For a successful design of an engineering system it is essential to pay careful attention to its dynamic response. This is particularly true, in the case of nonlinear systems, since they can exhibit very complex dynamic behaviour, including multiple co-existing stable solutions and chaotic motions, characterized by large sensitivity to initial conditions. In some systems nonlinear characteristics are desired and designed for, but in other cases they are unwanted and can cause fatigue and failure. A type of dynamical system which is highly nonlinear is discontinuous or non-smooth systems. In this work, systems with impacts are primarily investigated, and this is a typical example of a discontinuous system. To enhance or optimize the performance of dynamical systems, some kind of control can be implemented. This thesis concerns implementation of low-cost control strategies for discontinuous systems. Low-cost control means that a minimum amount of energy is used when performing the control actions, which is a desirable situation regardless of the application. The disadvantage of such a method is that the performance might be limited as compared with a control strategy with no restrictions on energy consumption. In this work, the control objective is to enforce a continuous or discontinuous grazing bifurcation of the system, whichever is desirable. In Paper A, the dynamic response and bifurcation behaviour of an impactoscillator with dry friction is investigated. For a one-degree-of-freedom model of the system, analytical solutions are found in separate regions of state space. These are then used to perform a perturbation analysis around a grazing trajectory. Through the analysis, a condition on the parameters of the system is derived, which assures a continuous grazing bifurcation. It is also shown that the result has bearing on the dynamic response of a two-degree-of-freedom model of the system. A low-cost active control strategy for a class of impact oscillators is proposed in Paper B. The idea of the control method is to introduce small adjustments in the position of the impact surface, at discrete moments in time, to assure a continuous bifurcation. A proof is given for what control parameters assures the stabilization. In Paper C, the proposed low-cost control method is implemented in a quarter-car model of a vehicle suspension, in order to minimize impact velocities with the bumpstop in case of high amplitude excitation. It is shown that the control method is effective for harmonic road excitation. / QC 20101118

In the theoretical section of presented diploma thesis are discussed various nanoparticles such as micelles and liposomes, solid lipid nanoparticles and polymeric nanoparticles. Special attention was focused on copolymer PLGA. There are characterized different procedures in the preparation of nanoparticles. From the approches for nanoparticles evaluation are chosen measuring size of nanoparticles and their zeta potential. The experiment was almost unambiguously focused on study of effect of diffrent factors on nanopartlicles size and distribution from linear PLGA and PLGA used for branching of tripentaerythritol and polyacrylic acid. Keywords: nanoparticles, size, size distribution, zeta potential, interactions of nanoparticles

[pt] Suspensões correspondem a uma classe de materiais amplamente utilizada em uma grande variedade de aplicações e indústrias. Devido à sua extrema versatilidade, elas têm sido foco de inúmeros estudos nas últimas décadas. Suspensões também são muito flexíveis e podem apresentar diferentes propriedades reológicas e respostas macroscópicas dependendo da escolha dos parâmetros usados como entrada no sistema. Mais especificamente, a resposta reológica de suspensões está intimamente associada ao arranjo microestrutural das partículas que compõem o meio e a fatores externos, como o quão confinadas elas se encontram e a rigidez das partículas. No presente estudo, o efeito da rigidez, confinamento e vazão na microestrutura de suspensões altamente concentradas é avaliado usando Dinâmica Dissipativa de Partículas com Núcleo Modificado. Precedento este estudo principal, foram necessárias outras duas etapas para garantir um sistema de simulação confiável e representativo, que consistiu, essencialmente, na realização de estudos paramétricos para compreender e estimar os valores adequados para os parâmetros de interacção parede-partícula. O presente trabalho aborda estudos paramétricos realizados para auxiliar na escolha dos parâmetros de entrada para evitar a penetração de partículas em um sistema delimitado por paredes. Inicialmente um sistema mais simples, composto por solvente e paredes é construído e os parâmetros de interação e densidades de parede foram ajustados. Em seguida as interações são definidas para suspensões. Neste último caso, vários parâmetros desempenham um papel na penetração e a maneira tradicional de investigar esses efeitos seria exaustiva e demorada. Por isso, optamos por usar uma abordagem de Machine Learning para realizar este estudo. Uma vez ajustados os parâmetros, o estudo de confinamento pôde ser realizado. O objetivo principal deste estudo foi entender como a microestrutura de suspensões concentradas é afetada pela vazão, rigidez das partículas e confinamento. Verificou-se que partículas muito flexíveis sempre formam um aglomerado gigante independente da razão de confinamento; a diferença está em quão compactadas são as partículas. No caso de partículas rígidas, um confinamento mais forte leva à formação de aglomerados maiores. O estudo final aborda um estudo de aprendizado de máquina realizado para prever a reologia de suspensões não confinadas. Com este trabalho foi possível entender e ajustar parâmetros de simulação e desenvolver um domínio computacional que permite estudar sistematicamente efeitos do confinamento em suspensões. / [en] Suspensions correspond to a class of materials vastly used in a large set of applications and industries. Due to its extreme versatility, they have been the focus of numerous studies over the past decades. Suspensions are also very flexible and can display different rheological properties and macroscopic responses depending on the choice of parameters used as input in the system. More specifically, the rheological response of suspensions is intimately associated to the microstructural arrangement of the particles composing the medium and external factors, such as how strongly they are confined and particle rigidity. In the present study, the effect of particle rigidity, confinement and flow rate on the microstructure of highly concentrated suspensions is studied using CoreModified Dissipative Particle Dynamics. Preceding this main study, two other steps were necessary to guarantee a reliable and realistic simulation system, which consisted, essentially, on performing parametric studies to understand and estimate the appropriate values for wall-particle interaction parameters. The present work address parametric studies performed to assist the input parameters choice to prevent particle penetration in a wall-bounded system. Initially a simpler system, composed of solvent and walls, is built and the interaction parameters and wall densities were adjusted. Following, the interactions are set for suspensions. In the latter case multiple parameters play a role in penetration and the traditional way to investigate these effects would be exhaustive and time consuming. Hence, we choose to use a Machine Learning approach to perform this study. Once the parameters were adjusted, the study of confinement could be carried out. The main goal of this study was to understand how the microstructure of concentrated suspensions is affected by flow rate, particle rigidity and confinement. It was found that very soft particles always form a giant cluster regardless the confinement ratio; the difference being on how packed the particles are. In the rigid case, a stronger confinement leads the formation of larger clusters. The final study addresses a machine learning study carried out to predict the rheology of unconfined suspensions. The main contribution of this work is that it was possible to understand and adjust simulation parameters and develop a computational domain that enables to systematically study confinement effects on suspensions.

