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排序方式: 共有338条查询结果,搜索用时 218 毫秒
41.
在产业转移背景下,考虑港口服务货运需求与刺激货运需求的双重功效,研究海上丝绸之路沿线产业承接地的港口投资建设问题。首先,在现实交通运输网络中加入虚拟链接构建超级网络,用以刻画制造业的转移、生产和运输过程。其次,建立制造业承接地港口投资决策优化模型,用运输阻抗、地价和工资三个内生变量描述港口投资、产业转移与区域经济之间均衡关系。模型以产业承接地港口收益最大为目标,确定承接地港口的投资规模及费率水平。最后,以斯里兰卡的科伦坡口为例进行数值分析,计算海上丝绸之路沿线港口需求与供给间正向反馈的数量关系及上确界,为优化沿线港口投资实现投资利益最大化提供依据。 相似文献
42.
The isotopic compositions of carbon compounds in landfill leachate provide insights into the biodegradation pathways that dominate the different stages of waste decomposition. In this study, the carbon geochemistry of different carbon pools, environmental stable isotopes and compound-specific isotope analysis (CSIA) of leachate dissolved organic carbon (DOC) fractions and gases show distinctions in leachate biogeochemistry and methane production between the young area of active waste emplacement and the old area of historical emplacement at the Trail Road Landfill (TRL). The active area leachate has low DOC concentrations (<200 mg l?1) dominated by fulvic acid (FA=160 mg l?1), and produces CH4 dominantly by CO2 reduction (D? excess=20.6‰). Leachate generated in the area of older waste has high DOC (>4770 mg l?1) dominated by FA (4482 mg l?1) and simple fatty acids (acetic=1008 mg l?1 and propionic=608 mg l?1), and produces CH4 by the acetate fermentation pathway (D? excess=9.8‰). CSIA shows an advanced degradation and a progressive accumulation of 13C of fatty acids in leachate from the older area. The enriched 13C value of FA (?20 and?26‰ for the older and active parts, respectively,) and of low molecular weight DOC (?8 and?27‰) as well as of the bulk DOC (?21 and?25‰) shows more advanced degradation in the older part of the landfill, which is consistent with the shift in the humic/FA ratios (0.05 and 0.18). The 13C enrichment of acetate (?12‰) above the 13C of DOC (?21‰) and of propionic acid (?19‰), in older leachate, suggests that this acetate has not evolved from the simple degradation of larger organic molecules, but by homoacetogenesis from the enriched dissolved inorganic carbon (DIC) pool (8‰) and H2, which produce a more enriched 13C of acetate. In contrast, the 13C of the minor acetate in the active area (?17‰) indicates that CO2-reducing bacteria must be the primary consumers of H2, which has resulted in enriched 13CDIC (10‰) and depleted 13CCH4 (?58‰). 相似文献
43.
Yang Bai Xiang Yao Jiandong Wang Jin-Long Wang Si-Cheng Wu Shi-Ping Yang Wei-Shi Li 《Tetrahedron》2019,75(33):4676-4685
Fullerene-based organic solar cells are generally suffering from severe microstructure evolution occurring in their bulk heterojunction active layers and thus are extremely stable. To address it, four polymerizable C70 fullerene derivatives, [6,6]-phenyl-C71-ethyl acrylate (PC71EA), [6,6]-phenyl-C71-propyl acrylate (PC71PrA), [6,6]-phenyl-C71-butyl acrylate (PC71BA), and [6,6]-phenyl-C71-pentyl acrylate (PC71PeA), have been designed, synthesized, and investigated. These fullerene compounds have a molecular structure, shape and size very like the conventional C70 fullerene acceptor, [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM), and have been found no different in their light absorption, redox potentials, and frontier orbital energy levels. Using these fullerene acrylates individually as acceptor and poly(3-hexylthiophene) as donor, organic solar cells have been fabricated and gave optimal efficiencies ranging from 3.32% to 4.16%, comparable to PC71BM-based reference cells (4.06%). Owing to their acrylate functionality, these fullerene derivatives can turn into insoluble upon heating, and thus endow their solar cell devices much better thermostability than PC71BM-based reference cells. The best one, coming from PC71PeA devices, reported an optimal efficiency of 4.16%, and maintained 91.7% efficiency after heat treatment at 150 °C for 35 h. As a sharp contrast, the PC71BM reference cell dropped its optimal efficiency from 4.06% to 0.48% only after 5 h heat treatment. X-ray diffraction, optical and atomic force microscopy, and space-charge-limited current method have been carried out to understand active layer structure, morphology, and charge mobility change during heat treatment. 相似文献
44.
Hao Dong Dawen Xu Wangsheng Liu Yaopeng Zhang Hao Guo 《Journal of Saudi Chemical Society》2019,23(8):1041-1048
An intramolecular-intermolecular cascade cyclization reaction via multi metal-carbene intermediates has been developed. This reaction uses catalytic amount of Nd(OTf)3, which actives both alkyne and aldehyde moieties. This protocol provides a novel strategy for the synthesis of phenanthro[9,10-b]furans. 相似文献
45.
