Ultra-wideband balun and power divider using coplanar waveguide to microstrip transitions

An ultra-wideband transition from coplanar waveguide (CPW) to a pair of microstrip lines is presented in this letter. It is shown that the proposed transition can be used to devise an ultra-wideband T-junction power divider with equally split in-phase output signals. More importantly, it is demonstrated that the out-of-phase magnetic currents in the slots of the CPW can be utilized to achieve an out-of-phase power divider or a balun. Both the T-junction power divider and the balun benefit from compact size and good performance over an ultra wide frequency band from 3 to 16 GHz. Prototypes of both proposed devices are fabricated and measured to provide an experimental verification on the concept and numerically predicted features.     

Copper-doped flower-like molybdenum disulfide/bismuth sulfide photocatalysts for enhanced solar water splitting

A facile synthesis approach to fabricate Cu-doped MoS₂/Bi₂S₃ (Cu-MoS₂/Bi₂S₃) photocatalysts is reported. The photocatalyst samples with varying amounts of Cu are applied in the photocatalytic splitting of water to produce H₂ under the irradiation of simulated solar light. The Cu-MoS₂/Bi₂S₃ photocatalysts with an optimum Cu loading of 20 mol% exhibited high photocatalytic performance, achieving a total H₂ yield of 32.4 μmol/h after 6 h of reaction. The photoactivity of the Cu-doped sample was shown to have risen more than 40% than that of pure MoS₂/Bi₂S₃. The improved performance is attributed to the impurity states generated within Cu-doped MoS₂, which serve as trapping sites for photogenerated electrons. The effective charge transfer mechanism achieved was evidenced by photoelectrochemical measurements. Based on the experimental results obtained, a plausible mechanism for the photocatalytic process associated with Cu-MoS₂/Bi₂S₃ was proposed.     

A first-principles investigation on mechanical and metallic properties of titanium carbides under pressure

The titanium carbides are potential candidates to achieve both high hardness and refractory property. We carried out a structural search for titanium carbides at three pressures of 0 GPa, 30 GPa and 50 GPa. A phase diagram of the Ti-C system at 0 K was obtained by elucidating formation enthalpies as a function of compositions, and their mechanical and metallic properties of titanium carbides were investigated systematically. We also discussed the relation of titanium concentration to the both mechanical and metallic properties of titanium carbides. It has been found that the average valence electron density and tractility improved at higher concentrations of titanium, while the degree of covalent bonding directionality decreased. To this effect, the hardness of titanium carbide decreases as the content of titanium increases. Our results indicated that the titanium content significantly affected the metallic properties of the Ti-C system.     

过渡圆角尺寸对错拐曲轴强度影响分析

利用有限元分析方法,研究探讨了错拐曲轴结构过渡圆角尺寸改变时轴颈圆角处应力变化规律,以某90°V6柴油机错拐曲轴为例,分别模拟5种不同结构方案在相同工况下轴颈过渡圆角处应力情况,并对薄弱部位进行疲劳强度分析、校核。其模拟结果表明:增大过渡圆角尺寸在不同程度上降低各轴颈过渡圆角处的应力峰值,并作为提高曲轴疲劳强度的一种有效手段,为错拐曲轴设计及结构优化提供参考。     

Dehydrogenation and hydrogenation characteristics of MgH2 with transition metal fluorides

The effect of transition metal fluorides on the dehydrogenation and hydrogenation of MgH₂ has been investigated. Many of the fluorides show a considerable catalytic effect on both the dehydrogenation temperature and hydrogenation kinetics of MgH₂. Among them, NbF₅ and TiF₃ most significantly enhance the hydrogenation kinetics of MgH₂. It is suggested that hydride phases formed by the reaction between MgH₂ and these transition metal fluorides during milling and/or hydrogenation play a key role in improving the hydrogenation kinetics of MgH₂.     

Fluid flow in micro-channels

We consider the problem of liquid and gas flow in micro-channels under conditions of a small Knudsen and Mach numbers, that correspond to continuum model. Data from the literature on pressure drop in circular, rectangle, triangular and trapezoidal micro-channels with hydrodynamic diameter ranging from 1.01 μm to 4010 μm are analyzed. The Reynolds number at transition from laminar to turbulent flow is considered. Attention is paid to comparison between predictions of the conventional theory and experimental data, obtained during the last decade, as well as to discussion of possible sources of unexpected effects which were revealed by a number of previous investigations.     

