Dissertations / Theses on the topic 'Preloads'
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Woodend, Dianne. "The effect of sucrose and safflower oil preloads on satiety, mood and memory." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0021/MQ49777.pdf.
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Nettles, A. T. "The effects of tensile preloads on the impact response of carbon/epoxy laminates." Diss., This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-06062008-154902/.
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Regan, Paula J. "Influence of macronutrient preloads on appetite and metabolic parameters in liver and renal transplant recipients." Thesis, Queen Margaret University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271521.
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Jakel, Roland. "Analyzing a bolted, conical hub-shaft-connection with finite friction contact in Creo Simulate 3.0: Best practices for working with large displacement analysis, bolt preloads and finite friction contact." Technische Universität Chemnitz, 2018. https://monarch.qucosa.de/id/qucosa%3A21441.
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Der Vortrag beschreibt, wie mittels des Kontaktmodells mit endlicher Reibung in
Creo Simulate 3.0 ein Schwungrad mit axial verschraubtem mit Kegel-Presssitz
berechnet werden kann. Da in Creo Simulate 3.0 des Softwareentwicklers PTC das
Kontaktmodell mit endlicher Reibung nur für die Theorie großer Verformungen
implementiert ist, nicht jedoch für einfache Analysen mit kleinen Deformationen,
muss der Anwender einige softwareseitige Einschränkungen geschickt umgehen. Es
werden Vorgehensweisen vorgeschlagen, wie der Anwender dies bewerkstelligen
kann. Ein besonderer Schwerpunkt liegt dabei auf der Modellierung von Schrauben
sowie der Einstellung der Schraubenvorspannung. Rechenergebnisse des Programms
werden mit analytischen Lösungen verglichen.The presentation describes how to analyze a flywheel with axially bolted hub-shaft- connection using a conical press fit with help of the finite friction contact model in Creo Simulate 3.0. Since Creo Simulate 3.0 from PTC offers a finite friction contact model implementation just for large displacement analysis, but not for simple analyses with small displacements, the user has to work around a couple of code specific limitations. Best practices are proposed how to do this. Special attention is paid on bolt modeling and preload adjustment. Analysis results are compared with analytical solutions.
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Xu, Weiwei. "Effect of Bolted Joint Preload on Structural Damping." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4794.
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Bolted joints are integral parts of mechanical systems, and bolt preload loss is one of the major failure modes for bolted joint structures. Understanding the damping and frequency response to a varying preload in a single-bolted lap-joint structure can be very helpful in predicting and analyzing more complicated structures connected by these joints.
In this thesis, the relationship between the bolt preload and the natural frequency, and the relationship between the bolt preload and the structural damping, have both been investigated through impact hammer testing on a single-bolted lap-joint structure. The test data revealed that the bolt preload has nonlinear effects on the structural damping and on the natural frequency of the structure. The damping ratios of the test structure were determined to increase with decreasing preload. An increase in structural damping is beneficial in most engineering circumstances, for it will reduce the vibrational response and noise subjected to external excitations. It was also observed that the modal frequency increased with increasing preload, but remained approximately constant for preload larger than 30% in the bolt yield strength. One application for studying the preload effect is the detection for loose bolts in structures. The possibility of using impact testing for estimating preload loss has been confirmed, and the modal damping was determined to be a more sensitive indicator than the natural frequency in a single-bolted lap-joint structure.
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Lundin, Malin. "Left atrial functions: effects of increased and decreased preload." Thesis, Örebro universitet, Institutionen för hälsovetenskap och medicin, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:oru:diva-44928.
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Thomas, Anthony H. 1981. "Strain based preload measurement in drive axle pinion bearings." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/30322.
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Thesis (S.M. and S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.Includes bibliographical references (leaf 44).
Bearing setting has a significant impact on bearing life and system performance. A strain based load measurement technique that has been previously developed and patented will be used to measure preload in automotive drive axle pinion bearings. This technique utilizes strain gages placed in notches that have been machined into the outer diameter of a bearing cup. The performance of two gage types, semiconductor and metal foil, are compared. Preload in the pinion bearings is simulated in a machine by applying an axial load to a bearing assembly. The bearing assembly is rotated at various speeds and temperatures for each set of axial loads. Two notch geometries are compared for each set of tests conducted. An effort has been made to develop a finite element model that can be used to verify the results of the gage calibration. The results of the calibration reveal that metal foil and semiconductor gages can provide preload measurements that are accurate to within 3.7% and 7.7% of the full scale input load (73 lbs. and 155 lbs.) respectively.
by Anthony H. Thomas, II.
S.M.and S.B.
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Jacobs, Nicholas R. "Displacement of Screw-Retained Single Crowns into New Generation Narrow Diameter Implants with Conical and Conical/Hex Internal Connections and their Performance when Cyclically Loaded." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1566144926275455.
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Preuss, Jason Lee. "Design and analysis of a composite flywheel preload loss test rig." Thesis, Texas A&M University, 2004. http://hdl.handle.net/1969.1/100.
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Flywheel energy storage units have become a viable alternative to electrochemical batteries in applications such as satellites, uninterrupted power supplies, and hybrid vehicles. However, this performance is contingent upon safe operation since these flywheels can release their stored energy almost instantaneously upon failure. The research presented here investigates a health monitoring technology that may give an early indication of degraded material properties in a concentric ring composite flywheel. The existence of degraded material properties is manifested as a change in mass eccentricity due to asymmetric growth of the outermost flywheel ring. A test rig concept to investigate the technology is developed in detail using a systems engineering design process. Successful detection of the change in mass eccentricity was verified analytically through dynamic modeling of the flywheel rotor and magnetic suspension system. During steady state operation detection was determined to be feasible via measurements of the magnetic bearing currents and shaft position provided by the magnetic suspension feedback sensors. A rotordynamic analysis was also conducted and predicts successful operation to the maximum operating speed of 50,000 Rpm.
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Åkerblom, Mats. "Gearbox noise : Correlation with transmission error and influence of bearing preload." Doctoral thesis, KTH, Maskinkonstruktion (Inst.), 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9899.
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The five appended papers all deal with gearbox noise and vibration. The first paper presents a review of previously published literature on gearbox noise and vibration. The second paper describes a test rig that was specially designed and built for noise testing of gears. Finite element analysis was used to predict the dynamic properties of the test rig, and experimental modal analysis of the gearbox housing was used to verify the theoretical predictions of natural frequencies. In the third paper, the influence of gear finishing method and gear deviations on gearbox noise is investigated in what is primarily an experimental study. Eleven test gear pairs were manufactured using three different finishing methods. Transmission error, which is considered to be an important excitation mechanism for gear noise, was measured as well as predicted. The test rig was used to measure gearbox noise and vibration for the different test gear pairs. The measured noise and vibration levels were compared with the predicted and measured transmission error. Most of the experimental results can be interpreted in terms of measured and predicted transmission error. However, it does not seem possible to identify one single parameter, such as measured peak-to-peak transmission error, that can be directly related to measured noise and vibration. The measurements also show that disassembly and reassembly of the gearbox with the same gear pair can change the levels of measured noise and vibration considerably. This finding indicates that other factors besides the gears affect gear noise. In the fourth paper, the influence of bearing endplay or preload on gearbox noise and vibration is investigated. Vibration measurements were carried out at torque levels of 140 Nm and 400 Nm, with 0.15 mm and 0 mm bearing endplay, and with 0.15 mm bearing preload. The results show that the bearing endplay and preload influence the gearbox vibrations. With preloaded bearings, the vibrations increase at speeds over 2000 rpm and decrease at speeds below 2000 rpm, compared with bearings with endplay. Finite element simulations show the same tendencies as the measurements. The fifth paper describes how gearbox noise is reduced by optimizing the gear geometry for decreased transmission error. Robustness with respect to gear deviations and varying torque is considered in order to find a gear geometry giving low noise in an appropriate torque range despite deviations from the nominal geometry due to manufacturing tolerances. Static and dynamic transmission error, noise, and housing vibrations were measured. The correlation between dynamic transmission error, housing vibrations and noise was investigated in speed sweeps from 500 to 2500 rpm at constant torque. No correlation was found between dynamic transmission error and noise. Static loaded transmission error seems to be correlated with the ability of the gear pair to excite vibration in the gearbox dynamic system.QC 20100923
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Åkerblom, Mats. "Gearbox noise : correlation with transmission error and influence of bearing preload /." Stockholm : Maskinkonstruktion, Kungliga Tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9899.
