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Thermal Behavior During the Selective Laser Melting Process of Ti-6Al-4V Powder in the Point Exposure Scan Pattern
摘要： Currently, there are two main scan patterns, including the continuous exposure scan pattern and the point exposure scan pattern, during the selective laser melting (SLM) process. The point exposure scan pattern allows a three-dimensional (3-D) printer to build ?ner detail features as a static molten pool that is more stable than a dynamic one. However, there has been limited theoretical research on the thermal behavior characteristics during the process in the point exposure scan pattern. Therefore, in this study, the simulation of thermal behavior during SLM of Ti-6Al-4V powder in the point exposure scan pattern was performed. The temperature evolution behavior of di?erent positions and the e?ects of exposure time on the temperature evolution behavior of di?erent positions, temperature distributions, and dimensions of the molten pool were investigated. The results showed that the direct exposure position and unexposed position had signi?cantly di?erent temperature evolution behaviors under a given condition, and the changed exposure time had the greatest in?uence on the direct exposure position compared with unexposed position. Moreover, the thermal accumulation e?ect of a former exposure point on a later one decreased with increasing exposure time. In addition, with the increase of exposure time, the maximum temperature of the molten pool was enhanced and the surface morphology of the molten pool changed from an approximate ellipse to an approximate circle. Besides, the molten pool dimensions were found to increase with exposure time, which indicated that the exposure time played an important role in the stability of the molten pool and the metallurgical bonding in the process. Furthermore, the dimensions of the molten pool and metallurgical bonding in the cross-sectional view were obtained through experiments. Good agreement was obtained when comparing the simulated results with the experimental ones.
关键词： Point exposure scan pattern,Selective laser melting,Ti-6Al-4V,Exposure time,Thermal behavior
更新于2025-09-11 14:15:04
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[IEEE 2019 21st International Conference on Transparent Optical Networks (ICTON) - Angers, France (2019.7.9-2019.7.13)] 2019 21st International Conference on Transparent Optical Networks (ICTON) - Direct Laser Writing Using Chalcogenide Thin Films
摘要： Direct laser writing has been performed in thin AMTIR-1 layers. By using 10 ns laser pulses, 250 nm thick lines have been written by tightly focusing the laser beam on the thin film layers. The possibility to enhance this resolution by using the Sb2Te3 material as super-resolution mask is also discussed.
关键词： saturable absorption,direct laser writing,Z-scan,super-resolution,nonlinear optics,chalcogenide glasses
更新于2025-09-11 14:15:04
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QUALITY IMPROVEMENT OF LASER TREATMENT (QUILT)A New Retinal Laser Simulation System for Training in Resource-Poor Countries
摘要： In resource-poor countries, there is a reported lack of quality and structured retinal laser training in residency and hospital eye programs. This unmet training need has been validated in current international diabetic retinopathy screening centers. Quality Improvement of Laser Treatment (QUILT) is a novel laser photocoagulation simulator that contains modules for laser treatment of PDR, diabetic macular edema (DME), retinal vein occlusion, and laser retinopexy. The primary objective of the QUILT simulation is to introduce a new bespoke application to support practical skills training in retinal laser treatment in countries where laser training is suboptimal for ophthalmologists and trainees/residents. The application was first developed as an online application but has subsequently been developed as a standalone application that can be downloaded or copied onto individual laptops or computers, so that the training is not dependent on a good internet connection.
关键词： diabetes,simulator,proliferative diabetic retinopathy,laser training,simulation,pattern scan laser,retinopexy,macular edema
更新于2025-09-11 14:15:04
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A study on microhardness and microstructural evolution of titanium/zirconium diboride cermet coatings with varying scan speeds during laser cladding on Ti6Al4V substrate
摘要： Titanium/zirconium diboride cermet coatings were deposited at different laser scan speeds on Ti–6Al–4V alloy using laser cladding technique. Microhardness of the coatings was compared with the microhardness of the substrate, while the microstructural morphologies of coatings were evaluated via scanning electron microscope with energy dispersive spectroscopy. In addition, resultant grain sizes of the coatings were observed and phases formed within the coatings were also examined. The microhardness of the coatings was seen to be four times harder than the substrate. Scanning electron microscopic images exhibited a refinement in grain size and the development of distinct microstructural features. X-ray diffraction patterns showed significant hard phases such as Al2Zr and Ti3B4 which may be responsible for the sky-rocketed microhardness values of the coatings. This study proffers profound insight on the influence of laser scan speed, during deposition, on the microhardness and microstructural morphology of titanium/zirconium diboride cermet coatings.
