• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 420
  • 187
  • 34
  • 28
  • 24
  • 11
  • 11
  • 11
  • 10
  • 10
  • 10
  • 9
  • 5
  • 4
  • 3
  • Tagged with
  • 780
  • 161
  • 139
  • 99
  • 97
  • 83
  • 66
  • 64
  • 57
  • 55
  • 54
  • 54
  • 46
  • 46
  • 42
  • 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.
111

Response Inhibition to High Calorie Food Cues Among Adolescents Following Active and Sedentary Video Game Play Using a Go/No-Go Task: A Randomized Crossover Study

Smith, Joshua L 01 December 2017 (has links)
Sedentary behaviors, such as leisure time computer use and sedentary video games, are significant barriers to regular physical activity and contribute to high rates of overweight and obesity among adolescents. Sedentary screen time can adversely affect food intake and food selection. Active video games may be a promising way of increasing daily physical activity levels among adolescents. Active video games may help modulate response inhibition and food intake. PURPOSE: Compare the effects of an acute bout of active and sedentary video gaming on N2 amplitudes (while viewing high calorie and low calorie images), Stroop Color Word Test (Stroop test) performance and ad libitum eating. METHODS: We used a within-subjects randomized crossover design with counterbalanced treatment conditions was used among 65 participants (31 girls, 34 boys; age = 13.5 ± 1.1 year; height = 161.4 ± 10.2 cm; weight = 52.5 ± 12.3 kg; BMI = 19.9 ± 3.3 kg·m2). Participants completed 2 separate video gaming sessions, 7 days apart, while energy expenditure during sedentary and active video game play was measured using the K4b2 portable metabolic system. The K4b2 system provided metabolic equivalents (METs) which are used as a measure of energy cost of physical activity. After either 60 minutes of active or sedentary video game play, participants completed a go/no-go task while viewing high calorie and low calorie images while electroencephalogram (EEG) data were collected. N2 event related potential (ERP) amplitudes were measured during the viewing task. Participants also completed a Stroop task to measure response inhibition. Finally, participants were given high calorie and low calorie snacks to consume ad libitum. We used a repeated measures ANOVA was used to measure main and interaction effects for N2 ERP amplitudes within subjects. RESULTS: Active video game play relative to sedentary video games significantly increased METs (F = 543.1, p ≤ 0.0001) from 1.7 ± 0.35 to 5.0 ± 1.2 METs. A significant gender-by-condition interaction (F = 7.03, p ≤ 0.009) was observed for energy expenditure with boys (5.4 ± 1.1 METs) expending more energy during the active video game than girls (4.5 ± 1.1 METs). No significant differences were observed for the N2 component (F = 0.50, p = 0.48) between video game conditions nor between genders (F = 1.85, p = 0.17). There were no significant differences (F = 3.10, p = 0.08) in the total number of calories consumed between the 2 video gaming conditions. Results from the Stroop task showed no significant differences for word naming (F = 0.45, p = 0.49), congruent condition (F = 0.43, p = 0.52) and incongruent condition (F = 0.14, p = 0.71) between the active and sedentary video games. CONCLUSION: Sixty minutes of active video gaming increases energy expenditure to a moderate intensity level but does not alter behavioral response or response inhibition to high calorie or low calorie foods.
112

The Effects of a Three-Hour, After School Bout of Sedentary vs Active Behavior on Reward and Cognitive Control Activation in 8- to 9-Year-Old Children: A Randomized Crossover Study

