Academic literature on the topic 'Transition FST'

Les cycles de Rankine organique (ORC) apparaissent comme l'une des solutions pour répondre aux défis énergétiques et environnementaux actuels, en raison de leur important potentiel énergétique. L'un des composants clés des ORC est le détendeur, généralement une turbine. Pour les petits systèmes, cette dernière fonctionne dans les régimes transsoniques à supersoniques et peut être influencée par les propriétés de la vapeur organique utilisée, présentant ainsi des effets non idéaux. Dans cette étude, nous examinons les transitions de couche limite (CL) et le mécanisme des pertes au sein des turbines dans des conditions représentatives des ORC pour le fluide Novec649. Nous débutons par la présentation des premières simulations numériques directes (DNS) et des simulations à grandes échelles (LES) de CL transitionnant et turbulentes de Novec dans des conditions subsoniques élevées. Dans l'état turbulent, les profils des propriétés dynamiques de l'écoulement sont peu affectés par les propriétés du gaz et demeurent très proches de la DNS incompressible, malgré la vitesse élevée de l'écoulement subsonique, même si de véritables mais très faibles effets de compressibilité sont présents. Notre stratégie LES est validée par rapport à la DNS et est utilisée pour étudier l'influence de la fréquence et de l'amplitude du forçage sur l'état turbulent établi. Ensuite, pour la première fois, nous étudions, par LES, la transition induite par la turbulence extérieure (FST) de CL de gaz dense sur des plaques planes et autour du bord d'attaque d'une turbine. En raison du nombre de Reynolds élevé, les fines CL interagissent avec de larges structures turbulentes qui peuvent, pour des intensités relativement élevées, favoriser un mécanisme de transition non linéaire au lieu du mécanisme classique de transition par stries laminaires. Comparées au Novec, les CL d'air se révèlent légèrement plus instables mais conservent globalement des caractéristiques similaires, notamment en ce qui concerne les mécanismes de transition observés. Enfin, l'écoulement autour d'une configuration idéalisée d'aube est abordé au moyen de simulations DDES (Delayed Detached-Eddy Simulations), permettant une analyse fine des phénomènes instationnaires. À mesure que la non-idéalité de l'écoulement augmente, le rapport de pression diminue et les pertes augmentent. Comparativement à l'air, la capacité thermique élevée du Novec réduit les fluctuations de température, éliminant ainsi le phénomène dit de séparation d'énergie, tout en accentuant les fluctuations de pression dans le sillage. En comparaison avec les DDES, les simulations RANS conduisent à une sous-estimation des pertes d'environ 20%<br>Organic Rankine Cycle (ORC) systems appear as one of the solutions to answer the current energy and environmental challenges, owing to their significant potential for generating power. A key component for ORC is the expander, most often a turbine. For small systems, the latter works in the transonic to supersonic regimes and can be affected by the properties of the organic vapor used and exhibit strong non-ideal effects. In the present study, we investigate boundary layer (BL) transitions and losses mechanism in turbines under conditions representative of ORC for the organic vapor Novec649. We begin by reporting the first direct numerical simulation (DNS) and large-eddy simulations (LES) of transitional and turbulent BL of Novec at high-subsonic conditions. In the turbulent state, the profiles of dynamic flow properties are little affected by the gas properties and remain very close to incompressible DNS, despite the high-subsonic flow speed and even if genuine but very small compressibility effects are present. Our LES strategy is validated against the reference DNS and is used to investigate the influence of forcing frequency and amplitude on the established turbulent state. Then, for the first time, we investigate freestream turbulence (FST)-induced transition of dense-gas BL on flat plates and around the leading-edge of a turbine by means of LES. Due to the high Reynolds number conditions, the thin BL experience large-scale incoming turbulent structures which can, for relatively high intensities, promote a non-linear transition mechanism instead of the classical laminar streak transition mechanism. Compared to Novec flows, air BL are found to be slightly more unstable but retains overall similar characteristics, in particular concerning the transition mechanisms observed. Finally, the flow around an idealized blade vane configuration is tackle by means of Delayed Detached-Eddy Simulations (DDES), allowing fine-detail analysis of unsteady flow phenomena. As the non-ideality of the flow increases, a lower pressure ratio is achieved and the losses increases. With regards to air, Novec's high heat capacity reduces temperature fluctuations, suppressing the so-called energy separation phenomena, while accentuating pressure fluctuations in the wake. Compared to DDES, RANS simulations leads to an underestimation of the losses by about 20%

