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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.
51

A Theoretical and Experimental Comparison of Aluminum as an Energetic Additive in Solid Rocket Motors with Thrust Stand Design

Farrow, Derek Damon 01 August 2011 (has links)
The use of aluminum as an energetic additive in solid rocket propellants has been around since the 1950’s. Since then, much research has been done both on the aluminum material itself and on chemical techniques to properly prepare aluminum particles for injection into a solid propellant. Although initial interests in additives were centered on space limited applications, performance increases opened the door for higher performance systems without the need to remake current systems. This thesis aims to compare the performance for aluminized solid rocket motors and non-aluminized motors, as well as focuses on design considerations for a thrust stand that can be created easily at low cost for initial testing. A theoretical model is created for predicting propellant performance and the results are compared with experimental data taken from the thrust stand as well as existing data. What is seen at the end of testing is the non-aluminized grains follow the same trends as previously conducted tests and firings. The aluminized grains follow their expected trend but at a lower performance level due to grain degradation. However, the aluminized grains still show a specific impulse increase of 6%-23% over the non-aluminized grains.
52

THE NANNY’S NANNY : Filipina Migrant Workers and the ‘Stand-In’ Women at Home

Bäck , Hanna January 2008 (has links)
This article examines the case of Filipina women that substitute for Filipina migrant workers. Through semi-structured interviews in the Philippines this study draws attention to the experiences of the ‘stand-in’ women and demonstrates how the organisation of care in the transnational families is based on a system whereby female family members or friends are ascribed with a ‘natural’ responsibility to become social reproductive stand-ins for the migrated mothers. In the global transfer of social reproduction, hierarchies of women are maintained, based on intersectional power structures such as ethnicity, race, nationality, age, and class. But the stand-in women in the three-tier transfer of reproductive labour, or global care chain, do not  always occupy one single position, but actually shift in time and place between ‘the middle’ and ‘the bottom’ of the hierarchy. Regardless of location, Filipina women remain under the burden of their gendered duties and whether working abroad as domestic workers or acting as local stand-ins, they have to take on both local and global social reproductive work. They become the breadwinner in their families, at the same time as they are ascribed natural responsibility for households and families, as wives, mothers and stand-ins ‘at home’.
53

Electricity Supply Solutions for an Educational Center in Tanzania

Ålander, Atte January 2013 (has links)
The aim of this study was to investigate electricity supply solutions for an educationalcenter that is being built in Chonyonyo Tanzania. Off-grid power generation solutions andfurther optimization possibilities were studied for the case.The study was done for Engineers Without Borders in Sweden. Who are working withMavuno Project on the educational center. The school is set to start operating in year 2015with 40 girl students in the beginning. The educational center will help to improve genderequality by offering high quality education in a safe environment for girls in rural area.It is important for the system to be economically and environmentally sustainable. Thearea has great potential for photovoltaic power generation. Thus PV was considered as theprimary power generation and a diesel generator as a reliable backup. The system sizeoptimization was done with HOMER. For the simulations HOMER required componentdata, weather data and load data. Common components were chose with standardproperties, the loads were based on load estimations from year 2011 and the weather datawas acquired from NASA database. The system size optimization result for this base casewas a system with 26 kW PW; 5.5 kW diesel generator, 15 kW converter and 112 T-105batteries. The initial cost of the system was 55 875 €, the total net present cost 92 121 €and the levelized cost of electricity 0.264 €/kWh.In addition three optimization possibilities were studied. First it was studied how thesystem should be designed and how it would affect the system size to have night loads(security lights) use DC and could the system then be extended in blocks. As a result it wasfound out that the system size could be decreased as the inverter losses would be avoided.Also the system extension in blocks was found to be possible. The second study was aboutinverter stacking where multiple inverters can work as one unit. This type of connectionallows only the required number of inverters to run while shutting down the excess ones.This would allow the converter-unit to run with higher efficiency and lower powerconsumption could be achieved. In future with higher loads the system could be easilyextendable by connecting more inverters either in parallel or series depending on what isneeded. Multiple inverters would also offer higher reliability than using one centralizedinverter. The third study examined how the choice of location for a centralized powergeneration affects the cable sizing for the system. As a result it was found that centralizedpower generation should be located close to high loads in order to avoid long runs of thickcables. Future loads should also be considered when choosing the location. For theeducational center the potential locations for centralized power generation were found outto be close to the school buildings and close to the dormitories.
54

