bluuebunny/crossref_metadata_2025 huggingface dataset:
Accounting for defect characteristics in evaluations of testing techniques
Authors: Strecker Jaymie , Memon Atif M.
Published: July 2012

As new software-testing techniques are developed, before they can achieve widespread acceptance, their effectiveness at detecting defects must be evaluated. The most common way of evaluating testing techniques is with empirical studies, in which one or more techniques are tried out on software with known defects. However, the defects used can affect the performance of the techniques. To complicate matters, it is not even clear how to effectively describe or characterize defects. To address these problems, this article describes an experiment architecture for empirically evaluating testing techniques which takes both defect and test-suite characteristics into account. As proof of concept, an experiment on GUI-testing techniques is conducted. It provides evidence that the defect characteristics proposed do help explain defect detection, at least for GUI testing, and it explores the relationship between the coverage of defective code and the detection of defects.
A two-phase approximation for model checking probabilistic unbounded until properties of probabilistic systems
Authors: Jennings Paul , Ghosh Arka P. , Basu Samik
Published: July 2012

We have developed a new approximate probabilistic model-checking method for
untimed
properties in probabilistic systems, expressed in a probabilistic temporal logic (PCTL, CSL). This method, in contrast to the existing ones, does not require the untimed until properties to be
bounded
a priori, where the bound refers to the number of discrete steps in the system required to verify the until property. The method consists of two phases. In the first phase, a suitable system- and property-dependent bound
k
0
is obtained automatically. In the second phase, the probability of satisfying the
k
0
-bounded until property is computed as the estimate of the probability of satisfying the original unbounded until property. Both phases require only verification of bounded until properties, which can be effectively performed by simulation-based methods. We prove the correctness of the proposed two-phase method and present its optimized implementation in the widely used PRISM model-checking engine. We compare this implementation with sampling-based model-checking techniques implemented in two tools: PRISM and MRMC. We show that for several models these existing tools fail to compute the result, while the two-phase method successfully computes the result efficiently with respect to time and space.
Gamification
Authors: Deterding Sebastian
Published: July 2012

Social Mediator is a forum exploring the ways that HCI research and principles interact---or might interact---with practices in the social media world.

Joe McCarthy, Editor
Pervasive science
Authors: Quintana Chris
Published: July 2012

In this forum we celebrate research that helps to successfully bring the benefits of computing technologies to children, older adults, people with disabilities, and other populations that are often ignored in the design of mass-marketed products.

Juan Pablo Hourcade, Editor
The role of enticing design in usability
Authors: Siegel David A.
Published: July 2012

Evaluation and usability as a practice area has diversified its approaches, broadened the spectrum of UX issues it addresses, and extended its contribution into deeper levels of product-development decision making. This forum addresses conceptual, methodological, and professional issues that arise in the field's continuing effort to contribute robust information about users to product planning and design.

David Siegel and Susan Dray, Editors
Border gateway protocol (BGP) and traceroute data workshop report
Authors: claffy kc
Published: July 2012

On Monday, 22 August 2011, CAIDA hosted a one-day workshop to discuss scalable measurement and analysis of BGP and traceroute topology data, and practical applications of such data analysis including tracking of macroscopic censorship and filtering activities on the Internet. Discussion topics included: the surprisingly stability in the number of BGP updates over time; techniques for improving measurement and analysis of inter-domain routing policies; an update on Colorado State's BGPMon instrumentation; using BGP data to improve the interpretation of traceroute data, both for real-time diagnostics (e.g., AS traceroute) and for large-scale topology mapping; using both BGP and traceroute data to support detection and mapping infrastructure integrity, including different types of of filtering and censorship; and use of BGP data to analyze existing and proposed approaches to securing the interdomain routing system. This report briefly summarizes the presentations and discussions that followed.
Waveperf
Authors: Kriegel Joffrey , Broekaert Florian , Pegatoquet Alain , Auguin Michel
Published: July 2012

Multi-core processors are more and more present in the embedded and real-time world. This paper introduces a code generator software applied to the benchmarking of embedded platforms. This solution creates an application runnable on embedded multicore platform and compliant with both POSIX or Xenomai interface. Running the application outputs an execution trace for each thread of the benchmark. It is also used to check the interruption latency and the preemption of real-time platforms.
Linux on FPGA platforms
Authors: Kretz Moritz , Kugel Andreas
Published: July 2012

Accessing custom hardware peripherals from a soft-CPU realized on FPGA fabric is a common task. We use a Virtex-5 FPGA with a MicroBlaze soft-CPU running a standard Linux kernel as the core of our embedded system. In order to enable processes on the Linux system to communicate with custom peripherals on the FPGA a device driver is implemented to take advantage of the fast simplex link (FSL) bus and the resulting performance regarding throughput and latency is measured.
Paravirtualizing Linux in a real-time hypervisor
Authors: Legout Vincent , Lemerre Matthieu
Published: July 2012

This paper describes a new hypervisor built to run Linux in a virtual machine. This hypervisor is built inside Anaxagoros, a real-time microkernel designed to execute safely hard real-time and non real-time tasks. This allows the execution of hard real-time tasks in parallel with Linux virtual machines without interfering with the execution of the real-time tasks.

