Dipolar interactions and origin of spin ice in ising pyrochlore magnets

Recent experiments suggest that the Ising pyrochlore magnets Ho2Ti2O7 and Dy2Ti2O7 display qualitative properties of the nearest-neighbor "spin ice" model. We discuss the dipolar energy scale present in both these materials and discuss how spin-ice behavior can occur despite the presence of long-range dipolar interactions. We present results of numerical simulations and a mean field analysis of Ising pyrochlore systems. Based on our quantitative theory, we suggest that the spin-ice behavior in these systems is due to long-range dipolar interactions, and that the nearest-neighbor exchange in Dy2Ti2O7 is antiferromagnetic.     

Exact scalar field cosmologies in a higher derivative theory

We obtain exact cosmological solutions of a higher derivative theory described by the Lagrangian L=R+2αR ² in the presence of interacting scalar field. The interacting scalar field potential required for a known evolution of the FRW universe in the framework of the theory is obtained using a technique different from the usual approach to solve the Einstein field equations. We follow here a technique to determine potential similar to that used by Ellis and Madsen in Einstein gravity. Some new and interesting potentials are noted in the presence of R ² term in the Einstein action for the known behaviours of the universe. These potentials in general do not obey the slow rollover approximation.     

Synthesis and photovoltaic properties of 2,6‐bis(2‐thienyl) benzobisazole and 4,8‐bis(thienyl)‐benzo[1,2‐B:4,5‐B′]dithiophene copolymers

In an effort to design efficient low‐cost polymers for use in organic photovoltaic cells the easily prepared donor–acceptor–donor triad of a either cis‐benzobisoxazole, trans‐benzobisoxazole or trans‐benzobisthiazole flanked by two thiophene rings was combined with the electron‐rich 4,8‐bis(5‐(2‐ethylhexyl)‐thien‐2‐yl)‐benzo[1,2‐b:4,5‐b′]dithiophene. The electrochemical, optical, morphological, charge transport, and photovoltaic properties of the resulting terpolymers were investigated. Although the polymers differed in the arrangement and/or nature of the chalcogens, they all had similar highest occupied molecular orbital energy levels (?5.2 to ?5.3 eV) and optical band gaps (2.1–2.2 eV). However, the lowest unoccupied molecular orbital energy levels ranged from ?3.1 to ?3.5 eV. When the polymers were used as electron donors in bulk heterojunction photovoltaic devices with PC₇₁BM ([6,6]‐phenyl C₇₁‐butyric acid methyl ester) as the acceptor, the trans‐benzobisoxazole polymer had the best performance with a power conversion efficiency of 2.8%. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 316–324     

Orbital Angular Momentum in Scalar Diquark Model and QED

We compare the orbital angular momentum of the ‘quark’ in the scalar diquark model as well as that of the electron in QED (to order α) obtained from the Jaffe–Manohar decomposition to that obtained from the Ji relation. We estimate the importance of the vector potential in the definition of orbital angular momentum.     

Tuning the optical and electronic properties of 4,8-disubstituted benzobisoxazoles via alkyne substitution

In an effort to design new electron-deficient building blocks for the synthesis of conjugated materials, a series of new trans-benzobisoxazoles bearing halogen or alkynyl substituents at the 4,8-positions was synthesized. Additionally, the impact of these modifications on the optical and electronic properties was investigated. Theoretical calculations predicted that the incorporation of various alkynes can be used to tune the energy levels and band gaps of these small molecules. The targeted 4,8-disubstituted benzobisoxazoles were easily prepared in good yields using a two-step reaction sequence: Lewis acid catalyzed orthoester cyclization followed by Sonogashira cross-coupling. The experimentally determined HOMO values for these 4,8-disubstituted benzobisoxazoles ranged from -4.97 to -6.20 eV and showed reasonable correlation to the theoretically predicted values, with a percent deviation that ranged from 2.4-12.8%. However, the deviation between actual and predicted HOMO values was reduced to less than 3.5% when the theoretical values were extrapolated to the long-chain limit and compared to copolymers containing the 4,8-disubstituted benzobisoxazoles. Collectively, these results indicate that these 4,8-disubstituted trans-benzobisoxazoles can be used for the synthesis of new conjugated materials with electronic properties that are variable and predictable.     

An efficient one-pot synthesis of coumarin-amino acid derivatives as potential anti-inflammatory and antioxidant agents

Abstract

A series of seven coumarinyl-amino acid ester conjugates have been synthesized and characterized by NMR (¹H and 13C) and mass spectra. Further, the compounds were investigated for their therapeutic applications such as anti-inflammatory and antioxidant activities. Among the synthesized compounds most of the analogs showed good efficiency compared with the standard.