Controlled synthesis of Mn3O4/Co9S8–Ni3S2 on nickel foam as efficient electrocatalyst for oxygen evolution reaction

Advances in electrochemical interfaces have greatly facilitated the development of new energy systems that can replace traditional fossil fuels. Oxygen evolution reaction (OER) is the core reaction in the new energy conversion system to produce hydrogen. Here, nanorods structure of Mn₃O₄/Co₉S₈–Ni₃S₂/NF-4 was designed and assembled. The Mn₃O₄ has served as an appropriate matrix to build a composite structure with Co₉S₈–Ni₃S₂ to enhance the stability of catalyst. And the introduction of Mn regulated the electronic structure of Ni and Co, which increased the OER activity of matericals. Further characterization and electrochemical testing have suggested that between polymetallic can effectively optimize conductivity and enhance reaction kinetics. Mn₃O₄/Co₉S₈–Ni₃S₂/NF-4 can achieve overpotential of 188 mV at the current density of 10 mA cm^?2 in alkaline solution, with small Tafel slope of 43.2 mV dec^?1 and satisfactory stability of 30 h at 10 mA cm^?2. This work may show a feasible reference in the design of high-efficient OER catalysts.     

Sulfur vacancy and CdS phase transition synergistically boosting one-dimensional CdS/Cu2S/SiO2 hollow tube for photocatalytic hydrogen evolution

Constructing an efficient photoelectron transfer route to improve carrier separation efficiency is crucial for photocatalytic hydrogen evolution. In this work, CdS/Cu₂S/SiO₂ heterostructure with one-dimensional hollow tube morphology was designed by the solvothermal method using CuO/SiO₂ hollow tube as carrier. The hexagonal phase CdS and sulfur vacancies were adjusted simultaneously by the reduction strategy of NaBH₄ aqueous solution. CdS/CuS/SiO₂ with cubic phase CdS was synthesized in the absence of NaBH₄ aqueous solution. CdS/Cu₂S/SiO₂ was characterized by SEM, TEM, XRD, XPS, SPV and so on. The results showed that hexagonal CdS and sulfur vacancies benefited the separation of photo-generated carriers. As a consequence, the CdS/Cu₂S/SiO₂-10 composite exhibited a high photocatalytic hydrogen production rate (1196.98 μmol/g/h), and its performance almost 7.18 times than that of CdS/CuS/SiO₂. Moreover, CdS/Cu₂S/SiO₂-10 showed an excellent cyclic stability. This was attributed to the strong electron interaction of CdS/Cu₂S/SiO₂ heterostructure and the sulfur vacancy acted as an electron trap, enhancing the separation of photo-induced electrons and holes.     

Finite element method analysis of Fokker–Plank equation in stationary and evolutionary versions

The problems that often arise in stochastic dynamics can be investigated using the Fokker–Planck (FP) equation. The response of a such systems being subjected to additive and/or multiplicative random noise is represented by probability density function (PDF) that gives the full information about a response random character. Various analytic and semi-analytic solution methods have been developed for various systems to obtain results requested. However numerical approaches offer a powerful alternative. In particular the Finite Element Method (FEM) seems to be very effective. A couple of single dynamic linear/non-linear (Duffing and Van Der Pol type) systems under additive and multiplicative random excitations are discussed using FEM as a solution tool of the FP equation. The resulting PDFs are analyzed and if the analytic results exist mutually compared.     

The standard enthalpies of formation of some intermetallic compounds of early 4d and 5d transition metals by high temperature direct synthesis calorimetry

The standard enthalpies of formation of some intermetallic compounds of early 4d and 5d transition metals have been measured by high temperature direct synthesis calorimetry at 1373±2 K. The following results (in kJ/mol of atoms) are reported: ZrMn₂(−24.7±2.7); ZrMo₂(−5.8±5.3); Zr₁₁Os₄(−8.9±2.1); HfCr₂(−4.8±4.3); HfMn₂(−20.3±2.0); HfMo₂(−6.4±4.3); NbRh₃(−21.6±1.8); TaRh₃(−14.0±4.0).