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91.
Evan D.G. Fraser 《Global Environmental Change》2013,23(6):1662-1672
This paper examines four broad policy and public responses to the American Dust Bowl in the 1930s as a way of exploring how society today could address our own “food crisis”. More particularly, in the Dust Bowl some argued that solutions would be found by engineers and farmers who would develop new ways of watering dry fields. A second group believed that inappropriate political and economic incentives had led to bad farming practices prior to the drought and this contributed to wide-spread erosion. To this group, the best solutions included governmental regulation of farm practices. A third group focused on the welfare of individuals, arguing that creating a social safety net to protect marginalized families was the highest priority. Finally, there were commentators who advocated for a smaller scale, ecological, and holistic approach to farming. Today, the same four perspectives are present in debates about how to maintain global food security in light of population growth, high energy prices and climate change. Exploring the similarity of the discourses between today's food crisis and the one that hit American society 80 years ago reveals that advocates of the four different camps are motivated by very different principles. Briefly, proponents of technological solutions base many of their arguments on the assumption that human ingenuity is capable of producing extremely productive food systems. The managerial arguments, by contrast, are based on the idea that the natural environment can be rationally and efficiently managed using scientific principles. The social welfare narrative seeks to create a more equitable food system. Finally, the ecological and holistic narrative argues that diverse, small scale and local food systems are a prerequisite for long term sustainability. The primary contribution of this paper, therefore, is to expose these deeply held ontological tensions as a way of arguing that policy makers today must de-politicise arguments and use the principles embedded in all four narratives when designing programmes to ensure that the 21st century does not face a repeat of the crisis of the 1930s. 相似文献
92.
Yiannis Tsapras Rachel A. Street Keith Horne Alan Penny Fraser Clarke Hans Deeg Francisco Garzon Simon Kemp Maria Rosa Zapatero Osorio Alejandro Oscoz Abad Santiago Madruga Sanchez Carlos Eiroa Alcione Mora Antxon Alberdi rew Cameron John K. Davies Roger Ferlet Carol Grady Allan W. Harris Javier Palacios reas Quirrenbach Heike Rauer Jean Schneider Dolf de Winter Bruno Merin Enrique Solano 《Monthly notices of the Royal Astronomical Society》2001,325(3):1205-1212
In 1998 the EXPORT team monitored microlensing event light curves using a charge-coupled device (CCD) camera on the IAC 0.8-m telescope on Tenerife to evaluate the prospect of using northern telescopes to find microlens anomalies that reveal planets orbiting the lens stars. The high airmass and more limited time available for observations of Galactic bulge sources make a northern site less favourable for microlensing planet searches. However, there are potentially a large number of northern 1-m class telescopes that could devote a few hours per night to monitor ongoing microlensing events. Our IAC observations indicate that accuracies sufficient to detect planets can be achieved despite the higher airmass. 相似文献
93.
Teresa Mineo George W. Fraser Adrian Martindale Charly Feldman Riccardo Campana Giancarlo Cusumano Marco Feroci 《Experimental Astronomy》2014,37(1):69-84
The Large Observatory For X-ray Timing (LOFT) is one of the candidate missions selected by the European Space Agency for an initial assessment phase in the Cosmic Vision programme. It is proposed for the M3 launch slot and has broad scientific goals related to fast timing of astrophysical X-ray sources. LOFT will carry the Large Area Detector (LAD), as one of the two core science instruments, necessary to achieve the challenging objectives of the project. LAD is a collimated detector working in the energy range 2-50 keV with an effective area of approximately 10 m 2at 8 keV. The instrument comprises an array of modules located on deployable panels. Lead-glass microchannel plate (MCP) collimators are located in front of the large-area Silicon Drift Detectors (SDD) to reduce the background contamination from off-axis resolved point sources and from the diffuse X-ray background. The inner walls of the microchannel plate pores reflect grazing incidence X-ray photons with a probability that depends on energy. In this paper, we present a study performed with an ad-hoc simulator of the effects of this capillary reflectivity on the overall instrument performance. The reflectivity is derived from a limited set of laboratory measurements, used to constrain the model. The measurements were taken using a prototype collimator whose thickness is similar to that adopted in the current baseline design proposed for the LAD. We find that the experimentally measured level of reflectivity of the pore inner walls enhances the off-axis transmission at low energies, producing an almost flat-top response. The resulting background increase due to the diffuse cosmic X-ray emission and sources within the field of view does not degrade the instrument sensitivity. 相似文献
94.
