• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 276
  • 144
  • 121
  • 66
  • 30
  • 28
  • 20
  • 8
  • 6
  • 5
  • 5
  • 5
  • 5
  • 5
  • 5
  • Tagged with
  • 863
  • 556
  • 241
  • 104
  • 98
  • 97
  • 95
  • 84
  • 65
  • 61
  • 61
  • 56
  • 51
  • 51
  • 49
  • 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.
751

Contribuições para melhoria do desempenho e viabilidade de fabricação de scanners indutivos / Contributions to improve the performance, and the manufacture viability of inductive scanners

Oliveira, Luiz Claudio Marangoni de, 1975- 22 February 2006 (has links)
Orientador: Luiz Otavio Saraiva Ferreira / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-06T21:02:18Z (GMT). No. of bitstreams: 1 Oliveira_LuizClaudioMarangonide_D.pdf: 9710529 bytes, checksum: 4fc22426f2b4d1d845715c4742df71a2 (MD5) Previous issue date: 2006 / Resumo: Scanners são dispositivos que defletem um feixe luminoso e transfonnam um feixe puntual em uma linha de varredura, com amplitude e freqüência controladas. Diversos equipamentos utilizam este padrão luminoso para codificar ou decodificar infonnações, exemplos mais comuns são os leitores de código de barras de bancada, utilizados em supennercados, e as impressoras laser. V ários fenômenos podem ser empregados para defletir um feixe luminoso. Neste trabalho, os scanners utilizam o princípio da reflexão da luz por um espelho em movimento hannônico e ressonante sob ação de forças de origem eletromagnética. Tais forças são geradas pela interação de correntes induzi das na annadura, com o campo magnético produzido por ímãs pennanentes. A principal vantagem deste tipo de scanner é a ausência de conexões elétricas entre as partes móveis e fixas do dispositivo, o que simplifica o processo de fabricação e o toma mais robusto e menos suceptível a falhas. Parte dos scanners similares existentes atualmente são dispositivos eletro-mecânicos complexos, fabricados em série. Trabalhos anteriores demonstraram a viabilidade da geometria planar e da utilização de processos de fabricação em lotes, derivados da microeletrônica, neste tipo de scanner. Os protótipos fabricados, embora funcionais, apresentaram consumo de potência acima da média para este tipo de dispositivo, o que demonstrava a necessidade de melhorias em seu projeto. O processo de fabricação, embora confiável, foi desenvolvido com materiais e métodos baseados no Silício e originários da microeletrônica, o que dificultava sua implantação em indústrias em território nacional. Neste trabalho, foram pr9postos aprimoramentos à tecnologia dos scanners ressonantes planares atuados por indução para tomar seu desempenho compatível com o d~ dispositivos similares, e também para viabilizar sua fabricação utilizando materiais e métodos disponíveis no país. Uma metodologia de projeto, em conjunto com uma série de contribuições ao modelo, foi proposta e avaliada. Para viabilizar a fabricação propôs-se a utilização do Bronze-fosforoso, como material estrutural, e a utilização de foto-fabricação, como processo de fabricação. As contribuições propostas neste trabalho possibilitaram a redução do consumo de potência de 2, 2 W para cerca de 5 m W por grau óptico, e o aumento da freqüência de operação do circuito de cerca de 1 kHz para 4 kHz, com um ângulo de deflexão óptico típico de 20° pico-a-pico, parâmetros compatíveis com os de dispositivos similares, mas mecanicamente mais complexos e fabricados por processo serial / Abstract: Scanners are devices that deftects a light beam and converts a spot light in a well controlled amplitude and frequency scan line. Several applications uses the generated pattem to code or decode data, common examples ar,e barcode readers, and laser printers. A light beam can be deftected by different means. In this work, the scanner deftects the light by reftection in a moving mirror, in a resonant and harmonic movement, subjected to forces of electromagnetic nature. Such forces are generated by the interaction between an induced current in the armature, and a magnetic field, generated by permanent magnets. The main advantage of this kind of scanner is the absence of electrical connections between the mobile, and fixed parts of the device, that simplifies the fabrication process, and make its more reliable and less fault susceptible. Part of the similar devices available today are complex eIectro-mechanical devices, manufactured by serial processo Earlier works established that the planar geometry, and the use of batch fabrication process, derived from microelectronics, are feasible with this kind of device. A1though functional, the earlier prototypes presented a high power consumption, that shown the demand for an improved designo The Silicon-based fabrication process adopted makes the use of materiaIs and methods that are not readily accessible to the Brazilian industry. In this work improvements were proposed to the induction actuated planar resonant scanners technology. The goal was to make its performance compatible with the performance of similar devices, and to enable its fabrication using materiaIs and methods available to the Brazilian industry. A design m~thodology, and a set of model contributions were proposed and validated. The use of Phosphor-bronze, as structural material, and the photqfabrication process, as the machining method, were proposed as an option to the Silicon-based fabrication method. The contributions ofthis work had enabled the reduction ofthe power consumptlon from 2,2 W to about 5 m W per optical degree, and an increase in the working frequency from 1 kHz to 4kHz, with a optical deftection angle of about 20° peak-to-peak. Such parameters are fully compatible with similar devices, mechanically more complexes and manufactured by serial processes / Doutorado / Mecanica dos Sólidos e Projeto Mecanico / Doutor em Engenharia Mecânica
752

