Collaboration structures in Slovenian scientific communities

We combine two seemingly distinct perspectives regarding the modeling of network dynamics. One perspective is found in the work of physicists and mathematicians who formally introduced the small world model and the mechanism of preferential attachment. The other perspective is sociological and focuses on the process of cumulative advantage and considers the agency of individual actors in a network. We test hypotheses, based on work drawn from these perspectives, regarding the structure and dynamics of scientific collaboration networks. The data we use are for four scientific disciplines in the Slovene system of science. The results deal with the overall topology of these networks and specific processes that generate them. The two perspectives can be joined to mutual benefit. Within this combined approach, the presence of small-world structures was confirmed. However preferential attachment is far more complex than advocates of a single autonomous mechanism claim.     

Using a LRF sensor in the Kalman-filtering-based localization of a mobile robot

This paper deals with the problem of estimating the output-noise covariance matrix that is involved in the localization of a mobile robot. The extended Kalman filter (EKF) is used to localize the mobile robot with a laser range finder (LRF) sensor in an environment described with line segments. The covariances of the observed environment lines, which compose the output-noise covariance matrix in the correction step of the EKF, are the result of the noise arising from a range-sensor’s (e.g., a LRF) distance and angle measurements. A method for estimating the covariances of the line parameters based on classic least squares (LSQ) is proposed. This method is compared with the method resulting from the orthogonal LSQ in terms of computational complexity. The results of a comparison show that the use of classic LSQ instead of orthogonal LSQ reduce the number of computations in a localization algorithm which is a part of a SLAM (simultaneous localization and mapping) algorithm. Statistical accuracy of both methods is also compared by simulating the LRF’s measurements and the comparison proves the efficiency of the proposed approach.     

Developers’ perceptions of object-oriented frameworks - An investigation into the impact of technological and individual characteristics

Framework-based development is currently regarded as one of the most promising software development approaches, boasting increases in lead time, productivity and quality. However, many frameworks and framework-related projects still fail, which indicates that frameworks still have unsolved problems. In this article, we will identify and investigate the major framework characteristics and individual differences that impact the most important users’ perceptions about frameworks. To test the causal relationships between these factors, we performed an online survey and analyzed the results using structural equation modeling. The results support the technology acceptance model (TAM), which was used as an underlying theory. In addition, we found that framework characteristics and individual differences have a significant impact on users’ perceptions, especially in the case of voluntary framework use. Beside TAM constructs, the results also suggest an additional determinant for the acceptance of frameworks: “confidence”. Despite the limits of our research, we foresee future research activities as well as theoretical and practical implications. Our results might be used to develop acceptable frameworks and for the evaluation of existing frameworks, their constituent parts and framework-related guidelines.     

OntoPlus: Text-driven ontology extension using ontology content,structure and co-occurrence information

This paper addresses the process of semi-automatic text-driven ontology extension using ontology content, structure and co-occurrence information. A novel OntoPlus methodology is proposed for semi-automatic ontology extension based on text mining methods. It allows for the effective extension of the large ontologies, providing a ranked list of potentially relevant concepts and relationships given a new concept (e.g., glossary term) to be inserted in the ontology. A number of experiments are conducted, evaluating measures for ranking correspondence between existing ontology concepts and new domain concepts suggested for the ontology extension. Measures for ranking are based on incorporating ontology content, structure and co-occurrence information. The experiments are performed using a well known Cyc ontology and textual material from two domains – finances and, fisheries & aquaculture. Our experiments show that the best results are achieved by combining content, structure and co-occurrence information. Furthermore, ontology content and structure seem to be more important than co-occurrence for our data in the financial domain. At the same time, ontology content and co-occurrence seem to have higher importance for our fisheries & aquaculture domain.     

Shear resistance of longitudinally stiffened panels — Part 2: Numerical parametric study

This paper presents the FE analysis of the influence of different parameters on the shear resistance of panels with different arrangements of longitudinal stiffeners. The studied parameters were the stiffener bending stiffness, the panel aspect ratio, the stiffener position, the web slenderness and the flange rigidity. Longitudinal stiffeners of trapezoidal shape were compared to open T-stiffeners. The former proved to be more efficient, since a larger panel resistance is achieved, for which in addition a smaller stiffness of trapezoidal stiffeners is needed. Different features of the new Eurocode rules were verified against the FEA results as well. Three different procedures for the determination of panel slenderness were tested and the reduction of stiffener bending stiffness, prescribed due to a better correlation with tests on open stiffeners, was verified for both closed and open stiffeners. The influence of bending moment was also considered and the verification of shear and bending interaction was discussed. Finally, the flange contribution to shear resistance was critically analysed.     

