Computer Sciences Commons^™

Exploring The Design Space Of Multichannel Peer-To-Peer Live Video Streaming Systems, Miao Wang, Lisong Xu, Byrav Ramamurthy

School of Computing: Faculty Publications

Most of the commercial peer-to-peer (P2P) video streaming deployments support hundreds of channels and are referred to as multichannel systems. Recent research studies have proposed specific protocols to improve the streaming quality for all channels by enabling cross-channel cooperation among multiple channels. In this paper, we focus on the following fundamental problems in designing cooperating multichannel systems: 1) what are the general characteristics of existing and potential designs? and 2) under what circumstances should a particular design be used to achieve the desired streaming quality with the lowest implementation complexity? To answer the first question, we propose simple models based …

Redistricting Using Constrained Polygonal Clustering, Deepti Joshi, Leen-Kiat Soh, Ashok Samal

School of Computing: Faculty Publications

Redistricting is the process of dividing a geographic area consisting of spatial units—often represented as spatial polygons—into smaller districts that satisfy some properties. It can therefore be formulated as a set partitioning problem where the objective is to cluster the set of spatial polygons into groups such that a value function is maximized [1]. Widely used algorithms developed for point-based data sets are not readily applicable because polygons introduce the concepts of spatial contiguity and other topological properties that cannot be captured by representing polygons as points. Furthermore, when clustering polygons, constraints such as spatial contiguity and unit distributedness should …

An Efficient Water-Filling Algorithm For Power Allocation In Ofdm-Based Cognitive Radio Systems, Qilin Qi, Yaoqing Lamar Yang

School of Computing: Conference and Workshop Papers

In this paper, we present a new water-filling algorithm for power allocation in Orthogonal Frequency Division Multiplexing (OFDM) – based cognitive radio systems. The conventional water-filling algorithm cannot be directly employed for power allocation in a cognitive radio system, because there are more power constraints in the cognitive radio power allocation problem than in the classic OFDM system. In this paper, a novel algorithm based on iterative water-filling is presented to overcome such limitations. However, the computational complexity in iterative water-filling is very high. Thus, we explore features of the water-filling algorithm and propose a low-complexity algorithm using power-increment or …

Adaptive Energy-Efficient Task Partitioning For Heterogeneous Multi-Core Multiprocessor Real-Time Systems, Shivashis Saha, Jitender S. Deogun, Ying Lu

School of Computing: Conference and Workshop Papers

The designs of heterogeneous multi-core multiprocessor real-time systems are evolving for higher energy efficiency at the cost of increased heat density. This adversely effects the reliability and performance of the real-time systems. Moreover, the partitioning of periodic real-time tasks based on their worst case execution time can lead to significant energy wastage.

In this paper, we investigate adaptive energy-efficient task partitioning for heterogeneous multi-core multiprocessor realtime systems. We use a power model which incorporates the impact of temperature and voltage of a processor on its static power consumption. Two different thermal models are used to estimate the peak temperature of …

Hyscaleii: A High Performance Hybrid Optical Network Architecture For Data Centers, Shivashis Saha, Jitender S. Deogun, Lisong Xu

School of Computing: Conference and Workshop Papers

Tremendous growth in data-intensive cloud applications have resulted in an increased demand for highly scalable data center network (DCN) architectures with high throughput and low network complexity. In this paper, we propose HyScaleII to improve the performance of HyScale [17]. HyScaleII is a switchcentric high performance hybrid optical network based DCN architecture that has most of the desirable properties of a data center, e.g. high scalability, low diameter, high bisection width, fault-tolerance, and low network complexity. We also present an efficient and simple routing scheme called HySII routing, which exploits the structural properties of HyScaleII. In our experiments, HyScaleII …

Finding Suitable Programs: Semantic Search With Incomplete And Lightweight Specifications, Kathryn T. Stolee

School of Computing: Conference and Workshop Papers

Finding suitable code for reuse is a common task for programmers. Two general approaches dominate the code search literature: syntactic and semantic. While queries for syntactic search are easy to compose, the results are often vague or irrelevant. On the other hand, a semantic search may return relevant results, but current techniques require developers to write specifications by hand, are costly as potentially matching code need to be executed to verify congruence with the specifications, or only return exact matches. In this work, we propose an approach for semantic search in which programmers specify lightweight, incomplete specifications and an SMT …

Space-Efficient Algorithms For Reachability In Surface-Embedded Graphs, Derrick Stolee, N. V. Vinodchandran

