Magnetic field effect on an exciplex between N-vinyl carbazole grafted on cellulose acetate film and 1,4-dicyanobenzene

The present work emphasises the investigation of photoinduced electron transfer reaction between an electron-donor fluorophore, N-vinyl carbazole (VCZ), grafted on a polymeric cellulose acetate film and an electron-acceptor, 1,4-dicyanobenzene, in the presence of an external magnetic field that serves as a powerful tool to identify the spin states where the initial electron transfer occurs and to modulate the course of the reaction as desire. Here initial electron transfer occurs in the singlet spin state, and the formation of exciplex increases in the presence of magnetic field. The maximum field effect is obtained in the solvent with medium dielectric constant (ε_max) around 8.0. The ε_max value indicates that the extent of charge transfer in this exciplex is less compared to other similar systems studied so far, owing to the characteristic binding of VCZ to the polymeric backbone through oxygen atom. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3910–3915, 1999     

Stiff chain persistence lengths in liquid crystalline copolyesters

This paper describes a continuation of our X-ray diffraction work on the structure of the mesomorphic copolyesters prepared from p-hydroxybenzoic acid (HBA) and 2-hydroxy-6-naphthoic acid (HNA). The X-ray patterns of meltspun fibers of these copolymers show a series of aperiodic meridional maxima, and these are predicted by a model consisting of stiff extended chains of completely random copolymer sequence. The calculated intensity data are independent of the chain length for the model, except that the width of the peak at d≃2.1Å decreases with increasing chain length. For 58/42 copoly(HBA/HNA) the best agreement obtained is for a chain length of 11 monomers, and this corresponds to a correlation or persistence length for the stiff chain conformation in the solid state. This effect has been modeled for an infinite chain by deriving experimental monomer length distribution functions, from a survey of the conformations of models of typical random chain sequences. The distribution function is then incorporated into the intensity calculations and leads to prediction of peak widths that are comparable to those observed.     

Site Density Functional Theory and Structural Bioinformatics Analysis of the SARS-CoV Spike Protein and hACE2 Complex

The entry of the SARS-CoV-2, a causative agent of COVID-19, into human host cells is mediated by the SARS-CoV-2 spike (S) glycoprotein, which critically depends on the formation of complexes involving the spike protein receptor-binding domain (RBD) and the human cellular membrane receptor angiotensin-converting enzyme 2 (hACE2). Using classical site density functional theory (SDFT) and structural bioinformatics methods, we investigate binding and conformational properties of these complexes and study the overlooked role of water-mediated interactions. Analysis of the three-dimensional reference interaction site model (3DRISM) of SDFT indicates that water mediated interactions in the form of additional water bridges strongly increases the binding between SARS-CoV-2 spike protein and hACE2 compared to SARS-CoV-1-hACE2 complex. By analyzing structures of SARS-CoV-2 and SARS-CoV-1, we find that the homotrimer SARS-CoV-2 S receptor-binding domain (RBD) has expanded in size, indicating large conformational change relative to SARS-CoV-1 S protein. Protomer with the up-conformational form of RBD, which binds with hACE2, exhibits stronger intermolecular interactions at the RBD-ACE2 interface, with differential distributions and the inclusion of specific H-bonds in the CoV-2 complex. Further interface analysis has shown that interfacial water promotes and stabilizes the formation of CoV-2/hACE2 complex. This interaction causes a significant structural rigidification of the spike protein, favoring proteolytic processing of the S protein for the fusion of the viral and cellular membrane. Moreover, conformational dynamics simulations of RBD motions in SARS-CoV-2 and SARS-CoV-1 point to the role in modification of the RBD dynamics and their impact on infectivity.     

Higher-Order Nonclassicality in Photon Added and Subtracted Qudit States

Higher-order nonclassical properties of r photon added and t photon subtracted qudit states (referred to as rPAQS and tPSQS, respectively) are investigated here to answer: How addition and subtraction of photon can be used to engineer higher-order nonclassical properties of qudit states? To obtain the answer, higher-order moment of relevant bosonic field operators is first obtained and subsequently used to study the higher-order nonclassical properties (e.g., higher-order antibunching, higher-order squeezing, and higher-order sub-Poissonian photon statistics) of the corresponding states. These witnesses establish that rPAQS and tPSQS are highly nonclassical. To quantitatively establish this observation and to make a comparison between rPAQS and tPSQS, volumes of the negative part of Wigner function are computed. Finally, for the sake of verifiability of the obtained results, optical tomograms are also reported. Throughout the study, a particular type of qudit state named as a new generalized binomial state is used as an example.     

