Journal Articles
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Item Influence of disjoining pressure on the dynamics of steadily moving long bubbles inside narrow cylindrical capillaries(American Physical Society, 2014) Chaudhury, K.; Acharya, P.V.; Chakraborty, S.We study the influence of disjoining pressure for moving long bubbles inside cylindrical capillaries. Towards that end, consistent thin-film equations, for the annular region separating the bubble from the channel surface, are presented with specific emphasis on three different attributes: (a) the van der Waals interaction, formalized by the classical Lifshitz form of disjoining pressure; (b) the nonuniformity in film thickness, accommodated by the necessary corrections in the disjoining pressure; and (c) the electrostatic component of disjoining pressure, reminiscent of the electrostatic interactions in the presence of surface charges. The present thin-film analysis appositely uncovers the existence and the breakdown of the two-thirds power law for minimum film thickness behavior. This is attributed to the alteration in the characteristic length scales governing the underlying physics, as quantitatively established by our consistent scaling analysis. In the breakdown regimes, the characteristic length scales are found to be composed of the suitable combinations of the capillary number and the physics driven intrinsic length scales. The characteristics of the breakdown regime reported by us appear to match excellently with reported experimental data in the low capillary number regime. Towards unveiling the possible implications of slope and curvature dependence of disjoining pressure, our analysis reveals that the consequent correction term endorses an order two-thirds power of the capillary number contribution without alerting the governing length scales. The subsequent asymptotic analysis reveals that this correction may be neglected to the leading order approximation. Finally, we consider the electrostatic component of the disjoining pressure which may be realized in the presence of surface charges. Our analysis reveals that the significance of the electrostatic interaction is realized over a very small capillary number regime, leading towards the departure from the two-thirds power law type behavior. Reasonably good agreement is obtained with reported experimental data over this regime. © 2014 American Physical Society.Item Multi-response optimisation of surface texturing using artificial bee colony algorithm(Inderscience Publishers, 2016) Chakraborty, S.; Chakraborty, R.; Nagendrababu, K.; Talla, G.; Gangopadhyay, S.Determination of the optimal combination of process parameters plays a pivotal role in reducing manufacturing costs while enhancing rate of productivity and standard of quality of the product. This paper deals with fabrication of arrayed structures consisting of cylindrical pillars using reverse electro discharge machining (R-EDM) process, followed by optimisation of the process using artificial bee colony (ABC) algorithm. The influence of various machining parameters such as peak current (Ip), pulse-on time (Ton) and flushing pressure (Fp) on multiple performance measures in R-EDM like material removal rate (MRR), surface roughness (SR), taper and cylindricity error (CE) has been investigated using response surface methodology (RSM) based approach. In the course of this paper, the optimal parameters have been found to be Ip = 10 A; Ton = 179.091 ?s; Fp = 0.2 kg/cm2. The fast convergence and the high degree of closeness with the experimental data under optimal condition establishes the efficiency and robustness of the algorithm. © © 2016 Inderscience Enterprises Ltd.Item Tunable adhesion and slip on a bio-mimetic sticky soft surface(Royal Society of Chemistry, 2019) Bandyopadhyay, S.; Sriram, S.M.; Parihar, V.; das Gupta, S.; Mukherjee, R.; Chakraborty, S.Simultaneous tuning of wettability and adhesion of a surface requires intricate procedures for altering the interfacial structures. Here, we present a simple method for preparing a stable slippery surface, with an intrinsic capability of varying its adhesion characteristics. Cross-linked PDMS, an inherent hydrophobic material commonly used for microfluidic applications, is used to replicate the structures on the surface of a rose petal which acts as a high adhesion solid base and is subsequently oleoplaned with silicone oil. Our results demonstrate that the complex hierarchical rose petal structures can arrest dewetting of the silicone oil on the cross linked PDMS base by anchoring the oil film strongly even under flow. Further, by tuning the extent of submergence of the rose petal structures with silicone oil, we could alter the adhesion characteristics of the surface on demand, while retaining its slippery characteristics for a wide range of the pertinent parameters. We have also demonstrated the possible fabrication of gradient adhesion surfaces. This, in turn, may find a wide variety of applications in water harvesting, droplet maneuverability and no-loss transportation in resource-limited settings. © 2019 The Royal Society of Chemistry.Item Numerical modelling and analytical comparison of delamination during cryogenic drilling of cfrp(MDPI, 2021) Balan, A.S.S.; Kannan, C.; Jain, K.; Chakraborty, S.; Joshi, S.; Rawat, K.; F Alsanie, W.F.; Thakur, V.K.Carbon-Fibre-Reinforced Polymers (CFRPs) have seen a steady rise in modern industrial