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101.
By analyzing all archival Rossi X-ray timing explorer (RXTE) data of the neutron star low mass X-ray binary 4U1820-303, we investigate the detectability of simultaneous twin kHz quasi-periodic oscillations (QPOs) as a function of their frequency, width and root mean squared (RMS) amplitudes. In a blind search over the whole data set (spanning over about 10 years), we show that in continuous time intervals (2000–3000 s), twin QPOs are preferentially detected over narrow range of frequencies (100 Hz wide), leading to a clustering in the distribution of frequency ratios, and a gap around the point (600, 900) Hz in the correlation line that links the upper QPO frequency to the lower QPO frequency. A deficit of lower QPOs around 600 Hz had already been noticed by Belloni et al. [Belloni, T., Méndez, M., Homan, J., 2005. A&A 437, 209], it is now confirmed using a much larger data set. We show that the lack of twin QPOs within the gap is not due to a lack of sensitivity for QPO detection, if the parameters of the QPOs (RMS and width) can be interpolated within the gap, using values measured before and after. Since as previously noticed, the gap cannot be attributed to an incomplete sampling of the source states, it thus implies a sudden change of the QPO properties within the gap, either a loss of coherence or an amplitude decrease, or alternatively, that there may be forbidden frequencies in this system. 相似文献
102.
Jean-Claude Hippolyte Didier Bourls Rgis Braucher Julien Carcaillet Laëtitia Lanni Maurice Arnold Georges Aumaitre 《Geomorphology》2009,108(3-4):312-320
Sackungs are the largest gravitational deformation observed in mountains. They are characterized by the long-term slowness of the movements, but their mechanism is still not well understood. Nowadays cosmic ray exposure (CRE) dating methods allow dating the morphologic structures involved in sackung and can contribute at the understanding of their origin. In the Alps, the 5.3 km long Arcs sackung initiated during the activity of rock glaciers. Three samples from these faulted rock glaciers provide their first CRE ages and show that at 2000 m elevation these block accumulations moved during the Younger Dryas and stopped in early Holocene. Six 10Be ages of fault scarps show that the Arcs sackung lasted only a few thousand years and stopped at about 8462 ± 432 10Be yr. They also reveal that deformation migrated upslope in agreement with a mechanism of flexural toppling of vertical layers. This unique and long gravitational event, characterized by migration of the deformation, does not support earthquake shaking as triggering mechanism for individual faults. It shows that, in the upper Isère valley, slope deformation was delayed of several thousand years after glacial debuttressing, and is not anymore active despite its fresh morphology. 相似文献
103.
Sarah Lambart Didier Laporte Pierre Schiano 《Contributions to Mineralogy and Petrology》2009,157(4):429-451
We performed experiments in a piston-cylinder apparatus to determine the effects of focused magma transport into highly permeable
channels beneath mid-ocean ridges on: (1) the chemical composition of the ascending basalt; and (2) the proportions and compositions
of solid phases in the surrounding mantle. In our experiments, magma focusing was supposed to occur instantaneously at a pressure
of 1.25 GPa. We first determined the equilibrium melt composition of a fertile mantle (FM) at 1.25 GPa-1,310°C; this composition
was then synthesised as a gel and added in various proportions to peridotite FM to simulate focusing factors Ω equal to 3
and 6 (Ω = 3 means that the total mass of liquid in the system increased by a factor of 3 due to focusing). Peridotite FM
and the two basalt-enriched compositions were equilibrated at 1 GPa-1,290°C; 0.75 GPa-1,270°C; 0.5 GPa-1,250°C, to monitor
the evolution of phase proportions and compositions during adiabatic decompression melting. Our main results may be summarised
as follows: (1) magma focusing induces major changes of the coefficients of the decompression melting reaction, in particular,
a major increase of the rate of opx consumption, which lead to complete exhaustion of orthopyroxene (and clinopyroxene) and
the formation of a dunitic residue. A focusing factor of ≈4—that is, a magma/rock ratios equal to ≈0.26—is sufficient to produce
a dunite at 0.5 GPa. (2) Liquids in equilibrium with olivine (±spinel) at low pressure (0.5 GPa) have lower SiO2 concentrations, and higher concentrations in MgO, FeO, and incompatible elements (Na2O, K2O, TiO2) than liquids produced by decompression melting of the fertile mantle, and plot in the primitive MORB field in the olivine–silica–diopside–plagioclase
tetrahedron. Our study confirms that there is a genetic relationship between focused magma transport, dunite bodies in the
upper mantle, and the generation of primitive MORBs. 相似文献
104.
