Esta tese tem por objetivo o desenvolvimento de metodologias eficientes e de baixo custo para ajustar as propriedades elétricas de OFETs de canal p e de canal n, a fim de possibilitar a fabricação do circuito complementar orgânico, semelhante a uma estrutura CMOS. O desempenho do circuito complementar fabricado foi otimizado, e também foi confeccionado por impressão um OFETs de canal operando em baixas tensões. Para a fabricação do CMOS orgânico foi proposto um método baseado na seleção adequada do solvente da camada dielétrica para ajustar o desempenho elétrico dos OFETs de canal p e de canal n. Os solventes, MEK, nBA e DMSO foram selecionados para a dissolução do PMMA por apresentarem diferenças nos valores de momento de dipolo, de ponto de ebulição e de graus de ortogonalidade em relação as camadas semicondutoras de P3HT e de P(NDI2OD-T2) dos OFETs. A análise dos resultados dos OFETs de canal p e de canal n demonstrou que a metodologia proposta é adequada tanto para o ajuste das propriedades elétricas destes dispositivos quanto para a otimização do desempenho dos mesmos. Os melhores desempenhos elétricos para os OFETs de canal p e de canal n foram obtidos quando utilizados o DMSO e o MEK como solventes do PMMA, respectivamente, devido à perfeita ortogonalidade destes solventes em relação às camadas semicondutoras. Os OFETs de canal p que utilizaram o DMSO e os OFETs de canal n que utilizaram o nBA foram os que apresentaram desempenhos elétricos semelhantes, sendo portanto aplicados na fabricação do CMOS. Valores de ganho entre 6,8 e 7,8 e de margem de ruído entre 28,3 V e 34,5 V foram obtidos para inversores complementares fabricados nesta etapa do trabalho. OFETs de canal p utilizando uma blenda de PTAA: diF TES ADT como camada semicondutora, o PEDOT:PSS como eletrodos dreno/fonte e o P(VDF-TrFE-CFE) como camada dielétrica também foram fabricados neste trabalho. A técnica de blade-coating foi utilizada para a deposição dos eletrodos dreno/fonte e da camada semicondutora, ao passo que a técnica de spray-coating foi utilizada para a deposição da camada dielétrica. Da análise dos resultados foi possível inferir que a utilização de um dielétrico com elevada constante dielétrica (K), como o P(VDF-TrFE-CFE), possibilita o funcionamento dos transistores a baixas tensões (≤ 8 V), porém com valores de mobilidade reduzidos devido à elevada desordem dipolar na interface provocada por este dielétrico. Para minimizar esses efeitos, uma fina camada de um polímero fluorado foi depositada entre a camada semicondutora e a dielétrica pela técnica de blade-coating, constituindo assim uma bicamada dielétrica nos OFETs. Dos resultados das medidas elétricas dos OFETs constituídos pela bicamada dielétrica foi observada permanência do funcionamento destes dispositivos a tensões inferiores a 8 V com desempenho elétricos superiores a resultados já publicados na literatura. Por fim, inversores lógicos unipolares com transistores de carga foram fabricados com os OFETs que utilizaram a bicamada dielétrica, sendo obtidos valores de ganho entre 1,2 e 1,6 e de margem de ruído entre 56% e 68,5% de ½ VDD. / This thesis aimed to develop an efficient and low cost method to adjust the electrical properties of p- and n-channel OFETs to allow us to build an organic CMOS and the optimization of printed p-channel OFETs to work at low voltages. We proposed a method to fabricate the organic CMOS, based on the careful selection of dielectric solvent, which was adjusted to obtain the best performance of p- and n-channel OFETs. The dielectric solvents as MEK, nBA and DMSO were selected to dissolve the PMMA dielectric polymer due their different physical properties as dipole moment and boiling point and because they showed slightly different degrees of orthogonality to the P3HT and P(NDI2OD-T2) semiconductor layers of the OFETs. The results showed that the careful selection of the dielectric solvent not only allows to tune the electrical characteristics of the p- and n-channel OFETs, but also to improve the performance of these devices. The best performances were achieved when DMSO and MEK were used as dielectric solvents of the p and n-channel OFETs, respectively, as