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Wang, Lu, and 王璐. "Post-compressed plates for strengthening preloaded reinforced concretecolumns." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hub.hku.hk/bib/B50162664.
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Reinforced concrete (RC) columns are the primary load-bearing structural components in buildings. Over time these columns may need to be repaired or strengthened either due to defective construction, having higher loads than those foreseen in the initial design of the structure, or as a result of material deterioration or accidental damage. Three external strengthening methods, namely steel jacketing, concrete jacketing and composite jacketing, are commonly adopted for upgrading the ultimate load capacity of RC columns. Among these strengthening techniques for RC columns, steel jacketing, which is easy to construct, less prone to debonding and has better fire resistance than bonded plates, has been proven to be an effective retrofitting scheme and is the most commonly used.
Different methods for strengthening existing RC columns have been proposed in the literature. However, no matter which jacket is used to strengthen RC columns, the adverse effects of pre-existing loads on stress-lagging between the concrete core and the new jacket have yet to be solved. In order to deal with this problem, a new postcompression approach was proposed for strengthening preloaded RC columns. In this approach, the slightly precambered steel plates were used. The advantages of this ‘post-compressed plates’ (PCP) strengthening technique are that both the strength and deformability of existing columns can be enhanced and the design life of old buildings can be prolonged.
Due to the aforementioned advantages, the PCP strengthening technique was investigated in this study. To begin with, axial compression tests of the PCP strengthened columns were conducted. The overall response, in particular the internal force distribution between concrete and steel plates was obtained. It was observed that the plate thickness and preloading level had dominant effects on the behaviour of PCP strengthened columns. Subsequently, eccentric compression tests of PCP strengthened columns were undertaken. The behaviour of PCP strengthened columns was mainly affected by the degree of eccentricity and plate thickness. Placing flat and precambered steel plates on the tension and compression sides respectively of the RC columns and using post-compression method on the compression side can significantly improve the ultimate load capacity of RC columns under large eccentricity; while placing precambered steel plates on the side faces of the RC columns can significantly improve the ultimate load capacity of RC columns under small eccentricity. Finally, axial compression tests of PCP repaired fire-exposed columns were carried out. The ultimate load capacity of fire-exposed columns can be restored up to 72% of original level by using this post-compression approach. The corresponding theoretical models were also developed to predict the ultimate load capacity of PCP strengthened columns. Comparison of theoretical and experimental results showed that the theoretical models accurately predicted the load-carrying capacities of PCP strengthened columns.
According to the experimental and theoretical results, a unified design procedure for the PCP strengthened columns was proposed to aid engineers in designing this new type of PCP strengthened columns and to ensure proper column detailing for desirable performance. The design procedure was validated by the available experimental and theoretical results.published_or_final_version
Civil Engineering
Doctoral
Doctor of Philosophy
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Lin, Alvin Lai. "Design and implementation of a preload electronics architecture for a MEMS accelerometer." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/62988.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 99-101).
This thesis describes the design and implementation of an electronics system to provide rebalancing and readout for a force-rebalanced microelectromechanical accelerometer. A feedback control loop is devised using a novel preload architecture, compensating the proof mass of the sensor and providing an accurate acceleration measurement. This architecture is compared to alternative methods of linearizing the control loop. The electronics system is divided into analog and digital subsystems. The design is analyzed at several abstraction levels. The system is implemented for prototype testing with discrete components on a printed circuit board with a MEMS sensor attached. A computer program is implemented to receive and process the readout data using the serial port. The design methodology consists of a top-down design flow based on simulation. At each iteration in the design process, the lower level abstraction is verified with the previous model. Eventually, the design reaches the level of synthesizable digital logic and discrete analog components. This thesis describes the design process and implementation details for creating an accelerometer system prototype ready for lab testing. Detailed simulations indicate that the implemented design is likely to meet the design goals for a personal navigation system suitable for a human or land vehicle. Conclusions on design methodology and verification techniques are also presented.
by Alvin Lai Lin.
M.Eng.
14
Kovacs, Michelle. "The Effects of Caloric Preload and Dietary Restraint on Smoking and Eating Behavior." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4524.
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Abstract
Rates of smoking are elevated in eating-disordered populations, especially among females (Pomerleau & Snedecor, 2008; Klesges & Klesges, 1988). Restrained eaters ignore physiological cues of satiation and hunger, and instead attempt to employ cognitive control over decisions to eat. Additionally, they are prone to eat in a disinhibited manner after a salient emotional or food cue interrupts their restraint. This eating style is also associated with increased rates of smoking compared with the general population. Although there is a great deal of literature on the relationship between smoking and eating, the role of eating in momentary decisions regarding smoking remains to be explored. The current study tested whether a food prime, which has been found to elicit disinhibited eating in restrained eaters, could also motivate smoking as an alternative to eating. In a randomized two-arm (Prime/No-Prime) between-subjects design, it was hypothesized that smokers, particularly those high in eating restraint, receiving a food prime would be more likely to smoke than eat when given the option, compared to smokers who did not receive the food prime. Although main effects on smoking variables were not found, restraint status did moderate the effect of the food prime upon latency to first puff, number of puffs, and cigarette craving. Moreover, the moderation effect was reversed upon eating variables, suggesting that after a food prime, weight-control smokers appear to choose to smoke to prevent further food intake. This conclusion was bolstered by the finding that the moderation effect on smoking was further moderated by expectancies regarding the effect of smoking upon appetite and weight. In summary, this study identified psychological mechanisms that appear to underlie the population-based covariance between disordered eating and smoking.
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Roan, Earl Taylor. "Design of an STM and EPL control system and linear actuator preload diaphragm." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/40310.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 53-54).
Increasing demand for nano-scale machining processes in the semiconductor industry necessitates new mechanisms for nano-machining. A system capable of nano-scale machining of conductive material via Electronic Pen Lithography (EPL) may fit this niche. The purpose of this research is to develop a system capable of EPL based on a HexFlex six axis nano-manipulator. The system will also be capable of Scanning Tunneling Microscopy (STM), which is will locate the surface with the precision necessary for EPL and also allow the user to confirm the machined features immediately after machining. The import of this work is the development of a low-cost and compact system for nano-machining and nano-scale imaging. The impact of this work may improve the process for manufacturing semiconductors including circuitry, MEMS, and NEMS. The continued development of full six axis machining techniques may allow for the construction of features hitherto impossible to fabricate. This segment of the project focuses on the integration of the HexFlex, a micron stepper motor, precision mounts, a preload diaphragm, and an advanced control system capable of automated EPL and STM verification. Steady electron tunneling is first demonstrated, followed by STM imaging functionality. However, high-speed, high-accuracy EPL machining techniques are reserved for future work.
by Earl Taylor Roan.
S.B.
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Oliveira, Marcio Rodrigo de. "Estudo e implementação da otimização de Preload de dados usando o processador XScale." [s.n.], 2005. http://repositorio.unicamp.br/jspui/handle/REPOSIP/276447.
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Orientador: Guido Costa Souza AraujoDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Computação
Made available in DSpace on 2018-08-06T14:27:52Z (GMT). No. of bitstreams: 1 Oliveira_MarcioRodrigode_M.pdf: 1563381 bytes, checksum: 52e2e029998b3539a26f5c2b76284d88 (MD5) Previous issue date: 2005
Resumo: Atualmente existe um grande mercado para o desenvolvimento de aplicações para sistemas embutidos, pois estes estão fazendo parte crescente do cotidiano das pessoas em produtos de eletrônica de consumo como telefones celulares, palmtop's, agendas eletrônicas, etc. Os produtos de eletrônica de consumo possuem grandes restrições de projeto, tais como custo reduzido, baixo consumo de potência e muitas vezes alto desempenho. Deste modo, o código produzido pelos compiladores para os programas executados nestes produtos, devem executar rapidamente, economizando energia de suas baterias. Estes melhoramentos são alcançados através de transformações no programa fonte chamadas de otimizações de código. A otimização preload de dados consiste em mover dados de um alto nível da hierarquia de memória para um baixo nível dessa hierarquia antes deste dado ser usado. Este é um método que pode reduzir a penalidade da latência de memória. Este trabalho mostra o desenvolvimento da otimização de preload de dados no compilador Xingo para a plataforma Pocket PC, cuja arquitetura possui um processador XScale. A arquitetura XScale possui a instrução preload, cujo objetivo é fazer uma pré-busca de dados para a cache. Esta otimização insere (através de previsões) a instrução preload no código intermediário do programa fonte, tentando prever quais dados serão usados e que darão miss na cache (trazendo-os para esta cache antes de seu uso). Com essa estratégia, tenta-se minimizar a porcentagem de misses na cache de dados, reduzindo o tempo gasto em acessos à memória. Foram usados neste trabalho vários programas de benchmarks conhecidos para a avaliação dos resultados, dentre eles destacam-se DSPstone e o MiBench. Os resultados mostram que esta otimização de preload de dados para o Pocket PC produz um aumento considerável de desempenho para a maioria dos programa testados, sendo que em vários programas observou-se uma melhora de desempenho maior que 30%!
