• Applied Chemistry for Engineering
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• v.10 no.2
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• pp.268-274
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• 1999

The chitosan solution was prepared by dissolving chitosan into 2 wt % aqueous acetic acid solution and then chitosan beads were made by sol-gel method. The average molecular weight and the degree of deacetylation of the chitosan used here were determined to be $8.2{\times}10^5$ and 85%, respectively. chitosan beads were highly porous which was confirmed by SEM photography and BET. Adsorption equilibrium of $Cu^{2+}$ on porous chitosan beads could be represented by Sips equation. The diffusion of cupric ions in the chitosan beads could be explained by pore and surface diffusion mechanisms. Adsorption dynamics of $Cu^{2+}$ in fixed-bed could be simulated by linear driving force approximation (LDFA). It was proven that porous chitosan beads manufactured in this work are good adsorbents for the removal of $Cu^{2+}$.

• Molecules and Cells
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• v.25 no.3
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• pp.385-389
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• 2008

Septins are a family of filament-forming GTP-binding proteins involved in a variety of cellular process such as cytokinesis, exocytosis, and membrane dynamics. Here we report the biochemical and immunocytochemical characterization of a recently identified mammalian septin, SEPT12. SEPT12 binds GTP in vitro, and a mutation (Gly56 to Asn) in the GTP-binding motif abolished binding. Immunocytochemical analysis revealed that wild-type SEPT12 formed filamentous structures when transiently expressed in Hela cells whereas $SEPT12^{G56A}$ generated large aggregates. In addition, wild-type SEPT12 failed to form filaments when coexpressed with $SEPT12^{G56A}$. We also observed that GTP-binding by SEPT12 is required for interaction with SEPT11 but not with itself.

• Journal of Microbiology and Biotechnology
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• v.22 no.6
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• pp.754-762
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• 2012

Colbricon Superiore and Inferiore are two small adjacent high-mountain lakes located in the Paneveggio Natural Park (Italy) that offer the rare opportunity to study two iso-ecologic water environments differing only by area and volume in a ratio of 2:1 and 3:1, respectively. We took advantage of this setting to investigate phytoplankton dynamics, compare variability and productivity differences between the two basins, and assess size-dependent issues. The phytoplankton group of the Dinophyceae was chosen as the indicator organisms of ecological perturbation owing to their high sensitivity to environmental variations, as well as their acknowledged nature of versatile proxy to report global climatic changes. The study was conducted for over 10 years with fortnightly samplings. Results indicated that (a) the Dinophyceae communities in the smaller lake were significantly more resistant to changes exerted by the fluctuation of lakewater transparency and pH; and (b) the smaller lake sustained a consistently higher production with an average Dinophyceae density 1.73 fold higher than that of the larger lake. The coefficients of variation show that the chemical parameters in the smaller lake display higher time-related fluctuation while being spatially homogeneous and that such conditions correlate with a higher stability of the Dinophyceae assemblage. The use of this setting is also proposed as a model to test relationships between ecosystem production and physical stability.

• Journal of the Korean Ceramic Society
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• v.54 no.6
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• pp.506-510
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• 2017

One of the characteristics of polycrystalline graphene that determines its material properties is grain size. Mechanical properties such as Young's modulus, yield strain and tensile strength depend on the grain size and show a reverse Hall-Petch effect at small grain size limit for some properties under certain conditions. While there is agreement on the grain size effect for Young's modulus and yield strain, certain MD simulations have led to disagreement for tensile strength. Song et al. showed a decreasing behavior for tensile strength, that is, a pseudo Hall-Petch effect for the small grain size domain up to 5 nm. On the other hand, Sha et al. showed an increasing behavior, a reverse Hall-Petch effect, for grain size domain up to 10 nm. Mortazavi et al. also showed results similar to those of Sha et al. We suspect that the main difference of these two inconsistent results is due to the different modeling. The modeling of polycrystalline graphene with regular size and (hexagonal) shape shows the pseudo Hall-Petch effect, while the modeling with random size and shape shows the reverse Hall-Petch effect. Therefore, this study is conducted to confirm that different modeling is the main reason for the different behavior of tensile strength of the polycrystalline structures. We conducted MD simulations with models derived from the Voronoi tessellation for two types of grain size distributions. One type is grains of relatively similar sizes; the other is grains of random sizes. We found that the pseudo Hall-Petch effect and the reverse Hall-Petch effect of tensile strength were consistently shown for the two different models. We suspect that this result comes from the different crack paths, which are related to the grain patterns in the models.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.6
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• pp.577-582
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• 2016

