Le chant des dunes est un phénomène naturel qui a longtemps éveillé la curiosité des hommes du désert, de Marco Polo à R.A. Bagnold. Les observations scientifiques du XXème siècle ont montré que le son est émis par la vibration cohérente de la surface libre d'un écoulement de ces grains chantants, et que ce son est soumis à un phénomène de seuil qui dépend de beaucoup de paramètres. Pour comprendre le mécanisme qui synchronise le mouvement des grains entre eux, nous avons effectué deux voyages au Maroc et à Oman pour observer les dunes chantantes sur le terrain, dont nous avons rapporté plusieurs échantillons de sable chantant. En étudiant leurs propriétés microscopiques, nous avons montré que ces sables sont recouverts d'un vernis qui augmente leurs propriétés d'adhésion et de frottement. Grâce à une expérience à cisaillement variable, nous avons caractérisé la dépendance du seuil avec l'humidité et les paramètres d'écoulement. Dans une expérience d'avalanches, nous avons réussi à reproduire le chant des dunes sur le terrain, et nos observations montrent qu'une partie de l'écoulement a une vitesse homogène, comme un bloc solide. De plus, cette expérience montre aussi que la synchronisation ne peut être due à une onde acoustique dans le milieu granulaire. Nous avons alors développé un modèle basé sur l'interaction entre les chaînes de forces dans l'écoulement de cisaillement et la partie où la vitesse est homogène. Ce modèle a un bon accord quantitatif avec les mesures, et il permet de rendre compte de toutes les observations qualitatives faites sur le chant des dunes.

De leur source continentale à leur lieu de stockage ultime, les particules sédimentaires détritiques vont être produites en fonction de la nature et de l'intensité des processus continentaux : climat, contexte géodynamique. Sur les plates-formes, elles vont subir l'action des agents hydrodynamiques, vont se déplacer, constituer des corps sédimentaires qui seront préservés ou non selon la nature et l'intensité des processus : agitation s.l., apports sédimentaires, création d'espace par subsidence et variation du niveau marin... Enfin, dans les domaines océaniques profonds, elles vont se déposer.<br />L'objectif des travaux présentés dans ce mémoire est, par une approche sédimentologique, de reconstituer les conditions environnementales, tant sur les continents que sur les plates-formes, ayant conduit aux dépôts étudiés. Sur cette base, nous avons entrepris des études sur des dépôts du Pléistocène en mer du Nord ainsi que dans les mers de Chine de l'Est et du Sud. Cette époque, par sa proximité, permet des études à très haute résolution temporelle tandis qu'elle est caractérisée par des oscillations climatiques et eustatiques importantes et rapides. De plus, les dépôts les plus récents portent la trace de l'Homme.<br />Sur la plate-forme, l'étude des grands corps sableux, bancs et très grandes dunes, a permis de préciser les mécanismes de leur mise en place. A court terme, même dans les environnements dominés par la marée, l'importance de phénomènes sporadiques tels que les houles de tempêtes, a été démontrée. Ils impriment aux formes et à la structure des fonds marins leur marque tandis que les agents tidaux sont les pourvoyeurs du matériel sédimentaire. A plus long terme, ce ne sont plus les agents dynamiques qui conditionnent la préservation des corps sédimentaires mais la création d'espace disponible et l'importance des apports sédimentaires. Au niveau de l'estuaire de l'Authie, des séries de carottages nous ont aidé à mesurer les conséquences du mouvement vers le nord des divers ensembles sédimentaires sur le type de sédiment rencontré ainsi que sur les modifications d'un espace naturel convoité par l'Homme.<br />Dans les bassins profonds, en mer de Chine du Sud, nos études ont permis de préciser les sources du matériel sédimentaire et son transport en faisant la part des contributions éolienne, fluviatile et marine. L'étude des caractères sédimentologiques de la fraction détritique a permis également d'étudier la balance ntre l'érosion et l'altération sur les zones émergées ainsi que de voir quelle est la réponse des marqueurs détritiques aux changements climatiques globaux depuis 2 millions d'années.

