Physics

Shiv Nadar University is a comprehensive, multidisciplinary, research-focused, and student-centric University offering a full range of academic programs at the undergraduate, postgraduate and doctoral level. With state-of-the-art infrastructure, the University comprises of academic wings, sophisticated labs, international standard sports facilities, amphitheaters, auditorium, conference rooms and smart classrooms. The University&rsquo;s goal is to become internationally recognized for the quality of its research and creative endeavors and their applicability to improving quality of life, generating new insights and expanding the boundaries of human knowledge creativity. Committed to excellence in teaching, research and service, the University aims to serve the higher education needs of India and the world beyond.

Shiv Nadar University

A new analytical approximate expression for K distribution is proposed by expanding it in terms of orthogonal associated Laguerre polynomial. The expansion is truncated after first three terms, which yields a fairly close approximation to K distribution. The advantage of the proposed approximation is that the analytical closed form expression for bit error rate can be easily derived. KL measure is used to show the accuracy of the proposed approximation. The proposed approximate probability density function and bit error rate work well within the desired range of the channel parameter α, which is 1 &lt; α &lt; 2 and corresponds to the scintillation index value ranging from 2 to 3. We have also demonstrated the utility of our approximation for other quality of service metric such as fade probability. © 2009-2012 IEEE.

Computer Science and Engineering

(SoE) School of Engineering

(SoNS) School of Natural Sciences

Fulltext

IEEE Photonics Journal

A novel approximation for K distribution: Closed-form BER using DPSK modulation in free-space optical communication

The modifications of Poly(3-Hexylthiophene) (P3HT) thin films have been investigated by irradiating with 90 MeV Ni7+ ions at different fluences (1 × 109 to 1 × 1011 ions/cm2). Thin films have been characterized by micro-Raman Spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), UV-visible absorption Spectroscopy, Photoluminescence spectroscopy (PL), Atomic Force Microscopy (AFM) and small angle X-ray scattering (SAXS) analysis. The narrow FWHM of C=C mode and the larger intensity ratio of C-C and C=C modes are identified at low fluences. The IR active modes with increased intensity indicates the increased conjugation length, while the XRD analysis revels the improved crystallinity with enhanced molecular ordering. The XPS analysis shows that chemical bonding nature near the film surface is not affected by irradiation. The room temperature electrical conductivity is found to be increased from 2.48 × 10−6 to 1.35 × 10−5 Ω−1cm−1 at the fluence of 1 × 1010 ions/cm2. The temperature dependence of dc conductivity has been explained using Mott's variable range hopping model. SAXS detector images confirm the presence of ion tracks and density variation between the track core and halo regions. It is found that less intense heating effect in the halo region of ion path could induce the molecular ordering of P3HT. © 2016 Elsevier Ltd

World University root node

Vacuum

Ion irradiation induced modifications of P3HT: A donor material for organic photovoltaic devices

In the present work, the suitability of Aloe vera (AV) as a 'green reducing agent' has been investigated for the reduction of graphene oxide (GO). The extent of reduction was studied by varying the amount of AV. The physical and chemical properties of the GO and reduced graphene oxide (rGO) were investigated using UV-Vis spectrophotometry, FT-IR spectroscopy, High Resolution Transmission Electron Microscopy (HRTEM) and Selected Area Electron Diffraction (SAED). Partially reduced graphene oxide sheets obtained with 7.5 g of AV (rGO-7.5) demonstrated a maximum reduction efficiency of about 73\% as evident from FT-IR data. Cyclic voltammetry and electrochemical impedance spectroscopy studies revealed a significant enhancement in current density and a decrease in charge transfer resistance for the rGO-7.5 sample. Moreover, the as prepared rGO-7.5 sample showed a remarkable dye removal ability with a maximum efficiency of ∼98\%. The enhanced surface area, π-π interaction and strong electrostatic attraction were correlated with the dye removal capability. The adsorption kinetics were also studied and pseudo second order adsorption phenomena were confirmed. The recyclability of the rGO-7.5 sample was further investigated and an excellent desorption capability was established. © 2017 The Royal Society of Chemistry.

