Search

Purpose The purpose of this study was expected to simultaneously monitor the surface roughness of each solidified layer, the surface roughness of the metal powder, the outline of the solidified layer, and the height difference between the solidified layer and the metal powder. Design/methodology/approach In the proposed approach, color images with red, green and blue fringes are used to measure the shape of the built object using a three-step phase-shift algorithm and phase-unwrapping method. In addition, the surface roughness is extracted from the speckle information in the captured image using a predetermined autocorrelation function. Findings The feasibility and accuracy of the proposed system were validated by comparing it with a commercial system for an identical set of samples fabricated by a selective laser melting process. The maximum and minimum errors between the two systems are approximately 24% and 0.8%, respectively. Originality/value In the additive manufacturing field, the authors are the first to use fringe detection technology to simultaneously measure the profile of the printed layer and its surface roughness.

A low-cost, lateral off-axis non-IR imaging system is proposed to inspect the melt-pool in the Laser Powder Bed Fusion (L-PBF) processing of IN718 powder and stainless steel 316 L powder. In the proposed system, a perspective transformation method is applied to transform the captured side-view image into a top-view image and the melt-pool boundary is then determined based on an inspection of the gray-level intensity profile of the captured image and its first derivative. For the IN718 L-PBF process, the measurement results obtained for the melt-pool width and melt-pool length vary by no more than 13% and 3%, respectively, from the experimental results reported in the literature. For the SS316L, the measured melt-pool width is within 6% of the ex-situ measurements obtained by optical microscopy, while the melt-pool length differs by no more than 9% from the numerical predictions. Overall, the results show that the proposed system provides a viable means of detecting potential build failures during the L-PBF process and improving the yield of the fabrication process as a result.

Purpose Vancomycin-resistant enterococci infection is a worrying worldwide clinical problem. To evaluate the accuracy of GeneXpert vanA/vanB in the diagnosis of VRE, we conducted a systematic review in the study. Methods Experimental data were extracted from publications until May 03 2021 related to the diagnostic accuracy of GeneXpert vanA/vanB for VRE in PubMed, Embase, Web of Science and the Cochrane Library. The accuracy of GeneXpert vanA/vanB for VRE was evaluated using summary receiver to operate characteristic curve, pooled sensitivity, pooled specificity, positive likelihood ratio, negative likelihood ratio, and diagnostic odds ratio. Results 8 publications were divided into 3 groups according to two golden standard references, vanA and vanB group, vanA group, vanB group, including 6 researches, 5 researches and 5 researches, respectively. The pooled sensitivity and specificity of group vanA and vanB were 0.96 (95% CI, 0.93–0.98) and 0.90 (95% CI, 0.88–0.91) respectively. The DOR was 440.77 (95% CI, 37.92–5123.55). The pooled sensitivity and specificity of group vanA were 0.86 (95% CI, 0.81–0.90) and 0.99 (95% CI, 0.99–0.99) respectively, and those of group vanB were 0.85 (95% CI, 0.63–0.97) and 0.82 (95% CI, 0.80–0.83) respectively. Conclusion GeneXpert vanA/vanB can diagnose VRE with high-accuracy and shows greater accuracy in diagnosing vanA., Author summary Vancomycin-resistant enterococci (VRE), firstly identified in the mid-1980, is a type of antimicrobial resistance bacteria. In recent years, they were found more colonization in patients with critical diseases, showing new resistance to many antibacterial drugs, which is a worrisome clinical problem worldwide. Traditionally, VRE testing is performed mainly by culture which is a standard reference but requires complex steps and takes a long time. Currently, GeneXpert vanA/vanB were approved as a rapid and sensitive molecular assay for detecting VRE. However, the accuracy of GeneXpert vanA/vanB is without systematic-analyses in evidence-based medicine. Therefore, we conducted a data integration and analysis in this study. Finally, we draw a conclusion that GeneXpert vanA/vanB has a high accuracy diagnosing VRE in comparation with conventional culture and PCR. Furthermore, GeneXpert vanA/vanB shows more accuracy in diagnosing vanA. In addition, we suggest that an additional test is needed for further detecting vanB. This finding provides a promising direction for the diagnosis of VRE to a certain extent.

Accumulated spatters not only deteriorate the quality of the built parts in terms of surface roughness and/or density but also sabotage the whole fabrication process via damaging the powder re-coater. A cross-flow of inert gas inside the processing chamber is by far the only effective mean of removing the spouted spatters from the build platform. Despite the essential role, there are few efforts to investigate the interactions between the cross-flow dynamics and the spouted spatters, and hence, to optimize the design and settings of the cross-flow. Therefore, in this study, a coupled computational fluid dynamics (CFD) – discreate element method (DEM) simulation framework is proposed to study the interactions between the flow field and the spouted spatters during the single scan process. The simulation results for the maximum ejection distance and maximum ejection height of the spatters were shown to deviate from the numerical results reported in the literature by no more than 15%. Moreover, the simulation results for the distribution of the landing sites of the spatters were consistent with the experimental observations, which showed that a large number of large spatters landed near the scan track, while a small number of large spatters landed at a greater distance from the scan track. To the best of the authors’ knowledge, this study represents the first reported attempt to use a coupled CFD-DEM simulation framework to investigate the spatter dynamics within an LPBF chamber and to validate the results with experimental observations and published data. The proposed model is an important tool to optimize and calibrate the cross-flow inside the L-PBF processing chamber.

A three-dimensional numerical model is developed to investigate the melting and solidification process during the Selective Laser Melting (SLM) of IN718. The model utilizes the effective medium approach to solve the heat transfer and melt-flow dynamics within the melt-pool in a computationally efficient manner. In addition, the model replaces the built-in linear solidification function in commercial code ANSYS Fluent with a self-written non-linear solidification function in order to better describe the melt-pool formation during the SLM process. The simulation results obtained for the depth and width of the melt-pool are compared with the experimental data reported in the literature. Moreover, the simulated melt-pool length defined by the liquid-solid phase transition point of the melt-pool trailing edge is compared with the experimental observations obtained using a self-built in-situ inspection system. For the simulated melt-pool depth and width, no significant difference is found between the non-linear and linear models for the solidification behavior of IN718. However, the non-linear model provides a better prediction of the melt-pool length than the linear solidification function. Many studies have shown that the solid-liquid transition in the melting range of the material during cooling plays an important role in determining both the melt-pool length and the cooling rate of the SLM parts. As a result, the effects of the non-linear solidification behavior of IN718 are important not only in determining the melt-pool formation, but also in governing the liquid-solid transition process at the melt-pool tailing edge, which is one of the most important factors affecting the microstructure and residual stress accumulation of SLM printed parts.

Bit commitment is a fundamental cryptographic task that guarantees a secure commitment between two mutually mistrustful parties and is a building block for many cryptographic primitives, including coin tossing, zero-knowledge proofs, oblivious transfer and secure two-party computation. Unconditionally secure bit commitment was thought to be impossible until recent theoretical protocols that combine quantum mechanics and relativity were shown to elude previous impossibility proofs. Here we implement such a bit commitment protocol. In the experiment, the committer performs quantum measurements using two quantum key distribution systems and the results are transmitted via free-space optical communication to two agents separated with more than 20 km. The security of the protocol relies on the properties of quantum information and relativity theory. We show that, in each run of the experiment, a bit is successfully committed with less than 5.68*10^-2 cheating probability. Our result demonstrates unconditionally secure bit commitment and the experimental feasibility of relativistic quantum communication., 15 pages, 2 figures