Orientador: Celio Pasquini / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-04T14:28:43Z (GMT). No. of bitstreams: 1 Bueno_AerentonFerreira_M.pdf: 1724151 bytes, checksum: bf49a3496f1952d08541ce7184b5dcfd (MD5) Previous issue date: 2004 / Mestrado / Quimica Analitica / Mestre em Química

Das Ziel dieser Studie lag darin, die Auswirkung zentraler schlafbezogener Atemstörungen (zSBA) auf die zerebrale Oxygenierung bei Kindern mit Meningomyelozele (MMC) und Chiari-II-Malformation zu untersuchen. Im Schlaflabor der Universitäts-Kinderklinik Würzburg wurden Kinder mit MMC und Chiari-II-Malformation, bei denen zuvor eine zentrale Atemstörung diagnostiziert worden war, polysomnographisch untersucht. Zusätzlich zur standardisierten Polysomnographie (PSG) wurde die zerebrale Sauerstoffsättigung mittels Nahinfrarotspektroskopie (NIRS) abgeleitet. Die Nahinfrarotspektroskopie ermöglicht eine kontinuierliche, nicht-invasive Messung der zerebralen Oxygenierung. Diese Methode beruht auf der relativen Durchlässigkeit von Gewebe im Nahinfrarotbereich. Beim Durchtritt von Licht durch Gewebe kommt es zur Absorption durch die Chromophoren O2Hb und HHb. Mit Hilfe des modifizierten Lambert-Beer-Gesetzes können Veränderungen der Chromophorenkonzentration berechnet werden. Zusätzlich zu dieser Methode ist es mit dem NIRO-200-Gerät möglich, absolute Werte des Gewebeoxygenierungsindexes (TOI) zu ermitteln. Mittels Spatially Resolved Spectroscopy (SRS) wird die Änderung der Lichtabschwächung über eine Distanz gemessen und unter Verwendung einer modifizierten Diffusionsgleichung TOI berechnet. Die respiratorischen Ereignisse während der Polysomnographie wurden in Bezug auf die Dauer, den peripheren Sättigungsabfall, das Schlafstadium und die Veränderungen der zerebralen Sauerstoffsättigung ausgewertet. Die zerebralen Werte wurden mit dem NIRO-200-Gerät (Fa. Hamamatsu Phototonics) gemessen: oxygeniertes Hämoglobin (O2Hb), deoxygeniertes Hämoglobin (HHb) und der Gewebeoxygenierungsindex (TOI). Es konnte ein typisches Reaktionsmuster der zerebralen Parameter während zSBA beschrieben werden mit Abfall des O2Hb, zum Anstieg des HHb und zum Abfall des TOI. Zudem konnte gezeigt werden, dass zSBA mit sehr starken zerebralen Sauerstoffabfällen assoziiert sein können. Es zeigte sich eine starke Korrelation mit der Dauer einer Atemstörung, sowie dem Ausmaß des peripheren Sättigungsabfalls. Eine signifikante Korrelation mit dem Schlafstadium konnte nicht hergestellt werden. Je länger demnach eine Apnoe ist bzw. je stärker der peripher gemessene Sauerstoffabfall, desto stärker ist auch der zerebrale Sauerstoffabfall. Es ist zu vermuten, dass wiederkehrende Episoden von Hypoxie während zentraler Apnoen und zentraler Hypopnoen über Jahre zu Schädigungen des Gehirns führen und dadurch einen negativen Einfluss auf die Entwicklung von Kindern mit Chiari-II-Malformation haben bzw. eine neurologische Verschlechterung begünstigen. Daher erscheint es wichtig, zSBA möglichst frühzeitig aufzudecken und zu behandeln. / Central Apnea are very common in Children with Meningomyelocele and Chiari-II-Malfromation. Previous studies showed, that these central Apneas often are assotiated with peripheral Deoxygenation. To show, wether these deoxygenations are just a phenomenon of peripheral circulation or if they are affecting the cerebral oxygenation we used Near-infrared-Spectroskopy (NIRS). NIRS is a method for continously, noninvasively monitoring cerebral oxygenation (NIRO-200 Fa. Hamamatsu). This study shows, that there is a typical reaction of cerebral parameters: dedrease of oxygenatet heamoglobin, increase of deoxy-heamoglobin and decrease of tissue oxygenation index. In addition it is shown that the duration and the peripheral Desaturation have an impact on cerebral Deoxygenation.