applications due to their high strength-to-weight ratio and corrosion resistance. However, their potential is being hindered by delamination which is induced on them during machining operations. This has led to the adoption of new and innovative techniques like cryogenic-assisted machining which could potentially help reduce delamination. This study is aimed at investigating the effect of cryogenic conditions on achieving better hole quality with reduced delamination. In this paper, the numerical analysis of the drilling of CFRP composites is presented. Drilling tests were performed experimentally for validation purposes. The effects of cooling conditions and their subsequent effect on the thrust force and delamination were evaluated using ABAQUS/CAE. The numerical models and experimental results both demonstrated a significant reduction in the delamination factor in CFRP under cryogenic drilling conditions. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.Item Containerized deployment of micro-services in fog devices: a reinforcement learning-based approach(Springer, 2022) Nath, S.B.; Chattopadhyay, S.; Karmakar, R.; Addya, S.K.; Chakraborty, S.; Ghosh, S.K.The real power of fog computing comes when deployed under a smart environment, where the raw data sensed by the Internet of Things (IoT) devices should not cross the data boundary to preserve the privacy of the environment, yet a fast computation and the processing of the data is required. Devices like home network gateway, WiFi access points or core network switches can work as a fog device in such scenarios as its computing resources can be leveraged by the applications for data processing. However, these devices have their primary workload (like packet forwarding in a router/switch) that is time-varying and often generates spikes in the resource demand when bandwidth-hungry end-user applications, are started. In this paper, we propose pick–test–choose, a dynamic micro-service deployment and execution model that considers such time-varying primary workloads and workload spikes in the fog nodes. The proposed mechanism uses a reinforcement learning mechanism, Bayesian optimization, to decide the target fog node for an application micro-service based on its prior observation of the system’s states. We implement PTC in a testbed setup and evaluate its performance. We observe that PTC performs better than four other baseline models for micro-service offloading in a fog computing framework. In the experiment with an optical character recognition service, the proposed PTC gives average response time in the range of 9.71 sec–50 sec, which is better than Foglets (24.21 sec–80.35 sec), first-fit (16.74 sec–88 sec), best-fit (11.48 sec–57.39 sec) and mobility-based method (12 sec–53 sec). A further scalability study with an emulated setup over Amazon EC2 further confirms the superiority of PTC over other baselines. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.Item CoMCLOUD: Virtual Machine Coalition for Multi-Tier Applications over Multi-Cloud Environments(Institute of Electrical and Electronics Engineers Inc., 2023) Addya, S.K.; Satpathy, A.; Ghosh, B.C.; Chakraborty, S.; Ghosh, S.K.; Das, S.K.Applications hosted in commercial clouds are typically multi-tier and comprise multiple tightly coupled virtual machines (VMs). Service providers (SPs) cater to the users using VM instances with different configurations and pricing depending on the location of the data center (DC) hosting the VMs. However, selecting VMs to host multi-tier applications is challenging due to the trade-off between cost and quality of service (QoS) depending on the placement of VMs. This paper proposes a multi-cloud broker model called CoMCLOUD to select a sub-optimal VM coalition for multi-tier applications from an SP with minimum coalition pricing and maximum QoS. To strike a trade-off between the cost and QoS, we use an ant-colony-based optimization technique. The overall service selection game is modeled as a first-price sealed-bid auction aimed at maximizing the overall revenue of SPs. Further, as the hosted VMs often face demand spikes, we present a parallel migration strategy to migrate VMs with minimum disruption time. Detailed experiments show that our approach can improve the federation profit up to 23% at the expense of increased latency of approximately 15%, compared to the baselines. © 2013 IEEE.Item Monitoring COVID-19 Cases and Vaccination in Indian States and Union Territories Using Unsupervised Machine Learning Algorithm(Springer Science and Business Media Deutschland GmbH, 2023) Chakraborty, S.The worldwide spread of the novel coronavirus originating from Wuhan, China led to an ongoing pandemic as COVID-19. The disease being a contagion transmitted rapidly in India through the people having travel histories to the affected countries, and their contacts that tested positive. Millions of people across all states and union territories (UT) were affected leading to serious respiratory illness and deaths. In the present study, two unsupervised clustering algorithms namely k-means clustering and hierarchical agglomerative clustering are applied on the COVID-19 dataset in order to group the Indian states/UTs based on the pandemic effect and the vaccination program from the period of March, 2020 to early June, 2021. The aim of the study is to observe the plight of each state and UT of India combating the novel coronavirus infection