Rectification effect: A universal strategy for single-atom electrocatalysts to enhance oxygen reduction reaction

The M-Nxsingle-atom catalysts (SACs) are critical for efficient energy conversion technologies. However, most SACs with M-Nxmoiety (M: Fe, Co, or/and Mn) suffer the strong binding ability with OH* intermediates in oxygen reduction reaction (ORR), which becomes a bottleneck in accelerating the kinetics. Herein, a universal "rectification effect" strategy is proposed by constructing a p-n junction, where an n-type ZnS semiconductor longitudinally bridges withp-type M-Nxmoiety to weaken the interaction of M-Nxwith OH*. As expected, the a- ZnS/Fe-NSC electrocatalyst exhibits remarkable intrinsic activity in alkaline media with a half-wave potential of 0.90 V vs. RHE, and long-term durability (a shift of only 10 mV in E1/2 after 8,000 cycles). This phenomenon can be ascribed to the optimization of electronic structure, the S-MN4 site can effectively activate the M centre with the intermediate spin state which possesses one eg electron (t2g4 eg1) readily penetrating the antibonding it-orbital of oxygen. Moreover, it offers a superior power density and higher discharge voltage in Al-air batteries. This universal strategy provides a rational perspective for the design of SACs and electronic structure engineering to construct robust active sites for high-performance oxygen reduction

面向冷气推力器的高分辨率低噪声微流量传感器设计与标定

微流量传感器用于精确测量和控制流经推力器的气体流量,其性能直接影响冷气推力器系统的整体表现.针对当前微流量传感器分辨率低、噪声大和响应时间慢的问题,研制了一种基于恒温差原理的MEMS微流量传感器系统.该传感器采用了4个MEMS铂电阻构成恒温差架构,通过高精度恒温差驱动电路实现温差恒定,经过测温电桥将温度变化信号经过高精度程控放大器输入到24位高精度模数转换器（ADC）进行采样,实现了低噪声和高精度的微流量信号采集.测试结果显示,该微流量传感器在0.05～1 Hz等效输出噪声小于0.126μL·s–1·Hz–1/2,分辨率达到0.06μL·s–1,量程为0～1000μL·s–1,响应时间为1.2 ms.其测量分辨率高、噪声低、响应速度快,为空间引力波探测中的冷气推力器系统提供了关键的技术支持

Investigation of a New Stacking Pattern of Laminates with Approximately Constant Bending Stiffness

To achieve laminates with constant bending stiffness to match the high precision requirement of optical systems made of carbon fiber reinforced plastic (CFRP), a new method, the normalized direction factor of bending stiffness (NDFBS), is proposed based on the normalized geometric factor of bending stiffness. Using NDFBS and its variance (VNDFBS), we investigate two common stacking patterns, I and II ([(theta(1))(m)/(theta(2))(m)/& mldr;/(theta(p))(m)](S) and [(theta(1)/theta(2)/& mldr;/theta(p))(m)](S)) and our proposed new stacking pattern, Pattern III ([(theta(1)/theta(2)/& mldr;/theta(p))(S)](m)) based on the initial quasi-isotropic laminates, [theta(1)/theta(2)/& mldr;/theta(p)]. The bending stiffness of the stacking sequence [(45/-45/0/90)(S)](2) tends to be more uniform than that of [45/-45/0/90](2S), and the order of uniformity in bending stiffness of other stacking sequences is [(60/0/-60)(S)](4) > [60/0/-60](4S) > [(60/0/-60)(S)](2) > [60/0/-60](2S). Both theoretical deviations and experimental observations confirm that as the cycle number m increased, the uniformity in bending stiffness is improved gradually, except for that of Pattern I. As the cycle number increased, the speed of Pattern III approaching the constant bending stiffness was faster than that of Patterns I and II. Notably, to achieve a nearly identical uniformity in bending stiffness, only the square root of the cycle number of Pattern II was enough for Pattern III. Based on the same initial laminate and cycle number, Pattern III exhibited more uniform bending stiffness and strength, which are appropriate for precision optical components that require dimensional stability, such as space mirrors

Influence of elastomer film thickness and particle size on laser-induced microparticle launch

