Showing papers by "University of Trento published in 2003"

Neurofeedback Treatment for Attention-Deficit/Hyperactivity Disorder in Children: A Comparison with Methylphenidate

Abstract: Clinical trials have suggested that neurofeedback may be efficient in treating attention- deficit /hyperactivity disorder (ADHD). We compared the effects of a 3-month electroen- cephalographic feedback program providing reinforcement contingent on the production of cortical sensorimotor rhythm (12-15 Hz) and beta1 activity (15-18 Hz) with stimulant medication. Participants were ND 34 children aged 8-12 years, 22 of which were assigned to the neurofeedback group and 12 to the methylphenidate group according to their parents' preference. Both neurofeedback and methylphenidate were associated with improvements on all subscales of the Test of Variables of Attention, and on the speed and accuracy mea- sures of the d2 Attention Endurance Test. Furthermore, behaviors related to the disorder were rated as significantly reduced in both groups by both teachers and parents on the IOWA-Conners Behavior Rating Scale. These findings suggest that neurofeedback was effi- cient in improving some of the behavioral concomitants of ADHD in children whose parents favored a nonpharmacological treatment.

C-OWL: contextualizing ontologies

Abstract: Ontologies are shared models of a domain that encode a view which is common to a set of different parties. Contexts are local models that encode a party's subjective view of a domain. In this paper we show how ontologies can be contextualized, thus acquiring certain useful properties that a pure shared approach cannot provide. We say that an ontology is contextualized or, also, that it is a contextual ontology, when its contents are kept local, and therefore not shared with other ontologies, and mapped with the contents of other ontologies via explicit (context) mappings. The result is Context OWL (C-OWL), a language whose syntax and semantics have been obtained by extending the OWL syntax and semantics to allow for the representation of contextual ontologies.

Learning In a Constellation of Interconnected Practices: Canon or Dissonance?

Abstract: In this paper we argue that the learning of safety in a constellation of communities of practice is mediated by comparison among the perspectives of the world embraced by the co-participants in the production of this practice. Our discussion is based on two empirical research projects in which we investigated the accounts of the causes of accidents provided by the members of three different communities of practice (engineers, site foremen and main contractors), in a medium sized building firm. In the paper we suggest that comparison among perspectives is made possible by a discursive practice targeted on the alignment of elements both mental and material, within mutually accountable discursive positions. These alignments are provisional and unstable, they produce tensions, discontinuities and incoherence (cacophony) just as much as they produce order and negotiated meanings (consonance).

Phonon interpretation of the 'boson peak' in supercooled liquids

Abstract: Glasses are amorphous solids, in the sense that they display elastic behaviour. In crystalline solids, elasticity is associated with phonons, which are quantized vibrational excitations. Phonon-like excitations also exist in glasses at very high (terahertz; 10(12) Hz) frequencies; surprisingly, these persist in the supercooled liquids. A universal feature of such amorphous systems is the boson peak: the vibrational density of states has an excess compared to the Debye squared-frequency law. Here we investigate the origin of this feature by studying the spectra of inherent structures (local minima of the potential energy) in a realistic glass model. We claim that the peak is the signature of a phase transition in the space of the stationary points of the energy, from a minima-dominated phase (with phonons) at low energy to a saddle-point-dominated phase (without phonons). The boson peak moves to lower frequencies on approaching the phonon-saddle transition, and its height diverges at the critical point. Our numerical results agree with the predictions of euclidean random matrix theory on the existence of a sharp phase transition between an amorphous elastic phase and a phonon-free one.

Light transport through the band-edge states of Fibonacci quasicrystals.

Abstract: The propagation of light in nonperiodic quasicrystals is studied by ultrashort pulse interferometry. Samples consist of multilayer dielectric structures of the Fibonacci type and are realized from porous silicon. We observe mode beating and strong pulse stretching in the light transport through these systems, and a strongly suppressed group velocity for frequencies close to a Fibonacci band gap. A theoretical description based on transfer matrix theory allows us to interpret the results in terms of Fibonacci band-edge resonances.

