Microstructure and compressive behavior of Al-Y2O3 nanocomposites prepared by microwave-assisted mechanical alloying

In this study, Al–Y2O3 nanocomposites were synthesized via mechanical alloying and microwave-assisted sintering. The effect of different levels of yttrium oxide on the microstructural and mechanical properties of the Al–Y2O3 nanocomposites were investigated. The density of the Al–Y2O3 nanocomposites increased with increasing Y2O3 volume fraction in the aluminum matrix, while the porosity decreased. Scanning electron microscopy analysis of the nanocomposites showed the homogeneous distribution of the Y2O3 nanoparticles in the aluminum matrix. X-ray diffraction analysis revealed the presence of yttria particles in the Al matrix. The mechanical properties of the Al–Y2O3 nanocomposites increased as the addition of yttria reached to 1.5 vol. % and thereafter decreased. The microhardness first increased from 38 Hv to 81 Hv, and then decreased to 74 ± 4 Hv for 1.5 vol. % yttria. The Al–1.5 vol. % Y2O3 nanocomposite exhibited the best ultimate compressive strength and yielded a strength of 359 ± 7 and 111 ± 5 MPa, respectively. The Al–Y2O3 nanocomposites showed higher hardness, yield strength, and compressive strength than the microwave-assisted mechanically alloyed pure Al.This publication was made possible by NPRP Grant 7-159-2-076 from the Qatar National Research Fund (a member of the Qatar Foundation).Scopu

Modelling of Complex Plasmas

Nowadays plasmas are used for various applications such as the fabrication of silicon solar cells, integrated circuits, coatings and dental cleaning. In the case of a processing plasma, e.g. for the fabrication of amorphous silicon solar cells, a mixture of silane and hydrogen gas is injected in a reactor. These gases are decomposed by making a plasma. A plasma with a low degree of ionization (typically 10_5) is usually made in a reactor containing two electrodes driven by a radio-frequency (RF) power source in the megahertz range. Under the right circumstances the radicals, neutrals and ions can react further to produce nanometer sized dust particles. The particles can stick to the surface and thereby contribute to a higher deposition rate. Another possibility is that the nanometer sized particles coagulate and form larger micron sized particles. These particles obtain a high negative charge, due to their large radius and are usually trapped in a radiofrequency plasma. The electric field present in the discharge sheaths causes the entrapment. Such plasmas are called dusty or complex plasmas. In this thesis numerical models are presented which describe dusty plasmas in reactive and nonreactive plasmas. We started first with the development of a simple one-dimensional silane fluid model where a dusty radio-frequency silane/hydrogen discharge is simulated. In the model, discharge quantities like the fluxes, densities and electric field are calculated self-consistently. A radius and an initial density profile for the spherical dust particles are given and the charge and the density of the dust are calculated with an iterative method. During the transport of the dust, its charge is kept constant in time. The dust influences the electric field distribution through its charge and the density of the plasma through recombination of positive ions and electrons at its surface. In the model this process gives an extra production of silane radicals, since the growth of dust is not included. Results are presented for situations in which the dust signi_cantly changes the discharge characteristics, both by a strong reduction of the electron density and by altering the electric field by its charge. Simulations for dust with a radius of 2 mu-m show that the stationary solution of the dust density and the average electric field depend on the total amount of the dust. The presence of dust enhances the deposition rate of amorphous silicon 2 at the electrodes because of the rise in the average electron energy associated with the decrease of the electron density and the constraint of a constant power input. This increase of deposition rate has also been observed in experiments by others. To study the behavior of dust in a less complicated environment, experiments in non-reactive plasmas have been carried out by a number of research groups. In these experiments the dust particles are injected through the electrodes in an argon discharge. These experiments have shown very interesting phenomena. Dust particles start to interact with each other in the discharge and form two-dimensional Coulomb clusters. These experiments often show an appearance of a void, a dustfree region in the discharge. Similar experiments have also been carried out under microgravity. These experiments have shown three-dimensional Coulomb clusters of dust particles also with the appearance of a void. Also rotating dust clouds (vortices) near the edges of the electrodes have been observed, that tend to rotate as long as the plasmas is on. To understand the behavior of the particles, we have developed a two-dimensional fluid model for a dusty argon plasma in which the plasma and dust parameters are solved self-consistently to study the behavior of dust particles. Simulations for dust with a radius of 7.5 mu-m show that a double space charge layer is created around the sharp boundary of the dust crystal. The inter-particle interaction is taken into account by means of an equation of state for the dust. A central dust-free region (void) is created by the ion drag force. The contribution of the thermophoretic force, driven by the temperature gradient induced by gas heating from ion-neutral collisions and heating of the dust particle material by the recombining ions and electrons, can be neglected in the quasi-neutral center of the plasma. Inside this void a strong increase of the production of argon meta-stables is found. This phenomenon is in agreement with experimental observations, where an enhanced light emission is seen inside the void

Horn Antennas Loaded with Metamaterial for UWB Applications

YesIn this paper, a conical horn antenna has been designed for Ultra-Wideband ap-plications by loading its section with a metamaterial. The work aims first to compare results obtained by the wavelet-moment method to a simulation performed using HFSS. Secondly the conical horn is loaded with a very thin layer of metamaterial to enhance the radiation pattern and the bandwidth performance of the conical horn antenna and reduce the size of the antenna. The operating bandwidth of the proposed antenna is in the range of 10{13 GHz. The results obtained from HFSS and moment method are in good agreement.Electronics and Telecommunication

