A durabilidade das estruturas de concreto tem se tornado um assunto de interesse mundial nas últimas duas décadas. Os custos econômicos associados a reparos de estruturas de concreto são cada vez maiores, e cada vez mais a incidência de insucessos nessas intervenções corretivas que não resultam adequadas é reportada. No Brasil a técnica de intervenção corretiva mais utilizada é a de reparos localizados com argamassas base cimento modificadas com polímeros. Uma das patologias mais comumente apresentada quando do uso deste tipo de intervenção é a fissuração associada à retração. O presente trabalho pretende avaliar a influência das variáveis mais importantes e até de alguns parâmetros de dosagem, na fissuração devido à retração de argamassas de reparo. Para tal foi estudada uma família de argamassas com mesma consistência de traços 1:1,0, 1:1,5, 1:2,2 e 1:3,0; utilizando para estas um teor fixo de polímero e de aditivo superplastificante com relação à massa do cimento. Foram também avaliadas três argamassas de base cimento modificadas com polímeros disponíveis no país e comercializadas para o reparo de estruturas de concreto, de modo a classificar e comparar estas quanto à fissuração, em relação àquelas dosadas em laboratório. Para avaliar a tendência à fissuração das argamassas foram realizados ensaios de retração potencial livre, resistência à tração na flexão, módulo de elasticidade e retração restringida. Os resultados obtidos mostram que o modelo εj - ftj/Ecj conseguiu acusar a fissuração das argamassas que realmente fissuraram no ensaio de retração restringida. Esse modelo considera todas as variáveis influentes na fissuração medidas no programa experimental. Verificou-se também que para um estudo mais simplificado pode ser utilizado um modelo que considera apenas a retração livre, porém este se coloca sempre a favor da segurança. Para argamassas de uma mesma família pode-se dizer que há um traço que apresenta a menor tendência à fissuração. / The durability of concrete structures has become an issue of interest worldwide especially during the last two decades. The expenditures associated to the repair and rehabilitation of concrete structures is becoming increasingly higher, and the amount of unsucceeded repairs on concrete structures has been reported as unacceptable. In Brazil, patch repair with cement-based polymer modified mortars is the most widely technique used. One of the main causes of distress when using this type of repair has been found to be shrinkage cracking. The target of this research is to evaluate the effect of some significant properties and also some mix-design parameters on the cracking potential due to shrinkage of repair mortars. Therefore, a family of mortars with the same consistency with cement:sand proportions of 1:1,0, 1:1,5, 1:2,2 and 1:3,0; with a constant polymer and superplasticizer content related to the cement weight. Also, three industrialized polymer modified repair mortars from different manufacturers were evaluated, thus allowing classifying and comparing their cracking potential with the laboratory prepared mortars. For evaluating the cracking potential of the mortars the following tests were selected, free-shrinkage, flexural strength, elasticity modulus and restrained shrinkage. The results obtained show that the model εj - ftj/Ecj was able to distinguish the mortars that cracked during the restrained shrinkage testing from the mortars that did not crack. This model considers all of the variables measured during the experimental program affecting shrinkage related cracking. It was also verified that a more simplified study can considering only the free-shrinkage of the mortars can be applied; being that this model will always be in favor of security. For mortars of a same family it can be concluded that there is one mix-proportion that will present the least cracking tendency.

This project is a book which facilitates thinking about the ongoing climate crisis from a Degrowth perspective. Methods are to the greater part reading literature, watching interviews and also to a lesser extent conducting a survey, contacting a researcher and holding a workshop. The key visual tools that are used in this book are typography, infographics, illustration, layout and bookbinding. Firstly, the connection between personal experience and global warming is illustrated. Secondly, based on the severity and scope of the crisis, it is argued that radical societal change is required. Thirdly, the solution approach of shrinking the economy is investigated and suggested. Importantly, some key dynamics of capitalism are deconstructed, such as the accumulation of wealth and power, the exploitation of the global South, the disconnect of money and social value, the misconception of work and finally how these lead to disastrous greenhouse gas emissions as well. Essentially, shrinking the economy is identified as an absolute necessity to supporting and indeed extending human well-being to all.

