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Bibliografie tematiche / L-H transition

Letteratura scientifica selezionata sul tema "L-H transition"

Autore: Grafiati

Pubblicato: 8 giugno 2024

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Articoli di riviste sul tema "L-H transition":

1

Tsui, K. H., e C. E. Navia. "Tokamak L/H mode transition". Physics of Plasmas 19, n. 1 (gennaio 2012): 012505. http://dx.doi.org/10.1063/1.3671975.

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2

Chen, Liang, Guosheng Xu, Lingming Shao, Wei Gao, Yifeng Wang, Yanmin Duan, Shouxin Wang et al. "Comparison of dynamical features between the fast H-L and the H-I-L transition for EAST RF-heated plasmas". Physica Scripta 97, n. 1 (1 gennaio 2022): 015601. http://dx.doi.org/10.1088/1402-4896/ac4635.

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Abstract In this paper, a comparison of dynamical features between the fast H-L and the H-I-L transition, which can be identified by the intermediate phase, or ‘I-phase’, has been made for radio-frequency (RF) heated deuterium plasmas in EAST. The fast H-L transition is characterized by a rapid release of stored energy during the transition transient, while the H-I-L transition exhibits a ‘soft’ H-mode termination. One important distinction between the transitions has been observed by dedicated probe measurements slightly inside the separatrix, with respect to the radial gradient of the floating potential, which corresponds to the E × B flow and/or the electron temperature gradient. The potential gradient inside the separatrix oscillates and persists during the stationary I-phase, and shows a larger amplitude than that before the fast H-L transition. The reduction of the gradient leads to the final transition to the L-mode for both the fast H-L and the H-I-L transition. These findings indicate that the mean E × B flow shear and/or edge electron temperature gradient play a critical role underlying the H-L transition physics. In addition, the back transition in EAST is found to be sensitive to magnetic configuration, where the vertical configuration, i.e., inner strike-point located at vertical target, favours access to the H-I-L transition, while the horizontal shape facilitates achievement of the fast H-L transition. The divertor recycling level normalized to electron density is higher before the fast H-L transition, as compared to that before the I-phase, which strongly suggest that the density of the recycled neutrals is an important ingredient in determining the back transition behaviour.

3

Toda, Shinichiro, Sanae-I. Itoh, Masatoshi Yagi, Kimitaka Itoh e Atsushi Fukuyama. "Probabilistic Nature in L/H Transition". Journal of the Physical Society of Japan 68, n. 11 (15 novembre 1999): 3520–27. http://dx.doi.org/10.1143/jpsj.68.3520.

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4

Rozhansky, V., M. Tendler e S. Voskoboinikov. "Dynamics of the L - H transition". Plasma Physics and Controlled Fusion 38, n. 8 (1 agosto 1996): 1327–30. http://dx.doi.org/10.1088/0741-3335/38/8/031.

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5

Shaing, K. C., C. T. Hsu e P. J. Christenson. "L-H transition in tokamaks and stellarators". Plasma Physics and Controlled Fusion 36, n. 7A (1 luglio 1994): A75—A80. http://dx.doi.org/10.1088/0741-3335/36/7a/007.

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6

Fukuda, T. "`Hidden' variables affecting the L-H transition". Plasma Physics and Controlled Fusion 40, n. 5 (1 maggio 1998): 543–55. http://dx.doi.org/10.1088/0741-3335/40/5/003.

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7

Estrada, T., E. Ascasíbar, T. Happel, C. Hidalgo, E. Blanco, R. Jiménez-Gómez, M. Liniers, D. López-Bruna, F. L. Tabarés e D. Tafalla. "L-H Transition Experiments in TJ-II". Contributions to Plasma Physics 50, n. 6-7 (23 luglio 2010): 501–6. http://dx.doi.org/10.1002/ctpp.200900024.

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8

Schorlepp, Timo, Pavel Sasorov e Baruch Meerson. "Short-time large deviations of the spatially averaged height of a Kardar–Parisi–Zhang interface on a ring". Journal of Statistical Mechanics: Theory and Experiment 2023, n. 12 (1 dicembre 2023): 123202. http://dx.doi.org/10.1088/1742-5468/ad0a94.

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Abstract Using the optimal fluctuation method, we evaluate the short-time probability distribution P ( H ˉ , L , t = T ) of the spatially averaged height H ˉ = ( 1 / L ) ∫ 0 L h ( x , t = T ) d x of a one-dimensional interface h ( x , t ) governed by the Kardar–Parisi–Zhang equation ∂ t h = ν ∂ x 2 h + λ 2 ∂ x h 2 + D ξ x , t on a ring of length L. The process starts from a flat interface, h ( x , t = 0 ) = 0 . Both at λ H ˉ < 0 and at sufficiently small positive λ H ˉ the optimal (that is, the least-action) path h ( x , t ) of the interface, conditioned on H ˉ , is uniform in space, and the distribution P ( H ˉ , L , T ) is Gaussian. However, at sufficiently large λ H ˉ > 0 the spatially uniform solution becomes sub-optimal and gives way to non-uniform optimal paths. We study these, and the resulting non-Gaussian distribution P ( H ˉ , L , T ) , analytically and numerically. The loss of optimality of the uniform solution occurs via a dynamical phase transition of either first or second order, depending on the rescaled system size ℓ = L / ν T , at a critical value H ˉ = H ˉ c ( ℓ ) . At large but finite ℓ the transition is of first order. Remarkably, it becomes an ‘accidental’ second-order transition in the limit of ℓ → ∞ , where a large-deviation behavior − ln P ( H ¯ , L , T ) ≃ ( L / T ) f ( H ¯ ) (in the units λ = ν = D = 1 ) is observed. At small ℓ the transition is of second order, while at ℓ = O ( 1 ) transitions of both types occur.

9

Shaing, K. C., e P. J. Christenson. "Ion collisionality and L–H transition in tokamaks". Physics of Fluids B: Plasma Physics 5, n. 3 (marzo 1993): 666–68. http://dx.doi.org/10.1063/1.860511.

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10

Meyer, H., M. F. M. De Bock, N. J. Conway, S. J. Freethy, K. Gibson, J. Hiratsuka, A. Kirk et al. "L–H transition and pedestal studies on MAST". Nuclear Fusion 51, n. 11 (24 ottobre 2011): 113011. http://dx.doi.org/10.1088/0029-5515/51/11/113011.

