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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

Effects of Post-Glacial Range Expansions and Population Bottlenecks on Species Richness

Ödeen, Anders January 2001 (has links)
This thesis relates modern speciation theory to the effects of sudden changes in the range and size of populations. Special reference is made to the climatic oscillations during the Quaternary ice ages. A meta-analysis of laboratory experiments showed that support for allopatric speciation is weak, especially for the peripatric type of allopatric speciation. Furthermore, factors traditionally believed to increase the likelihood of speciation have had little effect on the generation of reproductive isolation in speciation experiments. However, the method of testing reproductive isolation appeared important, in the sense that experimentally derived sister populations were likely to demonstrate reproductive isolation from each other but not from the unaffected mother population. Raw data from mating tests showed that the poor isolation between mother and daughter populations was an effect of asymmetric mate preferences towards males from the mother population. This suggests that peripatric speciation can be effective in generating reproductive isolation between sister populations. The proposed mechanism is that males become less attractive to females by losing certain secondary sexual traits during population bottlenecks, and that females shift their preferences towards other male traits. Support for this mode of speciation is found in the widespread bird genus Motacilla (wagtails). This genus is characterised by extensive plumage variation and contains a large number of widely distributed taxa in the northern parts of its distribution. This thesis shows that taxonomic diversity of wagtails is inversely related to complexity in song and to diversity in molecular and mitochondrial markers. The northern taxa seem to be descendants of southern populations, which were subjected to bottlenecks during expansions into re-opened habitats after the last ice age. The bottlenecks would not only reduce genetic diversity but also inhibit cultural transmission of song to the leading edge of colonisers, allowing sexual selection on other traits, such as plumage. Rapid plumage differentiation among wagtail taxa appears to be a recurrent process and has lead to convergent evolution, making the currently recognised species Motacilla flava (Yellow Wagtail) polyphyletic.
42

Alternative Stable States in Size-Structured Communities : Patterns, Processes, and Mechanisms

Schröder, Arne January 2008 (has links)
Alternative stable states have been, based on theoretical findings, predicted to be common in ecological systems. Empirical data from a number of laboratory and natural studies strongly suggest that alternative stable states also occur in real populations, communities and ecosystems. Potential mechanisms involve population size-structure and food-dependent individual development. These features can lead to ontogenetic niche shifts, juvenile recruitment bottlenecks and emergent Allee effects; phenomena that establish destabilising positive feedbacks in a system and hence create alternative stable states. I studied the consequences of population size-structure for community dynamics at different scales of system complexity. I performed laboratory and ecosystem experiments. Small poecilliid fishes and planktonic invertebrates with short generation times and life spans were used as model organisms. This allowed me to assess the long-term dynamics of the populations and communities investigated. The main experimental results are: (a) An ontogenetic niche shift in individuals of the phantom midge Chaoborus made the population vulnerable to an indirect competitive recruitment bottleneck imposed by cladoceran mesozooplankton via rotifers. Consequentially the natural zooplankton food web exhibited two alternative attractors. (b) Body size determined the success of Poecilia reticulata invading resident population of Heterandria formosa and thus the type of alternative stable state that established. Small invaders were outcompeted by the residents, whereas large invaders excluded their competitor by predating on its recruits. (c) External juvenile and adult mortality altered the internal feedback structure that regulates a laboratory population of H. formosa in such a way that juvenile biomass increased with mortality. This biomass overcompensation in a prey population can establish alternative stable states with top-predators being either absent or present. The major conclusion is that size-structure and individual growth can indeed lead to alternative stable states. The considerations of these ubiquitous features of populations offer hence new insights and deeper understanding of community dynamics. Alternative stable states can have tremendous consequences for human societies that utilise the ecological services provided by an ecological system. Understanding the effects of size-structure on alternative stability is thus crucial for sustainable exploitation or production of food resources.
43

Automatisering av det interna flödet på ett tillverkande företag : En studie om den interna hanteringen av kretskortställningar och hur det kan effektiviseras i flödet

