• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 195
  • 60
  • 45
  • 32
  • 27
  • 17
  • 7
  • 7
  • 7
  • 5
  • 2
  • 2
  • 2
  • 1
  • 1
  • Tagged with
  • 449
  • 98
  • 66
  • 52
  • 50
  • 50
  • 49
  • 47
  • 45
  • 41
  • 35
  • 35
  • 34
  • 33
  • 32
  • 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

Hidrodescloração catalítica de bifenilas policloradas (PCB) em dióxido de carbono supercrítico / Catalytic hydrodechlorination of polychlorinated biphenyls (PCB) in supercritical carbon dioxide

Luiz Américo da Silva do Vale 17 February 2014 (has links)
A reação de hidrodescloração catalítica (HDC) de bifenilas policloradas (PCB) foi estudada em diversos sistemas reacionais: solventes orgânicos, dióxido de carbono supercrítico, presença e natureza de aditivos (bases e co-solventes) a temperaturas na faixa de 25 °C a 100 °C e pressões de 1 bar até 250 bar. Os reagentes utilizados foram um composto modelo (2,4- diclorobifenil), misturas comerciais de PCB (Aroclor, Ascarel) e outros compostos halogenados (clorobenzenos e bromoclorobenzeno). Os catalisadores avaliados, paládio suportado em carvão ativo (Pd/C), paládio suportado em sílica mesoporosa (Pd/SiO2), nanopartículas ferromagnéticas de paládio (FFSiNH2Pd), e nanopartículas ocas de paládio (PdNP) e de platina (PtNP), mostraram-se versáteis nas mais diversas condições, quer sejam condições supercríticas, presença ou não de água, presença e natureza da base e diferentes doadores de hidrogênio. Em dióxido de carbono, dois regimes reacionais foram avaliados: dióxido de carbono subcrítico, onde o gás atua como agente expansor da fase líquida ao se dissolver nela permitindo que a reação ocorra em uma fase líquida rica em gás hidrogênio; e dióxido de carbono supercrítico, sistema onde a temperatura influencia fortemente a reação e a pressão tende a ter efeito negativo sobre a velocidade de reação, devido a efeitos de diluição e de competição das moléculas do gás com as moléculas dos reagentes. A condição reacional ótima foi determinada para o regime supercrítico e dados cinéticos foram obtidos para os regimes sub- e supercrítico. / The catalytic hydrodechlorination reaction (HDC) of polychlorinated biphenyls (PCB) was studied in several reactional systems: organic solvents, supercritical carbon dioxide, presence and nature of additives (bases and co-solvents), in temperatures of 25 °C to 100 °C and pressures of 1 bar to 250 bar. The reagents used were: a model compound, 2,4-dichlorobiphenyl, commercial mixtures of PCB (Aroclor, Ascarel) and other halogenated compounds (chlorobenzenes and bromochlorobenzene). The catalysts evaluated, palladium supported in activated carbon (Pd/C), palladium supported in mesoporous silica (Pd/SiO2), palladium ferromagnetic nanoparticles (FFSiNH2Pd), and hollow palladium ((PdNP) and platinum (PtNP) nanoparticles, showed to be versatile in several conditions, either supercritical conditions, presence or not of water, nature of the base, and different hydrogen donors. In carbon dioxide, two reaction regimes were evaluated: subcritical carbon dioxide, where the gas acts as an expansion agent of the liquid phase when it dissolves in it, allowing that the reaction happens in a liquid phase rich in hydrogen; and supercritical carbon dioxide, a system where the temperature has a strong influence over the reaction and the pressure has a negative effect on the rate of the reaction, due to dilution and the competition of gas molecules with the reagents molecules for the catalyst. The optimal reaction condition was determined for the supercritical regime and kinetic data were obtained for both the sub and supercritical regimes.
112

Konstrukce německé paralaktické montáže astronomického dalekohledu / Construction of German Equatorial Mount