Resprouting is an important means of plant regeneration especially under conditions that do not favour regeneration through seeding such as frequent disturbances, low productivity, unfavourable soil conditions, extreme cold and limited understorey light availability. Sprouts may be advantageous over seedlings because they have higher survival and growth rates than seedlings, since they use resources from parent plants unlike seedlings that have to acquire their own resources. Resprouting is well documented for ecosystems that experience severe disturbances that damage aboveground biomass. For example, resprouting is important for plant persistence against fire in fire-prone savannas and Mediterranean shrub-lands, and hurricanes and cyclones in tropical forests. In these ecosystems, resprouting often results in multi-stemming, because this dilutes the risk of damage among many stems, improving the chances of individual survival. This study was conducted at coastal dune forest at Cape Vidal in north-eastern South Africa, where there is a high incidence of multi-stemmed trees due to resprouting in response to chronic disturbances of low severity. This study examines (1) the importance of resprouting to tree survival and dynamics in an environment where disturbance severity is low but pervasive, and (2) how this resprouting strategy differs from the more familiar sprouting response to severe disturbances such as fire and hurricanes. Analysis of the relationship between multi-stemming and a number of disturbances potentially causing multi-stemming revealed that stem leaning and substrate erosion were the most important disturbances associated with multi-stemming. There were fewer multistemmed trees on dune slacks that had a stable substrate and were protected from sea winds than on dune crests and slopes that had unstable substrate and were exposed to sea winds. Trees resprouted and became multi-stemmed from an early stage to increase their chances of survival against leaning caused by strong sea winds and erosion, and occasional slumping of the unstable dune sand substrate. These low severity disturbances are persistent and are referred to as chronic disturbances in this thesis. As a result of these chronic disturbances, both single and multi-stemmed trees had short stature because taller individuals that emerged above the tree canopy would be exposed to wind damage. Under chronic disturbances plants may manifest a phylogenetically determined sprouting response. However, in this study resprouting and multi-stemming were the results of the tree-disturbance interaction and not a property of a plant or species and were not phylogenetically constrained. Because the disturbances are predominantly of low severity, leaning trees were able to regain the vertical orientation of the growing section by turning upward (a process referred to as ‘turning up’ in this study) and hence survive without resprouting. Species that were prone to turning upward had a low incidence and degree of leaning of their individuals, low frequency of loss of primary stems and high abundance of individuals. Although turning up is less costly to the individual than resprouting, it could only be used by leaning trees that had small angles of inclination and were not eroded. High intensities of the latter require that individuals resprout to survive. The form and function of resprouting varied between seedlings and juvenile and mature trees. Resprouting in seedlings resulted in a single replacement shoot, unlike sprouting in juvenile and mature trees that resulted in multi-stemmed trees. Like sprouting in juvenile and mature trees, sprouting in seedlings was not phylogenetically constrained. Resprouting in seedlings increased seedling persistence; hence species with more sprout seedlings had larger individual seedlings and seedling banks. Resprouting in seedlings increased the chances of seedling recruitment, whereas resprouting in juvenile and mature trees increased the chances of an established plant maintaining its position in the habitat. After disturbances of high severity, which destroy the photosynthesizing parts, plants resprout using carbohydrates stored below- or above ground. In this study, good resprouters stored more carbohydrates both below- and above ground than poor resprouters. The carbohydrates were mobilized for resprouting after disturbance. More carbohydrates were stored in stems than in roots because the prevailing disturbances were mostly of low severity and hence above ground resources were readily available. Similar to storage by plants in severely disturbed habitats, carbohydrates were stored by reserve formation, which competes for carbohydrates with growth and maintenance and forms permanent storage, rather than accumulation, which temporarily stores carbohydrates in excess of demands for growth and maintenance. Stored carbohydrates are not necessary for resprouting of plants after disturbances of low severity because they can resprout using resources remobilized directly from the disturbed photosynthesizing parts. However, in this study, stored carbohydrates served as a bet-hedge against occasional severe disturbances that occurred in addition to chronic disturbances. Allocation of carbohydrates to permanent storage diverts them from growth and reproduction and hence good resprouters had lower growth rates, seed output, seed size and seedling recruitment than poor resprouters. However, the costs of these traits that resulted in low recruitment from seed by good resprouters, were compensated for by high persistence of established individuals of good resprouters through recruitment of sprout stems. This study demonstrates that resprouting is not only advantageous in severely disturbed environments, but also in environments where disturbances are of low severity but nevertheless confer an advantage on individuals that persist. Thus in forest environments where aboveground biomass is seldom destroyed and individuals are relatively long-lived, resprouting can confer significant fitness and selective advantage on individuals. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.

