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.     

Thermal degradation of composites of poly(methyl methacrylate) with alkoxysilane hydrolyzates

Organic-inorganic composites of poly(methyl methacrylate) with alkoxysilane hydrolyzates form transparent films. Their thermal and oxidative thermal degradation were studied by differential scanning calorimetry and thermogravimetric analysis.     

Nonlinear pulsed ultrasound beams radiated by rectangular focused diagnostic transducers

A numerical model for simulating nonlinear pulsed beams radiated by rectangular focused transducers, which are typical of diagnostic ultrasound systems, is presented. The model is based on a KZK-type nonlinear evolution equation generalized to an arbitrary frequency-dependent absorption. The method of fractional steps with an operator-splitting procedure is employed in the combined frequency-time domain algorithm. The diffraction is described using the implicit backward finite-difference scheme and the alternate direction implicit method. An analytic solution in the time domain is employed for the nonlinearity operator. The absorption and dispersion of the sound speed are also described using an analytic solution but in the frequency domain. Numerical solutions are obtained for the nonlinear acoustic field in a homogeneous tissue-like medium obeying a linear frequency law of absorption and in a thermoviscous fluid with a quadratic frequency law of absorption. The model is applied to study the spatial distributions of the fundamental and second harmonics for a typical diagnostic ultrasound source. The nonlinear distortion of pulses and their spectra due to the propagation in tissues are presented. A better understanding of nonlinear propagation in tissue may lead to improvements in nonlinear imaging and in specific tissue harmonic imaging. Published in Russian in Akusticheskiĭ Zhurnal, 2006, Vol. 52, No. 4, pp. 560–570. This article was translated by the authors.     

Efficient synthesis of enynecarbamates and their ring-closing metathesis/[4 + 2] Diels-Alder cycloaddition: synthesis of hexahydroisoquinolines

Enynes 5a-g were prepared in moderate to good yields from 1-(triphenylphosphoranylideneaminoalkyl)benzotriazoles. Ring-closing metathesis of 5a-f afforded functionalized dienes 6a-f, respectively, which were used in a Diels-Alder cycloaddition reaction in the synthesis of the corresponding hexahydroisoquinoline derivatives 7a-f.     

Adsorption properties of cermet and track-etched poly(ethylene terephthalate) membranes

The adsorption properties of cermet and track-etched poly(ethylene terephthalate) (PET-TM) membranes are compared with respect to proteins and water-soluble dyes. It is shown that the cermet membranes have a noticeably higher adsorption capacity (calculated per unit surface area) than the PET-TM. In this case, the character of adsorption of these substances on both types of membranes is quite similar and determined by the combination of ionic and hydrophobic interactions. The adsorption values of basic dyes are considerably higher than acid one because of the negative charge at the membrane surfaces. The isotherm of adsorption of the basic dye rhodamine 6G on PET-TM from aqueous solution is characterized by the inflection in the concentration range of lower than 1 µmol/l due to the presence of highly active adsorption sites on the surface. The adsorption of dyes considerably lowers on adding isopropanol to the aqueous solution. Using basic protein cytochrome C as an example, it is established that its adsorption on cermet membranes can be prevented by increasing solution ionic strength.Translated from Kolloidnyi Zhurnal, Vol. 67, No. 1, 2005, pp. 124–127. Original Russian Text Copyright © 2005 by Khataibe, Khokhlova, Trusov, Mchedlishvili.     

Protein and Dye Adsorption on Poly(ethylene terephthalate) Nucleopore Membranes Modified with Polymers

Adsorption of basic, neutral, and acidic proteins on poly(ethylene terephthalate) nucleopore membranes was studied as a function of solution pH. Higher adsorption values were observed for basic and neutral proteins and lower, for acidic proteins. The value of pH corresponding to maximal adsorption was somewhat lower than the isoelectric points of proteins, thus suggesting that the adsorption was governed by a combination of ionic and hydrophobic interactions between proteins and the membrane surface. Proteins were adsorbed in an associated form. Membrane surface was modified with poly(ethylene imine) and poly(ethylene glycol). Combined modification of the membranes with these polymers was found to substantially decrease the adsorption of basic and neutral proteins, as well as basic dye and to slightly increase the adsorption of acidic proteins. The modifying coating had a high hydrolytic stability.     

Influence of UV Pretreatment on Thermooxidative Degradation of Poly(Methyl Methacrylate) Films with Fullerene C<Subscript>60</Subscript> or C<Subscript>70</Subscript>

Wariation of the concentration of fullerenes C₆₀ and C₇₀ in poly(methyl methacrylate) films under UV exposure in atmospheric oxygen was studied. The mechanism of the influence exerted by addition of some photostabilizing polymers and xanthene dyes on the photooxidative degradation of fullerene in the polymer matrix was analyzed.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 6, 2005, pp. 1038–1042.Original Russian Text Copyright © 2005 by Troitskii, Khokhlova, Konev, Denisova, Novikova, Lopatin.     

Adsorption of dyes on activated carbon and graphitic thermal carbon black

The adsorption of a basic dye (Methylene Blue; MB) and an acidic dye (Acid Orange; AO) has been studied on three activated carbons (ACs; FAS, SKD, and BAU) significantly differing in their porous structures and surface concentrations of ion-exchange groups and on graphitic thermal carbon black (GTCB). The effective specific surface area of FAS, SKD, and BAU determined by dye adsorption is, respectively, 60, 50, and 40% of the BET nitrogen adsorption surface area. The MB uptake on ACs and GTCB increases with rising pH, while the AO uptake decreases. Addition of an electrolyte (0.3 M NaCl) virtually does not effect the adsorption of dyes on ACs and GTCB. It is suggested that hydrophobic interactions, and not ionic ones, are the major contributors to the adsorption of dyes on ACs.     

Spectral Modeling of Difference-Frequency Generation in the Case of Two-Frequency Interaction of Ultrasound Waves

Acoustical Physics - A spectral algorithm is considered for describing nonlinear generation of an acoustic wave of difference frequency formed as the interaction of two high-intensity pump waves...