Letteratura scientifica selezionata sul tema "Transition FST"
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Articoli di riviste sul tema "Transition FST"
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Nakagawa, Kosuke, Takahiro Tsukahara e Takahiro Ishida. "DNS Study on Turbulent Transition Induced by an Interaction between Freestream Turbulence and Cylindrical Roughness in Swept Flat-Plate Boundary Layer". Aerospace 10, n. 2 (30 gennaio 2023): 128. http://dx.doi.org/10.3390/aerospace10020128.
Testo completoAbstract (sommario):
Laminar-to-turbulent transition in a swept flat-plate boundary layer is caused by the breakdown of the crossflow vortex via high-frequency secondary instability and is promoted by the wall-surface roughness and the freestream turbulence (FST). Although the FST is characterized by its intensity and wavelength, it is not clear how the wavelength affects turbulent transitions and interacts with the roughness-induced transition. The wavelength of the FST depends on the wind tunnel or in-flight conditions, and its arbitrary control is practically difficult in experiments. By means of direct numerical simulation, we performed a parametric study on the interaction between the roughness-induced disturbance and FST in the Falkner–Skan–Cooke boundary layer. One of our aims is to determine the critical roughness height and its dependence on the turbulent intensity and peak wavelength of FST. We found a suppression and promotion in the transition process as a result of the interaction. In particular, the immediate transition behind the roughness was delayed by the long-wavelength FST, where the presence of FST suppressed the high-frequency disturbance emanating from the roughness edge. Even below the criticality, the short-wavelength FST promoted a secondary instability in the form of the hairpin vortex and triggered an early transition before the crossflow-vortex breakdown with the finger vortex. Thresholds for the FST wavelengths that promote or suppress the early transition were also discussed to provide a practically important indicator in the prediction and control of turbulent transitions due to FST and/or roughness on the swept wing.
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OVCHINNIKOV, VICTOR, MEELAN M. CHOUDHARI e UGO PIOMELLI. "Numerical simulations of boundary-layer bypass transition due to high-amplitude free-stream turbulence". Journal of Fluid Mechanics 613 (1 ottobre 2008): 135–69. http://dx.doi.org/10.1017/s0022112008003017.
Testo completoAbstract (sommario):
Direct numerical simulations (DNS) of bypass transition due to high-amplitude free-stream turbulence (FST) are carried out for a flat-plate boundary layer. The computational domain begins upstream of the plate leading edge and extends into the fully turbulent region. Thus, there is noad hoctreatment to account for the initial ingestion of FST into the laminar boundary layer. We study the effects of both the FST length scale and the disturbance behaviour near the plate leading edge on the details of bypass transition farther downstream. In one set of simulations, the FST parameters are chosen to match the ERCOFTAC benchmark case T3B. The inferred FST integral length scaleL11is significantly larger (RL=UL11/ν = 6580) than that employed in previous simulations of bypass transition (RL≃ 1000). An additional set of simulations was performed atRL= 1081 to compare the transition behaviour in the T3B case with that of a smaller value of FST length scale. The FST length scale is found to have a profound impact on the mechanism of transition. While streamwise streaks (Klebanoff modes) are observed at both values of the FST length scale, they appear to have clear dynamical significance only at the smaller value ofRL, where transition is concomitant with streak breakdown. For the T3B case, turbulent spots form upstream of the region where streaks could be detected. Spot precursors are traced to quasi-periodic spanwise structures, first observed as short wavepackets in the wall-normal velocity component inside the boundary layer. These structures are reoriented to become horseshoe vortices, which break down into young turbulent spots. Two of the four spots examined for this case had a downstream-pointing shape, similar to those found in experimental studies of transitional boundary layers. Additionally, our simulations indicate the importance of leading-edge receptivity for the onset of transition. Specifically, higher fluctuations of the vertical velocity at the leading edge of the plate result in higher levels of streamwise Reynolds stress inside the developing boundary layer, facilitating breakdown to turbulence.
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Verberck, B., A. V. Nikolaev e K. H. Michel. "Theoretical Model for the Structural Phase Transition and the Metal–Insulator Transition in Polymerized KC60". Fullerenes, Nanotubes and Carbon Nanostructures 12, n. 1-2 (2 gennaio 2005): 243–52. http://dx.doi.org/10.1081/fst-120027164.
Testo completo
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Hosseinverdi, Shirzad, e Hermann F. Fasel. "Role of Klebanoff modes in active flow control of separation: direct numerical simulations". Journal of Fluid Mechanics 850 (10 luglio 2018): 954–83. http://dx.doi.org/10.1017/jfm.2018.489.
Testo completoAbstract (sommario):
Our previous research has shown that an active flow control strategy using two-dimensional (2-D) harmonic blowing and suction with properly chosen frequency and amplitude can significantly reduce the separation region, delay transition to turbulence and can even relaminarize the flow. How such effective flow control for transition delay and relaminarization is affected by free-stream turbulence (FST) remains an open question. In order to answer this question, highly resolved direct numerical simulations (DNS) are carried out where very low-amplitude isotropic FST fluctuations are introduced at the inflow boundary of the computational domain. With FST the effectiveness of the flow control is not diminished, and the extent of the separated flow region is reduced by the same amount as for the zero FST case. However, a striking difference observed in the DNS is the fact that in the presence of even very low levels of FST, the flow transitions shortly downstream of the reattachment location of the bubble, contrary to the case without FST. It appears that this different behaviour for even very small levels of FST is caused by an interaction between the high-amplitude 2-D disturbances introduced by the flow control forcing and 3-D Klebanoff modes (K-modes) that are generated by the FST. The streamwise elongated streaks due to the K-modes cause a spanwise-periodic modulation of the basic flow and subsequently of the primary 2-D wave. The disturbances associated with this modulation exhibit strong growth and initiate the breakdown process to turbulence. Linear secondary instability investigations with respect to low-frequency 3-D disturbances are carried out based on the linearized Navier–Stokes equations. The response of the forced flow to the low-frequency 3-D disturbances reveals that the time-periodic base flow is unstable with respect to a wide range of 3-D modes. In particular, the wavelength associated with the spanwise spacing of the K-mode falls into the range of, and is in fact very close to, the most unstable 3-D disturbances. Results from the secondary instability analysis and the comparison with DNS results, support the conjecture that the forcing amplitude has a major impact on the onset and amplification rate of the K-modes: lowering the forcing amplitude postpones the onset of the growth of the K-modes and reduces the growth rate of the K-modes for a given FST intensity. The net effect of these two events is a delay of the transition onset. Nevertheless, the instability mechanism that governs the transition process is the same as previously identified, i.e. interaction of the K-mode and 2-D primary wave. Furthermore, for low levels of FST, the amplitude of the low-frequency K-modes scales linearly with the FST intensity in the approach boundary layer up to the secondary instability regime.