Submitted by Natalia de Souza Gonçalves (natalia.goncalves@ufpe.br) on 2015-05-08T13:02:32Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) tese_viviane_caetano.pdf: 8033577 bytes, checksum: 28662999951e39c3499407035284456e (MD5) / Made available in DSpace on 2015-05-08T13:02:32Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) tese_viviane_caetano.pdf: 8033577 bytes, checksum: 28662999951e39c3499407035284456e (MD5) Previous issue date: 2015-03-30 / PRH-28 / Neste trabalho foram construídos modelos empíricos multivariados utilizando a espectroscopia e imagens hiperespectrais na região do infravermelho próximo (NIR), visando determinar e mapear, respectivamente, o teor de dietilenoglicol (DEG), grupos carboxílicos terminais (GCT) e índice de viscosidade (IV) em amostras de fibras de poli(tereftalato de etileno)-PET. Cento e cinqüenta e duas amostras de fibras foram fornecidas pela empresa M&G (Cabo de Santo Agostinho-PE). Devido à dificuldade de obtenção de espectros representativos das fibras, foi empregado um acessório de amostragem, desenvolvido para este trabalho, e utilizados os espectros obtidos em dois equipamentos: Spectrum 400 (marca Perkin Elmer) e Diamond20 (marca AIT). Também foram adquiridas imagens hiperespectrais na região do NIR utilizando-se uma câmara SisuCHEMA SWIR (marca Specim Spectral Imaging Ltd.). Para ampliar as faixas de variações dos parâmetros estudados foram utilizadas a radiação gama nas doses de 25, 60, 120 e 200 kGy. Foram construídos e avaliados modelos por Regressão por Mínimos Quadrados Parciais (PLS) empregando diferentes técnicas de pré-processamentos: variação normal padrão combinada com suavização Savitzky-Golay ou derivada Savitzky-Golay, nas janelas de 15, 17 e 19 pontos (modo clássico) e 5, 7 e 9 pontos (modo por imagem). O algoritmo Jack-Knife foi empregado para seleção das variáveis significativas. Para escolha do número de fatores (PLS) foi usado a validação cruzada completa e para seleção dos conjuntos de calibração e validação externa foi empregado o algoritmo SPXY (Sample set Partitioning based on joint X-y distances). A capacidade preditiva dos modelos PLS foi avaliada de acordo com os erros de previsão (RMSEP) para o conjunto de validação externa. Os modelos construídos apresentaram resultados satisfatórios para o DEG e GCT, com valores do RMSEP equivalentes à estimativa da repetitividade do método de referência (cromatografia e titulação, respectivamente). Com os modelos construídos com os espectros médios das imagens foi possível obter os mapas de distribuição dos teores de DEG e GCT na fibra. Para o IV, os resultados não foram satisfatórios, pois os valores dos RMSEP’s foram maiores que a repetitividade do método de referência (3,88 UA). Ainda nesta tese, foi avaliada a possibilidade de prever regiões mais sujeitas ao Environmental stress cracking (ESC) em filmes de PET reciclado, utilizando imagens hiperespectrais na região do NIR e Análise discriminante por mínimos quadrados parciais (PLS-DA). Duas amostras foram utilizadas. Modelos satisfatórios só foram obtidos quando construídos com uma das amostras testadas. Esses resultados embora preliminares, abrem uma nova linha de pesquisa tratando da avaliação e compreensão do fenômeno de ESC empregando imagens hiperespectrais no NIR.

