Erosion of refractory carbides in high-temperature hydrogen from ab initio computations

Advanced concepts for in-space propulsion require coatings that are resistant to erosion in high temperature and pressure hydrogen. The erosion of refractory carbides of interest for this application (ZrC, NbC, HfC, and TaC) is investigated using combined ab initio thermodynamic computations and equilibrium product analyses. The carbides are shown to erode through a combination of four governing reactions, the relative extent of which depend on environmental conditions. The product profiles from these reactions are complex but exhibit lower hydrogen saturation at higher temperatures and lower pressures. A metric is derived to determine the applicability of equilibrium analyses for erosion rates, based on experimental conditions. Heritage mass loss experiments on ZrC in hydrogen satisfy the equilibrium criteria, and, correspondingly, the computed equilibrium erosion rate agrees quantitatively. The results suggest that previously postulated non-equilibrium effects, namely the prolonged incongruent vaporization originating from high carbon mobility, do not drive erosion over the hours-long timescales of the experiments. For specific in-space propulsion designs, comparisons of carbide performance show TaC and HfC outperform other carbides and meet the criteria needed to close designs.     

Microfluidic mixing using pulsating flows

Mixing of biological species in microfluidic channels is challenging since the mixing process is limited by the small mass diffusion coefficient of the species and by the dominance of viscous effects, captured by the low value of Reynolds number characteristic of laminar liquid flow in microchannels. This paper investigates the use of pulsating flows to enhance mixing in microflows. The dependence of the degree of mixing on various dimensionless groups is investigated. These dimensionless numbers are Strouhal number, pulse amplitude divided by base velocity, Reynolds number, location along the mixing channel normalized by the channel width, channel cross section aspect ratio, and phase difference between the inlet streams. The degree of mixing, observed to experience both spatial fluctuations down the mixing channel and temporal fluctuations over a pulsation cycle at the quasi-stationary state, is shown to be most sensitive to changes in pulsation amplitude and frequency. For a fixed pulsation amplitude and Reynolds number, the degree of mixing has a peak value for a certain Strouhal number above and below which the degree of mixing decreases. Increasing the pulsation amplitude improves mixing with the behavior becoming asymptotic at large pulsation amplitudes. The temporal fluctuations in the degree of mixing over a cycle at the quasi-stationary state decrease and the average degree of mixing increases downstream the mixing channel. The fluctuations are also smaller at higher values of the Strouhal number and are generally larger for larger pulsation amplitudes. This study also takes into account the rate of work input required to overcome viscous effects. While this power input is independent of the pulsation frequency, it exhibits a parabolic dependence on the pulsation amplitude. Finally, considering the dependence of the degree of mixing (mean and standard deviation), mixing length, and energy consumption on these dimensionless groups, examples of the trade-off that has to be made in choosing the operating conditions based on different constraints are presented.     

Multivariate Study on Phenanthrene Sorption in Soils

Batch tests and different statistical tools of data analysis were used to re-evaluate the overall effect of soil characteristics and liquid phase composition on the extent of phenanthrene adsorption in complex soil-water systems. The linear isotherm models was capable of adequately describing the equilibrium data under extremely varying conditions of soil type, environmental conditions (pH, temperature, ionic strength) and amendments (surfactant, oil, dispersing agent, glucose). Consistent with existing mechanistic models, the multivariate approach also identified the organic carbon content (foc) of soil as the key parameter controlling the phenanthrene adsorption constant (Kd) in nonamended systems (Koc was 17,700 mL/g). From studying the effect of the amendments, two interactions (surfactant-pH and surfactant-oil) and two main effects (surfactant and oil) have been detected. An empirical linear model of Kd as a function of foc, pH, oil content of soil, and surfactant dose was developed for the range of conditions studied. The proposed model and modeling approach can be adapted to other types of contaminants or variables for specific natural and engineered systems.     

Comparative study of dewatering characteristics of metal precipitates generated during treatment synthetic polymetallic and AMD solutions

The sludge dewatering characteristics expressed in terms of settling, filtration and centrifugation of metal precipitates generated during treatment of polymetallic solutions and synthetic acid mine drainage have been evaluated in this research. Results show that dewatering properties of metallic sludge vary depending on the type of matrix (Cl⁻; SO₄²⁻), precipitating agent, and metals present in effluent. Metal hydroxides (at pH 10.0) and metal phosphates precipitates (at pH 7.0) are amorphous in nature, thus difficult to dewater. In these treatment methods, the substitution of chloride matrix by sulphate one improves considerably dewatering properties (specific resistance to filtration = 6.60 × 10¹³ and 2.35 × 10¹³ m/kg for the chloride and sulphate matrix, respectively). In the case of sulphide and carbonate treatments (pH 8.0), precipitates obtained are semi crystalline, and crystalline form, respectively, and no influence of the matrix was detected on dewatering characteristics.     

