Local structure analysis of smoky and colorless topaz using single crystal Al NMR

The angular dependence of the ²⁷Al NMR spectrum was measured for single crystals of smoky and colorless topaz, Al₂SiO₄(F,OH)₂. Smoky topaz was obtained by irradiating high energy neutrons to colorless topaz. The quadrupole coupling constant e²Qq/h and the asymmetry parameter η were obtained from the analysis of the angular dependences of quadrupole splitting of the ²⁷Al NMR spectrum. The local structures around the aluminum atoms in smoky and colorless topaz were discussed from the magnitude and the direction of the electric field gradient. The directions of principal axes of the EFG tensor of ²⁷Al were close to the directions of Al-O and Al-F bonds. The difference in the bond lengths between Al(1)-F(1) and Al(1)-F(2) was found to affect the x and y components of the EFG tensor.     

Action de O- et N-nucléophiles sur les sels de phényl-3 benzopyrylium-1

3-Phenyl-1-benzopyrylium percholorates 1a, 1i react exculusively at C-2 with ethanol and isopropyl alcohol, affording mixed acetals 2a, 3a, 3i . Aqueous ammonia gives symmetrical secondary amines 4a, 4b or bis(3-phenyl-2H-1-benzopyran-2-yl)amines, while with aqueous aliphatic amines (40%) bis-acetals 5a, 5b or 2,2′-oxy-bis(3-phenyl-2H-1-benzopyrans) are characterized. In some other acidic conditions, 5a and 5b are also obtained.     

α Emission in proton induced reactions

The continuous spectra of theα particles emitted in reactions induced by protons on⁹³Nb,¹⁰⁷Ag,¹¹⁸Sn,¹⁶⁵Ho,¹⁶⁹Tm have been measured at several energies ranging from 20 to 45 MeV. The spectra have been analysed in the framework of the Exciton model assuming that the emittedα's pre-existed in the target nucleus and evaluating their energy distribution on the basis of nucleon-α scattering dynamics in nuclear matter. Nuclear Reactions⁹³Nb,¹⁰⁷Ag,¹¹⁸Sn,¹⁶⁵Ho,¹⁶⁹Tm(p,α...).E=20–45MeV; Measured \(\frac{{d\sigma (E_\alpha )}}{{dE_\alpha }}\) ; calculated \(\frac{{d\sigma (E_\alpha )}}{{dE_\alpha }}\) .     

Calculating Fractional-Parentage Coefficients for Six Body System in Translational Invariant Basis

In this paper we present an independent scheme for constructing fractional parentage coefficients using symmetry group apparatus in translationally invariantmodel space, suitable for the six-particle system composed of three-particle bi-clusters, where the presented subsystems have their own intrinsic clusterization. Simple expressions for corresponding antisymmetrization procedure are presented as well as computational results.

     

Mechanical properties of epoxy resins and glass/epoxy composites at cryogenic temperatures

The mechanical properties of four modified-epoxy resin systems were investigated. Tensile properties (including strength, modulus, and elongation), notch toughness, impact strength, the coefficient of linear thermal contraction, and thermal-shock resistance were determined for cast-resin specimens at 75, ?320, and ?423°F. Inter-laminar shear strengths (Naval Ordnance Laboratory horizontal shear and short-span shear) were obtained for glass-filament-wound-composite specimens at the three temperatures.

The two systems with the best cryogenic properties were a hybridepoxy/polyurethane (resin 4A) and a highly modified bisphenol-A epoxy (resin 2). In choosing the optimum system, the same tests (except for notch toughness, impact strength, and short-span shear) were performed on filament-wound-composite specimens at the three temperatures. In these tests the performance of resin 4A was better than, or at least comparable to, that of resin 2.     

Band-dependent quasiparticle dynamics in the hole-doped Ba-122 iron pnictides

We report on band-dependent quasiparticle dynamics in the hole-doped Ba-122 pnictides measured by ultrafast pump-probe spectroscopy. In the superconducting state of the optimal and over hole-doped samples, we observe two distinct relaxation processes: a fast component whose decay rate increases linearly with excitation density and a slow component whose relaxation is independent of excitation strength. We argue that these two components reflect the recombination of quasiparticles in the two hole bands through intraband and interband processes. We also find that the thermal recombination rate of quasiparticles increases quadratically with temperature in all samples. The temperature and excitation density dependence of the decays indicates fully gapped hole bands and nodal or very anisotropic electron bands.     

A Mountain Pass-type Theorem for Vector-valued Functions

The mountain pass theorem for scalar functionals is a fundamental result of the minimax methods in variational analysis. In this work we extend this theorem to the class of \(\mathcal{C}^{1}\) functions \(f:\mathbb{R}^{n}\rightarrow\mathbb{R}^{m}\), where the image space is ordered by the nonnegative orthant \(\mathbb{R}_{+}^{m}\). Under suitable geometrical assumptions, we prove the existence of a critical point of f and we localize this point as a solution of a minimax problem. We remark that the considered minimax problem consists of an inner vector maximization problem and of an outer set-valued minimization problem. To deal with the outer set-valued problem we use an ordering relation among subsets of \(\mathbb{R}^{m}\) introduced by Kuroiwa. In order to prove our result, we develop an Ekeland-type principle for set-valued maps and we extensively use the notion of vector pseudogradient.     

The effect of oxidation on the surface-near lattice relaxation in FeNi nanoparticles

The near-surface oxidation-induced lattice relaxation and compositional changes of FeNi alloy nano-particles are investigated. Using a newly developed transfer system, the particle structure was characterised by means of aberration-corrected HR-TEM prior to exposing the particles to ambient air. This allows for a comparison of oxidised and un-oxidised particles, respectively. Independent of the oxidation, the surface-near and/or interface-near metal lattice was found to be expanded by up to 3%. EELS profiles clearly reveal an enrichment of Fe at the particle surfaces. MD simulations in combination with HR-TEM contrast simulations were conducted to investigate the effect of the Fe enrichment on the structural relaxation. The results show that a surface-near over-stoichiometric enrichment of Fe indeed causes a dilation that counteracts a compression of the lattice at the particle surface as obtained for homogeneously alloyed particles. Besides, the large lattice mismatch between the metallic cores and the NiFe₂O₄ shells causes the formation of step dislocations in the close vicinities of the interface. In essence, the surface-near lattice relaxation in oxide free particles is found to be due to a segregation of Fe to the surface, whereas in the case of shell–core particles, no systematic influence of the oxide on the lattice relaxation was found.