“Compensation effect“ in heterogeneous catalysis

For a number of compared systems (different catalysts of the given process, similar reactions on one catalyst, the given reaction under different conditions, etc.), it is shown that the experimentally observed compensation effect is, in the majority of cases, the result of a change in the kinetic equation. Analysis of the experimental results confirms this conclusion.     

The influence of water on the friction forces of fibers in aramid fabrics

Fabrics based on high-impact organic fibers have an excellent potential to dissipate the energy of a ballistic impact. That is why they are used in protective helmets and flexible armor vests. The work of friction is the main mechanism of energy absorption in fabrics during a transverse impact. The friction forces of fibers were studied via the pullout of several neighboring fibers and via the transverse hardness indentation. The influence of water on indentation forces and pullout forces of Armos and Rusar fibers during their pullout from fabrics is studied. Water enhances friction force several-fold during the pullout of fibers. Consequently, the potential to dissipate the energy of an impact changes during a transverse action. The influence of moisture is irreversible in the Armos fabrics without a water-repellent coating, and drying does not lead to complete recovery of the friction forces of fibers. In the case of Rusar 56319 fabrics with a water-repellent coating, large drops of water roll off the fabric and only small drops influence the friction forces. A substantial variation in the indentation force is detected, thereby apparently providing evidence of the instability of the density of the fabric. An analysis of the mechanisms of energy dissipation is performed. The energy of the elastic deformation in an individual fiber is three times smaller than the kinetic energy of the fiber. Friction work can exceed the sum of kinetic energy and strain energy by an order of magnitude. The estimation of the value of the increase in the temperature of a fiber during an impact is performed. Heat is not emitted during an impact on an individual fiber in the case of the formation of a transverse wave during an inelastic impact. In the process of transmission of transverse and dilatational waves, the energy dissipation is proportionate to the impact velocity raised to the power of 8/3.     

Interfacial phenomena in starch/fumed silica at varied hydration levels

Hydrated powders of non-gelatinised starch and hydrogels of gelatinised starch alone or with addition of modified nanosilica (with grafted aminopropylmethylsilyl groups substituting one-third of surface silanols) were studied using broadband dielectric relaxation spectroscopy (DRS), thermally stimulated depolarisation current (TSDC) method and ¹H NMR spectroscopy with layer-by-layer freezing-out of bulk and interfacial waters. The ¹H NMR and TSDC techniques with the use of Gibbs–Thomson relation for the freezing point depression allow us to calculate: (i) the thermodynamic parameters of interfacial water weakly and strongly bound to polymer molecules and nanoparticles; (ii) size distributions of pores filled by structured water; (iii) surface area and volume of micro-, meso- and macropores. The DRS and TSDC results for hydrogels and hydrated powders with starch/modified fumed silica show that the β- and γ-relaxations of starch are strongly affected by water and functionalised silica nanoparticles which slow down both low- and high-frequency and low- and high-temperature relaxations.     

Ionic mobility and conductivity in PbSnF<Subscript>4</Subscript> doped with CaF<Subscript>2</Subscript> from the NMR and impedance spectroscopy data

The ionic mobility and conductivity in the crystalline phases of PbSnF_4–xCaF₂ systems (x = 2.5 mol.%, 5 mol.%, 7.5 mol.%, and 10 mol.%) in the temperature range of 150-500 K are studied by NMR and impedance spectroscopy. The parameters of ¹⁹F NMR spectra, types of ion motions, and ionic conductivity in the PbSnF₄ compound doped with calcium fluoride are found to be determined by the temperature and concentration of calcium fluoride. The specific conductivity of the crystalline phases in the PbSnF₄–CaF₂ systems is rather high at room temperature, and hence, one cannot exclude the possibility to use them for the creation of functional materials with a high ionic (superionic) conductivity.     

Synthesis of a conjugate of 3´-sialyllactoside with recombinant flagellin as a carrier protein and assessment of its immunological activity in comparison with that of a similar hemocyanin-based conjugate

In the framework of a project directed to the design of synthetic cancer vaccines based on carbohydrate chains of tumor-associated gangliosides, a new prototype cancer vaccine, a polyvalent carbohydrate-protein conjugate 1 with ～11 3´-sialyllactoside ligands conjugated to one molecule of recombinant flagellin was synthesized. Dendritic cell vaccines were designed using the conjugate 1 and a neoglycoconjugate 2 consisting of ～400 3´-sialyllactose residues linked to hemocyanin from a snail Megathura crenulata (KLH). Comparative ELISA study was conducted to assess the induction of carbohydrate-specific immunoglobulins IgM and IgG after immunization of mice with conjugates 1 and 2 and dendritic cells loaded with 1 and 2. Synthetic polyacrylamide carrier conjugated to 3´-sialyllactose ligands and B16F0 melanoma cells were used as coating antigens.     

A polysaccharide composite for water treatment to remove nitrates: Synthesis,properties, and utilization

A sorbent for water treatment to remove nitrates was prepared from readily available vegetable boipolymers: cellulose and starch. The adsorption characteristics of the polysaccharide composite were determined. Biodegradation of the spent composite in the course of its utilization was studied.     

Recombination processes in europium-doped cadmium iodide crystals

Results of comprehensive research into optical and luminescent-kinetic characteristics of europium-doped cadmium iodide crystals excited by nitrogen laser radiation, α-particles, and x-rays are presented. Crystals under study have been grown by the Bridgman–Stockbarger method. The doping EuCl₃ admixture was introduced into the charge in quantities of about 0.05 and 1.0 mol%. Impurity absorption detected in the near-edge region of the crystals is interpreted as part of the Eu²⁺ ion long-wavelength band associated with f–d-transitions. The cation impurity and matrix defects in CdI₂:Eu²⁺ crystals create complex centers responsible for emission with a maximum in the 580–600-nm region. The short component in the luminescence decay kinetics of weakly-doped crystal excited by α-particles and x-ray photons is due to the exciton emission characteristic of CdI₂. The slow component in the scintillation pulse results from recombination of charge carriers followed by creation of exciton-like states on the defect-impurity centers. Laser or x-ray excitation induces light-sum accumulation on the trapping levels at a depth of 0.2–0.6 eV that is mainly related to matrix microdefects. Trapping centers associated with the chlorine impurity are observed in the heavily-doped crystal. Photostimulated luminescence at 85 K arising at the electron stage of the recombination process is caused by recombination of electrons released from F-type centers with holes localized near the activator. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 358–364, May–June, 2009.