Kadhim Abed, Ahmed, Rappestad, Erik January 2023 (has links)
Purpose: The purpose of the study was to identify the current transport flow for circuit board racks and to investigate the potential implementation of an automated solution for the transportation of circuit board racks in order to increase efficiency in the flow. The research questions answered during this study were: What does the transport flow for circuit board racks look like today?  What could an automated transport flow for circuit board racks look like?  Is an automated transport flow for circuit board racks a sufficient solution to improve efficiency in the flow? Theoretical framework: The study applied several different theories, with waste being a central part. This, in combination with bottleneck identification, mapping, and automation, has been theories used to study the flow and find improvements. Method: A case study was conducted to analyze the transport flow of circuit board racks and identify potential improvements. The method included a literature review, observations, interviews, brainstorming, Value Stream Mapping, and spaghetti diagrams to collect and analyze data from different perspectives. Results: With a combination of theories and empirical data, an analysis of the current transport flow for the circuit board racks could be made. Furthermore, bottlenecks and waste were identified, and automated transport solutions linked to AMR systems were found as a potential solution for a more efficient transport flow. The result showed that an AMR system is the most advantageous solution. However, the study showed that the automated solution was not sufficient without eliminating the bottlenecks in order to generate maximum efficiency in the automated transport flow. Implications: This study has the implication of highlighting the challenges and opportunities of a more efficient transport flow using AMR systems. This includes an improved working environment, reduced work-related injuries, increased production efficiency by eliminating bottlenecks, and waiting times.
44

Повышение эффективности бизнес-процессов в сети салонов оптики в современных условиях : магистерская диссертация / Improving the efficiency of business processes in the network of optical salons in modern conditions

Спиринцова, Е. М., Spirintsova, E. M. January 2021 (has links)
Магистерская диссертация посвящена разработке методов повышения эффективности бизнес-процессов в сети салонов оптики. Выпускная квалификационная работа состоит из введения, трех глав, заключения и списка использованных источников. В первой главе рассмотрены теоретические аспекты управления бизнес-процессами. Во второй главе проведен анализ и дана оценка существующей ситуации в оптической сфере в России и в мире. Третья глава посвящена разработке рекомендаций по повышению эффективности бизнес-процессов на примере сети оптик «#1». / The master's thesis is devoted to the development of methods to improve the efficiency of business processes in the network of optical salons. The final qualifying work consists of an introduction, three chapters, a conclusion and a list of sources used. The first chapter discusses the theoretical aspects of business process management. The second chapter analyzes and evaluates the current situation in the optical sphere in Russia and in the world. The third chapter is devoted to the development of recommendations for improving the efficiency of business processes on the example of the optics network "#1".
45

Appling Machine and Statistical Learning Techniques to Intelligent Transport Systems: Bottleneck Identification and Prediction, Dynamic Travel Time Prediction, Driver Run-Stop Behavior Modeling, and Autonomous Vehicle Control at Intersections

Elhenawy, Mohammed Mamdouh Zakaria 30 June 2015 (has links)
In this dissertation, new algorithms that address three traffic problems of major importance are developed. First automatic identification and prediction algorithms are developed to identify and predict the occurrence of traffic congestion. The identification algorithms concoct a model to identify speed thresholds by exploiting historical spatiotemporal speed matrices. We employ the speed model to define a cutoff speed separating free-flow from congested traffic. We further enhance our algorithm by utilizing weather and visibility data. To our knowledge, we are the first to include weather and visibility variables in formulating an automatic congestion identification model. We also approach the congestion prediction problem by adopting an algorithm which employs Adaptive Boosting machine learning classifiers again something novel that has not been done previously. The algorithm is promising where it resulted in a true positive rate slightly higher than 0.99 and false positive rate less than 0.001. We next address the issue of travel time modeling. We propose algorithms to model travel time using various machine learning and statistical learning techniques. We obtain travel time models by employing the historical spatiotemporal speed matrices in conjunction with our algorithms. The algorithms yield pertinent information regarding travel time reliability and prediction of travel times. Our proposed algorithms give better predictions compared to the state of practice algorithms. Finally we consider driver safety at signalized intersections and uncontrolled intersections in a connected vehicles environment. For signalized intersections, we exploit datasets collected from four controlled experiments to model the stop-run behavior of the driver at the onset of the yellow indicator for various roadway surface conditions and multiple vehicle types. We further propose a new variable (predictor) related to driver aggressiveness which we estimate by monitoring how drivers respond to yellow indications. The performance of the stop-run models shows improvements after adding the new aggressiveness predictor. The proposed models are practical and easy to implement in advanced driver assistance systems. For uncontrolled intersections, we present a game theory based algorithm that models the intersection as a chicken game to solve the conflicts between vehicles crossing the intersection. The simulation results show a 49% saving in travel time on average relative to a stop control when the vehicles obey the Nash equilibrium of the game. / Ph. D.
46

