To see the other types of publications on this topic, follow the link: Selection pressures.
Dissertations / Theses on the topic 'Selection pressures'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Selection pressures.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Nilsson, Annika. "Bacterial adaptation to novel selection pressures /." Stockholm, 2005. http://diss.kib.ki.se/2005/91-7140-192-X/.
Full text
2
Seemiller, Eric S. "Selective pressures influencing color-vision in Neotropical primates." Kent State University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=kent1309883439.
Full text
3
Ball, Colleen. "Understanding pathogen selection pressures at the within- and between-host levels." Thesis, University of British Columbia, 2006. http://hdl.handle.net/2429/57.
Full textAbstract:
Many infectious pathogens, and in particular viruses, have an
extremely high rate of mutation. This can lead to rapid evolution
driven by selection pressures operating at both the within- and
between-host levels, as strains compete for resources within their
chosen host while also competing to effectively transmit to new
hosts. In the case of chronic viral infections, such as the human
immunodeficiency virus (HIV) or hepatitis C, substantial viral
evolution may take place within a single infected host. The fitness
of a pathogen has been studied at the between-host level and at the
within-host level, but linking the two levels of selection pressure
is a difficult problem that has yet to be studied satisfactorily.
We modify a simple model describing the within host dynamics of HIV
infection by including multiple pathogen strains with different
properties and allowing these strains to mutate. Within the host we
observe different strategies for pathogen success during different
stages of infection, which often leads to different strains
predominating within the host over the course of infection. We then
embed our within-host model into a Monte Carlo simulation that
models the interactions between infected individuals. This approach
allows us to combine selective pressure at the within-host level
with pressures at the between-host level and helps us to predict
which strains are most likely to be present within the population.
We show that under our model assumptions the co-existence of
multiple strains is possible and we explore the factors leading to
the success of a pathogen.
4
Hoggarth, E. A. "Strategies and pressures in the selection process for community service orders." Thesis, Birmingham City University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305740.
Full text
5
Hatchett, William. "The road toward sympatric speciation in whitefish. : The effects of divergent selection on European whitefish (Coregonus lavaretus) size and behavior, and effects on zooplankton communities." Thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-110741.
Full textAbstract:
For almost every organism there are large gaps in our knowledge about the processes that leads to speciation. The changes an organism undergoes before divergence has occurred have remained a mystery, as it is difficult to say whether or not a species is going to diverge and when. To investigate this unknown the European whitefish (Coregonus lavaretus) and the northern pike (Esox lucius) were studied, as they produce a repeatable and predictable pattern of speciation in sympatry. To investigate the changes in phenotypes and behaviour in whitefish that precedes divergence, two lake populations were examined, Gräsvattnet and Ringsjön. Gräsvattnet was used as a control, with a population of whitefish but an absence of pike, whereas Ringsjön has a population of whitefish that invaded from Gräsvattnet and a pike population. The presence of pike presumably exerts divergent selection on the whitefish population. Fish and zooplankton were surveyed in both lakes from 1970 to the present day, which allows us to compare how whitefish populations and their resources change in the presence and absence of pike. The results found in Ringsjön show; (1) a change in habitat use, (2) a change in diet from pelagic to benthic, (3) an increase in the relationship between individual body size and diet and (4) a decrease in average size over the course of the study. (1)The presence of pike is believed to have forced the whitefish into the pelagic which could be seen in the result, with an increase in individuals caught in the pelagic. (2) The change in diet is thought to be caused by a resource competition created by individuals being forced to use the pelagic. Although insignificant this led to an overall reduction in zooplankton abundance by almost 40% which could have intensified competition. The resource competition could then have been intensified further by the change in composition of zooplankton relative abundance. (3) The increase in relationship between individual body size and diet is thought to increase due to the resource competition between smaller and larger individuals in the pelagic. Smaller individuals are better competitors than larger individuals for pelagic resource which could have led to the larger individuals switching to a more benthic diet. (4) The decrease in average size is thought to be caused by negative selection for larger individuals. Larger individuals have switched to a more benthic diet, and although the individuals are larger they still face the risk of predation in the littoral zone as they have not outgrown the gape size of the pike. This could have led to the average size reduction that may be the first steps in speciation, and ultimately leading to the divergence of two morphs by sympatric speciation in Ringsjön. In Gräsvattnet over the course of the study there were few and small changes in whitefish size, zooplankton relative abundance in the diet and in the environment. The results in Gräsvattnet could however suggest resource competition for benthic resources. Although resource competition is thought to be an important factor in the speciation of whitefish, without predation pressure no speciation occurs. This result could suggest the importance of predation pressure in the speciation of whitefish.
6
Rowe, Candida L. "Multicomponent signals." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299417.
Full text
7
Pugach, Pavel. "The evolutionary response of the HIV-1 ENV complex to selection pressures in vitro /." Access full-text from WCMC:, 2007. http://proquest.umi.com/pqdweb?did=1428842531&sid=4&Fmt=2&clientId=8424&RQT=309&VName=PQD.
Full text
8
Siopis, Matthew James. "Wear at high sliding speeds and high contact pressures." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54854.
Full textAbstract:
Metal on metal wear at high sliding speeds and high contact pressures results in the melting of one or both of the sliding solid bodies due to heat generated at the contact interface. Understanding the influence of sliding speeds, contact pressures and material properties on wear rates is important in developing predictive models for designing more efficient and effective engineering system components. Typical engineering applications subjected to these extreme conditions include ultrahigh speed machining, rocket sleds, large caliber cannon, and electromagnetic launchers. Sliding speeds on the order of 1,000 m/s and contact pressures in excess of 100 MPa are common in these applications and difficult to replicate in a laboratory environment. A unique wedge experiment using a minor caliber electromagnetic launcher has been developed and implemented to characterize wear deposition of a 6061-T6 aluminum sliding body on several different guider materials of varying mechanical and thermal properties at sliding speeds from 0 – 1,200 m/s and contact pressures from 100 – 225 MPa. Optical microscopy and 3D profilometry were used to characterize and quantify the slider wear. Three distinct wear regions, plasticity dominated, severe plastic deformation and melt lubrication were observed. Test results provided evidence that the aluminum slider contact interface was molten. Modeling of the experimental wear data showed a dependence on pressure and velocity and guider material properties, density and specific heat. A predictive wear model was developed for the melt lubrication region as a tool for designing components subjected to similar operating conditions.
9
Garcia, Tiffany Sacra. "INTERACTING COLOR AND BEHAVIOR RESPONSES TO MULTIPLE SELECTION PRESSURES IN THE SISTER SALAMANDER SPECIES AMBYSTOMA BARBOURI AND AMBYSTOMA TEXANUM." UKnowledge, 2002. http://uknowledge.uky.edu/gradschool_diss/260.
Full textAbstract:
My research explores the complex strategies animals adapt to cope with multiple selection pressures. I studied the behavioral and color response of two salamander sister species, Ambystoma barbouri and A. texanum, to temperature, predation risk and ultraviolet radiation (UVR, 280-320 nm). Ambystoma barbouri undergo development in streams, while A. texanum larvae inhabit ponds. Thus, A. barbouri are exposed to increased habitat ephemerality, enhanced predation risk, and UVR exposure. I show how A. barbouri have evolved alternate coping mechanisms in response to these environmental factors, relative to A. texanum. In this comparison study, I've quantified the affects of these selection pressures on larval color change, refuge use and depth choice.I found Ambystoma barbouri to have a significantly darker mean color than A. texanum. Additionally, both species significantly change color to match their background and in response to temperature. When exposed to warm temperatures, early-stage larvae of both species became lighter. Both species also changed color over ontogeny, with larvae becoming significantly lighter over development. Remarkably, A. texanum larvae mediated risk from predatory fish chemical cues by visually assessing the degree to which they cryptically match their background. If cryptic, A. texanum larvae remained on that background color rather than in refuge. A. barbouri larvae preferred to hide in refuge or on dark backgrounds regardless of crypticity, butquickly change color to match their new background. I found that both species darken in response to UVR. When given the choice of refuge, both species spent significantly more time in hiding when UVR was present. When given a choice of water depth, larvae preferred deep water in the presence of UVR radiation.Adapting multiple color and behavioral responses to individual selection pressures help organisms mediate conflicting demands from multiple selection pressures. For example, when predatory fish are present, larvae should move to shallow water to avoid predation. In the presence of UVR, however, larvae should prefer deeper water. I found A. barbouri larvae choose deep water to avoid high UVR exposure despite the risk of predation. Evolving multiple behavioral strategies allows A. barbouri larvae to avoid UVR damage and mediate predation risk.
10
Frénoy, Antoine. "Second order selection pressures promoting the evolution and maintenance of cooperation in microbial and in silico systems." Thesis, Paris 5, 2014. http://www.theses.fr/2014PA05T050/document.
