• 한국생물공학회:학술대회논문집
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• 2003.10a
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• pp.499-503
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• 2003

In the study, we have obtained modified cellulase with higher cellulose degradation activity by molecular evolution method. Cellobiohydrolase(CBH I ) gene of Trichorderma reerri has been used. Cellulase mutant 228-G2 was selected and the activity of cellulase mutant 228-G2 was increased by 300% compared to original CBH I The 17 among 1542bases were found to be modified with mutant 228-G2.

• BMB Reports
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• v.49 no.11
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• pp.587-589
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• 2016

The circadian clock system enables organisms to anticipate the rhythmic environmental changes and to manifest behavior and physiology at advantageous times of the day. Transcriptional/translational feedback loop (TTFL) is the basic feature of the eukaryotic circadian clock and is based on the rhythmic association of circadian transcriptional activator and repressor. In Drosophila, repression of dCLOCK/CYCLE (dCLK/CYC) mediated transcription by PERIOD (PER) is critical for inducing circadian rhythms of gene expression. Pacemaker neurons in the brain control specific circadian behaviors upon environmental timing cues such as light and temperature cycle. We show that amino acids 657-707 of dCLK are important for the transcriptional activation and the association with PER both in vitro and in vivo. Flies expressing dCLK lacking AA657-707 in $Clk^{out}$ genetic background, homologous to the mouse Clock allele where exon 19 region is deleted, display pacemaker-neuron-dependent perturbation of the molecular clockwork. The molecular rhythms in light-cycle-sensitive pacemaker neurons such as ventral lateral neurons ($LN_vs$) were significantly disrupted, but those in temperature-cycle-sensitive pacemaker neurons such as dorsal neurons (DNs) were robust. Our results suggest that the dCLK-controlled TTFL diversify in a pacemaker-neuron-dependent manner which may contribute to specific functions such as different sensitivities to entraining cues.

• Journal of computational fluids engineering
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• v.11 no.3 s.34
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• pp.28-36
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• 2006

NSBT(No Slip Boundary Treatment) is a newly developed scheme for the treatment of a no slip condition on the solid wall of obstacle in a flow field. In our research, NSBT was used to perform LBM simulation of a flow over a circular cylinder to determine the flow feature and aerodynamics characteristic of the cylinder. To ascertain the applicability of NSBT on the complex shape of the obstacle, it was first simulated for the case of the flow over a circular and square cylinder in a channel and the results were compared against the solution of Navier-Stokes equation. The simulations were performed in a moderate range of Reynolds number at each cylinder position to identify the flow feature and aerodynamic characteristics of circular cylinder in a channel. The drag coefficients of the cylinder were calculated from the simulation results. We have numerically confirmed that the critical reynolds number for vortex shedding is in the range of 200$\sim$250. For the gap parameter $\gamma$ = 2 cases at Re > 240, the vortex shedding were symmetric and it resembled the Karmann vortex. As the cylinder approached to one wall, the vorticity significantly reduced in length while the vorticity on the other side elongated and the vorticity combined with the wall boundary-layer vorticity. The resultant $C_d$ by LBM concurred with the results of DNS simulation performed by previous researchers.

• Journal of Mechanical Science and Technology
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• v.18 no.8
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• pp.1479-1489
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• 2004

The effect of fluctuation of Equivalence Ratio (ER) in a turbulent reactive field has been studied in order to check the global combustion characteristics induced by the local fluctuation. When the flow is premixed on a large scale, closer examination on a small scale reveals that local fluctuations of ER exist in an imperfectly premixed mixture, and that these fluctuations must be considered to correctly estimate the mean reaction rate. The fluctuation effect is analyzed with DNS by considering the joint PDF of reactive scalar and ER, followed by modeling study where an extension of stochastic mixing models accounting for the ER fluctuation is reviewed and tested. It was found that models prediction capability as well as its potential is in favor to this case accounting the local ER fluctuation. However, the effect of local fluctuation did not show any notable changes on the mean global characteristics of combustion when statistical independence between the reactive scalar and ER field is imposed, though it greatly influenced the joint PDF distribution. The importance of taking into account the statistical dependency between ER and combustible at the initial phase is demonstrated by testing the modeled reaction rate.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.8
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• pp.702-710
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• 2007

Direct numerical simulation (DNS) is performed to investigate suppressed wake transition and occurrence of lock-on in the wake of a circular cylinder disturbed by sinusoidal perturbation at the Reynolds number of 220 (A-mode instability regime). The sinusoidal perturbation, of which the frequency is near twice the natural shedding frequency, is superimposed on the free stream velocity. It is shown that the wake transition behind the circular cylinder can be suppressed due to the perturbation of the free stream velocity. This change causes a jump in the Strouhal number from the value corresponding to A-mode instability regime to the value corresponding to retarded wake transition regime (extrapolated from laminar shedding regime) in the Strouhal-Reynolds number relationship. As a result, vortex shedding frequency is locked on the perturbation frequency depending not on the natural shedding frequency but on the modified shedding frequency.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.11
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• pp.1523-1534
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• 2000

