7,257 research outputs found
Antecedents of approach-avoidance achievement goal adoption in physical education: A longitudinal perspective
Interactions of arbuscular mycorrhizal fungi, critical loads of nitrogen deposition, and shifts from native to invasive species in a southern California shrubland
Anthropogenic nitrogen (N) deposition and invasive species are causing declines in global biodiversity, and both factors impact the diversity and functioning of arbuscular mycorrhizal (AM) fungi. Shifts in arbuscular mycorrhizal fungal (AMF) communities can generate feedback to native plants and affect their success, as was observed in California’s coastal sage scrub, which is a Mediterranean-type shrubland threatened by invasive grasses. As vegetation-type conversion from native shrubland to exotic annual grassland increased along a gradient of increasing N deposition, the richness of native plant species and of spore morphotypes decreased. Rapid declines in all plant and fungal values occurred at the critical load (CL) of 10–11 kg N·ha−1·year−1, indicating that AM fungi respond to the same environmental signals as the plants, and can be used to assess CL. Shrub root colonization also decreased along the N gradient, but colonization of the invasive grass was dominated by a fine AMF endophyte that was unresponsive to elevated N. A greenhouse experiment to assess AMF functioning showed that the native shrub Artemisia californica Less. had a negative growth response to an inoculum from high-N but not low-N soils, whereas the invasive grass Bromus rubens L. had a positive response to both inocula. Differential functioning of AM fungi under N deposition may in part explain vegetation-type conversion and the decline of this native shrubland
Knowing Where To Hit It: A Conceptual Framework for the Sustainable Development of the Himalayas
This paper originated in a short exploratory piece of work for the United Nations Environment Programme (UNEP), in the nature of a "strategic reconnaissance" of a complex knot of environmental-social problems. However, early forays indicated strong underlying parallels with issues being explored in other case studies in the Institutional Settings and Environmental Policies (INS) project at IIASA. For this reason, and despite its limited external resources, the Himalaya work written up here took its place as one part of a troika INS project, that also involved research on hazardous waste management and on energy policy modeling.
Though the main effort has been on hazardous waste management, the intellectual connections between these apparently diverse research fields have proved most instructive. These connections have to do with the ways in which uncertainties (both technical and social) are defined by institutions, especially regulatory and policy analytic bodies. The thrust of research on all these fronts has been to better characterise different kinds of uncertainty and to explore the origins and policy implications of conflicting problem definitions. The practical aim in this effort has been to encourage better policy design. An understanding of the institutional roots of uncertainty and of multiple problem definitions opens the way for an anticipatory style of policy formulation that is capable of evaluating the implementability, and thus viability, of different policy options and institutional arrangements. This strategic concern is a direct evolution from the previous work of the Risk Group--the predecessor to INS
Electric field sensing with a scanning fiber-coupled quantum dot
We demonstrate the application of a fiber-coupled quantum-dot-in-a-tip as a
probe for scanning electric field microscopy. We map the out-of-plane component
of the electric field induced by a pair of electrodes by measurement of the
quantum-confined Stark effect induced on a quantum dot spectral line. Our
results are in agreement with finite element simulations of the experiment.
Furthermore, we present results from analytic calculations and simulations
which are relevant to any electric field sensor embedded in a dielectric tip.
In particular, we highlight the impact of the tip geometry on both the
resolution and sensitivity.Comment: 10 pages, 4 figure
New calculations of the PNC Matrix Element for the 0 doublet in N
A new calculation of the predominantly isoscalar PNC matrix element between
the (E 8.7 MeV) states in N has
been carried out in a (0+1+2+3+4) model space with the
Warburton-Brown interaction. The magnitude of the PNC matrix element of 0.22 to
0.34 eV obtained with the DDH PNC interaction is substantially suppressed
compared with previous calculations in smaller model spaces but shows agreement
with the preliminary Seattle experimental data. The calculated sign is opposite
to that obtained experimentally, and the implications of this are discussed.Comment: REVTEX, 28 page
Quantum dot opto-mechanics in a fully self-assembled nanowire
We show that fully self-assembled optically-active quantum dots (QDs)
embedded in MBE-grown GaAs/AlGaAs core-shell nanowires (NWs) are coupled to the
NW mechanical motion. Oscillations of the NW modulate the QD emission energy in
a broad range exceeding 14 meV. Furthermore, this opto-mechanical interaction
enables the dynamical tuning of two neighboring QDs into resonance, possibly
allowing for emitter-emitter coupling. Both the QDs and the coupling mechanism
-- material strain -- are intrinsic to the NW structure and do not depend on
any functionalization or external field. Such systems open up the prospect of
using QDs to probe and control the mechanical state of a NW, or conversely of
making a quantum non-demolition readout of a QD state through a position
measurement.Comment: 20 pages, 6 figure
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