Orientadores: Ivo Milton Raimundo Junior, Maria Fernanda D'Oliveira Pimentel / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-13T12:57:52Z (GMT). No. of bitstreams: 1 Lima_KassioMichellGomesde_D.pdf: 3376040 bytes, checksum: c43fc17e739fb3c24ee4fa1b849c70ef (MD5) Previous issue date: 2009 / Resumo: Este trabalho descreve o desenvolvimento de sensores ópticos para determinação de benzeno, tolueno, etilbenzeno e xilenos (BTEX) e de íons metálicos em águas. Para a determinação de BTEX, monolitos de polidimetilsiloxano (PDMS) foram colocados dentro de um frasco preenchido com soluções aquosas dos compostos BTEX por um determinado tempo. Em seguida, a fase sensora era removida da solução, seca rapidamente e inserida num sistema de medidas, empregando-se um espectrofotômetro FT-NIR. Limites de detecção de 0,079; 0,12; 0,14 e 0,28 mg L para benzeno, tolueno, etilbenzeno e xilenos foram alcançados. A fase sensora foi aplicada a amostras de águas contaminadas por gasolina, quantificando teores de BT (benzeno e tolueno) sem diferença estatística, no nível de 95% de confiança, comparada a técnica GC-FID. A fase sensora também foi usada na determinação simultânea de BTX. Valores de RMSEP (raiz quadrada do erro médio quadrático de previsão) de 0,57 mg L para benzeno, 2,21 mg L para tolueno e 1,23 mg L para xilenos foram alcançados. Um fotômetro no infravermelho próximo baseado em LED (diodos emissores de luz) para a determinação de BTEX total foi desenvolvido. O instrumento desenvolvido opera com dois LED, um fotodiodo, um sistema de fibras ópticas para captação da radiação, célula de transmissão e um programa em Visualbasic.Net para controle e aquisição de dados. O instrumento pode ser uma alternativa viável, de baixo custo para a determinação de BTEX total em águas. Foi avaliado o comportamento do novo reagente luminescente di(hexafluorofosfato) de bis(1,10-fenantrolina)(2-(1H-imidazo[4,5- f][1,10]fenantrolina)Rutenio (II), abreviadamente [Ru(phen)2iip](PF6)2, no desenvolvimento de um sensor óptico para a determinação de íons metálicos em águas. A imobilização do reagente em matrizes poliméricas revelou que o sensor óptico e seletivo ao íon Cu(II), apresentando limite de detecção 32 mg L. O novo complexo de rutênio (II) foi aplicado numa determinação simultânea dos íons metálicos Cu(II) e Hg(II) em solução aquosa, alcançando valores de RMSEP de 2,12 mg L e 0,95 mg L, respectivamente / Abstract: This work describes the development of optical sensors for determination of benzene, toluene, ethylbenzene and xylenes (BTEX) and metal ions in water. For the determination of BTEX, monoliths of polydimethylsiloxane (PDMS) were inserted into a bottle filled with aqueous solutions of BTEX compounds for a pre-defined period of time. Afterwards the sensing phase was removed from the solution, dried and placed in the detection system of an FT-NIR spectrophotometer. Detection limits of 0.079, 0.12, 0.14 and 0.28 mg L for benzene, toluene, ethylbenzene and xylenes, respectively, have been achieved. The sensing phase was applied to the determination of benzene and toluene in water samples contaminated by gasoline, providing results that did not show statistical differences from those obtained by GC-FID at a confidence level of 95%. The sensing phase was also applied to the simultaneous determination of BTX in contaminated water, providing RMSEP values (root mean square error of prediction) of 0.57 mg L for benzene, 2.21 mg L for toluene and 1.23 mg L for xylenes. A near infrared photometer based on LED (light emitting diodes) for the determination of total BTEX was developed. The instrument operates with two LED as light sources and a photodiode as detector, a transmission cell connected to an optical fiber bundles; a VisualBasic.Net program was written for control and data acquisition. The instrument performance indicated that it can be a feasible and low cost alternative for the determination of total BTEX in water. Finally, it was evaluated the performance of the new luminescent reagent bis(1,10-phenanthroline)(2-(1H-imidazol-2- yl)-1H-imidazo[4,5-f][1,10]phenanthroline)ruthenium(II) di(hexafluorophosphate) for the development of an optical sensor for the determination of metal ions in water. The immobilization the reagent in the polymeric matrices showed that the optical sensor is selective to Cu (II) ion, providing a detection limit of 32 mg L. The new complex of ruthenium (II) was also applied to the simultaneous determination of Cu (II) and Hg (II) in aqueous solution, showing RMSEP values 2.12 mg L and 0.95 mg L, respectively / Doutorado / Quimica Analitica / Doutor em Ciências

