Minimization of Diffraction Losses in Big Gaps of Multi-Mode Waveguides

A systematic approach to design of low-loss miter bends and quasi-optical gaps in multi-mode waveguides is proposed. Several examples illustrate the approach. A mode filter based on a quasi-optical gap in the 31.75 mm diameter corrugated waveguide at frequency 84 GHz has been tested in low (mW) and high-power (200 kW, CW) experiments.     

Development of platinum-free catalyst and catalyst with low platinum content for cathodic oxygen reduction in acidic electrolytes

Studies are presented of the kinetics and mechanism of oxygen electroreduction on CoPd catalysts synthesized on XC 72 carbon black. As shown both in model conditions and in tests with the cathodes of hydrogen–oxygen fuel cells with proton conducting electrolyte, the CoPd/C system features higher activity as compared to Co/C. It is found by means of structural analysis that CoPd alloy is formed in the course of the catalyst synthesis. This provides the higher catalytic activity of the binary systems. CoPd/C catalyst is also more stable in respect to corrosion than Pd on carbon black. Measurements on a rotating ring–disc electrode show that the CoPd/C system provides preferential oxygen reduction to water in the practically important range of potentials (E > 0.7 V). The similarity of the kinetic parameters of the oxygen reduction reaction on CoPd/C and Pt/C catalysts points to a similar reaction mechanism. The slow step of the reaction is the addition of the first electron to the adsorbed and previously protonated O₂ molecule. Studies of the most active catalyst in the fuel cell cathodes are performed. Binary PtCo catalysts (metal atomic ratio of 1 : 1) with low platinum content (7.3 wt.%) modified by phosphorus or sulfur are developed and studied. It is demonstrated that the specific activity of the PtCoS/C (Pt : S = 1 : 1) catalytic system for the O₂ reduction reaction exceeds that of a commercial Pt/C catalyst (E-TEK). The tolerance of the catalyst modified with sulfur is at least six times higher than that of Pt/C (E-TEK).     

On the Correctness of the Well-Known Mathematical Model of Irradiation-Induced Swelling with the Influence of Stresses in the Problems of Elastic-Plastic Deformation Mechanics

Strength of Materials - The paper provides results of the study of correctness of the mathematical model that includes the influence of stresses on irradiation-induced swelling of metal in the...     

Two-dimensional modeling of the near-wellbore fracture tortuosity effect

A two-dimensional (2D) model is proposed for the hydraulic fracture propagating along some given curvilinear trajectory. The turning of the trajectory is conditioned by the difference between the perforation angle of a wellbore and the direction of the maximum principal in-situ stress. Two kinds of equations are coupled and solved numerically in the model: one-dimensional (1D) equations of a power-law fluid flow along the fracture trajectory and 2D equations of the linear elasticity for the rock mass. Based on numerous computations, it is ascertained that the pinching of the fracture occurs only if the trajectory is curvilinear and the in-situ stress in the formation is nonuniform (anisotropic compression). The influence of the fluid rheology and the perforation misalignment angle on the fracture width is investigated as well.