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Stefani, Mario Antonio. "Medidores de distância por triangulação a laser." Universidade de São Paulo, 1995. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-19032009-093741/.
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Os Medidores de Distância por Triangulação a Laser são sistemas optoeletrônicos destinados à medição de pequenas distâncias ou deslocamentos, sem contato físico direto. Estes equipamentos possuem um grande campo de aplicações industriais. Este trabalho descreve as diversas configurações que este equipamento pode se apresentar, discutindo suas vantagens relativas. São estudadas também as suas partes e os componentes mais indicados. O projeto detalhado de um medidor usando sensor tipo CCD, e apresentado. Algumas aplicações industriais deste modelo são relatadas e diversos métodos e sugestões de uso são apresentadas, com base nas experiências realizadas pelo autor.<br>Laser Triangulation Rangefinders are non-contact, optoelectronic devices for measurement of small displacements or distances. These devices offer a broad range of industrial applications. This work explains common configurations, parts and main components, comparing their advantages. A detailed project on a CCD based Laser Rangefinder is presented. Some industrial applications for that project are related, discussing practical aspects based on authors experience. Some potential applications are also suggested.
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Nissinen, I. (Ilkka). "CMOS time-to-digital converter structures for the integrated receiver of a pulsed time-of-flight laser rangefinder." Doctoral thesis, Oulun yliopisto, 2011. http://urn.fi/urn:isbn:9789514295478.
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Abstract The aim of this thesis was to develop time-to-digital converters (TDC) for the integrated receiver of a pulsed time-of-flight (TOF) laser rangefinder aiming at cm-level accuracy over an input range of 10 m – 15 m. A simple structure, a high integration level and low power consumption are the desired features for such a TDC. From the pulsed TOF laser rangefinder point of view an integrated receiver consisting of both the TDC and the receiver channel on the same die offers the possibility of manufacturing these laser rangefinders with a high integration level and at a low price to fulfil the needs of mass industrial markets. The heart of the TDC is a CMOS ring oscillator, the clock frequency of which is used to calculate the full clock cycles between timing signals, the positions of the timing signals inside the clock period being determined by storing the state of the phase of the ring oscillator for each timing signal. This will improve the resolution of the TDC. Also, additional delay lines are used to generate multiple timing signals, each having a time difference of a fraction of that of the ring oscillator. This will further improve the resolution of the whole TDC. To achieve stable results regardless of temperature and supply voltage variations, the TDC is locked to an on-chip reference voltage, or the resolution of the TDC is calibrated before the actual time interval measurement. The systematic walk error in the receiver channel caused by amplitude variation in the received pulse is compensated for by the TDC measuring the slew rate of the received pulse. This time domain compensation method is not affected by the low supply voltage range of modern CMOS technologies. Three TDC prototypes were tested. A single-shot precision standard deviation of 16 ps (2.4 mm) and a power consumption of 5.3 mW/channel were achieved at best over an input range of 100 ns (15 m). The temperature drifts of an on-chip voltage reference-locked TDC and a TDC based on the calibration method were 90 ppm/°C and 0.27 ps/°C, respectively. The results also showed that a pulsed TOF laser rangefinder with cm-level accuracy over a 0 – 15 m input range can be realized using the integrated receiver with the time domain walk error compensation described here<br>Tiivistelmä Väitöskirjatyön tavoitteena oli kehittää aika-digitaalimuunninrakenteita valopulssin kulkuajan mittaukseen perustuvan lasertutkan integroituun vastaanottimeen. Tavoitteena oli saavuttaa senttimetriluokan tarkkuus 10 m – 15 m mittausalueella koko lasertutkan osalta. Aika-digitaalimuuntimelta vaaditaan yksinkertaista rakennetta, korkeaa integroimisastetta ja matalaa tehonkulutusta. Integroitu vastaanotin sisältää sekä aika-digitaalimuuntimen että vastaanotinkanavan ja tarjoaa mahdollisuuden korkeasti integroidun lasertutkan valmistukseen halvalla teollisuuden massamarkkinoiden tarpeisiin. Aika-digitaalimuuntimen ytimenä toimii monivaiheinen CMOS-rengasoskillaattori. Aika-digitaalimuunnos perustuu rengasoskillaattorin täysien kellojaksojen laskentaan laskurilla ajoitussignaalien välillä. Lisäksi rengasoskillaatorin jokaisesta vaiheesta otetaan näyte ajoitussignaaleilla niiden paikkojen määrittämiseksi kellojakson sisällä, jolloin aika-digitaalimuuntimen erottelutarkkuutta saadaan parannettua. Erottelutarkkuutta parannetaan lisää viivästämällä ajoitussignaaleja viive-elementeillä ja muodostamalla näin useita erillisiä ajoitussignaaleja, joiden väliset viive-erot ovat murto-osa rengasoskillaattorin viive-elementin viiveestä. Aika-digitaalimuunnin stabiloidaan käyttöjännite- ja lämpötilavaihteluja vastaan lukitsemalla se integroidun piirin sisäiseen jännitereferenssiin, tai sen erottelutarkkuus määritetään ennen varsinaista aikavälinmittausta erillisellä kalibrointimittauksella. Vastaanotetun valopulssin amplitudivaihtelun aiheuttama systemaattinen ajoitusvirhe integroidussa vastaanotinkanavassa kompensoidaan mittaamalla vastaanotetun valopulssin nousunopeus aika-digitaalimuuntimella. Tällainen aikatasoon perustuva kompensointimetodi on myös suorituskykyinen nykyisissä matalakäyttöjännitteisissä CMOS-teknologioissa. Työssä valmistettiin ja testattiin kolme aika-digitaalimuunninprototyyppiä. Muuntimien kertamittaustarkkuuden keskihajonta oli parhaimmillaan 16 ps (2,4 mm) ja tehonkulutus alle 5,3 mW/kanava mittausetäisyyden olessa alle 100 ns (15 m). Sisäiseen jännitereferenssiin lukitun aika-digitaalimuuntimen lämpötilariippuvuudeksi mitattiin 90 ppm/°C ja kalibrointimenetelmällä saavutettiin 0,27 ps/°C lämpötilariipuvuus. Työssä saavutetut tulokset osoittavat lisäksi, että valopulssin kulkuajan mittaukseen perustuvalla lasertutkalla on saavutettavissa senttimetriluokan tarkkuus 0 – 15 m mittausalueella käyttämällä tässä työssä esitettyä integroitua vastaanotinta ja aikatason ajoitusvirhekompensointia
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Châteauneuf, François. "Dynamique et structure moléculaire en champ laser intense." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq26049.pdf.
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CHATEAUNEUF, FRANCOIS. "Dynamique et structure moleculaire en champ laser intense." Paris 11, 1997. http://www.theses.fr/1997PA112428.
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Ce travail aborde differents volets des problemes issus de l'interaction entre un champ laser intense et un systeme moleculaire. L'equivalence entre le traitement floquet vibronique et la propagation de fonctions d'onde nucleaires sur des courbes electroniques floquet est etablie et le domaine d'application de l'image floquet electronique pour un champ laser ultraviolet est bien delimite. Par une etude de la dissociation de l'ion moleculaire h#+#2 en champ infrarouge, le mecanisme clapet, un nouveau mecanisme de piegeage de la population vibrationnelle, est devoile. De plus, un nouveau traitement de l'ionisation tunnel en champ infrarouge permet desormais une approche paquets d'ondes simple de la dynamique d'ionisation dissociative en reduisant considerablement la taille du probleme initial. Par un calcul ne faisant intervenir que la premiere ionisation de la molecule neutre et la dissociation de l'ion, il est demontre que les fragments possedent deja des composantes d'energie cinetique comprises entre 0 et 1 ev/fragment. Enfin, une representation adiabatique du systeme molecule + champ est etudiee pour laquelle les manifestations de la structure moleculaire laser-induite sont decrites dans un nouvel hamiltonien effectif.
5
Hutt, K. W. "Far-infrared laser spectroscopy of disordered solids." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373250.
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Schapper, Florian. "Attosecond structure of high-order harmonics." Konstanz Hartung-Gorre, 2010. http://d-nb.info/1000540448/04.
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Nguyen, Nam Anh. "Représentations et structure électronique des molécules en champ laser intense." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/NQ66331.pdf.
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Ulanowski, Z. "Investigations of microbial physiology and cell structure using laser diffractometry." Thesis, University of Hertfordshire, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382603.
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Miura, Kiyotaka. "Studies on Modification of Glass Structure Using Ultrafast Pulse Laser." 京都大学 (Kyoto University), 2003. http://hdl.handle.net/2433/77753.
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GLOTIN, FRANCOIS. "Le laser a electrons libres clio et sa structure temporelle." Paris 7, 1994. http://www.theses.fr/1994PA077142.
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Clio est un laser a electrons libres fonctionnant en centre serveur de lumiere a orsay depuis 1992. Son milieu amplificateur est constitue par un faisceau d'electrons relativistes (30-60 mev), delivre par un accelerateur radiofrequence bati specialement pour cet usage. Cette these regroupe l'ensemble des resultats experimentaux majeurs obtenus sur clio pendant ses deux premieres annees de fonctionnement. Le faisceau laser, accordable continument entre 1,8 et 17,5 m, est caracterise en terme de puissance, largeur spectrale, rendement, etc une attention particuliere est portee a sa structure temporelle, etudiee par une methode d'autocorrelation du 2d ordre en intensite. Ceci a permis de definir differents regimes de fonctionnement, et mis en evidence la possibilite de generer des impulsions lasers de moins de 500 fs a mi-hauteur, correspondant a des puissances cretes de plusieurs dizaines de megawatts. La micro-structure temporelle du faisceau d'electrons est egalement etudiee, et peut etre mise en regard des resultats obtenus pour le laser. Il apparait notamment que les impulsions lasers peuvent etre beaucoup plus courtes que les paquets d'electrons. Les premiers resultats experimentaux concernant la generation de deux raies laser accordables independamment sont aussi presentes brievement
11
Dumont, Jean-Paul. "Etude de la structure spatiale de flammes turbulentes par laser." Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb37604738z.
