Efficient Post-processing Technique Research Articles

Laser powder bed fused 304L steel shot-peened with various ceramic shot sizes: Surface/subsurface characteristics, tensile behavior, and fatigue behavior

Shot peening is an efficient post-processing technique for eliminating surface manufacturing defects, inducing compressive residual stress, and improving the mechanical properties of laser powder bed fused (L-PBFed) metallic materials. With a series of microstructural characterizations, this work comprehensively evaluated the influence of ceramic shot size on the surface characteristics, subsurface characteristics, and mechanical properties, especially fatigue performance, of L-PBF manufactured 304L austenitic stainless steel (SS). The mechanical testing process was in situ observed using an infrared thermal camera, and the tensile-fractured and fatigue-fractured microstructures were systematically examined, aiming to explore the life improvement mechanisms caused by different ceramic shot sizes. The results revealed that when compared to small-sized AZB 100 shots, the large-sized AZB 300 shots could result in higher surface roughness, larger thickness reduction, more apparent surface gradient structure, higher strength, and longer fatigue lifetimes. The strength improvement could be associated with the size reduction of L-PBF induced subsurface defects, the grain refinement at the surface layer, and the α'-martensitic transformation during tensile deformation. The life improvement could be primarily attributed to the subsurface defect strengthening, which resulted in the fatigue crack initiation transition from subsurface defects to surface defects. During the fatigue process, the energy dissipation originating from the core materials dominated the thermal equilibrium temperature, whereas the density of micro-defects (crystalline defects) at the surface layer dominated the crack tip temperature. These findings provide a basic understanding of how to advance the shot peening process for L-PBFed materials.

Efficient Post-Processing techniques for enhancing performance of PeLEDs

Metal halide perovskites have gained significant attention as a hopeful research area for developing perovskite light-emitting diodes. Achieving high-quality and cost-effective perovskite light-emitting diodes is crucial for their commercialization. This report focuses on an effective postprocessing approach that enhances the performance of perovskite emissive thin films without the need for vacuum equipment. By employing annealing and plasma treatment, the method successfully reduces grain size, and increases photoluminescence quantum yield, carrier recombination rate, external quantum efficiency (∼20.5 %), and luminance (∼68000 cd/m2) of the perovskite emitters (MAPbBr3). The proposed technique offers a time-efficient and economical solution for fabricating efficient commercial devices.

Improved fatigue life of SLM-produced TC4 alloy treated by a pulsed magnetic field

Microstructural defects have been considered to be detrimental to fatigue life of SLM-produced TC4. To improve the fatigue property of the alloy, pulsed magnetic field (PMT) treatment, an efficient post-processing technique, was utilized in this work. The evolution concerning fatigue life, microstructure, stress state, and fatigue fracture behavior influenced by PMT was investigated. After the treatment, the average fatigue life under a certain load is increased by 471.13%, and the reliability of the life of the specimen is improved. The mechanism that PMT action on the microstructure lies in dislocation motion. It can be found dislocation density decreased evidently with more uniform distribution. Furthermore, with the influence of dislocation, superficial and internal residual stress (RS) of the material, in terms of magnitude, decreased by more than 60% and 10%, respectively. And superficial RS changed from a tensile state to a compressive state. Besides, the treated specimen exhibited better fracture behavior by comparatively analyzing microstructure alongside fatigue initiation. According to this comparison related to the primary slip system and dislocation, improvement of PMT on fatigue performance of SLM-ed TC4 can be validated.

Superconvergent postprocessing of the C1-conforming finite element method for fourth-order boundary value problems

We develop a very simple but efficient postprocessing technique for enhancing the accuracy of the C1-conforming finite element method for fourth-order boundary value problems. The key idea of the postprocessing technique is to add certain generalized Jacobi polynomials of degree larger than k to the Galerkin approximation of degree k. We prove that the postprocess improves the order of convergence of the Galerkin approximation under L2- and H2-norms. Numerical experiments are provided to illustrate the theoretical results. We also present computational results for a steady-state problem with to demonstrate the effectiveness of the postprocessing.

