Knowing Climate Change: Local Social Institutions and Adaptation in Indian Groundwater Irrigation     

Trevor Birkenholtz 《The Professional geographer》2013,65(3):354-362

SHORE FEATURES. Patrick C. Moyer.

LOKATE. Charles W. Smith.  相似文献   

Galaxy evolution in Hickson compact groups: the role of ram-pressure stripping and strangulation     

Jesper Rasmussen †  Trevor J. Ponman  Lourdes Verdes-Montenegro  Min S. Yun  Sanchayeeta Borthakur 《Monthly notices of the Royal Astronomical Society》2008,388(3):1245-1264

Galaxies in compact groups tend to be deficient in neutral hydrogen compared to isolated galaxies of similar optical properties. In order to investigate the role played by a hot intragroup medium (IGM) for the removal and destruction of H  i in these systems, we have performed a Chandra and XMM–Newton study of eight of the most H  i deficient Hickson compact groups. Diffuse X-ray emission associated with an IGM is detected in four of the groups, suggesting that galaxy–IGM interactions are not the dominant mechanism driving cold gas out of the group members. No clear evidence is seen for any of the members being currently stripped of any hot gas, nor for galaxies to show enhanced nuclear X-ray activity in the X-ray bright or most H  i deficient groups. Combining the inferred IGM distributions with analytical models of representative disc galaxies orbiting within each group, we estimate the H  i mass-loss due to ram-pressure and viscous stripping. While these processes are generally insufficient to explain observed H  i deficiencies, they could still be important for H  i removal in the X-ray bright groups, potentially removing more than half of the interstellar medium in the X-ray bright HCG 97. Ram pressure may also have facilitated strangulation through the removal of galactic coronal gas. In X-ray undetected groups, tidal interactions could be playing a prominent role, but it remains an open question whether they can fully account for the observed H  i deficiencies.  相似文献   

Helminth parasites of brown trout (Salmo Trutta L.) in Canterbury,New Zealand     

Trevor G. Dix 《新西兰海洋与淡水研究杂志》2013,47(2):363-374

Neopeltopsis pectinipes gen. et sp. nov. is described and figured from sublittoral marine algae at Wellington, New Zealand; the genus is an addition to the Peltidiidae Sars. The genus is compared with the other genera of the family, and a revised key is given to the genera of the Peltidiidae.  相似文献   

Biology of evechinus chloroticus (echinoidea: Echinometridae) from different localities   总被引：1，自引：1，他引：0  

Trevor G. Dix 《新西兰海洋与淡水研究杂志》2013,47(2):91-116

The distribution, general habits, morphological variation, food, associates and predators ‘Of the common endemic New Zealand echiooid Evechinus chloroticus (Val.) are considered.

Evechinus chloroticus is chiefly a rocky bottom dweller but adults, juveniles and very small individuals often occupy different microhabitats. The urchin is typically found in shallow subtidal situations (<12m) although considerable intertidal populations occur in some areas, particularly towards the north. A superimposed dispersion pattern of population and intra‐population clumping is typical and densities often exceed 50 adults/m².

Spine length, thickness and sharpness and test thickness vary between populations but no significant variation in test shape (height/diameter) was observed. Variations in spination are probably related to wave exposure while test thickness is at least in part related to nutrition.

In the localities where macroscopic algae are diverse and abundant, Evechinus is almost exclusively algivorous, but it predominantly browses material from the substrate where algae are sparse.

The rhabdocoele, Syndesmis sp. (in the gut) and various tiliates (in the gut and gonad) were commonly found in Evechinus. The urchin provides shelter and food for the clingfish Dellichthys morelandi, and the isopod Exosphaeroma sp. is probably also a close associate.

