Yonsei University

About: Yonsei University is a education organization based out in Seoul, South Korea. It is known for research contribution in the topics: Population & Cancer. The organization has 50162 authors who have published 106172 publications receiving 2279044 citations. The organization is also known as: Yonsei.

Directly Linked Porphyrin Arrays with Tunable Excitonic Interactions

Abstract: On the basis of the Ag(I)-promoted coupling reaction of Zn(II) 5,15-diaryl porphyrin that gave a meso−meso-linked diporphyrin, we developed a variety of directly linked porphyrin arrays including linear, windmill, gridlike, cyclic, and box architectures. Electronic and excitonic interactions are thus fine tuned by placing porphyrin chromophores in well-defined arrangements. Photoexcited-state dynamics of these porphyrin arrays, as revealed by various ultrafast laser-based measurements, are pertinent to photosynthetic light-harvesting antenna in terms of very efficient excitation energy hopping over many porphyrins and lack of a defect that acts as energy sink. The conformational flexibility of a meso−meso-linked diporphyrin has also been used for the fine tuning of excitonic interactions as demonstrated by strapped meso−meso diporphyrins and reversible switching of energy transfer in a triporphyrin. Triply linked porphyrin arrays have also been explored, which exhibit an exceptionally low HOMO−LUMO gap as...

The Y2 Isochrones for α-Element Enhanced Mixtures

Abstract: We present a new set of isochrones in which the effect of the α-element enhancement is fully incorporated. These isochrones are an extension of the already published set of Y2 Isochrones (our Paper I), constructed for the scaled-solar mixture. As in Paper I, helium diffusion and convective core overshoot have been taken into account. The range of chemical compositions covered is 0.00001 ≤ Z ≤ 0.08. The models were evolved from the pre-main-sequence stellar birthline to the onset of helium burning in the core. The age range of the full isochrone set is 0.1-20 Gyr, while younger isochrones of age 1-80 Myr are also presented up to the main-sequence turn-off. Combining this set with that of Paper I for scaled-solar mixture isochrones, we provide a consistent set of isochrones that can be used to investigate populations of any value of α-enhancement. We confirm the earlier results of Paper I that inclusion of α-enhancement effects further reduces the age estimates of globular clusters by approximately 8% if [α/Fe]= +0.3. It is important to note the metallicity dependence of the change in age estimates (larger age reductions in lower metallicities). This reduces the age gap between the oldest metal-rich and metal-poor Galactic stellar populations and between the halo and the disk populations. We also investigate whether the effects of α-enhancement can be mimicked by increasing the total metal abundance in the manner proposed by Salaris and collaborators. We find such simple scaling formulae are valid at low metallicities but not at all at high metallicities near and above solar. Thus, it is essential to use the isochrones rigorously computed for α-enhancement when modeling metal-rich populations, such as bright galaxies. The isochrone tables, together with interpolation routines have been made available via internet.

CD24 + cells from hierarchically organized ovarian cancer are enriched in cancer stem cells

Abstract: Cancer stem cells (CSCs) have been identified in solid tumors and cancer cell lines In this study, we isolated a series of cancer cell clones, which were heterogeneous in growth rate, cell cycle distribution and expression profile of genes and proteins, from ovarian tumor specimens of a patient and identified a sub-population enriched for ovarian CSCs defined by CD24 phenotype Experiments in vitro demonstrated CD24(+) sub-population possessed stem cell-like characteristics of remaining quiescence and more chemoresistant compared with CD24(-) fraction, as well as a specific capacity for self-renewal and differentiation In addition, injection of 5 x 10(3) CD24(+) cells was able to form tumor xenografts in nude mice, whereas equal number of CD24(-) cells remained nontumorigenic We also found that CD24(+) cells expressed higher mRNA levels of some 'stemness' genes, including Nestin, beta-catenin, Bmi-1, Oct4, Oct3/4, Notch1 and Notch4 which were involved in modulating many functions of stem cells, and lower E-cadherin mRNA level than CD24(-) cells Altogether, these observations suggest human ovarian tumor cells are organized as a hierarchy and CD24 demarcates an ovarian cancer-initiating cell population These findings will have important clinical applications for developing effective therapeutic strategies to treat ovarian cancer