Showing papers by "National Institute of Technology, Meghalaya published in 2019"
TL;DR: Current research trends in the field of AUVs and future research directions are presented and localization and navigation techniques such as inertial navigation to simultaneous localization and mapping being used in current AUVs are discussed in detail.
250 citations
TL;DR: In this paper, the updated concepts on the nature of π-π interactions and their use in various fields ranging from crystal engineering to materials science to biochemistry are discussed and discussed.
Abstract: The updated concepts on the nature of π–π interactions and their use in various fields ranging from crystal engineering to materials science to biochemistry are discussed. This is the opening paper...
188 citations
TL;DR: The developed topology requires less switch count and driver circuit count compared with the few recently developed RS MLI topologies and a modified version of fish swarm optimization algorithm is examined for computing optimum switching angles required to control the SDDS MLI.
Abstract: Recently multilevel inverters (MLIs) have received wide attention from industry and academia, as they are changing into a viable technology for diverse applications. To produce high-quality output using less switch count, development of novel reduced switch MLI (RS MLI) topologies has been a focus of current research theme. This paper presents design and control of a switched-diode dual source single switch MLI (SDDS MLI). The generalized SDDS MLI is first designed using an asymmetric basic unit. Proposed SDDS MLI requires less switch count and driver circuit count compared with the few recently developed RS MLI topologies. To improve the voltage quality by eliminating targeted low-order harmonics, a modified version of fish swarm optimization algorithm is examined for computing optimum switching angles required to control the SDDS MLI. Moreover, suitability and superiority of the derived algorithm are established by comparing with traditional selective harmonic elimination techniques. The developed topology is investigated through several MATLAB simulations as well as experimental tests in the laboratory applying the modified control approach.
112 citations
TL;DR: In this paper, a 2D unsteady simulation is performed for semicircular, Benesh, modified Bach and elliptical profiles keeping the overall rotor diameter in each case to be constant.
85 citations
TL;DR: The blade profiles and blade shapes of vertical-axis Savonius wind turbine rotors have undergone a series of changes over the past three decades as mentioned in this paper, and there is not a single piece of literature that gives a comprehensive and a systematic review of rotor blade profile and shape.
Abstract: The blade profiles and blade shapes of vertical-axis Savonius wind turbine rotors have undergone a series of changes over the past three decades. Wind turbine aerodynamicists have carried out numerous computational and experimental research to arrive at a suitable rotor blade design configuration so as to harvest maximum energy from the available wind. In most of the studies, the geometric and aerodynamic aspects of the rotor blade design have been reported. Interestingly enough, a couple of review papers got published in the area of Savonius rotors during the last one decade. However, there is not a single piece of literature that gives a comprehensive and a systematic review of Savonius rotor blade profiles and shapes. This paper aims to collate all the research findings related to these blade profiles/shapes and makes an attempt to highlight their features together with future recommendations.
46 citations
TL;DR: In this paper, photoswitchable acylhydrazone derivatives, Ac-1 and Ac-2, were reported to respond to light as well as to mechanical force. But they only exhibited a single mechanical response to a single input stimulus.
Abstract: The advancement of our understanding of stimuli-responsive molecular crystals has led to the realization that they hold great yet unexplored potential as adaptive materials. Although molecular crystals that exhibit a single mechanical response to a single input stimulus are now abundant, crystals that are capable of response to multiple stimuli are rather scarce. Here we report two photoswitchable acylhydrazone derivatives, Ac-1 and Ac-2, which respond to light as well as to mechanical force. Upon application of localized mechanical stress, the anhydrous (Ac-1a) and monohydrate (Ac-1h) crystals of Ac-1 undergo plastic shearing deformation and bending, whereas monohydrate crystals of Ac-2 undergo elastic deformation. When they are exposed to UV light, crystals of Ac-1h and Ac-2 undergo photoinduced bending; on the other hand, crystals of Ac-1a and thicker crystals of Ac-2 exhibit photosalient effect (light-induced leaping). It is demonstrated that the synergistic action of multiple stimuli (UV light and fo...
