N,N′-methylene-bis-acrylamide-crosslinked polyacrylamides as supports for dithiocarbamate ligands for metal ion complexation

The complexation behaviour of dithiocarbamate functions supported on polyacrylamides with varying extents (2-20 mol%) of N,N′-methylene-bis-acrylamide (NNMBA) crosslinks was investigated. The crosslinked polyacrylamides were prepared by the free radical solution polymerization of the monomers in water at 80°C using potassium persulphate as initiator. The dithiocarbamate ligands were introduced by polymer-analogous reaction involving transamidation with ethylenediamine and dithiocarbamylation with carbon disulphide and alkali. The complexation behaviour of these dithiocarbamate resins with the ligand functions in different macromolecular environments were investigated towards Co(II), Ni(II), Cu(II), Zn(II) and Hg(II) ions by a batch equilibration technique. The metal ion intake varied with the extent of the NNMBA-crosslinking. Thus the 8% crosslinked system has the highest complexation capacity. The values for metal ion intake followed the order Hg(II)> Cu(II)> Zn(II)> Ni(II)> Co(II). The time-course of complexation, the possibility of recycling and the swelling characteristics of the uncomplexed and complexed resins were considered, and IR characterization and thermal studies were undertaken. The swelling values of the complexed resins are lower than those of the uncomplexed resins. The thermal stability of dithiocarbamates varied with the extent of NNMBA-crosslinks and with the metal ion.     

Predominance of HLA-restricted cytotoxic T-lymphocyte responses to serotype-cross-reactive epitopes on nonstructural proteins following natural secondary dengue virus infection

We examined the memory cytotoxic T-lymphocytic (CTL) responses of peripheral blood mononuclear cells (PBMC) obtained from patients in Thailand 12 months after natural symptomatic secondary dengue virus infection. In all four patients analyzed, CTLs were detected in bulk culture PBMC against nonstructural dengue virus proteins. Numerous CD4+ and CD8+ CTL lines were generated from the bulk cultures of two patients, KPP94-037 and KPP94-024, which were specific for NS1.2a (NS1 and NS2a collectively) and NS3 proteins, respectively. All CTL lines derived from both patients were cross-reactive with other serotypes of dengue virus. The CD8+ NS1.2a-specific lines from patient KPP94-037 were HLA B57 restricted, and the CD8+ NS3-specific lines from patient KPP94-024 were HLA B7 restricted. The CD4+ CTL lines from patient KPP94-037 were HLA DR7 restricted. A majority of the CD8+ CTLs isolated from patient KPP94-024 were found to recognize amino acids 221 to 232 on NS3. These results demonstrate that in Thai patients after symptomatic secondary natural dengue infections, CTLs are mainly directed against nonstructural proteins and are broadly cross-reactive.     

Laser-induced breakdown spectroscopy analysis of solids using a long-pulse (150 ns) Q-switched Nd:YAG laser

Laser-induced breakdown spectroscopy (LIBS) measurements are typically carried out using pulses (<20 ns, >50 mJ) from a flashlamp-pumped electro-optically Q-switched Nd:YAG laser (EO-laser) or excimer laser. Here we report LIBS analyses of solids using an acousto-optically Q-switched Nd:YAG laser (AO-laser) producing 150 ns pulses of lower energy (10 mJ) at repetition rates up to 6 kHz. The high repetition rate allows increased spatial or depth sampling over a given time period compared to the EO-laser. Results of AO-laser based LIBS analysis of (1) steels, (2) soils, and (3) surface stains and dusts are described. Detection limits for Cr, Cu, Mn, Ni, and Si in steel ranged from 0.11 to 0.24% using a commercial polychromator-based detection system with limits 4--30 times lower achieved using a laboratory-based detection system. The minimum detectable masses of Ba, Cr, Mn, and Sr on a metal surface were estimated with 1.2 pg/shot achieved for Sr. Detection limits for Ba and Sr in soil were 296 and 52 ppm, respectively. The temperatures, spectra, and emission decay curves from plasmas generated by the AO- and EO-lasers are compared and some characteristics of particles ablated by the AO-laser are described.     

The generation-recombination mechanism of charge transport in a thin-film CdS/CdTe heterojunction

An n-CdS/p-CdTe heterostructure is studied. The heterostructure is obtained using the sequential growth of CdS and CdTe layers by electrochemical deposition and closed-space sublimation, respectively. The measured current-voltage characteristics are interpreted in the context of the Sah-Noyce-Shokley generation-recombination model for the depletion layer of a diode structure. The theory quantitatively agrees with the experimental results.     

The influence of oxidation on the structure and strength of graphite—II: Materials of different impurity content

Six polycrystalline graphites were manufactured to contain specific impurities, iron, vanadium and calcium, with two different concentrations. They were then oxidized in either dry air, CO₂ or H₂O so as to produce a uniform gasification profile within the samples and were tested for loss of compressive strength and Young's modulus. Mercury porosimeter measurements and scanning electron microscope observations were also made. Materials containing calcium suffered the greatest loss of mechanical properties for a given weight loss, with calcium producing the greatest catalytic effect for the graphite—H₂O reaction. For the materials doped with Ca and Fe there appeared to be little or no effect of impurity concentration on strength loss as a function of burn-off. Microscopic observations showed that the degradation of mechanical properties was due to gross gasification of the binder together with some weakening of filler particles.     

Studies on the hydrogenation of alkenes and alkynes using polymer coated silica-Pd catalysts

Palladium complexes of crosslinked polyacrylamide and poly-N-vinylimidazole coated on silica gel have been prepared and used as hydrogenation catalysts for alkenes, dienes and alkynes under ambient conditions. The characterisation of the catalysts, the kinetic and mechanistic aspects of the hydrogenation of a few substrates, the effect of temperature, selectivity and the recycling efficiency of the catalysts are presented. A comparison of their activity is made with other silica supported and silica free polymer-Pd catalysts.     

Optimization of preparation conditions on the dielectric properties of polyaniline

The dielectric response in the microwave field of polyaniline prepared at different temperatures and using different inorganic and organic dopants was studied. Chemical oxidative polymerization of aniline was done at low temperature (0–5°C), at room temperature, and at high (60°C) temperature using different inorganic dopants like HCl, HNO₃, H₂SO₄, HClO₄, etc. Polyaniline was also prepared with different organic dopants like camphor sulfonic acid, Toluene sulfonic acid, and Naphthalene sulfonic acid. All polymers formed were characterized using IR, TGA, DSC, and SEM, etc. The dielectric responses of all polymers are studied using cavity perturbation technique in the microwave field. The studies indicates that the polyaniline prepared with perchloric acid at room temperature shows higher conductivity and absorption coefficient compared with all other samples. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Analysis and prediction of laser cutting parameters of fibre reinforced plastics (FRP) composite materials

A theoretical model is presented considering the spatial distribution of the laser beam, interaction time between the laser and the work material, absorption coefficient of the laser beam at the laser wavelength and the thermal properties of the material. It is assumed that the laser energy is absorbed through the entire thickness of the material. The developed model predicts the various parameters in laser cutting of composite materials such as kerf width at the entry and at the exit, material removal rate and energy transmitted through the cut kerf. The theoretical analysis also determines the position of the beam with respect to the cutting front. Experiments for different laser and material combinations to evaluate the effects of cutting parameters on the cut quality were carried out to compare with the predicted results. The results obtained show very good agreement.