Dissertations / Theses on the topic 'Density'

In this study, the effects of organoclay loading, compatibilizer loading and polyethylene type on the morphology, rheology, thermal properties and mechanical properties of polyethylene/compatibilizer/organoclay nanocomposites were investigated. As compatibilizer, terpolymer of ethylene-methacrylate-glycidyl methacrylate (Lotader®
AX8900), as organoclay Cloisite®
15A were used. All samples were prepared by a co-rotating twin screw extruder, followed by injection molding. Considering ternary nanocomposites, highest impact strength results were obtained with 10% compatibilizer plus 2% organoclay
highest yield stress, elastic modulus, flexural strength, flexural modulus were obtained with 5% compatibilizer plus 4-6% organoclay. DSC data indicated that addition of organoclay and compatibilizer did not change the melting point remarkably
on the other hand it affected the crystallinity. The organoclay used had no nucleation effect on polyethylene, and the compatibilizer decreased the crystallinity of the matrix. X-ray diffraction showed that in all ternary nanocomposites and in binary nanocomposite of high density polyethylene with organoclay, layer separation associated with intercalation of the clay structure occurred,. The highest increase of interlayer gallery spacing was obtained with 10% compatibilizer plus 2% organoclay, which were 25%, 28% and 27% for HDPE, LLDPE and LDPE matrices respectively.

Master of Regional and Community Planning
Department of Landscape Architecture/Regional and Community Planning
Jason Brody
Today, achieving higher residential densities is an integral part of most discussions on concepts such as sustainability, placemaking, smart growth and new urbanism. It is argued that high density environments can potentially improve quality of life through a range of social benefits. In attempting to achieve these benefits, often times, developments that provide more than a certain number of dwelling units are considered desirable and successful high-density developments. However, understanding high residential density merely in terms of an increase in the number of dwelling units over an area of development might not help realize meaningful social benefits; in fact it could result in problems such as parking constraints, increased vehicular traffic, crowding, and eventually abandonment. This implies a dilemma of understanding high density environments holistically. Using literature review and design exploration as two key research methods, this project aims at resolving this dilemma by presenting a holistic understanding of desirable high-density environments. The research works on the idea that high densities are a matter of design and performance. Through synthesis of literature review and explorative design findings, this research focuses on the qualitative aspects of high density environments that make them meaningful and desirable. Through synthesis of literature review and design findings, the research finds that desirable high density environments should (a) Be Physically Compact; (b) Support Urbanity; and (c) Offer Livability and Sense of Place. These three qualitative aspects of high density environments are critical in determining how well such environments perform. The research further proposes eight meaningful goals and seventeen specific guidelines to achieve aforementioned three qualities that influence the performance of high density developments. In addition to these principles and guidelines, opportunities and challenges posed by explorative design exercises also allows identifying certain supplementary guidelines necessary to strengthen the framework. Together, these findings result in a theoretical framework that may be used as an effective design and evaluation tool in considering high density environments. This framework is named “Density Dynamics” to signify various morphological and socio-economic dynamics involved in a holistic understanding of high density environments.

Una metodologia denominata Scalar Mass Filtered Density Function (SFMDF) e’ stata uti- lizzata per condurre Large Eddy Simulation (LES) di flussi turbolenti con reazioni chimiche. La SFMDF descrive la distribuzione delle fluttuazioni di sottoscala delle concentrazioni delle specie chimiche e dell’entalpia. Il grande vantaggio della formulazione SFMDF risiede nel fatto che il termine sorgente che descrive l’effetto delle reazioni chimiche appare in forma chiusa e non deve essere modellato. Il metodo presentato in questa tesi di dottorato si basa sull’equazione di trasporto della SFMDF, che viene risolta con un metodo Monte Carlo. La SFMDF e’ in grado di fornire solo la concentrazione delle specie chimiche e l’entalpia: tutte le altre variabili devono essere calcolate da un solutore fluidodinamico. Questo tipo di approccio viene detto ibrido. Per questa tesi e’ stato sviluppato un solutore Monte Carlo in grado di risolvere l’equazione di trasporto della SFMDF in forma Lagrangiana. Questo codice e’ stato accoppiato a un codice fluidodinamico ai volumi finiti che opera su domini non strutturati sviluppato dalla University of Minnesota. I risultati dei test effettuati su mixing layer bi- e tri-dimensionali e su scie planari tridimensionali mostrano che il metodo e’ consistente e accurato.

