360 research outputs found
Transport Properties of Highly Aligned Polymer Light-Emitting-Diodes
We investigate hole transport in polymer light-emitting-diodes in which the
emissive layer is made of liquid-crystalline polymer chains aligned
perpendicular to the direction of transport. Calculations of the current as a
function of time via a random-walk model show excellent qualitative agreement
with experiments conducted on electroluminescent polyfluorene demonstrating
non-dispersive hole transport. The current exhibits a constant plateau as the
charge carriers move with a time-independent drift velocity, followed by a long
tail when they reach the collecting electrode. Variation of the parameters
within the model allows the investigation of the transition from non-dispersive
to dispersive transport in highly aligned polymers. It turns out that large
inter-chain hopping is required for non-dispersive hole transport and that
structural disorder obstructs the propagation of holes through the polymer
film.Comment: 4 pages, 5 figure
Temperature and Field Dependence of the Mobility in Liquid-Crystalline Conjugated Polymer Films
The transport properties of organic light-emitting diodes in which the
emissive layer is composed of conjugated polymers in the liquid-crystalline
phase have been investigated. We have performed simulations of the current
transient response to an illumination pulse via the Monte Carlo approach, and
from the transit times we have extracted the mobility of the charge carriers as
a function of both the electric field and the temperature. The transport
properties of such films are different from their disordered counterparts, with
charge carrier mobilities exhibiting only a weak dependence on both the
electric field and temperature. We show that for spatially ordered polymer
films, this weak dependence arises for thermal energy being comparable to the
energetic disorder, due to the combined effect of the electrostatic and thermal
energies. The inclusion of spatial disorder, on the other hand, does not alter
the qualitative behaviour of the mobility, but results in decreasing its
absolute value.Comment: 9 pages, 8 figures, submitted to Phys. Rev.
Revealing natural relationships among arbuscular mycorrhizal fungi: culture line BEG47 represents Diversispora epigaea, not Glomus versiforme
Background: Understanding the mechanisms underlying biological phenomena, such as evolutionarily conservative trait inheritance, is predicated on knowledge of the natural relationships among organisms. However, despite their enormous ecological significance, many of the ubiquitous soil inhabiting and plant symbiotic arbuscular mycorrhizal fungi (AMF, phylum Glomeromycota) are incorrectly classified.
Methodology/Principal Findings:
Here, we focused on a frequently used model AMF registered as culture BEG47. This fungus is a descendent of the ex-type culture-lineage of Glomus epigaeum, which in 1983 was synonymised with Glomus versiforme. It has since then been used as ‘G. versiforme BEG47’. We show by morphological comparisons, based on type material, collected 1860–61, of G. versiforme and on type material and living ex-type cultures of G. epigaeum, that these two AMF species cannot be conspecific, and by molecular phylogenetics that BEG47 is a member of the genus Diversispora.
Conclusions: This study highlights that experimental works published during the last >25 years on an AMF named ‘G. versiforme’ or ‘BEG47’ refer to D. epigaea, a species that is actually evolutionarily separated by hundreds of millions of years from all members of the genera in the Glomerales and thus from most other commonly used AMF ‘laboratory strains’. Detailed redescriptions substantiate the renaming of G. epigaeum (BEG47) as D. epigaea, positioning it systematically in the order Diversisporales, thus enabling an evolutionary understanding of genetical, physiological, and ecological traits, relative to those of other AMF. Diversispora epigaea is widely cultured as a laboratory strain of AMF, whereas G. versiforme appears not to have been cultured nor found in the field since its original description
Association of Caldendrin splice isoforms with secretory vesicles in neurohypophyseal axons and the pituitary
AbstractCaldendrin is a neuronal calcium-binding protein, which is highly enriched in the postsynaptic density fraction and exhibits a prominent somato-dendritic distribution in brain. Two additional splice variants derive from the caldendrin gene, which have unrelated N-termini and were previously only detected in the retina. We now show that these isoforms are present in neurohypophyseal axons and on secretory granules of endocrine cells. In light of the described interaction of the Caldendrin C-terminus with Q-type Cav2.1 calcium channels these data suggest that this interaction takes place in neurohypophyseal axons and pituitary cells indicating functions of the short splice variants in triggering Ca2+ transients to a vesicular target interaction
Literacy practices of primary education children in Andalusia (Spain): a family-based perspective
Primary school children develop literacy practices in various domains and situations in everyday life.
