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- 2018
- Lorentzian influence
- optical flow
- additive white Gaussian noise
- 2D vector
- Materials characterization
- laser additive manufacturing
- selective laser sintering
- Additive manufacturing
- selective laser melting
- Optoelectronic Information Science and Engineering
- Mechanical Engineering
- University of Johannesburg
- Assumption University
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Parallel domain decomposition methods for a quantum-corrected drift–diffusion model for MOSFET devices
摘要： In this paper, we describe parallel domain decomposition methods based on the restricted additive Schwarz (RAS) method for a quantum-corrected drift-diffusion (QCDD) model for MOSFET devices. We have developed hybrid Message Passing Interface (MPI)/OpenMP parallelization algorithms of the QCDD system. For internode parallelization, two extensions of the RAS method are newly developed for the QCDD model. For intranode parallelization, we combine the conjugate gradient (CG) and BiCGSTAB procedures with a splitting-up operator method to realize parallelization of the incomplete factorization. The parallel numerical results for a three-dimensional Si bulk n-MOSFET on a multi-core NEC SX-ACE parallel computer are demonstrated. The intranode parallel numerical results are further evaluated on a many-core Cray XC40 parallel computer.
关键词： Restricted additive Schwarz method,Domain decomposition method,Numerical methods,Device simulation,Semiconductor,quantum-corrected drift–diffusion model
更新于2025-09-23 15:21:21
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[IEEE 2018 9th International Conference on Ultrawideband and Ultrashort Impulse Signals (UWBUSIS) - Odessa, Ukraine (2018.9.4-2018.9.7)] 2018 9th International Conference on Ultrawideband and Ultrashort Impulse Signals (UWBUSIS) - Correlation Properties of Additive Linear High-Order Markov Chains
摘要： The aim of this paper is to study the statistical properties of the Nth order correlated Markov chains, which have a large application area in the UWB signal generation, transmission and processing. The state space of the chain under consideration is supposed to be a finite set of real numbers. The transition probability function is assumed to be homogeneous, additive and linear with respect to the values of random variable. The equations relating the correlation functions of the sequence to the memory function, which determined by the transition probability function, are derived and solved. The obtained analytical solutions for the correlation functions are compared with the results of numerical simulations. Examples of possible correlation scenarios in additive linear chains of higher orders are given. The obtained results can be useful both in analytical and simulative context, for example, for the modeling of the UWB transmission channels, for the refinement of transmitter and receiver design, for the enhancement of coding methods suitable for the UWB communication systems.
关键词： UWB channels,higher order Markov chain,memory function,linear additive high-order Markov chain,correlation function
更新于2025-09-23 15:21:21
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All 3D Printed Flexible ZnO UV Photodetector on Ultraflat Substrate
摘要： An all 3D printed flexible ZnO ultraviolet (UV) photodetector is demonstrated, where the 3D printing method is used not only for the electrode and photosensitive material but also for creating a substrate. An ultra-flat and flexible substrate capable of serving as the backbone layer is developed using a water-dissolvable polymer layer for surface planarization. A two layered printing followed by surface treatment is demonstrated for the substrate preparation. As a mechanical support but flexible, a thick and sparse thermoplastic polyurethane layer is printed. On its surface, a thin and dense polyvinyl alcohol (PVA) is then printed. A precise control of PVA reflow using micro-water droplet results in a flexible and extremely uniform substrate. A Cu-Ag nanowire network is directly 3D-printed on the flexible substrate for the conducting layer, followed by ZnO for photosensitive material. Unlike the planar two-dimensional printing that provides thin films, 3D printing allows the electrode to have a step height, which can be made like a dam to accommodate a thick film of ZnO. Photosentivity as a function of various ZnO thickness values was investigated to establish an optimal thickness for UV response. The device was also tested in natural sunlight along with stability and reliability.
