高耸桥墩保护性爆破拆除关键技术

为解决高耸钢砼桥墩上部倾斜导致的工程质量不合格问题,采用保护性控制爆破将上部倾斜部分钢砼桥墩予以拆除,同时保留下部未偏斜部分桥墩不受破坏。采用开设组合形状切口,预开定向窗、导向窗;设置组合高差卸荷槽,预伤钢筋弱化抗压抗拉能力为关键措施的控制爆破方案。方案实施取得了十分满意的效果,上部拟拆除部分桥墩顺利倾倒下坠,下部保留部分桥墩完好无损。采用保护性控制爆破技术能高效、安全地解决类似高耸钢砼桥墩(构筑物)部分拆除、部分保留利用的问题,并能取得可观的经济、社会效益。     

基于分形理论的黄河内蒙古段河势演变特征及其与凌汛灾害关联研究

寒区河道凌汛灾害河势“弯道效应”的量化评估十分重要。基于分形理论提出河道横断面-纵剖面-平面多维度河势分形维数计算方法及其物理机制，并探讨黄河内蒙古段不同维度河势演变分形特征及其与凌汛灾害的关联关系。结果表明，黄河内蒙古段不同维度河势均具有多尺度自相似分形特征，且具有多年记忆周期的长程相关性；冰坝（严重性冰塞）发生频次与河道主槽弯曲分形维数呈正相关指数型函数关系，与河相系数、深泓点高程和河段平均底坡分形维数负相关，与水深-面积分形维数正相关，总体表明冰坝灾害更易发生于主槽偏移摆动大、蜿蜒曲折、河湾发育程度高的宽浅型弯曲河道，研究成果可为凌汛期冰塞冰坝灾害易发河段诊断及预测提供重要理论依据。     

Osmotic pretreatment for instant controlled pressure drop dried apple chips: Impact of the type of saccharides and treatment conditions

Instant controlled pressure drop (ICPD) is an emerging drying technique that can produce fruit chips with crispy texture. To improve the qualities of ICPD-dried apple chips, six types of saccharides with different polymerization were used for osmotic pretreatment on apple slices. Firstly, the effects of different saccharides on the osmotic behavior and texture of ICPD-dried apple chips were evaluated. Then, the effects of osmotic conditions of a selected saccharide, i.e. stachyose, on the qualities of ICPD-dried apple chips were studied. The results showed that sucrose, raffinose, and stachyose could significantly enhance the crispness of the ICPD-dried apple chips. In addition, the ICPD-dried apple chips pretreated with stachyose possessed the highest T_g (29.74?°C) and superior porous structure compared with pretreatments using the other saccharides. Moreover, limited color change (ΔE) was found in the samples pretreated with stachyose at 40?°C for 30?min, as well as higher retention of polyphenols. In conclusion, it is confirmed that the types of saccharides significantly influence the qualities of the ICPD-dried apple chips, and osmotic pretreatment at 40?°C for 30?min using stachyose was suggested for improving the overall quality of ICPD-dried apple chips.     

海藻酸钠/脲醛树脂复合微胶囊的缓释动力学特性

采用两步法制备海藻酸钠/脲醛树脂复合微胶囊。在树脂化阶段引入海藻酸钠(SA)参与脲醛树脂(UF)的缩聚反应形成复合壳层,制备了阿维菌素复合微胶囊。通过FTIR、TG、SEM、粒度分析等表征微胶囊的结构特征、组成成分、表观形貌、粒度分布。结果表明,SA的引入可有效改善脲醛树脂微胶囊的团聚现象,提高药物的包覆率至60%以上。释放性能研究显示,复合微胶囊的缓释能力较脲醛树脂微胶囊提高,72 d累计释放率由27.5%增至44.5%,且释放速率受pH、温度的影响,25℃下酸性介质中27d累计释放率超过50%。释放行为均可用Korsmeyer-Pappas动力学模型进行描述。     

An analytical method for the analysis of trihalomethanes in ambient air using solid‐phase microextraction gas chromatography‐mass spectrometry: An application to indoor swimming pool complexes

A simple method for the collection and analysis of the four brominated and chlorinated trihalomethanes (THMs) in air samples is described. Ambient air samples were collected in pre‐prepared glass vials, with THM analysis performed using solid‐phase microextraction gas chromatography‐mass spectrometry, where the need for chemical reagents is minimized. Analytical parameters, including oven temperature program, solvent volume, incubation time, vial agitation, extraction time and temperature, as well as desorption time and temperature, were evaluated to ensure optimal method performance. The developed method allows for point‐in‐time quantification (compared to an average concentration measured over extended periods of time), with detection limits between 0.7 to 2.6 µg/m³. Excellent linearity (r² > 0.99), repeatability (3% to 11% RSD), and reproducibility (3% to 16% RSD) were demonstrated over a concentration range from 2 to 5000 µg/m³. The method was validated for the analysis of THMs in indoor swimming pool air and was used to investigate the occurrence of THMs in the air above 15 indoor swimming pools. This is the first study to report the occurrence of THMs in swimming pool air in Australia, and concentrations higher than those previously reported in other countries were measured.     

