Some regularities in the variation of the Balmer line profiles in the P Cyg spectrum

In the Coudé focus of the 2 m RCC telescope at the National Astronomical Observatory of the Bulgarian Academy of Science 47 spectrograms covering the range from 3500 to 4900 Å (about 1400 Å) with a reciprocal dispersion of 9 Å mm^–1 and a spectral resolution of 0.18 Å were obtained. The photometric and position behaviour of Balmer lines were investigated over a long time-scale, i.e. March 1981 to August 1982.The hydrogen line profiles were rectified in the way discribed by de Groot (1969). It is found that the absorption consists of three and sometimes four components. Their position behaviour may be expalined by the existence of two kinds of shells: pulsating and steadily expanding, and it is quite possible that shells of the first type may become shells of the second type in the outer parts of the P Cyg envelope.The total emission and absorption equivalent widths of the H11, H9, and H lines change with conspicuous minima and maxima. The amplitude of these variations increases with decrease in the upper quantum number. For example,W _tot ^abs change by about 38% for H and 22% for H9.Our data suggest a periodic change in the radial velocities, intensity of each separate absorption component, total equivalent widths and profiles.     

Evaluation of approaches to calculate debris-flow parameters for hazard assessment

Many different runout prediction methods can be applied to estimate the mobility of future debris flows during hazard assessment. The present article reviews the empirical, analytical, simple flow routing and numerical techniques. All these techniques were applied to back-calculate a debris flow, which occurred in 1982 at La Guingueta catchment, in the Eastern Pyrenees. A sensitivity analysis of input parameters was carried out, while special attention was paid to the influence of rheological parameters. We used the Voellmy fluid rheology for our analytical and numerical modelling, since this flow resistance law coincided best with field observations. The simulation results indicated that the “basal” friction coefficients rather affect the runout distance, while the “turbulence” terms mainly influence flow velocity. A comparison of the velocity computed on the fan showed that the analytical model calculated values similar to the numerical ones. The values of our rheological parameters calibrated at La Guingueta agree with data back-calculated for other debris flows. Empirical relationships represent another method to estimate total runout distance. The results confirmed that they contain an important uncertainty and they are strictly valid only for the conditions, which were the basis for their development. With regards to the simple flow routing algorithm, this methods could satisfactorily simulate the total area affected by the 1982 debris flow, but it was not able to directly calculate total runout distance and velocity. Finally, a suggestion on how different runout prediction methods can be applied to generate debris-flow hazard maps is presented. Taking into account the definition of hazard and intensity, the best choice would be to divide the resulting hazard maps into two types: “final hazard maps” and “preliminary hazard maps”. Only the use of numerical models provided final hazard maps, because they could incorporate different event magnitudes and they supplied output-values for intensity calculation. In contrast, empirical relationships and flow routing algorithms, or a combination of both, could be applied to create preliminary hazard maps. The present study only focussed on runout prediction methods. Other necessary tasks to complete the hazard assessment can be looked up in the “Guidelines for landslide susceptibility, hazard and risk zoning” included in this Special Issue.     

Zircon U–Pb and Hf isotopic study of gneissic rocks from the Chinese Altai: Progressive accretionary history in the early to middle Palaeozoic

Gneissic rocks in the Chinese Altai Mountains have been interpreted as either Paleozoic metasedimentary rocks or Precambrian basement. This study reports geochemical and geochronological data for banded paragneisses and associated gneissic granitoids collected along a NE–SW traverse in the northwestern Chinese Altai. Petrological and geochemical data suggest that the protoliths of the banded gneisses were possibly immature sediments with significant volcanic input and that the gneissic granitoids were derived from I-type granites formed in a subduction environment. Three types of morphological features can be recognized in zircons from the banded gneisses and are interpreted to correlate with different sources. Zircons from five samples of banded paragneiss cluster predominantly between 466 and 528 Ma, some give Neoproterozoic ages, and a few yield discordant Paleoproterozoic to Archean ages. Zircon Hf isotopic compositions indicate that both juvenile/mantle and crust materials were involved in the generation of the source rocks from which these zircons were derived. In contrast, zircons occur ubiquitously as elongated euhedral prismatic crystals in the four samples of the gneissic granitoids, and define single populations for each sample with mean ages between 380 and 453 Ma. The general absence of Precambrian inheritance and positive zircon ?Hf values for these granitoids suggest insignificant crustal contribution to the generation of the precursor magmas. Our data can be interpreted in terms of a progressive accretionary history in early to middle Palaeozoic times, and the Chinese Altai may possibly represent a magmatic arc built on a continental margin dominated by Neoproterozoic rocks.     

Phytoreduction and volatilization of mercury by ascorbate in Arabidopsis thaliana, European beech and Norway spruce

Mercury vapor (Hg⁰) emission from plants contributes to the atmospheric Hg cycle. Young barley (Hordeum vulgare L.) plants grown on a hydroponic cultivation medium containing Hg(II) have previously been shown to increase their Hg⁰ emission significantly by reduction of Hg(II) with endogenous ascorbic acid. Regarding the potential contribution to the Hg cycle from the vast forest-covered areas, it was important to investigate this mechanism in trees. The increase in Hg⁰ emission from young European beech plants cultivated on a HgCl₂ medium exceeded that from controls by ca. tenfold and was proportional to the Hg(II) concentration. From these experiments, a flux of 12.8 μg Hg⁰/h/m² was estimated at an exposure of the roots to 20 μM Hg(II). Mercury vapor release from homogenates of Norway spruce needles exceeded that from European beech leaves by a factor of 2.3–4, i.e. in proportion to the reported AA concentrations; the reduction was maximal at alkaline pH which is typical for AA. The 8.4-fold difference in Hg⁰ release between homogenates from wild-type Arabidopsis thaliana and from its AA-deficient mutant vtc 1-1 also paralleled the reported difference in AA levels of both species. It is concluded that the phytoreduction and vaporization of Hg by AA is an important mechanism as much for Hg detoxification in trees as for Hg emission to the atmosphere. The efficiency of this process seems to result from the optimal coordination of transfer and biochemical transformation of mercuric ions and Hg vapor. There is no evidence for a relevant difference in the mechanisms of biogenic Hg(II) reduction between grass plants and trees.     

