LES, DNS and RANS for the analysis of high-speed turbulent reacting flows

The purpose of this research is to continue our efforts in advancing the state of knowledge in large eddy simulation (LES), direct numerical simulation (DNS), and Reynolds averaged Navier Stokes (RANS) methods for the computational analysis of high-speed reacting turbulent flows. In the second phase of this work, covering the period 1 Sep. 1993 - 1 Sep. 1994, we have focused our efforts on two research problems: (1) developments of 'algebraic' moment closures for statistical descriptions of nonpremixed reacting systems, and (2) assessments of the Dirichlet frequency in presumed scalar probability density function (PDF) methods in stochastic description of turbulent reacting flows. This report provides a complete description of our efforts during this past year as supported by the NASA Langley Research Center under Grant NAG1-1122

Налоговые реформы в Украине и Грузии: эволюция приоритетов

The Georgian and Ukrainian tax systems both emerged after the collapse of the USSR, yet the tax reforms in the two countries pursued different trajectories and produced different outcomes. The article systematizes and compares the results of the tax reforms in Ukraine and Georgia. The study applies qualitative methods for historical analysis, for periodization of the reforms and for classifying their key priorities and the factors that influenced them. Quantitative methods are applied to compare the tax burden in Ukraine, Georgia and OECD countries. The success and failure of the tax reforms was measured by the index of economic freedom (including its component – the index of tax burden). The first hypothesis suggested that a reduction in the tax burden had a positive impact on the indicators of economic freedom; the second hypothesis stated that a reduction in the tax burden affected fiscal freedom but did not affect the index of economic freedom. Regression dependences of the average tax burden (including the tax burden resulting from social security contributions) and the index of economic freedom (including the index of tax burden) were built in the R environment. The regression analysis confirmed the first hypothesis for Ukraine and the second, for Georgia. This result can be explained by the fact that, unlike Ukraine, the Georgian tax reforms focused on institutional changes, which determined their success. In 1996–2018, Georgia rose in the ranking of economic freedom and joined the group of economically free countries. Moreover, this country has been steadily improving its position in the ranking. Ukraine, on the contrary, has remained in the group of economically unfree countries. Due to the unbalanced reforms and insufficient structural changes, the country’s government failed to ensure the desired effect from the tax burden reduction.For citationBedianashvili G., Ivanov Yu. B., Paientko T. V. Tax Reforms in Ukraine and Georgia: Changing Priorities. Journal of Tax Reform. 2019;5(2):107–128. DOI: 10.15826/jtr.2019.5.2.063Article infoReceived June 25, 2019; accepted July 27, 2019Становление и развитие налоговых систем Грузии и Украины имели одну отправную точку – распад СССР, но пути реформирования были разными, что повлияло на результаты реформ. Целью статьи является систематизация и сравнительный анализ результатов налоговых реформ двух стран. Качественные методы исследования применены для исторического анализа и периодизации налоговых реформ в Украине и Грузии. Выявлены факторы и приоритеты налоговых реформ в исследуемых странах. Изменения налоговых систем структурированы в соответствии с выделенными этапами. Количественные методы использованы для аналитического сравнения налоговой нагрузки в Украине, Грузии и странах ОЭСР. В качестве индикатора результатов налоговых реформ выбран индекс экономической свободы, и его составляющая – индекс налоговой нагрузки. Сформулированы две гипотезы: (1) снижение налоговой нагрузки положительно отразилось на показателях экономической свободы; (2) снижение налоговой нагрузки повлияло на фискальную свободу, но не повлияло на индекс экономической свободы. С помощью программной среды R построены регрессионные зависимости средней налоговой нагрузки (включая налоговую нагрузку по взносам на социальное страхование) и индекса экономической свободы (включая индекс налоговой нагрузки). Результаты регрессионного анализа показали, что для Украины подтвердилась первая гипотеза, для Грузии – вторая. Полученный результат объясняется тем, что проводя налоговые реформы, Грузия, в отличие от Украины, сделала акцент на институциональных изменениях в сфере налогообложения. Как результат, грузинские налоговые реформы оказались более успешными, и страна за период с 1996 по 2018 г. в рейтинге экономической свободы смогла подняться в группу экономически свободных стран и ежегодно повышать рейтинг в этой группе. Украина так и осталась в группе экономически несвободных стран, поскольку несбалансированность налоговых реформ, недостаточные институциональные и структурные изменения не дали ожидаемого эффекта от снижения налоговой нагрузки.Для цитированияБедианашвили Г., Иванов Ю. Б., Паентко Т. В. Налоговые реформы в Украине и Грузии: эволюция приоритетов // Journal of Tax Reform. – 2019. – Т. 5, № 2. – С. 107–128. – DOI: 10.15826/jtr.2019.5.2.063Информация о статьеДата поступления 25 июня 2019 г.; дата принятия к печати 27 июля 2019 г

Safety Recommendations for Evaluation and Surgery of the Head and Neck During the COVID-19 Pandemic

