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Thesis: B.S., Massachusetts Institute of Technology, Department of Mechanical Engineering, 1981 / Vita. / Includes bibliographical references. / by Paul Stephen Ranyak. / B.S. / B.S. Massachusetts Institute of Technology, Department of Mechanical Engineering

I nuläget finns flertalet företag som tillverkar distanser som är kompatibla med originalimplantat. Det finns dock ingen evidens för att dessa distanser är likvärdiga med originaldistanser när de används på originalimplantat. God passform hos implantatkomponenter är en viktig faktor för att undvika biologiska och tekniska komplikationer.Syftet med den här studien var att jämföra passformen mellan originaldistans och originlimplantat med kompatibel kopiadistans och originalimplantat.Material och metod: Fem originaldistanser och fem kompatibla distanser skruvades till originalimplantat. Provkroppar bäddades in och delade på mitten för att sedan analyseras i ljusmikroskop och SEM. Där mättes kontaktytans längd och mellanrummet mellan implantat och distans och distans och distansskruv. All data analyserades i SPSS.Resultatet: Implantatkoplex med kopiadistans hade fem gånger kortare kontaktyta mellan komponenterna och mellanrummet var större, vilket ger en försämrad stabilitet under andvändning. Analysen av distansskruvens yta visade morfologiska skillnader mot den inre ytan av distansen vilket kan leda till deformation och/eller fraktur av skruven.Konklusion: Användning av lågpris kopiadistanser till Astra originalimplantat kan leda till signifikant avvikande passform hos distansen och en lägre tolerans för stress hos distansskruven. / Nowadays there exist different abutments from different companies that are compatible to a certain manufacturer implant. But no scientific evidence exists on whether the fit of the compatible abutments are comparable to that of the genuine abutments when connected to the genuine implants. God fitting of implant components is an essential factor to avoid microgap formation in implant-abutment interface due to microgaps lead to biological and biomechanical complications. The aim of this study was to compare interface in original abutment and copy compatible abutment connected to original implant.Material and Methods: Five original abutments and five compatible abutments were connected to the original implants. The complex were sectioned in the middle and thereafter analyzed in a light microscope and SEM by measuring contact length and interface thickness between the implant and abutment and also between the abutment and abutment screw. All data was analyzed with SPSS-program.Result: Compatible implant complex had about five times shorter contact surface between components and interface was thicker which gives less stability under clinical function. The analyze of screw-abutment interface showed morphologic differences with the inner surface of the abutment which could lead to screw deformation and even fracture.Conclusion: Using low-cost compatible abutments connected to original Astra implants could lead to significant fit discrepancy of the copy abutments and lower stress tolerance in the abutment screw.

<p>Intermeshing counter-rotating twin screw extruders (ICRTSE) are used extensively in the polymer processing industry for pelletizing, devolatilization and extrusion of various plastic products. ICRTSE have better positive displacement ability and are more suitable for shear sensitive materials compared to other types of twin screw extruders.</p> <p>The objectives of this thesis are to understand the flow mechanism and the effects of screw geometries and processing conditions in the ICRTSE. First, a simple flow model based on a volume of the conveying element of ICRTSE was used to calculate flow rate. Since ICRTSE do not give complete positive displacement, the various leakage flows were identified and taken into account in the simple flow model. Although the simple flow model provided reasonable results in terms of flow rate, computer simulations were found necessary due to the limitations of simple flow model. Second, a 3D computer simulation of ICRTSE was developed for various screw geometries and processing conditions. Both Newtonian and non-Newtonian fluids were examined.</p> <p>It was shown the simple model based on geometrical parameters for pumping behaviour give reasonable prediction of flow rate. It was found that determination of negative pressure should be taken into account in numerical simulations. The pumping efficiency is influenced positively by the ratio of flight width-to-channel width but it is affected negatively by the screw pitch length. It is negligibly changed with screw speed. Finally, the dominant flow is shear flow in ICRTSE and therefore, dispersive mixing capacity is very limited due to a lack of elongational effects.</p> / Master of Applied Science (MASc)

This study evaluated effects of driving torques on screw direct withdrawal resistance (SDWR) from wood-based composites. The results on the screw seating torques indicated that the face-grain orientation of each material type had the highest mean load. The face-grain orientation of OSB had the highest mean load of 11.1 lb.in., and the MDF had the lowest mean load of 7lb.in.. For the screw stripping torques, the result showed the face-grain orientation of each material type had the highest mean load. The face-grain orientation of OSB had the highest load of 55.9 lb.in. Effects of torque levels on SDWR, the results indicated that the SDWR was lower at the torque level closer to the seating and stripping torque levels in OSB, whereas the SDWR was only lower in the torque level closer to the stripping torque within MDF and PB. Face-grain orientations of the each wood material had the highest SDWR.

