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McDonald, Jennifer Mary. "Building a model for binary star formation : the separate nuclei hypothesis revisited." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387669.
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Arvin, Scott Anthony. "Physically based mechanical metaphors in architectural space planning." Diss., Texas A&M University, 2004. http://hdl.handle.net/1969.1/395.
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Physically based space planning is a means for automating the conceptual design process by applying the physics of motion to space plan elements. This methodology provides for a responsive design process, allowing a designer to easily make decisions whose consequences propagate throughout the design. It combines the speed of automated design methods with the flexibility of manual design methods, while adding a highly interactive quality and a sense of collaboration with the design. The primary assumption is that a digital design tool based on a physics paradigm can facilitate the architectural space planning process. The hypotheses are that Newtonian dynamics can be used 1) to define mechanical metaphors to represent the elements in an architectural space plan, 2) to compute architectural space planning solutions, and 3) to interact with architectural space plans. I show that space plan elements can be represented as physical masses, that design objectives can be represented using mechanical metaphors such as springs, repulsion fields, and screw clamps, that a layout solution can be computed by using these elements in a dynamical simulation, and that the user can interact with that solution by applying forces that are also models of the same mechanical objects. I present a prototype software application that successfully implements this approach. A subjective evaluation of this prototype reveals that it demonstrates a feasible process for producing space plans, and that it can potentially improve the design process because of the quality of the manipulation and the enhanced opportunities for design exploration it provides to the designer. I found that an important characteristic of this approach is that representation, computation, and interaction are all defined using the same paradigm. This contrasts with most approaches to automated space planning, where these three characteristics are usually defined in completely different ways. Also emerging from this work is a new cognitive theory of design titled 'dynamical design imagery,' which proposes that the elements in a designer's mental imagery during the act of design are dynamic in nature and act as a dynamical system, rather than as static images that are modified in a piecewise algorithmic manner.
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Harper, Kevin M. "Challenging the Efficient Market Hypothesis with Dynamically Trained Artificial Neural Networks." UNF Digital Commons, 2016. http://digitalcommons.unf.edu/etd/718.
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A review of the literature applying Multilayer Perceptron (MLP) based Artificial Neural Networks (ANNs) to market forecasting leads to three observations: 1) It is clear that simple ANNs, like other nonlinear machine learning techniques, are capable of approximating general market trends 2) It is not clear to what extent such forecasted trends are reliably exploitable in terms of profits obtained via trading activity 3) Most research with ANNs reporting profitable trading activity relies on ANN models trained over one fixed interval which is then tested on a separate out-of-sample fixed interval, and it is not clear to what extent these results may generalize to other out-of-sample periods. Very little research has tested the profitability of ANN models over multiple out-of-sample periods, and the author knows of no pure ANN (non-hybrid) systems that do so while being dynamically retrained on new data. This thesis tests the capacity of MLP type ANNs to reliably generate profitable trading signals over rolling training and testing periods. Traditional error statistics serve as descriptive rather than performance measures in this research, as they are of limited use for assessing a system’s ability to consistently produce above-market returns. Performance is measured for the ANN system by the average returns accumulated over multiple runs over multiple periods, and these averages are compared with the traditional buy-and-hold returns for the same periods. In some cases, our models were able to produce above-market returns over many years. These returns, however, proved to be highly sensitive to variability in the training, validation and testing datasets as well as to the market dynamics at play during initial deployment. We argue that credible challenges to the Efficient Market Hypothesis (EMH) by machine learning techniques must demonstrate that returns produced by their models are not similarly susceptible to such variability.
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González, Gómez Andrés. "Nonlinear dynamics and smooth transition models." Doctoral thesis, Handelshögskolan i Stockholm, Ekonomisk Statistik (ES), 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:hhs:diva-541.
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During the last few years nonlinear models have been a very active area of econometric research: new models have been introduced and existing ones generalized. To a large extent, these developments have concerned models in which the conditional moments are regime-dependent. In such models, the different regimes are usually linear and the change between them is governed by an observable or unobservable variable. These specifications can be useful in situations in which it is suspected that the behaviour of the dependent variable may vary between regimes. A classical example can be found the business cycle literature where it is argued that contractions in the economy are not only more violent but also short-lived than expansions. Unemployment, which tends to rise faster during recessions than decline during booms, constitutes another example. Two of the most popular regime-dependent models are the smooth transition and the threshold model. In both models cases the transition variable is observable but the specification of the way in which the model changes from one regime to the other is different. Particularly, in the smooth transition model the change is a continuous whereas in the threshold model it is abrupt. One of the factors that has influenced the development of nonlinear models are improvements in computer technology. They have not only permitted an introduction of more complex models but have also allowed the use of computer-intensive methods in hypothesis testing. This is particularly important in nonlinear models because there these methods have proved to be practical in testing statistical hypothesis such as linearity and parameter constancy. In general, these testing situation are not trivial and their solution often requires computer-intensive methods. In particular, bootstrapping and Monte Carlo testing are now commonly used. In this thesis the smooth transition model is used in different ways. In the first chapter, a vector smooth transition model is used as a device for deriving a test for parameter constancy in stationary vector autoregressive models. In the second chapter we introduce a panel model whose parameters can change in a smooth fashion between regimes as a function of an exogenous variable. The method is used to investigate whether financial constraints affect firms' \ investment decisions. The third chapter is concern with linearity testing in smooth transition models. New tests are introduced and Monte Carlo testing techniques are shown to be useful in achieving control over the size of the test. Finally, the last chapter is devoted to the Smooth Permanent Surge model. This is a nonlinear moving average model in which a shock can have transitory or permanent effects depending on its sign and magnitude. Test for linearity and random walk hypothesis are introduced.Diss. Stockholm : Handelshögsk., 2004
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Lombard, Karin. "Revising the value shift hypothesis : South Africa's value dynamics between 1991 and 2001." Thesis, Stellenbosch : Stellenbosch University, 2001. http://hdl.handle.net/10019.1/52437.
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Thesis (MPhil)--Stellenbosch University, 2001.ENGLISH ABSTRACT: The World Values Survey has made a significant contribution to research in the field of values and value change, but a large amount of the research has been fashioned in a manner to tap values in industrialized and western states, rendering the theoretical models of explanation less than relevant for developing nations. This study aims to advance an understanding of value change within the South African context, particularly in light of the expansive political, social and economic changes to have transpired since 1990, whilst simultaneously addressing this issue of a lack of universal theory to understand value change. Primary amongst the theoretical frameworks addressing this issue of value change has been Ronald Inglehart's theory of a shift towards increased post-materialism in economically viable democratic countries. By subjecting survey data regarding value priorities from the South African rounds of the 1991, 1995 and 2001 World Values Survey to statistical analysis, the hypothesis of a similar situation in South Africa will be tested. After evaluating whether South Africa concurs with the post-materialist shift hypothesis, a unique dimension, including pre-materialist values, will be utilized in an attempt to establish whether South Africa has undergone any value change. This dimension is employed in the analysis of the 1995 and 2001 South African data, and whilst the value shift hypothesis promulgated by Inglehart appears largely unconcurred, an overall trend away from pre-materialism towards increased mixed type value priorities, with an ever so slight increase in materialists, has become evident. Although South Africa's value configuration is displaying an increasing convergence towards more moderate value orientations, most of the dynamics of change are manifesting themselves amongst and across various population sub-groups. South Africa's values are therefore undergoing relatively dramatic fluctuations, mainly reflected when the data are disaggregated for the various population sub-groups, the results indicating that longitudinal analysis along the pre-materialist/materialist continuum continues to be a more appropriate tool for tapping South Africa's underlying values. The consequences of these findings, for democratic consolidation, future political conflict, value change determinants and the appropriateness of this model for developing countries, will be assessed in detail. Consequently, by conducting these analyses, this research essay attempts to situate a global, but still largely Western theory, in a South African and developing world context. It thereby attempts to contribute towards filling a knowledge gap concerning the direction, degree and nature of the dynamics of value change.
