On contribution of pores into the effective elastic properties of carbon/carbon composites

In this paper, we discuss the effect of porosity on the effective elastic properties of unidirectional carbon/carbon composites (carbon fibers in pyrolytic carbon matrix) densified by chemical vapor infiltration (CVI). It is shown that CVI treatment results in formation of irregularly shaped pores randomly oriented in the plane perpendicular to the direction of fiber (transverse plane). These pores are analyzed using numerical conformal mapping procedure, and their contribution to the effective elastic properties is expressed in terms of the cavity compliance contribution tensor. Components of this tensor are found for a variety of typical pores shapes.     

Electrochemical boron-doped diamond film microcells micromachined with femtosecond laser: application to the determination of water framework directive metals

Planar electrochemical microcells were micromachined in a microcrystalline boron-doped diamond (BDD) thin layer using a femtosecond laser. The electrochemical performances of the new laser-machined BDD microcell were assessed by differential pulse anodic stripping voltammetry (DPASV) determinations, at the nanomolar level, of the four heavy metal ions of the European Water Framework Directive (WFD): Cd(II), Ni(II), Pb(II), Hg(II). The results are compared with those of previously published BDD electrodes. The calculated detection limits are 0.4, 6.8, 5.5, and 2.3 nM, and the linearities go up to 35, 97, 48, and 5 nM for, respectively, Cd(II), Ni(II) Pb(II), and Hg(II). The detection limits meet with the environmental quality standard of the WFD for three of the four metals. It was shown that the four heavy metals could be detected simultaneously in the concentration ratio usually measured in sewage or runoff waters.     

Macro- and Nanotribological Properties of Graphite Tribofilms: Influence of the Sliding Interface

Macrotribological studies of microcrystalline graphite powder reveal a drastic decrease in the friction coefficient when the experiments are carried out in the presence of low-viscosity liquids. The friction reduction is attributed to the simultaneous presence of particles and liquid in the sliding contact, but the mechanisms involved remain unclear. In order to contribute to the understanding of liquid action in friction reduction mechanisms, nanoscale investigations of the tribofilms have been performed using lateral force microscopy. Attention is devoted to the nanostructure of the film surfaces and their nanofriction behavior using an atomic force microscope. The influence of the tip/sample interfaces on friction properties is investigated by using AFM tips constituted of different compounds (silicon, gold/chromium alloy, silicon nitride or carbon-covered AFM tip) and by performing the nanofriction tests in air or liquid environments. The results indicate that the friction reduction observed at macroscale is attributed neither to the lowering of the shear strength of the carbon/carbon interface in the presence of liquid nor to the nanostructure of the film surface. Collective liquid/particles effects inside the contact during sliding are probably involved.     

Girls' math performance under stereotype threat: The moderating role of mothers' gender stereotypes.

Previous research on stereotype threat in children suggests that making gender identity salient disrupts girls' math performance at as early as 5 to 7 years of age. The present study (n = 124) tested the hypothesis that parents' endorsement of gender stereotypes about math moderates girls' susceptibility to stereotype threat. Results confirmed that stereotype threat impaired girls' performance on math tasks among students from kindergarten through 2nd grade. Moreover, mothers' but not fathers' endorsement of gender stereotypes about math moderated girls' vulnerability to stereotype threat: Performance of girls whose mothers strongly rejected the gender stereotype about math did not decrease under stereotype threat. These findings are important because they point to the role of mothers' beliefs in the development of girls' vulnerability to the negative effects of gender stereotypes about math. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

A contaminant trap as a tool for isolating and measuring the desorption resistant fraction of soil pollutants

Bioremediation of contaminated soils often leaves a desorption-resistant pollutant fraction behind in the soil, which in the present study was isolated with a combination of diffusive carrier and infinite diffusive sink. Such a diffusive sink was made by casting a composite of silicone and activated carbon into the bottom of a large glass. Field-contaminated soil samples were then suspended in a cyclodextrin solution and incubated in such glasses for the continuous trapping of PAH molecules during their release from the soil matrix. The PAH concentrations remaining in the soil were determined by exhaustive extraction and compared with a biodegradation experiment. The concentration decline in the first soil was faster in the contaminant trap than in the biodegradation experiment, but the halting of the biodegradation process before reaching the legal threshold level was well indicated by the contaminant trap. The PAH concentrations in the second soil hardly decreased in the traps at all, in good agreement with the biodegradation experiment. The PAHs in this soil appeared to be "stuck" by strong sorption. The contaminant trap proved to be a practical approach to the isolation and quantification of the desorption-resistant PAH fraction.     

