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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
781

Structural Investigations of Highly Strictive Materials

Yao, Jianjun 22 May 2012 (has links)
Ferroelectric (piezoelectric) and ferromagnetic materials have extensively permeated in modern industry. (Na1/2Bi1/2)TiO3-BaTiO3 (NBT-x%BT) single crystals and K1/2Na1/2NbO3 (KNN) textured ceramics are top environment-friendly candidates which have potential to replace the commercial lead zirconate titanate or PZT. High magnetostrictive strain (up to 400 ppm) of Fe-xat.%Ga makes this alloys promising alternatives to existing magnetostrictive materials, which commonly either contain costly rare-earth elements or have undesirable mechanical properties for device applications. These systems have common characteristics: compositional/thermal/ electrical dependent structural heterogeneity and chemical disorder on sub-micron or nano scale, resulting in diverse local structures and different physical properties. In this work, I have investigated domain and local structures of NBT-x%BT crystals, KNN ceramics and Fe-xat.%Ga alloys under various conditions, mainly by scanning probe and electron transmission techniques. In NBT-x%BT single crystals, polarized light, piezo-response force (PFM) and transmission electron (TEM) microscopies were used to study domain structures and oxygen octahedral tiltings. Hierarchical domain structures were found in NBT: a high-temperature tetragonal ferroelastic domain structure is elastically inherited into a lower temperature rhombohedral ferroelectric phase. Nanoscale domain engineering mechanism was found to still work in NBT-x%BT system and a modified phase diagram was proposed based on domain observations. An increased intensity of octahedral in-phase tilted reflections and a decrease in the anti-phase ones was observed, with increasing x as the morphotropic phase boundary (MPB) is approached. It was also found that Mn substituents favor the formation of long range ordered micro-sized ferroelectric domains and octahedral in-phase tilted regions near the MPB. Nano-size heterogeneous regions were observed within submicron domain structure, indicating that the nanoscale polarization dynamics are not confined by domain boundaries, and the high piezoelectricity of NBT-x%BT is due to a polarization dynamics with high sensitivity to electric field and a broadened relaxation time distribution. In KNN textured ceramics, an aging effect was found to exist in the orthorhombic single phase field, not only in the orthorhombic and tetragonal two-phase field as previously reported. No variation of phase structure was revealed between before and after aging states. However, pronounced changes in domain morphology were observed by both PFM and TEM: more uniform and finer domain structures were then found with aging. These changes were even more pronounced after poling the aged state. A large number of sub-micron lamellar domains within micron-domains were observed: suggesting a domain origin for improved piezoelectric properties. In Fe-xat.%Ga alloys, an underlying inhomogeneity from Ga atoms embedded into the α-Fe matrix was believed to be the origin of giant magneostrictive properties. I have systematically investigated the phase structure and nano-size heterogeneity of Fe-xat.%Ga alloys subjected to different thermal treatments using standard TEM and high resolution TEM for 10<x<30. Nano-precipitates were observed in all specimens studied: A2, D03 and B2 phases were found depending on x. Nano-precipitates of D03 were observed to be dominant for compositions near the magnetostriction peaks in the phase diagram. Quenching was found to increase the volume fraction of nanoprecipitates for x=19, near the first magnetostriction peak. With increasing x to 22.5, nanoprecipitates were observed to undergo a D03 – B2 transformation. A high density of D03 precipitates of nanoscale size was found to be the critical factor for the first maximum in the magnetostriction. / Ph. D.
782

Nanocomposite Dispersion: Quantifying the Structure-Function Relationship

Gibbons, Luke J. 04 November 2011 (has links)
The dispersion quality of nanoinclusions within a matrix material is often overlooked when relating the effect of nanoscale structures on functional performance and processing/property relationships for nanocomposite materials. This is due in part to the difficulty in visualizing the nanoinclusion and ambiguity in the description of dispersion. Understanding the relationships between the composition of the nanofiller, matrix chemistry, processing procedures and resulting dispersion is a necessary step to tailor the physical properties. A method is presented that incorporates high-contrast imaging, an emerging scanning electron microscopy technique to visualize conductive nanofillers deep within insulating materials, with various image processing procedures to allow for the quantification and validation of dispersion parameters. This method makes it possible to quantify the dispersion of various single wall carbon nanotube (SWCNT)-polymer composites as a function of processing conditions, composition of SWCNT and polymer matrix chemistry. Furthermore, the methodology is utilized to show that SWCNT dispersion exhibits fractal-like behavior thus allowing for simplified quantitative dispersion analysis. The dispersion analysis methodology will be corroborated through comparison to results from small angle neutron scattering dispersion analysis. Additionally, the material property improvement of SWCNT nanocomposites are linked to the dispersion state of the nanostructure allowing for correlation between dispersion techniques, quantified dispersion of SWCNT at the microscopic scale and the material properties measured at the macroscopic scale. / Ph. D.
783