Full textAbstract:
Cette thèse s'intéresse aux liens entre l'évolution de la coopération et la sélection de second ordre. Dans une première partie, nous montrons comment des organismes digitaux adaptent leurs génomes pour encoder les gènes liées à la coopération d'une manière plus contrainte (suppression d'évolvabilité), notamment à l'aide d'opérons et d'overlaps impliquant aussi des gènes essentiels. Dans une deuxième partie, nous testons expérimentalement cette vision des overlaps de gènes comme "contrainte évolutive" grâce à des outils d'algorithmique et de biologie synthétique que nous avons développés. Dans une troisième partie, nous utilisons des simulations par agents pour montrer comment une forme de division du travail peut être interprétée comme un système coopératif à la lumière de la théorie évolutive moderne. Dans une dernière partie, nous montrons que la dispersion spatiale des allèles coopératives obtenue par des phénomènes de "genetic hitchiking" joue un rôle important dans l'évolution de la coopération, quand bien même ce mécanisme de dispersion s'applique aussi à des allèles non coopératives, grâce à la "relatedness" (aux loci codant pour la coopération) crée par l'invasion locale de mutations bénéfiques (à des loci non liés à la coopération) et par l'équilibre complexe entre ces mutations bénéfiques et la robustesse mutationnelle. L'ensemble de ces résultats appelle à une prise en compte plus importante des pressions sélectives de second ordre dans l'étude de l'évolution sociale, et au développement de modèles plus réalistes qui permettraient d'intégrer de telles forces évolutives. Nous insistons également sur l'importance du paysage mutationnel dans l'étude des populations bactériennes, et montrons le potentiel croissant de la biologie synthétique comme outil d'étude de ce paysage et de l'évolution microbienne en généralIn the first part, I show how digital organisms adapt their genomes to encode cooperation-related genes in a more constrained way (evolvability suppression), especially using operons and overlaps also involving essential genes. In the second part, we experimentally test this view of gene overlaps as an evolutionary constraint, using both algorithmic and synthetic biology tools that we have developed. In the third part, I use agent-based simulations to show how a form of division of labour can be interpreted as a cooperative system in the light of modern evolutionary theory. In the final part, I show that the patterns of dispersal of cooperative alleles due to hitchhiking phenomena play an important role in the evolution of cooperation. The last result holds even though the hitchhiking mechanisms also applies to non-cooperative alleles, thanks to the relatedness (at cooperation-related loci) created by the local invasion of beneficial mutations (at loci not related to cooperation). The beneficial mutations form a complex and interesting equilibrium with mutational robustness, which I investigate using in silico evolution. On the whole, these results call for a more careful consideration of the second-order selection pressures in the study of social evolution, and show the necessity for more realistic models allowing to integrate such evolutionary forces. My thesis research specifically highlights the importance of the mutational landscape in the study of microbial populations and shows the increasing potential of synthetic biology as a tool to study such landscape and microbial evolution in general
11
Linhart, Rasmus, and Daniel Nyborg. "Adapt or die : A qualitative study on how institutional pressures influence the strategies of sustainable investors and their holdings." Thesis, Uppsala universitet, Företagsekonomiska institutionen, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-446936.
Full textAbstract:
Large institutional actors in the financial arena are moving their capital in a sustainable direction. This implies a change of the institutional norms and rules regarding sustainable investing. One of the problematic aspects of sustainable investing is how investors use different strategies to influence their holdings and what implications this choice might have on a sector level. The purpose of this paper is to empirically examine how the strategies from institutional investors are an expression of the current norms and rules in the field of sustainable investing. It also intends to illustrate how institutional pressures influence the strategies of investors and their holdings. By interviewing respondents from eleven institutional investors, we present data regarding norms and rules for sustainable investing and the consequences of the investor’s strategies. Our findings indicate there has been an immense increase in demand for sustainable products in recent years, resulting in institutional pressures that have influenced both the investors and their holdings. This exposes the field to selection processes which may force organizations to the point of adapt or die. Finally, our conclusion provides practical implications on what role institutional investors have in the quest for sustainable development.
12
Schmitt, Paulina. "Diversité moléculaire des effecteurs antimicrobiens chez l'huître creuse Crassostrea gigas : mise en évidence et rôle dans la réponse antimicrobienne." Thesis, Montpellier 2, 2010. http://www.theses.fr/2010MON20158/document.
Full textAbstract:
Ce travail a contribué à la compréhension des bases moléculaires de l'immunité de l'huître creuse par la caractérisation la diversité de trois effecteurs antimicrobiens de C. gigas et par l'appréhension du rôle de cette diversité dans les mécanismes de défense. Des analyses phylogénétiques de deux peptides antimicrobiens (AMPs), Cg-Défensines (Cg-Defs) et Cg-Proline rich peptide (Cg-Prp), et d'une protéine de type Bactericidal Permeability Increasing protein, Cg-BPI, nous a permis montrer la grande diversité pour les 2 AMPs, qui est générée par plusieurs mécanismes génétiques et par des pressions de sélection directionnelles, suggèrant une diversité fonctionnelle des variants. L'importance biologique de cette diversité a été étudiée pour trois variants de Cg-Defs. Une forte activité antimicrobienne a été mise en évidence contre les bactéries à Gram positive, mais celle-ci diffère selon les variants. De plus, nous avons démontré que le mécanisme d'action des Cg-Defs contre S. aureus repose sur l'inhibition de la biosynthèse du peptidoglycane par le piegeage de son précurseur, le lipide II. Finalement, l'expression des transcrits et la localisation de ces effecteurs en réponse à une infection par un Vibrio pathogène ont montré un réseau complexe des profils d'expression des différents antimicrobiens, au niveau des populations hémocytaires et des tissus d'huître, suggérant une interaction entre les antimicrobiens du fait de leur colocalization. La combinaison entre les familles ou entre les variants d'une même famille produit de fortes activités synergiques qui élargissent les spectres d'activité. Ainsi, la diversité produit par la coévolution entre hôte et pathogènes pourrait améliorer l'activité des AMPs d'huître, lui conférant une plus grande protection contre les pathogènes de son environnementThis work contributed to the knowledge of the molecular bases of oyster immunity by the characterization of the diversity of three antimicrobials of C. gigas and the understanding of the role played by their diversity in the oyster antimicrobial response. Phylogenetic analyses of two antimicrobial peptides (AMPs), Cg-Defensins (Cg-Defs) and Cg-Proline rich peptide (Cg-Prp), and one Bactericidal Permeability Increasing protein, Cg-BPI, led us to the identification of a high diversity for both AMPs. Further analyses showed that this diversity is generated by gene duplication, allelic recombination and directional selection pressures, suggesting their functional diversification. The biological meaning of AMP diversity was investigated for the three major variants of Cg-Defs, which revealed a strong but variable potency against Gram-positive bacteria. We evidenced that oyster defensins kill S. aureus through binding to the cell wall precursor lipid II, resulting in the inhibition of peptidoglycan biosynthesis. Finally, transcript expression and localization of oyster antimicrobials after a pathogenic infection evidenced a complex network in their expression profiles in hemocyte populations and oyster tissues, suggesting a potential interplay between antimicrobials as a result of their colocalization. Indeed, the combination of oyster antimicrobials produced strong synergistic activities that enlarged their antimicrobial spectra. Thus, the diversity of oyster antimicrobials may provide significant means in acquiring functional divergence, probably concerned in the evolutionary arms race between hosts and their pathogens.From our data, it would provide oysters with a higher protection against the potential pathogens from their environment
13
Peng, Xiong. "Aircraft environmental control systems modeling for configuration selection." Thesis, Cranfield University, 2013. http://dspace.lib.cranfield.ac.uk/handle/1826/8471.
Full textAbstract:
According to the statistics about civil transportation aircraft Environmental
Control system (ECS), the three-wheel high pressure water separation system
(HPWS) and low pressure water separation system (LPWS) are the most
common choices for the 150-seat airliners. Although the former has become the
mainstream configuration for air conditioning pack, the latter is still used on
Boeing 737-600/700. In order to compare the two configurations and choose the
better one for a specific aircraft, simulation and analysis are done.
The cabin heat load is calculated at first in order to calculate required engine
bleed air mass flow. Then a specific aircraft is defined so that required structural
dimensions and cabin comfort indexes can be obtained based on Airbus 320.
Thirdly, the component models are built by Matlab/Simulink according to the
fundamental knowledge of heat transfer and aerodynamics, the working
principles and mechanical dimensions of the components, the ambient
environmental parameters and some data from Airbus 320. Consequently, the
complete system model can be assembled. After confirming the validity of the
model by checking the required ram air mass flow and temperature deviation of
the state points referred to Airbus 320, the simulation model is used to do
analyze the specific aircraft. Finally, through comparing the different values of
ram air mass flow and turbine expansion ratio, as well as the system mass,
economic cost and reliability, the better configuration is selected.
It can be summarized that the three-wheel LPWS requires less ram air mass
flow (0.012kg/s) and a little lower expansion ratio (0.02) than the HPWS, and it
also has lower weight (63% of HPWS), lower (83% of HPWS) cost and higher
reliability (140% of HPWS), thus it is the suitable configuration for the specific
aircraft.
14
Smith, Robert Anthony. "A General Model for Continuous Noninvasive Pulmonary Artery Pressure Estimation." BYU ScholarsArchive, 2011. https://scholarsarchive.byu.edu/etd/3189.
Full textAbstract:
Elevated pulmonary artery pressure (PAP) is a significant healthcare risk. Continuous monitoring for patients with elevated PAP is crucial for effective treatment, yet the most accurate method is invasive and expensive, and cannot be performed repeatedly. Noninvasive methods exist but are inaccurate, expensive, and cannot be used for continuous monitoring. We present a machine learning model based on heart sounds that estimates pulmonary artery pressure with enough accuracy to exclude an invasive diagnostic operation, allowing for consistent monitoring of heart condition in suspect patients without the cost and risk of invasive monitoring. We conduct a greedy search through 38 possible features using a 109-patient cross-validation to find the most predictive features. Our best general model has a standard estimate of error (SEE) of 8.28 mmHg, which outperforms the previous best performance in the literature on a general set of unseen patient data.