We implemented this hypervisor and compared performances with other virtualization techniques. Our hypervisor does not yet provide high performance but gives correct results and we believe the design is solid enough to guarantee solid performances with its future implementation.
Performance implications of flash and storage class memories
Authors: Patel Naresh M.
Published: July 2012

The storage industry has seen incredible growth in data storage needs by both consumers and enterprises. Long-term technology trends mean that the data deluge will continue well into the future. These trends include the big-data trend (driven by data mining analytics, high-bandwidth needs, and large content repositories), server virtualization, cloud storage, and Flash. We will cover how Flash and storage class memories (SCM) interact with some of these major trends from a performance perspective.
Optimal queue-size scaling in switched networks
Authors: Shah Devavrat , Walton Neil , Zhong Yuan
Published: July 2012

We consider a switched (queueing) network in which there are constraints on which queues may be served simultaneously; such networks have been used to effectively model input-queued switches and wireless networks. The scheduling policy for such a network specifies which queues to serve at any point in time, based on the current state or past history of the system. In the main result of this paper, we provide a new class of online scheduling policies that achieve optimal average queue-size scaling for a class of switched networks including input-queued switches. In particular, it establishes the validity of a conjecture about optimal queue-size scaling for input-queued switches.
Minimizing slowdown in heterogeneous size-aware dispatching systems
Authors: Hyytiä Esa , Aalto Samuli , Penttinen Aleksi
Published: July 2012

We consider a system of parallel queues where tasks are assigned (dispatched) to one of the available servers upon arrival. The dispatching decision is based on the full state information, i.e., on the sizes of the new and existing jobs. We are interested in minimizing the so-called mean slowdown criterion corresponding to the mean of the sojourn time divided by the processing time. Assuming no new jobs arrive, the shortest-processing-time-product (SPTP) schedule is known to minimize the slowdown of the existing jobs. The main contribution of this paper is three-fold: 1) To show the optimality of SPTP with respect to slowdown in a single server queue under Poisson arrivals; 2) to derive the so-called size-aware value functions for M/G/1-FIFO/LIFO/SPTP with general holding costs of which the slowdown criterion is a special case; and 3) to utilize the value functions to derive efficient dispatching policies so as to minimize the mean slowdown in a heterogeneous server system. The derived policies offer a significantly better performance than e.g., the size-aware-task-assignment with equal load (SITA-E) and least-work-left (LWL) policies.
Bipartite graph structures for efficient balancing of heterogeneous loads
Authors: Leconte Mathieu , Lelarge Marc , Massoulié Laurent
Published: July 2012

This paper considers large scale distributed content service platforms, such as peer-to-peer video-on-demand systems. Such systems feature two basic resources, namely storage and bandwidth. Their efficiency critically depends on two factors: (i) content replication within servers, and (ii) how incoming service requests are matched to servers holding requested content. To inform the corresponding design choices, we make the following contributions. We first show that, for underloaded systems, so-called proportional content placement with a simple greedy strategy for matching requests to servers ensures full system efficiency provided storage size grows logarithmically with the system size. However, for constant storage size, this strategy undergoes a phase transition with severe loss of efficiency as system load approaches criticality.

To better understand the role of the matching strategy in this performance degradation, we characterize the asymptotic system efficiency under an optimal matching policy. Our analysis shows that -in contrast to greedy matching- optimal matching incurs an inefficiency that is exponentially small in the server storage size, even at critical system loads. It further allows a characterization of content replication policies that minimize the inefficiency. These optimal policies, which differ markedly from proportional placement, have a simple structure which makes them implementable in practice.

On the methodological side, our analysis of matching performance uses the theory of local weak limits of random graphs, and highlights a novel characterization of matching numbers in bipartite graphs, which may both be of independent interest.
Workload analysis of a large-scale key-value store
Authors: Atikoglu Berk , Xu Yuehai , Frachtenberg Eitan , Jiang Song , Paleczny Mike
Published: July 2012

Key-value stores are a vital component in many scale-out enterprises, including social networks, online retail, and risk analysis. Accordingly, they are receiving increased attention from the research community in an effort to improve their performance, scalability, reliability, cost, and power consumption. To be effective, such efforts require a detailed understanding of realistic key-value workloads. And yet little is known about these workloads outside of the companies that operate them. This paper aims to address this gap.

To this end, we have collected detailed traces from Facebook's Memcached deployment, arguably the world's largest. The traces capture over 284 billion requests from five different Memcached use cases over several days. We analyze the workloads from multiple angles, including: request composition, size, and rate; cache efficacy; temporal patterns; and application use cases. We also propose a simple model of the most representative trace to enable the generation of more realistic synthetic workloads by the community.

