In vitro adhesion of staphylococci to diamond-like carbon polymer hybrids under dynamic flow conditions

This study compares the ability of selected materials to inhibit adhesion of two bacterial strains commonly implicated in implant-related infections. These two strains are Staphylococcus aureus (S-15981) and Staphylococcus epidermidis (ATCC 35984). In experiments we tested six different materials, three conventional implant metals: titanium, tantalum and chromium, and three diamond-like carbon (DLC) coatings: DLC, DLC–polydimethylsiloxane hybrid (DLC–PDMS-h) and DLC–polytetrafluoroethylene hybrid (DLC–PTFE-h) coatings. DLC coating represents extremely hard material whereas DLC hybrids represent novel nanocomposite coatings. The two DLC polymer hybrid films were chosen for testing due to their hardness, corrosion resistance and extremely good non-stick (hydrophobic and oleophobic) properties. Bacterial adhesion assay tests were performed under dynamic flow conditions by using parallel plate flow chambers (PPFC). The results show that adhesion of S. aureus to DLC–PTFE-h and to tantalum was significantly (P < 0.05) lower than to DLC–PDMS-h (0.671 ± 0.001 × 10⁷/cm² and 0.751 ± 0.002 × 10⁷/cm² vs. 1.055 ± 0.002 × 10⁷/cm², respectively). No significant differences were detected between other tested materials. Hence DLC–PTFE-h coating showed as low susceptibility to S. aureus adhesion as all the tested conventional implant metals. The adherence of S. epidermidis to biomaterials was not significantly (P < 0.05) different between the materials tested. This suggests that DLC–PTFE-h films could be used as a biomaterial coating without increasing the risk of implant-related infections.     

Driver age and vehicle engine size effects on fault and severity in young motorcyclists accidents

This paper reports a study of the combined effect of driver age and engine size on accident severity and at-fault risk of young riders of two-wheelers. Data from the national accident database of Greece are used to calculate accident severity and relative fault risk rates. The induced exposure technique is applied due to the lack of exposure data. A log-linear analysis is then used to examine first- and second-order effects within three-variable groups. Accident severity modelling revealed a significant second-order interaction between severity, driver age and two-wheeler engine size. On the contrary, no second-order effects were identified in fault risk modelling. Moreover, a significant effect of driver age on accident fault risk was identified. The effect of engine size was not significant.     

Instantaneous frequency based spectral analysis of nuclear magnetic resonance spectroscopy data

Nuclear magnetic resonance spectroscopy signals are modelled as a sum of decaying complex exponentials in noise. The spectral analysis of these signals allowing for their decomposition and the estimation of the parameters of the components is crucial to the study of biochemical samples. This paper presents a novel Gabor filterbank/notch filtering instantaneous frequency (IF) estimator, that enables the extraction of weaker and shorter lived exponentials. This new approach is an iterative procedure where a Gabor filterbank is first employed to obtain a reliable estimate of the IF of the strongest component present. The estimated strongest component is then notch filtered, which un-masks weaker components, and the procedure repeated. The performance of this method was evaluated using an artificial signal and compared to the short time Fourier transform, reassigned STFT, and the original Gabor filterbank approach. The results clearly demonstrate its superiority in uncovering weaker signals and resolving components that are very close to one another in frequency. Furthermore, the new method is shown to be more robust than the ITCMP technique at low signal to noise ratios.     

Fuzzy control optimized by a Multi-Objective Particle Swarm Optimization algorithm for vibration suppression of smart structures

Smart structures include elements of active, passive or hybrid control. In this paper, a new Multi-Objective Particle Swarm Optimization (MOPSO), with a different velocity equation, for the calculation of the free parameters in active control systems is proposed and tested. A fuzzy control system is considered. Fuzzy control is a suitable tool for the systematic development of nonlinear active control strategies and can be fine tuned if no experience exists or if one designs more complicated control schemes. The usage of MOPSO with a combination of continuous and discrete variables for the optimal design of the controller is proposed. Numerical applications on smart piezoelastic beams are presented.     

MOF-tree: A spatial access method to manipulate multiple overlapping features

In this paper we investigate the manipulation of large sets of 2-dimensional data representing multiple overlapping features (e.g. semantically distinct overlays of a given region), and we present a new access method, the MOF-tree. We perform an analysis with respect to the storage requirements and a time analysis with respect to window query operations involving multiple features (e.g. to verify if a constraint defined on multiple overlays holds or not inside a certain region). We examine both the pointer-based as well as the pointerless MOF-tree representations, using as space complexity measure the number of bits used in main memory and the number of disk pages in secondary storage respectively. In particular, we show that the new structure is space competitive in the average case, both in the pointer version and in the linear version, with respect to multiple instances of a region quadtree and a linear quadtree respectively, where each instance represents a single feature. Concerning the time performance of the new structure, we analyze the class of window (range) queries, posed on the secondary memory implementation. We show that the I/O worst-case time complexity for processing a number of window queries in the given image space, is competitive with respect to multiple instances of a linear quadtree, as confirmed by experimental results. Finally, we show that the MOF-tree can efficiently support spatial join processing in a spatial DBMS.     