Known predators include the cymaitiid gastropods Charonia capax and C. rubicunda, the seastar Coscinasterias calamaria, and the blue cod Parapercichthys colias and snapper Chrysophrys auratus.  相似文献   

Formation and erosion of sediment cover in an experimental bedrock‐alluvial channel          下载免费PDF全文

Rebecca Hodge  Trevor Hoey  Georgios Maniatis  Emilie Leprêtre 《地球表面变化过程与地形》2016,41(10):1409-1420

Sediment grains in a bedrock‐alluvial river will be deposited within or adjacent to a sediment patch, or as isolated grains on the bedrock surface. Previous analysis of grain geometry has demonstrated that these arrangements produce significant differences in grain entrainment shear stress. However, this analysis neglected potential interactions between the sediment patches, local hydraulics and grain entrainment. We present a series of flume experiments that measure the influence of sediment patches on grain entrainment. The flume had a planar bed with roughness that was much smaller than the diameters of the mobile grains. In each experiment sediment was added either as individual grains or as a single sediment pulse. Flow was then increased until the sediment was entrained. Analysis of the experiments demonstrates that: (1) for individual grains, coarse grains are entrained at a higher discharge than fine grains; (2) once sediment patches are present, the different in entrainment discharge between coarse and fine grains is greatly reduced; (3) the sheltering effect of patches also increases the entrainment discharge of isolated grains; (4) entire sediment patches break‐up and are eroded quickly, rather than through progressive grain‐by‐grain erosion; (5) as discharge increases there is some tendency for patches to become more elongate and flow‐aligned, and more randomly distributed across the bed. One implication of this research is that the critical shear stress in bedrock‐alluvial channels will be a function of the extent of the sediment cover. Another is that the influence of sediment patches equalizes critical shear stresses between different grain sizes and grain locations, meaning that these factors may not need to be accounted for. Further research is needed to quantify interactions between sediment patches, grain entrainment and local hydraulics on rougher bedrock surfaces, and under different types of sediment supply. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Honing safety and reliability aspects for the second generation of Eurocode 7     

Trevor L.L. Orr 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2019,13(3):205-213

ABSTRACT

Ten years after their publication, the Eurocodes, including Eurocode 7 for Geotechnical design, are being revised taking into account experiences with their use and developments in design concepts and practices since their publication to produce a second generation of the Eurocodes. The objectives for this second generation of Eurocode 7 are to improve its ease of use, harmonise its structure with the other Eurocodes, reduce the number of nationally determined parameters, include measures for robustness and include sections on topics not covered in the current Eurocode 7, such as numerical methods, reinforced soil and ground improvement. The evolution of Eurocode 7 aims to hone its safety and risk assessment aspects by developing the concept of Geotechnical Categories, expanding the supervision, monitoring and maintenance requirements, and explicitly allowing for reliability differentiation.  相似文献   

北祁连东部两类Ⅰ型花岗岩定年及其地质意义     

吴才来  杨经绥  杨宏仪  郑秋光  史仁灯  陈松永  Joe Wooden  Trevor lreland 《地质学报》2005,79(2):286

  相似文献   

Isotopic records in CM hibonites: Implications for timescales of mixing of isotope reservoirs in the solar nebula   总被引：1，自引：0，他引：1  

Ming-Chang Liu  Kevin D. McKeegan  Kuljeet K. Marhas  Trevor R. Ireland 《Geochimica et cosmochimica acta》2009,73(17):5051-1532

