• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 71
  • 20
  • 20
  • 19
  • 4
  • 3
  • 2
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 166
  • 166
  • 36
  • 23
  • 22
  • 20
  • 19
  • 17
  • 16
  • 15
  • 11
  • 11
  • 10
  • 10
  • 9
  • 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.
11

Dynamické modely zemětřesného zdroje a seismicita / Dynamic models of earthquake source and modeling of seismicity

Kostka, Filip January 2015 (has links)
In the present thesis we perform modeling of earthquake source using laboratory derive rate-and-state laws of friction. We have developed a code in Fortran 90 for modeling a planar, two-dimensional fault with general dip and heterogeneous distribution of frictional parameters. We use a quasi-dynamic approximation and assume that the fault is submnerged in an infinite elastic half-space. We performed an extensive number of numerical experiments to study the effect of fricitonal parameters distribution on the spatio-temporal complexity of slip on fault. We also study the effect of the so called Coulomb stress changed on clock advance and clock delay of events. For this purpose we use both a homogeneous model and a model of random frictional parameteres which exhibits the Gutenberg-Richter frequency- size dependence in the range of two magnitudes. We find that the effect of Couloumb stress change is nontrivial and depends on factors such as the domain of stress load and the slip velocity on it. Powered by TCPDF (www.tcpdf.org)
12

An Impact Model for the Industrial Cam-follower System: Simulation and Experiment

Paradorn, Vasin 28 November 2007 (has links)
"Automatic assembly machines have many cam-driven linkages that provide motion to tooling. Newer machines are typically designed to operate at higher speeds and may need to handle products with small and delicate features that must be assembled precisely every time. In order to design a good tooling mechanism linkage, the dynamic behavior of the components must be considered; this includes both the gross kinematic motion and self-induced vibration motion. Current simulations of cam-follower system dynamics correlate poorly to the actual dynamic behavior because they ignore two events common in these machines: impact and over-travel. A new dynamic model was developed with these events. From this model, an insight into proper design of systems with deliberate impact was developed through computer modeling. To attain more precise representations of these automatic assembly machines, a simplified industrial cam-follower system model was constructed in SolidWorks CAD software. A two-mass, single-degree-of-freedom dynamic model was created in Simulink, a dynamic modeling tool, and validated by comparing to the model results from the cam design program, DYNACAM. After the model was validated, a controlled impact and over-travel mechanism was designed, manufactured, and assembled to a simplified industrial cam-follower system, the Cam Dynamic Test Machine (CDTM). Then, a new three-mass, two-degree-of-freedom dynamic model was created. Once the model was simulated, it was found that the magnitude and the frequency of the vibration, in acceleration comparison, of the dynamic model matched with the experimental results fairly well. The two maximum underestimation errors, which occurred where the two bodies collided, were found to be 119 m/s2 or 45% and 41 m/s2 or 30%. With the exception of these two impacts, the simulated results predicted the output with reasonable accuracy. At the same time, the maximum simulated impact force overestimated the maximum experimental impact force by 2 lbf or 1.3%. By using this three-mass, two-DOF impact model, machine design engineers will be able to simulate and predict the behavior of the assembly machines prior to manufacturing. If the results found through the model are determined to be unsatisfactory, modifications to the design can be made and the simulation rerun until an acceptable design is obtained."
13

Dynamic Modelling and Fault Feature Analysis of Gear Tooth Pitting and Spalling

Luo, Yang 21 February 2019 (has links)
Fault feature analysis of gear tooth spall plays a vital role in gear fault diagnosis. Knowing the characteristic of fault features and their evolution as a gear tooth fault progresses is key to fault severity assessment. This thesis provides a comprehensive (both theoretical and experimental) analysis of the fault vibration features of a gear transmission with progressive localized gear tooth pitting and spalling. A dynamic model of a one-stage spur gear transmission is proposed to analyze the vibration behavior of a gear transmission with tooth fault. The proposed dynamic model considers the effects of Time Varying Mesh Stiffness (TVMS), tooth surface roughness changes and geometric deviations due to pitting and spalling, and also incorporates a time-varying load sharing ratio, as well as dynamic tooth contact friction forces, friction moments and dynamic mesh damping ratios. The gear dynamical model is validated by comparison with responses obtained from an experimental test rig under different load and fault conditions. In addition, several methods are proposed for the evaluation of the TVMS of a gear pair with tooth spall(s) with curved bottom and irregular shapes, which fills the current research gap on modelling tooth spalls with irregular shapes and randomly distribution conditions. Experiments are conducted and the fault vibration features and their evolution as the tooth fault progresses are analyzed. Based on feature analysis, a new health indicator is proposed to detect progressive localized tooth spall.
14

