Academic literature on the topic 'Bubble form of breakdown'

Experimental investigations of laminar swirling jets had revealed a new form of vortex breakdown, named conical vortex breakdown, in addition to the commonly observed bubble form. The present study explores these breakdown states that develop for the Maxworthy profile (a model of swirling jets) at inflow, from streamwise-invariant initial conditions, with direct numerical simulations. For a constant Reynolds number based on jet radius and a centreline velocity of 200, various flow states were observed as the inflow profile’s swirl parameter $S$ (scaled centreline radial derivative of azimuthal velocity) was varied up to 2. At low swirl ($S=1$) a helical mode of azimuthal wavenumber $m=-2$ (co-winding, counter-rotating mode) was observed. A ‘swelling’ appeared at $S=1.38$, and a steady bubble breakdown at $S=1.4$. On further increase to $S=1.5$, a helical, self-excited global mode ($m=+1$, counter-winding and co-rotating) was observed, originating in the bubble’s wake but with little effect on the bubble itself – a bubble vortex breakdown with a spiral tail. Local and global stability analyses revealed this to arise from a linear instability mechanism, distinct from that for the spiral breakdown which has been studied using Grabowski profile (a model of wing-tip vortices). At still higher swirl ($S=1.55$), a pulsating type of bubble breakdown occurred, followed by conical breakdown at 1.6. The latter consists of a large toroidal vortex confined by a radially expanding conical sheet, and a weaker vortex core downstream. For the highest swirls, the sheet was no longer conical, but curved away from the axis as a wide-open breakdown. The applicability of two classical inviscid theories for vortex breakdown – transition to a conjugate state, and the dominance of negative azimuthal vorticity – was assessed for the conical form. As required by the former, the flow transitioned from a supercritical to subcritical state in the vicinity of the stagnation point. The deviations from the predictions of the latter model were considerable.

In a recent study, Sotiropoulos et al. (2001) studied numerically the chaotic particle paths in the interior of stationary vortex-breakdown bubbles that form in a closed cylindrical container with a rotating lid. Here we report the first experimental verification of these numerical findings along with new insights into the dynamics of vortex-breakdown bubbles. We visualize the Lagrangian transport within the bubbles using planar laser-induced fluorescence (LIF) and show that even though the flow fields are steady – from the Eulerian standpoint – the spatial distribution of the dye tracer varies continuously, and in a seemingly random manner, over very long observation intervals. This finding is consistent with the arbitrarily long šil'nikov transients of upstream-originating orbits documented numerically by Sotiropoulos et al. (2001). Sequences of instantaneous LIF images also show that the steady bubbles exchange fluid with the outer flow via random bursting events during which blobs of dye exit the bubble through the spiral-in saddle. We construct experimental Poincaré maps by time-averaging a sufficiently long sequence of instantaneous LIF images. Ergodic theory concepts (Mezić & Sotiropoulos 2002) can be used to formally show that the level sets of the resulting time-averaged light intensity field reveal the invariant sets (unmixed islands) of the flow. The experimental Poincaré maps are in good agreement with the numerical computations. We apply this method to visualize the dynamics in the interior of the vortex-breakdown bubble that forms in the wake of the first bubble for governing parameters in the steady, two-bubble regime. In striking contrast with the asymmetric image obtained for the first bubble, the time-averaged light intensity field for the second bubble is remarkably axisymmetric. Numerical computations confirm this finding and further reveal that the apparent axisymmetry of this bubble is due to the fact that orbits in its interior exhibit quasi-periodic dynamics. We argue that this stark contrast in dynamics should be attributed to differences in the swirl-to-axial velocity ratio in the vicinity of each bubble. By studying the bifurcations of a simple dynamical system, with manifold topology resembling that of a vortex-breakdown bubble, we show that sufficiently high swirl intensities can stabilize the chaotic orbits, leading to quasi-periodic dynamics.

There have been tried many types of liquids with different ranges of viscosity values that have been tested to form a single cavitation bubble. The purpose of these experiments was to observe the behaviour of cavitation bubbles in media with different ranges of absorbance. The most of the method was based on spark to induced superheat limit of liquid. Here we used arrangement of the laser-induced breakdown (LIB) method. There were described the set cavitation setting that affects the size bubble in media with different absorbance. We visualized the cavitation bubble with a 60 kHz high speed camera. We used here shadowgraphy setup for the bubble visualization. There were observed time development and bubble extinction in various media, where the size of the bubble in the silicone oil was extremely small, due to the absorbance size of silicon oil.

This article presents the sterilization of bacteria using cavitation bubbles. Cavitation generated by ultrasound creates a cavitation cloud. Therefore is more advantageous to generate the cavitation bubbles by laser-induced breakdown, because it is possible to generate individual bubbles for the purpose of study single impact and physical mechanism of acting. The cavitation bubble is generated by a Nd: YAG 532nm laser beam, a short 10ns pulse. Here, we used optics to focus the laser beam and a high-speed camera to visualize characteristics the bubble. We used the method of long-distance microscopy and shadowgraph lightening for the visualization. We used the particle image velocimetry (PIV) method to determine the interaction of the bubble with the surrounding liquid and solid surface. The main goal of the research is to use cavitation to sterilize bacteria and biofilm in impact of single bubble collapse on living cells.

Cavitation between rotating and immobile cylinders appears in the form of a regular chain of bubbles. The bubble sizes are practically equal, as well as the distances between the bubbles and their azimuthal locations. Though such a form of cavitation has been observed in numerous experiments (in particular, in the experiments with bearings), its nature was not clarified. The presented analysis shows that breakdown of the flow axial symmetry due to displacement of the axis of one of cylinders leads to the regular wave-similar three-dimensional flow perturbations. Their “wavelength” is predetermined by the minimal gap between cylinders. Though the flow between cylinders is not curl-free, these perturbations can be determined with the use of a velocity potential.

Cavitation between rotating and immobile cylinders appears in the form of a regular chain of bubbles. The bubble sizes are practically equal, as well as the distances between the bubbles and their azimuthal locations. Though such a form of cavitation has been observed in numerous experiments (in particular, in the experiments with bearings), its nature was not clarified. The presented analysis shows that breakdown of the flow axial symmetry due to displacement of the axis of one of cylinders leads to the regular wave-similar three-dimensional flow perturbations. Their "wavelength" is predetermined by the minimal gap between cylinders. Though the flow between cylinders is not curl-free, these perturbations can be determined with the use of a velocity potential. Keywords: Cavitation, circular cylinders, misaligned cylinders, non-viscous flow.

The goal of this study is to characterize the various breakdown states taking place in a swirling water jet as the swirl ratio S and Reynolds number Re are varied. A pressure-driven water jet discharges into a large tank, swirl being imparted by means of a motor which sets into rotation a honeycomb within a settling chamber. The experiments are conducted for two distinct jet diameters by varying the swirl ratio S while maintaining the Reynolds number Re fixed in the range 300<Re<1200. Breakdown is observed to occur when S reaches a well defined threshold Sc≈1.3–1.4 which is independent of Re and nozzle diameter used. This critical value is found to be in good agreement with a simple criterion derived in the same spirit as the first stage of Escudier & Keller's (1983) theory. Four distinct forms of vortex breakdown are identified: the well documented bubble state, a new cone configuration in which the vortex takes the form of an open conical sheet, and two associated asymmetric bubble and asymmetric cone states, which are only observed at large Reynolds numbers. The two latter configurations differ from the former by the precession of the stagnation point around the jet axis in a co-rotating direction with respect to the upstream vortex flow. The two flow configurations, bubble or cone, are observed to coexist above the threshold Sc at the same values of the Reynolds number Re and swirl parameter S. The selection of breakdown state is extremely sensitive to small temperature inhomogeneities present in the apparatus. When S reaches Sc, breakdown gradually sets in, a stagnation point appearing in the downstream turbulent region of the flow and slowly moving upstream until it reaches an equilibrium location. In an intermediate range of Reynolds numbers, the breakdown threshold displays hysteresis lying in the ability of the breakdown state to remain stable for S<Sc once it has taken place. Below the onset of breakdown, i.e. when 0<S<Sc, the swirling jet is highly asymmetric and takes the shape of a steady helix. By contrast above breakdown onset, cross-section visualizations indicate that the cone and the bubble are axisymmetric. The cone is observed to undergo slow oscillations induced by secondary recirculating motions that are independent of confinement effects.

Several genera of anuran amphibians deposit their eggs within mucous secretions that have been aerated by the parents to produce a foam or bubble spawn body. This is a dynamic medium for embryo development given that it gradually breaks down over time, and one that has been hypothesised to serve a variety of purposes including protecting embryos from external stresses, such as suboptimal temperatures, desiccation and predation. In this study, I provide additional details of bubble spawn production in the sandpaper frog, Lechriodus fletcheri. Field and laboratory observations showed that females aerate spawn while in inguinal amplexus, using flanged fingers to transport air bubbles into the mucous. While the frothed spawn is initially resistant to breakdown, it gradually loses bubbles and flattens out into a film. This temporal shift in structure is likely to be adaptive, as the resultant increase in surface area allows embryos to come in direct contact with the open water, which may accommodate their increased oxygen demands or ease extrication from the mass. I provide evidence that this process is controlled by the residing embryos, given that spawn in the absence of embryos does not break down, highlighting the ability of offspring to modify their immediate environment even before hatching occurs to ensure conditions remain suitable for their changing needs.