42 citations
TL;DR: This paper envision employing lessons learned from context-aware computing, specifically context sharing among interdependent vertical IoT applications to address this delay requirement of such unified IoT applications by enacting context share among Fog nodes for minimizing system delay.
Abstract: As the Internet of Things (IoT) paradigm is maturing, innovative, and novel services are being envisioned. An upcoming trend is the depiction of services enacted through seamless integration of multiple vertical IoT services, termed as cross-vertical or unified IoT services in this paper. Traditional Cloud-based centralized network architectures cannot cater to real-time responses demanded by such unified IoT applications. Moreover, introducing Fog nodes within the network architecture, though a promising alternative, cannot sustain the burden of a huge number of applications that culminates in massive data handling. In this paper, we envision employing lessons learned from context-aware computing, specifically context sharing among interdependent vertical IoT applications to address this delay requirement of such unified IoT applications by enacting context sharing among Fog nodes for minimizing system delay. The detailed network model and context sharing mechanism have been presented and the service time minimization has been framed as an optimization problem. Algorithms for context sharing and delay tolerant load balancing have been presented and simulation results carried out demonstrate the efficacy of the proposed methodology.
40 citations
TL;DR: In this article, a stable and highly active metal oxide based electrochemical supercapacitor is developed, where the Au-Fe2O3 nanocomposite has a tiny amount of gold (3 atomic % Au...
Abstract: Development of a stable and highly active metal oxide based electrochemical supercapacitor is a major challenge. Herein, we report a Au–Fe2O3 nanocomposite having tiny amount of gold (3 atomic % Au...
34 citations
TL;DR: In this paper, the effects of chalcogen atoms on organic field-effect transistors (OFETs) were investigated by studying a series of furan-flanked diketopyrrolopyrrole copolymers (PFDPPF-Si, PFDPPT-Si and PFDPPS-Si) with different CHs, where the siloxane-terminated chains are used as solubilizing groups.
34 citations
32 citations
18 Apr 2019
TL;DR: To reduce the search space and to obtain the quality assembly sequences, stability graph is considered and the fitness of assembly subsets is evaluated according to the user weights at each level before proceeding to the higher levels.
Abstract: Assembly sequence planning is one of the multi-model optimization problems, in which more than one objective function has to be optimized at a time to obtain the quality assembly sequence. Moreover...
TL;DR: In this paper, the effect of the phenyl/thiophene units on the aggregation behavior and detailed photophysical properties were investigated by UV-visible, steady-state, and time-resolved fluorescence spectroscopy.
Abstract: Diketopyrrolopyrrole derivatives containing phenyl and thiophene units adorned with alkoxynaphthalene (Naph-PDPP and Naph-TDPP) were synthesized by a Suzuki cross-coupling reaction. The effect of the phenyl/thiophene units on the aggregation behavior and detailed photophysical properties were investigated by UV-visible, steady-state, and time-resolved fluorescence spectroscopy. The absorption and fluorescence spectra of Naph-PDPP and Naph-TDPP in the solid-state exhibit red-shifted spectral patterns due to strong intermolecular interactions. The concentration-dependent photophysical properties reveal the formation of J-type aggregates at higher concentrations and in the solid state. The extent of aggregate formation is higher for Naph-TDPP. DFT and TD-DFT studies showed that Naph-TDPP containing a thiophene ring in the backbone adopts a more planar geometry than Naph-PDPP and undergoes strong π–π stacking interactions that favor the formation of J-aggregates. Scanning Kelvin probe measurements on the thin films of Naph-PDPP and Naph-TDPP were performed (both in the dark and under visible light) upon exposure to different volatile organic vapors (ethanol and triethylamine). The study reveals that under visible light illumination, the Naph-PDPP thin film has significant gas adsorption towards ethanol vapors and alters its sign of response.
