Sharif Digital Repository

An energy-based ordinary differential equation is derived for a plastic wave propagating through a Taylor impact test specimen. Using the definition of true strain, an analytical equation is presented to calculate the strain rate across the plastic wave front. Having considered a Johnson-Cook plasticity model for the projectile material, the derived energy equation accompanied by a governing kinematics relation and the strain rate equation is numerically integrated to obtain the final deformed profile of the specimen. The results of the energy based model are then compared with those of the commonly used momentum-based approach as well as the existing experimental data in literature for... 

A low-power high-speed two-stage dynamic comparator is presented. In this circuit, PMOS transistors are used at the input of the first and second stages of the comparator. At the evaluation phase, the second stage is activated after the first stage with a predetermined delay to achieve a controllable pre-amplifier gain. Also, the first stage is turned off after the delay to reduce overall power consumption. Simulation results in 0.18 μτη CMOS technology, prove that the proposed circuit reduces the power consumption by a factor of two and reduces comparison time as large as 210ps in the same budget of offset voltage compared to the conventional circuit. Moreover, the offset voltage and power... 

Abstract: Well testing is one of the important methods to provide information about the reservoir heterogeneity and boundary limits by analyzing reservoir dynamic responses. Despite the significance of well testing data, misinterpreted data can lead us to a wrong reservoir performance prediction. In this study, we focus on cases ignoring the adjacent well’s production history, which may lead to misinterpretation. The analysis was conducted on both homogeneous and naturally fractured reservoirs in infinite-acting and finite-acting conditions. The model includes two wells: one is “tested well” and the other is “adjacent one.” By studying different scenarios and focusing on derivative plots, it... 

A simple and appropriate procedure for the synthesis of quinazoline-2,4(1H,3H)-dione derivatives from isocyanides, aniline and isocyanate via the Cu-catalyzed intramolecular C-H activation reaction is reported. The advantages of this method are one-pot conditions, accessible starting materials-catalyst, high yield of products, and short reaction times. The structures are confirmed spectroscopically (1H-and13C-NMR, IR and EI-MS) and by elemental analyses. © 2020 Bentham Science Publishers  

A one-pot synthesis of functionalized benzo thiazine derivatives via a Cu-catalyzed, multicomponent reaction of isocyanides, aniline, and heterocumulenes in acetonitrile at room temperature was developed. Transition metal-catalyzed activation of C-H bonds under mild copper-catalytic reaction conditions, using simple and available starting materials, also obtaining a pure product with high yield without applying column chromatography are the major advantages of the applied method among the other ones used for this purpose. The structures are confirmed spectroscopically (1H- and 13C-NMR, IR, and EI-MS) and through elemental analyses. © 2019 The Chemical Society Located in Taipei & Wiley-VCH... 

A one-pot Cu-catalyzed synthesis of functionalized alkynyl imidamide by terminal alkynes, trichloroacetonitrile and aniline or benzyl amine is reported. The compounds were produced via coupling reaction of terminal alkynes with trichloroacetamidine. This method was performed under mild, ligand-free conditions and easy work-up method. © 2020, Bentham Science Publishers. All rights reserved  

In the last decade, there has been a swift development in several scientific research works in which the quartz crystal microbalance (QCM) technique has played a critical role in unravelling different aspects of energy and environmental materials and biological substances as well as all corresponding molecular interactions within those media. We comprehensively review the numerous types of surface chemistries, including but not limited to hydrogen bonding, hydrophobic and electrostatic interactions, self-assembled monolayers and ionic bonding, that are monitored using QCMs in a variety of fields such as energy and chemical industries in addition to the biology, medicine and nanotechnology... 

This paper presents a novel approach based on pulse transit time (PTT) for the estimation of blood pressure (BP). In order to achieve this goal, a data acquisition hardware is designed for high-resolution sampling of phonocardiogram (PCG) and photoplethysmogram (PPG). These two signals can derive PTT values. Meanwhile, a force-sensing resistor (FSR) is placed under the cuff of the BP reference device to mark the moments of measurements accurately via recording instantaneous cuff pressure. For deriving the PTT-BP models, a calibration procedure including a supervised physical exercise is conducted for each individual. The proposed method is evaluated on 24 subjects. The final results prove... 

Selective Laser Sintering (SLS) is a rapidly growing additive manufacturing process, because it has the capacity to build parts from a variety of materials. However, the dimensional accuracy of the fabricated parts in this process is dependent on the ability to control phenomena such as warpage and shrinkage. This research presents an optimization algorithm to find the best processing parameters for minimizing warpage. The finite element method was used to simulate the sintering of a layer of polymer powder, and the warpage of the layer was calculated. The numerical model was verified through comparison with experimental results. A back-propagation neural network was used to formulate the... 

In this paper, fundamental concepts of ultrasonics and characteristics of distinctive microstructures have been used to simply explain the effect of microstructure on the attenuation mechanism of ultrasonic waves in carbon steels. In addition, it has been shown that application of the second medium hardness instead of the bulk hardness is more appropriate to correlate the sound velocity and the microstructure  

This paper resolve the salinity-dependent interactions of polar components of crude oil at calcite-brine interface in atomic resolution. Molecular dynamics simulations carried out on the present study showed that ordered water monolayers develop immediate to a calcite substrate in contact with a saline solution. Carboxylic compounds, herein represented by benzoic acid (BA), penetrate into those hydration layers and directly linking to the calcite surface. Through a mechanism termed screening effect, development of hydrogen bonding between –COOH functional groups of BA and carbonate groups is inhibited by formation of a positively-charged Na+ layer over CaCO3 surface. Contrary to the common... 

In this study, direct electron transfer of myoglobin (Mb) on cadmium oxide (CdO) nanoparticles modified glassy carbon electrode (GCE) was investigated. Prepared CdO nanoparticles were studied by X-Ray diffraction (XRD) and UV-visible absorption methods. All electrochemical studies were performed by cyclic voltammetry (CV) and a potentiostat device. The cyclic voltammogram of Mb/ CdO Nps/ GCE showed a couple of stable redox and oxidative peaks at -470 and -370 mV at scan rate of 50 mVs-1, respectively. The formal potential (Eo) of myoglobin was calculated as -(420 ± 3) mV. Direct electrode transfer led to design a biosensor for determination of hydrogen peroxide (H2O2). The sensor sensitivity... 

Inorganic scale deposition has been found to affect many industrial processes, including water injection into the oil reservoirs. The incompatibility of high sulfate ion content of seawater with formation water containing calcium ions results in formation damage and production decline. In this study, several simultaneous techniques are utilized for qualitative and quantitative analyses of calcium sulfate scale to get more insight into the formation damage during smart water flooding at micro and nanoscales. In the experimental section, calcium sulfate deposition due to the mixing of the formation water and seawater samples was investigated using the dynamic quartz crystal microbalance...