Publication

Purpose: Surface electromyography (sEMG) is a non-invasive technique to characterize muscle electrical activity. The analysis of sEMG signals under muscle fatigue play a crucial part in the branch of neurorehabilitation, sports medicine, biomechanics, and monitoring neuromuscular pathologies. In this work, a method to transform sEMG signals to complex networks under muscle fatigue conditions using Markov transition field (MTF) is proposed. The importance of normalization to a constant Maximum voluntary contraction (MVC) is also considered. Methods: For this, dynamic signals are recorded using two different experimental protocols one under constant load and another referenced to 50% MVC from Biceps brachii of 50 and 45 healthy subjects respectively. MTF is generated and network graph is constructed from preprocesses signals. Features such as average self-transition probability, average clustering coefficient and modularity are extracted. Results: All the extracted features showed statistical significance for the recorded signals. It is found that during the transition from non-fatigue to fatigue, average clustering coefficient decreases while average self-transition probability and modularity increases. Conclusion: The results indicate higher degree of signal complexity during non-fatigue condition. Thus, the MTF approach may be used to indicate the complexity of sEMG signals. Although both datasets showed same trend in results, sEMG signals under 50% MVC exhibited higher separability for the features. The inter individual variations of the MTF features is found to be more for the signals recorded using constant load. The proposed study can be adopted to study the complex nature of muscles under various neuromuscular conditions.

Objective: Rolling element bearings are an essential part of rotating machinery. Sudden bearing failure may lead to catastrophic machine failure. Early bearing fault detection is essential to avoid machine failure. Vibration data received from bearings typically contain impulsive fault information. The characteristics acquired from the vibration signals generated by bearings are primarily used to identify bearing defects. The derived features might not be able to accurately pinpoint the failure’s timing due to background noise in the observed vibration signal. External noise reduction from the vibration signal is essential for extracting important features for effective fault diagnosis. A helpful de-noising method at present is variational mode decomposition (VMD). However, the VMD method alone may not eliminate the noise from the vibration data. Methods: The present work proposes a methodology for noise reduction combining VMD and an optimized Morlet filter. Initially, the signal is split using the VMD approach into various intrinsic mode functions (IMF), and the most efficient IMF is chosen using the maximum kurtosis criterion. Next, the golden ratio optimization method (GROM) based Morlet wavelet filter is applied to the effective IMF for reducing unwanted noise. The convolutional neural network (CNN) technique is then employed to identify the bearing defects. Conclusion: The proposed approach is tested upon bearing simulation datasets, bearing experimental datasets, gearbox experimental datasets, and sound datasets to validate its efficiency. The validation of the proposed algorithm using gear and sound datasets indicates its broad applicability.

Data acquisition from a vehicle operating in real driving conditions is extremely useful for analyzing the real-time behavior of the vehicle and its components. A few studies have measured the real-time data for a four-wheeler electric vehicle. However, no attempts have been reported to measure the real-time data and find the inverter efficiency for a two-wheeler electric vehicle. The present work has accomplished successful real-time data acquisition from a two-wheeler electric vehicle. The real-time current and voltage coming in and going out from the inverter, frequency of the motor operation, power factor, distance covered, and velocity have been measured. The inverter efficiency is found to be over 95% for over 80% of the total drive time, and the power factor for the motor is over 0.8 for almost 50% of the total drive time. A few insights on driver behavior and finally the torque-speed characteristics and two quadrant operation of the motor are discussed.

Polycarbosilane-derived SiCW/SiC composites were processed by spark plasma sintering (SPS). Whisker-reinforced composites were densified with faster rates to a maximum density of ~ 98%, indicative of positive influence of SiC whiskers on densification behavior. Electron backscattered diffraction study confirmed the presence of twins in the sintered composites. A misorientation angle of 60° resembled to {111} twin boundaries. Twin density was found to increase with SPS temperature and whisker contest. Twin boundaries were found to be responsible for β→α SiC transformation. Hardness increased sharply with the increase in whisker content and a decrease in grain size. The maximum hardness of 23.4 GPa was observed in 20% SiCW/SiC composite. Nanoindentation study reflects the positive effect of whiskers on hardness and elastic modulus.