An Improved Thermogravimetric Analysis Method for Respirable Coal Mine Dust and Comparison to Results by SEM-EDX

Agioutanti, Eleftheria 24 July 2019 (has links)
It has long been known that chronic exposures to high concentrations of respirable coal mine dust can lead to the development of lung diseases such as Coal Worker's Pneumoconiosis, commonly referred to as "black lung", and silicosis. Since the mid-1990s, an alarming resurgence of diseases has been documented in central Appalachia, where underground mining often necessitates significant extraction of rock strata along with the thin seams of coal. These circumstances have prompted concern over if or how changing dust composition might be a factor in contemporary disease prevalence. Until now, the total mass concentration and quartz mass fraction of respirable dust have been regulated and monitored in US coal mines. Unfortunately, however, these two metrics alone do not paint a full picture of dust composition. Earlier work in the author's research group established a preliminary thermogravimetric analysis (TGA) method for coal mine dust. The method is intended to allow estimation of three key mass fractions of the dust from separate sources: coal from the coal strata being mined; non-carbonate minerals from the rock strata being mined or drilled; and carbonates that are primarly sourced from application of rock dust products to the mine floor or ribs. However, accuracy of the preliminary method was substantially limited by poor dust recovery from the fibrous filter media used for sample collection. This thesis includes two studies: The first study aims to establish an improved TGA method. It uses smooth polycarbonate (PC) filters for dust sampling and a modified thermal ramping routine. The method is verified using laboratory-generated respirable dust samples. In the second study, the improved TGA method is used to analyze 75 respirable mine dust samples, collected in 15 US mines. Replicate samples are also analyzed by scanning electron microscopy using energy dispersive X-ray (SEM-EDX). TGA and SEM-EDX results are compared to gain insights regarding the analytical methods and general trends in dust composition within and between mines. / Master of Science / It has long been known that chronic exposures to excessive respirable coal mine dust can lead to the development of lung diseases such as Coal Worker’s Pneumoconiosis (“Black Lung”) and silicosis. Disease rates in central Appalachia have shown an alarming and unexpected increase since the mid-1990s, despite declining dust concentrations evident from regulatory compliance monitoring data. Clearly, there is a need to better understand coal mine dust composition, which will require additional analytical methods. Thermogravimetric analysis (TGA) has been proposed as one possible method, because it should allow estimation of three key dust components from separate sources: coal from the coal strata being mined; non-carbonate minerals from the rock strata being mined or drilled; and carbonates from application of rock dust products to the mine floor and ribs. However, preliminary work with TGA showed limited accuracy, mostly due to sampling materials. In this thesis, two studies were performed. The first study aims to establish an improved TGA method using smooth, polycarbonate (PC) filters. The second study demonstrates the method on a large number of mine dust samples, and compares the results to those gained by an alternative method that uses electron microscopy.
784

