Sharif Digital Repository

In traffic engineering, one of the problems presented by slate pavement, besides being costly to repair and maintain, is the insufficient resistance of bitumen against traffic loads in low temperatures. In this study, the effect of synthesized basalt modifier has been assessed via four different tests to improve bitumen performance. Hence, the enhancement of resistance to traffic loads at low temperatures as an essential problem of asphalt superstructure in traffic engineering has been taken into account. The bending beam rheometer test was conducted at three temperatures of-6°C,-12°C, and-18°C, and the softening point and permeability index tests were performed. A Fourier transform infrared... 

Let (Formula presented.) be a graph. A vertex coloring (Formula presented.) of (Formula presented.) is called (Formula presented.)-vertex coloring if (Formula presented.) for every vertex (Formula presented.) of (Formula presented.), where (Formula presented.) is the set of colors of vertices adjacent to (Formula presented.). Let (Formula presented.) be the maximum number of colors used in an (Formula presented.)-vertex coloring of (Formula presented.). We provide some lower and upper bounds for (Formula presented.) in terms of girth, diameter or size of (Formula presented.). Also, for every tree (Formula presented.), we obtain (Formula presented.). © 2018 World Scientific Publishing Company... 

Let G be a graph. A vertex coloring ψ of G is called N2-vertex coloring if |ψ(v)|≤ 2 for every vertex v of G, where ψ(v) is the set of colors of vertices adjacent to v. Let t2(G) be the maximum number of colors used in an N2-vertex coloring of G. We provide some lower and upper bounds for t2(G) in terms of girth, diameter or size of G. Also, for every tree T, we obtain t2(T). © 2018 World Scientific Publishing Company  

Artificial neural networks with multilayer feed forward topology and back propagation algorithm containing two hidden layers are implemented to predict the effect of chemical composition and tensile properties on the both impact toughness and hardness of microalloyed API X70 line pipe steels. The chemical compositions in the forms of "carbon equivalent based on the International Institute of Welding equation (CEIIW)", "carbon equivalent based on the Ito-Bessyo equation (CEPcm)", "the sum of niobium, vanadium and titanium concentrations (VTiNb)", "the sum of niobium and vanadium concentrations (NbV)" and "the sum of chromium, molybdenum, nickel and copper concentrations (CrMoNiCu)", as well... 

Dissimilar Al/Cu joints were produced through simple cold compression technique. The influence of different reductions (40, 53 and 66 %) on the joint strength was studied. Also, the effect of heat treatment on the joints’ mechanical characteristics was investigated using a modified miniature shear test. Microscopical examinations by means of optical and scanning electron microscopes were conducted and results confirmed that acceptable joints produced through 53 and 66 % deformations. According to the shear test results, it was revealed that post-weld heat treatment influenced the joint’s strength and caused strength enhancement in the samples which were not subjected to annealing prior to... 

Stress-relieved Al-Mn-Si specimens were constrained groove pressed (CGPed) and in the following, cold-rolled under different strains of 0.47, 0.8 and 1.27. Dual strained sheets were isothermally heat treated at 150, 250, and 350 °C. Microstructure survey revealed that generated shear-bands by CGP acted as talent sites for further strain-induced grain boundary migration (SIGBM) during annealing. SEM micrographs pointed out that coarse particles (1 μm <) had not preferential positions within the aluminum matrix and often comminuted into fine dispersoids (0.5 μm >) under heavy strains. Assessment of the softening fraction (Rrec) depicted that greater accumulated strains along with higher... 

Charpy impact energy of the produced Al6061-SiCp laminated nanocomposites by mechanical alloying was modeled by adaptive neuro-fuzzy interfacial systems (ANFIS) in both crack divider and crack arrester configurations. The model was constructed by training, validating and testing of 171 gathered input-target data. The thickness of layers, the number of layers, the adhesive type, the crack tip configuration and the content of SiC nanoparticles were five independent input parameters utilized for modeling. The output parameter was Charpy impact energy of the nanocomposites. The performance of the proposed models was evaluated by absolute fraction of variance, the absolute percentage error and... 

