453 research outputs found
Protected areas: providing natural solutions to 21st century challenges
Protected areas remain a cornerstone of global conservation efforts. The double impacts of climate change and biodiversity loss are major threats to achieving the Millennium Development Goals, especially those relating to environmental sustainability, poverty alleviation and food and water security. The growing awareness of the planet’s vulnerability to human driven changes also provides an opportunity to re-emphasize the multiple values of natural ecosystems and the services that they provide. Protected areas, when integrated into landuse plans as part of larger and connected conservation networks, offer practical, tangible solutions to the problems of both species loss and adaptation to climate change. Natural habitats make a significant contribution to mitigation by storing and sequestering carbon in vegetation and soils, and to adaptation by maintaining essential ecosystem services which help societies to respond to, and cope with climate change and other environmental challenges. Many protected areas could be justified on socioeconomic grounds alone yet their multiple goods and services are largely unrecognized in national accounting. This paper argues that there is a convincing case for greater investment in expanded and better-connected protected area systems, under a range of governance and management regimes that are specifically designed to counter the threats of climate change, increased demand and altered patterns of resource use. The new agenda for protected areas requires greater inclusivity of a broader spectrum of actors and rights holders, with growing attention to landscapes and seascapes protected by indigenous peoples, local communities, private owners and other actors which complement conservation areas managed by state agencies. Greater attention also needs to be focused on ways to integrate and mainstream protected areas into sustainable development, including promotion of “green” infrastructure as a strategic part of responses to climate change
Quasi-one-dimensional antiferromagnetism and multiferroicity in CuCrO
The bulk magnetic properties of the new quasi-one-dimensional Heisenberg
antiferromagnet, CuCrO, were characterized by magnetic susceptibility, heat
capacity, optical spectroscopy, EPR and dielectric capacitance measurements and
density functional evaluations of the intra- and interchain spin exchange
interactions. We found type-II multiferroicity below the N\'{e}el temperature
of 8.2(5) K, arising from competing antiferromagnetic nearest-neighbor () and next-nearest-neighbor () intra-chain spin exchange
interactions. Experimental and theoretical results indicate that the ratio
is close to 2, putting CuCrO in the vicinity of
the Majumdar-Ghosh point.Comment: 9 pages, 8 figures, submitted to PR
Optical study of orbital excitations in transition-metal oxides
The orbital excitations of a series of transition-metal compounds are studied
by means of optical spectroscopy. Our aim was to identify signatures of
collective orbital excitations by comparison with experimental and theoretical
results for predominantly local crystal-field excitations. To this end, we have
studied TiOCl, RTiO3 (R=La, Sm, Y), LaMnO3, Y2BaNiO5, CaCu2O3, and K4Cu4OCl10,
ranging from early to late transition-metal ions, from t_2g to e_g systems, and
including systems in which the exchange coupling is predominantly
three-dimensional, one-dimensional or zero-dimensional. With the exception of
LaMnO3, we find orbital excitations in all compounds. We discuss the
competition between orbital fluctuations (for dominant exchange coupling) and
crystal-field splitting (for dominant coupling to the lattice). Comparison of
our experimental results with configuration-interaction cluster calculations in
general yield good agreement, demonstrating that the coupling to the lattice is
important for a quantitative description of the orbital excitations in these
compounds. However, detailed theoretical predictions for the contribution of
collective orbital modes to the optical conductivity (e.g., the line shape or
the polarization dependence) are required to decide on a possible contribution
of orbital fluctuations at low energies, in particular in case of the orbital
excitations at about 0.25 eV in RTiO3. Further calculations are called for
which take into account the exchange interactions between the orbitals and the
coupling to the lattice on an equal footing.Comment: published version, discussion of TiOCl extended to low T, improved
calculation of orbital excitation energies in TiOCl, figure 16 improved,
references updated, 33 pages, 20 figure
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