This is an experimental and theoretical study of a laminar separation bubble and the associated transition dynamics in its early stages. The separation of a laminar boundary layer from a solid surface is prevalent in very many flow situations such as over gas turbine blades (especially in the low-pressure turbine stage) and the wings of micro-aero-vehicles (MAVs) that operate at fairly low Reynolds numbers. Flow separation occurs in such cases due to the presence of an adverse pressure gradient. The separated shear layer becomes unstable due to the presence of an inflection point and presumably transitions to turbulence rapidly. Eventually, there is reattachment back to the solid surface further downstream, if conditions are right. The region enclosed by the shear layer is called a laminar separation bubble and has been a subject of many studies in the past. The present experiments have been conducted in a closed-circuit wind tunnel. A separation bubble was obtained on the upper surface of a flat plate by appropriately contouring the top wall of the tunnel. Four different techniques were used for qualitative and quantitative study viz. surface flow visualisation, smoke flow visualisation, surface pressure measurements and hotwire anemometry. Response of the bubble to both natural as well as artificial (impulsive excitation) disturbance environment has been studied. Linear stability analyses (both Orr-Sommerfeld and Rayleigh calculations), in the spatial framework, have been performed for the mean velocity profiles starting from an attached adverse pressure gradient boundary layer all the way up to the front portion of the separation bubble region (i.e. up to the end of the dead-air region where linear evolution of disturbances could be expected). The measured velocity profiles (both attached and separated) were fitted with analytical model profiles for doing stability calculations. A separation bubble consists of aspects of both wall-bounded and wall-free shear layers and therefore both viscous and inviscid mechanisms are expected to be at play. Most of the studies in the literature point to the inviscid instability associated with the shear layer to be the main mechanism. The main aim of the present work is to understand the exact origin of the primary instability mechanism responsible for the amplification of disturbances. We argue that at least up to the front portion of the bubble, the instability mechanism is due to the inflectional mode associated with the mean velocity profile. However, the seeds of this inviscid inflectional instability could be traced back to the attached boundary layer upstream of separation. In other words, the inviscid inflectional instability of the separated shear layer should be logically seen as an extension of the instability of the upstream attached adverse-pressure-gradient boundary layer. This modifies the traditional view that pegs the origin of the instability in a separation bubble to the free shear layer outside the bubble with its associated Kelvin-Helmholtz mechanism. Our contention is that only when the separated shear layer has moved considerably away from the wall (and this happens near the maximum height of the mean bubble) that a description by Kelvin-Helmholtz instability paradigm with its associated scaling principles could become relevant. We also propose a new scaling for the most amplified frequency for a wall-bounded shear layer in terms of the inflection point height and the vorticity thickness, and show its universality. Next, we theoretically investigate the role played by the re-circulating region of the separation bubble in the linear instability regime. In the re-circulating region near the wall, associated with the so-called wall mode, the production of disturbance kinetic energy is found to be negative. This is a very interesting observation which has been cursorily noted in earlier studies. Here we show that the near-wall negative production region exerts a stabilising influence on the downstream travelling disturbances. A theoretical support for such a mechanism to exist close to the wall is presented. It is shown that the stabilising wall-proximity effect is not a peripheral aspect but has a significant effect on the overall stability especially for the waves close to the upper neutral branch. We demonstrate the appropriateness of inviscid analysis for the stability of the separated flow velocity profile away from the wall, by comparing the numerical solutions of Rayleigh and Orr-Sommerfeld equations. Following this, the analytical consequences of the Rayleigh equation such as the inflection point criterion and the Fjortoft criterion are derived for the wall-bounded inflectional velocity profiles. Furthermore, we also discuss the relevance of the negative production region towards flow control and management for the wall-bounded