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151.
SoEun Ahn Joseph E. de Steiguer Raymond B. Palmquist Thomas P. Holmes 《Climatic change》2000,45(3-4):493-509
Global warming due to the enhanced greenhouse effect through human activities has become a major public policy issue in recent years. The present study focuses on the potential economic impact of climate change on recreational trout fishing in the Southern Appalachian Mountains of North Carolina. Significant reductions in trout habitat and/or populations are anticipated under global warming since the study area is on the extreme margins of trout habitat of the eastern U.S. The purpose of this study is to estimate the potential welfare loss of trout anglers due to global warming. A nested multinomial logit model was developed and estimated to describe the angler's fishing choice behavior. The estimated median welfare loss (Compensating Variation) ranged from $5.63 to $53.18 per angler per single occasion under the various diminished trout habitat and/or population scenarios. 相似文献
152.
153.
Michael J. Glotter Raymond T. Pierrehumbert Joshua W. Elliott Nathan J. Matteson Elisabeth J. Moyer 《Climatic change》2014,126(3-4):319-335
Integrated Assessment Models (IAMs) that couple the climate system and the economy require a representation of ocean CO2 uptake to translate human-produced emissions to atmospheric concentrations and in turn to climate change. The simple linear carbon cycle representations in most IAMs are not however physical at long timescales, since ocean carbonate chemistry makes CO2 uptake highly nonlinear. No linearized representation can capture the ocean’s dual-mode behavior, with initial rapid uptake and then slow equilibration over ∽10,000 years. In a business-as-usual scenario followed by cessation of emissions, the carbon cycle in the 2007 version of the most widely used IAM, DICE (Dynamic Integrated model of Climate and the Economy), produces errors of ∽2°C by the year 2300 and ∽6°C by the year 3500. We suggest here a simple alternative representation that captures the relevant physics and show that it reproduces carbon uptake in several more complex models to within the inter-model spread. The scheme involves little additional complexity over the DICE model, making it a useful tool for economic and policy analyses. 相似文献
154.
Robert M. D’Anjou Nicholas L. Balascio Raymond S. Bradley 《Journal of Paleolimnology》2014,52(3):257-264
We report a new approach to locate and quantify cryptotephra in sedimentary archives using a continuously-imaging Flow Cytometer and Microscope (FlowCAM®). The FlowCAM rapidly photographs particles flowing in suspension past a microscope lens and performs semi-automated analysis of particle images. It has had primarily biological applications, although the potential sedimentological applications are numerous. Here we test the ability of this instrument to image irregularly shaped, vesicular glass shards and to screen sediment samples for the presence of cryptotephra. First, reference samples of basalt and rhyolite tephra (sieved <63 μm) were analyzed with the FlowCAM, demonstrating the ability of the instrument to photograph individual tephra shards. The highest-quality images were used to create a reference library of tephra particles, against which other particle morphologies could be automatically compared. Lake sediment samples with known concentrations of tephra were then analyzed. The tephra image library was used to perform pattern recognition calculations, automatically distinguishing tephra-like images from other particles in the sediment samples. The number of tephra shards identified by the FlowCAM technique was compared to manual counting using a polarizing light microscope, demonstrating that this rapid approach is capable of determining the relative concentrations of tephra in a given sediment sample. However, the FlowCAM systematically underestimates tephra concentrations relative to manual counts. We conclude that with a well-developed image library, the FlowCAM can be an effective tool for cryptotephra and sedimentological applications, but it may be inappropriate for large volume samples or if particle morphologies are outside the range of the image library. 相似文献
155.