This thesis focused on the transition from university education to the first year of teaching. This may be a difficult transition, with several researchers reporting that 20% to 25% of newly qualified teachers do not teach beyond the first five years (Fimian & Blanton, 1987; Goddard & O'Brien, 2003a; Keeffe, Patton, & Spooner-Lane, 2005; Mackel, 2002; Stevens, Parker, & Burroughs, 2007), and that some teachers may experience symptoms of burnout after just eight months of employment (Fimian & Blanton, 1987; Goddard & O'Brien, 2003a, 2003b, 2006; O'Brien, O'Keeffe, & Goddard, 2008). The aim of this thesis was to examine graduate preparedness for teaching, and identify a set of skills and personal resources that may ameliorate burnout and turnover intentions during the first year of employment. Theories of Person-Environment Fit, along with the adaptation approach to stress, were adopted as conceptual frameworks for the thesis, and possible determinants of Demands-Abilities and Supplies-Values Fit were examined as resources that may enhance graduate preparedness and prevent burnout and turnover intentions. More specifically, graduates‟ perceptions of their own competency (perceived competency), their teaching self-efficacy and the training pathways they had followed to obtain their qualifications were considered as factors that may enhance Demands-Abilities Fit; while the graduates‟ sense of commitment to their careers (career commitment), their expectations regarding the rewards associated with teaching (reward expectations) and their expectations of the difficulties they would face in the workplace (challenge expectations) were considered as factors that may impact on Supplies-Values Fit.<br>Thesis (PhD Doctorate)<br>Doctor of Philosophy in Organisational Psychology (PhD OrgPsych)<br>School of Psychology<br>Griffith Health<br>Full Text

At present the field of molecular electronics - also known as molecular semiconductors, organic semiconductors, plastic electronics or organic electronics - is dominated by organic materials, both polymeric and molecular, with much less attention being focused on transition metal based complexes despite the advantages they can offer. Such advantages include tuneable frontier orbitals through the ligand/metal interaction and the ability to generate stable paramagnetic species. Devices containing radical materials are particularly interesting in order to examine the interplay between conduction and spin - an effect which is not yet properly understood but can give rise to exotic behaviour. A series of homoleptic, bis-ligand Ni(II) and Cu(II) complexes were prepared using three structurally related phenolic oxime ligands, 2-hydroxy-5-t-octylacetophenone oxime (t-OctsaoH), 2-hydroxy-5-n-propylacetophenone oxime (n-PrsaoH) and 2- hydroxyacetophenone oxime (HsaoH). The complexes were characterised by single-crystal X-ray diffraction, cyclic voltammetry, UV/Vis spectroscopy, field-effect-transistor measurements, DFT/TD-DFT calculations and in the case of the paramagnetic species, EPR and magnetic susceptibility. Variation of the substituent on the ligand from t-octyl to n-propyl to H enabled electronic isolation of the complexes in the crystal structures of M(t-OctsaoH)2, which contrasted with π-stacking interactions observed in the crystal packing of M(n-PrsaoH)2 and of M(HsaoH) (M = Ni, Cu). This was further evidenced by comparing the antiferromagnetic interactions observed in samples of Cu(n-PrsaoH)2 and Cu(HsaoH)2 with the ideal paramagnetic behaviour for Cu(t-OctsaoH)2 down to 1.8 K. Despite isostructural single crystal structures for M(n-PrsaoH)2, thin-film X-ray diffraction and SEM revealed different morphologies depending on the metal and the deposition method employed. However, the complexes of