New insights into the morphological stability of eutectic and peritectic coupled growth

Both eutectic and peritectic alloys exhibit three-phase equilibria and are used in diverse practical applications ranging from casting and welding to growing superconducting crystals. In-situ composites formed by the diffusively coupled growth of two solid phases are ubiquitous in eutectic solidification. This growth, however, is generally only stable over a finite range of eutectic spacing. The addition of a dilute ternary impurity can destabilize the interface and produce coarse two-phase cellular structures. Whether coupled growth is theoretically possible in peritectic alloys has been a question for over 40 years. This article reviews the current status of phase-field modeling of polyphase solidification in eutectic and peritectic alloys. Also discussed are new findings from both simulations and experiments that shed new light on the similarities and differences between the morphological stability of eutectic and peritectic coupled growth. For more information, contact Alain Karma, Northeastern University, Physics Department and Center for Interdisciplinary Research on Complex Systems, Boston, MA 02115; e-mail a.karma@neu.edu.     

Use of artificial intelligence in analytical systems for the clinical laboratory

The incorporation of information-processing technology into analytical systems in the form of standard computing software has recently been advanced by the introduction of artificial intelligence (AI), both as expert systems and as neural networks.This paper considers the role of software in system operation, control and automation, and attempts to define intelligence. AI is characterized by its ability to deal with incomplete and imprecise information and to accumulate knowledge. Expert systems, building on standard computing techniques, depend heavily on the domain experts and knowledge engineers that have programmed them to represent the real world. Neural networks are intended to emulate the pattern-recognition and parallel processing capabilities of the human brain and are taught rather than programmed. The future may lie in a combination of the recognition ability of the neural network and the rationalization capability of the expert system.In the second part of the paper, examples are given of applications of AI in stand-alone systems for knowledge engineering and medical diagnosis and in embedded systems for failure detection, image analysis, user interfacing, natural language processing, robotics and machine learning, as related to clinical laboratories.It is concluded that AI constitutes a collective form of intellectual propery, and that there is a need for better documentation, evaluation and regulation of the systems already being used in clinical laboratories.     

Non-contact handling in microassembly: Acoustical levitation

Microassembly is currently of the utmost importance in industry. Nevertheless, the classical assembly processes are no longer usable for very small components, typically ranging from 10  m to 10 mm, since usually neglected surface forces disturb the handling task by inducing adhesion between the component and the gripper. A promising alternative to tackle surface forces consists in levitating the handled component. The various advantages of this contactless handling method are reviewed here and justify the choice of this approach. Consequently, the numerous physical principles suitable for contactless handling are briefly described together with their limitations. The evaluation shows that acoustic levitation is best fitted in the case of microassembly. A classification of literature applications is presented hereafter with special focus on acoustic levitation. Finally, the most common models of acoustical levitation are inspected in a general way. The described models come within the scope of non-linear acoustics.     

Les glissements de terrain du quartier Bélouizdad, Constantine, Algérie

In Constantine, Belouizdad district landslides are extensive (Fig. 1). They occur along a hillside largely urbanized, and cover over 30 hectares. Dozens of houses were destroyed. The formations raised by these movements correspond to the alternating of thick Miocene clays and conglomerates. These contain several aquifers. The study of these landslides is conducted on the basis of recognition by deep boreholes equipped with piezometers and inclinometers. The inclinometric measurements have revealed failure surfaces sometimes deep (20 to 30 m) and north displacement, towards the Rhumel wadi. The use of a stability calculation software “Talren” shows on the one hand, the high sensitivity of unstable Miocene formations in the presence of water and on the other hand, a significant revival of the safety factor by reducing the pore pressure. The recommended solutions are therefore a lowering of underground water levels. Two techniques are recommended : deep drainage trench or galleries combined with radiating drainage holes.     

Reactive and non-reactive transport modelling in partially water saturated argillaceous porous media around the ventilation experiment, Mont Terri

At Mont Terri Underground Research Laboratory (URL) Switzerland, a specific experiment has been performed in a tunnel, in order to investigate the hydro-mechano-chemical (HMC) perturbations induced in the argillaceous formation by forced ventilation. This experiment has been selected in the international project DECOVALEX to be used for process model development and validation. The numerical simulation of the geochemical response to the ventilation experiment (VE) is the object of the present paper, focusing on the transport of chloride as a conservative species and sulphate as a reactive species. Utilising the validated hydro-mechanical (HM) results from earlier steps of the DECOVALEX task, reactive and non-reactive transport models, incorporating the current understanding of the geochemistry at the site, were successfully constructed for the whole experimental period. The associated parametric and process uncertainty analyses clearly demonstrate that the basic HM understanding must be sound. However, to demonstrate this degree of robustness, the explicit inclusion of process representations of water desaturation, liquid vaporisation, species exclusion porosity, and redox processes, is required.     

