Dissertations / Theses on the topic 'Instability mechanisms'
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Valkhoff, Nienke Jeltje Marjoke. "Stabilization by competing instability mechanisms." [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 2006. http://dare.uva.nl/document/37776.
Full textAkl, Sherif Adel. "Wellbore instability mechanisms in clays." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/64569.
Full text"February 2011." Cataloged from PDF version of thesis.
Includes bibliographical references (p. 331-341).
This dissertation investigates the stability of wellbores drilled in Ko-consolidated clays using non-linear finite element method (FEM) and effective stress soil models to characterize the behavior of clay and unconsolidated shale formations. Two constitutive models are used: Modified Cam Clay (MCC; Roscoe and Burland, 1968), and MIT-E3 (Whittle and Kavvadas, 1994). These soil models are incorporated in the commercial finite element program ABAQUS TM through user material subroutines (Hashash, 1992). The wellbores are modeled by a quasi-3D finite element model to approximate the far field stresses and plane strain boundary conditions. The constitutive models are calibrated to the behavior of Resedimented Boston Blue Clay (RBBC), an analog shale material which is Ko-consolidated to stress levels ranging from 0.15MPa to 10.0 MPa. The thesis comprises three major parts. Part one analyzes the short-term wellbore instability during drilling in low permeability formations. The part focuses on the relationship between the mud pressure inside the wellbore and the undrained shear deformations within the formations. The analyses predict critical mud pressure values necessary to maintain wellbore stability at different deviation angles and stress histories. The MIT-E3 model predicted higher deformations at reference mud pressure and estimated higher values of mud pressures than the underbalanced limit to prevent failure in highly deviated wellbores in NC clays. The second part validates the numerical analyses by comparing model predictions to results of an extensive program of model borehole tests. The lab experiments are performed on high pressure Thick- Walled Cylinder (TWC devices) using RBBC as analog testing material (Abdulhadi, 2009). The MIT-E3 predictions demonstrated a very good match with results from the experiments. The results from the analyses illustrated the effect of the device boundary conditions on specimen behavior and validated approximate analytical methods for interpreting TWC results. Part three studies the effects of consolidation on long-term wellbore stability. Non-linear coupled consolidation analyses are performed to simulate the post-drilling, time-dependent deformations and pore pressures around the wellbore. The analyses consider two different boundary conditions on seepage at the cavity. The analyses show that consolidation generates extensive volumetric strains around the wellbore and cavity deformations can aggravate stability conditions in highly deviated wellbores.
by Sherif Adel Akl.
Ph.D.
Perkins, Adam Christopher. "Mechanisms of instability in Rayleigh-Bénard convection." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42768.
Full textThirthagiri, Eswary. "Mechanisms of genomic instability in oral cancer." Thesis, University of Bristol, 2005. http://hdl.handle.net/1983/dc1b9061-be5b-4839-a266-de82fd1da5cf.
Full textHackett, Jennifer. "Telomere dysfunction and mechanisms of genomic instability." Available to US Hopkins community, 2003. http://wwwlib.umi.com/dissertations/dlnow/3080673.
Full textChan, Kara Y. "MECHANISMS OF TRINUCLEOTIDE REPEAT INSTABILITY DURING DNA SYNTHESIS." UKnowledge, 2019. https://uknowledge.uky.edu/toxicology_etds/29.
Full textLieuwen, Tim C. "Investigation of combustion instability mechanisms in premixed gas turbines." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/20300.
Full textOzols, Agris. "Low-dose studies of genomic instability-mechanisms and targets." Thesis, Queen Mary, University of London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271260.
Full textLee, A. J. X. "An investigation of chromosomal instability survival mechanisms in cancer." Thesis, University College London (University of London), 2012. http://discovery.ucl.ac.uk/1344056/.
Full textBarsoum, Nader N. "Analysis and computation of instability mechanisms in rotating electrical machinery." Thesis, University of Newcastle Upon Tyne, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328149.
Full textZhu, Ting 1971. "Atomistic characterization of stress-driven configurational instability and its activation mechanisms." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/17954.
Full textIncludes bibliographical references (p. 145-156).
