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Search Results: 1 - 10 of 832 matches for " Jakub Chaloupka "
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Using Strategy Improvement to Stay Alive
Lubo? Brim,Jakub Chaloupka
Electronic Proceedings in Theoretical Computer Science , 2010, DOI: 10.4204/eptcs.25.8
Abstract: We design a novel algorithm for solving Mean-Payoff Games (MPGs). Besides solving an MPG in the usual sense, our algorithm computes more information about the game, information that is important with respect to applications. The weights of the edges of an MPG can be thought of as a gained/consumed energy -- depending on the sign. For each vertex, our algorithm computes the minimum amount of initial energy that is sufficient for player Max to ensure that in a play starting from the vertex, the energy level never goes below zero. Our algorithm is not the first algorithm that computes the minimum sufficient initial energies, but according to our experimental study it is the fastest algorithm that computes them. The reason is that it utilizes the strategy improvement technique which is very efficient in practice.
pi-Xi correlations in d+Au and Au+Au collisions at STAR
Petr Chaloupka
Physics , 2007, DOI: 10.1142/S0218301307007726
Abstract: Qualitative comparison of source sizes from pi-Xi correlations analyses in d+Au and Au+Au collisions at sqrt(s_NN)=200G GeV and sqrt(s_NN)=62 GeV is presented. For the most central Au+Au collisions at sqrt(s_NN)=200 GeV we report first quantitative results concerning size of the pi-Xi source and relative shift of the average emission points between pi and Xi showing that the homogeneity region of Xi source is smaller then that of pion and significantly shifted in the transverse direction.
Non-identical particle correlations at 62 and 200 GeV at STAR
Petr Chaloupka
Physics , 2005,
Abstract: We report on STAR analyses of p-lambda, p_bar-lambda_bar, p-lambda_bar, p_bar-lambda, p-p_bar and pi-Xi correlations in Au+Au collisions at sqrt(S_NN)=62 and 200 GeV. Measured source sizes in p(p_bar)-lambda(lambda_bar) and p-p_bar are shown to be in qualitative agreement with flow expectations. Interaction potential between p-lambda_bar, p_bar-lambda was investigated by measuring scattering length, thus showing that correlation analyses in heavy-ion collisions can be used to study strong interaction potential between hadrons. We present also analyses of pi-Xi correlations addressing independently on previous measurements the issue of Xi flow in heavy-ion collisions.
Economic policies for tobacco control in developing countries
Ross,H; Chaloupka,FJ;
Salud Pública de México , 2006, DOI: 10.1590/S0036-36342006000700014
Abstract: raising tobacco taxes can have an income distributional impact on the population. since lower socio-economic groups usually smoke more, they also contribute more to total cigarette tax collection. thus, those who can afford it least contribute the most in terms of tobacco taxes. this means that tobacco taxes are regressive. however, tobacco tax increases are likely to be progressive, decreasing the relative tax incidence on the poor, vis-à-vis the rich. this is based on the premise that the poor are likely to be more sensitive to price changes, and would thus reduce their cigarette consumption by a greater percentage than the rich in response to an excise tax-induced increase in cigarette prices. recent empirical studies confirm this hypothesis by demonstrating that the price responsiveness of cigarette demand increases with income. research in china confirmed that reducing cigarette expenditures could release household resources for spending on food, housing, and other goods that improve living standards. therefore, in the long run, tobacco control measures will reduce social inequality.
Millimetre-wave imaging with reduced number of degrees of freedom in array signal processing: concepts for enhanced angular resolution
G. Kotyrba,H. Chaloupka
Advances in Radio Science : Kleinheubacher Berichte , 2003,
Abstract: This paper deals with millimetre-wave imaging systems based on linear receiving arrays and is focused on the issue of angular resolution and coverage for arrays where the number M of ports is smaller than the number N of elements due to forming of subarrays. For a wide angular coverage a trade-off between a narrow beam width and a high side-lobe suppression is shown to occur which requires proper synthesis of the subarray pattern. Two concepts for an enhanced angular resolution are presented. The first uses a combination of a frequency dependent distribution network (frequency scanning) with array signal processing to enhance angular resolution by cost of a reduced range resolution. The second approach takes advantage of relative movements to enhance angular resolution via a combined angular and temporal (Doppler) processing.
