933 resultados para SUCCESSION
Resumo:
One habitat management requirement forced by 21st century relative sea-level rise (RSLR), will be the need to re-comprehend the dimensions of long-term transgressive behaviour of coastal systems being forced by such RSLR. Fresh approaches to the conceptual modelling and subsequent implementation of new coastal and peri-marine habitats will be required. There is concern that existing approaches to forecasting coastal systems development (and by implication their associated scarce coastal habitats) over the next century depend on a certain premise of orderly spatial succession of habitats. This assumption is shown to be questionable given the possible future rates of RSLR, magnitude of shoreline retreat and the lack of coastal sediment to maintain the protective morphologies to low-energy coastal habitats. Of these issues, sediment deficiency is regarded as one of the major problem for future habitat development. Examples of contemporary behaviour of UK coasts show evidence of coastal sediment starvation resulting from relatively stable RSLR, anthropogenic sealing of coastal sources, and intercepted coastal sediment pathways, which together force segmentation of coastal systems. From these examples key principles are deduced which may prejudice the existence of future habitats: accelerated future sediment demand due to RSLR may not be met by supply and, if short- to medium-term hold-the-line policies predominate, long-term strategies for managed realignment and habitat enhancement may prove impossible goals. Methods of contemporary sediment husbandry may help sustain some habitats in place but otherwise, instead of integrated coastal organization, managers may need to consider coastal breakdown, segmentation and habitat reduction as the basis of 21st century coastal evolution and planning.
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Modern intense ultrafast pulsed lasers generate an electric field of sufficient strength to permit tunnel ionization of the valence electrons in atoms(1). This process is usually treated as a rapid succession of isolated events, in which the states of the remaining electrons are neglected(2). Such electronic interactions are predicted to be weak, the exception being recollision excitation and ionization caused by linearly polarized radiation(3). In contrast, it has recently been suggested that intense field ionization may be accompanied by a two-stage 'shake-up' reaction(4). Here we report a unique combination of experimental techniques(5-8) that allows us to accurately measure the tunnel ionization probability for argon exposed to 50-fs laser pulses. Most significantly for the current study, this measurement is independent of the optical focal geometry(7,8), equivalent to a homogenous electric field. Furthermore, circularly polarized radiation negates recollision. The present measurements indicate that tunnel ionization results in simultaneous excitation of one or more remaining electrons through shake-up(9). From an atomic physics standpoint, it may be possible to induce ionization from specific states, and will influence the development of coherent attosecond extreme-ultraviolet-radiation sources(10). Such pulses have vital scientific and economic potential in areas such as high-resolution imaging of in vivo cells and nanoscale extreme-ultraviolet lithography.
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Success rates of reintroduction programs are low, often owing to a lack of knowledge of site-specific ecological requirements. A reintroduction program of European roe deer (Capreolus capreolus (L., 1758)) in a dry Mediterranean region in Israel provides an opportunity to study the bottleneck effect of water requirements on a mesic-adapted species. Four does were hand-reared and released in a 10 ha site consisting of an early succession scrubland and a mature oak forest. We measured daily energy expenditure (DEE) and water turnover (WTO) using the doubly labeled water technique during summer and winter. DEE was similar in the summer and winter, but there was a significant difference in WTO and in the source of gained water. In winter, WTO was 3.3 L/day, of which 67% was obtained from vegetation. In summer, WTO dropped to 2.1 L/day, of which only 20% was obtained from the diet and 76% was gained from drinking. When the water source was moved to a nonpreferred habitat, drinking frequency dropped significantly, but water consumption remained constant. In a dry Mediterranean environment, availability of free water is both a physiological contraint and a behavioral constraint for roe deer. This study demonstrates the importance of physiological and behavioral feasibility studies for reintroduction programs.
Resumo:
We present a scheme for the extraction of singlet states of two remote particles of arbitrary quantum spin number. The goal is achieved through post-selection of the state of interaction mediators sent in succession. A small number of iterations is sufficient to make the scheme effective. We propose two suitable experimental setups where the protocol can be implemented.
