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Volume 8, Number 2, February 2020

In this work the properties of iron oxide magnetic nanoparticles (MNPs) synthesized by electrochemical method using different water-alcohol proportions and alcohols have been investigated. The syntheses were carried out using 99% iron foils acting electrodes in a 0.04 M NaCl solutions at room temperature applying 22 mAcm-2 on the working electrode, mostly obtaining magnetite nanoparticles. The impact of the electrolyte in the size of the synthesized MNPs has been evaluated by transmission electron microscopy (TEM), X-ray diffraction (XRD), chronopotentiometric studies, and magnetic characterization. The results have shown that nanoparticles can be obtained in the range of 6 to 26 nm depending on the type of alcohol and the proportions in the mixture of water-alcohol. The same trend has been observed for all alcohols. As the proportion of these in the medium increases, the nanoparticles obtained are smaller in size. This trend is maintained until a certain proportion of alcohol: 50% for methanol, and 60% for the rest of alcohols, proportions where obtaining a single phase of magnetite is not favored.

Key Words
electrochemical synthesis; magnetic nanoparticle; conductivity; alcohol mixture; electrolyte

Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Quimica Fisica Aplicada, 28049 Madrid, Spain.

In this research, buckling and free vibration of rectangular polymeric laminate reinforced by graphene sheets are investigated. Various patterns are considered for augmentation of each laminate. Critical buckling load is evaluated for different parameters, including boundary conditions, reinforcement pattern, loading regime, and laminate geometric states. Furthermore, vibration analysis is investigated for square laminate. Elastic properties of the composite are calculated using a combination of both molecular dynamics (MD) and the rule of mixture (MR). Kinematics of the plate is approximated based on the first shear deformation theory (FSDT). The current analysis is performed based on the energy method. For the numerical investigation, Ritz method is applied, and for shape functions, Chebyshev polynomials are utilized. It is found that the number of layers is effective on the buckling load and natural frequency of laminates which made from non-uniform layers.

Key Words
buckling; free vibration; FG-laminates; molecular dynamics; boundary conditions; Ritz method

(1) Mehran Karimi Zeverdejani:
Department of Mechanical Engineering, Shahrekord University, Shahrekord, Iran;
(2) Yaghoub Tadi Beni:
Faculty of Engineering, Shahrekord University, Shahrekord, Iran;
(3) Yaghoub Tadi Beni:
Nanotechnology Research Center, Shahrekord University, Shahrekord, Iran.

In this paper, the free vibrations analysis of the nanoplates made of three-directional functionally graded material (TDFGM) with small scale effects is presented. To study the small-scale effects on natural frequency, modified strain gradient theory (MSGT) has been used. Material properties of the nanoplate follow an arbitrary function that changes in three directions along the length, width and thickness of the plate. The equilibrium equations and boundary conditions of nanoplate are obtained using the Hamilton's principle. The generalized differential quadrature method (GDQM) is used to solve the governing equations and different boundary conditions for obtaining the natural frequency of nanoplate made of three-directional functionally graded material. The present model can be transformed into a couple stress plate model or a classic plate model if two or all parameters of the length scales set to zero. Finally, numerical results are presented to study the small-scale effect and heterogeneity constants and the aspect ratio with different boundary conditions on the free vibrations of nanoplates. To the best of the researchers' knowledge, in the literature, there is no study carried out into MSGT for free vibration analysis of FGM nanoplate with arbitrary functions.

Key Words
vibration; nanoplate; three-directional functionally graded material (TDFGM); modified strain gradient theory (MSGT); generalized differential quadrature method (GDQM); size effect

(1) Kasra Dehshahri, Mohammad Zamani Nejad, Sima Ziaee, Abbas Niknejad:
Department of Mechanical Engineering, Yasouj University, Yasouj, Iran;
(2) Amin Hadi:
Cellular and Molecular Research Center, School of Medicine, Yasuj University of Medical Sciences, Yasuj, Iran.

The incorporation of carbon nanotubes in a polymer matrix makes it possible to obtain nanocomposite materials with exceptional properties. It's in this scientific background that this work was based. There are several theories that deal with the behavior of plates, in this research based on the Mindlin-Reissner theory that takes into account the transversal shear effect, for analysis of the critical buckling load of a reinforced polymer plate with parabolic distribution of carbon nanotubes. The equations of the model are derived and the critical loads of linear and parabolic distribution of carbon nanotubes are obtained. With different disposition of nanotubes of carbon in the polymer matrix, the effects of different parameters such as the volume fractions, the plate geometric ratios and the number of modes on the critical load buckling are analysed and discussed. The results show that the critical buckling load of parabolic distribution is larger than the linear distribution. This variation is attributed to the concentration of reinforcement (CNTs) at the top and bottom faces for the X-CNT type which make the plate more rigid against buckling.

Key Words
nanotubes; shear deformation; parabolic distribution; buckling; volume fractions

(1) Tayeb Si Tayeb, Mohamed Zidour, Houari Heireche, Abdelillah Benahmed:
Laboratory of Modeling and Multi-Scale Simulation, Department of Physics, Faculty of Exact Science University of Sidi Bel Abbes, Algeria;
(2) Tayeb Si Tayeb, Houari Heireche, Abdelillah Benahmed:
University Djillali Liabes of Sidi-Bel-Abbès, BP 89, Sidi Bel Abbès 22000, Algeria;
(3) Mohamed Zidour, Tayeb Bensattalah:
Université of tiaret, BP 78 Zaaroura, 14000 Tiaret, Algeria;
(4) Mohamed Zidour, Tayeb Bensattalah:
Laboratory of Geomatics and Sustainable Development, Ibn Khaldoun University of Tiaret, Algeria;
(5) E.A. Adda Bedia:
Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia.