Cleavage decohesion and shear dislocation nucleation are two basic modes of localized deformation in crystal lattices, which normally result from instability of the atomic configuration driven by mechanical forces. The critical state of instability and its thermal activation mechanisms can be quantitatively determined by analyzing the energetics of the lattice system. In this thesis, the unit processes of configurational instability of crystal lattices under various non-uniform structural and/or chemical environments are characterized by systematically probing the atomistic potential energy landscape of each system using the state of the art configurational space sampling schemes. The problems studied are homogeneous dislocation nucleation in a perfect crystal by nanoindentation, dislocation emission and cleavage decohesion at atomically sharp crack tips, and chemically-enhanced bond breaking in a wet silica nanorod. These processes are studied in a unified manner such that two important types of properties are determined: one is the athermal load at which the instability takes place instantaneously without the aid of thermal fluctuations, and the other is the stress-dependent activation energy used for an estimate of the kinetic rate of transition. Along the way, important aspects concerning the atomistic characterization of configurational instability are revealed. Of particular note is extending the continuum instability criterion to detect atomic defect nucleation. We demonstrate that a local instability criterion can be applied to identify dislocation nucleation in the case of indentation, considering that the relatively small strain gradient beneath the indenter will lead to a mode of long wavelength phonon instability suitable for a study
(cont.) by the local continuum approach. In addition, the chemical effect on stress-driven lattice instability is revealed via the study on reactivity of a silica nanorod with water. We identify distinct competing mechanisms of hydrolysis which are rate-controlling at different load regimes. The ensuing stress-mediated switch of rate-limiting steps of hydrolysis quantitatively demonstrates the impact of finding the detailed molecular mechanisms on a realistic estimate of the activation rate when configurational instability occurs within a chemically reactive environment. Implications regarding the analysis of chemically-assisted brittle fracture are also discussed.
by Ting Zhu.
Ph.D.
Ghaffarzadeh, K. "Carrier transport and instability mechanisms in oxide semiconductor thin film transistors." Thesis, University College London (University of London), 2011. http://discovery.ucl.ac.uk/1333220/.
Full textVENEZIANO, Lorena. "MECHANISMS OF CHROMOSOMAL INSTABILITY: RELATIONSHIP BETWEEN TUMOR SUPPRESSORS AND SAC GENES." Doctoral thesis, Università degli Studi di Palermo, 2017. http://hdl.handle.net/10447/219878.
Full textThe majority of solid tumors are characterized by aneuploidy that is believed to be the consequence of chromosomal instability (CIN). The mechanisms leading to aneuploidy and the pathway (s) that allows its tolerance are not completely understood. The Spindle Assembly Checkpoint (SAC) is a cellular surveillance mechanism that works to maintain the genomic balance in mitosis. Alterations of SAC components can induce aneuploidy but it is not clear if these defects are sufficient for tumorigenesis. In this process the genetic background of the cell plays an important role. It is known that p53 defects allow cells to quickly proliferate tolerating CIN. On the contrary, activation of wt-p53 counteracts aneuploidy. Less is known about the role of the p14ARF tumor suppressor to counteract aneuploidy. In this thesis, I investigate the relationship between some of the SAC genes that if depleted induce aneuploidy and tumor suppressor genes. First, to investigate the role of p14ARF to counteract aneuploidy it was ectopically expressed in HCT116 cells (near diploid) after MAD2 depletion a crucial component of the SAC. MAD2 posttranscriptional silencing induced high levels of aneuploid cells and aberrant mitosis that decreased when p14ARF was simultaneously expressed. In addition, p14ARF ectopic expression in MAD2-depleted cells induced apoptosis associated with increased p53 protein levels. This response was not detected in HCT116 p53KO cells suggesting that p14ARF counteracts aneuploidy activating apoptosis p53-dependent. Second, I wanted to probe the relationship between the motor protein CENP-E, which works only in the SAC signaling, and aneuploidy in human cells. To this aim I used two types of cells, human primary fibroblasts (IMR90) and near diploid cells (HCT116) lacking p14ARF, and analyzed the effects of CENP-E depletion up to four weeks. These experiments showed a different response for the two cell types. Aneuploidy was tolerated for longer times in cells lacking p14ARF expression rather than in primary cells. In addition the observations that the reduction of aneuploidy in IMR90 cells was proportional to the increase of p14ARF gene expression, and that its ectopic expression in HCT116 cells reduced aneuploidy confirm the ability of p14ARF to counteract aneuploidy. Third, to improve these results I generated HCT116 cells expressing a functional p14ARF to assess the effects of CENP-E depletion. Collectively, these results suggest that the tumor suppressor p14ARF may have an important role to contrast aneuploidy activating a p53-dependent apoptosis pathway and that it is generally involved to counterbalance aneuploidy induced by different stimuli.
