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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Smuggling: its importance in the trinational region in front of the spatial structure / Contrabando: importancia en la región trinacional frente a la estructura espacial

Chavarría Castillo, Cindy Cecilia, Casquero Jar, Carlos Alfredo, Martínez Castillo, Dionel 10 April 2018 (has links)
The research focuses on the contraband´s spatial interactions that arise front to spatial structure, organization and pre existing complementary links, we identified through a diachronic analysis, establishing our field of study as the geographic area we call Trinational Macro Region: southern Peru, northern Chile and western Bolivia. This activity generates spatial dynamics and flows that are developed in the context of globalization and these exploit existing comparative advantages, i.e. the status of being neighbouring countries, the strategic location with respect to South America and the rest of the world, the communication channels, the absence of the state in these regions and price differentiation between licit products and contraband ones. These dynamic and flows, these are spatialize under various strategies adopted to transport contraband, storage and distribution of products. / La investigación se centra en las interacciones espaciales del contrabando que surgen frentea una estructura espacial, organización y vínculos de complementariedad preexistentes, que identificamos mediante un análisis diacrónico, estableciendo como nuestro campo de estudio el área geográfica que denominamos macrorregión trinacional: el sur del Perú, el norte de Chiley el noroeste de Boliva. Esta actividad genera dinámicas espaciales y flujos que se desarrollan en el contexto de la globalización y aprovechan las ventajas comparativas existentes, es decir, la condición de ser países fronterizos, la localización estratégica con respecto a América del Sur y el resto del mundo, las vías de comunicación, la débil presencia del Estado en estas regiones y la diferenciación de precios entre los productos lícitos y los de contrabando. Estas dinámicas y flujos se espacializan bajo diversas estrategias que adopta el contrabando para el traslado, almacenamiento y distribución de los productos.
42

Probabilistic and deterministic analysis of the evolution : influence of a spatial structure and a mating preference. / Analyses probabilistes et déterministes pour l'évolution : influence d'une structure spatiale et d'une préférence sexuelle

Leman, Hélène 28 June 2016 (has links)
Cette thèse porte sur l'étude des dynamiques spatiales et évolutives d'une population à l'aide d'outils probabilistes et déterministes. Dans la première partie, nous cherchons à comprendre l'effet de l'hétérogénéité de l'environnement sur l'évolution des espèces. La population considérée est modélisée par un processus individu-centré avec interactions qui décrit les événements de naissances, morts, mutations et diffusions spatiales de chaque individu. Les taux des événements dépendent des caractéristiques des individus : traits phénotypes et positions spatiales. Dans un premier temps, nous étudions le système d'équations aux dérivées partielles qui décrit la dynamique spatiale et démographique d'une population composée de deux traits dans une limite grande population. Nous caractérisons précisément les conditions d'extinction et de survie en temps long de cette population. Dans un deuxième temps, nous étudions le modèle individuel initial sous deux asymptotiques : grande population et mutations rares de telle sorte que les échelles de temps démographiques et mutationnelles sont séparées. Ainsi, lorsqu'un mutant apparaît, la population résidente est à l'équilibre démographique. Nous cherchons alors à caractériser la probabilité de survie de la population issue de ce mutant. Puis, en étudiantle processus dans l'échelle des mutations, nous prouvons que le processus individu-centré converge vers un processus de sauts qui décrit les fixations successives des traits les plus avantagés ainsi que la répartition spatiale des populations portant ces traits. Nous généralisons ensuite le modèle pour introduire des interactions de type mutualiste entre deux espèces. Nous étudions ce modèle dans une limite de grande population. Nous donnons par ailleurs des résultats numériques et une analyse biologique détaillée des comportements obtenus autour de deux problématiques : la coévolution de niches spatiales et phénotypiques d'espèces en interaction mutualiste et les dynamiques d'invasions d'un espace homogène par des espèces mutualistes. Dans la deuxième partie de cette thèse, nous développons un modèle probabiliste pour étudier finement l'effet d'une préférence sexuelle sur la spéciation. La population est ici structurée sur deux patchs et les individus, caractérisés par un trait, sont écologiquement et démographiquement équivalents et se distinguent uniquement par leur préférence sexuelle: deux individus de même trait ont plus de chance de se reproduire que deux individus de traits distincts. Nous montrons qu'en l'absence de toute autre différence écologique, la préférence sexuelle mène à un isolement reproductif entre les deux patchs. / We study the spatial and evolutionary dynamics of a population by using probabilistic and deterministic tools. In the first part of this thesis, we are concerned with the influence of a heterogeneous environment on the evolution of species. The population is modeled by an individual-based process with some interactions and which describes the birth, the death, the mutation and the spatial diffusion of each individual. The rates of those events depend on the characteristics of the individuals : their phenotypic trait and their spatial location. First, we study the system of partial differential equations that describes the spatial and demographic dynamics of a population composed of two traits in a large population limit. We characterize precisely the conditions of extinction and long time survival for this population. Secondly, we study the initial individual-based model under two asymptotic: large population and rare mutations such as demographic and mutational timescales are separated. Thus, when a mutant appears, the resident population has reached its demographic balance. We characterize the survival probability of the population descended from this mutant. Then, by studyingthe process in the mutational scale, we prove that the microscopic process converges to a jump process which describes the successive fixations of the most advantaged traits and the spatial distribution of populations carrying these traits. We then extend the model to introduce mutualistic interactions between two species. We study this model in a limit of large population. We also give numerical results and a detailed biological behavior analysis around two issues: the co-evolution of phenotypic and spatial niches of mutualistic species and the invasion dynamics of a homogeneous space by these species. In the second part of this thesis, we develop a probabilistic model to study the effect of the sexual preference on the speciation. Here, the population is structured on two patches and the individuals, characterized by a trait, are ecologically and demographically similar and differ only in their sexual preferences: two individuals of the same trait are more likely to reproduce than two individuals of distinct traits. We show that in the absence of any other ecological differences, the sexual preferences lead to reproductive isolation between the two patches.
43

