| 1. |
- Chukalovsky, A. A., et al.
(författare)
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Study of singlet delta oxygen O 2 ( 1 δg) impact on H 2-O 2 mixture ignition in flow reactor : 2D modeling
- 2012
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Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 0010-2202 .- 1563-521X. ; 184:10-11, s. 1768-1786
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Tidskriftsartikel (refereegranskat)abstract
- Influence of electron excited singlet delta oxygen (SDO) molecules produced in direct current (DC) glow discharged plasma on the induction length decrease in the H2-O2 mixture has been studied via comprehensive two-dimensional (2D) numerical simulations. The sensitivity analysis of the induction length on SDO mole fractions and residual mole fractions of odd oxygen was carried out. The influence of the reaction H 2+O 2( 1g)H+HO2 on the ignition length was found to be negligible due to the presence of residual odd oxygen in the oxidizer flow. Two stages specify the ignition time decrease for the studied conditions: (1) chain initiation in reactions with residual odd oxygen and (2) the following chain-branching enhancement due to reaction H 2+O 2( 1g)O+OH. The last reaction is the key process for studied conditions when the concentration of SDO exceeds 4%. The estimated rate constant of this reaction was found to be about 2.510 13cm 3/s at 780K. The quenching reaction H 2+O 2( 1g)H 2+O 2 does not affect the ignition length.
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| 2. |
- Liberman, M. A., et al.
(författare)
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Deflagration-to-detonation transition in highly reactive combustible mixtures
- 2010
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Ingår i: Acta Astronautica. - : Elsevier BV. - 0094-5765 .- 1879-2030. ; 67:7-8, s. 688-701
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Tidskriftsartikel (refereegranskat)abstract
- The paper presents experimental, theoretical, and numerical studies of deflagration-to-detonation transition (DDT) in highly reactive hydrogen-oxygen and ethylene-oxygen mixtures. Two-dimensional reactive Navier-Stokes equations for a hydrogen-oxygen gaseous mixture including the effects of viscosity, thermal conduction, molecular diffusion, and a detailed chemical reaction mechanism are solved numerically. It is found that mechanism of DDT is entirely determined by the features of the flame acceleration in tubes with no-slip walls. The experiments and computations show three distinct stages of the process: (1) the flame accelerates exponentially producing shock waves far ahead from the flame, (2) the flame acceleration decreases and shocks are formed directly on the flame surface, and (3) the final third stage of the actual transition to a detonation. During the second stage a compressed and heated pocket of unreacted gas adjacent ahead to the flame the preheat zone is forming and the compressed unreacted mixture entering the flame produces large amplitude pressure pulse. The increase of pressure enhances reaction rate and due to a positive feedback between the pressure peak and the reaction the pressure peak grows exponentially, steepens into a strong shock that is coupled with the reaction zone forming the overdriven detonation wave. The proposed new physical mechanism of DDT highlights the features of flame acceleration in tubes with no-slip walls, which is the key factor of the DDT origin.
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| 3. |
- Liberman, M. A., et al.
(författare)
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On the mechanism of the deflagration-to-detonation transition in a hydrogen-oxygen mixture
- 2010
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Ingår i: Journal of Experimental and Theoretical Physics. - 1063-7761 .- 1090-6509. ; 111:4, s. 684-698
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Tidskriftsartikel (refereegranskat)abstract
- The flame acceleration and the physical mechanism underlying the deflagration-to-detonation transition (DDT) have been studied experimentally, theoretically, and using a two-dimensional gasdynamic model for a hydrogen-oxygen gas mixture by taking into account the chain chemical reaction kinetics for eight components. A flame accelerating in a tube is shown to generate shock waves that are formed directly at the flame front just before DDT occurred, producing a layer of compressed gas adjacent to the flame front. A mixture with a density higher than that of the initial gas enters the flame front, is heated, and enters into reaction. As a result, a high-amplitude pressure peak is formed at the flame front. An increase in pressure and density at the leading edge of the flame front accelerates the chemical reaction, causing amplification of the compression wave and an exponentially rapid growth of the pressure peak, which "drags" the flame behind. A high-amplitude compression wave produces a strong shock immediately ahead of the reaction zone, generating a detonation wave. The theory and numerical simulations of the flame acceleration and the new physical mechanism of DDT are in complete agreement with the experimentally observed flame acceleration, shock formation, and DDT in a hydrogen-oxygen gas mixture.
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| 4. |
- Dumanov, E. V., et al.