15
Lazzaroni, Michael John. "Optimizing solvent selection for separation and reaction." Thesis, Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-07092004-124758/unrestricted/lazzaroni%5Fmichael%5Fj%5F200407%5Fphd.pdf.
Full textAbstract:
Thesis (Ph. D.)--School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, 2005. Directed by Charles A. Eckert.Charles L. Liotta, Committee Co-Chair ; Charles A. Eckert, Committee Chair ; Amyn S. Teja, Committee Member ; J. Carson Meredith, Committee Member ; Rigoberto Hernandez, Committee Member. Vita. Includes bibliographical references.
16
Arranz, Jordi. "Selective pressures towards the evolution of cooperation, communication and cognition." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/383620/.
Full textAbstract:
One of the main problems in studying human origins from an evolutionary perspective is uniqueness: we have evolved to fill a social and cognitive niche that is so distinctive it renders useless the usual investigative tool of careful comparison with other, similar species. Features such as cognition, communication and cooperation reached, in humans, unprecedented levels of sophistication and complexity. These features not only converge to the social dimension but they also lack a clear function outside it, a fact that makes epiphenomenal explanations unlikely. The main goal of this thesis is to shed light on the conditions that led to the evolution of modern humans through the development of computational models. Our research hypothesis is based on the assumption that the human “primeval niche” lies in the intersection of three fundamental phenomena: cooperation, communication and cognition. We argue that these three elements are intimately connected and that their intersection is the ideal spot to explore the so called human cognitive explosion. The new internal selective pressures that arise from any cooperative environment trigger asymmetric competitive co-evolutionary arms races that can pull the population in the opposing directions of altruism and selfishness. Co evolutionary feedback loops usually stagnate due to their increasing biological cost, however, in the human case, the invention of communication and language as a tool for social cohesion opened up a new “medium”, where both co operators and defectors can play their own personal “battle” at a lower cost and at a faster pace. Following this, we re-implement and develop several models of the evolution of communication and cooperation. As this thesis progresses, the scope of our modelling efforts is narrowed towards the study of the emergence of the simplest cooperative mechanism that explicitly relies on communication and important cognitive abilities: indirect reciprocity. Our findings strongly suggest that primitive communication could have evolved in order to sustain cooperation through indirect reciprocity and therefore communication and, eventually, language could have evolved as a tool for social cohesion. Moreover, our results indicate that there are two different evolutionary paths towards this goal. The first includes low levels of gossip in a trusting environment governed by a moderately heterogeneous moral system. The second consists of high levels of gossip in a suspicious context governed by a homogeneous moral system. The main contribution of this thesis is a plausible evolutionary outline of the primeval niche that early humans occupied and its depiction through the interactions and interdependence of the three cornerstones of human nature: cognition, communication and cooperation.
17
Morran, Levi 1981. "Selective pressures that drive the evolution and maintenance of outcrossing." Thesis, University of Oregon, 2009. http://hdl.handle.net/1794/10458.
Full textAbstract:
xi, 103 p. : ill. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number.Although outcrossing is the most widespread mating system among animals and plants, the reason for this prevalence is not fully understood. Evolutionary theory has classified the potential selective pressures driving the evolution and maintenance of outcrossing into two broad categories: deleterious mutations and changing ecological conditions. Despite the inherent advantages of self-fertilization, exposure to either or both of these selective pressures is predicted to favor outcrossing over self-fertilization. I tested these predictions using experimental evolution in populations of Caenorhabditis elegans with genetically modified rates of outcrossing and selfing. I found that outcrossing reduces the fixation of deleterious mutations under mutation influx and that outcrossing expedites adaptation to a bacterial pathogen. Further, I identified facultative outcrossing, a novel life history characteristic, in specific C. elegans strains that predominantly reproduce by selfing but engage in outcrossing when stressed. The shift from a primarily selfing mating system to a predominantly outcrossing system is similar to the environmentally induced facultative sex observed in asexual species, which is thought to enable more rapid adaptation. Facultative outcrossing, although not previously documented, may play a major role in the life histories of many highly selfing species. Finally, most mutations are deleterious and therefore elevated mutation rates are generally thought to produce progressively larger reductions in fitness. Using the chemical mutagen ethylmethanesulfonate, I found the surprising result that populations exposed to a mutation rate at least fifty times greater than natural rates exhibited significantly greater fitness than populations exposed to substantially lower mutation rates. This unexpected fitness optimum may be the result of a volatile balance between the influx of deleterious mutations and compensatory mutations. This work confirms the predictions of several long-standing evolutionary theories by identifying both deleterious mutations and changing ecological conditions as selective pressures capable of driving the evolution and maintenance of outcrossing. These selective pressures, which are ubiquitous in nature, may explain the prevalence of outcrossing relative to selling. This dissertation includes previously published and co-authored materials.
Committee in charge: Barbara Roy, Chairperson, Biology; Patrick Phillips, Advisor, Biology; Karen Guillemin, Member, Biology; William Bradshaw, Member, Biology; Douglas Kennett, Outside Member, Anthropology
18
Dyess, Mark Vernon. "OPTIMIZATION OF THE MATERIAL SELECTION PROCESS FOR CRYOGENIC COMPOSITE OVERWRAPPED PRESSURE VESSELS." MSSTATE, 2008. http://sun.library.msstate.edu/ETD-db/theses/available/etd-03272008-163646/.
Full textAbstract:
The objective of this research was to develop a test methodology for the evaluation of materials for possible use in cryogenic composite overwrapped pressure vessels (COPVs). This paper investigates various micromechanical and macromechanical techniques to test the interaction between fibers and resins. Uniaxial tension testing was performed at ambient and cryogenic temperatures on neat resin samples, straight-sided composite specimens, and NOL ring specimens. COPVs were constructed and burst tested to provide a performance comparison. Results show resins suitable for use at cryogenic conditions display a LN2 temperature elongation to failure greater than 2% and an ambient temperature elastic modulus less than 35 MPa. NOL rings were determined to be the preferred composite test method rather than straight-sided specimens. Mechanical performance of the NOL rings compares well with actual COPV performance.
19
Poulimeneas, Dimitrios. "Back-pressure-like mechanisms on relay selection policies for cooperative diversity systems." Thesis, KTH, Reglerteknik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-167794.
Full textAbstract:
The topic of the current thesis is the reduction of the average packet delay in two-hop wireless cooperative networks with buffer-aided relays. This type of networks is of particular interest since it constitutes the building block for extended networks with multiple hops and numerous relays. Back-pressure-like algorithms are developed for the HRS and max − link relay selection schemes. First, an algorithm is developed and applied for both the HRS and the max − link protocols. It reduces the average delay considerably, but, in the case of the max − link the diversity of the system is reduced resulting in higher outage probabilities. For this reason, a new algorithm is developed that aims at maintaining a high diversity throughout the operation of the network. Distributed implementations of the algorithms are also discussed. The performance of the proposed algorithms is illustrated via simulations.
20
Angeles, Mary Stankovich. "Use of Dynamic Pool Size to Regulate Selection Pressure in Cooperative Coevolutionary Algorithms." NSUWorks, 2010. http://nsuworks.nova.edu/gscis_etd/78.
Full textAbstract:
Cooperative coevolutionary algorithms (CCEA) are a form of evolutionary algorithm that is applicable when the problem can be decomposed into components. Each component is assigned a subpopulation that evolves a good solution to the subproblem. To compute an individual's fitness, it is combined with collaborators drawn from the other subpopulations to form a complete solution. The individual's fitness is a function of this solution's fitness. The contributors to the comprehensive fitness formula are known as collaborators. The number of collaborators allowed from each subpopulation is called pool size. It has been shown that the outcome of the CCEA can be improved by allowing multiple collaborators from each subpopulation. This results in larger pool sizes, but improved fitness. The improvement in fitness afforded by larger pool sizes is offset by increased calculation costs. This study targeted the pool size parameter of CCEAs by devising dynamic strategies for the assignment of pool size to regulate selection pressure. Subpopulations were rewarded with a larger pool size or penalized with a smaller pool size based on measures of their diversity and/or fitness. Measures for population diversity and fitness used in this study were derived from various works involving evolutionary computation. This study showed that dynamically assigning pool size based on these measures of the diversity and fitness of the subpopulations can yield improved fitness results with significant reduction in calculation costs over statically assigned pool sizes.
21
Dennis, Aaron W. "Noninvasive Estimation of Pulmonary Artery Pressure Using Heart Sound Analysis." BYU ScholarsArchive, 2009. https://scholarsarchive.byu.edu/etd/1971.
Full textAbstract:
Right-heart catheterization is the most accurate method for estimating pulmonary artery pressure (PAP). Because it is an invasive procedure it is expensive, exposes patients to the risk of infection, and is not suited for long-term monitoring situations. Medical researchers have shown that PAP influences the characteristics of heart sounds. This suggests that heart sound analysis is a potential noninvasive solution to the PAP estimation problem. This thesis describes the development of a prototype system, called PAPEr, which estimates PAP noninvasively using heart sound analysis. PAPEr uses patient data with machine learning algorithms to build models of how PAP affects heart sounds. Data from 20 patients was used to build the models and data from another 31 patients was used as a validation set. PAPEr diagnosed these 31 patients for pulmonary hypertension with an accuracy of 77 percent.
