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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
191

O sujeito pronominal no português uruguaio da região fronteiriça Brasil - Uruguai / SUBJECT IN PORTUGUESE pronominal URUGUAYAN The border region BRAZIL - URUGUAY

Bottaro, Silvia Etel Gutierrez 04 December 2009 (has links)
Na presente pesquisa estudamos o comportamento do sujeito pronominal no português uruguaio (PU) falado na região de fronteira entre Brasil e Uruguai (Santana do Livramento-Rivera). Associando alguns pressupostos da Teoria de Princípios e Parâmetros (CHOMSKY, 1981), mais especificamente o Parâmetro do Sujeito Nulo (pro-drop), e da Sociolinguística Variacionista (WEINREICH, LABOV e HERZOG, 1968), analisamos uma amostra de língua oral composta de falas de 37 informantes, investigando as seguintes questões: (1) no português uruguaio teríamos uma mudança linguística em curso no que se refere ao Parâmetro do Sujeito Nulo, de modo que ele venha a se tornar um sujeito pronominal pleno?; (2) quais são os fatores linguísticos e sociais condicionantes dessa produção e em que direção vai essa tendência, português brasileiro (PB) ou espanhol (E)? A análise dos fatores sociais e linguísticos selecionados permitiu observar que o PU também passa por um processo de mudança paramétrica, ainda que mais lenta, devido ao fato de estar submetido à pressão simultânea de duas línguas, e se apresenta como uma língua em que, em alguns contextos, a realização do sujeito pronominal é plena e, em outros, ainda conserva as características das línguas pro-drop. Confirma-se, ainda, que essa disputa não está terminada, embora haja indícios nos dados da geração mais nova de que as regras do espanhol vêm ganhando alguma força, talvez pela pressão da escola e dos meios de comunicação. Tudo indica, então, que a base do PU é o PB, porém algumas características do E estão presentes nesse aspecto da gramática. A análise realizada confirma a maior parte das hipóteses iniciais e dá indícios de que o PU e o PB poderiam configurar-se como duas línguas distintas, da mesma forma que o PB e o PE, como aponta Galves (1998), isto é, tudo parece indicar que, mesmo quando os enunciados superficialmente se parecem, a língua interna (Língua-I) seria diferente e os enunciados dos falantes teriam estatutos diferentes, algo que, no entanto, será necessário demonstrar com um outro modelo de coleta de dados, de natureza mais introspectiva. / In this research we study the behavior of the pronominal subject in the Uruguayan Portuguese language (PU) spoken in the border region between Brazil and Uruguay (Santana do Livramento-Rivera). Associating some assumptions from the Theory of Principles and Parameters (CHOMSKY, 1981), specifically the Null Subject Parameter (pro-drop), and from the Variationist Sociolinguistics (WEINREICH, LABOV and HERZOG, 1968), we analyze a sample of spoken language consisting of 37 informants, in order to investigate the following questions: (1) would we have in the Uruguayan Portuguese language a language change in progress with regard to the Null Subject Parameter, so that it will become a full pronominal subject? (2) what are the linguistic factors and social conditions of production and in which direction will this trend, Brazilian Portuguese (BP) or Spanish (E)? The analysis of social factors and selected language programs suggests that the PU is also undergoing a process of parametric change, albeit slower, due to the fact of being subjected to the pressure of two languages simultaneously, and is presented as a language that, in some contexts, the performance of the pronominal subject is full, and in others it still retains the characteristics of pro-drop languages. It is also confirmed that this dispute is not over, although there are indications in the data of the younger generation that the rules of Spanish are gaining some strength, maybe due to the pressure of school and the media. The analysis confirms most of our initial hypothesis and provides evidence that the PU and CP could be framed as two distinct languages, in the same way as the PB and PE, as appointed by GALVES (1998), that is, everything seems to indicate that, even when the statements superficially resemble, the internal language (Language I) would be different and the production of the speakers would have different statutes, something which, however, would just be demonstrated by means of another more introspective model of data collection.
192

