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Rajesh Kumar

Publications and source records attributed to Rajesh Kumar.

At least 163 records · Page 9Linked to original sources

UAV-Assisted Heterogeneous Networks for Capacity Enhancement

Modern day wireless networks have tremendously evolved driven by a sharp increase in user demands, continuously requesting more data and services. This puts significant strain on infrastructure based macro cellular networks due to the inefficiency in handling these traffic demands, cost effectively. A viable solution is the use of unmanned aerial vehicles (UAVs) as intermediate aerial nodes between the macro and small cell tiers for improving coverage and boosting capacity. This letter investigates the problem of user demand based UAV assignment over geographical areas subject to high traffic demands. A neural based cost function approach is formulated in which UAVs are matched to a particular geographical area. It is shown that leveraging multiple UAVs not only provides long range connectivity but also better load balancing and traffic offload. Simulation study demonstrate that the proposed approach yields significant improvements in terms of 5th percentile spectral efficiency up to 38\% and reduced delays up to 37.5\% compared to a ground-based network baseline without UAVs.

cs.NI↗

Optical bandgap and bowing parameter for Fe doped LaGaO3

The polycrystalline samples of LaGa1-xFexO3 have been prepared by standard solid state reaction route. The phase purity of the prepared samples is confirmed by powder xray diffraction experiments followed by Rietveld analysis. It has been observed that the variation of lattice parameters is governed by Vegards law. The optical band gap of these samples is estimated using diffuse reflectance analysis and it is observed that the optical gap systematically decreases with Fe doping from 3.62 eV and attains the saturation value of approximately 1.9 eV at x equal to 0.4. The value of the bowing parameter b for the prepared solid solution LaGa1-xFexO3 is estimated to be 3.8eV.The xray absorption near edge spectroscopy XANES suggests that the Fe is in mixed valence state in all prepared samples and these mixed states of Fe due to offstoichiometry acts like electron doping in LaGa1-xFexO3 and thereby results in the reduction in the effective band gap. Our results may be useful to design the LaGaO3based light emitting diodes and new generation of semiconductor photo-detectors.

cond-mat.str-el↗

Authenticating users through their arm movement patterns

In this paper, we propose four continuous authentication designs by using the characteristics of arm movements while individuals walk. The first design uses acceleration of arms captured by a smartwatch's accelerometer sensor, the second design uses the rotation of arms captured by a smartwatch's gyroscope sensor, third uses the fusion of both acceleration and rotation at the feature-level and fourth uses the fusion at score-level. Each of these designs is implemented by using four classifiers, namely, k nearest neighbors (k-NN) with Euclidean distance, Logistic Regression, Multilayer Perceptrons, and Random Forest resulting in a total of sixteen authentication mechanisms. These authentication mechanisms are tested under three different environments, namely an intra-session, inter-session on a dataset of 40 users and an inter-phase on a dataset of 12 users. The sessions of data collection were separated by at least ten minutes, whereas the phases of data collection were separated by at least three months. Under the intra-session environment, all of the twelve authentication mechanisms achieve a mean dynamic false accept rate (DFAR) of 0% and dynamic false reject rate (DFRR) of 0%. For the inter-session environment, feature level fusion-based design with classifier k-NN achieves the best error rates that are a mean DFAR of 2.2% and DFRR of 4.2%. The DFAR and DFRR increased from 5.68% and 4.23% to 15.03% and 14.62% respectively when feature level fusion-based design with classifier k-NN was tested under the inter-phase environment on a dataset of 12 users.

cs.CV↗

Intrinsic Half-metallicity in Edge Fluorinated Armchair Boron Nitride Nanoribbons