Determining the change in PCR efficiency with cycle number and characterizing the effect of serial dilutions on the DNA signal

Hu, Cheng-Tsung 08 April 2016 (has links)
The ability to obtain deoxyribonucleic acid (DNA) profiles is generally considered a powerful tool when examining evidence associated with a crime scene. However, variability in peak heights associated with short tandem repeats (STR) signal complicates DNA interpretation; particularly, low-template complex mixtures, which are regularly encountered during evidentiary analysis. In order to elucidate the sources that cause peak height variability a dynamic model, which simulates; 1) the serial dilution process; 2) polymerase chain reaction (PCR); and 3) capillary electrophoresis (CE) was built and used to generate simulated DNA evidentiary profiles. In order to develop the dynamic model, PCR efficiencies were characterized. This was accomplished using empirical quantitative polymerase chain reaction (qPCR) data. Specifically, the ratios of fluorescent readings of two consecutive cycles were evaluated. It was observed that the efficiency fluctuated at early cycles; stabilized during the middle cycles; and plateaued during later cycles. The relationship between the change in efficiency and the concentration of amplicons was modeled as an exponential function. Subsequently, this exponential relationship was incorporated into the dynamic model as a part of the PCR module. Using the dynamic laboratory model, the effect of serially diluting a concentrated DNA extract to a low-template concentration was assessed in an effort to determine whether serially diluted samples are a good representation of evidence samples which contain low copy number of cells. To accomplish this, peak height variances and the frequency of drop-out between serially and non-serially diluted samples were compared. The results showed that diluting the sample had a substantial influence on allelic drop-out. However, the distributions of the observed peak heights did not consistently change; though, changes in peak height distributions became more pronounced with samples at lower targets. The peak height equivalency (PHE) was also used to aid in the determination of the effect of serial dilutions on reproducibility. There was not a major change in PHE between serially and non-serially diluted samples.
15

Management of Reference Frames in Simulation and its Applications

Kalaver, Satchidanand Anil 04 April 2006 (has links)
The choice of reference frames used in simulations is typically fixed in dynamic models based on modeling decisions made early during their development, restricting model fidelity, numerical accuracy and integration into large-scale simulations. Individual simulation components typically need to model the transformations between multiple reference frames in order to interact with other components, resulting in additional development effort, time and cost. This dissertation describes the methods for defining and managing different reference frames in a simulation, thereby creating a shared simulation environment that can provide reference frame transformations, comprising of kinematics and rotations, to all simulation components through a Reference Frame Manager. Simulation components can use this Reference Frame Manager to handle all kinematics and rotations when interacting with components using different reference frames, improving the interoperability of simulation components, especially in parallel and distributed simulation, while reducing their development time, effort and cost. The Reference Frame Manager also facilitates the development of Generic Dynamic Models that encapsulate the core service of dynamic model, enabling the rapid development of dynamic models that can be reused and reconfigured for different simulation scenarios and requirements. The Reference Frame Manager can also be used to introduce Intermediate Frames that bound the magnitudes of vehicle states, reducing roundoff error and improving numerical accuracy.
16