This research aims at exploring meanings, qualities and analytical abilities of density concept and its potential interpretations in architecture and sustainability fields. Despite the growing unsustainability of today's city facing an effective energy and environmental crisis, recent statistics have confirmed the increasing attractive power of metropolitan areas. Within the context of European compact city, new building models based on energy conservation principles account for an insignificant percentage compared to the great mass of existing city whose functioning remarkably affects the inefficiency of the whole metropolitan system. Therefore an approach determining design instruments and methods at urban and architectural scale must be found in order to set out conditions more appropriate to the compact city. At this analysis stage, the relationship between energy and form takes a central role in the variation of energy performances; at the same time the concept of density has showed the ability to describe the morphological performances of the built form. The general aim of the present research is to determine the relationships among built-form, energy and urban fabrics by the density parameter in compact city with Mediterranean climate. This research is composed by four interconnected parts. The first one examines the relationship among current urban and energy dynamics to comprehend the role and contribution of the building industry in the light of the scientific progress and the implementation of present operational and regulatory instruments. The second one investigates role and evolution of the density concept as parameter, design instrument and basis of theoretical categories, especially referring to interactions with urban form and sustainability. In the third part the analytical and interpretative abilities of density are employed in order to prove the environmental implications and verify the existence of interactions among urban sustainability indicators and density. Finally, the fourth part enquires into the relationships among form, building, density and energy set up in the compact fabrics in Rome and Barcelona by models and simulations in order to control the main formal, building and energy factors parametrically. The influence of urban morphology, built-form and constructive features on solar access and energy demand for conditioning are shown by different density indicators that are the more suitable to express reliable trends. Firstly results point out that the contribution of the built environment to the complex energy issue arisen by metropolitan systems must be focused on the reduction of the demand - even before on the consumption and impact - operating with multi-scale instruments and methods for the transformation of existing city. The density has a preferred role in the relationship between sustainability and form thanks to its interpretative skills and meanings undertaken as theoretical and design category. At the metropolitan scale, urban quality indicators and density do not always show evident relationships with energy and environmental implications. Built-form typology and constructive features are the main factors that occur on energy performances variation of urban fabrics. The investigation of these kind of performances by density parameters leads to the comprehension of the different energy behavior in each urban texture, offering a contribution to the energy analysis at urban scale. Methodology and the defined parameters of density show themselves as knowledge base for aware transformations of Mediterranean compact city as well as applications in other urban contexts both for existing and new constructions.
La ricerca esplora significati, proprietà e capacità analitiche del concetto di densità e delle sue possibili interpretazioni nell’ambito dell’architettura e della sostenibilità. Il suo obiettivo è la determinazione di relazioni tra costruito, energia e forma dei tessuti urbani della città compatta mediterranea ricorrendo alla densità quale parametro utile a decifrarne le specificità. A dispetto della sempre maggiore insostenibilità della città odierna, di fronte alla crisi energetica ed ambientale in atto, recenti statistiche hanno confermato il crescente potere attrattivo delle aree metropolitane. Nel contesto della città compatta europea, i nuovi modelli insediativi basati su principi di risparmio energetico rappresentano una percentuale insignificante rispetto alla città esistente che, nel funzionare, incide notevolmente sull’inefficienza dell’intero sistema metropolitano. In questo quadro, potrebbe essere risolutivo identificare un approccio che individui strumenti e metodi progettuali alla scala urbana piuttosto che a quella architettonica, utili a definire condizioni più appropriate e realmente incisivi per la città compatta. Se riferito in primo luogo a tale scala il rapporto tra energia e forma assume un ruolo centrale sulla variazione delle prestazioni energetiche; allo stesso tempo il concetto di densità appare un’efficace strumento di analisi delle prestazioni morfologiche del costruito. La ricerca si compone di cinque parti. La prima analizza la condizione odierna delle dinamiche urbane ed energetiche, per comprendere ruolo e contributo dell’edilizia alla luce dell’avanzamento del pensiero scientifico e degli strumenti operativi disponibili. La seconda affronta il significato e l’evoluzione del concetto di densità quale parametro di misura, strumento progettuale e fondamento teorico, facendo riferimento in particolare alle interazioni con la forma urbana e la sostenibilità. Nella terza si utilizzano le capacità analitiche della densità per comprovare le implicazioni ambientali e verificare l’esistenza di leggi di dipendenza tra indicatori di sostenibilità urbana e densità. La quarta pone le basi per la comprensione delle relazioni tra densità ed energia alla scala urbana. La quinta parte, infine, indaga tali relazioni nei tessuti compatti di Roma e Barcellona declinandole in termini di caratteri formali e costruttivi, con l’ausilio di modellazioni e simulazioni strutturate allo scopo di controllare i corrispondenti fattori. S’illustra l’influenza di morfologia urbana e caratteri tipologico-costruttivi su guadagno solare e domanda energetica per riscaldamento e climatizzazione, individuando per mezzo di differenti definizioni d’indicatori di densità, i più adeguati ad esprimere con queste leggi di variazione affidabili. I risultati evidenziano che il contributo dell’edilizia alla complessa questione energetica posta dai sistemi metropolitani deve concentrarsi sulla riduzione della domanda - ancor prima che su consumo e impatto - operando con strumenti e metodi interscalari per la trasformazione della città esistente. La densità ha un ruolo privilegiato nel rapporto forma-sostenibilità per capacità interpretative e significati assunti quale categoria teorica e progettuale. A scala metropolitana, indicatori di sostenibilità urbana e densità non sempre mostrano chiare relazioni con le implicazioni ambientali ed energetiche. Morfologia, tipologia e aspetti costruttivi sono i fattori che più intervengono sulla variazione delle prestazioni energetiche dei tessuti urbani. Analizzarli mediante parametri di densità conduce alla comprensione del diverso comportamento energetico, fornendo un contributo agli strumenti d’indagine a scala urbana e favorendo una connotazione più efficiente del costruito riconducibile alla dimensione della densità sostenibile. Il metodo e gli strumenti individuati si offrono come base di conoscenza per trasformazioni consapevoli della città compatta mediterranea
El presente estudio indaga significados, propiedad y capacidad analíticas del concepto de densidad y de su posible interpretación en el ámbito de la arquitectura y de la sostenibilidad. El principal objetivo es determinar las relaciones entre ambiente construido, energía y forma de los tejidos urbanos recurriendo a la densidad como parámetro útil para descifrar sus especificidades de la ciudad compacta mediterránea. A pesar de una siempre mayor insostenibilidad de la ciudad actual, frente a la crisis energética y ambiental en curso, estadísticas recientes han confirmado el creciente poder atractivo de las metrópolis. En el contexto de la ciudad europea, los modelos de asentamiento actuales, basados en principios de ahorro energético, constituyen un porcentaje insignificante frente a la ciudad existente que, funcionando, grava notablemente en consumo el sistema metropolitano. En esta situación, podría ser resolutivo identificar un acercamiento que identifique herramientas y métodos para el proyecto a escala urbana, que sean útiles para definir condiciones más apropiadas y sean realmente eficaces para la ciudad compacta. Si se refiere en primer lugar a dicha escala, la relación entre energía y forma asume una función central para la variabilidad de la prestación energética; al mismo tiempo el concepto de densidad parece una herramienta eficaz para analizar las prestaciones morfológicas del ambiente construido. La investigación se compone de cinco partes. La primera analiza las dinámicas urbanas y energéticas actuales, para entender capacidad y contribución de la construcción a la luz del avance del pensamiento científico y de las herramientas disponibles. La segunda trata el significado y la evolución del concepto de densidad como parámetro de medida, herramienta del proyecto y origen teórico de la arquitectura, con particular referencia a las interacciones con la forma urbana y la sostenibilidad. En la tercera se utilizan las capacidades analíticas de la densidad para comprobar las repercusiones ambientales y verificar la existencia de leyes de dependencia entre indicadores de sostenibilidad urbana y densidad. La cuarta explica las relaciones entre densidad y energía a la escala urbana. La quinta, finalmente, estudia estas relaciones en los tejidos compactos de Roma y Barcelona, explicándolas en función de forma i construcción, con el auxilio de modelos y simulaciones. Se muestra la influencia de la morfología urbana y las características tipológicas y constructivas sobre la captación solar y la demanda energética por calefacción y climatización, individualizando entre diferentes indicadores de densidad los más apropiados para representar tendencias fiables. Los resultados prueban que la contribución de la construcción a la compleja cuestión energética tiene que basarse en la reducción de la demanda - antes que del consumo y del impacto - utilizando herramientas y métodos multi-escalares para la transformación de la ciudad existente. La densidad tiene una función privilegiada en la relación forma-sostenibilidad que depende de sus capacidades analíticas y significados en calidad de categoría teórica y del proyecto. A escala metropolitana, los indicadores de sostenibilidad urbana y densidad no siempre muestran una relación clara con las repercusiones ambientales y energéticas. Morfología, tipología y aspectos constructivos son los factores que más influyen sobre la variación de la prestación energética de los tejidos urbanos. Analizarlos recurriendo a parámetros de densidad, lleva a entender el diferente comportamiento energético, contribuye a las investigaciones a escala urbana y favorece la eficiencia del ambiente construido, con lo cual se reconduce el análisis al concepto de densidad sostenible. La metodología y las herramientas individualizadas se ofrecen como base de conocimiento para orientar las transformaciones de la ciudad compacta mediterránea.