Paula Lindgren John Parnell Craig Norman Darren F. Mark Martin Baron Jens Orm Erik Sturkell James Conliffe Wesley Fraser 《Meteoritics & planetary science》2007,42(11):1961-1969
Abstract— The Ordovician Lockne impact structure is located in central Sweden. The target lithology consisted of limestone and black unconsolidated shale overlaying a Precambrian crystalline basement. The Precambrian basement is uranium‐rich, and the black shale is both uranium‐ and organic‐rich. This circumstance makes Lockne a good candidate for testing the occurrence of U‐Th‐rich bitumen nodules in an impact structure setting. U‐Th‐rich bitumen nodules are formed through irradiation; hence the increase in the complexity of organic matter by a radioactive (uranium‐ and thorium‐rich) mineral phase. U‐Th‐rich bitumen nodules were detected in crystalline impact breccia and resurge deposits from the impact structure, but samples of non‐impact‐affected rocks from outside the impact structure do not contain any U‐Th‐rich bitumen nodules. This implies that in the Lockne impact structure, the nodules are associated with impact‐related processes. U‐Th‐rich bitumen nodules occur throughout the geological record and are not restricted to an impact structure setting, but our studies at Lockne show that this process of irradiation can readily occur in impact structures where fracturing of rocks and a post‐impact hydrothermal system enhances fluid circulation. The irradiation of organic matter by radioactive minerals has previously been proposed as a process for concentration of carbon on the early Earth. Impact structures are suggested as sites for prebiotic chemistry and primitive evolution, and irradiation by radioactive minerals could be an important mechanism for carbon concentration at impact sites. 相似文献
95.
96.
This study performs a comprehensive feedback analysis on the Bureau of Meteorology Research Centre General Circulation Model,
quantifying all important feedbacks operating under an increase in atmospheric CO2. The individual feedbacks are analysed in detail, using an offline radiation perturbation method, looking at long- and shortwave
components, latitudinal distributions, cloud impacts, non-linearities under 2xCO2 and 4xCO2 warmings and at interannual variability. The water vapour feedback is divided into terms due to moisture height and amount
changes. The net cloud feedback is separated into terms due to cloud amount, height, water content, water phase, physical
thickness and convective cloud fraction. Globally the most important feedbacks were found to be (from strongest positive to
strongest negative) those due to water vapour, clouds, surface albedo, lapse rate and surface temperature. For the longwave
(LW) response the most important term of the cloud ‘optical property’ feedbacks is due to the water content. In the shortwave
(SW), both water content and water phase changes are important. Cloud amount and height terms are also important for both
LW and SW. Feedbacks due to physical cloud thickness and convective cloud fraction are found to be relatively small. All cloud
component feedbacks (other than height) produce conflicting LW/SW feedbacks in the model. Furthermore, the optical property
and cloud fraction feedbacks are also of opposite sign. The result is that the net cloud feedback is the (relatively small)
product of conflicting physical processes. Non-linearities in the feedbacks are found to be relatively small for all but the
surface albedo response and some cloud component contributions. The cloud impact on non-cloud feedbacks is also discussed:
greatest impact is on the surface albedo, but impact on water vapour feedback is also significant. The analysis method here
proves to be a␣powerful tool for detailing the contributions from different model processes (and particularly those of the
clouds) to the final climate model sensitivity.
Received: 15 June 2000 / Accepted: 10 January 2001 相似文献
97.
