Metamaterial‐based antennas for integration in UWB transceivers and portable microwave handsets

Two planar antennas based on metamaterial unit‐cells are designed, fabricated, and tested. The unit‐cell configuration consists of H‐shaped or T‐shaped slits and a grounded spiral. The slits essentially behave as series left‐handed capacitance and the spiral as a shunt left‐handed inductance. The unit‐cell was modeled and optimized using commercial 3D full‐wave electromagnetic simulation tools. Both antennas employ two unit‐cells, which are constructed on the Rogers RO4003 substrate with thickness of 0.8 mm and ε_r = 3.38. The size of H‐shaped and T‐shaped unit cell antennas are 0.06λ₀ × 0.02λ₀ × 0.003λ₀ and 0.05λ₀ × 0.02λ₀ × 0.002λ₀, respectively, where λ₀ is the free–space wavelength. The measurements confirm the H–shaped and T–shaped unit‐cell antennas operate across 1.2–6.7 GHz and 1.1–6.85 GHz, respectively, for voltage standing wave ratio (VSWR) < 2, which correspond to fractional bandwidth of ～140% and ～ 145%, respectively. The H‐shaped unit‐cell antenna has gain and efficiency of 2–6.8 dBi and 50–86%, respectively, over its operational range. The T‐shaped unit‐cell antenna exhibits gain and efficiency of 2–7.1 dBi and 48–91%, respectively. The proposed antennas have specifications applicable for integration in UWB wireless communication systems and microwave portable devices. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:88–96, 2016.     

Quality enhancement of video on demand implementation in peer-to-peer networks by optimum chunk length in the BitTorrent

BitTorrent in efficiency content distribution is a major concern efficiency among the researchers of this field with respect to streaming video on demand (VoD) production. BitTorrent is not appropriate for real-time applications; therefore, in order to apply it in VoD it should go through the necessary changes. Most of the available studies have greatly focused on changes in methods regarding chunk and peer selections method regarding BitTorrent, which proposed methods have improved the quality of VoD to a certain degree, while, the effect of chunk size on quality of video has been of less concern among them. Noting the fact that the buffer is used on VoD, the specified time for filling the buffer would allow for appropriate management of the chunk’s length. The Bit error rate and the time overhead of the operating algorithm parameters, somehow effect the chunk size. Because of bit error rate, the probability of correctly received chunks with great length is much less, that is, offering shorter pieces, while these pieces would lead to formation of more pieces in a buffer. The results indicate that a specific amount of time is required for obtaining the buffer’s content, and it must be dividable into more chunks. Running algorithms for each chunk generate a greater overhead which would result in of the QoS reduction. This overhead would make the bigger pieces perform better. As for the opposite impacts of these two parameters on the chunk size, in this article the optimal length of the chunks is found by considering both the effective characteristic. This optimal length is an established balance between the correctly received chunks’ rate and the greater rate of the buffer context obtained in a specified time.     

Implementing the homotopy continuation method in a hybrid approach to solve the kinematics problem of spatial parallel robots

In this paper, first the application of homotopy continuation method (HCM) in numerically solving kinematics problem of spatial parallel manipulators is investigated. Using the HCM the forward kinematics problem (F-Kin) of a six degrees of freedom (DOFs) 6–3 Stewart platform and the inverse kinematics problem (I-Kin) of a 3-DOF 3-PSP robot are solved. The governing equations of the kinematics problems of the robots are developed and embedded in the homotopy continuation function. The HCM is utilized in order to solve the nonlinear system of equations derived from the kinematics analysis of the robots. Then, to represent the real case application an initial guess far from the correct answer is selected. It is shown that, comparing with the Newton–Raphson method (NRM), the F-Kin calculation time for the Stewart robot is decreased by 43%. Therefore, using the HCM a hybrid method is suggested to solve the F-Kin of the Stewart robot. Furthermore, the HCM, as an innovative method, relieves other downsides of the conventional numerical methods, including a proper initial guess requirement as well as the problems of convergence.     

Copolymerization of butyl acrylate with styrene in presence on ZnCl2

Summary Copolymers of butyl acrylate-styrene were prepared in presence of ZnCl₂. The formation of a complex was determined by infrared spectroscopy. The copolymers were characterized by IR, NMR and by solubility. The study of their structure as a function of the initial monomer composition and the analysis of UV spectra showing varying intensity of the carbonyl peaks confirmed the presence of an alternating copolymer. The reactivity ratios of the two monomers were determined and found to be 0.1 for both butyl acrylate and styrene.     

