003355   BISWAS D, KARTHA S A (Civil Engineering Dep, Indian Institute of Technology Guwahati, Guwahati - 781 039, Email: debraj.biswasjgec@gmail.com) : Conceptual modeling of temperature effects on capillary pressure in dead-end pores. Sadhana 2019, 44(5), 117.

The effect of temperature on the liquid–gas interface and consequently on the capillary pressure in unsaturated dead-end pores is conceptually modeled in this paper. Trapping of non-wetting fluid (e.g., air) in the dead-end pores impacts the capillary pressure–saturation relationship and affects the continuous flow of wetting fluids. In the dead-end pore, which is assumed to be a simple vertical cylindrical capillary tube with one end closed and the other end open to the liquid body, the dependence of solid–liquid and solid–air interfacial tensions on temperature and its subsequent effects on the contact angles are deduced. A non-linear ordinary differential equation, using the Young–Laplace equation, in terms of a contact-angle-sensitive temperature function is derived and numerically solved using the fourth order Runge–Kutta method. This temperature function is used to obtain the capillary pressure–temperature relationship for a solid–liquid–air capillary system. Two example problems, first a glass–water–air capillary system and second a polytetrafluoroethylene–n-hexadecane–air capillary system, are solved here. A linear decrease in capillary pressure with temperature is observed, suggesting that entrapped air affects capillary pressure in dead-end pores. A similar linear decrease in capillary pressure, consistent with experimental observations, is observed for open-end pores.

17 illus, 2 tables, 72 ref

003383   KAMANI P L, MULLA M A (Electrical Engineering Dep, Sardar Vallabhbhai National Institute of Technology, Surat 395009, Email: kamanipiyush03@gmail.com) : Univariate equation-based SHE-PWM for multilevel inverter. Sadhana 2019, 44(5), 116.

This article presents a selective harmonic elimination-pulse-width modulation (SHE-PWM) method for cascaded H-bridge multilevel inverters. The concept of volt–second area balancing is applied to estimate the voltage ratings of the dc sources, which provides different voltage ratings of each dc source. The control of output voltage is achieved by varying switching notch created at the centre of each level. This method calculates switching angles in real time easily owing to the usage of univariate equations. A comparison study shows that the proposed method eliminates more harmonics compared with the conventional SHE-PWM methods. Simulation and experimental studies are conducted to validate the performance of the proposed SHE-PWM method.

5 illus, 11 ref

003419   STARBINO A V, SATHIYAVATHI S (Mechatronics Engineering Dep, Kongu Engineering Coll, Erode, Tamil Nadu, Email: starbino2013@gmail.com) : Real-time implementation of SMC–PID for Magnetic Levitation System. Sadhana 2019, 44(5), 115.

Magnetic levitation is significant in almost all arenas of engineering. This principle is used to levitate objects such as a bullet train, flywheel, etc. This paper presents an experimental set-up of Magnetic Levitation System (MLS) in which a ball is levitated to a desired position and is sustained at a desired level for a stipulated time. The ball position is measured using an optoelectronic sensor and a controller is used to determine the time span of the ball at desired heights. To achieve this, a Sliding Mode Controller (SMC) is designed in such a way so as to regulate the current, which in turn controls the position through an electromagnet. Real-time observations of such ball positions have been recorded and compared to those of conventional PID (Proportional Integral Derivative) and robust SMC. Disturbance rejection, servo operation and set point tracking have also been tested and verified for the same. The outcome of such results processed through MATLAB proves that SMC’s performance is predominant over other controllers.

19 illus, 1 table, 19 ref

003418   SINHA A, RAVIKRISHNA R V (Mechanical Engineering Dep, Indian Institute of Science, Bangalore, Karnataka, Email: er.anubhav@gmail.com) : Experimental studies on structure of airblast spray in crossflow. Sadhana 2019, 44(5), 113.

The present investigation is focused on experimental studies on the structure of airblast spray in crossflow. Atomizer is at a higher pressure than ambient and the airblast gas is expected to exhibit features generally found in under-expanded gas jets. High-speed images are captured using shadowgraphy technique. Certain wave-like structures observed in the near-nozzle region are attributed to shock–vortex interactions, generally observed in under-expanded gas jets. Proper Orthogonal Decomposition (POD) analysis has been carried out using these images. POD mode shapes clearly show signatures of shock–vortex oscillations and frequencies close to the screeching frequency observed in under-expanded jets. The POD modes are compared for different conditions and the significance of dynamic structures and their temporal behavior is discussed. Finally, a regime map is also proposed to characterize spray behavior in crossflow.

14 illus, 2 tables, 37 ref

003384   KAVITHA J, UMAMAHESWARI B (Electrical and Electronics Engineering Dep, Rajalakshmi Engineering Coll, Chennai - 602 105, Email: kavitha.j@rajalakshmi.edu.in) : Analysis of a novel disc-type hybrid stepper motor with field circuit model. Sadhana 2019, 44(5), 112.

This paper presents modelling and analysis of a novel disc-type hybrid stepper motor (DTHSM) and brings out its relative merits over the cylindrical version. The machine is characterized by winding free rotorand stator-placed field coils/permanent magnets, creating homopolar field. DTHSM has the advantage of providing independent space for the field and armature, while other stator field machines have to share the same core space for both the field and armature. This increases field strength both by permanent magnet as well as field coils to achieve increased torque and speed ranges. The machine parameters are obtained using a field circuit model and its performance is predicted using analytical equations. A 50-W, 200 steps DTHSM prototype is fabricated and tested. Aggregation of simulation and experimental results validates the effectiveness of the proposed configuration.

25 illus, 11 tables, 22 ref

003411   RATHOD S, KUMAR A, BEENAMOLE K S, RAY K P (Electronic and Radar Development Establishment (LRDE), Bangalore- 560 093, Email: somsing.rathod@lrde.drdo.in) : Miniaturized composite band pass filter using folded transmission lines for wideband radar. Sadhana 2019, 44(5), 111.

A composite design of Band Pass Filter (BPF) is developed with 3-dB fractional bandwidth (FBW) of more than 140%. This BPF is suitable for the development of wideband radar, communication and EW system in 1 to 6 GHz. Composite BPF design utilizes stepped impedance Low Pass Filter (LPF) along with the quarter wavelength (λg/4) short circuited stub. λg/4 short circuited stubs incorporated High Pass Filter (HPF) response which transforms overall design into BPF. Four cases of filter have been discussed. In case-I, the proposed BPF is developed with a size of 32.6 mm X 7.0 mm. Further in case-II, design has been realized with improved roll-off at the lower edge of the bandwidth (i.e., 1GHz). In case-III, developed design is 75 % lengthwise miniaturized that of case-I. Further in case-IV, about 55 % length-wise miniaturization is done. Case-III and IV have their response similar to that of the case-I with miniaturized design. All designs are simulated, optimized and fabricated over RT-Duroid 5880 substrate. For case-I, III and IV fabrication has been done on 20 mil thick substrate, whereas for case-II 31 mil thick substrate is used. Comparisons between all the cases have been presented in tables and S-parameter plots.

8 illus, 1 table, 11 ref

003425   VERMA P, OM H (Computer Science and Engineering Dep, Indian Institute of Technology (Indian School of Mines), Dhanbad - 826004, Email: pradeepikav.verma093@gmail.com) : A novel approach for text summarization using optimal combination of sentence scoring methods. Sadhana 2019, 44(5), 110.

In this paper, a novel multi-document summarization scheme based on metaheuristic optimization is introduced that generates a summary by extracting salient and relevant sentences from a collection of documents. The proposed work generates optimal combinations of sentence scoring methods and their respective optimal weights to extract the sentences with the help of a metaheuristic approach known as teaching–learning-based optimization. In addition, the proposed scheme is compared to two summarization methods that use different metaheuristic approaches. The experimental results show the efficacy of the proposed summarization scheme.

8 illus, 7 tables, 45 ref

003349   AGARWAL V, PARTHASARATHY H (MPAE Div, Netaji Subhas Univ of Technology, New Delhi, Email: vijaynt.agarwal@gmail.com) : Simultaneous estimation of parameter uncertainties and disturbance trajectory for robotic manipulator. Sadhana 2019, 44(5), 109.