The grain size of constrained groove pressed aluminum has been predicted through the genetic programming approach. “Sheet thickness,” “elongation,” “yield strength,” “ultimate tensile strength,” “total strain,” and “hardness,” along with “primary grain size” of the ultrafine-grained sheets were utilized as input parameters to obtain the ultimate grain size. A total number of 73 available data in the literature were gathered and randomly divided into 60 and 13 sets for algorithm training and testing, respectively. Among the presented models, the one with best performance utilized parameters of total strain, ultimate tensile strength, and primary grain size with 40 chromosomes, 10 head sizes,... 

The dynamic and static softening phenomena in Al-6Mg alloy were studied through interrupted two-stage hot compression test performed isothermally at 480°C and strain rate range of 0.001-0.1 s-1. The interruptions of 29 and 90 s were considered when the true strain reached 0.5. It was concluded that the effect of static softening on the flow stress was not highlighted by extending the interruption at a constant strain rate. Also, it was exhibited that softening rate highly enhanced with the strain rate decrement at a constant time. Moreover, the static and dynamic recrystallization was revealed as the dominant softening mechanisms at low and high strain rates, respectively  

Post-uniform deformation energy of materials is defined as absorbed energy per unit area after necking. The energy is constant for a material type and its experienced specific processing history and also depends on its mechanical parameters as workhardening exponent, strain rate sensitivity, post-necking extension and inhomogeneity factor. Different methods such as single and multiple tensile testing had been proposed in the literature to calculate tearing energy, but the effect of post-necking extension had not been expressed explicitly. A new model by implementing uniform and failure elongations with the combination of Unwin theory is introduced. Based on the model, it was shown that... 

The cause of about 10% of faults in induction machines is related to the rotor part. In this paper, an analytical method for general modeling of brushless doubly-fed machines (BDFMs) with broken rotor loops and end ring is presented. The approach is based on calculation of resistance and inductance matrices through the winding function of the machine, so the assumption of sinusoidal MMF is not needed. It is also shown that a fault in a loop can lead to faults in other parts of the rotor. To validate the method a simulation in MATLAB/Simulink is performed based on the D180-frame prototype BDFM  

In this study, lamination as extrinsic mechanism was considered to enhance damage tolerance of three-layer Al6061-5%vol. SiCp/Al1050/Al6061-5%vol. SiCp composites. To fabricate laminates of dissimilar interfacial adhesion, different rolling strains were applied during hot roll-bonding. The discrepancy in interfacial strength of laminates was examined by shear test while toughness values were studied using three-point bending test. It was revealed that both interfacial adhesion and damage tolerance were influenced by rolling strain. Interfacial bonding played the major role in the energy absorption during fracture which was quantified as initiation, propagation and total toughness. The... 

Functionally graded aluminum matrix composites (FGAMC) are new advanced materials with promising applications due to their unique characteristics in which composite nature is combined with graded structure. Different architectures of Al6061/SiCp composite laminates were fabricated by successive hot roll-bonding. For FGAMCs, two composite layers as outer strips and a layer of Al1050 as interlayer were applied. To investigate laminate toughness, the quasi-static three-point bending test was conducted in the crack divider orientation. Genetic programming as a soft computing technique was implemented to find mathematical correlations between architectural parameters and experimentally obtained... 

Purpose Whole genome sequencing of SARS-CoV2 is important to find useful information about the viral lineages, variants of interests and variants of concern. As there are not enough data about the circulating SARS-CoV2 variants in Iran, we sequenced 54 SARS-CoV2 genomes during the 5 waves of pandemic in Iran. Methods After viral RNA extraction from clinical samples collected during the COVID-19 pandemic, next generation sequencing was performed using the Nextseq platform. The sequencing data were analyzed and compared with reference sequences. Results During the 1st wave, V and L clades were detected. The second wave was recognized by G, GH and GR clades. Circulating clades during the 3rd...