Subjektspronomina i spanskaundervisningen : Om tolkningen av nollsubjektsparametern i undervisningen av spanska som L2 och hur den påverkar elevernas användning av subjektspronomina samt automatisering av verbböjning / Subject Pronouns in Spanish Teaching : About the interpretation of the null subject parameter in Spanish as asecond language and how it affects students' use of pronouns and their automation of verb inflections

Olsson, Carina January 2019 (has links)
The aim of this paper is to study whether there is a correlation between how subject pronouns are introduced in Spanish teaching and the pupils' difficulties regarding both their use and the understanding of verb conjugation. What is being investigated is: a) to what extent and in what contexts subject pronouns appear in Spanish textbooks, and b) how secondary education teachers of Spanish work with subject pronouns in the classroom. My conclusion is that the subject pronouns are under-represented in Spanish textbooks, probably due to the interpretation of the null subject parameter and Spanish as a pro-drop language. As far as the work with subject pronouns in the classroom is concerned, a more in-depth analysis needs to be carried out in order to be able to demonstrate a reliable correlation between the teaching method and the students' results. / Syftet med detta arbete är att studera om det finns ett samband mellan hur subjektspronomina introduceras i spanskaundervisningen och elevernas svårigheter kring både användandet av dessa och förståelsen för verbböjning. Det som undersöks är: a) i vilken utsträckning och i vilka sammanhang förekommer subjektspronomina i läromedel för undervisning i spanska, och b) hur högstadielärare i spanska arbetar med subjektspronomina i klassrummet. Min slutsats är att subjektspronomina finns underrepresenterade i läroböcker i spanska, förmodligen på grund av den tolkning som görs av nollsubjektsparametern och spanska som pro-drop språk. Vad gäller arbetet med subjektspronomina i klassrummet behöver en mer fördjupad analys genomföras för att det ska kunna påvisas ett tillförlitligt samband mellan undervisningsmetod och elevernas resultat.
193

Klang, form, struktur eller funktion? : En kvalitativ studie i hur gitarrlärare och gitarrelever ser på ackordundervisning på elgitarr.

Kvarnbrink, Johannes January 2019 (has links)
The purpose of this study was to investigate how a small selection of guitar teachers go about to teach chords on electric guitar, as well as how a small selection of guitar students have experienced the phenomena during their studies. To answer the research questions, two experienced guitar teacher and two guitar students were subjects to qualitative interviews. The theoretical perspective of the study was hermeneutic. The results showed that the methods employed by the teachers to a high degree related to how they have been taught and also learned by themselves. Another result is that the combination of systems, music theory and practical musical performance can help guitar students to reach a point of musical independence. The results provide an insight in how chordal playing on electric guitar can take place on a higher level, and also opens up for research within several areas of guitar education. / Syftet med denna studie var att undersöka hur ett mindre urval av gitarrlärare lär ut ackord på elgitarr, samt hur ett mindre urval gitarrelever upplevt att de undervisats i ackordspel. För att besvara forskningsfrågorna genomfördes kvalitativa intervjuer med två erfarna gitarrlärare, samt två gitarrelever som studerat elgitarr på musikgymnasium och folkhögskola. Studiens teoretiska perspektiv var hermeneutiskt. Resultaten visar att lärarna till stor del undervisar med metoder som fungerat för dem själva, samt att en kombination av system, musikteori och framförallt praktiskt musicerande kan ge gitarrelever de grundkunskaper som behövs för att vara självgående som elgitarrist. Resultat ger en inblick i hur ackordundervisning kan ta form på högre nivå, och öppnar upp för flera områden av framtida forskning i elgitarrmetodik.
194