Our analysis details many characteristics of the caching workload. It also reveals a number of surprises: a GET/SET ratio of 30:1 that is higher than assumed in the literature; some applications of Memcached behave more like persistent storage than a cache; strong locality metrics, such as keys accessed many millions of times a day, do not always suffice for a high hit rate; and there is still room for efficiency and hit rate improvements in Memcached's implementation. Toward the last point, we make several suggestions that address the exposed deficiencies.
Uniform approximation of the distribution for the number of retransmissions of bounded documents
Authors: Jelenkovic Predrag R. , Skiani Evangelia D.
Published: July 2012

Retransmission-based failure recovery represents a primary approach in existing communication networks, on all protocol layers, that guarantees data delivery in the presence of channel failures. Contrary to the traditional belief that the number of retransmissions is geometrically distributed, a new phenomenon was discovered recently, which shows that retransmissions can cause long (-tailed) delays and instabilities even if all traffic and network characteristics are light-tailed, e.g., exponential or Gaussian. Since the preceding finding holds under the assumption that data sizes have infinite support, in this paper we investigate the practically important case of bounded data units 0≤ L
b
≤ b. To this end, we provide an explicit and uniform characterization of the entire body of the retransmission distribution Pr[N
b
> n] in both
n
and
b
. This rigorous approximation clearly demonstrates the previously observed transition from power law distributions in the main body to exponential tails. The accuracy of our approximation is validated with a number of simulation experiments. Furthermore, the results highlight the importance of wisely determining the size of data units in order to accommodate the performance needs in retransmission-based systems. From a broader perspective, this study applies to any other system, e.g., computing, where restart mechanisms are employed after a job processing failure.
Pricing cloud bandwidth reservations under demand uncertainty
Authors: Niu Di , Feng Chen , Li Baochun
Published: July 2012

In a public cloud, bandwidth is traditionally priced in a pay-as-you-go model. Reflecting the recent trend of augmenting cloud computing with bandwidth guarantees, we consider a novel model of cloud bandwidth allocation and pricing when explicit bandwidth reservation is enabled. We argue that a tenant's utility depends not only on its bandwidth usage, but more importantly on the portion of its demand that is satisfied with a performance guarantee. Our objective is to determine the optimal policy for pricing cloud bandwidth reservations, in order to maximize social welfare, i.e., the sum of the expected profits that can be made by all tenants and the cloud provider, even with the presence of demand uncertainty. The problem turns out to be a large-scale network optimization problem with a coupled objective function. We propose two new distributed solutions --- based on chaotic equation updates and cutting-plane methods --- that prove to be more efficient than existing solutions based on consistency pricing and subgradient methods. In addition, we address the practical challenge of forecasting demand statistics, required by our optimization problem as input. We propose a factor model for near-future demand prediction, and test it on a real-world video workload dataset. All included, we have designed a fully computerized trading environment for cloud bandwidth reservations, which operates effectively at a fine granularity of as small as ten minutes in our trace-driven simulations.
Renewable and cooling aware workload management for sustainable data centers
Authors: Liu Zhenhua , Chen Yuan , Bash Cullen , Wierman Adam , Gmach Daniel , Wang Zhikui , Marwah Manish , Hyser Chris
Published: July 2012

Recently, the demand for data center computing has surged, increasing the total energy footprint of data centers worldwide. Data centers typically comprise three subsystems: IT equipment provides services to customers; power infrastructure supports the IT and cooling equipment; and the cooling infrastructure removes heat generated by these subsystems. This work presents a novel approach to model the energy flows in a data center and optimize its operation. Traditionally, supply-side constraints such as energy or cooling availability were treated independently from IT workload management. This work reduces electricity cost and environmental impact using a holistic approach that integrates renewable supply, dynamic pricing, and cooling supply including chiller and outside air cooling, with IT workload planning to improve the overall sustainability of data center operations. Specifically, we first predict renewable energy as well as IT demand. Then we use these predictions to generate an IT workload management plan that schedules IT workload and allocates IT resources within a data center according to time varying power supply and cooling efficiency. We have implemented and evaluated our approach using traces from real data centers and production systems. The results demonstrate that our approach can reduce both the recurring power costs and the use of non-renewable energy by as much as 60% compared to existing techniques, while still meeting the Service Level Agreements.
Rumor centrality
Authors: Shah Devavrat , Zaman Tauhid
Published: July 2012

We consider the problem of detecting the source of a rumor (information diffusion) in a network based on observations about which set of nodes possess the rumor. In a recent work [10], this question was introduced and studied. The authors proposed
rumor centrality
as an estimator for detecting the source. They establish it to be the maximum likelihood estimator with respect to the popular Susceptible Infected (SI) model with exponential spreading time for regular trees. They showed that as the size of infected graph increases, for a line (2-regular tree) graph, the probability of source detection goes to 0 while for d-regular trees with d ≥ 3 the probability of detection, say α
d
, remains bounded away from 0 and is less than 1/2. Their results, however stop short of providing insights for the heterogeneous setting such as irregular trees or the SI model with non-exponential spreading times.

