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.

IIT Madras

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.

World University root node

Department Of Physics

Journal of Physics Condensed Matter

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

In conventional linear array (CLA)–based elastography tissue compression in one direction (e.g., axial) leads to an expansion in all other directions (lateral, elevation). Therefore, the estimation of the lateral displacements and strains may provide additional information on the tissue mechanical properties. However, these are not exploited fully due to the inherent limitation in lateral sampling. Recently, a method named actuator-assisted beam translation (ABT) was demonstrated to address this issue, wherein the focused beam was translated at subpitch locations using an external bench-top setup. However, because such bench-top setup may be impractical for routine clinical use, an ultrasound transducer was customized to have an internal actuator. The performance of the customized transducer was studied through experiments on phantoms for rotation elastography application, which requires precise lateral displacement estimation. Furthermore, the results obtained from ABT was compared against the currently practiced spatial displacement compounding (SDC) method, which is known to yield better quality lateral displacement estimates than conventional approaches. The results show that the ABT method yields a full-width half-maximum (FWHM) value, taken from the lateral profile across a point scatterer, which is 65% and 24% smaller than that obtained using CLA and SDC methods, respectively. Furthermore, the contrast-to-noise ratio (CNR) estimated from rotation elastogram obtained using ABT method is better by 300% and 35% compared with that obtained by using CLA and SDC methods, respectively. Furthermore, the results demonstrate an additional advantage of having larger field of view (FoV) for the ABT method compared with spatial compounding approach. © The Author(s) 2019.

Ultrasonic Imaging

Actuator-assisted Subpitch Translation-capable Transducer for Elastography: Preliminary Performance Assessment

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.

Department of Aerospace Engineering

Journal of Engineering Materials and Technology, Transactions of the ASME

Relating porosity with ductility in a commercial AA7075 alloy: A combined experimental and numerical study

A Spoken dialogue system for an unseen language is referred to as Zero resource speech. It is especially beneficial for developing applications for languages that have low digital resources. Zero resource speech synthesis is the task of building text-to-speech (TTS) models in the absence of transcriptions. In this work, speech is modelled as a sequence of transient and steady-state acoustic units, and a unique set of acoustic units is discovered by iterative training. Using the acoustic unit sequence, TTS models are trained. The main goal of this work is to improve the synthesis quality of zero resource TTS system. Four different systems are proposed. All the systems consist of three stages- unit discovery, followed by unit sequence to spectrogram mapping, and finally spectrogram to speech inversion. Modifications are proposed to the spectrogram mapping stage. These modifications include training the mapping on voice data, using x-vectors to improve the mapping, two-stage learning, and gender-specific modelling. Evaluation of the proposed systems in the Zerospeech 2020 challenge shows that quite good quality synthesis can be achieved. © 2020 ISCA

Department of Computer Science and Engineering

Proceedings of the Annual Conference of the International Speech Communication Association, INTERSPEECH

Exploration of end-to-end synthesisers for zero resource speech challenge 2020

High performance thermoresponsive soft, controllable and reversible actuators are highly desirable for diverse applications. The practical implementation of the existing poly(N-isopropylacrylamide) (pNipam) based soft thermoresponsive actuators faces serious limitations due to their functional requirement of proximal bulk solvent medium. In this work, addressing this issue, we report the development of a bilayer based actuator composed of a solvent responsive biodegradable polymer and temperature responsive pNipam. The designed bilayer is capable of achieving reversible and irreversible actuation as needed when exposed to a physiological range of body temperature, without any solvent bath around. The solvent or water supplied by the pNipam layer at its lower critical solution temperature (LCST) builds a concentration gradient across the thickness of the polymer layer. The concentration gradient results in a strain gradient, causing an out-of-plane folding of the bilayer. The underlying coupled diffusion-deformation interaction during folding and unfolding is incorporated in the reported finite element model, capable of predicting actuation characteristics under different initial conditions. The combined experimental and modelling effort in this work highlights the possibility of engineering 2-dimensional films into complex 3-dimensional shapes, which could have potential applications in soft machines and robotics. © The Royal Society of Chemistry 2020.

Department of Mechanical Engineering

Soft Matter

Controlled shape morphing of solvent free thermoresponsive soft actuators

Surface coatings are mainly applied to protect concrete structures against various environmental conditions. However, the interface between the concrete and coating is a weak link, and interfacial delamination is the primary mode of failure. Fracture resistance is the main design criteria for these materials, and therefore, it is necessary to investigate possible causes of interfacial failure for preventive measures. To this end, we have investigated the potential failure mechanisms and measured interfacial strength by performing a pull‐off adhesion test on epoxy coated cement paste. From the pull‐off adhesion test, adhesive (interface) failure between cement paste and epoxy is predominantly observed. It is observed that the adhesive (interfacial) strength for the sample tested on 50th day is more than the 28 days hydrated sample. This is due to additional curing of cement paste samples after coating epoxy which leads to higher interfacial strength. We also present the phase‐field model (PFM) to predict the adhesive failure for this system. The results obtained from the PFM, i.e., load at failure and crack path are validated against experimental results. Finally, the influence of various material parameters such as elastic modulus and fracture energy of the interface on interfacial fracture behaviour is studied. © The Author(s) 2021.