AFRIKAANSE OPSOMMING: Hoewel die Wêreld Waardestudie sedert 1981 'n noemenswaardige bydrae gemaak het tot navorsing rakende waardes en waardeverandering, was dit tot dusver hoofsaaklik gefokus op waardes van geindustrialiseerde en westerse state. Dié fokus, het die studie grootliks van sy verklarende bruikbaarheid vir ontwikkelende lande ontneem. In hierdie opdrag sal daar gepoog word om die waardeveranderinge van Suid-Afrikaners, in die lig van die politieke- en ekonomiese omwentelinge sedert 1990, te beskryf. Dit sal gedoen word tesame met die aanspreek van die kwessie rondom die gebrek aan 'n universele teorie waarmee waardeverandering verklaar kan word. Ronald Inglehart se teorie, wat 'n skuif na post-materialistiese waardes in ekonomiese lewensvatbare state postuleer, was tot dusver die mees prominente teoretiese raamwerk wat waardeveranderinge beskryf het. Deur middel van die analise van die 1991, 1995 en 2001 data van die Suid-Afrikaanse rondte van die Wêreld Waardestudie, sal daar gepoog word om dié hipotese binne die plaaslike konteks te toets. Hierna sal 'n unieke dimensie, wat prematerialistiese waardes insluit, gebruik word om vas te stelof Suid-Afrikaners enige verandering in hul waarde oriëntasies ondergaan het. Hierdie dimensie is by die 1995 en 2001 studies ingesluit, en hoewel die resultate nie heeltemalooreenstem met Inglehart se hipotese nie, was daar 'n neiging weg van pre-materialisme in die rigting van meer gemenge waarde prioriteite, sowel as 'n baie klein toename in die aantal materialiste, merkbaar. Suid- Afrikaners blyk te beweeg in die rigting van meer gematigde waarde oriëntasies, en meeste van hierdie neigings manifesteer ditselfbinne en tussen die verskeie bevolkingsgroepe. Suid-Afrikaanse waardes ondergaan dus, in relatiewe terme, dramatiese veranderinge, wat veral na vore kom wanneer data vir die onderskeie bevolking sub-groepe afsonderlik geanaliseer word. Die resultate bevestig dat longitudinale analise in terme van 'n prematerialistiese/ materialistiese kontinuum steeds die beste metode is om waardeverandering binne die Suid-Afrikaanse konteks te meet. Die implikasies van hierdie bevindinge vir demokratiese konsolidasie, toekomstige politieke konflik, waardeveranderinge, en die toepaslikheid van die modelop ontwikkelende lande, sal in detail bespreek word. Hierdie studie poog gevolglik om 'n universele, maar hoofsaaklik steeds Westerse, teorie in 'n Suid- Afrikaanse en ontwikkelende staat perspektief te plaas. Daar word gehoop dat sodanige studie sal bydra om bestaande tekortkominge rakende die rigting, graad, en aard, van waardeveranderinge aan te spreek. The financial assistance of the National Research Foundation (NRF) towards this research is hereby acknowledged. Opinions expressed and conclusions arrived at, are those of the author and are not necessarily to be attributed to the National Research Foundation.
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Nochomovitz, Yigal Dov. "From topologies to dynamics: A study of the designability hypothesis for biological networks." Diss., Search in ProQuest Dissertations & Theses. UC Only, 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3261243.
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Smith, D. J. "Cooperative dynamics among hunter-gatherers : an experimental investigation of adaptive hypotheses." Thesis, University College London (University of London), 2017. http://discovery.ucl.ac.uk/1560248/.
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From small-scale food-sharing among hunter-gatherers to large-scale institutions in modern industrial societies, cooperation is central to human success. This thesis focuses on the former, exploring cooperative dynamics among the Agta, a Filipino hunter-gatherer population. I develop a novel experimental approach to exploring hunter-gatherer cooperative behaviour which simultaneously assesses the amount individuals cooperate and who they cooperate with. In contrast to much previous experimental literature, this non-anonymous design permits tests of specific theories for the evolution of cooperation, including: kin selection (cooperating with related individuals); reciprocity (cooperating with others who cooperate in return); and tolerated theft/demand sharing (taking from those with more resources), among other adaptive hypotheses. Using two experimental games – one exploring giving behaviour (donating resources to others) and another exploring demand sharing behaviour (taking resources from others) – I find that individuals from camps with a greater probability of repeated interactions give more to and take less from others. When individuals give to others it is directed towards kin and reciprocating partners, while when individuals take they do so from those with more resources, regardless of kinship or reciprocity. As predicted by theoretical models, this suggests that reciprocal transfers occur when interactions are repeated, while demand sharing occurs when repeated interactions are less likely. Differences in the frequency of repeated interactions may therefore explain some cross-cultural variation in forager food-sharing practices. This thesis also explores the effects of reputation on cooperative and interaction networks, finding that many aspects of forager social networks may reflect the trade of commodities in biological markets. Additionally, assessment of the ontogenetic roots of Agta cooperative behaviour suggests that 3 who children cooperate with, but not overall levels of cooperation, change over childhood in ways which are consistent with adaptive evolutionary hypotheses. These findings provide an insight into the evolutionary and ecological roots of hunter-gatherer cooperation.
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Karaköylü, Erdem Mustafa. "The foraging sorties hypothesis evaluating the effect of gut dynamics on copepod foraging behavior /." Diss., [La Jolla] : University of California, San Diego, 2010. http://wwwlib.umi.com/cr/ucsd/fullcit?p3398254.
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Thesis (Ph. D.)--University of California, San Diego, 2010.Title from first page of PDF file (viewed May 6, 2010). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.
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Troitiño, Malavasi Bruno Matias, and Llerena Alejandro Muñoz. "Hypothesis test of a new line balancing approach with dynamic allocation of assembly operations." Thesis, Högskolan i Skövde, Institutionen för teknik och samhälle, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:his:diva-8533.
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Assembly lines are no longer systems designed to produce as much as possible at the lower cost. Nowadays several factors such as mass customization and variation in demand have led the manufacturers to consider the flexibility of the assembly systems as one of the most important facts to take into account when designing an assembly line. In this context, this study attempts to test a new paradigm of the workload balance, which is based on a dynamic allocation of the assembly operations. In order to test the hypothesis, a real assembly system of engines has been used as a base model to implement the new approach. The work developed, uses the simulation as a means to carry out the study, which has required the development of several simulation scenarios. The hypothesis has been studied from two different approaches; on one hand a total dynamic allocation of assembly operations, which was expected to cause a wide operational range of the stations. On the other hand, the second approach implements a flow control which aims to reduce the operational range and workload fluctuations. The results obtained show a significant improvement of the system performance in comparison with the current assembly line. It has been found that any improvement implemented in the system is directly reflected in the total performance of the line, regardless if the improvement is made in a system constraint. Moreover, the results have proven a better response of the system to changes in the frequency of models production. Finally, based on the results, this study suggests several paths of future work in order to acquire the needed information to implement the hypothesis in the real world context.Flexa project
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Abbey-Lee, Robin N. "Relative Role of Dispersal Dynamics and Competition in Niche Breadth." FIU Digital Commons, 2012. http://digitalcommons.fiu.edu/etd/674.
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Among-individual variation in resource use is pervasive and may have ecosystem-wide effects. This variation between individuals can affect population niche breadth. My study determined if niche breadth was best explained by dispersal of individuals from locations with different prey resources driven by ecosystem level disturbance regimes or competition among individuals inhabiting a site, resulting in dietary partitioning. I used structural equation modeling to examine the direct and indirect effects of several environmental variables spanning gradients of disturbance, competition strength, and food availability on niche breadth of the Eastern Mosquitofish (Gambusia holbrooki). I evaluated two complementary models 1) allowing for only direct effects of disturbance on niche breadth and 2) limiting effects of disturbance on niche breadth to indirect effects via food availability and competitor densities. The partitioning hypothesis excluding direct effects of disturbance on niche breadth was best supported by my data.
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Picascia, Stefano. "Agent-based modelling of urban economic and cultural dynamics under the rent-gap hypotheses." Thesis, Manchester Metropolitan University, 2017. http://e-space.mmu.ac.uk/618397/.
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This work proposes a theoretically grounded, generative approach to the study of urban dynamics, based on the Critical Geography line of thought. We implemented a variant of the 'Rent-Gap theory of gentrification' in a set of agent- based models of varying degrees of abstraction. A stylised model of the theory - coupled with residential mobility and cultural exchange in a city-wide context - is capable of reproducing certain observed dynamics of the past century of urbanisa- tion. Cycles of investment, the formation of persistent pockets of disinvestment, the emergence and dissolution of culturally homogeneous areas, and phenomena such as gentrification were all dynamics emerging in the simulation solely as the product of profit-driven investment in housing. A more descriptive version of the model, informed with official data derived from the UK Census and the Land Registry, provides an empirical validation of the core tenets of the theory in the context of contemporary British cities. The descriptive model is also employed to hypothesise on the mechanics and possible outcomes of large scale regeneration programmes, demonstrating a potential impact in the formulation and evaluation of urban policy. Ultimately, this work wishes to challenge the view that theory might be an un- necessary extravagance in an era of large datasets and suggestions of 'algorithmic governance.' At the same time, it wishes to highlight the actuality and insightfulness of the critical geographical approach, especially in the wake of the decidedly urban nature of the current economic crisis.
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Arbic, Brian K. "Generation of mid-ocean eddies : the local baroclinic instability hypothesis." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/53047.
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Thesis (Ph.D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences and the Woods Hole Oceanographic Institution), 2000.Includes bibliographical references (p. 284-290).
by Brian Kenneth Arbic.
Ph.D.
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Moon, Jinyoung. "Selective accrual and dynamics of proteinaceous compounds during pedogenesis: testing source and sink selection hypotheses." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/77030.
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The emerging evidence of preferential accumulation and long residence time of proteinaceous compounds in soil are counter to the traditional view that their structure is readily broken down through microbial activity. The shift in thinking of their residence time is, however, heavily influenced by physical and chemical protections in soil, representing an important change for understanding global biogeochemical carbon and nitrogen cycling. We investigated the accumulation patterns of proteinogenic amino acids for a long term (thousands of years) related to their sources and sinks. We found clear patterns of change in the amino acids in a 4000 year-chronosequence adjacent to Lake Michigan, USA (Michigan chronosequence) and they were tightly related to the shifts in their biological sources, namely aboveground vegetative community (r2=0.66, p<0.0001) and belowground microbial community (r2=0.71, p<0.0001). Results also showed great variations of approximately 49% between seasons (summer and winter). Moreover, seasonal dynamic patterns (22% variations) of the amino acids in soil mineral associated fraction were rather counter to the conceptual view that it represents a slow soil organic pool with long residence times. The amino acids enriched in the mineral associated fraction, (e.g., positively charged, aromatic, and sulfur containing amino acids), tended to preferentially accumulate in whole soil pool during the 4000 years of ecosystem development. Their interaction with soil minerals, therefore, may play a critical role in the long-term sink and selective accumulation of proteinaceous compounds with some degree of the displacement. This was further confirmed by another chronosequence system near Haast River, New Zealand, which is geologically separated and climatically- and ecologically- different from the Michigan chronosequence. Common trends between two chronosequences suggested that either polar interactions or redox reactions may be relatively more important in the mineral interaction of amino acids than non-polar interactions. The consistency of results at two disparate locations in the southern and northern hemispheres is strong evidence that the processes of pedogenesis and ecosystem development are parsimonious and predictable. Our research demonstrated fundamental understanding of behavior of proteinaceous compounds at the molecular species level, and further provided their partitioning mechanisms associated with soil components.Ph. D.
