Effect of coarse particle volume fraction on the yield stress and thixotropy of cementious materials

International audienceIn order to help in modelling the yield stress of fresh concrete, we study the behavior of suspensions of coarse particles in a thixotropic cement paste. Our aim is to relate the yield stress of these mixtures to the yield stress of the suspending cement paste, to the time passed at rest, and to the coarse particle volume fraction. We present here procedures that allow for (i) studying a homogeneous and isotropic suspension, (ii) comparing the yield stress of a given cement paste to that of the same cement paste added with particles, and (iii) accounting for the thixotropy of the cement paste. We observe that the yield stress of these suspensions of cement paste with coarse particles follows the very simple Chateau-Ovarlez-Trung model {[}X. Chateau, G. Ovarlez. K.L. Trung, Homogenization approach to the behavior of suspensions of noncolloidal particles in yield stress fluids, J. Rheol. (2008) 52 489-506.], consistently with the experimental results of Mahaut et al. {[}F. Mahaut, X. Chateau, P. Coussot, G. Ovarlez, Yield stress and elastic modulus of suspensions of noncolloidal particles in yield stress fluids, J. Rheol. (2008) 52 287-313.] obtained with many different particles and suspending yield stress fluids. This consistency between the results obtained in various yield stress fluids shows that the yield stress of the suspension does not depend on the physicochemical properties of the suspending yield stress fluid; it only depends on its yield stress value. This shows that studies of suspensions in model yield stress fluids can be used as a general tool to infer the behavior of fresh concrete. Moreover, we show that the thixotropic structuration rate of the interstitial paste (its static yield stress increase rate in time) is not affected by the presence of the particles. As a consequence, it is sufficient to measure the thixotropic properties of the constitutive cement paste in order to predict the thixotropic structuration rate of a given fresh concrete. This structuration rate is predicted to have the same dependence on the coarse particle volume fraction as the yield stress

Unraveling the strain state of GaN down to single nanowires

GaN nanowires (NWs) grown by molecular beam epitaxy are usually assumed free of strain in spite of different individual luminescence signatures. To ascertain this usual assumption, the c/a of a GaNNW assembly has been characterized using both X-ray diffraction and Raman spectroscopy, with scaling the measurement down to the single NW. Free-standing single NWs have been observed free of strain defined as [c/a-(c/a)o]/(c/a)o within the experimental accuracy mounting to 1.25 × 10-4. However, in the general case, a significant portion of the NWs is coalesced, generating an average tensile strain that can be partly released by detaching the NWs from their substrates. It is concluded that at the scale of the single NW, the free surface and the residual doping do not generate a significant strain and only coalescence does

Les multiples facettes des inégalités écologiques

La notion d’inégalités environnementales se décline différemment selon les contextes culturels. Cette notion, telle qu’elle est apparue aux États-Unis, n’a de sens que dans une perspective d’action. Il s’agit de s’appuyer sur un environnement dégradé pour étayer les revendications de communautés ou d’ethnies défavorisées. En Europe, elle rejoint la notion, plus globale, de populations davantage exposées à des risques ou des contaminants, ou encore tributaires d’une faible qualité de leur milieu ambiant. Des politiques ou des situations environnementales et leurs implications sanitaires peuvent se conjuguer et renforcer des inégalités constatées sur le plan social.The notion of ecological inequalities is understood in very different ways depending on different cultural contexts. In the United States, where it has first developed, its only meaning is in an action perspective. The idea is to lean on degraded environmental conditions to strengthen the claims of unfavoured communities or ethnical groups. In Europe, it meets the more global notion of populations specifically exposed to risks or contaminating substances, or benefitting from weak quality surroundings. Policies, environmental situations and their health implications can meet and thus reinforce already identified social inequalities

The Behavioral and Cognitive Executive Disorders of Stroke: The GREFEX Study.

