A study of SAR remote sensing of internal solitary waves in the north of the South China Sea:I.Simulation of internal tide transformation   总被引：2，自引：1，他引：1  

FAN Zhisong  ZHANG Yuanling  SONG Mei 《海洋学报(英文版)》2008,27(4)

For settlement of the well-known problem of contemporary radar imaging models,i.e.,the pmblem of a general underestimation of radar signatures of hydrodynamic features over oceanic internal waves and underwater bottom topography in tidal watels at at high radar frequency bands(X-band and C-band),the impact of the ocean surface mixed layer turbulence and the significance of strat-ified oceanic model on SAR remote sensing of internal solitary waves are proposed.In the north of the South China Sea by utilizing seme observed data of background field the nonlinearity coefficient,the dispersion coefficient,the horizontal variability coefficient and the phase speed in the generalized K-dV equation are determined approximately.Through simulations of internal tide transfor-mation the temporal evolution and spatial distribution of the vertical displacement and horizontal velocity of intereal wave field are obtained.The simulation results indicate that the maximum amplitudes of internal solitary waves occur at depth 35 m,but the maximum current speeds take place at depth 20 m in this area of the sea(about 20°30'N,114°E)in August.It was noticed that considering the effects of flood current and ebb current respectively is appropriate to investigate influence of the background shear flow on coefficients of the K-dV equation.The obtained results provide the possibility for the simulation of SAR signatures of inter-nal solitary waves under considering the impact of ocean surface mixed layer turbulence in the companion paper.  相似文献   

投喂四种饵料对曼氏无针乌贼(Sepiella maindroni)繁殖性能的影响          下载免费PDF全文

樊晓旭  王春琳  邵银文  王津伟  宋超霞  蒋霞敏 《海洋与湖沼》2008,39(6):634-642

以双齿围沙蚕、泥鳅、黄鲫、福寿螺4种不同饵料强化培育胴长(6.50±0.20)cm的曼氏无针乌贼,用曼氏无针乌贼肝脏和卵巢的氨基酸与脂肪酸变化、亲体产卵量、卵径、卵子孵化率及其幼体成活率等指标来评价4种饵料对其繁殖性能的影响.结果表明,黄鲫组曼氏无针乌贼肝脏与卵巢中∑EAA、∑SEAA、∑EAA+SEAA、∑NEAA、∑AA含量在第一次卵巢成熟与第二次卵巢成熟时均显著高于其它投喂组(P＜0.05).黄鲫组乌贼肝脏DHA/EPA在第一次卵巢成熟时显著高于其它投喂组,在第二次卵巢成熟时DHA、DHA/EPA、∑n3PUFA、∑n6PUFA、∑n3/n6PUFA都显著高于其它投喂组(P＜0.05);该组乌贼第一次卵巢成熟卵巢DHA、∑n3PUFA、∑n6PUFA、∑n3/n6PUFA及在第二次卵巢成熟时卵巢DHA、DHA/EPA、∑n3PUFA、∑n3/n6PUFA均显著高于其它投喂组(P＜0.05),该组第二次卵巢成熟时∑n6PUFA百分含量与沙蚕组无显著差异(P＞0.05).产卵量多少顺序为黄鲫组＞沙蚕组＞泥鳅组＞福寿螺组(P＜0.05);孵化率高低顺序为黄鲫组＞福寿螺组＞泥鳅组＞沙蚕组(P＜0.05);所产卵子平均直径大小顺序为黄鲫组＞泥鳅组＞沙蚕组＞福寿螺组(P＜0.05);幼体成活率高低顺序为黄鲫组＞泥鳅组＞沙蚕组、福寿螺组(P＜0.05).各指标吻合程度高.  相似文献   

Sulfide and iron control on mercury speciation in anoxic estuarine sediment slurries   总被引：2，自引：0，他引：2  

Seunghee Han  Anna Obraztsova  Patrizia Pretto  Dimitri D. Deheyn  Joris Gieskes  Bradley M. Tebo   《Marine Chemistry》2008,111(3-4):214-220