Low density plasmas are found throughout the known universe. Therefore, accurate diagnostic methods have implications for our understanding of a variety of topics, ranging from star formation to the semi conductor industry. Low density plasmas are ubiquitous in the material processing industry. However, measurements of the electron temperature and density, two of the most fundamental plasma properties, are not straightforward. In the laboratory, we create a low density, radio frequency, helium plasma with a bi-Maxwellian electron distribution, similar to those found in the semiconductor processing industry. We use optical emission spectroscopy to perform a non invasive measurement of the plasma conditions. We compare this to measurements obtained using a Langmuir probe, a commonly used invasive diagnostic. The optical emission spectroscopy is found to be insensitive to electron density but good agreement is found between the two techniques for values of the temperature of the hot electron component of the bi-Maxwellian. Plasmas created with high-intensity lasers are able to recreate conditions similar to those found during astrophysical events. This development has led to these condi- tions being explored in laboratories around the world. An experiment was performed at the Rutherford Appleton Laboratory in Didcot, UK, investigating the properties of supersonic turbulent jets. For the first time a magneto-optic probe was used to measure the magnetic field in a low-density supersonic turbulent plasma. The results were compared to measurements taken using a magnetic-induction probe. Good agreement was found between measurements of the magnetic field strength within the plasma; however, the magnetic power spectra differ. We attribute this to the dif- ference in integration length between the two measurements. Statistical properties of the velocity field are inferred from the magnetic field measurements, which compare favourably to astrophysical observations and hydrodynamic simulations.

This thesis presents a brief review of gravitation and cosmology, and then gives an overview of the theory of cosmological perturbations; subsequently some applications are discussed, such as large-scale structure formation. Cosmological perturbations are here presented both in the Newtonian paradigm and in two di¤erent relativistic approaches. The relativistic approaches are (i) the metric approach, where small variations of the metric tensor are considered, and (ii) the covariant approach, which focusses on small variations of the curvature. Dealing with these two approaches also involves addressing the gauge problem –how to map an idealized world model into a more accurate world model.

Snow density is an important measure in hydrological applications. It is used to convert snow depth to the snow water equivalent (SWE). A model developed by Sturm et al. (2010) predicts the snow density by using snow depth, the snow age and a snow class defined by the location. In this work the model is extended to include seasonal weather variables and variables concerning the location. The model is tested and fitted for 4040 Norwegian snow depth and densities measurements in the period $1998-2011$. A Bayesian modeling framework is chosen. To do inference a Markov Chain Monte Carlo method with Gibbs sampler is used, and cross-validation is used for model evaluation. The final model improved the snow density predictions for the Norwegian data compared to the model of Sturm et al. (2010). In addition year specific measurements are performed in different areas, and included in the model by using random effects. The associated reduction in the prediction error is computed, indicating a significant improvement by utilizing information of annual snow measurements.

