• Analytical Science and Technology
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• v.11 no.6
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• pp.436-439
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• 1998

Ginseng saponins were analysed using reversed-phase high performance liquid chromatography with several columns. The optimum conditions were as following : reverse phase column; Novapak $C_{18}$ ODS column ($3.9mm{\times}150mm$, $5{\mu}m$), acetonitrile/water binary mobile phase gradient controller system, solvent flow rate; 1.5 mL/min, and UV (203 nm) detector. The complete separation of ginsenoside $Rb_1$, $Rb_2$, Rc, Rd, Re, Rf and $Rg_1$ was achieved within 50 min. The regression coefficients of the calibration curves for seven ginsenosides were 0.98~0.99.

• Journal of IKEEE
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• v.23 no.3
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• pp.800-804
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• 2019

This paper presents a dual-loop sub-sampling digital PLL for a 2.4 GHz IoT applications. The PLL initially performs a divider-based coarse lock and switches to a divider-less fine sub-sampling lock. It achieves a low in-band phase noise performance by enabling the use of a high resolution time-to-digital converter (TDC) and a digital-to-time converter (DTC) in a selected timing range. To remove the difference between the phase offsets of the coarse and fine loops, a phase offset calibration scheme is proposed. The phase offset of the fine loop is estimated during the coarse lock and reflected in the coarse lock process, resulting in a smooth transition to the fine lock with a stable fast settling. The proposed digital PLL is designed by SystemVerilog modeling and Verilog-HDL and fully verified with simulations.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.43 no.12 s.354
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• pp.55-64
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• 2006

This work proposes a calibration-free 14b 70MS/s 0.13um CMOS ADC for high-performance integrated systems such as WLAN and high-definition video systems simultaneously requiring high resolution, low power, and small size at high speed. The proposed ADC employs signal insensitive 3-D fully symmetric layout techniques in two MDACs for high matching accuracy without any calibration. A three-stage pipeline architecture minimizes power consumption and chip area at the target resolution and sampling rate. The input SHA with a controlled trans-conductance ratio of two amplifier stages simultaneously achieves high gain and high phase margin with gate-bootstrapped sampling switches for 14b input accuracy at the Nyquist frequency. A back-end sub-ranging flash ADC with open-loop offset cancellation and interpolation achieves 6b accuracy at 70MS/s. Low-noise current and voltage references are employed on chip with optional off-chip reference voltages. The prototype ADC implemented in a 0.13um CMOS is based on a 0.35um minimum channel length for 2.5V applications. The measured DNL and INL are within 0.65LSB and l.80LSB, respectively. The prototype ADC shows maximum SNDR and SFDR of 66dB and 81dB and a power consumption of 235mW at 70MS/s. The active die area is $3.3mm^2$.

• Journal of Communications and Networks
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• v.15 no.4
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• pp.383-397
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• 2013

In this paper, the sensitivity of massive antenna arrays and digital beamforming to radio frequency (RF) chain in-phase quadrature-phase (I/Q) imbalance is studied and analyzed. The analysis shows that massive antenna arrays are increasingly sensitive to such RF chain imperfections, corrupting heavily the radiation pattern and beamforming capabilities. Motivated by this, novel RF-aware digital beamforming methods are then developed for automatically suppressing the unwanted effects of the RF I/Q imbalance without separate calibration loops in all individual receiver branches. More specifically, the paper covers closed-form analysis for signal processing properties as well as the associated radiation and beamforming properties of massive antenna arrays under both systematic and random RF I/Q imbalances. All analysis and derivations in this paper assume ideal signals to be circular. The well-known minimum variance distortionless response (MVDR) beamformer and a widely-linear (WL) extension of it, called WL-MVDR, are analyzed in detail from the RF imperfection perspective, in terms of interference attenuation and beamsteering. The optimum RF-aware WL-MVDR beamforming solution is formulated and shown to efficiently suppress the RF imperfections. Based on the obtained results, the developed solutions and in particular the RF-aware WL-MVDR method can provide efficient beamsteering and interference suppressing characteristics, despite of the imperfections in the RF circuits. This is seen critical especially in the massive antenna array context where the cost-efficiency of individual RF chains is emphasized.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1951-1956
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• 2004

The transient nature and complex flow geometries of two-phase gas-liquid flows cause fundamental difficulties when measuring flow velocity using an electromagnetic flowmeter. Recently, a current-sensing flowmeter was introduced to obtain measurements with high temporal resolution (Ahn et $al.^{(1)}$). In this study, current-sensing flowmeter theory was applied to measure the fast velocity transients in slug flows. To do this, the velocity fields of axisymmetric gas-liquid slug flow in a vertical pipe were obtained using Volume-of-Fluid (VOF) method and the virtual potential distributions for the electrodes of finite size were also computed using the finite volume method for the simulated slug flow. The output signal prediction for slug flow was carried out from the velocity and virtual potential (or weight function) fields. The flowmeter was numerically calibrated to obtain the cross-sectional liquid mean velocity at an electrode plane from the predicted output signal. Two calibration parameters are required for this procedure: a flow pattern coefficient and a localization parameter. The flow pattern coefficient was defined by the ratio of the liquid resistance between the electrodes for two-phase flow with respect to that for single-phase flow, and the localization parameter was introduced to avoid errors in the flowmeter readings caused by liquid acceleration or deceleration around the electrodes. These parameters were also calculated from the computed velocity and virtual potential fields. The results can be used to obtain the liquid mean velocity from the slug flow signal measured by a current-sensing flowmeter.

