Partial clustering: maintaining connectivity in a low duty-cycled dense wireless sensor network
We consider a dense wireless sensor network where the radio transceivers of the sensor nodes are heavily duty-cycled in order to conserve energy. The chief purpose of the sensor network is surveillance and monitoring, where upon observation of certain event of interest, a sensor node generates a message and forwards it to a gateway located somewhere in or near the network. This forwarding relies on routes constructed using sensors whose radios are on/active. In order for such messages to reach the gateway with minimal delay, any sensor in the network should ideally have a route to the gateway consisting of active sensors at all times. Prior approaches to similar problems include clustering, virtual backbone, and connected dominating sets. Low energy consumption and good connectivity are potentially conflicting objectives. Our principal goal is to find an approach that results in the lowest possible duty cycle, and that provides better trade-off between the two objectives. In this paper we introduce the concept of partial clustering, which may be viewed as a generalized method of clustering. We compare the theoretical performance of different instances of partial clustering to that of standard clustering, and show that partial clustering can achieve lower duty cycle and provide greater flexibility in the trade-off between energy efficiency and connectivity. We then present a distributed algorithm based on the partial clustering method. Simulation results are provided to evaluate their effectiveness and energy efficiency.

title: Sound mobility models
abstract: Simulation has become an indispensable tool in the construction and evaluation of mobile systems. By using mobility models that describe constituent movement, one can explore large systems, producing repeatable results for comparison between alternatives. Unfortunately, the vast majority of mobility models---including all those in which nodal speed and distance or destination are chosen independently---suffer from decay; average speed decreases until converging to some long-term average. Such decay provides an unsound basis for simulation studies that collect results averaged over time, complicating the experimental process.This paper shows via analysis that such decay is inevitable in a wide variety of mobility models, including the most common in use today. We derive a general framework for describing this decay, and apply it to a number of practical cases. Furthermore, this framework allows us to transform any given mobility model into a stationary one: choose initial speeds from the steady-state distribution, and subsequent speeds from the original. This transformation provides sound models for simulation, eliminating variations in average nodal speed.

title: Optimal controlled flooding search in a large wireless network
abstract: In this paper we consider the problem of searching for a node or an object (i.e., piece of data, file, etc.) in a large wireless network. We consider the class of controlled flooding search strategies where query/search packets are broadcast and propagated in the network until a preset TTL (time-to-live) value carried in the packet expires. Every unsuccessful search attempt results in an increased TTL value (i.e., larger search area) and the same process is repeated. We derive search strategies that minimize the search cost in the worst-case, via a performance measure in the form of the competitive ratio between the average search cost of a strategy and that of an omniscient observer. This ratio is shown in prior work to be lower bounded by 4 among all deterministic search strategies. In this paper we show that by using randomized strategies this ratio is lower bounded by e. We derive an optimal strategy that achieves this lower bound, and discuss its performance under other performance criteria.

title: Random waypoint considered harmful
abstract: This study examines the random waypoint model widely used in the simulation studies of mobile ad hoc networks. Our findings show that this model fails to provide a steady state in that the average nodal speed consistently decreases over time, and therefore should not be directly used for simulation. We show how unreliable results can be obtained by using this model. In particular, certain ad hoc routing metrics can drop by as much as 40% over the course of a 900-second simulation using the random waypoint model. We give both an intuitive and a formal explanation for this phenomenon. We also propose a simple fix of the problem and discuss a few alternatives. Our modified random waypoint model is able to reach a steady state and simulation results are presented.

