The bivalve Lembulus bicuspidatus may enhance denitrification in shelf sediment at the Angola–Benguela Frontal Zone     

A Neumann  A Flohr 《African Journal of Marine Science》2018,40(1):91-96

We collected living individuals of the bivalve Lembulus bicuspidatus, which shows an unusual preference for the oxygen-deficient habitat found at the Angola–Benguela Frontal Zone of the southeastern Atlantic. With a series of incubation experiments with ¹⁵N-labelled nitrate as a tracer in combination with membrane-inlet mass spectrometry, we studied the potential contribution of L. bicuspidatus to nitrate reduction in the upper sediment layer. Our preliminary results suggest that L. bicuspidatus enhances nitrate reduction if the oxygen concentration is sufficiently low. The Lembulus-mediated nitrate reduction rate is then similar to the rate of microbial nitrate reduction in the surrounding sediment.  相似文献   

PROPAGATION OF 30—60 DAY LOW FREQUENCY OSCILLATIONS AND THEIR INFLUENCE UPON THE SUBTROPICAL WESTERLIES JET STREAM DURING NORTHERN HEMISPHERE WINTER          下载免费PDF全文

史玉光  李清泉 《Acta Meteorologica Sinica》1996,(2)

Based on daily ECMWF gridpoint data of two winters during 1981—1983 including an ENSOyear,propagation of low frequency oscillations(LFO)during Northern Hemisphere winters andtheir influences upon 30—60 day oscillations of the subtropical jet stream are studied with the sta-tistical methods as complex empirical orthogonal function(CEOF)and so on.Results show that inthe winter of a normal year(1981—1982),30—60 day oscillations in the subtropical zone aremainly in the northern and southern flanks of exit region of jet stream.In the ENSO year(1982—1983),they are mainly in the vicinity of entrance and exit regions of jet stream.Intraseasonalchanges of subtropical jet stream manifested themselves as latitudinal fluctuation or longitudinalprogression or regression of about 40 day period.There are marked differences between propagat-ing passages of low frequency modes responsible for changes of subtropical jet stream in the normalyear(1981—1982)and in the ENSO year(1982—1983).Changes of oscillation amplitude showobvious phases.In general,the one in late winter is stronger than that in early winter,strongestone occurs in February.  相似文献   

Hard X-ray spectrum of Mkn 421 during the active phase     

R. K. Manchanda 《Journal of Astrophysics and Astronomy》2001,22(2-3):145-154

Spectral measurement of Mkn 421 were made in the hard X-ray energy band of 20–200 keV using a high sensitivity, large area scintillation counter telescope on November 21, 2000 and these coincided with the onset of an active X-ray phase as seen in the ASM counting rates on board RXTE. The observed spectrum can not be fitted to a single power law similar to the PDS data of BeppoSAX. The data can be fitted both by a two component power-law function or a combination of an exponential function with a power law component at the high energies above 80 keV. We identify these components with those arising from the synchrotron self compton and the high energy power-law tail arising from the upgrading of the thermal photons due to multiple Compton scattering a la Cyg X-1. A comparison with the earlier data clearly suggests a spectral variability in the hard X-ray spectrum of the source. We propose a continuously flaring geometry for the source as the underlying mechanism for energy release.  相似文献   

The Dependence of Water Exchanges between the Kuroshio Water and Its Surroundings on the Characteristics of the Kuroshio‘s Meanders     

姜华  吴德星  万修全 《中国海洋湖沼学报》2003,21(4):335-344

Observation of fluid parcel pathways in the Kuroshio Stream revealed a striking crossstream pattern associated with the Kuroshio‘‘ s meanders. In order to understand the observed pattern, a two-dimensional kinematic model of a meandering jet was developed which could be used to examine the relationship between streamfunction patterns and fluid parcel trajectories. The experiments designed to investigate the dependence of the water exchanges between the Kuroshio water and its surroundings on the characteristics of the Kuroshio‘‘s meanders involved the downstream speed,phase speed and the amplitude of other propagating waves. The results suggested that fluid parcels could cross the meandering jet to and fro; and that the water exchanges between the Kuroshio and its surroundings increased with a) increasing meander amplitude, b) decreasing downstream speed, and c) increasing wave phase speed. The results also showed that when the meandering jet was disturbed by other propagating waves, more effective water exchanges could be induced.  相似文献   

