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1.
Iacopo Cavicchini H. Cecilia Heyworth Christopher J. Duffin Claudia Hildebrandt Michael J. Benton 《Proceedings of the Geologists' Association. Geologists' Association》2018,129(2):144-158
Rhaetian bone beds have been described from many locations in south-west England, around Bristol. One site that has never been reported is Stowey Quarry, some 13?km south of Bristol. This quarry yielded Lias, and revealed thin Rhaetian units in the quarry floor, including two bone beds, the basal Rhaetian bone bed, and a second, higher bone bed, also within the Westbury Formation. The fossil fauna of both includes elements typical of Rhaetian bone beds elsewhere, but showing differences in faunal composition between the two. The basal bone bed yielded more specimens and more species, with three taxa (Sargodon tomicus, Rhomphaiodon minor and Hybodus cloacinus) exclusive to this bed and eleven identified in total. Severnichthys acuminatus accounts for more than 50% of the countable teeth from the basal bone bed, followed by Gyrolepis albertii with 20%, Lissodus minimus with 14% and Rhomphaiodon minor with 9%. The basal bone bed, as ever, is dominated by chondrichthyans, whereas the upper bone bed is dominated by osteichthyans, which form 90% of the non-dental remains. The only unique taxon is Dapedium, and Gyrolepis albertii is the most abundant species with 45% of countable teeth, followed by Severnichthys acuminatus with 38% and Duffinselache holwellensis with 11%. These faunal differences, and the equally good condition of specimens between both samples confirms that the upper bone bed is independent of the basal bone bed, and is not a reworked subsample. 相似文献
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Stefano Urbini Iacopo Nicolosi Antonio Zeoli Sami El Khrepy Ahmed Lethy Mahfooz Hafez Mohamed El Gabry Ahmed El Barkooky Aly Barakat Mahomoud GOMAA Ali M. Radwan Mohamed El Sharkawi Massimo D’orazio Luigi Folco 《Meteoritics & planetary science》2012,47(11):1842-1868
Abstract– We detail the Kamil crater (Egypt) structure and refine the impact scenario, based on the geological and geophysical data collected during our first expedition in February 2010. Kamil Crater is a model for terrestrial small‐scale hypervelocity impact craters. It is an exceptionally well‐preserved, simple crater with a diameter of 45 m, depth of 10 m, and rayed pattern of bright ejecta. It occurs in a simple geological context: flat, rocky desert surface, and target rocks comprising subhorizontally layered sandstones. The high depth‐to‐diameter ratio of the transient crater, its concave, yet asymmetric, bottom, and the fact that Kamil Crater is not part of a crater field confirm that it formed by the impact of a single iron mass (or a tight cluster of fragments) that fragmented upon hypervelocity impact with the ground. The circular crater shape and asymmetries in ejecta and shrapnel distributions coherently indicate a direction of incidence from the NW and an impact angle of approximately 30 to 45°. Newly identified asymmetries, including the off‐center bottom of the transient crater floor downrange, maximum overturning of target rocks along the impact direction, and lower crater rim elevation downrange, may be diagnostic of oblique impacts in well‐preserved craters. Geomagnetic data reveal no buried individual impactor masses >100 kg and suggest that the total mass of the buried shrapnel >100 g is approximately 1050–1700 kg. Based on this mass value plus that of shrapnel >10 g identified earlier on the surface during systematic search, the new estimate of the minimum projectile mass is approximately 5 t. 相似文献
3.
The goal of this research was to implement an optimization model that allows definition of best management strategies in the forest sector. The case study is depicted in a coniferous stand (silver fir—Abies alba Mill.) of Tuscany (central Italy). Four ecosystem services were quantified from biophysical (timber produced, carbon stored, ecosystem diversity, recreational function) and economic (total economic value of the above parameters) perspective. The indicators are aggregated through a multi-objective approach (compromise programming). In the framework of forest seen as complex adaptive systems, different management strategies can lead to emergent reaction of forest functions. Due to nonlinear and non-continuous interactions as well as to the presence of feedbacks and loops among environmental and socioeconomic forest components, results are optimized by means of differential evolution and particle swarm algorithm. The genetic algorithm was applied to minimize the distance from ideal point. The best value of the decision variable (rotation period) was defined for different scenarios based on compensatory level of criteria, constraints and presence/absence of forest thinning. Conflicting trends and trade-offs are highlighted when different criteria were optimized. Among outputs, thinning intervention seems to reduce the performance of several criteria in the study area. Strengths and weaknesses of the model as well as potential future improvements are finally discussed.
