Metallic glasses: Mössbauer contribution, physical properties and applications

We report first on the essential contributions of Mössbauer spectrometry to investigate iron-based metallic glasses. In addition to the analysis of the distributions of hyperfine data in terms of Fe coordination and neighbours, Mössbauer spectrometry is able to estimate the magnetic anisotropy from the magnetic texture, which can be correlated to the solidification process. After an overview of the different physical properties of the amorphous metallic alloys we also present their most advanced applications.     

A Frequency Selection Criterion in Spatially Developing Flows

The possible existence of global modes or self-excited linear resonances in spatially developing systems is explored within the framework of the WKBJ approximation. It is shown that the existence and properties of the dominant global mode may be deduced from the variations of the local absolute frequency ω₀ with distance X. The main results are summarized in two theorems: (1) A system with no region of absolute instability does not sustain temporally growing global modes with an O(1) growth rate. (2) If the singularity X, closest to the real X-axis of the complex function ω₀(X) is a saddle point, the most unstable global mode has, to leading order in the WKBJ approximation, a complex frequency ω₀(X_s). Thus, it will be temporally growing only if ω₀(X_s) is positive.     

Polynomial operators and local approximation of solutions of pseudo-differential equations on the sphere

We study the solutions of an equation of the form Lu=f, where L is a pseudo-differential operator defined for functions on the unit sphere embedded in a Euclidean space, f is a given function, and u is the desired solution. We give conditions under which the solution exists, and deduce local smoothness properties of u given corresponding local smoothness properties of f, measured by local Besov spaces. We study the global and local approximation properties of the spectral solutions, describe a method to obtain approximate solutions using values of f at points on the sphere and polynomial operators, and describe the global and local rates of approximation provided by our polynomial operators. The research of this author was supported, in part, by grant DMS-0204704 from the National Science Foundation and grant W911NF-04-1-0339 from the U.S. Army Research Office     

Growth of Ni-Al alloys on Ni(1 1 1): (I) Formation of epitaxial Ni3Al from ultra-thin Al deposits

In this paper we describe the alloying process of ultra-thin Al layers (below 8 × 10¹⁵ Al/cm²) deposited on Ni(1 1 1). For this purpose Auger electron spectroscopy, low energy electron diffraction, and ion beam analysis-channelling measurements have been performed in situ in an ultra-high vacuum chamber. Al deposits formed at low temperature (about 130 K) are strained defective crystalline layers retaining the substrate orientation. Alloying takes place, with very progressive Ni enrichment, in a very broad temperature range between 250 K and 570 K. This feature shows that diffusion of the alloy species is more and more difficult when the Ni concentration increases. At 570 K a crystallographically and chemically ordered Ni₃Al phase is formed, and its order continuously improves upon annealing, up to 750 K. We have shown by ion beam methods that this alloy is three-dimensional, extending up to 16 (1 1 1) planes for the thickest deposits. The Ni₃Al phase can also be obtained directly by Al deposition at 750 K, but its crystalline quality is lower and the layer is probably formed of grains elongated along 〈1 1 −2〉 directions. The Al content of the thin Ni₃Al layers formed mostly dissolves in the bulk above 800 K. However a small amount of Al remains segregated at the Ni crystal surface.     

Heat exchanger design based on chaotic advection

Experiments on hydrodynamic and heat transfer behavior of the flow in a twisted curved channel were conducted in a water tunnel and also in two heat exchanger coils tested in a heat exchanger test facility. The flow regime, designated “chaotic advection,” is a subclass of laminar flow with high mixing properties. Preliminary results show that heat transfer is enhanced due to the chaotic trajectories generated in the flow.     

Plasmonic structure and electromagnetic field enhancements in the metallic nanoparticle-film system

We investigate the plasmonic structure of a metallic nanoparticle near a metallic thin film. We show that in the thin film limit, a virtual plasmon resonance composed of delocalized thin film plasmons is induced. We investigate how the physical properties of the virtual state depend on polarization, film thickness and nanoparticle-film separation. We show that the electromagnetic field enhancements associated with the virtual plasmon resonance are large, suggesting applications of metallic nanoparticle/thin film systems as substrates for surface enhanced spectroscopies and surface enhanced scanning probe microscopies. PACS 78.67.Bf; 73.20.Mf; 78.30.-j     

Oxygen—evloving Activity in PhotosystemⅡ Core Complex of Photosynthetic Membrane in the Presence of Native Lipid

The techniques of oxygen electrode polarography and Fourier transform infrared (FT‐IR) spectroscopy were employed to explore the involvement of digalactosyl diacylglycerol (DGDG) in functional and structural roles in the photosystem II core complex (PSIICC). It was shown that DGDG exhibited the ability to stimulate the oxygen evolution in PSIICC, which was accompanied by the changes in the structures of PSIICC proteins. The results revealed that there existed hydrogen‐bonding interactions between DGDG molecules and PSIICC proteins. It is most likely that the sites of PSIICC interaction with DGDG are in the extrinsic protein of 33 kDa.     

Existence of Equilibria in Economies with Externalities and Nonconvexities

We consider a general equilibrium model of an economy in which the production possibilities, the consumption sets and the preferences of the consumers are represented by set-valued mappings which depend on the environment to take into account the possibility of external effect. In order to encompass all kinds of nonconvexities, we do not put any convexity assumption either on the graph of the set-valued mapping which describes the technological possibilities or on the production set for a given environment. The firms are instructed to set their prices according to general pricing rules which may depend on the production plans of other producers and on consumption plans.We report an existence result of general equilibria. As in the model without external effects, the key hypotheses are bounded loss and survival assumptions. Nevertheless, we also assume that the set-valued mappings which describe the fundamentals of the economy are lower semi-continuous and have a closed graph.Our framework is sufficiently large to generalize previous works on the existence of competitive equilibria with externalities when the firms have convex production sets and on the existence of equilibria with general pricing rule without externality.     

Alternative chromatographic processes for no-carrier added 177Lu radioisotope separation

HPLC technique combined with the simple conventional column solid phase extraction (SPE) chromatography using di-(2-ethylhexyl)orthophosphoric acid (HDEHP) impregnated OASIS-HLB sorbent based SPE resins (OASIS-HDEHP) was developed for the separation of no-carrier added (n.c.a) ¹⁷⁷Lu from the bulk quantity of ytterbium target. This combination strategy was based on combining the advantages of the better resolution of HPLC separation of n.c.a ¹⁷⁷Lu from the few milligram level Yb target with the high capacity of the OASISHDEHP column for the separation of ¹⁷⁷Lu from the bulk Yb target. The production batches of several hundred mCi activity of n.c.a ¹⁷⁷Lu radioisotope separated from 50 mg Yb target activated in a nuclear reactor of medium neutron flux (Φ=5·10¹³ n·cm^?2·s^?1) were successfully performed using this combined separation technique. With the target irradiation in a reactor of higher thermal neutron flux or with the parallel run of several separation units, several Ci-s of n.c.a ¹⁷⁷Lu can be profitably produced on a commercial production basis.