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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.
161

Análise da antena planar de F-invertido pelo método das diferenças finitas no domínio do tempo

Andrade, Cássio Bento de January 2011 (has links)
Neste trabalho é apresentada uma análise da antena planar F-invertido (PIFA) com o objetivo de identificar os parâmetros geométricos que influenciam nas características de desempenho: frequência de ressonância, perda de retorno e largura de banda. Para realizar este estudo é desenvolvido um algoritmo em linguagem C baseado no método das Diferenças Finitas no Domínio do Tempo (FDTD). Duas PIFAs de geometria distintas foram investigadas. O primeiro modelo trata da geometria tradicional de elemento irradiador e plano de terra, ambos retangulares. Já o segundo modelo apresenta a fenda em formato de L no elemento irradiador, para operação em frequência dupla, e o plano de terra em formato de T, visando a aumentar a largura de banda. Os resultados da simulação do algoritmo identificam os parâmetros que influenciam no aumento nas duas larguras de banda, e são aplicados na prototipação de uma PIFA GSM-900 e GSM-1800. As medidas de laboratório do protótipo evidenciam os resultados previstos pelo algoritmo. / A Planar Inverted-F Antenna (PIFA) analysis is presented in this work, aiming to identify the geometric parameters that influence the antenna performance, such as resonant frequency, return loss and bandwidth. To accomplish this goal, an algorithm in C language based on the Finite-Difference Time-Domain (FDTD) method is developed. Two PIFAs with distinct geometries are investigated. The first one corresponds to a typicall rectangular patch and ground plane, The second model presents an L-shaped slot for dual frequency band operation, combined with a T-shaped ground plane, in order to increase the bandwidth. The simulated results obtained by algorithm identify the parameters that respond for both bandwidths enhancement, and are applied in a PIFA GSM-900/GSM-1800 practical project. The prototype’s measurements confirm the simulated results.
162

Análise da antena planar de F-invertido pelo método das diferenças finitas no domínio do tempo

Andrade, Cássio Bento de January 2011 (has links)
Neste trabalho é apresentada uma análise da antena planar F-invertido (PIFA) com o objetivo de identificar os parâmetros geométricos que influenciam nas características de desempenho: frequência de ressonância, perda de retorno e largura de banda. Para realizar este estudo é desenvolvido um algoritmo em linguagem C baseado no método das Diferenças Finitas no Domínio do Tempo (FDTD). Duas PIFAs de geometria distintas foram investigadas. O primeiro modelo trata da geometria tradicional de elemento irradiador e plano de terra, ambos retangulares. Já o segundo modelo apresenta a fenda em formato de L no elemento irradiador, para operação em frequência dupla, e o plano de terra em formato de T, visando a aumentar a largura de banda. Os resultados da simulação do algoritmo identificam os parâmetros que influenciam no aumento nas duas larguras de banda, e são aplicados na prototipação de uma PIFA GSM-900 e GSM-1800. As medidas de laboratório do protótipo evidenciam os resultados previstos pelo algoritmo. / A Planar Inverted-F Antenna (PIFA) analysis is presented in this work, aiming to identify the geometric parameters that influence the antenna performance, such as resonant frequency, return loss and bandwidth. To accomplish this goal, an algorithm in C language based on the Finite-Difference Time-Domain (FDTD) method is developed. Two PIFAs with distinct geometries are investigated. The first one corresponds to a typicall rectangular patch and ground plane, The second model presents an L-shaped slot for dual frequency band operation, combined with a T-shaped ground plane, in order to increase the bandwidth. The simulated results obtained by algorithm identify the parameters that respond for both bandwidths enhancement, and are applied in a PIFA GSM-900/GSM-1800 practical project. The prototype’s measurements confirm the simulated results.
163

Enhancing migration and reproduction of salmonid fishes:method development and research using physical and numerical modelling