TL;DR: In this article, nitrogen-doped porous carbon materials have been synthesized from nitrogen and oxygen rich triazine based polyimide (TPI-P/TPI N) frameworks using ZnCl2 as an activating agent at different temperatures (600 and 700 °C) for electrochemical energy storage applications.
Abstract: Nitrogen-doped porous carbon materials have been synthesized from nitrogen and oxygen rich triazine based polyimide (TPI-P/TPI-N) frameworks using ZnCl2 as an activating agent at different temperatures (600 and 700 °C) for electrochemical energy storage applications. The morphology and structural features of the materials were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption/desorption isotherms, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopic techniques. The resultant carbon materials possess large specific surface area and rich nitrogen contents. In particular, the material obtained at 700 °C (TPI-P-700) exhibits a surface area of up to 1650 m2 g−1 and a nitrogen content of up to 6.3%, and shows an excellent specific capacitance of 423 F g−1 in an aqueous acid electrolyte (1 M H2SO4) in a three electrode system. Moreover, the material also demonstrates nearly 100% capacitance retention up to 10 000 charge–discharge cycles. A symmetrical supercapacitor device assembled using TPI-P-700 as an active material delivered an energy density of 10.5 W h kg−1 at 0.5 A g−1.
TL;DR: In this paper, a comparison of the performance of dot-textured coated carbide tool with the groove-based and nontextured tool in machining AISI D2 steel is presented.
Abstract: Surface texturing is a method where there is a change in tribological properties due to change in surface characteristics. The present work is a comparison of the performance of dot-textured coated carbide tool with groove-textured and non-textured coated carbide tool in machining AISI D2 steel. Micro dot textures are made on the flank face using micro-electric discharge machining. Considering full factorial design, total 8 experiments are performed with cutting speed, feed and depth of cut as process parameters. For each parameter, two levels are considered. Flank wear and surface roughness are investigated to compare the function of dot-textured coated carbide tool with the groove-textured and non-textured coated carbide tool. In every condition, flank wear is less in machining with both types of textured tool in comparison to the non-textured coated carbide tool. In most of the cases, surface roughness is less for both types of textured tool than the non-textured tool. Comparing dot-textured tool over groove-textured tool, it is observed that dot-textured tool is better than the groove-textured tool in reducing flank wear and surface roughness. Analysis of white layer and micro hardness at the machined surfaces revealed that dot-texturing helps in minimizing the thickness of white layer and micro-hardness property in comparison to groove-textured and non-textured tool. Thus, dot texturing is found to be better in improving machinability than groove-textured and non-textured tool.
TL;DR: In this paper, the authors focused on the mechanical strength and durability of geopolymer concrete with heat activation (at different temperatures) and indicated a limitation for its application in the development of mobile applications.
Abstract: Most recent research has focused on the mechanical strength and durability of geopolymer concrete with heat activation (at different temperatures) and has indicated a limitation for its app...
TL;DR: This paper proposes a look-ahead strategy for Boolean functions using Memristor Aided LoGIC (MAGIC) design style in the memristive crossbar, which supports in-memory computing.
TL;DR: This paper elaborate the design, implementation, and testing of a system—FallSense, which is able to detect accidental falls of human beings in a precise way and achieves overall 16% improvement in comparison with the existing approaches, on an average.
Abstract: In this paper, we elaborate the design, implementation, and testing of a system— FallSense , which is able to detect accidental falls of human beings in a precise way. The distinguishing feature of FallSense is its endeavors beyond the scope of accelerometer, which is a component of traditional body sensor network. Along with this acceleration measuring unit, FallSense uses the benefits of an Internet-of-Things-enabled environment, which consists of a number of infrared transmitter–receiver pairs and ultrasonic sensors. Employing a fuzzy inference system, FallSense fuses the data from multiple sensors and becomes over sure before inferring that a fall has occurred. Depending on the inputs from multiple sensors, FallSense generates a value between 0 and 1, which signifies the chance of fall. Results show that multi-sensor-based FallSense achieves overall 16% improvement in comparison with the existing approaches, on an average. Beyond the theoretical modeling, this paper also practically implemented the same with the help of the real-sensing units.