In this work, a systematic approach is proposed to estimate the disturbance trajectory using a new generalized Lyapunov matrix valued function of the joint angle variables and the robot’s physical parameters using the maximum likelihood estimate (MLE). It is also proved that the estimated disturbance error remains bounded over the infinite time interval. Here, the manipulator is excited with a periodic torque and by the position and velocity data collected at discrete time points construct an ML estimator of the parameters at time t þ dt. This process is carried over hand in hand in a recursive manner, thus resulting in a novel unified disturbance rejection and parameter estimation in a general frame work. These parameter estimates are then analyzed for mean and covariance and compared with the Cramer Rao Lower Bound (CRLB) for the parametric statistical model. Using the Lyapunov method, convergence of the ‘‘disturbance estimation error’’ to zero is established. We assume that a Lyapunov matrix dependent on the link angle and form the energy corresponding to this matrix as a quadratic function of the disturbance estimate error. Using the dynamics of the disturbance observer, the rate of change of the Lyapunov energy is evaluated as a quadratic form in the disturbance error. This quadratic form is negative definite for the angular velocity in a certain range and for a certain structured form of the Lyapunov energy matrix. The most general form of the Lyapunov matrix is obtained that guarantees negative rate of increase of the energy and a better bound on the disturbance estimation error convergence rate to zero. This is possible only because we have used the most general form of the Lyapunov energy matrix.

11 illus, 25 ref

003399   OZMEN M (Industrial Engineering Dep, Erciyes Univ, Kayseri, Turkey, Email: mihrimah@erciyes.edu.tr) : Logistics competitiveness of OECD countries using an improved TODIM method. Sadhana 2019, 44(5), 108.

The Organization for Economic Co-operation and Development (OECD) provides a forum where governments can work together to increase the global welfare and to seek solutions to common problems through economic growth, where logistics plays an important role and contributes to financial stability. Evaluation of the logistics competitiveness of countries is a technical decision-making issue involving a variety of criteria. Most importantly, these criteria usually conflict with each other and they often act and react upon one another. As in logistics competitiveness as well as in many decision-making problems, the relationships among criteria are interdependent. Moreover, different dimensions and criteria weights also affect the evaluation results. By considering these situations, in order to handle these criteria interactions, Mahalanobis distance (MD) based TODIM (an acronym in Portuguese for Interactive and Multicriteria Decision Making) method has been developed and it has been applied to evaluate the logistics competitiveness of the OECD countries. Evaluation of the correlation between criteria develops the consideration outcomes (regarding sorting) to a certain degree with the traditional TODIM method.

2 illus, 5 tables, 50 ref

003375   HASSANZADEH R, DARVISHYADEGARI M (Urmia Univ of Technology, Urmia, Iran, Email: r.hassanzadeh@uut.ac.ir) : Analysis of heat and fluid flow around two co-rotating side-by-side cylinders. Sadhana 2019, 44(5), 107.

Analysis of the heat and fluid flow around two co-rotating side-by-side cylinders is the subject of this numerical study which is done at constant Reynolds and Prandtl numbers of 200 and 7.0, respectively. Both cylinders rotate in the counterclockwise direction with an identical rotating speed (RS) in the range from 0 to 4. On the other hand, several gap spaces between the rotating cylinders such as G/D = 1.5, 2.0, and 3.0 are considered in the present study. The obtained results are validated against the available data in the open literature. Many different results have been reported in this investigation. It is observed that co-rotating the cylinders deforms the wake region downstream of both cylinders which the vortex strength of the lower cylinder against the rotation is stronger than that of the upper cylinder. On the other hand, co-rotating the cylinders develops a negative lift force on both cylinders. Finally, it was concluded that rotating the side-by-side cylinders reduces the heat transfer rate between the fluid flow and cylinders in general. At whole RS and G/D values, the heat transfer rate of the upper cylinder is realized to be less than that of the lower cylinder.

20 illus, 3 tables, 42 ref

003364   ELSHARKAWY R, HINDY M, SEBAK A-R, SALEEB A, EL-RABAIE E-S M, RAGHEB A, ASHRAF M, ALSHEBEILI S (Electronics Research Institute, Dokki, Giza, Egypt, Email: raniarefaat85@eri.sci.eg) : Single- and double-beam reflect arrays for Ka band communication. Sadhana 2019, 44(5), 106.

The Ka band has found applications in satellite, and radar communications. It is also expected that this band will be utilized for 5G applications. This paper presents single- and double-beam microstrip reflectarrays with single layer and compact size for Ka band communications at 28 GHz. Three different unit cells are investigated in this paper. Single- and double-beam reflectarrays are investigated. The reflectarrays are designed at 28 GHz with a physical size of 10 λ x 10 λ. A pyramidal horn antenna is used for the feeding purpose. The focal-length-to-diameter (F/D) ratio is equal to one. Two different scenarios for single-beam reflectarrays are presented: one with a broadside direction and the other with a 10° tilt angle. The simulation results show that for the broadside single-beam scenario, it is possible to achieve a gain up to 28.5 dB, and a 1-dB gain-bandwidth up to 30.7 %. On the other hand, the presented reflectarray for the single-beam design at 10° tilt angle gives a gain of about 26.4 dB, a side lobe level (SLL) of about -15.6 dB, and a 19.3 % gain-bandwidth. For the double-beam reflectarray, four different designs at different angles of 5°, 10°, 15°, and 20° have been simulated and compared. Moreover, the simulation results on the double-beam reflectarray show that the double-beam design at 10° is better from the gain and SLL perspectives. Two prototypes for broadside single-beam reflectarrays have been fabricated and measured. The measurement results show a good match with the simulation results. Gain flatness is guaranteed for both the simulated and measured results over the band of interest.

26 illus, 3 tables, 25 ref

003353   ALKAN V (Mechanical Engineering Dep, Pamukkale Univ, 20070 Pamukkale, Denizli, Turkey, Email: alkanveysel@gmail.com) : Optimal design of the transversely vibrating Euler–Bernoulli beams segmented in the longitudinal direction. Sadhana 2019, 44(5), 102.

In this study, optimal design of the transversely vibrating Euler–Bernoulli beams segmented in the longitudinal direction is explored. Mathematical formulation of the beams in bending vibration is obtained using transfer matrix method, which is later coupled with an eigenvalue routine using the ‘‘fmincon solver’’ provided in Matlab Optimization Toolbox. Characteristic equations, namely frequency equations, for determining natural frequencies of the segmented beams for all end conditions are obtained and for each case, square of this equation is selected as a fitness function together with constraints. Due to the explicitly unavailable objective functions for the natural frequencies as a function of segment length and volume fraction of the materials, especially for the beams made of a large number of segments, initially, prescribed value is assumed for the natural frequency and then the variables minimizing objective function and satisfying the constraints are searched. Clamped–free, clamped–clamped, clamped–pinned and pinned–pinned boundary conditions are considered. Among the end conditions, maximum increment in the fundamental natural frequency is more pronounced for the case of clamped–clamped end condition and for this case, maximum increment up to 17.3274 % is attained. Finally, the beam configurations maximizing fundamental natural frequencies will be presented.

5 illus, 5 tables, 22 ref

003374   HANMAIAHGARI P R, KOTTAM R R, KAUSHIK M (Civil Engineering Dep, Indian Institute of Technology Kharagpur, Kharagpur 721 302) : Estimation and examination of linepack pressures in long liquid pipelines. Sadhana 2019, 44(5), 101.

In the past, many researchers have carried out water-hammer pressure analysis using Joukowsky equation. However, it has been observed that the computed pressure surge is no longer applicable based on the equation. The Joukowsky equation cannot be used even within the reflection time of the long pipeline. In such cases, the actual pressure rise due to the sudden closure of a quick acting valve will be several times more than that of the sudden increase in pressure as calculated by the Joukowsky equation. The phenomenon of rising pressure at the upstream of an instantaneously closed valve with the passage of time caused by the pipe friction is commonly called as linepacking. In this paper, various parameters affecting the linepack pressure have been thoroughly investigated. As the relative roughness increases, the resulting non-dimensional linepack pressure (P_LP / P₀) significantly increases and the proportionality constant was equal to 1.5. The linepack pressure was determined to be decreasing with increasing valve closure time. The dominant parameter that influences the linepack pressure is found to be the Reynolds number as compared to the Mach number, and the relative roughness. Furthermore, the linepack pressure is found to be proportional to frictional head loss (h_L / D) , and inversely proportional to inlet pressure (P₀ / γL₀) . Finally, a linear regression equation was developed in terms of non-dimensional variables to estimate the linepack pressure using hand calculations without undergoing numerical modeling procedures. The proposed equation was validated for sudden valve closure pressure histories available in the literature. The proposed method is applicable to long distance water supply pipelines where the linepack pressures are significant.

