• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 6518
  • 406
  • 279
  • 279
  • 279
  • 279
  • 279
  • 279
  • 215
  • 184
  • 101
  • 10
  • 10
  • 6
  • 4
  • Tagged with
  • 9704
  • 9704
  • 899
  • 805
  • 799
  • 787
  • 787
  • 787
  • 721
  • 680
  • 457
  • 449
  • 283
  • 281
  • 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.
21

Injectable In Situ Gellable Hydrogel-Microgel Composites For Drug Delivery

Sivakumaran, Daryl N. 09 1900 (has links)
<p>Hydrogels are water soluble polymer networks that are similar to the extra-cellular matrix of cells. Drug delivery systems based on hydrogels are of interest given their high biocompatibility. Obstacles with their use include their macroscopic dimensions (requiring surgical implantation) and quick elution of drugs from the swollen hydrogel matrix.<br /><br />These challenges can be addressed through the use of microgels, hydrogel particles with nanoscale dimensions. Microgels made from poly(N-isopropylacrylamide) (PNIPAM)) are of particular interest given that the effective diameter and water content of these microgels decreases at ~32°C. The degree of des welling and drug release rates can be tuned by controlling distributions of comonomers inside micro gels. Microgels can be immobilized within an injectable hydrogel network which is a liquid outside the body but quickly gels upon injection inside the body.<br /><br />The bulk, entrapping hydro gels were fabricated from carboxymethyl cellulose (CMC) and dextran modified with hydrazide (CMC A) and aldehyde (Dex B) functional groups. When mixed via co-injection through a needle at concentrations of 2 wt%, a hydrazone-crosslinked hydrogel network was formed. AA-NIPAM micro gels were synthesized via mixed precipitation-emulsion free radical polymerization in a dilute (~1 wt% monomer) aqueous solution and were co-injected with the B polymer for encapsulation inside the hydrogel.<br /><br />Current results show that the release of bupivacaine, a cationic local anesthetic, can be sustained over a period of up to 30 days using these composite hydrogel systems. Release rates scaled directly with the anionic functional group content of the micro gel. Release rates from the composite microgels appear to be driven by ion exchange between the microgel and drug as opposed to simple diffusion.<br /><br />The composite hydro gels, hydrogel pre-polymers, and microgels all showed no significant cytotoxicity to fibroblasts or myoblasts at concentrations up to 2mg/mL according to the MTT assay, suggesting their utility as effective in vivo drug delivery vehicles.</p> / Master of Applied Science (MASc)
22

Particle Movement in Paper Porous Media: Influence Factors and Model

Hsu, Hsuan Huan 06 1900 (has links)
<p>In recent years, paper-based analytical devices have been widely applied in many areas such as chemical analysis, disease diagnosis, and contaminant sensing. From the most common utility in pH paper to novel electrochemical sensing devices for monitoring heavy metals or glucose (2), paper-based analytical devices have shown great potential to become alternative analytical technologies. In paper based analytical device, commonly, the samples are transport by the capillary force from enter site toward the testing area. However, there is still not enough information of sample transportation in paper. This research focused on understanding the particle movement during elution in paper in order to provide some useful information for design and manufacture of paper analytical devices.</p> <p>There are many factors that influence the particle movement in paper, such as particle properties (i.e. surface potentials), paper properties (i.e. salt content on paper) and ambient factors (i.e. humidity). The effects of those factors on particle movement in paper were studied by the elution experiments. The elution experiments were conducted by vertically dipping the bottom 1 cm of paper strips (Whatman No.1) into polystyrene latex solutions. The latex solutions were eluted up by the capillary force of paper, which was spontaneously occured due to the porous structure of paper. Then, by varying the testing factors, respectively, the effects caused by those factors can be investigated.</p> <p>Since paper is composed of cellulose with many carboxyl groups, it is negatively charged. Therefore, the surface potential of particles was considered as an important factor that influences particle movement and deposition. More deposition was observed when particles with more positive charge were eluted in paper and vice versa. In addition, the influence of the flow velocity on particle movement during elution was also studied. The flow velocity was varied by changing the shape of paper strips. No obvious influence of the flow velocity on anionic particle deposition was observed, while the raise of the flow velocity increased cationic particle deposition. Moreover, the paticle (cationic and anionic) deposition was increased when latexes flowed through paper strips with salt content. The salt was dissolved once it contacted by the elution flow, which resulted in the increase of ionic strength in the elution flow. As a result, increased particle deposition were observed due to the reduced electrical double layer repulsive forces (particle-particle and anionic particle-paper surface) caused by increased ionic strength.</p> <p>Nevertheless, in all the experiments described before, it was noted that there was always a band shape of concentrated particles at the elution end (where elution flow stopped flowing forward). This phenomenon was caused by the mass flow (MFE), which occurred in order to refill the water loss due to evaporation. After the capillary flow reached the elution end, the suspended particles were carried continuously up to the elution end by MFE and concentrated gradually. To describe the movement of this evaporation-driven flow, the model suggested by Fries (29) (Eq. 4.2.11) was applied. The results predicted from this model fitted the experimental data well. The influences of evaporation on elution flow movement were further investigated based on this model. The effects of paper properties on the maximum elution distance were also examined based on the model of Fries (29) (Eq. 4.2.11). The results showed the influences of paper properties were in the order as: pore radius (capillary radius (Rs)) > permeability (K) ≒ thickness (δ) > contact angle (θs)> porosity (ϕ) (no effect).</p> / Master of Applied Science (MASc)
23

