Sharif Digital Repository

This paper introduces an analytical approach to obtain fundamental and harmonic load-pull contours using X-parameters. This method is proposed to obtain the optimum load impedance at different harmonics. This approach has been applied on a two port X-parameter model and its results are independently verified by ADS simulation  

Al-5083 and St-12 alloys sheets were friction stir lap welded at various travel and rotation speeds of the welding tool. Microscopic examinations indicate that the joint strength is due to the macroscopic and microscopic mechanical lockings and also atomic diffusion. The reaction zone of the welded joints consists of mixed layers of ultra-fine grains and the intermetallic compounds. The microhardness and nano indentation results prove that the intermetallic phase layer is more brittle in comparison to base metals and ultra-fine grain region. The fracture surfaces are a combination of brittle and ductile fractures. The fracture loads show that the joint strength improves significantly by... 

Platinum nanowires (PtNWs) were electrodeposited on the polycarbonate templates (PCTs) in aqueous solution of H2PtCl6 in triply distilled water. Nanowires with diameters of 50 and 100 nanometers were electrodeposited on the same condition. The kinetics of electrodeposition process was studied by electrochemical techniques such as voltammetry and chronoamperometry methods. Increasing the scan rate, the peaks shifted to more negative potentials and the current density also increased in each peak which was typical for a diffusion-control process. The potential range for the deposition of platinum nanowires was specified and consequently the potentiostatic i-t transients were utilized to produce... 

Hyperelastic materials have high deformability and nonlinearity in load-deformation behavior. Based on a phenomenological approach, these materials are treated as a continuum, and a strain energy density is considered to describe their hyperelastic behavior. In this paper, the mechanical behavior characterization of these materials is studied from the continuum viewpoint. For this purpose, the strain energy density is expressed as sum of independent functions of the mutual multiple of principal stretches. These functions are determined by applying the governing postulates on the form of the strain energy density. It is observed that a consistent strain energy density is expressible in terms... 

The reaction of 15-18 membered benzodiazacrown ethers with salicylaldehyde afforded n-membered O2N2-donor macrocyclic ligands mounted with 1,3-diazacyclohexane subrings (1-4) in high yields. The products were characterized by FT-IR, 1H, 13C NMR spectroscopy, elemental analyses, and single crystal X-ray studies. The solid state structures revealed strong intramolecular hydrogen bonding between the pendant phenolic group and the tertiary nitrogen of the corresponding macroring  

Emerging cloud workloads in today's modern data centers have large memory footprints that make the processor's caches to be ineffective. Since L1 data cache is in the critical path, high data cache miss rates degrade the performance. To fix the issue in traditional workloads, data prefetchers predict the needed data to hide the memory latency and ultimately improve performance. In this paper, we focus on the L1 data cache to answer the question on why state-of-the-art prefetching methods are inefficient for modern workloads in terms of performance and energy consumption? This is because L1 cache is the most important player affecting the processor performance. Results show that, on the one... 

Smart drug delivery systems (DDSs) have attracted the attention of many scientists, as carriers that can be stimulated by changes in environmental parameters such as temperature, pH, light, electromagnetic fields, mechanical forces, etc. These smart nanocarriers can release their cargo on demand when their target is reached and the stimulus is applied. Using the techniques of nanotechnology, these nanocarriers can be tailored to be target-specific, and exhibit delayed or controlled release of drugs. Temperature-responsive nanocarriers are one of most important groups of smart nanoparticles (NPs) that have been investigated during the past decades. Temperature can either act as an external... 

Based on the results of recent studies, comprehensive characterization of the behavior of infilled rock fractures under saturated and unsaturated conditions requires knowledge of morphological details of fracture surface, as well as state of stress of infill materials and their initial innate conditions (e.g., void ratio, water content, degree of saturation and dry density). This paper describes a semi-empirical equation to interpret the effects of wall-roughed nature of the fractures and presence of partially saturated fine materials within the fractures on the behavior of infilled rock fractures during shear. The proposed equation incorporates the soil-water retention curve parameters as... 

Three-dimensional graphenic adsorbents have been successfully synthesized by hydrothermal reduction and applied for deep removal of dibenzothiophene (DBT) from model fuel. The nanoporous spongelike structure of the graphenic compounds was confirmed using various characterization techniques. Reduced graphene oxide (rGO), carbon black-graphene composite (CB-G), and nickel-impregnated graphene (Ni-G) showed adsorption capacities of 41.8, 46.9, and 43.3 mg of DBT g-1, respectively, and the DBT concentration in the model fuel was diminished to less than 10 ppm. Thermodynamic parameters for the adsorption process evidenced feasible and exothermic adsorption on rGO and CB-G with negative enthalpy... 

Porous silicon samples were obtained by the electrochemical method and were impregnated with Pd by the electroless process. X-ray photoelectron spectroscopy illustrated that the surface of the samples is oxidized during the palladium deposition. Scanning electron microscopy showed how factors such as morphology and pre-oxidations of porous samples and the plating parameters including Pd-salt concentration, HCl concentration, temperature of the electroless solution and the time of process affect the growth and nucleation of Pd particles. Observations demonstrated that the illumination-assisted process on p-type samples has a drastic effect on the growth of palladium. Hydrogen sensing of these... 

