1,012,180 research outputs found

    A Distributed Frank-Wolfe Algorithm for Communication-Efficient Sparse Learning

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    Learning sparse combinations is a frequent theme in machine learning. In this paper, we study its associated optimization problem in the distributed setting where the elements to be combined are not centrally located but spread over a network. We address the key challenges of balancing communication costs and optimization errors. To this end, we propose a distributed Frank-Wolfe (dFW) algorithm. We obtain theoretical guarantees on the optimization error ϵ\epsilon and communication cost that do not depend on the total number of combining elements. We further show that the communication cost of dFW is optimal by deriving a lower-bound on the communication cost required to construct an ϵ\epsilon-approximate solution. We validate our theoretical analysis with empirical studies on synthetic and real-world data, which demonstrate that dFW outperforms both baselines and competing methods. We also study the performance of dFW when the conditions of our analysis are relaxed, and show that dFW is fairly robust.Comment: Extended version of the SIAM Data Mining 2015 pape

    LTR-retrotransposons in R. exoculata and other crustaceans

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    Transposable elements are major constituents of eukaryote genomes and have a great impact on genome structure and stability. They can contribute to the genetic diversity and evolution of organisms. Knowledge of their distribution among several genomes is an essential condition to study their dynamics and to better understand their role in species evolution. LTR-retrotransposons have been reported in many diverse eukaryote species, describing a ubiquitous distribution. Given their abundance, diversity and their extended ranges in C-values, environment and life styles, crustaceans are a great taxon to investigate the genomic component of adaptation and its possible relationships with TEs. However, crustaceans have been greatly underrepresented in transposable element studies. Using both degenerate PCR and in silico approaches, we have identified 35 Copia and 46 Gypsy families in 15 and 18 crustacean species, respectively. In particular, we characterized several full-length elements from the shrimp Rimicaris exoculata that is listed as a model organism from hydrothermal vents. Phylogenic analyses show that Copia and Gypsy retrotransposons likely present two opposite dynamics within crustaceans. The Gypsy elements appear relatively frequent and diverse whereas Copia are much more homogeneous, as 29 of them belong to the single GalEa clade, and species- or lineage-dependent. Our results also support the hypothesis of the Copia retrotransposon scarcity in metazoans compared to Gypsy elements. In such a context, the GalEa-like elements present an outstanding wide distribution among eukaryotes, from fishes to red algae, and can be even highly predominant within a large taxon, such as Malacostraca. Their distribution among crustaceans suggests a dynamics that follows a "domino days spreading" branching process in which successive amplifications may interact positively

    Persuasive system design does matter: a systematic review of adherence to web-based interventions

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    Background: Although web-based interventions for promoting health and health-related behavior can be effective, poor adherence is a common issue that needs to be addressed. Technology as a means to communicate the content in web-based interventions has been neglected in research. Indeed, technology is often seen as a black-box, a mere tool that has no effect or value and serves only as a vehicle to deliver intervention content. In this paper we examine technology from a holistic perspective. We see it as a vital and inseparable aspect of web-based interventions to help explain and understand adherence. Objective: This study aims to review the literature on web-based health interventions to investigate whether intervention characteristics and persuasive design affect adherence to a web-based intervention. Methods: We conducted a systematic review of studies into web-based health interventions. Per intervention, intervention characteristics, persuasive technology elements and adherence were coded. We performed a multiple regression analysis to investigate whether these variables could predict adherence. Results: We included 101 articles on 83 interventions. The typical web-based intervention is meant to be used once a week, is modular in set-up, is updated once a week, lasts for 10 weeks, includes interaction with the system and a counselor and peers on the web, includes some persuasive technology elements, and about 50% of the participants adhere to the intervention. Regarding persuasive technology, we see that primary task support elements are most commonly employed (mean 2.9 out of a possible 7.0). Dialogue support and social support are less commonly employed (mean 1.5 and 1.2 out of a possible 7.0, respectively). When comparing the interventions of the different health care areas, we find significant differences in intended usage (p = .004), setup (p < .001), updates (p < .001), frequency of interaction with a counselor (p < .001), the system (p = .003) and peers (p = .017), duration (F = 6.068, p = .004), adherence (F = 4.833, p = .010) and the number of primary task support elements (F = 5.631, p = .005). Our final regression model explained 55% of the variance in adherence. In this model, a RCT study as opposed to an observational study, increased interaction with a counselor, more frequent intended usage, more frequent updates and more extensive employment of dialogue support significantly predicted better adherence. Conclusions: Using intervention characteristics and persuasive technology elements, a substantial amount of variance in adherence can be explained. Although there are differences between health care areas on intervention characteristics, health care area per se does not predict adherence. Rather, the differences in technology and interaction predict adherence. The results of this study can be used to make an informed decision about how to design a web-based intervention to which patients are more likely to adher

