Despite that porcine spermatogonial stem cells (pSSCs) have been regarded as a practical tool for preserving eternally genetic backgrounds derived from pigs with high performance in the economic traits or phenotypes of specific human diseases, there were no reports about precise definition of niche conditions promoting proliferation and maintenance of pSSCs. Accordingly, we tried to determine niche conditions supporting proliferation and maintenance of undifferentiated pSSCs for short-term. For these, undifferentiated pSSCs were progressively cultured in different composition of culture medium, seeding density of pSSCs, type of feeder cells and concentration of growth factors, and then total number of and alkaline phosphatase (AP) activity of pSSCs were investigated at post-6 day culture. As the results, the culture of 4x105 pSSCs on mitotically in activated 2x105 STO cells in the mouse embryonic stem cell culture medium (mESCCM) supplemented with 30 ng/ml glial cell line-derived neurotrophic factor (GDNF) was identified as the best niche condition supporting effectively the short-term maintenance of undifferentiated pSSCs. Moreover, the optimized short-term culture system will be a basis for developing long-term culture system of pSSCs in the following researches.

Conductive polymer composites (CPCs) consist of a polymeric matrix and a conductive fil-er, for example, carbon black, carbon fibers,graphite or carbon nanotubes (CNTs). The criti-cal amount of the electrically conductive fillernecessary to build up a continuous conductive network, and accordingly, to make the material conductive; is referred to as the percolation threshold. From technical and economical viewpoints, it is desirable to decrease the conduc-tive-fillerpercolation-threshold as much as possible. In this study, we investigated the effect of polymer/conductive-fillerinteractions, as well as the processing and morphological devel-opment of low-percolation-threshold (Φc) conductive-polymer composites. The aim of the study was to produce conductive composites containing less multi-walled CNTs (MWCNTs) than required for pure polypropylene (PP) through two approaches: one using various mix-ing methods and the other using immiscible polymer blends. Variants of the conductive PP composite filledwith MWCNT was prepared by dry mixing, melt mixing, mechanofusion, and compression molding. The percolation threshold (Φc) of the MWCNT-PP composites was most successfully lowered using the mechanofusion process than with any other mixing method (2-5 wt%). The mechanofusion process was found to enhance formation of a perco-lation network structure, and to ensure a more uniform state of dispersion in the CPCs. The immiscible-polymer blends were prepared by melt mixing (internal mixer) poly(vinylidene fluoride) (PVD, PP/PVDF, volume ratio 1:1) filled with MWCN.

이 논문은 2009년 2월 20일 미국의 제9 연방순회항소법원에서 내려진 Video Software Dealers Association v. Arnold Schwarzenegger 사건에 대한 판결의 의미와 한국게임법제도에의 시사점을 검토한 것이다. 이 사건에서 제9 연방순회항소법원은 폭력성 비디오게임을 18세 미만의 미성년자에게 판매하거나 대여하는 것을 금지하는 캘리포니아 주법(州法)이 미국 연방헌법에 명시된 미성년자 (minor)의 권리를 침해한다는 판결을 내렸다. 이에 비해서 한국의 헌법재판소는 청소년보호를 위한 청소년유해매체물 제도와 사전등급분류 제도에 대해서는 합헌이라는 결정을 하였다. 헌법재판소는 미국의 제9 연방항소법원의 판결과 같이 음란과 폭력성을 구분하여 접근하고 있고, 폭력성 개념이 대해서 간접적으로 위헌적이라는 결정을 한 바 있다. 미국법원의 덜 제한적인 수단의 선택이라는 법리와 헌법재판소의 최소침해성 원칙에서 본다면 청소년유해매체물 제도와 사전등급분류 제도의 중첩 적용은 문제될 수 있으며, 이 중에서 더 강한 규제가 위헌이 될 소지가 있다.