成长群体中的相变：凝聚力如何持续
Phase transitions in growing groups: How cohesion can persist
摘要：
一个社会群体的凝聚力是该群体保持团结的倾向。它对社会组织的稳定和生存具有重要意义，如政党，研究团队或在线团体。实证研究表明，群体凝聚力受新成员加入过程和群体规模的影响。然而，对它们之间的相互作用仍然缺乏理论上的理解。为此，我们提出了一个模型，其中一组增长的嘈杂的新成员谁可以是两种不同类型的录取过程。在这个框架中，凝聚力被定义为相同类型的成员的分数，而接纳过程中的噪声代表了新候选人评估的随机性水平。该模型可以再现经验报告的减少凝聚力与组的大小。当接纳新的候选人只涉及一个群体成员的决定时，群体的增长会导致凝聚力的丧失，即使是在极小的噪声水平下。然而，当接纳需要几个群体成员的共识时，存在一个临界噪声水平，低于该临界噪声水平，不断增长的群体保持凝聚力。内聚相和非内聚相之间的过渡的性质取决于模型参数，并形成一个丰富的结构，让人想起铁磁材料中的临界现象。
英文摘要：
The cohesion of a social group is the group's tendency to remain united. It has important implications for the stability and survival of social organizations, such as political parties, research teams, or online groups. Empirical studies suggest that cohesion is affected by both the admission process of new members and the group size. Yet, a theoretical understanding of their interplay is still lacking. To this end, we propose a model where a group grows by a noisy admission process of new members who can be of two different types. Cohesion is defined in this framework as the fraction of members of the same type and the noise in the admission process represents the level of randomness in the evaluation of new candidates. The model can reproduce the empirically reported decrease of cohesion with the group size. When the admission of new candidates involves the decision of only one group member, the group growth causes a loss of cohesion even for infinitesimal levels of noise. However, when admissions require a consensus of several group members, there is a critical noise level below which the growing group remains cohesive. The nature of the transition between the cohesive and non-cohesive phases depends on the model parameters and forms a rich structure reminiscent of critical phenomena in ferromagnetic materials.
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