Preparation and Characterization of Acetic Acid-Functionalized Fe3O4@SiO2 Nanoparticles as an Efficient Nanocatalyst for the Synthesis of Nitrones in Water

Silicon - Magnetic materials grafted with acetic acid (Fe3O4@SiO2COOH MNPs) were successfully prepared from the incorporation of bromoacetic acid as a functional group on the surface of magnetite...     

Guided local buckling (GLB) theory for short braces

According to recent earthquake experiences and experimental results, the local buckling is the most important parameter for limiting the ductility of short braces and prevents earthquake energy absorption in larger drifts. A new theory is introduced to prevent harmful effects of local buckling and use it as an energy absorption device in braced frames. According to this theory oblique stiffeners are provided inside braces section and it is expected to divide lateral drift of the system to smaller deflections inside stiffeners intervals. As much as number of local buckling along braces increases, more energy will be absorbed and the fracture life of the sections increases considerably. This theory is supported by half-scale experimental results and numerical modeling. The obtained results represent uniform and stable energy absorption and reasonable system ductility.     

A low-loss compact six-bit DMTL phase shifter for phased array antenna applications

A phase shifter is one of the main components of radars and phased array systems. In this paper, a novel three-state two-bridge unit cell is presented for a compact low-loss six-bit distributed microelectromechanical systems (MEMS) transmission line (DMTL) phase shifter. The proposed unit cell includes a coplanar waveguide (CPW) transmission line, a MEMS bridge on the signal line, two metal-air-metal (MAM) capacitors on a glass substrate, and two additional electrodes under the MEMS bridge, near the signal line. Using these electrodes, it is possible to generate two different phase states employing the MEMS bridge, and the third state is produced by a metal-air-metal (MAM) bridge. Hence, the designed structure can generate three different phase shifts per unit cell (i.e., 5.625°, 11.25°, and 22.5° phase shifts). The novelty of this design is that the number of unit cells is considerably reduced from 64 in a conventional six-bit phase shifter to only 17 in our design. Therefore, the total length of the six-bit phase shifter and average loss are considerably reduced. The designed structure is calculated and simulated at 32 GHz using MATLAB and ANSOFT HFSS, respectively. According to the calculation and simulation results, the lateral size of the phase shifter is only 8.5 mm, the root mean square (RMS) phase error is 1.38°, and the average loss is 1.1 dB. The feasibility of the proposed design is investigated using the proposed fabrication process. The designed phase shifter can be easily scaled to other frequencies for radar and satellite applications with more bits.     

Reducing the undesirable effects of wind farms＇ high-penetration on frequency

This paper reviews the effects caused by a high penetration of wind farms on network frequency. Energy generation in wind farms that use induction generators （as installed in Manjil Power Plant） is simulated, and, assuming that wind farm units provide 10% of the network power, the effect on frequency is studied, and it is shown that such a high penetration of the wind farms has a destructive effect on network frequency. It will be shown that the negative effects can be compensated for by using stored energy, but in the absence of energy storage equipments like SMES （Super Magnetic Energy Storage）, this solution is beyond reach. An alternative method is presented that is based on Rotary Frequency Converter （RFC）, and, as can be seen in the simulations, the wind farm output creates fewer disturbances, and frequency variations can be controlled considerably.     

Non‐linear behavior of yielding damped braced frames

Since the nature of an earthquake is the energy which is released due to tectonic events, improvements of behaviour of structures based on energy concepts have been a matter of great concern. Input energy must be dissipated by structures in order to decrease earthquake damage. For this purpose the YDBF (yielding damped braced frame) system is presented, which acts as a fuse when an earthquake occurs. Because of the high ductility of this system, damage to the main structural elements such as columns is prevented, and because of the non‐linear behaviour of such a system, which is based on the yielding of ductile steel, YDBF increases hysteretic dissipated energy. This class of dampers often yields in high or intermediate earthquake shakes and their hysteretic loops are relatively thick and stable. In this research seven YDBF system are modelled. These models are tested with various percentages of opening and the results of structural behaviour due to variation of opening percentages are compared. Copyright © 2004 John Wiley & Sons, Ltd.