We predict intrinsic half-metallicity in armchair boron nitride nanoribbons (ABNNRs) via edge fluorination. The stability, electronic and magnetic properties of bare and edge fluorinated ABNNRs have been systematically analyzed by means of first-principles calculations within the local spin-density approximation (LSDA). The ribbons whose only edge-B atoms passivated with F atoms (i.e., edge-N atoms are un-passivated), regardless of width, are found half-metallic with a half-metal gap of 0.3 eV. A 100 \% spin polarized charge transport across the Fermi level is expected for such ribbons as the spin polarized states are $\sim$0.4 eV more stable than the spin un-polarized states and only single-spin conducting channels are present across the Fermi level owing to the gigantic spin splitting. The existence of half-metallicity is attributed to the localization of electronic charge at bare edge-N atoms as revealed from the analysis of Bloch states and projected density of states (PDOS).The sufficiently large half-metal gap (0.3 eV) with huge difference in the energies ($\sim$ 0.4 eV) of spin polarized and spin compensated states projects these half-metallic ABNNRs as potential candidate for spintronics applications.

cond-mat.mes-hall↗

Role of Metal Nanoparticles on porosification of silicon by metal induced etching (MIE)

Porosification of silicon (Si) by metal induced etching (MIE) process have been studies here to understand the etching mechanism. The etching mechanism has been discussed on the basis of electron transfer from Si to metal ion (Ag$^+$) and metal to H$_2$O$_2$. Role of silver nanoparticles (AgNPs) in the etching process has been investigated by studying the effect of AgNPs coverage on surface porosity. A quantitative analysis of SEM images, done using Image J, shows a direct correlation between AgNPs coverage and surface porosity after the porosification. Density of Si nanowires (NWs) also varies as a function of AgNPs fractional coverage which reasserts the fact that AgNPs governs the porosification process during MIE.

cond-mat.mes-hall↗

Half-metallicity in Armchair Boron Nitride Nanoribbons: A First-Principles Study

Using density functional theory, we predict half-metallicity in edge hydrogenated armchair boron nitride nanoribbons (ABNNRs). The predicted spin polarization is analyzed in detail by calculating electronic and magnetic properties of these hydrogenated ABNNRs by means of first-principles calculations within the local spin-density approximation (LSDA). ABNNRs with only edge B atoms passivated by H atoms are found to be half-metallic (regardless of their width) with a half-metal gap of 0.26 eV. Upto 100% spin polarized charge transport is predicted across the Fermi level owing to the giant spin splitting. Transmission spectrum analysis also confirms the separation of spin up and spindown electronic channels. It is revealed that H-passivation of only edge N atoms transforms non-magnetic bare ribbons into energetically stable magnetic semiconductors whereas hydrogenation of both the edges does not affect the electronic and magnetic state of bare ribbons significantly. The results are promising towards the realization of inorganic spintronic devices.

cond-mat.mes-hall↗

Time Dependent Analysis with Dynamic Counter Measure Trees

The success of a security attack crucially depends on time: the more time available to the attacker, the higher the probability of a successful attack. Formalisms such as Reliability block diagrams, Reliability graphs and Attack Countermeasure trees provide quantitative information about attack scenarios, but they are provably insufficient to model dependent actions which involve costs, skills, and time. In this presentation, we extend the Attack Countermeasure trees with a notion of time; inspired by the fact that there is a strong correlation between the amount of resources in which the attacker invests (in this case time) and probability that an attacker succeeds. This allows for an effective selection of countermeasures and rank them according to their resource consumption in terms of costs/skills of installing them and effectiveness in preventing an attack

cs.CR↗

Room temperature magnetodielectric studies on Mn doped LaGaO3

The polycrystalline samples of LaGa1-xMnxO3 (0<x<0.3) has been prepared by solid state reaction route. The phase purity of these samples has been confirmed by powder x-ray diffraction experiments carried out on BL-12 at Indus-2 synchrotron radiation source. The sample with x=0.2 shows significant change in the value of capacitance with the application of magnetic field. The observed results were understood by systematically analyzing magneto-capacitance (MC), magneto resistance (MR) and dielectric loss as a function of frequency. Our results and analysis suggests that the observed magneto dielectric (MD) coupling may be due to the MR effect of Maxwell-Wagner type and/or field induced dipolar relaxation. Further it is observed that the oxygen stoichiometry plays a very crucial role in observed MD coupling.

cond-mat.str-el↗

Interplay between Phonon Confinement and Fano Effect on Raman line shape for semiconductor nanostructures: Analytical study