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Più fonti

Tesi sul tema "L-H transition":

1

Meakins, Alexander James. "A study of the L-H transition in tokamak fusion experiments". Thesis, Imperial College London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.506162.

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2

Sayer, Min-hee Shin. "Evolution of radial force balance and radial transport over L-H transition". Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45911.

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Understanding of plasma confinement modes is an essential component in development of a fusion reactor. Plasma confinement directly relates to performance of a fusion reactor in terms of energy replacement time requirements on other design parameters. Although a variety of levels of confinement have been achieved under different operating conditions in tokamaks, tokamak confinement is generally identified as being either Low (L-mode--poor confinement) or High (H-mode--good confinement) In operation of a tokamak experiment, the plasma confinement condition generally changes from L-mode to H-mode over a few hundred milliseconds, sometimes quite sharply. Such a difference in transition period seems to be largely due to operating conditions of the plasma. Comparison of experimental data exhibits various distinctions between confinement modes. One noteworthy distinction between confinement modes is development of steep density and temperature gradients of electrons and ions in the plasma edge region of High confinement, H-modes, relative to Low-confinement, L-modes. The fundamental reason for the change for L-mode to H-mode is not understood. Previous studies have suggested i) the development of reduced diffusive transport coefficients that require a steepening of the gradients in a localized region in the edge plasma, the "transport barrier" in H-mode confinement ii) the radial force balance between pressure gradient forces and electromagnetic (radial electric field and VxB) forces require radial particle fluxes to satisfy a pinch-diffusion relation. A recent study suggests that the major difference between L-mode and H-mode are associated with the electromagnetic forces in the "pinch velocity" and the pressure gradient, not in the diffusion coefficients that multiplies the pressure gradient. The research will examine in detail the time evolution of the radial force balance and the particle and energy transport during the L-H transition. For the analysis, DIII-D shot #118897 is selected for transition between L- and H-mode confinements. Plasma conditions in L-mode, near the L-H transition and following the transition are selected for analysis of various parameter profiles. The initial analysis will be based on the four principal equations for plasma: particle balance, momentum balance, force balance and heat conduction. Based on these equations, specific equations have been derived: toroidal and radial momentum balances, diffusion coefficient, pinch velocity and heat conduction relation for calculation of parameters. The analysis of these equations, using the measured data, will establish how various terms in the radial force balance (radial electric field, VXB (electromagnetic) force, and pressure gradient) and the diffusive transport coefficients evolve over the confinement mode transition.

3

Walk, John Reel Jr. "The L- to H-mode transition and momentum confinement in Alcator C-Mod plasmas". Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/61271.

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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2010.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 63-64).
Using a spatially-resolving x-ray spectrometer system, toroidal impurity rotation in Alcator C-Mod plasmas was measured. The propagation of the rotational velocity from the edge to the core of the plasma column was measured during the L- to H-mode transition. Momentum transport was measured in both Ohmic and ICRF-heated discharges, which produced EDA and ELM-free H-modes. The momentum transport was modeled by a simplified diffusion model, in which momentum diffusivity was substantially higher than neoclassically predicted values.
by John Reel Walk, Jr.
S.B.

4

Liang, Anshu. "Understanding the low to high confinement transition in tokamak plasmas". Electronic Thesis or Diss., Aix-Marseille, 2023. http://theses.univ-amu.fr.lama.univ-amu.fr/230112_LIANG_826zuy182lisgpn946fzpk544n_TH.pdf.

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Les travaux présentés dans cette thèse sont consacrés à la compréhension du mécanisme physique de la transition L-H. Le mécanisme d'entraînement du cisaillement de vitesse dans le bord du plasma a été étudié à l'aide d'une injection de puissance d'entraînement à courant hybride inférieur (LHCD) sur le tokamak HL-2A en Chine. Il a été montré que l'augmentation du cisaillement de vitesse est principalement entraînée par le terme diamagnétique ionique du champ électrique radial Er. Au cours de la transition L-H, on observe que le terme diamagnétique ionique du champ électrique radial Er joue un rôle dominant dans l'augmentation du cisaillement de vitesse, tandis que les contributions des termes de vitesse poloïdal et toroïdal sont négligeables. Le cisaillement de vitesse doit atteindre une valeur critique pour permettre à la transition L-H de se produire. Cela signifie que la valeur critique joue un rôle de seuil de cisaillement de vitesse pour la transition L-H. De plus, l'effet stimulé de l'injection de faisceaux moléculaires supersoniques (SMBI) sur la transition L-H a également été étudié sur HL-2A. Les résultats suggèrent que le SMBI pourrait être une méthode fiable pour réduire le seuil de puissance de transition L-H et contrôler la transition L-H dans les futurs réacteurs de fusion. Enfin, des efforts ont été faits sur l'optimisation du couplage LHCD sur le tokamak WEST en France et une analyse du couplage de l'onde LH dans les plasmas WEST a été réalisée. L'analyse montre que le remodelage toroïdal du lanceur multijonction entièrement actif effectué avant son installation à WEST a été un succès
The works presented in this thesis are devoted to understand the physical mechanism of the L-H transition. The driving mechanism of the velocity shear in the plasma edge has been studied using lower hybrid current drive (LHCD) power injection on the HL-2A tokamak in China. It has been shown that the increase of the velocity shear is mainly driven by the ion diamagnetic term of the radial electric field Er. During the L-H transition, it is observed that the ion diamagnetic term of the radial electric field Er plays a dominant role in the increase of velocity shear, while the contributions of the poloidal and toroidal velocity terms are negligible. The velocity shear must reach a critical value to allow the L-H transition to occur. This means that the critical value plays a role as a velocity shear threshold for the L-H transition. In addition, the stimulated effect of supersonic molecular beam injection (SMBI) on the L-H transition has also been investigated on HL-2A. The results suggest that SMBI could be a reliable method for reducing the L-H transition power threshold and controlling the L-H transition in future fusion reactors. Finally, efforts have been made on the optimization of LHCD coupling on the WEST tokamak in France and an analysis of the LH wave coupling in WEST plasmas has been carried out. The analysis shows that the toroidal reshaping of the fully-active-multijunction launcher carried out before its installation in WEST was successful. The experiments have also shown that the reshaping of the passive-active-multijunction launcher is necessary in order to avoid overheating on the launcher front in long pulses

5

Berionni, Vincent. "Etude de l'impact des flux zonaux sur la turbulence dans les plasmas, sur la transition L-H et la production d'entropie". Palaiseau, Ecole polytechnique, 2014. https://pastel.archives-ouvertes.fr/tel-01314705.