相似文献4.
The main research question investigated in this paper is the following: will a post-NATO world emerge during the next decades? The relevance of such a question is a consequence of the political and economic changes that have seen the light as a result of the power shift of international relations after the end of the Cold War. In spite of this, some contradictory tendencies, such as the weakening of the European pole within the NATO block, the US-NATO enlargement and its military aggressiveness, are generating a number of significant obstacles to the emergence of a post-NATO world. We will argue that the existence of these obstacles could be interpreted as some steps toward the historical downsizing of the US-EU-NATO hegemony. A “post-NATO” world does not necessarily imply the end of NATO, but rather the end of its hegemonic military presence on the global stage. Firstly, we will put the question into context mentioning the debates around NATO’s future and underlining the path undertaken by the Alliance in the frame of the redefinition of the aims of its “strategic concepts”. In this perspective, we will underline the direct link which exists between US strategic needs and NATO’s evolution in the post-Cold war era. Secondly, we will argue that the recent process of military expansionism led by NATO is remarkably de-legitimizing its actions on the global stage. Such a process, along with the current world system shift toward the end of unipolarity, is likely to provoke dramatic consequences in terms of international insecurity and the spreading of war. Thirdly, we will briefly compare the US and Chinese foreign actions, arguing that the space of international legitimacy is radically changing. This fact represents another brick supporting the idea of the emergence of a post-NATO world system in the future of international relations. 相似文献
5.
David Balata Iacopo Bertocci Luigi Piazzi Ugo Nesti 《Estuarine, Coastal and Shelf Science》2008,79(3):533-540
This paper aimed to compare epiphyte assemblages of leaves and rhizomes of Posidonia oceanica exposed to different levels of concentration of nutrients. The same design including a potentially impacted meadow and two reference meadows was used in each of two locations, characterized by the presence of a city or of suspended cages of a fish farm, respectively. This allowed to test for the consistency of responses of epiphytic assemblages to different sources of eutrophication. In both studies, results documented differences in patterns of composition and abundance of epiphytic assemblages on leaves between disturbed and reference meadows, while assemblages on rhizomes did not appear sensitive to this kind of disturbance. Moreover, in potentially impacted meadows, both assemblages showed different patterns of spatial variability compared to reference assemblages. Species composition and abundance of epiphyte assemblages seemed suitable for detecting moderate nutrient increases, even if adequate sampling designs are needed to separate patterns related to the large natural spatial variability of these systems from those related to changes in environmental conditions. 相似文献
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Large woody debris(LWD) reduces the flow area,deviate the flow and increases the velocity in correspondence of the bridge pier,therefore increases the maximum scour hole depth and accelerates sediment removal.Logs and drifts accumulated on bridge piers are of different dimensions.According to logs characteristics and river morphology,drift accumulations can either extend downstream the bridge pier or they can accumulate totally upstream.This paper aims to analyze the effect of drift accumulation planimetry on bridge pier scour.The experimental investigation has been carried out at the PITLAB hydraulic centre of Civil Engineering Department,University of Pisa,Italy.Drift accumulation was characterized by different relative longitudinal lengths,flow area occlusions,length of longitudinal drift and downstream planimetrical positions relative to the pier center.The experimental investigation has been carried out in clear-water conditions.Several pier sizes,channel widths and sediment materials have been tested.Maximum scour hole in presence of drift accumulation have been compared to the maximum scour hole for an isolated pier.Finally,data were compared with previous literature findings,which highlight the effect of the downstream extension of drift accumulation on bridge pier scour.New relationships have been proposed to predict the effect of drift accumulation on bridge pier scour,both in terms of relative maximum scour and temporal scour evolution. 相似文献
7.
