A model of bead size based on the dynamic response of CMT-based wire and arc additive manufacturing process parameters

Purpose This paper aims at fabricating large metallic components with high deposition rates, low equipment costs through wire and wire and arc additive manufacturing (WAAM) method, in order to achieve the morphology and mechanical properties of manufacturing process, a bead morphology prediction model with high precision for ideal deposition of every pass was established. Design/methodology/approach The dynamic response of the process parameters on the bead width and bead height of cold metal transfer (CMT)-based AM was analyzed. A laser profile scanner was used to continuously capture the morphology variation. A prediction model of the deposition bead morphology was established using response surface optimization. Moreover, the validity of the model was examined using 15 groups of quadratic regression analyzes. Findings The relative errors of the predicted bead width and height were all less than 5% compared with the experimental measurements. The model was then preliminarily used with necessary modifications, such as further considering the interlayer process parameters, to guide the fabrication of complex three-dimensional components. Originality/value The morphology prediction of WAAMed bead is a critical issue. Most research has focused on the formability and defects in CMT-based WAAM and little research on the effect of process parameters on the morphology of the deposited layer in CMT-based WAAM has been conducted. To test the sensitivities of the processing parameters to bead size, the dynamic response of key parameters was investigated. A regression model was established to guide the process parameter optimization for subsequent multi-layer or component deposition.

Optical tweezers-based velocimetry: a method to measure microscale unsteady flows

In the study of micro-scale biological flows, velocimetry methods based on passive tracers, such as micro-PIV and micro-PTV, are well established to characterize steady flows. However, these methods become inappropriate for measuring unsteady flows of small amplitude, because, on these scales, the motion of passive tracers cannot be distinguished from Brownian motion. In this study, we use optical tweezers (OTs) in combination with Kalman filtering, to measure unsteady microscopic flows with high temporal accuracy. This method is referred to as optical tweezers-based velocimetry (OTV). The OTV method measures the nanometric displacements of a trapped bead, and predicts the instantaneous velocity of the flow by employing a Kalman filter. We discuss the accuracy of OTV in measuring unsteady flows with 1.5–70 $$\upmu$$ μ m s$$^{-1}$$ - 1 amplitudes and 10–90 Hz frequencies. We quantify how the bead size and the laser power affect the velocimetry accuracy, and specify the optimal choices for the bead size and laser power to measure different unsteady flows. OTV accurately measures unsteady flows with amplitudes as small as 3–6 $$\upmu$$ μ m s$$^{-1}$$ - 1 . We compare the accuracy of OTV and micro-PTV, and characterize the flow regime for which OTV outperforms micro-PTV. We also demonstrate the robustness of OTV by measuring the unsteady flow created by the cilia of green alga Chlamydomonas reinhardtii, and comparing with numerical predictions based on Stokes equations. An open-source implementation of the OTV software in Matlab is available through the 4TU.Centre for Research Data. Graphic abstract

Effect of Glass Bead Refractive Index on Pavement Marking Retroreflectivity Considering Passenger Vehicle and Airplane Geometries

Pavement marking retroreflectivity depends on several factors including but not limited to the type of retroreflective optics, binder, installation quality, marking condition, and measurement type/geometry. Texas A&M Transportation Institute (TTI) evaluated the retroreflectivity of 19 pavement marking panels, prepared with different types of glass bead at standard 30-m and non-standard measurement geometries. The non-standard geometries represented typical commercial airplane configurations. The primary purpose of the research was to evaluate the effects of the glass bead refractive index (RI) (1.5 versus 1.9) and the measurement geometry on pavement marking retroreflectivity. Results showed a decrease in retroreflectivity with an increase in observation and entrance angles for both 1.5 and 1.9 RI. The study showed higher retroreflectivity levels for high RI beads at all the geometries evaluated. The result showed that 1.9 RI beads exhibit an average of 171% (862 mcd/m2/lx) higher retroreflectivity at standard 30-m car geometry as well as 102% (193 mcd/m2/lx) higher retroreflectivity at airplane geometry compared with 1.5 RI beads. The study found that an increase in bead RI had a larger effect on retroreflectivity than did an increase in bead size. The effect of the measurement geometry on the retroreflectivity level of the markings highlights a limitation of using the 30-m car geometry to represent the visibility of markings from a pilot’s perspective. Additional work should be conducted to better assess the visibility of markings from various vehicle platforms and how to best represent the visibility through retroreflectivity measurement.