22
Schneider, Brandt Lawrence. "In vitro multistage carcinogenesis: A balance of genetic alterations and selective pressures." Diss., The University of Arizona, 1993. http://hdl.handle.net/10150/186542.
Full textAbstract:
The long latency of human tumors and the difficulty of transforming human cell lines has necessitated the investigation of rodent models which have helped propagate a general theory of carcinogenesis. This author has addressed the temporal and physiological significance of oncogene activation and tumor suppressor loss during malignant progression of nontumorigenic murine keratinocytes. The data presented here indicate that mechanisms of carcinogenesis may be dependent upon both the model system studied, and on innate environmental selective pressures. 7,12-dimethylbenz(a) anthracene initiation of murine keratinocytes resulted in tumorigenic phenotypes with transferrable dominant transforming activity. However, mutated Ha-ras alleles were not detected in the tumorigenic cell lines despite the direct correlation between chemical initiation and ras activation in vivo. Somatic cell hybrid studies implicated the loss of multiple tumor suppressors in the progression of a normal cell through a benign state to frank malignancy. While all hybrids were suppressed to varying degrees, nontumorigenic cells suppressed tumor formation to a greater extent than benign cells. Interestingly, a well differentiated carcinoma cell line also suppressed tumor formation, The implication of tumor suppressor loss in the formation of a benign papilloma was a novel finding. Results from these experiments revealed that disruption of differentiation programs is concomitant with tumorigenicity, and that the ability to differentiate in vitro is a prerequisite for tumor suppression in vivo. Indicative of an inability to differentiate, benign and malignant cell lines failed to express keratins K1 or K10 in response to high extracellular calcium concentrations. While differential northern analysis revealed that keratins K6 and K18 were predominately expressed by either non-tumorigenic or malignant cells, respectively, subtractive hybridization identified five putative gene sequences (Suz 1-4 and 6) expressed exclusively by non-tumorigenic cells. In summary, somatic cell hybrid studies helped assess the phenotypic dominance of a given stage of cancer. The isolation of genes whose expression is abrogated in malignant cells may further our insight into the role of gene loss during malignant conversion. Finally, a better understanding of the mechanisms of endogenous and exogenous selective pressures will enable the design of improved in vitro models of carcinogenesis.
23
Wilbert, Melissa. "Differential selective pressures acting upon the Influenza A genome : a comparative study /." Online version of thesis, 2008. http://hdl.handle.net/1850/7916.
Full text
24
Ollion, Charles. "Emergence of internal representations in evolutionary robotics : influence of multiple selective pressures." Phd thesis, Université René Descartes - Paris V, 2013. http://tel.archives-ouvertes.fr/tel-00948029.
Full text
25
Kovacs, Jennifer L. "Queen-specific selective pressures and caste dimorphism in the social wasp Vespula maculifrons." Diss., Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/37100.
Full textAbstract:
Within social insect colonies, sterile workers are responsible for brood care, while queens are the primary egg-layers. These reproductive caste differences are often accompanied by pronounced morphological distinctions. Queen and worker phenotypic differences are particularly remarkable considering caste is environmentally, rather than genetically, determined. Environmental caste determination can produce intralocus genetic conflict between castes, particularly when homologous traits are highly dimorphic. Therefore, when studying the evolution of social insect caste dimorphism, one must consider the genetic architecture underlying phenotypic expression as well as the selective pressures that have shaped caste morphology.
This dissertation presents the results of four studies that investigated factors affecting caste morphology in the social wasp Vespula maculifrons. The first two studies focused on identifying queen morphological traits that were positively associated with queen fitness and would therefore be subject to selection. Queen length, specifically gaster length, was positively associated with overwintering survival and was consistently associated with mating success. Both of these findings suggest that queen gaster length is under selection during two life-history events, mating and overwintering, in which workers do not participate. These findings provide empirical support for the adaptive evolution of a caste dimorphic trait.
The third and fourth studies used classical quantitative genetic and morphological analyses to examine the genetic architecture underlying caste dimorphism in V. maculifrons. I determined which traits were under caste-specific selection by analyzing trait allometries and the levels of genetic control, variation, and dimorphism of traits between castes. Little genetic variation for morphological trait size was detected for most worker and queen traits, suggesting a strong influence of environment on phenotypic variation. Additionally, analyses of trait allometries indicated that several queen traits (mass, thorax width and length) were under queen-specific selection. The relationship between thorax length, gaster length, and overall body size is further evidence of selection on length in queens.
Overall, these studies provide evidence for the importance of queen-specific selection in the evolution of caste dimorphism. When placed in the broader context of caste evolution, they point to the importance of life-history in shaping the genetic architecture underlying caste dimorphism.
26
Blake, Hunter B. "Avoiding Protoporphyrinogen Oxidase Inhibiting Herbicide Selection Pressure on Common Ragweed and Palmer amaranth in Soybean." Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/87390.
Full textAbstract:
Palmer amaranth (Amaranthus palmeri) and common ragweed (Ambrosia artemisiifolia) can cause detrimental soybean yield loss. Due to widespread resistance to glyphosate and ALS-inhibiting herbicides, growers rely on protoporphyrinogen oxidase inhibiting herbicides (PPO) such as flumioxazin applied preemergence (PRE) and fomesafen postemergence (POST) to control both weeds. Experiments were conducted with the overarching goal of reducing PPO selection pressure for Palmer amaranth and common ragweed. Flumioxazin alone PRE controlled Palmer amaranth near 100%. However, sulfentrazone combined with pyroxasulfone or pendimethalin provided similar control to flumioxazin. Acetochlor and linuron controlled common ragweed <74%, yet controlled Palmer amaranth >96%. Glufosinate applied POST controlled Palmer amaranth and common ragweed 74-100%, regardless of PRE treatment. Flumioxazin PRE followed by fomesafen POST controlled common ragweed well; however, several non-PPO herbicide treatments or programs with only 1 PPO-inhibiting herbicide provided similar common ragweed control as the 2 PPO system (flumioxazin followed by fomesafen). Treatments consisting of a PRE and POST herbicide controlled Palmer amaranth at least 80% and common ragweed 95%. To reduce PPO selection pressure, soybean producers growing glufosinate-resistant soybean may use flumioxazin PRE followed by glufosinate POST whereas non-glufosinate-resistant soybean growers should reduce PPO herbicide use by using a non-PPO herbicide PRE. Alternatively, these producers can effectively reduce PPO selection pressure by implementing residual combinations of a PPO-inhibiting herbicide + non-PPO with spectrums of weed control that overlap at either Palmer amaranth or common ragweed.Master of Science in Life Sciences
Soybean producers planted 35.4 million hectares in the US during 2018. Palmer amaranth (Amaranthus palmeri) and common ragweed (Ambrosia artemisiifolia) are both common and problematic in soybean production. The introduction of a glyphosate-resistant soybean cultivars coupled with glyphosate allowed soybean producers to easily control these weeds along with many other broadleaf and grass weeds. However, over reliance on glyphosate selected for biotypes of common ragweed and Palmer amaranth resistant to the herbicide. In response, soybean producers have reverted to preemergence (PRE) herbicides and alternative modes of action postemergence (POST) to control these herbicide-resistant weeds. One such herbicide mode of action is inhibition of protoporphyrinogen oxidase (PPO). Flumioxazin and fomesafen are both PPO-inhibiting herbicides and have been widely used in soybean, however increasing reliance on PPOs has selected for resistant common ragweed and Palmer amaranth biotypes. This research focused on reducing risk of PPO-inhibiting herbicide resistance development (“selection pressure”) by finding alternatives to or combinations with PPOinhibiting herbicides that would effectively control both weeds and thus preserve effectiveness of a valuable herbicide group. Of PRE herbicides applied alone, flumioxazin was the only treatment to control Palmer amaranth >79% 14 DA-PRE at Painter 2017. However, combination of PRE herbicides such as sulfentrazone or metribuzin in combination with pyroxasulfone, and pendimethalin + sulfentrazone, all controlled Palmer amaranth well. While metribuzin and pendimethalin alone did not provide as much control, a POST application of glufosinate coupled with these residual herbicides adequately controlled Palmer amaranth. Soybean producers can effectively control Palmer amaranth with a non-PPO PRE herbicide followed by glufosinate postemergence (POST) or residual combinations of a PPO + non-PPO while reducing risk of herbicide resistance development. Several PRE herbicide treatments adequately controlled common ragweed. During 2017, residual herbicides that controlled common ragweed at least 90% included flumioxazin, flumioxazin + clomazone, linuron, or metribuzin, fomesafen + linuron, and linuron + clomazone. All treatments controlled common ragweed greater than 94% during 2018, except metribuzin, linuron, and clomazone, which controlled the weed 75, 86, and 90%, respectively. Fomesafen alone or in combination with metribuzin controlled common ragweed 80 to 84%. Regardless of PRE, glufosinate POST controlled common ragweed 99% 56 and 70 days after planting (DAP). In fields infested with common ragweed yet to develop PPO resistance, growers should use a non-PPO herbicide in combination with flumioxazin PRE. Additionally, tank mixtures of effective MOAs PRE followed by glufosinate rather than a PPO POST may reduce herbicide selection pressure. The final study set out to determine which was more critical to controlling herbicideresistant Palmer amaranth and common ragweed in soybean, a PPO-inhibiting herbicide applied PRE or POST. Flumioxazin applied PRE controlled both weeds almost completely. Acetochlor and linuron did not control common ragweed as well, but controlled Palmer amaranth >96%. Both metribuzin and clomazone were weaker on common ragweed and Palmer amaranth. However, all PRE herbicide treatments followed by glufosinate or fomesafen controlled Palmer amaranth and common ragweed at least 80 and 95%, respectively. To reduce PPO selection pressure, soybean producers growing glufosinate-resistant soybean may use flumioxazin PRE followed by glufosinate POST whereas non-glufosinate-resistant growers should reduce PPO herbicide use by using a non-PPO herbicide PRE. Alternatively, these producers can effectively reduce PPO selection pressure by implementing residual combinations of a PPO-inhibiting herbicide + non-PPO with spectrums of weed control that overlap at either Palmer amaranth or common ragweed. Results from these experiments suggest PPO-inhibiting herbicides are critical for common ragweed and Palmer amaranth control. Previous research has shown effective tank mixtures with various effective MOAs has reduced the risk of herbicide resistance development. Protoporphyrinogen oxidase herbicides should be used sparingly and in combination with effective non-PPO herbicides to reduce selection pressure.
