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      Volume 44, Issue 6

      June 2019

    • Aerodynamic shape optimization of airfoils at ultra-low Reynolds numbers

      MEEDHU GEOGY UKKEN M SIVAPRAGASAM

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      The flow over NACA 0008 airfoil is studied computationally in the ultra-low Reynolds number regime Re ∈ [1000, 10000] for various angles of attack α ∈ [0°, 8°]. The laminar flow separation occurs even atlow angles of attack in this Reynolds number regime. The lift curve slope is far reduced from the inviscid thin airfoil theory value of Clα = 2π Significant increase in the values of drag coefficient is seen with a decrease in Re. Lift-to-drag ratios are consequently very low. An adjoint-based aerodynamic shape optimization methodology is employed to obtain improved aerodynamic characteristics in the ultra-low Re regime. Three differentobjective functions are considered, namely, (i) minimization of drag coefficient, Cd, (ii) maximization of lift coefficient, Cl, and (iii) maximization of lift-to-drag ratio, (Cl/Cd). Significant improvement in each of the objective functions is obtained.

    • Design and analysis of dual band implantable DGS antenna for medical applications

      B PRUDHVI NADH B T P MADHAV M SIVA KUMAR

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      An implantable antenna is designed for body area network, industrial scientific and medical applications with low specific absorption rate (SAR). The proposed antenna with defected ground structure (DGS) is designed on the FR4 substrate as well as on polyimide substrate. The designed antenna providing dualband characteristics at (Industrial scientific and medical) ISM band of 2.5 GHz and location application for emergency services (LAES) band at 4.2 GHz. The electromagnetic radiation is evaluated using the specific absorption rate in three layered phantom models and the SAR values of the antenna are evaluated by placing the antenna at different levels. The antenna distance is varied inside the skin layer to 5 mm away from the three layered model and observed the reduction in SAR, when moving away from skin tissue. The observed value of SAR satisfies the IEEE-C95-1-2005 standards at ISM operating band. The proposed antenna is tested on threelayered phantom model in simulation through HFSS and in the real time on artificial layers with the help of combinational analyzer (CNA) connection.

    • A provable secure key-escrow-free identity-based signature scheme without using secure channel at the phase of private key issuance

      SUBHAS CHANDRA SAHANA MANIK LAL DAS BUBU BHUYAN

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      The identity-based cryptosystems furnish us with simplest key management procedures. Yet, they have a very slow adoption in cryptography due to the key escrow problem and the necessity of a secure channel between the user and the Private Key Generator (PKG) to transmit the created private key to the user. In thispaper, we propose an identity-based signature scheme that not only solves the key escrow problem but also eliminates the requirement of the secure channel. The proposed scheme is secure against existential forgery under adaptively chosen message and ID attacks in the random oracle model assuming the hardness of theComputational Diffie–Hellmann Problem (CDHP). Furthermore, we compare the efficiency of our scheme to that of a similar established scheme.

    • Analytical modeling of exit Burr in drilling of Ti6Al4V alloy

      ANKIT RANA GANESH DONGRE SUHAS S JOSHI

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      Burrs affect precision components and cause assembly related problems, and in general, decrease manufacturing productivity. Drilling burr formation involves multiple stages that are influenced by variation in thrust forces, temperature, stress conditions, and deformation modes in the unsupported length of the workmaterialbelow the drill. Several of these have not been adequately investigated so far. Therefore, the objective of this work is to model the complex phenomena that occur just before the exit of the drill tip from the bottom surface of the hole, and up to the complete exit of the drill point from the work surface. Accordingly, two models have been developed: (i) to estimate onset of bending in conjunction with theory of plasticity, which leads to the formation of a small drill cap under the pressure of steady-state drilling thrust forces, and (ii) to evaluate exitburr size that involves stretching and bending of a thin layer below the drill tip, using the principle of energy conservation. It is observed that a fracture is initiated at the chisel edge corner resulting in the formation of a small drill cap. The exit burr size predicted by the model is within one standard deviation from the average burrheight as determined from the experimental data.