Superconvergent postprocessing of the discontinuous Galerkin time stepping method for nonlinear Volterra integro-differential equations

We propose a very simple but efficient postprocessing technique for improving the global accuracy of the discontinuous Galerkin (DG) time stepping method for solving nonlinear Volterra integro-differential equations. The key idea of the postprocessing technique is to add a higher order generalized Jacobi polynomial of degree k+1 with parameters (−1,0) to the DG approximation of degree k. We prove that the postprocessed DG approximations converge one order faster than the unprocessed DG approximations in the L2-, H1- and L∞-norms. Based on these postprocessed superconvergence results, we construct several a posteriori error estimators and prove that they are asymptotically exact as the step-size decreases. Numerical experiments are carried out to verify the theoretical results.

How Many Reindeer? UAV Surveys as an Alternative to Helicopter or Ground Surveys for Estimating Population Abundance in Open Landscapes

Conservation of wildlife depends on precise and unbiased knowledge on the abundance and distribution of species. It is challenging to choose appropriate methods to obtain a sufficiently high detectability and spatial coverage matching the species characteristics and spatiotemporal use of the landscape. In remote regions, such as in the Arctic, monitoring efforts are often resource-intensive and there is a need for cheap and precise alternative methods. Here, we compare an uncrewed aerial vehicle (UAV; quadcopter) pilot survey of the non-gregarious Svalbard reindeer to traditional population abundance surveys from ground and helicopter to investigate whether UAVs can be an efficient alternative technology. We found that the UAV survey underestimated reindeer abundance compared to the traditional abundance surveys when used at management relevant spatial scales. Observer variation in reindeer detection on UAV imagery was influenced by the RGB greenness index and mean blue channel. In future studies, we suggest testing long-range fixed-wing UAVs to increase the sample size of reindeer and area coverage and incorporate detection probability in animal density models from UAV imagery. In addition, we encourage focus on more efficient post-processing techniques, including automatic animal object identification with machine learning and analytical methods that account for uncertainties.

Development of material extrusion 3D printable ABS/PC polymer blends: influence of styrene–isoprene–styrene copolymer on printability and mechanical properties

ABSTRACT In this work, a series of 3D printable ABS/PC blends were successfully prepared via filament extrusion and fused deposition fabrication. Influence of styrene–isoprene–styrene (SIS) copolymer on printability and mechanical properties were examined. It was revealed that SIS not only enhances the compatibility of the two blend phases, but also enhances the 3D printability of the resulting materials. The effect of print temperature, bed temperature, print speed, layer thickness, number of shell and infill density on mechanical properties of the printed parts were investigated using the Taguchi experimental design method, and the samples were printed using optimized process parameters according to the Taguchi method. It was revealed that the optimization of extrusion multiplier was an efficient method to overcome voids in the printed parts. Interestingly, incorporation of SIS considerably improved the adhesion and distribution of the blend phases. In addition, with an increase in SIS content, tensile strength, yield strength, elastic modulus, and hardness were found to decrease, whereas Izod impact strength and percentage elongation values of the 3D-printable blend increased. Finally, an efficient post-processing technique was successfully employed to improve the aesthetics of additive manufactured specimens. This work provides a facile strategy to prepare new 3D-printable polymer blends with improved adhesion between phases and minimized voids in the printed parts.

Antenna Design and Analysis Using the Sequential Loading Method

This article presents a new method for accurately designing and analyzing an antenna or array. The proposed technique operates solely on the transfer admittance matrix of a perfect electrically conducting antenna fabric that is obtained using a full-wave simulator only once. The desired antenna, which must be a subset of the fabric, is then synthesized by progressively loading the fabric and applying a computationally efficient iterative postprocessing technique that transforms the stored admittance matrix into one that corresponds to the desired antenna or array. Given that the admittance matrix of the fabric is used as the basis for all subsequent antennas that can be represented by the fabric, it contains the solutions to an entire class of antennas. The proposed method is demonstrated by applying it to the class of colinear antennas up to five wavelengths long, arranged along a single axis. The method is validated by comparing its results to those obtained using a conventional full-wave simulator. The proposed method is applied first to the case of multiple loads located at arbitrary port locations along the fabric. Then, open-circuited loads are used to decimate the tips of a linear antenna to demonstrate that the method accurately predicts the response of an electrically shorter antenna. Finally, decimation is used to transform the fabric into an array of smaller antennas, where it is shown that mutual coupling effects are accurately predicted.

