28 June 2025, Volume 24 Issue 3

  

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  Preparation of TiO₂ nanosphere and resonance characteristic in visible band

  GAO Zhuo-yu, CEN Yi-hua, ZHANG Cheng-yun

  2025, 24(3): 1-9.

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  All-dielectric nanostructures support unique electromagnetic resonance modes in visible band, and have important application prospects in the fields of directional light scattering and nonlinear optical response. The nanostructures with various morphologies of high refractive index silicon (Si) have become important basic components of nanostructures in this field. The imaginary part of the refractive index of titanium dioxide (TiO₂) nanostructures with medium refractive index and wide band gap is close to 0 in visible band, and the extremely low absorption property leads to stronger scattering than silicon. To this end, TiO₂ nanospheres with different sizes were prepared by femtosecond (fs) laser-induced backward transfer method, and the regulation of size-dependent resonance mode in visible band was studied. Based on Mie theory, the multipole resonance mode was analyzed, and it was found that the magnetic dipole (MD) and electric dipole (ED) characteristic peaks of TiO₂ nanospheres of a hundred nanometers in diameter were broadened and overlapped, resulting in a mode coupling between them, and the ED resonance mode becomes not obvious, while the high-order magnetic quadrupole (MQ) resonance mode has the characteristics of narrow bandwidth. The numerical simulation results show that the MQ resonance mode has a stronger local field enhancement factor. Controlled tuning of size-dependent resonant modes can be applied to nanoscale displays and photonic devices.
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  Effect of trace Vanadium additions on the modification of high-performance 6xxx series aluminum alloys for automotive applications

  YAN Jia-lin, KE Bin, DENG Hao-wei, ZHANG Tao

  2025, 24(3): 10-19.

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  The 6xxx (Al-Mg-Si) series aluminum alloys, with moderate strength and good formability, are widely used in automotive structural parts. As vehicle products evolve and safety demands grow, traditional 6xxx extrusions can no longer meet performance requirements. Adding transition elements (retained in α-Al matrix via rapid solidification during casting and dispersed via high-temperature homogenization) effectively enhances alloy properties. Here, a 6xxx alloy extrusion was developed by modifying 6061 composition with 0.1 wt.% Vanadium (V), using three-stage homogenization, hot extrusion, and aging. Microstructure and mechanical properties were characterized via SEM, EBSD, and tensile testing. Results show the original alloy has coarse recrystallized grains, while the V-added alloy features fine recrystallized and partially recrystallized fibrous grains: core recrystallization fraction decreases from 62.7% to 29.2%, and average grain size refines from 93 μm to 11.8 μm. Homogenization spheroidizes needle-like β-Al(FeMnCrV)Si to spherical α-Al(FeMnCrV)Si phases. The V-added T6 extrusion exhibits +31 MPa UTS, +20 MPa YS, and +6.1% elongation vs. the original. Reduced extrusion speed causes near-surface abnormal grain growth in the V-added alloy, decreasing YS to the original level but maintaining higher UTS. This work demonstrates vanadium addition and homogenization effectively refine microstructure, while emphasizing extrusion process optimization to balance mechanical properties.
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  An investigation of color index for the bulge and the disk in the nearby spiral galaxy M81 (NGC 3031)

  MOU Shuang-qian, MIAO Jing-ren, MAO Ye-wei

  2025, 24(3): 20-30.

