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Experimentální zkoumání anodové oblasti hybridního plazmového hořáku s vodně-plynnou stabilizací DC oblouku. / Experimental Investigation of the Anode Area in the Hybrid Water-Gas DC Arc Plasma TorchOndáč, Peter January 2020 (has links)
This thesis focuses on an experimental study of the anode area of the hybrid water- gas DC arc plasma torch that is used in many industrial applications, including plasma spraying, hydrocarbon reforming, pyrolysis, and organic waste gasification. The effects of ambient pressure and plasma generation conditions on the torch's plasma jet were studied, with particular focus on the torch's anode area. Movement of the anode arc attachment is described in detail, including its speed, range of its motion on the anode surface, restrike periods, and the frequency of its many sudden decelerations and re-accelerations. It was found that the anode erosion can be compared relatively simply by quick processing of high-speed camera videos. The anode erosion was also measured directly. Many electric probe measurements were made in the anode area of this plasma torch for the first time. By using these electric probes, shock waves, turbulent vortices, and plasma potential fluctuations were studied directly. It was found that a mean plasma electric field and a mean plasma electrical conductivity in the anode area can be satisfactorily estimated also non-intrusively by quick processing of high-speed camera videos. Moreover, schlieren videos of the plasma jet in the anode area were created. 1
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Implementation And Performance Comparisons For The Crisfield And Stiff Arc Length Methods In FEASilvers, Thomas W. 01 January 2012 (has links)
In Nonlinear Finite Element Analysis (FEA) applied to structures, displacements at which the tangent stiffness matrix KT becomes singular are called critical points, and correspond to instabilities such as buckling or elastoplastic softening (e.g., necking). Prior to the introduction of Arc Length Methods (ALMs), critical points posed severe computational challenges, which was unfortunate since behavior at instabilities is of great interest as a precursor to structural failure. The original ALM was shown to be capable in some circumstances of continued computation at critical points, but limited success and unattractive features of the formulation were noted and addressed in extensive subsequent research. The widely used Crisfield Cylindrical and Spherical ALMs may be viewed as representing the 'state-of-the-art'. The more recent Stiff Arc Length method, which is attractive on fundamental grounds, was introduced in 2004, but without implementation, benchmarking or performance assessment. The present thesis addresses (a) implementation and (b) performance comparisons for the Crisfield and Stiff methods, using simple benchmarks formulated to incorporate elastoplastic softening. It is seen that, in contrast to the Crisfield methods, the Stiff ALM consistently continues accurate computation at, near and beyond critical points.
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Une stratégie nutritionnelle de réduction du phosphore (P) dans les effluents aquacoles : l'alimentation en phase des truites arc-en-ciel (Oncorhynchus mykiss) avec alternances d'un régime carencé et d'un régime équilibré en PKoko, Koffi Delagnoh Gabriel 13 April 2018 (has links)
L'étude a pour but de mettre au point une stratégie nutritionnelle de réduction de la charge en phosphore (P) des effluents piscicoles au Québec. Elle a duré 112 jours et consisté à évaluer les effets de trois types d'alternances répétées (à 1, 2 et 4 semaines) de régimes carencé ou RO (0,2 % P disponible) et équilibré ou RIO (0,3 % P disponible) en P sur la croissance et l'excrétion de P chez Oncorhynchus mykiss. Ces alternances ont été comparées à l'alimentation en continu avec RO, RIO et un régime témoin, bien équilibré, ou RG (0,5 % P disponible). Les alternances n'ont pas différé significativement (P<0,05) entre elles pour la croissance, la minéralisation des tissus et les rejets de P. Elles ont été globalement meilleures par rapport à l'alimentation en continu avec RO et RIO. C'est le RG ±en continu¿ qui a, cependant, eu des valeurs plus élevées pour la croissance, mais aussi des rejets de P plus élevés (4,2 contre 2 g de P par kg de poids frais). L'étude a montré qu'une alternance de régimes carencé et équilibré en P est une avenue intéressante pouvant permettre d'atteindre et même de dépasser l'objectif provincial du Québec en matière de rejet de P.