The aim of this paper is to analyse the effect introduced in the dynamics of a financial market when agents anticipate the occurrence of a correlation breakdown. What emerges is that correlation breakdowns can act both as a consequence and as a triggering factor in the emergence of financial crises rational bubbles. We propose a market with two kinds of agents: speculators and rational investors. Rational agents use excess demand information to estimate the variance-covariance structure of assets returns, and their investment decisions are represented as a Markowitz optimal portfolio allocation. Speculators are uninformed agents and form their expectations by imitative behavior, depending on market excess demand. Several market equilibria result, depending on the prevalence of one of the two types of agents. Differing from previous results in the literature on the interaction between market dynamics and speculative behavior, rational agents can generate financial crises, even without the speculator contribution.

The main idea of this paper is to understand the fundamental vortex breakdown mechanisms in the coaxial swirling flow field. In particular, the interaction dynamics of the flow field is meticulously addressed with the help of high fidelity laser diagnostic tools. Time-resolved particle image velocimetry (PIV) (${\sim}1500~\text{frames}~\text{s}^{-1}$) is employed in $y{-}r$ and multiple $r{-}\unicode[STIX]{x1D703}$ planes to precisely delineate the flow dynamics. Experiments are carried out for three sets of co-annular flow Reynolds number $Re_{a}=4896$, 10 545, 17 546. Furthermore, for each $Re_{a}$ condition, the swirl number ‘$S_{G}$’ is varied independently from $0\leqslant S_{G}\leqslant 3$. The global evolution of flow field across various swirl numbers is presented using the time-averaged PIV data. Three distinct forms of vortex breakdown namely, pre-vortex breakdown (PVB), central toroidal recirculation zone (CTRZ; axisymmetric toroidal bubble type breakdown) and sudden conical breakdown are witnessed. Among these, the conical form of vortex breakdown is less explored in the literature. In this paper, much attention is therefore focused on exploring the governing mechanism of conical breakdown. It is should be interesting to note that, unlike other vortex breakdown modes, conical breakdown persists only for a very short band of $S_{G}$. For any small increase/decrease in $S_{G}$ beyond a certain threshold, the flow spontaneously reverts back to the CTRZ state. Energy ranked and frequency-resolved/ranked robust structure identification methods – proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) respectively – are implemented over instantaneous time-resolved PIV data sets to extract the dynamics of the coherent structures associated with each vortex breakdown mode. The dominant structures obtained from POD analysis suggest the dominance of the Kelvin–Helmholtz (KH) instability (axial $+$ azimuthal; accounts for ${\sim}80\,\%$ of total turbulent kinetic energy, TKE) for both PVB and CTRZ while the remaining energy is contributed by shedding modes. On the other hand, shedding modes contribute the majority of the TKE in conical breakdown. The frequency signatures quantified from POD temporal modes and DMD analysis reveal the occurrence of multiple dominant frequencies in the range of ${\sim}10{-}400~\text{Hz}$ with conical breakdown. This phenomenon may be a manifestation of high energy contribution by shedding eddies in the shear layer. Contrarily, with PVB and CTRZ, the dominant frequencies are observed in the range of ${\sim}20{-}40~\text{Hz}$ only. We have provided a detailed exposition of the mechanism through which conical breakdown occurs. In addition, the current work explores the hysteresis (path dependence) phenomena of conical breakdown as functions of the Reynolds and Rossby numbers. It has been observed that the conical mode is not reversible and highly dependent on the initial conditions.

The complexity of multidisciplinary projects requires that many specialities and disciplines work together. In rail infrastructure projects, the term 'systems engineering (SE)' is being widely used, yet it is still loosely defined. This PhD thesis proposes the use of a Disciplinary Breakdown Structure (DBS), an approach that better integrates SE as it is currently understood with traditional project management (PM) to make PM more efficient. A review of PM, SE and their relationship, particularly in the rail sector, identified gaps in performance, the most significant of which is a lack of integration between the SE and PM activities. Case study material was examined and a survey was conducted. The results highlighted the lack of consensus and consistency of the definition of SE and its application by project practitioners at various levels. Interface management (IM) was identified as a key factor contributing in project failure or success. IM was reviewed in the context of SE and PM, and existing methods and solutions were examined. The DBS as a new solution, was developed and introduced to improve the IM life cycle from definition to closure. This solution is based on industry discipline sectors (in this case, the rail sector) and therefore it is independent from project specific requirement. Exploring more detail of the DBS revealed its capability in integrating SE and PM more generally. The DBS is a modular solution (with a potential to become an industry standard) that provides a basis for the rapid development of project-bespoke management systems, improving PM efficiency by saving time and resources. The approach has been tested in two major rail project case studies in the UK and one in Canada and the results, benefits, constraints and the areas of improvements are discussed in more detail.

This dissertation delivers a new computational framework for the automatic generation of geometric feature patterns for industrial design and architectural facades on free-form surfaces. Such patterns include holes in a speaker grill, showerhead holes, protrusions on ceramics or bumpy textures on a panel. These patterns play a key role in making a designed object aesthetically pleasing as well as functional. Computer Aided Design (CAD) systems currently offer tools for generating simple patterns, such as uniformly spaced rectangular or radial patterns. However, they are not applicable to more general cases required in industrial design, including arbitrarily shaped target geometry and graded feature sizes. These tools are limited in several ways: (1) They cannot be applied to free-form geometries used in industrial design, (2) Patterning of these features happens within a single working plane and is not applicable to highly curved surfaces, and (3) Created features lack anisotropy and spatial variations, such as changes in the size and orientation of geometric features within a given region. This thesis proposes a new method of taking input for a target region along with sizing metrics. It will generate feature patterns automatically in three steps: (1) packing isotropic or anisotropic cells tightly in a target region, (2) scaling features according to the specified sizing metrics, and (3) adding features on the base geometry. This approach automatically generates complex patterns that conform to the boundary of any specified region. User input of a small number of geometric features (called “seed features”) of desired size and orientation in preferred locations also can be specified within the target domain. These geometric seed features are then transformed into tensors and used as boundary conditions to generate a Riemannian metric tensor field. A form of the Laplace heat equation is used to generate the field over the target domain, subject to specified boundary conditions. The field represents the anisotropic pattern of the geometric features. The system is implemented as a plugin module in a commercial CAD package to add geometric features to the target region of the model using two set operations, union and subtraction. This method facilitates the creation of a complex pattern of hundreds of geometric features in minutes. All the features are accessible from the CAD system and can be manipulated individually if required by the user. This allows the industrial designer or architect to explore more alternatives by avoiding the tedious and time-consuming manual generation of these geometric patterns.

The main object of this thesis is the diagnostics of the diaphragm discharge generated in water solutions containing supporting electrolytes (mostly NaCl), and description of particular processes before and after discharge breakdown by DC non-pulsed voltage up to 2 kV. Although many applications of electric discharge in liquids have been developed during the last years, the exact mechanism of the discharge ignition is not sufficiently known up to now. Based on this reason, this work is focused on the investigation of processes before the discharge ignition, breakdown parameters and the discharge itself both in the irregular and stable regime. The theoretical part of the work presents proposed mechanisms of the discharge generation in water solutions including the description of particular kinds of known discharges. Diaphragm discharge is one of many possible configurations of electrical discharges in liquids. In fact, electrical discharge in water forms non-thermal plasma, which is generated by high voltage, and many physical and chemical processes are started in plasma channels (so-called streamers). Among physical processes, high electrical field, shock waves and last but not least emission of electromagnetic radiation in visible and ultra-violet radiation belongs. The most important chemical processes are generation of various active species as hydrogen peroxide, and OH radical. Three batch plasma reactors using a diaphragm configuration with different total volume (4 l, 100 ml and 50 ml) are employed in the presented work. The discharge is created in an orifice (a pin-hole) in the dielectric barrier separating two electrode parts of the reactor. DC non-pulsed high voltage up to 4 kV is used for the discharge generation. Electrodes are made of stainless steel or platinum, and they are installed in parallel to the diaphragm in a variable distance from the dielectric barrier in each reactor part. The dielectric barrier is made of PET or Shapal-MTM ceramics with the variable thickness (0.2?2 mm). One pin hole st the diaphragm center with diameter of 0.2?1.5 mm are used in contemporary experiments. Time resolved characteristics of current and voltage are recorded using four-channel oscilloscope which detected their output values. Parameters are measured by the constantly increasing DC voltage with a step of 100 V. The solutions containing sodium chloride electrolyte are used at five different conductivities. Recorded time resolved characteristics determine breakdown moment, and describe current and voltage in particular parts within the static current-voltage curve. The breakdown appeared at lower applied voltage when the electrode distance is enhanced. However, the electrode distances higher than 4 cm does not induce any significant change of the breakdown voltage. The influence of pin-hole diameter is less obvious in the studied range, but a slight enhancement of breakdown voltage is observed with the increasing pin-hole diameter. Current-voltage characteristic curve moves towards lower voltage with the diaphragm thickness enhancement. The work compares the influence of conductivity change on current-voltage characteristics as well as the effect of inorganic salt kind. By the conductivity enhancement, the measured current-voltage curve moves towards lower voltage which means that the breakdown voltage is decreased. Sizes of the reactors do not have any effect on the processes before and after discharge breakdown.

