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排序方式: 共有266条查询结果,搜索用时 93 毫秒
101.
Mubasher Jamil Yerlan Myrzakulov Olga Razina Ratbay Myrzakulov 《Astrophysics and Space Science》2011,336(2):315-325
The Modified Chaplygin Gas (MCG) model belongs to the class of a unified models of dark energy and dark matter. In this paper,
we have modeled MCG in the framework of f-essence cosmology. By constructing an equation connecting the MCG and the f-essence,
we solve it to obtain explicitly the pressure and energy density of MCG. As special cases, we obtain both positive and negative
pressure solutions for suitable choices of free parameters. We also calculate the state parameter which describes the phantom
crossing. 相似文献
102.
正1 Introduction Regosol in Eastern Siberia is intrazonal soil.In Priolkhonie region it occurs among chestnut soils,salt marshes and solonetzes.There are small information about Tagotskij hydrolaccolith in the research articles of geologists,archaeologists,and paleolimnologists when 相似文献
103.
A common way to construct a finite difference scheme is to satisfy a desired order of approximation, typically as high as
possible. For linear wave propagation problem approximation together with stability delivers convergence of the same order
as approximation. If a wave propagation proses is considered convergence to a plane wave solution can be derived analytically
by means of the dispersion analysis. However, mentioned techniques are applicable only to homogeneous media and provide no
knowledge of reflection/transmission coefficients. In this paper we prove that the only way to get second order accuracy of
the solution for media with discontinuous parameters is to use a conservative finite difference scheme of the second order,
and the only way to do this is to use the arithmetic mean for the density and the harmonic mean for the bulk modulus in the
vicinity of the interface. 相似文献
104.
The big Comacchio lagoons (NW Adriatic coast) have been experiencing a super-dense, long-term bloom of picocyanobacteria (PCB)
since 1985. This bloom has caused profound transformations in their ecosystem and has resulted in the loss of valuable fish
and clam resources. The composition, density and seasonal dynamics of this bloom and its impact on the ecosystem were studied
between spring and autumn 1995 and in the summer of 2001. The density of the blooming phytoplankton assemblages varied from
8 to 35 × 106 cells ml−1, and biomass from 20 to 40 g m−3, thus demonstrating a quasi-stable status since 1993. The share of pico + nanocyanobacterial fraction of the total phytoplankton
biomass was 98% in spring to early summer, and 92% in autumn. The remaining 0.2–5% comprised eukaryotic nano-algae. All components
of the animal food web were found to be drastically depleted in the lagoons. Their biomass range in the open lagoons areas
were: 2 to 20 mg m−3 of microzooplankton, 10 to 40 mg m−3 mesozooplankton, and 5 to 12 g m−2 macrozoobenthos. The share of filtering fauna in the whole ecosystem metabolism was less than 2%. The malfunction of the
deteriorated animal food web resulted in the hyper-accumulation of non-grazed microplankton biomass and detritus in the water
column and in bottom sediments. The sequence brought the acceleration of sulfide production and the accumulation of acid soluble
sulfides in the upper sediment layer of up to 700–800 mg S dm−3 of wet silt. The results of this study provide evidence that the state of ecological collapse continues in the lagoons since
1993. 相似文献
105.
The complex geology of Europa is evidenced by many tectonic and cryomagmatic resurfacing structures, some of which are “painted” into a more visible expression by exogenic alteration processes acting on the principal endogenic cryopetrology. The surface materials emplaced and affected by this activity are mainly composed of water ice in some areas, but in other places there are other minerals involved. Non-ice minerals are visually recognized by their low albedo and reddish color either when first emplaced or, more likely, after alteration by Europan weathering processes, especially sublimation and alteration by ionizing radiation. While red chromophoric material could be due to endogenic production of solid sulfur allotropes or other compounds, most likely the red substance is an impurity produced by radiation alteration of hydrated sulfate salts or sulphuric acid of mainly internal origin. If the non-ice red materials or their precursors have a source in the satellite interior, and if they are not merely trace contaminants, then they can play an important role in the evolution of the icy crust, including structural differentiation and the internal dynamics. Here we assume that these substances are major components of Europa's cryo/hydrosphere, as some models have predicted they should be. If this is an accurate assumption, then these substances should not be neglected in physical, chemical, and biological models of Europa, even if major uncertainties remain as to the exact identity, abundance, and distribution of the non-ice materials. The physical chemical properties of the ice-associated materials will contribute to the physical state of the crust today and in the geological past. In order to model the influence of them on the thermal state and the geology, we have determined the thermal properties of the hydrated salts. Our new lab data reveal very low thermal conductivities for hydrated salts compared to water ice. Lower conductivities of salty ice would produce steeper thermal gradients than in pure ice. If there are salt-rich layers inside the crust, forming salt beds over the seafloor or a briny eutectic crust, for instance, the high thermal gradients may promote endogenic geological activity. On the seafloor, bedded salt accumulations may exhibit high thermochemical gradients. Metamorphic and magmatic processes and possible niches for thermophilic life at shallow suboceanic depths result from the calculated thermal profiles, even if the ocean is very cold. 相似文献
106.
