118 research outputs found
The effects of stand characteristics on the understory vegetation in Quercus petraea and Q. cerris dominated forests
The shelterwood system used in Hungary has many effects on the composition and structure of the herb layer. The aim of our study was to identify the main variables that affect the occurence of herbs and seedlings in Turkey oak-sessile oak (Quercus cerris and Q. petraea) stands. The study was carried out in the BĂŒkk mountains, Hungary. 122 sampling plots were established in 50-150 year old oak forests, where we studied the species composition and structure of the understorey and overstorey. The occurence of herbs was affected by canopy closure, the heterogenity and patchiness of the stand, the slope and the east-west component of the aspect. The composition of saplings was significantly explained by the ratio of the two major oak species in the stand and the proximity of the adult plants. An important result for forest management was that sessile oaks were able to regenerate almost only where they were dominant in the overstorey
Structure Investigations of Molecular Crystals Containing the Ring System Cyclo-tris(2,6-pyridylformamidine) by Means of X-ray Powder Diffraction and Force-Field-Constrained Rietveld Refinement
Versatile Coordination of Cyclopentadienyl-Arene Ligands and Its Role in Titanium-Catalyzed Ethylene Trimerization
Cationic titanium(IV) complexes with ansa-(η5-cyclopentadienyl,η6-arene) ligands were synthesized and characterized by X-ray crystallography. The strength of the metal-arene interaction in these systems was studied by variable-temperature NMR spectroscopy. Complexes with a C1 bridge between the cyclopentadienyl and arene moieties feature hemilabile coordination behavior of the ligand and consequently are active ethylene trimerization catalysts. Reaction of the titanium(IV) dimethyl cations with CO results in conversion to the analogous cationic titanium(II) dicarbonyl species. Metal-to-ligand backdonation in these formally low-valent complexes gives rise to a strongly bonded, partially reduced arene moiety. In contrast to the η6-arene coordination mode observed for titanium, the more electron-rich vanadium(V) cations [cyclopentadienyl-arene]V(NiPr2)(NC6H4-4-Me)+ feature η1-arene binding, as determined by a crystallographic study. The three different metal-arene coordination modes that we experimentally observed model intermediates in the cycle for titanium-catalyzed ethylene trimerization. The nature of the metal-arene interaction in these systems was studied by DFT calculations.
Neoproterozoic to early Paleozoic extensional and compressional history of East Laurentian margin sequences: The Moine Supergroup, Scottish Caledonides
Neoproterozoic siliciclastic-dominated sequences are widespread along the eastern margin of Laurentia and are related to rifting associated with the breakout of Laurentia from the supercontinent Rodinia. Detrital zircons from the Moine Supergroup, NW Scotland, yield Archean to early Neoproterozoic U-Pb ages, consistent with derivation from the Grenville-Sveconorwegian orogen and environs and accumulation postâ1000 Ma. U-Pb zircon ages for felsic and associated mafic intrusions confirm a widespread pulse of extension-related magmatism at around 870 Ma. Pegmatites yielding U-Pb zircon ages between 830 Ma and 745 Ma constrain a series of deformation and metamorphic pulses related to Knoydartian orogenesis of the host Moinerocks. Additional U-Pb zircon and monazite data, and 40Ar/39Ar ages for pegmatites and host gneisses indicate high-grade metamorphic events at ca. 458â446 Ma and ca. 426 Maduring the Caledonian orogenic cycle.The presence of early Neoproterozoic silici clastic sedimentation and deformation in the Moine and equivalent successions around the North Atlantic and their absence along strike in eastern North America reflect contrasting Laurentian paleogeography during the breakup of Rodinia. The North Atlantic realm occupied an external location on the margin of Laurentia, and this region acted as a locus for accumulation of detritus (Moine Supergroup and equivalents) derived from the Grenville-Sveconorwegian orogenic welt, which developed as a consequence of collisional assembly of Rodinia. Neoproterozoic orogenic activity corresponds with theinferred development of convergent platemargin activity along the periphery of the supercontinent. In contrast in eastern North America, which lay within the internal parts of Rodinia, sedimentation did not commence until the mid-Neoproterozoic (ca. 760 Ma) during initial stages of supercontinent fragmentation. In the North Atlantic region, this time frame corresponds to a second pulse of extension represented by units such as the Dalradian Supergroup, which unconformably overlies the predeformed Moine succession