    • Impact analysis of mobile phone electromagnetic radiations on human electroencephalogram

      SUMAN PATTNAIK BALWINDER SINGH DHALIWAL S S PATTNAIK

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      The experimental study of electromagnetic interference of mobile phone radiations on brain waves is a contemporary research area and the ever-increasing use of mobile phones make it more imperative to explore the problem area in detail. Electromagnetic signal from mobile phones operating in Global System forMobile (GSM) and wide band code division multiple access (WCDMA), has been considered in this paper and their interference impacts have been analyzed on the human electroencephalogram (EEG). The impact on brain waves i.e., delta, theta, alpha, beta and gamma waves are analyzed in five modes namely ideal mode i.e., when mobile phone is not in use, transmission mode and the receiving modes of second generation (2G) and third generation (3G) networks. The data has been acquired from 75 young and healthy students of a post graduate institute while the students were making their routine calls. The acquired EEG signal is analyzed using various parameters viz.; Approximate Entropy(ApEn), Largest Lyapunov Exponent (LLE), Hurst Exponent (HE), Correlation dimension (CD) and the power of the brain waves have also been analyzed. It has been found thatdue to mobile phone usage, there is variation in the nonlinear parameters and increase in the power of the alpha brain waves at T5O1 during 3GRx and decrease in alpha power at the P4O2 channel in all modes. It has beenobserved that the change at the right temporal region is more, the side to which mobile phone was held. The Statistical analysis has also been done using SPSS software which shows significant variations at some of the channels in different modes.

    • Estimation of blood glucose by non-invasive method using photoplethysmography

      SHRADDHA HABBU MANISHA DALE RAJESH GHONGADE

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      This paper presents a system which estimates blood glucose level (BGL) by non-invasive method using Photoplethysmography (PPG). Previous studies have shown better estimation of blood glucose level using an optical sensor. An optical sensor based data acquisition system is built and the PPG signal of the subjects isrecorded. The main contribution of this paper is exploring various features of a PPG signal using Single Pulse Analysis technique for effective estimation of BGL values. A PPG data of 611 individuals is recorded over duration of 3 minutes each. BGL value estimation is performed using two types of feature sets, (i) Time andfrequency domain features and (ii) Single Pulse Analysis (SPA). Neural network is trained using above mentioned proposed feature sets and BGL value estimation is performed. First we validate our methodology using the same features used by Monte Moreno in his earlier work. The experimentation is performed on our owndataset. We obtained comparable results of BGL value estimation as compared with Monte Moreno, with maximum R² = 0.81. Further, BGL estimation using (i) Time and frequency domain features and (ii) Single Pulse Analysis (SPA) is performed and the resulting coefficient of determination (i.e., R²) obtained for reference vs. prediction are 0.84 and 0.91, respectively. Clarke Error Grid analysis for BGL estimation is clinically accepted, so we performed similar analysis. Using Time and frequency domain feature set, the distributions of data samples is obtained as 80.6% in class A and 17.4% in class B. 1% samples in zone C and Zone D. For Single Pulse Analysis technique (SPA) the distribution of data samples are 83% in class A and 17% in class B. The proposed features in SPA have shown significant improvement in R2 and Clarke Error grid analysis. SPA technique with the proposed feature set is a good choice for the implementation of system for measurement of non-invasive glucometer.

