Search

Nickel-based superalloys have attracted significant attention due to their outstanding high-temperature strength, corrosion resistance, and oxidation resistance, and are widely used in aerospace and other fields. This article provides a comprehensive review of the preparation methods, common grades, and microstructure and properties of additive manufactured nickel-based superalloys, summarizes the current issues, and proposes future areas for exploration. Nickel-based superalloys prepared by metal additive manufacturing technology have excellent performance, can achieve precise forming of complex components, and have minimal material waste during the manufacturing process. They are expected to become an important production process for nickel-based superalloys components in fields such as aerospace. Common methods for additive manufacturing of nickel-based superalloys include laser powder bed melting, directed energy deposition, and arc additive manufacturing. Powder bed melting is widely used for manufacturing high-precision and complex parts, but it has a relatively slow manufacturing speed and higher equipment and material costs. Directed energy deposition has higher degrees of freedom and flexibility and can be used to prepare functional gradient materials, but it has lower accuracy. Arc additive manufacturing has lower equipment and material costs and is suitable for rapid manufacturing of large parts, but the surface roughness of the alloy produced by this method is poor and requires additional processing or post-treatment. Nickel-based superalloys widely studied in the additive manufacturing process include IN625, Hastelloy X, and other solid solution strengthened alloys, as well as IN718, CM247LC, IN738LC, and other precipitation strengthened superalloys. Compared with traditional casting and forging methods, the unique layer-by-layer forming and rapid cooling and heating process of additive manufacturing result in a coarse columnar grain structure and a unique microstructure with a large number of fine grains. It also forms unique melt pool structures and dislocation cell structures. However, the alloys obtained by additive manufacturing generally require heat treatment to control grain structure and precipitated phases, which affects the mechanical properties of the alloy. In addition, the mechanical properties of additive manufactured nickel-based superalloys are also related to specific preparation methods and alloy types. Although additive manufacturing has been widely used in the preparation of nickel-based superalloys, there are still issues such as anisotropy in microstructure and properties, high sensitivity to alloy cracking, and a lack of corresponding specifications and standards. In the future, further exploration is needed in areas such as heat treatment, customization and development of specialized alloys, investigation of the process-structure-function relationship, and computational modeling.

The 6- DOF joint robot with offset wrist can’t satisfy the Pieper rule,thus there are no closed- form inverse kinematics solutions for them. Compared with non- offset robot,a numerical iterative algorithm that integrates the closed- form inverse solutions of non- offset robot with the modified Newton iteration method is obtained,and the inverse method is utilized to obtain the closed- form inverse solutions of the non- offset robot with the same configurations,and the solutions are considered as the initial values of the subsequent iteration. According to the forward kinematics,by combining the three components of position vector with the three independent elements of attitude matrix,a non- liner equation set which contains all joint variables can be obtained,and then the numerical inverse kinematics solutions for the robot with offset wrist can be searched with the modified Newton iteration method. A large number of tests indicate that the algorithm can meet the requirements of real- time control.

This study aimed to investigate the clinical characteristics, prognosis, and factors for survival of patients who underwent early-start peritoneal dialysis (PD) within 24 h after catheter insertion three years after PD. This study was conducted from January 1, 2013 to December 31, 2017. All adult patients who were diagnosed with end-stage renal disease (ESRD) and underwent PD for the first time within 24 h after catheter insertion in our hospital were included. All patients with PD were followed-up until they withdrew from PD, switching to hemodialysis, were transferred to other medical centers, underwent renal transplantation, died or were lost to follow-up, or continued to undergo dialysis until the end of the study period. The follow-up observation lasted three years. The number of eligible patients was 110, and switching to hemodialysis and death were the main reasons for patients to withdraw from PD. The 1-, 2-, and 3-year technical survival rates of patients were 89.1, 79.1, and 79.1% respectively, while the 1-, 2- and 3-year survival rates were 90, 81.8, and 81.8%, respectively. The Charlson comorbidity index, age, hemoglobin, serum albumin, diabetic nephropathy, chronic glomerulonephritis, and hypertensive renal damage were independent risk factors that affected the prognosis of PD patients. Under the condition of ensuring the quality of the PD catheter insertion, early-start PD within 24 h after catheter insertion is a safe treatment approach for ESRD patients.