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Vázquez, Rodríguez Liss. "Laser spectroscopy of tin across N=82." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS339.
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L’objectif de cette thèse est l'étude par spectroscopie laser colinéaire à haute résolution de la structure nucléaire des isotopes d’étain riches en neutrons, vers de la fermeture de couche N=82 et au-delà. Les structures hyperfines et les déplacements isotopiques le long de ¹⁰⁸⁻¹³⁴Sn ont été mesurés en utilisant l’expérience COLLAPS à ISOLDE au CERN. Deux expériences indépendantes, utilisant des propriétés de transitions complémentaires l’une à 452 et l’autre à 286 nanomètres, ont étudiées les états 5p6s ¹P₁ et 5p6s ³P₁ dans l'atome neutre. L'état singlet fournit une sensibilité élevée au moment quadrupolaire tandis que le triplet facilite une grande séparation magnétique. A partir d'une analyse auto-cohérente des deux ensembles de données, les spins nucléaires, les moments électromagnétiques et les rayons de charge ont été extraits. Les propriétés des isomères à vie longue des noyaux ¹¹³Sn, ¹²³Sn, ¹²⁸Sn ainsi que l'état fondamental de ¹³³Sn et ¹³⁴Sn ont été évalués pour la première fois. Les moments quadrupolaires des états 11/2⁻, déterminés avec une plus grande précision que les études précédentes, suivent une tendance presque linéaire. Un coude à N=82 dans la courbe des rayons a été observé pour la première fois. Des calculs de champ moyen fournissent une description précise des rayons et relient en outre la tendance globale aux corrélations provenant des fluctuations des moments quadrupolaires<br>The aim of this thesis is the study of nuclear structure properties of the neutron-rich Sn isotopes towards the N=82 shell closure and beyond by high-resolution collinear laser spectroscopy. The hyperfine structures and isotope shifts along ¹⁰⁸⁻¹³⁴Sn were measured using the COLLAPS instrumentation at ISOLDE, CERN. Two independent experiments using transitions with complementary properties, respectively at 452 and 286 nanometres studied the 5p6s ¹P₁ and the 5p6s ³P₁ states in the neutral atom. The singlet state provided high sensitivity to quadrupole moments while the triplet facilitated a large magnetic splitting. From a self-consistent analysis of the two data sets, nuclear spins, electromagnetic moments and charge radii have been extracted. The properties of the long-lived isomers in ¹¹³Sn, ¹²³Sn, ¹²⁸Sn and the ground state of ¹³³Sn and ¹³⁴Sn have been assessed for the first time. The quadrupole moments of the 11/2⁻ states, determined with much higher precision than in previous studies, have been found to follow a nearly linear trend. A "kink" in the radii trend at N=82 was observed for the first time. Beyond mean-field calculations provide an accurate description of the radii and further relate the overall trend to correlations stemming from the fluctuations of the quadrupole moments
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Winstead, Christopher Brooks. "Laser spectroscopy of small metal and semiconductor molecules." Diss., Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/31049.
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Breuer, John. "Dielectric laser acceleration of non-relativistic electrons at a photonic structure." Diss., Ludwig-Maximilians-Universität München, 2013. http://nbn-resolving.de/urn:nbn:de:bvb:19-161479.
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In dieser Arbeit berichten wir über die Beobachtung der dielektrischen Laserbeschleunigung nichtrelativistischer Elektronen mithilfe des inversen Smith-Purcell Effekts bei optischen Wellenlängen. Wenn die Phasengeschwindigkeit von evaneszenten Wellen nahe periodischer Gitterstrukturen mit der Elektronengeschwindigkeit übereinstimmt, kann eine vorwärtsgerichtete elektrische Feldkomponente das Elektron kontinuierlich beschleunigen. Dieser Effekt tritt jedoch nur im Nahfeld passender photonischer Strukturen auf, d.h., dass der Elektronenstrahl die Struktur in Abständen, die kleiner als die Wellenlänge sind, passieren muss.
Für die Beschleunigung nichtrelativistischer 28keV Elektronen verwenden wir die dritte Raumharmonische eines Quarzgitters, die mittels Lichtpulsen eines Titan-Saphir-Oszillators angeregt wird. Wir messen einen maximalen Energiegewinn von 280eV, was einem Beschleunigungsgradienten von 25MeV/m entspricht. Dieser Wert ist vergleichbar mit dem Gradienten heutiger Radiofrequenz-Linearbeschleuniger. Um diese Beschleunigung zu erfahren, passieren die Elektronen die Gitteroberfläche in einem Abstand von weniger als 100nm.
Im Rahmen dieser Arbeit beschreiben wir die Theorie der Elektronenbeschleunigung im Nahfeld von Gitterstrukturen und diskutieren Simulationsergebnisse zu dieser dielektrischen Laserbeschleunigung. Unsere Messergebnisse stimmen sehr gut mit den Simulationen überein und bestätigen deshalb die direkte Beschleunigung im Lichtfeld. Zusätzlich diskutieren wir die Elektronenbeschleunigung in Doppelgitterstrukturen, das Dephasieren nichtrelativistischer Elektronen, sowie den Raumladungseffekt, der den Spitzenstrahlstrom in diesen neuartigen, auf Mikrostrukturen basierenden Beschleunigern begrenzt.
Die hier verwendeten photonischen Gitterstrukturen können direkt aneinandergereiht werden und erfüllen damit die Voraussetzung für skalierbare Linearbeschleuniger. Außerdem sind unsere Strukturen kompatibel mit den Mikrostrukturen, an denen die dielektrische Laserbeschleunigung relativistischer Elektronen zeitgleich durch unsere Kollegen in Stanford demonstriert wurde. Das Potenzial dielektrischer Laserbeschleuniger liegt in dem bis zu zwei Größenordnungen höheren Beschleunigungsgradienten verglichen mit konventionellen Beschleunigereinrichtungen, was sich letztendlich auf die größere Zerstörschwelle dielektrischer Materialien bei optischen Wellenlängen im Vergleich zu Metallen im Radio- und Mikrowellenbereich zurückführen lässt, die eine erhöhte Oberflächenspannungsfestigkeit zur Folge hat. Dieser erhöhte Beschleunigungsgradient könnte den Bau von deutlich kompakteren und kostengünstigeren Beschleunigern erlauben. Wir geben einen Ausblick auf den möglichen Aufbau solcher zukünftiger optischen Beschleuniger und auf deren potentiellen Anwendungen in kompakten Freie-Elektronen-Lasern.<br>This thesis reports on the observation of dielectric laser acceleration of non-relativistic electrons via the inverse Smith-Purcell effect in the optical regime. Evanescent modes in the vicinity of a periodic grating structure can travel at the same velocity as the electrons along the grating surface. A longitudinal electric field component is used to continuously impart momentum onto the electrons. This is only possible in the near-field of a suitable photonic structure, which means that the electron beam has to pass the structure within about one wavelength.
In our experiment we exploit the third spatial harmonic of a single fused silica grating excited by laser pulses derived from a Titanium:sapphire oscillator and accelerate non-relativistic 28keV electrons. We measure a maximum energy gain of 280eV, corresponding to an acceleration gradient of 25MeV/m, already comparable with state-of-the-art radio-frequency linear accelerators. To experience this acceleration gradient the electrons approach the grating closer than 100nm.
We present the theory behind grating-based particle acceleration and discuss simulation results of dielectric laser acceleration in the near-field of photonic grating structures, which is excited by near-infrared laser light. Our measurements show excellent agreement with our simulation results and therefore confirm the direct acceleration with the light field. We further discuss the acceleration inside double grating structures, dephasing effects of non-relativistic electrons as well as the space charge effect, which can limit the attainable peak currents of these novel accelerator structures.
The photonic structures described in this work can be readily concatenated and therefore represent a scalable realization of dielectric laser acceleration. Furthermore, our structures are directly compatible with the microstructures used for the acceleration of relativistic electrons demonstrated in parallel to this work by our collaborators in Stanford. The potential of dielectric laser accelerators lies in the larger attainable acceleration gradients resulting in a more compact design as well as a lower cost of these devices compared with conventional accelerator facilities. This size reduction by potentially a factor of 100 is owed to the two orders of magnitude larger damage threshold of dielectric materials as compared to metals. We present an outlook towards the design of an envisioned large-scale dielectric laser accelerator and its possible application in future compact free electron lasers.
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Siegel, Thomas. "Imaging of molecular structure and dynamics using laser driven electron recollisions." Thesis, Imperial College London, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.522867.
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Mura, Matteo. "Estimating and mapping forest structure diversity using airborne laser scanning data." Doctoral thesis, Università degli studi del Molise, 2016. http://hdl.handle.net/11695/66275.
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Il tema trattato in questa tesi di dottorato è l'acquisizione e applicazione degli approcci e delle tecniche più efficaci che possono essere utilizzati per stimare e mappare indicatori di diversità strutturale delle foreste, nell’ottica di una più completa valutazione, gestione e monitoraggio della biodiversità in ambienti forestali.
La tesi è suddivisa in due sezioni principali, costituite da cinque diversi ma interdipendenti e organicamente collegati studi, rappresentati da altrettanti articoli pubblicati su riviste soggette al processo di referaggio, di seguito riportati in numeri romani come Studi I-V.
La prima sezione comprende tre studi, Studio I-II-III. I contenuti di questa sezione forniscono le basi conoscitive che verranno successivamente applicate per la stima e la mappatura della diversità strutturale in ambito forestale negli studi della seconda sezione (Studi IV e V).
Diversi progetti di cooperazione internazionale sono stati stipulati al fine di far fronte al problema della costante perdita di biodiversità a livello mondiale, e data la rilevanza che la diversità strutturale delle foreste ha in termini di diversificazione degli habitat, un monitoraggio costante del suo status su grandi aree è di indubbia necessità.