Department Of Civil Engineering

Fulltext

RILEM Technical Letters

Interfacial fracture behaviour between cement paste and epoxy coating ‐ an experimental and phase‐field approach

Failure of bioengineered meniscus implant after transplantation is a major concern owing to mechanical failure, lack of chondrogenic capability and patient specific design. In this article, we have, for the first time, fabricated a 3D printed scaffold with carbohydrate based self-healing interpenetrating network (IPN) hydrogels-based monolith construct for load bearing meniscus tissue. 3D printed PLA scaffold was surface functionalized and embedded with self-healing IPN hydrogel for interfacial bonding further characterized by micro CT. Using collagen (C), alginate (A) and oxidized alginate (ADA), we developed self-healing IPN hydrogels with dual crosslinking (Ca2+ based ionic crosslinking and Schiff base (A-A, A-ADA)) capability and studied their physicochemical properties. Further, we studied human stem cells behaviour and chondrogenic differentiation potential within these IPN hydrogels. In-vivo heterotopic implantation confirmed biocompatibility of the monolith showing the feasibility of using carbohydrate based IPN hydrogel embedded in 3D printed scaffold for meniscal tissue development. © 2020 Elsevier B.V.

Department Of Biotechnology

Department of Ocean Engineering

International Journal of Biological Macromolecules

Meniscal tissue engineering via 3D printed PLA monolith with carbohydrate based self-healing interpenetrating network hydrogel

The permanence of injected CO2 in deep saline aquifers mainly depends on caprock permeability. Thus, the main objective of this study is to investigate the effect of salinity level in the formation fluid on permeability of siltstone when advective flow of scCO2 is dominant. Siltstone caprock samples were fully saturated with different synthetic brines, which were similar to natural formation fluids. A chemical analysis was conducted for each saturated rock and brine samples to recognize the geo-chemical equilibrium between the formation fluid and caprock since the identification of final brine composition in rock pores is crucial to predict the possible interactions with scCO2 flow. Interestingly, the results show that the caprock is subjected to dissolution during saturation due to ion exchange between caprock minerals and cations in the pore fluid changing the brine elemental composition. The scCO2 permeability experiments were conducted for each saturated sample using a core flooding apparatus for a series of injection pressures. According to the results, scCO2 permeability significantly reduces at high salinity concentrations in brine due to deposition of different types of evaporites in rock pores which significantly depends on the elemental concentration of brine and caprock-brine interaction. It is known as CO2 dry-out phenomenon. © 2019

Energy

Effect of salinity on supercritical CO2 permeability of caprock in deep saline aquifers: An experimental study

The paper investigates the post-buckling behavior of micro-cantilevers within the framework of consistent couple stress theory. The theoretical foundation for carrying out the analysis is formulated in terms of moment and curvature which is apt for solving thin beam problems. A differential equation governing the deflection of micro-cantilever subjected to different boundary conditions is obtained from the developed moment-curvature relationship. Axially loaded micro-cantilevers are solved by using an efficient semi-analytical method which involves removal of singularity. On the other hand solutions to eccentrically loaded micro-cantilevers are determined with the help of purely numerical approach based on iterative shooting method. Profiles of post-buckled micro-cantilevers subjected to different loading conditions are furnished. The obtained results for the micro-cantilever display strong size-dependency due to presence of the material length scale parameter in the developed model. Also the non-classical theory results tend to those from classical theory when the length scale parameter is negligible as compared to the characteristic length of the structure. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.

Annals of Solid and Structural Mechanics

Post-buckling involving large deflection of micro-cantilever using the consistent couple stress theory

Building text-to-speech (TTS) synthesisers for Indian languages is a difficult task owing to a large number of active languages. Indian languages can be classified into a finite set of families, prominent among them, Indo-Aryan and Dravidian. The proposed work exploits this property to build a generic TTS system using multiple languages from the same family in an end-to-end framework. Generic systems are quite robust as they are capable of capturing a variety of phonotactics across languages. These systems are then adapted to a new language in the same family using small amounts of adaptation data. Experiments indicate that good quality TTS systems can be built using only 7 minutes of adaptation data. An average degradation mean opinion score of 3.98 is obtained for the adapted TTSes. Extensive analysis of systematic interactions between languages in the generic TTSes is carried out. x-vectors are included as speaker embedding to synthesise text in a particular speaker's voice. An interesting observation is that the prosody of the target speaker's voice is preserved. These results are quite promising as they indicate the capability of generic TTSes to handle speaker and language switching seamlessly, along with the ease of adaptation to a new language. Copyright © 2020 ISCA