1,591 research outputs found
Implications of changes in trophic diversity and food webs on fisheries and the environment
Most of the earth's ecosystems are experiencing slight to
catastrophic losses of biodiversity, caused by habitat
destruction, alien species introduction, climate change and
pollution (Wilcove et al., 1998). These human effects have
led to the extinction of native fish species, the collapse of their populations and the loss of ecological integrity and ecosystem functioning (Ogutu-Ohwayo & Hecky, 1991;
Witte et al. , 1992a; Mills et al., 1994; Vitousek et al., 1996).
Food webs are macro-descriptors of community feeding
interactions that can be used to map the flow of materials
and nutrients in ecosystems (Jepsen & Winemiller, 2002).
Comparative food web studies have been used to address theoretical questions such as 'does greater trophic connectivity increase stability?' (Cohen et al., 1990), and 'does the number of trophic levels increase with productivity?' (Briand & Cohen, 1987). Answers to such questions have obvious applications for natural resources management. From a multi-species fisheries standpoint, there is a need to understand consumer-resource dynamics within complex trophic networks
They want to tell us: Attention-aware Design and Evaluation of Ambient Displays for Learning
This paper explores the interaction between users and ambient displays and the evaluation thereof in a learning context. A formative design study examined the user attention towards ambient displays as well as the influence of different display designs. Experimental prototypes were varied on two design dimensions, namely representational fidelity and notification level, and deployed on a university campus. For the evaluation a combined approach using quantitative attention data as well as qualitative assessment methods was used. The results show a high degree of user interest in the displays over time, but do not provide clear evidence that the design of the displays influences the user attention. Nevertheless, the combination of quantitative and qualitative measurement does provide a more holistic view on user attention. The gathered insights can inform future designs and developments of ambient displays also beyond the learning context
Food web structure and mercury transfer in two contrasting Ugandan highland crater lakes (East Africa)
Abstract in English and FrenchVolcanic crater lakes scattered throughout western Uganda are important local sources of water and fish. Two representative but contrasting crater lakes near the Kibale National Park were sampled in 2000; the hyper-eutrophic Lake Saka, which is highly affected by agricultural practices, and the mesotrophic Lake Nkuruba that is still surrounded by intact forest. The food web structures in these
two lakes were assessed using stable nitrogen (d15N) and carbon (d13C) isotope analyses, and the mercury (THg) transfer patterns were quantified. The d15N results indicate that food webs in both lakes are abbreviated, with only one to two trophic levels from primary consumers. The Lake Saka biota had distinctively enriched d13C values compared with those in Lake Nkuruba, which may be due to 12C-limited phytoplankton blooms in this lake. In Lake Nkuruba, two introduced tilapiine species and the introduced guppy Poecilia reticulata fed predominantly upon invertebrates and decomposed terrestrial plant material. In Lake Saka, the introduced Nile perch Lates niloticus appeared to occupy the top trophic position, but stable isotope values of the endemic haplochromine cichlids exclude those as Nile perch prey items. THg was found to biomagnify through the food web, reaching highest concentrations in P. reticulata in Nkuruba, which tended to be higher than for L. niloticus in Saka, suggesting increased bioavailability of THg in Nkuruba. Maximum THg concentrations in fish never approached WHO recommended guidelines (200 ng g-1) designed to protect at-risk groups
Soil profile modification and cotton production
Hardpan soils of the southeastern Coastal Plains were
mixed to depths up to 0.61 m in an attempt to alleviate
strength problems associated with a subsurface pan. It
was hypothesized that mixing the dense, coarse-textured
E Horizon with the less dense Ap and the relatively
clayey B horizon would increase the water-holding
capacity of the E and decrease its strength. Mixed
soil did have a higher amount of water held than the
unmixed E, increasing it from 5 to 7% at -200 kPa
matric potential. This would reduce its strength by
approximately 0.1 MPa allowing easier root penetration
whether the increased water is available for uptake or
not. Although seed cotton in the deeply-mixed
treatments outyielded the moldboard-plowed treatments
by 233 kg/ha in one year, they were outyielded by 132
kg/ha in another year. The decrease in strength and
the increases of retention as a result of the mixing
were small and infiltration was unchanged.
