Community diversity and hazard events: understanding the evolution of local approaches to wildfire     

Paveglio  Travis  Edgeley  Catrin 《Natural Hazards》2017,87(2):1083-1108

Natural Hazards - Existing research indicates that distinct human populations may prepare for, experience, and recover from wildfires in different ways. However, research that helps explain...  相似文献   

Iron concretions within a highly altered unit of the Berlins Porphyry,New Zealand: an abiotic or biotic story?     

Cox  Toni L.  Oze  Christopher  Horton  Travis W. 《Mineralogy and Petrology》2017,111(2):173-181

Mineralogy and Petrology - The Berlins Porphyry located on the South Island of New Zealand provides an opportunity to examine iron concretions formed in a subterranean system. Specifically, an...  相似文献   

A Surface Model for Aeolian Dune Topography     

Travis Swanson  David Mohrig  Gary Kocurek  Man Liang 《Mathematical Geosciences》2017,49(5):635-655

A surface model for aeolian bedform topography is adapted from a surface model of subaqueous bedform topography. The aeolian bedform surface model is developed using a uniform grid with a cell-centered finite volume approximation of the sediment continuity equation. The resulting modeling framework approximates the dynamic motions of aeolian bedform topography driven by bedform field boundary conditions. The numerical model is applied to simulate bedforms growing from unimodal and bimodal transport regimes from both a fixed elevation (sediment source area) and within a domain with fully periodic boundary conditions. The rates at which modeled aeolian bedforms grow and morphologically mature are sensitive to the chosen boundary conditions. Video files of model simulations and source code for the presented aeolian bedform surface modeling framework are available in supplemental materials. The aeolian bedform surface model code is malleable and readily modified for exploratory study of dynamic bedform topography that inherits morphological traits from aeolian bedform field boundary conditions.  相似文献   

Mineralogical characterization of acid weathered phyllosilicates with implications for secondary martian deposits     

Travis S. Altheide  Vincent F. Chevrier 《Geochimica et cosmochimica acta》2010,74(21):6232-6248

The detection of phyllosilicates and sulfates on Mars has revealed a complex aqueous history which suggests distinct geochemical environments separated temporally and spatially. Recent observations by MRO CRISM in Mawrth Vallis have shown that phyllosilicate deposits exhibit a specific stratigraphy, which remains incompletely understood. Moreover, MER Spirit has evidenced association between phyllosilicates, amorphous silica and sulfates. We investigated the hypothesis that these parageneses resulted from the acidic weathering of older phyllosilicate deposits. We exposed nontronite (Fe-rich smectite), montmorillonite (Al-rich smectite) and kaolinite to H₂SO₄ solutions at pH 0, 2 and 4, and at a temperature of 60 °C. After the acid treatment, a combination of mineralogical techniques was used to assess the degree of alteration of the three phyllosilicate minerals. XRF, XRD and ESEM measurements show that nontronite was the most unstable when acid leached, followed by montmorillonite and then kaolinite. Progressive acidic leaching of nontronite leads to alteration of the phyllosilicate to amorphous silica, along with Fe-sulfate and anatase, and the formation of an acidic Al,Fe-rich solution. Alteration of montmorillonite resulted in the formation of Fe-, Al-, Ca- and Mg-sulfates, and a Al-rich leaching solution. Comparatively, leaching of kaolinite resulted in the formation of Al-sulfates and a Al-rich solution as well, with only slight alteration of the primary mineralogical features. The effects of acid leaching of the phyllosilicates were also observed in NIR reflectance spectra, allowing a comparison with CRISM spectra from Mawrth Vallis. Based on our results, we propose a new model where acid leaching of mixed phyllosilicate deposits leads to kaolinite overlaying montmorillonite, which in turn caps Fe,Mg-smectites. Leaching of cations and subsequent evaporation leads to sulfate deposits, as supported by geochemical modeling, while amorphous silica remains as a residue. Depending on the intensity (pH) and length of exposure of acidic leaching, our model can explain the stratigraphic distribution of phyllosilicates, and the association of sulfates, silica and smectites.  相似文献   

Young orogenic gold mineralisation in active collisional mountains, Taiwan   总被引：1，自引：0，他引：1  

