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Hanghang Tong Spiros Papadimitriou Christos Faloutsos Philip S. Yu Tina Eliassi-Rad 《Information Retrieval》2012,15(3-4):391-411
Given a graph, how to find a small group of ‘gateways’, that is a small subset of nodes that are crucial in connecting the source to the target? For instance, given a social network, who is the best person to introduce you to, say, Chris Ferguson, the poker champion? Or, given a network of people and skills, who is the best person to help you learn about, say, wavelets? We formally formulate this problem in two scenarios: Pair-Gateway and Group-Gateway. For each scenario, we show that it is sub-modular and thus it can be solved near-optimally. We further give fast, scalable algorithms to find such gateways. Extensive experimental evaluations on real data sets demonstrate the effectiveness and efficiency of the proposed methods. 相似文献
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Christos Katsanos Nikolaos Tselios Athanasios Tsakoumis Nikolaos Avouris 《Education and Information Technologies》2012,17(1):79-94
Many websites remain inaccessible for people with disabilities, despite the availability of relevant guidelines and tools.
This is mainly due to lack of appropriate training of Web designers on accessibility technology. In this paper, a project
based learning activity designed to instruct Web accessibility guidelines and good design practices is presented. The activity
is mediated by a web-based learning environment, which presents real-world examples of accessibility impasses that arise when
certain, established guidelines are violated, and then provides advice on how to avoid or resolve them. The learning material
contained in the tool is offered through a faceted browsing approach, thus enabling active exploration by the learner. A within-subjects
case study compared the learning effectiveness of traditional academic instruction (pre-condition) with the proposed project
based activity (post-condition) in the context of a University course. A significant improvement in students’ academic performance
and perceived learning was found. 相似文献
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Athanassios Protopapas Aikaterini Fakou Styliani Drakopoulou Christos Skaloumbakas Angeliki Mouzaki 《Reading and writing》2013,26(5):615-646
In this study we propose a classification system for spelling errors and determine the most common spelling difficulties of Greek children with and without dyslexia. Spelling skills of 542 children from the general population and 44 children with dyslexia, Grades 3–4 and 7, were assessed with a dictated common word list and age-appropriate passages. Spelling errors were classified into broad categories, including phonological (graphophonemic mappings), grammatical (inflectional suffixes), orthographic (word stems), stress assignment (diacritic), and punctuation. Errors were further classified into specific subcategories. Relative proportions for a total of 11,364 errors were derived by calculating the opportunities for each error type. Nondyslexic children of both age groups made primarily grammatical and stress errors, followed by orthographic errors. Phonological and punctuation errors were negligible. Most frequent specific errors were in derivational affixes, stress diacritics, inflectional suffixes, and vowel historical spellings. Older children made fewer errors, especially in inflectional suffixes. Dyslexic children differed from nondyslexic ones in making more errors of the same types, in comparable relative proportions. Spelling profiles of dyslexic children did not differ from those of same-age children with poor reading skills or of younger children matched in reading and phonological awareness. In conclusion, spelling errors of both dyslexic and nondyslexic children indicate persistent difficulty with internalizing regularities of the Greek orthographic lexicon, including derivational, inflectional, and word (stem) families. This difficulty is greater for children with dyslexia. 相似文献
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Christos Dimitriadis 《Roeper Review》2013,35(2):107-122
This article presents findings from a case study of an in-classroom program based on ability grouping for Year 2 (ages 6–7) primary (elementary) children identified as high ability in mathematics. The study examined the role of classroom setting, classroom environment, and teacher’s approach in realizing and developing mathematical promise. The teacher’s approach was found to be fundamental to revealing and developing mathematical promise. However, a large regular classroom with a range of ability, along with some common beliefs that link mathematical prowess with competence in numerical calculations and that dominate the classroom environment, pose some major challenges for the teacher as well as obstacles and threats to the development of mathematical promise. The article illuminates these issues and suggests possible solutions. 相似文献
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Yoann M. Garnier Christos Paizis Romuald Lepers 《European Journal of Sport Science》2019,19(2):166-176
