Dissertations / Theses on the topic 'N. Berg'

Thesis (MTh)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: The purpose of the study is to gain clarity on the conflict that occurs around the minister in the congregation. The following questions will be asked: Why did the conflict occur, what caused it and how was this conflict handled? If there was a better understanding of the cause of the conflict, it can be better managed in the future. The following research question is formulated: What were the biggest hurdles in the missional transformation process in the Dutch Reformed Congregation Op-die-Berg en how was this unlocked? The notion of members of what the essence of the essence and being of the church is and what they expect of the minister play a very important part in the changing context in which the congregation try to discover her missional vocation and actually live missionally. For the purpose of the study the work was done within the field of practical theology on the basis of Richard Osmer’s (2008) model of practical theology. He explored four questions that guided our interpretation and our response to the situation. The four questions are: What is going on? Why is this going on? What ought to be going on? How might we respond? Answering these questions is the four tasks of practical theological interpretation. These tasks are: The descriptive-empirical task; gathering information that help us discern patterns and dynamics in particular situations and contexts. The interpretive task; drawing on theories of the arts and sciences to have a better understanding of and explain why these patterns and dynamics are occurring. The normative task; using theological concepts to interpret particular situations and constructing ethical norms to guide our responses. The pragmatic task: determining strategies of action that will influence situations in ways that are desirable and entering into a reflective conversation. Together, these four tasks constitute the basic structure of practical theological interpretation. A metaphor to describe this process will be that of a spiral and not a circle. Chapters two to six is a discussion of these questions en tasks. The hermeneutical lens of the research is the question of the missio Dei and the role of the Trinitarian God in the transformation process. The research want to help members to answer the question: How might we respond? Thus, they will be able to understand the four questions of Osmer, but will also be able to live with spiritual discernment. The study describes a paradigm shift which the congregation experienced during the past twenty years. The influence of the Christendom paradigm as well as the influence of the business model of running an organization, in which most of the members operate, is challenged by the theology that developed from the missio Dei and the Trinity concepts. The study described the process in a rural community which changed its identity and culture. The influence of the ever-changing context was discussed. Postmodern society challenged the influence of patriarchy. The community and its relationships form the backdrop in the research. This study shows that transformation can’t happen if the minister is not willing to be transformed. The practice of faith-forming habits played an important role. Leadership had to lead through spiritual discernment. The changes that happened doesn’t happen because of a program, but is discovered on a journey of spiritual discernment.
AFRIKAANSE OPSOMMING: Die doel van die studie is om helderheid te verkry oor die konflik wat in die gemeente rondom die persoon van die leraar ontstaan het. Wat het daartoe aanleiding gegee en hoe is dit ontlont? As die faktore wat daartoe aanleiding gegee het, beter verstaan kan word, kan dit ook in die toekoms beter hanteer word. Die volgende navorsingsvraag is geformuleer: Wat was die moeilikste hekkies in die missionale transformasieproses in die Nederduitse Gereformeerde Gemeente Op-die-Berg en hoe is dit ontsluit? Lidmate se kerkbegrip en die rolverwagting van die leraar speel ʼn wesentlike rol in ʼn veranderende konteks waarin die gemeente strewe om sy missie nie net te ontdek nie maar ook uit te leef. Dit is ʼn prakties teologiese studie aan die hand van Richard Osmer (2008) se model waarin vier vrae gevra word. Osmer het vier vrae ontwikkel wat ons interpretasie en