result of the perfectly orthogonality of these solvents to the semiconductor layers. P-channel OFETs using DMSO and n-channel OFETs using nBA showed similar electrical characteristics and thus, they were used to construct the organic CMOS. The organic complementary inverters showed high gain and noise margin values in the range of 6,8 to 7,8 and 28,3 V to 34,5 V, respectively. Printed p-channel OFETs were also fabricated, in which the blend PTAA:diF TES ADT was used as semiconductor channel, PEDOT:PSS as the drain/source electrodes and P(VDF-TrFE-CFE) as the dielectric layer. The blade-coating technique was used to deposit the source/drain electrodes and the semiconductor layer, while the spray-coating technique was used to deposit the dielectric layer. It was observed that using high-k dielectric as P(VDF-TrFE-CFE) enable to reduce the operating voltage of the OFETs (≤8 V), however, this high-k dielectric also reduced the field effect mobility due the dipolar disorder at the semiconductor/dielectric interface. To minimize the dipolar issue at the interface, we inserted a thin fluoropolymer dielectric layer by blade-coating between the semiconductor and the high-k dielectric layers, thus constituting a dielectric bilayer on the OFETs. From the electrical measurements of the OFETs with the dielectric bilayer, it was observed that the devices were still working at 8 V and they also showed better performance in comparison to results already published. Finally, organic unipolar inverters with load transistors were fabricated using the p-channel OFETs with the dielectric bilayer and they showed reasonable performance, with gain and noise margin in the range of 1,2 to 1,6 and 56% e 68,5% of ½ VDD, respectively.

FundaÃÃo de Amparo à Pesquisa do Estado do Cearà / Esse trabalho doutoral tem como proposta fazer uso da Teoria ClÃssica dos Testes â TCT e da Teoria de Resposta ao Item â TRI como instrumentos na avaliaÃÃo da qualidade mÃtrica de testes de seleÃÃo, sob quatro aspectos de investigaÃÃo: AnÃlise da Validez do Construto; AnÃlise PsicomÃtrica dos Itens; Funcionamento Diferencial dos Itens â DIF; e FunÃÃo de InformaÃÃo. Para tanto, foram utilizados dados dos resultados das provas de PortuguÃs e MatemÃtica do concurso vestibular da Universidade Estadual do Estado do Cearà â UECE, de 2007, em que participaram 20.016 candidatos a 38 Cursos de GraduaÃÃo, somente na Capital do Estado. Para o tratamento desses dados, foram utilizados os seguintes softwares: SPSS, v15; BILOG-MG, v3.0; MULTILOG FOR WINDOWS, v1.0; e o TESTFACT v4.0. A primeira providÃncia foi verificar a dimensionaidade dessas provas. Para tanto se utilizou o MÃtodo de Kaiser-Guttman, Scree-plot, e o MÃtodo das Cargas Fatoriais e das Comunalidades da Matriz de Fatores. A constataÃÃo foi de que a prova de PortuguÃs apresentava caracterÃsticas multidimensionais, sendo, portanto, descartada, por nÃo atender aos pressupostos bÃsicos da Unidimensionalidade e IndependÃncia Local dos Itens. A prova de MatemÃtica, no entanto, por apresentar comportamento unidimensional, se tornou o foco deste trabalho. A anÃlise da Validez do Construto foi realizada por meio dos coeficientes Alpha de Cronbach e Kuder-Richardson, tendo gerado valores iguais a 0,685, alÃm da utilizaÃÃo, tambÃm, do mÃtodo das Cargas Fatoriais, com cargas entre 0,837 e 0,960, indicando intensa consistÃncia interna. A anÃlise psicomÃtrica dos itens foi realizada por meio dos Ãndices de dificuldade, discriminaÃÃo e acerto ao acaso, para ambas as teorias, indicando ser essa uma prova de dificuldade mediana, com bom comportamento discriminativo e baixo Ãndice de acerto ao acaso. A anÃlise do DIF foi realizada, segundo o gÃnero dos candidatos, pelos mÃtodos Delta-plot, Maentel-Haenszel, RegressÃo LogÃstica e ComparaÃÃo dos Betas, indicando resultados estatÃsticamente nÃo significativos, no que se concluiu nÃo apresentar, a prova, comportamento diferenciado, segundo o gÃnero. A anÃlise da FunÃÃo de InformaÃÃo da prova permitiu se observar que esta à particularmente vÃlida para candidatos com aptidÃo em torno de 0,8750 e que, a um nÃvel de confianÃa de 95%, 49,3% dos candidatos atenderiam a essa indicaÃÃo. Observou-se tambÃm que 90,6% dos candidatos, em ambos os processos, apresentaram o mesmo nÃvel de aptidÃo, indicando uma convergÃncia bastante razoÃvel entre os resultados gerados pela TCT e TRI, no entanto, no estudo amostral, a TRI identificou que 9,4% dos candidatos apresentaram maior aptidÃo para a realizaÃÃo de um curso superior que os selecionados pela TCT.

