• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 19
  • 8
  • 3
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 38
  • 5
  • 5
  • 4
  • 4
  • 4
  • 4
  • 4
  • 3
  • 3
  • 3
  • 3
  • 3
  • 3
  • 3
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Synthesized polyimide membranes for pervaporation separations of toluene/iso-octane mixtures

Xu, Wen Yuan 30 April 2014 (has links)
Separation of aromatic/aliphatic hydrocarbon mixtures by pervaporation has been of increasing interest in recent decades. Dozens of polymer materials have been reported for separations of benzene/cyclohexane and toluene/iso-ocatne mixtures. However, fundamental understanding of material structure and transport relations is not adequate to generalize guidelines for materials screening. The goals of this study are to tailor the structure of the polyimide materials, correlate the structure and transport relations, and establish guidelines for future materials. The 3, 5-Diaminobenzoic acid (DABA) containing polyimides were synthesized by both chemical and thermal solution imidization. The synthesized polyimides were formed into dense films by solution casting. The physical properties of the polyimides synthesized with monomers: 2, 2-bis (3, 4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA), 4, 6-trimethyl-1, 3-phenylendiamine (DAM) and DABA, were characterized by DSC, WAXD, GPC and density. The chemical structures were assessed by FTIR and NMR. The pervaporation and sorption of the synthesized polyimide membranes were tested in toluene/iso-octane mixtures at 100°C. The structure- transport property relations were established for the 6FDA-DAM/DABA membranes. The 6FDA-DAM/DABA polyimides were crosslinked by ethylene glycol. The pervaporation and sorption of the crosslinked membranes were tested in toluene/iso-octane mixtures at 100°C. Thermal imidization was found to give a higher imidization degree than chemical imidization. As a result, the polyimides made by chemical imidization contain a higher percentage of carboxylic acid groups than those made by thermal imidization. Chemical imidization gives higher film density, glass transition temperature and lower flux and higher selectivity for the toluene/iso-octane pervaporation than the thermally imidized membranes because of the higher carboxylic acid concentration. The chemically imidized membranes are slightly brittle after the crosslinking. Only the thermal imidization membranes have good flexibility and its pervaporation selectivity improves significantly after the crosslinking. Solubility selectivity and diffusivity selectivity of the 6FDA-DAM/DABA membranes were correlated with solubility parameters and fractional free volume, respectively. The structure-mass transport relations show that for the 6FDA-DAM/DABA membranes, both solubility selectivity and diffusivity selectivity contribute to the pervaporation selectivity. For the chemically imidized membranes, increased DABA concentration has a positive effect on solubility selectivity and diffusivity selectivity. For the thermally imidized membranes, increased DABA concentration has a significant effect on diffusivity selectivity only. / text
12

Development of improved ASP formulations for reactive and non-reactive crude oils

Yang, Hyun Tae 17 February 2011 (has links)
The ability to select low-cost, high-performance surfactants for a wide range of crude oils under a wide range of reservoir conditions has improved dramatically in recent years. Surfactant formulations (surfactant, co-surfactant, co-solvent, alkali, polymer, and electrolyte) were developed by using a refined phase behavior approach. Such formulations nearly always result in more than 90% oil recovery in core flood when good surfactants with good mobility control are used. The advances that have improved performance, reduced cost, increased robustness, and extended the range of reservoir conditions for these formulations are described in this work. There are thousands of possible combinations of the chemicals that could be tested for each oil and each chemical combination requires many observations over a long time period at reservoir temperature for proper evaluation. It would take too long, cost too much and in many cases not even be feasible to test all combinations. In practice the scientific understanding is used to match up the surfactant/co-surfactant/co-solvent characteristics with the oil characteristics, temperature, salinity, hardness and so forth. Synthesized and new surfactants with much larger hydrophobes and more branching than previously available were tested. New classes of co-solvents and co-surfactants with superior performance were test to improve aqueous solubility. These new developments resulted in improved ASP formulations for both oils that react with alkali to make soap and oils that do not. Many of these developments are synergistic and taken together represent a breakthrough in reducing the cost of chemical flooding and thus its commercial potential. / text
13

