Synthesis of calcium hydroxyapatite from calcium carbonate and different orthophosphate sources: A comparative study

The synthesis of calcium hydroxyapatite (Ca-HA) starting from calcium carbonate and different orthophosphate sources, including orthophosphoric acid, potassium, sodium and ammonium dihydrogen orthophosphates, was investigated under ambient conditions. The reaction started with calcium carbonate dissolution in an acid medium, followed by rapid precipitation of calcium cations with orthophosphate species to form calcium phosphate based particles which were in the size range of 0.4–1 μm. These particles then agglomerated into much larger ones, up to 350 μm in diameter (aggregates). These aggregates possessed an unstable porous structure which was responsible for the porosity of the final products. The highest specific surface area and pore volume were obtained with potassium dihydrogen orthophosphate. On the other hand, orthophosphoric acid led to the highest dissolution of calcium carbonate and the complete precipitation of orthophosphate species. Under ambient conditions, calcium phosphate based solid products of low crystallinity were formed. Different intermediates were identified and a reaction pathway proposed.     

Numerical simulation of hydrous transfer within fibrouscement slates

In situ distortion of fibrous-cement slates is brought about by exposure to different temperature and hygrometric gradients across the material. The aim of this research was to understand in detail the effect of each compositional change on the physical properties, and to use this knowledge for the manufacture of slates which would exhibit improved mechanical properties. A previous paper described the experimental measurements conducted to evaluate the impact of changing the composition of the slates on the physical properties controlling hydrous transfer. In the present paper, the physical parameters obtained from the experimental work are used in a numerical model. The numerical model, NSAT, employs a finite-element method to solve the non-linear diffusion equation. The numerical model was validated and subsequent simulations are described. A theoretical model has been obtained which shows good agreement between the results from practical tests at the experimental station and the predictions of the numerical model. The results also confirm the previous hypotheses of the industrial partner. The theoretical model obtained may be used for the prediction and specification of industrial materials having improved mechanical properties, and in particular, exhibiting less distortion.

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Résumé Les déformations locales dans les ardoises de fibrociment peuvent être engendrées par l'existence de gradients de température et d'hygrométrie au sein du matériau. Le but de ce travail est de comprendre en détail l'effet des modifications de composition des ardoises sur leurs propriétés physiques et d'utiliser ces connaissances dans la fabrication d'ardoises présentant de meilleures propriétés mécaniques. Un article précédent a décrit l'effet des traitements subis par les ardoises sur les paramètres physiques influant sur les transferts d'humidité. Dans cet article, les paramètres physiques sont utilisés dans un modèle numérique, NSAT. Le modèle numérique emploie la méthode des éléments finis pour résoudre l'équation non-linéaire de diffusion. D'abord le modèle numérique a été validé. Ensuite d'autres simulations plus complexes sont présentées. Les calculs numériques ont clairement mis en évidence les différents types de comportement de séchage qui correspondent aux diverses observations expérimentales du partenaire industriel. Le modèle numérique peut être utilisé pour la prévision et l'élaboration des matériaux industriels avec un meilleur comportement mécanique. En particulier, une dimunition de la déformation est attendue.

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Editorial note A. Raoof and T. H. Doan are working at the Laboratoire des Matériaux et des Structures du Génie Civil of LCPC, France, which is a RILEM Titular Member. A. Sabouraud is working at Pont-à-Mousson SA, France, which is a RILEM Titular Member.     

Design considerations for 60 GHz CMOS radios

With the availability of 7 GHz of unlicensed spectrum around 60 GHz, there is a growing interest in using this resource for new consumer applications requiring very high-data-rate wireless transmission. Historically, the cost of the 60 GHz electronics, implemented in the compound semiconductor technology, has been prohibitively expensive. A fully integrated CMOS solution has the potential to drastically reduce costs enough to hit consumer price points. System, circuit, and device-level barriers to a low-cost 60 GHz CMOS implementation are described, potential solutions are explored, and remaining challenges are discussed.     