Laser-induced microparticle impact testing (LIPIT) provides an effective experimental method for revealing the ultrahigh strain-rate dynamic response of materials by launching a single microparticle through laser-induced film expansion to impact a target material. Understanding the coupling effects of laser ablation and the dynamic responses of both the films and microparticles during the launch process in LIPIT is essential for achieving higher launch velocity of the microparticle. In this study, the influences of elastomer film thickness and microparticle diameter on the launch process are investigated by numerical simulations. The results show that the laser-induced plasma pressure experiences a sudden increase in the launch system with a thin or without elastomer film due to the inertial effect of microparticle and the reflection of laser-induced shock waves at the microparticle-film interface. As the elastomer film thickness increases, the onset time of the sudden increase in pressure delays and the amplitude of the peak pressure decreases. When the elastomer film thickness exceeds about 10 mu m, the influence of elastomer film thickness is negligible. Additionally, the microparticle launch velocity decreases with increasing elastomer film thickness. In a launch system without an elastomer film, increasing the microparticle diameter leads to a greater amplitude of the sudden increase in plasma pressure, resulting in a higher launch velocity. However, when the microparticle diameter exceeds 9.2 mu m, the launch velocity begins to decrease with increasing diameter. This study discloses the coupling effects during the microparticle launch process in LIPIT and provides insights into experimental design and optimization of the LIPIT system. (c) 2025 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution-NonCommercial 4.0International (CC BY-NC) license (https://creativecommons.org/licenses/by-nc/4.0/).</p

Self-organization of multiple shear bands in CoCrNi chemically complex medium entropy alloys

Complex concentrated alloys (CCAs), also known as medium/high entropy alloys (M/HEAs), possess a multitude of outstanding properties attributing to their distinctive chemically disor&shy; dered structure, which endows them with broad application prospects in many engineering fields. As a fundamental and ubiquitous non-equilibrium phenomenon, shear localization has received significant attention during past several decades. However, the collective behavior of multiple shear bands in CCAs or M/HEAs has not been comprehensively elucidated. Here, we tackle this problem in CoCrNi medium entropy alloy by thick-walled cylinders technology. Via the experi&shy; mental design, the specimens subjected to diverse deformations were effectively &quot;frozen&quot;, thereby facilitating the acquisition of the self-organization characteristics of multiple shear bands in distinct evolution stages. A notable scaling law of multiple shear band spacing was identified. To uncover the underlying physical mechanism of the scaling law, a multiple shear band energy dissipation evolution dynamics model was formulated. Subsequently, a competing map of shear band nucleation and growth was established. It is found that the coordinated propagation of stacking faults and twins may trigger the transformation from the face-centered cubic structure to the hexagonal close-packed structure and even amorphization in late stage of shear band growth. The amorphization regions possess a high probability of serving as nucleation sites with a pro&shy; pensity for void formation. Eventually, with the progression of void evolution, fracture occurs.</p

基于聚焦激光差分干涉(FLDI)技术的高超声速风洞来流扰动特征实验研究

风洞来流扰动是影响边界层转捩的关键因素之一.文章搭建并标定了一套对密度扰动敏感的非介入式聚焦激光差分干涉仪测量系统(focused laser differential interferometry, FLDI),对中国科学院力学研究所的JF8 A风洞开展了风洞来流扰动环境特征的实验研究.实验选取不同马赫数以及不同单位雷诺数的来流条件,通过FLDI的密度脉动测量,得到了较大尺寸激波风洞中自由来流扰动的规律.实验结果表明:在同一马赫数下,随着单位雷诺数的增加,密度脉动幅值逐渐上升,但归一化幅值逐渐下降;在同一单位雷诺数下,马赫数高的状态自由流滚降斜率更加平缓,这表明更多能量保留在更高频段.随着单位雷诺数的升高,密度脉动的归一化均方根值降低,该特征与典型的高超声速噪声风洞的皮托总压扰动水平随雷诺数变化的趋势相同.此外,短时功率谱密度(PSD)分析显示,随着单位雷诺数增加,自由流干扰环境的间歇性降低.本研究为高超声速风洞边界层转捩研究提供了重要的实验数据支撑

A spatio-temporal fusion method for non-destructive testing using infrared thermography