Benchmark Solution for Time-Dependent Natural Convection Flows with an Accelerated Full-Multigrid Method

A computational procedure is presented with an accelerated full-multigrid scheme for an efficient modeling of time-dependent buoyancy-driven flows. The smoother is the iterative red-and-black successive overrelaxation (RBSOR) scheme. In order to improve the convergence, an acceleration parameter, Γ, is implemented in the classical full-multigrid procedure. It is shown that an optimal value of Γ = 3.75 minimizes the number of iterations needed for convergence. Numerical results are presented and compared with available investigations for an 8:1 differentially heated enclosure and a square heated cavity. Solutions for Prandtl number Pr = 0.71, Rayleigh number Ra = 3.4 × 10⁵ for the 8:1 heated enclosure, and 10⁵ ≤ Ra ≤ 10⁹ for the square cavity are presented and show excellent agreement.     

Analysis of human male armpit sweat after fenugreek ingestion: Instrumental and sensory optimisation of the extraction method

In this study, we intend to develop a simple and selective procedure to extract compounds involved in the strong odour which appears after fenugreek ingestion (this odour is responsible of the so-called pseudo-maple syrup urine disease). Two procedures, solvent extraction and headspace solid-phase microextraction (HS-SPME), were employed to extract compounds from armpits sweat samples collected from two volunteer subjects. The HS-SPME extraction parameters were first optimised and then applied to extracts of armpit sweat collected from subjects after fenugreek ingestion. The sensory evaluation of the different extracts was carried by eight trained assessors; the HS-SPME and solvent extracts were, respectively, smelled by direct gas chromatography–olfactometry and direct olfaction. The results of sensory evaluation indicate that HS-SPME with a divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fibre, of 50/30 μm film thickness and 2 cm length, gives a global odour close to that of sweat after ingestion of fenugreek infusion.     

Bandwidth Estimation for IEEE 802.11-Based Ad Hoc Networks

Since 2005, IEEE 802.11-based networks are able to provide a certain level of Quality of Service by the means of service differentiation, thanks to the IEEE 802.11e amendment. However, no mechanism or method has been standardized to accurately evaluate the amount of resources remaining on a given channel. Such evaluation would however be a good asset for bandwidth-constrained applications. In multi-hop ad hoc networks, such evaluation becomes even more difficult. Consequently, despite the various contributions around this research topic, the estimation of the available bandwidth still represents one of the main issues in this field. In this article, we propose an improved mechanism to estimate the available bandwidth in IEEE 802.11-based ad hoc networks. Through simulations, we compare the accuracy of the estimation we propose to the estimation performed by others state of the art QoS protocols, BRuIT, AAC and QoS-AODV.     

Evaluation of the implementation fidelity of an ergonomic training program designed to prevent back pain

The aim of this study was to evaluate the implementation fidelity of a multidimensional ergonomic program designed to prevent back pain injuries among healthcare personnel. The program, provided by peer trainers included training intended to modify patient handling and transfer behaviour, trainee follow-up, prevention activities aimed at work environment improvements and follow-up monitors training. Two hundred twenty-one peer trainers at 139 Quebec healthcare institutions participated in our study. Only 61.5% were involved in training; most of them taught safe patient handling, positioning, transfer, and preparation techniques, which are the cornerstones of the program; 72.7% were involved in prevention activities, 46.1% in follow-up activities, and 10.7% in follow-up monitors training. The study results should help organizations anticipate and prevent potential discrepancies between prescribed and implemented programs.     

High-Performance Computation of Bézier Surfaces on Parallel and Heterogeneous Platforms

Bézier surfaces are mathematical tools employed in a wide variety of applications. Some works in the literature propose parallelization strategies to improve performance for the computation of Bézier surfaces. These approaches, however, are mainly focused on graphics applications and often are not directly applicable to other domains. In this work, we propose a new method for the computation of Bézier surfaces, together with approaches to efficiently map the method onto different platforms (CPUs, discrete and integrated GPUs). Additionally, we explore CPU–GPU cooperation mechanisms for computing Bézier surfaces using two integrated heterogeneous systems with different characteristics. An exhaustive performance evaluation—including different data-types, rendering and several hardware platforms—is performed. The results show that our method achieves speedups as high as 3.12x (double-precision) and 2.47x (single-precision) on CPU, and 3.69x (double-precision) and 13.14x (single-precision) on GPU compared to other methods in the literature. In heterogeneous platforms, the CPU–GPU cooperation increases the performance up to 2.09x with respect to the GPU-only version. Our method and the associated parallelization approaches can be easily employed in domains other than computer-graphics (e.g., image registration, bio-mechanical modeling and flow simulation), and extended to other Bézier formulations and Bézier constructions of higher order than surfaces.