Highly resolved numerical simulation of combustion in supersonic hydrogen–air coflowing jets

The present study is focused on the analysis of non-premixed combustion in high-velocity (supersonic) flows. The computations make use of a large eddy simulation (LES) model, which has been recently introduced to address combustion in high Reynolds number turbulent flows featuring moderate Damköhler values. We expect that the corresponding closure is able to account for the specificities encountered in high Mach number turbulent reactive flows featuring chemical reaction time scales with the same order of magnitude as flow time scales. The model takes finite-rate chemistry and micro-mixing effects into account within the framework of the partially stirred reactor (PaSR) concept, it is hereafter denoted by U-PaSR (unsteady partially stirred reactor). (i) In a first step of the present investigation, the capabilities of the U-PaSR closure hence proposed are evaluated through a detailed comparison performed between numerical results and the data obtained from an experimental study devoted to non-premixed combustion in supersonic co-flowing jets of hydrogen and vitiated air. The simulated test case corresponds to a well-documented experimental database that includes Raman scattering and laser-induced pre-dissociative fluorescence measurements. The comparisons performed between computational results and experimental data establish that the physical processes are well-described by the performed simulation. (ii) In a second step of this study, the flame structure and associated stabilization zone are analysed in the light of numerical simulation results. The post-processing to the computational results indeed confirms the importance of self-ignition processes, as well as the relevance of diagnostic tools recently introduced by Boivin et al. [1,2]. Considering the stabilization zone, it also emphasizes the essential importance of the pressure dynamics associated with the discharge of compressible coflowing jets into the atmosphere – an importance that was not so clearly evidenced from previous numerical simulations conducted on the same experimental benchmark.     

Identification of the Elastic–Plastic Behavior of Adhesively Bonded Structures Under Multi-Axial Loadings: Comparison of a Modified Arcan Test and a Tension/Compression–Torsion Test

Structural bonding is nowadays widespread in the industry. However, characterisation methods and 3D modelling of the adhesives need to be improved. The characterisation requires an experimental procedure to obtain a large experimental database under various loading cases, which represents a significant amount of data. The 3D modelling requires advanced models with several parameters to identify and generally uses inverse identification procedures, which can be time expensive. For a good accuracy, the constitutive models need to take into account the dependency on the hydrostatic stress and be written under the non-associated formalism. In this study, the experimental database is obtained via a modified Arcan test that can cover a wide range of loadings between tension, shear, mixed tension–shear, and mixed compression–shear. A second experimental campaign is realized with a tension/compression–torsion (TCT) test that can cover a greater range of loadings: from tension to compression and mixed tension/compression–shear, with an infinite possibility of mixed loadings. The modified Arcan database is used to identify a 3D elastic–plastic Mahnken–Schlimmer type model, according to an inverse identification procedure developed in a previous study. This model identification is validated on the experimental database coming from the TCT test: a numerical/experimental comparison is realized. This allows the validation of the model and emphasizes the benefits of the TCT test. Indeed, it proves that this test is well suited to characterize adhesive joints and presents several capacities that will be really useful for further studies, like an infinite range of non-proportional loadings available.     

Interplay between Selenium,Selenoproteins and HIV-1 Replication in Human CD4 T-Lymphocytes

The infection of CD4 T-lymphocytes with human immunodeficiency virus (HIV), the etiological agent of acquired immunodeficiency syndrome (AIDS), disrupts cellular homeostasis, increases oxidative stress and interferes with micronutrient metabolism. Viral replication simultaneously increases the demand for micronutrients and causes their loss, as for selenium (Se). In HIV-infected patients, selenium deficiency was associated with a lower CD4 T-cell count and a shorter life expectancy. Selenium has an important role in antioxidant defense, redox signaling and redox homeostasis, and most of these biological activities are mediated by its incorporation in an essential family of redox enzymes, namely the selenoproteins. Here, we have investigated how selenium and selenoproteins interplay with HIV infection in different cellular models of human CD4 T lymphocytes derived from established cell lines (Jurkat and SupT1) and isolated primary CD4 T cells. First, we characterized the expression of the selenoproteome in various human T-cell models and found it tightly regulated by the selenium level of the culture media, which was in agreement with reports from non-immune cells. Then, we showed that selenium had no significant effect on HIV-1 protein production nor on infectivity, but slightly reduced the percentage of infected cells in a Jurkat cell line and isolated primary CD4 T cells. Finally, in response to HIV-1 infection, the selenoproteome was slightly altered.     