My thesis consists of three chapters. The first chapter uses the Factor-augmented Error Correction Model in model averaging for predictive regressions, which provides significant improvements with large datasets in areas where the individual methods have not. I allow the candidate models to vary by the number of dependent variable lags, the number of factors, and the number of cointegration ranks. I show that the leave-h-out cross-validation criterion is an asymptotically unbiased estimator of the optimal mean squared forecast error, using either the estimated cointegration vectors or the nonstationary regressors. Empirical results demonstrate that including cointegration relationships significantly improves long-run forecasts of a standard set of macroeconomic variables. I also estimate simulation-based prediction intervals for six real and nominal macroeconomics variables. The results are consistent with the point estimates, which further support the usefulness of cointegration in long-run forecasts.<div><br></div><div>The second chapter is a Monte Carlo study comparing the finite sample performance of six recently proposed estimation methods designed for large-dimensional regressions with endogeneity. The methods are based on combining shrinkage estimation with two-stage least squares (2SLS) or generalized method of moments(GMM), where both the number of regressors and instruments can be large. The methods are evaluated in terms of bias and mean squared error of the estimators. I consider a variety of designs with practically relevant features such as weak instruments and heteroskedasticity as well as cases where the number of observations is smaller/larger than the number of regressors/instruments. The consistency results show that the methods using GMM with shrinkage provide smaller estimation errors than the methods using 2SLS with shrinkage. Moreover, the results support the use of cross-validation to select tuning parameters if theoretically derived parameters are unavailable. Lastly, the results indicate that all instruments should correlate with at least one endogenous regressor to ensure estimation consistency.<br></div><div><br></div><div>The third chapter is coauthored with Mohitosh Kejriwal. We present new evidence on the nexus between democracy and growth employing the dynamic common correlated effects (DCCE) approach advanced by Chudik and Pesaran (2015), which is robust to both parameter heterogeneity and cross-section dependence. The DCCE results indicate a positive and statistically significant effect of democracy on economic growth, with a point estimate between approximately 1.5-2% depending on the specification. We complement our estimates with a battery of diagnostic tests for heterogeneity and cross-section dependence that corroborate the use of the DCCE approach.<br></div>

京都大学 / 新制・課程博士 / 博士(情報学) / 甲第23314号 / 情博第750号 / 新制||情||128(附属図書館) / 京都大学大学院情報学研究科知能情報学専攻 / (主査)教授 山本 章博, 教授 鹿島 久嗣, 教授 河原 達也 / 学位規則第4条第1項該当 / Doctor of Informatics / Kyoto University / DFAM

Content: A characteristic of leather is that if it is gradually heated in aqueous solution it reaches a temperature where sudden and irreversible shrinkage occurs. This phenomenon is related to the denaturalization of the collagen protein that conforms the hide and is known as leather shrinkage. Specifically, the internal bonds break thus causing a shortening of the skin that can be up to a 35% from its original length. Accordingly, one of the most used methods to check the quality of the leather tanning process is the determination of the contraction temperature according to the ISO 3380:2015 standard. This method measures the leather shrinkage when constantly increasing the sample temperature. The shrinkage temperature corresponds to the temperature when the sample suddenly contracts. The value of this temperature indicates the degree of collagen stability and therefore, when higher, the leather will have better quality and resistance. The process of leather shrinkage can be divided in different stages. Several authors discriminate temperature A1 (when the first fibre starts to shrinkage), temperature C (when there is a massive shrinkage) and finally temperature A2 (when the last fibres are contracted individually). The method that describes the ISO 3380:2015 standard uses a device where the determination of the shrinkage temperature is performed visually by the laboratory technician. Consequently, the method tends to be imprecise and subjective. It should also be noticed that the device proposed by the standard does not allow differentiation between the different stages of the contraction process. There are other methods to determine leather shrinkage temperature including differential scanning calorimetry, microscopic hot table, thermogravimetric analysis, differential thermal analysis and thermomechanical analysis. All these methods involve complex devices and are only suitable for specialized personnel. In this work, a new device is developed to precisely measure the leather shrinkage temperature and to distinguish the different contraction stages. In addition, the proposed device is simple, easy to use and inexpensive, which facilitates its use in any industry. The developed system consists basically of a load cell to measure the strength produced by the shrinkage of the leather. With the logged data during the test a strength versus temperature graph is built. By means of its interpretation, the different stages of shrinkage can be determined. Different mathematical analysis of the logged data is proposed to determine the shrinkage stages temperatures, thus achieving a high degree of certainty and repeatability. Take-Away: A new device, simple and inexpensive, is developed to precisely measure the leather shrinkage temperature and to distinguish the different contraction stages.