    • A Legendre wavelet spectral collocation method for analysis of thermal radiation and slip in the oblique stagnation-point flow of Walters-B liquid towards a stretching surface

      M SAJID M NOVEEL SADIQ K MAHMOOD N ALI

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      A spectral collocation method based on Legendre wavelet is applied to analyse the slip and radiation effects in the flow of an elastico-viscous Walters-B fluid. The fluid is assumed to impinge obliquely on a stretching surface with linear stretching velocity. The governing system of equations is converted into dimensionless ordinary differential equations by invoking suitable similarity variables. The proposed iterative spectral technique for solving governing system of initial value problems is applied for obtaining the solutions. First, we extend Legendre wavelet and Legendre–Guass collocation points are computed for a large interval. Thedifferential equations are converted into a system of algebraic equations. The approximate solution is obtained by solving these algebraic equations. The proposed algorithm is implemented to obtain numerical results for different values of the pertinent parameters. The proposed algorithm controlled the overshooting and undershooting in velocity profiles. The presence of stretching and slip enhances the velocity and reduces the temperature of the fluid within the boundary layer.

    • A compact 4-to-8-bit nonbinary SAR ADC based on 2 bits per cycle DAC architecture

      KALPANA G BHAT T LAXMINIDHI M S BHAT

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      A compact programmable-resolution successive approximation register (SAR) analog to digital converter (ADC) for biosignal acquisition system is presented. The ADC features a programmable 4-to-8-bit DAC that makes the ADC programmable with 2 bits evaluated in each clock cycle. At low resolution with relaxed noise and linearity requirements, use of an increased clock speed improves energy efficiency. A single DAC architecture is used to generate references for 2 bits per cycle evaluation for all resolutions. Nonbinary switched capacitor circuits, least sensitive to parasitics, are proposed for the use in DAC for reference generation.The choice of architecture and circuit design are presented with mathematical analysis. The post-layout simulation of designed ADC in 90 nm CMOS process has 1.2 MS/s sampling rate at 8-bit mode with a power consumption of 185 μ achieving an ENOB of 7.6. The active area of designed ADC is 0.06 mm². The DAC resolution scaling and the use of variable sampling rate maximize efficiency at lower resolutions. Therefore, figure of merit (FOM) is degraded only by a factor of 4.7 for resolution scaling from 8 to 4 bits. This is a significant improvement over 16× degradation expected from 8-bit to 4-bit resolution scaling by truncating the bits.

    • Distributed interference-aware admission control and resource allocation for underlaying D2D communications in cellular networks

      SUSAN DOMINIC LILLYKUTTY JACOB

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      In this letter, we present a two-phase distributed resource allocation algorithm for a Device-to- Device (D2D) network underlaying a cellular network. In the first phase, D2D pairs learn resource block (RB) of the cellular user equipment (CUEs) to be used, while playing an interference minimization game. Each D2D pairis ensured an interference below an upper limit, which is chosen as the criterion for admission control. In the next phase, power allocation for the device pairs allocated to each RB is carried out to maximize their sum rate while ensuring a minimum rate to the CUEs using a pricing scheme. We perform simulations to evaluate the performance of the proposed scheme.

    • Streamlining multitemporal vegetation indices for dependable crop growth monitoring in Himalayan foothill region

      SANDEEP KUMAR SINGLA RAHUL DEV GARG OM PRAKASH DUBEY

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      Satellite data in conjunction with geoinformatics are used to study the land cover change dynamics, extraction of crop information and the monitoring of crop growth. The information derived from the satellite may contain contaminated values due to the atmospheric effects, geometric errors, snow and clouds. These contaminated values can be identified and eliminated using time series analysis to further streamline for agricultural monitoring and prognostic applications. The inherent advantages and disadvantages of existing streamlining methods limit their usability in particular situation. The method proposed in this study synergizesthe use of interpolation, running median and moving average. This has clearly shown the proposal’s capability in preserving the trend in the series in addition to streamlining the temporal profile of satellite data in the Himalayan foothills. This will make the road map for satisfactory crop growth monitoring and crop yieldestimation. Analysis based on the root mean square error and F-Test has been presented to deduce the results and interpretations.