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Carlsson, Michaela. "Vegetation succession in savanna determined by interaction of grazing, browsing and fire; a comparison between hypotheses." Thesis, Södertörn University College, School of Life Sciences, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:sh:diva-307.
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Studies in tropical regions have shown that trees and grasses respond differently to fire, grazing and browsing. In African savannas, the responses to fire, grazing and browsing are different, determined by negative or positive correlations. Browsing may have other consequences than grazing because instead of increasing woody biomass it reduces it, causing increase in grass growth, leading to increase in fuel that results in more intense fires and decrease in woody biomass. Fire and herbivory are an important interactive disturbance factors affecting vegetation succession and the tree-grass dynamics in savanna environment. Several of the fire-herbivory interactions are landscape level effects, which is shown in 2 models. My hypothesis is that the tree-grass balances are determined by interactions of both grazing and fire. There have come new scientific data about fire and herbivory and the interaction effects on tree-grass dynamic and succession in the savanna. By analyzing my hypothesis through a comparison between hypotheses, Intermediate disturbance hypothesis, Janzen-Connell hypothesis and the Huston hypothesis, I propose several scenarios of the savanna tree-grass dynamics in East Africa, as a result of this comparison.
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Buc, Calderon Cristian. "Temporal dynamics and neural architecture of action selection." Doctoral thesis, Universite Libre de Bruxelles, 2016. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/229408.
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In this thesis we pitted two views of action selection. On the one hand, a traditional view suggesting that action selection emerges from a sequential process whereby perception, cognition and action proceed serially and are subtended by distinct brain areas. On the other hand, an ecological view (formalized in the affordance competition hypothesis) advocating that action selection stems from the parallel implementation of potential action plans. In parallel, the competition between these action plans would be biased by relevant task factors. We first addressed the issue of the temporal dynamics of action selection processes in Chapter 2. We built a reaching task design that crucially gave equal opportunities for serial and parallel processing of cognitive and motor processes to occur. In our study, we first cued participants with probabilities associated to upcoming potential reaches. After several hundreds of milliseconds, participants were given a deterministic go signal indicating which target to reach for. They had to reach for the signaled target as fast as possible. Importantly, our design tries to cope with the biases involved in previous reaching tasks, allowing for a much more informative way to tackle the issue of serial versus parallel processing in action selection. We show that effects of action probability are not only present in the initiation time (i.e. the time it takes to initiate the movement), but crucially also in the movement time (i.e. the time interval between movement initiation and target reaching). Furthermore, an analysis of the movement trajectories showed that reach probability influenced the trajectories according to the predicted pattern. Thus, these results back up a system where cognitive and motor processes continuously interact with one another to come up with a decision. After clarifying the temporal dynamics, we concentrate our efforts on exposing the neural architecture of processes subtending action selection in Chapter 3. In a two-choice button press task, participants were first cued with predictive information regarding upcoming button presses. Crucially, we experimentally manipulated the amount of information in favor of specific button presses whilst adopting a design as similar as possible to those used in monkey neurophysiology (e.g. Cisek & Kalaska, 2005). Using fMRI, our results showed that as information in favor a button press increases, so does activity in the contralateral primary motor cortex, while activity in the ipsilateral primary motor cortex decreases. Moreover, we observed that primary motor regions are more tightly coupled with fronto-parietal areas in a condition involving a decision compared with a situation not implicating a decision between two button presses. Our results are compatible with an account predicting that decision-making emerges from motor areas, and therefore suggest that the architecture presented in the affordance competition hypothesis is not only valid in monkeys but also humans. In Chapter 4, we combine the findings acquired in the studies of chapter 2 and 3 with recent neurophysiological insights to develop a neuro-computational model capable of grasping the continuous interaction between cognitive and motor processes, responsible for the behavioral pattern in reach selection tasks. Our model functions on the principles of cascade forward models whereby activation at one stage of processing systematically spills to the next one, thereby substantially blurring the boundaries between perceptive, cognitive and motor processes. Contrary to most computational models confining action selection processes prior to action execution, our model allows for these processes to leak into action execution. Moreover, the threshold for action execution is not fixed, but rather dynamic and crucially depends on the activity pattern of the model’s primary motor neurons. We propose that the modification of the threshold is governed by the subthalamic nucleus, receiving direct input signals from the primary motor cortex and in turn imposing a dynamical brake on action execution. By including this dynamical threshold, our model has the advantage that it can release movement execution either rapidly or slowly depending on the context. Our model accounts not only for initiation times, but also movement times in reaching task studies. Furthermore, it can grasp the qualitative pattern of movement trajectories. This study suggests that to explain unfolding actions a classical fixed threshold is not sufficient, but rather an execution threshold level that is continuously being updated depending on the context is required.Doctorat en Sciences psychologiques et de l'éducation
info:eu-repo/semantics/nonPublished
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Thorarinsson, Johann Sigurdur. "Navigating in a dynamic world : Predicting the movements of others." Thesis, University of Skövde, School of Humanities and Informatics, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:his:diva-3146.
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The human brain is always trying to predict ahead in time. Many say that it is possible to take actions only based on internal simulations of the brain. A recent trend in the field of Artificial Intelligence is to provide agents with an “inner world” or internal simulations. This inner world can then be used instead of the real world, making it possible to operate without any inputs from the real world.
This final year project explores the possibility to navigate collision-free in a dynamic environment, using only internal simulation of sensor input instead of real input. Three scenarios will be presented that show how internal simulation operates in a dynamic environment. The results show that it is possible to navigate entirely based on predictions without a collision.
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Hossin, Muhammad Zakir. "Is the association between late-life morbidity and disability attenuated over time? : Exploring the dynamic equilibrium of morbidity hypothesis." Thesis, Stockholms universitet, Centrum för forskning om ojämlikhet i hälsa (CHESS), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-131507.
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Context: There is evidence suggesting that the prevalence of disability in late life has declined over time while the prevalence of disabling chronic diseases has increased. The dynamic equilibrium of morbidity hypothesis suggests that these seemingly contradictory trends are due to the attenuation of the morbidity-disability link over time. The aim of this study was to empirically test this assumption.Methods: Data were drawn from three repeated cross-sections of SWEOLD, a population-based survey among the Swedish men and women ages 77 and older. Logistic regression models were fitted to assess the trends in the prevalence of Activities of Daily Living (ADL) disability, Instrumental ADL (IADL) disability, and selected groups of chronic conditions. The changes in the associations between chronic conditions and disabilities were examined in both multiplicative and additive models.Results: Between 1992 and 2011, the odds of ADL disability significantly declined among women whereas the odds of IADL disability significantly declined among men. During the same period, the prevalence of most chronic morbidities including multimorbidity went up. Significant attenuations of the morbidity-disability associations were found for cardiovascular diseases, metabolic disorders, poor lung function, psychological distress, and multimorbidity.Conclusion: In agreement with the dynamic equilibrium hypothesis, this study concludes that the associations between chronic conditions and disability among the Swedish older adults have largely waned over time.
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Demharter, Samuel. "Novel applications for hierarchical natural move Monte Carlo simulations : from proteins to nucleic acids." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:c0ef3ba5-4fe0-4684-a0ce-202003cd79a5.
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Biological molecules often undergo large structural changes to perform their function. Computational methods can provide a fine-grained description at the atomistic scale. Without sufficient approximations to accelerate the simulations, however, the time-scale on which functional motions often occur is out of reach for many traditional methods. Natural Move Monte Carlo belongs to a class of methods that were introduced to bridge this gap. I present three novel applications for Natural Move Monte Carlo, two on proteins and one on DNA epigenetics. In the second part of this thesis I introduce a new protocol for the testing of hypotheses regarding the functional motions of biological systems, named customised Natural Move Monte Carlo. Two different case studies are presented aimed at demonstrating the feasibility of customised Natural Move Monte Carlo.
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Ortega, Nicole. "Flames and Frogs – The Impact of Environmental Disturbances on Host-Parasite Dynamics." Scholar Commons, 2018. https://scholarcommons.usf.edu/etd/7640.