Orientador: Ivo Milton Raimundo Junior / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-09T15:37:40Z (GMT). No. of bitstreams: 1 Panontin_Flavia_M.pdf: 2358588 bytes, checksum: 5556de1b55db28438143379cca4b4281 (MD5) Previous issue date: 2007 / Resumo: Um método para a determinação do volume de poros de sílicas, utilizadas como suportes de fases estacionárias para CLAE (Cromatografia Líquida de Alta Eficiência), foi desenvolvido utilizando a espectroscopia na região do infravermelho próximo (NIR). Foram preparadas amostras pela adição de sílica em soluções de diferentes concentrações de compostos de recobrimento, como polímeros, hidrocarbonetos lineares e ramificados, nujol, glicerol, entre outros, em meio de diclorometano ou metanol. Foram registrados espectros de reflectância difusa na região de 1100 a 2300 nm. Os espectros obtidos foram submetidos à primeira derivada e as intensidades em 1688 nm (primeiro sobretom de ligações C-H) foram empregadas para a construção de uma curva em função da carga inicial (massa recobrimento/massa total) da amostra. Foram obtidos dois ramos lineares, o primeiro (praticamente paralelo à abscissa) indica que a imobilização do reagente no interior dos poros da sílica, e o segundo mostra um aumento crescente dos valores de primeira derivada, indicando o recobrimento de sua superfície externa. A intersecção destas duas retas fornece o valor de carga equivalente ao total preenchimento dos poros. Os resultados obtidos de volume de poro são concordantes com os valores fornecidos pelo método padrão (BJH), apresentando desvios padrão menores que 10%. O método proposto apresenta boa reprodutibilidade, com desvios menores que 1,0%, sendo rápido, simples e não destrutivo o que mostra uma grande vantagem frente ao método BJH, que faz uso de equipamentos caros e procedimentos lentos / Abstract: A method for the determination of pore volume of silicas, used as stationary phases for HPLC (High Performance Liquid Chromatography) was developed using near infrared spectroscopy (NIR). Samples were prepared by the addition of silica in covering compounds solutions of different concentrations, as linear and ramified polymers, hydrocarbons, nujol, glycerol, and among others, using dichloromethane or methanol as solvents. Diffuse reflectance spectra were registered in the 1100 to 2300 nm region. Spectra were submitted to a first derivative pre-treatment and the intensities at 1688 nm (first overtone of C-H bonds) were used for the construction of a curve as a function of the initial load (covering/total mass) of the sample. Two linear branches were obtained; the first one (practically parallel to the abscissa) indicates the immobilization of the reagent in the interior silica pores, and the second one shows increasing values of first derivative, indicating the covering of its external surface. The intersession of these two straight lines supplies the load value that is equivalent to the total fulfilling of the pores. The results obtained for of pore volume are in agreement with those supplied by the standard method (BJH), presenting deviation lower than 10 %. The proposed method presents good reproducibility with standard deviation lower than 1.0 %, being fast, simple and no destructive technique, that is a great advantage over the BJH method, which uses expensive equipment and slow procedures / Mestrado / Quimica Analitica / Mestre em Química

This diploma thesis provides summary information about using of near infrared spectroscopy for monitoring of high oleic acid content in sunflower seed. The calibration for high oleic sunflower seed was performed by using calibration model PLS - „Partial least squares. Gas chromatography was used as a reference method. Based on this knowledge thirty samples of high oleic sunflower seeds were measured and evaluated on this calibration. The last part of diploma thesis consist of comparison of oleic acid results measured by near infrared spectroscopy and gas chromatography used as reference method, and discussion about the measurement accuracy and evaluation of suitability of using these methods.

In this thesis a near-infrared laser scanning confocal microscope (NIR-LSCM) is built to operate with optimal performance at 1550nm in combination with simultaneous LED light imaging at 970nm. For detection, a camera equipped with a complementary metal oxide semiconductor (CMOS) sensor and a superconducting nanowire single photon detector (SNSPD) are used for the LED part and the LSCM part, respectively. By using an SNSPD developed for operation in the NIR with a timing jitter of 19ps and a quantum efficiency (QE) of 85$\%$ instead of, for example, a photo-multiplier tube (PMT) or a single photon avalanche photo diode (SPAD), it has been demonstrated that limitations of existing systems can be reduced.  