To address the rapidly increasing demand for culturally and linguistically diverse school psychologists and training needs for international school psychology students in the USA, this study was grounded in the risk and resilience framework and used semi-structured interviews to explore the nuanced experiences of Asian international trainees in school psychology programs in the USA. Participants included 11 Asian international students who were enrolled in or recently graduated from school psychology programs in the USA. Thematic analysis revealed that Asian international school psychology students identified some assets they have brought to the program, including their diverse perspectives and experiences, awareness and commitment to social justice, and the potential to diversify the school psychology workforce. Participants also identified several challenges they were facing, such as acculturative stress, microaggression and discrimination, training program-related issues, and working restrictions related to their visa status. Moreover, they identified some effective strategies (i.e., seeking resources and increasing internal strengths) they have used to cope with these challenges. The findings provide important implications for school psychology graduate programs in the USA to improve the training experiences and training outcomes for international students from Asia and other countries.

BackgroundCompared to commonly-used green space indicators from downward-facing satellite imagery, street view-based green space may capture different types of green space and represent how environments are perceived and experienced by people on the ground, which is important to elucidate the underlying mechanisms linking green space and health.ObjectivesThis study aimed to evaluate machine learning models that can classify the type of vegetation (i.e., tree, low-lying vegetation, grass) from street view images; and to investigate the associations between street green space and socioeconomic (SES) factors, in Los Angeles County, California.MethodsSES variables were obtained from the CalEnviroScreen3.0 dataset. Microsoft Bing Maps images in conjunction with deep learning were used to measure total and types of street view green space, which were compared to normalized difference vegetation index (NDVI) as commonly-used satellite-based green space measure. Generalized linear mixed model was used to examine associations between green space and census tract SES, adjusting for population density and rural/urban status.ResultsThe accuracy of the deep learning model was high with 92.5% mean intersection over union. NDVI were moderately correlated with total street view-based green space and tree, and weakly correlated with low-lying vegetation and grass. Total and three types of green space showed significant negative associations with neighborhood SES. The percentage of total green space decreased by 2.62 [95% confidence interval (CI): -3.02, -2.21, p < 0.001] with each interquartile range increase in CalEnviroScreen3.0 score. Disadvantaged communities contained approximately 5% less average street green space than other communities.ConclusionStreet view imagery coupled with deep learning approach can accurately and efficiently measure eye-level street green space and distinguish vegetation types. In Los Angeles County, disadvantaged communities had substantively less street green space. Governments and urban planners need to consider the type and visibility of street green space from pedestrian's perspective.

We discuss the existence of solutions for the first-order multipoint BVPs on time scale : , , , where is a parameter, is a fixed number, , is continuous, is regressive and rd-continuous, , , , , and . For suitable , some existence, multiplicity, and nonexistence criteria of positive solutions are established by using well-known results from the fixed-point index.

By defining a new terminology, scatter degree, as the supremum of graininess functional value, this paper studies the existence of solutions for a nonlinear two-point dynamic boundary value problem on time scales. We do not need any growth restrictions on nonlinear term of dynamic equation besides a barrier strips condition. The main tool in this paper is the induction principle on time scales.

An exact multiplicity result of positive solutions for the boundary value problems , , , is achieved, where is a positive parameter. Here the function is and satisfies , for for some . Moreover, is asymptotically linear and can change sign only once. The weight function is and satisfies , for . Using bifurcation techniques, we obtain the exact number of positive solutions of the problem under consideration for lying in various intervals in . Moreover, we indicate how to extend the result to the general case.