Preparation of organic–inorganic nanocomposites with core‐shell structure by inorganic powders

Organic–inorganic nanocomposites with core‐shell structure were prepared in two steps. In the first step, the latex particles in the semibatch emulsion polymerization of butyl methacrylate (BMA), in the presence of methacrylic acid (MAA), were prepared. Small amounts of acrylic acid incorporated into the latex to have better interaction between the surface of particles and inorganic phase. MAA also increased the latex stability and decreased the amount of coagulum. In the second step, the core‐shell structures were prepared by coating the latex particles with three types of inorganic powders. Pectin coated precipitated calcium carbonate, alumina, and silica. The examinations show that pectin‐coated calcium carbonate has the best response than other types of calcium carbonate. Alumina was the second type of inorganic powder that was used for coating the core particles. Silicagel and fumed silica (Aerosil) were used for coating by silica. Scanning electron microscopy and transmission electron microscopy showed the particle morphology and the core‐shell structure, respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Dynamic task scheduling modeling in unstructured heterogeneous multiprocessor systems

An algorithm is proposed for scheduling dependent tasks in time-varying heterogeneous multiprocessor systems, in which computational power and links between processors are allowed to change over time. Link contention is considered in the multiprocessor scheduling problem. A linear switching-state space-modeling paradigm is introduced to enable theoretical analysis from a system engineering perspective. Theoretical analysis of this model shows its robustness against changes in processing power and link failure. The proposed algorithm uses a fuzzy decision-making procedure to handle changes in the multiprocessor system. The efficiency of the proposed algorithm is illustrated by several random experiments and comparison against a recent benchmark approach. The results show up to 18% average improvement in makespan, especially for larger scale systems.     

Quantum circuit physical design methodology with emphasis on physical synthesis

In our previous works, we have introduced the concept of “physical synthesis” as a method to consider the mutual effects of quantum circuit synthesis and physical design. While physical synthesis can involve various techniques to improve the characteristics of the resulting quantum circuit, we have proposed two techniques (namely gate exchanging and auxiliary qubit selection) to demonstrate the effectiveness of the physical synthesis. However, the previous contributions focused mainly on the physical synthesis concept, and the techniques were proposed only as a proof of concept. In this paper, we propose a methodological framework for physical synthesis that involves all previously proposed techniques along with a newly introduced one (called auxiliary qubit insertion). We will show that the entire flow can be seen as one monolithic methodology. The proposed methodology is analyzed using a large set of benchmarks. Experimental results show that the proposed methodology decreases the average latency of quantum circuits by about 36.81 % for the attempted benchmarks.     

Experimental Modeling of Gas–Solid Heat Transfer in a Pipe with Various Inclination Angles

Gas–solid flow in a pipe with different configurations (vertical, horizontal, and inclined positions) is studied experimentally. Air with temperature around 170°C and sand particles with mean diameter of 253 μm are used as gas and solid mediums, respectively. Effects of different parameters (pipe slope and solid particles feed rate) are studied on heat transfer rate between gas and solid particles. The Nusselt number decreases at lower solids feed rate in a dilute regime of the mixture; however, it increases at higher solids feed rates. Furthermore, results show that a higher Nusselt number takes place at the angles closer to 45 degrees.     

The effect of TiO2 additive on sinterability and properties of SiC-Al2O3-Y2O3 composite system

In the current research, the effects of TiO₂ additive on mechanical and physical properties of SiC bodies, sintered by liquid phase methods were investigated. Al₂O₃ and Y₂O₃ were used as sintering-aids (10?wt% in total) with an Al₂O₃/Y₂O₃ ratio of 43/57 to provide liquid phase during Sintering. TiO₂ was also used as the oxide additive with an amount ranging from 0 to 10?wt%. After scaling and mixing the starting materials by a planetary mill, the obtained slurry was dried at 100?℃ for four hours. The derived powders were finally pressed under a pressure of 90?MPa. The samples were then pyrolyzed and sintered at 600?℃ and 1900?℃, respectively under argon atmosphere for 1.5?h. Phase analysis showed no trace of TiO₂ after the sintering process, demonstrating the complete TiO₂ to TiC transformation. The results showed that an increase in TiO₂ content up to 5?wt%, led an improvement in all the measured properties including the relative density, hardness, Young's modulus, bending strength, indentation fracture resistance and the brittleness factor, reaching to 96.2%, 24.4?GPa, 395.8?GPa, 521?MPa, 5.8?MPa?m^1/2 and 286.5?×?10^?6 m^?1, respectively. However more than 5?wt% additive resulted in a decrease in all the above-mentioned properties. Microstructural studies demonstrated that crack deflection and crack bridging were the major mechanisms responsible for an increase in the indentation fracture resistance.     

Synthesis and Characterization of Polycarbonate/TiO2 Ultrafiltration Membranes: Critical Flux Determination

A novel polycarbonate (PC) membrane was modified with titanium dioxide via nonsolvent-induced phase separation method to improve its hydrophilicity and antifouling properties in a submerged membrane system for the removal of humic acid (HA) both with and without polyaluminum chloride (PAC) coagulant. The effect of TiO₂ additive on the morphology and performance of the nanocomposite membranes was studied by atomic force microscopy, field emission scanning electron microscopy, energy dispersive X-ray, mechanical properties, water contact angle, porosity, pure water flux, rejection tests, and antifouling parameters. The obtained results revealed that a higher critical flux was achieved by the PC/TiO₂ nanocomposite membrane. The flux recovery ratio of the neat PC membrane increased with the addition of TiO₂ nanoparticles and without PAC coagulant. HA removal for the PC nanocomposite membrane was higher than that of the neat PC membrane with and without PAC coagulant.