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The successful completion of this work is dedicated first to my grandparents for having always shown their unwavering love and encouragement in my journeys (most of which they kindly and politely only pretended to understand) and for having also served as life-long role models who upheld an unparalleled work ethic. To many whom I consider to be my chosen family, especially Ann Williams and Brittany Sears, who kept me laughing, but more importantly, kept my crazy train from derailing during these tumultuous years. To Wayne Price and Tom Jackman, who fostered the success of my career and are the epitome of patience and kindness. To DeAngelis, for the many hours of laughter, conversations, and adventuresome treks that further kindled my knowledge, love, and respect for Florida’s ecology. To family in Alabama who have either helped shape my brazen character or made this education possible. To Taego, the one to whom I am bound through so many of the stories that begin with, “Remember when…?” and who is often so kind and thoughtful though he still holds tightly to the stereotype of the selfish youngest sibling. Finally, to Fen for being my smiling, bright blue-eyed, spunky kid who has been on this journey with me from the get-go; for keeping me from getting too big for my britches; for your intrinsic fire that burns for equality, fairness, and friendship; and for inspiring me to be the best example of a mother that I can possibly be.
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Trifonov, Trifon [Verfasser], and Andreas [Akademischer Betreuer] Quirrenbach. "Planetary dynamics and high precision optical and near-IR spectroscopy. Testing the planetary hypothesis around evolved K-giants. / Trifon Trifonov ; Betreuer: Andreas Quirrenbach." Heidelberg : Universitätsbibliothek Heidelberg, 2014. http://d-nb.info/1177811251/34.
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Buhrmann, Thomas. "On the intrinsic control properties of muscle and relexes : exploring the interaction between neural and musculoskeletal dynamics in the framework of the equilbrium-point hypothesis." Thesis, University of Sussex, 2010. http://sro.sussex.ac.uk/id/eprint/6279/.
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The aim of this thesis is to examine the relationship between the intrinsic dynamics of the body and its neural control. Specifically, it investigates the influence of musculoskeletal properties on the control signals needed for simple goal-directed movements in the framework of the equilibriumpoint (EP) hypothesis. To this end, muscle models of varying complexity are studied in isolation and when coupled to feedback laws derived from the EP hypothesis. It is demonstrated that the dynamical landscape formed by non-linear musculoskeletal models features a stable attractor in joint space whose properties, such as position, stiffness and viscosity, can be controlled through differential- and co-activation of antagonistic muscles. The emergence of this attractor creates a new level of control that reduces the system's degrees of freedom and thus constitutes a low-level motor synergy. It is described how the properties of this stable equilibrium, as well as transient movement dynamics, depend on the various modelling assumptions underlying the muscle model. The EP hypothesis is then tested on a chosen musculoskeletal model by using an optimal feedback control approach: genetic algorithm optimisation is used to identify feedback gains that produce smooth single- and multijoint movements of varying amplitude and duration. The importance of different feedback components is studied for reproducing invariants observed in natural movement kinematics. The resulting controllers are demonstrated to cope with a plausible range of reflex delays, predict the use of velocity-error feedback for the fastest movements, and suggest that experimentally observed triphasic muscle bursts are an emergent feature rather than centrally planned. Also, control schemes which allow for simultaneous control of movement duration and distance are identified. Lastly, it is shown that the generic formulation of the EP hypothesis fails to account for the interaction torques arising in multijoint movements. Extensions are proposed which address this shortcoming while maintaining its two basic assumptions: control signals in positional rather than force-based frames of reference; and the primacy of control properties intrinsic to the body over internal models. It is concluded that the EP hypothesis cannot be rejected for single- or multijoint reaching movements based on claims that predicted movement kinematics are unrealistic.
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Kim, Yeongwoo. "Dynamic GAN-based Clustering in Federated Learning." Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-285576.
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As the era of Industry 4.0 arises, the number of devices that are connectedto a network has increased. The devices continuously generate data that hasvarious information from power consumption to the configuration of thedevices. Since the data have the raw information about each local node inthe network, the manipulation of the information brings a potential to benefitthe network with different methods. However, due to the large amount ofnon-IID data generated in each node, manual operations to process the dataand tune the methods became challenging. To overcome the challenge, therehave been attempts to apply automated methods to build accurate machinelearning models by a subset of collected data or cluster network nodes byleveraging clustering algorithms and using machine learning models withineach cluster. However, the conventional clustering algorithms are imperfectin a distributed and dynamic network due to risk of data privacy, the nondynamicclusters, and the fixed number of clusters. These limitations ofthe clustering algorithms degrade the performance of the machine learningmodels because the clusters may become obsolete over time. Therefore, thisthesis proposes a three-phase clustering algorithm in dynamic environmentsby leveraging 1) GAN-based clustering, 2) cluster calibration, and 3) divisiveclustering in federated learning. GAN-based clustering preserves data becauseit eliminates the necessity of sharing raw data in a network to create clusters.Cluster calibration adds dynamics to fixed clusters by continuously updatingclusters and benefits methods that manage the network. Moreover, the divisiveclustering explores the different number of clusters by iteratively selectingand dividing a cluster into multiple clusters. As a result, we create clustersfor dynamic environments and improve the performance of machine learningmodels within each cluster.ett nätverk ökat. Enheterna genererar kontinuerligt data som har varierandeinformation, från strömförbrukning till konfigurationen av enheterna. Eftersomdatan innehåller den råa informationen om varje lokal nod i nätverket germanipulation av informationen potential att gynna nätverket med olika metoder.På grund av den stora mängden data, och dess egenskap av att vara icke-o.l.f.,som genereras i varje nod blir manuella operationer för att bearbeta data ochjustera metoderna utmanande. För att hantera utmaningen finns försök med attanvända automatiserade metoder för att bygga precisa maskininlärningsmodellermed hjälp av en mindre mängd insamlad data eller att gruppera nodergenom att utnyttja klustringsalgoritmer och använda maskininlärningsmodellerinom varje kluster. De konventionella klustringsalgoritmerna är emellertidofullkomliga i ett distribuerat och dynamiskt nätverk på grund av risken fördataskydd, de icke-dynamiska klusterna och det fasta antalet kluster. Dessabegränsningar av klustringsalgoritmerna försämrar maskininlärningsmodellernasprestanda eftersom klustren kan bli föråldrade med tiden. Därför föreslårdenna avhandling en trefasklustringsalgoritm i dynamiska miljöer genom attutnyttja 1) GAN-baserad klustring, 2) klusterkalibrering och 3) klyvning avkluster i federerad inlärning. GAN-baserade klustring bevarar dataintegriteteneftersom det eliminerar behovet av att dela rådata i ett nätverk för att skapakluster. Klusterkalibrering lägger till dynamik i klustringen genom att kontinuerligtuppdatera kluster och fördelar metoder som hanterar nätverket. Dessutomdelar den klövlande klustringen olika antal kluster genom att iterativt välja ochdela ett kluster i flera kluster. Som ett resultat skapar vi kluster för dynamiskamiljöer och förbättrar prestandan hos maskininlärningsmodeller inom varjekluster.
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Lee, Dongwoo. "Essays on Economic Decision Making." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/89564.
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This dissertation focuses on exploring individual and strategic decision problems in Economics. I take a different approach in each chapter to capture various aspects of decision problems. An overview of this dissertation is provided in Chapter 1.
Chapter 2 studies an individual's decision making in extensive-form games under ambiguity when the individual is ambiguous about an opponent's moves. In this chapter, a player follows Choquet Expected Utility preferences, since the standard Expected Utility cannot explain the situations of ambiguity. I raise the issue that dynamically inconsistent decision making can be derived in extensive-form games with ambiguity. To cope with this issue, this chapter provides sufficient conditions to recover dynamic consistency.
Chapter 3 analyzes the strategic decision making in signaling games when a player makes an inference about hidden information from the behavioral hypothesis. The Hypothesis Testing Equilibrium (HTE) is proposed to provide an explanation for posterior beliefs from the player. The notion of HTE admits belief updates for all events including zero-probability events. In addition, this chapter introduces well-motivated modifications of HTE.
Finally, Chapter 4 examines a boundedly rational individual who considers selective attributes when making a decision. It is assumed that the individual focuses on a subset of attributes that stand out from a choice set. The selective attributes model can accommodate violations of choice axioms of Independence from Irrelevant Alternative (IIA) and Regularity.Doctor of Philosophy
This dissertation focuses on exploring individual and strategic decision problems in Economics. I take a different approach in each chapter to capture various aspects of decision problem. An overview of this dissertation is provided in Chapter 1. Chapter 2 studies an individual’s decision making in extensive-form games under ambiguity. Ambiguity describes the situation in which the information available to a decision maker is too imprecise to be summarized by a probability measure (Epstein, 1999). It is known that ambiguity causes dynamic inconsistency between ex-ante and interim decision making. This chapter provides sufficient conditions under which dynamic consistency is maintained. Chapter 3 analyzes the strategic decision making in signaling games in which there are two players: informed sender and uninformed receiver. The sender has a private information about his type and the receiver makes an inference about hidden information. This chapter suggests a notion of the Hypothesis Testing Equilibrium (HTE), which provides an alternative explanation for the receiver’s beliefs. The idea of the HTE can be used as a refinement of Perfect Bayesian Equilibrium (PBE) in signaling games to cope with the known limitations of PBE. Finally, Chapter 4 examines a boundedly rational individual who considers only salient attributes when making a decision. The individual considers an attribute only when it stands out enough in a choice set. The selective attribute model can accommodate violations of choice axioms of Independence from Irrelevant Alternative (IIA) and Regularity.
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Aunapuu, Maano. "Predators in low arctic tundra and their impact on community structure and dynamics." Doctoral thesis, Umeå : Department of Ecology and Environmental Science, Umeå university, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-354.
