We present the results of the linear analysis for the Parker-Jeans instability in the magnetized gas disks including the effect of cosmic-ray diffusion along the magnetic field lines. We adopted an uni-formly rotating two temperature layered disk with a horizontal magnetic fields and solved the perturbed equations numerically. Fragmentation of gases takes place and filamentary structures are formed by the growth of the instability. Nagai et al. (1998) showed that the direction of filaments being formed by the Parker-Jeans instability depends on the strength of pressure outside the unperturbed gas disk. We found that at some range of external pressures the direction of filaments is also governed by the value of the diffusion coefficient of CR along the magnetic field lines k.

Here we present a linear stability analysis and an MHD 2D model for the Parker-Jeans instability in the Galactic gaseous disk. The magnetic field is assumed parallel to a Galactic spiral arm, and the gaseous disk is modelled as a multi-component, magnetized, and isothermal gas layer. The model employs the observed vertical stratifications for the gas density and the gravitational acceleration in the Solar neighborhood, and the self-gravity of the gas is also included. By solving Poisson's equation for the gas density stratification, we determine the vertical acceleration due to self-gravity as a function of z. Subtracting it from the observed gravitational acceleration, we separate the total acceleration into self and external gravities. The linear stability analysis provides the corresponding dispersion relations. The time and length scales of the fastest growing mode of the Parker-Jeans instability are about 40 Myr and 3.3 kpc, respectively. In order to confirm the linear stability analysis, we have performed two-dimensional MHD simulations. These show that the Parker-Jeans instability under the self and external gravities evolves into a quasi-equilibrium state, creating condensations on the northern and southern sides of the plane, in an alternate manner.

To cletermine the role of mismatch repair in the clevelopment of oral squamolls cell carcinomas (OSCCs) , the prevalence of microsatellite instability (MSI), expression of I뼈LH1 ancll띠SH2 ， ancl hypennethylation of I뻐LH1 ancl hMSH2 were explorecl. Bya panel of five markers (BAT25, BAT26 , 02S123, 05S346, ancl 017~‘250 ， the so-callecl Bethescla markers) for screening of MSI, MSI was observecl in 5 of the 15 sqllamolls cell carcinomas (33.3%). As MSI is callsecl by the clysfllnction of MMR genes, this stucly examinecl the methylation status of CpG sites in the hMLH 1 ancl hMSH2 promoters ancl the expression hMLH1 ancl hMSH2. Becallse of inappr이)riate efficiency of fonnalin-frxecl ancl paraffin-embeclclecl samples for methylation-specific PCR (MS-PCR) of hMLH1 ancl hMSH2, the role of promoter hypelmethylation 띠 the clevelopment of MSI ancl expression of hMLH1 ancl hMSH2. meùlylation was failecl to clefìne. However, loss of nllclear staining of 1ψIILH 1 ancl hMSH2 were seen in nine (69.2%) ancl four (30.7%) of 13 OSCCs, while four ancl fìve all corresponcling normal epiùlelial tisslles showecl positive nllclear stι ining ofl마ILH1 and hMSH2. These data suggest that MSI anclloss of expression of hMLH1 ancl hMSH2 play a role in the carcinc핑enesis of oral sqllamolls cell carcinomas thollgh the role of promoter hypermethylation of hMLH1 ancl hMSH2 in MSI and their expresslon IS lIncertam

전통적으로 Cordyceps종은 한국을 포함한 동양에서 건강증진과 심장과 폐에 관련된 질환을 치료하는 약용식물의 하나로 사용되어왔다. 최근에 동충하초의 약리적 가치 때문에 큰번데기 동충하초를 포함한 몇가지 Cordyceps종의 인공재배에 관한 연구가 활발하게 이루어지고 있다. 본 연구에서는 큰번데기 동충하초를 in vitro에서 인공재배한 결과 자실체 형성이 불안정한 것을 관찰하였기에 보고하고자 한다.