Beurteilung bestehender Stahltragwerke: Empfehlungen zur Abschätzung der Restnutzungsdauer

Assessment of existing steel structures: recommendations for estimation of remaining fatigue life. The growing importance of sustainability affects new markets for the construction industry; the rehabilitation and refurbishment of existing buildings and civil engineering works is getting more and more into the focus of construction activities. This also applies to bridges as well where the quality management comprising the full life of a bridge has a long tradition. For bridges in particular the enormous increase of freight‐volume on roads and rails and the growing age of the bridges cause the question, whether the existing structures are still fit for use and whether or not they can be retrofitted and if so how that could be done. For decision making concerning measures for maintenance and refurbishment of a bridge or its substitution by a new bridge the value of the residual service life is very important. Therefore the bridge authorities have been cooperating for a long time to develop appropriate methods for determining the residual safety and service life of existing bridges. Also the International Technical‐Scientific Organisations as the ECCS and fip as well as Standard Organisations as ISO and CEN have cared for an international exchange of views and the harmonisation of methods. For steel bridges in particular the Technical Committee 6 – Fatigue – of the ECCS has taken over the task to develop a technical guidance for the assessment of existing steel bridges on the grounds of national experiences and the present state of the art [1]. This guidance has been prepared to serve as a basis for CEN/TC 250 – the CEN‐Technical Committee responsible for the structural Eurocodes – for future further development of these Eurocodes to include the assessment and retrofitting of existing structures. The result of the development of ECCS‐TC 6 is a technical‐scientific report which has been published by the Commission of the EU (DG‐Research – Joint Research Centre – JRC) in the frame of a cooperation agreement between the JRC and the ECCS. This report may be used as a technical recommendation as long as the revision of the Eurocodes has not been carried out. This contribution gives the main information from the JRC‐ECCS‐report [1], that can be downloaded free of charge from the e‐bookshop of the Commission.     

In situ characterization of nitrifying biofilm: Minimizing biomass loss and preserving perspective

Methods for characterizing nitrifying bacteria within biofilms are of key importance to understand and optimize the nitrification kinetics of attached growth treatment facilities. In this work, we propose an analytical protocol based upon environmental scanning electron microscopy (ESEM) and confocal laser scanning microscopy (CSLM) in combination with fluorescent in situ hybridization (FISH) to characterize the structure of nitrifying biofilm as it remains attached to the original reactor substratum. This protocol minimizes the loss of mass and distortion of in situ perspective commonly associated with traditionally applied microscopic techniques and thereby enables a more accurate estimation of the nitrifying biomass within biofilm attached to the substratum. The use of ESEM eliminates the destructive preparatory procedures associated with traditional scanning electron microscopy and thus the loss of mass and shrinking of the samples. ESEM is used in this study to evaluate the percent coverage of the substratum with biofilm and the biofilm thickness. CLSM-FISH is used to determine cell counts in the biofilm and to characterize the undisturbed substratum/biofilm interface. By hybridizing and analyzing the nitrifying biofilm using CLSM as it remains attached to the substratum, the loss of material and distortion of in situ perspective associated with the biofilm detachment process is minimized. Moreover, by conducting the CLSM analysis directly on the nitrifying biofilm as it remains attached to the substratum it is shown that cell counts at the substratum/biofilm interface differ significantly from that located above the interface.     

Mercury distribution in fish organs and food regimes: Significant relationships from twelve species collected in French Guiana (Amazonian basin)