关键词： ultraviolet radiation,UV detector,UV sensor,Printed electronics,3D printing,additive manufacturing
更新于2025-09-23 15:21:01
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Laser polishing of additively manufactured Ti-6Al-4V: Microstructure evolution and material properties
摘要： Laser polishing of metals consists of irradiating the part’s surface with a laser beam, thus generating a molten layer that is redistributed and resolidified to create a surface with reduced roughness. However, the process is also characterized by an instantaneous formation of heat-affected zones with consequent microstructural changes that influence the mechanical properties. In order to understand the microstructural evolution during laser polishing of Ti-6Al-4V laser-based powder bed fusion samples, a thermal model is applied in the current study to predict the dimensions of the melted zones and the heat-affected areas. Furthermore, the results obtained through simulations are discussed and compared to the experimental data, thereby establishing the validity of the process models. Finally, the experimental studies also include the evaluation of material hardness and residual stresses after laser polishing.
关键词： laser polishing,thermal model,material properties,additive manufacturing,microstructure evolution
更新于2025-09-23 15:21:01
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Characterization of IN 625 recycled metal powder used for selective laser melting
摘要： Additive manufacturing of high-quality materials by Selective Laser Melting depends not only on establishing appropriate process parameters, but also on the characteristics of the metal powders used and their stability over time or after recycling. The aim of the research was to characterize the IN 625 powder used over multiple manufacturing cycles with a Lasertec 30 SLM machine. In order to achieve the research’s goal, virgin and recirculated powder’s physical and technological characteristics were investigated. A decrease in all D-values (D10, D50, D90) of the powder size distribution was observed after multiple recirculation cycles showing a decrease of the powder dimensional range over time. Both virgin and recirculated powders are composed of mainly spherical particles, but elongated particles and satellite particles were observed as well. The dimensional evolution analysis showed a deviation from the powder ideal roundness, deviation that is more pronounced over multiple recirculation cycles. It was experimentally determined that the powders present a good ?owability based on the ?ow rate value obtained for both virgin and recirculated powders, con?rmed also by the Hausner ratio and angle of repose.
关键词： metallic powder,additive manufacturing,recycling,SLM,IN 625
更新于2025-09-23 15:21:01
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Dynamic Laser Absorptance Measured in a Geometrically Characterized Stainless-Steel Powder Layer
摘要： The relationship between real powder distributions and optical coupling is a critical building block for developing a deeper physical understanding of laser-additive manufacturing and for creating more reliable and accurate models for predictable manufacturing. Laser-light absorption by a metal powder is distinctly different from that of a solid material, as it is impacted by additional parameters, such as particle size, shape distribution, and packing. Here, we use x-ray computed tomography to experimentally determine these parameters in a thinly spread austenitic stainless-steel powder on a metal substrate, and we combine these results with optical absorptance measurements during a 1 ms stationary laser-light exposure to simulate the additive-manufacturing process. Within the thinly spread powder layer, the particle volume fraction changes continuously from near zero at the powder surface to a peak value of 0.72 at a depth of 235 μm, with the most rapid increase taking place in the first 100 μm. The relationship between this particle volume fraction gradient and optical absorptance is investigated using an analytical model, which shows that depth-averaged absorptance measurements can measure the predicted average value, but will fail to capture local effects that result from a changing powder density. The time-averaged absorptance remains at levels between 0.67 and 0.80 across a two orders of magnitude range in laser power, which is significantly higher than that observed in solid stainless-steel experiments. The dynamic behavior of the absorptance, however, reveals physical phenomena, including oxidation, melting, and vapor cavity (keyhole) formation, as well as quantifying the effect of these on the absorbed energy.
关键词： keyhole formation,laser-additive manufacturing,stainless-steel powder,x-ray computed tomography,optical coupling,optical absorptance,particle volume fraction
更新于2025-09-23 15:21:01
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Effect of laser shock processing on oxidation resistance of laser additive manufactured Ti6Al4V titanium alloy
摘要： The high-temperature oxidation resistance of laser additive manufactured (LAM) Ti6Al4V before and after laser shock processing (LSP) was investigated. The samples were oxidized at 400?800 °C for 1?50 h in air. The results revealed that the rate of weight gain of the Ti6Al4V fabricated through LAM decreased, and LSP had a positive effect on increasing the oxidation resistance. At an oxidation temperature of 700 °C, an aluminum-rich layer was observed in the cross-section before LSP. After LSP, the aluminum-rich layer changed to three layers. The aluminum-rich layer prevented the diffusion of oxygen, which improved the oxidation resistance of the Ti6Al4V.