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Hosseinverdi, Shirzad, e Hermann F. Fasel. "Numerical investigation of laminar–turbulent transition in laminar separation bubbles: the effect of free-stream turbulence". Journal of Fluid Mechanics 858 (12 novembre 2018): 714–59. http://dx.doi.org/10.1017/jfm.2018.809.
Testo completoAbstract (sommario):
The role of free-stream turbulence (FST) in the hydrodynamic instability mechanisms and transition to turbulence in laminar separation bubbles (LSBs) was investigated using direct numerical simulations (DNS). Towards this end, a set of highly resolved DNS have been carried out, where isotropic FST fluctuations with intensities from 0.1 % to 3 % are introduced to investigate the relevant physical mechanisms governing the interaction of separation and transition in LSBs. For disturbance-free simulations, i.e. without FST, laminar–turbulent transition involves a Kelvin–Helmholtz (KH) instability of the separated shear layer. For LSBs subjected to FST, vortical FST fluctuations penetrate the approaching attached laminar boundary layer upstream of the separation location and induce slowly growing low-frequency disturbances, so-called Klebanoff (K) modes, which cause a spanwise modulation with a distinct spanwise wavelength. Simultaneously, the FST enhances the initial levels of instability waves with frequencies in the frequency range of the KH instability, but at much smaller amplitude levels compared to the K-modes. Results from the calculations based on the linearized Navier–Stokes equations and comparison with DNS results reveal that the K-mode exhibits exponential growth in the separated shear layer until it reaches a peak amplitude. At the same time, two-dimensional (2D) disturbance waves are also exponentially amplified, in fact at larger growth rate compared to the K-mode, due to the primary (convective) shear-layer instability mechanism until they saturate downstream of the peak amplitude associated with the K-mode. Therefore, based on detailed spectral analysis and modal decompositions for the separation bubbles investigated, the transition process is the result of two different mechanisms: (i) strong amplification of high-frequency (order of the shedding frequency), essentially 2D or weakly oblique fluctuating disturbances and (ii) low-frequency, three-dimensional K-modes caused by FST. Depending on the intensity of the FST, one of these mechanisms would dominate the transition process, or both mechanisms act together and contribute simultaneously. The net effect of these two events is an acceleration of transition for an increased level of FST intensity, which in turn leads to a reduction of the extent of the separation bubble in streamwise and wall-normal directions. The ‘roll-up’ into spanwise large-scale vortical structures resulting from the shear-layer instability, and the eventual breakdown of these structures, strongly contribute to the reattachment process. The spanwise coherence of these ‘rollers’ deteriorates due to the presence of large-amplitude K-modes, thus effectively weakening their strength for high levels of FST intensities ($Tu>1\,\%$).
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Gall, N. R., E. V. Rut'kov e A. Ya Tontegode. "C60DECOMPOSITION ON SOME TRANSITION METAL AND SEMICONDUCTOR SURFACES". Fullerene Science and Technology 9, n. 2 (15 aprile 2001): 241–46. http://dx.doi.org/10.1081/fst-100102971.
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Konarev, Dmitri V., Gunzi Saito e Rimma N. Lyubovskaya. "Singlet‐Triplet Transition in the C60 2− Dianion". Fullerenes, Nanotubes and Carbon Nanostructures 12, n. 1-2 (2 gennaio 2005): 147–54. http://dx.doi.org/10.1081/fst-120027148.
Testo completo
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Balzer, Wolfgang, e H. F. Fasel. "Numerical investigation of the role of free-stream turbulence in boundary-layer separation". Journal of Fluid Mechanics 801 (21 luglio 2016): 289–321. http://dx.doi.org/10.1017/jfm.2016.424.
Testo completoAbstract (sommario):
The aerodynamic performance of lifting surfaces operating at low Reynolds number conditions is impaired by laminar separation. In most cases, transition to turbulence occurs in the separated shear layer as a result of a series of strong hydrodynamic instability mechanisms. Although the understanding of these mechanisms has been significantly advanced over the past decades, key questions remain unanswered about the influence of external factors such as free-stream turbulence (FST) and others on transition and separation. The present study is driven by the need for more accurate predictions of separation and transition phenomena in ‘real world’ applications, where elevated levels of FST can play a significant role (e.g. turbomachinery). Numerical investigations have become an integral part in the effort to enhance our understanding of the intricate interactions between separation and transition. Due to the development of advanced numerical methods and the increase in the performance of supercomputers with parallel architecture, it has become feasible for low Reynolds number application ($O(10^{5})$) to carry out direct numerical simulations (DNS) such that all relevant spatial and temporal scales are resolved without the use of turbulence modelling. Because the employed high-order accurate DNS are characterized by very low levels of background noise, they lend themselves to transition research where the amplification of small disturbances, sometimes even growing from numerical round-off, can be examined in great detail. When comparing results from DNS and experiment, however, it is beneficial, if not necessary, to increase the background disturbance levels in the DNS to levels that are typical for the experiment. For the current work, a numerical model that emulates a realistic free-stream turbulent environment was adapted and implemented into an existing Navier–Stokes code based on a vorticity–velocity formulation. The role FST plays in the transition process was then investigated for a laminar separation bubble forming on a flat plate. FST was shown to cause the formation of the well-known Klebanoff mode that is represented by streamwise-elongated streaks inside the boundary layer. Increasing the FST levels led to accelerated transition, a reduction in bubble size and better agreement with the experiments. Moreover, the stage of linear disturbance growth due to the inviscid shear-layer instability was found to not be ‘bypassed’.
