• Nuclear Engineering and Technology
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• v.55 no.3
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• pp.1061-1070
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• 2023

Over the last few years, lead-free inorganic metal perovskites have gained impressive ground in empowering satellites in space exploration owing to their material stability and performance evolution under extreme space environments. The present work has examined the versatility of eight such perovskites as space radiation shielding materials by computing their photon, charged particles and neutron interaction parameters. Photon interaction parameters were calculated for a wide energy range using PAGEX software. The ranges of heavy charged particles (H, He, C, N, O, Ne, Mg, Si and Fe ions) in these perovskites were estimated using SRIM software in the energy range 1 keV-10 GeV, and that of electrons was computed using ESTAR NIST software in the energy range 0.01 MeV-1 GeV. Further, the macroscopic fast neutron removal cross-sections were also calculated to estimate the neutron shielding efficiencies. The examined shielding parameters of the perovskites varied depending on the radiation type and energy. Among the selected perovskites, Cs₂TiI₆ and Ba₂AgIO₆ displayed superior photon attenuation properties. A 3.5 cm thick Ba₂AgIO₆-based shield could reduce the incident radiation intensity to half its initial value, a thickness even lesser than that of Pb-glass. Besides, CsSnBr₃ and La_0.8Ca_0.2Ni_0.5Ti_0.5O₃ displayed the highest and lowest range values, respectively, for all heavy charged particles. Ba₂AgIO₆ showed electron stopping power (on par with Kovar) better than that of other examined materials. Interestingly, La_0.8Ca_0.2Ni_0.5Ti_0.5O₃ demonstrated neutron removal cross-section values greater than that of standard neutron shielding materials - aluminium and polyethylene. On the whole, the present study not only demonstrates the employment prospects of eco-friendly perovskites for shielding space radiations but also suggests future prospects for research in this direction.

• Asian Pacific Journal of Cancer Prevention
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• v.13 no.11
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• pp.5627-5632
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• 2012

Background: The aim of the study was to determine the prevalence of shisha smoking and associated factors among medical students in Malaysia. Materials and Methods: A cross-sectional study was conducted at the Management and Science University from December 2011 until March 2012. The questionnaire consisted of five sections including socio-demographic, social environment, knowledge about shisha, psychosocial factors, and personal shisha smoking behavior. Obtained data were analyzed using Statistical Package for the Social Sciences (SPSS 13). T-test was used to determine the relationships between shisha smoking and socio-demographic characteristic. Results: A total number of 300 medical students participated in this study. Mean age was $22.5{\pm}2.5$ years. The majority were female, Malay, single, from urban areas (67%, 54%, 97%, 73%; respectively). The prevalence of shisha smoking among medical students was found to be 20%. The study revealed that many students believed that shisha does not contains nicotine, carbon monoxide, does not lead to lung cancer, dental problems and does not lead to cardiovascular diseases (25%, 20.7%, 22.3%, 29%, 26.7%; respectively). Age and sex were found to be significantly associated with smoking shisha status among medical students (p=0.029, p<0.001; respectively). Furthermore, having parents, siblings and friends smokers of shisha were found to be significantly associated with shisha smoking status (p<0.001, p<0.001, p<0.001; respectively). Furthermore, family problems, problems with friends, financial problems and university life were found to significantly associated with shisha smoking status among medical students (p<0.001, p=0.002, p<0.001, p=0.002; respectively). Conclusions: There is a high prevalence of shisha smoking and a poor knowledge about its impact on health among medical students. More attention is needed to focus on medical education in this regard. The policies that are currently employed in order to reduce the cigarettes smoking should be applied to shisha smoking and shisha products.

• Journal of Conservation Science
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• v.35 no.5
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• pp.403-415
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• 2019

According to oral tradition, the King Sejo's palanquin is indeed the palanquin of King Sejo, the 7^th monarch of the Joseon dynasty who reigned from 1455 to 1468, which was left behind after visiting the Magoksa temple. The palanquin is painted in five colors, mainly black, white, yellow, red and green. The chromaticity measurement of the yellow pigment showed that orpiment and gold are a noticeable distinction between the lightness and b^⁎ values. In the case of the red pigment, a^⁎ values of areas painted with cinnabar tend to measure at high values. As a result of the optical microscopy, scanning electron microscopy and energy dispersive spectroscopy analyses, it was determined that Chinese ink was used for the black pigment, lead white and white clay were used for the white, and orpiment and gold for the yellow. The red pigment was found to be the result of minium, cinnabar and red ocher, atacamite was used as green pigment. Though the analysis results of the cross sections on very small exfoliation fragments of pigments, it was confirmed that white clay and lead white were used for the preparation layer. In addition, several coloration techniques were considered based on these analyses.

• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.2
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• pp.17-26
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• 2024

In recent times, accidents involving structural elements, formwork, and shore have been persistently occurring during concrete pouring, especially in multi-story reinforced concrete (RC) structures. In previous studies, research on construction load analysis was mainly conducted for cases where the thickness of all slabs is constant. However, when the thickness of some slabs is different, the variation in the stiffness of slab cross-sections can lead to different distributions of construction loads, necessitating further investigation. In this study, the slab thickness was set as a variable, and the analysis of the distribution of construction loads was conducted, taking into account the influence of changes in slab thickness on the concrete stiffness and structure. It was confirmed that not only the concrete material stiffness but also the slab cross-section stiffness should be considered in the estimation of construction loads when the slab thickness changes. As the slab thickness increases, the maximum construction load and maximum damage parameter on the layer with increased thickness significantly increase, and it was observed that a thicker slab results in a higher proportion of construction load.

• Magazine of the Korea Concrete Institute
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• v.11 no.2
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• pp.197-208
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• 1999

The use of high-strength concrete which permits smaller cross sections, reduced dead loads, and longer spans has been getting more popular in tall buildings. However, there has been little research on behavior of high-strength concrete columns laterally reinforced with square ties and subjected to compressive loading. With the addition of transverse reinforcement which lead to triaxial compressive state, ductility behavior of high-strength column member shall be increased. In this study, rational quality and quantity evaluations were made to investigate the ultimate strength and strain ductility by confinement effect of tie reinforced high-strength concrete columns subject to uniaxial loads. Concrete failure theory at the triaxial compressive state and statistical results based on conventional experimental data were applied for this propose. Up to 185 columns, tested under monotonically increasing concentric loading, were evaluated in terms of strength and strain ductility. Analytical results show that confinement stress, maximum compressive strength, and increase of strain equations were developed with the consideration of concrete strength, yield strength, spacing, volumetric ratio, and configurations of tie reinforcement.

• Magazine of the Korean Society of Agricultural Engineers
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• v.44 no.3
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• pp.92-100
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• 2002

The advent or high-strength steel has enabled the arch structures to be relatively light, durable and long-spanned by reducing the cross sectional area. On the other hand, the possibility of collapse may be increased due to the slender members which may cause the stability problems. The limit analysis to estimate the ultimate load is based on the concept of collapse mechanism that forms the plastic zone through the full transverse sections. So, it is not appropriate to apply it directly to the instability analysis of arch structures that are composed with compressive members. The objective of this study is to evaluate the ultimate load carrying capacity of the parabolic arch by using the elasto-plastic finite element model. As the rise to span ratio (h/L) varies from 0.0 to 0.5 with the increment of 0.05, the ultimate load has been calculated fur arch structures subjected to uniformly distributed vertical loads. Also, the disco-elasto-plastic analysis has been carried out to find the duration time until the behavior of arch begins to show the stable state when the estimated ultimate load is applied. It may be noted that the maximum ultimate lead of the parabolic arch occurs at h/L=0.2, and the appropriate ratio can be recommended between 0.2 and 0.3. Moreover, it is shown that the circular arch may be more suitable when the h/L ratio is less than 0.2, however, the parabolic arch can be suggested when the h/L ratio is greater than 0.3. The ultimate load carrying capacity of parabolic arch can be estimated by the well-known formula of kEI/L$^3$where the values of k have been reported in this study. In addition, there is no general tendency to obtain the duration time of arch structures subjected to the ultimate load in order to reach the steady state. Merely, it is observed that the duration time is the shortest when the h/L ratio is 0.1, and the longest when the h/L ratio is 0.2.