Chaque année, le nombre de demandeur d’organe augmente en France comme dans le reste du monde. Pour combattre ce fléau, il existe aujourd’hui des technologies permettant d’imprimer du vivant, telle que la Bioimpression Assistée par Laser (LAB). Robuste et précise, cette méthode s’appuie sur les propriétés d’interaction laser-matière pour éjecter une bio-encre constituée de cellules vivantes. Pour éviter l’utilisation d’une couche absorbante sacrificielle, généralement utilisée, on focalise directement un faisceau laser dans la bioencre afin de générer un plasma puis une bulle de cavitation. La position de cette bulle est essentiellement maitrisée pas la longueur d’onde, et sa taille est gérée par l’énergie et la durée d’impulsion du laser. Ce sont les facteurs clés pour maîtriser l’éjection de matière biologique. Cependant, l’inhomogénéité locale apportée par les cellules perturbe l’impact du laser et donc la reproductibilité des jets, mais une fois imprimées, ces cellules sont viables et permettent de reconstruire des tissus vivants
Every year, the transplant waiting list gets bigger in France as in all over the world. To fight this curse, Bioprinting makes organ printing possible, especially with Laser Assisted Bioprinting (LAB). Robust and precise, this method use laser-matter interaction to eject a bioink made of living cells. To avoid the use of absorbing sacrificial layer, we directly focalize a laser beam into a living cells bioink, to create a plasma then a cavitation bubble. Its position, which is mainly driven by laser wavelength, and its size, managed by the energy and pulse duration, are the most important keys to control liquid jet ejection. However, the laser energy deposition and jet ejection is disturbed because of cells local concentration disparity, but when cells are printed, they are still viable and able to reconstruct living tissues

Ce travail de thèse concerne l’utilisation des décharges électriques de haute tension (DEHT) en milieu aqueux comme méthode d’extraction des polyphénols à partir de pépins de raisin.Les arcs électriques produits en milieu aqueux provoquent une succession de phénomènes (ondes de choc, bulles de cavitation) qui ont pour effet de fragmenter toute matière première située à proximité de l’arc électrique. L’objectif de cette thèse est d’étudier ces phénomènes afin d’améliorer la compréhension et l’efficacité des DEHT en tant que méthode d’extraction.Dans un premier temps, une étude des conditions d’apparition de l’arc électrique dans l’eau a permis de montrer que l’arc apparaît initialement dans des bulles de vapeur générées à la surface de l’électrode à cause de l’échauffement du liquide par effet Joule. Des mesures électriques, des prises de vues à haute vitesse, ainsi qu’une simulation numérique du problème ont permis de vérifier cette hypothèse. Une étude paramétrique des phénomènes générés par l’arc électrique (onde de choc et bulle de cavitation) a été menée. Grâce à des mesures de la pression des ondes de choc, des mesures de la taille des bulles de cavitation, et grâce des mesures électriques précises (notamment de la résistance électrique de l’arc), il apparaît que l’amplitude des phénomènes dépendent essentiellement de l’énergie dépensée dans l’arc. Cette énergie doit être distinguée de l’énergie totale d’une impulsion électrique, dont une partie est dépensée avant le claquage, mais également de l’énergie disponible au moment du claquage, dont une partie importante est dépensée dans le circuit électrique. La partition de cette énergie entre l’arc et le circuit électrique dépend du rapport entre la résistance du circuit et la résistance de l’arc. Ainsi une méthode pour augmenter significativement l’amplitude des phénomènes étudiés, et donc l’efficacité du procédé est d’améliorer le rapport entre ces résistances. Il a par exemple été observé qu’en augmentant la longueur de l’arc électrique de 2.5 mm à 2 cm, la résistance de l’arc augmente de 40 m à 0.55, et l’amplitude de l’onde de choc augmente de 135%. Pour finir, une étude paramétrique sur l’efficacité des DEHT comme procédé d’extraction des polyphénols des pépins de raisin a été menée. Entre autres, les effets sur l’extraction de la conductivité du liquide, du rapport liquide-solide, du nombre d’impulsion, de l’énergie par impulsion, de la distance inter-électrode ont été étudiés. Ces études ont mis en évidence l’importance de la répartition de l’énergie totale d’une impulsion en énergie dépensée avant le claquage, énergie dépensée au claquage dans le circuit électrique et énergie dépensée dans l’arc électrique. Ces études ont montré comment cette répartition est influencée par ces différents paramètres, et comment cela influence l’efficacité d’extraction. L’influence de la distance inter-électrode, et donc de la longueur de l’arc, a été particulièrement été mise en évidence par les résultats d’extraction
This thesis work focuses on the use of high voltage electrical discharges (HVED) in aqueous media as a method for extracting polyphenols from grape seeds. Electric arcs generated in an aqueous environment cause a succession of phenomena (shock waves, cavitation bubbles) that have the effect of fragmenting any raw material located near the electric arc. The objective of this thesis is to study these phenomena in order to improve the understanding and effectiveness ofHVED as an extraction method. First, a study of the conditions under which the electric arc appears in water showed that the arc initially appears in vapour bubbles generated on the electrode surface due to the heating of the liquid due to Joule effect. Electrical measurements, high-speed photography and a numerical simulation of the problem have allowed this hypothesis to be verified. A parametric study of the phenomena generated by the electric arc (shock wave and cavitation bubble) was carried out. Through measurements of shock wave pressure, of cavitation bubble size, and precise electrical measurements (including the electrical resistance of the arc), it appears that the amplitude of the phenomena depends essentially on the energy consumed in the arc. This energy mustbe distinguished from the total energy of an electrical pulse, part of which is spent before the breakdown. The energy spent in the electric arc must also be distinguishedfrom the energy available at electrical breakdown, as a significant part of breakdown energy is spent in the electrical circuit. The partition of breakdown energy between the arc and the electrical circuit depends on the ratio between the resistance of the circuit and that of the arc. Thus a method to significantly increase the amplitude of the studied phenomena (and therefore the efficiency of the process), is to improve the ratio between these resistances. For example, it has been observed that by increasing the length of the electric arc from 2.5 mm to 2 cm, the resistance of the arc increases from 40 m to 0.55, and the amplitude of the shock wave increases by 135%. Finally, a parametric study on the efficiency of DEHT as a process for extracting polyphenols from grape seedswas carried out. Among other things, the effects on the extraction of liquid conductivity, liquid-solid ratio, number of pulses, energy per pulse, and distance between electrodes were studied. These studies highlighted the importance of the distribution of the total pulse energy into energy spent before the breakdown, energy spent after breakdown in the electrical circuit and energy spent in the arc. These studies have shown howthis distribution is influenced by these different parameters, and how it influences extraction efficiency. The influence of the inter-electrode distance, and therefore the length of the arc, was particularly highlighted by the extraction results

The exact mechanism of the discharge in liquids ignition is not sufficiently known up to now. Although during the last years was achieved the great progress and overloading which some of them are written in this theoretical part of thesis. This thesis is divided into two experimental parts. When the first part deals with diagnostics of diaphragm discharge in electrolyte solutions and the second part is focused on its use for uncoiling (higher homogenization) of carbon nanotubes in solutions. In experiment 1, three different sized (4 l, 100 ml, 50 ml) diaphragm discharge configurations were used to diagnose diaphragm discharge in electrolyte solutions. Diagnostics is done through current and voltage waveforms with the addition of synchronized ICCD camera images that have been connected to a four-channel oscilloscope. The V-A characteristic can be described by three events occurring in the electrolyte solution with a gradual increase in voltage. Slowly increasing of the voltage in the solution leads first to electrolysis. The next phase is the formation of microbubbles or bubbles, which is characteristic of the curve by a slight decrease in the increase of the current passing between electrodes. The sudden increase in the current flow is characteristic of the last phase, namely the discharge phase. The distance of the electrodes from the diaphragm does not significantly affect the V-A characteristic. The higher diameter of the pin hole, therefore, has a higher voltage, but this does not affect the origin of bubble generation or breakdown. The higher thickness of diaphragm, the higher voltage is needed to the beginning of the bubbles generation, and consequently the discharge breakdown. Comparison of the voltage of the start generation of the bubbles and breakdown for PET diaphragms and diaphragms from the ceramic there was no mark able difference. One of the most important parameters is the conductivity of the electrolyte solution. The lower voltage is needed for the start generation of the bubbles at the higher solution conductivity, and also the discharge generation is observed at a lower breakdown voltage. The second experimental part is focused on the study of the diaphragm discharge effect on carbon nanotubes. A specially designed U-shaped reactor is used to modify carbon nanoparticles. Tap water and aqueous solutions of organic compounds are used as the electrolytic solutions. The discharge is generated by a non-pulsed DC high source with a voltage in the range of 0-2.8 kV supplied to platinum electrodes located in the electrolyte solution. The experimental results have shown that the diaphragm discharge has positive effects on the disintegration of clusters and agglomerates of carbon nanotubes. The primary effect on disintegration is probably the shock waves generated by the discharge. It turned out that it depends on the electrode configuration, where the treatment in anode space has far greater effects than the treatment in cathode half of the reactor. Effects of carbon nanotubes disintegration in solution are long-lasting and the treatment effect is not loosed after several months. There were detected no significant changes in the structure of plasma-treated nanotubes by Infra-red spectroscopy.