The present work investigates the mechanical responses of additively manufactured 17-4 PH Stainless Steel systematically using finite element method (FEM). Different simulations of tensile tests at room and elevated temperatures are performed on smooth and notched specimens for calculating the parameters of the Johnson-Cook material and damage model. The tensile strength of the 17-4 PH SS alloy notch bar is higher than the smooth bar at room temperature. ABAQUS (Explicit) is used for all FE calculations. Experimental data was used as input to perform all the elastic–plastic simulations in both 2D and 3D through the ABAQUS 6.14 software. The observed simulation results were correlated with the available literature. Strain rate and temperature dependent mechanical properties of AM 17-4 PH stainless steel in different processing conditions are also investigated in this study.

In this paper, crack growth in orthotropic materials subjected to dynamic loading is numerically studied using an adaptive phase-field method. The study starts with a coarse structured mesh and the adaptive refinement strategy based on a user-defined threshold on the phase-field variable is proposed for computational efficiency, and variable-node elements are employed to treat the hanging nodes as a result of local adaptive refinement. The Hughes-Hilbert-Taylor (HHT) time integration scheme is adopted for temporal discretization. The directionality of orthotropic materials is represented by a penalized second-order structural matrix, which is incorporated in the crack face energy density. Through numerical examples, the influence of the material orientation on the dynamic crack growth in orthotropic materials is studied and the reliability of the proposed framework is validated.

The role of wall-slip on the soluto-Marangoni instability that emerges in a two-fluid creeping two-dimensional Poiseuille flow is assessed within the framework of Orr-Sommerfeld analysis and species-transport system. Different wall-slip scenarios, namely S1 (slip at the upper wall), S2 (slip at the lower wall), S1S2 (symmetric slip at the upper and lower walls) are considered. The system instability is characterized by identifying unstable and stable zones in the m-n (viscosity ratio - depth ratio) plane for each of the slip conditions at the wall using asymptotic analysis for long-wave disturbances. Numerical simulations based on Chebyshev spectral collocation method reveals the emergence of two modes (M1 and M2) and corresponding stability features are displayed for typical values of Marangoni numbers, n, m and slip lengths. The occurrence of short-wave modes and the features of exchanging dominance between the short-wave modes in the presence of wall-slip for different slip condition are elucidated and the physical mechanism responsible for triggering the instability in the system are revealed through energy budget analysis. The channel system hosting less viscous fluid adjacent to the upper wall demonstrates interesting characteristics such as (among other things): stabilizing/destabilizing the emerging M1/M2 modes in system with no-slip by imposing S1/S2/S1S2 wall conditions and increasing the slip length; exchange of dominance of unstable modes beyond a threshold slip length for S1 slip type. The study thus presents possible means of stabilizing/destabilizing a creeping channel flow system by designing the walls of the channel with appropriate slip type relevant to the application.

The east coast of India is highly prone to devastating winds, torrential rainfall, and storm surges caused by tropical cyclones. The storm surge is affected by ocean basin characteristics involving the width and slope of the continental shelf. The bed roughness plays a major role in surge formation. The east coast of India is characterized by a broader shelf in the north and a narrow shelf in the south. This paper uses a hybrid Finite Volume Method–Finite Element Method based Shallow water equation (SWE) solver to predict the storm surges during different cyclone events, and the roughness parameter Manning’s n is used in bed friction calculations. The bottom friction coefficient parameterization involving bed roughness is used to calibrate the resistance to flow in the numerical model. The calibration exercises are carried out with different values of n for each surge simulations for different cyclones to predict the surface elevation. Different statistical parameters against the measured values are used to analyze the impact of varying n values on predicted surge levels, and the most suitable n value is carefully chosen. The relationship between n and the bed slope is established as an expression, to replace the formulations involving Manning’s n, thereby minimizing the usual computational efforts. The performance of the novel bed friction formulation involving the physical parameter in bed slope is demonstrated through statistical evaluations.