Nano, Maddalena. "Identification of the molecular mechanisms generating genetic instability in polyploid cells." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066263.
Full textPolyploidy, which derives from whole-genome duplication events, is normally a potent inhibitor of cell proliferation, but plays important roles during the early steps of tumorigenesis. However, how the gain of multiple sets of chromosomes promotes the generation of unbalanced karyotypes typical of cancer cells remains to be investigated. Using a number of conditions that affect cytokinesis, I established a model system to study the consequences of polyploidy in the neural stem cells (NSCs) of Drosophila and in the wing disc (WD). Importantly, while polyploidy is rapidly eliminated from the WD, polyploid NSCs continue to proliferate. Polyploid NSCs are characterized by early-onset genetic instability and two sources account for the generation of unstable karyotypes: mitotic errors and high-levels of DNA damage. DNA damage in polyploid NSCs arises, at least in part, from the inability of polyploid cells to restrain cell cycle progression in response to incomplete DNA replication. Surprisingly, I found that multiple nuclear domains in the same polyploid NSC can exhibit asynchrony in cell cycle progression, with delayed nuclear domains experiencing acute DNA damage at mitotic entry. I show that DNA damage in polyploid NSCs can be reduced over-expressing Chk1, the main downstream kinase engaged by ATR in the DNA damage response. I also show that uncontrolled proliferation of genetically unstable polyploid NSCs holds tumorigenic potential in transplantation assays. Overall, my results show that the tolerance to polyploidy is tissue dependent and that a complex network of events contributes to the generation of unbalanced karyotypes in polyploid NSCs
Nano, Maddalena. "Identification of the molecular mechanisms generating genetic instability in polyploid cells." Electronic Thesis or Diss., Paris 6, 2017. http://www.theses.fr/2017PA066263.
Full textPolyploidy, which derives from whole-genome duplication events, is normally a potent inhibitor of cell proliferation, but plays important roles during the early steps of tumorigenesis. However, how the gain of multiple sets of chromosomes promotes the generation of unbalanced karyotypes typical of cancer cells remains to be investigated. Using a number of conditions that affect cytokinesis, I established a model system to study the consequences of polyploidy in the neural stem cells (NSCs) of Drosophila and in the wing disc (WD). Importantly, while polyploidy is rapidly eliminated from the WD, polyploid NSCs continue to proliferate. Polyploid NSCs are characterized by early-onset genetic instability and two sources account for the generation of unstable karyotypes: mitotic errors and high-levels of DNA damage. DNA damage in polyploid NSCs arises, at least in part, from the inability of polyploid cells to restrain cell cycle progression in response to incomplete DNA replication. Surprisingly, I found that multiple nuclear domains in the same polyploid NSC can exhibit asynchrony in cell cycle progression, with delayed nuclear domains experiencing acute DNA damage at mitotic entry. I show that DNA damage in polyploid NSCs can be reduced over-expressing Chk1, the main downstream kinase engaged by ATR in the DNA damage response. I also show that uncontrolled proliferation of genetically unstable polyploid NSCs holds tumorigenic potential in transplantation assays. Overall, my results show that the tolerance to polyploidy is tissue dependent and that a complex network of events contributes to the generation of unbalanced karyotypes in polyploid NSCs
Martinez, Ramon, Hans-K. Schackert, Jens Plaschke, Gustavo Baretton, Hella Appelt, and Gabriele Schackert. "Molecular Mechanisms Associated with Chromosomal and Microsatellite Instability in Sporadic Glioblastoma multiforme." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-133546.
Full textDieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich
Martinez, Ramon, Hans-K. Schackert, Jens Plaschke, Gustavo Baretton, Hella Appelt, and Gabriele Schackert. "Molecular Mechanisms Associated with Chromosomal and Microsatellite Instability in Sporadic Glioblastoma multiforme." Karger, 2004. https://tud.qucosa.de/id/qucosa%3A27514.
Full textDieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.
Nayak, Sushma [Verfasser], and Anne [Akademischer Betreuer] Régnier-Vigourox. "Mechanisms of Chromosomal Instability in Glioblastoma / Sushma Nayak ; Betreuer: Anne Régnier-Vigourox." Heidelberg : Universitätsbibliothek Heidelberg, 2016. http://d-nb.info/1180613821/34.
