Extended Born-Oppenheimer equation for a three-state system

We present explicit forms of nonadiabatic coupling (NAC) elements of nuclear Schrodinger equation (SE) for a coupled three-state electronic manifold in terms of mixing angles of real electronic basis functions. If the adiabatic-diabatic transformation (ADT) angles are the mixing angles of electronic bases, ADT matrix transforms away the NAC terms and brings diabatic form of SE. ADT and NAC matrices are shown to satisfy a curl condition with nonzero divergence. We have demonstrated that the formulation of extended Born-Oppenheimer (EBO) equation from any three-state BO system is possible only when there exists a coordinate-independent ratio of the gradients for each pair of mixing angles. On the contrary, since such relations among the mixing angles lead to zero curl, we explore its validity analytically around conical intersection(s) and support numerically considering two nuclear-coordinate-dependent three surface BO models. Numerical calculations are performed by using newly derived diabatic and EBO equations and expected transition probabilities are obtained.     

Microindentation Hardness of Nanostructured Thermoplastic Materials

Summary: The micromechanical behaviour of various thermoplastics based nanocomposites was investigated with the aid of the microindentation technique. The materials studied were microphase separated styrene-butadiene block copolymer systems and several thermoplastics reinforced with nano-sized fillers having variable dimensionality. It was found that the microhardness behaviour of the nanocomposites studied was strongly influenced by the dimensionalities of the filler. Due to large surface to volume-ratio one- and two-dimensional fillers exhibit a far better reinforcing behaviour than the three dimensional ones. In case of nanostructured block copolymers, the microhardness is not determined by the total polystyrene (PS)/polybutadiene (PB) composition alone but diminishes gradually in presence of freely standing dangling polybutadiene chains even if the morphology of the systems remains unaltered.     

An efficient multi-use multi-secret sharing scheme based on hash function

In this work, a renewable, multi-use, multi-secret sharing scheme for general access structure based on the one-way collision resistant hash function is presented in which each participant has to carry only one share. As it applies the collision resistant one-way hash function, the proposed scheme is secure against conspiracy attacks even if the pseudo-secret shares are compromised. Moreover, high complexity operations like modular multiplication, exponentiation and inversion are avoided to increase its efficiency. Finally, in the proposed scheme, both the combiner and the participants can verify the correctness of the information exchanged among themselves.     

Well-Defined Ni(0) and Ni(II) Complexes of Bicyclic (Alkyl)(Amino)Carbene (MeBICAAC): Catalytic Activity and Mechanistic Insights in Negishi Cross-Coupling Reaction

Negishi cross-coupling reaction of organozinc compounds as nucleophiles with aryl halides has drawn immense focus for C−C bond formation reactions. In comparison to the well-established library of Pd complexes, the C−C cross-coupling of this particular approach is largely primitive with nickel-complexes. Herein, we describe the syntheses of Ni(II) complexes, [(^MeBICAAC)₂NiX₂] (X=Cl ( 1 ), Br ( 2 ), and I ( 3 )) by employing the bicyclic (alkyl)(amino)carbene (^MeBICAAC) ligand. The reduction of complexes 1 – 3 using KC₈ afforded the two coordinate low valent, Ni(0) complex, [(^MeBICAAC)₂Ni(0)] ( 4 ). Complexes 1 – 4 have been characterized by spectroscopic techniques and their solid-state structures were also confirmed by X-ray crystallography. Furthermore, complexes 1 – 4 have been applied in a direct and convenient method to catalyze the Negishi cross-coupling reaction of various aryl halides with 2,6-difluorophenylzinc bromide or phenylzinc bromide as the coupling partner in the presence of 3 mol % catalyst. Comparatively, among all-pristine complexes, 1 exhibit high catalytic potential to afford value-added C−C coupled products without the use of any additive. The UV-vis studies and HRMS measurements of controlled stochiometric reactions vindicate the involvement of Ni(I)−NI(III) cycle featured with a penta-coordinated Ni(III)-aryl species as the key intermediate for 1 whereas Ni(0)/Ni(II) species are potentially involved in the catalytic cycle of 4 .     