Preparation and application of visible-light-responsive Ni-doped and SnO2-coupled TiO2 nanocomposite photocatalysts

Soil contamination with petroleum hydrocarbons has caused critical environmental and health defects and increasing attention has been paid for developing innovative technology for cleaning up this contamination. In this work, the washing process of a soil column by ionic surfactant sodium dodecyl sulfate (SDS) was investigated. Water flow rate and the contamination duration (age) have been studied. The performance of water in the removal of diesel fuel was found to be non-negligible, while water contributed by 24.7% in the global elimination of n-alkanes. The effect of SDS is significant beyond a concentration of 8mM. After 4h of treatment with surfactant solution, the diesel soil content remains constant, which shows the existence of a necessary contact time needed to the surfactant to be efficient. The soil washing process at a rate of 3.2 mL/min has removed 97% of the diesel fuel. This surfactant soil remediation process was shown to be governed by the first-order kinetics. These results are of practical interest in developing effective surfactant remediation technology of diesel fuel contaminated soils.     

Comparison of chlorination and chloramination practices on microbial inactivation efficiencies within a scaled‐up water distribution network using central composite design

Disinfection practices reduce the incidence of water‐borne diseases but may result in formation of disinfection byproducts (DBPs) in raw water that are reported to be carcinogenic. Central composite design (CCD) was employed in the present study for optimization of disinfectant dose and contact time with the rationale to evaluate if an optimal balance could be achieved between minimal DBPs formation and effective microbial inactivation with either free or combined chlorine in treated water within a lab‐scale prototype network to simulate real water distribution network conditions. After a series of experimental runs based upon design of experiments (DoE) by CCD, dose was found to be the most significant factor (P < 0.01) in determining DBPs formation in both disinfectant’s applications. Where, contact time significantly (P < 0.01) affected bacterial inactivation in chlorination experiments, in contrast, dose was effective in chloramination experiments. Thus, it was concluded that the optimal balance may be achieved in the water networks with the help of multifactorial optimization when disinfectant dose was maintained near 3 mg/L as applied chlorine dose in both disinfection cases, while contact time was 62 and 155 min for chlorine and chloramine, respectively.     

3D Printing of Dual-Cure Networks Based on (Meth)acrylate/Bispropargyl Ether Building Blocks

In recent years, dual-cure chemistry has been exploited to realize interpenetrating networks (IPNs) that provide enhanced thermo-mechanical properties. In this contribution, photoinduced curing of (meth)acrylates is used to build the desired 3D structure, whereas the thermally triggered polymerization reaction of 2H-chromene functionalized building blocks is utilized to create the IPN. This strategy combines the advantages of traditional UV-curable monomers with high-performance thermosets. After the successful synthesis of the bispropargyl ether derivative, i.e., 4,4′-(propane-2,2-diyl)bis((ethynyloxy)benzene), its thermally induced conversion to the corresponding 2H chromene functionalized prepolymer is studied by Fourier-transform infrared spectroscopy and gel permeation chromatography. The network formation as well as the printability of various formulations containing different amounts of the thermo-curable building block is investigated. The obtained IPNs provide enhanced thermo-mechanical properties making these resins suitable for the additive manufacturing of functional 3D parts for high-performance applications.     

PROCESSUS – Integration of SEI CMM and ISO quality models

Integration of the two best-known quality management models for software production and maintenance, the Capability Maturity Model and the ISO 9001 Model (including ISO 9000-3) is of great interest for both the European and the American software market. The definition of a quality management model which would conform to the requirements of both models and use the advantages of each was a key goal of our research work within the project PROCESSUS.1 Research work was conducted in two steps: first, the detailed comparison of both models was made in order to define their common issues and specifics of each model, and secondly, the integrated model based on the results of the comparison was defined. In this paper the comparison method and results are described. Further, a method for the integration and a framework of the integrated model are presented. The core of our work is actually the content of the integrated model. Due to extensive content of the integrated model examples of some parts only are given in the appendix. The integrated model presented in this paper has already been successfully used in organizations which are cooperating in the project PROCESSUS o these organizations achieved the needed maturity for certification to the ISO 9001 standard and a maturity level near level 3 of CMM.