Determination of detection limits for elements in water by femtosecond laser-induced breakdown spectroscopy

We have evaluated the feasibility of using femtosecond laser-induced breakdown spectroscopy with time-resolved detection of the spectra for determination of trace concentrations of chemical elements in water. The laser plasma was generated on the surface of aqueous solutions by a single pulse from a titanium:sapphire laser (pulse duration 40 fs, pulse repetition frequency up to 1 kHz). We obtained the 3σ limits of detection (LODs) for Al, Ba, Ca, Cu, Fe, K, Mg, Na, Zn in water as 0.19, 0.08, 0.01, 0.78, 3.4, 0.006, 1, 0.0009, 2.5 mg/L respectively.     

Mott criterion application to analysis of electrical conductivity in Na-β-aluminates doped by yttrium

The mechanism of electrical conductivity in yttrium-doped Na-β-aluminate has been investigated in terms of the Mott criterion in the range from room temperature to 1073 K. The activation energies for electrical conduction and thermoelectromotive force are determined from high-temperature measurements. The results obtained and the data derived from optical measurements are in satisfactory agreement. It is shown that electrical conductivity is determined by nonlocalized states in the temperature range from 973 to 1073 K and by localized states in the range from room temperature to 973 K.     

Study of the paramagnetic centers in heterofullerides MnM′3-nC60 (M = K, Rb, Cs; M′ = Be, Mg, Ca, Ba; n = 1, 2)

New heterofullerides Cs₂MC₆₀, CsM₂C₆₀, Rb₂MC₆₀, K₂MC₆₀, and KM₂C₆₀ (M = Be, Mg, Ca, Ba) have been synthesized; the temperature dependences of the magnetic susceptibilities of these compounds in the temperature range from 4.2 to 297 K have been measured. Among these heterofullerides, K₂MgC₆₀, KMg₂C₆₀, K₂CaC₆₀, K₂BeC₆₀, and Rb₂BeC₆₀ pass to the superconducting state at temperatures T _c = 13–24.3 K. The paramagnetic electronic states of the compounds have been studied by EPR at temperatures of 105–300 K, which shows the existence of two types of paramagnetic centers, related to oxygen defects and conduction electrons.     

Phase transition in CdHfO<Subscript>3</Subscript>

The phase transition from an orthorhombic phase (space group Pnma) to a rhombohedral phase (space group R3m) of the CdHfO₃ hafnate is investigated using methods of structural analysis. It is shown that crystal lattices of both phases contain polar structural units (octahedra, cubooctahedra). On this basis, it is assumed that the orthorhombic and rhombohedral phases of the CdHfO₃ compound are the antiferroelectric and ferroelectric phases, respectively.     

Structure formation of fullerene-containing propylene oxide oligomers in deuterium water

Structure formation of propylene oxide oligomers with terminal hydrophobic aliphatic fragment and of oligo(propylene oxides) additionally containing covalently bonded fullerene C₆₀ in deuterium water was studied by small-angle neutron scattering. Propylene oxide chains containing a long hydrophobic fragment undergo organization into spherical micelles, whereas the fullerene(C₆₀)-containing derivatives form rodlike structures (elongated “chains” of cross-linked micelles).     

One‐Pot Method for Synthesizing Spherical‐Like Metal Sulfide–Reduced Graphene Oxide Composite Powders with Superior Electrochemical Properties for Lithium‐Ion Batteries

A facile, one‐pot method for synthesizing spherical‐like metal sulfide–reduced graphene oxide (RGO) composite powders by spray pyrolysis is reported. The direct sulfidation of ZnO nanocrystals decorated on spherical‐like RGO powders resulted in ZnS–RGO composite powders. ZnS nanocrystals with a size below 20 nm were uniformly dispersed on spherical‐like RGO balls. The discharge capacities of the ZnS–RGO, ZnO–RGO, bare ZnS, and bare ZnO powders at a current density of 1000 mA g^?1 after 300 cycles were 628, 476, 230, and 168 mA h g^?1, respectively, and the corresponding capacity retentions measured after the first cycles were 93, 70, 40, and 21 %, respectively. The discharge capacity of the ZnS–RGO composite powders at a high current density of 4000 mA g^?1 after 700 cycles was 437 mA h g^?1. The structural stability of the highly conductive ZnS–RGO composite powders with ultrafine crystals during cycling resulted in excellent electrochemical properties.     

Noise-resistant system of concealed information transfer on a chaotic delayed feedback oscillator with switchable delay time

We propose a system of concealed information transfer based on a delayed feedback oscillator with switchable chaotic regimes. The proposed system is analyzed numerically and experimentally. The dependences of the bit error rate during transmission of a binary information signal on the signal-to-noise ratio, attenuation of the signal in the communication channel, and the duration of the time interval during which a bit is transferred are constructed. The high stability of the system to noise and amplitude distortions of a signal in the communication channel is demonstrated.