752 research outputs found
Measures against the abandonment of common property summer pastures: experimental evidence from joint appropriation-provision games
Common property summer pastures constitute longstanding evidence that the tragedy of the commons can be prevented through self-organization. As a byproduct of their sustainable governance, high nature value farming systems with well-integrated patchy landscapes have existed for centuries. These common pool resourcesâwhich have historically needed protection from overexploitationâtoday suffer from underutilization, and their continued use is often contingent on government subsidies. The current study sought to identify which user, institutional, and resource attributes contribute to the sustainable use of high nature value summer pastures. Taking as our point of departure a recent field study of Swiss Alpine grazing lands, we set out to experimentally identify the most promising mechanisms for successful resource management in this context. To do so, we implement a controlled experiment that closely mirrors our field observations ("field-in-the-lab"), and parametrize our experiment to replicate field data. Our focus is on the institutional linkage of provision and appropriation. Our treatments varied across a range of parameters, ceteris paribus, to isolate which governance elements are most relevant; we did so to identify which policy options and scenarios should be prioritized in practical policy evaluations. It turns out that underappropriation appears to be the main management challenge for Swiss common property pastures today. Our analytical results suggest that current governance institutionsâand, more specifically, how they link appropriation to provision requirementsâmight need to be overhauled. The most promising avenues for doing so appear to be increased provision requirements, incentivized overprovision, and appropriation subsidies. Thus, our study highlights promising institutional adaptations at various governance levels that potentially counteract the decreasing use of high nature value common property pastures in Switzerland and elsewhere in Europe
Surface exposure ages imply multiple low-amplitude Pleistocene variations in East Antarctic Ice Sheet, Ricker Hills, Victoria Land
One of the major issues in (palaeo-) climatology is the response of Antarctic ice sheets to global climate changes. Antarctic ice volume has varied in the past but the extent and timing of these fluctuations are not well known. In this study, we address the question of amplitude and timing of past Antarctic ice level changes by surface exposure dating using in situ produced cosmogenic nuclides (10Be and 21Ne). The study area lies in the Ricker Hills, a nunatak at the boundary of the East Antarctic Ice Sheet in southern Victoria Land. By determining exposure ages of erratic boulders from glacial drifts we directly date East Antarctic Ice Sheet variations. Erosion-corrected neon and beryllium exposure ages indicate that a major ice advance reaching elevations of about 500m above present ice levels occurred between 1.125 and 1.375 million years before present. Subsequent ice fluctuations were of lesser extent but timing is difficult as all erratic boulders from related deposits show complex exposure histories. Sample-specific erosion rates were on the order of 20-45cmMa-1 for a quartzite and 10-65cmMa-1 for a sandstone boulder and imply that the modern cold, arid climate has persisted since at least the early Pleistocen
Solar Wind Neon from Genesis: Implications for the Lunar Noble Gas Record
Lunar soils have been thought to contain two solar noble gas components with distinct isotopic composition. One has been identified as implanted solar wind, the other as higher-energy solar particles. The latter was puzzling because its relative amounts were much too large compared with present-day fluxes, suggesting periodic, very high solar activity in the past. Here we show that the depth-dependent isotopic composition of neon in a metallic glass exposed on NASA's Genesis mission agrees with the expected depth profile for solar wind neon with uniform isotopic composition. Our results strongly indicate that no extra high-energy component is required and that the solar neon isotope composition of lunar samples can be explained as implantation-fractionated solar wind
Cosmic History and a Candidate Parent Asteroid for the Quasicrystal-bearing Meteorite Khatyrka
The unique CV-type meteorite Khatyrka is the only natural sample in which
"quasicrystals" and associated crystalline Cu,Al-alloys, including khatyrkite
and cupalite, have been found. They are suspected to have formed in the early
Solar System. To better understand the origin of these exotic phases, and the
relationship of Khatyrka to other CV chondrites, we have measured He and Ne in
six individual, ~40-{\mu}m-sized olivine grains from Khatyrka. We find a
cosmic-ray exposure age of about 2-4 Ma (if the meteoroid was <3 m in diameter,
more if it was larger). The U,Th-He ages of the olivine grains suggest that
Khatyrka experienced a relatively recent (<600 Ma) shock event, which created
pressure and temperature conditions sufficient to form both the quasicrystals
and the high-pressure phases found in the meteorite. We propose that the parent
body of Khatyrka is the large K-type asteroid 89 Julia, based on its peculiar,
but matching reflectance spectrum, evidence for an impact/shock event within
the last few 100 Ma (which formed the Julia family), and its location close to
strong orbital resonances, so that the Khatyrka meteoroid could plausibly have
reached Earth within its rather short cosmic-ray exposure age.Comment: Submitted to Earth and Planetary Science Letter
NNLO corrections to the total cross section for Higgs boson production in hadron-hadron collisions
We present the next-to-next-to-leading order (NNLO) corrections to the total
cross section for (pseudo-) scalar Higgs boson production using an alternative
method than those used in previous calculations. All QCD partonic subprocesses
have been included and the computation is carried out in the effective
Lagrangian approach which emerges from the standard model by taking the limit
where denotes the mass of the top quark. Our results
agree with those published earlier in the literature. We estimate the
theoretical uncertainties by comparing the -factors and the variation with
respect to the mass factorization/renormalization scales with the results
obtained by lower order calculations. We also investigate the dependence of the
cross section on several parton density sets provided by different groups.
