Earticle

대표적인 초고온용 복합재인 탄소-탄소 복합재(C/C복합재)는 우수한 내삭마성 및 고온에서의 강도를 바탕으로 함상용 유도무기의 발사 화염을 지지하는 함정 수직 발사대의 화염처리장치에 적용되고 있다. 이러한 C/C복합재는 화염처리장치 구조물에 고온용 접착제로 부착되어 있기 때문에 발사 화염 온도의 전달을 통한 접착면의 고온부가 및 박리 위험성 방지를 위한 저열전도도 구현이 필수적이다. 본 연구에서는 C/C 복합재 내 탄소 기재의 밀도 구배를 통해 저 열전도도를 구현하고, 성능을 분석하였다. 밀도 구배는 CVI(Chemical Vapor Infiltration)공정 시 온도의 구배를 통하여 구현되었으며, 밀도 구배와 열전도도의 상관성에 대하여 분석하였다. 본 연구를 통해 제안되는 밀도 구배 C/C 복합재는 저 열전도도를 통해 발사대 화염처리장치와 같이 고온용 접착제를 통해 구조물에 부착, 고온 환경에 노출되는 여러 분야에 응용 가능 할 것으로 예상된다.

Carbon material has been highlighted in broad research area in wide size-spectrum, such as nano-sized graphene for next generation opto-electrical device, carbon nanotube for advanced flexible device, and meter-sized cabron composite for new platform for high-performance automobile. Expecially, extraordinary physical properties of carbon based composites make it possible candidate as anti-ablative material in various thermal protection system in aero, space, and defense industry. For instance, carbon-carbon composite(C/C) with high density has been highlighted for its superior anti-ablative properties in extreme conditions and applied in gas management system(GMS) in vertical launcher system(VLS). However, high thermal conductivity of C/C composites from pyrolytic carbon structure, which has negative effect on the limitation of adhesive's working temperature, makes it difficult to apply on steel structure with even high-temperature adhesive. In this study, the density gradient in C/C was made by temperature-gradient during chemical vapour infiltration (CVI) process for lowering thermal conductivity (k) with sustaining its superior anti-ablative properties. The thermal gradient during CVI process consists gradient on crystallization reaction velocity and produces density gradient in intrinsic C/C composite, as scanning electron microstope(SEM) measurement has confirmed. Moreover, from the thermal conductivity (k) measurement, the lower thermal conductivity of density-gradient C/C than normal high-density homogeneous C/C also has been confirmed. This study suggests density gradient C/C with low thermal conductivity as possible candidate for wide application in anti-ablation applications.

커들란은 용액의 pH 7.0에서 salt 상태로 존재하기 때문에 커들란만이 액상에 녹아있는 경우에는 분리공정은 원심분리를 함으로써 분리가 가능하다. 그러나, 세포외 다당류로 생산된 커들란은 세포, 염 등의 무기물이 섞여 있기 때문에 이러한 물질을 제거하는 것이 커들란 분리의 중요한 변수가 되었다. 커들란의 생산을 위한 분리에 관한 보고는 원심분리 방법을 이용한 것으로 알려져 있으며 세포 및 불순물 등을 제거하여 순수한 커들란을 분리하기 위해 pH swing separation(pH가 높은 경우 커들란이 용액에 녹는 성질을 이용)을 이용하였으나 원심분리를 수 차례 반복해야 되기 때문에 소요되는 동력이 많이 필요하여 에너지 절감형 및 오염절감형의 새로운 공정의 개발이 필요하게 되었다. 본 연구에서는 pH swing separation에서 동력비가 많이 드는 단점을 감소시키기위하여 커들란의 물리 화학적인 특성을 고려한 분리공정을 개발하였다. 향후 공정 개선을 위한 지속적인 연구가 필요하며 완성시 경제적인 공정을 개발하는 것이 가능할 것이다.