This study examines foredune evolution along a 2100 m section of coast adjacent to the Tugela River. The foredunes vary in both height and shape along the study area and form the southern most extension of the Tugela foredune-ridge plain. Sand accumulation and erosion was measured at regular intervals over a 30 month period by tacheometric surveys. The foredunes and beaches are comprised of over 99 % sand. The sediment was predominantly composed of quartz and feldspar with subordinate lithic fragments. The quartz grains display conchoidal fractures and mechanical v-shaped pits and curved grooves. The beach and dune sand is well sorted and slightly negatively skewed with a mean grain size of 1.62 ф. The vegetation structure and floristic composition of the foredunes are explored. A range of factors influencing foredune morphology and evolution, including canopy density, height and distribution, wind velocity and a variety of ecological and environmental processes are examined. Ridge and swale morphology as well as alongshore variation in the dunefield could not be related to biological processes. The development of a foredune-ridge topography depends on a large sediment supply from the Tugela River over the long-term. Periods of high discharge introduce a fresh source of sediment to the littoral zone. Reworking of fluvial sediment landwards results in wide beaches. Onshore winds transport the sand from the beaches to the foredunes. Scaevola thunbergii encourages rapid vertical accretion and hummock dunes are formed. Lateral extensive invasion by seedlings may result in the hummock dunes joining to form coast parallel foredunes. Under periods of reduced sediment discharge erosion of the shoreline results in steep narrow beaches. Despite a negative beach budget foredunes continue to accrete vertically. Marine erosion results in either the complete destruction of embryo foredunes or their landward shift. Natural breaks in the dune crestline were attributed to changes in the delivery of sediment to the beaches. The processes operating in the study area conform to Psuty's (1988,1989) sediment budget model of foredune development. Sediment availability to the coastline produces characteristic morphologies. / Thesis (M.Sc.)-University of Natal, Durban, 1998.

Pine plantations have been established on secondary grassland on the dune systems of the Eastern Shores of Lake St Lucia, KwaZulu-Natal, South Africa for the past 40 years. These plantations have been progressively felled for the past six years, and will continue to be felled until the year 2011, by which time they will be eliminated. Space-for-time substitution was used to determine the direction of both woody and herbaceous vegetation succession and to predict possible future management implications for the Eastern Shores. Soil samples were taken from undisturbed grassland, grassland with trees, dune forest, pine plantations, and clearfelled areas at various successional stages. To determine the effects of the pine plantations on the soils of the area, soils were subjected to particle size analysis, and determination of pH, organic carbon, phosphorus, exchangeable bases, iron and aluminium. Minimal modification of the sandy soils by the pine plantations was found to have occurred. That which did occur was shown to be short-term, and to be ameliorated by the establishment of an indigenous woody understorey, resembling pioneer dune forest. Soil under plantations was shown to have a lower pH and cation exchange capacity than under opposite indigenous vegetation but no other direct effects were observed. The direction of succession was determined by the nature of the indigenous vegetation adjacent to the plantation. Pine plantations were shown to facilitate succession towards dune forest by the exclusion of fire, provision of perches and refugia for forest-dwelling animals, and creation of a forest environment for the establishment of trees. However, the extent of re-establishment of indigenous dune forest under pine plantations was shown to be directly related to the nature of the adjacent indigenous vegetation, be it grassland, grassland with trees or dune forest. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1998.

