On the complexity of some inductive logic programming problems

The bounded ILP-consistency problem for function-free Horn clauses is described as follows. Given at setE ⁺ andE ^? of function-free ground Horn clauses and an integerk polynomial inE ⁺∪E ^?, does there exist a function-free Horn clauseC with no more thank literals such thatC subsumes each element inE ⁺ andC does not subsume any element inE ^?? It is shown that this problem is Σ ₂ ^P complete. We derive some related results on the complexity of ILP and discuss the usefulness of such complexity results.     

Simultaneous localization and odometry self calibration for mobile robot

This paper presents both the theory and the experimental results of a method allowing simultaneous robot localization and odometry error estimation (both systematic and non-systematic) during the navigation. The estimation of the systematic components is carried out through an augmented Kalman filter, which estimates a state containing the robot configuration and the parameters characterizing the systematic component of the odometry error. It uses encoder readings as inputs and the readings from a laser range finder as observations. In this first filter, the non-systematic error is defined as constant and it is overestimated. Then, the estimation of the real non-systematic component is carried out through another Kalman filter, where the observations are obtained by two subsequent robot configurations provided by the previous augmented Kalman filter. There, the systematic parameters in the model are regularly updated with the values estimated by the first filter. The approach is theoretically developed for both the synchronous and the differential drive. A first validation is performed through very accurate simulations where both the drive systems are considered. Then, a series of experiments are carried out in an indoor environment by using a mobile platform with a differential drive.     

Mapping Twitter hate speech towards social and sexual minorities: a lexicon-based approach to semantic content analysis

ABSTRACT

Though there are currently no statistics offering a global overview of online hate speech, both social networking platforms and organisations that combat hate speech have recognised that prevention strategies are needed to address this negative online phenomenon. While most cases of online hate speech target individuals on the basis of ethnicity and nationality, incitements to hatred on the basis of religion, class, gender and sexual orientation are increasing. This paper reports the findings of the ‘Italian Hate Map’ project, which used a lexicon-based method of semantic content analysis to extract 2,659,879 Tweets (from 879,428 Twitter profiles) over a period of 7 months; 412,716 of these Tweets contained negative terms directed at one of the six target groups. In the geolocalized Tweets, women were the most insulted group, having received 71,006 hateful Tweets (60.4% of the negative geolocalized tweets), followed by immigrants (12,281 tweets, 10.4%), gay and lesbian persons (12,140 tweets, 10.3%), Muslims (7,465 tweets, 6.4%), Jews (7,465 tweets, 6.4%) and disabled persons (7,230 tweets, 6.1%). The findings provide a real-time snapshot of community behaviours and attitudes against social, ethnic, sexual and gender minority groups that can be used to inform intolerance prevention campaigns on both local and national levels.     

Noise reduction for instance-based learning with a local maximal margin approach

To some extent the problem of noise reduction in machine learning has been finessed by the development of learning techniques that are noise-tolerant. However, it is difficult to make instance-based learning noise tolerant and noise reduction still plays an important role in k-nearest neighbour classification. There are also other motivations for noise reduction, for instance the elimination of noise may result in simpler models or data cleansing may be an end in itself. In this paper we present a novel approach to noise reduction based on local Support Vector Machines (LSVM) which brings the benefits of maximal margin classifiers to bear on noise reduction. This provides a more robust alternative to the majority rule on which almost all the existing noise reduction techniques are based. Roughly speaking, for each training example an SVM is trained on its neighbourhood and if the SVM classification for the central example disagrees with its actual class there is evidence in favour of removing it from the training set. We provide an empirical evaluation on 15 real datasets showing improved classification accuracy when using training data edited with our method as well as specific experiments regarding the spam filtering application domain. We present a further evaluation on two artificial datasets where we analyse two different types of noise (Gaussian feature noise and mislabelling noise) and the influence of different class densities. The conclusion is that LSVM noise reduction is significantly better than the other analysed algorithms for real datasets and for artificial datasets perturbed by Gaussian noise and in presence of uneven class densities.     

Interferometric analysis of reorientational nonlinear phenomena at 10.6 microm in a nematic liquid crystal

We describe an infrared interferometric technique based on a two-dimensional spatial fringe analysis Fourier method for investigating the characteristic ring diffraction pattern generated by the self-phase-modulation effect induced in nematic liquid crystals (NLCs) by an infrared laser beam and for measuring the nonlinear refractive index of the NLCs. The experimental setup employs a Mach-Zehnder interferometer with a cw CO2 laser emitting at 10.6 microm and a pyroelectric optoelectronic sensor matrix to detect the modulated ring-pattern intensity distribution formed in the far field by a nematic E7 sample. A Fourier-transform-based analysis of the interference fringe pattern allows comparison of the measurements with the theoretical ring-pattern intensity distribution. We show that accurate determination of the nonlinear refractive index can be obtained by analyzing the two-dimensional phase distribution of the modulated ring pattern.     