Differenzielles Itemfunktionieren bedeutet für die Trendschätzung durch Linking in querschnittlich angelegten Large-Scale Assessments eine Voraussetzungsverletzung. Solche Voraussetzungsverletzungen können sich negativ auf die Eigenschaften von Trendschätzern auswirken, woraus sich Einschränkungen für die Interpretierbarkeit der Trendschätzung ergeben können. Die vorliegende Arbeit umfasst, eingebettet in einen Rahmungstext, drei Einzelbeiträge, die sich mit der Prüfung der Auswirkung differenziellen Itemfunktionierens unterschiedlicher Provenienz auseinandersetzen. Im ersten Einzelbeitrag wird die Interaktion von Linkingdesigns und Linkingmethoden mit zwischen Ländern und über die Zeit unsystematisch unterschiedlich funktionierenden Items untersucht. Dabei zeigte sich, dass die Wahl des Designs von großer Bedeutung sein kann, während der Performanzunterschied zwischen gängigen Linkingmethoden marginal war. Darüber hinaus führte der häufig praktizierte Ausschluss von differenziell funktionierenden Items zu einem Effizienzverlust. Im zweiten Einzelbeitrag wird die Unsicherheit der Trendschätzung, die entsteht, wenn Items zwischen Ländern und über die Zeit unsystematisch unterschiedlich funktionieren, quantifiziert und in die Berechnung der zugehörigen Standardfehler integriert. Im dritten Einzelbeitrag wird betrachtet, wie differenziellem Itemfunktionieren begegnet werden kann, das durch fehlende Werte und wechselnde Ausfallmechanismen zustande kommt. Wurden die fehlenden Werte inadäquat behandelt, verloren die Trendschätzer ihre Erwartungstreue und Konsistenz sowie an Effizienz. In der Summe wird in der vorliegenden Arbeit identifiziert und hervorgehoben, dass es in den untersuchten Bedingungen je nach Art des differenziellen Itemfunktionierens effektive Möglichkeiten des Umgangs mit diesem gibt, die potenziellen Einschränkungen bei der validen Interpretation der Trendschätzung zumindest teilweise entgegenwirken können. / Differential item functioning signifies a violation of the prerequisites required for trend estimation, which involves the linking of cross-sectional large-scale assessments. Such violations can negatively affect the properties of the trend estimators. Hence, the interpretability of trend estimates will be limited under such circumstances. Embedded within an overarching framework, three individual contributions that examine and deal with the effects of differential item functioning from different origins are presented in the current dissertation. The first article examines the interactions of linking designs and linking methods with items that show unsystematic and differential functioning between countries and across time. It showed that the choice of the design can be of great importance, whereas the difference in performance between common linking methods was marginal. In addition, the exclusion of differentially functioning items, an approach that is frequently used in practice, led to a loss of efficiency. In the second contribution, the uncertainty for the trend estimation resulting from items that show unsystematic and differential functioning between countries and across time is quantified and incorporated into the calculation of the trends' standard errors. The third article focuses on differential item functioning that is induced by missing values and nonresponse mechanisms that change over time. When the missing values were treated inappropriately, the trend estimators lost their unbiasedness, their consistency, and their efficiency. In sum, this dissertation identifies and emphasizes the ideas that, depending on the type of differential item functioning, there are effective ways to deal with it under the investigated conditions, and these can at least partially counteract potential limitations so that the trend estimates can still be interpreted validly.

