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Neglecting complex network structures underestimates delays in a large-capital project 忽略复杂的网络结构低估了大型项目的延迟
IF 2.7 Q1 MATHEMATICS, INTERDISCIPLINARY APPLICATIONS Pub Date : 2023-04-20 DOI: 10.1088/2632-072X/accef0
C. Ellinas, D. Avraam, C. Nicolaides
Completing large-scale projects on time is a daunting challenge, partly due to the intricate network of dependencies between a project’s activities. To support this challenge, existing theory focuses on predicting whether a delay in completing a single activity is likely to spread and impact downstream activities. Using fine-grained information from 68 546 activities and 84 934 pairs, associated with the delivery of a $1.86Bn infrastructure project, we show that the core mechanism that underpins existing theory underestimates delay propagation. To elucidate the mechanisms that drive delay, we generated null models that destroyed the structural and temporal correlations of the original project activity network. By doing so, we argue that this underestimation is the result of neglecting endogenous structural features within the project’s activity network. Formulating a new mechanism that utilizes both temporal and structural features may help improve our capacity to predict how delays spread within projects.
按时完成大型项目是一项艰巨的挑战,部分原因在于项目活动之间错综复杂的依赖关系网络。为了支持这一挑战,现有的理论侧重于预测完成单个活动的延迟是否可能蔓延并影响下游活动。使用来自68546个活动和84934对的细粒度信息,与18.6亿美元基础设施项目的交付相关,我们表明支撑现有理论的核心机制低估了延迟传播。为了阐明驱动延迟的机制,我们生成了零模型,该模型破坏了原始项目活动网络的结构和时间相关性。通过这样做,我们认为这种低估是忽视了项目活动网络内的内生结构特征的结果。制定一种利用时间和结构特征的新机制可能有助于提高我们预测延迟如何在项目中传播的能力。
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引用次数: 0
Smallworldness in hypergraphs 超图中的小世界性
IF 2.7 Q1 MATHEMATICS, INTERDISCIPLINARY APPLICATIONS Pub Date : 2023-04-18 DOI: 10.1088/2632-072X/acf430
Tanu Raghav, S. Boccaletti, S. Jalan
Most real-world networks are endowed with the small-world property, by means of which the maximal distance between any two of their nodes scales logarithmically rather than linearly with their size. The evidence sparkled a wealth of studies trying to reveal possible mechanisms through which the pairwise interactions amongst the units of a network are structured in a way to determine such observed regularity. Here we show that smallworldness occurs also when interactions are of higher order. Namely, by considering Q-uniform hypergraphs and a process through which connections can be randomly rewired with given probability p, we find that such systems may exhibit prominent clustering properties in connection with small average path lengths for a wide range of p values, in analogy to the case of dyadic interactions. The nature of small-world transition remains the same at different orders Q ( =2,3,4,5, and 6) of the interactions, however, the increase in the hyperedge order reduces the range of rewiring probability for which smallworldness emerge.
大多数现实世界的网络都具有小世界特性,即网络中任意两个节点之间的最大距离与网络大小成对数关系,而不是线性关系。这些证据激发了大量的研究,试图揭示可能的机制,通过这种机制,网络单元之间的成对相互作用以某种方式确定了这种观察到的规律性。在这里,我们表明小世界也会发生在高阶互动中。也就是说,通过考虑q -均匀超图和一个连接可以在给定概率p下随机重新连接的过程,我们发现这样的系统在广泛的p值范围内具有较小的平均路径长度时可能表现出突出的聚类性质,类似于二元相互作用的情况。在不同阶次Q(=2、3、4、5和6)的相互作用下,小世界转换的性质保持不变,但是,超边缘阶次的增加减少了小世界出现的重新布线概率的范围。
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引用次数: 0
Effects of active noise on transition-path dynamics 有源噪声对过渡路径动力学的影响
IF 2.7 Q1 MATHEMATICS, INTERDISCIPLINARY APPLICATIONS Pub Date : 2023-04-12 DOI: 10.1088/2632-072X/accc69
K. Goswami, R. Metzler
We propose an extension of the existing model describing a biomolecular reaction such as protein folding or ligand binding which is usually visualised as the barrier crossing of a diffusing particle in a double-well potential. In addition to the thermal noise, an active noise modelled in terms of an Ornstein–Uhlenbeck process is introduced to the dynamics. Within this framework, we investigate the transition-path properties of an underdamped particle surmounting an energy barrier, and we show explicitly how these properties are affected by the activity and persistence of the particle. Our theoretical study suggests that an active particle can cross the barrier at comparatively shorter timescales by lowering the (effective) barrier height. In particular, we study how the persistence time of the active force alters the transition-path time (TPT) at different friction limits. Interestingly, in one of our models we find a nonmonotonic behaviour of the TPT which is absent in the overdamped limit. The framework presented here can be useful in designing a reaction in a non-equilibrium environment, particularly inside a living biological cell in which active fluctuations keep the system out of equilibrium.