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  In this study, by analyzing the imaging data for the nearby spiral galaxy M81 (NGC 3031) obtained with the Spitzer Space Telescope at 3.6 μm and 4.5 μm, morphological parameters at the two bands and color index for the bulge and the disk of the galaxy are obtained, based on which, spatial distributions of the surface brightness and the color index for the galaxy and its substructures are deeply investigated. The software GALFIT is used to decompose the galaxy with two Sérsic components. By separating the bulge and the disk from the galaxy, images of the color index (3.6~4.5 μm) for the two substructures are created. In the results, the Sérsic index of M81 at 3.6 μm and 4.5 μm band is 4.27 and 5.13, respectively, confirming it as a classical bulge. The Sérsic index n ≈ 1.1 of the disk complies with the feature of an exponential disk. The effective radius of the bulge in the 3.6 μm band (72.24 arcsec) is smaller than in the 4.5 μm band (87.03 arcsec), and hence more compact in morphology, which may be related to the difference in sensitivity to stellar population properties at different bands. Analysis of the color index shows that the color difference between the bulge and the disk is not obvious (the color index is -0.08), but the overall color index for the galaxy (about -0.09) is bluer than those for the bulge and the disk. In the radial profiles, the color index of the disk decreases gradually with the radius, with the gradient about 0.33 mag/arcsec², suggesting a decrease in stellar population age from the center to the edge. The color index for the bulge slightly decreases within a small radial range (< 70 arcsec), with the gradient about 0.13 mag/arcsec², suggesting older central stars than those at outer areas. The overall color index for the galaxy shows a flat trend extending to large radii, suggesting similar ages for outer stars. In the center, the color index for the disk is larger than that for the bulge, which may be caused by different processes in the formation and evolution of different substructures. In the next work, we will conduct the multi-band decomposition of the galaxy, and construct spatially resolved spectral energy distributions for its substructure, respectively.
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  Estimation of oxygen abundance in HⅡ region of extragalactic galaxy NGC 0925

  I Lin-lin, WU Qi-ming, MAO Ye-wei, MO Shi-yin

  2025, 24(3): 31-41.

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  The oxygen abundance serves as a pivotal probe for unveiling the chemical evolution of galaxies. While estimating oxygen abundance via spectral emission lines remains the most prevalent approach, significant discrepancies among different methods for the same target source introduce substantial uncertainties in abundance determination and studies of galactic chemical evolution. In this study, by utilizing observational data for HⅡ regions in the extragalactic galaxy NGC 0925, obtained with the 2.16 m telescope in the National Astronomical Observatory′s, oxygen abundances are estimated through multiple methods. We compare and quantify the estimates from the four widely used strong-line diagnostics (N2, R23,O3N2, N2O2) and the Bayesian multi-line statistical inference NebulaBayes. In the Bayesian statistical inference, we generate 27 abundance estimates by adjusting different emission-line combinations. The observed spectral emission lines include seven features: [O Ⅱ] λ3727, [O Ⅲ] λ5007, [N Ⅱ] λ6583, [S Ⅱ] λ λ6717, 6731, Hα, and Hβ. Results demonstrate that the mean oxygen abundance derived from all methods is approximately 8.3 (in 12+log(O/H)), with the maximum and minimum estimates 9.068 and 7.179, respectively. Comparative analysis reveals that the Bayesian method exhibits strong consistency with the N2 index (12+log(O/H)~8.36 with the difference~0.085 dex) when adopting all the seven emission lines; the R23 method (12+log(O/H)~8.112) lead to the maximal difference (0.33 dex). Among the seven lines, [O Ⅱ] λ3727 and [N Ⅱ] λ6583 emerge as critical diagnostic features for oxygen abundance determination. Absence of them induces substantial difference (|Δ| > 0.3 dex), disrupts ionization equilibrium constraints, skews posterior probability distributions toward extreme values, and significantly enlarges uncertainty ranges. Conversely, exclusion of non-critical lines such as [S Ⅱ] λ λ6717, 6731 only causes subtle differences (|Δ| ≤ 0.1 dex) with upper and lower limits equal in uncertainties. These findings provide observational benchmarks for refining oxygen abundance calibration methodologies. Based on the analysis, we suggest prioritizing spectroscopic coverage of [O Ⅱ] λ3727 and [N Ⅱ] λ6583 in abundance determinations, coupled with Bayesian multi-line statistical constraints to reduce systematic errors. The results in this work offer methodological guidance for constructing high-precision models of galactic chemical evolution.
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  Study on human-induced vibration response of bridge based on Cellular Automata

  CAI Wei-qiang, LIU Ai-rong, HUANG You-qin, PAN Zhao-jie

  2025, 24(3): 42-51.