The performance of a number of existing dynamic subgrid-scale(SGS) models is evaluated in large-eddy simulations(LES) of two prototype transitional and turbulent shear flows, a planar jet and a channel flow. The dynamic SGS models applied include the dynamic Smagorinsky model(DSM);Germano et al. 1991, Lully 1992), the dynamic tow-component model(DTM; Akhavan et al. 2000), the dynamic mixed model(DMM;Zang et al, 1993). and the dynamic two-parameter model(DTPM; Salvetti & Banerjee 1995). The results are compared with those for DNS for their evaluation. The LES results demonstrate the superior performance of DTM with use of a sharp cutoff filter and DMM with use of a box filter, as compared to their respect counterpart DSM, in predicting the mean statistics, spectra and large-scale structure of the flow, Such features of DTM and DMM derive from the construction of the models in which tow separate terms are included to represent the SGS interactions; a Smagorinsky edd-viscosity term to account for the non-local interactions, and a local-interaction term to account for the nonlinear dynamics between the resolved and subgrid scales in the vicinity of the LES cutoff. As well, overall the SGS models using a sharp cutoff filter are more successful than those using a box filter in capturing the statistics and structure of the flow. Finally, DTPM is found to be compatible or inferior to DMM.

• Composites Research
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• v.18 no.5
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• pp.15-20
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• 2005

In this paper, damage induced acoustic emission in the composite plate in numerically simulated by using the three dimensional finite element method and explicit time integration. Acoustic source is modeled by equivalent volume source. To verify the proposed method, dynamic displacements due to the elastic wave are compared with the experiment when the fiber is broken in the single fiber embedded isotropic plate. For the laminated composite plates, the results are compared between homogenized model and DNS approach which models fibers and matrix separately. To capture high frequencies in the elastic wave, small time step size and a large number of meshes are required. The parallel computing technology is introduced to solve a large scale problem efficiently.

• Proceedings of the Korean Information Science Society Conference
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• 2000.10c
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• pp.532-534
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• 2000

IPv4(Internet Protocol version 4)의 차세대 버전인 IPv6는 기존 IPv4의 문제점인 주소부족 및 새로운 부가기능 등의 필요성 때문에 IETF(Internet Engineering Task Force)에서 IPv4를 대체하기 위해 개발한 프로토콜이다. 하지만 IPv4를 어느 한순간에 IPv6로 대체하는 것은 불가능하기 때문에 기존 IPv4와의 호환 및 연동을 위한 터널링 및 기타 여러 가지 transition mechanism들이 고려되고 있다. 이러한 mechanism들 중에서 최근 표준으로 발표된 NAT-PT(Network Address Translation $\square$ Protocol Translation)는 DNS-ALG (Domain Name System $\square$ Application Level Gateway)라는 개념을 도입하여 IPv4와 IPv6간의 양방향 주소변환 및 프로토콜 변환기능을 수행한다. 각각의 기능에서 주소 변환은 주소크기와 형식이 다른 IPv4와 Pv6간의 서로 상대 노드를 엑세스할 수 있도록 하고 프로토콜 변환은 다른 버전의 프로토콜을 사용하는 노드들이 상대노드가 보낸 패킷의 헤더정보를 이해할 수 있도록 한다. 그리고 이러한 기본적인 변환 외에 헤더정보의 정확한 전달을 위해서는 기존의 path MTU(Maximum Transgfer Unit) discovery 그리고 pseudo header checksum 등도 고려되어야 한다.

• 한국전산유체공학회:학술대회논문집
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• 2001.10a
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• pp.84-90
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• 2001

Secondary instability of flow past a circular cylinder is examined using direct numerical simulation at Reynolds number 220 and 250. The higher-order finite difference scheme is employed for the spatial distributions along with the second order Adams-Bashforth and the first order backward-Euler time integration. In x-y plane, the convection term is applied by the 5th order upwind scheme, and the pressure and viscosity terms are applied by the 4th order central difference. In spanwise, Navier-Stokes equation is distributed using Spectral Method. The critical Reynolds number for this instability is found to be about Re=190. The secondary instability leads re three-dimensionality with a spanwise wavelength about 4 cylinder diameters at onset (A-mode). Results of three-dimensional effect in wake of a circular cylinder are represented with spanwise and streamwise vorticity contours as Reynolds numbers.

• Journal of Mechanical Science and Technology
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• v.14 no.11
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• pp.1305-1318
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• 2000

The local wall shear stress in transitional boundary layer was estimated from the near-wall mean velocity data using the principle of Computational Preston Tube Method(CPM). The previous DNS and experimental databases of transitional boundary layers were used to demonstrate the accuracy of the method and to provide the applicable range of wall unit y(sup)+. The skin friction coefficients predicted by the CPM agreed well with those from previous studies. To reexamine the applicability of CPM, near-wall hot-wire measurement were conducted in developing transitional boundary layers on a flat plate with different freestream turbulence intensities. The intermittency profiles across the transitional boundary layers were reasonably obtained from the conditional sampling technique. An empirical correlation between the representative intermittency near the wall and free parameter K$_1$of the extended wall function of CPM has been newly proposed using the present and other experimental data. The CPM has been verified as a useful tool to measure the wall shear stress in transitional boundary layer with reasonable accuracy.