Quantitative analysis of surface treatment to enhance surface finish and mechanical characteristics of ABS parts

Lack of surface integrity and porosity are the key factors limiting the growth of fused deposition modelling (FDM) method. The method requires an efficient post processing technique which is consistent, controllable and predictable to improve surface finish without affecting geometrical and mechanical properties. This work aims to setup a novel method to treat FDM parts to improve surface quality as well as heat absorption, which in turn makes it suitable for high temperature applications. In this process, Acrylonitrile Butadiene Styrene (ABS) parts are treated with montmorillonite nanoclay via acetone bathing. The parameters like layer thickness, nanoclay content and immersion time were considered for the investigation. The roughness is measured based on the deviation from the least square plane fixed to the computed surface topography data sets, which allows to investigate the influence of smoothing parameters. Further, parts have been investigated for thermal and mechanical properties to predict optimal smoothing parameters. Results showed the proposed surface treatment method could effectively reduce the roughness of the ABS parts. In addition, nanoclay coating showed remarkable effect on the ultimate tensile strength (UTS), reflection of heat radiation resulting in the reduction of heat absorption.

Analytical modeling of laminated composite plates integrated with piezoelectric layer using Trigonometric Zigzag theory

The analytical solution for static analysis of laminated composite plate integrated with piezoelectric fiber reinforced composite actuator is obtained using a recently developed Trigonometric Zigzag theory. The kinematic field consists of five independent field variables accommodating non-linear variation of transverse shear strains through the thickness of the laminated composite plate. The principle of minimum potential energy is adopted to derive the governing equations of equilibrium. Navier’s solution technique is employed to convert the system of coupled partial differential equations into a system of algebraic equations. The electric potential is assumed to vary linearly through the thickness of the piezoelectric layer. The analytical formulation also does not include voltage as an additional primary variable. The response in the form of deflection and stresses are obtained for smart composite plates subjected to electro-mechanical loads and compared with the elasticity solutions and available results reported by other researchers in the existing literature. The transverse shear stresses are accurately determined by an efficient post-processing technique of integrating the equilibrium equations of elasticity. Parametric studies on actuation in the response of the smart composite plate are also presented graphically in order to have a clear understanding of the static behavior.

High temperature annealing effects on spectral, microstructural and laser damage resistance properties of sputtered HfO2 and HfO2-SiO2 mixture-based UV mirrors

Hafnium oxide is widely used as high refractive index material for making high power laser coatings for UV spectral range. Thermal annealing is one of the most efficient post-processing techniques for improving optical coating stress, its absorption, and resistance to laser radiation. In this article we investigate high temperature annealing effects on optical, microstructural, surface and laser radiation resistance properties of pure hafnia and two different hafnia-silica mixture-based sputtered dielectric mirrors for 266 nm wavelength. Three distinct annealing temperatures were selected for different coatings, leading to amorphous and polycrystalline phases of high refractive index layers. Annealing increased reflectance of all mirrors. Annealing at high temperatures that triggered crystallization considerably increased LIDT of all coatings. In addition, substantial increase in transmittance at shorter wavelength range was registered. Our results suggest that high temperature annealing above crystallization onset of HfO2 and HfO2-SiO2 mixture based dielectric mirrors has a great potential of increasing their damage resistance for UV laser pulses.

Efficient postprocessing technique for fabricating surface nanoscale axial photonics microresonators with subangstrom precision by femtosecond laser.

We demonstrated the subangstrom precise correction of surface nanoscale axial photonics (SNAP) micro-resonators by the femtosecond (fs) laser postprocessing technique for the first time. The internal stress can be induced by fs laser inscriptions in the fiber, causing nanoscale effective radius variation (ERV). However, the obtained ultraprecise fabrication usually undergoes multiple tries. Here, we propose a novel postprocessing technique based on the fs laser that significantly reduces the ERV errors and improves the fabrication precision without iterative corrections. The postexposure process is achieved at the original exposure locations using lower pulse energy than that in the initial fabrication process. The results show that the ERV is nearly proportional to the pulse energy of the postexposure process. The slope of the ERV versus the pulse energy is 0.07Å/nJ. The maximum of the postprocessed ERV can reach 8.0Å. The repeatability was experimentally verified by accomplishing the correction on three SNAP microresonators with the precision of 0.75Å. The developed fabrication technique with fs laser enables SNAP microresonators with new breakthrough applications for optomechanics and filters.