Furthermore, mixing of field samples was less
homogenous than lab samples. It is doubtful that the
level of improvement of cotton would warrant the effort
involved in the mixing operation.
Treatments at two sites were split into fertility
subplots. The only significant fertility difference
was between rates of N sidedressed when plants were
about 0.40 m tall. The 20 kg/ha rate outyielded the 67
kg/ha rate by up to 300 kg/ha presumably because the
higher rate encouraged vegetative growth and retarded
boll formation which in turn limited lint and seed
production. Interactions between tillage or mixing and
fertility were non-significant. Plants grew better in
the deeper disturbed soils in dryer years. Other crops
may respond more favorably to the mixing
Absence of Phase Stiffness in the Quantum Rotor Phase Glass
We analyze here the consequence of local rotational-symmetry breaking in the
quantum spin (or phase) glass state of the quantum random rotor model. By
coupling the spin glass order parameter directly to a vector potential, we are
able to compute whether the system is resilient (that is, possesses a phase
stiffness) to a uniform rotation in the presence of random anisotropy. We show
explicitly that the O(2) vector spin glass has no electromagnetic response
indicative of a superconductor at mean-field and beyond, suggesting the absence
of phase stiffness. This result confirms our earlier finding (PRL, {\bf 89},
27001 (2002)) that the phase glass is metallic, due to the main contribution to
the conductivity arising from fluctuations of the superconducting order
parameter. In addition, our finding that the spin stiffness vanishes in the
quantum rotor glass is consistent with the absence of a transverse stiffness in
the Heisenberg spin glass found by Feigelman and Tsvelik (Sov. Phys. JETP, {\bf
50}, 1222 (1979).Comment: 8 pages, revised version with added references on the vanishing of
the stiffness constant in the Heisenberg spin glas
Baryogenesis via lepton number violating scalar interactions
We study baryogenesis through lepton number violation in left-right symmetric
models. In these models the lepton number and CP violating interactions of the
triplet higgs scalars can give rise to lepton number asymmetry through
non-equilibrium decays of the triplet higgs and the right handed
neutrinos. This in turn generates baryon asymmetry during the electroweak
anomalous processes.Comment: 14 pages, UTPT-93-1
Water conservation under reduced tillage systems
Water is important for dryland crop production. Seldom is rainfall
sufficient or adequately distributed during a growing season so that dryland
crops can produce to their fullest potential. It is necessary to have
stored water available in the soil to supplement inadequate growing season
rainfall for economical crop production. Stored water is especially
important in the Inland Pacific Northwest of north central Oregon,
southeastern Washington, and northern Idaho, where 65% of annual
precipitation occurs during the six-month (Sept. 1 to Feb. 28) winter period
and 30% during the four-month (March 1 to June 30) growing season. Stored
water is also important in the Eastern Idaho Plateau where the low annual
precipitation is nearly evenly distributed over the months of the year.
The water balance equation tells us that change in water content in the
soil - precipitation + inflow - runoff + upward flow - drainage -
evapotranspiration (ET). Any cultural practice that decreases runoff or ET
can result in increased water in the soil. To store adequate quantities
of water, deep soils (> 60 inches) with good infiltration and water holding
capacity are required. Summer fallow has long been the traditional practice
for storing water in soils for later use by crops. Fallow periods vary from
14 to 15 months where winter small grains are seeded to 21 months where
spring small grains are seeded. Water storage efficiency for fallow is low,
ranging from 10 to 35% in the Great Plains and the Southwest; to 30-37% in
eastern Idaho and northern Utah; to 40-45% of precipitation in the Inland
Pacific Northwest (Evans and Lemon, 1957). Good water conservation yields
increased crop production, stability of production, and increased water use
efficiency. Soil tillage and residue management play significant roles in
collection and storage of precipitation in the soil.
