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Purpose The purpose of this paper is to provide a theoretical foundation for improving the selective laser melting (SLM) surface roughness. To improve the part’s surface quality during SLM process, the upper surface roughness of SLM parts was theoretically studied and the influencing factors were analyzed through experiments. Design/methodology/approach The characteristics of single track were first investigated, and based on the analysis of single track, theoretical value of the upper surface roughness would be calculated. Two groups of cubic sample were fabricated to validate SLM parts’ surface roughness, the Ra and relative density of all the cubic parts was measured, and the difference between theoretical calculation and experiment results was studied. Then, the effect of laser energy density on surface roughness was studied. At last, the SLM part’s surface was improved by laser re-melting method. At the end of this paper, the curved surface roughness was discussed briefly. Findings The SLM upper surface roughness is affected by the width of track, scan space and the thickness of powder layer. Measured surface roughness Ra value was about 50 per cent greater than the theoretical value. The laser energy density has a great influence on the SLM fabrication quality. Different laser energy density corresponds to different fabricating characteristics. This study divided the SLM fabrication into not completely melting zone, balling zone in low energy density, successfully fabricating zone and excessive melting zone. The laser surface re-melting (LSR) process can improve the surface roughness of SLM parts greatly without considering the fabricating time and stress accumulation. Originality/value The upper surface roughness of SLM parts was theoretically studied, and the influencing factors were analyzed together; also, the LSR process was proven to be effective to improve the surface quality. This study provides a theoretical foundation to improve the surface quality of SLM parts to promote the popularization and application of metal additive manufacturing technology.

Highlights We first report on H 11 Al 2 V 6 O 23.2 with large layer spacing as cathode for aqueous zinc-ion battery, which accelerates the diffusion of Zn 2+ . The graphene-wrapped H 11 Al 2 V 6 O 23.2 nanobelts can improve electronic conductivity, and potentially inhibit the dissolution of elements in the aqueous electrolyte. H 11 Al 2 V 6 O 23.2 @graphene exhibits high capacity and stable cycling stability even at an ultra-high mass loading of ~ 15.7 mg cm −2 . Rechargeable aqueous zinc-ion batteries (AZIBs) have their unique advantages of cost efficiency, high safety, and environmental friendliness. However, challenges facing the cathode materials include whether they can remain chemically stable in aqueous electrolyte and provide a robust structure for the storage of Zn 2+ . Here, we report on H 11 Al 2 V 6 O 23.2 @graphene (HAVO@G) with exceptionally large layer spacing of (001) plane (13.36 Å). The graphene-wrapped structure can keep the structure stable during discharge/charge process, thereby promoting the inhibition of the dissolution of elements in the aqueous electrolyte. While used as cathode for AZIBs, HAVO@G electrode delivers ideal rate performance (reversible capacity of 305.4, 276.6, 230.0, 201.7, 180.6 mAh g −1 at current densities between 1 and 10 A g −1 ). Remarkably, the electrode exhibits excellent and stable cycling stability even at a high loading mass of ~ 15.7 mg cm −2 , with an ideal reversible capacity of 131.7 mAh g −1 after 400 cycles at 2 A g −1 .

Overhanging surface is inherent geometric restraint during selective laser melting (SLM), which is suitable for various complex parts fabrication. In order to improve the fabricating quality of overhanging surface, a series of experiments were designed to investigate the effects of inclined angle, scanning speed, laser power, accumulated residual stress, and scanning vector length on overhanging surface fabrication. Analysis found that overhanging surface would warp easier when the inclined angle and the scanning speed became smaller and the warping trend will be larger as the laser power became larger. The relationships of laser power, scanning speed, and the critical inclined angle were mutual restraint, that is, larger inclined angle will be designed when the laser power becomes larger and scanning speed gets smaller, or vice versa: the selection of the fabricating parameters will be determined by established inclined angle of the overhanging surface. More serious warp would happen as the processing layers increased as a result of residual stress accumulation, and it was found that longer scanning vector were more helpful to stress accumulation, leading to more serious warp than shorter vector. At last, two effective methods were adopted to optimize overhanging surface fabrication, including adjusting part orientation to improve the inclined angle at the key position, and controlling regional parameters to reduce energy input. Above two ways were adopted to manufacture complex parts with typical overhanging surface, the results proved that adjusting part orientation and controlling regional parameters were effective ways to improve the fabricating quality of overhanging surface. In this study, the basis for building overhanging surface by SLM was provided from the view of process and design, and the preliminary solutions were proposed to manufacture complex metal parts with lower risk.

