Made available in DSpace on 2015-03-26T13:42:27Z (GMT). No. of bitstreams: 1 texto completo.pdf: 3965956 bytes, checksum: 7ee9799f71d65ccd8dd579d596629d39 (MD5) Previous issue date: 2012-07-23 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Karyological analysis of Geophagus brasiliensis (Quoy and Gaimard, 1824) was performed on 81 specimens from six localities, three geologically recent lakes and three stream collection sites. Techniques included conventional staining with Giemsa, NOR banding, C-banding and in situ hybridization (FISH) with 5S rDNA and 18s rDNA probes. The diploid number was 2n = 48 chromosomes, and fundamental number varied between 50-52. We observed four different karyotypes, based on heteromorphisms presented by the first chromosome pair and were not related to sex, NOR location or collection site. This heteromorphism is related to differences in the ratio arms, which led to variations in the karyotypic formulae (3sm +18 st +26 t; 2sm +20 st +26 t; 4sm +18 st +26 t). This heteromorphism may be related to chromosome rearrangements, such as pericentromeric inversions, deletions, and unequal crossing-over, which together with other processes, such as Muller s ratchet, background selection and dosage compensation caused size alterations in some chromosomes. The number of NORs varied within and between specimens, however most individuals had NOR bands in more than one chromosome pair, a distinctive feature of the Doce River populations. The 18S rDNA probe confirmed the presence of NORs in more than two chromosomes. The location of the 5S rDNA probe remained conserved in all samples, marking a pair of chromosomes. The heterochromatin blocks occurred predominantly in the centromeric / pericentromeric chromosomes, and this a characteristic of the Cichlidae family. Heterochromatin blocks in interstitial regions were observed in two pairs of chromosomes. The presence of two subtelocentric chromosomes, with fully heterochromatic small arms is a diagnostic feature of the populations of the Doce River Basin. We conclude that the populations of G. brasiliensis of the Rio Doce Basin present unique characteristics, as evidenced by four configurations of the first pair of chromosomes and different results obtained by banding techniques. Results suggest differential viability of the chromosomal variations described in this study. / A análise cariotípica de Geophagus brasiliensis (Quoy & Gaimard, 1824) foi realizada em 81 espécimes de seis localidades da bacia do rio Doce. Foram usadas as técnicas de coloração convencional com Giemsa, bandeamento NORs, bandeamento C e hibridização in situ (FISH) com sondas rDNA 18s e rDNA 5S. O número diplóide foi de 2n=48 cromossomos, com variação do número fundamental entre 50-52. Foram observados quatro diferentes cariótipos, com base em heteromorfismos apresentados pelo primeiro par cromossômico e não foram associados ao sexo, à NOR nem ao local de coleta. Esse heteromorfismo está relacionado com diferenças de razão de braços, o que acarretou variações nas fórmulas cariotípicas encontradas (3sm+18st+26t; 2sm+20st+26t; 4sm+18st+26t). Este heteromorfismo pode estar relacionado com rearranjos cromossômicos, como inversões pericentroméricas, deleções, e crossing-over desiguais, as quais, associadas a outros processos, como catraca de Muller, seleção de fundo e compensação de dosagem, determinaram a alteração do tamanho de alguns cromossomos. O número de NORs observadas teve variações intra e inter-individuais, contudo a maioria dos indivíduos apresentou marcações em mais de um par cromossômico, uma característica única das populações de G. brasiliensis da bacia do rio Doce. A sonda de rDNA 18S confirmou a presença de NORs em mais de dois cromossomos. A localização da sonda de rDNA 5S manteve-se conservada em todas as amostras, marcando par de cromossomos telocêntricos. Os blocos de heterocromatina ocorreram predominantemente nas regiões centroméricas/pericentromérica, sendo essa uma característica da família Cichlidae. Blocos de heterocromatina em regiões intersticiais foram observados em dois pares de cromossomos. A presença de dois subtelocêntricos apresentando seus braços menores totalmente heterocromáticos é uma característica diagnóstica das populações da bacia do rio Doce. Conclui-se que as populações de G. brasiliensis da bacia do rio Doce apresentam A análise cariotípica de Geophagus brasiliensis (Quoy & Gaimard, 1824) foi realizada em 81 espécimes de seis localidades da bacia do rio Doce. Foram usadas as técnicas de coloração convencional com Giemsa, bandeamento NORs, bandeamento C e hibridização in situ (FISH) com sondas rDNA 18s e rDNA 5S. O número diplóide foi de 2n=48 cromossomos, com variação do número fundamental entre 50-52. Foram observados quatro diferentes cariótipos, com base em heteromorfismos apresentados pelo primeiro par cromossômico e não foram