Rehabilitation is a dynamic process influenced by factors related to more than one field of ecology. It is therefore necessary to consider all these components when assessing the rehabilitation, although in the initial stages the successful revegetation of the disturbed areas is the most important criterion. Richards Bay Minerals, on whose mining site this project was carried out, is dredge mining heavy minerals on the north coast of Natal, where they have rehabilitated mined areas since 1978. This project has been carried out to establish: 1) The success of their dune forest rehabilitation using quantitative techniques. 2) The available seed bank in their rehabilitation stands. 3) The similarities in the succession taking place in rehabilitation stands compared to the revegetated stands in the vicinity of Richards Bay. 4) The best methods for creating alternative vegetation communities, especially grasslands, with a high species diversity on the mined tailings. This study reviews only the success of rehabilitation of the natural vegetation but other studies focusing on the insect, reptile, mammal and bird populations are also being undertaken by other researchers. No particular method of determining the success of vegetation rehabilitation has been chosen by restoration ecologists. Therefore in this study a broad range of quantitative techniques were used to show whether successional changes are occurring in the vegetation and physical environment. The results obtained from sampling the rehabilitated vegetation have shown that both the species richness and diversity are increasing as the returned vegetation matures. Levels of soil properties such as Sodium, Phosphate, Calcium and percentage organic matter have also risen with increasing stand age. Community complexity is also increasing with stand age, and TWINSPAN and DECORANA plots have separated out the differently aged stands based on their differences. A "pilot" study was done on the seed bank present in the rehabilitation stands. This has shown the presence of large amounts of early successional, mostly herbaceous species. Seeds of later successional and woody species were scarce which may be a result of the sampling intensity used. However seeds of late successional ground cover species were found in the older stands. Comparisons between the natural revegetation of disturbed areas in the vicinity of Richards Bay and the rehabilitation stands revealed similarities in both species composition and complexity. Species richness and diversity values are comparatively similar for the younger revegetated and older rehabilitation stands, and lWlNSPAN and DECORANA analysis techniques clustered the samples recorded from these areas in close proximity on their relative plots. The oldest revegetated sites contain a number of species found in the rehabilitated vegetation but as Acacia karroo has thinned-out in these stands many of these other species are now mature individuals. Attempts at rehabilitating an area of grassland at Richards Bay Minerals has not produced satisfactory species diversity and experimental manipulations were used to try and increase the diversity of the existing Eragrostis curvula dominated community. Of the several treatments used for the manipulation, a combination of burning and further topsoiling was the most successful in reducing Eragrostis importance and in increasing the species richness. Grassland topsoil spread directly onto the bare tailings produced an extensive vegetation covering over a short period but species richness was not significantly greater than for the existing Eragrostis dominated grassland, and further treatments and management needs to continue if this technique is to be employed. Only a limited amount of alien infestation of the rehabilitated areas was evident from the sampling undertaken during this research. As the removal of alien plants is an ongoing process and the rehabilitation stands are continuously monitored to identify any new invaders, this is not expected to become a problem. From the results of work done overseas and the rehabilitation carried out in South Africa it appears that it is possible to return natural vegetation communities on mined areas. That this is a lengthy process is to be expected but by manipulating the vegetation and continuously monitoring the process it may be possible to speed up development. Areas in need of further research have been identified based on the findings of this project. This will help to reinforce the undertaking of management proposals that will enhance the vegetation recovery and the success of the rehabilitation programme.

