Feasibility of age determination of deep-water bamboo corals (Gorgonacea; Isididae) from annual cycles in skeletal composition     

Ronald E. Thresher  Colin M. MacRae  Nick C. Wilson  Stewart Fallon 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(3):442-449

We test two hypotheses, that annual environmental cycles produce periodic variability in the skeletal composition of deep-water gorgonians, and that these cycles can be counted to determine the coral's age. Annual periodicity of deposition was tested by comparing the internode composition of bamboo corals live-collected 10 years apart in the Southern Ocean. The validity of the comparison was substantiated by growth rates for the 10-year interval (77–121 μm/yr) that were confirmed by radiocarbon analysis. Variability in Mg/Ca and possibly S/Ca, but not Sr/Ca or P/Ca, was consistent with annual cycles of deposition. However, spectral analysis of Mg/Ca data for a larger coral showed little or no spectral peak associated with an annual cycle of deposition (though there were peaks at periods of 4–5 and 11–15 years). The absence of an annual peak is likely to reflect growth rates that vary over time, coral cross-sections that change shape over time, and interannual differences in the seasonal range of environmental variability. The resulting subjectivity in what defines an annulus, along with evidence that the nature and extent of annual periodicity differs among sites, means that the technique is likely to be inherently imprecise and to require independent validation for each site and taxon before it can be applied.  相似文献   

Identifying step changes in single streamflow and evaporation records due to forest cover change     

Nick A. Chappell  Wlodek Tych 《水文研究》2012,26(1):100-116

Techniques that identify forestry‐induced changes to streamflow or evaporation are needed to assess available water resources. Equally, there is a growing appreciation that climate cycles may be having a profound impact on the land‐surface hydrology. The ability to see forestry‐induced change above the effects of climate dynamics, therefore, becomes a critical issue. Paired‐catchment analyses have proved very valuable in identifying change, but cannot quantify the relative impacts of climate and land‐cover change, and data from adjacent reference basins are not always available. Within this study, we examined whether step changes within single time‐series of streamflow or evaporation (P‐Q) could be identified without reference to those of a control catchment. The UC‐DHR method was used for this analysis, and included a special routine to allow a known change‐point (e.g. start of logging) to be specified or alternatively identified by the model. Data from three experimental catchments important for their seminal forestry impact studies were selected for the analyses. The study demonstrated that clear‐cutting 29% of the Hore catchment and 40% selective felling of the Berembun basin produced a step change in the discharge trend that was clearly observable above the climate‐related dynamics and uncertainty. In contrast, step changes in P‐Q following the same selective felling event or following 22% afforestation of the Upper Hodder basin were not larger than the uncertainty bands or magnitude of the inter‐annual cycles produced by the climate dynamics, respectively. This demonstrates that while step changes can be observed in single hydrological time‐series, errors within the observations can sometimes mask the identification of change. This masking of change is also possible where the longer‐term cyclical behaviour in Q or P‐Q from natural climate dynamics is large, while the spatial extent of forestry change is small. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Ottawa: the knowledge city and a labyrinth of obstacles     

Nick Novakowski 《GeoJournal》2010,75(6):553-565

This research provides a comparative examination of Ottawa as an archetype of a knowledge city. Among Canada’s four largest cities, Ottawa is unique in terms of the characteristics of its labor force, the nature of its employment mix, and its infrastructure. Since the high-tech downturn of 2001, some of Ottawa’s options as a knowledge city seem to be contracting, despite some simultaneously encouraging signs (like recovering employment levels in the high-tech sector). This raises a question about Ottawa’s potential longevity as a knowledge center. The challenge is to understand the inventory of obstacles faced by the city, and address the sort of alchemy required to maintain and improve its competitiveness as a knowledge city.  相似文献   

