• Journal of Microbiology and Biotechnology
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• v.18 no.7
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• pp.1257-1265
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• 2008

To lower the cost of ethanol distillation of fermentation broths, a high initial glucose concentration is desired. However, an increase in the substrate concentration typically reduces the ethanol yield because of insufficient mass and heat transfer. In addition, different operating temperatures are required to optimize the enzymatic hydrolysis (50$^{\circ}C$) and fermentation (30$^{\circ}C$). Thus, to overcome these incompatible temperatures, saccharification followed by fermentation (SFF) was employed with relatively high solid concentrations (10% to 20%) using a portion loading method. In this study, glucose and ethanol were produced from Solka Floc, which was first digested by enzymes at 50$^{\circ}C$ for 48 h, followed by fermentation. In this process, commercial enzymes were used in combination with a recombinant strain of Zymomonas mobilis (39679:pZB4L). The effects of the substrate concentration (10% to 20%, w/v) and reactor configuration were also investigated. In the first step, the enzyme reaction was achieved using 20 FPU/g cellulose at 50$^{\circ}C$ for 96 h. The fermentation was then performed at 30$^{\circ}C$ for 96 h. The enzymatic digestibility was 50.7%, 38.4%, and 29.4% after 96 h with a baffled Rushton impeller and initial solid concentration of 10%, 15%, and 20% (w/v), respectively, which was significantly higher than that obtained with a baffled marine impeller. The highest ethanol yield of 83.6%, 73.4%, and 21.8%, based on the theoretical amount of glucose, was obtained with a substrate concentration of 10%, 15%, and 20%, respectively, which also corresponded to 80.5%, 68.6%, and 19.1%, based on the theoretical amount of the cell biomass and soluble glucose present after 48 h of SFF.

• Journal of The Korean Society of Agricultural Engineers
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• v.60 no.5
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• pp.17-27
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• 2018

The objective of this study is to identify the priority area where the nonpoint source pollution (NPS) management is required and to set up the load reduction goals for the identified priority area. In this study, the load duration curve (LDC) was first developed using the flow and water quality data observed at 286 monitoring stations. Based on the developed LDC, the priority area for the NPS pollution management was determined using a three-step method. The 24 watersheds were finally identified as the priority areas for the NPS pollution management. The water quality parameters of concern in the priority areas were the total phosphorus or chemical oxygen demand. The load reduction goals, which were calculated as the percent reduction from current loading levels needed to meet target water quality, ranged from 67.9% to 97.2% during high flows and from 40.3% to 69.5% during moist conditions, respectively. The results from this study will help to identify critical watersheds for NPS program planning purposes. In addition, the process used in this study can be effectively applied to identify the pollutant of concern as well as the load reduction target.

• Journal of Korean Society of Water and Wastewater
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• v.10 no.2
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• pp.47-54
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• 1996

UASB reactor was operated for treating wastewater containing high sulfate to assess their performance, competition between sulfate-reducing bacteria(SRB) and methane-producing bacteria(MPB), and the change in the characteristics of microbial granules according to change of hydraulic retention time(HRT) in the reactor. The reactor was fed with a synthetic moderate strength wastes(glucose, 2000 mgCOD/l) containing high sulfate($2400mgSO_4{^{2-}}/l$). The organic loading rate(OLR) ranged from 1.5 to 3.0 gCOD/l.d as HRT maintained 15 to 30 hrs in the stage I. The COD removal efficiency was between 80 to 92%. During this period, methane yield rapidly decreased from 0.3 to 0.1 1 $CH_4$/gCODremoved. While sulfide concentration in the effluent increased from 80 to 200 mgS/l. This indicates that SRB becomes dominant over MPB at a relatively long HRT in the excess sulfate. When OLR of reactor maintained from 5 to 8 gCOD/l.d in the stage II, methane yield increased from 0.1 to 0.17 1 $CH_4$/gCODremoved regardless of decrease of COD removal efficiency. This indicates that SRB is more sensitive to the change of a short HRT than MPB. In the competition between SRB and MPB, about 30% of the removed COD was utilized by SRB at HRT of 30 hrs during the start-up period, while about 73% was used by SRB at HRT of 15hrs at the final step of second experimental stage. Whereas after shock exposure of OLR about 62% was utilized by SRB at HRT of 5hrs. It indicates that SRB is strongly suppressed by the wash-out of significant dispersed SRB since a large electron flow is distributed to the MPB. In addition, the granulation in the presence of high sulfate is unfavoured at a long HRT because of substrate transport limitations into MPB like Methanothrix spp. which is an important factor in the composition of the granules. Accordingly, granule sizes in the UASB reactor decreased with time due to weak network frame of granules by the decreased activity of MPB.