This thesis also demonstrates that it is possible to build a LSCM with commercially available optical components. It is also proved how important it is to consider the features of each optical component chosen as well as how all components work together as a system. Especially how important it is to consider lens coatings and splitting ratios for beamsplitters to realize a system with optimal performance for operation in the NIR. Thorough research in combination with a trial-and-error process was used to arrive at the final NIR-LSCM system setup presented in this thesis. As a final note, this thesis sheds light on some possible NIR-probes which are suitable for operation in combination with our system. / I detta projekt byggs ett nära-infrarött konfokalt laserskanningsmikroskop (NIR-LSCM) med optimal prestanda för våglängder kring 1550nm i kombination med samtidig LED-ljusavbildning vid 970nm. För detektering används en kamera utrustad med en komplementär metalloxidhalvledarsensor (CMOS) för LED-delen och en supraledande nanotrådsdetektor för detektion av enstaka fotoner (SNSPD) för LSCM-delen. Genom att använda en SNSPD optimerad för NIR med 19ps timing jitter och 85$\%$ kvanteffektivitet (QE) istället för exempelvis ett fotomultiplikatorrör (PMT) eller en enkelfoton lavinfotodiod (SPAD) har det bevisats att begränsningar av befintliga system kan reduceras. Detta projekt visar också att det är möjligt att bygga ett LSCM med kommersiellt tillgängliga optiska komponenter. Det har också bevisats hur viktigt det är att beakta egenskaperna hos varje vald optisk komponent samt hur alla komponenter fungerar tillsammans som ett system. Speciell fokus har lagts på hur viktigt det är att ta hänsyn till linsbeläggningar och delningsförhållanden för stråldelare för att realisera ett system med optimal prestanda för drift i NIR. Sammanfattningsvis användes grundliga förstudier av optiska komponenter och existerande NIR-system i kombination med en trial-and-error-process för att komma fram till den slutliga NIR-LSCM-systemuppsättningen som presenteras i detta projekt. Som en sista notering belyser detta projekt några möjliga NIR-prober som är lämpliga för drift i kombination med vårt system.

Abstract Purpose – To study the possibility of using a NIR hardware solution to photograph individuals in a private vehicle as well as an analysis of its images. Method – A study of existing theories around the NIR-method’s performance in selected conditions and individual tests were performed to examine if the literature statements were valid for this study. Two empirical tests have been carried out, the first was carried out at Kapsch test track and the other outside the test track in a single stationary test. An interview which formed the basis for the assessment on the quality of empirical data with a focus on computer-based detection of the number of individuals in the vehicle. Findings – The results have demonstrated the potential of the NIR method’s performance in a fully automated detection system for the number of individuals inside the vehicle. Empirical data indicates that the method can depict individuals inside vehicles of sufficiently high quality, but it is greatly affected by reflections, weather and light conditions. Implications – Result supports the assumption that the NIR method using an external light source can be used to image the interior through a varying number of weather and lightning conditions. The study originated until the results suggested that a NIR-based hardware setup can create images with high enough quality for the human eye to be able to detect the number of individuals inside the vehicle.If the overall performance into account, it suggests that the main problem with the use of the hardware set is to maintain the quality of the whole sample and that the crucial variables for the method’s performance is the influence of light and reflection conditions. Limitations – The major limitations have been that we limited ourselves to a subjective analysis of the selection and assessment on the image features for computer-based detection of the number of individuals in the vehicle. We were limited to two tests, one in tough conditions where only the driver was in the vehicle and the second stationary test, where the focus was on the number of people in vehicles and light sources impact on the result.

Submitted by Gizele Lima (gizele.lima@inpa.gov.br) on 2017-08-07T14:59:16Z No. of bitstreams: 2 Dissertação_mestrado_Carla Lang.pdf: 1090969 bytes, checksum: 1a54204915e84b680485beadcfce6175 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2017-08-07T14:59:16Z (GMT). No. of bitstreams: 2 Dissertação_mestrado_Carla Lang.pdf: 1090969 bytes, checksum: 1a54204915e84b680485beadcfce6175 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2014-05-21 / Amazon species identification in different ontogenetic stages by near infrared spectroscopy Precise identification of species requires high level of knowledge by taxonomists and presence of reproductive material. This represents a major limitation for those working with seedlings and juveniles, which differ morphologically from adults and do not bear reproductive