In this study, a multiscale method for solving a thermoelasticity problem for interphase in the polymeric nanocomposites is developed. Molecular dynamics simulation and finite element analysis were numerically combined to describe the geometrical boundaries and the local mechanical response of the interfacial region where the polymer networks were highly interacted with the nanoparticle surface. Also, the micrmechanical thermoelasticity equations were applied to the obtained equivalent continuum unit to compute the growth of interphase thickness according to the size of nanoparticles, as well as the thermal phase transition behavior at a wide range of temperatures. Accordingly, the equivalent continuum model obtained from the multiscale analysis provides a meaningful description of the thermoelastic behavior of interphase as well as its nanoparticle size effect on thermoelasticity at both below and above the glass transition temperature.

• BMB Reports
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• v.48 no.10
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• pp.583-588
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• 2015

Microtubule actin crosslinking factor 1 (MACF1), a widely expressed cytoskeletal linker, plays important roles in various cells by regulating cytoskeleton dynamics. However, its role in osteoblastic cells is not well understood. Based on our previous findings that the association of MACF1 with F-actin and microtubules in osteoblast-like cells was altered under magnetic force conditions, here, by adopting a stable MACF1-knockdown MC3T3-E1 osteoblastic cell line, we found that MACF1 knockdown induced large cells with a binuclear/multinuclear structure. Further, immunofluorescence staining showed disorganization of F-actin and microtubules in MACF1-knockdown cells. Cell counting revealed significant decrease of cell proliferation and cell cycle analysis showed an S phase cell cycle arrest in MACF1-knockdown cells. Moreover and interestingly, MACF1 knockdown showed a potential effect on cellular MTT reduction activity and mitochondrial content, suggesting an impact on cellular metabolic activity. These results together indicate an important role of MACF1 in regulating osteoblastic cell morphology and function.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.4
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• pp.301-305
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• 2012

In this work the mechanical behaviors of GaN nanowires are analyzed during tension, compression, and unloading deformations. The thermal conductivity of the nanowires at each deformed state is evaluated using an equilibrium Green-Kubo approach. Under tensile loading, the [0001]-oriented nanowires with hexagonal cross-sections undergo a phase transformation from wurtzite to a tetragonal structure. The phase transformation is not observed under compressive loading. The thermal conductivity decreases on going from compressive strains to tensile strains. The strain dependence of the thermal conductivity results from the relaxation time of phonon. A reverse transformation from the tetragonal structure to the wurtzite structure is observed during unloading. The thermal conductivities in the intermediate states are lower than the conductivity in the wurtzite structure at same strain. Such differences in the thermal conductivity between different atomic structures are mainly due to changes in the group velocity of phonon.

• Journal of the Korea Society of Computer and Information
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• v.15 no.12
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• pp.175-180
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• 2010

In this paper, we have investigated ultrahigh frequency nano-mechanical resonators, made of DWCNTs with various wall lengths, via classical molecular dynamics simulations. We have aimed our analysis on the frequency variations of these resonators with the DWCNT wall lengths. The results show that the variations can be well fitted by either the Pearson VII function when the resonant frequency of normalized by its maximum frequency is plotted as a function of the inner/outer wall length ratio L5/L10 for different values of the outer wall length L10, and the Gauss distribution function when the resonant frequency of normalized by its maximum frequency is plotted as a function of the outer/inner wall length ratio for different values of the inner wall length.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.168-168
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• 2000