This paper overcomes this limitation and establishes the effectiveness of rumor centrality for source detection for generic random trees and the SI model with a generic spreading time distribution. The key result is an interesting connection between a multi-type continuous time branching process (an equivalent representation of a generalized Polya's urn, cf. [1]) and the effectiveness of rumor centrality. Through this, it is possible to quantify the detection probability precisely. As a consequence, we recover all the results of [10] as a special case and more importantly, we obtain a variety of results establishing the
universality
of rumor centrality in the context of tree-like graphs and the SI model with a generic spreading time distribution.
Network forensics
Authors: Milling Chris , Caramanis Constantine , Mannor Shie , Shakkottai Sanjay
Published: July 2012

Computer (and human) networks have long had to contend with spreading viruses. Effectively controlling or curbing an outbreak requires understanding the dynamics of the spread. A virus that spreads by taking advantage of physical links or user-acquaintance links on a social network can grow explosively if it spreads beyond a critical radius. On the other hand, random infections (that do not take advantage of network structure) have very different propagation characteristics. If too many machines (or humans) are infected, network structure becomes essentially irrelevant, and the different spreading modes appear identical. When can we distinguish between mechanics of infection? Further, how can this be done efficiently? This paper studies these two questions. We provide sufficient conditions for different graph topologies, for when it is possible to distinguish between a random model of infection and a spreading epidemic model, with probability of misclassification going to zero. We further provide efficient algorithms that are guaranteed to work in different regimes.
Does lean imply green?
Authors: Bhattacharya Suparna , Rajamani Karthick , Gopinath K. , Gupta Manish
Published: July 2012

The presence of software bloat in large flexible software systems can hurt energy efficiency. However, identifying and mitigating bloat is fairly effort intensive. To enable such efforts to be directed where there is a substantial potential for energy savings, we investigate the impact of bloat on power consumption under different situations. We conduct the first systematic experimental study of the joint power-performance implications of bloat across a range of hardware and software configurations on modern server platforms. The study employs controlled experiments to expose different effects of a common type of Java runtime bloat, excess temporary objects, in the context of the SPECPower_ssj2008 workload. We introduce the notion of equi-performance power reduction to characterize the impact, in addition to peak power comparisons. The results show a wide variation in energy savings from bloat reduction across these configurations. Energy efficiency benefits at peak performance tend to be most pronounced when bloat affects a performance bottleneck and non-bloated resources have low energy-proportionality. Equi-performance power savings are highest when bloated resources have a high degree of energy proportionality.

We develop an analytical model that establishes a general relation between resource pressure caused by bloat and its energy efficiency impact under different conditions of resource bottlenecks and energy proportionality. Applying the model to different "what-if" scenarios, we predict the impact of bloat reduction and corroborate these predictions with empirical observations. Our work shows that the prevalent software-only view of bloat is inadequate for assessing its power-performance impact and instead provides a full systems approach for reasoning about its implications.
D-factor
Authors: Lim Seung-Hwan , Huh Jae-Seok , Kim Youngjae , Shipman Galen M. , Das Chita R.
Published: July 2012

Scheduling multiple jobs onto a platform enhances system utilization by sharing resources. The benefits from higher resource utilization include reduced cost to construct, operate, and maintain a system, which often include energy consumption. Maximizing these benefits, while satisfying performance limits, comes at a price -- resource contention among jobs increases job completion time. In this paper, we analyze slow-downs of jobs due to contention for multiple resources in a system; referred to as
dilation factor
. We observe that multiple-resource contention creates non-linear dilation factors of jobs. From this observation, we establish a general quantitative model for dilation factors of jobs in multi-resource systems. A job is characterized by a vector-valued loading statistics and dilation factors of a job set are given by a quadratic function of their loading vectors. We demonstrate how to systematically characterize a job, maintain the data structure to calculate the dilation factor (loading matrix), and calculate the dilation factor of each job. We validated the accuracy of the model with multiple processes running on a native Linux server, virtualized servers, and with multiple MapReduce workloads co-scheduled in a cluster. Evaluation with measured data shows that the D-factor model has an error margin of less than 16%. We also show that the model can be integrated with an existing on-line scheduler to minimize the makespan of workloads.
Characterizing continuous time random walks on time varying graphs
Authors: Figueiredo Daniel , Nain Philippe , Ribeiro Bruno , de Souza e Silva Edmundo , Towsley Don
Published: July 2012

In this paper we study the behavior of a continuous time random walk (CTRW) on a stationary and ergodic time varying dynamic graph. We establish conditions under which the CTRW is a stationary and ergodic process. In general, the stationary distribution of the walker depends on the walker rate and is difficult to characterize. However, we characterize the stationary distribution in the following cases: i) the walker rate is significantly larger or smaller than the rate in which the graph changes (time-scale separation), ii) the walker rate is proportional to the degree of the node that it resides on (coupled dynamics), and iii) the degrees of node belonging to the same connected component are identical (structural constraints). We provide examples that illustrate our theoretical findings.
Clustered embedding of massive social networks
Authors: Song Han Hee , Savas Berkant , Cho Tae Won , Dave Vacha , Lu Zhengdong , Dhillon Inderjit S. , Zhang Yin , Qiu Lili
Published: July 2012