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He, S., e M. Seddighi. "Turbulence in transient channel flow". Journal of Fluid Mechanics 715 (9 gennaio 2013): 60–102. http://dx.doi.org/10.1017/jfm.2012.498.
Testo completoAbstract (sommario):
AbstractDirect numerical simulations (DNS) are performed of a transient channel flow following a rapid increase of flow rate from an initially turbulent flow. It is shown that a low-Reynolds-number turbulent flow can undergo a process of transition that resembles the laminar–turbulent transition. In response to the rapid increase of flow rate, the flow does not progressively evolve from the initial turbulent structure to a new one, but undergoes a process involving three distinct phases (pre-transition, transition and fully turbulent) that are equivalent to the three regions of the boundary layer bypass transition, namely, the buffeted laminar flow, the intermittent flow and the fully turbulent flow regions. This transient channel flow represents an alternative bypass transition scenario to the free-stream-turbulence (FST) induced transition, whereby the initial flow serving as the disturbance is a low-Reynolds-number turbulent wall shear flow with pre-existing streaky structures. The flow nevertheless undergoes a ‘receptivity’ process during which the initial structures are modulated by a time-developing boundary layer, forming streaks of apparently specific favourable spacing (of about double the new boundary layer thickness) which are elongated streamwise during the pre-transitional period. The structures are stable and the flow is laminar-like initially; but later in the transitional phase, localized turbulent spots are generated which grow spatially, merge with each other and eventually occupy the entire wall surfaces when the flow becomes fully turbulent. It appears that the presence of the initial turbulent structures does not promote early transition when compared with boundary layer transition of similar FST intensity. New turbulent structures first appear at high wavenumbers extending into a lower-wavenumber spectrum later as turbulent spots grow and join together. In line with the transient energy growth theory, the maximum turbulent kinetic energy in the pre-transitional phase grows linearly but only in terms of ${u}^{\ensuremath{\prime} } $, whilst ${v}^{\ensuremath{\prime} } $ and ${w}^{\ensuremath{\prime} } $ remain essentially unchanged. The energy production and dissipation rates are very low at this stage despite the high level of ${u}^{\ensuremath{\prime} } $. The pressure–strain term remains unchanged at that time, but increases rapidly later during transition along with the generation of turbulent spots, hence providing an unambiguous measure for the onset of transition.
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Zhang, Guangsheng, Chenghao Wang, Lingmei Jiang, Yibo Wang, Bing Wang, Xiaoxu Wang, Haoran Liu, Lishuai Zong, Jinyan Wang e Xigao Jian. "Low Dielectric Constant Photocurable Fluorinated Poly (Phthalazinone Ether) Ink with Excellent Mechanical Properties and Heat Resistance". Polymers 15, n. 6 (20 marzo 2023): 1531. http://dx.doi.org/10.3390/polym15061531.
Testo completoAbstract (sommario):
The photosensitive resins for 3D printing technology have been widely applied throughout the advanced communication field due to their merits of high molding accuracy and fast processing speed. Regardless, they, in particular, should have better mechanical properties, heat resistance, and dielectric properties. Herein, photocurable fluorinated poly (phthalazinone ether) (FSt-FPPE) was utilized as a prepolymer to improve the performance of photosensitive resin. A series of UV-curable inks named FST/DPGs were prepared with FSt-FPPE and acrylic diluents of different mass fractions. The FST/DPGs were cured into films by UV curing and post-treatment. After curing, their properties were characterized in detail. In terms of heat resistance, glass transition temperature (Tg) could reach 233 °C and the 5% thermal decomposition temperature (Td5%) was 371 °C. The tensile strength surprisingly reached 61.5 MPa, and the dielectric constant (Dk) could be significantly reduced to 2.75. Additionally, FST/DPGs were successfully employed in UV-assisted direct writing (DIW) to print 3D objects that benefited from their commendable fluidity and rapid curing speed. A stiff cylinder sample with a smooth surface and distinct pattern was ultimately obtained, indicating their remarkable 3D printing adaptation. Such photosensitive resin for UV-assisted DIW exhibits tremendous potential in the electronic industry.
Tesi sul tema "Transition FST"
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Bienner, Aurélien. "Real-gas effects on freestream induced transition and losses in ORC turbine flows". Electronic Thesis or Diss., Paris, HESAM, 2024. http://www.theses.fr/2024HESAE016.
Testo completoAbstract (sommario):
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%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%
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Westwell, Jeremy R. "Fast infrared spectroscopy of excited states". Thesis, University of Nottingham, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262165.
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Yates, Kelley Anne. "Graduate Preparedness for the Transition to Teaching: An Examination of Predictors of Transitional Difficulties during the First Year of Employment". Thesis, Griffith University, 2011. http://hdl.handle.net/10072/367115.
Testo completoAbstract (sommario):
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.Thesis (PhD Doctorate)
Doctor of Philosophy in Organisational Psychology (PhD OrgPsych)
School of Psychology
Griffith Health
Full Text
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Richards, Martyn W. "Chemical reactions of caesium, tellurium and oxygen with transition metal alloys". Thesis, University of Nottingham, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.276201.
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Whyte, Alex. "Thin film studies of planar transition metal complexes". Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/7966.
Testo completoAbstract (sommario):
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.
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Hughes, Kevin Michael. "A mission in transition: Legitimacy, philosophical fit and student affairs cultures". W&M ScholarWorks, 2004. https://scholarworks.wm.edu/etd/1550154095.