New Paradigms for Automated Classification of Pottery

Hörr, Christian, Lindinger, Elisabeth, Brunnett, Guido 14 September 2009 (has links) (PDF)
This paper describes how feature extraction on ancient pottery can be combined with recent developments in artificial intelligence to draw up an automated, but still flexible classification system. These features include for instance several dimensions of the vessel's body, ratios thereof, an abstract representation of the overall shape, the shape of vessel segments and the number and type of attachments such as handles, lugs and feet. While most traditional approaches to classification are based on statistical analysis or the search for fuzzy clusters in high-dimensional spaces, we apply machine learning techniques, such as decision tree algorithms and neural networks. These methods allow for an objective and reproducible classification process. Conclusions about the "typability" of data, the evolution of types and the diagnostic attributes of the types themselves can be drawn as well.
753

Glaspärlor i Skandinavien : ett långtidsperspektiv

Karlsson, Maria January 2020 (has links)
New research has shed light on the origin of the Danish glass beads dating to the BronzeAge and the increase in long-distance exchange during this period. This has provided newknowledge about glass beads during the Bronze Age, which unlocked the question of whatit looks like in the rest of Scandinavia. To get a broader perspective I have chosen to studythe first evidence of early craft sites where glass beads were made in Scandinavia. Then acomparison is made between the Bronze and Iron Ages from a broader perspective, whichincludes both the use of glass beads and the glass productions sites. I have therefore chosento study glass beads from a long-term perspective, from the introduction of the first glassbeads in Scandinavia during the Early Bronze Age until the Vendel period when the firstglass beads were manufactured in Scandinavia. By studying glass beads from a long-termperspective, we can learn more about the significance of glass beads in society.
754

Plazmochemické odstraňování korozních vrstev bronzu / Plasma chemical removal of bronze corrosion layers

Miková, Petra January 2019 (has links)
The thesis deal with applying low-pressure low-temperature plasma to corrosion products layers on bronze. Layers of corrosion products on samples were artificially prepared. As a result, they had the same composition and could be irreversibly destroyed during experiments, which would not be possible with real archeological artifacts. Bronze, copper and tin alloy, samples were cut with respect to the size of the plasma-chemical device. XRF was used to determine the bronze composition. Before being corroded by the active medium, each sample was washed with ethanol and dried with a hot air stream. Until now, the procedure was the same for all samples. During formation of corrosion products layers, two factors have to be taken into account: the time consumption and the corrosiveness of the active environment. By focusing on one or the other factor, several groups of samples with differently degraded surfaces were created. The fastest way was to place samples in a corrosion chamber where sodium chloride solution was applied at the elevated temperature. The samples were corroded within a few days there. Longer, but in terms of corrosion products layers compactness better way proved procedure where the samples were sealed in the desiccator. At the desiccator bottom the Petri dish with an inorganic acid was placed, in our case, with hydrochloric acid inside. This method corroded the samples within one month. The longest but the most closed to the real live method was the burial of samples into soil or compost. However, this method corroded the samples within two years. Final step after the samples were removed from any corrosive environment, were dried under low pressure and were placed in a barrier film made bag together with moisture and oxygen absorbers. So prepared samples with layers of corrosion products have been treated in a low-pressure low-temperature plasma. Treatment was carried out in the apparatus which is based on the reactor: cylinder of quartz glass having a diameter of 100 mm and a length of 900 mm. The reactor was supplied with a working gas or a mixture of working gases with a total flow rate of 50 sccm. In our case, one is pure hydrogen or a combination with argon. A rotary oil pump was used to provide vacuum. The reactor base pressure was 10 Pa before treatment, while during the treatment it was 150 Pa. High-frequency generator (13.54 MHz) was used for supply the system with energy through two copper electrodes located outside the reactor. According to the energy delivery method, the treatment was carried out in a continuous or pulse mode. The sample temperature was monitored during the experiment and were evaluated the emission spectra from OES. The sample temperature was one of the key factors. The measurement was first done with a thermocouple, later switched to a thermocouple with optical data transmission. A safe temperature was set and then the whole process was controlled through it. In addition, the effect of the energy delivery method, value of the delivered power, sample size, presence of incrusted layers and composition of working gas were studied. After application of plasma, samples were analyzed by SEM – EDX and XRD. After the evaluation of the acquired knowledge and experience, a real artifact - a bronze chisel from the site of Boskovice - was treated. This documentation lacked the artifact, so it could be used to verify the lessons learned about plasma chemical reduction.
755