Resumo:
A National Frog Survey of Ireland is planned for spring 2011. We conducted a pilot survey of 25 water bodies in ten 0.25 km2 survey squares in Co. Mayo during spring 2010. Drainage ditches were the most commonly available site for breeding and, generally, two 100 m stretches of ditch were surveyed in each square. The restricted period for peak spawning activity renders any methodology utilizing only one site visit inherently risky. Consequently, each site was visited three times from late March to early April. Occurrence of spawn declined significantly from 72 % to 44 % between the first and third visit whilst the overall occurrence of spawn at all sites was 76 %. As the breeding season advanced, spawn either hatched or was predated and, therefore, disappeared. In those water bodies where spawning was late, however, greater densities of spawn were deposited than in those sites where breeding was early. Consequently, spawn density and estimated frog density did not differ significantly between site visits. Future surveys should nevertheless include multiple site visits to avoid biased estimation of species occurrence and distribution. Ecological succession was identified as the main threat present at 44 % of sites.
Resumo:
Evaluating the effectiveness of social work education has become a topic of major interest in the UK in the wake of a succession of child-care tragedies that have undermined confidence in the profession. However, many key aspects of social work education remain under-researched and/or contested and our knowledge of how students acquire and develop professional expertise remains limited. This paper reports on the first part of a longitudinal study aimed at developing evidence-based knowledge in this area by considering student perceptions at different stages of their social work education at Queen’s University Belfast. Focusing on the strengths and limitations of preparatory teaching, and their first experience of practice learning, this article considers the impact of demographic factors, including age, gender and experience, on how students experience the learning process. The findings indicate a significant level of disjunction between academic and practice learning and suggest that better integration between these two domains of learning is needed if social work students are to be more effectively prepared for the challenges they are likely to encounter in practice.
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A sediment succession from Hojby So, a lake in eastern Denmark, covering the time period 9400-7400 cal yr BP was studied using high-resolution geochemistry, magnetic susceptibility, pollen, macrofossil, diatom, and algal pigment analysis to investigate responses of the terrestrial and aquatic ecosystems to the 8.2 ka cold event. A reduced pollen production by thermophilous deciduous tree taxa in the period c. 8250-8000 cal yr BP reveal that the forest ecosystem was affected by low temperatures during the summer and winter/early-spring seasons. This finding is consistent with the timing of the 8.2 ka cold event as registered in the Greenland ice cores. At Hojby So, the climate anomaly appears to have started 200-250 yr earlier than the 8.2 ka cold event as the lake proxy data provide strong evidence for a precipitation-induced distinct increase in catchment soil erosion beginning around 8500 cal yr BP. Alteration of the terrestrial environment then resulted in a major aquatic ecosystem change with nutrient enrichment of the lake and enhanced productivity, which lasted until c. 7900 cal yr BP. (C) 2009 University of Washington. Published by Elsevier Inc. All rights reserved.
Resumo:
Fourier transform ion cyclotron resonance mass spectrometry experiments showed that liquid Group 1 metal salts of the bistriflamide anion undergoing reduced-pressure distillation exhibit a remarkable behavior that is in transition between that of the vapor-liquid equilibrium characteristics of aprotic ionic liquids and that of the Group 1 metal halides: the unperturbed vapors resemble those of aprotic ionic liquids, in the sense that they are essentially composed of discrete ion pairs. However, the formation of large aggregates through a succession of ion-molecule reactions is closer to what might be expected for Group I metal halides. Similar experiments were also carried out with bis{(trifluoromethyl)sulfonyl}amine to investigate the effect of H+, which despite being the smallest Group 1 cation, is generally regarded as a nonmetal species. In this case, instead of the complex ion-molecule reaction pattern found for the vapors of Group I metal salts, an equilibrium similar to those observed for aprotic ionic liquids was observed.
