Stability and rheology of dispersions of silicon nitride and silicon carbide

The relationship between the surface and colloid chemistry of commercial ultra-fine silicon carbide and silicon nitride powders was examined by a variety of standard characterization techniques and by methodologies especially developed for ceramic dispersions. These include electrokinetic measurement, surface titration, and surface spectroscopies. The effects of powder pretreatment and modification strategies, which can be utilized to augment control of processing characteristics, were monitored with these technologies. Both silicon carbide and nitride were found to exhibit silica-like surface chemistries, but silicon nitride powders possess an additional amine surface functionality. Colloidal characteristics of the various nitride powders in aqueous suspension is believed to be highly dependent on the relative amounts of the two types of surface groups, which in turn is determined by the powder synthesis route. The differences in the apparent colloidal characteristics for silicon nitride powders cannot be attributed to the specific absorption of ammonium ions. Development of a model for the prediction of double-layer characteristics of materials with a hybrid site interface facilitated understanding and prediction of the behavior of both surface charge and surface potential for these materials. The utility of the model in application to silicon nitride powders was demonstrated

Quechua to Spanish Cross-Linguistic Influence Among Cuzco Quechua-Spanish Bilinguals: The Case of Epistemology

Throughout the course of this dissertation, I respond to three related research goals. In order to investigate these goals, I gathered data from 169 members of two Cuzco, Peru non-profit governmental agencies, the Asociación Civil 'Gregorio Condori Mamani' Proyecto Casa del Cargador, 'Gregorio Condori Mamani' Civil Association House of the Carrier Project' and El Centro de Apoyo Integral a la Trabajadora del Hogar, 'Center for the Integral Support of Female Home Workers'. The majority of my participants speaks Quechua natively and acquired Spanish as an L2 during childhood or adolescence. I collected data from these two populations through the means of ethnography, demographic questionnaires, a social network analysis, a language attitudes study, elicitation of short narratives, role play interviews and a subjective reaction test. In response to my first research goal, I examine the nature of the semantics and pragmatics of the Cuzco Quechua epistemic system, including the epistemic suffixes, -mi/-n and -si/-s, and the Quechua verb past tenses, -rqa- and -sqa-. I find the Quechua epistemics to encode meaning beyond information source and level of certainty and to be affected by a variety of discourse factors. In my treatment of my second research goal, I find 31 different phonetic, morphosyntactic, and calque Quechua to Spanish cross-linguistic influence features to occur in my participants' speech. I also examine the specific case of the cross-linguistic influence of the Quechua epistemic system on the Spanish spoken by my participants. The presence of cross-linguistic influence in my participants' speech supports a model of child SLA in which the L1 plays a significant role in the acquisition of the L2. Finally, in response to my third research goal, I find various demographic characteristics, social network characteristics, and the language attitudes of my participants to correlate with their production of the 31 Quechua to Spanish phonetic, morphosyntactic, and calque cross-linguistic features. While presenting my results for my third research goal, I suggest that my participants may purposefully use various Quechua cross-linguistic features in order to identify themselves as Quechua speakers and distinguish themselves from native Spanish speakers, thereby creating an in-group variety of Spanish

Fractionation of Cell Mixtures Using Acoustic and Laminar Flow Fields

A fractionation method applicable to different populations of cells in a suspension is reported. The separation was accomplished by subjecting the suspension to a resonant ultrasonic field and a laminar flow field propagating in orthogonal directions within a thin, rectangular chamber. Steady, laminar flow transports the cell suspension along the chamber, while the ultrasonic field causes the suspended cells to migrate to the mid-plane of the chamber at rates related to their size and physical properties. A thin flow splitter positioned near the outlet divides the effluent cell suspension into two product streams, thereby allowing cells that respond faster to the acoustic field to be separated from those cells that respond more slowly. Modeling of the trajectories of individual cells through the chamber shows that by altering the strength of the flow relative to that of the acoustic field, the desired fractionation can be controlled. Proof-of-concept experiments were performed using hybridoma cells and Lactobacillus rhamnosus cells. The two populations of cells could be effectively separated using this technique, resulting in hybridoma/Lactobacillus ratios in the left and right product streams, normalized to the feed ratio, of 6.9 ± 1.8 and 0.39 ± 0.01 (vol/vol), respectively. The acoustic method is fast, efficient, and could be operated continuously with a high degree of selectivity and yield and with low power consumption

Fractionation of Cell Mixtures Using Acoustic and Laminar Flow Fields

A fractionation method applicable to different populations of cells in a suspension is reported. The separation was accomplished by subjecting the suspension to a resonant ultrasonic field and a laminar flow field propagating in orthogonal directions within a thin, rectangular chamber. Steady, laminar flow transports the cell suspension along the chamber, while the ultrasonic field causes the suspended cells to migrate to the mid-plane of the chamber at rates related to their size and physical properties. A thin flow splitter positioned near the outlet divides the effluent cell suspension into two product streams, thereby allowing cells that respond faster to the acoustic field to be separated from those cells that respond more slowly. Modeling of the trajectories of individual cells through the chamber shows that by altering the strength of the flow relative to that of the acoustic field, the desired fractionation can be controlled. Proof-of-concept experiments were performed using hybridoma cells and Lactobacillus rhamnosus cells. The two populations of cells could be effectively separated using this technique, resulting in hybridoma/Lactobacillus ratios in the left and right product streams, normalized to the feed ratio, of 6.9 ± 1.8 and 0.39 ± 0.01 (vol/vol), respectively. The acoustic method is fast, efficient, and could be operated continuously with a high degree of selectivity and yield and with low power consumption

