An adaptive Cartesian grid generation method for ‘Dirty’ geometry

Traditional structured and unstructured grid generation methods need a ‘water‐tight’ boundary surface grid to start. Therefore, these methods are named boundary to interior (B2I) approaches. Although these methods have achieved great success in fluid flow simulations, the grid generation process can still be very time consuming if ‘non‐water‐tight’ geometries are given. Significant user time can be taken to repair or clean a ‘dirty’ geometry with cracks, overlaps or invalid manifolds before grid generation can take place. In this paper, we advocate a different approach in grid generation, namely the interior to boundary (I2B) approach. With an I2B approach, the computational grid is first generated inside the computational domain. Then this grid is intelligently ‘connected’ to the boundary, and the boundary grid is a result of this ‘connection’. A significant advantage of the I2B approach is that ‘dirty’ geometries can be handled without cleaning or repairing, dramatically reducing grid generation time. An I2B adaptive Cartesian grid generation method is developed in this paper to handle ‘dirty’ geometries without geometry repair. Comparing with a B2I approach, the grid generation time with the I2B approach for a complex automotive engine can be reduced by three orders of magnitude. Copyright © 2002 John Wiley & Sons, Ltd.     

Burn-up measurements on nuclear reactor fuels using high performance liquid chromatography

Burn-up measurements on thermal as well as fast reactor fuels were carried out using high performance liquid chromatography (HPLC). A column chromatographic technique using di-(2-ethylhexyl) phosphoric acid (HDEHP) coated column was employed for the isolation of lanthanides from uranium, plutonium and other fission products. Ion-pair HPLC was used for the separation of individual lanthanides. The atom percent fissions were calculated from the concentrations of the lanthanide (neodymium in the case of thermal reactor and lanthanum for the fast reactor fuels) and from uranium and plutonium contents of the dissolver solutions. The HPLC method was also used for determining the fractional fissions from uranium and plutonium for the thermal reactor fuel.     

A low cost PC based card for heat-capacity measurements at low temperatures

We describe a simple, low cost pc based card for the measurement of heat capacity using adiabatic calorimetry at low temperatures. This card provides the control pulse to the sample heater as well as trigger pulse to the nano-voltmeter which monitors the sensor voltage (Ge sensor, Lake Shore Inc., USA). We have also added a 12 bit DAC on this card and this is used for remote setting of the heater current of an old SHE (now Biomagnetic, Inc., USA, model CCS) analog constant current source. Although this card is used here for heat-capacity measurements, the same can also be used for thermo-power and thermal-conductivity measurements.     

Charge density analysis of a pentaborate ion in an ammonium borate: toward the understanding of topological features in borate minerals

Structural and charge density distribution studies have been carried out on a single crystal data of an ammonium borate, [C(10)H(26)N(4)][B(5)O(6)(OH)(4)](2), synthesized by solvothermal method. Further, the experimentally observed geometry is used for the theoretical charge density calculations using the B3LYP/6-31G** level of theory, and the results are compared with the experimental values. Topological analysis of charge density based on the Atoms in Molecules approach for B-O bonds exhibit mixed covalent/ionic character. Detailed analysis of the hydrogen bonds in the crystal structure in the ammonium borate provides insights into the understanding of the reaction pathways that could result in the formation of borate minerals. The net atomic charges and electrostatic potential isosurfaces also give additional input to evaluate chemical and physical properties in such systems.     

Graphene-supported anatase TiO2 nanosheets for fast lithium storage

We have designed a unique hybrid structure by directly growing ultrathin anatase TiO(2) nanosheets onto graphene support for fast lithium storage. With exposed (001) high-energy facets, these TiO(2) nanosheets serve as ideal hosts for fast and efficient lithium storage. On the other hand, the graphene support serves as a highly conductive substrate that is beneficial to the high-rate performance.     

Physicochemical studies of some novel Y-shaped imidazole derivatives--a sensitive chemisensor

Some novel Y-shaped imidazole derivatives were developed for highly sensitive chemisensors for transition metal ions. A prominent fluorescence enhancement was found in the presence of transition metal ions such as Hg²⁺, Pb²⁺ and Cu²⁺ and it is due to the suppression of radiationless transitions from the n–π* state in the chemisensors. The HOMO–LUMO energies, electric dipole moment (μ) and the first-hyperpolarizability (β) values of the investigated molecule have been studied theoretically which reveal that the synthesized molecules have microscopic non-linear optical (NLO) behaviour with non-zero values.     

A physiochemical study of azo dyes: DFT based ESIPT process

Azo linked dye derivatives were synthesized and characterized by NMR, mass and elemental analysis. An excited state intramolecular proton transfer (ESIPT) in hydroxy Schiff base has been analyzed, and found that two distinct ground state isomers of I and II are responsible for the observed dual emission. DFT calculation on energy, dipole moment, charge distribution of the rotamers in the ground and excited states support the ESIPT process. PES calculation indicates that the energy barrier for the interconversion of two rotamers is too high in the excited state than the ground state. By varying the addition of base concentration to hydroxy Schiff base, two isobestic points were found which confirm the equilibrium among the trans enol form, anion and the cis enol form. Fluorescence quenching with metal ions reveal that hydroxy Schiff base can be used as a new fluorescence sensor to detect the Cu(2+) ion.     

Biosynthesis of silver nanoparticles using citrus sinensis peel extract and its antibacterial activity

Biosynthesis of silver nanoparticles (AgNPs) was achieved by a novel, simple green chemistry procedure using citrus sinensis peel extract as a reducing and a capping agent. The effect of temperature on the synthesis of silver nanoparticles was carried out at room temperature (25°C) and 60°C. The successful formation of silver nanoparticles has been confirmed by UV-vis, FTIR, XRD, EDAX, FESEM and TEM analysis and their antibacterial activity against Escherichia coli, Pseudomonas aeruginosa (gram-negative), and Staphylococcus aureus (gram-positive) has been studied. The results suggest that the synthesized AgNPs act as an effective antibacterial agent.     

Self-interaction artifacts on structural features of uranyl monohydroxide from Kohn�CSham calculations

Invoking a DFT?+?U approach, we explored self-interaction artifacts in results from Kohn?CSham (KS) density functional calculations on the geometry and the vibrational frequencies of uranyl monohydroxide and the corresponding tetra-aqua complex. Exchange?Ccorrelation functionals based on the local density approximation (LDA) and the generalized-gradient approximation (GGA) predict equilibrium geometries for [UO₂(OH)]⁺ that deviate from the results of hybrid DFT calculations and high-level wavefunction-based methods such as CCSD(T). LDA?+?U and GGA?+?U functionals with corrections for the insufficient localization of the U 5f shell yield better agreement, in particular for the angle U-O_h-H. At the LDA level, a linear coordination of the OH ligand results; with the +U correction, the angle U-O_h-H is reduced by ~35°, in good agreement with CCSD(T) results. At the GGA level, the bending angle is changed by ~20°. This relatively strong self-interaction artifact is traced back to a spurious ?? interaction between U 5f and O(p) orbitals which is less pronounced in the presence of further (aqua) ligands.