文献浏览

Editorial

Noticias

Contribución al análisis y estudio de las posibilidades de variación de la cantidad de yeso, CaSO4.2 H2O, como agresivo, del método acelerado de ensayo ASTM C 452. Parte I A

This research work, which will include four publications, was done as a result of the discussions, doubts and controversies which were originated some time ago about the ASTM C 452 method and specially on its 7.0% SO3 content. To clarify this two portland cements P-1 (14.11% C3A) and P-31 (7.62% C3), all it industriéi…

Modification of an Amposta origin bitumen by using tlie Friedel and Crafts reaction with toluyiene-2,4-diisocyanate

In this works, we have modified a bitumen from Amposta by using the Friedel and Crafts reaction with toluylene-2,4-diisocyanate in presence of aluminium trichloride, presenting as well as the characteristics of the original bitumen as the ones of the modification products. We have made technological test, aging of thi…

Characteristics of spanish fly ashes

The purpose of this study is the characterization of fly ashes produced by Spanish thermoelectric power plants, according to sampling taken in 1981 and 1982. The study takes in the following characteristics: physical characteristics (size distribution of particles, ...); chemical ones (chemical analysis...); and miner…

Glosario de términos relacionados con el deterioro de las piedras de construcción

Not available.

Determination of sulphides in cements by using potentiometry with a selective electrode of sulphides

A procedure for the determination of sulphides attackable by HCI (1 :3) in cements by means of a potentiometric determination with a selective electrodo of sulphides, is proposed.

Gd-DOTA: characterization of a new paramagnetic complex.

The relaxivity, biodistribution, and toxicity of the gadolinium-tetraazacyclododecanetetraacetic acid (Gd-DOTA) complex were evaluated. This cyclic complex has much greater in vitro stability (10(28)) than similar noncyclic complexes such as gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA) (10(23)) or gadoliniu…

A Microcrack Model of Dilatancy in Brittle Materials

For a solid containing preexisting flaws, overall nonlinear constitutive relations are developed on the basis of a model which endows a preexisting flaw with frictional and cohesive resistance, and which includes nucleation and growth of tension cracks at the preexisting flaw, as it deforms under the action of an over…

Application of the Rietveld Refinement Procedure in Assaying Powdered Mixtures

Abstract Results are given of an assessment of a Rietveld-type X-ray powder diffraction pattern fitting structure refinement technique for assaying powdered mixtures as an alternative to conventional discrete peak empirical methods of the type described by Klug and Alexander (1974) and Chung (1974). The values obtaine…

Effect of Cation Substitution on the Oxygen Semipermeability of Perovskite-type Oxides

Abstract Oxygen semipermeability of LnCoO3-based perovskite-type oxides changed drastically by the partial substitution of A site and B site cations, Ba and Cu being the most effective substituents, respectively. Host rare earth cations (Ln) also affected the oxygen semipermeability, which increased with a decrease in…

A Parabolic Density Profile for Grafted Polymers

We study the statistics of a grafted polymer brush, consisting of a set of monodisperse chains in solution, each attached irreversibly by one end to a flat surface. We use a self-consistent field method, valid in the limit of weak excluded volume and at moderately high surface coverage. Exploiting the fact that the ch…

Estimation of forms of Fe and Al - a review, and analysis of contrasting soils by dissolution and Mossbauer methods

Three methods have been used to extract iron (Fe) and aluminium (Al) from a wide range of soils. The three extractants were pyrophosphate reagent (p), acid-oxalate reagent (o), and dithionite-citrate reagent (d), and each reagent is thought to extract different forms of Fe and Al. The forms of Fe in the soils were stu…

Phase diagram and dynamics of Yukawa systems

The phase diagram and dynamical properties of systems of particles interacting through a repulsive screened Coulomb (Yukawa) potential have been calculated using molecular and lattice dynamics techniques. The phase diagram contains both a melting transition and a transition from fcc to bcc crystalline phases. These ph…

Continuum Damage Mechanics: Part I—General Concepts

Continuum Damage Mechanics (C.D.M.) has developed continuously since the early works of Kachanov and Rabotnov. It constitutes a practical tool to take into account the various damaging processes in materials and structures at a macroscopic continuum level. The main basic features of C.D.M. are considered in the first…

Electron structure of the 4f shells and magnetism of rare-earth metals

The relationship between magnetic properties of rare-earth metals and the electron structure of the f shell is considered. Simple concepts are used to show how many-electron quantum numbers of the spin, orbital and total angular momenta of the f shell are related to the Curie temperature, magnetic moment, magnetic ani…

Deoxycytidylate hydroxymethylase: purification, properties, and the role of a thiol group in catalysis

Deoxycytidylate (dCMP) hydroxymethylase from Escherichia coli infected with a T-4 bacteriophage amber mutant has been purified to homogeneity. It is a dimer with a subunit molecular weight of 28,000. Chemical modification of the homogeneous enzyme with N-ethylmaleimide (NEM) and 5,5'-dithiobis(2-nitrobenzoic acid) (DT…

Differences in the solution structures of oxidized and reduced cytochrome c measured by small-angle x-ray scattering

While X-ray crystallographic data on cytochrome c show the reduced and oxidized forms to have very similar structures, there is a considerable body of data, mostly from solution studies, that indicates the reduced form is more stable and that the interior of the protein is less accessible to solvent in this state. The…

Unusual thermal expansion behaviour of scandium vanadate at elevated temperatures

The thermal expansivity of zircon-type scandium vanadate (ScVO 4 ) was determined by the X-ray powder diffraction method in the temperature range 300-634 K. The thermal expansion is anisotropic at room temperature as it has a larger coefficient of expansion along the a direction than along the perpendicular direction…

Thermopower, conductivity and the Hall effect in V2O5gels

Conductivity, thermoelectric power and Hall effect measurements are reported for V 2 O 5 gels with relative concentrations of V 4+ of 0.005 and 0.11. Both the Seebeck and the Hall coefficient are negative. This is an exception to the rule that the sign anomaly effect should be observed for amorphous semiconductors, i.…