This study focused on the analysis of literacy practices of children aged 8–12 years from the perspec-
tive of their families. 1,843 families participated in the non-experimental explanatory study. The
children in these families speak Spanish as a first language and are schooled in this language. The
instrument used was a self-report questionnaire about children’s home-literacy practices. The data
obtained were analysed using categorical principal components analysis (CATPCA) and analysis of
variance (ANOVA). The results show the complex relationship between literacy practices developed
by children in the domains of home and school and the limited development of a literacy-promoting
‘third space’. In conclusion, the families in our study had limited awareness of their role as literacy-
promoting agents and thought of literacy learning as restricted to formal or academic spaces
Impact of contamination on the development of controlled inundation areas along the Scheldt estuary (poster)
One of the objectives of the SIGMA-plan of the River Scheldt is the construction of a controlled inundation area in Kruibeke-Bazel-Rupelmonde. However this area is contaminated with heavy metals due to aerial deposition. On the other hand, as an inundation area, it will be flooded with contaminated water from the Scheldt. Therefore it is necessary to estimate the impact of contamination on the potential nature development in these areas.A case study was carried out last two years in a VLINA-project at a tidal marsh along the River Scheldt. The distribution of the contaminants over the different compartments was investigated during two years. The compartments were the soil and pore water, but also the vegetation and the dominant group of macrobenthos. Beside this an estimation was made of the input of contaminants due to the sedimentation of particles during flooding. Other processes that were studied are the sorption and desorption processes, which affect the bioavailability, and the effect on the uptake of contaminants and the bioaccumulation in reed (Phragmites australis) and Oligochaeta are studied in detail. The above- and belowground biomass of reed (Phragmites australis) was measured
Confirmation of occurrence of Babesia vogeli in a dog in Windhoek, central Namibia
Although there is evidence of high seroprevalence of antibodies to Babesia spp. in dogs in
central Namibia, clinical babesiosis is rarely diagnosed. Rhipicephalus sanguineus sensu lato, the
vector of Babesia vogeli, is common in Namibia while Haemaphysalis elliptica, the vector of the
highly virulent but morphologically indistinguishable Babesia rossi, has rarely been recorded,
mainly in northern Namibia. On the basis of vector occurrence, clinical cases of canine
babesiosis in Windhoek, central Namibia, have been ascribed to B. vogeli. DNA extracted from
a blood smear made from a sick dog was subjected to the reverse line blot hybridisation assay.
The polymerase chain reaction amplicons hybridised with the B. vogeli–specific probe, but not
with the Babesia canis– and B. rossi–specific probes. Although attempts at cloning and
sequencing of the full-length 18S rRNA gene were unsuccessful, we can confirm that B. vogeli
occurs in central Namibia.http://www.jsava.co.zaam2016Veterinary Tropical Disease
Darkness visible: reflections on underground ecology
1 Soil science and ecology have developed independently, making it difficult for ecologists to contribute to urgent current debates on the destruction of the global soil resource and its key role in the global carbon cycle. Soils are believed to be exceptionally biodiverse parts of ecosystems, a view confirmed by recent data from the UK Soil Biodiversity Programme at Sourhope, Scotland, where high diversity was a characteristic of small organisms, but not of larger ones. Explaining this difference requires knowledge that we currently lack about the basic biology and biogeography of micro-organisms. 2 It seems inherently plausible that the high levels of biological diversity in soil play some part in determining the ability of soils to undertake ecosystem-level processes, such as carbon and mineral cycling. However, we lack conceptual models to address this issue, and debate about the role of biodiversity in ecosystem processes has centred around the concept of functional redundancy, and has consequently been largely semantic. More precise construction of our experimental questions is needed to advance understanding. 3 These issues are well illustrated by the fungi that form arbuscular mycorrhizas, the Glomeromycota. This ancient symbiosis of plants and fungi is responsible for phosphate uptake in most land plants, and the phylum is generally held to be species-poor and non-specific, with most members readily colonizing any plant species. Molecular techniques have shown both those assumptions to be unsafe, raising questions about what factors have promoted diversification in these fungi. One source of this genetic diversity may be functional diversity. 4 Specificity of the mycorrhizal interaction between plants and fungi would have important ecosystem consequences. One example would be in the control of invasiveness in introduced plant species: surprisingly, naturalized plant species in Britain are disproportionately from mycorrhizal families, suggesting that these fungi may play a role in assisting invasion. 5 What emerges from an attempt to relate biodiversity and ecosystem processes in soil is our extraordinary ignorance about the organisms involved. There are fundamental questions that are now answerable with new techniques and sufficient will, such as how biodiverse are natural soils? Do microbes have biogeography? Are there rare or even endangered microbes
Facilitating new forms of discourse for learning and teaching: harnessing the power of Web 2.0 practices
When asked what they would find most helpful to enable them to use technologies more in their teaching, most teachers say "give me examples, in my subject area" and "point me to relevant people I can discuss these issues with". Web 2.0 technologies - with their emphasis on sharing, networking and user production - seem to offer a potential solution. However uptake and use of web 2.0 sites such as blogs, social networking and wikis by teachers for sharing and discussing practice has being marginal so far. This paper focuses on work we are undertaking as part of the OU Learning Design Initiative (http://ouldi.open.ac.uk) and the Hewlett-funded Olnet initiative (http://olnet.org). A key focus of our work is the development of tools, methods and approaches to support the design of innovative learning activities and Open Educational Resources (OER). In this paper I want to focus on one strand of our work; namely how to leverage technologies to promote better sharing and discussing of learning and teaching ideas and designs
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