Synthesis-Structure-Property Relationships in Lead-Free Piezoelectric Materials

Maurya, Deepam 19 December 2012 (has links)
Piezoelectric materials find applications in multitude of devices such as sensors, actuators and energy harvesters. However, most of these piezoelectric materials utilize lead-based systems which are becoming serious problem owing to the restrictions imposed by regulatory agencies across the globe. In the functional ceramics community, currently there is no problem more important than to find a replacement for lead-based piezoelectrics used for actuators. The electromechanical properties required for actuators (high piezoelectric constant, high coupling factor, low loss, and high transition temperatures) for known lead-free compositions are, however, far inferior to those of lead-based systems. There are three lines of research for addressing this fundamental problem "C (i) search for new systems through a combination of theory-based prediction followed by experimental effort (doping, solid solutions having a morphotropic (M) or polymorphic (P) phase boundary (PB), (iii) stabilization of metastable phases or finding the high temperature triclinic systems, and (iii) improving the properties of known compositions through microstructure optimization, domain engineering and multilayering. All these approaches are challenging and require innovation to make a significant impact on the current state-of-the-art. In this thesis, the later line of research was focused which is promising for near future applications, as it builds upon the known material systems with high depoling temperatures that have demonstrated the potential to be practical. In the first chapter, a novel method for the synthesis of lead-free (1-x)(Na0.5Bi0.5)TiO₃ "C xBaTiO3 piezoelectric ceramics was investigated. Initially, multiple compositions around morphotrpic phase boundary (MPB) were synthesized to identify the optimum composition 0.93Na0.5Bi0.5TiO3-0.07BaTiO3 (NBT-BT) for electromechanical effect. The new synthesis method starts with the synthesis of Na2Ti6O13 (NTO) whiskers which are then transformed into lead-free NBT-BT ceramics. Synthesis of NTO whiskers was performed using molten salt synthesis (MSS) method. Tape casting method was used to align the whiskers in base matrix powder and subjected to various processing temperatures to elucidate the microstructure and texture evolution. For this, scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM) and energy dispersive spectroscopy (EDS) analysis were used as principal tools. The sintering process can be understood by dividing it into three stages, namely (i) transformation of monoclinic whiskers in to NBT-BT perovskite phase through topochemical reaction (<800°C), (ii) localized sintering confined on single whisker (800-1050°C), and (iii) liquid phase sintering as densification and grain growth occurs in the whole matrix (>1050°C). The concentric growth ledges observed on grain surfaces were found to be preferably confined on the corners of cubical grains indicating <111> growth direction. The Lotgering factor (f100) for the sintered matrix was found to decrease with increase in sintering temperature. The longitudinal piezoelectric constant (d33) of samples sintered for 20h at 1175°C, 1200°C and 1225°C was measured to be ~153 pC/N, ~216 pC/N and ~180 pC/N, respectively. Next, a novel method was developed for the synthesis of nanostructured lead-free ferroelectric NBT-BT whiskers with high aspect ratio using NTO as a host structure. High energy x-ray diffraction coupled with atomic pair distribution function (PDF) and Raman scattering analyses were used to confirm the average structure of lead-free NBT-BT whiskers as rhombohedral, i.e. a ferroelectricity enabling type. The HRTEM analysis revealed local monoclinic-type structural distortions indicating a modulated structure at the nanoscale in the MPB composition of lead-free NBT-BT whiskers. The structural rearrangement during the synthesis of lead-free NBT-BT whiskers was found to occur via translation of edge shared octahedra of NTO into a corner sharing coordination. The high temperature morphological changes depicting disintegration of isolated whiskers into individual grains due to higher grain boundary energy have been found to occur in a close analogy with Rayleigh-type instability. In lead-based ABO3 compounds, with B-site disorder, the origin of enhancement of piezoelectric properties near MPB has been associated with the presence of an intermediate monoclinic/orthorhombic state that bridges the adjacent ferroelectric rhombohedral and tetragonal phases. However, the origin of high piezoelectric response in lead-free ABO3 compounds with A-site disorder has not been conclusively established. In this thesis, a microscopic model derived from comparative analyses of HR-TEM and neutron diffraction was developed that explains the origin of high piezoelectric response in lead "C free MPB compositions of NBT-BT. Direct observation of nanotwins with monoclinic symmetry confirmed the presence of an intermediate bridging phase that facilitates a pathway for polarization reorientation. Monoclinic distortions of an average rhombohedral phase were attributed to localized displacements of atoms along the non-polar directions. These results provide new insight towards design of high performance lead "C free piezoelectric materials. Microstructure and domain structure play dominant role towards controlling the magnitude of piezoelectric coefficient and hysteretic losses in perovskites. Brick-wall like microstructure with large grain size and small domain size can provide significant enhancement in the magnitude of piezoelectric coefficient. A synthesis technique for lead-free piezoelectric NBT-BT system that can provide [001]pc/[012]Rh grain oriented ceramics with large grain size and an electrical poling technique that results