A model for material handling improvements when using automated storage systems: A case study / En modell för förbättringar av materialhantering genom användandet av automatiserade lagersystem: En fallstudie

Thongmal Larsson, Marie January 2010 (has links)
<p>The purpose of this thesis is to create a model of how to organize the placements of articles in an automated storage system in order to reduce time and cost related to the extractions. The model was developed during an investigation at a case company, and a comprehensive study of the material handling identified bottlenecks, whereof one was chosen to be further investigated: the automated storage system. The automated storage system is newly installed equipment, which required new working methods to be incorporated to the already existing working environment. The ABC-analysis was used in order to motivate how the articles should be placed in the automated storage. The goal for the new way of handling material was to put as little effort as possible on time related to the extraction of material. This due to the realization of material handling processes being a huge contributor to waste activities. This resulted in the development of the model and the suggestion that is given to the case company is to place the most frequent extracted articles close to the users. However, advantages must be held against disadvantages of rearrangements since the material handling will not be eliminated totally due to smaller improvements.</p> / <p>Syftet med denna uppsats är att skapa en modell för hur man ska organisera artikelplaceringar i ett automatiserat lagersystem för att reducera tid och kostnad relaterat till uttag av material. Modellen skapades genom en undersökning på ett fallföretag, en omfattande studie av materialhanteringen identifierade flaskhalsar, varav en valdes för fortsatt undersökning: det automatiserade lagersystemet. Det automatiserade lagersystemet är en nyinstallerad utrustning, som kräver att nya arbetsmetoder ska inkorporeras till den redan existerande arbetsmiljön. ABC-analysen användes för att motivera hur artiklarna ska placeras i det automatiserade lagret. Målet för det nya sättet att hantera material på var att så få insatser som möjligt skulle användas för uttag av material. Detta pågrund av insikten utav att materialhanteringsprocesser är en stor bidragande slöserifaktor. Detta resulterade i modellen och förslagen som ges till fallföretaget är att placera de mest frekvent använda artiklarna nära användaren. Emellertid så måste man väga fördelar mot nackdelar av en förändring eftersom materialhanteringen inte kommer att elimineras helt pågrund av mindre förbättringar.</p>
47

"Adaptation of the Marginal Budgeting for Bottlenecks model for planning, costing and budgeting in the educational sector".

