Recently, the thermal performance of the parabolic trough collector (PTC), augmented to be more applicable and efficient, received intensive research. These studies aimed to improve heat transfer in the receiver part, in order to decrease the heat loss, and enhance the heat transfer to the thermal fluid. Many previous review papers focused on the numerical sides rather than the experimental side. Several research papers recommended doing more research in the experimental field; in order to decrease the gap between the numerical and experimental results, as well as increase the confidence level of what has been done in the theoretical field researches. Regarding the recommendations of the recent papers to decrease the gap between numerical and experimental aspects, this review paper focused on the recent experimental research related to thermal enhancement performance in the receiver part of the parabolic solar collector. In this research, different categories of the enhancement methods are discussed in detail through this review, namely nanofluids, surface modifications, and inserts models or the two categories combined together. We discussed these categories for different parabolic troughs considering only the recent experimental research between the period from 2014 up to 2019. Some parameters were discussed, such as the main dimensions of the examined receiver and parabolic collector. Moreover, types of nanoparticle specifications and preparation methods with different base fluids were highlighted. In addition, we discussed different aspects of using inserts models and inlet and outlet surface modification methods. Finally, the main thermal efficiency and thermal performance enhancement results for each work were presented.
Authors:Ekhlas H. Karam, Noor S. Abdul-Jaleel, and Basma J. Salah
The control of higher order linear system is one of the main fields of research area that has been studied for decades because of the difficulty in designing a controller for such systems. One of the best approaches to solve this problem is by reducing the order of the system into a second orders, based on this reduction many approaches can be proposed for controlling the higher order system, therefore many reduction methods are suggested and developed for this purpose, one of these methods is the Mixed Reduction Method (MRM). The first contribution of this paper is to improve the efficiency of MRM by using a flower optimization algorithm.
The second contribution of this paper lies in proposing a hybrid Neuro-Robust deadbeat controller using Matlab facilities to control higher order linear systems based on the optimized MRM. Where the robust deadbeat control algorithm is combined with a modified adaptive radial basis neural network to improve the robustness and efficacy of the deadbeat controller, which is partially lost when designing this controller for the higher order based on model reduction. The suggested radial basis function neural network has a simple design. The proposed control scheme assures the stability of the overall closed loop-controlled system; therefore, it can be applied to control any linear higher order systems. Results of different simulation examples show the efficiency of the proposed hybrid controller (Neuro-robust deadbeat) in tracking different reference signals compared to the robust deadbeat controller.
Authors:Caturwati Ni Ketut, Yusuf Yusvardi, and Komara Fajar Muhamad
The availability of freshwater is increasingly becoming an international concern because of the increase in population and the diminishing forest area as a source of water, leading to a freshwater crisis. The coastal and swamp areas abound in water, but humans cannot consume it due to the quality. One effort that can be done in overcoming this problem is by treating existing raw water with solar distillation methods. However, the main obstacle faced in this method is the intensity of sunlight that is not stable throughout the day so that the productivity of distilled water is disrupted. Using the appropriate phase change material (PCM) is expected to make the distillation process smoother and increase the production of pure water. In this study, myristic acid was used as PCM in double slope solar distillation system. Through observation, it was obtained that the average water temperature in the basin equaled to 42.5 °C while the melting point of the myristic acid was 58 °C. This shows that the use of myristic acid as an energy storage through phase change process does not occur. Therefore, the use of myristic acid as PCM for increasing the productivity of solar distillation in these experiments is not effective because the melting point of PCM is higher than water temperature in the basin. Therefore, material with a phase change temperature below 42.5 °C is more appropriate to use in these conditions.
Authors:Varun Barthwal, M.M.S. Rauthan, and Rohan Varma
Virtual machine (VM) management is a fundamental challenge in the cloud datacenter, as it requires not only scheduling and placement, but also optimization of the method to maintain the energy cost and service quality. This paper reviews the different areas of literature that deal with the resource utilization prediction, VM migration, VM placement and the selection of physical machines (PMs) for hosting the VMs. The main features of VM management policies were also examined using a comparative analysis of the current policies. Many research works include Machine Learning (ML) for detecting the PM overloading, the selection of VMs from over-utilized PM and VM placement as the main activities. This article aims to identify and classify research done in the area of scheduling and placement of VMs using the ML with resource utilization history. Energy efficiency, VM migration counts and Service quality were the key performance parameters that were used to assess the performance of the cloud datacenter.
Due to recent changes in the labour market, recruitment and retaining employees have become more important than ever. Research dealing with the appearance of new generations in the labour market has found that they are less loyal to their employers, have high demands, and the key factors that they consider when choosing a job are salary, career opportunities, working environment, and work-life balance. As numerous studies in recent years have proved the importance of a healthy lifestyle in the context of labour, the question has arisen whether opportunities for sport participation and services supporting the well-being of employees have an influence on young people when they are seeking employment. We carried out an online survey to find out what students of the University of Debrecen think about the issue. The results were in line with the findings of previous studies, that is, young people look for high salaries, good working conditions, work-life balance and career opportunities when choosing a job. However, respondents did not identify sports opportunities and well-being benefits as major factors Yet, we found significant differences between different groups in terms of preference of particular factors, depending on sex, marital status, and whether someone does physical exercises regularly, and whether someone works while attending a university course or not.
