Charge plate technique in recoil study: Evidence for collection of recoil charged species from solid targets on metal electrodes

The occurrence of charge on recoil⁵⁶Mn produced by the (n,γ) reaction in polycrystalline potassium permanganate has been examined using the ‘charge plate technique’. From considerations of capture gamma ray decay schemes and internal conversion it appears that, in a condensed medium, the recoil atom develops charge after losing much of its initial kinetic energy which allows collection on charged electrodes. Preliminary findings were presented at the International Symposium on Radiochemistry and Radiation Chemistry, RC-41 BARC, Bombay, Feb. 4–6 (1991).     

Compounds of palladium halides with substituted imidazoles

Summary Compounds of the type PdL₂X₂ (L=1-methylimidazole, 1-vinylimidazole, 1-n-butylimidazole, 1,2-dimethylimidazole, 1-vinyl-2-methylimidazole, 1,2-dimethyl-5-nitroimidazole, 2-isopropyl-4(5)-nitroimidazole and 2-methyl-4(5)-nitro-imidazole; X=Cl or Br) are obtained by treating PdX₂ (1 mole) with solutions of the ligands L (2 moles). An excess of L gives PdL₄X₂ complexes (L=1-methylimidazole, 1-vinylimidazole, 1,2-dimethylimidazole and 1-vinyl-2-methylimidazole). The compounds were characterized by chemical analyses, molar conductivity measurements and i.r. spectra.     

Novel virtual user scheme to increase data confidentiality against eavesdropping in OCDMA network

We propose a novel technique to increase the confidentiality of an optical code division multiple access(OCDMA) system.A virtual user technique is analyzed and implemented to make an OCDMA system secure.Using this technique,an eavesdropper will never find an isolated authorized user’s signal.When authorized users and virtual users transmit data synchronously and asynchronously,network security increases by 25% and 37.5%,respectively.     

Structural,dielectric and optical properties of sol–gel synthesized 0.55Ba(Zr0.2Ti0.8)O3–0.45(Ba0.7Ca0.3)TiO3 ceramic

Lead-free polycrystalline ceramic 0.55Ba(Zr_0.2Ti_0.8)O₃–0.45(Ba_0.7Ca_0.3)TiO₃ (0.55BZT–0.45BCT) was synthesized by sol–gel method and the dielectric, impedance and optical properties of this ceramic were studied. X-ray diffraction analysis revealed the formation of pure perovskite phase with the coexistence of tetragonal and rhombohedral structures. The high value of dielectric constant (~6,985) with low dielectric loss (~0.013) was obtained at room temperature. Bulk and grain boundary resistances were measured by impedance analysis, which revealed negative temperature coefficient of resistance behaviour in this ceramic. The estimated value of optical band gap was found to be ~3.16 eV, which is related to the presence of intermediate energy levels. Two emission bands one at ~365 nm (UV region) and another at ~465 nm (blue region) were observed in photoluminescence spectrum at room temperature.     

Swift heavy ion irradiation effects on structural,optical properties and ac conductivity of polypyrrole nanofibers

Polypyrrole (PPy) nanofibers have been synthesized by interfacial polymerization method and irradiated with 160?MeV Ni¹²⁺ ions under vacuum with fluences in the range of 10¹⁰–10¹²?ions/cm². High-resolution transmission electron microscopy results show that upon swift heavy ion (SHI) irradiation the PPy nanofibers become denser. The crystallinity of PPy nanofibers increases upon SHI irradiation, while their d-spacing decreases. Upon SHI irradiation, the polaron absorption band gets red-shifted indicating reduction in the optical band gap energy of the irradiated PPy nanofibers. The indirect optical band gap energy is decreased as compared to corresponding direct optical band gap energy. The number of carbon atoms per conjugation length (N) and carbon atoms per cluster (M) of the SHI-irradiated PPy nanofibers increase with increasing the irradiation fluence. Fourier transform infrared spectra reveal the enhancement in intensity of some characteristic vibration bands upon SHI irradiation. The thermal stability of the PPy nanofibers is enhanced on SHI irradiation. The charge carriers in both pristine and irradiated PPy nanofibers follow the correlated barrier hopping mechanism. Scaling of ac conductivity reveals that the conduction mechanism is independent of the SHI irradiation fluence.     

Coumarins: antifungal effectiveness and future therapeutic scope

Molecular Diversity - The antifungals that are in current clinical practice have a high occurrence of a side effect and multidrug resistance (MDR). Researchers across the globe are trying to...     