Curdlan is one of biopolymer composed of β-1,3-glucan and dissolved in a alkali solution but formed salt under neutral or acid condition. It was produced by Agrobacterium species and the separation process is necessary to make pure curdlan from the culture broth. The pH swing separation method was a feasible separation process using solubility changes with the pH difference. however, this method requires a lot of acid and alkali solution also produces a lot of waste. Therefore, an efficient process which could save energy and minimize toxic waste was developed. A density gradient separation process was developed in this research. High density sucrose solution was used as a separation agent. Curdlan was separated from the culture broth when the density of the sucrose solution was 1.15 g/L. Since the curdlan was produced on the surface of cell wall, the pre-treatment of culture broth was necessary. Curdlan recovery yield was increased up to 83% with the homogenization of the culture broth and further increased up to 87% with the treatment of alkali-acid solution.

이산화탄소를 용매로하는 초임계유체 크로마토그래퍼(SFC)방법을 이용하여 어유로부터 EPA및 DHA를 고순도로 분리정제하는 연구를 하였다. 질산은 칼럼을 이용하는 초임계 이산화탄소의 초기 압력조건 변화가 저 지방산의 용해도 및 분리도에 미치는 영향을 조사하였는데 압력이 증가될수록 저지방산의 용해도는 증가되었고, 반면에 EPA와의 분리도는 감소하는 경향을 나타내었다. EPA의 분리정제 효율을 높이기 위해 초임계 이산화탄소에 대한 단계별 밀도구매 방법을 적용하였다. 적용 결과 초기에 저지방산이 먼저 분리되었고, 계속해서 92.1%~97.8%EPA 순도를 갖는 분획들을 얻을 수 있었다. 순도가 높은 3개의 분획의 평균 순도는 95.6%이었고 회수율은 30%에 달하였다

SupercriticaCO2 chromatography was applied for purification of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from fish oil. Various supercritical CO2 pressures were tested to find out the pressure effects on solubility and selectivity of low fatty acids in the silver nitrate column. The solubility of low fatty acids was increased as the supercntical CO2 Pressure increased. However, the selectiviy between low fatty acids and EPA waw decreased. Stepwise density gradient method was applied to increase the purification efficiency of EPA. Low fatty acids were easily separated at the early elution steps with low CO2 densities. Successive fractions containing 92.1~97.8% of EPA were collected. The average concentration of three purified fractions was 95.6% with the recovery rate of 30%.

이 논문에서는 서울, 부산, 대전, 대구, 광주의 5대 대도시를 분석대상으로 하여 도시별로 인구밀도 경사도 (Population Density Gradient)를 추정하였다. 기본적으로 우리나라 대도시의 인구밀도 경사도와 도심지역의 인구는 시간이 지남에 따라 감소하는 경향이 나타나고 있으며, 이는 교외화(Suburbanization)가 지속적으로 이루어지고 있음을 의미한다. 또한 더 나아가 도시의 어떤 특성들이 이러한 도심지역 인구 비율 감소에 영향을 주었는지를 1995년 우리나라 73개 도시의 동별 자료를 이용하여 분석하였다. 분석결과, 도시 거주자의 교육수준이 높을수록 그리고 재정자립도가 높거나 인구성장률이 높은 도시일수록 도심의 인구비율이 낮은, 즉 인구의 교외화가 발생한 것으로 분석되었다. 추가적으로 전철이나 지하철과 같은 교통시설이 잘 되어 있는 도시 일수록 그리고 금융보험업과 부동산 임대업 같은 정보 중심의 산업이 해당 도시의 핵심 산업인 도시는 도시발달 단계가 높은 도시로서 이들 도시에서는 도심의 거주 기능이 상실하는 도심공동화 현상이 발생하는 것으로 나타났다. 이러한 도심인구 비율 감소의 요인분석을 근거로 하여 도심공동화 현상을 해소하기 위한 시정부의 정책방안을 검토하였다. 도심공동화 현상에 대처하기 위해서는 도심의 주거기능 확보가 필요하며 이를 위해서는 도심의 주거지역을 조사하여 지역유형별로 파악할 필요가 있다. 주거기능과 상업기능이 혼재하여 주거지역으로서의 쾌적성을 상실한 지역과 주거기능이 비교적 잘 유지된 지역 등을 선별하여 다른 용도로의 전환을 억제할 수 있는 조치를 강구할 필요가 있다. 또한 인구 교외화는 높은 기동성을 가지면서 환경의 질을 중시하는 중간 소득계층을 중심으로 이루어지고 있다. 따라서 이러한 중간 소득계층에게 적합한 평형 및 설계를 통해 다양한 가격대의 주택을 공급함과 동시에 도심 정부는 도심의 주거환경과 생활 여건을 쾌적하게 유지할 수 있도록 무분별한 난개발을 억제하고 공원과 녹지공간의 확보를 위해 노력해야 할 것이다. 최근 이러한 구도심 활성화를 위한 노력의 일환으로 ‘도시재생’(산업구조의 변화나 신도시 위주의 도시 확장으로 상대적으로 낙후된 기존 도시에 새로운 기능을 도입)사업이 추진되고 있다. 이러한 정책은 국가적 차원에서도 필요하지만 근본적으로 지방자치단체와 민간이 함께 참여하여 추진하는 민관합동 대책이 동시에 추진될 때 더 큰 시너지 효과를 구현할 수 있을 것이다.

