Construction of large-volume tissue mimics with 3D functional vascular networks

We used indirect stereolithography (SL) to form inner-layered fluidic networks in a porous scaffold by introducing a hydrogel barrier on the luminal surface, then seeded the networks separately with human umbilical vein endothelial cells and human lung fibroblasts to form a tissue mimic containing vascular networks. The artificial vascular networks provided channels for oxygen transport, thus reducing the hypoxic volume and preventing cell death. The endothelium of the vascular networks significantly retarded the occlusion of channels during whole-blood circulation. The tissue mimics have the potential to be used as an in vitro platform to examine the physiologic and pathologic phenomena through vascular architecture.ope

The Peopling of Korea Revealed by Analyses of Mitochondrial DNA and Y-Chromosomal Markers

The Koreans are generally considered a northeast Asian group because of their geographical location. However, recent findings from Y chromosome studies showed that the Korean population contains lineages from both southern and northern parts of East Asia. To understand the genetic history and relationships of Korea more fully, additional data and analyses are necessary.We analyzed mitochondrial DNA (mtDNA) sequence variation in the hypervariable segments I and II (HVS-I and HVS-II) and haplogroup-specific mutations in coding regions in 445 individuals from seven east Asian populations (Korean, Korean-Chinese, Mongolian, Manchurian, Han (Beijing), Vietnamese and Thais). In addition, published mtDNA haplogroup data (N = 3307), mtDNA HVS-I sequences (N = 2313), Y chromosome haplogroup data (N = 1697) and Y chromosome STR data (N = 2713) were analyzed to elucidate the genetic structure of East Asian populations. All the mtDNA profiles studied here were classified into subsets of haplogroups common in East Asia, with just two exceptions. In general, the Korean mtDNA profiles revealed similarities to other northeastern Asian populations through analysis of individual haplogroup distributions, genetic distances between populations or an analysis of molecular variance, although a minor southern contribution was also suggested. Reanalysis of Y-chromosomal data confirmed both the overall similarity to other northeastern populations, and also a larger paternal contribution from southeastern populations.The present work provides evidence that peopling of Korea can be seen as a complex process, interpreted as an early northern Asian settlement with at least one subsequent male-biased southern-to-northern migration, possibly associated with the spread of rice agriculture

Achieving Fairness Between Uplink and Downlink Flows in Error-Prone WLANs

This letter considers an unfairness problem between uplink and downlink in 802.11 WLANs. One of existing solutions for this problem is giving a larger transmission opportunity (TXOP) limit to an AP than stations. This TXOP differentiation scheme, however, does not work well in error-prone environments since a packet bursting during a TXOP duration is terminated when a data transmission fails due to channel errors. To overcome this, we propose a new scheme in which an AP controls its minimum contention window size and TXOP limit dynamically according to the packet error rate and the number of stations. Our simulation results show that the proposed scheme provides fair channel accesses between uplink and downlink in error-prone 802.11 WLANs.X1199sciescopu

A Survey and Comparison of Multichannel Protocols for Performance Anomaly Mitigation in IEEE 802.11 Wireless Networks

Providing multichannel functionality can improve the performance of wireless networks. Although off-the-shelf IEEE 802.11 physical layer and medium access control specifications support multiple channels and multiple data rates, one of the major challenges is how to efficiently utilize available channels and data rates to improve network performance. In multirate networks, low-rate links severely degrade the capacity of high-rate links, which is known as performance anomaly. To overcome the performance anomaly problem, different data rate links can get equal air-time by exploiting time diversity and frequency diversity, or they can be separated over nonoverlapping channels. In this paper, we study existing multichannel protocols proposed to mitigate the performance anomaly problem by classifying them into single-radio protocols, multiradio single-hop protocols, and multiradio multihop protocols. To investigate the effectiveness of multichannel solutions for performance anomaly, we compare these protocols with well-known multichannel protocols that do not consider performance anomaly. In addition, this paper gives insightful research issues to design multichannel protocols that mitigate performance anomaly in IEEE 802.11 wireless networks. Copyright (c) 2012 John Wiley & Sons, Ltd.X1167sciescopu