Search results for "CERAMICS"
showing 10 items of 1599 documents
Reorientational dynamics in simple supercooled liquids
1998
Abstract The geometry of the reorientational dynamics in the van der Waals liquid, toluene, and the hydrogen bond network, glycerol, are compared. Both systems have contributions from small angle fluctuations. In glycerol the fraction of these small angle fluctuations is much larger than in toluene, due to the stronger anisotropic interactions in the former substance. The average reorientational angle in both systems is similar and on the order of 10 ∘ . In addition we analyze the stretching of the rotational correlation functions of rank one and two. In both cases we find that the second rank correlation function has a more pronounced stretching than the corresponding first rank correlatio…
Post-buckling analysis of cracked multilayered composite plates by pb-2 Rayleigh–Ritz method
2015
Abstract A pb-2 Rayleigh–Ritz variational approach for the analysis of post-buckling behavior of cracked composite plates is presented. The plate is modeled by the first order shear deformation theory taking geometric nonlinearities into account through the von Karman’s theory. General stacking sequences are considered. Cracks are modeled by using subdomain decomposition of the plate coupled with penalty techniques, used to augment the variational statement with the needed continuity conditions along the connected subdomains edges. Numerical procedures have been developed and used to validate the present solution by comparison with available literature results. Original results are then pre…
Unexpected metal-free synthesis of trifluoromethyl arenes via tandem coupling of dicyanoalkenes and conjugated fluorinated sulfinyl imines
2021
A novel strategy for the synthesis of policyclic trifluoromethyl arenes has been devised. It involves a DBU-promoted tandem cycloaromatization reaction of dicyanoalkenes and fluorinated conjugated sulfinyl imines. This unprecedented transformation is a metal-free and air-tolerant process that takes place from readily available starting materials under mild reaction conditions.
Unveiling the reaction mechanism of novel copper N-alkylated tetra-azacyclophanes with outstanding superoxide dismutase activity.
2020
Quantum chemical and multiscale calculations reveal the mechanistic pathway of two superoxide dismutase mimetic N-alkylated tetra-azacyclophane copper complexes with remarkable activity. The arrangement of the binding site afforded by the bulky alkyl substituents and the coordinated water molecule as a proton source play key roles in the reaction mechanism.
Microstructural study of titanium carbonitride elaborated by combustion synthesis
2007
Abstract The self-propagating high-temperature synthesis (S.H.S.) process, which is promising for the fabrication of ceramic materials, was chosen to elaborate titanium carbonitride materials. The influence of parameters such as nitrogen gas pressure and carbon ratio on the microstructure was studied. A single phase product of Ti(C,N) is obtained for a carbon ratio under 15 at.% and a nitrogen pressure of 36 MPa. The increase of the carbon ratio corresponds to a decrease of the maximum temperature reached during the synthesis. Time resolved X-ray diffraction measurements (TRXRD) with the synchrotron radiation were used to determine the reaction mechanisms. We could observe that the synthesi…
Computational simulations on the binding and reactivity of a nitrile inhibitor of the SARS-CoV-2 main protease.
2021
We present a detailed computational analysis of the binding mode and reactivity of the novel oral inhibitor PF-07321332 developed against the SARS-CoV-2 3CL protease. Alchemical free energy calculations suggest that positions P3 and P4 could be susceptible to improvement in order to get a larger binding strength. QM/MM simulations unveil the reaction mechanism for covalent inhibition, showing that the nitrile warhead facilitates the recruitment of a water molecule for the proton transfer step.
Chain-extending of Hydroxytelechelic Polybutadiene: Synthesis and Characterization
2010
Extension of hydroxytelechelic polybutadiene oligomers ( 3200 g/mol) is performed in mild conditions, in order to avoid backbone modifications, using succinic anhydride or methylenedicyclohexyl diisocyanate. The two routes present significative extension of the initial oligomers. Extension through the anhydride route, in the presence of DCC and DMAP, leads to new hydroxytelechelic oligomers ( 8000 g/mol). Extension through the diisocyanate route, catalyzed by DBTL at 65°C leads to hydroxytelechelic oligomers of higher average molecular weight ( 20000 g/mol). New materials are characterized by FTIR/1H-NMR and changes in their Tg according to , are discussed. The influence of reaction time on…
Mixed finite elements for nonlocal elastic multilayered composite plate refined theories
2020
Abstract A novel mixed finite element formulation for the layerwise analysis of nonlocal multilayered composite plates is presented. The finite elements are formulated starting from the weak form of a set of governing equations for the laminate layers that were deduced via the Reissner Mixed Variational Theorem. The primary variables, namely displacements and out-of-plane stresses, are expressed at layer level as through-the-thickness expansions of suitable selected functions with coefficients approximated by the finite element scheme. The through-the-thickness expansion order is considered as a free parameter. This way, finite elements for different refined higher order plate theories can …
Interaction of oxygen with Mo(100), Mo(110), and Mo(111) surfaces. RHEED and AES analyses of the molybdenum oxide nucleation and growth
1991
Abstract A study of the nucleation and growth of MoO 3 generated by interaction of oxygen with Mo(100), Mo(110), and Mo(111) single crystalline surfaces is investigated at high oxygen pressure (10 4 Pa) and low temperature (620 to 820 K). The results of RHEED and AES analyses prove that under these oxidation conditions, MoO 3 nucleates directly from the metal without intermediate formation of MoO 2 or nonstoichiometric molybdenum oxide such as Mo 4 O 11 . The structure and orientation of MoO 3 nuclei are characterized in relation with the parent molybdenum surface. On the Mo(110) and Mo(111) surfaces, which are faceting, the nucleation and growth of MoO 3 takes place by successive structura…
A preliminary comparison between finite element and meshless simulations of extrusion
2009
In this paper the extrusion process of a cross-shaped profile was investigated. In particular, the study was focused on the distortion of extruding profiles when the workpiece and die axis are not aligned. The process was simulated using the finite element method (FEM) and the natural element method (NEM), both implemented in an updated-Lagrangian formulation, in order to avoid the burden associated with the description of free surfaces in ALE or Eulerian formulations. Furthermore, an experimental equipment was developed in order to obtain reliable data in terms of deformed entity, required process load and calculated pressure. At the end, a comparison between the numerical predictions and …