reaksie op die situasie begelei. Die vier vrae is: Wat is aan die gebeur? Hoekom gebeur dit? Wat behoort te gebeur? Hoe behoort ons daarop te reageer? Om hierdie vier vrae te beantwoord, is die basis van prakties teologiese interpretasie. Die take wat voortvloei uit die vrae kan as volg beskryf word. Die deskriptief-empiriese taak: Hierdie taak behels die insameling van inligting sodat patrone en dinamika in gegewe situasies en kontekste geëvalueer kan word. Die interpretasie-taak: Die taak behels om deur middel van wetenskaplike metodes en teorieë beter te verstaan en te kan verduidelik waarom die spesifieke patrone en dinamika na vore kom. Die normatiewe taak is om met die hulp van teologiese konsepte die praktiese situasie te interpreteer. Etiese norme word daar gestel om die respons te begelei. Die pragmatiese taak ontwikkel strategieë wat die situasie positief sal beïnvloed en om oop reflekterende gesprek moontlik te maak. Die dinamiese interaksie en invloed van bogenoemde take op mekaar, ( vergelyk dit met die werking van ʼn spiraal in teestelling met die van ʼn sirkel), onderskei praktiese teologie van ander wetenskaplike navorsing. Veral die normatiewe en pragmatiese take is tot die wese van praktiese teologie. Die vier vrae en take word in hoofstuk twee tot ses bespreek. Die hermeneutiese lens van die navorsing, is die vraag na die missio Dei en die rol wat ʼn Trinitariese Godsbegrip in ʼn transformasieproses speel. Die studie wil lidmate help om die vraag te beantwoord: Hoe behoort ons te reageer op die situasie? Lidmate kry nie net in die studie ʼn verstaan van die vrae van Osmer nie, maar veral hoe om geloofonderskeidend in ʼn klein gemeente te lewe. Die studie beskryf die paradigmaskuif waardeur die gemeente van Op-die-Berg die afgelope twintig jaar beweeg het. Die invloed of houvas van die Christendom paradigma asook die uitwerking van die besigheidsmodel waarbinne meeste lidmate opereer, is uitgedaag deur ʼn nuwe verstaan van die missio Dei en die Triniteit. Die studie beskyf die proses en stryd wat ʼn klein plattelandse gemeente deurloop het tydens die skuif in identiteit en kultuur. Die invloed van die konteks word ook deeglik bespreek. Mens kan ook sê dat die postmoderne samelewing implikasies het vir patriargale sisteme. Die studie toon aan hoe sodanige verskuiwings baie van die predikant vra en dat dit net kan gebeur as die geestelike leiers van die gemeente leer om geloofonderskeidend te leef, veral deur die beoefening van geloofsgewoontes. Die gemeenskap en die onderlinge verhoudinge (koinonia) is die hele tyd op die spel. Die verandering wat gebeur het, is nie deur ʼn geïmplementeerde program bewerk nie, maar is op ʼn geloofsonderskeidende reis ontdek.

Adaptive LMS equalizers are widely used in digital communication systems for their simplicity in implementation. Conventional adaptive filtering theory suggests the upper bound of the performance of such equalizer is determined by the performance of a Wiener filter of the same structure. However, in the presence of a narrowband interferer the performance of the LMS equalizer is better than that of its Wiener counterpart. This phenomenon, termed a non-Wiener effect, has been observed before and substantial work has been done in explaining the underlying reasons. In this work, we focus on the Bit Error Rate (BER) performance of LMS equalizers. At first a model – the Gaussian Mixture (GM) model – is presented to estimate the BER performance of a Wiener filter operating in an environment dominated by a narrowband interferer. Simulation results show that the model predicts BER accurately for a wide range of SNR, ISR, and equalizer length. Next, a model similar to GM termed the Gaussian Mixture using Steady State Weights (GMSSW) model is proposed to model the BER behavior of the adaptive NLMS equalizer. Simulation results show unsatisfactory performance of the model. A detailed discussion is presented that points out the limitations of the GMSSW model, thereby providing some insight into the non-Wiener behavior of (N)LMS equalizers. An improved model, the Gaussian with Mean Square Error (GMSE), is then proposed. Simulation results show that the GMSE model is able to model the non-Wiener characteristics of the NLMS equalizer when the normalized step size is between 0 and 0.4. A brief discussion is provided on why the model is inaccurate for larger step sizes.