associados ao sexo, à NOR nem ao local de coleta. Esse heteromorfismo está relacionado com diferenças de razão de braços, o que acarretou variações nas fórmulas cariotípicas encontradas (3sm+18st+26t; 2sm+20st+26t; 4sm+18st+26t). Este heteromorfismo pode estar relacionado com rearranjos cromossômicos, como inversões pericentroméricas, deleções, e crossing-over desiguais, as quais, associadas a outros processos, como catraca de Muller, seleção de fundo e compensação de dosagem, determinaram a alteração do tamanho de alguns cromossomos. O número de NORs observadas teve variações intra e inter-individuais, contudo a maioria dos indivíduos apresentou marcações em mais de um par cromossômico, uma característica única das populações de G. brasiliensis da bacia do rio Doce. A sonda de rDNA 18S confirmou a presença de NORs em mais de dois cromossomos. A localização da sonda de rDNA 5S manteve-se conservada em todas as amostras, marcando par de cromossomos telocêntricos. Os blocos de heterocromatina ocorreram predominantemente nas regiões centroméricas / pericentromérica, sendo essa uma característica da família Cichlidae. Blocos de heterocromatina em regiões intersticiais foram observados em dois pares de cromossomos. A presença de dois subtelocêntricos apresentando seus braços menores totalmente heterocromáticos é uma característica diagnóstica das populações da bacia do rio Doce. Conclui-se que as populações de G. brasiliensis da bacia do rio Doce apresentam características únicas, associadas à existência de quatro configurações do primeiro par cromossômico e aos diferentes resultados obtidas nas técnicas de bandeamento realizadas. Os resultados também sugerem uma viabilidade diferenciada das variáveis cromossômicas descritas nesse trabalho.

Submitted by (ana.araujo@ufrpe.br) on 2016-07-07T12:58:08Z No. of bitstreams: 1 Juliana Katia da Silva.pdf: 2299995 bytes, checksum: 786d6f38a091474c4b7f97d00ef069a9 (MD5) / Made available in DSpace on 2016-07-07T12:58:08Z (GMT). No. of bitstreams: 1 Juliana Katia da Silva.pdf: 2299995 bytes, checksum: 786d6f38a091474c4b7f97d00ef069a9 (MD5) Previous issue date: 2009-02-16 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The understanding of the central mechanisms favouring sex and recombination in real populations is one of the fundamental issues in evolutionary biology. Based on a previous stochastic formulation to the study of sex, here we aim to investigate the conditions under which epistasis favours the fixation of the sexual mode of reproduction in a given population. Besides, we try to identify the evolutionary forces which contribute to this process. Our model considers a finite population model which assumes the existence of a recombination modifier allele which can activate the recombination mechanism. We have found that sex is very little favoured in a scenario of antagonistic epistasis, and this advantage only takes place in a narrow range of values of the selection coefficient, sd. On the other hand, synergistic epistasis favours recombination in a very broad domain. However, the major mechanism contributing to the spreading of the modifier allele depends on the range of values of sd. At large sd background selection favours recombination since it increases the efficacy of selection, while at low sd Muller’s ratchet is the leading mechanism. / O entendimento dos mecanismos centrais que favorecem o sexo e a recombinação nas populações é um das questões fundamentais, e que ainda se encontra indefinida, na Biologia Evolucionária. Diversos modelos e teorias têm sido propostos de forma a melhor compreender a predominância do sexo e recombinação na natureza. Uma teoria de sucesso deve ser capaz de mostrar que existem mecanismos que contrabalanceiem os custos imediatos associados à reprodução sexuada. Aqui nesta dissertação de mestrado fazemos uma extensão de um modelo estocástico para o estudo do sexo, de forma agora a verificarmos em que condições a epistasia (interação entre genes) favorece a fixação do modo de reprodução sexuado, e que mecanismos evolucionários contribuem para isto. Consideramos um modelo de população finita que assume a existência de um alelo modificador de recombinação que é então inserido em uma população inicialmente assexuada. O destino desse alelo é então analisado. Verificamos que o sexo é pouco favorecido quando consideramos o relevo com epistasia antagonística, tornando-se vantajoso em um pequeno intervalo de valores do parâmetro seletivo sd. Já no caso da epistasia sinergística, observamos uma grande vantagem para a recombinação em duas regiões distintas: uma para pequenos valores de sd, e neste caso é a Catraca de Muller o mecanismo responsável pela vantagem; e na segunda região para grandes valores de sd, o mecanismo responsável é o efeito Hill-Robertson, em que a recombinação atua de forma a aumentar a eficácia da seleção purificadora.

