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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.
431

Porovnání různých metod stanovení melitelnosti práškových pojiv / Comparison of the different methods for the determination of the powder binders grindability

Virágová, Tereza January 2017 (has links)
The aim of this thesis is to summarize the knowledge gained in the field of grinding medium-hard and hard materials. Work has focused on examining the grindability of the material using available laboratory mill. The part of the work is subsequent optimization of the grinding process on the device and evaluation of the results.
432

Vybraní hlavonožci (Cephalopoda) ordoviku pražské pánve a Baltiky(Estonsko a Švédsko): taxonomie, paleobiogeografie a paleoekologie / Selected cephalopods from the Ordovician of the Prague Basin (Bohemia) and Baltica (Estonia and Sweden): taxonomy, paleobiogeography and paleoecology

Aubrechtová, Martina January 2018 (has links)
This dissertation thesis is a summary of five studies published in peer- reviewed, impacted scientific journals. All of the publications are taxonomic revisions of previously unknown or little known collections of fossil cephalopods from the Early Paleozoic strata of Bohemia, Estonia and Sweden. Paleogeogra- phical and stratigraphical distributions of the respective taxa were summarized, refined and compared with contemporary fossil assemblages known from other regions. Implications on the paleoecology of the cephalopods and original envi- ronmental conditions were made. The text of the thesis is divided into three main parts. In the first part, the morphology of cephalopods is explained, stressing out the most important diagnostic characters used for their descriptions. The current systematics of the Cephalopoda is overviewed and the main cephalopod groups during the Ordovician are briefly introduced. The second part of the thesis describes the geological development and settings of the regions, from which the studied fossil cephalopods originate. The third and final part of the thesis provides a discussion and interpretation of the results of the published studies in the context of the previously published research. The genus Bactroceras Holm, 1898 and some members of the order Litui- tida were studied...
433

Plži, stromy, pH, podloží a epifytické lišejníky / Gastropods, trees, pH, subsoil and epiphytic lichens

Pelant, Filip January 2020 (has links)
Epiphytic lichens are under considerable grazing pressure due to invertebrate lichenivores, mostly gastropods. Preferences of tree-climbing gastropods affect vertical distribution of lichens, their habitat preferences and whole area of distribution. Higher grazing pressure is expected on sites with basic subsoil and sufficient sources of calcium, where the abundance of gastropods is higher. Most of researches about the topic of grazing pressure were therefore conducted on such sites, although this hypothesis has never been formally tested. Epiphytic communities are also affected by pH and other properties specific to its photophyte. Nevertheless, it is not known, if the same applies for grazing gastropods and how is the grazing pressure affected by tree species. I have addressed these questions in my thesis. I set an 80-days-long field transplantation experiment in the mixed forest of Moravský kras (South Moravia, Czech Republic). Glass fiber meshes with lichen thalli were placed on sixty trunks of three tree species (Carpinus betulus - hornbeam, Abies alba - fir, Fagus sylvatica - common beech) on both calcareous (limestone) and acidic (granodiorite) sites. Abundance and diversity of gastropods were measured. Determined grazing pressure was higher than pressure detected by other authors and was...
434

Analys av röda missfärgningar i Gåsgruvans marmor / Analysis of red discolouration found in crystalline limestone in Gåsgruvan quarry

