Multibubble sonolysis and sonoluminescence in molten elementary sulfur and sulfur—styrene mixture

The effect of saturation with argon, as well as styrene and iodine additives on the temperature dependence of multibubble sonoluminescence intensity in molten sulfur at 120–230 °C was studied. The shape of the temperature dependence with a maximum at 170–200 °C is determined by the viscosity variations related to the changes in the molecular structure of molten elemental sulfur. At high temperatures, cyclooctasulfane (S₈) molecules break to radical products, which then undergo polymerization that can be slowed down by the additives. Sulfurization of styrene during sonolysis of a sulfur—styrene mixture resulting in products of the thiophene series was detected. Unlike thermal sulfurization that affords 2,5-diphenylthiophene as a major product, sonochemical sulfurization results mainly in 2,4-diphenylthiophene. The mechanism of 2,4-diphenylthiophene formation initiated by the reaction of styrene molecules with S⁺ ions produced upon fragmentation of S₈ within cavitation bubbles is proposed. The glow of electronically excited S⁺* ions is responsible for the band with a maximum at 560 nm in the sonoluminescence spectrum of molten sulfur, which is suppressed by the styrene additive.     

A spectroscopic and computational study of Al(III) complexes in sodium cryolite melts: Ionic composition in a wide range of cryolite ratios

The structure of sodium cryolite melts was studied using Raman spectroscopy and quantum chemical calculations performed at the density functional theory level. The existence of bridged forms in the melts was argued first from the analysis of experimental Raman spectra. In the quantum chemical modelling emphasis was put on the construction of potential energy surfaces describing the formation/dissociation of certain complex species. Effects of the ionic environment were found to play a crucial role in the energetics of model processes. The structure of the simplest possible polymeric forms involving two Al centres linked through F atoms (“dimers”) was thoroughly investigated. The calculated equilibrium constants and model Raman spectra yield additional evidence in favour of the dimers. This agrees with a self-consistent analysis of a series of Raman spectra for a wide range of the melt composition.     

[Zn3(PO4)2(H2O)0.8(NH3)1.2]

The structure of the title compound, ammineaquadi‐μ₅‐phosphato‐trizinc(II), [Zn₃(PO₄)₂(H₂O)_0.8(NH₃)_1.2], consists of two parts: (i) PO₄ and ZnO₄ vertex‐sharing tetrahedra arranged in layers parallel to (100) and (ii) ZnO₂(N/O)₂ tetrahedra located between the layers. Elemental analysis establishes the ammine‐to‐water ratio as 3:2. ZnO₂(N/O)₂ tetrahedra are located at special position 4e (site symmetry 2) in C2/c. The two O atoms of ZnO₂(N/O)₂ are bonded to neighbouring P atoms, forming two Zn—O—P linkages and connecting ZnO₂(N/O)₂ tetrahedra with two adjacent bc plane layers. A noteworthy feature of the structure is the presence of NH₃ and H₂O at the same crystallographic position and, consequently, qualitative changes in the pattern of hydrogen bonding and weaker N/O—H...O electrostatic interactions, as compared to two closely related structures.     

Electron density distribution in BaPb<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3</Subscript> superconducting oxides studied by double nuclear magnetic resonance methods

The effect of charge disorder on the formation of an inhomogeneous state of the electron system in the conduction band in BaPb_{1 − x} Sb _x O₃ superconducting oxides is investigated experimentally by NMR methods. The NMR spectra of ¹⁷O are measured systematically, and the contributions from ¹⁷O atoms with different cation nearest surroundings are identified. It is found that microscopic regions with an elevated spin density of charge carriers are formed within two coordination spheres near antimony ions. Nuclei of the superconducting phase of the oxide (regions with an elevated antimony concentration) microscopically distributed over the sample are detected in compounds with x = 0.25 and 0.33. Experiments in which a double resonance signal of the spin echo of ¹⁷O-²⁰⁷Pb and ¹⁷O-¹²¹Sb are measured in the metal phase of BaPb_{1 − x} Sb _x O₃ oxides are carried out for the first time. The constants of indirect heteronuclear spin-spin ¹⁷O-²⁰⁷Pb interaction are determined as functions of the local Knight shift ₂₀₇ Ks. The estimates of the constants of the indirect interaction between the nuclei of the nearest neighbors (O-Pb and Pb-Pb atoms) and analysis of evolution of the NMR spectra of ¹⁷O upon a change in the antimony concentration are convincing evidence in favor of the development of a microscopically inhomogeneous state of the electron system in the metal phase of BaPb_{1 − x} Sb _x O₃ oxides.     