Abstract: Nowadays, there is a big market for applications for embedded systems, in products as celIular phones, palmtops, electronic schedulers, etc. Consumer electronics are designed under stringent design constraints, like reduced cost, low power consumption and high performance. This way, the code produced by compiling programs to execute on these products, must execute quickly, and also should save power consumption. In order to achieve that, code optimizations must be performed at compile time. Data preload consists of moving data from a higher leveI of the memory hierarchy to a lower leveI before data is actualIy needed, thus reducing memory latency penalty. This dissertation shows how data preload optimization was implemented into the Xingo compiler for the Pocket PC platform, a XScale based processor. The XScale architecture has a preload instruction, whose main objective is to prefetch program data into cache. This optimization inserts (through heuristics) preload instructions into the program source code, in order to anticipate which data will be used. This strategy minimizes cache misses, allowing to reduce the cache miss latency while running the program code. Some benchmark programs have been used for evaluation, like DSPstone and MiBench. The results show a considerable performance improvement for almost alI tested programs, subject to the preload optimization. Many of the tested programs achieved performance improvements larger than 30%
Mestrado
Otimização de Codigo
Mestre em Ciência da Computação
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Cui, Zheng. "FUEL: A Runtime Methodology to Preload Time Consuming UI-APIs for Android Apps." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu158768332631699.
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Subasic, Mustafa. "The effect of preload on the fatigue strength of additively manufactured 316L stainless steel." Thesis, KTH, Hållfasthetslära, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-285818.
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In this thesis an investigation of the effect of preload on the fatigue behaviour of additively manufactured (AM) 316L stainless steel parts with less than 5 % porosity, for both horizontal and vertical build direction, is presented. The specimens used were manufactured by selective laser melting (SLM) and cut by EDM. Preloads at two different magnitudes were used, below and above the yield strength of the material, and fatigue tests were performed on the specimens with and without the preloads. In addition, microstructural analysis was carried out in order to illustrate/quantify the defects and to realize the corresponding effect of the preload by use of white light interferometry (WLI), SEM and FEM modeling. It was found that the fatigue life and the fatigue limit clearly increase with increasing the preloads in both build directions, although the preload significance might be varied for different directions. This was attributed to the imposed compressive residual stresses and blunting of sharp defects after preloading.I detta examensarbete presenteras en undersökning på effekten av förbelastning på utmattningsbeteendet hos additivt tillverkade (AM) komponenter av 316L rostfritt stål med mindre än 5 % porositet, för både horisontell och vertikal byggriktning. Provstavarana tillverkades genom selektiv lasersmältning (SLM) och skars ut med trådgnist (EDM). Förspänningar i två olika storlekar användes, under och över materialets sträckgräns, och utmattningstester utfördes på provstavarna med och utan förspänningarna. Dessutom genomfördes mikrostrukturella analyser för att illustrera / kvantifiera defekterna och effekten av förspänningen med användning av vitt ljusinterferometri (WLI), SEM och FEM-modellering. Det visade sig att utmattningslivslängden och utmattningsgränsen tydligt ökar med ökad förspänning i båda byggriktningarna, även om förspänningens betydelse kan variera för olika riktningar. Denna positiva effekt på utmattningen kommer från de kompressiva restspänningarna och avstumpningen av skarpa defekter som uppstår efter förbelastningen.
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Paye, Anco Alex Aurelio, Castillo José Peña, and Sanchez Juan Franco. "Propuesta para la utilización de losas de entrepisos prefabricados y su evaluación costo-tiempo." Universidad Peruana de Ciencias Aplicadas (UPC), 2014. http://hdl.handle.net/10757/337192.
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La innovación tecnológica abarca aspectos como las mejoras en los procesos, los productos y en los servicios, orientados en estas mejoras es que tenemos por finalidad proponer sistemas innovadores de losas de entrepiso más ventajosos que el sistema de losas tradicionales actualmente usada por el sector de la construcción (Ghio, V. & Bascuñan, R. 2006). Es por esta razón que realizamos un estudio para determinar las diferencias entre las losas aligeradas en una y dos direcciones, losas macizas, losas prefabricadas compuestas con viguetas pretensadas y prefabricadas, losas compuestas con láminas colaborantes y las Prelosas, que en la actualidad se ofrece en la industria de la construcción. Ante un mercado tan exigente y competitivo es conveniente realizar un análisis de las tendencias del uso de losas de entrepisos prefabricadas y un diagnóstico de la evaluación costo y tiempo comparándolas con las losas del sistema tradicional, de esta manera podemos optar por una mejor alternativa de losa de entrepisos de acuerdo al tipo de obra y sus condiciones. En este análisis se demuestra que no siempre se toma una alternativa por su menor costo, sino también por otras ventajas como el tiempo, la calidad del producto, accesibilidad a la zona de trabajo, procesos constructivos seguros, reducción de gastos generales, etc.
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Evans, Brandon A. (Brandon Adam). "Development of kinematic coupling preload guidelines through design and testing of an adjustable micromanufacturing fixture." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/92063.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 111-117).
In the growing field of non-lithographic micromanufacturing, the ability to properly align a workpiece to a machine limits the attainable tolerances in micro-electro-mechanical-systems (MEMS) prototyping. This limit has created the need for a standard adjustable base for implementation into multiple precision machines, allowing for six-axis adjustment and alignment of workpiece stages that are moved between these machines. Such a fixture--a hybrid positioning fixture (HPF)--has been designed, fabricated, and tested. This HPF has demonstrated <50 nm and <1.5 [mu]rad 2[sigma] (95% confidence) static positional repeatability over 1000 separation-engagement cycles and equivalent 2[sigma] (95% confidence) path-following accuracy when used as a dynamic nano-stage. The HPF has also demonstrated adequate stiffness to ensure <50 nm positional accuracy over an adjustment range of ±5 [mu]m and ±100 [mu]rad in response to 2 N normal and lateral forces during micro-milling operations. The HPF is based upon a kinematic coupling concept, and experiments have been completed that show highly repeatability coupling can be obtained by loading the Hertzian kinematic contacts of the HPF past the fully plastic half-groove material limit. This is a novel result that allows for stiffness increases of ~2.5 and load capacity increases of ~15.5 over conventional kinematic couplings, which are typically loaded to the sub-surface elastic limit.
by Brandon A. Evans.
S.M.
21
Turk, Amanda C. (Amanda Christine). "Design and fabrication of a device to characterize spindle performance as a function of bearing preload." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/75453.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Page 98 blank. Cataloged from student submitted PDF version of thesis.
Includes bibliographical references (p. 83-84).
This paper describes the design and fabrication of an apparatus to characterize the performance of lathe spindles as a function of spindle bearing preload. The apparatus will be used to assist undergraduate students enrolled in 2.72 in understanding mechanical design concepts. In order to assess spindle performance, the apparatus measures the radial stiffness, radial error motion, and running torque of a spindle at different preload levels. The data obtained using the apparatus can be used by students to select the optimal preload level for a spindle. The apparatus was designed as four subsystems (one for each measurement) that were integrated into a cohesive measurement system. The apparatus is designed to be as small, light, and user-friendly as possible, in order for students to use it effectively. The apparatus is capable of measuring bearing preload up to 10,000 lbs with a linearity of 0.05% and radial error motion with an accuracy of +/-0.00012 in. (3 [mu]m). It can measure the radial stiffness of the spindle for applied loads up to 500 lbs and running torque up to 443 in-lbs (50 N-m). The fabrication and assembly of the mechanical apparatus, as designed, were completed.
by Amanda C. Turk.