Structures Related to the Emplacement of Shallow-Level Intrusions
A systematic view of the vast nomenclature used to describe the structures of shallow-level intrusions is presented here. Structures are organised in four main groups, according to logical breaks in the timing of magma emplacement, independent of the scales of features: (1) Intrusion-related structures, formed as the magma is making space and then develops into its intrusion shape; (2) Magmatic flow-related structures, developed as magma moves with suspended crystals that are free to rotate; (3) Solid-state, flow-related structures that formed in portions of the intrusions affected by continuing flow of nearby magma, therefore considered to have a syn-magmatic, non-tectonic origin; (4) Thermal and fragmental structures, related to creation of space and impact on host materials. This scheme appears as a rational organisation, helpful in describing and interpreting the large variety of structures observed in shallow-level intrusions
Monitoring and evaluation of sport-based HIV/AIDS awareness programmes: strengthening outcome indicators
There are number of Non-Governmental Organisations (NGOs) in South Africa that use sport as a tool to respond to Human
Immunodeficiency Virus/Acquired Immunodeficiency Syndrome (HIV/AIDS), however, little is reported about the outcomes
and impact of these programmes. The aim of this study is to contribute to a generic monitoring and evaluation framework by
improving the options for the use of outcome indicators of sport-based HIV/AIDS awareness programmes of selected NGOs in
South Africa. A qualitative method study was carried out with seven employees of five selected NGOs that integrate sport to
deliver HIV/AIDS programmes in South Africa. The study further involved six specialists/experts involved in the field of HIV/
AIDS and an official from Sport Recreation South Africa (SRSA). Multiple data collection instruments including desktop review,
narrative systematic review, document analysis, one-on-one interviews and focus group interview were used to collect
information on outcomes and indicators for sport-based HIV/AIDS awareness programmes. The information was classified
according to the determinants of HIV/AIDS. The overall findings revealed that the sport-based HIV/AIDS awareness
programmes of five selected NGOs examined in this study focus on similar HIV prevention messages within the key priorities
highlighted in the current National Strategic Plan for HIV/AIDS, STIs and TB of South Africa. However, monitoring and
evaluating outcomes of sport-based HIV/AIDS programmes of the selected NGOs remains a challenge. A need exists for the
improvement of the outcome statements and indicators for their sport-based HIV/AIDS awareness programmes. This study
proposed a total of 51 generic outcome indicators focusing on measuring change in the knowledge of HIV/AIDS and change in
attitude and intention towards HIV risk behaviours. In addition, this study further proposed a total of eight generic outcome
indicators to measure predictors of HIV risk behaviour. The selected NGOs can adapt the proposed generic outcomes and
indicators based on the settings of their programmes. A collaborative approach by all stakeholders is required, from
international organisations, funders, governments, NGOs and communities to strengthening monitoring and evaluation of
sport-based HIV/AIDS awareness programmes including other development programmes. This will assist the NGOs that use
sport for development to be able to reflect accurately the information about their HIV/AIDS activities and also be able to
contribute to on-going monitoring activities at a national and global level as well as to the Sustainable Development Goals.IS
Lewis Acid Promoted Titanium Alkylidene Formation: Off-Cycle Intermediates Relevant to Olefin Trimerization Catalysis
Highly Selective Olefin Trimerization Catalysis by a Borane-Activated Titanium Trimethyl Complex
Czochralski-type crystal growth system developed at the Central Research Institute for Physics
Der Einfluss der motivationalen Praxis der Eltern auf die Schulleistung : Welche Rolle spielt die soziokulturelle Herkunft und die Ăbergangsentscheidung?
- âŠ