Single-Collector Experiments and Modeling of Acoustically Aided Mesh Filtration

A model for the motion of particles driven by acoustic and hydrodynamic effects in the vicinity of a cylindrical collector has been previously reported. This trajectory model was developed to describe the essential physics that underlies an ultrasonically aided particle-filtration process in which a porous mesh is used to capture particles two orders of magnitude smaller than the pore size. To validate this trajectory model, experiments were performed to elucidate the detailed motion of particles in the neighborhood of a single cylindrical collector. Images of 54-μm-diameter polystyrene particles in aqueous suspension responding to acoustic and hydrodynamic forces were analyzed. Particle trajectories, calculated using only experimentally measured parameters as model inputs, well predicted the experimental observations. Adjustment of the local magnitude of the acoustic field, which accounts for spatial nonuniformities in the field, results in improvements in the correspondence between the trajectory predictions and the experimental observations

Transport Analysis and Model for the Performance of an Ultrasonically Enhanced Filtration Process

This paper presents an analysis of a filtration technique that uses ultrasound to aid the collection of small particles (tens of microns in diameter) from suspension. In this method, particles are retained within a porous mesh that is subjected to a resonant ultrasonic field, even though the pore size of the mesh is two orders of magnitude greater than the particle diameter. The role of acoustic forces in driving the retention phenomena has previously been studied on a micro-scale, which included modeling and experimental verification of particle motion and trapping near a single element of the mesh. Here, we build on this work to develop an overall transport model to predict macroscopic performance criteria such as breakthrough times and the dynamics of the filtration performance. Results from this model compare favorably to experimental studies of the filtration phenomena; simulation results scale appropriately with experimental results in which inlet feed concentration and flow rate are varied

An exploration of citizen’s attitudes towards waste recycling within the uMhlathuze Local Municipality in KwaZulu-Natal Province.

Master’s Degree. University of KwaZulu-Natal, Durban.ABSTRACT The success of municipal waste recycling highly depends on the attitudes and participation of individuals as citizens, to separate waste from source. The aim of this study was to explore the attitudes of citizens of UMhlathuze Local Municipality in Kwazulu-Natal, towards waste recycling. Understanding which attitudes shape the behaviour of the citizens with regards to waste recycling is essential for the municipality to achieve waste recycling targets. For this study, the quantitative research approach and combination of stratified, random and convenient sampling method were applied. The research involved 322 respondents from the three suburbs of the uMhlathuze Local Municipality: Meerensee, Aquadene and Esikhawini. The respondents were both male and female above 19 years of age. Data were collected by means of structured questionnaire distributed to the citizens of the 3 selected suburbs of the uMhlathuze Local Municipality. The data collected were analysed using descriptive and inferential statistics. The analysis conducted revealed that there are no statistical significant association between overall waste recycling behaviour and overall recycling attitude among the respondents, both those who separate waste for recycling and those who do not. However, the socio-demographic variables tested revealed that gender, nationality and income category are statistically significantly associated with recycling behaviour. General concern for the environment, culture and beliefs were significant predictors of negative or positive attitudes towards waste recycling. From the analysis, recommendations were made for uMhlathuze Local Municipality: to provide adequate recycling facility to create and sustain a recycling culture, implement penalties to instil recycling beliefs and incentives to motivate citizens. This research might probably guide the management of the municipality to reinforce attitudes, which promote desirable behaviours and overcome the attitudes hampering recycling behaviour among citizens in the municipality. Key words: citizens; attitudes; recycling behaviour; municipal waste.Abstract available in the PDF

Intensity and spectrum of light scattered from a fluid near its critical point.

Massachusetts Institute of Technology. Dept. of Physics. Thesis. 1974. Ph.D.MICROFICHE COPY ALSO AVAILABLE IN SCIENCE LIBRARY.Vita.Includes bibliographical references.Ph.D

Single-Collector Experiments and Modeling of Acoustically Aided Mesh Filtration

A model for the motion of particles driven by acoustic and hydrodynamic effects in the vicinity of a cylindrical collector has been previously reported. This trajectory model was developed to describe the essential physics that underlies an ultrasonically aided particle-filtration process in which a porous mesh is used to capture particles two orders of magnitude smaller than the pore size. To validate this trajectory model, experiments were performed to elucidate the detailed motion of particles in the neighborhood of a single cylindrical collector. Images of 54-μm-diameter polystyrene particles in aqueous suspension responding to acoustic and hydrodynamic forces were analyzed. Particle trajectories, calculated using only experimentally measured parameters as model inputs, well predicted the experimental observations. Adjustment of the local magnitude of the acoustic field, which accounts for spatial nonuniformities in the field, results in improvements in the correspondence between the trajectory predictions and the experimental observations