A compressible near-wall turbulence model for boundary layer calculations

A compressible near-wall two-equation model is derived by relaxing the assumption of dynamical field similarity between compressible and incompressible flows. This requires justifications for extending the incompressible models to compressible flows and the formulation of the turbulent kinetic energy equation in a form similar to its incompressible counterpart. As a result, the compressible dissipation function has to be split into a solenoidal part, which is not sensitive to changes of compressibility indicators, and a dilational part, which is directly affected by these changes. This approach isolates terms with explicit dependence on compressibility so that they can be modeled accordingly. An equation that governs the transport of the solenoidal dissipation rate with additional terms that are explicitly dependent on the compressibility effects is derived similarly. A model with an explicit dependence on the turbulent Mach number is proposed for the dilational dissipation rate. Thus formulated, all near-wall incompressible flow models could be expressed in terms of the solenoidal dissipation rate and straight-forwardly extended to compressible flows. Therefore, the incompressible equations are recovered correctly in the limit of constant density. The two-equation model and the assumption of constant turbulent Prandtl number are used to calculate compressible boundary layers on a flat plate with different wall thermal boundary conditions and free-stream Mach numbers. The calculated results, including the near-wall distributions of turbulence statistics and their limiting behavior, are in good agreement with measurements. In particular, the near-wall asymptotic properties are found to be consistent with incompressible behavior; thus suggesting that turbulent flows in the viscous sublayer are not much affected by compressibility effects

A near-wall two-equation model for compressible turbulent flows

A near-wall two-equation turbulence model of the K - epsilon type is developed for the description of high-speed compressible flows. The Favre-averaged equations of motion are solved in conjunction with modeled transport equations for the turbulent kinetic energy and solenoidal dissipation wherein a variable density extension of the asymptotically consistent near-wall model of So and co-workers is supplemented with new dilatational models. The resulting compressible two-equation model is tested in the supersonic flat plate boundary layer - with an adiabatic wall and with wall cooling - for Mach numbers as large as 10. Direct comparisons of the predictions of the new model with raw experimental data and with results from the K - omega model indicate that it performs well for a wide range of Mach numbers. The surprising finding is that the Morkovin hypothesis, where turbulent dilatational terms are neglected, works well at high Mach numbers, provided that the near wall model is asymptotically consistent. Instances where the model predictions deviate from the experiments appear to be attributable to the assumption of constant turbulent Prandtl number - a deficiency that will be addressed in a future paper

A review of near-wall Reynolds-stress

The advances made in second-order near-wall turbulence closures are summarized. All closures examined are based on some form of high Reynolds number models for the Reynolds stress and the turbulent kinetic energy dissipation rate equations. Consequently, most near-wall closures proposed to data attempt to modify the high Reynolds number models for the dissipation rate equation so that the resultant models are applicable all the way to the wall. The near-wall closures are examined for their asymptotic behavior so that they can be compared with the proper near-wall behavior of the exact equations. A comparison of the closure's performance in the calculation of a low Reynolds number plane channel flow is carried out. In addition, the closures are evaluated for their ability to predict the turbulence statistics and the limiting behavior of the structure parameters compared to direct simulation data

On the Finite-Time Complexity and Practical Computation of Approximate Stationarity Concepts of Lipschitz Functions

We report a practical finite-time algorithmic scheme to compute approximately stationary points for nonconvex nonsmooth Lipschitz functions. In particular, we are interested in two kinds of approximate stationarity notions for nonconvex nonsmooth problems, i.e., Goldstein approximate stationarity (GAS) and near-approximate stationarity (NAS). For GAS, our scheme removes the unrealistic subgradient selection oracle assumption in (Zhang et al., 2020, Assumption 1) and computes GAS with the same finite-time complexity. For NAS, Davis & Drusvyatskiy (2019) showed that $\rho$-weakly convex functions admit finite-time computation, while Tian & So (2021) provided the matching impossibility results of dimension-free finite-time complexity for first-order methods. Complement to these developments, in this paper, we isolate a new class of functions that could be Clarke irregular (and thus not weakly convex anymore) and show that our new algorithmic scheme can compute NAS points for functions in that class within finite time. To demonstrate the wide applicability of our new theoretical framework, we show that $\rho$-margin SVM, $1$-layer, and $2$-layer ReLU neural networks, all being Clarke irregular, satisfy our new conditions.Comment: 20 pages, 3 figures, ICML 202

Characteristics and strategies of a consistently profitable proprietary day trader at bursa Malaysia / Saw Imm Song, Ei Yet Chu and Tian So Lai

Proprietary day trading is relatively new in Malaysia. This study looks into the background characteristics, strategies, behaviour of an above average proprietary trader and factors that determined her success. Recent literature in the developed markets found that the majority of the day traders failed in the first year of trading. Few studies have looked into the winning characteristics and strategies of the traders. Contrary to the findings on failed traders, who traded actively, speculatively, and to their detriment, this case study found that a successful trader on the other hand is highly attentive and disciplined. On average the trader had executed approximately 20 counters per day for  about 100 transactions. More than 50% of the roundtrips transactions were completed within half an hour and 70% were completed within 2 hours.  The trader was most active in the morning for buy transactions and the majority of the roundtrips were completed in the afternoon. The trader usually holds large positions only for shorter periods to minimise huge losses and disposition effect.  It was evident that the trader employs scalping strategies that she profits from very short run and small movement of prices rather than employing fundamental analysis which requires longer term investment horizon. If the trader made profits in the morning, the likelihood is the trader will be more aggressive in the afternoon trades. The regression results reveal that factors that significantly explained the profitability of the trader were the transaction values and the time entering the trades. Market sentiment and duration of holding time do not significantly explain the profitability made by the trader. It shows that in a bullish market, the trader tended to trade more transactions; however that does not contribute significantly to the profits made

The effect of health-related quality of life on health service utilization and willingness to pay for treatment of Chinese with chronic hepatitis B infection

Conference Theme: Integrating HRQOL in Health Care Policy, Research, and PracticeOral Session: Measuring Health Outcomes in Chronic Disease: abstract no. 139

Transfusion-refractory anaemia in liver cirrhosis

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Relationship Between Joint/shared Activities with Marital Dissatisfaction, Flexibility, Cohesion, and Communication

Education Psycholog

Neuroprotective effects of minocycline on double-stranded RNA-induced neurotoxicity in cultured cortical neurons

1. Minocycline, memantine,and glycoconjugate were assessed for their ability to protect cultured primary cortical neurons against double-stranded RNA-induced neurotoxicity. 2. Minocycline but not memantine or glycoconjugate protected cultured cells and warrants further investigation.published_or_final_versio