关键词： Ti6Al4V titanium alloy,High-temperature oxidation resistance,Laser shock processing,Laser additive manufacturing
更新于2025-09-23 15:21:01
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Microstructure and properties of CeO2-doped CoCrFeMnNi high entropy alloy fabricated by laser metal deposition
摘要： Rare earth elements are usually regarded as e?cient additives for property enhancement of many types of alloys. In the present study, the CoCrFeMnNi high entropy alloy (HEA) was doped with CeO2, and such composites were for the ?rst time obtained by the laser metal deposition (LMD) process. The microstructure, phase compositions, microhardness and crystallographic texture of the HEA/CeO2 composites were investigated. It was demonstrated that CoCrFeMnNi HEA/CeO2 samples were successfully obtained by the LMD process. Meanwhile, small irregular shape oxides rich in Mn and Cr were observed in the HEA/ CeO2 composite. Rare earth element Ce was found to be evenly distributed throughout the sample. Heterogeneous dendritic microstructure with a long columnar grains oriented along the build direction was observed. The measured average microhardness is 181.72 ± 9.72 HV0.1.
关键词： Composite,CeO2,High entropy alloy,Laser metal deposition,Additive manufacturing,CoCrFeMnNi
更新于2025-09-23 15:21:01
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Fabrication of Laser Grade Yb: Y2O3 Transparent Ceramics with ZrO2 Additive through Hot Isostatic Pressing
摘要： Laser grade 8 at.% Yb: Y2O3 transparent ceramics were fabricated with ZrO2 as a sintering additive by using hot isostatic pressing. The hot isostatic pressed 8 at.% Yb: Y2O3 transparent ceramics have a small average grain size of 3 μm and a high transmittance of 82.8% in the near-infrared light region. Optical homogeneity is compromised slightly in the visible light region likely because of the presence of nano/micro-scaled pores. Laser output at 1076 nm reaches a maximum power of 1.1 W and a slope efficiency of 6.1%, indicating that the hot isostatic pressed 8 at.% Yb: Y2O3 transparent ceramics have a promising optical quality. An unusual laser damage is observed and believed to be related to ZrO2 additive associated defects.
关键词： ZrO2 additive,hot isostatic pressing,laser grade,Yb: Y2O3,transparent ceramics
更新于2025-09-23 15:21:01
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Understanding the effect of solvent additive in polymeric thin film: turning a bilayer in a bulk heterojunction like photovoltaic device
摘要： Here we report the effect of an additive solvent, the 1,8-diiodooctane (DIO) on the performance of a bilayer organic photovoltaic (OPV) device which active layer comprises the poly[2,7-(9,9-bis(2 ethylhexyl)-dibenzosilole)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole] (PSiF-DBT) as the electron donor material and C60 as the electron acceptor material. We observed that when the donor layer was treated with 1% of DIO the power conversion efficiency (PCE) of the device increase 138.4% in relation to the device with a non-treated donor layer and 21.3% in relation to the device containing a donor layer submitted to a thermal annealed. The main effects that lead to this increase in PCE are the large interfacial area between donor and acceptor materials and the improved conductivity at low voltages. The increase in polymer surface roughness leads to a more effective PSiF-DBT/C60 interface for exciton dissociation. This effect, as well as the increase in the conductivity, raised the short circuit current density (JSC) to 13.89 mA/cm2 and PCE to 4.84%. Our conclusions are supported by morphological analysis, chemical cross-sectional evaluations with advanced microscopy techniques, charge mobility measurements as well as by theoretical simulations of the devices in which the changes on the donor/acceptor interfacial area were considered. The outcomes suggest that, solvent additives could be an alternative treatment to replace the thermal annealing which imposes further difficulties to perform the lab-to-manufacturing upscaling.
关键词： solvent additive,PSiF-DBT,exciton dissociation,1,8-diiodooctane,C60,organic photovoltaic,power conversion efficiency
更新于2025-09-23 15:21:01