Philosophical Transactions of the Royal Society A最新文献_第5页

Open-flow mixing and transfer operators 开流混合和转移操作员

Philosophical Transactions of the Royal Society A Pub Date : 2021-12-21 DOI: 10.1098/rsta.2021.0028

Anna Klünker, Kathrin Padberg-Gehle, Jean-Luc Thiffeault

引用次数: 2

Opinion dynamics: public and private 舆论动态:公共和私人

Philosophical Transactions of the Royal Society A Pub Date : 2021-12-02 DOI: 10.1098/rsta.2021.0169

Subhadeep Roy, Soumyajyoti Biswas

引用次数: 3

New futures for cosmological models 宇宙学模型的新未来

Philosophical Transactions of the Royal Society A Pub Date : 2021-11-17 DOI: 10.1098/rsta.2021.0333

L. Fernández-Jambrina, R. Lazkoz

引用次数: 5

Self-regularization in turbulence from the Kolmogorov 4/5-law and alignment 湍流中的Kolmogorov 4/5律自正则化及其对准

Philosophical Transactions of the Royal Society A Pub Date : 2021-11-05 DOI: 10.1098/rsta.2021.0033

T. Drivas

{"title":"Self-regularization in turbulence from the Kolmogorov 4/5-law and alignment","authors":"T. Drivas","doi":"10.1098/rsta.2021.0033","DOIUrl":"https://doi.org/10.1098/rsta.2021.0033","url":null,"abstract":"A defining feature of three-dimensional hydrodynamic turbulence is that the rate of energy dissipation is bounded away from zero as viscosity is decreased (Reynolds number increased). This phenomenon—anomalous dissipation—is sometimes called the ‘zeroth law of turbulence’ as it underpins many celebrated theoretical predictions. Another robust feature observed in turbulence is that velocity structure functions Sp(ℓ):=⟨|δℓu|p⟩ exhibit persistent power-law scaling in the inertial range, namely Sp(ℓ)∼|ℓ|ζp for exponents ζp>0 over an ever increasing (with Reynolds) range of scales. This behaviour indicates that the velocity field retains some fractional differentiability uniformly in the Reynolds number. The Kolmogorov 1941 theory of turbulence predicts that ζp=p/3 for all p and Onsager’s 1949 theory establishes the requirement that ζp≤p/3 for p≥ 3 for consistency with the zeroth law. Empirically, ζ2⪆2/3 and ζ3⪅1, suggesting that turbulent Navier–Stokes solutions approximate dissipative weak solutions of the Euler equations possessing (nearly) the minimal degree of singularity required to sustain anomalous dissipation. In this note, we adopt an experimentally supported hypothesis on the anti-alignment of velocity increments with their separation vectors and demonstrate that the inertial dissipation provides a regularization mechanism via the Kolmogorov 4/5-law. This article is part of the theme issue ‘Mathematical problems in physical fluid dynamics (part 2)’.","PeriodicalId":20020,"journal":{"name":"Philosophical Transactions of the Royal Society A","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90595058","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 9

Optimal cooling of an internally heated disc 内部加热盘的最佳冷却

Philosophical Transactions of the Royal Society A Pub Date : 2021-10-25 DOI: 10.1098/rsta.2021.0040

Ian Tobasco

{"title":"Optimal cooling of an internally heated disc","authors":"Ian Tobasco","doi":"10.1098/rsta.2021.0040","DOIUrl":"https://doi.org/10.1098/rsta.2021.0040","url":null,"abstract":"Motivated by the search for sharp bounds on turbulent heat transfer as well as the design of optimal heat exchangers, we consider incompressible flows that most efficiently cool an internally heated disc. Heat enters via a distributed source, is passively advected and diffused, and exits through the boundary at a fixed temperature. We seek an advecting flow to optimize this exchange. Previous work on energy-constrained cooling with a constant source has conjectured that global optimizers should resemble convection rolls; we prove one-sided bounds on energy-constrained cooling corresponding to, but not resolving, this conjecture. In the case of an enstrophy constraint, our results are more complete: we construct a family of self-similar, tree-like ‘branching flows’ whose cooling we prove is within a logarithm of globally optimal. These results hold for general space- and time-dependent source–sink distributions that add more heat than they remove. Our main technical tool is a non-local Dirichlet-like variational principle for bounding solutions of the inhomogeneous advection–diffusion equation with a divergence-free velocity. This article is part of the theme issue ‘Mathematical problems in physical fluid dynamics (part 1)’.","PeriodicalId":20020,"journal":{"name":"Philosophical Transactions of the Royal Society A","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87705022","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 10

Effect of delay on the emergent stability patterns in generalized Lotka–Volterra ecological dynamics 时滞对广义Lotka-Volterra生态动态中涌现稳定性模式的影响

Philosophical Transactions of the Royal Society A Pub Date : 2021-10-22 DOI: 10.1098/rsta.2021.0245

