4 research outputs found
Research on Heat Source Model and Weld Profile for Fiber Laser Welding of A304 Stainless Steel Thin Sheet
No full textA heat source model is the key issue for laser welding simulation. The Gaussian heat source model is not suitable to match the actual laser weld profile accurately. Furthermore, fiber lasers are widely recognized to result in good-quality laser beam output, a narrower weld zone, less distortion, and high process efficiency, compared with other types of lasers (such as CO2, Nd : YAG, and diode lasers). At present, there are few heat source models for fiber laser welding. Most of researchers evaluate the weld profile only by the bead width and depth of penetration, which is not suitable for the laser keyhole welding nail-like profile. This paper reports an experimental study and FEA simulation of fiber laser butt welding on 1 mm thick A304 stainless steel. A new heat source model (cylindrical and cylindrical) is established to match the actual weld profile using Marc and Fortran software. Four bead geometry parameters (penetration depth, bead width, waist width, and depth of the waist) are used to compare between the experimental and simulation results. The results show that the heat source model of cylindrical and cylindrical can match the actual shape of the fiber laser welding feasibly. The error range of the penetration depth, bead width, waist width, and depth of the waist between experimental and simulation results is about 4.1 ± 1.6%, 2.9 ± 2.0%, 13.6 ± 7.4/%, and 18.3 ± 8.0%, respectively. In addition, it is found that the depth of penetration is more sensitive to laser power rather than bead width, waist width, and depth of the waist. Welding speed has a similar influence on the depth of penetration, weld width, waist width, and depth of the waist
Rapid and sensitive determination of ascorbic acid based on label-free silver triangular nanoplates
No full textIn this study, a new method for the detection of ascorbic acid (AA) was proposed. It was based on the protective effect of AA on silver triangular nanoplates (Ag TNPs) against Cl− induced etching reactions. Cl− can attack the corners of Ag TNPs and etch them, causing a morphological shift from triangular nanoplates to nanodiscs. As a result, the solution changes color from blue to yellow. However, in the presence of AA, the corners of Ag TNPs can be protected from Cl− etching, and the blue color of the solution remains unchanged. Using this effect, a selective sensor was designed to detect AA in the range of 0–40.00 μM with a detection limit of 2.17 μM. As the concentration of AA varies in this range, color changes from yellow to blue can be easily observed, so the designed sensor can be used for colorimetric detection. This method can be used to analyze fruit juice samples
Reconstruction of the Origin of a Neo-Y Sex Chromosome and Its Evolution in the Spotted Knifejaw, Oplegnathus punctatus
No full textSex chromosomes are a peculiar constituent of the genome because the evolutionary forces that fix the primary sex-determining gene cause genic degeneration and accumulation of junk DNA in the heterogametic partner. One of the most spectacular phenomena in sex chromosome evolution is the occurrence of neo-Y chromosomes, which lead to X1X2Y sex-determining systems. Such neo-sex chromosomes are critical for understanding the processes of sex chromosome evolution because they rejuvenate their total gene content. We assembled the male and female genomes at the chromosome level of the spotted knifejaw (Oplegnathus punctatus), which has a cytogenetically recognized neo-Y chromosome. The full assembly and annotation of all three sex chromosomes allowed us to reconstruct their evolutionary history. Contrary to other neo-Y chromosomes, the fusion to X2 is quite ancient, estimated at 48 Ma. Despite its old age and being even older in the X1 homologous region which carries a huge inversion that occurred as early as 55–48 Ma, genetic degeneration of the neo-Y appears to be only moderate. Transcriptomic analysis showed that sex chromosomes harbor 87 genes, which may serve important functions in the testis. The accumulation of such male-beneficial genes, a large inversion on the X1 homologous region and fusion to X2 appear to be the main drivers of neo-Y evolution in the spotted knifejaw. The availability of high-quality assemblies of the neo-Y and both X chromosomes make this fish an ideal model for a better understanding of the variability of sex determination mechanisms and of sex chromosome evolution
