• Herbal Formula Science
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• v.19 no.1
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• pp.183-194
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• 2011

Objectives : To estimate the shelf-life by long-term storage test of Pyungwi-san. Methods : Experiments were conducted to evaluate the stability such as the selected physicochemical, heavy metal, microbilogical experiment under an acceleration test and long-term storage test of Pyungwi-san in different storage under room temperature, refrigeration and freezing. Futhermore, HPLC analysis was performed for the determinations of glycyrrhizin in the Pyungwi-san on an Inertsil ODS-3 column(250 mm ${\times}$ 4.6 mm, 5 um) using solvent 35% acetonitrile include 0.05% phosphoric acid at 254 nm. The flow rate was 1.0 mL/min. Results : The significant change was not showed in pH, heavy metal, microbiological, identification test and quantitative analysis based on acceleration test and long-term storage test. Retention time of glycyrrhizin in HPLC chromatogram was about 16.065 min and calibration curve showed good linearity($R^2$ = 0.9999). The contents of glycyrrhizin in acceleration test and long-term storage test were 0.068~0.076 mg/mL and 0.066~0.077 mg/mL, respectively. Shelf-lifes of room temperature, refrigeration and freezing by long-term storage test were predicted 41, 24 and 34 months, respectively. Conclusions : The suggested shelf-life would be helpful on the storage and distribution of herbal medicine.

• KSBB Journal
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• v.20 no.3
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• pp.244-249
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• 2005

Chiral separation of racemic ibuprofen was achieved on a Kromasil KR100-5CHI-TBB column. Some chromatographic parameters (resolution, number of theoretical plates, HETP, capacity factor) are calculated under different separation conditions such as change of mobile phase compositions (hexane / t-BME : 85 / 15, 75 / 15, 65 / 35, 55 /45) as well as acetic acid concentrations for adjusting pH (0.1 to 1 $v/v\%$). Flow rate versus number of theoretical plates and HETP were compared to evaluate column efficiency. To determine the adsorption isotherms, PIM (Pulsed Input Method) was carried out. At concentrations of racemic ibuprofen between 0.1 and 0.3 mg/ml, S- and R-ibuprofen have the same retention time of 4.48 and 5.81 min. Ibuprofen isotherms show a linear form under concentrations of 0.3 mg/ml with eluent (hexane / t-BME = 55 / 45).

• Particle and aerosol research
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• v.12 no.4
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• pp.145-150
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• 2016

During the chemical mechanical planarization (CMP) process, slurry that comprises abrasive particles can directly affect the CMP performance and quality. Mainly, the large particles in the slurry can generate the defects on the wafer. Thus, many kinds of filters have been used in the CMP process to remove unwanted over-sized particles. Among these filters, the point-of-use (POU) filter is used just before the slurry is supplied onto the CMP pad. In the CMP research field, analysis of the POU filter has been relatively exceptional, and previous studies have not focused on the standardized filtration efficiency (FE) or filter performance. Furthermore, conventional evaluation methods of filter performance are not appropriate for POU filters, as the POU filter is not a membrane type, but is instead a depth type roll filter. In order to accurately evaluate the POU filter, slurry FE according to particle size was measured in this study. Additionally, a CMP experiment was conducted with filtered slurry to demonstrate the effects of filtered slurry on CMP performance. Depending on the flow rate and the filter retention size, the FE according to particle size was different. When the small and large particles have different FEs, the total filtration efficiency (TFE) can still have a similar value. For this reason, there is a need to measure the FE with respect to the particle size to verify the effects of the POU filter on the CMP process.