A novel superabsorbent hydrogel composite based on kappa-carrageenan (κC) was prepared by graft copolymerisation of acrylic acid (AA) in the presence of kaolin using methylenebisacrylamide (MBA) as a crosslinking agent and ammonium persulfate (APS) as an initiator. The synthetic variables (i.e. AA, MBA and APS concentration, and the amount of kaolin) affecting the water absorbency of the resulting superabsorbent composite were studied. Evidence of grafting and kaolin interaction was obtained by comparing the FTIR spectra of the initial substrates and of the superabsorbent composite. A new absorption band at 1722 cm-1 in the composite spectrum confirmed the kaolin-organic polymer linkage.... 

In this work, the synthesis, characterization, and kinetic investigation of the free-radical polymerization of 4-acetylaminobenzene propenoic ester (ABPE) and 4-methylbenzene propenoic ester (MBPE) were studied. The kinetic behaviors of ABPE and MBPE in the polymerization initiated by azobisisobutyronitrile in dimethylformamide solutions at temperatures between 50 and 120°C were investigated, and experimental and theoretical conversion-time curves were compared. Both monomers showed a polymerization ceiling temperature (T c ). Tc was calculated with experimental values of k pk1/2 with a constant concentration of 0.7 mol/L for monomers. Tc was about 141 and 131 °C for ABPE and MBPE,... 

This paper provides a perspective on the current knowledge and potential areas of future research related to electrostatics in fluidized beds. Aspects addressed include characterization techniques, interplay between electrostatics and hydrodynamics, charge control methods, applications of tribo-electrostatic fluidization systems, and computational simulations which account for electrostatic forces, as well as other forces. This is a complex research field involving fluid mechanics, powders, and electrical physics. © 2021 CFB 2021 - Proceedings of the 13th International Conference on Fluidized Bed Technology. All rights reserved  

Porous poly-silicon (PPS) samples, obtained by electrochemical anodization of p-type poly-silicon wafers, were doped with Pd by the electroless process. Rutherford backscattering spectroscopy shows that Pd has diffused a few micrometres into the PPS layer. Scanning electron microscopy and energy dispersive x-ray analysis results demonstrate the presence of Pd as dispersed clusters on the surface. The variation of the electrical resistance in the presence of dry air diluted with hydrogen at room temperature shows that Pd/PPS samples have the ability to sense hydrogen at levels down to several thousands of ppm. This value is far below the flammability limit of hydrogen gas. It was found that... 

This paper proposes a new medium-access control (MAC) protocol designed for wireless sensor networks. A wireless sensor network is an array of large number of sensors interconnected by a multi-hop ad-hoc network. The primary objective for the sensor network is achieving to low-power consumption while latency is usually less important compare to traditional wireless networks. This characteristic of sensor network motivates the design of new MAC layer so that power consumption is reduced. In this paper, a novel traffic-aware algorithm based on distributed node schedule management (DMD) protocol is introduced that utilizes distributed dynamic node scheduling strategy to dramatically increase... 

In smart antenna systems, The localization and direction of desired source(s) must be known. In this paper, we introduce a method called "DMSAE" (Direction finding of Multiple Sources by Alternating Eliminations) to find the radio directions of signals impinging on an arbitrary antenna array and the number of the signals. This method which is based on the Minimum Variance Distortionless Response (MVDR) algorithm, can not only detect the direction and the number of sources, simultaneously, but also has better resolution ability compared to the other conventional direction finding algorithms. This method can also detect very weak sources when other powerful sources exist in the environment. In... 

Enhancing oil extraction from oil sands with a hydraulic fracturing technique has been widely used in practice. Due to the complexity of the actual process, modelling of hydraulic fracturing is far behind its application. Reproducing the effects of high pore pressure and high temperature, combined with, complex stress changes in the oil sand reservoir, requires a comprehensive numerical model which is capable of simulating the fracturing phenomenon. To capture all of these aspects in the problem, three partial differential equations, i.e., equilibrium, flow, and heat transfer, should be solved simultaneously in a fully implicit (coupled) manner. A fully coupled thermo-hydro-mechanical... 

A damage plastic constitutive model for metals is proposed in this paper. An anisotropic damage tensor and a damage surface are adopted to describe the degradation of the mechanical properties of metals. The model is developed within the thermodynamic framework and creates an anisotropic damage plastic model with the ability to describe the plastic and damage behavior of iron based materials. According to the principle of strain energy equivalence between the undamaged and damaged materials, the linear elastic constitutive equations for the damaged material expressed a stiffness tensor in the damaged configuration. The damaged material is modeled using the constitutive laws of the undamaged... 

In this investigation, in-situ precipitation of vanadium carbides was employed to reinforce Fe-13Mn and Fe-13Mn-3W alloys by means of conventional melting and casting route. Microstructures were characterized by optical and scanning electron microscopy techniques.Mechanical properties of the materials were determined by hardness, impact toughness and tension tests. It was observed that tungsten improved the strength of the matrix and the reinforcements as well as tensile properties and work hardening rate of the VC-reinforced composite. Ball mill abrasion test was utilized to simulate impact-abrasion wear condition using two types of abrasive minerals. The results showed that the degree of... 

A multicomponent polysaccharide obtained from dried tubers of certain natural terrestrial orchids was chemically modified by sulfonation using chlorosulfonic acid-dimethylformamide (HClSO3-DMF) complex as a reagent. For a structural characterization of salep sulfate 1H nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) spectra, and Thermogravimetric analysis (TGA) curves were recorded. The sulfate content of modified salep was determined using elemental analysis. This modified biopolymer was used to prepare a new environment-friendly heavy metal ion adsorbent, salep sulfate-graft-polyacrylic acid hydrogel (SS-g-PAA). Swelling rate and equilibrium water absorbency in various...