4,841 research outputs found
A review of the processes and effects of droughts and summer floods in rivers and threats due to climate change on current adaptive strategies
Europe is expected to experience a greater frequency of floods and droughts as precipitation and evapotranspiration patterns are modified by climate change in future. Several large scale drought and flooding events have occurred in Europe since 2000. Studies of drought are rare but indicate important impacts on freshwater habitats, water quality, plants and animals, which may have wider consequences for ecosystem functioning. The main factors determining the impacts of droughts and floods are event duration and seasonality of the event. A diverse habitat distribution and the presence of refugia at the reach scale confer the most resilience against droughts and floods. Management measures will also be impacted particularly with regard to riparian zones, channel morphology, flow and floodplain connectivity. However there is a conflict between management actions that target the effects of drought, and those that target floods.
This report reviews information on droughts and aseasonal floods (summer floods) published since 2000 with a principal focus on small lowland rivers. Using several recent (post 2000) reviews on these topics, we describe abiotic and biotic effects of droughts and floods, providing recent European examples where possible. We explain the current status of droughts and summer floods in Europe, and where the main sources of data can be found. We highlight the threats posed by these phenomena to some of the most common current adaptive management strategies in place in the EU. To this end we use measures already described within REFRESH under Deliverables 1.1 and 1.2, and we focused solely on adaptive measures relating to riparian zones, channel morphology, flow and floodplain connectivity
Andreev's Theorem on hyperbolic polyhedra
In 1970, E. M. Andreev published a classification of all three-dimensional
compact hyperbolic polyhedra having non-obtuse dihedral angles. Given a
combinatorial description of a polyhedron, , Andreev's Theorem provides five
classes of linear inequalities, depending on , for the dihedral angles,
which are necessary and sufficient conditions for the existence of a hyperbolic
polyhedron realizing with the assigned dihedral angles. Andreev's Theorem
also shows that the resulting polyhedron is unique, up to hyperbolic isometry.
Andreev's Theorem is both an interesting statement about the geometry of
hyperbolic 3-dimensional space, as well as a fundamental tool used in the proof
for Thurston's Hyperbolization Theorem for 3-dimensional Haken manifolds. It is
also remarkable to what level the proof of Andreev's Theorem resembles (in a
simpler way) the proof of Thurston.
We correct a fundamental error in Andreev's proof of existence and also
provide a readable new proof of the other parts of the proof of Andreev's
Theorem, because Andreev's paper has the reputation of being ``unreadable''.Comment: To appear les Annales de l'Institut Fourier. 47 pages and many
figures. Revision includes significant modification to section 4, making it
shorter and more rigorous. Many new references include
Integrating professional development into a quality improvement framework in community pharmacy
Recent Biological Research in Greenland
The first two authors present a brief outline of research in plant taxonomy, geography and ecology; tree planting and future work. Dr. Dunbar reviews terrestrial and fresh-water faunistic studies: marine biological and fisheries investigations in West Greenland and its offshore waters
The No-Triangle Hypothesis for N=8 Supergravity
We study the perturbative expansion of N=8 supergravity in four dimensions
from the viewpoint of the ``no-triangle'' hypothesis, which states that
one-loop graviton amplitudes in N=8 supergravity only contain scalar box
integral functions. Our computations constitute a direct proof at six-points
and support the no-triangle conjecture for seven-point amplitudes and beyond.Comment: 43page
The impact of governance on management research
The rigor versus relevance debate of management research is ongoing. We
contribute to this discussion by contrasting alternative assumptions about
generating management knowledge and linking knowledge generation to academic
governance. Specifically, we show that knowledge-by-representation dominates
the field and is reinforced by the governance structures and processes guiding
our academic management journals, peer review, and business school practices.
We propose governance changes in academic publishing to encourage innovative
research that may also generate knowledge-by-exemplification with strong ties
to management practice
Observation of enhanced transmission for s-polarized light through a subwavelength slit
Enhanced optical transmission (EOT) through subwavelength apertures is
usually obtained for p-polarized light. The present study experimentally
investigates EOT for s-polarized light. A subwavelength slit surrounded on each
side by periodic grooves has been fabricated in a gold film and covered by a
thin dielectric layer. The excitation of s-polarized dielectric waveguide modes
inside the dielectric film strongly increases the s-polarized transmission.
Transmission measurements are compared with a coupled mode model and show good
qualitative agreement. Adding a waveguide can improve light transmission
through subwavelength apertures, as both s and p-polarization can be
efficiently transmitted.Comment: 11 pages, 3 figures, submitted to Applied Physics Letter
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Tracer concentration profiles measured in central London as part of the REPARTEE campaign
There have been relatively few tracer experiments carried out that have looked at vertical plume spread in urban areas. In this paper we present results from two tracer (cyclic perfluorocarbon) experiments carried out in 2006 and 2007 in central London centred on the BT Tower as part of the REPARTEE (Regent’s Park and Tower Environmental Experiment) campaign. The height of the tower gives a unique opportunity to study vertical dispersion profiles and transport times in central London. Vertical gradients are contrasted with the relevant Pasquill stability classes. Estimation of lateral advection and vertical mixing times are made and compared with previous measurements. Data are then compared with a simple operational dispersion model and contrasted with data taken in central London as part of the DAPPLE campaign. This correlates dosage with non-dimensionalised distance from source. Such analyses illustrate the feasibility of the use of these empirical correlations over these prescribed distances in central London
<sup>14</sup>C AMS at SUERC: improving QA data from the 5 MV tandem AMS and 250 kV SSAMS
In 2003, a National Electrostatics Corporation (NEC) 5MV tandem accelerator mass spectrometer was installed at SUERC, providing the radiocarbon laboratory with 14C measurements to 4–5‰ repeatability. In 2007, a 250kV single-stage accelerator mass spectrometer (SSAMS) was added to provide additional 14C capability and is now the preferred system for 14C analysis. Changes to the technology and to our operations are evident in our copious quality assurance data: typically, we now use the 134-position MC-SNICS source, which is filled to capacity. Measurement of standards shows that spectrometer running without the complication of on-line δ13C evaluation is a good operational compromise. Currently, 3‰ 14C/13C measurements are routinely achieved for samples up to nearly 3 half-lives old by consistent sample preparation and an automated data acquisition algorithm with sample random access for measurement repeats. Background and known-age standard data are presented for the period 2003–2008 for the 5MV system and 2007–2008 for the SSAMS, to demonstrate the improvements in data quality
MHV-Vertices for Gravity Amplitudes
We obtain a CSW-style formalism for calculating graviton scattering
amplitudes and prove its validity through the use of a special type of
BCFW-like parameter shift. The procedure is illustrated with explicit examples.Comment: 21 pages, minor typos corrected, proof added in section
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