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6

Haupricht, Tim Jakobus Thomas [Verfasser], L. H. [Akademischer Betreuer] Tjeng e T. [Akademischer Betreuer] Michely. "Transition metal impurities in wide bandgap oxides: fundamental model systems for strongly correlated oxides / Tim Jakobus Thomas Haupricht. Gutachter: L. H. Tjeng ; T. Michely". Köln : Universitäts- und Stadtbibliothek Köln, 2011. http://d-nb.info/1038168260/34.

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7

Friis, Zachary W. "An investigation of MARFE induced H-L back transitions". Available online, Georgia Institute of Technology, 2005, 2005. http://etd.gatech.edu/theses/available/etd-09072005-155104/.

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Thesis (M. S.)--Nuclear and Radiological Engineering, Georgia Institute of Technology, 2006.
Dr. Cassiano de Oliveira, Committee Member ; Dr. John Mandrekas, Committee Member ; Dr. Weston M. Stacey, Committee Chair. Includes bibliographical references.

8

Friis, Zachary Ward. "An investigation of MARFE induced H-L back transitions". Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7494.

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The common observation that the onset of a core MARFE (edge localized, poloidally asymmetric, highly radiating region) is followed immediately by a High-to-Low confinement mode transition in DIII-D was investigated by comparing a theoretical prediction of the threshold non-radiative power across the separatrix needed to maintain H-mode with an experimental determination of the non-radiative power flowing across the separatrix. It was found that in three shots with continuous gas fueling that the increased neutral influx associated with the MARFE formation caused a sharp increase in the predicted threshold non-radiative power crossing the separatrix that was required for the plasma to remain in H-mode to a value comparable to the experimental power crossing the separatrix, indicating a theoretical prediction of a H-L transition in agreement with experimental observation.

9

Alnaser, Fatimah Abdulameer. "Youth transitions and social change in Kuwait : tensions between tradition and modernity". Thesis, University of Glasgow, 2018. http://theses.gla.ac.uk/30774/.

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Within the social sciences, there is extensive literature on youth transitions as a key context for understanding how social changes and complex contemporary life have an impact on young people’s lives, focusing generally on the ‘global north’. However, far too little attention has been paid to exploring youth transitions in the ‘global south’. Even if it is acknowledged that youth research in the global south has grown in recent years, and has discovered different youth experiences from those in northern contexts, these studies have still been narrow and mostly based on theoretical rather than new empirical work. This research addresses the research gap by investigating young people’s transition from education to the labour market, and exploring the impact of social changes on their lives beyond the global north, in Kuwaiti society. It provides insight into how contemporary young people are constructing and negotiating their pathways to work within a complex reality in which traditional norms and cultural restrictions come into conflict with modernity. It highlights the role of certain variables that continue to mould their transition, including family, gender, religion, education, and government policies. It demonstrates that the rapid change and the compressed manner of modernity in Kuwait have made young people live in a state of tension and contradiction between modernity and tradition, agency and structure, and individual and collective ways of life. It shows how the unique nature of modernity and its consequences in Kuwaiti society have made the young people’s experience distinct from that described in other contexts. This study draws on data generated through questionnaires and interviews. It involves a sample of 1,120 secondary school students, and 24 young adults who had recently entered the labour market. The thesis, which reports the results, challenges existing models in the youth studies literature and critically assesses general sociological theories which tend to be northern-centric. In considering the ideas of the German sociologist Ulrich Beck on modernisation and individualisation, it is difficult to apply his western ideas to the Kuwaiti context. This thesis therefore calls for a cosmopolitan sociology, claiming the need to re-define the concepts within social sciences in such a way that can be easily and flexibly used in a variety of global contexts.

10

Rufinus, Jeffrey. "Antenna-plasma coupling during the L- to H-mode transition in the ion-cyclotron range of frequencies". 1991. http://catalog.hathitrust.org/api/volumes/oclc/25330417.html.

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Thesis (M.S.)--University of Wisconsin--Madison, 1991.
Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 41-50).

Libri sul tema "L-H transition":

1

(Firm), Drouot-Richelieu. Tableaux modernes: P. Aizpiri, A. Barbier, E.C. Benezit, E. Bourdin, M. Boulet, Y. Brayer, G. Cambier, Carlos-Reymond, J. Carzou, P. Charavel, V. Charreton, H.C. Delpy, A. Dignimont, J. Dunoyer, A. Dunoyer de Segonzac, G. d'Espagnat, S. Ferat, L. Fini, Frank-Boggs, L. Genin, M. Girard, N. Giuffrida, H. Goetz, A. Guillaumin, A. Hambourg, N. Henon, C. Hilaire, J.B. Jongkind, M. Journod, L. Laborit, P. Laprade, P. Laroche, M. Laurencin, E. de La Villeon, H. Lebasque, A. Lhote, J. Le Guennec, M. Luce, D. Lucas, E. Maclet, H. Manguin, A. Marquet, M. Martin, Mayeux, Meg, P.E. Montezin, J.P. Pascin, R. Quence, L. Touchagues, J.B. Valadie, L. Valtat, Vander Hacehenn, M. de Vlaminck, C. Wauthier, F. Witte, F. Ziem ; tableaux du XIXe siècle ; bijoux ; argenterie ; verrerie "art nouveau" et modernes ; Extrême-Orient, paravants, vases, pagode en serpentine, statuette en jade ; sculptures ; meubles et objets d'art, commode transition par E. Avril, pair de fauteuils par I. Nadal, bibliothèque par P. Defriche, Bureau par P. Sormani, tapis. Paris: Drouot-Richelieu, 2001.

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Capitoli di libri sul tema "L-H transition":

1

"The impact of the Chinese criminal law in Hong Kong H . L . F U". In Hong Kong in Transition, 160–71. Routledge, 2003. http://dx.doi.org/10.4324/9780203222775-20.

