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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.
401

Etude de la purification d'un matériau par fusion solidification''zone Melting''.

Manaa, Mongi 15 April 2005 (has links) (PDF)
Ce travail de thèse est consacré à l'étude d'un modèle transitoire qui tient compte des effets multidimensionnels dans le procédé de purification par fusion de zone. Nous avons étudié les effets des principaux paramètres gouvernant le processus de purification à savoir: la vitesse de translation des sources de chauffage et de refroidissement, l'intensité de flux de chauffage, l'intensité de flux de refroidissement, la largeur de la zone fondue et en fin le rapport d'aspect géométrique. Ces différents paramètres influent de façon importante sur le processus de purification, sur son efficacité et sur le degré de purification atteint après un ou plusieurs passages des sources. Une application dans le cas du matériau SiGe à très faible concentration a été simulée à l'aide d! u code de calcul par éléments finis Castem 2000. Le résultat de cette simulation a montré la difficulté de résolution numérique pour un nombre de Lewis très grand. Afin d'atteindre l'objectif visé, une étape importante dans cette étude a été consacrée à la détermination d'un couple (nombre de Lewis dans le liquide et rapport des coefficients de diffusion des espèces) pour que le processus de purification soit correctement représenté. Pour ce faire, nous avions étudié la fusion d'une tranche par une source immobile et choisir un couple convenable de ces 2 paramètres déterminants qui nous permet d'atteindre l'objectif visé. Afin d'analyser l'effet de chacune des grandeurs évoquées ci-dessus sur la purification, une deuxième étape a été consacrée à l'étude de la ! phase de purification proprement dite en adoptant une étu! de param étrique.
402

Analysis of Metal to Composite Adhesive Joins in Space Applications / Analys av limförband mellan metall och kompositmaterial i rymdtillämpningar

Fors, Fredrik January 2010 (has links)
<p>Within the European space programme, a new upper stage engine (Vinci) for the Ariane 5 launcher is being developed, and the Volvo Aero Corporation (VAC) is contributing with tur-bines for the fuel turbopumps. This MSc thesis investigates the possibility of designing the Turbine Exhaust Duct (TED) of the Vinci-engine in a carbon fibre composite material with adhesively attached titanium flanges. The focus of the project has been on stress analyses of the adhesive joints using Finite Element Methods (FEM), more specifically by using a cohe-sive zone material (CZM) to model the adhesive layer. Analysing adhesive joints is complex and an important part of the work has been to develop and concretise analysis methods for future use within VAC.</p><p>To obtain the specialised material parameters needed for a CZM analysis, FE-models of ten-sile test specimens were analysed and the results compared to those of equivalent experimen-tal tensile tests. These parameters were then used when analysing the TED geometry with load cases specified to simulate the actual operation conditions of the Vinci engine. Both two-dimensional axisymmetric and fully three-dimensional models were analysed and, addition-ally, a study was performed to evaluate the effect of cryogenic temperatures on the strength of the joint.</p><p>The results show that the applied thermal and structural loading causes local stress concentra-tions on the adhesive surface, but the stresses are not high enough to cause damage to the joint if a suitable joint design is used. Cryogenic temperatures (-150 °C) caused a significant strength reduction in the tensile specimens, partially through altered adhesive properties, but no such severe effects were seen in the temperature-dependent FE-analyses of the TED. It should be pointed out however, that some uncertainties about the material parameters exist, since these were obtained in a rather unconventional way. There are also several other impor-tant questions, beside the strength of the adhesive joint, that need to be answered before a metal-composite TED can be realised.</p> / <p>Volvo Aero deltar i utvecklingen av Vinci, en ny motor till det övre steget i den europeiska Ariane 5-raketen. Detta examensarbete behandlar möjligheten att tillverka ett turbinutlopp (TED) till vätgasturbinen i Vinci-motorn i kompositmaterial med flänsar i titan för att på så sätt uppnå en viktbesparing gentemot den tidigare konstruktionen i gjuten Inconel 718. Fokus har legat på att analysera hållfastheten i de limfogar som är tänkta att sammanfoga huvudröret med flänsarna, genom analyser med finita elementmetoden (FEM). Ett viktigt syfte har även varit att, för Volvo Aeros räkning, samla praktiska erfarenheter angående numerisk analys av limfogar, särskilt med användning av kohesiva zon-element för att modellera limfogen.</p><p>FEM-analyser har gjorts av provstavsmodeller, där resultaten sedan jämförts med experimen-tella dragprovsresultat för att ta fram lämpliga material- och modelleringsparametrar för ana-lys med kohesiva zonelement. Därefter tillämpades dessa parametrar i analyser av den verkli-ga TED-geometrin med relevanta lastfall framtagna för att simulera driftsförhållandena i Vin-ci-motorn. Lastfallsanalyser med både tvådimensionellt axisymmetriska och tredimensionella geometrimodeller genomfördes, liksom uppskattningar av limfogens styrka vid kryogena driftstemperaturer.</p><p>Resultaten pekar entydigt mot att en limfog med en ändamålsenlig tvärsnittsgeometri skulle hålla för de angivna lasterna utan att ta skada. De spänningskoncentrationer som uppstår ger lokalt höga spänningar i limmet, men inte på nivåer som skulle kunna orsaka brott. Det finns dock en viss osäkerhet angående riktigheten i materialparametrarna då en något okonventio-nell metod användes för att ta fram dessa. Flera stora frågor finns fortfarande kvar att besvara innan en metall-komposit konstruktion kan realiseras, inte minst hur flödeskammarens kom-plicerade geometri skall kunna tillverkas i kompositmaterial.</p>
403