White, Mary Linn 01 April 2018 (has links)
PURPOSE: To compare the effects of after-school sedentary versus active play on activation in the reward and cognitive control regions of the brain to pictures of high- and low-calorie foods. METHODS: 32 children (12 girls, 20 boys; age 8.7 ± 0.5 years; height 137.9 ± 6.9 cm; weight 32.4 ± 6.2 kg) participated in a randomized crossover study with counterbalanced treatment conditions. Conditions took place on separate days after school and included three hours of active or sedentary play. After each condition, neural activation in reward and cognitive control regions of the brain were assessed using functional magnetic resonance imaging (fMRI) while participants completed a go/no-go task involving pictures of high- and low-calorie foods. General response inhibition was measured by the Stroop task. Hunger was measured upon arrival to the testing facility and just prior to fMRI scans. Mixed effects models were used to evaluate main and interaction effects. RESULTS: Significant stimulus by condition interactions were found in the right superior parietal cortex, right postcentral gyrus and accumbens area (p <<> 0.05). High- versus low-calorie pictures of food elicited significantly different activation bilaterally in the orbitofrontal cortex (p <<> 0.01). Stroop task performance diminished significantly following the sedentary condition compared to the active condition (F = 6.79, p <<> 0.01). Subjective feelings of hunger were not different between conditions at any point. CONCLUSION: Sedentary behavior significantly decreased response inhibition and brain activation to pictures of high-calorie foods in areas of the brain important to the modulation of food intake. Decreased attention, reward, and response inhibition, following sedentary behavior, may contribute to disinhibited eating that can lead to overweight and obesity.
113

Predicting Reaction Time from Temporal Performance Indicators on a Go/No-Go Task in Children with Attention Deficit Hyperactivity Disorder

Hwang, Michelle 17 April 2009 (has links)
No description available.
114

Decompiling Go : Using metadata to improve decompilation readability / Dekompilering av Go : Att använda metadata för att förbättra dekompileringens läsbarhet

Grenfeldt, Mattias January 2023 (has links)
Malware written in Go is on the rise, and yet, tools for investigating Go programs, such as decompilers, are limited. A decompiler takes a compiled binary and tries to recover its source code. Go is a high-level language that requires runtime metadata to implement many of its features, such as garbage collection and polymorphism. While decompilers have to some degree used this metadata to benefit manual reverse engineering, there is more that can be done. To remedy this, we extend the decompiler Ghidra with improvements that increase the readability of the decompilation of Go binaries by using runtime metadata. We make progress towards enabling Ghidra to represent Go's assembly conventions. We implement multiple analyses: some which reduce noise for the reverse engineer to filter through, some which enhance the decompilation by adding types, etc. The analyses are a mix of reimplementations of previous work and novel improvements. The analyses use metadata known beforehand but in new ways: applying data types at polymorphic function call sites, and using function names to import signatures from source code. We also discover previously unused metadata, which points to promising future work. Our experimental evaluation compares our extension against previously existing extensions for decompilers using multiple readability metrics. Our extension improves on metrics measuring the amount of code, such as lines of code. It also decreases the number of casts. However, the extension performs worse on other metrics, producing more variables and glue functions. In conclusion, our extension produces more compact code while also increasing its informativeness for the reverse engineer. / Datorvirus skrivna i Go ökar, men verktyg för att undersöka Go-program, såsom dekompilatorer, är begränsade. En dekompilator tar en kompilerad binär och försöker återskapa dess ursprungliga källkod. Go är ett högnivåspråk som kräver metadata under körtid för att implementera många av dess funktionaliteter, såsom automatisk minneshantering och polymorfism. Medan dekompilatorer i någon mån har använt denna metadata för att gynna manuell reverse engineering, så finns det mer som kan göras. För att åtgärda detta bygger vi en utökning till dekompilatorn Ghidra som förbättrar dekompileringens läsbarhet för Go-binärer genom att använda körtidsmetadata. Vi gör framsteg mot att få Ghidra att kunna representera Gos assemblerkonventioner. Vi implementerar flera analyser: några som minskar bruset för undersökaren att filtrera bort, några som förbättrar dekompileringen genom att lägga till datatyper, etc. Vissa analyser är återimplementationer av tidigare arbeten, och vissa är originella. Analyserna använder tidigare känd metadata, men på nya sätt: de applicerar datatyper vid anrop till polymorfiska funktioner, och använder funktionsnamn för att importera funktionssignaturer från källkod. Vi upptäcker även tidigare okänd metadata, som är lovande att undersöka i framtida studier. Vår experimentella utvärdering jämför vår utökning mot tidigare existerande utökningar av dekompilatorer med hjälp av flera läsbarhetsmått. Vår utökning förbättrar mått av mängd kod, såsom antal kodrader. Den minskar också antalet typkonverteringar. Dock så presterar utökningen sämre på andra mått och producerar fler variabler och limfunktioner. Sammanfattningsvis producerar vår utökning mer kompakt kod samtidigt som den ökar mängden användbar information tillgänglig för undersökaren.
115

