The Relationship Between Biomechanical-Anthropometrical Parameters and the Force Exerted on the Head When Heading Free Kicks in Soccer

Background: Soccer is a contact sport in which the players are frequently faced with the risk of injury. It has been shown that the force exerted on the head during heading can be as much as 500–1200 Newton (N). Objectives: The main objective of this study was to determine whether there was any relationship between the force exerted on the head and several biomechanical and anthropometrical parameters related to heading free kicks. Patients and Methods: A total of 16 semi-professional soccer players with at least 5 years experience participated in this study. The mean age, height, and weight of the study participants were 21.36 ± 5.67, 178 ± 5.99 cm, and 70.55 ± 8.55 kg, respectively. To measure the force exerted on the heads of the players, a pressure gauge was installed on their foreheads. Each participant was asked to defend the ball using the heading technique three times. A camera with a sampling frequency of 150 frames per second was used to record the moment of impact between the ball and head during each heading event. For each participant and replicate, the ball and head velocity (m/s) as well as the angular body changes (degrees) were calculated using MATLAB and AutoCAD softwares, respectively. Descriptive statistics, including means and standard deviations were used to describe the data. Pearson correlation coefficient (alpha = 0.05) was used to examine potential relationships between the variables of interest. Results: Significant correlations existed between the force exerted on the head during heading, participant age, body mass, body fat percentage, and head perimeter (P < 0.05). Conclusions: The study revealed the significance of anthropometric variables related to heading, such as age and head perimeter. Therefore, it was concluded that these variables should be considered when teaching and practicing the heading technique with players of different ages and anthropometric sizes

Performance Analysis of Solar Combined Ejector-Vapor Compression Cycle Using Environmental Friendly Refrigerants

In this study, a new model of a solar combined ejector-vapor compression refrigeration system has been considered. The system is equipped with an internal heat exchanger to enhance the performance of the cycle. The effects of working fluid and operating conditions on the system performance including COP, entrainment ratio (ω), compression ratio (rp) and exergy efficiency were investigated. Some working fluids suggested are: R114, R141b, R123, R245fa, R600a, R365mfc, R1234ze(e) and R1234ze(z). The results show that R114 and R1234ze(e) yield the highest COP and exergy efficiency followed by R123, R245fa, R365mfc, R141b, R152a and R600a. It is noticed that the COP value of the new solar ejector-vapor compression refrigeration cycle is higher than that of the conventional ejector cycle with R1234ze(e) for all operating conditions. This paper also demonstrates that R1234ze(e) will be a suitable refrigerant in the solar combined ejector-vapor compression refrigeration system, due to its environmental friendly properties and better performance.   ABSTRAK: Kajian ini menganalisa model baru sistem penyejukan mampatan gabungan ejektor-wap solar.Sistem ini dilengkapi dengan penukar haba dalaman untuk meningkatkan prestasi kitaran.Kesan bendalir bekerja dan keadaan operasi pada prestasi sistem termasuk COP, nisbah pemerangkapan (ω), nisbah mampatan (rp) dan kecekapan eksergi telah disiasat.Beberapa bendalir bekerja yang dicadangkan adalah: R114, R141b, R123, R245fa, R600a, R365mfc, R1234ze(e) dan R1234ze(z).Hasil kajian menunjukkan R114 dan R1234ze(e) menghasilkan COP dan kecekapan eksergi tertinggi diikuti oleh R123, R245fa, R365mfc, R141b, R152a dan R600a.Didapati nilai COP kitaran penyejukan mampatan bagi ejektor-wap solar baru adalah lebih tinggi daripada kitaran ejektor konvensional dengan R1234ze(e) bagi semua keadaan operasi.Kertas kerja ini juga menunjukkan bahawa R1234ze(e) boleh menjadi penyejuk yang sesuai dalam sistem penyejukan mampatan gabungan ejektor -wap solar, kerana ianya mempunyai prestasi yang lebih baik serta sifatnya yang lebih mesra alam sekitar.   KEYWORDS: environmental friendly refrigerants; solar combined ejector-vapor compression cycle; R1234ze(e

Convection Heat Transfer Modeling of Nano-fluid Tio 2 Using Different Viscosity Theories

Abstract: In this paper, the effects of adding nanoparticles including Tio2 to a fluid media for purpose of free convection heat transfer improvement were analyzed

Solar collectors and photovoltaics as combined heat and power systems: A critical review

A main method to increase the solar energy utilization efficiency is to combine heat and power generation together. In this paper, a critical review of the literature on solar combined heat and power systems (CHP) is conducted, which includes solar photovoltaic/thermal systems, concentrated photovoltaic/thermal systems, and various combination with different solar collectors and applications. It shows that there are serious gaps in this field, which calls for more research. The modeling and analysis of the electrical parts of the CHP systems are not adequate, and there are limited studies on the economic and exergy assessments of the solar concentrating CHP systems. The solar collectors for combined CHP were focused on optimizing the performance of the maximum average useful power generation and minimum total heat transfer area, little environment impact analysis was conducted. Careful exergy, economic and environmental analysis on both electronic and thermal performance is suggested, especially for large CHP system. Also, further studies are recommend for investigating the hybrids of concentrating collectors with CHP, with considering the economic issues

An experimental investigation of a hybrid photovoltaic/thermoelectric system with nanofluid application