Palaeobotanical evidence of wildfires in the Late Palaeozoic of South America – Early Permian, Rio Bonito Formation, Paraná Basin, Rio Grande do Sul, Brazil

Fossil charcoal, as direct evidence of palaeowildfires, has repeatedly been reported from several plant-bearing deposits from the Late Palaeozoic of the Northern Hemisphere. In contrast charcoal reports from the Late Palaeozoic deposits of the Southern Hemisphere are relatively rare in comparison to the Northern Hemisphere. Although the presence of pyrogenic coal macerals has repeatedly been reported from Late Palaeozoic coals from South America, no detailed anatomical investigations of such material have been published so far. Here is presented an anatomical analysis of charcoal originating from Early Permian sediments of the Quitéria Outcrop, Rio Bonito Formation, Paraná Basin, located in the central-eastern portion of Rio Grande do Sul, Brazil. This charcoal comes from two different coaly facies, and it was possible to scrutinize between three types, based on anatomical characters of the charcoal. Two of these charcoal types can be correlated to gymnosperm woods, and the other type corresponds to strongly permineralized bark with characteristic features of lycopsids. The presence of charcoal in different facies, ranging from parautochtonous to allochtonous origin, indicates that different vegetation types, i.e. plants which grew under wet conditions in the lowland as well as in the more dry hinterland, have experienced wildfires. Taking into account previous petrographic and lithological analyses from the facies in which the charcoal occurs and from the conditions of the wood and bark fragments, it was possible to speculate that the intensity of such wildfires most probably corresponds to forest-crown fires. Moreover, it is possible to state that wildfires have been a more or less common element in distinct Late Palaeozoic terrestrial ecosystems in the South American part of Gondwana. The data support previous assumptions on the occurrence of wildfires in the Early Permian of the Paraná Basin which were based solely on coal-petrographic data.     

Defect properties of albite

Knowledge of the defect properties of Lunar and Mercurian minerals has recently become important, with the advent of models which attempt to explain the formation of the thin exosphere of these celestial bodies. Here, we have calculated the formation energies of sodium and oxygen vacancies in the mineral albite (NaAlSi₃O₈), as well as the Schottky defect energy for the removal of a Na₂O unit. We have employed both the supercell and Mott–Littleton approaches, using Kohn–Sham density functional theory and classical interatomic potential methods. As well as reporting the defect energies and structures, we comment upon the relative merits of the methods used.     

Exploring the gap of the digital divide

While much of the literature related to the digital divide focuses on either technology penetration in developed countries or the introduction of new technology to the poor and disadvantaged in the developing world, this paper pays attention to the middle-classes in a developing country which is connected to the Internet but under poor conditions. The digital divide is examined by investigating how the uneven distribution of Internet connection influences distance education students’ participation in higher education. Empirically, the paper is informed by a qualitative study of distance education in Indonesia. The main conclusion is that while in more peripheral areas students may not gain much from the use of new technology, the use of this technology may be useful for the further development of such regions. In central areas the new technology seems to contribute to students’ study situations more effectively and the daily environment empowers the students’ study activities, rather than vice versa.     

How a court, a commissioner and a lobby group brought European transport policy to life in 1985

Until the mid-1980s, transport policy was considered by many as one of the least successful domains of the European integration project. However, from the early 1990s onwards, there are clear signs of a single European transport policy, along with the accompanying implementation of infrastructure projects. What is the explanation for such a change in pace? This paper aims to offer insight in these processes by looking at the mechanisms which form and transform this policy domain. To understand the state of a policy domain and its dynamics over time an institutional approach is taken. Two concepts in political science, ‘policy arrangements’ and ‘supranational governance’ are combined and used as a framework to analyse the European transport policy domain. This analysis describes the development of several elements: organisations, rules, the transnational society, power, resources, and the central transport discourse. It demonstrates that all of these elements have developed from an intergovernmental setting towards a more supranational one. This development was slow in the first decennia when European transport policy was rather passive, but it picked up speed in the 1980s and 1990s. In the pivotal year of 1985, pressure from the transnational society resulted in a rapid change of the rules, the resources and the discourse.     

Detection of free vertical convection and double-diffusion in groundwater monitoring wells with geophysical borehole measurements

Two algorithms for in-situ detection and identification of vertical free convective and double-diffusive flows in groundwater monitoring wells or boreholes are proposed. With one algorithm the causes (driving forces) and with the other one the effects (convection or double-diffusion) of vertical transport processes can be detected based on geophysical borehole measurements in the water column. Five density-driven flow processes are identified: thermal, solutal, and thermosolutal convection leading to an equalization, as well as saltfingers and diffusive layering leading to an intensification of a vertical density gradient. The occurrence of density-driven transport processes could be proven in many groundwater monitoring wells and boreholes; especially shallow sections of boreholes or groundwater monitoring wells are affected dramatically by such vertical flows. Deep sections are also impaired as the critical threshold for the onset of a density-driven flow is considerably low. In monitoring wells or boreholes, several sections with different types of density-driven vertical flows may exist at the same time. Results from experimental investigations in a medium-scale testing facility with high aspect ratio (height/radius = 19) and from numerical modeling of a water column agree well with paramters of in-situ detected convection cells.