Antiga Vila Boa de Goiás: experiências e memórias na/da Cidade Patrimônio

Gomide, Cristina Helou 14 May 2007 (has links)
Made available in DSpace on 2016-04-27T19:31:30Z (GMT). No. of bitstreams: 1 Cristina H Gomide.pdf: 4702508 bytes, checksum: 966788e51f5d917c3bdd11b7c565ba2f (MD5) Previous issue date: 2007-05-14 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This research points the patrimonial history of the City of Goiás, that was politician-administrative headquarters since the colonial period until the decade of 1930, when occurred the transference from the state capital of the former Vila Boa de Goiás to Goiânia - planned city for the new capital of the state of Goiás at that epoch. Investigating the history of this city, I perceived that the idea of the historic-patrimonial city was shaping itself while fortify the image of one city that appeared in local press divulgations as "root of the goiana culture". Since 1950, when the first actions of the SPHAN in the City of Goiás had occurred, I concentrate my reflections into the politics of buildings inventorying that were considered patrimonial, and I begun to scan inside the former Vila Boa de Goiás, the trajectory of the responsible agency for the preservation of historical, artistic and cultural things in Brazil. Based upon this investigation, I realized some landmarks in this process. In 1978 IPHAN promoted another falling inventorying in the city, extending the patrimony notion and considering important real urban webs. From 1997 to 1999, dialoguing with inhabitants who had remained in the Cidade de Goiás even after the transference of the capital for Goiânia, I noticed that the history of the transference of the capital brought to them discomfort and hurt, while these people alluded, many times to the image of the city that was abandoned after that change. Until that moment, the "marasmus" of the city - one of the factors pointed to justify the change of the capital - appeared as something negative, although the urban space leaded into the notion of historical patrimony and those inhabitants worried themselves to defend the space wich they lived in. From 2003 the 2005, worried to understand the way as the inhabitants of the historical city saw and lived this city, I treated to look for people who live in less supplied quarters of former Vila Boa. In that period, more engaged to the city as a patrimonical place and more vinculated to the touristic practical that envolved the city, some inhabitants intercrossed themselves to the local touristic movement, although they still felt detached, in many cases, from the dynamic of the so called city historical center. In 2007 february I was with a new way of looking and thinking about that subject, when I tried to dialogue with people who work and live the daily dynamics of the historical center of Goiás. I talked with confectioner, artisans, managers and workers of shops located there. I realized a notable transformation in the ways that people see and live this city. The "marasmus" before told as part of the hurt from the transference of the capital, today had changed into a significative form of "tranquillity", expressing itself, to them, as quality of life. Intercrossed at the construction history of a hegemonicly memory built of the local patrimony, these habitants re-signify the traditions doing part of the memory like a part of its lives. At last, analysing especially touristic and propagandistic folders (destined to the trajectory of the city visitor), postcards, newspapers articles, literary and verbal narratives, I appoint in this thesis the experiences and the memories expressions in and of the Patrimonial City succeeding to perceive the way how inhabitants live and mean that city / Este trabalho aborda a história patrimonial da Cidade de Goiás, que foi sede político-administrativa desde o período colonial até a década de 1930, quando ocorreu a transferência da capital estadual da antiga Vila Boa de Goiás para Goiânia cidade planejada para se a nova capital do estado de Goiás à época. Investigando a história desta cidade, percebi que a idéia de cidade histórico-patrimonial foi se construindo à medida que se reforçava a imagem de uma cidade que aparecia nos discursos da imprensa local como raiz da cultura goiana . Partindo de 1950, quando ocorreram as primeiras ações do SPHAN na Cidade de Goiás, foquei minhas reflexões nas políticas de tombamento dos bens considerados patrimoniais e comecei a mapear, na antiga Vila Boa de Goiás, a trajetória do órgão responsável pela preservação de bens históricos, artísticos e culturais no Brasil. Com base nesta investigação, percebi alguns marcos neste processo. Em 1978 o já então IPHAN promoveu outra leva de tombamentos na cidade, ampliando a noção de patrimônio e considerando importantes verdadeiras malhas urbanas. De 1997 a 1999, em diálogo com moradores que permaneceram na Cidade de Goiás mesmo após a transferência da capital para Goiânia, percebi que a história da transferência da capital lhes gerava desconforto e mágoa, e estes aludiam, muitas vezes à imagem da cidade que foi abandonada depois do acontecimento. Até este momento, o marasmo da cidade um dos fatores apontados para justificar a mudança da capital aparecia como algo negativo, ainda que o espaço urbano já se movimentasse em torno na noção de patrimônio histórico e estes moradores se preocupassem em defender o espaço em que residiam. De 2003 a 2005, preocupada em compreender o modo como os moradores da cidade histórica viam e viviam esta cidade, tratei de procurar pessoas que residem em bairros menos abastados da antiga Vila Boa. Neste período, mais engajados à cidade patrimônio e às práticas turísticas que a envolviam, alguns moradores se entrecruzavam ao movimento turístico local, mas ainda se viam desvinculados, em muitos casos, da dinâmica do chamado centro histórico da cidade. Em fevereiro de 2007, já com um novo olhar, procurei dialogar com pessoas que trabalham e vivem cotidianamente a dinâmica do centro histórico de Goiás. Conversei com doceiras, artesãs, empresários(as) e trabalhadores(as) de lojas ali localizadas. Percebi uma transformação notável nos modos de ver e viver esta cidade. O marasmo antes narrado como parte da mágoa da transferência da capital, hoje se inscreve de forma significativa como tranqüilidade , traduzindo-se, para eles, como qualidade de vida. Entrecruzados à história de construção de uma memória hegemonicamente construída do patrimônio local, estes moradores re-significam tradições e desta memória, parte de suas vidas. Enfim, utilizando-me, sobretudo da análise de folders turísticos e propagandísticos (destinados à trajetória do visitante da cidade), cartões-postais, artigos de jornais locais, narrativas literárias e narrativas orais, trato aqui de apontar as expressões das experiências e das memórias na e da Cidade Patrimônio logrando perceber o modo como os moradores a vivem e significam
116

