New-type of Multi-purpose Standard Radon Chamber in South Korea

Radon is an inert and a radioactive gas which is colorless, tasteless and odorless. As the radon decay proceeds, and if DNA damage continues beyond repair capacity of cells in the human body, it can cause severe health problems such as lung cancer in the long-term. There is a tendency that those countries where legal restriction on radon is strict, various studies related to radon are under way. In South Korea, radon has been regulated under recommendation level. Even though there are about 3 standard radon chambers in Korea, they have not been in an active use because of lack of demand. Also, most of them are specialized in calibration of radon detectors only. Recently, Korean government started giving some attention to radon issue and supporting radon research fields. Thus, this study was carried out to develop a new type of radon chamber for multi-purpose such as 1) radon emission rate from natural and artificial radon sources; 2) calibration of radon detectors; 3) evaluation of radon mitigation efficiency. Keywords: Radon, Radon Chamber, Indoor Air Quality, Chamber Desig

Correlation between the dynamics of polar nanoregions and temperature evolution of central peaks in Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 ferroelectric relaxors

Acoustic properties of Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 have been investigated in a wide temperature range. The sound velocity of acoustic phonons showed a deviation from its high-temperature linear behavior at the Burns temperature TB~730 K. Upon cooling, acoustic properties exhibited significant changes at about 550 K in polarization state and width of the central peak in addition to changes in frequency and damping of acoustic phonons. This finding suggests that, besides TB, another intermediate characteristic temperature exists in the evolution of relaxor dynamics, which might be related to the formation of long-lived polar nanoregions and associated local strain fields

Central peaks, acoustic modes, and the dynamics of polar nanoregions in Pb[(Zn1/3Nb2/3)xTi1−x]O3 single crystals studied by Brillouin spectroscopy

Temperature dependence of acoustic behaviors and quasielastic central peaks (CPs) of Pb[(Zn1/3Nb2/3)xTi1−x]O3 (PZN-xPT) single crystals with x=4.5% and 9% have been investigated in a temperature range of 300–900 K by using the Brillouin light scattering. The temperature dependence of the C11 elastic constant of both crystals showed a deviation from normal lattice anharmonicity at the Burns temperature (TB) of about 730 K upon cooling, indicating the onset of the electrostrictive coupling between the polar nanoregions (PNRs) and the longitudinal acoustic (LA) waves. Upon further cooling, depolarized CP began to appear at a certain temperature (Td) located in 500–550 K, which was accompanied by substantial softening of the C44 elastic constant below this temperature suggesting anisotropic electrostrictive coupling between PNRs and the two acoustic waves. In addition, the onset of significant increase in the acoustic damping of both acoustic waves at Td could be seen from the temperature dependence of the linewidth of Brillouin doublets. These results suggested that electrostrictive coupling of the strain to the square of the local polarization of PNRs and the resultant order-parameter fluctuations are enhanced not at TB but at a much lower temperature of Td, which may be ascribed to a local structural transformation occurring in PNRs at Td. This suggestion is consistent with recent studies on PZN-xPT single crystals reporting the appearance of strong acoustic emission signals [M. Roth et al., Phys. Rev. Lett. 98, 265701 (2007)] and substantial changes in the Raman spectrum [O. Svitelskiy, Phys. Rev. B 72, 172106 (2005)] at almost the same temperature. From the comparison of the present results to those of two typical relaxors, Pb(Mg1/3Nb2/3)O3 and Pb(Mg1/3Ta2/3)O3, it was suggested that the existence of an intermediate characteristic temperature Td below TB may be considered as a more common characteristic in the temperature evolution of PNRs of relaxor ferroelectrics

Enhancement on Radon Adsorption Property of GAC using Nano-size Carbon Colloids

Granular activated carbon (GAC) is well-known as an efficient adsorbent against a number of gaseous pollutants. Radon is one of those pollutants, and radon has been classified as the second leading cause of lung cancer in USA. This study was to enhance the radon removal efficiency with applying nano-technology. Nano-size carbon colloids (NCC) was produced through electrolysis which is simple and cheap. NCC was used for impregnation with activated carbon. Surface areas of both NCC-treated and non-treated activated carbon did not show a significant difference. However, the results of radon removal efficiency show that impregnated carbon with NCC could capture about 1.3 ~ 2 times of more radon gas compared to non-treated activated carbon. It is assumed that nano-size carbon colloids might have filled up meso-pores, and meso-pores turned into micro-pores eventually. Because meso-pores initially accounted for large portion of whole pores, more radon could be captured to NCC-impregnated activated carbon. Keywords: Radon, Nano-Size Carbon Collid, Activated Carbo

Micro-Brillouin scattering study of ferroelectric relaxor Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 single crystals under the electric field along the [001] direction