8 illus, 6 tables, 22 ref

003403   PRINCY S S, SREEJA B S, MANIKANDAN E, RADHA S (Electronics and Communication Engineering Dep, SSN Coll of Engineering, Chennai- 603 110, Email: sasiprincys@ssn.edu.in) : Design of polarisation-dependent multiband terahertz frequency-selective surface using two resonators. Pramana– J Phys 2019, 92(6), 92.

The aim of this paper is to present the frequency-selective surface (FSS) filter operating in the terahertz regime, emphasising on its polarisation-dependent nature. The FSS filter consists of two-concentric hexagonalshaped metal strips embossed on a gold layer over the teflon substrate, created in the form of a split ring resonator (SRR). The emphasised polarisation-dependent nature of the FSS structure has been proved by analysing the frequency response. Numerical simulation has been done using the CST microwave studio software. Resonance occurs at five frequencies in the transverse electric (TE) mode and at four frequencies in the transverse magnetic (TM) mode, describing the polarisation-dependent nature of the proposed FSS filter structure.

6 illus, 1 table, 14 ref

003370   GHAFORYAN H (Optics and Laser Engineering Dep, Bonab Univ, Bonab, Iran, Email: drghaforyan@gmail.com) : Energy of electrons at the interaction of femtosecond laser with argon nanocluster. Pramana– J Phys 2019, 92(5), 81.

The interaction of intense femtosecond laser pulses with argon nanoclusters is studied using nanoplasma model. Based on the dynamic simulations, ionisation process, heating, and expansion of an argon nanocluster irradiated by an intense femtosecond laser pulse are investigated. The analytical calculation provides ionisation rate for different mechanisms and time evolution of hydrodynamic pressure for various pulse shapes. In this work, the dependence of laser intensity, initial ion density and pulse shape on the electron pressure, the density of electrons and electron temperature are presented. It is noticed that the negative and positive chirped pulses and initial ion density implement some modifications on the current calculation models. It is found that reducing the initial ion density at a laser intensity of about 1×10¹⁶ W/hboxcm² increases the energy of electrons. By applying a positive chirp laser pulse during interaction with nanoclusters, both electron density and ultimately electron pressure are improved by about 22 %.

6 illus, 31 ref

002257   YULIHARSINI S, NASUTION I D, AGUSNAR H, RITONGA P W U (Sumatera Utara Univ, Medan, Indonesia, Email: sriyuliharsini@yahoo.com) : Effect of e-glass fiber addition on mechanical properties of heat-polymerized acrylic resin denture base. J Evolution Med Dent Sci 2019, 8(12), 872-8.

Heat-polymerized acrylic resins are commonly used as denture base, but they have relatively low mechanical properties such as impact strength, transverse strength, and modulus of elasticity that made them susceptible to fracture during clinical application. Various modifications were made to improve the mechanical properties of heat-polymerized acrylic resins, one of them was with the addition of E-glass fiber. We wanted to determine the effect of E-glass fiber (chopped strands of 3 mm size) with 1 % and 1.5 % weight concentration addition on mechanical properties (impact strength, transverse strength, and modulus of elasticity) of heatpolymerized acrylic resin denture base material and the correlation between them. Ninety samples of heat-polymerized acrylic resin were divided into 9 groups, consisting of impact strength, transverse strength and modulus of elasticity testing group. Each testing group consisting of group without and with addition of 1 % and 1.5 % E-glass fiber. Impact strength test was performed using Charpy impact tester, while transverse strength and modulus of elasticity were performed using the Universal Testing Machine. After the test, fracture surface of the samples was evaluated and scanning electron microscope view was taken. The effect of E-glass fiber addition to impact, transverse strength and modulus of elasticity on heatpolymerized acrylic resin was analysed with one-way ANOVA statistical test. Pearson Correlation test was then performed to determine the correlation between impact, transverse strength and modulus of elasticity. There was an effect of E-glass fiber addition (chopped strands of 3 mm size) with 1 % and 1.5 % weight concentration to impact strength p=0.0001 (p<0.05); transverse strength p=0,002 (p<0,05); and modulus of elasticity p=0.002 (p<0.05). Pearson Correlation test showed that there was no correlation between impact and transverse strength (r=0.311 and p=0.094) (p>0.05); impact strength and modulus of elasticity (r=0.284 and p=0.128) (p>0.05); and transverse strength with modulus of elasticity (r= -0.044 and p=0.816) (p>0.05). Addition of 1 % and 1.5 % E-glass fiber can improve the impact strength, transverse strength, and modulus of elasticity of heatpolymerized acrylic resin denture base and the addition of 1 % E-glass fiber can increase a balanced of impact strength, transverse strength, and modulus of elasticity of heat-polymerized acrylic resin denture base.

4 illus, 4 tables, 31 ref

002242   RAGHUWANSHI S K, PANDEY P S (Electrical Engineering Dep, Indian Institute of Technology (Indian School of Mines), Dhanbad - 826 004) : Finite element method analysis of propagation in a non magnetic coupled waveguide structure having α-power refractive index profile. Indian J Pure Appl Phys 2019, 57(3), 188-95.

The work presented in the paper is a numerical study of a waveguiding component. The structure studied is a coupler consisting of three closely-coupled weakly-guiding one-dimensional waveguides. The refractive index profile of the coupler has been allowed to vary arbitrarily. The scalar finite element method (FEM) has been used to separately extract the TE and TM modes supported by this coupler and propagate them along the structure using a beam propagation method (BPM). We excite structure with Eigen mode profile which can be well approximated by Gaussian shape pulse. The effect of waveguide separation has been well demonstrated by using an example. The Crank-Nicolson (CN) scheme has been used to stabilize the propagation and transparent boundary conditions (TBC) which have been used to absorb energy leaked by the waveguides to the outer boundaries. The work’s main finding is that the coupling period of the structure can be changed by altering the index profile of the middle waveguide; step-, parabolic- and triangular-profile distributions have been studied and compared. In FEM analysis we have used the variable discretization step (δ) for the better accuracy of the results.

14 illus, 22 ref

002254   VISHWESHWARA P S, GNANASEKARAN N, ARUN M (Mechanical Engineering Dep, National Institute of Technology Karnataka, Mangalore, Karnataka - 575 025, Email: gnanasekaran@nitk.edu.in) : Simultaneous estimation of unknown parameters using a-priori knowledge for the estimation of interfacial heat transfer coefficient during solidification of Sn–5wt %Pb alloy—an ANN-driven Bayesian approach. Sadhana 2019, 44(4), 100.

The present methodology focuses on model reduction in which the prevalent one-dimensional transient heat conduction equation for a horizontal solidification of Sn–5wt%Pb alloy is replaced with Artificial Neural Network (ANN) in order to estimate the unknown constants present in the interfacial heat transfer coefficient correlation. As a novel approach, ANN-driven forward model is synergistically combined with Bayesian framework and Genetic algorithm to simultaneously estimate the unknown parameters and modelling error. Gaussian noise is then added to the temperature distribution obtained using the forward approach to represent real-time experiments. The hallmark of the present work is to reduce the computational time of both the forward and the inverse methods and to simultaneously estimate the unknown parameters using a-priori engineering knowledge. The results of the present methodology prove that the simultaneous estimation of unknown parameters can be effectively obtained only with the use of Bayesian framework.

18 illus, 9 tables, 47 ref

002240   LOH Z P, MO K H, TAN C G, YEO S H (Civil Engineering Dep, Malaya Univ, Kuala Lumpur, Malaysia, Email: khmo@um.edu.my) : Mechanical characteristics and flexural behaviour of fibre-reinforced cementitious composite containing PVA and basalt fibres. Sadhana 2019, 44(4), 98.