Duehring, Momo E. 14 May 2015 (has links)
Already in its Education Strategy, adopted by the Executive Board in 2007, UNICEF fully obligates to the international commitment to universal education and defines its contribution to national efforts to fulfil children’s right to education. In September 2010, UNICEF further published a special report on a study showing that an equity-focused approach to child survival and development is the most practical and cost-effective way of meeting the health MDGs for children. For the modelling process of the research a simulation was run employing the Marginal Budgeting for Bottlenecks (MBB) model, jointly developed by the World Bank and UNICEF. This model has been widely used in international public health research to design and test development strategies. In its consistency with the human-right based approach, the MBB model addresses bottlenecks in the capacity of duty-bearers to fulfil human-rights as well as barriers of the capacity of right-holders to claim their rights. Using the MBB model, policymakers and researchers can simulate varying configurations of service delivery modes to expand access of coverage and measures to encourage usage. For each strategy, the model generates the predicted impact on intervention coverage and outcomes, overall cost and cost-effectiveness. UNICEF’s global refocus on equity and the most disadvantaged children makes it necessary to introduce improved planning and monitoring instruments. In this context, the MBB model is used as a budgeting and simulation tool for UNICEF interventions in health and nutrition. UNICEF aims to use harmonized tools across different sectors to reduce transaction costs and to improve comparison and sharing of lessons learned between the different sectors. However, it is also important to adapt and develop instruments based on the diverse needs of different sectors to ensure best results. Therefore, the main purpose of this research is to find an answer to following question: Can, and if so, how can the Marginal Budgeting for Bottlenecks model, developed for the health sector, be adapted for planning, costing and budgeting allocations in the education sector? An adapted Marginal Budgeting for Bottleneck model for education could be applied for a comprehensive sector analysis, comparing intervention alternatives and setting policy goals and strategies. It could further be used to monitor the implementation of major sector reforms with regard to the comparison of potential versus actual impact of interventions on learning achievements. Applying two production functions, the MBB model applies the basic principle of Cost-Effectiveness Analysis, comparing the costs of education interventions with the corresponding expected impact on increased service coverage. However, detailed inputs, outputs, outcomes and impacts and the corresponding correlations would need to be defined for an Service Production Function (inputoutput) and an Education Production Function (output-outcome/impact). Further, a selection of globally proved remedial actions to overcome sector bottlenecks need to be specified. Education interventions largely depend on the country context and different countries and regions apply different remedial actions. Since the relationship of input and impact is not as linear as the illness-treatment relationship in health, international research and comparison of effective interventions would need to be conducted. The MBB model is applying service coverage determinants of both, supply and demand side. Therefore the approach could be a helpful instrument in the context of the Human Rights-based Approach as used within programming of the United Nations and UNICEF. However, applying further analysis on humanitarian aspects of programming always depends on the availability of disaggregated information. Based on the outline of the Service Coverage Concept and the Marginal Budgeting for Bottlenecks model and the conceptual adaptation of the MBB model for its use in education, following suggestions can be made for the Service Delivery Modes and Service Coverage Determinants: Overall, an MBB model in education could have added value for education planning, budgeting and impact simulation. However, it has to be considered that applying the model requires extensive data input for all six Service Coverage Determinants for each of the five Service Deliver Modes. Although, the MBB model could be adjusted to only cover a certain sub-sector within Quality Education for All. Five Service Delivery Modes Ten Sub-Packages 1. Pre-School Education 1.1 Public Early Childhood Education 1.2 Private Early Childhood Education 2. Formal Basic Education 2.1 Public Formal Basic Education 2.2 Private Basic Education 3. Non-Formal Basic Education 3.1 Public Non-Formal Basic Education 3.2 Private Non-Formal Basic Education 4. (Lower) Secondary Education 4.1 Public Secondary Education 4.2 Private Secondary Education 5. Adult Literacy, Continuing Education 5.1 Youth and Adult Literacy Interventions 5.2 Continuing Education Six Service Coverage Determinants Indicator Supply side 1. Availability of essential commodities Pupil-Classroom Ratio by grade Pupil-Textbook Ratio 2. Availability of human resources Pupil-Teacher Ratio (or Pupilqualified Teacher Ratio) by grade 3. Geographic and financial accessibility School-Distance School-Costs by grade Demand side 4. Initial Utilization Net-Enrolment Ratio (or Gross- Enrolment Ratio) by grade 5. Continuous Utilization Survival Rate by grade 6. Effective Utilization Graduation Ratio Graduation Test Scores Overall, an MBB model in education could have added value for education planning, budgeting and impact simulation. However, it has to be considered that applying the model requires extensive data input for all six Service Coverage Determinants for each of the five Service Deliver Modes. Although, the MBB model could be adjusted to only cover a certain sub-sector within Quality Education for All.
48

