A one-dimensional model of a current-sheet with a static electric potential is considered. Free electrons and protons move in opposite directions under the influence of the potential and we seek a solution for the potential in a bounded region in space (over the sheet width). The general solution is found to be plasma oscillations. Then introducing a short wavelength, monochromatic wave as a perturbation, it is shown by the method of stationary phase that electrons in resonance give a growth- (damping-) rate similar to the Landau formula. There is the possibility, however, that the wave can both grow and damp in different regions when traversing the sheet as it will sample electrons from various parts of the zero-order distribution function. 相似文献
Using the observed data for metric and hectometric type III radio bursts, the dependence of burst characteristics on the solar longitude has been examined over a wide frequency range. It is found that there exists an east-west asymmetry for the extension of metric type III bursts into hectometric wavelength range. In particular, hectometric bursts are rarely observed for solar flares associated with metric bursts eastward solar longitude 60°E. Furthermore, for eastern longitudes, the low frequency radio observations show a large dispersion in drift time interval. 相似文献
The profiles of the resonance lines of Caii have been studied in two large disk flares and in the surrounding plage. In the brightest portions of the flares no self-reversal in the central emission core was detected; self-reversed cores were present in the less bright portions of the flares. We find that as the intensity of the emission core increases the separation of the H2 and K2 peaks decreases monotonically, becoming unobservable at intensities near to 0.90 the local continuum. Possible reasons for the behavior of the H and K lines in flares are considered. It is suggested that the largest density enhancements in flares are found near the strongest magnetic field. 相似文献
To improve the water supply in Bogota, Colombia, 38 km of tunnels were excavated through the Cretaceous and Tertiary sedimentary rocks. After four months in operation, a number of fall-outs and slides in the shotcrete-lined parts of the longest tunnel stopped the water flow completely. The majority of the fall-outs occurred in the Fomeque formation, which is dominated by black shales with interbedded layers of siltstone and some limestones.
Several rock samples from the Fomeque formation have been analyzed with respect to swellability and petrography/mineralogy. Swelling pressures varying from 014 MPa (siltstone) to 45 MPa (shale) have been measured on intact rock specimens. The siltstone does not show cracking or slaking after storage in water for several weeks. The shale disintegrates almost immediately when submerged. Representative samples of the two rock types were chosen for comprehensive mineralogical and textural analyses. The rocks show a marked difference in textures. The siltstone is homogeneous, massive and cryptocrystalline to fine grained, while the shale is microcrystalline to cryptocrystalline with a penetrative slaty cleavage.
Before the tunnel was filled with water, extensive draining and drying-out of the rock masses along the tunnel periphery took place. This resulted in heavy cracking and fissuring, especially along the cleavage planes of the shales. The cracking reduced the general strength of the rocks, but, more importantly, caused a dramatic increase in the permeability and in the exposed rock surface area. When the tunnel was filled, water entered all new fissures in the shales and the exposed and partly dehydrated illite/smectite started to swell. The swelling of the mixed layered silicates is believed to be the initiating factor causing most of the fall-outs and slides in the Chingaza tunnel. 相似文献
The stability properties of a source-sink driven flow in a two-layer, rotating fluid is considered. A steady flow in an annulus has been determined previously (Maeland, 1982) by Ekman-layer dynamics at the interface of the two layers; in this paper, the stability will be studied by linear, inviscid theory. For a given configuration, the two parameters which govern the stability of the basic flow are the internal Froude numbers of each layer. The growth rates for the instabilities are calculated by a simple numerical method (matrix method). 相似文献
Documentary data provide long time series and sometimes high-resolution, detailed data from historical times to the present and can give valuable information about palaeoclimate, and for the prediction of future climates. In this paper, documentary data containing qualitative information on climate, in the form of a diary written by the farmer I.G. Grude, and two newspapers, were used for the reconstruction of the palaeoclimate at Jæren, in the county of Rogaland, in southwestern Norway, during the period 1821–50. An index method to quantify the qualitative climate data was developed and used for a low-resolution reconstruction of winter, summer and annual temperatures. A high-resolution climate reconstruction of temperature and precipitation for the winter of 1837/38 is also presented, making use of a method that keeps the climate data in a qualitative form. The climate reconstructions are compared to an instrumental temperature series from Bergen, for the same period. The two data sets are in good agreement except for summer temperature (annual temperature: r = 0.75, winter temperature: r = 0.77, summer temperature: r = 0.44). Compared to average temperatures during 1961–90, the instrumental data from Bergen during the 1821–50 period show slightly different temperatures: annual average was 0.3°C lower, winter 0.4°C lower, and summer 0.1°C lower than at present, implying conditions consistent with the "Little Ice Age" climate. 相似文献