Integration of Long Baseline Positioning System And Vehicle Dynamic Model

Chiou, Ji-Wen 04 August 2011 (has links)
Precise positioning is crucial for the success of navigation of underwater vehicles. At present, different instruments and methods are available for underwater positioning but few of them are reliable for three-dimensional position sensing of underwater vehicles. Long baseline (LBL) positioning is the standard method for three-dimensional underwater navigation. However, the accuracy of LBL positioning suffers from its own drawback of relatively low update rates. To improve the accuracy in positioning an underwater vehicle, integration of additional sensing measurements in a LBL navigation system is necessary. In this study, numerical simulation and experiment are conducted to investigate the effect of interrogate rate on the accuracy of LBL positioning. Numerical and experimental results show that the longer the interrogate rate, the greater the LBL positioning error. In addition, no reply from a transponder to transceiver interrogation is another major error source in LBL positioning. The experimental result also shows that the accuracy of LBL positioning can be significantly improved by the integration of velocity sensing. Therefore, based on Kalman filter, this study integrates a LBL system with vehicle dynamic model to improve the accuracy of positioning an underwater vehicle. For conducting the positioning experiments, a remotely operated vehicle (ROV) with dedicated Graphic User Interface (GUI) is designed, constructed, and tested. To have a precise motion simulation of ROV, a nonlinear dynamic model of ROV with six degrees of freedom (DOF) is used and its hydrodynamic parameters are identified. Finally, the positioning experiment is run by maneuvering the ROV to move along an ¡§S¡¨ trajectory, and Kalman filter is adopted to propagate the error covariance, to update the measurement errors, and to correct the state equation when the measurements of range, depth, and thruster command are available. The experimental result demonstrates the effectiveness of the integrated LBL system with the ROV dynamic model on the improvement of accuracy of positioning an underwater vehicle.
17

Detailed Measurements Of Dynamic Stability Derivatives Under Roll Oscillations For Standard Dynamic Model In Ankara Wind Tunnel

Nacakli, Yavuz 01 January 2003 (has links) (PDF)
The subject of this experimental investigation is to measure the dynamic stability derivatives in roll plane for an oscillating combat aircraft model by using forced oscillation technique. In forced oscillation technique the model is forced to oscillate around the center of gravity according to a harmonic motion of small amplitude and low frequency. The aerodynamic reactions are measured by an internal balance placed inside the model. The thesis presents a brief description of the test rig and the measurement system. The theory of dynamic stability derivatives and forced oscillation technique are also explained. The data is collected and analyzed by using a data acquisition system written with under the Labview programming language. Systematic analysis of the static and dynamic tests results and effect of various parameters (angle of attack, sideslip angle, oscillation frequency and amplitude, wind velocity) on these results are presented. Comparison of the present results with previous results obtained in other test facilities is also given. Design and manufacture process of a new angle of attack mechanism is also given in this thesis.
18

Toxicokinetics and Bioaccumulation of Metals in Wood Frog Tadpoles (Lithobates sylvaticus) Exposed to Sediment Near Oil Sands Mining in Northern Alberta

Moeun, Brian 20 September 2018 (has links)
Bitumen extraction in the Athabasca oil sands in Alberta releases metals to the region. In this study, I performed an uptake-elimination experiment with wood frog tadpoles (Lithobates sylvaticus) to determine the bioaccumulation potential of metals from exposure to MacKay River sediment, an area affected by oil sands contamination, and to uncontaminated reference sediment. Wood frog tadpoles, Gosner stages 28-32, were exposed to two sediments: (1) MacKay River sediment that is enriched in petrogenic hydrocarbons from natural and anthropogenic sources; and (2) an uncontaminated reference sediment. Tadpole exposures to sediments lasted 4 days, followed by a depuration phase for an additional 4 days where tadpoles were allowed to eliminate excess metals from their bodies. The metal concentrations at various time points during the uptake and elimination phases were determined in order to define toxicokinetic parameters, such as uptake and elimination first order rate constants, accumulation by ingestion, and assimilation efficiencies for specific metals. It was determined that tadpoles exposed to the MacKay sediment had higher concentrations of Al, Co, Cu, Cr, Mg, Ni, Pb, V, and Zn throughout the uptake phase of the study compared to tadpoles exposed to reference sediment. We also observed little to no decrease in concentrations of Al, Co, Cu, Cr, Mg, Ni, Pb, V, and Zn throughout the elimination phase of the study. In addition, biota-sediment accumulation factors (BSAF) revealed that Cu, Zn, Cr, and V had among the highest bioaccumulation potential in our trials. The experiment was subsequently repeated by preventing direct contact of the tadpoles to sediment with a screen, exposing tadpoles only to metals in water. By comparing tadpole exposures to metals from ‘aqueous’ and ‘aqueous +sediment’ in separate trials, and by tracking sediment ingestion rates, I am able to show that sediment ingestion constitutes the primary source of metal bioaccumulation by tadpoles. Not only were metal concentrations higher in tadpoles that were ingesting sediment, but they also had greater metal uptake rates compared to tadpoles that were only exposed to contaminated water. It was also determined that assimilation efficiencies were higher in tadpoles exposed to reference sediment compared to ones exposed to MacKay River sediment. Using toxicokinetic parameters defined by the uptake-elimination experiment, I developed a computational model using STELLATM system dynamics software to accurately estimate first order uptake and depuration rate constants for metals in exposed aquatic animals. The model estimated metal uptake and depuration kinetics with a mean relative error of 2.25 ± 0.93 % (±SE, n=9) for the uptake study and 2.53 ± 2.61 % (±SE, n=9) for the depuration study. With increased oil-sands production anticipated, we recommend continued monitoring of contaminants from oil-sands for the purpose of understanding the potential risks they may have on northern Alberta’s ecosystems.
19

