Studies of accretion flows around rotating black holes – III. Shock oscillations and an estimation of the spin parameter from QPO frequencies     

S. Mondal  P. Basu  S. K. Chakrabarti † 《Monthly notices of the Royal Astronomical Society》2009,396(2):1038-1045

In the present communication of our series of papers dealing with the accretion flows in the pseudo-Kerr geometry, we discuss the effects of viscosity on the accretion flow around a rotating black hole. We find the solution topologies and give special attention to the solutions containing shocks. We draw the parameter space where standing shocks are possible and where the shocks could be oscillating and could produce quasi-periodic oscillations (QPOs) of X-rays observed from black hole candidates. In this model, the extreme locations of the shocks give the upper limits of the QPO frequencies  (ν_QPO)  which could be observed. We show that both the viscosity of the flow and the spin of the black hole a increase the QPO frequency while, as expected, the black hole mass reduces the QPO frequencies. Our major conclusion is that the highest observed frequency gives a strict lower limit of the spin. For instance, a black hole exhibiting  ν_QPO∼ 400  and  700 Hz  must have the spin parameters of   a > 0.25  and  >0.75  , respectively, provided viscosity of the flow is small. We discuss the implications of our results in the light of observations of QPOs from black hole candidates.  相似文献   

A failed outburst of H1743−322     

F. Capitanio  T. Belloni  M. Del Santo  P. Ubertini 《Monthly notices of the Royal Astronomical Society》2009,398(3):1194-1200

We report on a campaign of X-ray and soft γ-ray observations of the black hole candidate (BHC) H1743−322 (also named IGR J17464-3213), performed with the RXTE , INTEGRAL and Swift satellites. The source was observed during a short outburst between 2008 October 03 and November 16. The evolution of the hardness–intensity diagram throughout the outburst is peculiar, in that it does not follow the canonical pattern through all the spectral states (the so-called q-track pattern) seen during the outburst of black hole transients. On the contrary, the source only makes a transition from the hard state to the hard–intermediate state. After this transition, the source decreases in luminosity and its spectrum hardens again. This behaviour is confirmed by both spectral and timing analyses. This kind of outburst has been rarely observed before in a transient BHC.  相似文献   

The Influence of Viscosity on the Truncation of Accretion Disks Around Black Holes     

Qiang Niu 《Chinese Astronomy and Astrophysics》2009

  相似文献   

2007年梅雨锋降水的大尺度特征分析   总被引：13，自引：1，他引：12  

陶诗言  卫捷  张小玲 《气象》2008,34(4):3-15

2007年6-7月在华南、长江中下游以及淮河流域先后出现东西走向静止锋暴雨,引起粤东和淮河流域洪涝灾害.分析了这3个地区静止锋暴雨的动力学、热力学结构的异同点.2007年7月引起淮河洪涝的主要强降水是7月8-9日的暴雨,分析了引起这场强暴雨的大气环流特征以及梅雨锋深厚的锋生过程和气旋生成过程.主要结论为:(1)华南前汛期降水、长江梅雨期降水以及淮河强降水出现时东西向静止锋在动力学和热力学的结构相同,可通称为"梅雨锋".(2)2007年淮河静止锋暴雨的出现,是由于中国东部上空有深厚高空槽发展,诱导梅雨锋上气旋生成过程和深厚的锋生过程.气旋生成过程和锋生过程使梅雨锋上出现强烈的上升运动,形成了致洪暴雨.  相似文献   

适于深部取心钻探井超高温聚磺钻井液体系研究   总被引：4，自引：0，他引：4  

黄聿铭 《地质与勘探》2017,53(4):773-779

东北松辽盆地强水敏泥岩、泥页岩、凝灰岩发育,地温梯度高达4.1℃/100m。深井钻进过程中易出现井壁失稳、钻井液抗温能力不足等复杂情况,研制深部取心钻进配套用超高温钻井液具有迫切的工程需要。通过造浆土、抗温抗盐处理剂、防塌剂等处理剂优选及复配试验,完成了抗高温聚磺钻井液配方设计。钠土与凹凸棒土复配保证了高温钻井液具有合适的粘土胶粒浓度,处理剂优选在满足良好护胶性能的基础上充分考虑了其粘度效应。综合测试结果表明,该聚磺钻井液在230℃条件下连续加热滚动24h后性能稳定,且具备良好的抑制性、润滑性及一定的抗污染能力。在东北松辽盆地某深井连续取心钻进过程中取得了良好的应用效果。  相似文献   

Adaptation of diet in a changed environment: Increased consumption of lobster krill Munida gregaria (Fabricius, 1793) by Argentine hake          下载免费PDF全文

Mauro Belleggia  Diego Giberto  Claudia Bremec 《Marine Ecology》2017,38(4)

