Effect of Thermomechanical Fatigue on Precipitation Microstructure in Two Precipitation-Hardened Cast Aluminum Alloys

Thermal loading induces modifications of the precipitation microstructure of Al–Si–Cu–Mg alloys. This study focuses on the effect of deformation on precipitation microstructure during thermomechanical loadings. Several specimens were thermomechanically cycled while others were exposed to the same thermal cycles without any mechanical loading. The nature and morphological characteristics of the precipitation microstructure of the thermomechanically cycled specimens are compared to those of the thermally aged ones, using transmission electron microscopy (TEM), in order to assess the effect of deformation on the precipitation microstructure and especially on the kinetics of precipitate growth. The absence of any significant effect of superimposed straining during thermal cycling is discussed. Implications for the prevision of yield strength degradation during service operation are briefly presented.

     

Functional and molecular properties of calcium precipitated soy glycinin and the effect of glycation with κ-carrageenan

This study describes an extraction process for the preparation of highly purified calcium precipitated glycinin (11S). Initial extraction of soy proteins using isoelectric precipitation at pH 6.8 followed by cryo-precipitation yielded 4.2% product (11S) recovery with 98% protein purity for the control extracted with NaOH. Addition of calcium chloride (CaCl₂) doubled the extraction yield (9%) compared to the control and when two other salts were used (i.e., sodium (Na₂SO₄) and ammonium (NH₄)₂SO₄ sulfate, average yields of 4.4% and 5.17%, respectively). Thermal and molecular stability under varying conditions (pH, salts, SDS as a protein structure perturbing agent), and effect of glycation on functional and structural properties were investigated. Size exclusion chromatography and electrophoresis confirmed the predominance of a major band with MW of ～342 kDa with 98.4% purity. Differential scanning calorimetry (DSC) yielded one endothermic transition peak at 95.5 °C. Denaturation temperatures were >100 °C for all salt concentrations studied. The pH had a dominant influence on the structural properties of glycinin. In the presence of NaCl and CaCl₂ (0.2–1 M), the protein structure showed very little denaturation and no aggregation bands were observed even on heating to 95 °C. Lower SDS concentrations (0.5–1%) resulted in denaturation and aggregation, while at 2% SDS only denaturation was observed. Glycation did not alter the conformational structure of protein. Improvements in surface properties were observed with moderate degree of glycation (6–24 h).     

Factors responsible for rapid dissipation of acidic herbicides in the coastal lagoons of the Camargue (Rhône River Delta, France)

This study was aimed at investigating which processes cause acidic herbicides (e.g., bentazone, MCPA and dichlorprop) to rapidly disappear in the lagoons of the Rhône delta, which are peculiar brackish and shallow aquatic environments. The use of the model MASAS (Modeling of Anthropogenic Substances in Aquatic Systems) revealed that sorption, sedimentation, volatilization, flushing and abiotic hydrolysis had a minor role in the attenuation of the investigated herbicides. Laboratory scale biodegradation and photodegradation studies were conducted to better assess the significance of these two processes in the natural attenuation of herbicides in brackish (lagoons) waters with respect to fresh waters (canals draining paddy fields). Herbicide biodegradation rates were significantly lower in lagoon water than in canal water. Consequently, photodegradation was the main dissipation route of all investigated herbicides. The contribution of indirect photolysis was relevant for MCPA and dichlorprop while direct photolysis dominated for bentazone removal. There is a need to further investigate the identity of phototransformation products of herbicides in lagoons.     

Functional group modification in a non-ionic extracellular schizophyllan polysaccharide

Summary Chemical modification of schizophyllan, a neutral fungal polysaccharide which assumes a triple helical structure in aqueous solution,was performed at room temperature in DMSO in the presence of triethylamine and dimethyl-4 aminopyridine. No molecular weight degradation results from the modification.The modified polysaccharide which contains 2.3 phtalic acid groups per repeat unit behaves as a polyelectrolyte in aqueous solution. Due to the presence of charged acidic groups a single chain conformation is evidenced in both DMSO and aqueous solution.     

Spatial contrast detection for colour patterns under selective chromatic adaptation

This paper reports the results of a fundamental study investigating the filtering characteristics of the colour mechanisms that encode spatial information. The shape of the contrast sensitivity function of the human visual system with red, green and blue stimuli was investigated under selective chromatic adaptation, and at eccentricities of 0°, 13° and 26°. The results are compared with those obtained with an achromatic test, at the same eccentricities. The band-pass character of the contrast sensitivity function is brought to light for the three selective chromatic adaptation states obtained. It is more pronounced in peripheral than in foveal vision, whatever the temporal frequency tested. The authors suggest an interpretation of the shape changes of the contrast sensitivity curves based on the neurological properties of achromatic and chromatic mechanisms. The functional exploration of the neurophysiological and optical properties of the visual system may be useful to display designers and users as far as the system efficiency for using colour as an information code is concerned.     

Twenty-four-hour ambulatory EEG monitoring in infantile spasms

Twenty-four-hour ambulatory EEG (AEEG) recordings were performed in 74 infants with West Syndrome (WS) who had not received corticosteroids before the recording. EEG analysis was performed visually for interictal background activity as well as for ictal events: spasms (isolated or in clusters) and other seizures either generalized or partial. Six hundred fifty-four seizures were recorded in 67 patients. Partial seizures (PS) were noted in 31 infants (51% of symptomatic WS cases, 33% of cryptogenic WS cases). In 14 patients, PS were immediately followed by a cluster of spasms consisting of a single ictal event. Patients with PS had an asymmetrical interictal background activity in 85% of cases, with no return to hypsarrhythmia between spasms in a given cluster. AEEG is a reliable method to detect and analyze ictal events in infants with WS. In this population, patients with unfavorable outcome of both epilepsy and psychomotor development have PS. Therefore, the existence of PS may contribute to etiologic diagnosis and prognostic evaluation.     

