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In this work, the influence of bias and electric field intensity on the electrochemical migration of SAC305 solder alloy is investigated using a self-designed in-situ thin electrolyte film device. The results indicate that when the bias is 0.5 V, a compact passivation film forms on the sample surface, effectively inhibiting dendrite growth. When the applied bias reaches 0.75 V, it is observed that specific corrosion products are generated between the two plates, and the occurrence of dendritic growth phenomena is still absent. Dendrite development is observed when a bias voltage of 1 V is applied. Regarding the electrode reactions, when the applied bias falls below 1.5 V, a notable polarization resistance is encountered in the anode reaction. In this case, the cathode reaction primarily entails the process of oxygen reduction. As the applied voltage climbs to 1.5 V, the anodic potential shows an increase, leading to a reduction in the polarization resistance of the anodic process that determines the rate of the electrochemical reaction. At this time, the cathode potential exhibits a comparatively negative value, leading to the progressive occurrence of the hydrogen evolution process. Additionally, the influence mechanism of bias on ECM is also proposed.

Q345B carbon steel as well as Q450NQR1 and S500AW weathering steels were subjected to outdoor exposure corrosion tests in coal environments and indoor periodic immersion accelerated corrosion tests with a simulated coal leaching solution. The corrosion kinetics were studied by the weight loss method, and the corrosion morphology and corrosion product composition were observed and analyzed by scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction. Afterward, correlation analysis of the indoor and outdoor tests was carried out by the gray correlation analysis method. The results show that the relationship between the corrosion weight loss and corrosion time of the three steels conforms to follow the exponent power law. In particular, Q450NQR1 steel has the best corrosion resistance. The types of corrosion products and the distribution of elements in the rust layer of the three steels are similar in the indoor and outdoor tests. The gray correlation degrees of the three steels in the indoor and outdoor tests are all greater than 0.6; thus, the two corrosion tests have a good correlation. Based on this, the accelerated simulation test method of the coal leaching solution is determined, and life prediction models of three steels in coal leaching solution are established to simulate the corrosion of the bottom board and side board.

The hippocampus is closely related to many brain diseases, such as Alzheimer's disease. Accurate measurement of the hippocampus is helpful for clinicians in identifying lesions and then diagnosing and treating the related brain diseases. Therefore, accurate segmentation of the hippocampus is of vital significance for the in‐depth study of many brain diseases. However, the accurate measurement of the hippocampus depends on its accurate segmentation, and hippocampal segmentation has always been a challenging problem due to the small size, irregular shape, and fuzzy boundaries with surrounding tissues of the hippocampus. With the development of machine learning, many innovative methods have been proposed to segment the hippocampus. The purpose of this survey is to provide a comprehensive overview of hippocampal segmentation in brain MRI images using machine learning methods. First, a brief introduction to hippocampal segmentation in brain MRI images is given. Then, common evaluation metrics of hippocampal segmentation are introduced. Next, brain hippocampal segmentation methods based on traditional machine learning and deep learning are described. Subsequently, some common open datasets and toolkits applied to brain hippocampal segmentation are presented. Finally, objective conclusions regarding hippocampal segmentation in brain MRI images using machine learning methods are drawn, and future developments and trends are identified for brain hippocampal segmentation.

The computed tomography angiography (CTA) Spot Sign is an effective means of predicting hematoma expansion (HE) in the context of spontaneous intracerebral hemorrhage (ICH). We investigated whether continuous CTA source images could differentiate the Spot Sign and blood vessels in the hematoma, and whether it would improve Spot Sign accuracy as an HE predictor. We screened for the presence of CTA Spot Sign in individuals affected by spontaneous ICH within 24 h of symptom development. Based on our findings, we determined the sensitivity, specificity, and positive/negative predictive values of this sign as a predictor of HE both on its own and following the exclusion of blood vessels. In addition, a receiver-operating characteristic approach was used to assess the accuracy of Spot Sign with and without elimination of vascular interference. A total of 265 patients were included in this study. The Spot Sign was observed in 100 patients, including in 29 patients wherein it was confirmed to be blood vessels as determined based upon continuous CTA source images. With respect to predicting HE, Spot Sign sensitivity, specificity, positive predictive values, and negative predictive values were 57%, 71%, 48% and 78%, respectively. Following the exclusion of blood vessels, these values were 57%, 87%, 68% and 81%, respectively. Spot Sign area under the curve after excluding blood vessels was 0.718, which was higher than that of the Spot Sign (0.638). After continuous CTA, source images are used to exclude blood vessels in the hematoma, the Spot Sign is thus more accurate in predicting HE.