• Analytical Science and Technology
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• v.13 no.1
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• pp.27-33
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• 2000

Simultaneous separation and analysis of Ni(II), Pd(II), Co(II), Cu(II) and Hg(II) in peperidinedithiocarbamate (PDTC) chelates were investigated by reversed phase liquid chromatography. The optimum conditions for the separation of PDTC metal chelates were examined with respect to the pH, extraction solvent, and mobile phase strength on Novapak $C_{18}$ column using methanol/water mixture as mobile phase. All metal PDTC chelates were eluted in an acceptable range of capacity factor value ($0{\leq}log\;k^{\prime}{\leq}1$). The linear calibration curves were obtained in the concentration range of $0{\sim}1.2{\mu}g/mL$ for five metal ions, and also good precision in the range of 1.96~3.41% RSD was obseved. Under the optimum conditions, trace metat ions in the composite water sample were successfully separated and determined with relative error of ${\pm}2.0%$.

• Analytical Science and Technology
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• v.19 no.6
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• pp.519-528
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• 2006

An analytical method for the determination of thyroid hormones in urine samples has been studied by using solid-phase extraction and high-performance liquid chromatography/diode array detector/electro-spray mass spectrometry. Seven thyroid hormones were successfully separated by gradient elution on the reverse phase Hypersil ODS column (4.6 mm I.D., 100 mm length, particle size $5{\mu}m$) with ammonium formate buffer and acetonitrile, and UV spectra and mass fragment could be confirmed. The extraction recoveries of thyroid hormones in the urine samples (pH 3) were in the range of 89.0-113.1% with solid-phase extraction by C18, followed by elution with 4 ml of methanol/ammonium hydroxide (9 : 1). The calibration curves showed good linearity with the correlation coefficients ($r^2$) varying from 0.992 to 0.998 and the detection limits of all analytes were obtained in the range of 2-4 ng/ml (3.8-13.0 pmol/ml).

• Bulletin of the Korean Chemical Society
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• v.27 no.6
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• pp.875-880
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• 2006

A new, simple and fast flow injection analysis (FIA) method has been developed for the indirect determination of nitrite. The proposed indirect automatic method is based on the oxidation of nitrite to nitrate using a lead(IV) dioxide oxidant microcolumn where the flow of the sample through the microcolumn reduces the $PbO_2$ solid phase reagent to Pb(II), which is measured by flame atomic absorption spectrometry. The absorbance of Pb(II) are proportional to the concentration of nitrite in the samples. The calibration curve was linear up to 30 mg $L ^{-1}$, with a detection limit of 0.11 mg $L ^{-1}$ for a 400 mL injected sample volume and a sampling rate of about 80 $h ^{-1}$. The results exhibit no interference from the presence of large amounts of ions. The developed procedure was found to be suitable for the determination of nitrite in foodstuffs and wastewaters. A relative standard deviation better than 0.9% was obtained in a repeatability study. The reliability of the method was established by parallel determination against the standard method.

• Korean Journal of Computational Design and Engineering
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• v.16 no.6
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• pp.391-396
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• 2011

Gait is walking attitude and indicating state. The body's gait is a good mix in the center of body mechanics and exercises to wake up gently at the same time switch is a pass which is complicated at legs various joints. The shifting action what swing phase and stance phase rhythmic movement of body. One from piece moves with different dot. Especially plain walking and stair walking as a vehicle has been used frequently. Characteristics of the stair walking while the balanced the horizontal and vertical movement. Stair walking often takes place in everyday. It requires large range more than walking at plain in the moment and joint range of gait motion. And consistently applied to joints and various types of loads at legs joint may involve joint disorders. In this study, spastic cerebral palsy existing artificial limbs for disabled people when developing calibration equinus deformity patients induce muscle pain when walking on stairs independently, to reduce the research. Comparing the characteristics of the walking up the stairs for analysis patellofemoral joint pain as a result it is to provide engineering data.

• Bulletin of the Korean Chemical Society
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• v.25 no.7
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• pp.1019-1024
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• 2004

The present paper is focused on simultaneous sorption concentration of gold (III) and silver (I) from thiocyanate solutions using high-selective anion exchanger AN-25 and subsequent separation of these ions at various concentrations of thiocarbamide (eluent). As a result, silver (I) ions are completely eluted from AN-25 and gold (III) ions remain in the resin phase and can be determined directly in the solid phase by diffuse reflection spectroscopy. It is proposed to use the sorption-spectroscopic method for Au(III) determination in aqueous solutions. The calibration curve is linear in the concentration range of 1-19 mg/L (sample volume is 10.0 mL) and the detection limit is 0.05 ${\mu}g/mL$. The presence of Cu(II), Co(II), Fe(II) do not hinder this determination. Au(III) was determined in industrial solutions.