flows. It appears fruitful to divide the separation bubble region into two parts with respect to the nature of disturbance dynamics: one outside the mean dividing streamline (which behaves as an amplifier) and the other inside the bubble corresponding to the re-circulating region (having oscillator type characteristics). To explore the oscillator-like behaviour of the bubble further, we have carried out spatio-temporal stability analysis of the reversed flow velocity profiles and determined the conditions for the onset of absolute instability. We contend that the presence of the negative production region for the upstream travelling waves has a restraining effect arresting the tendency of the flow (both wall-free and wall-bounded) to become absolutely unstable and thereby requiring a particular threshold of the backflow velocity to be crossed for its realisation. Moreover, the delay in the onset of absolute instability for a wall-bounded profile as compared to a free shear layer is attributed to a certain ‘negative-drag’ effect of the wall on the overall flow which increases the group velocities for the wall-bounded flows. A related theme in the literature regarding the dynamics of laminar separation bubbles is the so-called ‘bursting’ of the bubble wherein there is a sudden increase in the length and height of the bubble as some critical conditions are reached. Bubbles before bursting are termed as ‘short’ bubbles and those after bursting as ‘long’ bubbles. In this work, we provide a criterion to predict bursting which is a refinement over the existing criteria. The proposed criterion takes into account not just the length of the bubble but also the maximum height and it is shown to be more universal in differentiating short bubbles from the long ones, as compared to the other criteria. We also present a hypothesis regarding the sequence of events leading to bubble bursting by relating its onset to the instability of the re-circulating region. For this we observe that as the amount of backflow velocity is increased for a reversed flow velocity profile, the inflection point moves inside the mean dividing streamline and this happens before the onset of absolute instability. This causes a vorticity maximum to develop inside the re-circulating region which could lead to the instability of the closed streamlines with respect to two-dimensional cylindrical disturbances. The actual bursting process may be expected to involve non-linear interactions of the disturbances and the long bubble could be a nonlinearly saturated state of the instability of the re-circulating region. In order to explore the three-dimensionality associated with the bubble, extensive surface flow visualisation experiments have been performed. The surface streamline pattern is obtained for the entire span of the plate for three different freestream velocities. The patterns have been interpreted using topological ideas and various critical points have been identified. It is shown that the arrangement of critical points satisfies the ‘index theorem’ which is a topological necessity and the streamline patterns are ‘structurally stable’. An interesting observation from these patterns is the presence of three-dimensionality upstream of the separation line close to the wall even though the oncoming flow is nominally two-dimensional. Using the critical point theory, we propose a hypothesis which could be used to construct a semi-empirical model wherein the critical points are assigned with a quantity called ‘strength’ for determining the extent of upstream influence of a given separation line. Finally, we derive a necessary condition for the existence of inviscid spatial instability in plane parallel flows. It states that for spatial instability the curvature of the velocity profile should be positive in some region of the profile. This includes Rayleigh’s inflection point theorem (which was proposed and proved by Rayleigh for temporal instability) as a special case. It thus provides a rigorous basis for applying the inflection point criterion to the flows in the framework of spatial stability theory (which we have used extensively in the present thesis). Moreover, the condition derived here is more general as it also includes velocity profiles with the curvature positive everywhere which are excluded by Rayleigh’s theorem in the temporal framework. An example of such a profile is presented (Couette-Poiseuille flow with adverse pressure gradient) and it is shown that this flow is an exceptional case which is temporally stable but spatially unstable. Eigenvalue calculations as well as energy considerations suggest that the mechanism governing instability of this flow is inviscid and non-inflectional in character. This is a new result which could have important implications in understanding the instability dynamics of parallel flows.