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Karlsson, Viktor, and Emil Nygren. "Beating the Swedish Market : A dynamic approach to Value Investing using Modern Portfolio Theory." Thesis, Södertörns högskola, Institutionen för ekonomi och företagande, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:sh:diva-16465.
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Previous research has confirmed the existence of a value premium in a wide array of markets and using this value stock anomaly has yielded superior performance. This thesis investigates if one could take advantage of the existence of a value premium to deploy a dynamic investment strategy on the Swedish stock market (OMXS30) with focus on minimizing risk to achieve higher risk adjusted performance than the stock market index. The investment strategy implemented use Market-to-Book-Value to screen for both entry and exit signals and Modern Portfolio Theory, using the minimum-variance portfolio with short-selling constraints, to allocate assets within the portfolio. The investment strategy is evaluated using the Modigliani-Modigliani Risk Adjusted Performance measure. Conclusions from the thesis are that the strategy does outperform the Swedish stock market index, both in terms of nominal return and risk-adjusted performance. The suboptimal behaviour of investors where they overreact to signals and unconsciously rely on heuristics is used to explain why this is possible. Market-to-Book-Value, using the first quartile as entry signal and third quartile as exit signal, is considered to be a successful key ratio to screen for value stocks.
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Sigman, Daniel M. "The Role of Biological Production in Pleistocene Atmospheric Carbon Dioxide Variations and the Nitrogen Isotope Dynamics of the Southern Ocean." Ft. Belvoir : Defense Technical Information Center, 1997. http://handle.dtic.mil/100.2/ADA342811.
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Thesis (Ph. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution Joint Program in Oceanography/Applied Ocean Science and Engineering, 1997."September 1997." "Funding was provided by National Science Foundation Grant OCE-9201286, National Science Foundation Graduate Fellowship Program, and the JOI/USSAC Ocean Drilling Graduate Fellowship Program." Includes bibliographical references (p. 152-153).
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Murphy, Raegan. "Exploring a meta-theoretical framework for dynamic assessment and intelligence." Thesis, Pretoria : [s.n.], 2007. http://upetd.up.ac.za/thesis/available/etd-09302007-162044.
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Erasmus, Natasja. "The relationship between maternal employment and teenage character traits / Erasmus N." Thesis, North-West University, 2011. http://hdl.handle.net/10394/7341.
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The purpose of the study is to determine the relationship between maternal employment and teenage character traits.
Statistics show a significant increase in women entering the labour market and although demographics are changing rapidly, social attitudes and policies may lag behind, and the concept of mothers as principal caretakers and fathers as economic providers remains very much in place. The profound and sometimes contradictory convictions of individual members about working mothers and their children paralleled those of countless others and professional people where matched only by the equally profound lack of facts on which these convictions might be based.
The objective of the study is to measure the perceived character traits of teenage children in terms of self confidence, locus of control, independence, time management and ambition. The questions were measured within two different scenarios: the first, within households where both parents are employed, and the second, within households where only the father is employed. The aim of the study is to determine if there is any correlation between maternal employment and the presence or lack of presence of the specified character traits.
The empirical study was conducted using the quantitative research method with a non–probability sample. The data collection method used for the purpose of this study was in the form of questionnaires, based on the Likert scale. The content validity of the questionnaire was evaluated by a subject matter expert, while the face validity was determined by the Statistical Consultation Services of the North West University. Analysis of completed questionnaires involved descriptive statistics and practical significance.
The target population, high school teachers within the North West and Gauteng Province, consisted of 70 participants.
Based on the findings emanating from the research, there were no noticeable difference found between teenagers within households where both parents are employed and households where only the father is employed, although the results indicated a tendency for children within households where both parents are employed to be slightly more self confident, lean more towards an internal lotus of control, have higher ambition and are less dependent than those teenagers from households where only the father is employed. These findings, although not noticeable, agree with the literature.
There were limitations that had an impact on the results of this study. The limited population resulted in a small sample. The sample indicated that 41 percent have five years or less experience. Participants indicated that they are not always aware of the household dynamics. Additional limitations include the strict ethical roadblocks when conducting research on children.
It was recommended that a more comprehensive study should follow, which should include the participation of mothers and teenagers alike. This will give the researcher a distinct and clear result of what the influences could be within the household dynamics.Thesis (M.B.A.)--North-West University, Potchefstroom Campus, 2012.
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Chen, Xi. "Climate and landscape controls on seasonal water balance at the watershed scale." Doctoral diss., University of Central Florida, 2014. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/6263.
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The main goal of this dissertation is to develop a seasonal water balance model for evaporation, runoff and water storage change based on observations from a large number of watersheds, and further to obtain a comprehensive understanding on the dominant physical controls on intra-annual water balance. Meanwhile, the method for estimating evaporation and water storage based on recession analysis is improved by quantifying the seasonal pattern of the partial contributing area and contributing storage to base flow during low flow seasons.
A new method for quantifying seasonality is developed in this research. The difference between precipitation and soil water storage change, defined as effective precipitation, is considered as the available water. As an analog to climate aridity index, the ratio between monthly potential evaporation and effective precipitation is defined as a monthly aridity index. Water-limited or energy-limited months are defined based on the threshold of 1. Water-limited or energy-limited seasons are defined by aggregating water-limited or energy-limited months, respectively.
Seasonal evaporation is modeled by extending the Budyko hypothesis, which is originally for mean annual water balance; while seasonal surface runoff and base flow are modeled by generalizing the proportionality hypothesis originating from the SCS curve number model for surface runoff at the event scale. The developed seasonal evaporation and runoff models are evaluated based on watersheds across the United States. For the extended Budyko model, 250 out of 277 study watersheds have a Nash-Sutcliff efficiency (NSE) higher than 0.5, and for the seasonal runoff model, 179 out of 203 study watersheds have a NSE higher than 0.5.
Furthermore, the connection between the seasonal parameters of the developed model and a variety of physical factors in the study watersheds is investigated. For the extended Budyko model, vegetation is identified as an important physical factor that related to the seasonal model parameters. However, the relationship is only strong in water-limited seasons, due to the seasonality of the vegetation coverage. In the seasonal runoff model, the key controlling factors for wetting capacity and initial wetting are soil hydraulic conductivity and maximum rainfall intensity respectively. As for initial evaporation, vegetation is identified as the strongest controlling factor. Besides long-term climate, this research identifies the key controlling factors on seasonal water balance: the effects of soil water storage, vegetation, soil hydraulic conductivity, and storminess.
The developed model is applied to the Chipola River watershed and the Apalachicola River basin in Florida for assessing potential climate change impact on the seasonal water balance. The developed model performance is compared with a physically-based distributed hydrologic model of the Soil Water Assessment Tool, showing a good performance for seasonal runoff, evaporation and storage change.Ph.D.
Doctorate
Civil, Environmental and Construction Engineering
Engineering and Computer Science
Environmental Engineering
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Bayer, Petr. "Použitelnost ložového popele z vitrifikovaného lignitového uhlí v kompozitních cementech." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2014. http://www.nusl.cz/ntk/nusl-217052.
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Předložená magisterská práce se zabývá možným použitím vitrifikovaného lignitového lóžového popele jako náhrada slinku v kompozitních cementech. Byly zkoumány vlivy přidaného vitrifikovaného lóžového popele, jeho jemnosti, alkalických roztoků a jejich koncentrací. Byly připraveny kompozitní cementy v souladu s normou DIN EN 197 – 1. V těchto cementech bylo nahrazeno 30 % slinku vitrifikovaným lóžovým popelem. Konkrétně byly připraveny kompozitní cementy s vitrifikovaným lóžovým popelem o jemnosti 5549 cm2/g a 8397 cm2/g. Dále byly přidány alkalické roztoky hydroxidů a síranů vždy o dvou různých koncentracích, za účelem stimulace pucolánové a/nebo geopolymerní reakce. Mechanické vlastnosti připravených vzorků byly charakterizovány mechanickým testováním na prizmách s rozměry 40×40×160 mm, jak je specifikováno v normě DIN EN 196 – 1. Byla provedena nedestruktivní měření dynamického elastického modulu a destruktivní testovaní na pevnosti v tlaku a v ohybu. Distribuce velikosti částic a chemická analýza vstupních materiálů byla vykonána pomocí laserové granulometrie a rentgenové fluorescence. U zatvrdlých kompozitů bylo dále zkoumáno po 2 a 28 dnech hydratace fázové složení s využitím metody rentgenové difrakce a mikrostruktura s využitím skenovací elektronové mikroskopie. Výsledky ukázaly, že mechanické vlastnosti jsou nezávislé na množství přidaných alkálií stejně jako na jemnosti přidaného vitrifikovaného lóžového popele. Nicméně, znatelně nižší mechanické pevnosti byly pozorovány pro vzorky, které byly aktivovány hydroxidy, pravděpodobně kvůli brzké tvorbě silikátového hydrogelu. Vzorky aktivované sírany nedosáhly pevností jako referenční malta.
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Kuklik, Robert G. "Capital Asset Prices Modelling - Concept VAPM." Doctoral thesis, Vysoká škola ekonomická v Praze, 2008. http://www.nusl.cz/ntk/nusl-196945.