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Investigation of the functioning of a liquefied-gas micro-satellite propulsion systemWeyer, Robert Bernhard 12 1900 (has links)
Thesis (MScEng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: The focus of this thesis is on the investigation of the functioning of a liquefied-gas
thruster. Such a thruster could be used to provide secondary propulsion to a microsatellite
in orbit. A general overview of the need for thrusters in micro-satellites is put
forward in the introduction. Motivation for deciding to investigate a liquefied-gas
system is presented. Recent developments in the field of micro-satellites are
discussed as well as their relevance to the project undertaken. Fundamental
background theory relevant to the engineering problems associated with the
development and analysis of such a system is also presented. Computer programs
were written to simulate such a liquefied-gas thruster system. The experimental work
carried out to analyse the system from a practical view-point is documented.
Attention is also given to the measurement and calibration techniques used to obtain
experimental data.
One-dimensional fully explicit transient mathematical models of the thruster system
were developed to model the system using both compressed air and butane as
propellants. These models were incorporated into computer programs used to
simulate the transient behaviour of the system. Although it is intended to use butane
as the propellant onboard a satellite, the reason for modelling and simulating a system
using compressed air is because air is a convenient fluid to work with from both a
theoretical and practical point of view.
An experimental model of a thruster system was designed, built and tested using air
and butane as propellants. Most of the model was built using perspex to allow for the
observation of the two-phase behaviour of the propellant inside the system. Locally
purchased components were used for the solenoid and fill valves. Readily available
butane lighter fluid was used for butane testing. Self-made heating elements were
used to provide heat input to the propellant. Testing was done at different back
pressures ranging from 100 kPa down to 20 kPa in a vacuum chamber.
Good comparison between theoretical and experimental results was obtained for air.
Theoretical results for peak thrusts tended to over predict experimental results by approximately 15 % for a system exhausting to a pressure of 100 kPa. Peak thrusts as
high as 0.2 N were obtained for vacuum tests conducted at an absolute pressure of 20
kPa.
Peak thrusts of approximately 50 mN were achieved for experimental testing III
atmospheric conditions using butane with a starting pressure of between 270 and 290
kPa. Typical average thrusts of between 20 mN and 30 mN were noted for butane
testing with initial pressure of between 200 to 300 kPa. Peak thrusts of over 0.1 N
were observed for vacuum testing at an absolute pressure of 20 kPa. An equation to
correlate the experimentally determined average thrust as a function of pulse duration
and starting pressure was developed. This correlated most of the experimental data to
within ±25 %. Theoretical results for butane testing are able to predict peak thrusts
within approximately 20 % for starting pressures in the range of 200 to 300 kPa.
Since the project was an exploratory investigation into a liquefied-gas thruster, some
additional aspects relating to such systems were also given attention. The effect of
liquid propellant motion or sloshing was considered and recommendations regarding
the design and placement of the propellant tanks were made. The use of heat pipes as
an alternative to electrical heating elements was investigated and some elementary
design aspects are presented graphically. The management of the liquid propellant
using surface tension devices was examined qualitatively.
Recommendations relating to future projects in the field of simple, low-cost
propulsion systems for micro-satellites are put forward. More specifically these
recommendations are with regard to: thermo-fluid modelling of the propellant, future
experimental work to be done, techniques to measure small thrusts and vacuum
chamber testing. / AFRIKAANSE OPSOMMING: Die tesis ondersoek die funksionering van 'n vervloeidegas stuwer. So 'n stuwer kan
gebruik word om sekondêre aandrywing aan 'n mikro-satelliet in 'n wentelbaan te
verskaf. 'n Algemene oorsig oor die behoeftes van stuwers vir mikro-satelliete word
voortgesit in die inleiding. Redes vir die gebruik van 'n vervloeidegas stuwer word
bespreek. Onlangse ontwikkelinge in die veld van mikro-satelliet aandrywing word
bespreek asook die toepaslikheid daarvan. Fundamentele teoretiese agtergrond
verbonde aan die ontwikkeling en analise van so 'n stuwer stelsel word ook gegee.
Rekenaarprogramme is geskryf om die gedrag van so 'n stuwer stelsel te simuleer.
Eksperimentele werk is gedoen om die stelsel vanuit 'n praktiese oogpunt te analiseer.
Aandag word ook gegee aan die metings- en kalibrasietegnieke soos toegepas vir die
eksperimentele werk.