M. Tech. Electrical Engineering. / Discusses node location as a major problem when considering several areas of application based on wireless sensor networks. Many localisation algorithms have been proposed in the literature to solve the problem of locating sensor nodes in WSN. However, most of these algorithms have poor localisation accuracy and high computational cost. Due to these limitations, this research study considers the modelling of an efficient and robust localisation scheme to determine the location of individual sensor nodes in WSN. To successfully solve this task, this research study focuses on the aspect of improving the position accuracy of wireless sensor nodes in WSN. The study considers a distance based cooperative localisation algorithm called Curvilinear Component Analysis Mapping (CCA-MAP) to accurately localise the sensor nodes in WSN. CCA-MAP is used because it delivers improved position accuracy and computational efficiency.

Syftet med denna studie har varit att undersöka och jämföra hur fyra professionella inom olika människovårdande yrkesgrupper uppfattar sina möjligheter att uppmärksamma och hjälpa barn som upplever föräldrars konflikter med anledning av separation. Studien har genomförts med hjälp av en kvalitativ metod genom att intervjua en: skolkurator, skolpsykolog, samordnare och familjerättssekreterare. De teoretiska utgångspunkter vi använt oss av är professionsteori med begreppen jurisdiktion och handlingsutrymme samt nyinstitutionell teori inbegripande begreppet organisatoriskt fält. Utifrån dessa teorier och begrepp har vi undersökt och jämfört hur en skolkurator, en skolpsykolog, en samordnare och en familjerättssekreterare enskilt och i jämförelse med varandra beskriver sitt arbeta, om problematiken framkommer i yrkesgruppernas arbete samt hur de arbetar i möten med barn. Alla informanter beskriver att barn kan må dåligt av föräldrars konflikt med anledning av separation. I vissa fall, och i olika utsträckning kan detta komma till uttryck i mötet med de professionella i studien. De uttryck hos barnen som lyfts fram i studien är dåligt mående, beteendeproblem, koncentrationssvårigheter och försämrade skolprestationer. Representanterna från de olika professionerna har olika förutsättningar att hjälpa dessa barn beroende på deras olika utgångspunkter och arbetsuppgifter / The purpose of this qualitative study is to examine and compare how professionals in four groups in Human Services perceive their possibilities to see, understand and help children who experience parental conflicts due to separation. A qualitative method has been used, where the selection of participants was made through appropriate sampling. The theoretical basis applied involves professional theory with the concepts jurisdiction and scope for action, as well as new institutional theory including the concept organizational field. Based on these theories and concepts we have examined and compared how the professionals from four occuapational groups; school counselor, school psychologist, coordinator and secretary of family law, individually and in comparison with each other, describe their work with this type of problems and how they act in meetings with children. The results show that the professionals have the experience that children may feel bad about the conflict between their parents in connection with separation. In some cases, and to a varying extent, this may be expressed in meetings with the professional groups in the study. The reactions of the children highlighted in the study are bad mood, behavioral problems, difficulty to concentrate and deteriorating school performance. The professionals from the different professional groups, depending on their jurisdiction and scope for action, have different abilities to help the children showing these reactions.

