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Showing papers by "Ghulam Ishaq Khan Institute of Engineering Sciences and Technology published in 2017"


Journal ArticleDOI
TL;DR: In this article, the effect of chemical and thermal reduction on the quality of chemically synthesized graphene and its derivatives was explored using Raman spectroscopy and X-ray diffraction, field emission scanning electron microscopy (FESEM) and atomic force microscopy.
Abstract: Large-scale fabrication of graphene and reduced graphene oxide (rGO) is important for industrial and research applications of this material. Chemical solution methods offer a low-cost alternate to produce rGO with high yield. This research is to explore the effect of chemical and thermal reduction on the quality of chemically synthesized graphene and its derivatives. A top-down process involved the chemical oxidation of the precursor graphite powder (size ~10 μm) using a concentrated mixture of sulphuric acid and nitric acid. Oxidized graphite powder was thermally exfoliated at 1,050°C for 30 s to produce graphene oxide (GO). Chemical reduction in GO sheets with sodium borohydride led to the formation of rGO. Characterization by Raman spectroscopy revealed an intensity ratio of 2D/G bands of rGO as approximately 0.5 indicating a multi-layered structure. X-ray diffraction, field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) results indicated a multi-layered rGO wit...

86 citations


Journal ArticleDOI
TL;DR: A cell association scheme that selectively mutes certain small-cell base stations and covers end users by cell range extension (via cell biasing) for achieving load balancing and a signal-to-interference plus noise ratio (SINR) distribution are proposed.
Abstract: To meet the ever-growing traffic demand and address the cell capacity shortage problem, associating end users to various tiers of cells in a multitier cellular network appears to be a promising approach. In this paper, we consider a nonuniform heterogeneous cellular network (NuHCN) and propose a cell association scheme that selectively mutes certain small-cell base stations (BSs) and covers end users by cell range extension (via cell biasing) for achieving load balancing. The envisaged NuHCN is comprised of two tiers of BSs, i.e., macro- and small-cell BSs, deployed according to three independent homogeneous Poisson point processes for BSs and end users, respectively. Accordingly, the available space is divided into two subspaces. In the inner subspace, the end users are associated only with a macrocell BS based on the unbiased maximum received power scheme since the small-cell BSs therein are deactivated. In the outer subspace, where the macrocell BS coverage is comparatively poor, the end users are associated with either a macrocell BS or a microcell BS based on the biased/unbiased maximum received power scheme. Cell range extension-based cell association allows the macrocell users in the outer subspace to efficiently utilize the resources of the lightly loaded small-cell BSs, resulting in improved network coverage and capacity. Based on the proposed cell association scheme, we analyze the signal-to-interference plus noise ratio (SINR) distribution and deduce expressions for coverage probability and rate coverage. Numerical results show that, contrary to the uniform case, biasing has distinct effects on the coverage and rate performance of an NuHCN.

58 citations


Journal ArticleDOI
TL;DR: Numerical simulation results are provided to show the superiority and the advantages of the proposed controller such as robustness to external disturbances, no chattering, less control effort and accurate output tracking, thus proposed controller can be considered as a suitable choice for designing automatic insulin pumps for diabetes patients.

57 citations


Journal ArticleDOI
TL;DR: The results show that DIHM achieves superior coherency detection and outperforms the compared methods in both pixel level and coherent region level average particle error rates, average coherent number error (CNE) and F-score.

52 citations


Journal ArticleDOI
TL;DR: In this article, the authors present the results of an analysis of the Carbon, water and land footprints of the worldwide from 1995 to 2009, and compare the outcomes for the two approaches for four world regions (i.e., EU, OECD, BRIC and RoW) for four different perspectives in worldwide environmental policies.
Abstract: The traditional approach of accounting of environmental pressure in the Kyoto Protocols follows the production-based accounting, which attributes all environmental pressures generated from production activities within a country boundary to that country total environmental pressure However, the major flaws of this approach is that it does not take into account the environmental pressures embodied in imports and so build stimulus for shifting of environmental pressures abroad An alternative approach to include environmental pressures associated with imports to the country and subtract export related environmental pressures is the consumption-based approach or footprint approach This approach has been widely considered as an alternative way to more adequately allot responsibilities between the emitters and final consumers This study compares and discusses the concepts of both approaches, showing the results of an empirical analysis and going into the application of the two different perspectives in worldwide environmental policies This paper presents the results of an analysis of the Carbon, water and land footprints of the worldwide from 1995 to 2009, and compares the outcomes for the two approaches for four world regions (ie EU, OECD, BRIC and RoW) The analysis is based on a multi-region input output (MRIO) model to assess these environmental pressures The proposed model uses the world-input-output-database (WIOD) covering 35 sectors and 41 countries The results show that during the entire study period, the carbon emissions, land use and water use for the EU and OECD regions are higher in the consumer approach than in the producer approach The results further indicate that, for the BRIC and rest of the world (RoW) regions, the carbon emission, land and water use are higher in the producer approach than in the consumer approach