Master of Science

The research focuses on the value of the teacher´s competence for students with deficiency of motivation for learning and development. A teacher’s socio-emotional competence may give these students energy to seize their own future and contribute to positive personal development for themselves. This research contributes to the understanding of the content of the social inter-action between teacher and student. Relations that develop have significance for the student’s development and growth. Main topics in this connection are: How important is human inter-action between teacher and student as a basic condition for learning and development? What encourages and what obstructs positive inter-action between teacher and student? Are teachers and school-leaders conscious of the positive inter-action and how does this express itself? Finally one may ask the question: Can guidelines be developed for the practice and understanding of positive inter-action? Knowledge and understanding is based on the use of different scientific methods. In essence the use of method is qualitative in a retrospective perspective. The qualitative investigations have both been individual and collective/group based. Students, teachers and school-leaders who participated in the research were my collaboraters associated with a certain schoolclass during the years 1976 – 1980. The individual part has consisted of experiences and acts written down in journals or “books of retrospection”. The collective or group-based part is attached to a seminar were the participants have been gathered in order to reflect upon their common experiences from this particular period of their school days. The result of these group-based investigations have been compared with the content of my journals. Examinations with a broader scope have been carried out to detect trends in the content of relations between adults and young people in today’s society both at school and during spare time. The empirical data give reasons to discuss the social inter-active learning- and developing-perspective. In this discussion the significance of human inter-action between teacher and student is closely attached to kognitive- and social competence. Essential in this regard is knowledge of what kind of actions encourage or obstruct the development of the processes that result in personal growth or recognition/acknowledgement, and how significant these processes are as a basis for the kognitive learning. The results show that many students have a need for untraditional structures in relation to their own development. Modification of behaviour often occurs in connection to emotional learning, in situations where psychodynamic surplus and motivation for kognitive development and growth is created. The teacher has to make an effort to find the students “home ground” through careful observations and spontanious actions in his/her encounter with the student. Through a joint adventure/stay on the student’s arena, opportunities for insight into important values for meaningful, constructive and confluent didactic processes can be created. This type of inter-action often creates a break from traditional structures in school. The results of the investigations in this thesis suggest a great significance for the processes involving positive inter-action between teacher and student and therefore gives these processes great attention. This thesis defines the untraditional as a form of necessary nonstructure where the consequencies of our social actions in a learning perspective is central.
Godkänd; 2000; 20061116 (haneit)

Adaptive Least Mean Square (LMS) equalizers are widely used in digital communication systems primarily for their ease of implementation and lack of dependence on a priori knowledge of input signal statistics. LMS equalizers exhibit non-Wiener characteristics in the presence of a strong narrowband interference and can outperform the optimal Wiener equalizer in terms of both mean square error (MSE) and bit error rate (BER). There has been significant work in the past related to the analysis of the non-Wiener characteristics of the LMS equalizer, which includes the discovery of the shift in the mean of the LMS weights from the corresponding Wiener weights and the modeling of steady state MSE performance. BER performance is ultimately a more practically relevant metric than MSE for characterizing system performance. The present work focuses on modeling the steady state BER performance of the