Jančařík, Julius January 2011 (has links)
Purpose of this master´s thesis is a construction proposal of German Equatorial Mount capable to load capacity to 20kg inclusive both shaft-actuators. The solution contains design options of actuators of mount, design proposal of partial systems and parts and calcualtions. More is contain drafts of overal assembly, motor pinion and shaft.
113

Wide Bandgap Semiconductor Components Integration in a PCB Substrate for the Development of a High Density Power Electronics Converter / Intégration dans un substrat PCB de composants à semi-conducteur grand gap pour le développement d’un convertisseur d’électronique de puissance à forte densité

Zhang, Shuangfeng 30 November 2018 (has links)
Les nouveaux composants à semi-conducteur de type grand gap ont été développés pour des applications de conversion de puissance en raison de leurs hautes fréquences de commutation (de centaine kHz à quelques MHz) et pertes faibles. Afin de bien profiter ses avantages, la technologie des circuits imprimés (PCB) est intéressante pour une intégration à haute densité de puissance grâce à sa flexibilité et son faible coût. Cependant, à cause de la mauvaise conductivité thermique du matériau FR-4 utilisé pour le substrat PCB et la haute densité de puissance réalisée, il est primordial de trouver des solutions thermiques pour améliorer les performances thermiques de la structure de PCB. Dans cette thèse, trois solutions thermiques pour les structures de PCB ont été proposées, y compris des solutions avec des vias thermiques, de cuivre épais sur le substrat de PCB ainsi que des dispositifs de refroidissement thermoélectrique (TEC). Nos études sont basées sur la modélisation électrothermique et la méthode d’éléments finis en 3D. Tout d’abord, l’optimisation des paramètres des vias (diamètre, épaisseur de placage, surface formée par des vias, la distance entre des vias etc.) a été réalisée pour optimiser l’effet de refroidissement. Ensuite, on constate que les performances thermiques des structures de PCB peuvent être améliorées en utilisant cuivre épais sur le substrat de PCB. Cuivre épais augmente le flux thermique latéral dans la couche de cuivre. Les influences de l’épaisseur de cuivre (35 à 500 µm) ont été étudiées. Cette solution est facile à réaliser et peut être combinée à d’autres solutions de refroidissement. Enfin, le dispositif thermoélectrique comme les modules Peltier est une technologie de refroidissement local. Les influences des paramètres de Peltier (Propriétés du matériau thermoélectrique, nombre d’éléments Peltier, distance entre la source de chaleur et les dispositifs Peltier, etc.) ont été identifiées. Il est démontré que des modules Peltier ont l’application potentielle pour le développement d’intégration de PCB attendu que son active contrôle des températures. / The emerging wide bandgap (WBG) semiconductor devices have been developed for power conversion applications instead of silicon devices due to higher switching frequencies (from few 100 kHz to several MHz) and lower on-state losses resulting in a better efficiency. In order to take full advantage of the WBG components, PCB technology is attractive for high power density integration thanks to its flexibility and low cost. However, due to poor thermal conductivity of the commonly used material Flame Retardant-4 (FR4), efficient thermal solutions are becoming a challenging issue in integrated power boards based on PCB substrates. So it is of the first importance to seek technological means in order to improve the thermal performances. In this thesis, three main thermal management solutions for PCB structures have been investigated including thermal vias, thick copper thickness on the PCB substrate as well as thermoelectric cooling (TEC) devices. Our studies are based on the electro-thermal modeling and 3D finite element (FE) methods. Firstly, optimization of the thermal via parameters (via diameter, via plating thickness, via-cluster surface, via pattern, pitch distance between vias etc.) has been realized to improve their cooing performances. We presented and evaluated thermal performances of the PCB structures by analyzing the thermal resistance of the PCB substrate with different thermal vias. Secondly, it is found that thermal performances of the PCB structures can be enhanced by using thick copper thickness on top of the PCB substrate, which increases the lateral heat flux along the copper layer. Influences of the copper thickness (35 µm to 500 µm) has been discussed. This solution is easy to realize and can be combined with other cooling solutions. Thirdly, thermoelectric cooler like Peltier device is a solid-state cooling technology that can meet the local cooling requirements. Influences of Peltier parameters (Thermoelectric material properties, number of Peltier elements, distance between the heating source and the Peltier devices etc.) have been identified. All these analyses demonstrate the potential application of Peltier devices placed beside the heating source for PCB structures, which is a benefit for developing the embedding technology in such structures.
114