Dave Craw  Phaedra Upton  Bing-Sheng Yu  Travis Horton  Yue-Gau Chen 《Mineralium Deposita》2010,45(7):631-646

Gold-bearing vein systems in the high mountains of Taiwan are part of the youngest tectonic-hydrothermal system on Earth. Tectonic collision initiated in the Pliocene has stacked Eocene–Miocene marine sedimentary rocks to form steep mountains nearly 4 km high. Thinner portions of the sedimentary pile (∼5 km) are currently producing hydrocarbons in a fold and thrust belt, and orogenic gold occurs in quartz veins in thicker parts of the pile (∼10 km) in the Slate Belt that underlies the mountains. Metamorphic fluids (2–5 wt.% NaCl equivalent) are rising from the active greenschist facies metamorphic zone and transporting gold released during rock recrystallisation. Metamorphic fluid flow at the Pingfengshan historic gold mine was focussed in well-defined (4 km³) fracture zones with networks of quartz veins, whereas large surrounding volumes of rock are largely unveined. Gold and arsenopyrite occur in several superimposed vein generations, with ankeritic alteration of host rocks superimposed on chlorite–calcite alteration zones as fluids cooled and became out of equilibrium with the host rocks. Mineralising fluids had δ¹⁸O near +10‰, δ¹³C was between −1‰ and −6‰ and these fluids were in isotopic equilibrium with host rocks at ∼350°C. Ankeritic veins were emplaced in extensional sites in kink fold axial surfaces, formed as the rock mass was transported laterally from compressional to extensional regimes in the orogen. Rapid exhumation (>2 mm/year) of the Slate Belt is causing a widespread shallow conductive thermal anomaly without igneous intrusions. Meteoric water is penetrating into the conductive thermal anomaly to contribute to crustal fluid flow and generate shallow boiling fluids (∼250°C) with fluid temperature greater than rock temperature. The meteoric-hydrothermal system impinges on, but causes only minor dilution of, the gold mineralisation system at depth.  相似文献   

Near-infrared spectroscopic search for the close orbiting planet HD 75289b     

J. R. Barnes  C. J. Leigh  H. R. A. Jones  Travis S. Barman  D. J. Pinfield  A. Collier Cameron  J. S. Jenkins 《Monthly notices of the Royal Astronomical Society》2007,379(3):1097-1107

We present a search for the near-infrared spectroscopic signature of the close orbiting extrasolar giant planet HD 75289b. We obtained ∼230 spectra in the wavelength range 2.18–2.19 μm using the Phoenix spectrograph at Gemini South. By considering the direct spectrum, derived from irradiated model atmospheres, we search for the absorption profile signature present in the combined star and planet light. Since the planetary spectrum is separated from the stellar spectrum at most phases, we apply a phase-dependent orbital model and tomographic techniques to search for absorption signatures.
Because the absorption signature lies buried in the noise of a single exposure we apply a multiline deconvolution to the spectral lines available in order to boost the effective signal-to-noise ratio (S/N) of the data. The wavelength coverage of 80 Å is expected to contain ∼100 planetary lines, enabling a mean line with S/N of 800 to be achieved after deconvolution. We are nevertheless unable to detect the presence of the planet in the data and carry out further simulations to show that broader wavelength coverage should enable a planet like HD 75289b to be detected with 99.9 per cent confidence. We investigate the sensitivity of our method and estimate detection tolerances for mismatches between observed and model planetary atmospheres.  相似文献   

Structure of Cl-containing silicate and aluminosilicate glasses: A Cl MAS-NMR study     

Travis O. Sandland  Jonathan F. Stebbins  James D. Webster 《Geochimica et cosmochimica acta》2004,68(24):5059-5069

