3714 research outputs found
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Nanostructural design of superstrong metallic materials by severe plastic deformation processing
No full textUltrafine-grained (UFG) metallic materials processed by severe plastic deformation (SPD) techniques often exhibit significantly higher strengths than those calculated by the well-known Hall-Petch equation. These higher strengths result from the fact that SPD processing not only forms the UFG structure but also leads to the formation of other nanostructural features, including dislocation substructures, nanotwins and nanosized second-phase precipitations, which further contribute to the hardening. Moreover, the analysis of strengthening mechanisms in recent studies demonstrates an important contribution to the hardening due to phenomena related to the structure of grain boundaries as a non-equilibrium state and the presence of grain boundary segregations. Herein, the principles of the nanostructural design of metallic materials for superior strength using SPD processing are discussed
Environmental embrittlement behavior of high-entropy alloys
No full textHigh entropy alloys (HEAs), as a new class of structural materials, have attracted extensive interest from numerous metallurgical scientists and engineers. Benefiting from their unique microstructural features and outstanding mechanical performance, HEAs have shown significant potential for applications in many engineering fields, even under extreme conditions. In particular, when exposed to hydrogen and/or intermediate-temperature environments, these HEAs inevitably suffer from severe environmental embrittlement (EE) issues, e.g., hydrogen embrittlement (HE) and intermediate-temperature embrittlement (ITE), resulting in serious premature intergranular failure. In this work, we critically review the state-of-the-art advances of EE in previously reported HEA systems. Particular focus is given to novel strategies to enhance the resistance to EE in different HEAs. Two critical embrittlement phenomena, namely, HE and ITE, are highlighted separately. Finally, we provide perspectives on future research directions and opportunities for EE-resistant HEAs
Recent advances in shape selectivity of MFI zeolite and its effect on the catalytic performance
No full textMFI zeolite characterized by uniform pore size, adjustable acidity, and high-temperature resistance has a broad application prospect in catalytic reactions. However, controlling the product distribution of zeolite as a catalyst is still confronting great challenges and applications. It is considered as an effective way to control the product distribution by developing and improving new zeolites to modulate their shape selective effect. In recent years, researchers have achieved remarkable successes in investigating the shape selective modulation of zeolites on catalytic reaction and molecular diffusion. The microporous channels of MFI zeolite are the main places for the entry and exit of reactants or product molecules. This review provides the research progress of the shape-selective modulation of MFI zeolite channels and its influence on a series of catalytic performances in recent years. The shape-selective modulation of microporous channels of zeolite, encapsulation of micropores to metals, catalysis of mesoporous zeolite, and the distribution of framework Al were all systematically discussed. The development of advanced catalysts still faces great challenges and potential applications. Finally, we discussed the problems to be addressed urgently in the field of zeolite catalysts in the future
Radical skeletal metastatic site irradiation in high-risk neuroblastoma: systematic review and proposal for a randomised trial: a report from the SIOPEN Radiotherapy Committee
No full textAim: Neuroblastoma has a variable outcome depending on age, stage, and molecular pathology. Distant metastatic disease is the central feature of high-risk disease. Recommendations for irradiating persistent metastatic deposits with curative intent after systemic therapy vary. It is unclear to what extent this practice may improve local control or survival. This study systematically reviewed the evidence for skeletal metastatic site irradiation and made evidence-based recommendations for clinical practice.Methods: We systematically reviewed the literature on radical radiotherapy of persistent metastases after chemotherapy. The aim was to determine whether a position could be taken regarding metastatic site irradiation in combined modality treatment protocols aiming for a cure and whether recommendations could be formulated.Results: The initial search yielded 445 results. After the title and abstract review, 13 full papers were retrieved. Ten papers were found suitable for data extraction. One additional paper was identified. All 11 were graded as Centre for Evidence-Based Medicine Step 4 in quality; there was no high-level evidence. There are suggestions of benefit for skeletal site irradiation in high-risk neuroblastoma; however, there is no certainty, and it was not possible to recommend a particular treatment policy.Conclusion: We recommend that consideration is given to a randomised evaluation of the benefits of radiotherapy to a limited number of residual post-induction-chemotherapy metastatic sites in good responders. This practice could be incorporated as an amendment to existing trials
Recent advances in organocatalytic cascade reactions for enantioselective synthesis of chiral spirolactone skeletons
No full textChiral spirolactones, including spiropropyllactones, spirobutyrolactones, and spirovalerolactones, are important heterocyclic frameworks that attracted the attention of organic and medicinal chemists because these motifs constitute the core structure of several natural products and bioactive molecules. The absolute configuration and the substituents on the fully substituted spirocyclic stereocenter of the lactone can potentially enhance specificity for ligand-protein binding and enhance bioavailability, potency, and metabolic stability. So, intensive attention from chemists has been paid to the synthetic methods leading to such prominent structural motifs. The synthetic methods can be divided into two main classes. The first approach takes advantage of the presence of the existing lactone structure and focuses on its functionalization. The second approach is the lactone framework constructed from various precursors in a direct spirolactonization reaction. In this review, for convenience in reading, the recent advances in the synthesis of spirolactones are summarized and discussed according to the two major organocatalytic asymmetric synthetic routes: (i) using the lactone-related frameworks as building blocks; and (ii) direct spirolactonization reaction using various reagents. This review also describes both the mechanisms and related transformations, and gives some insights into challenging issues in this research field, which will enlighten the future development of this field
An overview of intelligent image segmentation using active contour models
