Investigations of selected mechanical, wear properties and transparency of alumina obtained by combined PIM and SPS techniques

Loghman Estarki Mohammad Reza,Abedi Vellashani Faezeh,Moinifard Farzad,Milani Mostafa,Kumar Anjan,Ghazi Mohammad Reza,Sardarian Mehran 한국세라믹학회 2022 한국세라믹학회지 Vol.59 No.6

To produce transparent alumina pieces, alpha-alumina nanoparticles with diff erent amounts of MgO sintering aid were dispersed in a paraffi n-polypropylene-based binder system. The alumina-binder feedstock was optimized for the powder injection molding (PIM) method. After binder removal, the green body piece was sintered through the spark plasma sintering method. Rheometric tests, Vickers measurement, three-point bending fl exural test, and Archimedes test were used for the feed fl uidity, hardness, fl exural strength, and density of the sintered pieces, respectively. Next, IR and visible transmission of SPSed bodies were measured. The results showed that a combination of PIM and SPS methods with 500 ppm sintering aid causes higher IR and visible transmission than the sample with 600 ppm sintering aid. In addition, the hardness of as- obtained transparent alumina was in the range of 16–16.5 GPa. The fl exural strength of the as-obtained transparent sample (with 500 ppm MgO) was more than SPSed with 600 ppm MgO sintering aid.

Cytotoxic Activity Evaluation and QSAR Study of Chromene-based Chalcones

Loghman Firoozpour,Alireza Foroumadi,Najmeh Edraki,Maryam Nakhjiri,Saeed Emami,Maliheh Safavi,Sussan Kabudanian Ardestani,Mehdi Khoshneviszadeh,Abbas Shafiee 대한약학회 2012 Archives of Pharmacal Research Vol.35 No.12

Chalcone and chromene motifs are synthetic or naturally occurring scaffolds with significant cytotoxic profile. Two types of novel regioisomeric chromene-chalcone hybrids, namely 1-(6-chloro or 6-methoxy-2H-chromen-3-yl)-3-phenylprop-2-en-1-one (Type A) and 3-(6-chloro or 6-methoxy-2H-chromen-3-yl)-1-phenylprop-2-en-1-one (Type B), both with different substituents on the phenyl ring attached to propenone linkage, have been evaluated for their cytotoxic activity against breast cancer cell lines (MCF-7 and MDA-MB-231). The results indicate that type A of chromene-chalcones demonstrated better cytotoxic profile than type B especially in MDA-MB-231 cell line. In addition, the growth inhibitory activity of most of the target compounds is higher than Etoposide as a reference drug. QSAR analysis of these novel compounds demonstrated that topological and geometrical parameters are among the important descriptors that influence the cytotoxic activity profile of compounds.

Effects of motion direction and power of Er,Cr:YSGG laser on pull-out bond strength of fiber post to root dentin in endodontically-treated single-canal premolar teeth

Loghman Rezaei-Soufi,Leili Tapak,Mahsa Forouzande,Reza Fekrazad 한국생체재료학회 2019 생체재료학회지 Vol.23 No.4

Background: Inadequate retention and gradual debonding of intracanal post from root dentin is a major cause of failure of endodontically treated teeth restored with fiber post. Main body: This study aimed to assess the effect of surface treatment of quartz fiber posts with different powers and motion directions of Er,Cr:YSGG laser on their pull-out bond strength to root dentin in endodontically treated premolar teeth. In this study, 105 fiber posts were divided into 7 groups according to their surface treatment with different powers of Er,Cr:YSGG laser at 2780 nm wavelength, 20 Hz frequency and 150 μs pulse duration in circumferential (C) or longitudinal (L) motion directions: Control group (no treatment), 0.5W laser in longitudinally (L0.5), 1.0W laser in longitudinally (L1), 1.5W laser in longitudinally (L1.5), 0.5W laser in circumferentially (C0.5), 1.0 W laser in circumferentially (C1) and 1.5W laser in circumferentially (C1.5). After cementation, pull-out bond strength was measured in Newton (N). Each sample was inspected under a stereomicroscope at × 25 magnification to determine the mode of failure. Two samples of each group were inspected under a scanning electron microscope (SEM). Data were analyzed using two-way ANOVA and Tukey’s test with significant level of 0.05. The pull-out bond strength of 0.5W groups had significant differences with the control group (P = 0.009). The bond strength of 1.0W and 1.5W groups were not significantly different (P = 0.630) but were higher than the control and 0.5W groups (P < 0.001). Motion direction of laser irradiation had no significant effect on the bond strength (P = 0.384). The interaction effect of power and motion direction of laser irradiation had no significant effect on the bond strength (P = 0.092). Conclusion: Fiber posts treated with 0.5, 1.0 and 1.5W Er,Cr:YSGG laser showed higher bond strength to dentin compared to posts with no surface treatment. However, the motion directions of laser irradiation had no significant effect on the bond strength. In order to minimize damage to post surface and achieving maximum bond strength, longitudinal surface treatment of posts with 1.0W power of Er,Cr:YSGG laser is recommended.

