Mechanical and durability characteristics of concrete containing EAF slag as aggregate

The present study aims to investigate the opportunity to largely substitute natural aggregates of traditional concrete with Black/Oxidizing Electric Arc Furnace (EAF) slag. Compressive and tensile strength, elastic modulus and durability characteristics (accelerated aging, freezing and thawing, wetting and drying) of concrete containing EAF slag as aggregate according to Fuller’s ideal grading curve were experimentally investigated. This study aims to improve the scarce database of mechanical and durability tests on this type of concrete and give some insights to improve durability properties of concrete made with EAF slag, not only using modern agents and additives, but also working on the actual grading curve of aggregates used, closely connected to the overall durability for any kind of concrete. Concrete made with EAF slag as aggregate showed good strength characteristics since, in normal environmental conditions, strength properties of the conglomerate containing EAF slag are totally comparable (or even better) than those observed for traditional concrete. Conversely, the typical chemical and physical properties of EAF slag, such as the high content in calcium and magnesium oxides inclined to hydration, may be a limit for the durability of the resulting concrete: on one hand the durability can be strongly improved even in critical freezing/thawing environmental conditions by a small amount of air-entraining agent, on the other hand, this conglomerate still remains rather vulnerable to repeated cycles of wetting and drying.     

Thermodynamic and economic optimization of a MCFC-based hybrid system for the combined production of electricity and hydrogen

In this paper, a biogas fuelled power generation system is considered. The system is based on a molten carbonate fuel cell (MCFC) stack integrated with a micro gas turbine for electricity generation, coupled with a pressure swing absorption system (PSA) for hydrogen production.     

Optical fiber Bragg gratings. Part II. Modeling of finite-length gratings and grating arrays

A model of both uniform finite-length optical fiber Bragg gratings and grating arrays is presented. The model is based on the Floquet-Bloch formalism and allows rigorous investigation of all the physical aspects in either single- or multiple-periodic structures realized on the core of a monomodal fiber. Analytical expressions of reflectivity and transmittivity for both single gratings and grating arrays are derived. The influence of the grating length and the index modulation amplitude on the reflected and transmitted optical power for both sinusoidal and rectangular profiles is evaluated. Good agreement between our method and the well-known coupled-mode theory (CMT) approach has been observed for both single gratings and grating arrays only in the case of weak index perturbation. Significant discrepancies exist there in cases of strong index contrast because of the increasing approximation of the CMT approach. The effects of intragrating phase shift are also shown and discussed.     

Fire behaviour of polyester–clay nanocomposites

The aim of this study was on the one hand, to compare the fire behaviour of polyester/clay nanocomposites with that of the neat polymers added with the conventional flame retardant melamine isocyanurate (MIC) and on the other hand, to study the effect of the flame retardant added to the nanocomposites. Polyester/clay nanocomposites were prepared by using polybutylene terephthalate (PBT) and a co‐polyester elastomer as polymeric matrices and a commercial organoclay as filler. As verified by X‐ray diffractometry (XRD) and transmission electron microscopy (TEM) intercalated structures were obtained by mixing the molten polymer with the layered silicate in a corotating twin screw extruder. The fire behaviour of these materials was investigated by means of an oxygen consumption calorimetry (Cone Calorimeter). Peak heat release rate of 3‐mm thick samples measured at 50 kW/m² external heat flux was reduced by a factor of 2–3 by the addition of organically modified montmorillonite to the polymers. The further addition of MIC did not give a significant improvement in the behaviour of the materials. Copyright © 2005 John Wiley & Sons, Ltd.     