Eendimensionele volle eksplisiete wiskundige modelle is ontwikkelom die
oorgangsgedrag van die stuwer-stelsel te simuleer met beide lug en butaan as
dryfmiddel. Hierdie modelle is geïnkorporeer in die rekenaar programme om die
stuwer stelsel te simuleer. Alhoewel dit beoog word om butaan as die dryfmiddel aan
boord die satelliet te gebruik, is lug ook gebruik vir simulasie weens sy gerieflikheid
as 'n vloeier uit beide 'n teoretiese en 'n praktiese oogpunt.
'n Eksperimentele model van die stuwer stelsel is ontwerp, gebou en getoets met beide
lug en butaan as dryfmiddels. Die model is hoofsaaklik uit perspex gebou sodat die
twee-fase gedrag van die butaan uitgebeeld kon word. Vrylik beskikbare butaan
aansteker vloeistof IS gebruik VIr butaan toetsing. Selfvervaardigde
verhittingselemente is gebruik om hitte aan die dryfmiddel te verskaf. Toetse is
gedoen deur verskeie omgewingsdrukke varieërend van 100 kPa af tot 20 kPa in 'n
vakuumtenk te gebruik.
Goeie ooreenstemming tussen die teoretiese en eksperimentele resultate vir die
toetsing van lug is verkry. Die teoretiese resultate neig om die piek stukrag 15 % hoër
te voorspel as die eksperimentele resultate vir 'n stelsel wat tot 'n omgewingsdruk van
100 kPa by die uitlaat. Piek stukragte van meer as 0.2 N is gekry vir vakuum toetse
wat gedoen is by 'n omgewingsdruk van 20 kPa. Tydens eksperimentele toetsing met butaan teen 'n aanvanklike druk tussen 270 en
290 kPa, in atmosferiese toestande, is piek stukragte van ongeveer 50 mN behaal.
Tipiese gemiddelde stukragte van tussen 20 en 30 mN is waargeneem vir butaan
toetsing teen 'n aanvanklike druk tussen 200 en 300 kPa. Piek stukragte van meer as
0.1 N is behaal vir vakuum toetse met 'n absolute druk van 20 kPa. 'n Vergelyking
om die gemiddelde stukrag, wat eksperimenteel bepaal is, as 'n funksie van puls
tydsduur en aanvanklike druk te korreleer, is ontwikkel. Die meeste eksperimentele
data se afwyking van die korrelasie-vergelyking was minder as 25 %. Teoretiese
resultate vir butaantoetse het piek stukragte binne 20 % van die eksperimenteel
metings korrek voorspel vir aanvanklike drukke tussen 200 tot 300 kPa.
Weens die feit dat die projek 'n oorhoofse ondersoek in In vervloeidegas stuwer
behels, is aandag ook gegee aan addisionele aspekte wat verband hou met sulke
stelsels. Die effek van die vloeistof-dryfmiddel se onstabiele beweging in sy tenke is
in ag geneem en voorstelle vir die ontwerp en plasing van die dryfmiddel tenke is
gemaak. Die gebruik van hitte pype as 'n alternatief vir elektriese verhittingselemente
is ondersoek. Verskeie ontwerp aspekte word grafies voorgestel. Die bestuur van die
vloeistof-dryfmiddel deur van oppervlak spannings apparaat gebruik te maak, is
kwalitatief ondersoek.
Voorstelle vir verdere navorsing in die veld van eenvoudige, lae-koste stuwer stelsels
vir mikro-satelliete is gemaak. Meer spesifiek is hierdie voorstelle gerig op die
termo-vloeidinamiese modellering van die dryfmiddel, verdere eksperimentele
navorsing, tegnieke om klein stukragte te meet en vakuumtenk toetse.
