interacts Ca2+ independently with partially zippered SNARE complexes, the plasma membrane, phospholipids, and other components to form a primed pre-fusion state that is ready for fast release. However, membrane fusion is inhibited until the arrival of Ca2+ reorients the Ca2+-binding loops of the C2 domain to perturb the lipid bilayers, help bridge the membranes, and/or induce membrane curvatures, which serves as a power stroke to activate fusion. This chapter reviews the evidence supporting these models and discusses the molecular interactions that may underlie these abilities.

Dual power generation modes for thermally regenerative electrochemical cycle integrated with concentrated thermal photovoltaic and phase change material storage

A dual power stroke system that generates electricity during the day and night is proposed. The model consists of concentrated thermal photovoltaic (CPV/T), thermally regenerative electrochemical cycle (TREC), and phase change material (PCM) storage. During the daytime, the concentrated thermal photovoltaic generates electricity directly and supplies hot water to raise the charging temperature of the thermally regenerative electrochemical cycle. To reduce the discharging temperature of the thermally regenerative electrochemical cycle and to avoid losing heat to the environment, a phase change material storage is used to store the heat. During the nighttime, the stored heat in the storage is used back to raise the charging temperature of the regenerative cycle. The discharging temperature is reduced using a finned heat sink. Raising the charging temperature of the regenerative cycle and reducing the discharging temperature will generate electricity during the day and night. An analytical model is developed and validated to investigate the effect of different parameters like solar radiation intensity, water mass flow rate, and temperature in the concentrated thermal photovoltaic and ambient temperature on efficiency and the power produced. The solar radiation, water inlet temperature, and mass flow rate impact the system's performance during the daytime. The ambient temperature is a primary influencer during the nighttime. The efficiency of the regenerative cycle and photovoltaic cells can reach 7.11 % and 15.74 % during the daytime. During the nighttime, the regenerative cycle is the only source of electricity and has an efficiency of up to 6.13 %. Using the proposed model presents a powerful solution for the energy problem in remote areas during the day and night times.

Piston Compression Ring Elastodynamics and Ring–Liner Elastohydrodynamic Lubrication Correlation Analysis

Friction loss in an internal combustion engine largely depends on elastohydrodynamic lubrication. The piston compression ring is a contributor to such parasitic losses in the piston subsystem. The complex elastodynamics of the ring are responsible for the transient and regime-altering film that affects the elastohydrodynamic lubrication of the ring liner contact conjunction. The current paper will discuss the ring radial, lateral deformation, and axial twist, and its effect on the film profile of the compression ring and its subsequent effect on tribological characteristics like elastohydrodynamic pressure, friction, and lubricant. A finite difference technique is used to solve the elastohydrodynamic issue of elastodynamic piston compression by introducing the elastodynamically influenced film thickness into the lubrication model. The results show that consideration of the elastodynamics predicts a 23.53% reduction in friction power loss in the power stroke due to the elastodynamic ring compared to the rigid ring. The elastodynamic effect improves the lubricant oil flow into the conjunction. A finite element simulation predicts a von-Mises stress of 0.414 N/mm2, and a maximum deformation of 0.513 µm at the core and coating interface is observed at the ring–ring groove contact. The sustainability of EHL in this case largely depends on the ring–liner elastodynamics.

Variational and phase response analysis for limit cycles with hard boundaries, with applications to neuromechanical control problems

Motor systems show an overall robustness, but because they are highly nonlinear, understanding how they achieve robustness is difficult. In many rhythmic systems, robustness against perturbations involves response of both the shape and the timing of the trajectory. This makes the study of robustness even more challenging. To understand how a motor system produces robust behaviors in a variable environment, we consider a neuromechanical model of motor patterns in the feeding apparatus of the marine mollusk Aplysia californica (Shaw et al. in J Comput Neurosci 38(1):25–51, 2015; Lyttle et al. in Biol Cybern 111(1):25–47, 2017). We established in (Wang et al. in SIAM J Appl Dyn Syst 20(2):701–744, 2021. https://doi.org/10.1137/20M1344974) the tools for studying combined shape and timing responses of limit cycle systems under sustained perturbations and here apply them to study robustness of the neuromechanical model against increased mechanical load during swallowing. Interestingly, we discover that nonlinear biomechanical properties confer resilience by immediately increasing resistance to applied loads. In contrast, the effect of changed sensory feedback signal is significantly delayed by the firing rates’ hard boundary properties. Our analysis suggests that sensory feedback contributes to robustness in swallowing primarily by shifting the timing of neural activation involved in the power stroke of the motor cycle (retraction). This effect enables the system to generate stronger retractor muscle forces to compensate for the increased load, and hence achieve strong robustness. The approaches that we are applying to understanding a neuromechanical model in Aplysia, and the results that we have obtained, are likely to provide insights into the function of other motor systems that encounter changing mechanical loads and hard boundaries, both due to mechanical and neuronal firing properties.