Soybean producers planted 35.4 million hectares in the US during 2018. Palmer amaranth (Amaranthus palmeri) and common ragweed (Ambrosia artemisiifolia) are both common and problematic in soybean production. The introduction of a glyphosate-resistant soybean cultivars coupled with glyphosate allowed soybean producers to easily control these weeds along with many other broadleaf and grass weeds. However, over reliance on glyphosate selected for biotypes of common ragweed and Palmer amaranth resistant to the herbicide. In response, soybean producers have reverted to preemergence (PRE) herbicides and alternative modes of action postemergence (POST) to control these herbicide-resistant weeds. One such herbicide mode of action is inhibition of protoporphyrinogen oxidase (PPO). Flumioxazin and fomesafen are both PPO-inhibiting herbicides and have been widely used in soybean, however increasing reliance on PPOs has selected for resistant common ragweed and Palmer amaranth biotypes. This research focused on reducing risk of PPO-inhibiting herbicide resistance development (“selection pressure”) by finding alternatives to or combinations with PPOinhibiting herbicides that would effectively control both weeds and thus preserve effectiveness of a valuable herbicide group. Of PRE herbicides applied alone, flumioxazin was the only treatment to control Palmer amaranth >79% 14 DA-PRE at Painter 2017. However, combination of PRE herbicides such as sulfentrazone or metribuzin in combination with pyroxasulfone, and pendimethalin + sulfentrazone, all controlled Palmer amaranth well. While metribuzin and pendimethalin alone did not provide as much control, a POST application of glufosinate coupled with these residual herbicides adequately controlled Palmer amaranth. Soybean producers can effectively control Palmer amaranth with a non-PPO PRE herbicide followed by glufosinate postemergence (POST) or residual combinations of a PPO + non-PPO while reducing risk of herbicide resistance development. Several PRE herbicide treatments adequately controlled common ragweed. During 2017, residual herbicides that controlled common ragweed at least 90% included flumioxazin, flumioxazin + clomazone, linuron, or metribuzin, fomesafen + linuron, and linuron + clomazone. All treatments controlled common ragweed greater than 94% during 2018, except metribuzin, linuron, and clomazone, which controlled the weed 75, 86, and 90%, respectively. Fomesafen alone or in combination with metribuzin controlled common ragweed 80 to 84%. Regardless of PRE, glufosinate POST controlled common ragweed 99% 56 and 70 days after planting (DAP). In fields infested with common ragweed yet to develop PPO resistance, growers should use a non-PPO herbicide in combination with flumioxazin PRE. Additionally, tank mixtures of effective MOAs PRE followed by glufosinate rather than a PPO POST may reduce herbicide selection pressure. The final study set out to determine which was more critical to controlling herbicideresistant Palmer amaranth and common ragweed in soybean, a PPO-inhibiting herbicide applied PRE or POST. Flumioxazin applied PRE controlled both weeds almost completely. Acetochlor and linuron did not control common ragweed as well, but controlled Palmer amaranth >96%. Both metribuzin and clomazone were weaker on common ragweed and Palmer amaranth. However, all PRE herbicide treatments followed by glufosinate or fomesafen controlled Palmer amaranth and common ragweed at least 80 and 95%, respectively. To reduce PPO selection pressure, soybean producers growing glufosinate-resistant soybean may use flumioxazin PRE followed by glufosinate POST whereas non-glufosinate-resistant growers should reduce PPO herbicide use by using a non-PPO herbicide PRE. Alternatively, these producers can effectively reduce PPO selection pressure by implementing residual combinations of a PPO-inhibiting herbicide + non-PPO with spectrums of weed control that overlap at either Palmer amaranth or common ragweed. Results from these experiments suggest PPO-inhibiting herbicides are critical for common ragweed and Palmer amaranth control. Previous research has shown effective tank mixtures with various effective MOAs has reduced the risk of herbicide resistance development. Protoporphyrinogen oxidase herbicides should be used sparingly and in combination with effective non-PPO herbicides to reduce selection pressure.
27
Howard, Lesley. "Membership representation in the issue-focus selection process of national environmental nonprofit organizations." Thesis, Virginia Tech, 1994. http://hdl.handle.net/10919/42067.
Full textAbstract:
Public interest groups, environmental nonprofit organizations (ENPOs) among
them, play a large role in the formulation and implementation of public policy. Much of
their legitimacy comes from their claim that they represent their members' interests. This
thesis examines ENPO communication forms to ascertain whether and how ENPOs seek
their members' opinions, and if so, whether or not those opinions influence the ENPOs'
issue-focus selection process, which is the issues on which the ENPO's financial and
human resources will be expended.
The research addresses these questions at two related levels of representation: internal to the organization (e. g., how do ENPOs seek their members' opinions) and inter - organizational (e.g., what role do ENPOs play in the political arena). On the level of internal democracy, elitist theory and Seymour Martin Lipset's "factors that encourage organizational democracy" provide a base for interpreting the results. At the inter-organizational level both pluralist and elitist theories of democratic governance provide the base for interpretation of the results. Finally, speculation is made about ENPO membership as "symbolic" political participation
The results suggest that support for both pluralist and elitist interpretation of both
internal and inter-organizational democracy may be appropriate. All ENPOs use a variety of
communication forms to inform their members, and all ENPO survey respondents stated
that they are open to membership suggestions. The findings also suggest that another
appropriate interpretation of ENPO membership may be that membership is a symbolic
purchase of political participation.
Master of Urban Affairs
28
Guerreiro, Lara Sofia Fernandes. "Influência do uso de enrofloxacina no aparecimento de resistência às quinolonas mediada por plasmídeos em Escherichia coli de vitelos." Master's thesis, Universidade Técnica de Lisboa. Faculdade de Medicina Veterinária, 2012. http://hdl.handle.net/10400.5/4589.
Full textAbstract:
Dissertação de Mestrado em Segurança AlimentarO conhecimento sobre a presença e frequência de genes de resistência às quinolonas mediada por plasmídeos (RQMP) em estirpes comensais de Escherichia coli de origem bovina é escasso a nível mundial. Foram estudadas um total de 237 amostras de E. coli de vitelos saudáveis previamente isoladas após pressão selectiva in vivo de enrofloxacina (ENR) e caracterizadas quanto à resistência aos antibióticos: 101, 79 e 57 isolados relativos a T0, T1 (6 semanas após administração de ENR) e T2 (10 semanas após administração de ENR), respectivamente. Os isolados foram caracterizados fenotipicamente por determinação da Concentração Inibitória Mínima (CIM) para os antimicrobianos ácido nalidíxico (AN), ciprofloxacina (CIP) e levofloxacina (LEV) e os resultados interpretados segundo os critérios epidemiológicos (ECOFF) estabelecidos pelo EUCAST. A frequência de genes de RQMP (qnr, aac(6’)-Ib-cr e qepA) foi determinada através de amplificação por PCR e sequenciação nucleotídica. A proporção de isolados de E. coli resistentes ao AN em T0, T1 e T2 foi de, respectivamente: 52,5% (n=53; CIM 64->256 μg/ml), 100% (n=79; CIM 128->256 μg/ml) e 82,5% (n=47; CIM 128->256 μg/ml). A resistência à CIP em T0, T1 e T2 foi de, respectivamente: 52,5% (n=53; CIM 0,125->256 μg/ml), 100% (n=79; CIM 0,25-128 μg/ml) e 89,5% (n=51; CIM 0,25-64 μg/ml). A resistência à LEV em T0, T1 e T2 foi de, respectivamente: 46,5% (n=47; CIM 0,5-64 μg/ml), 100% (n=79; CIM 0,5-64 μg/ml) e 87,7% (n=50; CIM 0,5-32 μg/ml). No que respeita aos determinantes de RQMP nos 237 isolados estudados, foram identificados: 11,8% (n=28) positivos para genes qnr (qnrB2, n=4; qnrD, n=11; qnrS1, n=13); e 0,8% (n=2) isolados positivos para o gene aac(6’)-Ib-cr. Da análise da frequência dos genes de RQMP nos isolados de E. coli observou-se: em T0, 3% de genes qnr (todos qnrS1) e 2% do gene aac(6’)-Ib-cr; em T1, 15,2% de genes qnr (10,1% qnrD e 5,1% qnrS1); em T2, 22,8% de genes qnr (7% qnrB2, 5,3% qnrD e 10,5% qnrS1). Os dados obtidos evidenciam um aumento significativo da prevalência de isolados resistentes ao longo do tempo de colheita, sugerindo que a pressão selectiva imposta pela exposição à ENR tem influência no aparecimento de resistência às quinolonas. Observou-se um aumento significativo da frequência de genes de RQMP ao longo do estudo longitudinal e mais de 80% dos isolados positivos para RQMP foram resistentes às quinolonas. Este é, para o nosso conhecimento, o primeiro estudo que descreve a identificação de resistência às quinolonas por qnrD em isolados de E. coli de bovinos.
