Photoionising shocks in SNRs and AGN     

Michael A. Dopita 《Astrophysics and Space Science》1995,233(1-2):215-230

A high velocity radiative shock, or one moving into high-metallicity gas, provides an efficient means to generate a strong local UV photon field. The optical emission from the shock and precursor region is dominated by the photoionised gas, rather than by the cooling region, and the total optical + UV emission scales as the mechanical energy flux through the shock. In this paper, such models are applied to oxygen-rich supernova remnants and AGN. For AGN, the degree of magnetic support in the post-shock gas is an important parameter. LINER and cooling flow spectra can be understood as resulting from high velocity shocks without precursors, while Seyfert 1.5–2 galaxy emission line ratios result from high velocity shocks with their photoionised precursor HII regions. This model explains the problem of the high electron temperatures observed in both classes of object.  相似文献   

Internal shocks in a relativistic wind as a source for gamma-ray bursts?     

R. Mochkovitch  V. Maitia  R. Marques 《Astrophysics and Space Science》1995,231(1-2):441-444

We investigate the recent proposal made by Rees and Mészáros (1994) that GRBs result from internal shocks in the relativistic wind emerging from two coalesced neutron stars. Using a simple model of that wind, where a large number of layers with different Lorentz factors interact through a series of mildly relativistic shocks we compute the efficiency of the process and the time profile of the resulting burst. We show that a great variety of profiles can be obtained using plausible initial distributions of Lorentz factors in the wind. However, the rather low overall efficiency (< 10%) of the process and limits imposed on the burst duration can be used to put severe constraints on the nature of the energy source.  相似文献   

An interview with C.V. Theis     

John D. Bredehoeft 《Hydrogeology Journal》2008,16(1):5-9

  相似文献   

Enacting things through numbers: Taking nature into account/ing     

Kristin Asdal 《Geoforum》2008,39(1):123-132

In this article I make use of a combination of actor-network-theory, governmentality studies and feminist studies of science to show how nature is done or enacted within politics and administration. In particular I show how it relates to the theories and practices of economics and accounting. I explore the process by which the ‘critical limits’ of nature under the impact of acidification was created as a part of the politics and negotiations about acid rain. I demonstrate that even though the outcome was not ‘Nature’ as such, understood as a form of moral high-ground, the effect of this process was to produce ‘a nature as a whole’, in a process of unification. This I argue can only be understood relationally: ‘Nature’ is taken into account by way of accounting. In doing this I engage with Latour’s work on the politics of Nature and argue that nature is not necessarily such a deadly tool to politics as is sometimes taken for granted. Before we throw Nature out with our empirical studies of sciences, natures and politics, in the plural, we need to look first at how Nature-wholes emerge, are enacted, and take part in politics.  相似文献   

Nonlinear magneto-acoustic waves in the solar atmosphere     

Csar A. Mendoza-Briceo  Miguel H. Ibez  Valery M. Nakariakov 《Dynamics of Atmospheres and Oceans》2001,34(2-4)

The weakly nonlinear evolution of quasi-isentropic magnetoacoustic waves in the solar atmosphere is analyzed. The plasma is assumed to be initially homogeneous, in thermal equilibrium and with a straight and homogeneous magnetic field frozen in. Additionally, the plasma is assumed to be cooled by the standard cooling function in the range of 10⁴ K<T<10⁷ K and heated by a mechanism which is proportional to the density and temperature. The range of temperature where the plasma is isentropically unstable, the e-folding time for thermal instability and the corresponding time and length-scale for wave breaking are found.  相似文献   

Auswirkung von Schwermetallgemischen auf die biologische Behandlung naphthalinsulfonsäurehaltiger Abwässer     

H. Pack  D. C. Hempel 《洁净——土壤、空气、水》1997,25(6):306-310

Effect of Mixtures of Heavy Metals on the Biological Treatment of Sewages Containing Naphthalenesulfonic Acid Biological wastewater treatment processes can be destabilized considerably by heavy metals. In this investigation, the effect of loadings of heavy metals on the degradation of naphthalene-2-sulfonic acid (2NS) by immobilized bacteria in continuously operated airlift-loop reactors was studied. Shock loadings with mixtures of cadmium and nickel, or cadmium and zinc, respectively, resulted in increases in inhibition compared to those observed with the single metals. In contrast, the 2NS-degradation was less inhibited by shock loadings with mixtures of nickel and zinc than by the single metal ions. Repeated shock loadings up to 100 mg L^?1 nickel and 1000 mg L^?1 zinc effected an adaptation of the microorganisms. Continuous loadings with up to 10 mg L^?1 cadmium and nickel each, or with 50 mg L^?1 nickel and 210 mg L^?1 zinc, respectively, did not inhibit the degradation of 2NS. The permanent loadings led to an adaptation of the bacteria with an increased biosynthesis of proteins from 0.2 to 0.5 g g^?1 cell dry weight. However, if the immobilized cells were incubated with mixtures of cadmium and nickel, the specific polysaccharide content decreased to less than 0.2 g g^?1 cell dry weight, resulting in a detachment of the biofilms.  相似文献   