Chris B. Folkes Heather M. Wright Raymond A. F. Cas Shanaka L. de Silva Chiara Lesti Jose G. Viramonte 《Bulletin of Volcanology》2011,73(10):1427-1454
From detailed fieldwork and biotite 40Ar/39Ar dating correlated with paleomagnetic analyses of lithic clasts, we present a revision of the stratigraphy, areal extent
and volume estimates of ignimbrites in the Cerro Galán volcanic complex. We find evidence for nine distinct outflow ignimbrites,
including two newly identified ignimbrites in the Toconquis Group (the Pitas and Vega Ignimbrites). Toconquis Group Ignimbrites
(~5.60–4.51 Ma biotite ages) have been discovered to the southwest and north of the caldera, increasing their spatial extents
from previous estimates. Previously thought to be contemporaneous, we distinguish the Real Grande Ignimbrite (4.68 ± 0.07 Ma
biotite age) from the Cueva Negra Ignimbrite (3.77 ± 0.08 Ma biotite age). The form and collapse processes of the Cerro Galán
caldera are also reassessed. Based on re-interpretation of the margins of the caldera, we find evidence for a fault-bounded
trapdoor collapse hinged along a regional N-S fault on the eastern side of the caldera and accommodated on a N-S fault on
the western caldera margin. The collapsed area defines a roughly isosceles trapezoid shape elongated E-W and with maximum
dimensions 27 × 16 km. The Cerro Galán Ignimbrite (CGI; 2.08 ± 0.02 Ma sanidine age) outflow sheet extends to 40 km in all
directions from the inferred structural margins, with a maximum runout distance of ~80 km to the north of the caldera. New
deposit volume estimates confirm an increase in eruptive volume through time, wherein the Toconquis Group Ignimbrites increase
in volume from the ~10 km3 Lower Merihuaca Ignimbrite to a maximum of ~390 km3 (Dense Rock Equivalent; DRE) with the Real Grande Ignimbrite. The climactic CGI has a revised volume of ~630 km3 (DRE), approximately two thirds of the commonly quoted value. 相似文献
156.
Heather M. N. Wright Chiara Lesti Raymond A. F. Cas Massimiliano Porreca José G. Viramonte Chris B. Folkes Guido Giordano 《Bulletin of Volcanology》2011,73(10):1567-1582
Columnar jointing is thought to occur primarily in lavas and welded pyroclastic flow deposits. However, the non-welded Cerro
Galán Ignimbrite at Paycuqui, Argentina, contains well-developed columnar joints that are instead due to high-temperature
vapor-phase alteration of the deposit, where devitrification and vapor-phase crystallization have increased the density and
cohesion of the upper half of the section. Thermal remanent magnetization analyses of entrained lithic clasts indicate high
emplacement temperatures, above 630°C, but the lack of welding textures indicates temperatures below the glass transition
temperature. In order to remain below the glass transition at 630°C, the minimum cooling rate prior to deposition was 3.0 × 10−3–8.5 × 10−2°C/min (depending on the experimental data used for comparison). Alternatively, if the deposit was emplaced above the glass
transition temperature, conductive cooling alone was insufficient to prevent welding. Crack patterns (average, 4.5 sides to
each polygon) and column diameters (average, 75 cm) are consistent with relatively rapid cooling, where advective heat loss
due to vapor fluxing increases cooling over simple conductive heat transfer. The presence of regularly spaced, complex radiating
joint patterns is consistent with fumarolic gas rise, where volatiles originated in the valley-confined drainage system below.
Joint spacing is a proxy for cooling rates and is controlled by depositional thickness/valley width. We suggest that the formation
of joints in high-temperature, non-welded deposits is aided by the presence of underlying external water, where vapor transfer
causes crystallization in pore spaces, densifies the deposit, and helps prevent welding. 相似文献
157.
J. C. Raymond 《Astrophysics and Space Science》1995,233(1-2):231-237
Fairly simple models can explain the emission from non-radiative shock waves in supernova remnants. This talk reviews some of the more robust diagnostics of shock parameters and some of the implications for the physics of collisionless shock waves in interstellar gas. The Hopkins Ultraviolet Telescope observed several non-radiative shocks during the ASTRO-2 mission, and the spectra have interesting implications for the physics of collisionless shocks. 相似文献
158.
