• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 43
  • 19
  • 16
  • 4
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 100
  • 34
  • 20
  • 20
  • 13
  • 11
  • 9
  • 9
  • 8
  • 7
  • 7
  • 7
  • 7
  • 7
  • 6
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

CW Mid-infrared NH3 Lasers

Kroeker, David Francis 03 1900 (has links)
This thesis describes a series of experiments that were undertaken to extend the limits of output power and wavelength coverage of optically pumped mid-infrared lasers. Initially, two new CW Raman lasers operating at wavelengths of 11.5 and 12.5 pm were developed. Maximum powers of 650 and 150 mW were produced, with pump powers of 11 and 3.3 W, respectively. The effect of the pump offset on the output power was then determined by measuring the efficiency of an NHg laser pumped at frequency offsets of 94 and 274 MHz. In lasers operating in pure NH3, the larger pump offset required a greater pump intensity to reach threshold, but efficiency increased with pump offset. Higher NH3 pressures could be used at larger pump offsets and the improved efficiency was attributed to reduced saturation effects at the higher operating pressures. Experiments carried out with NHg inversion lasers have greatly increased the output powers available at a large number of wavelengths in the 10 to.14 pm range. In a buffered NH3 mixture, the sR(5,0) transition was pumped on resonance. C^llis;o^r^s with either — or Ar buffer gases were effective in thermalizing the rotational populations in the v>2=1 vibrational level and producing gain on a wide range of frequencies. Output powers as large as 3.5 W on a single line and greater than 5 W multi-line were produced, at efficiencies of 20 and 30 % respectively. The number of lasing wavelengths increased substantially, as more than forty ortho-NH3 transitions were observed to lase in a grating-tuned cavity. The optical pumping technique was then used for the first time to produce line-tunable lasing on para-NH3 transitions. The sR(5,l) transition was pumped near resonance and 24 para-transst'lons were observed to lase. In total, lasing was achieved on 65 different transitions in 14NH3, with wavelengths of 10.3 to 13.8 pm. / Thesis / Master of Science (MSc)
12

Espectroscopia de dois fotons do ion Gd+3 em estruturas perovskitas / Two photon spectroscopy in perovskite crystal

Nunes, Luiz Antonio de Oliveira 15 April 1988 (has links)
Através da absorção de um e de dois fótons estudamos as diferentes transições do íon \'Gd POT.+3\' e GGG. Utilizando técnicas espectroscópicas com laser pulsado e laser contínuo, analisamos a influência do campo cristalino sobre o íon. Estes resultados estão em concordância com as previsões advindas da teoria de grupo. A partir da análise dos espectros de luminescência das amostras de GdAl\'O IND.3\', conseguimos detectar pequenos traços de impurezas nas mesmas. Não conseguimos detectar nenhuma anomalia nos espectros obtidos, de modo a não acreditarmos na existência de alguma interação Gadolínio - Galdoíno, acima da temperatura de transição de fase. Laser de corante contínuo de alta resolução, laser de corante pulsado foram construídos para a realização dos experimentos. Também desenvolvemos os equipamentos eletrônicos envolvidos. / The different transitions of \'Gd POT.3+\' ion in samples of GdAl\'O IND.3\' and GGG were studied by means of the absorption of one and two photons. The crystalline field influence an the ion was studied by using spectroscopic techniques with pulsed laser as well as continuous laser. These results are in agreement with the group theory prediction. From the luminescence spectrum of this sample little impurities aspects in the GdA1\'O IND.3\' sample were detected. No anomaly was detected in the spectra obtained so that we believed there is no \'Gd POT.3+\'-\'Gd POT.3+\' interaction above the phase transition temperature. High resolution continuous dye laser and pulsed die laser were built up to carry out the experiments. The electronic equipment used in the experiment was developed by us.
13