Konsten att mäta tjänstekvalitet : En utvärdering av tre instrument för att mäta tjänstekvalitet i kollektivtrafiken

Rashid, Paola, Fessehazion, Shannet January 2009 (has links)
<p>The purpose of this study is to analyze and evaluate the suitability of the three instruments SERVQUAL, SERVPERF and Zone of tolerance to measure service quality, from the respondents' perspective. This study has been carried out by a quantitative method in which respondents answered three questionnaires, which was based on the three instruments. The SERVQUAL instrument is a revised version based on criticism by Carman (1990). It is based on the five dimensions; reliability, responsiveness, assurance, empathy and tangibility, with 22 items in which each dimension is associated with a number of items. SERVPERF is the instrument most similar to SERVQUAL and is also composed of the same five dimensions. The Zone of tolerance instrument is based on a three-column format of SERVQUAL, where each items is answered in the form of respondent's minimum service level, desired service level, and the perception of SL's service performance. The Zone of tolerance questionnaire consists of eight dimensions, including three new ones (convenience, connection, comfort) and 38 items.</p><p>The theoretical frame of reference that includes Grönroos model of service quality, and the three instruments form the basis of the results, analysis and conclusion. In this study, we concluded that Zone of tolerance is the most suitable instrument for measuring the quality of service in public transport according to the respondents, thus it best describes the feelings that the respondents feel about the service quality of SL. There was however no significant difference between the Zone of tolerance and the SERVPERF instrument in this regard. The Zone of tolerance instrument was the most specific of the three, but we found that the instrument may undergo additional changes to make it more suitably. Although most respondents felt that the Zone of tolerance instrument was the best descriptive of how the respondents felt regarding the service quality of SL, a large proportion of respondents (49 %) found this instrument as the one that worst describe the feelings they felt regarding the service quality of SL. A large proportion (72 %) of respondents believe that the Zone of tolerance instrument is the most difficult to understand. This may be because it includes many items and that every item must answer three times, a rather unusual format. The fact that this instrument was the last one in the scheme may have a negative effect. Since respondents in the assessment of the last instrument certainly became bored and therefore may have led to the instrument not receiving as much attention as the two previous instruments.</p>
404

Can tidal power promote sustainable integrated coastal development in Bangladesh?

Salequzzaman, Md. January 2003 (has links)
Thesis (Ph. D.)--Murdoch University, 2003. / Title from PDF title page (viewed on Apr. 23, 2007). Includes bibliographical references (p. [363]-422).
405

Collaboration toward a more integrated national ocean policy assessment of several United States federal interagency coordination groups /

Kuska, Gerhard F. January 2006 (has links)
Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Biliana Cicin-Sain, College of Marine and Earth Studies. Includes bibliographical references.
406

