Study of the peak effect phenomenon in single crystals of 2H-NbSe2

The weakly pinned single crystals of the hexagonal 2H-NbSe₂ compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of the peak effect phenomenon in three crystals of 2H-NbSe₂, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability effects and pinning.     

Dynamics of colloid silver nanoparticles in an evaporating water drop

The method of photon correlation spectroscopy is used to investigate the distribution of the diffusion coefficient of silver nanoparticles in an evaporating water drop given that the drop base area remains unchanged (the pinning condition). It is established that the capillary flow dominates over the diffusion nanoparticle motion in redistribution of concentration of the dissolved nanoparticles.     

Novel nonperipheral octa-3-hydroxypropylthio substituted metallo-phthalocyanines: synthesis,characterization, and investigation of their electrochemical,photochemical and computational properties

The current study describes the synthesis, electrochemical, computational, and photochemical properties of octa (3-hydroxypropylthio) substituted cobalt (II) ( 4 ), copper (II) ( 5 ), nickel (II) ( 6 ) and zinc(II) ( 7 ) phthalocyanine derivatives. These novel compounds were characterized by elemental analysis,¹H,¹³C NMR, FT-IR, UV-Vis, and MS. The redox behaviors of these metallo-phthalocyanines were investigated by the cyclic voltammetric method. The optimized molecular structure and gauge-including atomic orbital (GIAO)¹H and¹³C NMR chemical shift values of these phthalocyanines in the ground state had been calculated by using B3LYP/6–31G(d,p) basis set. The outcomes of the optimized molecular structure were given and compared with the experimental NMR values. The photochemical properties including photodegradation and singlet oxygen generation of zinc(II) phthalocyanine were studied in DMSO solution for the determination of its photosensitizer behaviors.     

Nuclear magnetic resonance study of self-diffusion in liquid crystals

A simple and accurate pulsed-gradient nuclear magnetic resonance technique for measuring coefficients of self-diffusion in liquid crystals is described. It is based on exciting sharp response signals with long weak pulses. The method uses an extremely weak radio-frequency field, which eliminates the problem of radio-frequency heating of the sample. The temperature dependencies of coefficients of self-diffusion for two liquid crystals, 5CB (4-pentyl-4(')-cyanobiphenyl) and EBBA (N-(4-ethoxybenzylidene)-4-butylaniline), are presented.     

An improved broadband decoupling sequence for liquid crystals and solids

Recently we developed an efficient broadband decoupling sequence called SPARC-16 for liquid crystals ?J. Magn. Reson. 130, 317 (1998). The sequence is based upon a 16-step phase cycling of the 2-step TPPM decoupling method for solids ?J. Chem. Phys. 103, 6951 (1995). Since then, we have found that a stepwise variation of the phase angle in the TPPM sequence offers even better results. The application of this new method to a liquid crystalline compound, 4-n-pentyl-4'-cyanobiphenyl, and a solid, L-tyrosine hydrochloride, is reported. The reason for the improvement is explained by an analysis of the problem in the rotating frame.     

Cloused cycle of production of ulltrafine polytetrafluoroethylene and new areas of use of fluoropolymer manufacture waste

The features of processes of ultrafine polytetrafluoroethylene manufacture of waste technological polytetrafluoroethylene by hydrothermal method and thermal degradation with an exhaustive fluorination in the presence of cobalt trifluoride were studied. Compositions and properties of gaseous and solid products of pyrolysis and recycling in ultrafine polytetrafluoroethylene manufacture were determined. Methods of use of ultrafine polytetrafluoroethylene, gaseous products, and spent catalyst were developed. On the basis of the experiments a closed scheme of producing ultrafine polytetrafluoroethylene was proposed in view of its application with recycling of accompanying gas fraction, and separating manufacture waste with recycling of cobalt trifluoride catalyst and using the resulting cobalt difluoride for producing composite coatings and lubricants.     

Development of the method for determination of the content of softwood component in lignins

Methods for the quantitative treatment of IR Fourier spectra for the determination of relative contents of pine and birch lignin in wood were studied.     

Fast protonic conductivity in crystalline benzenehexasulfonic acid hydrates

We report on the crystal structures of two hydrates of benzenehexasulfonic acid, its water sorption isotherm, temperature- and humidity-dependent conductivity, along with ¹H NMR studies. At comparable humidities and temperatures, this crystalline material shows conductivity similar to Nafion, which conducts protons via liquid water channels. We believe that the presented discovery of fast protonic conductivity in benzenehexasulfonic acid at low humidities is encouraging for further efforts in developing highly sulfonated polymers as membranes for fuel cells.     

Study of magnetoresistance and conductance of bicrystal grain boundary in La0.67Ba0.33MnO3 thin film

La_0.67Ba_0.33MnO₃ (LBMO) thin film is deposited on a 36.7°C SrTiO₃ bicrystal substrate using laser ablation technique. A microbridge is created across bicrystal grain boundary and its characteristics are compared with a microbridge on the LBMO film having no grain boundary. Presence of grain boundary exhibits substantial magnetoresistance ratio (MRR) in the low field and low temperature region. Bicrystal grain boundary contribution in MRR disappears at temperature T>175 K. At low temperature, I-V characteristic of the microbridge across bicrystal grain boundary is nonlinear. Analysis of temperature dependence of dynamic conductance-voltage characteristics of the bicrystal grain boundary indicates that at low temperatures (T<175 K) carrier transport across the grain boundary in LBMO film is dominated by inelastic tunneling via pairs of manganese atoms and tunneling through disordered oxides. At higher temperatures (T>175 K), magnetic scattering process is dominating. Decrease of bicrystal grain boundary contribution in magnetoresistance with the increase in temperature is due to enhanced spin-flip scattering process.