Samir K H. Safi, Olajide Idris Sanusi and Afreen Arif
This study aims to evaluate linear mixed data sampling (MIDAS), nonlinear artificial neural networks (ANNs) and a hybrid approach for exploiting high-frequency information to…
Abstract
Purpose
This study aims to evaluate linear mixed data sampling (MIDAS), nonlinear artificial neural networks (ANNs) and a hybrid approach for exploiting high-frequency information to improve low-frequency gross domestic product (GDP) forecasting. Their capabilities are assessed through direct forecasting comparisons.
Design/methodology/approach
This study compares quarterly GDP forecasts from unrestricted MIDAS (UMIDAS), standalone ANN and ANN-enhanced MIDAS models using five monthly predictors. Rigorous empirical analysis of recent US data is supplemented by Monte Carlo simulations to validate findings.
Findings
The empirical results and simulations demonstrate that the hybrid ANN-MIDAS performs best for short-term predictions, whereas UMIDAS is more robust for long-term forecasts. The integration of ANNs into MIDAS provides modeling flexibility and accuracy gains for near-term forecasts.
Research limitations/implications
The model comparisons are limited to five selected monthly indicators. Expanding the variables and alternative data processing techniques may reveal further insights. Longer analysis horizons could identify structural breaks in relationships.
Practical implications
The findings guide researchers and policymakers in leveraging mixed frequencies amidst data complexity. Appropriate modeling choices based on context and forecast horizon can maximize accuracy.
Social implications
Enhanced GDP forecasting supports improved policy and business decisions, benefiting economic performance and societal welfare. More accurate predictions build stakeholder confidence and trust in statistics underlying critical choices.
Originality/value
This direct forecasting comparison offers unique large-scale simulation evidence on harnessing mixed frequencies with leading statistical and machine learning techniques. The results elucidate their complementarity for short-term versus long-term modeling.
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Mandeep Singh, Deepak Bhandari and Khushdeep Goyal
This study aims to examine the corrosion and flexural behaviour of advanced hybrid aluminium matrix nanocomposites (HAMNCs) made with a vacuum-assisted stir die casting (two-layer…
Abstract
Purpose
This study aims to examine the corrosion and flexural behaviour of advanced hybrid aluminium matrix nanocomposites (HAMNCs) made with a vacuum-assisted stir die casting (two-layer feeding) and reinforced with titanium oxide (TiO2) and yttrium oxide (Y2O3) nanoparticles. The previous researchers have shown that TiO2 and Y2O3 nanoparticles make aluminium composites much more resistant to corrosion and wear.
Design/methodology/approach
Salt spray corrosion tests were done on the samples over time as well as the pre-and post-corrosion morphology of the test samples was also investigated. The density, porosity and energy dispersive X-ray of the fabricated samples were observed.
Findings
It was observed that a lower corrosion rate of 0.127 mils/year and 0.573 mils/year was seen in the Al/5 Wt.%TiO2/5 Wt.%Y2O3 (HAMNC1) and Al/7.5 Wt.%TiO2/2.5 Wt.%Y2O3 (HAMNC3), respectively. It was evident from the results that the pores and densities of the samples varied with the filler concentrations and matrix filler wettability. HAMNC1 has the lowest values of density and porosity at 2.568 g/cm3 and 9.91%, respectively. At the same time, a significant improvement in the flexural strength of 72 N/mm2 was also seen in the HAMNC1 configuration.
Practical implications
The proposed hybrid samples are well suited for aerospace and automobile structural components such as brake drums, discs, engine cylinders and fins.
Originality/value
The mixed influence evaluation of TiO2 and Y2O3 nanoparticles with pure Al on composite samples has not been studied. This research aims to examine the combined influence of nanoparticles on the corrosion aspects of two-step feeding vacuum stir casted products, as well as their morphology.
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Severe plastic deformation (SPD) has provided new opportunities in investigations of enhanced mechanical properties like high strength and ductility by permitting grain refinement…
Abstract
Purpose
Severe plastic deformation (SPD) has provided new opportunities in investigations of enhanced mechanical properties like high strength and ductility by permitting grain refinement to a nanometer level, especially ultra‐fine grained and nanocrystalline metals and alloys. These materials have been attracting more and more research interest during the past few decades due to scientific curiosity and their engineering potentials with a significant advancement in their understanding. The purpose of this paper is to find the relationship between processing, structures and properties of these novel materials with the ultimate goal of producing a model to account for the grain size changes at the nano‐scale.
Design/methodology/approach
In this paper, specimens with various grain sizes from 23 to 80 μm are obtained via processing by SPD, using equal channel angular press (ECAP) technique. The effect of grain size on the hardness properties of nanostructured copper alloy has been investigated using micro‐hardness testing of the samples to test the mechanical properties of this material.