Particle-Laden Drop Impingement on a Solid Surface

Ok, Hyunyoung 13 July 2005 (has links)
An experimental study on impaction of a single drop on solid surfaces was conducted to show the effects of particles on the impact process. The parameters were: volume fraction of particles (0 to 0.3), particle size (0.47 to 250 micron), and ratio of particle size to drop size (0.00017 to 0.074). The effect of particle volume fraction on the spreading process depended on impact speed and substrate. At low impact speed, particles had little effect on the spreading except for surfaces where the equilibrium contact angle was low. For high impact speed, the influence of particles on spreading can be described by the effective viscosity. The effect of particle size on the spreading process also depended on impact speed and substrate. At low impact speed, the drop did not have enough kinetic energy to overcome the energy barrier associated with the large particles. For particle-laden liquids, retraction was affected by particle parameters. When pure liquid drops retracted from the maximum spreading ratio, the retraction appeared to be symmetric around the point of impaction while retraction of the particle-laden drop was sometimes asymmetric. Rebounding on the Teflon film depended on impact speed, particle volume fraction, and particle size. The impact speed must reach a critical value for rebounding to occur. Bouncing results suggested that the probability of bouncing decreased as viscosity increased, impact speed increased, and surface tension decreased. The non-wetting behavior and bouncing probably involved an air layer between the surface and the drop. When a low-velocity liquid drop impacts on a surface, ejection of a secondary drop from the top of the impacting drop was sometimes observed. When Renardy et al.'s (2003) criterion for the range of velocities for existence of a capillary wave was applied to for a 3.2-mm water drop; the range was between 0.2 to 1.5 m/s. However, drop ejection was observed at lower impact speed. When apparent viscosity of the particle-laden liquid obtained from Krieger's equation (1972) was used in the pure liquid models for predicting the maximum spreading ratio, good agreement between model predictions and experimental results was obtained when Park et al's model (2003) was used.
195

Strength of Megathrust Faults: Insights from the 2011 M=9 Tohoku-oki Earthquake

Brown, Lonn 27 August 2015 (has links)
The state of stress in forearc regions depends on the balance of two competing factors: the plate coupling force that generates margin-normal compression, and the gravitational force, that generates margin-normal tension. Widespread reversal of the focal mechanisms of small earthquakes after the 2011 Tohoku-oki earthquake indicate a reversal in the dominant state of stress of the forearc, from compressive before the earthquake to tensional afterwards. This implies that the plate coupling force dominated before the earthquake, and that the coseismic weakening of the fault lowered the amount of stress exerted on the forearc, such that the gravitational force became dominant in the post-seismic period. This change requires that the average stress drop along the fault represents a significant portion of the fault strength. Two cases are possible: (1) The fault was strong and the stress drop was large or nearly-complete (e.g. from 50 MPa to 10 MPa), or (2) that the fault was weak and the stress drop was small (e.g. from 15 MPa to 10 MPa). The first option appears to be consistent with the dramatic weakening associated with high-rate rock friction experiments, while the second option is consistent with seismological observations that large earthquakes are characterized by low average stress drops. In this work, we demonstrate that the second option is correct. A very weak fault, represented by an apparent coefficient of friction of 0.032, is sufficient to put the Japan Trench forearc into margin-normal compression. Lowering this value by ~0.01 causes the reversal of the state of stress as observed after the earthquake. A slightly stronger fault, with a strength of 0.045, does not agree well with the observed spatial extent of normal faulting for the same coseismic reduction in strength. We also calculate distributions of stress change on the fault and average stress drop values for the Tohoku-oki earthquake, as predicted from 20 published rupture models which were constrained by seismic, tsunami, and geodetic data. Our results reconcile seismic observations that average stress drops for large megathrust events are low with laboratory work on high-rate weakening that predicts very high or complete stress drop. We find that, in all rupture models, regions of high stress drop (20 – 55 MPa) are probably indicative of dynamic weakening during seismic slip, but that the heterogeneous nature of fault slip does not allow these regions to become widespread. Also, coseismic stress increase on the fault occurs in many parts of the fault, including parts of the area that experienced high slip (> 30 m). These two factors ensure that the average stress drop remains low (< 5 MPa). The low average stress drop during the Tohoku earthquake, consistent with values reported for other large earthquakes, makes it unambiguous that the Japan Trench megathrust is very weak. / Graduate
196