S.B.
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Braxton, Joi Requan. "Effect of preload on the response of mouse trachea smooth muscle to cholinergic stimulation a thesis /." San Antonio : UTHSC, 2008. http://learningobjects.library.uthscsa.edu/cdm4/item_viewer.php?CISOROOT=/theses&CISOPTR=33&CISOBOX=1&REC=10.
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Cierocka, Joanna, and Jiayue Tang. "Vibrational tests of preloaded rubber vibration isolators : A cam controlled displacement excitation." Thesis, Linnéuniversitetet, Institutionen för maskinteknik (MT), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-53703.
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Vibrations are very common phenomenon. It influences structures and generates acoustic noise which might be harmful to human beings. The vibration isolator was invented to reduce the effect from vibrations. However, the behavior of rubber material, which many vibration isolators are made of, is hard to predict. Consequently, vibration tests are needed to obtain the dynamic properties of rubber isolator.In this case, a six-year old LORD 2204-5 rubber isolator provided by Atlas Copco was tested. The aim of this paper is to obtain the FRF (Frequency Response Function) diagram which can describe the property of the rubber material. Moreover, the influence of aging of rubber material on the dynamic properties was studied.As the vibration test should simulate the working environment of the isolators that are both a static load from the structure and a dynamic force from the engine, a new excitation method was designed. The camshaft with the shape of an epitrochoid induced the sinusoidal signal of the isolator and the frame transferred the static load from the hydraulic machine. The artificial aging was performed in a hot air oven in 90°C for 42 hours, which according to Arrhenius equation should be equivalent to six years of natural aging. The vibration isolator was tested again after being aged.The obtained data showed that the aging process decreased the stiffness of the material. The results were corresponding with other studies regarding aging of rubber.
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Dunn, Jonathan Mark. "Determining the stiffness characteristics of a preloaded bolted joint using finite element analysis." Thesis, University of Bath, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320326.
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Richards, Jason Halbert. "Turn-of-the-nut tightening of anchor bolts." Texas A&M University, 2004. http://hdl.handle.net/1969.1/443.
Full textAbstract:
Double-nut anchor bolt systems are used in the erection of traffic signal poles, high-mast luminaries, and other highway appurtenances. An absence of a tightening standard for such systems decreases the confidence in their performance under fatigue loading. Past research has shown that a tightening standard should include the development of preload in the anchor bolt sufficient to provide adequate resistance to fatigue failure. Preload should be measured by a turn-of-the-nut method.
Laboratory progressive tightening tests were performed in order to monitor the stress ranges occurring in the bolt at various locations of interest at various degrees of turn-of-the-nut tightness. Tests were performed on six diameters of anchor bolt ranging from 1 to 2-1/4 inches in diameter and two different categories of thread pitch: UNC and 8UN. Plots of stress range versus degree of tightness were developed for each test and evaluated to find the minimum degree of turn-of-the-nut at which stress range inside the nuts dropped below that outside the nuts. This shift was considered to be the principle theoretical indication of adequate performance. A fatigue test which saw failure outside the double-nut connection was set down as the practical indicator of adequate fatigue performance.
The 2 inch 8UN bolt was chosen as the critical specimen due to its overall low generation of preload during tightening tests. Theoretical testing showed that 1/24 turn-of-the-nut would guarantee sufficient fatigue performance. Two practical fatigue tests of the bolt at that tightness saw one positive and one negative failure.
After actual lab tests, finite element modeling was used to investigate the behavior of the bolt. It was found that performance did not see improvement until 1/12 turn-of-the-nut.
After all results were considered, a standard of 1/6 turn-of-the-nut or refusal of tightening by specified methods was recommended, provided a minimum of 1/12 turn-of-the-nut was achieved. This value allows for ease of measurement, sufficient tightness, degree of safety, and has been shown in past testing not to cause failure through over-tightening. However, tightening to only 1/12 turn-of-the-nut still provided adequate performance.
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Cravotta, Stefan, and Emanuele Grimolizzi. "Simulation of vehicle impact into a steel building : A parametric study on the impacted column end-connections." Thesis, KTH, Bro- och stålbyggnad, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-172341.
Full textAbstract:
Understanding the true behaviour of impacted structures is the only way to assess their robustness under exceptional events such as vehicle collision. The primary objective of this master’s thesis was to perform a finite element parametric investigation on the influence that some parameters have in steel buildings subjected to vehicle impacts. The parameters chosen for the study, involved uncertainties in the material definition and in the load configuration of the bolts used in the impacted column end-connections. By using the Abaqus software, a finite element model of the structure has been created. The five storey steel building considered has been modelled in a simplified manner with the exception of the impacted area which, instead, has been defined in a more detailed fashion. During the simulations, different preload conditions have been used, comparing cases with and without the preload force. Regardless its variation, it has not been observed any increase in the structural resistance. On the other hand, the simulation provided interesting results for what concerns the material variations in the bolts. Although the changes have been small in magnitude, the effect on the structural response during the impact was remarkable. For all the cases considered, an increase of the material ductility, achieved by increasing the ultimate strain at failure, entailed higher resistance of the connections. Various failure modes have been observed when the material properties have been changed. Having clarified the influence of the assumptions made, the results provided helpful information in sight of future studies. Although the model still needs to be validated, the research clarified which of the parameters investigated are to be collected with more attention. Keywords: Vehicle collision, steel building, FE model, Abaqus/Explicit, parametric investigation, bolt preload, bolt material.
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Scherer, Rebecca Elizabeth. "Settlement Analyses of Grade Supported Tanks Constructed with the Use of Prefabricated Wick Drains and an Earth Preload." ScholarWorks@UNO, 2011. http://scholarworks.uno.edu/td/1345.
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In the design of tank foundations several design techniques are considered. This study focuses on grade supported tanks constructed under an extensive preload and instrumentation program. Settlement estimation methods were performed and compared to field instrumentation data taken at the project sites. Three project sites were selected for this study. The geotechnical investigations were performed by Eustis Engineering Services, L.L.C. and included both undisturbed soil borings and cone penetrometer tests. Conclusions were made about the accuracy of the calculations and how assumptions affect the settlement computation results.
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Andersson, Amanda, and Adam Eklund. "Vidareutveckling av friktionsbetingat förband för fixering av tankar." Thesis, Mälardalens högskola, Akademin för innovation, design och teknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-40251.