Full textZhang, Yu. "Mechanisms of chromosomal instability induced by unstable DNA repeats in yeast S.cerevisiae." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/52185.
Full textSpeth, Raymond L. 1981. "Fundamental studies in hydrogen-rich combustion : instability mechanisms and dynamic mode selection." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/61525.
Full textThis electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 121-127).
Hydrogen-rich alternative fuels are likely to play a significant role in future power generation systems. The emergence of the integrated gasification combined cycle (IGCC) as one of the favored technologies for incorporating carbon capture into coal-based power plants increases the need for gas turbine combustors which can operate on a range of fuels, particularly syngas, a hydrogen-rich fuel produced by coal gasification. Lean premixed combustion, the preferred high-efficiency, low-emissions operating mode in these combustors, is susceptible to strong instabilities even in ordinary fuels. Because hydrogen-rich fuels have combustion properties which depend strongly on composition, avoiding the dynamics that energize combustion instability across all operating conditions is a significant challenge. In order to explore the effect of fuel composition on combustion dynamics, a series of experiments were carried out in two optically-accessible laboratory-scale combustors: a planar backward-facing step combustor and an axisymmetric swirlstabilized combustor. Fuels consisting of carbon monoxide and hydrogen, or propane and hydrogen were tested over a range of equivalence ratios and at various inlet temperatures. Dynamic pressure and chemiluminescence measurements were taken for each case. High-speed video and stereographic particle imaging velocimetry were used to explore the dynamic interactions between the flame and the flow field of the combustor. Stable, quasi-stable, and unstable operating modes were identified in each combustor, with each mode characterized by a distinct dynamic flame shape and acoustic response which is dependent on the composition of the reactants and the inlet temperature. In both combustors, the quasi-stable and unstable modes are associated with acoustically driven flame-vortex interactions in the combustion-anchoring region. In the planar combustor, the flame is convoluted around a large wake vortex, which is periodically shed from the step. In the swirl-stabilized combustor, the flame shape is controlled by the dynamics of the inner recirculation zone formed as a result of vortex breakdown. In both cases, the unstable mode is associated with velocity oscillation amplitudes that exceed the mean flow velocity. The apparent similarity between the response curves and flame dynamics in the two combustors indicate that the intrinsic local dynamics--instead of global acoustics--govern the flame response. Analysis shows that for each combustor, the pressure response curves across a range of operating conditions can be collapsed onto a single curve by introducing an appropriate similarity parameter that captures the flame response to the vortex. Computations are performed for stretched flames in hydrogen-rich fuels and the results are used to explain the observed similarity and to define the form of the similarity parameter. This similarity parameter works equally well for both experiments across fuel compositions and different inlet conditions, demonstrating that it fundamentally embodies the reciprocity between the flow and the combustion process that drives the instability. A linear model of the combustor's acoustics shows that the onset of combustion instability at a particular frequency can be related to a time delay between the velocity and the exothermic response of the flame that is inversely proportional to the local burning velocity. This analysis captures the impact of the fuel composition and operating temperature on the mode selection through an appropriately-weighted strained flame consumption speed, further emphasizing the influence of local transport-chemistry interactions on the system response. This new result confirms the role of turbulent combustion dynamics in driving thermoacoustic instabilities.
by Raymond Levi Speth.
Ph.D.
Zong, Zhixin. "Studies on the mechanisms of solid state and solution instability of drugs." Diss., University of Iowa, 2011. https://ir.uiowa.edu/etd/2795.
Full textDere, Ruhee J. "The molecular mechanisms involved in the genetic instability of the CCTG. CAGG repeats associated with myotonic dystrophy type 2." Texas A&M University, 2005. http://hdl.handle.net/1969.1/3783.
Full textGrant, David. "Failure mechanisms and instrumentation systems for an induced slope failure project." Thesis, University of Southampton, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243134.
Full textGrant, David. "Instrumentation systems for and failure mechanisms of an induced slope failure project." Thesis, University of Southampton, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243025.
Full textModise, Thero. "Genomic Instability and Gene Dosage Obscures Clues to Virulence Mechanisms of F. tularensis species." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/72885.
Full textPh. D.
Stanger, Jonathan Jeffrey. "Charge Transfer Mechanisms in Electrospinning." Thesis, University of Canterbury. Physics and Astronomy, 2008. http://hdl.handle.net/10092/1667.
