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| 2. |
- Moskalenko, S. A., et al.
(författare)
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Two-Dimensional Electron-Hole System under the Influence of the Chern-Simons Gauge Field Created by the Quantum Point Vortices
- 2021
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Ingår i: Semiconductors (Woodbury, N.Y.). - : Pleiades Publishing Ltd. - 1063-7826 .- 1090-6479. ; 55:SUPPL 1, s. S35-S48
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Tidskriftsartikel (refereegranskat)abstract
- The Chern-Simons (CS) gauge field theory was widely used to explain and to deeper understand the fractional quantum Hall effects. In this work, we apply the Chern-Simons gauge field theory to a two-dimensional (2D) electron-hole (e-h) system in a strong perpendicular magnetic field under the influence of the quantum point vortices creating by the Chern-Simons (CS) gauge field. The composite electron-hole particles with equal integer positive numbers phi of the attached quantum point vortices are described by the dressed field operators that obey to either the Fermi or Bose statistics depending on the even or odd numbers phi. It is shown that the phase operators, as well as the vector and scalar potentials of the CS gauge field, depend on the difference between the electron and the hole density operators. They vanish in the mean field approximation, when the average values of the electron and of the hole densities coincide. Nevertheless, even in this case, quantum fluctuations of the CS gauge field lead to new properties of the 2D e-h system. It is found that the numbers of vortices attached to each electron and hole are the same. This result is not obvious, and a different distribution of vortices in the environment of electron-hole pairs could be expected. A simple analytical formula is obtained for the shift of the magnetoexciton energy level at the point k = 0 due to the influence of the CS gauge field.
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| 3. |
- Podlesny, I. V., et al.
(författare)
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Metastable bound states of the quasi–bimagnetoexcitons in the lowest Landau levels approximation
- 2020
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : Elsevier B.V.. - 1386-9477 .- 1873-1759. ; 115
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Tidskriftsartikel (refereegranskat)abstract
- Four different spin structures of two electrons and of two holes situated on the lowest Landau levels (LLLs) are taken into account to investigate possible bound states of the two-dimensional magnetic biexciton formed of two magnetoexcitons with opposite wave vectors and antiparallel dipole moments. The singlet and triplet states of the spins of two electrons and of two holes separately, as well as of two para- and two ortho-magnetoexcitons are considered. The general expressions describing the binding energy of the bound states and the normalization conditions characterized by the effective spin parameter η=±1,±1/2 for the corresponding wave functions are derived. The most favorable of the four considered spin configurations happened to be the triplet-triplet spin structure of two electrons and of two holes. In its frame a metastable bound state with activation barrier comparable with two ionization potentials of the magnetoexciton is revealed.
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| 4. |
- Bellafronte, Natália Tomborelli, et al.
(författare)
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A survey of preoperative surgical nutrition practices, opinions, and barriers across Canada
- 2024
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Ingår i: Applied Physiology, Nutrition and Metabolism. - : National Research Council Canada. - 1715-5312 .- 1715-5320. ; 49:5, s. 687-699
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Tidskriftsartikel (refereegranskat)abstract
- Malnutrition is prevalent among surgical candidates and associated with adverse outcomes. Despite being potentially modifiable, malnutrition risk screening is not a standard preoperative practice. We conducted a cross-sectional survey to understand healthcare professionals' (HCP) opinions and barriers regarding screening and treatment of malnutrition. HCPs working with adult surgical patients in Canada were invited to complete an online survey. Barriers to preoperative malnutrition screening were assessed using the Capability Opportunity Motivation-Behaviour model. Quantitative data were analyzed using descriptive statistics and qualitative data were analyzed using summative content analysis. Of the 225 HCPs surveyed (n=111 dietitians, n=72 physicians, n=42 allied healthcare professionals), 96%-100% agreed that preoperative malnutrition is a modifiable risk factor associated with worse surgical outcomes and is a treatment priority. Yet, 65% (n=142/220; dietitians: 88% vs. physicians: 40%) reported screening for malnutrition, mostly in the postoperative period (n=117) by dietitians (n=94), and just 42% (48/113) of non-dietitian respondents referred positively screened patients to a dietitian for further assessment and treatment. The most prevalent barriers for malnutrition screening were related to opportunity, including availability of resources (57%, n=121/212), time (40%, n=84/212) and support from others (38%, n=80/212). In conclusion, there is a gap between opinion and practice among surgical HCPs pertaining to malnutrition. Although HCPs agreed malnutrition is a surgical priority, the opportunity to screen for nutrition risk was a great barrier.
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| 5. |
- Dai, P., et al.