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Scania CV AB is one of the world’s leading companies within heavy vehicles. The company have a broad selection of trucks, which all are equipped with gas, or fuel tanks, depending on the fuel type of the truck, The trucks also contain air tanks that are used for braking and air suspension. The tanks are assembled with straps, where the rubber spacers constitutes a protective layer between the tank and the strap, to protect the tank from wear. When installing different types of tanks there is a need for elements in the joint that increases the friction, compensates for manufacturing defects, prevents wear and permits electrical insulation. This has traditionally been done with rubber spacers. However, the rubber spacers increase the uncertainty of the actual preload of the joint, and movements in the joint usually make the spacers slip out of its position. The purpose of the project is to generate knowledge on what characteristics and conditions that affects the performance of the friction joint, and to find a conceptual solution of the underlaying problem. The following questions were created to be able to fulfill the purpose of the project: F1: Which underlying causes generate preload loss in the straps when assembling various tanks? F2: Which underlying causes makes rubber spacers tend to slip out of its position in various tank installations?F3: What operations need to be undertaken to prevent the preload loss in the straps and that the rubber spacers slip out of its position? A case study and a literature review was conducted. The literature review was done to get an overall understanding of all of the different subjects that can be of relevance in this project. The data was collected from books, research papers and scientific articles. Data was also collected from interviews, technical reports, deviation reports, legal requirements, drawings, statistics from the field quality and observations in production. The case study is based on a product development process where several different product development tools have been used. The case study also include material testing in terms of friction and settlement testing. The project resulted in a concept in the shape of a rubber spacer which is based on the existing solution that Scania is using today. The solution consists of four components: geometries that prevent the rubber from slipping away known as flanges and geometries in the shape of tips of a fir tree, rounded short sides and a dimpled underside. The size of the spacer will vary because of the different types of tank and strap sizes. The project also resulted in a design guideline, that will provide guidelines and guidance for further work and future design.Scania CV AB är ett av de världsledande företagen inom tunga fordon. Deras utbud av lastbilar är brett, och lastbilarna är utrustade med gas-, eller bränsletankar, beroende på fordonets drivmedel. Lastbilarna är även utrustade med trycktankar som används vid inbromsning och luftfjädring. Tankarna är monterade med spännband, där gummimellanlägg utgör ett skydd mellan tank och spännband för att skydda tanken mot nötning. Vid installation av olika lastbilstankar finns behov av element i förbandet som ökar friktionen, kompenserar formfel, förhindrar nötning, och medger elektrisk isolation. Detta har traditionellt gjorts genom att använda gummimellanlägg i förbandet. Gummimellanlägg ökar dock osäkerheten i den faktiska förspänningen av förbandet, samt rörelser i konstruktionen ofta får mellanlägget att vandra ur position. Syftet med projektet är att skapa förståelse för vilka egenskaper och förutsättningar som påverkar prestandan av ett friktionsbetingat förband, samt att hitta konceptuell lösning på grundproblematiken. För att kunna fullgöra syftet har följande frågeställningar utformats:F1: Vilka orsaker ligger till grund för att förspänningen i spännbanden släpper vid montering av diverse fordonstankar?F2: Vilka orsaker ligger till grund för att gummimellanlägg tenderar att vandra ur position i olika tankinstallationer?F3: Vilka åtgärder kan vidtas för att motverka att förspänningen i spännbanden släpper och att gummimellanläggen vandrar ur position? I arbetet har en fallstudie och en litteraturstudie genomförts. Litteraturstudien utfördes för att skapa övergripande förståelse i ämnen som kan vara relevanta för arbetet. Den insamlade informationen härrör från böcker, forskningsavhandlingar och vetenskapliga artiklar. Data har även samlats in i form av intervjuer, tekniska rapporter, felrapporter, lagkrav, ritningar, statistik i fältkvaliteten, och observationer i produktionen. Fallstudien baseras på en produktutvecklingsprocess där flera produktutvecklingsverktyg har använts. I fallstudien ingår även materialprov i form av friktion och sättning. Arbetet resulterade i ett koncept i form av ett gummimellanlägg och baseras på Scanias befintliga lösning. Lösningen består av fyra komponenter: geometrilåsning i form av flänsar och så kallade grantoppar, rundade kortsidor och gropig undersida. Storleken kan däremot variera på grund av spännbandens och tankarnas breda storleksspann. Arbetet har även resulterat i en design-guideline, som ska ge riktlinjer och vägledning för fortsatt arbete och framtida konstruktion.
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Aron, Adrian. "The utility of bioimpedance cardiography in assessing the influence of obstructive sleep apnea hypopnea syndrome on cardiac function." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/72996.
Full textAbstract:
Obstructive Sleep Apnea Hypopnea Syndrome (OSAHS) is a breathing disorder characterized by recurrent episodes of upper airway collapse during sleep. Measuring cardiac function in OSAHS patients may provide information to help delineate not only chronic effects of autonomic imbalance and ventricular loading in the diseases state, but also possible beneficial effects of clinical treatments. Objectives (Study 1): The aim of this study was to determine the reproducibility of select cardiac variables when monitoring a simulated sleep apnea event using a new improved bioimpedance cardiography system. Methods: Fifteen apparently healthy males were tested on three different days in a protocol requiring their performance of two 15 sec and two 30 sec forced and sustained inspiratory efforts against a closed epiglottis (Müeller Maneuver-MM). Results: Changes in cardiac output (CO), heart rate (HR), stroke volume (SV), myocardial contractility index (MCI) and systemic vascular resistance (SVR) were similar during 15 sec and 30 sec MM in all three days. During 30 sec MM, these changes in cardiac function were pronounced in comparison to the minimal variations observed for the 15 sec MM challenge test.
Objectives (Study 2): The aim of this study was to characterize the cardiac responses to negative intrathoracic pressure in OSAHS patients with and without hypertension versus healthy subjects. Methods: Two groups of 10 OSAHS patients, one without HTN and one with HTN were compared with a control group. Each subject underwent two 30 sec (MM) as previously described. Results: During MM, there were similar changes in SV, HR and SVR in all three groups. CO was lower during MM in controls compared to OSAHS groups, whereas MCI decreased during MM in both controls and OSAHS+HTN groups (-7.5% and -1.7%, respectively) compared with an increase in OSAHS group (11.8%). During a Post-MM, both OSAHS groups showed return of cardiac responses toward their pre-MM baseline within 30 sec. Conclusions: The new bioimpedance cardiograph evaluated in this study was found to be reliable for measuring acute changes in cardiac responses to this breathing challenge test. OSAHS may cause acute changes in selected cardiac parameters during and immediately after a breathing challenge test.Ph. D.
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Zimandy, Adam Joseph Charles. "Prevailing Torque Locking Feature Wear-out." Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/4424.
Full textAbstract:
This thesis provides much needed representative sample data for reuse life of fully seated and torqued locknuts. Most national requirements for prevailing torque locking fasteners only specify unseated reuse life. This could create a potentially dangerous situation if unseated is misinterpreted for seated. This thesis provides comparative data for seated verses unseated configuration. Six aerospace, 3 all-metal and 3 nylon insert, and one non-aerospace locknuts were tested at preloads levels of unseated, 66%, 75%, and 85% of yield of bolt. The locknuts tested are MS21043-4, NAS1291-4, NAS1805-4, MS17825-4, MS21044D4, NAS1021N4, and Grade 8. A fixture was created in order to allow for the simultaneous data collection of the applied preload and torque, along with the removal of preload without loosening the locknut. The results from testing indicate the number of reuse cycles is greater for nylon locknuts than the all-metal locknuts. Large losses, on the order of 20-50%, in prevailing torque occur between the first and second cycle of each locknut under all preloads. Tightening Torque required to achieve a certain preload was found to increase with reuse. Application of lubrication to nylon locknuts had a significant effect, reducing the reuse life and prevailing torque performance. The testing indicated the effect of preload reduced the number of reuse cycles to failure, failure occurs when the prevailing torque is measured outside the range of 3.5 to 30 in-lb. All locknuts survived unseated and 66% Y preload testing,
except MS21043 which lasted about 14.5 reuse cycles at 66% Y and NAS1805 which survived 8 reuse cycles for unseated and 12.67 reuse cycles at 66% Y. NAS1805's loss of reuse life is due to hardness and material compatibility issues. The scatter of the torque measurements was low for the first three to five cycles, then as the coatings and lubrications are worn the scatter increases. The data collected from testing agrees with the torque friction equation.
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Watral, Adrienne. "Design and engineering of low-cost centimeter-scale repeatable and accurate kinematic fixtures for nanomanufacturing equipment using magnetic preload and potting." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/65317.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, February 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 127-130).
This paper introduces a low-cost, centimeter-scale kinematic coupling fixture for use in nanomanufacturing equipment. The fixture uses magnetic circuit design techniques to optimize the magnetic preload required to achieve repeatability on the order of 100 nanometers. The fixture achieves accuracy to within one micrometer via an adjustable interface composed of UV curing adhesive between the mating kinematic coupling components. The fixture is monitored by a micro-vision system and moved by a six-axis nanopositioner until proper alignment is achieved, at which point the fixture position is permanently set by UV light. This thesis presents design rules and insights for design of a general accurate and repeatable kinematic fixture and presents a case study of fixtures used for tool exchange on dip pen nanolithography machines. A prototype fixturing assembly was fabricated and tested for repeatability and stability in six degrees of freedom. The test results concluded that the fixture has a 1-o- 3-D translational repeatability of 87 nanometers and a 3-D stability of 344 nanometers over 48 hours. This is an order of magnitude improvement on past low-cost accurate and repeatable fixture designs. This optimized accurate and repeatable kinematic fixture will enable repeatable, accurate, quick, and elegant tool change, thus advancing the manufacturing capabilities of nanofabrication techniques.
by Adrienne Watral.
S.M.
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Cheatham, Christopher. "Statistical analysis of fastener vibration life tests." [Tampa, Fla.] : University of South Florida, 2007. http://purl.fcla.edu/usf/dc/et/SFE0002275.