The explosive growth of social networks has created numerous exciting research opportunities. A central concept in the analysis of social networks is a proximity measure, which captures the closeness or similarity between nodes in the network. Despite much research on proximity measures, there is a lack of techniques to efficiently and accurately compute proximity measures for large-scale social networks. In this paper, we embed the original massive social graph into a much smaller graph, using a novel dimensionality reduction technique termed Clustered Spectral Graph Embedding. We show that the embedded graph captures the essential clustering and spectral structure of the original graph and allow a wide range of analysis to be performed on massive social graphs. Applying the clustered embedding to proximity measurement of social networks, we develop accurate, scalable, and flexible solutions to three important social network analysis tasks: proximity estimation, missing link inference, and link prediction. We demonstrate the effectiveness of our solutions to the tasks in the context of large real-world social network datasets: Flickr, LiveJournal, and MySpace with up to 2 million nodes and 90 million links.
TCAM-based NFA implementation
Authors: Peng Kunyang , Dong Qunfeng
Published: July 2012

Regular expression matching as the core packet inspection engine of network systems has long been striving to be both fast in matching speed (like DFA) and scalable in storage space (like NFA). Recently, ternary content addressable memory (TCAM) has been investigated as a promising way out, by implementing DFA using TCAM for regular express matching. In this paper, we present the first method for implementing NFA using TCAM. Through proper TCAM encoding, our method matches each input byte with one single TCAM lookup --- operating at precisely the same speed as DFA, while using a number of TCAM entries that can be close to NFA size. These properties make our method an important step along a new path --- TCAM-based NFA implementation --- towards the long-standing goal of fast and scalable regular expression matching.
Stable and efficient pricing for inter-domain traffic forwarding
Authors: Anshelevich Elliot , Hate Ameya , Kar Koushik , Usher Michael
Published: July 2012

We address the question of strategic pricing of inter-domain traffic forwarding services provided by ISPs, which is also closely coupled with the question of how ISPs route their traffic towards their neighboring ISPs. Posing this question as a non-cooperative game between neighboring ISPs, we study the properties of this pricing game in terms of the existence and efficiency of the equilibrium. We observe that for "well-provisioned" ISPs, Nash equilibrium prices exist and they result in flows that maximize the overall network utility (generalized end-to-end throughput). For general ISP topologies, equilibrium prices may not exist; however, simulations on a large number of realistic topologies show that best-response based simple price update solutions converge to stable and efficient prices and flows for most topologies.
Measuring and characterizing home networks
Authors: DiCioccio Lucas , Teixeira Renata , Rosenberg Catherine
Published: July 2012

This paper presents the design and evaluation of HomeNet Profiler, a tool that runs on an end-system in the home to collect data from home networks. HomeNet Profiler collects a wide range of measurements including: the set of devices, the set of services (with UPnP and Zeroconf), and the characteristics of the WiFi environment. Since the release of HomeNet Profiler in April 2011, we have collected data from over 2,400 distinct homes in 46 different countries.
Comparing metro-area cellular and WiFi performance
Authors: Sommers Joel , Barford Paul
Published: July 2012

Cellular and 802.11 WiFi offer two compelling connectivity options for mobile users. The goal of our work is to better understand performance characteristics of these technologies in diverse environments and conditions. To that end, we compare and contrast cellular and Wifi performance using crowd-sourced data from speedtest.net. We consider spatio-temporal performance aspects (e.g., upload and download throughput and latency) using over 3 million user-initiated tests initiated in 15 different metro areas, collected over 15 weeks. In these preliminary results, we find that WiFi performance generally exceeds cellular performance, and that observed characteristics are highly variable across different locations and times of day. We also observe diverse performance characteristics resulting from the rollout of new cell access technologies and service differences among local providers.
Modeling randomness in network traffic
Authors: Laner Markus , Svoboda Philipp , Rupp Markus
Published: July 2012

A continuous challenge in the field of network traffic modeling is to map recorded traffic onto parameters of random processes, in order to enable simulations of the respective traffic. A key element thereof is a convenient model which is simple, yet, captures the most relevant statistics.

This work aims to find such a model which, more precisely, enables the generation of multiple random processes with arbitrary but jointly characterized distributions, auto-correlation functions and cross-correlations. Hence, we present the definition of a novel class of models, the derivation of a respective closed-form analytical representation and its application on real network traffic.

Our modeling approach comprises: (i) generating statistical dependent Gaussian random processes, (ii) introducing auto-correlation to each process with a linear filter and, (iii) transforming them sample-wise by real-valued polynomial functions in order to shape their distributions. This particular structure allows to split the parameter fitting problem into three independent parts, each of which solvable by standard methods. Therefore, it is simple and straightforward to fit the model to measurement data.
Congestion control meets medium access
Authors: Bodas Shreeshankar , Shah Devavrat , Wischik Damon
Published: July 2012

