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We investigate specific models for a dark energy universe leading to Quasi-Rip and Pseudo-Rip cosmologies. In the Quasi-Rip model the equation of state parameter w is less than ?1 in the first stage, but becomes larger than ?1 in the second stage. In the Pseudo-Rip model the Hubble parameter tends to a constant value in the remote future, although w is always less than ?1. Conditions for the appearance of the Quasi-Rip and the Pseudo-Rip in terms of the parameters in the equation of state are determined. Analogies with the theory of viscous cosmology are discussed. 相似文献
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Iver M. Brook 《Estuaries and Coasts》1979,2(1):54-58
A lightweight, portable suction dredge has been used for five bottom types which usually present problems to benthic investigators. Water depth ranged from 0.25 m to 5 m. By use of a 0.25 m2 quadrat or using the suction end as a probe with the depth of penetration limited by a collar, quantitative samples were taken in coarse sand, fine flocculent mud, dense turtle grass (Thalassia testudinum), sparse turtle grass over coralline rubble (Porites sp.) and carbonate rock with an overlay of shell rubble. The samples consisted of the material retained by a collecting bag attached to the suction dredge. None of the commonly used benthic sampling devices could obtain samples at all stations. 相似文献
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The partial molal volume of silicic acid () in 0.725 M NaCl at 1°C was calculated from the measured volume change (Δ) due to the neutralization of anhydrous sodium metasilicate with HCl and the and obtained from the literature. , determined under experimental conditions of pH = 2.2, compares favorably with calculated from the measured volume change due to the hydrolysis of the meta-silicate salt at pH = 11 and from the partial molal volume due to electrostriction () of water by charged Si species present in the solution at the high pH. This agreement lends support to a semiempirical model for calculating in developed by Millero (1969). in 0.725 M NaCl needed for this calculation was also determined in this work. The rate of polymerization of Si(OH)4 at 1°C was monitored to insure that the monomer Si(OH)4 was the main Si species present during the determination of by neutralization of the alkali silicate. determined in this study compares favorably with the value calculated from high pressure solubility measurements. 相似文献
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Some aspects of viscous cosmological models, mainly of Bianchi type-I, are studied, in particular with the purpose of trying to obtain a natural explanation of why the entropy per baryon in the universe, ~ 109, is so large. Using the FRW metric it is first shown, in agreement with previous workers, that the expressions for the bulk viscosity as derived from kinetic theory in the plasma era is incapable of explaining the large value of. However it is possible to imagine the viscosity to be an impulse viscosity operative in one or several phase transitions in the early universe. This is the main idea elaborated on in the present paper. It is shown that in thek = 0 FRW space, an impulse bulk viscosity infl ~ 1060 g cm–1 s–1) acting at the phase transition at the end of the inflationary epoch corresponds to the correct entropy. If the space is anisotropic, it is natural to exploit the analogy with classical fluid dynamics to introduce the turbulent viscosity concept. This is finally discussed, in relation to an anisotropy introduced in the universe via the Kasner metric. 相似文献
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With the rising cost of oil the electric power generating companies are turning to coal as a fuel source. Large amounts of fly ash are produced as a by product of coal combustion. This fly ash must then be disposed of, with the oceans being considered an alternative to land fill disposal. This research investigated the sorptive behavior of the surface-associated arsenic and utilized the results to project arsenic's impact on the water column during the ocean disposal of fly ash.Several acid digests were investigated to determine an effective method of arsenic recovery from fly ash. Of these, the HCl digest was the most effective technique, yielding 100% arsenic recoveries from fly-ash particles. The arsenic content of the fly ashes studied varied from 69 ± 11 μg g−1 to 323 ± 24 μg g−1, reflecting differences in the arsenic content of the source coal. In both seawater and freshwater there is an increase in arsenic desorption with increasing pH. The greatest release of arsenic occurred at pH 12 with generally over 80% of the surface arsenic released.Fly ash in contact with seawater and freshwater can exhibit either acidic or alkaline tendencies depending upon the soluble elemental composition on the surface of the flyash particle. The acidic ashes were shown to leach a greater percentage of arsenic (16.9%) than the more alkaline ashes (8.2%). During these leaching studies in seawater, arsenic was found to leach in both the pentavalent and trivalent oxidation state. The pentavalent state was predominant, comprising 77% of the arsenic initially desorbed.The dissolution in seawater of arsenic was utilized to assess the possible impact of the ocean disposal of fly ash. Based upon these data it appears that the natural levels of arsenic in the water column would not be significantly increased. Further research is needed on the fate of fly-ash particles in marine sediments. 相似文献
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Eric C. Brevik 《Journal of Paleolimnology》1999,22(3):253-257
Several discontinuous, segmented strandlines that mark the former shores of Lake Agassiz can be found in eastern North Dakota. These strandlines are difficult to map and correlate because of their segmented nature. Better mapping would benefit researchers working on a number of problems involving Lake Agassiz including dating the strandlines, reconstructing the lake's history, and calculation of asthenosphere viscosity beneath the Lake Agassiz basin. Elongated soil delineations representing beach-indicative soils with a north-northwest trend and extending from currently mapped areas of the Herman strandline were identified on Grand Forks County soil maps. This information was combined with the geologic map of Grand Forks County in an attempt to better define the location of the Herman strandline in the southern part of the county. This approach worked well, and it is recommended that similar studies be attempted on other Lake Agassiz strandlines in North Dakota and the surrounding area. 相似文献
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Detailed simulations based on quasi-linear theory are presented for fundamental ( $f_{\rm p}$ ) emission of type III bursts produced in non-Maxwellian, suprathermal, background coronal plasma by injection of energetic electrons during flares with a power-law or Maxwellian velocity distribution, where $f_{\rm p}$ is the electron plasma frequency. The background plasma is assumed to have a kappa (κ) distribution, as inferred from solar wind data and proposed by theories for the corona and solar wind. The predicted type III beam speeds, Langmuir wave levels, and the drift rate and flux of $f_{\rm p}$ emission are strongly sensitive to the presence of suprathermal background electrons in the corona. The simulations show the following results. i) Fast beams with speeds $v_{\rm b}>0.5c$ are produced for coronal background electrons with small κ (κ?5) by injected electrons with power-law spectra. ii) Moderately fast beams with $v_{\rm b} \approx0.3\,\mbox{--}\,0.5c$ are generated in coronal plasma with κ?8 by injections of power-law or Maxwellian electrons. iii) Slow beams with $v_{\rm b}<0.3c$ are produced for coronal background electrons with large κ (κ>8), including the asymptotic limit κ→∞ where the electrons are Maxwellian, for both power-law and Maxwellian injections. The observation of fast type III beams (with $v_{\rm b}>0.5c$ ) thus suggests that these beams are produced in coronal regions where the background electron distribution has small κ by injected electrons with power-law spectra, at least when such beams are observed. The simulations, from the viewpoint of type III bursts, thus support: i) the presence, at least sometimes, of suprathermal background electrons in the corona and the associated mechanisms for coronal heating and solar wind acceleration; ii) power-law spectra for injected energetic electrons, consistent with observations of such electrons in situ and of X-ray emission. 相似文献