    Using Gameplay Patterns to Gamify Learning Experiences

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    Gamification refers to the use of gaming elements to enhance user experience and engagement in non-gaming systems. In this paper we report the design and implementation of two higher education courses in which ludic elements were used to enhance the quality of the learning experience. A game can be regarded as a system of organised gameplay activities, and a course can be regarded as a system of organised learning activities. Leveraging this analogy, analysing games can provide valuable insights to organise learning activities within a learning experience. We examined a sample of successful commercial games to identify patterns of organisation of gameplay activities that could be applied to a course design. Five patterns were identified: quest structure, strategic open-endedness, non-linear progression, orientation, and challenge-based reward. These patterns were then used to define the instructional design of the courses. As a result, courses were organised as systems of quests that could be tackled through different strategies and in a non-linear way. Students received frequent feedback and were rewarded according to the challenges chosen, based on mechanics common in quest-based games. The courses involved two lecturers and 70 students. Learning journals were used throughout the term to collect data regarding student perceptions on the clarity and usefulness of the gamified approach, level of motivation and engagement in the courses, and relevance of the activities proposed. Results show that students felt challenged by the activities proposed and motivated to complete them, despite considering most activities as difficult. Students adopted different cognitive and behavioural strategies to cope with the courses’ demands. They had to define their own team project, defining the objectives, managing their times and coordinating task completion. The regular and frequent provision of feedback was highly appreciated. A sense of mastery was promoted and final achievement was positively impacted by the gamified strategy

    Genomic insights into the rapid emergence and evolution of MDR in Staphylococcus pseudintermedius.

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    OBJECTIVES: MDR methicillin-resistant Staphylococcus pseudintermedius (MRSP) strains have emerged rapidly as major canine pathogens and present serious treatment issues and concerns to public health due to their, albeit low, zoonotic potential. A further understanding of the genetics of resistance arising from a broadly susceptible background of S. pseudintermedius is needed. METHODS: We sequenced the genomes of 12 S. pseudintermedius isolates of varied STs and resistance phenotypes. RESULTS: Nine distinct clonal lineages had acquired either staphylococcal cassette chromosome (SCC) mec elements and/or Tn5405-like elements carrying up to five resistance genes [aphA3, sat, aadE, erm(B), dfrG] to generate MRSP, MDR methicillin-susceptible S. pseudintermedius and MDR MRSP populations. The most successful and clinically problematic MDR MRSP clones, ST68 SCCmecV(T) and ST71 SCCmecII-III, have further accumulated mutations in gyrA and grlA conferring resistance to fluoroquinolones. The carriage of additional mobile genetic elements (MGEs) was highly variable, suggesting that horizontal gene transfer is frequent in S. pseudintermedius populations. CONCLUSIONS: Importantly, the data suggest that MDR MRSP evolved rapidly by the acquisition of a very limited number of MGEs and mutations, and that the use of many classes of antimicrobials may co-select for the spread and emergence of MDR and XDR strains. Antimicrobial stewardship will need to be comprehensive, encompassing human medicine and veterinary disciplines to successfully preserve antimicrobial efficacy

    Frequent Elements with Witnesses in Data Streams

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    Detecting frequent elements is among the oldest and most-studied problems in the area of data streams. Given a stream of mm data items in {1,2,,n}\{1, 2, \dots, n\}, the objective is to output items that appear at least dd times, for some threshold parameter dd, and provably optimal algorithms are known today. However, in many applications, knowing only the frequent elements themselves is not enough: For example, an Internet router may not only need to know the most frequent destination IP addresses of forwarded packages, but also the timestamps of when these packages appeared or any other meta-data that "arrived" with the packages, e.g., their source IP addresses. In this paper, we introduce the witness version of the frequent elements problem: Given a desired approximation guarantee α1\alpha \ge 1 and a desired frequency dΔd \le \Delta, where Δ\Delta is the frequency of the most frequent item, the objective is to report an item together with at least d/αd / \alpha timestamps of when the item appeared in the stream (or any other meta-data that arrived with the items). We give provably optimal algorithms for both the insertion-only and insertion-deletion stream settings: In insertion-only streams, we show that space O~(n+dn1α)\tilde{O}(n + d \cdot n^{\frac{1}{\alpha}}) is necessary and sufficient for every integral 1αlogn1 \le \alpha \le \log n. In insertion-deletion streams, we show that space O~(ndα2)\tilde{O}(\frac{n \cdot d}{\alpha^2}) is necessary and sufficient, for every αn\alpha \le \sqrt{n}.Comment: Fixed the statement of Lemma 5.1, introduction update
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