Dissipative-acoustic instability in accretion disks at a nonlinear stage     

A. V. Khoperskov  S. S. Khrapov  E. A. Nedugova 《Astronomy Letters》2003,29(4):246-257

Nonstationary hydrodynamic models of a viscous accretion disk around a central compact object were constructed. Two different numerical methods (TVD and SPH) are used to study the dynamics of dissipatively unstable acoustic perturbations at the nonlinear stage in terms of the standard α-disk model. The standard disk accretion in the Shakura-Sunyaev model is unstable against acoustic waves for various parameters of the system. If the α parameter, which specifies the level of turbulent viscosity, exceeds α?0.03, then a complex nonstationary system of small-scale weak shock waves is formed. The growth rate of the perturbations is higher in the central disk region. For α?0.2, the relative shock amplitude can exceed 50% of the equilibrium disk parameters. The reflection of waves from the disk boundaries and their nonlinear interaction are important factors that can produce unsteady accretion. The luminosity of such a disk undergoes quasi-periodic oscillations at a level of several percent (?5%) of the equilibrium level.  相似文献   

碱消解-高效液相色谱-电感耦合等离子体质谱法测定生物样品中的甲基汞和乙基汞   总被引：7，自引：2，他引：5  

杨红霞  刘崴  李冰 《岩矿测试》2008,27(6):405-408

建立了碱消解-高效液相色谱-电感耦合等离子体质谱联用系统测定生物样品中甲基汞(MeHg)与乙基汞(EtHg)的分析方法。为提高灵敏度,选用微流量的PFA雾化器,在优化的检测条件下,MeHg及EtHg检出限可达到0.036μg/L和0.03μg/L;线性范围达到4个数量级,两条工作曲线线性相关系数为1。对1.78μg/L MeHg、1.65μg/L EtHg的混合标准溶液重复测定7次,色谱峰面积的相对标准偏差(RSD)分别为1.79%和1.44%。对标准物质BCR 464(金枪鱼)的分析结果表明,测定值与标准值基本吻合,但略低于标准值;甲基汞和乙基汞的加标回收率分别为85.9%和84.5%。高效液相色谱与质谱联用技术的高灵敏度和低检出限能够满足生物样品中汞形态定量分析的要求。  相似文献   

河口涨落潮槽水动力特征及河槽类型判定   总被引：4，自引：0，他引：4  

刘高峰  沈焕庭  吴加学  吴华林 《海洋学报》2005,27(5):151-156

在前人对河口冲刷槽研究的基础上,选择长江口南支、新桥水道、南小泓和南港主槽作为典型涨、落潮槽研究对象,以2001年洪季和2003年枯季实测资料为根据,比较分析了长江口涨落潮槽的水流、泥沙、优势流和优势沙等动力特征,结果表明用单一因子分析河槽性质不够全面.提出了一个(无量纲因子)河槽类型系数(λ)来综合表述河槽的多种水文泥沙特征,可以较全面地用多个影响因子来合理地判断河槽类型.  相似文献   

海洋平台沉垫的波浪载荷试验研究   总被引：2，自引：0，他引：2  

姚美旺  张承懿  缪国平  季春群 《海洋工程》1997,(4)

本文通过对海洋平台沉垫的波浪载荷试验研究分析，着重研究了在规则波中平台沉垫总体波浪载荷和局部水动压力分布的情况，定性地考察了非线性影响、浅水影响的重要性，为今后波浪理论中粘性的引入，进而考虑粘性与波浪运动的非线性相互干扰提供实测依据  相似文献   

