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101.
We present a novel experiment with the capacity to independently measure both the electron density and the magnetic field
of the solar corona. We achieve this through measurement of the excess Faraday rotation resulting from propagation of the
polarised emission from a number of pulsars through the magnetic field of the solar corona. This method yields independent
measures of the integrated electron density, via dispersion of the pulsed signal and the magnetic field, via the amount of
Faraday rotation. In principle this allows the determination of the integrated magnetic field through the solar corona along
many lines of sight without any assumptions regarding the electron density distribution. We present a detection of an increase
in the rotation measure of the pulsar J1801-2304 of approximately 170 rad m2 at an elongation of 0.96° from the centre of the solar disc. This corresponds to a lower limit of the magnetic field strength
along this line of sight of >41.8 nT. The lack of precision in the integrated electron density measurement restricts this
result to a limit, but application of coronal plasma models can further constrain this to approximately 0.5 μT, along a path
passing 2.7 solar radii from the solar limb, which is consistent with predictions obtained using extensions to the source
surface models published by the Wilcox Solar Observatory. 相似文献
102.
This paper deals with the theoretical aspects of nonaqueous phase liquid (NAPL)‐dissolution‐induced instability in two‐dimensional fluid‐saturated porous media including solute dispersion effects.After some weaknesses associated with the previous work are analyzed and overcome, a comprehensive dimensionless number, known as the Zhao number, is proposed to represent the main driving force and three controlling mechanisms of an NAPL‐dissolution system that has a finite domain. The linear stability analysis is carried out to derive the critical value of the comprehensive dimensionless number of the NAPL‐dissolution system in a limit case as the ratio of the equilibrium concentration to the density of the NAPL approaches zero. As a result, a theoretical criterion that can be used to assess the instability of planar NAPL‐dissolution fronts in two‐dimensional fluid‐saturated porous media of finite domains has been established. Not only can the present theoretical results be used for the theoretical understanding of the effect of solute dispersion on the instability of an NAPL‐dissolution front in the fluid‐saturated porous medium of either a finite domain or an infinite domain, but also they can be used as benchmark solutions for verifying numerical methods employed to simulate detailed morphological evolution processes of NAPL‐dissolution fronts in two‐dimensional fluid‐saturated porous media. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
103.
Destructive tsunamis are infrequent comparedwith other natural disasters, andtheir evidences tend to disappear quickly.Conventional data acquisition havebeen limited in coverage and tend to beunreliable. Readily available andtransient data should be collectedby field survey teams as soon as possible.Since tsunamis are always triggered by the simultaneous or in-advanceoccurrence of another phenomena, they can be considered close to thesource as a syndrome, leaving a variety of almost simultaneous effectsat the nearby coasts. By observating the evidence left bythese local interaction effects, the surveyors should be able to identifyand evaluate at least the maximum horizontal extension and the verticalreach of the inundation. High water marks and lines of landward limitof sea grass, debris or sediment deposited, may help in this identification and measurement process.Guidelines to conduct post-tsunami field surveys and standards for theobservations have been established by the International Coordination Groupfor the Tsunami Warning System in the Pacific (ICG/ITSU) upon agreement with the scientific community. A Post-Tsunami Survey Field Guide was published by the Intergovernmental Oceanographic Commission (IOC) of UNESCO. 相似文献
104.
Finite element analysis of flow patterns near geological lenses in hydrodynamic and hydrothermal systems 总被引:2,自引:0,他引:2
Chongbin Zhao B. E. Hobbs H. B. Mühlhaus & A. Ord 《Geophysical Journal International》1999,138(1):146-158
We use theoretical and numerical methods to investigate the general pore-fluid flow patterns near geological lenses in hydrodynamic and hydrothermal systems respectively. Analytical solutions have been rigorously derived for the pore-fluid velocity, stream function and excess pore-fluid pressure near a circular lens in a hydrodynamic system. These analytical solutions provide not only a better understanding of the physics behind the problem, but also a valuable benchmark solution for validating any numerical method.
Since a geological lens is surrounded by a medium of large extent in nature and the finite element method is efficient at modelling only media of finite size, the determination of the size of the computational domain of a finite element model, which is often overlooked by numerical analysts, is very important in order to ensure both the efficiency of the method and the accuracy of the numerical solution obtained. To highlight this issue, we use the derived analytical solutions to deduce a rigorous mathematical formula for designing the computational domain size of a finite element model. The proposed mathematical formula has indicated that, no matter how fine the mesh or how high the order of elements, the desired accuracy of a finite element solution for pore-fluid flow near a geological lens cannot be achieved unless the size of the finite element model is determined appropriately.