M(n-PrsaoH)2 and M(HsaoH) failed to demonstrate significant charge transport in an FET device despite displaying the ability to form π- stacking structures. A series of planar Ni(II), Cu(II) and Co(II) dibenzotetraaza[14]annulenes (dbtaa) and dinapthotetraaza[14]annulenes (dntaa) were synthesised and studied crystallographically, optically, electrochemically and magnetically. Thin films of each of these complexes have been prepared by vacuum deposition to evaluate the field-effect transistor (FET) performance as well as the morphology and crystallinity of the film formed. Single crystal data revealed that Ni(dbtaa) and Cu(dbtaa) are isomorphous to each other, with Co(dbtaa) displaying a different crystallographic packing. The electrochemistry and UV/Vis absorption studies indicate the materials are redox active and highly coloured, with molar extinction coefficients as large as 80,000 M-1cm-1 in the visible region. The paramagnetic Cu(II) and Co(II) complexes display weak 1-dimensional antiferromagnetic interactions and were fit to the Bonner-Fisher chain model. The data revealed that the Co(II) species possesses much stronger magnetic exchange interactions compared with the Cu(II) complex. Each of the materials formed polycrystalline films when vacuum deposited and all showed ptype field-effect transistor behaviour, with modest charge carrier mobilities in the range of 10-5 to 10-9 cm2 V-1 s-1 . SEM imaging of the substrates indicates that the central metal ion, and its sublimation temperature, has a crucial role in defining the morphology of the resulting film. Structurally related Cu(II) and Ni(II) dithiadiazoletetraaza[14]annulene (dttaa) macrocycles were synthesised and studied in the context of their thin film electrochemical, conducting and morphological properties. Both the Ni(II) and Cu(II) complexes were found to be volatile under reduced pressure, which allowed crystals of both materials to be grown and the single crystal structures solved. Interestingly, the crystal packing of these heterocyclic macrocycles varies depending on whether the central metal ion is Cu(II) or Ni(II), which is in contrast to the analogous dibenzotetrazaannulenes complexes. Soluble Ni(II) analogues containing benzoyl groups on the meso- positions of the macrocycle (dttaaBzOR) were also prepared and contrasted with the insoluble Ni(dttaa) complexes in terms of their solution optical and electrochemical properties. Thin film electrochemical studies of Cu(dttaa) and Ni(dttaa) showed chemically reversible oxidative processes but on scanning to reductive potentials the films disintegrated almost immediately as the bulky counter tetrabutylammonium cation entered the thin film. FET studies undertaken on polycrystalline films of both complexes, using various device configurations and surface treatments, failed to realise any gate effect. Thin film XRD measurements indicate that films of both complexes formed by vacuum deposition are crystalline and contain a mixture of molecular alignments, with molecules aligning “edge on” and “face down” to the substrate. SEM imaging failed to effectively resolve the morphology of the films implying the sizes of the crystallites are small, which may help to explain the lack of FET effect. A series of bis-ligand diimine Ni, Cu and Pd complexes have been synthesised from the ligand 4,5-bis(dodecyloxy)benzene-1,2-diamine (dbdaH2). The same ligand was also used to prepare a series of soluble Cu(II) and Ni(II) tetraaza[14]annulene macrocycles. All the bis-ligand diimine complexes were found to suffer from instability in air due to the ease at which the complexes are oxidised. The Ni complex, Ni(dbda)2, was found to display a NIR transition in the region of 971 to 1024 nm depending on the polarity of the solvent that the molecule is dissolved in. Solution electrochemistry studies of Ni(dbda)2 reaffirmed the facile nature of the first oxidative process, with the HOMO energy calculated at -4 eV by hybrid-DFT. This compound failed to yield semiconducting behaviour in an FET device despite the use of surface treatments aimed at promoting suitable molecular alignment across the conducting channel.

Thesis (M.A.)--Kent State University, 2010.<br>Title from PDF t.p. (viewed May 26, 2010). Advisor: Robyn Parker. Keywords: organizational socialization; proactive newcomers; nontraditional graduate students; socialization tactics. Includes bibliographical references (p. 114-122).