Arborização urbana de Catalão (GO): caracterização e proposta para a requalificação do sistema viário / Urban forestry Catalan (GO): characterization and proposal for the upgrading of the road system

ROCHA, Ione Soares da Silva 16 June 2011 (has links)
Made available in DSpace on 2014-07-29T14:44:42Z (GMT). No. of bitstreams: 1 Dissertacao Ione Soares Silva Rocha - parte 1.pdf: 2557270 bytes, checksum: 01b14bef4ecb8f358f355e2befe37e0b (MD5) Previous issue date: 2011-06-16 / In this research, the main goal is to describe and understand the urban afforestation in the road space of Catalão (Go), specifically, a delimited and interesting space, which the main object is the tree. In this way, the research about afforestation in this profile for studies and analysis, and the works realized using this ideas could also allow another goal, that was to offer, according to the principles of the primitive nature in the place, and the intention to improve the ecodynamics in Catalão city, actions for the requalification of the afforestation in the road urban system. The theoretical discussion is done by the ecodynamic approach, using the specialized literature giving emphasis also to the perception of the landscape,using other ways, for better comprehension of the subject, like soil analysis, trees total inventory, questionnaires to obtain the population perceptions and opinion. Through approaches, like reviews literature, field and laboratory researches, searching to understand the problems that exist in the urban afforestation of monitoring road, like to check if the afforestation how is made today is according to the place ecodynamic, and presents a proposal for the problems that arose in this analysis of the afforestation. The afforestation can be improved by the observance of the laws that are legal and the ones that are academic and scientific, some are Federal and Constitucional, others are from the state and the municipality, and rules that are related to the ecosystems nature that still remaining in the space cut for this study and that allows to observe and conclude about the ecodynamic of this space in study. / Nesta pesquisa, propôs-se a caracterizar e compreender a arborização urbana do espaço viário de Catalão (GO), especificamente, um espaço de interesse e delimitado, no qual o objeto principal em discussão é a árvore. Desta forma, esta pesquisa sobre a arborização no recorte para estudo e análise, e os trabalhos a partir daí realizados permitiram também cumprir outra meta deste trabalho, que era propor, conforme os princípios da Natureza Primitiva do lugar, e com a intenção de melhorar a ecodinâmica do Município de Catalão (GO), ações para a requalificação da arborização do sistema viário urbano. A discussão teórica se fez por meio da abordagem ecodinâmica, utilizando-se de suporte em literatura especializada, dando ênfase também à percepção, à Paisagem, recorrendo a instrumentos, para melhor compreensão do assunto, como análises de solos, inventário total das árvores, questionários para obter a percepção e opinião da população. Por meio de metodologias, como revisões em literaturas, pesquisas de campo e de laboratórios, buscou-se compreender os problemas existentes na arborização urbana de acompanhamento viário, como verificar se a arborização como é hoje realizada está de acordo com a ecodinâmica do lugar, e apresentar propostas para os problemas que se evidenciaram nesta análise da arborização. A arborização pode melhorar mediante a observância das normas já existentes de cunho legal e acadêmico-científico, sendo algumas das Leis Constitucionais de nível Federal, outras Estaduais ou Municipais e normas ligadas à própria Natureza dos ecossistemas ainda persistentes no espaço recortado para este estudo e que permitem observar e concluir sobre a ecodinâmica desse espaço em estudo.
117

Circuitos sociais da fotografia votiva em Trindade (GO): caminhos para uma reflexão sobre a fotografia popular / Social circuits of votive photography in Trindade (GO): paths for a reflection on popular photography