Changing characteristics of arctic pressure ridges   总被引：1，自引：1，他引：0  

Peter Wadhams  Nick Toberg 《Polar Science》2012,6(1):71-77

The advent of multibeam sonar permits us to obtain full three-dimensional maps of the underside of sea ice. In particular this enables us to distinguish the morphological characteristics of first-year (FY) and multi-year (MY) pressure ridges in a statistically valid way, whereas in the past only a small number of ridges could be mapped laboriously by drilling. In this study pressure ridge distributions from two parts of the Arctic Ocean are compared, in both the cases using mainly data collected by the submarine “Tireless” in March 2007 during two specific grid surveys, in the Beaufort Sea at about 75° N, 140° W (N of Prudhoe Bay), and north of Ellesmere Island at about 83° 20′ N, 64° W. In the Beaufort Sea the ice was mainly FY, and later melted or broke up as this area became ice-free during the subsequent summer. N of Ellesmere Island the ice was mainly MY. Ridge depth and spacing distributions were derived for each region using the boat's upward looking sonar, combined with distributions of shapes of the ridges encountered, using the Kongsberg EM3002 multibeam sonar. The differing shapes of FY and MY ridges are consistent with two later high-resolution multibeam studies of specific ridges by AUV. FY ridges are found to fit the normal triangular shape template in cross-section (with a range of slope angles averaging 27°) with a relatively constant along-crest depth, and often a structure of small ice blocks can be distinguished. MY ridges, however, are often split into a number of independent solid, smooth blocks of large size, giving an irregular ridge profile which may be seemingly without linearity.Our hypothesis for this difference is that during its long lifetime an MY ridge is subjected to several episodes of crack opening; new cracks in the Arctic pack often run in straight lines across the ridges and undeformed ice alike. Such a crack will open somewhat before refreezing, interpolating a stretch of thin ice into the structure, and breaking up the continuity and linearity of the ridge crest. Many such episodes over a number of years can cause the ridge to become simply a series of blocks. This has implications for ridge strength and for permeability to spilled oil. As the percentage of MY ice in the Arctic diminishes, Arctic ridging will be more and more dominated by FY ridges, and we discuss the implications of this change of character of the ice underside in the light of the statistics that we have generated for the two types of ridge.  相似文献   

Assessing ground cover at patch and hillslope scale in semi-arid woody vegetation and pasture using fused Quickbird data     

Carlos Muñoz-Robles  Paul FrazierMatthew Tighe  Nick ReidSue V. Briggs  Brian Wilson 《International Journal of Applied Earth Observation and Geoinformation》2012,14(1):94-102

The amount and distribution of vegetation and ground cover are important factors that influence resource transfer (e.g. runoff, sediment) in patterned semi-arid landscapes. Identifying and describing these features in detail is an essential part of measuring and understanding ecohydrological processes at hillslope scales that can then be applied at broader scales. The aim of this study was to develop a comprehensive methodology to map ground cover using high resolution Quickbird imagery in woody and non-woody (pasture) vegetation. The specific goals were to: (1) investigate the use of several techniques of image fusion, namely principal components analysis (PCA), Brovey transform, modified intensity-hue-saturation (MIHS) and wavelet transform to increase the spatial detail of multispectral Quickbird data; (2) evaluate the performance of the red and near-infra-red bands (NIR), the difference vegetation index (DVI), and the normalised difference vegetation index (NDVI) in estimating ground cover, and (3) map and assess spatial and temporal changes in ground cover at hillslope scale using the most appropriate method or combination of methods. Estimates of ground cover from the imagery were compared with a subset of observed ground cover estimates to determine map accuracy. The MIHS algorithm produced images that best preserved spectral and spatial integrity, while the red band fused with the panchromatic band produced the most accurate ground cover maps. The patch size of the ground cover beneath canopies was similar to canopy size, and percent ground cover (mainly litter) increased with canopy size. Ground cover was mapped with relative accuracies of 84% in the woody vegetation and 86% in the pasture. From 2008 to 2009, ground cover increased from 55% to 65% in the woody vegetation and from 40% to 45% in the pasture. These ground cover maps can be used to explore the spatial ecohydrological interactions between areas of different ground cover at hillslope scale with application to management at broader scales.  相似文献   

RE J1034+396: the origin of the soft X-ray excess and quasi-periodic oscillation     

Matthew Middleton  Chris Done  Martin Ward  Marek Gierli&#;ski  Nick Schurch 《Monthly notices of the Royal Astronomical Society》2009,394(1):250-260

The X-ray quasi-periodic oscillation (QPO) seen in RE J1034+396 is so far unique amongst active galactic nuclei (AGN). Here, we look at another unique feature of RE J1034+396, namely its huge soft X-ray excess, to see if this is related in any way to the detection of the QPO. We show that all potential models considered for the soft energy excess can fit the 0.3–10 keV X-ray spectrum, but the energy dependence of the rapid variability (which is dominated by the QPO) strongly supports a spectral decomposition where the soft excess is from low-temperature Comptonization of the disc emission and remains mostly constant, while the rapid variability is produced by the power-law tail changing in normalization. The presence of the QPO in the tail rather than in the disc is a common feature in black hole binaries (BHBs), but low-temperature Comptonization of the disc spectrum is not generally seen in these systems. The main exception to this is GRS 1915+105, the only BHB which routinely shows super-Eddington luminosities. We speculate that the super-Eddington accretion rates lead to a change in disc structure, and that this also triggers the X-ray QPO.  相似文献   