Heat of dilution and density data for poly(β-propiolactone) and poly(ε-caprolactone) in dioxane

Solution properties of two polyesters, poly(β-propiolactone) and poly(?-caprolactone) in dioxane have been studied. Data reported are: polymer densities, thermal expansion coefficients, thermal pressure coefficients, solution densities (volume changes on mixing: (ΔV_M) and heats of dilution (ΔH₁). It is found that the solution properties of the two polyesters in dioxane differ; e.g. poly(β-propiolactone): ΔV_M < 0; ΔH₁ > 0; poly(?-caprolactone): ΔV_u > 0; ΔH₁ < 0. Flory's theory is used to interpret these results. The theory contains one adjustable parameter (X₁₂) which is fixed by fitting the theory to the heat of dilution data. Sign and order of magnitude of the volume changes on mixing are then correctly predicted.     

Visible and infrared mapping spectrometer for exploration of comets,asteroids, and the saturnian system of rings and moons

The science objectives and system design for a Visible and Infrared Mapping Spectrometer (VIMS), an imaging spectrometer for planetary exploration, are described. The instrument development is the result of a collaboration between scientists and engineers from the United States, Italy, and France. NASA has selected VIMS as a facility instrument for the Comet Rendezvous Asteroid Flyby (CRAF) Mission, and as a candidate facility instrument for the Cassini Mission to explore Saturn and its rings and moons. (A facility instrument is provided by the project for the use of a science team which was selected on the basis of individual competitive science proposals.) VIMS covers the spectral range from 0.35 to 5.2 μm with a nominal spatial resolution of 0.5 milliradians (pixel size) and spectral resolutions (spectral width) of 7 nm at 0.35–1.0- μm wavelength and 16nm at 1.0–5.2-μm wavelength. The nominal pixel size is 0.5 × 0.5 mrad². The two separate missions are scheduled to be launched by NASA from the Eastern Test Range at Cape Canaveral, Florida, using the Titan IV Launch Vehicle. The planned launch date for the Cassini Mission is November 1995. The planned launch date for the CRAF Mission is February 1996.     

Modern perspectives in supercomputer-aided microwave circuit design

The computer-aided simulation and design of microwave integrated circuits often leads to large-size numerical jobs, especially for modern multiple-device MMIC subsystems such as distributed mixers and amplifiers. When this is the case, the use of large computer systems such as vector processors may become very attractive, because of the dramatic reduction of wall-clock time and of the related improvement of cost-to-performance ratio. This paper discusses the application of supercomputers to the solution of a number of such advanced microwave circuit CAD problems. An overview of the performance of general-purpose vectorized algorithms such as system solvers and Fast Fourier Transforms is first presented, in order to give a feeling of the potential of this class of machines in microwave CAD applications. Then a few typical microwave engineering problems are specifically addressed, including the statistical design (yield optimization) of linear circuits, the analysis of nonlinear circuits under multitone excitation, and the optimization of ultrabroadband nonlinear subsystems. In each case, a possible vectorization strategy is studied in depth, and the structure and performance of a specific highly vectorized algorithm are described in detail.     

Augmented scene modeling and visualization by optical and acoustic sensor integration

In this paper, underwater scene modeling from multisensor data is addressed. Acoustic and optical devices aboard an underwater vehicle are used to sense the environment in order to produce an output that is readily understandable even by an inexperienced operator. The main idea is to integrate multiple-sensor data by geometrically registering such data to a model. The geometrical structure of this model is a priori known but not ad hoc designed for this purpose. As a result, the vehicle pose is derived and model objects can be superimposed upon actual images, thus generating an augmented-reality representation. Results on a real underwater scene are reported, showing the effectiveness of the proposed approach.     

Materialization of fragmented views in multidimensional databases

The most effective technique to enhance performances of multidimensional databases consists in materializing redundant aggregates called views. In the classical approach to materialization, each view includes all and only the measures of the cube it aggregates. In this paper we investigate the benefits of materializing views in vertical fragments, aimed at minimizing the workload response time. We formalize the fragmentation problem as a 0–1 integer linear programming problem, which is then solved by means of a standard integer programming solver to determine the optimal fragmentation for a given workload. Finally, we demonstrate the usefulness of fragmentation by presenting a large set of experimental results based on the TPC-H benchmark.