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1
Vallès, Eduard 1971. "La influència de l’art català sobre Picasso a través de dues generacions: Santiago Rusiñol i Isidre Nonell com a paradigmes (1897-1904)." Doctoral thesis, Universitat de Barcelona, 2016. http://hdl.handle.net/10803/670359.
Texte intégralRésumé :
Aquesta tesi tracta sobre la influència que l’art català va exercir sobre Picasso durant els anys que aquest artista va residir a Catalunya. Aquesta influència no es planteja en abstracte sinó que es vehicula a través d’un parell d’artistes concrets, Santiago Rusiñol i Isidre Nonell. La tria és deguda a que van ser els artistes més representatius de les dues generacions amb les que es relacionà Picasso. Santiago Rusiñol pertanyia a la vella generació modernista, de la que era el principal referent. Isidre Nonell, sense ser un líder en sentit estricte, va ser l’artista més emblemàtic de la següent generació, que suposava un trencament respecte als postulats de la generació que representava Rusiñol, de manera que Picasso va evolucionar de la primera cap a la segona. El motiu d’escollir aquests dos artistes és degut a que responen a la condició de “paradigmes”, no només perque entre tots dos abasten bona part dels registres de l’art català del seu temps, sinó per que en alguns casos fins i tot en són els capdavanters.
La recerca s’ha centrat en els diversos nivells d’influència possibles, des de l’exercit pels mateixos artistes de forma directa, fins els que, de manera el·líptica, provenen de les propostes o dicursos que tots dos representaven. Això donarà lloc a que s’eixampli el camp d’estudi, per porositat, cap a altres artistes que puntualment van intersseccionar amb Rusiñol o Nonell i que, d’una u altra manera, van influir sobre l’obra picassiana. Aquesta recerca s’ha realitzat, bàsicament, en base al mètode formal i a l’iconogràfic, en el ben entès que s’ha comparat l’obra dels tres artistes. Tot plegat ha permès descobrir noves influències i, de retruc, noves lectures de l’obra de joventut de Picasso. Però les influències sobre Picasso tenen gairebé sempre una naturalesa multidireccional i, quan es produeixen, no sempre resulten explícites atès que Picasso normalment el·ludeix la còpia directa i empra formes d’apropiació més subtils, que també consignem en aquesta tesi.
Si bé és coneguda la vinculació de Picasso amb l’art català durant els seus anys barcelonins, a dia d’avui no s’havia analitzat amb tanta profunditat la incidència de dues personalitats com Rusiñol o Nonell sobre l’obra picassiana. Malgrat que aquesta tesi estableix una comparativa entre Picasso i dos artistes concrets, l’objectiu final resideix en elaborar un discurs unitari per agragació dels dos cossos teòrics. En definitiva, demostrar com la influència de l’art català sobre Picasso no només fou una realitat sinó que va tenir lloc a través dels seus principals representants i en un grau d’intensitat inconegut fins a dia d’avui.<br>This thesis considers the influence of Catalan art on Picasso during the period when he lived in Catalonia. This subject is explored not in the abstract but through two particular artists, Santiago Rusiñol and Isidre Nonell, chosen because they were the most representative artists of the two generations with which Picasso mixed. Rusiñol belonged to the old Modernista generation and was its leading light. Isidre Nonell was not a leader per se, but he was the most iconic artist of the following generation, which broke with the postulates of Rusiñol’s circle, meaning that Picasso shifted from the earlier to the later generation. The reason for this choice of two particular artists is that they are ‘paradigms’, not just because they encompass many of the registers of Catalan art of their time, but because in some instances they even led them.
The research focuses on the various possible levels of influence these artists exercised, from the direct inspiration they gave to the more elliptical stimulus provided by the works and discourses they represented. As a result, the field of study widens to encompass other artists who crossed paths by chance with Rusiñol or Nonell and who, in one way or another, influenced Picasso’s work. Above all, this research has been carried out on the basis of the formal and iconographic method, inasmuch as works by the three artists have been compared. This has revealed new influences and, in consequence, new readings of Picasso’s work in his youth. Nevertheless, the influences on Picasso are in almost all instances multidirectional in nature and, when they occur, they are not always explicit, since Picasso normally avoided direct copying and inclined towards more subtle forms of appropriation, as is also confirmed in this thesis.
While Picasso’s link with Catalan art during his years in Barcelona is well known, the impact of Rusiñol or Nonell on his work has not been analysed in any great depth to date. Even though this thesis draws a comparison between Picasso and these two particular artists, the ultimate aim is to formulate a single discourse combining two bodies of theory. In short, the goal is to demonstrate that the influence of Catalan art on Picasso was not just a reality but that it was transmitted through its two luminaries and was of a hitherto unknown strength.<br>Esta tesis trata sobre la influencia que ejerció el arte catalán sobre Picasso durante los años en que este artista residió en Catalunya. Esta influencia no se plantea en abstracto sino que se vehicula a través de dos artistas concretos, Santiago Rusiñol e Isidro Nonell. La elección se debe a que fueron los artistas más representativos de las dos generaciones con las que se relacionó Picasso. Santiago Rusiñol pertenecía a la vieja generación modernista, de la que era su principal referente. Isidre Nonell, sin ser un líder en sentido estricto, sería el artista más emblemático de la siguiente generación, que suponía una ruptura respecto a los postulados de la generación que representaba Rusiñol, de manera que Picasso basculó de la primera hacia la segunda. El motivo de escoger dos artistas concretos es debido a que ostentan la condición de “paradigmas”, no sólo porque entre ambos abarcan buena parte de los registros del arte catalán de su tiempo, sino porque en algunos casos incluso los lideran.
La investigación se ha centrado en los diversos niveles de influencia posibles, desde el ejercido por los propios artistas de forma directa, hasta el que, de manera elípitica, procede de las propuestas o discursos que ambos representaban. Ello provocará que el campo de estudio se ensanche, por porosidad, hacia otros artistas que eventualmente interseccionaron con Rusiñol o Nonell, y que de una manera u otra influyeron sobre la obra picassiana. Esta investigación se ha realizado, sobretodo, en base al método formal y al iconográfico, en la medida que se han comparado obras de los tres artistas. Ello ha permitido descubrir nuevas influencias y, en consecuencia, nuevas lecturas de la obra de juventud de Picasso. No obstante, las influencias sobre Picasso tienen casi siempre una naturaleza multidireccional y, cuando se producen, no siempre son explícitas pues normalmente Picasso elude la copia directa y tiende hacia formas de apropiación más sutiles, que también consignamos en esta tesis.
Si bien es conocida la vinculación de Picasso con el arte catalán durante sus años en Barcelona, a dia de hoy no se había analizado con tanta profundidad la incidencia de dos personalidades como Rusiñol o Nonell sobre la obra de Picasso. A pesar de que esta tesis establece una comparativa entre Picasso y dos artistas concretos, el objectivo final consiste en elaborar un discurso unitario por agregación de dos cuerpos teóricos. En definitiva, demostrar que la influencia del arte catalán sobre Picasso no tan solo fue una realidad sino que se vehiculó a través de sus principales representantes y en un grado de intensidad hasta hoy desconocido.
2
Power, Stephen Charles. "Topics in the theory of nonself-adjoint operator algebras." Thesis, University of Edinburgh, 1987. http://hdl.handle.net/1842/15654.
Texte intégral
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Rybka, Ana Cecilia Poloni. "Folatos, capacidade antioxidante e trans-2-nonenal em cerveja brasileira." [s.n.], 2010. http://repositorio.unicamp.br/jspui/handle/REPOSIP/254275.
