Fabrication of high surface area graphitic nanoflakes on carbon nanotubes templates

Graphitic nanoflakes were fabricated on the carbon nanotubes templates for increasing the surface area utilizing bias assisted microwave plasma enhanced chemical vapor deposition (MWPECVD). The analysis of morphologies and structures were achieved by means of scanning electron microscopy and transmission electron microscopy. The surface area of graphitic nanoflakes, carbon nanotubes (CNTs) and graphitic nanoflakes/CNTs were 57.44 m²/g, 90.31 m²/g and 130.96 m²/g from BET measurement, respectively. The cyclic voltammetry was used to calculate the active area of platinum catalysts in 1 M sulfuric acid from hydrogen adsorption peak. An enhancement of activity could be observed from the calculation of CV results. This may be attributed to the small particle size and high dispersion of platinum particles coated on graphitic nanoflakes/CNTs. These high surface area materials could be used as catalysts supports or electrode for fuel cell applications.     

压痕法确定纤维复合材料界面影响区蠕变特性的数值模拟法

研究由平头压痕蠕变试验来确定纤维复合材料界面影响区蠕变性能参数的可行性。利用有限元蠕变分析确定在定压痕应力下的压痕蠕变率，重点放在稳定压痕蠕变率和复合材料材料界面影响区的蠕变性能参数的关系上。计算结果表明，界面影响区的剪应力沿纤维轴向在蠕变的主要过程中均匀分布，并且保持不变；详细地研究了压头大小对压痕蠕变响应的影响：提出两种方法由压痕蠕变试验来确定界面影响区蠕变性能参数，并给出了算例。这些结果也有利于准确认识平头压痕蠕变试验从而拓宽其应用范围。     

Surface modification of macroporous Al2O3 tubes with carbon-doped TiO2 intermediate layer and preparation of highly permeable palladium composite membranes for hydrogen separation

ABSTRACT

To prepare H₂-permeable palladium composite membranes, a novel carbon-doped microporous TiO₂ intermediate layer was introduced to modify the surface of macroporous Al₂O₃ substrates. The Pd/TiO₂–C/Al₂O₃ membrane was prepared via electroless plating, and thereafter, carbon residue in the intermediate layer was removed by calcination in air, yielding a Pd/TiO₂/Al₂O₃ membrane. Experimental results indicate that the carbon residue shrinks the pore size of the intermediate layer and facilitates a decrease of membrane defects. Additionally, carbon removal induces a higher effective membrane area at the permeate side, which enhances hydrogen permeability. Furthermore, the apparent activation energy (E_A) and stability of the as-prepared Pd/TiO₂/Al₂O₃ membrane were investigated.     

Spatial ecology of Bay of Quinte walleye (Sander vitreus): Annual timing,extent, and patterns of migrations in eastern Lake Ontario

Walleye (Sander vitreus) are the top nearshore predator in the Bay of Quinte and eastern Lake Ontario, where they have strong ecological and socio-economic impacts. The population is known to migrate seasonally; however, the precise timing and extent are not well defined. This study used acoustic telemetry to provide a fisheries-independent measure of timing, extent, and seasonal distribution of migration in Lake Ontario and to examine the influence of sex, spawning river, size, and year. Annual detection histories were used to determine the timing of migrations into and out of the spawning rivers, departure from the Bay of Quinte post-spawn, and the pre-spawn return to the Bay of Quinte. Sequence analysis was subsequently used to examine how fish occupy defined regions of eastern Lake Ontario annually and identify patterns in migration strategy. Spawning site fidelity was high for both rivers (91–97%) and annual residency within the Bay of Quinte was low (9.5%). Females spent less time in spawning rivers, migrated to the main lake earlier, and generally travelled further than males. Larger fish also migrated to the main lake first and travelled further, and differences in timing between spawning rivers were minor. Annual differences in timing were observed and were most likely related to environmental differences between years. Cluster analysis was used to identify groups of fish which utilized unique annual migration strategies and demonstrated sex and size had an important influence on the variability in annual spatial occupancy, but the importance of spawning river and year was minimal.     

Dreissena in Lake Ontario 30 years post-invasion

We examined three decades of changes in dreissenid populations in Lake Ontario and predation by round goby (Neogobius melanostomus). Dreissenids (almost exclusively quagga mussels, Dreissena rostriformis bugensis) peaked in 2003, 13 years after arrival, and then declined at depths <90 m but continued to increase deeper through 2018. Lake-wide density also increased from 2008 to 2018 along with average mussel lengths and lake-wide biomass, which reached an all-time high in 2018 (25.2 ± 3.3 g AFTDW/m²). Round goby densities were estimated at 4.2 fish/m² using videography at 10 to 35 m depth range in 2018. This density should impact mussel populations based on feeding rates, as indicated in the literature. While the abundance of 0–5 mm mussels appears to be high in all three years with measured length distributions (2008, 2013, 2018), the abundance of 5 to 12 mm dreissenids, the size range most commonly consumed by round goby, was low except at >90 m depths. Although the size distributions indicate that round goby is affecting mussel recruitment, we did not find a decline in dreissenid density in the nearshore and mid-depth ranges where goby have been abundant since 2005. The lake-wide densities and biomass of quagga mussels have increased over time, due to both the growth of individual mussels in the shallower depths, and a continuing increase in density at >90 m. Thus, the ecological effects of quagga mussels in Lake Ontario are likely to continue into the foreseeable future.     