    • Improving bounds on outage probability in correlated Rayleigh fading environment

      ARVIND DHAKA SIDDHARTHA CHAUHAN VIDHYACHARAN BHASKAR AMITA NANDAL

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      In this letter, we propose a limiting criterion to improve the bounds on outage probability for n-correlated Rayleigh fading channel. We use a threshold-based limiting distribution to yield explicit bounds on probability. This work takes into consideration the effect of correlated noise signal to the receiver, which is ageneralization based on the power and noise correlation vectors. The approach proposed in this paper is different from many other existing bounds and it provides strong information to improve the results for the bounds on the outage probability.

    • Devanagari ancient documents recognition using statistical feature extraction techniques

      SONIKA NARANG M K JINDAL MUNISH KUMAR

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      Devanagari ancient document recognition process is drawing a lot of consideration from researchers nowadays. These ancient documents contain a wealth of knowledge. However, these documents are not available to all because of their fragile condition. A Devanagari ancient manuscript recognition system isdesigned for digital archiving. This system includes image binarization, character segmentation and recognition phases. It incorporates automatic recognition of scanned and segmented characters. Segmented characters mayinclude basic characters (vowels and consonants), modifiers (matras) and various compound characters (characters formed by joining more than one basic characters). In this paper, handwritten Devanagari ancient manuscripts recognition system has been presented using statistical features extraction techniques. In feature extraction phase, intersection points, open endpoints, centroid, horizontal peak extent and vertical peak extent features are extracted. For classification, Convolutional Neural Network, Neural Network, Multilayer Perceptron,RBF-SVM and random forest techniques are considered in this work. Various feature extraction and classification techniques are considered and compared to the recognition of basic characters segmented from Devanagari ancient manuscripts. A data set, of 6152 pre-segmented samples of Devanagari ancient documents, is considered for experimental work. Authors have achieved 88.95% recognition accuracy using a combination of all features and a combination of all classifiers considered in this work by a simple majority voting scheme.

    • Hot machining of Ti–6Al–4V: FE analysis and experimental validation

      ASIT KUMAR PARIDA KALIPADA MAITY

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      Machining process is a nonlinear process where high stress, temperature and strain are generated in the primary and secondary shear zone. It is difficult to determine these parameters experimentally and also consumes time. In this study, finite-element method (FEM) is applied to hot machining of Ti–6Al–4V alloyusing DEFORM software. The simulations are used to investigate the effect of heating temperature on cutting force, cutting temperature, stress, strain and chip morphology for various machining conditions. The predicted results are compared to results obtained in room temperature and hot machining conditions. From this analysis, it is observed that hot machining reduces the cutting force, and changes the chip morphology. To validate the simulation results, an experimental trial is performed and positive coherence is achieved.

    • Partial dentures by centrifugal casting assisted by additive manufacturing

      GURPARTAP SINGH RUPINDER SINGH SARBJIT SINGH

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      This research work focuses on preparation of partial dentures (as functional prototypes) by additive manufacturing (AM)-assisted centrifugal casting (CC). The master pattern for partial dentures was prepared on fused deposition modelling (FDM) set-up (established by AM technique at low cost). The final dentures asfunctional prototypes were prepared with a nickel–chromium (Ni–Cr)-based alloy by varying different proportions of Ni% (N) by weight %. The other input parameters were powder to water P/W ratio (W) and pH value (H) of water used for mixing the investment. The samples prepared were ascertained for dimensional deviation (Δd), surface finish (Ra) and micro-hardness (HV) as output parameters. Finally, multifactor optimization has been applied on output parameters of functional prototypes prepared. This study highlights that partial denture prepared with W-100/15, H-7 and N-61% gives overall better results from mechanical properties and dimensional accuracy viewpoint. The results are also supported by photo-micrographic analysis.