Further we study which part of the coefficient functions dominates the cross
section. This is of interest for the resummation of large corrections which
occur near the boundary of phase space. It turns out that depending on the
definition of the total cross section the latter is dominated by the the
soft-plus-virtual gluon corrections represented by and
terms. PACS numbers: 12.38.-t, 12.38.Bx, 13.85.-t,
14.80.Gt.Comment: 61 pages, LaTeX, 15 postscript figures. With respect to the previous
version a more thorough comparison is made between two definitions of the
soft plus virtual gluon approximation. Misprints are corrected and references
are changed. Figs. 8a, 9a are changed into Figs. 8,9 respectively and Figs.
8b, 9b are droppe
Presolar He and Ne Isotopes in Single Circumstellar SiC Grains
Noble gas isotopes in presolar silicon carbide (SiC) dust grains from primitive meteorites provide, together with major element isotopic compositions, insight into the nucleosynthetic output of different types of evolved stars >4.5 Gyr ago. We report here new results from helium and neon isotopic analyses of single presolar SiC grains with sizes between 0.6 and 6.3 ÎŒm using an ultrahigh sensitivity mass spectrometer. These noble gas studies were complemented by an ion microprobe study (NanoSIMS) of Si, C, and N isotopic compositions of the same grains. About 40%, or 46 of the 110 grains analyzed, contain nucleosynthetic 22Ne and/or 4He from their parent stars above our mass spectrometer's detection limit. We discuss the possible stellar sources using isotopic ratios as constraints combined with new model predictions for low- to intermediate-mass (1.5, 2, 3, and 5 Mâ) asymptotic giant branch (AGB) stars of different metallicities (1, 1/2, 1/3, and 1/6 Zâ). Most SiC grains are of the mainstream type and originated in low-mass AGB stars. We find a higher-than-expected percentage of A/B type grains, with some containing 22Ne and/or 4He. In addition, we find one noble gas-rich nova grain candidate, one supernova grain (X-type grain), and one 22Ne-rich X- or Z-type grain candidate
Search for New Particles Decaying to Dijets at CDF
We have used 106 pb^-1 of data collected with the Collider Detector at
Fermilab to search for new particles decaying to dijets. We exclude at the 95%
confidence level models containing the following new particles: axigluons and
flavor universal colorons with mass between 200 and 980 GeV/c, excited quarks
with mass between 80 and 570 GeV/c^2 and between 580 and 760 GeV/c^2, color
octet technirhos with mass between 260 and 480 GeV/c^2, W' bosons with mass
between 300 and 420 GeV/c^2, and E_6 diquarks with mass between 290 and 420
GeV/c^2.Comment: 18 pages, 4 figures, 1 table. Submitted to Physical Review D Rapid
Communications. Postscript file of paper is also available at
http://www-cdf.fnal.gov/physics/pub97/cdf3276_dijet_search_prd_rc.p
Measurement of Rapidity Distribution for High Mass Drell-Yan ee Pairs at CDF
We report on the first measurement of the rapidity distribution dsigma/dy
over nearly the entire kinematic region of rapidity for e^+e^- pairs in the
Z-boson region of 66116 GeV/c^2.
The data sample consists of 108 pb^{-1} of ppbar collisions at \sqrt{s}=1.8 TeV
taken by the Collider Detector at Fermilab during 1992--1995. The total cross
section in the -boson region is measured to be 252 +- 11 pb. The measured
total cross section and d\sigma/dy are compared with quantum chromodynamics
calculations in leading and higher orders.Comment: 7 pages, 3 figures. Submitted to Physical Review Letter
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