normalized LMS (NLMS) equalizer operating in the presence of a strong narrowband interference. Initial observations showed that a 2 dB improvement in MSE may result in two orders of magnitude improvement in BER. However, some differences in the MSE and BER behavior of the NLMS equalizer were also seen, most notably the significant dependence (one order of magnitude variation) of the BER behavior on the interference frequency, a dependence not seen in MSE. Thus, MSE cannot be used as a predictor for the BER performance; the latter further motivates the pursuit of a separate BER model. The primary contribution of this work is the derivation of the probability density of the output of the NLMS equalizer conditioned on a particular symbol having been transmitted, which can then be leveraged to predict its BER performance. The analysis of the NLMS equalizer, operating in a strong narrowband interference environment, resulted in a conditional probability density function in the form of a Gaussian Sum Mixture (GSM). Simulation results verify the efficacy of the GSM expression for a wide range of system parameters, such as signal-to-noise ratio (SNR), interference-to-signal (ISR) ratio, interference frequency, and step-sizes over the range of mean-square stable operation of NLMS. Additionally, a low complexity approximate version of the GSM model is also derived and can be used to give a conservative lower bound on BER performance. A thorough analysis of the MSE and BER behavior of the Bi-scale NLMS equalizer (BNLMS), a variant of the NLMS equalizer, constitutes another important contribution of this work. Prior results indicated a 2 dB MSE improvement of BNLMS over NLMS in the presence of a strong narrowband interference. A closed form MSE model is derived for the BLMS algorithm. Additionally, BNLMS BER behavior was studied and showed the potential of two orders of magnitude improvement over NLMS. Analysis led to a BER model in the form of a GSM similar to the NLMS case but with different parameters. Simulation results verified that both models for MSE and BER provided accurate prediction of system performance for different combinations of SNR, ISR, interference frequency, and step-size. An enhanced GSM (EGSM) model to predict the BER performance for the NLMS equalizer is also introduced, specifically to address certain cases (low ISR cases) where the original GSM expression (derived for high ISR) was less accurate. Simulation results show that the EGSM model is more accurate in the low ISR region than the GSM expression. For the situations where the derived GSM expression was accurate, the BER estimates provided by the heuristic EGSM model coincided with those computed from the GSM expression. Finally, the two-interferer problem is introduced, where NLMS equalizer performance is studied in the presence of two narrowband interferers. Initial results show the presence of non-Wiener characteristics for the two-interferer case. Additionally, experimental results indicate that the BER performance of the NLMS equalizer operating in the presence of a single narrowband interferer may be improved by purposeful injection of a second narrowband interferer.
PHD

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Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior
Analisam-se as oito fotografias produzidas no Brasil, componentes da obra O ber?o da desigualdade (2009), cuja autoria ? de Sebasti?o Salgado (imagens e legendas) e Cristovam Buarque (textos po?ticos), buscando apresentar possibilidades interpretativas de signos mediadores de problem?ticas sociais. Al?m das fotografias, tamb?m se consideram os escritos complementares das imagens, que em conjunto discutem a tem?tica da desigualdade socioeducacional no mundo. Delineia-se uma an?lise cr?tica dos signos imagens, legendas e textos po?ticos , refletindo-se sobre a ocorr?ncia da semiose no processo interpretativo e a representa??o da sociedade por meio destes textos. A investiga??o baseia-se na semi?tica de Peirce especificamente na Teoria dos Interpretantes na linguagem fotogr?fica e na teoria da imagem. Considera-se relevante a linguagem como interface entre o ser social e a sociedade para a percep??o do campo s?cio-comunicacional. A fotografia pode at? n?o ser vista como uma ferramenta de transforma??o social, mas pode ser compreendida como um signo componente do movimento de transforma??o, sendo carregada de potencialidades influenciadoras do pensamento e das a??es humanas quer culturais, quer ideol?gicas