Lo Studio I dimostra come questo risultato può essere affrontato in modo efficiente integrando dati a terra, come quelli rilevati durante le indagini di tipo inventariale, e da dati rilevati, in particolare quelli derivanti da scansione laser aerea (ALS), i quali hanno dimostrato di essere uno strumento affidabile nel caratterizzare la struttura del bosco. Nel caso specifico dello Studio I viene mostrato come i dati ALS vengano utilizzati nella stima di un comune attributo forestale come la biomassa epigea, utilizzando dati a terra rilevati secondo un originale schema di campionamento stratificato a due fasi.
Al fine di essere utilizzato come valida fonte di informazione per la pianificazione di strategie di conservazione, congiuntamente con la stima areale del parametro di interesse, una mappattura dettagliata che mostra come la diversità strutturale si distribuisce spazialmente è di grande utilità. Lo Studio II presenta una vasta meta-analisi e analisi bibliografica, effettuata durante il periodo il dottorato, in cui è mostrato come la tecnica parametrica della k-NN è, tra gli altri, quella più utilizzata ed efficace per la stima e spazializzazione di attributi forestali, sia come singolo attributo che come combinazione di essi, atti a formare indici sintetici. Questa tecnica può essere ulteriormente migliorata implementando una fase di ottimizzazione avente lo scopo di impostare i parametri del metodo k-NN per ottenere le migliori prestazioni possibili di stima. Lo Studio III scende nel dettaglio di questa fase, confermando che se l’ottimizzazione è effettuata prima di eseguire la procedura di k-NN, la performance nelle previsioni migliorata in maniera rilevante.
Nella seconda e ultima sezione, i metodi sperimentati nella prima sezione sono applicati in due diversi studi. Lo Studio IV descrive l'uso dei dati ALS e di quelli a terra per la stima del valori medi degli indici di diversità strutturali sull’area di studio, in un contesto dove le stime derivanti dal modello fungono da supporto migliorando la precisione della stima rispetto ad una stima basata solo sull’utilizzo dei dati rilevati a terra. Lo studio propone inoltre il calcolo degli intervalli di confidenza di tali stime e la mappatura degli indici esaminati. Lo Studio V è strutturato come un approccio metodologico, portandosi un passo avanti rispetto allo Studio IV. Questo è la sintesi di tutto ciò che è stato acquisito e applicato finora, e propone la mappattura e la stima di un indice sintetico di diversità strutturale (SDI) ottenuto tramite la capacità di un’ottimizzata k-NN nello stimare attributi di interesse in maniera simultanea, sintetizzandoli in un unico e più comprensivo indice di diversità strutturale.<br>The topic of this doctoral thesis is the investigation of the most effective approaches and techniques that can be used to predict and map indicators of forest structural diversity, in a perspective of a more comprehensive assessment, management and monitoring of biodiversity in forest environments.
The thesis is subdivided in two main sections, made up of five different but interdependent and organically connected studies, represented by as many published peer-reviewed original research articles, hereafter reported in Roman numerals as Studies I-V.
The first section comprises the studies I-II-III. The contents of this section set the basis of methods and know-how that are subsequently used to estimate and map forest structure diversity in Studies IV and V.
Several international cooperation projects has been stipulated in order to cope with the issue of the constantly loss of biodiversity at global scale, and because of the relevant influence that forest structure has on biodiversity, forest structure diversity needs to be to assessed and monitored on large areas.
In Study I is demonstrated how this achievement can be efficiently tackled coupling ground data, such as those measured during forest inventory surveys, and remotely sensed data, in particular the ones derived from airborne laser scanning (ALS), which has proved to be a reliable source to characterize forest structure. The specific case of Study I presents how ALS data support the estimates of a common forest parameter, in such case forest above ground biomass (AGB), using field data gathered in a novel two-phase tessellation stratified sampling (TSS) design.
In order to be used as a valid source of information for planning conservation strategies, along with the estimation, a detailed map showing the spatial patterns of structural diversity is of great usefulness. Study II presents an extensive meta-analysis carried out during the doctoral time frame where is demonstrated that the non-parametric k-NN is, among the others, the most used and effective technique to spatial predict and map forest attributes, alone or combined together to form synthetic indices. This technique can be further improved implementing an optimization step aimed to set the k-NN parameters in order to achieve the best prediction performance possible. Study III demonstrates that, if an optimization phase is carried out before running the k-NN procedure, the performance in the predictions improved sensibly.
In the second and last section, the methods experimented in the first section are applied in two different research studies. Study IV describes the use of ALS data and ground data for the areal estimate of mean values of two forest structural diversity indices in a model-assisted framework. Along with the areal estimates, the study proposes the calculation of the confidence intervals of such estimates and the mapping of the investigated indices. Study V is framed as a methodological paper that takes a step further than Study IV, showing how, using the capability of an optimized k-NN techniques in predict simultaneously different parameters, is possible to map a more comprehensive structural diversity index (SDI) combining different forest structural diversity indices.
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Miller, Jordan Mitchell. "Estimation of individual tree metrics using structure-from-motion photogrammetry." Thesis, University of Canterbury. Geography, 2015. http://hdl.handle.net/10092/11035.
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The deficiencies of traditional dendrometry mean improvements in methods of tree mensuration are necessary in order to obtain accurate tree metrics for applications such as resource appraisal, and biophysical and ecological modelling. This thesis tests the potential of SfM-MVS (Structure-fromMotion with Multi-View Stereo-photogrammetry) using the software package PhotoScan Professional, for accurately determining linear (2D) and volumetric (3D) tree metrics. SfM is a remote sensing technique, in which the 3D position of objects is calculated from a series of photographs, resulting in a 3D point cloud model. Unlike other photogrammetric techniques, SfM requires no control points or camera calibration. The MVS component of model reconstruction generates a mesh surface based on the structure of the SfM point cloud.
The study was divided into two research components, for which two different groups of study trees were used: 1) 30 small, potted ‘nursery’ trees (mean height 2.98 m), for which exact measurements could be made and field settings could be modified, and; 2) 35 mature ‘landscape’ trees (mean height 8.6 m) located in parks and reserves in urban areas around the South Island, New Zealand, for which field settings could not be modified.
The first component of research tested the ability of SfM-MVS to reconstruct spatially-accurate 3D models from which 2D (height, crown spread, crown depth, stem diameter) and 3D (volume) tree metrics could be estimated. Each of the 30 nursery trees was photographed and measured with traditional dendrometry to obtain ground truth values with which to evaluate against SfM-MVS estimates. The trees were destructively sampled by way of xylometry, in order to obtain true volume values. The RMSE for SfM-MVS estimates of linear tree metrics ranged between 2.6% and 20.7%, and between 12.3% and 47.5% for volumetric tree metrics. Tree stems were reconstructed very well though slender stems and branches were reconstructed poorly.
The second component of research tested the ability of SfM-MVS to reconstruct spatially-accurate 3D models from which height and DBH could be estimated. Each of the 35 landscape trees, which varied in height and species, were photographed, and ground truth values were obtained to evaluate against SfM-MVS estimates. As well as this, each photoset was thinned to find the minimum number of images required to achieve total image alignment in PhotoScan and produce an SfM point cloud (minimum photoset), from which 2D metrics could be estimated. The height and DBH were estimated by SfM-MVS from the complete photosets with RMSE of 6.2% and 5.6% respectively. The height and DBH were estimated from the minimum photosets with RMSE of 9.3% and 7.4% respectively. The minimum number of images required to achieve total alignment was between 20 and 50. There does not appear to be a correlation between the minimum number of images required for alignment and the error in the estimates of height or DBH (R2 =0.001 and 0.09 respectively). Tree height does not appear to affect the minimum number of images required for image alignment (R 2 =0.08).
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DeBolt, Frederick C. "Analysis of thermal effects produced by incident laser radiation on a structure /." Online version of thesis, 1991. http://hdl.handle.net/1850/10788.
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Cotton, Charles E. "A computational study of thiocyanate based laser flash photolysis reporters." Virtual Press, 2006. http://liblink.bsu.edu/uhtbin/catkey/1348346.
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Radical chemistry has always been a very active area of research. This is due to the fact that radicals are both very numerous in variety and very reactive. A radical is any chemical species that possesses one or more unpaired electrons. These unpaired electrons usually lead to the extremely reactive characteristics of the chemical species. This reactivity can be beneficial; this is true in the case of polymer chemistry. For instance, some plastics are synthesized through a radical chain reaction. In addition, radicals are used in the synthesis of novel organic compounds with the goal of creating new pharmaceuticals. Radical reactivity can be detrimental as well; radicals have been implicated in a number of ailments including heart disease and cancer. One particular view of cancer cells is that their DNA is somehow mutated; a radical could cause this mutation. In fact, one radical species in particular is known to oxidize DNA, the hydroxyl radical.Unfortunately, the electronic structures of most radicals do not lend themselves to direct study by modem spectroscopic methods. Recently, researchers have discovered that hydroxyl radical, being very reactive in nature, easily complexes with other species. If these complexes are spectrosopically active, then we can study the radical reactivity indirectly through a "reporter" molecule. One such approach uses the transient visible absorbance of the complexes of hydroxyl radical with the thiocyanate anion. In addition, there is other experimental evidence that suggests that thiocyanate anion complexes with other radicals as well. These experiments have been very successful in improving our understanding of radical chemistry, but very little is known about the electronic structure or connectivities of these complexes.Our research is comprised of a systematic theoretical study of the structure, vibrational frequencies, and spectroscopic properties of complexes of hydroxyl radical with thiocyanate anion. In addition, we will investigate the structures, vibrational frequencies, and spectroscopic properties of complexes of thiocyanate anion and other radical species.The ultimate goal of our research is to determine the feasibility of utilizing thiocyanate anion as an LFP reporter for radical species other than hydroxyl radical.Our theoretical approach is based in computerized, mathematical models of the properties of the species being studied, based on quantum mechanics and density functional theory as implemented in the computational chemistry software Gaussian 03. Our study includes calculations that provide the energies, optimized geometry, vibrational frequencies, charge and spin densities, and other properties of the various species. This consists of the various isolated radicals and anions, complexes, transitions states, pre-reactive complexes, and structural isomers.<br>Department of Chemistry
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Allouche, Billal. "Étude de composés à structure TTB en couches minces et multicouches." Electronic Thesis or Diss., Amiens, 2015. http://www.theses.fr/2015AMIE0007.