We compare two time series models: an ARMA(1,1)-ACD(1,1)-NIG model against an ARMA(1,1)-GARCH(1,1)-NIG model. Their out-of-sample performance is of interest rather than their in-sample properties. The models produce one-day ahead forecasts which are evaluated using three statistical tests: VaR-test, VaRdur-test and Berkowitz-test. All three tests are concerned with the the tail events, since our time series models are often used to estimate downside risk. When the two models are applied to data on Canadian stock market returns, our three statistical tests point in the direction that the ACD model and the GARCH model perform similarly. The difference between the models is small. We finish with comments on the model uncertainty inherit in the comparison.

Magnetic Resonance Electrical Impedance Tomography (MREIT) algorithms using current density distribution have been proposed in the literature. The current density distribution can be determined by using Magnetic Resonance Current Density Imaging (MRCDI) technique. In MRCDI technique, all three components of magnetic flux density should be measured. Hence, object should be rotated inside the magnet which is not trivial even for small size objects and remains as a strong limitation to clinical applicability of the technique. In this thesis, 2D MRCDI problem is investigated in detail and an analytical relation is found between Bz, Jx and Jy. This study makes it easy to understand the behavior of Bz due to changes in Jx and Jy. Furthermore, a novel 2D MRCDI reconstruction algorithm using one component of B is proposed. Iterative FT-MRCDI algorithm is also implemented. The algorithms are tested with simulation and experimental models. In simulations, error in the reconstructed current density changes between 0.27% - 23.00% using the proposed algorithm and 7.41% - 37.45% using the iterative FT-MRCDI algorithm for various SNR levels. The proposed algorithm is superior to the iterative FT-MRCDI algorithm in reconstruction time comparison. In experimental models, the classical MRCDI algorithm has the best reconstruction performance when the algorithms are compared by evaluating the reconstructed current density images perceptually. However, the J-substitution algorithm reconstructs the best conductivity image by using J obtained from the proposed algorithm. Finally, the iterative FT-MRCDI algorithm shows the best performance when the reconstructed current density images are verified by using divergence theorem.

During the last three years, my practice has mainly consisted of installation works; compositions of images, texts, video, constructions, produced and found objects, drawings etcetera. This thesis serves to present an overview of my practice during these three years, to contextualize my work and work method and to discuss my future artistic intentions.

With the advent of the information technology, the amount of data we are facing today is growing in both the scale and the dimensionality dramatically. It thus raises new challenges for some traditional machine learning tasks. This thesis is mainly concerned with manifold aligned density estimation problems. In particular, the work presented in this thesis includes efficiently learning the density distribution on very large-scale datasets and estimating the manifold aligned density through explicit manifold modeling. First, we propose an efficient and sparse density estimator: Fast Parzen Windows (FPW) to represent the density of large-scale dataset by a mixture of locally fitted Gaussians components. The Gaussian components in the model are estimated in a "sloppy" way, which can avoid very time-consuming "global" optimizations, keep the simplicity of the density estimator and also assure the estimation accuracy. Preliminary theoretical work shows that the performance of the local fitted Gaussian components is related to the curvature of the true density and the characteristic of Gaussian model itself. A successful application of our FPW on principled calibrating the galaxy simulations is also demonstrated in the thesis. Then, we investigate the problem of manifold (i.e., low dimensional structure) aligned density estimation through explicit manifold modeling, which aims to obtain the embedded manifold and the density distribution simultaneously. A new manifold learning algorithm is proposed to capture the non-linear low dimensional structure and provides an improved initialization to Generative Topographic Mapping (GTM) model. The GTM models are then employed in our proposed hierarchical mixture model to estimate the density of data aligned along multiple manifolds. Extensive experiments verified the effectiveness of the presented work.

There are situations in the framework of quasi-Monte Carlo integration where nonuniform low-discrepancy sequences are required. Using the inversion method for this task usually results in the best performance in terms of the integration errors. However, this method requires a fast algorithm for evaluating the inverse of the cumulative distribution function which is often not available. Then a smoothed version of transformed density rejection is a good alternative as it is a fast method and its speed hardly depends on the distribution. It can easily be adjusted such that it is almost as good as the inversion method. For importance sampling it is even better to use the hat distribution as importance distribution directly. Then the resulting algorithm is as good as using the inversion method for the original importance distribution but its generation time is much shorter.
Series: Preprint Series / Department of Applied Statistics and Data Processing

This dissertation investigates the performance of two-class classi cation credit scoring data sets with low default ratios. The standard two-class parametric Gaussian and naive Bayes (NB), as well as the non-parametric Parzen classi ers are extended, using Bayes' rule, to include either a class imbalance or a Bernoulli prior. This is done with the aim of addressing the low default probability problem. Furthermore, the performance of Parzen classi cation with Silverman and Minimum Leave-one-out Entropy (MLE) Gaussian kernel bandwidth estimation is also investigated. It is shown that the non-parametric Parzen classi ers yield superior classi cation power. However, there is a longing for these non-parametric classi ers to posses a predictive power, such as exhibited by the odds ratio found in logistic regression (LR). The dissertation therefore dedicates a section to, amongst other things, study the paper entitled \Model-Free Objective Bayesian Prediction" (Bernardo 1999). Since this approach to Bayesian kernel density estimation is only developed for the univariate and the uncorrelated multivariate case, the section develops a theoretical multivariate approach to Bayesian kernel density estimation. This approach is theoretically capable of handling both correlated as well as uncorrelated features in data. This is done through the assumption of a multivariate Gaussian kernel function and the use of an inverse Wishart prior.
Dissertation (MSc)--University of Pretoria, 2017.
The financial assistance of the National Research Foundation (NRF) towards this research is hereby acknowledged. Opinions expressed and conclusions arrived at, are those of the authors and are not necessarily to be attributed to the NRF.
Statistics
MSc
Unrestricted

