High temperature syntheses of novel nitrido- and oxonitrido-silicates and sialons using rf furnaces

The high-temperature reaction of pure metals with silicon diimide Si(NH)2 in a specially developed radiofrequency furnace has been successfully applied to the synthesis of novel highly condensed nitridosilicates. With SrCO3 as an additional starting material this procedure has now been extended to the synthesis of oxonitridosilicates and oxonitridoaluminosilicates (sialons). Two novel sialons SrSiAl2 O3 N2 [space group P21 21 21 (no. 19), a=491.89(6), b=789.73(7), c=1134.94(18) pm, Z=4] and SrErSiAl3 O3 N4 [space group P63 mc (no. 186), a=606.53(3), c=985.90(8) pm, Z=2] have been obtained as coarsely crystalline materials. According to single crystal X-ray diffraction both compounds adopt structure types which are unprecedented for sialons. They derive from the nitridosilicates LnSi3 N5 (Ln=La, Ce, Pr, Nd) and MYbSi4 N7 (M=Sr, Ba, Eu), respectively, by partial substitution of Si by Al and N by O. For SrSiAl2 O3 N2 and SrErSiAl3 O3 N4 an unambiguous crystallographic differentiation between the tetrahedral centres (Al and Si) as well as the bridging atoms of the framework structures (N and O) seems reasonable

High-temperature synthesis, single-crystal X-ray and neutron powder diffraction, and materials properties of Sr3Ln10Si18Al12O18N36 (Ln = Ce, Pr, Nd)

The novel oxonitridoaluminosilicates (sialons) Sr3Ln10Si18Al12O18N36 (Ln = Ce, Pr, Nd) were obtained by the reaction of the respective lanthanide metals with Si(NH)2, SrCO3, and AlN using a radiofrequency furnace at temperatures between 1550–1650°C. The crystal structures of the isotypic sialons were determined by single-crystal X-ray investigations (Sr3Ce10Si18Al12O18N36: I3m, Z = 2, a = 1338.2(2) pm, R1 = 0.0333; Sr3Pr10Si18Al12O18N36: a = 1334.54(6) pm, R1 = 0.0296; Sr3Nd10Si18Al12O18N36: a = 1332.85(6) pm, R1 = 0.0271) and in the case of Sr3Pr10Si18Al12O18N36 with powder neutron diffraction as well. The three-dimensional sialon network is built up by SiON3, SiN4, and AlON3 tetrahedra. Besides the bridging O and N atoms of the sialon network there are isolated O2− which are tetrahedrally coordinated by Sr and Ln. The crystallographic differentiation of Si/Al and O/N seemed to be possible by a careful evaluation of the single-crystal X-ray diffraction data combined with lattice energy calculations using the MAPLE concept (Madelung Part of Lattice Energy). In the case of Sr3Pr10Si18Al12O18N36 the differentiation of O and N and the proposed ordering was completely confirmed by powder neutron diffraction

Multiphysics simulations of collisionless plasmas

Collisionless plasmas, mostly present in astrophysical and space environments, often require a kinetic treatment as given by the Vlasov equation. Unfortunately, the six-dimensional Vlasov equation can only be solved on very small parts of the considered spatial domain. However, in some cases, e.g. magnetic reconnection, it is sufficient to solve the Vlasov equation in a localized domain and solve the remaining domain by appropriate fluid models. In this paper, we describe a hierarchical treatment of collisionless plasmas in the following way. On the finest level of description, the Vlasov equation is solved both for ions and electrons. The next courser description treats electrons with a 10-moment fluid model incorporating a simplified treatment of Landau damping. At the boundary between the electron kinetic and fluid region, the central question is how the fluid moments influence the electron distribution function. On the next coarser level of description the ions are treated by an 10-moment fluid model as well. It may turn out that in some spatial regions far away from the reconnection zone the temperature tensor in the 10-moment description is nearly isotopic. In this case it is even possible to switch to a 5-moment description. This change can be done separately for ions and electrons. To test this multiphysics approach, we apply this full physics-adaptive simulations to the Geospace Environmental Modeling (GEM) challenge of magnetic reconnection

The bright and dark side of staging: Investment performance and the varying motivations of private equity firms

Previous papers that examined investment decisions by private equity funds are divided on whether staging has a positive or negative effect on returns. We believe these opposing views can be reconciled by studying when staging is used during the life of the investment relationship: We find that staging has a positive effect on investment returns in the beginning of the investment relationship, consistent with the notion that staging helps mitigate information asymmetry. However, staging appears to be negatively associated with returns when used prior to the exit decision. Our unique dataset allows us to measure these intertemporal effects precisely.Private equity Staging Investment decisions Liquidation

Duration of effect of the mouthwash CB12 for the treatment of intra-oral halitosis: a double-blind, randomised, controlled trial.

Halitosis occurs in approximately 30% of the adult population and has a negative social and psychological impact on affected individuals. Mouthwashes may be used to prevent unpleasant odour, with long-duration of effect being a desirable attribute. The aim of this study was to assess the long-term efficacy of CB12 (a mixture of 0.3% zinc acetate and 0.025% chlorhexidine) for the treatment of intra-oral halitosis. Thirty-four subjects with confirmed intra-oral halitosis were randomized into a double-blind, controlled, cross-over study to one of 2 groups; (i) CB12-water-water or (ii) water-CB12-CB12. Each group comprised 3 treatments, each given evening and morning (12 h apart) on consecutive study days, with a 5 d washout between treatments. Intra-oral halitosis was assessed objectively by measuring concentrations of hydrogen sulphide, methyl mercaptan, dimethyl sulphide and total volatile sulphur compound (VSC) concentrations and subjectively using organoleptic score (OLS). These were measured at baseline, 12 h after the evening rinse (i.e. 12 h overnight assessment) and 12 h after the daytime rinse (i.e. 12 h day time assessment). CB12 significantly reduced mean hydrogen sulphide, methyl mercaptan, dimethyl sulphide and VSC concentrations, with a duration of effect lasting 12 h, whether assessed overnight (all p  ⩽  0.0003 versus water) or during the day (all p  ⩽  0.0007 versus water). CB12's effect on OLS was also evident for 12 h overnight (p  =  0.0043). CB12 was well-tolerated. In conclusion, CB12 showed a clear and durable effect on intra-oral halitosis which lasted at least 12 h, both during the day and overnight, with consistent effect on both objective and subjective variables