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Abstract: In a typical pressurized water reactor, neutron detectors located outside the reactor core monitor reactor power. In addition, they are also used to measure the reactivity of the control rods. A novel approach to calculate the ex-core neutron detector response in a typical pressurized water reactor using the Monte Carlo technique is presented. A detailed ex-core model of the Krško nuclear power plant was developed using the Monte Carlo neutron transport code MCNP. Due to the location of the ex-core neutron detectors, the hybrid code ADVANTG is used to generate variance reduction parameters to accelerte the convergence of the results outside the reactor core. To use ADVANTG, the fixed neutron source had to be reconstructed from the criticality core calculation. This paper presents the sensitivity analysis of the response of the ex-core detectors to the neutron data libraries used, the description of the fixed neutron source and the ADVANTG parameters. It was found that a pin-wise description of the neutron source for at least two rows of fuel assemblies at the core periphery is necessary for accurate results. Our results show the importance of a correct description of the prompt neutron spectra in the high energy region and the impact this has on the response of the ex-core detectors. The method in which the prompt neutron fission spectra for important fission nuclides are weighted by the calculated reaction rates has been shown to be the best approximation, with deviations from the reference calculation within statistical uncertainty. The effect of nuclear data libraries on the response of the ex-core detector was investigated, and the difference between the ENDF/B-VII.0 and the ENDF/B-VIII.0 nuclear data libraries was ∼11%. When the deficient evaluation of the 56Fe isotope included in the ENDF/B-VIII.0 nuclear data library was replaced by the improved evaluation from the IAEA INDEN project, the differences decreased to ∼3.7%. In addition, neutron flux redistributions due to control rod movement were investigated and flux redistribution factors were updated using Monte Carlo particle transport methods. The reaction rate redistribution factors obtained with methods presented in this paper are within 1% agreement with the currently used factors.
Keywords: MCNP, ADVANTG, pressurized water reactor, Monte Carlo neutron transport, control rod, neutron flux redistribution factor, rod insertion, krško nuclear power plant
Published in DKUM: 29.11.2024; Views: 0; Downloads: 2
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Abstract: Reputation and reciprocity are key mechanisms for cooperation in human societies, often going hand in hand to favor prosocial behavior over selfish actions. Here we review recent researches at the interface of physics and evolutionary game theory that explored these two mechanisms. We focus on image scoring as the bearer of reputation, as well as on various types of reciprocity, including direct, indirect, and network reciprocity. We review different definitions of reputation and reciprocity dynamics, and we show how these affect the evolution of cooperation in social dilemmas. We consider first-order, second-order, as well as higherorder models in well-mixed and structured populations, and we review experimental works that support and inform the results of mathematical modeling and simulations. We also provide a synthesis of the reviewed researches along with an outlook in terms of six directions that seem particularly promising to explore in the future.
Keywords: pattern formation, Monte Carlo method, complex network, evolutionary game theory, cooperation, social physics
Published in DKUM: 20.06.2024; Views: 154; Downloads: 13
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Abstract: Razumevanje razvoja sodelovanja med posamezniki, ki so v osnovi sebični, je eden najpomembnejših izzivov današnjega časa, ki vzbuja zanimanje raziskovalcev iz različnih področij. V ta namen znanstveniki integrirajo evolucijsko teorijo iger z naprednimi metodami s področja znanosti o omrežjih in metodami statistične fizike. V doktorski disertaciji smo s pomočjo takega interdisciplinarnega pristopa raziskali, kako različni tipi mobilnosti oziroma mešanj igralcev na različnih interakcijskih mrežah vplivajo na evolucijo in promocijo sodelovanja v igri javnih dobrin. V ta namen smo raziskovalno delo razdelili v štiri sklope. V prvem delu smo pokazali, da uvedba mešanja igralcev v igri javnih dobrin na regularnem omrežju omogoči prehod iz stanja sistema vpetega v prostorsko mrežo v stanje dobro mešane populacije, kjer struktura interakcijske mreže več nima bistvenega pomena na evolucijsko dinamiko. Izkaže se, da je v primeru mešanja najbližjih sosedov za to potrebna večja frekvenca mešanja kot pri mešanju naključnih igralcev. Nadalje smo pokazali, da oba načina mešanja zavirata evolucijski uspeh kooperatorjev. V nadaljevanju smo raziskavo razširili na področje kompleksnih omrežij, ki podajajo realnejši opis interakcij med posamezniki. V drugem delu doktorske disertacije smo tako igro javnih dobrin postavili na naključno omrežje, vpeto v hiperbolični prostor in v model vključili asortativno in