Will the iron age of superconductivity become the Mössbauer age?

The discovery of new iron-containing high-temperature superconductors is considered in relation to their studies by means of the Mössbauer effect. The importance of the relevant results for the problem of the coexistence of magnetism and superconductivity and the stability of superconductivity against to disorder is shown by analyzing the available literature data.     

Effect of broken ice on the wave resistance of an amphibian air-cushion vehicle in nonstationary motion

The uniformly accelerated motion of an amphibian air-cushion vehicle on the surface of a basin covered by finely small ice floes is considered. Institute of Machine Science and Metallurgy, Far-Eastern Division, Russian Academy of Sciences, Komsomol'sk-on-Amur 681005. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 6, pp. 48–53, November–December, 1999.     

The kinetics and mechanism of dissolution of gold in solutions of thiocarbamide with an oxidizer

The kinetics and mechanism of dissolution of gold in solutions of thiocarbamide (T) in the presence of Fe₂(SO₄)₃ as an oxidizer were studied. The dependences of the rate of dissolution of gold on the concentration ratio between iron(III) and T and pH were determined, and optimum solution compositions for the dissolution of gold were found. The compositions of gold(I) complexes formed in the boundary double layer ([Au{(NH₂)₂C=S}₂]⁺) and in the bulk ([Au{(NH₂)₂C=S}₃]⁺) were determined. The diffusion and kinetic components of the overall reaction of gold dissolution in solutions of T in the presence of the oxidizer were obtained by the rotating disc method. The first-order rate constants at 278–333 K, k _Au = 3.5 × 10^?5?2.73 × 10^?4 s^?1, and the activation energies at 278–295 K (E _a = 13.4 kJ/mol, which is evidence that dissolution value characteristic of kinetically controlled reactions) were determined for the dissolution of gold in solutions of T. The composition of the adsorption sulfide-containing film on the surface of gold was studied by Auger electron spectroscopy. The film, which inhibited gold dissolution, consisted of gold(I) hydrosulfide (AuHS) and sulfide (Au₂S). The solubility products of these compounds and their solubilities in aqueous solutions were calculated.     

Kinetics of Gold Dissolution in Thiosemicarbazide Solutions

The kinetics of gold dissolution in thiosemicarbazide solutions was studied relative to the ratio of ferric ion and thiosemicarbazide concentrations as well as pH. The composition of the complex formed was found to be [Au(NH₂)₂NHC=S₃]⁺. The rate constants for gold dissolution were determined at 278-298 K along with the stability, dissociation, and equilibrium constants at 288 K. The activation energy at 288 K was also found.     

Functional polymer colloids with ordered interior

Polymer colloids with internal ordering were synthesized using hydrolytic condensation of octadecyl-dimethyl(3-trimethoxysilylpropyl)ammonium chloride (ODMACl) and a mixture of ODMACl and the trisodium salt of the triacetic acid N-(trimethoxysilylpropyl)ethylenediamine (TANED). The structure and morphology of these colloids were studied with small-angle X-ray scattering, transmission electron microscopy, nuclear magnetic resonance, sedimentation in ultracentrifuge; and other methods. When polymer colloids are obtained from a single precursor (ODMACl), their local structure, molecular weight characteristics, and morphology strongly depend on the reaction conditions, while lamellar ordering remains nearly unaffected. Use of a mixture of cationic and anionic silanes (ODMACl and TANED) as precursors in hydrolytic condensation results in novel zwitterionic copolymer colloids with two-dimensional hexagonal packing. Interaction of the ODMACl quaternary ammonium groups with the three carboxy groups of TANED leads to replacement of sodium and chloride ions and formation of gegenions, resulting in a molar ratio ODMACl:TANED = 3:1 (each TANED molecule contains three carboxy groups). Due to their ordered interior, polyODMACl (PODMACl) and PODMACl-TANED colloids can be used as templates for controlled positioning of nanoparticles within these colloids. For example, lamellar ordering controls Pt nanoparticle formation within PODMACl colloids providing Pt nanoparticle alignment within the lamellar structure. Loading of PODMACl-TANED colloids with iron salts followed by pH increase results in the formation of iron oxide nanoparticles located within PODMACl-TANED cylinders.     

