Department of Applied Mechanics

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

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Motor sequence learning data collected continuously for fifteen days of practice using a novel glove-based typing device

Finger pressing task data collected with and without post-trial performance feedback

Exercise-induced muscle damage is a condition which results in the loss of muscle function due to overexertion. Muscle fatigue is a precursor of this phenomenon. The characterization of muscle fatigue plays a crucial role in preventing muscle damage. In this work, an attempt is made to develop signal processing methods to understand the dynamics of the muscle’s electrical properties. Surface electromyography signals are recorded from 50 healthy adult volunteers under dynamic curl exercise. The signals are preprocessed, and the first difference signal is computed. Furthermore, ascending and descending slopes are used to generate a binary sequence. The binary sequence of various motif lengths is analyzed using features such as the average symbolic occurrence, modified Shannon entropy, chi-square value, time irreversibility, maximum probability of pattern and forbidden pattern ratio. The progression of muscle fatigue is assessed using trend analysis techniques. The motif length is optimized to maximize the rho value of features. In addition, the first and the last zones of the signal are compared with standard statistical tests. The results indicate that the recorded signals differ in both frequency and amplitude in both inter- and intra-subjects along the period of the experiment. The binary sequence generated has information related to the complexity of the signal. The presence of more repetitive patterns across the motif lengths in the case of fatigue indicates that the signal has lower complexity. In most cases, larger motif length resulted in better rho values. In a comparison of the first and the last zones, most of the extracted features are statistically significant with p &lt; 0.05. It is observed that at the motif length of 13 all the extracted features are significant. This analysis method can be extended to diagnose other neuromuscular conditions.&nbsp;

Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine

Characterization of surface electromyography signals of biceps brachii muscle in fatigue using symbolic motif features

We study the effect of shear on the line plumes in turbulent mixed convection (MC) and Rayleigh Bénard convection (RBC) for a decade range of near-wall Rayleigh numbers (2.3 × 106 ≤ Raw ≤ 2.17 × 109) and shear Reynolds numbers (802 ≤ Re ≤ 15000) for a Prandtl number range of 0.7 ≤ Pr ≤ 10.1 in air and water. Plumes are visualised in mixed convection in air by smoke while the plumes in RBC in water are detected from the planar PIV fields using the horizontal divergence criteria [Vipin K. and Puthenveettil B. A., ExHFT-8, Lisbon, 2013]. In addition to our planforms we measure the plume spacings from the planforms of Gilpin et al. [J. Heat Transfer 100, 71 (1978)], Pirozzoli et al. [J. Fluid Mech. 821, 482 (2017)] and by Blass et al. [arXiv:1904.11400 , physics.flu-dyn]. The mean plume spacing λ increase with increase in Re while they decrease with increase in Raw, in addition to being a function of Pr. We propose a common scaling law that captures this complex dependence of the mean plume spacing on Raw, Re and Pr, λ* = λ− λo = SZsh/D, where S = Re3/Raw is the shear parameter, Zsh is the viscous shear length, D is a function of Pr and λ0 the plume spacing in the absence of shear.

Proceedings of the 25th National and 3rd International ISHMT-ASTFE Heat and Mass Transfer Conference (IHMTC-2019)

Quantifying Near-Wall Plumes in the Presence of Shear in Turbulent Convection

This study investigates the effect of randomness in the forcing on a harmonically excited bilinear impact oscillator with a soft barrier. The system parameter range considered coincides with regimes in which multiple stable attractors coexist. The random component superimposed on the harmonic excitations is shown to lead to qualitatively different dynamical behaviours at different parameter values, due to the presence of multiple coexisting attractors. This is classified as P-bifurcation. Wavelet analysis and recurrence quantification-based tools have been employed to show that these qualitative changes are due to noise-induced intermittency in the system. © 2020, Springer Nature B.V.

Nonlinear Dynamics

Stochastic P-bifurcation in a nonlinear impact oscillator with soft barrier under Ornstein–Uhlenbeck process

<a href="https://www.sciencedirect.com/topics/chemistry/endotoxin">Bacterial endotoxins</a> such as <a href="https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/lipopolysaccharide">lipopolysaccharides</a> (LPS) are major contaminants of most pharmaceutical and consumer products. We report an antibiotic-mediated <a href="https://www.sciencedirect.com/topics/engineering/plasmonics">plasmonic</a> <a href="https://www.sciencedirect.com/topics/engineering/biosensors">biosensor</a> for LPS detection based on a facile U-bent <a href="https://www.sciencedirect.com/topics/engineering/fiber-optic-probe">fiber optic probe</a> (UFOP) technology. <a href="https://www.sciencedirect.com/topics/engineering/biomimetics">Biomimetic</a> self-assembled layer of <a href="https://www.sciencedirect.com/topics/engineering/octadecyltrichlorosilane">octadecyltrichlorosilanes</a> (OTS) were functionalized on the surface of <a href="https://www.sciencedirect.com/topics/engineering/optical-fibers">optical fiber</a> probes to hydrophobically entrap LPS from aqueous solutions. The binding of LPS molecules was monitored in real-time by measuring the change in <a href="https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/refraction-index">refractive index</a> (RI) in the <a href="https://www.sciencedirect.com/topics/engineering/evanescent">evanescent</a> layer. To add specificity and <a href="https://www.sciencedirect.com/topics/engineering/signal-amplification">signal amplification</a>, the bound LPS molecules were further tagged with antimicrobial polymyxin-B conjugated <a href="https://www.sciencedirect.com/topics/chemistry/gold-nanoparticle">gold nanoparticles</a> (PMB-AuNPs) in a sandwich format. The assay was extensively optimized by investigating the role of experimental parameters like OTS concentration, <a href="https://www.sciencedirect.com/topics/engineering/incubation-time">incubation time</a> and addition of a silver reduction step at the end of the assay. The lower limit of detection (LOD) for LPS was found to be 0.4 ng/mL with a 36-fold improved sensitivity upon silver enhancement. The total assay time was 1 h. The assay was also found to be highly specific in the presence of common biopharmaceutical components and could thus serve as an efficient endotoxin detection platform for quality control testing during therapeutic development.