Ledarens och deltagarnas beteende vid drop-in-idrott : En kvalitativ studie kring drop-in-idrott på Ersboda

Brolin, Jonatan, Eriksson, Johan Unknown Date (has links)
May 2010 a project called drop-in sports was started to get boys and girlsin the ages of 13-20 more physically active and keep them away from  committing crime. With the slogan ”come as you are, whenever you want and do what you want for free ” spontaneous sports was organized. To evaluate the project a research of the activity was carried out, where two of the objectives were to investigate how responsibility and empowerment is taken. Twelve hours of observations studies were used to collect data about leadership decision-making and democratic values in forms of respect, everybody’s right to play and influence. The study concluded that variations in the leaders decision-making affected the participant’s influence during activities. In terms of everybody’s right to play the study showed that, girls and younger participants were not included in the same scale at indoor activity as outside. Finally results showed that presence of leaders made an impact in respect and conflict management.
197

The influence of academic self-confidence on mathematics achievement / Erika van der Bergh

Van der Bergh, Erika January 2013 (has links)
It seems as if there is a continued problem with mathematical performances nationally. The rate, at which FET (Further Education and Training) phase learner s discontinue Mathematics as a result of poor mathematical performances, is of great concern. This research study determined how academic self-confidence could have an influence on learners’ abilities to perform in Mathematics. The literature review confirmed that there could be a link between academic self-confidence and mathematical performance. Consequently, the researcher wanted to establish if the same could be found at a school where the emphasis is very much on mathematical achievement. The school is based in Northern Johannesburg (D10) in Gauteng, South Africa. By applying an explanatory mixed method approach (quantitative, followed by qualitative methods), the researcher identified a clear link between this school’s learners’ abilities to perform in Mathematics and their academic self-confidence. Amongst others, positive links were also identified between the learner s’ comprehension of Mathematics, their problem- solving skills as well as educator assistance, which in turn influence their academic self - confidence and consequently al so their performance s. A cycle of mathematical influences was identified that demonstrated that the influence i s not only working one way, but that a cycle forms; academic self-confidence influences the learner’s ability to perform in mathematics and mathematical performance s al so influence academic self - confidence, causing a continuous cycle of influence. / MEd (Learner Support), North-West University, Vaal Triangle Campus, 2013
198

Study of the interaction of older adults with touchscreen / Etude de l'interaction de personnes âgées avec des écrans tactiles

Genaro Motti Ader, Lilian 21 March 2016 (has links)
Utiliser une tablette ou un smartphone est désormais courant. Cependant, les effets de l'âge sur les capacités motrices nécessaires pour l'exécution des gestes d'interaction tactile n'ont pas été suffisamment pris en compte lors de la conception et de l'évaluation des systèmes interactifs, une des raisons qui a empêché l'inclusion numérique de ce groupe d'utilisateurs. L'objectif de cette thèse est d'étudier l'interaction des personnes âgées avec les écrans tactiles afin d'identifier des problèmes d'utilisabilité sur des supports variés (smartphone et tablette, doigt et stylet). Pour cette étude, nous avons conçu un système interactif constitué de jeux de type puzzle numérique tactiles, où le geste d'interaction drag-and-drop (glisser-déposer) est employé pour positionner les cibles. Dans ce contexte, une attention particulière a été portée à l'analyse des mouvements de l'utilisateur. L'analyse des postures du poignet durant l'interaction a permis d'élucider la relation entre les caractéristiques des mouvements des personnes âgées avec leurs performances, à savoir, des temps plus longs et une augmentation du nombre d'erreurs par rapport aux utilisateurs adultes plus jeunes. Prendre en compte la variabilité des capacités motrices des utilisateurs lors des phases de conception et évaluation des systèmes interactifs est nécessaire pour comprendre leurs difficultés et améliorer l'ergonomie et utilisabilité de l'interaction tactile. / Tablets and smartphones have become mainstream technologies. However, the aging effects on the motor skills implied on tactile interaction haven't been enough considered during the design and evaluation of tactile interactive systems, what prevent this group of older adult users to be digitally included successfully. This thesis aims to study the interaction of older adults with touchscreens in order to identify usability issues on different devices and input modalities (smartphone and tablet, finger and stylus). To this study, we designed an interactive system consisted of tactile puzzle games and using drag-and-drop interaction for positioning the puzzle pieces into their corresponding targets. In this framework, a special attention was given to the analysis of the movements of the user. The analysis of the postures of the users' wrists during interaction allowed to elucidate the relationship between the characteristics of the movements of older adults and their performances, particularly concerning the longer times needed for executing the gestures of interaction as well as the increased error rates of this group of users when compared to younger adults. Taking into account the variability of users' motor skills during the design and evaluation of interactive systems is necessary to better understand their difficulties as well as to improve the ergonomics and the usability levels of tactile interaction.
199