Introduction and Background: Spiral bevel gears are ubiquitous in numerous power transmission systems. The exigent demands such as high performance, more strength and less noise in helicopter drives can be met by selecting the optimal geometrical design parameters. However, a comprehensive study on the influences of geometric parameters on the transmission system dynamics is not found in the literature. Objective: Therefore, in this study, the effects of geometric design parameters such as spiral angle, pressure angle and pitch cone angle on the spiral bevel gear set dynamic characteristics for various boundary conditions are studied. Method: Firstly, the analytical modelling of coupled lateral-axial–torsional vibrations of the spiral bevel gear set is derived theoretically under few assumptions. Then the emphasis on the effects of geometric parameters on the dynamic characteristics such as critical speeds, coupled mode shapes and unbalance vibration response of the gear pair supported by flexible and rigid boundary conditions are investigated numerically. Results: Under rigid support conditions, it is observed that there is no remarkable influence of geometric parameters on the critical speeds. However, the unbalance response amplitudes at and around the resonance peaks are notably affected. Whereas the critical speeds and unbalance responses are essentially affected by the variation of axial and torsional stiffness at the supports. Meanwhile, the influence of geometric parameters on the critical speeds corresponding to torsional and axial modes is remarkable for the flexible support conditions. Furthermore, the steady-state response due to combined torsional and unbalance excitations is also studied, and the results show that the geometric parameters influence the axial, lateral and torsional responses. Conclusion: The results obtained through this study are useful in the design of the spiral bevel gear set.

Leaders and organizations worldwide faced tough decisions while responding to the complications of operating during the pandemic, COVID-19. Schools were not exempt from this mayhem. The rapid need for transition to virtual classrooms stressed teachers even as they battled with the virus. Teachers required a compassionate leader during the crisis. With stress at an all-time high, accompanied by uncertainty about the future, compassionate leadership was a crucial factor to navigate through such crises. Regarding compassionate leadership of school principals, researchers are yet to thoroughly study its conceptual and empirical relationship with teacher attitudes and behaviours. Although evolving research addresses the outcomes of compassionate leadership, little is known about how compassionate school principals impact work attitudes and behaviours of teachers. Hence, we present a broad theoretical framework of how compassionate leadership of school principals influences teacher work attitudes and job performance. Mainly, we analyse the relationships between compassionate leadership and teachers’ resilience, work engagement, psychological well-being, and job performance. We base our study on trust, positive emotions, and self-efficacy theories to explain the compassionate leadership process. We advance research propositions and discuss the implications for future research and compassionate leadership practices at schools.

The study focuses on the polarization dynamics of the ferroelectric phase under an external magnetic field in a trilayered magnetoelectric (ME) composite of 0.94(Na0.5Bi0.5TiO3)-0.06BaTiO3 (NBT-BT)/CoFe2O4(CFO)/NBT-BT. With the estimation of gradient size of the strain across the interface, the thin films with varying top layer (NBT-BT) thicknesses were fabricated. The piezoelectric displacement curves revealed the linear characteristics for the 30 nm NBT-BT ME composite due to the presence of dominant interfacial strain. Time-resolved polarization switching studies confirmed the role of interfacial strain on the time scale of polarization switching of the ferroelectric phase. Magnetic field-assisted piezoresponse force microscopy studies confirmed the presence of nonlinear contribution like polarization rotation in the 100 nm NBT-BT ME composite. The interfacial strain was found to operate in a way that imposes constraints on the polarization rotation in a spatial region of ∼20-30 nm away from the interface. However, at a spatial region >30 nm, the interfacial strain was found to supplement the field-induced strain and assisted the polarization rotation to happen. The spatial-dependent behavioral analysis of the interface strain on the polarization dynamics will help in using the ME composite for targeted device applications such as actuators or energy harvesters.