Borges , Déborah Rodrigues 18 May 2015 (has links)
Submitted by Cláudia Bueno (claudiamoura18@gmail.com) on 2016-01-08T16:41:41Z No. of bitstreams: 2 Tese - Déborah Rodrigues Borges - 2015.pdf: 7645607 bytes, checksum: 94245b9a6f9e64bb23dc539f1f74e8f5 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2016-01-11T06:34:11Z (GMT) No. of bitstreams: 2 Tese - Déborah Rodrigues Borges - 2015.pdf: 7645607 bytes, checksum: 94245b9a6f9e64bb23dc539f1f74e8f5 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2016-01-11T06:34:11Z (GMT). No. of bitstreams: 2 Tese - Déborah Rodrigues Borges - 2015.pdf: 7645607 bytes, checksum: 94245b9a6f9e64bb23dc539f1f74e8f5 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2015-05-18 / Circuitos sociais da fotografias votiva em Trindade (GO): caminhos para uma reflexão sobre a fotografia popular proposes a new look at the field of popular photography, which consists of massive photographic practices, whose images are endowed with senses widely shared, through analysis of practices, uses and functions of photographic ex-votos in the context of Sala dos Milagres at the Basílica do Divino Pai Eterno in Trindade, a city located in the metropolitan area of Goiânia, capital of Goiás. The ex-votos are objects made by devotees and deposited on religious pilgrimage sites as thanks for graces received or as a way to beg the intervention of saints in favor of certain persons and / or situations. In Trindade(GO), we identified, from the analysis of photographic ex-votos deposited in the Sala dos Milagres and interviews with pilgrims, devotees of the Divino Pai Eterno and employees of the sanctuary, the dynamics of institutionalization of votive picture and the tensions in this process. Thus, we highlight the importance of the materiality of photographic artifacts, performances of individuals and assemblies in space as defining elements of the dynamics of meanings production of photographic ex-votos. / La investigación Circuitos Sociais da Fotografia Votiva em Trindade (GO): caminhos para uma reflexão sobre a fotografia popular propone una nueva mirada a la esfera de la fotografía popular, consistente en prácticas fotográficas de carácter masivo, cuyas imágenes están dotadas de sentidos ampliamente compartidos, a través del análisis de las prácticas, usos y funciones de los ex-votos fotográficos en el contexto de la Sala dos Milagres de la Basílica do Divino Pai Eterno em Trindade, ciudad situada en el área metropolitana de Goiânia, capital de Goiás. Los ex-votos son objetos hechos por los devotos y depositados en lugares de peregrinación religiosa como agradecimiento por las gracias recibidas o como una manera de pedir la intervención de las entidades religiosas a favor de ciertas personas y / o situaciones. En Trindade (GO), identificamos a partir del análisis de ex-votos fotográficos depositados en la Sala dos Milagres y entrevistas con los peregrinos, devotos del Divino Pai Eterno y empleados del santuario, la dinámica de institucionalización de la imagen votiva y las tensiones de este proceso. Así, destacamos la importancia de la materialidad de los artefactos fotográficos, de las actuaciones de los individuos y de los montajes en el espacio como elementos definidores de la dinámica de la producción de significados de los ex-votos fotográficos. / A pesquisa Circuitos sociais da fotografias votiva em Trindade (GO): caminhos para uma