We estimated population density gradients for five major cities of Korea, namely, Seoul, Pusan, Daejeon, Taegu and Gwangju to explain changes in the internal spatial structure of cities. Basically, population density gradients of large cities in Korea and population in the city center areas tend to decline over the time, which indicates the suburbanization is continuously taking place. Furthermore, we have analyzed the effects of basic characteristics of a city on the size of population in central areas of the city. Higher education level of residents, high level of financial independence, high level of population growth rate, and high ratio of automobile users caused suburbanization reducing population in the city center. Additionally, cities with good subway and other public transportation facilities, and cities with active information processing sectors where the finance, security and real estate industry becomes a core industry are considered to be cities with high level of urban development. In such cities, the phenomenon of city center doughnut hole in which residential function is eradicated from the city center takes place. In order to avoid a rapid decrease of city center’s population, the city center must maintain residential functions. To achieve this goal, it is essential to investigate the dynamics of the residential areas in a city in depth and to acquire a full understanding of the factors causing the differences in city center's population shares among various cities.

목적: 본 논문은 임신부의 혈액 내 태아유핵적혈구를 임신 초기와 임신중기 중 언제 더 많이 얻을 수 있는지에 관하여 연구하고자 하였다. 연구 방법: 임신 초기와 중기의 임신부의 혈액 10 mL으로부터 유핵적혈구를 다른 삼투압을 이용한 double percoll gradient방법을 이용하여 분리하였으며 Magnetic activated cell sorting방법과 Kleihauer-Betke 염색 및 Fluorescence In Situ Hybridization (FISH)를 이용하여 태아의 성과 염색체 이수성을 진단하였다. 결과: 임신 초기에 얻은 유핵 적혈구의 수는 9.88이었고 임신중기에 얻은 유핵적혈구는 14.88이었으며 이들간에는 통계적인 유의성이 없었다 (P=0.07). 임신 초기에 얻은 Y염색체를 가진 유핵적혈구의 수는 5.73이었고 임신 중기에 얻은 Y염색체를 가진 유핵적혈구의 수는 8.22로 역시 두 군간에 유의한 차이가 없었다 (P=0.56). 그러나 임신 초기에 Y염색체를 가진 유핵 적혈구의 퍼센트는 임신중기의 경우보다 유의하게 높았다 (P=0.049). 이 방법을 이용하여 태아 이수성을 가진 7명의 임신부에게서 얻은 혈액으로부터 얻은 유핵적혈구는 18.4개였다. 결론: 따라서 퍼콜의 삼투압과 double gradient method는 임신 초기와 중기 모두에서 유핵 적혈구를 분리하는데 매우 유용한 방법으로 생각된다.