Massive migration is one the most significant phenomena of China's urbanization. In the thirty years since the "Reform and Open Up" policy began, Guangzhou has experienced economic growth and urban expansion and attracted a vast number of migrants. Seen as the product of the rapid urbanization, urban villages accommodate the majority of migrants by providing low-rent housing, but at the same time cause many social problems. This thesis aim at improving the migrants' standard of living, helping them gradually integrate into the city, and enhancing the potential for social interactions in the neighborhood.
Master of Architecture

The local likelihood method of Copas (1995a) allows for the incorporation into our parametric model of influence from data local to the point t at which we are estimating the true density function g(t). This is achieved through an analogy with censored data; we define the probability of a data point being considered observed, given that it has taken value xi, as where K is a scaled kernel function with smoothing parameter h. This leads to a likelihood function which gives more weight to observations close to t, hence the term ‘local likelihood’. After constructing this local likelihood function and maximising it at t, the resulting density estimate f(tiOt) can be described as semi-parametric in terms of its limits with respect to h. As h--oo, it approximates a standard parametric' fit f(I.O) whereas when h decreases towards 0, it approximates the non - parametric kernel density estimate. My thesis develops this idea, initially proving its asymptotic superiority over the standard parametric estimate under certain conditions. We then consider the improvements possible by making smoothing parameter h a function of /, enabling our semi parametric estimate to vary from approximating y(l) in regions of high density to f(t,0) in regions where we believe the true density to be low. Our improvement in accuracy is demonstrated in both simulated and real data examples, and the limits with respect to h and the new adaption parameter oo are examined. Methods for choosing h and oo are given and evaluated, along with a procedure for incorporating prior belief about the true form of the density into these choices. Further practical examples illustrate the effectiveness of I these ideas when applied to a wide range of data sets.

Data clustering is a data analysis technique that groups data based on a measure of similarity. When data is well clustered the similarities between the objects in the same group are high, while the similarities between objects in different groups are low. The data clustering technique is widely applied in a variety of areas such as bioinformatics, image segmentation and market research. This project conducted an in-depth study on data clustering with focus on density-based clustering methods. The latest density-based (CFSFDP) algorithm is based on the idea that cluster centers are characterized by a higher density than their neighbors and by a relatively larger distance from points with higher densities. This method has been examined, experimented, and improved. These methods (KNN-based, Gaussian Kernel-based and Iterative Gaussian Kernel-based) are applied in this project to improve (CFSFDP) density-based clustering. The methods are applied to four milestone datasets and the results are analyzed and compared.

The effects of polyethylene, (PE), type, compatibilizer type and organoclay type on the morphology, rheological, thermal, and mechanical properties of ternary low density polyethylene (LDPE), high density polyethylene (HDPE), and linear low density polyethylene (LLDPE), matrix nanocomposites were investigated in this study. Ethylene &ndash
Methyl acrylate &ndash
Glycidyl methacrylate terpolymer (E-MAGMA) and Ethylene &ndash
Butyl acrylate- Maleic anhydrate terpolymer (E-BA-MAH) were used as the compatibilizers. The organoclays selected for the study were Cloisite 30B and Nanofil 8. Nanocomposites were prepared by means of melt blending via co-rotating twin screw extrusion process. Extruded samples were injection molded to be used for material characterization tests. Optimum amounts of ingredients of ternary nanocomposites were determined based on to the mechanical test results of binary blends of PE/Compatibilizer and binary nanocomposites of PE/Organoclay. Based on the tensile test results, the optimum contents of compatibilizer and organoclay were determined as 5 wt % and 2 wt %, respectively. XRD and TEM analysis results indicated that intercalated and partially exfoliated structures were obtained in the ternary nanocomposites. In these nanocomposites E-MA-GMA compatibilizer produced higher d-spacing in comparison to E-BA-MAH, owing to its higher reactivity. HDPE exhibited the highest basal spacing among all the nanocomposite types with E-MA-GMA/30B system. Considering the polymer type, better dispersion was achieved in the order of LDPE<
LLDPE<
HDPE, owing to the linearity of HDPE, and short branches of LLDPE. MFI values were decreased by the addition of compatibilizer and organoclay to the matrix polymers. Compatibilizers imparted the effect of sticking the polymer blends on the walls of test apparatus, and addition of organoclay showed the filler effect and increased the viscosity. DSC analysis showed that addition of compatibilizer or organoclay did not significantly affect the melting behavior of the nanocomposites. Degree of crystallinity of polyethylene matrices decreased with organoclay addition. Nanoscale organoclays prevented the alignment of polyethylene chains and reduced the degree of crystallinity. Ternary nanocomposites had improved tensile properties. Effect of compatibilizer on property enhancement was observed in mechanical results. Tensile strength and Young&rsquo
s modulus of nanocomposites increased significantly in the presence of compatibilizers.