reflexão sobre a fotografia popular propõe um novo olhar sobre o campo da fotografia popular, constituído por práticas fotográficas de caráter massivo, cujas imagens são dotadas de sentidos amplamente compartilhados, através de análises sobre as práticas, usos e funções da fotografia como ex-voto no contexto da Sala dos Milagres da Basílica do Divino Pai Eterno em Trindade, município localizado na região metropolitana de Goiânia, capital de Goiás. Os ex-votos são objetos elaborados por devotos e depositados em locais de peregrinação religiosa como agradecimento por graças recebidas ou como forma de suplicar a intervenção das entidades religiosas em favor de determinadas pessoas e/ou situações. Em Trindade (GO), identificamos, a partir da análise de fotografias votivas depositadas na Sala dos Milagres e de entrevistas realizadas com romeiros, devotos do Divino Pai Eterno e funcionários do santuário, as dinâmicas de institucionalização da fotografia votiva, bem como as tensões existentes nesse processo. Com isso, destacamos a importância da materialidade dos artefatos fotográficos, as performances dos sujeitos e as montagens no espaço como elementos definidores das dinâmicas de produção de sentidos dos ex-votos fotográficos.
118

Kommunikation med hjälp av digitala verktyg i grundsärskolan. : Kan appen Widgit Go bidra till utveckling?

Calén, Ulrika, Susann, Genegård Ivarsson, Nyberg, Mona January 2015 (has links)
Syftet med denna studie har varit att ta reda på om digitala hjälpmedel kan skapa möjligheter till kommunikation och samspel för elever i grundsärskolan. Vi har valt att studera surfplatta och appen Widgit Go. Intresset för studien uppkom då vi i våra verksamheter sett att många elever i grundsärskolan har begränsningar i sin förmåga att kommunicera. Många elever är i behov av stöd och kompensatoriska hjälpmedel för att kunna tala om vad de vill och för att bli förstådda. I våra verksamheter används surfplattor och våra erfarenheter är att de kan vara ett bra hjälpmedel för kommunikation om det används på rätt sätt. Studien är inspirerad av aktionsforskning och de metoder vi använt är intervjuer, observationer samt reflekterande samtal. Studiens fokus har varit på pedagogernas arbete med Widgit Go som kommunikativt hjälpmedel, samt på förändringar som gjorts under studiens gång för att anpassa appen efter elevernas behov. Resultatet i studien visar att alla deltagande pedagoger anser att Widgit Go och surfplatta bidrar till ökad kommunikation och ökat samspel hos eleverna och en stor fördel är att den kan formas efter individens behov. Pedagogerna har även stött på vissa tekniska svårigheter med appen. Det finns flera olika appar till surfplatta som kan stödja elever i deras kommunikation och vad som passar eleven är individuellt. I denna studie har enbart appen Widgit Go studerats och vi kan därför inte uttala oss om andra liknande appar. Studien har i jämförelse med tidigare forskning kommit fram till liknande resultat, det vill säga att digitala hjälpmedel bidrar till ökad kommunikation och ökat samspel hos elever i grundsärskolan, men att appar behöver anpassas för individen. Då studien är inspirerad av aktionsforskning så bidrar den mest med kunskap för den egna praktiken eller liknande praktiker. Aktionsforskning kan vara en givande metod för att utveckla den egna praktiken genom att tillsammans söka kunskap om den egna undervisningen.
119

