Physics

<p>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.</p>

Shiv Nadar University

One of the less well-understood ambiguities of quantization is emphasized to result from the presence of higher-order time derivatives in the Lagrangians resulting in multiple-valued Hamiltonians. We explore certain classes of branched Hamiltonians in the context of nonlinear autonomous differential equation of Liénard type. Two eligible elementary nonlinear models that emerge are shown to admit a feasible quantization along these lines. © 2015 World Scientific Publishing Company.

(SoNS) School of Natural Sciences

World University root node

Fulltext

Modern Physics Letters A

Exploring branched Hamiltonians for a class of nonlinear systems

A series of donor-acceptor-donor (D-A-D) scheme based organic molecules was studied to examine the dependence of molecular structure and electronic properties on the D/A ratio and the strength of the acceptor moiety, using first-principles density-functional-theory based calculations. Thiophenes were taken as the donor moiety and a series of benzo-X-diazoles and benzobis-X-diazoles (X = O, S, Se, and Te) were considered to account the strength of the acceptor moieties. The role of different exchange-correlation functionals was also investigated to search for the functional that best describes the properties of such D-A-D based molecules. Our systematic calculations reveal that both the D/A ratio and the strength of the acceptor moiety largely affect the energy gap between energies of the highest occupied molecular orbital (H) and the lowest unoccupied molecular orbital (L). In thiophene-benzo-X-diazole molecules, the H-L gap varies from 7\% to 25\%, whereas in thiophene-benzobis-X-diazoles, it can be tuned from 40\% to 80\%, by changing the D/A ratio from 0.5 to 4.0. In the latter case, higher steric hindrance (>50°) between A-A units disrupts the conjugation length with the increase in acceptor units. This leads to a monotonic decrease of the H-L gap with the increase in the D/A ratio, and a larger variation as compared to the case for thiophene-benzo-X-diazoles. On accounting for the effect of strength of the acceptor moiety, we observed that the H-L gap of the bis molecule was roughly 1 eV smaller than its respective non-bis configuration. A decrease in the H-L gap was also found on moving from S to Se to Te. Quantitatively, the H-L gap of the investigated molecules was found within a wide range of 0.2-2.4 eV, which not only is smaller than the H-L gap of isolated thiophene or the benzo-(bis)X-diazole molecules but also lies in the desired range for the applications in optoelectronic devices, including solar cells. Thus, our study affirms that by choosing a suitable acceptor moiety and the D/A ratio, the structural and electronic properties of D-A-D based materials can be widely tuned. Through this work we emphasize the need to understand the tuning of molecular properties by examining the structure-property correlation, which is essential for rational design of high performing novel organic materials. © 2015 American Chemical Society.

Journal of Physical Chemistry C

Dependence of the Structure and Electronic Properties of D-A-D Based Molecules on the D/A Ratio and the Strength of the Acceptor Moiety

In this paper we will discuss the range of large tensor to scalar ratio, r, obtainable from a sub-Planckian excursion of a single, slow roll driven inflaton field. In order to obtain a large r for such a scenario one has to depart from a monotonic evolution of the slow roll parameters in such a way that one still satisfies all the current constraints of, such as the scalar amplitude, the tilt in the scalar power spectrum, running and running of the tilt close to the pivot scale. Since the slow roll parameters evolve non-monotonically, we will also consider the evolution of the power spectrum on the smallest scales, i.e. at s (k ∼ 1016 Mpc-1)<∼ 10-2, to make sure that the amplitude does not become too large. All these constraints tend to keep the tensor to scalar ratio, r <∼ 0.1. We scan three different kinds of potential for supersymmetric flat directions and obtain the benchmark points which satisfy all the constraints. We also show that it is possible to go beyond r >∼ 0.1 provided we relax the upper bound on the power spectrum on the smallest scales.

Journal of Cosmology and Astroparticle Physics

Bound on largest r &lt;∼ 0.1 from sub-Planckian excursions of inflaton

Abstract: In view of the recent interest in the pMSSM with light third generation squarks, we consider a hitherto neglected scenario where the lighter bottom squark (formula presented) is the next lightest supersymmetric particle (NLSP) which co-annihilates with the lightest supersymmetric particle (LSP), the dark matter (DM) candidate. Since the co-annihilation cross section receives contributions from both electroweak and strong vertices, it is relatively large. As a result relatively large NLSP-LSP mass difference (25-35 GeV) is consistent with the PLANCK data. This facilitates the LHC signatures of this scenario. We consider several variants of the sbottom NLSP scenario with and without light stops and delineate the parameter space allowed by the PLANCK data. We point out several novel signal (e.g., (formula presented) which are not viable in the stop NLSP scenario of DM production. Finally, we consider gluino (formula presented) decays in this scenario and using the current ATLAS data in the jets (with or without b-tagging) + (formula presented) channel, obtain new limits in the (formula presented) mass plane. We find that for (formula presented) upto 500 GeV, (formula presented)≥ 1.1-1.2 TeV in this scenario.