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2

Fusi Aizpúrua, Juan Pablo. "Centre and Periphery 1900-1936: National Integration and Regional Nationalisms Reconsidered". In Élites and Power in Twentieth-Century Spain, 33–44. Oxford University PressOxford, 1990. http://dx.doi.org/10.1093/oso/9780198228806.003.0003.

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Abstract Regional nationalisms have been in Spain like the Anglo-Irish question in British politics, ‘One of those desperate problems of internal government which admit of no smooth and satisfying solutions’, to put it in H. A. L. Fisher’s classic words. This became evident in the years between 1900 and 1936 and has remained so ever since. Basque nationalism constituted the main obstacle to political stability in the transition towards democracy after General Franco’s death in 1975.

3

Blow, David. "Anomalous scattering". In Outline of Crystallography for Biologists. Oxford University Press, 2002. http://dx.doi.org/10.1093/oso/9780198510512.003.0013.

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X-rays set the electronic charges around atoms vibrating, and these vibrations generate radiation of the same frequency, which is propagated in all directions. This is the coherent scattering that gives rise to diffraction effects. Normally, the electrons vibrate in step with the incident beam. If, however, the incident photons have an energy close to a transition energy which can bring the atom to an excited state, the electronic vibration gets out of step. Instead of re-radiating in phase with the incident beam, the radiated energy has a different phase. Also, the intensity of coherent scattering is reduced, because some energy is absorbed to bring about the transition. This effect is called anomalous scattering. More detail is given in Box 8.1. Figure 8.1 shows how X-ray absorption varies with wavelength near the transition energy. X-rays become rapidly less penetrating as wavelength increases, but this trend is interrupted by a sharp ‘edge’ at a wavelength that corresponds to an electronic transition. In practice, at the wavelengths of X-rays convenient for diffraction experiments (less than 1.6 Å) atoms lighter than phosphorus or sulphur behave as normal scatterers because they have no transitions of corresponding energy. At wavelengths very near the energy of an electronic transition, anomalous scattering can become a significant fraction of the total scattering. In this chapter the atoms which are scattering anomalously are referred to as heavy atoms, H. Useful anomalous scatterers can be far lighter than the heavy elements needed for macromolecular isomorphous replacement. From iron (Z=26) to palladium (Z = 46) the K absorption edges are at convenient wavelengths. Much heavier atoms (the lanthanides and beyond) give strong anomalous effects from the L edges, at useful wavelengths. Remember that the X-ray scattering power of an atom is measured by comparison with the scattering of an electron. At low scattering angle and ‘normal’ wavelengths, an atom scatters according to the number of electrons it contains (Box 5.2). At wavelengths close to the absorption edge, the atomic scattering factor includes an ‘anomalous’ component, shown in Fig. 8.2, and presented in algebraic form in Box 8.2.

4

Li, Jie Jack, Chris Limberakis e Derek A. Pflum. "Carbon−Carbon Bond Formation". In Modern Organic Synthesis in the Laboratory. Oxford University Press, 2008. http://dx.doi.org/10.1093/oso/9780195187984.003.0011.

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Reviews: (a) Vicarion, J. L.; Badia, D.; Carillo, L.; Reyes, E.; Etxebarria, J. Curr. Org. Chem. 2005, 9, 219-235. (b) Mahrwald, R. Ed. In Modern Aldol Reactions; Wiley-VCH: Weinheim, 2004; Vol. 1., pp. 1-335 (c) Mahrwald, R. Ed. In Modern Aldol Reactions; Wiley-VCH: Weinheim, 2004; Vol. 2., pp. 1-345.(d) Machajewski, T. D.; Wong, C.-H. Angew. Chem. Int. Ed. 2000, 39, 1352-1375. (e) Carriera, E. M. In Modern Carbonyl Chemistry; Otera, J.; Wiley-VCH: Weinheim, 2000; Chapter 8: Aldol Reaction: Methodology and Stereochemistry, 227-248. (f) Paterson, I.; Cowden, C. J.; Wallace, D. J. In Modern Carbonyl Chemistry; Otera, J.; Wiley-VCH: Weinheim, 2000; Chapter 9: Stereoselective Aldol Reactions in the Synthesis of Polyketide Natural Products, pp. 249-298. (g) Franklin, A. S.; Paterson, I. Contemp. Org. Synth. 1994, 1 317-338. (h) Heathcock, C. H. In Asymmetric Synthesis; Morrison, J. D., Ed.; Academic Press: Orlando, Fl.; 1984; Vol. 3., Chapter 2: The Aldol Addition Reaction, pp. 111-212. (i) Mukaiyama, T. Org. React. 1982, 28, 203-331. Since the early 1980s, aldol condensations involving boron enolates have gain great importance in asymmetric synthesis, particularly the synthesis of natural products with adjacent stereogenic centers bearing hydroxyl and methyl groups. (Z)-Boron enolates tend to give a high diastereoslectivity preference for the syn-stereochemistry while (E)-boron enolates favor the anti-stereochemistry. Because the B-O and B-C bonds are shorter than other metals with oxygen and carbon, the six membered Zimmerman–Traxler transition state in the aldol condensation tends to be more compact which accentuates steric interactions, thus leading to higher diastereoselectivity. When this feature is coupled with a boron enolate bearing a chiral auxillary, high enantioselectivity is achieved. Boron enolates are generated from a ketone and boron triflate in the presence of an organic base such as triethylamine. Reviews: (a) Abiko, A. Acc. Chem. Res. 2004, 37, 387-395. (b) Cowden, C. J. Org. React. 1997, 51, 1-200.

5

Taber, Douglass. "Transition Metal-Mediated C-C Ring Construction: The Stoltz Synthesis of (-)-Cyanthiwigin F". In Organic Synthesis. Oxford University Press, 2011. http://dx.doi.org/10.1093/oso/9780199764549.003.0077.