48 citations


Journal ArticleDOI
TL;DR: The kinetic study showed that adsorption followed pseudo-second order kinetics, and the most commonly used isotherm models, Freundlich, Langmuir and Temkin, were applied to experimental data using linear regression technique, however, The Temkin model fits better to experimentalData.

39 citations


Journal ArticleDOI
TL;DR: The present study aims to design a chaotic-advection-based passive micromixer with enhanced mixing efficiency by designing a serpentine-shaped microchannel with sinusoidal side walls and increasing the A/λ ratio.
Abstract: Sample mixing is difficult in microfluidic devices because of laminar flow. Micromixers are designed to ensure the optimal use of miniaturized devices. The present study aims to design a chaotic-advection-based passive micromixer with enhanced mixing efficiency. A serpentine-shaped microchannel with sinusoidal side walls was designed, and three cases, with amplitude to wavelength (A/λ) ratios of 0.1, 0.15, and 0.2 were investigated. Numerical simulations were conducted using the Navier–Stokes equations, to determine the flow field. The flow was then coupled with the convection–diffusion equation to obtain the species concentration distribution. The mixing performance of sinusoidal walled channels was compared with that of a simple serpentine channel for Reynolds numbers ranging from 0.1 to 50. Secondary flows were observed at high Reynolds numbers that mixed the fluid streams. These flows were dominant in the proposed sinusoidal walled channels, thereby showing better mixing performance than the simple serpentine channel at similar or less mixing cost. Higher mixing efficiency was obtained by increasing the A/λ ratio.

38 citations


Journal ArticleDOI
TL;DR: A tractable analytical network model abating ICI using reverse frequency allocation (RFA) scheme along with cell range expansion-based user association is developed and demonstrated that selective sBS deployment outperforms other deployment methods.
Abstract: To meet the current cellular capacity demands, proactive offloading is required in heterogeneous cellular networks (HetCNets) comprising of different tiers of base stations (BSs), e.g., small-cell BSs (sBSs) and conventional macro-cell BSs (mBSs). Each tier differs from the others in terms of BS transmit power, spatial density, and association bias. Consequently, the coverage range of each tier BSs is also different from others. Due to low transmit power, a fewer number of users are associated to an sBS as compared with mBS. Thus, inefficient utilization of small-cell resources occurs. To balance the load across the network, it is necessary to push users to the underloaded small cells from the overloaded macro-cells. In co-channel deployed HetCNets, mBSs cause heavy inter-cell interference (ICI) to the offloaded users, which significantly affects the network performance gain. To address this issue, we develop a tractable analytical network model abating ICI using reverse frequency allocation (RFA) scheme along with cell range expansion-based user association. We probabilistically characterize coverage probability and user rate while considering RFA with and without selective sBS deployment. Our results demonstrate that selective sBS deployment outperforms other deployment methods.

38 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of laser processing parameters on the weld pool shape, pulse overlap, oxide formation, and microstructure were studied using scanning electron and optical microscope, and it was found out that laser peak power had a significant influence on the FZ oxygen contents and grain size whereas, both peak power and heat input per unit length were important in defining the welding pool shape.
Abstract: Pulsed Nd-YAG laser was employed in bead on plate configuration for welding of 1.6 mm thick Ti-5Al-2.5Sn alloy sheet. The effect of laser processing parameters on the weld pool shape, pulse overlap, oxide formation, and microstructure were studied using scanning electron and optical microscope. It was found out that laser peak power had a significant influence on the FZ oxygen contents and grain size whereas, both peak power and heat input per unit length were important in defining the weld pool shape. Processing parameters for full penetration welds with acceptable joint properties and low oxygen contents were selected for further study in terms of residual stresses and mechanical properties. Formation of acicular α and α′ martensite in fusion and heat affected zone, led to an increase in microhardness by about 55 HV0.2 as compared to base metal. Induced residual stresses were found to be significantly less than the yield strength resulting in plate deformation less than 1 mm. Transverse residual stresses present at different depths below the surface tend to counter effect each other resulting in tensile strength of welded specimen becoming nearly equal to that of the base metal.