A new approach to business fluctuations: heterogeneous interacting agents, scaling laws and financial fragility

Abstract: In this paper we discuss a scaling approach to business fluctuations. Our starting point consists in recognizing that concepts and methods derived from physics have allowed economists to (re)discover a set of stylized facts which have to be satisfactorily accounted for in their models. Standard macroeconomics, based on a reductionist approach centered on the representative agent, is definitely badly equipped for this task. On the contrary, we show that a simple financial fragility agent-based model, based on complex interactions of heterogeneous agents, is able to replicate a large number of scaling type stylized facts with a remarkable high degree of statistical precision.

Will silicon be the photonic material of the third millenium

Abstract: Silicon microphotonics, a technology which merges photonics and silicon microelectronic components, is rapidly evolving. Many different fields of application are emerging: transceiver modules for optical communication systems, optical bus systems for ULSI circuits, I/O stages for SOC, displays, .... In this review I will give a brief motivation for silicon microphotonics and try to give the state-of-the-art of this technology. The ingredient still lacking is the silicon laser: a review of the various approaches will be presented. Finally, I will try to draw some conclusions where silicon is predicted to be the material to achieve a full integration of electronic and optical devices.

Emotional prejudice, essentialism, and nationalism - The 2002 Tajfel lecture

Abstract: In explaining differences between groups, people ascribe the human essence to their ingroup and consider outgroups as less human. This phenomenon, called infra-humanization, occurs outside people's awareness. Because secondary emotions (e.g. love, hope, contempt, resentment) are considered uniquely human emotions, people not only attribute more secondary emotions to their ingroup than to outgroups, but are reluctant to associate these emotions with outgroups. Moreover, people behave less cooperatively (in terms of altruism, imitation, and approach) with an outgroup member who expresses himself through secondary emotions. Infra-humanization occurs for high and low status groups, even in the absence of conflict between groups. It does not occur when the outgroup target is adequately individualized, by a complete name or through perspective taking, for instance.

Role of the interface region on the optoelectronic properties of silicon nanocrystals embedded in SiO 2

Abstract: Light-emitting silicon nanocrystals embedded in ${\mathrm{SiO}}_{2}$ have been investigated by x-ray absorption measurements in total electron and photoluminescence yields, by energy filtered transmission electron microscopy and by ab initio total energy calculations. Both experimental and theoretical results show that the interface between the silicon nanocrystals and the surrounding ${\mathrm{SiO}}_{2}$ is not sharp: an intermediate region of amorphous nature and variable composition links the crystalline Si with the amorphous stoichiometric ${\mathrm{SiO}}_{2}.$ This region plays an active role in the light-emission process.

Semantic coordination: a new approach and an application

Abstract: Semantic coordination, namely the problem of finding an agreement on the meaning of heterogeneous semantic models, is one of the key issues in the development of the Semantic Web. In this paper, we propose a new algorithm for discovering semantic mappings across hierarchical classifications based on a new approach to semantic coordination. This approach shifts the problem of semantic coordination from the problem of computing linguistic or structural similarities (what most other proposed approaches do) to the problem of deducing relations between sets of logical formulae that represent the meaning of concepts belonging to different models. We show how to apply the approach and the algorithm to an interesting family of semantic models, namely hierarchical classifications, and present the results of preliminary tests on two types of hierarchical classifications, web directories and catalogs. Finally, we argue why this is a significant improvement on previous approaches.

On the behavioral consequences of infrahumanization: the implicit role of uniquely human emotions in intergroup relations.

Abstract: Four experiments confirmed the hypothesis that people discriminate the out-group on the basis of the expression of uniquely human emotions. In Study 1, using a lost e-mail paradigm, the expression of a uniquely human emotion resulted in "nicer" replies when the sender was an in-group compared with an out-group member. The same pattern of results was obtained in Studies 2 and 3 using a conformity paradigm. In addition, perceived similarity was measured and proposed as a potential underlying mechanism (Study 3). Finally, using an approach-avoidance procedure, Study 4 showed that people not only deprive the out-group of positive consequences as in the former studies but that people also act against the out-group. The role of infrahumanization underlying prejudice and discrimination is discussed.