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The key objective of this thesis is the outline of an alternative capital market modeling framework, the Volatility Asset Pricing Model, VAPM, inspired by the innovative dual approach of Mandelbrot and Hudson using the method based on synthesis of two seemingly antagonistic factors -- the volatility of market prices and their serial dependence determining the capital markets' dynamics. The pilot tests of this model in various periods using the market index as well as a portfolio of selected securities delivered generally satisfactory results. Firstly, the work delivers a brief recapitulation regarding the concepts of a consumer/investor choice under general conditions of hypothetical certainty. Secondly, this outline is then followed by a description of the "classical" methodologies in the risky environment of uncertainty, with assessment of their corresponding key models, i.e. the CAPM, SIM, MIM, APTM, etc., notwithstanding results of the related testing approaches. Thirdly, this assessment is based on evaluation of the underlying doctrine of Efficient Market Hypothesis in relation to the so called Random Walk Model. Fourthly, in this context the work also offers a brief exposure to a few selected tests of these contraversial concepts. Fifthly, the main points of conteporary approaches such as the Fractal Dimension and the Hurst Exponent in the dynamic framework of information entropy are subsequently described as the theoretical tools leading to development of the abovementioned model VAPM. The major contribution of this thesis is considered its attempt to apply the abovementioned concepts in practice, with the intention to possibly inspire a further analytical research.
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Biagini, Giulio. "Studio delle Problematiche ed Evoluzione dello Streaming Adattivo su HTTP." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/15474/.
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Negli ultimi anni abbiamo assistito ad un notevole aumento del traffico dati mobile, trend confermato anche per il futuro, generato in gran parte da dispositivi smart e perlopiù legato alla metodica di accesso e scambio dati nota con il nome di video streaming. Si stima infatti che circa l'80% della bandwidth mobile mondiale nel 2021 sarà utilizzata per lo scambio di dati audio/video. Risulta dunque di fondamentale importanza per i provider di rete e dei servizi di video streaming, soprattutto quelli forniti on-demand, cercare di comprendere quali sono i parametri che maggiormente influenzano la cosiddetta QoE - Quality of Experience sperimentata dagli utenti finali, in modo da garantire loro il miglior servizio possibile (QoS - Quality of Service), mantenendo comunque alti i profitti.
Nell'ambito delle applicazioni e servizi di video streaming, in particolare, la qualità percepita dagli utenti finali risulta fortemente influenzata da diversi effetti di degradazione che possono verificarsi a causa di cattive condizioni di rete, soprattutto nello specifico ambito della mobilità.
Da questi studi risulta come, ad esempio, gli utenti preferiscono sperimentare effetti di degradazione temporale durante la riproduzione di contenui multimediali piuttosto che effetti di degradazione della qualità, risultati da cui derivano scelte implementative quali, ad esempio, l'utilizzo del protocollo TCP e la nascita del cosiddetto HTTP-based adaptive streaming, ovvero quella tecnica che permette di adattare la qualità dei segmenti scaricati in base al throughput, in modo da minimizzare il numero di interruzioni del servizio e massimizzare, al contempo, la qualità del media in download.
Dopo una rapida analisi delle principali tecnologie oggi utilizzate, si evince come vi sia la necessità di definire un unico formato per il manifest e per la struttura dei segmenti. Si arriva così alla definizione dello standard MPEG-DASH con le proprie euristiche di adattamento.
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Ruthberg, Richard, and Steven Zhao. "Interest Rate Parity and Monetary Integration: A Cointegration Analysis of Sweden and the EMU." Thesis, KTH, Matematik (Inst.), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-146277.
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This thesis provides a thorough analysis of the covered- and uncovered interest parity conditions (CIP, UIP) as well as the forward rate unbiasedness hypothesis (FRUH) for Sweden and the European Economic and Monetary Union (EMU). By studying data on interbank rates in Sweden (STIBOR) and the EMU (EURIBOR) as well as the corresponding spot- and forward exchange rates, monetary integration and country-specific risks are determined and analyzed with direct applications to the potential entry of Sweden into the EMU. As interest rate parity in general gives insight into market efficiency and frictions between the chosen regions, such points are discussed in addition to EMU entry. Drawing on past studies that mainly studied one condition in isolation, a nested formulation of interest rate parity is instead derived and tested using cointegration and robust estimation methods. The results point to a strict rejection of the FRUH for all horizons except the shortest and a case where CIP only holds for the 6-month horizon and partially over one year. This implies, based on the nested formulation, that UIP is rejected for all horizons as well. Ultimately, the study concludes that a Swedish entry into the EMU is not motivated given the lackluster results on UIP and due to the lack of monetary integration.Den här uppsatsen presenterar en djupgående analys av det kurssäkrade- och icke-kurssäkrade ränteparitetsvillkoret samt den effektiva marknadshypotesen på valutaterminer för Sverige och den europeiska ekonomiska och monetära unionen (EMU). Genom att studera data på interbankräntor i Sverige (STIBOR) och EMU (EURIBOR) samt respektive spot- och valutaterminskurser så skattas och analyseras monetär integration samt landsspecifika risker med en direkt tillämpning på Sveriges eventuella inträde i EMU. Eftersom ränteparitet generellt ger insikt i marknadseffektivitet och friktioner regioner emellan, diskuteras även dessa punkter utöver ett eventuellt EMU-inträde. Genom att bygga på föregående studier som i huvudsak studerar ränteparitetsvillkoren var för sig, härleds en sekventiell formulering av villkoren som sedan testas med kointegration och robusta estimeringsmetoder. Resultaten ger att den effektiva marknadshypotesen strikt förkastas på alla tidshorisonter förutom på en dag respektive en vecka, samt att kurssäkrad ränteparitet håller på 6 och delvis 12 månaders sikt. Baserat på den sekventiella formuleringen så innebär detta att icke-kurssäkrad ränteparitet inte håller på någon tidshorisont. Slutligen, baserat på både resultat och diskussion, är ett svenskt inträde i EMU inte motiverbart givet negativa resultat för icke-kurssäkrad ränteparitet och avsaknaden av fullständig monetär integration mellan regionerna.
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Levy, Yariv Z. "Multiscale modeling of human addiction: A computational hypothesis for allostasis and healing." 2013. https://scholarworks.umass.edu/dissertations/AAI3556264.
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This dissertation presents a computational multiscale framework for predicting behavioral tendencies related to human addiction. The research encompasses three main contributions. The first contribution presents a formal, heuristic, and exploratory framework to conduct interdisciplinary investigations about the neuropsychological, cognitive, behavioral, and recovery constituents of addiction. The second contribution proposes a computational framework to account for real-life recoveries that are not dependent on pharmaceutical, clinical, and counseling support. This exploration relies upon a combination of current biological beliefs together with unorthodox rehabilitation practices, such as meditation, and proposes a conjecture regarding possible cognitive mechanisms involved in the recovery process. Further elaboration of this investigation leads on to the third contribution, which introduces a computational hypothesis for exploring the allostatic theory of addiction. A person engaging in drug consumption is likely to encounter mood deterioration and eventually to suffer the loss of a reasonable functional state (e.g., experience depression). The allostatic theory describes how the consumption of abusive substances modifies the brain's reward system by means of two mechanisms which aim to viably maintain the functional state of an addict. The first mechanism is initiated in the reward system itself, whereas the second might originate in the endocrine system or elsewhere. The proposed computational hypothesis indicates that the first mechanism can explain the functional stabilization of the addict, whereas the second mechanism is a candidate for a source of possible recovery. The formal arguments presented in this dissertation are illustrated by simulations which delineate archetypal patterns of human behavior toward drug consumption: escalation of use and influence of conventional and alternative rehabilitation treatments. Results obtained from this computational framework encourage an integrative approach to drug rehabilitation therapies which combine conventional therapies with alternative practices to achieve higher rates of consumption cessation and lower rates of relapse.
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Khodja, Abdellah. "Investigations of transport phenomena and dynamical relaxation in closed quantum systems." Doctoral thesis, 2015. https://repositorium.ub.uni-osnabrueck.de/handle/urn:nbn:de:gbv:700-2015031713128.
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The first part of the present Phd thesis is devoted to transport investigations in disordered quantum systems. We aim at quantitatively determining transport parameters like conductivity, mean
free path, etc., for simple models of spatially disordered and/or percolated quantum systems in the limit of
high temperatures and low fillings using linear response theory. We find the transport behavior for some models to be in accord with a Boltzmann equation, i.e., long mean free paths, exponentially decaying currents although there are no band-structures to start from, while this does not apply to other models even though they are also almost completely delocalized. The second part of the present PhD thesis addresses the issue of initial state independence (ISI) in closed quantum system. The relevance of the eigenstate thermalization hypothesis (ETH) for the emergence of ISI equilibration is to some extent addressed. To this end, we investigate the Heisenberg spin-ladder and check the validity of the ETH for the energy difference operator by examining the scaling behavior of the corresponding ETH-fluctuations, which we compute using an innovative numerical method based on typicality related arguments. While, the ETH turns out to hold for the generic non-integrable models and may therefore serve as the key mechanism for ISI for this cases, it does not hold for the integrable Heisenberg-chain. However, close analysis on the dynamic of substantially out-of-equilibrium initial states indicates the occurrence of ISI equillibration in the thermodynamic limit regardless of whether the ETH is violated. Thus, we introduce a new parameter $v$, which we propose as an alternative of the ETH to indicate ISI equillibration in cases, in which the ETH does not strictly apply.
