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Seminar khoa học của GS.TSKH. Phạm Đức Chính, TS. Lê Nguyễn Minh Thông

Vào 9h00 ngày 05/4/2024, Viện IAST tổ chức buổi trao đổi học thuật tại Phòng A901 với nội dung chi tiết như sau: 

GS.TSKH. Phạm Đức Chính trình bày về "Minimum energy bounds onlongitudinal elastic constantsof transversely isotropicunidirectional composites"

Tóm tắt: 

We consider the n-component transversely isotropicunidirectional elastic composites, the longitudinalaxis of which is parallel to those of the transverselyisotropic components as well as the generators of thecylindrical phase boundaries between them. Fromthe minimum energy and complementary energyprinciples, with appropriate constant strain andpiece-wise constant stress trial fields, optimizationand iteration techniques, a set of bounds for themacroscopic (effective) longitudinal elastic constants of the composites (including the simple lower arithmetic average estimate for longitudinal Young modulus Eeff ≥ EV) are constructed. Numerical examples are provided to illustrate the obtained.

TS. Lê Nguyễn Minh Thông trình bày về "First-principles study of methane oxidation over modified ZIF-204"

Tóm tắt: 

The direct oxidation of methane over oxo-doped ZIF-204 is studied relying on first-principles DFT-based calculations. Doped oxo ligand stabilizes on the mono-copper site with a formation energy of 1.06 eV. Methane interacts with Cu metal via a so-called η2 mode with the physisorption energy of 0.24 eV, arising from a polarization of methane under the electrostatic attraction of the Cu2+ cation. With doped oxo, presenting of electrons in O_pz orbital accounts for the adsorption of methane via a hydrogen bonding with an adsorption energy of 0.30 eV. Given the initial adsorption configurations, the oxidation of methane occurs via either a concerted direct oxo insertion mechanism or a hydrogen-atom abstraction radical rebound mechanism. Calculating transition state barriers, the reactions via concerted direct oxo insertion mechanism occur without energy barriers. Whereas, reactions via the hydrogen atom abstraction radical rebound mechanism are barrierless for the dissociation of C-H bond of CH4, and a small barrier of 0.16 eV for the recombination of C-O bond to form CH3OH. Those negligible energy barriers propose a favorable catalyst for the oxidation of methane over the modified ZIF-204