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  • 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.
41

three dimensional electrophotographic printing through layered manufacturing : an exploration into personal fabrication

Mahale, Tushar Ramkrishna 03 June 2003 (has links)
A machine capable of making ?anything? has always existed in the realm of science fiction. The advent of the Rapid Prototyping machines partially fulfilled the realization of a personal fabricator by breaking the boundaries on the geometric form that could be realized through a machine in a single set up. The proliferation of the rapid prototyping machines into the industry and finally for domestic use, has been hampered by their costs, size and process limitations. The current trends in the Rapid Prototyping industry has been to develop machines capable of manufacturing parts in functionally graded materials. In order to achieve this, there is a need to develop means to precisely deposit a controlled combination of materials within the volume of a part. Electrophotography has been used for decades for monochrome and multicolor dry toner printing. The application of electrophotography for the generation of 3D parts through layered manufacturing has been left mostly unexplored. This thesis suggests guidelines for the development of an electrophotography based rapid prototyping process that would be cost effective in comparison with current commercial rapid prototyping technologies, as well as have the capability of depositing multiple materials. The initial research involved attempts to adapt a commercial electrophotographic printer to print in 3D. Later, experiments were conducted to indigenously build an electrophotography based layered manufacturing system. The research involved the development of transmission systems, development of power supplies to facilitate electrostatic charging, testing of polygon mirror based laser-scanning system, development of fusing and pressing station and experiments with multiple materials. Though a electrophotography based rapid prototyping machine was not realized at the end of this research, substantial evidence was generated to validate future research towards the development of such a system. Future work would involve the development of a completely automated system. Upon the completion of this system, further research could be carried out in the fields of personal fabrication, micro Rapid Prototyping, materials with directional properties, bio and materials, direct write technologies for printing circuits and functionally graded materials.
42

College Student Computer Use and Ergonomics

Noack, Karen Lee 05 June 2003 (has links)
Student computer users are at risk for Musculoskeletal Disorders (MSDs), such as carpal tunnel syndrome and tendonitis, and tension neck syndrome. Past research has identified repetition, duration, and posture as contributors to the development of MSDs in the computer work environment and these risk factors are present in the activities of student computer users as well as professional computer users. A web-based questionnaire was administered to 234 undergraduate and graduate college students majoring in either engineering or humanities and social sciences. The results of this study were compared with the results of a previous survey of professional workers that has a similar question structure. Sixty four percent of college students reported assuming an awkward posture at least 'sometimes' while using a desktop computer. On the 24-hour clock, college students reported their computer use to be at least 'somewhat likely' between the hours of 8:00 a.m. ? 2:00 a.m., while for professional workers the time period was reduced to the 12 hours between 6:00 a.m. ? 6:00 p.m. The survey also showed that college students work on the computer for closer to 90 minutes before taking a break, while the professional workers worked closer to 60 minutes before taking a break. In participants under 35 years of age, graduate students reported on average 33.7 weekly computing hours, compared to the 35.2 hours reported by professional workers. In general, college students reported a higher frequency of upper extremity discomfort than professional workers, and female participants reported higher discomfort than their male counterparts. There is still much to be learned about college students? interaction with computers, their risk of developing MSDs, and means by which risk can be reduced. The importance of incorporating ergonomics in the daily life of student computer users is apparent; it is believed that college students are likely to enter the workforce with poor computing habits and that appropriate education while the students are still in college is necessary to reduce the lifetime risk of developing these disorders.
43

Using Clothoidal Spirals to Generate Smooth Tool Paths for High Speed Machining

Pamali, Abhinand P 21 May 2004 (has links)
We present a new and innovative method to generate Contour Parallel tool paths using Clothoidal spirals for 2.5D pocket milling. The tool paths generated by the proposed method are more suitable for High Speed Machining compared to the traditional tool paths. Mechanical parts, such as those in Aerospace industry, Mold and Dies industry, etc require large volumes of milling operations. Modern High Speed CNC Machines are used in making of these parts. Although the High Speed CNC machines can provide very high spindle speed, due to various reasons, it has not been possible to use their High speed capabilities to their full extent. Two of the main reasons being, complex pocket geometry and complex tool path geometry. Most pockets are made up of sharp corners. In the traditional contour parallel pocket milling tool paths, as the cutting tool approaches these corners, they have to undergo a sudden change in directions and the acceleration of the tool has to be instantaneously decreased. Also, there is an instantaneous increase in the chip volume and the resultant forces acting on the cutting tool. In our proposed method we smooth these sharp corners of the traditional tool path by using Clothoidal spirals. The Clothoidal curves which have traditionally been used for Highways and Rail track design, have an unique property, according to which, the curvature of the Clothoidal spirals varies linearly with the length of the curve. By using these curves of uniformly varying curvature, we reduce the magnitude of the sudden direction changes that the cutting tool has to undergo at the sharp pocket corners. The cutting tool is subjected to lesser resultant forces and has a comparatively uniform acceleration. Machining time is also expected to be reduced by our proposed method.
44