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Hernandez, Alan. "Use of Anaerobic Adhesive for Prevailing Torque Locking Feature on Threaded Product." Scholar Commons, 2015. http://scholarcommons.usf.edu/etd/5700.
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The purpose of this research is to determine if anaerobic adhesive can be used as a prevailing torque locking feature. Maintaining preload in critical joints is the usual standard that anaerobic adhesives are held to in aerospace and other industry. To test if anaerobic adhesive can be used as a prevailing torque locking feature a test procedure was developed and implemented to measure the removal torque of threaded fasteners after an allotted cure time. In total, 191 threaded fasteners of different material and coatings were tested in the unseated and seated states with various strengths and varieties of anaerobic adhesive. A series of three tests were conducted: initial use, reuse with no added anaerobic adhesive, and a third test with added product to the bolt and nut to see how removal torque would behave in these conditions. It was found that using anaerobic adhesive as a prevailing torque locking feature is viable in many cases. No published work to date analyzes anaerobic adhesive at the standard of a prevailing torque locking feature.
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Ramadoss, Vivek. "Analysis of capillary forces in electrowetting and precision self assembly." [Tampa, Fla] : University of South Florida, 2008. http://purl.fcla.edu/usf/dc/et/SFE0002439.
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Cheyne, William Spencer. "The effect of negative intrathoracic pressure on heart-lung interaction in the presence of elevated lung volume and increased right ventricular preload and afterload." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/55262.
Full textAbstract:
While the hemodynamic effects of spontaneous respiration are normally considered minimal, large increases in negative intrathoracic pressure (ITP) are known to impair left ventricular (LV) function. Increased negative ITP is a hallmark of obstructive respiratory disease, and is often accompanied by elevations in lung volume and changes to the pulmonary vasculature, both of which have adverse effects on LV function through both series and direct ventricular interaction (DVI). While the hemodynamic effects of these stressors in isolation are generally well established, the interaction of these mechanisms, and their summative effect on LV function, has not been investigated.
This study examined the hemodynamic effects of increased negative ITP, dynamic lung hyperinflation (DH), increased pulmonary vascular resistance (PVR) and increased preload (VL) alone and in combination in healthy, spontaneously breathing humans using echocardiography to evaluate LV volumes and geometry. Reducing ITP on inspiration to -20 cmH₂O significantly decreased LV SV by 7% (p<0.001), due to a reduced LV end-diastolic volume (LVEDV). DVI was implicated in this reduction, as evidenced by a significant increase in the radius of septal curvature (RSC) (p=0.002), indicating leftward septal shift. DH alone also decreased LV SV by 12% (p=0.001) and, in combination with increased negative ITP, caused a greater reduction in LVEDV than either condition in isolation (p=0.001). This LV under-filling was exacerbated by increased PVR, resulting in a 14% decrease in LV SV (p=0.001), which appears to be partially mediated by DVI, as indicated by significant increases in RSC (p=0.001). Under these conditions, when preload was increased by acute VL, we observed a paradoxical further decrease in LVEDV (-16%, p<0.001) and thus LV SV (-21%, p<0.001). Together with the observed increase in RSC (p=0.001), this is strong evidence for the role of DVI in impairing LV filling under these conditions.
In conclusion, large increases in lung volume have a considerable deleterious effect on cardiac function. Moreover, at high volumes, DH may play a larger role than the associated increases in negative ITP in influencing hemodynamics. These findings have important implications for better understanding altered cardiopulmonary interaction in obstructive respiratory disease.Graduate Studies, College of (Okanagan)
Graduate
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Cyprian, Rudolf. "Aktivní řízení předpětí hlavy obráběcího stroje." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2013. http://www.nusl.cz/ntk/nusl-230921.
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This Master’s Thesis introducing active preload control of machine tool head supported by a company TOSHULIN, a.s. It presents a way of creating models from rigid body models to flexible bodies and finally to multi-body systems with control loop. The goal of this thesis is create active preload control using a piezo-stack system for simplified linear model of ma-chine tool head.
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Salam, Jamal Mohamad. "Application of cyclic uniaxial compression testing to investigate the effects of preload and other factors on the structural properties of concrete affected by alkali silica reaction." Thesis, Queen Mary, University of London, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261641.
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Laine, Daniel Petri. "Effect of axial preloads on confined concrete." 2004. http://link.library.utoronto.ca/eir/EIRdetail.cfm?Resources__ID=94923&T=F.
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"The Effects of Meal Preloads on Glycemia, Insulinemia and Satiety." Master's thesis, 2012. http://hdl.handle.net/2286/R.I.14935.
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abstract: Background: Obesity is considered one of the most serious public health issues worldwide. Small, feasible lifestyle changes are necessary to obtain and maintain weight loss. Clinical evidence is inconclusive about whether meal preloading is an example of a small change that could potentially increase the likelihood of weight loss and weight maintenance. Objective: The aim of this study is to determine if consuming 23 grams of peanuts, as a meal preload, before a carbohydrate-rich meal will lower post prandial glycemia and insulinemia and increase satiety in the 2 hour period after a carbohydrate-rich meal. Design: 15 healthy, non-diabetic adults without any known peanut or tree nut allergies were recruited from a campus community. A randomized, 3x3 block crossover design was used. The day prior to testing participants refrained from vigorous activity and consumed a standard dinner meal followed by a 10 hour fast. Participants reported to the test site in the fasted state to complete one of three treatment meals: control (CON), peanut (NUT), or grain bar (BAR) followed one hour later by a carbohydrate-rich meal. Satiety, glucose and insulin were measured at different time points throughout the visit. Each participant had a one-week washout period between visits. Results: Glucose curves varied between treatments (p=.023). Blood glucose was significantly higher one hour after ingestion of the grain bar compared to the peanut and control treatments (p<.001). At 30 minutes after the meal, the control glucose was significantly higher than for the peanut or grain bar (p=.048). Insulin did vary significantly between treatments (p<.001). The insulin change one hour after grain bar consumption was significantly higher than after the peanut or control at the same time point (p<.001). The change in insulin one hour after peanut consumption was significantly higher than for the control treatment (p=.002). Overall satiety, expressed as the 180 minute AUC, differed significantly between treatments (p=.001). One hour after preload consumption, peanut and bar consumption was associated with greater satiety than the water control (p<.001). At 30 minutes post-meal, the grain bar was associated with greater satiety versus the water control (p=.049). The bar was also associated with greater satiety versus peanut and control at 60 and 90 minutes post-meal (p=.003 and .034, respectively). At 120 minutes post-meal, the final satiety measurement, the bar was still associated with greater satiety than the peanut preload (p=.023). Total energy intake, including test meal, on treatment days did not differ significantly between treatment (p=.233). Conclusions: Overall satiety, blood glucose and blood insulin levels differed at different time points depending on treatment. Both meal preloads increased overall satiety. However, grain bar ingestion resulted in sustained satiety, greater than the peanut preload. Grain bar ingestion resulted in an immediate glycemic and insulinemic response. However, the response was not sustained after the test meal was ingested. The results of this study suggest that a low-energy, carbohydrate-rich meal preload may have a positive impact on weight maintenance and weight loss by initiating a sustained increase in overall satiety. More research is needed to confirm these findings.Dissertation/Thesis
M.S. Nutrition 2012
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Watson, Linda Ernestine. "A novel nutritional approach to the management of type 2 diabetes: effects of nutritional preloads on postprandial blood glucose and gastric emptying in type 2 diabetes mellitus." Thesis, 2018. http://hdl.handle.net/2440/115410.
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This thesis focuses on the impact of dietary protein and fibre preloads on postprandial blood glucose and gastric emptying in type 2 diabetes mellitus.
Key themes relate to:
1) The longitudinal evaluation of gastric emptying in type 2 diabetes
2) The evaluation of gastric emptying as measured by means of a ¹³C-octanoic acid breath test in older adults with type 2 diabetes
3) The evaluation of the acute effects of low dose ‘preloads’ of whey and guar, given alone or in combination before a meal, on postprandial glycaemia, GLP-1, insulin, and gastric emptying
4) The evaluation of the effects of 12 weeks’ treatment with a whey/guar preload on gastric emptying, postprandial glycaemia, and glycated haemoglobin (HbA1c), in type 2 diabetes.