One of the central goals in finance is to find better models for pricing and hedging financial derivatives such as call and put options. We present a semi-nonparametric approach to risk-neutral density extraction from option prices which is based on an extension of the concept of mixture density networks. The central idea is to model the shape of the risk-neutral density in a flexible, non-linear way as a function of the time horizon. Thereby, stylized facts such as negative skewness and excess kurtosis are captured. The approach is applied to a very large set of intraday options data on the FTSE 100 recorded at LIFFE. It is shown to yield significantly better results in terms of out-of-sample pricing in comparison to the basic Black-Scholes model and to an extended model adjusting the skewness and kurtosis terms. From the perspective of risk management, the extracted risk-neutral densities provide valuable information about market expectations. (author's abstract)
Series: Report Series SFB "Adaptive Information Systems and Modelling in Economics and Management Science"

Densification of soil during construction of earth structures is achieved through the process of compaction by application of mechanical energy to obtain the required engineering properties of the soil for a particular project such as hydraulic conductivity, soil strength and compressibility. These properties are dependent on attainment of high compaction densities normally achieved at specific moisture contents for a given compactive effort. The optimum moisture content and maximum dry density for a particular soil is determined by means of Proctor tests in the laboratory. A relative compaction index is then used to correlate the laboratory values with the field compaction values obtained using in-situ tests. The Sand Cone (SC) and Nuclear Density Gauge (NDG) are the common field tests used to the dry density and moisture content of the soil for purposes of quality control of the compaction process. The sand cone is a laborious test that involves excavation of part of the compacted layer and requires a 24-hour waiting period to obtain the moisture content of the soil through the laboratory oven method. The NDG on the other hand is less laborious, however it uses a radioactive source that is a potential health hazard and therefore requires strict handling, storage and maintenance of the equipment to maintain safety standards. The Electrical Density Gauge (EDG) is an alternative in-situ test that is quicker, safer and easier to maintain since it uses electric current to measure the compaction characteristics of the soil. The objective of the study was to determine the repeatability, accuracy and applicability of the EDG on South African soils by comparing its measurements for dry density and moisture content in the laboratory and in the field to the results from the sand cone and oven method. In the laboratory, a clean sand and a clayey sand were tested at the optimum moisture content and at ± 3% of the optimum moisture content. The soils were compacted to 200 mm using the RT74 rammer and the compaction values first tested using the EDG then followed by the sand cone test at the centre of the EDG test spot. The moisture content of the excavated sample from the sand cone test was determined using the oven method. For the field tests, the compaction characteristics of a sandy gravel and three uniformly graded sands were tested in-situ using the EDG followed by the sand cone test. Overall, the EDG measurements were repeatable based on test-retest comparison of the paired measurements. EDG results for moisture content were consistent with the values obtained from the laboratory oven method especially in the uniformly graded sands. However, the density measurements differed from the results of the sand cone test, which was considered the reference test for determination of field soil density. It is recommended that the EDG calibration relationship for bulk density be revised in order to improve the accuracy of the density measurements.

Many information technology artefacts can be found in today’s cars. The interaction with these artefacts is the driver’s secondary task while driving the car in a safe way is the primary task. When designing interfaces for in-vehicle usage, measures have to be taken in order to make the interaction with the artefact suit the in-vehicle environment. One of these measures is to have the appropriate screen density level, which is the amount of information present on the screen.

This thesis compares the usability of two integrated in-vehicle display prototypes, one with low screen density and one with high screen density. The usability comparison considers both safety and user preferences. Safety was measured by a Lane Change Test (LCT) which measures distraction of a primary task while performing a secondary task, and user preferences was measured with a questionnaire. Before the comparison was made, controls and a graphical user interface were designed.

Results showed no significant difference in driver distraction between performing tasks on the high screen density display and the low screen density display. However, a vast majority of the users preferred high screen density over low. Furthermore, the distraction levels for both the high and the low screen density displays were below the proposed 0.5 meter limit for allowed driver distraction. The results indicate that in-vehicle displays can have a high level of screen density without imposing a level of distraction on the driver that is unsuitable for driving.

Thesis (Ph. D.)--University of California, San Diego and San Diego State University, 2006.
Title from first page of PDF file (viewed June 21, 2006). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 121-139).

Is it possible to increase physical density whilst limiting the perception of density? This thesis outlines the main determinants of perceived urban density, exploring alternative parameters to those commonly used to define density. The study uses Hong Kong as an urban case study. Findings suggest high perceived density is seen as a negative aspect of urban life in Hong Kong. To create a satisfactory urban environment, means of reducing the perception of density are welcome. A number of candidate urban parameters were investigated and their effects on the perception of density are discussed. Plot ratio has a significant but weak correlation with perceived density. This suggests actual physical density has minor influences on the perception of urban density. However, urban developments with similar plot ratios can exhibit very different urban forms and are thus likely to be perceived differently. This thesis demonstrates spatial openness is a key factor in the perception of density. This study used the sky view factor as a measure of spatial openness. According to findings, the perception of density decreases with increasing sky view. This thesis illustrates the application of the findings through the development of a speculative urban plan for an old district of Hong Kong. The use of the sky view factor coupled with other modelling techniques such as passive zone analysis provides a good indication of spatial openness and urban daylight availability. These output parameters can be used as a basis for performance comparison. The sky view factor provides an indicator for assessing the performances of urban design both in terms of human perception and urban micro-climate, and so this work can shed light on the formulation of new urban planning policy.