Texte intégralRésumé :
Orientador: Helena Teixeira Godoy<br>Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos<br>Made available in DSpace on 2018-08-15T07:36:05Z (GMT). No. of bitstreams: 1
Rybka_AnaCeciliaPoloni_D.pdf: 1201100 bytes, checksum: 1057a41b652a7de5fa122bc5691bea97 (MD5)
Previous issue date: 2010<br>Resumo: No presente trabalho foram adaptados e aplicados métodos para a determinação do teor de folatos, avaliação de capacidade antioxidante e quantificação do composto trans-2-nonenal em cervejas brasileiras. Foram avaliadas 5 marcas de cervejas tipo Pilsen, sem álcool e Malzbier, nas embalagens lata e garrafa âmbar. Para determinação dos folatos (ácido fólico - AF, 10-metil-ácido fólico - 10Metil, 5-metiltetraidrofolato - 5Metil, 5-formiltetraidrofolato - 5Formil e 10-formil-ácido fólico - 10Formil) vitaminas do complexo B, empregou-se um método utilizando a cromatografia líquida de alta eficiência (CLAE). Na etapa cromatográfica utilizou-se coluna C18 e eluição por gradiente com fase móvel composta por ácido acético 2,0% ajustado a pH 2,8 e acetonitrila, a uma vazão de 0,5 mL/min. A detecção foi realizada com o detector de arranjo de diodos a 290nm para o AF e o 10Metil; e com detector de fluorescência a ?exc. 290nm e ?emis. 360nm na detecção do 5Metil e 5Formil; e a ?exc. 290nm e ?emis. 445nm para o 10Formil. Após sua validação, o método apresentou coeficientes de correlação variando de 0,9970 a 0,9999, limites de detecção de 0,07 a 2,42 mg/100mL, e de quantificação entre 0,22 e 8,07 mg/100mL. Os coeficientes de variação (CV) ficaram entre 0,75 e 5,01% e a precisão intermediária entre 1,20 e 9,99%. Os ensaios de recuperação nos níveis avaliados estiveram entre 92 e 107%. Os folatos encontrados nas cervejas analisadas foram o 10Metil, o 5Metil e o 10Formil e os níveis totais da vitamina variaram de 18,26 a 23,99 µg/100mL. Estas vitaminas foram monitoradas durante a vida de prateleira da bebida (6 meses), sendo avaliadas na cerveja recém fabricada e a cada 2 meses subseqüentes. De modo geral o teor de folatos decresceu ao longo da vida de prateleira, e não foi possível constatar o efeito do tipo de embalagem sobre a vitamina. A avaliação em diferentes lotes resultou em grande variação, com CVs de até 52,42%. Para estabelecer o teor de fenólicos totais foi aplicado o método de Folin-Ciocalteau, pelo qual foram encontrados 47,05, 18,67 e 21,83 mg/100mL em equivalentes de ácido gálico (EAG), na cerveja Malzbier, Pilsen sem álcool e Pilsen, respectivamente. O tipo de embalagem utilizada, lata ou garrafa, apresentou relevância para o teor de fenólicos totais somente para a cerveja Pilsen, e a cerveja sem álcool foi a que mais apresentou variação do teor entre marcas. Para avaliação da capacidade antioxidante foram realizados ensaios utilizando o radical 2,2- difenil -1- picrilhidrazil (DPPH) e o poder antioxidante de redução do ferro (FRAP). Os dois ensaios indicaram a cerveja Malzbier com maior capacidade antioxidante, corroborando com o teor de fenólicos totais. Para identificação e quantificação do trans-2- nonenal, um dos principais responsáveis pelo sabor envelhecido em cervejas, foi utilizado o método de headspace com microextração em fase sólida e cromatografia gasosa acoplada à espectrometria de massas (HS-SPME-GC-MS). Foi utilizada coluna 5%-fenilmetilpolisiloxano (HP-5MS) e a condição cromatográfica empregada teve inicio em temperatura de 60ºC, variando 3 ºC/min até atingir 100ºC. Em seguida, uma rampa de 10 ºC/min até atingir 200ºC e permanência a 200ºC por sete minutos para limpeza da coluna. O gás de arraste (hélio) teve vazão constante de 1,0 mL/min. Os íons monitorados para a identificação (m/z) foram 55, 70 e 83 (fonte de ionização de 70eV), após verificação do espectro de massas do composto. O teor de trans-2-nonenal encontrado variou de 0,11 a 0,46 µg/L nas cervejas em lata, estando acima de seu threshold. Para este composto foi encontrada diferença significativa entre amostras de um mesmo tipo de cerveja, porém não houve diferença significativa entre os três tipos de cerveja analisados. Este trabalho demonstrou que a cerveja brasileira possui substâncias benéficas à saúde humana, com teor similar a de outros alimentos, e que o trans-2-nonenal ainda é presente em quantidades acima do threshold na bebida, podendo comprometer sua qualidade. De modo geral, a embalagem, lata ou garrafa, não influenciou no teor das substâncias analisadas e a cerveja Malzbier se destacou pela maior capacidade antioxidante<br>Abstract: In the present study methods were adapted and applied to quantify levels of folate, antioxidant capacity assessment and E-2-nonenal quantification in Brazilian beers. 5 brands of Pilsen, non-alcoholic and Malzbier beers were used, in can and amber bottle. For determination of folates (folic acid - FA, 10-methyl-folic acid - 10Methyl, 5-methyltetrahydrofolate - 5Methyl, 5-formyltetrahydrofolate - 5Formyl and 10-formyl-folic acid - 10Formyl) B vitamins, a method using liquid chromatography (HPLC) was employed. In the chromatographic step a C18 column was used and was applied a gradient elution with mobile phase consisting of an acetic acid 2.0% solution adjusted to pH 2.8 and acetonitrile, at a flow rate of 0.5 mL / min. The detection was performed with the diode array detector at 290nm for FA and 10Methyl, and with a fluorescence detector at ?exc. 290nm and ?emis. 360nm in the detection of 5Methyl and 5Formyl, and at ?exc. 290nm and ?emis. 445nm for the 10Formyl. After its validation, the method presented correlation coefficients ranging from 0.9970 to 0.9999 mg/100 mL, detection limits from 0.07 to 2.42 mg/100 mL and quantification limits between 0.22 and 8.07 mg/100 mL. The standard deviation (SD) was between 0.75 and 5.01% and intermediate precision was from 1.20 to 9.99%. Tests of recovery levels were resulted between 92 and 107%. Folates found in beers were 10Methyl, 5Methyl and 10Formyl. The total folate levels found among types of fresh beers ranged from 18.26 to 23.99 µg/100mL. These vitamins were monitored during beer shelf life (6 months), being evaluated in freshly brewed beer and at every subsequent 2 months. Overall levels of folate found decreased over the shelf life, but it was not possible to verify the effect of package to protect beer against degradation of the vitamins. Evaluation in different batches showed a great variation, with SD up to 52.42%. To determine the total phenolic content was applied the Folin-Ciocalteau method, by which they were found 47.05, 18.67 and 21.83 in mg/100mL equivalents gallic acid (EGA) for Malzbier beer, alcohol-free Pilsen and Pilsen, respectively. The type of packaging used, can or bottle, had relevance to the total phenolic content only for Pilsen beer. Nonalcoholic beer showed the highest variation. To evaluate the antioxidant capacity, tests using the radical 2,2 - diphenyl -1 - picrylhydrazyl (DPPH) and the ferric reduction antioxidant power (FRAP) were performed. The two tests indicated the beer Malzbier has the highest antioxidant capacity, which agrees with the content of total phenolics. For identification and quantification of E-2-nonenal, a major cause of aged flavor in beers, it was used a headspace method with micro solid phase extraction and gas chromatography technique coupled with mass spectrometry (HS-SPME-GC-MS). A 5%- phenyl-methylpolisiloxane (HP-5MS) column was used. The chromatographic conditions used beginning in temperature of 60 ºC, ranging from 3 ºC / min up to 100 ºC. Then, ramp of 10 °C / min until 200 ºC and then stay at 200 ºC for seven minutes to clean the column. The carrier gas (helium) had constant flow of 1.0 mL / min. The monitored ions were 55, 70 and 83 (m/z) (source of ionization 70eV), after verification of mass spectra of the compound. Levels of E-2-nonenal ranged from 0.11 to 0.46 µg/L in beer cans, being above its threshold. For this compound significant difference was found between samples of the same type of beer, but there was no significant difference between the three types of analyzed beer. This study showed that the Brazilian beer have beneficial substances to human health, with similar content to other food, and that the E-2-nonenal is still present in quantities above the threshold in the beverage, which can compromise its quality. In general, the packaging, can or bottle, did not influence the content of the analyzed substances, and Malzbier beer stood out for greater antioxidant capacity<br>Doutorado<br>Doutor em Ciência de Alimentos
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McGahan, Jeremy. "The development of correlations between HMA pavement performance and aggregate shape properties." Texas A&M University, 2005. http://hdl.handle.net/1969.1/3351.
Texte intégralRésumé :
The physical characteristics of aggregates (form, angularity, and texture) are
known to affect the performance of hot mix asphalt (HMA) pavements. Efforts to
develop relationships between these aggregate characteristics and aggregate performance
in HMA pavements have been limited in the past due to inherent inaccuracies in the
methods used to measure these characteristics. The recently developed Aggregate
Imaging System (AIMS) offers an opportunity to accurately measure aggregate shape
characteristics allowing them to be properly related to asphalt performance.
This research focused on relating the aggregate characteristics of form,
angularity, and texture measured using AIMS to laboratory performance measurements
on a wide variety of HMA mixes. The performance of these mixes was evaluated in
three projects carried out by the Federal Highway Administration (FHWA) and the
Texas Transportation Institute (TTI). During this research, a database of the volumetric,
performance, and aggregate shape measurements for mixes used in these projects was
created. Statistical analysis was conducted to correlate HMA performance parameters to
volumetric and aggregate shape characteristics. The results show the dominant effect
that aggregate shape properties have on HMA performance.
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Villarreal, Evert. "Recovering Carl Sandburg: politics, prose, and poetry after 1920." Diss., Texas A&M University, 2006. http://hdl.handle.net/1969.1/4167.
Texte intégralRésumé :
Chapter I of this study is an attempt to articulate and understand the factors that have contributed to Carl Sandburg's declining trajectory, which has led to a reputation that has diminished significantly in the twentieth century. I note that from the outset of his long career of publication - running from 1904 to 1963 - Sandburg was a literary outsider despite (and sometimes because of) his great public popularity though he enjoyed a national reputation from the early 1920s onward. Chapter II clarifies how Carl Sandburg, in various ways, was attempting to re-invent or re-construct American literature. Indeed, beginning in 1922, a very complex creative imagination - one not seen before - began to manifest itself in Sandburg's works. As a result, readers begin to see how Sandburg's view of the role of the writer was shifting - from one of a radical political poet into one of a writer who experimented with several genres. Chapter III examines the two separately published biographies of Abraham Lincoln - Abraham Lincoln: The Prairie Years (1926) and Abraham Lincoln: The War Years (1939) - and reveals how Sandburg incorporates a new perspective that was radically different from the Lincoln biographies that preceded it. Chapter IV turns to Sandburg's celebration of the theme of "the People." The chapter explores four works - The American Songbag (1927), Good Morning, America (1928), The People, Yes (1936), and Remembrance Rock (1948). These works, like all of his previous works, are an effort to make life possible to the common man. Finally, Chapter V reminds readers of Sandburg's stature as witness to the labor problem - perhaps the most significant problem of the twentieth century. I argue that the only way to recover Sandburg correctly is to assess the political ideology present in each of his published works.
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Biju, Cletus Anila. "Drying characteristics of New Zealand Chestnuts." The University of Waikato, 2007. http://hdl.handle.net/10289/2268.
