36,451 research outputs found

    Complexities of (U-Th)/he zircon thermochronology through the lens of zonation and deep time

    No full text
    The zircon (U-Th)/He (zircon-He) system is a dating tool used to date low-temperature geologic events that occur in the upper four kilometers of Earth‚Äôs crust. The zircon-He system is defined by the kinetic interactions of radiation damage accumulation and annealing, and He diffusion. The kinetics of the zircon-He system were developed using idealized samples and conditions, which do not always translate well to the complex samples and settings that researchers attempt to date when using the zircon-He system. I seek to better understand how the defining elements of the zircon-He system interact when applied to complex natural samples and deep-time thermal histories. I first explore the role of radiation damage zonation in zircon on annealing kinetics. Annealing is the thermally activated process by which chemical bonds reform after being broken by radiation damage. Radiation damage directly impacts the diffusion of He from the crystal lattice and is a key factor in defining the kinetics of the zircon (U-Th)/He system. Damage accumulates within a crystal as a function of time and U and Th concentration. The total level of radiation damage in a zircon crystal is governed by the thermally-activated, kinetic process of annealing, which in turn influences the interpretation of zircon (U-Th)/He dates for thermal histories. Several annealing models have been defined for the zircon system based on measurements in natural crystals; however, few studies have investigated how multiple levels of radiation damage due to zonation of actinides within a crystal may influence the annealing process. Here I use Raman spectroscopy to map the full-width half maximum (FWHM) of the 3(SiO4) band, a proxy for radiation damage, in zircon crystals from the Lucerne pluton (Maine, USA) with heterogeneous distributions of U and Th. I compare FWHM maps before and after annealing these crystals at laboratory times and temperatures. These maps show that each damage zone within a single zircon acts as an isolated domain that is dictated by an independent set of annealing kinetics. Thermally activated annealing decreases radiation damage in all radiation damage zones; however, the rate of annealing is not consistent across all zones. I identify specific FWHM damage levels present post-annealing regardless of laboratory time temperature conditions: FWHM modes at 2-5 cm-1, 10-15 cm-1, and 25-30 cm-1. I attribute these persistent damage modes to variable annealing kinetics that are partially dependent on the level of pre-annealing damage, combined with the inability of high-damage crystals, or zones within crystals, to fully recover their crystallinity. These findings therefore show that zircon crystals with non-uniform distributions of U and Th can anneal to create long-lived damage zones at specific damage levels, which has implications for treating the zircon (U-Th)/He chronometer as a multi-domain diffusion system. Next, I apply the zircon-He system to the geologically complex deep-time thermal history of the Eastern Grand Canyon. I demonstrate the power of zircon-He thermochronology to resolve cooling events of Precambrian basement exposures below the Great Unconformity surface in the Grand Canyon. I combine new zircon-He data with previous 40Ar/39Ar mica and K-spar results to model the 1 Ga, thermal history of these basement rocks. Forward and inverse models of zircon-He date-effective uranium (eU) concentration, a proxy for radiation damage, suggest that the main phase of Precambrian cooling to <200 ¬įC was between 1350 and 1250 Ma, after the Yavapai orogeny. This result agrees with K-spar 40Ar/39Ar thermochronology showing rapid post-1400 Ma cooling and both are consistent with the 1255 Ma depositional age for the Unkar Group. The data and models are highly sensitive to