Pre-normative research on the use of mixed recycled aggregates in unbound road sections

This paper presents and discusses the results arising from a pre-normative study aimed at determining the physical, chemical and mineralogical characteristics of mixed recycled aggregates produced from the treatment of mixed rubble for use in unbound structural layers of road. The results of this research show that the combined presence of concrete and ceramic materials induces pozzolanic reactions, which contribute to an increase in the bearing capacity of the compacted mixed recycled aggregate. From an analysis of their chemical characteristics, it can be inferred that the total sulphur compound content, the gypsum content and soluble salt contents can be regulated with reference to the water soluble sulphates test, given the high correlation that exists between those parameters. Generally, mixed recycled aggregates with ceramic material contents below 35%, organic matter contents below 0.8% and water soluble sulphate contents below 0.4% constitute a granular material that is technically feasible for use in unbound structural road sections.     

Freeze–thaw resistance of blended cements containing calcined paper sludge

This work deals with the frost resistance of blended cements containing calcined paper sludge (source for metakaolin) as partial Portland cement replacements. Freeze–thaw tests were performed on blended cement mortars containing 0%, 10% and 20% waste paper sludge calcined at 650 °C for 2 h. Cement mortar specimens were exposed to freezing and thawing cycles until the relative dynamic modulus of elasticity fell below 60%. The performance of the cement mortars was assessed from measurements of weight, ultrasonic pulse velocity, compressive strength, mercury intrusion porosimetry and SEM. Failure of the control cement mortar occurred before 40 freeze/thaw cycles, while cement mortar containing 20% calcined paper sludge failed after 100 cycles. After 28 and 62 freezing and thawing cycles, cement blended with 10% and 20% calcined paper sludge exhibited a smaller reduction in compressive strength than the control cement.     

Numerical study of electromagnetic wave propagation through layered structures with chiral media

In this paper, the characteristics of layered structures (photonic or electromagnetic bandgaps), including chiral media, are studied by means of two different numerical methods, one in the time domain (finite differences in the time domain, FDTD) and the other in the frequency domain (coupled‐mode method, CMM). The results (reflection and transmission coefficients for a plane wave normally incident over a layered structure) obtained by means of both well different techniques are practically identical. Copyright © 2009 John Wiley & Sons, Ltd.     

Quantitative correlations among textural characteristics of C–S–H gel and mechanical properties: Case of ternary Portland cements containing activated paper sludge and fly ash

The hydraulic activity of ternary Portland cements containing different proportions of commercial thermally activated paper sludge (APS(I)) and fly ash (FA) from coal combustion was evaluated from the textural characterization of the C–S–H gels formed during hydration. The study was accomplished by means of the specific surface area (SSA) and pore-size distribution (PSD), which were measured by the sorption isotherms of nitrogen gas and the BET method. The microstructure was characterized by scanning electron microscopy (SEM). The incorporation of such admixtures (APS and FA) clearly revealed an increase in both porosity and SSA. This effect decreased with the progress of hydration, together with a refinement of the nano-porous structure of C–S–H. In addition, high correlations were found between nano-structural characteristics of the C–S–H gel and mechanical compressive strengths.     

Cations in Inorganic Solids

Abstract

Until recently, cations have been considered as small “isolated” entities, occupying the spaces in close-packed arrays of large anions. An inspection however of cation subarrays reveals that some kind of interaction must exist between them, as they reproduce both the topology and the distances of their parent metal structures.

Up to now, the existence of clusters has been identified with metal-rich compounds or with compounds in which the metal atoms have unsaturated valences. However, from the results reported here, it can be stated that cations recognize themselves in forming aggregates in such a way that the world of clusters also comes into the field of fully ionic compounds, wherein metal atoms have saturated valences.

This kind of interaction has already been observed in silver(I) and gold(I) compounds (and is known as the auriphilic effect or as d ¹⁰-d ¹⁰ interactions); but examples are reported here of similar interactions between cations of the alkaline-earth metals. Group 13 elements, lanthanides, Sc, Ti and Y, indicating that this effect is a general feature of inorganic solids. Although some explanations have been reported, the reasons for such interactions remain unclear. This is an open question challenging theoretical chemists.

These new ideas are placed in the context of similar ones developed recently, which give to cations a more relevant ôle in determining crystal structures. Thus, the old ideas of Lebedev regarding the protagonism of “large” cations in the formation of crystal structures is discussed together with the more recent ideas of O'Keeffe and Hyde which describe the crystal structures of oxides as oxygen-stuffed alloys.

In many oxides, the cations occupy octahedral or tetrahedral holes in close-packed arrays of anions. It is true that in many other structures, the cations reproduce the topology of the structures of elements or simple alloys, but it is also true that the structure of the parent metal is often preserved in its oxides.     

A Look at 25 Years of Data

Is 25 years enough time to build up a coherent body of knowledge that can help point to useful principles? As a testbed for helping us answer this question, software testing techniques are a good place to start. Few software practices are as important as testing, and testing techniques are amenable to measurement and reasoning about their effectiveness. Because they're aimed at removing faults, measuring the number and type of such removed faults seems like a natural part of applying these techniques. To make sense of this data, Universidad Politecnica de Madrid researchers have spent some time worrying about how to put 25 years' worth of work together usefully.     

Wireless and Optical-Integrated Access Network With Peer-To-Peer Connection Capability

We show a bidirectional optical access network with dynamic channel allocation capability of decimeter-wave band optical radio-over-fiber (RoF) and baseband signals. The network can be configured enabling peer-to-peer connectivity, and is based on a simple access point (AP) unit. The proposed RoF architecture is highly scalable, both in terms of channels and APs.     

Modelling multiple discontinuities in rectangular waveguidepartially filled with non-reciprocal ferrites

This work analyzes multiple 3D discontinuities between rectangular ferrite-loaded waveguides. Each uniform section of waveguide is analyzed by means of Schelkunoff's method with improved convergence. Combining this method with the mode matching method allows the analysis of multiple discontinuities to be simplified. The theoretical results obtained in this way agree quite well with measurements     

Combining the FDTD Method and Rational-Fitting Techniques for Modeling Active Devices Characterized by Measured S -Parameters

Most extensions of the original finite-difference time-domain (FDTD) method to incorporate lumped components are based on equivalent-circuit models. However, for active components, most manufacturers provide only the measured S-parameters of the device. This letter proposes the combination of the two-port lumped-network FDTD method and rational-fitting techniques to incorporate linear active devices characterized by measured 5-parameters into FDTD simulators. To this end, first the Y-parameters are obtained, which are then approximated by rational functions of the frequency over the band of interest. The polynomial coefficients resulting from the rational fitting are directly used to feed the FDTD simulation. The approach proposed here is applied to the calculation of the S-parameters of a microstrip amplifier. The results obtained are compared with those provided by the commercial simulator advanced design system and with measurements.