Design and construction of a portable wireless module

Rashed, Lauk January 2020 (has links)
In this thesis, a wireless module in form of a portable peripheral printed circuit board that can connect to a master device, periodically sending values from a sensor, has been developed to the company Biotage. A literature study has been made on antennas and PCB-design for high frequency applications and a prototype has been designed through CAD software. This thesis handles the design process behind the module which consists of choosing suitable components, measurements/matching of an antenna and design of a suitable rechargeable power supply module. The prototype resulted in a portable, fully wireless device with a long expected battery life with the help of Bluetooth Low Energy technology and low power usage components.
115

Profil lakasové aktivity v kulturách houby Trametes versicolor během degradace endokrinně disruptivní látky Delor 103 / Laccase activity profiling in Trametes versicolor cultures degrading endocrine-disrupting compound Delor 103

Plačková, Martina January 2011 (has links)
In this work endocrine disrupting potential of Delor 103, a commercial mixture of PCB congeners, was studied along with its effect on production of laccase by the ligninolytic fungus Trametes versicolor. Using a gene-reporter yeast assay for evaluation of hormonal activity Delor 103 showed an androgenic activity with an EC50 value of 2.29. 10-2 mg/l. Chlorbenzoic acids, Delor 103 potential metabolites resulting from microbial degradation, displayed on the other hand an estrogenic activity, indicating possible changes in hormonal activity of Delor 103 during its microbial degradation. The addition of Delor 103 to mineral medium T. versicolor cultures resulted in an up to 257times higher laccase activities detected in fungal cultures. Delor 103 induced enzymes showed different pI values from those of control cultures. In a complex malt-extract glucose medium (MEG) the stimulation effect of Delor 103 was kept down. Further, the production of laccase and synthesis of different pI forms depended strongly on the growth phase of fungal cultures. Exponencially growing cultures of T. versicolor were able to produce up to 7 different pI forms of laccase in responce to Delor 103 whereas stationary cultures produced only 4 enzyme forms with higher pI values. Stimulation of laccase activities in T. versicolor,...
116

ATT UTVECKLA EN KRETSKORTSPROTOTYP : UTVECKLING AV EN SMART PILLERDOSA

Hallberg, Anders, Lindberg, Jonathan January 2019 (has links)
Allt fler människor är beroende av medicinering för sin överlevnad. Dessa hittas främst i de äldre åldersgrupperna. Många av dessa tar medicin dagligen och bördan av medicinering är påtaglig. På grund av deras problematik skapas en oerhörd stress i samband med medicinering eftersom dessa människor har särskilt svårt att minnas när den ska intas, vilken dos, men också vilken medicin. En del behöver ta medicin så ofta som 8 ggr på en dag.Dessa människor behandlas av läkare. Läkare bedömer medicineringens verkningsgrad baserat på patientens förmåga och vilja att återge korrekt information medicineringens följsamhet. Allt för ofta återger patienten fel information.Vi har fått i uppgift att vidareutveckla en prototyp för en ”smart” pillerdosa vars mål är att förbättra patientens upplevelse av medicinering samt ge läkaren ett pålitligt och säkert sätt att följa sina patienters följsamhet till medicinering.Vi har vidareutvecklat en tidigare framtagen prototyp genom att utveckla en ny prototyp som implementerar alla önskvärda funktioner på ett måttanpassat kretskort.Fördelarna med en speciellt framtagen kretskortsprototyp gentemot en modulbaserad prototyp undersöks med avseende på storleksförminskning, energieffektivisering samt kostnadseffektivisering.Ett lämpligt tillvägagångsätt för att utveckla en kretskortsprototyp, resultatet av undersökning samt rekommendationer för vidareutveckling avhandlas och presenteras i rapporten.En kretskortsprototyp enligt angivna specifikationer utvecklades på utsatt tid. Undersökningarna visade att storleksförminskning, energieffektivisering samt kostnadseffektivisering kunde uppnås. / More and more people are dependent on medication for their survival. These are mainly found in older age groups. Many of these are medicated daily and the burden of medication is noticeable. Because of their problems, enormous stress is associated with medication because it is particularly difficult to remember when it is to be taken, which dose, but also which medicine. Some need to take medicine as often as eight times in one day.These people are treated by doctors. Doctors assess the effectiveness of medication based on the patient's ability and willingness to recall accurate information regarding their compliance with medication. All too often, the patient recalls wrongful information.We have been given the task of further developing a prototype for a "smart" pillbox whose goal is to improve the patient's experience in medication and give the doctor a reliable and safe way to follow the patients' compliance with medication.We have further developed a previous prototype by creating a new prototype that implements all the desired features on a customized circuit board.The advantages of a specially developed circuit board prototype against a modular prototype are investigated regarding size reduction, energy efficiency and cost efficiency.A suitable approach for developing a circuit board prototype, the results of the investigation and recommendations for further development are discussed and presented in the report.A circuit board prototype according to the stated specifications was successfully developed in the specified timeframe. The investigation showed that greater sizereduction, energy-efficiency and cost-efficiency were possible to achieve.
117

