Phase transformations in the Mn-Ge system and in Ge x Mn1 ? x diluted semiconductors

Results of an X-ray diffraction study as well as magnetic and electrical measurements of the solid-state reactions in Ge/Mn polycrystalline films of an 80/20 atomic composition have been presented. It has been shown that the ferromagnetic Mn₅Ge₃ phase is formed first on the Ge/Mn interface after annealing at ??120°C. The further increase in the annealing temperature to 300°C leads to the beginning of the synthesis of the Mn₁₁Ge₈ phase, which becomes dominating at 400°C. The existence of new structural transitions in the Mn-Ge system in the region of ??120 and ??300°C has been predicted on the basis of the presented results and results obtained earlier when studying solid-state reactions in different film structures. The supposition about the general chemical mechanisms of the synthesis of the Mn₅Ge₃ and Mn₁₁Ge₈ phases during the solid-state reactions in the Ge/Mn films of the 80/20 atomic composition and the phase separation in Ge _x Mn_{1 ? x} (x > 0.95) diluted semiconductors has been substantiated.     

Polymorphic transformations in γ-irradiated amino acids and dipeptides

There is an unexpected decrease in infra-red absorption band intensities of amino acids and dipeptides on irradiation with γ-rays at very high dose rates. The infra-red evidence together with X-ray crystallographic studies leads to the postulation of weak bond formation which increases the degree of molecular association in the irradiated material. A marked increase in infra-red absorption at low dose rate earlier reported⁽¹⁾ has not been observed.     

Widths in the conversion of Σ and Ξ hyperons in nuclear matter

The widths of the conversion processes N, N in nuclear mattter were calculated based on the model of single-boson exchange. It was established that the conversion width for is significantly reduced by the interference of the contributions of separate mesons to the conversion amplitude. The conversion width obtained for in nuclear matter turned out to be less than 1 MeV.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 79–84, March, 1988.     

Momentum dependence of hadronic production of the ?-meson and its width in nuclear matter

Information on the properties of the ? meson in the nuclear environment has been derived from its production in proton collisions with C, Cu, Al, and Au nuclear targets. The experiment was carried out with 2.83?GeV protons at the Cooler Synchrotron COSY, with the ? being detected via its K ^?+? K ^?? decay using the ANKE magnetic spectrometer. The measured dependence of the production cross section on the nuclear mass number has been compared with calculations within three different nuclear models. These suggest a significant broadening of the width of the ? in medium relative to its vacuum value. The ANKE results obtained in the momentum range 0.6?p _? ?c are compared with data from photoproduction experiments at slightly higher momenta.     

Is there nuclear pinning of vortices in superfluid pulsars?

We develop a fully consistent semianalytical model in order to study the vortex-nucleus interaction in the inner crust of neutron stars. In the framework of the local-density approximation and assuming a constant pairing gap and a square-well nuclear potential, the model takes into account all energy contributions and determines unambiguously the structure of the vortex core. The results show that, irrespective of the value of the pairing gap, only interstitial pinning takes place all along the inner crust. This is in contrast with all existing calculations, which predict nuclear pinning in the deeper layers of the crust. Should further studies confirm this surprising result, the explanation of pulsar glitches in terms of depinning of vortices will have to be carefully revisited.     

Antikaon production in proton-nucleus reactions and the K− properties in nuclear matter

We calculate the momentum-dependent potentials for K⁺ and K⁻ mesons in a dispersion approach at nuclear density ϱ₀ using the information from the vacuum K⁺N and K⁻N scattering amplitudes, however, leaving out the resonance contributions for the in-medium analysis. Whereas the K⁺ potential is found to be repulsive (≈ + 25 MeV) and to show only a moderate momentum dependence, the K⁻ self-energy at normal nuclear matter density turns out to be ≈ − 140 ± 25 MeV at zero momentum roughly in line with K⁻ atomic data, however, decreases rapidly in magnitude for higher momenta. The antikaon production in p + A reactions is calculated within a coupled channel transport approach and compared to the data at KEK including different assumptions for the antikaon potentials. Furthermore, detailed predictions are made for p+¹²C and p+²⁰⁷Pb reactions at 2.5 GeV in order to determine the momentum-dependent antikaon potential experimentally.     

