Sandy soils in silty loess:The loess system of Matmata (Tunisia)

International audienceThe purpose of this study is to better understand the system of Quaternary loess-palaeosol sequences (LPS) of the Matmata region in southern Tunisia. Results from a combination of predominantly classical methods (grain size and mineral analysis, CaCO3- content estimation, environmental magnetism) indicate strong soil formation phases during which the conditions of sedimentation changed drastically. The heavy mineral analysis underlines northwest, west and southwest provenances of the loessic material. Furthermore, we discuss the process of soil formation in LPS and explain why these soils are very sandy in comparison to the loess units. During phases of soil formation, the northwestern sediment transport path was blocked while sandy material was blown dominantly from the southwestern Grand Erg. Therefore, we present a conceptual model including a provenance analysis of the loessic material that support and improve earlier results of Coudé-Gaussen and collaborators.Dans cette étude, nous présentons un modèle conceptuel pour une meilleure compréhension du système de séquences de loess paléosol (LPS) dans la région de Matmata située dans le sud de la Tunisie. Les résultats d'une combinaison de méthodes principalement classiques (analyse granulométrique, analyse minéralogique, détermination de la teneur en CaCO3, magnétisme environnemental) indiquent des phases de formation importante de sols au cours desquelles les conditions de sédimentation ont fondamentalement changé. L'analyse des minéraux lourds met en évidence une origine nord-ouest, ouest et sud-ouest du matériel loessique. En outre, nous discutons la nature de la formation des sols et expliquons pourquoi ces sols sont si sableux par rapport aux unités de loess. Pendant les phases de formation des sols, le trajet des sédiments en provenance du nord-ouest a été bloqué alors que les matériaux sableux pouvaient encore être soufflés à partir du Grand Erg au sud-ouest. Notre modèle conceptuel de la provenance du lœss à Matmata soutient et précise les conclusions de Coudé-Gaussen et collaborateurs

Hochfeste multifunktionale Verbundwerkstoffe auf Basis von Portlandzement und Kohlenstoffkurzfasern

In der vorliegenden Arbeit werden Kohlenstoffkurzfasern (0,2 bis 10 mm) in Portlandzementmörtel homogen dispergiert und der resultierende Verbundwerkstoff hinsichtlich seiner 3-Punkt Biegezugfestigkeit und einaxialen Druckfestigkeit untersucht. Es wird die Fasergeometrie, der Fasergehalt und die Oberflächenchemie der Verstärkungsfasern hinsichtlich einer hohen Biegezugfestigkeit der resultierenden Faser-Zement-Komposite untersucht und optimiert. Außerdem wird ein Verfahren zur Ausrichtung von Kohlenstoffkurzfasern in Portlandzementleim vorgestellt, das es ermöglicht, die Biegezugfestigkeit der mit dieser Methode hergestellten Proben noch weiter zu steigern, als es durch homogen dispergierte Fasern möglich wäre. In Hinblick auf eine praktische Anwendung dieser Zementleimsysteme mit gerichteten Kurzfasern wird der 3D-Druck als vielversprechendes Verfahren für eine automatisierte Verarbeitungstechnologie untersucht. Neben mechanisch hochfesten Verbundwerkstoffen, wird ebenso der Einsatz von elektrisch leitfähigem Portlandzementmörtel mit homogen dispergierten Kohlenstoffkurzfasern als intelligentes Heizsystem vorgeschlagen

From Micro to Nano: A Toolbox for Tuning Crystal Size and Morphology of Benzotriazolate-Based Metal–Organic Frameworks

Scaling down the size of metal–organic framework (MOF) particles is a challenging but important task for extending the spectrum of potential MOF applications. Herein, we describe downsizing particles of MFU-4, a benzobistriazolate-based Zn­(II)-MOF, which can be prepared by either solvothermal or microwave-assisted synthesis. We report on combining various synthetic strategies leading to a production of nanosized MOF crystals of well-defined sizes and shape. Our approaches include varying reaction time, temperature, solvent choice, and amount of additives (alkali hydroxides or selected amines) in order to gain control over the nucleation process. As a result, the crystal sizes can be tuned over a broad range, from 40 nm large globular particles up to 5 μm cubic crystals with narrow size distributions. Additionally, the article offers a comparison of different techniques used to determine the particle size of crystals. These include dynamic light scattering, X-ray powder diffraction (from Scherrer equation), and transmission electron microscopy

Adverse effects of low occuptional cadmium exposure on renal and oxidative stress biomarkers in solderers.

Objectives Recent studies suggest adverse health effects after low exposure to cadmium (Cd). Brazing with Cd-containing solder exposes workers to Cd. The purpose of this study was to assess: (1) indicators of Cd exposure in blood (Cd-B)/ urine (Cd-U); (2) the association between Cd-B, Cd-U and renal and oxidative stress biomarkers. Methods In this cross-sectional study Cd-B, Cd-U, renal (ie, N-acetyl-β-D-glucosaminidase/urinary intestinal alkaline phosphatase (IAP)/microalbumin/beta-2-microglobulin/retinol binding protein and oxidative stress markers (ie, derivatives of reactive oxygen metabolites/glutathione peroxidase/superoxide dismutase (SOD)/ advanced oxidation protein products/8-hydroxy-2′-deoxyguanosin/8-isoprostanes) were determined in 36 solderers. Results Multiple linear regression analysis adjusting for age and pack-years of smoking show that IAP is statistically significantly associated with Cd-B (B=0.24; SE=0.11) and Cd-U (B=0.15; SE=0.07). Also SOD is statistically significantly associated with Cd-B (B=62.96; SE=29.62). The association between SOD and Cd-U is of borderline statistical significance (B=37.69; SE=19.59). Conclusions While there is still some debate as whether the Cd-induced tubular effects are reversible or not, IAP and SOD appear as sensitive and potentially useful early biomarkers for the health surveillance of workers exposed to low levels of Cd