    • Precision assembly method of a kind of small interference fitting parts

      ZHIFENG LOU XINGYUAN WANG YUE WANG XIAODONG WANG CHONGLIN XU ZHIZE WANG

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      Interference fitting parts are widely used in many engineering applications. Press-fit method is commonly used for assembling interference fitting parts, but most of press-fit instruments cannot meet assembly requirements of small precision parts for poor accuracies of positioning, alignment and pressing displacement’smeasurement. In this paper, the press-fit method of a kind of small precision interference fitting parts was introduced. In order to achieve a reasonable assembly of the interference fitting parts, the influence of aligning error and positioning error on assembly accuracies were analyzed by finite element method (FEM). Furthermore, the relation between pressing force and displacement were also analyzed to obtain a reasonable range of force–displacement curves, which can be used for assembly quality estimation. An automatic press-fit instrumentwas developed. Through analyzing relation between pressing force and the instrument’s elastic deformation, press-fit displacement error was compensated to increase assembly accuracy. A kind of machine vision device with upper and lower CCDs was used to detect relative situation of parts, and calibration method of themachine vision device was proposed. The assembly experiments showed that press-fit force–displacement curve was consistent with the predicted values. The parts’ relative position deviation was less than ±5 μm, and parallelism deviation was less than 10 μm, which meet the requirements of the assembly accuracy index.

    • A non-linear ductile damage growth law at elevated temperature

      MANOJ KUMAR SACHIN S GAUTAM PRAKASH M DIXIT

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      Continuum damage mechanics (CDM) model is commonly used for the prediction of ductile fracture. For numerical simulation of ductile fracture in impact or high-temperature problems, the damage growth law that incorporates the effect of high temperature is needed. Experimentally, it has been observed that damage growth decreases with temperature. However, the damage growth law at high temperature is not easily available in the literature. In the present work, a damage growth law at high temperature is proposed for steel, based on the experimental measurement of damage carried out at IIT Kanpur.

    • Deep echo state network with reservoirs of multiple activation functions for time-series prediction

      YONGBO LIAO HONGMEI LI

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      In this paper, an improved deep echo state network is proposed, named as multiple activation functions deep echo state network (MAF-DESN), where states are activated by multiple activation functions. A sufficient condition for MAF-DESN is given to guarantee that MAF-DESN possesses the echo state property.Finally, the MAF-DESN is applied to chaotic time-series predictions and compared to other ESN deformation models and popular LSTM. Simulation results show that under same network size condition, MAF-DESN possesses stronger explanatory power in chaotic far-infrared laser predictions (R-square=0.9537, others≤.6487), and better fitting ability in daily foreign exchange rates (MAE=0.0040, others≥0.0047) and chaotic far-infrared laser (MAE=3.4042, others≥4.9021). In high-dimension-input task, MAF-DESN improved the performance when the results were compared (R-square=0.4274, others≤0.3975 and MAE=5.2221, others≥7.6876), while the train time of MAF-DESN did not increase when compared to DESN.

    • Hybrid bi-dimensional empirical mode decomposition based enhancement technique for extreme low contrast UAV thermal images

      R THILLAINAYAGI K SENTHIL KUMAR

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      The performance of automatic target detection and classification systems are typically affected by reduced contrast quality introduced by external interferences. In particular for Unmanned Aerial Vehicle (UAV) captured thermal surveillance images, the effect is more evident. This advises the use of contrast enhancementtechnique as a solution to enhance the reduced contrast of hot regions for efficient target detection. In this paper, a simple and novel enhancement technique based on singular value decomposition (SVD) using Bi-Dimensional Empirical Mode Decomposition (BEMD) is proposed to enhance the hot regions in extreme low contrast thermal images captured by UAV. In the first step, the technique decomposes the thermal image into Intrinsic Mode Functions (IMFs) and residue by using BEMD. In the second step, it applies Contrast Limited AdaptiveHistogram Equalization (CLAHE) in the residue for local contrast enhancement and then calculates the singular value matrix. In the third step, residue component is rescaled for further improvement of hot regions using scaling factor. In the fourth step, a detail enhanced IMF components are generated using gray scale transformation. Finally, the contrast enhanced residue undergoes Inverse BEMD (IBEMD) together with the detailed enhanced IMFs for enhanced image generation. Experimental results demonstrate that the proposed techniqueeffectively enhances the contrast and details in the image with less visual artefacts than other state-of-the-art techniques.

