Sharif Digital Repository

The employment of tissue engineering scaffolds in the reconstruction of the damaged bone tissues has shown remarkable promise since they significantly facilitate the healing process. Fabrication of highly porous biocompatible scaffolds with sufficient mechanical strength is still challenging. In this regard, polymers have been widely utilized to construct three-dimensional (3D) porous scaffolds due to their excellent processability and biocompatibility. However, insufficient mechanical strength and inappropriate degradation rate of the monophasic polymer scaffolds in the bone regeneration process, as the main challenges, limit their extensive clinical application. The incorporation of... 

A novel voltammetric biosensor based on nano-TiO2/nafion/carbon nanoparticles modified glassy carbon electrode (TiO2/N/CNP/GCE) was developed for the determination of dobutamine (DBA). Characterization of the surface morphology and property of TiO2/N/CNP layer was carried out by the scanning electron microscopy and atomic force microscopy. The electrochemical performance of the modified electrode was investigated by means of the cyclic voltammetry, differential pulse voltammetry and electrochemical impedance spectroscopy techniques. Effective experimental variables, such as the scan rate, pH of the supporting electrolyte, drop size of the casted modifier suspension and accumulation... 

The performance of an HTPB/N2O hybrid motor was experimentally investigated. A hybrid motor was designed and manufactured in a laboratory with the purpose of studying the effects of various parameters on the motor's performance, including fuel regression rate and specific impulse. A series of tests were conducted to find a correlation between the fuel regression rate and the oxidizer's mass flux. The effects of chamber's pressure on the regression rate as well as other performance parameters were investigated. While the burning rate did not change dramatically, both the efficiency and ISP of the motor increased. The local fuel regression rate and the fuel port were also calculated. In... 

Chatter is a limiting factor in machining systems with adverse effects for workpiece surface, tool and machine life and material removal rate. Proper modelling of this phenomenon requires that the dynamic characteristics of the machining system is known. It is common to obtain the dynamic of the system by modal tests in stationary condition. However, the vibration characteristics of a machine change between its operating and resting mode. The goal of this work is to study vibrations in boring using the vibrational characteristic in operational conditions using the operating deflection shape method. In this paper, vibration characteristics of the in the boring bar is obtained by both modal... 

A gas turbine which output 18MW power exploded after 3h of ordinary operation and after 4,785 starts. The turbine's rotor had undergone repair after 77,000 operating hours. A piece was cut from the failed marriage bolt and tested using atomic absorption spectrometry in order to know the grade of the alloy. It was found that the marriage bolt is made from ASTM A193 B16 steel which is suitable. Hardness and microhardness measurement was also determined and showed that it was within the range of the specified hardness for ASTM A193 B16 steel. The marriage bolt's mechanical properties also meet technical specifications and showed that it contained anti-corrosion properties. Visual examination... 

Biodegradable magnesium implants possess excellent mechanical properties and biocompatibility, which make them suitable candidates to be employed as temporary structures for the bone regeneration purposes. However, there are still important challenges which limit their extensive use in biomedical applications, where the most important ones include implant-associated infection, rapid degradation rate and the need for improved mechanical properties. Silver, which is a strong antimicrobial agent, has been extensively used for improving the mentioned challenges in biodegradable Mg alloys either as alloying element or incorporation in the protective coating. Ag addition has been reported to have... 

3D porous PLA-graphite composite scaffolds are recently introduced as promising candidates in tissue engineering practices owing to their significantly enhanced mechanical strength in comparison with pure PLA. However, they mainly suffer from low degradation rate as well as undesirable hydrophobic surface. In this regard and to address such challenges, Mg particles, as one of the lightest metallic fillers, were added to PLA-graphite scaffolds via the fused deposition modeling (FDM) technique. The obtained results indicated that introduction of 1 wt% Mg inhibited polymeric chain mobility of PLA, and hence, increased the glass transition temperature. Also, Mg particles behaved as nucleating... 

For the present article, a pulsating heat pipe (PHP) is fabricated and tested experimentally by bending a copper tube. The effects of working fluid, heat input, charging ratio, inclination angle, magnets location, and ferrofluid (magnetic nanofluid) volumetric concentration have been investigated on the thermal performance of this PHP. Experimental results show that using ferrofluid as a working fluid improves the thermal performance of the PHP significantly. Moreover, applying a magnetic field on a ferrofluidic PHP reduces its thermal resistance. By changing the inclination angle of the PHP from vertical mode to angles close to the horizontal mode, the present PHP has a constant and... 

In this article, the control of an electrohydrodynamic 3D printer is studied. The proposed controller has a hybrid piecewise linear feedback form which is designed based on a hybrid model of the printer. The hybrid model is obtained via a gray box identification process whose structure is proposed utilizing the results of the finite element simulation of the printer within the COMSOL Multiphysics software. The asymptotic stability of the hybrid control combined with a hybrid observer is proven using the Lyapunov theory. In addition, the obtained control is applied to the finite element model of the printer to check its performance which shows the success of the controlled system in tracking... 

Pentamode metamaterials are a type of extremal designer metamaterials, which are able to demonstrate extremely high rigidity in one direction and extremely high compliance in other directions. Pentamodes can, therefore, be considered as building blocks of exotic materials with any arbitrarily selected thermodynamically admissible elasticity tensor. The pentamode lattices can then be envisioned to be combined to construct intermediate extremal materials, such as quadramodes, trimodes, and bimodes. In this study, we constructed several primary types of anisotropic pentamode lattices (with midpoint positioning of 10%, 15%, 20%, 25%, 30%, 35%, and 42% of the main unit cell diagonal) and then... 

