arXiv subjects

Viktor Begun

Publications and source records attributed to Viktor Begun.

17 recordsLinked to original sources

arXiv2024

Data Requirements and Prediction Scaling for Long-Term Failure Forecasts in Wind Turbines

We investigate the key factors that enable early failure forecasting in wind turbines. For this purpose, we analyze studies with long-term forecasts and compare their main features: prediction time, methods, targeted components, dataset size, and check the effect of using additional sensors. We found that the size of the dataset is the main factor and that an approximate linear scaling holds: the number of forecast days is twice the size of the dataset, measured in turbine years. We also observe that the data allow us to quantify the meaning of "big" and "long" in the terms "big data" and "long-term" forecasts, which are found to be ten turbine years and two weeks.

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arXiv2024

Cost-optimized probabilistic maintenance for condition monitoring of wind turbines with rare failures

We propose a method, a model, and a form of presenting model results for condition monitoring of a small set of wind turbines with rare failures. The main new ingredient of the method is to sample failure thresholds according to the profit they give to an operating company. The model is a multiple linear regression with seasonal components and external regressors, representing all sensor components except for the selected one. To overcome the scarcity of the training data, we use the median sensor values from all available turbines in their healthy state. The cumulated deviation from the normal behavior model obtained for this median turbine is calibrated for each turbine at the beginning of the test period and after known failures. The proposed form of presenting results is to set a scale for possible costs, control for random maintenance, and show a whole distribution of costs depending on the free model parameters. We make a case study on an open dataset with SCADA data from multiple sensors and show that considering the influence of turbine components is more critical than seasonality. The distribution, the average, and the standard deviation of maintenance costs can be very different for similar minimal costs. Random maintenance can be more profitable than reactive maintenance and other approaches. Our predictive maintenance model outperforms random maintenance and competitors for the whole set of considered turbines, giving substantial savings.

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arXiv2018

Estimation of the freeze-out parameters reachable in the AFTER@LHC project

Estimation of the freeze-out parameters as the function of rapidity in Pb+Pb collisions at $\sqrt{s_{NN}}=72$ GeV in the AFTER@LHC project is performed. The conventional hadron resonance gas model is used for the analysis of the events generated by the UrQMD model. The results indicate that one may obtain at least $2.5$ times increase of baryon chemical potential $μ_B$ in the forward rapidity range as compared to the mid-rapidity. The $μ_B$ values in the rapidity range of $0 < y < 4.5$ for AFTER@LHC are comparable to that covered by the RHIC Beam Energy Scan program. Thus, a rapidity scan in the AFTER@LHC project provides a complementary approach to study the QCD phase diagram.

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arXiv2017

Multi moment cancellation of participant fluctuations

We summarize the new method for the correction of participant fluctuations in high energy nucleus-nucleus collisions. It allows to estimate a fluctuation baseline in comparison to a useful signal. In particular cases of a weak signal compared to baseline, it allows to cancel the baseline contribution from participants.

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arXiv2017

Resonances in a sudden chemical freeze-out model

The prediction for $p_T$ spectra of various resonances produced in Pb+Pb collisions at 2.76 TeV at the LHC in equilibrium and non-equilibrium models is made. It includes the $η$, $ρ$(770), $Σ$(1385), $Λ$(1520), and $Ξ$(1530). The apparent differences may allow to distinguish between the models.

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arXiv2017

Multi moment cancellation of participant fluctuations - MMCP method

We propose a new way to correct for finite centrality bin width effect i.e. participant fluctuations in fluctuation analysis in high energy nucleus-nucleus collisions. The MMCP method allows to separate participant fluctuations and obtain fluctuations from one participant - a source - from a combination of the experimentally measured first four moments. The EPOS model is used for the numerical check of the MMCP for the net electric charge fluctuations in the forward rapidity region in Ar+Sc reactions at beam momentum 150 GeV/c. We show that using the existing methods - decreasing a centrality bin width, or using the Centrality Bin Width Correction procedure, one may still leave some residual participant fluctuations in the sample. Moreover, we show that the Centrality Bin Width Correction procedure may alter the fluctuation measures. The most important advantage of the MMCP is it's precision even when the amount of measured events does not allow to decrease the centrality bin width, or the experimental determination of participants is difficult, e.g. in collider experiments. Even for the largest centrality bin in the considered case, $c=0-20\%$, the relative error of the MMCP for the scaled variance of a source is below 2\%. It is especially important in determination of the base line of the fluctuations in the search for the QCD Critical Point and the signals of the QCD phase transition.