Game Theoretic Analysis of a Distribution System in Supply Chain

Yuan, Pei-Lun 20 June 2003 (has links)
We consider a distribution system in which one supplier provides a single product to several retailers at the beginning of a selling season. The supplier has infinite capacity. The customer demand at each retailer is randomly distributed. Customers who encounter a stockout at one retailer may search other retailers for the product. We study the effects of this market search behavior under both decentralized and centralized control. For the decentralized control model, we show the necessary and sufficient conditions for the existence of a Nash equilibrium, and the sufficient conditions for its uniqueness. For the centralized control model, we find that the payoff function is submodular, and thus we can only obtain allocations that are locally optimal for the entire supply chain. We also design a channel coordination mechanism to match the allocations in the decentralized control model with one of the local optimal allocations under centralized control.
45

Nano-scale Molecular Docking and Assembly Simulator (NanoDAS) with Haptic Force-Torque Rendering and Energy Minimization for Computer-Aided Molecular Design (CAMD)

Lai-Yuen, Susana Karina 30 June 2005 (has links)
The objective of this research is to investigate and develop computational and haptic interface techniques to facilitate the design of molecular docking and molecular assembly for computer-aided molecular design (CAMD). Nano-scale molecular docking and molecular assembly are vital for the discovery and development of medicines, nano-scale devices, and new materials. In this paper, a new method called NanoDAS (Nano-scale Docking and Assembly Simulator) is presented to determine the feasibility of a ligand molecule reaching the binding site of a receptor molecule. To improve the design of molecular docking process, effective user intervention is necessary and is introduced through the use of a 5-DOF (degrees of freedom) force-torque feedback Haptic device developed at our research lab. Through the force-torque feedback haptic interface, a user is able to feel the forces exerted on the ligand by the receptor and find a feasible path using the proposed NanoDAS. The user is also able to determine whether the ligand can actually dock into the receptor by considering its conformational changes using a proposed energy minimization algorithm. The developed techniques can be used in Computer-Aided Molecular Design (CAMD) and Computer-Aided Drug Design (CADD) applications. Computer implementations and practical examples of the proposed methods are also presented.
46

A TEACHING JOB SHOP CONTROL SYSTEM WITH REAL-TIME INVENTORY MANAGEMENT

Maxwell, Andrew Charles 08 July 2005 (has links)
This thesis presents a teaching job shop control system for running in assembly laboratories at colleges and universities in preparing Industrial Engineering students for challenges faced in real-world factories. Current techniques fail to encompass this idea of training for students like the proposed method does. Microsoft Access was used in creating a database that is the center point in this new system. Inventory is managed using this database system and added if parts are created in the manufacturing lab and moved to the assembly area. The system will stop if parts are low until new parts are created. In this new system, a pallet with an unfinished product on it moves down a conveyor system until it reaches the next workstation. At this station, the station operator scans a barcode on the pallet. This barcode contains what product is on this pallet. Based on this information, an ordered list of tasks appears on the workstation computer screen and must be done before the pallet can be moved on. When all tasks have been completed at a station, the station operator clicks ?done? on the screen and then can either move to the next pallet or end the run. Statistics are kept on the quality of the final products and parts as well as a work-in-process and on a goal percentage of good products out at the end of a one-hour time frame. Administrators will be able to assign tasks and parts to products and stations, as well as be able assign the goal ahead of time.
47

Investigation of Factors Associated with Prevalence and Severity of Musculoskeletal Symptoms Among the Workers in Clinical Specialties of Radiologic Technology: An Ergonomic and Epidemiological Approach

Lamar, Sabrina Lyons 20 July 2004 (has links)
Little research has been done to investigate the combination of biomechanical and work organization factors associated with musculoskeletal symptoms among radiologic technologists. This cross-sectional study used a written self-report questionnaire to evaluate levels of job-related psychological stress, exposure to ergonomic stressors, and 12-month and 7-day prevalence of musculoskeletal complaints in radiologic technologists who worked in hospital or clinic-based settings in one health system. Written surveys based on interviews and direct observations of radiologic technologists and adapted from the Job Content Questionnaire and the Nordic Questionnaire were used to elicit information about psychological stress from a control-demands theory approach, work organization factors, categories of work performed, types of equipment utilized, prevalence and severity of musculoskeletal symptoms, and specific personal and health factors. Associations between personal factors, the type of work performed and the presence and severity of musculoskeletal symptoms were explored through statistical analysis. Work stress factors for radiologic technologists sin this study were compared to similar health technologists and nurses from a previously established database of Job Content Questionnaire scores. RESULTS: Radiologic technologists have a high prevalence of low back symptoms that are likely to interfere with work and leisure activities. Patient positioning was associated with an increased prevalence of low back symptoms. Transporting equipment was associated with an increased risk of experiencing right hand/wrist symptoms and dominant hand/wrist symptoms. Working as a sonographer was associated with increased risk of experiencing symptoms in the right shoulder, dominant shoulder, right hand/wrist and dominant hand/wrist. Positioning patients was associated with greater risk of experiencing musculoskeletal symptoms in the low back. Technologists in this study were older and had more education than other health care technologists from previous research using the Job Content Questionnaire. They had better scores for decision authority, decision latitude and supervisor support than the other technologists. However, they also had higher levels of physical exertion and psychological demands than the other technologists. They had a similar distribution of males versus females, and scores for created skills, job insecurity, total social support, co-worker support and job dissatisfaction as the other health technologists. Technologists in this study were older than nurses in previous research conducted with the Job Content Questionnaire. They had higher scores for decision authority and reported higher levels for psychological demands than the nurses in previous research. CONCLUSIONS: This group of radiologic technologists had a very high prevalence of musculoskeletal symptoms that were likely to interfere with work and leisure activities. Tasks related to patient handling and positioning and transporting equipment were associated with higher prevalence of symptoms. Results of this study may provide direction for future research efforts toward quantifying biomechanical exposures for radiologic technologists.
48