in smaller domain size will have significant impact on the electromechanical response. In this research, a synthesis technique was developed and the processing variables that play deterministic role in achieving the large grain brick-wall like microstructure were explained. Interfaces in the microstructure were found to be coherent at the atomic scale facilitating the domain wall motion with applied electric field. The piezoelectric response was found to increase monotonously with the incease in the degree of texturing and optimized microstructure was found to provide 200% enhancement in the magnitude of piezoelectric coefficient as compared to its random form. In order to understand the mechanism of enhanced piezoelectric response in textured NBT-BT, in-situ neutron diffraction experiments revealed that characteristically different structural responses are induced in textured and randomly-oriented NBT-BT ceramics upon application of electric fields (E), which are likely related to the varying coherence lengths of polar nano regions and internal stresses induced by domain switching. In conjunction to focus on NBT-BT, new lead-free piezoelectric materials with enhanced piezoelectric response were synthesized. This study provides fundamental understanding of the enhanced piezoelectric instability in lead-free piezoelectric (1-x) BaTiO₃-xA(Cu1/3Nb2/3)O3₃ (A: Sr, Ba and Ca and x = 0.0-0.03) solid solutions. These compositions were found to exhibit large d33 of ~330 pC/N and electromechanical planar coupling constant (kp)~ 46% at room temperature. The piezoelectric instability in these compositions was found to increase with x despite monotonous decrease in the long range polar ordering. High energy X-ray diffraction coupled with PDFs indicated increase in local polarization. Raman scattering analysis revealed that substitutions on A and B-site both substantially perturbed the local octahedral dynamics and resulted in localized nano polar regions with lower symmetry. These localized polar distortions were found to persist much above the Curie temperature (Tc). Polarization "C electric field (P-E) hysteresis loop analysis indicated presence of the internal bias that was found to be correlated with the formation of polar defects. This defect structure was found to modulate the domain structure resulting in nano domains and broad domain walls with higher mobility as revealed through analysis from HR-TEM and piezoresponse force microscopy (PFM). The presence of nano domains and local structural distortions smears the Curie peak resulting in diffuse order-disorder type phase transitions. The electron paramagnetic resonance (EPR) investigations revealed that substitution of Cu²⁺ takes place on octahedral sites that are distorted due to Jahn-Teller effect. The A-sites were distorted by substitution of Sr and Ca on Ba-site possessing different ionic radii and electronegativity. The effect of these distortions on the variations in physical property was modeled and analyzed within the context of nanodomains and phase transitions. As an application, the solid solution with nominal composition of (1-x)BaTiO₃-xBa(Cu1/3Nb2/3)O₃ (BCN) (x = 0, 0.025) was synthesized by conventional mixed oxide route, followed by compositional modification with varying concentration of Sn, as given by the formulation: 0.975 BaTi1-ySnyO₃ "C 0.025 Ba(Cu1/3Nb2/3)O₃ (y = 0.05, 0.06, 0.075, 0.1). Room temperature XRD patterns showed decrease in tetragonality of BT after modifying with BCN (BT-BCN). Modifications with Sn lead to further decrement in tetragonality and the room temperature structure became cubic at 6.0 at% doping level. The decrement in tetragonality was accompanied by lowering of Tc.  BT-BCN doped with 6 and 7.5 at% Sn were found to exhibit diffuse phase transition accompanied by high dielectric constant "Ý 7000, low loss tangent "Ü 1% and grain size in the submicron regime ("Ü 1 "Ìm). These compositions were found to be promising for Y5V type multilayer ceramic capacitors (MLCCs). Lastly, the dielectric and ferroelectric responses of compositionally graded bilayer and trilayer composites consisting of BT and 0.975BaTiO₃-0.025Ba(Cu1/3Nb2/3)O₃ (BT-BCN) were investigated. Two types of graded bilayer samples were synthesized, one with same thickness of BT and BT-BCN while other with different layer thicknesses. The graded trilayer sample consisted of BT layer sandwiched between two BT-BCN layers of equal thickness. SEM and TEM images showed a sharp interface with needle-shape domains across the interface. The domain size on BT-side was found to be larger than that on BT-BCN-side. The temperature dependence of dielectric response for all composite systems was found to exhibit shifting of characteristic Curie peak compared to constituent material which was associated to coupling between layers. Moreover, the differences in grain size, tetragonality, domain mobility of each layer was found to perturb the electrical response of composite. The polarization mismatch between uncoupled BT and BT-BCN established internal electric field in composite specimen and defined new polarization states in each layer by perturbing free energy functional of the composite specimen. Dynamic hysteresis behaviors and power-law scaling relations of all specimens were determined from P"CE field hysteresis loop measurements as a function of frequency. All systems were found to exhibit similar dynamic scaling relationships. Hysteresis area, Pr and EC decreased with increasing frequency due to delayed response, but increased with increasing applied electric field due to enhancement of driving force. Trilayer system was found to exhibit strong internal-bias field and double hysteresis behavior. The coupling effect resulting due to polarization mismatch between layers had substantial influence on the dynamic hysteresis behavior and power-law scaling relations. / Ph. D.
785