Ověřování původních technologií pro výrobu uměleckých odlitků / Verification of the original technologies used for art castings

Hřebíček, Lukáš January 2008 (has links)
This diploma thesis is describing making of the same art casting by using different foundry technologies/ moulds (ceramic shell mould, several types of plaster moulds including anhydride gypsum and also natural sand mould). In this thesis there is also description of casting the famous piece of bull from “Byci skala” (Bull Rock). The bull was cast into traditional clay mould which is believed to be the original technology. Also the original shape of the bull casting was reconstructed, i.e. a copy of the original bull casting made. As the main achievement of this work is an overview and comparison of several technologies suitable for making art castings.
756

Transitions vers des états électroniques complexes et des structures super périodiques dans les bronzes mono phosphates de tungstènes / Transitions toward complex electronic states and super-periodic structures in the monophosphate tungsten bronzes family.

Duverger-Nédellec, Elen 01 December 2017 (has links)
Les matériaux conducteurs de basse dimensionnalité électronique peuvent présenter des transitions vers des états électroniques complexes tels que la supraconduction, les Ondes de Densité de Spins (ODS) et les Ondes de Densité de Charges (ODC). La coexistence de plusieurs de ces instabilités au sein d’un même matériau a donné lieu à une recherche active de nouveaux systèmes conducteurs quasi-bidimensionnels. Dans cette thèse nous avons choisi de nous intéresser à la famille des Bronzes MonoPhosphate de Tungstène à tunnels pentagonaux (MPTBp), de formule chimique (PO2)4(WO3)2m ; l’un des principaux intérêts réside dans la possibilité de contrôler directement la dimensionnalité du matériau et sa densité de porteurs en faisant varier la valeur de m (2 ≤ m ≤ 14). Dans la littérature il a été montré que certains termes de cette famille (m=4, 5, 6) admettent des états ODC successifs alors que d’autres (m=10) présentent des ordres de type ferro électrique ; l’objectif de cette thèse est alors de montrer l’effet de la dimensionnalité du matériau sur l’apparition et la stabilité de ces états électroniques dans les MPTBp. Pour cela, des mesures de transport électronique, des études des structures modulées incommensurables et commensurables par diffraction des rayons X avant et après chaque transition et des mesures de diffusion inélastique ont été effectuées sur plusieurs termes à valeur de m pair. Dans ce travail nous avons pu montrer l’existence d’un état ODC pour les termes m=2, 4, 6, 8 et 10, caractérisé par la formation d’amas de tungstène dans certaines régions du matériau, accompagné, pour les m=8 et 10, de l’installation progressive d’une mise en ordre de type anti-ferroélectrique des déplacements des atomes de tungstène. Un phénomène de dépiégeage d’ODC a été observé pour le terme quasi-unidimensionnel m=2, ce qui n’avait encore jamais été reporté chez les MPTBp. Un couplage électron-phonon fort a pu être mis en évidence pour les hauts termes (m ≥ 8) à la fois via les analyses structurales, l’observation de transitions résistives du premier ordre mais également par des mesures de diffusion inélastique des rayons X. Pour ces hauts termes, une transition de type ordre-désordre est alors à envisager. / Conductive materials with low electronic dimensionality can present some transitions toward complex electronic states as superconductivity, Spin Density Waves (SDW) and Charge Density Waves (CDW). The coexistence of several of these instabilities in the same material leads to bustling investigations on new quasi-bidimensional conductors. In this thesis, we chose to study the MonoPhosphate Tungsten Bronzes with pentagonal channels family (MPTBp), of chemical formula (PO2)4(WO3)2m ; one of the main interests of this family is the possibility to directly control the compound’s dimensionality and its carriers density by varying m value (2 ≤ m ≤ 14). In the literature, it’s been shown that some MPTBp members (m=4, 5, 6) present successive CDW states whereas others (m=10) show ferroelectric-type orders. The aim of this thesis is thus to bring into light the effect of the material’s dimensionality on the appearance and the stability of these electronic states in the MPTBp family. In this way, transport measurements, X-Rays diffraction studies of the commensurate and incommensurate modulated structures below and above each transition and inelastic scattering measurements were done on several members with even value of m. In this work we reveal the existence of a CDW state for the m=2, 4, 6, 8 and 10 members, characterized by the formation of tungsten clusters in some areas of the crystal. For the m=8 and 10 members, the CDW is accompanied by a gradual installation of an anti-ferroelectric-like ordering of the tungsten atoms displacements. A CDW depinning phenomenon was observed for the quasi-unidimensional m=2 member, which has never been reported before in the MPTBp family. A strong electron-phonon coupling was evidenced for the high terms of the family (m ≥ 8) by structural analysis, first order resistive transitions observation and by X-Rays inelastic scattering measurements. For these high terms, an order-disorder transition must be considered.
757