Meng Zang Chaocheng Zhao Yongqiang Wang Shuiquan Chen 《Journal of Saudi Chemical Society》2019,23(6):645-654
Along with the rapid development of industry, VOCs gradually move into the spotlight, and now become a kind of harmful environmental pollutants that cannot be overlooked. This paper introduces the hazards of VOCs and the common catalytic combustion catalysts, noble metal catalysts and non-noble metal catalysts, for the elimination of VOCs. Perovskite catalysts, as one of the non-noble catalysts, play an important role in the field of catalytic combustion in recent years. According to the classification of elements doping in perovskites, the research achievements in the past five years were analyzed and reviewed. In addition, this paper also analyzes and elaborates the reaction kinetics and QSAR/QSPR models for the introduction of structural properties and reaction mechanisms. 相似文献
46.
Yong Zhang Yonghai Liu Shuai Zhang Lei Shi Wei Wang Hao Li 《Tetrahedron letters》2019,60(22):1463-1466
An acid-promoted 2-component Mannich annulation reaction of readily available acetylbenzaldehydes and secondary amines has been reported. The approach provides a simple and efficient method under mild conditions to synthesize 3-aminoindan-1-one derivatives in moderate to good yields. 相似文献
47.
面对一个分布在新地理区域的新市场,合理规划区域服务影响力的发展战略对企业至关重要。本文假设企业的服务影响力在地理区域上的发展可以用其地理上分布的立足点来表示。单个立足点覆盖有限范围内的地理区域,并且在一个特定时刻用所有立足点所覆盖地理区域的总和来表示企业该时刻的发展状态。由于资源限制,企业对经济发展迅速的区域的覆盖必须在一定时间内逐步完成。因此,在发展时期内如何确定立足点的位置并使其位于知名城市中,是企业管理者亟待解决的问题。针对这个问题,本文首先基于时间序列预测方法建立了区域经济指标评估模型;然后使用集合覆盖理论提出了以成本和满意度为目标的选址优化模型并使用分支定界算法求解该模型;最后,使用从“一带一路”地区收集的数据对模型进行了检验。结果表明,该方法对有相关问题的企业具有较大的参考价值。 相似文献
48.
Degradation behaviors of porous scaffolds play an important role in the engineering process of a new tissue. In this study, three-dimensional porous silk fibroin/chitosan (SFCS) scaffolds were successfully prepared by freeze-drying method. In vitro degradation behaviors of SFCS scaffolds have been systematically investigated up to 8 weeks in phosphate buffer saline (PBS) solution at 37 °C. The following properties of the scaffolds were measured as a function of degradation time: pore morphology, structure, weight loss, and wet/dry weight value. The pH value of the PBS solution during degradation was also detected. SFCS scaffolds maintained its porous structure till 6 weeks of degradation. During the first 2 weeks, the pH value fluctuated in a narrow range from 6.53 to 6.93. SFCS scaffolds degraded much more quickly during the first 2 weeks, and the weight loss reached 19.28 wt% after 8 weeks of degradation. The degradation process affects little SFCS scaffolds' swelling properties. 相似文献
49.
Marianne Stranger Agnieszka Krata Velichka Kontozova-Deutsch Felix Deutsch Anna Worobiec Edward Roekens 《Microchemical Journal》2008,90(2):93-98
Nitrogen dioxide (NO2) concentrations were used to evaluate the air quality before and after the infrastructural change of an important traffic artery in Mortsel, Antwerp (Belgium). During the reconstruction works two pairs of traffic lanes were reduced to one in each direction. Two sampling campaigns were conducted: the first one before the works in 2003 and the second one in 2005, after the road works were finished. Sampling was performed on a weekly base with the use of passive diffusion tubes on the streets, and also indoors in nearby houses. The samples were analyzed by ion chromatography, from which data the NO2 concentrations in air could be calculated. These results were compared with NO2 values from the air monitoring station 42R801 of the Flemish Environment Agency in Borgerhout, Antwerp. On the base of different NO2 concentrations, correlated well with the traffic density, sampling locations were classified into three groups as follows: 1) ‘heavily polluted’ (heavy traffic); 2) ‘moderately polluted’ (medium traffic); or 3) ‘less polluted’ (low traffic density). Sampling sites located further from the road works, enclosed to the group ‘less polluted’, showed the lowest NO2 concentrations. The highest NO2 level was found for the locations close to reconstruction works, which belonged to the group ‘heavily polluted’. The contribution of NO2 was at the same level before and after the road works. During the first campaign it ranged from 30 ± 7 µg/m3 to 71 ± 11 µg/m3 and during the second sampling it was between 36 ± 17 µg/m3 and 73 ± 17 µg/m3. These modernization works had no impact on preventing the traffic-related pollutant as NO2 and as a consequence no significant effect on the air quality in the studied region. It has been proven that the impact of traffic on the air quality is unmistakably high and simply reduction of the number of the traffic lanes, intended to discourage the traffic flow, had apparently no environmentally advantageous effect. 相似文献
50.
Active noise control has been applied to a variety of systems in order to improve performance without the increases in size and weight that would otherwise be required by traditional passive noise control treatments. This paper investigates the application of an active noise control system to the control of generator noise in the master cabin of a luxury yacht. A multichannel, multi-tonal active noise control system employing loudspeakers and microphones in the master cabin of the yacht is investigated. It is shown that, due to the high number of engine orders produced by the generator, in order to achieve significantly perceptible levels of noise attenuation it is necessary to control at least 7 individual orders. A controller is investigated which targets 19 engine orders and it is shown to achieve in excess of 5 dB broadband attenuation, whilst achieving up to 23 dB attenuation in individual orders. This corresponds to a 23% reduction in the Zwicker loudness. 相似文献