The structural system that discreterized from continuous shells is frequently used to make a large space structures. As well these structures show the unstable phenomena when a load level over the limit load, and snap-through and bifurcation are most well known of it. For the collapse mechanism, rise-span ratio, element stiffness and load mode are main factor, which it give an effect to unstable behavior. In our real situation, most structures have semi-rigid joint that has middle characteristic between pin and rigid joint. So the knowledge of semi-rigid joint is very important problem of stable large space structure. And the instability phenemena of framed space structures show a strong non-linearity and very sensitive behavior according to the joint rigidity For this reason In this study, we are investigating to unstable problem of framed structure with semi-rigidity and to grasp the nonlinear instability behavior that make the fundamental collapse mechanism of the large space frame structures with semi-rigid joint, by proposed the numerical analysis method. Using the incremental stiffness matrix in chapter 2, we study instability of space structures.

가상환경시스템은 매우 현실감 있는 정보를 제공할 수 있다는 점에서 산업, 의료, 교육훈련 등에 널리 사용되고 있다. 그러나 아직 많은 가상환경 시스템에서 부정적 요인으로 멀미, 시각피로, 방향감각 상실로 대표되는 cybersickness중세를 수반하고 있어 그 사용과 확산에 제약이 되고 있다. 이러한 cybersickness문제에 대응하기 위해서는 우선 이것을 객관적으로 측정, 평가할 수 있는 방법의 개발이 필요하다. 이러한 방법들 중의 하나로 신체동요의 정도를 평가 지표로 사용할 수 있다. 이번 연구에서는 45 명의 피실험자들을 대상으로 가상현실 운전시뮬레이터를 운전하기 전과 후의 신체동요 정도를 힘판(force platform)을 이용해 측정하였다. 특히 본 실험에 사용된 가상현실 운전시뮬레이터는 피실험자에게 운동판(motion platform)을 이용해 운동감을 제공할 수 있었고, 피실험자의 멀미 현상이 검지되면, 시야각을 1/3로 줄여주는 멀미 완화 피드백(feedback) 시스템이 연결되어 있었다. 그래서 motion의 제공여부와 feedback의 제공 여부도 실험의 독립변수로 추가하였다. 실험 결과, 가상현실 체험 후 유의한 차이는 아니나 피실험자들의 신체동요가 약간 증가하는 것이 관측되었다. motion과 feedback에 대한 분석에서는, 유일하게 motion을 제공하는 것이 제공 안할 때에 비해 좌우 방향의 신체동요가 더 적어지는 것으로 나타났다. 신체동요를cybersickness의 지표로 사용하기 위해서는 추후연구가 더 요청된다.

The structure system that is discreterized by continuous shells is usually used to make a large space structures and these structures show the collapse mechanisms that are captured at over the limit load, and snap-through and bifurcation are most well known of it. For the collapse mechanism, rise-span ratio, element stiffness and load mode are main factor, which it give an effect to unstable behavior. Moreover, resist force of structure can be reduced by initial condition and initial imperfection significantly. In order to investigate the instability of shell structures, the finite deformation theory can be applied and it becomes a nonlinear mathematics in which use equation of tangential stiffness incrementally. With an initial imperfection, using simple example and Flow Truss Dome, the buckling characteristics of space truss is main purpose of this paper, and unstable behavior is studied by proposed the numerical method. Also, by using MIDAS, this research work analyzes displacements and inner forces as the design load of model, and the ratio of buckling load of design load is investigated.