School of Computing: Conference and Workshop Papers

This work presents a log-space reduction which compresses an n-vertex directed acyclic graph with m(n) sources embedded on a surface of genus g(n), to a graph with O(m(n) + g(n)) vertices while preserving reachability between a given pair of vertices. Applying existing algorithms to this reduced graph yields new deterministic algorithms with improved space bounds as well as improved simultaneous time space bounds for the reachability problem over a large class of directed acyclic graphs. Specifically, it significantly extends the class of surface-embedded graphs with log-space reachability algorithms: from planar graphs with O(log n) sources, to graphs with …

Mobile Data Harvesting In Wireless Underground Sensor Networks, John Tooker, Mehmet C. Vuran

School of Computing: Conference and Workshop Papers

Wireless Underground Sensor Networks (WUSNs) allow for continuous field monitoring without interfering with aboveground activities, such as plowing or football games. Due to the increased path loss in soil, it is challenging to ensure that a large-scale underground network is connected while still being cost effective in terms of deployment and maintenance.

In this paper, a practical WUSN architecture is developed, consisting of mobile nodes that harvest data from stationary underground nodes. To this end, the impacts of packet size and error control schemes on network performance are investigated through field experiments. By developing a better understanding of the wireless …

Amplifying Tests To Validate Exception Handling Code, Pingyu Zhang, Sebastian Elbaum

School of Computing: Conference and Workshop Papers

Validating code handling exceptional behavior is difficult, particularly when dealing with external resources that may be noisy and unreliable, as it requires: 1) the systematic exploration of the space of exceptions that may be thrown by the external resources, and 2) the setup of the context to trigger specific patterns of exceptions. In this work we present an approach that addresses those difficulties by performing an exhaustive amplification of the space of exceptional behavior associated with an external resource that is exercised by a test suite. Each amplification attempts to expose a program exception handling construct to new behavior by …

Sensing Through The Continent: Towards Monitoring Migratory Birds Using Cellular Sensor Networks, David Anthony, William P. Bennett, Mehmet C. Vuran, Matthew B. Dwyer, Sebastian Elbaum, Anne Lacy, Mike Engels, Walter Wehtje

School of Computing: Conference and Workshop Papers

This paper presents CraneTracker, a novel sensor platform for monitoring migratory birds. The platform is designed to monitor Whooping Cranes, an endangered species that conducts an annual migration of 4, 000 km between southern Texas and north-central Canada. CraneTracker includes a rich set of sensors, a multi-modal radio, and power control circuitry for sustainable, continental-scale information delivery during migration. The need for large-scale connectivity motivates the use of cellular technology in low-cost sensor platforms augmented by a low-power transceiver for ad-hoc connectivity. This platform leads to a new class of cellular sensor networks (CSNs) for time-critical and mobile sensing applications. …

A Study Of Correlations Between The Definition And Application Of The Gene Ontology, Yuji Mo

Department of Computer Electronics and Engineering: Dissertations, Theses, and Student Research

When using the Gene Ontology (GO), nucleotide and amino acid sequences are annotated by terms in a structured and controlled vocabulary organized into relational graphs. The usage of the vocabulary (GO terms) in the annotation of these sequences may diverge from the relations defined in the ontology. We measure the consistency of the use of GO terms by comparing GO's defined structure to the terms' application. To do this, we first use synthetic data with different characteristics to understand how these characteristics influence the correlation values determined by various similarity measures. Using these results as a baseline, we found that …

The R Journal (December 2011) 3(2): Complete Issue, The R Foundation

The R Journal

Contributed Research Articles

Creating and Deploying an Application with (R)Excel and R, Thomas Baier, Erich Neuwirth, and Michele De Meo

glm2: Fitting Generalized Linear Models with Convergence Problems, Ian C. Marschner

Implementing the Compendium Concept with Sweave and DOCSTRIP, Michael Lundholm

Watch Your Spelling! Kurt Hornik and Duncan Murdoch

Ckmeans.1d.dp: Optimal k-means Clustering in One Dimension by Dynamic Programming, Haizhou Wang and Mingzhou Song

Nonparametric Goodness-of-Fit Tests for Discrete Null Distributions, Taylor B. Arnold and John W. Emerson

Using the Google Visualisation API with R, Markus Gesmann and Diego de Castillo

GrapheR: a Multiplatform GUI for Drawing Customizable Graphs in …

Rainbow: An R Package For Visualizing Functional Time Series, Han Lin Shang

The R Journal

Recent advances in computer technology have tremendously increased the use of functional data, whose graphical representation can be infinite-dimensional curves, images or shapes. This article describes four methods for visualizing functional time series using an R add-on package. These methods are demonstrated using age-specific Australian fertility data from 1921 to 2006 and monthly sea surface temperatures from January 1950 to December 2006.

