Exploring the use of information visualization for digital libraries

This paper presents the findings from a study conducted to explore the current and future use of information visualization (IV) for digital libraries (DL). A series of query techniques and participatory design workshops were employed with the goal of actively involving users in identifying the key characteristics and applications of IV for DLs. The methodology employed, key findings and overall conclusions are presented and discussed.     

On scaling the IEEE 802.11 to facilitate scalable wireless networks

The IEEE 802.11 MAC protocol has gained widespread popularity and has been adopted as the de-facto layer 2 protocol for wireless local area networks (WLANs). However, it is well known that as the number of competing stations increases, the performance of the protocol degrades dramatically. Given the explosive growth in WLANs’ usage, the question of how to sustain each user’s perceived performance when a large number of competing stations are present, is an important and challenging open research problem.Motivated by this, in this paper we analyze the behavior of 802.11-based WLANs as the number of competing stations increases, and attempt to provide concrete answers to the following fundamental questions: (i) is there a set of system and protocol parameters that we can scale in order to sustain each individual user’s perceived performance, and (ii) what is the minimum scaling factor?Using theoretical analysis coupled with extensive simulations we show that such a set of parameters exists, and that the minimum scaling factor is equal to the factor by which the number of users increases. Our results reveal several important scaling properties that exist in today’s 802.11-based wireless networks, and set guidelines for designing future versions of such networks that can efficiently support a very large number of users.     

Power efficiency through tuple ranking in?wireless sensor network monitoring

In this paper, we present an innovative framework for efficiently monitoring Wireless Sensor Networks (WSNs). Our framework, coined KSpot, utilizes a novel top-k query processing algorithm we developed, in conjunction with the concept of in-network views, in order to minimize the cost of query execution. For ease of exposition, consider a set of sensors acquiring data from their environment at a given time instance. The generated information can conceptually be thought as a horizontally fragmented base relation R. Furthermore, the results to a user-defined query Q, registered at some sink point, can conceptually be thought as a view V. Maintaining consistency between V and R is very expensive in terms of communication and energy. Thus, KSpot focuses on a subset V??(?V) that unveils only the k highest-ranked answers at the sink, for some user defined parameter k. To illustrate the efficiency of our framework, we have implemented a real system in nesC, which combines the traditional advantages of declarative acquisition frameworks, like TinyDB, with the ideas presented in this work. Extensive real-world testing and experimentation with traces from UC-Berkeley, the University of Washington and Intel Research Berkeley, show that KSpot provides an up to 66% of energy savings compared to TinyDB, minimizes both the size and number of packets transmitted over the network (up to 77%), and prolongs the longevity of a WSN deployment to new scales.     

A comprehensive solution for application‐level adaptation

Driven by the emergence of mobile and pervasive computing there is a growing demand for context‐aware software systems that can dynamically adapt to their run‐time environment. We present the results of project MADAM that has delivered a comprehensive solution for the development and operation of context‐aware, self‐adaptive applications. The main contributions of MADAM are (a) a sophisticated middleware that supports the dynamic adaptation of component‐based applications, and (b) an innovative model‐driven development methodology that is based on abstract adaptation models and corresponding model‐to‐code transformations. MADAM has demonstrated the viability of a general, integrated approach to application‐level adaptation. We discuss our experiences with two real‐world case studies that were built using the MADAM approach. Copyright © 2008 John Wiley & Sons, Ltd.     

A Glance into Social and Evolutionary Aspects of an Artifact Ecology for Collaborative Learning through the Lens of Distributed Cognition

There is steadily growing interest in the design and evaluation of digitally enhanced spaces in the real-world where users use, combine, and appropriate different physical and digital tools based on the task at hand. Under the notion of “ubiquitous computing,” researchers have explored tools and theories to analyze, understand, and model users in complex socio-technical systems. Yet, even though theoretical approaches play a significant role in the work of practitioners, there is a general difficulty in applying them, pushing researchers to explore methodological frameworks with clearer guidelines. Using the distributed cognition for teamwork (DiCoT) framework, we study collaboration and communication patterns, physical movement, and social structures of two groups of learners working on a design problem as they evolve over a 3-month period. Through an in-depth investigation, we present detailed accounts of the social and evolutionary models of DiCoT for each group. Our analysis enriches the DiCoT framework by identifying five new principles: social emersion and social circles of privacy for the social model, and continuity, mutual adaptation, and semantics of body for the evolutionary model. This article contributes to HCI research by refining and extending the existing DiCoT framework and elaborating on two dimensions that have previously been under-developed in the literature.     