Canada is a major global producer of pulse products including pulse starch, which notably contributes to a healthy diet. Strategically, Canada is taking steps to research methods of adding greater value to these crop products, and functional foods like resistant starch are particularly interesting. The primary objectives of this study were to develop an effective reactive extrusion process to produce gelatinized lipid complexed pea starches with enhanced enzyme resistance and examine the effects of bulk lipid complexing conditions on physicochemical and functional properties of extruded pea starches. One type of commercially available pea starch, Nutri-Pea, was chosen as the research subject in this study. A number of methods including; Englyst digestion method, differential scanning calorimetry (DSC), infrared spectroscopy (FTIR), contact angle, titrations, residence time distribution (RTD) and rapid visco analysis (RVA) were used to characterize the properties of extruded pea starches. The effects of feed formulation and extrusion conditions on lipid complexing and Englyst digestion profiles were systematically examined on two mixing devices. An extensive kinetics study was conducted on a lab scale twin-screw compounder, DSM-Xplore. The process was then scaled up to produce bulk lipid complexed pea starch on a Leistritz twin-screw extruder. The results showed that lipid complexing and digestion profiles were highly dependent on feed moisture and induced screw shear. Reactive extrusion of pea starches under optimized conditions achieved a significant but moderate increase in either resistant starch (RS) content (from 13.3% to 20.2%) or slowly digestible starch (SDS) content (from 7.85% to 23.3%) compared to their native counterparts. However, RS and SDS content could not be improved simultaneously based on the pea starch and extrusion process in this study. Increased degree of substitution (DS) was found for myristic acid complexed pea starches (nominal DS= ~0.8) when compared to palmitic acid complexed pea starch (nominal DS= ~0.5). Contact angle measurements, FTIR and DSC thermograms confirmed the presence of lipids. Lipid complexed starch films showed increasing hydrophobicity with increasing lipid content. As an alternative product compared to functional foods, the modified starch was considered as a biodegradable film for industrial applications. The material was produced at the highest moisture content for extruded native starch and two concentrations of lipid complexed starch using an intensive screw design. Preliminary results show that increasing lipid content and adding 1% glycerol to samples decreases the force per film thickness required to puncture films. However further investigation is required to determine effect of heat and moisture deformation. / Thesis / Master of Applied Science (MASc) / Incorporation of pulses into food products has been a major area of Canadian research for its potential to create new avenues of enzyme resistant food starches. Extrusion cooking is commonly used in industry for producing various food products such as snacks and cereals but little research has been reported on using an extruder to rapidly produce resistant pulse starches as a functional ingredient on a large scale; resistant starch is a functional food beneficial to humans in the same manner as insoluble fiber but exhibits improved textural properties. This study aimed to develop an effective reactive extrusion process to produce lipid complexed pea starches with enhanced enzyme resistance (i.e. increased slowly digestible starch (SDS) and resistant starch (RS) content) by an examination of the effects of reaction conditions on the properties of extrusion products. The lipid complexed pea starches under optimized conditions achieved a significant but moderate increase in either RS content or SDS content depending on the sample formulation compared to their native counterparts. However, RS and SDS content could not simultaneously be improved in this study.

As exploration in space increases through the use of larger telescopes, more sophisticated structures, and physical exploration, the use of autonomous robots will become instrumental to build and maintain the infrastructures required for this exploration. These systems must be autonomous to deal with the infeasibility of teleoperation due signal delay and task complexity. The reality of using robots in the real world without direct human input will require the autonomous systems to have the capability of responding to errors that occur in an assembly scenario on their own. As such, a system must be in place to allow for the sequencing and allocation of tasks to the robotic workforce autonomously, giving the ability to re-plan in real world stochastic environments. This work presents four contributions towards a system allowing for the autonomous sequencing and allocation of tasks for in-space assembly problems. The first contribution is the development of the Stochastic Assembly Problem Definition (SAPD) to articulate all of the features in an assembly problem that are applicable to the task sequencing and allocation. The second contribution is the formulation of a mixed integer program to solve for assembly schedules that are optimal or a quantifiable measurement from optimal. This contribution is expanded through the development of a genetic algorithm formulation to utilize the stochastic information present in the assembly problem. This formulation extends the state-of-the-art techniques in genetic algorithms to allow for the inclusion of new constraints required for the in-space assembly domain. The third contribution addresses how to estimate a robot's ability to complete a task if the robot must be assigned to a task it was previously not expected to work on. This is accomplished through the development of four metrics and analyzed through the use of screw theory kinematics. The final contribution focuses on a set of metrics to guide the selection of a good scheduling method for different assembly situations. The experiments in this work demonstrate how the developed theory can be utilized and shows the scheduling systems producing the best or close to the best schedules for assemblies. It also shows how the metrics used to quantify and estimate robot ability are applied. The theory developed in this work provides another step towards autonomous systems that are capable of assembling structures in-space without the need for human input. / Doctor of Philosophy / As space exploration continues to progress, autonomous robots are needed to allow for the necessary structures to be built in-space, on Mars, and on the Lunar surface. Since it is not possible to plan for every possible thing that could go wrong or break, the robots must be able to figure out how to build and repair structures without human input. The work presented here develops a framework that allows this in-space assembly problem to be framed in a way the robots can process. It then provides a method for generating assembly schedules that describe very good, if not the best way to complete the assembly quickly while still taking into account randomness that may be present. Additionally, this work develops a way to quantify and estimate how good robots will be at a task they have not attempted before. Finally, a set of considerations are proposed to aid in determining what scheduling method will work best for different assembly scenarios. The experiments in this work demonstrate how the developed theory can be used and shows the scheduling systems producing the best or close to the best schedules for assemblies. It also shows how the methods used to define robot ability are applied. The work developed here provides another step towards autonomous systems that are capable of assembling structures in-space without the need for human input.