Simulations of liquid metal flows over plasma-facing component edges and application to beryllium melt events in JET

Navier-Stokes simulations of liquid beryllium flows over the straight edge of plasma-facing components are carried out in conditions emulating upper dump plate melting observed experimentally in JET. The results demonstrate the existence of three main hydrodynamic regimes featuring various degrees of downstream flow attachment to the underlying solid surface. Transitions between these regimes are characterized by critical values of the Weber number, which quantifies the relative strength of fluid inertia and surface tension, thereby providing a general stability criterion that can be applied to any instance of transient melt events in fusion devices. The predictive capabilities of the model are tested by comparing numerical output with JET data regarding the morphology of the frozen melt layers and the location of beryllium droplets splashed onto nearby vacuum vessel surfaces as a result of disruption current quench plasmas interacting with the solid beryllium tiles protecting the upper main chamber regions. Simulations accounting for the coupling between fluid flow and heat transfer confirm the key role played by re-solidification as a stabilizing process, as previously found through macroscopic melt dynamics calculations performed with the MEMOS-U code. The favourable agreement found between the simulations and the general characteristics of the JET beryllium upper dump plate melt splashing give confidence that the same approach can be applied to estimate the possibility of such mechanisms occurring during disruptions on ITER.

9. Governing from Below

This chapter studies a key aspect of delegation in British politics: decentralization and local/national self-government. It deals with local government in England, and government in the devolved territories/nations of Scotland, Wales, and Northern Ireland. Decentralization in British politics has formed into a complex pattern, where there are different dynamics in the various territories: relative centralization in England, power-sharing in Northern Ireland, pragmatic devolution in Wales, and then a strong push towards independence in Scotland. For a question about how centralized or decentralized British politics is, the answer would need to be based on where a person lives, with England rehearsing the conventional arguments about constitutional centralization and the rest of the country increasing decentralization, if not a form of federalism. The chapter then assesses the question of the rationale and general stability of the system, with respect to the integrity of the UK as a whole.

General stability and exponential growth of nonlinear variable coefficient wave equation with logarithmic source and memory term

This paper is concerned with the asymptotic stability and instability of solutions to a variable coefficient logarithmic wave equation with nonlinear damping and memory term. This model describes wave travelling through nonhomogeneous viscoelastic materials. By choosing appropriate multiplier and using weighted energy method, we prove the exponential decay of the energy. Besides, we also obtain the instability at the infinity of the solutions in the presence of the nonlinear damping.

Dying AdS Schwarzschild black hole

The criteria for thermal stability of a most general quantum black hole derived by us appeared in the form of a series of inequalities connecting second-order derivatives of black hole mass with respect to its parameters, which determine the mass of the black hole. These nullify the concept of positivity of specific heat as the sole criteria for thermal stability. Using this most general stability criterion, we prove here that AdS Schwarzschild black holes are no longer stable anywhere in their parameter space if cosmological constant is allowed to vary. We also calculate the fluctuations of both horizon area and cosmological constant of this black hole. We calculate specific heat of it and compare this with Hawking’s prediction.

The Resilience of Foreign Remittances in the Time of Pandemic: Bangladesh Perspective

Foreign remittances have contributed significantly to Bangladesh’s overall economic development through the years. More than half a million Bangladeshi citizens work abroad, which lessens the country’s labour market burden. As a result, Bangladesh deemed a big beneficiary of remittances, earning USD 21.8 billion in 2020. It is inseparably linked to economic matters and influenced Bangladesh’s economic strengths. However, it endured appallingly during the recent worldwide COVID-19 outbreak and has already seen remittance inflows fall. This article examines the effects of foreign remittances on the COVID-19 issue and the link between remittances and the general stability of Bangladesh’s economy. Also, suggested some possible courses of action to face these challenges in an effective way. The recommendations derived from this study findings will aid to increase the valuable remittances and overall welfare for the society.

On the Backward Path Tracking Control of N-Trailer Systems

This paper considers the lateral control of articulated wheeled vehicles in backward motion. The parameterized articulated vehicle is composed of a car-like truck and N passive trailers, resulting in one single steerable axle. First a nonlinear path tracking control law based on exact linearization of an offset model is reviewed and the general stability conditions of such systems is presented. Second, a stability analysis for some vehicle cases is performed and verified in simulation. The possible application of this path tracking control law in real world articulated vehicles is discussed, and its limitations are shown.

Some aspects of consideration of initial imperfections in the calculations of stability of thin-walled elements of open profile

Performed analysis of the initial geometric imperfections influence on the stability of the open C-shaped bars. Test tasks were solved in MSC Nastran, which is based on the finite element method. Imperfections are given in different formulations: the general stability loss of an ideal bar, of wavy bulging of walls and shelves, of deplanation of a bar. To model imperfections, has been developed a program which for the formation of new coordinates of the nodes of the "deformed" model, the components of a vector similar to the form of stability loss are added to the corresponding coordinates of the middle surface of the bar. In this way, you can set initial imperfections in the forms of stability loss of the bar with different amplitude. Researches made with different values of the imperfection amplitude and eccentricity of applied efforts. All tasks are performed in linear and nonlinear staging. The conclusion is made regarding the influence of initial imperfections form and imperfection amplitude on the critical force in nonlinear calculations. It was found that the most affected are imperfections, which are given in the form of total loss of stability. It was revealed the influence of the imperfection amplitude on the magnitude of the critical force for such imperfections. The influence of imperfections amplitude given in the form of wavy bulging walls and in the form of deplanations is not affected on the value of the critical force.