我们提出了现有模型的扩展,该模型描述了生物分子反应,如蛋白质折叠或配体结合,通常被视为双阱势中扩散粒子的屏障穿越。除了热噪声外,还引入了基于Ornstein-Uhlenbeck过程建模的主动噪声。在此框架内,我们研究了克服能量势垒的欠阻尼粒子的过渡路径特性,并明确地展示了这些特性如何受到粒子的活性和持久性的影响。我们的理论研究表明,通过降低(有效)势垒高度,活性粒子可以在相对较短的时间尺度内穿过势垒。特别地,我们研究了在不同摩擦极限下,主动力的持续时间如何改变过渡路径时间(TPT)。有趣的是,在我们的一个模型中,我们发现了在过阻尼极限中不存在的TPT的非单调行为。本文提出的框架可以用于设计非平衡环境中的反应,特别是在活性波动使系统处于不平衡状态的活生物细胞内。
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引用次数: 3
Sparse block-structured random matrices: universality 稀疏块结构随机矩阵:通用性
IF 2.7 Q1 MATHEMATICS, INTERDISCIPLINARY APPLICATIONS Pub Date : 2023-03-23 DOI: 10.1088/2632-072X/acc71a
G. M. Cicuta, M. Pernici
We study ensembles of sparse block-structured random matrices generated from the adjacency matrix of a Erdös–Renyi random graph with N vertices of average degree Z, inserting a real symmetric d × d random block at each non-vanishing entry. We consider several ensembles of random block matrices with rank r < d and with maximal rank, r = d. The spectral moments of the sparse block-structured random matrix are evaluated for N→∞ , d finite or infinite, and several probability distributions for the blocks (e.g. fixed trace, bounded trace and Gaussian). Because of the concentration of the probability measure in the d→∞ limit, the spectral moments are independent of the probability measure of the blocks (with mild assumptions of isotropy, smoothness and sub-Gaussian tails). The effective medium approximation is the limiting spectral density of the sparse block-structured random ensembles with finite rank. Analogous classes of universality hold for the Laplacian sparse block-structured ensemble. The same limiting distributions are obtained using random regular graphs instead of Erdös–Renyi graphs.
我们研究了由具有N个平均度为Z的顶点的Erdös–Renyi随机图的邻接矩阵生成的稀疏块结构随机矩阵的集合,插入了实对称d × d随机块。我们考虑秩为r的随机块矩阵的几个集合 < d和具有最大秩的r = d.对于N,评估稀疏块结构随机矩阵的谱矩→∞ , d有限或无限,以及块的几个概率分布(例如,固定轨迹、有界轨迹和高斯)。由于d中概率测度的集中→∞ 极限,谱矩与块的概率测度无关(具有各向同性、光滑性和亚高斯尾的温和假设)。有效介质近似是具有有限秩的稀疏块结构随机系综的极限谱密度。拉普拉斯稀疏块结构系综具有类似的普适性类。使用随机正则图代替Erdös–Renyi图获得了相同的极限分布。
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引用次数: 0
Online identity as a collective labeling process 网络身份作为一个集体标签的过程
IF 2.7 Q1 MATHEMATICS, INTERDISCIPLINARY APPLICATIONS Pub Date : 2023-03-21 DOI: 10.1088/2632-072X/acc62c
Alexander T. J. Barron, Marijn ten Thij, J. Bollen
Expressing identity socially involves a balance between conformity and innovation. One can adopt existing labels to express belonging to a certain community or introduce new labels to express an individual sense of identity. In such a process of co-creation, the existing identity labels of a community shape one’s sense of identity, while individual expression changes that of a community. Social media has introduced new opportunities to study the expression of collective identity. Here we study the group behavior of individuals defining their identities with hashtag self-labels in their Twitter profiles from mid-2017 through 2019. These timelines of personal self-labeling show behavior incorporating innovation, conservation, and social conformity when defining self. We show that the collective co-labeling of popular concepts in the context of identity, such as #resist and #maga, follow the dynamics of a modified Yule–Simon model balancing novelty and conformity. The dynamics of identity expression resemble the collective tagging processes of folksonomies, indicating a similarity between the collective tagging of external objects and the collective labeling of ourselves. Our work underpins a better understanding of how online environments mediate the evolution of collective identity which plays an increasingly important role in the establishment of community values and identity politics.
