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Radon anomalies in soil gas caused by seismic activity
Boris Zmazek, Mladen Živčić, Ljupčo Todorovski, Sašo Džeroski, Janja Vaupotič, Ivan Kobal, 2004, original scientific article

Abstract: At the Orlica fault in the Krško basin, combined barasol detectors were buried in six boreholes, two along the fault itself and four on either side of it, to measure and record radon activity, temperature and pressure in soil gas every 60 minutes for four years. Data collected have been analysed in a manner aimed at distinguishing radon anomalies resulting from environmental parameters (air and soil temperature, barometric pressure, rainfall) from those caused solely by seismic events. The following approaches have been used to identify anomalies: (i) ± 2σ deviation of radon concentration from the seasonal average, (ii) correlation between time gradients of radon concentration and barometric pressure, and (iii) prediction with regression trees within a machine learning program. In this paper results obtained with regression trees are presented. A model has been built in which the program was taught to predict radon concentration from the data collected during the seismically inactive periods when radon is presumably influenced only by environmental parameters. A correlation coefficient of 0.83 between measured and predicted values was obtained. Then, the whole data time series was included and a significantly lowered correlation was observed during the seismically active periods. This reduced correlation is thus an indicator of seismic effect.
Keywords: radon in soil gas, environmental parameters, earthquakes, correlation, regression trees, forecasting
Published in DKUM: 15.05.2018; Views: 1059; Downloads: 67
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Productivity and economic growth in the European Union : impact of investment in research and development
Andreja Nekrep, Sebastjan Strašek, Darja Boršič, 2018, original scientific article

Abstract: This paper focuses on investment in research and development as a factor of labour productivity and economic growth. Our analysis confirms the link between expenditure for research and development (expressed in % of GDP) and labour productivity (expressed in the number of hours worked) based on selected data for EU Member States in the period 1995-2013. A causal link between variables of the concave parabola was confirmed, and the value of expenditure for research and development (2.85% of EU GDP) maximising productivity (per hour of work) was determined based on the examined data. In accordance with these findings, EU’s target of reaching 3% of GDP spent on research and development to be achieved by 2020 seems in support of reaching maximum productivity in the EU.
Keywords: investment in research and development, productivity, economic growth, correlation, panel analysis
Published in DKUM: 03.05.2018; Views: 1050; Downloads: 138
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The influence of broadband regulation in EU on the development of the regulated technology
Andrej Mihevc, 2011, original scientific article

Abstract: The aim of the article is to answer the question if the level of intensity of `ex ante` regulation (also `regulation`) imposed by NRA (national regulatory Authority or regulators) influence on the development of incumbent DSL technology against other Access technologies. There are several approaches which support the basic idea of regulation, that Ćex anteĆ regulation promotes the competition. The approaches must be also based on the size of themarket. In the internet world there are different access technologies. OpenAccess is crucial for the development of competition. Regulators have to ensure, that also new entrants can reach end users through the facilities of the incumbent operator. Based on the approach of three criteria, European Commission defines two wholesale relevant access markets both based on DSL technology (`bitstream` access and unbundled local loop) susceptible to sector specific `ex ante` regulation. In the last stage also optical access isincluded on the relevant markets. Other technologies are still not equivalent to incumbent DSL technology according to the opinion of the commission. The intensity of regulation influences on the competition conditions. It influences on the level where and at which point of the investment ladder entrants will enter the market through wholesale inputs or through building its own infrastructure.
Keywords: regulation, market analyses, broadband, correlation, DSL technology
Published in DKUM: 22.01.2018; Views: 818; Downloads: 304
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Asymmetric correlation of sovereign bond yield dynamics in the Eurozone
Silvo Dajčman, 2013, original scientific article