In order to understand the role of sulfate and Fe(III) reduction processes in the net production of monomethylmercury (MMHg), we amended anoxic sediment slurries collected from the Venice Lagoon, Italy, with inorganic Hg and either potential electron acceptors or metabolic byproducts of sulfate and Fe(III) reduction processes, gradually changing their concentrations. Addition of sulfide (final concentration: 0.2–6.3 mM) resulted in an exponential decrease in the sulfate reduction rate and MMHg concentration with increasing concentrations of sulfide. Based on this result, we argue that the concentration of dissolved sulfide is a critical factor controlling the sulfate reduction rate, and in turn, the net MMHg production at steady state. Addition of either Fe(II) (added concentration: 0–6.1 mM) or Fe(III) (added concentration: 0–3.5 mM) resulted in similar trends in the MMHg concentration, an increase with low levels of Fe additions and a subsequent decrease with high levels of Fe additions. The limited availability of dissolved Hg, associated with sulfide removal by precipitation of FeS, appears to inhibit the net MMHg production in high levels of Fe additions. There was a noticeable reduction in the net MMHg production in Fe(III)-amended slurries as compared to Fe(II)-amended ones, which could be caused by a decrease in the sulfate reduction rate. This agrees with the results of Hg methylation assays using the enrichment cultures of anaerobic bacteria: whereas the enrichment cultures of sulfate reducers showed significant production of MMHg (4.6% of amended Hg), those of Fe(III), Mn(IV), and nitrate reducers showed no production of MMHg. It appears that enhanced Fe(III)-reduction activities suppress the formation of MMHg in high sulfate estuarine sediments.  相似文献   

Evaluation of ENVISAT ASAR data for sea surface wind retrieval in Hong Kong coastal waters of China   总被引：2，自引：1，他引：1  

XU Qing  LIN Hui  ZHENG Quanan  XIU Peng  CHENG Yongcun  LIU Yuguang 《海洋学报(英文版)》2008,27(4):57-62

The C-band wind speed retrieval models, CMOD4, CMOD - IFR2, and CMOD5 were applied to retrieval of sea surface wind speeds from ENVISAT （European environmental satellite） ASAR （advanced synthetic aperture radar） data in the coastal waters near Hong Kong during a period from October 2005 to July 2007. The retrieved wind speeds are evaluated by comparing with buoy measurements and the QuikSCAT （quick scatterometer） wind products. The results show that the CMOD4 model gives the best performance at wind speeds lower than 15 m/s. The correlation coefficients with buoy and QuikSCAT winds are 0.781 and 0.896, respectively. The root mean square errors are the same 1.74 m/s. Namely, the CMOD4 model is the best one for sea surface wind speed retrieval from ASAR data in the coastal waters near Hong Kong.  相似文献   

White spot syndrome virus envelope protein VP124 involved in the virus infection     

ZHU Yanbing  WU Chenglin  YANG Feng 《海洋学报(英文版)》2008,27(4):130-136

White spot syndrome virus （WSSV） is one of the major shrimp pathogens causing large economic losses to shrimp farming. In an attempt to identify the envelope proteins involved in the virus infection, purified WSSV virions were mixed with three antisera against WSSV envelope proteins （VP39, VP124 and VP187 ）, individually. And then they were injected intramuscularly into crayfish （Procambarus clarkii） to conduct in vivo neutralization assays. The results showed that for groups injected with virions only and groups injected with the mixture of virions and antiserum against VP124, the crayfish mortalities were 100% and 60% on the 8th day postinfection, individually. The virus infection could be delayed or neutralized by antibody against the envelope protein VP124. Quantitative PCR was used to further investigate the influence of three antisera described above on the virus infection. The results showed that the antiserum against VP124 could restrain the propagation of WSSV in crayfish. All of the results suggested that the viral envelope protein VP124 played a role in WSSV infection.  相似文献   

面向应用的高校GIS教学探索与实践   总被引：8，自引：2，他引：6  

党安荣  刘钊  贾海峰 《地理信息世界》2007,5(2):9-14

高校GIS教学是近年来国内探讨的热点教学问题之一,涉及到GIS专业课程体系设置、教学内容设置、实践环节设置、教学体制改革等多个方面;但这些探讨主要是针对GIS专业学士学位与硕士学位教学而引发的,较少关注非GIS专业学位的GIS教学问题.本文通过分析清华大学GIS教学发展与现状,结合作者在GIS教学中的探索与实践,从教学平台、教学内容、授课形式、考试方式、教学效果等几个方面,讨论如何开展针对非GIS专业、面向应用的高校GIS教学模式,与全国高校GIS教育工作者共勉.  相似文献   