Full textDiemuodeke, Ogheneruona Endurance. "Modelling of Liquid Breakup Mechanisms in Engineering Systems." Thesis, Cranfield University, 2014. http://dspace.lib.cranfield.ac.uk/handle/1826/9289.
Full textColosio, A. "MECHANISMS MEDIATING REPLICATION FORK COLLAPSE AND PROCESSING IN CHECKPOINT DEFECTIVE CELLS." Doctoral thesis, Università degli Studi di Milano, 2014. http://hdl.handle.net/2434/234147.
Full textWebster, Gregory Daniel. "Level and Instability of Global and Domain-Specific Self-Esteem as Differential Predictors of Aggression." W&M ScholarWorks, 2001. https://scholarworks.wm.edu/etd/1539626333.
Full textGrabsch, Heike Irmgard. "Clinicopathological and molecular factors related to chromosomal instability and its underlying genetic mechanisms in gastric cancer." Thesis, University of Leeds, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.551249.
Full textCHOUDHARY, RAMVEER. "MECHANISMS CONTROLLING THE INTEGRITY OF CONVERGING FORKS DURING REPLICATION TERMINATION." Doctoral thesis, Università degli Studi di Milano, 2018. http://hdl.handle.net/2434/559540.
Full textCheng, Boqian. "The mechanisms underlying flow-induced instability of cylinder arrays in cross-flow : an investigation of system parameters." Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=28437.
Full textAn in-line square array with pitch-to-diameter ratio P/d = l.5 has been tested in both water- (with low mass ratio, $m/pd sp2$ = 6.5) and air-flow (with high mass ratio, $m/pd sp2$ = 860). The effect of fluidelastic coupling between cylinders on the critical flow velocity for fluidelastic instability was investigated via frequency detuning experiments, including an extreme case of one flexible cylinder in an otherwise rigid cylinder array. The water tunnel experimental results showed that fluidelastic coupling between cylinders in water-flow has little effect on the critical flow velocity for fluidelastic instability, whereas the wind tunnel experimental results demonstrated that fluidelastic coupling between cylinders in airflow has a significant effect on the critical flow velocity. Therefore, for the cases with low mass ratio parameter the negative fluid damping mechanism dominated the fluidelastic instability of the array; however, for cases with high mass ratio, fluidelastic instability of the array was controlled by fluid stiffness effects.
An in-line square array with P/d = l.5 was also tested in the wind tunnel, with cylinders with high and low levels of mechanical damping. The experimental results showed that fluidelastic coupling between cylinders with low mechanical damping has a more significant effect on the critical flow velocity for fluidelastic instability than with high mechanical damping in airflow (with high mass ratio, $m/pd sp2$ = 860); hence, fluid stiffness-controlled mechanism becomes more important for fluidelastic instability of the array with low mechanical damping in airflow. Next, an in-line square array with P/d = 3.0 was tested in the wind tunnel. The results showed that one flexible cylinder becomes unstable when positioned in row 2 of the array; however, it does not become unstable when positioned in rows 3 or 4. This suggests that P/d has a large effect on fluidelastic instability behaviour of in-line square arrays.
Finally, a new constrained-mode approach, with a one-cylinder-kernel, has been developed for the instability analysis of both in-line and staggered arrays. The approach was developed to reduce the computational effort when a fully flexible cylinder array has to be analyzed, in order to take into account fluidelastic coupling; between cylinders.
Smith, Michael James. "Implications of anthocyanin instability and metabolism : impact on discovery of intake biomarkers and in vitro mechanisms of action." Thesis, University of East Anglia, 2016. https://ueaeprints.uea.ac.uk/61980/.
Full textPalanca-Wessels, Maria Corinna. "In vitro analysis of cultured Barrett's esophagus cells : insights into mechanisms of genomic instability and possible therapeutic strategies /." Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/4995.
Full textPaisie, Carolyn Anne. "Definition of mechanisms of mutation generation in tissues and embryonic stem cellsof the constitutive Fhit knockout mouse." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1436542716.
Full textGogolin, Sina [Verfasser]. "MYCN-dependent and -independent mechanisms targeting drug-induced DNA damage response and chromosomal instability in neuroblastoma cells / Sina Gogolin." Hannover : Bibliothek der Tierärztlichen Hochschule Hannover, 2013. http://d-nb.info/1030142882/34.
Full textLees, Hayley Diane. "Molecular mechanisms of premature ageing in a worm model of human Werner syndrome." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:080df619-828b-4248-b03f-c4aeb31f1672.
