Sharif Digital Repository

This paper presents the results of an experimental study on the application of strapping technique for retrofit of concrete compressive specimens. In this technique, standard strapping devices, which are used in the packaging industry, are applied to post-tension high strength metal strips around the concrete columns. Experimental program included axial compressive tests on 72 cylindrical and prismatic compressive specimens, which were actively confined by pre-stressed metal strips. The effects of various parameters on strength and ductility of confined concrete were studied including compressive strength of concrete, mechanical volumetric ratio of confining strips, post-tensioning force in... 

This paper presents the results of experimental and analytical study on a new technique of seismic retrofitting of concrete columns. In this technique, standard strapping devices, which are used in the packaging industry, are used to post-tension metal strips around concrete columns. The two ends of the strip are tightened in sealed clamps to maintain the pre-stress force in the strip. Experimental program included axial compressive tests on 30 cylindrical as well as 30 prismatic small-scale columns which were actively confined by pre-stressed metal strips. Longitudinal and lateral strain of concrete and strain in the strips were monitored. Test Results showed significant increase in... 

Introduction: Some tinnitus subjects habituate to their tinnitus but some others do not and complain of its annoyance tremendously. Normal sensory memory and change detection processes are needed for detecting the tinnitus signal as a prediction error and habituation to tinnitus. The purpose of this study was to compare auditory mismatch negativity as the index of sensory memory and change detection among the studied groups to search for the factors involving in the perception of tinnitus and preventing habituation in decompensated tinnitus subjects. Methods: Electroencephalography was recorded from scalp electrodes in compensated tinnitus, decompensated tinnitus, and no tinnitus control... 

In this paper a new method of modeling shear force-displacement relationship for confined masonry walls by neural networks has been presented. Although the mathematical models have been very useful in the simulations so far, however developing more accurate models is necessary. While developing precise mathematical models for highly hysteretic materials is itself challenging and practically cumbersome, the use of learning algorithms is an attractive alternative. The issue of material modeling by neural networks has been a challenging one itself, noticing available neural networks have some limitations in the learning of non-linearity. In this paper a new type neural network, called Prandtl... 

A new model is proposed to predict the Forming Limit Diagrams (FLDs) of Tailor Welded Blanks (TWBs). This model is derived by modification of the Marciniak and Kuczynski (MK) analysis and imposing the weld constraints to deformation state of each blank at each strain increment. Based on this model, it is possible to predict the strains of both weaker and stronger blanks once necking occurs. By comparison to the experimental results of two laser welded TWBs, it is demonstrated that this model provides a close prediction of FLD of TWBs, when necking occurs far from the weld line at a region out of HAZ (Heat Affected Zone) and close to it so that it is affected by the weld line constraints  

The aim of this work is to produce two layered thin-walled Cu/Al composite tube by the spin-bonding process. The process is utilized to bond the aluminum tube into the copper one at thickness reductions of 20-60% and process temperatures of 25°C, 130°C, and 230°C. The bond strength is measured by T-peeling test, and the bond interfaces are examined by metallography and scanning electron microscopy (SEM). The results show that after a threshold thickness reduction of about 30%, the bond strength increased with the amount of deformation. SEM fractography of the peel surfaces confirms that the copper oxide film is broken in a shear manner during deformation. Severe shear strains applied during... 

A novel SPD process for manufacturing of high strength tubes and cylinders by accumulative spin-bonding (ASB) is proposed. It is demonstrated that due to incremental deformation in this process, high strain rate without considerable temperature rise is achieved. This is accompanied with a high value of Zener-Hollomon parameter as a characteristic of this SPD process. ASB was applied to a commercially pure aluminum up to four cycles and its effects on the microstructure and mechanical properties were examined by optical microscopy, TEM, EBSD, microhardness and tension tests. The results show that ultra-fine grains are developed during the process by formation of subgrains at early stages... 

Utilizing the so-called tube spinning, a cold-bonding process entitled as "spin-bonding" is developed to produce seamless thin-walled clad tubes and cylinders. By this method, two layers of AA 1050 tubes were successfully bonded together to form a clad tube at room temperature. Based on mechanical aspects of the tube spinning process, the mechanism of spin-bonding is explained in two stages: surface preparation before occurrence of a stable bond and bond strengthening thereafter. The effects of process temperature, thickness reduction, feed rate and roller attack angle as the parameters of tube spinning on the bond strength are studied. It is shown that the bond strength increases by... 

In this study, ultrafine grained aluminum sheets AA1050 and AA5052 are incrementally cryo-rolled after precooling in liquid nitrogen. Cryogenic deformation is considered as an effective approach to postpone saturation of the grain refinement by conventional severe plastic deformation. However, for a quantitative understanding of the resulted microstructure and mechanical properties, accurate values of the deformation parameters (strain, strain rate and temperature) are needed. The aim of this study is, therefore, to find values of the applied cryo-rolling parameters. As the experimental measurements of parameters such as temperature are infeasible in the thin specimens, a FEM simulation is... 

Strain rate sensitivity (m-value) of ultrafine grain (UFG) AA 1050 and AA 5052 sheets processed by accumulative roll-bonding is investigated versus strain rate by stress relaxation (SR) test at ambient temperature. The results show a weak viscous nature of deformation for AA 5052 specimens as compared to AA 1050 ones. So that much less stress relaxation and negligible strain rate sensitivity are obtained for this material due to dislocation and grain boundary mobility limitation caused by Mg solute atoms. In order to formulate strain rate sensitivity of UFG aluminum as a function of strain rate, three phenomenological and two empirical models are developed and assessed by the experimental... 