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arXiv2016

Charge conservation effects for high order fluctuations

The exact charge conservation significantly impacts multiplicity fluctuations. The result depends strongly on the part of the system charge carried by the particles of interest. Along with the expected suppression of fluctuations for large systems, charge conservation may lead to negative skewness or kurtosis for small systems.

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arXiv2016

Fluctuations as a test of chemical non-equilibrium at the LHC

It is shown that large chemical potential leads to the significant increase of multiplicity fluctuations for bosons, and makes the fluctuations infinite in the case of Bose-Einstein condensation. It allows to distinguish between the models that explain the anomalous proton to pion ratio and the low transverse momentum enhancement of pion spectra in Pb+Pb collisions at the LHC within chemical equilibrium or non-equilibrium models. The effects of resonance decays, finite size of the system, requirements to the event statistics, different momentum cuts, and limited detector acceptance are considered. The obtained results show the possibility to observe a substantial increase of the normalized kurtosis for positively or negatively charged pions in the case of non-equilibrium or partial pion condensation using currently measured data.

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arXiv2016

Participant number fluctuations for higher moments of a multiplicity distribution

The independent participant model is generalized for skewness and kurtosis. The obtained relations allow to calculate the fluctuations of an arbitrarily high order. From the comparison with the SPS and the LHC data it is found that the participants are not nucleons. The contribution of the participant fluctuations increases with the order of fluctuations. The 5% centrality bins selected for the analysis at the LHC by ALICE seems to be too large. The fluctuations measures are dominated by the fluctuations of participants there. The method to quantify the value of participant number fluctuations experimentally is proposed.

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arXiv2016

Irrelevance of $f_{0}(500)$ in bulk thermal properties

We discuss why the scalar-isoscalar resonance $f_{0}(500)$ should in practice not be included in thermal models describing the freeze-out of heavy-ion collisions. Its contribution into pion multiplicities is in principle relevant because it is light and it decays only into pions. However, it is cancelled to a very good numerical precision by the non-resonant scalar-isotensor repulsion among pions. Our approach is an application of a well-known theorem relating spectral function to phase shifts. The numerical results are solely based on pion-pion scattering data and thus model independent.

hep-ph↗

arXiv2016

Thermodynamics and kinetics of Gribov-Zwanziger plasma with temperature dependent Gribov parameter

A Gribov-type dispersion relation is treated as an effective description of interacting gluons forming a hot medium. Temperature dependence of the Gribov parameter is determined from the fit to the lattice Yang-Mills results describing thermodynamic functions. To maintain thermodynamic consistency of the approach, a temperature dependent bag pressure is introduced. The results obtained for equilibrium functions are generalised in the next step to non-equilibrium conditions. We derive formulas for the bulk and shear viscosity coefficients within the relaxation time approximation. We find evidence for largely enhanced bulk viscosity in the region of the phase transition.

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arXiv2015

Cancellation of the sigma meson in thermal models

The by now well-established scalar-isoscalar resonance $f_{0}(500)$ (the $σ$ meson) seems potentially relevant in the evaluation of thermodynamic quantities of a hadronic gas, since its mass is low. However, we recall that its contribution to isospin-averaged observables is, to a surprising accuracy, canceled by the repulsion from the pion-pion scalar-isotensor channel. As a result, in practice one should not incorporate $f_0(500)$ in standard hadronic resonance-gas models for studies of isospin averaged quantities. In our analysis we use the formalism of the virial expansion, which allows one to calculate the thermal properties of an interacting hadron gas in terms of derivatives of the scattering phase shifts, hence in a model-independent way directly from experimentally accessible quantities. A similar cancellation mechanism occurs for the scalar kaonic interactions between the $I=1/2$ channel (containing the alleged $K_{0}^{\ast}(800)$ or the $κ$ meson) and the $I=3/2$ channel.