ABSTRACT - The current knowledge about the presence and frequency of pasmid-mediated quinolone resistance (PMQR) genes in commensal Escherichia coli strains from cattle is scarce. Two hundred and thirty seven E. coli samples isolated from healthy calves were studied after in vivo enrofloxacin (ENR) selective pressure and previously characterized regarding antimicrobial susceptibility, including: 101, 79 and 57 isolates from T0, T1 (six weeks after ENR administration) and T2 (10 weeks after ENR administration), respectively. The phenotypic characterization was performed using Minimum Inhibitory Concentration (MIC) determinantion for nalidixic acid (NAL), ciprofloxacin (CIP) and levofloxacina (LEV) by the microdilution method and the results were interpreted according to EUCAST definitions of epidemiological cut-off values (ECOFF). PMQR genes (qnr, aac(6’)-Ib-cr and qepA) frequency was performed by PCR amplification and nucleotide sequencing. NAL resistant E. coli isolates in T0, T1 and T2 were, respectively: 52,5% (n=53; MICs 64 to >256 μg/ml), 100% (n=79; MICs 128 to >256 μg/ml) and 82,5% (n=47; MICs 128 to >256 μg/ml). CIP resistant isolates in T0, T1 and T2 were, respectively: 52,5% (n=53; MICs 0,125->256 μg/ml), 100% (n=79; MICs 0,25-128 μg/ml) and 89,5% (n=51; MICs 0,25-64 μg/ml). LEV resistant isolates in T0, T1 and T2 were, respectively: 46,5% (n=47; MICs 0,5-64 μg/ml), 100% (n=79; MICs 0,5-64 μg/ml) and 87,7% (n= 50; MICs 0,5-32 μg/ml). From the 237 E. coli isolates tested: 11,8% (n=28) harboured qnr genes (qnrB2, n=4; qnrD, n=11; and qnrS1, n=13) and 0,8% (n=2) were found positive for the aac(6’)-Ib-cr gene. The analysis of PMQR genes in E. coli at the different sampling times showed that: at T0, qnr genes were detected in 3% of the isolates (all found to be qnrS1) and 2% carried the aac(6’)-Ib-cr gene; at T1, 15,2% of the isolates carried qnr genes (10,1% qnrD and 5,1% qnrS1); and at T2, 22,8% of the isolates were found positive for qnr genes (7% qnrB2, 5,3% qnrD and 10,5% qnrS1). The results reveal an increased prevalence of resistant isolates along the time, suggesting that ENR selective pressure influences the emergence of quinolone resistance. A significant increased frequency of PMQR genes along the longitudinal study was observed and more than 80% of PMQR positive isolates were quinolone resistant. This is to our knowledge the first report on PMQR qnrD gene in E. coli isolates from cattle.
29
Claverie, Thomas. "Cheliped morphology, behaviour and selective pressures in the squat lobster Muninda rugosa (Fabricius, 1775)." Thesis, University of London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.520463.
Full text
30
Hermansen, Russell A., Brian K. Mannakee, Wolfgang Knecht, David A. Liberles, and Ryan N. Gutenkunst. "Characterizing selective pressures on the pathway for de novo biosynthesis of pyrimidines in yeast." BioMed Central Ltd, 2015. http://hdl.handle.net/10150/610280.
Full textAbstract:
BACKGROUND: Selection on proteins is typically measured with the assumption that each protein acts independently. However, selection more likely acts at higher levels of biological organization, requiring an integrative view of protein function. Here, we built a kinetic model for de novo pyrimidine biosynthesis in the yeast Saccharomyces cerevisiae to relate pathway function to selective pressures on individual protein-encoding genes. RESULTS: Gene families across yeast were constructed for each member of the pathway and the ratio of nonsynonymous to synonymous nucleotide substitution rates (dN/dS) was estimated for each enzyme from S. cerevisiae and closely related species. We found a positive relationship between the influence that each enzyme has on pathway function and its selective constraint. CONCLUSIONS: We expect this trend to be locally present for enzymes that have pathway control, but over longer evolutionary timescales we expect that mutation-selection balance may change the enzymes that have pathway control.
31
Taljaard, Francois George. "Analytical control valve selection for mine water reticulation systems / F.G. Taljaard." Thesis, North-West University, 2012. http://hdl.handle.net/10394/9703.
Full textAbstract:
Some of the largest and deepest mines in the world are situated in South Africa. Underground temperatures and humidity can be controlled by means of complex chilled water reticulation system. A cascade pumping system is used to pump the used water from the underground levels back to the surface.
The dewatering process is energy intensive. Large volumes of water are used during the general mine drilling periods (06:00 to 12:00). During blasting periods (15:00 to 18:00) a minimum amount of personnel are underground, yet large volumes of water are still sent underground due to a lack of control. Reducing the water sent underground, will reduce the amount of water pumped back to the surface; resulting in significant energy savings.
Water flow and pressure can be managed by installing control valves at appropriate positions throughout the water reticulation system. Selecting a control valve is typically governed by constraints such as cavitation, water hammer, flashing, safety ratings and control range. A basic set of calculations can be used to determine whether a valve conforms to a specific scenario. However, scenarios calculated by engineers are not indicative of all applied system scenarios.
When control valves are installed, to optimise the operation of a system, it affects the system’s characteristics. Sampled system data will therefore no longer provide adequate readings to help with selecting the correct control valve. An analytical control valve selection method has been developed and implemented. The case study shows the results and practical implications of applying this method in the mining industry. Implementing the analytical valve selection method is shown to be viable, realising electrical energy cost savings for the mine by reducing power requirements from Eskom. Analytical control valve selection for mine water reticulation systemsThesis (MIng (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2013.
32
Morgan, Julian Rees. "Selective estimation of sound pressure and intensity in determinations of transmission loss." Thesis, Liverpool John Moores University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.253702.
Full text
33
Orkwis, Brianne. "Novel acid phosphatase in Candida glabrata suggests dynamic selective pressures on the phosphate starvation response." Click here for download, 2009. http://proquest.umi.com.ps2.villanova.edu/pqdweb?did=1934097791&sid=1&Fmt=2&clientId=3260&RQT=309&VName=PQD.
Full text
34
Rodríguez-Vivas, Roger Iván. "The effect of selection pressure on the genotype and phenotype of acaricide resistance in Phipicephalus (Boophilus) microplus." Thesis, University of Liverpool, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501584.
Full textAbstract:
Acaricides have played a pivotal role in the control of the tick Rhipicephalus (Boophilus) microplus. As a consequence of extensive use, R. (B.) microplus has developed resistance to all major classes of acaricides, especially to pyrethroids. The thesis describes field and laboratory research undertaken in Yucatan, Mexico and Liverpool, UK to investigate pyrethroid resistance (PR) in R. (B.) microplus. For the first time gDNA of R. (B.) microplus was sequenced around the target single nucleotide polymorphism (SNP) in the sodium channel gene associated with PR and three new SNPs were identified.
35
Hyde, Timothy Paul. "A cross-over randomised controlled trial of selective pressure impressions for lower complete dentures and laboratory investigations into impression pressure variation." Thesis, University of Leeds, 2011. http://etheses.whiterose.ac.uk/1761/.
Full textAbstract:
Part I of this Thesis gives a brief outline of the history and evidence for impression techniques for complete dentures. The literature review suggested there was a paucity of high quality evidence for impression techniques for complete dentures, especially in the form of randomised controlled trials (Jokstad et al 2002, Harwood 2008). The literature review from Part I suggested that selective pressure impressions for complete dentures required evidence on three levels; firstly, in-vitro evidence on the numerous factors that affect pressure, secondly evidence that within a specific impression technique the pressure is re-distributed, and thirdly evidence that the specific impression technique provides patient benefit. Part II, III and IV of this Thesis address each of these issues in turn. Part II of the Thesis uses laboratory based in-vitro impression pressure research to investigate new issues and re-address old controversies where the evidence in the literature was conflicting or deficient. Part III investigates the specific distribution of pressure within the impression technique used for the clinical trial of Part IV, concluding that the pressure was distributed in a specific and useful way, which was clinically significant. The Clinical Trial reported in Part IV of this Thesis, had the primary objective of assessing patient preference for a specific selective pressure impression for complete dentures. The cross-over, randomised, controlled, clinical trial (RCT) was performed comparing a selective pressure impression with a placebo and an alternative method of redistributing pressure. Patients who had shown a specific pressure related clinical problem were recruited for the study. The results show that the preference for the selective pressure impression was greater than that of the other two techniques. The work of this Thesis introduces dentists to a successful impression technique and provides them with clear, clinically relevant and useful evidence for that impression technique.
