Morphological control of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> particles via glycothermal process

Acicular magnetite (Fe₃O₄) powders were synthesized through new glycothermal dehydration by using crystalline α-FeOOH as precursor and glycols as solvent. When ethylene glycol was used as solvent, the phase was in-situ transformed from acicular α-FeOOH to α-Fe₂O₃ and finally to Fe₃O₄ at 270 °C for 6 h without morphological change. When water was added as a co-solvent in glycothermal reaction, Fe₃O₄ powders were synthesized through dissolution–recrystallization process at 230 °C for 3 h. The volume ratio of ethylene glycol to water (E/W) in the reaction has a strong effect on the morphology of the synthesized Fe₃O₄ particles. The particle shape of Fe₃O₄ particles changed from needle to sphere when the water content in E/W volume ratio increased from 0.5 to 1 mL in mixed glycothermal condition. When the water were added by more than 10 ml, the particle shape of Fe₃O₄ changed from sphere to octahedron truncated with the {100} faces and finally distinct octahedron with only {111} faces. Also, it is demonstrated that the size of Fe₃O₄ particles can be controlled from 1–2 μm to 100–200 nm by varying the reaction conditions such as the volume ratio of water to ethylene glycol and additive in glycothermal reaction.     

Direct Numerical Simulation of Turbulent Flow in a Square Duct: Analysis of Secondary Flows

A direct numerical simulation of turbulent flow in a square duct was performed for a Reynolds number based on bulk streamwise velocity and duct height equal to 4,440. The mechanism by which secondary flows are generated in a square duct was investigated. Two counterrotating secondary flows occur around the duct corner. These secondary flows were found to play a key role in momentum transfer between the corner and center of the duct. A conditional quadrant analysis was performed in the local maximum and minimum regions of the wall shear stress in order to characterize the pattern of the mean secondary flows.     

Series compensation method to mitigate harmonics and voltage sags and swells

The use of a series compensator (SC) to improve power quality is investigated. The role of the compensator is not only to mitigate the effects of voltage sag and swell, but also to control the level of harmonic distortions in the network. This is accomplished through extension of the voltage injection scheme of the SC by the incorporation of load current feedback and an external inductive filter. The compensation process is accompanied by an exchange of energy between the SC and the external network. Through a phase adjustment technique, it is shown that the voltage quality across the terminals of the protected load can be controlled. Simulation studies, supported by laboratory experiments, show that the resulting series compensation scheme is effective in improving the supply quality of the power system.     

Control of M-H Loop Shape in Perpendicular Recording Media by Ion Implantation

We have investigated the properties of CoCrPt-SiO₂ perpendicular recording media as influenced by Co ion implantation, and have shown that a substantial change of the M-H loop squareness and a control of coercivity (H_c) over a wide range are feasible. Thin films of Ta(5 nm)/Ru(20 nm)/CoCrPt-SiO ₂ (15 nm) were deposited and then subjected to the ion implantation with various acceleration energies, doses, and incident angles. It has been found that the cobalt ion implantation significantly alters the magnetic properties of CoCrPt-SiO ₂. In the case of the near-perpendicular implantation at 60 KV, the M-H loop became much squarer but there was a decrease of coercivity 4300 to 2100 Oe. There was no noticeable decrease of the saturation magnetization by implantation. The reason for the significantly increased squareness by near-perpendicular implantation is mainly attributed to the increase of exchange coupling between the grains by cobalt ion implantation     

Optical and electrical properties of p-type transparent conducting CuAlO2 thin film

P-type transparent conducting CuAlO₂ thin films were prepared by e-beam evaporation and wet-oxidation technique. CuAlO₂ film was preferentially (006) oriented after wet-oxidation. The transmittance varied from 20 to 85% and the resistivity varied from 5 × 10^− 3 to 4 Ω cm with wet-oxidation conditions. The nature of p-type films was confirmed by the positive hall coefficient. Optical band gap was estimated to be in the range of 3.96-4.20 eV. These behaviors were due to the decrease of oxygen deficient state in the film as oxidation progresses. Microstructural observations of films showed smooth morphology with 23.2-29.7 Å rms roughness.     

