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The article examines the problems of the emergence and development of the flow of refugees from Ukraine during the first half of 2022 as a complex phenomenon that depends on rational (economic) and irrational (social-psychological) factors. The phenomenological model, created on the basis of the Burgers’ equation, which reproduces the process of the involvement of the new refugees to the flow and the resistance of the environment to the formation of this flow, made it possible to analyze such subtle effects as the existence of a hub country, where the initial accumulation of refugees takes place, followed by redistribution, and the influence of infrastructure problems in the exit country. Transitional regimes from the infrastructural problems prevailing in the country of exit to the predominant influence of the hub-country effects are also considered. It is concluded that the entry to new levels of the refugee flow could be achieved due to the effects of emotional and economic (rational) behavior of refugees replenishing the hub, i.e., a stepwise development of the refugee flow is possible if new hubs would be created, or the existing hub will be freed up from overloading. On the basis of mathematical modeling, it is shown that in the case when the refugee flow is restrained by infrastructural problems in the exodus country, the exit to the stationary regime is delayed. Identification of the proposed model was carried out based on the empirical data on the refugee flow development using the apparatus of incorrect problems of the mathematical physics. A comparison of the dynamic effects of the refugee flow development from Ukraine with similar processes in Syria and Iraq was carried out, which allowed for identification of the zones of influence of infrastructure problems and the hub effect in the refugee flow development. The use of the concept of refugees’ economic independence (self-sufficiency), which was developed in 2018 by the Office of the United Nations High Commissioner for Refugees, was proposed as a basis for policy formation in the field of refugee assistance. The consequences of the discrete use of this concept in the case of refugees from Syria are analyzed, and the dynamics of employment opportunities for these refugees in countries with similar and different socio-cultural conditions were compared. A conclusion was made about the fundamental difference in the employment trends in those types of countries. The authors formulated proposals regarding the utilization of the Monte Carlo methods and the learning model for researching the peculiarities of the process of Ukrainian refugees achieving a certain level of economic independence (self-sufficiency), determining the typical time of reaching such a level, obtaining the distribution of probabilities of getting the first job depending on the initial competencies and skills of refuges, their education, experience, and foreign languages mastery.

With the widespread use of unmanned aerial vehicles in the aviation industry, the importance of detailed examination of propellers, whose task is to provide thrust, has also increased. A propeller is a part that is formed by attaching more than one aerodynamically shaped blade to a hub and produces thrust by being rotated by a motor. The amount of thrust that is produced by a propeller depends on some parameters such as diameter, number of blades, pitch angle, etc. The aim of this study is to investigate the thrust distribution along a propeller diameter section with the gradual increase of the hub diameter. Related studies show that the maximum thrust of a propeller is obtained in the region between 75% and 85% of the propeller length. In order to obtain the necessary data, numerical flow analyzes were made and the results were discussed. As a conclusion, at the very closer to the root of the propeller blade, the amount of produced thrust is considerably low compared to the near tip of the propeller. Therefore, the thrust loss due to the increase of the propeller hub diameter is negligible and maximum thrust is obtained in the expected region. [ABSTRACT FROM AUTHOR]

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An optimal marine propeller design method is proposed, which integrates the lifting line and surface panel method and is characterized by the use of the surface panel method to take the hub effect into consideration. By developing an integrated approach instead of an iterative method for the calculation of the interaction between the hub and the designed blades, the hub effects on the optimal circulation can be accounted for throughout the theoretical design procedure. This new integrated method provides a fast and accurate enough method to model the straight forward hub surface, in the optimal propeller design. A systematic design procedure from the basic design inputs to the blade geometry determination is performed and the designed propellers are validated by the surface panel method and the RANS method. The design and analysis cases are considered by different approaches with comparison and validation. And a comparative study including different hub geometries is also performed to reveal the mechanism of the hub effect on the distributions of the propeller optimal loads. [ABSTRACT FROM AUTHOR]

This article analyses the effects of Regional Trade Agreements (RTAs) on bilateral trade in Africa. A structural gravity equation is estimated over the period 1955–2014. The overall effect of RTAs on African trade is strong, but depending on the nature of the RTAs, there is a decreasing impact over time. While Economic Integration Agreements (EIAs) still favour trade in Africa, there was no trade creation coming from Free Trade Agreements between 1990 and 2014. However, the provisions of RTAs do not have a negative impact on trade: agreements that include behind-the-border policies do not significantly deter bilateral trade. To explain the declining impact of RTAs, we look at their redistributive impact between members states. There is no evidence that large countries disproportionally export diversified goods due to RTAs (no 'home effect'). Countries with a good international network ('hub effect') benefited more than other countries of RTAs between 1955 and 1990 but this is however less true on the most recent period (1990–2014). [ABSTRACT FROM AUTHOR]

For a long period of time, researchers have been using analytical models to predict wake characteristics behind wind turbines in wind farms. Early models were weak and just depicted an approximation of wake shape. Based on those models, wake profile looks like a hat. A large number of analytical and numerical simulations were performed to predict the velocity profile in wind farm; some of them can predict both wake shape and velocity magnitude while some cannot reach the real magnitude of the velocity. In this study, a hybrid method based on blade element momentum (BEM) and computational fluid dynamics (CFD) is employed in order to investigate the actual shape of the wake using actuator disc (AD) model which represents the wind turbine. Different turbulence models are examined to investigate the effect of turbulence models on wake shape. It is shown that the wake shape depends on the induction factor which is calculated using (BEM) theory and assuming a constant induction factor leads to some errors. Comparison between recent study and old analytical models shows that the numerical approach is more accurate almost in far wake because of considering the effect of turbulence. Again, in the recent survey, a simple model is presented in order to simulate the hub. It is concluded that the hub has a great effect on downstream wake and should be taken into account. In this new approach, the error of wake modeling using AD significantly decreased. [ABSTRACT FROM AUTHOR]

The home market effect (HME) is a distinguishing feature of the “new” trade theory. It is customarily defined as disproportionate positive causation from expenditure to production. Recently it has been argued that this dynamic definition of the HME is problematic in a multi-country framework, because it neglects third country effects. In this paper, we show that more than one exogenous parameter change is needed to overturn the dynamic HME. An isolated increase in the size of the home country will unambiguously lead to an over-proportional domestic industry expansion. We then illustrate with some specific scenario what type of third country effects can “swamp” the HME. [ABSTRACT FROM AUTHOR]