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Physica
North-Holland
Physica

North-Holland

0378-4371

Physica/Journal Physica
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    Noise and noise propagation in transition cascade of colonic cells with four coupled feedback regulations

    Zhou, Bin-qianApata, Charles OmotomideZhou, Yi-fanJiang, Long...
    14页
    查看更多>>摘要：Noise and noise propagation are vital in various biological processes. In a phenotypic transition cascade of colonic cells, there are three compartments: stem cells (SCs), transit-amplifying cells (TACs), and fully differentiated cells (FDCs). Instead of pure linear feedback (L) or pure saturation feedback (S) in regulating SCs and TACs differentiation, four coupled feedbacks including LL, LS, SL, and SS are considered to compare the impacts of different feedbacks on noise and noise propagation of cells. Rather than LL feedback and LS feedback, SL feedback and SS feedback have obvious advantages: Firstly, the characteristics of cells steady states changing with the parameter are more consistent with the tumor development. Secondly, as long as the key parameter is adjusted reasonably, the strong correlation between any two fluctuations of cells can be effectively utilized or avoided. Finally, although there is no direct interaction between SCs and FDCs, the noise in SCs can propagate to FDCs by TACs. And the transmitted noise from upstream cells can cause the large total noise of downstream cells even the number of downstream cells is large. The strong correlation and noise propagation between upstream and downstream cells may be the theoretical basis of the targeted therapy, which can achieve dual or even triple-drug targeted anti-tumor therapy by acting on different targets in the upstream or downstream pathways. Therefore, SL feedback or SS feedback may be a better choice for SCs and TACs to adjust their differentiation rather than LL feedback and LS feedback. This work is an extension and application of the elementary fluctuation theory of statistical physics in life system. (C) 2021 Elsevier B.V. All rights reserved.
      原文链接:
    • NSTL
    • Elsevier

    Super-random states in vehicular traffic - Detection & explanation

    Krbalek, MilanSeba, FrantisekKrbalkova, Michaela
    14页
    查看更多>>摘要：This article deals with specific states of traffic flow on a two-lane freeway, in which statistical fluctuations of microscopic quantities (inter-vehicle gaps) are significantly higher than in systems with absolutely random events (Poisson systems). These anomalous states (super-random) are detected in empirical traffic data, specifically in the fast lane at traffic densities up to 25 vehicles per kilometer. The origin of these states is then explained mathematically (using the theory of balance particle systems and tools of random matrix theory), physically (by means of an one-dimensional particle gas subjected to local perturbations caused by overtaking cars) and empirically (using an analogy with phenomena observed in photon counting experiments). In the article we show that overtaking maneuvers, when vehicles from a slow lane are injected into a fast-lane stream of faster moving vehicles, disrupt a local balance in microstructure of fast-lane stream and cause atypical arrangement of vehicular positions, that is very rare, generally. With help of original numerical model we demonstrate that the anomalous states detected are identical to equilibrium states formed in a stochastic particle gas with a potential containing, in addition to a repulsive component, also an attractive component. (C) 2021 Published by Elsevier B.V.
      原文链接:
    • NSTL
    • Elsevier

    A rumor spreading pairwise model on weighted networks

    Jing, WenjunLi, YiZhang, XiaoqinZhang, Juping...
    10页
    查看更多>>摘要：The heterogeneity in edge weights plays a crucial role in the spread of a rumor on networks. To investigate the effects of weight distribution on a rumor spreading, we employ an ISR pairwise model on weighted regular random networks in this paper. The basic reproductive ratio of this model is derived, and it indicates that the heterogeneity in transmission rate leads to a fall in the basic reproductive ratio when the average transmission rate is fixed. Besides, by assuming that the transmission rate is a linear function of the edge weight, numerical simulation results of the model on networks with a bimodal weight distribution show that weight heterogeneity has a complex impact on the dynamics of a rumor. When we fix the proportions of two weights but vary their values to keep a constant average weight, increasing the heterogeneity in weight distribution slows down the initial growth rate, the final size and the maximum influence of a rumor, but increases the duration for rumor spreading. However, if we change both the values and proportions of two weights, only the mean and variance of the weight distribution are not able to provide sufficient information to predict the dynamics of a rumor. Moreover, we get similar simulation results in the case of nonlinear transmission rate. (C) 2021 Published by Elsevier B.V.
      原文链接:
    • NSTL
    • Elsevier

