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Online reading behavior can be regarded as a "new" form of cultural capital in today’s digital world. However, it is unclear whether "traditional" mechanisms of cultural and social reproduction are also found in this domain, and whether they manifest uniformly across countries at different stages of development. This article analyzes whether the early home literacy environment has an impact on informational online reading behavior among adolescents and whether this association varies between countries with different levels of digitalization and educational expansion. Data from the 2009 Programme for International Student Assessment (PISA) were used for the empirical analyses. The results of regression models with country-fixed effects indicate a positive association between literacy activities in early childhood and informational online reading at age 15. This association was quite stable across countries. These findings are discussed in light of cultural and social reproduction theory and digital divide research.
The toolbox for imaging molecules is well-equipped today. Some techniques visualize the geometrical structure, others the electron density or electron orbitals. Molecules are many-body systems for which the correlation between the constituents is decisive and the spatial and the momentum distribution of one electron depends on those of the other electrons and the nuclei. Such correlations have escaped direct observation by imaging techniques so far. Here, we implement an imaging scheme which visualizes correlations between electrons by coincident detection of the reaction fragments after high energy photofragmentation. With this technique, we examine the H2 two-electron wave function in which electron–electron correlation beyond the mean-field level is prominent. We visualize the dependence of the wave function on the internuclear distance. High energy photoelectrons are shown to be a powerful tool for molecular imaging. Our study paves the way for future time resolved correlation imaging at FELs and laser based X-ray sources.
Secretins form multimeric channels across the outer membrane of Gram-negative bacteria that mediate the import or export of substrates and/or extrusion of type IV pili. The secretin complex of Thermus thermophilus is an oligomer of the 757-residue PilQ protein, essential for DNA uptake and pilus extrusion. Here, we present the cryo-EM structure of this bifunctional complex at a resolution of ~7 Å using a new reconstruction protocol. Thirteen protomers form a large periplasmic domain of six stacked rings and a secretin domain in the outer membrane. A homology model of the PilQ protein was fitted into the cryo-EM map. A crown-like structure outside the outer membrane capping the secretin was found not to be part of PilQ. Mutations in the secretin domain disrupted the crown and abolished DNA uptake, suggesting a central role of the crown in natural transformation.
Patients who undergo endovascular repair of aortic aneurysms (EVAR) require life-long surveillance because complications including, in particular, endoleaks, aneurysm rupture, and graft dislocation are diagnosed in a certain share of the patient population and may occur at any time after the original procedure. Radiation exposure in patients undergoing EVAR and post-EVAR surveillance has been investigated by previous authors. Arriving at realistic exposure data is essential because radiation doses resulting from CT were shown to be not irrelevant. Efforts directed at identification of factors impacting the level of radiation exposure in both the course of the EVAR procedure and post-EVAR endovascular interventions and CTAs are warranted as potentially modifiable factors may offer opportunities to reduce the radiation. In the light of the risks found to be associated with radiation exposure and considering the findings above, those involved in EVAR and post-EVAR surveillance should aim at optimal dose management.
We have determined the crystal structures of two decachlorocyclopentasilanes, namely bis(tetra-n-butylammonium) dichloride decachlorocyclopentasilane dichloromethane disolvate, 2C16H36N+·2Cl−·Si5Cl10·2CH2Cl2, (I), and bis(tetraethylammonium) dichloride decachlorocyclopentasilane dichloromethane disolvate, 2C8H20N+·2Cl−·Si5Cl10·2CH2Cl2, (II), both of which crystallize with discrete cations, anions, and solvent molecules. In (I), the complete decachlorocyclopentasilane ring is generated by a crystallographic twofold rotation axis. In (II), one cation is located on a general position and the other two are disordered about centres of inversion. These are the first structures featuring the structural motif of a five-membered cyclopentasilane ring coordinated from both sides by a chloride ion. The extended structures of (I) and (II) feature numerous C—H⋯Cl interactions. In (II), the N atoms are located on centres of inversion and as a result, the ethylene chains are disordered over equally occupied orientations.
