Towards a more efficient dynamic mesh adaptation methodology for continuum discretization in complex engineering problems

A novel and efficient method of adaptive mesh generation, for dynamically adaptive unstructured grids, is proposed. A locally refined triangulation is constructed on a coarse background mesh, subdividing each triangle in the refinement region R into four congruent sub-triangles iteratively, by connecting edge midpoints, until triangles of a prescribed lengthscale are obtained. The unavoidable propagation outside the refinement region R is restricted to a single triangle in the coarse background mesh. The triangles, in the immediate vicinity of region R, are broken down using the concept of iterated function systems, widely used in fractal modeling, by recursive generation of sub-triangles with a gradation towards the region R triangles. A quantitative assessment of the present algorithm proves its superiority over other comparable models reported in the literature. The time cost of the algorithm is linear, and the method can be easily extended to three dimensions.     

Novel synthesis of biodegradable poly(lactide-co-ethylene glycol) block copolymers

Biodegradable and amphiphilic diblock copolymers [polylactide-block-poly(ethylene glycol)] and triblock copolymers [polylactide-block-poly(ethylene glycol)-block-polylactide] were synthesized by the anionic ring-opening polymerization of lactides in the presence of poly(ethylene glycol) methyl ether or poly(ethylene glycol) and potassium hexamethyldisilazide as a catalyst. The polymerization in toluene at room temperature was very fast, yielding copolymers of controlled molecular weights and tailored molecular architectures. The chemical structure of the copolymers was investigated with ¹H and ¹³C NMR. The formation of block copolymers was confirmed by ¹³C NMR and differential scanning calorimetry investigations. The monomodal profile of the molecular weight distribution by gel permeation chromatography provided further evidence of block copolymer formation as well as the absence of cyclic species. Additional confirmation of the block copolymers was obtained by the substitution of 2-butanol for poly(ethylene glycol); butyl groups were clearly identified by ¹H NMR as polymer chain end groups. The effects of the copolymer composition and lactide stereochemistry on the copolymer properties were examined. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2235–2245, 2007     

Preparation and characterisation of CoS2 nanomaterial in aqueous cationic surfactant medium of cetyltrimethylammonium bromide (CTAB)

Cobalt disulfide is an important nanomaterial in the field of material chemistry due to its interesting catalytic and electromagnetic properties. We herein report the simple solution phase preparation of nanoparticles of cobalt disulfide in micellar medium of cationic surfactant cetyltrimethylammonium bromide (CTAB) and also by way of capping with thiophenol. The product has been characterized using spectroscopic and electron microscopic and magnetic moment measurements. The presence of disulfide bond is clearly evident from the 480 cm⁻¹ peak in the infrared spectrum. The thiol passivated particles prepared in aqueous and ethanol medium has been found to have different compositions as observed from the ESIMS study.     

Redox responsive activity regulation in exceptionally stable supramolecular assembly and co-assembly of a protein

Supramolecular assembly of biomolecules/macromolecules stems from the desire to mimic complex biological structures and functions of living organisms. While DNA nanotechnology is already in an advanced stage, protein assembly is still in its infancy as it is a significantly difficult task due to their large molecular weight, conformational complexity and structural instability towards variation in temperature, pH or ionic strength. This article reports highly stable redox-responsive supramolecular assembly of a protein Bovine serum albumin (BSA) which is functionalized with a supramolecular structure directing unit (SSDU). The SSDU consists of a benzamide functionalized naphthalene-diimide (NDI) chromophore which is attached with the protein by a bio-reducible disulfide linker. The SSDU attached protein (NDI-BSA) exhibits spontaneous supramolecular assembly in water by off-set π-stacking among the NDI chromophores, leading to the formation of spherical nanoparticles (diameter: 150–200 nm). The same SSDU when connected with a small hydrophilic wedge (NDI-1) instead of the large globular protein, exhibits a different π-stacking mode with relatively less longitudinal displacement which results in a fibrillar network and hydrogelation. Supramolecular co-assembly of NDI-BSA and NDI-1 (3 : 7) produces similar π-stacking and an entangled 1D morphology. Both the spherical assembly of NDI-BSA or the fibrillar co-assembly of NDI-BSA + NDI-1 (3 : 7) provide sufficient thermal stability to the protein as its thermal denaturation could be completely surpassed while the secondary structure remained intact. However, the esterase like activity of the protein reduced significantly as a result of such supramolecular assembly indicating limited access by the substrate to the active site of the enzyme located in the confined environment. In the presence of glutathione (GSH), a biologically important tri-peptide, due to the cleavage of the disulfide bond, the protein became free and was released, resulting in fully regaining its enzymatic activity. Such supramolecular assembly provided excellent protection to the protein against enzymatic hydrolysis as the relative hydrolysis was estimated to be <30% for the co-assembled protein with respect to the free protein under identical conditions. Similar to bioactivity, the enzymatic hydrolysis also became prominent after GSH-treatment, confirming that the lack of hydrolysis in the supramolecularly assembled state is indeed related to the confinement of the protein in the nanostructure assembly.

