10 research outputs found
Wavelet-based Adaptive Techniques Applied to Turbulent Hypersonic Scramjet Intake Flows
The simulation of hypersonic flows is computationally demanding due to large
gradients of the flow variables caused by strong shock waves and thick boundary
or shear layers. The resolution of those gradients imposes the use of extremely
small cells in the respective regions. Taking turbulence into account
intensives the variation in scales even more. Furthermore, hypersonic flows
have been shown to be extremely grid sensitive. For the simulation of
three-dimensional configurations of engineering applications, this results in a
huge amount of cells and prohibitive computational time. Therefore, modern
adaptive techniques can provide a gain with respect to computational costs and
accuracy, allowing the generation of locally highly resolved flow regions where
they are needed and retaining an otherwise smooth distribution. An h-adaptive
technique based on wavelets is employed for the solution of hypersonic flows.
The compressible Reynolds averaged Navier-Stokes equations are solved using a
differential Reynolds stress turbulence model, well suited to predict
shock-wave-boundary-layer interactions in high enthalpy flows. Two test cases
are considered: a compression corner and a scramjet intake. The compression
corner is a classical test case in hypersonic flow investigations because it
poses a shock-wave-turbulent-boundary-layer interaction problem. The adaptive
procedure is applied to a two-dimensional confguration as validation. The
scramjet intake is firstly computed in two dimensions. Subsequently a
three-dimensional geometry is considered. Both test cases are validated with
experimental data and compared to non-adaptive computations. The results show
that the use of an adaptive technique for hypersonic turbulent flows at high
enthalpy conditions can strongly improve the performance in terms of memory and
CPU time while at the same time maintaining the required accuracy of the
results.Comment: 26 pages, 29 Figures, submitted to AIAA Journa
Исследование кинетики термически активированных изменений состава и свойств торфяных гуминовых кислот
Изучены изменения состава и свойств гуминовых кислот вследствие предварительной термообработки торфа до 250 °С: элементный и функциональный состав, концентрация парамагнитных центров, термическая устойчивость, содержание гидролизуемых веществ. Получены кинетические закономерности процессов декарбоксилирования и дегидратации при термической деструкции гуминовых кислот
Transition Prediction for Scramjet Intakes Using the γ-Re_θ_t Model Coupled to Two Turbulence Models
Neuroactive steroids: Focus on human brain
Studies in experimental animals have revealed important roles of neuroactive steroids in the control of central nervous system functions during physiological and pathological conditions, suggesting that they may represent good candidates for the development of neuroprotective strategies for neurodegenerative and psychiatric disorders. Even if the characterization of the roles played by neuroactive steroids in humans is still at the beginning, several data are already available showing that they may be synthesized within the human CNS. Among the different enzymes, a prominent role is dedicated to aromatase that synthesizes estradiol whose neuroprotective effects have been described in experimental animals. Neuroactive steroid levels are modified by neurodegenerative conditions (i.e. Alzheimer's and Parkinson's diseases, multiple sclerosis) or in other mental diseases (i.e. schizophrenia), and may have an important role in physiological conditions, as the reorganization of grey and white matter during human puberty and adolescence or as a consequence of emotional responses. The interaction of some neuroactive steroids (i.e., allopregnanolone and isopregnanolone) with GABA-A receptor is particularly important in mood disorders. The presumptive role of estradiol and progesterone in neuroprotection is here discussed by comparing contradictory data that have been collected in humans. In conclusion, the state of the art of our knowledge of the role of neuroactive steroids in the normal and pathological human brain suggests several lines of future therapeutic developments in the treatments of neurological, neurodegenerative and affective disorders. © 2011 IBRO.Peer Reviewe