We have studied the nonlinear evolution of a magnetized disk of isothermal gas, which is sustained by its self-gravity. Our objective is to investigate how the Jeans, Parker, and convective instabilities compete with each other in structuring/de-structuring large scale condensations in such disk. The Poisson equation for the self-gravity has been solved with a fourth-order accurate Fourier method along with the Green function, and the MHD part has been handled by an isothermal TVD code. When large wavelength perturbations are applied, the combined action of the Jeans and Parker instabilities suppresses the development of the convection and forms a dense core of prolate shape in the mid-plane. Peripheral structures around it are filamentary. The low density filaments connect the dense core to the diffuse upper region. On the other hand, when small wavelength perturbations are applied, the disk develops into an equilibrium state which is reminiscent of the Mouschovias's 2-D non-linear equilibrium of the classical Parker instability under an externally given gravity.

As a companion to an adiabatic version developed by Ryu and his coworkers, we have built an isothermal magnetohydrodynamic code for astrophysical flows. It is suited for the dynamical simulations of flows where cooling timescale is much shorter than dynamical timescale, as well as for turbulence and dynamo simulations in which detailed energetics are unimportant. Since a simple isothermal equation of state substitutes the energy conservation equation, the numerical schemes for isothermal flows are simpler (no contact discontinuity) than those for adiabatic flows and the resulting code is faster. Tests for shock tubes and Alfven wave decay have shown that our isothermal code has not only a good shock capturing ability, but also numerical dissipation smaller than its adiabatic analogue. As a real astrophysical application of the code, we have simulated the nonlinear three-dimensional evolution of the Parker instability. A factor of two enhancement in vertical column density has been achieved at most, and the main structures formed are sheet-like and aligned with the mean field direction. We conclude that the Parker instability alone is not a viable formation mechanism of the giant molecular clouds.

The characteristics of structural behavior for a cable dome shows a strong nonlinearity and very sensitive by the initial imperfection. The instability phenomenon of Geiger-type cable dome structure is generated due to the in-plane twisting near the critical load level. In this study, therefore, the effect of bracing reinforcement resisting to the in-plane twisting is investigated for the Geiger-type model reinforced by bracing. The effect of initial imperfection is also studied because the structural instability phenomenon of shell-like structure is very sensitive according to the initial condition.

Many models of globular cluster formation assume the presence of cold dense clouds in early universe. Here we re-examine the Fall & Rees (1985) model for formation of proto-globular cluster clouds (PGCCs) via thermal instabilities in a protogalactic halo. We first argue, based on the previous study of two-dimensional numerical simulations of thermally unstable clouds in a stratified halo of galaxy clusters by Real et al. (1991), that under the protogalactic environments only nonlinear (δ≳1) density inhomogeneities can condense into PGCCs without being disrupted by the buoyancy-driven dynamical instabilities. We then carry out numerical simulations of the collapse of overdense douds in one-dimensional spherical geometry, including self-gravity and radiative cooling down to T = 10 4 K. Since imprinting of Jeans mass at 10 4 K is essential to this model, here we focus on the cases where external UV background radiation prevents the formation of H2 molecules and so prevent the cloud from cooling below 10 4 K. The quantitative results from these simulations can be summarized as follows: 1) Perturbations smaller than Mmin ~(10 5.6 M⊙)(nh/0.05cm-3)-2 cool isobarically, where nh is the unperturbed halo density, while perturbations larger than Mmax ~(10 8 M⊙)(nh/0.05 cm-3)-2 cool isochorically and thermal instabilities do not operate. On the other hand, intermediate size perturbations (Mmin < Mpgcc < Mmax) are compressed supersonically, accompanied by strong accretion shocks. 2) For supersonically collapsing clouds, the density compression factor after they cool to Tc = 10 4 K range 10 2.5 - 10 6, while the isobaric compression factor is only 10 2.5. 3) Isobarically collapsed clouds (M < Mmin) are too small to be gravitationally bound. For supersonically collapsing clouds, however, the Jeans mass can be reduced to as small as 10 5.5 M⊙(nh/0.05 cm-3)-1/2 at the maximum compression owing to the increased density compression. 4) The density profile of simulated PGCCs can be approximated by a constant core with a halo of p∝ r-2 rather than a singular isothermal sphere.