Optical analogue of electronic Bloch oscillations

Abstract: We report on the observation of Bloch oscillations in light transport through periodic dielectric systems. By introducing a linear refractive index gradient along the propagation direction the optical equivalent of a Wannier-Stark ladder was obtained. Bloch oscillations were observed as time-resolved oscillations in transmission, in direct analogy to electronic Bloch oscillations in conducting crystals where the Wannier-Stark ladder is obtained via an external electric field. The observed oscillatory behavior is in excellent agreement with transfer matrix calculations.

Structural Properties of XPath Fragments

Abstract: We study structural properties of each of the main sublanguages of XPath [8] commonly used in practice First, we characterize the expressive power of these language fragments in terms of both logics and tree patterns Second, we investigate closure properties, focusing on the ability to perform basic Boolean operations while remaining within the fragment We give a complete picture of the closure properties of these fragments, treating XPath expressions both as functions of arbitrary nodes in a document tree, and as functions that are applied only at the root of the tree Finally, we provide sound and complete axiom systems and normal forms for several of these fragments These results are useful for simplification of XPath expressions and optimization of XML queries

On the structure of finite perimeter sets in step 2 Carnot groups

Abstract: In this article we study codimension 1 rectifiable sets in Carnot groups and we extend classical De Giorgi ’s rectifiability and divergence theorems to the setting of step 2 groups Related problems in higher step Carnot groups are discussed, pointing on new phenomena related to the blow up procedure

A digital architecture for support vector machines: theory, algorithm, and FPGA implementation

Abstract: In this paper, we propose a digital architecture for support vector machine (SVM) learning and discuss its implementation on a field programmable gate array (FPGA). We analyze briefly the quantization effects on the performance of the SVM in classification problems to show its robustness, in the feedforward phase, respect to fixed-point math implementations; then, we address the problem of SVM learning. The architecture described here makes use of a new algorithm for SVM learning which is less sensitive to quantization errors respect to the solution appeared so far in the literature. The algorithm is composed of two parts: the first one exploits a recurrent network for finding the parameters of the SVM; the second one uses a bisection process for computing the threshold. The architecture implementing the algorithm is described in detail and mapped on a real current-generation FPGA (Xilinx Virtex II). Its effectiveness is then tested on a channel equalization problem, where real-time performances are of paramount importance.

Channel bifurcation in braided rivers: Equilibrium configurations and stability

Abstract: [1] We investigate the equilibrium configurations and the stability of river bifurcations in gravel braided networks. Within the context of a one-dimensional approach, the nodal point conditions play a crucial rule, as pointed out by Wang et al. [1995] who propose an empirical relationship relating water and sediment flow rates into the downstream branches. In the present paper, an alternative formulation of nodal point conditions is proposed based on a quasi two-dimensional approach. The results show that, if the Shields parameter of the upstream channel is large enough, the system only admits of one solution with both branches open, which is invariably stable. As the Shields parameter of the upstream channel decreases, two further stable solutions appear characterized by a different partition of water discharge into the downstream branches: in this case, the previous solution becomes unstable. Theoretical findings are confirmed by the numerical solution of the nonlinear one-dimensional equations.

Evaluating and designing Web site quality

Abstract: There are many reasons to evaluate a Web site's quality. The growth of e-commerce, for example, has made a company's success more dependent on the quality of its Web site, whether its goal is commerce or content presentation. We developed the 2QCV3Q model to help site owners and developers evaluate Web site quality and incorporate these findings into site design. Starting with the assumption that a Web site is a hypermedia system primarily concerned with communication, we used classical rhetoric to create this model.

Formal Reasoning Techniques for Goal Models

Abstract: Over the past decade, goal models have been used in Computer Science in order to represent software requirements, business objectives and design qualities. Such models extend traditional AI planning techniques for representing goals by allowing for partially defined and possibly inconsistent goals. This paper presents a formal framework for reasoning with such goal models. In particular, the paper proposes a qualitative and a numerical axiomatization for goal modeling primitives and introduces label propagation algorithms that are shown to be sound and complete with respect to their respective axiomatizations. In addition, the paper reports on experimental results on the propagation algorithms applied to a goal model for a US car manufacturer.