(författare)
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Mixed exciton-plasmon collective elementary excitations of the Bose-Einstein condensed two-dimensional magnetoexcitons with motional dipole moments
- 2013
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Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 250:1, s. 115-127
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Tidskriftsartikel (refereegranskat)abstract
- The collective elementary excitations of the two-dimensional (2D) magnetoexcitons in the state of their BoseEinstein condensation (BEC) with nonzero wave vector k and inplane parallel oriented motional dipole moments are investigated in the HartreeFockBogoliubov approximation (HFBA). The breaking of the gauge symmetry is achieved using the Bogoliubov theory of quasiaverages and the KeldyshKozlovKopaev (KKK) method. The starting Hamiltonian and the Green's functions are determined using the integral two-particle operators instead of the single-particle Fermi operators. The infinite chains of equations of motion for the multioperator four- and six-particle Green-s functions are truncated following the Zubarev method and introducing a small parameter of the perturbation theory related with the lowest Landau levels (LLLs) filling factor and with the phase-space filling factor. The energy spectrum of the collective elementary excitations consists of the mixed excitonplasmon energy braches, mixed excitonplasmon quasienergy branches as well as the optical and acoustical plasmon energy branches. The exciton branches of the spectrum have gaps related with the negative values of the chemical potential and attractive interaction between the 2D megnetoexcitons with inplane, parallel oriented motional dipole moments. The slopes of the mixed excitonplasmon branches are determined by the group velocities of the moving condensed excitons in the laboratory reference frame. The acoustical and optical plasmon energy branches are gapless. Their dependence on the small wave vectors accounted from the condensate wave vector k is linear and quadratic, respectively, with saturation in the range of high values of the wave vectors.
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| 5. |
- Gustafsson, U. O., et al.
(författare)
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Guidelines for perioperative care in elective colonic surgery : enhanced recovery after surgery (ERAS(®)) society recommendations
- 2013
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Ingår i: World Journal of Surgery. - : Springer. - 0364-2313 .- 1432-2323. ; 37:2, s. 259-284
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Forskningsöversikt (refereegranskat)abstract
- BACKGROUND: This review aims to present a consensus for optimal perioperative care in colonic surgery and to provide graded recommendations for items for an evidenced-based enhanced perioperative protocol.METHODS: Studies were selected with particular attention paid to meta-analyses, randomised controlled trials and large prospective cohorts. For each item of the perioperative treatment pathway, available English-language literature was examined, reviewed and graded. A consensus recommendation was reached after critical appraisal of the literature by the group.RESULTS: For most of the protocol items, recommendations are based on good-quality trials or meta-analyses of good-quality trials (quality of evidence and recommendations according to the GRADE system).CONCLUSIONS: Based on the evidence available for each item of the multimodal perioperative care pathway, the Enhanced Recovery After Surgery (ERAS) Society, International Association for Surgical Metabolism and Nutrition (IASMEN) and European Society for Clinical Nutrition and Metabolism (ESPEN) present a comprehensive evidence-based consensus review of perioperative care for colonic surgery.
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| 6. |
- Gustafsson, U. O., et al.
(författare)
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Guidelines for perioperative care in elective colonic surgery : enhanced recovery after surgery (ERAS®) society recommendations
- 2012
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Ingår i: Clinical Nutrition. - Amsterdam, Netherlands : Elsevier. - 0261-5614 .- 1532-1983. ; 31:6, s. 783-800
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Forskningsöversikt (refereegranskat)abstract
- Background: This review aims to present a consensus for optimal perioperative care in colonic surgery and to provide graded recommendations for items for an evidenced-based enhanced perioperative protocol.Methods: Studies were selected with particular attention paid to meta-analyses, randomised controlled trials and large prospective cohorts. For each item of the perioperative treatment pathway, available English-language literature was examined, reviewed and graded. A consensus recommendation was reached after critical appraisal of the literature by the group.Results: For most of the protocol items, recommendations are based on good-quality trials or meta-analyses of good-quality trials (quality of evidence and recommendations according to the GRADE system).Conclusions: Based on the evidence available for each item of the multimodal perioperative-care pathway, the Enhanced Recovery After Surgery (ERAS) Society, International Association for Surgical Metabolism and Nutrition (IASMEN) and European Society for Clinical Nutrition and Metabolism (ESPEN) present a comprehensive evidence-based consensus review of perioperative care for colonic surgery.
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| 7. |
- Hakioglu, T., et al.