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Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico
In vitro and in animal models, APE1, OGG1, and PARP-1 have been proposed as being involved with inflammatory response. In this work, we have investigated if the SNPs APE1 Asn148Glu, OGG1 Ser326Cys, and PARP-1 Val762Ala are associated to meningitis and also developed a system to enable the functional analysis of polymorphic proteins. Patients with bacterial meningitis (BM), aseptic meningitis (AM) and controls (non-infected) genotypes were investigated by PIRA-PCR or PCR-RFLP. DNA damages were detected in genomic DNA by Fpg treatment. IgG and IgA were measured from plasma and the cytokines and chemokines were measured from cerebrospinal fluid samples using Bio-Plex assays. The levels of NF-?B and c-Jun were measured in CSF by dot blot assays. A significant (P<0.05) increase in the frequency of APE1 148Glu allele in BM and AM patients was observed. A significant increase in the genotypes Asn/Asn in control group and Asn/Glu in BM group was also found. For the SNP OGG1 Ser326Cys, the genotype Cys/Cys was more frequent (P<0.05) in BM group. The frequency of PARP-1 Val/Val genotype was higher in control group (P<0.05). The occurrence of combined SNPs increased significantly in BM patients, indicating that these SNPs may be associated to the disease. Increasing in sensitive sites to Fpg was observed in carriers of APE1 148Glu allele or OGG1 326Cys allele, suggesting that SNPs affect DNA repair activity. Alterations in IgG production were observed in the presence of SNPs APE1Asn148Glu, OGG1Ser326Cys or PARP-1Val762Ala. Reductions in the levels ofIL-6, IL-1Ra, MCP-1/CCL2and IL-8/CXCL8 were observed in the presence of APE1148Glu allele in BM patients, however no differences were observed in the levels of NF-?B and c-Jun considering genotypes and analyzed groups. Using APE1 as model, a system to enable the analysis of cellular effects and functional characterization of polymorphic proteins was developed using strategies of cloning APE1 cDNA in pIRES2-EGFP vector, cellular transfection of the construction obtained, siRNA for endogenous APE1 and cellular cultures genotyping. In conclusion, we obtained evidences of an effect of SNPs in DNA repair genes on the regulation of immune response. This is a pioneering work in the field that shows association of BER variant enzymes with an infectious disease in human patients, suggesting that the SNPs analyzed may affect immune response and damage by oxidative stress level during brain infection. Considering these data, new approaches of functional characterization must be developed to better analysis and interactions of polymorphic proteins in response to this context
Estudos in vitro e em modelos animais sugerem que as prote?nas de reparo de DNA da via de reparo por excis?o de bases (do ingl?s, BER) APE1, OGG1 e PARP-1 est?o envolvidas tamb?m na resposta inflamat?ria. Neste trabalho foi investigado se os SNPs APE1 Asn148Glu, OGG1 Ser326Cys e PARP-1 Val762Ala associam-se ? meningite, e foi desenvolvido um sistema para an?lise funcional destas variantes polim?rficas. Os gen?tipos de pacientes com meningite bacteriana (MB), meningite ass?ptica (MA) e n?o infectados (controles) foram investigados por PIRA-PCR ou PCR-RFLP. Danos no DNA gen?mico foram detectados por meio de tratamento com Fpg. IgG e IgA foram titulados no plasma e citocinas e quimiocinas foram mensuradas em amostras de l?quor atrav?s de ensaios em Bio-Plex. Os n?veis de NF-?B e c-Jun foram dosados no l?quor dos pacientes por meio de dot blot. Foi observado um aumento significativo (P<0.05) na frequ?ncia do alelo APE1 148Glu nos casos de MB e MA. Os gen?tipos Asn/Asn no grupo controle e Asn/Glu no grupo da MB tamb?m apresentaram relevante aumento em suas frequ?ncias (P<0.05). Para o SNP OGG1 Ser326Cys, o gen?tipo Cys/Cys esteve mais frequente (P<0.05) nos casos de MB. A frequ?ncia do gen?tipo PARP-1 Val/Val foi mais alta no grupo controle (P<0.05). A ocorr?ncia combinada dos SNPs foi significativamente alta nos pacientes com MB, indicando que estes SNPs podem estar associados ? doen?a. Os portadores do alelo APE1 148Glu ou OGG1 326Cys apresentaram um n?mero maior de s?tios sens?veis ? Fpg, sugerindo que os SNPs afetam a atividade de reparo do DNA. Altera??es na s?ntese de IgG foram observadas na presen?a dos SNPs APE1 Asn148Glu, OGG1 Ser326Cys ou PARP-1 Val762Ala. Redu??es nos n?veis de IL-6, IL-1Ra, MCP-1/CCL2 e IL-8/CXCL8 foram