Full textGomez, Giraldo Evelio Andres. "Observations of energy transfer mechanisms associated with internal waves." University of Western Australia. Centre for Water Research, 2007. http://theses.library.uwa.edu.au/adt-WU2007.0045.
Full textVogt, Damian. "Experimental Investigation of Three-Dimensional Mechanisms in Low-Pressure Turbine Flutter." Doctoral thesis, KTH, Energy Technology, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-205.
Full textThe continuous trend in gas turbine design towards lighter, more powerful and more reliable engines on one side and use of alternative fuels on the other side renders flutter problems as one of the paramount challenges in engine design. Flutter denotes a self-excited and self-sustained aeroelastic instability phenomenon that can lead to material fatigue and eventually damage of structure in a short period of time unless properly damped. The design for flutter safety involves the prediction of unsteady aerodynamics as well as structural dynamics that is mostly based on in-house developed numerical tools. While high confidence has been gained on the structural side unanticipated flutter occurrences during engine design, testing and operation evidence a need for enhanced validation of aerodynamic models despite the degree of sophistication attained. The continuous development of these models can only be based on the deepened understanding of underlying physical mechanisms from test data.
As a matter of fact most flutter test cases treat the turbomachine flow in two-dimensional manner indicating that the problem is solved as plane representation at a certain radius rather than representing the complex annular geometry of a real engine. Such considerations do consequently not capture effects that are due to variations in the third dimension, i.e. in radial direction. In this light the present thesis has been formulated to study three-dimensional effects during flutter in the annular environment of a low-pressure turbine blade row and to describe the importance on prediction of flutter stability. The work has been conceived as compound experimental and computational work employing a new annular sector cascade test facility. The aeroelastic response phenomenon is studied in the influence coefficient domain having one blade oscillating in various three-dimensional rigid-body modes and measuring the unsteady response on several blades and at various radial positions. On the computational side a state-of-the-art industrial numerical prediction tool has been used that allowed for two-dimensional and three-dimensional linearized unsteady Euler analyses.
The results suggest that considerable three-dimensional effects are present, which are harming prediction accuracy for flutter stability when employing a two-dimensional plane model. These effects are mainly apparent as radial gradient in unsteady response magnitude from tip to hub indicating that the sections closer to the hub experience higher aeroelastic response than their equivalent plane representatives. Other effects are due to turbomachinery-typical three-dimensional flow features such as hub endwall and tip leakage vortices, which considerably affect aeroelastic prediction accuracy. Both effects are of the same order of magnitude as effects of design parameters such as reduced frequency, flow velocity level and incidence. Although the overall behavior is captured fairly well when using two-dimensional simulations notable improvement has been demonstrated when modeling fully three-dimensional and including tip clearance.
Moritz, Benjamin [Verfasser], and Peter [Akademischer Betreuer] Becker. "Prevention and prediction of production instability of CHO-K1 cell lines by the examination of epigenetic mechanisms / Benjamin Moritz. Betreuer: Peter Becker." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2015. http://d-nb.info/107914031X/34.
Full textQuinlan, John Mathew. "Investigation of driving mechanisms of combustion instabilities in liquid rocket engines via the dynamic mode decomposition." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54343.
Full textPetit, Tom. "Compréhension et modélisation d’essais de ténacité avec pop-in : application à l’aluminium 6061-T6 et influence de l’irradiation neutronique." Thesis, Paris Sciences et Lettres (ComUE), 2018. http://www.theses.fr/2018PSLEM019/document.