Tammela, S. (Simo) 03 November 2013 (has links)
Abstract Dam building for hydropower production, dredging for log floating and drainage of peatlands have massively affected migrating salmonid populations in Finland. Increased sedimentation and changes in hydraulic conditions have destroyed the majority of spawning and rearing habitats in freshwater brooks and dam building has stopped migration upstream at river mouths. This thesis examines the current state of drained forest brooks, possibilities for restoration and methods to assist migration in rivers used for hydropower. Drainage down to the mineral soil has caused massive erosion and sedimentation in headwater brooks. The surface layer of a sand bed is constantly moving, preventing vegetation growth, while shortcuts created during drainage increase flow velocity and reduce retention time. The cross-sectional and longitudinal profiles become homogeneous and biodiversity is severely reduced. A simple wooden brook restoration structure was developed in laboratory experiments. Fish migration problems past a hydropower dam and reproduction possibilities offered by a natural-like bypass channel were studied in the river Oulujoki, the mouth of which was blocked by a hydropower dam in the late 1940s. Public pressure for remedial structures has grown since then and was given a boost after a fishway was opened at Merikoski, in the river mouth, in 2003. This thesis examined the next dam upstream, Montta at Muhos, which was studied separately as a partial and sole natural-like bypass. A natural-like bypass can offer stable conditions for spawning and rearing and can be designed precisely, through water flow and habitat modelling, to match desired conditions. The most important section in a fishway is ultimately the entrance. Fishway discharge is often merely a fraction of whole river discharge and the attractivity of the entrance can be increased by pumping additional discharge to the lowest part of the fishway. The hydraulics of a twin-slot vertical slot fishway were studied here by laboratory flume testing and 2D water flow modelling. Water flow and habitat modelling proved to be good tools in designing partly natural-like bypasses. However, fish behaviour should be closely monitored in any natural-like fishways already built, in order to verify the results of habitat modelling. / Tiivistelmä Jokien patoaminen vesivoiman tuotantoon, ruoppaaminen puunuiton helpottamiseksi sekä latvapurojen ojitukset metsän kasvun edistämiseksi ovat voimakkaasti vaikuttaneet vaeltavien lohikalakantojen vaellus- ja lisääntymismahdollisuuksiin. Muuttuneet hydrauliset olosuhteet ja lisääntynyt sedimentaatio ovat tuhonneet lohikalojen lisääntymisalueet ja patoaminen on katkaissut ylösvaelluksen lisääntymispaikoille. Väitöstyö koostuu viidestä artikkelista, joissa esitellään uusia menetelmiä ja ratkaisuja lohikalojen vaelluksen ja lisääntymisen ennallistamiseksi. Kaksi artikkelia keskittyy ojituksesta kärsivien latvapurojen nykytilaan, kunnostusmahdollisuuksiin sekä kunnostusrakenteen kehittämiseen. Paikoin ojituksen seurauksena on ollut massiivinen mineraalimaan eroosio ja hienon hiekan sedimentoituminen puroihin. Puroihin on kertynyt paksuja hiekkakerroksia, joiden pintakerros on jatkuvassa liikkeessä. Pintakerroksen jatkuva liike estää kasvillisuuden kasvamisen. Osittain ojitus on myös oikaissut puroja, jolloin virtausnopeudet ovat kasvaneet ja veden viipymä lyhentynyt. Purojen pituus- ja poikkileikkauksen vaihtelu ja biodiversiteetti ovat on vähentyneet huomattavasti. Laboratoriokokeissa kehitettiin yksinkertainen puusta rakennettava kunnostusrakenne hiekoittuneiden purojen kunnostamiseksi. Kolme artikkelia käsittelee Oulujokea, kalateiden suunnittelua ja kalatierakenteita. Vuonna 2003 rakennettu Merikosken kalatie kasvatti paineita kalatierakentamiseen Oulujoen muille voimalaitoksille. Erityisesti väitöstyö keskittyi Montan voimalaitoksen ohitukseen suunniteltuun kalatiehen, jota tutkittiin virtausmallinnuksen avulla kokonaan ja osittain luonnonmukaisena ohitusuomana. Luonnonmukainen ohitusuoma voidaan suunnitella toimimaan kutukanavan tyyppisenä uomana, jonka tarkoitus on tarjota vakaat virtausolosuhteet lohikalojen lisääntymistä varten. Virtaus- ja habitaattimallinnuksen avulla uoma voidaan suunnitella tarkasti haluttujen virtausolosuhteiden mukaisesti. Kalatien toimivuuden kannalta tärkeintä on että kalat löytävät kalatien sisäänkäynnin. Kalatien virtaama on usein vain murto-osa koko joen virtaamasta, joten sisäänkäynnin houkuttavuutta voidaan lisätä lisävettä pumppaamalla. Kaksirakoisen pystyrakokalatien hydrauliikkaa tutkittiin sekä laboratorio- että virtausmallilla.
164

Ocenění společnosti Kimex group / Valuation of KIMEX GROUP corporation

Köhler, Tomáš January 2008 (has links)
Goal and content of this thesis is market value determination of KIMEX GROUP corporation to the date of 1.1.2008 based on public available documentation and management consultation.
165

A Tagmemic Analysis of Coherence in the Writing of Descriptive Texts by College Students

Kent, Carolyn E. (Carolyn Elizabeth) 08 1900 (has links)
For this study an attempt was made to bridge the disciplines of linguistics and composition in order to examine factors contributing to textual coherence. Pairs of descriptive texts written by fifty college students were examined in order to identify the factors which differentiate quality and topic. Students were asked to compose a descriptive paragraph on the topic of fall. They were then encouraged to use their five senses, given leaves, and asked to compose a paragraph describing the leaves. The pairs of texts thus elicited were evaluated for preference by readers. The ANOVA revealed a significant difference (p=.001) between the two topics with fall texts preferred over the more specific leaves texts. Results suggest that encouraging students to use their five senses does not improve their writing. It may be more important to move through various levels of abstraction than to merely focus on sensory detail. The texts were also scored holistically by two trained evaluators. Results of this grading were used to choose five high- and five low-coherence texts on each of the two topics. These 20 texts were then analyzed in terms of the tagmemic referential hierarchy. A MANOVA was done to examine the dependent variables of Slot (location in time or space), Role (purpose or reason), and Cohesion (sociocultural context) in relation to quality and topic for these texts. Slot was found to be significant for both quality (p=.025) and topic (p=.004). Role was significant only for quality (p=.001). Cohesion was nonsignificant for either quality or topic. These results suggest that students should: (a) be encouraged to locate their texts in time and space in order to develop an adequate context for readers; (b) be encouraged to include purposes and reasons for the statements they make; and (c) be encouraged, where appropriate, to include a focus on humans and their activities (either literal or figurative) since such reference is a distinguishing feature of high-coherence texts.
166