Chlorine-35 magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra were collected at 14.1 and 18.8 Tesla fields to determine the atomic scale structural environments of the chloride ions in anhydrous and hydrous silicate and aluminosilicate glasses containing 0.2 to 0.7 wt% Cl. NMR peaks are broad and featureless, but are much narrower than the total chemical shift range for the nuclide in inorganic chlorides. Peak widths are primarily due to quadrupole interactions and to a lesser extent to chemical shift distributions. Peak positions are quite different for the Na- and Ca-containing glasses, suggesting that most Cl⁻ coordination environments contain network modifier cations. Comparison of peak positions and shapes for silicate and aluminosilicate glasses containing either Na or Ca suggests that there is no obvious contribution from Cl⁻ bonded to Al, and relative quantitation of peak areas indicates that there is no systematic undercounting of ³⁵Cl spins in the aluminous vs. the Al-free samples. In Ca-Na silicate glasses with varying Ca/(Ca + Na), the mixed-cation glasses have intermediate chemical shifts between those of the end members, implying that there is not a strong preference of either Ca²⁺ or of Na⁺ around Cl⁻. Hydrous Na-aluminosilicate glasses with H₂O contents up to 5.9 wt% show a shift to higher frequency NMR signal with increasing H₂O content, while the quadrupole coupling constant (C_Q) remains constant at ∼3.3 MHz. However, the change in frequency is much smaller than that expected if H₂O systematically replaced Na⁺ in the first-neighbor coordination shell around Cl⁻. A series of hydrous Ca-aluminosilicate glasses with H₂O contents up to 5.5 wt% show no shift in NMR signal with increasing H₂O content. The C_Q remains constant at ∼4.4 MHz, again suggesting no direct interaction between Cl⁻ and H₂O in these samples.  相似文献   

Hydrothermal convection in carbonaceous chondrite parent bodies     

Bryan J. Travis  Gerald Schubert 《Earth and Planetary Science Letters》2005,240(2):234-250

Numerical simulations of the thermal evolution of carbonaceous chondrite parent bodies indicate a period of several million years during which convective motion of water could occur. The present study considers variations of permeability, radiogenic heating, and body radius. The model accounts for the radial variation of gravity within the body, melting of ice, freezing of liquid water, and variable water properties and incorporates a realistic equation of state for water. Some regions of a parent body experience no pore water flow while other regions experience hundreds of pore volumes of liquid water flow. The spatial heterogeneity in pore water flow reflects the convective pattern in the body. Hydrothermal alteration of minerals inside the parent body will accordingly vary greatly with location in the body, and one parent body could be the source of chemically diverse meteorites.  相似文献   

Galileo Photopolarimetry of Jupiter at 678.5 nm     

C.J. BraakJ.F. de Haan  J.W. Hovenier  L.D. Travis 《Icarus》2002,157(2):401-418

Brightness and linear polarization measurements at 678.5 nm for four south-north strips of Jupiter are studied. These measurements were obtained in 1997 by the Galileo photopolarimeter/radiometer. The observed brightness exhibits latitudinal variations consistent with the belt/zone structure of Jupiter. The observed degree of linear polarization is small at low latitudes and increases steeply toward higher latitudes. No clear correlations were observed between the degree of linear polarization and the brightness. The observed direction of polarization changes from approximately parallel to the local scattering plane at low latitudes to perpendicular at higher latitudes. For our studies, we used atmospheric models that include a haze layer above a cloud layer. Parameterized scattering matrices were employed for the haze and cloud particles. On a pixel-wise basis, the haze optical thickness and the single-scattering albedo of the cloud particles were derived from the observed brightness and degree of linear polarization; results were accepted only if they were compatible with the observed direction of polarization. Using atmospheric parameter values obtained from Pioneer 10 and 11 photopolarimetry for the South Tropical Zone and the north component of the South Equatorial Belt, this analysis yielded acceptable results for very few pixels, particularly at small phase angles. However, for almost all pixels, acceptable results were found when the parameterized scattering matrix of the cloud particles was adjusted to produce more negative polarization for single scattering of unpolarized light, especially at large scattering angles, similar to some laboratory measurements of ammonia ice crystals. Using this adjusted model, it was found that the derived latitudinal variation of the single-scattering albedo of the cloud particles is consistent with the belt/zone structure, and that the haze optical thickness steeply increases toward higher latitudes.  相似文献   

Anomalous bathymetry, 3D edge driven convection, and dynamic topography at the western Atlantic passive margin     

Travis Ramsay  Russell Pysklywec 《Journal of Geodynamics》2011,52(1):45-56

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