Using The Google Visualisation Api With R, Markus Gesmann, Diego De Castillo

The R Journal

The googleVis package provides an interface between R and the Google Visualisation API to create interactive charts which can be embedded into web pages. The best known of these charts is probably the Motion Chart, popularised by Hans Rosling in his TED talks. With the googleVis package users can easily create web pages with interactive charts based on R data frames and display them either via the local R HTTPhelp server or within their own sites.

Ckmeans.1d.Dp: Optimal K-Means Clustering In One Dimension By Dynamic Programming, Haizhou Wang, Mingzhou Song

The R Journal

The heuristic k-means algorithm, widely used for cluster analysis, does not guarantee optimality. We developed a dynamic programming algorithm for optimal one-dimensional clustering. The algorithm is implemented as an R package called Ckmeans.1d.dp. We demonstrate its ad vantage in optimality and runtime over the standard iterative k-means algorithm.

Implementing The Compendium Concept With Sweave And Docstrip, Michael Lundholm

The R Journal

This article suggests an implementation of the compendium concept by combining Sweave and the LATEX literate programming environment DOCSTRIP.

Content-Based Social Network Analysis Of Mailing Lists, Angela Bohn, Ingo Feinerer, Kurt Hornik, Patrick Mair

The R Journal

Social Network Analysis (SNA) provides tools to examine relationships between people. Text Mining (TM) allows capturing the text they produce in Web 2.0 applications, for example, however it neglects their social structure. This paper applies an approach to combine the two methods named “content-based SNA”. Using the R mailing lists, R-help and R-devel, we show how this combination can be used to describe people’s interests and to find out if authors who have similar interests actually communicate. We find that the expected positive relationship between sharing interests and communicating gets stronger as the centrality scores of authors in the communication …

Watch Your Spelling!, Kurt Hornik, Duncan Murdoch

The R Journal

We discuss the facilities in base R for spell checking via Aspell, Hunspell or Ispell, which are useful in particular for conveniently checking the spelling of natural language texts in package Rd files and vignettes. Spell checking performance is illustrated using the Rd files in package stats. This example clearly indicates the need for a domain-specific statistical dictionary. We analyze the results of spell checking all Rd files in all CRAN packages and show how these can be employed for building such a dictionary.

Nonparametric Goodness-Of-Fit Tests For Discrete Null Distributions, Taylor B. Arnold, John W. Emerson

The R Journal

Methodology extending nonparametric goodness-of-fit tests to discrete null distributions has existed for several decades. However, modern statistical software has generally failed to provide this methodology to users. We offer a revision of R’s ks.test() function and a new cvm.test() function that fill this need in the R language for two of the most popular nonparametric goodness-of-fit tests. This paper describes these contributions and provides examples of their usage. Particular attention is given to various numerical issues that arise in their implementation.

Portable C++ For R Packages, Martyn Plummer

The R Journal

Package checking errors are more common on Solaris than Linux. In many cases, these errors are due to non-portable C++ code. This article reviews some commonly recurring problems in C++ code found in R packages and suggests solutions.

Glm2: Fitting Generalized Linear Models With Convergence Problems, Ian C. Marschner

The R Journal

The R function glm uses step-halving to deal with certain types of convergence problems when using iteratively reweighted least squares to fit a generalized linear model. This works well in some circumstances but non-convergence remains a possibility, particularly with a non standard link function. In some cases this is be cause step-halving is never invoked, despite a lack of convergence. In other cases step-halving is invoked but is unable to induce convergence. One remedy is to impose a stricter form of step halving than is currently available in glm, so that the deviance is forced to decrease in every iteration. …

Creating And Deploying An Application With (R)Excel And R, Thomas Baier, Erich Neuwirth, Michele De Meo

The R Journal

We present some ways of using R in Excel and build an example application using the package rpart. Starting with simple interactive use of rpart in Excel, we eventually package the code into an Excel-based application, hiding all details (including R itself) from the end user. In the end, our application implements a service oriented architecture (SOA) with a clean separation of presentation and computation layer

Grapher: A Multiplatform Gui For Drawing Customizable Graphs In R, Maxime Hervé

The R Journal

This article presents GrapheR, a Graphical User Interface allowing the user to draw customizable and high-quality graphs without knowing any R commands. Six kinds of graph are available: histograms, box-and-whisker plots, bar plots, pie charts, curves and scatter plots. The complete process is described with the examples of a bar plot and a scatter plot illustrating the legendary puzzle of African and European swallows’ migrations.