Performance comparativa entre R290/R600a (50:50) e R134a para drop-in em refrigerador dom?stico

Almeida, Igor Marcel Gomes 20 December 2010 (has links)
Made available in DSpace on 2014-12-17T14:58:05Z (GMT). No. of bitstreams: 1 IgorMGA_DISSERT_1-100.pdf: 3498388 bytes, checksum: 478be24ae351a921f1a23bafc58492ef (MD5) Previous issue date: 2010-12-20 / This research this based on the seminar on Use of Natural Fluids in Refrigeration and Air-Conditioning Systems conducted in 2007 in Sao Paulo. The event was inserted in the National Plan for Elimination of CFCs, coordinated by the Ministry of Environment and implemented by the United Nations Development Programme (UNDP). The objective of this research is analyze the performance of the hydrocarbons application as zeotropic mixtures in domestic refrigerator and validate the application of technical standards for pull down and cycling (on-off) tests to the mixture R290/R600a (50:50) in domestic refrigerator. It was first developed an computational analysis of R290/R600a (50:50) compared to R134a and other mass fractions of the hydrocarbons mixtures in the standard ASHRAE refrigeration cycle in order to compare the operational characteristics and thermodynamic properties of fluids based on the software REFPROP 6.0. The characteristics of the Lorenz cycle is presented as an application directed to zeotropic mixtures. Standardized pull down and cycling (on-off) tests were conducted to evaluate the performance of the hydrocarbons mixture R290/R600a (50:50) as a drop-in alternative to R134a in domestic refrigerator of 219 L. The results showed that the use of R290/R600a (50:50) with a charge of refrigerant reduced at 53% compared to R134a presents reduced energy performance than R134a. The COP obtained with hydrocarbon mixture was about 13% lower compared to R134a. Pull down times in the refrigerator compartments for fluids analyzed were quite close, having been found a 4,7% reduction in pull down time for the R290/R600a compared to R134a, in the freezer compartment. The data indicated a higher consumption of electric current from the refrigerator when operating with the R290/R600a. The values were higher than about 3% compared to R134a. The charge of 40 g of R290/R600a proved very low for the equipment analyzed / Esta pesquisa est? baseada no semin?rio Uso de Fluidos Naturais em Sistemas de Refrigera??o e Ar-Condicionado realizado em 2007 na cidade de S?o Paulo. O evento esteve inserido no Plano Nacional de Elimina??o de CFC?s, coordenado pelo Minist?rio do Meio Ambiente e implementado pelo Programa das Na??es Unidas para o Desenvolvimento (PNUD). O objetivo do trabalho ? analisar a performance da aplica??o de hidrocarbonetos como misturas zeotr?picas em refrigerador dom?stico e validar a aplica??o das normas t?cnicas de ensaios de abaixamento de temperatura e ciclagem para a mistura R290/R600a (50:50) em refrigerador dom?stico. Foi desenvolvida primeiramente uma an?lise computacional do R290/R600a (50:50) em rela??o ao R134a e outras fra??es de massa da mistura de hidrocarbonetos operando no ciclo de refrigera??o padr?o ASHRAE de modo a comparar as caracter?sticas operacionais e termodin?micas destes fluidos com base no software REFPROP 6.0. As caracter?sticas do ciclo Lorenz s?o apresentadas como aplica??o direcionada ?s misturas zeotr?picas. Ensaios normalizados de abaixamento de temperatura e ciclagem foram desenvolvidos para avaliar a performance da mistura de hidrocarbonetos R290/R600a (50:50) como uma alternativa de drop-in do R134a em refrigerador dom?stico de 219 litros de capacidade. Os resultados mostraram que a utiliza??o do R290/R600a (50:50) com uma carga reduzida em 53% da carga de R134a apresenta desempenho energ?tico ligeiramente inferior ao R134a. O COP obtido para a opera??o com a mistura de hidrocarbonetos foi cerca de 13% inferior em rela??o ao R134a. Os tempos de abaixamento de temperatura nos compartimentos do refrigerador para os fluidos analisados foram bastante pr?ximos, tendo sido verificada uma redu??o de 4,7% no tempo de abaixamento para o R290/R600a em compara??o ao R134a, no compartimento do freezer. Foi verificado um maior consumo de corrente el?trica do refrigerador quando operando com o R290/R600a. Os valores obtidos foram superiores cerca de 3% em rela??o ao R134a. A carga de 40 g do R290/R600a se mostrou diminuta para o equipamento analisado
200

