On shock-induced light-fluid-layer evolution

Shock-induced light-fluid-layer evolution is firstly investigated experimentally and theoretically. Specifically, three quasi-one-dimensional helium gas layers with different layer thicknesses are generated to study the wave patterns and interface motions. Six quasi-two-dimensional helium gas layers with diverse layer thicknesses and amplitude combinations are created to explore the Richtmyer–Meshkov instability of a light-fluid layer. Due to the multiple reflected shocks reverberating inside a light-fluid layer, the speeds of the two interfaces gradually converge, and the layer thickness saturates eventually. A general one-dimensional theory is adopted to describe the two interfaces’ motions and the layer thickness variations. It is found that, for the first interface, the end time of its phase reversal determines the influence of the reflected shocks on it. However, the reverberated shocks indeed lead to the second interface being more unstable. When the two interfaces are initially in phase, and the initial fluid layer is very thin, the two interfaces’ spike heads collide and stabilise the two interfaces. Linear and nonlinear models are successfully adopted by considering the interface-coupling effect and the reverberated shocks to predict the two interfaces’ perturbation growths in all regimes. The interfacial instability of a light-fluid layer is quantitatively compared with that of a heavy-fluid layer. It is concluded that the kind of waves reverberating inside a fluid layer significantly affects the fluid-layer evolution.

The question on the existence of black holes

Simulation shows that general relativity would lead to the existence of black holes if gravitation is always attractive. However, although we observed an invisible and extremely heavy object governs the orbits of stars at the center of our galaxy, we still cannot determine the existence of a black hole. Thus, one may ask whether black holes actually exist. Einstein’s general relativity has been established, because its prediction on the bending of light rays has been confirmed by observation. However, Einstein’s prediction on the increment of weight for a piece of metal as the temperature increases is proven incorrect by experiments, which actually show a reduction of weight. This leads to the necessary existence of repulsive gravitational force, which has been demonstrated by a charged capacitor hovering above the earth. Thus, Einstein, Newton, Galileo, and Maxwell all made the error of overlooking the repulsive gravitational charge-mass interaction. Thus, it is necessary to rejustify the existence of black holes, because gravity is not always attractive. Moreover, repulsive gravitational force makes it necessary to extend general relativity to a five-dimensional theory. Thus, to find out whether black holes exist, it is necessary to investigate the repulsive gravitation and a five-dimensional space.

De Sitter braneworld and gravitational waves

We study the braneworld theory constructed by multi scalar fields. The model contains a smooth and infinitely large extra dimension, allowing the background fields propagating in it. We give a de Sitter solution for the four-dimensional cosmology as a good approximation to the early universe inflation. We show that the graviton has a localizable massless mode, and a series of continuous massive modes, separated by a mass gap. There could be a normalizable massive mode, depending on the background solution. The gravitational waves of massless mode evolve the same as the four dimensional theory, while that of the massive modes evolve greatly different from the massless mode.

Methods of determination of the gas-dynamic characteristics of a jet nozzle of an aerodynamic object

The efficiency of aerodynamic objects with jet engines is the result of many factors, among which nozzle parameters are of great importance in relation to the general engine design and the energy source, that determines the composition and properties of the engine working medium. In this respect, an urgent need was to calculate nozzle gas-dynamic characteristics and geometric parameters at various designing and testing stages of jet engines. Relatively simple calculations involving a large number of assumptions and detailed modeling with regard to the maximum possible number of factors are the basis of the existing modeling approaches. In the present work, the problem was to assess an agreement between such modeling methods of a specific ‘high-energy material – working medium – nozzle’ system and the experimental ones. The calculations using one-dimensional nozzle theory and the gas dynamics modeling method revealed a 6 % difference in the results of various parameters. At the same time, a closer agreement was noted between the experimental data and the results predicted by the gas dynamics modeling method. Moreover, in comparison to one-dimensional theory, the gas dynamics modeling method of an engine jet nozzle is more labor-intensive and expensive for calculations. Therefore, from the practical viewpoint, it is advisable to give preference to one-dimensional theory to calculate the engine construction and to verify calculations with the use of the modeling methods.