Findings
The results reveal that the copper alloys processed by SPD using ECAP technique after various passes differ in the grain size and mechanical properties. The hardness test exhibits grained size dependence according to Hall‐Petch relationship from room temperature. The increase in the hardness with number of passages suggest increasing in strain during deformation, as the passes increase the smaller grain size can be produced.
Originality/value
The paper usefully shows how nanostructured materials by SPD technique will offer a possible solution to the problem of using light metals for certain applications by increasing the strength of materials which could be used in structures where previously strength requirement in various industries, including such as, for example, transportation, medical devices and electronics. Understanding the relationship between processing, structures and properties will enhance the performance of metals and alloys in a target application which is important in improving the mechanical properties of engineering materials that are necessary fundamental for applications of lightweight materials and structures. The influences of structural parameters, such as grain size, grain shape on plastic deformation which is important parameters in study the mechanical properties of nanostructured materials.
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Bhavya Swathi I., Suvarna Raju L. and Perumalla Janaki Ramulu
Friction stir processing (FSP) is overviewed with the process variables, along with the thermal aspect of different metals.
Abstract
Purpose
Friction stir processing (FSP) is overviewed with the process variables, along with the thermal aspect of different metals.
Design/methodology/approach
With its inbuilt advantages, FSP is used to reduce the failure in the structural integrity of the body panels of automobiles, airplanes and lashing rails. FSP has excellent process ability and surface treatability with good corrosion resistance and high strength at elevated temperatures. Process parameters such as rotation speed of the tool, traverse speed, tool tilt angle, groove design, volume fraction and increase in number of tool passes should be considered for generating a processed and defect-free surface of the workpiece.
Findings
FSP process is used for modifying the surface by reinforcement of composites to improve the mechanical properties and results in the ultrafine grain refinement of microstructure. FSP uses the frictional heat and mechanical deformation for achieving the maximum performance using the low-cost tool; the production time is also very less.
Originality/value
100
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Rajat Yadav, Vijay Kumar Dwivedi, Anas Islam and Shashi Prakash Dwivedi
Aluminium metal matrix composite (AMMC) is most popular in various industrial applications such as aerospace, automobile, marine, sports and many others. In common practice…
Abstract
Purpose
Aluminium metal matrix composite (AMMC) is most popular in various industrial applications such as aerospace, automobile, marine, sports and many others. In common practice, silicon carbide, aluminum oxides, magnesium oxide, graphene and carbon nano tubes are the major reinforcing elements to prepare the AMMC. The purpose of this paper is to develop AMMCs reinforce with eggshell (ES) and rice husk ash (RHA).
Design/methodology/approach
Stir casting process is used for preparation of AMMC. From past few years, more emphasis is given to prepare the AMMCs using agro waste such as rice husk and/or ES as reinforcing materials. In this method, after the Al-matrix material is melted; it is stirred vigorously to form vortex at the surface of the melt, and the reinforcement material is then introduced at the side of the vortex. Stir casting process is a vortex and vigorous method to prepare the AMMCs. First, aluminum alloy (AA3105) is melted in the furnace when metal is in semisolid form. Reinforcement, i.e. ES and RHA are preheated at temperature 220°C and 260°C, respectively.
Findings
The result of AMMC shows that the tensile strength and hardness increased by using 22.41% and 45.5%, respectively, at 4.75 Wt.% each reinforcement, i.e. ES and RHA, and 1% Cr. The toughness and ductility of metal matrix composite (MMCs) have decreased up to 23.31% and 19.23% respectively by using 1% Cr, 4.75 wt. % ES and by 4.75 wt. % RHA of composite material.
Originality/value
In this work, Cr, waste ES and RHA have been used to develop green MMC to support the green revolution as promoted/suggested by United Nations, thus reducing the environmental pollution.
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One of the most innovative materials available today is polyester resin, which finds application in a wide range of industries, including consumer products, automotive, aircraft…
Abstract
Purpose
One of the most innovative materials available today is polyester resin, which finds application in a wide range of industries, including consumer products, automotive, aircraft, marine, construction, sports and renewable energy, due to its impressive mechanical properties and low cost. In recent years, significant progress has been achieved in the development of polyester resin composites. This paper aims to provide an overview of the recent advances in the field of polyester resin composites.
Design/methodology/approach
The review introduces the properties of polyester resins and the fabrication techniques used to prepare polyester resin composites. It provides an overview of the reinforcement materials such as fibers and nanoparticles that are commonly used to enhance the properties of the composites. Recent advances in the use of fillers such as nanocellulose, graphene and carbon nanotubes are also discussed. This work highlights the latest developments in the functionalization of polyester resin composites, which aims to improve the properties of the composite materials for specific applications in diverse fields such as aerospace, biomedical and energy. It highlights how collaborations worldwide, business and academia are working together to advance polyester resin composite technologies.