late-stage reheating due to burial beneath ~ 3-4 km of Phanerozoic strata prior to the Laramide orogeny; models that best match observed date-eU correlations show maximum temperatures of 140-160 ¬įC, in agreement with apatite (U-Th)/He and fission-track data. Forward and inverse models also test for the age of carving of Grand Canyon; they support a multi-stage cooling model involving 25-15 Ma cooling from 100 to 50 ¬įC during partial carving of Eastern Grand Canyon, with post- 6 Ma rapid cooling indicated by 3 to 7 Ma zircon-He dates over a wide range of high eU. The zircon-He data capture basement exhumation below the Great Unconformity during the Mesoproterozoic (1300-1250 Ma), and ‚Äúyoung‚ÄĚ (20-0 Ma) carving of Grand Canyon. Finally, I assess the role of zonation in creating secondary dispersion in zircon-He data. High-levels of secondary dispersion can be seen in the zircon-He data collected from the Eastern Grand Canyon. Dispersion in zircon-He data can lead to greater levels of uncertainty in modeled thermal histories. Dispersive datapoints were determined as those datapoints that deviate from the average date-eU trendline of the binned data by more than 2 standard deviations. All dispersive datapoints were targeted as potentially having severe zonation, which can create unaccounted for complexities in the kinetics applied to the zircon-He system. CL images were collected for zircon separates from the Eastern Grand Canyon and showed a range of zonation patterns from no zonation and concentric zonation to chaotic, non-concentric zonation. I ran two inverse models to see if the addition of zonation information increases the probability of various thermal events in the Eastern Grand Canyon thermal history. One inverse model used data without any zonation information and the other used data with zonation information based on anonymous zonation styles identified in CL image. I also created forward models to see if the level of secondary dispersion could be modeled by artificially creating zircon-He data with zoned eU information data. I found that the addition of zonation information to my inverse models does not increase the probability of known thermal events but creates a less complex thermal history. The artificially zoned data does not fully explain the level of secondary dispersion seen in the measured zircon-He data. Of the seven dispersive datapoints identified in the zircon-He data, only three datapoints were captured by the artificially zoned data, leaving the two oldest and two youngest dispersive datapoints unexplained. I attribute the decrease in complexity of the zoned thermal history, and the inability of artificially zoned data to account for all secondary dispersion, to an overly simplified morphology of zonation in both my inverse and forward models. I suggest that He diffusion kinetics should include the option for the use of a multi-domain diffusion (MDD) model where domains are separated by fast-pathways of diffusion. The introduction of a non-nested MDD would allow for zonation information from chaotic zones to be better modeled and could ultimately reduce dispersion in zircon-He data. The collective results of this dissertation show both the utility of zircon-He thermochronology and areas where the method can be expanded and improved upon. Proper kinetic models for describing radiation damage annealing and He diffusion in zircon with heterogeneous uranium and thorium distribution would allow for zircon-He users to better understand the complexities and dispersion found in their zircon-He data. The potential for zoned zircon to produce additional dates and thermal history information using the zircon-He method, particularly in deep-time settings, makes improving the communal understanding and application of the underlying kinetics of the zircon-He methods all the more imperative.U of I OnlyAuthor requested U of Illinois access only (OA after 2yrs) in Vireo ETD syste

