Numerical study of an oscillating smaller cylinder in the wake of an upstream larger cylinder     

TAN Soon Keat 《中国海洋大学学报(英文版)》2012,11(2):111-117

A numerical study of flow around two tandem cylinders with unequal diameters was carried out. The upstream larger cylinder was fixed and the downstream smaller cylinder was allowed to oscillate in the transverse direction only. Comparisons of the experimental and numerical results were made to investigate the effects of the gap ratio on the maximum vibration amplitude and vortex shedding frequency. The results showed that the vibration response of the smaller cylinder was significantly affected by the presence of the upstream larger cylinder, and resulted in greatly reduced vibration amplitudes. With an increasing gap ratio, the vibration amplitude increased. However, the magnitude was lower than that corresponding to a single cylinder (with the same diameter as that of the downstream smaller cylinder) under the same flow conditions.  相似文献   

Size fraction and class composition of phytoplankton in the Antarctic marginal ice zone along the 140°E meridian during February–March 2003     

Fuminori Hashihama  Toru Hirawake  Sakae Kudoh  Jota Kanda  Ken Furuya  Yukuya Yamaguchi  Takashi Ishimaru 《Polar Science》2008,2(2):109-120

We investigated the size fraction and pigment-derived class compositions of phytoplankton within the euphotic zone of the Antarctic marginal ice zone between 63.3°S and 66.5°S along the 140°E meridian on two consecutive cruises in the late austral summer and early austral autumn of 2003. We observed significant temporal and spatial variations in phytoplankton size and taxonomic composition, although chlorophyll a concentrations were generally below 1 μg l⁻¹ during both periods. Microphytoplankton (>20 μm), mainly diatoms, were prominent in the euphotic zone in the southernmost area around 66.5°S during late summer. In the rest of the study area during both cruises, the phytoplankton community was dominated by pico- and nano-sized populations (<20 μm) throughout the euphotic zone. The small-size populations mostly consisted of diatoms and haptophytes, although chlorophytes were dominant in extremely cold water (−1.5°C) below the overlying warm water around 65.5°S during late summer. From late summer to early autumn, chlorophytes declined in abundance, probably due to increasing temperature within the euphotic zone (−1 to 0°C). These pico- and nano-phytoplankton-dominated populations were often accompanied by relatively high concentrations of ammonium, suggesting the active regeneration of nutrients within the small-size plankton community.  相似文献   

青藏高原北部地区7级以上地震前地震活动特征     

陈春梅  任雪梅 《东北地震研究》2015,(2)

发现青藏高原北部7级以上地震前震中区普遍存在5级以上地震空段,空段时间在7~33年之间,且在青海发生的7级以上地震前震中区还存在ML≥4.0级地震空区,四川北部的7级以上地震前弱震活动出现显著增强现象。未来2~8年间青藏高原北部有可能发生7级以上地震,其危险区域为祁连地震带西部、甘肃东南部、宁夏和内蒙西部。  相似文献   

天然闪锌矿矿物学特征与光催化性能     

沈灿  鲁安怀  谷湘平 《岩石矿物学杂志》2017,36(6):807-816

本文采集了我国19个产地的天然闪锌矿进行矿物学和光催化性能研究。样品皆为立方Zn S结构,化学成分变化较大,其中Fe对闪锌矿中Zn的替代范围为0.235%~14.826%(质量分数,下同),Cd对闪锌矿中Zn的替代范围为0.133%~1.576%。闪锌矿中Fe含量由低到高,导致颜色由浅变深直至呈黑色,半导体禁带宽度由大变小,估算获得天然闪锌矿的禁带宽度范围为3.18~2.28 e V,明显低于纯Zn S禁带宽度3.68 e V,光催化响应均在可见光范围。验证光催化实验结果表明含Fe较低、含Cd较高的天然闪锌矿可见光催化还原降解甲基橙的效果较佳,如可见光下1 g/L闪锌矿样品(含铁4.262%,含镉1.576%)对30 mg/L甲基橙催化反应4 h后的脱色降解率达到82.11%。天然闪锌矿中Fe含量影响着禁带宽度和光响应范围,Cd含量影响着光催化性能,为高附加值开发利用贱金属资源天然闪锌矿提供了科学依据。  相似文献   