36
Goulois, Joffrey. "Diversité des modes de résistance de cible aux antivitamines K chez les rongeurs." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSE1048/document.
Full textAbstract:
Les populations de rongeurs sont responsables de nombreux problèmes économiques et sanitaires. Pour ces raisons certains rongeurs sont qualifiés de nuisibles, tels que le rat brun, le rat noir et la souris domestique. En conséquence, leurs populations doivent être gérées. Cette gestion implique des mesures sanitaires et écologiques strictement indispensables mais passe aussi par l'utilisation de produits chimiques toxiques. Dans le cadre de la lutte chimique, les AVKs sont actuellement les molécules les plus utilisées. Ces AVKs inhibent la coagulation sanguine et sont à l'origine d'hémorragies mortelles. La cible pharmacologique des AVK est l'enzyme VKOR, codée par le gène vkorc1. Cependant, l'utilisation intensive des AVKs depuis les années 1950 a eu pour conséquence, chez les rongeurs, la sélection de résistance à ces molécules. La résistance de cible a été bien étudiée chez le rat brun mais est très peu connue chez la souris domestique et le rat noirRodent populations are responsible for many economic and health problems. For these reasons different rodents species are called pests and particularly brown rats, house mice and black rats. Their populations need to be managed. This management involves health and environmental measures strictly necessary but is also based on the use of toxic chemicals. As part of chemical control, the AVKs are currently the most commonly used molecules. These AVKs inhibit blood coagulation and are the cause of fatal bleeding. The pharmacological target of AVK is the VKOR enzymatic activity, encoded by the vkorc1 gene. However, the intensive use of AVKs since the 1950s has led to the development of resistance to these molecules. The target resistance has been well studied in the brown rat, but little is known in the house mouse and the black rat
37
Boone, Johnathan. "Three essays concerning information transmission." Diss., [La Jolla] : University of California, San Diego, 2010. http://wwwlib.umi.com/cr/ucsd/fullcit?p3397279.
Full textAbstract:
Thesis (Ph. D.)--University of California, San Diego, 2010.Title from first page of PDF file (viewed March 29, 2010). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.
38
Procházka, Ondřej. "Metody detekce selekce v DNA sekvencích." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2016. http://www.nusl.cz/ntk/nusl-242086.
Full textAbstract:
The topic of semestral thesis is methods to detect selection in DNA sequences. In the begining of the thesis we will describe molecular evolution. It will be written what made the evolution and how the evolution is shown. Moreover there are gen mutations and mechanisms of diffuse and fixation. It will be defined what pozitive, negative and neutral selection is. The thesis is focused on evolution distance of synonymous and nonsynonymous substitution. There will be described three methods – Nei-Gojobori, Li-Wu-Luo and Comeron. All these methods will be described with mathematic formulas. There will be statistic test to decide what kind of selection ti is – there will be used z-test. In the practical part, there will be information about developed software what counts selection pressure from sequences from databazes in format GenBank and it shows parts where selection is. The software will be used for two data sets with two different genetic codes. The result will be discussed. We will discuss results of all three methods of selection pressure and influence of input parametrs.
39
Kinnell, Peter Ken. "The development of selective strain coupling structures for a novel MEMS resonant pressure sensor." Thesis, University of Birmingham, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.422766.
Full textAbstract:
This thesis proposes a novel form of MEMS (micro electro mechanical system) resonant pressure sensor. The sensor incorporates a MEMS silicon resonator that is coupled to a macro scale metallic diaphragm. The combination of a large metallic diaphragm with a micro engineered MEMS resonator required an innovative selective strain coupling structure to be designed. Without the proposed coupling structure, unwanted packaging or thermally induced strain would severely degrade sensor performance, resulting in resonator misalignment, or unwanted strain loading. The feasibility of the proposed device is investigated though analysis and characterisation work performed on a prototype resonator, and a prototype selective coupling structure. These devices allowed fabrication processes to be developed, and their predicted performance to be verified. The prototype resonator demonstrated high quality factors of 28,000 - 30,000 in a vacuum, and resonant frequencies within 10% of modelled predictions. The selective coupling structure was shown to provide a reduction of resonator misalignment of 100: 1, while providing selective strain coupling of 900:1. Following this a fabrication route for producing the fully integrated resonator and selectively coupling structure was developed. This device was electrically tested to determine its resonant characteristics, and quality factors greater that 40,000 were demonstrated.
40
Lucas, Nina. "Microplasma stamps - an atmospheric pressure plasma source for the area selective modification of surfaces." Aachen Shaker, 2008. http://d-nb.info/993157238/04.
Full text
41
Zhang, Zhipeng, Wenckstern Holger von, Jörg Lenzner, and Marius Grundmann. "Wavelength-selective ultraviolet (Mg,Zn)O photodiodes: Tuning of parallel composition gradients with oxygen pressure." American Institute of Physics, 2016. https://ul.qucosa.de/id/qucosa%3A23555.
Full textAbstract:
We report on ultraviolet photodiodes with integrated optical filter based on the wurtzite (Mg,Zn)O
thin films. Tuning of the bandgap of filter and active layers was realized by employing a
continuous composition spread approach relying on the ablation of a single segmented target in
pulsed-laser deposition. Filter and active layers of the device were deposited on opposite sides of a
sapphire substrate with nearly parallel compositional gradients. Ensure that for each sample position
the bandgap of the filter layer blocking the high energy radiation is higher than that of the
active layer. Different oxygen pressures during the two depositions runs. The absorption edge is
tuned over 360 meV and the spectral bandwidth of photodiodes is typically 100 meV and as low as
50 meV.
42
Fiedler, Lindsey J. "Evolutionary Dynamics of Influenza Type B in the Presence of Vaccination: An Ecological Study." Scholar Commons, 2019. https://scholarcommons.usf.edu/etd/7786.
Full textAbstract:
Understanding the evolutionary dynamics of influenza type B in human hosts is a public health concern as we strive to minimize the disease burden in seasonal epidemics. Vaccination is considered the best defense against contracting influenza, and everyone over the age of 6 months is advised to get vaccinated before each season. The effect that vaccine-acquired immunity has on the evolution of influenza B remains unclear. In the U.S., vaccine-uptake is irregular across the states, and the differing coverages present an opportunity to study how vaccination influences viral evolution. This thesis analyzes the evolutionary patterns of influenza B in the presence of vaccine-induced selective pressure. Using an ecological study design, estimates on statewide vaccination coverages from the Centers for Disease Control and Prevention were related to influenza B sequence data. The phylogenies and the frequencies of single nucleotide polymorphisms for high and low coverage states across three influenza seasons were compared to evaluate if there was evidence of vaccination influencing evolution. Overall, the results show that vaccination does not significantly impact the evolutionary dynamics of influenza B with both high and low coverage states showing interspersed phylogenetic trees and similar antigenic diversities.
43
Su, Yung-Chieh. "Selection of Prediction Methods for Thermophysical Properties for Process Modeling and Product Design of Biodiesel Manufacturing." Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/32675.
Full textAbstract:
To optimize biodiesel manufacturing, many reported studies have built simulation models to quantify the relationship between operating conditions and process performance. For mass and energy balance simulations, it is essential to know the four fundamental thermophysical properties of the feed oil: liquid density (Ï L), vapor pressure (Pvap), liquid heat capacity (CpL), and heat of vaporization (Î Hvap). Additionally, to characterize the fuel qualities, it is critical to develop quantitative correlations to predict three biodiesel properties, namely, viscosity, cetane number, and flash point. Also, to ensure the operability of biodiesel in cold weather, one needs to quantitatively predict three low-temperature flow properties: cloud point (CP), pour point (PP), and cold filter plugging point (CFPP). This article presents the results from a comprehensive evaluation of the methods for predicting these four essential feed oil properties and six key biodiesel fuel properties. We compare the predictions to reported experimental data and recommend the appropriate prediction methods for each property based on accuracy, consistency, and generality. Of particular significance are (1) our presentation of simple and accurate methods for predicting the six key fuel properties based on the number of carbon atoms and the number of double bonds or the composition of total unsaturated fatty acid methyl esters (FAMEs) and (2) our posting of the Excel spreadsheets for implementing all of the evaluated accurate prediction methods on our group website (www.design.che.vt.edu) for the reader to download without charge.Master of Science
44
Lucas, Nina [Verfasser]. "Microplasma Stamps – An Atmospheric-Pressure Plasma Source for the Area-Selective Modification of Surfaces / Nina Lucas." Aachen : Shaker, 2009. http://d-nb.info/1126378402/34.
Full text
45
Stagaman, Keaton. "Investigating the Role of Immunity and Other Selective Pressures on the Assembly of the Gut Microbiota in Zebrafish and Humans." Thesis, University of Oregon, 2016. http://hdl.handle.net/1794/20455.
Full textAbstract:
Over the past few decades, it has become increasingly apparent that host-associated microbial communities play an integral role in the development, physiology, and health of their host organisms. All hosts have evolved mechanisms to filter the microbial taxa that comprise their resident intestinal microbial community, or gut microbiota. Utilizing the zebrafish as a model host organism, we documented the development of the gut microbiota through time, and found a significant shift in the composition of the gut microbiota after the onset of adaptive immunity.