The infrared thermography, as a non-contact and highly sensitive non-destructive testing (NDT) method, has been extensively applied in various fields such as aerospace, construction, and industrial manufacturing industry. Current post-processing of dynamic thermal sequences relies mainly on thermal images' spatial information without incorporating temporal data, compromising defect detection accuracy and efficiency. To address this challenge, we propose a spatio-temporal fusion thermography (STFT) method that enables high-precision of surface defects detection. The method primarily establishes a theoretical model by integrating spatial and temporal gradient information from dynamic thermal sequences, with thermal propagation being estimated using optical flow method. The verification experiment on metal surface defects indicates that the STFT method is capable of reliably detecting surface microcracks as small as 3 mu m in width. And it can effectively eliminate the impact of uneven temperature distribution on the test specimens and significantly improves the signal-to-noise ratio (SNR) of the defect images. The proposed method holds great potential for broad application in the field of industrial non-destructive testing, such as detecting surface or near surfac cracks and pitting defects in gears

Instability in centrifugally stable shear flows

We investigate the linear instability of flows that are stable according to Rayleigh's criterion for rotating fluids. Using Taylor-Couette flow as a primary test case, we develop large-Reynolds-number-matched asymptotic expansion theories. Our theoretical results not only aid in detecting instabilities previously reported by Deguchi (Phys. Rev. E, vol 95, 2017, p. 021102(R)) across a wide parameter range, but also clarify the physical mechanisms behind this counterintuitive phenomenon. Instability arises from the interaction between large-scale inviscid vortices and the viscous flow structure near the wall, which is analogous to Tollmien-Schlichting waves. Furthermore, our asymptotic theories and numerical computations reveal that similar instability mechanisms occur in boundary layer flows over convex walls

Hierarchical heterogeneous microstructure for enhanced wear resistance of CoCrFeMnNi high-entropy alloy coatings via in-situ rolling assisted laser cladding

Heterogeneous high-entropy alloys (HEAs) are promising materials due to their excellent mechanical properties. In this study, hierarchical heterostructures were introduced into CoCrFeMnNi HEA via an in-situ rolling (ISR) assisted laser cladding (LC) process. The microstructural evolution and tribological behavior of the ISR-assisted LC coating were investigated. Results indicate that porosity and surface roughness are significantly reduced, as the plastic flow during ISR-assisted LC closes pore and fills the surface valley. ISR induces a gradient distribution of dislocation density and grain size along the depth direction, and the thermal effect of subsequent laser track deposition leads to a tilted-strip distribution of grain size and geometrically necessary dislocations (GNDs) along the overlapping direction. During ISR-assisted LC process, the combined effects of deformation and recrystallization reduce the average grain size from 93.84 mu m to 32.47 mu m, decrease the texture intensity from 9.83 to 4.23, and extend the strain depth to 950 mu m. The reduction in porosity, increase in microhardness, and hierarchical heterostructure strengthening collectively enhance the wear resistance of the ISR-assisted LC coating. The volume wear rate reduces significantly from 1.740 x 10-4 mm3 center dot N- 1 center dot m- 1 to 0.133 x 10-4 mm3 center dot N- 1 center dot m- 1. This study provides a novel approach for the design of wear-resistant HEA coatings

Hierarchical heterogeneous microstructure for enhanced wear resistance of CoCrFeMnNi high-entropy alloy coatings via in-situ rolling assisted laser cladding

Heterogeneous high-entropy alloys (HEAs) are promising materials due to their excellent mechanical properties. In this study, hierarchical heterostructures were introduced into CoCrFeMnNi HEA via an in-situ rolling (ISR) assisted laser cladding (LC) process. The microstructural evolution and tribological behavior of the ISR-assisted LC coating were investigated. Results indicate that porosity and surface roughness are significantly reduced, as the plastic flow during ISR-assisted LC closes pore and fills the surface valley. ISR induces a gradient distribution of dislocation density and grain size along the depth direction, and the thermal effect of subsequent laser track deposition leads to a tilted-strip distribution of grain size and geometrically necessary dislocations (GNDs) along the overlapping direction. During ISR-assisted LC process, the combined effects of deformation and recrystallization reduce the average grain size from 93.84 mu m to 32.47 mu m, decrease the texture intensity from 9.83 to 4.23, and extend the strain depth to 950 mu m. The reduction in porosity, increase in microhardness, and hierarchical heterostructure strengthening collectively enhance the wear resistance of the ISR-assisted LC coating. The volume wear rate reduces significantly from 1.740 x 10-4 mm3 center dot N- 1 center dot m- 1 to 0.133 x 10-4 mm3 center dot N- 1 center dot m- 1. This study provides a novel approach for the design of wear-resistant HEA coatings