Texte intégralRésumé :
Chestnut is a relatively new nut crop to New Zealand and they do grow well in New Zealand conditions. Research to date in New Zealand indicated that New Zealand chestnuts present some unique features compared to chestnuts world wide. The two main unique problems with New Zealand chestnuts are the susceptibility to fungal disease Phomopsis (accounting for 40% loss of nuts at the wholesale markets) and the difficulty in the removal of the inner skin called the pellicle. No systematic drying trials had been performed on New Zealand chestnuts and therefore this research investigated the drying characteristics of New Zealand chestnuts to establish optimum drying conditions. The study also investigated the influence of the shell and pellicle on the drying process and the efficacy of shell and pellicle removal of New Zealand chestnuts under a range of moisture contents since the moisture content is a key factor which determines this efficiency. The drying trials were carried out at a temperature of 30 C because preliminary studies indicated that higher temperatures resulted in extensive surface deterioration. Experimental drying curves are considered the only adequate preliminary step for determination of drying characteristics of a food material and the curves clearly indicated that there are two distinct falling rate periods. It was concluded that the first falling rate period corresponded to the period during which the surface of the nut reaches equilibrium moisture content and the second falling rate period occurred as the moisture movement from interior of the nut to the surface was the rate limiting factor. Hence a diffusion based model was used to estimate the apparent moisture diffusivity in chestnuts. The average apparent moisture diffusivity in chestnuts obtained at 30 C was 6.21x 10-11m2s-1. The study revealed that the pellicle is the most significant barrier to mass transfer; considerably more so than the shell. The shelling and peeling efficiency of New Zealand chestnuts were carried out at various moisture contents using a custom-made mechanical shelling machine. The mechanical shell removal of New Zealand chestnuts was accomplished with an efficiency of 94% at the desired storage moisture content of 40%. However mechanical pellicle removal of New Zealand chestnuts proved practically impossible although American varieties (Carolina and Revival) exhibited 100% peeling efficiency.
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Ciochina, Roxana. "STUDIES TOWARD SYNTHESIS OF POLYCYCLIC POLYPRENYLATED ACYLPHLOROGLUCINOLS." UKnowledge, 2006. http://uknowledge.uky.edu/gradschool_diss/291.
Texte intégralRésumé :
Polycyclic polyprenylated acylphloroglucinols (PPAPs) are a class of compounds that reveal intriguing biological activities and interesting and challenging chemical structures. These products are claimed to possess antioxidant, antiviral, and antimitotic properties. Increasing interest is related to their function in the CNS as modulators of neurotransmitters associated to neuronal damaging and depression. All these features make PPAPs targets for synthesis. We decided to focus our own initial efforts in this area on the type A PPAP, nemorosone because we thought that its fairly simple structure relative to other PPAPs would present fewer hurdles as we developed our methodology.In the past decade many approaches to the synthesis of the bicyclo[3.3.1]nonane-2,4,9-trione structure of type A PPAPs have been reported, but only two total syntheses of any PPAP, garsubellin A by Shibasaki and Danishefsky, have been published recently, near the end of 2005. All approaches have relied on the ??,????-annulation of a three-carbon bridge onto a cyclohexanone, although the methods used to execute this annulation differ dramatically. The methods most often used to form the two new C–C bonds have involved classical carbonyl chemistry.We have developed a short and efficient synthetic approach to the bicyclo[3.3.1]nonane skeleton of the PPAPs that involves a novel three-carbon ??,????-annulation of a sterically hindered cyclic ??-keto ester with 3,3-diethoxypropyne. The alkynylation reaction permits the construction of the two contiguous quaternary centers of the PPAPs in reasonable yield and without complications from side reactions. We have also successfully applied a recently developed syn hydrosilylation to the very hindered product of this alkynylation reaction. Our methodology received positive feedback already, and we see this total synthesis of nemorone as an ideal platform for the implementation of new synthetic methodologies.
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Galan, Cherrez Andres Moroni. "Design and Evaluation of a CMOS Contact-Imaging System for Microfluidics." BYU ScholarsArchive, 2017. https://scholarsarchive.byu.edu/etd/7219.
Texte intégralRésumé :
A CMOS contact-imaging system for microfluidics is presented. The microsystem integrates a five-layer PDMS microfluidic network and a CMOS image sensor fabricated in a standard 0.18 µm technology. The CMOS image sensor consists of two 10×1-pixel array, an amplifier, and a control logic. The imager is able to achieve a low dark signal of 1.67 mV/s, a maximum integration time of 514 s, and a high dynamic range of 75.2 dB at 1 s integration time. The microfluidic device integrates several actuated valve to achieve a fully automated lab-on-a-chip. This work also presents a quantitative comparison of the photomultiplier tube (PMT) and the CMOS contact-imaging system. The CMOS-microfluidic device is validated using an on-chip chemiluminescent analyte.
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Durrant, Creighton. "If Then, Elsewhere." ScholarWorks@UNO, 2011. http://scholarworks.uno.edu/td/118.
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Nicoloso, Steven P. "An Investigation of Carrier Recovery Techniques for PSK Modulated Signals in CDMA and Mulipath Mobile Environments." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/35869.
Texte intégralRésumé :
The challenge of carrier recovery for digitally phase modulated, suppressed-carrier signals has been the target of much attention in mobile radio system design for many years. Code division multiple access (CDMA) cellular systems are now being deployed in mobile environments, and the performance of carrier recovery for CDMA is much less well understood. CDMA systems typically utilize lower bit energies, relying instead upon coding gain for reliable performance. As an additional challenge, the multiple access interference (MAI) inherent to direct-sequence spread-spectrum (DSSS) signalling further hampers many carrier recovery techniques.
This thesis first surveys general carrier recovery strategies, conventional as well as new, and then applies them to the particular task of recovering a suppressed carrier in mobile CDMA systems. First some of the theory surrounding conventional, closed-loop, carrier recovery techniques and several newer open-loop estimation structures, based on the maximum likelihood (ML) principle is presented. A novel decision-feedback ML phase estimator is proposed. The statistical behavior of this new structure as well as the related squaring estimator are examined and are shown to be equivalent to the stochastic performance of classical closed-loop techniques.
Candidate receivers based upon closed- and open-loop carrier recovery structures are proposed and then examined via simulation. Both forward and reverse cellular links are examined under a variety of both of single-path and multipath conditions. The notion of exploiting cyclostationary MAI in CDMA systems by applying adaptive receiver techniques is also examined, especially as this scheme relies to some extent upon coherent carrier recovery for its promising performance enhancements. This work concludes with recommendations of the best carrier recovery strategies for the variety of environments examined and suggestions for future research are made.<br>Master of Science
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Mizusawa, George A. "Performance of Hyperbolic Position Location Techniques for Code Division Multiple Access." Thesis, Virginia Tech, 1996. http://hdl.handle.net/10919/30542.
Texte intégralRésumé :
The Federal Communications Commission (FCC) recently adopted rules requiring cellular telephone, Personal Communication System (PCS) and Specialized Mobile Radio (SMR) licensees to provide two dimensional automatic location information (ALI) for a user requesting E-911 service. These wireless service providers will need to utilize effective position location (PL) technology in order to meet FCC rules. Hyperbolic PL systems are one such technology that can provide accurate PL information using the existing cellular/PCS infrastructure and without requiring additional hardware/software implementation within the mobile unit. In recent years, the IS-95 Code Division Multiple Access (CDMA) system has gained increasing popularity in North America because of the many advantages it offers over existing air interfaces. However, CDMA systems present some unique challenges to the effectiveness of hyperbolic position location systems.
This thesis investigates the performance of the hyperbolic PL technique in CDMA systems. The effect of multipath and shadowed mobile radio environments, the location of the user within the cell, and configuration and number of base stations on the accuracy of the hyperbolic PL technique is investigated. The effect of the power control scheme required in CDMA system operation on the performance of the hyperbolic system is also demonstrated. The simulation results provide insight to the limitations and effectiveness of hyperbolic position location systems within CDMA systems.<br>Master of Science
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Saldanha, Kevin J. "Performance Evaluation of DECT in Different Radio Environments." Thesis, Virginia Tech, 1996. http://hdl.handle.net/10919/37003.
Texte intégralRésumé :
DECT is a cordless telephone standard whose applications are broadening with the advent of PCS services, wireless local loop (WLL), and the increasing demand for high data-rate wireless local area networks (WLANs). This thesis investigates the performance of DECT in different channel conditions.
DECT is simulated using the Signal Processing WorkSystem (SPW) software in different channels including the additive white Gaussian noise (AWGN) channel, the flat faded Rayleigh channel, the frequency selective faded Rayleigh channel, and the Ricean channel. The effect of cochannel and adjacent channel interference is also investigated.
In order to quantify the RF channel dispersive properties, and other parameters that determine performance in a radio channel, channel impulse response measurements at 1.9 GHz are made. Parameters that help describe the radio channel are identified and calculated from the recorded power delay profile measurements.
Finally, a mean-opinion-score (MOS) rating was performed for National Semiconductor Corporation's implementation of DECT in the indoor, indoor-to- outdoor, and outdoor environments. A comparison is made between the MOS and propagation measurements. It is found that the performance of DECT is very closely related to the RMS delay spread and the path loss in the RF channel.<br>Master of Science
13
Lekutai, Gaviphat. "Adaptive Self-Tuning Neuro Wavelet Network Controllers." Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/30603.
Texte intégralRésumé :
Single layer feed forward neural networks with hidden nodes of adaptive wavelet functions (wavenets) have been successfully demonstrated to have potential in many applications. Yet applications in the process control area have not been investigated. In this paper an application to a self-tuning design method for an unknown nonlinear system is presented. Different types of frame wavelet functions are integrated for their simplicity, availability, and capability of constructing adaptive controllers. Infinite impulse response (IIR) recurrent structures are combined in cascade to the network to provide a double local structure resulting in improved speed of learning. In particular, neuro-based controllers assume a certain model structure to approximate the system dynamics of the "unknown" plant and generate the control signal. The capability of neuro-controllers to self-tuning of an unknown nonlinear plants is then illustrated through design examples. Simulation results demonstrate that the self-tuning design methods are directly applicable for a large class of nonlinear control systems.<br>Ph. D.
14
Vasavada, Yash M. "Performance Evaluation of a Frequency Modulated Spread-Spectrum System." Thesis, Virginia Tech, 1996. http://hdl.handle.net/10919/36758.
Texte intégralRésumé :
Analog frequency modulated (FM) systems offer advantages of reliable speech quality and simplicity, whereas code division multiple access (CDMA) systems promise high capacity, resistance to multipath fading, and simplified frequency planning. In this thesis, we investigate the performance of a wireless local loop (WLL) system that uses the frequency modulation with the CDMA technique.