107.
The main incentives for Russia's and Ukraine's participation in the first commitment period of the Kyoto Protocol were its mechanisms. The opportunities that the anticipated post-2012 mechanisms will offer Russia and Ukraine are explored in light of the lessons from Joint Implementation (JI) and the Green Investment Scheme (GIS) during this first period. Four key factors that explain the success of these mechanisms are identified: the design of the mechanisms, the role of the private sector in their implementation, the coordination required, and the political will gained. Even though a weak rule of law, problems with policy implementation, and the ambiguous role of private-sector actors are not ‘make or break’ issues, they are likely to defer future mechanisms. Success and failure will, rather, hinge on the priority these factors are accorded by the top leadership. It is likely that simple mechanisms that only involve a few actors will be less complicated to set up and run than, for instance, emissions trading schemes (which require domestic burden sharing). Project-based options in which domestic actors have gained experience may be better suited. However, any lessons prior to the new mechanisms taking a clearer shape must be considered as preliminary.Policy relevanceThe Kyoto Protocol mechanisms, despite their problems, provided Russia and Ukraine with their main incentives for participation in the Protocol's first commitment period. As the chances that these countries will participate in the second commitment period seem slim, the opportunities that the anticipated post-2012 mechanisms will offer Russia and Ukraine are explored in light of the lessons from JI and GIS. The key factors that have determined the success and failure of these mechanisms are likely to be of relevance to future mechanisms. It is argued that – of the post-2012 options available – simple mechanisms with few actors involved should be chosen. Project-based options rather than emissions trading schemes may be more likely to succeed due to experience gained by domestic actors. 相似文献
108.
109.
Olga Solomina Vincent Jomelli Georg Kaser Alcides Ames Bernhard Berger Bernard Pouyaud 《Global and Planetary Change》2007,59(1-4):225
This paper is a comparison and compilation of lichenometric and geomorphic studies performed by two independent teams in the Cordillera Blanca, Peru, in 1996 and 2002 on 66 “Little Ice Age” moraines of 14 glaciers. Using eleven new control points, we recalibrated the initial rapid growth phase of the previously established Rhizocarpon subgenus Rhizocarpon growth curve. This curve was then used to estimate the age of “Little Ice Age” moraines. The time of deposition of the most prominent and numerous terminal and lateral moraines on the Pacific-facing side of the Cordillera Blanca (between AD 1590 and AD 1720) corresponds to the coldest and wettest phase in the tropical Andes as revealed by ice-core data. Less prominent advances occurred between AD 1780 and 1880. 相似文献
110.
The Source Regions of Impulsive Solar Electron Events 总被引:1,自引:0,他引:1
Benz Arnold O. Lin Robert P. Sheiner Olga A. Krucker Säm Fainberg Joe 《Solar physics》2001,203(1):131-144
Low-energy (2–19 keV) impulsive electron events observed in interplanetary space have been traced back to the Sun, using their interplanetary type III radiation and metric/decimetric radio-spectrograms. For the first time we are able to study the highest frequencies and thus the radio signatures closest to the source region. All the selected impulsive solar electron events have been found to be associated with an interplanetary type III burst. This allows to time the particle events at the 2 MHz plasma level and identify the associated coronal radio emissions. Except for 5 out of 27 cases, the electron events were found to be associated with a coronal type III burst in the metric wavelength range. The start frequency yields a lower limit to the density in the acceleration region. We also search for narrow-band spikes at the start of the type III bursts. In about half of the observed cases we find metric spikes or enhancements of type I bursts associated with the start of the electron event. If interpreted as the plasma emission of the acceleration process, the observed average frequency of spikes suggests a source density of the order of 3×108 cm–3 consistent with the energy cut-off observed. 相似文献