• Journal of the Korean Electrochemical Society
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• v.16 no.3
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• pp.162-168
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• 2013

$Li_2MnO_3-LiMO_2$(M=Ni, Co, Mn) nano-composite is a promising cathode material for xEV application due to its high theoretic capacity. However high voltage operating system of $Li_2MnO_3-LiMO_2$(M=Ni, Co, Mn) has worked as a hurdle in its application because of the inherent demerits, such as cycle life degradation and gas evolution. In order to enhance cell performance of $Li_2MnO_3-LiMO_2$(M=Ni, Co, Mn)/graphite cell, we examined electrolyte mainly composed of FEC, fluroalkyl ether and $LiPF_6$ (F-based EL). F-based EL showed much better discharging retention ratio than 1.3 M $LiPF_6$ EC/EMC/DMC (3/4/3, v/v/v) (STD). Furthermore gas evolution, especially CO and $CO_2$ during $60^{\circ}C$ storage for 30 days was dramatically reduced owing to thermal stable SEI formation effect of F-based EL.

• Korean Journal of Weed Science
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• v.18 no.2
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• pp.154-160
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• 1998

This study was conducted to develop a foliar applied herbicide mixture covering wide spectrum weeds in dry direct seeded rice. Uniform precision central composite design(UPCCD) was employed to evaluate the effect of herbicide mixture among cyhalofop-butyl(cyhalofop), bispyribenzoxim and pyrazosulfuron-ethyl(pyrazosulfuron) having different weed control spectrum and to determine the best application rates of the three herbicide mixtures. The partial additive effect was observed in the mixture of cyhalofop and bispyribenzoxim with pyrazosulfron against Echinochloa crus-galli Beauv var crus-galli L., attributed to the negative interaction between cyhalofop and bispyribenzoxim system. Additive effect was observed in the mixture of bispyribenzoxim and pyrazosulfuron against Cyperus serotinus R. and Aneilema keisak H. but cyhalofop had no effect on these weeds. The most appropriate rate of the mixture of cyhalofop with bispyribenzoxim and pyrazosulfuron was 100 : 12 : 10g ai/ha exhibiting $ED_{90}$ against three weeds such as E. crus-galli, C. serotinus and A. keisak.

• Restorative Dentistry and Endodontics
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• v.29 no.6
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• pp.489-497
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• 2004

Objective: The purpose of this study was to investigate the viscoelastic properties related to handling characteristics of composite resins, Methods: A custom designed vertical oscillation rheometer (VOR) was used for rheological measurements of composites. The VOR consists of three parts: (1) a measuring unit, (2) a deformation induction unit and (3) a force detecting unit, Two medium viscous composites, Z100 and Z250 and two packable composites, P60 and SureFil were tested. The viscoelastic material function, including complex modulus $E^{*}$ and phase angle ${\delta}$, were measured. A dynamic oscillatory test was used to evaluate the storage modulus (E'), loss modulus (E") and loss tangent ($tan{\delta}$) of the composites as a function of frequency ($\omega$) from 0.1 to 20 Hz at $23^{\circ}C$. Results: The E' and E" increased with increasing frequency and showed differences in magnitude between brands. The $E^{*}s$ of composites at ${\omega}{\;}={\;}2{\;}Hz$, normalized to that of Z100, were 2.16 (Z250), 4,80 (P60) and 25.21 (SureFil). The magnitudes and patterns of the change of $tan{\delta}$ of composites with increasing frequency were significantly different between brands. The relationships between the complex modulus $E^{*}$, the phase angle ${\delta}$ and the frequency \omega were represented by frequency domain phasor form, $E^{*}{\;}(\omega){\;}={\;}E^{*}e^{i{\delta}}{\;}={\;}E^{*}{\angle}{\delta}$. Conclusions: The viscoelasticity of composites that influences handling characteristics is significant different between brands, The VOR is a relatively simple device for dynamic, mechanical analysis of high viscous dental composites. The locus of frequency domain phasor plots in a complex plane is a valuable method of representing the viscoelastic properties of composites.

• Restorative Dentistry and Endodontics
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• v.25 no.2
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• pp.243-253
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• 2000