A numerical model for simulating Hortonian overland flow on tropical hillslopes with vegetation elements     

Ayodele E. Ajayi  Nick van de Giesen  Paul Vlek 《水文研究》2008,22(8):1107-1118

This paper describes a two‐dimensional hydrodynamic model that characterizes surface runoff process resulting from a varying rainfall intensity event, on an infiltrating soil surface. The soil surface has spatially varied soil physical, hydraulic and microtopographic characteristics. Infiltration process is modelled with the Philip two‐term equation and the time before ponding approximated with the time compression algorithm. Vegetation is modelled as a dynamic component with the modified Gash model. The equation is solved with a modified second order Leapfrog explicit finite difference scheme with centred time and space derivatives. The model was validated with standard analytical solutions. Evaluation with results from field campaigns in the Volta Basin of West Africa during the 2002 rainfall season indicates good agreement, with r² values ranging from 0·89 to 0·96. The developed method will be useful in studying the dynamics of surface runoff generation under complex microtopographic conditions, spatially varying soil hydraulic characteristics and temporally dynamic rainfall intensity, as found in many tropical catchments. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Aperture synthesis observations of individual molecular clouds in M33     

Christine D. Wilson  Nick Scoville 《Astrophysics and Space Science》1989,156(1-2):269-273

Aperture synthesis maps of six fields in the nearby spiral galaxy M33 have revealed the presence of a population of molecular clouds whose masses, sizes, velocity widths, and brightness temperatures are similar to Galactic giant molecular clouds. The masses of the clouds obtained from the virial theorem and from the integrated CO flux are in relatively good agreement, suggesting that the conversion factor from CO flux to molecular mass in M33 is unlikely to be much different from the value measured in our own Galaxy. The star formation properties of these regions are under study with deep optical CCD imaging and near-infrared data.  相似文献   

An asymptotic theory of combined wave refraction and diffraction     

Philip L. -F. Liu  Carlos J. Lozano  Nick Pantazaras 《Applied Ocean Research》1979,1(3):137-146

A uniformly valid asymptotic theory for water waves is presented, which accounts for the combined effects of refraction due to slowly varying water depth and diffraction by a semi-infinite thin break water. The present theory is more rigorous and generical than the approximate solution developed by Liu and Mei, which becomes invalid near the edge and the tip of the breakwater. The effects of wave breaking are ignored.  相似文献   

Gold-Related Sulfide Mineralization and Ore Genesis of the Penjom Gold Deposit, Pahang, Malaysia     

Kamar Shah Ariffin  Nick J. Hewson 《Resource Geology》2007,57(2):149-169

The Penjom gold deposit lies on the eastern side of the Raub‐Bentong Suture line within the Central Belt of Permo‐Triassic rocks, near Kuala Lipis, Pahang, Malaysia. The geology of the deposit is dominated by a sequence of fine‐ to coarse‐grained rhyolitic to rhyodacitic tuff, tuff‐breccia and a minor rhyolitic–rhyodacitic volcanic series, associated with argillaceous marine sedimentary rocks consisting of shale with subordinate shalely limestone of Padang Tungku Formation and Pahang Volcanic Series. Fine‐ to coarse‐grained tonalite and quartz porphyry intruded this unit. The main structural features of the area are north–south‐trending left‐lateral strike‐slip faults and their subsidiaries, which generally strike north–south and dip moderately to the east (350°–360°/40°–60°). Mineralization at the Penjom gold deposit is structurally controlled and also erratic laterally and vertically. The gold mineralization can be categorized as (i) gold associated with carbonate‐rich zones hosted within dilated quartz veins carrying significant amount of sulfides; (ii) gold disseminated within stockwork of quartz–carbonate veins affiliated with tonalite; and (iii) gold often associated with arsenopyrite and pyrite in quartz–carbonate veins and stringers hosted within shear zones of brittle–ductile nature in all rock types and in brittle fractured rhyodacitic volcanic rocks. Sphalerite, chalcopyrite, tetrahedrite and pyrrhotite are the minerals accompanying the early stage of gold mineralization. These minerals also suffered from local brittle deformation. However, most of the gold mineralization took place after the deposition of these sulfides. Galena appears somewhat towards the end of gold mineralization, whereas tellurium and bismuth accompanied gold contemporaneously. The gold mineralization occurred most probably due to the metamorphogenic deformational origin concentrated mostly in the shear zone. The mineralization is strongly controlled by the wall rock (e.g. graphitic shale), the sulfide minerals and fluid–rock interaction.  相似文献