My diploma thesis is focused on a comparison of direct-current and high frequency (15-80 kHz) electric discharge, which generates non-thermal plasma in water solution of sodium chloride. Mainly current-voltage and Lissajous charts are discussed in the first part of this thesis. These charts describe different discharge phases: electrolysis, bubble formation, discharge breakdown and discharge regular operation in a pin-hole of a dielectric barrier. Influence of frequency, electrolyte conductivity, thickness of the diaphragm (or length of the capillary) and pin-hole diameter on discharge breakdown and bubble generation was studied, too. Measurements were realized in a polycarbonate reactor with total volume of 110 ml, which was divided by a changeable polyacetal insulating wall. This wall divided the reactor into two approximately equal spaces with one stainless steel planar electrode in each part. The Shapal-MTM ceramic discs (thickness of 0.3–1.5 mm and diameter of the central pin-hole of 0.3-0.9 mm) were mounted in the centre of the insulating wall. Initial conductivity of sodium chloride solution was chosen within the interval of 100900 S/cm. The second part of my thesis compares an influence of the direct-current (DC) and high frequency (HF) power sources on physical solution properties (conductivity, pH and temperature) and generation of hydrogen peroxide. A plasma reactor with total volume of 4 l and with mixing set up was divided into two equal spaces with one planar platinum electrode in each part. Diaphragm with thickness of 0.6 mm and pin-hole diameter of 0.6 mm was installed in the middle of the separating wall. Experiment was held at discharge operation of 45 W for 40 minutes with both power sources. Detection of hydrogen peroxide was realised by using a titanium reagent forming a yellow complex, which was analysed by absorption spectroscopy. If HF discharge power is plotted as a function of applied frequency, exponential decrease of frequency with increasing power can be observed. Higher breakdown voltage is necessary for thicker dielectric barriers, on the other hand for bigger diameter of the pin-hole lower breakdown voltage and higher power is needed in DC as well as in HF regime. Breakdown voltage is decreased by the increasing conductivity in both regimes; due to more charge carriers in the higher conductivity lower breakdown voltage is needed. However frequency in HF regime and DC discharge power increases. HF discharge power is decreased by the increasing conductivity. Solution conductivity and temperature are increased by initial conductivity value in both discharge regimes. Solution pH drops to acidic conditions when HF or DC positive regime is applied due to the generation of reactive species and electrolysis (in DC regime). However solution becomes alkaline when DC negative regime is applied. Concentration of hydrogen peroxide is produced linearly when HF or DC negative regime is applied and it depends on initial solution conductivity.

[ES] El principal desafío en los motores turbina de gas empleados en aviación reside en aumentar la eficiencia del ciclo termodinámico manteniendo las emisiones contaminantes por debajo de las rigurosas restricciones. Ésto ha conllevado la necesidad de diseñar nuevas estrategias de inyección/combustión que operan en puntos de operación peligrosos por su cercanía al límite inferior de apagado de llama. En este contexto, el concepto Lean Direct Injection (LDI) ha emergido como una tecnología prometedora a la hora de reducir los óxidos de nitrógeno (NOx) emitidos por las plantas propulsoras de los aviones de nueva generación. En este contexto, la presente tesis tiene como objetivos contribuir al conocimiento de los mecanismos físicos que rigen el comportamiento de un quemador LDI y proporcionar herramientas de análisis para una profunda caracterización de las complejas estructuras de flujo de turbulento generadas en el interior de la cámara de combustión. Para ello, se ha desarrollado una metodología numérica basada en CFD capaz de modelar el flujo bifásico no reactivo en el interior de un quemador LDI académico mediante enfoques de turbulencia U-RANS y LES en un marco Euleriano-Lagrangiano. La resolución numérica de este problema multi-escala se aborda mediante la descripción completa del flujo a lo largo de todos los elementos que constituyen la maqueta experimental, incluyendo su paso por el swirler y entrada a la cámara de combustión. Ésto se lleva a cabo través de dos códigos CFD que involucran dos estrategias de mallado diferentes: una basada en algoritmos de generación y refinamiento automático de la malla (AMR) a través de CONVERGE y otra técnica de mallado estático más tradicional mediante OpenFOAM. Por un lado, se ha definido una metodología para obtener una estrategia de mallado óptima mediante el uso del AMR y se han explotado sus beneficios frente a los enfoques tradicionales de malla estática. De esta forma, se ha demostrado que la aplicabilidad de las herramientas de control de malla disponibles en CONVERGE como el refinamiento fijo (fixed embedding) y el AMR son una opción muy interesante para afrontar este tipo de problemas multi-escala. Los resultados destacan una optimización del uso de los recursos computacionales y una mayor precisión en las simulaciones realizadas con la metodología presentada. Por otro lado, el uso de herramientas CFD se ha combinado con la aplicación de técnicas de descomposición modal avanzadas (Proper Orthogonal Decomposition and Dynamic Mode Decomposition). La identificación numérica de los principales modos acústicos en la cámara de combustión ha demostrado el potencial de estas herramientas al permitir caracterizar las estructuras de flujo coherentes generadas como consecuencia de la rotura de los vórtices (VBB) y de los chorros fuertemente torbellinados presentes en el quemador LDI. Además, la implementación de estos procedimientos matemáticos ha permitido tanto recuperar información sobre las características de la dinámica de flujo como proporcionar un enfoque sistemático para identificar los principales mecanismos que sustentan las inestabilidades en la cámara de combustión. Finalmente, la metodología validada ha sido explotada a través de un Diseño de Experimentos (DoE) para cuantificar la influencia de los factores críticos de diseño en el flujo no reactivo. De esta manera, se ha evaluado la contribución individual de algunos parámetros funcionales (el número de palas del swirler, el ángulo de dichas palas, el ancho de la cámara de combustión y la posición axial del orificio del inyector) en los patrones del campo fluido, la distribución del tamaño de gotas del combustible líquido y la aparición de inestabilidades en la cámara de combustión a través de una matriz ortogonal L9 de Taguchi. Este estudio estadístico supone un punto de partida para posteriores estudios de inyección, atomización y combus
[CA] El principal desafiament als motors turbina de gas utilitzats a la aviació resideix en augmentar l'eficiència del cicle termodinàmic mantenint les emissions contaminants per davall de les rigoroses restriccions. Aquest fet comporta la necessitat de dissenyar noves estratègies d'injecció/combustió que radiquen en punts d'operació perillosos per la seva aproximació al límit inferior d'apagat de flama. En aquest context, el concepte Lean Direct Injection (LDI) sorgeix com a eina innovadora a l'hora de reduir els òxids de nitrogen (NOx) emesos per les plantes propulsores dels avions de nova generació. Sota aquest context, aquesta tesis té com a objectius contribuir al coneixement dels mecanismes físics que regeixen el comportament d'un cremador LDI i proporcionar ferramentes d'anàlisi per a una profunda caracterització de les complexes estructures de flux turbulent generades a l'interior de la càmera de combustió. Per tal de dur-ho a terme s'ha desenvolupat una metodología numèrica basada en CFD capaç de modelar el flux bifàsic no reactiu a l'interior d'un cremador LDI acadèmic mitjançant els enfocaments de turbulència U-RANS i LES en un marc Eulerià-Lagrangià. La resolució numèrica d'aquest problema multiescala s'aborda mitjançant la resolució completa del flux al llarg de tots els elements que constitueixen la maqueta experimental, incloent el seu pas pel swirler i l'entrada a la càmera de combustió. Açò es duu a terme a través de dos codis CFD que involucren estratègies de mallat diferents: una basada en la generación automàtica de la malla i en l'algoritme de refinament adaptatiu (AMR) amb CONVERGE i l'altra que es basa en una tècnica de mallat estàtic més tradicional amb OpenFOAM. D'una banda, s'ha definit una metodologia per tal d'obtindre una estrategia de mallat òptima mitjançant l'ús de l'AMR i s'han explotat els seus beneficis front als enfocaments tradicionals de malla estàtica. D'aquesta forma, s'ha demostrat que l'aplicabilitat de les ferramente de control de malla disponibles en CONVERGE com el refinament fixe (fixed embedding) i l'AMR són una opció molt interessant per tal d'afrontar aquest tipus de problemes multiescala. Els resultats destaquen una optimització de l'ús dels recursos computacionals i una major precisió en les simulacions realitzades amb la metodologia presentada. D'altra banda, l'ús d'eines CFD s'ha combinat amb l'aplicació de tècniques de descomposició modal avançades (Proper Orthogonal Decomposition and Dynamic Mode Decomposition). La identificació numèrica dels principals modes acústics a la càmera de combustió ha demostrat el potencial d'aquestes ferramentes al permetre caracteritzar les estructures de flux coherents generades com a conseqüència del trencament dels vòrtex (VBB) i dels raigs fortament arremolinats presents al cremador LDI. A més, la implantació d'estos procediments matemàtics ha permès recuperar informació sobre les característiques de la dinàmica del flux i proporcionar un enfocament sistemàtic per tal d'identificar els principals mecanismes que sustenten les inestabilitats a la càmera de combustió. Finalment, la metodologia validada ha sigut explotada a traves d'un Diseny d'Experiments (DoE) per tal de quantificar la influència dels factors crítics de disseny en el flux no reactiu. D'aquesta manera, s'ha avaluat la contribución individual d'alguns paràmetres funcionals (el nombre de pales del swirler, l'angle de les pales, l'amplada de la càmera de combustió i la posició axial de l'orifici de l'injector) en els patrons del camp fluid, la distribució de la mida de gotes del combustible líquid i l'aparició d'inestabilitats en la càmera de combustió mitjançant una matriu ortogonal L9 de Taguchi. Aquest estudi estadístic és un bon punt de partida per a futurs estudis de injecció, atomització i combustió en cremadors LDI.
[EN] Aeronautical gas turbine engines present the main challenge of increasing the efficiency of the cycle while keeping the pollutant emissions below stringent restrictions. This has led to the design of new injection-combustion strategies working on more risky and problematic operating points such as those close to the lean extinction limit. In this context, the Lean Direct Injection (LDI) concept has emerged as a promising technology to reduce oxides of nitrogen (NOx) for next-generation aircraft power plants In this context, this thesis aims at contributing to the knowledge of the governing physical mechanisms within an LDI burner and to provide analysis tools for a deep characterisation of such complex flows. In order to do so, a numerical CFD methodology capable of reliably modelling the 2-phase nonreacting flow in an academic LDI burner has been developed in an Eulerian-Lagrangian framework, using the U-RANS and LES turbulence approaches. The LDI combustor taken as a reference to carry out the investigation is the laboratory-scale swirled-stabilised CORIA Spray Burner. The multi-scale problem is addressed by solving the complete inlet flow path through the swirl vanes and the combustor through two different CFD codes involving two different meshing strategies: an automatic mesh generation with adaptive mesh refinement (AMR) algorithm through CONVERGE and a more traditional static meshing technique in OpenFOAM. On the one hand, a methodology to obtain an optimal mesh strategy using AMR has been defined, and its benefits against traditional fixed mesh approaches have been exploited. In this way, the applicability of grid control tools available in CONVERGE such as fixed embedding and AMR has been demonstrated to be an interesting option to face this type of multi-scale problem. The results highlight an optimisation of the use of the computational resources and better accuracy in the simulations carried out with the presented methodology. On the other hand, the use of CFD tools has been combined with the application of systematic advanced modal decomposition techniques (i.e., Proper Orthogonal Decomposition and Dynamic Mode Decomposition). The numerical identification of the main acoustic modes in the chamber have proved their potential when studying the characteristics of the most powerful coherent flow structures of strongly swirled jets in a LDI burner undergoing vortex breakdown (VBB). Besides, the implementation of these mathematical procedures has allowed both retrieving information about the flow dynamics features and providing a systematic approach to identify the main mechanisms that sustain instabilities in the combustor. Last, this analysis has also allowed identifying some key features of swirl spray systems such as the complex pulsating, intermittent and cyclical spatial patterns related to the Precessing Vortex Core (PVC). Finally, the validated methodology is exploited through a Design of Experiments (DoE) to quantify the influence of critical design factors on the non-reacting flow. In this way, the individual contribution of some functional parameters (namely the number of swirler vanes, the swirler vane angle, the combustion chamber width and the axial position of the nozzle tip) into both the flow field pattern, the spray size distribution and the occurrence of instabilities in the combustion chamber are evaluated throughout a Taguchi's orthogonal array L9. Such a statistical study has supposed a good starting point for subsequent studies of injection, atomisation and combustion on LDI burners.
Belmar Gil, M. (2020). Computational study on the non-reacting flow in Lean Direct Injection gas turbine combustors through Eulerian-Lagrangian Large-Eddy Simulations [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/159882
TESIS