The purpose of this in vitro study was to evaluate dentin bonding by two different dentin bonding systems(DBS) using acetone based primer or adhesive [All Bond 2(AB2), One Step(OS)] when they were applied by wet or dry bonding technique. Morphology of resin-dentin interface and hybrid layer thickness(HLT) were investigated using Confocal Laser Scanning Microscope(CLSM) and compared to shear bond strength(SBS). 72 extracted sound human molars were randomly divided into 4 groups of 18 teeth each - Group 1.(AW); AB2 by wet bonding. Group 2(AD); AB2 by dry bonding. Group 3.(OW); OS by wet bonding, Group 4.(OD); OS by dry bonding. In 6 teeth of each group, notch-shaped class V cavities(depth 2mm) were prepared on buccal and lingual surface at the cementoenamel juction(12 cavities per group). To obtain color contrast in CLSM observation, bonding resins of each DBS were mixed with rhodamine B and primer of AB2 was mixed with sodium fluorescein. Prepared teeth of each group were treated with AB2, OS, respectively according to the manufacturer's instructions except for dentin surface moisture treatment after acid etching. In group 1 and 3, after acid etching, excess water was removed with wet tissue(Kimwipes), leaving consistently shiny, visibly hydrated dentin surface. In group 2 and 4, dentin surface was dried for 10 seconds at 1 inch distance. The treated teeth were then packed with composite resin(${\AE}$litefil) and light-cured. 12 microscopic samples($60{\sim}80{\mu}m$ thickness) of each group were obtained after longitudinal section and grinding(Exakt cutting and grinding system). Morphological investigation of resin-dentin interface and HLT measurement using CLSM were done. For measurement of SBS, remaining 12 teeth of each group were flattened occlusally to remove all enamel and grinded to 500 grit SiC(Pedemet Specimen Preparation Equipment). After applying DBS on the exposed dentin surface, composite resin was applied in the shape of cylinder, which has 5mm diameter, 1.5mm thickness, and light cured. SBS was measured using Instron with a crosshead speed of 0.5mm/min. It was concluded as follows, 1. HLT of AW(mean: $2.59{\mu}m$) was thicker than any other group, and followed by AD, OW, OD in descending order(mean; 2.37, 2.28, $1.92{\mu}m$). Only OD had statistically significant differences(p<0.05) to AW and AD. 2. There were intimate contact of resin and dentin at the interface in wet bonding groups, but gaps or irregular interfaces were observed in dry bonding groups. 3. The length, diameter, density of resin tags were various even in the same group without significant differences between groups and lots of adhesive lateral branches were observed. 4. There were no statistically significant difference of SBS between AB2 and OS, but SBS of wet bonding groups were significantly higher(p<0.05) than dry bonding groups. 5. There were no consistent relationships between HLT and SBS.

• Elastomers and Composites
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• v.38 no.3
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• pp.235-242
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• 2003

A vulcanization reaction characteristics of an isoprene rubber (IR)-modified natural rubber/carbon black (NR/CB) composite was studied using in-situ electrical property measuring technique. Since the electrical conductivity of the sample composite would be changed continuously during the vulcanization reaction by rearranging of the carbon black particles within the sample, volume resistivity (${\rho}$) might be obtained as a function or reaction time. A stabilization time ($t_i$), maximum reaction speed time ($t_p$), and volume resistivity at that time(${\rho}_p$) were defined from the data for the Arrhenius analysis. Volume resistivity ${\rho}$ showed a comparatively high value of ${\sim}10^8$ order before the reaction started, and dramatically decreased to be stabilized within $1{\sim}2$ minutes as soon as the reaction started. As the more time elapsed, thereafter, ${\rho}$ decreased monotonously to a certain constant value through a peak, ${\rho}_p$ at time $t_p$, which was considered as the maximum reaction rate. As a result, while $t_i$ values were comparatively constant as $1{\sim}2$ minutes, $t_p$ values showed to become shorter and shorter as the reaction temperature.

• Journal of the Korean Magnetics Society
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• v.18 no.4
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• pp.136-141
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• 2008

In this study, the magnetic(static and high-frequency) and microwave absorbing properties have been investigated in Ru-Co substituted M-hexaferrites($BaFe_{12-2x}Ru_xCo_xO_{19}$). The powders and sintered specimens were prepared by conventional ceramic processing technique. With the calcined powders, the composite specimens were prepared using the silicone rubber as a matrix material. The substitution ratio of Ru-Co to obtain in-plane magnetic anisotropy, thus having the minimum coercivity, is much smaller (about x=0.3) than the previously reported Ti-Co substituted specimen. Owing to this low substitution, the specimen has a large value of saturation magnetization($M_s$=65 emu/g). Ferromagnetic resonance behavior and microwave absorbing frequency band is strongly influnced by the coercvity which can be controlled by Ru-Co substitution ratio. It is found that the M-hexaferrites with planar magnetic anisotropy by doping Ru-Co in both sintered and composite form have superior microwave absorbing properties in GHz frequency range.

• Fibers and Polymers
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• v.7 no.4
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• pp.442-445
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• 2006

The purpose of this study was to compare the subjective fabric hand evaluation and wear comfort of PET treated by Ultraviolet and to evaluate the subjective results from the investigation of microclimate temperature. The subjective hand evaluation was performed by 20 subjects (age: 20-25) with 5-point scale questionnaires to investigate the change of PET knit fabrics treated for different times, specifically, 0, 30 and 90 minutes. The questionnaires were composite with 8 questions; roughness, smoothness, wetness, stiffness, coolness, touch, preference, and comfort. In order to evaluate sensations of wear comfort, we made garments with UV treated fabric and five female students were tested. They walked at the speed of 6.7 km/ hr for 15 minutes in an environment, which was controlled at $29^{\circ}C,\;75{\pm}5%$ RH. Before and after exercising, the microclimate under clothing and subjective wear comfort was measured. The results of subjective evaluation of fabric hand were that untreated and treated for 30 minutes PET were recognized as similar and have a good evaluation on comfort, preference, and touch. According to the result of wear comfort, clothing treated by UV for 90 minutes had the lowest value on the thermal and humidity sensations. In addition, the value of tactile and comfort sensation was the highest on the clothing treated by UV for 90 minutes. In the case of objective evaluation, PET treated for 90 minutes was the lowest on microclimate humidity. PET irradiated by UV for 90 minutes was more 'cool' in thermal sensation and more 'dry' in wet sensation. Accordingly, it was consistent with the result of subjective wear comfort.