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The sediments of Like Fimon N Italy contain the first continuous archive of the Late Pleistocene environmental and climate history of the southern Alpine foreland We present here the detailed palynological record of the interval between Termination II and the List Glacial Maximum The age-depth model is obtained by radiocarbon dating in the uppermost part of the record Downward we con elated major forest expansion and contraction events to isotopic events in the Greenland Ice core records via a stepping-stone approach involving intermediate correlation to isotopic events dated by TIMS U/Th in Alpine and Apennine stalagmites and to pollen records from mime cores of the Iberian margin Modelled ages obtained by Bayesian analysis of deposition are thoroughly consistent with actual ages with maximum offset of +/- 1700 years Sharp expansion of broad-leaved temperate forest and of sudden water table rise mark the onset of the Last Interglacial after a treeless steppe phase at the end of penultimate glaciation This event is actually a two-step process which matches the two step rise observed in the isotopic record of the nearby Antro del Corchia stalagmite respectively dated to 132 5 +/- 2 5 and 129 +/- 1 5 ka At the interglacial decline mixed oak forests were replaced by oceanic mixed forests the latter persisting further for 7 ka till the end of the Eemian succession Warm-temperate woody species are still abundant at the Eemian end corroborating a steep gradient between central Europe and the Alpine divide at the inception of the last glacial After a stadial phase marked by moderate forest decline a new expansion of warm broad leaved forests interrupted by minor events and followed by mixed oceanic forests can be identified with the north-alpine Saint Germain I The spread of beech during the oceanic phase is a valuable circumalpine marker The subsequent stadial-interstadial succession lacking the telocratic oceanic phase is also consistent with the evidence at the north alpine foreland The Middle Wurmian (full glacial) is marked by persistence of mixed forests dominated by conifers but with significant lime and other broad leaved species A major Arboreal Pollen decrease is observed at modelled age of 38 7 +/- 0 5 ka (larch expansion and last occurrence of lime) which his been related to Heinrich Event 4 The evidence of afforestation persisting south of the Alps throughout most of MIS 3 contrasts with a boreal and continental landscape known for the northern alpine foreland pointing to a sharp rainfall boundary at the Alpine divide and to southern air circulation This is in agreement with the Alpine paleoglaciological record and is supported by the pressure and rainfall patterns designed by mesoscale paleoclimate simulations Strenghtening the continental high pressure during the full glacial triggered cyclogenesis in the middle latitude eastern Europe and orographic rainfall in the eastern Alps and the Balkanic mountains thus allowing forests development at current sea level altitudes (C) 2010 Elsevier Ltd All rights reserved
Resumo:
The site Pilgrimstad in central Sweden has often been cited as a key locality for discussions of ice-free/ice-covered intervals during the Early and Middle Weichselian. Multi-proxy investigations of a recently excavated section at Pilgrimstad now provide a revised picture of the climatic and environmental development between similar to 80 and 36 ka ago. The combination of sedimentology, geochemistry, OSL and 14C dating, and macrofossil, siliceous microfossil and chironomid analyses shows: (i) a lower succession of glaciofluvial/fluvial, lacustrine and glaciolacustrine sediments; (ii) an upper lacustrine sediment sequence; and (iii) Last Glacial Maximum till cover. Microfossils in the upper lacustrine sediments are initially characteristic for oligo- to mesotrophic lakes, and macrofossils indicate arctic/sub-arctic environments and mean July temperatures > 8 degrees C. These conditions were, however, followed by a return to a low-nutrient lake and a cold and dry climate. The sequence contains several hiatuses, as shown by the often sharp contacts between individual units, which suggests that ice-free intervals alternated with possible ice advances during certain parts of the Early and Middle Weichselian.
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The impact of burning and grazing on plant, ground beetle and spider species was investigated experimentally in stands of varying ages (burnt in 1982 and 1988 and unburnt plots) on an area of heather moorland in County Antrim, north-east Ireland. Burning initiated complex succession pathways which appear to have characteristic plant and invertebrate species associations. Removal of Calluna dominance initiated a period of high plant species diversity. Investigation of initial post-fire regeneration suggested that the frequency of occurrence of plant species changed over time and was affected by grazing. Grouping of species by the position of their renewal bud, i.e. their life-form, did not account for all observed interspecific variation. The dominant species after burning were Eriophorum vaginatum, E. angustifolium and Vaccinium myrtillus. Studies of vegetation canopy structure showed that, even with the exclusion of the main grazing herbivores, Calluna will not re-establish itself as the dominant species until several years after burning. The ground beetle Nebria salina was trapped more often on plots burnt in 1988 than on unburnt plots or those burnt in 1982. In comparison, Pterostichus niger and Carabus granulatus were trapped in greater numbers on plots burnt in 1982 than on unburnt plots and plots burnt in 1988. The large species Carabus problematicus and Carabus glabratus were trapped in greater numbers on unburnt plots. Similarly, more of the spiders Ceratinella brevipes and Centromerita concinna were trapped on the plots burnt in 1982. In comparison, Lepthyphantes zimmermanni and Robertus lividus were trapped more often on unburnt plots than on plots burnt in 1982 and 1988. Results are discussed with respect to the importance of the continuation of traditional heathland management practices.