No description available.

The work of the Cal Poly Tissue Engineering Lab is primarily focused on the fabrication, characterization, and improvement of “Blood Vessel Mimics” (BVMs), tissue engineered constructs used to evaluate cellular response to vascular medical devices. Currently, cells are grown onto fibrous, porous tubes made using an in-house electrospinning process from PLGA, a biocompatible co-polymer. The adhesion and proliferation of cells in a BVM is reliant on the micro-scale structure of the PLGA scaffold, and as such it is of great importance for the electrospinning process to consistently produce scaffolds of similar morphologies. Additionally, it has been shown that cell proliferation increases with scaffolds of smaller fibers and pores than the current electrospinning protocol can produce. Finally, the Tissue Engineering Lab has interest in testing devices in more tortuous BVM bioreactor designs, however the use of relatively rigid PLGA scaffolds has severely limited the ability to construct more complicated vessel geometries. The overall goal of this thesis was to improve fabrication and characterization of electrospun polymer scaffolds for BVM use. The specific aims of this thesis were to: 1) Improve scaffold characterization by comparing two techniques for fiber diameter measurement and implementing a technique for pore area measurement. 2) Reduce scaffold fiber diameter and pore area by investigating humidity and solvent composition electrospinning parameters. 3) Reduce process variability by developing a more specific electrospinning protocol. 4) Improve scaffold consistency and use by understanding and reducing PLGA scaffold shrinkage. 5) Identify and evaluate more flexible polymers as potential alternatives for electrospun BVM scaffolds. In order to accomplish these aims, first, several BVM and outside literature images were taken and evaluated with current and prospective fiber diameter techniques, and with 2 prospective pore area techniques to characterize accuracy and consistency of each method. It was found that the prospective fiber diameter measurement technique was not superior to the current method. The techniques developed for pore area measurement were found to produce results that differed significantly from each other and from the published value for a given image. Next, changes to environmental and solution composition parameters were made with the hopes of reducing fiber diameter and pore area of electrospun PLGA scaffolds. Changes in relative humidity did not appear to significantly affect scaffold fiber diameter while changes to solvent composition, specifically the use of acetone, resulted in fibers significantly smaller than those regularly achieved in the BVM lab. Next, several sources of variability in the electrospinning protocol were identified and subsequently altered to improve consistency and usability. Specifically, this included redefining the precision with which PLGA mass was measured, repositioning electrical equipment to reduce the effect of stray electrostatic forces on the polymer solution jet, attempting to control the temperature and humidity inside the electrospinning enclosure, and improving the ease with which scaffolds are removed from their mandrels through alternative mandrel surface treatments. In addition to overall process variability, the issue of scaffold shrinkage during BVM use was investigated and two possible treatments, exposure to either ethanol or elevated temperatures, were proposed based on previous electrospinning literature results. Each was tested for their effectiveness in mitigating shrinkage through exposure to BVM setup-mimicking conditions. It was found that both treatments reduced scaffold shrinkage compared to control samples when exposed to BVM setup-mimicking conditions. Finally, 3 flexible polymers were selected and electrospun to compare against typical PLGA results and to conduct a kink radius test as a metric for measuring flexibility as it pertains to the proposed BVM lab application. It was concluded that two types of thermoplastic polyurethane (tPU) were not acceptable electrospinning materials for use in the BVM lab. Additionally, while polycaprolactone (PCL) could be successfully electrospun it could not undergo the amount bending required for more tortuous BVM bioreactor designs without kinking. Overall, the work in this thesis provided insight into multiple scaffold characterization techniques, reduced overall electrospinning variability in the fabrication and use of PLGA scaffolds, and defined processing parameters that have been shown to yield scaffolds with smaller morphological features than all prior Tissue Engineering Lab work. By creating better, more effective scaffolds, researchers in the Tissue Engineering Lab can more accurately mimic the structure and properties of native blood vessels; this, in turn, will result in BVM cell responses that more closely resemble that of native tissue. Creating consistent and appropriate BVMs will then lead to impactful contributions to the existing body of tissue engineering research and to better preclinical device testing.