The magnesium isotopic compositions of 26 hibonite-bearing inclusions from the CM chondrite Murchison, as well as isotopic measurements on a subset of these samples for oxygen, titanium, and lithium-beryllium-boron are reported along with oxygen isotopic data for an additional 13 hibonites that were previously investigated for other isotope systems (magnesium, potassium, calcium, and titanium) and rare earth element concentrations. Magnesium isotopic compositions divide CM hibonites into two distinct populations which correlate perfectly with their mineralogy and morphology, as previously discovered by Ireland [Ireland T. R. (1988) Correlated morphological, chemical, and isotopic characteristics of hibonites from the Murchison carbonaceous chondrite. Geochim. Cosmochim. Acta52, 2827-2839]: Spinel-HIBonite spherules (SHIBs) bear evidence of in situ²⁶Al decay, whereas PLAty-Crystals (PLACs) and Blue AGgregates (BAGs) either lack resolvable ²⁶Mg-excesses or exhibit ²⁶Mg deficits by up to ∼4‰. High precision, multiple collector SIMS analyses show that 6 of 7 SHIBs investigated fall on a single correlation line implying ²⁶Al/²⁷Al = (4.5 ± 0.2) × 10⁻⁵ at the time of isotopic closure, consistent with the “canonical” ²⁶Al abundance characteristic of internal isochrons in many calcium-aluminum-rich inclusions (CAIs). One SHIB sample exhibits Δ²⁶Mg^∗ consistent with a “supracanonical” ²⁶Al/²⁷Al ratio of (6.4 ± 0.5) × 10⁻⁵. The PLAC hibonites contain highly anomalous titanium isotopic compositions, with δ⁵⁰Ti values ranging from −80‰ to almost +200‰, whereas SHIBs generally lack large Ti isotopic anomalies.Eight out of 11 ²⁶Al-free PLAC hibonite grains record ¹⁰B/¹¹B excesses that correlate with Be/B; the inferred initial ¹⁰Be/⁹Be ratio of (5.1 ± 1.4) × 10⁻⁴ is lower than the best-constrained ¹⁰Be/⁹Be of (8.8 ± 0.6) × 10⁻⁴ in a CV CAI. The data demonstrate that ¹⁰Be cannot be used as a relative chronometer for these objects and that most of the ¹⁰Be observed in CAIs must be produced by irradiation of precursor solids in the early solar system. The lack of ²⁶Al in PLAC hibonites indicates that significant amounts of ²⁶Al were not formed in the same spallogenic processes that made ¹⁰Be in PLAC precursors. This is most easily understood as indicating very early formation of the PLAC hibonites, prior to the incorporation and mixing of ²⁶Al into the solar nebula, although an alternative scenario, which invokes irradiation under different solar flare conditions, cannot be ruled out. Lithium isotopes are normal within uncertainties, probably reflecting contamination and/or postcrystallization exchange.The oxygen isotopic compositions of SHIBs and PLACs are all highly ¹⁶O-enriched, but are not derived from a homogeneous reservoir: Δ¹⁷O values span a range of ∼−28‰ to −15‰. The ranges of ¹⁶O-enrichment in SHIBs and PLACs overlap and are less “anomalous” than the most ¹⁶O-enriched compositions found in meteorites [Kobayashi S., Imai H. and Yurimoto H. (2003) New extreme ¹⁶O-rich chondrule in the early solar system. Geochem. J.37, 663-669]. Both PLACs and SHIBs formed in ¹⁶O-enriched reservoirs characterized by small-scale heterogeneities in the gas phase. If such heterogeneities were generated by an admixture of relatively ¹⁶O-poor gas created by self-shielding during CO photolysis and transported to the hot inner regions of the accretion disk, then this process must have been initiated very early on, prior to the arrival of fresh radioactivity into the inner solar system. Oxygen isotope heterogeneities persisted throughout the formation interval of PLACs, CAI precursors, and SHIBs which could be as long as 3 × 10⁵ years based on ²⁶Al records.One SHIB and one BAG exhibit mass fractionated oxygen isotopic compositions similar to those seen in FUN inclusions and in several platy hibonite crystals [Lee T., Mayeda T. K. and Clayton R. N. (1980) Oxygen isotopic anomalies in Allende inclusion HAL. Geophys. Res. Lett.7, 493-496; Ireland T. R., Zinner E. K., Fahey A. J. and Esat T. M. (1992) Evidence for distillation in the formation of HAL and related hibonite inclusions. Geochim. Cosmochim. Acta56, 2503-2520; Ushikubo T., Hiyagon H. and Sugiura N. (2007) A FUN-like hibonite inclusion with a large ²⁶Mg-excess. Earth Planet. Sci. Lett.254, 115-126]. The suite of mass-fractionated hibonites exhibit a range of isotopic properties, including ²⁶Al/²⁷Al ratios from below detection to a “canonical” level and oxygen and titanium anomalies that are not exceptional by PLAC standards. This suggests that F (fractionation) processes—evaporation under (oxidizing) conditions—are not necessarily associated with sampling a special isotopic reservoir.  相似文献   