The present paper explores forced vibrational properties of porosity-dependent functionally graded (FG) cylindrical nanoshells exposed to linear-type or triangular-type impulse load via classical shell theory (CST) and nonlocal strain gradient theory (NSGT). Employing such scale-dependent theory, two scale factors accounting for stiffness softening and hardening effects are incorporated in modeling of the nanoshell. Two sorts of porosity distributions called even and uneven have been taken into account. Governing equations obtained for porous nanoshell have been solved through inverse Laplace transforms technique to derive dynamical deflections. It is shown that transient responses of a nanoshell are affected by the form and position of impulse loading, amount of porosities, porosities dispensation, nonlocal and strain gradient factors.

Key Words
dynamic analysis; transient vibrations; nanoshell; porous FGMs; nonlocal strain gradient theory

(1) Seyed Sajad Mirjavadi, Masoud Forsat, Alireza Farrokhi Nia, A.M.S. Hamouda:
Department of Mechanical and Industrial Engineering, Qatar University, P.O. Box 2713, Doha, Qatar;
(2) Salman Badnava:
Department of Computer Science and Engineering, College of Engineering, Qatar University, P.O. Box 2713 Doha, Qatar.

This paper studies forced vibrational behavior of porous nanocrystalline silicon nanoshells under radial dynamic loads using strain gradient theory (SGT). This type of material contains many pores inside it and also there are nano-size grains which define the material character. The formulation for nanocrystalline nanoshell is provided by first order shell theory and a numerical approach is used in order to solve nanoshell equations. SGT gives a scale factor related to stiffness hardening provided by nanograins. For more accurate description of size effects due to nano-grains or nano-pore, their surface energy influences have been introduced. Surface energy of inclusion exhibit extraordinary influence on dynamic response of the nanoshell. Also, dynamic response of the nanoshell is affected by the scale of nano-grain and nano-pore.

Key Words
nanocrystalline material; forced vibration; porous nanoshell; strain gradient; Mori-Tanaka scheme

Al-Mustansiriah University, Engineering Collage P.O. Box 46049, Bab-Muadum, Baghdad 10001, Iraq.

This study presents the hygro-thermo-electromagnetic mechanical vibration attributes of elastically restrained piezoelectric nanobeam considering effects of beam surface for various elastic non-ideal boundary conditions. The nonlocal Eringen theory besides the surface effects containing surface stress, surface elasticity and surface density are employed to incorporate sizedependent effects in the whole of the model and the corresponding governing equations are derived using Hamilton principle. The natural frequencies are derived with the help of differential transformation method (DTM) as a semi-analytical-numerical method. Some validations are presented between differential transform method results and peer-reviewed literature to show the accuracy and the convergence of this method. Finally, the effects of spring constants, changing nonlocal parameter, imposed electric potential, temperature rise, magnetic potential and moisture concentration are explored. These results can be beneficial to design nanostructures in diverse environments.

Key Words
mechanical vibration; piezoelectric nanobeam; non-ideal boundary condition; size dependent effects

(1) Farzad Ebrahimi, Mohammadreza Kokaba:
Mechanical Engineering Department, Engineering Faculty, Imam Khomeini International University, Qazvin, Iran;
(2) Gholamreza Shaghaghi:
Young Researchers and Elites Club, Science and Research Branch, Islamic Azad University, Tehran, Iran;
(3) Rajendran Selvamani:
Department of Mathematics, Karunya University, Coimbatore 641114, Tamil nadu, India.

The objectives of this research were the reduction of membrane fouling and improvement of sludge properties by using synthesized H-ZSM-5 and NH4-ZSM-5 zeolites. These two nano zeolites were synthesized and added to the membrane bioreactor (MBR). Three similar MBRs with the same operational condition were used in order to evaluate their effect on the mentioned matters. The evaluated parameters were trans-membrane pressure (TMP), Fourier-transform infrared spectroscopy (FTIR), particle size distribution (PSD), soluble microbial product (SMP), extracellular polymeric substances (EPS) and, excitation-emission matrix (EEM). The MBR0 was without any additional zeolite while 0.4 g/L of H-ZSM-5 and NH4-ZSM-5 were added to MBRHZSM-5 and MBRNH4ZSM-5, respectively. The COD removal of the MBR0, MBRH-ZSM-5 and MBRNH4-ZSM-5 were 87.5%, 93.3% and 94.6%, respectively. The TMP of the MBRH-ZSM-5 was 45% less than MBR0 whereas the reduction for MBRNH4-ZSM-5 was 65.5%. Also results showed that both H-ZSM-5 and NH4-ZSM-5 caused reduction in protein and polysaccharide related EPS but the NH4-ZSM-5 had better performance toward the elimination of organic compounds.

Key Words
submerged membrane bioreactor; NH4-ZSM-5; H-ZSM-5; membrane fouling

(1) Zahra Sadat Sajadian, Hossein Hazrati, Mohammad Rostamizadeh:
Faculty of Chemical Engineering, Sahand University of Technology, Tabriz, Iran;
(2) Hossein Hazrati, Mohammad Rostamizadeh:
Environmental Engineering Research center, Sahand University of Technology, Tabriz, Iran.

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