21,653 research outputs found
Historical changes (1905-2005) in external phosphorus loads to Loch Leven, Scotland, UK
This article reviews historical changes in
the total phosphorus (TP) inputs to Loch Leven,
Scotland, UK. Data derived from palaeolimnological
records suggest that inputs in the early 1900s were
about 6 t TP year-1 (0.45 g TP m-2 year-1). By
1985, this had risen to about 20 t TP year-1
(1.5 g TP m-2 year-1) due to increases in runoff
from agricultural land and discharges from point
sources. By the late 1970s, increased TP inputs were
causing serious degradation of lake water quality.
Most noticeably, there had been an increase in
cyanobacterial blooms. A catchment management
plan was implemented in the early 1990s. This
resulted in a 60% reduction in the annual TP input
between 1985 (20 t TP year-1/1.5 g TP m-2 year-1)
and 1995 (8 t TP year-1/0.6 g TP m-2 year-1). The
main reduction was associated with better control of
point source discharges, but attempts were also made
to reduce inputs from diffuse sources. The reduction in
external TP loading to the lake led to a marked decline
in TP retention by the lake each year
Classification and area estimation of land covers in Kansas using ground-gathered and LANDSAT digital data
Ground-gathered data and LANDSAT multispectral scanner (MSS) digital data from 1981 were analyzed to produce a classification of Kansas land areas into specific types called land covers. The land covers included rangeland, forest, residential, commercial/industrial, and various types of water. The analysis produced two outputs: acreage estimates with measures of precision, and map-type or photo products of the classification which can be overlaid on maps at specific scales. State-level acreage estimates were obtained and substate-level land cover classification overlays and estimates were generated for selected geographical areas. These products were found to be of potential use in managing land and water resources
Non-Equilibrium Dynamics of Correlated Electron Transfer in Molecular Chains
The relaxation dynamics of correlated electron transport (ET) along molecular
chains is studied based on a substantially improved numerically exact path
integral Monte Carlo (PIMC) approach. As archetypical model we consider a
Hubbard chain containing two interacting electrons coupled to a bosonic bath.
For this generalization of the ubiquitous spin-boson model, the intricate
interdependence of correlations and dissipation leads to non-Boltzmann thermal
equilibrium distributions for many-body states. By mapping the multi-particle
dynamics onto an isomorphic single particle motion this phenomenon is shown to
be sensitive to the particle statistics and due to its robustness allows for
new control schemes in designed quantum aggregates.Comment: 5 pages, 4 figure
Secondary literacy across the curriculum: Challenges and possibilities
This paper discusses the challenges and possibilities attendant upon successfully implementing literacy across the curriculum initiatives – or ‘school language policies’ as they have come to be known - particularly at the secondary or high school level. It provides a theoretical background to these issues, exploring previous academic discussions of school language policies, and highlights key areas of concern as well as opportunity with respect to school implementation of such policies. As such, it provides a necessary conceptual background to the subsequent papers in this special issue, which focus upon the Secondary Schools’ Literacy Initiative (SSLI) – a New Zealand funded programme that aims to establish cross-curricular language and literacy policies in secondary schools
Can Long-Range Nuclear Properties Be Influenced By Short Range Interactions? A chiral dynamics estimate
Recent experiments and many-body calculations indicate that approximately
20\% of the nucleons in medium and heavy nuclei () are part of
short-range correlated (SRC) primarily neutron-proton () pairs. We find
that using chiral dynamics to account for the formation of pairs due to
the effects of iterated and irreducible two-pion exchange leads to values
consistent with the 20\% level. We further apply chiral dynamics to study how
these correlations influence the calculations of nuclear charge radii, that
traditionally truncate their effect, to find that they are capable of
introducing non-negligible effects.Comment: 6 pages, 0 figures. This version includes many improvement
Segregation by thermal diffusion in granular shear flows
Segregation by thermal diffusion of an intruder immersed in a sheared
granular gas is analyzed from the (inelastic) Boltzmann equation. Segregation
is induced by the presence of a temperature gradient orthogonal to the shear
flow plane and parallel to gravity. We show that, like in analogous systems
without shear, the segregation criterion yields a transition between upwards
segregation and downwards segregation. The form of the phase diagrams is
illustrated in detail showing that they depend sensitively on the value of
gravity relative to the thermal gradient. Two specific situations are
considered: i) absence of gravity, and ii) homogeneous temperature. We find
that both mechanisms (upwards and downwards segregation) are stronger and more
clearly separated when compared with segregation criteria in systems without
shear.Comment: 8 figures. To appear in J. Stat. Mec
Three-dimensional simulations of laser-plasma interactions at ultrahigh intensities
Three-dimensional (3D) particle-in-cell (PIC) simulations are used to
investigate the interaction of ultrahigh intensity lasers (
W/cm) with matter at overcritical densities. Intense laser pulses are
shown to penetrate up to relativistic critical density levels and to be
strongly self-focused during this process. The heat flux of the accelerated
electrons is observed to have an annular structure when the laser is tightly
focused, showing that a large fraction of fast electrons is accelerated at an
angle. These results shed light into the multi-dimensional effects present in
laser-plasma interactions of relevance to fast ignition of fusion targets and
laser-driven ion acceleration in plasmas.Comment: 2 pages, 1 figur
Utilizing remote sensing of Thematic Mapper data to improve our understanding of estuarine processes and their influence on the productivity of estuarine-dependent fisheries
LANDSAT thematic mapper (TM) data are being used to refine and validate a stochastic spatial computer model to be applied to coastal resource management problems in Louisiana. Two major aspects of the research are: (1) the measurement of area of land (or emergent vegetation) and water and the length of the interface between land and water in TM imagery of selected coastal wetlands (sample marshes); and (2) the comparison of spatial patterns of land and water in the sample marshes of the imagery to that in marshes simulated by a computer model. In addition to activities in these two areas, the potential use of a published autocorrelation statistic is analyzed
Population Dynamics on Complex Food Webs
In this work we analyse the topological and dynamical properties of a simple
model of complex food webs, namely the niche model. In order to underline
competition among species, we introduce "prey" and "predators" weighted overlap
graphs derived from the niche model and compare synthetic food webs with real
data. Doing so, we find new tests for the goodness of synthetic food web models
and indicate a possible direction of improvement for existing ones. We then
exploit the weighted overlap graphs to define a competition kernel for
Lotka-Volterra population dynamics and find that for such a model the stability
of food webs decreases with its ecological complexity.Comment: 11 Pages, 5 Figures, styles enclosed in the submissio
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