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Why are there six degrees of separation in a social network?
I. Samoylenko, D. Aleja, E. Primo, Karin Alfaro-Bittner, E. Vasilyeva, K. Kovalenko, D. Musatov, A. M. Raigorodskii, R. Criado, M. Romance, David Papo, Matjaž Perc, B. Barzel, Stefano Boccaletti, 2023, izvirni znanstveni članek

Opis: A wealth of evidence shows that real-world networks are endowed with the small-world property, i.e., that the maximal distance between any two of their nodes scales logarithmically rather than linearly with their size. In addition, most social networks are organized so that no individual is more than six connections apart from any other, an empirical regularity known as the six degrees of separation. Why social networks have this ultrasmall-world organization, whereby the graph’s diameter is independent of the network size over several orders of magnitude, is still unknown. We show that the “six degrees of separation” is the property featured by the equilibrium state of any network where individuals weigh between their aspiration to improve their centrality and the costs incurred in forming and maintaining connections. We show, moreover, that the emergence of such a regularity is compatible with all other features, such as clustering and scale-freeness, that normally characterize the structure of social networks. Thus, our results show how simple evolutionary rules of the kind traditionally associated with human cooperation and altruism can also account for the emergence of one of the most intriguing attributes of social networks.
Ključne besede: degree distribution, network evolution, complex network, small-world network, social physics
Objavljeno v DKUM: 16.07.2024; Ogledov: 1; Prenosov: 0
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Swarmalators under competitive time-varying phase interactions
Gourab Kumar Sar, Sayantan Nag Chowdhury, Matjaž Perc, Dibakar Ghosh, 2022, izvirni znanstveni članek

Opis: Swarmalators are entities with the simultaneous presence of swarming and synchronization that reveal emergent collective behavior due to the fascinating bidirectional interplay between phase and spatial dynamics. Although different coupling topologies have already been considered, here we introduce time-varying competitive phase interaction among swarmalators where the underlying connectivity for attractive and repulsive coupling varies depending on the vision (sensing) radius. Apart from investigating some fundamental properties like conservation of center of position and collision avoidance, we also scrutinize the cases of extreme limits of vision radius. The concurrence of attractive–repulsive competitive phase coupling allows the exploration of diverse asymptotic states, like static π, and mixed phase wave states, and we explore the feasible routes of those states through a detailed numerical analysis. In sole presence of attractive local coupling, we reveal the occurrence of static cluster synchronization where the number of clusters depends crucially on the initial distribution of positions and phases of each swarmalator. In addition, we analytically calculate the sufficient condition for the emergence of the static synchronization state. We further report the appearance of the static ring phase wave state and evaluate its radius theoretically. Finally, we validate our findings using Stuart–Landau oscillators to describe the phase dynamics of swarmalators subject to attractive local coupling.
Ključne besede: swarmalators, time-varying couplings, synchronization, competitive phase coupling
Objavljeno v DKUM: 16.07.2024; Ogledov: 2; Prenosov: 0
.pdf Celotno besedilo (3,26 MB)
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Eco-evolutionary dynamics of multigames with mutations
Sourav Roy, Sayantan Nag Chowdhury, Prakash Chandra Mali, Matjaž Perc, Dibakar Ghosh, 2022, izvirni znanstveni članek

Opis: Most environments favor defection over cooperation due to natural selection. Nonetheless, the emergence of cooperation is omnipresent in many biological, social, and economic systems, quite contrary to the well-celebrated Darwinian theory of evolution. Much research has been devoted to better understanding how and why cooperation persists among selfinterested individuals despite their competition for limited resources. Here we go beyond a single social dilemma since individuals usually encounter various social challenges. In particular, we propose and study a mathematical model incorporating both the prisoner’s dilemma and the snowdrift game. We further extend this model by considering ecological signatures like mutation and selfless one-sided contribution of altruist free space. The nonlinear evolutionary dynamics that results from these upgrades offer a broader range of equilibrium outcomes, and it also often favors cooperation over defection. With the help of analytical and numerical calculations, our theoretical model sheds light on the mechanisms that maintain biodiversity, and it helps to explain the evolution of social order in human societies.
Ključne besede: public goods, cooperation, mutation, social physics, evolutionary dynamics
Objavljeno v DKUM: 15.07.2024; Ogledov: 25; Prenosov: 0
.pdf Celotno besedilo (4,97 MB)
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Glucose-stimulated calcium dynamics in beta cells from male C57BL/6J, C57BL/6N, and NMRI mice : a comparison of activation, activity, and deactivation properties in tissue slices
Viljem Pohorec, Lidija Križančić Bombek, Maša Skelin, Jurij Dolenšek, Andraž Stožer, 2022, izvirni znanstveni članek