Submitted by (ana.araujo@ufrpe.br) on 2016-08-09T13:23:57Z No. of bitstreams: 1 Oscar Felipe Falcao Raposo.pdf: 947805 bytes, checksum: 8fe5720f628d5178eea9572acc985b50 (MD5) / Made available in DSpace on 2016-08-09T13:23:57Z (GMT). No. of bitstreams: 1 Oscar Felipe Falcao Raposo.pdf: 947805 bytes, checksum: 8fe5720f628d5178eea9572acc985b50 (MD5) Previous issue date: 2006-10-24 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / We investigate the evolution of asexual populations subject to a large supply of deleterious mutations such that Muller’s ratchet operates. In this regime, the accumulation of deleterious mutations takes place continuously with the resulting loss of the least-loaded class of individuals. In the current work, we study the effect of the supply of beneficial mutations on the ratchet’s speed. We also examine how the rate of substitution of favorable mutations as well as the mean selective effect of favorable mutations that reach fixation is compared to those assuming a population at equilibrium. We observe that under Muller’s ratchet, the rate of fixation of advantageous mutations is higher than that predicted for an equilibrium population. The difference between the rate supposing an equilibrium regime and that for the non-equilibrium case becomes larger as we increase the rate of deleterious mutations. On the other hand, the mean selective effect of beneficial mutations that reach fixation is smaller than the expected value for the equilibrium situation. / Nós investigamos a evolução das populações assexuadas sujeita à ocorrência de um fluxo contínuo de mutações deletérias, onde a Catraca de Muller opera. Neste regime, a acumulação de mutações deletérias ocorre continuamente com a conseqüente perda da classe de indivíduos mais adaptados. Na nossa dissertação nós estudamos o efeito das mutações benéficas na velocidade da catraca. Nós examinamos como a taxa de substituição das mutações benéficas como também o efeito seletivo médio das mutações favoráveis que alcançam a fixação é comparada àquelas que supõem uma população em equilíbrio. Nós observamos que sob o regime de não-equilíbrio, a taxa de fixação das mutações vantajosas é mais elevada do que aquela estimada para uma população em equilíbrio. A diferença entre a taxa que supõe um regime de equilíbrio e aquela para um regime de não-equilíbrio torna-se maior quando aumentamos a taxa de mutações deletérias. Por outro lado, o efeito seletivo médio das mutações benéficas que alcançam a fixação é menor do que o valor previsto para a situação de equilíbrio.

<div>My dissertation consists of three chapters in the field of managerial economics and experimental economics. The first chapter studies the ratchet effect and the possible ways to mitigate it. Specifically, I conduct a controlled experiment to test the effectiveness of job rotation in eliminating the ratchet effect. Additionally, I compare effort provision between the situation where agents are rotated exogenously and the situation where the principal rotates agents endogenously. The experiment shows that the ratchet effect is effectively reduced both when workers are informed that they will be rotated in the future and when a principal has a costly option of rotating agents.</div><div> </div><div><br></div><div>The second and third chapter are based on joint work with Prof. Yaroslav Rosokha. In the second chapter, we study a single-queue system in which human servers have discretion over the effort with which to process orders that arrive stochastically. We show theoretically that the efficient outcome in the form of high effort can be sustained in the subgame perfect equilibrium if the interactions are long term (even when each server has a short-term incentive to free ride). In addition, we show that queue visibility plays an important role in the type of strategies that can sustain high-effort equilibrium. In particular, we show that limiting feedback about the current state of the queue is beneficial if servers are patient enough. We conduct a controlled lab experiment to test the theoretical predictions and find that when the queue is visible, human subjects cooperate if the queue is long, but defect if the queue is short. We also find that cooperation is hard to achieve when the queue is not visible. </div><div><br></div><div>In the third chapter, we report another lab experiment to test the theory developed in the second chapter. In the new experiment, we provide a more natural queueing frame for the subjects rather than the neutral language used in the second chapter. We also increase the number of matches in each treatment. We find that effort increases with the expected duration of the interaction. We also find that visibility has a strong impact on the strategies that human subjects use to provide effort. As a result, providing less visibility makes servers more willing to provide high effort if they are patient enough.</div>

No description available.