Studying participation networks in collaboration using mixed methods

This paper describes the application of a mixed-evaluation method, published elsewhere, to three different learning scenarios. The method defines how to combine social network analysis with qualitative and quantitative analysis in order to study participatory aspects of learning in CSCL contexts. The three case studies include a course-long, blended learning experience evaluated as the course develops; a course-long, distance learning experience evaluated at the end of the course; and a synchronous experience of a few hours duration. These scenarios show that the analysis techniques and data collection and processing tools are flexible enough to be applied in different conditions. In particular, SAMSA, a tool that processes interaction data to allow social network analysis, is useful with different types of interactions (indirect asynchronous or direct synchronous interactions) and different data representations. Furthermore, the predefined types of social networks and indexes selected are shown to be appropriate for measuring structural aspects of interaction in these CSCL scenarios. These elements are usable and their results comprehensible by education practitioners. Finally, the experiments show that the mixed-evaluation method and its computational tools allow researchers to efficiently achieve a deeper and more reliable evaluation through complementarity and the triangulation of different data sources. The three experiments described show the particular benefits of each of the data sources and analysis techniques.     

Conversational natural language understanding interfacing city event information

The article describes aspects of the development of a conversational natural language understanding (NLU) system done during the first year of the European research project CATCH-2004 (Converse in AThens Cologne and Helsinki) [http://www.catch2004.org]. The project is co-funded by the European Union in the scope of the IST programme (IST 1999-11103).

Its objectives focus on multi-modal, multi-lingual conversational natural language access to information systems. The paper emphasises on architecture, and telephony-based speech and NLU components as well as aspects of the implementation of a city event information (CEI) system in English, Finnish, German and Greek. The CEI system accesses two different databases in Athens and Helsinki using a common retrieval interface. Furthermore the paper singles out methodologies involved for acoustic and language model of the speech recognition component, parsing techniques and dialog modelling for the conversational natural language subsystem. For the implementation it outlines an incremental system refinement methodology necessary to adapt the system components to real-life data. It addresses the implementation of language specific characteristics and a common dialog design for all four languages, but also deals with aspects towards a multilingual conversational system. Finally, it presents prospects for further developments of the project.     

Evolution of faceted taxonomies and CTCA expressions

A faceted taxonomy is a set of taxonomies each describing the application domain from a different (preferably orthogonal) point of view. CTCA is an algebra that allows specifying the set of meaningful compound terms (meaningful conjunctions of terms) over a faceted taxonomy in a flexible and efficient manner. However, taxonomy updates may turn a CTCA expression e not well-formed and may turn the compound terms specified by e to no longer reflect the domain knowledge originally expressed in e. This paper shows how we can revise e after a taxonomy update and reach an expression e′ that is both well-formed and whose semantics (compound terms defined) is as close as possible to the semantics of the original expression e before the update. Various cases are analyzed and the revising algorithms are given. The proposed technique can enhance the robustness and usability of systems that are based on CTCA and allows optimizing several other tasks where CTCA can be used (including mining and compressing). Yannis Tzitzikas is Assistant Professor in the Computer Science Department at University of Crete (Greece) and Associate Researcher in Information Systems Lab at FORTH-ICS (Greece). Before joining UofCrete and FORTH-ICS, he was postdoctoral fellow at the University of Namur (Belgium) and ERCIM postdoctoral fellow at ISTI-CNR (Pisa, Italy) and at VTT Technical Research Centre of Finland. He conducted his undergraduate and graduate studies (MSc, PhD) in the Computer Science Department at University of Crete. In parallel, he was a member of the Information Systems Lab of FORTH-ICS where he conducted basic and applied research around semantic-network-based information systems within several EU-founded research projects. His research interests fall in the intersection of the following areas: information systems, information indexing and retrieval, conceptual modeling, knowledge representation and reasoning, and collaborative distributed applications. His current research revolves around faceted metadata and semantics (theory and applications), the P2P paradigm (focusing on conceptual modeling issues, query evaluation algorithms and automatic schema integration techniques), and flexible interaction schemes for information bases. The results of his research have been published in more than 40 papers in refereed international conferences and journals, and he has received one best paper award (CIA'2003).     

A Low-Voltage 5-GHz Downconversion Mixer Employing A Second Harmonic Injection Linearization Technique

In this paper, a low-voltage CMOS mixer topology, appropriate for operation in the 5-GHz frequency band, is presented. The mixer combines several design techniques in order to achieve high linearity performance with minimum current consumption in a restricted 1-V supply. The proposed mixer utilizes an integrated transformer to improve the high frequency performance and to achieve large LO to RF isolation. In addition, a novel linearization technique based on second harmonic injection, is introduced to optimize linearity performance. The design is being implemented in a 0.13-mum CMOS technology.