太湖三山岛击变岩的发现及其意义   总被引：7，自引：0，他引：7  

傅成义  王赐银 《地理学报》1990,45(2):253-256,T002

太湖三山岛击变岩,宏观特征表现为崩解裂理;微观特征出现石英颗粒的晶体弯曲、多组微页理的面型特征、机械双晶、震变玻璃、焦石英及柯石英相变产生的放射状裂隙等,是陨石撞击地表的一种特殊地质现象。它的发现,是太湖成因研究中的重要进展。  相似文献   

H2 fluorescence in HH 7 and DR 21     

A. Fernandes  P. Brand  M. Burton 《Astrophysics and Space Science》1995,233(1-2):45-50

We present evidence for Ly pumping of the Lyman band system of molecular hydrogen in Herbig-Haro 7 and the bipolar outflow DR 21. For this study we have measured several vibrational-rotational emission lines of H₂ whose energy levels are widely spaced and ranging from 6000 (v = 1) to 25000 Kelvin (v = 4). We show that the near-infrared H₂ emission from the shocked gas in HH 7 can be well described by a bow C-type shock. The enhanced emission observed from the higher energy levels (v > 3) can be well modelled by employing the Ly pumping mechanism.In the DR 21 outflow the multi-line study showed that different physical conditions exist in the eastern and western emission lobes. The higher H₂ line ratios measured in the eastern lobe suggests a higher Ly pump rate which may be locally produced in the fast bowshocks. The FUV radiation field emanating from the central HII regions may in addition be exciting the Lyman and Werner bands of H₂ in the molecular lobes.We show that the observed H₂ emission can be interpreted in terms of a simple model consisting of a C-type bowshock, which produces the low excitation H₂ emission, and a FUV radiation field with enough Ly line radiation to produce the high excitation H₂ emission through fluorescence.  相似文献   

Scydmobisetia gen. nov., the first definite Glandulariini from Upper Cretaceous Burmese amber (Coleoptera: Staphylinidae: Scydmaeninae)     

《Cretaceous Research》2016

The Glandulariini (=Cyrtoscydmini) includes about 60 genera comprising over 70% of the extant species of Scydmaeninae. This successful group is today very common and abundant in forests of all continents. However, while extinct representatives of much smaller extant tribes, as Clidicini, Eutheiini and Cephenniini, were described from Cretaceous deposits, named genera and species of Glandulariini were so far known only from much younger Baltic, Sicilian and Dominican ambers. Here we report the first genus and species of definite Glandulariini from the Upper Cretaceous Burmese amber, Scydmobisetia vetutissima Jałoszyński and Yamamoto, gen. and sp. nov. Scydmobisetia is the first known glandulariine beetle with a pair of very long vertexal sensilla chaetica, previously not found in this tribe, but common among unrelated Staphylinidae. The new genus shows similarities to the extant genera Anthicimimus, Sciacharis, Spinosciacharis and Horaeomorphus, but S. vetutissima has protibial modifications typical of males of some extant species of Euconnus. We discuss the apparent disproportion in the oldest fossil record of various tribes of scydmaenines as a result of identification problems, and not the lack of known fossils.  相似文献   

Cretaceous amber inclusions of Spain and Myanmar demonstrate early diversification and wide dispersal of Cephenniitae (Coleoptera: Staphylinidae: Scydmaeninae)     

《Cretaceous Research》2016

The taxonomic status of previously misplaced species of an ant-like stone beetle from Spanish amber (Albian) is clarified. Specimens of Kachinus magnificus (originally placed as incertae sedis within Scydmaenitae) were re-examined and their characters were found different from those of the type species of Kachinus from Myanmar amber. Consequently, Archeutheia gen. nov. is proposed to accommodate the Spanish species, resulting in Archeutheia magnifica comb. nov. Moreover, in a comprehensive phylogenetic analysis Archeutheia was placed as a sister group to extant Eutheia, within the tribe Eutheiini of Cephenniitae. A specimen of an undetermined genus from Myanmar amber clearly belonging in Cephenniini is also recorded. Both taxa represent the first definite Cretaceous Cephenniitae, a supertribe whose recent members are distributed on all continents but are especially diverse in the Oriental and East Palaearctic regions. This finding demonstrates a diversification of two presently most species-rich tribes of Cephenniitae already in Early Cretaceous. Archeutheia is strikingly similar to the extant species of Eutheia and Veraphis, showing male dimorphic characters (modified protrochanters) and antennal cavities characteristic of Palaearctic Eutheiini. This fact suggests a long morphological stability in the supertribe. A previously proposed hypothesis of an early presence of the Cephenniitae in the Northern Hemisphere is for the first time supported by the fossil record, and the palaeolocalities (western Europe and Southeast Asia) demonstrate a wide distribution of Cephenniitae in the Cretaceous and an early split of its ancestral lineage.  相似文献