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[Objective] The construction of new energy demonstration cities is an important measure to achieve sustainable and high-quality development in China, and a comprehensive and objective evaluation of its impact on green and low-carbon development performance is crucial for the further promotion of new energy pilot cities. [Methods] Based on the panel data of 282 prefecture-level cities in China from 2006 to 2019, this study analyzed whether the construction of new energy demonstration cities has achieved green and low-carbon development by using the propensity score matching and difference-in-differences methods. [Results] The findings are as follows: (1) The construction of new energy demonstration cities significantly improved the level of green and low-carbon development. (2) Further mechanism test found that the new energy demonstration city policy promoted the green and low-carbon development of pilot cities through fiscal subsidies and financial support, forcing industrial enterprises to transform and upgrade green, but the policy has not significantly promoted green technology innovation. (3) The new energy demonstration city policy had a heterogeneous impact in different regions. The green and low-carbon development level of the western pilot cities has been significantly improved, while the policy effect of the eastern and central pilot cities was not significant; and the new energy demonstration city policy had a positive effect on the green and low-carbon development of resource-based cities, while the policy effect of non-resource-based cities was not obvious. [Conclusion] This paper argues that China should further promote green technology innovation, moderately increase the level of fiscal subsidies and financial support at an appropriate time, and force industrial enterprises to transform and upgrade green, promote the green and low-carbon development of pilot cities, which will have a positive demonstration effect on driving the green and low-carbon development of cities across the country.

42CrMo is an ultra-high-strength, low-alloy structural steel. To enhance its surface wear resistance and prolong the service life of components, surface strengthening techniques are commonly applied. In this study, a numerical model for the laser phase transformation hardening of 42CrMo was established. The temperature field and metallurgical transformations during the laser phase transformation hardening process were investigated through numerical simulation, and the morphology of the hardened layer after laser surface treatment was predicted. The effects of key process parameters on the temperature field and the characteristics of the hardened layer were identified. The optimal parameters for single-pass laser phase transformation hardening were found to be a laser power of 1200 W, a scanning speed of 20 mm/s, and a spot diameter of 6 mm. The accuracy of the simulation results was validated through laser phase transformation hardening experiments. The results indicate that under these optimal conditions—laser power of 1200 W and a scanning speed of 20 mm/s—the hardening effect is maximized. The surface hardness reaches a maximum of 782 HV0.2, with a cross-sectional hardness peaking at 875 HV0.2, which is three to four times higher than the base material's hardness, with an average surface hardness of 745 HV0.2. [ABSTRACT FROM AUTHOR]

Non-immersed cavitation jets represent an advanced surface treatment technology, characterized by their ability to generate cavitation in an air environment. Owing to their simple structure, these jets have found widespread application. In this study, both numerical and experimental investigations of non-immersed cavitation jets, incorporating fluid–solid coupling, are conducted. The microforming effects on T2 copper foils, induced by non-immersed cavitation jets, are analyzed by comparing simulation results with the experimental data, thereby validating the efficacy of this technique in foil microforming. Additionally, the flow field characteristics of the non-immersed cavitation jet are examined, focusing on the transient distributions of velocity, vortex structures, cavitation bubbles, and pressure at various dimensionless impact distances. The findings confirm that non-immersed cavitation jets are effective for microforming T2 copper foils, with an optimal dimensionless impact distance of 40 under the specified process parameters. The study also reveals that the non-immersed cavitation jet flow is inherently unstable, with the impact distance significantly influencing the evolution of vortex structures and cavitation bubbles. This research offers critical insights into the physical mechanisms underlying non-immersed cavitation jet microforming and provides both a theoretical foundation and experimental guidance for optimizing jet parameters to enhance microforming precision in future applications. [ABSTRACT FROM AUTHOR]

