激光功率对低碳钢表面激光熔覆钛合金涂层组织和性能的影响

目的 利用激光熔覆简便、高效的特点,在低碳钢表面开发低成本、短流程的耐蚀钛合金涂层,拓宽钛合金在海洋工程装备上的应用。方法 选择球形纯钛粉末,采用同步送粉式激光熔覆技术在低碳钢表面制备一层薄的钛合金涂层。通过单色红外测温仪对熔池的温度变化进行监测。利用光学显微镜(OM)、扫描电子显微镜(SEM)、能谱仪(EDS)和X射线衍射仪(XRD)等表征涂层的宏观形貌、微观形貌和相组成。借助万能试验机和维氏硬度计测试涂层的结合强度、剪切强度和硬度。使用电化学工作站在NaCl(质量分数3.5%)溶液中测试涂层的极化曲线和阻抗(EIS),以评价涂层的耐蚀性能。结果 采用激光熔覆技术在低碳钢表面成功制备了一层薄的耐蚀钛合金涂层。激光功率的选择对在低碳钢表面制备性能良好的钛合金涂层至关重要。一方面,激光功率会影响熔池的温度演变,随着功率的降低,熔池的最高温度降低,熔池寿命缩短。通过引入粉末沉积密度(ρ_PDD)和单位面积有效能量输入(E_eff)进一步描述工艺参数与涂层质量之间的关系。结果表明,在ρ_PDD(0.009 g/mm²     

A survey of histamine content in seafood sold in markets of nine countries

Histamine content was investigated in some fresh scombroid fish including tuna (Thunnus spp), mackerel (Scomber Japonicus) etc, and non-scombroid fish including mahi–mahi (Coryphaena hippurus), sardine (Sardina pilchardus), herring (Clupea harengus) etc, and fish products (sauce, dried fish) which came from Fiji, Germany, the Netherlands, Norway, Thailand, Cambodia, the Philippines, Japan and China. Histamine was detected in 35 of the 159 fish samples tested for a detection rate of about 21%. Fish samples exceeding 50 ppm histamine occurred in about 9% of the samples with 5 samples exceeding 500 ppm of which 2 were above 1000 ppm. Fish sold in markets in some countries may cause a histamine risk to consumers while other countries may have the necessary controls in place.     

One-step synthesis of biochar-supported potassium-iron catalyst for catalytic cracking of biomass pyrolysis tar

In this work, K–Fe bimetallic catalyst supported on porous biomass char was synthesized via a one-step synthesis method by pyrolysis of biomass (peanut shells) after impregnation of a small amount of potassium ferrate (PSC–K₂FeO₄), and was evaluated for the cracking of biomass pyrolysis tar. Control experiments using the pure char (PSC) and char-supported catalysts after impregnation of KOH (PSC–KOH) and FeCl₃ (PSC–FeCl₃) were also performed for comparison. The as-prepared PSC-K₂FeO₄ possessed a porous structure with the dispersion of particles/clusters of Fe metal, K₂CO₃ and KFeO₂ on the char support. Tar cracking experiments showed that the PSC-K₂FeO₄ exhibited excellent catalytic activity on the cracking of biomass pyrolysis tar in the temperature range of 600–800 °C, and the obtained tar conversion efficiencies were obviously higher than that in the control experiments, particularly at relatively lower temperatures (600 and 700 °C). The yields of combustible gas compounds including CO, H₂ and CH₄ increased significantly using PSC-K₂FeO₄ as the catalyst due to the enhanced tar cracking and reforming reactions. The porous structure and the active crystal structures of the spent catalyst were well retained, indicating the potential for efficient and long-term utilization of the catalyst in tar cracking. PSC-K₂FeO₄ exhibited excellent reusability during the five times reuse under the same conditions without regeneration, which showed almost no obvious decrease in the tar conversion efficiency and gas yields.     

Sputter-etching treatment of proton-exchange membranes: Completely dry thin-film approach to low-loading catalyst-coated membranes for water electrolysis

Simultaneous plasma etching of a proton-exchange membrane (PEM) and deposition of a cerium oxide layer during reactive magnetron sputtering leads to the formation of a pronounced fiber-like structure on its surface. The level of structural porosity can be adjusted by varying the working pressure during the process. A PEM treated this way can be subsequently coated with a thin layer of iridium, forming an anode-side catalyst-coated membrane (CCM) for applications in water electrolysis. Due to the significantly enlarged surface of the membrane, there is no necessity for any additional, potentially corroding, support nanoparticles to achieve efficient in-cell operation. Moreover, utilizing a rotatory frame-shaped substrate holder and a multitarget deposition apparatus, the sputter-etching process can be used in the preparation of a full anode/cathode thin-film CCM in a single vacuum entry. This structure yields remarkable performance characteristics in an electrolyzer cell, considering its low combined noble metal loading of just 220 μg cm⁻². Using this completely dry process for CCM manufacturing may facilitate efficient large-scale future production.     

