Twitter, a microblogging service less than three years old, commands more than 41 million users as of July 2009 and is growing fast. Twitter users tweet about any topic within the 140-character limit and follow others to receive their tweets. The goal of this paper is to study the topological characteristics of Twitter and its power as a new medium of information sharing.We have crawled the entire Twitter site and obtained 41.7 million user profiles, 1.47 billion social relations, 4, 262 trending topics, and 106 million tweets. In its follower-following topology analysis we have found a non-power-law follower distribution, a short effective diameter, and low reciprocity, which all mark a deviation from known characteristics of human social networks [28]. In order to identify influentials on Twitter, we have ranked users by the number of followers and by PageRank and found two rankings to be similar. Ranking by retweets differs from the previous two rankings, indicating a gap in influence inferred from the number of followers and that from the popularity of one's tweets. We have analyzed the tweets of top trending topics and reported on their temporal behavior and user participation. We have classified the trending topics based on the active period and the tweets and show that the majority (over 85%) of topics are headline news or persistent news in nature. A closer look at retweets reveals that any retweeted tweet is to reach an average of 1, 000 users no matter what the number of followers is of the original tweet. Once retweeted, a tweet gets retweeted almost instantly on next hops, signifying fast diffusion of information after the 1st retweet.To the best of our knowledge this work is the first quantitative study on the entire Twittersphere and information diffusion on it.

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We present a simple yet robust method for fabricating angled, hierarchically patterned high-aspect-ratio polymer nanohairs to generate directionally sensitive dry adhesives. The slanted polymeric nanostructures were molded from an etched polySi substrate containing slanted nanoholes. An angled etching technique was developed to fabricate slanted nanoholes with flat tips by inserting an etch-stop layer of silicon dioxide. This unique etching method was equipped with a Faraday cage system to control the ionincident angles in the conventional plasma etching system. The polymeric nanohairs were fabricated with tailored leaning angles, sizes, tip shapes, and hierarchical structures. As a result of controlled leaning angle and bulged flat top of the nanohairs, the replicated, slanted nanohairs showed excellent directional adhesion, exhibiting strong shear attachment (Ϸ26 N/cm 2 in maximum) in the angled direction and easy detachment (Ϸ2.2 N/cm 2 ) in the opposite direction, with a hysteresis value of Ϸ10. In addition to single scale nanohairs, monolithic, micro-nanoscale combined hierarchical hairs were also fabricated by using a 2-step UV-assisted molding technique. These hierarchical nanoscale patterns maintained their adhesive force even on a rough surface (roughness <20 m) because of an increase in the contact area by the enhanced height of hierarchy, whereas simple nanohairs lost their adhesion strength. To demonstrate the potential applications of the adhesive patch, the dry adhesive was used to transport a large-area glass (47.5 ؋ 37.5 cm 2 , second-generation TFT-LCD glass), which could replace the current electrostatic transport/ holding system with further optimization.biomimetics ͉ gecko ͉ angled etching ͉ slanted nanohair ͉ hierarchical nanohair A dhesive are used in many aspects of the daily life. With increasing demands for various applications in the industry, new adhesives have been developed that use thermoplastic, UV or light curing, rubbery and pressure-sensitive materials (1). In general, such man-made adhesives have high (sometimes extremely strong) adhesion strength but are not easily detached. Furthermore, they are seldom reusable because the surfaces are quickly contaminated by adhering materials because of their tacky nature. In contrast, nature has created its own adhesives with unique structures and functions. For example, mussels generate specialized adhesive proteins, allowing for strong adhesion to wet surfaces, which is not easily achievable with man-made adhesives (2).In addition, dry adhesion mechanism in gecko lizards has attracted much attention because it provides strong, yet reversible attachment against surfaces of varying roughness and orientation. Such unusual adhesion capability is attributed to arrays of millions of fine microscopic foot hairs (setae), splitting into hundreds of smaller, nanoscale ends (spatulae), which form intimate contact to various surfaces by van der Waals forces with strong adhesion (Ϸ10

verprovisioning is widely used by packet network engineering teams to protect networks against network element failure and support the rapid growth of traffic volume. So far, this approach has been successful in maintaining simple, scalable, highly available, and robust networks. It is important to realize that in packet networks which do not perform call admission control, there is often no way to control the amount or types of traffic entering the network. The provisioning problem therefore lies in figuring out how much excess capacity is required to provide robustness (e.g., resilience to multiple simultaneous link failures) and scalability. The current tools for network management, such as Simple Network Management Protocol (SNMP), are limited in their capabilities, since they only provide highly aggregated statistics about the traffic (e.g., average traffic load over fiveminute intervals) and do not give insight into traffic dynamics on timescales appropriate for events such as packet drops. Another example is the demand traffic matrix, which is a crucial input to many network planning, provisioning, and engineering problems, but is difficult to obtain with available tools [1,2].Detailed traffic measurements are necessary to assess the capacity requirements and efficiently engineer the network. In this article we first describe the architecture and capabilities of the IPMON system. Then we point out the challenges we faced in collecting terabytes of data, and include our solutions to data sanitization. In the remainder of the article we AbstractNetwork traffic measurements provide essential data for networking research and network management. In this article we describe a passive monitoring system designed to capture GPS synchronized packet-level traffic measurements on OC-3, OC-12, and OC-48 links. Our system is deployed in four POPs in the Sprint IP backbone. Measurement data is stored on a 10 Tbyte storage area network and analyzed on a computing cluster. We present a set of results to both demonstrate the strength of the system and identify recent changes in Internet traffic characteristics. The results include traffic workload, analyses of TCP flow round-trip times, out-of-sequence packet rates, and packet delay. We also show that some links no longer carry Web traffic as their dominant component to the benefit of file sharing and media streaming. On most links we monitored, TCP flows exhibit low out-of-sequence packet rates, and backbone delays are dominated by the speed of light.

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