Fibre-reinforced cementitious composite (FRCC) is a type of composite that uses high volume of fibres to attain ductile properties. In this research, the effects of two different fibres, namely polyvinyl alcohol (PVA) and basalt, on the mechanical properties of FRCC such as compressive, splitting tensile and flexural strengths were investigated. The fibres were used in varying volume fraction, which includes 1.0 %, 1.5 % and 2.0 % and a hybrid combination of 1.5 % basalt fibre with 1.5 % PVA fibre for the preparation of the FRCC. The results showed that while the fibres had minimal effect on the compressive strength of FRCC, significant improvements in the splitting tensile and flexural strengths were found. In the comparison of the flexural performances, the introduction of PVA fibre in FRCC led to superior properties and it exhibited more ductile failure mode compared with basalt fibre and the optimum fibre dosage to be added was determined to be 1.5 %.

9 illus, 4 tables, 38 ref

002252   TUTAR M, AYDIN H, DURMUS A (Mechanical Engineering Dep, Bursa Uludag Univ, Bursa, Turkey, Email: hakanay@uludag.edu.tr) : The effect of duplex surface treatment on erosion performance of QRO 90 Supreme steel. Sadhana 2019, 44(4), 93.

In this study, CrN and TiAlN thin films were deposited on plasma-nitrided QRO 90 Supreme hot work tool steel by physical vapor deposition process and analysed with regard to their erosion performance under hydro-abrasive erosion conditions. The as-received specimens were quenched to room temperature from 1050$°$C and tempered gradually at 605$°$C for 2 h and at 560$°$C for 4 h. These specimens were plasma-nitrided for 10 h at 500 C at a pressure of 250 Pa in a gas mixture of 80 % N₂ + 20 % H2 and then coated with TiAlN or CrN coatings by cathode arc evaporation. The specimens were characterized by metallographic techniques, SEM, EDS and micro-hardness test. Plasma nitriding and duplex surface treatments significantly increased the hardness of the specimens and thus significantly reduced the erosion of the specimens. The hardnesses on the surface of plasma-nitrided, CrN-deposited and TiAlN-deposited QRO 90 steels were 1092 HV_0.025, 2436 HV_0.025 and 3578 HV_0.025, respectively. TiAlN-coated specimens were about 17-fold harder than the as-received specimens and over 3-fold harder than the plasma-nitrided specimens. The erosion resistance of CrN-coated specimens was increased by a factor of 3.6 and 1.5 compared with that of the as-received and plasma-nitrided specimens, respectively. A brittle fracture phenomenon was observed on the eroded surface of the duplex-treated specimens while a ductile material removal was observed on the as-received and the tempered specimens. The plasma-nitrided specimens showed a mixed behaviour of ductility and brittleness.

11 illus, 3 tables, 41 ref

002241   MAHTABI G, TARAN F (Water Engineering Dep, Zanjan Univ, Zanjan 45371-38791, Iran, Email: ghmahtabi@gmail.com) : Effect of weep hole and cut-off wall on hydraulic gradient and uplift pressure under a diversion dam. Sadhana 2019, 44(4), 92.

In hydraulic structures such as diversion or gravity dams constructed on a porous foundation, the difference in water levels between upstream and downstream results in water seepage through the porous soil under the dam. This seepage flow generates uplift pressure under the structure that may cause a crack on the concrete surface of the structure’s floor. In this condition, the exit gradient may exceed the critical value and cause the piping phenomenon. In this study, the effect of the weep hole and cut-off wall on the uplift pressure and the hydraulic gradient under a diversion dam was investigated experimentally and numerically. For this purpose, four weep holes (diameter = 1 cm) were embedded along the longitudinal axis of the stilling basin. The weep holes were examined in single and combined modes. The experiments were conducted in three upstream water heads of 10, 15, and 20 cm. The results showed that in terms of seepage losses, hydraulic gradient, and uplift pressure, the binary combinations of weep holes are better than the other modes. Among the binary combinations, the combination of the two closest weep holes to the dam toe (weep holes 1 and 2) had the most proper performance. In the supplementary experiments, a cut-off wall in two depths (10 and 15 cm) was placed at the dam heel in addition to the best modes of weep holes combination. Overall, the simultaneous use of cut-off wall (especially 15 cm) and weep holes improved the hydraulic condition of seepage phenomenon under the dam.

10 illus, 18 ref

002244   RAMESH N T, ARAKERI J H (Mechanical Engineering Dep, Indian Institute of Science, Bangalore - 560 012, Email: nikhilesh.tumuluru@gmail.com) : Actively and passively aspirated temperature sensors in a windless environment like greenhouses. Sadhana 2019, 44(4), 91.

Windless environments are prevalent in greenhouses, where precise temperature control is critical to the health of plants and errors in temperature measurement must be avoided. A mathematical model based on heat balance is used to estimate the error in temperature sensors under different conditions and sensor geometries. The model is then applied to two geometries and solved numerically. The sensors used are a T-type thermocouple and a Sensirion SHT 75. Experiments are carried out in a greenhouse prototype to replicate conditions in a greenhouse and validate the error model. Active ventilation of the sensors is provided by a fan and passive ventilation is provided using a model built on the concept of a ‘solar chimney’. It is shown that even small flow rates can decrease the error shown by unventilated sensors by as much as 10$°$C.

11 illus, 3 tables, 8 ref

002243   RAI S, TRIPATHY P, NAYAK S K (Electrical and Electronics Engineering Dep, National Institute of Technology Nagaland, Dimapur, Nagaland 797 103, Email: rai.shekha@gmail.com) : Using sparsity to estimate oscillatory mode from ambient data. Sadhana 2019, 44(4), 90.

In this paper, a sparse-technique-based representation of the signal over a learned dictionary and random decrement technique are explored to extract the oscillatory mode from the ambient data. The main contribution of the present work is to design a dictionary and compute the coefficients that best represent the clean signal to estimate the modes. In this work, the noise embedded in the ambient signal is minimized by representing the ambient signal in sparse domain with respect to the dictionary. Comparison between the proposed method and other methods such as nonlinear filtering, etc., has been done on the test signal, two-area power system on the data generated through simulation in Matlab, two-area data simulated on real-time digital simulator and real measurement from Phasor data concentrator (PDC) of Indian power system and Western Electricity Coordinating Council (WECC) network.

6 illus, 7 tables, 31 ref

002248   SAI C Y, MOKHTAR N, YIP H W, BAK L L M, HASAN M S, AROF H, CUMMING P, ADENAN N A M (Electrical Engineering Dep, Malaya Univ, Kuala Lumpur, Malaysia, Email: norrimamokhtar@um.edu.my) : Objective identification of pain due to uterine contraction during the first stage of labour using continuous EEG signals and SVM. Sadhana 2019, 44(4), 87.

This study aimed to assess the utility of electroencephalography (EEG) as an objective marker of pain during the first stage of labour. EEG and cardiotocography (CTG) data were obtained from 10 parturient women during their first stage of labour. The study subjects reported the extent of their pain experienced due to uterine contractions, which were recorded by the CTG tracing. Simultaneous 16-channel EEG traces were obtained for spectral analysis and a subsequent machine learning classification using Support Vector Machine (SVM) aiming to predict the pain experienced in relation to uterine contractions. It was found that pain due to uterine contraction correlated positively with relative delta and beta band activities and negatively with relative theta and alpha band activities of the EEG signals. SVM using the spectral activities, statistical and non-linear features of the EEG classified the state of pain with 83% accuracy using a classification model generalizable across subjects. Furthermore, dimension reduction using Principal Component Analysis (PCA) successfully reduced the number of features used in the classification while achieving a maximum classification accuracy of 84%. Continuous EEG affords the means to assess objectively maternal pain experienced during the active contraction phase of the first stage of labour. Monitoring of the pain experience using EEG signals may complement the clinical decision-making process behind administration of epidural anaesthesia during labour. We envision future studies to investigate EEG markers of pain in other clinical states, aiming to generalize the use of EEG as an objective method of pain assessment.

10 illus, 4 tables, 44 ref

002250   SARAVANAKUMAR J, SHAMEEM C A, VENKATESH T N (CTFD Div, CSIR-National Aerospace Laboratories, Bengaluru - 560 017, Email: tnv@nal.res.in) : Development of a potential vortex-hazard index to predict cruise-level wake turbulence encounters. Sadhana 2019, 44(4), 86.

