Ultraviolet spectroscopy of Asteroid (4) Vesta     

Jian-Yang Li  Dennis Bodewits  Lori M. Feaga  Wayne Landsman  Michael F. A’Hearn  Max J. Mutchler  Christopher T. Russell  Lucy A. McFadden  Carol A. Raymond 《Icarus》2011,216(2):640-649

We report a comprehensive review of the UV–visible spectrum and rotational lightcurve of Vesta combining new observations by Hubble Space Telescope and Swift Gamma-ray Burst Observatory with archival International Ultraviolet Explorer observations. The geometric albedos of Vesta from 220 nm to 953 nm are derived by carefully comparing these observations from various instruments at different times and observing geometries. Vesta has a rotationally averaged geometric albedo of 0.09 at 250 nm, 0.14 at 300 nm, 0.26 at 373 nm, 0.38 at 673 nm, and 0.30 at 950 nm. The linear spectral slope as measured between 240 and 320 nm in the ultraviolet displays a sharp minimum near a sub-Earth longitude of 20°, and maximum in the eastern hemisphere. This is consistent with the longitudinal distribution of the spectral slope in the visible wavelength. The photometric uncertainty in the ultraviolet is ∼20%, and in the visible wavelengths it is better than 10%. The amplitude of Vesta’s rotational lightcurves is ∼10% throughout the range of wavelengths we observed, but is smaller at 950 nm (∼6%) near the 1-μm band center. Contrary to earlier reports, we found no evidence for any difference between the phasing of the ultraviolet and visible/near-infrared lightcurves with respect to sub-Earth longitude. Vesta’s average spectrum between 220 and 950 nm can well be described by measured reflectance spectra of fine particle howardite-like materials of basaltic achondrite meteorites. Combining this with the in-phase behavior of the ultraviolet, visible, and near-infrared lightcurves, and the spectral slopes with respect to the rotational phase, we conclude that there is no global ultraviolet/visible reversal on Vesta. Consequently, this implies a lack of global space weathering on Vesta, as previously inferred from visible–near-infrared data.  相似文献   

The state‐of‐the‐art in marine navigation     

H. Bâkiiz  H. M. Ng 《Marine Geodesy》2013,36(3):209-217

Tide gauges distributed all over the world provide valuable information for monitoring mean sea level changes. The statistical models used in estimating sea level change from the tide gauge data assume implicitly that the random model components are stationary in variance. We show that for a large number of global tide gauge data this is not the case for the seasonal part using a variate-differencing algorithm. This finding is important for assessing the reliability of the present estimates of mean sea level changes because nonstationarity of the data may have marked impact on the sea level rate estimates, especially, for the data from short records.  相似文献   

Light‐dependence of photosynthesis and growth in cyanobacteria: Implications for their dominance in eutrophic lakes     

Max M. Tilzer 《新西兰海洋与淡水研究杂志》2013,47(3):401-412

In eutrophic lakes cyanobacteria are favoured relative to other phytoplankton, both under stratified and mixed conditions. During stratification, gas vacuole formation allows the accumulation of dense surface scums which attain the highest possible area‐specific photosynthetic rates in aquatic environments owing to high irradiances, near‐complete harvesting of impinging light, and minimal light inhibition and photo‐oxidation. During moderate mixing, high yields of biomass can be achieved by effective light harvesting for photosynthesis (aided by phycobilin pigments) and low maintenance energy requirements at low mean irradiances. Howevrr, nitrogen fixation competes for energy and reductant with photosynthesis, and leads to a decline of light‐saturated maximum growth rates. Wind‐driven vertical mixing and lateral advection are the main causes for the instability of cyanobacterial blooms in hyper‐eutrophic lake ecosystems.  相似文献   

Field calibration of a formula for entrance mixing of river inflows to lakes: Lake Taupo,North Island,New Zealand     

Robert H. Spigel  Clive Howard‐Williams  Max Gibbs  Scott Stephens  Barry Waugh 《新西兰海洋与淡水研究杂志》2013,47(4):785-802

Field measurements were used to validate predictions for the initial dilution of negatively buoyant, cold‐water inflows to Lake Taupo, as part of a study to quantify mixing processes associated with the two largest inflows to the lake. The predictions were made using a formulation originally derived for positively buoyant, warm‐water inflows to cooling ponds. The formulation predicts the total dilution of an inflow during its inertia‐dominated phase between its entrance to the lake and the point where buoyancy forces are great enough to cause the inflow to plunge and form a submerged density current. In one of the measured inflows, the inflowing jet was free to entrain from both sides; in the other, entrainment was restricted on one side by attachment of the inflowing jet to the shoreline of a bay just upstream of the plunge point. In the former example, the unmodified coefficients from the cooling pond formulation provided an excellent prediction of initial dilution. In the latter example, entrainment was reduced and different coefficients were derived. In both examples the inflows remained attached to the lake bed throughout their course until their liftoff at depths of 45–55 m to form interflows. The difference between coefficients for the two inflows indicates that the coefficient values should be considered site‐specific. The formulation is not valid for inflows that separate from the bottom of the inflow channel before plunging. The entrance mixing formulation was incorporated in a more general model of lake stratification, DYRESM, which already includes a well‐documented routine for routing underflows down submerged channels on the bed of a lake. Application of the model to the inflows measured in Lake Taupo gave good results for two model outputs that were not involved in the calibration of the entrance mixing formulation, but that are affected by the result of the initial dilution calculation—the temperatures in the river plume after it has plunged, and the insertion depth.  相似文献   

