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The analysis of chemical states and morphology in nanomaterials is central to many areas of science. We address this need with an ultrahigh-resolution scanning transmission soft x-ray microscope. Our instrument provides multiple analysis tools in a compact assembly and can achieve few-nanometer spatial resolution and high chemical sensitivity via x-ray ptychography and conventional scanning microscopy. A novel scanning mechanism, coupled to advanced x-ray detectors, a high-brightness x-ray source, and high-performance computing for analysis provide a revolutionary step forward in terms of imaging speed and resolution. We present x-ray microscopy with 8-nm full-period spatial resolution and use this capability in conjunction with operando sample environments and cryogenic imaging, which are now routinely available. Our multimodal approach will find wide use across many fields of science and facilitate correlative analysis of materials with other types of probes.

Experiments have shown that precipitation can affect the mechanical properties of zirconium alloy, but the interaction mechanism between dislocations and Nb precipitates in zirconium alloys is still unclear. Thus, a systematic molecular dynamics study was performed to investigate the interaction between edge dislocations and Nb precipitates. It was found that the dislocation passed through Nb precipitate by shear mechanism or bypass mechanism of forming jogs, and the critical resolved shear stress increased with the diameter of the precipitate. After completion of the interaction, dislocations formed jogs due to climb when the precipitates were larger than 2 or 3 nm. Some atoms in the precipitate were more disordered after dislocation shearing, and dislocation fragments were generated around the precipitate, both of which lead to the precipitate hardening. The calculation of obstacle strength further confirmed that unsheared Nb precipitates until hundreds of nanometers were the weak obstacle for dislocations. [ABSTRACT FROM AUTHOR]

With its excellent strength and toughness, ductile iron is widely utilized in marine applications, including ship propellers, rudders, ship cabin pumps, valves, and pipes. Laser cladding is an emerging environmentally-friendly surface-strengthening technology. Numerous corrosion pits on the cladding layer surface accelerate the corrosion failure process. It is of great significance to quantitatively reveal the evolution of microscopic corrosion transients on the cladding layer and to analyze the interaction mechanism between adjacent corrosion pits. In this article, a cladding layer of IN625 was prepared on the surface of QT600 ductile iron. The microscopic morphology and Energy Dispersive Spectroscopy (EDS) were used to observe the cladding layer. The relationship among ion concentration, ion migration, pH, electrode potential and corrosion rate was analyzed by numerical simulation. Electrochemical corrosion experiments were conducted using the CorrTest electrochemical workstation. The results show that the IN625 cladding layer can effectively improve the corrosion resistance of QT600 ductile iron. The polarization curves show that the corrosion current density decreases by two orders of magnitude, and the corrosion rate decreases by 395.5 times after laser cladding. This study can provide new ideas and methods to enhance the service performance enhancement of ductile iron laser cladding layers in marine environments. [ABSTRACT FROM AUTHOR]

Drawing on the code theory of Basil Bernstein, this study set out to examine how primary school teachers operationalize and experience their teaching practice with respect to the weak framing that may underpin teacher-pupil interaction, and how this practice is regulated by certain variables. Questionnaires were completed by 2,238 primary school teachers in China. The findings revealed that the teachers performed weak framing mainly through an invisible pedagogy in interactions with students, which was significantly affected by an interplay between student-based authority, students' linguistic codes and use of textbooks. An elaborated code generates two crucial advantages: it reduces the impact of the constraints of textbooks and traditional pedagogy on student-based teacher authority, and facilitates the teachers in implementing weak framing. Therefore, providing scaffolding resources to underachieving students to assist them in acquiring an elaborated code could be the key to ameliorating the phenomenon of cultural reproduction.

Interaction between turbulence and an airfoil is a significant aerodynamic noise source for many engineering applications when turbulence in the wake of upstream blades interacts with the leading edge of downstream blades. Modeling the oncoming turbulence as harmonic gusts is a common approach to study the noise generated by turbulence–airfoil interaction. In former studies, it has been found that the sound reduces with the increase in airfoil thickness. However, this is not always true for high-reduced frequency cases. This paper studies airfoil thickness effects using a computational aeroacoustics approach based on the spectral/hp element method. It is found that the sound pressure decreases with the increase in thickness for low-reduced frequency gusts. However, the sound pressure increases in the upstream direction and declines downstream with the increase in thickness for high-reduced frequency cases. To reveal its mechanism, a semi-analytical method and the convective Ffowcs Williams–Hawkings equation are used for low- and high-reduced frequency, respectively, to analyze the radiated noise. For low-reduced frequency cases, the sound reduction due to thickness is caused by the decrease in amplitude in the leading edge region and the increase in phase difference along the airfoil. For high-reduced frequency cases, the phase difference in the upstream observer is much more significant than the downstream observer's due to the convective effect. The increase in phase difference results in a cancellation effect, which leads to a different behavior upstream. [ABSTRACT FROM AUTHOR]

Although the rapid expansion of urban rail transit offers convenience to citizens, the issue of subway vibration cannot be overlooked. This study investigates the spatial distribution characteristics of vibration in the Fayuan Temple historic and cultural reserve. It involves using a V001 magnetoelectric acceleration sensor capable of monitoring low amplitudes with a sensitivity of 0.298 V/(m/s2), a measuring range of up to 20 m/s2, and a frequency range span from 0.5 to 100 Hz for in situ testing, analyzing the law of vibration propagation in this area, evaluating the impact on buildings, and determining the vibration reduction scheme. The reserve is divided into three zones based on the vertical vibration level measured during the in situ test as follows: severely excessive, generally excessive, and non-excessive vibration. Furthermore, the research develops a dynamic coupling model of vehicle–track–tunnel–stratum–structure to verify the damping effect of the wire spring floating plate track and periodic pile row. It compares the characteristics of three vibration reduction schemes, namely, internal vibration reduction reconstruction, periodic pile row, and anti-vibration reinforcement or reconstruction of buildings, proposing a comprehensive solution. Considering the construction conditions, difficulty, cost, and other factors, a periodic pile row is recommended as the primary treatment measure. If necessary, anti-vibration reinforcement or reconstruction of buildings can serve as supplemental measures. [ABSTRACT FROM AUTHOR]

Atomically precise Au nanoclusters (NCs) with discrete energy levels can be used as photosensitizers for CO2 reduction. However, tight ligand capping of Au NCs hinders CO2 adsorption on its active sites. Here, a new hybrid material is obtained by anchoring of thiol functionalized terpyridine metal complexes (metal=Ru, Ni, Fe, Co) on Au NCs by ligand exchange reactions (LERs). The anchoring of Ru and Ni complexes on Au25 NC (Au25−Ru and Au25−Ni) leads to adequate CO2 to CO conversion for photocoupled electrocatalytic CO2 reduction (PECR) in terms of high selectivity, with Faradaic efficiency of CO (FECO) exceeding 90 % in a wide potential range, remarkable activity (CO production rate up to two times higher than that for pristine Au25PET18) and extremely large turnover frequencies (TOFs, 63012 h−1 at −0.97 V for Au25−Ru and 69989 h−1 at −1.07 V vs. RHE for Au25−Ni). Moreover, PECR stability test indicates the excellent long‐term stability of the modified NCs in contrast with pristine Au NCs. The present approach offers a novel strategy to enhance PECR activity and selectivity, as well as to improve the stability of Au NCs under light illumination, which paves the way for highly active and stable Au NCs catalysts. [ABSTRACT FROM AUTHOR]