Variation in tree and shrub diversity across space, along environmental gradients and through time in a temperate forest in eastern North America / Forest diversity across space and environmental gradients

Munoz, Sophia January 2016 (has links)
The variation in community composition among sites is often used to gain insight into the processes of plant community assembly. In this study, we looked for evidence of environmentally and spatially mediated community assembly mechanisms in a temperate forest in eastern North America. To test this, we measured, identified and mapped all woody stems ≥1 cm in diameter at breast height (DBH) in 12 ha of a 20 ha forest plot. We used principal coordinates of neighbor matrices (PCNM) to obtain variables that modelled spatial processes (eg. dispersal, drift) at the community level. Topographic variables (slope, elevation, convexity, aspect) were used to model environmental conditions. Variation partitioning was used to isolate the unique and shared effects of topographic and spatial variables on community composition. We were also interested in studying how associations with the environment change with tree size. For this we assessed the abundance of a subset of focal species in response to topography as well as human disturbance. Species abundance were divided into three stem size classes: small (< 5 cm), medium (≥5 cm and < 15), and big (≥15 cm). We found that topography and space jointly explained 63% of the variation in community composition. This variation was almost entirely spatially structured with the component of pure topography only contributing 1% to the total explained variation. A redundancy analysis showed that slope and elevation were the most important topographic variables structuring the distribution of trees. The focal species had largely independent distributions across the environmental gradients and three of the five species showed within-species differences associated with size class effects on the relationship with topography and human disturbance. The implications of these results are relevant to conservation efforts and suggest that large contiguous areas of heterogeneous environments are essential in maintaining biodiversity. / Thesis / Master of Science (MSc)
44

