SEM-EDS and XPS Studies of the High Temperature Oxidation Behaviour of Inconel 718

 The oxidation in air under isothermal conditions of Inconel 718 has been investigated at 900 °C. We have studied the firsts stages of the high temperature oxidation mechanism. The oxidised samples were examined using a number of surface analytical techniques including XPS and SEM-EDS. The results have shown that minor alloying elements strongly influence the oxidation behaviour of the alloy: Previous studies had shown that the rate of the external oxide scale growth and the intergranular oxide penetration during oxidation of Inconel 718 at 900 °C in air are lower than those of Inconel X or Incoloy 800. We suggest that the formation of a quasi continuous scale of the intermetallic phase Ni₃Nb at the oxide-alloy interface could have an important contribution to the good oxidation resistance of Inconel 718.     

Study of Thin Films of High Temperature Superconductors Based on YBaCuO by EPMA

 An analytical model of an effective atomic number, Z _eff, for simultaneous calculation of composition and thickness of films on substrates that allows for backscattering processes is presented. Comparison of dependencies of ϕ(ρz) parameters for film elements on electron beam energy, on atomic numbers of a film and a substrate and on film thickness was done. The errors inherent in EPMA have been determined by comparing experimental data obtained on YBa₂Cu₃O_7−x bulk crystals with model calculations. Possibility of EPMA as an effective technique for investigation of spatially inhomogeneous objects was demonstrated by studying the correlation between composition and local superconducting properties (values of critical temperature and critical current) of these films.     

Independent Directed Triangles in a Directed Graph

If D is a directed graph of order n≥3 with , then D contains independent directed triangles. Moreover, the condition on the minimum degree is sharp in general. Revised: April 19, 1999     

The Stability of Magnetic VorticesRID="*"ID="*"Research on this paper was supported by NSERC under grant N7901

We study the linearized stability of n-vortex (n∈ℤ) solutions of the magnetic Ginzburg–Landau (or Abelian Higgs) equations. We prove that the fundamental vortices (n = ± 1) are stable for all values of the coupling constant, λ, and we prove that the higher-degree vortices (|n|≥ 2) are stable for λ < 1, and unstable for λ > 1. This resolves a long-standing conjecture (see, eg, [JT]). Received: 16 November 1998 / Accepted: 3 January 2000 RID="*" ID="*"Research on this paper was supported by NSERC under grant N7901 RID="**" ID="**"Present address: Courant Institute, 251 Mercer St., New York, NY 10012, USA.&para;E-mail: gustaf&commat;cims.nyu.edu     

$$L^p$$-Fourier asymptotics,Hardy-type inequality and fractal measures

Suppose \(\mu \) is an \(\alpha \)-dimensional fractal measure for some \(0<\alpha <n\). Inspired by the results proved by Strichartz (J Funct Anal 89:154–187, 1990), we discuss the \(L^p\)-asymptotics of the Fourier transform of \(fd\mu \) by estimating bounds of

$$\begin{aligned} \underset{L\rightarrow \infty }{\liminf }\ \frac{1}{L^k} \int _{|\xi |\le L}\ |\widehat{fd\mu }(\xi )|^pd\xi , \end{aligned}$$

for \(f\in L^p(d\mu )\) and \(2<p<2n/\alpha \). In a different direction, we prove a Hardy type inequality, that is,

$$\begin{aligned} \int \frac{|f(x)|^p}{(\mu (E_x))^{2-p}}d\mu (x)\le C\ \underset{L\rightarrow \infty }{\liminf }\frac{1}{L^{n-\alpha }} \int _{B_L(0)}|\widehat{fd\mu }(\xi )|^pd\xi \end{aligned}$$

where \(1\le p\le 2\) and \(E_x=E\cap (-\infty ,x_1]\times (-\infty ,x_2]\ldots (-\infty ,x_n]\) for \(x=(x_1,\ldots x_n)\in {\mathbb R}^n\) generalizing the one dimensional results by Hudson and Leckband (J Funct Anal 108:133–160, 1992).

     

Access to well-defined isolated Fe(II) centers on silica and their use in oxidation

Well-defined Fe(II) isolated sites are obtained by reaction of diaryl-N,N'-diazadiene bis(neosilyl) iron (1) with an aerosil silica, SiO(2-(700)). This system can be used as a precursor for the catalytic oxidation of cyclohexene into cyclohexene oxide, cyclohexenol and cyclohexenone in the presence of H(2)O(2).     

On the fragmentation dynamics of NH3 → NH2 + H. II. Diatomics-in-molecules potential energy surfaces

The earlier developed diatomics-in-molecules (DIM) model structure for ammonia is used to design a model potential energy surface describing the hydrogen abstraction from H(SINGLEBOND)NH₂ in the A˜ state. The adequate model representation of the dissociation process serves to illustrate that even a DIM model of a large size with respect to both the dimensions of the DIM polyatomic basis set and diatomic mixing matrices is amenable to adjustment to target properties. The only proviso in the step of adjusting the DIM surfaces by effective manipulation of diatomic interaction matrices is that the DIM diatomic bases need to be orthogonal. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 62: 659–668, 1997     

Interpreting early land management through compound specific stable isotope analyses of archaeological soils

Compound specific stable isotope analyses of managed soils using isotope ratio mass spectrometry have been undertaken as a means of determining early land use practices. delta (15)N amino acid signals demonstrate differences between manured grassland, unmanured grassland and continuous cereal cultivation under long-term experimental land use control conditions, with delta (15)N in hydrophobic amino acids providing the most distinctive signals. Analysis of early modern/medieval and of Bronze age anthropogenic soils from Orkney demonstrates that such signals are retained in archaeological contexts. delta (13)C analyses of n- alkanoic acid components of the fossil, Bronze Age, anthropogenic soils suggest a major terrestrial input to these soils, with uniform composition of formation materials. Surficial soils demonstrate the assimilation of isotopically lighter carbon, providing a means of assessing the mobility of the n- alkanoic acids within soils and sediments. Copyright 1999 John Wiley & Sons, Ltd.