关键词： titanium/zirconium diboride cermet coatings,laser cladding technique,Ti6Al4V substrate,laser scan speed
更新于2025-09-11 14:15:04
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Improvement of the third order nonlinear optical properties of nematic liquid crystal under the influence of different compositional percentage of doped SWCNT and the external electric field
摘要： In this research, the nematic liquid crystal (NLC) was doped with varying concentration (0-1 % wt.) of single walled carbon nanotubes (SWCNTs) at room temperature to study the nonlinear optical (NLO) properties of E5CN7@CNT cell.The third order NLO properties such as the nonlinear susceptibility, the nonlinear refraction (NLR) and the nonlinear absorption (NLA) were determined by using Z-scan techniques. The nonlinear studies have been done using a continuous wave (CW) He: Ne laser at 632.8 nm.Doping SWCNTs to eutectic uniaxial NLC (E5CN7) enhanced the third order nonlinear susceptibility, ??(3) and consequently the nonlinearity properties of composite systems improved.It is found that at lower concentration of CNTs (c< 0.75 % wt.), the third order nonlinear susceptibility are increased, but for concentration 0. 5<c<1 % wt., the third order nonlinear susceptibility are decreased. The negative sign of the observed NLR index, indicates that the E5CN7@CNT exhibits self-defocusing type optical nonlinearity. The two photon absorption (TPA) behavior, corresponding to negative sign NLA of samples. The reorientation of samples molecules amplifies upon the application of electric field, then nonlinearity increases.
关键词： Composite materials,Nematic liquid crystal,Carbon nanotubes,Third order nonlinear susceptibility,Nonlinear optics,Electric field,Z-scan method
更新于2025-09-10 09:29:36
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Crystal growth, Hirshfeld surface analysis, DFT study and third order NLO studies of Thiourea 4 dimethyl aminobenzaldehyde
摘要： In this work we investigate the crystal growth and the characterization of Thiourea 4 dimethyl aminobenzaldehyde (TDA) crystal. The Molecular geometry shows good agreement with Experimental and Theoretical (HF and DFT) bond lengths and bond angles. From X-ray diffraction studies it shows that the structure belongs to monoclinic structure and experimental, refinement data also discussed. Hirshfeld surface analysis used to clarify the intermolecular interactions in a visual manner. Vibrational assignments of TDA crystal is discussed by FT-IR and FT-Raman spectroscopic studies. The assignments are compared with Density Functional Theory calculation and it shows good agreement with experimental data. The Frontier molecular orbital energy gap is found by TD-DFT method with HOMO-LUMO calculation. The Third order NLO studies for TDA organic crystal is done by Z-scan technique and Optical parameters like Non linear and Linear refractive index are calculated.
关键词： Z-scan Technique,DFT,Hirshfeld surface analysis,X-Ray diffraction,Molecular Geometry.
更新于2025-09-10 09:29:36
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Investigation of combined kV/MV CBCT imaging with a high-DQE MV detector
摘要： Purpose: Combined kV-MV CBCT imaging has been proposed for two potentially important image-guided radiotherapy applications: 1) scan time reduction (STR) and 2) metal artifact reduction (MAR). However, the feasibility of these techniques has been in question due to the low detective quantum efficiencies (DQEs) of commercially available electronic portal imagers (EPIDs). The goal of the work was to test whether a prototype high DQE MV detector can be used to generate acceptable quality pre-treatment CBCT images at acceptable dose levels. Methods: 6MV and 100kVp projection data were acquired on a Truebeam system (Varian, Palo Alto, CA). The MV data were acquired using a prototype EPID containing two scintillators 1) a standard copper-gadolinium oxysulfide (Cu-GOS) screen having a zero-frequency DQE (DQE(0)) value of 1.4%, and 2) a prototype focused cadmium tungstate (CWO) pixelated “strip” with a DQE(0) = 22%. The kV data were acquired using the standard onboard imager (DQE(0) = 70%). The angular spacing of the MV projections was 0.81° and the source output was 0.03 MU/projection while the kV projections were acquired with an angular spacing of 0.4° at 0.3 mAs/projection. Image quality was evaluated using 1) an 18-cm diameter electron density phantom (CIRS, Norfolk, VA) with nine contrast inserts and 2) the resolution section of the 20-cm diameter Catphan phantom (The Phantom Laboratory, Greenwich, NY). For the MAR studies, two opposing CIRS phantom inserts were replaced by steel rods. The reconstruction methods were based on combining MV and kV data into one sinogram. The MAR reconstruction utilized mostly kV raw data with only those rays corrupted by metal requiring replacement with MV data (total absorbed dose = 0.7 cGy). For the STR study, projections from partially overlapping 105° kV and MV acquisitions were combined to create a complete data set that could have been acquired in 18 sec (absorbed dose = 2.5 cGy). MV-only (4.3 cGy) and kV-only (0.3 cGy) images were also reconstructed. Results: The average signal-to-noise ratio (SNR) of the inserts in the MV-only CWO and GOS CIRS phantom images were 0.62x and 0.12x the SNR of the inserts in kV-only image, respectively. The limiting spatial resolutions in the MV-only GOS, MV-only CWO, and kV-only Catphan images were 3 lp/cm, 6 lp/cm, and 8 lp/cm, respectively. In the combined kV/CWO STR reconstruction, all contrast inserts were visible while only two were detectable in the kV/Cu-GOS image due to high levels of noise (average SNRs of kV/CWO and kV/GOS inserts were 0.97x and 0.18x the SNR of the kV-only inserts, respectively). In the kV-MV MAR reconstructions, streaking artifacts were substantially reduced with all inserts becoming clearly visible in the kV/CWO image while only two were visible in the kV/Cu-GOS image (average SNRs of the kV/CWO and kV/Cu-GOS CIRS with metal inserts were 0.94x and 0.35x the SNRs of the kV-only CIRS without metal inserts). Conclusions: We have demonstrated that a high-DQE MV detector can be applied to generating high quality combined kV-MV images for SRT and MAR. Clinically acceptable doses were utilized.