Analysis of Patellar Height of the Cranial Cruciate Ligament Deficient Canine Stifle Following Three Tibial Osteotomy Procedures.

Crimi, Christopher Scott 03 October 2008 (has links)
The cranial cruciate ligament (CCL) plays a significant role in providing functional stability to the canine stifle joint and has been the topic of an increasing amount of attention in the veterinary community. The objective of this study was to evaluate the effects of CCL deficiency and common procedures for treatment of a ruptured CCL on patellar location within the trochlear groove. Five identical and anatomically accurate physical models of the left hind limb of a healthy dog were constructed using a combination of rapid-prototyping technologies and casting techniques. One model remained the intact control, one simulated a CCL deficient stifle and each of the remaining models underwent one of the three tibial osteotomy procedures to be examined: the Tibial Plateau Leveling Osteotomy (TPLO), Tibial Tuberosity Advancement (TTA), and the Triple Tibial Osteotomy (TTO). Physical testing via a custom testing apparatus was carried out for five stifle positions (75º, 96º, 113º, 130º, 148º) representing the normal range of motion of a large-breed dog. Confirmation of a cranial translation following transection of the CCL was in good agreement with literature. Cranial cruciate transection also caused a slight proximal shift of the patella with respect to the trochlear groove. The results of the models further suggest that both the TPLO and TTO procedures result in a more proximally located patella with respect to the trochlear groove, while the TTA results in a more distally located patella.
49

STATISTICAL ANALYSIS OF NOVEL DIELECTRIC MATERIALS FOR MICROELECTRONICS

Hunt-Lowery, Alisa 23 November 2004 (has links)
This research analyzes the re-oxidation annealing process of Barium titanate thin films on copper foils made by Chemical Solution Deposition. During this anneal, the temperature and oxygen pressure settings must be optimized to ensure the elimination of oxygen vacancies without oxidizing the copper foil substrate. This research utilizes Design of Experiments (DOE) to study the impact of re-oxidation furnace temperature and pressure on the dielectric loss tangent response. Two designs of experiments were run. The first experiment, a 32 DOE, examined a large range of temperature and pressure levels. Due to the high susceptibility of uncontrollable factors such as humidity and film position in the crystallization anneal furnace, an adequate model could not be developed. However, the temperature at 550ºC and a pressure of 10-5 Torr yielded a lower mean and standard deviation of the loss tangent response. A second and smaller scale experiment, a 22 with a center point, was run around 550ºC and 10-5 Torr to determine if more optimal temperature and pressure settings existed in the local area. Two second order response surface models were developed from two crystallization anneals that were statistically significant. The most significant finding was that the optimum level for temperature and pressure in the re-oxidation anneal furnace in this experiment is 550ºC and 2x10-5 Torr. While the models concluded that the temperature, pressure, temperature quadratic, and interaction between pressure and temperature were important effects in the model, there were differences in the curvature of the models due to the temperature quadratic effect.
50

Electron Beam Melting of Advanced Materials and Structures, mass customization, mass personalization

Mahale, Tushar Ramkrishna 04 December 2009 (has links)
Layered manufacturing has for long been used for the fabrication of non-functional parts using polymer-based processes. Developments in laser beam and electron beam welding technologies and their adoption to layered manufacturing has made it possible to fabricate high-density functional parts in metal irrespective of the level of complexity. The Electron Beam Melting (EBM) process by Arcam AB is one such layered manufacturing process that utilizes a focused electron beam to process metal powder, layer by layer, in a vacuum environment. Research conducted as part of this body of work, looks into the development of both bulk materials in the form of metal alloys and ceramic metal-matrix composites as well as the development of tunable mechanical & thermal metamaterials. Simulation models to approximate electron beam melting were suggested using commercial finite element analysis packages. A framework was developed based on the finite difference method to simulate layered manufacturing using Arcam ABâs electron beam melting process. The outputs from the simulation data could be used for the better understanding the local melting, grain evolution, composition and internal stresses within a freeform-fabricated metal parts.

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