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Contact-based biometric applications primarily use prints from a finger or a palm for a single instance in different applications. For access control, there is an enrollment process using one or more templates which are compared with verification images. In forensics applications, randomly located, partial, and often degraded prints acquired from a crime scene are compared with the images captured from suspects or existing fingerprint databases, like AFIS. In both scenarios, if we need to use handprints which include segments from the finger and palm, what would be the solution? The motivation behind this is the concept of one single algorithm for one hand. Using an algorithm that can incorporate both prints in a common processing framework can be an alternative which will have advantages like scaling to larger existing databases. This work proposes a method that uses minutiae or minutiae-like features, Delaunay triangulation and graph matching with invariant feature representation to overcome the effects of rotation and scaling. Since palm prints have a large surface area with degradation, they tend to have many false minutiae compared to fingerprints, and the existing palm print algorithms fail to tackle this. The proposed algorithm constructs Delaunay triangulated graphs (DTG) using minutiae where Delaunay triangles form from minutiae, and initiate a collection of base triangles for opening the matching process. Several matches may be observed for a single triangle match when two images are compared. Therefore, the set of initially matched triangles may not be a true set of matched triangles. Each matched triangle is then used to extend as a sub-graph, adding more nodes to it until a maximum graph size is reached. When a significant region of the template image is matched with the test image, the highest possible order of this graph will be obtained. To prove the robustness of the algorithm to geometrical variations and working ability with extremely degraded (similar to latent prints) conditions, it is demonstrated with a subset of partial-quality and extremely-low-quality images from the FVC (fingerprint) and the THUPALMLAB (palm print) databases with and without geometrical variations. The algorithm is useful when partial matches between template and test are expected, and alignment or geometrical normalization is not accurately possible in pre-processing. It will also work for cross-comparisons between images that are not known a priori. [ABSTRACT FROM AUTHOR]

Due to the development of printing materials, light-cured 3D printing is playing an increasingly important role in industrial and consumer markets for prototype manufacturing and conceptual design due to its advantages in high-precision and high-surface finish. Despite its widespread use, it is still difficult to achieve the 3D printing requirements of large volume, high resolution, and high speed. Currently, traditional light-cured 3D printing technologies based on stereolithography, such as regular DLP and SLA, can no longer meet the requirements of the processing size and processing rate. This paper introduces a dynamic projection of 3D printing technology utilizing a digital micro-mirror device (DMD). By projecting the ultraviolet light pattern in the form of "animation", the printing resin is continuously cured in the exposure process to form the required three-dimensional structure. To print large-size objects, the three-dimensional model is sliced into high-resolution sectional images, and each layer of the sectional image is further divided into sub-regional images. These images are dynamically exposed to the light-curing material and are synchronized with the scanning motion of the projection lens to form a static exposure pattern in the construction area. Combined with the digital super-resolution, this system can achieve the layering and fine printing of large-size objects up to 400 × 400 × 200 mm, with a minimum feature size of 45 μm. This technology can achieve large-size, high-precision structural printing in industrial fields such as automobiles and aviation, promoting structural design, performance verification, product pre-production, and final part processing. Its printing speed and material bending characteristics are superior to existing DLP light-curing 3D printing methods. [ABSTRACT FROM AUTHOR]

Ceramic 3D printing is a promising technology that overcomes the limitations of traditional ceramic molding. It offers advantages such as refined models, reduced mold manufacturing costs, simplified processes, and automatic operation, which have attracted a growing number of researchers. However, current research tends to focus more on the molding process and print molding quality rather than exploring printing parameters in detail. In this study, we successfully prepared a large-size ceramic blank using screw extrusion stacking printing technology. Subsequent glazing and sintering processes were used to create complex ceramic handicrafts. Additionally, we used modeling and simulation technology to explore the fluid model printed by the printing nozzle at different flow rates. We adjusted two core parameters that affect the printing speed separately: three feed rates were set to be 0.001 m/s, 0.005 m/s, and 0.010 m/s, and three screw speeds were set to be 0.5 r/s, 1.5 r/s, and 2.5 r/s. Through a comparative analysis, we were able to simulate the printing exit speed, which ranged from 0.0751 m/s to 0.6828 m/s. It is evident that these two parameters have a significant impact on the printing exit speed. Our findings show that the extrusion velocity of clay is approximately 700 times faster than the inlet velocity at an inlet velocity of 0.001–0.010 m/s. Furthermore, the screw speed is influenced by the inlet velocity. Overall, our study sheds light on the importance of exploring printing parameters in ceramic 3D printing. By gaining a deeper understanding of the printing process, we can optimize printing parameters and further improve the quality of ceramic 3D printing. [ABSTRACT FROM AUTHOR]