Objective: The aim of our study was to make a practical comparative evaluation of the first and second trimesters in order to determine the period during which a higher yield of fetal nucleated red blood cells (FNRBCs) can be obtained. Methods: NRBCs were isolated from maternal blood during the first and second trimesters of pregnancy using double Percoll gradients with different osmolarities. Magnetic activated cell sorting was performed with Kleihauer-Betke stain. We isolated fetal NRBCs from 10 mL of samples of maternal blood and determined fetal sex and fetal aneuploidy by fluorescence in situ hybridization (FISH). Results: The average number of NRBCs was 9.85 in samples obtained during the first trimester and 14.88 in samples obtained during the second trimester (P=0.07). The average number of NRBCs with Y chromosome signals was 5.73 in the first trimester and 8.22 in second trimester (P=0.56). However, the percentage of NRBCs with Y chromosome signals in the first trimester (70.6%) was significantly higher than in the second trimester (59.8%) (P=0.049). We diagnosed the blood samples from 7 pregnant women having fetal aneuploidy using this method and the number of NRBCs was 18.4. Conclusion: The method using Percoll osmolarity and a double density gradient system may be a very useful method for separation of NRBCs in the first trimester of pregnancy and also in the second trimester.

In order to obtain high proportion of Y sperm the semen was laid over 6%,10% and 20% bovine serum albumin. Separated sperm were stained with quinacrine mustard in order to see F - body which could be seen in human Y sperm. But we could'nt find F-body in the bull sperm. So sperm were compared with size of sperm head. As a result of observation separated sperm was small in size of length and width of sperm head as compared with control sperm. So it was found that the proportion of Y sperm showed a marked increase in separated layer. Then the higher albumin density was, the higher the proportion of Y sperm which had smaller head and faster motility was. But the higher albumin density was, the lower the recovery rate of sperm was. So it was hard to separate Y sperm in oligospermia.

Formation of a steep plasma density gradient in the middle-latitude ionosphere during geomagnetic storms and the latitudinal migration of its location depending on the storm phase are suggested to be associated with the ionospheric signature of the plasmapause. We test this idea by using the satellite and ground observation data during the 11 April 2001 storm. The locations of the steep plasma density gradient identified by TOPEX/Poseidon (2001 LT) and DMSP (1800 and 2130 LT) satellites coincide with the ionospheric footprints of the plasmapause identified by the IMAGE satellite. This observation may support the dependence of the middle-latitude plasma density gradient location on the plasmapause motion, but does not explain why the steep density gradient whose morphology is largely different from the morphology of the middle-latitude ionization trough during quiet period is formed in association with the plasmapause. The ionospheric disturbances in the total electron content (TEC) maps shows that the steep TEC gradient is formed at the boundary of the positive ionospheric storm in low-middle latitudes and the negative ionospheric storm in middle-high latitudes. We interpret that the thermospheric neutral composition disturbance in the dayside is confined within the middle-high latitude ionospheric convection zone. The neutral composition latitudes and, therefore, the locations of the steep plasma density gradient coincide with the footprints of the plasmapause. The TEC maps show that the appearance of the steep plasma density gradient in the pre-midnight sector during the recovery phase is related to the co-rotation of the gradient that is created during the main phase.

ObjectiveTo compare the degree of efficiency between density gradient centrifugation (DGC) method and an extended horizontal swim-up (SU) method. MethodsA total of 97 couples undergoing in vitro fertilization were enrolled in the study. Semen samples were divided into three aliquots and treated using DGC, extended horizontal SU, and combined methods. DNA fragmentation and chromatin decondensation were detected in native semen samples and their three corresponding aliquots. The corresponding mature oocytes of each semen sample were divided into two sibling cultures. The first sibling culture was microinjected with semen pellets from DGC, and the second sibling culture was microinjected with semen pellets from the combination of both methods. Fertilization rate and embryonic development were assessed at day 3. ResultsDNA fragmentation and chromatin decondensation was significantly low in DGC and extended horizontal SU samples; however, the rates of DNA fragmentation and chromatin decondensation were significantly lower in extended horizontal SU samples than in DGC samples. The lowest rates of DNA fragmentation and chromatin decondensation corresponded to the samples treated with both methods. The highest rates of DNA fragmentation and chromatin decondensation corresponded to the samples treated with DGC. No significant difference was found in the fertilization rate or day 3 embryos between sibling cultures. ConclusionThe combination of DGC and the extended horizontal SU techniques is best for giving the lowest rates of sperm DNA fragmentation and chromatin decondensation.