Application of Tidal Model for Tide Correction in Hydrographic Survey

Lee, Meng-lin 24 August 2007 (has links)
It is necessary to subtracting the tidal height from the observed depth to derived real depth while conduct hydrographic survey. The tidal data can be collected by conventional tide gauge or by using real time kinematics (RTK) GPS survey in the near shore region. However, when setting up tidal instruments in the offshore areas, many restricts still remained due to many factors such as topography, weather, and sea state. On contrary, the RTK GPS survey method has the limitation on the radio transmitting range. Therefore, the tidal zone method integrates the tidal station data to calculate the offshore tide data which can solve these problems. Generally, the tidal zone is constructed by using real tidal station data around the narrow channel. But the tide data is not possible to integrate on both side of the Taiwan Strait due to the vertical datum is not identical due to current political separation. To overcome this problem, this study proposed tidal zone method based on the tidal height derived from a tide numerical model. The tidal zone method is consequently applied to improve the accuracy of the offshore hydrographic survey. After processing the tide data derived from the model output and performing harmonic analysis, this study utilized the analysis result to draw a co-tidal chart to demonstrate the tidal characteristics for the purpose of establishing the tidal zone of the Taiwan Strait. This study also accomplished correspondent tidal zones for all the tide stations of Taiwan west coast within 12 miles territorial waters. This study further proposed a virtual station method for offshore hydrographic survey tide correction which applied the analysis result of each numerical model grid point as a virtual tidal station to derive the offshore tide correction values with spatial continuous characteristics. This study selected three experiment areas based on the multi-beam echo sounder survey data acquired offshore Ma-Liuo tide station. The direct tide station correction, tidal zone correction, and virtual station correction methods are applied to the hydrographic survey data to evaluate the performance of the tidal zone and virtual station correction methods. According to the experiment results, the tidal zone and virtual station correction method improve 20 and 16 cm respectively over the direct tide station correction method in the offshore area with the distance 25 km to the Ma-Liuo tide station. It indicates that the feasibility of the tidal zone method and it can improve the hydrographic survey results significant while the tide characteristics are different. Tidal zone can provide the required information to decide a proper reference tide station according to the tidal characteristics for the hydrographic survey data post-processing.
407

Analysis of Taiwan-Fujlan¡¦s Regional Economic Development

Chen, Mei-yin 06 September 2007 (has links)
Fujian is the closest province between Taiwan and China. Fujian is also the important area that Taiwan¡¦s businesses invested in China. The economical development and industrial structure in Taiwan and Fujian is very closely. Fujian is the key area that for the Taiwan ¡¥s businesses entering to China. It is necessary to understand the trade relation and history between Taiwan and Fujian, the economical position in Fujian, the plan of the west side of the Straits and the compare with other economical area. The study researched and analysed the history of Fujian, Xizmen economical zone, the Quanzhou pattern and the plan of the west side of the Straits to know the regional economical development between Fujian and Taiwan.
408

Inverse modeling to predict effective leakage area

Qi, Te 14 November 2012 (has links)
The purpose of this research is to develop a new approach to estimate the effective leakage area using the inverse modeling process as an alternative to the blower door test. An actual office building, which is the head quarter of Energy Efficiency Hub, was used as an example case in this study. The main principle of the inverse modeling process is comparing the real monitor boiler gas consumption with the result calculated from the EnergyPlus model with a dynamic infiltration rate input to find the best estimation of the parameter of effective leakage area (ELA). This thesis considers only the feasibility of replacing the blower door test with the calibration approach, so rather than attempting an automated calibration process based on inverse modeling we deal with generating a first estimate and consider the role of model uncertainties that would make the proposed method less feasible. There are five steps of the whole process. First, we need to customize our own actual weather data (AMY) needed by the energy model (EnergyPlus model), which can help increase our quality of the result. Second, create the building energy model in EnergyPlus. Third, create a multi-zone model using CONTAM with different ELA estimation of each facade to calculate the dynamic infiltration rate of each ELA estimate. Fourth, input the dynamic infiltration rate got from the CONTAM model to EnergyPlus model and output the boiler energy consumption. Fifth, compare the boiler gas consumption from the model and the real monitor data and find the best match between the two and the corresponding ELA, which gives the best estimate from the whole inverse modeling process. From the simulation result comparison, the best estimation of the total building ELA from the inverse modeling process is the 23437cm2 at 4pa, while the result from the blower door test is 10483cm2 at 4pa. Because of the insufficient information of the building and also the uncertainty of the input parameters, the study has not led to a definite statement whether the proposed calibration of the ELA with consumption data can replace a blower door test to get an equally valid or even better ELA estimate, but it looks feasible. As this this case study is done in a deterministic context, the full feasibility test should be conducted under uncertainty. A first step towards this will talk be discussed in chapter 4.
409