Density functional theory (DFT) has become a central aspect of quantum chemistry and provides the mainstay of chemical calculations. The advantage of DFT methods lies in their relatively inexpensive computational cost and their dealing with an experimentally tangible quantity, i.e. the density. The chief drawback is its lack of well-defined path from approximation to exactitude. Consequently many models and approaches have emerged, and been enthusiastically advocated, often with little more justification than "it works". This thesis begins with an overview of traditional quantum chemical theory and methods, and places DFT within this framework. In chapters 5 and 6 new model systems are presented, and novel methods to derive exchange functionals that are exact for these model systems are developed. By taking this approach, rather than the more pragmatic one of data fitting, the successes and failures can be traced to the underlying soundness of the model and/or the method used in the derivation. In the development of these functionals some difficulties were encountered with convergence of the self-consistent field calculations. These problems are addressed in chapter 7. The observation that a molecular density is very close to that given by the superposition of its constituent atoms, leads naturally to the idea of modelling a density by a sum of nuclear centred, spherically symmetric 'Stewart Atoms'. However, attempts at constructing Stewart atoms in the past have been thwarted by slow basis set convergence. In chapter 8 we overview the work that has been undertaken on Stewart atoms and present several formalisms in which the theory has been developed. Chapter 9 deals with the problem of constructing accurate representations of Stewart atoms. Several different approaches are considered and the most accurate is determined. Applications of the Stewart atoms are considered in chapter 10.

The first part of our work, we describe investigations into the formal and conceptual aspects of density functional theory. These have been in four main areas. The first, is the theory of the derivative discontinuity, where we extended the theory to density matrix functionals, and carried out calculations of the effects of the discontinuity. Our second investigation concerned a new channel concept, namely, the shape and local chemical potentials. These describe the electron donating or accepting power of a density fragment. We demonstrated in simple model systems, that chemical features such as shell structure, or atoms in molecules, could be characterised as regions of constant shape chemical potential. Our third investigation concerned the homogeneous scaling of the Kohn-Sham kinetic energy. We disproved certain existing relations in the literature; we then went on to derive simple bounds on the kinetic energy, and to numerically calculate the approximate scaling of the kinetic energy in atomic systems. Our fourth investigation concerned an improved Lieb-Oxford bound for the exchange-correlation energy. By improving the numerical optimisation in the last part of the proof, we were able to tighten the bound. The second part of our work focused on the search for new energy functionals, and procedures for developing new functionals. Our efforts have been in two areas. The first was an investigation of the correlation functional of Hartree-Fock-Kohn-Sham theory. We observed the deficiencies of current functionals in the reproduction of the correlation potential, and attempted to correct this by fitting a functional to best reproduce numerical correlation potentials. In doing so, we observed the highly non-local nature of correlation in Hartree-Fock-Kohn-Sham theory, and the important effect of the derivative discontinuity on the energy. The second investigation attempted an exhaustive study of the Generalised Gradient Approximation (GCA), within a well-defined ab initio model. We developed a rigorous fitting methodology, and constructed well-converged fits to conclusively explore the limits of the accuracy of the GCA. A large number of observations were made concerning the choice of functional basis, the importance of additional gradient corrections, and the role of exact exchange. We also applied our fitting methodology to the construction of approximate Kohn-Sham kinetic energy functionals, with some success.

We have studied the charge density wave (CDW) repolarization dynamics in blue bronze (K0.3MoO3) by applying symmetric bipolar square-wave voltages of different frequencies to the sample and measuring the changes in infrared transmittance, proportional to CDW strain. The frequency dependence of the electro-transmittance was fit to a modified harmonic oscillator response and the evolution of the parameters as functions of voltage, position, and temperature are discussed. We found that resonance frequencies decrease with distance from the current contacts, indicating that the resulting delays are intrinsic to the CDW with the strain effectively flowing from the contact. For a fixed position, the average relaxation time for most samples has a voltage dependence given by τ0 ∼ V −p, with 1 < p < 2. The temperature dependence of the fitting parameters shows that the dynamics are governed by both the force on the CDW and the CDW current: for a given force and position, both the relaxation and delay times are inversely proportional to the CDW current as temperature is varied. The long delay times (∼ 100 μs) for large CDW currents suggest that the strain response involves the motion of macroscopic objects, presumably CDW phase dislocation lines. We have done frequency domain simulations to study charge-density-wave (CDW) polarization dynamics when symmetric bipolar square current pulses of different frequencies and amplitudes are applied to the sample, using parameters appropriate for NbSe3 at T = 90 K. The frequency dependence of the strain at one fixed position was fit to the same modified harmonic oscillator response and the behavior of the parameters as functions of current and position are discussed. Delay times increase nonlinearly with distance from the current contacts again, indicating that these are intrinsic to the CDWwith the strain effectively flowing from the contact. For a fixed position and high currents the relaxation time increases with decreasing current, but for low currents its behavior is strongly dependent on the distance between the current contact and the sample ends. This fact clearly shows the effect of the phase-slip process needed in the current conversion process at the contacts. The relaxation and delay times computed (∼ 1 μs) are much shorter than observed in blue bronze (> 100 μs), as expected because NbSe3 is metallic whereas K0.3MoO3 is semiconducting. While our simulated results bear a qualitative resemblance with those obtained in blue bronze, we can not make a quantitative comparison with the K0.3MoO3 results since the CDW in our simulations is current driven, whereas the electro-optic experiment was voltage driven. Different theoretical models predict that for voltages near the threshold Von, quantities such as the dynamic phase velocity correlation length and CDW velocity vary as ξ ∼ |V/Von − 1| −ν and v ∼ |V/Von − 1|ξ with ν ∼ 1/2 and ζ = 5/6. Additionally, a weakly divergent behavior for the diffusion constant D ∼ |V/Von − 1|−2ν+ζ is expected. Motivated by these premises and the fact that no convincing experimental evidence is known, we carried out measurements of the parameters that govern the CDW repolarization dynamic for voltages near threshold. We found that for most temperatures considered the relaxation time still increases for voltages as small as 1.06Von indicating that the CDW is still in the plastic and presumably in the noncritical limit. However, at one temperature we found that the relaxation time saturates with no indication of critical behavior, giving a new upper limit to the critical regime, of |V/Von − 1| < 0.06.