在社会上表达身份认同涉及从众和创新之间的平衡。人们可以采用现有的标签来表达对某个社区的归属,也可以引入新的标签来表示个人的认同感。在这样一个共同创造的过程中,一个社区现有的身份标签塑造了一个人的身份感,而个人的表达则改变了一个社区的身份感。社交媒体为研究集体身份的表达提供了新的机会。在这里,我们研究了2017年年中至2019年期间,在推特个人资料中使用标签自标签定义身份的个人的群体行为。这些个人自我标签的时间线显示了在定义自我时结合创新、保护和社会整合的行为。我们表明,在身份背景下,流行概念的集体共标记,如#resist和#maga,遵循了平衡新颖性和一致性的修正Yule–Simon模型的动力学。身份表达的动力学类似于民族学的集体标记过程,表明外部对象的集体标记和我们自己的集体标记之间的相似性。我们的工作为更好地理解网络环境如何介导集体身份的演变奠定了基础,集体身份在建立社区价值观和身份政治中发挥着越来越重要的作用。
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引用次数: 0
Information parity increases on functional brain networks under influence of a psychedelic substance 在迷幻物质的影响下,大脑功能网络的信息平价增加
IF 2.7 Q1 MATHEMATICS, INTERDISCIPLINARY APPLICATIONS Pub Date : 2023-03-07 DOI: 10.1088/2632-072X/acc22b
A. Viol, G. Viswanathan, Oleksandra Soldatkina, Fernanda Palhano-Fontes, H. Onias, D. D. de Araujo, Philipp Hoevel
The physical basis of consciousness is one of the most intriguing open questions that contemporary science aims to solve. By approaching the brain as an interactive information system, complex network theory has greatly contributed to understand brain process in different states of mind. We study a non-ordinary state of mind by comparing resting-state functional brain networks of individuals in two different conditions: before and after the ingestion of the psychedelic brew Ayahuasca. In order to quantify the functional, statistical symmetries between brain region connectivity, we calculate the pairwise information parity of the functional brain networks. Unlike the usual approach to quantitative network analysis that considers only local or global scales, information parity instead quantifies pairwise statistical similarities over the entire network structure. We find an increase in the average information parity on brain networks of individuals under psychedelic influences. Notably, the information parity between regions from the limbic system and frontal cortex is consistently higher for all the individuals while under the psychedelic influence. These findings suggest that the resemblance of statistical influences between pair of brain regions activities tends to increase under Ayahuasca effects. This could be interpreted as a mechanism to maintain the network functional resilience.