and to monitor their vaccination status. The research study will be helpful to the government and to the frontline workers coping to restrict the transmission of the virus in India. Also, the results of the study will provide a source of information for future research regarding the COVID-19 pandemic in India. © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.Item Geo-Distributed Multi-Tier Workload Migration Over Multi-Timescale Electricity Markets(Institute of Electrical and Electronics Engineers Inc., 2023) Addya, S.K.; Satpathy, A.; Ghosh, B.C.; Chakraborty, S.; Ghosh, S.K.; Das, S.K.Virtual machine (VM) migration enables cloud service providers (CSPs) to balance workload, perform zero-downtime maintenance, and reduce applications' power consumption and response time. Migrating a VM consumes energy at the source, destination, and backbone networks, i.e., intermediate routers and switches, especially in a Geo-distributed setting. In this context, we propose a VM migration model called Low Energy Application Workload Migration (LEAWM) aimed at reducing the per-bit migration cost in migrating VMs over Geo-distributed clouds. With a Geo-distributed cloud connected through multiple Internet Service Providers (ISPs), we develop an approach to find out the migration path across ISPs leading to the most feasible destination. For this, we use the variation in the electricity price at the ISPs to decide the migration paths. However, reduced power consumption at the expense of higher migration time is intolerable for real-time applications. As finding an optimal relocation is $\mathcal {NP}$NP-Hard, we propose an Ant Colony Optimization (ACO) based bi-objective optimization technique to strike a balance between migration delay and migration power. A thorough simulation analysis of the proposed approach shows that the proposed model can reduce the migration time by 25%-30% and electricity cost by approximately 25% compared to the baseline. © 2008-2012 IEEE.Item A Single Source Quadruple Boost Nine-Level Switched-Capacitor Inverter with Reduced Components and Continuous Input Current(Institute of Electrical and Electronics Engineers Inc., 2024) Kumar, D.; Raushan, R.; Chakraborty, S.The multilevel inverter (MLI) serves as a pivotal class of power electronic converters, well-suited for high-power applications at medium voltage levels, ensuring superior power quality. While designing an MLI, there is a motif among the number of components, voltage stress on the semiconductor devices, and its voltage-boosting ability. A single source nine-level switched-capacitor based novel inverter with reduced components has been proposed in this paper. The proposed H-bridge based switched capacitor inverter topology employs nine switches, two capacitors, two diodes, and one DC source. The inverter has a quadruple voltage boost and the ability to draw continuous input current from the DC supply and self-voltage balance with a voltage ripple of less than 5%. A comprehensive study of performance parameters, design consideration, and loss analysis of the proposed inverter is also incorporated. A level-shifted pulse width modulation technique is implemented to operate the inverter for unity to 0.5 lagging load power factors and 1-0.2 modulation indices. The dynamic responses of the proposed switched capacitor inverter topology are obtained through MATLAB simulation for analysis and further validated by hardware prototype. © 2013 IEEE.Item Unveiling the mass-loading effect on the electrochemical performance of Mn3O4 thin film electrodes: a combined computational and experimental study(Institute of Physics, 2024) Pramitha, A.; Hegde, S.S.; Badekai Ramachandra, B.R.; Yadav K, C.; Chakraborty, S.; Ravikumar, A.; George, S.D.; Sudhakar, Y.N.; Raviprakash, Y.The remarkable storage performance of manganese oxide (Mn3O4) makes it an appealing option for use as electrodes in electrochemical capacitors. However, the storage kinetics were significantly influenced by the mass loading of the electrode. Herein, we have inspected the dependency of mass loading on the storage performance of the spray pyrolyzed Mn3O4 thin film electrodes along with the correlation of structural and morphological characteristics. X-ray diffraction and Raman spectroscopic studies proven the formation of spinel Mn3O4 with a tetragonal structure. Morphological analysis revealed that all films exhibited fibrous structures with interconnected patterns at higher mass loadings. Moreover, the surface roughness and wettability of the electrode surface were influenced by variations in mass loading. Notably, thin-film electrode with a mass loading of 0.4 mg cm?2 exhibited the highest specific capacitance value of 168 F g?1 at 5 mV s?1 in a three-electrode system. Further, electrochemical impedance spectroscopic studies showed that there were noticeable changes in the capacitive behaviour of the electrode with respect to variations in mass loading. Moreover, the Dunn approach was employed to differentiate the underlying storage mechanism of the Mn3O4 electrode. Additionally, first-principles Density Functional Theory (DFT) studies were carried out in connection with the experimental study to comprehend the structure and electronic band structure of Mn3O4. This study underscores the critical importance of mass loading for enhancing the storage performance of Mn3O4 thin-film electrodes. © 2024 The Author(s). Published by IOP Publishing Ltd.