A new closed-loop frequency-domain model is developed to incorporate the water hammer effect with pump rotordynamics, in order to investigate the sub-synchronous instability problem observed in a field pump. Seal flow-rate perturbations due to eccentricity are calculated from Soulas and San Andres's seal code. A complete transfer function matrix between rotor motion and reaction force due to pressure perturbation is developed in detail. Stability analysis with transfer-function'add-in' modules is conducted in XLTRC2. Seal clearances and the reaction force angle are found to be important in shifting natural frequencies and damping. The sub-synchronous instability observed in field is duplicated successfully with double-clearance seals.

Many of the celestial bodies we know are found to be magnetized:the Earth, many of the planets so far discovered, the Sun and other stars,the interstellar space, the Milky Way and other galaxies.The reason for that is still to be fully understood, and this work is meant to be a step in that direction. The dynamics of the interstellar medium is dominated by events likesupernovae explosions that can be modelled as irrotational flows.The first part of this thesis is dedicated to the analysis of some characteristics of these flows, in particular how they influencethe typical turbulent magnetic diffusivity of a medium, and it is shownthat the diffusivity is generally enhanced, except for some specific casessuch as steady potential flows, where it can be lowered.Moreover, it is examined how such flows can develop vorticity when they occur in environments affected by rotation or shear,or that are not barotropic. Secondly, we examine helical flows, that are of basic importance for the phenomenon of the amplification of magnetic fields, namely the dynamo.Magnetic helicity can arise from the occurrence of an instability: here we focus on theinstability of purely toroidal magnetic fields, also known as Tayler instability.It is possible to give a topological interpretation of magnetic helicity.Using this point of view, and being aware that magnetic helicity is a conserved quantity in non-resistive flows,it is illustrated how helical systems preserve magnetic structureslonger than non-helical ones. The final part of the thesis deals directly with dynamos.It is shown how to evaluate dynamo transport coefficients with two of the most commonly used techniques, namely theimposed-field and the test-field methods.After that, it is analyzed how dynamos are affected by advectionof magnetic fields and material away from the domain in which theyoperate.It is demonstrated that the presence of an outflow, likestellar or galactic winds in real astrophysical cases,alleviates the so-calledcatastrophic quenching, that is the damping of a dynamoin highly conductive media, thus allowing the dynamo process to work better. / <p>At the time of the doctoral defence the following paper was unpublished and had a status as follows: Paper nr 5: Submitted</p>

Various premixed flame phenomena are studied by means of direct numerical simulations of the complete system of hydrodynamic equations. Rigorous study of flame dynamics is essential for all premixed combustion problems where multidimensional effects cannot be disregarded.The present thesis consists of six parts. The first part deals with the fundamental problem of curved stationary flames propagation in free-slip tubes of different widths. It is shown that only simple "single-hump" slanted stationary flames are possible in tubes wider than some stability limit. The flame dynamics is shown to be governed by a large-scale stability mechanism resulting in a highly slanted flame front.The second part of the thesis is dedicated to studies of acceleration and fractal structure of outward freely propagating flames. It is shown that the development of Landau-Darrieus instability results in the formation of fractal-like flame front structure. Two-dimensional simulation of radially expanding flames displays a radial growth with 1.25 power law temporal behavior. It is shown that the fractal excess for 2D geometry obtained in thenumerical simulation is in good agreement with theoretical predictions.In third part the flame acceleration in tubes with non-slip at the walls is studied in the extremely wide range of flame front velocity. Flame accelerates from small initial velocity to supersonic speed in the laboratory reference frame. Flame acceleration undergoes three stages: 1) initial exponential acceleration in the quasi-isobaric regime, 2) almost linear increase of the flame speed to supersonic values, 3) saturation to a stationary high-speed deflagration velocity, which is correlated with the Chapman-Jouguet deflagration speed. The saturation velocity is in line with previous experimental results.In fourth part the role of viscous stress in heating of the fuel mixture in deflagration-to-detonation transition in tubes is studied both analytically and numerically. The developed analytical theory determines temperature distribution ahead of an accelerating flame. The heating effects of viscous stress and the compression wave become comparable at sufficiently high values of the Mach number. Viscous stress makes heating and explosion of the fuel mixture preferential at the walls.In fifth part we reveal the physical mechanism of ultra-fast flame acceleration in obstructed channels used in modern experiments on detonation triggering. It is demonstrated that delayed burning between the obstacles creates a powerful jet-flow, driving the acceleration. The flame front accelerates exponentially; theanalytical formula for the growth rate is obtained. The theory is validated by extensive direct numerical simulations and comparison to previous experiments.The last part of the thesis concerns the transition from deflagration to detonation. It is found that in sufficiently wide free-slip channels and for sufficiently fast flames Landau-Darrieus instability may invoke nucleation of hot spots within the wrinkled flame folds, triggering an abrupt transition from deflagrative to detonative combustion. Results on DDT in channels with non-slip at the walls are also presented. / QC 20100915