Energieffektivisering av laddningssystemet till vindmätarutrustning

Westlund, Oskar, Älgsjöö, Marcus January 2012 (has links)
Behovet av elektricitet blir allt viktigare i dagens samhälle. Runt om i världen finns än idag platser där tillgängligheten till det fasta elnätet är begränsad. Oftast är det platser som ligger avlägset och terrängen gör det ekonomiskt oförsvarbart att ansluta sig till det befintliga elnätet. Det kan vara platser som fjäll, öar och skogsområden. På dessa platser används ett fristående elsystem som står för elförsörjningen. Det allra vanligaste systemet är ett hybridsystem som använder sig av två eller flera energikällor vanligtvis en förnyelsebar och en kompletterande fossil energikälla. Examensarbetet som görs i samarbete med Arise Windpower AB går ut på att energieffektivisera och undersöka ett befintligt fristående elsystem som används som vindmätarutrustning, SODAR. Detta ska göras utifrån tre huvudaspekter, lågt underhåll, låg driftkostnad och hög driftsäkerhet. Projektgruppen har genomfört en omfattande energianalys på systemet för att se vart i systemet man kan göra energieffektiviseringar. För att komma fram till systemets brister och ge förslag på olika åtgärder har projektgruppen besökt objektet för att få en överblick hur systemet är kopplat och vilka komponenter som ingår. Systemets energiflöde har noggrant mätts upp med flera olika verktyg och sammanställts i tabeller och diagram för att få en tydlig bild över energiflödet. För att genomföra detta har solcellernas teoretiska årsgenerering beräknas utifrån ett webbaserat kalkyleringsprogram. Dieselgeneratorns totala drifttid loggas i systemet och den informationen har projektgruppen tagit del av för att sammanställa och beräkna den tillförda energin.SODAR är ett meteorologiskt instrument för att mäta vindhastigheter och vindens karakteristik. En högtalare sänder ut akustiska ljudpulser och en mottagare analyserar retursignalen. En dator behandlar sedan signalen och beräknar vindhastigheten. SODAR används främst inom vindkraftprojektering men även på flygplatser för att mäta turbulensgraden i luften. Meteorologer använder sig av denna mätutrustning för att förutspå kommande väderleksrapporter med hjälp av vind, temperatur samt ändringar i luftens kemiska sammansättning. Vid förstudien av ett vindkraftsprojekt placeras en SODAR ut på den tänkta platsen under minst ett år för att få så tillförlitliga mätvärden som möjligt. Mätutrustningen är enkel att flytta då hela systemet är inbyggt i en vanlig släpvagn. Resultatet från analysen visade en låg batteriverkningsgrad. Huvudslutsatsen för att energieffektivisera systemet är att kontrollera batteristatusen samt optimera laddningsförloppet. Detta kan göras genom att reglera laddningsspänningen beroende på omgivningstemperaturen. För att uppnå ett billigare energipris i systemet kan SODAR:n kompletteras med ett småskaligt vindkraftverk alternativt en bränslecell istället för dagens dieselgenerator.
55

Humor Alert: Muslim and Arab Stand-Up Comedy in Post-9/11 United States

Micu, Andreea 2012 May 1900 (has links)
After 9/11, American stand-up comedy includes an increasing presence of Arab and Muslim comedians whose humor engages some of the recurring Islamophobic stereotypes circulating in the United States. These comedians combine self-deprecating humor and critique of American society. In doing so, they continue a rich tradition of American ethnic comedy, first used by other minorities to negotiate positive recognition of their ethnicities in American society. Although Arab and Muslim American stand-up comedy continues to grow, there is little academic analysis of it. My research attempts to fill this gap. I examine two video-recorded comedy tours, Allah Made Me Funny and The Axis of Evil, and draw on my experiences as participant observer at the 8th annual edition of the New York Arab American Comedy Festival. In my examination, I explore Arab and Muslim American stand-up comedy after 9/11 as a set of performances that challenge Islamophobic political discourses and contest stereotypical representations of Arabs and Muslims circulating in the media and popular culture. I begin this thesis with a discussion that defines Islamophobia after 9/11 as a pervasive ideological formation and explores the relationship between Islamophobia and stereotypical representations of Arabs and Muslims in the media and popular culture. Second, I identify political activism, personal narrative, as well as both artistic and historical opportunism as complex and interrelated dimensions of this stand-up comedy. Third, I examine how Arab and Muslim American comedians use humor to navigate the poles of their hyphenated identities and negotiate their belonging in American society. Finally, I examine the ways in which stand-up comedy reverses the discourses and representations of Islamophobia by drawing on Mikhail Bakhtin's theory of the carnivalesque.
56