Fenômeno fotoeletrocatalítico mediada por UV/TiO2: da rápida imobilização do TiO2 P25 em eletrodos de ouro ao seu comportamento na fotooxidação do sistema modelo EDTA em células de camada delgada irradiadas por LED UV / The photoelectrocatalytic phenomenon mediated by UV/TiO2: from the quick immobilization of the P25 TiO2 on gold electrodes to its behavior on the photooxidation of the model system EDTA in thin layer-type cells irradiated by UV LED

Alexandre Luiz Bonizio Baccaro 22 February 2017 (has links)
O demorado tratamento térmico, comum no preparo de fotocatalisadores e sua imobilização em substratos, foi contornado nesta tese, em que se investigaram duas estratégias de modificação de eletrodos de ouro com TiO2 P25. A primeira consiste em promover a formação de uma nanocamada pela simples exposição do metal por 1 min à suspensão aquosa de TiO2 (10 g L-1 em HCl 0,1 mol L-1); na segunda, deposita-se uma pequena alíquota (5 ou 8 &#181;L) da suspensão diretamente no substrato (drop coating) para secá-lo em seguida por irradiação com lâmpada incandescente (60 W a 20 cm), obtendo-se bons resultados de uma a três camadas depositadas. Comprovou-se grande aumento da estabilidade da suspensão aquosa e duplicação da atividade fotocatalítica do nanofilme de TiO2 em decorrência da repulverização de P25 comercial em almofariz, melhoria inalcançável por sonicação da suspensão. O tamanho de partícula médio obtido por DLS para o TiO2 disperso em meio de HCl 0,1 mol L-1 atingiu 103±3 nm, enquanto que o filme depositado na superfície do ouro (observado por MEV e caracterizado por EDS) não ultrapassou 100 nm de espessura, sendo dominado por partículas de diâmetro de 20 (anatase) a 30 nm (rutilo), observadas por MET. A estabilidade da suspensão é susceptível ao ânion do ácido utilizado, sendo que resultados igualmente satisfatórios foram obtidos com HCl e HclO4 0,1 mol L-1, enquanto que para a mesma concentração de H2SO4 o TiO2 sofreu sedimentação rápida e o eletrodo preparado com a suspensão apresentou fotoatividade 10x menor. Filmes de espessuras bastante distintas (100 nm e 2 m) depositados a partir de suspensão 10 g L-1 por contato e drop coating com gota de 5,0 &#181;L, respectivamente, foram comparados em relação à sua capacidade de transporte de elétrons e resposta eletroquímica ao Fe(CN)6 3 1,0 mmol L-1, sendo que a carga líquida formal de oxidação do EDTA 1,0 mmol L-1 é apenas 50 % maior para o filme 20x mais espesso, além de gerar distorções consideráveis nas ondas voltamétricas do sistema-sonda reversível em relação ao filme nanométrico e à superfície polida. Com eletrodos modificados pelo protocolo otimizado de drop coating (8,0 &#181;L de TiO2 2 g L-1), testou-se o efeito da presença de diferentes eletrólitos de suporte (ácidos 0,1 mol L-1) em processos anódicos de fotooxidação em geral. A curva de decaimento da fotocorrente iph com o tempo pode ser descrita por uma equação de decaimento exponencial duplo iph = i0 + A1 exp(k1t) + A2 exp( k21t), permitindo distinguir as contribuições da fotocorrente de oxidação da água (i0) e de termos referentes a dois tipos de sítio superficiais, sendo um de cinética rápida e outro de cinética lenta. A seguinte ordem foi determinada para a fotocorrente total inicial (iph0 total) dos eletrólitos: HNO3 > HClO4 > HCl > H1SO4 > H3PO4 e as explicações propostas para tal se embasam