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Mitchell, Julie B. "Exploring Midcareer Women's Graduate School Transition: Department Socialization Tactics and Perceived Fit". [Kent, Ohio] : Kent State University, 2010. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=kent1270745471.
Testo completoAbstract (sommario):
Thesis (M.A.)--Kent State University, 2010.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).
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Conteh, Emmanuel. "Youth livelihoods in transition : poverty, 'fast money' and diamonds in Kono District, Sierra Leone". Thesis, University of Reading, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.553030.
Testo completoAbstract (sommario):
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).
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Atawa, Bienvenu. "Mobilité moléculaire et vieillissement physique des composés amorphes chiraux". Thesis, Normandie, 2018. http://www.theses.fr/2018NORMR125/document.
Testo completoAbstract (sommario):
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 αIn 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
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Bowers, Carla J. "The freshman transition process /". view abstract or download file of text, 2007. http://proquest.umi.com/pqdweb?did=1421620451&sid=1&Fmt=2&clientId=11238&RQT=309&VName=PQD.
Testo completoLibri sul tema "Transition FST"
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St. Antony's College (University of Oxford) e Markaz Muḥammad ʻUmar Bashīr lil-Dirāsāt al-Sūdānīyah, a cura di. Sudan: A long transition into two states. Umm Durmān: Markaz Muḥammad ʻUmar Bashīr lil-Dirāsāt al-Sūdānīyah, 2012.
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Mʼrad, Hatem. Transitions arabes: Révoltes, gouvernance et géopolitique. Tunis: Nirvana, 2018.
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Agency, OECD Nuclear Energy, a cura di. Strategic and policy issues raised by the transition from thermal to fast nuclear systems. Paris: Nuclear Energy Agency, Organisation for Economic Co-operation and Development, 2009.
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K, Rosati Dariusz, a cura di. Transition countries in the first quarter 1998: Widening gap between fast and slow reformers. [Vienna, Austria]: Vienna Institute for International Economic Studies, 1998.
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Agency, OECD Nuclear Energy, a cura di. Strategic and policy issues raised by the transition from thermal to fast nuclear systems. Paris: Nuclear Energy Agency, Organisation for Economic Co-operation and Development, 2009.
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Kreinovich, Vladik. Fast parallel algorithms that compute transitive closure of a fuzzy relation. [Washington, DC?: National Aeronautics and Space Administration, 1993.
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Erkelens, L. J. J. Investigation on MLS approach path interception and transition techniques, Part I: Fast-time computer simulations. Amsterdam: National Aerospace Laboratory, 1985.
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(Kathmandu, Nepal) Media Foundation. Healing the wounds: Stories from Nepal's transitional justice process. Kathmandu: Media Foundation, 2011.
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Yao, Huang, e Zhu Yunkuan, a cura di. Yong you shi jie: Hong tu di zhi qing qing tu wen ji. Kunming Shi: Yunnan min zu chu ban she, 2004.
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Authority, Financial Services. Investigation of complaints against the FSA: Feedback on CP73 and "final" text.Consultation on transitional arrangements. Londoon: Financial Services Authority, 2001.
Cerca il testo completoCapitoli di libri sul tema "Transition FST"
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Bakchinov, A. A., M. M. Katasonov, P. H. Alfredsson e V. V. Kozlov. "Control of Boundary Layer Transition at High Fst by Localized Suction". In IUTAM Symposium on Mechanics of Passive and Active Flow Control, 159–64. Dordrecht: Springer Netherlands, 1999. http://dx.doi.org/10.1007/978-94-011-4199-4_26.
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Bardin, Sébastien, Alain Finkel, Jérôme Leroux e Laure Petrucci. "FAST: Fast Acceleration of Symbolic Transition Systems". In Computer Aided Verification, 118–21. Berlin, Heidelberg: Springer Berlin Heidelberg, 2003. http://dx.doi.org/10.1007/978-3-540-45069-6_12.
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Böller, Florian. "Fast-Track Towards a Hegemonic Transition? COVID-19 and the Decline of US Hegemony". In Hegemonic Transition, 259–80. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-74505-9_13.
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Simon, Sindee L., e Yung P. Koh. "The Glass Transition and Structural Recovery Using Flash DSC". In Fast Scanning Calorimetry, 433–59. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-31329-0_14.
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Gao, Yulai, Bingge Zhao, Bin Yang e Christoph Schick. "Fast Scanning Calorimetry of Phase Transitions in Metals". In Fast Scanning Calorimetry, 691–721. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-31329-0_21.
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Ma, Jianfeng, Changguang Wang e Zhuo Ma. "Security Protocols for Fast BSS transition". In Security Access in Wireless Local Area Networks, 135–73. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-642-00941-9_4.
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Cangialosi, Daniele, Angel Alegría e Juan Colmenero. "Cooling Rate Dependent Glass Transition in Thin Polymer Films and in Bulk". In Fast Scanning Calorimetry, 403–31. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-31329-0_13.
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White, Andrew S., Kate N. Sirota, Scott R. Frohn, Sara E. Swenson e Kathleen Moritz Rudasill. "Children’s Temperament and the Transition to Kindergarten: A Question of “Fit”". In Kindergarten Transition and Readiness, 225–45. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-90200-5_10.
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Combs, Danny. "Slow to Go Fast". In Supporting Neurodivergent and Autistic People for Their Transition into Adulthood, 77–82. New York: Routledge, 2023. http://dx.doi.org/10.4324/9781003353959-15.
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Berg, Jana. "Which Person Is Presumed to Fit the Institution? How Refugee Students’ and Practitioners’ Discursive Representations of Successful Applicants and Students Highlight Transition Barriers to German Higher Education". In European Higher Education Area: Challenges for a New Decade, 211–27. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-56316-5_15.