The performance of the FM CDMA system is affected by the choice of the frequency demodulation method. Performance of different state-of-art DSP based FM demodulators is evaluated. Design improvements with threshold extension, pre-deemphasis, and voice companding techniques are explored, and the limitations of the DSP based FM demodulation methods are identifed.
The transmitter, the channel, and the receiver of the FM CDMA system are simulated for particular values of FM bandwidth and spread-spectrum processing gain. The capacity supported by the FM CDMA sysem is estimated with different levels of orthogonal as well as non-orthognal multiple access interference. The performance of the FM CDMA system in AWGN, multipath fading, Doppler spread, and nonlinear signal processing effects is predicted. A power control algorithm for the FM CDMA system is proposed, and its effect on the system performance is studied.
The capacity of the FM based wireless system may saturate as the system evolves. An adaptive FM CDMA interference cancelation technique and a digital modulation with CDMA are two approaches investigated as ways to improve system capacity.<br>Master of Science
15
Appel, Justin Ronald. "Sensitivity Calculations For Conservation Laws With Application To Discontinuous Fluid Flows." Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/30476.
Texte intégralRésumé :
Flow sensitivities are the derivatives of the variables that describe the fluid flow with respect to the parameters that determine the fluid flow. Sensitivities are of interest in their own right and are also of use in flow optimization, control and design and in the calculation of perturbed flows. Problems arise in all sensitivity calculation methods in the presence of discontinuities and other complexities such as shock waves, contact discontinuities and rarefaction waves that commonly occur in super and hypersonic inviscid, compressible fluid flows. Flow sensitivities are calculated using finite difference quotients, automatic differentiation and the sensitivity equation method for a variety of numerical methods. Explanations for the inaccuracies arising in the numerical approximations and implications these inaccuracies have on different applications are discussed. Possible corrections for the inaccuracies are outlined.<br>Ph. D.
16
Juneja, Vikas. "Locating Structural Damage in Real Time Using Contrast Maximization." Diss., Virginia Tech, 1996. http://hdl.handle.net/10919/30372.
Texte intégralRésumé :
A technique to identify structural damage in real time using limited instrumentation is presented, Contrast maximization is used to find the excitation forces that maximize the difference in the response of the damaged structure and the analytical response of the undamaged structure. The optimal excitations are then matched against a database of optimal excitations to locate the damage. To increase the reliability of the approach when modeling and measurement errors are present, the contrast maximization approach is then combined with an approach based on changes in frequency signature to develop the average angle technique. A damage detectability measure is defined which, for a given level and location of damage and a given amount of modeling and measurement errors, compares the magnitude of the damage to the magnitude of errors in a single number. The success of the average angle technique in damage detection is quantitatively defined by a success factor. The technique is first tested analytically on a 132 degree of freedom truss. The structure can be either equipped with active members or collocated shakers/sensors. The technique has a high success rate in damage detection. The technique is then tested numerically on a 36 degree of freedom truss equipped with 3 collocated shakers/sensors. To simulate experimental conditions, an extensive study is carried out in the presence of numerical noise. It is seen that the success factor in the presence of noise depends upon the success factor in the absence of noise and the damage detectability measure. The members are classified into three groups based on the success factor in the presence of noise. A mathematical relationship between the damage detectability measure and the success factors with and without noise is developed using linear regression. Using the results of numerical simulations in the presence of noise and this mathematical relationship, we find members where we expect to locate damage experimentally, for a given amount of damage and given amount of noise. A similar truss is built and the FEM model of the structure is corrected using experimental data. The average angle technique is applied to locate damage in a member when the member has a low level of damage (25%). The damage detectability measure indicated that the measurement errors are large compared to the damage and it is difficult to detect damage in most detectable locations. The steps taken to rectify that are described and after each step we show the improvement in damage detectability. The average angle technique is used to locate damage in 5 members. The experimental results indicate that the technique can robustly identify the damaged member with limited instrumentation.<br>Ph. D.
17
Villeneuve, Pierre V. "A Numerical Study of the Sensitivity of Cloudy-Scene Bidirectional Reflectivity Distribution Functions to Variations in Cloud Parameters." Diss., Virginia Tech, 1996. http://hdl.handle.net/10919/30336.
Texte intégralRésumé :
The goal of this research has been to characterize the sensitivity of the earth's
shortwave bidirectional reflectivity distribution function (BRDF) to variations in
cloud parameters. The BRDF is a remote sensing tool used to predict the flux
reflected from a given earth scene from a satellite-based measurement of the
reflected intensity. The BRDF is necessary in order to account for the anisotropic
nature of the shortwave radiation field. A shortwave atmospheric radiation
Monte-Carlo ray-trace model has been developed as part of this research to predict
the earth-reflected radiation field at the top of the atmosphere. This model was
developed while paying special attention to clouds including realistic
three-dimensional cloud fields characterized by fundamental physical properties.
This model was used to predict the BRDF for various cloud fields where a single
cloud parameter was varied as part of the sensitivity analysis. The results show that
the shortwave BRDF is very sensitive to changes in cloud vertical thickness and
mean cloud size. This sensitivity is also strongly dependent on the direction from
which the scene is observed. In a related analysis, a study was done of the error
associated with using a BRDF from one scene to retrieve fluxes from a second
scene. The model was also used to predict images of cloud fields for comparison
with experimental data from the Rutherford Appleton Laboratories satellite-based
Along Track Scanning Radiometer (ATSR). Finally the output from the radiation
model was integrated with the end-to-end radiative electrothermal model of a
practical earth radiation budget instrument. This integrated model was used to
predict the instrument response to scanning a realistic partly-cloudy earth scene.<br>Ph. D.
18
Zhang, Michael Tao. "Electrical, Thermal, and EMI Designs of High-Density, Low-Profile Power Supplies." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/30316.
Texte intégralRésumé :
This work presents the analyses and designs of high-density, low-profile power supplies, including the electrical, thermal, and EMI aspects. Emphasis is placed on forward and flyback converters.
The efficiency improvements of employing synchronous rectification are theoretically derived and experimentally verified in forward and flyback converters. The performances of synchronous rectifiers in forward converters are analyzed with regards to transformer reset and SR driven method. The effectiveness of synchronous rectification in flyback converters is evaluated in various operation modes and control schemes. The paralleling techniques utilized to realize high-density, low-profile power conversion are presented. Current sharing in transformer paralleling is addressed and evaluated in forward topology. The performance and the operation principles of one-choke and two-choke interleaved forward converters are analyzed.
The thermal management of high-density power supplies in sealed enclosures is optimized using computational fluid dynamics simulations. The theoretical limit of power density due to thermal constraint is determined. In addition, the thermal-design optimization guidelines are given and verified experimentally.
A systematic methodology is developed to facilitate the analysis and design of conducted EMI problems in high-density power supplies. Partial element equivalent circuit method is employed for parasitic parameter extraction. Layout and packaging are optimized to minimize conducted EMI noises. Noise predictions by Saber simulations are confirmed by experimental measurements.<br>Ph. D.
19
Keller, Benjamin J. "Algorithms and Orders for Finding Noncummutative Gröbner Bases." Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/30506.
Texte intégralRésumé :
The problem of choosing efficient algorithms and good admissible orders for computing Gröbner bases in noncommutative algebras is considered. Gröbner bases are an important tool that make many problems in polynomial algebra computationally tractable. However, the computation of Gröbner bases is expensive, and in noncommutative algebras is not guaranteed to terminate. The algorithm, together with the order used to determine the leading term of each polynomial, are known to affect the cost of the computation, and are the focus of this thesis.
A Gröbner basis is a set of polynomials computed, using Buchberger's algorithm, from another set of polynomials. The noncommutative form of Buchberger's algorithm repeatedly constructs a new polynomial from a triple, which is a pair of polynomials whose leading terms overlap and form a nontrivial common multiple. The algorithm leaves a number of details underspecified, and can be altered to improve its behavior. A significant improvement is the development of a dynamic dictionary matching approach that efficiently solves the pattern matching problems of noncommutative Gröbner basis computations. Three algorithmic alternatives are considered: the strategy for selecting triples (selection), the strategy for removing triples from consideration (triple elimination), and the approach to keeping the set interreduced (set reduction).
Experiments show that the selection strategy is generally more significant than the other techniques, with the best strategy being the one that chooses the triple with the shortest common multiple. The best triple elimination strategy ignoring resource constraints is the Gebauer-Müller strategy. However, another strategy is defined that can perform as well as the Gebauer-Müller strategy in less space.
The experiments also show that the admissible order used to determine the leading term of a polynomial is more significant than the algorithm. Experiments indicate that the choice of order is dependent on the input set of polynomials, but also suggest that the length lexicographic order is a good choice for many problems. A more practical approach to chosing an order may be to develop heuristics that attempt to find an order that minimizes the number of overlaps considered during the computation.<br>Ph. D.
20
Valero, Carlos Alberto. "Applications of Qualitative and Quantitative Techniques of Management in Administrative/Academic Decision-Making in Institutions of Higher Education in Virginia." Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/30653.
Texte intégralRésumé :
The purpose of this study was to examine the status and extent to which
administrators of colleges and universities in the state of Virginia apply
qualitative and quantitative techniques of management in planning, directing,
reporting, and controlling activities for enhancing their administrative and
academic decision-making capability. The study was directed to the top and
operative organizational levels in two categories of administrators (nonacademic
and academic) to determine the types of managerial techniques used, degrees of
familiarity with these techniques, frequency of use, managerial benefits and
constraints, and individual and organizational factors involved in using such
techniques. The qualitative and quantitative techniques were selected from
diverse sources of related literature. The study followed guidelines of
exploratory and descriptive research. Data were collected through a
questionnaire mailed to 288 administrators of twelve randomly selected colleges
and universities in Virginia. The study was limited to institutions granting at least
a four-year baccalaureate degree and having a total enrollment of at least 1,000
students. Data were analyzed using descriptive statistics and factorial analysis of
variance to describe administrators1 decision-making capability in terms of the
extent of utilization of the selected techniques. Based upon a 55 percent response
rate, the findings show that administrators have moderate knowledge about the
techniques and their extent of use is fairly low. No significant statistical
differences in the degree of familiarity and extent of use with various
management techniques (qualitative and quantitative) either by category of
administrator assignment (nonacademic and academic) and by level or type of
administrator (executive and operative) was found. The most reported techniques
related to familiarity and extent of use were Brainstorming, Checklists,
Benchmarking and Cost-Benefit Analysis. Respondents positively use and
perceive the value of qualitative techniques more favorably than the quantitative
techniques for decision-making. Results of this study may be of benefit to both
practitioners and academicians. Based upon this study1s findings, practical
implications are discussed. Limitations and suggestions also are made for future
research into this topic.<br>Ph. D.