Background Medical students experience depression and anxiety at a higher rate than the general population or students from other specialties. While there is a growing literature on the high prevalence of depression and anxiety symptoms and about potential risk factors to the prevalence of depression and anxiety symptoms among medical students, there is a paucity of evidence focused on the prevalence of depression and anxiety symptoms and associations with family function, social support and coping styles in Chinese vocational medicine students. This study aims to investigate the prevalence of depression and anxiety symptoms among Chinese medical students and assess the correlation between depression/anxiety symptoms and family function, social support and coping styles. Methods A sample of 2057 medical students from Chongqing Medical and Pharmaceutical College in China was investigated with a self-report questionnaire, which included demographic information, Zung self-rating depression scale, Zung Self-Rating Anxiety Scale, Family APGAR Index, Social Support Rating Scale and Trait Coping Style Questionnaire. Results The prevalence of depression and anxiety symptoms among the medical students was 57.5 and 30.8%, respectively. Older students(≥20 years) experienced higher levels of depression and anxiety. More depression and anxiety symptoms were exhibited among students with big financial burden, big study-induced stress and poor sleep quality. Students with large employment pressure showed more anxiety symptoms. Students who live alone or had bad relationship with their lovers or classmates or friends showed higher depression and anxiety scores. Depression and anxiety symptoms had highly significant correlations with family functioning, social support and coping style. Conclusions Academic staffs should take measures to reduce depression and anxiety among medical students and to provide educational counseling and psychological support for students to cope with these problems.

Increasing antibiotic resistance in multidrug-resistant (MDR) Gram-negative bacteria (MDR-GNB) presents significant health problems worldwide, since the vital available and effective antibiotics, including; broad-spectrum penicillins, fluoroquinolones, aminoglycosides, and β-lactams, such as; carbapenems, monobactam, and cephalosporins; often fail to fight MDR Gram-negative pathogens as well as the absence of new antibiotics that can defeat these \"superbugs\". All of these has prompted the reconsideration of old drugs such as polymyxins that were reckoned too toxic for clinical use. Only two polymyxins, polymyxin E (colistin) and polymyxin B, are currently commercially available. Colistin has re-emerged as a last-hope treatment in the mid-1990s against MDR Gram-negative pathogens due to the development of extensively drug-resistant GNB. Unfortunately, rapid global resistance towards colistin has emerged following its resurgence. Different mechanisms of colistin resistance have been characterized, including intrinsic, mutational, and transferable mechanisms. In this review, we intend to discuss the progress over the last two decades in understanding the alternative colistin mechanisms of action and different strategies used by bacteria to develop resistance against colistin, besides providing an update about what is previously recognized and what is novel concerning colistin resistance.

Biphasic and multiphasic compounds have been well clarified to achieve extraordinary electrochemical properties as advanced energy storage materials. Yet the role of phase boundaries in improving the performance is remained to be illustrated. Herein, we reported the biphasic vanadate, that is, Na1.2V3O8/K2V6O16·1.5H2O (designated as Na0.5K0.5VO), and detected the novel interfacial adsorption–insertion mechanism induced by phase boundaries. First‐principles calculations indicated that large amount of Zn2+ and H+ ions would be absorbed by the phase boundaries and most of them would insert into the host structure, which not only promote the specific capacity, but also effectively reduce diffusion energy barrier toward faster reaction kinetics. Driven by this advanced interfacial adsorption–insertion mechanism, the aqueous Zn/Na0.5K0.5VO is able to perform excellent rate capability as well as long‐term cycling performance. A stable capacity of 267 mA h g−1 after 800 cycles at 5 A g−1 can be achieved. The discovery of this mechanism is beneficial to understand the performance enhancement mechanism of biphasic and multiphasic compounds as well as pave pathway for the strategic design of high‐performance energy storage materials. A novel interfacial adsorption–insertion mechanism is observed in biphasic Na1.2V3O8/K2V6O16·1.5H2O cathode for aqueous Zn‐ion battery. The numerous phase boundaries in biphasic material could absorb H+ and Zn2+ ions and facilitate the subsequent ions insertion process. This advanced mechanism could bring about enhanced capacity as well as faster reaction kinetics, thus leading to brilliant capacity and remarkable long‐term cycling stability.

