Sharif Digital Repository

Hydrogels have been recognized as crucial biomaterials in the field of tissue engineering, regenerative medicine, and drug delivery applications due to their specific characteristics. These biomaterials benefit from retaining a large amount of water, effective mass transfer, similarity to natural tissues and the ability to form different shapes. However, having relatively poor mechanical properties is a limiting factor associated with hydrogel biomaterials. Controlling the biomechanical properties of hydrogels is of paramount importance. In this work, firstly, mechanical characteristics of hydrogels and methods employed for characterizing these properties are explored. Subsequently, the most... 

Development of predictive multi-organ models before implementing costly clinical trials is central for screening the toxicity, efficacy, and side effects of new therapeutic agents. Despite significant efforts that have been recently made to develop biomimetic in vitro tissue models, the clinical application of such platforms is still far from reality. Recent advances in physiologically-based pharmacokinetic and pharmacodynamic (PBPK-PD) modeling, micro- and nanotechnology, and in silico modeling have enabled single- and multi-organ platforms for investigation of new chemical agents and tissue-tissue interactions. This review provides an overview of the principles of designing... 

Organ-on-chip (OOC) platforms have attracted attentions of pharmaceutical companies as powerful tools for screening of existing drugs and development of new drug candidates. OOCs have primarily used human cell lines or primary cells to develop biomimetic tissue models. However, the ability of human stem cells in unlimited self-renewal and differentiation into multiple lineages has made them attractive for OOCs. The microfluidic technology has enabled precise control of stem cell differentiation using soluble factors, biophysical cues, and electromagnetic signals. This study discusses different tissue- and organ-on-chip platforms (i.e., skin, brain, blood–brain barrier, bone marrow, heart,... 

This survey investigated the cultural identity of Iranian English language teachers. Accordingly, a cultural identity model was proposed a priori, based on which a questionnaire was developed and piloted on 50 Iranian English language teachers (α = 0.87). The developed questionnaire was then administered to 636 male and female Iranian English language teachers. The results of confirmatory factor analysis showed that the model was fit and eight components namely 1) religious beliefs, 2) history, 3) customs, 4) manners and behaviors, 5) Persian language, 6) literature and art, 7) parents’ influence and 8) family relations were confirmed to form the core of Iranian cultural identity. The... 

The present mixed-methods research examined the identity and attitude of Iranian English language learners as a result of their participation in an online critical reflective course. The participants were 38 English language students who attended ten online sessions within a five-month English language course. Their online posts underwent inductive qualitative content analysis and subsequently five themes were extracted. In addition, the content of the first and last two sessions were analysed quantitatively. A validated questionnaire was also administered and 18 participants were interviewed. Qualitative and quantitative content analyses of the data revealed eight finalised codes. The... 

Terephthalic acid is generally produced via oxidation of p-xylene. In this process, a large quantity of residue is produced containing cobalt, manganese, and bromine catalysts as well as by-products such as benzoic acid. Our purpose is to totally recover this residue. Extraction by water has been used as an efficient method to recover catalyst from this residue. In this study, the best condition for extraction was obtained at water/residue dilution ratio of 6: 1, extraction temperature of 45°C and extraction time of 40 min. Efficiency of catalyst recovery was 92 wt % at these conditions. The catalyst containing extracted solution can be reused in the oxidation process after being... 

This survey research investigated the attitude of Iranian Azeri native speakers towards Azeri language. A questionnaire was developed and its reliability was estimated (r = 0.74) through a piloting phase on 54 Azeri native speakers. The participants, for the main phase of this study, were 400 Azeri native speakers with different social and educational backgrounds and from some densely Azeri-populated provinces in Iran. They completed either the online or the printed version of the survey, the results of which indicated that Iranian Azeri native speakers have a high level of positive attitude towards their mother tongue in spite of the negligence of this language in the Iranian educational... 

To ameliorate high collision, a nefarious side effect of route discovery stage of reactive routing protocols in wireless networks, jitter mechanisms are proposed which enforce wireless nodes to postpone their transmission for a random amount of time so as to reduce probability of simultaneous transmission. Although it has been shown that jitter mechanisms can dramatically improve reactive routing protocols, it was not until recently that jitter mechanisms have been subjected to study. In this paper, different random distributions are proposed for jittering mechanisms and also shaping function, with the aim of which a simple routing protocol like AODV becomes sensitive to any arbitrary... 

In recent years, the rapid evolution of multirotor technology has driven innovation in aerial platforms tailored for diverse applications, ranging from imaging and agriculture to search and rescue missions. This article introduces a heuristic quadrotor design capable of shape-shifting through adjustable arm angles, thereby modulating its flight dynamics to improve maneuverability and facilitate safe, fast descent maneuvers. Additionally, a sophisticated control strategy termed the adaptive gain-scheduled Proportional-Integral-Derivative (PID) controller is proposed, meticulously engineered to enhance the stability and command-following of the quadrotor. This methodology integrates... 

Attitude states are critical parameters in the control, navigation, and guidance of aerial robotics. Various models, including Euler angles, rotation matrices, and quaternions, are used to represent the orientation of multirotors. The performance of a quadrotor's attitude controller is significantly influenced not only by optimal gain design but also by the structure and strategy of error allocation and control command management. Given the dynamic behavior of the quadrotor, challenges arise with the Proportional-Integral-Derivative (PID) controller, which, as a Single Input Single Output (SISO) controller, struggles to manage the system's channels independently. This paper presents three... 