Hesser, Sarina January 2020 (has links)
Detta arbetes mål har varit att hjälpa företaget SMA Mineral att utreda de rödamissfärgningar som allt oftare påträffats i deras marmor. Rapporten är högst visuellpå mikroskopisk nivå, och avhandlar vad missfärgningarna beror på. Provmaterialhar undersökts och karakteriserats mineralogiskt och geokemiskt, och typer avmissfärgningen har identifierats. Även en förklaring över de geologiska processersom ger upphov till missfärgningarna har formats. De metoder som använts underarbetet är egna undersökningar med komplement av en litteraturstudie påavhandlingar som handlar om just missfärgningar i marmor. Provmaterial harinhämtats från tre olika platser i gruvan, dessa har sågats och tvättats och några haräven slipats och polerats. Detta material har sedan använts genom hela arbetet.Optiska observationer med hjälp av binokulär har dokumenterats digitalt, detta gavinformation om att missfärgningen ligger mellan karbonatkristallerna, och sannolikthar varit av en mer löslig karaktär i ett tidigare skede. Utifrån detta kategoriserasmissfärgningen till två olika typer. Typ A förekommer som asymmetriska,koncentrerade fläckar på och mellan kristaller men till synes oregelbundet, medantyp B följer mikrofina sprickor och kan ses i bandade regelbundna formationer imaterialet. Järnrika kristaller upptäcktes i missfärgningarnas omedelbara närhet ochhär skapades hypotesen om att det är järnoxider som orsakat föroreningarna. ÄvenSEM-analyser har gjorts för att kunna identifiera den geokemiska sammansättningenav missfärgningarna. Resultaten från SEM- och XRF-analyserna bekräftade tesen, dåjärn förekom i varierande grad i samtliga analyser utom en. Dessutom hittadeshematit som i sig lämnar röda spår, samt ren rost i form av goetit. Ävenlitteraturstudien bekräftade att förekomster av järnrika mineral i marmor förr ellersenare kommer att orsaka missfärgningar. / The goal of this project has been to assist SMA mineral, a limestone producer, tofind the source of red discolourations found in their crystalline limestone. Thediscolouration has appeared on a more regular basis than before and is starting tobecome a problem for the company.This is a highly visual report focused on a microscopical level, that follows thestudy and finding of the origin of the red discolourations. Specimens from threedifferent locations in the quarry have been collected, then cut to proper sizes to fitthe needs for the scans and examinations suited for the project. Some of the sampleswere polished to fit the requirements of SEM. The material has been opticallyanalysed through a binocular microscope and documented with high resolutionimages. This was the first major breakthrough, since the discolouration showed tobe placed between the carbonate crystals, and appeared to have been more of asolution-like substance at some point. Based on the findings, the discolourationcould be categorised inte two types, type A appears as an irregular spotting oncrystal surfaces with a deeper red colour, whilst type B can be found in fine cracksin the material and follows a more regular pattern. Lots of minerals rich in ironwere also found in close proximity to the discolourations, which led to a hypothesisthat iron oxides might be the source of the problem. The thesis was confirmed bySEM- and XRF analyses of the material. Iron in different weight-percentages wasfound in all of the analyses except for one.The mineralogical and geochemical properties of the discolouration has beendefined, and the geological process that leads to the discolouration is explained.
435

Betongens hållfasthetsutveckling vid användning av olika ersättare för portlandklinker : En laborativ studie / Concrete strength development in the use of different replacement for clinker : An experimental study

Nilsson, Daniel, Lundgren, Dennis January 2012 (has links)
Tillverkning av portlandklinker står för ungefär fem procent av världens totala koldioxidutsläpp. Det finns därför ett allmänt intresse att minska användandet av portlandklinker. Klinkern kan antingen ersättas av andra cementerande material, eller så kan nya cementsnåla recept utformas. I den här rapporten har två cement med inmald flygaska respektive slagg från Cementa AB undersökts. För att undersöka klinkerersättnings-materialens potential har tester för tryckhållfasthet, uttorkningskrympning, bindetid, värmeutveckling och arbetbarhet utförts. Resultaten visar att skillnaderna mellan försökscementen och byggcementet är så pass små att båda bör kunna användas som byggcement. Ytterligare har ultrafiller av kalksten använts som ersättare för att minska cementhalten i betongen. Det går lika bra att delvis ersätta försökscementen med ultrafiller som det gör för byggcementet. Med cementsnåla recept och större del ersättningsmaterial finns det stora möjligheter att spara på energi och miljö. Detta borde i framtiden kunna leda till ett bättre och mer miljövänligt byggmaterial. / Manufacture of clinker is responsible for about five percent of the total global carbon dioxide emissions. Therefore, there is a general interest in reducing the use of clinker. Clinker can either be replaced by other cementitious materials, or reduced by using lean-cement recipes. This report examines two experimental cements, one with fly ash and one with slag, developed by Cementa AB. To examine the potential of clinker replacement materials, tests for compressive strength, drying shrinkage, initial setting, heat generation and workability, were performed. The results show that the differences between the experimental cements and the reference are so small that both are useable as building cements. In addition, an ultrafine filler of limestone is used as a replacement material for further reduction of the clinker content in concrete. It was also found, that it is just as efficient to partly replace the experimental cements with ultrafine filler as in the reference cement. There are great opportunities to save energy and the environment impact with both clinker-saving cement recipes and with cement replacement materials. This should lead to a better, more environmentally friendly, building material in the future.
436

Eigenschaften und Genese periglazialer Deckschichten auf Carbonatgesteinen des Muschelkalks in einem Teilgebiet der ostthüringischen Triaslandschaft: Genesis and properties of periglacial slope deposits on calcareous rocks of the Muschelkalk formation in an area of the eastern Thuringian Triassic landscape.

