Two leaks detection in viscoelastic pipeline systems by means of transient

This paper presents a technique for detecting and locating leaks in a single viscoelastic pipe, by means of transient analysis. The system studied is a reservoir-pipe-valve structure. The viscoelastic behavior of the pipe wall material is modeled by a generalized KelvinVoigt model. To determine the leak location, the mathematical formulation has been solved by the method of characteristics. The approach by the method of characteristics is often chosen because it is based on the concept of acoustic wave propagation which is the main mechanism of all transient events considered. The presence of the two leaks in a pipe partially reflects pressure waves initiated by the sudden closure of a downstream shut-off valve. These waves affect the shape and the amplitude of the time-history-pressure. The computed results describe the influence of the presence of two leaks on pressure time-history and the effect of leaks locations and sizes on the pressure signal behavior. The effect of the pipe wall viscoelasticity on the two leaks detection and sizing is also discussed. The leaks discharges are determined by resolving two independent equations derived from literatures and based on transient analysis. The friction and leaks depths effects on two leaks locations and sizing are involved.     

MIE determination and thermal degradation study of PA12 polymer powder used for laser sintering

Pulverized materials such as metallic or polymer powders play a considerable role in many industrial processes. Their use requires the introduction of preventive safeguards to control the plant's safety.PA12 polymer powder processing by laser sintering is characteristic of this tendency. The present work concerns PA12 powder (bimodal particle size distribution: 10 μm and 55 μm) and relates to explosion sensitivity and the thermal degradation of this powder, which can occur during laser sintering. Minimum Ignition Energy is determined using a modified Hartmann tube combined with the Langlie method developed in the PRISME Laboratory. This study shows the influence of parameters such as distance between the electrodes, powder concentration and arc power on MIE values. Theses parameters vary in the range of 3–6 A for the current intensity of the spark and the electrode gap in the range of 2.5–4 mm. The MIE is obtained for a spark gap of 3 mm and current intensity of the 4 A spark in our device. It shows that the MIE is less than 40 mJ for concentrations approaching 1000 g/m³. At lower concentrations (under 150 g/m³) the MIE increases but discrepancies in measurements appear, probably because of the static electricity that creates strong irregularities in dust dispersion. The second part of this study concerns the thermal degradation of the PA12 which is performed by thermogravimetric experiments coupled with mass spectrometric (MS) analysis for gas investigation. The mass loss measurement combined with the gas analysis allows the principal stages of degradation to be determined so as to calculate the kinetics parameter PA12. Experiments have been performed for different heating rates between 1 and 30 K min^?1 and the reproducibility of experiments has been verified. The activation energy is determined using two methods: Freidman and KAS. For a reaction rate of between 0.2 and 0.6, the activation energy is nearly constant. The KAS method gives a value of E_a = 250 kJ mol^?1 and the Friedman method gives E_a = 300 kJ mol^?1. The gas analysis by MS shows that oxidation begins at over 350 °C and finishes at under 650 °C with the formation of CO₂ and H₂O. Other major peaks with an m/z ratio of 29, 28 and 30 are noticed in this range of temperature. They show the presence of intermediate species such as C₂H₆, NO or CH₂O. The presence of HCN is also detected (m/z ratio of 27).     

Diversity trends in Neogene European ungulates and rodents: large-scale comparisons and perspectives

The ungulate and rodent fossil records are often used independently to understand mammalian evolutionary history. Few studies have directly compared both records over long time periods and large geographic areas. Here, we compiled two datasets of European fossil localities containing rodents and/or ungulates over 20 My (Early Miocene–Early Pliocene) and processed the data with the same methodology. We counted the raw diversity and calculated a measure of evenness (Pielou’s index). After controlling for potential biases on diversity estimators, we identify the evenness index as a more reliable estimator bringing interesting insights into the way both mammal groups are structured by biotic or abiotic factors. In this study, we consider that an uneven distribution of the species richness among families, when only some families successfully diversify within the “continental-scale community”, represents a lower adaptability of this community to the environmental context. Pielou’s index is used to estimate this adaptability through time. The responses of ungulates and rodents to environmental changes are very divergent, especially facing the climatic changes known since the Middle Miocene. The general patterns suggest that rodent broad-scale assemblages are affected by all kinds of perturbations, even short biotic and abiotic events, but show a better adaptability when facing long-term abiotic changes. Unlike rodents, the ungulate assemblages show more stability in periods of relative environmental stability but show less adaptability to long-term climatic changes. Life-history traits of mammals can help explain patterns of diversity and biogeography at different spatial scales and may probably partly explain the opposite patterns evidenced here.     