On mathematical modeling of shaped charge penetration

Clipii, Tudor January 2008 (has links)
<p>Shaped charges are a well established type of projectile, subjected to a lot of research ever since emerging as a viable technology in the 1940s. The penetration achieved by shaped charges decreases with increased standoff distance. This is often attributed to the shaped charge jet losing its coherence. The Swedish Defence Research Agency however, noted no such loss of coherence in its experiments. An alternative explanation to the decrease of penetration was instead proposed. The object of this thesis was to investigate this proposed theory. To this end, the hydrocode Autodyn was used, modelling the impact of a high-velocity projectile into a generic target and analysing the resulting behaviour of the target. Several setups were used and several parameters were considered when evaluating the results. The conclusion of this thesis is that the alternative explanation offered is not supported by the observed behaviour of the target in the computer model.</p>
57

Λειτουργία και τεχνικοοικονομική μελέτη ενός αυτόνομου φωτοβολταϊκού συστήματος

Παπαδημητράκης, Αλέξανδρος 26 October 2009 (has links)
Κεντρικός άξονας της εργασίας είναι η παρουσίαση της δομής ενός αυτονόμου φωτοβολταϊκού συστήματος, καθώς και η τεχνικοοικονομική μελέτη ενός τέτοιου συστήματος. Επίσης μέσα από αυτήν την εργασία θα βγουν συμπεράσματα για την λειτουργία ενός τέτοιου συστήματος σε μεταβατική κατάσταση υπό τις δυσμενέστερες συνθήκες. Ξεκινώντας παραθέτουμε τους λόγους για τους οποίους υπάρχει έντονη ανάγκη για την ανάπτυξη των ανανεώσιμων πηγών ενέργειας(ΑΠΕ), όπως είναι η μόλυνση του περιβάλλοντος από τις συμβατικές πηγές, η εξάντληση των αποθεμάτων του πετρελαίου αλλά και άλλων πηγών ηλεκτρικής ενέργειας, καθώς επίσης και μια σειρά από πολιτικοοικονομικούς λόγους με πρώτο την ιδιοπαραγωγή ηλεκτρικής ενέργειας. Εν συνεχεία στο κεφάλαιο 2 αναλύεται το φωτοβολταϊκό φαινόμενο σε όλη του την έκταση, το πώς δηλαδή μετατρέπεται η ηλιακή ακτινοβολία σε ηλεκτρική με την βοήθεια των ιδιοτήτων των ημιαγώγιμων υλικών που χρησιμοποιούνται στα ηλιακά πλαίσια. Ακόμη αναλύονται τα ηλεκτρικά χαρακτηριστικά των φωτοβολταϊκών, για να δωθεί έτσι και μαθηματικά η σχέση μετατροπής της ηλιακής ενέργειας σε ηλεκτρική. Στο κεφάλαιο 3 γίνεται η παρουσίαση της μπαταρίας. Αρχικά δίνεται η αρχή λειτουργίας και τα είδη των μπαταριών (επαναφορτιζόμενες η μη). Στη συνέχεια εξετάζονται τα χαρακτηριστικά μεγέθη, δηλαδή η χωρητικότητα, το βάθος εκφόρτισης-DOD, η στάθμη φόρτισης-SOC και ο συντελεστής φόρτισης της μπαταρίας, που δίνει την απόδοση ισχύος της. Στο κεφάλαιο 4 εξετάζουμε στα μέρη του, ένα τυπικό αυτόνομο φωτοβολταϊκό σύστημα. Σκοπός του κεφαλαίου είναι να δείξει τη λειτουργία των ηλεκτρονικών μετατροπέων, τον έλεγχο τους και την καταπολέμηση των αρμόνικων που παράγουν αυτοί. Αναλυτικά παρουσιάζεται ο μετατροπεας συνεχούς τάσης DC/DC, ο τρόπος με τον oποίο γίνεται ο έλεγχος του. Επίσης εξηγείται ο καθοριστικός ρόλος του στην λειτουργία του συστήματος. Το ίδιο γίνεται και για τον αντιστροφέα συνεχούς-εναλλασσομενου DC/AC, που είναι μια εξαπαλμική γέφυρα με IGBT μετατροπείς. Τέλος γίνεται και μια εισαγωγή στο θέμα των αρμονικών συνιστωσών που παράγουν οι μετατροπείς μας. Δίνονται στοιχεία για τους κανονισμούς μέσω των οποίων γίνεται και η επιλογή των μετατροπέων και των φίλτρων που χρησιμοποιούνται για τον περιορισμό των αρμονικών συνιστωσών. Στο κεφάλαιο 5 παρουσιάζονται