    • Thermal fatigue analysis of H13 steel die adopted in pressure-diecasting process

      V A GIRISHA MANOJ M JOSHI L J KIRTHAN A BHARATISH RAMAKRISHNA HEGDE

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      The thermal fatigue of die casting die steels causes reduction in tool life and seriously affects the surface conditions such as microstructure, hardness, surface finish and residual stresses. The improvement of die life by suitably modifying the die design assumes utmost importance for die designers. In this regard, a key issue is the size and location of cooling channels relative to the surface of the die, which affect the thermal stresses and fatigue life of dies. This paper focuses on thermal fatigue analysis of pressure-die-casting die steel H13 andanalyses the effect of coolant channel location on temperature distribution and fatigue parameters such as life, damage, equivalent alternating stress and biaxiality using ANSYS Workbench 15.0 finite-element package. Increase in wall thickness (location of coolant channel from base) caused an increase in temperature and decrease in die life, which led to increase in volume porosity and hence crack initiation. The optimum coolant channel location from the base is obtained as 1 mm, which corresponds to minimum normal stress of149.1 MPa, fatigue life of 4.1 ×10⁵ cycles, fatigue damage of 2436.9 and equivalent alternating stress of 100.62 MPa.

    • Minimum cost berth allocation problem in maritime logistics: new mixed integer programming models

      BOBIN CHERIAN JOS M HARIMANIKANDAN CHANDRASEKHARAN RAJENDRAN HANS ZIEGLER

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      The berth allocation problem (BAP) involves decisions on how to allocate the berth space and to sequence maritime vessels that are to be loaded and unloaded at a container terminal involved in the maritime logistics. As the berth is a critical resource in a container terminal, an effective use of it is highly essential tohave efficient berthing and servicing of vessels, and to optimize the associated costs. This study focuses on the minimum cost berth allocation problem (MCBAP) at a container terminal where the maritime vessels arrive dynamically. The objective comprises the waiting time penalty, tardiness penalty, handling cost and benefit of early service completion of vessels. This paper proposes three computationally efficient mixed integer linear programming (MILP) models for the MCBAP. Through numerical experiments, the proposed MILP models arecompared to an existing model in the literature to evaluate their computational performance. The computational study with problem instances of various problem characteristics demonstrates the computational efficiency of the proposed models.

    • Estimation of dilution in laser cladding based on energy balance approach using regression analysis

      SHITANSHU SHEKHAR CHAKRABORTY SAMIK DUTTA

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      Laser cladding is a complex manufacturing process involving more than 19 variables related to laser source, workpiece movement, powder-substrate material combinations, clad geometry, powder flow dynamics, shrouding gas flow and so on. Significant research efforts have been directed to analytical-numericalempiricalmodelling of laser cladding and also in-process monitoring and control of the process. Still, due to complicated physics there is a dearth of simple analytical model for estimation of dilution in laser cladding. Its experimental measurement requires suitable micrographs of the clad cross section perpendicular to the clad path. This is a time-consuming and destructive way of measurement. Numerical models are time consuming to evaluate and hence not suitable for fast decision making or real-time control implementation. The analytical models available, despite having many approximations, are a little complicated, require fair amount computer programming and often need suitable prior guessing of range of output parameters for adjustment of constant values in the models. This poses some challenges for use and having an intuitive guidance, for a beginner/unskilled operator. Besides, their complexity may erect barrier in the way of their implementation for real time monitoring and control. This work proposes a simple linear regression model, formed based on energy balance approach, to estimate dilution in laser cladding. After fitting to a set of data, within a suitable process parameter window, for a particular clad-substrate material combination, this model can estimate dilution as a function of input/easily measureable parameters, viz. laser power, scan speed, clad width and clad height. The model fitted well to the experimental data taken from literature.