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Trois composés de structure Bronze de Tungstène Quadratique ont été étudiés sous forme de couches minces élaborées par ablation laser. Il s'agit de Pb2KNb5O15 (PKN), GdK2Nb5O15 (GKN) et K3Li2Nb5O15 (KLN). Les deux premiers composés correspondent aux compositions extrêmes (x = 0 et x = 1) choisies à partir de la solution solide Pb2(1-x)K(1+x)GdxNb5O15 (PKGN) étudiée au préalable sous forme de céramique au LPMC. Ces composés ont été déposés avec succès sur les trois substrats STO, MgO et GG. La température de dépôt a été établie pour être supérieure ou égale à 700°C, tandis que l'orientation et la qualité cristalline des couches dépendent de la pression partielle d'oxygène, variant de 0,01 à 0,3 mbar. Les propriétés cristallographiques et les relations d'épitaxie ont été analysées au moyen d'un diffractomètre 4-cercles implanté au sein du LPMC. La couche de GKN s'épitaxie (001) sur les deux substrats, MgO et STO, avec des microstructures différentes. La maille GKN est contractée sur les deux substrats et ne présente aucune transition de phase en dessous de 600°C. Elle présente, en dessous de 140°C, une commutation résistive avec une bonne endurance et une rétention moyenne. La couche de PKN est orientée [001] à basse pression et [530] à haute pression, sur le même substrat platiné (STO ou GG) ou sur un substrat MgO non tamponné. La couche de KLN orientée [001] a montré aussi une bonne qualité cristalline sur le substrat MgO. Les couches de GKN et de PKN sont transparentes dans le visible. Celles de GKN et KLN présentent des propriétés ferroélectriques macroscopiques. L'association de GKN et BT en superréseaux n'ont pas permis d'amplifier la réponse ferroélectrique<br>Three compounds with Tetragonal Tungsten Bronze (TTB) type struc-ture were studied as thin films grown by Pulsed Laser Deposition from pure oxide ceramics. These compounds are Pb2KNb5O15 (PKN), GdK2Nb5O15 (GKN) and K3Li2Nb5O15 (KLN). PKN and GKN correspond to the compositions (x = 0 and x = 1) selected from the solid solution Pb2(1-x)K(1+x)GdxNb5O15 (PKGN), previously studied as ceramics in LPMC. The deposition parameters were optimized to grow oriented thin films. The films were integrated in parallel plate capacitor structures in order to evaluate their electrical properties. GKN film was successfully epitaxially grown on two different substrates, MgO and STO, with different microstructures. GKN unit cell is oriented [001] and is under stress that removed the phase transition and led to resistive switching in GKN films. Promising endurance and retention performances were been demonstrated below 140°C. The obtained films suffer initially from leakage current that was reduced by thermal treatment in oxygen rich atmosphere. Indeed, leakage and resistive switching were found due to oxygen vacancies created during the deposition process. The orientation of PKN thin film was also controlled on Pt coated substrates. [001] ([530]) orientation was achieved using low (high) pressure during the growth process. Crystalline quality of KLN [001] thin film was significantly enhanced using MgO substrate. CV measurements performed on different films, demonstrate the ferroelectric properties in GKN and KLN thin films. However, Coupling GKN and BT in superlattices did not allow enhanced ferroelectric properties. Transparency of GKN and PKN films was demonstrated and their different optical parameters were determined
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Allouche, Billal. "Étude de composés à structure TTB en couches minces et multicouches." Thesis, Amiens, 2015. http://www.theses.fr/2015AMIE0007/document.
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Trois composés de structure Bronze de Tungstène Quadratique ont été étudiés sous forme de couches minces élaborées par ablation laser. Il s'agit de Pb2KNb5O15 (PKN), GdK2Nb5O15 (GKN) et K3Li2Nb5O15 (KLN). Les deux premiers composés correspondent aux compositions extrêmes (x = 0 et x = 1) choisies à partir de la solution solide Pb2(1-x)K(1+x)GdxNb5O15 (PKGN) étudiée au préalable sous forme de céramique au LPMC. Ces composés ont été déposés avec succès sur les trois substrats STO, MgO et GG. La température de dépôt a été établie pour être supérieure ou égale à 700°C, tandis que l'orientation et la qualité cristalline des couches dépendent de la pression partielle d'oxygène, variant de 0,01 à 0,3 mbar. Les propriétés cristallographiques et les relations d'épitaxie ont été analysées au moyen d'un diffractomètre 4-cercles implanté au sein du LPMC. La couche de GKN s'épitaxie (001) sur les deux substrats, MgO et STO, avec des microstructures différentes. La maille GKN est contractée sur les deux substrats et ne présente aucune transition de phase en dessous de 600°C. Elle présente, en dessous de 140°C, une commutation résistive avec une bonne endurance et une rétention moyenne. La couche de PKN est orientée [001] à basse pression et [530] à haute pression, sur le même substrat platiné (STO ou GG) ou sur un substrat MgO non tamponné. La couche de KLN orientée [001] a montré aussi une bonne qualité cristalline sur le substrat MgO. Les couches de GKN et de PKN sont transparentes dans le visible. Celles de GKN et KLN présentent des propriétés ferroélectriques macroscopiques. L'association de GKN et BT en superréseaux n'ont pas permis d'amplifier la réponse ferroélectrique<br>Three compounds with Tetragonal Tungsten Bronze (TTB) type struc-ture were studied as thin films grown by Pulsed Laser Deposition from pure oxide ceramics. These compounds are Pb2KNb5O15 (PKN), GdK2Nb5O15 (GKN) and K3Li2Nb5O15 (KLN). PKN and GKN correspond to the compositions (x = 0 and x = 1) selected from the solid solution Pb2(1-x)K(1+x)GdxNb5O15 (PKGN), previously studied as ceramics in LPMC. The deposition parameters were optimized to grow oriented thin films. The films were integrated in parallel plate capacitor structures in order to evaluate their electrical properties. GKN film was successfully epitaxially grown on two different substrates, MgO and STO, with different microstructures. GKN unit cell is oriented [001] and is under stress that removed the phase transition and led to resistive switching in GKN films. Promising endurance and retention performances were been demonstrated below 140°C. The obtained films suffer initially from leakage current that was reduced by thermal treatment in oxygen rich atmosphere. Indeed, leakage and resistive switching were found due to oxygen vacancies created during the deposition process. The orientation of PKN thin film was also controlled on Pt coated substrates. [001] ([530]) orientation was achieved using low (high) pressure during the growth process. Crystalline quality of KLN [001] thin film was significantly enhanced using MgO substrate. CV measurements performed on different films, demonstrate the ferroelectric properties in GKN and KLN thin films. However, Coupling GKN and BT in superlattices did not allow enhanced ferroelectric properties. Transparency of GKN and PKN films was demonstrated and their different optical parameters were determined
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Wang, Xi. "Studies on Property and Structure Modification of Inorganic Glasses with Femtosecond Laser." 京都大学 (Kyoto University), 2011. http://hdl.handle.net/2433/151983.
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Whitaker, Iain Robert. "The structure and properties of autogenous laser beam welds in aluminium alloys." Thesis, University of Nottingham, 1994. http://eprints.nottingham.ac.uk/28427/.
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Autogenous laser beam welds were made in sheets of the aluminium alloys 8090, 8009 and 6061. The Al-Li based alloy 8090 was subjected to both continuous wave CO2 and pulsed Nd:YAG thermal cycles with average powers of 1.5-3.8 kW and 0.8- 0.9 kW respectively. The two techniques were compared for their influence on the 8090 solidified weld pool shape, the fusion zone microstructure and microhardness, the HAZ and the susceptibility of the fusion zone to post-weld heat treatment. It was found that CO2 keyhole welding is preferable to Nd:YAG welding, under the welding conditions investigated, as essential elements such as Li and Mg were lost by evaporation during Nd:YAG processing. Microscopy of the 8090 CO2 weld fusion zone revealed that the solidification mode was sensitive both to the temperature gradient and growth rate during solidification, with a transformation from cellular to equiaxed dendritic growth occurring from the weld pool edge to the weld centre. The secondary dendrite arm spacing was found to be 2-5µm and the metastable phase δ (Al3Li) was present after welding with a very fine homogeneous distribution of -5nm diameter spheres. Porosity was identified as a major welding defect and was attributed to two distinct formation mechanisms. Firstly, the release of hydrogen gas during welding caused spherical gas bubbles throughout the weld pool. Secondly, the delicate balance of forces within the keyhole resulted in larger irregular shaped pores at the weld centre-line towards the weld root. This second type of pore was virtually absent in full penetration welds. The influence of heating rate to the solution treatment temperature on 8090 CO2 weld metal was assessed and the weld metal grain size was found to be most uniformly small after a heating rate of 1 K/min. A TEM investigation confirmed that the grain boundary pinning dispersoid β(Al3Zr) was responsible for inhibiting grain growth. However, the microhardness and notch-tensile strength of the CO2 weld metal did not depend on the weld metal grain size. Instead, it was suggested that the residual cast structure was responsible for determining the mode of failure and fracture strength. Microstructural studies of CO2 laser welds in RSIPM 8009 and wrought 6061 confirmed the cooling rate of 102-103 K/s predicted for CO2 welds in 8090. However, the 8009 CO2 weld metal did not solidify by epitaxial growth from the fusion boundary, which was the case for CO2 welds in 8090 and 6061. Instead, solidification in 8009 weld pools occurred via many isolated events on primary intermetallic particles. The intermetallic particles had the stoichiometry Al4.5(Fe,V,Si) with the AI.mFe tetragonal lattice parameters. It was qualitatively shown that the 8009 weld microhardness had an inverse relationship with the volume fraction of intermetallic particles. Chemical analysis of the 6061 weld metal confirmed that even when aluminium is alloyed with volatile elements such as Mg it is mostly retained within the weld pool during CO2 keyhole laser welding. It was found that a much higher power was required to obtain a deep penetration weld in 6061 than in either of the other alloys.