BACKGROUND: Many studies have highlighted the high prevalence of executive disorders in stroke. However, major uncertainties remain due to use of variable and non-validated methods. The objectives of this study were: 1) to characterize the executive disorder profile in stroke using a standardized battery, validated diagnosis criteria of executive disorders and validated framework for the interpretation of neuropsychological data and 2) examine the sensitivity of the harmonization standards protocol proposed by the National Institute of Neurological Disorders and Stroke and Canadian Stroke Network (NINDS-CSN) for the diagnosis of Vascular Cognitive Impairment. METHODS: 237 patients (infarct: 57; cerebral hemorrhage: 54; ruptured aneurysm of the anterior communicating artery (ACoA): 80; cerebral venous thrombosis (CVT): 46) were examined by using the GREFEX battery. The patients' test results were interpreted with a validated framework derived from normative data from 780 controls. RESULTS: Dysexecutive syndrome was observed in 88 (55.7%; 95%CI: 48-63.4) out of the 156 patients with full cognitive and behavioral data: 40 (45.5%) had combined behavioral and cognitive syndromes, 29 (33%) had a behavioral disorder alone and 19 (21.6%) had a cognitive syndrome alone. The dysexecutive profile was characterized by prominent impairments of initiation and generation in the cognitive domain and by hypoactivity with disinterest and anticipation loss in the behavioral domain. Cognitive impairment was more frequent (p = 0.014) in hemorrhage and behavioral disorders were more frequent (p = 0.004) in infarct and hemorrhage. The harmonization standards protocol underestimated (p = 0.007) executive disorders in CVT or ACoA. CONCLUSIONS: This profile of executive disorders implies that the assessment should include both cognitive tests and a validated inventory for behavioral dysexecutive syndrome. Initial assessment may be performed with a short cognitive battery, such as the harmonization standards protocol. However, administration of a full cognitive battery is required in selected patients

Cancer screening in France: subjects’ and physicians’ attitudes

International audienceOBJECTIVE: Since screening for cancer has been advocated, funded, and promoted in France, it is important to evaluate the attitudes of subjects in the general population and general practitioners (GPs) toward cancer screening strategies. METHODS: EDIFICE is a nationwide opinion poll that was carried out by telephone among a representative sample of 1,504 subjects living in France and aged between 40 and 75 years and among a representative sample of 600 GPs. The questionnaire administered to subjects queried about previous screening for cancer. RESULTS: Ninety-three percent of women stated that they had undergone at least one mammography. Although rated "A" recommendation-strongly recommended-by the US Preventive Services Task Force, screening for colorectal cancer received less attention than prostate cancer screening which is rated "I"-insufficient evidence-(reported screening rates of 25% and 36%, respectively). Six percent of subjects stated that they had undergone lung cancer screening. GPs' attitudes toward cancer screening showed similar inconsistencies. CONCLUSIONS: It thus appears that understanding of cancer screening practices in the French general population does not match scientific evidence. To a lesser extent, this also holds for GPs

Secondary organic aerosol origin in an urban environment: Influence of biogenic and fuel combustion precursors

Source contributions of organic aerosol (OA) are still not fully understood, especially in terms of quantitative distinction between secondary OA formed from anthropogenic precursors vs. that formed from natural precursors. In order to investigate the OA origin, a field campaign was carried out in Barcelona in summer 2013, including two periods characterized by low and high traffic conditions. Volatile organic compound (VOC) concentrations were higher during the second period, especially aromatic hydrocarbons related to traffic emissions, which showed a marked daily cycle peaking during traffic rush hours, similarly to black carbon (BC) concentrations. Biogenic VOC (BVOC) concentrations showed only minor changes from the low to the high traffic period, and their intra-day variability was related to temperature and solar radiation cycles, although a decrease was observed for monoterpenes during the day. The organic carbon (OC) concentrations increased from the first to the second period, and the fraction of non-fossil OC as determined by C analysis increased from 43% to 54% of the total OC. The combination of C analysis and Aerosol Chemical Speciation Monitor (ACSM) OA source apportionment showed that the fossil OC was mainly secondary (>70%) except for the last sample, when the fossil secondary OC only represented 51% of the total fossil OC. The fraction of non-fossil secondary OC increased from 37% of total secondary OC for the first sample to 60% for the last sample. This enhanced formation of non-fossil secondary OA (SOA) could be attributed to the reaction of BVOC precursors with NO emitted from road traffic (or from its nocturnal derivative nitrate that enhances night-time semi-volatile oxygenated OA (SV-OOA)), since NO concentrations increased from 19 to 42 μg m from the first to the last sample