Many chemicals are released into surface water and biodegradation is one important mechanismto remove the contaminants. Their actual concentrations in water depend on their persistence.The OECD 309 test is the most recognized method to assess the persistence of chemicals in theaquatic environment. However, the quantity of sediment used in the OECD 309 suspensiontests is not clearly defined. To investigate the influence of sediment concentrations and thebacterial cell count on the biodegradation, we compared the biodegradation rate constants of amixture of organic chemicals in suspension tests with 5 different water-sediment ratios. Thesediment concentrations were 125, 50, 20, 8 and 3 g L-1. The 5 test systems were spiked with129 chemicals including pharmaceuticals, agrochemicals, food additives, and cosmetics at aconcentration of 1 μg mL-1 each. The chemical degradation was monitored by analyzing thewater subsamples collected at different time points during the 14-day incubation period. It wasthe first time that the effects of sediment concentrations on biodegradation were systematicallystudied for a broad range of chemicals. The bacterial cell count was measured to test whether itcorrelated with sediment concentration and biodegradation rate constant. In the present study,k could be quantified for at least 2 sediment concentrations for 10 chemicals. The resultsshowed that the biodegradation rate constants of the chemicals, k, were positively correlatedwith sediment concentration for 10 chemicals; 6 of these correlations were significant. The totalbacterial cell count showed a positive correlation with sediment concentration, but it was notsignificant. Also, k was positively correlated with total cell count, but these correlations werenot significant for any of 10 chemicals. It is concluded that sediment plays an important role inchemical biodegradation. Sediment-associated total cell count can be one factor contributing tothis effect. The variable results of chemical biodegradation rate constants caused by differentsediment concentrations in the present suspension tests suggest the need for a standardizedsediment concentration in OECD 309 tests.

No description available.

This qualitative study explored the relationship between ten African American girls’ experiences with discipline practices and their academic identity in middle school. In the U.S., Black girls continue to suffer from inequitable treatment in school discipline resulting in disparate academic outcomes and have higher suspension rates than all other students including boys. This study attempted to answer the central question: what is the relationship between students’ experiences with school discipline practices and their academic identity? Ten African American girls associated with a middle school in New York fit the following criteria: (1) students in grades 6-8; a female student (2) self-identified as being African American (3) have received an out of school suspension in the previous school year. A one-on-one interview was conducted with the girls individually. The five major themes were related to: (a) good vs. bad student, (b) strict rules, (c) negative and positive teacher-student relationships, (d) different treatment by black and white teachers, and (e) role of peers. The conclusions derived from the study were: (1) African American girls educational experiences are influenced by teachers’ and administrators’ lack of cultural knowledge and understanding; thus, teachers and administrators can reflect how their biases manifest themselves in disciplinary actions, educational outcomes and student participation (2) teachers and administrators can work together to develop different ways to support African Americans to feel welcome and safe in school. (3) Teachers and administrators need to review and revise the current school discipline policies that are too harsh. Addressing these issues will help support African American girls to be successful in middle school. / Educational Leadership