Sierra Leone, one of the world's poorest countries, is still recovering from a protracted civil war in which diamonds were implicated as the main source of financing for rebel activity. The view that diamonds still present a significant threat in the post-conflict period are based on fears that the high numbers of youth gangs (principally comprised of ex-combatants and school dropouts) in mining camps could threaten the delicate peace that was so difficult to establish. But despite growing concerns over the sector's growth, minimal research has been carried out to identify what drives youths to participate in the sector. Moreover, the country's Poverty Reduction Strategy Paper (PRSP) and allied policies fail to articulate what ultimately motivates youths to move to the mines or the extent to which these individuals depend on the sector for their livelihoods. A broadened understanding of these drivers is an important first step towards designing effective policies for poverty reduction, as well as minimising the probability of future civil violence. It is against this background that this thesis examines prevailing livelihood diversification patterns among youths m diamondiferous regions of Sierra Leone, and critically analyses the policy implications of their movements. The thesis draws upon research carried out in Kono District, which has the highest concentration of artisanal miners in Sierra Leone. Relevant primary documents, as well as feedback from interviews with key informants, focus group discussions with youth, and life histories of selected miners informed the analysis. The thesis concludes that there is no single factor driving youth movement into Sierra Leone's diamond mining camps: that migration is largely determined by individual circumstances. The country's youth diggers, therefore, should no longer be viewed as a iii homogenous entity similar in the way in which they are categorised in the literature and by policy makers. A distinct pattern, however, emerged from the analysis, which can be used to categorise particular individuals in the camps visited: 1) those looking to 'get rich quick', most of whom are ex-combatants; and 2) those driven by hardship, the majority of whom are farmers originating from the North of the country ('Northerners'), who, unlike most ex- combatants interviewed, have migrated to diamond-rich communities such as Kono to escape poverty. Despite carrying out the bulk of the laborious mining activity in Kono, most of the youth diggers (both ex-combatants and Northerners) consulted remain poverty-stricken. The lack of required skills for gainful employment, high illiteracy rates, solid networks and a sense of 'shame' have trapped many youth diggers in these camps. This is problematic from a policy standpoint because no single aspect of the country's PRSP attempts to address the very different issues and circumstances facing ex-combatants and Northerners. Further, the major initiatives implemented by Government and donors to improve the welfare of the country's diamond diggers and dependent communities have done little to address the specific problems facing youth diggers. The findings suggest there is a need for increased collaboration between key stakeholders, including the Government of Sierra Leone, large-scale mining companies, non- governmental organisations and local leaders. Specifically, there is need to broaden understanding of the dynamics on the ground and to enhance the capacity of these diggers to pursue alternative livelihoods. To achieve this, a broad policy mix is needed - specifically, a blueprint that emphasises the implementation of more sustainable alternative livelihoods, farm and non-farm, that would appeal to a range of youths (Northerners and ex-combatants).

Dans le cadre de cette thèse, nous avons réalisé l’étude de systèmes amorphes moléculaires chiraux en évaluant leur vieillissement, leur mobilité ainsi que leur capacité à recristalliser en fonction de la composition énantiomérique du matériau. Pour limiter les facteurs additionnels à la chiralité, ce travail s’est concentré sur des systèmes modèles formant des conglomérats stables : N-acetyl-α-methylbenzylamine (Nac-MBA) et 5-ethyl-5-methylhydantoin (12H). De ces travaux il ressort que l’impact le plus spectaculaire de la chiralité est exprimé dans la propension à la cristallisation ou l’habilité à former un verre (qui augmente de façon inversement proportionnelle de l’excès enantiomérique (ee)). Les cinétiques de vieillissement sont implicitement impactées par l’ee : Celles-ci sont plus lentes pour les ee importants. Enfin, il semble que les processus de relaxation ainsi que les temps associés soient identiques quelle que soit l’ee, bien que le comportement à la cristallisation soit lui significativement impacté. A noter que la signature la plus manifeste de la chiralité dans l’état amorphe du Nac-MBA s’exprime dans l’intensité diélectrique des processus D et α<br>In the framework of this thesis, we carried out the study of amorphous chiral molecular systems by evaluating their molecular mobility, the evolution of physical properties during aging and the recrystallization behavior as function of the initial enantiomeric excess (ee). In order to avoid factors additional to chirality itself, we focused on enantiomeric systems forming stable conglomerates (full chiral discrimination in the solid state) by choosing two model compounds: 5-ethy-5-methylhydantoin (12H) and N-acetyl-α-methylbenzylamine (Nac-MBA). From this thesis it was shown that the most spectacular effects of chirality in the amorphous state is expressed in the GFA or the crystallization propensity. The GFA increases as the ee decreases. The kinetics of physical aging is implicitly impacted by chirality. Glassy pure enantiomer requires more time to reach equilibrium than that of an intermediate composition. This situation is hypothetically due to constraints effects mostly resulting from a strong nucleation behavior in the glass state at high ee. Furthermore, the time scale of all the processes (D, α, βJG, γ) and the evolution of their temperature dependency are approximatively identical even though the crystallization behavior is highly impacted by ee. it seems that molecular mobility would not be a key parameter in the crystallization behavior of Nac-MBA. The main expression of chirality in amorphous Nac-MBA is evidenced in the signature of the dielectric strength of both D and α processes