A dual-band multiple-input multiple-output microstrip antenna with metamaterial structure for LTE and WLAN applications

A method to enhance the gain of microstrip dual-band multiple-input multiple-output (MIMO) antenna using partially reflective surface (PRS) layer is introduced and investigated in this paper. The proposed antenna consists of two FR4 substrates. The lower substrate has two radiating patches with parasitic elements that are supplied independently and create the MIMO property of the antenna. The upper substrate which is known as superstrate is arrays of PRS unit cells. The PRS layer printed on either side of a dielectric substrate and causes the antenna gain to increase in both frequency bands. The proposed antenna is appropriate for LTE (2.4–3.1 GHz) and WLAN (5.1–5.8 GHz) applications. The measured values of S₁₁ and S₂₂ parameters of the antenna are less than −10 dB and its FBR and gain are 12.5 dB and 5dBi, respectively. The average half power beam-width (HPBW) is roughly 108^○.     

Optimal damper placement based on base moment in steel building frames

A new damper optimization method for finding optimal size and location of the added viscous dampers is proposed based on the elastic base moment in planar steel building frames. A Fourier Transform is applied to the equation of the motion and the transfer function in terms of the fundamental natural frequency of the structures is defined. The transfer function amplitude of the elastic base moment evaluated at the first natural circular frequency of the structure is chosen as a new objective function in the minimization problem. The damper coefficients of the added viscous dampers are taken into consideration as design variables in a steel planar building frame. The transfer function amplitude of the elastic base moment is minimized under an active constraint on the sum of the damper coefficients of the added dampers and the passive constraints on the upper and lower bounds of the added dampers. The optimal damper design presented in this paper is compared with other optimal damper methods based on top displacement, top absolute acceleration and base shear. A ten-storey steel planar building frame is chosen to be rehabilitated with the optimal dampers. The optimal damper allocation is obtained for the transfer function amplitude of the elastic base moment then compared with the other damper optimization methods in terms of the transfer function response. The results of the proposed method show that the method can also be beneficial to decrease both the base moment and the interstorey drift ratios in some frequency regions.     

Lactic Acid: An Efficient and Green Catalyst for the One-Pot Five-Components Synthesis of Highly Substituted Piperidines

ABSTRACT

Polyfunctionalized heterocyclic compounds have an important role in the drug discovery process and analysis of drugs in late development. Piperidines and their analogues have received attention owing to their biological activities, because of the importance of these heterocycle compounds, there is still a need to improve the ways for green synthesis of these compounds. In this study, lactic acid was applied as a green and efficient catalyst for the one-pot five-component synthesis of highly substituted piperidines from the reaction between aromatic aldehydes, aromatic amines, and b-ketoester at ambient temperature. This methodology has a number of advantages such as: use of easy access and green catalyst, short reaction times, high yields, and easy work-up (just simple filtration).     

Review of bipolar plates in PEM fuel cells: Flow-field designs

The polymer electrolyte membrane (PEM) fuel cell is a promising candidate as zero-emission power source for transport and stationary cogeneration applications due to its high efficiency, low-temperature operation, high power density, fast start-up, and system robustness. Bipolar plate is a vital component of PEM fuel cells, which supplies fuel and oxidant to reactive sites, removes reaction products, collects produced current and provides mechanical support for the cells in the stack. Bipolar plates constitute more than 60% of the weight and 30% of the total cost in a fuel cell stack. For this reason, the weight, volume and cost of the fuel cell stack can be reduced significantly by improving layout configuration of flow field and use of lightweight materials. Different combinations of materials, flow-field layouts and fabrication techniques have been developed for these plates to achieve aforementioned functions efficiently, with the aim of obtaining high performance and economic advantages. The present paper presents a comprehensive review of the flow-field layouts developed by different companies and research groups and the pros and cons associated with these designs.     

ZrOCl2·8H2O as an environmentally friendly and recyclable catalyst for the chemoselective synthesis of 2-aryloxazolines and bis-oxazolines under thermal conditions and microwave irradiation

The reactions of arylnitriles with β-aminoalcohols to prepare 2-aryloxazolines has been efficiently carried out in the presence of catalytic amounts of ZrOCl₂·8H₂O using heat or microwave irradiation. Synthesis of mono- and bis-oxazolines from dicyanobenzenes was accomplished with high selectivity using this catalyst. Chemoselective conversion of arylnitriles to their corresponding 2-oxazolines in the presence of alkylnitriles was also achieved by this method. The use of ZrOCl₂·8H₂O catalyst is feasible because of its easy availability, easy handling, stability, easy recovery, reusability, good activity and eco-friendly.     

Simulation of refrigerant flow boiling in serpentine tubes

Numerical simulations were conducted to investigate the refrigerant flow boiling in a horizontal serpentine round tube with the Eulerian multiphase flow model and a phase-change model for the mass transfer. Correspondingly, an experimental investigation was conducted to provide validation and data for the simulations. The liquid/vapor phase distributions show stratification in horizontal tubes, indicating the buoyancy force caused by gravity acceleration is dominant, especially when the vapor void fraction is sufficiently high. The adiabatic bend sections served to redistribute the vapor phase, which was induced by the centrifugal force and re-condensation of the vapor (due to thermal non-equilibrium of two phases). The phase distributions in the bend sections showed the competitive influence of buoyancy force and centrifugal force at different operating conditions. In all cases, the numerical simulations appear reasonably consistent with the experimental observations. In particular, the simulation very well explains the bend effects on flow reconstruction and thermal non-equilibrium release observed in the experiments.     

CFD Simulation of Gas Distribution Performance of Gas Inlet Systems in Packed Columns

Packed columns are widely used in the chemical process industries. The optimum operation of these columns requires an even distribution of gas and liquid flows. This paper describes a method for modeling the flow pattern which develops above the gas inlet system using a computational fluid dynamics (CFD) approach. The uniformity of the gas flow through the packing is assessed by means of a maldistribution factor, M_F. Several factors which affect gas distribution, such as gas inlet type, gas inlet diameter and the distance between gas inlet and column bottom, were analyzed. It was found that gas distribution is more uniform as the inlet diameter and bottom distance are increased. Comparison of experimental data with a CFD simulation for several types of gas inlets, such as straight, slope and bend inlets, shows good agreement.     

CFD Simulation of Mass Transfer Efficiency and Pressure Drop in a Structured Packed Distillation Column

The pressure drop and mass transfer efficiency for two‐phase flow in a structured packed column were simulated using a commercial CFD package, CFX version 10. The distillation of the methanol/isopropanol system was carried out in a 0.073 m diameter column, with an element composed of a ceramic structured packing and 0.053 m in height. The Height Equivalent to Theoretical Plate (HETP) value varied from 0.106–0.146 m. Pressure drop experiments were measured with an air/water system. The pressure drops at the flooding and loading points were ca. 173 and 580 Pa/m of packing, respectively. HETPs and pressure drops calculated from the Computational Fluid Dynamics (CFD) model were compared to their experimental counterparts. The average relative error between CFD predictions and the experimental data for the prediction of dry pressure drop, irrigated pressure drop and mass transfer efficiency are 20.3 %, 23 % and 9.15 %, respectively. In all cases, the CFD predictions show a good agreement with the experimental data, indicating that CFD is a reliable, cost saving and suitable technique for the design and optimization of separation processes.