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This paper aims to present the results of a design optimization study for the impeller of a small mixed‐flow compressor. The objective of the optimization is to obtain an impeller geometry that could minimize a cost function based on the specific thrust and the thrust specific fuel consumption of a small turbojet engine.

The design methodology is based on an optimization process that uses a configurational database for various compressor geometries. The database is constructed using design of experiments and the compressor configurations are generated using one‐dimensional in‐house design codes, as well as various tools and programs of the Agile Engineering Design System^®, which is a commercially available turbomachinery design system developed at Concepts NREC. The cost function variations within the design space are represented through a neural network. The optimum configuration that minimizes the cost function is obtained using a direct search optimization procedure.

The optimization study generated a small 86 mm diameter mixed‐flow impeller with a 50° meridional exit angle. The optimized compressor, as well as the engine that it is designed for, were shown to have improved performance characteristics.

Preliminary performance and flow analysis of the optimized impeller show shock structures and possible shock‐boundary layer interactions within the blade passages indicating further geometrical fine tuning may be required based on more detailed computational studies or experimental tests.

A further study including the effect of diffuser is required to carry the results to a more practical level.

The originality and the value of the paper comes mainly from two different aspects: combining various in‐house and commercial turbomachinery design codes in one robust methodology to obtain an optimum mixed‐flow compressor impeller that will maximize the performance requirements of a small unmanned air vehicle (UAV) turbojet engine under restricted size and power conditions; and investigation of the design optimization and analysis of a mixed‐flow compressor that could have potential applications in small jet engines to be used in high‐performance UAV applications. Design optimization studies on this type of compressor are very limited in the open literature. For many years, these compressors have been disregarded because of their bulky design in large‐scale engines. However, as mentioned above, they present a great potential for small‐scale jet engines by supplying enough pressure rise, as well as high mass flow rate compared to their centrifugal counterparts.

While there are enormous studies on the determinants of environmental degradation, empirical studies on the effect of renewable energy consumption and economic growth on the environment remain limited. The purpose of this paper is to examine the asymmetric effect of renewable energy consumption and economic growth on environmental degradation in 31 selected sub-Saharan African countries spanning from 1990 to 2018.

To examine possible asymmetric effects of the exogenous variables on environmental degradation, we used the panel nonlinear autoregressive distributed lag approach and secondary data was sourced from the World Bank (2021).

The cointegration test results suggest that there is a long-run cointegration among the variables whereas our main findings indicate that environmental degradation responds asymmetrically to changes in renewable energy consumption and economic growth. The results further reveal that both positive and negative shocks in renewable energy consumption reduce environmental degradation. On the other hand, positive and negative shocks in economic growth increase environmental degradation in the long run.

The implications of this study include the need for policymakers in sub-Saharan Africa to encourage the utilization of renewable energy as it reduces environmental degradation. Also, governments in the subregion should gradually replace the usage of fossil fuels by adapting renewable energy sources so as to achieve higher economic growth.

The positive and negative shocks of renewable energy consumption and economic growth on environmental degradation are examined to ascertain their asymmetric relationships.

This paper aims to analyze and give directions for advancing research in stock market volatility highlighting its features, structural breaks and emerging developments. This study offers a platform to research the benchmark studies to know the research gap and give directions for extending future research.

The author has performed the literature review, and, reference checking as per the snowballing approach. Firstly, the author has started with outlining and simplifying the significance of the subject area, the review illustrating the various elements along with the research gaps and emphasizing the finding.

This work summarizes the studies covering the volatility, its properties and structural breaks on various aspects such as techniques applied, subareas and the markets. From the review’s analysis, no study has clarified the supremacy of any model because of the different market conditions, nature of data and methodological aspects. The outcome of this research work has delivered further magnitude to research the benchmark studies for the upcoming work on stock market volatility. This paper has also proposed the hybrid volatility models combining artificial intelligence with econometric techniques to detect noise, sudden changes and chaotic information easily.

The author has taken the research papers from the scholarly journal published in the English language only and the author may also consider other nonscholarly or other language journals.

To the best of the author’s knowledge, this research work highlights an updated and more comprehensive framework examining the properties and demonstrating the contemporary developments in the field of stock market volatility.

This article tackles the intersection of mothering and labor through the author's own experience as a feminist mother/manager from Istanbul, Turkey. It aims to revisit the first years of motherhood, exploring the struggle to invent a peculiar maternal subjectivity in opposition and negotiation with the patriarchal institution of motherhood, the new definition of maternal labor in a highly digital, neoliberal context and the issue of marital fairness in a dual-income heterosexual marriage.

The article presents an autoethnographic, retrospective and introspective inquiry into the first seven years of the author's mothering experience in order to offer an in-depth exploration of the various aspects of contemporary maternal labor.

The article shows how maternal labor has shifted in nature and expanded in scope in a contemporary non-Western context. It investigates the dissolution of the spatial, temporal and sensorial boundaries between the managerial labor dedicated to the workplace, and to the family. Highlighting the similarities of the two forms of labor, the article manifests the materiality, tangibility and visibility of maternal labor.

Further intersectional studies shall be beneficial to redefine maternal labor in different contexts.

Departing and diverting from the terms “invisible labor” and “mental load”, the article suggests a shift in terminology to stress the multifaceted medley of managerial tasks mothers undertake today.

The article provides an original take on maternal labor through the first-hand experience of a middle-class, professional mother from Istanbul, Turkey.