A well‐replicated decadal‐term (2005–2014) stomach content data set was analysed in order to infer inter‐annual fluctuations in the diet of the Argentine hake, Merluccius hubbsi, an opportunistic predator in the San Jorge Gulf (SJG) ecosystem in the Southwest Atlantic. Ten research cruises were carried out each year during January from 2005 to 2014. A total of 18,461 specimens of Me. hubbsi was analysed, of which 6,777 (36.71%) contained food in their stomachs. The diet of Me. hubbsi changed markedly from 2011 onwards, with much greater consumption of the lobster krill Munida gregaria compared to the years before 2011. The frequency of occurrence (%F) of Mu. gregaria in the stomach contents of Argentine hake increased from the year 2009 onwards, most noticeably since 2011, and mostly over the southern region of the SJG. The main predators of Mu. gregaria in the SJG are two species of teleost fish (pink cusk eel, Genypterus blacodes, Argentine seabass, Acanthistius brasilianus) and three Rajidae skates (Zearaja chilensis, Psammobatis spp. and Sympterygia bonapartii), which exhibited decreased catches in the years analysed. The increased consumption of Mu. gregaria by Me. hubbsi, coupled with decreased trends in abundance of the main predators of the lobster krill during the last decade, indicate that top‐down trophic dynamic control occurs in the SJG ecosystem.  相似文献   

Food web and fish stock changes in central Chile: comparing the roles of jumbo squid (Dosidicus gigas) predation,the environment,and fisheries     

《Deep Sea Research Part II: Topical Studies in Oceanography》2013

We analyzed recent food web and fish stock changes in the central Chile marine ecosystem, comparing the roles of jumbo squid (Dosidicus gigas) as predator, the environment, and fishing. To accomplish this we used food web modeling and the Ecopath with Ecosim software (EwE). The principal fish stocks have experienced wide decadal fluctuations in the past 30 years, including stock collapses of horse mackerel (Trachurus murphyi) and hake (Merluccius gayi), and there was a large influx of jumbo squid during the mid-2000s. We used two EwE models representing the food web off central Chile to test the hypothesis that predation by jumbo squid has been significant in explaining the dynamics of the main fishing resources and other species in the study area. Results indicate that predation by jumbo squid on fish stocks is lower than that of other predators (e.g. hake) and the fishery. Long-term fluctuations (1978–2004) in the biomass of the main fish stocks (as well as other components of the food web) seem to be related to fishing and to variation in primary production, rather than to predation by jumbo squid alone. Jumbo squid seems to play a role as predator rather than prey in the system, but its impacts are low when compared with the impacts of other predators and fishing. Therefore, we conclude that jumbo squid predation on its prey was not the primary force behind the collapse of important fish stocks off central Chile. Future efforts should be directed to better understanding factors that trigger sudden increases in jumbo squid abundance off central Chile, as well as modeling its trophic impacts.  相似文献   

Geomorphology and glacial history of Rauer Group, East Antarctica     

Duanne A. White  Ole Bennike  Simon L. Harley  Kevin Kiernan  Bernd Wagner 《Quaternary Research》2009,72(1):80-90

The presence of glacial sediments across the Rauer Group indicates that the East Antarctic ice sheet formerly covered the entire archipelago and has since retreated at least 15 km from its maximum extent. The degree of weathering of these glacial sediments suggests that ice retreat from this maximum position occurred sometime during the latter half of the last glacial cycle. Following this phase of retreat, the ice sheet margin has not expanded more than ∼ 1 km seaward of its present position. This pattern of ice sheet change matches that recorded in Vestfold Hills, providing further evidence that the diminutive Marine Isotope Stage 2 ice sheet advance in the nearby Larsemann Hills may have been influenced by local factors rather than a regional ice-sheet response to climate and sea-level change.  相似文献   

麦垛山煤矿副立井井筒检查孔施工技术及涌水量预算     

马力 《中国煤炭地质》2009,(11):50-52

针对井简俭查孔施工中的技术难点,采取了钻前修建钻错底座,使用合理的钻具组合,强化套管作业过程,按照不同地层．选用不同的泥浆配方的技术措施,从而使井筒检查孔的质量达到了设计及规范的要求。根据抽水试验成果．运用稳定流的裘布农公式进行水文地质参数的计算,采用大井法进行井筒涌水量的预算。预算井筒涌水量为6454．96m^3／d．该成果与流量测井结果较为吻合,可以作为建井工程设计的依据。  相似文献   

煤矿采掘工作面覆岩观测孔施工技术应用——以山西省黄岩汇井田15100采掘工作面为例     

田立强  ;范士彦  ;李毅  ;张心彬  ;翁士忠 《中国煤炭地质》2009,(3):58-62

以山西省黄岩汇井田15100采掘工作面所施工的两个“三带”观测孔为例,介绍了通过冒落带角、导水裂缝角和导水裂缝带的计算来确定钻孔位置的基本方法。针对覆岩观测孔的施工难点,提出了相应的应对措施,并详细说明了GC-2观测孔施工中出现的各种问题及解决方法。认为钻孔冲洗液法是目前煤矿取得“三带”数据较为精确的方法,根据钻孔冲洗液漏失量的大小及覆岩的开裂情况,对“三带”进行了划分：在钻进中覆岩一般开裂,冲洗液漏失量小于1L/（s·m）为弯曲带;钻进中覆岩严重开裂,冲洗液漏失量大于1.0L/（s·m）为导水裂缝带;钻进中覆岩出现掉钻,冲洗液漏失量大于1.0L/（s·m）为冒落带。  相似文献