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X. Peter Zhang of the University of South Florida extended (Organic Lett. 2009, 11, 2273) Co-catalyzed asymmetric cyclopropanation to the activated ester 2. The product 3 readily coupled with amines. André B. Charette of the Université de Montréal showed (J. Am. Chem. Soc. 2009, 131, 6970) that even α-olefins such as 4 could be cyclopropanated in high ee with the diazo amide 5. Xue-Long Hou of the Shanghai Institute of Organic Chemistry established (J. Am. Chem. Soc. 2009, 131, 8734) conditions for the enantioselective coupling of 7 and 8 to give 9 , in which sidechain chirality was also controlled. Tristan H. Lambert of Columbia University found (J. Am. Chem. Soc. 2009, 131, 7536) that “methylene” could be transferred in an intramolecular sense from the epoxide of 10 to the alkene, delivering the cyclopropane 11 in high ee. Yuichi Kobayashi of the Tokyo Institute of Technology established (Organic Lett . 2009, 11, 1103) that the 2-picolinoxy leaving group worked well for the SN2' coupling with 13 to give 14. Chang Ho Oh of Hanyang University developed (J. Org. Chem. 2009, 74, 370) a new route to cyclopentenones such as 16, by gold-catalyzed cyclization of diynes such as 15. David J. Procter of the University of Manchester used (J. Am. Chem. Soc. 2009, 131, 7214; Tetrahedron Lett . 2009, 50, 3224) SmI2 to cyclize 17 to 18 and 19 to 20, each with high diastereocontrol. Yoshiaki Nishibayashi of the University of Tokyo devised (Angew. Chem. Int. Ed. 2009, 48, 2534) Ru catalysts for the cyclization of an enyne such as 21 to the cyclohexadiene 22. Laurel L. Schafer of the University of British Columbia developed (J. Am. Chem. Soc. 2009, 131, 2116) a Zr catalyst for the diastereocontrolled cyclization of amino alkenes such as 23. Hongbin Zhai of the Shangahi Institute of Organic Chemistry showed (J. Org. Chem. 2009, 74, 2592) that the Mo-mediated cyclization of 25 also proceeded with high diastereocontrol. Even more impressive was the selectivity Kozo Shishido of the University of Tokushima demonstrated (Tetrahedron Lett . 2009, 50, 1279) for the cyclization of 27.

6

Lambert, Tristan H. "C–O Ring Construction: The Reisman Synthesis of (–)-Acetylaranotin". In Organic Synthesis. Oxford University Press, 2015. http://dx.doi.org/10.1093/oso/9780190200794.003.0048.

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The Prins cyclization is a powerful approach for the construction of oxygen-containing heterocycles. B.V. Subba Reddy at the Indian Institute of Technology has reported (Tetrahedron Lett. 2012, 53, 3100) an approach to 2,6-dioxabicyclo[3.2.1]octanes 2 by way of a tandem Prins reaction/intramolecular acetalization of the diol 1 and a variety of aldehydes. Christine L. Willis of the University of Bristol utilized (Angew. Chem. Int. Ed. 2012, 51, 3901) nontraditional γ, δ-unsaturated alcohols 3 for a Prins-type strategy to access bicyclic heterocycles 5, while Zhenlei Song of Sichuan University employed (Angew. Chem. Int. Ed. 2012, 51, 5367) a bis(silyl) homoallylic alcohol 7 in the synthesis of structures such as 8, corresponding to the B ring of the bryostatins. In a mechanistically related process, the conversion of unsaturated ketones 9 to tetrahydropyranyl products 11 by treatment with a boronic acid 10 and triflic anhydride was described (Org. Lett. 2012, 14, 1187) by Aurelio G. Csáky at the Universidad Complutense in Spain. A powerful approach to heterocycles is via the ring expansion of smaller, and especially strained, ring systems. Jon T. Njardarson of the University of Arizona has been exploring such strategies and has reported (Angew. Chem. Int. Ed. 2012, 51, 5675) the conversion of vinyl oxetanes to dihydropyrans via catalysis by transition metals or Brønsted acids. The use of a chiral catalyst such as 13 allowed for the enantioselective conversion of divinyl oxetane 12 to enantioenriched dihydropyran 14. Meanwhile, Amir H. Hoveyda at Boston College and Richard R. Schrock at MIT have developed (J. Am. Chem. Soc. 2012, 134, 2788) a highly reactive and stereoselective catalyst for the ring-opening/cross-metathesis of several ring systems such as 15 with enol ethers. Notably, reactions occur rapidly (e.g., 10 min) using as little as 0.15 mol% catalyst. An alkynyl cyclopropyl ketone such as 17 can be converted (Angew. Chem. Int. Ed. 2012, 51, 4112) to products 18 by treatment with a gold/silver catalyst mixture, as shown by Zhongwen Wang at Nankai University. Notably, the oxabicyclic ring structure contained within 18 is present in a diversity of natural product structures.

7

Taber, Douglass. "Developments in Alkene Metathesis". In Organic Synthesis. Oxford University Press, 2011. http://dx.doi.org/10.1093/oso/9780199764549.003.0024.

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Abstract (sommario):

Alkene metathesis has been extended to increasingly complex starting materials and products. Nitriles are good donors to coordinatively-unsaturated transition metal centers, so tend to inhibit the reaction. Ren He of Dalian University of Technology has found (Tetrahedron Lett. 2007, 48, 4203) that inclusion of the loosely-coordinating 2-methyl pyridine in the reaction enables facile cross-coupling with acrylonitrile 2. Although crosscoupling with (Z, Z)-sorbate is not efﬁcient, Dennis P. Curran of the University of Pittsburgh has shown (Organic Lett. 2007, 9, 5) that cross-coupling with (E, Z)-sorbate 5 works well. For large scale work, he has developed a Hoveyda-type catalyst with a perﬂuoro tail, that is recoverable in 70% recrystallized yield from the reaction mixture. Shigefumi Kuwahara of Tohoku University has reported (Tetrahedron Lett. 2007, 48, 3163) a practical alternative for direct metathesis to deliver (E, E)-dienyl esters. Continuing the investigation of tandem Ru-catalyzed reactions, Marc L. Snapper of Boston College effected (Organic Lett. 2007, 9, 1749) metathesis with methacrolein 8a, then added Ph3P and diazoacetate, to give the diene 11. A range of common Ru catalysts worked well for this transformation. In an alternative approach to trisubstituted alkene construction, Stellios Arseniyadis and Janine Cossy of ESPCI Paris have demonstrated (Organic Lett. 2007, 9, 1695) that inclusion of Cl-catecholborane 14 allows clean cross metathesis with the lactone 13. The construction of tetrasubstituted alkenes has been more challenging. Yann Schrodi of Materia, Inc. (Organic Lett. 2007, 9, 1589) has described a catalyst 17 that is particularly effective. Complex 17 was superior to a catalyst reported (Organic Lett. 2007, 9, 1339) shortly earlier by Robert H. Grubbs of Caltech. Debendra K. Mohapatra of the National Chemical Laboratory, Pune, and Professor Grubbs, in a new approach to macrocyclic stereocontrol, have made (Tetrahedron Lett. 2007, 48, 2621) the remarkable observation that the cyclization of the bis ether 19a gave 20 in a 9:1 E / Z ratio, while cyclization of the diol 9b gave only Z - 21. Oligomer formation can often compete in such medium ring-forming reactions. Deryn E. Fogg of the University of Ottawa has raised (J. Am. Chem. Soc. 2007, 129, 1024) the cautionary (but happy!) observation that while the cyclization, for instance, of 22 proceeded efficiently to give 23, at an intermediate point in the transformation the product was more than half oligomer.