RSC Advances

Aloe vera assisted facile green synthesis of reduced graphene oxide for electrochemical and dye removal applications

Nanoscale evidence of self-recovery in resistive switching (RS) behavior was found in TiO2-x film by conductive atomic force microscopy when exposed to Ar+-ions above a threshold fluence of 1 × 1016 ions cm-2. This revealed an evolution and gradual disappearance of bipolar RS-loops, followed by reappearance with increasing number of voltage sweep. This was discussed in the realm of oxygen vacancy (OV) driven formation, dissolution and reformation of conducting filaments. The presence of OVs in ion-beam irradiated TiO2-x films was evidenced by decreasing trend of work function in scanning-Kelvin probe microscopy, and was further verified by x-ray absorption near edge spectroscopy at Ti and O-K edges. © 2017 IOP Publishing Ltd.

Journal of Physics D: Applied Physics

Nanoscale self-recovery of resistive switching in Ar+ irradiated TiO2-x films

The sum of Wishart matrices has an important role in multiple-input multiple-output (MIMO) multiple access channel (MAC) and MIMO relay channel. In this paper, we present a new closed-form expression for the marginal density of one of the unordered eigenvalues of a sum of $K$ complex central Wishart matrices having covariance matrices proportional to the identity matrix. The expression is general and allows for any set of linear coefficients. The derived expression is used to obtain the ergodic sum-rate capacity for the MIMO-MAC and MIMO relay cases, both as closed-form expressions. We also present a very simple expression to approximate the sum of Wishart matrices by one equivalent Wishart matrix. The agreement between the exact eigenvalue distribution and numerical simulations is perfect, whereas for the approximate solution the difference is indistinguishable. © 1967-2012 IEEE.

IEEE Transactions on Vehicular Technology

On the Exact and Approximate Eigenvalue Distribution for Sum of Wishart Matrices

The interaction of phospholipids with the peripheral membrane proteins like spectrin is important not only to understand the various physiological functions of cells, but also to gain insight into the mechanism involved in the self-assembly of polymer-like long chain molecules at the soft surfaces and interfaces. The lipid head-group specificity of adsorption of spectrin to supported phopsholipid bilayer model membranes has been investigated using the X-ray reflectivity (XRR) technique. Model lipid bilayers composed of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) head groups have been prepared on a soft polymer cushion and the XRR measurements have been carried out from the bilayers immersed in a water bath using high-energy synchrotron X-rays. Our results suggest that in PC-based membranes the spectrin chains form a uniform layer on top of the bilayer with their chains lying on the membrane surface, while in PE-based membranes with relatively smaller head groups, the spectrin chains are attached only through a few possible binding sites with the rest of the part projected out of the membrane surface. In addition, the reflectivity profiles reveal the penetration of spectrin polypeptide chains through the PE bilayer in its fluid phase. Pressure-area isotherm measurements on Langmuir monolayers also support similar observations on the adsorption of spectrin molecules to the membranes composed of PC and PE. The observed results were explained using a qualitative model based on the ion-mediated protein interaction in the PC-based membrane. © CopyrightEPLA, 2017.

Differential adsorption of a membrane skeletal protein, spectrin, in phospholipid membranes

This work describes a simple wet chemical synthesis of iron oxide (Fe3O4) nanoparticles (NPs) capped with terephthalic acid (TA) and their application for the individual detection of Hg(II), Pb(II) and Cd(II) ions as well as simultaneous and selective detection of Hg(II), Pb(II) and Cd(II) ions by electrochemical approach. Terephthalic acid capped Fe3O4 NPs were first characterized by cyclic voltammetry (CV) using redox couples Fe(CN)63&nbsp;−/4&nbsp;−, thereafter square wave anodic stripping voltammetry (SWASV) was utilized for the detection of Hg(II), Pb(II) and Cd(II) ions. Optimization of experimental parameters such as deposition time, deposition potential and pH value of the electrolyte towards electrochemical detection of target heavy metal ions was also carried out in SWASV method. Under optimized experimental conditions limit of detection (LOD) values for individual analysis of Hg(II), Pb(II) and Cd(II) ions were found to be 0.1, 0.05&nbsp;μM and 0.01&nbsp;μM respectively, whereas the LOD values for the simultaneous analysis of Hg(II), Pb(II) and Cd(II) ions were found to be 0.3&nbsp;μM, 0.04&nbsp;μM and 0.2&nbsp;μM respectively. © 2017 Elsevier B.V.

