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271.
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273.
Pasquale Blasi Elena Amato Damiano Caprioli 《Monthly notices of the Royal Astronomical Society》2007,375(4):1471-1478
Particle acceleration at non-relativistic shocks can be very efficient, leading to the appearance of non-linear effects due to the dynamical reaction of the accelerated particles on the shock structure and to the non-linear amplification of the magnetic field in the shock vicinity. The value of the maximum momentum, p max , in these circumstances cannot be estimated using the classical results obtained within the framework of test-particle approaches. We provide here the first attempt at estimating p max in the cosmic ray modified regime, taking into account the non-linear effects mentioned above. 相似文献
274.
275.
Extreme-ultraviolet data from EIT/SOHO (1996–2002), soft X-ray data from Yohkoh (1991–2001), and magnetic field data from MDI/SOHO (1996–2002) and Kitt Peak Observatory, NSO/NOAO (1991–2002) are analyzed
together in the form of synoptic maps for the investigation of solar cycle variations of the corona and their relation to
the magnetic field. These results show new interesting relations between the evolution of the topological structure of the
corona, coronal heating and the large-scale magnetic field. The long-lived coronal structures are related to complexes of
solar activity and display quasi-periodic behavior (in the form of impulses of coronal activity) with periods of 1.0–1.5 year,
in the axisymmetric distribution of EUV and X-ray fluxes during the current solar cycle 23. In particular, during the second
maximum of this cycle the solar corona became somewhat hotter than it was in the period of the first maximum. 相似文献
276.
Michael Zemcov Mark Halpern Colin Borys Scott Chapman Wayne Holland Elena Pierpaoli Douglas Scott 《Monthly notices of the Royal Astronomical Society》2003,346(4):1179-1188
We have detected the Sunyaev–Zel'dovich (SZ) increment at 850 μm in two galaxy clusters (Cl 0016+16 and MS 1054.4−0321) using the Submillimetre Common User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope. Fits to the isothermal β model yield a central Compton y parameter of (2.2 ± 0.7) × 10−4 and a central 850-μm flux of Δ I 0 = 2.2 ± 0.7 mJy beam−1 in Cl 0016. This can be combined with decrement measurements to infer y = (2.38 ±0.36 0.34 ) × 10−4 and v pec = 400±1900 1400 km s−1 . In MS 1054 we find a peak 850-μm flux of Δ I 0 = 2.0 ± 1.0 mJy beam−1 and y = (2.0 ± 1.0) × 10−4 . To be successful such measurements require large chop throws and non-standard data analysis techniques. In particular, the 450-μm data are used to remove atmospheric variations in the 850-μm data. An explicit annular model is fit to the SCUBA difference data in order to extract the radial profile, and separately fit to the model differences to minimize the effect of correlations induced by our scanning strategy. We have demonstrated that with sufficient care, SCUBA can be used to measure the SZ increment in massive, compact galaxy clusters. 相似文献
277.
汪啸风 STOUGE Svend 王传尚 MALETZ J?rg 阎春波 BAGNOLI Gabriella 祁玉平 RAEVSKAYA Elena G 《华南地质与矿产》2022,38(1):1-26
根据对中国小阳桥剖面高精度生物、层序、化学和磁性地层学综合研究的新成果及其与绿岬全球界线层型剖面(GSSP)的详细对比,进一步厘定了加拿大绿岬"金钉子"剖面所定义的奥陶系底界划分与对比的标志,并指出:(1)与所定义的全球标准奥陶系底界相当的界线位于小阳桥剖面块状叠层石灰岩之上19.9 m处的薄层纹层灰岩中(BD-24层... 相似文献
278.
Elena Zubieta Juan C. Larrasoaña Alaitz Aldaz Javier Casalí Rafael Giménez 《地球表面变化过程与地形》2021,46(6):1103-1110
In gully erosion, the detached soil can be transported over long distances along the landscape. The eroded material can be redistributed and/or deposited on the soil surface along the landscape and then eventually be buried by newly eroded and deposited sediment. There can be significant variability of the soil conditions (e.g., texture and moisture content) over which the eroded material travels. The eroded material can be detected through the use of magnetic tracers attached to or mixed with the eroded soil. In this study we evaluated the degree to which the magnetic signal of the magnetite is conditioned by (i) burial depth of tracer, (ii) condition of soil covering the tracer and (iii) tracer concentration. In the laboratory containers were filled with a specific soil. In the filling process, a 0.5-cm layer of a soil–magnetite mixture was interspersed in the soil profile at a certain depth. Experiments encompassed three different soil–tracer concentrations (1000:1, 200:1, 100:1), four burial depths of tracer (0 cm, 3 cm, 5 cm and 10 cm from soil surface), and two different soils. In each case, the magnetic susceptibility was measured with a susceptometer. Experiments were repeated with different soil moisture contents. If the tracer is located under the soil surface, a minimum soil–tracer concentration of 200:1 is required for its correct detection. The intensity of the magnetic signal decreases dramatically with the vertical distance of the tracer from the soil surface. The maximum detection depth for the tracer's magnetic signal is strongly dependent on the natural magnetic susceptibility of the soil, which masks the tracer's signal. Variation in soil moisture content does not significantly affect the magnetic signal. For extensive field studies, the soil–tracer volume to be handled would be very high and therefore, it is necessary to explore new tracer application techniques. 相似文献
279.
This paper investigates the specific contributions of river network geomorphology, hillslope flow dynamics and channel routing to the scaling behavior of the hydrologic response as function of drainage area. Scaling relationships emerged from the observations of geomorphological and hydrological data and were reproduced in previous works through mathematical models, for both idealized self-similar networks and natural basins. Recent literature highlighted that scale invariance of hydrological quantities depends not only on the metrics of the drainage catchment but also on effective flow routing. In this study we employ a geomorphological width function scheme to test the simple scaling hypothesis adopting more realistic dynamic conditions than in previous approaches, specifically taking into account the role of hillslopes. The analysis is based on the derivation of the characteristic distributions of path lengths and travel times, inferred from DEM processing and measurements of rainfall and runoff data. The study area is located in the Tiber River region (central Italy).Results indicate that, while scaling properties clearly emerge when the hydrologic response is defined on the basis of the sole geomorphology, scale invariance is broken when less idealized flow dynamics are taken into account. Lack of scaling appears in particular as a consequence of the catchment to catchment variability of hillslope velocities. 相似文献
280.
Obtaining natural oscillatory modes of bays and harbors via Empirical Orthogonal Function analysis of tsunami wave fields 总被引:1,自引:1,他引:0
To a tsunami wave, bays and harbors represent oscillatory systems, whose resonance (normal) modes determine the response to
tsunami and consequently the potential hazard. The direct way to obtain the resonance modes of a water reservoir is by solving
the boundary problem for the eigenfunctions of the linearized shallow-water wave equation. The principal difficulty of posing
such a problem for a basin coupled to an ocean is specifying the boundary between the two. The technique developed in this
work allows the normal modes of a semi-enclosed water body to be obtained without a-priori restricting the resonator area.
The technique utilizes complex Empirical Orthogonal Function analysis of modeled tsunami wave fields. On the examples of Poverty
Bay in New Zealand and Monterey Bay in California (United States), we demonstrate that the normal modes can be identified
and isolated using the EOFs of a data set comprised of the concatenated time-series collected from different tsunami scenarios
in a basin. The analysis of the modeled tsunami wave fields for the normal modes can also answer the question of how likely
and under which conditions the different modes are exited, due to feasible natural events. 相似文献