Managing the memory hierarchy in GPUs

Dublish, Saumay Kumar January 2018 (has links)
Pervasive use of GPUs across multiple disciplines is a result of continuous adaptation of the GPU architectures to address the needs of upcoming application domains. One such vital improvement is the introduction of the on-chip cache hierarchy, used primarily to filter the high bandwidth demand to the off-chip memory. However, in contrast to traditional CPUs, the cache hierarchy in GPUs is presented with significantly different challenges such as cache thrashing and bandwidth bottlenecks, arising due to small caches and high levels of memory traffic. These challenges lead to severe congestion across the memory hierarchy, resulting in high memory access latencies. In memory-intensive applications, such high memory access latencies often get exposed and can no longer be hidden through multithreading, and therefore adversely impact system performance. In this thesis, we address the inefficiencies across the memory hierarchy in GPUs that lead to such high levels of congestion. We identify three major factors contributing to poor memory system performance: first, disproportionate and insufficient bandwidth resources in the cache hierarchy; second, poor cache management policies; and third, high levels of multithreading. In order to revitalize the memory hierarchy by addressing the above limitations, we propose a three-pronged approach. First, we characterize the bandwidth bottlenecks present across the memory hierarchy in GPUs and identify the architectural parameters that are most critical in alleviating congestion. Subsequently, we explore the architectural design space to mitigate the bandwidth bottlenecks in a cost-effective manner. Second, we identify significant inter-core reuse in GPUs, presenting an opportunity to reuse data among the L1s. We exploit this reuse by connecting the L1 caches with a lightweight ring network to facilitate inter-core communication of shared data. We show that this technique reduces traffic to the L2 cache, freeing up the bandwidth for other accesses. Third, we present Poise, a machine learning approach to mitigate cache thrashing and bandwidth bottlenecks by altering the levels of multi-threading. Poise comprises a supervised learning model that is trained offline on a set of profiled kernels to make good warp scheduling decisions. Subsequently, a hardware inference engine is used to predict good warp scheduling decisions at runtime using the model learned during training. In summary, we address the problem of bandwidth bottlenecks across the memory hierarchy in GPUs by exploring how to best scale, supplement and utilize the existing bandwidth resources. These techniques provide an effective and comprehensive methodology to mitigate the bandwidth bottlenecks in the GPU memory hierarchy.
49

A model for material handling improvements when using automated storage systems: A case study / En modell för förbättringar av materialhantering genom användandet av automatiserade lagersystem: En fallstudie

Thongmal Larsson, Marie January 2010 (has links)
The purpose of this thesis is to create a model of how to organize the placements of articles in an automated storage system in order to reduce time and cost related to the extractions. The model was developed during an investigation at a case company, and a comprehensive study of the material handling identified bottlenecks, whereof one was chosen to be further investigated: the automated storage system. The automated storage system is newly installed equipment, which required new working methods to be incorporated to the already existing working environment. The ABC-analysis was used in order to motivate how the articles should be placed in the automated storage. The goal for the new way of handling material was to put as little effort as possible on time related to the extraction of material. This due to the realization of material handling processes being a huge contributor to waste activities. This resulted in the development of the model and the suggestion that is given to the case company is to place the most frequent extracted articles close to the users. However, advantages must be held against disadvantages of rearrangements since the material handling will not be eliminated totally due to smaller improvements. / Syftet med denna uppsats är att skapa en modell för hur man ska organisera artikelplaceringar i ett automatiserat lagersystem för att reducera tid och kostnad relaterat till uttag av material. Modellen skapades genom en undersökning på ett fallföretag, en omfattande studie av materialhanteringen identifierade flaskhalsar, varav en valdes för fortsatt undersökning: det automatiserade lagersystemet. Det automatiserade lagersystemet är en nyinstallerad utrustning, som kräver att nya arbetsmetoder ska inkorporeras till den redan existerande arbetsmiljön. ABC-analysen användes för att motivera hur artiklarna ska placeras i det automatiserade lagret. Målet för det nya sättet att hantera material på var att så få insatser som möjligt skulle användas för uttag av material. Detta pågrund av insikten utav att materialhanteringsprocesser är en stor bidragande slöserifaktor. Detta resulterade i modellen och förslagen som ges till fallföretaget är att placera de mest frekvent använda artiklarna nära användaren. Emellertid så måste man väga fördelar mot nackdelar av en förändring eftersom materialhanteringen inte kommer att elimineras helt pågrund av mindre förbättringar.
50