encontradas na presen?a do alelo APE1 148Glu em amostras de pacientes com MB, no entanto n?o foram encontradas diferen?as nos n?veis de NF-?B e c-Jun considerando os gen?tipos e os grupos analisados. Utilizando APE1 como modelo, foi desenvolvido um sistema que possibilita a express?o e caracteriza??o funcional das enzimas polim?rficas estudadas e seus efeitos na c?lula, por meio de clonagem, utilizando o vetor pIRES2-EGFP e cDNA de APE1, transfec??o celular da constru??o obtida, inibi??o por siRNA de APE1 end?gena e genotipagem de culturas celulares. Em conclus?o, foram obtidas evid?ncias de um efeito significativo dos SNPs nos genes de reparo de DNA na regula??o da resposta imunol?gica. Este ? um trabalho pioneiro na ?rea, que demonstra a associa??o de variantes das enzimas da via BER com uma doen?a infecciosa em humanos, sugerindo que os SNPs estudados podem afetar a resposta imune e o impacto do n?vel de estresse oxidativo durante a infec??o cerebral. Desta forma, novos meios de an?lise funcional devem ser desenvolvidos para estudo de prote?nas polim?rficas e suas intera??es neste contexto
2020-01-01

Master's thesis compares the standard for digital terrestrial television broadcasting of the first generation DVB-T/H and the second generation DVB-T2 with particular emphasis on the modulator, a security channel interference, the signal from the transmitting environment itself and the modulation signal. The following description of specific models of transmission channels for fixed, portable and mobile reception of digital terrestrial signal. Comparison with the particular relates of the transmission parameters for different types of reception of digital terrestrial television with achieving efficiency and effectiveness of transmission at the level of laboratory measurements and computer simulation.

International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California
Bit errors often occur in a wireless communications link when impairments alter the transmitted signal. It is advantageous to be able to predict how well a system will tolerate transmission problems. This paper details laboratory performance measurements and comparisons in terms of evaluating configurations of a digital receiver for Feher patented Quadrature Phase Shift Keying (FQPSK-B) demodulation. The transmitted signal is subjected to calibrated levels of impairments while the receiver performance is monitored in real-time.

Bivalves play a marked role in coastal marine ecosystems, impacting primary productivity with a strong top-down control on phytoplankton communities. In addition, they are an important food source for higher trophic levels, including humans. However, bivalves can be impaired by several external factors, either biotic or abiotic, natural or anthropogenic. Exposure to these stressors, coupled with intensive farming, raised the need for adequate management of the wild populations and farmed production. To improve the difficult balance between ecological and socio-economic interests, it must be investigated how bivalves cope with external stressors. For this reason, the effects caused by the following stressors were studied in the present thesis: (i) harmful algal blooms (HABs) and (ii) climate change drivers in the seawater, such as warming (W) and acidification (A). HABs are increasing in frequency, intensity, persistence and geographic distribution, but are ambiguous regarding their ecological impacts and physiological effects on bivalves. A strong relationship is emerging between HABs and climate change drivers, what may affect both shellfisheries and wild populations. Hence, the objectives of this work are: 1) To determine whether native and invasive species cope with exposure to HABs differently, providing new insights on species-specificities and ecosystem functioning fragilities in the presence of invasive species and HABs; 2) To evaluate how commercially valuable bivalve species cope with simultaneous exposure to several climate change drives and HABs, providing new insights on how environmental changes affects toxicokinetics, physiological and genotoxic bivalves responses, under HABs; 3) To assess, marine biotoxins bioaccessibility, contributing for new information relevant for risk assessment. Different approaches were used to achieve these goals. Complementary field and laboratory works were performed to assess toxicokinetics patterns of marine biotoxins in native vs. invasive bivalve species. Bivalves were exposed to toxic blooming algae