Performance Characterization of Pharmaceutical Removal by Horizontal Subsurface Flow Constructed Wetlands Using Multivariate Analysis          下载免费PDF全文

Dongqing Zhang  Wangdong Ni  Richard M. Gersberg  Wun Jern Ng  Soon Keat Tan 《洁净——土壤、空气、水》2015,43(8):1181-1189

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Encounters with an unearthly mudstone: Understanding the first mudstone found on Mars          下载免费PDF全文

Juergen Schieber  David Bish  Max Coleman  Mark Reed  Elisabeth M. Hausrath  John Cosgrove  Sanjeev Gupta  Michelle E. Minitti  Kenneth S. Edgett  Mike Malin 《Sedimentology》2017,64(2):311-358

The Sheepbed mudstone forms the base of the strata examined by the Curiosity rover in Gale Crater on Mars, and is the first bona fide mudstone known on another planet. From images and associated data, this contribution proposes a holistic interpretation of depositional regime, diagenesis and burial history. A lake basin probably received sediment pulses from alluvial fans. Bed cross‐sections show millimetre to centimetre‐scale layering due to distal pulses of fluvial sediment injections (fine‐grained hyperpycnites), fall‐out from river plumes, and some aeolian supply. Diagenetic features include mineralized synaeresis cracks and millimetre‐scale nodules, as well as stratiform cementation. Clay minerals were initially considered due to in situ alteration, but bulk rock chemistry and mineralogy suggests that sediments were derived from variably weathered source rocks that probably contained pre‐existing clay minerals. X‐ray diffraction analyses show contrasting clay mineralogy in closely spaced samples, consistent with at least partial detrital supply of clay minerals. A significant (ca 30 wt%) amorphous component is consistent with little post‐depositional alteration. Theoretical modelling of diagenetic reactions, as well as kinetic considerations, suggest that the bulk of diagenetic clay mineral formation occurred comparatively late in diagenesis. Diagenetic features (synaeresis cracks and nodules) were previously thought to reflect early diagenetic gas formation, but an alternative scenario of synaeresis crack formation via fabric collapse of flocculated clays appears more likely. The observed diagenetic features, such as solid nodules, hollow nodules, matrix cement and ‘raised ridges’ (synaeresis cracks) can be explained with progressive alteration of olivine/glass in conjunction with centrifugal and counter diffusion of reactive species. Anhydrite‐filled fractures in the Sheepbed mudstone occurred late in diagenesis when fluid pressures built up to exceed lithostatic pressure. Generating fluid overpressure by burial to facilitate hydraulic fracturing suggests a burial depth of at least 1000 m for the underlying strata that supplied these fluids.  相似文献   

Comparisons of traditional and novel stochastic models for the generation of daily precipitation occurrences     

W.W. Ng  U.S. Panu 《Journal of Hydrology》2010,380(1-2):222-236

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Thule Fishing Revisited: The Economic Importance of Fish at the Pembroke and Bell Sites,Victoria Island,Nunavut     

Lauren Norman  T. Max Friesen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):261-278

Geografisk Tidsskrift—Danish Journal of Geography 110(2):261–278, 2010

In a comprehensive overview of evidence for fishing in the Thule period of the eastern North American Arctic, Whitridge (2001) noted that fish bones are either extremely rare or absent in archaeofaunal samples, despite the fact that artifact assemblages typically contain a variety of fishing implements. In this paper, we present new faunal data from two sites on southeastern Victoria Island, Nunavut, which offer a marked contrast to this pattern. The Pembroke site, located just north of Cambridge Bay, is a small Thule site probably occupied during an early migration into the region. The Bell site, located on the Ekalluk River, is a more substantial site, occupied for a much longer duration during the Thule period. These sites are located in areas devoid of many taxa preferred by Thule peoples, which led the sites' occupants to rely on caribou and fish for much of their winter subsistence. At the Bell site, storage of caribou and fish was critical for winter survival. However, the occupants of the Pembroke site appear to have been unable to acquire sufficient stores during the fall, and therefore relied on fishing through the ice during winter to supplement their inadequate stores. Although both sites indicate a more important economic role for fish than has been recorded on any other eastern Arctic Thule winter site, the use of fish at the two sites differs markedly, adding nuance to archaeologically known Thule subsistence patterns.  相似文献   

The Evolution and Research Trends of Port Geography     

Adolf K. Y. Ng 《The Professional geographer》2013,65(1):65-86

Despite the long existence of port geography research, there has been no systematic investigation on its evolution and research trends. Hence, through investigating 155 port geography articles featured in geography journals between 1956 and 2011, this article studied the evolution and research trends of port geography. The article argues that port geography had gradually evolved from a secondary and encyclopedic subdiscipline within transport and human geographies to a primary and specialized one. Such a trend had blurred its “geographicalness,” however, with port geography moving toward the more applied and interdisciplinary transportation. The article also indicates that further research would be required to understand the communication between port geography and other disciplines, as well as philosophical and epistemological issues.  相似文献   

Spatial data infrastructures in context: north and south,edited by Zorica Nedovic-Budic,Joep Crompvoets and Yola Georgiadou     

Max Craglia 《International journal of geographical information science》2013,27(10):1997-1999

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