The research presented in this dissertation integrates data and theory to examine three important topics in biology. In the first chapter, I investigate genetic variation at two loci involved in a genetic incompatibility in the genus Xiphophorus. In this genus, hybrids develop a fatal melanoma due to the interaction of an oncogene and its repressor. Using the genetic variation data from each locus, I fit evolutionary models to test for coevolution between the oncogene and the repressor. The results of this study suggest that the evolutionary trajectory of a microsatellite element in the proximal promoter of the repressor locus is affected by the presence of the oncogene. This study significantly advances our understanding of how loci involved in both a genetic incompatibility and a genetically determined cancer evolve. Chapter two addresses the role polyploidy, or whole genome duplication, has played in generating flowering plant diversity. The question of whether polyploidy events facilitate diversification has received considerable attention among plant and evolutionary biologists. To address this question, I estimated the speciation and genome duplication rates for 60 genera of flowering plants. The results suggest that diploids, as opposed to polyploids, generate more species diversity. This study represents the broadest comparative analysis to date of the effect of polyploidy on flowering plant diversity. In the final chapter, I develop a computational method for designing disease surveillance networks. The method is a data-driven, geographic optimization of surveillance sites. Networks constructed using this method are predicted to significantly outperform existing networks, in terms of information quality, efficiency, and robustness. This work involved the coordinated efforts of researchers in biology, epidemiology, and operations research with public health decision makers. Together, the results of this dissertation demonstrate the utility of applying quantitative theory and statistical methods to data in order to address complex, biological processes. / text

The Signal protocol can be considered state-of-the-art when it comes to secure messaging, but advances in quantum computing stress the importance of finding post-quantum resistant alternatives to its asymmetric cryptographic primitives. The aim is to determine whether existing post-quantum cryptography can be used as a drop-in replacement for the public-key cryptography currently used in the Signal protocol and what the performance trade-offs may be. An implementation of the Signal protocol using commutative supersingular isogeny Diffie-Hellman (CSIDH) key exchange operations in place of elliptic-curve Diffie-Hellman (ECDH) is proposed. The benchmark results on a Samsung Galaxy Note 8 mobile device equipped with a 64-bit Samsung Exynos 9 (8895) octa-core CPU shows that it takes roughly 8 seconds to initialize a session using CSIDH-512 and over 40 seconds using CSIDH-1024, without platform specific optimization. To the best of our knowledge, the proposed implementation is the first post-quantum resistant Signal protocol implementation and the first evaluation of using CSIDH as a drop-in replacement for ECDH in a communication protocol.

A ratchet is an asymmetric, non-equilibrated system that can produce a directed current of particles without the need for macroscopic potential gradients. In rocked quantum electron ratchets, tunnelling and wave-reflection can induce reversals in the direction of the net current as a function of system parameters. An asymmetric quantum point contact in a GaAs/GaAlAs heterostructure has been studied experimentally as a realisation of a quantum electron ratchet. A Landauer model predicts reversals in the direction of the net current as a function of temperature, amplitude of the rocking voltage, and Fermi energy. Artifacts such as circuit-induced asymmetry, also known as self-gating, were carefully removed from the experimental data, which showed net current and net differential conductance reversals, as predicted by the model. The model also predicts the existence of a heat current where the net electron current changes sign, as equal numbers of high and low energy electrons are pumped in opposite directions. An idealised quantum electron ratchet is studied analytically as an energy selective electron heat engine and refrigerator. The hypothetical device considered consists of two electron reservoirs with different temperatures and Fermi energies. The reservoirs are linked via a resonant state in a quantum dot, which functions as an idealised energy filter for electrons. The efficiency of the device approaches the Carnot value when the energy transmitted by the filter is tuned to that where the Fermi distributions in the reservoirs are equal. The maximum power regime, where the filter transmits all electrons that contribute positively to the power, is also examined. Analytic expressions are obtained for the power and efficiency of the idealised device as both a heat engine and as a refrigerator in this regime of operation. The expressions depend on the ratio of the voltage to the difference in temperature of the reservoirs, and on the ratio of the reservoir temperatures. The energy selective electron heat engine is shown to be non-endoreversible, and to operate in an analogous manner to the three-level amplifier, a laser based quantum heat engine. Implications for improving the efficiency of thermionic refrigerators and power generators are discussed.