Testo completoAbstract (sommario):
Abstract During recent years, German higher education institutions implemented a variety of support programs for refugees on their way to higher education. This newly highlighted questions of widening participation and informal as well as formal access barriers to higher education. This paper looks into discourses on successful students as a form of knowledge that implicitly highlights transition barriers to higher education. The qualitative study is based on expert interviews with teachers, program coordinators and student counsellors as well as interviews with prospective refugee students in a case study of a preparatory college (‘Studienkolleg’) and a university in a case study of one city in Germany. They are analysed using Keller’s (Forum qualitative Sozialforschung/Forum Qualitative Social Research 8(2), Art. 19:1–32, 2007) approach to discourse analysis. The paper describes personal, institutional and structural characteristics of ideal higher education transitions. Institutional presuppositions and assumptions about individual characteristics, the social organisation of time, academic practices and knowledges as well as discursively represented norms are discussed as crucial factors influencing higher education transitions. The paper ends with a working hypothesis on the influence of discourses on transitions and recommends that institutional settings should develop more awareness of and adapt to diverse applicants and students in order to widen access to higher education.
Atti di convegni sul tema "Transition FST"
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Delbari, Mohamadreza, Robin Neuder, Alejandro Jiménez-Sáez, Arash Asadi e Vahid Jamali. "Fast Transition-Aware Reconfiguration of Liquid Crystal-Based RISs". In 2024 IEEE International Conference on Communications Workshops (ICC Workshops), 214–19. IEEE, 2024. http://dx.doi.org/10.1109/iccworkshops59551.2024.10615422.
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Jain, Ishita, S. Katiyar e Subrata Sarkar. "Influence of Varying Freestream Turbulence on Flow Transition Over Distributed Surface Roughness". In ASME Turbo Expo 2024: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2024. http://dx.doi.org/10.1115/gt2024-124283.
Testo completoAbstract (sommario):
Abstract High-fidelity Large Eddy Simulations (LES) are used to investigate the influence of distributed surface roughness on the spatially developing laminar boundary layer under varying freestream turbulence (FST) levels of 0.07 to 6%. The inlet Reynolds number based on the momentum thickness and freestream velocity is 360. The square-shaped (SQ) riblets that are employed in the present study are homogeneous in the spanwise direction and distributed in a series along the streamwise length. The aspect ratio (s/k) considered here is 3, where k is the riblet height, and s is the longitudinal spacing between the consecutive rows of riblets. The instantaneous flow structures reveal a Λ vortex-induced breakdown for FST levels below 3.2%, attributed to the near wall streamwise vortices arising from embedded recirculation regions between riblets. On the contrary, at a high FST level of 6%, the flow is characterized by low- and high-speed streaks generated via shear sheltering, resulting in the turbulent flow downstream. Moreover, an exponential growth of velocity fluctuations is apparent for a lower FST, which becomes algebraic for a higher FST. The onset and end of transition shift progressively upstream with an increase in FST. Interestingly, the flow features exhibit self-similarity in the turbulent region irrespective of FST levels.
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Wang, Taiyang, Yaomin Zhao, John Leggett e Richard D. Sandberg. "Direct Numerical Simulation of an HPT Stage: Unsteady Boundary Layer Transition and the Resulting Flow Structures". In ASME Turbo Expo 2023: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2023. http://dx.doi.org/10.1115/gt2023-102213.
Testo completoAbstract (sommario):
Abstract In the present study, we investigate the unsteady boundary layer transition based on the direct numerical simulation (DNS) database of a high-pressure turbine (HPT) stage (Zhao and Sandberg, GT2021-58995), focusing on the transition mechanisms on the rotor blade, which are affected by the incoming periodic wakes and also by the background free-stream turbulence (FST) introduced at the inlet. Based on the fully-resolved DNS flow fields, we are able to provide detailed analysis of the flow structures responsible for the transition, and two distinctive paths to laminar-turbulent transition have been identified. The first path is the typical bypass transition via the instability of Klebanoff streaks, which happens when the transition region is not directly affected by the wake. It is noted that the suction-side boundary layer is disturbed at the leading edge, resulting in the formation of streamwise streaks. These streaky structures endure varicose instability in the region with adverse pressure-gradient (APG), then quickly break down into turbulent spots, which then evolves into fully turbulence. The other transition path is a consequence of the direct interaction between the wake structures and the blade boundary layer, when the wake apex starts to affect the transitional region. To be specific, the wake structures seem to directly interact with the separation bubble in the APG region, causing sudden break down into turbulence. The turbulent boundary layer induced by the periodic wake are usually followed by a calmed region as the wake travels away from the passage. It is also observed that the recovery to a calmed region can be impacted by the FST, as the calmed region in case with no FST is much longer compared to cases with stronger FST.
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Matsubara, Masaharu, P. Henrik Alfredsson e K. Johan A. Westin. "Boundary Layer Transition at High Levels of Free Stream Turbulence". In ASME 1998 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/98-gt-248.
Testo completoAbstract (sommario):
Transition to turbulence in laminar boundary layers subjected to high levels of free stream turbulence (FST) can still not be reliably predicted, despite its technical importance, e.g. in the case of boundary layers developing on gas turbine blades. In a series of experiments in the MTL-wind tunnel at KTH the influence of grid-generated FST on boundary layer transition has been studied, with FST-levels up to 6%. It was shown from both flow visualisation and hot-wire measurements that the boundary layer develops unsteady streaky structures with high and low streamwise velocity. This leads to large amplitude low frequency fluctuations inside the boundary layer although the mean flow is still close to the laminar profile. Breakdown to turbulence occurs through an instability of the streaks which leads to the formation of turbulent spots. Accurate physical modelling of these processes seems to be needed in order to obtain a reliable prediction method.
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Rath, P. K. "Uncertainties in nuclear transition matrix elements of neutrinoless ββ decay". In THE 2013 UKM FST POSTGRADUATE COLLOQUIUM: Proceedings of the Universiti Kebangsaan Malaysia, Faculty of Science and Technology 2013 Postgraduate Colloquium. AIP Publishing LLC, 2013. http://dx.doi.org/10.1063/1.4856554.