    Order-disorder transition in a linear system of anti-parallel magnetic dipoles with long-range interactions

    Dimitrov, R.Dimitrova, O., VArda, L.
    29页
    查看更多>>摘要：In the present study, we investigate the magnetic ordering of a system with a large number of nanomagnetic dipoles, approximated as point dipoles, arranged on a regular ring, and having anti-parallel (anti-ferromagnetic) ordering at zero external magnetic fields. We can impose different restrictions on the degrees of freedom of the dipoles: dipoles along the ring and dipoles perpendicular to the ring. When the dipoles are along the ring, the model is called the phi-model (the dipoles are along the phi-coordinate of the cylindrical coordinate system) or head-to-tail model. When the dipoles are perpendicular to the plane of the ring the model is called the z-model (the dipoles are along the z-axis of the cylindrical coordinate system), and when the dipoles are along the radials of the ring, the model is called the r-model (the radial model). The z-and the r- models are similar to the one-dimensional Ising chain model (spins 'up' or 'down'): the only difference is that in the z-and r-models the interactions are dipolar long-range ones. By a combination of numerical and analytical methods, we have found the exact ground states of the models, which are degenerated. A perfectly ordered system is possible only at zero temperature: by increasing the temperature the perfect order is destroyed. Employing the Monte Carlo simulation, we show that in a system of magnetic dipoles forming a linear chain, similar to the one-dimensional Ising chain model, there are no phase transitions in the thermodynamics limit, when N -> infinity, except at zero temperature. The system continuously transforms from a perfectly-ordered state at zero temperature to a perfectly-disordered state at very high temperatures. However, the disordered states of the models consist of perfectly ordered domains, where the ordering corresponds to one of the degenerated ground states. With the temperature, the average size of the domains decreases to zero (at very high temperatures), and numerically this size is equal to the correlation length. For finite-sized models the perfectly ordered state is kept to some critical temperature depending on the number of dipoles: T-1 approximate to 4.8/In (N/2) for the head-to-tail model, T-c approximate to 1.8/In (N/2) for the z- and radial models, T-c is the temperature when the first defect appears in the perfectly-ordered ground state,measured in J = mu(0)m(2)/4 pi r(0)(3) units, where m is the dipole moment of the dipoles, ro the nearest distance between 6 them. Introducing quasi-dipoles, in the present study we investigate the basic properties of the z-models, such as the internal energy, the heat capacity, the order parameter, the correlation length, etc. Employing Boltzmann's statistics, we have obtained the exact solution of the z- and Id Ising models. The zero-temperature state of the z-model is a perfectly ordered configuration of anti-parallel pairs of dipoles, and it is degenerated because inverting the directions of the dipoles does not change the energy of the configuration. When the model consists of N odd number of dipoles, in the ground state there is a natural 'defect' - a non-paired dipole, which degenerates additionally N-times the ground state and increases the energy per dipole of the ground state. For any large number of dipoles (N similar to 100) this effect becomes negligible. We have obtained exact analytical expressions for the energy and the magnetic field of the z-model at zero temperature. (C) 2021 Elsevier B.V. All rights reserved.
      原文链接:
    • NSTL
    • Elsevier