Depth and temperature selection of lake charr (Salvelinus namaycush) ecotypes in Lake Superior revealed by popup satellite archival tags

Lake charr exhibit morphological diversity in large North American lakes, largely attributed to habitat partitioning. Bathythermal habitats of lean lake charr have been assessed but remain largely unknown for other lake charr ecotypes. Popup satellite archival tags (PSATs) were used to determine depth and temperature profiles of lean (n = 15), siscowet (n = 16) and redfin (n = 3) lake charr ecotypes in Lake Superior during segments of the year. Monthly median depths of leans were < 20 m throughout the year while the median depth of redfins was 24–32 m (June-September). Monthly median depth of siscowets ranged from 103 to 204 m but they exhibited four distinctive patterns: deep (>80 m), shallow (<10 m), extreme vertical movements (>80–0 m), and high frequency vertical movements between 100 and 125 m. Siscowets were the most stenothermal with habitat temperatures generally 4–5 °C but not exceeding 12 °C. Leans were found as low as 0 °C (January-March) and up to 15 °C (July-September). Median monthly habitat temperatures for redfins were 1–3 °C colder than leans during July-September. PSATs confirmed that siscowets exhibit extreme vertical movements and may feed near the surface. The timing and duration of the extreme vertical movements exhibited by siscowets did not appear to be associated with time of day (i.e., not diel vertical movements) and may be described as opportunistic movements presumably related to foraging. Data obtained from the PSATs reinforces the view that lake charr are highly adaptive and can thrive in cold, oligotrophic lakes by optimizing the use of the entire water column.     

风拖曳力系数和曼宁系数对风暴潮流模拟的影响

利用0205号威马逊台风期间实测风暴增水和风暴潮流数据,采用NCEP FNL和台风模型风场的融合风场作为驱动项,建立了覆盖东海的三维风暴潮流数值模型,研究风拖曳力系数和曼宁系数对风暴增水和风暴潮流的影响。计算结果表明:(1)风拖曳力系数取值应考虑随风速变化。表层风暴潮流受风拖曳力系数影响较大,中层和底层风暴潮流基本不受影响。(2)风暴潮流结构在一定程度上取决于曼宁系数;曼宁系数对中层和底层风暴潮流影响大于表层,曼宁系数越大,底摩擦阻力越大,风暴潮流垂向分层越明显。(3)风暴增水和风暴潮流对曼宁系数的响应不同,建立模型时,应同时率定风暴增水和风暴潮流。     

自重施加方式对高拱坝廊道结构应力及配筋的影响

自重工况一般是高拱坝内廊道配筋设计的控制工况,由于高拱坝施工过程的特殊性及复杂性,有限元计算中自重有多种施加方式。结合工程实例,对高拱坝基础廊道结构进行三维有限元分析,比较不同自重施加方式对廊道结构应力及配筋的影响。研究结果表明:按整体自重考虑时,廊道结构应力及配筋面积明显偏小;全部按分缝自重考虑时,廊道结构应力及配筋面积明显大于按施工过程考虑自重的结果;为符合实际施工过程及结构承载规律,保证结构安全及经济合理,在拱坝结构的有限元计算中应按照施工过程考虑自重荷载。该研究成果对泄洪孔结构的应力分析也具有参考价值。     

Influence of activated carbon pore structure on oxygen reduction at catalyst layers supported on rotating disk electrodes

Carbon materials are often used as catalyst supports, and for catalysts in electrodes of a polymer electrolyte fuel cell, carbon black has been used. Recently, it was found, however, that activated carbon could replace carbon black and besides, significantly improve the activity of the electrode catalyst layer for oxygen reduction. In the present study, to optimize the pore structure of activated carbon for further activity improvement, the influence of the pore structure on the activity was investigated using activated carbon of various specific surface areas and mean pore diameters. A catalyst layer was formed from activated carbon loaded with platinum and a polymer electrolyte. The activity of the layer was measured in an oxygen-saturated perchloric acid solution, supporting the layer on a rotating glassy carbon disk electrode. We found that increases in the specific surface area and mean pore diameter increased the activity and that the latter was more effective than the former mainly due to the enhanced mass-transfer in the pores; the catalyst layer formed from activated carbon with the largest mean pore diameter was the most active. Unless pores excessively develop and lose connections between particles, a large pore diameter is therefore desired for the fuel cell electrodes.     

基于泄洪移民区域分汊河道泄流相互影响的模型试验研究

基于政府的组织行为、政府的协调行为和政府的监督行为与行洪移民区域后期扶持的具体工作的研究,治淮工程移民安置方案产生31.2亿元的投资。移民区域的大小与安全行洪区范围直接相关,分汊河道行洪的最佳分流比决定了行洪的安全与否。为了探讨复杂并联泄洪河道中不同的闸门控制对泄流的影响,论文结合淮河入江水道归江控制段模型试验,对复杂分汊并联河道的分流比及其流态对河道的稳定等进行了分析研究。通过对所采集的水位流量资料进行理论分析,按照不同的闸门开度组合,结合水面流态,系统分析入江水道中下段分汊并联河道在不同的流量下最优闸门开度组合及支汊分流比。单闸控制,主汊河道闸门开度一定时,分流比随着总泄流量增加而减小,两支汊河道分流比基本相同,且随总泄流量增加而增加。双闸控制,主汊河道和支汊河道闸门组合调节时,主汊分流比同单闸控制,支汊分流比变化量来自主汊,不影响其他支汊河道分流比。最优闸门开度为主汊单闸控制2/3开度,最优分流比为76%、12%、12%,在此分流比下行洪,将保持移民后期区域不扩大或缩小。