Our objectives are to discuss insights in water conservation gained under
the STEEP (Solutions to Economic and Environmental Problems) program
(Oldenstadt et al., 1982) during these last ten years and problems that
remain. New research information will be discussed under topics of crop
residues, conservation tillage systems, fallow and models
Action research in physical education: focusing beyond myself through cooperative learning
This paper reports on the pedagogical changes that I experienced as a teacher engaged in an action research project in which I designed and implemented an indirect, developmentally appropriate and childâcentred approach to my teaching. There have been repeated calls to expunge â or at least rationalise â the use of traditional, teacherâled practice in physical education. Yet despite the advocacy of many leading academics there is little evidence that such a change of approach is occurring. In my role as teacherâasâresearcher I sought to implement a new pedagogical approach, in the form of cooperative learning, and bring about a positive change in the form of enhanced pupil learning. Data collection included a reflective journal, postâteaching reflective analysis, pupil questionnaires, student interviews, document analysis, and nonâparticipant observations. The research team analysed the data using inductive analysis and constant comparison. Six themes emerged from the data: teaching and learning, reflections on cooperation, performance, time, teacher change, and social interaction. The paper argues that cooperative learning allowed me to place social and academic learning goals on an even footing, which in turn placed a focus on pupilsâ understanding and improvement of skills in athletics alongside their interpersonal development
Coherently Scattering Atoms from an Excited Bose-Einstein Condensate
We consider scattering atoms from a fully Bose-Einstein condensed gas. If we
take these atoms to be identical to those in the Bose-Einstein condensate, this
scattering process is to a large extent analogous to Andreev reflection from
the interface between a superconducting and a normal metal. We determine the
scattering wave function both in the absence and the presence of a vortex. Our
results show a qualitative difference between these two cases that can be
understood as due to an Aharonov-Bohm effect. It leads to the possibility to
experimentally detect and study vortices in this way.Comment: 5 pages of ReVTeX and 2 postscript figure
CCL2 and CCR2 regulate pain-related behaviour and early gene expression in post-traumatic murine osteoarthritis but contribute little to chondropathy
SummaryObjectiveThe role of inflammation in structural and symptomatic osteoarthritis (OA) remains unclear. One key mediator of inflammation is the chemokine CCL2, primarily responsible for attracting monocytes to sites of injury. We investigated the role of CCL2 and its receptor CCR2 in experimental OA.DesignOA was induced in 10 weeks old male wild type (WT), Ccl2â/â and Ccr2â/â mice, by destabilisation of the medial meniscus (DMM). RNA was extracted from whole joints at 6Â h and 7 days post-surgery and examined by reverse transcription polymerase chain reaction (RT-PCR). Gene expression changes between naĂŻve and DMM-operated mice were compared. Chondropathy scores, from mice at 8, 12, 16 and 20 weeks post DMM were calculated using modified Osteoarthritis Research Society International (OARSI) grading systems. Changes in hind paw weight distribution, as a measure of pain, were assessed by Linton incapacitance.ResultsAbsence of CCL2 strongly suppressed (>90%) selective inflammatory response genes in the joint 6Â h post DMM, including arginase 1, prostaglandin synthase 2, nitric oxide synthase 2 and inhibin A. IL6, MMP3 and tissue inhibitor of metalloproteinase 1 were also significantly suppressed. Similar trends were also observed in the absence of CCR2. A lower average chondropathy score was observed in both Ccl2â/â and Ccr2â/â mice at 12, 16 and 20 weeks post DMM compared with WT mice, but this was only statistically significant at 20 weeks in Ccr2â/â mice. Pain-related behaviour in Ccl2â/â and Ccr2â/â mice post DMM was delayed in onset.ConclusionThe CCL2/CCR2 axis plays an important role in the development of pain in murine OA, but contributes little to cartilage damage
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