Fanconi anaemia (FA) is an inherited disorder characterized by bone marrow failure, cancer predisposition and congenital abnormalities. The 12 known FA genes have been implicated in homologous recombination (HR), a process involved in telomere maintenance. A complex of at least 7 FA proteins promotes FANCD2 monoubiquitination and nuclear foci formation. FANCD2 colocalizes and interacts with HR proteins, however the role of FANCD2 in HR is unclear. Telomeres in dividing human somatic cells shorten until they reach a critical length, triggering most cells to undergo senescence or apoptosis. Rare immortal cells escape this crisis by expressing telomerase, or activating the Alternative Lengthening of Telomeres (ALT) pathway, which involves HR. FA core complex proteins and FANCD2 colocalize with telomeric foci in ALT, but not telomerase positive cells. Localization of FANCD2 to ALT telomeric foci requires monoubiquitination by the FA core complex, but is independent of ATM and ATR. FANCD2 primarily colocalizes with ALT telomeric DNA within ALT-associated PML bodies (APBs). Electron spectroscopic imaging and FISH experiments show that APBs contain extra-chromosomal telomeric repeat (ECTR) DNA that is non-nucleosomal. Depletion of FANCD2 causes marked increases in ECTR in ALT, but not telomerase positive cells. Overexpression of BLM, the helicase mutated in Bloom syndrome, also causes an ALT-specific increase in ECTR DNA. FANCD2 coimmunoprecipitates with BLM in ALT cells, and FANCD2 localization to ALT telomeric foci requires BLM expression. FANCD2-depleted ALT cells have reduced viability, signs of mitotic catastrophe, and multiple types of telomeric abnormalities, including increases in telomeric recombination, entanglements, colocalization with DNA repair proteins, and expression of fragile site characteristics. SiRNA depletion of FANCD2 does not cause overexpression of BLM, however codepletion of BLM with FANCD2 suppresses the telomere phenotypes caused by FANCD2 knockdown. Together this suggests that FANCD2 regulates BLM-dependent recombination and amplification of telomeric DNA within ALT cells.

Magnetohydrodynamic (MHD) flows in annular channels are of great current interest due to experimental search for the so-called magnetorotational instability (MRI) which is important for astrophysical applications (accretion disk physics, magnetic dynamo effect). <p>The main point of MRI experiments is to study the stability of liquid metal rotating in an external magnetic field. Two different types of fluid rotation are proposed: Taylor-Couette flow between rotating coaxial cylinders and electrically driven flow in transverse magnetic field. The implementation of MRI experiments and explanation of experimental results requires a theoretical study of the equilibrium and the stability of MHD flow in an annular channel. This is one of the main tasks of present thesis.<p>For study of equilibrium Taylor-Couette and electrically driven flows, a numerical code is developed which is based on the finite difference scheme with Jacobi iterations. The structure of flows is calculated for different parameters of the experiment. Effect of the inertia on the rotation profiles is investigated in detail. The approximate analytical expressions are obtained for radial profiles of rotation that can be used for optimization of the experimental device for MRI investigation. Equilibrium Taylor-Couette and electrically driven flows are compared from the perspective of experimental studies of MRI.<p>The spectral stability of electrically driven flow is studied by solving the eigen-value problem. This study is performed in the frames of both ideal and dissipative MHD models. It is shown that electrically driven flow can be destabilized through the mechanism of MRI if fluid velocity exceeds some instability threshold, which is determined by non-axisymmetric modes. The obtained results are compared with available experimental data.<p>A general variational method is developed for the stability study of MHD flows of ideal compressible fluids. It is shown that the linearized dynamics of such fluids has an infinite set of invariants. A necessary and sufficient stability criterion can be obtained after inclusion of one or several such invariants in analysis. An analytical example is presented to confirm the fruitfulness of the developed method.