区际资本流动与区域发展差距——对中国银行间信贷资本流动的分析   总被引：3，自引：1，他引：2  

陈东  樊杰 《地理学报》2011,66(6):723-731

一国经济发展初期,区际资本流动通常是导致区域发展差距形成、扩大的重要原因--资本往往从发展条件较差的地区流向发展条件较好的地区,从而产生“好者更好、差者更差”的马太效应。银行间信贷资本流动是区际资本流动的重要形式。本文通过构建计量方法对中国区域发展差距扩大阶段(1978-2003 年) 银行间信贷资本的区际流动方向进行测度,并分析其成因。计量结果发现,存在区际间信贷资本流动的年份,资本并未从发展条件较差的中西部地区流向发展条件较好的东部地区,而呈现相反的流动。这表明银行间信贷资本的区际流动至少在一定程度上缩小而不是扩大了区域发展差距。进一步分析发现,政府对信贷的管制以及市场环境的变化分别导致了1994年以前以及1994 年以后的银行间信贷资本流动。  相似文献   

Definition and interests of reciprocity and reciprocity gap principles for groundwater flow problems     

Nejla T. Hariga  Amel Ben Abda  Rachida Bouhlila  Jean-Raynald de Dreuzy 《Advances in water resources》2010

We introduce the reciprocity and reciprocity gap principles for flow problems in hydrogeology and illustrate their interest in addressing identification problems. The reciprocity principle is derived from mechanics and establishes for flow problems a relationship between different sets of forcing terms, including sources, sinks and boundary conditions, and the resulting head fields. The reciprocity gap principle compares different head fields resulting from the same forcing terms applied to different structures. We give general 2D expressions of the reciprocity and reciprocity gap principles for transient flow problems and give two examples of applications for the identification of transmissivity values and interfaces between different transmissivities. Identification capacities of the reciprocity and reciprocity gap principles yielding direct inversion methods could be used as initial guesses for more advanced inverse problem methodologies.  相似文献   

Characteristics of Seismic Activity in a 3-Dimensional Space before the Wen'an Earthquake,Hebei Province by Relocation of Small Earthquakes in the China's Capital Area     

Xue Yan  Zhou Longquan  Ma Hongsheng  Liu Jie 《中国地震研究》2010,24(4):404-414

Characteristics of seismic activity before the M5.1 earthquake in Wen'an,Hebei Province on July 4,2006 are analyzed by relocation of small earthquakes in the China's capital area,and some results are obtained as follows:① The seismic activity of M L ≥3.0 in the middle part of the Hebei plain seismic belt displayed a feature of strengthening (lasting 43 months) quiescence (17 months) five years before the Wen'an earthquake.Simultaneously,the strain release curve showed a variation process of accelerating-flatting.② A seismogenic gap in a three-dimensional space,located at the depth of 15km ～ 20km,with 70km long in latitude direction and 90km long in longitude orientation,was formed by M≥2.0 earthquakes four years prior to the Wen'an earthquake.The initial rupture point of the Wen'an earthquake is situated at the bottom of the gap.③ The focal depths of earthquakes with M L ≥2.0 in the middle part of the Hebei plain seismic belt gradually increased from 10km to 30km during the period from April,2003 to October,2004.Meanwhile,the seismic activity obviously strengthened in the middle and lower crust (from 20km to 30km in depth).  相似文献   

Boundaries Make a Difference: The Effects of Spatial and Temporal Parameters on Conservation Planning*     

Patrick R. Huber  Steven E. Greco  James H. Thorne 《The Professional geographer》2013,65(3):409-425

Conservation planning and resulting ecological target identification require selection of both a planning area boundary and temporal baseline or reference condition. We examined the effects that these selections can have on resulting amount and location of identified conservation targets. A gap analysis for California was conducted using five different sets of ecoregion boundaries to identify and compare existing conservation shortfalls in major land cover type representation in protected areas using a threshold of 30 percent per ecoregion per type as the minimum required for future ecological viability. Another gap analysis was run for a single ecoregion using two temporal baselines (current and pre-1900) for the land cover followed by a comparison of identified conservation needs. We found that the boundaries of different ecoregional schemes affected both the total area needed to meet the per ecoregion land cover conservation goals and the spatial location of underprotected land cover types. Choice of temporal baseline also had a significant effect on the establishment of conservation targets for the highly human-impacted Central Valley ecoregion. To meet the given conservation threshold using a historic rather than contemporary baseline, a substantial amount of restoration is required. The results can help identify areas of both conservation needs consensus and those that vary widely based on the chosen planning boundary, as well as aid in the selection of appropriate restoration targets in degraded ecosystems. Because all landscapes are continuous in nature and planning area boundaries are discrete, similar results are likely to be found in analyses conducted in other regions.  相似文献   