Abstract: This paper examines the symmetry of correlation of sovereign bond yield dynamics between eight Eurozone countries (Austria, Belgium, France, Germany, Ireland, Italy, Portugal, and Spain) in the period from January 3, 2000 to August 31, 2011. Asymmetry of correlation is investigated pair-wise by applying the test of Yongmiao Hong, Jun Tu, and Guofu Zhou (2007). Whereas the test of Hong, Tu, and Zhou (2007) is static, the present paper provides also a dynamic version of the test and identifies time periods when the correlation of Eurozone sovereign bond yield dynamics became asymmetric. We identified seven pairs of sovereign bond markets for which the null hypothesis of symmetry in correlation of sovereign bond yield dynamics can be rejected. Calculating rolling-window exceedance correlation, we found that the time-varying upper- (i.e. for positive yield changes) and lower-tail correlations (i.e. for negative yield changes) for pair-wise observed sovereign bond markets normally follow each other closely, yet during some time periods (for most pair-wise observed countries, these periods are around the September 11 attack on the New York City WTC and around the start of the Greek debt crisis) the difference in correlation does increase. The results show that the upper- and lower-tail correlation was symmetric before the Eurozone debt crisis for most of the pair-wise observed sovereign bond markets but has become much less symmetric since then.
Keywords: asymmetric correlation, sovereign bonds, Eurozone, financial crisis
Published in DKUM: 03.08.2017; Views: 775; Downloads: 304
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Phase equilibrium measurements and data correlation for the ternary system oleic acid + 1-octanol + carbon dioxide
Chiara Giulia Laudani, Mateja Primožič, Željko Knez, Maja Leitgeb, 2009, original scientific article

Abstract: A study of the high-pressure phase equilibria in the ternary system oleic acid/1- octanol/supercritical CO2 was performed to obtain information for optimization of enzymatic synthesis of n-octyl oleate. Equilibrium data were measured at temperatures of 308.15, 323.15 and 343.15 K over a pressure range from 1 to 25 MPa. Two different apparatuses: a Variable Volume View Cell and a Batch Stirred Tank were used employing synthetic and static-analytic measurement methods, respectively. The measured solubility of dense CO2 in the binary liquid mixture oleic acid/1-octanol covered the range from 0.0781 to 0.7686 of CO2 molar fraction. CO2 solubility increased with increasing pressure up to 10 MPa. At higher pressures, no significant increase was observed. The Soave-Redlich-Kwong equation-of-state (SRK-EoS) with quadratic mixing rules was successfully used for data correlation in the whole P-T-x region studied.
Keywords: data correlation, 1-octanol, oleic acid, supercritical carbon dioxide, Soave-Redlich-Kwong equation-of-state, vapor-liquid equilibria
Published in DKUM: 05.07.2017; Views: 978; Downloads: 94
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Characterization of heterogeneous arc welds through miniature tensile testing and Vickers-hardness mapping
Stjin Hertelé, Jonas Bally, Nenad Gubeljak, Primož Štefane, Patricia Verleysen, Wim De Waele, 2016, original scientific article

Abstract: The heterogeneity of arc-welded connections is often ignored in structural assessments, giving rise to inaccuracies. Improved assessments taking into account heterogeneity require the characterization of local constitutive properties. We have compared two methods to do this: Vickers-hardness mapping and miniature tensile testing. Whereas the former is more straightforward to apply, the latter provides full-range stress-strain data. This paper discusses an experimental comparison of both methods on a heterogeneous arc weld. Miniature tensile tests were performed, using digital image correlation to measure the strain. The specimens were indented to compare their stress-strain response with Vickers hardness. Notwithstanding that small natural flaws invalidated some tests, reliable stress-strain curves were obtained. Vickers hardness testing is a convenient alternative if the yield and ultimate tensile strength are the only points of interest and the corresponding conversion inaccuracy is acceptable.
Keywords: arc weld, heterogeneity, hardness, miniature tensile testing, digital image correlation
Published in DKUM: 14.03.2017; Views: 793; Downloads: 361
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The variation of F2 progenies derived from interspecific crosses between Phaseolus vulgaris and Phaseolus coccineus
Anton Ivančič, Metka Šiško, 2003, original scientific article