Full textPop-in is a phenomenon of crack propagation instability observed during toughness tests on some materials. This phenomenon has been observed on the 6061-T6 aluminum alloy, which has been identified as an essential structural element of the core of the Jules Horowitz research reactor. This thesis was initiated to understand the origin of this phenomenon on 6061-T6 aluminum and to propose a physics-based modeling, usable for the exploitation and interpretation of toughness tests, especially in the irradiated state.The different origins identified in the literature have been experimentally tested. Different aging times (4/8/12/16h) were applied to obtain different mechanical behaviors. Tensile tests with image correlation have shown that the observed pop-ins are not due to a PLC effect. Nor do they correspond to microstructural heterogeneity; they are not linked to different fracture mechanisms, because the rupture is typically ductile, whether a pop-in is involved or not. These mechanisms and the different microstructures were compared using several techniques (SEM, EBSD, EDS, Atom Probe Tomography, tomography, synchrotron laminography and nanolaminography). Pop-ins are therefore only the result of an acceleration of the ductile fracture.In fact, they are due to an interaction between two parameters: the reduced material crack growth toughness (i.e. the low tearing modulus), and the significant compliance of the test device (i.e. the low stiffness). In order to investigate this second parameter, an innovative setup has been designed to vary the machine stiffness during toughness tests. Two analytical criteria, one based on the load-opening curve, the other on the J-integral, have been established, making it possible to reliably quantify the conditions for initiation and arrest of pop-in.To take into account the central role of hardening for ductile propagation, a new stress-controlled nucleation criterion has been introduced into a single GTN model. This makes it possible to simulate and capture by finite elements the various J-Δa toughness curves by modifying only the elastoplastic law. By adding springs in the models and with an adapted control, the pop-ins are successfully simulated, and remain exploitable with the analytical criteria.Studies on irradiated specimens carried out in hot cells have shown that the increase in pop-ins with irradiation results from the decrease in the tearing modulus, itself due to hardening. As in the non-irradiated state, pop-ins thus appear solely because of the interaction between the tearing modulus and the test device stiffness, and not because of a range of industrial development not mastered
Smart, Una Margaret. "Chaos in the Rayleigh-Taylor instability." Thesis, Queen's University Belfast, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317526.
Full textZhou, Yang. "Numerical instability investigations for thin membranes." Doctoral thesis, KTH, Strukturmekanik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-209155.
Full textQC 20170616
Skryabin, Dmitry Vladimirovich. "Modulational instability of optical solitary waves." Thesis, University of Strathclyde, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366995.
Full textTaute, Katja. "Microtubule mechanics and the implications for their assembly." Doctoral thesis, Universitätsbibliothek Leipzig, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-86861.
Full textSchneider, Alexandra Patrizia. "Aerodynamic and aeroelastic investigation of a composite fan for ultra-high-bypass-ratio aircraft engines." Electronic Thesis or Diss., Ecully, Ecole centrale de Lyon, 2024. http://www.theses.fr/2024ECDL0018.
Full textModern low-speed Ultra-High Bypass Ratio (UHBR) fans operate predominantly on the flat part of the compression characteristic, have shorter intake lengths, and employ flexible, lightweight, composite blades. These changes promote the evolution of different types of instabilities with multi-physical interactions such as convective non-synchronous vibration (NSV). To enable further technological ad-vancements, experimental benchmark data on representative geometries required. Within this con-text, the European project CATANA was initiated at Ecole Centrale de Lyon. The open-test-case fan stage ECL5 was designed, following industrial guidelines, and tested experimentally on the facility ECL-B3. This thesis presents the experimental results of the CATANA project. The experimental investiga-tion of the ECL5 reference configuration shows that all design goals have been reached. The machine is operational in a wide range and aerodynamic performance at design condition is exactly coincident with the numerical prediction. In contrast, instability mechanisms are more complex than predicted by the employed numerical methods. Through application of synchronized multi-physical instrumenta-tion, the involved complex fluid-structure interaction is resolved. The analysis of the influence of in-flow conditions and geometrical and structural system symmetry allows to identify the sensitivity of aerodynamic and structural characteristics and the behavior close to the stability limit. The investiga-tion of a second rotor configuration featuring structural mistuning highlights the importance of geo-metrical blade-to-blade variations. They cause an asymmetry of the aerodynamic field at the blade tip and suppress coherently propagating aerodynamic disturbances resulting in a delayed onset of NSV. The results presented in this thesis provide a comprehensive multi-physical characterization of the ECL5 fan stage and serve as a benchmark data set for the validation of numerical simula-tions
Chau, P. Y. Pauline. "Mechanism of genomic instability in Prelamin A based premature ageing." Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/HKUTO/record/B39557352.
Full textChau, P. Y. Pauline, and 周珮然. "Mechanism of genomic instability in Prelamin A based premature ageing." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B39557352.
Full textPitayu, Laras. "Mitochondrial Disorders Linked to mtDNA instability : From Therapy to Mechanism." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112233.
