Sharif Digital Repository

The properties of self-compacting concrete (SCC) can be manipulated by the addition of nano-montmorillonite (NMMT) clays. This paper presents the results of an experimental investigation on incorporating small dosages of NMMT clays (.25, .50, .75 and 1.00% addition by mass of total cementitious material) into SCC. Tests were conducted on fresh and hardened specimens to measure workability (by slump flow, V-funnel and L-box), mechanical (by compressive and splitting tensile strengths), durability (electrical resistivity and water penetration) and microstructural (X-ray diffraction and scanning electron microscopy) properties of control and NMMT-reinforced SCCs. The results showed that the... 

The properties of self-compacting concrete (SCC) can be manipulated by the addition of nano-montmorillonite (NMMT) clays. This paper presents the results of an experimental investigation on incorporating small dosages of NMMT clays (.25,.50,.75 and 1.00% addition by mass of total cementitious material) into SCC. Tests were conducted on fresh and hardened specimens to measure workability (by slump flow, V-funnel and L-box), mechanical (by compressive and splitting tensile strengths), durability (electrical resistivity and water penetration) and microstructural (X-ray diffraction and scanning electron microscopy) properties of control and NMMT-reinforced SCCs. The results showed that the... 

The use of manipulators in space missions has become popular, as their applications can be extended to various space missions such as on-orbit servicing, assembly, and debris removal. Due to space reachability limitations, such robots must accomplish their tasks in space autonomously and under severe operating conditions such as the occurrence of faults or uncertainties. For robots and manipulators used in space missions, this paper provides a unique, robust control technique based on Model Predictive Path Integral Control (MPPI). The proposed algorithm, named Planner-Estimator MPPI (PE-MPPI), comprises a planner and an estimator. The planner controls a system, while the estimator modifies... 

This paper presents the results of an experimental study on retrofitting RC beams using FRP strengthening and RC jacketing. Three-point loadings are applied to twelve strengthened beams and three reference specimens to put the two techniques into perspective. Formation of first cracks, FRP debonding, and onset of concrete crushing are compared and discussed. Load-deflection behavior, failure modes, and crack propagation patterns are studied extensively. The experiments demonstrate that the RC jacketed beams exhibit a flexural failure identical to the reference beams. However, the FRP strengthened beams fail in a relatively small deflection due to the premature FRP debonding. Furthermore, the... 

The isomerization of D-glucose to D-fructose using the immobilized glucose isomerase, as a typical model system of solid-liquid enzyme reactions has been carried out in a novel type of two-impinging-jets reactor (TIJR), which is characterized by a rotating inner cylinder in a stationary one. Because of the impinging process, turbulence, and complex trajectory of the solid particles within the reactor, the fractional conversion of glucose obtained in the TIJR increased dramatically compared to that obtained by conventional reaction systems. A compartment model was considered to describe the pattern of flow [residence time distribution (RTD) of solid particles] within the TIJR. Considering... 

In this article, the problem of simultaneous heat, mass, and momentum transfer in the developing region of tubular reactors with homogeneous chemical reaction and laminar power-law fluid flow under unsteady-state conditions has been solved. In this regard, the general governing equations were solved using finite-difference method and analyzed carefully. Moreover, the influences of various parameters and dimensionless numbers such as power-law index, heat of reaction, reaction order, and Damköhler number value on the numerical results were investigated. In addition, the numerical results obtained for the fully-developed velocity distribution of Newtonian fluid flow and Sherwood number value... 

A new nonlinear Time to Digital Converter (TDC) based on time difference amplification is the proposed. A new gain compensation method is presented to expand the DR of conventional × 2 Time Amplifiers (TAs). Instead of conventional gain compensation approach based on changing strength of current sources, the proposed technique uses current difference which results more stable gain over wider DR. In order to avoid two different paths of the stages, a sign bit detection part is the proposed at the front of the TDC to allow using one path of stages for both positive and negative input time differences. As a result, the most advantages of the proposed TDC are its high resolution, wide DR, and... 