Cosmogenic 21Ne analysis of individual detrital grains: Opportunities and limitations     

Alexandru T. Codilean  Paul Bishop  Trevor B. Hoey  Finlay M. Stuart  Derek Fabel 《地球表面变化过程与地形》2010,35(1):16-27

We use a numerical model describing cosmogenic nuclide acquisition in sediment moving through the upper Gaub River catchment to evaluate the extent to which aspects of source area geomorphology and geomorphological processes can be inferred from frequency distributions of cosmogenic ²¹Ne (²¹Ne_c) concentrations in individual detrital grains. The numerical model predicts the pathways of sediment grains from their source to the outlet of the catchment and calculates the total ²¹Ne_c concentration that each grain acquires along its pathway. The model fully accounts for variations in nuclide production due to changes in latitude, altitude and topographic shielding and allows for spatially variable erosion and sediment transport rates. Model results show that the form of the frequency distribution of ²¹Ne_c concentrations in exported sediment is sensitive to the range and spatial distribution of processes operating in the sediment's source areas and that this distribution can be used to infer the range and spatial distribution of erosion rates that characterise the catchment. The results also show that lithology can affect the form of the ²¹Ne_c concentration distribution indirectly by exerting control on the spatial pattern of denudation in a catchment. Model results further indicate that the form of the distribution of ²¹Ne_c concentrations in the exported sediment can also be affected by the acquisition of ²¹Ne_c after detachment from bedrock, in the diffusive (hillslope) and/or advective (fluvial) domains. However, for such post‐detachment nuclide acquisition to be important, this effect needs to at least equal the nuclide acquisition prior to detachment from bedrock. Copyright © 2009 John Wiley and Sons, Ltd.  相似文献   

Assessing the significance of wet-canopy evaporation from forests during extreme rainfall events for flood mitigation in mountainous regions of the United Kingdom     

Trevor Page  Nick A. Chappell  Keith J. Beven  Barry Hankin  Ann Kretzschmar 《水文研究》2020,34(24):4740-4754

There is increased interest in the potential of tree planting to help mitigate flooding using nature-based solutions or natural flood management. However, many publications based upon catchment studies conclude that, as flood magnitude increases, benefit from forest cover declines and is insignificant for extreme flood events. These conclusions conflict with estimates of evaporation loss from forest plot observations of gross rainfall, through fall and stem flow. This study explores data from existing studies to assess the magnitudes of evaporation and attempts to identify the meteorological conditions under which they would be supported. This is achieved using rainfall event data collated from publications and data archives from studies undertaken in temperate environments around the world. The meteorological conditions required to drive the observed evaporation losses are explored theoretically using the Penman–Monteith equation. The results of this theoretical analysis are compared with the prevailing meteorological conditions during large and extreme rainfall events in mountainous regions of the United Kingdom to assess the likely significance of wet canopy evaporation loss. The collated dataset showed that event Ewc losses between approximately 2 and 38% of gross rainfall (1.5 to 39.4 mm day⁻¹) have been observed during large rainfall events (up to 118 mm day⁻¹) and that there are few data for extreme events (>150 mm day⁻¹). Event data greater than 150 mm (reported separately) included similarly high percentage evaporation losses. Theoretical estimates of wet-canopy evaporation indicated that, to reproduce the losses towards the high end of these observations, relative humidity and the aerodynamic resistance for vapour transport needed to be lower than approximately 97.5% and 0.5 to 2 s m⁻¹ respectively. Surface meteorological data during large and extreme rainfall events in the United Kingdom suggest that conditions favourable for high wet-canopy evaporation are not uncommon and indicate that significant evaporation losses during large and extreme events are possible but not for all events and not at all locations. Thus the disparity with the results from catchment studies remains.  相似文献