Detailed study of an hydrological system of valleys, a delta and lakes in the Southwest Thaumasia region, Mars     

Nicolas Mangold  Véronique Ansan 《Icarus》2006,180(1):75-87

The occurrence of fluvial activity and standing bodies of water on early Mars is the subject of debate. Using MOC, MOLA, and THEMIS data, we identify a whole set of landforms in the Thaumasia region which attest to water flows during geologically long periods of more than thousand years. A thick fan-delta is identified within an impact crater at the outlet of a deep valley. Ponded water filled and overflowed this crater's rim, creating entrance and exit breaches and an outlet valley. These landforms show that the 25-km diameter impact crater contained a lake up to 600 m deep. At the head of this crater's deep contributing valley, a closed depression may have contained another lake, but depositional landforms are not evident in this headward basin. Alternatively, groundwater discharge may have supplied the valley, but the observed landforms are not consistent with a sudden release of water, as is usually invoked for the large martian outflows channels. Stratigraphic relationships show that this hydrological activity occurred during the Hesperian period, thus relatively late in the history of martian valley network development.  相似文献   

Distribution and community structure of estuarine copepods     

Rolland S. Fulton 《Estuaries and Coasts》1984,7(1):38-50

Distribution, abundance, and community structure were studied over a 30 month period in the planktonic copepod community of the estuaries near Beaufort, North Carolina. Many of the copepod species showed a demersal distribution during the day and entered the surface waters at night. Several species were largely confined to vegetated littoral areas during the day. The copepod community showed consistent trends of seasonal abundance and succession of dominant species which differed greatly from those found by previous workers, whose methods were inadequate to sample quantitatively the small, demersal copepods which dominated the community. Copepod abundances were higher than found in previous studies and were correlated with water temperature. Species composition changed from a winter community dominated byCentropages spp., to a spring community dominated byAcartia tonsa, to a summer community jointly dominated byParacalanus crassirostris andOithona spp. Copepods were much more important grazers in these estuaries than previous studies had concluded.  相似文献   

Modeling the risk of robbery in the city of Tshwane,South Africa     

Nicolas Kemp  Antony Cooper 《制图学和地理信息科学》2021,48(1):29-42

ABSTRACT

In this study, we model the risk of robbery in the City of Tshwane in South Africa. We use the collective knowledge of two prominent spatial theories of crime (social disorganization theory, and crime pattern theory) to guide the selection of data and employ rudimentary geospatial techniques to create a crude model that identifies the risk of future robbery incidents in the city. The model is validated using actual robbery incidences recorded for the city. Overall the model performs reasonably well with approximately 70% of future robbery incidences accurately identified within a small subset of the overall model. Developing countries such as South Africa are in dire need of crime risk intensity models that are simple, and not data intensive to allocate scarce crime prevention resources in a more optimal fashion. It is anticipated that this model is a first step in this regard.  相似文献   

Centimeter Accuracy for the French Transportable Laser Ranging Station (FTLRS) through Sub-System Controls     

J. Nicolas  F. Pierron  E. Samain  F. Barlier 《Surveys in Geophysics》2001,22(5-6):449-464

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Magnetostratigraphy of the lower member of the hadar formation (Ethiopia): Evidence for a short normal event in the mammoth subchron     

Endale Tamrat  Nicolas Thouveny  Maurice Taieb 《Studia Geophysica et Geodaetica》1996,40(3):313-335

Summary Rock magnetism and magnetostratigraphy of the lower part of the Hadar Formation (Afar, Ethiopia) is presented after analysis of multiple new collection of samples from over 84 horizons. The Hadar Formation is composed of lacustrine, lake margin, fluvial and flood plain sediments and known for important Pliocene vertebrate faunas including Australopithecus afarensis. Hysteresis measurements, thermomagnetic analysis, growth and decay of isothermal remanent magnetisation are used to unravel the complex magnetic mineralogy of the different representative lithologies. Ferrimagnetic minerals of magnetite or titanomagnetite in composition, in the stable pseudo-single domain (PSD) size range are found to be the main carriers of the remanence. In most sites the characteristic remanence was isolated using stepwise thermal demagnetisation. The overall mean direction for about 72 horizons (434 samples) is D=358·6°, I=7° (k=17·9, α₉₅=4°) implying some 14° of inclination shallowing, related to sediment compaction due to the very rapid sedimentation history of the site. Five successive polarity zones (N1-R1-N2-R2-N3) are identified and correlation with the lower Gauss chron of the astronomically calibrated geomagnetic polarity time scale (GPTS) is proposed using the existing⁴⁰Ar/³⁹Ar ages. This implies the existence of a short normal polarity event (N2), identified on six different sites, within the reversed Mammoth subchron, called the Kada-Hadar event. The age calculated for the Kada-Hadar event, using linear interpolation of the dated horizons, assuming a constant rate of sedimentation is 3.246 Ma and its duration is about 8 kyr.  相似文献   

The February 1996 earthquake sequence in the eastern Pyrenees: first results     

A. Rigo  A. Souriau  H. Pauchet  A. Grésillaud  M. Nicolas  C. Olivera  S. Figueras 《Journal of Seismology》1997,1(1):3-14