TL;DR: In this article, a pseudocapacitive mechanism becomes increasingly operative when H+ ions are intercalated easily into the enhanced van der Waals gap of layered material α-Fe2O3 in Au-α-Fe 2O3-Mn3O4 nanocomposite.
TL;DR: Insight is provided into the interaction dynamics and energetics of the binding of 6HF to HEWL and the ligand 6HF is found to bind near to Trp 62 and Trp 63 residues of HewL.
Abstract: The interaction of 6-hydroxyflavone (6HF) with hen egg white lysozyme (HEWL) has been executed using multi-spectroscopic and computational methods. Steady state fluorescence studies indicat...
Journal Article•
TL;DR: A novel 5-level MLI using fewer switch count suitable for standalone PV system is presented and firefly assisted genetic algorithm (FAGA) based selective harmonic elimination (SHE) technique is developed to effectively control and reduced the harmonics from the designed system.
Abstract: The rapid advancement in the power electronic sector has evolved multilevel inverter (MLI) for different applications. Now a day’s MLIs are chosen over the conventional two level inverters because of several advantages like less voltage stress, less electromagnetic interference, reduced filter size requirement, etc. However, the conventional MLIs require more device components to synthesize more levels. Considering this fact, this paper presents a novel 5-level MLI using fewer switch count suitable for standalone PV system. Furthermore, to effectively control and reduced the harmonics from the designed system, firefly assisted genetic algorithm (FAGA) based selective harmonic elimination (SHE) technique is developed. The targeted low-order harmonics from the output voltage of the proposed PV-MLI is eliminated using the FAGA algorithm. Existing firefly algorithm (FA) and genetic algorithm (GA) are also implemented for this purpose to verify the superiority of FAGA. Incremental conductance (IC) algorithm is used to yield the maximum power from the PV system. Simulation study of the overall system is carried out in MATLAB environment and the obtained results are discussed individually. An experimental test setup is developed finally to validate the working of PV integrated MLI with the SHE control scheme.
TL;DR: In this article, the authors investigated analytically the two-dimensional heat transfer and entropy generation characteristics of axi-symmetric, incompressible viscous fluid flow in a horizontal circular pipe.
Abstract: The present paper investigates analytically the two-dimensional heat transfer and entropy generation characteristics of axi-symmetric, incompressible viscous fluid flow in a horizontal circular pipe.The flow is subjected to an externally applied uniform suction across the wall in normal direction and a constant radial magnetic field. Constant wall temperature is considered as the thermal boundary condition.The reduced Navier-Stokes equations in a cylindrical coordinate system are solved to obtain the velocity and temperature distributions. The velocity distributions are expressed in terms of stream function and thesolution is obtained using the Homotopy Analysis Method (HAM). Validation with earlier non-magnetic solutions in the literature is incorporated. The effects of various parameters on axial and radial velocities, temperature, axial and radial entropy generation numbers, and axial and radial Bejan numbers and are presented graphically and interpreted at length. Streamlines, isotherms, pressure, entropy generation number and Bejan number contours are also visualized. Increasing magnetic body force parameter shifts the peak of the velocity curve near to the axis where as it accelerates the radial flow. The study is relevant to thermodynamic optimization of magnetic blood flows and electromagnetic industrial flows featuring heat transfer.
TL;DR: In this paper, a numerical and experimental approach has been presented in order to detect the LDR frequency of aluminium plate having circular flat bottom hole (FBH) and delaminated glass fibre reinforced polymer composite (GFRP) plates.
TL;DR: In this paper, a nonlinear active plus proportional integral sliding mode control (NA-PISMC) is proposed to control microscopic chaos in the deterministic dynamics of the chemical reactor system.