    • Road risk assessment using fuzzy Context-free Grammar based Association Rule Miner

      S SARANYADEVI R MURUGESWARI S BATHRINATH

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      Road traffic accidents are a major social concern as well as a crucial issue for the public in recent days due to the risk factors involved. Analysing and identifying the major risk factors of road accident is still a challenging task. In this paper, a fuzzy Context-free Grammar (FCFG)-based association rule mining (ARM)technique is proposed to categorize a heterogeneous road accident dataset into two categories based on the critical factors such as total number of accidents (TA), persons killed (PK) and persons injured (PI). The role of the fuzzy grammar in this paper is to govern the entire algorithm using the prescribed grammar rules to proceed further. The considered road accident dataset does not have class labels; hence there is a need to assign class labels for the available data instance. The accident data with assigned class labels are given as input to K-nearestneighbour (KNN) machine learning algorithm in order to train the classifier for testing purpose. Further, the collected test data from the user are utilized by the KNN classifier for carrying out the performance analysis of the proposed algorithm. The case study is conducted on the National Highway roads, India, to examine theproposed approach. The experimentations are executed for road accident records using MATLAB software and the analysis is made using the following performance measures: accuracy, recall or sensitivity, precision or specificity and F1 score. A comparative study is accomplished with existing algorithms in order to show that the proposed algorithm works with improved accuracy of more than 83%. The results suggested that the road users are responsible for the acceptance or rejection of safe or un-safe roads, respectively.

    • Effect of magnetic field on the time-dependent flow due to a disk with non-torsional oscillation and a Newtonian fluid at infinity rotating about distinct axes

      H VOLKAN ERSOY

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      This work aims to study the effect of magnetic field on the time-dependent flow of an insulated disk executing non-torsional oscillation in its own plane and a Newtonian fluid at infinity while they are initially rotating at the same speed about two vertical axes. It is shown that the presence of a magnetic field causes aresistive force and the required time to reach the periodic state becomes shorter. Further, it is demonstrated that there is an excellent agreement between the exact solution that is appropriate for all values of time and the periodic solution that is valid after the periodicity of the flow starts.

    • Fabrication of third generation Al–Li alloy by friction stir welding: a review

      MD PARWEZ ALAM A N SINHA

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      Aerospace industry stimulates research for new materials to reduce the weight of it thereby reduction of fuel consumption. Aluminium–Lithium alloys have become a good alternative due to its inherent properties. Nevertheless, joining of these materials by traditional welding is difficult. Friction stir welding process considered as an ideal joining process for these materials due to low heat input. This paper reviews the fabrication of the latest generation of Al–Li alloy by friction stir welding. In addition, it also presents and discusses the effect of process parameters on microstructure, mechanical properties and precipitate distribution in friction stir welded joint of Al–Li alloy.

    • Optimization of WEDM process of mould material using Kriging model to improve technological performances

      TRUNG-THANH NGUYEN QUOC-DUNG DUONG

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      Improving the technical performance of the wire electro-discharge machining (WEDM) process is an effective solution to decrease manufacturing costs. This paper addresses a multi-response optimization to simultaneously improve the cutting area rate CAR and decrease the kerf width AKW, while the average surfaceroughness ASR is predefined as a constraint. The processing conditions considered include the pulse-on time Ton, the current I, the voltage V and the wire speed S. A WEDM machine was adopted in conjunction with the Box–Behnken matrix to conduct experimental trials for machining of SKD61 steel. Highly nonlinear relationships between machining parameters and technological outputs were developed using the Kriging models. Finally, an archive-based micro-genetic algorithm (AMGA) was used to resolve the trade-off analysis among threeresponses and determine the optimal values of the processing factors. The results showed that a set of feasible solutions can be determined for the low kerf width as well as the surface roughness and the high cutting area rate. The selection of optimum parameters could help the WEDM operators to save the machining costs and time. The combination of the Kriging model and AMGA could be considered as an intelligent approach for modelling WEDM processes and predicting optimal results.

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