人格測驗一直是企業進行人力資源管理活動時的一個重要工具。大部分的人格測驗都是自陳量表，且沒有標準答案，因此在甄選情境時，應徵者對於人格測驗是否會有意圖地作假，一直是個很重要的研究議題。過去在研究測驗作假的議題上，主要有2種典範：（1）在人格測驗中設有一個量尺（scale）專門測量受試者是否意圖作假，（2）比較作假動機較高者和較低者對人格測驗反應的差異，來檢查是否有作假。 以往的研究大多從古典測驗理論的觀點來探討社會期許量表的作答，在古典測驗理論架構下，僅能就量表總分來判斷受試者的答題傾向，而本研究認為具有不同動機的受試者的作假企圖會反應在不同的題目上面，而非以一個概括的總分來決斷受試者是否有作假。透過試題反應理論（Item Response Theory, IRT）能分析每一個試題的特徵，再加上輔以DIF（Differential Item Functioning）的分析方法，徹底探討社會期許量表中的每個試題對不同群體的受試者產生不同的效果，另外，也透過同樣的方法分析人格測驗中的每個題目，從題目的層次探討：在不同的作假動機下，受試者的作答是否會展現不同的作答組型；接著，再從量表的層次，探討在不同的作假動機下，受試者在社會期許量表及人格測驗的作答是否會展現不同的因素結構。而由於作假可視為一種有意識地操弄作答，以造成良好的印象，因此，本研究也探討應徵不同職務者，是否會「朝向應徵的工作所期望的方向」來作答（作假），同樣的，透過題目的層次和量表的層次來探究這個問題。 本研究樣本乃自北部某顧問公司資料庫取得，為實際應徵工作或在職者之作答資料，為達成研究目的，共分析四組樣本，分別是一般應徵者樣本7,000人，非應徵者樣本7,000人，應徵行銷業務職務者3,974人，和應徵研發工程職務者3,974人。所有樣本皆填答「員工甄選人格量表」和「社會期許量表」二個研究工具，然後以SPSS 15.0 for Windows、 LISREL 8.72、以及 poly-SIBTEST等程式軟體進行資料分析。 研究結果發現： （1） 非應徵者、應徵者、以及應徵不同職務者在社會期許量表和人格五個量表的得分，並不全然支持應徵者得分較非應徵者高的假設，不論是量表總分或個別題項得分之差異，雖然大多數是應徵者得分較高，但亦有約25%以上的題目是應徵者和非應徵者之間沒有差異，甚或非應徵者得分高過應徵者。 （2） 社會期許量表和人格五個量表當中都檢測出DIF題目，且當中有些是應徵者傾向高估，亦有些是非應徵者傾向高估自己的分數，因此形成每一樣本組獨特的作答反應組型。 （3） 跨群組的因素結構恆等性檢定結果顯示，人格五個量表在不同樣本群組的因素結構皆有所差異，但在社會期許量表的結構只在「非應徵者vs. 應徵者」及「非應徵者 vs. 應徵研發工程職類者」兩個比較組中有差異。 （4） 綜合應徵者、非應徵者、和應徵不同職務者在平均數差異、DIF分析、及人格因素結構恆等性之分析等指標，本研究判斷，應徵者在人格測驗上的作假，主要是為了形成「良好印象」的作假，此良好印象與社會期許量表所測者較無關，但與應徵職務特性所期望者較有關。 本研究最主要的突破在於從IRT DIF的方法學從題目層次探討人格測驗的作假議題，並且綜合探討社會期許量表和人格測驗的作假效果，此一突破是植基於本研究所欲探討的人格測驗並無標準答案之特點，因而運用DIF檢測方法來評估是否不同的受試群體（應徵者/非應徵者）在個別題項上，選擇某個選項的機率不同（即使他們的能力相同），而據以判斷不同群體受試者是否具有不同的反應組型；此外，研究結果也初步反映出應徵不同職務者的確有朝向其所應徵的職務所期望的方向作答的傾向。最後，本研究亦針對研究結果，從實務應用的角度以及方法學的角度，提出討論與建議。

Le système de recombinaison Xer est impliqué dans la monomerisation des réplicons bactériens, comme les plasmides et les chromosomes, dans une grande variété de bactéries. Ce système est un système de recombinaison site-spécifique composé de deux tyrosine recombinases, soit XerC et XerD. Ils agissent ensemble afin de convertir les chromosomes dimériques en monomères en agissant à un site spécifique près du terminus de la réplication, appelé le site dif. Les gènes Xer et leur site d’action sont identifiés dans plusieurs bactéries gram positives et gram négatives. Staphylococcus aureus représente une bactérie gram positive qui contient un système XerCD/dif. Elle est impliqué dans plusieurs maladies humaines, tels que des infections cutanées, des gastroentérites, et le syndrome de choc toxique, pour en nommer quelques