Effect of Doping and Electrotransfer on Contact Melting in Cadmium–Indium and Cadmium–Tin Systems

X-rays are used to investigate phase formation upon contact melting, including cases of electrotransfer, in Cd–In and Cd–Sn systems upon adding small amounts of sodium to cadmium. The nucleation of two-component intermetallic compounds is established. The microhardness of diffusion zones along interlayers is measured. An attempt is made to explain the obtained results.     

β-NMR and nuclear spin diffusion in a spatially disordered subsystem

The results of theoretical and experimental investigations of delocalization of nuclear polarization in spatially disordered media are presented. The experiment is based on the measurement of a depolarization of β-active ⁸Li impurity nuclei (β-nuclei) in the spatially disordered subsystem of ⁸Li-⁶Li nuclei in LiF single crystals. The process is determined by the dipole-dipole interaction in this subsystem and by its dipole interactions with nuclei of the ⁷Li¹⁹F matrix. It is effective in a wide range of external magnetic fields H ₀ = 200–3000 G owing to proximity of g-factors. The kinetics of a depolarization of β-nuclei at the ⁶Li concentration c = 0.15–10.06% in fields H ₀ = 200 and 1210 G is investigated. A satisfactory explanation of the results is based on the numerical-analytical simulation of the process.     

Optics and spectroscopy of cooperative laser-electron nuclear processes in atomic and molecular systems – new trend in quantum optics

A consistent QED perturbation theory approach is applied to calculation of the electron-nuclear γ-transition spectrum of nucleus in the multicharged ion. The intensities of satellites are defined within the relativistic version of the energy approach (Gell-Mann and Low S-matrix formalism). As example, the nuclear transition in the isotope with the energy 14.41 keV is considered. The results of the relativistic calculation for the electron-nuclear γ-transition spectrum (a set of electron satellites) of the nucleus in a multicharged atomic ion FeXIX are presented. The possible experiments for observation of the new effect in the thermalized plasma of the O-like ions are discussed. A consistent quantum approach to calculation of the electron-nuclear γ transition spectrum (a set of vibration-rotational satellites in a molecule) of nucleus in a molecule is proposed and based on the Dunham model potential approximation for potential curves of the diatomic molecules. Model proposed generelizes the well known Letokhov-Minogin model. The estimates are made for vibration-rotation-nuclear transition probabilities in a case of the emission and absorption spectrum of nucleus ¹²⁷I (E⁽⁰⁾_γ=203 keV) in the molecule of H¹²⁷I.     

The sublimation growth of AlN fibers: transformations in?morphology & fiber direction

The growth of AlN fibers using sublimation method was investigated in the temperature range from 1600 °C to 2000 °C. Large-scale AlN fibers are obtained with diameters from 100 nm to 50 μm and lengths up to several millimeters. The fiber morphology and growth direction are characterized by X-ray diffraction (XRD), field emission scanning electron microscope (SEM), high-resolution transmission electron microscopy (HRTEM), and Raman scattering. The fibers change from wire-like to prism-like in morphology and increase in diameter as rising temperatures, accompanying a transformation in axial direction from [10 ] to [0001]. The transformation in the growth direction is discussed in terms of AlN structure and supersaturation of AlN gas species. These results provide useful information for controlling the growth of large-scale AlN fibers.     

Electron beam-induced structural transformations of MoO3 and MoO3?x crystalline nanostructures

Electron beam-induced damage and structural changes in MoO₃ and MoO_3−x single crystalline nanostructures were revealed by in situ transmission electron microscopy (TEM) examination (at 200 kV) after few minutes of concentrating the electron beam onto small areas (diameters between 25 and 200 nm) of the samples. The damage was evaluated recording TEM images, while the structural changes were revealed acquiring selected area electron diffraction patterns and high resolution transmission electron microscopy (HRTEM) images after different irradiation times. The as-received nanostructures of orthorhombic MoO₃ were transformed to a Magnéli’s phase of the oxide (γ-Mo₄O₁₁) after ~10 min of electron beam irradiation. The oxygen loss from the oxide promoted structural changes. HRTEM observations showed that, in the first stage of the reduction, oxygen vacancies generated by the electron beam are accommodated by forming crystallographic shear planes. At a later stage of the reduction process, a polycrystalline structure was developed with highly oxygen-deficient grains. The structural changes can be attributed to the local heating of the irradiated zone combined with radiolysis.     