L’érosion éolienne est un phénomène complexe avec des interactions entre la couche limite atmosphérique, le transport des particules et la déformation des dunes. Dans cette thèse des simulations numériques de transport de particules solides sur des dunes fixes ou déformables sont effectuées. L’écoulement turbulent est calculé par des simulations des grandes échelles (LES) couplée avec une méthode de frontières immergées. Les particules solides sont tractées par une approche Lagrangienne. L’entraînement des particules, leur interaction avec la surface et leur dépôt sont pris en compte par des modèles physiques complets d’érosion. D’un point de vue numérique, une méthode de frontières immergées a été introduite pour simuler les écoulements turbulents sur des frontières mouvantes. Le nouveau solveur a été validé en effectuant des comparaison avec les résultats expérimentaux de Simoens et al. (2015) dans le cas d’une colline Gaussienne. D’un point de vue physique, des modèles complets ont été développés pour l’érosion éolienne en se basant sur les forces agissant sur les particules. Des modèles instantanés pour l’envol, le roulement et le glissement des particules sont développés pour initier le mouvement des particules. Leur rebond et le splash sont également pris en compte. Des équations Lagrangiennes sont utilisées pour simuler la trajectoire des particules solides dans l’air. Une équation de transport d’un lit de particules a également été développée pour les cas de glissement et de roulement des particules sur la surface. La déformation de la dune est effectuée en faisant le bilan des particules qui s’envolent et se déposent. Ces modèles ont été validés en comparant les résultats de simulation avec les résultats expérimentaux de Simoens et al. (2015) sur les profils de concentration autour d’une colline Gaussienne. Enfin, des simulations numériques d’une dune sinusoïdale déformable sont effectuées. La forme de la dune simulée est comparée avec les résultats expérimentaux de Ferreira and Fino (2012). Un bon agrément est obtenu a t = 2.0 min, par contre la hauteur de la dune est sous-estimée entre 4.0 min et 6.0 min. Les résultats numériques montrent que la zone de recirculation diminue progressivement quand la dune se déforme. L’érosion, due à l’envol et au splash, est important a l’avant de la dune tandis que les particules se déposent a l’arrière de la dune. Le modèle de splash a été modifié pour prendre en compte l’effet de la pente, ce qui a permis une meilleure estimation de la hauteur de la dune a t = 4.0 min. / Wind erosion is a complex dynamic process consisting in an atmospheric boundary layer, aeolian particle transport, sand dune deformation and their intricate interactions. This thesis undertakes this problems by conducting three-dimensional numerical simulations of solid particle transport over a fixed or deformable sand dune. Turbulent flow is calculated by a developed numerical solver (Large-eddy simulation (LES) coupled with immersed boundary method (IBM)). Solid particle trajectories are tracked by a Lagrangian approach. Particle entrainment, particle-surface interactions and particle deposition are taken into account by physical comprehensive wind erosion models. Firstly, a new numerical solver has been developed to simulate turbulent flows over moving boundaries by introducing the IBM into LES. Two canonical simulation cases of a turbulent boundary layer flow over a Gaussian dune and over a sinusoidal dune are performed to examine the accuracy of the developed solver. Recirculation region characteristics, mean streamwise velocity profiles, Reynolds stress profiles as well as the friction velocity over the dune are presented. In the Gaussian case, a good agreement between experimental data and simulated results demonstrates the numerical ability of the improved solver. In the sinusoidal case, the developed solver with wall modeling over the immersed boundary shows a better performance than the pure one, when a relatively coarse grid is used. Secondly, physical comprehensive modeling of wind erosion is described in detail, based on the forces acting an individual particle. An instantaneous entrainment model for both lifting and rolling-sliding modes is proposed to initialize particle incipient motions. Lagrangian governing equations of aeolian particle motion are presented and used to simulate the trajectories of solid particles. Particularly, Lagrangian governing equations of bed-load particle motion are originally deduced and applied to model the particle rolling-sliding movement on the bed surface. In addition, particle-surface interactions are taken into account by probabilistic rebound/splash models. Thirdly, numerical simulations of particle transport over a fixed Gaussian dune and over a deformable sinusoidal dune are carried out. In the fixed Gaussian case, an overall good agreement on the particle concentration profiles over the dune between the simulated results and the experimental data of Simoens et al. (2015) preliminarily validates the ability and accuracy of the developed numerical solver coupled with physical comprehensive wind erosion models. In the deformable sinusoidal case, the simulated dune shapes are compared with the experimental ones of Ferreira and Fino (2012). A good agreement between them is observed at t = 2.0 min and an obvious underestimate of the dune shape is shown at t = 4.0 min and t = 6.0 min. By analyzing the simulated results, it is shown that the recirculation zone behind the dune is gradually reduced as the dune deforms and that windward erosion and lee side deposition is observed. It is also shown after testing that the splash entrainment is important for the lee side erosion. Moreover, a preliminary attempt is presented to apply an improved splash model with accounting for the bed slope effect to the simulation of sand dune deformation. A better performance on the simulated dune shape is achieved at t = 4.0 min in comparison with the experimental one.