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Cosmos greenstone terrane : insights into an Archaean volcanic arc, associated with komatiite-hosted nickel sulphide mineralisation, from U-Pb dating, volcanic stratigraphy and geochemistryDe Joux, Alexandra January 2014 (has links)
The Neoarchaean Agnew-Wiluna greenstone belt (AWB) of the Kalgoorlie Terrane, within the Eastern Goldfields Superterrane (EGS) of the Yilgarn Craton, Western Australia, contains several world-class, komatiite-hosted, nickel-sulphide ore bodies. These are commonly associated with felsic volcanic successions, many of which are considered to have a tonalite-trondhjemite-dacite (TTD) affinity. The Cosmos greenstone sequence lies on the western edge of the AWB and this previously unstudied mineralised volcanic succession contrasts markedly in age, geochemistry, emplacement mechanisms and probable tectonic setting to that of the majority of the AWB and wider EGS. Detailed subsurface mapping has shown that the footwall to the Cosmos mineralised ultramafic sequence consists of an intricate succession of both fragmental and coherent extrusive lithologies, ranging from basaltic andesites through to rhyolites, plus later-formed felsic and basaltic intrusions. The occurrence of thick sequences of amygdaloidal intermediate lavas intercalated with extensive sequences of dacite lapilli tuff, coupled with the absence of marine sediments or hydrovolcanic products, indicates the succession was formed in a subaerial environment. Chemical composition of the non-ultramafic lithologies is typified by a high-K calc-alkaline to shoshonite signature, indicative of formation in a volcanic arc setting. Assimilation-fractional crystallisation modelling has shown that at least two compositionally distinct sources must be invoked to explain the observed basaltic andesite to rhyolite magma suite. High resolution U-Pb dating of several units within the succession underpins stratigraphic relationships established in the field and indicates that the emplacement of the Cosmos succession took place between ~2736 Ma and ~2653 Ma, making it significantly older and longer-lived than most other greenstone successions within the Kalgoorlie Terrane. Extrusive periodic volcanism spanned ~50 Myrs with three cycles of bimodal intermediate/felsic and ultramafic volcanism occurring between ~2736 Ma and ~2685 Ma. Periodic intrusive activity, related to the local granite plutonism, lasted for a further ~32 Myrs or until ~2653 Ma. The Cosmos succession either represents a separate, older terrane in its own right or it has an autochthonous relationship with the AWB but volcanism initiated much earlier in this region than currently considered. Dating of the Cosmos succession has demonstrated that high-resolution geochronology within individual greenstone successions can be achieved and provides more robust platforms for interpreting the evolution of ancient mineralised volcanic successions. The geochemical affinity of the Cosmos succession indicates a subduction zone was operating in the Kalgoorlie Terrane by ~2736 Ma, much earlier than considered in current regional geodynamic models. The Cosmos volcanic succession provides further evidence that plate tectonics was in operation during the Neoarchaean, contrary to some recently proposed tectonic models.
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Subduction zone processes and continental crust formation in the southern Central Andes : insights from geochemistry and geochronologyJones, Rosemary Ellen January 2014 (has links)
Subduction zones, such as the Andean convergent margin, are the sites at which new continental crust is generated, and where subducting material is either recycled to the crust via arc magmatism or transferred to the deep mantle. The composition of arc magmas and associated new continental crust reflects variable contributions from mantle, crustal and subducted reservoirs. Insights into crustal growth and recycling processes in the southern Central Andes, specifically in the Pampean flat-slab segment, have been gained by utilising a range of petrological, geochronological and geochemical techniques. These techniques have been applied to a suite of Late Cretaceous (~73 Ma) to Late Miocene (~6 Ma) intrusive (granitoids) and extrusive (basalts to rhyolites) arc rocks collected from an east - west transect across the Andean Cordillera. The oxygen and hafnium isotopic composition of the accessory mineral zircon allows mantle-derived melts contaminated with older, upper continental crustal to be identified. Boron isotopic compositions of melt inclusions, combined with concentrations of certain incompatible trace elements, can be used to assess the source and influence of fluids derived from subducting material on the melt source region. The southern Central Andes provides a particularly interesting area to study these processes as the thickness of the continental crust has increased significantly over the course of the Cenozoic (from ~35 km to >50 km) and the angle of the subducting Nazca plate has shallowed since ~18 Ma, causing the position of the volcanic arc to migrate to the east. In order to unravel the complexities involved with constraining the contributions to arc magmas at an active continental margin, a range of geochronological, geochemical, and geothermobarometric techniques, including high resolution, micro-analysis of mineral phases and melt