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Watmuff, Jonathan H. "Effects of Weak Free Stream Nonuniformity on Boundary Layer Transition (Keynote Paper)". In ASME/JSME 2003 4th Joint Fluids Summer Engineering Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/fedsm2003-45685.
Testo completoAbstract (sommario):
Experiments are described in which well-defined FSN (Free Stream Nonuniformity) distributions are introduced by placing fine wires upstream of the leading edge of a flat plate. Large amplitude spanwise thickness variations are present in the downstream boundary layer resulting from the interaction of the laminar wakes with the leading edge. Regions of elevated background unsteadiness appear on either side of the peak layer thickness, which share many of the characteristics of Klebanoff modes, observed at elevated Free Stream Turbulence (FST) levels. However, for the low background disturbance level of the free stream, the layer remains laminar to the end of the test section (Rx ≈ l.4×106) and there is no evidence of bursting or other phenomena associated with breakdown to turbulence. A vibrating ribbon apparatus is used to demonstrate that the deformation of the mean flow is responsible for substantial phase and amplitude distortion of Tollmien-Schlichting (TS) waves. Pseudo-flow visualization of hot-wire data shows that the breakdown of the distorted waves is more complex and occurs at a lower Reynolds number than the breakdown of the K-type secondary instability observed when the FSN is not present.
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Zhang, Lifang, Fei Wang, Jian-Hua Yan e Ke-Fa Cen. "NO concentration sensing at 1.79 μm transition using tunable diode laser absorption spectroscopy". In THE 2013 UKM FST POSTGRADUATE COLLOQUIUM: Proceedings of the Universiti Kebangsaan Malaysia, Faculty of Science and Technology 2013 Postgraduate Colloquium. AIP Publishing LLC, 2014. http://dx.doi.org/10.1063/1.4872112.
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Miki, Kenji, e Ali Ameri. "Improved Prediction of Losses With Large Eddy Simulation in a Low-Pressure Turbine". In ASME Turbo Expo 2021: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/gt2021-59095.
Testo completoAbstract (sommario):
Abstract There is a need to improve predictions of losses resulting from large eddy simulations (LES) of low-pressure turbines (LPT) in gas turbines. This may be done by assessing the accuracy of predictions against validation data and understanding the source of any inaccuracies. LES is a promising approach for capturing the laminar/turbulent transition process in a LPT. In previous studies, the authors utilized LES to model the flow field over a Variable Speed Power Turbine (VSPT) blade and successfully captured characteristic features of separation/reattachment and transition on the suction side at both the cruise (positive incidence) and take-off conditions (negative incidence) and as well, simulated the effect of free-stream turbulence (FST) on those phenomena. The predicted pressure loading profiles agreed well with the experimental data for both a high and a low FST case at a Reynolds number of Reex = 220,000. In this paper, we present wake profiles resulting from computations for a range of FST values. Although the predicted wake profiles for the lowest FST case (Tu = 0.5%) matched the experimental data, at higher FST (Tu = 10–15%,) the wake was wider than the experimentally measured wake and for both cases were displaced laterally when compared to the experimental measurements. In our investigation of the causes of the said discrepancies we have identified important effects which could strongly influence the predicted wake profile. Predicted losses were improved by assuring the validity of the flow solution. This was done by utilizing spectral analysis to scrutinize the dynamic behavior of the wake and determine solution accuracy resulting from low mesh density and low accuracy of convective modeling.
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Menéndez, Javier. "Theoretical uncertainties in the nuclear matrix elements of neutrinoless double beta decay: The transition operator". In THE 2013 UKM FST POSTGRADUATE COLLOQUIUM: Proceedings of the Universiti Kebangsaan Malaysia, Faculty of Science and Technology 2013 Postgraduate Colloquium. AIP Publishing LLC, 2013. http://dx.doi.org/10.1063/1.4861134.
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Cui, J., V. Nagabhushana Rao e P. G. Tucker. "Numerical Investigation of Contrasting Flow Physics in Different Zones of a High-Lift Low Pressure Turbine Blade". In ASME Turbo Expo 2015: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/gt2015-43200.
Testo completoAbstract (sommario):
Using a range of high fidelity large eddy simulations, the contrasting flow physics on the suction surface, pressure surface and endwalls of a low pressure turbine blade (T106A) was studied. The current paper attempts to provide an improved understanding of the flow physics over these three zones under the influence of different inflow boundary conditions. These include: (a) the effect of wakes at low and high turbulence intensity on the flow at mid-span and (b) the impact of the state of the incoming boundary layer on endwall flow features. On the suction surface, the pressure fluctuations on the aft portion significantly reduced at high Free-Stream Turbulence (FST). The instantaneous flow features revealed that this reduction at high FST is due to the dominance of ‘streak-based’ transition over the ‘Kelvin-Helmholtz’ based transition. Also, the transition mechanisms observed over the turbine blade were largely similar to those on a flat plate subjected to pressure gradients. On pressure surface, elongated vortices were observed at low FST. The possibility of the co-existence of both the Görtler instability and the severe straining of the wakes in the formation of these elongated vortices was suggested. While this was true for the cases under low turbulence levels, the elongated vortices vanished at higher levels of background turbulence. At endwalls, the effect of the state of the incoming boundary layer on flow features has been demonstrated. The loss cores corresponding to the passage vortex and trailing shed vortex were moved farther from the endwall with a turbulent boundary layer when compared to an incoming laminar boundary layer. Multiple horse-shoe vortices, which constantly moved towards the leading edge due to a low-frequency unstable mechanism, were captured.
Rapporti di organizzazioni sul tema "Transition FST"
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Guttenberg, S. Fast flux test facility, transition project plan. Office of Scientific and Technical Information (OSTI), novembre 1994. http://dx.doi.org/10.2172/10103903.
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Reisch, Tobias, Jan Hurt, Johannes Stangl, Liuhuaying Yang e Stefan Thurner. Expected Workforce Requirements for the Green Transition. Rat für Forschung und Technologieentwicklung, aprile 2023. http://dx.doi.org/10.22163/fteval.2023.602.