21
Vergara, John Paul C. "Sorting by Bounded Permutations." Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/30401.
Texte intégralRésumé :
Let P be a predicate applicable to permutations. A permutation that satisfies P is called a generator. Given a permutation $pi$, MinSort_P is the problem of finding a shortest sequence of generators that, when composed with $pi$, yields the identity permutation. The length of this sequence is called the P distance of $pi$. Diam_P is the problem of finding the longest such distance for permutations of a given length. MinSort_P and Diam_P, for some choices of P, have applications in the study of genome rearrangements and in the design of interconnection networks.
This dissertation considers generators that are swaps, reversals, or block-moves. Distance bounds on these generators are introduced and the corresponding problems are investigated. Reduction results, graph-theoretic models, exact and approximation algorithms, and heuristics for these problems are presented. Experimental results on the heuristics are also provided.
When the bound is a function of the length of the permutation, there are several sorting problems such as sorting by block-moves and sorting by reversals whose bounded variants are at least as difficult as the corresponding unbounded problems. For some bounded problems, a strong relationship exists between finding optimal sorting sequences and correcting the relative order of individual pairs of elements. This fact is used in investigating MinSort_P and Diam_P for two particular predicates.
A short block-move is a generator that moves an element at most two positions away from its original position. Sorting by short block-moves is solvable in polynomial time for two large classes of permutations: woven bitonic permutations and woven double-strip permutations. For general permutations, a polynomial-time (4/3)-approximation algorithm that computes short block-move distance is devised. The short block-move diameter for length-n permutations is determined.
A short swap is a generator that swaps two elements that have at most one element between them. A polynomial-time 2-approximation algorithm for computing short swap distance is devised and a class of permutations where the algorithm computes the exact short swap distance is determined. Bounds for the short swap diameter for length-n permutations are determined.<br>Ph. D.
22
Brown, Dewayne Randolph. "A New Digital Relay for Dispersed Storage and generation (DSG) Units." Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/30594.
Texte intégralRésumé :
A dispersed storage and generation system consists of both a source of energy for conversion to electricity and a means to interconnect this unit to the electric utility system. Most dispersed generators connected to the utility distribution system are less than 5 MW. A new emerging problem arises when a utility circuit breaker is opened while a capacitor-bank bus and load bus is energized very near a dispersed storage and generation unit. A new resonant- detecting relay will be developed that has the ability to trip if dangerously high off-nominal frequency voltages are produced at the capacitor-bank bus or load bus during this condition (self-excitation). Self-excitation may lead to severe overvoltages, and may induce undesirable transients in neighoring circuits (low power and control circuits being particularly vulnerable) on the connected network. It can create harmonics that can fail surge arrestors or cause transformer saturation. The new relay will be able to detect this condition at the inter-tie and trip the cogeneration facility. In order to make this multifunction relay cost effective, it includes protection functions for traditional relay functions such as directional inverse time-delay overcurrent, directional instantaneous overcurrent, islanding, loss-of- excitation, differential, overfrequency, underfrequency, overvoltage, undervoltage, negative-sequence current, check-synchronism, and directional power. Also, the new relay will have metering capability.<br>Ph. D.
23
Clark, Richard L. Jr. "Influence of the Interphase on the Mechanical Properties of Nylon 66 Composites." Diss., Virginia Tech, 1996. http://hdl.handle.net/10919/30385.
Texte intégralRésumé :
The mechanical properties of glass fiber and carbon fiber reinforced nylon 66 were investigated using both microscopic and macroscopic testing techniques. The objective was to determine how different interphase morphologies affect the adhesion and properties such as damping, ultimate stress and strain, and modulus of the composite. This was accomplished using a modified fiber pull-out test on single filament composites, and dynamic mechanical analysis, vibrational adhesion testing, and uni-axial tension testing on bulk composite samples. Additional techniques such as scanning electron microscopy, profilometry, thermogravimetric analysis, differential scanning calorimetry, and water absorption measurements were performed to assist in data interpretation. The specific interphase that forms in both glass reinforced and high modulus carbon fiber reinforced nylon 66 is termed transcrystallinity. Previous work has shown that this region can be altered by the addition of a specific diluent, poly(vinyl pyrrolidone), as either a blend to the matrix or as a fiber sizing. The diluent serves to dampen nucleation on the fiber surface thus causing the interphase to change from transcrystalline in nature to spherulitic. The changes in composite properties that the different interphases produce were examined.
Results from the modified fiber pull-out test showed that the interfacial shear strength decreases as the interphase becomes more spherulitic. Scanning electron microscopy revealed a more cohesive fracture surface of the samples having a transcrystalline interphase.
Dynamic mechanical analysis showed that the damping behavior of E-glass/nylon 66 composites does not change with PVP sizing, while carbon fiber/nylon 66 composites showed a decrease in damping with the addition of sizing. Vibrational adhesion testing showed similar effects in the loss tangent of both composites versus fiber sizing. In addition, uni-axial tensile testing revealed an increase in the ultimate strength and toughness of both composites. On the other hand, neither the ultimate strain or modulus was a strong function of fiber sizing.<br>Ph. D.
24
McKeel, Scott Andrew. "Numerical Simulation of the Transition Region in Hypersonic Flow." Diss., Virginia Tech, 1996. http://hdl.handle.net/10919/30731.
Texte intégralRésumé :
The current state of transition region modeling is investigated through a literature search. The six most promising transition region models from the literature search were implemented in the Navier-Stokes code GASP. Baldwin-Lomax is an algebraic turbulence model in which the authors discuss how it can be used to simulate the transition region. Wilcox developed a procedure to use the low-Reynolds number k - w model as a transition region model where a roughness strip is used to fix the transition point. Schmidt and Patankar developed production term modifications for low-Reynolds number k - e models to correct for the problems these models have in simulating the transition region. Warren, Harris and Hassan developed a one equation turbulence model that accounts for the first and second mode disturbances in the transition region. The algebraic transition region model of ONERA/CERT controls the amount of eddy viscosity added to the molecular viscosity. The linear combination model of Dey and Narasimha combines a fully laminar and fully turbulent flow field through the indeterminacy to form the transitional flow field.
GASP is a compressible Navier-Stokes code which has a practical lower working limit of M = .1. The majority of experimental data for transitional flow exists below this limit. The test cases found above this limit and used here were all in the hypersonic regime. The results from the six transition region models were compared against the experimental test cases found for a variety of cones and ramps. Two models produced inadequate results on these test cases. The Wilcox model did not function as it was intended. The algebraic transition region model overpredicted the heat transfer in the turbulent region for several cases and did not transition in regions of large adverse pressure gradients. Several models performed adequately. The Baldwin and Lomax model provide fast estimates of the transition region. The Warren, Harris and Hassan model, the Schmidt and Patankar model, and the linear combination model produced adequate results on the test cases for this work and are worthy of attention on other test cases.
Modifications were made to the Schmidt and Patankar model and the algebraic transition region model to improve their predictions on the current test cases. A turbulent spot was introduced into the boundary layer for the Schmidt and Patankar model which facilitated in the use of the model. Also, the maximum production allowed was recalibrated and allowed to grow exponentially to improve transition region simulating for the test cases presented here. The empirical transition function from the algebraic transition region model was recalibrated for the hypersonic test cases used in this work.<br>Ph. D.
25
Kontogeorgakis, Christos. "Millimeter Through Visible Frequency Waves Through Aerosols: Particle Modeling, Reflectivity and Attenuation." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/37049.
Texte intégralRésumé :
This thesis addresses the problem of modeling atmospheric aerosol (such as haze and fog) particle-size distributions in order to predict the effects (such as attenuation and reflectivity) that these particles have upon the propagation of electromagnetic waves of micrometer range wavelengths. Specifically, an inversely proportional to the fourth power of the particle diameter model is used for haze and the gamma and lognormal distribution models are used for fog. In the case of fog the models are developed based on data consisting of measured fog particle-size distributions at five locations. In this relatively big amount of data, the gamma distribution model is an accurate fit for all the cases and, also, the resulted size distribution does not depend on the altitude. This leads to considerably simpler formulations which yield a linear relationship between the reflectivity factor and the liquid water content. The knowledge of one parameter appears to be enough for defining the model and subsequently predicting reflectivity and attenuation. Attenuation and reflection in haze are found to be insignificant for millimeter wavelengths and somewhat appreciable for the visible ones. In fog, attenuation is found to be extremely high for the infrared-to-visible wavelengths and very low for the millimeter ones.<br>Master of Science
26
Smith, Michael D. "Estimation of Future Manufacturing Costs for Nanoelectronics Technology." Thesis, Virginia Tech, 1996. http://hdl.handle.net/10919/36515.
Texte intégralRésumé :
In this report, a future scenario concerning the economic direction of the computing industry has been presented. This future scenario was based on past developments within the computing industry. The continued miniaturization of semiconductor components was discussed based on observed trends for transistors. The physical limitations for transistor devices were also addressed. The use of x-ray lithography for the construction of devices on a 3nano-scale2 was considered. Next, cost trends within the microelectronics industry were explored. Although the cost per transistor has been observed to decrease, total equipment costs and facilities costs were observed to rise.
