General Enantioselective Synthesis of Butyrolactone Natural Products via Ruthenium‐SYNPHOS®‐Catalyzed Hydrogenation Reactions

Enantioselective syntheses of several paraconic acids have been achieved using catalyzed asymmetric hydrogenation of β‐keto esters with SYNPHOS^® as a ligand. This strategy allowed the short synthesis of biologically active (−)‐methylenolactocin 1 , (−)‐protolichesterinic acid 2 , (−)‐phaseolinic acid 3 and (+)‐roccellaric acid 4 .     

Stability,magnetic, electronic,elastic, thermodynamic,optical, and thermoelectric properties of Co2TiSn,Co2ZrSn and Co2HfSn Heusler alloys from calculations using generalized gradient approximation techniques

Structural, magnetic, electronic, elastic, thermodynamic, optical, and thermoelectric properties of full-Heusler alloys Co₂YSn (Y?=?Ti; Zr; Hf) were determined using density functional theory-based WIEN2k code within GGA and GGA?+?U approximations for exchange correlation functions. The calculated formation energies and elastic parameters demonstrate the stability of these alloys. It was also observed that the studied compounds have a ductile structure and exhibit anisotropic behavior. The magnetic moment of these systems is equal to 2 μ_B, which conforms to the Slater–Pauling rule. In addition, the half-metallic ferrimagnetic behavior and good bandgap in the minority spin are showed for all compounds. The optical properties are systematically studied by computing the optical parameters. The existence of bandgaps with minimal energy loss in IR and visible regions makes these materials suitable candidates for optoelectronic devices. The thermoelectric properties of these systems were also examined in terms of temperature and chemical potential.

     

Evaporation-induced evolution of the capillary force between two grains

The evolution of capillary forces during evaporation and the corresponding changes in the geometrical characteristics of liquid (water) bridges between two glass spheres with constant separation are examined experimentally. For comparison, the liquid bridges were also tested for mechanical extension (at constant volume). The obtained results reveal substantial differences between the evolution of capillary force due to evaporation and the evolution due to extension of the liquid bridges. During both evaporation and extension, the change of interparticle capillary forces consists in a force decrease to zero either gradually or via rupture of the bridge. At small separations between the grains (short & wide bridges) during evaporation and at large volumes during extension, there is a slight initial increase of force. During evaporation, the capillary force decreases slowly at the beginning of the process and quickly at the end of the process; during extension, the capillary force decreases quickly at the beginning and slowly at the end of the process. Rupture during evaporation of the bridges occurs most abruptly for bridges with wider separations (tall and thin), sometimes occurring after only 25 % of the water volume was evaporated. The evolution (pinning/depinning) of two geometrical characteristics of the bridge, the diameter of the three-phase contact line and the “apparent” contact angle at the solid/liquid/gas interface, seem to control the capillary force evolution. The findings are of relevance to the mechanics of unsaturated granular media in the final phase of drying.     

Energetic and exergetic parametric study of a SOFC-GT hybrid power plant

A parametric study is conducted on a hybrid SOFC-GT cycle as part of a national program aiming to improve the efficiency of the actual gas turbine power plants and to better undertake the future investigations. The proposed power plant is mainly constituted by a Gas Turbine cycle, a SOFC system, and an ammonia water absorption refrigerating system. An external pre-reformer is installed before the SOFC. Heat recovery systems are adopted to valorize the waste heat at the SOFC and GT exhausts. The gas from the SOFC exhaust is also used as additional supply for the combustion chamber. An extraction is performed on the gas Turbine in order to feed the SOFC cycle by thermal heat flux at medium pressure.The equations governing the electrochemical processes, the energy and the exergy balances of the power plant components are established. Numerical simulation using EES software is performed. The influences of key operating parameters, such as humidity, pre-reforming fraction, extraction fraction from the Gas Turbine and fuel utilization on the performances of the SOFC-GT hybrid system are analyzed. Obtained results show that the integration of the SOFC enhances significantly the hybrid overall cycle efficiency. The increase of the ambient temperature and humidity reduces the system efficiencies. The utilization factor has a negative effect on the SOFC temperature and voltage. That leads to a decrease in the power plant performances. While the pre-reforming fraction, has a positive effect on the indicated parameters.     

Role of Zinc Oxide and Nickel Nanoparticles on EMI Shielding Behavior of Chopped Carbon Fibre/Electrospun Fibrous Cobalt Epoxy Composites in X and Ku Band Microwave Frequencies

Silicon - This work investigated the microwave scattering parameters along with mechanical properties of a wave shielding magnetic nickel nanoparticles Ni-chopped carbon fibre CCF-Electrospun...     

Synthesis of Mg-stabilized nitrogen-rich alpha-sialons along Si3N4–0.5Mg3N2:3AlN line via field-assisted sintering

The present study reports for the first time the synthesis and evaluation of magnesium (Mg)-doped nitrogen-rich (N-rich) sialon ceramics exploring the possible existence of Mg-stabilized single-phase alpha-sialon (on the Mg-alpha-sialon plane). Mg-stabilized N-rich sialons, with the general formula of Mg_xSi_12−2xAl_2xN₁₆ having x value in the range of 0.2–2.2 for the composition laying along the Si₃N₄–0.5Mg₃N₂:3AlN line, were synthesized at 1500°C, using nano-size starting powder precursors and field-assisted (or spark plasma) sintering technique. Consolidated sialon ceramic samples were characterized for their microstructure, phase stability regime, and physical and mechanical properties. Although a relatively low synthesis temperature was adopted, well densified sialon samples were achieved; however, the densification of the samples became difficult with a higher x value (containing high Mg₃N₂/AlN content). Contrary to what was expected to take place, a single-phase Mg-doped sialon was not obtained near the N-rich line (on Mg-alpha-sialon plane). Such distinctive behavior in Mg-doped sialons was supposed to be due to the formation of a highly stable Mg-containing aluminum nitride polytype phase, which consumed most of the high-temperature transient liquid phase. Mg-doped N-rich sialon sample having the maximum amount of alpha phase depicted a remarkable hardness (HV₁₀) of 21.4 GPa and a fracture toughness of 3.5 MPa m^1/2.