An Efficient Evolution Method From TDM-PON to Next-Generation PON

An efficient evolution method from a time-division-multiplexing passive optical network (TDM-PON) is proposed and demonstrated for a next-generation PON. A single-type three-port wavelength band combiner/splitter enables a simple and efficient evolution of TDM-PON maintaining the current PON infrastructure and wavelength plan. The crosstalk between the TDM-PON and next-generation PON is negligibly small     

A 2.4-GHz Low-Power Low-IF Receiver and Direct-Conversion Transmitter in 0.18-μm CMOS for IEEE 802.15.4 WPAN Applications

In this paper, a low-power low-IF receiver and a direct-conversion transmitter (DCT) suitable for the IEEE standard 802.15.4 radio system at the 2.4-GHz band are presented in 0.18-mum deep n-well CMOS technology. By using vertical NPN (V-NPN) bipolar junction transistors in the baseband analog circuits of the low-IF receiver, the image rejection performance is improved and the power consumption is reduced. In addition, by applying the V-NPN current mirrored technique in a DCT, the carrier leakage is reduced and the linearity performance is improved. The receiver has 10 dB of noise figure, -15 dBm of third-order input intercept point, and 35 dBc of image rejection. The transmitter has more than -2 dBm of transmit output power, -35 dBc of local oscillator leakage, and -46 dBc of the transmit third harmonic component. The receiver and transmitter dissipate 6 and 9 mA from a 1.8-V supply, respectively     

Self-Aligned Wafer-Level Integration Technology With High-Density Interconnects and Embedded Passives

This paper presents a polymer-based wafer-level integration technology suitable for integrating RF and mixed-signal circuits and systems. In this technology, disparate dies can be integrated together using a batch fabrication process. Very high density die-to-die interconnects with widths currently as small as 25 mum are implemented. To demonstrate the capabilities of this technology, a 10-GHz receiver front-end implemented in 0.18-mum CMOS technology is integrated with a high-resistivity Si substrate and embedded passives. By adjusting the input matching of the receiver using the embedded passives fabricated on the high-resistivity Si substrate, the input matching and conversion gain of the front-end receiver are improved     

High-Power 1.3-μm Quantum-Dot Superluminescent Light-Emitting Diode Grown by Molecular Beam Epitaxy

In this letter, we demonstrate the improved performance of 1.3-mum seven-layered InAs-GaAs quantum-dot superluminescent light-emitting diodes by the engineering of the epitaxial growth conditions alone, namely the thickness of the low-temperature GaAs spacer layer between quantum-dot layers. For laser devices, a significant reduction in threshold current density and increase in external efficiency is observed, while for superluminescent diode structures, a ~4 fold increase in CW power at a given drive current is obtained     

Improving Quality of Service and Assuring Fairness in WLAN Access Networks

As public deployment of wireless local area networks (WLANs) has increased and various applications with different service requirements have emerged, fairness and quality of service (QoS) are two imperative issues in allocating wireless channels. This study proposes a fair QoS agent (FQA) to simultaneously provide per-class QoS enhancement and per-station fair channel sharing in WLAN access networks. FQA implements two additional components above the 802.11 MAC: a dual service differentiator and a service level manager. The former is intended to improve QoS for different service classes by differentiating service with appropriate scheduling and queue management algorithms, while the latter is to assure fair channel sharing by estimating the fair share for each station and dynamically adjusting the service levels of packets. FQA assures (weighted) fairness among stations in terms of channel access time without decreasing channel utilization. Furthermore, it can provide quantitative service assurance in terms of queuing delay and packet loss rate. FQA neither resorts to any complex fair scheduling algorithm nor requires maintaining per-station queues. Since the FQA algorithm is an add-on scheme above the 802.11 MAC, it does not require any modification of the standard MAC protocol. Extensive ns-2 simulations confirm the effectiveness of the FQA algorithm with respect to the per class QoS enhancement and per-station fair channel sharing