• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 6451
  • 404
  • 270
  • 270
  • 270
  • 270
  • 270
  • 270
  • 211
  • 184
  • 101
  • 10
  • 10
  • 6
  • 4
  • Tagged with
  • 9608
  • 9608
  • 877
  • 787
  • 785
  • 779
  • 767
  • 767
  • 707
  • 668
  • 449
  • 439
  • 277
  • 275
  • 256
  • 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.

Developing, implementing, and assessing coupled-tank experiments in an undergraduate chemical engineering curriculum

Inampudi, Narendra Kumar. Pinhero, Patrick J. January 2009 (has links)
Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 18, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Thesis advisor: Dr. Patrick J. Pinhero. Includes bibliographical references.

Heat transfer to granular beds from vibrating plates

Stephan, David George January 1955 (has links)
No description available.


Doggart, Jason January 2011 (has links)
<p>In recent years, there has been a strong interest in the use of drop-on-demand inkjet printing for the fabrication of organic thin-film transistors (OTFTs). This method would allow for roll-to-roll fabrication of low-end, disposable, and large-area electronics such as RFID tags, sensors, and flexible displays at a small fraction of the current costs. A great deal of research has already yielded new materials which are solution processable and have demonstrated excellent perfonnance when incorporated into OTFTs. One of the largest obstacles to the commercialization of this technology is the development of a successful strategy for the inkjet printing process. In order for this printing process to be successful, it must be able to deposit the components of the OTFTs such that they have sufficient resolution, excellent film thickness unifonnity and excellent perfonnance.</p> <p>Here a strategy is developed which allows for high resolution printing of source and drain electrodes with excellent film uniformity. By simultaneously optimizing dot-to-dot spacing and solvent composition, near-perfect film uniformity and very high resolution can be obtained. Resolution is further improved via increasing the viscosity of the ink and decreasing the surface roughness of the substrate.</p> <p>The inkjet printing system is further investigated and optimized for printing with silver nanoparticle ink. By using the design of experiments method, we detennined the independent influence of silver nanoparticle mass fraction, solvent composition, substrate surface energy, substrate temperature and dot-to-dot spacing on printed line width, line thickness and film uniformity. Furthennore, this method also allowed for the detennination of the influence of variable interaction, allowing a complete understanding of the system to be developed. This knowledge was used to develop a non-linear computer optimization program such that optimal variable settings could be detennined. As a result of this study, highly conductive silver lines with excellent resolution and film uniformity were inkjet printed and incorporated in high perfonnance OTFTs.</p> <p>A novel method for printing source and drain electrodes with a very small channel length was also developed. A silver nanoparticle ink with a large concentration of free alkylamine stabilizer was used in this study. The excess alkylamine formed a hydrophobic boundary around printed silver features, which repelled any ink subsequently deposited near the original feature. This allowed for source and drain electrodes to be printed with very narrow channel length with no need for any intelmediate processing steps. Furthennore, the self-alignment nature of this technique allowed the process to automatically correct for slight printing errors, resulting in transistor arrays with very narrow channel length distributions.</p> / Master of Applied Science (MASc)