Testo completoAbstract (sommario):
In dieser Arbeit wird die erwartete zusätzliche Arbeitsnachfrage untersucht, die durch das Wachstum der Produktion grüner Produkte in Österreich entstehen wird. Hier schätzen wir ab, wie viele zusätzliche Mitarbeiter benötigt werden und in welchen Wirtschaftssektoren sie beschäftigt sein werden, um die identifizierten Branchen zu fördern. Wir stellen fest, dass Österreichs fünf vielversprechendste Möglichkeiten zur grünen Diversifizierung den größten Arbeitskräftebedarf in den Sektoren "Maschinen und Geräte" sowie "Reparatur von Maschinen und Geräten" verursachen werden. Die insgesamt geschätzte Zunahme der Arbeitsnachfrage in allen Sektoren beträgt etwa 6,30 Mitarbeiter. Die Ergebnisse dieser Studie sind über ein Online-Dashboard zugänglich und können erforscht werden, das die die Untersuchung von maßgeschneiderten Szenarien ermöglicht. Das Dashboard ist veröffentlicht unter: https://ecto.rfte.at/
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Dalabajan, Dante, Ruth Mayne, Blandina Bobson, Hadeel Qazzaz, Henry Ushie, Jacobo Ocharan, Jason Farr et al. Towards a Just Energy Transition: Implications for communities in lower- and middle-income countries. Oxfam, dicembre 2022. http://dx.doi.org/10.21201/2022.9936.
Testo completoAbstract (sommario):
More frequent or intense floods, heatwaves, wildfires, droughts and typhoons devastate people’s homes, livelihoods and the natural world. A clean energy transition is urgently needed to reduce carbon emissions and prevent the impacts worsening. Wealthy countries have the prime historic responsibility for the climate crisis and therefore for its mitigation. But as the clean energy transition gathers speed, it inevitably also impacts lower-income, lower-emitting countries and communities. This research report, written by 20 co-authors from Africa, Asia, Latin America, the Middle East, the US and Europe, investigates the implications of the energy transition for them, and asks how the world can achieve a truly just, as well as fast, transition. The findings highlight the stark choice facing humanity. If the transition is undertaken with justice and respect for communities’ rights at its heart, it offers an unprecedented opportunity to simultaneously mitigate the climate crisis and reduce poverty and inequality. Conversely, an unjust transition, which entrenches or exacerbates inequalities, risks generating public resistance and slowing the transition with devastating human consequences.
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Ahrens L., E. Raka, L. Ratner e S. P. Yamin. Transition Jump Using ? ? Produced by the Polarized Proton Fast Quadrupoles. Office of Scientific and Technical Information (OSTI), luglio 1986. http://dx.doi.org/10.2172/1131538.
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Shoales, Gregory A., e Scott A. Fawaz. E-8/B-707 Wing Station 320 Transition Fit Fastener Finite Element Analysis. Fort Belvoir, VA: Defense Technical Information Center, marzo 2004. http://dx.doi.org/10.21236/ada430478.
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Samach, Alon, Douglas Cook e Jaime Kigel. Molecular mechanisms of plant reproductive adaptation to aridity gradients. United States Department of Agriculture, gennaio 2008. http://dx.doi.org/10.32747/2008.7696513.bard.
Testo completoAbstract (sommario):
Annual plants have developed a range of different mechanisms to avoid flowering (exposure of reproductive organs to the environment) under adverse environmental conditions. Seasonal environmental events such as gradual changes in day length and temperature affect the timing of transition to flowering in many annual and perennial plants. Research in Arabidopsis and additional species suggest that some environmental signals converge on transcriptional regulation of common floral integrators such as FLOWERING LOCUS T (FT). Here we studied environmental induction of flowering in the model legume Medicago truncatula. Similarly to Arabidopsis, the transition to flowering in M. truncatula is hastened by long photoperiods and long periods of vernalization (4°C for 2-3 weeks). Ecotypes collected in Israel retain a vernalization response even though winter temperatures are way above 4°C. Here we show that this species is also highly responsive (flowers earlier) to mild ambient temperatures up to 19°C simulating winter conditions in its natural habitat. Physiological experiments allowed us to time the transition to flowering due to low temperatures, and to compare it to vernalization. We have made use of natural variation, and induced mutants to identify key genes involved in this process, and we provide here data suggesting that an FT gene in M.truncatula is transcriptionally regulated by different environmental cues. Flowering time was found to be correlated with MtFTA and MtFTB expression levels. Mutation in the MtFTA gene showed a late flowering phenotype, while over-expressing MtFTA in Arabidopsis complemented the ft- phenotype. We found that combination of 4°C and 12°C resulted in a synergistic increase in MtFTB expression, while combining 4°C and long photoperiods caused a synergistic increase in MtFTA expression. These results suggest that the two vernalization temperatures work through distinct mechanisms. The early flowering kalil mutant expressed higher levels of MtFTA and not MtFTB suggesting that the KALIL protein represses MtFTA specifically. The desert ecotype Sde Boker flowers earlier in response to short treatments of 8-12oc vernalization and expresses higher levels of MtFTA. This suggests a possible mechanism this desert ecotype developed to flower as fast as possible and finish its growth cycle before the dry period. MtFTA and FT expression are induced by common environmental cues in each species, and expression is repressed under short days. Replacing FT with the MtFTA gene (including regulatory elements) caused high MtFTA expression and early flowering under short days suggesting that the mechanism used to repress flowering under short days has diversified between the two species.The circadian regulated gene, GIGANTEA (GI) encodes a unique protein in Arabidopsis that is involved in flowering mechanism. In this research we characterized how the expression of the M.truncatula GI ortholog is regulated by light and temperature in comparison to its regulation in Arabidopsis. In Arabidopsis GI was found to be involved in temperature compensation to the clock. In addition, GI was found to be involved in mediating the effect of temperature on flowering time. We tested the influence of cold temperature on the MtGI gene in M.truncatula and found correlation between MtGI levels and extended periods of 12°C treatment. MtGI elevation that was found mostly after plants were removed from the cold influence preceded the induction of MtFT expression. This data suggests that MtGI might be involved in 12°C cold perception with respect to flowering in M.truncatula. GI seems to integrate diverse environmental inputs and translates them to the proper physiological and developmental outputs, acting through several different pathways. These research enabled to correlate between temperature and circadian clock in M.truncatula and achieved a better understanding of the flowering mechanism of this species.