Design and Implementation of 4-Stroke Topology in Electric Drives

Retianza, Darian Verdy January 2018 (has links)
The 4-Stroke inverter topology is investigated and implemented in thisthesis as a method to damp the oscillation at the MOSFET drain-sourcevoltage when reverse recovery occurs. The aim is lower ElectromagneticInterference source level from the power inverter. The designprocess is coming from analyzing the appropriate inductor, making asimulation in LTSPICE and making a high-performance six-layer PCBfor the high current application. Finally, the prototype is tested in differentcontrol timing, radiated emission test and conducted emissiontest. / 4-taktsomvandlarens topologi undersöks och implementeras i dennaavhandling som en metod för att dämpa oscillation när reverse recoverysker i slutstegets MOSFET. Syftet är att dämpa elektromagnetiskstörning från kraftomvandlaren. Designprocessen är att analyseralämplig induktans, göra en simulering i LTSPICE och designa ett högpresterande6-lager PCB för kraftiga strömmar. Slutligen testas prototypenmed olika kontrolltider, elektromagnetisk emission och elektromagnetiskkonduktion.
118

Phase Noise Performance of a PLL Frequency Synthesizer when Powered by Silent Switchers

Basu, Sampriti January 2023 (has links)
In use today are ‘normal’ DC-DC switching regulators with considerable switching noise and ringing, which is bad for noise-sensitive applications. This project involves a solution based on ‘Silent Switchers’ to prove its effectiveness in reducing noise. This idea is then coupled into identifying the susceptibility of a PLL synthesizer to ensure we understand the sensitivity of this type of component and if this can be used with a silent switcher. A particular PLL synthesizer evaluation board is currently powered by linear regulators, which is used as a basis for comparing results. A new board involving silent switchers is designed and manufactured. Phase noise measurements are done to evaluate if silent switchers are a suitable alternative for power supply. / Idag används ’vanliga’ DC-DC switching regulatorer med betydande kopplingsbrus och ringningar, vilket är dåligt för bruskänsliga applikationer. Detta projekt innefattar en lösning baserad på Silent Switchersför att bevisa dess effektivitet när det gäller att minska bruset från dessa regulatorer. Denna lösning används sedan till att identifiera känsligheten hos en PLL-synthesizer för att se till att vi förstår känsligheten hos denna typ av component och om den kan användas med en Silent Switcher". Som referens för studien används ett särskilt PLL-synthesizer- utvärderingskort, drivet av linjära regulatorer. Ett nytt kort med Silent Switchers"istället för linjära regulatorer har konstruerats och tillverkats. Fasbrusmätningar görs på båda korten för att utvärdera om Silent Switchers"är ett lämpligt alternativ för denna applikation.
119