Importance The rapidly expanding novel coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2, has challenged the medical community to an unprecedented degree. Physicians and health care workers are at added risk of exposure and infection during the course of patient care. Because of the rapid spread of this disease through respiratory droplets, health care workers who come in close contact with the upper aerodigestive tract during diagnostic and therapeutic procedures, such as otolaryngologists–head and neck surgeons, are particularly at risk. A set of safety recommendations was created based on a review of the literature and communications with physicians with firsthand knowledge of safety procedures during the COVID-19 pandemic. Observations A high number of health care workers were infected during the first phase of the pandemic in the city of Wuhan, China. Subsequently, by adopting strict safety precautions, other regions were able to achieve high levels of safety for health care workers without jeopardizing the care of patients. The most common procedures related to the examination and treatment of upper aerodigestive tract diseases were reviewed. Each category was reviewed based on the potential risk imposed to health care workers. Specific recommendations were made based on the literature, when available, or consensus best practices. Specific safety recommendations were made for performing tracheostomy in patients with COVID-19. Conclusions and Relevance Preserving a highly skilled health care workforce is a top priority for any community and health care system. Based on the experience of health care systems in Asia and Europe, by following strict safety guidelines, the risk of exposure and infection of health care workers could be greatly reduced while providing high levels of care. The provided recommendations, which may evolve over time, could be used as broad guidance for all health care workers who are involved in the care of patients with COVID-19

The counter-propagating Rossby-wave perspective on baroclinic instability. Part III: Primitive-equation disturbances on the sphere

Baroclinic instability of perturbations described by the linearized primitive quations, growing on steady zonal jets on the sphere, can be understood in terms of the interaction of pairs of counter-propagating Rossby waves (CRWs). The CRWs can be viewed as the basic components of the dynamical system where the Hamiltonian is the pseudoenergy and each CRW has a zonal coordinate and pseudomomentum. The theory holds for adiabatic frictionless flow to the extent that truncated forms of pseudomomentum and pseudoenergy are globally conserved. These forms focus attention on Rossby wave activity. Normal mode (NM) dispersion relations for realistic jets are explained in terms of the two CRWs associated with each unstable NM pair. Although derived from the NMs, CRWs have the conceptual advantage that their structure is zonally untilted, and can be anticipated given only the basic state. Moreover, their zonal propagation, phase-locking and mutual interaction can all be understood by ‘PV-thinking’ applied at only two ‘home-bases’—potential vorticity (PV) anomalies at one home-base induce circulation anomalies, both locally and at the other home-base, which in turn can advect the PV gradient and modify PV anomalies there. At short wavelengths the upper CRW is focused in the mid-troposphere just above the steering level of the NM, but at longer wavelengths the upper CRW has a second wave-activity maximum at the tropopause. In the absence of meridional shear, CRW behaviour is very similar to that of Charney modes, while shear results in a meridional slant with height of the air-parcel displacement-structures of CRWs in sympathy with basic-state zonal angular-velocity surfaces. A consequence of this slant is that baroclinically growing eddies (on jets broader than the Rossby radius) must tilt downshear in the horizontal, giving rise to up-gradient momentum fluxes that tend to accelerate the barotropic component of the jet

Thermal and mechanical properties of hemp fabric-reinforced nanoclay-cement nano-composites

The influence of nanoclay on thermal and mechanical properties of hemp fabric-reinforced cement composite is presented in this paper. Results indicate that these properties are improved as a result of nanoclay addition. An optimum replacement of ordinary Portland cement with 1 wt% nanoclay is observed through improved thermal stability, reduced porosity and water absorption as well as increased density, flexural strength, fracture toughness and impact strength of hemp fabric-reinforced nanocomposite. The microstructural analyses indicate that the nanoclay behaves not only as a filler to improve the microstructure but also as an activator to promote the pozzolanic reaction and thus improve the adhesion between hemp fabric and nanomatrix

Abrasion resistance and compressive strength of unprocessed rice husk ash concrete

This paper investigates the effects of adding natural rice husk ash collected from uncontrolled burning and without previous grinding (NRHA) as cement replacement in concrete. To obtain an adequate particle size, NRHA was mixed with coarse aggregate for a convenient period of time before adding the other components. Compressive strength, water absorption, porosity, and abrasion resistance expressed as weight loss were examined. Test results show that decreasing the particle size through mixing with coarse aggregate improved the compressive strength, reduced the permeability, and increased the abrasion resistance of concrete. By mixing NRHA with aggregate for 8 min, abrasion resistance improved by 10.35 and 23.62% over the control concrete at 28 and 91 days, respectively. Incorporating NRHA in concrete by grinding with coarse aggregate during the mixing process could be suitable for making normal-strength concrete and for applications where abrasion resistance is an important parameter. In addition, using NRHA as a partial replacement cement contributes to the reduction of CO2 emissions due to the production of cement

Status of Turbulence Modeling for Hypersonic Propulsion Flowpaths

This report provides an assessment of current turbulent flow calculation methods for hypersonic propulsion flowpaths, particularly the scramjet engine. Emphasis is placed on Reynolds-averaged Navier-Stokes (RANS) methods, but some discussion of newer meth- ods such as Large Eddy Simulation (LES) is also provided. The report is organized by considering technical issues throughout the scramjet-powered vehicle flowpath including laminar-to-turbulent boundary layer transition, shock wave / turbulent boundary layer interactions, scalar transport modeling (specifically the significance of turbulent Prandtl and Schmidt numbers) and compressible mixing. Unit problems are primarily used to conduct the assessment. In the combustor, results from calculations of a direct connect supersonic combustion experiment are also used to address the effects of turbulence model selection and in particular settings for the turbulent Prandtl and Schmidt numbers. It is concluded that RANS turbulence modeling shortfalls are still a major limitation to the accuracy of hypersonic propulsion simulations, whether considering individual components or an overall system. Newer methods such as LES-based techniques may be promising, but are not yet at a maturity to be used routinely by the hypersonic propulsion community. The need for fundamental experiments to provide data for turbulence model development and validation is discussed