Bullmann, Heike 01 November 2010 (has links)
Periglaziale Deckschichten auf carbonatreichen Gesteinen der geologischen Formation des Muschelkalks sind bisher nur peripher Gegenstand wissenschaftlicher Untersuchungen innerhalb der Deckschichtenfor-schung. Um diese Lücke zu schließen, widmet sich die vorliegende Arbeit dem Aufbau des oberflächenna-hen Untergrundes im Muschelkalk in einem Teilgebiet in der ostthüringischen Triaslandschaft. Die Ergebnisse zeigen, dass die periglazialen Deckschichten in Abhängigkeit von lithologischen Gesteins-merkmalen und Relieffaktoren (Exposition, Neigung) eine hohe räumliche Heterogenität hinsichtlich der stoff-lichen Zusammensetzung, der vertikalen Gliederung und Gründigkeit aufweisen. Sie sind in Basislagen (LB), Mittellagen (LM) und Hauptlagen (LH) gegliedert, die ihrerseits eigenständige Schichten beinhalten können. Die Lagenbildungen über carbonatreichen Gesteinen des Muschelkalks weisen Besonderheiten im Aufbau, in den stofflichen Eigenschaften und in ihrer Genese auf. Die Basislagen sind in der Regel mehrgliedrig entwickelt und können bis zu drei, faziell zu unterscheidende Substratkomplexe enthalten. Dies sind i) eine skelettfreie Kalksteinbraunlehm-Fließerde (LB-F), ii) ein Kalk-steinbraunlehmschutt (LB-1) und iii) ein Kalksteinschutt (LB-2). Die Zweiteilung der Basislagenschutte sowie die Abfolge LB-1/ LB-2 (LB-1 über LB-2) können als charakteristische Merkmale der Basislagenbildung über Muschelkalk herausgestellt werden. Skelettfreie Kalksteinbraunlehme (LB-F) stellen eine Besonderheit auf Carbonatgesteinen dar, da vergleichbare Bildungen auf quarz- und silikatreichen Standorten fehlen. Die Hauptlagen werden in eine schluffreiche (LH) und tonreiche (LHT) Fazies unterschieden. Beide zeichnen sich durch eine vollständige Skelettfreiheit aus, die ebenfalls als übergreifendes Merkmal über Muschelkalk gelten kann. Zwei Mittellagentypen sind mit skelettfreier Mittellage (LM) und skeletthaltiger Mittellage (LMs) vertreten. Die Genese der Basislagenabfolge LB-F/ LB-1/ LB-2 fand vollständig im Weichselglazial statt und schließt eine periglaziale Genese der Kalksteinbraunlehme ein. Die Beteiligung von Spülprozessen an der (Geli-) Solifluktion hat die Akkumulation von Lösungsrückständen (= Kalksteinbraunlehm) gefördert. Die Zweiteilung der Basisschutte kann ebenfalls durch die Mitwirkung ablualer Prozesse erklärt werden. Die Kalksteinbraun-lehm-Fließerde entstand synsedimentär zur Bildung der Basislagenschutte durch laterale Ausspülung. Die Variabilität der Lössedimente wird neben Luv-/Lee-Effekten und präsedimentäre karstartige Hohlformen vor allem auch über eine differenzierte periglaziale Bodenfeuchte- und Vegetationsverteilung gesteuert. In der Arbeit wurden u.a. der gU/fU-Quotient, pedogene Eisenoxide (Feo, Fed), Gesamteisengehalt (Fet), Fet/Ton-Quotient und (Fed-Feo/(Fet/Ton)-Quotient (nach GÜNSTER et al. 2001) sowie die Korrelation von Tongehalt und pedogenem Eisen für alle oben genannten Substrate ermittelt. Eine integrative Betrachtung dieser Parameter ist grundsätzlich geeignet, primäre Sedimenteigenschaften der Substrate herauszustellen und eine pedogenetische Überprägung abzugrenzen. Darüber hinaus erlauben sie Aussagen zur Genese. Der Tongehalt der Mittellagen konnte neben der Überformung durch Tonverlagerung als sedimentogene Ei-genschaft belegt werden. Kalksteinbraunlehme mit weniger als 65% Tongehalt müssen nicht grundsätzlich lösslehmbeeinflusst sein. Rezente Lösungsprozesse und eine rezente Weiterbildung der Kalksteinbraunleh-me konnten auch im Liegenden mächtigerer Lösssedimente nachgewiesen werden. Es wird gezeigt, wie die periglazialen Decksedimente in ihrer räumlichen, vertikalen und stofflichen Variabilität Einfluss auf die Heterogenität der Bodendecke nehmen.
437

Mikroproportionering av cement : För minskning av koldioxidutsläpp

Haj Hamido, Ahmad, Salem, Majd Eddin January 2023 (has links)
This study has investigated the effect of replacing limestone with different percentages of limestone powder (5%, 10% and 15%) using the T KS method on the compressive strength of the mortar. The results have shown that the compressive strength of the mortar has decreased with curing time (at day 14) and with an increase in the proportion of limestone powder, contrary to what has been expected. This decrease in strength was attributed to the occurrence of delayed ettringite formation (DEF) in the mortar samples. DEF is a phenomenon that occurs in concrete and mortar when the conditions for ettringite formation are not optimal, which leads to the formation of a more expansive form of ettringite at a later stage. The presence of limestone aggregates in the mortar mix has been shown to contribute to the formation of DEF, resulting in the lower compressive strength values observed. This effect becomes greater the smaller the size of the limestone granules.The results suggest that caution should be exercised when using limestone powder as a replacement in mortar mixes, as it may lead to DEF and reduced compressive strength.
438