• Steel and Composite Structures
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• v.21 no.1
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• pp.217-247
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• 2016

Five extended cylindrical reticulated shells are proposed by changing distribution rule of diagonal rods based on three fundamental types. Modeling programs for fundamental types and extended types of cylindrical reticulated shell are compiled by using the ANSYS Parametric Design Language (APDL). On this basis, conditional formulas are derived when the grid shape of cylindrical reticulated shells is equilateral triangle. Internal force analysis of cylindrical reticulated shells is carried out. The variation and distribution regularities of maximum displacement and stress are studied. A shape optimization program is proposed by adopting the sequence two-stage algorithm (RDQA) in FORTRAN environment based on the characteristics of cylindrical reticulated shells and the ideas of discrete variable optimization design. Shape optimization is achieved by considering the objective function of the minimum total steel consumption, global and locality constraints. The shape optimization for three fundamental types and five extended types is calculated with the span of 30 m~80 m and rise-span ratio of 1/7~1/3. The variations of the total steel consumption along with the span and rise-span ratio are analyzed with contrast to the results of shape optimization. The optimal combination of main design parameters for five extended cylindrical reticulated shells is investigated. The total steel consumption affected by distribution rule of diagonal rods is discussed. The results show that: (1) Parametric modeling method is simple, efficient and practical, which can quickly generate different types of cylindrical reticulated shells. (2) The mechanical properties of five extended cylindrical reticulated shells are better than their fundamental types. (3) The total steel consumption of cylindrical reticulated shells is optimized to be the least when rise-span ratio is 1/6. (4) The extended type of three-way grid cylindrical reticulated shell should be preferentially adopted in practical engineering. (5) The grid shape of reticulated shells should be designed to equilateral triangle as much as possible because of its reasonable stress and the lowest total steel consumption.

• Journal of the Microelectronics and Packaging Society
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• v.23 no.2
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• pp.11-18
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• 2016

This study focused on examining the possibility for recycling of Fe-Si electric sheet. We manufactured Fe-6.5Si mother alloy using by Fe-Si electric sheet scrap for transformer core materials. And then, soft magnetic alloy powder which diameter and shape were $45{\sim}150{\mu}m$ and sphere type was prepared by gas atomization process. As we compared to commercial Fe-6.5Si powder, its diameter distribution and microstructure of recycled powder was a similar. To investigate the possibility of reusing the soft magnetic composite sheet for electronics, recycled powder was treated to have a high aspect ratio (AR), and we finally obtained the 65~66 AR and $2.3{\mu}m$ thickness powder. To release the residual stress of powder, heat treatment was conducted under $300{\sim}400^{\circ}C$, $N_2$ gas. And then, soft magnetic sheet was made by tape casting process using by those powders. After the density and permeability of tape was measured, and we confirmed that the recycled Fe-Si electric sheet scrap was possible to reuse the soft magnetic materials of electronics.

• Steel and Composite Structures
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• v.35 no.5
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• pp.611-625
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• 2020

Experimental investigation and finite element analysis of corroded cold-formed steel (CFS) columns are presented. 11 tensile coupon specimens and 6 stub columns of corroded CFS that had a channel section of C160x60x20 were subjected to monotonic tensile tests and axial compression tests, respectively. The degradation laws of the mechanical properties of the tensile coupon specimens and stub columns were analysed. An appropriate finite element model for the corroded CFS columns was proposed and the influence of local corrosion on the stability performance of the columns was studied by finite element analysis. Finally, the axial capacity of the experimental results was compared with the predictions obtained from the existing design specifications. The results indicated that with an increasing average thickness loss ratio, the ultimate strength, elastic modulus and yield strength decreased for the tensile coupon specimens. Local buckling deformation was not noticeable until the load reached about 90% of the ultimate load for the non-corroded columns, while local buckling deformation was observed when the load was only 40% of the ultimate load for the corroded columns. The maximum reduction of the ultimate load and critical buckling load was 57% and 81.7%, respectively, compared to those values for the non-corroded columns. The ultimate load of the columns with web thickness reduced by 2 mm was 53% lower than that of the non-corroded columns, which indicates that web corrosion most significantly affects the bearing capacity of the columns with localized corrosion. The results predicted using the design specifications of MOHURD were more accurate than those predicted using the design specifications of AISI.