Electrical characterization of thermally reduced graphite oxide

Jewell, Ira 07 July 2010 (has links)
This thesis describes the transport properties observed in thermally treated graphite oxide (GO), which holds promise as an economical route to obtaining graphene. Graphene is a material consisting of a single atomic plane of carbon atoms and was first isolated as recently as 2004. Several isolation techniques have been investigated, including mechanical exfoliation, chemical vapor deposition, and the reduction (by various methods) of chemically synthesized graphite oxide. Two fundamental questions are pursued in this work. The first is concerned with the maximum electrical conductivity that can be achieved in atomically thin reduced graphite oxide samples (rGO). As produced, GO is insulating and of little use electronically. By heating and exposure to reducing atmospheres, however, the conductivity can be increased. Through the lithographic definition and fabrication of four-point contact structures atop microscopic samples of GO, the resistance of the sample can be monitored in situ as the reduction process takes place. It was discovered that the resistance of few-layer GO could be decreased by an order of magnitude when heated to 200 °C and subsequently cooled back to room temperature in forming gas. Final resistivities were on the order of 0.5 Ω-cm. An ambipolar field effect was observed in the thermally treated samples, with resistance decreasing by up to 16 % under a substrate bias of ±20 V. Mobilites were inferred to be on the order of 0.1 cm²/V-s. It was also found that the presence of forming gas during reduction decreased the resistance of the GO samples by roughly one half. The second question that this work begins to answer is concerned with the distance that electrons can travel in such thermally-reduced GO before spin-randomizing scattering. The answer can be elucidated with the aid of magnetoresistance measurements using ferromagnetic contacts to inject a spin-polarized current through the sample. The observation of the magnetoresistive effect with the contacts separated by a certain distance can be taken as evidence of a spin coherence length in the material of at least that distance. Though this experiment has not yet been carried out, progress has been made toward its possibility; specifically in the fabrication and characterization of independently switchable magnetic contacts. By exploiting magnetic shape anisotropy, contact pairs have been fabricated and demonstrated to differ in magnetic coercivity by up to 8 Oe. / Graduation date: 2011
120

Exploring Unease : A Study of How Unease is Produced in Kazuo Ishiguro’s Never Let Me Go

Greijdanus, Wouter January 2014 (has links)
This paper deals with the novel Never Let Me Go by Kazuo Ishiguro and explores the feeling of unease established by the author. The theoretical framework for this paper is based on questions of humanity and thus makes use of existentialism as established by Sartre and Kierkegaard. Initially the essay explores how the setting of the novel helps establish a familiar world with unfamiliar elements. After that questions of humanity are raised and how these questions relate to the clones by showing that the clones have human qualities yet are not treated as human. These questions are expanded in the following part about ethical issues and it is shown that the reader is tempted by the author to cross certain ethical boundaries leading to a feeling of unease. Special attention is given to freedom of choice in the third part of the analysis and it is shown how the choices of the clones are very limited, especially if they are considered human. The fourth part then discusses the narrative perspective and how the narrator Kathy H. is used by the author to establish a connection and a perception of the narrator as human.

Page generated in 0.0514 seconds