• Journal of the Microelectronics and Packaging Society
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• v.22 no.1
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• pp.43-49
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• 2015

By the trends of electronic package to be smaller, thinner and more integrative, organic printed circuit board is required to be finer Cu trace pitch. This paper reports on a study of failure mechanism for PCB with fine Cu trace pitch using biased HAST. In weibull analysis of the biased HAST lifetime, it is found that the acceleration factor (AF) of between $135^{\circ}C/90%RH/3.3V$ and $130^{\circ}C/85%RH/3.3V$ is 2.079. A focused ion beam (FIB) was used to polish the cross sections to reveal details of the microstructure of the failure mode. It is found that $Cu_xO/Cu(OH)_2$ colloids and Cu dendrites were formed at anode (+) and at cathode (-), respectively. Thus, this gives the evidence that Cu dendrites formed at cathode by $Cu^{2+}$ ion migration lead to a short failure between a pair of Cu nets.

• Wind and Structures
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• v.23 no.2
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• pp.127-142
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• 2016

Aerodynamic effects, such as drag force and flow-induced vibration (FIV), on civil engineering structures can be minimized by optimally modifying the structure shape. This work investigates the turbulent wake of a square prism with its faces modified into a sinusoidal wave along the spanwise direction using three-dimensional large eddy simulation (LES) and particle image velocimetry (PIV) techniques at Reynolds number $Re_{Dm}$ = 16,500-22,000, based on the nominal width ($D_m$) of the prism and free-stream velocity ($U_{\infty}$). Two arrangements are considered: (i) the top and bottom faces of the prism are shaped into the sinusoidal waves (termed as WSP-A), and (ii) the front and rear faces are modified into the sinusoidal waves (WSP-B). The sinusoidal waves have a wavelength of $6D_m$ and an amplitude of $0.15D_m$. It has been found that the wavy faces lead to more three-dimensional free shear layers in the near wake than the flat faces (smooth square prism). As a result, the roll-up of shear layers is postponed. Furthermore, the near-wake vortical structures exhibit dominant periodic variations along the spanwise direction; the minimum (i.e., saddle) and maximum (i.e., node) cross-sections of the modified prisms have narrow and wide wakes, respectively. The wake recirculation bubble of the modified prism is wider and longer, compared with its smooth counterpart, thus resulting in a significant drag reduction and fluctuating lift suppression (up to 8.7% and 78.2%, respectively, for the case of WSP-A). Multiple dominant frequencies of vortex shedding, which are distinct from that of the smooth prism, are detected in the near wake of the wavy prisms. The present study may shed light on the understanding of the underlying physical mechanisms of FIV control, in terms of passive modification of the bluff-body shape.

• Journal of the Korean Wood Science and Technology
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• v.33 no.6 s.134
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• pp.8-16
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• 2005

Fire-killed trees of Korean red pine are valuable resources for industrial uses. It is common only believed that fire-killed trees are too weak and brittle to use in construction purposes. The misunderstandings of fire-killed trees lead these valuable resources abandonment. The purposes of this research are focused on scrutinization of material properties of fire-killed trees to facilitate industrial uses of these resources. The sample logs were collected from the forest fire site of the eastern coast area in which the most catastrophic wild fire had taken place in 2000. Fire-killed Korean red pines were classified into 3 levels by the degree of fire damage so called light, medium and heavy, then their physical, mechanical and chemical properties were compared with sound trees. No significant difference in physical appearances were found in the cross sections by degree of damage compared to sound tree but bark char. Investigation on mechanical and chemical properties indicates that forest fire did not impact significantly in lowering the strength of damaged trees. It was concluded that there was any limitation of forest fire-killed trees of Korean red pine in industrial utilization.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.585-588
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• 2003

Bi-2223 superconducting wires were fabricated by stacking, drawing process with different precursor powders and different heat-treatment histories. The precursor powders were 2 kinds of Pb content. And a part of the tapes were experienced pre-annealing process which caused tetragonal structure of Bi-2212 phase to orthorhombic structure of it was during drawing process. We confirmed the transformation of Bi-2212 phase from tetragonal structure to orthorhombic structure and reduction of second phases. AC magnetization analysis were performed in order to investigate the fraction of Bi-2223 phase in Bi-2223/Ag HTS tape. The cross sections of 55 filaments and 61 filaments were investigated after rolled in order to understand deformation mechanism of superconducting cores. We could achieve best Ic of 70 A class at the Bi-2223/Ag tape using low Pb content of precursor powder and experienced pre-annealing process. AC magnetization analysis was useful to investigate the fraction of Bi-2223 phase in the Bi-2223/Ag tape.