Trend extrapolation was next used to predict the future cost per transistor and the number of transistors per chip. By taking the product of these two predicted quantities, an equation for the future manufacturing cost per chip was determined. A parametric cost estimation model (VHSIC Model) for the prediction of avionics computer system costs was modified to reflect the future performance parameters of nanoelectronics. Using data from the x86 design of Intel Microprocessor Chips, undetermined parameters of the Modified VHSIC Model were calculated. Next, future performance parameters were used in the model to predict the initial selling price of future chips. The resulting predictions from this model indicated that chip prices are expected to increase while the price per electronic function will decrease. Finally, profit-time models for semiconductor chips and transistors were derived. These models were used to predict the future profit for a chip or transistor.<br>Master of Engineering
27
Prakash, Divya. "Bi-criteria Scheduling Problems on Parallel Machines." Thesis, Virginia Tech, 1995. http://hdl.handle.net/10919/36732.
Texte intégralRésumé :
Mathematical programming has not been used extensively for the solution of scheduling problems. Moreover, the study of bicriteria problems on single and parallel machines is an open field for research. This thesis is aimed at developing algorithms to solve bicriteria problems more efficiently and in reasonable amount of time and with little compromise on the optimality of the solutions obtained. Two classes of problems are considered. The first class consists of scheduling unit duration tasks on parallel machines. Various combinations of primary and secondary criteria are considered and optimal seeking algorithms of polynomial time complexity are developed. The second class of problems assume general processing time tasks. An algorithm is developed for the primary criterion of total tardiness and the secondary criterion of total flow time. This algorithm is based on the solution of the underlying mathematical program and makes use of dominance relationship among the jobs and fixing of variables. Experimental results are presented regarding its performance.<br>Master of Science
28
Tenace, Stephen M. "Aperture." Thesis, Virginia Tech, 1991. http://hdl.handle.net/10919/32734.
Texte intégralRésumé :
In the beginning God created the world.
Waste and void, waste and void.
And darkness was upon the face of the deep.
And when there were men, in their various ways,
they struggled in torment towards God.
Blindly and vainly, for man is a vain thing,
and man without God is a seed upon the wind:
driven this way and that, and finding no place
of lodgment and germination.
They followed the light and the shadow, and
the light led them forward to light
and the shadow led them to darkness,
Worshipping snakes or trees,
worshipping devils rather than nothing:
crying for life beyond life,
for ecstasy not of the flesh.
Waste and void.
Waste and void.
And darkness on the
face of the deep.
Choruses from
â The Rockâ
T.S. Eliot<br>Master of Architecture
29
Walker, Kenroy A. "The Aspirations Formation of Disadvantaged Jamaican Male Youths." Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/30383.
Texte intégralRésumé :
This study examined the aspirations formation of disadvantaged Jamaican male youths. The design of the study was a Type 3 holistic design which considered the global nature of multiple cases, and focused on the impact of work, family, school, peers and siblings on subjects1 aspirations. Six case studies were conducted using observations, focus groups, taped interviews and document inspection techniques. Data were analyzed using McCraken's coding techniques. The results showed that the youths' aspirations were leveled, reflected realities f their employment possibilities, and were patterned after their father's occupations. The youths' reluctance to raise their aspirations signals the need for Jamaican policy makers to address the problems caused by low aspirations among youths. Recommendations for further research are offered.<br>Ph. D.
30
Watson, George W. "Beyond the Psychological Contract: Ideology and the Economic Social Contract." Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/30413.
Texte intégralRésumé :
By combining normative philosophy and empirical social science, I craft a research framework for assessing
differential expectations of economic justice within the economic social contract of the United States. I argue
that distinct viewsof such a contract grounded in the tradition of individualism and communitarianism
manifest in people's judgments about economic justice. We empirically test these hypotheses on a sample of
270 subjects, finding broad support for the theoretical framework.<br>Ph. D.
31
Migliozzi, Joseph P. "Feasibility Study of Partially Restrained Connections." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/36545.
Texte intégralRésumé :
In recent years the idea of using partially restrained connections in building structures has become more practical and economical. Partially restrained connections resist moment and also allow rotation, therefore distributing the moments and stresses more evenly throughout the element. Combining this idea with steel joists, which are also quite common in construction, makes for shallower story heights and lower steel weights. This initial study analyzes partially restrained connections for both hot rolled shapes and steel joists using non-composite and composite construction. The designs are than compared with respect to complexity, practicality, serviceability and economics. The results of this study show that partially restrained joist connections are economically superior to comparable hot rolled member designs.<br>Master of Science
32
Kraus, Cynthia A. "Floor Vibration Design Criterion For Cold-Formed C-Shaped Supported Residential Floor Systems." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/36612.
Texte intégralRésumé :
Annoying floor vibration due to normal human activity was investigated for cold-formed C-shaped residential floors systems. Dynamic impact and static loading tests were performed on twelve full size laboratory floors and five two-joist line laboratory floors to determine the influencing characteristics of annoying vibrations in metal framed floors. Similar tests were conducted on eleven floors located in existing houses. Subjective evaluation, in terms of annoying vibration levels, of all floors was recorded. Four existing floor vibration criteria were investigated: 1) Australian Standard. Domestic Metal Framing Code, 2) Swedish Building Technology Design Guide developed by Professor Sven Ohlsson, 3) United States Proposed Timber Floor Vibration Criterion developed by James Johnson, and 4) Canadian Timber Floor Criterion developed by Donald Onysko. Data collected from testing was used to determine which of the four existing criteria best classified the perceived vibration level of the floors. One criterion is suggested as the most suitable for predicting the perceived vibration level of metal framed residential floors.
Three methods to predict the vertical deflection of a floor subject to a concentrated load at mid-bay were examined. The results of applying these methods to the laboratory floors were compared to the actual measured values. The method which correlated the best with the measured values was selected for use in the proposed criterion.<br>Master of Science
33
Mitchell, Sarah. "Bodies of Knowledge: The Influence of Slaves on the Antebellum Medical Community." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/36885.
Texte intégralRésumé :
The influence of slaves on the south is well documented in areas such as agriculture, music, diet, religion and language. This thesis extends the list to include medicine. It also suggests that the importance of cultural transfer to America from places other than Europe has been overlooked in the history of medicine. The medical influence of slaves took the form of botanical remedies, many of them with an African origin, and were disseminated through the treatments of slave healers. Slave medical knowledge offered a viable alternative for whites to both nineteenth-century “heroic” practices and to alternative methods, such as homeopathy and Thomsonianism. In addition, the slave’s body itself was a vehicle of medical influence. Informed by nineteenth-century beliefs about the differences between whites and blacks, antebellum physicians performed experiments upon slave bodies that they could not and did not perform on whites’. Transfer of slave medical knowledge was facilitated by personal contact between individuals, by the publicity surrounding slaves who were set free for revealing cures, through the services of slave healers, through newspapers and medical journals in which whites wrote of slave treatments and acknowledged the source of the information, and through word of mouth. This study uses the theme of ambivalence to reconcile the conflicting attitudes of southern physicians and slaveowners towards slave medical knowledge.<br>Master of Arts
34
Kaufman, Matthew Douglas. "Variable-Complexity Response Surface Approximations For Wing Structural Weight in HSCT Design." Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/36566.
Texte intégralRésumé :
A procedure for generating and using a polynomial approximation to wing bending material weight of a High Speed Civil Transport (HSCT) is presented. Response surface methodology is used to fit a quadratic polynomial to data gathered from a series of structural optimizations. Several techniques are employed in order to minimize the number of required structural optimizations and to maintain accuracy. First, another weight function based on statistical data is used to identify a suitable model function for the response surface. In a similar manner, geometric and loading parameters that are likely to appear in the response surface model are also identified. Next, rudimentary analysis techniques are used to find regions of the design space where reasonable HSCT designs could occur. The use of intervening variables along with analysis of variance reduce the number of polynomial terms in the response surface model function. Structural optimization is then performed by the program GENESIS on a 28-node Intel Paragon. Finally, optimizations of the HSCT are completed both with and without the response surface.<br>Master of Science
35
Riess, Janet T. "Student Satisfaction with the Cooperative Education Program at Virginia Tech." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/36649.
Texte intégralRésumé :
The Cooperative Education component of Career Services at Virginia Polytechnic Institute and State University is undergoing a Business Process Re-engineering to develop the "Best Cooperative Education" program. The components considered in this process are the employers, the students, the staff, and the University faculty.
To determine what the students think of the present program and what they might want from an ideal program, a survey was developed and sent to all students currently enrolled in the program and the program participants who graduated in 1996. Participants were surveyed on three different areas: conducting a job search, assessing their experience on the job, and program administration. In addition, they were given the opportunity to comment on why they chose to participate in co-op, what the benefits were for participation, and what changes they would like to see in the program.
Results of the survey showed that the main reason for choosing to participate in the program was to gain experience of all kinds. This experience included the "real world," the corporate culture, interpersonal skills, making contacts, having a better sense of self-worth, verifying choice of a major, and making links between classroom learning and on the job experience. Earning money to finance their education was a distant second choice.
Increases in the mean responses of questions about the jobs being meaningful, challenging, utilizing skills and abilities, helping in classroom learning, involving well-defined projects, providing a variety of tasks and activities, allowing independent actions, and helping with classroom learning showed that as the students completed more work terms, they more strongly agreed that their job provided these attributes. They believed their colleagues at work were concerned about their professional growth and development and two-thirds would go to work for the company if given an opportunity.
Telephone interviews are becoming more popular and should be included in skills-building sessions with prospective co-op students, according to the respondents. While most students found their jobs through Career Services and a co-op job fair, several departments provided the services in-house for their own students.
Suggestions for improving the program clearly revealed that the students expect help and support through the whole process--finding the job, preparing to go to the workplace, and throughout their remaining undergraduate experience whether they are at school or at work.
The students' preferences for program services may be difficult to provide within the current department culture where the goal is to do more with less. Career Services may need to make some decisions about how to spend their resources.<br>Master of Arts
36
Yatsko, Michael S. "Ethnicity in Festival Landscapes: An Analysis of the Landscape of Jaialdi '95 as a Spatial Expression of Basque Ethnicity." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/36552.