Full textThe instability of mitochondrial DNA (mtDNA) in form of mtDNA depletion (quantitative instability) or large deletion (qualitative instability) is one of the most common cause of mitochondrial diseases.. One of the genes responsible for human mtDNA stability, POLG, is exploited in this study. POLG encodes the human mitochondrial polymerase gamma. In human, POLG mutations are a major cause of mitochondrial disorders including hepatic insufficiency; Alpers syndrome, progressive external ophthalmoplegia, sensory neuropathy and ataxia. They are also associated with Parkinsonism. Currently, there is no effective and disease-specific therapy for these diseases. Based on the conservation of mitochondrial function from yeast to human, we used Saccharomyces cerevisiae and Caenorhabditis elegans as first pass filters to identify chemical compounds that suppresses mtDNA instability in cultured fibroblasts of a POLG-deficient patient. We found three potential candidates, MRS2, MRS3 and MRS4, from a chemical screening of nearly 2000 compounds in yeast. MRS3 is the most efficacious in stabilizing mtDNA in yeast, filamentous fungi, worm and patient fibroblasts. This unsuspected compound, clofilium tosylate (CLO), belongs to a class of antiarrhythmic agents for cardiovascular disease. Two other antiarrhythmic agents (FDA-approved) sharing common pharmacological properties and chemical structure with CLO also show potential benefit for POLG deficiency in C. elegans. Using a chemogenomic approach in yeast, we also discovered that a mitochondrial fission actor Fis1 is implicated in the mechanism of action of CLO. Fis1 is important for cellular viability in a slightly toxic concentration of CLO and is required for the mtDNA stabilizing potency of CLO. Our findings provide evidence of the first mtDNA-stabilizing compound that may be an effective pharmacological alternative for the treatment of POLG-related diseases and uncover a new connection between the mitochondrial fission process and mtDNA replication
Ketidakstabilan DNA mitokondria (mtDNA) dalam bentuk pengurangan kopi mtDNA di dalam sel (ketidakstabilan kuantitatif), atau pun dalam bentuk delesi pada sekuens mtDNA (ketidakstabilan kualitatif) merupakan salah satu penyebab penyakit mitokondria. Salah satu gen yang bertanggung jawab dalam menjamin kestabilan mtDNA adalah POLG. Gen POLG mengkode protein polimerase gamma pada manusia, yang mereplikasi dan mereparasi mtDNA di dalam mitokondria. Mutasi pada gen POLG dapat menyebabkan penyakit kelainan mitokondria pada manusia, seperti gagal ginjal, sindrom Alpers, Progressive External Ophtalmoplegia, neuropati sensorial, ataxia dan bisa dikaitkan dalam beberapa gejala Parkinsonisme. Saat ini, belum ada terapi obat yang dapat mengatasi penyakit – penyakit tersebut. Berdasarkan kesamaan evolutif dari ragi hingga manusia, pada studi ini kami menggunakan Saccharomyces cerevisiae dan Caenorhabditis elegans untuk mengidentifikasi molekul obat yang berpotensi mengatasi ketidakstabilan mtDNA dari fibroblas pasien manusia yang memiliki mutasi gen POLG. Kami mengidentifikasi tiga kandidat potensial, yakni MRS2, MRS3 dan MRS4 dari penapisan kurang lebih 2000 molekul obat dengan menggunakan ragi. MRS3 adalah kandidat yang paling berkhasiat dan mampu mengatasi ketidakstabilan mtDNA pada ragi, Podospora, cacing dan fibroblas manusia. MRS3 adalah alias bagi clofilium tosylate (CLO), sebuah molekul antiaritmia untuk penyakit kardiovaskuler. Pada studi ini, kami juga menguji aktifitas dua molekul antiaritmia lain yang tergabung dalam kelas yang sama dengan CLO, dan menemukan bahwa kedua molekul ini juga berpotensi mengatasi defisit POLG pada cacing C. elegans. Dengan menggunakan metode kemogenomik pada ragi, kami juga mengidentifikasi sebuah aktor prosesus pembelahan mitokondria, Fis1, yang berpotensi terlibat dalam mekanisme seluler CLO. Fis1 dibutuhkan untuk: (1) kelangsungan hidup ragi pada konsentrasi toksik CLO dan (2) efek CLO dalam menstabilkan mtDNA pada ragi. Keseluruhan studi ini membuktikan potensi CLO sebagai molekul penstabil mtDNA yang pertama, yang dapat dikembangkan sebagai salah satu alternatif terapi obat untuk penyakit – penyakit mitokondria terkait mutasi POLG. Melalui studi ini, juga diungkap adanya hubungan antara kestabilan mtDNA dan prosesus pembelahan mitokondria