Application of constructed wetland on wastewater treatment

Chen, Zhong-Xun 02 September 2008 (has links)
Constructed wetland (CW) system is one natural purifying process. Using the CW systems to treat industrial wastewater or domestic sewage has been extensively application in many countries. Constructed wastewater treatment wetland must depend on the optimal operation parameters to achieve the best treatment efficiency. The objective of this research was to evaluate the effectiveness of Kaoping River Rail Bridge Constructed Wetland (KPCW) on contaminated river water treatment. The major influents came from the treated industrial wastewater from a paper mill [Yuen Foong Yu paper manufacturing company (System A)] and local drainage system (Chu Liao River) containing untreated domestic wastewater (System B).Results from this study show that the measured flow rates for Systems A and B systems were 10,968 and 13,147 m3/day, respectively. The hydraulic loading rates (HLR) and hydraulic retention time (HRT) for Systems A and B were 0.085 and 0.096 m/day, and 5.4 and 10.7 d, respectively. The average removal efficiencies for both systems ranged from 63.4-71.7% for biochemical oxygen demand (BOD), 39.5-44.4% for chemical oxygen demand (COD), 28.1-39.5% for ammonia nitrogen (NH4-N), 17.1-40.3% for total nitrogen (TN), 5.4-45.5% for total phosphorus (TP), and 91.1-98.7% for total coliform (TC). Reduction in suspend solid (SS) concentration was ineffective in both systems. This was due to the irregular harvest of the plants in the wetland. Results from the effluent probability method (EPM) evaluation indicate that the removal efficiency increased with the increase in influent pollutant concentration. Moreover, variations in pollutant loading rate (PLR) would affect both the removal rates and effluent concentrations. The experience obtained from this project will be helpful in designing similar natural water treatment systems for river water quality improvement for other river basins.
14

Minimização do efeito de anomalia em redes IEEE 802.11 usando SNR para controlar o CW / WLAN 802.11 anomaly mitigation using SNR to control backoff contention window

Ferreira, Debora Meyhofer 30 July 2007 (has links)
Orientadores: Michel Daoud Yacoub, Omar Carvalho Branquinho / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-08T18:59:46Z (GMT). No. of bitstreams: 1 Ferreira_DeboraMeyhofer_M.pdf: 1183194 bytes, checksum: 3c93692fbad066caa7e514b9442843d9 (MD5) Previous issue date: 2007 / Resumo: A Ethernet existe há mais de 20 anos e a ¿wireless ethernet¿ (ethernet sem fio), conhecida como o padrão 802.11, há mais de sete anos. Extensões do padrão original, tais como o 802.11g, foram criados para garantir maiores taxas de transmissão. No entanto, existem condições que afetam o seu desempenho. Um desses casos, conhecido como performance anomaly, ou anomalia de desempenho, ocorre quando em uma rede infraestruturada existem estações móveis (STAs) transmitindo com taxas diferentes. Nesse caso, uma STA a uma taxa baixa ocupa o canal por um longo período, degradando o desempenho das demais estações e comprometendo o funcionamento de toda a rede. Esse trabalho constata e quantifica essa anomalia e determina um método de priorizar as STAs com uma taxa de transmissão alta, objetivando a redução do efeito da anomalia. Essa priorização é feita alterando-se a janela de contenção de acordo com a relação sinal ruído da STA. O mecanismo é modelado matematicamente e avaliado através de simulação com o software Network Simulator / Abstract: Ethernet exists more than 20 years and the wireless Ethernet, known as IEEE 802.11, for more than seven years. Extensions of the original standard, as IEEE 802.11g, are been created to guarantee higher transmission rates. However, some conditions there are that affect the performance of the network. One of them, known as Performance Anomaly, occurs when in an infrastructured WLAN stations (STAs) operate at different rates. In such a case, the low rate STA rate captures the channel for a long time, penalizing the higher rate stations, thence degrading the performance of the network. This work substantiates and quantifies such an anomaly and proposes a method to mitigate the effect of it, prioritizating the higher STAs. This mitigation is is carried out using Signal to Noise Ratio as a criterion to control the Contention Window variation. The mechanism is modeled mathematically and evaluated by means of simulation using the software Network Simulator / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica
15

Espectroscopia de dois fotons do ion Gd+3 em estruturas perovskitas / Two photon spectroscopy in perovskite crystal