disasortativno mešanje igralcev. Ugotovili smo, da oba tipa mešanja zavirata razvoj sodelovanja ne glede na arhitekturo omrežja, a je vpliv disasortativnega mešanja večji v primerjavi z asortativnim mešanjem. Naslednji tip interakcijske mreže, s katerim se še boljše opišemo realne interakcije, so večplastna soodvisna omrežja, ki smo jih v raziskave vključili v naših naslednjih dveh raziskavah. Soodvisnost med dvema omrežjema smo vpeljali s koristnostno funkcijo in pokazali, da lahko parameter pristranskosti učinkovito vpliva na raven sodelovanja. Pokazali smo, da asortativne medmrežne povezave med dvema skalno neodvisnima omrežjema spodbujajo kooperacijo v igri javnih dobrin v nekoliko večji meri kot naključne in disasortativne povezave. V zadnjem sklopu raziskav smo prišli do presenetljivih zaključkov. Rezultati mešanja na dvoplastnem soodvisnem omrežju, kjer posamezna plast predstavlja naključno omrežje, vpeto v hiperbolični prostor, kažejo, da lahko mešanje znotraj posamezne plasti omrežja, kjer je sodelovanje prvotno uspešno, močno oslabi evolucijsko uspešnost kooperatorjev na tej plasti, medtem ko jo za določene vrednosti normaliziranega sinergijskega faktorja spodbuja sodelovanje na drugi plasti omrežja. Rezultati doktorske disertacije predstavljajo pomemben prispevek k znanstvenemu raziskovanju na področju razumevanja razvoja in vzdrževanja sodelovanja, s poudarkom na uporabi evolucijske teorije iger, kompleksnih omrežij in mobilnosti igralcev.
Keywords: evolucijska teorija iger, igra javnih dobrin, sodelovanje, mešanje, kompleksna omrežja, večplastna omrežja, simulacije Monte Carlo
Published in DKUM: 05.06.2024; Views: 120; Downloads: 21
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Abstract: The main goal of the master's thesis was the analysis of air resistance on the body in motion in a model that does not require solving the Navier-Stokes equations, but works on the basis of mechanics and statistical physics. The model was a Monte Carlo (MC) simulation of the motion of ideal gas molecules in a closed container in which a body was placed, moving along one of the axes. For the most part of calculations, the approach was used when the body was fixed in the middle of the simulation cell, and one of the components of the molecular velocity had an additional term that simulated the flow, as if the body was moving at this speed in the opposite direction. First of all, a linear dependence of the drag force on speed was found for low flow speed for a flat plate, which was predicted by linear drag law. For high molecular flow rates, the quadratic dependence predicted by the Bernoulli equation was clearly observed. The results of calculating the corresponding resistivity coefficients for the flat plate were in agreement with the analytical values for both regimes of speeds. By analogy, a simulation was made for a spherical body, which also demonstrated a strong quadratic dependence at high speeds and the drag coefficient value is approximately equal to the analytical one. In the following, we studied systematically ellipsoids with circular cross-section, where we varied the ratio between semiaxes in the direction of motion and perpendicular direction, respectively. The results for the ellipsoid showed that the drag coefficient value is maximum for a flat plate (a limiting case of an ellipsoid, when the semiaxis in the direction of motion tends to 0) and decreases with stretching of the body along the flow axis. When the Maxwell distribution of molecular speeds that was mainly used was replaced with uniform Root-Mean-Square (RMS) speed the results for drag coefficient were slightly different.
Keywords: Air resistance, drag force, quadratic drag law, drag coefficient, Monte Carlo (MC) simulation, Maxwell distribution.
Published in DKUM: 13.10.2021; Views: 1038; Downloads: 62
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Abstract: Perceptual researchers often argue that natural selection supports veridical perceptions, respectively those that accurately reflect the environment. They also claim that beings whose perceptions are truer are also more fit. This assumption was tested using standard tools of evolutionary game theory in a simple environment. The result was that more veridical perceptions are not necessarily more successful. In the majority of the parameter space, veridical perceptions are extinct in competition with simplified perceptions, based on adaptive behavior in a given environment. In the thesis, we build upon mentioned territorial games introduced by Mark, Marion, and Hoffman in 2010, and extend four of their territory perception and selection strategies with two novel ones that together constitute a model of technological readiness valley of death. Whenever utility of a resource is not monotonous in the amount of that resource, the technological valley of death emerges. While the development of the science behind these models is in its infancy, modeling and understanding the phenomenon may shed light on progress and related phenomena in society.
Keywords: evolution, perception, utility, Monte Carlo simulation, game theory
Published in DKUM: 22.11.2019; Views: 1781; Downloads: 182
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