inclusions, have been applied. High resolution, U-Pb dating of magmatic zircon has improved regional stratigraphy in the Pampean flat-slab segment (between ~29 and 32 °S) and provided an accurate temporal constraint for geochemical and geothermobarometric data. The results of in-situ O and Lu-Hf isotope analysis of zircon show both distinct temporal and spatial variations across the Andean arc. The observed isotopic variability is attributed to variable contamination of mantle-derived melts with distinct Andean basement terranes, which vary east – west in composition and age. ‘Mantle-like’ δ18O(zircon) values, juvenile initial ƐHf(zircon) values and a lack of inherited, xenocrystic zircon cores, suggests the Late Cretaceous (~73 Ma) to Eocene (~39 Ma) plutons located in the Principal Cordillera of Chile, experienced very little interaction with the upper continental crust. Amphibole – plagioclase geothermobarometry indicates these calc-alkaline granitoids, which form extensive north – south trending belts, were emplaced at shallow depths in the crust (~4 – 5 km). Therefore the Late Cretaceous to Late Eocene is interpreted as a period of significant upper crustal growth. The isotopic variability in the Late Oligocene (~26 Ma) to Late Miocene (~6 Ma) arc magmatic rocks demonstrates that during thickening of the continental crust and migration of the Andean arc to the east, arc magmas assimilated Late Paleozoic to Early Mesozoic basement. In addition, arc magmas erupted/emplaced in the Argentinean Precordillera (i.e. farthest east from the trench) assimilated a Grenville-aged (~ 1330 – 1030 Ma) basement. The youngest arc magmas (~6 Ma) erupted in the Frontal Cordillera also show evidence for the assimilation of this ancient basement terrane, potentially signalling under-thrusting beneath the Frontal Cordillera. Overall, the later part of the Cenozoic represents a period of crustal reworking. Boron concentrations and isotope ratios measured in pyroxene hosted melt inclusions and for the first time in zircon hosted melt inclusions, are higher than the values expected for the mantle wedge and show significant variations with time. The source of the Paleocene (~61 Ma) arc magmas were influenced by fluids primarily derived from altered oceanic crust. Lower δ11B values and boron concentrations obtained for Oligocene (25 – 23 Ma) arc magmatic rocks reflects a diminished influence of slab-derived fluids reflecting a greater depth to the top of the slab. Fluids derived from serpentinite influenced the source of the arc magmas after ~19.5 Ma. This has been linked with the intersection of the Juan Fernández Ridge, a volcanic seamount chain associated with hydrated and serpentinised oceanic lithosphere.
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Investigation into possible mechanisms of light pollution flashover of 275kv transmission lines as a cause of unknown outagesKleinhans, Kevin 03 1900 (has links)
Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005. / The cause of the largest number of faults on the Eskom main transmission system is unknown. It is believed that a non-uniform pollution layer along an insulator string is the reason for these anomalous flashovers. This non-uniform pollution layer results in the highest electric field strength, and thus the highest voltage, across the cleanest and driest discs. There thus exists a strong possibility that the anomalous flashover phenomenon is caused by a combination of mechanisms involving the pollution and air breakdown flashover mechanisms. This research project attempted to prove that flashover of the insulators is possible in accordance with the above model. Various experiments were set up in the high voltage laboratory and at a natural test site with a low source impedance supply attempting to simulate the conditions that lead to flashover in accordance with the hypothesis. All the tests done have not proven the non-uniform light pollution flashover mechanism successfully. However, future research has proposed an air breakdown flashover mechanism in light pollution conditions where the polluted part of the insulator string has a specific non-uniform distribution. Full scale testing in conditions similar to the normal operating conditions is proposed to prove the validity of this new hypothesis.
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Large scale plasma density perturbations in the polar F-region ionosphere2015 February 1900 (has links)
The most compelling evidence of the complex interaction between the geomagnetic field of the Earth and the magnetic field of the Sun is found in the polar ionosphere. Large scale F-region plasma density perturbations result from the coupling between the two fields. Plasma density enhancements known as ionization patches, and depletions can have lifetimes of several hours in the F region and are almost always present everywhere throughout the nighttime polar ionosphere. The perturbations can seed ionospheric irregularities that severely hamper communication and navigational networks, even during times of subdued geomagnetic activity. Up until recently, it has been difficult to study the perturbations due to the remoteness of their location. In the past decade an array of optical and radio instruments have been deployed to the Canadian sector of the Arctic, enabling a more thorough sampling of the polar ionosphere and the large scale perturbations therein.