Luiz Antonio de Oliveira Nunes 15 April 1988 (has links)
Através da absorção de um e de dois fótons estudamos as diferentes transições do íon \'Gd POT.+3\' e GGG. Utilizando técnicas espectroscópicas com laser pulsado e laser contínuo, analisamos a influência do campo cristalino sobre o íon. Estes resultados estão em concordância com as previsões advindas da teoria de grupo. A partir da análise dos espectros de luminescência das amostras de GdAl\'O IND.3\', conseguimos detectar pequenos traços de impurezas nas mesmas. Não conseguimos detectar nenhuma anomalia nos espectros obtidos, de modo a não acreditarmos na existência de alguma interação Gadolínio - Galdoíno, acima da temperatura de transição de fase. Laser de corante contínuo de alta resolução, laser de corante pulsado foram construídos para a realização dos experimentos. Também desenvolvemos os equipamentos eletrônicos envolvidos. / The different transitions of \'Gd POT.3+\' ion in samples of GdAl\'O IND.3\' and GGG were studied by means of the absorption of one and two photons. The crystalline field influence an the ion was studied by using spectroscopic techniques with pulsed laser as well as continuous laser. These results are in agreement with the group theory prediction. From the luminescence spectrum of this sample little impurities aspects in the GdA1\'O IND.3\' sample were detected. No anomaly was detected in the spectra obtained so that we believed there is no \'Gd POT.3+\'-\'Gd POT.3+\' interaction above the phase transition temperature. High resolution continuous dye laser and pulsed die laser were built up to carry out the experiments. The electronic equipment used in the experiment was developed by us.
16

Human Detection Using Ultra Wideband Radar and Continuous Wave Radar

Ahmed, Atheeq January 2017 (has links)
A radar works by radiating electromagnetic energy and detecting the reflected signal returned from the target. The nature of the reflected signal provides information about the target’s distance or speed. In this thesis, we will be using a UWB radar and a CW radar to help detect the presence and rough location of trapped survivors by detecting their motions. Range is estimated in the UWB radar using clutter removal with SVD and for the dual frequency CW Radar using STFT and median filtering. The effect of the algorithm parameters on their performance was analyzed. The performance of the implemented algorithms with regards to small motion detection, distance estimation and penetration capability was analyzed. Both systems are certainly capable of human detection and tracking.
17

Traffic Surveillance Using Low Cost Continuous Wave (CW) Doppler Radars

Yang, Wu 12 September 2012 (has links)
No description available.
18

Design of a Continuous-Wave Synthetic Aperture Radar System with Analog Dechirp

Edwards, Matthew C. 12 March 2009 (has links) (PDF)
This thesis presents a design methodology for continuous wave (CW) synthetic aperture radar (SAR) systems. The focus is on design considerations specific to small, low-power systems suitable for operation on small aircraft and unmanned aerial vehicles (UAVs). Well-known results which have been derived in other works, such as the radar equation, are explained in the context of low-power, CW systems. Additionally, design issues unique to CW SAR are addressed and the results generalized. A method for controlling feedthrough between antennas is developed, and the resulting limitations on swath width are discussed. Methods are developed which allow an engineer to design a CW SAR system to obtain a given swath width, resolution, and data rate, and necessary tradeoffs are discussed. Using the proposed methodology, designs for two specific SAR systems are developed. Example sections outline the design of two small SAR systems called microASAR and microBSAR. These sections present a real-world application of the methodology and offer explanations of the rationale behind many of the design choices. Straightforward methods for testing different aspects of a completed SAR system are developed and presented. These procedures are carried out using microASAR hardware, and the results are used to validate the design methodology.
19