Syftet med denna uppsats är att undersöka socialtjänstens perspektiv på hur föräldrar förändrar sina roller för att på bästa sätt kunna ta sitt föräldraansvar efter en separation, speciellt om en förälder brister i sin omsorg kring barnet och hur socialtjänsten ser på sin roll i den processen. Vi har genomfört tre fokusgruppsintervjuer; en barnutredningsgrupp och två grupper från familjerätten. Alla enheter vi besökte ligger i Stockholm. Respondenterna har i fokusgrupperna fått reflektera och diskutera sina uppfattningar kring temana föräldraansvar, oro kring den andre förälderns förmåga, roller i och kring familjen samt socialtjänstens roll. Vårt resultat har analyserats med hjälp av rollteorin och mentaliseringsbegreppet. Resultatet visade att i omskapandet av föräldrarollerna efter separation är samarbete samt att minimera konflikter mellan föräldrar grundläggande. I de fall socialtjänsten är i kontakt med föräldrarna så har även de en roll i föräldraansvaret, de strävar efter att vägleda föräldrarna mot ett fullgott ansvarstagande och se till att föräldrarna behåller barnperspektivet med barnets behov i fokus. Om en förälder har förmågan att mentalisera en annan människas situation och ser dennes behov så underlättar det omskapandet av föräldrarollen efter separation precis som det vidare underlättar om föräldrar har en fungerande kommunikation mellan varandra. Den roll som är mest komplex enligt oss är den som en orolig förälder har kring barnets vistelse hos den andra föräldern. Oavsett hur relationen till den andre är så ligger det i bådas ansvar att alltid säkerställa att barnet har det bra och inte far illa. / The purpose of this paper is to examine the perspective of the Swedish social services with regard to how parents change their roles in order to best take parental responsibility following separation. We particularly examine the perspective of the social services with regard to cases in which a parent has shortcomings in his or her care of the child and how the social services view their own role in this process. We conducted three focus group interviews: one involving a child protection investigation group and two involving family law groups. All of the units visited were in Stockholm, Sweden. The respondents in the focus groups were asked to reflect and discuss their views on the themes of parental responsibility, concern about the other parent’s capacity, roles in and involving the family, and the role of the social services. Our results were analysed using role theory and the concept of mentalisation. The results showed that in changing parental roles following separation, cooperation and minimising conflict between parents is fundamental. In cases in which the social services have contact with the parents, they too have a role in parental responsibility since they endeavour to guide the parents towards taking an adequate level of responsibility and ensure that the parents maintain a children’s perspective in which the needs of the child are in focus. If a parent has the ability to mentalise another person’s situation and see his or her needs, the changing of the parental role following separation is facilitated. Likewise, it also is beneficial if parents are able to communicate with each other. The role that is most complex, in our view, is that of a concerned parent with regard to the child staying with the other parent. Regardless of the nature of their relationship, it is the responsibility of both parents to always ensure that the child receives adequate care and does not come to harm.

Phase-redistribution and full-phase separation data were generated for two-phase (air-water) flow splitting at an equal-sided impacting tee junction with a horizontal inlet and inclined outlets. The flow loop incorporated a tee junction machined in an acrylic block with the three sided having an equal diameter of 13.5 ± 0.1 mm I.D. Both sets of experiments were conducted at a nominal pressure (Ps) of 200 kPa (abs) and near-ambient temperature (Ts). The operating conditions for the phase-redistribution experiments were as follows: inlet superficial liquid velocities (JL1) ranging from 0.01 to 0.18 m/s, inlet qualities (x1) ranging from 0.1 to 0.9, mass split ratios (W3/W1) from 0 to 1.0, and outlet inclination angles ranging from horizontal to vertical. These inlet conditions corresponded to inlet flow regimes of stratified, wavy, and annular. Phase-redistribution data revealed that the redistribution of phases depended on the inlet conditions, the mass split ratio at the junction, and the inclination angle of the outlets. The magnitude of the inclination effect was dependent on the inlet flow regime. The phase redistribution in stratified flow was very sensitive to the outlet angle and full separation could be achieved at angles as low as 0.7°. Wavy flow was less sensitive to the outlet angle and annular flow was even less sensitive to the outlet angle. The capability of a single impacting tee junction to perform as a full phase separator has been examined. Experimental data were obtained for the limiting inlet conditions under which full separation was attainable at various outlet inclinations (θ) of 2.5°, 7.5°, 15°, 30°, 60°, 75°, and 90°. Full separation data have shown that a single impacting tee junction can perform as a full-phase separator for some inlet conditions. Flow phenomena near the limiting conditions were observed and a simple correlation based on the similarity between these flow phenomena and the phenomenon of liquid entrainment in small upward branches was developed. This correlation was capable of accurate prediction of the data in terms of magnitude and trend.