M. Saeedian, E. Pigani, A. Maritan, S. Suweis, S. Azaele

{"title":"Effect of delay on the emergent stability patterns in generalized Lotka–Volterra ecological dynamics","authors":"M. Saeedian, E. Pigani, A. Maritan, S. Suweis, S. Azaele","doi":"10.1098/rsta.2021.0245","DOIUrl":"https://doi.org/10.1098/rsta.2021.0245","url":null,"abstract":"Understanding the conditions of feasibility and stability in ecological systems is a major challenge in theoretical ecology. The seminal work of May in 1972 and recent developments based on the theory of random matrices have shown the existence of emergent universal patterns of both stability and feasibility in ecological dynamics. However, only a few studies have investigated the role of delay coupled with population dynamics in the emergence of feasible and stable states. In this work, we study the effects of delay on generalized Loka–Volterra population dynamics of several interacting species in closed ecological environments. First, we investigate the relation between feasibility and stability of the modelled ecological community in the absence of delay and find a simple analytical relation when intra-species interactions are dominant. We then show how, by increasing the time delay, there is a transition in the stability phases of the population dynamics: from an equilibrium state to a stable non-point attractor phase. We calculate analytically the critical delay of that transition and show that it is in excellent agreement with numerical simulations. Finally, following a similar approach to characterizing stability in empirical studies, we investigate the coefficient of variation, which quantifies the magnitude of population fluctuations. We show that in the oscillatory regime induced by the delay, the variability at community level decreases for increasing diversity. This article is part of the theme issue ‘Emergent phenomena in complex physical and socio-technical systems: from cells to societies’.","PeriodicalId":20020,"journal":{"name":"Philosophical Transactions of the Royal Society A","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90717695","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 5

Physics-inspired analysis of the two-class income distribution in the USA in 1983–2018 1983-2018年美国两阶层收入分配的物理学启发分析

Philosophical Transactions of the Royal Society A Pub Date : 2021-10-07 DOI: 10.1098/rsta.2021.0162

D. Ludwig, V. Yakovenko

{"title":"Physics-inspired analysis of the two-class income distribution in the USA in 1983–2018","authors":"D. Ludwig, V. Yakovenko","doi":"10.1098/rsta.2021.0162","DOIUrl":"https://doi.org/10.1098/rsta.2021.0162","url":null,"abstract":"The first part of this paper is a brief survey of the approaches to economic inequality based on ideas from statistical physics and kinetic theory. These include the Boltzmann kinetic equation, the time-reversal symmetry, the ergodicity hypothesis, entropy maximization and the Fokker–Planck equation. The origins of the exponential Boltzmann–Gibbs distribution and the Pareto power law are discussed in relation to additive and multiplicative stochastic processes. The second part of the paper analyses income distribution data in the USA for the time period 1983–2018 using a two-class decomposition. We present overwhelming evidence that the lower class (more than 90% of the population) is described by the exponential distribution, whereas the upper class (about 4% of the population in 2018) by the power law. We show that the significant growth of inequality during this time period is due to the sharp increase in the upper-class income share, whereas relative inequality within the lower class remains constant. We speculate that the expansion of the upper-class population and income shares may be due to increasing digitization and non-locality of the economy in the last 40 years. This article is part of the theme issue ‘Kinetic exchange models of societies and economies’.","PeriodicalId":20020,"journal":{"name":"Philosophical Transactions of the Royal Society A","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-10-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87393211","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 15

Growth of Sobolev norms and loss of regularity in transport equations 输运方程中Sobolev范数的增长和正则性的丧失

Philosophical Transactions of the Royal Society A Pub Date : 2021-09-30 DOI: 10.1098/rsta.2021.0024

Gianluca Crippa, T. Elgindi, Gautam Iyer, A. Mazzucato

引用次数: 7

Spreading of fake news, competence and learning: kinetic modelling and numerical approximation 假新闻传播、能力与学习:动力学建模与数值逼近

Philosophical Transactions of the Royal Society A Pub Date : 2021-09-28 DOI: 10.1098/rsta.2021.0159

Jonathan Franceschi, L. Pareschi

{"title":"Spreading of fake news, competence and learning: kinetic modelling and numerical approximation","authors":"Jonathan Franceschi, L. Pareschi","doi":"10.1098/rsta.2021.0159","DOIUrl":"https://doi.org/10.1098/rsta.2021.0159","url":null,"abstract":"The rise of social networks as the primary means of communication in almost every country in the world has simultaneously triggered an increase in the amount of fake news circulating online. The urgent need for models that can describe the growing infodemic of fake news has been highlighted by the current pandemic. The resulting slowdown in vaccination campaigns due to misinformation and generally the inability of individuals to discern the reliability of information is posing enormous risks to the governments of many countries. In this research using the tools of kinetic theory, we describe the interaction between fake news spreading and competence of individuals through multi-population models in which fake news spreads analogously to an infectious disease with different impact depending on the level of competence of individuals. The level of competence, in particular, is subject to evolutionary dynamics due to both social interactions between agents and external learning dynamics. The results show how the model is able to correctly describe the dynamics of diffusion of fake news and the important role of competence in their containment. This article is part of the theme issue ‘Kinetic exchange models of societies and economies’.","PeriodicalId":20020,"journal":{"name":"Philosophical Transactions of the Royal Society A","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90198503","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 8

An Elo-type rating model for players and teams of variable strength 可变强度球员和球队的elo型评分模型

Philosophical Transactions of the Royal Society A Pub Date : 2021-09-28 DOI: 10.1098/rsta.2021.0155

Bertram Düring, Michael Fischer, Marie-Therese Wolfram

引用次数: 4