Indian Association for the Cultivation of Science

About: Indian Association for the Cultivation of Science is a education organization based out in Kolkata, India. It is known for research contribution in the topics: Catalysis & Excited state. The organization has 3867 authors who have published 10457 publications receiving 220098 citations.

Graphene Oxide-Based Supramolecular Hydrogels for Making Nanohybrid Systems with Au Nanoparticles

Abstract: In the presence of a small amount of a proteinous amino acid (arginine/tryptophan/histidine) or a nucleoside (adenosine/guanosine/cytidine), graphene oxide (GO) forms supramolecular stable hydrogels. These hydrogels have been characterized by field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray diffraction (XRD) analysis, Raman spectroscopy, and rheology. The morphology of the hydrogel reveals the presence of nanofibers and nanosheets. This suggests the supramolecular aggregation of GO in the presence of an amino acid/nucleoside. Rheological studies of arginine containing a GO-based hydrogel show a very high G′ value (6.058 × 104 Pa), indicating the rigid, solid-like behavior of this gel. One of these hydrogels (GO-tryptophan) has been successfully utilized for the in situ synthesis and stabilization of Au nanoparticles (Au NPs) within the hydrogel matrix without the presence of any other external reducing and stabilizing agents to make Au NPs containing the GO-based ...

The magnetic and other properties of the free electrons in graphite

Abstract: 1. Graphite crystals have a large free-electron diamagnetism, which is directed almost wholly along the hexagonal axis. Over the whole range of temperature over which measurements have been made, namely, from 90 to 1270$^{\circ}$ K, this free-electron diamagnetism of graphite per carbon atom is found to be equal to the Landau diamagnetism per electron of a free-electron gas obeying Fermi-Dirac statistics and having a degeneracy temperature of 520$^{\circ} $ K. 2. From this experimental result it is concluded (a) that the number of free or mobile electrons in graphite is just one per carbon atom; (b) that the effective mass of these electrons for motion in the basal plane is just their actual mass, showing that the movements in this plane are completely free and uninfluenced by the lattice field; (c) that on the other hand their effective mass for motion along the normal to the basal plane is enormous, about 190$^{3}$ times the actual mass, which indicates that the mobile electrons belonging to any given basal layer of carbon atoms are tightly bound to the layer, though, according to (b), they can migrate quite freely over the whole of the layer; (d) that this tight binding accounts for the observed low degeneracy temperature of the electron gas in the crystal. 3. The electron gas in graphite thus conforms to a simple model which is easily amenable to theoretical treatment, and it has a low degeneracy temperature which is conveniently accessible for experimenting. It therefore forms a suitable medium for studying the properties of an electron gas. 4. The conclusions stated in 2 are in accord with the quantal views of the electronic structure of graphite, and also with its Brillouin zones. There is one zone which can just accommodate three electrons per atom, and the energy discontinuities at all of its boundary surfaces are large. There is a bigger zone which can just accommodate all the four valency electrons, but the energy discontinuities at those of its faces that are perpendicular to the basal plane are very small.

Micellization and interfacial behavior of binary and ternary mixtures of model cationic and nonionic surfactants in aqueous NaCl medium

Abstract: Mixed micelle formation and interfacial properties of aqueous binary and ternary combinations of hexadecyltrimethylammonium bromide (C(16)Br), hexadecylbenzyldimethylammonium chloride (C(16)BzCl) and polyoxyethylene (20) cetyl ether (Brij58) at 25 degrees C in 30 mM aqueous NaCl have been studied in detail employing tensiometric and fluorimetric techniques. The micellar and adsorption characteristics like composition, activity coefficients, mutual interaction parameters and free energy of micellization have been estimated using the theoretical approaches of Clint, Rosen, Rubingh, Blankschtein et al., Rubingh-Holland and Maeda. A comprehensive account of the comparative performance of these models on the selected cationic-cationic-nonionic surfactant mixtures at constant ionic strength has been presented. The Blankschtein model predicted lower synergism than from Rubingh's method because it neglects the contribution due to steric interaction between surfactant head groups of different sizes and charges. Free energy of micellization calculated using Maeda's approach, which employs interaction parameter and micellar mole fraction from Rubingh's model as inputs, shows good correlation with that calculated from commonly used phase separation model. The present study also reveals that the modified Rubingh-Holland method along with the Rosen's model can be applied to analyze the interfacial characteristics of ternary surfactant mixtures with a fair degree of success thereby widening the domain of applicability of this model.

Inflation driven by Einstein-Gauss-Bonnet gravity

Abstract: We have explicitly demonstrated that scalar coupled Gauss-Bonnet gravity in four dimensions can have nontrivial effects on the early inflationary stage of our Universe. In particular, we have shown that the scalar coupled Gauss-Bonnet term alone is capable of driving the inflationary stages of the Universe without incorporating slow roll approximation, while remaining compatible with the current observations. Subsequently, to avoid the instability of the tensor perturbation modes we have introduced a self-interacting potential for the inflaton field and have shown that, in this context as well, it is possible to have an inflationary scenario. Moreover, it turns out that presence of the Gauss-Bonnet term is incompatible with the slow roll approximation and hence one must work with the field equations in the most general context. Finally, we have shown that the scalar coupled Gauss-Bonnet term attains smaller and smaller values as the Universe exits from inflation. Thus, at the end of the inflation, the Universe makes a smooth transition to Einstein gravity.

Occurrence of ribbons of cyclic water pentamers in a metallo-organic framework formed by spontaneous fixation of CO2

Abstract: In the reaction of equimolar amounts of copper(II) acetate with 2,2′-dipyridylamine (DPA) in aqueous tetrahydrofuran, in presence of KOH, aerial CO2 is spontaneously fixed to the carbonate anion yielding [Cu(DPA)(CO3)]·3H2O (1). X-ray crystallography shows the presence of zigzag ribbons of cyclic water pentamers in the channels of a chain-like metallo-organic framework. The water ribbons are stabilised by hydrogen bonds to the metallo-organic backbone. Each (H2O)5 pentamer is approximately planar.