The present study focusses on vortex breakdown (VB), which occurs in axially convected swirling flows and is characterized by the development of an internal stagnation point and regions of reverse flow. VB has been observed or utilized in a variety of situations including flow over delta wings, tornadoes, re whirls, turbomachinery, fuel injectors and combustors. Flows where VB is observed include swirling round jets with non-swirling and negligible co flow. The experimental study of Billant et al., (1998) has shown VB characteristics unique to this family of flows. In addition to the commonly observed bubble form of breakdown (BVB) the experiments revealed a new form, referred to as conical form of breakdown (CVB). Features of these forms (especially the latter) remain mostly unexplored. This serves as motivation for the present numerical investigation of VB in swirling jets. In this study, a survey of different VB states (laminar and turbulent) observed with varying flow parameters has been carried out using numerical simulations, along with investigations on hysteresis effects and bistability phenomenon. Previous theoretical models for VB have been assessed using these results. Helical instabilities that were observed to arise in the simulations have been examined using the tools of stability analysis. Three-dimensional numerical simulations were carried out using the open-source incompressible flow solver incompact3d in a Cartesian coordinate framework to study a swirling jet entering an adequately large domain to prevent con nement effects. The swirling jet was modelled using the axisymmetric and steady `Maxworthy' in flow pro le (Ruith et al., 2004), with the main control parameter as the swirl number, S, representing the relative rate of rotation in comparison to the centreline axial velocity of the jet. The Reynolds number (Re) was chosen based on the jet radius and centreline axial velocity. The long-time flow states achieved with varying S and initial conditions are reported for Re = 200 and 1000. For the latter case, where the flow transitioned to turbulence, large eddy simulations were carried out using the explicit fi ltering approach. Both local and global stability analyses have been performed to examine instabilities. Selective frequency damping and axisymmetric simulations using ANSYS Fluent have been used to compute base flows. For Re = 200, BVB and CVB were observed and could be clearly distinguished by the distinct spatial structure of the recirculation zone. These different VB forms could be further classi ed based on unique characteristics into different types. For BVB, the following types were identi ed{ steady one-celled BVB, one-celled BVB with spiral tail, pulsating BVB, two-celled BVB with spiral tail and asymmetric BVB. The categorization as one-celled and two-celled was based on the number of toroidal structures that could be identi fied within the bubble, while the pulsating BVB was observed to be an intermediate state between the two. The term `spiral tail' is used to denote the presence of a helical mode that developed in the wake of the bubble which had no signifi cant effect on the axisymmetric upstream portions of the bubble. In contrast, for the asymmetric BVB, a helical mode was present, which caused asymmetric motion of the entire bubble. Two types of CVB were identifi ed{ regular and wide-open{ the latter with an approximately radial expansion of the flow downstream to the stagnation point. Comparisons with different experimental results showed strong similarities in features for most flow states. Hysteresis studies established the coexistence of different types of BVB with the regular CVB in overlapping ranges of swirl numbers, confo rming that these are bistable forms. Remarkable differences in length scales involved for the two forms could be observed when comparing time-averaged flow structure. A hysteresis plot is provided based on the maximum radius achieved by a streamline starting from the in flow plane at an arbitrary radius. It was additionally seen that the two-celled BVB with spiral tail and asymmetric BVB coexist (along with regular CVB) over a small range of swirls. For Re = 1000, a transition to turbulence was observed, leading to some interesting differences in the flow states observed. At low swirls, the stagnation point occurred only intermittently in time, in contrast to the steady VB observed for equivalent S for Re = 200. For swirls above this, a two-celled BVB with a turbulent wake was observed for a large swirl range. The stagnation point at the bubble's nose was lost at swirls just above those for which BVB was observed. For this range, a spiral coherent structure was seen to arise intermittently in the bubble's wake, accompanied by streamwise oscillatory motions in the flow. At higher swirls, this motion was subdued and the spiral downstream of the bubble was lost, while the stagnation point at the bubble's nose eventually reappeared. The streamwise oscillations of the bubble being a common feature to all long-time flow states observed, these states are collectively referred to as oscillating BVB. For even higher swirls, turbulent regular and wide-open types of CVB were observed. Bistability of oscillating BVB and regular CVB, and additionally, between regular and wide-open CVB were established using hysteresis studies. The stark differences in length scales associated with the bistable bubble and conical forms were reduced due to turbulence, indicating that CVB might be misidenti ed as BVB at high Re. Indeed, it is speculated that some of the VB states reported in experimental studies of Liang and Maxworthy, (2005) are likely the CVB. The bistable regular and wide-open types of CVB were found to have considerable differences in the length scales of respective recirculation zones. The two VB states for which helical modes were observed, the BVB with spiral tail and asymmetric BVB, were examined using stability analysis. A closely related flow state to BVB with spiral tail is the spiral vortex breakdown (SVB). In previous studies, SVB was identi ed to arise due to the instability of a nonlinear steep global mode. Assuming weakly non-parallel flow, a local spatio-temporal analysis coupled with a WKBJ framework was used to show that the global mode associated with BVB with spiral tail differed from that of the SVB, with the linear frequency selection criterion (Chomaz et al., 1991) better predicting the global frequency. Using tools of global stability analysis, the asymmetric type of BVB was shown to arise due to a different unstable mode that has strong energy content in the bubble region. It was observed in the simulations that the base state was strongly modifi ed by the instability. The stability analysis using the mean flow made better predictions as compared to that based on the base flow for this type of BVB. Two theories developed by Benjamin, (1962) and Brown and Lopez, (1990) towards explaining VB were assessed. It was observed that the prediction from the former theory, that the flow becomes subcritical downstream of VB, was confi rmed based on simulation results. However, other aspects of the theory, which have not been scrutinized in previous studies displayed a trend opposite to that observed in the present simulations as well as other available experimental results. That is, the conjugate states predicted by the theory, modelling the flow downstream of VB, were found to better resemble the primary state upstream of VB with increasing swirl. This contradicts the observation that the bubble increases in size with swirl. Reasons for why the predictions display this trend, based on analogies to gasdynamic shockwaves, are provided. The theory of Brown and Lopez, (1990) was found to give qualitatively similar predictions for BVB, but deviated strongly from the numerical results for CVB. A major highlight of this study is the signifi cance of the initial conditions in determining the VB form or type achieved, with results showing the coexistence of three distinct pairs of long-time flow states in overlapping parametric ranges for swirling jets. Though emphasized by Billant et al., (1998), many later studies on swirling jets have generally neglected this aspect. Similarly, as this study shows, the CVB is a distinct form of VB that has not been clearly identifi ed in previous studies on swirling jets. These results might aid in better understanding features of the elementary flow confi guration of swirling jets and allow for more informed developments of design and control strategies in practical applications.

