Indian Institute of Technology Madras
  • Chennai, Tamilnadu, India
Recent publications
This chapter introduces porous medium concepts used in modelling fluid flow and heat and mass transfer in biological systems. With the advancements in biology, health and medicine becoming interdisciplinary, physical and mathematical concepts are being increasingly invoked to model biological processes. Porous medium modelling of bio-fluid and heat flows is an interesting and useful approach to simplify and understand biological phenomena.
In this chapter we discuss introductory concepts, starting with an understanding of the definition of a porous medium. We proceed to define and discuss other terminologies like porosity, connectivity, consolidation, percolation, tortuosity, homogeneity, isotropy and anisotropy. The concept of volume averaging is also introduced from first principles. These basic concepts and terminology that characterize a porous medium are to be understood before formulating the governing conservation equations of mass, momentum and heat for analysing transport phenomena in such porous media.
In this chapter, we take a historical approach to introduce some key ideas in flow through porous media. Later in the chapter, we will place these historically significant developments into a theoretical framework that is based on the volume averaging procedure and concept of representative elemental volume (REV) introduced in Chap. 1. For this, we shall begin with conventional definitions of flow variables prevalent in porous medium literature.
In this short chapter, the radiative transport equation (RTE) valid for a porous medium is first presented. The volume-averaged energy equations when LTE and LTNE conditions prevail, introduced in Chaps. 2 and 4 are reintroduced with the radiative flux term present. The coupling between the RTE and the energy equation is discussed briefly. Various effective properties, relevant to radiative energy transport in porous media that must be determined to solve the RTE are also mentioned. The content is largely based on the review chapter by Prof. Howell, in the Handbook of Porous Media, 1st Edition, ed. Vafai (2000).
In this and the next chapters, we shall discuss, respectively, forced and natural convection heat transfer in a porous medium. An excellent research monograph by Nield and Bejan (2006) with extensive coverage of material segregated in relevant subtopics of convection in porous media is already available. Additionally, recent compilations by Ingham et al. (2004); Bejan et al. (2004); Vadász (2008) and the two handbooks on porous media (Vafai 2000, 2005) discuss both basic and advanced topics and ongoing research pertaining to convection in porous media. Hence, we shall restrict our discussion of convection in porous media only to the fundamentals and advanced material that are less discussed elsewhere. Readers are encouraged to consult the above texts for additional material.
This chapter introduces a few current research topics that involve porous medium modelling discussed in the preceding chapters. Each section is treated as a separate case study, providing details on the fundamental equations and modelling involved. Most of the topics chosen are based on the author’s involvement in the associated research and should by no means be considered either exhaustive or superior to other ongoing research. The selection should enthuse those readers who wish to pursue research in transport in porous media.
The monograph on convection in porous media by Nield and Bejan (2006) provides elaborate cataloguing and exposition of research in natural convection configurations for several decades. Repeating the analysis is redundant, and hence, only the adopted basic analysis is provided in this chapter. Appendix II provides a list of heat transfer solutions and correlations, with relevant references. For advance subject material, Nield and Bejan (2006) may be consulted.
Although the therapeutic efficacy and commercial success of monoclonal antibodies (mAbs) are tremendous, the design and discovery of new candidates remain a time and cost-intensive endeavor. In this regard, progress in the generation of data describing antigen binding and developability, computational methodology, and artificial intelligence may pave the way for a new era of in silico on-demand immunotherapeutics design and discovery. Here, we argue that the main necessary machine learning (ML) components for an in silico mAb sequence generator are: understanding of the rules of mAb-antigen binding, capacity to modularly combine mAb design parameters, and algorithms for unconstrained parameter-driven in silico mAb sequence synthesis. We review the current progress toward the realization of these necessary components and discuss the challenges that must be overcome to allow the on-demand ML-based discovery and design of fit-for-purpose mAb therapeutic candidates.
We report the effect of grain boundary diffusion of the Nd-Cu eutectic phase and the influence of Nb on the microstructure and magnetic properties of Nd-Fe-B melt-spun ribbons. The Atom probe tomography analysis indicated the presence of Nb clusters (∼10 nm), which possibly restricts grain growth during diffusion annealing while facilitating Nd-Cu grain boundary decoration. Correspondingly, the coercivity was enhanced from the initial 1.2 T of the as-prepared to 2.1 T for the 20 wt.% Nd-Cu diffusion annealed (600°C, 2 h). Incidentally, the as-diffused sample exhibited a high coercivity of ∼1 T at 150°C, making it suitable for high-temperature applications.