This thesis deals with the comparison of volumetric and stress variations in different formulations of cast floor self-leveling screeds during maturation. These changes were measured by several methods. Furthermore, the strength parameters of the test materials were compared. The test specimens were cured in metallic and elastic forms. The microstructure of these samples were monitored by scanning electron microscopy. In conclusion, the suitability of the tested methods for the given type of flooring materials was evaluated.

Air entraining admixtures are surfactants, that are commonly used in Portland cement materials, because they form and stabilize small air bubbles distributed in the binder, thereby changing the pore size distribution. The aim of these additives is to increase the durability of the cured binder, especially in climatic conditions, where it must withstand low temperatures, and simultaneously improving the workability in the plastic state. The effect of air entraining admixtures in alkali-activated slag was studied for certain properties. Air entraining admixtures were able to entrain the air in the alkali-activated matrix, they changed the pore size distribution, which resulted in a reduction in capillary pressure in the porous complex, and there was a reduction of shrinkage under autogenous conditions, respectively. The improvement of workability is certainly also positive, but on the other hand there has been a bad effect on flexural strength and compressive strength. The morphology of the air entrained binder was observed by scanning electron microscopy, and simultaneously the effect of air entrained admixtures on hydration was observed by isothermal calorimetry.

The Soil Water Retention Curve (SWRC) of different soils has been researched thoroughly by multiple Geotechnical Engineers. The interpretation of the SWRC for a specific soil leads to the identification of certain properties of the soil. The SWRC typically involves a plot of suction measurements (on a logarithmic scale) against the volumetric water content or degree of saturation of the soil. This project aims to determine a manner in which concrete properties (such as durability, porosity, shrinkage, strength and stiffness) can be estimated through suction measurements. The Dew Point PotentiaMeter (WP4C) apparatus was used to measure the suctions of different concrete mixtures, as well as to derive the water retention curve of concrete. A cement paste study was first conducted to determine whether this apparatus is able to deliver representative results, which it is. It was discovered that the water retention curve of concrete is similar to a bimodal SWRC identified by Geotechnical Engineers. Thereafter, a mortar study was completed to determine if the water retention curves can be used to estimate different concrete properties. Three different porosity tests were investigated during this research study, namely the X-ray test, the Mercury Intrusion Porosimetry (MIP) test and a simple test method described in the durability index testing procedure manual assembled by University of Cape Town, University of the Witwatersrand and CoMSIRU. It was concluded that the MIP test and the simple test method described in the durability index testing procedure manual gave the most comparable results with regards to literature. The shrinkage of the concrete mixture was investigated to determine a relationship between the suctions and the shrinkage of the concrete. Different strength tests of all the concrete mixtures were also investigated, namely the flexural test, the compressive test, the splitting cylinder test and the E-value test (stiffness). It was concluded that there was a definite trend between the suction measurements and the specific concrete properties tested. The water retention curve has the potential to describe various properties of different concrete mixtures. / Dissertation (MEng (Structural Engineering))--University of Pretoria, 2020. / Civil Engineering / MEng (Structural Engineering) / Unrestricted