This paper looks at the problem of designing medium access algorithm for wireless networks with the objective of providing high throughput and low delay performance to the users, while requiring only a modest computational effort at the transmitters and receivers. Additive inter-user interference at the receivers is an important physical layer characteristic of wireless networks. Today's Wi-Fi networks are based upon the abstraction of physical layer where inter-user interference is considered as noise leading to the 'collision' model in which users are required to co-ordinate their transmissions through Carrier Sensing Multiple Access (CSMA)-based schemes to avoid interference. This, in turn, leads to an inherent performance trade-off [1]: it is impossible to obtain high throughput and low delay by means of low complexity medium access algorithm (unless P=NP). As the main result, we establish that this trade-off is primarily due to treating interference as noise in the current wireless architecture. Concretely, we develop a simple medium access algorithm that allows for simultaneous transmissions of users to the same receiver by performing joint decoding at receivers, over time. For a receiver to be able to decode multiple transmissions quickly enough, we develop appropriate congestion control where each transmitter maintains a "window" of undecoded transmitted data that is adjusted based upon the "feedback" from the receiver. In summary, this provides an efficient, low complexity "online" code operating at varying rate, and the system as a whole experiences only small amount of delay (including decoding time) while operating at high throughput.
Characterizing the impact of the workload on the value of dynamic resizing in data centers
Authors: Wang Kai , Lin Minghong , Ciucu Florin , Wierman Adam , Lin Chuang
Published: July 2012

Energy consumption imposes a significant cost for data centers; yet much of that energy is used to maintain excess service capacity during periods of predictably low load. Resultantly, there has recently been interest in developing designs that allow the service capacity to be dynamically resized to match the current workload. However, there is still much debate about the value of such approaches in real settings. In this paper, we show that the value of dynamic resizing is highly dependent on statistics of the workload process. In particular, both slow time-scale non-stationarities of the workload (e.g., the peak-to-mean ratio) and the fast time-scale stochasticity (e.g., the burstiness of arrivals) play key roles. To illustrate the impact of these factors, we combine optimization-based modeling of the slow time-scale with stochastic modeling of the fast time scale. Within this framework, we provide both analytic and numerical results characterizing when dynamic resizing does (and does not) provide benefits.
Smartphones vs. laptops
Authors: Papapanagiotou Ioannis , Nahum Erich M. , Pappas Vasileios
Published: July 2012

In this work we present the differences and similarities of the web browsing behavior in most common mobile platforms. We devise a novel Operating System (OS) fingerprinting methodology to distinguish different types of wireless devices (smartphone vs laptops) as well as operating system instances (iOS, Android, BlackBerry etc.). We showcase that most of the multimedia content in smartphone devices is delivered via Range-Requests, and a large portion of the video transfers are aborted. We also show that laptop devices have more intelligent browser caching capabilities. We investigate the impact of an additional browser cache, and demonstrate that a 10MB browser cache that is able to handle partial downloads in smartphones would be enough to handle the majority of the savings. Finally, we showcase that caching policies need to be amended to attain the maximum possible savings in proxy caches. Based on those optimizations the emulated proxy cache provides 10%-20% in bandwidth savings.
Introduction to network experiments using the GENI cyberinfrastructure
Authors: Aikat Jay , Jeffay Kevin
Published: July 2012

In this tutorial, we will introduce the SIGMETRICS/Performance community to the vast testbeds, tools and resources openly available through the GENI (Global Environment for Network Innovations) project. We will present details about the distributed computing resources available on GENI for researchers interested in simulation as well as measurement-based performance evaluation experiments. We will demonstrate simple experiments on GENI, and leave them with information on how to run experiments for research and education using GENI resources.
Interferon regulatory factor-2 is protective against hepatic ischemia-reperfusion injury
Authors: Klune John R. , Dhupar Rajeev , Kimura Shoko , Ueki Shinya , Cardinal Jon , Nakao Atsunori , Nace Gary , Evankovich John , Murase Noriko , Tsung Allan , Geller David A.
Published: June 2012

Interferon regulatory factor (IRF)-1 is a nuclear transcription factor that induces inflammatory cytokine mediators and contributes to hepatic ischemia-reperfusion (I/R) injury. No strategies to mitigate IRF1-mediated liver damage exist. IRF2 is a structurally similar endogenous protein that competes with IRF1 for DNA binding sites in IRF-responsive target genes and acts as a competitive inhibitor. However, the role of IRF2 in hepatic injury during hypoxic or inflammatory conditions is unknown. We hypothesize that IRF2 overexpression may mitigate IRF1-mediated I/R damage. Endogenous IRF2 is basally expressed in normal livers and is mildly increased by ischemia alone. Overexpression of IRF2 protects against hepatic warm I/R injury. Furthermore, we demonstrate that IRF2 overexpression limits production of IRF1-dependent proinflammatory genes, such as IL-12, IFNβ, and inducible nitric oxide synthase, even in the presence of IRF1 induction. Additionally, isograft liver transplantation with IRF2 heterozygote knockout (IRF2+/−) donor grafts that have reduced endogenous IRF2 levels results in worse injury following cold I/R during murine orthotopic liver transplantation. These findings indicate that endogenous intrahepatic IRF2 protein is protective, because the IRF2-deficient liver donor grafts exhibited increased liver damage compared with the wild-type donor grafts. In summary, IRF2 overexpression protects against I/R injury by decreasing IRF1-dependent injury and may represent a novel therapeutic strategy.
Enteral nutrients potentiate glucagon-like peptide-2 action and reduce dependence on parenteral nutrition in a rat model of human intestinal failure
Authors: Brinkman Adam S. , Murali Sangita G. , Hitt Stacy , Solverson Patrick M. , Holst Jens J. , Ney Denise M.
Published: June 2012

