Owing to gravitational instability, an initially Gaussian density field develops non-Gaussian features as the Universe evolves. The most prominent non-Gaussian features are massive haloes, visible as clusters of galaxies. The distortion of high-redshift galaxy images because of the tidal gravitational field of the large-scale matter distribution, called cosmic shear, can be used to investigate the statistical properties of the large‐scale structure (LSS) . In particular, non-Gaussian properties of the LSS will lead to a non-Gaussian distribution of cosmic-shear statistic. The aperture mass ( M ap) statistics, recently introduced as a measure for cosmic shear, is particularly well suited for measuring these non-Gaussian properties. In this paper we calculate the highly non-Gaussian tail of the aperture mass probability distribution, assuming Press–Schechter theory for the halo abundance and the 'universal' density profile of haloes as obtained from numerical simulations. We find that for values of M ap much larger than its dispersion, this probability distribution is closely approximated by an exponential, rather than a Gaussian. We determine the amplitude and shape of this exponential for various cosmological models and aperture sizes, and show that wide-field imaging surveys can be used to distinguish between some of the currently most popular cosmogonies. Our study here is complementary to earlier cosmic-shear investigations, which focused more on two- and three-point statistical properties. 相似文献
Submerged macrophyte vegetation has been mapped in four calcareous groundwater-fed streams in Bavaria (southern Germany) in order to compare and assess two different methods of river bioindication. The first one, the trophic index of macrophytes (TIM), is a tool to assess the trophic status of running waters. In contrast, the reference index (RI) is an ecological index which evaluates the difference between a reference community and the actual submerged vegetation, depending on the river type, as required by the Water Framework Directive. Water nutrient concentrations were measured once at selected sites in all water courses.The TIM reflects water phosphorus concentrations, accounting also for nutrients enrichment in the sediment, and is not influenced by shading, depth, substrate and flow velocity of the water course. The TIM is very sensitive to small variations in P concentration when the P level is low, while the index tends to a maximum as soluble reactive phosphorus (SRP) and total phosphorus (Ptot) exceed a certain value.The RI indicates river ecological status which is not only influenced by trophic status but by every factor leading to a deviation of the actual macrophyte community from the reference community. In the investigated rivers the RI indicated reduced flow velocity caused by milldams and shading by riparian vegetation, in addition to trophic status.In rivers that are at the boundary between two different river types, classification of river type can play a crucial role for river status assessment. Incorrect classification of river type can lead to both, a “too good” and “too bad” assessment. 相似文献
Tourmaline alteration and high boron contents are typical features of the magmatic-hydrothermal systems of the Bolivian tin
province. The average boron content in melt inclusions of quartz phenocrysts from tin porphyry systems is 225 ppm (1σ-variation
range: 110–420 ppm; n=12) and suggests a magmatic boron input to the hydrothermal tin systems, and not shallow post-magmatic leaching of boron
from pelitic country rocks. Boron data from melt inclusions correlate positively with cesium, rubidium and arsenic, and negatively
with lithium, titanium and zirconium, and define magmatic fractionation trends. The generally high B, As, Cs and Li contents
in melt inclusions suggest involvement of pelitic source lithologies undepleted in these fluid-mobile components, i.e. first-cycle
metamorphic rocks. Magmatic fractionation modified the trace-element contents within a one-log-unit range. Bulk-rock Nd isotope
data (ɛNd−5 to −10) are in agreement with the dominantly intracrustal geochemical signature of the Bolivian tin porphyry systems, but
also imply a variable but minor mantle input. The metallogeny of the tin belt is likely a consequence of intracrustal melting
of Lower Paleozoic pelitic and slightly carbonaceous source material, combined with an extended magmatic evolution. The long-lived
thermal preparation of the root zones of the silicic systems is provided by mafic magma which also leaves a chemical imprint
in the form of the hybrid dacitic bulk composition of the tin porphyry systems.
Received: 6 August 1998 / Accepted: 19 August 1999 相似文献
The relationship between the macrophyte vegetation and the nutrient concentration of the water and the sediment of a stream was studied. The small stream is fed by calcareous groundwater. The alteration in the macrophyte vegetation of the stream Rotbach from oligotrophic community towards more eutrophic species is associated with an increasing concentration of nutrients in the sediment. Particularly the concentration of SRP-P in the interstitial water changes significantly.
