Electronic States of Cobalt Ions in EuBaCo2O5 + δ Layered Cobaltites

JETP Letters - The oxygen K-edge X-ray absorption spectra in EuBaCo2O5.52 ± 0.02 and EuBaCo2O5.24 ± 0.02 cobaltites are measured at temperatures of 300 and 440 K, which are below and...     

Experimental investigation of three-dimensional flow instabilities in a rotating lid-driven cavity

The swirling flow between a rotating lid and a stationary cylinder is studied experimentally. The flow is governed by two parameters: the ratio of container height to disk radius, h, and the Reynolds number, Re, based on the disk angular velocity, cylinder radius and kinematic viscosity of the working liquid. For the first time, the onset of three-dimensional flow behavior is measured by combining the high spatial resolution of particle image velocimetry and the temporal accuracy of laser Doppler anemometry. A detailed mapping of the transition scenario from steady and axisymmetric flow to unsteady and three-dimensional flow is investigated for 1 ≥ h ≥ 3.5. The flow is characterized by the development of azimuthal modes of different wave numbers. A range of different modes is detected and critical Reynolds numbers and associated frequencies are identified. The results are compared to the numerical stability analysis of Gelfgat et al. (J Fluid Mech 438:363–377, 2001). In most cases, the measured onset of three-dimensionality is in good agreement with the numerical results and disagreements can be explained by bifurcations not accounted for by the numerical stability analysis.     

Synthesis and characterization of A4[Re6Q8L6]@SiO2 red-emitting silica nanoparticles based on Re6 metal atom clusters (A = Cs or K, Q = S or Se, and L = OH or CN)

Metal atom clusters constitute very promising candidates as luminophores for applications in biotechnology because they are nanosized entities offering robust luminescence in the near-infrared field (NIR). However, they cannot be used as prepared for biological applications because of potential toxic effects and quenching of the clusters' luminescence in aqueous media, and they therefore need to be dispersed in a biocompatible matrix. We describe herein the encapsulation of octahedral rhenium clusters, denoted as A(4)[Re(6)Q(8)L(6)] (A = Cs or K, Q = S or Se, and L = OH or CN), in silica nanoparticles by a water-in-oil microemulsion process, paying particular attention to the clusters' stability. The obtained A(4)[Re(6)Q(8)L(6)]@SiO(2) nanoparticles are 30 nm in size with good monodispersity and a perfectly spherical shape, as shown by scanning electron microscopy (SEM). The presence of cluster units inside the silica matrix was evidenced by scanning transmission electron microscopy in annular dark-field mode (ADF-STEM). From the point of view of their optical properties, the A(4)[Re(6)Q(8)L(6)]@SiO(2) nanoparticles show red and NIR emission under UV excitation, even when dispersed in water. The evolution of the structural and luminescence properties of clusters before and after encapsulation was followed by Raman and photoluminescence spectroscopy.     

The first example of stereoselective self-assembly of a cryptand containing four asymmetric intracyclic phosphane groups

The rac stereoisomer of a novel cryptand containing two bridgehead nitrogen and four asymmetric phosphorus atoms in the 16-membered core cycle was obtained stereoselectively via the reaction of bis(mesitylphosphino)propane, formaldehyde, and meta-xylylenediamine in the course of a covalent self-assembly process.     

Study of sodium interaction with calcium nitrate and carbonate in alkali metal chloride melts by IR and Raman spectroscopy

In the IR and Raman spectra of molten eutectic mixtures of alkali metal chlorides with additions of calcium nitrate and carbonate (without the introduction of sodium), vibrations of NO₃⁻ and CO₃²⁻ groups of symmetry D _3h were detected. After the introduction of sodium metal into the melts of oxygen-containing salts in amounts equal to the stoichiometric content of oxygen-containing groups, the spectra did not show the characteristic frequencies of the NO₂⁻ group or CO₃²⁻ vibrations, which is evidence of the complete oxidation of the alkali metal accompanied by reduction of the nitrate and carbonate groups to nitrogen dioxide and carbon dioxide, respectively. The results of spectroscopic studies are presented.     

Gamma-ray emission from thunderstorm discharges

Fine features of gamma-ray radiation registered during a thunderstorm at Tien-Shan Mountain Cosmic Ray Station are presented. Long duration (100-600 ms) gamma-ray bursts are found. They are for the first time identified with atmospheric discharges (lighting). Gamma-ray emission lasts all the time of the discharge and is extremely non-uniform consisting of numerous flashes. Its peak intensity in the flashes exceeds the gamma-ray background up to two orders of magnitude. Exclusively strong altitude dependence of gamma radiation is found. The observation of gamma radiation at the height 4-8 km could serve as a new important method of atmospheric discharge processes investigation.     

Simple method for solving transport equations describing the propagation of cosmic-ray nucleons in the atmosphere

A simple and efficient method is proposed for solving transport equations that describe the propagation of cosmic-ray protons and neutrons in the atmosphere at high energies. It is shown that, upon taking into account a non-power-law character of the primary spectrum, a growth of total cross sections for inelastic nucleon-nucleus interactions, and violation of scaling in such interactions, the effective absorption ranges of nucleons come to be dependent not only on energy but also on the depth in the atmosphere. The results of the calculations are compared with available experimental data.     

Modal liquid crystal lenses

Abstract

When considering the possibility of commercially viable applications for discotic liquid crystals it is worth noting that in the case of calamitic liquid crystals some 80 to 90 years elapsed between their discovery in 1888 and their first application in displays. Since discotic mesophases were only discovered in 1977 [ll, it is not surprising that the first applications are yet to be realized.     

Intermolecular interactions in metal-containing polymers based on 2,4-toluylene diisocyanate and open-chain analogs of crown ethers

The interaction of 2,4-toluylene diisocyanate with open-chain analogs of crown ethers containing potassium alcoholate groups is studied, and the mechanism of stabilization of the formed O-polyisocyanate end units via intermolecular interactions is proposed. The electron delocalization in intermolecular cyclic structures may be responsible for electron-transfer processes in the polymers under study.