Journal of High Energy Physics

Gluino mass limits with sbottom NLSP in coannihilation scenarios

We report a Li7 nuclear magnetic resonance (NMR) study of a frustrated three-dimensional spin-12 antiferromagnet Li2CuW2O8 and also explore the effect of nonmagnetic dilution. The magnetic long-range ordering in the parent compound at TN≃3.9K was detected from the drastic line broadening and a peak in the spin-lattice relaxation rate (1/T1). The NMR spectrum above TN broadens systematically and its full width at half maximum (FWHM) tracks the static spin susceptibility. From the analysis of FWHM vs static susceptibility, the coupling between the Li nuclei and Cu2+ ions was found to be purely dipolar in nature. The magnitude of the maximum exchange coupling constant is Jmax/kB≃13K. NMR spectra below TN broaden abruptly and transform into a double-horn pattern reflecting the commensurate nature of the spin structure in the ordered state. Below TN, 1/T1 follows a T5 behavior. The frustrated nature of the compound is confirmed by persistent magnetic correlations at high temperatures well above TN. The dilution of the spin lattice with nonmagnetic Zn atoms has dramatic influence on TN that decreases exponentially similar to quasi-one-dimensional antiferromagnets, even though Li2CuW2O8 has only a weak one-dimensional anisotropy. Heat capacity of doped samples follows power law (Cp T$\alpha$) below TN and the exponent ($\alpha$) decreases from 3 in the parent compound to 1 in the 25% doped sample.

Physical Review B - Condensed Matter and Materials Physics

Frustrated three-dimensional antiferromagnet Li2CuW2O8: Li 7 NMR and the effect of nonmagnetic dilution

Hexagonal $\alpha$-Ru trichloride single crystals exhibit a strong magnetic anisotropy and we show that upon applying fields up to 14 T in the honeycomb plane the successive magnetic order at T1=14K and T2=8K could be completely suppressed, whereas in the perpendicular direction the magnetic order is robust. Furthermore, the field dependence of $\chi$(T) implies coexisting ferro- and antiferromagnetic exchange between in-plane components of Ru3+ spins, whereas for out-of-plane components a strong antiferromagnetic exchange becomes evident. Ru101 zero-field nuclear magnetic resonance in the ordered state evidence a complex (probably noncoplanar chiral) long-range magnetic structure. The large orbital moment on Ru3+ is found in density-functional calculations.

Anisotropic Ru3+ 4d5 magnetism in the $\alpha$-RuCl3 honeycomb system: Susceptibility, specific heat and zero-field NMR anisotropic Ru3+4d5 magnetism in the ⋯ M. Majumder et al.

We have demonstrated that the gel-like mesophase of Cetyltrimethylammonium bromide (CTAB) can be synthesized by judicial adjustment of water to surfactant molar ratio (W0), without using any additional salts, gelating agents or co-surfactants. Gel formation was found to be highly dependent on the water to surfactant molar ratio (W0), with the lowest value of W0 (41.5) resulting in rapid gel formation. Environmental scanning electron microscope (ESEM) analysis revealed that the gel was comprised of interconnected cylindrical structures. The presence of hydrogen bonding in the gel-like mesophase was confirmed by Fourier Transform Infrared spectroscopy (FTIR) analysis. Rheology measurements revealed that all the gel samples were highly viscoelastic in nature. Furthermore, Au and Ag containing CTAB gels were explored as precursors for the preparation of spherical Gold (Au) and Silver (Ag) nanoparticles using Sodium borohydride (NaBH4) as reducing agent. The effects of NaBH4 concentration on the particle size and morphology of the Au and Ag nanoparticles have also been studied. © 2015 Elsevier B.V.

Materials Chemistry and Physics

Fast and facile preparation of CTAB based gels and their applications in Au and Ag nanoparticles synthesis

We provide a proof to a recent conjecture by Forrester (2014 J. Phys. A: Math. Theor. 47 065202) regarding the algebraic and arithmetic structure of Meijer G-functions which appear in the expression for probability of all eigenvalues real for the product of two real Gaussian matrices. In the process we come across several interesting identities involving Meijer G-functions. © 2015 IOP Publishing Ltd.

Journal of Physics A: Mathematical and Theoretical

Exact evaluations of some Meijer G-functions and probability of all eigenvalues real for the product of two Gaussian matrices

Gold nanoparticles (Au NPs) were synthesized using Au containing CTAB gel as a precursor. The effect of concentration of NaBH4 on the structural, optical, catalytic and electrochemical properties of the Au NPs was also investigated. With the increase of NaBH4 concentration from 0.1 to 0.15 M, an increase in the particle size and change in the morphology from spherical to elliptical was observed. Absorption and emission properties of the Au NPs were also probed using UV–Vis and photoluminescence spectroscopy respectively. Synthesized Au NPs samples were explored as catalyst for the reduction of 4-nitrophenol to 4-aminophenol. Catalytic activity of Au NPs samples prepared using 0.1 and 0.15 M concentration of NaBH4 were also compared. It was found that Au NPs prepared using lower concentration of NaBH4 (Au-0.1) exhibits better catalytic activity compared to the other Au NPs sample (Au-0.15). Synthesized Au NPs were also utilized as electrode material for the detection of Pb2+ ions, results show that Au NPs modified glassy carbon electrode can detect very low concentration of Pb2+ ions (2 µM). Au-0.1 sample exhibited better electrochemical performance compared to the Au-0.15 sample. © 2015, Springer Science+Business Media New York.

Journal of Materials Science: Materials in Electronics

Optical, structural, catalytic and electrochemical properties of the Au nanoparticles synthesized using CTAB based gels

We investigate bicomplex Hamiltonian systems in the framework of an analogous version of the Schrodinger equation. Since in such a setting three different types of conjugates of bicomplex numbers appear, each is found to define, in a natural way, a separate class of time reversal operator. However, the induced parity (P)-time (T)-symmetric models turn out to be mutually incompatible, except for two of them which could be chosen uniquely. The latter models are then explored by working within an extended phase space. Applications to the problems of harmonic oscillator, inverted oscillator and isotonic oscillator are considered and many new interesting properties are uncovered for the new types of PT symmetries. © 2015 IOP Publishing Ltd.