关键词： high DQE,scan time reduction,metal artifact reduction,CBCT imaging,MV detector
更新于2025-09-10 09:29:36
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[Ocular Trauma] Anatomy and Examination in Ocular Trauma || Imaging Examination
摘要： Technology advances at a great pace. Particularly in medicine and, one may venture to say, even more so in the field of ophthalmology. Yet, regarding ocular trauma, the physician stands between multiple crossroads when deciding which imaging examination method to choose from. He must find balance between cost-benefit, medicolegal purposes, immediate or intermediate availability, and prioritizing strategy-modifying information, more often than not relying on century-old techniques, mixed with state-of-the-art technologies, and always based on solid clinical evaluation to make the best decision in a reasonably short time. This chapter will attempt to introduce the imaging examination techniques of X-ray, computed tomography scan, magnetic resonance imaging, B-ultrasound, biomicroscopy, optical coherence tomography, and specular microscopy now available for the assessment in ocular trauma, their working mechanisms, scopes, as well as their strong and weak points.
关键词： Computed tomography scan,Ocular trauma,Magnetic resonance imaging,B-ultrasound,Optical coherence tomography,Specular microscopy,Examination,X-ray,Biomicroscopy,UBM
更新于2025-09-10 09:29:36
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Synthesis, crystal growth, structural, spectral, thermal, optical characteristics and density functional theory calculations of a novel third-order nonlinear optical material: 4-acetylanilinium dihydrogen phosphate (4AADP) single crystals
摘要： Single crystals of 4-acetylanilinium dihydrogen phosphate (4AADP), a novel third-order nonlinear optical material has been synthesized and successfully grown by the slow evaporation solution growth technique using acetone as a solvent at room temperature. The single crystal X-ray diffraction analysis implies that 4AADP crystallized into a monoclinic crystal system with the centrosymmetric space group P21/c. The molecular structure of the grown 4AADP compound was evidently established by using 1H and 13C NMR spectral analysis. The vibrational behavior of the chemical bond and discrete functional groups of the grown crystal were identified using FT-IR and FT-Raman spectral analysis. UV-Visible-Near Infrared spectral analysis shows that the grown crystal was highly transparent in the entire visible range above 365 nm. The 4AADP compound was thermally stable up to 195 oC and it was ascertained by thermogravimetric and differential scanning calorimetric analysis. The photoactive behavior of the material was established from photoluminescence studies. The ionization energy (I) and electron affinity (A) were computed from the energy gap values of HOMO and LUMO orbitals respectively. The Molecular electrostatic potentials and Mulliken charges have also been calculated theoretically by applying DFT/B3LYP method. The nonlinear absorption coefficient (β), third order nonlinear refractive index (n2) and third-order nonlinear optical susceptibility (χ3) were calculated from Z-scan measurements, reveals that the grown crystal of 4AADP could serve as a promising source for nonlinear optical devices.
关键词： Crystal growth,Density functional theory,Z-scan,Thermal analysis,Spectral studies
更新于2025-09-10 09:29:36
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Tunable optical nonlinearity of Au-TiO2 nanocomposites
摘要： The present work is focused on the correlation studies of Fermi energy level and optical nonlinearity of Au-TiO2 nanocomposites. The Fermi energy and optical nonlinearity are found to be nearly proportionally related with respect to concentration of Au. The observed shift in Fermi level with increasing concentration of Au is due to charge transfer between TiO2 and Au in the presence of ultraviolet light irradiation during the formation of Au-TiO2 nanocomposites. The estimated third order optical nonlinearity was found to increase from 3.80×10-6 to 9.69×10-6 esu with increase in Au concentrations from 0 to 1.0×10-2 M. This observed increment in nonlinearity is due to the enhancement of local electric field created by excitation of surface plasmon resonance that affects the Fermi energy level or work function.
关键词： Work function,Z-scan technique,Nanocomposites,Surface plasmon resonance,Optical nonlinearity
更新于2025-09-10 09:29:36