The increasing prevalence of multirotors necessitates the development of new configurations for specific applications. Innovative morphing of multirotors has enhanced their stability, maneuverability, agility, and overall performance. The utilization of Artificial Intelligence (AI) in robotics has enabled robots to exhibit autonomous behaviors in areas such as control, path planning, state estimation, system identification, and image processing. This paper introduces a novel approach to improving the control system of an adjustable arm-Angle quadrotor through the integration of a self-Tuning Proportional-Integral-Derivative (PID) controller, utilizing an Actor-Critic-based Neural Network... 

In recent years, descriptive evaluation has been introduced as a new model for educational evaluation of Iranian students. The current descriptive evaluation method is based on four-valued logic. Assessing all students with only four values is led to a lack of relative justice and creation of unrealistic equality. Also, the complexity of the evaluation process in the current method increases teacher error’s likelihood. As a suitable solution, in this paper, a fuzzy descriptive evaluation system has been proposed. The proposed method is based on fuzzy logic, which is an infinite-valued logic, and it can perform approximate reasoning on natural language propositions. By the proposed fuzzy... 

Structural, microstructural and mechanical properties in roll bonding of AA5052 and polypropylene sheets have been evaluated in this study. The surface roughness of the AA5052 sheets, rolling temperature and the surface energy of polymer were selected as the bonding variables. The findings indicated that an increase in the surface energy of polypropylene by grafting maleic anhydride would result in higher bonding strength due to chemical interaction between the AA5052 and the maleic anhydride grafted polypropylene (PP-g-MAH). In fact, this reaction caused the formation of an interphase layer at the polymer side of the interface and the diffusion of aluminum into the PP-g-MAH layer. It was... 

Structural, microstructural and mechanical properties in roll bonding of AA5052 and polypropylene sheets have been evaluated in this study. The surface roughness of the AA5052 sheets, rolling temperature and the surface energy of polymer were selected as the bonding variables. The findings indicated that an increase in the surface energy of polypropylene by grafting maleic anhydride would result in higher bonding strength due to chemical interaction between the AA5052 and the maleic anhydride grafted polypropylene (PP-g-MAH). In fact, this reaction caused the formation of an interphase layer at the polymer side of the interface and the diffusion of aluminum into the PP-g-MAH layer. It was... 

Fracture process of fiber-reinforced concrete notched beams is investigated here. Polypropylene macrosynthetic fibers are utilized for reinforcing concrete specimens, and a high-strength mix design is used to produce strong bonds between the embossed polypropylene fibers and the cementitious matrix of beams. Considering different locations for the notch, this study focuses on bridging mechanism under different conditions using both experimental and numerical approaches. First mode of fracture occurs due to opening of crack faces. This mode of failure is simulated by imposing symmetric boundary conditions on middle-notched beams. Inducing the notch with an offset from the middle, mixed-mode... 

In this paper, the impression of surface oxidization on the aluminum nanopowders is investigated using the reactive molecular dynamics (MD) method under the triaxial compression tests. Validation of the computational model is examined with the experimental results, which demonstrates an acceptable accuracy of the numerical simulations. The MD simulations are performed in three stages; relaxing the nanopowders at 300 K and 0.1 MPa, confining the nanopowders under hydrostatic pressure, and imposing the deviatoric stress through the triaxial compression. Evolutions of the relative density with pressure, stress with strain, and dislocation density with strain are derived together with the... 

Fracture process of fiber-reinforced concrete notched beams is investigated here. Polypropylene macrosynthetic fibers are utilized for reinforcing concrete specimens, and a high-strength mix design is used to produce strong bonds between the embossed polypropylene fibers and the cementitious matrix of beams. Considering different locations for the notch, this study focuses on bridging mechanism under different conditions using both experimental and numerical approaches. First mode of fracture occurs due to opening of crack faces. This mode of failure is simulated by imposing symmetric boundary conditions on middle-notched beams. Inducing the notch with an offset from the middle, mixed-mode... 

Multirotors have attracted much attention in recent years. During the design phase, both designers and users are often curious about whether an assembled multirotor can meet their expectations, including hover endurance, system efficiency, maximum load capacity, maximum pitch angle, and maximum flight distance. Traditionally, multirotor performance evaluation involves multiple flight tests or relying on experience, which can be time-consuming and expensive. To solve this challenge, this algorithm is proposed for extensive offline design and evaluation. This algorithm primarily focuses on performance metrics linked to the propulsion system, encompassing components such as motors, propellers,... 

In this paper, a computational atomistic-continuum multiscale framework is presented for the simulation of the nano-powder compaction process using a cone-cap plasticity model. The atomistic representative volume element (RVE) comprises of nano-powder particles that is used to perform the molecular dynamics analysis in order to capture the mechanical behavior of nano-powder material. The periodic boundary condition is applied over the atomistic RVE to satisfy the inter-scale kinematic compatibility, and the stress tensor is derived according to the inter-scale energetic consistency principals from the nanoscale at each material point of the powder component. A multiscale framework is...