The concentrations of dissolved and particulate polycyclic aromatic hydrocarbons (PAHs) were monitored in waters of the Rhône River (France) every fortnight for a full calendar year, from June 1994 to May 1995. All flood events occurring over the course of the experiment were sampled at higher frequency to better quantify the impact of these extreme hydrological episodes on the annual export of PAHs to the Mediterranean Sea. This time-series indicates that more than 90% of the annual load of particulate PAHs is transported during flood episodes, with 77% discharged during the course of only one extreme flood event occurring in November 1994. During these intense events, riverine particles are depleted in PAHs while at low river discharge particles are PAH-enriched. Dissolved PAHs were less variable and less abundant than adsorbed PAHs, consistently with the low solubility of these compounds. 相似文献
105.
HABIB Ammara CHEN Bin SHI Guangyu IWASAKA Yasunobu NATH Debashis KHALID Bushra TAN Saichun MAHMOOD Tariq JIAO Reguang NTWALI Didier 《大气和海洋科学快报》2019,(1):12-20
塔克拉玛干沙漠是亚洲沙尘气溶胶的重要源地。为探讨塔克拉玛干地区沙尘气溶胶的理化特性与时空变化,研究其环境与气候效应,本文分析了四个季节在中国敦煌(塔克拉玛干沙漠内)取得的探空气球观测数据,包括气溶胶的数浓度、粒径分布、质量浓度及在西风主导下的水平输送通量。气溶胶数浓度的垂直廓线显示,来自沙漠地区的矿物粒子对局地环境与气候有重要影响,且所有季节都存在长距离输送。粒子谱分布显示局地有大量粗粒子输入。结果说明,源于塔克拉玛干沙漠的沙尘气溶胶的背景输送有着重要的科学意义,需进一步研究其对东亚和西太平洋地区环境与气候的影响。 相似文献
106.
107.
108.
Monitoring chemical contamination levels in the Mediterranean based on the use of mussel caging 总被引:3,自引:0,他引:3
Andral B Stanisiere JY Sauzade D Damier E Thebault H Galgani F Boissery P 《Marine pollution bulletin》2004,49(9-10):704-712
Within the framework of the biointegrator network (RINBIO), 92 man-made cages containing mussels (Mytilus galloprovincialis), distributed over 1800 km of the French Mediterranean coast, made it possible to assess chemical contamination by heavy metals (Cd, Hg, Zn, Pb, Cu, Ni, Cr, As) and organic compounds (DDT, PCBs, HAP). The caging technique was adopted to compensate for the scarcity of natural shellfish stocks in the Mediterranean and to enable comparison of the sites regardless of their physicochemical and trophic characteristics. Models linking a biometric parameter (the condition index) to pollutant levels make it possible to adjust raw data on contamination for a reference individual, by making a clear distinction between physiological factors (growth) and environmental ones. The results demonstrate significant levels of pollutants in sites heretofore unsampled; the pollution occurs at limited areas, and the sources have been identified. Moreover, average contamination levels are comparable to those measured in wild species and in other areas. Overall, the research demonstrates the reliability of this methodological approach for monitoring marine pollution, especially in the Mediterranean. 相似文献
109.
The local and convective accelerations of steep irregular wave events have been investigated. These properties are measured by a two-camera PIV technique. Furthermore, the experiments are compared with two different theories including a fully nonlinear and a simplified analytical model. An important result is that the convective term is of the same order of magnitude and of opposite sign as the local acceleration. The convective acceleration term can therefore not be neglected in acceleration and force estimates. 相似文献
110.