Spatial distribution of cadmium and lead in the sediments of the western Anzali wetlands on the coast of the Caspian Sea (Iran)   总被引：1，自引：0，他引：1  

Rasool Zamani-Ahmadmahmoodi  Abbas Esmaili-Sari  Jahangard Mohammadi  Alireza Riyahi Bakhtiari  Mozhgan Savabieasfahani 《Marine pollution bulletin》2013

Spatial distribution patterns of total cadmium (Cd) and lead (Pb), their bioavailable fractions and total organic matter in sediment from Anzali wetlands are provided. Total sediment Pb was higher than Cd (34.95 versus 0.024 μg/g dry weight). The geoaccumulation index indicated that the sediment was “uncontaminated”, but some stations were categorized as “unpolluted” to “moderately polluted”. Less than 0.01 of Pb existed in exchangeable and carbonate fractions. The sum of exchangeable and carbonate-bound fractions of Cd was 42%, suggesting that Cd poses high risk to the aquatic ecosystems. Total Cd and Pb exhibited positive relationships with total organic matter. Considering spatial distribution maps of total and bioavailable fractions of metals suggested that high concentrations of metals does not necessarily indicate high bioavailable fraction. The methodologies we used in this study can be in more effective management of aquatic ecosystems, as well as ecological risk assessment of metals, and remediation programs.  相似文献   

Vecteur de la pollution metallique du bassin versant de l’Oued El Bey vers le Golfe de Tunis (Tunisie)     

Samia Khadhar  Ammar Mlayah  Anis Chekirben  Abdelkrim Charef  Malika Methammam  Shabou Nouha 《水文科学杂志》2013,58(8):1803-1812

Résumé

L’Oued El Bey, qui draine 60% de la charge polluante hydrique de plusieurs agglomérations urbaines du Nord-Est de la Tunisie, est un exemple représentatif du transfert des métaux lourds résultant de l’activité industrielle et urbaine. Il fournit une indication sur le devenir et la répartition des métaux lourds dans le Golfe de Tunis. Dans la fraction dissoute, Cd, Pb, Co et Hg ne sont pas détectés mais Zn varie entre 0,01 et 0,07 μg/L. Les concentrations du Mn, Zn, As, Ni, Pb, Cu et du Cd sont très élevées dans la fraction particulaire par rapport à la fraction dissoute, avec un coefficient de partage Kd de l’ordre de 10⁶, ainsi que dans les sédiments du lit de l’oued pour Pb et Zn. La pollution par les métaux la plus élevé de l’Oued El Bey a été trouvée pour Zn, Pb et Cu: les concentrations variaient respectivement entre 1698,9 et 14575, de 0 à 2153,7 et de 0 à 3431,8 μg/g. La variation spatiale des teneurs en métaux lourds confirme l’effet des eaux usées rejetées dans l’Oued El Bey. Les teneurs de ces métaux lourds dans les trois phases dissoute, particulaire (MES) et sédiments confirment que la MES constitue le vecteur de transport principal via la Sebkha Soliman vers le golfe. L’examen des rapports des différents éléments (Pb, Cu et Cd) par rapport au Zn dans les sédiments de l’oued montre une augmentation au niveau de la confluence de l’Oued El Bey et de son affluent l’Oued El Meleh, ce qui signifie que les apports sédimentaires de cet affluent contrôlent la signatutue chimique des sédiments de l’Oued El Bey.

Editeur Z.W. Kundzewicz; Editeur associé B. Touaibia

Citation Khadhar, S., Mlayah, A., Chekirben, A., Charef, A., Methammam, M., Nouha, S., et Khemais, Z., 2013. Bassin versant Oued El Bey: vecteur de transport de la pollution métallique vers le Golfe de Tunis (Tunisie). Hydrological Sciences Journal, 58 (8), 1803–1812.  相似文献