Stjärnornas krig : kampen om it-kompetensen fortsätter / Star Wars : the battle for IT-workforce continues

Bergmark, Kristina, Öman, Elias January 2013 (has links)
Sammanfattning Titel: Stjärnornas krig – kampen om IT-kompetensen fortsätter Författare: Kristina Bergmark och Elias Öman Handledare: Agneta Hugemark Lärosäte: Uppsala Universitet Datum: 2013-06-04 Syfte: Uppsatsens syfte är att ge en ökad insyn i vad som uppfattas som attraktivt hos en arbetsgivare av arbetskraft med IT-kompetens som arbetar inom organisationen 3. Uppsatsen ämnar också ge insyn i vilka krav och normer denna arbetskraft tvingas underkasta sig till följd av sitt medlemskap i denna organisation. Metod: Datainsamlingen skedde genom kvalitativa semistrukturerade intervjuer. Intervjuerna genomfördes med 6 anställda på företagets 3:s IT-avdelning och 2 HR-anställda inom organisationen. Materialet analyserades och diskuterades utifrån de teoretiska begreppen kollektiva resurser och zone of indifference. Den tidigare forskning som behandlades fokuserade i huvudsak på motivation hos arbetskraft med IT-kompetens samt personalstyrning genom identitetsskapande. Resultat/slutsats: Det som uppfattades som attraktivt av denna typ av personer med IT- kompetens som arbetade inom organisationen 3 var autonomi, hög grad av eget ansvar, utvecklingsmöjligheter, en icke hierarkisk arbetsmiljö, återkoppling och feedback, föränderlighet och flexibilitet. Gällande krav och normer fann vi att man var tvungen att vara starkt engagerad, effektiv, konstant sträva efter sin egen och företagets utveckling och alltid vara en ”utmanare” i branschen. Nyckelord: Sociologi, zone of indifference, kollektiva resurser, IT, krav, makt
410

An experimental investigation of the flow around impulsively started cylinders

Tonui, Nelson Kiplanga't 10 September 2009
A study of impulsively started flow over cylindrical objects is made using the particle image velocimetry (PIV) technique for Reynolds numbers of Re = 200, 500 and 1000 in an X-Y towing tank. The cylindrical objects studied were a circular cylinder of diameter, D = 25.4 mm, and square and diamond cylinders each with side length, D = 25.4 mm. The aspect ratio, AR (= L/D) of the cylinders was 28 and therefore they were considered infinite. The development of the recirculation zone up to a dimensionless time of t* = 4 following the start of the motion was examined. The impulsive start was approximated using a dimensionless acceleration parameter, a*, and in this research, the experiments were conducted for five acceleration parameters, a* = 0.5, 1, 3, 5 and 10. The study showed that conditions similar to impulsively started motion were attained once a* ¡Ý 3.<p> A recirculation zone was formed immediately after the start of motion as a result of flow separation at the surface of the cylinder. It contained a pair of primary eddies, which in the initial stages (like in this case) were symmetrical and rotating in opposite directions. The recirculation zone was quantified by looking at the length of the zone, LR, the vortex development, both in terms of the streamwise location and the cross-stream spacing of the vortex centers, a and b, respectively, as well as the circulation (strength) of the primary vortices, ¦£.<p> For all types of cylinders examined, the length of the recirculation zone, the streamwise location of the primary eddies and the circulation of the primary eddies increase as time advances from the start of the impulsive motion. They also increase with an increase in the acceleration parameter, a*, until a* = 3, beyond which there is no more change, since the conditions similar to impulsively started conditions have been achieved. The cross-stream spacing of the primary vortices is relatively independent of Re, a* and t* but was different for different cylinders.<p> Irrespective of the type of cylinder, the growth of the recirculation zone at Re = 500 and 1000 is smaller than at Re = 200. The recirculation zone of a diamond cylinder is much larger than for both square and circular cylinders. The square and diamond cylinders have sharp edges which act as fixed separation points. Therefore, the cross-stream spacing of the primary vortex centers are independent of Re, unlike the circular cylinder which shows some slight variation with changes in Reynolds number.<p> The growth of the recirculation is more dependent on the distance moved following the start of the impulsive motion; that is why for all types of cylinders, the LR/D, a/D and ¦£/UD profiles collapse onto common curves when plotted against the distance moved from the start of the motion.

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