Properties of Sb2S3 and Sb2Se3 thin films obtained by pulsed laser ablation

The properties of Sb₂S₃ and Sb₂Se₃ thin films of variable thickness deposited onto Al₂O₃, Si, and KCl substrates are investigated by the method of pulsed laser ablation. The samples are obtained at a substrate temperature of 180°C in a vacuum chamber with a residual pressure of 10^?5 Torr. The thickness of the films amounted to 40–1500 nm. The structure of the bulk material of the targets and films is investigated by the methods of X-ray diffraction and transmission high-energy electron diffraction, respectively. The electrical properties of the films are investigated in the temperature range of 253–310 K. It is shown that the films have semiconductor properties. The structural features of the films determine their optical parameters.     

Computerized segmentation of whole-body bone scintigrams and its use in automated diagnostics

Bone scintigraphy or whole-body bone scan is one of the most common diagnostic procedures in nuclear medicine used in the last 25 years. Pathological conditions, technically poor image resolution and artefacts necessitate that algorithms use sufficient background knowledge of anatomy and spatial relations of bones in order to work satisfactorily. A robust knowledge based methodology for detecting reference points of the main skeletal regions that is simultaneously applied on anterior and posterior whole-body bone scintigrams is presented. Expert knowledge is represented as a set of parameterized rules which are used to support standard image-processing algorithms. Our study includes 467 consecutive, non-selected scintigrams, which is, to our knowledge the largest number of images ever used in such studies. Automatic analysis of whole-body bone scans using our segmentation algorithm gives more accurate and reliable results than previous studies. Obtained reference points are used for automatic segmentation of the skeleton, which is applied to automatic (machine learning) or manual (expert physicians) diagnostics. Preliminary experiments show that an expert system based on machine learning closely mimics the results of expert physicians.     

Chemical Ecology of Cave-Dwelling Millipedes: Defensive Secretions of the Typhloiulini (Diplopoda,Julida, Julidae)

Cave animals live under highly constant ecological conditions and in permanent darkness, and many evolutionary adaptations of cave-dwellers have been triggered by their specific environment. A similar “cave effect” leading to pronounced chemical interactions under such conditions may be assumed, but the chemoecology of troglobionts is mostly unknown. We investigated the defensive chemistry of a largely cave-dwelling julid group, the controversial tribe “Typhloiulini”, and we included some cave-dwelling and some endogean representatives. While chemical defense in juliform diplopods is known to be highly uniform, and mainly based on methyl- and methoxy-substituted benzoquinones, the defensive secretions of typhloiulines contained ethyl-benzoquinones and related compounds. Interestingly, ethyl-benzoquinones were found in some, but not all cave-dwelling typhloiulines, and some non-cave dwellers also contained these compounds. On the other hand, ethyl-benzoquinones were not detected in troglobiont nor in endogean typhloiuline outgroups. In order to explain the taxonomic pattern of ethyl-benzoquinone occurrence, and to unravel whether a cave-effect triggered ethyl-benzoquinone evolution, we classed the “Typhloiulini” investigated here within a phylogenetic framework of julid taxa, and traced the evolutionary history of ethyl-benzoquinones in typhloiulines in relation to cave-dwelling. The results indicated a cave-independent evolution of ethyl-substituted benzoquinones, indicating the absence of a “cave effect” on the secretions of troglobiont Typhloiulini. Ethyl-benzoquinones probably evolved early in an epi- or endogean ancestor of a clade including several, but not all Typhloiulus (basically comprising a taxonomic entity known as “Typhloiulus sensu stricto”) and Serboiulus. Ethyl-benzoquinones are proposed as novel and valuable chemical characters for julid systematics.     

Online Segmentation and Clustering From Continuous Observation of Whole Body Motions

This paper describes a novel approach for incremental learning of human motion pattern primitives through online observation of human motion. The observed time series data stream is first stochastically segmented into potential motion primitive segments, based on the assumption that data belonging to the same motion primitive will have the same underlying distribution. The motion segments are then abstracted into a stochastic model representation and automatically clustered and organized. As new motion patterns are observed, they are incrementally grouped together into a tree structure, based on their relative distance in the model space. The tree leaves, which represent the most specialized learned motion primitives, are then passed back to the segmentation algorithm so that as the number of known motion primitives increases, the accuracy of the segmentation can also be improved. The combined algorithm is tested on a sequence of continuous human motion data that are obtained through motion capture, and demonstrates the performance of the proposed approach.