Investigation into the pedagogical value of demonstrating deliberate design deficiencies in PCB design instruction

Sunedal, Björn January 2021 (has links)
Universities and other higher education institutions have been struggling with high levels of student dropouts and poor graduation rates for a long time. As a result, there has been an interest in modifying traditional teaching techniques and implementing new ones to improve student learning outcomes. Interactive Lecture Demonstrations (ILD) is one such teaching technique which has shown positive results in terms of improving student learning outcomes. An audio recorder and player application with the addition of a DC/DC converter was developed. Six different PCB versions of the audio application were created, containing different combinations of deliberate design deficiencies. The deliberate design deficiencies came in the form of different configurations of decoupling capacitors and ground planes. The DC/DC converter served as a noise source to expose weaknesses in the design. In order to make certain that design deficiencies were exposed effectively, the conversion frequency of the DC/DC converter was switchable between a "high" and a "low" setting. The "low" conversion frequency setting was chosen to comfortably fall in the frequency range of human hearing. Measurements of voltage (time domain and spectral), current spectrum, audio spectrum and radiated emissions were collected. Audio recordings illustrating the impact of decoupling capacitors and interference from the DC/DC converter were performed. The measurement results and audio recordings were used to produce an ILD in video format. The ILD was structured around a modified version of the PODS (Predict-Observe-Discuss-Synthesize) model, which is a four-step process used in ILDs. The ILD contained four separate demonstrations that covered the impact of decoupling capacitors, ground topology and the DC/DC converter on the audio quality and radiated emissions. The ILDs were presented in such a way that the measurement results and audio recordings were correlated with the underlying design theory. Students who had taken either one of two courses related to PCB and electronics design offered at the Royal Institute of Technology (KTH) in the spring of 2019 and 2020 were invited to view the ILD video. The effectiveness of the ILD presentation in terms of pedagogic value was measured via a survey which the students were asked to fill out after watching the video. The results were overall very positive. The feedback received indicate that the students found the demonstrations to be informative and educational. By being able to see and hear the effects of neglecting good PCB design practices in two key areas, the demonstrations were able to provide a more realistic and real-world view of the consequences of neglecting to adhere to good design practices in these two areas that may not be apparent in the theoretical literature. In addition, since PCB design is such a vast subject, the results motivates further developments and study of the ILD concept related to other PCB design concepts such as transmission lines, layer ordering, signal integrity (crosstalk, timing, noise, etc), and others. / Universitet och andra högre lärosäten har länge kämpat mot höga nivåer av studentavhopp och låg genomströmning. Som en följd av detta har det funnits ett intresse att göra förändringar i de traditionella undervisningsmetoderna samt att implementera nya sådana. Interaktiva föreläsningsdemonstrationer (Interactive Lecture Demonstrations, ILD) är en undervisningsmetod som har visat på positiva resultat gällande studenters förmåga att uppnå läromålen. En ljudinspelnings- och uppspelningstillämpning med en likspänningsomvandlare konstruerades. Sex olika kretskort med en kombination av olika avsiktliga konstruktionsbrister producerades. De avsiktliga konstruktionsbristerna innefattade olika kombinationer av avkopplings-kondensatorer och jordplan. Likspänningsomvandlaren agerade som en störningskälla vars syfte var att blottlägga svagheter i konstruktionen. För att säkerställa att konstruktionsbristerna skulle kunna blottläggas tydligt var omvandlingsfrekvensen på likspänningsomvandlaren ställbar mellan ”hög” och ”låg”. Omvandlingsfrekvensen på inställningen ”låg” valdes så att den med god marginal hamnade inom frekvensområdet för mänsklig hörsel. Matningar av spänning (tids- och frekvensdomän), strömspektrum, ljudspektrum och utstrålad radioenergi genomfördes. Ljudinspelningar som belyste inverkan av avkopplings-kondensatorerna och störningar från likspänningsomvandlaren samlades in. Mätningarna och ljudinspelningarna användes för att producera en ILD i videoformat. ILD:erna konstruerades kring en modifierad version av PODS-modellen (Predict- Observe- Discuss- Synthesize, ung. Förutspå-Observera-Diskutera-Inlärning), vilken är en fyrstegsprocess för ILD:er. ILD:en innehöll fyra separata demonstrationer som belös avkopplingskondensatorernas, jordtopologins och likspänningsomvandlarens inverkan på ljudkvaliteten och den utstrålade radioenergin. ILD:en presenterades på ett sådant sätt att mätresultaten och ljudinspelningarna korrelerades till den bakomliggande konstruktionsteorin. Studenter som hade läst endera av två kurser relaterade till kretskorts- och elektronik-konstruktion vid Kungliga Tekniska högskolan (KTH) under våren 2019 och 2020 mottog en inbjudan att titta på videon. Utvärdering av effektiviteten hos ILD-presentationen gällande dess pedagogiska värde gjordes via en enkät vilka studenterna ombads att fylla i efter att de tittat på videon. Resultatet var övervägande positivt. Återkopplingen tyder på att studenterna tyckte att demonstrationerna var informativa och lärorika. Genom att kunna se effekterna av att försumma god PCB-konstruktionssed inom två nyckelområden så lyckades demonstrationerna ge en mer realistisk syn på konsekvenserna av att inte följa god konstruktionssed på ett sätt som inte är uppenbart i den teoretiska litteraturen. Eftersom att PCB-konstruktion är ett så pass omfattande ämnesområde så motiverar resultaten vidare utveckling och studier av ILD-konceptet inom andra PCB-konstruktionskoncept, t.ex transmissionsledningar, lager-ordning, signalintegritet (¨överhörning, timing, brus, etc), samt andra.
120

