• 한국발생생물학회지:발생과생식
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• 제21권1호
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• pp.1-10
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• 2017

The use of human mesenchymal stem cells (hMSCs) in cell-based therapy has attracted extensive interest in the field of regenerative medicine, and it shows applications to numerous incurable diseases. hMSCs show several superior properties for therapeutic use compared to other types of stem cells. Different cell types are discussed in terms of their advantages and disadvantages, with focus on the characteristics of hMSCs. hMSCs can proliferate readily and produce differentiated cells that can substitute for the targeted affected tissue. To maximize the therapeutic effects of hMSCs, a substantial number of these cells are essential, requiring extensive ex vivo cell expansion. However, hMSCs have a limited lifespan in an in vitro culture condition. The senescence of hMSCs is a double-edged sword from the viewpoint of clinical applications. Although their limited cell proliferation potency protects them from malignant transformation after transplantation, senescence can alter various cell functions including proliferation, differentiation, and migration, that are essential for their therapeutic efficacy. Numerous trials to overcome the limited lifespan of mesenchymal stem cells are discussed.

• Archives of Plastic Surgery
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• 제39권6호
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• pp.585-592
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• 2012

During the past decade, many studies using platelet-rich plasma (PRP) or adipose-derived stem cells (ASCs) have been conducted in various medical fields, from cardiovascular research to applications for corneal diseases. Nonetheless, there are several limitations of practical applications of PRP and ASCs. Most reports of PRP are anecdotal and few include controls to determine the specific role of PRP. There is little consensus regarding PRP production and characterization. Some have reported the development of an antibody to bovine thrombin, which was the initiator of platelet activation. In the case of ASCs, good manufacturing practices are needed for the production of clinical-grade human stem cells, and in vitro expansion of ASCs requires approval of the Korea Food and Drug Administration, such that considerable expense and time are required. Additionally, some have reported that ASCs could have a potential risk of transformation to malignant cells. Therefore, the authors tried to investigate the latest research on the efficacy and safety of PRP and ASCs and report on the current state and regulation of these stem cell-based therapies.

• 한국세라믹학회지
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• 제48권2호
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• pp.152-159
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• 2011

The green and hard machining characteristics of dental ceramics are of great interest to dental industry. The green bodies of TZP/$Al_2O_3$ composites were prepared by the cold isostatic pressing, and machined on the CNC lathe using PCD (polycrystalline diamond) insert under various machining conditions. With increasing nose radius of PCD insert, surface roughness initially increased due to increased cutting resistance, but decreased by the onset of sliding fracture. The lowest surface roughness was obtained at spindle speed of 1,300 rpm and lowest feed rate. Hard bodies were prepared by pressureless sintering the machined green bodies at several temperatures. The grinding test for sintered hard body was conducted using electroplated diamond bur with different grit sizes. During grinding, grain pull out in the composite was occurred due to thermal expansion mismatch between the alumina and zirconia. The strength of the composite decreased with alumina contents, due to increased surface roughness and high monoclinic phase transformed during grinding process. The final polished samples represented high strength by the elimination of a phase transformation layer.

• 한국자동차공학회논문집
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• 제18권2호
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• pp.61-66
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• 2010

A virtual manufacturing system that is composed of JMatPro, a material modeler and $DEFORM^{TM}$-HT, a finite element package is applied to the hot press forming process: high temperature material properties for each phase such as flow stress, elastic modulus, Poisson's ratio, thermal expansion coefficient, in addition to TTT curve are predicted by JMatPro and taken into $DEFORM^{TM}$-HT to predict the material behavior considering phase transformation and heat transfer simultaneously. In order to verify the accuracy of computation, the residual stress and the springback were compared with the experimental measurements. Both the predicted and measured principal residual stresses and amount of springback were in good agreement. It was also found that the residual stresses generated from hot press forming are not negligible as it has been generally assumed, although the springback deformation is quite small.

• 한국주거학회논문집
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• 제17권2호
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• pp.63-75
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• 2006

The exploration of the spatial structure of a particular urban area, or the analysis of the tendencies of spatial consumption among urbanites, can be a literary-geographical attitude, shifting literary interests toward geography. It may also constitute a field of cultural geography that reads texts as cultural symbols. Based on this kind of attitude, the paper reads the literature of Park Wan So, particularly the popular novels that involve urban and residential spaces of Seoul, as a cultural text that carries a kind of symbolism. It proceeds with the idea that most popular novels reflect the mass phenomena of its times, and that representing real cultural experiences through text, it becomes a means of generalizing the identity shared by the anonymous masses and the characteristics of particular places. Hence the individuality of Park Wan So, who moved to Seoul during the Japanese colonial period and hence forth lived as a middle-class citizen, is inseparable from her literary work. With this attitude and methodology, the paper argues that in the urban space of metropolitan Seoul, the modern ambivalent gaze of the colonial period shifted toward increasingly new value systems, and was replaced by a dichotomous view, and furthermore, that the contents of this dichotomous view has experienced a multivalent transformation through the accumulation of time and the expansion of space.