Effect of Epigallocatechin Gallate on shear bond strength of composite resin to bleached enamel: an in vitro study

Loghman Rezaei-Soufi,Zahra Khamverdi,Shahin Kasraei,Negin Ronasi,Shiva Rostami 대한치과보존학회 2013 Restorative Dentistry & Endodontics Vol.38 No.4

Objectives The aim of this study was to determine the effect of epigallocatechin gallate (EGCG) on the shear bond strength of composite resin to bleached enamel. Materials and Methods Ninety enamel surfaces of maxillary incisors were randomly divided into 9 groups as follows: G1: control (no bleaching); G2: bleaching; G3: bleaching and storage for seven days; G4 - 6: bleaching and application of 600, 800 and 1,000 µmol of EGCG-containing solution for 10 minutes, respectively; G7 - 9: bleaching and application of 600, 800 and 1,000 µmol of EGCG-containing solution for 20 minutes, respectively. The specimens were bleached with 30% hydrogen peroxide gel and a composite resin cylinder was bonded on each specimen using a bonding agent. Shear bond strength of the samples were measured in MPa. Data was analyzed using the two-way ANOVA and Tukey HSD tests (α = 0.05). Results The maximum and minimum mean shear bond strength values were observed in G1 and G2, respectively. Time and concentration of EGCG showed no significant effects on bond strength of the groups (p > 0.05). Multiple comparison of groups did not reveal any significant differences between the groups except for G2 and all the other groups (p < 0.05). Conclusions There is a significant decrease in bond strength of composite resin to enamel immediately after bleaching. A delay of one week before bonding and the use of EGCG increased bond strength of composite resin to bleached enamel. Objectives The aim of this study was to determine the effect of epigallocatechin gallate (EGCG) on the shear bond strength of composite resin to bleached enamel. Materials and Methods Ninety enamel surfaces of maxillary incisors were randomly divided into 9 groups as follows: G1: control (no bleaching); G2: bleaching; G3: bleaching and storage for seven days; G4 - 6: bleaching and application of 600, 800 and 1,000 µmol of EGCG-containing solution for 10 minutes, respectively; G7 - 9: bleaching and application of 600, 800 and 1,000 µmol of EGCG-containing solution for 20 minutes, respectively. The specimens were bleached with 30% hydrogen peroxide gel and a composite resin cylinder was bonded on each specimen using a bonding agent. Shear bond strength of the samples were measured in MPa. Data was analyzed using the two-way ANOVA and Tukey HSD tests (α = 0.05). Results The maximum and minimum mean shear bond strength values were observed in G1 and G2, respectively. Time and concentration of EGCG showed no significant effects on bond strength of the groups (p > 0.05). Multiple comparison of groups did not reveal any significant differences between the groups except for G2 and all the other groups (p < 0.05). Conclusions There is a significant decrease in bond strength of composite resin to enamel immediately after bleaching. A delay of one week before bonding and the use of EGCG increased bond strength of composite resin to bleached enamel.

Creep damage evaluation of thick-walled spheres using a long-term creep constitutive model

Abbas Loghman,Nader Shokouhi 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.10

This paper describes a numerical model developed for the computation of creep damages in a thick-walled sphere subjected to an internal pressure and a thermal gradient. The model predicts the creep damage histories during the life of the sphere, owing to variations in stresses with time and through-thickness variations. The creep damage fraction is based on the Robinson’s linear life fraction damage rule, which has been incorporated in a nonlinear time-dependent stress analysis. Following the stress histories, the effective stress histories are obtained and the creep damages are calculated and summed during the life of the sphere. The material long-term creep properties up to the rupture and creep rupture data are defined by the Θ projection concept [1]. The damage histories up to 38 years are calculated and the results show that the maximum damages are always located at the inner surface of the sphere, while the outer surface of the vessel sustains minimum damages.

Comparison of seismic behavior of long period SDOF systems mounted on friction isolators under near-field earthquakes

Vahid Loghman,Faramarz Khoshnoudian 국제구조공학회 2015 Smart Structures and Systems, An International Jou Vol.16 No.4

Friction isolators are one of the most important types of bearings used to mitigate damages of earthquakes. The adaptive behavior of these isolators allows them to achieve multiple levels of performances and predictable seismic behavior during different earthquake hazard levels. There are three main types of friction isolators. The first generation with one sliding surface is known as Friction Pendulum System (FPS) isolators. The double concave friction pendulum (DCFP) with two sliding surfaces is an advanced form of FPS, and the third one, with fully adaptive behavior, is named as triple concave friction pendulum (TCFP). The current study has been conducted to investigate and compare seismic responses of these three types of isolators. The structure is idealized as a two-dimensional single degree of freedom (SDOF) resting on isolators. The coupled differential equations of motion are derived and solved using state space formulation. Seismic responses of isolated structures using each one of these isolators are investigated under seven near fault earthquake motions. The peak values of bearing displacement and base shear are studied employing the variation of essential parameters such as superstructure period, effective isolation period and effective damping of isolator. The results demonstrate a more efficient seismic behavior of TCFP isolator comparing to the other types of isolators. This efficiency depends on the selected effective isolation period as well as effective isolation damping. The investigation shows that increasing the effective isolation period or decreasing the effective isolation damping improves the seismic behavior of TCFP compared to the other isolators. The maximum difference in seismic responses, the base shear and the bearing displacement, for the TCFP isolator are calculated 26.8 and 13.4 percent less than the DCFP and FPS in effective isolation damping equal to10%, respectively.