The onset of colorectal cancer (CRC) is often attributed to gut bacterial dysbiosis, and thus gut microbiota are highly relevant in devising treatment strategies. Certain gut microbes, like Enterococcus spp ., exhibit remarkable anti-neoplastic and probiotic properties, which can aid in silver nanoparticle (AgNPs) induced reactive oxygen species (ROS)-based CRC treatment. However, the effects of AgNPs on gut microbial metabolism have not been reported thus far. In this study, a detailed systems-level understanding of ROS metabolism in Enterococcus durans ( E. durans ), a representative gut microbe, was gained using constraint-based modeling, wherein, the critical association between ROS and folate metabolism was established. Experimental studies involving low AgNP concentration treatment of E. durans cultures confirmed these modeling predictions (an increased extracellular folate concentration by 52%, at the 9 th h of microbial growth, was observed). Besides, the computational studies established various metabolic pathways involving amino acids, energy metabolites, nucleotides, and SCFAs as the key players in elevating folate levels on ROS exposure. The anti-cancer potential of E. durans was also studied through MTT analysis of HCT 116 cells treated with microbial culture (AgNP treated) supernatant. A decrease in cell viability by 19% implicated the role of microbial metabolites (primarily folate) in causing cell death. The genome-scale modeling approach was then extended to extensively model CRC metabolism, as well as CRC– E. durans interactions in the context of CRC treatment, using tissue-specific metabolic models of CRC and healthy colon. These findings on further validation can facilitate the development of robust and effective cancer therapy.
Pile foundations are adopted if a soil of low bearing capacity extends to a considerable depth or if the structure is heavy or the settlement due to the structure is large. It transfers the load to a strong, stable stratum of soil. The behaviour of soil in slope and piles embedded in it is an elaborated soil-structure interaction problem. This paper presents the results of experimental investigations on a single pile subjected to lateral load by varying relative density of soil in the horizontal and sloping ground with three different slopes of 1V: 2H, 1V: 2.5H and 1V: 3H. The lateral load carrying capacity of the pile is considerably decreased when the lateral load is applied in the direction of the slope. It is found that the lateral load carrying capacity of the pile is increased for higher relative density of sand and the lateral capacity of the pile is greater in flatter slope than in steeper slope. The effect of different slopes on normalized lateral load versus displacement for the lateral load applied in the direction along and against slope is quantified. A set of empirical equations are formulated to determine the deflection, fixity depth and moment for the pile in sloping ground.
Single-cell patterning technologies are rapidly evolving, where single cells are positioned in spatially distinct areas, thus providing a platform for several biological and biomedical, therapeutics, and diagnostics applications. By considering the cellular heterogeneity and providing more statistical power, single-cell patterning outperforms precise cellular analysis than conventional bulk patterning, where average data can be acquired with millions of cells together. A crucial step in cell patterning is to regulate cell adhesion on a substrate by adapting several physical and biochemical strategies for substrate modification and patterning. In this article, we briefly discuss different biochemical as well as physical approaches for the surface modification and cellular adhesion. Moreover, we also emphasize in-depth single-cell patterning by using different physiochemical and physical approaches and their biological and biomedical applications. Finally, single-cell printing, its advantages, limitations, and future challenges are also elaborated.
Cooling of turbine blades is necessary for longer durability and better thermal efficiency of the turbines. Turbine blade cooling is fulfilled by passing a coolant through the serpentine channel roughened with turbulators. In this work, the combined effect of the centrifugal buoyancy and the Coriolis force on heat transfer of a square duct roughened with ribs is studied using Large Eddy Simulation (LES). Simulations are carried for a Reynolds number based on bulk velocity of 20,000 with staggered square (SQ) rib, Backward step (BS) rib, and Forward step (FS) rib on the leading and trailing wall. The heat transfer performance of the square duct roughened with ribs is compared at rotation numbers Ro=0.35,0.67 and Richardson numbers Ri=0.0,12.0,28.0. The heat transfer augmentation for SQ-, BS-, and FS-ribs for Ro=0.67 and Ri=28 is 4.2%, 8.6% and 14.9%, respectively, higher than that without the effects of buoyancy. The friction coefficient for SQ-, BS-, and FS-ribs for Ro=0.67 and Ri=28 is 12.8%, 14.8% and 13.3% respectively higher than that without buoyancy.
With COVID-19 pandemic forcing academic institutions to shift to emergency remote teaching (ERT), teachers worldwide are attempting several strategies to engage their learners. Even though existing research in online learning suggests that effectiveness of the online session is more dependent on pedagogical design rather than technology feature, teachers may still focus on the intricacies of the technology. In this paper, we present the evolution of an active learning pedagogy, supported by technology (eBook reader—BookRoll, Analytics Dashboard—LAViEW), for an undergraduate physics classroom across a semester that was affected by the lockdown due to pandemic. The technology-enhanced pedagogy evolved in three phases—technology used in “Content Focus” mode, technology used in “Problem Focus” mode and technology used in “Learning Dialogue Focus” mode. The entire activities were designed and implemented within the technology-enhanced and evidence-based education and learning (TEEL) ecosystem, which supported integration of learning technologies with analytics system. Comparison of the student’s learning logs indicated that there was a sustained engagement in the learning activities conducted during the blended (before lockdown) and online mode (during lockdown). We had conducted one-way ANOVA to compare the post-test scores for each teaching phase and found statistically significant differences in the latter phases. A preliminary qualitative analysis of the learner artifacts generated as memos in BookRoll during each phase revealed that students were posing conceptual clarifications during the latter phases. These were also having greater alignment with the session agenda and showed construction of new knowledge based on the seed knowledge provided during the instructor–learner interaction sessions. The study provides key insights into how reflection and practice by both learner and teacher improves the acceptance of technology-enabled pedagogy.