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arXiv2015

Bose-Einstein condensation of pions in heavy-ion collisions at the CERN Large Hadron Collider (LHC) energies

We analyse in detail the possibility of Bose-Einstein condensation of pions produced in heavy-ion collisions at the beam energy $\sqrt{s_{\rm NN}}$ = 2.76 TeV. Our approach is based on the chemical non-equilibrium thermal model of hadron production which has been generalised to include separately the contribution from the local zero-momentum state. In order to study both the hadronic multiplicities and the transverse-momentum spectra, we use the Cracow freeze-out model which parameterises the flow and space-time geometry of the system at freeze-out in a very economic way. Our analysis indicates that about 5% of all pions may form the Bose-Einstein condensate.

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arXiv2015

Thermal model for Pb+Pb collisions at $\sqrt{s}_{NN} = 2.76$ TeV with explicit treatment of hadronic ground states

Various explanations of the anomalous proton to pion ratio at the LHC are discussed. The special emphasis is set on the Cracow thermal model with single freeze-out. This model allows to get a good agreement for both the mean hadron multiplicities and the spectra. Moreover, the values of the fit parameters indicate the possibility of pion Bose condensation in the most central collisions at the LHC. Therefore, a modification of the thermal framework is proposed that explicitly allows for the condensation in the ground state. The generalised model makes a link between equilibrium and non-equilibrium thermal models. It also suggests that the pion condensation may be formed in the central collisions.

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arXiv2014

Explanation of hadron transverse-momentum spectra in heavy-ion collisions at sqrt(sNN) = 2.76 TeV within chemical non-equilibrium statistical hadronization model

Chemical non-equilibrium version of the statistical hadronization model combined with a single-freeze-out scenario is used to analyze the transverse-momentum spectra of pions, kaons and protons produced in heavy-ion collisions at sqrt(sNN) = 2.76 TeV. With the statistical parameters found in earlier studies of hadronic ratios and two new geometric parameters determined by the absolute normalization and slopes of the spectra, we obtain a very good agreement between the data and the model predictions. In particular, the enhancement of pions observed at the very low transverse-momenta is very well reproduced. In the chemical non-equilibrium approach, this effect may be naturally interpreted as the onset of pion condensation in heavy-ion collisions. We further stress that the chemical non-equilibrium explains not only the proton yield but the proton spectra as well.

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arXiv2014

Transverse-momentum spectra of strange particles produced in Pb+Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV in the chemical non-equilibrium model

We analyze the transverse-momentum spectra of strange hadrons produced in Pb+Pb collisions at the collision energy $\sqrt{s_{\rm NN}}=2.76$ TeV. Our approach combines the concept of chemical non-equilibrium with the single-freeze-out scenario. The two ideas are realized in the framework of the Cracow model, whose thermodynamic parameters have been established in earlier studies of the ratios of hadron multiplicities. The geometric parameters of the model are obtained from the fit to the spectra of pions and kaons, only. Using these parameters, we obtain an excellent description of the spectra of protons and the $K_S^0$, $K^*(892)^0$, and $ϕ(1020)$ mesons. A satisfactory description is also obtained for the $Λ$, $Ξ$ and $Ω$ hyperons. Further improvement of the hyperon spectra may be achieved if we assume that they are emitted from a smaller, internal part of the system but at the same thermodynamic conditions. Our work not only includes all particle species measured up to now in heavy-ion collisions at the LHC energies but, in addition, discusses the centrality dependence of the particle production.

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arXiv2007

Bose-Einstein Condensation of Pions

Particle number fluctuations are studied in the ideal pion gas approaching Bose-Einstein condensation. Two different cases are considered: Bose condensation of pions at large charge densities $ρ_Q$ and Bose condensation at large total densities of pions $ρ_π$. Calculations are done in grand canonical, canonical and microcanonical ensembles. At high collision energy, in the samples of events with a fixed number of all pions, $N_π$, one may observe a prominent signal. When $N_π$ increases the scaled variances for particle number fluctuations of both neutral and charged pions increase dramatically in the vicinity of the Bose-Einstein condensation line. As an example, the estimates are presented for $p+p$ collisions at the beam energy of 70 GeV.

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