Effect of a sweeping air stream and gas–phase aspect ratio of an isothermal Stefan diffusion column on the experimental estimation of binary gas diffusivities

The Stefan column consists of liquid A evaporating into an inert/stagnant gas B with a sweeping B stream at the top. It was designed to estimate binary gas diffusivities, D_AB’s, but “end effects” such as gas mixing at the top and interfacial curvature have been either ignored or uncorrelated to the operational settings. This study’s hypothesis is that gas mixing at the top and the gas–phase aspect ratio affect D_AB estimation in the acetone (A)-ambient air (B) system at 50?°C. The sweeping stream Reynolds number (Re) and the gas–phase aspect ratio (AR?=?initial gas phase height to column internal diameter) were the variables tested. Isothermal evaporation-diffusion experiments were conducted in which the temporal interfacial descent was tracked. The settings were 492 ≤ Re ≤ 5378 and AR between 5 and 15. A 1D transport model allowed determination of the experimental diffusivity, D_AB,exp, by nonlinear regression. For Re < 600, the D_AB,exp errors relative to D_AB,CE (predicted by the Chapman–Enskog kinetic theory for low-density gases) were small and unrelated to AR, while for Re > 600 the errors increased considerably with Re and were inversely proportional to AR. This study is the first to relate the column’s operational settings to the D_AB estimation errors. The column should be operated at low sweeping gas Re and large AR for accurate D_AB,exp’s. The low Re region deserves further study, while the present transport model may have to be replaced by computational fluid dynamics simulations to account for the multidimensional gas flow patterns.     

Hydrogen carriers: Production,transmission, decomposition,and storage

Recognizing the potential role of liquid hydrogen carriers in overcoming the inherent limitations in transporting and storing gaseous and liquid hydrogen, a complete production and use scenario is postulated and analyzed for perspective one-way and two-way carriers. The carriers, methanol, ammonia and toluene/MCH (methylcyclohexane), are produced at commercially viable scales in a central location, transmitted by rail or pipelines for 2000 miles, and decomposed near city gates to generate fuel-cell quality hydrogen for distribution to refueling stations. In terms of the levelized cost of H₂ distributed to the stations, methanol is less expensive to produce ($1.22/kg-H₂) than MCH ($1.35/kg-H₂) or ammonia ($2.20/kg-H₂). Levelized train transmission cost is smaller for methanol ($0.63/kg-H₂) than ammonia ($1.29/kg-H₂) or toluene/MCH system ($2.07/kg-H₂). Levelized decomposition cost is smaller for ammonia ($0.30–1.06/kg-H₂) than MCH ($0.54–1.22/kg-H₂) or methanol ($0.43–1.12/kg-H₂). Over the complete range of demand investigated, 10–350 tpd-H₂, the levelized cost of H₂ distributed to stations is aligned as methanol « ammonia ~ MCH. With pipelines at much larger scale, 6000 tpd-H₂, the levelized cost decreases by ~1 $/kg-H₂ for ammonia and MCH and much less for methanol. Methanol is a particularly attractive low-risk carrier in the transition phase with lower than 50-tpd H₂ demand.     

Comparison of horizontal and vertical electric field in the treatment of river sediment by electro-dewatering

The aim of this study was to evaluate and compare the effectiveness of horizontal (H-EDW) and vertical (V-EDW) electro-dewatering fields, in terms of dewatering and energy consumption, for the treatment of river sediment. The influence of the sludge thickness (3, 4, 5, 6, 7?cm) and the applied voltage (10?30?V) were examined. V-EDW was found to significantly improve dewatering and reduce process time, while H-EDW has the potential to save energy but results in sludge containing greater moisture. As the applied voltage was increased from 10?V to 30?V, the final dry solids content and energy consumption increased for both modes. Increased sludge thickness from 3?cm to 7?cm was found to have a negative influence on the final dry solid content of the sludge for V-EDW, but is not a significant influence with H-EDW. The results demonstrate that H-EDW is an effective dewatering method and has potential for continuous operation and energy efficiency for industrial-scale applications.