Selection in a spatially structured population

Straulino, Daniel January 2014 (has links)
This thesis focus on the effect that selection has on the ancestry of a spatially structured population. In the absence of selection, the ancestry of a sample from the population behaves as a system of random walks that coalesce upon meeting. Backwards in time, each ancestral lineage jumps, at the time of its birth, to the location of its parent, and whenever two ancestral lineages have the same parent they jump to the same location and coalesce. Introducing selective forces to the evolution of a population translates into branching when we follow ancestral lineages, a by-product of biased sampling forwards in time. We study populations that evolve according to the Spatial Lambda-Fleming-Viot process with selection. In order to assess whether the picture under selection differs from the neutral case we must consider the timescale dictated by the neutral mutation rate Theta. Thus we look at the rescaled dual process with n=1/Theta. Our goal is to find a non-trivial rescaling limit for the system of branching and coalescing random walks that describe the ancestral process of a population. We show that the strength of selection (relative to the mutation rate) required to do so depends on the dimension; in one and two dimensions selection needs to be stronger in order to leave a detectable trace in the population. The main results in this thesis can be summarised as follows. In dimensions three and higher we take the selection coefficient to be proportional to 1/n, in dimension two we take it to be proportional to log(n)/n and finally, in dimension one we take the selection coefficient to be proportional to 1/sqrt(n). We then proceed to prove that in two and higher dimensions the ancestral process of a sample of the population converges to branching Brownian motion. In one dimension, provided we do not allow ancestral lineages to jump over each other, the ancestral process converges to a subset of the Brownian net. We also provide numerical results that show that the non-crossing restriction in one dimension cannot be lifted without a qualitative change in the behaviour of the process. Finally, through simulations, we study the rate of convergence in the two-dimensional case.
45

Group structure and behaviour in microfinance : empirics from Sierra Leone

Sabin, Nicholas Edward January 2014 (has links)
The use of group lending for poverty alleviation is a widespread feature of modern microfinance. The structure of joint-liability credit - if one member defaults the others are held financially responsible - produces a natural tension between a borrower's social and economic interests. This study integrates theory from economics, sociology, and behavioural experiments to address the question, "How do social and economic mechanisms interact to shape a microcredit group's financial behaviour?" The empirical analysis involves an original dataset from a microfinance institution in Sierra Leone. The total dataset includes 7,025 joint-liability borrowers involved in 47,931 repayment transactions from 2005 to 2011. The empirical methods used are diverse: ethnographic fieldwork, GPS spatial analysis, social affiliation survey design, and multilevel statistical analysis of loan performance data. The original work is structured as three distinct papers. In the first paper, I examine social collateral, the formal use of a borrower's relationships as security against loan default. How does a group's spatial structure affect the efficacy of social collateral? Spatial concentration improves a group's economic performance up to a certain level after which the effect reverses and performance declines. The relationship is driven by a social trade-off between ability and willingness to enforce the loan. Further, groups that consist of multiple spatial fragments produce worse performance. Spatially fragmented groups are prone to splitting into social factions. In the second paper, I question what drives the self-selection process of microcredit group formation. The results show that group leaders prefer members with pre-existing social ties, who are spatially proximate, and have matching business types. The preference for socio-spatial factors is likely motivated by reducing the risk of strategic default by group members. In the third paper, I explore how economic cooperation in small groups evolves over years of repeated interaction. Despite the selective retention of better performing groups, average cooperation rates consistently decline, in terms of contribution and effort. Further, variance across groups continues to increase over 30 months of repeated interaction, suggesting that convergence to a stable cooperation rate has not occurred. Given that group lending exhibits many of the factors found to promote cooperation in laboratory experiments, it is surprising to find such a marked decline in this field setting. Overall, this thesis contributes to economic sociology by dissecting the difficult trade-offs between social and economic motives in group lending and offers policy implications for microfinance institutions regarding group formation heuristics, contract design, and loan management.
46

Sociálně-prostorová struktura města Mostu / Socio-spatial structure of the town Most

Syrovátková, Veronika January 2015 (has links)
The purpose of this diploma thesis is to analyze social-spatial structure of the town Most from the point of view of human ecology. The period under consideration is from 1991 to 2011. There is attempt to define local typology of the city, i.e. areas with similarities in the socioeconomic characteristic, its changes and also describe a transformation processes behind it. Trends in spatial differentiation of people are analyzed according to factor ecology. It means that there are used methods of multidimensional statistics like factor analysis and cluster analysis, because of defining the type and strength of certain factors which are specific to the urban areas.
47

Relations entre structures de peuplement végétal et bioagresseurs de la culture principale dans les agroforêts tropicales. Application aux agroforêts à cacaoyers et à 3 bioagresseurs : la moniliose (Moniliophthora roreri) au Costa Rica, la pourriture brune (Phytophthora megakarya) et les mirides (Sahlbergellasingularis) au Cameroun. / Relationship between vegetation structure and pest and disease in tropical agroforests. Application to cocoa agroforest and Frosty Pod Rot (Moniliophthora roreri) in Costa Rica and Black Pod (Phytophthora megakarya) and Mirid (Sahlbergellasingularis) in Cameroon.