Failure envelopes and plastic potentials for eccentrically loaded surface footings on undrained soil
M. Fraser Bransby 《国际地质力学数值与分析法杂志》2001,25(4):329-346
The failure envelope in V–M space for surface foundations on undrained material under eccentric loading can be determined using an extended version of the scaling (or effective area) concept of Meyerhof. A similar displacement transformation allows production of the plastic potential. The two‐dimensional finite element analyses of fully attached foundations subject to combined vertical (V) and moment (M) loading have been used to calculate appropriate scaling points for deduction of the failure envelope and plastic potential. Failure envelopes and plastic potentials are presented for footings on uniform and non‐uniform undrained material and it is seen that the equivalent ‘critical state’ or ‘parallel point’ lies slightly beneath the peak moment capacity. For accurate prediction of failure envelopes for footings on non‐uniform strength soil, consideration must be made of the apparent reduction of the soil heterogeneity as the area of footing in contact with the soil decreases. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
98.
Here we present new adaptive optics observations of the Quaoar–Weywot system. With these new observations we determine an improved system orbit. Due to a 0.39 day alias that exists in available observations, four possible orbital solutions are available with periods of ~11.6, ~12.0, ~12.4, and ~12.8 days. From the possible orbital solutions, system masses of 1.3–1.5 ± 0.1 × 1021 kg are found. These observations provide an updated density for Quaoar of 2.7–5.0 g cm?3. In all cases, Weywot’s orbit is eccentric, with possible values ~0.13–0.16. We present a reanalysis of the tidal orbital evolution of the Quaoar–Weywot system. We have found that Weywot has probably evolved to a state of synchronous rotation, and has likely preserved its initial inclination over the age of the Solar System. We find that for plausible values of the effective tidal dissipation factor tides produce a very slow evolution of Weywot’s eccentricity and semi-major axis. Accordingly, it appears that Weywot’s eccentricity likely did not tidally evolve to its current value from an initially circular orbit. Rather, it seems that some other mechanism has raised its eccentricity post-formation, or Weywot formed with a non-negligible eccentricity. 相似文献
99.
S. Sembay G. Branduardi‐Raymont J.P. Eastwood D.G. Sibeck A. Abbey P. Brown J.A. Carter C.M. Carr C. Forsyth D. Kataria S. Kemble S. Milan C.J. Owen A.M. Read L. Peacocke C.S. Arridge A.J. Coates M.R. Collier S.W.H. Cowley A.N. Fazakerley G. Fraser G.H. Jones R. Lallement M. Lester F.S. Porter T. Yeoman 《Astronomische Nachrichten》2012,333(4):388-392
AXIOM (Advanced X‐ray Imaging Of the Magnetosphere) is a concept mission which aims to explain how the Earth's magnetosphere responds to the changing impact of the solar wind using a unique method never attempted before; performing wide‐field soft X‐ray imaging and spectroscopy of the magnetosheath, magnetopause and bow shock at high spatial and temporal resolution. Global imaging of these regions is possible because of the solar wind charge exchange (SWCX) process which produces elevated soft X‐ray emission from the interaction of high charge‐state solar wind ions with primarily neutral hydrogen in the Earth's exosphere and near‐interplanetary space (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
100.
Water vapor plays an important role in the global climate system. A clear relationship between water vapor and solar activity can explain some physical mechanisms of how solar activity influences terrestrial weather/climate changes. To gain insight of this possible relationship, the atmospheric precipitable water vapor (PWV) as the terrestrial climate response was observed by ground-based GPS receivers over the Antarctic stations. The PWV changes analyzed for the period from 2003 to 2008 coincided with the declining phase of solar cycle 23 exhibited following the solar variability trend. Their relationship showed moderate to strong correlation with 0.45 < R 2 < 0.93 (p < 0.01), on a monthly basis. This possible relationship suggests that when the solar-coupled geomagnetic activity is stronger, the Earth’s surface will be warmer, as indicated by electrical connection between ionosphere and troposphere. 相似文献