Theoretical Raman line shape functions have been studied to take care of quantum confinement effect and Fano effect individually and jointly. The characteristics of various Raman line shapes have been studied in terms of the broadening and asymmetry of Raman line shapes. It is shown that the asymmetry in the Raman line-shape function caused by these two effects individually does not add linearly to give asymmetry of line-shape generated by considering the combined effect. This indicates existence of interplay between the two effects. The origin of interplay lies in the fact that Fano effect itself depends on quantum confinement effect and in turn provides an asymmetry. This can not be explained by considering the two effects contribution independent of each other.

cond-mat.mes-hall↗

Effect of silicon resistivity on its porosification using metal induced chemical etching

A comparison of porous structures formed from silicon (Si) wafers with different resistivities has been reported here based on the morphological studies carried out using scanning electron microscope (SEM). The porous Si samples have been prepared using metal induced etching (MIE) technique from two different Si wafers having two different resistivities. It is observed that porous Si containing well aligned Si nanowires are formed from high resistivity (1-20 $Ω$cm) Si wafer whereas interconnected pores or cheese like structures are formed from low resistivity (0.02 $Ω$cm ) Si wafers after MIE. An explanation for the different porosification processes has also been proposed based on the initial doping level where number of dopants seems to be playing an important role on the etching process. Visible photoluminescence have been observed from all the porous samples possibly due to quantum confinement effect.

cond-mat.mes-hall↗

Geometrical Localization Algorithm for 3-D Wireless Sensor Networks

In this paper, we propose an efficient range free localization scheme for large scale three dimensional wireless sensor networks. Our system environment consists of two type of sensors, randomly deployed static sensors and global positioning system equipped moving sensors. These moving anchors travels across the network field and broadcast their current locations on specified intervals. As soon as the sensors which are deployed in random fashion receives three beacon messages (known locations broadcasted by anchors), they computes their locations automatically by using our proposed algorithm. One of our significant contributions is, we use only three different beacon messages to localize one sensor, while in the best of our knowledge, all previously proposed methods use at least four different known locations. The ability of our method to localize by using only three known locations not only saves computation, time, energy, but also reduces the number of anchors needed to be deployed and more importantly reduces the communication overheads. Experimental results demonstrate that our proposed scheme improves the overall efficiency of localization process significantly. Important Note: Final version of this paper is accepted and published by Journal of Wireless Personal Communication, Springer : June, 2014 The final version of publication is available at link.springer.com Link: http://link.springer.com/article/10.1007\%2Fs11277-014-1852-6

cs.NI↗

Micro-Raman and field emission studies of silicon nanowires prepared by metal assisted chemical etching

Micro-Raman scattering and electron field emission characteristics of silicon nanowires (SiNWs) synthesized by metal assisted chemical etching (MACE) are investigated. Scanning electron microscopy images reveal the growth of well aligned vertical SiNWs. Raman shift and size relation from bond-polarizability model has been used to calculate exact confinement sizes in SiNWs. The Si optical phonon peak for SiNWs showed a downshift and an asymmetric broadening with decreasing diameter of the SiNWs due to quantum confinement of optical phonons. The field emission characteristics of these SiNWs are studied based by carrying out current-voltage measurements followed by a theoretical analysis using Fowler-Nordheim equation. The electron field emission increased with decreasing diameter of SiNWs. Field emission from these SiNWs exhibits significant enhancement in turn-on field and total emission current with decreasing nanowire size. The reported results in the current study indicate that MACE is a simple technique to prepare well-aligned SiNWs with potentials for applications in field emission devices.

cond-mat.mes-hall↗

Comparison of porous silicon prepared using metal-induced etching (MIE) and laser-induced etching (LIE)

Porous silicon (p-Si), prepared by two routes (metal induced etching (MIE) and laser induced etching (LIE)) have been studied by comparing the observed surface morphologies using SEM. A uniformly distributed smaller (submicron sized) pores are formed when MIE technique is used because the pore formation is driven by uniformly distributed metal (silver in present case) nanoparticles, deposited prior to the porosification step. Whereas in p-Si, prepared by LIE technique, wider pores with some variation in pore size as compared to MIE technique is observed because a laser having gaussian profile of intensity is used for porosification. Uniformly distribute well-aligned Si nanowires are observed in samples prepared by MIE method as seen using cross-sectional SEM imaging. A single photoluminescence (PL) peak at 1.96 eV corresponding to red emission at room temperature is observed which reveals that the Si nanowires, present in p-Si prepared by MIE, show quantum confinement effect. The single PL peak confirms the presence of uniform sized nanowires in MIE samples. These vertically aligned Si nanowires can be used for field emission application.

