A simple analytical model to study and control azimuthal instabilities in annular combustion chambers

This study describes a simple analytical method to compute the azimuthal modes appearing in annular combustion chambers and help analyzing experimental, acoustic and large eddy simulation (LES) data obtained in these combustion chambers. It is based on a one-dimensional zero Mach number formulation where N burners are connected to a single annular chamber. A manipulation of the corresponding acoustic equations in this configuration leads to a simple dispersion relation which can be solved by hand when the interaction indices of the flame transfer function are small and numerically when they are not. This simple tool is applied to multiple cases: (1) a single burner connected to an annular chamber (N = 1), (2) two burners connected to the chamber (N = 2), and (3) four burners (N = 4). In this case, the tool also allows to study passive control methods where two different types of burners are mixed to control the azimuthal mode. Finally, a complete helicopter chamber (N = 15) is studied. For all cases, the analytical results are compared to the predictions of a full three-dimensional Helmholtz solver and a very good agreement is found. These results show that building very simple analytical tools to study azimuthal modes in annular chambers is an interesting path to control them.     

Photodétecteurs en intégration monolithique sur guides optiques : modélisation et vérifications expérimentales

The authors developed a model on optical guided structures with complex refractive indices, on 9 desktop-computer. This model allows to predict the coupling efficiency of photodetectors monolithically integrated with optical waveguides. An oscillatory behaviour of the absorption coefficient versus the absorbing layer thinkness has been pointed out. Comparisons with experimental resuylts obtained with device made in different laboratories show a good agrement     

Single carbon nanotube transistor at GHz frequency

We report on microwave operation of top-gated single carbon nanotube transistors. From transmission measurements in the 0.1-1.6 GHz range, we deduce device transconductance gm and gate-nanotube capacitance Cg of micro- and nanometric devices. A large and frequency-independent gm approximately 20 microS is observed on short devices, which meets the best dc results. The capacitance per unit gate length of 60 aF/microm is typical of top gates on a conventional oxide with epsilon approximately 10. This value is a factor of 3-5 below the nanotube quantum capacitance which, according to recent simulations, favors high transit frequencies fT=gm/2piCg. For our smallest devices, we find a large fT approximately 50 GHz with no evidence of saturation in length dependence.     

Application of Monte Carlo calculation and OEDIPE software for virtual calibration of an in vivo counting system

OEDIPE (a French acronym standing for 'Tool for Personalized Internal Dose Assessment'), developed by IRSN, is used to perform virtual calibration of a real in vivo counting system. The system, installed recently at Le Vésinet, consists of four Broad Energy germanium detectors. CT images of Livermore torso phantom are used to create a voxel phantom after segmentation using Dosigray software. Virtual calibration using the voxel phantom was validated by the comparison of peak efficiencies between Monte Carlo calculation and phantom experiments using lung sources 152Eu and 241Am at different chest wall thickness (CWT = 19, 25, 30, 43 mm). The comparison between virtual calibration and physical phantom experiments shows that the relative deviations are within +/- 10% in the energy range of 59.5-1408 keV, and within +/- 30% for 17.5 keV photons.     

Efficient Telomerization of Butadiene with Starch in Water: The Role of the Surfactant

The synthesis of hydrophobic starch was performed via palladium-catalyzed telomerization of butadiene with native starch. This reaction is efficiently performed in water in the presence of neutral or cationic surfactant with high HLB. After optimization of the reaction conditions, TOF up to 446 was achieved.     

Laser Melting of Spark Plasma-Sintered Zirconium Carbide: Thermophysical Properties of a Generation IV Very High-Temperature Reactor Material

Melting temperatures of zirconium carbide were investigated in validating a novel thermal analysis technique for refractory materials. Commercial ZrC_0.96 powder was densified by spark plasma sintering to >96% relative density after 6–30 min at 2173–2453 K under 40–100 MPa. Sintered ceramics were heated to >4000 K via pulsed laser heating. Mean values for solidus and liquidus transitions were 3451 and 3608 K, respectively, in fair agreement with the present phase diagram. Postmelting analysis revealed dendritic microstructure and composition consistent with single-phase ZrC. Subsurface gas porosity and ZrC–C eutectic indicate complex processes occurring during melting and freezing.     

A Mutant D‐Fructose‐6‐Phosphate Aldolase (Ala129Ser) with Improved Affinity towards Dihydroxyacetone for the Synthesis of Polyhydroxylated Compounds

A mutant of D ‐fructose‐6‐phosphate aldolase (FSA) of Escherichia coli, FSA A129S, with improved catalytic efficiency towards dihydroxyacetone (DHA), the donor substrate in aldol addition reactions, was explored for synthetic applications. The k_cat/K_M value for DHA was 17‐fold higher with FSA A129S than that with FSA wild type (FSA wt). On the other hand, for hydroxyacetone as donor substrate FSA A129S was found to be 3.5‐fold less efficient than FSA wt. Furthermore, FSA A129S also accepted glycolaldehyde (GA) as donor substrate with 3.3‐fold lower affinity than FSA wt. This differential selectivity of both FSA wt and FSA A129S for GA makes them complementary biocatalysts allowing a control over donor and acceptor roles, which is particularly useful in carboligation multi‐step cascade synthesis of polyhydroxylated complex compounds. Production of the mutant protein was also improved for its convenient use in synthesis. Several carbohydrates and nitrocyclitols were efficiently prepared, demonstrating the versatile potential of FSA A129S as biocatalyst in organic synthesis.     

Crystal Structure of the Human Monoacylglycerol Lipase,a Key Actor in Endocannabinoid Signaling

2‐Arachidonoylglycerol plays a major role in endocannabinoid signaling, and is tightly regulated by the monoacylglycerol lipase (MAGL). Here we report the crystal structure of human MAGL. The protein crystallizes as a dimer, and despite structural homologies to haloperoxidases and esterases, it distinguishes itself by a wide and hydrophobic access to the catalytic site. An apolar helix covering the active site also gives structural insight into the amphitropic character of MAGL, and likely explains how MAGL interacts with membranes to recruit its substrate. Docking of 2‐arachidonoylglycerol highlights a hydrophobic and a hydrophilic cavity that accommodate the lipid into the catalytic site. Moreover, we identified Cys201 as the crucial residue in MAGL inhibition by N‐arachidonylmaleimide, a sulfhydryl‐reactive compound. Beside the advance in the knowledge of endocannabinoids degradation routes, the structure of MAGL paves the way for future medicinal chemistry works aimed at the design of new drugs exploiting 2‐arachidonoylglycerol transmission.