A pair of counter-rotating trailing vortices formed as a consequence of lift generation poses a potential threat to the encountering aircraft. In recent years, incidents/accidents involving wake turbulence confrontation at cruise altitude are increasing due to increase in the number of super-heavy category aircraft. The vertical separation distance between two airplanes guided by the Federal Aviation Administration (FAA) could be inadequate in certain cases. In this article, a new approach has been proposed to predict the probable area of the persistence of trailing vortices produced by large aircraft. It includes the development of an index with multiple atmospheric effects on the vortices. Also, the impact of the wake from a distinct airplane is incorporated. The performance assessment of the index in predicting the cruise-level wake vortex encounters has been made using various scenarios that happened in the recent past. Weather Research and Forecasting (WRF) model is employed to simulate the atmospheric flow conditions of chosen situations. We found that the method successfully predicts all the cases considered in this study.

16 illus, 2 tables, 31 ref

002253   VERMA A, SAXENA R K (Mechanical Engineering Dep, Sant Longowal Institute of Engineering and Technology, Longowal, Sangrur - 148 106, Email: rksaxena04@yahoo.com) : A new method to generate artificial microstructure of dual phase steel using Teacher-Learner Based Optimization. Sadhana 2019, 44(4), 85.

The dual phase steels are widely used in the manufacturing and automobile industry. The micromechanical analysis of the dual phase steel using microstructure based representative volume elements is the effective methodology for the estimation of its macroscopic properties. The real microstructure of the dual phase steels obtained using different microscopic analysis methods depicts the two main constituents viz. martensite inclusion in the ferrite matrix. The distribution of martensite in ferrite matrix exhibits a number of control parameters to define its characteristics. Generation of the artificial microstructure of dual phase steel based on these controlling parameters is advantageous to get a-priori estimate of the macroscopic properties and behavior. In the present work, a model is proposed for predicting the artificial microstructure of dual phase steel. The volume fraction of martensite and connectivity of the martensite in the ferrite matrix are used as controlling parameters to generate the artificial microstructure using the Teacher-Learner Based Optimization algorithm. The model has effectively predicted the microstructure of the DP590 steel. The artificial microstructure is applied for getting the tensile flow curve of the material using the finite element method. The predicted tensile response of the material is in good agreement with the experimental observations for DP590 steel. The model can be effectively applied to predict the artificial microstructure and subsequent micromechanical analysis of the dual phase steels.

23 illus, 2 tables, 55 ref

002237   GUPTA A, GHOSH A (Aerospace Engineering Dep, Indian Institute of Technology Kharagpur, Kharagpur - 721 302, Email: anup@aero.iitkgp.ac.in) : NURBS-based thermo-elastic analyses of laminated and sandwich composite plates. Sadhana 2019, 44(4), 84.

Present research work is based on the unique properties of isogeometric analysis (IGA) like smarter, faster and cheaper analysis for the thermo-elastic bending of laminated and sandwich composite plates. IGA, based on isoparametric concept, is a breakthrough in the area of structural analysis, which employs non-uniform rational B-spline (NURBS) as a basis function to represent less erroneous geometry. Unlike finite-element method (FEM), increasing the polynomial order in IGA gives higher continuous basis functions naturally and easily with reduced computational cost. A procedure has been developed for thermo-elastic bending analysis of laminated composite plates and sandwich structures using IGA approach. The developed NURBS-based code is validated and computational efficacy of thermo-elastic analysis is investigated. A detailed parametric study has been carried out for the quadratic, cubic and quartic NURBS elements with respect to the variation of temperature. Different types of temperature profiles have been considered. Change of deflections, stresses and moment resultants are analysed with an aim to understand the thermo-elastic behaviour of laminated and sandwich composite plates. Several thermo-elastic numerical examples have been analysed extensively. Obtained numerical results are compared with available literature to show the advantage of current formulation.

11 illus, 12 tables, 37 ref

002239   JAMUNAA D, MAHANTI G K, AL ATTAR F N H (Electronics and Communication Engineering Dep, National Institute of Technology, Durgapur - 713 209, Email: gautammahanti@yahoo.com) : Design of phase-only reconfigurable planar array antenna in selected phi cuts using various meta-heuristic optimization algorithms. Sadhana 2019, 44(4), 83.

In this paper, a pattern synthesis based on a multiobjective optimization algorithm is proposed for the generation of a reconfigurable pencil/flat top dual-beam planar antenna array built using isotropic antenna elements in selected phi cuts. These beams claim the same amplitude excitations and differ from each other in phase excitations. Zero-phase excitations are used in pencil beam and these phases are updated with optimum phases for the flat top beam. All the excitations are obtained using Moth–flame optimization algorithm. With the support of the fitness functions, care is taken to control the expected values of the radiation pattern parameters to remain under certain fixed limit. In addition, synthesis is also done for the provision of a null in a particular direction for rejection of interference in the pencil beam in two different phi cuts. To suppress the mutual coupling effects, dynamic range ratio is kept under a threshold limit. Simulation results show the effectiveness of this proposed synthesis for phi cut planes. This algorithm is compared and proved to be better in many aspects over the standard meta-heuristic algorithms like Artificial Bee Colony and Imperialist Competitive algorithms in terms of performance parameters.

9 illus, 4 tables, 24 ref

002236   GULERIA A, SWAMI D, SHARMA A, SHARMA S (Indian Institute of Technology Mandi, Kamand - 175 005, Email: abhayguleria92@gmail.com) : Non-reactive solute transport modelling with time-dependent dispersion through stratified porous media. Sadhana 2019, 44(4), 81.

We present a numerical solution of the mobile–immobile model (MIM) with time-dependent dispersion coefficient to simulate solute transport through heterogeneous porous media. Observed experimental data of non-reactive solute transport through hydraulically coupled stratified porous media have been simulated using asymptotic and linear time-dependent dispersion functions. Non-Gaussian breakthrough curves comprising long tails are simulated well with the MIM incorporating asymptotic time-dependent dispersion model. The system is under the strong influence of physical nonequilibrium, which is evident by variable mass transfer coefficient estimated at different down-gradient distances. Asymptotic time-dependent functions are capable of capturing the rising limb of the solution phase breakthrough curves with improved accuracy, whereas tailing part simulation capabilities are similar for both asymptotic and linear time-dependent dispersion functions. Further, the temporal moment analysis demonstrated increased spreading, variance for linear dispersion model as compared with asymptotic dispersion model. It is also observed that the first-order mass transfer coefficient varies inversely with travel distance from the input source. It can be concluded from the study that MIM with time-dependent dispersion function is simpler yet sensitive to account for medium’s heterogeneity in a better manner even for small observation distances from the source.

9 illus, 2 tables, 53 ref

002251   SONI R P, GAVARA M R (Mechanical Engineering Dep, Indian Institute of Technology Guwahati, Guwahati - 781 039, Email: gmadhu@iitg.ac.in) : Mixed convection heat transfer of water about a vertical surface of variable heat flux with density inversion. Sadhana 2019, 44(4), 80.

Laminar mixed convection boundary layer flow of water about a vertical plate is studied including density inversion effects. The plate surface is subjected to an arbitrary heat flux that is a function of vertical distance from the leading edge. Both aiding and opposing mixed convection situations are considered in the study. The dimensionless forms of stream function and temperature are expanded in terms of perturbation elements and universal functions. The differentials of the heat flux, which are functions of vertical distance, are used as perturbation elements to obtain universal functions. The results for universal functions required to find temperature and velocity profiles are obtained. The obtained universal functions are valid for any arbitrary wall heat flux variation. The universal applicability of results is demonstrated for power-law variation of wall heat flux. The velocity and temperature variation, boundary layer thickness, Nusselt numbers and skin friction coefficient are presented for various values of mixed convection parameter, wall flux power index, for both aiding and opposing mixed convection. For a given combination of Grashof and Reynolds numbers, the heat transfer rates and skin friction coefficient are found to increase almost linearly with wall flux power index, in the parameter range of the study, for both the cases of aiding and opposing mixed convection. The present results of special cases are found to match well with the results available in the literature.

14 illus, 5 tables, 26 ref

002234   DAS B, PAL S, BAG S (Mechanical Engineering Dep, Indian Institute of Technology Guwahati, Guwahati - 781 039, Email: swarupbag@iitg.ac.in) : Probing defects in friction stir welding process using temperature profile. Sadhana 2019, 44(4), 79.