cond-mat.mes-hall↗

Convergence analysis of a finite volume scheme for solving non-linear aggregation-breakage population balance equations

This paper presents stability and convergence analysis of a finite volume scheme (FVS) for solving aggregation, breakage and the combined processes by showing Lipschitz continuity of the numerical fluxes. It is shown that the FVS is second order convergent independently of the meshes for pure breakage problem while for pure aggregation and coupled equations, it shows second order convergent on uniform and non-uniform smooth meshes. Furthermore, it gives only first order convergence on non-uniform grids. The mathematical results of convergence analysis are also demonstrated numerically for several test problems.

math.NA↗

A Fast Compressive Sensing Based Digital Image Encryption Technique using Structurally Random Matrices and Arnold Transform

A new digital image encryption method based on fast compressed sensing approach using structurally random matrices and Arnold transform is proposed. Considering the natural images to be compressed in any domain, the fast compressed sensing based approach saves computational time, increases the quality of the image and reduces the dimension of the digital image by choosing even 25 % of the measurements. First, dimension reduction is utilized to compress the digital image with scrambling effect. Second, Arnold transformation is used to give the reduced digital image into more complex form. Then, the complex image is again encrypted by double random phase encoding process embedded with a host image; two random keys with fractional Fourier transform are been used as a secret keys. At the receiver, the decryption process is recovered by using TwIST algorithm. Experimental results including peak-to-peak signal-to-noise ratio between the original and reconstructed image are shown to analyze the validity of this technique and demonstrated our proposed method to be secure, fast, complex and robust.

cs.CR↗

Fast Ion Surface Energy Loss and Straggling in the Surface Wake Fields

We have measured the stopping powers and straggling of fast, highly ionized atoms passing through thin bilayer targets made up of metals and insulators. We were surprised to find that the energy losses as well as the straggling depend on the ordering of the target and have small but significantly different values on bilayer reversal. We ascribe this newly found difference in energy loss to the surface energy loss field effect due to the differing surface wake fields as the beam exits the target in the two cases. This finding is validated with experiments using several different projectiles, velocities, and bilayer targets. Both partners of the diatomic molecular ions also display similar results. A comparison of the energy loss results with those of previous theoretical predictions for the surface wake potential for fast ions in solids supports the existence of a self-wake.

physics.atom-ph↗

Evolution of Asymmetric Raman line-shape from nano-structures

A step-by-step evolution of an asymmetric Raman line-shape function from a Lorentzian line-shape is presented here for low dimensional semiconductors. The evolution reported here is based on the phonon confinement model which is successfully used in literature to explain the asymmetric Raman line-shape from semiconductor nano-structures. Physical significance of different terms in the theoretical asymmetric Raman line-shape has been explained here. Better understanding of theoretical reasoning behind each term allows one to use the theoretical Raman line-shape without going into details of theory from first principle. This will enable one to empirically derive a theoretical Raman line-shape function for any material if information about its phonon dispersion, size dependence etc is known.

cond-mat.mes-hall↗

Fabrication of silicon nanocrystals using sequential Au ion implantation

Silicon nanocrystals are produced using a two-stage gold ion implantation technique. First stage implantation using low energy ions leads to the formation of an amorphous Si (a-Si) layer. A subsequent high energy Au irradiation in the second stage is found to produce strained Si NCs. An annealing at a temperature as low as 500$^o$C is seen to result in strain free NCs showing quantum confinement effects. Higher temperature annealing of the samples is found to result in growth in size from recrystallization of the a-Si matrix. Raman Scattering, X-ray diffraction (XRD) and Rutherford Backscattering spectrometry (RBS) have been used to study the effect of annealing on the samples and the size of Si NCs formed. The data could be well explained using a phonon confinement model with an extremely narrow size distribution. XRD results go in line with Raman analysis.

cond-mat.mes-hall↗