739 research outputs found
A 37 GHz Millimeter-Wave Antenna Array for 5G Communication Terminals
No full textThis work presents, design and specific absorption rate (SAR) analysis of a 37 GHz antenna, for 5th Generation (5G) applications. The proposed antenna comprises of 4-elements of rectangular patch and an even distribution. The radiating element is composed of copper material supported by Rogers RT5880 substrate of thickness, 0.254 mm, dielectric constant (εr), 2.2, and loss tangent, 0.0009. The 4-elements array antenna is compact in size with a dimension of 8 mm × 20 mm in length and width. The radiating patch is excited with a 50 ohms connector i.e., K-type. The antenna resonates in the frequency band of 37 GHz, that covers the 5G applications. The antenna behavior is studied both in free space and in the proximity of the human body. Three models of the human body, i.e., belly, hand, and head (contain skin, fat, muscles, and bone) are considered for on-body simulations. At resonant frequency, the antenna gives a boresight gain of 11.6 dB. The antenna radiates efficiently with a radiated efficiency of more than 90%. Also, it is observed that the antenna detunes to the lowest in the proximity of the human body, but still a good impedance matching is achieved considering the −10 dB criteria. Moreover, SAR is also being presented. The safe limit of 2 W/kg for any 10 g of biological tissue, specified by the European International Electro Technical Commission (IEC) has been considered. The calculated values of SAR for human body models, i.e., belly, hand and head are 1.82, 1.81 and 1.09 W/kg, respectively. The SAR values are less than the international recommendations for the three models. Furthermore, the simulated and measured results of the antenna are in close agreement, which makes it, a potential candidate for the fifth-generation smart phones and other handheld devices
Laser welding of polypropylene using two different sources
No full textIn this paper, laser weldability of neutral polypropylene has been investigated using fibre and carbon dioxide lasers. A design of experiment (DoE) was conducted in order to establish the influence of the main working parameters on the welding strength of the two types of laser. The welded samples were characterized by carrying out visual and microscopic inspection for the welding morphology and cross-section, and by distinguishing the tensile strength. The resulting weld quality was investigated by means of optical microscopy at weld cross-sections. The tensile strength of butt-welded materials was measured and compared to that of a corresponding bulk material
State-of-the-Art Technologies, Challenges, and Prospects
No full textFunding Information: This review was prepared as part of research supported by the Alexander von Humboldt Foundation through a postdoctoral fellowship awarded to Dr. Muhammad Ali Inam. This work was financed by national funds from FCT—Fundação para a Ciência e a Tecnologia, I.P., under the scope of the project UID/50006/2023 of the Associate Laboratory for Green Chemistry—LAQV REQUIMTE. Publisher Copyright: © 2025 by the authors.The contamination of drinking water sources with selenium (Se) oxyanions, including selenite (Se(IV)) and selenate (Se(VI)), contains serious health hazards with an oral intake exceeding 400 µg/day and therefore requires urgent attention. Various natural and anthropogenic sources are responsible for high Se concentrations in aquatic environments. In addition, the chemical behavior and speciation of selenium can vary noticeably depending on the origin of the source water. The Se(VI) oxyanion is more soluble and therefore more abundant in surface water. Se levels in contaminated waters often exceed 50 µg/L and may reach several hundred µg/L, well above drinking water limits set by the World Health Organization (40 µg/L) and Germany (10 µg/L), as well as typical industrial discharge limits (5–10 µg/L). Overall, Se is difficult to remove using conventionally available physical, chemical, and biological treatment technologies. The recent literature has therefore highlighted promising advancements in Se removal using emerging technologies. These include advanced physical separation methods such as membrane-based treatment systems and engineered nanomaterials for selective Se decontamination. Additionally, other integrated approaches incorporating photocatalysis coupled adsorption processes, and bio-electrochemical systems have also demonstrated high efficiency in redox transformation and capturing of Se from contaminated water bodies. These innovative strategies may offer enhanced selectivity, removal, and recovery potential for Se-containing species. Here, a current review outlines the sources, distribution, and chemical behavior of Se in natural waters, along with its toxicity and associated health risks. It also provides a broad and multi-perspective assessment of conventional as well as emerging physical, chemical, and biological approaches for Se removal and/or recovery with further prospects for integrated and sustainable strategies.publishersversionpublishe
Development of a numerical methodology for flowforming process simulation of complex geometry tubes