A stable composite film of silver nanoparticles (Ag NPs) decorated on reduced graphene oxide is prepared by a two-step simple procedure. The surface morphology of the modified electrode is characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The electrochemical behavior of tinidazole (TNZ) on the surface of the modified electrode is investigated by linear sweep voltammetry and electrochemical impedance spectroscopy. The prepared composite electrode acts as a highly sensitive platform for the voltammetric determination of TNZ, leading to a significant increase in the reduction peak current of TNZ. The effects of experimental parameters such as the... 

Here in, for the first time, we report a new and simple procedure for preparing reduced graphene oxide/nickel-cobalt double layered hydroxide composite on the nickel foam (Ni-Co LDH/rGO/NF) via a fast and simple two-step electrochemical method including potentiostatic routes in the presence of CTAB as a cationic surfactant. Graphene oxide coated nickel foam prepared by simple immersion method. After that, the prepared electrode reduced electrochemically to obtain rGO/NF electrode. Finally, the rGO/NF electrode was used as cathode for electrodeposition of Ni-Co LDH in the presence of CTAB as cationic surfactant. The prepared electrodes were characterized by field emission scanning electron... 

Miniaturization of electronic devices with portable, flexible and wearable characteristics created a great demand for high-performance microscale energy storage devices with lightweight and flexible properties. Among the energy storage devices, wire-shaped supercapacitors (WSSCs) have recently received tremendous attention due to their tiny volume, wearability, high flexibility and potential applications in the next-generation portable/wearable electronic devices. Herein, we successfully fabricated a porous dendritic Ni-Cu film on Cu wire substrate (CWE) for fabrication of high-performance wire-type supercapacitors. The porous structure with dendritic morphology provides a high surface area,... 

Here in, for the first time, we report a new and simple procedure for preparing reduced graphene oxide/nickel-cobalt double layered hydroxide composite on the nickel foam (Ni-Co LDH/rGO/NF) via a fast and simple two-step electrochemical method including potentiostatic routes in the presence of CTAB as a cationic surfactant. Graphene oxide coated nickel foam prepared by simple immersion method. After that, the prepared electrode reduced electrochemically to obtain rGO/NF electrode. Finally, the rGO/NF electrode was used as cathode for electrodeposition of Ni-Co LDH in the presence of CTAB as cationic surfactant. The prepared electrodes were characterized by field emission scanning electron... 

The ability of 5G wireless communication networks to effectively and simultaneously interact with incoming signals is made possible by antenna arrays, which play a vital role in assisting the functioning of 5G wireless communication networks. The utilization of beamforming enables the enhancement of signal strength, expansion of coverage area, and reduction of interference, thereby optimizing the performance of the communication networks. This paper introduces a deep learning approach that utilizes a deep neural network (DNN). This approach establishes an appropriate framework to implement beamforming for planar antenna arrays. The DNN utilizes the desired radiation pattern as an input to... 

The deployment of 5G networks requires advanced antenna technologies to meet the increasing demands for high-capacity and low-latency communication. Antenna arrays, known for their beamforming capabilities, are vital in achieving these goals. However, sidelobes in the antenna radiation pattern can introduce errors and significantly impact the system's overall performance. This paper proposes a novel beamforming optimization technique for linear antenna arrays (LLA) in 5G networks. Our approach leverages the power of metaheuristic algorithms, precisely the Grasshopper Optimization Algorithm (GOA), to optimize the array configuration and reduce the Sidelobe Levels (SLL). The main objective is... 

The aim of this study was to investigate the applicability of acoustic emission (AE) technique to evaluate delamination crack in glass/epoxy composite laminates under quasi-static and fatigue loading. To this aim, double cantilever beam specimens were subjected to mode I quasi-static and fatigue loading conditions and the generated AE signals were recorded during the tests. By analyzing the mechanical and AE results, an analytical correlation between the AE energy with the released strain energy and the crack growth was established. It was found that there is a 3rd degree polynomial correlation between the crack growth and the cumulative AE energy. Using this correlation the delamination... 

Electrohydrodynamic (EHD) printing is a novel technology used for fabricating high-resolution part features from a wide range of materials. Due to the multiphysics dynamics and the multiphase nature of the microdroplet formation in the EHD printers, modeling of this phenomenon is complicated. In this paper, the formation of a droplet in an EHD printer—under a pulsed electrical field—is simulated using a new numerical model which couples the fluid flow, the electric field distribution and the movement of the electric charges under dynamic and transient conditions. The level-set method is applied to the entire multiphysics domain in order to study the formation of the droplet. The presented... 

The electrohydrodynamic (EHD) 3D printing technology is an Additive Manufacturing (AM) method that can be used in the manufacture of submicron-size structures. In this process, which is based on the formation of Taylor jet from a metallic ink, the investigation of particles reaction and aggregate formation in ink during printing is of great importance. In this paper, a new Finite Element model based on particle tracing in fluids is presented that couples the different physics that govern an EHD phenomenon. Vortex flow caused by boundary shear stress was observed in the ink jet; which was more like the Marangoni phenomenon in a stationary drop. By experimentally validating the presented model... 

In this paper, bulk and suspension free radical polymerization of styrene in batch reactor has been modelled. This research contains two parts. In the first part, the derivation of a mathematical model from kinetics of reactions was performed. The solution of this mathematical model required roughly 10000-50000 stiff-differential equations to be solved simultaneously. However, the number of equations were reduced to only five non-stiff differential equations and six algebraic equations using moment model and quasi-steady-state assumption. Due to an enormous increase in viscosity during polymerization, the system translates into diffusion-controlled state, which causes gel and glassy effects....