Current progresses and trends in carbon nanomaterials-based electrochemical and electrochemiluminescence biosensors

The enormous potential of biosensors in medical diagnostics has motivated scientists to develop newer innovative tools and advance biosensing technologies. The use of cell, organelles, nucleotides, aptamers, antibodies, affibodies, proteins, peptides, molecules, and printed polymers, merged with nanotechnology, offers excellent tools to prepare highly sensitive and advanced biosensors. Therefore, the current decade has witnessed a rapid surge in the fabrication of different nanomaterial-based biosensors. Among them, carbon nanomaterials (CNMs) have emerged highly attractive in the fabrication of both electrochemical and electrochemiluminescence (ECL) biosensors. On one hand, CNMs bear prominent electrical conductivity, large surface area to immobilize adequate amount of biomolecules, an enhanced loading capacity, improved biocompatibility, and active site for electrochemical reaction. Additionally, CNMs could be chemically modified for the covalent coupling with the biomolecules. On the other hand, both electrochemical and ECL biosensors allow for cost-effective, rapid, and real-time detection with excellent sensitivity and selectivity, with the capability of integrating different biomolecules and CNMs on the same chip. However, currently there is not a single review, which includes CNM-based electrochemical and ECL biosensors' current progress and trends. Therefore, this review intends to survey the current progress and future trends in CNM-based electrochemical and ECL biosensors.     

Elastic instability of bilayer graphene using atomistic finite element

In-plane elastic instability of bilayer graphene sheets is investigated using atomistic finite element approaches. The equivalent homogenised properties of graphene sheet are expressed in terms of the thickness, equilibrium lengths and force-field models used to represent the C–C bonds of the graphene lattice. The covalent bonds are represented as structural beams with stretching, bending, torsional and shear deformation, and the strain energies associated to affine deformation mechanisms. The overall mechanical properties and geometric configurations of the nano-structures represented as truss assemblies are then calculated minimising the total potential energy associated to the loading, thickness and average equilibrium lengths of the bonds. Different boundary conditions and aspect ratios are considered for both bilayer and single-layer graphene sheets. The bilayer graphene sheets are found to be offering remarkably higher buckling strengths as compared to single-layer sheets.     

Bright Vortex Solitons in Bose Condensates

We suggest the possibility of observing and studying bright vortex solitons in attractive Bose-Einstein condensates in three dimensions with a radial trap. Such systems lie on the verge of critical stability and we discuss the conditions of their stability. We study the interaction between two such solitons. Unlike the text-book solitons in one dimension, the interaction between two radially trapped and axially free three-dimensional solitons is inelastic in nature and involves exchange of particles and deformation in shape. The interaction remains repulsive for all phase between them except for 0.     

Micellar catalyzed redox reactions of bilirubin in CTAB medium. A pulse radiolysis study

The reaction of CO with bilirubin which is not detectable in homogeneous aqueous medium proceeds almost with diffusion controlled rate in CTAB micellar system. This could be explained on the basis of catalysis caused by the possible electrostatic surface potential of cationic CTAB Micelles. The rate constant for the oxidation of bilirubin by haloperoxyl radicals have been shown to increase with increasing solvent polarity. Although the polarity effect was small, it followed a trend in the expected direction. Micellar effect was not observed in the oxidation reactions when alcohol was present in high concentration. But a small increase in the rate constant was observed when alcohol concentration was lower. © 1994 John Wiley & Sons, Inc.     

Pervaporation separation of aqueous chlorophenols by a novel polyurethane urea–poly (methyl methacrylate) interpenetrating network membrane

A novel polymer membrane system consisting of interpenetrating network (IPN) of hydroxy terminated polybutadiene (HTPB) based polyurethane urea (PUU)–poly (methyl methacrylate) (PMMA) has been designed and developed as highly permselective membrane for pervaporation separation of toxic p-chlorophenol and 2,4-dichlorophenol from their dilute aqueous solutions. It was observed that 3 ppm 2,4-dichlorophenol in water could be reduced to 0.3 ppm 2,4-dichlorophenol using a PUU–PMMA IPN membrane of 28 cm² area and 150 μm thickness. This membrane has shown high selectivity towards p-chlorophenol and 2,4-dichlorophenol at very low concentration in feed. Feed concentration of p-chlorophenol was varied from 1000 to 7000 ppm and that of 2,4-dichlorophenol was varied from 3 to 4000 ppm. Fifty seven percent 2,4-dichlorophenol in permeate was obtained from 3 ppm concentration in feed compared to 87% 2,4-dichlorophenol in permeate from 1000 ppm in feed. Pervaporation studies were carried out by varying the temperature of feed, membrane thickness and PMMA content in the membrane. The results of this investigation have revealed that these membranes would be suitable for separation of chlorophenols from industrial effluents.