Abstract: Interspecific hybridisation within the genus Phaseolus represents an importantsource of genetic variation which can be very useful in breeding programmes based on recurrent selection. The aim of this investigation was to analyse the phenotypic variation and relationships among the most important quantitative traits in F2 generation materials derived from crosses P. vulgaris x P. coccienus. P. vulgaris was used as female while P. coccineus as male parent. The F2 material was composed of 825 individuals which originated from open pollination of 65 F1 plants. The most variable quantitative trait was the number of flowers per inflorescence, which varied from 0 to 57 (CV=45,8 %). The second was the inflorescence length which varied from 2.5 to 74 cm (CV=39,0 %). The highest value (CV=70.4 %) was obtained for floral colour (a qualitative trait which was transformed into a special numerical scale).The correlation analysis showed that there were close relationships among the number of leaves, number of flowers, number of pods, number of seedsand the length of the growth period. For practical breeding, the most useful is probably the correlation between the number of inflorescences and the number of seeds per plant (r=0.503 and 0.560) because the number of inflorescences can be easily determined at the beginning of the hybridisation period, and the number of seeds is more or less directly associated with the yield. For the final visual selection, at the end of the vegetation period, the most useful trait is the number of pods, which is highly correlated with the number of seeds (r=0.740 and 0.916)
Keywords: interspecific hybrids, Phaseolus vulgaris x P. coccineus, hybridisation technique, phenotypic variation, phenotypic correlation coefficients
Published in DKUM: 10.07.2015; Views: 967; Downloads: 31
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Regression analysis of variables describing poultry meat supply in European countries
Miro Simonič, Ksenija Dumičić, Gabrijel Devetak, 2012, original scientific article

Abstract: In this paper, based on the analysis of official FAOSTAT and EUROSTAT data on poultry meat for 38 European countries for years 2007 and 2009, two hypotheses were examined. Firstly, considering four clustering variables on poultry meat, i.e. production, export and import in kg/capita, as well as the producer price in US $/t, using descriptive exploratory and cluster analysis, the hypothesis that the clusters of countries may be recognized was confirmed. As a result six clusters of similar countries were distinguished. Secondly, based on multiple regression analysis, this paper proofs that there exists the statistically significant relationship of poultry meat production on export and import of that kind of meat, all measured in kg/capita. There is also a high correlation between production, as a dependent, and each of two independent variables.
Keywords: poultry meat, marketing strategy, cluster analysis, correlation, multiple regression
Published in DKUM: 10.07.2015; Views: 1002; Downloads: 358
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Constructing domain-specific semantic dictionaries to supplement domain-specific knowledge bases
Goran Hrovat, Milan Ojsteršek, published scientific conference contribution

Abstract: Semantic dictionaries as well as knowledge bases are im- portant source of information for natural language process- ing. Using corpus and algorithms for constructing semantic space, we can quickly construct semantic dictionary, which is exploit to supplement the knowledge base. Algorithm for constructing semantic space, COALS was chosen. Semantic distance between terms in semantic space reveals their sim- ilarity, which is used to add semantic relationships in the dictionary. Semantic dictionary also serves to assist in iden- tifying entities and in relation extraction, to supplement the knowledge base.
Keywords: semantic space, correlation, semantic dictionary, knowledge base
Published in DKUM: 22.06.2015; Views: 1270; Downloads: 36
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Establishing the stochastic nature of intracellular calcium oscillations from experimental data
Matjaž Perc, Anne K. Green, C. Jane Dixon, Marko Marhl, 2008, original scientific article

Abstract: Calcium has been established as a key messenger in both intra- and intercellular signaling. Experimentally observed intracellular calcium responses to different agonists show a variety of behaviors from simple spiking to complex oscillatory regimes. Here we study typical experimental traces of calcium oscillations in hepatocytes obtained in response to phenylephrine and ATP. The traces were analyzed with methods of nonlinear time series analysis in order to determine the stochastic/deterministic nature of the intracellular calcium oscillations. Despite the fact that the oscillations appear, visually, to be deterministic yet perturbed by noise, our analyses provide strong evidence that the measured calcium traces in hepatocytes are prevalently of stochastic nature. In particular, bursting calcium oscillations are temporally correlated Gaussian series distorted by a monotonic, instantaneous, time-independent function, whilst the spiking behavior appears to have a dynamical nonlinear component whereby the overall determinism level is still low. The biological importance of this finding is discussed in relation to the mechanisms incorporated in mathematical models as well as the role of stochasticity and determinism at cellular and tissue levels which resemble typical statistical and thermodynamic effects in physics.
Keywords: dynamic systems, stochastic processes, cellular signaling, calcium oscillations, time series analyses, noise, temporal correlation
Published in DKUM: 07.06.2012; Views: 1453; Downloads: 117
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