36 citations


Journal ArticleDOI
TL;DR: The proposed approach converts an uncertain graph to a certain graph by predicting about the existence of the edges in the uncertain graph by using a classifier, and shows that the proposed approach performs better than the other four methods.

33 citations


Journal ArticleDOI
TL;DR: In this article, a green GaAlInN-based light-emitting diode (LED) has been proposed with peak emission wavelength of ∼510nm, and the proposed structure has significantly reduced electrostatic field in the active region.

Journal ArticleDOI
TL;DR: A set of visualization metrics to quantify visualization techniques and a framework for optimizing the layout of a visualization technique is presented, based on an evolutionary algorithm which uses treemaps as a case study.

Journal ArticleDOI
TL;DR: Simulation results are presented to show that the proposed pre-processing method called illumination normalization using ICA increases the accuracy rate of several baseline face recognition systems (FRSs) and showed improved performance of baseline FRSs when using the Extended Yale-B databases.
Abstract: In this work, we separate the illumination and reflectance components of a single input image which is non-uniformly illuminated. Considering the input image and its blurred version as two different combinations of illumination and reflectance components, we use the conventional independent component analysis (ICA) to separate these two components. The separated reflectance component, which is an illumination normalized version of the input image, can then be used as an effective pre-processed (illumination normalized) image for different computer vision tasks e.g. face recognition. To this end, we present simulation results to show that our proposed pre-processing method called illumination normalization using ICA increases the accuracy rate of several baseline face recognition systems (FRSs). The proposed method showed improved performance of baseline FRSs when using the Extended Yale-B databases.

Journal ArticleDOI
01 Jun 2017
TL;DR: In this paper, the authors investigated a suitable set of friction stir processing parameters to form AL7075T651/TiN nano composite and quantified the effect of these variations on the composite through several microstructural and mechanical tests.
Abstract: Friction stir processing is a novel material fabrication technique. This study was undertaken in order to investigate a suitable set of friction stir processing parameters to form AL7075T651/TiN nano composite. A number of samples were produced by varying the process parameters, namely, tool-pin geometry, number of passes and the direction of tool rotation. The pin geometries employed include triangular, square and threaded taper; the passes were varied over two levels (i.e. 2 and 4) and the tool rotation was changed as clockwise and counter clockwise between the successive passes. The effect of these variations on the composite was quantified through several microstructural and mechanical tests. The increase in the number of passes was observed to improve various characteristics of the composite (i.e. distribution of TiN particles, grain refinement and mechanical properties). The effect of tool geometry, however, was associated with the choice of the number of passes. The change in the direction of tool ...

Journal ArticleDOI
TL;DR: In this paper, two spin valve junctions were constructed from directly grown graphene on Ni electrode (DG) and transferred graphene (TG), and the magnetoresistance (MR) ratio for DG device was found to be higher than TG device i.e. 0.73% and 0.14%, respectively.

Journal ArticleDOI
TL;DR: In this paper, a high resistive strain gauge is reported that can measure large mechanical deformation with higher sensitivity, and the printed structure is the same as common for strain gauge.
Abstract: Tremendous increase in the number of sold micro sensing units have been reported in recent years. This research presented a resistance strain gauge of conductive carbon paste printed on flexible substrate through Micro-dispensing direct write (MDDW) technique. A high resistive strain gauge is reported that can measure large mechanical deformation with higher sensitivity. The printed structure is the same as common for strain gauge. The electrical characterization is carried out followed by gauge factor (G.F) calculation. Besides formal testing for strain, the strain gauge sensitivity were tested towards humid and warm environment. Microscopic characterization is carried out for surface morphology and particle sizing. A strain gauge for tensile test application is also presented in this work. The research concluded with the fabrication of a low cost high gauge factor strain gauge with sensitivity towards humid and warm environment.

Journal ArticleDOI
TL;DR: In this paper, the indentation fracture toughness of bulk metallic glass alloys in the partially crystalline composite state has been studied and corner cracking was observed on indentation in all the compositions above a certain critical load.
Abstract: Indentation fracture toughness of (Fe0·5Co0.5)69 − xNb6B25 + x (x = 0, 2, 4) bulk metallic glass alloys in the partially crystalline (intrinsic composite) state has been studied. Corner cracking was observed on indentation in all the compositions above a certain critical load. High hardness with values in excess of 1100HV was obtained for all the alloy compositions. Indentation fracture toughness measured through various empirical relations was found to be

Journal ArticleDOI
TL;DR: In this paper, a solution-processed visible wavelength organic photodiode (OPD) using donor/acceptor dyad of zinc phthalocyanine (ZnPc) and [6,6]-phenyl-C71-butyric-acid methyl ester (PC71BM), respectively, has been demonstrated.