8

Hryshyna, Nataliia, Larysa Hryshyna e Petr Karas. "TRENDS AND PROSPECTS OF DIGITAL TRANSFORMATION OF THE UKRAINIAN ECONOMY IN THE CONDITIONS OF EUROPEAN INTEGRATION". In GLOBAL DIGITAL TRENDS AND THEIR IMPACT ON NATIONAL ECONOMIC PROGRESS. OKTAN PRINT, 2024. http://dx.doi.org/10.46489/gdtatione-05-24-11.

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The processes of globalization, scientific and technical development of many countries and informatization of society require significant changes within the sphere of economic activity. Traditional economic activity is being restructured in the direction of using information, communication and digital technologies, which causes its transition from one that consumes resources to an economy that creates them. The development of digital technologies has activated a deepened interest in the establishment of the digital economy's foundations and the study of its impact on the economic growth of many countries. Digital transformations contribute to the development of small and medium-sized businesses, smart transport management, increased safety and improvement of ecology, improvement of housing and communal services, electronic interaction with local authorities, improvement of the population's level of digital skills. In Ukraine, at the state level, considerable attention is paid to the use of digital transformations for the development of the economy and society. Digitization is defined as a mechanism of economic growth due to the ability of technologies to positively influence the efficiency, effectiveness, cost and quality of economic, public and personal activities. This is reflected in the Digitalization Strategy of Ukraine until 2030 [1]. Choosing to cooperate with the countries of the European Union is an important stage in the development of Ukraine's economy. This has led to the development and approval of the strategic document known as the Digital Compass 2030 [2]. The main four directions are highlighted, which include the development of highly qualified specialists in the field of digital technologies, safe and effective sustainable digital infrastructure, digital transformation of business, digitization of public services, which in turn include specific goals for the formation of a prosperous digital future of the country. Literary review. Research on the development of digital transformations in the economy is reflected in many scientific works of foreign and domestic economists, including I. Irtyshcheva, L. Ligonenko, H. Lopushnyak, O. Mykhaylenko, S. Mishchenko, K. Pugachevska, M. Rudenko, I. .Strutynska, B. Teteryatnik, A. Khripko and others. [3,4,5,6,7]. In particular, the results of the study of prerequisites, challenges and drivers of digital transformation of domestic business structures are noted in the scientific works of I. Strutynska [6]. The author formulated the methodological provisions of the digital transformation of business structures, which provide for the systematic structuring of business processes, business models, factors, indicators of the processes of digital transformation of enterprises. Analytical assessment of Ukraine's position in the global indices of the digital economy is reflected in the works of M. Rudenko [7]. But at the same time a significant number of problems digital transformation of Ukraine's economy in war conditions remain insufficiently disclosed.

9

Succi, Sauro. "Flows At Moderate Reynolds Number". In The Lattice Boltzmann Equation for Fluid Dynamics and Beyond, 97–109. Oxford University PressOxford, 2001. http://dx.doi.org/10.1093/oso/9780198503989.003.0007.

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Abstract In this chapter we present the application of LBE to the problem of transitional flows at moderate Reynolds numbers. This is an important area of theoretical and applied fluid mechanics, one that relates mainly with the onset of nonlinear instabilities and their effects on the transport properties of the unsteady flow configuration. The regime of Reynolds numbers at which these instabilities take place is usually not too high, of the order of thousands, and consequently basically within reach of present day computer capabilities. Nonetheless, following the entire evolution of these highly dynamic transitional flows requires very long integrations with short time-steps which demand conspicuous computational power. Which is why, again, efficient numerical methods are in great demand. As we shall see, LBE has good credentials to meet this demand. 7.1 Moderate Reynolds flows in simple geometry Let us consider a rectangular channel of length L and height H . The fluid enters the channel from the left side (inlet) and flows steadily down the channel under the effect of a constant pressure drop ΔP = P i P o between the inlet and outlet section. At the top and bottom boundaries the flow speed vanishes (noslip boundary condition) as a result of the drag exerted by the rigid walls. This is how dissipation balances the momentum input from the pressure gradient. If the Reynolds number is small enough, typically below 2000 in a real pipe, occasional fluctuations are unable to break the one-dimensional symmetry of the flow so that the nonlinear terms of the Navier–Stokes equations, (∂buaub ), vanish identically and have no effect on the evolution of the flow.

10

"Preclinical analysis of developmental transitions in the extinction of learned fear From infancy through adolescence to adulthood BriDget L. caLLagHan, steLLa Li, jee H. kim, anD rick ricHarDson". In Changing Emotions, 95–102. Psychology Press, 2013. http://dx.doi.org/10.4324/9780203075630-18.

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Atti di convegni sul tema "L-H transition":

1

Martinell, Julio J. "A Model of Self-Consistent L-H Transition Based on Finite-β Drift Waves". In PLASMA PHYSICS: 11th International Congress on Plasma Physics: ICPP2002. AIP, 2003. http://dx.doi.org/10.1063/1.1594015.

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2

Lam, N. T., J. E. Scharer e M. Bettenhausen. "Effects of the L- to H-Mode Transition in BPX on a Recessed Coil Antenna". In Radio frequency power in plasmas. AIP, 1992. http://dx.doi.org/10.1063/1.41703.