Kinetics of The Synthesis of High Impact Polystyrene

Richmond, John 05 1900 (has links)
<p>This thesis reports on an experimental and theoretical investigation of the kinetics of free radical polymerization of styrene in the presence of dissolved polybutadiene. A kinetic model which accounts for the grafting of polystyryl radicals on polybutadiene backbone and the concomitant effect on the rate of polymerization of styrene was developed. This model is in reasonable agreement with experimental measurements.</p> / Master of Engineering (ME)
24

An Appraisal of The Lignin/Activated Carbon Adsorption System

Rankin, Paul 04 1900 (has links)
<p>The pore structure of a wide array of activated carbons has been evaluated by nitrogen adsorption and mercury penetration techniques. Carbons were found to exhibit total surface areas and pore volumes in the range 93 - 1500 m²/g and 0.34 -1.8 cm³/g respectively. The Darco carbons contain significant pore structure in all pores up to 1000 Ǻ radius. Columbia carbon contains negligible pore structure in pores of greater than approximately 20 Ǻ radius. Special "A" carbon contains virtually all its limited pore structure in pores of 20 - 200 Ǻ radius.</p> <p>A kraft lignin, Indulin A.T., has been shown by Ultra-filtration and Gel Filtration techniques to exist in aqueous solution as a variety of different molecular weight fragments, with molecular weights ranging from approximately 4,000 to greater than 300,000. Each fragment is characterised by a unique molecular weight, hydrodynamic radius, characteristic diffusivity, solubility and color and TOC content. The concentration, and color and TOC content per molecule of each species in solution determines overall solutions color and TOC. The change in overall solution color and/or TOC with change in solution pH and solution age has been shown to be associated with an alteration in the molecular distribution, and hence the relative concentrations, of the various fragments in solution.</p> <p>Adsorption of lignin from aqueous solution onto activated carbon has been shown to proceed by a selective adsorption mechanism. Here the smallest adsorbable fragments are preferentially adsorbed initially, with progressive preferential adsorption of increasingly larger fragments as either contact time or carbon dosage is increased. Correlations between observed adsorption behaviour and pore structure for various carbons tend to support Chen's hypothesis that each fragment will adsorb preferentially into pores of approximately 3.3 to 6.1 times its hydrodynamic radius. It appears that carbon pore structure in pores of greater than 16 Ǻ radius is primarily responsible for adsorption of color and TOC from aqueous lignin solution. Adsorption of each species appears to occur by an ion exchange or concentration-precipitation mechanism.</p> <p>Most activated carbons contain sufficient pore structure in pores of greater than 16 Ǻ radius to bring about good color and TOC removals at resonably low carbon dosages. Columbia carbon, however, is incapable of removing the bulk of lignin fragments, and hence the major portion of color and TOC, from solution due to lack of adequate pore structure in pores of greater than 15 Ǻ radius. Similarly, Special "A" cannot effectively adsorb the low molecular weight fragments from solution due to a deficiency of pore structure in pores of less than 16 - 20 Ǻ. Good color and TOC removals are, however, possible with Special "A", as its limited pore structure is specific to adsorption of the fragments responsible for the bulk of overall solution color and TOC.</p> / Master of Engineering (ME)
25