This paper presents a new low-power reduced comparator flash ADC. The proposed ADC uses dynamic comparators to perform a high-speed low-power conversion. In order to reduce offset and kick-back noise effect of conventional dynamic comparators, a new comparator with a higher pre-amplifier gain along with the mathematical analysis is presented. The proposed 4bit ADC is simulated in 0.18um with 1.8-υ supply voltage. SNDR and SFDR of the ADC are 23dB and 26.5dB, respectively. The ADC consumes only 0.95mw at the sampling rate of 400MS/s. © 2017 IEEE  

Time amplifiers (TAs) are the key building blocks of the two-step time-to-digital converters. High resolution TAs suffer from inaccuracy the gain due to employing meta-stability behavior of the SR latches. In the proposed method, two offset NAND gates are placed in parallel with the NAND gates of the conventional SR latch to get a linear re-configurable gain. Gain of the TA is controlled only by the driving strength of the NAND gates. To confirm the effectiveness of the proposed method, an 8-bit two step time to digital converter (TDC) was designed and laid-out in 0.18- μm CMOS technology. Using a supply voltage of 1.2 V, the proposed TDC consumes 1.1 mW at 30 MS/s throughput. © 2004-2012... 

In this article, adsorption of p-xylene, m-xylene, o-xylene, and ethylbenzene on Na-BETA type zeolite in liquid phase at 15, 25, and 35 °C has been studied and the single adsorption isotherms have been obtained and reported. The Langmuir isotherm model was used to describe the experimental adsorption isotherm data. It was found that p-xylene is more strongly adsorbed component followed by ethylbenzene, m-xylene and o-xylene. This means that this adsorbent is selective for p-xylene. Using Langmuir isotherm model, the saturation adsorption capacities of the adsorbent were obtained as follows 143 mg/g for p-xylene, 105 mg/g for ethylbenzene, 83 mg/g for m-xylene, and 68 mg/g for o-xylene at 25... 

Heterogeneous solid catalysts comprising CaO and ZrO 2 mixed oxides with various Ca-to-Zr molar ratios were synthesized by means of coprecipitation method. These synthesized mixed oxide catalysts were used for the transesterification of waste cooking oil (WCO) as feedstock with methanol to produce biodiesel fuel (BDF) at 65 °C and 1 atm. The influences of Ca-to-Zr molar ratio, catalyst loading, methanol-to-oil molar ratio, and the reaction time on the BDF yield were carefully investigated. In addition, the stability of prepared solid catalysts was studied. These catalysts were characterized by using techniques of X-ray diffraction, X-ray florescence, X-ray photoelectron spectroscopy, surface... 

Dual-phase (DP) steels with different martensite contents were produced by subjecting a low carbon steel to various heat treatment cycles. In order to investigate the effect of dynamic strain aging (DSA) on mechanical properties, tensile specimens were deformed 3% at 300 °C. Room temperature tensile tests of specimens which deformed at 300 °C showed that both yield and ultimate tensile strengths increased, while total elongation decreased. The fatigue limit increased after pre-strain in the DSA temperature range. The effects of martensite volume fraction on mechanical properties were discussed  

A numerical study was conducted on the transient behavior of a hydrodynamically fully developed, laminar flow of power-law fluids in the thermally developing entrance region of circular ducts with taking into account the effects of viscous dissipation, axial conduction, and variations of viscosity with temperature. In this regard, the unsteady-state thermal energy and momentum equations were solved numerically using a finite-difference method, whereas the steady-state thermal energy equation with constant wall heat flux as the boundary condition was solved analytically as the initial condition of the former. The numerical procedure used in the present work was validated with an analytical... 

Dual phase (DP) steels with network and fibrous martensite were produced by intercritical annealing heat treatment cycles. Some of these steels were deformed at dynamic strain aging temperatures. Room temperature tensile tests of specimens deformed at 300 °C showed that both yield and ultimate tensile strengths for both morphologies increased, while total elongation decreased. Fatigue test results before and after high temperature deformation showed that dynamic strain aging has a stronger effect on fatigue properties of dual phase steels with fibrous martensite. Cracks in DP steels with fibrous martensite propagate in a tortuous path in soft ferrite phase, while they pass of both hard and... 

Time amplifiers (TA) are the key building blocks of the two-step time-to-digital converters. High resolution TAs suffer from inaccuracy the gain due to employing meta-stability behavior of the SR latches. In the proposed method, two offset NAND gates are placed in parallel with the NAND gates of the conventional SR latch to get a linear re-configurable gain. Gain of the TA is controlled only by the driving strength of the NAND gates. To confirm the effectiveness of the proposed method, an 8-bit two step time to digital converter (TDC) was designed and laid-out in 0.18 μ m CMOS technology. Using a supply voltage of 1.2V, the proposed TDC consumes 1.1mW at 30MS/s throughput. IEEE