Validity of Holocene Analogs for Ancient Carbonate Stratigraphic Successions: Insights from a Heterogeneous Pleistocene Carbonate Platform Deposit

Hazard, Colby 01 February 2015 (has links) (PDF)
Observations of modern carbonate depositional environments and their accompanying depositional models have been used for decades in the reconstruction and interpretation of ancient carbonate depositional environments and stratigraphic successions. While these Holocene models are necessary for interpreting their more ancient counterparts, they inherently exclude important factors related to the erosion, diagenesis, and ultimate preservation of sediments and sedimentary structures that are ubiquitous in shallow marine carbonate environments. Andros Island, Bahamas is an ideal location to examine the validity of Holocene conceptual models, where geologically young (Late Pleistocene) limestones can be studied immediately adjacent to their well-documented modern equivalents. For this study, two 3D ground-penetrating radar (GPR) datasets (200 MHz and 400 MHz) were collected at a schoolyard in northwest Andros. These surveys reveal the geometries and internal characteristics of a peloidal-oolitic sand wave and tidal channel in unprecedented detail. These two prominent features are underlain by low-energy lagoonal wackestones and packstones, and are bordered laterally to the northwest by wackestones-packstones intermixed with thin sheets of peloidaloolitic grainstone. A deeper radar surface is observed at approximately 6 m depth dipping gently to the west, and is interpreted to be a karstified exposure surface delineating the base of a complete depositional sequence. Interpretation of the 3D radar volumes is enhanced and constrained by data from three cores drilled through the crest and toe of the sand wave, and through the tidal channel. This study is the first of its kind to capture the complex heterogeneity of a carbonate depositional package in three dimensions, where various depositional environments, sedimentary structures, and textures (mudstone to grainstone) have been preserved within a small volume.The results from this study suggest that the degree of vertical and lateral heterogeneity in preserved carbonate successions is often more complex than what can be observed in modern depositional environments, where sediments can generally only be observed in two dimensions, at an instant in time. Data from this study demonstrate the value of using two overlapping GPR datasets at differing resolutions to image the internal characteristics of a complete carbonate depositional package in three dimensions. From these datasets, a depositional model similar to other Holocene and Pleistocene carbonate depositional models is derived.
439

Porosity and Cement Development In Pleistocene Key Largo Limestone, Key Largo Florida

Cooper, Lorie Debra 05 1900 (has links)
<p> A detailed petrographic study of the Pleistocene Key Largo Limestone Formation, Key Largo, Florida, was undertaken observing three units of varying ages. From oldest to youngest, these are: Q4A (age unknown); Q4B, (180,000 years B.P.), and Q5, (125, 000 years B.P.). Fifty thin sections from four cored wells were point counted. Porosity remained constant for all three units at 28.5% as did total cements at 27.5%. These are still very porous rocks relative to ancient carbonates, which generally show 0-2% porosity. Q5 is diagenetically less mature than Q4B and Q4A, with the persistence of aragonite (which is being leached) and solution-enhanced interparticle porosity. Q5 has been exposed to a vadose environment. Multiple generation cements in Q4B indicate two periods of vadose exposure coincident with known Pleistocene eustatic sea level fluctuations. Moldic porosity is predominant in Q4B. Vague horizons of macroscopic vuggy porosity act as pathways of directed flow for percolating fluids precipitating late stage cements and stains rich in iron. Q4A has been interpreted as a beachrock in part, deposited at pH's greater than 9, resulting in dissolution of quartz grains. Of special interest in Q4A is the probable exploitation of a quartz substrate by endolithic borers. </p> / Thesis / Bachelor of Science (BSc)
440

Numerical Insights Into the Effect of Spacing on Axial Resistance of Auger Cast Piles

Correa Prada, Edgar Camilo 01 January 2023 (has links) (PDF)
The present thesis evaluates numerically and experimentally if the axial capacity of Auger Cast Piles (ACPs) constructed in interbedded layers of granular soil and Limestone should be reduced as a function of pile spacing. The numerical component of this thesis includes a series of parametric studies that consider different sets of normalized spacings, stiffness ratios, relative densities, unconfined compressive strengths, and installation effects for multiple subsurface conditions. The experimental program designed herein involves the construction of multiple components for a laboratory testing program of small-scale physical models that will validate the results of the numerical models in terms of capacities, efficiency ratios and normalized spacings.

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