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101.
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   
102.
The photometry of G and K subdwarfs in the Vilnius photometric system permits us to recognize them photometrically and to determine their metallicity, despite the presence of interstellar reddening. The weakening of the strong metallic lines in their spectra can also be used to estimate their metallicity.  相似文献   
103.
Summary Contour maps of any meteorological variable cannot give radius or area of influences around the measurement station by considering the records at surrounding sites. The main purpose of this paper is to propose a trigonometric point cumulative semivariogram (TPCSV) concept for deciding on a spatial dependence function and then its use for regional prediction. The TPCSV provides a unique opportunity for the establishment of a regional objective prediction method whereby the radius of influence helps to predict wind velocity at any site by using the weighted averages. The spatial correlations and weightings are obtained through the TPCSV provided that the distance between two sites is known. If the slope of TPCSV is greater than 80° after some distance, then beyond this distance the regional correlation is considered as negligible. The implementation of the proposed methodology is presented for 68 wind velocity measurement stations in Turkey. The proposed method yields the least prediction error compared with other objective methodologies. It is seen that areas of influence at Central Anatolia are generally bigger than coastal areas of Turkey.  相似文献   
104.
Ninety-eight clay mineral samples from the YSDP102 core were analyzed by x-ray diffractometer to study the four clay minerals: illite, chlorite, kaolinite and smectite. Twenty-eight samples had been analyzed on the laser particle-siz eanalyzer to reveal the particle features of the sediments. Distribution of the clay minerals and the particle characteristics in the YSDP102 core show that the core experienced three different depositional periods and formed three different sedimentary intervals due to different sediment sources and different depositional environments. Features of the clay minerals and the heavy minerals in the YSDP102 core indicate that coarse-grained sediments and fine-grained sediments result from different sources. The Yellow Sea Warm Current has greatly influenced the sedimentary framework of this region since the current‘s formation.  相似文献   
105.
Evapotranspiration is a source of water vapour to the atmosphere, and as a crucial indicator of landscape behaviour its accurate measurement has widespread implications. Here we investigate errors that are prevalent and systematic in the closed-path eddy-covariance measurement of latent heat flux: the attenuation of fluxes through dampened cospectral power at high frequencies. This process is especially pronounced during periods of high relative humidity through the adsorption and desorption of water vapour along the tube walls. These effects are additionally amplified during lower air temperature conditions. Here, we quantify the underestimation of evapotranspiration by a closed-path system by comparing its flux estimate to simultaneous and adjacent measurements from an open-path sensor. We apply models relating flux loss to relative humidity itself, to the lag time of the cross-correlation peak between the water vapour and vertical wind velocity signals, and to models of cospectral attenuation relative to the cospectral power of simultaneous sensible heat-flux measurements. We find that including the role of temperature in modifying the attenuation–humidity relationship is essential for unbiased flux correction, and that physically based cospectral attenuation methods are effective characterizers of closed-path instrument signal loss relative to the unattenuated flux value.  相似文献   
106.
Characterization of atmospheric surfactants in bulk precipitations was carried out by adsorption study at the mercury electrode/solution interface using phase sensitive AC voltammetry. The structure and permeability of the adsorbed organic films at the mercury electrode was tested using the redox processes of lead and cadmium ions as electrochemical tools. The effects of organic matter from the bulk precipitations (rainwater and melted snow) were compared to those obtained for aqueous solutions of model substances: aromatic hydrocarbon (naphtalene), anionic surfactant (sodium dodecylbenzene sulfonate, NDBS), protein (albumine) and selected model substances suggested to be representative of water soluble organic compounds (WSOC) in atmospheric water (monocarboxylic, dicarboxylic, and polyacidic compounds and levoglucosan). It was found that substances like humic acid and 3-hydroxybutanoic acid may play an important role in atmospheric heterogeneous chemistry because of their surface active potential.  相似文献   
107.
A series of new radio-continuum (λ=20 cm) mosaic images focused on the NGC?300 galactic system were produced using archived observational data from the VLA and/or ATCA. These new images are both very sensitive (rms?=60 μJy) and feature high angular resolution (<10?″). The most prominent new feature is the galaxy’s extended radio-continuum emission, which does not match its optical appearance. Using these newly created images a number of previously unidentified discrete sources have been discovered. Furthermore, we demonstrate that a joint deconvolution approach to imaging this complete data-set is inferior when compared to an immerge approach.  相似文献   
108.
109.
The accumulation of sediment in river channels is a phenomenon that is not only influenced by the channel morphology, but also by the physical and geographical characteristics and the endogenous and exogenous processes taking place in the catchment. This paper presents an analysis of the impact the changes in lithological conditions have on the morphological and morphometric parameters of the Udava River channel and their relation to the channel accumulation forms representative of the river’s longitudinal profile as well as of its planform. Results document when accumulation forms occur and what is their spatial distribution within the longitudinal and cross-sectional river profiles. More resistant structures created sections with a lower degree of sedimentation, while in depression segments the degree of sedimentation was higher. With the increase in longitudinal slope, the impact of channel width on the average channel bar size increased. Also a difference in the accumulation was observed between the left and right bank which could be possibly explained by the impact of Coriolis force.  相似文献   
110.
Aurass  H.  Vršnak  B.  Hofmann  A.  Rudžjak  V. 《Solar physics》1999,190(1-2):267-293
We analyze radio observations, magnetograms and extrapolated field line maps, Hα filtergrams, and X-ray observations of two flare events (6 February 1992 in AR 7042 and 25 October 1994 in AR 7792) and study properties, evolution and energy release signatures of sigmoidal loop systems. During both events, the loop configuration seen in soft X-ray (SXR) images changes from a preflare sigmoidal shape to a relaxed post-flare loop system. The underlying magnetic field system consists of a quadrupolar configuration formed by a sheared arcade core and a remote field concentration. We demonstrate two possibilities: a sigmoidal SXR pattern can be due to a single continuous flux tube (the 1992 event). Alternatively, it can be due to a set of independent loops appearing like a sigmoid (the 1994 event). In both cases, the preflare and post-flare loops can be well reproduced by a linear force-free field and potential field, respectively, computed using preflare magnetograms. We find that thermal and non-thermal flare energy release indicators of both events become remarkably similar after applying spatial and temporal scale transformations. Using the spatial scaling between both events we estimated that the non-thermal energy release in the second event liberated about 1.7 times more energy per unit volume. A two-and-a-half times faster evolution indicates that the rate of the energy release per unit volume is more than four times higher in this event. A coronal type II burst reveals ignition and propagation of a coronal shock wave. In contrast, the first event, which was larger and released about a 10 times more energy during the non-thermal phase, was associated with a CME, but no type II burst was recorded. During both events, in addition to the two-ribbon flare process an interaction was observed between the flaring arcade and an emerging magnetic flux region of opposite polarity next to the dominant leading sunspot. The arcade flare seems to stimulate the reconnection process in an `emerging flux-type' configuration, which significantly contributes to the energy release. This regime is characterized by the quasiperiodic injection of electron beams into the surrounding extended field line systems. The repeated beam injections excite pulsating broadband radio emission in the decimetric-metric wavelength range. Each radio pulse is due to a new electron beam injection. The pulsation period (seconds) reflects the spatial scale of the emerging flux-type field configuration. Since broadband decimetric-metric radio pulsations are a frequent radio flare phenomenon, we speculate that opposite-polarity small-scale flux intrusions located in the vicinity of strong field regions may be an essential component of the energy release process in dynamic flares.  相似文献   
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