Enhanced dielectric permittivity in poly (vinylidene) fluoride/multiwalled carbon nanotubes nanocomposite thin films fabricated by pulsed laser deposition

The fabrication of high quality thin films of poly (vinylidene fluoride) embedded with multiwalled carbon nanotubes using pulsed laser deposition technique is reported. The prepared films were characterized for structural, morphology and dielectric properties. The morphology analysis revealed uniform dispersion of multiwalled carbon nanotubes throughout the polymer matrix. X-ray diffraction results suggested that the poly (vinylidene fluoride) film is in amorphous phase while addition of multiwalled carbon nanotubes showed presence of crystalline peaks in the nanocomposites films. It was interesting to note that the nanocomposite films exhibits significant enhancement of the ferroelectric β-phase as evidenced by the X-ray diffraction and Fourier transform infrared spectroscopy results. The dielectric analysis shows a remarkable enhancement in the dielectric permittivity of nanocomposites with lower loss and conductivity level. The results can be attributed to the formation of minicapacitor network and relatively higher percolation threshold in the nanocomposites.     

Solute transport and composition profile during direct metal deposition with coaxial powder injection

Direct metal deposition (DMD) with coaxial powder injection allows fabrication of three-dimensional geometry with rapidly solidified microstructure. During DMD, addition of powder leads to the interaction between laser and powder, and also the redistribution of solute. The concentration distribution of the alloying element is very important for mechanical properties of the deposited clad material. The evolution of concentration distribution of carbon and chromium in the molten pool is simulated using a self-consistent three-dimensional model, based on the solution of the equations of mass, momentum, energy conservation and solute transport in the molten pool. The experimental and calculated molten pool geometry is compared for model validation purposes.     

Induced Electronic and Thermal Effects of 86 MeV Nickel Ions in Bisphenol-A Polycarbonate

Bisphenol-A polycarbonate films were irradiated with 86 MeV swift heavy nickel ions at varying fluences, ranging from 1 × 10¹¹ to 1 × 10¹³ ions cm^?2, under vacuum at room temperature, to analyze the induced electrical and thermal modifications. AC conductivity measurements and UV-visible spectroscopy, Fourier transform infra-red (FTIR) spectroscopy, thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) techniques were applied to analyze the changes. A significant, exponential increase in conductivity at higher frequency was observed with the increase of nickel ion fluence. UV-visible analysis corroborated the results of the AC conductivity measurement, revealing the increase in size of the carbon clusters embedded in the polymer network, with the increase of heavy ion fluence. FTIR analysis revealed the formation of alkene and alkyne end groups at higher doses, which further supported the suggestion that the variation in electrical properties induced by the ion irradiation of the polymer was due to development of a carbonaceous phase inside the polymer due to the irradiation. Thermal analysis, i.e., TGA and DSC patterns, showed that chain-scission was the leading phenomena in the heavy ion-irradiated polycarbonate samples, resulting in degradation of their thermal stability.     

Hydrogen atom abstraction from Piperazine by hydroxyl radical: a theoretical investigation

Dual level of quantum mechanical calculations have been carried out for hydrogen abstraction from Piperazine [HN(CH₂CH₂)₂NH] initiated by OH radical. Geometry optimisation and frequency calculations of all species involved in the titled reaction have been performed at M06-2X/6-31+G(d,p) level of theory. For the accuracy in the thermochemistry and kinetics data, single-point energy calculations have been further carried out at coupled cluster CCSD(T) method along with 6-311G(d,p) basis set. An energy profile diagram for the reaction has been plotted along with pre-reactive and post-reactive complexes at entrance and exit channels. Intrinsic reaction coordinates (IRCs) calculations have been performed for identification of real transition states that connect it via reactant to product. Our result shows that the H-atom abstraction takes place from the C–H position of Piperazine. The rate constant is calculated using canonical transition state theory (CTST) is found to be 2.86 × 10^?10 cm³ molecule^?1 s^?1 which is in good agreement with the reported experimental rate constant (2.38 ± 0.28) × 10^?10 cm³ molecule^?1 s^?1 at 298 K. We have also reported rate constant for the temperature range 300–500 K. Using group-balance isodesmic reaction, the standard enthalpies of formation for Piperazine and product radicals generated by hydrogen abstraction are reported. The branching ratios for both reaction channel (i.e. H-abstraction from –CH₂ and –NH position of Piperazine) are found to be 93% and 7%, respectively. The calculated atmospheric life time of Piperazine is found to be 0.97 hour.