Assessment of fecal DNA extraction protocols for metagenomic studies

Background Shotgun metagenomic sequencing has improved our understanding of the human gut microbiota. Various DNA extraction methods have been compared to find protocols that robustly and most accurately reflect the original microbial community structures. However, these recommendations can be further refined by considering the time and cost demands in dealing with samples from very large human cohorts. Additionally, fungal DNA extraction performance has so far been little investigated. Results We compared 6 DNA extraction protocols, MagPure Fast Stool DNA KF Kit B, Macherey Nagel™ NucleoSpin™®Soil kit, Zymo Research Quick-DNA™ Fecal/Soil Microbe kit, MOBIO DNeasy PowerSoil kit, the manual non-commercial protocol MetaHIT, and the recently published protocol Q using 1 microbial mock community (MMC) (containing 8 bacterial and 2 fungal strains) and fecal samples. All samples were manually extracted and subjected to shotgun metagenomics sequencing. Extracting DNA revealed high reproducibility within all 6 protocols, but microbial extraction efficiencies varied. The MMC results demonstrated that bead size was a determining factor for fungal and bacterial DNA yields. In human fecal samples, the MagPure bacterial extraction performed as well as the standardized protocol Q but was faster and more cost-effective. Extraction using the PowerSoil protocol resulted in a significantly higher ratio of gram-negative to gram-positive bacteria than other protocols, which might contribute to reported gut microbial differences between healthy adults. Conclusions We emphasize the importance of bead size selection for bacterial and fungal DNA extraction. More importantly, the performance of the novel protocol MP matched that of the recommended standardized protocol Q but consumed less time, was more cost-effective, and is recommended for further large-scale human gut metagenomic studies.

Design of cellulose derivative and alginate based smart polymers to develop stomach specific floating drug delivery system

Background: Polysaccharide based gastro-retentive drug delivery systems (GRDDSs) can retain in the gastric fluid of stomach for longer time and release entrapped drug in controlled and localized manner, which can ensure optimal drug concentration at the site of action with improved bioavailability and reduced side effects of acid suppressive drugs like ranitidine. Objective: The objective of present study was to design smart polymers for gastro-retentive drug delivery of ranitidine through ionic-gelation of carboxymethyl cellulose (CMC) and sodium alginate (ALG). Methods: The optimal reaction conditions for synthesis of beads were evaluated by varying reaction parameters during synthesis and were obtained as [CMC] = 1.5% (w/v), [ALG] = 0.5% (w/v) and [CaCl2] = 0.1 M with maximum equilibrium swelling ratio (2922.50±0.90)%. The drug loading was carried out by simultaneous and swelling equilibrium methods. Beads were characterized by SEM, PXRD, FTIR, TGA, bead size and swelling studies. Results: Increase in Ca2+ ions and ALG concentration resulted in decrease in swelling capacity and increase in bead size. Beads got collapsed in phosphate buffer solution and swelling had been occurred through non-Fickian diffusion mechanism. Floating beads with (51.05±0.25)% entrapment efficiency for simultaneous drug loading method exhibited Fickian diffusion mechanism and best fitted in Higuchi model. The diffusion coefficient and initial rate of drug release in simulated gastric fluid demonstrated swelling controlled gastro-retentive release of ranitidine. Conclusion: These smart polymeric beads have potential to use as a promising candidate for the design of GRDDSs meant for the treatment of gastric ulceration and gastro-oesophageal reflux disease.