Cosmic cloaking of rich extra dimensions

We present arguments that show why it is difficult to see rich extra dimensions in the universe. Conditions are found where significant size and variation of the extra dimensions in a Kaluza–Klein compactification lead to a black hole in the lower-dimensional theory. The idea is based on the hoop conjecture concerning black hole existence, as well as on the observation that dimensional reduction on macroscopically large, twisted, or highly dynamical extra dimensions contributes positively to the energy density in the lower-dimensional theory and can induce gravitational collapse. A threshold for the size is postulated on the order of [Formula: see text][Formula: see text]m, whereby extra dimensions of length above this level must lie inside black holes, thus cloaking them from the view of outside observers. The threshold depends on the size of the universe, leading to speculation that in the early stages of evolution truly macroscopic and large extra dimensions would have been visible.

CFD tool application in predicting the behavior of a centrifugal fan designed by one-dimensional theory

Computational fluid dynamics (CFD) is the most current technology in the fluid flow study. Experimental methods for predicting the turbomachinery performance involve greater time consumption and financial resources compared to the CFD approach. The purpose of this article is to present the analysis of CFD simulation results in a centrifugal fan. The impeller was calculated using the one-dimensional theory and the volute the principle of constant angular momentum. The ANSYS-CFX software was used for the simulation. The turbulence model adopted was the SST. The simulation provided the characteristic curves, the pressure and velocity distribution, and the static and total pressure values at impeller and volute exit. An analysis of the behavior of the pressure plots, and the loss and recovery of pressure in the volute was performed. The results indicated the characteristic curves, the pressure and velocity distribution were consistent with the turbomachinery theory. The pressure values showed the static pressure at volute exit was smaller than impeller exit for some flow rate. It caused the pressure recovery coefficient negative. This work indicated to be possible design a centrifugal fan applying the one-dimensional theory and optimize it with the CFD tool.

TOWARDS A MULTI-DIMENSIONAL THEORY OF TEMPORAL CONTROL IN THE GIG ECONOMY

This paper proposes a multi-dimensional theory of temporal control in the gig economy. Specifically, we focus on different types of platform-based temporal control and their respective effects on (a) workers’ autonomy, (b) value of free time, and (c) their social and political connectedness. Theoretically, we draw on the sociology of time and normative time literature in political theory. Empirically, the framework is informed by the synthesis of the literature about algorithms in the gig economy, with particular attention to the methods of temporal control. Meanwhile, we draw insights from a larger comparative project that examines algorithmic labor control and resistance across ride-hailing platforms (Uber and Lyft), TaskRabbit, and delivery platforms (DoorDash, Uber Eats, and Instacart) in the United States. The project interviewed 50 gig workers between 2017 and 2020. Through a systematic synthesis of primary and secondary materials, this paper contributes to understanding temporalities and work autonomy in the gig economy, and more broadly, flexible workplaces where the boundaries between work and non-work time become blurred.

1092Questioning health inequality as policy agenda in Korea: using Luke’s three-dimensional theory of power

Focus of Presentation Health inequality is an important public health concern in Korea. However, policies to reduce health inequalities still falls behind. This research focus on political agenda making process of health inequality. To achieve this aim, we utilized Lukes’ three-dimensional theory of power to explain current state of ‘health inequality’ as political agenda in South Korea. Findings We conducted 12 in-depth interviews with 6 policymakers and 6 practitioners, and focus-group interview with 5 researchers in 2016. From the qualitative analysis, we constructed 3 main themes. First theme, the perception, participants’ perspective on health inequality varied widely. Some participants assumed health inequality in Korea as an inevitable social condition, not even a problem to be tackled. Despite differing views on the condition, most participants attributed health inequality as result of accumulated result of socio-economic inequality. Second theme, the barriers, many claimed health inequality too abstract, complex, and ambiguous concept to be politicized. Policy actors saw current political apathy to paucity of empirical evidence, which was the complete opposite to the researchers. Third theme, the supression, was analyzed using luke's theory of power. On first dimension, the pluralistic power, conservative government has been marginalizing overal inequality issue. On second dimension, two major obstacles of growth-first policy and result-ased management of bureaucratic organization were found. On third dimension, the governmentality, 3 mechanisms that suppress health inequality were found. Those were medicalization of health, neoliberal discourse that individualize health as personal asset, and policy monopoly by 'health insurance' that absorbe every health-related issue. Conclusions/Implications In conclusion, we derived five propositions for making health inequality a policy agenda in Korea. Strong political leadership to tackle structrual inequality is needed, more decentralized, democratic governance system should be founded, intersectoral approach and comprehensive intervention for health inequality should be implemented, alternative health regime to reorganized current medicalization of health should suffuse, finally, more knowledge and experience to denaturalize health inequality should be followed. Key messages To tackle health inequality, power that supress health equity becoming policy agenda should be anlalized.