Gidoin, Cynthia 09 December 2013 (has links)
La valeur potentielle des agro-forêts tropicales comme modèle d'intensification écologique de l'agriculture est un sujet d'intérêt croissant. Les agro-forêts tropicales sont des agroécosystèmes caractérisés par une forte diversité végétale et une diversité d'organisation spatiale des individus. Les structures complexes de ces agroécosystèmes en font des systèmes « proches » des écosystèmes naturels. Cette complexité améliorerait la fourniture de nombreux services écosystémiques. Dans ce travail, nous nous sommes intéressés au service de régulation naturelle des bio-agresseurs des cultures. Notre hypothèse est que la complexité de structure (composition et structure spatiale) des agro-forêts influence la présence et l'intensité d'attaque des bio-agresseurs de la culture principale. En effet, l'augmentation de la diversité végétale à l'échelle de la parcelle diminuerait l'intensité d'attaque de bio-agresseurs spécialistes via la diminution de l'abondance de la ressource. Inversement, cette diversité amplifierait celle des bio-agresseurs généralistes via l'introduction potentielle d'hôtes alternatifs. Une diversité de structures spatiales d'individus associés est aussi susceptible d'influencer le microclimat et par son biais les bio-agresseurs des cultures. Pourtant, l'importance relative de l'effet de la composition (via la dilution ou l'amplification de la ressource) et de la structure spatiale (via l'altération du microclimat) du peuplement végétal sur l'intensité d'attaque de bio-agresseurs a rarement été étudiée. L'objectif de ce travail est de quantifier les interactions entre les caractéristiques de composition et de structure spatiale du peuplement végétal d'agroécosystèmes complexes et l'intensité d'attaque de bio-agresseurs de la culture principale à l'échelle de la parcelle. Ce travail est appliqué aux agro-forêts à cacaoyers du Costa Rica et du Cameroun. En effet, la culture du cacaoyer est l'une des rares encore réalisée traditionnellement au sein d'agro-forêts dans la majorité des pays producteurs. Nous nous intéresserons à trois bio-agresseurs du cacaoyer choisis pour leurs caractéristiques de dissémination et de développement contrastées : au Costa Rica, la moniliose sur un réseau de parcelles installées dans la région de Talamanca ; au Cameroun la pourriture brune et les mirides sur un réseau de parcelles installées dans la région Centre. Dans un premier temps nous avons construit des typologies descriptives des structures spatiales des agro-forêts à cacaoyers du Costa Rica et du Cameroun afin d'identifier la variabilité des structures spatiale des agro-forêts au sein d'une même région. Ces typologies ont permis d'identifier des structures spatiales horizontales variées allant de la régularité à l'agrégation significatives des arbres d'ombrage selon les pays étudiés. Dans un deuxième temps nous avons identifié et hiérarchisé les caractéristiques de composition et de structure spatiale à l'échelle de la parcelle agroforestière qui influencent l'intensité d'attaque de la moniliose au Costa Rica ; et de la pourriture brune et des mirides au Cameroun. La structure spatiale du peuplement végétal joue un rôle prépondérant dans l'ensemble de nos résultats. L'agrégation des arbres forestiers augmente l'intensité d'attaque de la moniliose au Costa Rica et la densité des mirides au Cameroun. La pourriture brune quant à elle augmente lorsque la densité des individus de la strate basse augmente à l'échelle de la parcelle. Pour finir, nous montrons que la quantité de tissus sensible plutôt que la composition en hôte explique l'intensité de la moniliose et la densité en miride. Ces résultats sont discutés en fonction des nombreux mécanismes qui relient la structure de la végétation aux bio-agresseurs et des caractéristiques de ces bio-agresseurs. Notre travail fournit une description