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3

"Adsorption of hydrogen sulphide (H2S) using xerogel synthesized from palm kernel shell biochar". In Sustainable Processes and Clean Energy Transition. Materials Research Forum LLC, 2023. http://dx.doi.org/10.21741/9781644902516-14.

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Abstract: Xerogel is a typical porous material with a large internal surface area, causing them to have significant gas adsorption. Adsorption performance was investigated to determine the potential contribution of xerogel to removing Hydrogen Sulphide (H2S) in this research. Adsorption is a well-known energy-efficient approach for removing acid gases at low temperatures. H2S gas harms human health, such as headaches, eye irritation, and loss of smell if exposed to a low concentration. Furthermore, the physical and chemical properties of the raw material and synthesized xerogel were evaluated by various techniques: Fourier Transform Infrared Spectroscopy (FTIR), thermogravimetric Analysis (TGA), and Scan Electron Microscopy (SEM). Results showed that the removal of H2S increased with increasing adsorbent mass from 3 to 12 g and decreased flow rate from 40 to 26 L/h. The maximum Adsorption capacity of Xerogel for H2S was 27.5 mg/g, and the surface area was 0.2686 m2/g. This research shows the significant potential of using adsorbent materials obtained from waste to absorb H2S.

4

Righi, E. "Influence of plasma proximity to the vessel on the L-H transition in JET ICRF heated plasmas". In RADIO FREQUENCY POWER IN PLASMAS:14th Topical Conference. AIP, 2001. http://dx.doi.org/10.1063/1.1424156.

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5

Kumar, Ravi, Pradeep Singh e S. Sarkar. "Transition of a Laminar Separated Boundary Layer Under Varying Adverse Pressure Gradient". In ASME Turbo Expo 2022: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/gt2022-83045.

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Abstract This paper describes the effects of pressure gradients on the transition of a laminar separation bubble (LSB) formed over the flat plate. The measurements were performed using electronically scanned pressure (ESP) and hot-wire anemometer. The different adverse pressure gradients (APG) are achieved by changing the opening angle (α) of the upper boundary of the domain. The experiments were performed for α = 7°, 9.5° and 11.5° at a Re of 2 × 105 (based on the inlet freestream velocity and plate length) and freestream turbulence intensity (fst) of 1.02%. The onset of separation and transition occurs at x / L = 0.39, 0.449 respectively with reattachment at 0.491 for α = 7°. As APG increases, the separation, transition and reattachment shift upstream with respect to α = 7° leading to the reduction in bubble length. The decrease in the length of LSB is attributed to the earlier transition. Moreover, the growth rate of fluctuations increases with increasing APG. The power spectra of streamwise fluctuations illustrate that the transition occurs via K-H instability for all APG and the predominant shedding frequency increases with increasing pressure gradient. Moreover, the self-similarity of normalized urms profiles in the second half of the bubble show the presence of viscous instability.

6

Darbandi, Masoud, e Shidvash Vakilipour. "Numerical Study of Flow and Heat in Long Micro and Nano Channels". In ASME 2008 First International Conference on Micro/Nanoscale Heat Transfer. ASMEDC, 2008. http://dx.doi.org/10.1115/mnht2008-52077.

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In this work, we extend a numerical tool capable of solving compressible and incompressible gas flows to study the momentum and heat transfer rates in micro/nano channels with high aspect ratio (L/H = 8000), where the compressibility effect is dominant. The constant heat flux thermal boundary condition is firstly applied at the wall. Next, the flow regime is extended to the early transition regime employing a high order slip velocity boundary condition based on the kinetic theory assumptions. The accuracy of the present results in the slip flow regimes is evaluated against other available theoretical and experimental results. The thermal and compressibility effects on the pressure and Knudsen number distribution are extensively studied along the channel at early transition regimes up to Kn = 0.5. Likely, this Knudsen is the highest one to be reached via applying the foregoing boundary conditions.

7

Marmet, L., K. Hakuta e B. P. Stoicheff. "Second-harmonic generation in atomic hydrogen at Lyman-α". In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1990. http://dx.doi.org/10.1364/oam.1990.fo3.

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We have observed second-harmonic generation in atomic hydrogen in the Lyman-α region, with and without an applied dc electric field, Ea. Experiments with a continuous atomic beam were carried out by using a pulsed dye laser tuned to 243 nm for excitation of the n = 2-1 transition. The laser beam was focused 0.4 mm below the H-source nozzle, where the H-atom density was estimated to be 5 × 1013 cm-3. Measurements of second-harmonic generation (SHG) at ~122 nm were made at various electric fields up to ~27 kV/cm. It was shown that the SH signal produced at E a = 0 occurs because of a charge-separation field of ~800 V/cm that is caused by three-photon ionization. Measurements of the SHG and ion current were found to vary as I2 L and I3 L , respectively. At high fields (E a > 10 kV/cm) the SH signal at the center of the Stark-split components decreased somewhat from the peak value, but the ion current (corresponding to photon absorption) approached zero. This observation is a clear demonstration of a similar effect, predicted by Harris et al.1 of efficient nonlinear conversion with induced transparency, and it suggests the possibility of obtaining intense Lyman-a radiation.

8

Wang, Qiang, Chi Zhou, Zhaoyuan Guo, Peigang Yan, Guotai Feng e Zhongqi Wang. "Study on Numerical Methods for Conjugate Heat Transfer Simulation of an Air Cooling Turbine". In ASME 2008 International Mechanical Engineering Congress and Exposition. ASMEDC, 2008. http://dx.doi.org/10.1115/imece2008-66740.

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The effects of several numerical methods, including computational grids, coupling method, transition model and inner cooling air flow prediction, on the conjugate simulations were studied in the research. Firstly a finite difference conjugate solver was developed. Such solver included an N-S solver and a thermal conduction module for fluid flow and solid thermal conduction, respectively. Then conjugate simulations of an air cooling turbine were carried out. There were four kinds of conjugate simulations: the first one employs different types of computational grids, including H-type grids and O-type grids, for discretizing near-wall regions in fluid zone; the second one employs different coupling methods including indirect and direct ones; the third one employs different models including the B-L and q-ω turbulence models, and the AGS transition model; and the forth one employs different turbulence models for the prediction of flows in the cooling channels. All of the numerical results have been compared to the experimental result. Finally it concludes that to accurately predict thermal and aerodynamic load of the air cooled turbine, the conjugate simulation should employ O-type girds to discretize the near wall regions in the fluid zone, use the direct coupling method to transfer data between solid and fluid domains, and utilize the transition model to predict accurate flow details within the boundary layers, and also account for flows in the cooling air channels.

