• Korean Journal of Materials Research
• /
• v.33 no.7
• /
• pp.295-301
• /
• 2023

Thermoelectric (TE) energy harvesting, which converts available thermal resources into electrical energy, is attracting significant attention, as it facilitates wireless and self-powered electronics. Recently, as demand for portable/wearable electronic devices and sensors increases, organic-inorganic TE films with polymeric matrix are being studied to realize flexible thermoelectric energy harvesters (f-TEHs). Here, we developed flexible organic-inorganic TE films with p-type Bi_0.5Sb_1.5Te₃ powder and polymeric matrices such as poly(3,4-eethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and poly (vinylidene fluoride) (PVDF). The fabricated TE films with a PEDOT:PSS matrix and 1 wt% of multi-walled carbon nanotube (MWCNT) exhibited a power factor value of 3.96 µW·m^-1·K^-2 which is about 2.8 times higher than that of PVDF-based TE film. We also fabricated f-TEHs using both types of TE films and investigated the TE output performance. The f-TEH made of PEDOT:PSS-based TE films harvested the maximum load voltage of 3.4 mV, with a load current of 17.4 µA, and output power of 15.7 nW at a temperature difference of 25 K, whereas the f-TEH with PVDF-based TE films generated values of 0.6 mV, 3.3 µA, and 0.54 nW. This study will broaden the fields of the research on methods to improve TE efficiency and the development of flexible organic-inorganic TE films and f-TEH.

• Proceedings of the International Microelectronics And Packaging Society Conference
• /
• 2001.11a
• /
• pp.75-87
• /
• 2001

Three different kinds of substrate used in this study : bare Cu substrate, Ni-P/Cu substrate with a Ni-P layer thickness of $5\mu\textrm{m},$ and Au/Ni-P/Cu substrate with the Ni-P and Au layers of $0.15\mu\textrm{m}$ and $5\mu\textrm{m}$ thickness respectively. The wettability of various Sn-base solders was affected by the substrate metal finish used, i.e., nickel, gold and copper. On the Au/Ni-F/Cu substrate, Sn-base solders wet better than any of the other substrate metal finishes tested. The interfacial reaction between various substrate and Sn-base solder was investigated at $70^{\circ}C,$ $100^{\circ}C,$ $120^{\circ}C,$ $150^{\circ}C,$ $170^{\circ}C$ and $200^{\circ}C$ for reaction times ranging from 0 day to 60 day. Intermetallic phases was formed along a Sn-base solder/ various substrate interface during solid-state aging. The apparent activation energy for growth of Sn-Ag/Cu, Sn-Ag-Bi/Cu, and Sn-Bi/Cu couples were 65.4, 88.6, and 127.9 Kj/mol, respectively. After isothermal aging, the fracture surface shoved various characteristics depending on aging temperature and time, and the types of BGA pad.

• Journal of the Korean Ceramic Society
• /
• v.40 no.1
• /
• pp.52-61
• /
• 2003

$SrBi_2Ta_2O_9(SBT)$and$ZrO_2$thin films for MFIS structure(Metal-Ferroelectric-Insulator-Semiconductor) were deposited by RF magnetron sputtering method. In order to investigate the effect of heat treatment of insulator layers and MFIS structure, the insulator layers were heat treated from $550^{circ}C;to; 850^{\circ}C$in conventional furnace or RTA furnace under$O_2$and Ar ambient, respectively. After then, C-V characteristics and leakage current were measured. The capacitor with 20 nm thick $ZrO_2$layer treated at RTA$750^{circ}C;in;O_2$ atmosphere had the largest memory window. The C-V and leakage current characteristics of the$Pt/SBT(260nm)/ZrO_2(20nm)/Si$structure were better than those of$Pt/SBT(260nm)/Si$ structure. These results showed that$ZrO_2$films took a role of buffer layer effectively.

• Nuclear Engineering and Technology
• /
• v.51 no.3
• /
• pp.860-866
• /
• 2019

The lead element or its salts are good radiation shielding materials. However, their toxic effects are high. Due to less toxicity of bismuth salts, the radiation shielding properties of the bismuth salts have been investigated and compared to that of lead salts to establish them as a better alternative to radiation shielding material to the lead element or its salts. The transmission geometry was utilized to measure the mass attenuation coefficient (${\mu}/{\rho}$) of different salts containing lead and bismuth using a high-resolution HPGe detector and different energies (between 81 and 1333 keV) emitted from point sources of $^{133}Ba$, $^{57}Co$, $^{22}Na$, $^{54}Mn$, $^{137}Cs$, and $^{60}Co$. The experimental ${\mu}/{\rho}$ results are compared with the theoretical values obtained through WinXCOM program. The theoretical calculations are in good agreement with their experimental ones. The radiation protection efficiencies, mean free paths, effective atomic numbers and electron densities for the present compounds were determined. The bismuth fluoride ($BiF_3$) is found to have maximum radiation protection efficiency among the selected salts. The results showed that present salts are more effective for reducing the intensity of gamma photons at low energy region.

