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Design issues adumbrate conclusions on LED-mediated bycatch risk reduction of cetaceans and turtles in fishing nets: A comment on Bielli et al. (2020)
摘要： Worldwide, bycatch is one of the biggest threat to the long-term viability of cetaceans and turtles (Reeves et al., 2013; Wallace et al., 2013), or marine megafauna in general (Lewison et al., 2004). Reducing marine megafauna bycatch is urgent: Bielli et al. (2020) reported a decreased risk of bycatch for cetaceans and turtles by small-scale fisheries targeting elasmobranchs in Peruvian waters when green visible spectrum light emitting diodes (LEDs) were added on fishing nets. To estimate the causal effect of LEDs on bycatch, some nets had LEDs (treatment) and some nets had none (control). Due to intrinsic difficulties of collecting relevant data in realistic settings while not overburdening fishermen with additional constraints, nets with LEDs were, on average, shorter than nets without. The ratio of effort (in km of net soaked per day) in treatment versus control amounts to 40%. Because of this systematic difference between treatment and control in the experimental design, less bycatch (in absolute numbers) is expected in treatment than in control conditions. This may be taken into account in the statistical analysis of data. However, such a design results in treatment and effort being intrinsically confounded: estimating the causal effect of LEDs on bycatch with these data is problematic as any estimated effect will be model-dependent (Rubin, 2008).
关键词： Causal analysis,Marine megafauna,Design of experiments,Covariate overlap,Bycatch
更新于2025-09-23 15:19:57
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The effect of spot overlap ratio on femtosecond laser planarization processing of SiC ceramics
摘要： Silicon carbide ceramics are widely used in many fields owing to their excellent mechanical properties such as good wear resistance, thermal stability, and chemical corrosion resistance. The laser planarization processing can effectively achieve the functional, practical, and engineering process, satisfying the demands of the assembly precision. Therefore, different spot overlap ratios were utilized to investigate the effect of femtosecond laser planarization processing on silicon carbide ceramic samples. Various scanning speeds and laser repetition frequencies were matched to achieve different spot overlap ratios under the premise of fixed laser incident angle and single pulse energy. Under different parameters, the ablation depth, surface roughness, surface morphology, oxidation, and residual stress were compared. The result showed that at the same spot overlap ratio, the ablation depth and surface roughness are basically maintained at a stable value despite the difference in the scanning speed and repetition rate. The surface oxidation phenomenon remarkably decreased at the spot overlap ratio less than 90%. The decrease in the overlap ratio leads to the transition of the low frequency nano-ripple and the high frequency nano-ripple, and the surface residual stress converted from tensile stress to compressive stress. Combining processing requirements with ablation quality, the parameters are divided into three parts to fit three processes based on the spot overlap ratios. The variation in the spot overlap ratios as the guidelines had good potential in guiding the parameter range selection.
关键词： Residual stress,Spot overlap ratios,Femtosecond laser,Silicon carbide ceramics,Planarization processing
更新于2025-09-23 15:19:57
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[IEEE 2019 IEEE Asia Pacific Conference on Wireless and Mobile (APWiMob) - BALI, Indonesia (2019.11.5-2019.11.7)] 2019 IEEE Asia Pacific Conference on Wireless and Mobile (APWiMob) - Performance of LED Overlap in Visible Light Communication System
摘要： In this paper, we consider an indoor Visible Light Communication (VLC) system with a placement technique with and without an overlap formed, using four and five Light Emitting Diodes (LED), placements on a room roof. To support the better received signal power, this paper evaluated the performance of LED overlap using the 3-Watt transmit power. We did a computer simulation using the dimension closed communication 5x5x3 m3. In this paper, we found that the VLC system with an overlap was better than the one without an overlap. The result showed that the received power could reach the minimum Bit Error Rate (BER) threshold around -18 dBm for VLC system without an overlap and -20 dBm for VLC system with an overlap. From the simulation, it obtained that communication link coverage with an overlap was about 25 m2.
关键词： Overlap,Bit Error Rate,Coverage,Visible Light Communication
更新于2025-09-19 17:13:59
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Optimization of the pulse width and injection time in a double-pass laser amplifier
摘要： We have optimized the input pulse width and injection time to achieve the highest possible output pulse energy in a double-pass laser ampli?er using two Nd:YAG rods. For this purpose, we have extended the Frantz–Nodvik equation by simultaneously including both spontaneous emission and pump energy variation. The effective pump energy of the ?ash lamp was 8.84 J for each gain medium. The energy of 1 J could be ampli?ed to an output energy of 12.17 J with the maximum achieved extraction ef?ciency of 63.18% when an input pulse having a pulse width of 168 μs is sent 10 μs after the absorbed pump energy becomes the maximum value.