Opis: Although mice are a very instrumental model in islet beta cell research, possible phenotypic differences between strains and substrains are largely neglected in the scientific community. In this study, we show important phenotypic differences in beta cell responses to glucose between C57BL/6J, C57BL/6N, and NMRI mice, i.e., the three most commonly used strains. High-resolution multicellular confocal imaging of beta cells in acute pancreas tissue slices was used to measure and quantitatively compare the calcium dynamics in response to a wide range of glucose concentrations. Strain- and substrain-specific features were found in all three phases of beta cell responses to glucose: a shift in the dose-response curve characterizing the delay to activation and deactivation in response to stimulus onset and termination, respectively, and distinct concentration-encoding principles during the plateau phase in terms of frequency, duration, and active time changes with increasing glucose concentrations. Our results underline the significance of carefully choosing and reporting the strain to enable comparison and increase reproducibility, emphasize the importance of analyzing a number of different beta cell physiological parameters characterizing the response to glucose, and provide a valuable standard for future studies on beta cell calcium dynamics in health and disease in tissue slices.
Ključne besede: beta cell, mouse models, calcium imaging, glucose-dependence, tissue slice
Objavljeno v DKUM: 15.07.2024; Ogledov: 17; Prenosov: 0
.pdf Celotno besedilo (4,45 MB)
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Kolmogorov compression complexity may differentiate different schools of Orthodox iconography
Daniel Peptenatu, Ion Andronache, Helmut Ahammer, Richard Taylor, Ioannis Liritzis, Marko Radulovic, Bogdan Ciobanu, Marin Burcea, Matjaž Perc, Tuan D. Pham, 2022, izvirni znanstveni članek

Opis: The complexity in the styles of 1200 Byzantine icons painted between 13th and 16th from Greece, Russia and Romania was investigated through the Kolmogorov algorithmic information theory. The aim was to identify specific quantitative patterns which define the key characteristics of the three different painting schools. Our novel approach using the artificial surface images generated with Inverse FFT and the Midpoint Displacement (MD) algorithms, was validated by comparison of results with eight fractal and non-fractal indices. From the analyzes performed, normalized Kolmogorov compression complexity (KC) proved to be the best solution because it had the best complexity pattern differentiations, is not sensitive to the image size and the least affected by noise. We conclude that normalized KC methodology does offer capability to differentiate the icons within a School and amongst the three Schools.
Ključne besede: iconography, complexity, Kolmogorov compression, art, physics
Objavljeno v DKUM: 15.07.2024; Ogledov: 19; Prenosov: 0
.pdf Celotno besedilo (6,05 MB)
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Universality of political corruption networks
Alvaro F. Martins, Bruno R. da Cunha, Quentin S. Hanley, Sebastián Gonçalves, Matjaž Perc, Haroldo V. Ribeiro, 2022, izvirni znanstveni članek

Opis: Corruption crimes demand highly coordinated actions among criminal agents to succeed. But research dedicated to corruption networks is still in its infancy and indeed little is known about the properties of these networks. Here we present a comprehensive investigation of corruption networks related to political scandals in Spain and Brazil over nearly three decades. We show that corruption networks of both countries share universal structural and dynamical properties, including similar degree distributions, clustering and assortativity coefficients, modular structure, and a growth process that is marked by the coalescence of network components due to a few recidivist criminals. We propose a simple model that not only reproduces these empirical properties but reveals also that corruption networks operate near a critical recidivism rate below which the network is entirely fragmented and above which it is overly connected. Our research thus indicates that actions focused on decreasing corruption recidivism may substantially mitigate this type of organized crime.
Ključne besede: corruption, network, politics, universality, social physics
Objavljeno v DKUM: 15.07.2024; Ogledov: 15; Prenosov: 0
.pdf Celotno besedilo (7,26 MB)
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Risk assessment of COVID-19 epidemic resurgence in relation to SARS-CoV-2 variants and vaccination passes
Tyll Krüger, Krzysztof Gogolewski, Marcin Bodych, Anna Gambin, Giulia Giordano, Sarah Cuschieri, Thomas Czypionka, Matjaž Perc, Elena Petelos, Magdalena Rosińska, Ewa Szczurek, 2022, izvirni znanstveni članek

Opis: The introduction of COVID-19 vaccination passes (VPs) by many countries coincided with the Delta variant fast becoming dominant across Europe. A thorough assessment of their impact on epidemic dynamics is still lacking. Here, we propose the VAP-SIRS model that considers possibly lower restrictions for the VP holders than for the rest of the population, imperfect vaccination effectiveness against infection, rates of (re-)vaccination and waning immunity, fraction of never-vaccinated, and the increased transmissibility of the Delta variant. Some predicted epidemic scenarios for realistic parameter values yield new COVID-19 infection waves within two years, and high daily case numbers in the endemic state, even without introducing VPs and granting more freedom to their holders. Still, suitable adaptive policies can avoid unfavorable outcomes. While VP holders could initially be allowed more freedom, the lack of full vaccine effectiveness and increased transmissibility will require accelerated (re-)vaccination, wide-spread immunity surveillance, and/or minimal long-term common restrictions.
Ključne besede: SIRS model, vaccination pass, stability analysis
Objavljeno v DKUM: 15.07.2024; Ogledov: 17; Prenosov: 1
.pdf Celotno besedilo (2,06 MB)
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Use of emulsion-templated, highly porous polyelectrolytes for in vitro germination of chickpea embryos : a new substrate for soilless cultivation
Janja Majer Kovačič, Terezija Ciringer, Jana Ambrožič-Dolinšek, Sebastijan Kovačič, 2022, izvirni znanstveni članek