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Patterson, P. E. The Complete Fast Fourier Transform and Cascaded Transition-Band Filters to Reduce the Noise of Deconvolution. Office of Scientific and Technical Information (OSTI), gennaio 2000. http://dx.doi.org/10.2172/776348.
Testo completo
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Gamez, Daniel H. Benjamin, Fredrik von Malmborg, Johan Nordensvärd, Martin Björklund, Lina La Fleur e Emma Skogsmo. Politics and Policy Processes for Green Energy Transition and Climate Neutrality: A Project Report. Linköping University Electronic Press, agosto 2024. http://dx.doi.org/10.3384/9789180758079.
Testo completoAbstract (sommario):
This policy report outlines the group research on advocacy, decision-making, and EU policy change towards green energy transition and climate neutrality, focusing on resource- and energy-efficient buildings, as well as energy efficiency more broadly within the EU's Fit for 55 legislative packages. The research also includes analyses of advocacy and decision-making related to EU policy change for decarbonizing maritime shipping. The project explores how stakeholder coalitions shape policies for sustainable environments since decision-making is influenced by stakeholders and conflicts of interest. By providing better insight into EU policy change dynamics, this report offers valuable knowledge that can enhance policymakers' understanding of how to influence future EU policies on energy efficiency and building energy performance, as well as a clean energy transition more broadly, promoting Swedish interests. It highlights the complexity of decision-making in energy efficiency and climate impact reduction within the EU while also underscoring the influence of stakeholders and conflicts of interest. As a result, actors with inadequate grasp of political dynamics can hinder effective energy policy design and implementation, posing challenges to achieving climate goals and sustainable development. Similarly, since negotiations are key to advance regulation, it is found that less politicization and polarization facilitate deliberative negotiations and policy-oriented learning, among other things. Thus, strategic advocacy is crucial for Swedish policymakers aiming to successfully influence future EU energy and climate policies.
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Strambo, Claudia, Patricio Calles Almeida e Elisa Arond. Energy transition ambitions of four national oil and gas companies in South America. Stockholm Environment Institute, novembre 2023. http://dx.doi.org/10.51414/sei2023.059.
Testo completoAbstract (sommario):
This report explores what (if any) diversification strategies national oil and gas companies (NOGCs) are employing to engage in an energy transition, with a focus on four South American countries: Argentina, Brazil, Colombia and Ecuador.The authors identify how four South American NOGCs are preparing to transform in the face of climate change and the energy transition. They do so by looking at these companies’ publicly stated ambitions regarding diversification: they focus in particular on whether and how these companies are leaving fossil fuels behind, as a sign of transforming their core business and moving towards a more structural transformation overall in society. The four South American NOGCs are Ecopetrol (Colombia), Petrobras (Brazil), Yacimientos Petrolíferos Fiscales (YPF, Argentina) and EP Petroecuador (Ecuador). While all four companies are controlled by their national governments, three are also public companies that are traded on domestic and international stock markets. This report can serve as a resource for comparative analysis and to inform transition strategies in oil and gas–producing countries, for energy and finance researchers, professionals working within NOGCs, and policymakers shaping NOGCs’ missions, strategies and investments. Key messages National oil and gas companies, or NOGCs, must transform to survive and fit into a new global dynamic for mitigating the impacts of climate change. While navigating their roles in generating public revenue and domestic employment, enabling public services, and other characteristics, they will also have to overcome institutional barriers in order to accelerate their diversification into non-fossil fuel businesses. Diversification to new low-carbon businesses is a part of but not the priority for decarbonization for four of South America’s NOGCs. These four South American NOGCs have limited capacity to expand into new low-carbon businesses. More research is needed to assess and strengthen South American NOGCs’ preparedness for a transition to a low-carbon future, including factors such as financial, technical and managerial capabilities, and their role in national and global political economies.
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Walsh, Alex. The Contentious Politics of Tunisia’s Natural Resource Management and the Prospects of the Renewable Energy Transition. Institute of Development Studies (IDS), febbraio 2021. http://dx.doi.org/10.19088/k4d.2021.048.
Testo completoAbstract (sommario):
For many decades in Tunisia, there has been a robust link between natural resource management and contentious national and local politics. These disputes manifest in the form of protests, sit-ins, the disruption of production and distribution and legal suits on the one hand, and corporate and government response using coercive and concessionary measures on the other. Residents of resource-rich areas and their allies protest the inequitable distribution of their local natural wealth and the degradation of their health, land, water, soil and air. They contest a dynamic that tends to bring greater benefit to Tunisia’s coastal metropolitan areas. Natural resource exploitation is also a source of livelihoods and the contentious politics around them have, at times, led to somewhat more equitable relationships. The most important actors in these contentious politics include citizens, activists, local NGOs, local and national government, international commercial interests, international NGOs and multilateral organisations. These politics fit into wider and very longstanding patterns of wealth distribution in Tunisia and were part of the popular alienation that drove the uprising of 2011. In many ways, the dynamic of the contentious politics is fundamentally unchanged since prior to the uprising and protests have taken place within the same month of writing of this paper. Looking onto this scene, commentators use the frame of margins versus centre (‘marginalization’), and also apply the lens of labour versus capital. If this latter lens is applied, not only is there continuity from prior to 2011, there is continuity with the colonial era when natural resource extraction was first industrialised and internationalised. In these ways, the management of Tunisia’s natural wealth is a significant part of the country’s serious political and economic challenges, making it a major factor in the street politics unfolding at the time of writing.