unes. Bien que les gènes codant les protéines XerC et XerD ont été identifiés, il y a beaucoup d’inconnu sur leur mode d’action au site dif. Des mutations dans XerC ont été obtenues, mais aucune dans XerD, suggérant que ce gène pourrait être essentiel pour cet organisme. Les études présentées dans ce mémoire ont permis de commencer à mieux caractériser XerD de S. aureus, en séquençant le gène et en faisant des tests de liaison à l’ADN. Elles ont montré que la recombinase XerD se lie au site dif d’Eschericia coli seul et de façon coopérative avec la recombinase XerC d’E. coli. XerD de S. aureus est, aussi, efficace dans la complémentation de XerD muté d’E. coli dans la réaction de recombinaison chromosomique. Cependant, elle ne démontre pas cette même capacité de complémentation lors de la recombinaison plasmidique aux sites cer. / The Xer recombination system is involved in the monomerisation of bacterial replicons, such as plasmids and chromosomes, in a wide variety of bacteria. This system is a site-specific recombination system comprised of two tyrosine recombinases, XerC and XerD, which act in concert to convert dimeric chromosomes to monomers by acting at a specific site near the terminus of replication called the dif site. Xer genes and their site of action have been identified in many gram positive and gram negative bacteria. Staphylococcus aureus represents a gram positive bacterium containing a XerCD/dif system. It is a bacteria implicated in many human diseases, such as skin infections, gastroenteritis and toxic shock syndrome, to name a few. Although the genes encoding the XerC and XerD proteins have been identified, not much is known about their mode of action on the dif site. Mutations in xerC have been obtained, but none in xerD, suggesting that this gene may be essential for this organism. The work presented in this paper has allowed us to better understand the XerD protein of S. aureus, not only in the sequencing of the xerD gene but also in the performing of DNA binding assays. It has been shown that XerD binds to the dif site of E. coli, not only alone but also in cooperativity with E. coli XerC. S. aureus XerD is also capable of complementing the mutated XerD protein in E. coli when it comes to chromosomal recombination. However, it does not demonstrate this same ability to complement XerD regarding recombination at the plasmidic cer sites.