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Aires, Matilde Proença. "Dynamic delivery pricing model applied to two-sample hypothesis testing." Master's thesis, 2019. https://hdl.handle.net/10216/122853.
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Wang, Chia-Ching, and 汪家慶. "Developing a Dynamic QoS Prediction via Hypothesis Testing and Collaborative Filtering." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/ex9x34.
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碩士國立交通大學
資訊科學與工程研究所
104
During development of service-based systems (SBS), the quality of services (QoS) plays an important role at helping select more suitable services, based on QoS values. There are several QoS prediction approaches proposed; however, in an open and dynamic network environment, QoS values cannot be predicted accurately because the collected or derived QoS values may not indicate the realistic software quality. The inaccuracy caused by the deviation of QoS values cannot provide users an effective way to select services. In this thesis, we propose a framework to dynamic QoS Prediction via Hypothesis Testing and Collaborative Filtering. Using Hypothesis Testing is to remove deviation value and to improve accuracy of QoS prediction. The experimental results indicate that our approach has higher prediction accuracy than other methods.
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Seetharam, Yudhvir. "The dynamics of market efficiency: testing the adaptive market hypothesis in South Africa." Thesis, 2016. http://hdl.handle.net/10539/21982.
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A thesis submitted to the School of Economic and Business Sciences, Faculty of Commerce,
Law and Management, University of the Witwatersrand in fulfilment of the requirements for
the degree of Doctor of Philosophy (Ph/D).
Johannesburg, South Africa
June 2016In recent years, the debate on market efficiency has shifted to providing alternate forms of the hypothesis, some of which are testable and can be proven false. This thesis examines one such alternative, the Adaptive Market Hypothesis (AMH), with a focus on providing a framework for testing the dynamic (cyclical) notion of market efficiency using South African equity data (44 shares and six indices) over the period 1997 to 2014. By application of this framework, stylised facts emerged. First, the examination of market efficiency is dependent on the frequency of data. If one were to only use a single frequency of data, one might obtain conflicting conclusions. Second, by binning data into smaller sub-samples, one can obtain a pattern of whether the equity market is efficient or not. In other words, one might get a conclusion of, say, randomess, over the entire sample period of daily data, but there may be pockets of non-randomness with the daily data. Third, by running a variety of tests, one provides robustness to the results. This is a somewhat debateable issue as one could either run a variety of tests (each being an improvement over the other) or argue the theoretical merits of each test befoe selecting the more appropriate one. Fourth, analysis according to industries also adds to the result of efficiency, if markets have high concentration sectors (such as the JSE), one might be tempted to conclude that the entire JSE exhibits, say, randomness, where it could be driven by the resources sector as opposed to any other sector. Last, the use of neural networks as approximators is of benefit when examining data with less than ideal sample sizes. Examining five frequencies of data, 86% of the shares and indices exhibited a random walk under daily data, 78% under weekly data, 56% under monthly data, 22% under quarterly data and 24% under semi-annual data. The results over the entire sample period and non-overlapping sub-samples showed that this model's accuracy varied over time. Coupled with the results of the trading strategies, one can conclude that the nature of market efficiency in South Africa can be seen as time dependent, in line with the implication of the AMH.
MT2017
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Kim, Won Dae. "Handedness, limb selection, and reach control: a test of the dynamic dominance hypothesis." 2008. http://hdl.handle.net/1969.1/ETD-TAMU-3183.
Full textAbstract:
This study examined the generalization of the Dynamic Dominance Hypothesis (DDH) in regard to limb dominance, limb selection, and limb action. This study was inspired by the finding that limb selection changes from dominant-arm to nondominant-arm occur around an object position of 80° for right-handers and 100° for left-handers after passing the body midline (90°) into contralateral hemispace.
For Study 1 and Study 2, 10 right-handed and 10 left-handed adults participated and reaching with the right and left arms of right- and left-handers was made to each of nine targets using free-choice and forced-choice paradigms. The purpose of Study 1 was to determine the relationship between limb selection and the DDH among both handedness groups. Thus, Study 1 addressed the following questions: Can the DDH explain why people select their nondominant hand for reaching into their contalateral hemispace? Do predictions of the DDH hold for right- and left-handers? Our results suggest that control efficiency with regard to a reduction in degrees of freedom in reaching movements seems to be a more fundamental cause for the limb selection phenomenon rather than the DDH. Also, our data reveal that kinematic differences between right- and left-handers with regard to utilization of joints for reaching explain limb selection differences between both handedness groups. The aim of Study 2 was to extend generalization of the DDH using a wide range of movement speed. Thus, Study 2 addressed the following question: Do propositions of the DDH hold for a wide range of speeds? Our data indicate the DDH does not hold for either slow or fast speed in reaching movements. Rather, a change in kinematics with regard to utilization of joints in reaching movements is associated with movement speed.
Considered together, our data indicate that the DDH is an inadequate explanation of differences in limb selection, limb dominance (handedness), and limb action (speed). Rather, our findings with regard to control efficiency seem to be more fundamental and justified explanations for limb differences in the control of reaching based on the context of our task.
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Blake, Adam J. "The effects of soil and plant nutrients on the oviposition preference, larval performance and spatial dynamics of Ceutorhynchus obstrictus and its parasitoids." Master's thesis, 2010. http://hdl.handle.net/10048/1549.
Full textAbstract:
The effects of nitrogen and sulfur fertilization on the oviposition, feeding preferences, and larval performance of Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae) on Brassica napus L. were examined in a series of laboratory experiments. The associations between C. obstrictus adults, larvae and parasitoids, and environmental factors including plant vigor indicators and soil and plant nutrients were evaluated within two commercial fields of B. napus in southern Alberta. Nitrogen fertilization, and sulfur fertilization at low levels of nitrogen fertilization had positive effects on oviposition preference. Nitrogen had a positive effect on larval development times and no effect on larval weights. Within one field, gravid C. obstrictus females were dissociated with high levels of plant nutrients including nitrogen. The synthesis of the lab and field experiments seems to support the plant stress and the preference-performance hypotheses. Differences in olfactory and visual cues are identified as a possible mechanism for the observed differences.Ecology
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Larter, Nicholas C. "Plant-herbivore dynamics associated with an erupting ungulate population : a test of hypotheses." Thesis, 1994. http://hdl.handle.net/2429/7089.
Full textAbstract:
This study tests some of the predictions made by two competing hypotheses of plant
community and herbivore dynamics: the equilibrium hypothesis, both the original four-stage
model proposed by Riney (1964) and Caughley (1970a), and the two-stage model proposed
by Sinclair (1979) and Houston (1982), and the facilitation and feedback hypothesis
(McNaughton, 1979). This is one of the rare occasions where these predictions have been
tested on an erupting indigenous herbivore population subjected to predation; the
Mackenzie wood bison (Bison bison athabciscae) population which was reintroduced in
1963. Recently the population split into two subpopulations: the Mackenzie Bison
Sanctuary (MB S) which is stabilizing, and the Mink Lake (ML) which is increasing. The
aims of this study were to determine 1) if the plant community dynamics were consistent
with either of the hypotheses, 2) if herbivore dynamics and demographics were consistent
with either of the hypotheses, and 3) the impact of predation on the system.
Net primary production of sedges and grasses in areas of willow savannas that were
excluded from grazing was similar in MBS and ML, but the standing crop in areas not
excluded from grazing was consistently lower in MBS than ML. This difference appears
to be a direct result of different grazing pressures. Species composition of willow savannas
in MBS had more unpalatable and less preferred species than savannas in ML. These
results were consistent with the predictions and assumptions of both models of the
equilibrium hypothesis but not the facilitation and feedback hypothesis. Forage quality was
not different between MBS and ML with the possible exception of higher levels of some
cations found in forages growing in MBS.
The two subpopulations appear to be distinct and are at different stages of eruptive
oscillation. The demographic characteristics of these subpopulations agree with the
predictions of the four-stage model of the equilibrium hypothesis: the MBS subpopulation
experienced a negative instantaneous growth rate (r), animals in ML had significantly
(p
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Hersh, Michelle Heather. "The Role of Seedling Pathogens in Temperate Forest Dynamics." Diss., 2009. http://hdl.handle.net/10161/1357.
Full textAbstract:
Fungal pathogens likely play an important role in regulating populations of tree seedlings and preserving forest diversity, due to their ubiquitous presence and differential effects on survival. Host-specific mortality from natural enemies is one of the most widely tested hypotheses in community ecology to explain the high biodiversity of forests. The effects of fungal pathogens on seedling survival are usually discussed under the framework of the Janzen-Connell (JC) hypothesis, which posits that seedlings are more likely to survive when dispersed far from the parent tree or at low densities due to pressure from host-specific pathogens (Janzen 1970, Connell 1971). One of the key challenges to assessing the importance of JC effects has been to identify and quantify the effects of the large numbers of potential pathogens required to maintain host diversity. The primary objectives of this research were to (1) characterize the fungi associated with seedling disease and mortality for a number of important southeastern US forest tree species; and (2) determine if these associations are consistent with the Janzen-Connell hypothesis in terms of differential effects on seedling survival.