Improving photovoltaic efficiency is fundamental to the large scale utilization of solar energy and reduction of carbon emission. In this field, reducing the temperature of the Photovoltaic (PV) panel will increase its efficiency and power production. Utilizing hybrid photovoltaic/thermoelectric (PV/TE) systems is an effective way to simultaneously release the excess heat of the PV panel and use this heat to produce power. The cooling method used for the thermoelectric module (TEM) plays an important role in the system efficiency as well as the produced power. A new nanofluid-based cooling method for a hybrid photovoltaic/thermoelectric system is proposed in this work and compared with the conventional cooling methods experimentally. To this end, five different cooling methods were investigated experimentally, namely natural cooling, forced air cooling, water cooling, SiO2/water nanofluid cooling, and Fe3O4/water nanofluid cooling. The results showed the promise of SiO2/water nanofluid cooling, which yielded the highest power and efficiency, showing 54.29% and 3.35% improvement, while Fe3O4/water nanofluid cooling showed 52.40% and 3.13% improvement in power production and efficiency respectively, comparing with the natural cooling method

Energy analysis and shadow modeling of a rectangular type salt gradient solar pond

In calculating the total solar energy input into a salt gradient solar pond, the current method is insufficient mainly caused by two problems. Firstly, the existing equations of solar pond energy analysis can be only used for momentary calculations but it is very time-consuming for long time periods. Secondly, the shading effect inside the pond affects significantly the energy storage performance of the pond, especially in small ones. To solve the first problem, the mean values of variable parameters during the concerned time period is proposed in this work and the ‘first mean value theorem for definite integrals’ is used to derive the average values. For the second problem, a rectangular pond with vertical walls is investigated as an example, and the exact sunny areas in different depths of the pond are calculated at different time conditions. The experimental data of a published study is used for the validation. The energy efficiency of the low convective zone of the experimental pond is calculated theoretically, which shows a good agreement with the experimental value. The experimental data and theoretical results for the energy efficiency are 9.68% and 11.38% for January, 17.54% and 18.92% for May, and 28.11% and 30.94% for August, respectively. The modified equations can be used to predict a pond performance before its construction

Novel ZnO-Ag/MWCNT nanocomposite for the photocatalytic degradation of phenol

A novel Ag-doped ZnO nanoparticle with different amount of multi-walled carbon nano tubes (MWCNTs) was developed, aiming to shift the band edge toward longer wavelength. New particles were produced in a simple wet synthesis method and assessed toward the removal of phenol under UV-A illumination. The photocatalysts were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) with an energy-dispersive X-ray (EDX) spectroscopy analysis, transition electron microscopy (TEM), BET surface area analyzer, UV–vis diffuse reflectance spectroscopy (DRS) and photoluminescence spectroscopy (PL). The results indicated that all the samples containing MWCNTs exhibit higher photocatalytic activity than the bare ZnO and Ag doped ZnO nanoparticles. At a 10% MWCNT addition, the novel particle achieved a photocatalytic conversion rate of 81% in removing 100 ppm phenol under UV-A light irradiation after 240 min. The pH value, initial concentration and catalyst dosage were also found to influence the particle’s photocatalytic performance significantly

Metabolic risk factors and risk of Covid-19: A systematic review and meta-analysis

Objective Based on the epidemiologic findings of Covid-19 incidence; illness and mortality seem to be associated with metabolic risk factors. This systematic review and meta-analysis aimed to assess the association of metabolic risk factors and risk of Covid-19. Methods This study was designed according to PRISMA guidelines. Two independent researchers searched for the relevant studies using PubMed, Web of Science, Cochrane Library, and Scopus. The search terms developed focusing on two main roots of "Covid-19"and "metabolic risk factors". All relevant observational, analytical studies, review articles, and a meta-analysis on the adult population were included in this meta-analysis. Meta-analysis was performed using the random effect model for pooling proportions to address heterogeneity among studies. Data were analyzed using STATA package version 11.2, (Stata- Corp, USA). Results Through a comprehensive systematic search in the targeted databases we found 1124 papers, after running the proses of refining, 13 studies were included in the present meta-analysis. The pooled prevalence of obesity in Covid-19 patients was 29 (95 CI: 14-47). For Diabetes and Hypertension, these were 22 (95 CI: 12 33) and 32 (95 CI: 12 56), respectively. There was significant heterogeneity in the estimates of the three pooled prevalence without any significant small-study effects. Such warning points, to some extent, guide physicians and clinicians to better understand the importance of controlling co-morbid risk factors in prioritizing resource allocation and interventions. Conclusion The meta-analysis showed that hypertension is more prevalent than obesity and diabetes in patients with Covid-19 disease. The prevalence of co-morbid metabolic risk factors must be adopted for better management and priority settings of public health vaccination and other required interventions. The results may help to improve services delivery in COVID-19 patients, while helping to develop better policies for prevention and response to COVID-19 and its critical outcomes. © 2020 Moazzami et al

Experimental investigation of PV/T and thermoelectric systems using CNT/ water nanofluids

This study investigated experimentally the thermal performance of a Photovoltaic-thermal (PV/T) and thermoelectric (TE) system using the application of two nanofluids. Single-walled Carbon nanotube/water (SWCNT/water) and multi-walled Carbon nanotube/water (MWCNT/water), with a mass fraction of 0.02% were assessed as the working fluid of the PV/T system. Examinations were done from 10:00 to 16:30 daily in November 2021 at Tarbiat Modares University, Tehran, Iran. Different parameters were measured during the experimental tests including fluid inlet and outlet temperatures, volume flow rate, solar irradiance, and ambient and cell surface temperatures. The results showed that the highest performance of the solar system was measured using the application of SWCNT/water nanofluid. The PV/T surface temperature decreased using nanofluids compared to pure water. It was found that the output generated power and efficiency improved using nanofluid application whereas application of SWCNT/water was more effective compared to MWCNT/water nanofluid. Also, the application of the two nanofluids improved the performance of the TE module compared to pure water. The highest values of TE electric current, voltage, generated power, and efficiency were obtained using the application of SWCNT/water nanofluid