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31.
Ioannis Basdekis Iosif Klironomos Ioannis Metaxas Constantine Stephanidis 《Universal Access in the Information Society》2010,9(2):185-190
This communication reports on the results of a web accessibility audit of public Web sites in Greece. The audit was conducted
in 2008 by the Human Computer Interaction Laboratory of the Institute of Computer Science of FORTH, in its capacity as the
Greek National Contact Centre of the European Design for All e-Accessibility Network. In an earlier e-Accessibility study
in 2004, that evaluated approximately 250 public and commercial Web sites in Greece, 73% of the sample failed to meet the
most basic requirements for web accessibility (). Four years later, in the context of a re-audit, a similar sample was examined for compliance with the same web accessibility
standard (WCAG 1.0), as set by the Web Accessibility Initiative of the World Wide Web Consortium. The accessibility checks
were conducted during the period from March to September 2008. A comparison of the results indicates that although new web
development technologies may have been employed, instead of improving the overall status of e-accessibility, this has resulted
in a serious deterioration in overall accessibility levels. Such findings—85% of sites failed to comply with Level A—suggest
that Greek Web sites are likely to present even more significant access barriers to people with disability than in the past.
As Web Accessibility is poorly understood and, until today, new platforms have failed to deliver products that conform to
WCAG, the need emerges for a concrete legislative framework to set accessibility specifications for all public Web sites in
Greece. 相似文献
32.
ROSy+: 3D Object Pose Normalization Based on PCA and Reflective Object Symmetry with Application in 3D Object Retrieval 总被引:1,自引:0,他引:1
Konstantinos Sfikas Theoharis Theoharis Ioannis Pratikakis 《International Journal of Computer Vision》2011,91(3):262-279
A novel pose normalization method based on 3D object reflective symmetry is presented. It is a general purpose global pose
normalization method; in this paper it is used to enhance the performance of a 3D object retrieval pipeline. Initially, the
axis-aligned minimum bounding box of a rigid 3D object is modified by requiring that the 3D object is also in minimum angular
difference with respect to the normals to the faces of its bounding box. To estimate the modified axis-aligned bounding box,
a set of predefined planes of symmetry are used and a combined spatial and angular distance, between the 3D object and its
symmetric object, is calculated. By minimizing the combined distance, the 3D object fits inside its modified axis-aligned
bounding box and alignment with the coordinate system is achieved. The proposed method is incorporated in a hybrid scheme,
that serves as the alignment method in a 3D object retrieval system. The effectiveness of the 3D object retrieval system,
using the hybrid pose normalization scheme, is evaluated in terms of retrieval accuracy and demonstrated using both quantitative
and qualitative measures via an extensive consistent evaluation on standard benchmarks. The results clearly show performance
boost against current approaches. 相似文献
33.
34.
Ioanna Lykourentzou Ioannis Giannoukos Vassilis Nikolopoulos George Mpardis Vassili Loumos 《Computers & Education》2009,53(3):950-965
In this paper, a dropout prediction method for e-learning courses, based on three popular machine learning techniques and detailed student data, is proposed. The machine learning techniques used are feed-forward neural networks, support vector machines and probabilistic ensemble simplified fuzzy ARTMAP. Since a single technique may fail to accurately classify some e-learning students, whereas another may succeed, three decision schemes, which combine in different ways the results of the three machine learning techniques, were also tested. The method was examined in terms of overall accuracy, sensitivity and precision and its results were found to be significantly better than those reported in relevant literature. 相似文献
35.
36.
37.