射电喷流中湍动阿耳芬波对相对论电子的加速     

马春玉 《天文学报》1996,37(1):28-34

本文通过数值求解带电粒子与Ａｌｆｖｅｎ波湍动相互作用的动力学方程，得到了相对论电子在射电喷流中被加速随时间演化的解．高能电子可以加速到Ｌｏｒｅｎｔｚ因子γｙ～１０６，且形成稳态的幂律谱，尽管其谱指数Ｓ≈ｌ比观测值小，但粒子加速时间约为１０１２－１０１４秒，小于射电斑的寿命１０７年．粒子能谱指数几乎与Ａｌｆｖｅｎ波谱指数和能量损失函数无关．能量损失对加速上限有较大影响．  相似文献   

软硬互层金刚石复合片钻头在地浸砂岩型铀矿中的研究及应用          下载免费PDF全文

要二仓  邢预恩  杨爱军 《探矿工程》2008,35(1):68-70

针对近年在巴音戈壁盆地及鄂尔多斯盆地钻探所遇到的复杂地质情况,研究试验了PDC钻头,在地浸砂岩铀矿钻探生产中取得了良好的效果,并制定总结了相应的钻进参数.  相似文献   

渤海中南部悬浮物海洋调查资料分析   总被引：6，自引：0，他引：6  

苏健  江文胜  孙文心 《中国海洋大学学报(自然科学版)》2001,31(5):647-652

对于悬浮物 (SPM)的研究目前已引起诸多学者关注。作者利用 1998和 1999年的中德合作海洋调查所获得的资料进行分析。主要进行三个方面的工作 :研究悬浮物与透明度的关系 ;研究悬浮物与浊度的关系 ;估计海底剪切速度。并为研究悬浮物输运提供资料和作前期研究  相似文献   

江苏大丰潮滩潮流边界层特征研究   总被引：7，自引：0，他引：7  

李占海  高抒  陈沈良 《海洋工程》2007,25(3):53-60

2003年7月中小潮期间使用MIDAS-400用户化数据采集系统在江苏大丰潮滩上进行了垂向多层位同步的流速和悬沙浓度观测。根据观测资料研究了潮流作用下的潮滩底部边界层过程,结果表明,观测地点的潮汐不对称现象十分明显,落潮流速、历时和输水输沙量皆明显大于涨潮;在潮周期内的多数时间里流速剖面符合对数分布,但在风力较强、水流快速增加和流速缓慢的情况下,流速剖面常偏离对数分布;悬沙颗粒垂向混合均匀,悬沙浓度剖面符合Rouse公式;落潮时的底部切应力和摩阻流速明显大于涨潮,摩阻流速与各水层流速通常有较好的线性关系;滩面糙度主要与沙纹形态和推移质运动强度有关,它与摩阻流速存在密切关系;悬沙浓度具有明显的减阻效应,受其影响,摩阻流速和底部切应力分别减小了28%~41%和40%~62%。  相似文献   

南海中沙天然气水合物资源远景区海底沉积物的物理力学性质研究   总被引：3，自引：0，他引：3  

魏巍 《海岸工程》2006,25(3):33-38

根据南海中沙天然气水合物远景区沉积物样品的分析资料,从物理力学特征各方面对本区海底沉积物进行了综合工程地质特征研究。结果表明,本区海底沉积物类型全部为淤泥,工程地质性质相近,以高含水率、高孔隙比、低密度及高塑性为主要特征,抗剪强度很小,压缩系数均大于0.5。土体沉积环境为水动力强度较弱的深海半深海环境。  相似文献   

First results from the North Iceland experiment     

C. Riedel  A. Tryggvason  B. Brandsdottír  T. Dahm  R. Stéfansson  M. Hensch  R. Böðvarsson  K. S. Vogfjord  S. Jakobsdottír  T. Eken  R. Herber  J. Holmjarn  M. Schnese  M. Thölen  B. Hofmann  B. Sigurdsson  S. Winter 《Marine Geophysical Researches》2006,27(4):267-281

Between June 2004 and September 2004 a temporary seismic network was installed on the northern insular shelf of Iceland and onshore in north Iceland. The seismic setup aimed at resolving the subsurface structure and, thus, the geodynamical transition from Icelandic crust to typical oceanic crust along Kolbeinsey Ridge. The experiment recorded about 1,000 earthquakes. The region encloses the Tjörnes Fracture Zone containing the Husavik–Flatey strike-slip fault and the extensional seismic Grimsey Lineament. Most of the seismicity occurs in swarms offshore. Preliminary results reveal typical mid-ocean crust north of Grimsey and a heterogeneous structure with major velocity anomalies along the seismic lineaments and north–south trending subsurface features. Complementary bathymetric mapping highlight numerous extrusion features along the Grimsey Lineament and Kolbeinsey Ridge. The seismic dataset promises to deliver new insights into the tectonic framework for earthquakes in an extensional transform zone along the global mid-ocean ridge system.  相似文献