• Geomechanics and Engineering
• /
• v.37 no.4
• /
• pp.395-418
• /
• 2024

The epicentral region of earthquakes is typically where liquefaction-related damage takes place. To determine the maximum distance, such as maximum epicentral distance (R_e), maximum fault distance (R_f), or maximum hypocentral distance (R_h), at which an earthquake can inflict damage, given its magnitude, this study, using a recently updated global liquefaction database, multiple ML models are built to predict the limiting distances (R_e, R_f, or R_h) required for an earthquake of a given magnitude to cause damage. Four machine learning models LSTM (Long Short-Term Memory), BiLSTM (Bidirectional Long Short-Term Memory), CNN (Convolutional Neural Network), and XGB (Extreme Gradient Boosting) are developed using the Python programming language. All four proposed ML models performed better than empirical models for limiting distance assessment. Among these models, the XGB model outperformed all the models. In order to determine how well the suggested models can predict limiting distances, a number of statistical parameters have been studied. To compare the accuracy of the proposed models, rank analysis, error matrix, and Taylor diagram have been developed. The ML models proposed in this paper are more robust than other current models and may be used to assess the minimal energy of a liquefaction disaster caused by an earthquake or to estimate the maximum distance of a liquefied site provided an earthquake in rapid disaster mapping.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2010.09a
• /
• pp.349-356
• /
• 2010

In this study, a new design method of pile bent structure considering plastic hinge was proposed on the basis of the beam-column model. Based on the analysis results, it is found that the positioning of plastic hinge on the pile bent structure was influenced by nonlinear behavior of material and p-$\Delta$ effect. Moreover, concrete cracking began to occur at the joint section between the pile and column in case of pile bent structure with different cross-sections. The plastic hinge can be developed on the pile bent structure when large displacement was occurred, and pile bent structures can be maintained well only if it is developed on the column part. Therefore, in this study, the optimized cross-section ratio between column and pile was analyzed to induce the plastic hinge at the joint section between the pile and column. Based on this, the optimized diameter ratio of pile and column can be obtained below the inflection point of the bi-linear curve depending on the relations between column-pile diameter ratio($D_c/D_p$) and normalized lateral cracking load ratio($F/F_{Dc=Dp}$). And through this study, it is founded that in-depth limit($L_{As}$=0.4%) normalized by the pile length($L_P$) are proportionally decreased as the pile length($L_P/D_P$) increases up to $L_P/D_P$=17.5, and beyond that in-depth limit converges to a constant value. Finally, it is found that the proposed limit depth by taking into account the minimum concrete-steel ratio would be more economical design of the pile bent structure.

• Earthquakes and Structures
• /
• v.17 no.5
• /
• pp.477-487
• /
• 2019

Understanding the behavior of skew bridges under the action of earthquakes is quite challenging due to the combined transverse and longitudinal responses even under unidirectional hit. The main goal of this research is to assess the response of skew bridges when subjected to longitudinal and transversal earthquake loading. The effect of skew on the response considering two- and three- span bridges with skew angles varying from 0 to 60 degrees is illustrated. Various pier fixities (and hence stiffness) and cross-section shapes, as well as different abutment's bearing articulations, are also studied. Finite-element models are established for modal and seismic analyses. Around 900 models are analyzed under the action of the code design response spectrum. $Vis-{\grave{a}}-vis$ modal properties, the higher the skew angle, the less the fundamental period. In addition, it is found that bridges with skew angles less than 30 degrees can be treated as straight bridges for the purpose of calculating modal mass participation factors. Other monitored results are bearings' reactions at abutments, shear and torsion demand in piers, as well as deck longitudinal displacement. Unlike straight bridges, it has been typically noted that skew bridges experience non-negligible torsion and bi-directional pier base shears. In a complementary effort to assess the accuracy of the conducted response spectrum analysis, a series of time-history analyses are applied under seven actual earthquake records scaled to match the code design response spectrum and critical comparisons are performed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.14 no.6
• /
• pp.648-654
• /
• 2003