Proposed dynamic error control techniques for QoS improvement of wireless 3D video transmission

SummaryError control techniques like error resilience (ER) and error concealment (EC) are efficient techniques to ameliorate the lost macroblocks (MBs) in the 3D video (3DV) communication system. In this paper, we propose efficient and adaptive hybrid ER‐EC algorithms for 3DV transmission over error‐prone wireless channels. At the encoder, adaptive preprocessing ER mechanisms are proposed through using the context adaptive variable length coding entropy, slice structured coding modes, and explicit flexible macroblock ordering mapping. They are used to assist the suggested EC techniques at the decoder to accurately reconstruct the erroneous MBs and frames. At the decoder, an efficient postprocessing EC technique with multiproposition methods is proposed to dynamically select the convenient EC hypothesis method based on the size of the lost MBs, the faulty view, and the frame type. It conceals the received erroneous MBs of intra‐encoded and inter‐encoded frames of the transmitted 3DV by exploiting the temporal, spatial, and inter‐view correlations among frames and views. To further improve the decoded 3DV quality, a weighted overlapping block motion and disparity compensation technique is used to reinforce the performance of the suggested ER‐EC techniques. Experimental results on various 3DV streams prove that the suggested techniques have considerably acceptable subjective and objective 3DV performance. They achieve an improved average peak signal‐to‐noise ratio gain by almost 2.85 dB compared to the conventional error control algorithms at a packet loss rate = 40%.

A hybrid algorithm for speckle noise reduction of ultrasound images

Background and objectiveMedical images are contaminated by multiplicative speckle noise which significantly reduce the contrast of ultrasound images and creates a negative effect on various image interpretation tasks. In this paper, we proposed a hybrid denoising approach which collaborate the both local and nonlocal information in an efficient manner. The proposed hybrid algorithm consist of three stages in which at first stage the use of local statistics in the form of guided filter is used to reduce the effect of speckle noise initially. Then, an improved speckle reducing bilateral filter (SRBF) is developed to further reduce the speckle noise from the medical images. Finally, to reconstruct the diffused edges we have used the efficient post-processing technique which jointly considered the advantages of both bilateral and nonlocal mean (NLM) filter for the attenuation of speckle noise efficiently. MethodsThe performance of proposed hybrid algorithm is evaluated on synthetic, simulated and real ultrasound images. The experiments conducted on various test images demonstrate that our proposed hybrid approach outperforms the various traditional speckle reduction approaches included recently proposed NLM and optimized Bayesian-based NLM. ResultsThe results of various quantitative, qualitative measures and by visual inspection of denoise synthetic and real ultrasound images demonstrate that the proposed hybrid algorithm have strong denoising capability and able to preserve the fine image details such as edge of a lesion better than previously developed methods for speckle noise reduction. ConclusionsThe denoising and edge preserving capability of hybrid algorithm is far better than existing traditional and recently proposed speckle reduction (SR) filters. The success of proposed algorithm would help in building the lay foundation for inventing the hybrid algorithms for denoising of ultrasound images.

Improvement of surface integrity of Nimonic C 263 super alloy produced by WEDM through various post-processing techniques

Wire electrical discharge machining (WEDM) process provides a cost effective solution to generate complicated shapes in various exotic materials, irrespective of their hardness. However, WEDM process removes the material by thermal erosion mechanism which in term affects the topography and mechanical characteristics of the material. In view of this, an effort is needed to eliminate the adverse effect of WEDM process on the final product surface. Therefore, the present work evaluates surface morphology, surface roughness, elemental composition, micro-hardness and residual stress of the machined surface produced by various WEDM strategies such as, rough cut and finish cut. Two post-processing techniques namely, grinding and etching-grinding are proposed to remove recast layer and also to improve the surface integrity of the machined surface. The proposed strategy found to be an efficient post-processing technique for complete removal of recast layer and generation of surface with an average surface roughness as low as 0.024 μm, high compressive residual stress as high as 500 MPa and basic elemental composition. The basic mechanism of these process are also explained in details.