A Markov random field approach to spatio-temporal contextual image classification

Abstract: Markov random fields (MRFs) provide a useful and theoretically well-established tool for integrating temporal contextual information into the classification process. In particular, when dealing with a sequence of temporal images, the usual MRF-based approach consists in adopting a "cascade" scheme, i.e., in propagating the temporal information from the current image to the next one of the sequence. The simplicity of the cascade scheme makes it attractive; on the other hand, it does not fully exploit the temporal information available in a sequence of temporal images. In this paper, a "mutual" MRF approach is proposed that aims at improving both the accuracy and the reliability of the classification process by means of a better exploitation of the temporal information. It involves carrying out a bidirectional exchange of the temporal information between the defined single-time MRF models of consecutive images. A difficult issue related to MRFs is the determination of the MRF model parameters that weight the energy terms related to the available information sources. To solve this problem, we propose a simple and fast method based on the concept of "minimum perturbation" and implemented with the pseudoinverse technique for the minimization of the sum of squared errors. Experimental results on a multitemporal dataset made up of two multisensor (Landsat Thematic Mapper and European Remote Sensing 1 synthetic aperture radar) images are reported. The results obtained by the proposed "mutual" approach show a clear improvement in terms of classification accuracy over those yielded by a reference MRF-based classifier. The presented method to automatically estimate the MRF parameters yielded significant results that make it an attractive alternative to the usual trial-and-error search procedure.

Web service composition as planning

Abstract: We show how the service composition problem can be viewed as a planning problem in which state descriptions are ambiguous and operator definitions are incomplete. We then discuss the problem of interpreting documents (which describe the world state), and introduce a semantic type matching algorithm. The matching algorithm together with an interleaved search and execution algorithm allow for basic automated ser-

Comments on the Stress-Energy Tensor Operator in Curved Spacetime

Abstract: The technique based on a *-algebra of Wick products of field operators in curved spacetime, in the local covariant version proposed by Hollands and Wald, is strightforwardly generalized in order to define the stress-energy tensor operator in curved globally hyperbolic spacetimes. In particular, the locality and covariance requirement is generalized to Wick products of differentiated quantum fields. Within the proposed formalism, there is room to accomplish all of the physical requirements provided that known problems concerning the conservation of the stress-energy tensor are assumed to be related to the interface between the quantum and classical formalism. The proposed stress-energy tensor operator turns out to be conserved and reduces to the classical form if field operators are replaced by classical fields satisfying the equation of motion. The definition is based on the existence of convenient counterterms given by certain local Wick products of differentiated fields. These terms are independent from the arbitrary length scale (and any quantum state) and they classically vanish on solutions of the Klein-Gordon equation. Considering the averaged stress-energy tensor with respect to Hadamard quantum states, the presented definition turns out to be equivalent to an improved point-splitting renormalization procedure which makes use of the nonambiguous part of the Hadamard parametrix only that is determined by the local geometry and the parameters which appear in the Klein-Gordon operator. In particular, no extra added-by-hand term g αβQ and no arbitrary smooth part of the Hadamard parametrix (generated by some arbitrary smooth term ``ω 0 '') are involved. The averaged stress-energy tensor obtained by the point-splitting procedure also coincides with that found by employing the local ζ-function approach whenever that technique can be implemented.

Integrating security and systems engineering: towards the modelling of secure information systems

Abstract: Security is a crucial issue for information systems. Traditionally, security is considered after the definition of the system. However, this approach often leads to problems, which translate into security vulnerabilities. From the viewpoint of the traditional security paradigm, it should be possible to eliminate such problems through better integration of security and systems engineering. This paper argues for the need to develop a methodology that considers security as an integral part of the whole system development process. The paper contributes to the current state of the art by proposing an approach that considers security concerns as an integral part of the entire system development process and by relating this approach with existing work. The different stages of the approach are described with the aid of a case study; a health and social care information system.