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盧志偉 and Chi-wai Lo. "Improvement of semiconductor laser diodes' characteristics by using diffused quantum wells structure." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1997. http://hub.hku.hk/bib/B31215592.
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Lavvafi, Hossein. "EFFECTS OF LASER MACHINING ON STRUCTURE AND FATIGUE OF 316LVM BIOMEDICAL WIRES." Case Western Reserve University School of Graduate Studies / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=case1352743353.
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Kurian, Sachin. "Process-Structure-Property Relationship Study of Selective Laser Melting using Molecular Dynamics." Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/104115.
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Selective Laser Melting (SLM), a laser-based Additive Manufacturing technique has appealed to the bio-medical, automotive, and aerospace industries due to its ability to fabricate geometrically complex parts with tailored properties and high-precision end-use products. The SLM processing parameters highly influence the part quality, microstructure, and mechanical properties. The process-structure-property relationship of the SLM process is not well-understood. In the process-structure study, a quasi-2D model of Micro-Selective Laser Melting process using molecular dynamics is developed to investigate the localized melting and solidification of a randomly-distributed Aluminum nano-powder bed. The rapid solidification in the meltpool reveals the cooling rate dependent homogeneous nucleation of equiaxed grains at the center of the meltpool. Long columnar grains that spread across three layers, equiaxed grains, nano-pores, twin boundaries, and stacking faults are observed in the final solidified nanostructure obtained after ten passes of the laser beam on three layers of Aluminum nano-powder particles. In the structure-property study, the mechanical deformation behavior of the complex cellular structures observed in the SLM-fabricated 316L Stainless Steel is investigated by performing a series of molecular dynamics simulations of uniaxial tension tests. The effects of compositional segregation of alloying elements, distribution of austenite and ferrite phases in the microstructure, subgranular cell sizes, and pre-existing (grown in) nano-twins on the tensile characteristics of the cellular structures are investigated. The highest yield strength is observed when the Nickel concentration in the cell boundary drops very low to form a ferritic phase in the cell boundary. Additionally, the subgranular cell size has an inverse relationship with mechanical strength, and the nano-twinned cells exhibit higher strength in comparison with twin-free cells.<br>Master of Science<br>Additive Manufacturing's (AM) rise as a modern manufacturing paradigm has led to the proliferation in the number of materials that can be processed, reduction in the cost and time of manufacturing, and realization of complicated part geometries that were beyond the capabilities of conventional manufacturing. Selective Laser Melting (SLM) is a laser-based AM technique which can produce metallic parts from the fusion of a powder-bed. The SLM processing parameters greatly influence the part's quality, microstructure, and properties. The process-structure-property relationship of the SLM process is not well-understood. In-situ experimental investigation of the physical phenomena taking place during the SLM process is limited because of the very small length and time scales. Computational methods are cost-effective alternatives to the challenging experimental techniques. But, the continuum-based computational models are ineffective in modeling some of the important physical processes such as melting, nucleation and growth of grains during solidification, and the deformation mechanisms at the atomistic scale. Atomistic simulation is a powerful method that can offset the limitations of the continuum models in elucidating the underlying physics of the SLM process. In this work, the influence of the SLM process parameters on the microstructure of the Aluminum nano-powder particles undergoing μ-SLM processing and the mechanical deformation characteristics of the unique cellular structures observed in the SLM-fabricated 316L stainless steel are studied using molecular dynamics simulations. Ten passes of the laser beam on three layers of Aluminum nano-powder particles have unfolded the formation mechanisms of a complex microstructure associated with the SLM process. The study on the deformation mechanisms of 316L stainless steel has revealed the contribution of the cellular structures to its superior mechanical properties.
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Lo, Chi-wai. "Improvement of semiconductor laser diodes' characteristics by using diffused quantum wells structure /." Hong Kong : University of Hong Kong, 1997. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19003341.
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Taylor, Douglas John. "Structure and properties of laser-fired, sol-gel derived tungsten oxide films." Diss., The University of Arizona, 1995. http://hdl.handle.net/10150/187173.
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This investigation focuses on the use of laser radiation to fire sol-gel derived oxide films. The main emphasis of this work was to make high quality tungsten oxide films with good electrochromic properties. Laser firing was done with a carbon dioxide laser operated in continuous mode. The laser-fired tungsten oxide films were measured for density, composition, crystallinity and electrochromic behavior. Analytical tools included multi-angle ellipsometry, FTIR, TEM, XRD, spectrophotometry and electrochemistry. The effect of process variables (laser power, spot size and translation speed) on the extent of film densification and microstructural evolution was investigated. Thermal modeling of laser-heated sol-gel films was studied to further understand the laser firing process and to estimate firing temperatures. Temperature calculations were based on laser parameters, sample geometry and target materials. Properties characteristic of firing temperature were used to verify the thermal modeling. For laser-fired films, the properties at the calculated temperatures agreed well with the properties of similar furnace-fired films. The modeling also provided the thermal profiles seen by the laser heated materials. Laser firing was shown to be a feasible technique to make good quality electrochromic films. By precisely controlling the irradiation, the microstructure of tungsten oxide films was tailored to produce the desired electrochromic properties. Transmission electron microscopy showed film microstructures that varied from completely amorphous to fully crystalline. Corresponding optoelectrochemical measurements indicated a decrease in electrochromism with increasing crystallinity. The effects of density/porosity and coating composition are also discussed. It is proposed that laser firing of sol-gel derived films can be used for optics, sensors, graded index materials, and electrochromic windows. The ability to heat localized regions afforded by laser firing is advantageous for writing lines and patterns in these films. Windows with graded electrochromic properties can be made by dynamically changing the laser firing conditions as the beam rasters through a workpiece. Similarly, electrochromic signs can be written into a window--after the pattern is written by laser densification, the remaining film is etched away, leaving the pattern.
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Golalikhani, Maryam. "Structure and electronic properties of atomically-layered ultrathin nickelate films." Diss., Temple University Libraries, 2015. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/353844.
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Physics<br>Ph.D.<br>This work presents a study on stoichiometry and structure in perovskite-type oxide thin films and investigates the role of growth–induced defects on the properties of materials. It also explores the possibility to grow thin films with properties close or similar to the ideal bulk parent compound. A novel approach to the growth of thin films, atomic layer-by-layer (ALL) laser molecular beam epitaxy (MBE) using separate oxide targets is introduced to better control the assembly of each atomic layer and to improve interface perfection and stoichiometry. It also is a way to layer materials to achieve a new structure that does not exist in nature. This thesis is divided into three sections. In the first part, we use pulsed laser deposition (PLD) to grow LaAlO3 (LAO) thin films on SrTiO3 (STO) and LAO substrates in a broad range of laser energy density and oxygen pressure. Using x-ray diffraction (θ-2θ scan and reciprocal space mapping), transmission electron microscopy (TEM) and x-ray fluorescence (XRF) we studied stoichiometry and structure of LAO films as a function of growth parameters. We show deviation from bulk–like structure and composition when films are grown at oxygen pressures lower than 10-2 Torr. We conclude that the discussion of LAO/STO interfacial properties should include the effects of growth–induced defects in the LAO films when the deposition is conducted at low oxygen pressures, as is typically reported in the literature. In the second part, we describe a new approach to atomically layer the growth of perovskite oxides: (ALL) laser MBE, using separate oxide targets to grow materials as perfectly as possible starting from the first atomic layer. We use All laser MBE to grow Ruddlesden–Popper (RP) phase Lan+1NinO3n+1 with n = 1, 2, 3 and 4 and we show that this technique enables us to construct new layered materials (n=4). In the last and main section of this thesis, we use All laser MBE from separate oxide targets to build the LaNiO3 (LNO) films as near perfectly as possible by depositing one atomic layer at a time. We study the thickness dependent metal-insulator transition (MIT) in ultrathin LNO films on an LAO substrate. In LNO, the MIT occurs in thin films and superlattices that are only a few unit cells in thickness, the understanding of which remains elusive despite tremendous effort devoted to the subject. Quantum confinement and structure distortion have been evoked as the mechanism of the MIT; however, first-principle calculations show that LaNiO3 remains metallic even at one unit cell thickness. Here, we show that thicknesses of a few unit cells, growth–induced disorders such as cation stoichiometry, oxygen vacancies, and substrate-film interface quality will impact the film properties significantly. We find that a film as thin as 2 unit cells, with LaO termination, is metallic above 150 K. An oxygen K-edge feature in the x-ray absorption spectra is clearly inked to the transition to the insulating phase as well as oxygen vacancies. We conclude that dimensionality and strain are not sufficient to induce the MIT without the contribution of oxygen vacancies in LNO ultrathin films. Dimensionality, strain, crystallinity, cation stoichiometry, and oxygen vacancies are all indispensable ingredients in a true control of the electronic properties of nanoscale strongly–correlated materials.<br>Temple University--Theses
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Qian, Bin. "Laser sintered materials with Non-equilibrium structures." Doctoral thesis, Stockholms universitet, Institutionen för material- och miljökemi (MMK), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-101096.