    Modeling the dynamics of pedestrian evacuation in a complex environment

    Liu, QiujiaLu, LinjunZhang, YijingHu, Miaoqing...
    20页
    查看更多>>摘要：The study of crowd evacuation dynamics is important for the management of public safety, and crowd evacuation dynamics models can be used to simulate the behaviors of pedestrians during an evacuation. In this paper, we propose a new force model for simulation of the evacuation of complex environments. In comparison to existing models, this model considers more environmental factors to make it applicable to complex emergency environments. By verification using real data, the model is demonstrated to be able to predict evacuation efficiency and better reproduce the microscopic behavior of pedestrians under extreme conditions. We discuss the impact of the presence of different kinds of hazards and different types of obstacles in the environment on pedestrian evacuation performance and put forward suggestions for crowd evacuation management. (C) 2021 Published by Elsevier B.V.
      原文链接:
    • NSTL
    • Elsevier

    Recurrence analysis of urban traffic congestion index on multi-scale

    Wu, JiaxinZhou, XubingPeng, YiZhao, Xiaojun...
    16页
    查看更多>>摘要：As for the increasing traffic pressure in urban cities, it is of great significance to analyze the complex traffic system and grasp the recurrence characteristics of traffic state to better solve the problem of traffic congestion. This paper combines the multi-scale theory and recurrence analysis, which carries out the qualitative and quantitative multiscale recurrence analysis of the traffic congestion index (TCI) in a period of time in Beijing, China, and further, analyzes the recurrence state of each day in a week, as well as mines the recurrence law. The empirical results reveal that the low-frequency components of the dynamic characteristics of TCI play a major role in the long-term traffic state prediction. The traffic state between weekdays and weekends tends to change, and the state on weekdays is more regular, whereas on Friday, as the critical day for rest days, it is more complex and random. The conclusion of this paper will play a fundamental role in grasping the essential law of Beijing's traffic system and analyzing the traffic congestion problem and the urban traffic system, which has strong practical significance. (C) 2021 Elsevier B.V. All rights reserved.
      原文链接:
    • NSTL
    • Elsevier

    Thermostatistics in deformed space with maximal length

    Bensalem, SalaheddineBouaziz, Djamil
    13页
    查看更多>>摘要：The method for calculating the canonical partition function with deformed Heisenberg algebra, developed by Fityo (Fityo, 2008), is adapted to the modified commutation relations including a maximal length, proposed in 1D by Perivolaropoulos (Perivolaropoulos, 2017). Firstly, the one-dimensional maximum length formalism is extended to arbitrary dimensions. Then, by employing the adapted semiclassical approach, the thermostatistics of an ideal gas and a system of harmonic oscillators (HOs) is investigated. For the ideal gas, the results generalize those obtained recently by us in 1D (Bensalem and Bouaziz, 2019), and show a complete agreement between the semiclassical and quantum approaches. In particular, a stiffer real-like equation of state for the ideal gas is established in 3D; it is consistent with the formal one, which we presented in the aforementioned paper. The modified thermostatistics of a system of HOs compared to that of an ideal gas reveals that the effects of the maximal length depend on the studied system. On the other hand, it is observed that the maximal-length effects on some thermodynamic functions of the HOs are analogous to those of the minimal length, studied previously in the literature. Finally, by analyzing some experimental data, we argue that the maximal length might be viewed as a characteristic scale associated with the system under study. (C) 2021 Elsevier B.V. All rights reserved.
      原文链接:
    • NSTL
    • Elsevier

    Rank-size distributions for banks: A cross-country analysis

    Lupi, ClaudioPietrovito, FilomenaCerqueti, RoyPozzolo, Alberto Franco...
    14页
    查看更多>>摘要：Rank-size analysis is a powerful methodological instrument for describing the main features of a unified system by moving from an available sample of its disaggregated elements. We here study the rank-size relationship of banks' total assets in a sample of 13 advanced economies. We show that a standard power-law function is unable to provide an adequate fit of the data, while a Discrete Generalized Beta Distribution provides a statistically satisfactory fit, being able to capture the behaviour of the distribution at low and high ranks. We then analyse the relationship between the parameters of the Discrete Generalized Beta Distribution estimated in each country and the main features of the country's banking industry. Our results point to a connection with the degree of development of the banking sector and with some regulatory and institutional characteristics, but no relationship with riskiness. (C) 2021 Elsevier B.V. All rights reserved.
      原文链接:
    • NSTL
    • Elsevier