Opis: The application of highly porous and 3D interconnected microcellular polyelectrolyte polyHIPE (PE-PH) monoliths based on (3-acrylamidopropyl)-trimethylammonium chloride as soilless cultivation substrates for in vitro embryo culture is discussed. The embryo axes isolated from chickpea seeds are inoculated onto the surface of the monoliths and allowed to germinate. Germination study show that the newly disclosed PE-PH substrate performs much better than the conventionally used agar as the germination percentage, shoot and root length, fresh and dry weight as well as the number of leaves are enhanced. The PE-PHs exhibit a higher absorption capacity of the plant growth medium, that is, 36 g·g–1 compared to agar, that is, 20 g·g–1, and also survive autoclaving conditions without failing. The key advantage over standard agar substrates is that they can be reused several times and also without prior sterilization. These results suggest that PE-PHs with exceptional absorption/retention properties and robustness have great potential as soilless substrates for in vitro plant cultivation.
Ključne besede: absorption, catalyst supports, germination, plants, porosity
Objavljeno v DKUM: 15.07.2024; Ogledov: 22; Prenosov: 0
.pdf Celotno besedilo (4,70 MB)
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Disaggregated data on age and sex for the first 250 days of the COVID-19 pandemic in Bucharest, Romania
Marian-Gabriel Hâncean, Maria Cristina Ghiţǎ, Matjaž Perc, Jürgen Lerner, Iulian Oană, Bianca-Elena Mihǎilǎ, Adelina Alexandra Stoica, David-Andrei Bunaciu, 2022, izvirni znanstveni članek

Opis: Experts worldwide have constantly been calling for high-quality open-access epidemiological data, given the fast-evolving nature of the COVID-19 pandemic. Disaggregated high-level granularity records are still scant despite being essential to corroborate the effectiveness of virus containment measures and even vaccination strategies. We provide a complete dataset containing disaggregated epidemiological information about all the COVID-19 patients officially reported during the first 250 days of the COVID-19 pandemic in Bucharest (Romania). We give the sex, age, and the COVID-19 infection confirmation date for 46.440 individual cases, between March 7th and November 11th, 2020. Additionally, we provide context-wise information such as the stringency levels of the measures taken by the Romanian authorities. We procured the data from the local public health authorities and systemized it to respond to the urgent international need of comparing observational data collected from various populations. Our dataset may help understand COVID-19 transmission in highly dense urban communities, perform virus spreading simulations, ascertain the effects of non-pharmaceutical interventions, and craft better vaccination strategies.
Ključne besede: disaggregated data, age, sex, COVID-19, pandemic, Romania
Objavljeno v DKUM: 15.07.2024; Ogledov: 16; Prenosov: 0
.pdf Celotno besedilo (3,24 MB)
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Occupations and their impact on the spreading of COVID-19 in urban communities
Marian-Gabriel Hâncean, Jürgen Lerner, Matjaž Perc, Iulian Oană, David-Andrei Bunaciu, Adelina Alexandra Stoica, Maria Cristina Ghiţǎ, 2022, izvirni znanstveni članek

Opis: The current pandemic has disproportionally afected the workforce. To improve our understanding of the role that occupations play in the transmission of COVID-19, we analyse real-world network data that were collected in Bucharest between August 1st and October 31st 2020. The data record sex, age, and occupation of 6895 patients and the 13,272 people they have interacted with, thus providing a social network from an urban setting through which COVID-19 has spread. Quite remarkably, we fnd that medical occupations have no signifcant efect on the spread of the virus. Instead, we fnd common transmission chains to start with infected individuals who hold jobs in the private sector and are connected with non-active alters, such as spouses, siblings, or elderly relatives. We use relational hyperevent models to assess the most likely homophily and network efects in the community transmission. We detect homophily with respect to age and anti-homophily with respect to sex and employability. We note that, although additional data would be welcomed to perform more in-depth network analyses, our fndings may help public authorities better target under-performing vaccination campaigns.
Ključne besede: occupation, urban community, spreading of disease, covid-19
Objavljeno v DKUM: 15.07.2024; Ogledov: 3; Prenosov: 0
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