In this work, common volume measurements from the Rankin Inlet Super Dual Auroral Radar Network (SuperDARN), Resolute Bay Incoherent Scatter Radar - North (RISR-N) and Optical Mesosphere and Thermosphere Imagers (OMTI) system at Resolute Bay are employed to investigate the generation mechanisms, transport properties, and optical and radio signatures of the large scale perturbations. A model connecting the optical signatures of patches to their velocity profile through the ionosphere is introduced and applied to OMTI data. In addition, an algorithm is developed to detect the presence of patches using RISR-N. Using the algorithm, a survey of patches sampled over several days is conducted, providing a comprehensive account of the variable polar ionosphere in terms of its plasma state parameters. Furthermore, the algorithm is used to diagnose patches as a primary source of coherent backscatter for the Rankin Inlet SuperDARN radar. Lastly, the generation of a deep plasma density depletion is analyzed using the three aforementioned instruments. Using a model, it is shown that such perturbations can be forged by intense frictional heating events in the polar ionosphere on a time scale of 15 minutes, and can subsequently be transported through the region.
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PHYSICOCHEMICAL MODIFICATIONS AND APPLICATIONS OF CARBON NANO-ONIONS FOR ELECTROCHEMICAL ENERGY STORAGEBorgohain, Rituraj 01 January 2013 (has links)
Carbon nano-onions (CNOs), concentrically multilayered fullerenes, are prepared by several different methods. We are studying the properties of two specific CNOs: A-CNOs and N-CNOs. A-CNOs are synthesized by underwater arc discharge, and N-CNOs are synthesized by high-temperature graphitization of commercial nanodiamond. In this study the synthesis of A-CNOs are optimized by designing an arc discharge aparatus to control the arc plasma. Moreover other synthesis parameters such as arc power, duty cycles, temperature, graphitic and metal impurities are controlled for optimum production of A-CNOs. Also, a very efficient purification method is developed to screen out A-CNOs from carboneseous and metal impurities. In general, A-CNOs are larger than N-CNOs (ca. 30 nm vs. 7 nm diameter). The high surface area, appropriate mesoporosity, high thermal stability and high electrical conductivity of CNOs make them a promising material for various applications. These hydrophobic materials are functionalized with organic groups on their outer layers to study their surface chemistry and to decorate with metal oxide nanoparticles. Both CNOs and CNO nanocomposites are investigated for application in electrochemical capacitors (ECs). The influences of pH, concentration and additives on the performance of the composites are studied. Electrochemical measurements demonstrate high specific capacitance and high cycling stability with high energy and power density of the composite materials in aqueous electrolyte.
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Étude géologique de l'arc de Castellane dans la région de Saint-Auban (A.-M.) : zone subalpine méridionaleFujiwara, Hajime 01 June 1968 (has links) (PDF)
Cette région fait partie de la zone subalpine méridionale, plus précisément de la branche est de l'Arc de Castellane ( environs de St Auban ). On y observe des terrains sédimentaires secondaires et tertiaires. fortement plissés, et qui appartiennent à la couverture sédimentaire de la zone externe alpine, dont le socle n'apparait qu'à plusieurs dizaines de kilomètres au Nord, dans le dôme permien de Barrot. La structure actelle résulte de la superposition de plusieurs phases tectoniques , parmi lesquelles on distingue facilement une phase anté-nummulitique relativement tranquille déformée par une ou plusieurs phases ultérieures, difficiles à dater du fait de l'absence de terrains plus récents que l'Oligocène inférieur. Au cours de ces derniers mouvements se sont produits des chevauchements vers le Sud qui sont le trait le plus caractéristique de la structure de la région. Il en résulte des redoublements de la série, en particulier du niveau repère que constituent les calcaires du Jurassique supérieur, ossature du relief. qui forment une succession de barres regardant au Sud et dominant des dépressions synclinales. Les faciès du Mésozoique et du Nummulitique montrent de nombreuses variations, car cette légion se situe : - au Jurassique et au Crétacé: à la limite des domaines provençaux et vocontiens ; - au Nummulitique: en bordure du bassin marin alpin. le but essentiel de ce mémoire est l'explication d 'une carte détaillée au 1/20 000 destinée à être utilisée pour la publication ultérieure de la feuille Castellane au 1/50 000 de la carte géologique de la France. Nous nous sommes donc surtout attachés à décrire les structures plutôt qu'a en détailler la stratigraphie .
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