Glucagon-like peptide-2 (GLP-2) is a nutrient-dependent, proglucagon-derived gut hormone that shows promise for the treatment of short bowel syndrome (SBS). Our objective was to investigate how combination GLP-2 + enteral nutrients (EN) affects intestinal adaption in a rat model that mimics severe human SBS and requires parenteral nutrition (PN). Male Sprague-Dawley rats were assigned to one of five groups and maintained with PN for 18 days: total parenteral nutrition (TPN) alone, TPN + GLP-2 (100 μg·kg−1·day−1), PN + EN + GLP-2(7 days), PN + EN + GLP-2(18 days), and a nonsurgical oral reference group. Animals underwent massive distal bowel resection followed by jejunocolic anastomosis and placement of jugular catheters. Starting on postoperative day 4, rats in the EN groups were allowed ad libitum access to EN. Groups provided PN + EN + GLP-2 had their rate of PN reduced by 0.25 ml/day starting on postoperative day 6. Groups provided PN + EN + GLP-2 demonstrated significantly greater body weight gain with similar energy intake and a safe 80% reduction in PN compared with TPN ± GLP-2. Groups provided PN + EN + GLP-2 for 7 or 18 days showed similar body weight gain, residual jejunal length, and digestive capacity. Groups provided PN + EN + GLP-2 showed increased jejunal GLP-2 receptor (GLP-2R), insulin-like growth factor-I (IGF-I), and IGF-binding protein-5 (IGFBP-5) expression. Treatment with TPN + GLP-2 demonstrated increased jejunal expression of epidermal growth factor. Cessation of GLP-2 after 7 days with continued EN sustained the majority of intestinal adaption and significantly increased expression of colonic proglucagon compared with PN + EN + GLP-2 for 18 days, and increased plasma GLP-2 concentrations compared with TPN alone. In summary, EN potentiate the intestinotrophic actions of GLP-2 by improving body weight gain allowing for a safe 80% reduction in PN with increased jejunal expression of GLP-2R, IGF-I, and IGFBP-5 following distal bowel resection in the rat.
Protein kinase Cδ differentially regulates cAMP-dependent translocation of NTCP and MRP2 to the plasma membrane
Authors: Park Se Won , Schonhoff Christopher M. , Webster Cynthia R. L. , Anwer M. Sawkat
Published: June 2012

Cyclic AMP stimulates translocation of Na+/taurocholate cotransporting polypeptide (NTCP) from the cytosol to the sinusoidal membrane and multidrug resistance-associated protein 2 (MRP2) to the canalicular membrane. A recent study suggested that protein kinase Cδ (PKCδ) may mediate cAMP-induced translocation of Ntcp and Mrp2. In addition, cAMP has been shown to stimulate NTCP translocation in part via Rab4. The aim of this study was to determine whether cAMP-induced translocation of NTCP and MRP2 require kinase activity of PKCδ and to test the hypothesis that cAMP-induced activation of Rab4 is mediated via PKCδ. Studies were conducted in HuH-NTCP cells (HuH-7 cells stably transfected with NTCP). Transfection of cells with wild-type PKCδ increased plasma membrane PKCδ and NTCP and increased Rab4 activity. Paradoxically, overexpression of kinase-dead dominant-negative PKCδ also increased plasma membrane PKCδ and NTCP as well as Rab4 activity. Similar results were obtained in PKCδ knockdown experiments, despite a decrease in total PKCδ. These results raised the possibility that plasma membrane localization rather than kinase activity of PKCδ is necessary for NTCP translocation and Rab4 activity. This hypothesis was supported by results showing that rottlerin, which has previously been shown to inhibit cAMP-induced membrane translocation of PKCδ and NTCP, inhibited cAMP-induced Rab4 activity. In addition, LY294002 (a phosphoinositide-3-kinase inhibitor), which has been shown to inhibit cAMP-induced NTCP translocation, also inhibited cAMP-induced PKCδ translocation. In contrast to the results with NTCP, cAMP-induced MRP2 translocation was inhibited in cells transfected with DN-PKCδ and small interfering RNA PKCδ. Taken together, these results suggest that the plasma membrane localization rather than kinase activity of PKCδ plays an important role in cAMP-induced NTCP translocation and Rab4 activity, whereas the kinase activity of PKCδ is necessary for cAMP-induced MRP2 translocation.
Exposing cardiomyocytes to subclinical concentrations of doxorubicin rapidly reduces their creatine transport
Authors: Darrabie Marcus D. , Arciniegas Antonio Jose Luis , Mantilla Jose Gabriel , Mishra Rajashree , Vera Miguel Pinilla , Santacruz Lucia , Jacobs Danny O.
Published: June 2012