REACTIVE EXTRUSION OF PHOSPHATE CROSSLINKED POTATO STARCH

Wang, Gang 06 1900 (has links)
<p>Biobased engineering materials from natural polymers such as potato starch and sisal fiber have increasingly attracted more attention compared with their petroleum counterparts due to biodegradability, environmental protection, and sustainable development. A novel biobased composite was developed based on phosphate crosslinked thermoplastic potato starch and sisal cellulose fiber aimed at improving mechanical properties and hydrophobicity.</p> <p>First of all, potato starch has a much narrow processing window in extrusion machinery for manufacturing thermoplastic starch. Statistical analysis of differential scanning calorimetry data aided in extrusion processing design and optimization.</p> <p>Then, bulk crosslinking of potato starch with sodium trimetaphosphate in the presence of rheological controlling additives (xanthan gum and glycerol) was investigated. Batch kinetics for the reaction was studied using in-situ attenuated total reflectance infrared spectroscopy monitoring. The spectra data were processed by multivariate analysis to reveal vibrational bands related to crosslinking and to identify important variables for reaction optimization. A kinetics model was created to facilitate developing a reactive extrusion process for bulk starch phosphate crosslinking. The effects of hydrocolloidal xanthan gum and glycerol on starch crosslinking reaction were also evaluated.</p> <p>Furthermore, gelatinized starch with processing additives was crosslinked with and without natural sisal fiber using sodium trimetaphosphate within a co-rotating intermeshing twinscrew extruder. The produced biocomposites were characterized using infrared spectroscopy, sessile drop contact angle measurement, moisture content determination and tensile mechanical testing. Comparison of experiment data and calculated values from modified Tsai-Halpin model confirmed crosslinkages formed between the crosslinked starch matrix and sisal fibers. The mechanical properties of the biocomposites were significantly improved, but the moisture sensitivity was increased due to reduced crystallinity caused by crosslinking.</p> <p>Finally, hydrophobicity of the starch biocomposite was improved by surface modification with Hydrores 266MB dispersion. Improvement of hydrophobicity is essential to maintaining superior mechanical properties of the biocomposites in surroundings with high relative humidity.</p> / Master of Applied Science (MASc)
26

An Application of Tube Settlers in The Secondary Clarification of Domestic Wastewater

Mendis, Bertrand John 08 1900 (has links)
<p>The North-End Water Pollution Control Centre (NEWPCC) in Winnipeg, Manitoba, treats an average annual flow of 60 MGD. During peak periods, spring run-off and storms, flows to the plant exceeds 110 MGD. The capacity of the ten secondary clarifiers limit the capacity of the plant to 65 MGD.</p> <p>This report discusses the results of an attempt to upgrade the capacity of the existing clarifier at Winnipeg with the use of tube settlers. This experimental programme monitored variables which govern both the biological conditioning within the aeration tank (DO, SRT, F/M, etc.) and the hydraulic effects on the clarifier (Q and QR). A 5½ inch ID, 5 feet high transparent plexiglass column was used to monitor the zone settling velocities of various mixed liquor concentrations, from which flux plots were drawn and the limiting hydraulic and solids loadings were determined.</p> <p>A discontinuous or pulse input of Rhodamine WT dye was used to trace the hydraulic behaviour within the clarifier. The overflow was monitored continuously and the underflow or return was monitored by frequent batch sampling.</p> <p>The results indicate that under good biological conditioning (clarification limiting), the clarifier with tube settlers treated flows up to 11.5 MGD or 2000 GPD/sq.ft. of clarifier surface area (or 167 GPD /sq.ft. of tube settler area) at solids loadings of 50 to 60 lbs/day/sq.ft. This is 80% greater than the flows handled by a similar clarifier with no tubes. Under upset biological conditions (thickening limiting), the tube settlers could not handle flows in excess of 6.5 MGD or 1100 GPD/sq.ft. of clarifier surface area (or 93.2 GPD/sq.ft. of tube settling area) at solids loadings of 45 lbs/d/sq.ft.</p> <p>Although no significant short circuiting was found in the overflow, the underflow experienced serious short circuiting problems. As the underflow was increased beyond 2.5 MGD or 430 GPD/sq.ft. of clarifier surface area, short circuiting occurred deteriorating the effluent quality. Since the tracer studies were conducted during periods of thickening limiting, it is not known if the short circuiting in the underflow was singularly responsible for the deterioration of effluent quality, or if it was an interaction between thickening limitation and the short circuiting in the underflow. This is contradictory to the established design criteria of secondary clarifiers which state that an increase in underflow would increase the ability of the clarifier to handle a greater solids loading.</p> <p>Now that the ground work has been laid in correlating tube settler performance to thickener design, future studies should pursue the possibility of establishing predictive capability of tube settler performance in secondary clarification of domestic wastewater.</p> / Master of Engineering (ME)
27

