The chemical composition and structure of 30 Doradus

Spectrophotometry of many regions within 30 Doradus in the Large Magellanic Cloud provides chemical abundances and densities for this nebular complex. The helium to hydrogen abundance ratio is about one-tenth by number and the heavier elements are underabundant compared to Orion, with nitrogen showing the greatest deficit. The forbidden lines of singly-ionized sulphur show wide density variations across this object. The distribution of the intensities in these sulphur lines suggests that supernova shocks may have played an important role in producing the composite appearance of this giant HII region.     

Early diagenetic remineralization of sedimentary organic C in the Gulf of Papua deltaic complex (Papua New Guinea): Net loss of terrestrial C and diagenetic fractionation of C isotopes

Oceania supplies ∼40% of the global riverine flux of organic carbon, approximately half of which is injected onto broad continental shelves and processed in shallow deltaic systems. The Gulf of Papua, on the south coast of the large island of New Guinea, is one such deltaic clinoform complex. It receives ∼4 Mt yr⁻¹ particulate terrestrial organic carbon with initial particle C_org loading ∼0.7 mg m⁻². C_org loading is reduced to ∼0.3 mg m⁻² in the topset-upper foreset zones of the delta despite additional inputs of mangrove and planktonic detritus, and high net sediment accumulation rates of 1-4 cm yr⁻¹. Carbon isotopic analyses (δ¹³C, Δ¹⁴C) of ΣCO₂ and C_org demonstrate rapid (<100 yr) remineralization of both terrestrial (δ¹³C <−28.6) and marine C_org (δ¹³C ∼−20.5) ranging in average age from modern (bomb) (Δ¹⁴C ∼60) to ∼1000 yr (Δ¹⁴C ∼−140). Efficient and rapid remineralization in the topset-upper foreset zone is promoted by frequent physical reworking, bioturbation, exposure, and reoxidation of deposits. The seafloor in these regions, particularly <20 m, apparently functions as a periodically mixed, suboxic batch reactor dominated by microbial biomass. Although terrestrial sources can be the primary metabolic substrates at inshore sites, relatively young marine C_org often preferentially dominates pore water ΣCO₂ relative to bulk C_org in the upper foreset. Thus a small quantity of young, rapidly recycled marine organic material is often superimposed on a generally older, less reactive terrestrial background. Whereas the pore water ΣCO₂ reflects both rapidly cycled marine and terrestrial sources, terrestrial material dominates the slower overall net loss of C_org from particles in the topset-upper foreset zone (i.e. recycled marine C_org leaves little residue). Preferential utilization of C_org subpools and diagenetic fractionation of C isotopes supports the reactive continuum model as a conceptual basis for net decomposition kinetics. Early diagenetic fractionation of C isotopes relative to the bulk sedimentary C_org composition can produce changes in ¹⁴C activity independent of radioactive decay. In the Gulf of Papua topset-upper foreset, Δ¹⁴C of pore water ΣCO₂ averaged ∼ 300‰ greater than C_org sediment between ∼1-3 m depth in deposits. Diagenetic fractionation and decomposition aging of sedimentary C_org compromises simple application of ¹⁴C for determination of sediment accumulation rates in diagenetically reactive deposits.     

A prolonged flare in the blazar 3C 454.3

We present an analysis of data from multi-frequency monitoring of the blazar 3C 454.3 in 2010–2012, when the source experienced an unusually prolonged flare with a duration of about two years. This corresponds to the orbital period of the companion in a scenario in which two supermassive black holes are present in the nucleus of 3C 454.3. The flare’s shape, duration, and amplitude can be explained as a result of precession, if the plane of the accretion disk and the orbital plane of the binary are coincident. We detected small-scale structure of the flare, on time scales of no more than a month. These features probably correspond to inhomogeneities in the accretion disk and surrounding regions, with sizes of the order of 10¹⁵ cm. We estimated the size of the accretion disk based on the dynamical and geometrical parameters of this binary system: its diameter is comparable to the size of the orbit of the supermassive binary black hole, and its thickness does not exceed the gravitational radius of the central black hole. The presence of characteristic small-scale features during the flare makes it possible to estimate the relative time delays of variations in different spectral ranges: from gamma-ray to millimeter wavelengths.     

Anatomy of the Mondoñedo Nappe basal shear zone (NW Spain)

This paper analyses a major shear zone from the Iberian Hercynian belt which forms the basal thrust of the Mondoñedo Nappe. The shear zone developed by ductile deformation under amphibolite facies metamorphic conditions and later by brittle-ductile deformation in greenschists facies. Folds in the shear zone are asymmetric, very tight, 1C or similar class and frequently developing sheath geometries. The sheath folds originated by non-coaxial flow superimposed on earlier irregularities. The fabric of quartzitic rocks in the shear zone changes from bottom to top from ultramylonites through blastomylonitic rocks to non-mylonitic tectonites. c-axis fabrics vary across the shear zone, but show a dominant monoclinic symmetry. The blastomylonitic rocks include the fabrics representing the highest temperatures. The main foliation of the schists results from flattening of an earlier foliation, recording occasional microfolds. The use of different kinematic criteria has allowed an analysis of their validity as well as an assessment of movement direction towards the foreland of the orogen.     