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This thesis is focused on achieving materials with non-equilibrium structures fabricated by high-energy laser sintering. The chosen precursor materials have rigid and inert structures like high-melting point ceramics or metals. It was necessary to use real-time monitoring of temperature and spectrum profiles for selecting the optimal laser parameters for the laser sintering process. This monitoring was done by an off-axial setup that also controls the surface morphologies during the laser irradiation process. The laser focal spot receives very high temperatures and subsequent extreme cooling rates within a short time period. New non-equilibrium structures will emerge ruled by kinetics, huge temperature gradients or stresses and freeze by quenching in solid state. These material structures were found to form at different length scales from nano- to macro-level, frequently by a hierarchical ordering. This opens a method to engineer materials with both hierarchical and non-equilibrium structures by a single operation in both metal and ceramics by laser sintering. In the Co-Cr-Mo alloy system, structures on three levels of lengths were observed, namely i) nano-level structures dominated by the grain boundary segregation; ii) micron-level structures characterized by the interlocked clusters of columns; and iii) macro-level structures defined by the selected laser scan patterns. The non-equilibrium structures of the Co-Cr-Mo alloy are related to mechanical, corrosion and bio-compatibility properties. In ZrO2 ceramics, the final product had a non-equilibrium nano- and micron-sized structure created by uneven absorption of laser energy and rupture. The structure inside the micron-sized grains is formed through ordered coalescence of nano-crystals. Properties of the laser sintered materials were established and related to the observed structures. The materials properties might be tailored by controlling the structures in different levels and potential applications of the new materials will be given.<br><p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Accepted. Paper 3: Accepted. Paper 4: Submitted. Paper 5: Manuscript.</p>
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Kley, Markus. "Development of dispersion relationships for layered cylinders using laser ultrasonics." Thesis, Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/20846.
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Critchley, Andrew Duncan James. "Structure of free radicals." Thesis, University of Newcastle Upon Tyne, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327188.
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Fathalah, Ahmed A. A. "Microstructural Observations of Laser-Sintered Specimens for Prosthodontic Applications." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1366286613.
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Khazaei, Hamid Reza. "III-V high-speed electro-optic laser modulators using slow wave structure technique." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0019/NQ48886.pdf.
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Skinner, Lawrie Basil. "Structure and phase behaviour of aluminate glasses, produced using levitation and laser heating." Thesis, University of Bristol, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.495812.
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In this thesis aluminate glasses have been made using aerodynamic levitation and laser heating techniques. Three sub-systems are studied in detail. First the structure of (Nd₂0₃)o.₃₇₅(Al₂0₃)o.₆₂₅ (Nd₃Al₅0₁₂) glass was measured by neutron and x-ray diffraction techniques at the first order difference level. Using this data full structural models consistent with the diffraction measurements were made. From these Nd₃Al₅0₁₂ glass is found to consist of predominantly tetrahedral AlO, with on average 0.8 non-bridging oxygen per tetrahedron. The Average Nd-0 coordination is found to be 7.0(2), which results form a combination of 6.2(2) Nd-0 at 2.42(4)A and a further 1.2(2) Nd at 2.7(4)A, No significant amount of Nd-0 is found at the longer 2.91A crystal structure distance.
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Studer, Dominik [Verfasser]. "Probing atomic and nuclear structure properties of promethium by laser spectroscopy / Dominik Studer." Mainz : Universitätsbibliothek Mainz, 2020. http://d-nb.info/1212691989/34.
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Le, Blanc François. "La Spectroscopie laser appliquée à la physique nucléaire." Habilitation à diriger des recherches, Université Paris-Diderot - Paris VII, 2001. http://tel.archives-ouvertes.fr/tel-00001401.
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L'étude de la forme du noyau atomique est un sujet fondamental puisqu'elle constitue un excellent laboratoire pour tester et valider les différents modèles nucléaires. La mesure du moment quadrupolaire électrique et du rayon de charge nucléaire (signant tous deux la forme du noyau) et du moment dipolaire magnétique, apporte des renseignements précieux pour déterminer la structure nucléaire. En particulier, les valeurs des moments magnétiques sont importantes à caractériser car elles sont fortement liées au degré de pureté des fonctions d'onde décrivant une configuration nucléaire donnée. La spectroscopie atomique, et plus particulièrement la spectroscopie laser, est un moyen précis et inhabituel pour caractériser des observables liées à la forme du noyau : on extrait la variation du rayon de charge entre deux noyaux à partir du déplacement isotopique et le moment quadrupolaire à l'aide de la structure hyperfine ; on observe le noyau à partir du cortège électronique. Depuis plus de 10 ans, nous avons fondé un groupe de spectroscopie laser à l'IPN d'Orsay en collaboration avec le Laboratoire Aimé Cotton d'Orsay, l'université McGill à Montréal et l'Institut de Physique de Mayence. Nous avons ainsi construit un système expérimental baptisé PILIS à Orsay puis COMPLIS au CERN pour étudier la forme des noyaux loin de la vallée de stabilité. Grâce aux résultats obtenus avec cet ensemble expérimental, 7 thèses (une canadienne, trois allemandes et deux françaises) ont été soutenues sur les noyaux d'or, de platine et d'iridium. Un développement du système et une nouvelle de mesure sur les noyaux d'étain riches en neutrons viennent de débuter et doivent faire l'objet d'une nouvelle thèse.
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Augier, Frédéric. "Structure locale du champ hydrodynamique dans les écoulements dispersés liquide-liquide concentrés." Toulouse, INPT, 2001. http://www.theses.fr/2001INPT009G.
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L'objectif de ce travail est de caractériser la structure du champ hydrodynamique dans deux écoulements dispersés liquide-liquide de type homogène et de zone de mélange, par les mesures locales, simultanées et instantanées des champs de vitesse des deux phases, de la fraction volumique et du diamètre des gouttes. Ces mesures sont menées pour des fractions volumiques de la phase dispersée pouvant atteindre 40%, à l'aide d'une technique originale adaptée de la Vélocimétrie par Images de Particules en milieu optiquement homogène, développée et validée dans le cadre de ce travail. Les phases continue (mélange eau-glycérol) et dispersée (heptane) sont localement différenciées par la présence dans la phase continue d'un traceur fluorescent (rhodamine 6G). La technique est d'abord appliquée à l'étude d'écoulements homogènes co-courants dans l'objectif de caractériser l'influence de la fraction volumique de la phase dispersée sur la force de traînée diphasique et sur la turbulence des deux phases. Les résultats expérimentaux sont comparés à des modèles existants et /ou à des données de la littérature. Des éléments intéressants concernant la structure instantanée du champ hydrodynamique sont mis en évidence. Dans un deuxième temps, des zones de mélange diphasiques présentant, soit un gradient de vitesse, soit un gradient de fraction volumique, font l'objet de mesures locales par la même technique. Dans le premier cas, on constate que, par rapport au cas monophasique, la présence de la phase dispersée conduit à une expansion plus rapide de la zone de mélange et à une sensible modification de la turbulence produite par le cisaillement. Dans le deuxième cas, l'écoulement est piloté par les variations à grande échelle de la densité du mélange. Enfin, des comparaisons avec des simulations numériques sont effectuées afin d'évaluer la capacité d'outils numériques actuels à prédire ces différents écoulements liquide-liquide.
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Casale, Marco. "Réalisation d'un laser DFB hybride sur substrat de verre." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENT011/document.
Full textAbstract:
Les besoins actuels des systèmes de télécommunications et des capteurs optiques poussent à réaliser des circuits intégrés optiques présentant toujours plus de fonctions sur un même substrat. Atteindre un tel niveau d'intégration est difficile, car les matériaux et les procédés technologiques employés pour implémenter les différentes fonctions optiques ne sont pas toujours compatibles entre eux. Cette thèse s'inscrit dans la problématique de l'intégration des fonctions optiques actives (émission, amplification) et passives (multiplexage, filtrage, etc.) sur substrat passif et reporte la réalisation d'un laser DFB hybride tridimensionnel par échange d'ions sur verre passif et report de plaque d'un verre actif codopé Er3+:Yb3+. Ce laser est constitué d'un guide canal de Bragg, sélectivement enterré dans le substrat passif, et chargé par un guide plan, réalisé dans le verre actif (dopé avec une concentration massique de 2,3% en Er2O3 et 3,6% en Yb2O3). Il est caractérisé par une émission monomode de (420±15) µW à 1534 nm, pour (390±20) mW de puissance de pompe injectée. Ce dispositif ouvre ainsi la voie vers l'intégration de fonctions actives, localisées à la surface du substrat passif, avec des fonctions passives, réalisées en exploitant le volume et la surface du même substrat<br>The current needs of optical telecommunications and sensors require developing integrated optical circuits providing different and heterogeneous functions on the same substrate. The main issue is the incompatibility between the manufacturing processes of these optical functions. This work deals with the integration of active (emission, amplification) and passive (multiplexing, filtering, etc.) functions on a passive glass substrate. Its aim is to develop a DFB three-dimensional hybrid laser by ion-exchange in passive glass. This laser is made of a Bragg channel waveguide, selectively buried in the passive glass substrate, loaded by a plane waveguide, defined at the surface of an Er3+:Yb3+ codoped active glass wafer. It emits a (420±15) µW laser signal at 1534 nm for (390±20) mW injected pump power. Hence this device opens the way towards the integration of active functions, located at the surface of the passive glass substrate, with passive ones, spreading at its surface and in its volume
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Masbernat, Olivier. "Structure d'un écoulement dispersé liquide-liquide à contre-courant." Toulouse, INPT, 1989. http://www.theses.fr/1989INPT026G.