Speech Defect Analysis Using Hidden Markov Models
Z. Chaloupka,J. Uhlir
Radioengineering , 2007,
Abstract: The main aim of this paper is the analysis of speech deteriorated by a very rare disease, which induce epileptic seizures in a part of brain responsible for speech production. Speech defects, represented mostly by the combination of missing and mismatched phonemes, are sought and examined in the spectral and time domain. An algorithm, proposed in this paper, is based on Hidden Markov Models (HMMs) and it is most suitable for the speech recognition tasks. The algorithm is able to analyze in both time and spectral domains simultaneously; in the spectral domain as a log-likelihood score and in the time domain as a forced time alignment of the HMMs. The suggested algorithm works properly in the time domain. The results for the spectral domain are not credible, because the algorithm have to be tested on more data (not available at the time of paper preparation).
A vignette model for distributed teaching and learning
Marcel Chaloupka,Tony Koppi
Research in Learning Technology , 1998, DOI: 10.3402/rlt.v6i1.10983
Abstract: The notion of convergence of disparate technologies has become popular with governments, computing and business sectors in the 1990s; but how has the convergence been implemented in the educational sector? One evident area of convergence in education has been the use of the Internet. But according to Gosper et al (1996), the most likely strategies for implementation are to use the Internet as a repository of reference, lecture materials and the presentation of the lectures. This could imply that the full potential of distributed learning through convergence might never be achieved. How can we implement good learning strategies following sound educational methodologies today, while not producing legacy systems or piecemeal content that could constrain future developments? In making it possible for distributed learning to occur, there are best-practice considerations applicable to most educational environments.
The origin of strong correlations and superconductivity in Na$_x$CoO$_2$
G. Khaliullin,J. Chaloupka
Physics , 2007, DOI: 10.1103/PhysRevB.77.104532
Abstract: We propose a minimal model resolving a puzzle of enigmatic correlations observed in sodium-rich Na$_x$CoO$_2$ where one expects a simple, free motion of the dilute $S=1/2$ holes doped into a band insulator NaCoO$_2$. The model also predicts singlet superconductivity at experimentally observed compositions. The model is based on a key property of cobalt oxides -- the spin-state quasidegeneracy of CoO$_6$ octahedral complex -- leading to an unusual physics of, {\it e.g.}, LaCoO$_3$. We show that correlated hopping between $t_{2g}$ and $e_g$ states leads to the spin-polaron physics at $x\sim 1$, and to an extended s-wave pairing at larger doping when coherent fermionic bands are formed.
Orbital order and possible superconductivity in LaNiO3/LaMO3 superlattices
Jiri Chaloupka,Giniyat Khaliullin
Physics , 2010, DOI: 10.1103/PhysRevLett.100.016404
Abstract: A hypothetical layered oxide La_2NiMO_6 where NiO_2 and MO_2 planes alternate along the c-axis of ABO_3 perovskite lattice is considered theoretically. Here, M denotes a trivalent cation Al, Ga,... such that MO_2 planes are insulating and suppress the c-axis charge transfer. We predict that correlated e_g electrons in the NiO_2 planes develop a planar x^2-y^2 orbital order driven by the reduced dimensionality and further supported by epitaxial strain from the substrate. Low energy electronic states can be mapped to a single-band t-t'-J model, suggesting favorable conditions for high-T_c superconductivity.
Spin polaron theory for the photoemission spectra of layered cobaltates
J. Chaloupka,G. Khaliullin
Physics , 2007, DOI: 10.1103/PhysRevLett.99.256406
Abstract: Recently, strong reduction of the quasiparticle peaks and pronounced incoherent structures have been observed in the photoemission spectra of layered cobaltates. Surprisingly, these many-body effects are found to increase near the band insulator regime. We explain these unexpected observations in terms of a novel spin-polaron model for CoO_2 planes which is based on a fact of the spin-state quasidegeneracy of Co^{3+} ions in oxides. Scattering of the photoholes on spin-state fluctuations suppresses their coherent motion. The observed ``peak-dip-hump'' type lineshapes are well reproduced by the theory.
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