Impact of storm Xynthia in 2010 on coastal agricultural areas: the Saint Laurent de la Prée research farm’s experience

Storm Xynthia crossed France’s western coast between 28th February and 1st March 2010. It hit the Vendée and Charente-Maritime departments hardest, as storm surge flooded up to 23,000 ha of coastal agricultural areas (i.e. polders), causing severe damage to farming operations. However, farm-level damage in the aftermath of seawater flooding is an issue that has rarely been explored in the literature. Here we investigated the effects of storm Xynthia on agriculture at the farm scale. We focused on the case study of Saint Laurent de la Prée research farm, a mixed crop–livestock system that was severely hit. All damages were described and economic losses were quantified for the years 2010 and 2011. The results show numerous consequences of the storm in terms of crop and fodder production losses, but also farm infrastructure repairs, crop restoration and animal health problems. Economic damage costs were high, reaching €71,720 in 2010 (€500/ha flooded) and €56,195 (€390/ha) in 2011 for the case study farm. The discussion highlights the farm-level impacts of seawater flooding and the crucial factors that can explain the damage caused to agriculture by storm events in coastal areas. The results are also discussed in the wider context of global warming which is expected to cause sea level rise and more frequent storm events in the future. The vulnerability of coastal agricultural areas to storms thus exposes broader issues of coastal flooding risk management and specifically the allied protection–remediation–adaptation measures. The conclusions underline the need for future research to address prospective scenarios and subsequent adaptive strategies.     

Leak detection of hydrogen–natural gas mixtures in pipes using the characteristics method of specified time intervals

This paper presents a technique for detection and location of leaks in a single pipe, by means of transient analysis, of hydrogen–natural gas mixtures flows. The method uses transient pressure waves initiated by the sudden closure of a downstream shut-off valve. The presence of a leak in a pipe partially reflects these pressure waves and allows for the location of the leak. Pressure waves are governed by two coupled non-linear, hyperbolic partial differential equations with pressure dependent coefficients. The fluid pressure and velocity are considered as two principal dependent variables. To determine the leak location, the mathematical formulation has been solved by the characteristics method of specified time intervals. The computed results describe the influence of the leak on pressure time-history and the effect of hydrogen mass fraction in the mixture on the leak discharge behaviour. It was found that transient pressure is much important in the case of hydrogen than that in the case of natural gas.     

Occurrence of PCDD/Fs and dioxin-like PCBs in superficial sediment of Portuguese estuaries

Superficial sediments collected from seven estuarine systems located along the Portuguese coast were analyzed for 7 polychlorinated dibenzo-p-dioxins (PCDDs), 10 polychlorinated dibenzofurans (PCDFs), and 12 dioxin-like polychlorinated biphenyls (dl-PCBs). Total PCDD/F concentration ranged from 4.6 to 464 pg g^?1 dry weight (dw), while that of dl-PCBs varied from 26.6 to 8,693 pg g^?1 dw. In general, the highest PCDD/F and dl-PCB concentrations were associated with densely populated and industrially impacted areas. Additionally, PCDD/F revealed a predominance of octachlorodibenzodioxin (OCDD) to total PCDD/Fs, while PCB 118 was the major contributor to total dl-PCBs. This study provided a global perspective of the contamination status of Portuguese estuaries by dioxin-like compounds and allowed a comparison between the investigated systems and other systems worldwide. PCDD/F and dl-PCB levels found in the collected sediments were lower than those of highly impacted areas from different parts of the globe. Nevertheless, comparison with guidelines and quality standards from other countries indicated that some Portuguese estuarine areas with a high industrialization level present PCDD/F and dl-PCB concentrations in superficial sediment that may constitute a risk to aquatic organisms.     

Distribution and assessment of heavy metal toxicity in sediment cores from Bizerte Lagoon,Tunisia

To examine the state of pollution of Bizerte Lagoon which is exposed to intense anthropogenic pressure, two sediment cores were taken at two sites, one undergoes the dual effects of both marine waters arriving from the Mediterranean Sea through the Channel, and also of freshwater from the Tinja River; the other core is located at the center of the lagoon where water depth is maximal (12 m). Heavy metal concentrations in the two cores were assessed, with calculated enrichment factors and geo-accumulation indexes. Core sediments were also studied for chemical speciation and their monosulfide contents were measured. Results from enrichment factors and geo-accumulation indexes show an accumulation of Cd, Zn, Cr, and Pb, while chemical speciation revealed a risk only from Cd and Mn. Comparison of sequential extraction values with those of acid volatile sulfides revealed that non-toxic effects may be caused by any of the studied metals in the sediment.