Detection of defects in friction stir welding process is a challenging task since most of the defects are internal or subsurface. An attempt has been made to explore the methodologies based on temperature signal for possible detection of defects in friction stir welding process using different tool profiles. The presence of defect is affected by temperature diffusion and is better reflected by the change of temperature over time. Temperature signals are acquired using thermocouples inserted in specific locations on advancing and retreating side of the welds. The rate of change of temperature and wavelet-analysis-based indicator computed from temperature signal against each experiment reveal appreciable difference for defective and defect-free welds. Threshold values are computed that clearly set a boundary for classifying the defective welds from defect-free welds. The proposed approaches can effectively reduce the post-processing steps essential for other nondestructive evaluation of the welds and can work as a first level of safeguard in the identification of defects during friction stir welding process. The methodologies can be extended towards monitoring of the process in industrial applications.

5 illus, 1 table, 32 ref

002235   GAJBHIYE N L, ESWARAN V (Mechanical and Aerospace Engineering Dep, Indian Institute of Technology Hyderabad, Hyderabad - 502 285, Email: eswar@iith.ac.in) : Effect of radial magnetic field on the natural convection in a semi-circular curved enclosure for different aspect ratios. Sadhana 2019, 44(4), 78.

The problem of natural convection in a (2D) semi-circular curved enclosure in the presence of a radial magnetic field is numerically studied in this paper. The selected configuration is such that the convective flow is driven by a mean temperature gradient also directed radially, and the effects of enclosure aspect ratio and the strength of the applied magnetic field are considered. Numerical simulations are carried out using a (3D) MHD code developed by our research group, first at a fixed Ra = 10⁵ and Pr = 0.71 for aspect ratios A = 2, 4, 6, 8 and Hartmann numbers in the range Ha = 0-100. As the aspect ratio is increased, a Rayleigh– Be´nard-like convection with the convective cells formed near the symmetric central portion of the enclosure, where the mean temperature gradient is anti-parallel to the gravity, is found to be triggered. Except at the transition, the effect of the imposed radial magnetic field is found to decrease the fluid motion in general, and the convective motion is completely suppressed at Ha = 100 irrespective of the aspect ratio. The critical Hartmann number for the onset of (R–B-like) convection is found to decrease with an increase in the aspect ratio. Numerical simulations are also attempted at a fixed A = 10 and Ra = 8000 for Prandtl numbers Pr = 10, 0.1, 0.01 and Hartmann numbers Ha = 0, 3, 6, 9, 12. In the absence of the applied magnetic field, the flow is found to exhibit periodic oscillations of increased amplitude and time-period when Pr is decreased, except at Pr = 10, where a steady-state solution is found. For Pr = 0:01, the oscillatory flow is observed to persist even when the magnetic field strength is increased in the range Ha = 3-12. Moreover, the temporal frequency of these flow oscillations is found to be nearly the same for Ha$\le$9.

17 illus, 1 table, 17 ref

002238   HEYDARI F, AMADEH A A, OJO O O, HASANNIYA M H, TAMIZIFAR M (Federal Univ of Technology Akure, Akure, Nigeria, Email: ojooladimeji90@yahoo.com) : Microstructure and mechanical properties of autobody steel joined by friction stir spot welding. Sadhana 2019, 44(3), 73.

This work investigates the microstructural features and mechanical properties of joints of lowcarbon steel friction stir spot welded by changing tool rotational speed and dwell time. Microstructural evaluation, peeling, tension-shear and micro-hardness tests were employed to characterize the properties of the welded joints. The results show that an increase in the tool rotational speed promotes the formation of more weld flash, and it equally changes the flash morphology from ring flash to a combination of ring and serrated flashes. A fine immediate tool contact region is formed in the stir zone (SZ) and the width of the ITCR increases with the tool rotational speed and tensile-shear failure load. Besides the ITCR, the SZ uniquely consists of the shoulder undersurface region (SZ I) and vortex region (SZ II) with average grain sizes of about 10.9 and 16.66 $\mathrm{\mu }$m, respectively. An increase in tool rotational speed improves the micro-hardness, and the average diameter of the weld nugget (from 4.5 to 5.5 mm). Base metal–nugget interface failure (650 rpm) and base metal neckinginduced failure (1250 rpm) are the two forms of weld failure obtained in the welded samples.

10 illus, 2 tables, 36 ref

002247   SAHIN Y, TING N S (Electrical Electronics Engineering Dep, Bitlis Eren Univ, Bitlis, Turkey, Email: eee.yakupsahin@gmail.com) : Design and application of a novel snubber cell for soft switched PWM DC–DC converters. Sadhana 2019, 44(3), 71.

This paper introduces a novel active snubber cell for soft switching PWM DC–DC converters. In the proposed converter, the main switch is turned on under zero voltage transition (ZVT) and turned off under zero voltage switching (ZVS). The auxiliary switch and all of the other semiconductors in the converter are turned on and off with soft switching (SS). There is no extra voltage stress on the semiconductor devices. Besides, the proposed converter has simple structure and ease of control due to common ground. In this treatise, the theoretical and mathematical analysis of the proposed converter are presented and the design procedure of converters is also provided. The simulation study at 100 kHz switching frequency and 600 W output power are conducted. The experimental prototype of converter is operated under same conditions. Both the simulation and the experimental prototype exhibits similar performances. Ultimately, the efficiency of the proposed converter is 95.7 % at nominal power.

8 illus, 4 tables, 26 ref

002255   WU S, GONG S, GAO H (Harbin Institute of Technology, Harbin 150001, People’s Republic of China, Email: gaohm@hit.edu.cn) : Arc characteristics of GTAW under high pressure. Sadhana 2019, 44(3), 70.

The characteristics of GTA (gas tungsten arc) under high pressure has been studied in this paper to reveal the special arc phenomenon from the ambient pressure. A totally new hyperbaric GTAW experiment system has been built, including a hyperbaric environment simulator (0.1-3.5 MPa), an automatic GTAW machine with cooling, the moving equipment, a camera with filter and a central control unit. The arc morphology, the electric static characteristic, the arc voltage and arc length are studied with the increment of ambient pressure from 0.1 to 3.5 MPa, respectively. The relationship between the ambient pressure and the arc voltage is deduced according to the balance of heat-input and heat-output. The deduced function also verified the results from the welding experiment.

9 illus, 1 table, 16 ref

002256   YADAV S, PATHAK V K, GANGWAR S (Mechanical Engineering Dep, Madan Mohan Malaviya Univ of Technology, Gorakhpur, Uttar Pradesh - 273 016, Email: sukritiyadav09@gmail.com) : A novel hybrid TOPSIS-PSI approach for material selection in marine applications. Sadhana 2019, 44(3), 58.

Selection of material in engineering design process is a difficult and elusive task due to enormous number of dissimilar materials availability. For effective selection of materials, the designers have to take into account a number of definite qualitative and quantitative criteria. In the same context, this paper proposes a hybrid TOPSIS-PSI approach for effective material selection in marine applications. In this paper, the selection index value has been calculated by using logical combination of PSI and TOPSIS algorithm and these values have been ranked in ascending or descending order. The highest preference selection index value has been taken as the best alternative for the marine application. To prove the effectiveness of the proposed hybrid TOPSIS-PSI algorithm, two practical examples are considered and the result shows that the proposed procedure provides satisfactory results when compared with past literature. Furthermore, hybrid procedure is performed for selection of best wt.% combination among hybrid aluminum nanocomposites for marine applications based on its physical, mechanical and corrosive behavior. The result reveals that 9 wt.% and 6 wt.% reinforced hybrid aluminum nanocomposites have optimum combination of all physical, mechanical and corrosion properties, respectively according to hybrid TOPSIS-PSI approach.

3 illus, 19 tables, 35 ref

002249   SAMADI E, ALIPOOR G (Electrical Engineering Dep, Hamedan Univ of Technology, Hamedan 6516913733, Iran, Email: samadi@stu.hut.ac.ir) : Efficient band selection for improving the robustness of the EMD-based cepstral features. Sadhana 2019, 44(3), 54.

Mel-Frequency Cepstral Coefficients (MFCC) are features widely and successfully used for various speech processing applications. These features are extracted using Fourier transform. However, this transform suffers from some crucial restrictions when used for analyzing nonlinear and non-stationary signals such as speech. To address this problem, in the present study, we investigate the application of Empirical Mode Decomposition (EMD) in extracting more efficient and robust features for automatic gender identification. In particular, in the proposed approach, the speech signal is first decomposed into a set of narrow-band oscillatory modes, using EMD, from which mel-frequency cepstral features can be extracted. On the other hand, multi-band decomposition of all modes results in some redundant and even irrelevant features that can degrade the performance of the classification. Therefore, we propose to efficiently select the most discriminative frequency bands over all modes. The minimal-redundancy-maximal-relevance (mRMR) feature selection algorithm is also examined for this purpose. The proposed EMD-based features are then extracted by applying DCT on log power values calculated over the selected mel-scale bands of the IMFs. Simulation results show that, using the proposed features for automatic gender identification considerably improves the performance of the system, in particular in noisy environments.

