Turbulence Driven Tearing Modes

The effect of a turbulent background of density, electrostatic, and magnetic fluctuations on the growth of tearing modes is considered assuming three-wave interaction. It is found that, depending on the background conditions, the turbulence can cause anomalous electron resistivity or viscosity, leading to enhanced growth rate.     

Development of long-lifetime metal-ligand probes for biophysics and cellular imaging

Metal-ligand complexes containing ruthenium, osmium, or rhenium display a high photostability, with polarized emission and decay times from 100 ns to 100 Μs. Such probes have considerable potential in biophysics, clinical chemistry, and fluorescence microscopy. In this review we sumrecent developments from this laboratory on the spectral properties of conjugatable metalligand complexes. We also suggest how improved probes can be developed based on the selection of organic ligands.     

Synthesis and characterization of polyaniline–zirconium dioxide and polyaniline–cerium dioxide composites with enhanced photocatalytic degradation of rhodamine B dye

For the first time, chloroform and 2-butanol were used as solvent systems for the preparation of ZrO₂–PANI and CeO₂–PANI composites. Solubility of the synthesized composites was studied in chloroform, N-methyl-2-pyrrolidinone (NMP), and in mixture of toluene?+?2-propanol (2:1). XRD and cyclic voltammetry data showed that the ZrO₂–PANI and CeO₂–PANI composites possess both crystalline and amorphous domains indicating some sort of conductivity. TGA results showed that ZrO₂–PANI composite have a better thermal stability than pure PANI; however, CeO₂–PANI composite has lower thermal stability than pure PANI. The conjugated unsaturated structure of PANI is responsible for the enhanced photocatalytic properties of ZrO₂–PANI and CeO₂–PANI. Photocatalytic results showed that, at photolysis time of 60 min, rhodamine B (RhB) dye was degraded up to 34 and 35% by ZrO₂–PANI and CeO₂–PANI, respectively. The degradation products of RhB were quantified by LC–MS and GC–MS, and accordingly, a detailed pathway was proposed.     

Markovnikov versus anti‐Markovnikov addition and C–H activation: Pd–Cu synergistic catalysis

Copper‐ and palladium‐mediated transmetalation and coupling reactions are the backbone to several synthetic methodologies in organic chemistry for C–C bond formation. Computer‐aided simulations using density functional theory (DFT) (B3LYP‐D3 functional with 6‐31G** and effective core potential (ECP)‐LACVP** for heavy atoms for optimizations and cc‐pVTZ(?f) and ECP‐LACV3P** for single‐point calculations) was used to shed light on the probable mechanism of a novel synergistic Cu/Pd catalysts for the coupling of alkene, (Bpin)2 (where, pin = pinacolate), and vinyl‐ or aryl‐halogenated analogues. Every single conceivable pathway was carefully contemplated, and the base minimum energy pathway was found effectively. The copper‐catalyzed nucleophilic generation yields anti‐Markovnikov product using styrene as an alkene. This study affirms quantitatively and accurately how the reaction proceeds and at which steps of the synergistic catalysis the demand of the transmetalation and nucleophile formation for the C–C coupling using phosphine ligands arise. We conclude that the E and Z selectivity depends on the stereochemistry of the substrates used.     

Magnetic and optical properties of Gd-Tl substituted M-type barium hexaferrites synthesized by co-precipitation technique

The substitution of numerous cations into hexagonal ferrite has been extensively used to endow novel properties and functionalities for various applications. In the present work Gd-Tl substituted barium hexaferrites prepared by co-precipitation process, having the composition Ba_0.75Cu_0.25(Gd_xTl_0.5-x)Fe_11.5O₁₉ (x = 0.0, 0.25 and 0.50). The hexaferrite formation during calcination of sample x = 0.25 was confirmed by TGA/DSC which was processed at 1000 °C for 3 h. The analysis of X-ray diffraction depicts the existence of magneto-plumbite structure with the formation of a minor secondary α–Fe₂O₃ phase x ≤ 0.0 and BaFe₂O₄ phase x ≤ 0.50. UV–Vis spectra reveal the dropping down behavior in the optical energy band gap from 2.47 eV to 1.74 eV. The grains with hexagonal platelet-like shape having size of 0.415–0.446 μm of magnetic powder nanoparticles (MPs) are observed by SEM images. The energy dispersive spectrometer (EDS) analysis was employed for presence of ferrite elements within a single particle. Hysteresis loops signifies the magnetization (M_s) and remnant magnetization (M_r) first increases up to x = 0.25 then reduces with the substitution (x) increment; contrarily, the coercivity (H_c) exhibited initially decreased with maximum content of Tl at x = 0.0 then increases at x = 0.25 after that it decreases at x = 0.50. Maximum values such as M_s (51.727 emu/g), M_r (28.061 emu/g), and H_c (4.057 kOe) are attained for x = 0.25 at room temperature. The synthesized magnetic nanoparticles are found to be suitable for microwave absorbing materials, permanent magnets, catalyst, high density recording media and optoelectronic devices.     