The four individual papers in this thesis all explore some aspect of the relationship between productivity and the density of economic activity. The first paper (co-authored with Martin Andersson, and Johan Klaesson) establishes the general relationship between regional density and average labor productivity; a relationship that is particularly strong for workers in interactive professions. In the paper, we also caution that much of the observed differences are not causal effects of density, but driven by sorting of actors to dense environments. Paper number two (co-authored with Martin Andersson, and Johan Klaesson) addresses the attenuation of density externalities with space. Using data on the neighborhood-level, and information on first- and second-order neighboring areas, we conclude that the neighborhood effects are stronger for highly educated workers, and that the attenuation of the effect is sharp. In the third paper, I estimate an individual-level wage equation to assess appropriate levels of aggregation when analyzing density externalities. I conclude that failure to use data on the neighborhood level will severely understate the  benefits of working in the central parts of modern cities. The fourth paper departs from the conclusions of the previous chapters, and asks whether firms position themselves to benefit from density externalities. Judging by job switching patterns, the attenuation of density externalities are a real issue for the metropolitan workforce. Employees, especially those in interactive professions, tend to move short distances between employers, consistent with clustering to take advantage of significant but sharply attenuating human capital externalities.

Mammographic density (MD), created predominantly by increased stromal tissue, is a major breast cancer risk factor, though little is known about the biological mechanisms mediating it. Tamoxifen prevents breast cancer in a subset of high risk women via mechanisms that appear dependent on reduction of MD. Animal models suggest tamoxifen remodels the mammary stroma to a tumour-inhibitory phenotype. This study aims to analyse the effect of tamoxifen on human breast fibroblast function and identify pro-tumourigenic pathways contributing to density-associated risk. Methods Primary human breast fibroblasts from normal, high risk or breast cancer patients were treated with hydroxytamoxifen (100nM-5μM). Fibroblast function was analysed by measuring: proliferation, expression of stromal proteins fibronectin and collagen 1; effects on TGF-β signalling and up-regulation of myofibroblast marker SMA. Genome wide analysis was performed using RNA-Seq. Significantly deregulated pathways were validated by PCR, western blotting and mass spectrometry. Results Fibroblasts from 23 patients were treated with hydroxytamoxifen. All patients showed reduced proliferation with treatment. 62% of patients showed reduced fibronectin expression. TGF- β-mediated up-regulation of SMA and fibronectin were consistently inhibited by tamoxifen. RNA-Seq analysis revealed down-regulation of Wnt signalling, an established profibrogenic and pro-tumourigenic pathway. In addition, there was significant modulation of many metabolic pathways, including components of the microsomal anti-oestrogen binding site (AEBS). Binding of tamoxifen to the AEBS inhibits cholesterol epoxide hydrolase (ChEH) enzyme activity, promoting an anti-tumourigenic phenotype. The effects of tamoxifen on fibroblasts could be partly replicated using tesmilifene, a commercially available 5 inhibitor of ChEH. Mass spectrometry analysis confirmed an altered cholesterol metabolite profile in tamoxifen treated fibroblasts. Conclusion These data indicate that tamoxifen can directly remodel the mammary stromal microenvironment, generating a less 'reactive' stroma. Thus, tamoxifen impacts on multiple pathways, many independent of the oestrogen receptor, to create a tumourinhibitory microenvironment. This offers exciting potential for patient monitoring and alternative breast cancer prevention strategies.

A major theme in geometric measure theory is establishing global properties, such as rectifiability, of sets or measures from local ones, such as densities or tangent measures. In establishing sufficient conditions for rectifiability it is useful to know what local properties are possible in a given setting, and this is the theme of this thesis. It is known, for 1-dimensional subsets of the plane with positive lower density, that the tangent measures being concentrated on a line is sufficient to imply rectifiability. It is shown here that this cannot be relaxed too much by demonstrating the existence of a 1-dimensional subset of the plane with positive lower density whose tangent measures are concentrated on the union of two halflines, and yet the set is unrectiable. A class of metrics are also defined on R, which are functions of the Euclidean metric, to give spaces of dimension s (s > 1), where the lower density is strictly greater than 21-s, and a method for gaining an explicit lower bound for a given dimension is developed. The results are related to the generalised Besicovitch 1/2 conjecture. Set functions are defined that measure how easily the subsets of a set can be covered by balls (of any radius) with centres in the subset. These set functions are studied and used to give lower bounds on the upper density of subsets of a normed space, in particular Euclidean spaces. Further attention is paid to subsets of R, where more explicit bounds are given.

Thesis: S.M., Massachusetts Institute of Technology, Department of Physics, 2009.
Cataloged from PDF version of thesis.
Includes bibliographical references (page 35).
Inflation is a substantial modification to the big bang theory, and supernatural inflation is a hybrid inflation motivated from supersymmetry. In this thesis we carry out a one dimensional numerical simulation to verify the untested analytic approximation of Radall et al. The results show a good agreement for a wide range of parameters. We also propose a new method for calculating density perturbations in hybrid inflation, which shows an excellent agreement with the simulation in one dimension.
by Nguyen Thanh Son.
S.M.