• Particle and aerosol research
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• v.12 no.4
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• pp.127-134
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• 2016

A multiwall carbon nanotube (MWCNT)/graphene (GR) composite was synthesized for an enhanced supercapacitor. Aerosol spray pyrolysis (ASP) was employed to synthesize the MWCNT/GR composites using a colloidal mixture of MWCNT and graphene oxide (GO). The effect of the weight ratio of the MWCNT/GO on the particle properties including the morphology and layered structure were investigated. The morphology of MWCNT/GR composites was generally the shape of a crumpled paper ball, and the average composite size was about $5{\mu}m$. MWCNT were uniformly dispersed in GR sheets and the MWCNT not only increase the basal spacing but also bridge the defects for electron transfer between GR sheets. Thus, it was increasing electrolyte/electrode contact area and facilitating transportation of electrolyte ion and electron in the electrode. Electrochemical data demonstrate that the MWCNT/GR (weight ratio=0.1) composite possesses a specific capacitance of 192 F/g at 0.1 A/g and good rate capability (88% capacity retention at 4 A/g) using two-electrode testing system.

• Korean Chemical Engineering Research
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• v.53 no.2
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• pp.131-136
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• 2015

The nanostructural graphene/vanadium oxide (graphene/$V_2O_5$) composite with enhanced capacitance was synthesized by the electro-deposition in 0.5 M $VOSO_4$ solution. The morphology of composites was characterized using scanning electron microscopy (SEM), x-ray diffraction pattern (XRD), and x-ray photoelectron spectroscopy (XPS). The oxidation states of the electro-deposited vanadium oxide was found to be $V^{5+}$ and $V^{4+}$. The morphology of the prepared graphene/$V_2O_5$ composite exhibits a netlike nano-structure with $V_2O_5$ nanorods in about 100 nm diameter, which could lead a better contact between electrolyte an electrode. The composite with a deposition time of 4,000 s exhibits the specific capacitance of $854mF/cm^2$ at a scan rate of 20 mV/s and the capacitance retention of 53% after 1000 CV cycles.

• Korean Journal of Materials Research
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• v.30 no.1
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• pp.14-21
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• 2020

Carbon supports for dispersed platinum (Pt) electrocatalysts in direct methanol fuel cells (DMFCs) are being continuously developed to improve electrochemical performance and catalyst stability. However, carbon supports still require solutions to reduce costs and improve catalyst efficiency. In this study, we prepare well-dispersed Pt electrocatalysts by introducing titanium dioxide (TiO₂) into biomass based nitrogen-doped carbon supports. In order to obtain optimized electrochemical performance, different amounts of TiO₂ component are controlled by three types (Pt/TNC-2 wt%, Pt/TNC-4 wt%, and Pt/TNC-6 wt%). Especially, the anodic current density of Pt/TNC-4 wt% is 707.0 mA g^-1_pt, which is about 1.65 times higher than that of commercial Pt/C (429.1 mA g^-1_pt); Pt/TNC-4wt% also exhibits excellent catalytic stability, with a retention rate of 91 %. This novel support provides electrochemical performance improvement including several advantages of improved anodic current density and catalyst stability due to the well-dispersed Pt nanoparticles on the support by the introduction of TiO₂ component and nitrogen doping in carbon. Therefore, Pt/TNC-4 wt% may be electrocatalyst a promising catalyst as an anode for high-performance DMFCs.

• Journal of Service Research and Studies
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• v.9 no.4
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• pp.19-40
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• 2019

Mobility as a Service is a service conception to achieve the intelligent transportation system. Its aims to improve the travel experience. In one platform, it connects various transportation modes to offer service and users only need to pay in one time for the whole travel. But the single MaaS platform easily faces the problems such as low user traffic, low retention rate and the access to markets of the this service is still unfound. From the perspective of bicycle-sharing, this research makes the MaaS concept into bicycle-sharing to build a better service model. The bicycle-sharing combine with the MaaS concept is innovative in business model, travel model and service architecture. In addition, this research also tests users' expectations for service model. The research shows that MaaS-based bicycle-sharing could offer flexible and convenient travel experience in the aspects of combined transportation, travel, transfer and payment, and it also makes it possible to make travel services according to need, and sustainable transport.