Full textAbstract:
Le travail de recherche conduit dans le cadre de cette these a pour objet l'etude theorique et experimentale de l'hydrodynamique d'un ecoulement disperse liquide-liquide a contre-courant en conduite verticale. Le but de ce travail est de contribuer a l'amelioration de la connaissance, a l'echelle locale, des mecanismes fondamentaux de transport de masse, de quantite de mouvement, d'energie et des proprietes geometriques internes de l'ecoulement en milieu diphasique. Le cas particulier traite est une dispersion fluidisee a contre-courant d'un ecoulement d'eau descendant. Sur le plan experimental, les investigations en ecoulement liquide-liquide (mesure de vitesse, taux de presence et turbulence) necessite une metrologie et un traitement du signal approprie, dans le but de discriminer les informations provenant de chacune des phases. Nous avons developpe une technique nouvelle de mesure simultanee de vitesse et de taux de presence, utilisant l'anemometrie-doppler laser ainsi qu'une sonde capacitive hyperfrequence. Sur le plan theorique, nous avons choisi l'approche du modele a deux fluides dans lequel nous avons pris en compte le transport de la turbulence et la distribution des tailles de gouttes suivant l'axe de l'ecouldmdng; cette modelisation nous a conduits a une simulation de l'ecoulement etudie
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Lee, Alex C., and alexanderlee@aapt net au. "Utilising airborne scanning laser (LiDAR) to improve the assessment of Australian native forest structure." The Australian National University. Fenner School of Environment and Society, 2008. http://thesis.anu.edu.au./public/adt-ANU20090127.222600.
Full textAbstract:
Enhanced understanding of forest stocks and dynamics can be gained through improved forest measurement, which is required to assist with sustainable forest management decisions, meet Australian and international reporting needs, and improve research efforts to better respond to a changing climate. Integrated sampling schemes that utilise a multi-scale approach, with a range of data sourced from both field and remote sensing, have been identified as a way to generate the required forest information. Given the multi-scale approach proposed by these schemes, it is important to understand how scale potentially affects the interpretation and reporting of forest from a range of data.
¶
To provide improved forest assessment at a range of scales, this research has developed a strategy for facilitating tree and stand level retrieval of structural attributes within an integrated multi-scale analysis framework. The research investigated the use of fine-scale (~1m) airborne Light Detection and Ranging (LiDAR) data (1,125 ha in central Queensland, and 60,000 ha in NE Victoria) to calibrate other remotely sensed data at the two study sites. The strategy refines forest structure mapping through three-dimensional (3D) modelling combined with empirical relationships, allowing improved estimation of maximum and predominant height, as well as foliage and crown cover at multiple scales. Tree stems (including those in the sub-canopy) were located using a height scaled crown openness index (HSCOI), which integrated the 3D density of canopy elements within the vertical profile into a two-dimensional spatial layer. The HSCOI modelling also facilitated the reconstruction of the 3D distribution of foliage and branches (of varying size and orientation) within the forest volume.
¶
Comparisons between forests at the Queensland and NE Victorian study sites indicated that accurate and consistent retrieval of cover and height metrics could be achieved at multiple scales, with the algorithms applicable for semi-automated use in other forests with similar structure. This information has facilitated interpretation and evaluation of Landsat imagery and ICESat satellite laser data for forest height and canopy cover retrieval. The development of a forest cover translation matrix allows a range of data and metrics to be compared at the plot scale, and has initiated the development of continuous transfer functions between the metrics and datasets. These data have been used subsequently to support interpretation of SAR data, by providing valuable input to 2D and 3D radar simulation models. Scale effects have been identified as being significant enough to influence national forest class reporting in more heterogeneous forests, thus allowing the most appropriate use and integration of remote sensed data at a range of scales. An empirically based forest minimum mapping area of 1 ha for reporting is suggested. The research has concluded that LiDAR can provide calibration information just as detailed and possibly more accurately than field measurements for many required forest attributes. Therefore the use of LiDAR data offers a unique opportunity to bridge the gap between accurate field plot structural information and stand to landscape scale sampling, to provide enhanced forest assessment in Australia.
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Jamison, Steven P. "Laser site-selective spectroscopy of rare-earth ions in crystals of the fluorite structure." Thesis, University of Canterbury. Physics, 1998. http://hdl.handle.net/10092/8172.
Full textAbstract:
Site-selective laser spectroscopy, Zeeman infrared and optical absorption have been employed to investigate trivalent dysprosium centers in rare-earth doped alkaline-earth fluoride crystals. These studies have characterised the two dominant centers in SrF₂:Dy³⁺ which are determined to be the fluorine compensated C₄ᵥ and C₃ᵥ centers analogous to those observed in other SrF₂:RE³⁺ systems. The C₃ᵥ center is shown to correspond to the J-center of Sr₁:Er³⁺, rather than the B-center reported for SrF₂:Ho³⁺. In CaF₂:Dy³⁺ three single Dy³⁺ ion centers have been characterised, corresponding to the C₄ᵥ , C₃ᵥ and cubic centers. Cluster centers involving more than one Dy³⁺ ion are also present in CaF₂:0.05%Dy³⁺, and such centers undergo efficient non-radiative cross-relaxation. This cross-relaxation eliminates the possibility of a direct investigation of the laser spectroscopy of these cluster centers, leading to the consideration of double doped systems. The laser spectroscopy of CaF₂:Dy³⁺:Eu³⁺ reveals a cluster center with efficient Dy³⁺→’Eu³⁺ energy transfer. Through a correlation of the Eu³⁺ fluorescence with previous studies of CaF₂:Eu³⁺ this center has been determined to be a heterogeneous R-center dimer. The double doped CaF₂:Dy³⁺:Gd³⁺ system has enabled the Dy³⁺ R-center fluorescence to be investigated. The polarised fluorescence of the C₄ᵥ centers in CaF₂:Dy³⁺ and SrF₂:Dy³⁺ has been analysed in terms of both electric dipole and magnetic dipole transition moments, from which it is shown that magnetic dipole processes are significant for Dy³⁺ fluorescence.
The temperature dependence of fluorescence polarisation in praseodymium and europium doped CaF₂ and SrF₂ has been employed to investigate ionic motion in the C₄ᵥ centers. These experiments have enabled the barrier energies for interstitial reorientation to be determined in a site-selective manner. An anomalous temperature dependence of the polarisation anisotropy is observed in the Pr³⁺ C₄ᵥ centers, and has been shown to be a consequence of energy transfer between the C₄ᵥ centers.
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Aquilina, Charles Albert. "Estimating Floodplain Vegetative Roughness using Drone-Based Laser Scanning and Structure from Motion Photogrammetry." Thesis, Virginia Tech, 2008. http://hdl.handle.net/10919/99795.
Full textAbstract:
We compared high-resolution drone laser scanning (DLS) and structure from motion (SfM) photogrammetry-derived vegetation heights at the Virginia Tech StREAM Lab to determine Manning's roughness coefficient. We utilized two calibrated approaches and a calculated approach to estimate roughness from the two data sets (DLS and SfM), then utilized them in a two-dimensional (2D) hydrodynamic model (HEC-RAS). The calculated approach used plant characteristics to determine vegetative roughness, while the calibrated approaches involved adjusting roughness values until model outputs approached values of field data (e.g., velocity probe and visual observations). We compared the model simulations to seven actual high-flow events during the fall of 2018 and 2019 using measured field data (velocity sensors, groundwater well height, marked flood extents). We used a t-test to find that all models were not significantly different to water surface elevations from our 18 wells in the floodplain (p > 0.05). There was a decrease in RMSE (-0.02 m) using the calculated compared to the calibrated models. Another decrease in RMSE was found for DLS compared to SfM (-0.01 m). This increase might not justify the increased cost of a DLS setup over SfM (~$150,000 versus ~$2,000), though future studies are needed. Our results inform hydrodynamic modeling efforts, which are becoming increasingly important for management and planning as we experience increasing high-flow events in the eastern United States due to climate change.<br>Master of Science<br>We compared high-resolution drone laser scanning (DLS) and structure from motion (SfM) photogrammetry-derived vegetation heights at the Virginia Tech StREAM Lab to improve flood modeling. DLS uses laser pulses to measure distances to create a three-dimensional (3D) point cloud of the landscape. SfM combines overlapping aerial images to create a 3D point cloud. Each method has limitations, such as cost (DLS) and accuracy (SfM). These remote sensing methods have been increasingly used to provide inputs to flood models, due to lower cost, and increased accuracy compared to airplane or satellite-based surveys. Quantifying roughness or resistance to flow can be extremely difficult and results in flood model accuracy problems. We used two forms of a calibrated approach, and a calculated approach to estimate roughness from the two data sets (DLS and SfM) which were then used in a two-dimensional (2D) flood model. We compared the model results to measured field data from seven actual high-flow events in Fall 2018 and 2019. We used statistics to determine compare the various techniques. We found that model results were not significantly different from measured water-surface elevations measured in the floodplain during floods. We also used root mean square error (RMSE) to measure the differences between modeled and observed data. There was slight decrease (-0.02 m) in error when comparing model results using the calculated and calibrated techniques. The error also decreased (-0.01 m) for simulations using the DLS versus SfM data sets. The improved accuracy due to the use of DLS might not be justified based on the increased cost of a DLS setup to SfM (~$150,000 versus ~$2,000), though future studies are needed. Insights from this analysis will help improve flood modeling, particularly as we plan for increasing high-flow events in the eastern Unites States due to climate change.
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Aquilina, Charles A. "Estimating Floodplain Vegetative Roughness using Drone-Based Laser Scanning and Structure from Motion Photogrammetry." Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/99795.