Mahmood, Maaz January 2009 (has links)
<p>This thesis considers the problem of nonlinear predictive control design and applications. A predictive control formulation is presented which expands on the set of initial conditions for which closed-loop stability can be achieved. The key idea in this control design is to utilize control-law independent characterization of the process dynamics subject to constraints via model predicative controllers. An application of this idea is presented to the case of linear process systems for which characterizations of the null controllable region (the set of initial conditions from where closed-loop stability can be achieved subject to input constraints) are available. A predictive controller is designed that achieves closed-loop stability for every initial condition in the null controllable region. For nonlinear process systems, the constraints within the predictive controller are formulated to require the process to evolve within the region from where continued decay of the Lyapunov function value is achievable and incorporated in the predictive control design, thereby expanding on the set of initial conditions from where closed-loop stability can be achieved. The proposed method is illustrated using a chemical reactor example, and the robustness with respect to parametric uncertainty and disturbances demonstrated via application to a styrene polymerization process.</p> <p>In addition, we also consider the application of the predictive control design to the problem of handling actuator faults in nonlinear continuous-time processes and transport-reaction systems. Specifically, we consider faults that preclude the possibility of continued operating at the nominal equilibrium point using the existing robust or reconfiguration-based fault-tolerant control approaches. The key consideration is to operate the plant using the depleted control action at an appropriate safe-park point to prevent onset of hazardous situations as well as enable smooth resumption of nominal operation upon fault-repair. For the case of continuous-time nonlinear process systems we consider the presence of input constraints, uncertainty, and availability of limited measurements. First a Lyapunov-based predictive controller with an explicitly characterized stability region is developed to handle the aforementioned conditions. This control design is then subsequently used to develop a safe-parking framework in the presence of uncertainty, and availability of limited measurements. The proposed framework is illustrated using a chemical reactor example and demonstrated on a styrene polymerization process. Finally, we consider the problem of model predictive control and handling actuator faults in transport-reaction processes described by quasi-linear parabolic partial differential equations (PDEs) subject to input constraints. A Lyapunov-based model predictive controller is designed which accounts for the distributed nature of transport-reaction processes and provides an explicit characterization of the set of initial conditions from where closed-loop stability of the parabolic PDE system is guaranteed. Similar to the continuous time case, this control design is then subsequently used to develop a safe-parking framework for handling actuator faults in transport-reaction processes. The proposed framework is illustrated on a diffusion-reaction process</p> / Master of Applied Science (MASc)

Ultrafiltration of Alkalilignin Through Dynamic Membranes Formed of Feed Constituents

Horsti, Seppo Markku 12 1900 (has links)
<p>Membranes formed by constituents of ultrafiltration feed solutions on a support structure are called dynamic membranes. Lignin has the ability to form a self-rejecting membrane potentially useful for separating lignin from pulping wastes.</p> <p>Lignin solutions and pulp mill wastes were circulated past support tubes at different operating conditions. A typical product flux was about 7 gal/ft²day with about 99% rejection. The effect of the feed solution concentration, the pore size of the support structure and the cross-flow velocity were small on the membrane performance. A temperature increase from 30ºC to 70ºC increased the product flux by 130%. A higher operating pressure increased the product flux only slightly above a critical pressure of about 80 psi. The product flux was highly dependent on the pH, being e.g. 30 gal/ft²day at pH2 and 7.5 gal/ftday at pH//.</p> <p>Some chemical additives, reported to alter liquid conformation, were tested and the best results were given by addition of formaldehyde. It increased the product flux at pH2 from 30 gal/ft²day to 42 gal/ft²day. A pretreatment of the carbon support tubes by hydrochloric acid improved the product flux from 6 gal/ft²day to 16 gal/ft²day but the beneficial effect, in this case, was time dependent.</p> / Master of Engineering (ME)

Immune Response to Synthesized Pnipam-Based Graft Hydrogels Containing Chitosan and Hyaluronic Acid

Al-Haydari, Mariam D. 09 1900 (has links)
<p>p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.5px Helvetica}</p> <p>Biomaterials are thought to be the magical solution to improving the quality of life and lengthening lifespans of human beings. To date, there is no biomaterial that can completely escape immune responses. However, successes have recently been made in reducing immune responses to biomaterials.P(N-isopropylacrylamide) (PNIPAM), chitosan , and hyaluronan are examples of polymers that are gaining great interest in the field of biomaterials. The most attractive property of PNIPAM is thermo-responsiveness. Adequate literature has been published on improving the mechanical strength of PNIPAM, but not much has been published on host response to PNIPAM based graftpolymers. Chitosan and hyaluronan are generally considered non-toxic and nonimmunogenic.</p> <p>The first part of this project focuses on the synthesis and characterization of hyaluronan-grafted-chitosan-grafted-P(NIPAM-co-acrylic acid), while the second part examines the effect of grafting on the extent of immune reaction compared to P(NIPAM-co-acrylic acid) alone. The incorporation of chitosan into P(NIPAM-co-acrylic acid), and hyaluronan into chitosan-grafted-P(NIPAM-coacrylic acid) was confirmed by Fourier Transform Infrared Spectroscopy, Nuclear Magnetic Resonance , 2,4,6-trinitrobenzenesulfonic acid (TNBS), and Lower Critical Solution Temperature (LCST) experiments. The optimum molecular p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.5px Helvetica}</p> <p>weight for P(NIPAM-co-acrylic acid) that could provide sufficient amount of reactive sites while maintaining LCST below 37°C was found to be in the range of 2-2.5kDa. Western blotting results demonstrated that incorporating chitosan into P(NIPAM-co-acrylic acid) reduces the amount of fibrinogen, fibronectin, and vitronectin adsorbed, and eliminates complement component 3 (C3) adsorption.</p> <p>Furthermore, incorporating hyaluronan eliminates more inflammatory proteins including fibrinogen and reduces Immunoglobulin G (lgG) adsorption. Chitosan-grafted-P(NIPAM-co-acrylic acid) elicited lower levels of inflammatory cytokine release compared to P(NIPAM-co-acrylic acid), but higher than hyaluronan-grafted-chitsan-grafted-P(NIPAM-co-acrylic). In vitro and in vivo results revealed lowest density of leukocytes adhesion to hyaluronan containing surface compared to the other surfaces. The extent and duration of inflammation was reduced on chitosan-grafted-P(NIPAM-co-acrylic acid) and hyaluronangrafted-chitosan-grafted-P(NIPAM-co-acrylic acid) hydrogels.</p> / Master of Applied Science (MASc)