This project was a synthesis of studies of the disciplinary actions received by middle and high school African-American students in public schools. This synthesis was conducted for three reasons: (1) to identify and collect studies on the variables associated with the disciplining of African-American students, (2) to examine how the variables contribute to African-American students being disproportionately disciplined when compared to other ethnic groups, and (3) to examine how the variables could be managed so that the need to discipline African-American students is reduced. Twenty-nine variables were identified from a synthesis of 13 studies. These variables were placed into three categories: personal variables, environmental variables, and institutional variables. Twenty-three variables were found to be associated with the number of disciplinary actions received by African-American students. These variables are listed below by category: Personal variables. Parental involvement, socioeconomic status, fondness of teacher, ethnicity, gender, feelings of alienation (powerlessness, normlessness), attitude toward peers, and social involvement (participation in school activities, number of positions of responsibility, frequency of association with adults, and frequency of association with African-Americans). Environmental variable. Peer pressure. Institutional variables. Enforcement of school rules, organizational climate, sports activities, school violence, desegregation (influx of black students), level of satisfaction with the school environment (student activities, communication, school work, and decision-making opportunities), and in combination, perceived leader behaviors, perceived school climate, and school size. Ten variables that contribute to the disproportionate number of disciplinary actions received by African-American students when compared to other ethnic groups were found. These variables are listed below by category: Personal variables. Grades in the previous semester, past discipline record, socio- economic status, ethnicity, gender, feelings of alienation (personal incapacity, guidelessness). Environmental variable. School socioeconomic status. Institutional variables. Student demeanor rating, desegregation (influx of African-American students). Recommendations were made for managing the variables to reduce the need to discipline African-American students. Recommendations included implementing initiatives on working with students in poverty, providing cultural diversity workshops for faculty, and analyzing discipline data for disparities in the number of disciplinary actions received by students. / Ph. D.

The purpose of this work is to find a method of determining the average particle size in samples of clays and ceramical materials, and to attempt to classify their physical properties according to the size of the particles. Such data should be useful to compare the properties of clays, to match different samples for uniformity, and to better control processes where clays are used, as for instance in manufacture of paper, rubber, and burned wear. / M.S.

<i>Pinus taeda</i> L. suspension culture cells were used to develop a model system to study the process of lignification occurring during the early stages of cell wall formation and maturation. Chemical, biochemical and histochemical analyses of the <i>P. taeda</i> suspension cultures grown with 2,4-dichlorophenoxyacetic acid (2,4-D) as the growth regulator did not provide conclusive evidence for lignin deposition. On the other hand, cultures in which 2,4-D was substituted with α-naphthaleneacetic acid (NAA) were shown to lignify. During this induction of lignification, limited cell wall thickening occurred since transmission electron microscopy of the 2,4-D grown cells showed only primary walls while the average cell wall thickness of the NAA-grown cells was consistent with secondary (S₁) layer formation. Despite the possibility of only limited lignin deposition in the 2,4-0 grown cells, secondary metabolism had occurred as evidenced by reversed-phase and chiral chromatographic separations which revealed the ability of these cells to produce enantiomerically pure (-)-matairesinol. Administrations of [1-¹³C], [2-¹³C ] and [3-¹³C ] specifically labeled phenylalanines to the <i>P. taeda</i> suspension cultures in medium containing NAA allowed the determination of lignin bonding patterns <i>in situ</i> by solid-state ¹³C NMR spectroscopy of the resulting ¹³C enriched cells. Aqueous and organic solvent extractions and protease treatment yielded ¹³C enriched cell walls for solid-state ¹³C NMR spectroscopic analyses of the cell wall bound lignin component. Subsequently, an isolated lignin derivative from these cell walls was analyzed by solution-state ¹³C NMR spectroscopy and verified the assignments made in the solid-state. Accordingly, the above experiments represent the first demonstration of lignin bonding patterns <i>in situ</i> in a <i>Pinus</i> species as well as a suspension culture. This culture system possesses great potential as a model to thoroughly study the early stages of lignification. / Ph. D.

Inappropriate behavior among students has long been a point of great concern and contention for public schools in the United States. Our national school discipline rates have reached an all-time high. As suspension and expulsion rates continue to grow at schools across the country, so do racial disparities. Over the past 4 decades, the K, "12 suspension rates have doubled for White students but tripled for Black students. In Arlington County Public Schools (ACPS), inappropriate student behavior that may result in suspension is classified as either "zero-tolerance" (for which the student must be suspended) or "nonzero-tolerance" (for which the school administrator can choose between suspension and other forms of discipline). Suspension is assumed to be one of the more severe forms of discipline. This study analyzes the impact that student ethnicity had on suspensions in ACPS during school years 2006 to 2011. The results indicate that Hispanic and Black students are suspended more than White and Asian students. However, when the administrator has the option to suspend, results suggest that Blacks and Whites are given the benefit of the doubt but Hispanics are not. Possible causes of the relationship between ethnicity and inappropriate behavior are provided. Reasoning for school administrators' possible leniency with Blacks and their possible lack of leniency with Hispanics is also provided. Areas of future study are recommended. / Ed. D.