Wear identification in rotor-bearing systems by measurements of dynamic bearing characteristics

During operation of rotating machines, journal and bearing mechanisms are progressively worn down. To prevent catastrophic failure of a rotating system, it is necessary both to detect wear precisely, without shutting down and dismantling the machinery and to predict future replacement needs. In this work, Computational Fluid Dynamics (CFD) analysis is used to solve the Navier–Stokes equations. Diagrams of bearing characteristics such as relative eccentricity, attitude angle, lubricant side flow and friction coefficient versus Sommerfeld number are presented for various wear depths and used for online wear identification. A graphical detection method is analytically presented to identify the wear depth associated with the measured dynamic bearing characteristics.     

Graphs of linear clique-width at most 3

A graph has linear clique-width at most k if it has a clique-width expression using at most k labels such that every disjoint union operation has an operand which is a single vertex graph. We give the first characterisation of graphs of linear clique-width at most 3, and we give the first polynomial-time recognition algorithm for graphs of linear clique-width at most 3. In addition, we present new characterisations of graphs of linear clique-width at most 2. We also give a layout characterisation of graphs of bounded linear clique-width; a similar characterisation was independently shown by Gurski and by Lozin and Rautenbach.     

Extending WebDAV With Multiple-Granularity Locking

In distributed Web authoring, shared documents can be accessed concurrently by multiple authors who must be coordinated to avoid conflicts. The current Web standard for distributed authoring and versioning uses a two-phase locking to coordinate concurrent access. As the degree to which authors work concurrently may vary though among cooperative sessions, it is necessary to extend the aforementioned standard so as to support a multitude of lock granularity levels. In this paper, we first examine related protocols from the database literature, and then, we comment on their suitability for distributed authoring in the World Wide Web. Our main contribution is a multiple-granularity locking protocol, in which the locks are optional and they convey the meanings of access mode, locking scope, and locking effect. This protocol allows synchronous collaboration by guaranteeing a conflict-free environment and avoiding update loss while it also supports version control. Specifically, by identifying and timestamping object versions, the protocol preserves author intention and operation causality, which were possible so far with operational transformation only. The protocol's efficiency, finally, is demonstrated by a real test with human users and evaluated with simulation experiments, which reveal significant advantages over other protocols of this kind.     

Damage and loading rate effects on the microfailure behaviour of Al2O3-ceramics studied by SEM

A scanning electron microscopy (SEM)-X-ray combined experimental approach to qualitative and semi-quantitative characterization of microfailure behaviour of an Al₂O₃-ceramic material in terms of induced damage is presented. The qualitative approach was based on representative fractographical images and data obtained by SEM whereas the semi-quantitative approach was based on a new technique of the X-ray electron probe microanalysis (X-ray EPMA) capable to detect the localized subsurface damage. The damage was induced by a simple rotary notch-cutting procedure where the associated damage parameters can be controlled by the cutting rate. By correlating certain characteristic macro- and microfractographic features/patterns with well-known microfailure mechanisms it was possible to make qualitatively, in an indirect way, evident the existence of induced damage which was assumed to be ideal brittle having only microcracking component. In the same correlating way the stimulating effect of internal pores on the damage development was deduced. Observed loading rate effects on the fractographic behaviour expressed by changes in fracture roughness and micromorphology were attributed to pore-assisted microcracking linkage. Low porosity under high loading rates tends to lower the fractographic roughness, a fact which can be related with a reduction in the ability of energy dissipation. On the other hand, high porosity under increasing loading rates leads to non observable changes in the fractographic roughness, a fact which is indicative of corresponding no appreciable changes in the dissipative character of the material. The measured local damage distribution ahead of the notch-tip shows a monotonic increasing of damaging effects toward the tip. By means of this distribution the total or average damage degree and process zone length ahead of the notch-tip were evaluated. The increase of these two damage parameters is not proportional to the increase in the cutting speed i.e. the rate of damage development. Finally, by assuming brittle damage an experimental approaching procedure for the estimation of the induced energy required for the microcracking damage was proposed.