    Análisis de la conductividad térmica y resistencia a compresión del hormigón en las estructuras termoactivas

    Full text link
    En el presente trabajo se lleva a cabo el an√°lisis del hormig√≥n para su empleo como parte de las llamadas estructuras termoactivas. Se analiz√≥ la conductividad t√©rmica de diferentes tipos de hormig√≥n, as√≠ como su resistencia a compresi√≥n, y el reparto de temperaturas en el interior de una losa termoactiva de hormig√≥n. Las estructuras termoactivas basan su funcionamiento en el aprovechamiento de la inercia t√©rmica del hormig√≥n para llevar a cabo el proceso de climatizaci√≥n de los edificios. Para ello se incorpora una serie de conductos, para transportar un fluido caloportador, en el interior de los elementos estructurales de hormig√≥n armado de los edificios. Estos sistemas requieren temperaturas medias para su funcionamiento, por lo que permiten el aprovechamiento de energ√≠as renovables como la geotermia de baja entalp√≠a. En el trabajo se llev√≥ a cabo una campa√Īa experimental de probetas de hormig√≥n H-25, elaboradas con tres tipos de cemento diferentes (CEM I, CEM II y CEM III) combinados con dos tipos de √°rido (de origen calizo y origen sil√≠ceo) en el que se estudi√≥ por una parte la resistencia a compresi√≥n del hormig√≥n, y por otra parte la conductividad t√©rmica del hormig√≥n en tres grados de humedad diferentes (0%, 50% y 100% de humedad). Los resultados obtenidos indicaron que las muestras elaboradas con cemento del tipo CEM I y √°rido calizo ofrecieron valores de resistencia a compresi√≥n superiores a las de las muestras elaboradas con cemento CEM II, CEM III y √°rido sil√≠ceo. Por otra parte, de los ensayos t√©rmicos se obtuvieron valores de conductividad superiores en las muestras elaboradas con cemento CEM II, √°rido sil√≠ceo, y con un 100% de humedad. Del estudio de la resistencia del hormig√≥n, y la conductividad t√©rmica se puede concluir que el hormig√≥n elaborado con cemento de tipo CEM II y √°rido sil√≠ceo result√≥ m√°s adecuado para su empleo en los elementos estructurales de hormig√≥n armado, siempre que los requerimientos estructurales no se vean comprometidos. Al contrario de lo que se esperaba, el empleo de cemento CEM III, de origen sider√ļrgico, no supuso el aumento de la conductividad t√©rmica de las muestras de hormig√≥n analizadas. Para el an√°lisis del reparto de temperaturas en el interior de una losa termoactiva se realiz√≥ una muestra f√≠sica de losa de hormig√≥n con un sistema de tubos embebidos por los que se hizo circular el agua, y una serie de termopares en el interior del hormig√≥n a diferentes profundidades de la cara exterior de la losa. En cada termopar se analiz√≥ el reparto de temperaturas con 3 temperaturas de agua diferentes (30¬ļC, 40¬ļC y 50¬ļC), combinadas con 2 supuestos de temperatura ambiente de la sala en la que se realizaron los ensayos: la temperatura preexistente y la temperatura ambiente aumentada hasta 28¬ļC mediante el empleo del sistema de aire acondicionado de la sala. Los resultados conseguidos mostraron que con una temperatura del agua de 30¬ļC el hormig√≥n de la losa alcanza temperaturas m√°s pr√≥ximas a las del fluido caloportador que con temperaturas de 40¬ļC o 50¬ļC. Se comprob√≥ que el estrato con temperaturas m√°s estables de la losa se dio en los termopares m√°s alejados de las tuber√≠as y m√°s pr√≥ximos a la cara externa de la losa, y que el sistema alcanz√≥ la estabilizaci√≥n de las temperaturas tras 9 horas aproximadamente de funcionamiento. Del an√°lisis del reparto de temperaturas dentro del hormig√≥n de una losa termoactiva se puede concluir que el sistema es apropiado para el empleo de temperaturas medias del fluido caloportador, que se consiguen temperaturas m√°s estables en planos a una cierta distancia del sistema de tuber√≠as, y que el sistema resulta m√°s eficiente durante per√≠odos largos de funcionamiento. ----------ABSTRACT---------- The aim of the project is to study the concrete used in reinforced concrete structures of thermally active building systems (TABS). To that purpose the thermal conductivity and compressive strength of different kinds of concrete samples were analized, as well as the distribution of temperatures inside a sample of thermally activated concrete slab. Thermally active structures are based on thermal inertia of concrete for being used as part of the heating and cooling systems of buildings. To this purpose, a system of pipes with heat transfer fluid is embedded into concrete structures for heating and cooling different parts of buildings. As low temperatures are required for these heating and cooling systems, renewable energies such as geothermal energy are successfully used for climate control of buildings. For this reason different specimens and testing procedures were proposed to study. On the one hand the compressive strength of concrete made with three different types of cement (CEM I, CEM II and CEM III) and two different kinds of aggregate (limestone and siliceous). On the other hand, thermal conductivity of concrete were also studied at three different levels of humidity (0%, 50% and 100% of humidity). Results from tests showed that specimens made of concrete with CEM I and limestone aggregate had a higher compressive strength, while conductivity tests showed that concrete made with cement CEM II, siliceous aggregate and humidity of 100% had higher values of conductivity than the other specimens. In conclusion, concrete made of cement type CEM II and siliceous aggregate improves the conductivity of concrete for its use on thermal active structures. Thermal conductivity is also improved by high levels of humidity in concrete. Contrary to the expectations, concrete specimens made of cement CEM III did not show higher thermal conductivity levels than concrete made of cement CEM I and CEM II. In order to analize the distribution of heat inside of the concrete of a thermally active concrete slab, a sample with embedded tubes with water and thermocouples was made. The temperature at each thermocouple was analized depending on the distance to the tube system, water temperature (30¬ļC, 40¬ļC and 50¬ļC) and two different options for room temperature: the preexisting temperature and 28¬ļC of temperature by using air conditioning. Results from this part of the study showed that temperatures of concrete during the working period were closer to water temperature when this was 30¬ļC rather than 40¬ļC or 50¬ļC. The temperatures of concrete were more stable closer to surface levels rather than closer levels to tubes. The temperatures of the system reached its maximum values after 9 hours of use aproimately. In conclusion to this part of the study, the system results more suitable for using medium value temperatures for water, the location of the tubes system should be at the middle plane of the slab for stable temperatures at the exterior surface of the slab, and that the use of the system is more effective for long operative periods