Texte intégralRésumé :
Ethnic festivals are dynamic socio-spatial phenomena in
American society in which rationalized spaces are
transformed into "festival space" and the cultural landscapes
within the boundaries of the festivals are transfigured into
festival landscapes. The landscapes of ethnic festivals
generate, via a colorful assortment of cultural performances
and symbols, metaphors of ethnicity and spatial expressions
of social processes which influence ethnic groups. As a
metaphor of ethnicity, festival landscapes have become both
a tool for the ethnic boundary maintenance of ethnic groups
and a form of symbolic ethnicity for many assimilated
individuals. This thesis analyzes the landscape of the Basque
festival, Jaialdi '95, as a tool for the ethnic boundary
maintenance for the American Basque community and the
Basque colony in Boise, Idaho, and as a form of symbolic
ethnicity for assimilated American Basques.<br>Master of Science
37
Jyothikumar, Jagannathan. "All-fiber Spectral Filters based on LP01 - LP11 Mode Coupling and Applications in Wavelength Division Multiplexing and Dispersion Compensation." Thesis, Virginia Tech, 1996. http://hdl.handle.net/10919/30559.
Texte intégralRésumé :
All-fiber spectral filters have the advantages of providing low coupling loss and being readily integrated into fiber-optic networks. Spectral filters made of single-mode identical or dissimilar core parallel fibers provide 3-dB spectral widths on the order of 1 to 10 nm. A spectral filter made of single-mode and dual-mode fibers and operating based on coupling of power between LP01 and LP11 modes is proposed for applications as narrowband demultiplexers and as broadband mode converters with spectral widths of fraction of 1 nm to few 10 nm, respectively.
With appropriate choice of parameters, filters can be designed such that the LP01 mode of the single-mode fiber is phase matched with the LP11 mode of the dual-mode fiber at a desired wavelength. Thus, significant exchange of power between these two modes can occur. The coupled-mode theory of parallel dielectric waveguides is used to analyze the proposed filter. Transmission expressions are derived from the governing coupled-mode equations and evaluated numerically for example cases.
Two cases corresponding to maximum power coupling at 1.33 mm and 1.55 mm wavelengths are examined. Design data and transmission characteristics versus wavelength for these two cases are presented. The influence of the distance between fiber cores on peak transmission wavelength, spectral width, and coupling length is investigated. The application of the proposed filter as mode converter, which is required in the implementation of dispersion compensation using LP11 mode, is elucidated.<br>Master of Science
38
MacMillin, Peter Edward. "Trim, Control, and Performance Effects in Variable-Complexity High-Speed Civil Transport Design." Thesis, Virginia Tech, 1996. http://hdl.handle.net/10919/36717.
Texte intégralRésumé :
Numerous trim, control requirements and mission generalizations have been made to our previous multidisciplinary design methodology for a high speed civil transport. We optimize the design for minimum take off gross weight, including both aerodynamics and structures to find the wing planform and thickness distribution, fuselage shape, engine placement and thrust, using 29 design variables. While adding trim and control it was found necessary to simultaneously consider landing gear integration. We include the engine-out and crosswind landing requirements, as well as engine nacelle ground strike for lateral-directional requirements. For longitudinal requirements we include nose-wheel lift-off rotation and approach trim as the critical conditions. We found that the engine-out condition and the engine nacelle ground strike avoidance were critical conditions. The addition of a horizontal tail to provide take-off rotation resulted in a signiffcant weight penalty, and that penalty proved to be sensitive to the position of the landing gear. We include engine sizing with thrust during cruise and balanced field length conditions. Both the thrust during cruise and balanced field length constraints were critical. We include a subsonic leg in our mission analysis. The addition of a subsonic mission requirement also results in a large weight penalty.<br>Master of Science
39
Bhogaraju, Prabhakar V. "A Case-Based Reasoner for Evaluating Crop Rotations in Whole-Farm Planning." Thesis, Virginia Tech, 1996. http://hdl.handle.net/10919/36817.
Texte intégralRésumé :
I have worked on a Case-Based Reasoning (CBR) system that evaluates crop rotations for their soil erosion and risk of insect pest problems. The purpose of this system is to provide decision support for an automated whole-farm planner (CROPS). CROPS (Buick et al., 1992) generates crop rotation plans that can address some of the environmental, economic and legislative pressures facing natural resource managers. To generate and recommend a crop rotation plan CROPS requires estimates on the soil erosion risks and pesticide pollution potential of the crop rotation. In this research I have designed and prototyped a system that can assist CROPS in the process of whole-farm planning by providing information required for determining the soil erosion risks and the pesticide pollution potential of crop rotations. Inputs for the system include: a crop rotation, its tillage and residue management practices, and field conditions. Soil erosion risk is quantified using the C-value. Pest risks are likelihood of pest outbreaks that require control in a crop rotation. CBR was the chosen methodology for system implementation. In CBR, solutions to new problem situations are derived from retrieving and adapting solutions to similar problem situations experienced in the past. The system was prototyped using Esteemâ ¢, a CBR development shell, and runs on a PC under the MS. Windowsâ ¢, operating system.<br>Master of Science
40
Radtke, Philip J. "Basal Area Growth and Crown Dynamics in a Loblolly Pine Spacing Trial." Thesis, Virginia Tech, 1996. http://hdl.handle.net/10919/36950.
Texte intégralRésumé :
Relationships between the culmination of basal area growth and degree of crown closure in loblolly pine (Pinus taeda L.) were investigated. A spacing trial established on the low Appalachian Piedmont and Atlantic Coastal Plain provided the data for the investigation. Test plots were planted at densities ranging from 303 to 2723 stems per acre, and at various rectangular and square spacings. Annual stem and crown measurements were used to derive the sought-after relationships.
The age of basal area culmination was found to be inversely related to both planting density and site index. Crown closure was advanced on sites of relatively high quality, exhibiting an approximately linear increase with time from planting until the age of basal area culmination. The slope of this trend increased with planting density. The degree of crown closure at the age of basal area culmination was significantly higher on narrowly-spaced plots than it was on widely-spaced plots; however, it did not vary significantly with site index. Although crown closure is generally accelerated on high quality sites, the relatively early culmination of basal area growth on such sites offsets the increase - the net result being that crown closure at culmination age does not vary significantly with site differences. Crown closure indices can be used to determine whether or not a stand has reached the culmination of basal area growth; however, more readily available information on spacing and site index can be used to make the same prediction. The results of this study might be most useful to modelers of early stand dynamics in loblolly pine and other commercially important pines.<br>Master of Science
41
Batongbacal, Alan L. "A User-Extensible Architecture for Visualization and Analysis of Time-Series Trace Data." Thesis, Virginia Tech, 1996. http://hdl.handle.net/10919/30387.
Texte intégralRésumé :
This thesis describes the design and implementation of Chitra95, a software system developed for the visualization and analysis of time-series trace data. Chitra95 is based upon two earlier generations of Chitra and is aimed at producing a system with broad applicability and utility in this area of research.
This thesis contributes to the area of software design for trace visualization and analysis by proposing a set of design principles towards achieving the goals of system extensibility, reusability, reliability, testability and verifiability.
These design principles are demonstrated by Chitra95, a software architecture proposed in this thesis for visualization and analysis of time-series trace data. This architecture is novel in its combination of independence from problem domain semantics; optimization for user-extensibility and code reusability; freedom from any specific user interface model; ability to simultaneously produce an integrated application and a reusable toolkit of parts that may either be customized into a turnkey system or integrated into other software systems; support for enhanced reliability, testability and verifiability; and support for an interface to the World Wide Web and for remote execution. Finally, this thesis makes the specific contribution of a data structure for representing large traces that permits the maintenance of multiple versions of a trace and retains the ability to undo modifications made to a trace.<br>Master of Science
42
Favor, Craig M. "Evaluation of A "Floating" Aerobics Floor." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/37023.
Texte intégralRésumé :
Aerobics dance floors often produce annoying floor vibrations in adjacent parts of a building due to the rhythmic impact of the aerobicists. Various types of shock absorbing aerobics and dance floors are widely used to prevent injuries to the participants, but the floors may not prevent vibrations in adjacent areas of the building. The purpose of this investigation is to evaluate a temporary "floating" concrete aerobics floor designed to prevent the force and vibrations induced by rhythmic exercises from being transmitted to the existing building floor system.
The test floor is a concrete slab mounted on pressurized air springs. A series of tests was conducted to determine the vibration characteristics of the floor and the forces transferred to the supporting floor system. Experienced aerobicists compared the response of the "floating" floor to existing aerobics floors. Based on the experimental results, vibration characteristics and a prediction of the force transmitted to the supporting floor by the "floating" floor system were determined. Recommendations are made in terms of the feasibility of the "floating" floor concept, additional testing to be performed, and possible applications.<br>Master of Science
43
Munro, Jennifer L. "An Examination of the Credit Card Payment Practices of College Students." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/36590.
Texte intégralRésumé :
Every year, young adults graduate from high school and enter college. Often, college is the first opportunity students have to manage money. For some students, this means owning and managing their first credit cards. Colleges and universities frequently allow credit card vendors to solicit on campus. This practice is subject to criticism by the popular media, which reports horror stories of college students falling victim to great credit card debt.
This study examined the credit card payment practices of college students at a large research institution. To explore the null hypotheses, a convenience sampling technique was employed, and a pencil and paper survey was administered. The researcher sat at a table with a large sign advertising "free stuff" to participants. Participants who completed the instrument were rewarded with a candy bar or small prize. Participants were asked to complete a 50-item questionnaire about their credit card payment practices and were subsequently categorized into two subgroups: students who use their credit cards as a convenience and pay their balance each month; and, students who leave a debt on the card each month. The researcher identified eight locations on the campus where the study was conducted that attracted large numbers of students. Locations included: two dining halls; two residence halls; the black cultural center; an area between the library and the campus bookstore; and, the Graduate Student Assembly. The researcher collected 310 usable surveys to conduct the analysis.
