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排序方式： 共有76条查询结果，搜索用时 171 毫秒
31.
Erik Kuulkers Rudy Wijnands Michiel van der Klis 《Monthly notices of the Royal Astronomical Society》1999,308(2):485-492
It is known that the overall (mean) intensity of the low-mass X-ray binary Cyg X-2 varies on time-scales from a day to months, independently of the variations on time-scales of hours to a day by which the source moves between the horizontal, normal and flaring branches.
We present RXTE PCA observations of Cyg X-2, taken when its overall intensity was near its lowest values, in 1996 October and 1997 September. For the first time we perform a study of the fast timing behaviour at such low intensities. During the 1996 October observations, the source was in the left part of the horizontal branch, and during the 1997 September observations was most likely in the lower parts of the normal branch and flaring branch.
We find that the properties of the very low-frequency noise during the 1997 September observations are consistent with a monotonic decrease in its strength and power-law index as a function of overall intensity. In contrast, the strength of the ∼6 Hz normal branch quasi-periodic oscillations does not vary monotonically with overall intensity. They are strongest at medium overall intensity and weaker both when the overall intensity is low and when the overall intensity is high. 相似文献
We present RXTE PCA observations of Cyg X-2, taken when its overall intensity was near its lowest values, in 1996 October and 1997 September. For the first time we perform a study of the fast timing behaviour at such low intensities. During the 1996 October observations, the source was in the left part of the horizontal branch, and during the 1997 September observations was most likely in the lower parts of the normal branch and flaring branch.
We find that the properties of the very low-frequency noise during the 1997 September observations are consistent with a monotonic decrease in its strength and power-law index as a function of overall intensity. In contrast, the strength of the ∼6 Hz normal branch quasi-periodic oscillations does not vary monotonically with overall intensity. They are strongest at medium overall intensity and weaker both when the overall intensity is low and when the overall intensity is high. 相似文献
32.
The subject of measuring the performance of registries has been a topic of policy discussions in recent years at the regional level due to the recasting of the European Union (EU) port state control (PSC) directive which introduces incentives for flags which perform better. Since the current method used in the EU region entails some shortcomings, it has therefore been the subject of substantial scrutiny. Furthermore, the International Maritime Organization (IMO) developed a set of performance indicators which however lacks the ability to measure compliance as set out in one of its strategic directions towards fostering global compliance. This article develops a methodology to measure flag state performance which can be applied on the regional or global level and to other areas of legislative interest (e.g. recognized organizations, Document of Compliance Companies). The proposed methodology overcomes some of the shortcomings of the present method and presents a more refined, less biased approach of measuring performance. To demonstrate its usefulness, it is applied to a sample of 207,821 observations for a 3-year time frame and compared to the current method. 相似文献
33.
Michel?G.?J.?Den?ElzenEmail author Michiel?Schaeffer Paul?L.?Lucas 《Climatic change》2005,71(3):277-301
During the negotiations on the Kyoto Protocol, Brazil proposed allocating the greenhouse gas emission reductions of Annex I Parties according to the relative effect of a country’s historical emissions on global temperature increase. This paper analyses the impact of scientific uncertainties and of different options in policy implementation (policy choices) on the contribution of countries’ historical emissions to indicators of historical responsibility for climate change. The influence of policy choices was found to be at least as large as the impact of the scientific uncertainties analysed here. Building on this, the paper then proceeds to explore the implications of applying the Brazilian Proposal as a climate regime for differentiation of future commitments on the global scale combined with an income threshold for participation of the non-Annex I regions. Under stringent climate targets, such a regime leads to high emission reductions for Annex I regions by 2050, in particular for Europe and Japan. The income threshold assumptions strongly affect the Annex I reductions, even more than the impact of another burden-sharing key. A variant of the Brazilian Proposal, allocating emission reductions on the basis of cumulative emissions since 1990, would lead to a more balanced distribution of emission reductions. 相似文献
34.
This article utilizes central place theory (CPT) to navigate the “deluge” brought about by big data. While originating in the 1930s, CPT is a theoretical monument of 1960s spatial science. CPT aims to understand settlement geographies based on consumption behavior and is often presented as a singular, outdated, and rationalist theory. After critically reviewing the history of CPT, we assess the microfoundations of Christaller’s CPT – the threshold and range of goods – for various central functions in Louisville, Kentucky. The microfoundations are estimated through data from social media platforms Foursquare and Twitter. These sources alleviate many of the operationalization issues that traditionally hamper empirical use of CPT. The empirical application of CPT reveals that: (i) central functions have typical ranges and thresholds relating central places to population spread; (ii) central functions cluster based on an approximate hierarchical structure. The findings indicate the ongoing importance of CPT in shaping urban-economic geographies. 相似文献
35.
Oliver Sachs Eberhard J. Sauter Michael Schlüter Michiel M. Rutgers van der Loeff Kerstin Jerosch Ola Holby 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(8):1319-1335
For the investigation of organic carbon fluxes reaching the seafloor, oxygen microprofiles were measured at 145 sites in different sub-regions of the Southern Ocean. At 11 sites, an in situ oxygen microprofiler was deployed for the measurement of oxygen profiles and the calculation of organic carbon fluxes. At four sites, both in situ and ex situ data were determined for high latitudes. Based on this data set as well as on previous published data, a relationship was established for the estimation of fluxes derived by ex situ measured O2 profiles. The fluxes of labile organic matter range from 0.5 to 37.1 mg C m?2 d?1. The high values determined by in situ measurements were observed in the Polar Front region (water depth of more than 4290 m) and are comparable to organic matter fluxes observed for high-productivity, upwelling areas like off West Africa. The oxygen penetration depth, which reflects the long-term organic matter flux to the sediment, was correlated with assemblages of key diatom species. In the Scotia Sea (～3000 m water depth), oxygen penetration depths of less than 15 cm were observed, indicating high benthic organic carbon fluxes. In contrast, the oxic zone extends down to several decimeters in abyssal sediments of the Weddell Sea and the southeastern South Atlantic. The regional pattern of organic carbon fluxes derived from microsensor data suggests that episodic and seasonal sedimentation pulses are important for the carbon supply to the seafloor of the deep Southern Ocean. 相似文献
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39.
Michael A. Dopita Michiel Reuland Wil van Breugel Wim de Vries S. A. Stanford Huub Röttgering George Miley Bram Venemans Hy Spinrad Steve Dawson Arjun Dey Mark Lacy Daniel Stern Andrew Bunker 《Astrophysics and Space Science》2007,311(1-3):305-309
We present results from a Keck optical and near IR spectroscopic study of the giant emission line halos of the z>3 High Redshift Radio Galaxies (HiZRGs) 4C 41.17, 4C 60.07 and B2 0902+34. The outer regions of these halos show quiet kinematics
with typical velocity dispersions of a few hundred km s−1 and velocity shears consistent with rotation. The inner regions contain shocked, clumpy cocoons of gas closely associated
with the radio lobes with disturbed kinematics and expansion velocities and/or velocity dispersions >1000 km s−1. We also find evidence for the ejection of chemically enriched material in 4C 41.17 up to a distance of ∼60 kpc along the
radio-axis. We infer that these HiZRGs are undergoing a final jet-induced phase of star formation with the ejection of most
of their interstellar medium before evolving to become “red and dead” Elliptical galaxies. 相似文献
40.