Journal ArticleDOI
TL;DR: In this article, the vertical field effect transistors (FETs) with h-BN/Gr/MoS2/Mo multi-heterostructures were fabricated and a high current ON-OFF ratio of 106 was demonstrated with a highcurrent density of ∼105 A cm−2.
Abstract: Two-dimensional layered materials, such as graphene (Gr) and molybdenum disulfide (MoS2), have become fascinating and exciting candidates for next-generation electronic device materials. Their vertical combinations have led to novel electronic and photonic devices. We fabricated vertical field-effect transistors (FETs) with h-BN/Gr/MoS2/Mo multi-heterostructures. A facile route was followed to design high-quality vertical FETs with improved performance. MoS2 was directly transferred to SiO2/h-BN/Gr without using any polymer, which produced a clean interface between Gr and MoS2. A high current ON–OFF ratio of ∼106 was demonstrated with a high current density of ∼105 A cm−2. Our results were attributed to the high-quality bottom Gr on h-BN, the top-most molybdenum metal contact, and the clean interface between Gr and MoS2. The photoresponse of vertical FETs was also investigated under deep ultraviolet irradiation. The current density and photocurrent response of these vertical devices were strongly dependent on the back-gate voltage.

Journal ArticleDOI
TL;DR: In this paper, the authors proposed a methodological innovation on the study of suitable policy instrument against the raise of CO2emissions, which is based on the approach of the Macro Multipliers (MM) that leads with the recognition of the impact of all those industries responsible for CO2 emissions.

Journal ArticleDOI
TL;DR: The modeling for relaxation process of important synaptic behaviors, excitatory post-synaptic current (EPSC), has been updated as a stretched-exponential function with voltage factors in a more quantitative way to better simulate, realize and thus control neuromorphic computing.
Abstract: Recently, advanced designs and materials emerge to study biologically inspired neuromorphic circuit, such as oxide semiconductor devices. The existence of mobile ions in the oxide semiconductors could be somewhat regarded to be similar with the case of the ions movements among the neurons and synapses in the brain. Most of the previous studies focus on the spike time, pulse number and material species: however, a quantitative modeling is still needed to study the voltage dependence of the relaxation process of synaptic devices. Here, the gate pulse stimulated currents of oxide semiconductor devices have been employed to mimic and investigate artificial synapses functions. The modeling for relaxation process of important synaptic behaviors, excitatory post-synaptic current (EPSC), has been updated as a stretched-exponential function with voltage factors in a more quantitative way. This quantitative modeling investigation of representative synaptic transmission bias impacts would help to better simulate, realize and thus control neuromorphic computing.

Journal ArticleDOI
01 Oct 2017-Carbon
TL;DR: In this paper, a large hysteresis effect was reported by constructing graphene-tungsten disulfide heterostructure (GWH), where the semiconducting WS2 acts as a channel in field effect transistor geometry while graphene works as charge trapping interfacial layer.

Journal ArticleDOI
TL;DR: In this paper, performances of an organic electron donor-π-bridge-electron acceptor (Dπ-A) type RK1 dye and the most common metallic N719 dye-sensitized solar cells (DSSCs) were compared.
Abstract: In this work, performances of an organic electron donor–π-bridge–electron acceptor (D–π–A) type RK1 dye and the most common metallic N719 dye based dye-sensitized solar cells (DSSCs) were compared. To gain insight into the behavior of these devices, current–voltage and impedance spectroscopic measurements were performed. From the current–voltage data, the parameters of cells including open-circuit voltage, short-circuit current, fill factor, solar energy-to-electricity conversion efficiency, series resistance, shunt resistance, and ideality factor were extracted. The RK1 based cell showed higher photovoltage, higher short-circuit current, solar energy-to-electricity conversion efficiency, higher shunt resistance and ideality factor. Using the Mott-Schottky plots, electrical properties of the cells were investigated and lower electron concentration was found for the RK1-DSSC. This high performance can be attributed to the higher absorption coefficient of the RK1 dye and relatively higher induced positive band-shift of the conduction band edge of the TiO2 semiconductor. The trends of the recombination resistance and the chemical capacitance as observed in the measured impedance spectra have also confirmed high photovoltaic performance of the RK1 based cell. Impedance spectra of the devices were observed both voltage and frequency dependent. At low frequencies, significant contribution of trap states was observed.