Fracture instability and limit strength condition in structures with re-entrant corners

When considering a structural element with a re-entrant corner, the experimental analysis shows how the fracture strength increases with the angle of the corner. Thus, the strength increases with a decrease of the mass of the structure, in contrast to what we are used to observe in different kind of collapses, e.g., plasticity. To predict this behaviour, a non-local theory, basically based on the Novozhilov’s hypothesis of existence of a fracture quantum, is herein presented. Theoretical predictions for the strength of finite structures (e.g., finite plates under tension or beams under bending) by varying both angle and relative depth of the corner are presented: accordingly, simple formulas, useful in the design of such structures, are provided. The theory is then compared with experimental and numerical results, showing a relevant agreement.     

Mild stress stimuli built into a non-immersive virtual environment can elicit actual stress responses

The experience of Virtual Reality (VR) can lead to unwanted or wanted psychological stress reactions. Highly immersive VR games for instance utilise extreme, life-threatening, or dangerous situations to achieve those responses from their players. There is also sufficient evidence that in clinical settings and specific situations, such as fear of heights or post-traumatic stress, virtual stimuli can lead to perceived stress for clients. However, there is a gap in research targeting everyday, mild emotional stimuli, which are neither extreme nor specific and which are not presented in an immersive system. To what extent can common stimuli in a non-immersive virtual environment elicit actual stress reactions for its users? We developed a desktop VR system and evaluated it in a study with 54 participants. We could show that virtual stimuli in a common, domestic family environment led to a significant increase in perceived stress as measured by quantitative (self-reports) and qualitative (semi-structured interviews analysed with a General Inductive Approach (GIA)) responses. The results also showed that the introduction of virtual stimuli induced significantly higher levels of perceived workload and sense of presence and led to different physiological reactions. These findings have implications for the design and implementation of non-immersive VR systems.     

Differences Between People Who Use Only Facebook and Those Who Use Facebook Plus Twitter

Facebook (FB) and Twitter are popular social networking sites. This study examined differences between those who use both sites versus only FB, to test the hypothesis that mono-users differ in their personality characteristics from users active in both websites. Participants were 205 undergraduate students: 96 only used FB, 109 used FB and Twitter. Participants who used both sites reported significantly lower loneliness, higher number of FB friends, and lower number of minutes spent online, as compared to those who used only FB. Loneliness was positively associated with FB use only in those who used FB alone but was negatively associated with and negatively predicted both FB and Twitter use in those who used both websites. Findings suggest that more intense use of online interactions is more frequently found in mono-users (people using only Facebook) as compared to those using both websites, and it is predicted by increased feelings of loneliness. The current study findings provide additional insights on what personality factors may make some people prone to excessive use of social networking sites.     

A high frequency cMUT probe for ultrasound imaging of fingerprints

Fingerprint imaging using ultrasound has been investigated for several years and has shown to be a valid alternative to optical scanners. Capacitive micro-machined ultrasound transducers (cMUT) is an emerging MEMS technology that can be profitably exploited in biometric applications, like fingerprint or palm print.In this work a FEM model of a cMUT is proposed and used to design a 192-element array with a frequency band centered at 12.5 MHz. A cMUT array was manufactured by means of a proprietary fabrication process and an ultrasound probe was assembled and experimentally characterized. Comparison between simulation and experimental results has shown a quite good agreement. The cMUT probe was operated at a frequency of 12 MHz and used to produce images of fingerprints, the quality of which was quite satisfactory.     

Towards a Logic for Performance and Mobility

Klaim is an experimental language designed for modeling and programming distributed systems composed of mobile components where distribution awareness and dynamic system architecture configuration are key issues. StocKlaim [R. De Nicola, D. Latella, and M. Massink. Formal modeling and quantitative analysis of KLAIM-based mobile systems. In ACM Symposium on Applied Computing (SAC). ACM Press, 2005. Also available as Technical Report 2004-TR-25; CNR/ISTI, 2004] is a Markovian extension of the core subset of Klaim which includes process distribution, process mobility, asynchronous communication, and site creation. In this paper, MoSL, a temporal logic for StocKlaim is proposed which addresses and integrates the issues of distribution awareness and mobility and those concerning stochastic behaviour of systems. The satisfiability relation is formally defined over labelled Markov chains. A large fragment of the proposed logic can be translated to action-based CSL for which efficient model-checkers exist. This way, such model-checkers can be used for the verification of StocKlaim models against MoSL properties. An example application is provided in the present paper.