水动力条件差异导致潮坪分形特征变化实例研究   总被引：8，自引：0，他引：8       下载免费PDF全文

贾永刚  付元宾  许国辉  单红仙  曹雪晴 《海洋学报》2003,25(3):59-67

研究区位于1964～1976年黄河由刁口流路入海时形成的三角洲潮坪.为进行石油开采在潮坪上构筑的交通设施对波浪形成了良好的屏障,水动力条件具有显著差异的屏障两侧潮坪是研究潮坪特征对水动力条件响应的天然实验场所.在屏障两侧各选择一典型区,实测地貌形态,取样品进行粒度成分分析,根据实测资料分析确定潮坪分形特征.发现水动力环境的强弱决定着潮坪的形貌、沉积物粒度分维值的变化规律.水动力环境强的一侧潮坪滩面分维值高,且随着初始计算网格宽度增大迅速降维;表层沉积物粒度分维值小,且离散性大.相反,在另一侧潮坪滩面分维值低,且随着初始计算网格宽度增大分维值无显著变化;表层沉积物粒度分维值高,且具有较好的一致性.当初始计算网格宽度增大到某个值时,两侧潮坪形貌分维值渐趋一致.在屏障两侧各沿一条与屏障大角度相交的测线取样,并各选择一点采取不同深度的样品做分析计算,发现在水动力条件弱的一侧,样品的粒度分维值表现为远离屏障逐步降维、随深度增加分维值增大的规律;相反一侧粒度分维值变化的规律性很不明显.讨论了水动力环境对潮坪分形特征影响机理.  相似文献   

沟槽内海底管道的水动力特性研究   总被引：1，自引：0，他引：1  

邢至庄  张日向  郭建江 《海洋工程》1997,(4)

基于水力模型实验，引入相对沟形系数αｒ，获得了以αｒ为表征的相对水动力系数与ＫＣ数的关系；对于浅沟而言，这种关系较有规律性。根据所设计沟形的αｒ值和所选定的ＫＣ值，应用本文结果，可以方便地判断其力折减程度和掩护效果  相似文献   

A perturbation solution for nonlinear structural response to oscillatory flow     

A.W. Lipsett   《Applied Ocean Research》1986,8(4):183-189

  相似文献   

几丁糖酯原料药稳定性研究     

吕志华  赵峡  徐家敏 《中国海洋大学学报(自然科学版)》2001,31(6):842-848

该文建立高效凝胶渗透色谱法 (HPGPC) ,明胶比浊法 ,氧瓶燃烧法三种分析方法考察海洋硫酸多糖药物几丁糖酯的稳定性 ,采用这三种方法分别考察几丁糖酯原料药在高温、高湿、强光照射及加速条件下分子量及分布宽度、样品中硫酸根含量及样品含量的变化情况。结果表明 :三种方法均适用于几丁糖酯的稳定性考察 ,几丁糖酯在上述影响因素条件下稳定性良好  相似文献   

Comparative performance of ADAPT and Laurec-Shepherd methods for estimating fish population parameters and in stock management     

Patterson  K. R.; Kirkwood  G. P. 《ICES Journal of Marine Science》1995,52(2):183-196

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Jason-1: Assessment of the System Performances     

J. Perbos  P. Escudier  F. Parisot  G. Zaouche  P. Vincent  Y. Menard  F. Manon  G. Kunstmann  D. Royer  L. -L. Fu 《Marine Geodesy》2003,26(3):147-157

On 7 December 2001, Jason-1 was successfully launched by a Boeing Delta II rocket from the Vandenberg Air Force Base, California. The Jason-1 satellite will maintain the high accuracy altimeter service provided since 1992 by TOPEX/Poseidon (T/P), ensuring the continuity in observing and monitoring the Ocean Dynamics (intraseasonal to interannual changes, mean sea level, tides, etc.). Despite one-fourth the mass and power, the Jason-1 system has been designed to have basically the same performance as T/P, measuring sea surface topography at a centimetric level. This new CNES/NASA mission also provides near real-time data for sea state and ocean forecast. The first two months of the Jason-1 mission have been dedicated to the assessment of the overall system. The goals of this assessment phase were:

1. To assess the behavior of the spacecraft at the platform and payload levels (Jason-1 being the first program to call on the PROTEUS versatile multimission platform for Low and Medium Earth Orbit Missions developed in partnership between Alcatel Space and CNES);

2. To verify that platform performance requirements are met with respect to Jason-1 requirements;

3. To verify that payload instruments performance requirements evaluated at instrument level are met;

4. To assess the performance of the Jason-1 Ground System.

This article will display the main outputs of the assessment of the system. It will demonstrate that all the elements of the onboard and ground systems are within the specifications. Provision of data to the Jason-1 Science Working Team started at the end of March 2002. This is the goal of a six-month phase after closure of the initial assessment phase to derive the error budget of the system in terms of altimetry user products.  相似文献