Abstract: This paper puts forward the microscopic chaos control in the deterministic dynamics of the chemical reactor system. First, the dynamic behavior of the chemical reactor system is explored for some of the parameters and chaotic behavior is investigated. Phase plane, bifurcation plots and Lyapunov exponents are presented to verify the chaotic behavior. Second, nonlinear active plus proportional integral sliding mode control (NA-PISMC) is proposed to control microscopic chaos in the chemical reactor system. A proportional integral switching surface is proposed to achieve the stability condition of the error dynamics and controller is designed by using the relevant variables of the chemical system. Unlike the open loop and open plus closed loop control techniques, the design of proposed controller does not require the parameter perturbation. The required stability condition is derived based on Lyapunov stability theory. Simulation is done in MATLAB environment. Numerical simulation results are presented in order to show the effective performances of the proposed controller design. Simulation results correspond that the objectives of chaos existence and chaos control are achieved successfully.
TL;DR: In this article, the authors investigated the thermo-hydraulic performance improvement of a solar air duct by deploying modified conical vortex generators (VGs) on the absorber plate heated with uniform heat flux of 1000 W/m2.
Abstract: The present work investigates the thermo-hydraulic performance improvement of a solar air duct by deploying modified conical vortex generators (VGs) on the absorber plate heated with uniform heat flux of 1000 W/m2. Half and truncated half conical VGs at six different angle of attacks are considered for numerical simulation at a wide relevant range of Reynolds number varying from 3000 to 15,000. Commercial CFD tool, ANSYS FLUENT is used for simulating eighty four simulations on three dimensional model of VG integrated solar air heater with turbulent flow. RNG k-e turbulent model is employed to solve the complex governing equations of CFD. Results are analysed in detail based on different performance parameters namely Nusselt number (Nu), friction factor (f), thermal enhancement factor (Numod/Nus), friction factor enhancement factor (fmod/fs) and thermohydraulic performance parameter (THPP). The modified geometries are found to enhance Nu by about 7% and 4% compared to that of a smooth and conical VG integrated duct respectively. However there is an enhancement of 21% and 16% in local Nu due to the modifications in conical VG. Optimization based on performance at different angle of attack is carried out for both the modified conical VGs. At a higher Reynolds number value, truncated conical VG gives higher value of THPP. A maximum THPP of 1.06 is obtained for half conical VG at an angle of attack of 60° as compared to 1.02 for conical VG. The results are further supported and explained by exploring the temperature field, x-velocity, static pressure, turbulent kinetic energy and helicity contours. Modified conical VG shows a remarkable enhancement in overall performance as compared to conical VG.
TL;DR: In this article, the effect of the lift and the drag on the rotor performance was investigated for the elliptical-bladed Savonius wind turbine rotor and the results showed that the average lift and drag coefficients of the rotor were 1.31, 0.48, and 0.26, respectively.
Abstract: The elliptical-bladed Savonius wind turbine rotor has become a subject of interest because of its better energy capturing capability. Hitherto, the basic parameters of this rotor such as overlap ratio, aspect ratio, and number of blades have been studied and optimized numerically. Most of these studies estimated the torque and power coefficients (CT and CP) at given flow conditions. However, the two important aerodynamic forces, viz., the lift and the drag, acting on the elliptical-bladed rotor have not been studied. This calls for a deeper investigation into the effect of these forces on the rotor performance to arrive at a suitable design configuration. In view of this, at the outset, two-dimensional (2D) unsteady simulations are conducted to find the instantaneous lift and drag forces acting on an elliptical-bladed rotor at a Reynolds number (Re) = 0.892 × 105. The shear stress transport (SST) k–ω turbulence model is used for solving the unsteady Reynolds averaged Navier–Stokes equations. The three-dimensional (3D) unsteady simulations are then performed which are then followed by the wind tunnel experiments. The drag and lift coefficients (CD and CL) are analyzed for 0–360 deg rotation of rotor with an increment of 1 deg. The total pressure, velocity magnitude, and turbulence intensity contours are obtained at various angles of rotor rotation. For the elliptical-bladed rotor, the average CD, CL, and CP, from 3D simulation, are found to be 1.31, 0.48, and 0.26, respectively. The average CP for the 2D elliptical profile is found to be 0.34, whereas the wind tunnel experiments demonstrate CP to be 0.19.