Relational Neighborhood Inverse Consistency For Constraint Satisfaction: A Structure-Based Approach For Adjusting Consistency And Managing Propagation, Robert J. Woodward

School of Computing: Dissertations, Theses, and Student Research

Freuder and Elfe [1996] introduced Neighborhood Inverse Consistency (NIC) as a local consistency property defined on the values in the variables' domains of a Constraint Satisfaction Problem (CSP). Debruyne and Bessiere [2011] showed that enforcing NIC on binary CSPs is ineffective on sparse graph and too costly on dense graphs. In this thesis, we propose Relational Neighborhood Inverse Consistency (RNIC), an extension of NIC defined as a local consistency property on the tuples of the relations of a CSP. We characterize RNIC for both binary and non-binary CSPs, and propose an algorithm for enforcing it whose complexity is bounded by …

Use Of Constraint Solving For Testing Software Product Lines, Jiangfan Shi

School of Computing: Dissertations, Theses, and Student Research

A new software engineering methodology, software product line (SPL) engineering, has been increasingly studied in academia and adopted inindustry in the past decade. It allows the delivery of similar, but customized, software products to customers in the same domain within a short timeperiod. Software product line engineering produces an SPL by defining feature commonality and variability, and is supported by a well-managed asset base. SPL engineering can improve productivity from three to ten times, however, we require more efficient testing methods, so that we canensure the correctness of SPLs with the same resource allocation percentage as in the traditional software …

Location Cheating: A Security Challenge To Location-Based Social Network Services, Mai Ren

School of Computing: Dissertations, Theses, and Student Research

Location-based mobile social network services such as Foursquare and Gowalla have grown exponentially over the past several years. These location-based services utilize the geographical position to enrich user experiences in a variety of contexts, including location-based searching and location-based mobile advertising. To attract more users, the location-based mobile social network services provide real-world rewards to the user, when a user checks in at a certain venue or location. This gives incentives for users to cheat on their locations.

In this thesis, we investigate the threat of location cheating attacks, find the root cause of the vulnerability, and outline the possible …

Distributed Algorithms For Energy Savings In The Core Network, Lin Liu

School of Computing: Dissertations, Theses, and Student Research

Recently, many efforts have been undertaken to reduce the energy consumption of core networks. Bundle link is a commonly deployed technique in core networks to combine several high-speed physical sublinks into a virtual connection to achieve bandwidth upgrade flexibility and network reliability. The traffic passing through a bundle link can be carried fully over the first few sublinks (bin packing) or evenly distributed over all sublinks (load balancing). In the current network when a bundle link is on, all of its sublinks are on, thus, selectively shutting down a few sublinks during periods of low traffic could save a large …

Efficient Traffic Crash And Snow Complaint Gis System, Anthony B. Ngo

School of Computing: Dissertations, Theses, and Student Research

We describe the design and implementation of a traffic crash and snow complaint GIS system developed for the Lincoln Public Works department. We also describe a novel geocoding algorithm that was used to move data from the older Criminal Justice Information System, which is a relational database, to the new GIS system. In addition, we describe the implementation of several indexing algorithms that enable the system to efficiently answer rectangular range queries and queries about the relative locations of moving objects. Finally, in many applications (on-line analysis or mobile GIS), we need to execute spatial query efficiently (fast and small), …

Chatbots In The Library: Is It Time?, Deeann Allison

University of Nebraska-Lincoln Libraries: Faculty Publications

This paper describes a pilot at the University of Nebraska-Lincoln for a chatbot that answers questions about the library and library resources. The chatbot was developed using a SQL database to store the question and answers using Artificial Intelligence Mark-up Language metadata. The user interface was built using PHP, adapted from Program-O. The open source PHP program was modified to support better display and the launching of URLs within the chatbot screen. Database content was created by “mining” library websites for information, and analyzing chat logs.

The chatbot answers questions from a variety of users from around the world. It …

Relational Neighborhood Inverse Consistency For Constraint Satisfaction, Robert J. Woodward, Shant Karakashian, Berthe Y. Choueiry, Christian Bessiere

School of Computing: Technical Reports

Freuder and Elfe [1996] introduced Neighborhood Inverse Consistency (NIC) as a new local consistency property for Constraint Satisfaction Problems (CSPs) that filters the domains of variables. Two advantages of the algorithm for enforcing NIC is that it automatically adapts its filtering power to the local connectivity of the network and has insignificant space overhead. In this document, we discuss Relational Neighborhood Inverse Consistency (RNIC), which is an extension of NIC to filter relations introduced in [Woodward et al., 2011a], how we enhance the propagation effectiveness by reformulating the dual graph of the CSP. We also describe an automated selection policy …