• Journal of the Korean Geotechnical Society
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• v.34 no.2
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• pp.5-17
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• 2018

In this study, the in-situ stress, strength and stress-strain characteristics with shear parameters (UU, CU, ${\bar{CU}}$) are analytically evaluated and the stability analyses are carried out under loading/unloading conditions. The in-situ stress and the stress-strain behaviour may become different according to input shear parameters in finite element analyses with construction step, Especially, if the internal friction angle in Mohr-Coulomb model is set to zero, the in-situ stress and the stress-strain behaviour might not be properly predicted. The results from CU parameter of total stress analysis have no significant difference with the results from CU of effective stress analysis. Therefore, in the numerical analysis for soft ground, CU parameters can be applied to predict in-situ stress and stress-strain behaviors. In addition, the calculation method was proposed to determine the shear parameter of Mohr-Coulomb model, which is corresponding to the shear strength equivalent to that of in-situ soil.

• Journal of Ocean Engineering and Technology
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• v.34 no.5
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• pp.285-293
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• 2020

This study evaluated the Hook-up installation of an offshore site construction process, which is the final step in an offshore site installation process. During Hook-up installation, the offshore structure can have a detrimental effect on the work stability due to low-frequency motion. Moreover, economic costs can be incurred by the increase in available days of a tugboat. Therefore, this study developed a numerical analysis program to assess the dynamic behavior of mooring systems during hook-up installation to analyze the generally performed installation process and determine when the tugboat should be released. In this program, the behavior of an offshore structure was calculated using Cummin's time-domain motion equation, and the mooring system was calculated by Lumped mass method (LMM). In addition, a tugboat algorithm for hook-up installation was developed to apply the Hook-up procedure. The model used in the calculations was the barge type assuming FPSO (Floating production storage and off-loading) and has a taut mooring system connected to 16 mooring lines. The results of the simulation were verified by comparing with both MOSES, which is a commercial program, and a calculation method for restoring coefficient matrix, which was introduced by Patel and Lynch (1982). Finally, the offset of the structure according to the number of tugboats was calculated using the hook-up simulation, and the significant value was used to represent the calculation result.

• Korean Journal of Metals and Materials
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• v.56 no.11
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• pp.835-843
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• 2018

In this work, we report a delta rosette strain sensor based on highly stretchable silver nanowire (AgNW) percolation piezoresistors. The proposed rosette strain sensors were easily prepared by a facile two-step fabrication route. First, three identical AgNW piezoresistive electrodes were patterned in a simple and precise manner on a donor film using a solution-processed drop-coating of the AgNWs in conjunction with a tape-type shadow mask. The patterned AgNW electrodes were then entirely transferred to an elastomeric substrate while embedding them in the polymer matrix. The fabricated stretchable AgNW piezoresistors could be operated at up to 20% strain without electrical or mechanical failure, showing a maximum gauge factor as high as 5.3, low hysteresis, and high linearity ($r^2{\approx}0.996$). Moreover, the sensor responses were also found to be highly stable and reversible even under repeated strain loading/unloading for up to 1000 cycles at a maximum tensile strain of 20%, mainly due to the mechanical stability of the AgNW/elastomer composites. In addition, both the magnitude and direction of the principal strain could be precisely characterized by configuring three identical AgNW piezoresistors in a delta rosette form, representing the potential for employing the devices as a multidimensional strain sensor in various practical applications.