Proton exchange membrane water electrolysis at high current densities: Investigation of thermal limitations

In this work the thermal limitations of high current density proton exchange membrane water electrolysis are investigated by the use of a one dimensional model. The model encompasses in-cell heat transport from the membrane electrode assembly to the flow field channels. It is validated by in-situ temperature measurements using thin bare wire thermocouples integrated into the membrane electrode assemblies based on Nafion® 117 membranes in a 5 cm² cell setup. Heat conductivities of the porous transport layers, titanium sinter metal and carbon paper, between membrane electrode assembly and flow fields are measured in the relevant operating temperature range of 40 °C – 90 °C for application in the model. Additionally, high current density experiments up to 25 A/cm² are conducted with Nafion® 117, Nafion® 212 and Nafion® XL based membrane electrode assemblies. Experimental results are in agreement with the heat transport model. It is shown that for anode-only water circulation, water flows around 25 ml/(min cm²) are necessary for an effective heat removal in steady state operation at 10 A/cm², 80 °C water inlet temperature and 90 °C maximum membrane electrode assembly temperature. The measured cell voltage at this current density is 2,05 V which corresponds to a cell efficiency of 61 % based on lower heating value. Operation at these high current densities results in three to ten-fold higher power density compared to current state of the art proton exchange membrane water electrolysers. This would drastically lower the material usage and the capital expenditures for the electrolysis cell stack.     

考虑面力效应的HFR-LWC梁抗爆理论模型与试验验证

现有的抗爆设计规范通常将面力效应看作一种潜在的安全系数,而对面力作用在爆炸加载过程中的变化规律及其对结构抗力的贡献不做深入探索.该文对近距离爆炸荷载进行适当简化,并考虑面力效应的影响,建立一种基于等效单自由度(SDOF)法的梁式构件抗近距离爆炸分析模型.专门设计了一套面力加载装置,对8根考虑面力效应的混杂纤维轻骨料混凝...     

Single and competitive adsorption affinity of heavy metals toward peanut shell-derived biochar and its mechanisms in aqueous systems

Converting peanut shells into biochar by pyrolysis was considered an environmentally friendly and efficient method for agricultural solid waste disposal. The properties of peanut shell-derived biochar (PBC) under different temperature and its adsorption capacity of heavy metals were investigated. It was found that PBC400 exhibited the highest cumulative capability for heavy metals elimination in single solute because of its high specific surface area and rich functional groups. Furthermore, the competitive adsorption revealed that PBC had a substantial difference in adsorption affinity from diverse heavy metal ions, sorption capacity decreased as Pb²⁺ > Cu²⁺ > Cd²⁺ > Ni²⁺ > Zn²⁺, which was lower than in a single solute. The adsorption process using selected biochar was optimized with respect to pH, reaction time, adsorbent dose, and initial concentration of heavy metals. The kinetic data was well fitted with PSO model, and the Langmuir model was adopted for adsorption equilibrium data in both cases of single solutes and mixed solutes for all heavy metals, which indicated that the removal course was primarily explained by monolayer adsorption, and chemical adsorption occupied an important role. Therefore, peanut shells derived biochar could be a potential and green adsorbent for wastewater treatment.     

基于CiteSpace的《水资源保护》创刊35年文献计量分析

基于CiteSpace软件对《水资源保护》1985—2020年的4 060篇有效文献进行计量分析,对相应文献作者、研究单位及关键词进行共现分析与突现性检测,探究了《水资源保护》创刊以来研究主题演变、历史热点、核心作者及研究机构的发展脉络。结果表明：自创刊以来《水资源保护》刊文量呈现整体上升的趋势;受国家政策和社会热点的影响,研究方向由创刊初期的偏重水资源开发利用转向新千年的“人水和谐”视角下的水资源综合利用,再到近年来的以人水系统耦合过程、机制及其保护和影响研究为核心的综合研究;研究内容由单要素分析跃迁为多要素耦合研究,由传统的水质或水量分析上升为最严格的水资源管理制度导向下的水资源及虚拟水开发与管控;时空尺度不断开拓,时空分辨率进一步细化,研究视角由单一分散走向交叉融合;研究手段由传统的地面观测、统计分析迈向多源数据支持下的过程监测与数字耦合模拟,知识性研究弱化,方法性研究不断深化。     

Two simple and efficient algorithms for Jordan sorting and polygon cutting and clipping

This paper deals with the Jordan sorting problem: Given n intersection points of a Jordan curve with the x-axis in the order in which they occur along the curve, sort these points into the order in which they occur along the x-axis. The worst-case time complexity of this problem is θ(n). Unfortunately, the known O(n) time algorithms are too complicated, which causes that they are difficult to implement and slow for the inputs of sizes that are of practical interest. In this paper, two algorithms for Jordan sorting are presented. The first algorithm is extremely simple. Although its worst-case time complexity is O(nlogn), it is shown that the worst time is achieved only for special inputs. For most inputs, a better performance can be expected. Furthermore, an improved O(nlog logn) worst-case time algorithm is presented. For the input sequences of size from 4 to 10⁵, the algorithms are compared with Quicksort, with the algorithm based on splay trees and with the O(n) time algorithm proposed by Fung et al. The results show that our algorithms are faster. The relevant implementation details are given.