SUMMARYIn an open transmission access environment, the system operating conditions tend to be pushed close to the stability limits. Small signal stability, commonly in the form of low frequency oscillations, is considered to be a crucial factor since it limits the amount of power transfer through interconnected transmission lines under severe disturbances. This paper presents a novel approach to the assessment of the total transfer capability (TTC) using small signal stability-based security constrained optimal power flow (SSS-SCOPF), thereby enhancing small signal sense under a set of credible contingencies while maximizing power transfer. The eigenvalue perturbation method is used to derive the small signal stability constraint included in SSS-SCOPF, which is a linear inequality expressed in terms of the control parameters. In order to reduce the computational burden, Bender's decomposition method is applied to partition the TTC problem with the small signal stability constraint into an iterative two-stage mathematical programming problem. It is then solved by the primal-dual interior point method (PDIPM) in a master-sub problem iteration manner until no constraint violation occurs for each contingency. The effectiveness of the proposed method is clearly validated by comparison with the conventional optimal power flow (OPF) and SCOPF under the same array of transactions, base case, and line outages for the New England 39-bus system.

Seeding autologous cells with a medium containing collagen onto the scaffold showed the largest cell population and might generate the best matrix on the scaffold.

Apoptosis occurs during embryonic development, and is related to early embryonic loss. It is important to produce high-quality blastocysts in vitro for research on the establishment of embryonic stem (ES) cells and transgenic animal production. Therefore, our objectives were to compare the anti-apoptotic effect of bovine aggregate v. nonaggregate IVF embryos and to determine whether aggregation could improve the quality of bovine embryos. The cumulus–oocyte complexes were matured for 20–22 h, and the oocytes were fertilized with cryo-preserved bovine sperm using the swim-up method. After removal of the zona pellucida (ZP), three 4-cell-stage embryos (3X) were aggregated by co-culture in an aggregation hole that was made by an aggregation needle on the culture dish. Embryos were cultured either singularly (1X, ZP removed) or in aggregates of three (3X), and IVF intact embryos served as a control. Five days after aggregation, the developmental rate was observed. The numbers of total cells and apoptotic cells were determined by TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling) assay using blastocyst-stage embryos. Moreover, the mRNA expression pattern related to apoptosis and embryo quality was verified by real-time PCR of the aggregated (3X) and nonaggregated (1X) embryos (at least 3 embryos). The percentage of blastocysts was higher in the 3X aggregated embryos (41.3%) compared with that of the 1X ZP-free embryos (24.3%), whereas there was no significant difference in the 1X embryos and the intact controls (24.3 and 25.8%, respectively; P < 0.05). The total cell number of blastocysts also increased approximately threefold (P < 0.05) in 3X aggregated embryos compared with that of 1X controls. In contrast, the percentage of TUNEL-positive cells, an indication of apoptotic cells, was decreased by approximately threefold in 3X aggregated embryos when compared with that of 1X embryos (7.7 and 2.6%, respectively). The mRNA levels for the Oct-4, NANOG, and bcl-2 genes were higher (P < 0.05) and for the Bax gene were lower in the 3X aggregated embryos than for those of the 1X controls. Therefore, our results indicated that aggregation of bovine IVF embryos at a 4-cell stage could promote the quality and suppress the apoptosis of bovine pre-implantation-stage embryos produced in vitro. Further studies are required to investigate the quality of the aggregated embryos in terms of increasing the establishment rate of ES cell lines by seeding on the feeder layer and raising the efficiency of embryo transfer. This work was supported by the BioGreen 21 Program (#20070401034031, #20080401034031), Rural Development Administration, Republic of Korea (HK).

Porcine embryonic stem cells (ESC) can be a useful tool for the production of a transgenic animal and the study of developmental gene regulation. The study of porcine parthenogenetic ESC might also provide advantages in the understanding of changes in human parthenogenetic embryonic stem cells in the culture environment. Because human embryonic stem cells must be maintained stably for therapeutic uses, parthenogenetic porcine embryonic stem cells can give us precious information to help understand human parthenogenetic embryonic stem cells. Three putative porcine embryonic stem cell lines were derived from 99 parthenogenetic embryos. Cumulus-oocyte complexes were collected from prepubertal gilt ovaries and matured in vitro. Diploid parthenogenetic zygotes were produced by electrical activation followed by cytochalasin B treatment to suppress second polar body extrusion. Embryos were cultured to the blastocyst stage. Hatched blastocysts were directly cultured on mitomycin C-inactivated murine embryonic fibroblasts as feeder layers. Primary colonies were formed after 7 days of culture, and the colonies were transferred to new culture dishes 7 days after. They were passsaged every 5 days by physical dissociation, with one colony divided into small clumps and maintained for over 30 passages. These cells morphologically resembled human embryonic stem cells and consistently expressed the markers of pluripotent cells such as alkaline phosphatase, NANOG, OCT-4, SSEA-1, SSEA-4, TRA-1-60, and TRA-1-81. They could be maintained holding the previous characteristics after cryopreservation. Furthermore, we conducted experiments to confirm the expression patterns of the imprinted genes Igf2 and H19 in these ESC and IVF/parthenogenetic blastocysts using quantitative real-time PCR. At the blastocyst stage, the 2 genes were expressed in a parental-specific manner according to their origins in normal fertilized embryos and uniparental embryos. The putative parthenogenetic ESC, on the other hand, showed a high expression of Igf2, the paternally expressed gene, when compared with their blastocyst counterparts. Current work aims to confirm the authenticity of these ESC via teratoma formation in severe combined immunodeficiency mice following injection with these putative parthenogenetic ESC. This work was supported by the BioGreen 21 Program (#20070401034031, #20080401034031), Rural Development Administration, Republic of Korea (HK).

Although epigenetic reprogramming during germ cell development has extensively been studied in the mouse, little is known about the timing of imprinting accomplishment in the pig. Therefore, the aim of this study was to investigate the timing of epigenetic reprogramming in porcine primordial germ cells (PGC) through short-term culture as well as to confirm the differences of epigenetic features between PGC and embryonic germ cells (EGC). The present study aimed to investigate mRNA expression pattern of imprinted genes in cultured PGC that were derived from embryos at Day 25 to 30 of pregnancy. The overall expression pattern can be separated into 3 different features: no changes in all PGC regardless of embryonic day, gradual increases through embryonic day, and extreme increases in PGC derived from embryos at Day 30. Of 8 imprinted genes, Grb10, Peg10, and Snrpn transcripts were retained through all stages. The expression level of H19, Igf2, Igf2r, and Peg1/Mest progressively increased in PGC derived at later stages of embryo development. Interestingly, Xist and Nnat transcripts showed extremely high levels of expression in PGC derived from embryo at Day 30 of pregnancy. The expression level of these transcripts was 3- to 4-fold higher in PGC derived from embryo at Day 30 of pregnancy compared with that of the others. Our results indicated that analysis of the imprinted gene expression level in short-term cultured PGC may in part reflect epigenetic modifications during germ cell development in pig. This study could help us understand how epigenetic reprogramming is maintained or lost during germ cell development. Further study will be carried out to compare imprinted gene expression patterns between the porcine PGC and EGC. This work was supported by the BioGreen 21 Program (#20070401034031, #20080401034031), Rural Development Administration, Republic of Korea (HK).