(författare)
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The influence of the Rashba spin-orbit coupling on the two-dimensional magnetoexcitons
- 2011
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 23:34, s. 345405-
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the Rashba spin-orbit coupling (RSOC) on the two-dimensional (2D) electrons and holes in a strong perpendicular magnetic field leads to different results for the Landau quantization in different spin projections. In the Landau gauge the unidimensional wave vector describing the free motion in one in-plane direction is the same for both spin projections, whereas the numbers of Landau quantization levels are different. For an electron in an s-type conduction band they differ by one, as was established earlier by Rashba (1960 Fiz. Tverd. Tela 2 1224), whereas for heavy holes in a p-type valence band influenced by the 2D symmetry of the layer they differ by three. The shifts and the rearrangements of the 2D hole Landau quantization levels on the energy scale are much larger in comparison with the case of conduction electron Landau levels. This is due to the strong influence of the magnetic field on the RSOC parameter. At sufficiently large values of this parameter the shifts and rearrangements are comparable with the hole cyclotron energy. There are two lowest spin-split Landau levels for electrons as well as four lowest ones for holes in the case of small RSOC parameters. They give rise to eight lowest energy bands of the 2D magnetoexcitons, as well as of the band-to-band quantum transitions. It is shown that three of them are dipole-active, three are quadrupole-active and two are forbidden. The optical orientation under the influence of circularly polarized light leads to optical alignment of the magnetoexcitons with different orbital momentum projections in the direction of the external magnetic field.
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| 8. |
- Ivanou, M. F., et al.
(författare)
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Flame acceleration and DDT of hydrogen-oxygen gaseous mixtures in channels with no-slip walls
- 2011
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Ingår i: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487. ; 36:13, s. 7714-7727
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen-oxygen flame acceleration and transition from deflagration to detonation (DDT) in channels with no-slip walls were studied theoretically and using high resolution simulations of 2D reactive Navier-Stokes equations, including the effects of viscosity, thermal conduction, molecular diffusion, real equation of state and a detailed chemical reaction mechanism. It is shown that in "wide" channels (D > 1 mm) there are three distinctive stages of the combustion wave propagation: the initial short stage of exponential acceleration; the second stage of slower flame acceleration; the third stage of the actual transition to detonation. In a thin channel (D < 1 mm) the flame exponential acceleration is not bounded till the transition to detonation. While velocity of the steady detonation waves formed in wider channels (10, 5, 3, 2 mm) is close to the Chapman Jouguet velocity, the oscillating detonation waves with velocities slightly below the CJ velocity are formed in thinner channels (D < 1.0 mm). We analyse applicability of the gradient mechanism of detonation ignition for a detailed chemical reaction model to be a mechanism of the deflagration-to-detonation transition. The results of high resolution simulations are fully consistent with experimental observations of flame acceleration and DDT in hydrogen-oxygen gaseous mixtures.
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| 9. |
- Ivanov, M. F., et al.
(författare)
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Hydrogen-oxygen flame acceleration and deflagration-to-detonation transition in three-dimensional rectangular channels with no-slip walls
- 2013
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Ingår i: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487. ; 38:36, s. 16427-16440
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen-oxygen flame acceleration and the transition from deflagration to detonation (DDT) in channels with no-slip walls are studied using high resolution simulations of 3D reactive Navier-Stokes equations, including the effects of viscosity, thermal conduction, molecular diffusion, real equation of state and detailed (reduced) chemical reaction mechanism. The acceleration of the flame propagating from the closed end of a channel, which is a key factor for understanding of the mechanism of DDT, is thoroughly studied. The three dimensional modeling of the flame acceleration and DDT in a semi-closed rectangular channel with cross section 10 x 10 mm and length 250 mm confirms validity of the mechanism of deflagration-to-detonation transition, which was proposed earlier theoretically and verified using 2D simulations. We show that 3D model contrary to 2D models allows to understand clearly the meaning of schlieren photos obtained in experimental studies. The numerical schlieren and numerical shadowgraph obtained using 3D calculations clarify the meaning of the experimental schlieren and shadow photos and some earlier misinterpretations of experimental data.
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| 10. |
- Kiverin, A. D., et al.
(författare)
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Mechanisms of ignition by transient energy deposition : Regimes of combustion wave propagation
- 2013
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Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - 1539-3755 .- 1550-2376. ; 87:3, s. 033015-
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Tidskriftsartikel (refereegranskat)abstract
- Regimes of chemical reaction wave propagating in reactive gaseous mixtures, whose chemistry is governed by chain-branching kinetics, are studied depending on the characteristics of a transient thermal energy deposition localized in a finite volume of reactive gas. Different regimes of the reaction wave propagation are initiated depending on the amount of deposited thermal energy, power of the source, and the size of the hot spot. The main parameters which define regimes of the combustion waves facilitated by the transient deposition of thermal energy are acoustic time scale, duration of the energy deposition, ignition time scale, and size of the hot spot. The interplay between these parameters specifies the role of gasdynamical processes, the formation and steepness of the temperature gradient, and speed of the spontaneous wave. The obtained results show how ignition of one or another combustion regime depends on the value of energy, rate of the energy deposition, and size of the hot spot, which is important for the practical use and for risk assessment.
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