An earthquake with local magnitude (ML) 5.2 occurred February 18, 1996 in the eastern Pyrenees (France) near the town of Saint-Paul de Fenouillet. This event is the first of this magnitude in France to be well recorded instrumentally. Less than 24 hours after the main shock, we installed a temporary network of 30 seismological stations in the epicentral area to record the aftershock sequence. In this paper, we analyse the main shock and present the 37 largest aftershocks (1.8 Ml 3.4) in the two months following the main shock. These events are located using data from the permanent Pyrenean seismological network and the temporary network when available. We also determined eight fault plane solutions using the P-wave first motions. The main shock and the aftershocks are located inside the small Agly massif. This Hercynian structure sits some 8 km north of the North Pyrenean Fault, which is usually considered to be the suture between the Iberian and Eurasian plates. The mechanism of the main shock is a left-lateral strike-slip on an E–W trending fault. The fault plane solutions of the aftershocks are mostly E–W striking reverse faults, in agreement with the general north-south shortening of the Pyrenees. The aftershocks located down to 11 km depth, indicating that the Agly massif is deeply fractured. The main interpretations of these results are: (i) The main shock involved an E–W trending fault inside the highly fractured Agly massif, relaying the North Pyrenean Fault which had, at least in the last 35 years, a poor seismic activity along this segment; (ii) The Saint-Paul de Fenouillet syncline to the north and the North Pyrenean Fault to the south delimit a 15 km wide senestral shear zone. Such a structure is also suggested by the highly fractured pattern of the Agly massif and by small en echelon faults and secondary folds in the Saint-Paul de Fenouillet syncline; (iii) we suggest that the North Pyrenean Frontal Thrust, located less than 10 km north of the Agly massif, has a ramp geometry at depth below the Agly massif.  相似文献   

An introduction to the application and future use of Th in aquatic systems     

James T. Waples  Claudia Benitez-Nelson  Nicolas Savoye  Michiel Rutgers van der Loeff  Mark Baskaran   rjan Gustafsson 《Marine Chemistry》2006,100(3-4):166

²³⁴Th is an extremely useful radiotracer of particle dynamics in aquatic systems. Its utility, however, has yet to be realized by many within the aquatic science community. The reasons for this may in part be due to a lack of knowledge of how this nuclide has been used in the past as well as how and where ²³⁴Th might be profitably applied in future research. The purpose of this paper, then, is to examine the variety of ²³⁴Th applications that have been used to understand natural aquatic processes in four major areas: vertical transport, particle cycling, horizontal transport, and sediment dynamics. We provide a general overview of the possible applications of ²³⁴Th in the hopes of provoking an increased interest in the inherent potential and future application of ²³⁴Th in these systems. We end this paper with a discussion of future research avenues in the context of three specific regimes: (i) the upper 1000 m of the open ocean, (ii) coastal sediment/water processes and (iii) large freshwater lakes.  相似文献   

The whaling issue: Conservation,confusion, and casuistry     

Phillip J. Clapham  Simon Childerhouse  Nicolas J. Gales  Lorenzo Rojas-Bracho  Michael F. Tillman  Robert L. Brownell Jr. 《Marine Policy》2007

Morishita's “multiple analysis” of the whaling issue [Morishita J. Multiple analysis of the whaling issue: Understanding the dispute by a matrix. Marine Policy 2006;30:802–8] is essentially a restatement of the Government of Japan's whaling policy, which confuses the issue through selective use of data, unsubstantiated facts, and the vilification of opposing perspectives. Here, we deconstruct the major problems with Morishita's article and provide an alternative view of the whaling dispute. For many people in this debate, the issue is not that some whales are not abundant, but that the whaling industry cannot be trusted to regulate itself or to honestly assess the status of potentially exploitable populations. This suspicion has its origin in Japan's poor use of science, its often implausible stock assessments, its insistence that culling is an appropriate way to manage marine mammal populations, and its relatively recent falsification of whaling and fisheries catch data combined with a refusal to accept true transparency in catch and market monitoring. Japanese policy on whaling cannot be viewed in isolation, but is part of a larger framework involving a perceived right to secure unlimited access to global marine resources. Whaling is inextricably tied to the international fisheries agreements on which Japan is strongly dependent; thus, concessions made at the IWC would have potentially serious ramifications in other fora.  相似文献   

Modelling bathymetry by inverting satellite altimetry data: A review   总被引：3，自引：0，他引：3  

Stephane Calmant  Nicolas Baudry 《Marine Geophysical Researches》1996,18(2-4):123-134

With the advent of satellite altimetry it has become possible to determine the gravity field of the oceans on a global scale. This set of data can be used to predict the bathymetry of deep-seafloor features such as seamounts and ridges. During the last two decades, several algorithms which can be used to develop bathymetric predictions from satellite altimeter data have been published. The characteristics and quality of these algorithms are reviewed in this study. Based on this analysis, we suggest some guidelines for processing data towards the production of maps showing predicted bathymetry for economical purposes.  相似文献   

Spatial considerations for the Dakhla stock of Octopus vulgaris: indicators, patterns, and fisheries interactions     

Faraj  Abdelmalek; Bez  Nicolas 《ICES Journal of Marine Science》2007,64(9):1820-1828

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