In-situ investigation of crystallization and structural evolution of a metallic glass in three dimensions at nano-scale

The crystallization behaviour of metallic glasses (MGs) has been investigated since the discovery of these important functional materials in order to optimize their synthesis procedures and improve their performances. Methods including powder X-ray diffraction and transmission electron microscopy are usually combined to characterize the crystalline structure in these “amorphous” materials. Until now, these methods, however, have failed to show the crystallization of individual crystals in three dimensions. In this work, in-situ Bragg coherent X-ray diffraction imaging (BCDI) reveals the growth and the strain variation of individual crystals in the Fe-based MGs during annealing. There is preferential growth along the surface of the MG sample particles during the crystal formation and fractal structure formation around the developing crystal surfaces; there is also strain relaxation happening from the inner parts to the surfaces of the developing crystals while cooling. The work leads to propose that during the crystallization of Fe-based MGs, the growth of the individual crystals follows a two-step procedure; and at higher temperature after the first crystallization period of the Fe-based MGs, the crystallization of α-Fe could be a competitive process between the growth of α-Fe crystals and the erosion from other elements

Study on strengthening mechanism of Ti/Cu electron beam welding

Welding-brazing method is widely used for dissimilar metals welding. However, it is becoming increasingly difficult to further improve the connection strength by controlling the formation of the transition layer. In this study, an innovative welding method referred to as adjacent welding was addressed, which greatly improved the tensile strength of Ti/Cu dissimilar joint. The strength of new joint could reach up to 89% that of copper base metal, compared to the use of a traditional welding-brazing method which strength coefficient is within the limit of 70%. In order to determine the strengthening mechanism of adjacent welding, optical microscopy, SEM, EDS and XRD were applied for the analysis of microstructure and phase structure. Furthermore, tensile strength was also tested. The results show that due to the process of remelting and reverse solidification of intermetallic compounds (IMCs) layer, a less complex and thinner IMCs layer was formed and TiCu (553 HV) with high embrittlement existing in the front of titanium substrate was changed into Ti2Cu (442 HV). Performances of joints were optimized by these changes. An interpretation module was presented for the mechanism

基于最優電壓矢量的有源濾波器電流控制新方法

A novel hysteresis current control method for active power filter based on optimal voltage vector is suggested. The method jointly utilizes two sets of phase current difference comparators to determine the locations of the reference voltage vector and the current error vector. When the system reference voltage vector is changing rapidly and randomly which makes it difficult to estimate its location, the new method can fast detect its correct position by a single try-and-error process which is essential to the performance of active power filter. The related concept and formulation are presented. Computer simulation is conducted on a testing system and the results show that the method can fast determine optimal voltage vector, therefore effectively reduce current tracking error, and in the meanwhile apparently reduce switching frequency of voltage source inverter (VSI) and hence improve efficiency of active power filter noticeably. 提出了一種新的基于最優電壓矢量的有源濾波器滯環電流控制方法。該方法的特點是用一組滯環相間電流比較器和一組階梯式相間電流比較器相結合，快速、正確地判斷有源濾波器參考電壓空間矢量所在的區域，并由此決定最優電壓矢量及對有源濾波器實行滯環電流控制。用電磁暫態程序進行的計算機仿真結果表明，該方法能快速、正確地確定最優電壓矢量，從而可有效地降低開關頻率和提高有源濾波器的效率。其突出優點是在參考電壓空間矢量變化較快且難以預測的情況下，仍能快速跟蹤及確定其所在的區域，從而可有效地減少電流補償誤差，改善有源濾波器的性能

Investigating the effects of steel slag powder on the properties of self-compacting concrete with recycled aggregates

This study introduced both steel slag and recycled aggregate aiming to improve the sustainability performance of self-compacting concrete (SCC). Study focused on investigating the effects of steel slag powder on the properties of self-compacting concrete with recycled aggregate (SCRAC)

Semiparametric regression analysis for composite endpoints subject to componentwise censoring

Composite endpoints with censored data are commonly used as study outcomes in clinical trials. For example, progression-free survival is a widely used composite endpoint, with disease progression and death as the two components. Progression-free survival time is often defined as the time from randomization to the earlier occurrence of disease progression or death from any cause. The censoring times of the two components could be different for patients not experiencing the endpoint event. Conventional approaches, such as taking the minimum of the censoring times of the two components as the censoring time for progression-free survival time, may suffer from efficiency loss and could produce biased estimates of the treatment effect. We propose a new likelihood-based approach that decomposes the endpoints and models both the progression-free survival time and the time from disease progression to death. The censoring times for different components are distinguished. The approach makes full use of available information and provides a direct and improved estimate of the treatment effect on progression-free survival time. Simulations demonstrate that the proposed method outperforms several other approaches and is robust against various model misspecifications. An application to a prostate cancer clinical trial is provided