Interkulturelle Aspekte der Kriminalprognose

Schmidt, Stefanie 06 August 2018 (has links)
Wegen der hohen Diversität der Straftäterpopulation sind interkulturelle Aspekte auch bei der Kriminalprognose von großer Bedeutung. Allerdings werden diese Aspekte bisher weder in umfassenden Kriminaltheorien noch bei kriminalprognostischen Methoden explizit berücksichtigt. Die vorliegende Arbeit untersuchte anhand von vier Studien interkulturelle Aspekte der Kriminalprognose am Beispiel von Männern mit türkischem oder arabischem Migrationshintergrund (MH). Die kulturvergleichende, retrospektive Studie 1 zeigte, dass sich Täter ohne und mit türkischem oder arabischem MH hinsichtlich der Ausprägungen gängiger Risikofaktoren unterscheiden. Diese erwiesen sich für Täter ohne MH als valide, was jedoch nur mit Einschränkung für Täter mit türkischem MH galt. Bei Tätern mit arabischem MH war fast keiner der Risikofaktoren ein valider Prädiktor. Um etwaige Besonderheiten bei Personen mit türkischem oder arabischem MH zu ergründen, wurden in Studie 2.1 und Studie 2.2 forensische Experten befragt. Diese hielten migrations- und kulturbedingte Aspekte für genauso wichtig für die Erklärung von Delinquenz bei Personen mit türkischem oder arabischem MH wie gängige Risikofaktoren. Aus den subjektiven Relevanzbewertungen wurde ein Erklärungsansatz extrahiert, der neben gängigen Risikofaktoren auch migrations- und kultursensible Aspekte umfasst. Diese migrations- und kultursensiblen Faktoren wurden in Studie 3 validiert. Robuste Zusammenhänge mit Delinquenz fanden sich für folgende Faktoren: Einstellungen, die Gewalt befürworten bzw. gegen die Werte der Aufnahmegesellschaft gerichtet sind, ein globales Diskriminierungserleben und die soziale Unterstützung. Die Befunde unterstreichen zum einen die Notwendigkeit, interkulturelle Aspekte in Zukunft bei der Kriminalprognose zu berücksichtigen. Zum anderen sind die Theoriebildung und die empirischen Ergebnisse dieser Arbeit ein wichtiger Schritt hin zu einer kultursensiblen Kriminalprognose. / Due to the high diversity of offender population, intercultural aspects are very important for risk assessment. However, intercultural aspects are hardly addressed explicitly, neither in comprehensive crime theories nor in methods of risk assessment. Aiming to bridge this gap the current research project analysed intercultural aspects of risk assessment via four different studies taking men with a Turkish or Arab migration background (MB) as an example. The cross-cultural retrospective study 1 showed that offenders without a MB differ from offenders with a Turkish or Arab MB regarding the manifestation of well-known risk factors. Moreover, these risk factors proofed to be valid for offenders without a MB. For offenders with a Turkish MB, the validity was restricted. Critically, among offenders with an Arab MB nearly no risk factor was a valid predictor. To fathom potential particularities among people with a Turkish or Arab MB, forensic experts were surveyed in study 2.1. and 2.2. When explaining delinquency among people from Turkey or Arab countries, experts rated factors sensitive to migration and culture as relevant as common risk factors. Grounding on these individual ratings, a comprehensive theory was constructed which comprises common risk factors as well as risk factors sensitive to migration and culture. These culture and migration sensitive factors were validated in study 3. Robust correlations with delinquency were found for the following factors: attitudes approving violence or being directed against values of the host society, perceived global discrimination, and social support. On the one hand, the findings underline the necessity to take intercultural aspects into account in risk assessment. On the other hand, the theory construction and the empirical results of the current project already make an important step towards a culture-sensitive risk assessment.
20

Raízes de aplicações de complexos 2-dimensionais em superfícies fechadas / Roots of maps from 2-dimensional complexes into closed surfaces

Fenille, Marcio Colombo 01 February 2010 (has links)
Este texto é resultado de um estudo detalhado da teoria topológica de raízes para aplicações de complexos CW 2-dimensionais em superfícies fechadas (compactas e sem bordo). Diversas abordagens dos problemas envolvidos nesta teoria são apresentadas, algumas inclusive bastante diferenciadas com respeito aos parâmetros da teoria clássica / This text is the result of a detailed study of the topological root theory for maps from 2-dimensional CW complex into closed surfaces (compact and without boundary surfaces). Several approaches to the problems involved in this theory are presented, some of which are quite different with respect to the parameters of the classical theory

Page generated in 0.0453 seconds