Urban Transformation in China: From an Urban Ecological Perspective

Han, Ruibo January 2012 (has links)
China has undergone significant urban growth and industrialization over the last 30 years and its incredible development continues to move ahead at an increasingly rapid pace. In terms of urban expansion, China has just recently surpassed the world’s average urbanization rate of 50%, as it moves its massive population from rural to urban areas at an astonishing speed. It’s massive population and fast urbanizing speed aside, China is also unique in terms of its socio-political system and historical-cultural context: it is a hybrid of government planning and market forces. Since it encompasses a large part of the global population and has had a vastly different urbanization experience than that of Western countries, around which most theories are based, studying China’s urbanization is an opportunity to contribute to the field of urban studies in an unprecedented manner. However, these differences also make it difficult to develop a comprehensive study of China’s urban system since the predominant theories in the field are best suited to Western cities. This research rises to this challenge by systematically studying the relationship between the socioeconomic and biophysical processes in the Chinese urban system to understand the interaction between human and physical factors, and the landscape patterns that result from these interactions. This complex urban system is examined using a hierarchical, top-down approach. At the highest level is a Macro-scale analysis of the national urban system, followed by a study of the regional urban system: the JingJinJi Metropolitan Area at the Meso-scale, and finally a Micro-scale examination with a focus on the city of Beijing. Since urban systems develop over both time and space, the urban system is analyzed spatio-temporally on all three levels. Research at the national scale is composed of two parts. First, the challenges and opportunities of China’s urban development since the foundation of the People’s Republic of China in 1949 are investigated in a general context. The institutional barriers that impede the management and continuation of China’s urban development are also discussed. Rank-size Analysis and satellite images are used to present the structural transitions of city scaling and urban clusters. These changes come with a series of challenges that are also iterated and discussed. This is followed by an analysis of the spatial distribution and transition patterns of China’s urban system using Centrographic Analysis, particularly since the post-1979 reforms. Second, the Macro-scale research focuses on a study of the urban hierarchy that is based on inter-city interactions as determined by the Synthesized Gravity Model (SGM). Under this model socioeconomic variables are synthesized and represented by the Influential Factor, while the Function Distance is derived from a Network Analysis that is based on multiple transportation methods. As an improvement on the conventional Gravity Model (GM), the SGM is used to accurately establish and represent the nodal structure of China’s urban system, the evolution of its hierarchical structure, and the relationships that exist between the nodal structure and socioeconomic factors. The results based on the SGM indicate that China’s national urban system is characterized by the emergence of urban clusters with stronger inter-city interactions since the 1990s. However, development among cities within certain urban clusters is not even, although the general pattern indicates a lessening inequality among cities. Spatially, while most cities at the top of the hierarchy are located in the east of China, cities in the middle and west of the country are also gaining higher positions in the hierarchy over time. On the Meso-scale, the applicability of the Cellular Automata (CA)-based SLEUTH model for regional urban growth pattern is studied through a focus on the JingJinJi Metropolitan Area (Beijing-Tianjin-Hebei). By integrating socioeconomic factors into a modified SLEUTH model, the urban growth dynamics and future development scenarios of the area are simulated and predicted. The results based on the CA model show that this region is characterized by a dynamic development pattern with high spreading and breeding growth rules that relies greatly on the growing transportation systems. It also allows for the projection of three possible future urban growth scenarios, each occurring under different environmental and development conditions, showing the future urban growth with or without further intervention. This research confirms that four factors play essential roles in the formulation of the urban growth mechanism of the JingJinJi Metropolitan Area: Urban policies, Industry restructuring, Rural-urban migration, and Reclassification of urban boundaries. The Micro-scale study of Beijing is conducted from two perspectives: the social and natural. The social aspect adopts the factorial ecology approach to identify the social landscape patterns and the factors that have shaped Beijing’s social space in 1990 and 2000. The social mosaic has experienced a significant change due to suburbanization, resulting in a more dynamic and complex internal structure since the 2000s. From a natural perspective, Beijing’s physical landscape patterns are extracted by processing remotely sensed images that have the same temporal span. The physical change through landscape metrics demonstrates that Beijing’s expansion has generated a more complex and fragmented land use/cover pattern. Meanwhile, transportation systems play a significant role in urban expansion, although the expansion across the space (zonal rings and directional sectors) is not even. Finally, the relationship between the social and physical landscapes is quantitatively defined by the Geographically Weighted Regression (GWR) technique, using physical landscape metrics as dependent variables and social areas as independent variables. The GWR is able to demonstrate the relationship between the social and physical landscapes at this level: as a city’s social mosaic becomes more varied over time it results in the fragmentation of that city’s physical space.
14

A Comparative Evaluation of Functional Analytic Methods

Perkins, Crysta 05 1900 (has links)
The individual functional analysis (FA) is the most widely used method to identify variables that influence the occurrence of problem behavior. Researchers often modify the FA after the analysis reveals undifferentiated responding. The interview-informed synthesized contingency analysis (IISCA) is one of the most substantial variations of the FA that builds upon the FA modifications. We evaluated the use of the two different functional analytic methods, the FA and IISCA, and the subsequent function-based treatment to reduce problem behavior for three children with autism spectrum disorder (ASD). The individual FA and the IISCA demonstrated differentiated responding for all participants. The treatment based on the results from the traditional FA was effective for all children. We discuss the implications of these findings.
15