The primordial excitation and clearing of the asteroid belt—Revisited     

David P. O'Brien  Alessandro Morbidelli 《Icarus》2007,191(2):434-452

We have performed new simulations of two different scenarios for the excitation and depletion of the primordial asteroid belt, assuming Jupiter and Saturn on initially circular orbits as predicted by the Nice Model of the evolution of the outer Solar System [Gomes, R., Levison, H.F., Tsiganis, K., Morbidelli, A., 2005. Nature 435, 466-469; Tsiganis, K., Gomes, R., Morbidelli, A., Levison, H.F., 2005. Nature 435, 459-461; Morbidelli, A., Levison, H.F., Tsiganis, K., Gomes, R., 2005. Nature 435, 462-465]. First, we study the effects of sweeping secular resonances driven by the depletion of the solar nebula. We find that these sweeping secular resonances are incapable of giving sufficient dynamical excitation to the asteroids for nebula depletion timescales consistent with estimates for solar-type stars, and in addition cannot cause significant mass depletion in the asteroid belt or produce the observed radial mixing of different asteroid taxonomic types. Second, we study the effects of planetary embryos embedded in the primordial asteroid belt. These embedded planetary embryos, combined with the action of jovian and saturnian resonances, can lead to dynamical excitation and radial mixing comparable to the current asteroid belt. The mass depletion driven by embedded planetary embryos alone, even in the case of an eccentric Jupiter and Saturn, is roughly 10-20× less than necessary to explain the current mass of the main belt, and thus a secondary depletion event, such as that which occurs naturally in the Nice Model, is required. We discuss the implications of our new simulations for the dynamical and collisional evolution of the main belt.  相似文献   

Iron line profiles and self-shadowing from relativistic thick accretion discs     

Sheng-Miao Wu  Ting-Gui Wang 《Monthly notices of the Royal Astronomical Society》2007,378(3):841-851

We present Fe Kα line profiles from and images of relativistic discs with finite thickness around a rotating black hole using a novel code. The line is thought to be produced by iron fluorescence of a relatively cold X-ray-illuminated material in the innermost parts of the accretion disc and provides an excellent diagnostic of accretion flows in the vicinity of black holes. Previous studies have concentrated on the case of a thin, Keplerian accretion disc. This disc must become thicker and sub-Keplerian with increasing accretion rates. These can affect the line profiles and in turn can influence the estimation of the accretion disc and black hole parameters from the observed line profiles. We here embark on, for the first time, a fully relativistic computation which offers key insights into the effects of geometrical thickness and the sub-Keplerian orbital velocity on the line profiles. We include all relativistic effects such as frame-dragging, Doppler boost, time dilation, gravitational redshift and light bending. We find that the separation and the relative height between the blue and red peaks of the line profile diminish as the thickness of the disc increases. This code is also well suited to produce accretion disc images. We calculate the redshift and flux images of the accretion disc and find that the observed image of the disc strongly depends on the inclination angle. The self-shadowing effect appears remarkable for a high inclination angle, and leads to the black hole shadow being in this case, completely hidden by the disc itself.  相似文献   

A signature of the donor star in the extra-galactic X-ray binary LMC X−2     

R. Cornelisse  D. Steeghs  J. Casares  P. A. Charles  I. C. Shih  R. I. Hynes  K. O'Brien 《Monthly notices of the Royal Astronomical Society》2007,381(1):194-200

Two nights of phase-resolved medium-resolution Very Large Telescope spectroscopy of the extra-galactic low-mass X-ray binary LMC X−2 have revealed a 0.32 ± 0.02 d spectroscopic period in the radial velocity curve of the He  ii λ4686 emission line that we interpret as the orbital period. However, similar to previous findings, this radial velocity curve shows a longer term variation that is most likely due to the presence of a precessing accretion disc in LMC X−2. This is strengthened by He  ii λ4686 Doppler maps that show a bright spot that is moving from night to night. Furthermore, we detect narrow emission lines in the Bowen region of LMC X−2, with a velocity of   K _em= 351 ± 28 km s⁻¹  , that we tentatively interpret as coming from the irradiated side of the donor star. Since K _em must be smaller than K ₂, this leads to the first upper limit on the mass function of LMC X−2 of   f ( M ₁) ≥ 0.86  M_⊙  (95 per cent confidence), and the first constraints on its system parameters.  相似文献   

The Galaxy Evolution Explorer UV emission in shell galaxies: tracing galaxy 'rejuvenation' episodes     

R. Rampazzo  A. Marino  R. Tantalo  D. Bettoni  L. M. Buson  C. Chiosi  G. Galletta  R. Grützbauch  R. M. Rich 《Monthly notices of the Royal Astronomical Society》2007,381(1):245-262

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