Evaluation of liquid junction potentials and determination of pH values of strong acids at moderate ionic strengths

A new experimental approach is proposed for the evaluation of liquid junction potentials and single ion activities. Neither of these quantities can be experimentally measured without assumption. Furthermore, they are concentration dependent but without clearly defined functional relationships. Thus, a given assumption may be satisfactory to obtain these quantities at a given concentration, but will fail at another concentration. It is the intent of this paper to establish a functional relationship between the ratio of activity coefficients and the ionic strength, through which the liquid junction potentials may be computed, as well as the pH values at moderate ionic strengths (<1.0 m). Experimental results are presented and uncertainties are discussed.     

Synthesis of polyperfluoroalkylenetriazines

Four new s-triazine polymers were prepared by the mercury-induced coupling of bromodifluoromethyl-substituted ditriazinyl-perfluoroalkane derivatives. Each polymer was composed of CF₃-substituted s-triazin rings alternately joined with ? CF₂CF₂? segments and \documentclass{article}\pagestyle{empty}\begin{document}$\hbox{---}\hskip-5pt({\rm CF}_2 )_8 \hbox{---}$\end{document}, a mixture of ? (CF₃CFO(CF₂)₅OCF(CF₃)? and ? (CF₃)CFOCF₂CF(CF₃)OCF₂)₄? , ? CF₂OCF₂? , or ? CF₂SCF₂? , segments. All polymers were elastomeric and displayed high temperature stability on thermogravimetric analysis. The polymers containing either ? CF₂OCF₂? or ? CF₂SCF₂? segments showed high temperature limits slightly lower than the other two systems.     

Role of specular reflection of electrons in the radio frequency surface magneto impedance of metals

The effect of a parallel magnetic field on the 10-mHz surface resistance of gallium single crystals is reported. We suggest that the observed structure can be interpreted in terms of an angular dependence of the probability of specular reflection of the electron at the crystal surface. This model allows a quantitative determination from the data of the temperature-dependent electron mean free path for electron wave vectors with a narrow range that is determined by the magnetic field and crystal orientation.     

A 2D honeycomb-shaped network based on a starburst cluster: [Ag4(micro3-Cl)(PPh2(CH2)2PPh2)1.5{S2P(OR)2}3](R = Et, Pri)

The first 2D metal-organic framework utilizing PPh2(CH2)2PPh2 (dppe) units as the linkers and tetranuclear silver clusters, [Ag4(micro3)-Cl){S2P(OR)2}3], as the network nodes in the formation of the honeycomb-shaped layer structure is reported.     

Planarity relations for the sextic centrifugal distortion constants of triangular triatomic molecules

Four linearly independent linear combinations of the ten sextic centrifugal distortion coefficients of triangular triatomic molecules are presented. These combinations are formed in such a way that the resulting expressions depend only on the equilibrium geometry and the harmonic force field parameters of the molecule, quantities which are ordinarily known to considerably better precision than the sextic constants. The relations obtained thus constitute a set of planarity constraints on the ten sextic coefficients which arise in connection with the Nielsen-Amat expansion of the Darling-Dennison Hamiltonian. The planarity expressions can be utilized to effect a reduction of the sextic portion of the Hamiltonian.     

Dependence of the closed-shell repulsive interaction on the overlap of the electron densities

The relationship between the closed-shell repulsive interactions and overlap of the electron densities is investigated. It is found that the repulsive interactions vary in almost direct proportion to the absolute size of the density overlaps.     

Optical and structural properties of Sr-Nb-phosphate glasses

This research studied optical and structural properties of SrO-Nb₂O₅-P₂O₅ glasses containing 0 ~ 25 mol% Nb₂O₅ and 35 ~ 60 mol% SrO using spectra of UV-Vis, FTIR and XPS. Our aim was to work new moldable glasses which are colorless with high refractive index and transmittance, and their correlation with glass structure. Nb₂O₅ plays the role as an intermediate of glass formation, and transforms the role to network-former or glass-modifier depending on composition. Refractive index increases monotonically with Nb₂O₅ content at the expense of transmittance, and specific coloring which occurs in ternary compositions with the ratio P₂O₅/SrO > 1. This effect arises from much increased [Nb³⁺ and Nb⁴⁺] fraction, as quantitatively deconvoluted in Nb3d XPS spectra, in the ligand [NbO₆]_octahedral which is supported by FTIR and O1s XPS spectra. As the ratio P₂O₅/SrO ≤ 1, Nb₂O₅ is more of a network former and [NbO₆]_octahedral structure turns into [NbO₄]_tetrahedron with partial Nb-O…(Sr) bonding turns into (Nb-O-Nb)_tetrahedron, coloring disappears.     

Influence of Scholarships on STEM Teachers: Cluster Analysis and Characteristics

Science, technology, engineering, and mathematics (STEM) teachers' perceptions about the influence of scholarship on their decision to teach and to teach in a high‐needs school were examined using cluster analysis. Three hundred and four STEM scholars, who were currently teaching, and who received funding from 45 institutions located throughout the United States responded to this national survey that was part of a larger cross‐sectional program evaluation. Three disparate clusters were identified: less committed to becoming a teacher and teaching in a high‐needs school, highly committed to becoming a teacher but not to teaching in a high‐needs school, and highly committed to becoming a teacher and teaching in a high‐needs school. Furthermore, the results indicated that the recipient's race and the time when the scholar learned about the scholarship were related to cluster membership. These results can be used to target STEM majors who may be influenced by scholarships to enter teaching and to teach in high‐needs schools.     

Modeling complexity in musical rhythm

This article constructs a tree structure for the music rhythm using the L‐system. It models the structure as an automata and derives its complexity. It also solves the complexity for the L‐system. This complexity can resolve the similarity between trees. This complexity serves as a measure of psychological complexity for rhythms. It resolves the music complexity of various compositions including the Mozart effect K488. © 2009 Wiley Periodicals, Inc. Complexity, 2010