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Radioactividad natural en materiales de construcción
Some materials usually employed in building edification have been analyzed for their radioactive contents. The specific activities of all the gamma rays emisors present in fourteen differents samples have been determined. In all the cases, only low activities (under 2 Bq/g) have been found for these samples collected…
La plancha de plomo en cubiertas y fachadas
A description is given of the properties of lead sheet for roofing and cladding purposes. Basic rules as far as installations are concerned are given, specially with respect to dimensions of the pieces, characteristics of Joints and fixings, and watertightness conditions. Compatibility of lead with other building mate…
Modelos probabilísticos de los contenidos porcentuales de pérdida al fuego, residuo insoluble y SO3 de cementos P-350 fabricados en España
Limits fixed in Codes for the chemical characteristics of cements have been established with semi-empirical methods, given the complexity of influencing phenomena, without correspondence between these values and the physico-chemical or mechanical properties as durability or strength. Knowledge of statistical distribut…
Un método empírico para el proporcionamiento de mezclas de Morteros de Cemento Portland para Albañilería
In Colombian ways and means, since the application of no traditional constructive systems is growing up, and having recourse to the new Seismic Construction Code, it is necessary to work with cement mortars of defined and reproducible characteristics. An analysis of the variability affecting the mortars behaviour was…
Alternative use of the SMP‐buffer solution to determine lime requirement of soils
A close relationship was found between the pH of soil suspensions in the SMP buffer solution (pHsmp) and the potential acidity of soils (H + Al) extracted by a neutral calcium acetate solution (r = 0.98), for twenty six soil samples of the State of Sao Paulo, Brazil, This relationship was represented by the equation l…
Acoustoelastic waves in orthotropic media
The equations of acoustoelasticity are formulated in both natural and initial frames of reference and applied to investigate the propagation of ultrasonic waves in orthotropic elastic solids with initial stresses. The foundation of the equations is re-examined for the purpose of applying them to the measurement of res…
Electro-Optical Effects of a Small-Pitch Blue-Phase System
A system which shows a relatively large blue-phase range is investigated. Owing to the small value of the cholesteric pitch the blue-phase shows no Bragg-reflections in visible light. Nevertheless, electric-field induced birefringence shows quite large values. The response times are a few tens of microseconds below 10…
Epoxidized Natural Rubber
Abstract When natural rubber is epoxidized under carefully controlled conditions, it can be converted to a totally new polymer with some properties more akin to speciality rubbers and some properties that appear to be advantageous for tire treads. Three levels of epoxidation have been extensively evaluated. They were…
Electrochemical Characteristics of “Polyaniline” Cathodes and Anodes in Aqueous Electrolytes
The quinoid-benzenoid-diimine form, (=(C6H4)=N-(C6H4)-N=)x of “polyaniline” shows excellent cathode characteristics including recyclability when used in conjunction with a zinc anode in an aqueous electrolyte of (l. 0M ZnCl2 + 0. 5M NH4Cl) having a pH of ∼ 4. The reduced form of this material, (-(C6H4)-N(H)-(C6H4)-N(H…
Excited-state properties of a triply ortho-metalated iridium(III) complex
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTExcited-state properties of a triply ortho-metalated iridium(III) complexK. A. King, P. J. Spellane, and Richard J. WattsCite this: J. Am. Chem. Soc. 1985, 107, 5, 1431–1432Publication Date (Print):March 1, 1985Publication History Published online1 May 2002Published inissue…
“Polyaniline”: Interconversion of Metallic and Insulating Forms
“Polyaniline” has been synthesized in various forms both chemically and electrochemically in aqueous media. The qulnoid-benzenoid-diimine form, an insulator, is doped by dilute aqueous protonic acids to the metallic regime ([sgrave] = 5 ohm−1cm−1; compressed pellet) to give the corresponding iminium salt. This represe…
Estimation of effective interresidue contact energies from protein crystal structures: quasi-chemical approximation
ABSTRACT: Effective interresidue contact energies for proteins in solution are estimated from the numbers of residue-residue contacts observed in crystal structures of globular proteins by means of the quasi-chemical approximation with an approximate treatment of the effects of chain connectivity. Employing a lattice…
Trends in the plasmon dispersion of insulators and semiconductors
Starting from the dielectric function of a two-band model, a generalised Horie formula (1959) for the wavevector-dependent frequency omega p (q), of the valence plasmon is derived. The dispersion is determined by band-structure effects and the q-dependence of the oscillator strength. The latter is calculated using kp…
Collective modes in molten alkaline earth chlorides: III. Inelastic neutron scattering from molten MgCl 2 and CaCl 2
For part II, see ibid., vol.17, p.4725 (1984). Measurements of the inelastic neutron scattering spectrum of molten MgCl 2 show directly the existence of a weak soft mode in the momentum transfer range 1.5<Q<1.8 AA -1 . Such modes are not directly observed in molten CaCl 2 and have not been seen in other molten salts.…
X-ray diffraction study of the quasi-one-dimensional conductors (MSe4)2I (M=Ta and Nb)
Resistivity and X-ray diffraction measurements have been made for the quasi-one-dimensional conductors (MSe 4 ) 2 I (M=Ta and Nb). (TaSe 4 ) 2 I is known to undergo a phase transition at T c approximately=260K. A phase transition of (NbSe 4 ) 2 I was found to take place at T c approximately=210K. Non-linear conduction…
Low-frequency current noise with a 1/ f spectrum in solids
The problem of low-frequency current noise with a 1/ f spectrum in solids (flicker noise) is reviewed. The fundamental general properties of this noise are described: frequency-dependence of the spectral density, time-dependence of the correlation function, form of the distribution function of the fluctuations, depend…
Extended Affine Root Systems I (Coxeter transformations)
§ 1. Root System Belonging to a Quadratic Form § 2. Marked Extended Affine Root System (R
Potential models for ionic oxides
The authors present a systematic approach to the derivation of empirical potential parameters for binary oxides; they also consider their modification for use in mixed oxide systems. Shell-model potentials are used but, unlike the case of the alkali halides within which polarisability and short-range interaction param…
[2 + 2] Photocycloadditions in the Synthesis of Chiral Molecules
A strategy for the synthesis of chiral molecules that receives growing popularity among organic chemists employs the photochemically mediated [2 + 2] cycloaddition reaction. These reactions can be performed on a multigram scale and often proceed with high yield and with stereocontrol. These features, in combination wi…