structures. Near-infrared spectroscopy (FT-NIR) was previously shown to be effective in species discrimination of adult plants, so if young and adults have the same spectral signature, discriminant functions based on FT-NIR spectra of adults can be used to identify young. We tested this with a sample of 419 plants in 16 species within Protium and Crepidospermum (Burseraceae). We obtained 12 spectral readings per leaf, from adaxial and abaxial surfaces of dried leaves and compared the rate of correct predictions of species with discriminant functions for different combinations of readings. We obtained an average, over all species, of 75% correct identifications of young plants by discriminant equations developed based only on adults, when the most informative wavelengths were selected. Most species were well predicted (75-100% correct identifications) and only three had poor predictions (27-60%). This occurred despite of the spectra of young individuals being distinct of those of adults when species were analyzed individually. When young and adults individuals are included in the same discriminant function, correct predictions of external samples attained 99%. Some of the poorly predicted species were re-evaluated by an expert in the family in a blind procedure and proven to be a mixture of samples in different species. Even considering some limitations, concluded that FT-NIR has a high potential in identification of species even in different ontogenetic stages. Key words: Burseraceae, leaves, species discrimination, FT-NIR, ontogenetic stages / A identificação das espécies de plantas exige um alto nível de conhecimento de taxonomistas e a presença de material reprodutivo. Isso representa uma das grandes limitações para quem trabalha com plântulas e juvenis, os quais diferem morfologicamente dos adultos e ainda não apresentam estruturas reprodutivas. Estudos prévios demonstraram que a espectroscopia do infravermelho próximo (FT-NIR) é eficaz na discriminação de espécies de plantas em estádio adulto, logo se indivíduos jovens e adultos possuirem uma assinatura espectral semelhante, funções discriminantes baseadas em leituras espectrais de indivíduos adultos poderiam ser usadas para identificar plântulas e juvenis. Testamos isto com uma amostra de 429 espécimes de 16 espécies dentre os gêneros Protium e Crepidospermum (Burseraceae). Para isso coletamos 12 leituras espectrais, abaxial e adaxial, de folhas secas e comparamos as taxas de predições corretas das espécies para diferentes conjuntos de dados e modelos discriminantes. Obtivemos uma média, sobre todas as espécies, de 75% de acertos nas identificações dos jovens quando as funções discriminantes foram construídas com base nos adultos e com a seleção dos comprimentos de onda mais informativos. A maior parte das espécies foi bem predita (75-100% de identificações corretas) e apenas três espécies tiveram baixas predições (27-60%). Isso ocorreu devido os espectros dos jovens serem distintos dos espectros dos adultos quando as espécies foram analisadas individualmente. Quando jovens e adultos foram incluídos na função discriminante, amostras externas foram preditas corretamente, alcançando 99% de acerto. Algumas das espécies mal preditas foram novamente avaliadas por um perito da família por um procedimento cego e comprovou-se uma mistura de amostras de diferentes espécies. Mesmo considerando algumas limitações, concluimos que a FT-NIR tem um elevado potencial na identificação de espécies, mesmo em diferentes estádios ontogenéticos. Palavras chave: Burseraceae, folhas, discriminação de espécies, FT-NIR, fases ontogenéticas

Die Transkranielle Gleichstromstimulation (tDCS) stellt ein Verfahren zur nicht-invasiven und schmerzfreien Stimulation des Gehirns dar. Ziel dabei ist es die kortikale Erregbarkeit zu modulieren, indem das Ruhemembranpotenzial der Nervenzellen verschoben wird. Anodale tDCS führt dabei zu einer Depolarisierung des Membranpotenzials und somit zur Zunahme der neuronalen Aktivität. Kathodale tDCS hat durch die Hyperpolarisierung des Membranpotenzials eine Abnahme der neuronalen Aktivität zur Folge. Durch den exzitatorischen Effekt nach anodaler Stimulation und den inhibitorischen Effekt nach kathodaler Stimulation stellt die tDCS eine vielversprechende Option in der Therapie neurologischer oder neuropsychiatrischer Erkrankungen dar. In vorliegender Studie sollten die Auswirkungen der transkraniellen Gleichstromstimulation über dem linken dorsolateralen präfrontalen Kortex (DLPFC) auf Arbeitsgedächtnisprozesse untersucht werden. Die Effekte der tDCS wurden an 56 gesunden Versuchspersonen getestet, die randomisiert drei Stimulationsgruppen zugeordnet wurden (anodale, kathodale und Sham-Stimulation). Stimuliert wurde mit 2 mA bei einer Elektrodengröße von 35 cm². Stimulationsort war dabei der linke DLPFC, die Referenzelektrode wurde über dem linken Mastoid