Physics

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Bit error rate (BER) and channel capacity are two important metrics to assess the performance of free-space optical communication (FSOC) systems. Due to the fading of the optical signal owing to the atmospheric effects, these two quantities behave as random variables. Most of the studies in this direction have focused on the calculation of only the average of these quantities. However, since the complete information about a random variable is encoded in its distribution, it is more informative to examine the latter itself. In this work, the authors derive exact probability density function (PDF) expressions for the BER and the channel capacity for an arbitrary irradiance model. In particular, they investigate these exact results for log-normal, gamma-gamma, and K distributions. For the BER analysis, they focus on the binary phase shift keying and quadrature phase shift keying modulation schemes. The authors' analytical reults are found to be in conformity with Monte Carlo simulations. The exact PDFs of the BER and the channel capacity reveal that there are several instances when the average is unable to capture the actual behaviour of these quantities, and therefore one must be careful in drawing conclusions based on the first moment only. © The Institution of Engineering and Technology 2019

(SoNS) School of Natural Sciences

Computer Science and Engineering

(SoE) School of Engineering

Fulltext

IET Communications

Exact distributions for bit error rate and channel capacity in free-space optical communication

In the present study, an ionic liquid (IL), known as green solvent, 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4) with four carbons in the hydrophobic chain (C-4) has been used as an additive to modify the self-assembled aggregates of an anionic surfactant sodium dodecyl sulfate (SDS) and then the evolution of the liquid crystalline phases has been investigated. Small angle synchrotron x-ray diffraction study has revealed an unprecedented phase sequence where a hexagonal phase (HI) of direct cylindrical micelles is observed to evolve to another hexagonal phase (HII) of, again, direct cylindrical micelles with a lamellar phase (Lα) as the intermediate. The rheological data and the theoretical calculations have confirmed the phases. To understand such a phase behaviour of the system, the work is extended by considering the ionic liquids with the same head group but of shorter (C-2) and longer (C-10) hydrocarbon chains compared to BMIM-BF4. While the shorter chain IL causes the hexagonal phase to form rectangular (R) phase, the longer chain is observed to induce the lamellar phase (Lα). The molecular mechanism of appearance of such different phases has been discussed. © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group.

Liquid Crystals

Re-entrant direct hexagonal phases in a lyotropic system of surfactant induced by an ionic liquid

A clear understanding of the surface chemical reactivity of tungsten (W) films is indispensable for photocatalytic, sensing and memory applications, especially in the presence of WO x (0 ≤ x ≤ 3) for low thicknesses. Here, surface reactivity of the film through diffusion of oxygen and its ability to make bonds with W is identified by X-ray photoelectron spectroscopy (XPS). Further inspection of XPS valence band spectra confirms the possible hybridization of W 5d and O 2p electrons in the presence of defect states near Fermi level. Exploration of surface morphology by scanning electron microscopy (SEM) reveals agglomeration of grains with increasing film thickness. Detailed microstructural and grazing-incidence X-ray diffraction (GIXRD) studies suggest the formation of β W nanocrystallites in amorphous matrix, and establish a knowledge of thickness dependent phase transformation of W beside surface oxidation. The nonlinear surface current–voltage characteristics at low thickness further indicates dimensional phase change owing to the involvement of point defects. We also report a detailed study of interstitial and vacancy mediated diffusion probability of oxygen in W films, where the estimated diffusion constant is found to be relatively higher than that of other body-centered cubic transition metals. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.

World University root node

Journal of Materials Science: Materials in Electronics

Probing the impact of surface reactivity on charge transport in dimensional phase changed tungsten films

This paper presents a plasma display device (PDD) based on laser-induced graphene nanoribbons (LIGNs), which were directly fabricated on polyimide sheets. Superior field electron emission (FEE) characteristics, viz. a low turn-on field of 0.44 V/µm and a large field enhancement factor of 4578, were achieved for the LIGNs. Utilizing LIGNs as a cathode in a PDD showed excellent plasma illumination characteristics with a prolonged plasma lifetime stability. Moreover, the LIGN cathodes were directly laser-patternable. Such superior plasma illumination performance of LIGN-based PDDs has the potential to make a significant impact on display technology. © 2019 by the authors. Licensee MDPI, Basel, Switzerland.

Nanomaterials

Laser-patternable graphene field emitters for plasma displays

The largest eigenvalue distribution of the Wishart?Laguerre ensemble, indexed by Dyson parameter and Laguerre parameter a, is fundamental in multivariate statistics and finds applications in diverse areas. Based on a generalisation of the Selberg integral, we provide an effective recursion scheme to compute this distribution explicitly in both the original model, and a fixed-trace variant, for a, non-negative integers and finite matrix size. For = 2 this circumvents known symbolic evaluation based on determinants which become impractical for large dimensions. Our exact results have immediate applications in the areas of multiple channel communication and bipartite entanglement. Moreover, we are also led to the exact solution of a long standing problem of finding a general result for Landauer conductance distribution in a chaotic mesoscopic cavity with two ideal leads. Thus far, exact closed-form results for this were available only in the Fourier?Laplace space or could be obtained on a case-by-case basis. © 2019 IOP Publishing Ltd.

