Engineering Substrate Interactions for High Luminescence Efficiency of Transition‐Metal Dichalcogenide Monolayers

It is demonstrated that the luminescence efficiency of monolayers composed of MoS₂, WS₂, and WSe₂ is significantly limited by the substrate and can be improved by orders of magnitude through substrate engineering. The substrate affects the efficiency mainly through doping the monolayers and facilitating defect‐assisted nonradiative exciton recombinations, while the other substrate effects including straining and dielectric screening play minor roles. The doping may come from the substrate and substrate‐borne water moisture, the latter of which is much stronger than the former for MoS₂ and WS₂ but negligible for WSe₂. Using proper substrates such as mica or hexagonal boron nitride can substantially mitigate the doping effect. The defect‐assisted recombination depends on the interaction between the defect in the monolayer and the substrate. Suspended monolayers, in which the substrate effects are eliminated, may have efficiency up to 40% at room temperatures. The result provides useful guidance for the rational design of atomic‐scale light emission devices.     

Impact of slide diamond burnishing additional parameters on fatigue behaviour of 2024‐T3 Al alloy

One of the methods for increasing fatigue life of symmetric rotary metal components is slide diamond burnishing (SDB). This method is implemented on conventional and computer numerical control machine tools by means of simple equipment, which is its main advantage. The SDB basic parameters are diamond insert radius, burnishing force, feed rate, and burnishing velocity. The additional ones are number of passes, working scheme, and lubrication conditions. The effect of SDB additional parameters on the fatigue behaviour of 2024‐T3 Al alloy was experimentally studied. Groups of smooth and notched hourglass‐shaped specimens were slide burnished using different combinations of additional SDB parameters and then were subjected to bending fatigue tests. The residual stresses, introduced by SDB, were measured by X‐ray diffraction technique. The near‐surface microstructure of the slide‐burnished specimens was investigated. Based on the results obtained, it was established that SDB produces two main effects, which depend on SDB additional parameters. The essence of the macroeffect is creation of residual compressive stresses in the superficial and subsurface layers. This stresses retard the formation and growth of fatigue macrocracks and thus increase the lifetime of slide‐burnished components. The microeffect is expressed in modifying the microstructure of the surface and subsurface layers, correspondingly, refining the grain and homogenizing and reducing the pores in the material. Such microstructure is characterized by increased plasticity and fatigue crack resistance. The fatigue life depends on the combination of these two effects. Thus, the desired fatigue behaviour of the slide‐burnished component can be ensured through an appropriate selection of the governing additional SDB parameters.     

Numerical evaluation on single-row trenched-hole film cooling performances on turbine guide vane under engine-representative conditions

A numerical investigation is performed to study the effects of transverse trenches on the film cooling performances of single row film cooling holes on the turbine guide vane, under the engine-representative conditions. Two trenches are investigated in the current study, including a conventional straight trench and a novel serrated trench, both having the same slot width of 2.5d and depth of 0.75d. With the presence of trenches, the kidney vortices are effectively destroyed at the suction side, replaced by a pair of secondary vortices originating from the edge of trench slot, with a sense of rotation opposite to the kidney-vortex pair. However, at the pressure side, the kidney vortices remain clearly in the trenched-hole cases. The roles of trenched-hole on the film cooling enhancement behave more pronounced on the pressure surface when compared to the respective one on the suction surface. On the pressure surface, the serrated trench displays a more obvious role in the film cooling enhancement when compared to the straight trench. Combined with the effects of trenched-hole on the enthalpy loss coefficient, it is suggested that the trenches are more reasonably used on the pressure surface.     

宽带低频放大器的设计

文中讨论了宽带低频放大器的设计。宽带网络采用有源低通滤波器和有源高通滤波器组合而成。在电路设计中,有源滤波电路和放大电路采用同一放大模块,这样简化了电路,缩小了体积,提高了产品的可靠性。通过分析低通滤波器和高通滤波器的设计过程,给出了试验数据、滤波器波形和宽带低频放大器电路图,再经过调整得到较好的通频带波形。该放大器在10～85kHz这个范围内,有较好的增益平坦度和稳定的性能,电压增益为60dB,满足设计要求。     

Friction and wear properties of cu and fe-based P/M bearing materials

The performances of porous bearings under different operating conditions were experimentally investigated in this study. Material groups studied are 90%Cu+10%Sn bronze and 1%C + % balance Fe iron-based self-lubricating P/M bearings at constant (85%) density. In the experiments, the variation of the coefficient of friction and wear ratio of those two different group materials for different sliding speeds, loads, and temperatures were investigated. As a result, the variation of the friction coefficient - temperature for both constant load, and constant sliding speed, friction coefficient - average bearing pressure, PV - wear loss and temperature-wear loss curves were plotted and compared with each other for two materials, separately. The test results showed that Cu-based bearings have better friction and wear properties than Fe-based bearings.     

高等级施工控制测量与精度分析

文章以东坪水利站工程为例，阐述了在地形复杂务件下，利用精密经纬仪、测距仪、水准仪进行二等施工控制网测量，及施工控制网的数据处理、测边网与边角网的精度比较。     

Investigation of the most suitable location of insulation applying on building roof from maximum load levelling point of view

In this study, the maximum load levelling of periodic heat flux entering a room through a composite roof consisting of different insulation layer has been evaluated for different insulation positions in the roof. A numerical model based on implicit finite difference scheme was applied for 12 different roof configurations during typical winter and summer days. For this purpose, total insulation thickness was kept constant and insulation was placed as equally two pieces and as equally three pieces in different locations within the roof thickness. Then, insulation layers were moved 1 cm at a time across the roof thickness for 12 different configurations. Maximum and minimum values of periodic heat fluxes for each sweeping process in the roof were calculated for achieving the maximum levelling of the heat flux entering through the roof. It was found that the best load levelling was achieved in the case where three pieces insulation of equal thickness were placed one at the outdoor surface of the roof, the second piece of insulation was placed in the middle of the roof and third piece of insulation was placed at the indoor surface of the roof.