Full textAbstract:
We compared high-resolution drone laser scanning (DLS) and structure from motion (SfM) photogrammetry-derived vegetation heights at the Virginia Tech StREAM Lab to determine Manning's roughness coefficient. We utilized two calibrated approaches and a calculated approach to estimate roughness from the two data sets (DLS and SfM), then utilized them in a two-dimensional (2D) hydrodynamic model (HEC-RAS). The calculated approach used plant characteristics to determine vegetative roughness, while the calibrated approaches involved adjusting roughness values until model outputs approached values of field data (e.g., velocity probe and visual observations). We compared the model simulations to seven actual high-flow events during the fall of 2018 and 2019 using measured field data (velocity sensors, groundwater well height, marked flood extents). We used a t-test to find that all models were not significantly different to water surface elevations from our 18 wells in the floodplain (p > 0.05). There was a decrease in RMSE (-0.02 m) using the calculated compared to the calibrated models. Another decrease in RMSE was found for DLS compared to SfM (-0.01 m). This increase might not justify the increased cost of a DLS setup over SfM (~$150,000 versus ~$2,000), though future studies are needed. Our results inform hydrodynamic modeling efforts, which are becoming increasingly important for management and planning as we experience increasing high-flow events in the eastern United States due to climate change.<br>Master of Science<br>We compared high-resolution drone laser scanning (DLS) and structure from motion (SfM) photogrammetry-derived vegetation heights at the Virginia Tech StREAM Lab to improve flood modeling. DLS uses laser pulses to measure distances to create a three-dimensional (3D) point cloud of the landscape. SfM combines overlapping aerial images to create a 3D point cloud. Each method has limitations, such as cost (DLS) and accuracy (SfM). These remote sensing methods have been increasingly used to provide inputs to flood models, due to lower cost, and increased accuracy compared to airplane or satellite-based surveys. Quantifying roughness or resistance to flow can be extremely difficult and results in flood model accuracy problems. We used two forms of a calibrated approach, and a calculated approach to estimate roughness from the two data sets (DLS and SfM) which were then used in a two-dimensional (2D) flood model. We compared the model results to measured field data from seven actual high-flow events in Fall 2018 and 2019. We used statistics to determine compare the various techniques. We found that model results were not significantly different from measured water-surface elevations measured in the floodplain during floods. We also used root mean square error (RMSE) to measure the differences between modeled and observed data. There was slight decrease (-0.02 m) in error when comparing model results using the calculated and calibrated techniques. The error also decreased (-0.01 m) for simulations using the DLS versus SfM data sets. The improved accuracy due to the use of DLS might not be justified based on the increased cost of a DLS setup to SfM (~$150,000 versus ~$2,000), though future studies are needed. Insights from this analysis will help improve flood modeling, particularly as we plan for increasing high-flow events in the eastern Unites States due to climate change.
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Vrána, Radek. "STUDY OF ENERGY ABSORPTION IN MICRO – STRUT LATTICE STRUCTURE PRODUCED BY SELECTIVE LASER MELTING." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-401608.
Full textAbstract:
Předložená dizertační práce je součástí většího výzkumného projektu, který si klade za cíl využití mikro prutové konstrukce vyrobené technologií SLM jako absorbér rázové energie s přesně navrženými vlastnostmi. Hlavním cílem práce je vývoj numerického modelu deformačního chování mikro-prutové konstrukce vyrobeného technologií Selective Laser Melting (SLM) z materiálu AlSi10Mg. Aby bylo možné dosáhnout hlavního cíle dizertační práce, bylo nutné analyzovat vliv procesních parametrů technologie SLM na tvorbu vnitřních materiálových vad a drsnost povrchu při výrobě mikro-prutové konstrukce. Tyto imperfekce degradují její mechanické vlastnosti a jejich odstranění zlepší možnosti a přesnost numerické predikce. Výsledky ukazují významný vliv dvou hlavních parametrů – skenovací rychlosti laseru a výkonu laseru. Na základě těchto poznatků byly dále definovány parametry vstupní energie Ein a lineární energie Elin, které zahrnují oba zmíněné parametry a byly definovány jejich limitní hodnoty pro minimalizaci vzniklých imperfekcí. Deformační chování vyrobené mikro-prutové konstrukce bylo analyzováno na navrženém pádové zařízení, které umožňuje testování s dopadovou energií až 120 J. Deformační chování je vyhodnocováno s využitím obrazové analýzy záznamu vysoko rychlostní kamery a silového průběhu z tenzometru. Výsledky analýzy byly využity pro validaci numerického modelu v programu ANSYS Explicit, do kterého byly implementovány poznatky o reálném tvaru vyrobeného mikro-prutového materiálu ve formě eliptického modelu geometrie a informace o reálných mechanických vlastnostech ve formě vyvinutého materiálového modelu. Výsledné porovnání výsledků experimentu s predikcí numerického modelu ukazují dobrou shodu v místě maximálního zatížení Fmax (odchylka 5 %) i průběhu celé deformace vzorku. Tyto poznatky budou v budoucnu využity při návrhu absorbéru energie s definovanými mechanickými vlastnostmi.
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Tsai, Yao-Hsuan, and 蔡耀萱. "Passive Micro-Structure Laser Speckle Suppression Mechanism for Laser Scanning Projection System." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/58435815807911471680.
Full textAbstract:
碩士<br>國立臺灣科技大學<br>光電工程研究所<br>98<br>There is a major problem called Laser speckle in laser projection
display system which reduces the contrast and quality of the projection
image. In order to eliminate Laser speckle phenomena, the system
adopted nowadays applied vibrational mechanical device to make the
speckle pattern vary with time to reduce speckle contrast. These devices,
however, would perplex the system’s design and increase the cost.
In order to solve the deficiencies, we tried to find out a new method
by using the micro laser scanning projection system’s MEMS scanner as
time-varying engine. This method successfully boiled the speckle image
with only one device added into the optical path in the projection system,
and no mechanical devices was needed. In chapter 5 of the paper, we
simulated the speckle phenomena for laser scanning projection display
system and compared the results with our speckle suppression method.
We found out that the speckle contrast reduced 30% by the reflective
phase modulator, which proved the new method was efficient.
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Yu, Shi-Han, and 于世珩. "Novel Package Vertical Structure of Emission Laser." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/33621969084587625316.
Full textAbstract:
碩士<br>國立交通大學<br>電子物理系<br>86<br>This thesis is to study a novel technology of the fabrication of a vertical emitting semiconductor laser. This technique is a combination of an edgeemitting semiconductor laser and a silicon micro-machining W-groove which has forty-five degree mirror-like oblique planes made by oxidation- smooth method. With the edge emitting semiconductor laser packaged on the middle of the W-groove, reflected light will be perpendicular to the incident light, that is, as a vertical emitting semiconductor laser. This vertical emitting structure with simplifying laser package has the advantage for automation and cost lower.
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Lin, Wei-Han, and 林韋翰. "Exploring Laser Induced Breakdown Activating Structure Fluid." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/db25e4.
Full textAbstract:
碩士<br>國立交通大學<br>電子物理系所<br>106<br>We explored laser induced breakdown activating structured fluid for the activating structured fluid appliance. In the experiment, we tried different cone angle Axicon and Diffractive Optical Element to produce structured light. From the Gaussian beam transformed to the pattern. In the result of the experiment, DOE transformed structured laser induced breakdown could make the pressure's had the structured space. The structured space made the fluid toward the special direction. In addition, we took the PDMS coating to microfluidic device. In the future, we could combine two results to appliance in the biochip.
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Chen, Yu-Wen, and 陳煜文. "Precision Analysis for Laser Scanner to Structure Monitoring." Thesis, 2015. http://ndltd.ncl.edu.tw/cgi-bin/gs32/gsweb.cgi/login?o=dnclcdr&s=id=%22103TIT05653093%22.&searchmode=basic.
Full textAbstract:
碩士<br>國立臺北科技大學<br>土木與防災研究所<br>103<br>As an island which located on the junction of plates, Taiwan usually suffers from typhoons and earthquakes. Often, the external force will cause invisible threats to the structure. As time goes by, these potential factors will result in damages. Structure refers to such as factories, buildings, bridges, towers and other metal-material buildings etc. In Taiwan, many structures are affected by natural disasters and result in damages. These can lead to losses of the society. Thus, monitoring the stability of structures becomes important. In general, structural monitoring is through structure analysis with the original structure design. The place to install the monitoring sensor will be evaluated after the determination of professional engineers. Afterward, It will be evaluated whether it is stable or not by the monitoring data. However, it can not monitor the entire structure. In this research, the laser scanner is adopted as the wholeness and high accuracy are taken into account. It can achieve high accuracy of distance measurement, scan the entire target, and record the three dimensional coordinates. Several experiments were added during the monitoring in this research to test whether the accuracy of laser scanner on scanning structure can detect the variation of the structure. In the results of indoor and outdoor experiments, the node displacement was detected in the point cloud data. The amount of the displacement is similar with other monitoring instruments and proved the benefits of laser scanner on structural monitoring. If the monitoring can compare with structure finite element method, the appropriateness of laser scanner on structural monitoring will be more definitely approved.
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Kuo, Chin-Liang, and 郭晉良. "Fabrication of 3D Micro Structure using Excimer Laser." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/qm8r23.
Full textAbstract:
碩士<br>國立成功大學<br>機械工程學系碩博士班<br>90<br>This study applies excimer laser micro-machining technology for manufacturing 3D axially symmetrical micro-structures. It is based on a work-piece rotation or mask rotation method in conjunction with the unique capabilities of an excimer laser micro-machining system. Specially designed laser masks have been developed for machining various kinds of 3D surface profiles. The goal is to understand the feasibility of this micro-machining method and its accuracy in producing a given profile of structure surface. Surface roughness and machining speed are also under evaluation.
The research is carried out on three different polymer materials, namely, PMMA, PC, and PS. Axially symmetrical micro-structures with concave and convex surfaces are manufactured by the mask rotation method. The surface profiles have been characterized and compared with their theoretical counterparts. Good agreement is observed. Furthermore, PC and PS have better surface roughness in comparison to PMMA. The machining time for each structure is limited to few minutes, which is very satisfactory.
In order to overcome several limitations on the excimer laser micro-machining system, this work also re-developed the optical system for the laser beam so that the machining can be carried out on an optical table. This greatly enhances the performance of the micro-machining system and its flexibility. A commercial optical analysis software (ZEMAX) has also been used for analyze the system. The work presented in this thesis can be very useful to future studies on excimer laser micro-machining and LIGA-like MEMS technology development.