Mosaic DNA imports with interspersions of recipient sequence after natural transformation of Helicobacter pylori

Helicobacter pylori colonizes the gastric mucosa of half of the human population, causing gastritis, ulcers, and cancer. H. pylori is naturally competent for transformation by exogenous DNA, and recombination during mixed infections of one stomach with multiple H. pylori strains generates extensive allelic diversity. We developed an in vitro transformation protocol to study genomic imports after natural transformation of H. pylori. The mean length of imported fragments was dependent on the combination of donor and recipient strain and varied between 1294 bp and 3853 bp. In about 10% of recombinant clones, the imported fragments of donor DNA were interrupted by short interspersed sequences of the recipient (ISR) with a mean length of 82 bp. 18 candidate genes were inactivated in order to identify genes involved in the control of import length and generation of ISR. Inactivation of the antimutator glycosylase MutY increased the length of imports, but did not have a significant effect on ISR frequency. Overexpression of mutY strongly increased the frequency of ISR, indicating that MutY, while not indispensable for ISR formation, is part of at least one ISR-generating pathway. The formation of ISR in H. pylori increases allelic diversity, and contributes to the uniquely low linkage disequilibrium characteristic of this pathogen

Synthesis of T-Nb2O5 thin-films deposited by Atomic Layer Deposition for miniaturized electrochemical energy storage devices

Atomic Layer Deposition has been used to grow 30 to 90 nm-thick amorphous Nb2O5 films onto Pt current collectors deposited on Si wafer. While T-Nb2O5 polymorph is obtained by further annealing at 750 °C, the film thickness and the resulting electrode areal capacity are successfully controlled by tuning the number of ALD cycles. The electrochemical analysis reveals a lithium ion intercalation redox mechanism in the T-Nb2O5 electrode. An electrode areal capacity of 8 μAh cm-² could be achieved at 1 C, with only 40% capacity loss at 30 C(2 minutes discharging time). This paper aims at demonstrating the use of Atomic Layer Deposition method in the fabrication of Nb205-based on-chip micro-devices for Internet of Things (IoT) applications

Relevance of cyclin D1b expression and CCND1 polymorphism in the pathogenesis of multiple myeloma and mantle cell lymphoma

BACKGROUND: The CCND1 gene generates two mRNAs (cyclin D1a and D1b) through an alternative splicing at the site of a common A/G polymorphism. Cyclin D1a and b proteins differ in their C-terminus, a region involved in protein degradation and sub-cellular localization. Recent data have suggested that cyclin D1b could be a nuclear oncogene. The presence of cyclin D1b mRNA and protein has been studied in two hemopathies in which cyclin D1 could be present: multiple myeloma (MM) and mantle cell lymphoma (MCL). The A/G polymorphism of CCND1 has also been verified in a series of patients. METHODS: The expression of cyclin D1 mRNA isoforms has been studied by real-time quantitative PCR; protein isoforms expression, localization and degradation by western blotting. The CCND1 polymorphism was analyzed after sequencing genomic DNA. RESULTS: Cyclin D1 mRNA isoforms a and b were expressed in mantle cell lymphoma (MCL) and multiple myeloma (MM). Cyclin D1b proteins were present in MCL, rarely in MM. Importantly, both protein isoforms localized the nuclear and cytoplasmic compartments. They displayed the same short half-life. Thus, the two properties of cyclin D1b recognized as necessary for its transforming activity are missing in MCL. Moreover, CCND1 polymorphism at the exon/intron boundary had no influence on splicing regulation in MCL cells. CONCLUSION: Our results support the notion that cyclin D1b is not crucial for the pathogenesis of MCL and MM