Reservoir Management Using a Network Flow Optimization Model Considering Quadratic Convex Cost Functions on Arcs

The allocation of water resources between different users is a hard task for water managers because they must deal with conflicting objectives. The main objective is to obtain the most accurate distribution of the resource and the associated circulating flows through the system. This induces the need for a river basin optimization model that provides optimized results. This article presents a network flow optimization model to solve the water allocation problem in water resource systems. Managing a water system consists in providing water in the right proportion, at the right place and at the right time. Time expanded network allows to take into consideration the temporal dimension in the decision making. Since linear cost functions on arcs present many limitations and are not realistic, quadratic convex cost functions on arcs are considered here. The optimization algorithm developed herein extend the cycle canceling algorithm developed for linear cost functions. The methodology is applied to manage the three reservoirs of La Haute-Vilaine’s watershed located in the north west of France to protect a three vulnerable areas from flooding. The results obtained with the algorithm are compared to a reference scenario which consists in considering reservoirs transparent. The results show that the algorithm succeeds in managing the reservoir releases efficiently and keeps the flow rates below the vigilance flow in the vulnerable areas.     

Pesticides in the Rhône river delta (France): Basic data for a field-based exposure assessment

The pesticide concentration levels flowing into paddy fields and surrounding lagoons of the Rhône river delta were investigated over a period of 6 months in 2004. Water samples were collected at the outlets of the major ditches and in the lagoons in order to study the seasonal variation in pesticide concentrations and the spatial contamination profile. Twenty four pesticides were monitored, mainly herbicides and insecticides. Rice pesticides accounted for 90% of the detection rates while the pesticides transported by the Rhône river water dissolved phase only accounted for 10%. Pretilachlor, oxadiazon, MCPA and bentazone herbicides were found at the highest frequencies into the effluent waters of ditches with maximum concentration levels of 1.2, 0.8, 2.5 and 1.6 μg/L, respectively. Only one insecticide, tebufenozide, was sporadically detected at a maximum concentration level of 0.12 μg/L. There were two main peaks of contamination. The first one in April corresponded to the use of pre-emergence herbicides (oxadiazon and pretilachlor) and the second one in June was related to the post-emergence herbicides (MCPA and bentazone). These concentration peaks were well correlated with the pesticide application period time and rapid pesticide transfer (1–2 weeks) from fields to lagoons were observed. Increased loads of the pre-emergence herbicides were induced by the specific management of paddy fields which includes water emptying of fields before and after rice seeding. Pesticide dissipation into the lagoons occurred very quickly and the duration of the exposure of non-target aquatic organisms to high pesticide concentrations (in total a few μg/L level) was no longer than 2 weeks. According to the physico-chemical properties of the chemicals, contrasting results were observed when studying the spatial variation in pesticide concentrations through the lagoons. The concentrations of bentazone and MCPA, two substances with high phototransformation abilities, quickly decreased between the ditches and the lagoons while the oxadiazon and pretilachlor concentrations were more homogeneous.     

Occurrence of 2,4-dichlorophenol and of 2,4-dichloro-6-nitrophenol in the Rhone River Delta (Southern France)

The compounds 2,4-dichlorophenol (2,4-DCP) and 2,4-dichloro-6-nitrophenol (6-nitro-2,4-DCP) have been detected at microg L(-1) levels (10(-9)-10(-8) M) during the summer season 2005 in the water of the Rh?ne river delta. Compound 2,4-DCP would mainly derive from the transformation of the herbicide dichlorprop, heavily used in flooded rice farming (1400 kg in the delta region in 2005), in addition to being an impurity of the commercial herbicide. Field data show a fast concentration decrease of 2,4-DCP in the period June 21st to July 5th, accompanied by a corresponding increase of 6-nitro-2,4-DCP. This could imply a possible nitration process of 2,4-DCP into 6-nitro-2,4-DCP, with quite elevated yield (33%). Nitration of 2,4-DCP can be induced by photoproduced *NO2, the reaction kinetics (calculated in the presence of Fe(III) + nitrite under irradiation as model system) being d[6-nitro-2,4-DCP]/dt = 650 [2,4-DCP] [*NO2]. Interestingly, the yield of the process (38%) is similar to that suggested by field data. An indirect assessment of [*NO2] in surface water in different sites of the Rh?ne delta indicated that 2,4-DCP could be transformed into 6-nitro-2,4-DCP in a couple of weeks or less in the shallow water (10 cm depth) of the rice fields, a time scale that is compatible with field data. Photonitration of 2,4-DCP is thus a possible process to account for the occurrence of 6-nitro-2,4-DCP in the Rh?ne delta.     

Establishment of atmospheric pollution standards for motor vehicles

First we classify the various emission standards applying to light vehicles, the conditions under which the emissions are measured and the environmental standards. We then describe the way in which a standard is established according to the basic principles and procedures involved in determining acceptable environmental concentrations in practice. We refer to the economic and political considerations involved in deciding on a standard and, as an example, to the positions adopted by the various parties concerned in France when drafting the 15.05 standard. In response to the atmospheric pollution caused by motor vehicles, all the industrial countries have, some earlier than others, drawn up regulations designed to limit the extent of this pollution, to protect the environment and reduce the public health risk. Both environmental and emission standards are aimed at reducing the risks to the environment and in particular to man, arising From the presence of particular pollutants. The procedure concerned in establishing these standards is a complicated one involving scientific, economic and political considerations; furthermore, there is a great diversity of standards.