précise de la structure d'agro-écosystèmes tropicaux complexes. / The potential value of tropical agroforests as a model for ecological intensification of agriculture is a subject of increasing interest. Tropical agroforests are agroecosystems characterized by high plant diversity and a complex spatial structure of individuals. With their forest-like structures, agroforests are close to natural ecosystems. The complex structure of agroforests would seem to improve the provision of numerous ecosystem services.This work concerned natural pest and disease regulation services in complex agroecosystems. Our hypothesis was that complex agroforest structures (composition and spatial structure) influence the pest and disease attack intensity on the main crop. Indeed, an increase in plant diversity in agroecosystems is known to reduce specialized pest and disease attack intensity due to a decrease in resource abundance and density on a plot scale. Conversely, plant diversity could increase the generalist pest and disease attack intensity due to the potential introduction of alternative hosts. Moreover, diversity in plant spatial structure has an impact on microclimatic conditions and, thereby, on the pest and disease attack intensity. However, the relative importance of host composition effects on pest and disease intensity, due to resource dilution or amplification, and plant spatial structure effects, due to microclimatic alteration, is still unknown.Our objective was to quantify interactions between the composition and spatial structure characteristics of agroforests and the pest and disease attack intensity on a plot scale.This work was applied to cacao agroforests in Costa Rica and Cameroon. Indeed, cacao is one of the last crops still to be grown in traditional agroforests in the majority of producing countries. The study was conducted on two cacao diseases and one pest chosen for their contrasting spread and development characteristics: in Costa Rica, Frosty Pod Rot (FPR) intensity was studied in cacao agroforests in the Talamanca region; in Cameroon, Black Pod (BP) intensity and mirid density were studied in cacao agroforests in the Centre region.Firstly, we established shade tree spatial structure typologies for cacao agroforests in Costa Rica and Cameroon, in order to identify spatial structure diversity in the same region. A diversity of spatial structures was identified ranging from significant regularity to significant aggregation, depending on the shade tree stand and country studied.Secondly, we identified and classified the host composition, amount of sensitive tissue and the spatial structure characteristics of the associated plants, according to their explanatory power in explaining FPR intensity, BP intensity and mirid density in cacao agroforests. The spatial structure of the associated plants was a crucial characteristic of agroforests in explaining FPR and BP intensity and mirid density. Indeed, forest tree regularity decreased FPR intensity in Costa Rica and mirid density in Cameroon. The BP intensity was reduced by a decrease in the density of individuals belonging to strata lower than or equal to the cacao tree stratum. Lastly, the amount of sensitive tissue rather than the host composition variables explained the increase in FPR intensity in Costa Rica and the mirid density in Cameroon. Our results are discussed in line with several mechanisms that explain plant diversity and pest and disease relationships.Our work provides a precise description of complex tropical agroecosystem structures. We quantified the relationship between observed plant structures and the pest and disease regulation ecosystem service. In the context of agroecology, this work opens up prospects for identifying and understanding ecological mechanisms involved in natural pest and disease regulation in cacao agroforests on a plot scale.
48

