155 research outputs found
Effects of breeding habitat and field margins on the reproductive performance of Skylarks (Alauda arvensis) on intensive farmland
Field margin management is a common measure employed in Europe to support farmland bird populations. In this study we found and analysed 237 nests of the Skylark Alauda arvensis in the Netherlands over a period of 6 years to determine the effects of arable field margins and breeding crop on nest-level reproductive success. Additionally, the effect of field margins on predation was investigated and food availability in crops and field margins was compared. Neither clutch size, nest survival nor nestling body weight were improved by field margin availability, irrespective of the breeding crop used. However, the choice of breeding crop had important effects. Nestling weight was significantly lower in cereals than in grassland and lucerne, corresponding with the low prey densities present in cereals. Nest survival was lowest in grassland due to frequent silage cutting. Predation rates were highest in cereals but were not affected by field margin proximity. The highest reproductive success was achieved in lucerne, which was mown twice a year and retained a suitable height for breeding throughout the breeding season. We conclude that field margins are not sufficient to maintain a Skylark population in this intensively farmed area. The presumably more subtle effects of increased food availability cannot compensate for the high nest failure rates resulting from agricultural operations and predation. In this and similar areas, the provisioning of safe nesting habitat throughout the breeding season is essential to improve breeding performance. Our research suggests that this can be achieved by reducing the frequency of silage cutting on grassland and by increasing the surface area of lucerne.Conservation Biolog
Shuttling an electron spin through a silicon quantum dot array
Coherent links between qubits separated by tens of micrometers are expected
to facilitate scalable quantum computing architectures for spin qubits in
electrically-defined quantum dots. These links create space for classical
on-chip control electronics between qubit arrays, which can help to alleviate
the so-called wiring bottleneck. A promising method of achieving coherent links
between distant spin qubits consists of shuttling the spin through an array of
quantum dots. Here, we use a linear array of four tunnel-coupled quantum dots
in a 28Si/SiGe heterostructure to create a short quantum link. We move an
electron spin through the quantum dot array by adjusting the electrochemical
potential for each quantum dot sequentially. By pulsing the gates repeatedly,
we shuttle an electron forward and backward through the array up to 250 times,
which corresponds to a total distance of approximately 80 {\mu}m. We make an
estimate of the spin-flip probability per hop in these experiments and conclude
that this is well below 0.01% per hop.Comment: 11 pages, 3 main figures, 6 appendix figure
Does livestock predation reflect in negative local perceptions of Ethiopian wolves in South Wollo?
Conservation Biolog
Boundary relations and generalized resolvents of symmetric operators
The Kre\u{\i}n-Naimark formula provides a parametrization of all selfadjoint
exit space extensions of a, not necessarily densely defined, symmetric
operator, in terms of maximal dissipative (in \dC_+) holomorphic linear
relations on the parameter space (the so-called Nevanlinna families). The new
notion of a boundary relation makes it possible to interpret these parameter
families as Weyl families of boundary relations and to establish a simple
coupling method to construct the generalized resolvents from the given
parameter family. The general version of the coupling method is introduced and
the role of boundary relations and their Weyl families for the
Kre\u{\i}n-Naimark formula is investigated and explained.Comment: 47 page
Forty years of Leiden environmental science: the history of the Leiden Institute of Environmental Sciences (CML) 1978-2018
Forty years of Leiden environmental sciences relates the story of CML, today one of the Faculty of Science’s eight institutes but with its roots in a more or less in dependent group of ex-activists within the university. Back in the day, many of those at the top of the university would probably have had trouble accepting that ‘those upstarts’ would still be around forty years on – not locked away in some cubbyhole with their stencil duplicator, but as a professor, assistant professor or even a dean. Today they are professors emeritus or have retired: Helias Udo de Haes, Wouter de Groot, Gerard Barendse, Gjalt Huppes, Gerard Persoon, Hans de Iongh and Jan Boersema – which doesn’t stop most of them just carrying on working. And a new generation of environmental scientists is now leading CML’s research and teaching: Geert de Snoo, Arnold Tukker, Martina Vijver, Peter van Bodegom, Jeroen Guinée, Ester van der Voet and René Kleijn.Industrial EcologyConservation Biolog
The CHEK2 1100delC mutation identifies families with a hereditary breast and colorectal cancer phenotype
Because of genetic heterogeneity, the identification of breast
cancer-susceptibility genes has proven to be exceedingly difficult. Here,
we define a new subset of families with breast cancer characterized by the
presence of colorectal cancer cases. The 1100delC variant of the cell
cycle checkpoint kinase CHEK2 gene was present in 18% of 55 families with
hereditary breast and colorectal cancer (HBCC) as compared with 4% of 380
families with non-HBCC (P<.001), thus providing genetic evidence for the
HBCC phenotype. The CHEK2 1100delC mutation was, however, not the major
predisposing factor for the HBCC phenotype but appeared to act in synergy
with another, as-yet-unknown susceptibility gene(s). The unequivocal
definition of the HBCC phenotype opens new avenues to search for thi
The multifunctional roles of vegetated strips around and within agricultural fields : A systematic map protocol.
Background: Agriculture and agricultural intensification can have significant negative impacts on the environment, including nutrient and pesticide leaching, spreading of pathogens, soil erosion and reduction of ecosystem services provided by terrestrial and aquatic biodiversity. The establishment and management of vegetated strips adjacent to farmed fields (including various field margins, buffer strips and hedgerows) are key mitigation measures for these negative environmental impacts and environmental managers and other stakeholders must often make decisions about how best to design and implement vegetated strips for a variety of different outcomes. However, it may be difficult to obtain relevant, accurate and summarised information on the effects of implementation and management of vegetated strips, even though a vast body of evidence exists on multipurpose vegetated strip interventions within and around fields. To improve the situation, we describe a method for assembling a database of relevant research relating to vegetated strips undertaken in boreo-temperate farming systems (arable, pasture, horticulture, orchards and viticulture). Methods: We will search 13 bibliographic databases, 1 search engine and 37 websites for stakeholder organisations using a predefined and tested search string that focuses on a comprehensive list of vegetated strip synonyms. Non-English language searches in Danish, Finnish, German, Spanish, and Swedish will also be undertaken using a web-based search engine. We will screen search results at title, abstract and full text levels, recording the number of studies deemed non-relevant (with reasons at full text). A systematic map database that displays the meta-data (i.e. descriptive summary information about settings and methods) of relevant studies will be produced following full text assessment. The systematic map database will be displayed as a web-based geographical information system (GIS). The nature and extent of the evidence base will be discussed
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