Governments, institutions, and organisations are being persuaded by the UN Sustainable Development Goals (SDG) to include environmental-social-governance (ESG) measures in their disclosure systems and sustainable management practices. With the outbreak of the Covid-19 pandemic, institutional investors are shifting their focus from profit-making to sustainable and ethical investment. Investors are majorly focussing on ESG measures with financial incentives while making investment decisions. Empirical evidences indicate that firms disclosing ESG measures are likely to outperform others by reducing the risk and enhancing the economic performance, although the results may vary. ESG measures not only promote economic incentives but also encourage sustainable production through value accretive supply chain mechanism. The present study tries to explore the ESG disclosure-Corporate Financial Performance (CFP) nexus w.r.t the presence of sustainable value chains, considering the panel data of 1,170 firm-level observations from 2012 to 2020. In order to resolve endogeneity issue, we use Generalized Methods of Moments (GMM) and system GMM approach. The study also focuses on the presence of foreign ownership along with the environmental and social supply chain management practices in ESG–CFP nexus. The findings highlight ESG as an indicator of a sustainable manufacturing strategy and support the link between ESG and CFP.
Post monsoonal agricultural Crop Residue Burning (CRB) over northwestern India is believed to severely affect the air quality of the megacity of Delhi. However, the mechanistic understanding remains elusive. Long-term satellite observations (2007-2020) of aerosol properties during CRB season (Oct 20th to Nov 20th) indicate a distinct airshed of CRB plume transport from Northwestern India (source region) to greater Delhi (downwind region). Theoretically, the smoke concentration should disperse downwind, and the CRB-associated PM 2.5 enhancement over Northern India should be inversely proportional to the distance from the CRB source region. However, the in-situ PM 2.5 observations illustrate that smoke-associated enhancement in PM 2.5 over greater Delhi (downwind region) is disproportionately large compared to the source region. In this study, we examine satellite, radiosonde, and ground-based observations along with reanalysis data to provide robust evidence that aerosol-boundary layer-PM 2.5 associations via semi-direct effect can explain the above heterogeneity. Vertically resolved satellite observations indicate that as the emitted CRB-smoke plumes travel downwind, a portion of the transported smoke plume injected relatively at a higher altitude leads to the formation of an elevated smoke layer over greater Delhi. These elevated smoke layers tend to suppress the mixing height via inducing strong temperature inversion, thereby severely constraining the daytime dilution effect of shallow boundary layers. Along with direct advection of smoke particles, enhanced accumulation of local urban emissions due to these semi-direct impacts can lead to the observed disproportionate PM 2.5 enhancements over Delhi during CRB haze periods. Thus, control of the local anthropogenic emissions could bring relief during the extreme haze episodes over Delhi.
This study presents an integrated model to shed light on the factors influencing individuals’ likelihood and frequency of usage of bus transit in Bengaluru, India, with a focus on the role of individuals’ subjective perceptions of service quality. Typically, subjective perceptions of transit service characteristics such as comfort, cleanliness, reliability, and safety are measured using Likert rating scale questions in travel surveys. A shortcoming with many such surveys is that the Likert rating scale questions do not include a “don’t know” response category for the respondents to express their unfamiliarity and lack of opinion on the transit service. For this reason, some respondents who are not familiar with and do not have an opinion about the transit system are likely to choose the neutral response to Likert scale questions. At the same time, travelers who are familiar with and/or informed about the transit system may also choose the neutral response to state their opinion neutrality. As a result, some travelers’ unfamiliarity with (and lack of opinion about) transit services may be confounded with the informed perceptions of those who are familiar with transit. This is because those who are unfamiliar with the transit system are less likely to use it and more likely to state neutral responses than those who are familiar with the system. Ignoring such influence of travelers’ unfamiliarity can potentially distort the ordinal scale of Likert variables, result in biased parameter estimates and distorted implications about the influence of perceptions on transit usage. To address this concern, this study uses a generalized heterogeneous data model (GHDM) that allows a joint econometric analysis of the influence of individuals’ perceptions of transit service quality on their likelihood of transit use and frequency of use and at the same time disentangle unfamiliarity from informed perceptions. The empirical results shed light on: (a) the role of individuals’ demographic variables and subjective perceptions on their use and frequency of use of the bus transit system in Bengaluru, (b) the importance of separating unfamiliarity from informed opinions on transit service quality, (c) the need to include an option for respondents to reveal their unfamiliarity in Likert rating scale survey questions on perceptions, and (d) demographic segment-specific strategies for attracting new riders and enhancing ridership of current users of the bus transit system in Bengaluru.