Rezidenční suburbanizace v okrese Kladno: proměna sociálního prostředí / Residential suburbanization in Kladno district: change of social environment

Slavíček, Martin January 2018 (has links)
Since the second half of the 1990s a residential suburbanization process has occurred in the Czechia. Within the process residents move from cities to municipalities that are located in their outskirts. The general aim of the thesis is to evaluate the social environment in Kladno district which is change just as a consequence of the residential suburbanization process. Within the general aim, the thesis sets out three partial objectives: To characterize the process of residential suburbanization in Kladno district, to evaluate changes in the socio- spatial structure of Kladno district with the main focus on the suburban municipalities, and to evaluate the social environment in the selected suburban municipality in Kladno district. There are quantitative methods used in the work. To accomplish the first and second partial objectives is used the analysis of statistical data from Czech Statistical Office. To accomplish the third partial objective is used a questionnaire survey, which investigate how respondents interact with native and new residents and how they engage in social and political life in Buštěhrad. The thesis is based on concepts of social environment and community question. Key words: residential suburbanization, socio-spatial structure, social structure, social climate, social...
49

都市空間結構與公共支出關係之研究 / Urban Spatial Structure and Public Expenditures

潘依茹, Pan, Yi Ju Unknown Date (has links)
人口在空間上分布的差異形成集中發展抑或分散發展型態,相對地對於地方財政的支出亦有不同程度的影響。在現今台灣省各地方政府普遍存在著財源短絀之情形下,農地釋出政策的實施所造成都市規模的擴張,是否會引發地方財政加重的趨勢,實有深究的必要。因此本研究的目的,乃在於探討都市空間結構的差異對公共支出的變化影響效果,並進一步提出土地發展政策涵義。   針對上述,本研究擬藉由人口密度斜率此變數,作為都市空間結構之指標,進而瞭解都市發展型態之差異對地方公共支出的影響。所謂人口密度斜率乃是隨著距離的增加,人口在空間上的變化情形。其次,以中位數投票模型理論及官僚模型理論為基礎,建立模型並進行測試,同時為因應農地釋出政策的實施,在台灣省各市鄉鎮都市計畫區農業區釋出的假設前題下,進行模擬分析。   經本研究結果發現,就總體而言,台灣省各市鄉鎮目前之都市空間結構有分散發展的趨勢,並有無效率的現象;次就農地釋出而言,在不考慮人口規模聚集經濟的情況下,過多的土地開發,將會有惡化現存地方財政不足之趨勢。 / The difference of population spreads in the spatial will result in the pattern of concentrated development or dispersed development. Oppo-sitely, the difference pattern will influence to local public expenditures. On the condition that the local government often exists short tag of finance in Taiwan, so to practice policy of agriculture land release which should result in the extension of urban scale whether will increase the final burden or not, has necessary to discuss. Thus, the propose of this study is to discuss that the difference of urban spatial structure has what effect of change influence to pubhc expenditure, and father want to propose the meaning of land development policy.   As above that, this study uses the population density gradient to be the guide of urban spatial structure, and then want to understand the difference of urban development pattern has what influence to local public ex-penditure. Population density describes how rapidly the density falls off with distance. Next, based on the median voter theory and bureaucracy theory to built the model and test it, then for to practice the policy of agriculture land release, this study on the assumption that all agriculture area of urban planned area will be released in Taiwan progresses simulation and analysis which wants to know the influence of agriculture land release.   According to the result of this study, we find, fister, the present con-dition of local public in Taiwan, urban spatial structure has the tend of dis-persed development, and cause to nonefficiency. Second, if the agriculture land release do not consider the agglomeration economics of population scale, then to development too many lands will worse present local final.
50

多核心都市地價空間結構型態之研究-以台北市為例 / The spatial structure of land price of polycentric city - A case study in Taipei

林倩玫, Lin, Chan May Unknown Date (has links)
本研究可分為兩部份,第一部份以CBD為中心,向外擴展之地價空間結構變化情形之測試,主要是方法上的應用。運用較富彈性且能符合多核心都市測試需要之三次雲形函數來測試台北市之地價空間結構。研究發現都市發展方向會影響地價空間結構之變化,而傳統單核心模型之單一核心之假設及無考慮方向性,並不能充份描述現代大都市之真實空間結構。   第二部份則為了解各核心對地價影響情形,及在空間上互動關係進行多核心模型之測試。研究發現地價為都市空間中多核心互動的結果。而相同屬性、規模的核心間有排斥效果,不同屬性、規模的核心間則有吸引效果。藉由多核心之分散健全發展,與交通建設之密切配合,將可使都市之地價及都市空間結構更加健全發展。 / This research is divided to two parts. First part is to test the structural variance of the land price which extends by CBD. The method, the cubic spline function, is flexible and it can match the need of the polycentric city. From the test, we find the different directions which will affect the spatial structural variance of the land price. But the factor of the direction isn't included in the hypothesis of the traditional monocentric model, and it can't be described the true spatial structure of modern city sufficiently.   Another is the test that to understand the land price variance situation by the different centers and the interactions of them.By this test, it shows that land price is the result of the polycentric interactions of urban spatial structure. We also find there is a repelling effect between the same character and scale centers; vise versa.

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