• 한국세라믹학회지
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• 제32권12호
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• pp.1337-1348
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• 1995

TZP/SUS- and ZT/SUS-functionally gradient materials (FGM) were fabricated by pressureless sintering in Ar-atmosphere. The sintering defects such as warping, frustrum formation, splitting and cracking which originated from shrinkage and sintering behaviors of metal and ceramics different from each other could be controlled by the adjustment with respect to the particle size and phase type of zirconia. The residual stresses generated on the metal and ceramic regions in FGM were characterized with X-ray diffraction method, and relaxed as the thickness and number of compositional gradient layer were increased. The residual stress states in TZP/SUS-FGM have irregular patterns by means of the different sintering behavior and cracking at ceramic-monolith. While in ZT/SUS-FGM, compressive stress is induced on ceramic-monolith by the volume expansion of monoclinic ZrO2 at phase transformation. Also, compressive stress is induced on metal-monolith by the constraint of warping which may be created to the metal direction by the difference of coefficient of thermal expansions. As a consequence, it has been verified that the residual stress generated on FGM is dominantly influenced by the thickness and number of compositional gradient layer, and the sintering defects and residual stress can be controlled by the constraint of the difference of shrinkage and sintering behaviors of each component.

• 한국재료학회지
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• 제13권4호
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• pp.213-218
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• 2003

Fibrous monolithic control of$ Al_2$$O_3$ -$ZrO_2$composite was investigated by multi-pass extrusion process. To obtain sound $Al_2$$O_3$-X $O_2$sintered bodies, burning out and sintering process were carefully carried out. The sintered bodies showed continuous, fibrous monolithic microstructure without any swelling. Many microcracks were observed at the $Al_2$$O_3$-$ZrO_2$interfaces due to the mismatching of thermal expansion coefficient between $Al_2$$O_3$ and $ZrO_2$phase. Most of m- $ZrO_2$grains included twin defects such as (001), (010) and (011) type to accommodate the phase transformation induced stress.

• 대한치과기공학회지
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• 제19권1호
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• pp.55-61
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• 1997

To observe the difference of the special liquid influencing to the fitness of casting body among the many elements influencing to the die fitness of the casting body, we fit L/P ratio each investment, using two kinds of phosphate bonded investment, divided the density of the special liquid by 5 groups(Density 100, 75, 50, 25, 0), made 10 copying per each group and experiment 10 groups, totally 100 copying and finally we could get the result as following ; 1) In such a case of CB-30, the casting fitness of the density 100 of special liquid, group 6, was the best and in order of the density 75, 50, 25, 0 the fitness is better. 2) In such of Denti-vest, the fitness of the density 100 of the special liquid, group 1, was the best and in order of the density 75, 50, 25, 0 the fitness is better. 3) Therefore we should change the density according to the transformation of the environment as investing because of increasing the expansion of phosphate bonded investment, as increasing the density of the special liquid.

• 한국세라믹학회지
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• 제51권2호
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• pp.82-87
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• 2014

Due to the revised Korean standard KS L 5201 for Ordinary Portland Cement (OPC), the use of mixed cement has grown from 5% to 10%. This study investigates the hydration behavior of $C_3A$, asit is a cement mixture that is more commonly used than granulated blast furnace slag or limestone alone. Paste samples were prepared with either granulated blast furnace slag or limestone alone. Each sample was compared with the widely used Rietveld method with a cement mixture containing blast furnace slag or limestone. The hydration behavior of $C_3A$ in each OPC sample was assessed and results were analyzed. Granulated blast furnace slag promotes a high initial level of ettringite, but as the days passed, it promotes an increase in monosulfate, leading to cracks and expansion due to the penetration of sulfates in the solution. However, when limestone is added to the mixture, a transformation of ettringite to monosulfate occurs in the presence of the $CaCO_3$ in the limestone. It is considered that this produces hemi-carbonate and mono-carbonate and thus maintains the ettringite level.

• 한국사회복지학
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• 제42권
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• pp.169-198
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• 2000

This paper attempts to analyze the early retirement in the OECD countries and discuss implication of that in the old age policy in Korea. The increase of the early retirement in the almost all OECD countries is a common fact. Especially the rate of early retirement rapidly increased in the 1980s, mostly reflecting the high rate of unemployment and states' policies to reduce it. However, it varies across countries: the unemployment compensation pathway in France, the mixture of social assistance and private insurance in England, VUT in Netherland, the privatization of the early retirement in the U. S., and partial retirement and labor market policy in Sweden. The early retirement in the advanced countries contributes to de-institutionalization and de-standardization in life course model. It resulted in the erosion of the ordinary conception that the retirement was the beginning of the old age. And the last phase of life course became blurred. With respect to the problem of the early retirement, there is a big difference between Korea and the OECD countries. Above all, the retirement age is 55 years in many companies and the public pension is not universalized in Korea. Accordingly the policy for income security of the old age in Korea should be connected with social security policy such as the gradual extension of the retirement age and the expansion of the public pension and labor market policy such as job training for the old age, transformation of the seniority wage system etc.