species under climate change scenarios in laboratory controlled conditions to assess toxicokinetics as well as physiological and genotoxic responses. Naturally contaminated bivalves were used to investigate their role as vectors of marine biotoxins to humans through in vitro digestion methodology. Relevant new data were obtained regarding the effects of several marine biotoxins in bivalves. Assessing accumulation of regulated and non-regulated biotoxins in native (Ruditapes decussatus) and invasive (R. philippinarum) clam species from Aveiro Lagoon revealed that higher toxin content, particularly regarding OA-group, the most abundant and frequent toxins in the Portuguese coast, is reached by native species. Accumulation of lower toxin levels by invasive clam may then favour farmers interest for their production. The kinetics and genotoxicity study in native and invasive clams reinforced the existence of species-specific behaviours. Exposure to the dinoflagellate Prorocentrum lima, an OA and dinophysistoxin-1 producer, increases the pressure over native clams, with higher toxin accumulation and genetic damage, as well as early and increased induction of DNA repair activity. Invasive clams, on the other hand, are better adapted to cope with these challenges. Investigation of the effects of combined exposure to multiple stressors revealed that W, A and HABs alter the accumulation/elimination dynamics of Paralytic Shellfish Poisoning (PSP) toxins in mussels (Mytilus galloprovincialis). Lower accumulation levels and slower elimination rates were observed. The predicted climate change scenarios and exposure to HABs may then lead to lower contamination levels but to longer harvesting closures. Simultaneous exposure to altered environmental conditions and HABs also had significant impacts in the antioxidant system and DNA integrity, resulting in an organ-specific modulation of the antioxidant response, increasing genetic damage and preventing/retarding DNA damage repair. However, the DNA damage observed seems to be non-oxidative. While the investigation of factors enhancing the elimination of toxins was not a main objective of this study, it was shown that acidification might promote PSP toxins elimination in mussels. Finally, the bioaccessibility studies revealed a significant reduction in the OA group content available after in vitro digestion, suggesting an overestimation of exposure to these biotoxins and an over-conservative approach in safety levels definition and risk assessment studies. This was the first study assessing bioaccessibility of OA-group toxins, pointing to in vitro digestion as a promising tool to obtain accurate data regarding toxin ingestion from bivalves to the consumer. Overall, the complexity of the relation between HABs, bivalves and the environmental factors to consider in marine biotoxins management is increasing, and only continuous and extensive monitoring of environmental, biological and anthropogenic conditions may allow for a healthier balance between environmental and socio-economic interests.
Os bivalves desempenham um papel fundamental nos ecossistemas marinhos costeiros, limitando a produtividade primária através de um forte mecanismo de controlo descendente (top-down) sobre as comunidades fitoplanctónicas e constituindo uma importante fonte de alimento para níveis tróficos superiores, incluindo o Homem. No entanto, os bivalves são afetados negativamente por diversos fatores externos, sejam estes bióticos ou abióticos, naturais ou antropogénicos. A exposição a estes fatores, juntamente com a exploração intensiva, leva a que seja necessária a implementação de uma gestão adequada, quer das populações selvagens, quer da produção em viveiros. Para melhorar esta gestão e alcançar o difícil equilíbro entre os interesses ecológicos e socioeconómicos é então necessário entender como os bivalves lidam com estes fatores. Na presente tese foram estudados os efeitos provocados por (i) blooms de algas tóxicas (HABs do inglês harmful algal blooms) e (ii) alterações das condições climáticas da água do mar, nomeadamente o aumento da temperatura (W) e acidificação (A). Os HABs são fenómenos que estão a aumentar em frequência, intensidade, persistência e abrangência geográfica, mas cujos impactos ecológicos e efeitos fisiológicos em bivalves são ainda ambíguos. Concomitantemente com a pressão causada pelo aumento da procura de bivalves como alimento para as populações humanas, fortes indícios apontam para uma relação entre a