Energy input is crucial in the manufacturing of high-density metal part with smooth surface. In this article, the authors had studied the single-track, multi-track, and multi-layer and had obtained four types of typical tracks, including regular and thick shape, regular and thin shape, regular but occasionally broken shape, irregular and pre-balling shape. The analysis of single- and multi-track experiments showed that the regular and thin shape was the most suitable for selective laser melting (SLM) fabrication. Multi-track experiments proved that dense and smooth surface can be obtained when the overlapping rate was around 30% based on the regular- and thin-shaped track. As a result of the heat accumulation effect during multi-track and multi-layer fabrication, it was possible to obtain ideal track type with less energy input. In multi-layer experiment, the gradually thicken layer was the reason for the surface quality deterioration. The inter-layer stagger scanning strategy, which can improve the quality of the end-use part, was used in this experiment. By testing the 316 L stainless steel samples fabricated by the SLM process, the microstructure can be identified as composed of fine equiaxed and columnar grains, and the samples had higher tensile strength and hardness than castings of the same material, but with lower elongation. The experiments had proved that SLM process can directly produce high dense 316 L stainless steel part with smooth surface.

Zinc (Zn) is considered a promising biodegradable metal for implant applications due to its appropriate degradability and favorable osteogenesis properties. In this work, laser powder bed fusion (LPBF) additive manufacturing was employed to fabricate pure Zn with a heterogeneous microstructure and exceptional strength-ductility synergy. An optimized processing window of LPBF was established for printing Zn samples with relative densities greater than 99% using a laser power range of 80 ∼ 90 W and a scanning speed of 900 mm s −1 . The Zn sample printed with a power of 80 W at a speed of 900 mm s −1 exhibited a hierarchical heterogeneous microstructure consisting of millimeter-scale molten pool boundaries, micrometer-scale bimodal grains, and nanometer-scale pre-existing dislocations, due to rapid cooling rates and significant thermal gradients formed in the molten pools. The printed sample exhibited the highest ductility of ∼12.1% among all reported LPBF-printed pure Zn to date with appreciable ultimate tensile strength (∼128.7 MPa). Such superior strength-ductility synergy can be attributed to the presence of multiple deformation mechanisms that are primarily governed by heterogeneous deformation-induced hardening resulting from the alternative arrangement of bimodal Zn grains with pre-existing dislocations. Additionally, continuous strain hardening was facilitated through the interactions between deformation twins, grains and dislocations as strain accumulated, further contributing to the superior strength-ductility synergy. These findings provide valuable insights into the deformation behavior and mechanisms underlying exceptional mechanical properties of LPBF-printed Zn and its alloys for implant applications. A superior strength-ductility synergy was achieved in pure zinc printed by laser powder bed fusion. A heterogeneous microstructure with bimodal grains and dislocations was obtained. Back-stress hardening, massive dislocations and twins are dominant in deformation. Deformation mechanisms responsible for the strength-ductility synergy were revealed.

Due to the high capacity of impurities in its structure, calcite is regarded as one of the most attractive minerals to trap heavy metals (HMs) and radionuclides via substitution during coprecipitation/crystal growth. As a high-reactivity mineral, calcite may release HMs via dissolution. However, the influence of the incorporated HMs and radionuclides in calcite on its dissolution is unclear. Herein, we reported the dissolution behavior of the synthesized calcite incorporated with cadmium (Cd), cobalt (Co), nickel (Ni), zinc (Zn), and uranium (U). Our findings indicated that the HMs and U in calcite could significantly change the dissolution process of calcite. The results demonstrated that the incorporated HMs and U had both inhibiting and enhancing effects on the solubility of calcite, depending on the type of metals and their content. Furthermore, secondary minerals such as smithsonite (ZnCO 3 ), Co-poor aragonite, and U-rich calcite precipitated during dissolution. Thus, the incorporation of metals into calcite can control the behavior of HMs/uranium, calcite, and even carbon dioxide.

Vegetables are crucial to a human diet as they supply the body with essential vitamins, minerals, etc . Heavy metals that accumulate in plants consequently enter the food chain and endanger people's health. Studying the spatial distribution and chemical forms of elements in plant/vegetable tissues is vital to comprehending the potential interactions between elements and detoxification mechanisms. In this study, leek plants and soil from vegetable gardens near lead–zinc mines were collected and cultivated with 500 mg L −1 PbNO 3 solutions for three weeks. Micro X-ray fluorescence was used to map the distribution of Pb and other chemical elements in leek roots, and X-ray absorption near-edge spectroscopy was used to assess the Pb speciation in leek roots and leaves. These findings demonstrated that Pb, Cu, Mn, Cr, Ti and Fe were detected in the outer rings of the root's cross section, and high-intensity points were observed in the epidermis. Zn, K and Ca, on the other hand, were distributed throughout the root's cross section. Leek root and leaf contained significant quantities of lead phosphate and basic lead carbonate at more than 80%, followed by lead sulfide (19%) and lead stearate (11.1%). The capacity of leek roots to convert ambient lead into precipitated lead and fix it on the root epidermis and other inner surfaces is a key mechanism for reducing the toxic effects of Pb.