Step and Step-Nc as a Tool for Big Data in Cloud Manufacturing

The terms big data, cloud manufacturing, predictive and additive manufacturing, and Internet of Things (IoT) are being most commonly used in the manufacturing industry nowadays. These terms are related to the fourth industrial revolution that emphasizes automation and data exchange between manufacturing tools/elements. Communication occurs between machines, products and even technicians or operators through various technologies while creating records of each interaction resulting in rapid growth of amount of data to be stored. Data acquisition is not a major issue since a structure or framework can properly connect these data in improving manufacturing efficiency. However, lack of effort in collecting and storing manufacturing data in the whole product life cycle process has made integration to be almost difficult to achieve. In this study, the adoption of STEP-NC method/technique was demonstrated in suiting the current explosion of big data in the industrial and manufacturing sector. The proposed methodology was developed through a study of an entity file structure and hierarchical concept in STEP and STEP-NC in gathering manufacturing data in a unified database. The challenge would be in making sense of the data, revealing the patterns in it and using them for operational improvements. The outcome of this study will be useful to support strategic decision making in product manufacturing

Islamic perspectives of integrating Muslim cemeteries planning with recreational areas in urban setting

The provision of Muslim cemeteries is a requirement stemming from the Quranic teaching that Muslims are buried upon death. Simultaneously, the provision of recreational areas is equally important for a healthy living environment and be part of the ten percent calculation of open spaces required by planning guideline. Due to the scarcity of land particularly in the urban area, one of the ways is to integrate these two types of land uses. This study seeks to examine the Islamic perspective of integrating Muslim cemeteries planning with recreational areas. Using content analysis, Islamic injunctions of the Quran and Hadith were examined together with their exegesis by Muslim scholars. In principle, it is permissible to integrate Muslim cemeteries with the recreational areas provided that their sanctity is preserved. There are limitations of recreational activities that could be done there and only the area with severe land scarcity is allowed to do so. Consequently, a specific planning guidelines for a hybrid cemetery is required as the current GP-010A and GP-005A are standing alone in guiding the cemeteries and open spaces planning respectively. This shariah permissibility based on Maslahah mursalah helps to address the requirement of recreational areas and Muslim cemeteries in an urban setting

Machinability And Surface Quality Of Hybrid Composite CFRP/Al2024

oai:myjas.www.journal.unisza.edu.my:article/1The use of hybrid composite has increased due to their special mechanical and physical properties. However, machining of composite materials is extremely difficult due to non-homogeneous, anisotropic and highly abrasive characteristics. The performance of machined surface quality of CFRP/Al2024 was described using two level full factorial methodology. Trimming test was performed under dry conditions using 6mm diameter of burr tools end mills. The factors investigated were spindle speed(N), feed rate(fr) and depth of cut(dc), furthermore Ra CFRP and Ra Al2024 were the response variables. This work aims to minimize the machined surface quality of CFRP/Al2024 between 1μm to 2μm. The finding of this empirical study has shown that, the best estimated value of fr should be 500 mm/min to 530 mm/min, N is between and 2313.870 rpm to 2336.042 rpm. For both response spindle speed is the most significant effect followed by Feed rate and Depth of Cut

Adaptação ao cultivo e valorização de Lavandula luisieri

Foram estudadas diversas populações de Lavandula luisieri (Rozeira) Rivas-Martínez endémicas da Península Ibérica (Beira Interior, Castilla-la-Mancha e Andaluzia; acessos de Casal da Fraga, Mata, Penamacor e Vila Velha de Ródão – Portugal; Toledo e Sevilha – Espanha), comparando as populações relativamente ao óleo essencial (quantitativamente e qualitativamente), assim como, a sua actividade insecticida sobre pragas fitófagas (Spodoptera littoralis, Mysus persicae e Leptinotarsa decemlineata). Em função dos seus componentes escolheram-se as duas populações mais interessantes em termos da sua actividade biológica (Penamacor e Toledo) e instalaram-se dois campos produtivos em Castelo Branco e Saragoça, por forma a inferir sobre a influência do local de produção na qualidade do material vegetal obtido. Será fornecida informação técnica sobre a instalação destes campos

A systemic analysis of the usage of safety items among Malaysian private vehicle users

In such a large road transportation system, human factor plays a very significant role in ensuring a desirable balance between transport demand and safe operations. This paper presents a systemic analysis of three safety items, namely seatbelt for adult car occupants, child safety seats (CSS) for young occupants and helmet for motorcyclists, of which the success level is highly reliant on the road users’ willingness to utilise them according to the recommended and proper usage. In a temporal view of road crashes, these safety items were part of ‘during-crash’ passive safety components i.e. to provide protection during the crash impact phase. This analysis includes the safety items benefits and issues, related road safety strategic programmes, current legal framework, and local research findings based on observational studies. The use of both helmet and seatbelt was mandatory but the move has so far produced mixed results. Meanwhile, CSS usage and acceptance are on the rise, although still at a nascent stage. This situation can be considered as ‘below satisfactory compliance level’, hence a more inclusive solution is needed, including the introduction of technology, to influence or compel road users to wear such safety items while on the road