In-plane magnetization with high coercivity in terbium iron garnet thin films deposited on Pt/Si substrate by PLD

We report on the growth of terbium iron garnet (TbIG, Tb₃Fe₅O₁₂) thin films having anomalously large coercivity and in-plane easy axis of magnetization. The TbIG thin films were prepared at room temperature (RT) on Pt/Si(1 0 0) substrates by pulsed laser deposition technique. The films deposited at RT were X-ray amorphous and do not show any magnetic order. Annealing of the RT deposited film at 900 °C resulted into fully textured (532) TbIG film. Atomic force microscopy and cross-sectional scanning electron microscopy studies of the TbIG films showed good surface quality with an average surface roughness of 5.0 nm and thickness of about 300 nm, respectively. The M-H loops measured at 20 K for TbIG films, exhibit about an order of magnitude enhancement in the coercivity value (H_c) than the single crystal. In-plane and out-of-plane M-H loops revealed that the easy axis of the magnetization lies within the film’s plane. In-plane magnetization combining with large H_c value of the TbIG thin film may be of scientific interest for the possible applications.     

Stability of nonthermodynamic equilibrium cation distribution frozen during pulsed laser deposition of Co-ferrite thin films

Co-ferrite thin films were prepared by pulsed laser deposition technique at room temperature, and magnetization was studied as a function of annealing temperature (T _A ) and annealing time. One set of films was quenched immediately after annealing while the other set was furnace cooled. Spontaneous magnetization value, 4π M _S , of the quenched films was observed to be higher than the furnace cooled films in all the cases. Magnetization increases monotonically up to T _A =650°C and then became nearly constant with the increase in T _A . Magnetization values even higher than the Co-ferrite bulk value of 5300 G was observed in the quenched films annealed at and above 650°C. In the case of furnace cooled films, magnetization decreased with the increase in annealing time, while it remained nearly constant in quenched films. Coercivity values of the quenched films were always found to be lower than those of the furnace cooled films. The observed magnetic properties in the films were attributed to the cation distribution and the grain sizes.     

Kinetic and mechanistic studies on the complexation and anation of dioxotetracyanomolybdate (IV) with 2,2′-bipyridyl in aqueous solution

Dioxotetracyanomolybdate(IV) has been found to form a 1 : 2 complex with 2,2′-bipyridyl. The kinetics of the reaction has been studied over the pH range 5.3–8.7 by visible spectrophotometry under pseudo conditions. The effect of the 2,2′-bipyridyl and dioxotetracyanomolybdate(IV), temperature, ionic strength, and pH on the reaction rate was determined. The reaction follows first-order kinetics with respect to dioxotetracyanomolybdate(IV) ion and fractional-order kinetics with respect to 2,2′-bipyridyl. Values for the outer-sphere complex formation constant (K_os2) and rate constants (k₂) were also calculated from the kinetic data. It was found that rate of the reaction increases with the decreasing pH. The following rate equation based on the outersphere complexation equilibrium preceding the associative interchange has been derived. On the basis of the observed results probable mechanism has been proposed. © 1996 John Wiley & Sons, Inc.     

Separation of trace amounts of rhodium(III) with tri-n-butyl phosphate from nitric acid and sodium trichloroacetate media

A new method for the quantitative extraction and separation of trace amounts of rhodium from nitric acid and sodium trichloroacetate media has been established based on the formation of an ion-association complex of hexahydrated rhodium cation Rh(H₂O)₆ ³⁺ and the trichloroacetate (TCA) anion in tri-n-butyl phosphate (TBP). The effect of various factors (solvent, pH, sodium trichloroacetate, shaking time, phase volume ratio, composition of the extracted species, foreign ions, transformation of rhodium chlorocomplexes into hexahydrated cation, etc.) on the extraction and back-extraction of rhodium has been investigated. The method can be combined with subsequent FAAS determination of rhodium. The procedure was applied to determine rhodium traces in chloroplatinic acid and palladium chloride. Received: 17 March 2000 / Revised: 15 May 2000 / Accepted: 19 May 2000