Findings
The study emphasizes how urgent it is to adopt sustainable practices, which, in turn, is driving research into polyester resins that are recycled and biobased to create a circular economy. Constant advancements open up new possibilities for application development and improve performance, such as nanotechnology and smart materials. Furthermore, businesses are being revolutionized by sophisticated production processes like 3Dimensional printing and Internet of Things integration, which enable mass customization and real-time monitoring. These partnerships advance the sector and encourage the use of polyester resin composites in environmentally friendly applications. The remarkable mechanical, thermal and chemical capabilities of polyester resin composites are highlighted, showcasing their importance in a range of applications.
Originality/value
The study is a major step toward a sustainable tomorrow since it highlights the potential of polyester resin composites to build a more durable and environmentally friendly future. This review paper summarizes the recent advances in the development of polyester resin composites, highlighting their potential for advancing technologies in various fields. The knowledge gained from this review paper will undoubtedly aid researchers in designing novel polyester resin composite materials with tailored properties for specific applications.
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While most West European nations were formed around pre-existing entities that could be called “countries” before the modern age, this was not the case in the Middle East. Some…
Abstract
While most West European nations were formed around pre-existing entities that could be called “countries” before the modern age, this was not the case in the Middle East. Some entities, like Egypt, did have a clear political and cultural identity before colonialism, others, like Algeria, did not. This chapter discusses the four states of the Maghreb: Morocco, Algeria, Tunisia and Libya, through the perspective of “country creation” going into and coming out of colonial rule. We can see here two “models” of fairly similar types of historical development, one showing a gradual process through a protectorate period to relatively stable modern nations, another through violent conquest and direct colonization ending in violent liberation and military and wealthy but fragile states. The article asks whether these models for the history of country creation and the presence or absence of pre-colonial identities can help explain the modern history and nature of these states in the Arab Spring and the years thereafter. Then, a more tentative attempt is made to apply these models to two countries of the Arab east, Syria and Iraq. While local variations ensure that no model can be transferred directly, it can show the importance of studying the historical factors that go into the transition from geographical region to a country with people that can form the basis of a nation.
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Jamilu Iliyasu, Suleiman O. Mamman, Attahir B. Abubakar and Aliyu Rafindadi Sanusi
The recent Russia–Ukraine conflict highlights the geopolitical importance of natural gas, especially in Europe. In this light, this study examines the impact of the Russia–Ukraine…
Abstract
Purpose
The recent Russia–Ukraine conflict highlights the geopolitical importance of natural gas, especially in Europe. In this light, this study examines the impact of the Russia–Ukraine conflict on the spread of price bubbles from European natural gas to international energy prices.
Design/methodology/approach
The Generalized Supremum Augmented Dickey-Fuller (GSADF) test is employed to detect the occurrence of price bubble episodes while the Dynamic Logit Model is used to examine price bubble contagion between the two markets. Further, a tri-variate VAR model is used to examine the determinants of the price bubble.
Findings
The findings reveal multiple bubble episodes in both European natural gas and international energy prices. Further, evidence of bilateral contagion between European natural gas and the international energy market is found. In addition, the Russia–Ukraine conflict triggers price bubble episodes in both markets. Finally, a counterfactual analysis suggests that the conflict increases the bubble contagion from the European natural gas market to the international energy market by about 40%. These findings imply that the Russia–Ukraine conflict is a significant driver of high upside risks to bubble occurrence and subsequent contagion to both European natural gas and international energy prices.
Originality/value
To the best of our knowledge, this study contributes new empirical evidence that the Russian–Ukrainian conflict significantly impacts the spread of price bubbles from the European natural gas market to international energy markets.
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Purpose: This chapter looks specifically at the sources of economic policy uncertainty in Nigeria, and discusses their impact on the Nigerian economy while drawing implications…
Abstract
Purpose: This chapter looks specifically at the sources of economic policy uncertainty in Nigeria, and discusses their impact on the Nigerian economy while drawing implications for Africa. It identifies factors that transmit uncertainty in economic policy in Nigeria and draw implications for other African countries.
Methodology: This chapter uses a literature survey methodology to identify the sources of economic policy uncertainty in Nigeria.
Findings: The identified sources of economic policy uncertainty in Nigeria are: the frequent changes in central bank policy, unexpected changes in government policy, political interference, unexpected fall in global oil price, recession, and unethical practices.
Implications: The implication of the study is that rising economic policy uncertainty in Nigeria can have a significant effect on the Nigerian economy and for connected African countries.
Originality: Previous studies have not examined the sources of economic policy uncertainty in Nigeria.