    Mixed convection stagnation-point flow of Cross fluid over a shrinking sheet with suction and thermal radiation

    Jamaludin, AnuarNazar, RoslindaPop, Ioan
    17页
    查看更多>>摘要：This work focuses on numerically investigating the mixed convection stagnation-point flow and heat transfer in an incompressible Cross fluid over a permeable shrinking sheet, with suction and thermal radiation effects. The governing equations defining the current problem have been first transformed into the ordinary differential equations through similarity transformations. The resulting equations obtained are then solved numerically using the bvp4c programmed in MATLAB, revealing dual (upper and lower branch) solutions for both assisting and opposing flow regions. Stability analysis has been employed afterwards to determine a stable solution between them. Following from there, the upper branch solution has been found to be stable, while the lower branch solution is unstable. In addition, the study has established that the Weissenberg number, the Prandtl number and the suction parameter are strongly influenced to uplift the range of existence for dual solutions. (C) 2021 Elsevier B.V. All rights reserved.
      原文链接:
    • NSTL
    • Elsevier

    The 2020 global stock market crash: Endogenous or exogenous?

    Song, RuiqiangShu, MinZhu, Wei
    15页
    查看更多>>摘要：Starting on February 20, 2020, the global stock markets began to suffer the worst decline since the Great Recession in 2008, and the COVID-19 has been widely blamed on the stock market crashes. In this study, we applied the log-periodic power law singularity (LPPLS) methodology based on multilevel time series to unravel the underlying mechanisms of the 2020 global stock market crash by analyzing the trajectories of 10 major world stock market indexes from both developed and emergent stock markets, including the S&P 500, the DJIA, and the NASDAQ from the United State, the FTSE from the United Kingdom, the DAX from Germany, the NIKKEI from Japan, the CSI 300 from China, the HSI from Hong Kong, the BSESN from India, and the BOVESPA from Brazil. In order to effectively distinguish between endogenous crash and exogenous crash in stock market, we proposed using the LPPLS confidence indicator as a classification proxy. The results show that the apparent LPPLS bubble patterns of the super-exponential increase, corrected by the accelerating logarithm-periodic oscillations, have indeed presented in the price trajectories of the seven indexes: S&P 500, DJIA, NASDAQ DAX, CSI 300, BSESN, and BOVESPA, indicating that the large positive bubbles have formed endogenously prior to the 2020 stock market crash, and the subsequent crashes for the seven indexes are endogenous, stemming from the increasingly systemic instability of the stock markets inherently, while the well-known external shocks, such as the COVID-19 pandemic, the corporate debt bubble, and the 2020 Russia-Saudi Arabia oil price war, only served as sparks during the 2020 global stock market crash. In contrast, the crashes in the three remaining indexes: FTSE, NIKKEI, and HSI, are exogenous and hence are perhaps the only crashes truly due to the COVID-19 pandemic. We also found that in terms of the regime changes of the stock markets, no obvious LPPLS negative bubble pattern has been observed in the price trajectories of the 10 stock market indexes, indicating that the regime changes from a bear market to a bull market in late March 2020 are exogenous, stemming from external factors. The unprecedented market and economy rescue efforts from federal reserves and central banks across the world in unison may have played a critical role in quelling the 2020 global stock market crash in the nick of time. This paper creates a paradigm for future studies in real-time crash detection and underlying mechanism dissection. It serves to warn us of the imminent risks in not only the stock market but also other financial markets and economic indexes. (C) 2021 Elsevier B.V. All rights reserved.
      原文链接:
    • NSTL
    • Elsevier