Fanconi anaemia (FA) is an inherited disorder characterized by bone marrow failure, cancer predisposition and congenital abnormalities. The 12 known FA genes have been implicated in homologous recombination (HR), a process involved in telomere maintenance. A complex of at least 7 FA proteins promotes FANCD2 monoubiquitination and nuclear foci formation. FANCD2 colocalizes and interacts with HR proteins, however the role of FANCD2 in HR is unclear. Telomeres in dividing human somatic cells shorten until they reach a critical length, triggering most cells to undergo senescence or apoptosis. Rare immortal cells escape this crisis by expressing telomerase, or activating the Alternative Lengthening of Telomeres (ALT) pathway, which involves HR. FA core complex proteins and FANCD2 colocalize with telomeric foci in ALT, but not telomerase positive cells. Localization of FANCD2 to ALT telomeric foci requires monoubiquitination by the FA core complex, but is independent of ATM and ATR. FANCD2 primarily colocalizes with ALT telomeric DNA within ALT-associated PML bodies (APBs). Electron spectroscopic imaging and FISH experiments show that APBs contain extra-chromosomal telomeric repeat (ECTR) DNA that is non-nucleosomal. Depletion of FANCD2 causes marked increases in ECTR in ALT, but not telomerase positive cells. Overexpression of BLM, the helicase mutated in Bloom syndrome, also causes an ALT-specific increase in ECTR DNA. FANCD2 coimmunoprecipitates with BLM in ALT cells, and FANCD2 localization to ALT telomeric foci requires BLM expression. FANCD2-depleted ALT cells have reduced viability, signs of mitotic catastrophe, and multiple types of telomeric abnormalities, including increases in telomeric recombination, entanglements, colocalization with DNA repair proteins, and expression of fragile site characteristics. SiRNA depletion of FANCD2 does not cause overexpression of BLM, however codepletion of BLM with FANCD2 suppresses the telomere phenotypes caused by FANCD2 knockdown. Together this suggests that FANCD2 regulates BLM-dependent recombination and amplification of telomeric DNA within ALT cells.

No description available.

No description available.

Magnetohydrodynamic (MHD) flows in annular channels are of great current interest due to experimental search for the so-called magnetorotational instability (MRI) which is important for astrophysical applications (accretion disk physics, magnetic dynamo effect). <p>The main point of MRI experiments is to study the stability of liquid metal rotating in an external magnetic field. Two different types of fluid rotation are proposed: Taylor-Couette flow between rotating coaxial cylinders and electrically driven flow in transverse magnetic field. The implementation of MRI experiments and explanation of experimental results requires a theoretical study of the equilibrium and the stability of MHD flow in an annular channel. This is one of the main tasks of present thesis.<p>For study of equilibrium Taylor-Couette and electrically driven flows, a numerical code is developed which is based on the finite difference scheme with Jacobi iterations. The structure of flows is calculated for different parameters of the experiment. Effect of the inertia on the rotation profiles is investigated in detail. The approximate analytical expressions are obtained for radial profiles of rotation that can be used for optimization of the experimental device for MRI investigation. Equilibrium Taylor-Couette and electrically driven flows are compared from the perspective of experimental studies of MRI.<p>The spectral stability of electrically driven flow is studied by solving the eigen-value problem. This study is performed in the frames of both ideal and dissipative MHD models. It is shown that electrically driven flow can be destabilized through the mechanism of MRI if fluid velocity exceeds some instability threshold, which is determined by non-axisymmetric modes. The obtained results are compared with available experimental data.<p>A general variational method is developed for the stability study of MHD flows of ideal compressible fluids. It is shown that the linearized dynamics of such fluids has an infinite set of invariants. A necessary and sufficient stability criterion can be obtained after inclusion of one or several such invariants in analysis. An analytical example is presented to confirm the fruitfulness of the developed method.

This dissertation describes instability as a problem with a variety of sources and explains Publius' contribution to understanding the importance of these problems for politics and political theory. Using the Federalist and Publius' reading in political theory, history, and politics to ground my analysis, I explain the concept of instability as a multi-faceted problem that requires different solutions. I show that instability arises from one or a combination of four distinct notions: stasis or factional conflict, corruption, the mutability of the laws, and changing global conditions. My dissertation suggests that one of the primary goals of ancient and modern democracies was to solve the political challenges posed by instability. I further argue that the sources of instability remain relevant because they allow us to describe the problem of instability in a way that is theoretically and practically useful for understanding the role that democracy plays in addressing them. Finally, I suggest that describing and addressing the patterns of instability were central to Publius' interpretation of history and political theory and that recognizing and tackling these patterns are a part of the scope of modern political science and are central to the study of democratic politics. / Dissertation