It is well established that the rate of gastric emptying plays a major role in determining the early postprandial glycaemic response, and that interventions that slow gastric emptying can reduce postprandial glycaemic excursions in type 2 diabetes. Gastric emptying is regulated by inhibitory feedback arising from the interaction of nutrients with the small intestine, mediated in part by the secretion of gut hormones. Gastric emptying is often disordered in people with type 2 diabetes; the emptying of solids and/or nutrient liquids is abnormally delayed in up to 30-50% with patients with longstanding type 2 diabetes, while gastric emptying may be accelerated in ‘early’ type 2 diabetes, although this has not been a consistent observation. Dietary strategies that slow gastric emptying, such as the use of ‘preloads’ (small quantities of macronutrient given in advance of the main meal), represent an appealing approach to reducing postprandial glycaemia. However, if modulating the rate of gastric emptying is to be developed further as a therapeutic strategy for postprandial glycaemic control, additional information is required about the natural history of gastric emptying in these patients. In the study reported in Chapter 2, I explored how the rate of gastric emptying changed over an interval of some 14 years in a group of patients with type 2 diabetes.
The intra-individual variation of gastric emptying in health is modest, so that emptying is highly reproducible, although there is substantial inter-individual variation. Studies from tertiary referral centres involving patients with longstanding (typically 8-12 years) type 2 diabetes, relatively poor glycaemic control (HbA1c >8.5%), and a high prevalence of microvascular complications, indicate that 30-50% have abnormally delayed emptying of solids and/or nutrient liquids, whether studied by scintigraphy or stable isotope breath test, while a few have rapid emptying. Conversely, patients with ‘early’ type 2 diabetes (< 2 years) and/or an absence of autonomic neuropathy have been reported to have abnormally rapid emptying for solids and/or liquids, although this has not been observed in all series. Gastric emptying has a profound impact on control of glycaemia in type 2 diabetes, such that more rapid emptying of a glucose drink is associated with a higher blood glucose response. Scintigraphy is the gold standard technique used to quantify gastric emptying, but requires exposure of patients to ionising radiation and access to specialised equipment and personnel to undertake the assessment. An alternative method of measuring gastric emptying is by means of a stable isotope breath test, which can be used in an office-based setting, and has been validated against scintigraphy in both health and type 2 diabetes. There is also conflicting information regarding the effect of ageing on gastric emptying, with reports that emptying is either slowed, accelerated, or unchanged when compared to the young. When assessing the effects of type 2 diabetes on gastric emptying, it is important to select an age-matched healthy control group, particularly since type 2 diabetes cohorts tend to be older than the general population. In the study reported in Chapter 3, I evaluated the rate of gastric emptying using a ¹³C-octanoic acid breath test in community-based patients with type 2 diabetes, and compared this with age-matched healthy controls.
Nutritional strategies to reduce postprandial glycaemia are attractive, and represent the greatest opportunity for optimising glycaemic control at an affordable cost as the healthcare demands of society escalate. Both the rate of gastric emptying, and the actions of the incretin hormones, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), are major determinants of postprandial glycaemic excursions. In type 2 diabetes, the insulinotropic effect of GIP is diminished, whereas GLP-1 retains its capacity to stimulate insulin secretion, and also slows gastric emptying and suppresses glucagon secretion and energy intake. Stimulation of GLP-1 secretion is appealing in the management of type 2 diabetes. Whey protein, a by-product of the cheese-making process, can reduce postprandial glycaemia when taken with, or before, a meal, through interrelated mechanisms including enhancement of insulin and gut hormone secretion, slowing of gastric emptying, and reductions in appetite and energy consumption. Guar gum is a viscous soluble fibre, and when given with a meal, can decrease postprandial glycaemic excursions by slowing gastric emptying and inhibiting small intestinal absorption of glucose, associated with reduced, rather than increased plasma insulin levels, as well as attenuation of plasma GLP-1. Accordingly, combining both guar gum and whey protein in a dietary supplement may be advantageous. However, the relative contribution of whey and guar to glucose-lowering and slowing of gastric emptying when used alone, and whether their actions are additive or synergistic when given together, are uncertain. In the study reported in Chapter 4, I evaluated the comparative acute effects of whey protein and guar gum preloads, either alone or in combination, on postprandial glycaemia, GLP-1, insulin, and gastric emptying in type 2 diabetes.
For the majority of people with type 2 diabetes who have relatively good overall glycaemic control (HbA1c ≤ 7.9%), postprandial glycaemia predominates over fasting blood glucose in contributing to HbA1c. Indeed, a ‘target’ HbA1c of ≤ 7% is difficult to achieve without minimizing postprandial glycaemic excursions. We have previously established that acute administration of high doses of whey protein preloads (50g) slows gastric emptying of the subsequent meal. An acute study in subjects with type 2 or pre-diabetes reported a preload incorporating low-dose whey (17g) together with guar (5g) slows gastric emptying and reduces postprandial glycaemia. However, it remains to be determined if a ‘pre-load’ strategy to reduce glycaemia are sustained with long-term use. Similarly, while a pre-load slows gastric emptying acutely, it is unknown whether this effect is sustained with daily pre-load administration. Moreover, whey supplements incur a substantial energy burden, so it is also important to determine if patients compensate by adjusting their overall intake with long-term use. In the study reported in Chapter 5, I evaluated the effects of a twice daily low dose whey/guar preload taken 15 minutes before breakfast and dinner over 12 weeks, in 79 patients with type 2 diabetes and relatively good glycaemic control treated with diet or metformin only, on HbA1c, gastric emptying, postprandial glycaemia and body weight and composition, in a single-blind, randomized, placebo-controlled trial.Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, Adelaide Medical School, 2018
41
Patel, Vipulkumar Ishvarbhai. "Nonlinear inelastic analysis of concrete-filled steel tubular slender beam-columns." Thesis, 2013. https://vuir.vu.edu.au/22015/.
Full textAbstract:
High strength thin-walled concrete-filled steel tubular (CFST) slender beam-columns
may undergo local and global buckling when subjected to biaxial loads, preloads or
cyclic loading. The local buckling effects of steel tube walls under stress gradients have
not been considered in existing numerical models for CFST slender beam-columns. This
thesis presents a systematic development of new numerical models for the nonlinear
inelastic analysis of thin-walled rectangular and circular CFST slender beam-columns
incorporating the effects of local buckling, concrete confinement, geometric
imperfections, preloads, high strength materials, second order and cyclic behavior.
In the proposed numerical models, the inelastic behavior of column cross-sections is
simulated using the accurate fiber element method. Accurate constitutive laws for
confined concrete are implemented in the models. The effects of progressive local
buckling are taken into account in the models by using effective width formulas. Axial
load-moment-curvature relationships computed from the fiber analysis of sections are
used in the column stability analysis to determine equilibrium states. Deflections caused
by preloads on the steel tubes arising from the construction of upper floors are included
in the analysis of CFST slender columns. Efficient computational algorithms based on
the Müller’s method are developed to obtain nonlinear solutions. Analysis procedures
are proposed for predicting load-deflection and axial load-moment interaction curves for
CFST slender columns under axial load and uniaxial bending, biaxial loads, preloads or
axial load and cyclic lateral loading. The numerical models developed are verified by comparisons of computer solutions
with existing experimental results and then utilized to undertake extensive parametric
studies on the fundamental behavior of CFST slender columns covering a wide range of
parameters. The numerical models are shown to be efficient computer simulation tools
for designing safe and economical thin-walled CFST slender beam-columns with any
steel and concrete strength grades. The thesis presents benchmark numerical results on
the behavior of high strength thin-walled CFST slender beam-columns accounting for
progressive local buckling effects. These results provide a better understanding of the
fundamental behavior of CFST columns and are valuable to structural designers and
composite code writers.
42
Esfahbod, Behdad. "Preload: An adaptive prefetching Daemon." 2006. http://link.library.utoronto.ca/eir/EIRdetail.cfm?Resources__ID=450330&T=F.
Full text
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Luo, Kai Hong, and 羅凱鴻. "Detection of Ball Screw Preload." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/86621045755210910448.