Patterns in megabenthic assemblages on a seamount summit (Ormonde Peak,Gorringe Bank,Northeast Atlantic) 
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下载免费PDF全文 Manuela Ramos Iacopo Bertocci Fernando Tempera Gonçalo Calado Mónica Albuquerque Pedro Duarte 《Marine Ecology》2016,37(5):1057-1072
Gettysburg and Ormonde are two shallow peaks located on the Gorringe seamount about 200 and 240 km WSW off Cape St. Vincent (Portugal, NE Atlantic), within the Portuguese Economic Exclusive Zone. Despite the ecological importance of the biological assemblages on these peaks and the need to preserve seamounts as valuable habitats, no management plans have been yet implemented at this site, which only recently has been included in the list of Sites of Community Importance of Portugal. Video imagery collected using a ROV during the 2011 Oceana campaigns was used here to analyse qualitative and quantitative patterns of benthic assemblage composition at the summit of the seamount (between 30 and 230 m depth). The results suggest that Ormonde is a biologically important area made up of vulnerable marine ecosystem elements that change significantly with depth. These include: kelp beds, in the euphotic zone; encrusting coralline algal communities and solitary colonies or mixed associations of suspension‐feeders (scleractinians, gorgonians, antipatharians, encrusting demosponges and ascidians), at the lower limit of the euphotic zone; mixed coral gardens and erect sponges, in the disphotic zone; and dense sponge aggregations, on the upper slope. These results were further used to propose amendments to the European Nature Information System habitat classification as a tool to work towards resolving the seamounts management issue. The results also provide information on taxa and habitats with high ecological value and classified as threatened or vulnerable, which is essential for the implementation of the cornerstones of Europe's biodiversity conservation policy, namely the OSPAR Convention and the EU Habitats Directive. 相似文献
8.
J. C. Raymond J. L. Kohl G. Noci E. Antonucci G. Tondello M. C. E. Huber L. D. Gardner P. Nicolosi S. Fineschi M. Romoli D. Spadaro O. H. W. Siegmund C. Benna A. Ciaravella S. Cranmer S. Giordano M. Karovska R. Martin J. Michels A. Modigliani G. Naletto A. Panasyuk C. Pernechele G. Poletto Peter L. Smith R. M. Suleiman L. Strachan 《Solar physics》1997,175(2):645-665
The Ultraviolet Coronagraph Spectrometer on the SOHO satellite covers the 940–1350 Å range as well as the 470–630 Å range in second order. It has detected coronal emission lines of H, N, O, Mg, Al, Si, S, Ar, Ca, Fe, and Ni, particularly in coronal streamers. Resonance scattering of emission lines from the solar disk dominates the intensities of a few lines, but electron collisional excitation produces most of the lines observed. Resonance, intercombination and forbidden lines are seen, and their relative line intensities are diagnostics for the ionization state and elemental abundances of the coronal gas. The elemental composition of the solar corona and solar wind vary, with the abundance of each element related to the ionization potential of its neutral atom (First Ionization Potential–FIP). It is often difficult to obtain absolute abundances, rather than abundances relative to O or Si. In this paper, we study the ionization state of the gas in two coronal streamers, and we determine the absolute abundances of oxygen and other elements in the streamers. The ionization state is close to that of a log T = 6.2 plasma. The abundances vary among, and even within, streamers. The helium abundance is lower than photospheric, and the FIP effect is present. In the core of a quiescent equatorial streamer, oxygen and other high-FIP elements are depleted by an order of magnitude compared with photospheric abundances, while they are depleted by only a factor of 3 along the edges of the streamer. The abundances along the edges of the streamer (‘legs’) resemble elemental abundances measured in the slow solar wind, supporting the identification of streamers as the source of that wind component. 相似文献
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Sediment load plays a fundamental role in natural river morphology evolution. Therefore, the correct assessment of the role
of the sediment load on natural or anthropic pools morphology downstream of river grade control structures, such as rock chute
or block ramps, is of fundamental interest for preserving the fish habitat and the river morphology. This work presents an
experimental study on the sediment load influence on rectangular expanding pools downstream of block ramps in live-bed conditions.
Several longitudinal and transversal expanding ratios have been tested. Ramp slopes were varied between 0.083 and 0.25. The
effect of the pool geometry and the sediment load on hydraulic jump downstream of block ramp as well as scour morphologies
and flow patterns have been analyzed. Equations were derived to evaluate the maximum scour hole depth, the longitudinal distance
of the section in which it occurs, and the maximum water elevations both in the pool and in the downstream contraction. 相似文献