Financial intermediaries are recognized to promote the efficiency of resource allocation by mitigating problems of incentives, asymmetric information and contract incompleteness. The role played by financial intermediaries is perceived so crucial that these institutions have received all over the world the greatest attention of regulators. Differences in regulatory regimes as well as in the real economies have produced a large variety in the characteristics of financial sectors and of individual intermediaries. In particular, in different places and times it is possible to observe banking sectors more or less competitive, populated by credit intermediaries of different sizes and with different levels of specialization. This variety of institutions raises interesting questions about the features of a well functioning financial intermediation sector. These questions have inspired an important body of economic literature which, however, is still inconclusive in many aspects. This dissertation includes three studies all intending to contribute in this direction. Chapter 2 Recent empirical works have found evidence consistent with larger banks having lower incentives to collect soft information and, in particular, to lend to small firms which are typically regarded as relatively opaque borrowers. Another market segment affected by relatively high levels of opaqueness is that of long-term loans and the reason is that, as emphasized in the corporate finance literature, short-term maturities are useful for the purpose of screening and monitoring investment projects. It is therefore interesting to assess whether large and small banks differ in their propensity to issue long-term loans, a type of investigation which has not been conducted yet. The reason why small and large banks might be expected to have a different propensity to issue long-term loans has to do with two notions. First, the effectiveness of a short-term maturity as a screening and monitoring device is preserved only if parties anticipate that, when payments are due, the lender will not be willing to extend the maturity, otherwise the initial short-term loan is de facto a long-term one. The problem may rise if the liquidation of insolvent firms produces lower payoffs than their refinancing: under these circumstances, as suggested by theories on renegotiation, liquidation is not implemented no matter what is written on the contract (parties can easily avoid the inefficiency that would result from liquidation, for example by simply granting a new loan). Second, at a more specific level theories on renegotiation suggest that the ability to commit to not extend thematurity decreases with bank size.1 Small banks are therefore predicted to issue shorter-term loans and to make a better selection of projects. The results are consistent with this prediction. Controlling for other characteristics of both the demand- and the supply-side as well as for the type of guarantee supplied, small banks have lower proportions of long-term loans to total loans and lower proportions of non performing loans to total loans. It should be pointed out that this does not imply that small banks are necessarily more efficient since short-term maturities also have costs; in particular, short-term maturities can interfere with the incentives of good types by inducing short-termism (the inflation of shortterm results at the expenses of total profitability). Moreover, beyond the ability to commit other supply-side features are shown to be relevant in the determination of the maturity, at least with specific classes borrowers. In particular, the findings are also consistent with the presence of economies of scale in lending at long maturities to firms in more technical and innovative industries. Since providing the right incentives to high quality entrepreneurs and to firms in innovative sectors is more likely to be a priority in more advanced countries, a policy implication is that these economies need more the presence of large credit institutions and the more so if venture capital and stock market are of limited size. Chapter 3 As already emphasized, theories on renegotiation suggest that the ability of banks to commit to a given course of action is an important factor for efficiency and that such ability depends on observable characteristics, like bank size. An important aspect which has not been analyzed in the theoretical literature is the effect that competition among banks exert on their ability to commit. The theoretical model presented in chapter 3 tries to provide an answer to this question. More specifically, the model studies the effects of competition among banks when these are subject to dynamic commitment problems which may result in excess refinancing of insolvent borrowers (soft budget constraint) as well as in excess termination of profitable ones (ratchet effect and short-termism). The building assumption is that, because of priority schemes and relationship lending, competition is harsher for new lending than for lending to ongoing projects. The main conclusion is that there exists a trade-off between the benefits that competition brings by disciplining low quality borrowers and the costs implied by worsening the incentives of good ones. The model also allows to look at the effects of competition on stability. This is done in two ways by looking at the extent to which competition interferes with the procyclicality of the banking sector and by studying if competition may eliminate or add inefficient equilibria. The main policy implication is that the optimal level of competition of a banking system is positively related to the quality of the underlying economy. If taken together, the results of chapters 2 and 3 also provide a theory about local or regional banks which is not based on any aprioristic assumption about the technology of these type of intermediaries. As long as these institutions can be seen as banks with a relatively high market power and a relatively small size (they are often important players at a local level although of limited size), both chapters 2 and 3 suggest that these intermediaries can more easily commit to a tough stance at the refinancing stage, with positive effects on their ability to screen out bad projects but with negative effects on their ability to incentivize good types and to fund more technical and innovative firms. In other words, these institutions might promote growth at earlier stages of development, although they are not sufficient to address the incentive issues of more advanced economies. Interestingly, this interpretation of the role of local banks is totally distinct from the traditional one which is based on the aprioristic assumption that these banks are good in doing relationship lending. Chapter 4 Conflicts of interest of economic institutions carrying out a variety of functions are considered a widespread phenomenon severely limiting the efficiency that can be achieved. These worries are often taken as justification for regulations imposing transparency requirements or tougher measures like separation of functions. At the same time, contract theory suggests that the effects of opportunistic behavior can be limited by adopting appropriate incentive schemes. The third study, chapter 4, tries to understand from a theoretical point of view to what extent the use of incentive schemes can address the distortions posed by the presence of conflicts of interest. The universal bank is regarded as a (common) agent serving different clients with potentially conflicting interests: for example, it may buy assets on behalf of investors and sell assets on behalf of issuing firms. The clients offer incentive schemes to the bank and they behave non-cooperatively. The bank decides a level of effort and, when firewalls are absent, a level of collusion, modelled as a costly and unproductive redistribution of wealth among the clients (for example, the banks can at no cost sell the securities it is underwriting to the funds it manages and can do so at the price it likes). Firewalls are defined as all legal or economic devices imposing a real separation of functions and therefore preventing the bank from colluding as specified above. The main conclusion is that in the absence of firewalls the equilibrium incentive schemes are steeper. This means that the equilibrium level of effort is higher and may compensate the (ex post) inefficiency of collusion. In other words, not only appropriate incentive schemes can eliminate the distortions posed by conflicts of interest but, at least in principle, their presence may even be necessary for efficiency (this happens if effort is a public good for the two principals so that the allocation without firewalls is characterized by under-provision of effort). At the same time, the allocation without firewalls is shown to be the least efficient in the presence of one naive player who does not recognize the existence of the conflict of interest. As long as transparency requirements can be considered tools to improve market participants’ sophistication, these results suggest why and how this type of regulation can work. Moreover, the model allows to draw conclusions about the desirability of tougher regulation prescribing a more or less neat separation of functions. With sophisticated economic agents, who can address the distortions posed by conflicts of interest by choosing appropriate incentive schemes, separation of functions is unnecessary or even detrimental for efficiency. On the other hand, more or less powerful firewalls are desirable if market participants are not considered sufficiently sophisticated to be able to react to the presence of conflicts of interest and if transparency requirements cannot increase their sophistication. In few words, the optimal regulation of conflicts of interest is softer in situations involving professionals who are more likely to realize and to react by choosing an appropriate incentive scheme or, more generally, for institutions operating in advanced economies where the average level of market participants sophistication is higher.

Spatio-temporal control of the self-ordered structures by use of the time-dependent oscillatory fields of zero-time average, either deterministic (temporally regular) or noisy (temporally irregular) ones, has today become a fundamental field of multidisciplinary research in a wide variety of the highly nonlinear systems of the different physical origin. The self-ordered bistable fronts in the essentially dissipative systems of the reaction-diffusion type, that are formulated by parabolic partial differential equations, are investigated in the dissertation. The objective of the research is to investigate new possibilities of controlling the directed net motion of the self-ordered bistable fronts by the deterministic and stochastic zero-mean ac forces using computer modeling and analytic tools. In order to achieve the objective mathematical and numerical models were applied, computer software was created and new possibilities of controlling the directed net motion of bistable fronts by use of the zero-average periodic, quasi-periodic and bounded noise fields were investigated. / Savaime susidarančių lokalizuotų struktūrų valdymas deterministiškai (reguliariai) arba stochastiškai (atsitiktinai) osciliuojančiais laukais, kurių vidutinė vertė yra nulis, yra plačiai paplitęs įvairiose terpėse. Disertacijoje nagrinėjami savame susidarantys bistabilūs frontai disipatyviose sistemose, kurios aprašomos netiesinėmis parabolinėmis diferencialinėmis lygtimis su dalinėmis išvestinėmis. Disertacijos tikslas yra ištirti kryptingo bistabilių frontų dreifo valdymo nuliniais laukais galimybes, taikant kompiuterinį modeliavimą bei analitinius metodu. Tikslui pasiekti buvo sudaryti matematinis bei skaitinis modeliai, sukurta programinė įranga ir skaitiškai ištirtos savaiminių bistabilių frontų valdymo galimybės, naudojant periodinius, kvaziperiodinius ir stochastinius nulinius laukus.