Doxorubicin is commonly used to treat leukemia, lymphomas, and solid tumors, such as soft tissue sarcomas or breast cancer. A major side effect of doxorubicin therapy is dose-dependent cardiotoxicity. Doxorubicin's effects on cardiac energy metabolism are emerging as key elements mediating its toxicity. We evaluated the effect of doxorubicin on [14C]creatine uptake in rat neonatal cardiac myocytes and HL-1 murine cardiac cells expressing the human creatine transporter protein. A significant and irreversible decrease in creatine transport was detected after an incubation with 50–100 nmol/l doxorubicin. These concentrations are well below peak plasma levels (5 μmol/l) and within the ranges (25–250 nmol/l) for steady-state plasma concentrations reported after the administration of 15–90 mg/m2 doxorubicin for chemotherapy. The decrease in creatine transport was not solely because of increased cell death due to doxorubicin's cytotoxic effects. Kinetic analysis showed that doxorubicin decreased Vmax, Km, and creatine transporter protein content. Cell surface biotinylation experiments confirmed that the amount of creatine transporter protein present at the cell surface was reduced. Cardiomyocytes rely on uptake by a dedicated creatine transporter to meet their intracellular creatine needs. Our findings show that the cardiomyocellular transport capacity for creatine is substantially decreased by doxorubicin administration and suggest that this effect may be an important early event in the pathogenesis of doxorubicin-mediated cardiotoxicity.
Examining the Impact of Nitrous Acid Chemistry on Ozone and PM over the Pearl River Delta Region
Authors: Zhang Rui , Sarwar Golam , Fung Jimmy C. H. , Lau Alexis K. H. , Zhang Yuanhang
Published: July 2012

The impact of nitrous acid (HONO) chemistry on regional ozone and particulate matter in Pearl River Delta region was investigated using the community multiscale air quality (CMAQ) modeling system and the CB05 mechanism. Model simulations were conducted for a ten-day period in October 2004. Compared with available observed data, the model performance for NOx, SO2, PM10, and sulfate is reasonably good; however, predictions of HONO are an order of magnitude lower than observed data. The CB05 mechanism contains several homogenous reactions related to HONO. To improve the model performance for HONO, direct emissions, two heterogeneous reactions, and two surface photolysis reactions were incorporated into the model. The inclusion of the additional formation pathways significantly improved simulated HONO compared with observed data. The addition of HONO sources enhances daily maximum 8-hour ozone by up to 6 ppbV (8%) and daily mean PM2.5by up to 17 ug/m3(12%). They also affected ozone control strategy in Pearl River Delta region.
CUDAICA: GPU Optimization of Infomax-ICA EEG Analysis
Authors: Raimondo Federico , Kamienkowski Juan E. , Sigman Mariano , Fernandez Slezak Diego
Published: July 2012

In recent years, Independent Component Analysis (ICA) has become a standard to identify relevant dimensions of the data in neuroscience. ICA is a very reliable method to analyze data but it is, computationally, very costly. The use of ICA for online analysis of the data, used in brain computing interfaces, results are almost completely prohibitive. We show an increase with almost no cost (a rapid video card) of speed of ICA by about 25 fold. The EEG data, which is a repetition of many independent signals in multiple channels, is very suitable for processing using the vector processors included in the graphical units. We profiled the implementation of this algorithm and detected two main types of operations responsible of the processing bottleneck and taking almost 80% of computing time: vector-matrix and matrix-matrix multiplications. By replacing function calls to basic linear algebra functions to the standard CUBLAS routines provided by GPU manufacturers, it does not increase performance due to CUDA kernel launch overhead. Instead, we developed a GPU-based solution that, comparing with the original BLAS and CUBLAS versions, obtains a 25x increase of performance for the ICA calculation.
QoS Supported IPTV Service Architecture over Hybrid-Tree-Based Explicit Routed Multicast Network
Authors: Wen Chih-Chao , Wu Cheng-Shong
Published: July 2012

With the rapid advance in multimedia streaming and multicast transport technology, current IP multicast protocols, especially PIM-SM, become the major channel delivery mechanism for IPTV system over Internet. The goals for IPTV service are to provide two-way interactive services for viewers to select popular program channel with high quality for watching during fast channel surfing period. However, existing IP multicast protocol cannot meet above QoS requirements for IPTV applications between media server and subscribers. Therefore, we propose a cooperative scheme of hybrid-tree based on explicit routed multicast, called as HT-ERM to combine the advantages of shared tree and source tree for QoS-supported IPTV service. To increase network utilization, the constrained shortest path first (CSPF) routing algorithm is designed for construction of hybrid tree to deliver the high-quality video stream over watching channel and standard quality over surfing channel. Furthermore, the Resource Reservation Protocol- Traffic Engineering (RSVP-TE) is used as signaling mechanism to set up QoS path for multicast channel admission control. Our simulation results demonstrated that the proposed HT-ERM scheme outperforms other multicast QoS-based delivery scheme in terms of channel switching delay, resource utilization, and blocking ratio for IPTV service.