意识的物理基础是当代科学试图解决的最有趣的开放性问题之一。复杂网络理论将大脑视为一个相互作用的信息系统,对理解不同心理状态下的大脑过程有很大贡献。我们通过比较个体在两种不同条件下的静息状态功能大脑网络来研究一种不寻常的心理状态:摄入迷幻饮料死藤水之前和之后。为了量化脑区连接之间的功能、统计对称性,我们计算了脑功能网络的成对信息奇偶性。与通常只考虑局部或全局尺度的定量网络分析方法不同,信息奇偶性对整个网络结构的两两统计相似性进行量化。我们发现,在迷幻药影响下,个体大脑网络的平均信息平价有所增加。值得注意的是,在迷幻影响下,所有人的边缘系统和额叶皮层区域之间的信息均等度都一贯较高。这些发现表明,在死藤水的作用下,对大脑区域活动的统计影响的相似性倾向于增加。这可以解释为维持网络功能弹性的一种机制。
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引用次数: 1
Growing inequality in systems showing Zipf’s law 系统中不断增长的不平等体现了齐夫定律
IF 2.7 Q1 MATHEMATICS, INTERDISCIPLINARY APPLICATIONS Pub Date : 2023-03-02 DOI: 10.1088/2632-072X/acc0c1
Giordano De Marzo, F. Attili, L. Pietronero
A central problem in economics and statistics is the assessment of income or wealth inequality starting from empirical data. Here we focus on the behavior of Gini index, one of the most used inequality measures, in presence of Zipf’s law, a situation which occurs in many complex financial and economical systems. First, we show that the application of asymptotic formulas to finite size systems always leads to an overestimation of inequality. We thus compute finite size corrections and we show that depending on Zipf’s exponent two distinct regimes can be observed: low inequality, where Gini index is less than one and maximal inequality, where Gini index asymptotically tends to its maximal value one. In both cases, the inequality of an expanding system slowly increases just as effect of growth, with a scaling never faster than the inverse of the size. We test our computations on two real systems, US cities and the cryptocurrency market, observing in both cases an increase of inequality that is completely explained by Zipf’s law and the systems expanding. This shows that in growing complex systems finite size effects must be considered in order to properly assess if inequality is increasing due to natural growth processes or if it is produced by a change in the economical structure of the systems. Finally we discuss how such effects must be carefully considered when analyzing survey data.
经济学和统计学的一个核心问题是从实证数据开始评估收入或财富不平等。在这里,我们关注基尼指数的行为,基尼指数是最常用的不平等指标之一,在齐普夫定律的存在下,这种情况发生在许多复杂的金融和经济系统中。首先,我们证明了渐近公式在有限尺寸系统中的应用总是会导致对不等式的高估。因此,我们计算了有限大小的校正,并表明根据Zipf指数,可以观察到两种不同的状态:低不等式,其中Gini指数小于1,最大不等式,其中基尼指数渐近趋向于其最大值1。在这两种情况下,扩张系统的不平等性都会随着增长的影响而缓慢增加,其比例永远不会快于规模的倒数。我们在美国城市和加密货币市场这两个真实系统上测试了我们的计算,在这两种情况下都观察到不平等的增加,这完全可以用齐普夫定律和系统的扩张来解释。这表明,在不断增长的复杂系统中,必须考虑有限规模效应,以便正确评估不平等是由于自然增长过程而增加,还是由于系统经济结构的变化而产生。最后,我们讨论了在分析调查数据时必须如何仔细考虑这些影响。
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引用次数: 1
A scientific portrait of Giorgio Parisi: complex systems and much more 乔治·帕里西的科学肖像:复杂的系统和更多
IF 2.7 Q1 MATHEMATICS, INTERDISCIPLINARY APPLICATIONS Pub Date : 2023-03-01 DOI: 10.1088/2632-072X/acb8a1
L. Cugliandolo
This article summarises the outstanding scientific career of Giorgio Parisi, who was awarded the 2021 Nobel Prize in Physics, with special emphasis on his contributions to the description of the equilibrium properties of disordered systems.