To demonstrate the effect of body posture on the occupant dynamic response under a spacecraft high-level re-entry acceleration overload, seat-dummy system models with typical body positions, including supine and lying positions, are established in this study using Pro-E and HyperWorks software. A Human Model for Safety (HUMOS version II) dummy was used in the model. Seat-dummy system models were calibrated and validated according to actual centrifugal test data. The effect of body posture on the overload response of key body organs, including the heart, lung, diaphragm, liver, and abdominal viscera are demonstrated and analyzed under a high-level acceleration overload (a peak value of 6.4 g as input). Simulation results show that the displacement and deformation of the diaphragm are the most important factors affecting human tolerance to re-entry overload. The acting force of the diaphragm from other organs' inertial reaction in supine position is larger than that in the lying position. Therefore, spacecraft designers should focus more on the mechanical status of human internal organs and provide a body posture for better protection of the crew during spacecraft re-entry. [ABSTRACT FROM AUTHOR]

TC4 titanium alloy is widely used in aerospace, petrochemical, pharmaceutical and other fields, which accounts for about 60% of the current titanium alloy products. Water Cavitation Peening (WCP) is a new material surface modification process and has great development potential. The improvement of the water cavitation peening is severely limited by the correlation and coupling between process parameters. Therefore, the influence law of each process parameter is the key problem that needs to be resolved. TC4 titanium alloy as research object is took and four main process parameters of WCP under four working conditions is construct (four factors and four levels orthogonal). The influence of process parameters on three evaluation indexes is studied, such as the surface residual stress, the surface roughness and the microhardness. Then, the fuzzy mathematics comprehensive evaluation is used to optimize. Results show that the peening time has the greatest influence on strengthening effect and the nozzle diameter has the least. The optimized combination is that the nozzle diameter is 1.4 mm, the incident pressure is 40 MPa, the dimensionless target distance is 72.5 and peening time is 27.5 min. The corresponding surface residual stress, the surface roughness and the microhardness can reach −612 MPa, 0.76 μm, and 405 HV respectively. [ABSTRACT FROM AUTHOR]

An in-depth study of friction and wear requires analysis of the surface morphologies and contact status of friction pairs in mechanical systems. The bearing area curve is introduced for the calculation of wear, and combined with the concept of repositioning. The application of fast calculation of wear amount and improved three-dimensional characterization of a bearing area curve is achieved by this new method. The best roughness surface is used as the target surface to extract the target bearing area curve. The influence of microtexture parameters on the bearing area curve is studied to determine the optimal microtexture parameters. The test results show that a matching texture surface has a short run-in time and the lowest friction coefficient after stabilization among the surfaces studied herein, and the presence of a texture changes the wear mechanism from the original adhesive wear to abrasive wear and improves the tribological performance. The best texture parameters and laser process parameters are determined, which provide new ideas for the optimal design of surface topography. [ABSTRACT FROM AUTHOR]

A novel interface strengthening and toughening method of Steel/PEEK joints was proposed in this article. The multi-scale combined features consisting of macro grooves and micro conical hole array were constructed on the steel sheet surface. The shearing fracture behavior of the Steel/PEEK joints was studied to reveal the influence law and mechanism of the diameter-to-depth ratio γ of micro conical holes on the infiltration effect of molten PEEK, the maximum shear force and the energy absorption property. Results indicated that the Steel/PEEK joints with different multi-scale combined features possessed great infiltration effect and achieved a much larger maximum shear force than the joints without multi-scale combined feature (the largest improvement was approximately 360% when the γ of micro conical hole was 1.5). The joints also underwent a typical three-stage failure process. As the γ of the micro conical holes decreased, the maximum shear force almost increased linearly and the absorbed energy increased exponentially. The load-carrying capacity and energy absorption property of the steel/30% short carbon fiber-reinforced PEEK joint did not improve considerably as desired owing to the non-ideal infiltration effect. [ABSTRACT FROM AUTHOR]

Micro-feature arrays and large-area complex microscopic features on thin metallic sheet play an important role in micro-components. A novel technique-submerged water-jet cavitation shocking-is presented to generate micro-feature arrays on 304 stainless foils in this paper. High-speed camera shadowgraph images of the cavitation cloud were employed to analyze the impact zone. Then the forming depth, uniformity of forming depth and the thickness distribution of the micro-feature arrays were also studied. The results show that the forming region can be categorized into the jet-impact-zone, the bubble-impact-zone and the periphery-impact-zone radially. Bubble-impact-zone peaks in the depth of array micro-forming. The forming depth increases with time while the uniformity decreases with time. The forming parts have a uniform thickness distribution. [ABSTRACT FROM AUTHOR]