Accurate Cell-Centered Discretizations for Modeling Multiphase Flow in Porous Media on General Hexahedral and Simplicial Grids

Summary We introduce an accurate cell-centered method for modeling Darcy flow on general quadrilateral, hexahedral, and simplicial grids. We refer to these discretizations as the multipoint-flux mixed-finite-element (MFMFE) method. The MFMFE method is locally conservative with continuous fluxes and can be viewed within a variational framework as a mixed finite-element method with special approximating spaces and quadrature rules. We study two versions of the method: with a symmetric quadrature rule on smooth grids and a nonsymmetric quadrature rule on rough grids. The framework allows for handling hexahedral grids with nonplanar faces defined by trilinear mappings from the reference cube. Moreover, the MFMFE method allows for local elimination of the velocity, which leads to a cell-centered pressure system. Theoretical and numerical results demonstrate first-order convergence on rough grids. Second-order superconvergence is observed on smooth grids. We also discuss a new splitting scheme for modeling multiphase flows that can treat higher-order transport discretizations for saturations. We apply the MFMFE method to obtain physically consistent approximations to the velocity and a reference pressure on quadrilateral or hexahedral grids, and a discontinuous Galerkin method for saturations. For higher-order saturations, we propose an efficient post-processing technique that gives accurate velocities in the interior of the gridblocks. Computational results are provided for flow in highly heterogeneous reservoirs, including different capillary pressures arising from different rock types.

Efficient postprocessing of edge maps for image segmentation based on greedy correction cost minimization

A highly efficient postprocessing technique which enables the result of edge detection to be used for image segmentation is proposed. The method starts from an edge map obtained by a standard edge detection tool, e.g., Canny edge detector, and corrects it to obtain an edge map in which every edge point belongs to a closed boundary of an image region. The correction of the original edge map assumes removing some of the existing edge points as well as inserting virtual edge points. The proposed edge map correction procedure consists of two stages: (1) edge linking, which closes the gaps in edge contours by inserting virtual edge elements, and (2) edge pruning, which rejects spurious contours thereby avoiding over-segmentation. The edge pruning procedure performs an iterative greedy minimization of a correction cost function, while keeping all contours of the edge map closed. The proposed approach is evaluated using a set of standard test images.

Reverse reconciliation for continuous variable quantum key distribution

An efficient and practical post-processing technique based on reverse reconciliation for continuous variable quantum key distribution is proposed and simulated with low-density parity check (LDPC) codes. MultiLevel Coding/MultiStage Decoding, which fully utilizes optimization technique such as vector quantization and iterative decoding and the optimal channel coding most close to the Shannon limit, was used to realize efficient reverse reconciliation algorithm. Simulation results showed that the proposed method can improve the secure key distribution rate to 2.2 kb/s and the coding efficiency to 0.89 over 20 km in single-mode optical fiber. Moreover, there still is room for much improvement.

Combinatorial Algorithms for Fast Clock Mesh Optimization

Clock mesh has been widely used to distribute the clock signal across the chip. Clock mesh is driven by a top-level tree and a set of mesh buffers. We present fast and efficient combinatorial algorithms to simultaneously identify the candidate locations as well as sizes of the buffers driving the clock mesh. We show that such a sizing offers a better solution than inserting buffers of uniform size across the mesh. Due to the high redundancy, a mesh architecture offers high tolerance toward variations in clock skew. However, such a redundancy comes at the expense of mesh wire length and power dissipation. Based on survivable network theory, we formulate the problem to reduce the clock mesh by retaining only those edges that are critical to maintain redundancy. Such a formulation offers designer the option to tradeoff between power and tolerance to process variations. We present efficient postprocessing techniques to reduce the size of the mesh buffers after mesh reduction. Experimental results indicate that our techniques can result in <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">power savings up to 28% with less than 3.3% delay penalty</i> . We also present driver models that can help in simulating the clock mesh. Such models achieve near-HSPICE accuracy with significant speedup in run time.

A Higher-Order Formulation of the Mimetic Finite Difference Method

A new mimetic finite difference method for the diffusion problem is developed by using a linear interpolation for the numerical fluxes. This approach provides a higher-order accurate approximation to the flux of the exact solution. In analogy with the original formulation, a family of local scalar products is constructed to satisfy the fundamental properties of local consistency and spectral stability. The scalar solution field is approximated by a piecewise constant function. A computationally efficient postprocessing technique is also proposed to get a piecewise quadratic polynomial approximation to the exact scalar variable. Finally, optimal convergence rates and accuracy improvement with respect to the lower-order formulation are shown by numerical examples.