Journal of Electroanalytical Chemistry

Terephthalic acid capped iron oxide nanoparticles for sensitive electrochemical detection of heavy metal ions in water

Verhandlungen der Deutschen Physikalischen Gesellschaft

Spin liquid behavior in the triangular lattice iridate Ba3InIr2O9

Ionic liquids (ILs) are potential candidates for new antimicrobials due to their tunable antibacterial and antifungal properties that are required to keep pace with the growing challenge of bacterial resistance. To a great extent their antimicrobial actions are related to the interactions of ILs with cell membranes. Here, we report the effects of ILs on the nanoscopic dynamics and phase behaviour of a dimyristoylphosphatidylcholine (DMPC) membrane, a model cell membrane, as studied using neutron scattering techniques. Two prototypical imidazolium-based ILs 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM[BF4]) and 1-decyl-3-methylimidazolium tetrafluoroborate (DMIM[BF4]), which differ only in terms of the alkyl chain length of cations, have been used for the present study. Fixed Elastic Window Scan (FEWS) shows that the incorporation of ILs affects the phase behaviour of the phospholipid membrane significantly and the transition from a solid gel to a fluid phase shifts to lower temperature. This is found to be consistent with our differential scanning calorimetry measurements. DMIM[BF4], which has a longer alkyl chain cation, affects the phase behaviour more strongly in comparison to BMIM[BF4]. The pressure-area isotherms of the DMPC monolayer measured at the air-water interface show that in the presence of ILs, isotherms shift towards higher area-per lipid molecule. DMIM[BF4] is found to shift the isotherm to a greater extent compared to BMIM[BF4]. Quasielastic neutron scattering (QENS) data show that both ILs act as a plasticizer, which enhances the fluidity of the membrane. DMIM[BF4] is found to be a stronger plasticizing agent in comparison to BMIM[BF4] that has a cation with a shorter alkyl chain. The incorporation of DMIM[BF4] enhances not only the long range lateral motion but also the localised internal motion of the lipids. On the other hand, BMIM[BF4] acts weakly in comparison to DMIM[BF4] and mainly alters the localised internal motion of the lipids. Any subtle change in the dynamical properties of the membrane can profoundly affect the stability of the cell. Hence, the dominant effect of the IL with the longer chain length on the dynamics of the phospholipid membrane might be correlated with its cytotoxic activity. QENS data analysis has provided a quantitative description of the effects of the two imidazolium-based ILs on the dynamical and phase behaviour of the model cell membrane, which is essential for a detailed understanding of their action mechanism. © 2017 The Royal Society of Chemistry.

Soft Matter

Effects of ionic liquids on the nanoscopic dynamics and phase behaviour of a phosphatidylcholine membrane

A novel nanocomposite consisting of π-conjugated 2-aminoterephthalic acid (ATA) coated iron oxide (Fe3O4) nanoparticles and reduced graphene oxide (RGO) has been synthesized using a facile combination of wet-chemistry and low-power sonication. The ATA-Fe3O4/RGO nanocomposites exhibited a high specific capacitance of the order of 576 F g−1; significantly higher than that of pristine Fe3O4 (132 F g−1) and RGO (60 F g−1) counterparts, indicative of a synergistic effect between the ATA-Fe3O4 and RGO components. Furthermore, the maximum energy storage density was calculated to be 75 W h kg−1 (at a current density of 6 A g−1). The charging-discharging analysis showed promising long-term stability with nearly 86\% retention of the capacitance after 5000 cycles. The superior capacitive behaviour of these ATA-Fe3O4/RGO nanocomposites is attributed to the synergistic effect of the π-conjugated ATA coating on Fe3O4 which enhances the pseudo-capacitive charge transfer process of Fe3O4 and works in conjunction with the surface functional groups (such as carboxylic, amino and amide) present on the RGO surface, providing enhanced double layer capacitance. Thus, the current system exploits the advantages of both the double layer capacitors and pseudocapacitors in a hybrid structure. © The Royal Society of Chemistry.