Machine Learning and Computer Vision for PCB Verification

Yang, Chen January 2020 (has links)
Digitizing printed circuit boards (PCB) from images with computer science techniques is efficient in analyzing the PCB circuit. This automatic optic processing could help electronic engineers have a faster and more in-depth insight into complex multilayer PCB. This automatic optic processing could help electronic engineers have a faster and more in-depth insight of complex multi- layer PCB. In this thesis, multiple machine learning and computer vision methods for extracting PCB circuits are investigated, designed, and tested with real- world PCB data. PCB image dataset is collected by professional delayer engineers, that consist of every layer of PCB and Xray 3D models of the whole PCB. Region of interest (RoI) cropping and image alignment are applied firstly as in the pre- process stage. Detection and localization of electronic components are implemented with deep learning networks (Faster RCNN), unsupervised machine learning clustering (XOR-based K- means), and multiple template matching, their accuracy results are 71.2%, 82.3% and 96.5%, respectively. For the multilayer circuit extraction, the metallic print circuit is segmented in YCbCr color space, then the connection of every circuit net is obtained. / Digitalisering av tryckta kretskort (PCB) från bilder med datavetenskapstekniker är effektivt för att analysera PCB: s kretsar. Denna automatiska optiska bearbetning kan hjälpa elektroniska ingenjörer att få en snabbare och mer djupgående inblick i komplexa flerlagers PCB. I denna avhandling undersöks, designas och testas flera maskininlärnings- och datorvisionsmetoder för att extrahera PCB- kretsar med verkliga PCB- data. PCB- bilddataset samlas av professionella de-layer-ingenjörer, som består av varje lager av PCB och röntgen 3Dmodeller av hela PCB. Beskärning av region av intresse (RoI) och bildjustering tillämpas först som i förprocessstadiet. Upptäckt och lokalisering av elektroniska komponenter implementeras med djupinlärningsnätverk (Faster RCNN), utan tillsyn av maskininlärningskluster (XOR- based K- means) och flera mallmatchningar. För extraktion med flera lager kretsar är den metalliska utskriftskretsen segmenterad i YCbCr- färgutrymme, då erhålls anslutningen av varje kretsnät.

Page generated in 0.0307 seconds