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The late-glacial vegetation development in northern Norway in response to climate changes during the Allerod, Younger Dryas (YD), and the transition to the Holocene is poorly known. Here we present a high-resolution record of floral and vegetation changes at lake Lusvatnet, south-west Andoya, between 13500 and 8000 cal b.p. Plant macrofossil and pollen analyses were done on the same sediment core and the proxy records follow each other very closely. The core has also been analyzed using an ITRAX XRF scanner in order to check the sediment sequence for disturbances or hiatuses. The core has a good radiocarbon-based chronology. The Saksunarvatn tephra fits very well chronostratigraphically. During both the Allerod and the Younger Dryas time-periods arctic vegetation prevailed, dominated by Salix polaris associated with many typically arctic herbs such as Saxifraga cespitosa, Saxifraga rivularis and Oxyria digyna. Both periods were cold and dry. Between 12450 and 12250 cal b.p. during the Younger Dryas chronozone, the assemblage changed, particularly in the increased abundance of Papaver sect. Scapiflora and other high-Arctic herbs, suggesting the development of polar desert vegetation mainly as a response to increased aridity. After 11520 cal b.p. a gradually warmer and more oceanic climate initiated a succession to dwarf-shrub vegetation and the establishment of Betula woodland after 1,000 years at c. 10520 cal b.p. The overall late-glacial aridity contrasts with oceanic conditions in southern Norway and is probably related to sea-ice extent.
Resumo:
A certain type of rural support has emerged since agricultural restructuring of the 1980s. The article draws on research from the UK and Canada to suggest that support in both countries is derived from a patrilineal culture that still dominates family farming in both countries. Such a way of life, it is argued, involves the majority of farming men and women across generations working increasingly hard to ensure farm survival in order to facilitate an overall pattern of farm succession via the male or ‘patrilineal’ line. The article begins by providing a conceptualisation of patrilineal family farming drawing on insights from gender-informed work on farming identities, political-economy approaches from agricultural geography and the cultural turn in rural studies. This section will provide theoretical direction for discussion of the research findings. Here the article presents a discussion of the context to and typologies of organisations that emerged and five key findings derived from research conducted with members of the organisations in the UK and Canada. This assists in developing the argument that the emergent organisations are responding to and supporting this way of life and highlights some of the potential implications of doing so. The article has two aims. Firstly, it suggests that family farming in the UK and Canada continues to be predominantly structured by a way of life transmitted across generations which has the overall prerequisite of maintaining farm survival to enable patrilineal succession. Secondly, it suggests that a particular type of support for farming families emerged as a response to perceived threats to this way of life and provides evidence of its enduring nature.
Resumo:
During the past decade, a new culture of pedagogic research has emerged in social work in the UK. A succession of child-care tragedies that have led to government and public criticism of social work have highlighted the need for improvements to professional standards and stimulated renewed interest in social work education. Research aimed at developing knowledge of ‘what works’ in the educational process have included studies of student experiences and the perspectives of other stakeholders including service users and practice teachers. However, there has been little systematic investigation of the role of academics in social work education and their perceptions of what needs to be done to improve the quality of provision. This paper aims to address this gap in research by examining the perceptions of academics about their work. The authors utilise an adaptation of the conceptual model developed by Fraser and Bosanquet (2006) as a theoretical framework for analysing the findings and exploring the complex interrelationship between academic perspectives and the variety of concepts, ideas and stakeholder expectations that shape pedagogical practice. The findings should provide important lessons of relevance to educators in the UK and in other countries seeking to develop social work education.
Resumo:
Marine radiocarbon bomb-pulse time histories of annually resolved archives from temperate regions have been underexploited. We present here series of Delta C-14 excess from known-age annual increments of the long-lived bivalve mollusk Arctica islandica from 4 sites across the coastal North Atlantic (German Bight, North Sea; Tromso, north Norway; Siglufjordur, north Icelandic shelf; Grimsey, north Icelandic shelf) combined with published series from Georges Bank and Sable Bank (NW Atlantic) and the Oyster Ground (North Sea). The atmospheric bomb pulse is shown to be a step-function whose response in the marine environment is immediate but of smaller amplitude and which has a longer decay time as a result of the much larger marine carbon reservoir. Attenuation is determined by the regional hydrographic setting of the sites, vertical mixing, processes controlling the isotopic exchange of C-14 at the air-sea boundary, C-14 content of the freshwater flux, primary productivity, and the residence time of organic matter in the sediment mixed layer. The inventories form a sequence from high magnitude-early peak (German Bight) to low magnitude-late peak (Grimsey). All series show a rapid response to the increase in atmospheric Delta C-14 excess but a slow response to the subsequent decline resulting from the succession of rapid isotopic air-sea exchange followed by the more gradual isotopic equilibration in the mixed layer due to the variable marine carbon reservoir and incorporation of organic carbon from the sediment mixed layer. The data constitute calibration series for the use of the bomb pulse as a high-resolution dating tool in the marine environment and as a tracer of coastal ocean water masses.