στοιχεία από την οικονομική επιστήμη πάνω στα οποία θα βασιστεί η οικονομική μελέτη που πραγματοποιείται στο κεφάλαιο 7. Οι οικονομικοί δείκτες που χρησιμοποιήθηκαν στην εργασία αυτή είναι η Καθαρή Παρούσα Αξία (NPV), ο Εσωτερικός Βαθμός Απόδοσης (IRR), και η Έντοκη Περίοδος Αποπληρωμής (ΕΠΑ). Επίσης στο κεφάλαιο αυτό δόθηκαν στοιχεία για τις μεθόδους αποπληρωμής δανείων, καθώς επίσης αναλύθηκαν οι κλασσικές και οι σύγχρονες μορφές χρηματοδότησης ενός επενδυτικού σχεδίου. Στο κεφάλαιο 6 πραγματοποιείται ο τεχνικός σχεδιασμός του συστήματος. Με βάση τον τόπο εγκατάστασης και τα στοιχεία ακτινοβολίας και θερμοκρασίας γίνεται η επιλογή της κλίσης των συλλεκτών. Στη συνέχεια και με βάση τις απαιτήσεις του φορτίου γίνεται καθορισμός της ισχύος αιχμής, του πλήθους και της οργάνωσης των φωτοβολταϊκών πλαισίων. Τέλος με βάση τις απαιτήσεις για επάρκεια ηλεκτρικής ενέργειας για συνεχή λειτουργία του συστήματος καθορίζεται το μέγεθος των συσσωρευτών. Στο κεφάλαιο 7 πραγματοποιείται η οικονομική μελέτη για δυο διαφορετικά επενδυτικά σχέδια, με τη βοήθεια των οικονομικών δεικτών που αναφέρθησαν παραπάνω. Τα δυο σενάρια διαφέρουν ως προς τον τρόπο χρηματοδότησης (επιχορήγηση-δανειοδότηση) και με την εξέταση τους βγαίνουν πολύ χρήσιμα συμπεράσματα για την επενδυτική αξία τους. Η μελέτη αυτή μπορεί να χρησιμεύει και σαν οδηγός για άλλες παρομοίου τύπου μελέτες. Στο κεφάλαιο 8 παρουσιάζεται το σύστημα που εξετάζουμε στο πρόγραμμα εξομοίωσης PSCAD. Ο λόγος που γίνεται η εξομοίωση είναι για να μελετηθεί ακολούθως η μεταβατική ευστάθεια του συστήματος, δηλαδή η απόκριση του συστήματος σε αλλαγές του φορτίου μας. Στο σημείο αυτό πρέπει να τονιστεί ότι το PSCAD είναι από τα καταλληλότερα προγράμματα για το σκοπό αυτό, γιατί τα μοντέλα που διαθέτει ανταποκρίνονται σε μεταβατικές συνθήκες. Στο κεφάλαιο 9 πραγματοποιείται η μελέτη μεταβατικής ευσταθείας, αλλάζοντας βηματικά το μηχανικό φορτίο του κινητήρα, που αποτελεί το φορτίο του συστήματος μας. Για να έχουμε αποτελέσματα προς την ασφαλή πλευρά το σύστημα έχει μελετηθεί χωρίς την παρουσία μπαταρίας, δηλαδή υπό τις δυσμενέστερες συνθήκες. Στο κεφάλαιο αυτό δίνονται και εξηγούνται με φυσικό τρόπο τα γραφήματα που φανερώνουν την τελική κατάσταση του συστήματος, εάν δηλαδή το σύστημα οδηγήθηκε στην αστάθεια η όχι. Τέλος στο κεφάλαιο 10 υπάρχει ο επίλογος της εργασίας με ταυτόχρονη προσθήκη και των σημείων οπού επιδέχεται επέκταση η εργασία. / -
58

On mathematical modeling of shaped charge penetration

Clipii, Tudor January 2008 (has links)
Shaped charges are a well established type of projectile, subjected to a lot of research ever since emerging as a viable technology in the 1940s. The penetration achieved by shaped charges decreases with increased standoff distance. This is often attributed to the shaped charge jet losing its coherence. The Swedish Defence Research Agency however, noted no such loss of coherence in its experiments. An alternative explanation to the decrease of penetration was instead proposed. The object of this thesis was to investigate this proposed theory. To this end, the hydrocode Autodyn was used, modelling the impact of a high-velocity projectile into a generic target and analysing the resulting behaviour of the target. Several setups were used and several parameters were considered when evaluating the results. The conclusion of this thesis is that the alternative explanation offered is not supported by the observed behaviour of the target in the computer model.
59