No description available.

This practicum is a reference for vertical gardeners in cold climates. Winnipeg, Manitoba is explored, however findings may be applied to other cities in similar climates. First, the history of vertical gardening is discussed, then the types of vertical gardens currently on the market are described. These can be classified into two categories: soil bearing or non-soil bearing. Most designs are modular pre-planted systems that can be attached to any wall, as long as it satisfies the structural requirements recommended by the manufacturer. The benefits of vertical gardening have been shown to be rather extensive, covering a wide range of areas. Aesthetic improvement, reduction of the Urban Heat Island (UHI) effect, improvement of air quality, stormwater absorption, noise reduction, native habitat integration, reduction of heating and cooling costs for buildings, food production, marketing, and biophilia are all benefits explored in detail. Difficulties associated with vertical gardening are discussed, specifically the lack of knowledge and awareness of vertical gardens, lack of empirical evidence (or missing details in existing research), overall cost and lack of financial incentives, lack of industry codes, and various associated risks. Design framework exists within microclimate conditions unique to vertical gardens, as well as neighbourhood and regional (micro)climates. Theories relating to the study of green walls covered include the human ecosystem model, urban reconciliation ecology, habitat templating, the urban cliff hypothesis, and wall ecology. Suitable habitat templates identified for vertical gardens in Winnipeg are cliffs, sand dunes, alvars, mixed grass prairie and prairie potholes. Design parameters to be followed for vertical garden design in Winnipeg are to ensure that lightweight materials are used, to provide insulation to protect plants from sudden temperature changes, to choose plants that grow in the region and are adapted to grow in areas with limited soil, increased wind, varying degrees of sunlight (depending on orientation), and increased pollution and salt spray depending on location. / October 2015

[pt] Quando se visualiza a profusão de signos gráficos de empresas, atualmente expostos no meio social, se manifestam várias indagações, dentre as quais uma é fundamental: o que possibilita a estas imagens gráficas deterem tamanha força, capaz de permitir o seu reconhecimento como representante da empresa a que pertence, ou como sinal de indicação da marca de produtos a que se devota o consumo? O propósito deste trabalho de pesquisa é apresentar o entendimento de como o signo gráfico empresarial atinge essa força, que aqui se entende por eficiência. Tal como efetuamos nossa análise do fenômeno, a eficiência do signo gráfico empresarial não pode ser compreendida a partir das características técnicas de sua configuração, mas pela construção cultural de um campo simbólico de produção - o campo do design. Esse fenômeno somente foi possível porque ocorreram transformações sociais de grande proporção, que aprofundaram sobremaneira a ruptura inicial de instauração da Idade Moderna. Uma delas foi a alteração do modelo de visualidade no século XIX, a qual possibilitou ao campo do design efetivar seus princípios legítimos de produção de imagens gráficas, e assim justificar, na sociedade, o domínio de sua fabricação. Outra alteração consistiu na mudança do modelo de satisfação subjetiva, que forneceu as bases do insaciável consumo moderno. Essa mudança ofereceu oportunidade para que se instituíssem a importância das marcas - imagens projetadas a partir de valores atribuídos aos empreendimentos - e a força de seus signos gráficos. Para a articulação dessas duas alterações com a análise da eficiência do signo gráfico, foram empregados os seguintes autores: Jonathan Crary e Colin Campbell, que contribuíram respectivamente com indicações relevantes das alterações que permitiram aos indivíduos das sociedades modernas, visualizar e consumir de maneira autônoma. Na análise do funcionamento do campo do design, utilizou-se um autor fundamental, Pierre Bourdieu, que explicita, por meio de sua teoria de produção dos campos simbólicos, a maneira pela qual um bem simbólico - por exemplo, uma imagem gráfica - alcança o reconhecimento como legítimo. A partir dessa produção simbólica do campo, é possível compreender que a eficiência do signo gráfico empresarial depende de sua legitimação, levada a efeito de maneira precisa entre os diversos agentes e instituições das instâncias desse campo autônomo do design, em luta constante por legitimidade na hierarquia social. / [en] When one visualizes the profusion of company graphic signs currently displayed in the social area, several questions arise, but nevertheless one is