Catalytic asymmetric reactions in which water is a substrate are rare. Enantioselective transition-metal-catalyzed insertion of carbenes into the O–H bond of water can be used to incorporate water into the stereogenic center, but the reported chiral catalysts give good results only when α-aryl-α-diazoesters are used as the carbene precursors. Herein we report the first highly enantioselective O–H bond insertion reactions between water and α-alkyl- and α-alkenyl-α-diazoesters as carbene precursors, with catalysis by a combination of achiral dirhodium complexes and chiral phosphoric acids or chiral phosphoramides. Participation of the phosphoric acids or phosphoramides in the carbene transfer reaction markedly suppressed competing side reactions, such as β-H migration, carbene dimerization, and olefin isomerization, and thus ensured good yields of the desired products. Fine-tuning of the ester moiety facilitated enantiocontrol of the proton transfer reactions of the enol intermediates and resulted in excellent enantioselectivity. This protocol represents an efficient new method for preparation of multifunctionalized chiral α-alkyl and α-alkenyl hydroxyl esters, which readily undergo various transformations and can thus be used for the synthesis of bioactive compounds. Mechanistic studies revealed that the phosphoric acids and phosphoramides promoted highly enantioselective [1,2]- and [1,3]-proton transfer reactions of the enol intermediates. Maximization of molecular orbital overlap in the transition states of the proton transfer reactions was the original driving force to involve the proton shuttle catalysts in this process.

A highly efficient asymmetric Michael addition of thiols to exocyclic enones was achieved by using chiral spiro phosphoramide catalysts. The precisely chiral control in the protonation of the enol intermediate ensured high enantioselectivity. The reaction features high activity (yields up to 99%, turnover numbers up to 8400) and high enantioselectivity (up to 97% ee) with a broad substrate scope, and it has the potential for wide application in the synthesis of chiral sulfides.

Next-generation sequencing (NGS) technologies have fostered an unprecedented proliferation of high-throughput sequencing projects and a concomitant development of novel algorithms for the assembly of short reads. However, numerous technical or computational challenges in de novoassembly still remain, although many new ideas and solutions have been suggested to tackle the challenges in both experimental and computational settings. In this review, we first briefly introduce some of the major challenges faced by NGS sequence assembly. Then, we analyze the characteristics of various sequencing platforms and their impact on assembly results. After that, we classify de novoassemblers according to their frameworks (overlap graph-based, de Bruijngraph-based and string graph-based), and introduce the characteristics of each assembly tool and their adaptation scene. Next, we introduce in detail the solutions to the main challenges of de novoassembly of next generation sequencing data, single-cell sequencing data and single molecule sequencing data. At last, we discuss the application of SMS long reads in solving problems encountered in NGS assembly. This review not only gives an overview of the latest methods and developments in assembly algorithms, but also provides guidelines to determine the optimal assembly algorithm for a given input sequencing data type.

Next‐generation sequencing (NGS) technologies have fostered an unprecedented proliferation of high‐throughput sequencing projects and a concomitant development of novel algorithms for the assembly of short reads. However, numerous technical or computational challenges in de novoassembly still remain, although many new ideas and solutions have been suggested to tackle the challenges in both experimental and computational settings. In this review, we first briefly introduce some of the major challenges faced by NGS sequence assembly. Then, we analyze the characteristics of various sequencing platforms and their impact on assembly results. After that, we classify de novoassemblers according to their frameworks (overlap graph‐based, de Bruijngraph‐based and string graph‐based), and introduce the characteristics of each assembly tool and their adaptation scene. Next, we introduce in detail the solutions to the main challenges of de novoassembly of next generation sequencing data, single‐cell sequencing data and single molecule sequencing data. At last, we discuss the application of SMS long reads in solving problems encountered in NGS assembly. This review not only gives an overview of the latest methods and developments in assembly algorithms, but also provides guidelines to determine the optimal assembly algorithm for a given input sequencing data type. Author summary:In this review, we focus on the main challenges facing de novoassembly and its solusions. Firstly, we introduce some of the major challenges faced by de novoassembly. Secondly, we analyze the characteristics of various sequencing platforms and their impact on assembly results, and introduce the characteristics of each assemblers and their adaptation scene. Thirdly, we introduce in detail the solutions to the main challenges of de novoassembly. Finally, we discuss the latest methods and developments in de novoassembly.

Pharmaceuticals and biologically active natural products usually contain multiple stereocenters. The development of catalytic asymmetric reactions for the direct construction of complex motifs containing three nonadjacent stereocenters is a particularly important and formidable challenge. In this paper, we report an unprecedented method for the direct asymmetric construction of complex chiral amines with 1,3,5- or 1,3,4-stereocenters from readily available achiral and racemic starting materials. The reaction was made possible by the development of highly efficient chiral ammonium catalysts that serve three distinct functions: promoting efficient kinetic resolution by chiral recognition of racemic electrophiles, promoting asymmetric C–C bond forming reactions by recognizing enantiotropic faces of achiral nucleophiles, and mediating a highly stereoselective protonation of carbanions. Using these trifunctional catalysts, the reaction of imines and tulipane derivatives proceeded in a highly regio-, chemo-, and stereoselective manner to produce synthetically useful yields of complex chiral amines. We believe that trifunctional catalysis can be applied in a variety of asymmetric transformations for the streamlined asymmetric synthesis of complex chiral molecules with multiple stereocenters.