Within a multidisciplinary research programme set up in French Guiana (Amazonian basin), twelve fish species from six food regimes were collected from the upper part of the Maroni River in order to analyze mercury (Hg) distribution in six organs (gills, liver, kidneys, skeletal muscle, stomach, and intestine) and to look for a relationship between Hg organotropism and food regimes. As many studies have shown, mercury biomagnification leads to extremely marked differences in muscle accumulation levels: the average ratio between extreme concentrations measured in piscivorous and herbivorous species was almost 500. A first principal component analysis on primary Hg concentration variables showed that biomagnification had a marked effect, masking differences between Hg distribution in the organs according to fish species and their food regimes. In order to avoid this, we determined ratios between Hg concentrations measured in the different organs and in the skeletal muscle, considered as the reference tissue for biomagnification effects. A new principal component analysis using these normalized values, in conjunction with a Ward's hierarchical clustering method, revealed that there is a link between Hg organotropism and the food regimes, with comparatively high [Hg]gills/[Hg]muscle ratios for the herbivorous species; high [Hg]intestine-liver-kidneys/[Hg]muscle ratios for the benthivorous and periphytophagous species, and, in contrast, ratios of less than 1 in the different organs for the piscivorous and omnivorous species. Our determinations of methylmercury (MMHg) percentages in the food consumed by the fish (aquatic macrophytes, terrestrial material from the river banks, biofilms, benthic invertebrates, fish muscle tissues), according to the different food regimes (herbivorous, periphytophagous, benthivorous, omnivorous, carnivorous, piscivorous), showed that this criterion can account for the differences in Hg distribution in the fish organs. For instance, the periphytophagous and benthivorous fish species ingest biofilms and small benthic invertebrates with quite low MMHg burdens (18% and 35 to 52% of Hgtotal, respectively). The highest [Hg]organs/[Hg]muscle ratios were observed for the liver and kidneys, the two principal target organs for inorganic Hg in fish. On the other hand, the piscivorous species ingest a large amount of fish of varying size, with high MMHg percentages in their muscle tissue (nearly 80%); Hg organotropism is characterized by high MMHg concentrations in the skeletal muscle and comparatively low [Hg]organs/[Hg]muscle ratios.     

Effect of shear stress and growth conditions on detachment and physical properties of biofilms

Detachment is one of the major processes determining the physical structure and microbial functionalities of biofilms. To predict detachment, it is necessary to take the mechanical properties of the biofilm and the effect of both hydrodynamic and growth conditions into account. In this work, experiments were conducted with biofilms developed under various shear stresses and with various substrate natures. In addition, two cases were considered in order to differentiate between the effect of hydrodynamic factors and growth factors: the biofilms were directly grown under the targeted shear stress (τ) condition or they were precultivated under very low shear stress (0.01 Pa) and then exposed to high shear stress in the range of 0.1-13 Pa. An exponential and asymptotic decrease of the biofilm thickness and mass with increasing τ was observed in both cases. On contrary density, expressed as the biofilm dry mass on a known substratum divided by the average thickness increased with τ. Denitrifying biofilms always showed greater thickness and density than oxic biofilms. These results showed the presence of a compact basal layer that resisted shear stresses as high as 13 Pa whatever the culture conditions. Above this basal layer, the cohesion was lower and depended on the shear stress applied during biofilm development. The application of shear stress to the biofilms resulted in both detachment and compression, but detachment prevailed for the upper part of the biofilms and compression prevailed for the basal layers. A model of biofilm structure underlying the stratified character of this aggregate is given in terms of density and cohesion.     

The new era of the livestock production in Mongolia: Consequences on streams of the Great Lakes Depression

Mongolia, a landlocked country of the Central Asian plateau, is experiencing a significant modification of herding practices coupled with an increase in livestock numbers. These modifications lead to increasing impacts of grazing on the Mongolian steppes with major consequences on the waterbodies. We researched the impacts of grazing intensity on the streams of the Great Lakes Depression in northwestern Mongolia. We assessed the level of watershed and stream bank erosion and the type of vegetation structure. We calculated the livestock densities per watershed and linked them to the stream water discharge through a new metric (I_CU). I_CU was created as a function of cattle unit density and water discharge, having water discharge at a stream section reflecting its location in the drainage and therefore accounting for the surface area drained upstream. We measured also the major nutrients in the stream water and researched the causalities between the grazing and the impairment of watersheds and streams. Our results suggest that the increase of livestock numbers is reaching beyond the grassland and affecting the stream ecosystem. Two major impacts were highlighted by this study, 1) the extensive watershed and stream bank erosion and 2) the increase in concentration of suspended particles and orthophosphate in stream systems. When compared with past values from literature, our results show recent eutrophication of the streams compared to the pre-liberalization of the herding activity in Mongolia (before 1991). Consequently the continued uncontrolled increase of livestock numbers could threaten the conservation of the Mongolian waterbodies, with notable consequences on the life of the nomadic population of the Central Asian Plateau.