The application of interrupted die motion during the deformation process in a servo press cycle is known to enhance the forming limit of metallic materials. This observation is generally attributed to the transient effects associated with stress relaxation phenomenon. However, attempts to model stress relaxation behaviour using physically based constitutive formulations in the finite element method are scarce. In this work, a modified version of the Kocks–Mecking–Estrin (KME) dislocation density model is used to evaluate the substructural changes during relaxation. An ‘uncoupled’ elasto-viscoplastic approach is employed to accommodate the plastic strain rate effect. This modelling approach is implemented in the commercial finite element software via a user material subroutine. The model is validated through simulations of interrupted uniaxial tensile tests for aluminium alloy AA7075 under two different aging conditions. The implemented model is shown to closely capture the experimental results and account for changes in dislocation density and the athermal component of flow stress during relaxation. Subsequently, the model is applied to simulate monotonic and interrupted hole expansion tests (HET), and the results are discussed qualitatively.

This paper presents adaptive, graded and uniform mesh schemes to approximate the solution of a fractional order advection-diffusion model, which generally shows a weak singularity at the initial time level. The temporal fractional derivative in the underlying problem is described in a Caputo form and is discretized by means of L1 scheme on a nonuniform mesh. The space derivative is discretized on a uniform mesh employing a fourth-order compact finite difference scheme. The adaptive grid is generated via equidistribution of a positive monitor function. Stability and convergence results for the proposed method on graded mesh are established. Numerical examples are provided to study the accuracy and efficiency of the proposed techniques and to support the theoretical results. A discussion about the advantages of the graded and adaptive meshes over the uniform one is also presented. The CPU times for the proposed numerical schemes are provided.

The Split Hopkinson Pressure Bar (SHPB) technique is most commonly used to study the dynamic behaviour of materials when subjected to high-speed impact. The influence of the specimen size and shape plays a predominant role in estimating the flow stress behaviour of the Al 2014 alloy that is widely used in aerospace applications. In the present study, numerical analysis is carried out on three specimen shapes—Circular, Square, Demi-bull-nosed; and the corresponding L/D ratios of 0.5, 1 and 1.5 are estimated for the various specimen shapes. Flow stress–strain curves are compared with each other and found that the demi-bull-nosed specimens have shown moderate stresses, which could be a substitute for the circular specimens during their non-availability. These specimens were further analysed for their dynamic behaviour for the three strain rates of 2857.1/s, 5714.3/s and 8571.43/s. The variation of L/D or L/S ratios revealed that the lower ratio of 0.5 resulted in higher flow stresses with large deformation behaviour. The simulation results were further validated with the available experimental results of compression SHPB, which are in tandem with each other.

Thermoelectric textiles, constructed from thermoelectric materials and fabric, offer unique advantages compared to other types as they facilitate thermal energy harvesting from the human body and conform exceptionally well to dynamic body curves. This underscores their potential for on-body applications in electricity generation. In this investigation, we present a tellurium-free polymer-based textile thermoelectric prototype manufactured through a cost-effective method known as the solution drop-casting process. Two organic polymers, PEDOT:PSS and PVDF, are judiciously employed at optimized concentrations. At 300 K, the resulting PEDOT:PSS + PVDF/fabric thermoelectric film could exhibit an impressive output power factor of 60 nW/mK2. The processed thermoelectric film could retain its electronic properties after 500 bending cycles, which confirms its extraordinarily flexible nature. When subjected to a temperature gradient of 35 K, the textile thermoelectric prototype could generate a noteworthy output voltage and power of 3.8 mV and 2.7 nW, respectively, at 300 K. Importantly, when in contact with a human wrist and subjected to a temperature difference of ∼3 K, the prototype produced a 0.2 mV output voltage, which is reliable. Above all, the prototype exhibited an outstanding output voltage of approximately 13 mV, when its cold-end and hot-end were at 236 and 277 K, respectively. This corroborated the compatibility and superior energy generation performance of the investigated textile thermoelectrics under cold environmental conditions. Our study emphasizes the feasibility of Te-free, nontoxic polymer-based textile thermoelectric fabric for power generation using the human body and other low-grade heat available below and at room temperature.