Development of Photonic Integrated Microchip-Based

Kowpak, Thomas M. 10 1900 (has links)
<p>Microchip-based flow cytometry holds promise in replacing conventional flow cytometers, thus providing less expensive point of care alternatives. Although final products are far off, a strong step towards these goals involves developing easy, reliable processes and improved functionality. This study is part of a larger project to develop a photonic integrated microchip-based flow cytometer using optical designs and simulations to imposed stringent requirements in device fabrication. Thus the goal of this work was to perform material selection, process development and device fabrication to meet the stringent optical requirements with an overview of device testing to demonstrate the achievements.<br /> Materials needed careful selection and include an SU-8 2025 structural layer, Pyrex substrate and a polydimethylsiloxane (PDMS) sealing layer. Mismatched properties of SU-8 and Pyrex have previously provided poor bonding, namely due to surface chemistry and thermal expansion differences. To overcome this, a thin intermediate layer of polymer was introduced relaxing stresses and allowing for chemical linkages. A rough range of 186-600nm was effective and limited optical deterioration.<br /> Sealing SU-8 devices with PDMS was previously accomplished using mechanical means or low pressure reversible bonding. Strong irreversible bonding was achieved by coating oxygen plasma treated PDMS with 3-aminopropyltrimethoxysilane (APTMS) and bonding the amino groups to residual epoxy molecules on SU-8 surfaces via polycondensation reactions. Bonding could not be broken through rigorous pressure testing, with devices withstanding on average O.6-0.7MPa and up to 2.2MPa before failing at the inlet fluidic connection.<br /> Post processing procedures required a rough dicing saw compromising the SU-8 structural layer. Reversibly sealed PDMS helped reduce chipping and protect against debris. An intermediate layer thickness of 186nm was efficient and 600nm provided no further improvement.<br /> These developed processes met the optical constraints imposed and quality devices were fabricated, capable of coupling high power light through on-chip waveguides, exciting fluorescence in microchannels and providing beam shaping.</p> / Master of Applied Science (MASc)

Encapsulation of Gases in Zeolite 3A and Temperature Programmed Desorption of the Trapped Gases

Chan, Yun-cheung 10 1900 (has links)
<p>Gases (Ar, N₂ and CO₂) were encapsulated in zeolite 3A at high temperature (350ºC) and pressure (maximum pressure obtained from a gas cylinder). Temperature programmed desorption (TPD), with a linear temperature schedule, was applied to study the kinetics of the release of the trapped gases. The TPD spectra for argon show two peaks ( a large peak at about 350ºC and small one at about 500ºC, for a heating rate of 17ºC per minute) and there is only one peak in the spectra for nitrogen and carbon dioxide. The spectra obtained were analysed using a diffusion equation (Fick's Second Law of diffusion) taking into account the shape and size distribution of the particles. The effect of water addition was shown to enhance the rate of desorption of the trapped gases.</p> / Master of Engineering (ME)

The influence of paper surface chemistry on the activity of immobilized antibodies