Synthesis, characterization, reaction mechanism and kinetics of 3,4-dihydro-2H-1,3-benzoxazine and its polymer

Liu, Jingping January 1995 (has links)
No description available.
16

Tough bio-based elastomer nanocomposites with high performance for engineering applications

Wei, T., Lei, L., Kang, H., Qiao, B., Wang, Z., Zhang, L., Coates, Philip D., Hua, K-C., Kulig, J. January 2012 (has links)
No / Biomass feedstock is a viable alternative to finite fossil fuel resources to provide many of the same—plus others that petrochemicals cannot—chemical building blocks required to fabricate durable and high-performance materials. We demonstrate here for the first time a new generation of synthesized elastomers, namely bio-based engineering elastomers (BEE). These are of particular significance because they are synthesized from monomers derived from biomass, by routes which are suitable for large scale production, and they exhibit thermo-mechanical properties at least equivalent to current commercial petrochemical-derived elastomers. Bio-based monomers in large scale production, such as sebacic acid, itaconic acid, succinate acid, 1,3-propanediol, and 1,4 butanediol are chosen to generate the first synthetic BEE matrix through melting polycondensation—a comparatively simple reaction scheme offering good control and the potential for low cost, large-scale production. A novel linear BEE, an almost non-crystalline copolyester elastomer with low glass transition temperature (Tg) containing double bonds is designed and synthesized using multiple monomers (to help suppress crystallization). Silica nanoparticles are then introduced into the BEE matrix to achieve significant strengthening and improved environmental stability. Chemical crosslinks formed by peroxide and the pendant double bonds in the copolyester macromolecules endow the BEE with both the necessary high elasticity and required environmental stability. The BEE nanocomposites obtained exhibit excellent thermomechanical properties, such as an ultimate tensile strength of 20 MPa.
17

FUNCTIONAL ANALYSES: A COMPARISON OF ISOLATED AND SYNTHESIZED CONTINGENCIES

Graley, Devin N. 01 January 2019 (has links)
The purpose of the study was to compare traditional functional analysis procedures (isolated contingencies) to functional analysis procedures which are modified to include nuanced environmental variables (synthesized contingencies) for children in an outpatient setting in order to determine sensitivity to the isolated or synthesized contingencies. A multi-element design embedded into a multi-treatment design was used to evaluate differentiated rates of challenging behavior across the two analyses for three children exhibiting challenging behaviors. The results supported the utility of the traditional functional analysis (FA) procedures when compared to that of the interview informed synthesized contingency analysis (IISCA) for one of three participants.
18

Comportamento mecânico de compósitos asfálticos com argila calcinada sob flexão a quatro pontos

Silva, Antonio Cleiton Lopes da 31 March 2014 (has links)
Submitted by Geyciane Santos (geyciane_thamires@hotmail.com) on 2015-10-02T14:43:08Z No. of bitstreams: 1 Dissertação - Antonio Cleiton Lopes da Silva.pdf: 4158609 bytes, checksum: df0a9c601a830a898dc186dd5c7baec7 (MD5) / Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2015-10-02T20:01:05Z (GMT) No. of bitstreams: 1 Dissertação - Antonio Cleiton Lopes da Silva.pdf: 4158609 bytes, checksum: df0a9c601a830a898dc186dd5c7baec7 (MD5) / Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2015-10-02T20:07:10Z (GMT) No. of bitstreams: 1 Dissertação - Antonio Cleiton Lopes da Silva.pdf: 4158609 bytes, checksum: df0a9c601a830a898dc186dd5c7baec7 (MD5) / Made available in DSpace on 2015-10-02T20:07:11Z (GMT). No. of bitstreams: 1 Dissertação - Antonio Cleiton Lopes da Silva.pdf: 4158609 bytes, checksum: df0a9c601a830a898dc186dd5c7baec7 (MD5) Previous issue date: 2014-03-31 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In mechanistic analysis, the complex modulus is a parameter of fundamental importance for the construction of constitutive models of the behavior of asphalt concrete. Among the more modern options for obtaining it, are the bending tests to four points, widespread in Europe. As an alternative to national evaluation of these parameters, in this study is carried out four-points bending tests to obtain the dynamic modulus and phase angle of the asphalt concrete, employing conditions representative of the Amazônia on the coarse aggregate and temperature on the road surface, with almost 60 ° C for many hours a day. As aggregate, against a regional shortage of stone material, we used the ASAC - Synthesized Calcined Clay Aggregate, promising material in front of plenty of raw materials and feasibility financial and technical. As a result of the tests, it has been found dynamic modulus and phase angle at different frequencies and temperatures. Master curves were constructed by applying the principle of time-temperature superposition and data fit to a phenomenological model representing the dynamic module by a continuous function. Furthermore, it was demonstrated that some imperfections recorded by the device in low loads are not only noise or errors but arise from interference of natural vibration of the beam. Finally, considering the local conditions of temperature and traffic, the dynamic module presented abrupt change, showing a drop of up to 93.3 % in value, in which the surface appears very susceptible to permanent deformation, recurring problem in pavements local asphalt. / Na análise mecanicista, o módulo complexo é um parâmetro de importância fundamental para construção de modelos constitutivos do comportamento do concreto asfáltico. Dentre as opções mais modernas para sua obtenção, encontram-se os testes de flexão a quatro pontos, amplamente difundidos pela Europa. Como alternativa nacional para avaliação desses parâmetros, no presente estudo realiza-se testes de flexão a quatro pontos para obtenção do módulo dinâmico e ângulo de fase do concreto asfáltico, empregando-se condições representativas da Amazônia no tocante ao agregado graúdo e temperatura, que na superfície dos pavimentos alcança quase 60°C por longas horas do dia. Como agregado graúdo, ante a escassez regional de material pétreo, utilizou-se o ASAC – Agregado Sinterizado de Argila Calcinada, material promissor diante da abundância de matéria prima e viabilidade financeira e técnica. Como resultado dos testes, obteve-se pontualmente o módulo dinâmico e ângulo de fase a diversas frequências e temperaturas. Construíram-se curvas mestras aplicando-se o princípio da superposição tempo-temperatura e ajustaram-se os dados a um modelo fenomenológico, representando-se o módulo dinâmico por uma função contínua. Além disso, demonstrou-se que algumas imperfeições registradas pelo equipamento em condições de baixas solicitações não são apenas ruídos ou erros, mas decorrem da interferência da vibração natural da viga. Por fim, consideradas as condições locais de temperatura e tráfego, o módulo dinâmico apresentou variações abruptas, apresentando queda de até 93,3% em seu valor, situação em que o pavimento apresenta-se muito suscetível a deformações permanentes, problema recorrente nos pavimentos asfálticos locais.
19

