A theoretical insight into the reducing properties of bicyclic dithia hydrocarbons and hetero-bicyclic dithiolopyrrolone compounds with rotation-restricted planar disulfide linkage

Structural Chemistry - The current study primarily involves the investigation of reducing properties of dithia-substituted bicyclic hydrocarbons. Adiabatic electron affinities (AEA) of the selected...     

The chemist’s concept of molecular structure

The concept of molecular structure is fundamental to the practice and understanding of chemistry, but the meaning of this term has evolved and is still evolving. The Born–Oppenheimer separation of electronic and nuclear motions lies at the heart of most modern quantum chemical models of molecular structure. While this separation introduces a great computational and practical simplification, it is neither essential to the conceptual formulation of molecular structure nor universally valid. Going beyond the Born–Oppenheimer approximation introduces new paradigms, bringing fresh insight into the chemistry of fluxional molecules, proteins, superconductors and macroscopic dielectrics, thus opening up new avenues for exploration. But it requires that our ideas of molecular structure need to evolve beyond simple ball-and-stick-type models.

The heavy-ion spin-orbit interaction

An expression for the induced spin-orbit potential in a heavy-ion collision is derived by making and adiabatic approximation to the effective interaction in second-order perturbation theory. An explicit form for the induced spin-orbit interaction for the case of a projectile of arbitrary ground state spin S is given and is shown to be equivalent to the result obtained using the methods of geometrical magnetism.     

A Computational Approach to Determine Average Reservoir Pressure in a Coalbed Methane (CBM) Well Flowing Under Dominant Matrix Shrinkage Effect

Desorption of gas from coal matrix alters the pore volume of fracture network. Consequently, cleat porosity and permeability of reservoir changes as pressure depletes. The method of standard pressure analysis calculations produces incorrect results in the case of coalbed methane reservoirs producing under dominant matrix shrinkage effect. The change in cleat porosity and permeability due to shrinkage of coal matrix following gas desorption with pressure depletion invalidates the underlying assumptions made in the derivation of diffusivity equation. Consequently, equations of pseudo-steady state commonly used in conventional reservoirs no longer remain valid as the porosity and permeability values change with pressure depletion. In this paper, effort has been made to describe pseudo-steady-state flow in coalbed methane reservoirs in the form of a new equation that accounts for pressure dependency of cleat porosity and permeability due to shrinkage of coal matrix. The concept of Al-Hussainy et al. (1966) has been extended to define a new pseudo-pressure function which assimilates within itself the pressure dependence of porosity and permeability Palmer and Mansoori (1998). Equation has been used to relate the cleat porosity with pressure. The equation-based computational method suggested in this paper finds its usefulness in estimating average reservoir pressure for any known flowing bottom hole pressure and thus reducing the frequency of future pressure buildup tests. The new equation is also useful in predicting reservoir pressure under the situation when coal matrix shrinks below desorption pressure. The equation used in the computational method has been validated with the help of numerical simulator CMG-GEM.     

An unprecedented polyborate ester anion: X-ray diffraction studies on [1,8-C10H6(NMe2)2H][B5O6(OMe)4

The slow hydrolysis of B(OMe)3 in a CH2Cl2 solution in the presence of 1,8-C10H6(NMe2)2 (5:1 ratio) led to the formation of the novel isolated pentaborate ester anion [B5O6(OMe)4]-, which was characterized by a single-crystal X-ray diffraction study as the salt [1,8-C10H6(NMe2)2H][B5O6(OMe)4].     

Competitive adsorption of toxic heavy metal contaminants by gum kondagogu (Cochlospermum gossypium): A natural hydrocolloid

Gum kondagogu (Cochlospermum gossypium), a naturally occurring tree biopolymer, is exploited as a biosorbent to remove metal ions from aqueous solutions. The removal efficiency of toxic metals by gum kondagogu was determined quantitatively in the order Cd²⁺ > Cu²⁺ > Fe²⁺ > Se²⁺ > Pb²⁺ > total Cr > Ni²⁺ > Zn²⁺ > Co²⁺ > As²⁺ at pH 5.0 ± 0.1 and temperature 25 ± 2 °C by inductively coupled plasma-mass spectrometry (ICP-MS). The biosorption (%) of various metal ions tested was found to be in the range of 97.3–16.7%, at pH 5.0. The morphological and mechanisms of interaction of toxic metal ions with gum kondagogu were assessed by scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM-EDXA) and X-ray diffraction (XRD) spectrum. The analysis indicated that biosorption process included morphological changes, precipitation, complexation and ion exchange mechanism for the removal of metal ions by the gum. XRD analysis indicated the amorphous nature of gum kondagogu, which facilitate metal biosorption. The metal ions adsorption leads to its deposition on the gum kondagogu matrix in a crystalline state.     

Recovery of plutonium from carbonate wash solutions

A novel method has been developed for recovery of plutonium and uranium from carbonate wash solutions generated during solvent wash process involved in the reprocessing of high burn up FBTR fuel. The proposed method involves a selective coprecipitation of Pu and U by adding ammonium hydroxide to the pre acidified carbonate wash solution. Substantial removal of DBP by successive steps of coprecipitation, completely eliminates the possibility of undesired solid formation which is mainly due to the presence of high content of DBP. By adopting this method, an excellent decontamination factor for DBP has been achieved without any crud/solid formation. Phosphate content in the final oxide product meets the product specifications. Flowsheet condition necessary for the recovery process for plutonium from the aqueous carbonate solution is formulated and adopted in the CORAL facility.     

Modeling quasi-static crack growth with the extended finite element method Part II: Numerical applications

In Part I [Int. J. Solids Struct., 2003], we described the implementation of the extended finite element method (X-FEM) within Dynaflow™, a standard finite element package. In our implementation, we focused on two-dimensional crack modeling in linear elasticity. For crack modeling in the X-FEM, a discontinuous function and the near-tip asymptotic functions are added to the finite element approximation using the framework of partition of unity. This permits the crack to be represented without explicitly meshing the crack surfaces and crack propagation simulations can be carried out without the need for any remeshing. In this paper, we present numerical solutions for the stress intensity factor for crack problems, and also conduct crack growth simulations with the X-FEM. Numerical examples are presented with a two-fold objective: first to show the efficacy of the X-FEM implementation in Dynaflow™; and second to demonstrate the accuracy and versatility of the method to solve challenging problems in computational failure mechanics.