Evaluation of Properties of Concrete Without Cement Produced Using Fly Ash-Based Geopolymer

The use of ordinary Portland cement (OPC) in the construction industry is inevitable. The huge production of OPC and its use in infrastructural development pose an environmental impact. Greenhouse gas emitted increases the global temperature and it is an alarming sign to everybody on the planet. Concrete is the most consuming material which is produced by using OPC and it is proven that OPC contributes a lot to CO₂ emission. Hence in this study attempt is made to produce concrete by using environment-friendly material like fly ash along with alkaline activators, which is termed Geo polymer concrete. The by-product fly ash is widely available worldwide. It is a by-product of thermal power plants. The use of fly ash in concrete produces less expensive and more cost-effective concrete than concrete made up using OPC. Due to its high silicate and alumina content, fly ash reacts with an alkaline solution to create an aluminosilicate gel that binds the aggregate and results in high-quality concrete. Fly ash is finer than cement, it occupies the pores of cement after hydration. This would result in denser concrete which gives higher strength. In comparison to ordinary concrete, fly ash-based geopolymer concrete offers better resistance to aggressive environments and high temperatures. In the present study, an alkaline activator of molarity 8 is used to prepare geopolymer concrete. The test specimens are cast and cured for 28 days. Test results indicate that an alkaline liquid fly-ash ratio (0.4) produces higher mechanical properties. Hence, geopolymer concrete produced in this study is found to be cost-effective and environment friendly.     

Combinatorial Mapping of Surface Energy Effects on Diblock Copolymer Thin Film Ordering

Combinatorial gradient techniques are used to map the morphology dependence of thin symmetric diblock copolymer films on film thickness and substrate surface energy. An inversion from symmetric to anti‐symmetric lamellar morphology occurs with a progressive change in surface energy. An intermediate neutral region is found between these limiting types of ordering. The width ω of this transitional energy range scales as a power of copolymer mass M, ω ∝ M^1.9.

Optical photograph of a combinatorial map of the thin‐film block‐copolymer morphology on a film thickness and surface energy gradient. Island and holes on the surface scatter light causing the film to appear cloudy (lighter in color) in the areas where they exist. The darker areas do not have surface features and do not scatter light.     

Measurement and modeling of stress concentration around a circular notch

When designing composite materials, the presence of stress concentration at locations such as circular nothces is unavoidable. Such locations in structural elements arise from joints required to form a structure. The stress concentration, observed around the notch, is quantified by the stress concentration factorK. This quantity is normally calculated analytically and/or numerically and is an important design parameter. In this work, the experimental technique of remote laser Raman microscopy is used for the in situ measurement ofK in Kevlar 49 fiber/epoxy composite plates containing a circular hole. The results obtained by this technique are compared with those calculated analytically and by finite element analysis. Both analytical and numerical methods underestimate the experimental results for maximumK by approximately 10 percent, which is considered reasonable within experimental error. In addition, very good agreement between analytical and experimental data is obtained for the decay of the stress concentration factor as a function of distance from the edge of the hole. The numerical results, however, overestimate the decayK with distance from the notch boundary and only converge at relatively large distances.B. P. Arjyal has obtained his PhD from the Materials Department, Queen Mary & Westfield College, University of London, London, E1 4NS, United Kingdom.     

Investigating the Molecular Architecture of Hyperbranched Polymers

Hyperbranched polymers constitute a unique class of branched macromolecules, where structural complexity is complemented by relative ease of synthesis. The increasing interest in the study of these materials is due to their distinctive properties, inherently tied to their complex molecular architecture, and is augmented by the continual growth of applications like catalysis, viscosity modifiers, and sensors. We report a structural model for HBPs based on fractal scaling of both mass and connectivity. This model is shown to be of use in understanding small angle scattering data, especially in comparison with nuclear magnetic resonance spectroscopy for structural characterization.

     

Kosterlitz-thouless transition and self-duality in three dimensions

A class of self-dual globally symmetric Z_N models in three dimensions is presented. The limit N → ∞ is a type of anisotropic U(1) model (XY model) dual to a gas of integer point charges, interacting via a logarithmic potential in three dimensions. The latter is, at low temperature, nothing but a sine-Gordon theory with an anisotropic, logarithmic propagator. It therefore has a low-temperature Kosterlitz-Thouless phase and KT phase transition to a massive phase.The relation of the U(1) model to the thermodynamics of a helical magnet along the ferromagnetic-helical phase boundary in zero applied field (or to the smectic A to amectic C phase boundary in a liquid crystal) is indicated.     

Cross-over behavior of the nonlinear σ-model with quadratically broken symmetry

We study the nonlinear σ-model near two dimensions in the presence of a quadratic symmetry breaking, which gives a mass to M of the N fields. Using a renormalization scheme, proposed earlier, which includes the anisotropy mass explicitly, and making sure that the renormalized mass is a physical parameter, we calculate explicitly, to first order in d-2: the flow patterns of the temperature (coupling constant); the crossover in temperature and external magnetic field of the order-parameter (the average classical field); and the cross-over in momentum of the two-point Green function.