    Re-entrant relaxor ferroelectric behaviour in Nb-doped BiFeO 3 ‚ÄďBaTiO 3 ceramics ‚Ć

    Get PDF
    BiFeO3‚ÄďBaTiO3 (BF‚ÄďBT) solid solutions exhibit great promise as the basis for high temperature piezoelectric transducers and energy storage dielectrics, but the fundamental mechanisms governing their functional properties require further clarification. In the present study, both pure and niobium-doped 0.7BF‚Äď0.3BT ceramics are synthesized by solid state reaction and their structure‚Äďproperty relationships are systematically investigated. It is shown that substituting a low concentration of Ti with Nb at a level of 0.5 at% increases the resistivity of BF‚ÄďBT ceramics and facilitates ferroelectric switching at high electric field levels. Stable planar piezoelectric coupling factor values are achieved with a variation from 0.35 to 0.45 over the temperature range from 100 to 430 ¬įC. In addition to the ferroelectric-paraelectric phase transformation at the Curie point (‚ąľ430 ¬įC), a frequency-dependent relaxation of the dielectric permittivity and associated loss peak are observed over the temperature range from ‚ąí50 to +150 ¬įC. These effects are correlated with anomalous enhancement of the remanent polarization and structural (rhombohedral) distortion with increasing temperature, indicating the occurrence of a re-entrant relaxor ferroelectric transformation on cooling. The results of the study provide new insight into the thermal evolution of structure and the corresponding functional properties in BF‚ÄďBT and related solid solutions

    Structural Characterization of Geopolymers with the Addition of Eggshell Ash

    Get PDF
    It is well known that geopolymers are a new group of binder materials of alumosilicate origin. Geopolymers are made by the reaction of precursor aluminosilicate materials with alkaline activator solutions. The current research relates to a low-cost and eco-friendly procedure, suitable of being implemented in two easy steps. The first step is the production of a solid phase based on fly ash (Obrenovac, Serbia) and eggshell ash as waste materials rich in calcium. The second step is alkali activating the solid phase using an alkaline activator (a mixture of NaOH and Na2SiO3) and procedures in proper laboratory conditions. Four samples with different eggshell ash content were synthesized. The concentration of used NaOH was 12 mol dm‚ąí3. The structural properties of all investigated samples were analyzed by XRD (X-ray diffraction), DRIFT (diffuse reflectance infrared Fourier transform), SEM (scanning electron microscopy) and UV/Vis spectroscopy analysis. XRD determined the amorphous halo with the presence of quartz as the crystal phase in all of the investigated samples. These results were confirmed by DRIFT analysis. The morphology of the samples was determined by SEM analysis. UV/Vis showed that the material could be a potential adsorbent

    Variable optical elements for fast focus control

    Full text link
    In this Review, we survey recent developments in the emerging field of high-speed variable-z-focus optical elements, which are driving important innovations in advanced imaging and materials processing applications. Three-dimensional biomedical imaging, high-throughput industrial inspection, advanced spectroscopies, and other optical characterization and materials modification methods have made great strides forward in recent years due to precise and rapid axial control of light. Three state-of-the-art key optical technologies that enable fast z-focus modulation are reviewed, along with a discussion of the implications of the new developments in variable optical elements and their impact on technologically relevant applications

    The effect of orthophosphoric acid on energy-intensive parameters of porous carbon electrode materials