This study had implications for several constituencies. First, students may benefit because establishing a credit history is important for obtaining loans to buy cars, houses, and finance the college education of future children. By better understanding the credit card payment practices of college students, college student affairs officers may better program to the financial needs of students. Credit card companies may benefit from this research, as well. Given a better understanding of the payment practices of college students, credit card companies may be able to better administer their student credit card programs to meet the limitations of students. Parents may also benefit from this research. Parents often do not understand how, or why their children become burdened with credit card debt. This information may help parents better prepare their students for the financial implications of credit cards. The results revealed several interesting trends. Students who use their credit cards wisely are primarily white, lower division students (Freshmen, Sophomores) who acquired their cards prior to enrolling in college. Those who use less judicious payment practices include minorities, upper division (Juniors, Seniors) and graduate students, those who acquired their cards during college, and those with more than three cards. These findings suggest that credit card payment practices deteriorate as students approach adulthood. This trend may contribute to the rapidly increasing level of personal debt in the United States, and is one which merits attention by college and university students and administrators.<br>Master of Arts
44
Kabra, Sunil. "A Technique For Estimating System-Wide Phasors In Real Time." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/36532.
Texte intégralRésumé :
The objective of this study is to investigate the application of Synchronized Phasor Measurement techniques in real time estimation of power system phasors. The WSCC System is a very large power system network constituted by a number of electric utilities and power companies. The system was analyzed and equivalents developed to suit the purpose of this project. Using these equivalents, the system was simulated for various contingencies to analyze its behavior. The purpose is to develop a technique for estimating the voltage phasors at all major substation buses of the system from a limited number of available real time phasors at a fixed set of substations. The system load flow was computed for various possible loading situations. Various loading patterns were created around a base summer time load flow case. Using the results from these computations, an empirical relationship was developed between phasors from a fixed set of locations and the unknown phasors at the rest of the system buses.<br>Master of Science
45
Weissbart, Erich J. "The Leached Layer Formed On Wollastonite In An Acid Environment." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/36517.
Texte intégralRésumé :
Experiments were carried out in a fixed-bed external recycle mixed flow reactor to measure the rate of dissolution and the development of a leached layer on wollastonite. Each experiment ran for approximately 24 hours and the release rates of Si and Ca in the interval from 14 to 24 hours were analyzed. Each experiment began with an incongruent stage where Ca was released faster than the silica that remained on the surface to form the leached layer. The silica release rate after 14 hours was 2.13 x 10-9 ( 1.03 x 10-9, 1 , n=67) mol/m2/sec, and this rate appeared to be independent of pH from pH 2 to 6 at 25 degrees C. BET surface area measurements of reacted wollastonite showed large increases in BET Asp over the course of experiments even though both the Ca and Si release rates decreased. These large increases of measured Asp were the result of the growing internal porosity of the leached layer, and much of this surface does not seem to contribute to Si release rates. From these data, we infer that the overall reaction for the hydrolysis of wollastonite in an acid environment is best explained by two relatively independent reactions. First, Ca is removed from the crystal leaving behind linear silica polymers; then the silica polymers are released into solution where they hydrolyze to form H4SiO4. nCaSiO3 + 2nH+ nCa2+ + (H2SiO3)n (H2SiO3)n + nH2O n(H4SiO4) As the leached layer grows in thickness, the Ca release rate slows because it is controlled by transport through the leached layer. A model of Ca diffusion through the leached layer shows that the leached layer grows thicker at lower pH and presents a longer diffusion path for Ca transport into the solution. This diffusion limited reaction offsets the faster rate of the Ca hydrolysis reaction so that at steady state the Ca rates should also become equal to the Si release rate.<br>Master of Science
46
Ely, Paul T. "Internal Damping Rates of Construction Cranes." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/36524.
Texte intégralRésumé :
The conveyance of payloads by construction cranes generates pendulations of the payload. This research provides a critical design parameter for the development of a device that aids in reduction of these pendulations. Previous research developed a tuned mass damping system, that effectively attenuated the energy of a pendulating payload. In order to be effective the internal damping rate of the tuned mass damper must be at least twice that of the system to be damped. Prototypes of a tuned mass damping system have achieved damping rates between 6 and 12 %, making cranes with damping rates below 3% attractive. This research indicates that the internal damping rate of construction cranes is on the order of one percent, suggesting that a tuned mass damping system could be retrofitted to today's construction cranes.
This thesis is an investigation of the internal damping rates of construction cranes. Three hydraulic and two lattice boom cranes were tested. The motion of pendulating payloads was modeled after a simple pendulum. The internal damping rate was calculated using logarithmic decrement technique. Light to medium duty cranes were tested with loads similar to those used in duty cycle operations. Damping tests were performed both perpendicular and parallel to the mast of the crane. Values were calculated from data extracted from videos of a payload oscillating over a measurement scale.
A FMC Link Belt 25-ton hydraulic crane was tested at 6.4 % of capacity and displayed damping rates between 0.25 and 0.6 %. A 50-ton FMC Link Belt was tested at 10 % of capacity and had damping rates of 0.18 % for both tests. The third hydraulic crane was a 60-ton P&H T-600XL. The test parallel to the mast was performed at 6 % of capacity having a damping rate of 0.22 %. The test-performed perpendicular to the mast was at 3.5 % of capacity with a damping rate of 0.65 %.
Two lattice boom cranes with capacities of 70 and 100 tons were tested. The 70-ton LIMA 778c's damping rates were 0.06 and 1.3 percent. This test was performed at 15 % of capacity. The 100-ton Link Belt LS318 was tested at 6.8 % of capacity and had damping rates between 0.07 and 0.08 percent.<br>Master of Science
47
Mathes, Andrew R. "Experimental Analysis of an Advanced-Design, Quasi-Radial Diffuser Receiving an Oscillating Jet." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/36982.
Texte intégralRésumé :
Methods of experimental analysis of airflow through an advanced-design, quasi-radial
diffuser receiving an oscillating jet induced by a rotating baffle were devised and
performed. The initially unsteady flow was found to lose its unsteadiness as it progressed
through the diffuser and exited into the atmosphere. Within the diffuser, regions of slow
flow in the lee of ventilation holes exist due to entrainment. The addition of a
convergence insert across from these holes increased flow speeds, but also deflected the
flow farther away from the holes, aiding separation. The predominantly steady flow over
a flat plate upon which the exiting flow impinged produced an asymmetric static pressure
profile. This was probably due to the mechanism that set up the oscillations in the flow,
the rotating baffle.<br>Master of Science
48
Broderick, Kevin Dee. "Constructing A Successful Therapeutic Experience With Adolescent Clients: A Qualitative Study Of Adolescent Experiences In Family Therapy." Thesis, Virginia Tech, 1996. http://hdl.handle.net/10919/36753.
Texte intégralRésumé :
Traditionally, therapists and researchers have not asked adolescents about their family therapy experience. This qualitative study was designed to solicit in-depth feedback from adolescents who have recently participated in family therapy to broaden our understanding of their experiences in counseling. Interviews were conducted with 10 adolescents, between the ages of 14 and 20, to discover what helps teenagers have a successful family therapy experience. From the interviews, five main categories emerged; (1) client/therapist relationship, (2) talking and being heard in both individual and family sessions, (3) gaining insight during therapy, (4) taking personal responsibility for making therapy work, and (5) seeing positive results. Feedback from the adolescents is used to suggest ways family therapists might enhance their effectiveness with adolescent clients and a model for treatment success is presented.<br>Master of Science
49
Lian, Keng Jin. "Adaptive Antenna Arrays for Satellite Personal Communication Systems." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/36949.
Texte intégralRésumé :
Since about the turn of the decade, several proposals have come forth for personal communication services implemented by means of multiple satellite systems. These satellite systems are similar to current terrestrial cellular technologies, which are still relatively new and have numerous technical problems associated with them. As a result, these satellite systems will also experience some of the similar problems. Two of such problems are the issue of multipath and interference. These problems may result in significant link degradation and affect overall capacity. To overcome this problem, adaptive antenna arrays on handheld terminals are proposed. This technique is believed to be better than omni-directional antennas which radiate in all directions. Adaptive antenna arrays have the ability to adapt to the changing environment and null out the interference. The LMS algorithm was investigated and used in the simulation of the adaptive array. The performance of the LMS array was discussed in detail. In the case of a multipath, an alternate approach was proposed where a diversity combiner is used to phase shift the multipath and combine the Signal of Interest and multipaths constructively.<br>Master of Science
50
Zabaronick, Noel A. "Eye Tracking Using Fiber Optics and Computer Vision Techniques." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/30540.
Texte intégralRésumé :
We describe a system for tracking the motion and determining the velocity of the human eye using a combination of fiber optics and imaging optics integrated with a CCD camera, a framegrabber, and a PC. Systems such as the one we describe are needed for monitoring location of interest for better human-computer interfaces and virtual reality simulations, for monitoring pilot cognitive skills during flight simulations, and for detecting the early warning signs of driver drowsiness. Where some eye-tracking devices are cumbersome because they require a person to limit head motion to remain in view of a camera or uncomfortable because they require the use of an elaborate headpiece, our proposed system is as simple to wear as a pair of eyeglasses, with the only added weight to the glasses being that of a fiber optic bundle.
This fiber bundle guides the image of an 880 nm LED illuminated eye as it is reflected from a hot mirror built into the eyeglass assembly. The guided image is focused onto a CCD and the camera’s output is linked to a PC framegrabber card. Software written in Microsoft Visual C++ locates the user’s pupil in each video image and tracks the motion and velocity of the pupil over time.
The prototype system tracks the center of the pupil to an accuracy of only 1/5 of the pupil size. This diminished accuracy results from the minimized computation scheme of pupil detection. The technique relies on edge detection and direction of image gradient over very few pixels so that the system is optimized for speed. Many other methods of pupil detection could be investigated in future research in order to optimize such a system for other parameters.<br>Master of Science