(författare)
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Autoignition and detonation development from a hot spot inside a closed chamber : Effects of end wall reflection
- 2021
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier. - 1540-7489 .- 1873-2704. ; 38:4, s. 5905-5913
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Tidskriftsartikel (refereegranskat)abstract
- The advancement of highly boosted internal combustion engines (ICEs) with high thermal efficiency is mainly constrained by knock and super-knock, respectively, due to the end gas autoignition and detonation development. The pressure wave propagation and reflection in a small confined space may strongly interact with local end gas autoignition, leading to combustion characteristics different from those in a large chamber or open space. The present study investigates the transient autoignition process in an iso-octane/air mixture inside a closed chamber under engine-relevant conditions. The emphasis is given to the assessment of effects of the pressure wave-wall reflection and the mechanism of extremely strong pressure oscillation typical for super-knock. It is found that the hot spot induced autoignition in a closed chamber can be greatly affected by shock/pressure wave reflection from the end wall. Different autoignition modes respectively from the hot spot and the end wall reflection are identified. A non-dimensional parameter quantifying the interplay between different length and time scales is introduced, which helps to identify different autoignition regimes including detonation development near the end wall. It is shown that detonation development from the hot spot may cause super-knock with devastating pressure oscillation. However, the detonation development from the end wall can hardly produce pressure oscillation strong enough for the super-knock. The obtained results provide a fundamental insight into the knocking mechanism in engines under highly boosted conditions.
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| 6. |
- Liberman, Michael A.
(författare)
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Combustion Physics : Flames, Detonations, Explosions, Astrophysical Combustion and Inertial Confinement Fusion
- 2021
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- This book provides the latest achievements and original research work in physics of combustion processes and application of the methods developed in combustion physics for astrophysical problems of stars burning, supernovae explosions and a confined thermonuclear fusion. All the materials in the book are presented in a concise and easily accessible way, but at the same time provides a deep physical inside in the phenomena considered. It is an effective theoretical course with the direct practical implications in engineering fields of engine’s development, energy production, safety issues inherent to terrestrial combustion, as well as in thermonuclear combustion in the inertial fusion. This book is aimed at university students, Ph.D. students and engineers, as well as professionals in combustion, energy-related research, astrophysics and researchers in neighboring fields.
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| 7. |
- Liberman, Michael A.
(författare)
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Hydrogen atom in a magnetic field as an exactly solvable system without dynamical symmetries?
- 2022
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Ingår i: Physics Letters A. - : Elsevier BV. - 0375-9601 .- 1873-2429. ; 445
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Tidskriftsartikel (refereegranskat)abstract
- According to the generally accepted classification, there are supersymmetric superintegrable systems for which the Schrödinger equation is separable in more than one coordinate system and which admit an exact solution. A classic example of a superintegrable system is a hydrogen atom. It is believed that the converse is also true: an exactly solvable system has many integrals of motion corresponding to the separation constants of the Schrödinger equation in more than one coordinate system, which also means a high symmetry group of the system. It is shown that the existence of an exact solution for a hydrogen atom in an arbitrary strong uniform magnetic field apparently contradicts this classification.
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| 8. |
- Qian, Chengeng, et al.
(författare)
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Convergence properties of detonation simulations
- 2020
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Ingår i: Geophysical and Astrophysical Fluid Dynamics. - : Taylor & Francis. - 0309-1929 .- 1029-0419. ; 114:1-2, s. 58-76
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Tidskriftsartikel (refereegranskat)abstract
- We present a high-resolution convergence study of detonation initiated by a temperature gradient in a stoichiometric hydrogen-oxygen mixture using the PENCIL CODE and compare with a code that employs a fifth order weighted essentially non-oscillating (WENO) scheme. With Mach numbers reaching 10-30, a certain amount of shock viscosity is needed in the PENCIL CODE to remove or reduce numerical pressure oscillations on the grid scale at the position of the shock. Detonation is found to occur for intermediate values of the shock viscosity parameter. At fixed values of this parameter, the numerical error associated with those small wiggles in the pressure profile is found to decrease with decreasing mesh width like down to . With the WENO scheme, solutions are smooth at , but no detonation is obtained for . This is argued to be an artifact of a decoupling between pressure and reaction fronts.
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| 9. |
- Qian, Chengeng, et al.
(författare)
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On the mechanism of “tulip flame” formation : The effect of ignition sources
- 2023
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Ingår i: Physics of fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 35:11
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Tidskriftsartikel (refereegranskat)abstract
- The initial stages of hydrogen-air flame propagation in tubes and the mechanism of tulip flame formation are investigated using a high-order numerical code to solve the fully compressible reactive Navier-Stokes equations for a spark or planar igniting flame at the closed end of a tube and propagating to the opposite closed or open end. It is shown that the mechanism of tulip flame formation is universal for both sparked and planar ignited flames in tubes with both ends closed. Flame front inversion results from the tulip-shaped profile of the unburned gas axial velocity near the flame front, which is the result of the superposition of the unburned gas flow generated by the accelerating flame and the reverse flow generated by the rarefaction wave during flame deceleration. In a half-open tube, this mechanism is valid for spark ignited flames. In the case of planar ignition, there is no rarefaction wave, but the growth of bulges on the sidewalls leads to the formation of a tulip flame.
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