Commercially pure aluminum sheets, AA 1050, are processed by accumulative roll bonding (ARB) up to eight cycles to achieve ultrafine-grained (UFG) aluminum as primary material for mechanical testing. Optical microscopy and electron backscattering diffraction analysis are used for microstructural analysis of the processed sheets. Strain rate sensitivity (m-value) of the specimens is measured over a wide range of strain rates by stress relaxation test under plane strain compression. It is shown that the flow stress activation volume is reduced by decrease of the grain size. This reduction which follows a linear relation for UFG specimens, is thought to enhance the required effective (or... 

Plane strain compression (PSC) test was used to study the flow stress of ultrafine grained commercially pure aluminum at large strains. AA 1050 sheets were processed by various Accumulative Roll-Bonding (ARB) cycles up to 10 cycles as the initial specimens for the test. An approach was developed to measure the coefficient of friction and to suppress its effect on the results. It is shown that as a result of having an anisotropy parameter (R-value) of less than one, Von-Mises tensile strengths are significantly higher than PSC strengths. Comparing these strengths, the R-value as an average anisotropy parameter of rolling and transverse directions is estimated for the ARBed sheets, where it is... 

Abstract Flow behavior of ultrafine grained (UFG) AA 1050 sheets processed by Accumulative Roll-Bonding (ARB) and its viscous nature are investigated by plane strain compression test (PSC) along with stress relaxation. Occurrence of dynamic recovery is validated by TEM observations as the microstructural explanation of the flow softening at the start of deformation of the 8-cycles specimen. Significant recovery of the UFG specimens during the stress relaxation test is also disclosed. It is discussed that neither the internal stress (σi) nor the density of mobile dislocations are constant during the test. The possible effects of these two factors as well as contribution of the... 

Background: Human papillomavirus (HPV)-associated malignancy remain a main cause of cancer in men and women. Cancer immunotherapy has represented great potential as a new promising cancer therapeutic approach. Here, we report Mesenchymal stem cells (MSCs) as a carrier for the delivery of oncolytic Newcastle disease virus (NDV) for the treatment of HPV-associated tumor. Methods: For this purpose, MSCs obtained from the bone marrow of C57BL mice, then cultured and characterized subsequently by the flow cytometry analysis for the presence of cell surface markers. In this study, we sought out to determine the impacts of MSCs loaded with oncolytic NDV on splenic T cell and cytokine immune... 

In this research, Ag-Al2O3 nanostructures have been prepared via combustion synthesis and ammonium acetate and urea have been applied as fuels. The prepared Ag-Al2O3 nanostructures were characterized by DTA, XRD, SEM, TEM, and BET spectroscopy. The effect of different ratios of silver to alumina and fuel percentage on morphology and particle size of prepared products were investigated. The results showed that using ammonium acetate fuel led to the production of Ag-γ-Al2O3 nanocompounds, while using urea produced Ag-α-Al2O3. Also, the photocatalytic activity of Ag-Al2O3 nanostructures for Congo red degradation was evaluated by UV-Vis diffuse reflectance spectroscopy. The photocatalytic... 

Time reversal is a technique in which a signal is pre-filtered such that it focuses both in time and space. Spatial focusing reduces interference to other co-existing systems and temporal focusing concentrates the received power in a very short interval. Energy detector is a practical receiver for ultra-wideband (UWB) time reversed signals due to its low-complexity and low-cost implementation. However, selection of an optimum integration interval to minimize the bit error rate is a major problem. Weighted energy detection is an effective technique to overcome this problem and enhance the performance of energy detectors. However, this improvement is achieved at the expense of non-trivial... 

In this paper, the problem of coarse timing synchronization in orthogonal frequency-division multiplexing (OFDM) systems is investigated, and two new timing metrics with better performance are presented. The new metrics take advantage of two novel differential normalization functions that are based on the fourth-order statistics and are designed depending on the value of carrier frequency offset (CFO). The proposed timing metrics are theoretically evaluated using two different class separability criteria. It is shown that the new schemes considerably increase the difference between the correct and wrong timing points in comparison with previous methods. The computational complexity of the... 

Due to role of polymer in increasing sweep efficiency during oil recovery, much attention has been paid to the using polymer solutions in enhanced oil recovery methods. In spite of the existence of the great researches in this area, the role of nanoparticles in modification of the polymer performance in the presence of salts has not been examined before. Furthermore, there is no information about how the dispersed silica nanoparticles affect the heavy oil recovery during the polymer flooding in the presence of divalent cations. In this study, a series of polymer flooding experiments are performed in a quarter five-spot glass micromodel saturated with heavy oil. Solutions of polyacrylamide... 

By displacing oil in porous media with other fluid, different mechanisms of fluid displacing occur. The importance of understanding the trapping mechanisms like pore body filling is irrefutable. Pore body filling mechanism with a coordination number of four has different events like I0, I1, I2 and I3. Previous studies showed that the event of I0 occurs when the pore is only filled by a compressible non-wetting phase, but this study showed that this event could also occur by an incompressible non-wetting phase. Trapping mechanisms can be examined in a glass micro-model. In this research, a glass micro-model with three different patterns was used. Results showed that at two spots of the...