Proximity effects of a layered periodic structure on miniaturization of patch antennas

A miniaturized microstrip antenna on a planar layered periodic structure is proposed, designed and fabricated. The proposed structure miniaturizes patch antennas in the microwave band. With varying the parameters of the proposed structure, the achieved miniaturization factor can be adjusted in the range 2.6–4.2. Numerical and experimental results are presented. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Lattice-based certificateless public-key encryption in the standard model

The notion of certificateless public-key encryption (CL-PKE) was introduced by Al-Riyami and Paterson in 2003 that avoids the drawbacks of both traditional PKI-based public-key encryption (i.e., establishing public-key infrastructure) and identity-based encryption (i.e., key escrow). So CL-PKE like identity-based encryption is certificate-free, and unlike identity-based encryption is key escrow-free. In this paper, we introduce simple and efficient CCA-secure CL-PKE based on (hierarchical) identity-based encryption. Our construction has both theoretical and practical interests. First, our generic transformation gives a new way of constructing CCA-secure CL-PKE. Second, instantiating our transformation using lattice-based primitives results in a more efficient CCA-secure CL-PKE than its counterpart introduced by Dent in 2008.     

Mitigation of Crystallization Fouling in a Single Heated Tube Using Projectiles of Different Sizes and Hardness

Fouling of heat exchangers is a prevalent operating drawback in many process industries. Efficient chemical inhibitors have predominantly been used for many years to combat deposit formation. Nevertheless, new stringent environmental legislations limit their utilization. On-line mitigation techniques, such as propulsion of projectiles at different injection rates, can also be utilized, which can, in turn, minimize the need for chemical inhibitors. Nevertheless, the experimental data are scarce and nonconclusive. In this experimental study, two spherical-type projectiles of different sizes and hardness have been used to clean the inner surface of a single heated tube that was subjected to the deposition of calcium sulfate. Projectiles were then introduced at different injection rate of every 2, 5, 10, 15, and 30 min. The experimental results show that (i) the projectiles would expedite initial nucleation of crystals even if they are soft and easy to propel inside the tube; (ii) fouling can only be mitigated if the projectiles exert a shear force such that the corresponding removal rate is greater than the net rate of the deposition; and finally (iii) harder projectiles with larger surface contact area are more efficient in cleaning the surface compared to those that are softer.     

Adsorptive desulfurization and denitrogenation of model fuel by mesoporous adsorbents (MSU-S and CoO-MSU-S)

Adsorption of heterocyclic sulfur- and nitrogen-containing compounds by mesostructure adsorbent (MSU-S) and its modified form with cobalt oxide is studied using model fuel. The results of characteristic tests (XRD, N₂ adsorption–desorption, FTIR, and SEM) indicate that CoO impregnation causes a negative impact on mesoporous structure, crystalline phase, and particle shape along with a positive effect on surface ion exchange. CoO modification increased the adsorption loadings of DBT and BT to about 33.6% and 45.7%, respectively. For nitrogen compounds adsorption with the model fuel, adsorption loadings of quinoline and carbazole increase by 6.7% and 8.6%, respectively. Data fitting for carbazole, DBT, and BT is achieved better by the Langmuir model than the Freundlich model, and the data of quinoline fitted very well to the Freundlich model for CoO-MSU-S.     

Probabilistic approach to multi-objective Volt/Var control of distribution system considering hybrid fuel cell and wind energy sources using Improved Shuffled Frog Leaping Algorithm

Deregulation and restructuring in power systems, the ever-increasing demand for electricity, and concerns about the environment are the major driving forces for using Renewable Energy Sources (RES). Recently, Wind Farms (WFs) and Fuel Cell Power Plants (FCPPs) have gained great interest by Distribution Companies (DisCos) as the most common RES. In fact, the connection of enormous RES to existing distribution networks has changed the operation of distribution systems. It also affects the Volt/Var control problem, which is one of the most important schemes in distribution networks. Due to the intermittent characteristics of WFs, distribution systems should be analyzed using probabilistic approaches rather than deterministic ones. Therefore, this paper presents a new algorithm for the multi-objective probabilistic Volt/Var control problem in distribution systems including RES. In this regard, a probabilistic load flow based on Point Estimate Method (PEM) is used to consider the effect of uncertainty in electrical power production of WFs as well as load demands. The objective functions, which are investigated here, are the total cost of power generated by WFs, FCPPs and the grid; the total electrical energy losses and the total emission produced by WFs, FCPPs and DisCos. Moreover, a new optimization algorithm based on Improved Shuffled Frog Leaping Algorithm (ISFLA) is proposed to determine the best operating point for the active and reactive power generated by WFs and FCPPs, reactive power values of capacitors, and transformers’ tap positions for the next day. Using the fuzzy optimization method and max-min operator, DisCos can find solutions for different objective functions, which are optimal from economical, operational and environmental perspectives. Finally, a practical 85-bus distribution test system is used to investigate the feasibility and effectiveness of the proposed method.