Duk-Geun Hong

The resolution of stratigraphic inconsistency in the luminescence ages of marine terrace sediments from Korea

Several sets of marine terraces are exposed along the southeastern coast of the Korean peninsula. The formation ages of these terraces have attracted considerable attention because they provide essential information on local crustal stability. Over the last few years considerable effort has been put into the determination of these ages using optically stimulated luminescence (OSL) dating of the marine sediments from which the terraces were built. For several sites, the results of dose recovery tests and other OSL characteristics, including the dependence of equivalent dose on heat treatment prior to stimulation, have been described in detail elsewhere (Quat. Sci. Rev. 22 (2003) 407). However, it has been found that the samples from one site exhibit various undesirable OSL characteristics, which result in stratigraphically inconsistent OSL ages. In this paper, we investigate these characteristics, and use luminescence component separation to resolve this inconsistency. The resolved OSL ages obtained as such are then used for the discussion on the local crustal stability of the southeastern coast of Korea during the Late Pleistocene.

Sensitivity enhancement of spectral surface plasmon resonance biosensors for the analysis of protein arrays

A novel method for sensitivity enhancement of spectral surface plasmon resonance (SPR) biosensors was presented by reducing the refractive index of the sensing prism in the analysis of protein arrays. Sensitivity of spectral SPR biosensors with two different prisms (BK-7, fused silica) was analyzed by net shifts of resonance wavelength for specific interactions of GST–GTPase binding domain of p21-activated kinase-1 and anti-GST on a mixed thiol surface. Sensitivity was modulated by the refractive index of the sensing prism of the spectral SPR biosensors with the same incidence angle. The sensitivity of a spectral SPR biosensor with a fused silica prism was 1.6 times higher than that with a BK-7 prism at the same incidence angle of 46.2°. This result was interpreted by increment of the penetration depth correlated with evanescent field intensity at the metal/dielectric interface. Therefore, it is suggested that sensitivity enhancement is readily achieved by reducing the refractive index of the sensing prism of spectral SPR biosensors to be operated at long wavelength ranges for the analysis of protein arrays.

Determination of trap parameters for thermoluminescence glow peaks of red thermoluminescence of quartz from Japan

Red thermoluminescence in quartz has been generally observed in samples from volcanic deposits or archaeological burnt materials. Red thermoluminescence emission quartz has gained attention as a radiation dosimeter for thermoluminescence dating due to the high-dose saturation level and long-term stability of the thermoluminescence signal. The technique for this application can be improved with an understanding of various trap parameters associated with thermoluminescence glow peaks. The repeated initial rise and computerized glow curve deconvolution methods are used to determine the number of thermoluminescence glow peaks and trap parameters for red thermoluminescence from two types of quartz (Tazawa and Yuda samples) from Japan. For both quartz samples, the glow curves were best described as a superposition of seven glow peaks with activation energies of 0.76–1.95 eV and 0.89–1.91 eV for the Tazawa and Yuda samples, respectively. These results provide useful information for the investigation of the intrinsic characteristics of quartz crystals in the research fields relevant to dating and dosimetry.

Property of a CZT Semiconductor Detector for Radionuclide Identification

Compound semiconductors of high Z value material have been studied intensively for X-ray and γ -ray spectroscopy at room temperature. CdZnTe has wide band gap energy as 1.6 eV and can provide high quantum efficiency with reasonably good energy resolution at room temperature. This study is aimed at determining radionuclide analysis ability by measuring energy resolution of CZT detector which will be applied at nuclear material identification purpose. For experiment we used a CZT detector (5 × 5 × 5 mm3) which is manufactured by eV Products. We have performed our measurement at varied temperatures similar to the outdoor environment for the investigation about temperature dependence of energy resolution and peak centroid fluctuation of CZT detector by using gas cooling and Peltier cooling methods. In order to test radionuclide identification we used various radionuclide samples; plutonium, europium and other standard sources. Pulse height spectra were obtained by standard electronics which consists of a preamplifier, a shaping amplifier, and a multi-channel analyzer.

Inhibitory coherence in a heterogeneous population of subthreshold and suprathreshold type-I neurons

We study inhibitory coherence (i.e. collective coherence by synaptic inhibition) in a population of globally coupled type-I neurons, which can fire at arbitrarily low frequency. No inhibitory coherence is observed in a homogeneous population composed of only subthreshold neurons, which exhibit noise-induced firings. In addition to subthreshold neurons, there exist spontaneously firing suprathreshold neurons in a noisy environment of a real brain. To take into consideration the effect of suprathreshold neurons on inhibitory coherence, we consider a heterogeneous population of subthreshold and suprathreshold neurons and investigate the inhibitory coherence by increasing the fraction of suprathreshold neurons Psupra. As Psupra passes a threshold P*supra, suprathreshold neurons begin to synchronize and play the role of coherent inhibitors for the emergence of inhibitory coherence. Thus, regularly oscillating population-averaged global potential appears for Psupra > P*supra. For this coherent case, suprathreshold neurons exhibit sparse spike synchronization (i.e. individual potentials of suprathreshold neurons consist of coherent sparse spikings and coherent subthreshold small-amplitude hoppings). By virtue of their coherent inhibition, sparsely synchronized suprathreshold neurons suppress the noisy activity of subthreshold neurons. Thus, subthreshold neurons exhibit hopping synchronization (i.e. only coherent subthreshold hopping oscillations without spikings appear in the individual potentials of subthreshold neurons). We also characterize the inhibitory coherence in terms of the ?statistical-mechanical? spike-based and correlation-based measures, which quantify the average contributions of the microscopic individual spikes and individual potentials to the macroscopic global potential. Finally, the effect of sparse randomness of synaptic connectivity on the inhibitory coherence is briefly discussed.

Development of an immunosensor with angular interrogation-based SPR spectroscopy

We present a self-constructed immunosensor with angular interrogation-based-surface plasmon resonance (SPR) spectroscopy in order to analyse antigen–antibody interactions. The SPR intensity, resonance angle and full width at half maximum (FWHM) were significantly affected by the thickness of an Au film. The optimal thickness for the Au film thickness as an active metal for surface plasmons was determined to be approximately 45 nm, as respects the SPR intensity and the FWHM of SPR spectrum. The detection limit of the sensor based on the minimal refractive index variation was found to be 1.4 × 10−4. The interaction of C-reactive protein (CRP) with anti-CRP on a 45 nm Au film was successfully analysed with the self-constructed SPR sensor. We suggest that the SPR sensor can be used as a useful tool for the analysis of immunoreactions.

Optical dating of the hydroponic farm at Korea

For age determination, the single aliquot regenerative-dose (SAR) method was applied to quartz from archaeological materials, using luminescence stimulated by blue light. The quartz samples were extracted from sediment from the hydroponic farm related to rice cultivation in an area of archaeological interest in Buyeo, south of Seoul. The optically stimulated luminescence (OSL) dates obtained offered good agreement with the ages derived by typological assessment and 14C ages. These ages should contribute significantly to interpretation of the history of rice cultivation in Korea.