Wang, Jingyun 08 1900 (has links)
<p>p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.5px Times; color: #3a3a3a} p.p2 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.5px Times; color: #242424} span.s1 {color: #242424} span.s2 {color: #4e4e4e} span.s3 {color: #3a3a3a} span.s4 {color: #606060}</p> <p>With a long-term view to developing bioactive paper that can detect pathogens both in the laboratory and in the field, it is important to understand whether wet-strength papers are suitable supports for antibodies. This thesis describes the influence of polyamide-epichlorohydrin (PAE) and polyvinylamine (PVAm), which are typical wet-strength resins, on antibody activity. Two kinds of antibodies were employed: conventional Anti-Rabbit IgG (AR-Ab, whole molecules) and engineered anti-So aureus single domain antibody with cellulose binding domain (CBM-Ab). The results of the activity studies surprisingly showed that the typical loadings of reactive, cationic wet-strength polymers, used to strengthen wet paper, did not interfere with the antibody assays. However, higher content of wet-strength resins impeded the function of antibody. Also, conventional AR-Ab adsorbed very well and retained its functionality on paper surface without the aid of cellulose binding domain. A preliminary study was also performed to investigate the effect of alkylketene dimer (AKD), as a sizing agent, on AR-Ab activity. The results in the early stage revealed that AR-Ab functioned better on AKD-treated papers than on original paper.</p> / Master of Applied Science (MASc)

Use of Supercritical Carbon Dioxide in the Processing of Thermoplastic Elastomer Nanocomposites

Zhuang, Zijin 08 1900 (has links)
<p>Polymer-layered silicate (PLS) nanocomposites are of great interest presently due to their</p> <p>significant enhancement of properties compared to conventional polymeric materials. However, achieving a high extent of exfoliation, which refers to the complete separation and uniform dispersion of clay layers, is a key challenge in the preparation of PLS nanocomposites, particular for non-polar polymers like polyolefins. Recently, several novel processing technologies utilizing scCO₂ as an exfoliation aid have been developed. But how to achieve an optimal processing method by which fully exfoliation occurs with the aid of scCO₂ has not been fully studied.</p> <p>A novel clay-CO₂ injector apparatus was designed and constructed for this project in order to maintain the organoclay in suspension with scCO₂ during its melt compounding into a nanocomposite. Thermoplastic polyolefin elastomer (TPO) based nanocomposites were prepared by three methods: 1) directly injecting the CO₂ into a twin screw extruder (TSE); 2) injecting an organoclay-CO₂ suspension along with its compatibilizer into a twin screw extruder; and 3) injecting the organoclay-CO₂ suspension into a single screw extruder (SSE). Under Method 1 both as-supplied organoclay and a previously scCO₂- pretreated organoclay (from batch) were tested, while for the other two methods only the as-supplied material was used. The structure and properties of the resultant</p> <p>nanocomposites were characterized by X-ray diffraction (XRD), transmission electron</p> <p>microscopy (TEM), rheology and mechanical testing.</p> <p>It was found scCO₂ has a great influence on the morphology of clay within TPO nanocomposites. When preconditioned in scCO₂, chain mobility of surfactant within clay interlayers increased and led to further cation exchange reactions, thus resulted in an expansion in interlayer spacing and greater chance for penetration of large polymer specimen. It was shown in XRD patterns and TEM graphs that nanocomposites prepared using these pretreated organoclays (s-C20A) improved the degree of exfoliation over those based on as-supplied organoclay, in the absence of CO₂. On the other hand, the clay-CO₂ injector could also be beneficial for achieving an exfoliation structure. With increasing CO₂ pressure, the mobility of surfactantlcompatibilizers chains increased, allowing greater intercalation of matrix chains and further delamination under shear flow. The greatest exfoliation structure so far was achieved by maintaining the C20A/CO₂ suspension above the critical pressure of the gas during first-pass melt compounding in a single screw extruder then following with a second-pass through a twin screw extruder which provided sufficient shear stress for further exfoliation without the plasticizing effect of CO₂. Both pretreating clays and clay-CO₂ injection approaches showed improvement in clay dispersion over conventional nanocomposites melt compounding method. However, this improved exfoliation structure did not directly bring on improvement of rheological and mechanical properties. A possible thermo oxidative degradation was considered to be responsible for the reduction in rheological and mechanical properties.</p> / Master of Applied Science (MASc)

Page generated in 0.1325 seconds