Multi-laser selective laser melting (SLM) technology has attracted extensive attention for greatly improving forming efficiency. In this study, a 3D finite element (FE) model is established to obtain the temperature field of AlSi10Mg powder in different number of scans. The number of scans are equal to 1, 2, and 4. The FE analysis is conducted with the heat flux, convective and conductive heat-transfer taken into account. It showed that the maximum temperature, the width, and the depth of the melt pool increased by 0.61%, 10.29%, and 8.92% when the number of scans N used is equal to 2. They increased by 6.4%, 43.21%, and 43.73% when N is 4, respectively. The proper molten pool width (112.5 μm) and depth (36.76 μm) were obtained for a high dense product. SLM of AlSi10Mg powder was also experimentally performed using uniform processing conditions, and the microstructures of the SLM-fabricated samples were investigated to verify the reliability of the physical model. Good agreement is obtained.
Rayleigh wave is often used in geological exploration. Spectra analysis to Rayleigh wave and layering with velocity and drilling data can provide bases for the research of drilling data, and make the data accurate and reliable.
The four new Laser welding technologies of aluminium alloy and their process features were introduced,such as laser-GMA hybrid welding arc,laser welding with filler wire,dual-beam laser welding and laser-assisted friction stir welding.Based on these,the research progress of the above methods for welding aluminium alloy was reviewed.
ABSTRACT Hence, N,S‐CDs with photoluminescent property were simply synthesized via a one‐step hydrothermal method. Combined with the commercial reagent Ce 4+ , a ratiometric fluorescence assay for ascorbic acid (AA) detection was established. Ce 4+ , possessing oxidization, could directly oxidize o‐phenylenediamine (OPD) to form the yellow fluorescent product oxOPD. Under the excitation wavelength of 370 nm, oxOPD had a maximum fluorescence emission at 562 nm. Meanwhile, due to the occurrence of the inner filter effect (IFE), oxOPD quenched the fluorescence of N,S‐CDs. However, ascorbic acid (AA) inhibited the oxidation of Ce 4+ , causing the fluorescence of oxOPD at 562 nm to decrease, accompanied by an increase in the fluorescence belonging to N,S‐CDs at 450 nm. Thus, a Ce 4+ ‐assisted ratiometric fluorescence method was established for AA detection. The two fluorescence output signals in this method had opposite changing trends, which could reduce system errors and improve the accuracy. This method was successfully applied to the determination of AA in drugs and fruits.
In order to study the influence by non-uniformity of illumination on testing performance of optical measurement system, the causes of non-uniformity were analyzed. We constructed the relationship model between interval distance of LED light source and illumination. The distribution of illumination with different intervals of LED were simulated. Then relationship model between viewing-field angle at object plane of optical system and illumination was established. Influence of viewing-field angle at object plane on distribution of illumination was studied. The experimental results indicate that non-uniform light source and wide viewing-field angle are two main causes for non-uniformity in optical imaging system. Larger interval distance of LED or viewing-field angle will result in non-uniformity of illumination.
In X-ray imaging system, with the change of parameters in material quality, volume, object distance and else of the target objects, manual adjustments of tube voltage and tube current are often needed to get ideal imaging results. Whereas human interventions are often subjective that cannot meet the automation development of X-ray detection system. In view of the above problems, a method for objective quality evaluation in images which is based on weighted local entropy is presented in the paper. Parameters adaptive adjustment in X-ray detection system can be based on this method. The validity of the approach is proved by experiment and comparative analysis with the traditional image quality evaluation function.
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