This led us to hypothesize that adaptive immunity is an important determinant of gut microbiota composition. We tested this hypothesis using wild type and rag1-/- zebrafish, which lack a functional adaptive immune system. Additionally we tested the robustness of the effects of adaptive immunity to dispersal of microbes between immune-compromised and immune-competent genotypes. We found that adaptive immunity had less of an effect on the composition of the gut microbiota than we expected, although there were intriguing differences in the nature of selection imposed when adaptive immunity was present than when it was absent.
Because “westernization”, or market-integration, has been associated with significant changes in the human microbiota and certain health risks, we used similar analyses to those we applied to the zebrafish system to determine whether market-integration alters the filtering effects of inflammation and intestinal helminth parasites on the intestinal microbial community. We found that market-integration increased inter-subject dissimilarity and reduced inter-subject dispersal. Even small changes in the inflammation marker, CRP, were associated with differences in the gut microbiota, but these effects were reduced in the presence of helminth infection, which has been hypothesized to affect the microbiota by reducing inflammation.
In total, this dissertation provides evidence for the nature and importance of host filters of the gut microbiota across two vertebrate species, as well as providing a framework for future studies of the effects of such filters on the assembly of the gut microbiota.
This dissertation includes previously published, and unpublished, co-authored material.
46
Mathisen, Peter. "Environmental factors selecting for predation resistant and potentially pathogenic bacteria in aquatic environments." Doctoral thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-133338.
Full textAbstract:
The long history of co-existence of bacteria and their protozoan predators in aquatic environments has led to evolution of protozoa resistant bacteria (PRB). Many of these bacteria are also pathogenic to humans. However, the ecological drivers determining the occurrence of different types of PRB in aquatic environments, and the eco-evolutionary link between bacterial adaptation and the resulting implications for mammalian hosts are poorly known. This thesis examines the impact of nutrients and predation on PRB, as well as the ecological and evolutionary connection between their life in aquatic environments and mammalian hosts. In the first study seven bacterial isolates from the Baltic Sea were investigated for their plasticity of adaptation to predation. The response to predation showed large variation where some bacteria rapidly developed a degree of grazing resistance when exposed to predators. The rapid adaptation observed may result in bacterial communities being resilient or resistant to predation, and thus rapid adaptation may be a structuring force in the food web. With the aim to elucidate the link between occurrence of PRB and environmental conditions, a field study and a laboratory experiment were performed. In both studies three PRB genera were found: Mycobacterium, Pseudomonas and Rickettsia. PRB were found both in oligotrophic and eutrophic waters, indicating that waters of all nutrient states can harbor pathogenic bacteria. However, the ecological strategy of the PRB varied depending on environmental nutrient level and disturbance. Using an advanced bioinformatic analysis, it was shown that ecotypes within the same PRB genus can be linked to specific environmental conditions or the presence of specific protozoa, cyanobacteria or phytoplankton taxa. These environmental conditions or specific plankton taxa could potentially act as indicators for occurrence of PRB. Finally, using four mutants (with specific protein deletions) of the pathogenic and predation resistant Francisella tularensis ssp. holarctica, I found evidence of an eco-evolutionary connection between the bacterium´s life in aquatic and mammalian hosts (aquatic amoeba Acanthamoeba castellanii and a murine macrophage). To a large extent F. t. holarctica use similar mechanisms to persist predation by protozoa and to resist degradation by mammal macrophages. To summarize I found a link between predation resistant bacteria in aquatic environments and bacteria that are pathogenic to mammals. Further, I showed that different environmental conditions rapidly selects for PRB with either intracellular or extracellular lifestyles. This thesis provides insights regarding environmental conditions and biomarkers that can be used for assessment of aquatic environments at risk for spreading pathogenic bacteria.Medfinansiärer var även: Swedish Ministry of Defence (A4040, A4042, A404215, A404217), Swedish Minestry of Foreign Affairs (A4952), Swedish Civil Contingencies Agency (B4055)
47
Backlund, Ingrid. "Evaluation of a selective media for the detection of gram-positive bacteria in leg ulcers and pressure wounds." Thesis, Uppsala universitet, Institutionen för kvinnors och barns hälsa, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-254614.
Full textAbstract:
Hard-to-heal ulcers are resource intensive due to the fact that they are difficult to treat and especially vulnerable to bacterial invasion. The bacterial culture contaminating these wounds often consist of several different bacterial organisms that originate from endogenous sources. Necrotic material in ischemic ulcers provide nutrition which support bacterial reproduction, increasing the risk of infection. Determining causative pathogen in infected ulcers proves to be difficult when culturing swab samples, however Staphylococcus aureus and hemolytic streptococci generally act as primary pathogens. The aim of the study was to investigate if the detection rate increased for S. aureus and hemolytic streptococci when culturing swab samples from ulcers on Columbia CNA; a media selective for gram-positive bacteria. In the experimental procedure the inhibitory action of CNA upon gram-negative bacterial growth was evaluated, using simulated ulcer samples (n=6) containing bacterial quality control strains in arbitrary concentrations. Additionally, patient samples (n=51) were cultured and screened for primary pathogens to investigate differences in the detection rate for CNA and the current culture media; Blood agar, Chocolate agar, Gentian violet blood agar and CLED agar. Results from simulated ulcer samples showed excellent inhibitory function regarding the antibiotic substances of the CNA agar. Culturing patient samples from lower leg- and pressure ulcers on CNA, provided indications of diverse circumstances yielding higher respectively lower detection rate concerning S. aureus and hemolytic streptococci. Samples containing mixed flora with gram-negative bacteria generated higher detection rate and samples containing S. aureus yielded a lower detection rate when culturing on CNA, compared with that of the routine method.
48
Boknevitz, Katherine Lynn Michelle. "Synthesis and Characterization of BN-tryptophan and its Incorporation into Proteins & the Cation-π Binding Ability of BN-indole:." Thesis, Boston College, 2020. http://hdl.handle.net/2345/bc-ir:108710.
Full textAbstract:
Thesis advisor: Shih-Yuan LiuDescribed herein are two projects on the application and effects of BN/CC isosterism on indole-containing compounds. In the first chapter, the synthetic route to an unnatural boron and nitrogen-containing analogue of tryptophan (BN-tryptophan) via late-stage functionalization of BN-indole is disclosed and its spectroscopic properties are reported with respect to the natural amino acid, tryptophan. The incorporation of BN-tryptophan into proteins expressed in E. coli using selective pressure incorporation, a residue specific method of unnatural amino acid incorporation, is then reported and its reactivity and fluorescence in the proteins characterized. In the second chapter, the synthesis of a BN-indole-containing aromatic scaffold is reported and the cation-π binding ability characterized by nuclear magnetic resonance (NMR) monitored titrations is disclosed. The resulting chemical shifts were analyzed using a non-linear curve fitting procedure and the extracted association constants (Ka’s) compared with the natural indole scaffold. Computations were also performed to support the titration results
Thesis (PhD) — Boston College, 2020
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
49
Lucas, Nina Verfasser], and Stephanus [Akademischer Betreuer] [Büttgenbach. "Microplasma Stamps – An Atmospheric-Pressure Plasma Source for the Area-Selective Modification of Surfaces / Nina Lucas ; Betreuer: Stephanus Büttgenbach." Braunschweig : Technische Universität Braunschweig, 2019. http://d-nb.info/1231992492/34.
Full text
50
Stiegelmeier, Elenice Weber. "Modelo de otimização para o controle de plantas daninhas usando programação não linear inteira mista." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/18/18153/tde-04062012-165249/.
Full textAbstract:
Este trabalho propõe um modelo de otimização dinâmico para o controle da infestação por plantas daninhas usando aplicação seletiva de herbicida em um sistema anual de colheita da cultura do milho. A densidade do banco de sementes da população de plantas daninhas a frequência dos alelos dominante e recessivo são tomadas como variáveis de estado. A variável de controle é dada pela função de dose-resposta. O objetivo é reduzir o uso de herbicida, maximizar o lucro em um período pré-determinado de tempo e minimizar os impactos ambientais causados pelo uso excessivo de herbicida. O modelo de otimização leva em consideração a diminuição da eficácia do herbicida ao longo do tempo causada pela pressão seletiva. O problema de otimização dinâmico envolve variáveis inteiras e contínuas que foram modeladas como um problema de programação não linear inteiro misto (MINLP). O problema MINLP foi resolvido por enumeração implícita usando o método branch and bound. Simulações numéricas de uma estratégia ótima ilustra o manejo da planta daninha Bidens subalternans em uma plantação de milho com utilização da seleção de uma sequência de dois herbicidas. A solução obtida é comparada com a solução do problema com aplicação de uma sequência de somente um único herbicida.A dynamic optimization model for weed infestation control using selective herbicide application in a corn crop system is presented. The seed bank density of the weed population and frequency of dominant and recessive alleles are taken as state variables of the growing cycle. The control variable is taken as the dose response-function. The goal is to reduce herbicide use, maximize profit in a pre-determined period of time and minimize the environmental impacts caused by excessive use of herbicides. The dynamic optimization model takes into account the decreased herbicide efficacy over time due to weed resistance evolution caused by selective pressure. The dynamic optimization problem involves integer and continuous variables which are modeled as a mixed integer nonlinear programming (MINLP) problem. The MINLP problem was solved by an implicit enumeration known as branch and bound method. Numerical simulations for a case study illustrate the management of the Bidens subalternans in a corn crop by selecting a sequence of two herbicides. The solution presented is compared to the solution of a sequence of only one herbicide.