TL;DR: In this paper, two well known Lotka-Volterra (LV) type and Rosenzweig-MacArthur (RM) predator-prey models incorporating time delay into the logistic growth term are considered.
Abstract: Modeling population dynamics using delay differential equations and exploring the impacts of harvesting in predator-prey systems are among few of the thrust areas of research in theoretical and applied ecology. Many results are established to understand distinct dynamics under population harvesting. However, comparatively less attention is paid to explain the explicit harvesting effects when populations fluctuate due to time delay. In this contribution, two well known Lotka–Volterra (LV) type and Rosenzweig–MacArthur (RM) predator-prey models incorporating time delay into the logistic growth term are considered. The analysis and the obtained results are summarized as follows. (a) Firstly, the dynamics of both the models, by considering the time delay as the bifurcation parameter, is analyzed. Some of the parameter conditions for the delay induced stability switching are improved and corrected in comparison to the earlier works. The delay induced stability results are derived and found to be similar for both the models. (b) We investigate whether harvesting of either prey or predator can locally stabilize (respectively, destabilize) the system when the unharvested system dynamics is at non-equilibrium (respectively, stable steady state) mode due to time delay. It is observed that harvesting can induce stability and instability switching depending upon the dynamics mode of the unharvested system. (c) In the same framework, we examine if a stable steady state can be obtained when predator is harvested towards Maximum Sustainable Yield (MSY) level. Unlike the case of non-delayed LV type and RM predator-prey models, it is found that harvesting the predator towards MSY in the delayed models does not guarantee a stable stock. The new results compared to the existing literature might contribute in enriching fishery management policy and theoretical ecology as a whole.
TL;DR: This paper considered mobile electric vehicles (EVs) network as an energy storage and their charging/discharging is done by balance state-of-charge (SOC) holder technique taking into consideration future driving demand of EV owners using battery SOC controller.
Abstract: Massive penetration of nonsynchronous units with power electronics devices in the future grid could diminish the rotational inertia of a power system and inevitably jeopardize the frequency stability. Several adaptations are made accordingly in the power system to provide a short-term inertial support. In this paper, synchronous power concept is used for inertia emulation (IE) in high voltage direct current (HVdc) transmission links for frequency control. However, the energy reserves capacity such as direct current (dc) link capacitances or distributed generations for IE are limited and therefore required additional energy storage. This paper considered mobile electric vehicles (EVs) network as an energy storage and their charging/discharging is done by balance state-of-charge (SOC) holder technique taking into consideration future driving demand of EV owners using battery SOC controller. Cooperative contributions from HVdc links and EVs during perturbation exceptionally damp the oscillation and peak deviation in grid frequency as well as in tie-line power. To validate the efficacy of proposed framework, numerous time domain simulation results are presented.
01 Jul 2019
TL;DR: This work provides optimized superframe order values that achieve trade-offs between delay and power consumption as demanded by user-provided QoS requirements corresponding to different contexts.
Abstract: In this paper, we analyze the superframe structure of the Medium Access Control (MAC) sublayer of IEEE 802.15.4 protocol (ZigBee), designed for Low-Rate Wireless Personal Area Networks (LR-WPANs), and evaluate the effects of the inactive portion of a superframe on average delay, and average power consumption. The four-dimensional Markov chain-based analysis of the slotted Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) algorithm presented in this work considers backoff freezing and acknowledged packet transmission that are not studied in the existing works. The analytical results prove that the performance of LR-WPANs depends significantly on the length of a superframe's active portion. We introduce a variable—Superframe duration-Beacon interval Ratio (SBR), which is utilized by tuning a few MAC parameters to achieve 35 percent reduced delay, on an average, compared to the existing state of the art. The results show that the proposed model also yields improved performance in terms of power consumption, for short and medium contention windows. In addition to the proposed analysis, this work provides optimized superframe order values that achieve trade-offs between delay and power consumption as demanded by user-provided QoS requirements corresponding to different contexts.