Basic Science

Network Congestion Relieved by Removing Links

Dr. Zhang Guoqing et al., from the Institute of Computing Technology, CAS, proposed a novel method to alleviate network traffic congestion by simply removing links. The proposed counter-intuitive strategy utilizes “betweeness” to identify and remove certain links to mitigate network congestion. Their research work, appeared in Physical Review E and Scientia Sinica Informationis, revealed the necessary condition that the method stands. Alleviating network congestion has always been on the hot spot in network science and network engineering. Dr. Zhang acutely sensed that, the underlying structure of network itself greatly affects the QOS of the network transmission. In the past several years, his team thoroughly analyzed some real-world networks and classical network models, such as scale-free, random and small-world networks. And they find out that by removing certain high-weight links according to betweenness value in a network, the overall capacity of the network can be increased. At the same time, the study also shows that the results of capacity expansion depend on specific networks, and the greater the heterogeneity of a network is, the better the effect is. The method is practically easy to implement in modern communication and transportation networks, and will help reduce overall network operation cost.

No Significant Classical Bulge Found in Milky Way

Recently the study on the Galactic bar/bulge, participated and completed by Dr. Shen Juntai at the Shanghai Astronomical Observatory, has made new progress. The bar/bulge model generated by Shen deepened understanding on the Milky Way structure. His Milky Way bar/bulge model was recently highlighted on the home page of the U.S. National Optical Astronomical Observatory, and has been widely used by the international astronomy community. Previously, astronomers natively thought that the Milky Way has a classical bulge produced in galaxy mergers. In fact the Galactic bulge looks boxy-shaped in the solar perspective. The computer simulation performed by Shen suggests that a large scale bar structure can form from the evolution of a thin galactic disk with small random velocities. Then the ''buckling instability'' in the vertical direction of the disk thickens the inner part of the bar in a short time to make a boxy structure, which resembles the Milky Way bulge as seen from the Sun. Based on more modeling, Shen further suggests that the classical bulge component of the Milky Way, if exists, should be rather small. This study implies that the Milky Way is a massive pure-disk galaxy without a significant classical bulge component. The formation of such massive pure-disk galaxies poses an acute challenge to the current standard galaxy formation picture.