Variable range hopping conduction and percolation networks in the pellets formed from pristine and boron-doped carbon nanohorn particles

Resistivity of pelletized carbon nanohorn particles (CNHs) decreased immediately as the pressure for making the pellet increased. This behavior can be fitted by a power scaling relation with quasi-2-dimensional percolating conducting channels. Similarly, the resistivity of a pelletized boron-doped CNHs (B-CNHs) also decreased rapidly as a function of boron concentration in the region of low boron contents (<∼0.5%). On the other hand, the characteristic temperature for variable range hopping (VRH) conduction indicated different behavior, showing almost constant values for pristine CNHs and drastic changes for B-CNHs. By analyzing these experimental results using VRH theory it was found that the resistivity drop for B-CNHs can be explained by the increase of the electronic density of states at the Fermi level of nanohorns due to substitutional doping of boron in the sp² bonded carbon network which is unlike the percolation for pristine CNHs.     

Dissolution dynamic nuclear polarization–enhanced magnetic resonance spectroscopy and imaging: Chemical and biochemical reactions in nonequilibrium conditions

Hyperpolarization techniques, in particular dissolution dynamic nuclear polarization (D-DNP), make a contribution to overcoming sensitivity limitations of magnetic resonance (MR) spectroscopy through signal enhancement, leading to the study of new fields of research in real time. Utilizing the large signal enhancement initially produced on small molecules, it has become possible to study systems with low γ nuclei, such as ¹³C, ¹⁵N, and ²⁹Si. This review summarizes recent studies that have extended the applicability of D-DNP into various areas of research, especially for systems in nonequilibrium conditions that involve in vivo metabolic/molecular MR imaging for early stage disease diagnosis and real-time MR analysis of various chemical/biochemical reactions for kinetic and mechanistic studies. This review also deals with the theoretical aspects of DNP mechanisms and experimental arrangements of the dissolution setup.     

Multiple Darboux–B?cklund transformations via truncated Painleve′ expansion and Lie point symmetry approach

For a given truncated Painleve′ expansion of an arbitrary nonlinear Painleve′ integrable system, the residue with respect to the singularity manifold is known as a nonlocal symmetry, called the residual symmetry, which is proved to be localized to Lie point symmetries for suitable prolonged systems. Taking the Korteweg–de Vries equation as an example, the n-th binary Darboux–Ba¨cklund transformation is re-obtained by the Lie point symmetry approach accompanied by the localization of the n-fold residual symmetries.     

Diffusivity in water and fluorescence properties of?organic nanoparticles produced in?flames

Rotational and translational diffusion properties in water of nano organic carbon (NOC) particles collected from premixed laminar ethylene/air flames have been investigated using both time resolved fluorescence polarisation anisotropy (TRFPA) and fluorescence correlation spectroscopy (FCS). Insight into the NOC sizes, structures and rigidity has been gained through diffusion properties exploiting their fluorescence in different spectral ranges. The TRFPA measurements revealed the presence of two classes of particles. The first composed of particles with a mean size of 1.5?nm which absorb and fluoresce in the UV, and a second class composed of slightly larger particles, about 2.2?nm, which absorb and fluoresce in the visible and were also detected by FCS. From FCS measurements particle concentration and fluorescence quantum yield have been evaluated.     

Relayed magnetization transfer from nuclear Overhauser effect and chemical exchange observed by in vivo ³¹P MRS in rat brain

The ³¹P magnetization transfer effects among nuclear magnetic resonances (NMRs) of phosphocreatine (PCr), γ-adenosine-5'-triphosphate (γ-ATP) and inorganic phosphate (Pi) have been attributed to the chemical exchange reactions among PCr, ATP and Pi catalyzed by creatine kinase (CK) and ATPase enzymes and, therefore, are commonly applied in situ to measure chemical exchange fluxes involving two chemically coupled CK and ATPase reactions (i.e., PCr↔ATP↔Pi) by selectively saturating γ-ATP resonance. Besides the expected reductions in the Pi and PCr NMR signals upon saturating γ-ATP resonance, one particularly interesting phenomenon showing decreases in α-ATP and β-ATP signals was also observed. The underlying mechanism was investigated and identified via saturating NMR of β-ATP in the present study. The unique relayed magnetization transfer effects through spin diffusion were observed in the rat brain using in vivo ³¹P magnetic resonance spectroscopy.