Supramolecular structure directing unit regulated co-assembly of a protein produces a highly stable fibrillar nanostructure and glutathione responsive release of the protein in its active state.     

Pressure effects on diffusion in liquid ammonia : A simulation study using a combination of isobaric-isothermal and microcanonical molecular dynamics

The effects of pressure on translational and rotational diffusion in liquid ammonia are investigated by means of molecular dynamics simulations. Calculations are done at two different temperatures and at many different pressures by using a two-part protocol involving molecular dynamics in isobaric-isothermal ensemble in the first part and in microcanonical ensemble in the second part. Our results are analyzed in terms of pressure-induced changes in structural properties such as packing and hydrogen bond properties. Also, the present results of liquid ammonia are compared with corresponding results for other hydrogen bonded liquids that were reported in recent years.      

Synthesis and optical properties of triphenylene-based conjugated dendrons

Conjugated dendrons based on triphenylene building blocks have been synthesized. Such dendrons exhibit broader absorption wavelength range and higher absorption coefficients than their phenyl analogs. They also possess extended excited state lifetimes and high fluorescence quantum yields in dilute solutions. In the solid state, these dendrons are highly aggregated, resulting in significantly broadened and red-shifted emissions, whose decay transients depend strongly on the detection wavelength.     

Characterization and electrical transport properties of polyaniline and multiwall carbon nanotube composites

Polyaniline/multiwalled carbon nanotube (PANI/MWNT) composites were prepared by in situ polymerization. Scanning electron microscope, X‐ray diffraction, Fourier transform infrared, Uv‐Visible spectroscopy, Fluorescence spectrophotometry were done to characterize the PANI/MWNT composites. Thermal stability was measured by thermogravimetry analysis. The thermal stability of PANI/MWNT composites becomes higher than PANI. Electrical transport properties of different PANI/MWNT composites were investigated in the temperature range 77 ≤ T ≤ 300 K with and without magnetic field up to 1 T. The dc resistivity of PANI/MWNT composites shows different behavior compared to the sample without MWNT. The room temperature dc magnetoconductivity of the samples is negative; however, its sign changes to positive by lowering the temperature, which has been explained by hopping type charge transport. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1767–1775, 2010     

Esterification and ketalization of levulinic acid with desilicated zeolite β and pseudo-homogeneous model for reaction kinetics

To maximize the production of esters (E), keto (K) and keto-ester (KE) by esterification and ketalization of levulinic acid (LA) has been reacted using diols such as 1,2-propane diol (PDOL),1,2-ethane diol (EDOL), and 1,2,3-propane triol or glycerol (TRIOL) with desilicated Hβ. This work aims to assess the conversion and selectivity for the production of esters using conventional and microwave-irradiated (MWI) reactors. Catalysts characterizations were performed using NH₃-temperature programme desorption, Brunauer, Emmett and Teller surface area (BET), Barrett, Joyner, and Halenda (BJH), scanning electron microscope, transmission electron microscope, and dynamic light scattering. Operating parameters such as reaction temperature (170–180°C), reaction time (20–80 min), feed composition (LA:PDOL/EDOL/TRIOL, 1:8/10/12), and microwave energy (300–500 watt) have been systematically investigated. Note that 99–100% conversion was achieved with the product selectivity of E (40%), K (30%), and KE (30%) with1,2-EDOL; E (56%), K (2%), and KE (17%) with 1,2-PDOL; E (69%), K(0%), and KE (22%) with TRIOL using D-Hβ as a solid catalyst in an MWI reactor. Reaction paths and kinetics were studied using pseudo-homogeneous (PH) model.     

Strain rate and flame orientation statistics in the near-wall region for turbulent flame-wall interaction

Flame–wall interaction (FWI) in premixed turbulent combustion has been analysed based on a counter-flow like configuration at the statistically stationary state. For the present configuration, the two FWI sub-zones, i.e the influence zone and the quenching zone, can be identified from the DNS results. Detailed analysis of the important quantities, such as the flame temperature, flame–wall distance, wall heat flux, flame curvature and dilatation (including the flame normal and tangential strain rates), and some orientation relations between the flame normal and the principal strain rate directions, have been reported, together with the physical explanations. All these statistical results are determined by the relative strengths of the wall heat flux, thermal expansion and the flame–turbulence interaction.