Full textAbstract:
碩士國立中正大學
機械工程學系暨研究所
99
This study aims to establish the relation between the ball screw preload and the ball pass frequency; and then develop an intelligent on-line system for detecting whether the ball screw preload still takes effect. The ball screw vibration spectra blurred by the unsteady ball passing in the recycling tube is improved using the Vold-Kalman -filter order tracking(VKFOT) technique. Two methods that quantify the preload in a ball screw are proposed. The first is to determine the ball passing order ni a ball screw vibration spectra for ball screws with varying preload. The second is to quantify the participation in percentage of each vibration order during the period that the nut is traveling on the ball screw. And these two measures can be represented in a single tine-order plot. With these two measures, detecting the preload in a ball screw automatically and intelligently becomes feasible. Results from experiments show that the ball passing order is 11.5 for a ball screw with a preload of 1.5%; and 11.1 for a ball screw with a preload of 4% approximately. That is, the ball passing order of a ball screw with large preload is smaller than that with a light preload. With the proposed technique, the diagnostic system can detect whether the preload of a ball screw is still in effect with accuracy higher than 80%.
44
Ibrahim, Safwat A. H. "Preloaded frame structures." Thesis, 1987. http://spectrum.library.concordia.ca/3975/1/ML35555.pdf.
Full text
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Tuan, Yu-Chiang, and 段玉強. "Preload-Controlled and Friction Compensation with Ballscrew." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/42505851193249393044.
Full textAbstract:
碩士國立中正大學
機械工程學系
85
AbstractHigh speed precise positioning is very important technology in industry. To improve accuracy and to increase products, like semiconductor and MEMs technology, high speed precise positioning is used. So the goal of this research is high speed precise positioning.There is a backlash program in ballscrew, so if we want to eliminate backlash and increase stiffness, we get preload to ballscrew. But the preload is high so that the friction is increase. So we design a preload tuning machine to change preload of ballscrew and fine tuning of positioning.The coarse positioning using ballscrew , the controller is used the traditional PID controller and IP control, and the position accuracy is up to 1 mm, and change to piezoactuator to fine tune and the position accuracy is up to 0.1mm.
46
Li, Chi-Rung, and 李起榮. "Development of Ball Screw Preload Detection Technology." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/55987538877378499067.
Full textAbstract:
碩士國立中正大學
機械工程學系暨研究所
101
There are two purposes of this research. Firstly, a technique based on the method of Angular Velocity Vold-Kalman Filtering Order Tracking (AV VKF-OT) for monitoring the occurrence of preload loss of a ball screw in a feed drive system is proposed. Secondly, a method to measuring the ball screw friction torque induced by the preload is introduced. In detecting the preload loss in a ball screw feed drive system, it is worthy of noting that both the ball pass order and the vibration amplitude change corresponding to the major ball pass order along the screw shaft are monitored. It shows that the vibration amplitude of the ball screw without preload is not only higher than those with preloads but also varies strongly when the nut is traveling along the ball screw shaft. It also shows that the vibration amplitude variation along the shaft without preload is much larger than those with preload. Taking not only the change of BPO but also the vibration amplitude variation as well into account, experimental results show that the accuracy in detecting the occurrence of preload loss can be improved up to 93% approximately. On the other hand, the ball pass order changes little as the temperature rises from 25.5℃to 36.3℃. It concludes that the preload appears to be unaffected in this temperature range. For measuring the ball screw friction torque induced by the preload, a platform that consists of loadcells and accelerometers is introduced. The torque measured using this platform does not include the friction torque from bearings and thus it reflects the torque induced only by the preload on the ball screw.. Experiment results show that the torque induced by ball screw preload is 71% to 80% of that measured using the traditional torque sensor. That is, for a ball screw feed drive system, the ball screw preload costs 71-80% of the torque from motor, whereas the bearing accounts for the remaining 20-30%.
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Huang, Hung-Chun, and 黃弘竣. "Technology development of ball screw preload detection technology." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/56840817465277235150.
Full textAbstract:
碩士國立中正大學
機械工程學系暨研究所
100
A technique based on the method of Angular Velocity Vold-Kalman Filtering Order Tracking (AV VKF-OT) for monitoring the occurrence of preload loss of a ball screw in a feed drive system is proposed. Experimental results show that the friction caused by the preload tends to reduce the ball pass frequency. Therefore, the proposed technique focuses on measuring the change of the ball pass frequency instead of the ball screw vibration when the nut is traveling on the ball screw shaft. Results from both simulations and experiments show that the AV VKF-OT can successfully detect the small order change in an order spectrum of a preloaded ball screw and and provides a much better performance as compared to the traditional order tracking in terms of order resolution and order accuracy. Tests also conducted in several ball screw drive systems with varying preloads ranging from 1.5% to 7% provided by the ball screw manufacturer to access the performance of the proposed method. It concludes that the proposed technique so far has an accuracy of 70% approximately in determining whether the preload of ball screw exists. Simply attaching an accelerometer near the return tube, the proposed method provides an economic and reliable way in detecting the preload loss and is easy to be integrated in a prognosis system for ball screw.
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Chian, Shin-Yan, and 錢信諺. "Diagnosis of Ball Screw Preload Loss by Acoustic signals." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/98581380192628287141.
Full textAbstract:
碩士國立彰化師範大學
機電工程學系
99
The ball screws of mechanical transmission elements are used as the fast moving components in recent years. There are some issues when the inner elements of ball screw operate in high speed: (1) impact force of internal ball rolling and sliding on the raceway and returning pipe (2) friction and heat due to poor lubrication (3) wear effect when ball screw operates for a longtime and renders the preload loss problem. In this thesis, the microphone was used to detect and distinguish the sounds from the background noise, motor, coupling, ball screw and nut when the feed system in operation. Both of accelerometer and microphone validate the data acquisition signals for diagnosis. Hilbert Huang transform (HHT), Short-Term Fourier Transform (STFT) and Marginal Spectrum are used to analyze the characteristics of ball screw stiffness. The experiment results show (1) optimization method for finding microphone position is provided. (2) The dominated frequency of the 2%, 4% and 6% preload ball screw is about 320Hz, 450 Hz and 850 Hz through sound and vibration signals (3) Different preload ball screws by using the HHT and STFT analysis can be realized through the acoustic signals. This diagnosis method realizes the purposes of prognostic effectiveness on knowing the preload loss and utilizing convenience.
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Sun, Ming-Hua, and 孫明華. "Experimental Investigation on Preload for Wear of Ball Screw." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/37872409121680029546.
Full textAbstract:
碩士國立中興大學
機械工程學系
90
Ball screw is often used in the precise positioning which is the key technique of processing and mechanism motion. The friction force can be highly reduced by using the ball screw, because it transmits the power through rolling contact between the ball and nut, and between the ball and screw. But after operating for a period, wear will happen on the screw, ball, and nut, which will generate the clearance and cause the effect of preload disappear gradually. In this paper, the wear conditions of ball screw under different preloads and external loads have been discussed. The main factors of causing wear are the applied force on the ball and the rolling distance of the ball. Wear equations obtained from other researches have been studied in this paper to understand the relationships of the wear parameters. An analysis of the ball rolling the surface also have been done to understand the applied force on the ball under preload and external load. In order to understand the wear conditions of the ball screw under operation, a testing platform has been set up. By adjusting the preload and external load on the ball screw, different applied force conditions on the ball can be obtained. The wear amount was measured under different rolling distance to study the relationships between the wear conditions and the preload and external load. Also the factor of assembly and disassembly during the testing was analyzed in this research. The purpose of this research is trying to provide the information of wear conditions of ball screw under different loading conditions which can help the machine designers to understand more about the characteristic of the ball screw.
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Huang, Jing-ting, and 黃靖婷. "Gel preloaded microchips for DNA analysis." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/38493746211245001543.
Full textAbstract:
碩士國立成功大學
化學工程學系碩博士班
95
In this study, we proposed and demonstrated fabrication of the gel preloaded microchips for DNA analysis. The photocurable polyacrylamide gel solution was first pre-loaded inside the open microchannels, followed by UV curing and drying. The microchannels with dried gel were covered with a PMMA film and sealed via vacuum and heating. The results showed that distribution of the dried gel in microchannels was uniform, and the apparent swelling ratio of the gel in the microwell was larger than its free swelling ratio. Furthermore, there is no race tracking observed in the microchannel and the pore size distribution inside the microchannel is similar to that obtained by using common fabrication technique. DNA separation was also reasonably well. This fabrication technique yields excellent packaging of the polymer based DNA separation microchips ready for use with fast loading capability and increased portability.