Two dimensional time-dependent creep analysis of a thick-walled FG cylinder based on first order shear deformation theory

Abbas Loghman,Reza K. Faegh,Mohammad Arefi 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.26 No.5

In this paper the time-dependent creep analysis of a thick-walled FG cylinder with finite length subjected to axisymmetric mechanical and thermal loads are presented. First order shear deformation theory (FSDT) is used for description of displacement components. Inner and outer temperatures and outer pressure are considered as thermo-mechanical loadings. Both thermal and mechanical loadings are assumed variable along the axial direction using the sinusoidal distribution. To find temperature distribution, two dimensional heat transfer equation is solved using the required boundary conditions. The energy method and Euler equations are employed to reach final governing equations of the cylinder. After determination of elastic stresses and strains, the creep analysis can be performed based on the Yang method. The results of this research indicate that the boundaries have important effects on the responses of the cylinder. The effect of important parameters of this analysis such as variable loading, non-homogeneous index of functionally graded materials and time of creep is studied on the behaviors of the cylinder.

Synthesis and Antibacterial Activity of N-[5-(chlorobenzylthio)- 1,3,4-thiadiazol-2-yl] Piperazinyl Quinolone Derivatives

Firoozpour, Loghman,Emami, Saeed,Mansouri, Shahla,Ebrahimabadi, Abdolrasoul H.,Asadipour, Ali,Amini, Mohsen,Saeid-Adeli, Nosratollah,Shafiee, Abbas,Foroumadi, Alireza 대한약학회 2007 Archives of Pharmacal Research Vol.30 No.2

A series of N-[5-(chlorobenzylthio)-1,3,4-thiadiazol-2-yl] piperazinyl quinolones derivatives (4a-I) have been synthesized by reaction of piperazinyl quinolones with 5-chloro-2-(chlorobenzylthio)-1,3,4-thiadiazoles. Their structures were confirmed by elemental analysis, IR and NMR spectra. The antibacterial activities of 4a-I against a variety of Gram-positive and Gram-negative bacteria were determined. Several compounds showed a good antibacterial activity against Gram-positive bacteria among which, compound 4e with a 2-chlorobenzylthio moiety in ciprofloxacin derivative, exhibited high activities against Staphylococcus aureus and Staphylococcus epidermidis (MIC=0.06 ${\mu}$g/mL). The structure-activity relationship (SAR) study revealed that the position of chlorine atom on benzyl moiety would dramatically affect the antibacterial activities of the synthesized compounds.

Effect of particle content, size and temperature on magneto-thermo-mechanical creep behavior of composite cylinders

A. Loghman,A. Askari Kashan,M. Younesi Bidgoli,A. R. Shajari,A. Ghorbanpour Arani 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.4

The effects of particle content, particle size, operating temperature and magnetic field on steady-state creep behavior of thick-walled rotating cylinders made of Al-SiC composites have been investigated. Loading is composed of a uniform magnetic field in axial direction,steady-state heat conduction in radial direction and an inertia body force due to rotation. The composite creep constitutive equation has been described by Norton's law in which the creep parameters are functions of particle size, temperature and particle content. The composite properties are radial dependent based on volume fraction of SiC reinforcement. It has been found that the minimum effective creep strain rate belongs to a composite identified by 25% SiC at the inner and 5% at the outer surfaces. Therefore this composite has been selected for the design of the cylinder. It has been concluded that increasing particle size and operating temperature significantly increases the effective creep strain rates. It has also been illustrated that magnetic field decreases the stresses and the effective creep strain rates.

Nonlinear stability of non-axisymmetric functionally graded reinforced nano composite microplates

Abbas Loghman,Ali Ghorbanpour Arani,Ali Akbar Mosallaie Barzoki 사단법인 한국계산역학회 2017 Computers and Concrete, An International Journal Vol.19 No.6

The nonlinear buckling response of nano composite anti-symmetric functionally graded polymeric microplate reinforced by single-walled carbon nanotubes (SWCNTs) rested on orthotropic elastomeric foundation with temperature dependent properties is investigated. For the carbon-nanotube reinforced composite (CNTRC) microplate, a uniform distribution (UD) and four types of functionally graded (FG) distribution are considered. Based on orthotropic Mindlin plate theory, von Kármán geometric nonlinearity and Hamilton’s principle, the governing equations are derived. Generalized differential quadrature method (GDQM) is employed to calculate the non-linear buckling response of the plate. Effects of FG distribution type, elastomeric foundation, aspect ratio (thickness to width ratio), boundary condition, orientation of foundation orthotropy and temperature are considered. The results are validated. It is found that the critical buckling load without elastic medium is significantly lower than considering Winkler and Pasternak medium.