No full textThe active contour model (ACM) approach in image segmentation is regarded as a research hotspot in the area of computer vision, which is widely applied in different kinds of applications in practice, such as medical image processing. The essence of ACM is to make use ofuse an enclosed and smooth curve to signify the target boundary, which is usually accomplished by minimizing the associated energy function by means ofthrough the standard descent method. This paper presents an overview of ACMs for handling image segmentation problems in various fields. It begins with an introduction briefly reviewing different ACMs with their pros and cons. Then, some basic knowledge in of the theory of ACMs is explained, and several popular ACMs in terms of three categories, including region-based ACMs, edge-based ACMs, and hybrid ACMs, are detailedly reviewed with their advantages and disadvantages. After that, twelve ACMs are chosen from the literature to conduct three sets of segmentation experiments to segment different kinds of images, and compare the segmentation efficiency and accuracy with different methods. Next, two deep learning-based algorithms are implemented to segment different types of images to compare segmentation results with several ACMs. Experimental results confirm some useful conclusions about their sharing strengths and weaknesses. Lastly, this paper points out some promising research directions that need to be further studied in the future
GMAW welding procedure expert system based on machine learning
No full textIn order to simplify the robot preparation before welding and improve the automation of the whole welding process, an intelligent expert system for Gas Metal Arc Welding is designed in this paper. In the system, the user inputs the initial welding information and the output interface displays suitable welding procedure parameter schemes. The user can choose the schemes according to the actual requirements or directly generate the welding procedure specification required by the enterprise format for direct use. In addition, the system also combines the database technology and XGBoost algorithm in the field of machine learning, migrates the model trained on the data set to predict the welding raw data, accumulates more data for daily use to optimize the model, which makes the whole system more systematic and intelligent, and achieves the goal of more accurate use
Life cycle oriented low carbon manufacturing of mechanical equipment: method and application
No full textMechanical equipment is a significant contributor to carbon emissions. By analyzing the life cycle carbon emissions of mechanical equipment, it can be obtained that the consumption of materials and energy are the key factors. Focusing on decreasing material and energy consumption in the life cycle of mechanical equipment, a series of low carbon design strategies are proposed, including material selection, lightweight design, and design for disassembly and recycling; specifically, in this paper, low carbon operation strategies on the machine and workshop levels are discussed. Operations including power matching, energy recovery, and transmission chain shortening can be performed at the machine level, as well as scheduling and production optimization at the workshop level. The proposed method is applied to a piece of typical equipment, a hydraulic forming press, and results show that the proposed low carbon manufacturing methods have significant carbon emission reduction potential. Combined with current research hotspots, the integration of design methods and tools and the carbon emission reduction techniques enabled by intelligent manufacturing are future directions
Risk of hepatocellular carcinoma development in long-term nucles(t)ide analog suppressed patients with chronic hepatitis B
No full textAim: In long-term nucleos(t)ide analog (NA) suppressed patients with chronic hepatitis B (CHB), hepatocellular carcinoma (HCC) can still develop. Few data exist on the incidence and the predictors of HCC development beyond the first five years in long-term treated patients. To assess the prevalence, incidence, and risk factors for HCC development in a real-life cohort of successfully NA-treated CHB patients for more than five years.Methods: All CHB patients under NAs for ≥ 60 months with stable virologic response were enrolled. HCC surveillance was carried out using liver ultrasound and dosing of serum alpha-fetoprotein every year in patients with CHB and every six months in cirrhotic patients. The baseline PAGE-B score was calculated for each patient.Results: 343 patients (76% male, 86% HBeAg-negative, 30% cirrhotic) were enrolled. During a median (IQR) follow-up of 144 (105-182) months, 21 patients (6%) developed HCC despite virologic suppression (incidence rate 40 cases/1000 person-years follow-up). In multivariate analysis, higher PAGE B score [adjusted Hazard Ratio, aHR 1.26 (95%CI: 1.13-1.54), P = .022] and cirrhosis [aHR 9.71 (95%CI: 2.02-46.48), P = .005] were predictors of HCC development. PAGE B score showed a significant association with HCC (R2 0.225, P < .001) and good prognostic capacity (AUC 0.863) of HCC.Conclusions: Our results confirm that in successfully NA-treated CHB patients, sustained viral replication suppression does not abolish the risk of HCC. The PAGE-B score could be a useful tool for identifying high-risk subjects
Non-invasive prenatal diagnosis (NIPD): current and emerging technologies
No full textPrenatal testing is important for the early detection and diagnosis of rare genetic conditions with life-changing implications for the patient and their family. Gaining access to the fetal genotype can be achieved using gold-standard invasive sampling methods, such as amniocentesis and chorionic villus sampling, but these carry a small risk of miscarriage. Non-invasive prenatal diagnosis (NIPD) for select rare monogenic conditions has been in clinical service in England since 2012 and has revolutionised the field of prenatal diagnostics by reducing the number of women undergoing invasive sampling procedures. Fetal-derived genomic material is present in a highly fragmented form amongst the maternal cell-free DNA (cfDNA) in circulation, with sequence coverage across the entire fetal genome. Cell-free fetal DNA (cffDNA) is the foundation for NIPD, and several technologies have been clinically implemented for the detection of paternally inherited and de novo pathogenic variants. Conversely, a low abundance of cffDNA within a high background of maternal cfDNA makes assigning maternally inherited variants to the fetal fraction a significantly more challenging task. Research is ongoing to expand available tests for maternal inheritance to include a broader range of monogenic conditions, as well as to uncover novel diagnostic avenues. This review covers the scope of technologies currently clinically available for NIPD of monogenic conditions and those still in the research pipeline towards implementation in the future
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