Journal of Physics A: Mathematical and Theoretical

Recursion scheme for the largest-Wishart-Laguerre eigenvalue and Landauer conductance in quantum transport

A new realization of extended quantum-mechanical supersymmetry (QM SUSY) with central extension is investigated. We first show that two different sets of d+2 (d+1) supercharges for d=even (odd), each of which satisfies an N=d+2 (d+1) extended QM SUSY algebra without central extension, are hidden in the four-dimensional mass spectrum of the (4+d)-dimensional Dirac action. We then find that the whole set of the supercharges forms an N=2d+4 (2d+2) extended QM SUSY algebra with central charges for d=even (odd). The representation of the supersymmetry algebra is shown to be 1/2-Bogomol'nyi-Prasad-Sommerfield states that correspond to a short representation for the supersymmetry algebra with a central extension. We explicitly examine the four-dimensional mass spectrum of the models with the hyperrectangle and the torus extra dimensions, and discuss their supersymmetric structures. © 2019 authors. Published by the American Physical Society.

Physical Review D

Extended supersymmetry with central charges in higher dimensional Dirac action

V51 nuclear magnetic resonance (NMR) and magnetization studies on CeTi1-xVxGe3 have been performed to explore the evolution from the ferromagnetic (x=0.113) to the antiferromagnetic Kondo lattice state (x=1), with focus on the emergence of a possible ferromagnetic quantum critical point (FMQCP) at xc≈0.4. From the temperature dependence of the nuclear spin-lattice relaxation rate, 1/T1T and the Knight shift, K, for x=0.113 and x=1 a considerable competition between ferro- A nd antiferromagnetic correlations is found. Around the critical concentration (x=0.35,0.405), quantum-critical spin fluctuations entail weak antiferromagnetic spin fluctuations admixed with ferromagnetic spin fluctuations. The FMQCP in CeTi1-xVxGe3 therefore is not purely ferromagnetic in nature.

Physical Review B

Competing magnetic correlations across the ferromagnetic quantum critical point in the Kondo system CeTi1-x VxGe3: V 51 NMR as a local probe

Graphene oxide (GO) is an attractive precursor for graphene, provided by the well-known wet-chemical oxidative process. The intercalation of acid in graphite is considered as a crucial step, and its subsequent oxidation holds special relevance in synthesis. So far, the above chemistry is dominated by usage of H2SO4. Recently, H3PO4 appeared as a suitable intercalant for graphite. However, its role is not well understood in the formation of GO, especially when present as a co-acid with H2SO4. Additionally, a relatively lower toxicity of H3PO4 as compared to H2SO4, elimination of toxic NaNO3 usage, and a facile purification protocol are encouraging in terms of low-cost production of GO with a reduced environmental impact. Here, we report the systematic synthesis and characterization of GOs prepared with the variation in the ratio of H2SO4 and H3PO4. Ab initio simulations revealed that intercalation is primarily affected because of the usage of a mixture of co-acids. Interestingly, the ratio of the acids dictated the nature of the functionalities, extent of the defects, and morphology of the GOs, accounting for a pronounced effect on thermal stability, contact angle, zeta potential, and hydrodynamic size. The oxidation mechanism showed a predominance of H2SO4 content, whereas H3PO4 is found to mainly govern the intercalation of graphite, thereby affecting the acid-based intercalation-oxidation chemistry of graphite. The as-prepared GO suspension exhibited a high adsorption capacity for methylene blue dye removal in water, suggesting its potential as an adsorbent material in water treatment. The utility of the two acids affects the acid-based intercalation-oxidation chemistry of graphite and simultaneously may open up new opportunities for synthesized GOs, on tenets of green chemistry, in a wide arena of applications. © 2019 American Chemical Society.

Chemistry

ACS Omega

Control of Functionalities in GO: Effect of Bronsted Acids as Supported by Ab Initio Simulations and Experiments

Quantum and noncommutative corrections to the Newtonian law of inertia are considered in the general setting of Verlinde's entropic force postulate. We demonstrate that the form for the modified Newtonian dynamics (MOND) emerges in a classical setting by seeking appropriate corrections in the entropy. We estimate the correction term by using concrete coherent states in the standard and generalized versions of Heisenberg's uncertainty principle. Using Jackiw's direct and analytic method, we compute the explicit wavefunctions for these states, producing minimal length as well as minimal products. Subsequently, we derive a further selection criterium restricting the free parameters in the model in providing a canonical formulation of the quantum corrected Newtonian law by setting up the Lagrangian and Hamiltonian for the system. © 2019 World Scientific Publishing Company.

International Journal of Modern Physics B

Quantum, noncommutative and MOND corrections to the entropic law of gravitation

The controlled incorporation of defect species in amorphous oxide (AO) for regulating charge transport properties is highly demanding and challenging, especially for resistive switching (RS) memories. Here, we use pulsed electron beam deposition technique to engineer the growth of AO films, which show a large decrease (â33\%) in the t2g-eg gap. Our collective experiments and density functional theory (DFT) based ab initio simulations reveal the presence of undercoordinated TiO5 units, causing a decrease in the t2g-eg gap. Further, the importance of TiO5 in facilitating excess electron localization is demonstrated, showing an evolution of a broad defect band within the energy gap. The origin of this band (singly charged oxygen vacancy) is resolutely established by X-ray photoelectron spectroscopy and electron paramagnetic resonance measurements and is also supported by calculated partial charge density and Bader charge analysis. The preeminence of singly charged oxygen vacancies cause a low-current level (up to 1-5 nA) RS operation with a gradual change of resistance states, which could set their path for the energy-efficient neuromorphic computing application. Finally, a new model based on probabilistic Markov chain algorithm is also developed to unfold the gradual change of resistance states from the fundamental defect interaction perspective. © 2019 American Chemical Society.