Integrative modelling of glucocorticoid induced apoptosis with a systems biology approach

Chen, Daphne Wei-chen January 2013 (has links)
Glucocorticoids (GCs) have an important role in anti-inflammation, apoptosis and immunomodulatory activity. GCs exert their effect by binding to their receptor, glucocorticoid receptor (GR), which subsequently triggers receptor dimerisation, nuclear translocation and eventually causes impact on transcriptional activity. Such regulatory mechanism is complex as it is not only controlled at the transcription level, but also at the post translational level with other contributing factors such as protein stability and cofactor recruitment. Glucocorticoids are commonly used as part of the chemotherapeutical protocols for lymphoid malignancies and have been successfully implicated in treating childhood acute lymphoblastic leukaemia (ALL). Nevertheless, resistance and side effects such as muscle atrophy and osteoporosis still occur frequently.With the advance in high-throughput technology, vast amount of data on various scales, including genomics, proteomics, and metabolomics make the molecular study of cancer more complicated. The rise of systems biology helps the scientist to address this problem with the use of computation. Although the concept and the approach may vary depending on the research fields, the ultimate goal remains the same which is to create a comprehensive understanding of biological processes and to forecast outcome.The goal of this body of work is to better understand glucocorticoid induced apoptosis in acute lymphoblastic leukaemia by adopting a systems biology approach. As the Bcl-2 family, particularly Bim is known to be a key determinant of GC-induced apoptosis, we investigated the molecular mechanism of GC induction of Bim. By adopting ordinary differential equation modelling approach, we were able to make prediction and investigate details of Bim regulation by GCs. Further to this, we carried out an integrated microarray analysis in various ALL to study GC resistance and identified crucial candidate gene c-Jun as a regulator of Bim and Erg as a determinant for GC resistance. These results allowed us to refine our models and enabled more answers to be addressed. In conclusion, our findings not only suggest potential regulatory mechanisms for determining GC sensitivity, they also aid us to find potential biomarkers for determining GC resistance. More importantly, this study represents a successful example for utilising systems biology to study the genetic complexity in cancer.
20

Parametric Studies on UAV Flying Qualities

Lesiário, Ana January 2009 (has links)
When developing an aircraft, one of several important aspects is to predict and properly design the dynamic behaviour of the aircraft. This holds for manned aircraft as well as for UAVs. The optimal dynamic behaviour for an aircraft depends on the mission or purpose: for a certain use an aircraft should be agile, other may require a more stable one. In aeronautics, the properties that describe the aircraft ecacy with respect to some task are known as ying qualities, and our goal is to study their dependence on some design parameters. As a test model we use an existing UAV. After deriving its 6-DOF dynamic model and assessing its baseline characteristics, we perform parametric studies. The strategy followed is divided in two steps: the rst consists on analyzing ying qualities sensitivity to changes in model parameters. The second step studies how specific design changes affect model parameters. Because the rst step only depends on the dynamic model form, we verify, by testing two other dierent aircrafts, that conclusions drawn from this step are valid to other congurations. Finally we show how results from parametric studies can be used to improve the UAV ying qualities regarding a certain mission, through the introduction of slight modications on baseline design.

Page generated in 0.1161 seconds