Mohylová kultura střední doby bronzové v severozápadních Čechách / The Middle Bronze Age Tumulus Culture in North-Western Bohemie

Franková, Daniela January 2011 (has links)
The aim of the thesis The Middle Bronze Age tumulus culture in north-western Bohemia is to contribute to a deeper understanding of the Middle Bronze Age, and generally to expand our knowledge about this field of prehistoric history of north-western region. The work is divided into three main parts. The first one deals with the analysis of settlement of the tumulus culture in Dobroměřice. The analysis focuses mainly on the findings of the various movable objects, pursuant to which the settlement is situated chronologically. Second, we focused attention on the Middle Bronze Age tombs. He created a list of 51 currently known tomb files. By far the largest space was devoted to typological-chronological analysis of the find of the Fund, both in bronze and ceramic artefacts and the findings of other materials. Based on this analysis has succeeded individual graves units classified chronologically. The theme of the final chapter is the evaluation of sites by the accumulation of all known sites of the Middle Bronze Age in the study area. With made-geographical analysis of settlement can be considered on an overall The Middle Bronze settlement in the region.
758

Využití podpovrchové vody ve starším pravěku střední Evropy / Groundwater use in the Central European prehistory up to the Bronze Age.

Folejtarová, Lenka January 2017 (has links)
The thesis is about exploitation of groundwater in the Neolithic, Eneolithic and Bronze age in the Central Europe. Important part of work is catalog gathering findings of wells to the year 2016. All gathered data from literature are applied to the database and evaluated. Findings, evalution of structure and environment are followed up. The table of the most common types of construction is also done. Interpretation of finds is final part of work. The part of work are also map data and illustrated appendix. Key words: Central Europe; Neolithic; Eneolithic; Bronze Age; water management; water use; well; groundwater
759

Africké skalní umění: případová studie z údolí Oukaïmeden / African Rock Art: A Case Study in the Oukaïmeden Walley

Půtová, Barbora January 2020 (has links)
The subject of the thesis is the description, analysis and interpretation of rock art. The first, theoretic, part is dedicated to the research strategy, documentation, dating, conservation and presentation of rock art. It also analyses the relation between rock art and landscape, since differences in how different cultures perceived the landscape led rock art creators to different perception of the environment and to different forms of creative expression. The first part of the dissertation presents approaches rock art and methods of its interpretation from the landscape, historic, sociologic, ritual, artistic and aesthetic perspective. The second part of the dissertation discusses African rock art in the Oukaïmeden Valley, set in the central part of the High Atlas in Morocco. The dissertation focuses on particular archaeologic sites, art techniques applied, distinguishing features and other specificities of the local rock art. Special attention is paid to the motifs, development changes and dating of rock art in the Oukaïmeden Valley. Rock art first appeared there in the Late Neolithic and was further developed in the Bronze Age and continued until the Libyan-Berber period. The dissertation also presents interpretation of rock art motifs including analysis of their function and meaning of their positioning...
760

Použití symbolů v minojské a mykénské ikonografii / The Use of Symbols in Minoan and Mycenaean Iconography

Matoušková, Monika January 2020 (has links)
This Master thesis deals with symbolic objects appearing in the Bronze Age Aegean art in the 3rd and especially the 2nd millennium BCE. Recurrent types of scenes and motifs speak for the fact that there must have existed a complex iconographic system of Minoan and Mycenaean art. An analytical method aiming at single elements of composite scenes may bring us closer to better understanding of this system and to its more objective interpretation. The study, therefore, focuses on the iconography of each individual symbol and also discusses its possible parallels in art of the neighbouring Bronze Age cultures. Nonetheless, the Aegean iconographic system was not strictly codified throughout the entire Bronze Age and some of the themes evolved or were specific only for certain eras. For that reason, the studied material is treated in a diachronic approach so as to stress the iconographic evolution of the symbols' use. The aim is to provide a profound analysis of the rules applied to the symbols in Minoan and Mycenaean art, to investigate their possible origins, and finally to examine their mutual interconnections.

Page generated in 0.0208 seconds