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  Pedestrian walking behavior exhibits strong subjectivity, and the dynamic response of footbridges under random crowd loading has attracted widespread attention. This study considers subjective behaviors in pedestrian walking, such as following, overtaking, and avoidance, and establishes a pedestrian flow model using Cellular Automata. Based on the modal superposition method, an efficient computational approach for human-induced vibration response is developed. The variation of resonant response with crowd density and the influence of bridge frequency on the most critical crowd density are analyzed. The results indicate that: ① At high crowd densities, pedestrian step frequency may decrease, causing the frequency of walking loads to deviate from the natural frequency of the bridge. As a result, the resonant response does not necessarily increase with higher crowd density; ② Under high-density crowd conditions, attention should be paid to the impact of the second harmonic of walking forces on bridge vibration response, as it may induce significant resonant responses in higher-frequency modes.
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  Assessment of the integrity of multi-girder widened bridges based on dynamic response spectrum

  SUN Zhi-hai, ZHANG Jun-ping, WEI Bin, HUANG He-hao, ZHANG Tai-quan

  2025, 24(3): 52-60.

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  To evaluate the integrity of multi-girder widened bridges, a quantitative evaluation method based on response spectrum similarity for transverse cooperative working performance was established. The study focused on a short- and medium-span girder bridge in Guangdong province, constructed in 1996 and widened in 2012. Vertical acceleration sensors were installed at the mid-span bottom of each girder. Leveraging the characteristics of structural health monitoring data, a high-quality dynamic response spectrum was obtained through the ensemble averaging algorithm. The evaluation index was then constructed using the calculated acceleration spectrum to comprehensively assess the bridge's integrity. The analysis results indicated that the acceleration spectrum patterns of each girder were highly consistent, with similar characteristic frequencies. The spectral similarity between adjacent girders exceeded 0.90, reflecting good transverse cooperative working performance. The first singular value spectra of the new and old bridges were highly similar, with a singular value spectrum similarity of 0.91, demonstrating that the widened bridge continues to exhibit cooperative performance effectively. These findings confirm the integrity of the multi-girder widened bridge, consistent with conclusions drawn from various quasi-static time-domain responses, thereby validating the feasibility and scientific basis of the proposed evaluation method.
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  Simplified method for reduction effect of viscous fluid damper on deck displacement of cable-stayed bridge under pulse-type earthquakes

  SONG Kun

  2025, 24(3): 61-69.

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  This study examined the relationship between the seismic responses of cable-stayed bridges and the parameters of pulse-type ground motions. Based on this analysis, a simplified single-degree-of-freedom method for calculating longitudinal deck displacement was developed. The method's effectiveness was validated using various seismic inputs and bridge structures. Furthermore, the study analyzed the deck displacement response characteristics of cable-stayed bridges equipped with viscous dampers under different pulse waves and evaluated the dampers' shock-absorption performance during actual pulse-type earthquakes. The results provide a basis for rapidly determining viscous damper parameters and designing shock-absorption systems for cable-stayed bridges in pulse-type earthquake conditions.
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  Complexation pattern of complex emerging contaminants in water and the mechanism of iron-carbon surface enhanced degradation

  AO Li-shen, NAN Yi-chen, WANG Yu-meng, LIAO Wei-xiang, HU Chun

  2025, 24(3): 70-78.

