Size of flatfish larvae at transformation, functional demands and historical constraints     

J. W. M. Osse  J. G. M. Van den Boogaart 《Journal of Sea Research》1997,37(3-4)

At hatching the larvae of flatfish closely resemble the bilateral symmetric larvae of other teleosts, especially perciforms. Literature data show that transformation to asymmetric benthic juveniles normally occurs at body lengths between 10 and 25 mm. Unexpectedly, minimal size at its completion (including eye migration) can be 4.1 mm SL and maximal size is over 72 mm. In this paper we consider the functional requirements for a successful switch from a symmetric pelagic larva to a typical asymmetric juvenile benthic flatfish partly based on evidence from other teleosts. The unfavourable period of eye migration and transition to a benthic habitat requires some food reserves and rewiring and/or recalibration of vision and gravity-associated structures utilised previously by the still symmetric larvae for e.g. food detection. Binocular fixation of the prey probably occurs in that stage. Critical or sensitive periods occurring during development of fish larvae suggest that a completely functional symmetric stage of development must precede transformation. The normal size range in flatfish larvae at transformation seems to confirm our considerations. Recent data on temperature effects during development provide an explanation for metamorphosis at the minimal size. Some evidence for paedomorphic heterochrony in flatfish larvae is presented.  相似文献   

Upstream migration and reproductive patterns of a population of allis shad in a small river (L'Aulne, Brittany, France)   总被引：2，自引：0，他引：2  

Acolas  M.L.; Veron  V.; Jourdan  H.; Begout  M.L.; Sabatie  M.R.; Bagliniere  J.L. 《ICES Journal of Marine Science》2006,63(3):476-484

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Migration pattern of two salmon stocks in the Baltic Sea     

Kallio-Nyberg  I.; Ikonen  E. 《ICES Journal of Marine Science》1992,49(2):191-198

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AEL—1型风向,风速仪     

郑宝兴  李伟 《台湾海峡》1990,9(3):283-286

本文介绍并叙述了AEL-1型风向、风速仪的设计原理,仪器各部分的电路设计,工作过程及系统软件。该仪器适用于气象台站、工矿企业、海上浮标及科研单位等部门。  相似文献   

GPS测量船舶航速算法浅析     

胡飞荣 《全球定位系统》2008,33(1):46-48

简要介绍了GPS的定位原理和测速原理,并对利用GPS测试船舶航速的四种算法进行了说明。在多个船舶航速算例的基础上,进行了分析并得出结论。  相似文献   

高放废物处置库天然类比及其有关的地球化学问题     

郭永海  王驹  王志明  刘淑芬  宗自华  周佳 《物探与化探》2008,32(5):574-577

介绍了高放废物处置库天然类比研究的主要内容,重点阐述了类比研究中涉及的地球化学问题,包括核素溶解度和化学形态研究、核素迁移速率研究、核素迁移影响因素研究,并总结相关问题研究取得的成果和认识.  相似文献   

The distribution and geological significance of carbazole compounds in Silurian paleo-pools of the Tarim Basin,Northwest China     

LIU Luofu HUO Hong GUO Yongqiang CHEN Lixin LI Shuangwen ZHAO Yande LI Yan WANG Ping CHEN Zhijun 《中国地球化学学报》2008,27(1):1-8

The results presented in this paper indicated that the carbazole-type compounds have high thermal stability and also show stability in oxidation and bio-degradation. This kind of compounds still has high concentrations and a complete distribution in the analyzed dry asphalt samples, showing that they are particularly useful in the study of hydrocarbon migration of the paleo-pools. The difference in the contents of nitrogen compounds in the Silurian dry asphalts from the Awati, Tabei and Tazhong areas is attributed to the difference in the extent of oxidation and （or） bio-degradation for the areas; the Awati and Tabei areas underwent relatively strong oxidation and bio-degradation. During the first stage of hydrocarbon pool formation in the Silurian system in the Tazhong and Tabei areas of the Tarim Basin （at the end of the Silurian period） and at the second stage in the Awati area （in Permian）, the hydrocarbons experienced a long-distance migration.  相似文献   

Petroleum Migration Direction of the Silurian Paleo-pools in the Tarim Basin, Northwest China   总被引：1，自引：0，他引：1  

LIU Luofu  ZHAO Ye  HUO Hong  CHEN Lixin  CHEN Yuanzhuang  ZHAO Suping  LI Chao  LI Shuangwen  GUO Yongqiang  LI Yan 《《地质学报》英文版》2008,82(1):174-183