Culture-based methods and ribosomal DNA (rDNA) sequencing were used to characterize the fungal community in recently dead and live seedlings of thirteen common tree species in a temperate mixed hardwood forest (North Carolina, USA), with the goal of identifying putative seedling pathogens. Cultures were initially classified and grouped into 130 operational taxonomic units (OTUs) using 96% internal transcribed spacer (ITS) sequence similarity; 46% of all OTUs were found only once. Using rarefaction, it was concluded that the richness of the system was not fully sampled and likely included over 200 taxa (based on non-parametric richness estimators). Species richness did not differ between sampling sites or among the five most common hosts sampled. The large ribosomal subunit (LSU) region of rDNA was then sequenced for representative samples of common OTUs and refined identifications using a constrained maximum likelihood phylogenetic analysis. Phylogenetic placement verified strong BLAST classifications, and allowed for placement of unknown taxa to the order level, with many of these unknowns placed in the Leotiomycetes and Xylariales (Sordariomycetes).
Next, a hierarchical Bayesian model was developed to predict the effects of multiple putative fungal pathogens on individual seedling survival, without forcing the effects of multiple fungi to be additive. The process of disease was partitioned into a chain of events including incidence, infection, detection, and survival, and conditional probabilities were used to quantify each component individually, but in the context of one another. The use of this modeling approach was illustrated by examining the effects of two putative fungal pathogens,
Finally, the model was used to assess the impacts of these fungi on seedling survival, alone and in combination, using data on five potential fungal pathogens and five hosts. Multi-host fungi had differential effects on seedling survival depending on host identity, and multiple infections may impact survival even when single infections do not. Evaluating these interactions among multiple plant and fungal species generates a set of targeted hypotheses of specific plant-fungal combinations that could help us better understand pathogen-driven diversity maintenance at larger scales than previously possible. Building on these results, some recommendations are provided as to how the Janzen-Connell hypothesis can be re-evaluated with respect to host specificity, pathogen distribution, and environmental context.
Dissertation
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Benduhn, François [Verfasser]. "Implications of aerosol growth dynamics and aerosol-cloud interaction to the sun-cloud-climate hypothesis / vorgelegt von François Benduhn." 2008. http://d-nb.info/990526925/34.
Full text
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Alizamir, Saed. "Essays on Optimal Control of Dynamic Systems with Learning." Diss., 2013. http://hdl.handle.net/10161/8066.
Full textAbstract:
This dissertation studies the optimal control of two different dynamic systems with learning: (i) diagnostic service systems, and (ii) green incentive policy design. In both cases, analytical models have been developed to improve our understanding of the system, and managerial insights are gained on its optimal management.
We first consider a diagnostic service system in a queueing framework, where the service is in the form of sequential hypothesis testing. The agent should dynamically weigh the benefit of performing an additional test on the current task to improve the accuracy of her judgment against the incurred delay cost for the accumulated workload. We analyze the accuracy/congestion tradeoff in this setting and fully characterize the structure of the optimal policy. Further, we allow for admission control (dismissing tasks from the queue without processing) in the system, and derive its implications on the structure of the optimal policy and system's performance.
We then study Feed-in-Tariff (FIT) policies, which are incentive mechanisms by governments to promote renewable energy technologies. We focus on two key network externalities that govern the evolution of a new technology in the market over time: (i) technological learning, and (ii) social learning. By developing an intertemporal model that captures these dynamics, we investigate how lawmakers should leverage on such effects to make FIT policies more efficient. We contrast our findings against the current practice of FIT-implementing jurisdictions, and also determine how the FIT regimes should depend on specific technology and market characteristics.
Dissertation
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Weinert, Friedel. "Leibniz’s Defence of Heliocentrism." 2017. http://hdl.handle.net/10454/11760.
Full textAbstract:
yesThis paper discusses Leibniz’s view and defence of heliocentrism, which was one of the main achievements of the Scientific Revolution (1543-1687). As Leibniz was a defender of a strictly mechanistic worldview, it seems natural to assume that he accepted Copernican heliocentrism and its completion by figures like Kepler, Descartes and Newton without reservation. However, the fact that Leibniz speaks of the Copernican theory as a hypothesis (or plausible assumption) suggests that he had several reservations regarding heliocentrism. On a first approach Leibniz employed two of his most cherished principles to defend the Copernican hypothesis against the proponents of geocentrism: these were the principle of the relativity of motion and the principle of the equivalence of hypotheses. A closer analysis reveals, however, that Leibniz also appeals to dynamic causes of planetary motions, and these constitute a much stronger support for heliocentrism than his two philosophical principles alone.
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Hladík, Jan. "Inherentní nestabilita finančních trhů." Master's thesis, 2016. http://www.nusl.cz/ntk/nusl-352721.
Full textAbstract:
The main aim of this presented diploma thesis is to help build a systematic understanding of the political and social foundations of global financial markets, their operations and impacts on the global power affairs. The thesis highlights the dynamic complexity of the post financial crisis state of the World with its itra- and inter-social features. It instrumentaly uses critique of a free market agenda and neo-classical economy which contrasts the Efficient Markets Hypothesis with Hyman Minsky's Financial Instability Hypothesis (FIH), taking into account the dynamic complexity of financial markets. This approach offers analytical tools that can account for crisis through processes endogenous to contemporary financial capitalism. I shall argue that a financially complex system is, according to the FIH, inherently flawed and unstable. After a theoretical and historical review, the thesis discusses various aspects of the process of austerity regime and its social consequences. This provides an opportunity for analyses of the ongoing existence of interstate competition, of militarised foreign policy, and of other international, at times violent conflicts. In an effort to make sense of some of these phenomena, I instrumentaly use the study of geoeconomics that builds on some fundamental assumptions...
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"Development, growth and ultrastructure of the floral nectar spur of Centranthus ruber (L.) DC (Valerianaceae)." Thesis, 2013. http://hdl.handle.net/10388/ETD-2013-07-1117.
Full textAbstract:
The main objective of this research project was to study the growth and development of the floral nectar spur of Centranthus ruber (L.) DC. Nectar spurs are tubular floral outgrowths, generally derived from the perianth organs, which typically contain secreted floral nectar. The morphological characteristics of the spur, particularly the length, determine which floral visitors will be able to access the nectar reward pooled at the spur tip. Therefore, nectar spurs are ecologically important for the development of specialised pollinator interactions and have been demonstrated to act as key innovations in the evolution of some taxa.
Morphological and anatomical characteristics of the spur and floral nectary were investigated using light and scanning electron microscopy. Ultrastructural features of the nectar spur, particularly the floral nectary within, were assessed using transmission electron microscopy. Nectar in C. ruber is produced by a trichomatous nectary which runs along the entire, inner abaxial surface of the spur. The nectary is aligned with the single vascular bundle which runs along the abaxial side of the spur, through the sub-nectary parenchyma, and back up the adaxial side. The secretory trichomes are unicellular and, in late development, they develop a thick layer of secondary wall ingrowths which vastly increases the surface area of the plasma membrane for nectar secretion. Elongate, non-secretory trichomes occupy the entire remaining circumference of the spur’s inner epidermis, but their density is reduced compared to the secretory trichomes.
The cellular basis for spur growth is poorly characterized in the literature. Until recently, it was assumed that all nectar spurs grow by the constant production of new cells via up to three potential meristematic regions (the meristem hypothesis, Tepfer 1953). The cellular basis for spur growth in C. ruber was investigated by cell file counts and cell length and width measurements along the lateral side of nectar spurs in each of the developmental stages. DAPI stained spurs were also examined with Confocal/Apotome microscopy to determine the timing and position of cell division activity throughout spur development. It was determined that elongation of the spur epidermal cells contributes much more to spur growth than cell division. In early development, division is the primary driver of spur growth and the cells are isotropic. However, as development progresses, cell division activity slows down and the spur cells become increasingly anisotropic until anthesis.
The patterns of nectar secretion were determined by assessing the volume, solute concentration and carbohydrate composition of the nectar throughout flowering phenology in two C. ruber plants. Nectar volumes and solute amounts rose initially, followed by an eventual decline in both as phenology progressed towards senescence. Because this study was conducted on greenhouse grown plants, it can be assumed that nectar was not removed by insects, suggesting that it is likely reabsorbed following secretion. High performance liquid chromatography (HPLC) analysis determined that C. ruber's nectar is sucrose dominant and that nectar composition remains stable following anthesis throughout floral phenology.
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TVARDÍKOVÁ, Kateřina. "Jak ptáci poznávají predátory - význam úplnosti vizuální informace." Master's thesis, 2009. http://www.nusl.cz/ntk/nusl-51165.
Full textAbstract:
Pair-wise preferential experiments were used to reveal dangerous predator differentiation and ability of amodal completion by four tit species. Firstly was revealed that the tits{\crq} behaviour towards the feeder was in agreement with predictions of the dynamic risk assessment theory. The presence of any predator at the feeder lowered the number of visits to the feeder. Likewise, the tits evaluated the sparrowhawk as more dangerous than the kestrel because its presence lowered the number of visits more than the kestrel. Secondly, we observed tits{\crq} reactions to both partly occluded and amputated dummy of sparrowhawk in two different treatments (torsos vs. complete dummy of pigeon, torsos vs. complete dummy of sparrowhawk). All birds clearly classified both torsos as ``full-featured{\crqq} predators and kept away of them when pigeon on the second feeder. However, when sparrowhawk was presented on the second feeder, number of visits to amputated predator was higher than to occluded one. Birds risked arriving to ``utter{\crqq} amputated torso while the fear of ``full-featured{\crqq} occluded torso stayed without change when second feeder did not provide safe alternative. Such discrimination between torsos needs ability of amodal completion.