The ongoing competition between traditional vehicle manufacturers and technology companies for quickly developing autonomous vehicles (AVs) and gaining early traction in the market is well known. However, some issues need to be cleared regarding the antecedents of the behavioral intention to use AVs. In this context, we conducted a meta-analysis using the TIS (Technological, Individual, and Security) framework, to understand the convergence and divergence of the factors influencing the behavioral intention to use AV technology. This meta-analysis tested the hypotheses using a database of 65 studies obtained from 58 articles with the cumulative sample size of 37,076. The study identified perceived usefulness, attitude, trust, safety, hedonic motivation, and social influence as the critical antecedents of AV adoption. Several of the relationships investigated in the study were moderated by factors such as level of automation, vehicle ownership and culture. The results revealed fewer incentives for the public to accept AVs. Theoretical contributions and recommendations to practitioners and policymakers have also been discussed.
Auxetics are the class of cellular structures which possess a negative Poisson’s ratio. Negative Poisson’s ratio is achieved through the careful design of the structures. Generally, auxetic structures are not feasible to manufacture using the conventional manufacturing processes due to the unit cell’s complex geometry, additive manufacturing help in alleviating this issue. Material extrusion/Fused Filament Fabrication (FFF) is the most simple, reliable, and low-cost additive manufacturing process in use. The mechanical performance of FFF processed auxetics is influenced by both geometrical parameters of auxetics and printing parameters. The careful selection of these parameters is of prime priority to avoid premature failure of printed structures. In the present work, the re-entrant diamond auxetic mechanical metamaterial is fabricated via FFF using the most commonly used FFF feedstock material, Acrylonitrile Butadiene Styrene (ABS). Initially, efforts are made to fine-tune the FFF process parameters to process these complicated geometrical structures. The ideal deformation parametric zone is defined with preliminary experiments to avoid premature failure of the re-entrant diamond structure. Experimental investigation of the effect of auxetic geometrical parameters and FFF process parameters on the quasi-static in-plane compressive performance is systematically evaluated using the design of experiments. The grey-based optimisation method is considered to optimise influential parameters for combined responses. Further, the re-entrant diamond auxetic metamaterial is reinforced with short carbon and glass fibre, and studied at optimal parametric levels. Reinforcements have enhanced the specific strength and stiffness of the structure with the loss of energy absorption characteristics. Microscopic studies confirm the predominant failure modes as a bond failure for CF-ABS and fibre breakage for GF-ABS. This study also aims to serve as fabrication guidelines to process complicated cellular composite structures via FFF.
The present study reports the low-velocity impact (LVI) performance of carbon woven reinforced polymer (CWRP) composites with varying temperatures. The fabrication of carbon woven lamina and carbon woven reinforced two-layered laminate (named CWRP-1 and CWRP-2) was done using a vacuum-assisted resin transfer molding (VARTM) process. CWRP-1 samples were tested at varying impact velocities of 1, 2, 3, and 4 m/s at −25, 25, and 50 °C for each incident velocity. CWRP-2 samples were tested at room temperature at varying incident velocities to determine the effect of multiple woven layers. The impact resistance of the first-crack load, peak impact load, and absorbed energies were recorded and evaluated under different loading conditions. In addition, the Weibull probability method is adapted to forecast failure behavior as a function of load. Visual inspection, optical microscopy, and scanning electron microscope (SEM) images were used to assess the damage pattern and failure morphologies in forecasting the failure phases during LVI. The low-velocity impact behavior of CWRP-1 at −25 °C with various velocities was shown to be random due to the polymer matrix freezing condition. The softening of the resin matrix at 50 °C is responsible for the difference in damage tolerance. The relevance of multiple layered composites for better impact resistance characteristics was demonstrated during testing of CWRP-2 at room temperature. Overall, the results of this experiment showed that CWRP lamina and laminates are highly sensitive to the impact velocities and external temperatures.
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Sanga Mitra
  • Department of Computer Science and Engineering
Sundararajan Natarajan
  • Department of Mechanical Engineering
Ramesh L Gardas
  • Department of Chemistry
Surendran Sankunny
  • Department of Ocean Engineering
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Sardar patel road, Adyar, 600036, Chennai, Tamilnadu, India
Head of institution
Professor Bhaskar Ramamurthy
Website
www.iitm.ac.in