6 illus, 4 tables, 20 ref

002246   ROY R (Electronics and Electrical Communication Engineering Dep, Indian Institute of Technology, Kharagpur - 721 302, Email: rajatroy@ece.iitkgp.ac.in) : Brief report: Extremely dense general relativistic polytropes of index n = 1. Pramana – J Phys 2019, 92(4), 63.

Polytropic gas spheres of index 1 and extremely high central densities are analysed with the help of general relativistic field equations. Parameters such as the radius and mass are calculated for different central densities. The limiting values of these quantities are obtained and the physical nature of sound waves in these bodies is verified.

1 table, 13 ref

002245   RAZAVI S M, ZAHIRI S H, KARIMI S (Electrical Engineering Dep, Neyshabur Univ, Neyshabur, Iran, Email: razavi@neyshabur.ac.ir) : Electrical features in AlGaN/GaN high electron mobility transistors with recessed gate and undoped region in the barrier. Pramana – J Phys 2019, 92(4), 56.

This study considers electrical parameters of AlGaN/GaN high electron mobility transistor (HEMT) with the recessed gate and un-doped region (URG-HEMT) in the barrier layer. We have investigated the main electrical factors such as the lateral electric field, breakdown voltage (V_B), drain current (I_D), threshold voltage (V_T), output conductance (g_o) and gate capacitance (C_g). Simulation findings compare these parameters in the single heterostructure (SH-HEMT), recessed gate (RG-HEMT) and the proposed (URG-HEMT) structures. Regarding the simulation outcomes, the maximum lateral field in the URG is less than those in the SH and RG HEMTs. This improves the breakdown voltage of the suggested device up to 160 V, while the breakdown voltage in the SH and RG transistors is about 90 V. Therefore, breakdown voltage of the reported device is about 80% larger than that of the other transistors. Also, undoped region in the novel transistor reduces the output conductance and gate-to-drain capacitance. But, the recessed gate and undoped regions in the URG structure decrease in 2-DEG electron density and then reduce drain current.

6 illus, 20 ref

000995   CHOI I-C, KIM H C (Chemical Engineering Dep, Hoseo Univ, Chungnam 31499, Republic of Korea, Email: heonchan@hoseo.edu) : A study on decomposition of environmentally noxious gas with simultaneous synthesis of metal oxide powder in transferred DC thermal plasma. Asian J Chem 2019, 31(2), 449-52.

Carbon dioxide was directly decomposed by a transferred DC thermal plasma and the effects of plasma induced current on the decomposition efficiency were investigated. The thermal plasma system was operated in a way that the metal oxide particles could be simultaneously produced from an anodic bulk metal (Zn) placed on a carbon crucible, so as to continuously consume atomic and molecular oxygens (O and O₂) generated from the CO₂ decomposition. As the induced current increased from 120 to 160 A by 20 A, the decomposition efficiency increased almost linearly from 53 to 68 %. The amount of ZnO particles produced from the bulk also increased and the particle crystallinity was improved. Although the concentration of carbon monoxide in the effluent was sharply increased at 160 A, further destruction can be done by re-circulating the effluent to plasma chamber.

5 illus, 10 ref

001070   REDDY M C S, SRIDEVI K, JAHAN S M S, REDDY G V S (Basic Sciences Dep, G.P.R. Engineering Coll (Autonomous), Kurnool - 518 007, Email: mcsr.gprec@gmail.com) : Aqueous solubility enhancement and desorption of Sudan III dye from contaminated soil using plant based natural surfactant. Asian J Chem 2019, 31(1), 89-98.

A plant based natural surfactant was extracted from fruit pericarp of Sapindus mukorossi, commonly known as soap nuts. The natural surfactant was used for the treatment of the soils which were contaminated with hydrophobic organic compounds like organic dye, Sudan III and the dye was removed/recovered from the soils. This biosurfactant has great advantages when used in environmental remediation as it is environment friendly in nature. Using a simple water extraction of fruit pericarp powder, the natural surfactant was prepared. The natural surfactant solutions were employed to enhance the aqueous solubility of hydrophobic organic compounds like organic dye, Sudan III and to desorb organic dye Sudan III from contaminated soils in batch experiments. The performance of natural surfactant for the removal of Sudan III was compared with that of commercial surfactants like sodium dodecyl sulphate (SDS) (anionic surfactant), cetyltrimethylammonium bromide (CTAB) (cationic surfactant) and Triton X-100 (TX 100) (non-ionic surfactant). The aqueous solubility enhancement of Sudan III dye in presence of 0.04 M of NaCl was increased in case of non-ionic surfactants like natural surfactant (NS) and TX 100. The solubility of Sudan III dye in presence of 0.04 M of NaCl was decreased in case of ionic surfactants like SDS and CTAB. The desorption behaviour observed for natural surfactant was similar to TX 100 solutions. The natural surfactant solution performance was more or less similar to synthetic surfactants and the removal capacity of surfactant was given in increasing order as TX 100 > NS > SDS > CTAB.

11 illus, 5 tables, 49 ref

001067   RANI A, SURESH S, KUMAR A (Chemical Engineering Dep, Maulana Azad National Institute of Technology, Bhopal - 462 003, Email: sureshpecchem@gmail.com) : Different techniques for separation of Brackish water. Asian J Chem 2019, 31(1), 9-17.

The lack of water is usually depicted in volumetric or absolute terms. The most scarcity studies focus on how the 'problem' of scarcity is raised, therefore to overcome this issue the first step is heating of an air stream by using solar energy for heating of an air stream and in the next step to seawater adding into the hot air in imperative to moisten, then final step is a humid air cooling providing potable water as a condensate. The conventional technique for seawater desalination is to vapourize salty water and afterward condense the rising vapour being free of salt. Using fossil fuels as an energy source, these desalination plants are planned as multi-stage evaporator plants. This technique is the foundation for a day-to-day production of million cubic meters of water. This review is focused on the performance analysis of different techniques such as multistage flash distillation, multi-effect distillation, vapour-compression distillation, solar humidification, electrodialysis reversal, reverse osmosis, nanofiltration, forward osmosis, solar desalination for separation of brackish water. Based on literature discussion with their remarks from different techniques, solar desalination has achieved 87 % of efficiency and lower the total dissolved solids content as 40 ppm. Moreover, cost of distilled water per liter $ 0.029 from solar desalination plant. With this advantages, solar desalination has more attractive technique while compare to other towards better future and balanced eco-system.

12 illus, 1 table, 34 ref

001043   MOHADESZADEH M, KARIMPOUR A, PARIZ N (Electrical Engineering Dep, Ferdowsi Univ of Mashhad (FUM) Campus, Mashhad, Khorasan Razavi, Iran, Email: n-pariz@um.ac.ir) : Synchronisation of fractional-order complex systems and its application. Pramana – J Phys 2019, 92(2), 29.

In this paper, a passive control scheme based on the fractional-order calculus is proposed. We study the modified complex projective synchronisation between two identical fractional-order complex chaotic systems, and its application in the secure communication. The fractional-order complex chaotic Lorenz system is employed to encrypt the emitted signal. In the transmitter module, the information signal is modulated into one parameter of the Lorenz system. It is assumed that the same parameter is unknown in the receiver module. In order to synchronise two systems with different initial conditions, the controllers and an appropriate parameter update rule are designed. Theoretical analysis and numerical simulations show that this method is feasible and robust to some extent in the presence of channel noise.

9 illus, 37 ref

001060   PRAKASH P, SINGH J P, ROY B K (Electrical Engineering Dep, National Institute of Technology, Silchar - 788 010, Email: pankaj.prakash988@gmail.com) : Fractional-order memristor-based chaotic system with a stable equilibrium point, its fractional-order PI-based sliding mode control and switching synchronisation. Pramana – J Phys 2019, 92(2), 19.