The importance of telling new climate stories—stories that center the persistence of life itself, that embrace comedy and radical hope. “How dare you?” asked teenage climate activist Greta Thunberg at the United Nations in 2019. How dare the world's leaders fiddle around the edges when the world is on fire? Why is society unable to grasp the enormity of climate change? In Beyond Climate Breakdown, Peter Friederici writes that the answer must come in the form of a story, and that our miscomprehension of the climate crisis comes about because we have been telling the wrong stories. These stories are pervasive; they come from long narrative traditions, sanctioned by capitalism, Hollywood, and social media, and they revolve around a myth: that the nation exists primarily as a setting for a certain kind of economic activity. Stories are how we make sense of the world and our place in it. The story that “the economy” takes priority over everything else may seem foreordained, but, Friederici explains, actually reflect choices made by specific people out of self-interest. So we need new stories—stories that center the persistence of life, rather than of capitalism, stories that embrace contradiction and complexity. We can create new stories based on comedy and radical hope. Comedy never says no; hope sprouts like a flower in cracked concrete. These attitudes require a new way of thinking—an adaptive attitude toward life that slips the narrow yoke of definition.

The global market in antiquities has been described as a grey market. We provide a breakdown of the meanings and implications of this greyness. Usually the term refers to the mixing of recently looted antiquities with those that can be sold legally, thus the antiquities market is grey because illicit objects are sold via a public and purportedly legitimate network of dealers and auction houses. This is supported by a second form of greyness: the ethically grey status of individual looted objects after time and their passage through jurisdictions via multiple trades obscures or overwrites their illicit origins. It is also supported by a greying of ethical judgment, achieved through a discourse that permits the purchase of illicit objects in constructed circumstances of “saving” or “preserving” artifacts.

This chapter follows naturally out of the previous one in its presentation of a case of theology crystallizing into Jewish law. It examines various instances of concrete law that involve the divine name and its use in everyday life. The rabbinic allows for the exploitation of the most sacred for the most mundane, drawing the divine into the horizontal plane of human relationships. The first instance discussed is where classical rabbis allowed the name YHVH to form an integral part of the common salutation. The second examined is allowing the name’s effacement in order to repair a spousal breakdown. God disappears so that love can reappear. The third instance involves a battle to eradicate evil in the world. God’s name remains incomplete as long as that evil exists.

Horror cinema grants bodies and images a precarious hold on sense and order: from the zombie’s gory disintegration to the vampire’s absent reflection and from the shaky camerawork of ‘found footage’ horror to the spectacle of shattering glass in the Italian giallo. Addressing classic horror movies alongside popular and innovative contemporary works, Visceral Screens shows how they have rendered the human form as a type of ‘image-body’, mediated by optical effects, chromatic shifts, glitches and audiovisual fragmentation. The question of signification is central to this metaphorical exchange, since horror frequently pushes both bodies and media to the limits of their expressive capacity. Conducting their own anatomies of the screen, cutting across bodies and media alike, horror films revel in the breakdown of frames, patterns and figures, exposing the seams between matter and meaning.

While writers such as Friel and Murphy seemed to provide a certain continuity in the closing years of the twentieth century, a new generation of writers emerged in the 1990s for whom the Irish dramatic tradition seemed less an inheritance than a foil to be played against (or with) or, in some cases, an irrelevance. For instance, while Martin McDonagh’s work was sometimes associated with British ‘in-yer-face’ theatre of the 1990s, to some commentators his work made more sense as a subversion of an earlier Irish tradition. In the case of Conor McPherson, the breakdown of a community that made a shared theatre culture possible was registered in a turn to monologue, while writers such as Mark O’Rowe and Enda Walsh showed a freedom of dramatic form and a set of dramatic concerns reflecting immersion in a mediatized, globalized late modernity.

Psychopharmacological drugs have effects on selfhood in ways that often overlap with the treatment of mental disorders, but the effects also go beyond the domain of disorder into the sphere of enhancement. To what extent this is and will be the case depends, of course, on the definition and understanding of mental disorder. The psychotropic effects on selfhood can be mapped out by distinguishing groups of traits that belong to personality and that form dimensions of selfhood, but they can also be distinguished by acknowledging different layers of selfhood-pre-reflective embodied self, reflective self, and narrative self. The effects of psychopharmacological drugs in some cases normalize the alienating experiences of the breakdown of pre-reflective selfhood, in other cases they rather bring about changes in basic dimensions of selfhood and personality, such as temperament and emotional dispositions.

The joint discovery of sensibility and subjectivity is the hallmark of early Romanticism in Russia. In the 1780s and 1790s, younger writers—mostly amateur men of letters and the occasional noble woman—extended older debates about the elements of style and correct verse form. Writers were able to move between classical models and more experimental forms of subjectivity. Debate about the purpose of literature and its national cultural orientation and obligations intensified in the 1820s. At the end of the period covered in this chapter we see the breakdown of support for literature conceived as playful and gentlemanly. The advent of a full-blown Romantic movement, supported by the growth of the reading public, proliferation of literary journals, and the establishment of literary criticism as an institution, caused more writers to take entrenched positions and break with the past.

Further objections to miracles, such as moral and theological objections, are examined. These give valuable cautions. If miracles are possible, then their extreme rarity is troubling from the point of view of justice; a complete impossibility might be easier to understand. Augustine was right to oppose the idea that miracles represent a breakdown of lawful order. Christian commitment involves a duty of honesty and straight-dealing in questions of healthcare. Jesus himself strongly opposed the mindset that asks for impressive marvels rather than help in living right. Notwithstanding all this, we affirm, in company with other Christians, that after Jesus of Nazareth was dead, he was given new life in an embodied, tangible, visible, audible, coherent, insightful, dynamic form. We affirm this out of a sense of duty and in response to evidence, but we acknowledge that the evidence does not on its own compel the response.

AbstractStudies on participation tend to focus on describing the process. The exact form of their involvement, along with its effects on architecture and the lived environment, is rarely discussed. The aim of this article is to better understand the effects of participation in the long run after the initial involvement. This will be done by studying three rehabilitation projects in the Paris region. Our aim was to gather the opinions of those who had not made their voices heard through the official channels of consultation. Above all, it was to give visibility to, and understand the meanings of, the appropriation of spaces which have become invisible simply because they are used in ways which seem to go against the norm.