No full textPublisher Copyright: © 2017 Author(s).Nowadays, the incremental flowforming process is widely explored because of the usage of complex tubular products is increasing due to the light-weighting trend and the use of expensive materials. The enhanced mechanical properties of finished parts combined with the process efficiency in terms of raw material and energy consumption are the key factors for its competitiveness and sustainability, which is consistent with EU industry policy. As a promising technology, additional steps for extending the existing flowforming limits in the production of tubular products are required. The objective of the present research is to further expand the current state of the art regarding limitations on tube thickness and diameter, exploring the feasibility to flowform complex geometries as tubes of elevated thickness of up to 60 mm. In this study, the analysis of the backward flowforming process of 7075 aluminum tubular preform is carried out to define the optimum process parameters, machine requirements and tooling geometry as demonstration case. Numerical simulation studies on flowforming of thin walled tubular components have been considered to increase the knowledge of the technology. The calculation of the rotational movement of the mesh preform, the high ratio thickness/length and the thermomechanical condition increase significantly the computation time of the numerical simulation model. This means that efficient and reliable tools able to predict the forming loads and the quality of flowformed thick tubes are not available. This paper aims to overcome this situation by developing a simulation methodology based on FEM simulation code including new strategies. Material characterization has also been performed through tensile test to able to design the process. Finally, to check the reliability of the model, flowforming tests at industrial environment have been developed.Peer reviewe
Material saving by means of CWR technology using optimization techniques
No full textPublisher Copyright: © 2017 Author(s).Material saving is currently a must for the forging companies, as material costs sum up to 50% for parts made of steel and up to 90% in other materials like titanium. For long products, cross wedge rolling (CWR) technology can be used to obtain forging preforms with a suitable distribution of the material along its own axis. However, defining the correct preform dimensions is not an easy task and it could need an intensive trial-and-error campaign. To speed up the preform definition, it is necessary to apply optimization techniques on Finite Element Models (FEM) able to reproduce the material behaviour when being rolled. Meta-models Assisted Evolution Strategies (MAES), that combine evolutionary algorithms with Kriging meta-models, are implemented in FORGE® software and they allow reducing optimization computation costs in a relevant way. The paper shows the application of these optimization techniques to the definition of the right preform for a shaft from a vehicle of the agricultural sector. First, the current forging process, based on obtaining the forging preform by means of an open die forging operation, is showed. Then, the CWR preform optimization is developed by using the above mentioned optimization techniques. The objective is to reduce, as much as possible, the initial billet weight, so that a calculation of flash weight reduction due to the use of the proposed preform is stated. Finally, a simulation of CWR process for the defined preform is carried out to check that most common failures (necking, spirals,.) in CWR do not appear in this case.The research leading to these results received funding from the European Union´s Seventh Framework Program, managed by REA-Research Executive Agency (FP7/2007-2013) under grant agreement No. 606171 FP7-SME-2013-1 (CoVaForm). The research leading to these results received funding from the European Union's Seventh Framework Program, managed by REA-Research Executive Agency (FP7/2007-2013) under grant agreement No. 606171 FP7-SME-2013-1 (CoVaForm).Peer reviewe
Advances in green processing of seed oils using ultrasound‐assisted extraction: A review
No full textA growing interest in green bio‐refining technology using ultrasound to extract high‐added value compounds has been observed in the last decades. Therefore, it is of critical importance to consider the impact of the ultrasound technology on the efficiency of oil extraction from seeds as well as on the properties of extracted oils. The cavitation phenomena induced by ultrasound enhance the oil yield as it shatters the primary cell wall of the seeds and makes an easy release of oil. Thus, the higher oil yield is obtained when ultrasound‐assisted extraction (UAE) is used as compared to conventional methods. The properties of UAE oil such as crystallization, free fatty acid content, and oxidative stability are influenced by the ultrasonic time, temperature, intensity, and type of solvent employed during extraction. It can be concluded that UAE is a more efficient technique, which allows the use of alternative green solvents and the production of high‐quality products.Fil: Mushtaq, Anam. Universidad de Agricultura. Instituto Nacional de Ciencia y Tecnología de Alimentos. Faisalabad; Pakistán.Fil: Roobab, Ume. Universidad Tecnológica del Sur de China. Escuela de Ciencia e Ingeniería de Alimentos. Guangzhou; China.Fil: Denoya, Gabriela Inés. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto Tecnología de Alimentos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET); Argentina.Fil: Inam‐Ur‐Raheem, Muhammad. Universidad de Agricultura. Instituto Nacional de Ciencia y Tecnología de Alimentos. Faisalabad; Pakistán.Fil: Gullón, Beatriz. Universidad de Vigo. Campus Ourense. Facultad de Ciencias. Departamento de Ingeniería Química; España.Fil: Lorenzo, Jose Manuel. Parque Tecnológico de Galicia. Centro Tecnológico de la Carne de Galicia; España.Fil: Barba, Francisco J. Universidad de Valencia. Facultad de Farmacia, Medicina Preventiva y Salud Pública. Departamento de Ciencia de Alimentos. Toxicología y Medicina Forense. Nutrición y Ciencia de Alimentos; España.Fil: Zeng, Xin‐An. Universidad Tecnológica del Sur de China. Escuela de Ciencia e Ingeniería de Alimentos. Guangzhou; China.Fil: Wali, Asif. Universidad Internacional de Karakoram. Departamento de Agricultura y Tecnología de Alimentos; Pakistán.Fil: Aadil, Rana Muhammad. Universidad de Agricultura. Instituto Nacional de Ciencia y Tecnología de Alimentos. Faisalabad; Pakistán
Effect of management on reproductive performances of the Achai cattle in the Hindu Kush (Northern Pakistan)
No full textThis study evaluates the effect of management on the undocumented Achai cattle reproductive performance in transhumant farming systems (TFS) and in sedentary farming systems (SFS) in northwestern Pakistan. Data were collected from 172 households in TFS and 270 households in SFS to analyze the effect of farming systems, parity, and calving season on key reproductive traits. The results show that farming systems significantly affect pubertal age, while parity has no significant effect on any of the key traits. The calving season significantly affects the postpartum anoestrus interval in TFS only. More than 50% of the cows in both systems have postpartum anoestrus intervals and calving intervals within the recommended values for cows in tropical countries. Achai cows have high first-service conception rates (70% and 71% for TFS and SFS, respectively) and require a relatively small number of services per conception (1.53 ± 0.06 and 1.48 ± 0.05 SE for TFS and SFS, respectively). This local breed thus warrants conservation under both farming systems
Point, surface and volumetric heat sources in the thermal modelling of selective laser melting
No full textSelective laser melting (SLM) is a powder based additive manufacturing technique suitable for producing high precision metal parts. However, distortions and residual stresses within products arise during SLM because of the high temperature gradients created by the laser heating. Residual stresses limit the load resistance of the product and may even lead to fracture during the built process. It is therefore of paramount importance to predict the level of part distortion and residual stress as a function of SLM process parameters which requires a reliable thermal modelling of the SLM process. Consequently, a key question arises which is how to describe the laser source appropriately. Reasonable simplification of the laser representation is crucial for the computational efficiency of the thermal model of the SLM process. In this paper, first a semi-analytical thermal modelling approach is described. Subsequently, the laser heating is modelled using point, surface and volumetric sources, in order to compare the influence of different laser source geometries on the thermal history prediction of the thermal model. The present work provides guidelines on appropriate representation of the laser source in the thermal modelling of the SLM process.Computational Design and Mechanic
Computationally efficient thermal-mechanical modelling of selective laser melting
No full textThe Selective laser melting (SLM) is a powder based additive manufacturing (AM) method to produce high density metal parts with complex topology. However, part distortions and accompanying residual stresses deteriorates the mechanical reliability of SLM products. Modelling of the SLM process is anticipated to be instrumental for understanding and predicting the development of residual stress field during the build process. However, SLM process modelling requires determination of the heat transients within the part being built which is coupled to a mechanical boundary value problem to calculate displacement and residual stress fields. Thermal models associated with SLM are typically complex and computationally demanding. In this paper, we present a simple semi-analytical thermal-mechanical model, developed for SLM that represents the effect of laser scanning vectors with line heat sources. The temperature field within the part being build is attained by superposition of temperature field associated with line heat sources in a semi-infinite medium and a complimentary temperature field which accounts for the actual boundary conditions. An analytical solution of a line heat source in a semi-infinite medium is first described followed by the numerical procedure used for finding the complimentary temperature field. This analytical description of the line heat sources is able to capture the steep temperature gradients in the vicinity of the laser spot which is typically tens of micrometers. In turn, semi-analytical thermal model allows for having a relatively coarse discretisation of the complimentary temperature field. The temperature history determined is used to calculate the thermal strain induced on the SLM part. Finally, a mechanical model governed by elastic-plastic constitutive rule having isotropic hardening is used to predict the residual stresses.Computational Design and Mechanic
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