Yoonseok Choi

Solvent sublation using 8-hydroxyquinoline as a ligand for determination of trace elements in water samples

Abstract Solvent sublation was studied to separate and pre-concentrate a trace of Co(II), Cu(II) and Ni(II) as 8-hydroxyquinoline (oxine, HQ) complexes for their determination. The experimental conditions such as pH of solution, amount of HQ as a ligand and stirring time were investigated to optimize complex formation. Amount of surfactant and type of solvent were optimized for efficient sublation. The analyte ions in a 1.0 l sample were formed as metal–oxine complexes by the addition of 1.2% HQ 10 ml to the solution of pH 9.0 adjusted with NaOH solution. The solution was stirred for 30 min with a mechanical stirrer. Then 4 ml of 0.4% cetyltrimethylammonium bromide (CTAB) was added to the solution. After the solution was stirred for a further 20 min, it was transferred to a flotation cell and the complexes were floated by bubbling a nitrogen gas and extracted into 25 ml of methylisobutyl ketone (MIBK) on the surface of the aqueous solution. The analytes in the organic phase were determined by graphite furnace atomic absorption spectrophotometry (GF-AAS). This sublation method was applied to real samples and recoveries of 84–120% were obtained in the spiked samples.

Glucose Transporter-1 Expression in Squamous Cell Carcinoma of the Tongue

PURPOSE Tumor cells are known to express hypoxia-related proteins such as glucose transporter-1 (Glut-1). These hypoxia-induced changes may allow tumor cells to survive under sustained hypoxic microenvironments, and the surviving tumor cell under hypoxia may develop a more aggressive phenotype and so result in a poor prognosis. MATERIALS AND METHODS The Glut-1 expression was analyzed by immunohistochemistry, and its association with the prognosis was assessed in 60 patients with squamous cell carcinoma of the tongue. RESULTS The Glut-1 expression was diffuse with a membranous pattern, and the median percentage of Glut-1 positive tumor cells was 60% (range: 0.0 approximately 90.0%). A high Glut-1 expression (the percentage of positive tumor cells >or= the median value, 60%) was associated with the location of primary lesion, lymph node metastasis status and disease stage (p<0.05). The expression of Glut-1 was correlated with the Ki-67 expression (r=0.406, p=0.001). Microvessel density, as represented by CD31 staining, was also correlated with the Glut-1 expression although its significance is weak (r=0.267, p=0.039). On the univariate analysis, the group with a high Glut-1 expression showed poorer overall survival than the group with a low Glut-1 expression (p<0.05). However, the Glut-1 expression failed to show any independent prognostic significance on the multivariate analysis. CONCLUSION The expression of Glut-1 may be useful for predicting the prognosis and determining the treatment strategy for the management of squamous cell carcinoma of the tongue.

Performance analysis of adaptive equalizer design for CCK-OFDM wireless LAN

An adaptive equalizer scheme is presented in OFDM system for IEEE 802.11a, g wireless LAN. Conventional OFDM system employs a guard interval and a 1-tap frequency-domain equalizer (FEQ) to prevent delay spread distortions. This scheme is simple to implement, but provides low spectral efficiency due to the use of the guard interval. Moreover its performance is poor because of the lack of multipath diversity and the energy loss contained within the guard Interval. In the case where the channel impulse response (CIR) is larger than the guard interval, the system performance is limited by the intersymbol and intercarrier interference. The proposed equalizer scheme consists of an adaptive time-domain equalizer (TEQ) and a 1-tap FEQ using long training OFDM symbols in the preambles. Its performance is better than that of the conventional OFDM system under severe delay spread and noise power conditions, especially in the case where the CIR is larger than the guard interval. This enables a reduction in the size of the guard interval and thus the spectral efficiency of the OFDM system can be improved.

Design of a baseband modem for IEEE 802.11g wireless LAN systems

The paper presents the design and performance of a baseband modem for wireless LAN systems. The modem fully complies with the IEEE 802.11g standard draft 4.0. It is capable of operating in any of available modes such as ERP-DSSS/CCK, ERP-OFDM, Extended Rate PBCC, and CCK-OFDM. It offers different data rates from 1 Mbps to 54 Mbps and handles DBPSK, DQPSK, QPSK, 8-PSK, BPSK, 16-QAM, and 64-QAM modulation schemes. We show the BER performance of the presented modem as the result of simulation under AWGN and multipath channels.

Time preference and savings behaviour

ABSTRACT A number of studies have examined various determinants of savings rate. This article contributes to this literature by empirically testing whether the time preference (discounting behaviour) is another important determinant of savings rate. To this end, we estimate the hyperbolic Euler equation using the generalized method of moments (GMM) to examine whether the short-run discount factor can account for savings behaviour. The empirical results show that people exhibit short-run patience (impatience) when savings rate increases (decreases), which is in line with the theoretical prediction. This result implies that the time preference also plays an important role in determining savings behaviour. Various sets of instruments and different sample periods do not reverse the main finding.

Hyperbolic Discounting and Consumer Patience: The Case of Korea

ABSTRACT In this article, we test whether the consumption pattern in Korea exhibits a time-inconsistent discounting behavior compared to the conventional exponential discounting. We derive the quasi-hyperbolic Euler equation and estimate it using the generalized method of moments (GMM). The estimation results show that Korean consumers exhibit a time-inconsistent quasi-hyperbolic discounting behavior in general, but the pattern of inconsistency in consumption behavior, in particular the degree of impatience, depends on the estimation period, in particular whether it includes financial crisis periods in 1997–98 and 2008–11.