Studies of inorganic nanoparticles as collectors for flotation

Naderizand, Behnam January 2011 (has links)
<p>The goal of my work was to synthesize an appropriate inorganic nanoparticle as a collector for flotation of glass beads and also to prepare thin films of nickel sulfide. The first step was preparing a very uniform thin layer of nickel sulfide for model adhesion studies. The method employed was successive ionic layer adsorption and reaction (SILAR). The characterization experiments showed a weak deposited layer of nickel sulfide on glass, which was very uneven at low SILAR deposition cycles and very porous at high SILAR deposition cycles.</p> <p>In the next step, commercial grades of precipitated calcium carbonate (PCC) and colloidal silica were employed as collectors for the flotation of glass beads. Also, stearic acid treatments were carried out on untreated PCC samples. Despite that the mean particle size of PCC particles were in the nano range, they aggregated in aqueous solution and particle size increased to the micron range. Therefore, deposition of these particles onto glass beads was very low and consequently flotation results were not satisfactory. Also, silica particles aggregated when the pH increased to 9 which is the flotation operating pH. These particles did not show good deposition onto glass beads nor good flotation ability. The reasons could be hydrophilicity and aggregation of colloidal silica.</p> <p>In another series of experiments, stearic acid treated PCC nanoparticles were synthesized with a carbonation method and characterized with electrophoretic mobility, dynamic light scattering, FTIR and contact angle measurements. The flotation experiments have also been carried out and the results showed high recovery percentage of glass beads.</p> <p>Moreover, silica nanoparticles have been prepared by the Stober method and modified with aminopropyltriethoxy silane (APTS) and mercaptopropyltrimethoxy silane (MPTS) in solvent and aqueous media with post-modification and co-condensation methods. However, flotation results of glass beads when APTS modified silica nanoparticles were employed as collector were not satisfactory which can again related to their hydrophilic characteristics.</p> / Master of Applied Science (MASc)
28

Design for Dynamic Performance: Application to an Air Separation Unit

Cao, Yanan 04 1900 (has links)
<p>The significant effect that the design of a plant can have on its dynamic performance has led to methodologies for systematic analysis of the interaction between design and control, and for inclusion of dynamic performance considerations in plant design. In this thesis, an optimization-based framework is presented for improving the agility of a N<sub>2</sub> plant in response to the highly dynamic market, particularly demand and electricity price fluctuations. In this research, a decomposition optimization strategy is followed to identify limiting plant constraints and investigate selected design modifications using a rigorous dynamic air separation plant model. The plant model comprises of dynamic models for the distillation column with an integrated reboiler/condenser and a primary heat exchanger, and algebraic models for a compressor and turbine. The models presented follow first principles and/or empirical approaches. An index reduction procedure is utilized to reduce a high-index dynamic distillation model to an index-1 system. The proposed plant model is validated and reconciled using plant data through parameter estimation. Excellent prediction accuracy is obtained.</p> <p>Steady state optimization is the first tier of the optimization problem. In this stage, different scenarios in terms of demand changes and electricity price fluctuations are explored. In all optimized cases, the liquid nitrogen (LN<sub>2</sub> ) production rate and rate of evaporation remain at their lower bounds due to the zero revenue for LN<sub>2</sub> product and the high cost of evaporation. It is demonstrated that operating close to the maximum allowable impurity level is optimal as it gives a high recovery rate. Two major findings in this stage are: (1) the operating window of the plant is defined by the flooding constraint of the distillation column and the surge constraint of the compressor when the feed flow rate is considered; and (2) there is a break-even point between revenue generated from and compression cost required by one mole of air feed into the system when electricity price fluctuates.</p> <p>Dynamic optimization is performed to switch the system from the base case operating point to the new operating point determined from the steady state optimization without violating plant constraints . At rajectory tracking objective function with endpoint constraints to "pin-down" the final states to the pre-determined optimal values is solved in each case. With optimized control action, a fast transition without constraint violations can be achieved. Plants can complete the transit ion in less than 30 minutes with step-like responses of gas nitrogen (GN<sub>2</sub> ) production. Two plant modifications for aiding transitions are evaluated: (1) introducing external LN<sub>2</sub> during transit ions for cases of increasing demand, and (2) allowing a vent stream after the compressor for cases of decreasing demand. Even though for this particular plant setup (impurity requirements, tray design, etc.), introducing external LN<sub>2</sub> may not be cost-effective, this design modification is very attractive as it allows a smaller operating safety margin in the impurity requirement, which could result in more profitable steady state operation.</p> / Master of Applied Science (MASc)
29