本文总结了获得2021年诺贝尔物理学奖的乔治·帕里西杰出的科学生涯,特别强调了他对描述无序系统平衡性质的贡献。
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引用次数: 3
Exploring 3D community inconsistency in human chromosome contact networks 探索人类染色体接触网络中的三维群落不一致性
IF 2.7 Q1 MATHEMATICS, INTERDISCIPLINARY APPLICATIONS Pub Date : 2023-02-28 DOI: 10.1088/2632-072X/acef9d
Dolores Bernenko, Sang Hoon Lee, L. Lizana
Researchers have developed chromosome capture methods such as Hi-C to better understand DNA’s 3D folding in nuclei. The Hi-C method captures contact frequencies between DNA segment pairs across the genome. When analyzing Hi-C data sets, it is common to group these pairs using standard bioinformatics methods (e.g. PCA). Other approaches handle Hi-C data as weighted networks, where connected node pairs represent DNA segments in 3D proximity. In this representation, one can leverage community detection techniques developed in complex network theory to group nodes into mesoscale communities containing nodes with similar connection patterns. While there are several successful attempts to analyze Hi-C data in this way, it is common to report and study the most typical community structure. But in reality, there are often several valid candidates. Therefore, depending on algorithm design, different community detection methods focusing on slightly different connectivity features may have differing views on the ideal node groupings. In fact, even the same community detection method may yield different results if using a stochastic algorithm. This ambiguity is fundamental to community detection and shared by most complex networks whenever interactions span all scales in the network. This is known as community inconsistency. This paper explores this inconsistency of 3D communities in Hi-C data for all human chromosomes. We base our analysis on two inconsistency metrics, one local and one global, and quantify the network scales where the community separation is most variable. For example, we find that TADs are less reliable than A/B compartments and that nodes with highly variable node-community memberships are associated with open chromatin. Overall, our study provides a helpful framework for data-driven researchers and increases awareness of some inherent challenges when clustering Hi-C data into 3D communities.
研究人员开发了Hi-C等染色体捕获方法,以更好地了解DNA在细胞核中的3D折叠。Hi-C方法捕获整个基因组中DNA片段对之间的接触频率。在分析Hi-C数据集时,通常使用标准生物信息学方法(如PCA)对这些对进行分组。其他方法将Hi-C数据处理为加权网络,其中连接的节点对表示3D邻近的DNA片段。在这种表示中,可以利用复杂网络理论中开发的社区检测技术,将节点分组为包含具有相似连接模式的节点的中尺度社区。虽然有几种成功的尝试以这种方式分析Hi-C数据,但报告和研究最典型的社区结构是很常见的。但在现实中,通常有几个有效的候选人。因此,根据算法设计,专注于略微不同的连接特征的不同社区检测方法可能对理想节点分组有不同的看法。事实上,如果使用随机算法,即使是相同的社区检测方法也可能产生不同的结果。这种模糊性是社区检测的基础,每当交互跨越网络中的所有规模时,大多数复杂网络都会共享这种模糊性。这就是所谓的社区不一致。本文探讨了所有人类染色体的Hi-C数据中3D群落的这种不一致性。我们的分析基于两个不一致性指标,一个是局部指标,另一个是全局指标,并量化社区分离变化最大的网络规模。例如,我们发现TAD不如A/B区室可靠,并且具有高度可变节点群落成员资格的节点与开放染色质相关。总的来说,我们的研究为数据驱动的研究人员提供了一个有用的框架,并提高了人们对将Hi-C数据聚类到3D社区时的一些固有挑战的认识。
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引用次数: 0
Production process networks: a trophic analysis 生产过程网络:营养分析
IF 2.7 Q1 MATHEMATICS, INTERDISCIPLINARY APPLICATIONS Pub Date : 2023-02-20 DOI: 10.1088/2632-072X/acbd7c
Aurélien Hazan
In this article, production process databases originating from environmental sciences, more specifically from life cycle inventory (LCI), are considered as bipartite directed random networks. To model the observed directed hierarchical connection patterns, we turn to recent development concerning trophic coherence. Extending the scope to include bipartite networks, we compare several LCI networks to networks from other fields, and show empirically that they have high coherence and belong to the loopless regime, or close to its boundary.
在本文中,源自环境科学的生产过程数据库,更具体地说,源自生命周期清单(LCI),被认为是二部分有向随机网络。为了对观察到的定向层次连接模式进行建模,我们转向最近关于营养一致性的发展。将范围扩展到包括二部分网络,我们将几种LCI网络与其他领域的网络进行了比较,并从经验上表明它们具有高度一致性,属于无环状态,或接近其边界。
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引用次数: 0
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Journal of Physics Complexity
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