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  Emerging contaminants are widely detected in actual natural water bodies and have been the subject of considerable research interest due to their high ecotoxicity and the difficulty of their removal by conventional water treatment technologies. However, there is a paucity of literature on the mechanisms of pollutant interactions and their removal in actual water bodies under coexistence states. In this paper, we investigated the interactions between bisphenol A (BPA), which has a high detection rate in natural water bodies, and its coexisting pollutants, such as tetracycline (TC), diphenhydramine (DP), and phenytoin (PHT), as well as their transformation kinetics on the surface of the iron-carbon catalyst. A series of characterization tools were used to probe the pollutants interactions and electron transfer, confirming the formation of BPA-TC/DP/PHT composite complexes by BPA with TC, DP and PHT, respectively. The adsorption coordination of the composite complex with the surface of the iron-carbon catalyst resulted in a larger surface charge leaving the domain, which triggered the electron capture conduction on the surface of dissolved oxygen in water and the surface cleavage of the adsorbed complexes. The BPA degradation rate decreased to 62.1%, 53.6% and 70.0%, respectively, however, the degradation rates of BPA-complexed TC, DP and PHT increased by 17.2%, 31.6% and 44.8%, respectively, and the corresponding reaction rate constants increased by 2.195, 1.810 and 3.459 times, respectively. The products are low toxicity or harmless substances, and the catalytic system with environmental benefits.
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  Mechanism of the influence of disinfectant dosing strategy on disinfection by-products of drinking water pipe network

  ZHANG Po-jun, LIU Xin-kai, LIN Yan-liang, SHEN Kai-feng, CHEN You-yi, LU Xiao-qin, HU Chun, XING Xue-ci

  2025, 24(3): 79-88.

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  This study is designed to thoroughly investigate the impact mechanisms of chlorine disinfectant dosing strategies on the formation of disinfection by-products (DBPs) in drinking water cast iron pipelines. Secondary chlorination can effectively maintain the residual chlorine concentration in water, thereby ensuring long-term disinfection efficacy. The experimental data demonstrates that under the condition of 1.0 mg·L^-1 chlorine dosing at the water plant and an additional 1.0 mg·L^-1 secondary chlorination (Group 1-1), the control of DBPs in the simulated pipeline network effluent on the fifth day is optimal, with the concentration of trihalomethanes (THMs) being only 37.44 μg·L^-1 and virtually no nitrogen-containing DBPs generated. Further investigation revealed that the extracellular polymeric substances (EPS) in the effluent of Group 1-1 on the fifth day exhibit a higher proportion of β-sheet and α-helix protein secondary structures. This endows the suspended biofilm in the water with both coagulability and hydrophobicity, thereby inhibiting the chemical reactivity between EPS substances and chlorine disinfectants, leading to a significant reduction in the formation of DBPs, especially nitrogen-containing DBPs. During the water distribution process following chlorine disinfection in cast iron pipelines, EPS substances, primarily proteinaceous in nature, serve as a crucial source of DBPs precursors. Combining the protein/polysaccharide ratio and Zeta potential of EPS in water can significantly enhance the potential estimation accuracy of DBPs formation. The findings of this study provide a vital theoretical foundation and technical support for optimizing chlorine disinfectant dosing strategies in drinking water disinfection and pipeline distribution processes.
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  Study on CSI-free intelligent reflecting surface assisted communication optimization based on received signal strength

  PENG Kai, HUANG Gao-fei

  2025, 24(3): 89-99.

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  An IRS-assisted broadcast communication system composed of a transmitter, an intelligent reflecting surface (IRS), and multiple receivers was investigated, focusing on a novel IRS phase-shift optimization scheme that does not require channel state information (CSI). Existing research on optimizing IRS-assisted communication systems commonly assumes that CSI can be obtained. However, because IRS typically contains a large number of reflecting elements, the overhead for channel estimation increases with the number of these elements, making the acquisition of CSI prohibitively costly and limiting the practical applicability of such methods. To address this challenge, a scheme is proposed that utilizes only the received signal strength observed by the receivers to optimize the IRS phase shifts, aiming to maximize the minimum received signal power at receivers. Due to the lack of CSI, the received signal power cannot be derived through analytical expressions, preventing the use of conventional convex optimization approaches. To solve this problem, the system optimization is modeled as a Markov Decision Process (MDP), and a deep reinforcement learning algorithm based on proximal policy optimization is introduced to determine the optimal IRS phase shifts. Simulation results show that the proposed scheme achieves favorable system performance.