na adsortividade dos ânions no TiO2 e na reatividade dos respectivos traps formados. O mesmo modelo de ajuste matemático foi utilizado para avaliar a fotoatividade do eletrodo modificado pela sua irradiação sucessiva e repetida em HNO3 0,1 mol L-1 (sem EDTA), sendo observada redução significativa principalmente nos parâmetros relativos aos sítios de reação e, assim, sugere-se um impedimento dos mesmos através, p. ex., da formação de peróxidos superficiais. Na presença também de EDTA, a carga líquida total despendida na sua fotooxidação se mantém relativamente constante nas sucessivas irradiações. Por fim, os experimentos de fotooxidação do EDTA sob varredura de potencial revelaram uma região de relação linear entre a fotocorrente e o potencial aplicado ao eletrodo modificado com TiO2 que se estende até a região de saturação de fotocorrente ser atingida, comportamento compatível com filmes nanoparticulados porosos não-dopados. A inclinação da região linear aumenta em função da [EDTA], como se os valores de condutância (di/dE) se elevassem dependendo da reação interfacial. Ajuste de modelo matemático hiperbólico correlacionando a (foto)resistência do filme em função da fotocorrente de saturação R = R0 + kIsph1, fornece resistência ôhmica do filme R0 de 5,0 k&#937; e uma constante atrelada ao fotopotencial de 237 mA &#937;. Já a curva monotônica de fotocorrente de saturação (Isph) com a [EDTA] apresenta comportamento linear até cerca de 0,7 mmol L-1, sugerindo-se que nessa região o controle por transporte de massa é a etapa limitante do processo global. Acima dessa concentração o coeficiente angular diminui gradualmente à medida que a reação de cinética de captura das lacunas passa a ser o determinante até um limite máximo (aparentemente 5,0 mmol L-1 de EDTA, nas condições do experimento) onde a disponibilidade de lacunas fotogeradas passa a governar. / The lengthy thermal treatment is a common step during the preparation and immobilization of photocatalysers on substrates, which by the way, was overcome in this thesis by the investigation of two strategies of modification of gold electrodes with P25 TiO2. The first one consists in promoting the formation of a nanolayer by the simple exposure of the metal surface to an aqueous suspension of TiO2 (10 g L-1 on 0.1 mol L-1 HCl) during 1 min; the second involves the deposition of a small drop (5 or 8 L) of the suspension on the gold substrate (drop coating) and its drying by irradiation with an incandescent lamp (60 W at 20 cm far), with worthy results also for two or three deposited layers. The stability of this aqueous suspension was appreciably improved by the repulverization of commercial P25 in a grinding mortar. As a consequence the photocatalytic activity conferred to the electrode by the formation of the TiO2 nanofilm doubled. Such improvements cannot be attained by bath sonication of the suspension. The average particle size determined by DLS for the TiO2 dispersed in 0.1 mol L-1 HCl was 103±3 nm, while the film deposited on the surface of gold consisted of particles of 20 nmn (anatase) and 30 nm (rutile) characterized by TEM and barely achieved a thickness of 100 nm (characterized by SEM and EDS). The stability of the modifying suspension is susceptible to the type of anion of the electrolyte. Good results were found with 0.1 mol L-1 HCl and HClO4, but not with 