The effects of habitat fragmentation on the demography and population genetic structure of Uromys Caudimaculatus

Streatfeild, Craig Anthony January 2009 (has links)
Habitat fragmentation can have an impact on a wide variety of biological processes including abundance, life history strategies, mating system, inbreeding and genetic diversity levels of individual species. Although fragmented populations have received much attention, ecological and genetic responses of species to fragmentation have still not been fully resolved. The current study investigated the ecological factors that may influence the demographic and genetic structure of the giant white-tailed rat (Uromys caudimaculatus) within fragmented tropical rainforests. It is the first study to examine relationships between food resources, vegetation attributes and Uromys demography in a quantitative manner. Giant white-tailed rat densities were strongly correlated with specific suites of food resources rather than forest structure or other factors linked to fragmentation (i.e. fragment size). Several demographic parameters including the density of resident adults and juvenile recruitment showed similar patterns. Although data were limited, high quality food resources appear to initiate breeding in female Uromys. Where data were sufficient, influx of juveniles was significantly related to the density of high quality food resources that had fallen in the previous three months. Thus, availability of high quality food resources appear to be more important than either vegetation structure or fragment size in influencing giant white-tailed rat demography. These results support the suggestion that a species’ response to fragmentation can be related to their specific habitat requirements and can vary in response to local ecological conditions. In contrast to demographic data, genetic data revealed a significant negative effect of habitat fragmentation on genetic diversity and effective population size in U. caudimaculatus. All three fragments showed lower levels of allelic richness, number of private alleles and expected heterozygosity compared with the unfragmented continuous rainforest site. Populations at all sites were significantly differentiated, suggesting restricted among population gene flow. The combined effects of reduced genetic diversity, lower effective population size and restricted gene flow suggest that long-term viability of small fragmented populations may be at risk, unless effective management is employed in the future. A diverse range of genetic reproductive behaviours and sex-biased dispersal patterns were evident within U. caudimaculatus populations. Genetic paternity analyses revealed that the major mating system in U. caudimaculatus appeared to be polygyny at sites P1, P3 and C1. Evidence of genetic monogamy, however, was also found in the three fragmented sites, and was the dominant mating system in the remaining low density, small fragment (P2). High variability in reproductive skew and reproductive success was also found but was less pronounced when only resident Uromys were considered. Male body condition predicted which males sired offspring, however, neither body condition nor heterozygosity levels were accurate predictors of the number of offspring assigned to individual males or females. Genetic spatial autocorrelation analyses provided evidence for increased philopatry among females at site P1, but increased philopatry among males at site P3. This suggests that male-biased dispersal occurs at site P1 and female-biased dispersal at site P3, implying that in addition to mating systems, Uromys may also be able to adjust their dispersal behaviour to suit local ecological conditions. This study highlights the importance of examining the mechanisms that underlie population-level responses to habitat fragmentation using a combined ecological and genetic approach. The ecological data suggested that habitat quality (i.e. high quality food resources) rather than habitat quantity (i.e. fragment size) was relatively more important in influencing giant white-tailed rat demographics, at least for the populations studied here . Conversely, genetic data showed strong evidence that Uromys populations were affected adversely by habitat fragmentation and that management of isolated populations may be required for long-term viability of populations within isolated rainforest fragments.

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