In this paper, we discuss a new fractional-order memristor-based three-dimensional chaotic system with a stable equilibrium point. The proposed system belongs to the category of hidden attractors dynamical system. The system is new in the sense that it is a fractional-order memristor-based chaotic system and exhibits hidden attractors. The chaotic behaviour of the system is accessed by various numerical techniques such as Lyapunov exponents, bifurcation diagrams, instantaneous phase plot, attractor analyses and frequency spectrum plots. A fractional-order proportional integral (PI)-based sliding mode control is designed for chaos suppression of the proposed system. Further, the switching synchronisation of the new system in the form of the master and the slave systems is presented.

16 illus, 1 table, 32 ref

001009   GHIASI E K, SALEH R (Mechanical Engineering Dep, Islamic Azad Univ, Mashhad, Iran, Email: r-saleh@mshdiau.ac.ir) : Nonlinear stability and thermomechanical analysis of hydromagnetic Falkner–Skan Casson conjugate fluid flow over an angular–geometric surface based on Buongiorno’s model using homotopy analysis method and its extension. Pramana – J Phys 2019, 92(1), 12.

This paper aims to provide stability and thermomechanical analysis of hydromagnetic Falkner–Skan Casson conjugate fluid flow over an angular–geometric wedge-shaped surface. Based on the Buongiorno’s model, the governing boundary-layer equations are derived and solved iteratively using the homotopy analysis method (HAM). Furthermore, the HAM-series solution is optimised by minimising its squared residual errors. It is shown that the proposed approach can serve as an efficient criterion for accurately solving nonlinear problems.

12 illus, 7 tables, 40 ref

001080   SIMO H, DOMGUIA U S, DUTT J K, WOAFO P (Mechanical Engineering Dep, Indian Institute of Technology Delhi, Hauz Khas, New Delhi - 110 016, Email: hsimo2015@yahoo.fr) : Analysis of vibration of pendulum arm under bursting oscillation excitation. Pramana – J Phys 2019, 92(1), 3.

We investigate numerically the responses of the single pendulum and double pendulum arms coupled to a nonlinear RLC-circuit shaker through a magnetic field. These systems can be used to build a robotic device or an automat. The nonlinear RLC circuit is a Duffing oscillator that generates electric bursting oscillations. We first examine the dynamical behaviour of the single pendulum arm. Time series shows that the pendulum arm exhibits bursting oscillation. When the natural frequency w₂ < 1, the shape of the bursting in the electrical part is different from that observed in the pendulum arm and if w₂ > 1, the shape is the same. We then explore the behaviour of a double pendulum arm powered by electric bursting oscillations. Time series are also used to explore the behaviour of each pendulum arm. The results show that the displacement of each pendulum arm undergoes bursting oscillations resulting from the transfer of the electronic signal. The shape of bursting of the first pendulum is different from that of the second pendulum for some values of w₁. The shape, period and amplitude of the bursting oscillations depend on various control parameters.

6 illus, 8 tables, 34 ref

000998   DAS R, BAISHYA S (Electronics and Communication Engineering Dep, National Institute of Technology, Silchar - 788 010, Email: rajashree18das@gmail.com) : Analytical modelling of electrical parameters and the analogue performance of cylindrical gate-all-around FinFET. Pramana – J Phys 2019, 92(1), 2.

This paper presents the cylindrical gate-all-around (GAA) silicon on insulator (SOI) FinFET, which not only eliminates the corner effect but also shows high on-drain current (I_ON) ($~$10⁻² A), low leakage current (I_OFF) ($~$10⁻¹⁰ A), high I_ON/I_OFF (10⁸ > 10⁶) and reduced subthreshold swing (SS) (64.55 mV/dec, which is nearest to the Boltzmann limit of 60 mV/dec). To have a better understanding of the working principles, analytical modelling of electrical parameters such as surface potential, threshold voltage, drain current and SS has been carried out by solving two-dimensional Poisson’s equation using superposition principle. The behaviour of threshold voltage, drain current and SS has been investigated for different dimensional and electrical parameters such as channel lengths, channel radius, gate work functions, dielectric constants, drain-to-source voltages and channel concentrations. The physics-based models have been cross-examined with extracted three-dimensional TCAD simulation results. The modelled values show good agreement with the simulated data. Moreover, analogue performances such as transconductance, output conductance, intrinsic gain and gate capacitance for different channel lengths and radii of the presented device are also studied.

19 illus, 1 table, 33 ref

001103   YUAN H, PAN Y, LIU X (Zhengzhou Univ, Zhengzhou 450002, People’s Republic of China, Email: Xianhu.liu@zzu.edu.cn) : Large-scale formation of shish-kebab in water-assisted injection-moulded high-density polyethylene with a high-molecular weight. Bull Mater Sci 2019, 42(1), 40.

To promote flow-induced orientation and reserve the formation of the shish-kebab structure, a modified injectionmoulding technology named water-assisted injection moulding (WAIM), was applied to provide twice the shear flow and a rapid cooling rate on high-molecular weight high-density polyethylene (HDPE) melt in a mould cavity. Large-scale distribution of highly oriented shish-kebab was successfully achieved in a WAIM sample with a high-molecular weight. More importantly, the high-orientation degree of lamellae (larger than 0.4) in the thickness direction for a high-molecular weight WAIM sample is > 60 %, which is much more than a conventional injection-moulded sample (15 %). This work provides a new insight to achieve injection-moulded products with enhanced oriented structures.

4 illus, 1 table, 31 ref

001024   KAVIMANI V, PRAKASH K S, THANKACHAN T (Mechanical Engineering Dep, Anna Univ Regional Campus, Coimbatore - 641 046, Email: manikavi03@gmail.com) : Investigation of graphene-reinforced magnesium metal matrix composites processed through a solvent-based powder metallurgy route. Bull Mater Sci 2019, 42(1), 39.

In the present investigation, AZ31 alloy is homogeneously reinforced with 0.2, 0.3, 0.4 and 0.5 wt % of reduced graphene oxide (r-GO) nanosheets for the first time through a series of methodologies involving solvent processing, mechanical alloying, cold pressing and finally sintering under argon atmosphere at 560$°$C. Scanning Electron Microscopy (SEM) assisted with energy-dispersive X-ray analysis revealed that this inventive fabrication route is useful to easily disperse r-GO into the matrix material and thereby attain methodical homogeneity with a uniform particle size. The attained results show that amongst the others, addition of 0.4 wt % r-GO have obviously improved the hardness up to 64.6 HV and also yielded a better inhibition efficiency of 84 % on corrosion. Any further increase of r-GO content resulted for significant decrease in the wear rate up to the level of 2.6 mm³ Nm⁻¹.

9 illus, 2 tables, 28 ref

001099   WU C Y, CHEN J H, KUO C G, TWU M J, PENG S W, HSU C Y (Mechanical Engineering Dep, Lunghwa Univ of Science and Technology, Taoyuan 33306, Taiwan, Email: cyhsu@mail.lhu.edu.tw) : Effects of deposition parameters on the structure and properties of ZrN, WN and ZrWN films. Bull Mater Sci 2019, 42(1), 38.

This paper examines optimal settings for deposition parameters for transition metal nitride (ZrN, WN and ZrWN) thin films that are deposited on tungsten carbide tools and glass substrates using direct current (DC) reactive sputtering with pure Zr and W metal targets and Ar plasma and N₂ reactive gases. Experiments using the grey-Taguchi method are conducted to study the effects of deposition parameters (substrate plasma etching time, N₂/(N₂ + Ar) flow rate, deposition time and substrate temperature) on a film that is deposited on a cutting tool that is used for dry machining and on the films’ mechanical properties. The substrates’ surfaces are etched using oxygen plasma pretreatment. It is clear that the coated film is homogeneous, very compact and exhibits perfect adherence to the substrate. The results of grey relational analysis show for the dry turning AISI 304 stainless steel that the surface roughness is approximately R_a = 0.70 μm and that the flank wear is approximately 14.02 μm. The grey relational analysis shows that the period for which the substrate (tungsten carbide tool) is under plasma-etched pretreatment has the most significant effect on both the surface roughness and flank wear. The coated films are analysed using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction and a nano-indenter. The ternary nitride (ZrWN)-coated specimens exhibit better mechanical properties than binary nitride (ZrN and WN) specimens. The optimum ZrWN coating exhibits the greatest hardness (H), elastic modulus (E) and H/E values.

9 illus, 10 tables, 20 ref