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Melt Spun of Continuous Polycarbosilane Fibers
Congresos, Seminarios y Cursos. Noticias, ferias y exposiciones
Behaviour of alkaline cement mortars reinforced with acrylic and polypropylene fibres
In the present work, the behaviour of alkaline cement mortars reinforced with fibres of different nature (acrylic and polypropylene fibres) is studied. Also the chemical stability of those fibres in strong alkaline medium has been investigated. Three different matrixes have been used: glass blast furnace slag activate…
Fabrication of Graded Nickel–Alumina Composites with a Thermal‐Behavior‐Matching Process
Composites of nickel and Al 2 O 3 with compositionally graded microstructures were fabricated from powders through an empirically determined thermal‐behavior‐matching process that was designed to minimize processing‐induced stresses. Compositions ranged from pure Al 2 O 3 to pure nickel. Specimen geometries included r…
Charge density on thin straight wire, revisited
The question of the equilibrium linear charge density on a charged straight conducting “wire” of finite length as its cross-sectional dimension becomes vanishingly small relative to the length is revisited in our didactic presentation. We first consider the wire as the limit of a prolate spheroidal conductor with semi…
Study of the medieval lead cames used in the stained glass windows of the Monastery of Pedralbes (Barcelona)
This work includes an study of the glass windows of the "Monasterio de Pedralbes", in Barcelona, concerning lead as their main element.
Low energy phonon spectrum and its parameterization in pure KTaO3 under 80 K
High resolution data on low energy phonon branches (acoustic and soft optic) along the three principal symmetry axes in pure KTaO3 were obtained by cold neutron inelastic scattering between 10 and 80 K. Additional off-principal axis measurements were performed to characterize the dispersion anisotropy (away from the <…
Equilibrium Polymerization Behavior of 1,4-Dioxan-2-one in Bulk
To clarify the equilibrium polymerization behavior of 1,4-dioxan-2-one, PDO, bulk polymerization was investigated with Sn(II) ethylhexanoate or triethylaluminum over a range of 60−180 °C. The thermodynamic parameters Δ H ls, Δ S ls, and ceiling temperature for the polymerization were −14.1 kJ mol -1, −26.1 J mol -1 K…
Vibrational Study of the FeCl3-Doped Dimer of Polyaniline; A Good Model Compound of Emeraldine Salt
In this paper, optical and vibrational properties of the FeCl 3 -doped dimer of polyaniline, a model compound of emeraldine salt are presented. This oligomer is synthesized according to the method reported by Zaghal et al.. A complete assignment of the fundamental in-plane Raman and infrared modes (1700−600 cm -1 ) of…
Perovskite-like crystals of the Ruddlesden-Popper series
The layer perovskite-like structures of the so-called Ruddlesden-Popper phases have been analyzed in terms of crystal chemistry. The geometrical boundaries of the existence ranges of these compounds with multilayer stacks are determined and new phases of this type are predicted. The possible variants of related struct…
The broad Brillouin doublets and central peak of KTaO_3
The incipient ferroelectric KTaO3 presents low-T Brillouin spectra anomalies,e.g. a broad central peak (CP), and some additional Brillouin doublets (BD), whose origin is interpreted in terms of phonon-density fluctuation processes. A parameterisation from new extensive high-resolution neutron-scattering measurements i…
A comparison of Monte-Carlo simulations using RESTRAX and McSTAS with experiment on IN14
Monte-Carlo simulations of a focusing supermirror guide after the monochromator on the IN14 cold neutron three-axis spectrometer, I.L.L. were carried out using the instrument simulation programs RESTRAX and McSTAS. The simulations were compared to experiment to check their accuracy. Comparisons of the flux ratios over…
Percolative phase separation induced by nonuniformly distributed excess oxygen in low-dopedLa1−xCaxMnO3+δ(x<~0.2)
Zero-field ${}^{139}\mathrm{La}$ and ${}^{55}\mathrm{Mn}$ nuclear magnetic resonances were studied in ${\mathrm{La}}_{0.8}{\mathrm{Ca}}_{0.2}{\mathrm{MnO}}_{3+\ensuremath{\delta}}$ with different oxygen stoichiometries \ensuremath{\delta}. The signal intensity, peak frequency, and line broadening of the ${}^{139}\math…
Memory in the aging of a polymer glass
Low-frequency dielectric measurements on plexiglass (PMMA) show that cooling and heating the sample at constant rate give a hysteretic dependence on temperature of the dielectric constant . A temporary stop of cooling produces a downward relaxation of . Two main features are observed: i) when cooling is resumed goes b…
Nonlinear conduction in charge-orderedPr0.63Ca0.37MnO3:Effect of magnetic fields
Nonlinear conduction in a single crystal of charge-ordered ${\mathrm{Pr}}_{0.63}{\mathrm{Ca}}_{0.37}{\mathrm{MnO}}_{3}$ has been investigated in an applied magnetic field. In zero field, the nonlinear conduction, which starts at $T<{T}_{\mathrm{CO}},$ can give rise to a region of negative differential resistance (N…
Controlled phase separation in La0.5Ca0.5MnO3
A systematic study of phase separation effects in polycrystalline ${\mathrm{La}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_{3}$ obtained under different thermal treatments is reported. Samples with average grain size ranging from 200 to 1300 nm were studied. Magnetic and electrical measurements show quantitative differen…
Structural and magnetic study of Tb 1 − x Ca x MnO 3 perovskites
The crystal and magnetic structures of ${\mathrm{Tb}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}$ series have been studied by x-ray and neutron-diffraction techniques. Macroscopic magnetic properties have been characterized using ac magnetic susceptibility measurements. The relationships between structural…
Elastic moduli of model random three-dimensional closed-cell cellular solids
Most cellular solids are random materials, while practically all theoretical results are for periodic models. To be able to generate theoretical results for random models, the finite element method (FEM) was used to study the elastic properties of solids with a closed-cell cellular structure. We have computed the dens…