• The Journal of Engineering Geology
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• v.29 no.3
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• pp.237-249
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• 2019

The roughness changes on a fracture surface were analyzed via a multi-stage compression test under high temperatures to assess how the cracks in a rock mass affect groundwater movement. The analyzed samples consist of coarse granitic rocks from approximately 40 and 270 m depth, and fine granitic rocks from 500 m depth. The compression test was conducted on $20{\times}40{\times}5mm$ samples using a loading system where the pressure increases in 10 MPa increments to 120 MPa. A high-resolution 3D confocal laser scanning microscope (CLSM) was used to observe the surface changes, including the roughness changes, at each pressure step. The roughness change was calculated based on the roughness factor. The experimental results indicate that the roughness of the fracture surface varies with rock type under the stepwise pressure conditions. These data provide a basis for predicting groundwater flow along rock fractures.

• Smart Structures and Systems
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• v.7 no.4
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• pp.303-317
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• 2011

A specially designed tendon, which is proposed by embedding an FBG sensor into the center king cable of a 7-wire strand tendon, was applied to monitor the prestress force and load transfer of ground anchor. A series of tensile tests and a model pullout test were performed to verify the feasibility of the proposed smart tendon as a measuring sensor of tension force and load transfer along the tendon. The smart tendon has proven to be very effective for monitoring prestress force and load transfer by measuring the strain change of the tendon at the free part and the fixed part of ground anchor, respectively. Two 11.5 m long proto-type ground anchors were made simply by replacing a tendon with the proposed smart tendon and prestress forces of each anchor were monitored during the loading-unloading step using both FBG sensor embedded in the smart tendon and the conventional load cell. By comparing the prestress forces measured by the smart tendon and load cell, it was found that the prestress force monitored from the FBG sensor located at the free part is comparable to that measured from the conventional load cell. Furthermore, the load transfer of prestressing force at the tendon-grout interface was clearly measured from the FBGs distributed along the fixed part. From these pullout tests, the proposed smart tendon is not only expected to be an alternative monitoring tool for measuring prestress force from the introducing stage to the long-term period for health monitoring of the ground anchor but also can be used to improve design practice through determining the economic fixed length by practically measuring the load transfer depth.

• Journal of Microbiology and Biotechnology
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• v.31 no.10
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• pp.1455-1464
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• 2021

Trehalose is a non-reducing disaccharide in increasing demand for applications in food, nutraceutical, and pharmaceutical industries. Single-step trehalose production by trehalose synthase (TreS) using maltose as a starting material is a promising alternative process for industrial application due to its simplicity and cost advantage. Pseudomonas monteilii TBRC 1196 was identified using the developed screening method as a potent strain for TreS production. The TreS gene from P. monteilii TBRC 1196 was first cloned and expressed in Escherichia coli. Purified recombinant trehalose synthase (PmTreS) had a molecular weight of 76 kDa and showed optimal pH and temperature at 9.0 and 40℃, respectively. The enzyme exhibited >90% residual activity under mesophilic condition under a broad pH range of 7-10 for 6 h. Maximum trehalose yield by PmTreS was 68.1% with low yield of glucose (4%) as a byproduct under optimal conditions, equivalent to productivity of 4.5 g/l/h using enzyme loading of 2 mg/g substrate and high concentration maltose solution (100 g/l) in a lab-scale bioreactor. The enzyme represents a potent biocatalyst for energy-saving trehalose production with potential for inhibiting microbial contamination by alkaline condition.

• Journal of the Korean Geotechnical Society
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• v.37 no.12
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• pp.89-105
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• 2021

In this paper, feasibility study was carried out to evaluate necessity of seismic design of earth retaining structures in a deep excavation. Dynamic behavior of retaining system was analyzed using FLAC, a finite difference analysis program. It was shown that maximum bending moments of retaining walls and axial forces of supports were increased up to 98% and 87% during earthquake, respectively, compared to final excavation step, which indicates that dynamic earth pressure has a large effect on a retaining system. The stability of retaining system designed according to current design specifications was evaluated using structural forces obtained by numerical analysis, and effect of earthquake loading on structural design was analyzed.