Diamond MIS(Metal-Insulator-Semiconductor) diodes and MISFETs(Metal-Insulator-Semiconductor Field Effect Transistors) were fabricated by employing various fluorides as gate insulator, and their electrical properties were closely investigated by means of C-V measurements. The A1/BaF$_2$/diamond MIS structure exhibited outstanding electrical properties. The MIS diode showed a very low surface state density of ∼10$\^$10//$\textrm{cm}^2$ eV near the valence band edge, and the observed effective mobility(${\mu}$$\_$eff/) of the MISFET was 400 $\textrm{cm}^2$/Vs, which is the highest value obtained until now in the diamond FET. From the chemiphysical point of view, the above result might be explained by the reduction of adsorbed-oxygen on the diamond surface via strong chemical reaction by the constituent Ba atom in the insulator during the film deposition(Oxygen-Gettering Effect).

• The Journal of Korean Medicine Ophthalmology and Otolaryngology and Dermatology
• /
• v.17 no.1
• /
• pp.131-142
• /
• 2004

The purpose of this research was to investigate cytotoxity of Sunbanhwalmyungeum extract. Cytotoxity was determined by MTT assay method. After tumor cell lines(G361, BI6F10, MDA, A549) transplantation, the extracts of SunBangHwalMyungEum and its composition oriental medicines were administered, cytotoxity was measured by absorbance. The results were obtained as follows. 1. Sunbanhwalmyungeum extract and its composition oriental medicines extracts showed the concentration was higher, the more cytotoxity increased. 2. Both water and ethanol extracts of Sunbanhwalmyungeum showed excellent cytotoxity against G361, B16F10, MDA, A549 and high cytotoxity over 80$\%$ against G361, B16F10, MDA except A549 at the concentration of 1000ppm. 3. In water extract, Rhei Radix et Rhizoma, Gleditsiae Spina, Trichosanthis Radix, Glycyrrhizae Radix, Ledebouriellae Radix showed excellent cytotoxity. In ethanol extract, Gleditsiae Spina, Citri Pericarpium, Trichosanthis Radix, Paeoniae Radix Rubra, Myrrha showed excellent cytotoxity. 4. Rhei Radix et Rhizoma, Gleditsiae Spina, Trichosanthis Radix, Paeoniae Radix Rubra showed high cytotoxity in both water and ethanol extrats. 5. In water extract, Glycyrrhizae Radix, Ledebouriellae Radix, Myrrha showed high cytotoxity against A361, Lonicerae Flos, Olibanum, Fritillariae cirrhosae Bulbus, Paeoniae Radix Rubra, Manitis Squama against B16F10, Paeoniae Radix Rubra, Manitis Squama against MDA, Rhei Radix et Rhizoma, Angelicae gigantis Radix against A549. 6. In ethanol extract, Lonicerae Flos, Trichosanthis Radix showed high cytotoxity against G361, Rhei Radix et Rhizoma, Angelicae gigantis Radix, Gleditsiae Spina, Olibanum, Angelicae dahuricae Radix, Fritillariae cirrhosae Bulbus, Paeoniae Radix Rubra, Glycyrrhizae Radix, Ledebouriellae Radix, Myrrha against B16F10, Rhei Radix et Rhizoma, Manitis Squama against MDA, Citri Pericarpium, Manitis Squama against A549.

• MALSORI
• /
• no.37
• /
• pp.73-85
• /
• 1999

The prosodic characteristics of Korean particles in read speech were examined in this paper based on K-ToBI labeling system in order to see whether they are prosodically weak form like functions words in English. Acoustic measurements and statistical analysis were done focusing on the distribution of particles over a variety of prosodic positions, prosodic positional effects on the phonetic realization of particles, and acoustic strength of particles compared to those of their surrounding syllables. The panicles were distributed rather equally over all 4 prosodic positions with the highest frequency at IP-medial/AP-final position and the lowest at IP-medial/AP-medial position except that topic marker 'Un/nUn' showed preference for IP-final/AP-final position. There was a significant prosodic positional effect on the duration and F0 of the particles. Duration was the longest at IP-final/AP-final position and interestingly, at IP-medial/AP-medial position while F0 was the highest at IP-final/AP-medial Position as expected. The comparison of the acoustic properties of the particles with those of neighbor syllables showed that duration was generally significantly longer and energy also showed larger values, if not significant, in particles suggesting that the particles in Korean are not prosodically weaker like function words in English.