    Get PDF
    The effect of orthophosphoric acid concentration as an activating agent on the porous structure of carbon materials derived from apricot pits and energy-intensive parameters of electrochemical capacitors formed on their basis is studied. It is found that changing the ratio of the mass of the activating agent to the mass of the raw material in acid-activated porous carbon materials (PCMs), one can control the pore size distribution in the range of 0.5-20 nm and specific surface area in the range of 775-1830 m2/g. The use of cyclic voltammetry, impedance spectroscopy and chronopotentiometry made it possible to set the capacitive nature of charge accumulation processes in acid-activated PCMs, as well as to determine the contribution of a certain size of pores to the specific capacitance of PCM/electrolyte system

    Biological impacts of marine heatwaves

    Get PDF
    Climatic extremes are becoming increasingly common against a background trend of global warming. In the oceans, marine heatwaves (MHWs)‚ÄĒdiscrete periods of anomalously warm water‚ÄĒhave intensified and become more frequent over the past century, impacting the integrity of marine ecosystems globally. We review and synthesize current understanding of MHW impacts at the individual, population, and community levels. We then examine how these impacts affect broader ecosystem services and discuss the current state of research on biological impacts of MHWs. Finally, we explore current and emergent approaches to predicting the occurrence and impacts of future events, along with adaptation and management approaches. With further increases in intensity and frequency projected for coming decades, MHWs are emerging as pervasive stressors to marine ecosystems globally. A deeper mechanistic understanding of their biological impacts is needed to better predict and adapt to increased MHW activity in the Anthropocene

    Anu√°rio cient√≠fico da Escola Superior de Tecnologia da Sa√ļde de Lisboa - 2021

    Get PDF
    √Č com grande prazer que apresentamos a mais recente edi√ß√£o (a 11.¬™) do Anu√°rio Cient√≠fico da Escola Superior de Tecnologia da Sa√ļde de Lisboa. Como institui√ß√£o de ensino superior, temos o compromisso de promover e incentivar a pesquisa cient√≠fica em todas as √°reas do conhecimento que contemplam a nossa miss√£o. Esta publica√ß√£o tem como objetivo divulgar toda a produ√ß√£o cient√≠fica desenvolvida pelos Professores, Investigadores, Estudantes e Pessoal n√£o Docente da ESTeSL durante 2021. Este Anu√°rio √©, assim, o reflexo do trabalho √°rduo e dedicado da nossa comunidade, que se empenhou na produ√ß√£o de conte√ļdo cient√≠fico de elevada qualidade e partilhada com a Sociedade na forma de livros, cap√≠tulos de livros, artigos publicados em revistas nacionais e internacionais, resumos de comunica√ß√Ķes orais e p√≥steres, bem como resultado dos trabalhos de 1¬ļ e 2¬ļ ciclo. Com isto, o conte√ļdo desta publica√ß√£o abrange uma ampla variedade de t√≥picos, desde temas mais fundamentais at√© estudos de aplica√ß√£o pr√°tica em contextos espec√≠ficos de Sa√ļde, refletindo desta forma a pluralidade e diversidade de √°reas que definem, e tornam √ļnica, a ESTeSL. Acreditamos que a investiga√ß√£o e pesquisa cient√≠fica √© um eixo fundamental para o desenvolvimento da sociedade e √© por isso que incentivamos os nossos estudantes a envolverem-se em atividades de pesquisa e pr√°tica baseada na evid√™ncia desde o in√≠cio dos seus estudos na ESTeSL. Esta publica√ß√£o √© um exemplo do sucesso desses esfor√ßos, sendo a maior de sempre, o que faz com que estejamos muito orgulhosos em partilhar os resultados e descobertas dos nossos investigadores com a comunidade cient√≠fica e o p√ļblico em geral. Esperamos que este Anu√°rio inspire e motive outros estudantes, profissionais de sa√ļde, professores e outros colaboradores a continuarem a explorar novas ideias e contribuir para o avan√ßo da ci√™ncia e da tecnologia no corpo de conhecimento pr√≥prio das √°reas que comp√Ķe a ESTeSL. Agradecemos a todos os envolvidos na produ√ß√£o deste anu√°rio e desejamos uma leitura inspiradora e agrad√°vel.info:eu-repo/semantics/publishedVersio
    • ‚Ķ
    corecore