Olefin/paraffin separation is a large potential market for membrane applications. Carbon molecular sieve membranes (CMS) are promising for this application due to the intrinsically high separation performance and the viability for practical scale-up. Intrinsically high separation performance of CMS membranes for olefin/paraffin separations was demonstrated. The translation of intrinsic CMS transport properties into the hollow fiber configuration is considered in detail. Substructure collapse of asymmetric hollow fibers was found during Matrimidﾮ CMS hollow fiber formation. To overcome the permeance loss due to the increased separation layer thickness, 6FDA-DAM and 6FDA/BPDA-DAM polyimides with higher rigidity were employed as alternative precursors, and significant improvement has been achieved. Besides the macroscopic morphology control of asymmetric hollow fibers, the micro-structure was tuned by optimizing pyrolysis temperature protocol and pyrolysis atmosphere. In addition, unexpected physical aging was observed in CMS membranes, which is analogous to the aging phenomenon in glassy polymers. For performance evaluation, multiple "proof-of-concept" tests validated the viability of CMS membranes under realistic conditions. The scope of this work was expanded from binary ethylene/ethane and propylene/propane separations for the debottlenecking purpose to mixed carbon number hydrocarbon processing. CMS membranes were found to be olefins-selective over corresponding paraffins; moreover, CMS membranes are able to effectively fractionate the complex cracked gas stream in a preferable way. Reconfiguration of the hydrocarbon processing in ethylene plants is possible based on the unique CMS membranes.

Phase-redistribution and full-phase separation data were generated for two-phase (air-water) flow splitting at an equal-sided impacting tee junction with a horizontal inlet and inclined outlets. The flow loop incorporated a tee junction machined in an acrylic block with the three sided having an equal diameter of 13.5 ± 0.1 mm I.D. Both sets of experiments were conducted at a nominal pressure (Ps) of 200 kPa (abs) and near-ambient temperature (Ts). The operating conditions for the phase-redistribution experiments were as follows: inlet superficial liquid velocities (JL1) ranging from 0.01 to 0.18 m/s, inlet qualities (x1) ranging from 0.1 to 0.9, mass split ratios (W3/W1) from 0 to 1.0, and outlet inclination angles ranging from horizontal to vertical. These inlet conditions corresponded to inlet flow regimes of stratified, wavy, and annular. Phase-redistribution data revealed that the redistribution of phases depended on the inlet conditions, the mass split ratio at the junction, and the inclination angle of the outlets. The magnitude of the inclination effect was dependent on the inlet flow regime. The phase redistribution in stratified flow was very sensitive to the outlet angle and full separation could be achieved at angles as low as 0.7°. Wavy flow was less sensitive to the outlet angle and annular flow was even less sensitive to the outlet angle. The capability of a single impacting tee junction to perform as a full phase separator has been examined. Experimental data were obtained for the limiting inlet conditions under which full separation was attainable at various outlet inclinations (θ) of 2.5°, 7.5°, 15°, 30°, 60°, 75°, and 90°. Full separation data have shown that a single impacting tee junction can perform as a full-phase separator for some inlet conditions. Flow phenomena near the limiting conditions were observed and a simple correlation based on the similarity between these flow phenomena and the phenomenon of liquid entrainment in small upward branches was developed. This correlation was capable of accurate prediction of the data in terms of magnitude and trend.

Within this thesis, the dominant conceptualisations of the state/market and the national/global within international political economy are put into a critical scrutiny. It is emphasized that within most of the analyses of globalisation and the state, these conceptualisations are built in a dualist manner and that the internal relation between them is ignored. Within this context, it will be focused on three prominent approaches in contemporary international political economy literature, namely regulation approach, neo-Gramscian approach and open Marxism which scrutinise the relation between globalisation and the state. Through an analysis of the methodological and conceptual frameworks of regulation and neo-Gramscian approaches with a particular focus on the relationship they posit between globalisation and the state, the political/ economic and the national/ global conceptualisations of these approaches will be criticised for being dualist. Such a criticism will be developed by deriving insights from open Marxist perspective which provides a relational conception of the political/economic and the global/national and, through emphasizing that globalism is inherent in capitalism and capital is a global social relation which cannot be taken as separate from labour, perceives the state and market as internally related forms of capitalist social relations of production.

Thesis (Ph. D.)--University of Lund, 1995. / Published dissertation. Includes bibliographical references.

Thesis (Ph. D.)--University of Lund, 1995. / Published dissertation. Includes bibliographical references.