Authors:Adebayo Surajudeen Adekunle, Adekunle Akanni Adeleke, Peter Pelumi Ikubanni, Peter Olorunleke Omoniyi, Tajudeen Adelani Gbadamosi, and Jamiu Kolawole Odusote
Heat treatment industries require various quenching media to improve the properties of the materials to be quenched. Petroleum based mineral (PBM) oil, a non-biodegradable oil, is popular amongst others quenchants in heat treatment processes. Recently, biodegradable oils mostly in their raw, unblended and unbleached forms have been employed for quenching of various engineering materials. Therefore, the present study examined the effects of some selected bio-quenchants in blended raw (BR) and blended bleached (BB) forms on the mechanical properties and microstructure of solution heat treated aluminum (Al)-alloy. Edible vegetable oil (70% by volume) was blended with 30% by volume of jatropha oil to form the bio-quenchant oils. Another set of bio-quenchants were formed by bleaching the raw oils before mixing so as to reduce the oxidation level and contaminations in the oil. The Al-alloy is solution heat treated at 500 °C and soaked for 15 min in an electric muffle furnace before quenching in the various established bio-quenchants. Results showed that samples treated in blended raw melon (BRM) oil have higher tensile strength of 151.76 N/mm2 while samples quenched in blended bleached melon (BBM) oil have higher hardness value of 61.00 HRC. In accordance to the results obtained the bio-quenchants were found to be effective replacement to the PBM oil.
Authors:Donika Maloku, Péter Balogh, Attila Bai, Zoltán Gabnai, and Péter Lengyel
The article highlights the worldwide dissemination of precision agriculture scientific researches published from the period of 1996–2018, data gathered in the Scopus citation database, using the science mapping method. The findings show that there is a constant rise in the number of publications in precision agriculture. The USA is not only leading in the adoption of precision agriculture technologies but also in the publication of papers, accompanied by China placed in second place. The most frequent keywords highlighted the main topics authors concentrated on more, and the national affiliation of most cited papers was the USA. The main prominence and contributions of the results present scientific research trends in precision agriculture in the last two decades, and demonstrate the main countries, authors and organizations who have contributed, and were more productive in this area.
The main idea of the current paper consists in introducing the fractional order calculus in a control system. To control the system, an adaptive control technique with reference model is used. The fractional order models for the plant and reference model are obtained. To achieve the performances imposed by the fractional order reference model, a fractional order adaptive control law is proposed, which is a combination of two methods (MIT and Lyapunov stability). The original contribution in this paper is the use of fractional order calculus in the combined MIT and Lyapunov stability method and showing the dynamic behavior of the system. Several simulations are used to emphasize the effectiveness and benefits of the proposed method.
Authors:A. Ferchichi, S. Harrabi, M. Feki, and H. Fellah
Both the immature and mature Vicia faba L. seeds are used for human consumption. However, there is a lack of information on the phytochemical composition and the potent biological properties of the immature seeds. The aim of the present study was to establish the profile of bioactive lipids as well as the antibacterial, antioxidant, and α-amylase and α-glucosidase inhibitory capacities of the immature and mature Vicia faba L. seeds. The studied petroleum ether extracts contain different bioactive compounds such as β-sitosterol, lupeol, β-amyrin, α-tocopherol, and γ-tocopherol. The extracts of the immature seeds exhibited higher antioxidant and antibacterial activities than those of mature ones. All tested extracts exerted higher inhibition on α-glucosidase than α-amylase. The immature seeds appeared as promising sources of natural antioxidants, antibacterial compounds, and α-amylase and α-glucosidase inhibitors. Thus, the immature Vicia faba L. seeds have a great potential as functional foods providing health beneficial properties.
Authors:L. Ben Haj Said, S. Bellagha, and K. Allaf
The present study deals with the impact of storage time on the quality of dehydrofrozen versus conventionally frozen apple. Samples were submitted to freezing as fresh fruit or following the first stage of air drying. The quality was evaluated along a freezing storage period of 18 months under -18 °C. Thaw exudate water (TEW), total colour difference (TCD), and total polyphenol content (TPC) of dehydrofrozen/thawed samples were assessed regarding the water content (W) versus the frozen storage time (FST) (0-18 months). Dehydrofreezing exhibited significant effects on TEW and TCD of dehydrofrozen/thawed apples. Indeed, the lower the W, the lower the TEW content and TCD of partially dried frozen/thawed samples. TPC losses were significant for samples without any pre-dehydration stage and decreased when initial water content decreased. The 18-month frozen storage at -18 °C had the most insignificant effects on all quality response variables for the previously most dried samples. Thus, adequate drying of fruit before freezing is a relevant way to maintain the stability of fruit quality during long-term storage.