DcAFF (discontinuous aligned fibre filament) is a novel material for fused filament fabrication (FFF) 3D printing made of highly aligned discontinuous fibres produced using high performance discontinuous fibre (HiPerDiF) technology. It reinforces a thermoplastic matrix to provide high mechanical performance and formability. Accurate printing of DcAFF poses a challenge, especially for complex geometries, because: (i) there is a discrepancy between the path where the filament experiences the adhering pressure from the filleted nozzle and the nozzle path; and (ii) the rasters display poor adhesion to the build platform immediately after deposition, which causes the filament to be dragged when the printing direction changes. This paper explains the implication of these phenomena on steering capabilities and examines the techniques for improving DcAFF printing accuracy. In the first approach, the machine parameters were adjusted to improve the quality of the sharp turning angle without changing the desired path, but this showed insignificant effects in terms of precision improvements. In the second approach, a printing path modification with a compensation algorithm was introduced. The nature of the inaccuracy of the printing at the turning point was studied with a first-order lag relationship. Then the equation to describe the deposition raster inaccuracy was determined. A proportional–integral (PI) controller was added to the equation to calculate the nozzle movement in order to bring the raster back to the desired path. The applied compensation path is shown to give an accuracy improvement in curvilinear printing paths. This is particularly beneficial when printing larger circular diameter curvilinear printed parts. The developed printing approach can be applied with other fibre reinforced filaments to achieve complex geometries. [ABSTRACT FROM AUTHOR]

In the context of the use of AM, particularly in the L-PBF technique, the printability characterization of material occurs through the identification of its printability map as a function of printing process parameters. The printability map identifies the region where the powder melting is optimal and ensures a dense and defect-free material. Identifying the zones affected by physical phenomena that occur during the printing process which lead to material defects such as keyhole, lack of fusion and balling mode is also possible. Classical methods for the characterization of material and the identification of its printability map require the printing of a large number of specimens. The analysis of the specimens is currently time-consuming and costly. This paper proposed a methodology to identify optimal process parameters in L-PBF using an integrated single and multi-tracks analyses embedded in an overall algorithm with detailed metrics and specific factors. The main scope is to speed up the identification of printability window and, consequently, material characterization, reducing the number of micrographic analyses. The method is validated through an experimental campaign assessing the material microstructure in terms of porosity and melt pool evaluation. The case study on IN718 superalloy shows how the application of the proposed method allows an important reduction of micrographic analysis. The results obtained in the case study are a reduction of 25% for the complete definition of the printability map and more than 90% for identifying the zone with a high productivity rate. [ABSTRACT FROM AUTHOR]

Compared with conventional reactors that are designed by traditional micromachining technology, the use of 3D-printing technology to manufacture multichannel large-volume microchannel reactors as reaction equipment to remove low-concentration NOX by the wet method is simple and convenient, and the processing cost is low. The results showed that when the concentration of NO was 400 ppm, the mixed solution of (NH2)2CO mass fraction of 3% and H2O2 concentration of 0.5 mol/L was used, and the flow rates of gas and liquid were 100 mL/min, respectively, under the experimental conditions of pH = 11, solution temperature of 20 °C and 500 mL solution recycling for 20 min, the best removal effect of NOX was achieved, and the removal efficiency was 100%. When the O2 content in the flue gas was increased and the number and length of microchannels were increased, the NOX removal efficiency increased accordingly, which was conducive to the rapid and efficient reaction. The application of the microchannel reactor presents a new method for improving the air quality and reducing environmental pollution in the future. [ABSTRACT FROM AUTHOR]

In this research, the effects of fumed silica (FS) on the Ultraviolet (UV)-ink rheological behavior and processing windows were discussed. Objects using different concentrations of FS inks were printed by the modified UV-Direct ink writing (DIW) printer. The function of fumed silica in the ink-based system has been verified, and the processing scope has been expended with a suitable amount of FS combined with the UV light. The results show that the combination of a suitable amount of FS with the UV-DIW system reaches fast and accurate printing with a larger processing window compared to the non-UV system. However, an excessively high concentration of FS will increase the yield stress of the ink, which also increases the requirement of extrusion unit and the die-swelling effects. [ABSTRACT FROM AUTHOR]

Research and technological advancements in 3D concrete printing (3DCP) have led to the idea of applying it to offshore construction. The effect of gravity is reduced underwater, which can have a positive effect on 3DCP. For basic verification of this idea, this study printed and additively manufactured specimens with the same mortar mixture in air and underwater and evaluated properties in the fresh state and the hardened state. The mechanical properties were evaluated using the specimens produced by direct casting to the mold and specimens produced by extracting from the additive part through coring and cutting. The results of the experiment show that underwater 3D printing required a greater amount of printing output than in-air 3D printing for a good print quality, and buildability was improved underwater compared to that in air. In the case of the specimen layered underwater, the density and compressive strength decreased compared to the specimen layered in air. Because there are almost no effects of moisture evaporation and bleeding in water, the interlayer bond strength of the specimen printed underwater was somewhat larger than that printed in air, while there was no effect of the deposition time interval underwater. [ABSTRACT FROM AUTHOR]