Výzkum efektivních způsobů odsávání / Research on Effective Methods of Exhausting

Pech, Ondřej January 2017 (has links)
Many production technologies generate a variety of gas pollutants, which are unhealthy. The aim is therefore to minimize the content of such gas pollutants in the work environment. The highest capture efficiency of gas pollutants offers the local exhausting. Its disadvantage is the necessity to surround the source of pollutants, or to be as close as possible which is usually not technically or technologically possible. A possible alternative is to use a reinforced exhaust system that achieves greater capture distances. In the initial stage of the solution of the dissertation, a review of reinforced exhaust systems was carried out. Further, an existing measurement system was modified for measurements with the partition above the exhaust slot and the measurement system was partially automated. In order to investigate the case with pollutants having a lower density than the air, the workbench - the partition was moved above the exhaust slot. Based on of the literature review, a modification of the reinforced slot exhaust system was proposed. The modification consisted in the adjustment of the air inlet adjustment where a set of holes and a tube assembly were used instead of the slot. Such setup allowed for higher flow turbulence and thus for an increased exhaust efficiency. Subsequently, the inlet streams from the slot, holes and tubes were visualized by the smoke method. Further measurements were carried out by the tracer gas method for the determination of the exhaust efficiency. Measurements of velocity fields in front of the proposed configurations of the reinforced slot exhaust hood were also carried out. In conclusion, an energy performance assessment was carried out by means of the measurement of the electric power input to the fans with the determination of the electric loss power.
167

Materiálový tisk světelných dozimetrů / Material printing of light dosimeters

Kabelková, Markéta January 2019 (has links)
This diploma thesis is focused on material printing of light dosimeters, especially printing of dosimeters for visible light and two types of UV radiation dosimeters. The aim of this work was to convert optimized systems from laboratory scale to pilot plant and to prepare individual systems for large-scale printing. The experimental part deals with the preparation and gradual scaling of compositions to a pilot scale, including optimization of individual components. Problems which were found during scaling up are discussed. A roll-to-roll material printer with slot-die technique was used to convert to a pilot scale. The prepared layers were exposed and their color changes was studied in detail. In addition to printing optimization, the thicknesses of the prepared layers and their resistance were determined, as well as tests of shelf life and reaction of dosimeters to ozone. According to the tests which were performed, guidelines for quality control of light dosimeters printing were compiled.
168

Absorpční charakteristiky namáhaných drážkových izolací / Dielectric absorption characteristics of stressed slot insulations

Přikryl, Tomáš January 2010 (has links)
Master's thesis is monitoring changes in basic dielectric properties. Monitoring changes in absorbency of characteristics and temporal dependences in rezistance with change of relative humidity. On the colection samples were measured temporal dependences charged and uncharged currents in ambient temperature and 0%, 55%, 75%, 95% relative humidity. The next part of my work is monitoring temporal dependences interior rezistance in the time of ageing in different humidities. Experiments were made on material ISONOM NKN and NMN.
169

Štěrbinová anténní řada na bázi vlnovodu integrovaného do substrátu / Slot Antenna Array Based on Substrate Integrated Waveguide

Sedláček, Petr January 2012 (has links)
The Master’s Thesis deals with the design of slot antenna array based on the substrate integrated waveguide (SIW). Various supply methods are described and the design procedure is approached. The antenna array was designed for Wi-Fi band of 5 GHz in the Ansoft HFSS simulation software. The optimalized parameters are impedance bandwidth (low reflection coefficient at antenna input in the desired frequency band) and the gain (the maximum value). As the result of the work 3 antenna arrays based on the substrate integrated waveguide are designed and fabricated: antenna arrays 2x1, 2x2 and antenna array 2x2 supplemented with housing for outdoor use. The work also contains a comparison of simulated and measured parameters of antennas.
170

Lineárně polarizovaná štěrbinová anténní řada na bázi HMSIW / HMSIW linearly polarized slot antenna array

Horák, Lukáš January 2016 (has links)
In this work is proposed a HMSIW linearly polarized slot antenna arrays. The first antenna array is composed of four U-shape slots and the second antenna array is composed of four U-shape slots with three patches placed near the magnetic wall of HMSIW. The patches improve radiating parametrs of the proposed antenna array. The proposed antenna arrays are manufactured a measured.

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