Polyelectrolyte-based conductive hydrogels are being extensively explored for applications in energy storage and as electrode materials for batteries. We synthesized ionically crosslinked sodium carboxymethyl cellulose (NaCMC), esterified NaCMC, and Ca2+ doped esterified NaCMC hydrogels. This work aims to understand the effect of Ca2+ ions on the NaCMC and esterified NaCMC. FTIR, SEM, Rheology and EIS studies were performed to understand the structure and dynamics of hydrogels. Results confirmed that Ca2+ ions have an important role in determining the rheological and dielectric response of hydrogels. Power law behavior was observed in their rheological response with exponent (n) of 0.81 for G′ and 0.76 for G″ of ionically crosslinked NaCMC, 5.38 for G′ and 4.70 for G″ of esterified NaCMC, whereas, negative exponents −1.44 for G′ and −1.10 for G″ of Ca2+ ion doped esterified NaCMC. Ionically crosslinked NaCMC hydrogels have relaxation times (τ) in the range of 8.9 × 10−5 s–2.8 × 10−5 s may be due to the formation of temporary dipoles by electrostatic bridge formations with dc conductivity of (0.1 S/cm–5 S/cm), whereas, esterified NaCMC showed relaxation times (10−3 s–8.9 × 10−5 s) with increasing ester crosslinks and dc conductivity of (0.05 S/cm–0.8 S/cm). Interestingly, Ca2+ ion doped esterified hydrogels showed multiple dielectric relaxations on Ca2+ ion addition with different relaxation times may be due to change in ionic environment. The understanding obtained from this work may be useful for designing tuneable hydrogels with optimum electrical and mechanical properties.

In mixed traffic condition, vehicles with varying static and dynamic characteristics share the same road space. The smaller vehicles frequently try to manoeuvre through the gaps available between larger vehicles. In this scenario, the use of conventional vehicle-following models which considers the effect of single (overlapping) leader may become inappropriate. The influence of multiple leaders and their combinations on the response of the subject vehicle is a crucial research gap identified from the literature survey. In the multiple leader cases, the follower does not merely adjust to the relative speed and spacing with the primary (overlapping) leader, but judiciously responds to subsidiary (non-overlapping) leader attributes also. Present study formulates a model structure for vehicle-following manoeuvre in mixed traffic by incorporating the multiple leader dynamic variables. The spatial orientation of multiple leaders along with vehicle types and dynamic variables are found to have a substantial role, thus resulting in realistic representation of mixed traffic. These characteristics have the potential to enhance existing following behaviour models and improve the realism of microscopic modelling in mixed traffic conditions. Simulation models that integrate these attributes could find practical applications in more accurate assessments of traffic management and operational strategies.

Incubators play an instrumental role in nurturing startups and creating a vibrant ecosystem. But as the ecosystem evolves, incubators also need to reinvent themselves to stay relevant. Against a burgeoning startup ecosystem in India, this roundtable deliberates on the future of incubation. The experts discuss what services incubators should offer, how they should measure their impact and how they can become financially sustainable.

The Belle II experiment started data-taking in March 2019. The silicon vertex detector (SVD), part of the Belle II tracking system, has been operating smoothly and reliably. The data quality has been confirmed through various metrics such as a good signal-to-noise ratio and precise spatial resolution. The radiation damage effects have been continuously monitored, showing good agreement with our expectations. So far, no harmful impact due to the radiation damage on the detector performance has been observed. Additionally, the radiation tolerance of SVD sensors for future high-luminosity runs has been examined in a new irradiation campaign. In the high-luminosity runs, an increase in hit-occupancy is also expected due to the beam-induced backgrounds. To enhance the robustness of offline software in a high-background environment, new algorithms of background suppression using hit-time information have been developed.