AbstractThis chapter introduces various extended non-destructive testing (ENDT) techniques for surface quality assessment, which are first characterized, then enhanced, and finally applied to assess the level of pre-bond contaminations intentionally applied to carbon fiber reinforced plastic (CFRP) adherends following the procedures described in the previous chapter. Based on two user cases comprising different scenarios that are characteristic of either aeronautical production or repair, the detailed tests conducted on two types of sample geometry, namely flat coupons and scarfed pilot samples with a more complex shape, form the basis for applying the advanced ENDT procedures for the monitoring of realistic and real aircraft parts, as will be described in Chap. 10.1007/978-3-319-92810-4_5. Specifically, the reported investigations were performed to assess the surface quality of first ground and then intentionally contaminated CFRP surfaces using the following ENDT tools: the aerosol wetting test (AWT), optically stimulated electron emission (OSEE), two differently implemented approaches based on electronic noses, laser-induced breakdown spectroscopy (LIBS), Fourier-transform infrared (FTIR) spectroscopy, laser-induced fluorescence (LIF), and laser vibrometry.

In a bid to atone for its midcentury actions, the San Francisco Redevelopment Agency, beginning in the 1980s, set about planning a “jazz preservation district” to be located in the Fillmore neighborhood. Along with a program for small-business loans, the SFRA initiative originally took the form of a combined multiplex and jazz venue, pairing AMC Theaters with an outpost of the New York-based Blue Note club. While this first proposal was never realized, the SFRA did later succeed in launching a different mixed-use project that mixed affordable and market-rate housing with a branch of the Oakland-based Yoshi’s jazz club. Chapter 6 examines the economic and cultural challenges facing the Fillmore redevelopment district at the turn of the millennium.

This chapter assesses how professors grade students. It argues that the practice of grading is replete with problems. Grades are a kind of language. They are meant to be a form of communication. They are sometimes meant to communicate to students how well they’ve mastered a set of material. Most colleges calculate grade point averages (GPAs) and compare students to one another. Grades are also sometimes meant to communicate to outsiders something about how good a student is, and how he or she compares to other students from other universities. However, the grading and GPA systems are such a mess that they largely fail to accomplish these goals. In some cases, the mathematics used to calculate an average final grade in a class are incoherent. In nearly all cases, the mathematics used to calculate students’ GPAs are also incoherent.

Abstract For achieving better fuel-air mixing within a short distance or for improved atomization of liquid fuels counter rotating swirler designs are preferred in gas turbine engine combustors. In this study, vortex breakdown phenomenon is investigated in co and counter rotating swirlers using CFD. The swirler assembly consists of two axial swirlers, an inner and an outer swirler both with straight vanes. Swirler vane angles are varied from 30° to 60° in steps of 10° while keeping inner and outer swirler vane angles equal. CFD simulations are performed with air at ambient conditions as the working fluid at a constant mass flow rate. It is observed that strong shear layers are created in counter swirl flows due to the opposite flow rotation. The shear layers result in rapid decay of inner swirler tangential velocities for the counter swirlers compared to the co-swirlers. The tangential velocity decay is characterized with a parameter named tangential velocity integral (TVI). TVI was observed to decay faster for the counter swirl flows compared to the co-swirl flows. The faster decay in TVI for the counter swirlers is found to result in a stronger adverse pressure gradient in the axial direction at the center. The strong adverse pressure gradient resulted in higher pressure excess ratios (PER) for the counter swirlers. The higher PERs are observed to induce vortex breakdown in counter swirlers even at low vane angles whereas in co-swirlers vortex breakdown is not observed except for the highest vane angle. It is demonstrated that vortex breakdown could be suppressed in counter swirlers using a converging mixer passage. The converging mixer passage creates a favorable pressure gradient that counters the adverse pressure gradient due to swirl decay, resulting in breakdown suppression.

In this paper, large-eddy simulation of the transition process in a separation bubble is compared to experimental results. The measurements and simulations are conducted under low free-stream turbulence conditions over a flat plate with a streamwise pressure distribution typical of those encountered on the suction side of turbine airfoils. The computational grid is sufficiently refined that the effects of sub-grid scale turbulence are adequately represented by the numerical dissipation of the computational algorithm. The large-eddy simulations are shown to accurately capture the transition process in the separated shear layer. The results of these simulations are used to gain further insight into the breakdown mechanisms in transitioning separation bubbles.

This paper presents experimental results on separation-bubble transition at low Reynolds number and low freestream turbulence, measured on an airfoil using particle image velocimetry (PIV). The two-dimensional PIV measurements have been performed over the suction surface of a low-Reynolds-number airfoil in a water tow-tank facility. Reynolds numbers, based on airfoil chord length and towing speed, of 40,000 and 65,000 have been examined at various angles of incidence, providing a range of streamwise pressure distributions and transitional separation-bubble geometries. The types of bubbles observed range from a short and thick bubble with separation near the leading edge of the airfoil, to a long and thin bubble with separation far downstream of the suction peak. The PIV measurements facilitate visualization of the vortex dynamics associated with separation-bubble transition. The growth of instability waves within the separated shear layer and eventual breakdown into turbulence is documented through the instantaneous vector fields. For all cases examined, large-scale vortex shedding and multiple reverse-flow zones are observed in the reattachment region. A technique for estimating the location of transition onset based on statistical turbulence quantities is presented, and comparisons are made to existing transition models.

A simple Hamiltonian dynamical systems model for vortex breakdown of the bubble-type (B-type) is developed and analyzed. This model is constructed using the flow induced by two point vortices moving in a half-plane immersed in an ideal (= inviscid and incompressible) fluid with an ambient uniform horizontal velocity. It is shown — using a combination of modern dynamical systems theory and numerical analysis — that the flows generated by this model capture most of the dynamical features exhibited in B-type vortex breakdown, including the existence of chaotic regimes. Examples are provided to illustrate the variety and complexity of vortex breakdown type flows that can be produced with these models.

The use of the silicone known as Poly-dimethylsiloxane (PDMS) in microfluidic and other activities has increased enormously. By means of a laser short pulse, optical breakdown of the liquid contained in a microchannel (squared cross-section with 100 μm sides) can occur; as a consequence plasma is generated and a gaseous bubble suddenly expands. The expansion of such a bubble can be so violent that the channel walls deform considerably and in some cases the detachment of the top wall from the PDMS channel is verified. Measurements of channel width reveal a relative increase up to 45% for the tested conditions. Due to the elasticity of PDMS and surface energy values, surprisingly the top wall and channel reattach. Contrary to widely known cavitation where damage to the wall is manifested in form of pitting, we observe no permanent damage for the experimental conditions studied. We envisage the use of PDMS material in other types of applications with high relative volumetric change, such as microexplosions, ultrasonic cavitation and the like, in which there is a cyclic stress load of the PDMS material. We present a compact method to predict the reliability of PDMS for its use in cavitational events occurring inside of microfluidic channels (by force balance and energy conservation analysis).

Abstract Production logging tools (PLTs) and formation testing, even in logging while drilling (LWD) conditions during underbalanced drilling, are key technologies for assessing the productivity potential of a gas well and therefore to maximize recovery. Gas bubble detection sensors are key components in determining the fluid phases in the reservoir and accurately quantify recoverable reserves, optimize well placement, geosteering and to qualify the production ability of the well. We present here a new nonlinear autoregressive - breakdown artificial intelligence (AI) detection framework for PLT gas bubble detection sensors that categorize in real-time whether and which sensors become unreliable or have broken down during the logging measurements. AI tools allow the automatization of this method that is critical during data quality control of post-drilling PLT, but it is essential when the measurements are performed in LWD as data assessment and processing need to occur in real time. This AI framework was validated on both a training and testing dataset, and exhibited strong classification performance. This method enables accurate real-time breakdown detection for gas bubble detection sensors.

Abstract A high-quality precision-controlled turntable apparatus was fabricated to probe the dynamic behavior of a viscous fluid contained in a cylindrical container. Vortex breakdown(s) produced by a rotating endwall disk was visualized by using a fluorescent dye injection technique, and its flow field was measured by using a particle image velocimetry. This flow is characterized by two non-dimensional parameters, i.e., the height-to-radius ratio H/R and the rotating Reynolds number Re = Ω2/v. Limiting boundaries for single, double and triple vortex breakdowns in steady flow were re-plotted to compare with the previous visualization studies of Escudier. The locations of stagnation points of the vortex breakdown bubble(s) in steady flow were measured quantitatively. The overall experimental results in the steady flow were in excellent agreement with Escudier’s data. In unsteady flow, the amplitude and time period of periodic axial oscillation, and the polar angle and time period of precession, were measured. The domains for periodic axial oscillation and for precession in unsteady flow were delineated.