关键词： pump energy variation,input pulse optimization,spontaneous emission,Frantz–Nodvik equation,pulse overlap
更新于2025-09-19 17:13:59
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On the Analysis and Comparison of Decoupled Modal Gain Equalization Systems for Four-Mode (4a??M)-EDFAs
摘要： Space-Division Multiplexing (SDM) has gained considerable interest as a promising means to increase transmission capacity per fiber. For proper use of this technology, optical components of transmission line including Erbium-Doped Fiber Amplifiers (EDFAs) need to be re-examined. In this work we analyze modal gain equalization systems obtained from extended Giles model for 4M-EDFA. We introduced a simpler method of calculation of two radial overlap factors extracted from the model using standard B-V curve thus proposing two decoupled systems for Modal Gain Equalization. In Decoupled Mode-Specific Pump Combination (MSPC) system so obtained, Maximum Differential Modal Gain (DMG) was reduced to 1.55 dB with mean gain of about 28.72 dB. For Modified Erbium Doped Profile (MEDP) system we obtained an optimum Multi-Well Profile. The maximum DMG here showed further reduction to 1.3254 dB with mean gain of about 24.24 dB. Further we report investigation on evolution of ASE for 4M-EDFA for the first time with new performance metric namely ASE ratio to indicate the deviation of noise between four modes. The ASE levels reached in MEDP are smaller than MSPC system thus enabling reduction in Noise Figure. Simulation results and comparison indicated that in MEDP, DMG is more sensitive to variation in length, concentration and wavelength. Our designed MEDP and MPC system as well as simple 4M-EDFA system gave good pre-amplification performance for data rates smaller than 15 Gb/s.
关键词： Doping profiles,Erbium Doped Profile,Overlap Factors,Modal Gain Equalization,ASE Ratio,SDM Amplifiers
更新于2025-09-19 17:13:59
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Influence of Process Parameters and Deposition Strategy on Laser Metal Deposition of 316L Powder
摘要： In blown powder additive manufacturing technologies the geometrical stability of the built parts is more complex with respect to more conventional powder bed processes. Because of this reason, in order to select the most suitable building parameters, it is important to investigate the shape and the properties of the single metal bead formation and the effect that a scan track has on the nearby ones. In the present study, a methodology to identify an appropriate laser metal deposition process window was introduced, and the effect of the building parameters on the geometry of circular steel samples was investigated. The effect of the scanning strategy on the deposited part was also investigated. This work draws the attention to the importance of the obtainment of the most suitable melt pool shape, demonstrating that the laser power and the scanning strategy have a strong influence not only on the shape but also on the mechanical properties of the final component.
关键词： steel,additive manufacturing,melt pool,overlap,scanning strategy,directed energy deposition,AISI 316L
更新于2025-09-16 10:30:52
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Effects of Laser Beam Parameters on Bendability and Microstructure of Stainless Steel in Three-Dimensional Laser Forming
摘要： In this study, the e?ects of beam diameter and hatch spacing between the scanning paths on the bendability and microstructural behavior of an AISI 316 stainless-steel sheet in three-dimensional laser forming were investigated. The strain on the heating lines and that between the scanning tracks were numerically investigated to elucidate the e?ects of process parameters. The strain on heating lines and that between scanning tracks were numerically investigated. The increase in hatch spacing caused a larger amount of counter bending to be retained in the una?ected areas between the tracks through a process dominated by a temperature gradient mechanism (TGM), and also caused a lower deformation. The formation of small equiaxed dendrite grains instead of coarse and inhomogeneous austenite grains occurred during the process at a larger beam diameter and smaller hatch spacing, which increased the bendability of the material, owing to the decrease in anisotropy in the microstructure. Moreover, the increase in the grain size of the reheated overlap region of the deformed sample led to a higher bendability. Under these conditions, the microhardness was also increased owing to the grain boundary strengthening e?ect.