The present study assessed neuromuscular and corticospinal changes during and after a fatiguing submaximal exercise of the knee extensors in different modes of muscle contraction. Twelve subjects performed two knee extensors exercises in a concentric or eccentric mode, at the same torque and with a similar total impulse. Exercises consisted of 10 sets of 10 repetitions at an intensity of 80% of the maximal voluntary isometric contraction torque (MVIC). MVIC, maximal voluntary activation level (VAL) and responses of electrically evoked contractions of the knee extensors were assessed before and after exercise. Motor evoked potential amplitude (MEP) and cortical silent period (CSP) of the vastus medialis (VM) and rectus femoris (RF) muscles were assessed before, during and after exercise. Similar reductions of the MVIC (?13%), VAL (?12%) and a decrease in the peak twitch (?12%) were observed after both exercises. For both VM and RF muscles, MEP amplitude remained unchanged during either concentric or eccentric exercises. No change of the MEP amplitude input–output curves was observed post-exercise. For the RF muscle, CSP increased during the concentric exercise and remained lengthened after this exercise. For the VM muscle, CSP was reduced after the eccentric exercise only. For a similar amount of total impulse, concentric and eccentric knee extensor contractions led to similar exercise-induced neuromuscular response changes. For the two muscles investigated, no modulation of corticospinal excitability was observed during or after either concentric or eccentric exercises. However, intracortical inhibition showed significant modulations during and after exercise. 相似文献
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Christos V. Massalas George I. Tzivanidis John T. Katsikadelis 《Journal of The Franklin Institute》1978,306(6):449-455
In this paper, a solution is presented to the buckling problem of a continuous beam resting on a tensionless foundation model that was proposed by Winkler and by Reissner. 相似文献
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Stella Vosniadou Christos Ioannides 《International Journal of Science Education》2013,35(10):1213-1230
A theoretical framework based on cognitive/developmental research is described. It is argued that science learning is a gradual process during which initial conceptual structures based on children's interpretations of everyday experience are continuously enriched and restructured. Conceptual change also involves increased metaconceptual awareness, cognitive flexibility, and theoretical coherence. Some of the implications of this research for the development of science curricula and for instruction are discussed. It is also argued that while cognitive/developmental research can provide us with important information about the process of learning science, it does not provide much information about the external, environmental variables that can facilitate cognitive performance and conceptual change. What is needed in the future is the development of a theory of learning that bridges science education and cognitive/developmental research. Such a theory should specify the mechanisms that can take an individual from one level of cognitive performance to the next and relate them to situational and cultural factors. 相似文献
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The diverse array of contributions to the discipline of e-government, from evaluative frameworks and conceptual models to guidelines for initiatives and implementation architectures, evidences the requirement, both from the researcher's and the practitioner's standpoint, of sound theoretical foundations that can be applied directly in practice. We propose a cycle between theory and practice where theoretical approaches will support informed empirical studies of initiatives and enable the processes for future implementations, the analysis of which will lead to more encompassing theories. Upon this proposition, we present a theoretical analysis of e-government evolution and subsequently test the results of this analysis against two real-life cases. The juxtaposition of the theoretical positions and the practical findings leads us to the development of a set of guidelines for the analysis and design of e-government information systems. We frame these guidelines into an existing reference model for information systems development. Thus, the paper's contribution lies on three axes: first, the furthering of a theoretical perspective of e-government; second, the combination of theory and practice in the effort to understand practical particularities of the field; and third, the introduction of a usable set of design guidelines that can be applied in future implementations. 相似文献
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Sebastian Hoenen Christos Kolympiris Wilfred Schoenmakers Nicholas Kalaitzandonakes 《Research Policy》2014
A long stream of research has documented the positive effects that patents bring about to emerging firms in high technology industries. The general consensus is that patents contribute to firm growth because they confer monopolistic market rights, offer protection from competitors, increase the negotiating position of patent holders and other benefits. What has received relatively less attention in the literature is whether patents act as a signal that attracts investors such as venture capital firms. The handful of studies that have addressed that question has not analyzed whether the signaling function of patents decreases after the initial attraction of venture capital, as information asymmetries between investors and target firms reduce. In this study we hypothesize that patent activity has a signaling value that diminishes once information asymmetries between investors and funded firms lessen. To study our proposition we draw upon a longitudinal dataset of more than 580 U.S.-based biotechnology firms to empirically demonstrate that biotechnology firms that have submitted patent applications substantially increase the level of funding they receive for their first round of financing. In line with a reduction of information asymmetries once the initial investment has materialized, patent applications and granted patents have no effect on the growth of venture capital funds raised during the second round of financing. We conclude the study with a discussion of avenues for new research, implications for policy makers that consider the usefulness of the current patent system and with insights that can be employed by managers of firms in knowledge intensive areas such as biotechnology. 相似文献