In terms of the macrophyte vegetation the stream can be divided into 4 floristic zones, A-D. The zones are labelled in a sequence according to their sediment's nutrient content. The chemical analyses of the water and the sediment show the highest concentrations in zone D. It is characterized by the presence of Zannichellia palustris. The zones A-C have almost the same very low nutrient concentration in the water but show a different content of nutrients in the sediment, particularly of the SRP-P in the interstitial water. Zone A which is dominated by Chara hispida shows the lowest SRP-P in the interstitial water. Within zone B which is characterized by Mentha aquatica and Nasturtium officinale and even more in zone C where Chara hispida is less abundant and Elodea canadensis occurs, the SRP-P content is elevated.
The nutrient concentration in the sediment is clearly associated with changes in the macrophyte vegetation of the stream Rotbach. 相似文献
Specialized to the Lie series based perturbation method of Kirchgraber and Stiefel (1978) a new computer algebra package called
ANALYTOS has been developed for constructing analytical orbital theories either in noncanonical or canonical form. We present
results on the (extended) Main Problem of orbital theory of artificial earth satellites and related issues. The order of the
solutions achieved is generally one order higher than those known from literature. Moreover, the analytical orbits have been
checked succesfully against precise numerical ephemerides.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
The numerical prediction of fog requires a very high vertical resolution of the atmosphere. Owing to a prohibitive computational effort of high resolution three dimensional models, operational fog forecast is usually done by means of one dimensional fog models. An important condition for a successful fog forecast with one dimensional models consists of the proper integration of observational data into the numerical simulations. The goal of the present study is to introduce new methods for the consideration of these data in the one dimensional radiation fog model PAFOG. First, it will be shown how PAFOG may be initialized with observed visibilities. Second, a nudging scheme will be presented for the inclusion of measured temperature and humidity profiles in the PAFOG simulations. The new features of PAFOG have been tested by comparing the model results with observations of the German Meteorological Service. A case study will be presented that reveals the importance of including local observations in the model calculations. Numerical results obtained with the modified PAFOG model show a distinct improvement of fog forecasts regarding the times of fog formation, dissipation as well as the vertical extent of the investigated fog events. However, model results also reveal that a further improvement of PAFOG might be possible if several empirical model parameters are optimized. This tuning can only be realized by comprehensive comparisons of model simulations with corresponding fog observations. 相似文献
We investigate how strong gravitational lensing in the concordance ΛCDM cosmology is affected by the stellar mass in galaxies. We extend our previous studies, based on ray tracing through the Millennium Simulation, by including the stellar components predicted by galaxy formation models. We find that the inclusion of these components greatly enhances the probability for strong lensing compared to a 'dark matter only' universe. The identification of the 'lenses' associated with strong-lensing events reveals that the stellar mass of galaxies (i) significantly enhances the strong-lensing cross-sections of group and cluster haloes and (ii) gives rise to strong lensing in smaller haloes, which would not produce noticeable effects in the absence of the stars. Even if we consider only image splittings ≳10 arcsec, the luminous matter can enhance the strong-lensing optical depths by up to a factor of 2. 相似文献
The constant‐head permeameter test (CHPT) is widely used in sandy samples as a standard method in the laboratory to investigate hydraulic conductivity (K). However, it neither can be used to consistently determine directional hydraulic conductivity (DHC) nor guarantee the comparability of measured K values of samples with different sizes. Therefore, this paper proposes an integrated laboratory method, called modified CHPT (MCHPT), for the efficient determination and verification of consistent DHC values in fine‐to‐medium sandy sediments, based on a new methodological framework. A precise and standardized procedure for preparing the experimental setup of MCHPT was conducted, based on the integrated experimental setup of CHPT and tracer tests. Moreover, a formula was yielded for the time‐optimized sample saturation control. In comparison with grain size‐based methods, the validity of consistent Kh and Kv values determined by MCHPT was convincing. 相似文献