9

Ahuja, Suresh K. "Visco-Elastic Modulus and Intercalation of Polymer Chains in Epoxy Nano-Composites". In ASME 2007 International Mechanical Engineering Congress and Exposition. ASMEDC, 2007. http://dx.doi.org/10.1115/imece2007-42503.

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Polymer nano-composites (PNC) are polymers which are reinforced with less than 5% by volume of nano-sized particles with high aspect ratios (L/h > 300). Compared to conventional composites, where the reinforcement is on the order of microns, the nano-composites are reinforced on the order of a few nanometers with advantages in processing and toughness. Nano-composites of epoxy clay have been studied where epoxy is mixed at high shear rates with clay. In our method of making nano-composites, an epoxy, Diglycidyl ether of bisphenol (DGEBA) A was mixed under high shear with organically modified mica type silicate (OMTS) either of benzyl dimethyl stearyl ammonium (BDSMA) or of methyl bishydroxyethyl stearyl ammonium chloride ion exchange with sodium montmorillonite. Nano-composites of epoxy cured with hexahydrophthalic anhydride (70%) with polyether polyol (25%) were made also under high shear both at 90C and 120C. Heat of reaction and transition temperature of epoxy nano-composite was compared with cured epoxy nano-composite. Analysis by X-Ray Diffraction was used to determine peaks, spacing and interfacial region. Dynamic visco-elastic measurements were used to distinguish between the nano-composites from two organically modified mica type silicates. Effect of increase in concentration and temperature on visco-elastic modulus of nano-composites was analyzed in terms of intercalation of polymer chains.

10

Haustein, Herman D., e Barak Kashi. "The Importance of Viscous Dissipation in Micro-Tube and Micro-Gap Flows". In ASME 2018 16th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/icnmm2018-7704.

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Abstract (sommario):

Increasing heat flux density of modern micro-electronic devices has promoted a transition to liquid-based forced convection cooling. The miniaturization and maldistribution of micro-electronic heat generating elements (e.g. transistors and laser diodes) has promoted a similar decrease in size of cooling flow elements, specifically, micro-channels, micro-gaps and micro-jets. Convection heat transfer scaling laws do not contain a scale-factor in dimensionless form, and heat transfer coefficient (HTC) should continually increase with a decrease in size, as h∝1/d. However, extremely high HTCs are not found at tens of microns, which can be explained by the emergence of a typically neglected effect — heating by viscous dissipation. Traditionally, dissipation is only associated with high-Mach gas flows or high-viscosity oil flows. Nonetheless, it reemerges in micro-cooling, as shown here through theoretical analysis of simple cases. The extreme near-wall gradients and high L/d ratios, of these flows reintroduce dissipation as significant. When flow diameters reach a critical size, on the scale of tens of microns at Re = 2,000, depending on flow configuration, rate and liquid properties, the energy generated by dissipation is sufficient to counteract the inherent increase of HTC and the trend reverses. This maximum in HTC is the absolute lower limit to the cooling element size, a matter which has not been properly addressed. The present study lays a framework of recommendations and limitations for future cooling studies, thereby curbing the ongoing trend of flow miniaturization.

Rapporti di organizzazioni sul tema "L-H transition":

1

Hinton, F. L. Theory of the L-H transition. Office of Scientific and Technical Information (OSTI), settembre 1994. http://dx.doi.org/10.2172/10189786.

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2

Zhang, Y. Z., e S. M. Mahajan. A self-consistent turbulence generated scenario for L-H transition. Office of Scientific and Technical Information (OSTI), ottobre 1992. http://dx.doi.org/10.2172/10185633.

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3

Chang, Zuoyang, e J. D. Callen. Modeling particle transport during the L-H transition and ELM crashes. Office of Scientific and Technical Information (OSTI), ottobre 1991. http://dx.doi.org/10.2172/5003314.

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4

Zweben, S., R. Hager, K. Hallatschek, S. Kaye, T. Munsat, F. Poli, A. Roquemore, Y. Sechrest e D. Stotler. Quiet Periods in Edge Turbulence Preceding the L-H Transition in NSTX. Office of Scientific and Technical Information (OSTI), aprile 2010. http://dx.doi.org/10.2172/981661.

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5

Zhang, Y. Z., e S. M. Mahajan. A self-consistent turbulence generated scenario for L-H transition. [Banana polarization currents]. Office of Scientific and Technical Information (OSTI), ottobre 1992. http://dx.doi.org/10.2172/6996152.

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6

Isichenko, M. B., e P. H. Diamond. Transport suppression by diamagnetic phase shift as a possible mechanism to the L to H transition. Office of Scientific and Technical Information (OSTI), settembre 1994. http://dx.doi.org/10.2172/10103907.

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7

Coda, S., M. Porkolab e K. H. Burrell. Edge turbulence measurements during the L- to H-mode transition by phase contrast imaging on DIII-D. Office of Scientific and Technical Information (OSTI), luglio 1995. http://dx.doi.org/10.2172/195738.

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8

Carter, Troy. Final report for DOE DE-SC0016073: Towards a comprehensive, self-consistent, and predictive theory of the L-H transition. Office of Scientific and Technical Information (OSTI), settembre 2020. http://dx.doi.org/10.2172/1659671.

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9

S.M. Kaye, C.E. Bush, E. Fredrickson, B. LeBlanc, R. Maingi e S.A. Sabbagh. L-H Mode Transitions in the National Spherical Torus Experiment. Office of Scientific and Technical Information (OSTI), luglio 2003. http://dx.doi.org/10.2172/814726.

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10

Punjabi, A. L to H mode transitions and associated phenomena in divertor tokamaks. Office of Scientific and Technical Information (OSTI), settembre 1990. http://dx.doi.org/10.2172/5362928.

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