Tribological behavior of composites fabricated by reactive SPS sintering in Ti-Si-C system

In this study, wear and friction behavior of two based-composites from the Ti-Si-C system, (40 wt% TiC; 28 wt% Ti₅Si₃; 17 wt% Ti₃SiC₂) and (18 wt% TiC; 26 wt% Ti₅Si₃; 41 wt% Ti₃SiC₂) reinforced by 15 wt% of large size SiC (100-150 µm) particles were investigated. The four-phase composites exhibited approximatively the same friction coefficient (µ ~ 0.9) under high loads (10 N and 7 N). The composite with high Ti₃SiC₂ showed higher wear rate values by one order of magnitude. However, under 1 N, the composite with high TiC content showed a higher running-in period and a lower steady state µ value (0.37 after 1000 m sliding distance). Scanning electron microscopy, Energy Dispersive X-Ray and Raman spectroscopy analysis of the worn surfaces of the two composites revealed that oxidation was the dominant wear mechanism. The oxidation process and the removal kinetics of the oxides during sliding controlled the tribological behavior of the composites. The influence of processing variables on microstructures development and wear mechanisms of the composites is discussed.     

Synthesis of fatty hydroxamic acids catalyzed by the lipase ofMucor miehei

Biotechnological synthesis of a new class of amphiphilic molecules—fatty hydroxamic acids—was carried out using the lipase ofMucor miehei by reacting hydroxyl amine with the fatty acids in their free or methyl ester form. Concurrently with enzymatic synthesis, chemical synthesis of hydroxamic fatty acids has also been developed by adapting methods that already existed for water-soluble acids. Different parameters were studied to determine the optimum operating conditions: temperature, molar ratio of reagents, quantity of biocatalyst and length of reaction. A general method, whatever the type of fatty acids used, is described.     

INFLUENCE OF MATERIAL REMOVAL ON THE DYNAMIC BEHAVIOR OF THIN-WALLED STRUCTURES IN PERIPHERAL MILLING

Machining is a material removal process that alters the dynamic properties during machining operations. The peripheral milling of a thin-walled structure generates vibration of the workpiece and this influences the quality of the machined surface. A reduction of tool life and spindle life can also be experienced when machining is subjected to vibration. In this paper, the linearized stability lobes theory allows us to determine critical and optimal cutting conditions for which vibration is not apparent in the milling of thin-walled workpieces. The evolution of the mechanical parameters of the cutting tool, machine tool and workpiece during the milling operation are not taken into account. The critical and optimal cutting conditions depend on dynamic properties of the workpiece. It is illustrated how the stability lobes theory is used to evaluate the variation of the dynamic properties of the thin-walled workpiece. We use both modal measurement and finite element method to establish a 3D representation of stability lobes. The 3D representation allows us to identify spindle speed values at which the variation of spindle speed is initiated to improve the surface finish of the workpiece.     

Neutronic characterization of the MEGAPIE target

The MEGAPIE project aimed to design, build and operate a liquid metal spallation neutron target of about 1 MW beam power in the SINQ facility at the Paul Scherrer Institut (Villigen, Switzerland). This project is an important step in the roadmap towards the demonstration of the accelerator driven system (ADS) concept and high power liquid metal targets in general. Following the design phase, an experimental program was defined to provide a complete characterization of the facility by performing a “mapping” of the neutron flux at different points, from the center of the target to the beam lines. The neutronic performance of the target was studied using different experimental techniques with the goals of validating the Monte Carlo codes used in the design of the target; additionally, the performance was compared with the solid lead targets used before and after the MEGAPIE experiment.     

Co/SiO2 catalysts prepared from Co2(CO)8 for CO hydrogenation into alcohols and hydrocarbons: characterization by magnetic methods and temperature-programmed hydrogenation

The hydrogenation of carbon monoxide over Co/SiO₂ catalysts obtained by reduction of precursors prepared by the reaction of dicobaltoctacarbonyl with silica gives rise to a mixture of alcohols and hydrocarbons. The chain growth probability for hydrocarbon synthesis is similar to that observed over conventional catalysts prepared by the ammonia method (=0.74) with a comparable metal dispersion (metal particle size 4 nm). Alcohol formation yields a smaller chain growth probability (=0.42). Magnetic measurements have shown that in the latter catalyst, small cobalt clusters (1 nm) are likely to be present together with the cobalt particles (4 nm), this observation reconciles apparently conflicting results from the literature. It has been speculated that alcohol formation might be related to the presence of these clusters according to a concerted mechanism. Furthermore, the observation of large amounts of acetates by temperature-programmed hydrogenation, not detected in hydrocarbon selective catalysts, suggests that they may play a role in ethanol synthesis.