Training Behavior Professionals to Use the Interview-Informed Synthesized Contingency Analysis (IISCA): Extension

Markham, Eric Nicholas 12 1900 (has links)
The current investigation replicated and extended previous research on training of behavior professionals to implement functional assessment and analysis procedures. Specifically, the study extended procedures described by Metras to train board certified behavior analysts (BCBAs) to administer two components of the Interview Informed Synthesized Contingency Analyses (IISCA) by: (1) conducting the study in the context of a large residential/training facility for adults with ID, (2) including a participant who served as a behavior analyst for a caseload of individuals who lived and received services at the facility, and (3) adjusting the vignettes and interview scripts to reflect the change in context. This current study shows that, following a brief training sequence, the participant was able to accurately administer the open-ended interview and construct a synthesized test and control condition.
20

Study of high temperature and high density plasmoids in axially symmetrical magnetic fields

Berger, T., Konheiser, J., Anikeev, A. V., Prikhodko, V. V., Bagryansky, P. A., Kolesnikov, E. Yu., Soldatkina, E. I., Tsidulko, Yu. A., Noack, K., Lizunov, A. A. January 2009 (has links)
Within the framework of an Institutional Partnership of the Alexander von Humboldt Foundation, the Budker Institute of Nuclear Physics Novisibirsk (BINP) and Forschungszentrum Dresden-Rossendorf worked together in a joint project devoted to the research at the coupled GDT-SHIP facility of the BINP with the focus on the study of plasma phenomena within the SHIP mirror section. The project began at July 1st, 2005 and ended on August 30th, 2008. It included work packages of significant theoretical, computational and analyzing investigations. The focus of this final report is on the presentation of results achieved whereas the work that was done is described briefly only. Chapter 2 illustrates the GDT-SHIP facility and describes shortly the planned topics of the SHIP plasma research. Chapter 3 explains the main extensions and modifications of the Integrated Transport Code System (ITCS) which were necessary for the calculations of the fast ion and neutral gas particle fields in SHIP, describes briefly the scheme of computations and presents significant results of pre-calculations from which conclusions were drawn regarding the experimental program of SHIP. In chapter 4, the theoretical and computational investigations of self-organizing processes in two-component plasmas of the GDT-SHIP device are explained and the results hitherto achieved are presented. In chapter 5, significant results of several experiments with moderate and with enhanced plasma parameters are presented and compared with computational results obtained with the ITCS. Preparing neutron measurements which are planned for neutron producing experiments with deuterium injection, Monte Carlo neutron transport calculations with the MCNP code were also carried out. The results are presented. Finally, from the results obtained within the joint research project important conclusions are drawn in chapter 6.

Page generated in 0.0318 seconds