This dissertation served two purposes. The first was to develop a method of detecting differential item functioning (DIF) within tests containing both dichotomously and polytomously scored items. The second was related to gender and aimed a) to investigate if those items that were functioning differently for girls and boys showed any characteristic properties and, if so, b) determine if these properties could be used to predict which items would be flagged for D1F. The method development was based on the Mantel-Haenszel (MH) method used for dichotmously scored items. By dichotomizing the polytomously scored items both types of item could be compared on the same statistical level as either solved or non-solved items. It was not possible to compare the internal score structures for the two gender groups, only overall score differences were detected. By modelling the empirical item characteristic curves it was possible to develop a MH method for identifying nonuniform DIF. Both internal and external ability criteria were used. Total test score with no purification was used as the internal criterion. Purification was not done for validity reasons, no items were judged as biased. Teacher set marks were used as external criteria. The marking scale had to be transformed for either boys or girls since a comparison of scores for boys and girls with the same marks showed that boys always got higher mean scores. The results of the two MH analyses based on internal and external criterion were compared with results from P-SIBTEST. All three methods corresponded well although P-SIBTEST flagged considerably more items in favour of the reference group (boys) which exhibited a higher overall ability. All 200 items included in the last 15 annual national tests in physics were analysed for DIF and classified by ten criteria The most significant result was that items in electricity were, to a significantly higher degree, flagged as DIF in favour of girls whilst items in mechanics were flagged in favour of boys. Items in other content areas showed no significant pattern. Multiple-Choice items were flagged in favour of boys. Regardless of the degree of significance by which items from different content areas were flagged on a group level it was not possible to predict which single item would be flagged for DIF. The most probable prediction was always that an item was neutral. Some possible interpretations of DIF as an effect of multidimen-sionality were discussed as were some hypotheses about the reasons why boys did better in mechanics and girls in electricity. / digitalisering@umu

Le système de recombinaison Xer est impliqué dans la monomerisation des réplicons bactériens, comme les plasmides et les chromosomes, dans une grande variété de bactéries. Ce système est un système de recombinaison site-spécifique composé de deux tyrosine recombinases, soit XerC et XerD. Ils agissent ensemble afin de convertir les chromosomes dimériques en monomères en agissant à un site spécifique près du terminus de la réplication, appelé le site dif. Les gènes Xer et leur site d’action sont identifiés dans plusieurs bactéries gram positives et gram négatives. Staphylococcus aureus représente une bactérie gram positive qui contient un système XerCD/dif. Elle est impliqué dans plusieurs maladies humaines, tels que des infections cutanées, des gastroentérites, et le syndrome de choc toxique, pour en nommer quelques unes. Bien que les gènes codant les protéines XerC et XerD ont été identifiés, il y a beaucoup d’inconnu sur leur mode d’action au site dif. Des mutations dans XerC ont été obtenues, mais aucune dans XerD, suggérant que ce gène pourrait être essentiel pour cet organisme. Les études présentées dans ce mémoire ont permis de commencer à mieux caractériser XerD de S. aureus, en séquençant le gène et en faisant des tests de liaison à l’ADN. Elles ont montré que la recombinase XerD se lie au site dif d’Eschericia coli seul et de façon coopérative avec la recombinase XerC d’E. coli. XerD de S. aureus est, aussi, efficace dans la complémentation de XerD muté d’E. coli dans la réaction de recombinaison chromosomique. Cependant, elle ne démontre pas cette même capacité de complémentation lors de la recombinaison plasmidique aux sites cer. / The Xer recombination system is involved in the monomerisation of bacterial replicons, such as plasmids and chromosomes, in a wide variety of bacteria. This system is a site-specific recombination system comprised of two tyrosine recombinases, XerC and XerD, which act in concert to convert dimeric chromosomes to monomers by acting at a specific site near the terminus of replication called the dif site. Xer genes and their site of action have been identified in many gram positive and gram negative bacteria. Staphylococcus aureus represents a gram positive bacterium containing a XerCD/dif system. It is a bacteria implicated in many human diseases, such as skin infections, gastroenteritis and toxic shock syndrome, to name a few. Although the genes encoding the XerC and XerD proteins have been identified, not much is known about their mode of action on the dif site. Mutations in xerC have been obtained, but none in xerD, suggesting that this gene may be essential for this organism. The work presented in this paper has allowed us to better understand the XerD protein of S. aureus, not only in the sequencing of the xerD gene but also in the performing of DNA binding assays. It has been shown that XerD binds to the dif site of E. coli, not only alone but also in cooperativity with E. coli XerC. S. aureus XerD is also capable of complementing the mutated XerD protein in E. coli when it comes to chromosomal recombination. However, it does not demonstrate this same ability to complement XerD regarding recombination at the plasmidic cer sites.