title: Modeling TCP performance with proxies
abstract: This paper investigates TCP dynamics and performance over proxies that shorten the TCP feedback loop by segmenting the end-to-end connection. Such proxies are often used to improve the TCP performance, e.g. a splitting/spoofing proxy in satellite communication, and more commonly, a web cache. Through analysis, we attempt to develop a basic understanding of the properties of TCP dynamics when such proxies are used, and further obtain design principles of systems involving such proxies. We present simple models capturing some features of the proxy performance in both the lossless and lossy scenarios. Due to the complexity involved, detailed analysis is only available in the lossless scenario, and our discussion in the lossy scenario is largely limited to steady-state behavior. Nevertheless we are able to obtain useful insight. We identify conditions under which using a proxy provides significant or marginal performance gain by investigating factors including initial window size, congestion level of the proxy, and the level of asymmetry between the segments segregated by the proxy. We also discuss how these conditions affect the deployment and provisioning of such systems.

title: Data-gathering wireless sensor networks: organization and capacity
abstract: In this paper we study the transport capacity of a data-gathering wireless sensor network under different communication organizations. In particular, we consider using a flat as well as a hierarchical/clustering architecture to realize many-to-one communications. The capacity of the network under this many-to-one data-gathering scenario is reduced compared to random one-to-one communication due to the unavoidable creation of a point of traffic concentration at the data collector/receiver. We introduce the overall throughput bound of λ = W/n per node, where W is the transmission capacity, and show under what conditions it can be achieved and under what conditions it cannot. When those conditions are not met, we constructively show how λ = Θ(W/n) is achieved with high probability as the number of sensors goes to infinity. We also show how the introduction of clustering can improve the throughput. We discuss the trade-offs between achieving capacity and energy consumption, how transport capacity might be affected by considering in-network processing and the implications this study has on the design of practical protocols for large-scale data-gathering wireless sensor networks.

title: An Evaluation of the Use of Problem-Based Learning Software By Middle School Students
abstract: Research has shown the potential of a problem-based approach to enhance students' learning. The interactive nature of hypermedia technology and its ability to deliver information in different media formats can provide unique capabilities for implementing problem-based learning (PBL) environments. Yet, we know little about the types of tools that are effective in supporting students' learning in a hypermedia supported PBL environment. The purpose of this study was to investigate both the use of tools and design features in a piece of PBL software and their effectiveness on middle school students' learning. The findings of this study show that students who were exposed to the PBL environment increased their achievement scores from pre to posttest more than those students who learned the same content in the traditional classroom. Students' reading ability was found to be a better predictor for their achievement in PBL than their math ability. However, the brief treatment of the study had only limited impact on students' attitude toward learning science. The findings of the study and their implications are discussed in detail.

title: A prototype mobile-agent application
abstract: Mobile agents, a relatively new paradigm for distributed software development, has become an accessible technology in recent years. The potential bene-ts of this paradigm, including the reduction of network bandwidth consumption and latency, promise to revolutionize distributed applications A number of research institutions and industrial entities have engaged in the development of elaborate supporting systems for this technology, and the deployment of its applications can be expected to proliferate. This paper describes a small-scale project under-taken to explore the feasibility of this technology, the technical issues, and its eeects on network applications .

title: On the retention of female computer science students

title: The History and Status of Chinese Americans in Librarianship
abstract: This article reviews the brief history of Chinese Americans in the United States and their contributions to librarianship. Despite the hardships and challenges they faced, Chinese American librarians made great contributions to the building of East Asian libraries, to the cataloging of East Asian and Chinese collections, and to the development of library automation. They have advanced information technologies, promoted multicultural and diversity library services, and participated in library management and administration. Chinese Americans are active in library and information science education, in professional associations, in international librarianship, in national library and information services policy making and programming, and national policy making. Pioneers and key figures are identified with their accomplishments. The origin, purpose, programs, and activities of the Chinese American Librarians Association are also described.

title: Applying Design Patterns in Distributing a Genetic Algorithm Application
abstract: -This paper describes an experiment that employs an incremental approach to distribute a genetic algorithm application. The incremental approach allows the application to be initially developed for a standalone system, and then extended to run on multiple systems concurrently. For the extension, design patterns are employed wherever appropriate. The use of design patterns in the experiment is described, and the outcome of the experiment, including quantitative measurements, is presented.