Once the finite element computational model has been appropriately designed and validated in a hydrodynamic system, it is used to examine general pore-fluid flow patterns near geological lenses in hydrothermal systems. Some interesting conclusions on the behaviour of geological lenses in hydrodynamic and hydrothermal systems have been reached through the analytical and numerical analyses carried out in this paper. 相似文献
Since a geological lens is surrounded by a medium of large extent in nature and the finite element method is efficient at modelling only media of finite size, the determination of the size of the computational domain of a finite element model, which is often overlooked by numerical analysts, is very important in order to ensure both the efficiency of the method and the accuracy of the numerical solution obtained. To highlight this issue, we use the derived analytical solutions to deduce a rigorous mathematical formula for designing the computational domain size of a finite element model. The proposed mathematical formula has indicated that, no matter how fine the mesh or how high the order of elements, the desired accuracy of a finite element solution for pore-fluid flow near a geological lens cannot be achieved unless the size of the finite element model is determined appropriately.
Once the finite element computational model has been appropriately designed and validated in a hydrodynamic system, it is used to examine general pore-fluid flow patterns near geological lenses in hydrothermal systems. Some interesting conclusions on the behaviour of geological lenses in hydrodynamic and hydrothermal systems have been reached through the analytical and numerical analyses carried out in this paper. 相似文献
105.
Daniel Lluch-Belda Daniel B. Lluch-Cota Salvador E. Lluch-Cota 《Journal of Oceanography》2003,59(4):503-513
The information on the transitional areas between the temperate and tropical domains at the southern extent of the California
Current System is reviewed and described, particularly searching for the relative isolation or interchange between the western
coast of the Baja California peninsula and the Gulf of California, as well as mechanisms that permit the existence of sizeable
stocks of California sardine. Biological Action Centers that have high productivity throughout the year, as opposed to the
rest of the coastal area, are found in both the western coast of the peninsula at the Sebastián Vizcaíno—Punta Eugenia region
and in the Ballenas Channel inside the gulf; these features support large biomasses of sardine throughout the full year and
serve as long term refuges during adverse periods. The role of the Sebastián Vizcaino sardine stock as the primary group for
expansion is examined.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
106.
The highly vulnerable Pacific southwest coast of Mexico has been repeatedly affected by local, regional and remote source
tsunamis. Mexico presently has no national tsunami warning system in operation. The implementation of key elements of a National
Program on Tsunami Detection, Monitoring, Warning and Mitigation is in progress. For local and regional events detection and
monitoring, a prototype of a robust and low cost high frequency sea-level tsunami gauge, sampling every minute and equipped
with 24 hours real time transmission to the Internet, was developed and is currently in operation. Statistics allow identification
of low, medium and extreme hazard categories of arriving tsunamis. These categories are used as prototypes for computer simulations
of coastal flooding. A finite-difference numerical model with linear wave theory for the deep ocean propagation, and shallow
water nonlinear one for the near shore and interaction with the coast, and non-fixed boundaries for flooding and recession
at the coast, is used. For prevention purposes, tsunami inundation maps for several coastal communities, are being produced
in this way. The case of the heavily industrialized port of Lázaro Cárdenas, located on the sand shoals of a river delta,
is illustrated; including a detailed vulnerability assessment study. For public education on preparedness and awareness, printed
material for children and adults has been developed and published. It is intended to extend future coverage of this program
to the Mexican Caribbean and Gulf of Mexico coastal areas. 相似文献
107.
108.
In order to investigate the effect of material anisotropy on convective instability of three-dimensional fluid-saturated faults, an exact analytical solution for the critical Rayleigh number of three-dimensional convective flow has been obtained. Using this critical Rayleigh number, effects of different permeability ratios and thermal conductivity ratios on convective instability of a vertically oriented three-dimensional fault have been examined in detail. It has been recognized that (1) if the fault material is isotropic in the horizontal direction, the horizontal to vertical permeability ratio has a significant effect on the critical Rayleigh number of the three-dimensional fault system, but the horizontal to vertical thermal conductivity ratio has little influence on the convective instability of the system, and (2) if the fault material is isotropic in the fault plane, the thermal conductivity ratio of the fault normal to plane has a considerable effect on the critical Rayleigh number of the three-dimensional fault system, but the effect of the permeability ratio of the fault normal to plane on the critical Rayleigh number of three-dimensional convective flow is negligible. 相似文献
109.
The Quaternary: its character and definition 总被引:5,自引:0,他引:5
Martin J. Head Philip Gibbard Amos Salvador 《《幕》》2008,31(2):234-238
The Quaternary, is characterised by the development of widespread glaciations in mid-northern latitudes. As a chronostratigraphic term it has attracted vigorous debate. The Quaternao; as accepted by the International Union for Quaternary Research and proposed by the International Commission on Stratigraphy, begins at 2.6 Ma within a 2.8-2.4 Ma interval of profound change in Earth's climate system. 相似文献
110.
Hernández-Sánchez Rosa Isabel Castellanos Francisco Herrera-Barrientos Jaime Belmonte-Jiménez Salvador Isidro 《Natural Resources Research》2021,30(6):4207-4218
Natural Resources Research - Adequate management of water resources in aquifer systems implies knowledge of the different parameters of hydrological balance. However, only limited data exist for... 相似文献