The interaction of an SNR blastwave with clouds of various sizes determines the appearance of the SNR in all wavelength bands, and it may determine the overall evolution of the remnant. The Cygnus Loop provides excellent examples of the interaction with both large and small clouds at various stages, and its brightness, large size and low reddening make it a natural target for study. We consider X-ray, optical and UV observations of features at the eastern edge of the Cygnus Loop to look for evidence of cloud evaporation, turbulent stripping from a cloud and pressure enhancement associated with the blastwave-cloud interaction. We consider the effects of the sputtering of dust grains on the temperature derived from ROSAT spectra and we briefly consider the clumpiness of Hα emission to be expected from compression of a turbulent magnetic field. 相似文献
159.
Dion Brandt Wolf Uwe Reimold Raymond J. Durrheim 《Meteoritics & planetary science》1994,29(3):379-384
Abstract— The genesis of the 1.13-km-diameter Pretoria Saltpan crater has long been the focus of a controversy. Its origin has been explained by either meteorite impact or “cryptoexplosive” volcanic activity, but it was recently confirmed, through detailed petrographic and chemical analysis of a breccia layer forming part of the crater fill, that the crater was formed by impact. As the limited previous geophysical work failed to support an impact origin, a more detailed gravity and magnetic study was conducted. A possible 400-m-diameter circular crater located 3 km to the southwest of the main crater was also investigated with geophysical methods, including resistivity, seismics and ground-probing radar. The gravity signature of the main crater is compatible with that of a simple impact crater and the magnetic signature (no magnetic anomaly could be detected) rules out the possibility of a central magnetic volcanic body below the crater-fill sediments. The results for the possible twin or satellite crater are inconclusive. As it is the only such feature in the entire region, it should not be overlooked. A drilling program may reveal interesting results. 相似文献
160.
Steven J. OSTRO Lance A. M. BENNER Michael C. NOLAN Christopher MAGRI Jon D. GIORGINI Daniel J. SCHEERES Stephen B. BROSCHART Mikko KAASALAINEN David VOKROUHLICKÝ Steven R. CHESLEY Jean‐Luc MARGOT Raymond F. JURGENS Randy ROSE Donald K. YEOMANS Shigeru SUZUKI Eric M. de JONG 《Meteoritics & planetary science》2004,39(3):407-424
Abstract— We observed 25143 Itokawa, the target of Japan's Hayabusa (MUSES‐C) sample‐return mission, during its 2001 close approach at Arecibo on twelve dates during March 18‐April 9 and at Goldstone on nine dates during March 20‐April 2. We obtained delay‐Doppler images with range resolutions of 100 ns (15 m) at Arecibo and 125 ns (19 m) at Goldstone. Itokawa's average circular polarization ratio at 13 cm, 0.26 ± 0.04, is comparable to that of Eros, so its cm‐to‐m surface roughness probably is comparable to that on Eros. Itokawa's radar reflectivity and polarization properties indicate a near‐surface bulk density within 20% of 2.5 g cm?3. We present a preliminary estimate of Itokawa's shape, reconstructed from images with rather limited rotation‐phase coverage, using the method of Hudson (1993) and assuming the lightcurve‐derived spin period (12.132 hr) and pole direction (ecliptic long., lat. = 355°, ?84°) of Kaasalainen et al. (2003). The model can be described as a slightly asymmetrical, slightly flattened ellipsoid with extents along its principal axes of 548 times 312 times 276 m ± 10%. Itokawa's topography is very subdued compared to that of other asteroids for which spacecraft images or radar reconstructions are available. Similarly, gravitational slopes on our Itokawa model average only 9° and everywhere are less than 27°. The radar‐refined orbit allows accurate identification of Itokawa's close planetary approaches through 2170. If radar ranging planned for Itokawa's 2004 apparition succeeds, then tracking of Hayabusa during its 2005 rendezvous should reveal Yarkovsky perturbation of the asteroid's orbit. 相似文献