[en] The vapor slope of temperature-entropy saturation boundary of working fluids has a significant effect on the efficiency and the safety of thermodynamic processes. Therefore, how to predict the vapor slope efficiently and quickly is worth studying. In this work, the vapor slope represented by the slope angle is firstly correlated with the reduced temperature, the molecular weight, 10 molecular groups and a topological index. The 10 molecular groups can cover most working fluids employed in thermodynamic cycles. The chosen topological index is able to distinguish all the isomers of working fluids. The relationship between the slope angle and these variables is established by an artificial neural network. A total of 4338 data points for 54 working fluids are used to create this network. These data are calculated from the highly accurate Helmholtz energy equation at the reduced temperature range of 0.6–1. The predicted results from molecular groups show a good agreement with desired slope angles. The average absolute deviations for training, validation and test sets are 0.68%, 0.64%, 0.68%, respectively. In the selection and design of working fluids, the established model can be easily employed to predict the saturated vapor slope only from the molecular structures. - Highlights: • The saturated vapor slope is represented by the slope angle. • The slope angle is firstly predicted from molecular groups. • The average absolute deviation of the established model is 0.67%.

[en] The effect of tungsten (W) content and grain boundary misorientation angle (GBMOA) on crack blunting of nanocrystalline Ni-W alloy (20–100 nm) is researched theoretically, considering the coupled effects of dislocations and grain boundaries (GBs). In our proposed model, W atoms are clustered in the dislocation free region (DFZ), impeding dislocation slip, and W additions lead to GB segregation so that the boundary energy is reduced. The dislocations emitted from the crack tip are stopped at or/and penetrated through GBs, which depends on the total force acting on the dislocations as well as the critical penetration stress. The critical penetration stress is bound up with GB energy and residual Burgers vector. The number of dislocations emitted from the crack tip and penetrated through GB is calculated by using W content and GBMOA. The results show that an increase in W content decreases the critical penetration stress and increases the number of dislocations emitted from the crack tip. The critical stress intensity factors by considering the interactions between dislocations and GBs are larger than those of dislocations stayed at GBs. It is demonstrated that crack blunting depends significantly on both W content and GBMOA.

[en] Using seismic geophones to get stratum information is a common method of petroleum geophysical exploration technology. Optical fibre distributed acoustic sensor (DAS) is one of the most advanced sound field detection technologies. It has most advantages of distributed continuous monitoring, such as deployment, high cost performance ratio, wide range measurement and so on. In this paper, a distributed acoustic sensing technology using interferometric demodulation is researched. Basic principal of the DAS, demodulation algorithm, and parameter test are introduced in detail. Ground geophysical prospecting test for petroleum is designed and carried out and a very clearly seismic section image is drawn out. DAS system performance and test data are discussed in detail. The research provides a new approach to petroleum geophysical prospecting using optical fiber sensor technology. Convenient, big coverage and large data make it potentially better suited for geophysical prospecting applications. (paper)

[en] The electronic structure, photocatalytic properties and mechanism of Cu₂O with different Co-doped concentrations in visible light region are studied by first-principles calculation. The results show that intrinsic Cu₂O shows semiconductor characteristics, and the Co doped Cu₂O with 4.17% and 8.33% doping concentrations show metallic properties. The light absorption of Cu₂O in the visible region increases with the Co doping, and the photocatalytic efficiency enhances with increasing doping concentration. By analyzing the density of states, it is found that the enhanced light absorption of the two doped systems in the visible range is mainly caused by the intraband transition of Co 3d state electrons. The results found an effective way to improve the photocatalytic efficiency of Cu₂O in the visible region and promote the application of Cu₂O in photocatalysis. (paper)

[en] Degradation mechanisms that caused by repetitive insertion and extraction of the lithium ion on the electrodes can lead to a grand challenge for optimizing the design of silicon (Si) based anode with high capacity and rate capacity. However, with decreasing the electrode size into nanometer scale, the surface-to-volume ratio will become very high, meaning that surface effect will have a significant role in determining the mechanical behavior of the electrode. And these effects suppress crack nucleation and propagation, which may become a resistance to brittle fracture. In our work, we establish a theoretical model to study the diffusion induced stress (DIS) evolution and firstly discuss the crack growth by using stress intensity factor (SIF) coupled with surface effects. The results show that DIS, especially the tensile stress, would decrease noticeably due to the surface mechanism. Surface cracks will propagate when SIF is larger than the fracture toughness of materials. It can also be revealed that smaller particles exhibit higher structural integrity. Significantly, the critical nanoparticle electrode size is arrived, below which the anode will not be broken and this value is in good agreement with experimental observations. Overall, the present work maybe provides physical underpinnings for optimized structural design to mitigate the mechanical degradation in high-performance anodes for Li-ion batteries.

[en] Solid-state magnetic refrigeration systems that operate near room temperature have been proposed and studied in recent years because of their potential to improve system performance. Most solid-state MR systems require a thermal switch to control the heat transport; however, the thermal switches proposed to date are of limited applicability because of their complicated structures, low thermal conductivity, low durability, and high cost. Therefore, this study investigated an alternative type of thermal switch that is much easier to implement in practical solid-state MR systems, and the performance of the proposed thermal switch was validated by numerical simulation. The results showed that the proposed thermal switch is effective in the solid-state magnetic refrigeration system. Moreover, increasing the number of unit elements effectively improves the system performance. For the solid-state magnetic refrigeration system with certain number of unit elements, the operating frequency can also be optimized to achieve the best performance. In addition, the system performance could be further improved by utilizing a magnetocaloric material with increased thermal conductivity.