basic: what enables these graphic images to have so much strength which allows them to be recognized as representative of the companies to which they belong or as sign indicative of the trademarks of products whose consumption is desired? The purpose of this research work is to present the understanding of how the company graphic sign attains this strength, which in this work is understood as efficiency. As we perform our analysis of the phenomenon, the efficiency of the company graphic sign cannot be comprehended based on the technical characteristics of its configuration, but rather as the cultural construction of a symbolic field of production – the design field. This phenomenon was possible only because large-scale social transformations took place which greatly deepened the initial breakthrough of the establishment of the Modern Age. One of these was the change in the model for visualizing in the 19th century which enabled the design field to achieve its legitimate principles of graphic image production and thus justify to society the mastery of their production. Another change involved the shift in the model of subjective satisfaction, which furnished the bases for modern insatiable consumption. This change offered the opportunity for instituting the importance of trademarks – images projected based on values attributed to the undertakings – and the strength of their graphic signs. For the articulation of these two changes with the analysis of the graphic sign´s efficiency, the following authors were utilized: Jonathan Crary and Colin Campbell, who contributed respectively with relevant indications of these changes which allowed individuals in modern societies to visualize and consume in an independent way. In the analysis of the design field´s functioning, a fundamental author was utilized: Pierre Bourdieu, who makes explicit, by means of his theory of symbolic field production, the way in which a symbolic asset – for example, a graphic image – achieves recognition as legitimate. Based on this symbolic field production, it is possible to comprehend that the efficiency of the company graphic sign depends on its legitimizing, carried out in a precise way among the various agents and institutions on the levels of this independent field of design, in a constant struggle for legitimacy in the social hierarchy. / [fr] Quand on visualise la profusion des signes graphiques des entreprises actuellement exposés dans la société, plusieurs indagations se manifestent, cependant, une nous semble fondamentale: qu’est-ce que possibilite à ces images graphiques d’avoir telle force qui permet que l’on les reconaisse comme représentant de l’entreprise à laquelle elles appartiennent ou même comme indication de la marque des produits de consommation? L’objectif de ce travail est de comprendre comment le signe graphique d’une entreprise gagne cette force, qui dans ce travail on appelera efficacité. Selon la façon dont nous avons effectué notre analyse de ce phénomène, l’efficacité du signe graphique d’une entreprise ne peut pas être comprise à partir des caractéristiques techniques de sa configuration, mais à partir de la construction culturelle d’un champ symbolique de production – le champ du design. Cela a été possible grâce aux grandes transformations sociales qui ont aprofondi la rupture iniciale d’instauration de l’âge moderne. Une de ces transformations fût le changement de modèle de visualité au XIXème siècle qui a possibilité au champ du design d’effectuer ses príncipes légitimes de production des images graphiques et ainsi de justifier dans la société le domaine de sa fabrication. Une autre tranformation fût le changement de modèle de satisfaction subjective qui a donné les bases de la consommation exagérée de la modernité. Ce changement offrit l’opportunité de l’institution et de l’importance des marques – images projetées à partir des valeurs attribuées aux entreprises – et la force de leurs signes graphiques. Pour articuler ces deux changements deux auteurs ont été utilisés: Jonathan Crary et Colin Campbell qui ont fourni des indications relevantes à propos de ces changements qui permirent aux individus des sociétés modernes de visualiser et de consommer de manière autonome. Dans l’analyse du fonctionnement du champ du design, on a utilisé un auteur fondamental, Pierre Bourdieu qui explicite à travers sa théorie du champ de production symbolique, la façon dont un bien symbolique, une image graphique par exemple, obtient la reconnaissance comme légitime. À partir de cette production symbolique du champ, il est possible de comprendre que l’efficacité du signe graphique d’une entreprise dépend de sa propre légitimation parmi plusieurs agents et institutions de ce champ autonome du design, en lutte pour la légitimation dans l’hiérarchie sociale.