NMR study of the electric field gradient in the paramagnetic phase of M<Subscript>3</Subscript>V<Subscript>2</Subscript>O<Subscript>8</Subscript> (M = Co,Ni) compounds

The NMR spectra and the decay of a spin echo signal from ⁵¹V nuclei in Kagome-staircase Co₃V₂O₈ (CVO) and Ni₃V₂O₈ (NVO) single crystals are measured in the temperature range 30–300 K and a magnetic field H ₀ = 20 kOe. The orientation dependences of the ⁵¹V NMR line shape are used to determine the electric field gradient (EFG) parameters, namely, quadrupole frequency ν _Q and asymmetry parameter η. These parameters for NVO and CVO are ν _Q = 180(10) kHz, η = 0.5(1) and ν _Q = 130(10) kHz, η = 0.6(1), respectively. A comparison of the results of calculating EFG tensors with a point charge model and the NMR data indicates that the crystallographically equivalent vanadium atoms in the Ni₃V₂O₈ and Co₃V₂O₈ compounds differ in the EFG axis orientation. M₃V₂O₈ crystals are found to have vanadium positions (V1, V2) with different orientations of the z axis, which specifies the direction of the principal value of EFG (V _zz ): these orientations lie in the bc plane and make an angle of either +51(5)° (V1) or −51(5)° (V2) with axis c. In the temperature range 30–300 K, the EFG tensor components and the local symmetry of the charge surrounding of the vanadium positions in NVO and CVO oxides are found to change insignificantly.     

Apatite type lanthanum silicate and composite anode half cells

Apatite type rare earth silicates are being extensively studied as electrolyte material for intermediate temperature solid oxide fuel cells (SOFC). In this paper we presents results on synthesis of Al and/or Fe-doped ATLS, the design of compatible anode materials, thermal expansion properties and co-sintering of half-cells from expansion matched materials using the advanced pulsed electric current sintering (PECS) technique. The issues related to the co-sintering of half cells have been addressed successfully by the combined use of nano powders and PECS.     

Synthesis and characterization of doped apatite-type lanthanum silicates for SOFC applications

A series of iron- and/or aluminium-doped apatite-type lanthanum silicates (ATLS) La_9.83Si_{6 ‐ x ‐ y}Al_xFe_yO_26 ± δ (x = 0, 0.25, 0.75, and 1.5, y = 0, 0.25, 0.75, and 1.5) were synthesized using the mechanochemical activation (MA), solid state reaction (SSR), Pechini (Pe) and sol-gel (SG) methods. The total conductivity of the prepared materials was measured under air in the temperature range 600-850 °C using 4-probe AC impedance spectroscopy. Its dependence on composition, synthesis method, sintering conditions and powder particle size was investigated. It was found that for electrolytes of the same composition, those prepared via mechanochemical activation exhibited the highest total specific conductivity, which was improved with increasing Al- and decreasing Fe-content. The highest conductivity value at 700 °C, equal to 2.04 × 10^− 2 S cm^− 1, was observed for the La_9.83Si₅Al_0.75Fe_0.25O_26 ± δ electrolyte. La_9.83Si_4.5Fe_1.5O_26 ± δ electrolyte samples synthesized using the Pechini method exhibited higher conductivity when sintered conventionally than when spark-plasma sintering (SPS) was used.     

Development of an Instrument to Assess Attitudes Toward Science,Technology, Engineering,and Mathematics (STEM)

There is a need for more students to be interested in science, technology, engineering, and mathematics (STEM) careers to advance U.S. competitiveness and economic growth. A consensus exists that improving STEM education is necessary for motivating more students to pursue STEM careers. In this study, a survey to measure student (grades 4–6) attitudes toward STEM and STEM careers was developed and administered to 662 students from two STEM‐focused and three comprehensive (non‐STEM‐focused) schools. Cronbach's alphas for the whole survey and subscales indicated a high internal consistency. Statistically significant difference in means between students attending the STEM‐focused and comprehensive schools on the two subscales of the survey and the overall survey were found. However, the explained variance for these results was approximately 1%. The survey is a useful tool to assess efficacy of STEM education programs on student attitudes toward STEM and STEM careers.     

A High‐Quality Professional Development for Teachers of Grades 3–6 for Implementing Engineering into Classrooms

With the increasing emphasis on integrating engineering into K‐12 classrooms to help meet the needs of our complex and multidisciplinary society, there is an urgent need to investigate teachers' engineering‐focused professional development experiences as they relate to teacher learning, implementation, and student achievement. This study addresses this need by examining the effects of a professional development program focused on engineering integration, and how teachers chose to implement engineering in their classrooms as a result of the professional development. 198 teachers in grades 3–6 from 43 schools in 17 districts participated in a yearlong professional development program designed to help integrate the new state science standards, with a focus on engineering, into their teaching. Posters including lesson plans and student artifacts were used to assess teachers' engineering practices and the implementation in their classrooms. Results indicated that the majority of the teachers who participated in the professional development were able to effectively implement engineering design lessons in their classrooms suggesting that the teachers' success in implementing engineering lessons in their classroom was closely related to the structure of the professional development program.     

The reduction of Ag(I) by α‐silylamines R2NCH2SiX3

The introduction of the organosilicon substituent into the α‐position of an amino group results in cardinal change of the amine reactivity irrespective of the coordination state of silicon. Amines R₂NCH₂SiX₃ [R = Me, Et, PhCH₂, CH₂SiX₃; SiX₃ = SiMe₃, Si(OEt)₃, Si(OCH₂CH₂)₃N] easily react with AgNO₃, to give the corresponding ammonium salts (R₂NH⁺ CH₂SiX₃)·NO₃^?. At the same time, Ag(I) is reduced to Ag(0). The interaction of N‐methyl‐N,N‐bis(silatranylmethyl)amine with AgNO₃ has been investigated by EPR spectroscopy. It was proven that the reaction involved a single electron transfer stage with the formation of cation radical of this amine. A mechanism of the reaction is proposed. Copyright © 2006 John Wiley & Sons, Ltd.