Integrated Plant Modeling and Optimization Under Uncertainty

Gerardi, David 12 1900 (has links)
<p>A centralized optimization strategy is proposed to determine optimal raw material purchasing and plant operation practices as applied to the steel processing industry. Primary steelmaking can be separated into three sub-areas: cokemaking, ironmaking, and steelmaking. Raw materials are purchased on the open market for each area and include coal, iron ore pellets, and scrap steel. Many raw material vendors exist, providing products varying in quality and price. Additionally, the processing of raw materials within each area has an impact on its neighbours and, therefore, it is desired to determine the least costly method of both purchasing and processing the raw materials to make steel of acceptable quality.</p> <p>This work studies the modeling of primary steelmaking using a combination of mass balances and empirical relationships. The model, in addition to process constraints, is combined with a cost objective function and solved using a mixed-integer nonlinear programming (MINLP) solver. Various case studies are shown that illustrate the strong connection between the cokemaking and ironmaking as the carbon, volatile matter, and phosphorous contents of the coals and pellets have a large impact raw material selection. The centralized optimization results are then compared to the classic decentralized approach showing a clear reduction in cost.</p> <p>Raw material uncertainty is incorporated using two-stage stochastic programming. The formulation considers numerous raw material quality scenarios and the optimizer is required to make purchasing decisions based on the probability of each scenario occurring. The results indicate that by making a slightly more expensive raw material purchase, the frequency of constraint violation during processing can be significantly reduced.</p> <p>Multi-period optimization is also studied to determine how multi-tiered raw material pricing affects purchasing decisions. Steel demand forecasting is combined with the Multi-period formulation to make planning decisions over an entire year. Case studies are provided that illustrate how multi-tiered pricing can significantly change the slate of raw materials purchased. A rolling horizon optimization approach is then incorporated to determine how decisions change throughout the year in the face of errors in demand forecasting.</p> / Master of Engineering (ME)
30

Energy Efficient Model Predictive Building Temperature Control

Wallace, Matt January 2011 (has links)
<p>Sustainability considerations have placed increasing emphasis on the energy efficient operation and control of temperature control systems. It is estimated that the use of advanced control structures could lead to valuable savings in energy expenditure (up to 15-20 %) . This work considers the problem of developing a model predictive control (MPC) algorithm for temperature control in buildings. To this end, a cascade control structure was designed to regulate the room temperature subject to heat load disturbances, such as outdoor conditions or changes in the internal gains (i .e., number of people in a room). The inner loop of the cascade control structure involved controlling key variables of a vapor compression cycle (VCC), namely the superheat and supply air temperature (from the evaporator), by manipulating the compressor speed and valve opening (components in the VCC). Linear inputoutput models were appropriately identified for the VCC using a detailed first-principles model (adapted from Thermosys) for eventual utilization in a predictive control design. Then, closed loop simulations were performed by interfacing the VCC model with EnergyPlus (developed by the U.S . Department of Energy) , which was used to model realistic room temperature behavior. The control performance using a predictive controller (in the inner loop) was then evaluated against PI control.</p> / Master of Applied Science (MASc)

Page generated in 0.1746 seconds