The results obtained in this paper indicate that carbazole-type compounds have high thermal stability and also show stability in oxidation and bio-degradation. This kind of compounds still has a high concentration and complete distribution in the analyzed dry asphalt samples, showing that they are particularly useful in studying petroleum migration of paleo-pool. During the basin＇s first-stage of oil-gas pool formation in the Silurian in Tazhong and Tabei areas of Tarim Basin （at the end of Silurian period） and the second-stage in the Awati area （in Permian）, the petroleum experienced a long-distance migration. During the formation of the Silurian paleo-pools in Tazhong Uplift at the end of Silurian, the petroleum mainly came from the lower and middle Cambrian source rocks in the Manjiaer sag. The petroleum migrated towards the southwest-south entering the Silurian reservoir beds in Tazhong first. Then, it further migrated within Silurian from northwest to southeast along the highs of the Structural Belts to the region of the Silurian pinchout boundary in Tazhong. In Tabei Uplift, during the first-stage of pool formation, the petroleum was also from the lower and middle Cambrian source rocks in the Manjiaer sag. It migrated northwest entering the Silurian reservoir beds in the Tabei Uplift firstly, and then the migration continued in the same direction within the Silurian reservoirs and finally the petroleum was trapped in higher positions. During the second-stage pool formation in the Silurian beds in the areas around Awati sag, the petroleum mainly came from the lower-middle Cambrian source rocks in the Awati sag. The petroleum migrated from the generation center to Silurian reservoirs in all directions around the sag through major paths, and the petroleum was finally trapped in higher locations.  相似文献   

Origin of Oils in “Subtle pools” in the Dongying Depression, Bohai Bay Basin, China     

Li Sumei  Jiang Zhengxue  Liu Keyu  Qiu Guiqiang  Gao Yongjin 《《地质学报》英文版》2008,82(1):184-196

Subtle traps or oil pools have become an important exploration play in the Dongying Depression, Bohai Bay Basin, east China. Despite recent successes in exploration, the formation mechanisms of subtle traps are still not well understood. The majority of subtle oil pools in the Dongying Depression are developed in the middle interval of the Es3 Member of the Paleogene Shahejie Formation with the subtle traps being primarily of lenticular basin-floor turbidite sands encompassed in mudstones. Oil in the subtle traps was previously thought to have migrated directly from the surrounding source rocks of the same formation （Es3）. Detailed geochemical investigation of 41 oils and 41 rock samples from the depression now indicates that the oils from the subtle traps cannot be correlated well with the surrounding Es3 source rocks, which are characterized by high Pr/ Ph （〉1）, low Gammacerane/C30hopane, representing a freshwater lacustrine setting. In contrast the oils features low Pr/Ph （〈1） and relatively high Gammacerane content, showing a genetic affinity with the underlying Es4 source rocks, which also have the same qualities, indicating a brackish lacustrine setting. Oils in the Es3 subtle traps are probably derived from mixed sources with the contribution from the upper Es4 source rocks predominating. Therefore unconventional oil migration and accumulation mechanisms need to be invoked to explain the pooling of oils from the ES4 source rocks, which probably came through a thick low interval of the Es3 source rocks with no apparent structural or stratigraphic pathways. We suggest that the subtle oil migration pathway probably plays an important role here. This finding may have significant implications for future exploration and the remaining resource evaluation in the Dongying Depression.  相似文献   

葛店矿双庙扩大区三维地震勘探     

张彦湘 《中国煤炭地质》2008,20(2):53-56

葛店煤矿双庙扩大区位于豫、皖两省交界处。勘探区为一轴向北北东向的不对称向斜构造,地层倾角26°～30°,测区深部有岩浆岩侵入体,严重影响煤层赋存形态;地表条件复杂,村庄密集、河流较多,测区东侧塌陷区水塘大面积分布．三维地震勘探野外施工难度大。本区地震勘探观测系统设计为12线18炮制,为避免偏移归位及叠加次数降低等问题,在向斜轴部两侧、村子周边及河岸处适当加密炮点,并在塌陷区利用钢钎插置检波器以保证CDP点完整性。数据处理采取了叠前反褶积、叠前时间偏移等技术,数据处理效果显著。遵循多波组对比、多个数据体综合解释的原则,以纵向、横向和任意时间剖面相结合,充分利用三维可视化技术进行地震资料解释。本次勘探成果查明了主采煤层三2^2、二2煤层的构造形态及埋藏深度;解释落差5m以上断层34条,其中修改原有断层5条;另外新发现小于5m的异常断点22个。经巷道验证煤层底板标高误差0．43％～1．96％,巷道已揭露断层7条,与解释成果基本一致。  相似文献