This study presents new carbon-carbon (C/C) composite that has a density gradient within single material, and estimates its heat conduction performance by a numerical method. To address the high heat conduction of a high-density C/C, which can cause adhesion separation in the steel structures of vertical launching systems, density gradient carbon-carbon (DGCC) composite is proposed due to its exhibiting low thermal conductivity as well as excellent ablative resistance. DGCC is manufactured by hybridizing two different carbonization processes into a single carbon preform. One part exhibits a low density using phenolic resin carbonization to reduce heat conduction, and the other exhibits a high density using thermal gradient-chemical vapor infiltration for excellent ablative resistance. Numerical analysis for DGCC is performed with a heat conduction problem, and internal temperature distributions are estimated by the forward finite difference method. Material properties of the transition density layer, which is inevitably formed during DGCC manufacturing, are assumed to a combination of two density layers for numerical analysis. By comparing numerical results with experimental data, we validate that DGCC exhibits a low thermal conductivity, and it can serve as highly effective ablative material for vertical launching systems.

The propagation of an intense laser pulse through an upward density-gradient plasma in a self-modulated laser wakefield acceleration (SM-LWFA) is investigated by using particle-in-cell (PIC) simulations. In the fully relativistic and kinetic PIC simulations, the relativistic and kinetic effects including Landau damping enhance the electron dephasing. This electron dephasing is the most important factor for limiting the energy of accelerated electrons. However, the electron dephasing, which is enhanced by relativistic and kinetic effects in the homogeneous plasma, can be forestalled through the detuning process arising from the longitudinal density gradient. Simulation results show that the detuning process can effectively maintain the coherence of the laser wake wave in the spatiotemporal wakefield pattern, hence considerable energy enhancement is achievable. The spatiotemporal profiles are analyzed for the detailed study on the relativistic and kinetic effects. In this paper, the optimum slope of the density gradient for increasing electron energy is presented for various laser intensities.

This study was carried out to evaluate the possibility of sex preselection by gradients methods using bovine serum albumin in rabbits. Artificial insemination was performed with sperm from the top and bottom layer of rabbit semen separated by bovine serum albumin gradients. Various characteristics of separated sperm, and the conception rate and secondary sex ratio at artificial insemination with separated sperm were compared. The results obtained were as follows. 1. The sperm from the bottom layer showed significanty high value in motility, percent of normal sperm and progressive motility as compared with control sperm and the sperm and the sperm from the top layer. 2. The conception rate of sperm from the bottom layer was higher than that of the top layer. But secondary sex ratio was not altered by this methods.

The dielectrophoretic technique was used to prepare density gradient polymers, polystyrene doped with a dipolar modifier, diphenyl sulfide. We have measured concentration gradients of the dopant by UV/Nis spectroscopy as a function of time in a nonuniform electric field. Measured concentration data at different positions of the sample confirmed that a concentration gradient arose after a nonuniform electric field was applied to the system, these data were used to compare the concentration profile with that predicted by the dielectrophoresis equation.

Objective: The aim of this study was to compare the efficacy of swim-up and density gradient centrifugation (DGC) for reducing the amount of sperm with fragmented DNA, sex chromosome aneuploidy, and abnormal chromatin structure. Methods: Semen samples were obtained from 18 healthy male partners who attended infertility clinics for infertility investigations and were processed with swim-up and DGC. The percentages of sperm cells with fragmented DNA measured by the sperm chromatin dispersion test, normal sex chromosomes assessed by fluorescence in situ hybridization, and abnormal chromatin structure identified by toluidine blue staining were examined. Results: The percentage of sperm cells with fragmented DNA was significantly lower in the swim-up fraction (9.7%, p= 0.001) than in the unprocessed fraction (27.0%), but not in the DGC fraction (27.8%, p= 0.098). The percentage of sperm cells with normal X or Y chromosomes was comparable in the three fractions. The percentage of sperm cells with abnormal chromatin structure significantly decreased after DGC (from 15.7% to 10.3%, p= 0.002). The swim-up method also tended to reduce the percentage of sperm cells with abnormal chromatin structure, but the difference was not significant (from 15.7% to 11.6%, p= 0.316). Conclusion: The swim-up method is superior for enriching genetically competent sperm.