ocorrência de HABs e os parâmetros de alterações climáticas, o que pode afectar quer a indústria, quer as populações de bivalves selvagens. Assim, os objetivos deste trabalho são: 1) Determinar se as espécies nativas e invasoras lidam com a exposição a HABs de maneira diferente, dando particular atenção às respostas específicas de cada espécie e às fragilidades do ecossistema em relação à presença de espécies invasoras e ocorrência dos referidos blooms; 2) Avaliar como espécies de bivalves de elevado valor comercial lidam com a exposição simultânea a alterações climáticas e HABs, focando o efeito destas modificações ambientais na toxicocinética, respostas fisiológicas e genotoxicidade exibida pelos bivalves; 3) Avaliar a bioacessibilidade das biotoxinas marinhas, focando a obtenção de informação relevante para estudos de avaliação de risco. Foram realizados trabalhos complementares de campo e laboratório, de modo a avaliar os padrões de toxicocinética de biotoxinas marinhas em espécies nativas e invasoras. Em laboratório, foram expostos bivalves a algas tóxicas em condições alteradas, simulando a ocorrência de HABs sob cenários previstos de alterações climáticas, de modo a avaliar toxicocinética, respostas fisiológicas e genotoxicidade. Exemplares naturalmente contaminados foram utilizados para investigar o papel dos bivalves como vectores de biotoxinas marinhas para humanos, através da simulação da digestão in vitro. O estudo da acumulação de biotoxinas marinhas regulamentadas e não regulamentadas em espécies de amêijoa nativa (Ruditapes decussatus) e invasora (R. philippinarum) na Ria de Aveiro revelou que a espécie nativa acumula, recorrentemente, concentrações de toxinas mais elevadas, particularmente no que toca a toxinas grupo do ácido ocadaico (OA do inglês Okadaic acid), sendo estas as toxinas mais abundantes e frequentes na costa Portuguesa. A acumulação de menores concentrações por parte da amêijoa invasora pode promover o interesse dos produtores na sua exploração. A avaliação da cinética e da genotoxicidade em amêijoas nativas e invasoras reforçou a existência de comportamentos específicos para cada espécie. A exposição a Prorocentrum lima, dinoflagelado produtor de OA e dinofisistoxina 1, aumenta a pressão sobre a espécie nativa, uma vez que esta apresenta as concentrações de toxina mais elevadas, os maiores níveis de dano genético e ainda uma indução mais precoce e intensa dos mecanismos de reparação de dano no ADN. A espécie invasora, por outro lado, está melhor adaptada para lidar com estes desafios. O estudo dos efeitos de fatores múltiplos combinados revelou que a exposição a W, A e HABs altera a dinâmica de acumulação/eliminação de toxinas paralisantes (PSP) em mexilhões (Mytilus galloprovincialis). Os cenários previstos de alterações climáticas e a exposição a HABs sugerem níveis de contaminação mais baixos, mas períodos de interdição de apanha mais prolongados. A exposição simultânea a condições ambientais alteradas e HABs também teve um impacto significativo no sistema antioxidante e na integridade do ADN, resultando numa modulação da resposta antioxidante especifica para cada órgão, aumentando o dano genético e prevenindo/atrasando a sua reparação. O dano encontrado no ADN parece, no entanto, não ser oxidativo. Embora a investigação de fatores que favoreçam a rápida eliminação de toxinas não constasse dos objetivos deste estudo, foi demonstrado que a acidificação pode promover a eliminação de toxinas PSP em mexilhões. Por último, os estudos de bioacessibilidade revelaram uma redução na quantidade de toxinas do grupo-OA disponível após a digestão in vitro, sugerindo uma sobrestimação da exposição a estas biotoxinas e recomendando uma abordagem conservadora na definição dos níveis de segurança e na subsequente avaliação do risco. Este foi o primeiro estudo a determinar a bioacessibilidade das toxinas do grupo-OA e sugere a técnica de digestão in vitro como uma ferramenta promissora na obtenção de dados rigorosos no que diz respeito à ingestão de toxinas através de bivalves e a acessibilidade destes compostos no organismo humano. De um modo geral, a complexidade da relação entre HABs, bivalves e os fatores ambientais a serem considerados na gestão de biotoxinas marinhas está a aumentar, e apenas uma contínua e extensiva monitorização das condições ambientais, biológicas e antropogénicas pode permitir um melhor equilíbrio entre os interesses ambientais e socio-económicos.
Programa Doutoral em Ciência, Tecnologia e Gestão do Mar