Interactions among Silvicultural Intensity, Genotype, and Environment and Their Effects on the Growth and Mortality of Loblolly Pine and Slash Pine Families

Zhai, Lu 16 December 2013 (has links)
Managed pine forests are central to the economic vitality of the southeastern US. Over the past fifty years, the productivity of managed pine forests of this region have increased significantly with the development of new silvicultural technologies and the use of improved tree genetic material. Of the pine species present in the southeastern US, loblolly pine has arguably been the most intensively studied and widely planted by forest managers. Efficient operational deployment of improved genetic materials requires an understanding of how possible site conditions and silvicultural treatment may interact to affect maximum yield. There are a wide range of site conditions in the south as the result of regional climate gradients, soil type and soil drainage patterns. On the western edge of loblolly pine’s natural extent, Texas has a drier climate than areas to the east, and in Louisiana, there are also poorly drained Ultisols that are found in areas with little relief and are prone to flooding. However, on the basis of 10-year forest inventory data of pure-family plots from three different sites and under two levels of cultural regime intensity, my study found that superior genotype, Lob 5 from South Carolina, still showed best performance in the Western Gulf area, and high intensive treatment could improve stand growth and resistance to wind damage significantly. Further, my study compared the stand production and dynamics between pure- and mixed-family plots. I found that Lob 5 and Lob 4 showed the growth traits of competitive ideotype, and low intensive treatment increased the deployment effect significantly for competitive ideotype. Finally, my study examined leaf area index (LAI) and foliar nitrogen concentration (foliar N). The result showed that fast growing genotype had lower LAI and foliar N than slow growing one. It indicated that fast growing genotype had high resource use efficiency and nutrient requirement. This research provided critical information to guide industrial forest management in the WG (Western Gulf) area. First, introduced superior genotype continued to show good performance in this area. Second, combination of good genotype and high intensive treatment would increase plantation production significantly. Third, identification of ideotype would increase the accuracy of growth potential estimation in progeny test.
60

Lived Experiences of Primary-Aged Māori Students Exposed to Disciplinary Exclusions

Bowden, Anne-Maree January 2008 (has links)
This qualitative research study aims to document the lived experiences of several primary-aged Māori students, and the impact on their caregivers, when these students have been stood down, suspended or excluded from their school. In order to contextualise the students’ narratives, data from primary school site personnel, the principals and Board of Trustees chairperson of the students’ schools were gathered. The research also involved interviews with Ministry of Education and Group Special Education personnel, to gain an understanding of the Ministry’s perspective on how it meets the differing needs of students, caregivers and schools. An analysis of the two schools’ policy and procedures, and relevant documents, with regard to stand-down, suspension and exclusion of primary-aged students was also undertaken. Qualitative research methodologies enabled me to explore the lived experiences of these young people excluded from primary school, from the subjects’ own frame of reference. Data were collected using participant observations, document analysis, and in-depth semi-structured interviews. Kaumātua support for both the researcher, and the whānau involved, was sought with the aim of ensuring that the research proceeded in culturally appropriate and safe ways. The research aimed to keep the students’ stories central to the discussions. One of the key themes that emerged from the students’ narratives was the impact of being repeatedly framed by focusing solely on their behaviour. The impact of institutionalised racism evident within these educational life histories highlights the children’s struggle to persevere and survive in what they describe as hostile, racist, uncaring school environments. A key issue as outlined by the caregivers in this study has been the lack of understanding and support from or genuine partnership with their children’s education providers. The caregivers spoke of the effect that the disciplinary exclusion had on their relationship with their child and on their lives. Eventually the caregivers too become angry about, disengaged from and disillusioned with an education system that allows young people to be removed from schools, based solely on their behaviour. The themes that emerged from discussions with schools centred on lack of support and follow-up from government agencies. School personnel were critical of the length of time it took to access support packages from the Ministry of Education. They discussed the impact of Tomorrow’s Schools, particularly the current legislation on stand-downs, suspensions and exclusions. School personnel suggest their ability to manage high needs students is further complicated by the existence of kiwi suspensions and geographical school zones. This thesis stresses that it is critical for the students’ voices to remain central to discussions concerning their own education, so their creative ideas for possible solutions can help to create pathways forward.

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