Understanding MIDI. The key to creating and conducting the music toyour own MTV video

The Musical Instrument Digital Interface (MIDI) specifies the standard hardware and data format that allow devices to communicate with one another. Developed by researchers in Japan, MIDI Specification 1.0 made its debut in 1983. Soon afterwards, Roland introduced the MPU-401 (MIDI Processor Unit model 401), which gave PC users the power of MIDI. By providing an affordable way to interconnect musical devices, MIDI opened the door to the music world for computer users     

Gadolinium‐Doped Persistent Nanophosphors as Versatile Tool for Multimodal In Vivo Imaging

Recent breakthroughs in the rational development of multifunctional nanocarriers have highlightened the advantage of combining the complementary forces of several imaging modalities into one single nanotool fully dedicated to the biomedical field and diagnosis applications. A novel multimodal optical‐magnetic resonance imaging nanoprobe is introduced. Designed on the basis of a spinel zinc gallate structure doped with trivalent chromium and gadolinium, this nanocrystal bears the ability to serve as both a highly sensitive persistent luminescence nanoprobe for optical imaging, and a negative contrast agent for highly resolved magnetic resonance imaging (MRI). Additional proof is given that surface coverage can be modified in order to obtain stealth nanoparticles highly suitable for real‐time in vivo application in mice, showing delayed reticulo‐endothelial uptake and longer circulation time after systemic injection.     

Mass transfer variation within a packed bed and its relation to liquid distribution

The limiting current method is applied to characterize the local mass transfer in the axial, radial and angular directions throughout a packed bed of Pall rings. This is expressed in terms of the particle-to-fluid mass transfer coefficient of ferricyanide ions obtained from the limiting currents measured during its reduction to ferrocyanide at different locations in the bed. Particular focus is placed on the variability of the mass transfer coefficient with position in terms of the quantity MT_VAR, equivalent to the normalized deviation of the function Sh/Sc^0.33. The results confirm those reported by other researchers using more traditional liquid collection and tracer methods. Mass transfer coefficients throughout the bed closely follow normal distributions for the range of Re values investigated. When a multipoint distributor is used, MT_VAR is already low at the lowest flow rate (Re=95) considered and remains unchanged with any further increase in flow rate. In the case of a single-point distributor, on the other hand, MT_VAR decreases with increasing flow rate, but always remains significantly higher than that observed with the multipoint distributor. Moreover, the MT_VAR value depends on whether irrigated or full flow conditions prevail and on the cross-sectional area of the sampling electrodes, suggesting that local mass transfer variations are caused by local liquid velocity variations once the Pall rings are sufficiently wetted.     

SHAPES: A novel approach for learning search heuristics inunder-constrained optimization problems

Although much research in machine learning has been carried out on acquiring knowledge for problem-solving in many problem domains, little effort has been focused on learning search-control knowledge for solving optimization problems. This paper reports on the development of SHAPES, a system that learns heuristic search guidance for solving optimization problems in intractable, under-constrained domains based on the Explanation-Based Learning (EBL) framework. The system embodies two new and novel approaches to machine learning. First, it makes use of explanations of varying levels of approximation as a mean for verifying heuristic-based decisions, allowing heuristic estimates to be revised and corrected during problem-solving. The provision of such a revision mechanism is particularly important when working in intractable and under-constrained domains, where heuristics tend to be highly over-generalized, and hence at times will give rise to incorrect results. Second, it employs a new linear and quadratic programming-based weight-assignment algorithm formulated to direct search toward optimal solutions under best-first search. The algorithm offers a direct method for assigning rule strengths and, in so doing, avoids the need to address the credit-assignment problem faced by other iterative weight-adjustment methods     

Determination of fruit origin by using 26S rDNA fingerprinting of yeast communities by PCR–DGGE: preliminary application to Physalis fruits from Egypt

The determination of geographical origin is a demand of the traceability system of import–export food products. One hypothesis for tracing the source of a product is by global analysis of the microbial communities of the food and statistical linkage of this analysis to the geographical origin of the food. For this purpose, a molecular technique employing 26S rDNA profiles generated by PCR–DGGE was used to detect the variation in yeast community structures of three species of Physalis fruit (Physalis ixocarpa Brat, Physalis pubescens L, Physalis pruinosa L) from four Egyptian regions (Qalyoubia, Minufiya, Beheira and Alexandria Governments). When the 26S rDNA profiles were analysed by multivariate analysis, distinct microbial communities were detected. The band profiles of Physalis yeasts from different Governments were specific for each location and could be used as a bar code to discriminate the origin of the fruits. This method is a new traceability tool which provides fruit products with a unique biological bar code and makes it possible to trace back the fruits to their original location. Copyright © 2009 John Wiley & Sons, Ltd.     

High-pressure nitrogen gas alloying of Fe-Cr-Ni alloys

The melting of Fe-Cr-Ni alloys under 200 MPa nitrogen pressure has shown that nitrogen significantly improves the mechanical properties. Tensile strengths of these high-nitrogen alloys were found to be proportional to interstitial nitrogen concentration. The tensile strengths of nitrogen-alloyed steels could be significantly increased over comparable carbon-alloyed steels. The increase in tensile strength was found to be proportional to the square root of the interstitial nitrogen concentration indicating that the strengthening may be controlled by thermal effects.