Christophe Vandekerckhove Ioannis Kevrekidis Dirk Roose 《Journal of scientific computing》2009,39(2):167-188
The long-term dynamic behavior of many dynamical systems evolves on a low-dimensional, attracting, invariant slow manifold,
which can be parameterized by only a few variables (“observables”). The explicit derivation of such a slow manifold (and thus,
the reduction of the long-term system dynamics) is often extremely difficult or practically impossible. For this class of
problems, the equation-free framework has been developed to enable performing coarse-grained computations, based on short
full model simulations. Each full model simulation should be initialized so that the full model state is consistent with the
values of the observables and close to the slow manifold. To compute such an initial full model state, a class of constrained
runs functional iterations was proposed (Gear and Kevrekidis, J. Sci. Comput. 25(1), 17–28, 2005; Gear et al., SIAM J. Appl. Dyn. Syst. 4(3), 711–732, 2005). The schemes in this class only use the full model simulator and converge, under certain conditions, to an approximation
of the desired state on the slow manifold. In this article, we develop an implementation of the constrained runs scheme that
is based on a (preconditioned) Newton-Krylov method rather than on a simple functional iteration. The functional iteration
and the Newton-Krylov method are compared in detail using a lattice Boltzmann model for one-dimensional reaction-diffusion
as the full model simulator. Depending on the parameters of the lattice Boltzmann model, the functional iteration may converge
slowly or even diverge. We show that both issues are largely resolved by using the Newton-Krylov method, especially when a
coarse grid correction preconditioner is incorporated. 相似文献
38.
Apostolos Malatras Dimitris Geneiatakis Ioannis Vakalis 《International Journal of Information Security》2017,16(6):653-671
In the Internet era, users’ fundamental privacy and anonymity rights have received significant research and regulatory attention. This is not only a result of the exponential growth of data that users generate when accomplishing their daily task by means of computing devices with advanced capabilities, but also because of inherent data properties that allow them to be linked with a real or soft identity. Service providers exploit these facts for user monitoring and identification, albeit impacting users’ anonymity, based mainly on personal identifiable information or on sensors that generate unique data to provide personalized services. In this paper, we report on the feasibility of user identification using general system features like memory, CPU and network data, as provided by the underlying operating system. We provide a general framework based on supervised machine learning algorithms both for distinguishing users and informing them about their anonymity exposure. We conduct a series of experiments to collect trial datasets for users’ engagement on a shared computing platform. We evaluate various well-known classifiers in terms of their effectiveness in distinguishing users, and we perform a sensitivity analysis of their configuration setup to discover optimal settings under diverse conditions. Furthermore, we examine the bounds of sampling data to eliminate the chances of user identification and thus promote anonymity. Overall results show that under certain configurations users’ anonymity can be preserved, while in other cases users’ identification can be inferred with high accuracy, without relying on personal identifiable information. 相似文献
39.
Three-dimensional face recognition in the presence of facial expressions: an annotated deformable model approach 总被引:1,自引:0,他引:1
Kakadiaris IA Passalis G Toderici G Murtuza MN Lu Y Karampatziakis N Theoharis T 《IEEE transactions on pattern analysis and machine intelligence》2007,29(4):640-649
In this paper, we present the computational tools and a hardware prototype for 3D face recognition. Full automation is provided through the use of advanced multistage alignment algorithms, resilience to facial expressions by employing a deformable model framework, and invariance to 3D capture devices through suitable preprocessing steps. In addition, scalability in both time and space is achieved by converting 3D facial scans into compact metadata. We present our results on the largest known, and now publicly available, face recognition grand challenge 3D facial database consisting of several thousand scans. To the best of our knowledge, this is the highest performance reported on the FRGC v2 database for the 3D modality 相似文献
40.
Ioannis Tsivintzelis 《Polymer》2007,48(20):5928-5939
Microcellular polystyrene (PS) foams and porous structures of the biodegradable poly(d,l-lactic acid) (Pd,lLA) were prepared with the batch foaming technique (pressure quench) using supercritical CO2 as blowing agent. The effect of pressure, temperature and depressurization rate on the final porous structure was investigated. The results revealed that the size of the pores decreases and their population density increases with pressure increase, or decrease of temperature, and/or increase of the depressurization rate. The results were correlated by combining nucleation theory with NRHB model in order to account for and emphasize the physical mechanism related to nucleation of bubbles inside the supersaturated polymer matrix. A satisfactory agreement between correlations and experimental data was obtained indicating that the nucleation theory yields quantitative correlations when variables such as sorption, degree of plasticization, and surface tension of the system polymer-supercritical fluid are accurately described. 相似文献