Freeze–form Extrusion Fabrication (FEF) is an additive manufacturing process that extrudes high solids loading aqueous ceramic pastes in a layer–by–layer fashion below the paste freezing temperature for component fabrication. Due to effects such as the air bubble release, agglomerate breakdown, change in paste properties during extrusion as a result of liquid phase migration, etc., the extrusion force is difficult to control. In this paper, an adaptive controller is proposed to regulate the extrusion force. Recursive Least Squares is used to estimate extrusion force model parameters during fabrication and a low–order control scheme capable of tracking general reference trajectories is designed and implemented to regulate the extrusion process. Several parts were fabricated with the adaptive extrusion force controller. These results illustrate the need for extrusion force control and that variable reference extrusion force profiles are required to fabricate complex features.

The breakdown of tip leakage vortex has been investigated on a low-speed axial compressor rotor with moderate blade loading. Effects of the breakdown on the rotor aerodynamics are elucidated by Navier-Stokes flow simulations and visualization techniques for identifying the breakdown. The simulations show that the leakage vortex breakdown occurs inside the rotor at a lower flow rate than the peak pressure rise operating condition. The breakdown is characterized by the existence of the stagnation point followed by a bubble-like recirculation region. The onset of breakdown causes significant changes in the nature of the tip leakage vortex: large expansion of the vortex and disappearance of the streamwise vorticity concentrated in the vortex. The expansion has an extremely large blockage effect extending to the upstream of the leading edge. The disappearance of the concentrated vorticity results in no rolling-up of the vortex downstream of the rotor and the disappearance of the pressure trough on the casing. The leakage flow field downstream of the rotor is dominated by the outward radial flow resulting from the contraction of the bubble-like structure of the breakdown region. It is found that the leakage vortex breakdown plays a major role in characteristic of rotor performance at near-stall conditions. As the flow rate is decreased from the peak pressure rise operating condition, the breakdown region grows rapidly in the streamwise, spanwise and pitchwise directions. The growth of the breakdown causes the blockage and the loss to increase drastically. Then, the interaction of the breakdown region with the blade suction surface gives rise to the three-dimensional separation of the suction surface boundary layer, thus leading to a sudden drop in the total pressure rise across the rotor.

We have shown by experimental investigations that cellular surgery (microdissection, optoporation, and optoinjection) with Nd:YAG laser pulses of 1064 nm and 532 nm wavelength relies on nonlinear absorption leading to optical breakdown and plasma formation at the laser focus. The present study explores possibilities of refining the breakdown effects by employing shorter pulse durations and irradiances that generate plasmas below the threshold for shock wave and bubble formation. Optical breakdown in water at NA = 0.9 and NA = 1.3 was simulated numerically for wavelengths of 1064 nm, 532 nm and 355 nm, and pulse durations of 6 ns, 30 ps and 100 fs. We used a rate model that allows the calculation of the temporal evolution of the free electron density ρ during breakdown, ρ (t) could be followed separately for the free electrons generated by multiphoton ionization and avalanche ionization. We obtained excellent agreement between the calculated and measured threshold values for breakdown with 6-ns pulses. The simulations predict that the energy threshold for cellular surgery can be reduced by a factor of 350-2600 (depending on wavelength) when the pulse duration is reduced from 6 ns to 100 fs. The calculated breakdown energies for 100 fs pulses focused by an objective with NA = 1.3 are 0.6 nJ at 355 nm, 1.6 nJ at 532 nm, and 3.9 nJ at 1064 nm. With ns-pulses at 1064 nm, the breakdown threshold is very sharp, i. e. there is either no effect at all, or a dense plasma is formed causing a micro-explosion. With shorter wavelengths and pulse durations, the threshold is smoother, and electron densities may be produced that stay below the threshold for explosive vaporization and bubble formation. This creates the possibility of achieving highly localized plasma-mediated chemical or thermal changes in the cell. We conclude that both the reduced energy threshold and the smoother breakdown process with fs pulses bear a large potential for the refinement of intracellular surgery.

Genetic and biochemical analysis of glucosinolate breakdown: The effects of indole-3-carbinol on plant physiology and development Glucosinolates are a class of defense-related secondary metabolites found in all crucifers, including important oilseed and vegetable crops in the Brassica genus and the well-studied model plant Arabidopsis thaliana. Upon tissue damage, such as that provided by insect feeding, glucosinolates are subjected to catalysis and spontaneous degradation to form a variety of breakdown products. These breakdown products typically have a deterrent effect on generalist herbivores. Glucosinolate breakdown products also contribute to the anti-carcinogenic effects of eating cabbage, broccoli and related cruciferous vegetables. Indole-3-carbinol, a breakdown product of indol-3-ylmethylglucosinolate, forms conjugates with several other plant metabolites. Although some indole-3-carbinol conjugates have known functions in defense against herbivores and pathogens, most play as yet unidentified roles in plant metabolism, and possibly also plant development. At the outset, our proposal had three main hypotheses: (1) There is a specific detoxification pathway for indole-3-carbinol; (2) Metabolites derived from indole-3-carbinol are phloem-mobile and serve as signaling molecules; and (3) Indole-3-carbinol affects plant cell cycle and cell-differentiation pathways. The experiments were designed to enable us to elucidate how indole-3-carbinol and related metabolites affect plants and their interactions with herbivorous insects. We discovered that indole-3- carbinol rapidly and reversibly inhibits root elongation in a dose-dependent manner, and that this inhibition is accompanied by a loss of auxin activity in the root meristem. A direct interaction between indole-3-carbinol and the auxin perception machinery was suggested, as application of indole-3-carbinol rescued auxin-induced root phenotypes. In vitro and yeast-based protein interaction studies showed that indole-3-carbinol perturbs the auxin-dependent interaction of TIR1 with Aux/IAA proteins, supporting the notion that indole-3-carbinol acts as an auxin antagonist. Furthermore, transcript profiling experiments revealed the influence of indole-3-carbinol on auxin signaling in root tips, and indole-3-carbinol also affected auxin transporters. Brief treatment with indole-3-carbinol led to a reduction in the amount of PIN1 and to mislocalization of PIN2. The results indicate that chemicals induced by herbivory, such as indole-3-carbinol, function not only to repel herbivores, but also as signaling molecules that directly compete with auxin to fine tune plant growth and development, which implies transport of indole-3- carbinol that we are as yet unsuccessful in detecting. Our results indicate that plant defensive metabolites also have secondary functions in regulating aspects of plant metabolism, thereby providing diversity in defense-related plant signaling pathways. Such diversity of of signaling by defensive metabolites would be beneficial for the plant, as herbivores and pathogens would be less likely to mount effective countermeasures. We propose that growth arrest can be mediated directly by the herbivory-induced chemicals, in our case, indole-3-carbinol. Thus, glucosinolate breakdown to I3C following herbivory would have two outcomes: (1) Indole-3-carbinaol would inhibit the herbivore, while (2) at the same time inducing growth arrest within the plant. Thus, our results indicate that I3C is a defensive phytohormone that modulates auxin signaling, leading to growth arrest.

Recent books and articles have analyzed the causes of the global financial and economic crisis of 2007-09. Yet little attention has been paid to the quality of leadership in organizations that were at the epicentre of the storm, were victims of it, avoided it or even prospered from it. In the summer of 2009 a multi-disciplinary group of Ivey faculty decided to look at the leadership dimensions of the recent financial and economic crisis. We started by writing a working paper that laid out our preliminary views. We then engaged more than 300 business, public sector and not-for-profit leaders in small and large groups, as individuals and collectives, to get their reaction to this paper and, more generally, to discuss te role that organizational leadership played before, during and after the crisis. We examined leadership not just in the financial sector but also in many other public and private sector organizations that were affected by the crisis. In a sense, we were putting leadership on trial. Our aim in doing this was not to identify and assign blame. Rather, we examined leadership during this critical period in recent history to learn what we could, and use the learning to improve practice in leadership today and the development of next generation leaders. As we analyzed the role of leadership in this crisis we were faced with one major question: "Would better leadership have made a difference?" Our answer is unequivocal: "Yes!" We recognize that many people could argue it is unfair to criticize leaders whose decisions were based on their knowledge of the situation at the time and which only eventually, with the aid of 20/20 hindsight proved bad. We respect this view but we disagree with it. Some business and public sector leaders predicted better than others the bursting of the housing bubble and financial markets turmoil, positioned their organizations to avoid problems, and coped with them skillfully. Their organizations were not badly damaged by the crisis and some even prospered. Some governments and regulatory agencies' control and monitoring systems were superior to those in the U.S., the U.K., Ireland, Spain, Iceland and other countries that had to bail out their banks and other industries. Our evidence supports the conclusion that these companies, these agencies, these governments and these countries had better leadership. Good leadership mattered then and good leadership will matter in the future. We are presenting our conclusions about what good leadership involves in the form of a public statement of principles - a manifesto that addresses what good leaders do, who they are, and how they can be developed in organizations.