Biosensors and Bioelectronics

Plasmonic biosensors for bacterial endotoxin detection on biomimetic C-18 supported fiber optic probes

The two-dimensional (2D) inclined stroke plane kinematics of insect wing is studied for various stroke plane angles using the Immersed Boundary (IB) solver. The numerical results revealed the dominant lift enhancement mechanisms for this class of flows. The generated dipole was analyzed to find the maximum velocity, inclination and spread. The analysis of these dipole characteristics for the different stroke plane angles exposed the alternate method to study the vertical force variation with the stroke plane angles. Lift enhancement mechanisms and dipole characteristics complement the high vertical force coefficient for the stroke plane angle of 60˚ commonly used by dragonflies during hover. The location of the dipole identified a region of influence around the wing and demonstrated the role of the dipole jet in multi-body dynamics and wall effects. © 2020, Jilin University.

Journal of Bionic Engineering

Role of Dipole Jet in Inclined Stroke Plane Kinematics of Insect Flight

Flexoelectricity is the development of an electric field under an applied strain gradient. This effect is highly size-dependent and is significant at nanoscales. Unsymmetric magnetoelectric (ME) composites undergo bending deformations under a magnetic field that results in non-zero strain gradients. Hence, it is important to give due consideration to flexoelectricity, along with direct piezoelectricity in these composites. This article presents a finite-element model that predicts the static and dynamic behavior of ME nanobeams subjected to magnetic fields. The effect of material nonlinearity of the ferromagnetic phase and flexoelectricity in the ferroelectric phase on the ME coupling are determined, and the obtained results show agreement with the literature. It is found that flexoelectricity results in substantially higher static ME coefficients. However, the resonant ME response is weakened by flexoelectricity. The effect of surface elasticity on the ME coupling coefficient is also investigated by making use of the Gurtin-Murdoch theory. The surface effects are found to improve the ME coefficient at bending resonance, while its effect is trivial at static and axial resonant conditions. Furthermore, the effect of load resistance on the ME voltage and charge coefficients is determined. The results indicate clear changes in the trend between short-circuit and open-circuit conditions. © 1965-2012 IEEE.

IEEE Transactions on Magnetics

Effects of Flexoelectricity and Surface Elasticity on the Nonlinear Magnetoelectric Coupling in Unsymmetric Composites

Measurement of the viscoelastic properties of a cell using microscopic tracer particles has been complicated given that the medium viscosity is dependent upon the size of the measurement probe leading to reliability issues. Further, a technique for direct calibration of optically trapped particles in vivo has been elusive due to the frequency dependence and spatial inhomogeneity of the cytoplasmic viscosity, and the requirement of accurate knowledge of the medium refractive index. Here, we employ a recent extension of Jeffery's model of viscoelasticity in the microscopic domain to fit the passive motional power spectra of micrometer-sized optically trapped particles embedded in a viscoelastic medium. We find excellent agreement between the 0 Hz viscosity in MCF7 cells and the typical values of viscosity in literature, between 2 to 16 mPa sec expected for the typical concentration of proteins inside the cytoplasmic solvent. This bypasses the dependence on probe size by relying upon small thermal displacements. Our measurements of the relaxation time also match values reported with magnetic tweezers, at about 0.1 s. Finally, we calibrate the optical tweezers and demonstrate the efficacy of the technique to the study of in vivo translational motion. © 2020 IOP Publishing Ltd.

Department Of Physics

Journal of Physics Condensed Matter

Measurement of viscoelastic properties of the cellular cytoplasm using optically trapped Brownian probes

In this paper, the effect of porosity on the ductility of as-cast AA7075 (a commercial highstrength aluminum alloy) was investigated. The as-cast material was processed through hot upsetting, and specimens with different porosity content were achieved. These were then subjected to tensile and compression tests. It was shown that the tensile ductility exhibited a near sigmoidal dependence on the porosity content. Compressive ductility, on the other hand, was not affected by the initial porosity content. In addition, direct observations, on an X-ray microscope (XRM), enabled 3-dimensional imaging of the porosity evolution during plastic deformation. Numerical simulations using a homogenized damage model, the Gurson-Tvergaard-Needleman (GTN) approach, was used for predicting the mechanical responses. The continuum model, which accounted for the growth and coalescence of spherical voids, captured the overall experimental patterns reasonably well. © 2020 by ASME.