Yamada 등의 덩어리 증착에 관한 연구 이후 낮은 기판 온도에서 결정성이 뛰어난 금속박막성장(thin film growth)을 얻을 수 있는 방법으로 최근 덩어리 증착(cluster depositon) 방법에 관하여 많은 연구들이 진행되어 덩어리 충돌이 원자 충돌인 경우와 큰 차이를 보이는 결과를 얻었으며, 덩어리 증착시 기판 내부에 점결함(point defect)이 발생되지 않는다는 중요한 결과를 얻었다. 금속 덩어리를 사용한 금속박막성장은 높은 박막성장속도와 뛰어난 구조 재배열 효과를 얻을 수 있으며 기판의 격자 손상을 감소시키기 때문에 향후 나노미터 소자 개발에 응용성이 클 것으로 예상된다. 그러나 금속 덩어리와 금속 표면사이의 상호작용에서 발생되는 기본적인 역학(mechanism)은 분명하게 알려져 있지 않다. 지금까지 알루미늄 덩어리의 원자구조와 특성에 관한 연구는 수행되어졌지만 (4,5), 알루미늄 덩어리 증착에 관한 연구는 수행되지 않았다. 본 연구에서는 13~177개로 이루어진 큰 알루미늄 덩어리들의 증착에 관하여 Md(molecular dynamics) 방법을 사용하여 연구하였다. MD 시뮬레이션을 사용하여 덩어리 증착시 기판 표면과의 충돌 초기에 나타나는 덩어리 내부 원자들의 상관충돌효과(correlated collisions effect)에 의하여 덩어리 크기에 따른 증착현상과 여러 물리적 현상들을 관찰하였다. 덩어리 총 에너지가 증가할수록 기판의 최고 온도는 증가하며, 덩어리 크기가 클수록 상관충돌효과가 커지기 때문에 덩어리의 총 에너지에 다른 최고 증가 비율은 적어졌다. 시간에 따른 비정렬 원자수(disordered atom number) 비교를 통하여 덩어리가 클수록 구조 재배열이 더 잘 이루어진다는 것을 알 수 있었고, 원자당 에너지가 클수록 덩어리 원자들이 기판 내부로 더 깊이 들어갔고, 덩어리 크기가 클수록 상관충돌효과로 인하여 덩어리 원자들이 기판 내부로 더 깊이 들어가는 것을 알 수 있었고, 덩어리 크기가 클수록 상관충돌효과는 커지고 더욱 부드러운 증착이 이루어졌으며, 무엇보다도 덩어리 증착시 표면에서 구조 재배열이 잘 이루어지는 특징을 살펴볼 수 있었다. 이러한 알루미늄 덩어리를 생성하여 증착할 수 있을 경우, 뛰어난 재배열 효과를 이용하여 품질이 향상된 반도체 소자를 제조할 수 있을 것으로 사료된다.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.358-358
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• 2010

Ion beam bombardment at low energy forms nanosize patterns such as ripples, dots or wrinkles on the surface of polymers in ambient temperature and pressure. It has been known that the ion beam can alter the polymer surface that induces skins stiffer or the density higher by higher compressive stress or strain energies associated with chain scissions and crosslinks of the polymer. Atomic scale structure evolution in polymers is essential to understand a stress generation mechanism during the ion beam bombardment, which governs the nanoscale surface structure evolution. In this work, Molecular Dynamics (MD) simulations are employed to characterize the phenomenon occurred in bombardment between the ion beam and polymers that forms nanosize patterns. We investigate the structure evolution of Low Density Polyethylene (LDPE) at 300 K as the polymer is bombarded with Argon ions having various kinetic energies ranging from 100 eV to 1 KeV with 50 eV intervals having the fluence of $1.45\;{\times}\;1014 #/cm2$. These simulations use the Reactive Force Field (ReaxFF), which can mimic chemical covalent bonds and includes van der Waals potentials for describing the intermolecular interactions. The results show the details of the structural evolution of LDPE by the low energy Ar ion bombardment. Analyses through kinetic and potential energy, number of crosslinks and chain scissions, level of local densification and motions of atoms support that the residual strain energies on the surface is strongly associated with the number of crosslinks or scissored chains. Also, we could find an optimal Ar ion beam energy to make crosslinks well.