Status and restoration potential of heathlands and sand grasslands in the southwest of Luxembourg
(2017)
In Europe, semi-natural nutrient-poor ecosystems such as sand grasslands and heathlands have shown extreme declines in surface area and species richness within the last century. The remaining sites are hence of high conservation value. This study analysed the vascular plant species inventory of established and recently restored heathlands and sand grasslands in the southwest of Luxembourg. Analyses to explain differences in vegetation composition between “old” (remnant sites or sites restored a long time ago) and “new” (recently restored) sites in relation to environmental variables were carried out with DCAs and ANOVA/Mann-Whitney-U tests, respectively. The vegetation of old heathlands had few character species of typical heathland communities (Calluno-Ulicetea, Nardetalia), whereas new heathland sites were preponderantly marked by taxa of meso- or eutrophic grasslands and ruderal communities. New heathland sites mainly differed from old sites by higher soil phosphorus contents. Sand grassland vegetation was species-rich and composed by species of the Sedo-Scleranthetea and Festuco-Brometea. With increasing age of the sites, vegetation composition shifted to grass dominance with species of the Molinio-Arrhenateretea. New sand grasslands differed from old sand grasslands by higher soil pH, higher soil potassium content and lower graminoid cover. The differences between new and old sites of both habitat types could mainly be explained by successional processes or were a result of topsoil removal. In some cases, former anthropogenic impact at or in close proximity of restored sites resulted in unsuitable conditions, such as alkaline soil on former landfill sites or highly eutrophic soil due to intensive agriculture. Future management options for the study sites are discussed.
This study describes the vascular flora and community structure of grasslands occurring on heaps of waste rock left by former Zn-Pb mining in relation to the metal content in the soil and other environmental factors. The study was performed on 65 heaps scattered in agricultural land in southern Poland. The sites were described in terms of plant community characteristics, soil physicochemical properties, distance from woodland, altitude and local climate. The number of plant species and proportion of species of the Festuco-Brometea class decreased with increasing heavy metal (Cd, Pb, Zn) content in the soil, and increased with Ca content and pH of the soil. There was a negative relationship between the proportion of the later successional species and heavy metal content in the soil and a positive relationship between plants connected with the earlier stages of succession and metals. Floristic composition was also affected by distance from woodland and height above sea level. The investigated heaps were primarily colonised by native species dispersed by wind, characterised as competitive stresstolerant, ruderal and competitive strategy species. Three types of Carlino acaulis-Brometum erecti (CB) communities were distinguished: CB typicum – dominated by Brachypodium pinnatum, with the highest proportion of calcareous grassland species, CB festucetosum ovinae subass. nova – loose grassland with abundant facultative metallophytes, and the CB rubietosum caesi subass. nova with nutrientdemanding ruderal and woody plants invading from the nearby forest communities. The three subassociations represent different successional stages of Carlino acaulis-Brometum erecti, strongly dependent on both the substrate and spatial relations. The proportions of species traits, especially a high occurrence of endangered species and a very low proportion of alien species show that the post-mining habitats studied have a similar degree of ‘naturalness’ as valuable xerothermic grasslands on nonmetalliferous habitats. They thus may be considered as valuable objects for the protection of plant diversity.
This paper provides a comprehensive survey of the results of phytocoenological research into Alnus incana forests from the alliance Alnion incanae in the Dinarides. Stands from the south-eastern Dinarides (Alnetum incanae = Oxali-Alnetum incanae) were analyzed and compared with those from the north-western Dinarides (Lamio orvalae-Alnetum incanae). The comparison reveals significant differences in the floristic composition and in the degree of differentiation – and particularly in the presence of the species of the Illyrian floristic geoelement. Focus was placed on the area of western Croatia where a geographic variant of Helleborus dumetorum had previously been defined within the association Lamio orvalae-Alnetum incanae. Two of its subtypes, Salix alba and Alnus glutinosa, were determined in our research. The former subtype thrives on occasionally flooded, moist sites, where the floristic composition is dominated by hygrophytes. The latter subtype grows on elevated and drier terraces and is richer in mesophilous species from the surrounding zonal forests. A floristic-sociological comparison of the Lamio orvalae-Alnetum incanae with the related syntaxa indicates the presence of about fourty diagnostic species which accentuate its independence and the need to assess it at the level of an independent, regional association within the alliance Alnion incanae.