关键词： laser forming,track overlap,stainless steel,laser bending,bendability,hatch spacing
更新于2025-09-16 10:30:52
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Addressing K/L-edge overlap in elemental analysis from micro-X-ray fluorescence: bioimaging of tungsten and zinc in bone tissue using synchrotron radiation and laser ablation inductively coupled plasma mass spectrometry
摘要： Synchrotron radiation micro-X-ray fluorescence (SR-μXRF) is a powerful elemental mapping technique that has been used to map tungsten and zinc distribution in bone tissue. However, the heterogeneity of the bone samples along with overlap of the tungsten L-edge with the zinc K-edge signals complicates SR-μXRF data analysis, introduces minor artefacts into the resulting element maps, and decreases image sensitivity and resolution. To confirm and more carefully delineate these SR-μXRF results, we have employed laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to untangle the problem created by the K/L-edge overlap of the tungsten/zinc pair. While the overall elemental distribution results are consistent between the two techniques, LA-ICP-MS provides significantly higher sensitivity and image resolution compared with SR-μXRF measurements in bone. These improvements reveal tissue-specific distribution patterns of tungsten and zinc in bone, not observed using SR-μXRF. We conclude that probing elemental distribution in bone is best achieved using LA-ICP-MS, though SR-μXRF retains the advantage of being a non-destructive method with the capability of being paired with X-ray techniques, which determine speciation in situ. Since tungsten is an emerging contaminant recently found to accumulate in bone, accurately determining its distribution and speciation in situ is essential for directing toxicological studies and informing treatment regimes.
关键词： LA-ICP-MS,Overlap,X-ray spectroscopy (XPS | XRF | EDX),Analyte,Zinc,Tungsten
更新于2025-09-12 10:27:22
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A double raster laser scanning strategy for rapid die-less bending of 3D shape
摘要： Double raster scanning approach to 3D laser forming was investigated to obtain a large deformation with one-step laser irradiation, avoiding repetitive scanning. The magnitude of the deformation during raster scanning was found to be strongly dependent on the overlapping between adjacent passes, which can be controlled by changing their spacing and the beam diameter. Therefore, 3D deformation during raster scanning has been analyzed at various overlap ratios, whose effect on the temperature and strain distribution were discussed. As the heat transfer mode significantly influences the uniformity of the bending process, the variations in bending angles with negative and positive overlapping ratios have also been investigated. The ratio of the longitudinal and lateral curvatures decreased with the increasing overlap ratio. Therefore, the effect of the lateral side is more important for specifying the final symmetry of the part, playing a critical role in bending with higher overlap ratios. In a rectangular part, deformation of the lateral side was found to be more difficult, showing strong dependence on the length of the scanning track, compared with the space of the adjacent passes. Through process characterization, the double raster scanning process has been well understood and proved to be a feasible approach to 3D laser forming of rectangular parts.
关键词： Curvature,Overlap,Laser bending,Heat transfer,Laser forming,Raster scanning
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Determining the Waveguide Profile using the Overlap Integral
摘要： The determination of the index pro?le in guiding structures is a central problem in applied photonics, ranging from optical ?bers to femtosecond-written waveguides. A non-destructive and relatively easy method consists in the measurement of the index pro?le by measuring the transmitted ?eld. From the transmitted ?eld, the refractive index pro?le is computed by direct inversion of the Helmholtz equation. This technique is called near-?eld method. Here we present a new near-?eld method based upon the inversion of the overlap integral. From the waveguide theory, the power coupled to the m-th mode with pro?le ψm(x) from an input Ein(x) is am = (cid:2) Ein(x)ψ ? (x)dx. If the input Ein(x) is shifted by an amount x0, the overlap am(x0) is the convolution between the pro?le of the input beam Ein and the mode pro?le ψm. The convolution operator implicitly ?lters out the noise, but without creating distorsions or artifacts. An experimental measurement of the transmitted ?eld Eexp will be Nη, where η is a white Gaussian noise and N the noise amplitude. In the previous formulae P is the overall power given by |am(x0)|2. If both amplitude and phase of the transmitted ?eld are simultaneously measured, the overlap am can be inverted for any guided mode m. If only the intensity is measured, the overlap can be inverted only if the waveguide is monomodal. An example of the reconstructed mode in the case of intensity-only measurements is plotted in Fig. 1(a) for ψ0 = cosh(x/w) with w/λ = 4 and N/P = 1 × 10?4. The retrieved ?eld is very close to the exact one, with appreciable differences only for |x/λ | > 10. Important to stress, this range is larger than what it is achievable with a single direct measurement of the transmitted ?eld. The next step is to invert the Helmholtz equation, that is, to compute the second derivative of the retrieved mode. Direct application of the inversion protocol strongly enhances the noise, above all on the tails of the mode. The net result is the appearance of several fake oscillations, even where the retrieval of the mode is good. The problem can be overcome by ?tting the mode tails with a decaying exponential, in accordance with the waveguide theory. The reconstructed guide pro?les shown in Fig. 1(b) do not present arti?cial oscillations on the tails, showing a 10% error with respect to the original waveguide, the error depending slightly on the original signal-to-noise ratio N/P.
关键词： refractive index,overlap integral,Helmholtz equation,waveguide profile,near-field method
更新于2025-09-11 14:15:04