Performance comparison of language models for information retrieval

Vector Space Model (VSM), Statistical Language Model (SLM) and Inference Network are three distinguished language models. Instead of evaluating their performance directly, we estimate the information strategies founded on them using the known measures: precision and recall. What's more, we proposed the Sort Order Rationality (SOR) to make further performance comparison among different language models. All models are tested on a standard testing collection. Three important conclusions are attained: (1). The IR model combining the statistical language modeling and inference network approaches is better than that only founded on statistical language modeling approach. What's more, it is also better than that based on vector space modeling approach. (2). The performance of IR model based on VSM is similar to that based on SLM. (3). The Dirichlet priors method often is a better option to smooth a statistical language model. In some respects, these conclusions provide some experimental bases for constructing an efficient information retrieval system

Nucleation of fractal nanocrystallites upon annealing of Fe-based metallic glass

Bragg coherent X-ray diffraction imaging has been used to determine the structure of the initial clusters of α-Fe nano crystals which form upon annealing of an iron-based amorphous alloy or metallic glass. The method is able to identify the shapes and strain of these crystallites without any need for cutting the sample, so can visualize them in three dimensions in their intact state. In this way, the delicate dendritic structures on the exterior of the crystallites can be seen and its density versus radius relationship identifies a fractal dimension of the porous region that is consistent with diffusion-limited aggregation models. The crystal sizes were found to be around 60 nm after annealing at 700 °C growing to about 330 nm after annealing at 750 °C. This article introduces the BCDI method and describes its application to characterize previously recrystallized samples of iron-based amorphous alloys. It paves the way for a possible future in situ nucleation/growth investigation of the relationship between kinetics and nanostructure of metallic glass

Effects of climate change on the potential distribution of the threatened relict Dipentodon sinicus of subtropical forests in East Asia: Recommendations for management and conservation

Dipentodon sinicus Dunn. (Dipentodonaceae) is a rare and threatened relict plant species usually found co-dominating with other relict plants in subtropical forest patches in highly fragmented habitats of southwestern China, northern Vietnam and northeastern Myanmar of East Asia. To date, its management and conservation strategies in the light of climate change have not been explored. We evaluated effects of climate change on the distribution of climatically suitable areas of D. sinicus as found prevailing during the last glacial maximum (LGM), the mid-Holocene and the present time, and predicted the distribution of climatically suitable habitats in 2070 throughout East Asia. The results as derived from ecological niche modeling (ENM) show the current distribution to be limited to the prehistoric (the mid-Holocene and LGM) refugia, and to indicate decreasing probability of presence and a reducing range of distribution for 2070. In addition, the suitable areas predicted with high probability (0.5–1) only account for on average 9.8% of the total area of potential habitats (threshold‒1) among the models for the year 2070, thereby indicating that D. sinicus is highly vulnerable. Under all the future scenarios for the year 2070, 69–74.2% of potential habitats in China would be outside protected areas. We assess and propose priorities for protected areas, and provide suggestions for conservation management strategies.This study received financial support from Science and Technology Department of Yunnan University, China (2019YNU002), the Ministry of Science and Technology of China (2015FY210200-15), Ajuts a Grups de Recerca Consolidats” (grants nos. 2014-SGR514-GREB and 2017-SGR1116) from the Generalitat de Catalunya (Spain), Applied Basic Research Foundation of Yunnan Province, China (Grant No. 2019FB058), the Environment Research and Technology Development Fund (JPMEERF15S11407) of the Environmental Restoration and Conservation Agency of Japan, and the Kakenhi Grant Number 15H02833.Highlights Abstract Keywords 1. Introduction 2. Material and methods 2.1. Species 2.2. Occurrence data and ecological niche modeling 3. Results 3.1. Model performance and present potential distribution 3.2. Projected distribution during the mid-Holocene (ca. 6000 yr BP) and LGM (ca. 21,000 yr BP) 3.3. Projected distribution under future climate (2070) 4. Discussion 4.1. Effects of climate change on spatial distribution patterns of D. sinicus 5. Recommendations for future conservation efforts and management Declaration of competing interest Acknowledgements Appendix A. Supplementary data Reference