Journal ArticleDOI
TL;DR: In this paper, the angle dependent magnetoresistance (MR) in a spin valve for different orientations of applied magnetic field (B) has been investigated and the switching points of spin valve signals show a clear shift towards higher B for each increasing angle of the applied field, thus sensing the response for respective orientation of the magnetic field.

Journal ArticleDOI
TL;DR: In this paper, the magnetotransport properties of vertical spin valve structures incorporating graphene (Gr), Gr/Au and Gr/Al 2 O 3 intervening layers are elucidated, and an in-plane magnetic field is obliquely applied to the device with the purpose to vary the relative magnetizations of ferromagnetic electrodes (Co and Ni).

Journal ArticleDOI
TL;DR: In this article, the role of defects in the graphene interlayer and its influence on the spin valve signal is reported, and the emergence of D peak in Raman spectrum reveals defects in graphene layer.

Journal ArticleDOI
TL;DR: In this paper, a bead-on-plate (BoP) configuration was used for welding of 1.6mm thick Ti-5Al-2.5Sn plates, which led to the formation of complete α′ martensitic structure in laser welds and acicular α along with α− martensite within coarse prior β grains.
Abstract: Corrosion behavior of TIG and laser welded Ti–5Al–2.5Sn alloy was compared using different electrochemical techniques. Bead on plate (BoP) configuration was used for welding of 1.6 mm thick Ti–5Al–2.5Sn plates which led to the formation of complete α′ martensitic structure in laser welds and acicular α along with α′ martensite within coarse prior β grains was observed in TIG welds. Potentiodynamic and cyclic polarization were carried out in 5, 7 and 9 M HNO3 to study the effect of concentration on the galvanic corrosion of laser and TIG welded Ti–5Al–2.5Sn. The oxide layer developed after 192 h of immersion in fuming HNO3 was studied using electrochemical impedance spectroscopy (EIS) and SEM. All the samples showed good passivity but different oxidation behavior was observed mainly because of the surface modification after the welding operation.

Journal ArticleDOI
TL;DR: In this paper, the authors reported the electrical performance of graphene devices with the immobilization of cholesterol molecules and showed that the Dirac point position is gradually shifted towards negative gate voltage as cholesterol concentration increases.
Abstract: The intensive bio-effects on graphene surface is an attention-grabbing field which determine the capability of performing rapid detection of biomolecules with high accuracy. Here, we report the electrical performance of graphene devices with the immobilization of cholesterol molecules. In electrical transport measurements, the Dirac point position is gradually shifted towards negative gate voltage as cholesterol concentration increases which reveals the clear influence of cholesterol molecules on the graphene. This graphene surface modifications induce n-type doping and the charge carrier mobility is increased from ∼2000 cm 2 V −1 s −1 to ∼3900 cm 2 V −1 s −1 by increasing the cholesterol concentration. The detection of cholesterol molecules is further investigated by Raman spectroscopy, FTIR and AFM characterizations. The results indicate significant impact of cholesterol-graphene interaction on the performance of graphene devices. Furthermore, sensing approach can be quantitatively deployed for commercial use of portable graphene-based cholesterol sensing devices for biomedical applications.

Journal ArticleDOI
TL;DR: The pi-conjugated small molecular VOPcPhO was used to boost humidity sensing by Fatima et al. as discussed by the authors, which was the first work to address the problem of low humidity.
Abstract: Correction for ‘Compositional engineering of the pi-conjugated small molecular VOPcPhO : Alq3 complex to boost humidity sensing’ by Noshin Fatima et al., RSC Adv., 2017, 7, 19780–19786.

Journal ArticleDOI
TL;DR: In this paper, theoretical and experimental analysis of an AC-DC-AC inverter under DC link capacitor failure is presented, where the failure study conducted for this paper is the open circuit of the DC-link capacitor.
Abstract: In this paper theoretical and experimental analysis of an AC–DC–AC inverter under DC link capacitor failure is presented. The failure study conducted for this paper is the open circuit of the DC link capacitor. The presented analysis incorporates the results for both single and three phase AC input. It has been observed that the higher ripple frequency provides better ride through capability for this fault. Furthermore, the effects of this fault on electrical characteristics of AC–DC–AC inverter and mechanical properties of the induction motor are also presented. Moreover, the effect of pulsating torque as a result of an open circuited DC link capacitor is also taken into consideration. Theoretical analysis is supported by computer aided simulation as well as with a real time experimental prototype.