Electric-field effects on structural phase transitions have been studied in ferroelectric relaxor Pb[(Zn1/3Nb2/3)1–xTix]O3 single crystals with x=0.09 by the high-resolution micro-Brillouin scattering. Sharp phase transitions from cubic-to-tetragonal and then from tetragonal-to-rhombohedral phases have been observed under zero-field-cooling (ZFC) condition. For two phase-transition temperatures a noticeable thermal hysteresis was clearly observed, consistent with dielectric measurements. The temperature range of a tetragonal phase has been markedly extended under the electric field of E=6.7 kV/cm along the [001] direction. A large difference of the LA-mode frequency and damping between the ZFC and field-cooling processes indicated that the multidomain structure induces the increase of the acoustic damping due to the elastic scattering. In addition, it was found that the elastic stiffness coefficient c33 in the tetragonal coordinates shows a slight decrease. The first-order character of the cubic-to-tetragonal phase transition has been gradually changed into a second-order one under the increase of the electric field along the [001] direction, reflecting a general trend of the first-order ferroelectric phase transition. Although a clear specification of the low-temperature symmetry could not be accomplished from Brillouin scattering itself, these results give new insights into an electric-field-temperature phase diagram containing phase boundaries among cubic, tetragonal, and low-temperature phases

Ruin Theory for User Association and Energy Optimization in Multi-access Edge Computing

In this letter, a novel framework is proposed for analyzing data offloading in a multi-access edge computing system. Specifically, a two-phase algorithm, is proposed, including two key phases: \emph{1) user association phase} and \emph{2) task offloading phase}. In the first phase, a ruin theory-based approach is developed to obtain the users association considering the users' transmission reliability. Meanwhile, in the second phase, an optimization-based algorithm is used to optimize the data offloading process. In particular, ruin theory is used to manage the user association phase, and a ruin probability-based preference profile is considered to control the priority of proposing users. Here, ruin probability is derived by the surplus buffer space of each edge node at each time slot. Giving the association results, an optimization problem is formulated to optimize the amount of offloaded data aiming at minimizing the energy consumption of users. Simulation results show that the developed solutions guarantee system reliability under a tolerable value of surplus buffer size and minimize the total energy consumption of all users.Comment: This paper has been submitted to IEEE Wireless Communications Letter

Microheterogeneity and field-cooling effects on Pb[(Zn1/3Nb2/3)0.955Ti0.045]O3 single crystals probed by micro-Brillouin scattering

Microheterogeneity and field-cooling effects were investigated on Pb[(Zn1/3Nb2/3)0.955Ti0.045]O3 (PZN-4.5%PT) single crystals by using a high-resolution micro-Brillouin scattering. The temperature dependence of Brillouin shift showed a typical relaxor behavior with marked softening on approaching the diffuse phase transition, but also revealed a clear microareal variation in a rhombohedral phase below 150 °C which means a heterogeneity exists over a length scale of at least a few microns in PZN-4.5%PT. These two features seem to correlate with the coexistence of both micronsized domains and irregular nanosized domains, recently confirmed by high-resolution domain studies. This complex domain structure may make each microdomain represent different relaxor behaviors due to its own polar nanoregions and their dynamics. When the crystal was cooled under the electric field along the [001] direction from a cubic phase, two field-induced changes were observed in the Brillouin shift at around 143 °C and 106 °C. This observation is in good agreement with the dielectric measurements, meaning a medium-range ordered phase exists between short-range ordered and long-range order phases

Hysteresis in acoustic properties of ferroelectric relaxor Pb[(Zn1/3Nb2/3)0.955Ti0.045]O3 single crystals studied by Brillouin and dielectric spectroscopies

Acoustic and dielectric properties of Pb[(Zn1/3Nb2/3)1–xTix]O3 (PZN-xPT) single crystals with x=0.045 have been studied by the high-resolution micro-Brillouin scattering and dielectric spectroscopy in a wide temperature range. The softening of the Brillouin shift and the increase of dielectric relaxation time upon cooling indicated the formation of polar nanoregions (PNRs) and the slowing down of their dynamics. In contrast to the acoustic properties of typical model relaxors such as lead magnesioniobate, the change in the Brillouin shift near its minimum became sharper on heating compared to the change on cooling, pointing to the clear existence of hysteresis in the dynamics of the diffuse phase transition in PZN-4.5%PT. Since the number of PNRs will increase upon cooling, it may be expected that the kinetics of the phase transition would become slower, the lower the transition temperature resulting in the more sluggish, broad feature of the Brillouin shift observed during cooling. This result may indicate that the number and size of polar nanoregions, which are dependent on temperature, play an important role in the development of the mesoscopic ferroelectric order in PZN-4.5%PT