Differential item functioning (DIF) is present when examinees who have the same level of a trait have a different probability of correctly answering a test item intended to measure that trait (Shepard & Averill, 1981). The following study is a DIF analysis of the Herrmann Brain Dominance Instrument (HBDI), a preference profiling instrument developed by Herrmann International to help individuals identify their dominant preferences and then classify their level of dominance into four preference quadrants. Examinees who completed the American English version of the instrument were classified as the reference group and examinees of the International English version were classified as the focal group. Out of 105 items, 11 were manifesting a large amount of DIF and were flagged for further review. The POLYSIBTEST procedure was used to carry out the DIF analysis. POLYSIBTEST is an extension of the SIBTEST procedure, which is a conceptually simple method for analyzing DIF that uses a latent trait measure rather than an observed total score. The latent trait measure helps detect both uniform and nonuniform DIF and the POLYSIBTEST procedure is used for both dichotomous and polytomous items. Each of the four preference quadrants were analyzed separately to reduce incorrect findings as a result of ipsative scoring. The process used to complete the DIF analysis was documented so that additional language groups may be analyzed by Herrmann International.

No description available.

The surface gliding motility of Myxococcus xanthus is required for a multicellular developmental process initiated by unfavorable growth conditions. One form of the M. xanthus surface motility, social (S) gliding, is mediated by the extension and retraction of polarly localized type IV pili (Tfp). Besides Tfp, exopolysaccharides (EPS), another cell surface associated component, are also required for M. xanthus S motility. Previous studies demonstrated that the Dif chemotaxis-like signal transduction pathway is central to the regulation of EPS production in M. xanthus. Specifically, difA, difC and difE mutants were found to be defective in EPS production and S motility. DifA, DifC and DifE, homologous to methyl-accepting chemotaxis proteins (MCPs), CheW and CheA, respectively, are therefore positive regulators of EPS. This study, undertaken to better understand the regulation of EPS production, led to a few major findings. First, DifD and DifG, homologous to CheY and CheC, respectively, were found to be negative regulators of EPS production. Both DifD and DifG likely function upstream of the DifE kinase in EPS regulation. DifB, which has no homology to known chemotaxis proteins, was found not to be involved in EPS production. Secondly, this study led to the recognition that Tfp likely function upstream of the Dif pathway in the regulation of EPS production. Extracellular complementation experiments suggest that Tfp may act as sensors instead of signals for the Dif chemotaxis-like pathway. We propose a regulatory feedback loop that couples EPS production with Tfp function through the Dif signaling proteins. Lastly, we sought to identify additional genes involved in EPS production. Our efforts identified a mutation in a separate chemotaxis gene cluster as a suppressor of difA mutations, suggesting potential cross-talks among the multiple chemotaxis-like pathways in M. xanthus. In addition, we identified twenty-five previously uncharacterized genes that are predicted to be involved in M. xanthus EPS production. These genes appear to encode additional EPS regulators and proteins with biosynthetic function. / Ph. D.