platziert. Während der Stimulation führten die Versuchspersonen eine modifizierte N-Back-Aufgabe mit drei Bedingungen (0-Back, 1-Back und 2-Back) aus, um die Funktion des Arbeitsgedächtnisses hinsichtlich des Verhaltens erfassen zu können. Die Auswirkungen der tDCS auf die neuronale Aktivität wurden mittels funktioneller Nah-Infrarot-Spektroskopie (fNIRS) gemessen. Auf neuronaler Ebene erwarteten wir eine Zunahme der kortikalen Aktivität nach anodaler Stimulation innerhalb des linken DLPFC und gegenteilige Effekte nach kathodaler Stimulation. In vorliegender Untersuchung konnte lediglich eine Tendenz zu dieser Annahme beobachtet werden, eindeutige Signifikanzen blieben jedoch aus. Bei Betrachtung verschiedener Regions of Interest (ROIs) konnten nur signifikante Unterschiede zwischen der anodal und der kathodal stimulierten Gruppe nachgewiesen werden, was dafür spricht, dass die Auswirkungen der tDCS zwar in die intendierte Richtung gehen, die Effekte aber nicht stark genug sind, um auch signifikante Unterschiede zur Kontrollgruppe nachweisen zu können. Somit müssen wir davon ausgehen, dass sich die Neurone des DLPFC nur schwach durch die transkranielle Stimulation beeinflussen lassen. Desweiteren wurden die Verhaltensdaten während der N-Back-Aufgabe untersucht. Angenommen wurde eine Verbesserung der Arbeitsgedächtnisleistung durch anodale Stimulation und eine Verschlechterung durch kathodale Stimulation. Hier zeigte sich allerdings, dass sich unsere drei Stimulationsgruppen weder in der Anzahl der Fehler, noch in der Anzahl der richtigen Antworten, der Anzahl der verpassten Antworten oder in der mittleren Reaktionszeit signifikant voneinander unterscheiden. Dies lässt darauf schließen, dass die Stimulation des linken DLPFC keinen Einfluss auf das Verhalten während der Durchführung der Arbeitsgedächtnisaufgabe hat und somit auch die Arbeitsgedächtnisleistung nicht beeinflusst wird. Obwohl die Ergebnisse unserer Studie durch fehlende Signifikanzen nicht hypothesenkonform sind, konnten wir zusammenfassend dennoch eine Tendenz zur anodal-exzitatorischen und kathodal-inhibitorischen Wirkung der tDCS beobachten. Die weitere Erforschung der Auswirkungen der tDCS auf das Arbeitsgedächtnis scheint also sehr vernünftig, vor allem in Anbetracht der möglichen Etablierung der tDCS als Therapieoption neuropsychiatrischer Erkrankungen. Weiterführende Studien sollten die Wirksamkeit der tDCS weiter untersuchen und eine Optimierung der tDCS-induzierten Effekte überprüfen. Ansatzpunkte hierfür wären beispielsweise die Durchführung umfangreicherer Studien mit einem größeren Probandenkollektiv und veränderten Stimulationsparametern oder Studien, die die Auswirkungen der tDCS auf das Arbeitsgedächtnis auch bei psychiatrischen Patienten untersuchen. / Transcranial direct current stimulation (tDCS) is a non-invasive method to modulate cortical excitability. Anodal tDCS results in the depolarization of the neuronal membrane potential and has an increasing effect on neuronal activity whereas cathodal stimulation causes contrary effects by hyperpolarizing the neuronal membrane potential. Because of these effects tDCS is a promising tool in the therapy of mental disorders. In this study the effects of tDCS over the left dorsolateral prefrontal cortex (DLPFC) on working memory were investigated. We tested 56 healthy volunteers which were randomly related to three different stimulation groups (anodal, cathodal and sham stimulation). The electric field was generated with a current of 2 mA and an electrode size of 35 cm². The stimulation electrode was placed over the left DLPFC whereas the reference electrode was located over the left mastoid. While stimulation the subjects had to perform a modified n-back-task with three conditions (1-back, 2-back and 3-back) to determine the effects of tDCS on working memory performance. The impact of tDCS on neuronal activity was measured using functional near-infrared spectroscopy (fNIRS). Regarding neuronal activity, an increasing effect after anodal stimulation and an inhibiting effect after cathodal stimulation was expected. This study only revealed a tendency to this assumption, but statistical significance could not be proved. These findings demonstrate that tDCS only causes weak effects in cortical neurons of the DLPFC. Furthermore, working memory performance during the n-back-task was not influenced by tDCS since no significant difference between the three stimulation groups could be revealed. As tDCS is a promising option in the therapy of mental disorders, further studies with optimized parameters are necessary to examine the influence of tDCS on working memory. Extended sample sizes as well as changing the stimulation parameters should be considered in future studies. Moreover the impacts of tDCS can be investigated in patients suffering from mental disorders in purpose of proving more extinct results.