Hyun-seok Kim

Enhanced Arsenate Removal Performance in Aqueous Solution by Yttrium-Based Adsorbents

Arsenic contamination in drinking water has become an increasingly important issue due to its high toxicity to humans. The present study focuses on the development of the yttrium-based adsorbents, with basic yttrium carbonate (BYC), Ti-loaded basic yttrium carbonate (Ti-loaded BYC) and yttrium hydroxide prepared using a co-precipitation method. The Langmuir isotherm results confirmed the maximum adsorption capacity of Ti-loaded BYC (348.5 mg/g) was 25% higher than either BYC (289.6 mg/g) or yttrium hydroxide (206.5 mg/g) due to its increased specific surface area (82 m2/g) and surface charge (PZC: 8.4). Pseudo first- and second-order kinetic models further confirmed that the arsenate removal rate of Ti-loaded BYC was faster than for BYC and yttrium hydroxide. It was subsequently posited that the dominant removal mechanism of BYC and Ti-loaded BYC was the carbonate-arsenate ion exchange process, whereas yttrium hydroxide was regarded to be a co-precipitation process. The Ti-loaded BYC also displayed the highest adsorption affinity for a wide pH range (3–11) and in the presence of coexisting anionic species such as phosphate, silicate, and bicarbonate. Therefore, it is expected that Ti-loaded BYC can be used as an effective and practical adsorbent for arsenate remediation in drinking water.

High-frequency intermodulation analysis of cascode amplifier

By Volterra series analysis using only several device parameters (Cje,/spl beta/,/spl tau/, and rb), the high-frequency nonlinear behavior of cascode amplifiers is analyzed. To verify the validity of this simple analysis, theoretical analysis, simulation, and measurement of intermodulation behavior of cascode amplifier are compared. The results show that simple Volterra series analysis agrees with the simulation and measurement, varying with emitter degeneration inductor and bias current. This simple Volterra series analysis is suitable to estimate the nonlinear characteristics and gives an insight into the conceptual circuit analysis.

Cycling stability of Li metal in a mixed carbonate–ionic liquid electrolyte for lithium secondary batteries

Polymeric ionic liquids (PILs) containing a poly(ethylene glycol) methacrylate (POEM) coating layer significantly suppresses the reduction of the ionic liquid and of solvent molecules on Li metal anode in the Pyr14TFSI/carbonate electrolyte. Therefore, when Li metal was coated with the PILs–POEM, a cycling test performed with the electrolyte highlights an improved cycling stability.

Bias control technique for CDMA driver amplifier to decrease current

The ACPR requirement is constant over wide power range. ACPR at lower output power is excessive in conventional constant bias current. A new bias control technique to decrease bias current at lower power level is proposed by implementing hyperbolic tangent function (tanh) with offsets. It is verified indirectly by measurement. The measured bias current is reduced by the amount of 22% over the control range compared to the conventional one, in addition to meeting the ACPR requirement simultaneously over the entire range of output power.

A new linearity enhancing technique for ultra-wide dynamic range low noise amplifiers

This paper presents a new linearity enhancing technique for design of LNAs (Low Noise Amplifiers) which require high linearity and low power consumption for CDMA mobile station applications. In order to verify the feasibility of the proposed scheme over the conventional scheme, four different low noise amplifiers for 9000 MHz and 1.85 GHz applications have been designed, fabricated and measured using 0.5 /spl mu/m BiCMOS technology. The measured results of both 900 MHz and 1.85 GHz LNAs show that the proposed scheme consumes less than 50% of power that is required with conventional scheme, while maintaining comparable gain and linearity. Specifically, a 900 MHz LNA has NF of 1.65 dB, transducer power gain (S/sub 21/) of 16.5 dB and IIP3 of +3 dBm including gain controllability with power consumption of only 21 mW (3 V) using maximum f/sub T/ of 15 GHz BiCMOS technology.