0.1 mol L-1 H2SO4. This last medium causes fast sedimentation of TiO2 and generates electrodes with one tenth of the photoactivity achieved with the other acids. The effect of film thickness on the photoactivity was evaluated for films with 100 nm and 2.0 &#181;m prepared from a 10 g L-1 TiO2 suspension by the contact and drop coating (5 &#181;L) strategies, respectively. The electron transport across both films and the electrochemical response for the 1.0 mmol L-1 Fe(CN) 63- probe was compared. The formal net charge for the 1.0 mmol L-1 EDTA oxidation was only 50 % higher for the 20x thicker film that also considerably distorts the voltammetric waves of the aforementioned reversible probe. The effect of different supporting electrolytes (0.1 mol L-1 acids) on the anodic photooxidation processes in general was tested with electrodes modified by an optimized drop coating protocol (8.0 &#181;L of 2 &#181;g L-1 TiO2). The curve describing the photocurrent decay in function of time might be ascribed to an equation of double exponential decay iph = i0 + A1 exp(k1t) + A2 exp (k2t), which allows the distinction of the contribution of water oxidation (i0) from terms of two types of surface sites: a kinetically fast site and a slow one. The total initial photocurrent (iph0 total) of the following electrolytes decays in the order: HNO3 > HClO4 > HCl > H2SO4 > H3PO4; explanations comprise the adsorbability of each respective anion on TiO2 and the reactivity of the corresponding traps formed. Similar curve fitting applied to the data of photoactivity of the gold electrode during successive irradiations of its surface in 0.1 mol L-1 HNO3 (absence of EDTA) revealed that sites reactivities underwent considerable reduction. It is suggested that during repetitive experiments the sites are impaired by the formation of surface peroxides. However, in the presence of 1.0 mmol L-1 of EDTA, the formal net charge of oxidation of the organic species remains almost unaltered. Ultimately, the experiments concerning the photooxidation of EDTA under linear potential scan revealed a region of linear relation between the photocurrent and the potential applied to the electrode modified with a TiO2 film (nanometric or micrometric), which holds until the saturation photocurrent is attained. This behavior is typical for porous non-doped nanoparticulate electrodes. The slope of the linear region increase somewhat with the EDTA concentration, as though the conductance values (di/dE) were raised depending on the interfacial reaction rate. The fitting of a hyperbolic model R = R0 + kIsph-1 for the correlation of the (photo)resistence (R) of the film with the photocurrent of saturation (Isph) allows the estimation of an ohmic resistance of 5.0 k&#937;, and a photopotential related constant of 237 mA &#937;. The curve of correlation between Isph and the [EDTA] is linear fit until 0.7 mmol L-1, suggesting that in this initial region the mass transport to the interface is the limiting step of the global process. Above that concentration, the slope of the curve is gradually reduced as the kinetic of capture of the holes becomes the determining step and from 5.0 mmol L-1 on an asymptotic Isph is reached (under the conditions of the experiments), where the holes photogeneration might start governing.

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