The aim of our study was to reveal the differences in the species composition and soil properties of open sandy grasslands dominated by different Festuca species, Festuca vaginata and F. pseudovaginata. Due to the arid conditions, sandy grasslands are generally covered by xerothermic vegetation in which F. vaginata is a typical dominant species. Festuca pseudovaginata, a species newly described by the authors, can also gain dominance in sandy grasslands. However, species composition and soil properties of grasslands dominated by this recently discovered species are still undiscovered. Based on previous coenological studies, we hypothesised that the grasslands characterised by the endemic F. vaginata are more species-rich than those with F.pseudovaginata.
Coenological sampling was carried out in May 2009 at two study sites using the Braun-Blanquet method in quadrats of 2 m × 2 m. Five relevés were sampled in stands dominated by F. vaginata and F. pseudovaginata respectively at two study sites in Central Hungary, resulting in a total of twenty relevés. Analyses were based on the cover scores of vascular plant species and cryptogam crust and values of seven soil properties (pH [KCl], pH [H2O], humus, total N, Ca, P2O5 and K2O) measured in the 0–15 and 15–30 cm soil layers. Soil properties of the grasslands dominated by F. pseudovaginata and F. vaginata (dependent variables) were compared by linear mixed models, where ‘grassland type’ was the fixed factor and ‘site nested in grassland type’ was considered as random factor. Data were analysed by cluster analysis, fusion algorithm was a combinatorial method (minimising increase of variance), and the correlation was used as comparative function. We compared the cover of subordinate species by Mann-Whitney U test. We found that F. pseudovaginata and F. vaginata samples were well separated, and grasslands dominated by F. pseudovaginata had nearly two times more species than those dominated by F. vaginata. Based on the cluster analyses using plant cover and upper 0–15 cm soil layer data, F. pseudovaginata and F. vaginata groups could be well separated. Linear mixed models revealed that F. vaginata grasslands were typical on soils with higher pH, nitrogen, phosphorous and potassium contents compared to F. pseudovaginata grasslands, which indicates a tight connection between the properties of the upper soil layer and the vegetation in sandy grasslands.
Bromus racemosus L. is a rather rare grass species of moist meadows. It has strongly decreased in the course of the 20th century due to intensification of agricultural grassland management, and is therefore included in Red Lists of several European countries. Its winter annual life-cycle is remarkable for a species of permanent grasslands.
The aim of this study is to determine the habitat preference and optimal management of B. racemosus in the Netherlands and surrounding countries. Vegetation, soil and hydrological data from 28 sites in the Netherlands have been compared with B. racemosus cover, and with vegetation data from surrounding countries. The results indicate that B. racemosus is characteristic of Molinio-Arrhenatheretea meadows with good mineralisation and aftermath grazing. The optimum lies in grasslands of the alliance Alopecurion pratensis (Deschampsion cespitosae), but the species ranges from wetter Calthion palustris meadows to drier Arrhenatherion elatioris and Cynosurion cristati grasslands. It prefers intermediate nutrient levels and hydrological conditions (mesic sites), but within this range the highest cover is found in relatively nutrient rich and dry sites. Because of the absence of a seedbank and a low dispersal capability, B. racemosus is vulnerable to changes in grassland management. A management of mowing after 15 June and aftermath grazing is most suitable, since it enables fruit ripening and the maintenance of an open sward, needed for germination and development. The risk of extinction is likely to be higher in flat polders than in floodplain sites with natural relief, where the species may shift between belts in different years.