Observations and assessment of iron oxide nanoparticles in metal-polluted mine drainage within a steep redox gradient, and a comparison to synthetic analogs

Johnson, Carol A. 30 September 2014 (has links)
The complex interactions at the interfaces of minerals, microbes, and metals drive the cycling of iron and the fate and transport of metal(loid)s in contaminated systems. The former uranium mine near Ronneburg, Germany is one such system, where slightly acidic mine drainage crossing a steep redox gradient (groundwater outflow into a stream) forms and transforms iron (oxy)hydroxide nanoparticles. These particles interact with toxic metal(loid)s in water and sediments. Iron oxidizing and reducing bacteria also play a role in these processes. Biogeochemical reactions are influenced by nanoscale properties, and thus it is critical to probe environmental samples with appropriate techniques such as analytical transmission electron microscopy (TEM). This dissertation presents two studies on the iron (oxy)hydroxide mineral nanoparticles found in the Ronneburg mine drainage system. The first study uses TEM in conjunction with bulk analytical techniques to demonstrate the complexity of iron (oxy)hydroxide transformations at the steep redox gradient, and the partitioning of metal(loid)s within those mineral phases. An important result was the identification of Zn-bearing green rust platelets in the anoxic outflow water. Green rust minerals have only been identified in nature a handful of times, and we believe this work to be only the second to examine naturally occurring green rust using high resolution TEM (HR-TEM). Downstream of the outflow, aggregates of poorly crystalline iron oxide spheroids co-precipitated with amorphous silica formed and settled to the stream bed, where they aged to form nanoparticulate goethite and sequestered metals such as As and Zn. However, significant concentrations of Zn and Ni remained in the dissolved/nano (< 0.1 um) water fraction and continued downstream. The second study demonstrates that natural green rust nanoparticles and their synthetic analogs can be complex polycrystalline phases composed of crystallites only a few nanometers in size, and often include nano-regions of amorphous material. In addition to the typical pseudo-hexagonal platelet morphology, green rust nanorods were synthesized, which has not previously been reported. This work has important implications for the reactivity of green rust with biogeochemical interfaces in natural, anthropogenic, and industrial systems. A third study, presented in the appendix, characterizes the bacterial community at the Ronneburg mine drainage site and highlights iron oxidizers such as Gallionella sp., in particular those that form stalks of iron oxide nanoparticles. These biogenic stalks also contribute to the uptake of metal contaminants in water and sediments. The science of iron cycling is complex. It requires field-based exploration to enrich the contributions made by experimental, laboratory and modeling studies. This dissertation adds another chapter in the search for filling in missing pieces of this interconnected system. / Ph. D.
786

Morphological and Physiological Characteristics that Contribute to Insecticide Resistance in Bed Bug (Cimex lectularius L.) Eggs

Delong, Brittany E. 08 July 2014 (has links)
Although bed bug eggs are a difficult life stage to control with our currently labeled insecticides, few studies have examined how bed bug egg morphology and physiology is potentially related to pesticide resistance in bed bug eggs. Bed bug egg morphological features were examined using scanning electron microscopy (SEM) and the chorion and respiration structures were identified. Scanning electron microscopy photographs and bed bug egg measurements indicated there were no morphological differences between different bed bug egg strains (susceptible and resistant). Bed bug egg respiration rates measured by the amount of oxygen consumed (standard metabolic rate; SMR) also indicated there was no difference in SMR between different bed bug egg strains. Water conservation during respiration is vital to terrestrial insects. Therefore, similar patterns would be expected between egg water loss and respiration rates. However, susceptible strain eggs lost more water than one resistant strain of bed bug eggs, which was dissimilar from the respiration results, indicating that bed bug egg water loss and respiration are not directly related. Dose- response bioassays using two insecticide formulations (Temprid; imidacloprid/β-cyfluthrin, and Transport; acetamiprid/bifenthrin) indicated that bed bug eggs collected from pyrethroid resistant adult bed bug strains are also highly resistant. RNA sequencing of bed bug eggs from two resistant strains indicated that egg resistance may be directly related to the overexpression of multiple genes associated with insecticide resistance. / Master of Science in Life Sciences
787