Reduction of Deuterium Level Supports Resistance of Neurons to Glucose Deprivation and Hypoxia: Study in Cultures of Neurons and on Animals

The effect of a reduced deuterium (D) content in the incubation medium on the survival of cultured neurons in vitro and under glucose deprivation was studied. In addition, we studied the effect of a decrease in the deuterium content in the rat brain on oxidative processes in the nervous tissue, its antioxidant protection, and training of rats in the T-shaped maze test under hypoxic conditions. For experiments with cultures of neurons, 7–8-day cultures of cerebellar neurons were used. Determination of the rate of neuronal death in cultures was carried out using propidium iodide. Acute hypoxia with hypercapnia was simulated in rats by placing them in sealed vessels with a capacity of 1 L. The effect on oxidative processes in brain tissues was assessed by changes in the level of free radical oxidation and malondialdehyde. The effect on the antioxidant system of the brain was assessed by the activity of catalase. The study in the T-maze was carried out in accordance with the generally accepted methodology, the skill of alternating right-sided and left-sided loops on positive reinforcement was developed. This work has shown that a decrease in the deuterium content in the incubation medium to a level of −357‰ has a neuroprotective effect, increasing the survival rate of cultured neurons under glucose deprivation. When exposed to hypoxia, a preliminary decrease in the deuterium content in the rat brain to −261‰ prevents the development of oxidative stress in their nervous tissue and preserves the learning ability of animals in the T-shaped maze test at the level of the control group. A similar protective effect during the modification of the ²H/¹H internal environment of the body by the consumption of DDW can potentially be used for the prevention of pathological conditions associated with the development of oxidative stress with damage to the central nervous system.     

Kinetics of the Dissolution of Silver in Thiocarbamide Solutions

The dependence of the rate of solution of silver on the pH of the solution, the ratio of the iron(III) and thiocarbamide concentrations, and the temperature has been determined. The rate constants for the solution of silver (k _i = 2.3·10^–4 to 9.6·10^–4s^–1) at temperatures from 283-298 K have been calculated and from the temperature dependence of the rate constant the activation energies have been calculated: 68.84 kJ/mol for kinetic control of the rate of solution and 26.06 kJ/mol in the adsorption inhibition region.     

Small-angle X-ray scattering study of the structure of self-organized polymer matrices and formation of imbedded metal nanoparticles

The structures of self-organizing polymer matrices based on collapsed gels and polyoctadecylsiloxanes have been studied by the methods of conventional and anomalous X-ray small-angle scattering with the use of the laboratory and synchrotron sources of X-ray radiation. The process of formation of metal nanoparticles in such matrices is also studied, their size distributions are calculated, and the models of localization of these particles in the polymer matrices are suggested. It is shown that growth of metal particles is controlled by the structure of the polymer network and is limited by the dimensions of its cells. The electron-density profiles of polycondensed octadecylsiloxane matrices are also calculated.     

Electron and phonon effects in superconducting tunnel detectors of x-radiation

Nb/Al/AlO_x/Nb superconducting tunnel junctions were investigated in the role of x-ray detectors. Amplitude spectra of pulses arising upon irradiation of tunnel junctions of different sizes by ⁵⁵Mn x-radiation were recorded at a temperature T=1.4 K. We also analyzed the temporal shape of the pulses. We considered the influence of diffuse motion of nonequilibrium quasiparticles, the inverse tunneling effect, and exchange of 2Δ phonons between electrodes, on the characteristics of the tunnel detectors. It is shown that phonon processes can bring about changes in the amplitude, duration, and polarity of the signal. Fiz. Tverd. Tela (St. Petersburg) 41, 1168–1175 (July 1999)     

Assigning vibrational polyads using relative equilibria: application to ozone

We demonstrate how relative equilibria of a vibrating molecule, which are families of principal periodic orbits otherwise known as nonlinear normal modes, can be used to describe the global polyad structure of vibrational energy levels. The classical action integral n(E) computed along these orbits at different energies E corresponds to the polyad quantum number n so that the energy En of different relative equilibria describes the splitting of n-polyads. Further information on the internal polyad structure can be driven from the stability analysis of relative equilibria. We use the ozone molecule as a concrete example where n-polyads or "hyperpolyads" should be distinguished from the well-known polyads of the 1:1 stretching mode resonance; the stretching polyads are structural elements of hyperpolyads. We give dynamical interpretation of the relation between relative equilibria and n-polyads based on the normal form reduction in the limit of small vibrations near the equilibrium.