Dissolved Al in sediments and waters of the East China Sea: Implications for authigenic mineral formation

Numerous previous studies indicate that several different authigenic aluminosilicates form in the oceans. In this study we show, using dissolved Al distributions in sediments and waters from the nearshore regions of the East China Sea, that the process of aluminosilicate formation probably begins rapidly upon contact of detrital clays with seawater. Statistical analyses of dissolved Al-Si-H⁺ relations in surface sediments indicate that the minerals forming in East China Sea sediments low in dissolved Fe are dioctahedral chlorites with an average composition EX_0.91Mg_0.77Al_5.0Si_2.7O₁₀(OH)₈ (where EX = exchangeable + 1 cation). This composition is also consistent with dissolved Al and Si measurements as a function of salinity in turbid overlying waters. Results suggest a dissolution—reprecipitation mechanism for clay mineral reconstitution. This mechanism can help to explain why different authigenic clays are found in different areas of the oceans. In the East China Sea the total amount of authigenic clays present must constitute a very minor fraction of the bottom sediments. Thus, the formation of these minerals has a relatively small impact upon dissolved Si distributions. Clay mineral reconstitution in nearshore regions may provide a mechanism for buffering sediments and overlying waters with respect to pH, as the composition of minerals formed should be a direct function of the H⁺ activity in the surrounding environment.     

The importance of relict burrow structures and burrow irrigation in controlling sedimentary solute distributions

Some areas of the seafloor, particularly the deep sea, are characterized by large numbers of apparently uninhabited or relict burrow structures formed by macrobenthic organisms. Because of low sedimentation rates or lack of physical disturbance these structures are stable for long periods of time and could potentially influence solute diffusion patterns in surface sediments. A two-dimensional diffusionreaction model which allows for diffusive rather than advective transport within stagnant, water-filled burrows demonstrates that, in the absence of advective irrigation, relict burrow structures are unlikely in most cases to significantly alter average solute distributions from those predicted by one-dimensional vertical models. This conclusion assumes changes in diffusive transport properties alone and does not account for any effects of relict structures on reaction rates or physical ventilation of deposits by bottom currents. Significant changes (≥5%) in solute distributions are generally produced only when the ratio of the halfdistance between burrows to relict burrow radii is ≤10 and sedimentary diffusion coefficients are ≤60% that in free solution. Because solute distributions in stagnant burrow waters are nearly that in surrounding sediment, sediment-water solute fluxes are also essentially unaffected by relict burrows except at extremely high abundances or fairly large differential diffusion rates between sediment and free solution. In contrast, even at low abundance, biologically irrigated or physically ventilated burrows produce major changes in solute transport and build-up patterns.     

Monochromatic photographs of giantHii regions in the Magellanic Clouds

Narrow band-pass direct photographs have been secured of the central region of 30 Doradus and of several other nebulosities in the Magellanic Clouds. We have utilized an image tube camera attached to the Yale one-meter telescope at the Cerro Tololo Interamerican Observatory. Interference filters whose band passes were selected to allow for the radial velocities of the Magellanic Clouds have been utilized to record monochromatic images of [Nii] 6584, H, Hei 5876, and [Oiii] 5007. In 30 Doradus the main filamentary structures appear to be very similar in H, Hei, [Nii], and [Oiii] at least in the inner regions where most spectroscopic measurements have been made. The features appear to be material bounded rather than radiation bounded and the excitation differences are very small. Likewise, in NGC 346 in the Small Magellanic Cloud the [Oiii] and H images are very similar, but in N44 in the Large Magellanic Cloud excitation differences do appear. The implications of these observations for chemical compositions of nebulosities in the Magellanic Clouds would appear to be that spectroscopic and scanner studies should be supplemented by monochromatic photographs. Some nebulosities can be handled by simple models while for others excitation differences must be taken into account.Guest investigators at Cerro Tololo Interamerican Observatory operated by the Association of Universities for Research in Astronomy under contract with the National Science Foundation     

安徽女山麻粒岩包体：矿物学特征、下地壳地温曲线及其成因意义

女山玄武岩中麻粒岩包体的主要矿物组合为 Opx+Cpx+Pl,均呈条带状构造 ,具有细粒粒状变晶结构或不等粒结构。女山麻粒岩包体的斜方辉石及单斜辉石的化学成分都非常相似于华北太古代麻粒岩地体 ,而明显区别于汉诺坝麻粒岩包体。通过对世界上含石榴石麻粒岩的检验 ,表明 Wells(1977) :二辉石温度计与 Mc Carthy & Pati～no Douce(1998)的 Cpx+Pl+Qz压力计的温压计组合是计算麻粒岩平衡温压的可行方法 ,并得到了女山麻粒岩包体平衡温度分布于 80 9～ 899℃之间 ,主要集中于 85 0± 2 0 C,平衡压力为 0 .6 0～ 0 .95 GPa。由麻粒岩包体的平衡温压所建立起的女山地区下地壳地温曲线与 Xuet a1.(1998)建立的上地幔地温曲线上延部分非常吻合。根据地温线推得的“岩石学”Moho面深度为 31km土 ,与“地震”Moho面深度相一致 ,表明女山地区不具有明显的壳幔过渡带。女山地区缺乏强烈的底侵作用以及麻粒岩包体的特征矿物化学成分暗示了女山麻粒岩包体可能来源于华北克拉通结晶基底     

Theoretical models of planetary nebulae

Sets of theoretical models of spherically symmetrical gaseous nebulae are calculated for a fixed chemical composition and with central star, energy distributions given by Cassinelli (1971) and by Kunasz, Mihalas and Hummer (1975). A central region of constant densityN _H=100 cm^–3 is surrounded by a broken shell consisting of zones of different density and optical thickness. It is found that for a fixed chemical composition and central star flux, a considerable range can be found in the emitted fluxes of certain lines such as 4686 which are often used to fix the level of excitation of a nebula. Although it is possible to produce models yielding a variety of nebular line ratios in this way, these truncated inhomogeneous shell models have not reproduced the integrated spectra of nebulae that simultaneously show extreme features of high and low excitation with great strength-e.g. [Nii], [Oii] and 4686 Heii.