Análisis genético de la percepción del ácido salicílico en Arabidopsis thaliana. Caracterización de NRB4

Canet Perez, Juan Vicente 31 July 2012 (has links)
Interés del estudio: Profundizar en el conocimiento de algunos de los mecanismos de resistencia que han desarrollado las plantas frente a patógenos, tomando como referencia principal la interacción entre Arabidopsis thaliana y Pseudomonas syringae. Objetivos: 1- Desarrollar y validar un nuevo modelo para el estudio de la percepción del ácido salicílico (SA) basándose en el crecimiento de la planta, no en la inoculación de un patógeno y el posterior análisis de su crecimiento. 2- Aplicar este nuevo modelo para obtener información sobre las señales que empiezan tras la aplicación y/o inducción del SA y que desencadenan la activación de las defensas de la planta. Para ello se realizará un rastreo genético con el que se pretende responder a la pregunta de si el gen NPR1 es el único necesario para la percepción de esta hormona. 3- Clasificar los candidatos obtenidos por grupos de complementación. Mapear aquel grupo más interesante e iniciar su caracterización fenotípica. Elementos de la metodología a destacar: Se han utilizado metodologías tanto comunes a toda la biología molecular de plantas (mutagénesis, secuenciación de DNA, análisis de QTLs, inmunodetección de proteínas, cultivo in vitro de plantas, expresión transitoria de proteínas, doble híbrido en levadura, RT-qPCR, microscopía, análisis de transcriptomas, etc.), como más específicas del campo de la interacción planta-patógeno (cultivo de bacterias, inoculación de bacterias, tratamientos con inductores de resistencia, etc.). Resultados logrados: El análisis de la reducción del peso fresco de la planta provocada por la inducción de resistencia tras la aplicación del BTH (análogo del SA) constituye un modelo biológico válido y eficaz para el estudio de la percepción del SA en Arabidopsis. Además, permite realizar un rastreo genético en busca de mutaciones que afecten a la percepción del SA que ha permitido concluir que el gen NPR1 no es el único implicado en dicho proceso. Por una parte, los cinco parálogos de / Canet Perez, JV. (2012). Análisis genético de la percepción del ácido salicílico en Arabidopsis thaliana. Caracterización de NRB4 [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/16962
788

VESTIGIOS DE YESO. LOS REVESTIMIENTOS CONTINUOS HISTÓRICOS EN LAS FACHADAS DE LA VALENCIA INTRAMUROS: ESTUDIO HISTÓRICO, CARACTERIZACIÓN Y PROPUESTAS DE CONSERVACIÓN