• Archives of Pharmacal Research
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• v.3 no.1
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• pp.7-12
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• 1980

Ampliciline was synthesized from 6-amino-pencillanic acid (6-APA) and D-.alpha. phenylglycine methyl ester by using amplicilin synthesizing enzyme from Peudomonas melanogenum (IAM 1655). The whole cell enzyme was immobilized by entrapping it in the polyacrylamide gel lattices. The polymer used in the enzyme entrapment was made from 150 mg per ml of acrylamide monomer and 8 mg per ml of N, N'-methylenebisacrylamide. About 200 mg/whole cell enzyme was mixed in the polymer for entrapment. The maximal activity retention after immobilization was 56%. The optimal pH values for the whole cell enzyme and the immobilized whole cell enzyme were 6.0 and 5.9, respectively. The optimal temperature for the enzyme activity were the same for both type of preparations. The enzyme stabilities against pH and heat increased for immobilized whole cell enzyme. Immobilized cell was more stable especially in the acidic condition while both type were found to be very suceptible to thermal inactivation at a temperature above 4.deg.C. The kinetic constants obtained from Lineweaver-Burk plot based on two substate reaction mechanism showed somewhat higher value for immobilized whole cell enzyme as compared to the whole cell enzyme : the Km value for 6-APA were 7.0 mM and 12.5 mM while Km values for phenylglycine methyl ester were 4.5 mM and 8.2 mM, respectively. Using the immobilized whole cell enzyme packed in a column reactor, the productivity of ampiciline was studied by varying the flow rate of substrate solution. At the space velocity, SV, 0.14 hr$^{-1}$ the conversion was 45%. Operational stability found in terms of half life was 30 hr at SV = 0.2 hr.

• Bulletin of the Korean Chemical Society
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• v.35 no.10
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• pp.2974-2978
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• 2014

$Mn_3O_4$/multi-walled carbon nanotube (MWCNT) composites are prepared by chemically synthesizing $Mn_3O_4$ nanoparticles on a MWCNT film at room temperature. Structural and morphological characterization has been carried out using X-ray diffraction (XRD) and scanning and transmission electron microscopies (SEM and TEM). These reveal that polycrystalline $Mn_3O_4$ nanoparticles, with sizes of about 10-20 nm, aggregate to form larger nanoparticles (50-200 nm), and the $Mn_3O_4$ nanoparticles are attached inhomogeneously on MWCNTs. The electrochemical behavior of the composites is analyzed by cyclic voltammetry experiment. The $Mn_3O_4$/MWCNT composite exhibits a specific capacitance of $257Fg^{-1}$ at a scan rate of $5mVs^{-1}$, which is about 3.5 times higher than that of the pure $Mn_3O_4$. Cycle-life tests show that the specific capacitance of the $Mn_3O_4$/MWCNT composite is stable up to 1000 cycles with about 85% capacitance retention, which is better than the pure $Mn_3O_4$ electrode. The improved supercapacitive performance of the $Mn_3O_4$/MWCNT composite electrode can be attributed to the synergistic effects of the $Mn_3O_4$ nanoparticles and the MWCNTs, which arises not only from the combination of pseudocapacitance from $Mn_3O_4$ nanoparticles and electric double layer capacitance from the MWCNTs but also from the increased surface area, pore volume and conducting property of the MWCNT network.

• Journal of Digital Contents Society
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• v.17 no.5
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• pp.417-423
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• 2016

Recently smartphone has propagated all age groups rapidly due to the fact that the advance of media and the increase of smartphone penetration. In South Korea, high-school students' smartphone retention rate is 90.2%. This study proceed an analysis of high school students' smartphone usage by a feasibility study, and also by recording the log data of actual usage patterns of smartphone applications. The feasibility study investigates subject's smartphone usage, and the log data analysis measures the accurate usage recorded for about three months. We compared the feasibility study and the log data for the daily smartphone usage, and investigated the change of usage pattern during the weekdays, weekends, and the before, during and after exams. High-school students are unique group in capital area. As a result, we found that high-school students' smartphone usage pattern in capital area has not affected by weekday or weekend but has affected by the before, during and after exams.