The active fraction of soil organic matter, which includes organic debris and light organic fraction, plays a major role in nutrient cycling. In addition, particulate organic matter is a valuable index of labile soil organic matter and can reflect differences in various soil behaviors. Since soil organic matter bound to soil mineral particles has its density lower than soil minerals, we partitioned soil organic matter into debris ($<1.5g\;cm^{-3}$), light fraction ($1.5-2.0g\;cm^{-3}$), and heavy fraction ($>2.0g\;cm^{-3}$), based on high density $ZnCl_{2-}$ sucrose solutions. Generally, partitioned organic bands were clearly separated, demonstrating that the $ZnCl_{2-}$ sucrose solutions are useful for such a density gradient centrifugation. The available gradient ranges from 1.2 to $2.0g\;cm^{-3}$. Although there was not a statistically meaningful difference in organic debris and organomineral fractions among the examined soils, there was a general trend that a higher content of organic debris resulted in a higher proportion of light organomineral fraction. In addition, high clay content was associated with increased fraction of light organomineals. Partitioning of soil organic carbon revealed that carbon content is reduced in the heavy fraction than in the light fraction, reflecting that the light fraction contains more fresh and abundant carbon than the passive resistant fraction. It was also found that carbon contents in the overall organic matter, debris, light fraction, and heavy fractions may differ considerably in response to different farming practices.

Objective: Density gradient centrifugation (DGC) is frequently used to isolate high-motility fractions of spermatozoa. We compared the efficacy of four DGC media in terms of the percentage of morphologically normal spermatozoa, DNA fragmentation level, and hyaluronic acid (HA) binding ability. Methods: Thirty men with a total motile spermatozoa count > 80 million participated. Semen samples were divided into four aliquots, which were processed using PureSperm, PureCeption, Sidney, and SpermGrad media, respectively. The DNA fragmentation level was measured using the Halosperm assay kit and HA binding ability was measured using the HBA assay kit. Results: The mean percentage of morphologically normal spermatozoa was significantly enhanced after DGC using all four media (10.3%, 9.9%, 9.8%, and 10.7%, respectively; p< 0.05 for each when compared with 6.9% in raw semen). The DNA fragmentation level was significantly reduced after DGC using PureSperm, PureCeption, and SpermGrad media (6.0%, 6.5%, and 4.9%, respectively; p< 0.05 for each when compared with 11.2% in raw semen), but not after DGC using Sidney media (8.5%, p> 0.05). HA binding ability did not change after DGC using any of the four media. Conclusion: The four media were equally effective for obtaining a sperm fraction with highly motile, morphologically normal sperm. PureSperm, PureCeption, and SpermGrad media were equally effective for acquiring a sperm fraction with less DNA fragmentation.

All-solid-state batteries are promising energy storage devices in which high-energy-density and superior safety can be obtained by efficient cell design and the use of nonflammable solid electrolytes, respectively. This paper presents a systematic study of experimental factors that affect the electrochemical performance of all-solid-state batteries. The morphological changes in composite electrodes fabricated using different mixing speeds are carefully observed, and the corresponding electrochemical performances are evaluated in symmetric cell and half-cell configurations. We also investigate the effect of the composite electrode thickness at different charge/discharge rates for the realization of all-solid-state batteries with high-energy-density. The results of this investigation confirm a consistent relationship between the cell capacity and the ionic resistance within the composite electrodes. Finally, a concentration-gradient composite electrode design is presented for enhanced power density in thick composite electrodes; it provides a promising route to improving the cell performance simply by composite electrode design.