La Spina, Vincenzina 31 March 2015 (has links)
En el presente estudio se indican los principales resultados referentes a la invesƟ gación realizada sobre los revesƟ mientos conƟ nuos históricos en las fachadas de la Valencia intramuros (España), concretamente en los barrios de El Carme, Sant Francesc- Universitat, El Mercat, La Seu-Xerea, y Velluters. En esta zona casi la totalidad de los edifi cios residenciales de fi nales del siglo XVIII hasta principios del siglo XX están revesƟ dos por capas que protegen y a la vez decoran sus fábricas. Por tanto, se convierten en un rasgo disƟ nƟ vo de la imagen de la ciudad histórica y de la técnica construcƟ va local, y más cuando se ha podido descubrir su verdadera materialidad caracterizada por el uso de yeso. Esta tesis doctoral pretende contribuir a la puesta en valor de los revesƟ mientos de la ciudad parƟ endo del conocimiento de su historia, de la defi nición de su caracterización material y técnica, y de la necesaria conservación de los vesƟ gios que de ellos quedan. Se consideran vesƟ gios porque no son simples restos de algo material sino son también indicios de una memoria construcƟ va olvidada. Por lo tanto, el objeƟ vo central de la invesƟ gación ha sido profundizar en el conocimiento de sus caracterísƟ cas, peculiaridades, singularidades y parƟ cularidades para evidenciar los múlƟ ples valores: histórico, arquitectónico, cultural, material, tecnológico, construcƟ vo, etc. que atesoran. En este senƟ do, el estudio se divide en tres dimensiones temporales que han hecho posible conocer el pasado, el presente y el futuro de este elemento construcƟ vo, aplicando un enfoque mulƟ disciplinar que aúna los fundamentos, conocimientos y contenidos clave proporcionados por la Historia de la Arquitectura y de la Construcción, la Restauración Arquitectónica, la Geograİ a y sobre todo la Geología. De este modo , en la primera parte se intenta descubrir y conocer los revesƟ mientos conƟ nuos históricos desde una perspecƟ va histórica y construcƟ va a través del análisis de fuentes bibliográfi cas y archivísƟ cas, prestando especial atención al yeso como material de la tradición valenciana. En la segunda parte se pretende analizar e interpretar los revesƟ mientos conƟ nuos que revisten las fachadas de los edifi cios históricos de la ciudad parƟ endo del análisis químico y mineralógico de muestras pertenecientes a excavaciones arqueológicas y a edifi cios históricos, para así poder caracterizarlos y conocer su materialidad. Asimismo, ello ha hecho posible realizar una re-lectura analíƟ ca de toda la información obtenida gracias a su sistemaƟ zación en fi chas, así como establecer una posible evolución cronológica de los revesƟ mientos de la ciudad. Por úlƟ mo, en la tercera parte se aborda cómo intervenir y proteger este elemento construcƟ vo proponiéndose pautas a seguir y materiales más compaƟ bles con su realidad construcƟ va así como mecanismos para intentar evitar su constante pérdida. / La Spina, V. (2015). VESTIGIOS DE YESO. LOS REVESTIMIENTOS CONTINUOS HISTÓRICOS EN LAS FACHADAS DE LA VALENCIA INTRAMUROS: ESTUDIO HISTÓRICO, CARACTERIZACIÓN Y PROPUESTAS DE CONSERVACIÓN [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/48525 / Premios Extraordinarios de tesis doctorales
789

Ch4- IODP EXP 341 U-Pb Zircon Results for Lonestones

Wai Kehadeezbah Allen (14671736) 17 May 2024 (has links)
<p>This dataset includes U-Pb zircon summary excel file with datatables for all lonestones analyzed.This file also sorts data to include information of Rim and Core analyses were appropriate.</p> <p><br></p> <p>In addition, raw data for each individual sample are included that have detailed information regarding parameters during each analytical session. </p> <p><br></p> <p>All samples were analyzed at the University of Arizona Laserchron Center (NSF-EAR 1649254)</p> <p><br></p> <p>High Resolition Scanning Electron Microscopy Images are also included that were imaged at the University of Arizona Laserchron Center</p> <p><br></p>
790

A new combined approach using confocal and scanning electron microscopy to image surface modifications on quartzite

Pedergnana, A., Ollé, A., Evans, Adrian A. 10 February 2020 (has links)
Yes / Confocal microscopy has been increasingly employed in the field of traceology to acquire metrological data of surface changes on a micro-scale. However, its advantages for a traditional visual inspection of use-wear are rarely highlighted. As traditional optical microscopy (OM) has proven unable to entirely fulfil the prerequisites for an ideal observation of highly reflective and irregular materials, alternative ways for providing better observation conditions must be sought. In this contribution, we explore the combination of laser scanning confocal (LSCM) and scanning electron microscopy (SEM) micro-graphs for the visual characterisation of wear on quartzite and evaluate the potential of both techniques. / AHRC Fragmented Heritage project (AH/L00688X/1) at the University of Bradford, and of the MICINN-FEDER (PGC2018-093925-B-C32), the AGAUR (SGR 2017-1040) and the URV (2018PFR-URV-B2-91) projects at IPHES-URV. One of the authors (A.P.) was beneficiary of a Catalan pre-doctoral grant (2014FI B 00539), at the Rovira i Virgili University (URV), the IPHES and the Muséum national d’Histoire naturelle of Paris.

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