The article discusses the hitherto unknown correspondence between Danzig (present-day Gdańsk) botanist Jacob Breyne, his son Johann Philipp and James Petiver in last decade of seventeenth century. Their documents contacts one most important naturalists Polish-Lithuanian Commonwealth second half century members Royal Society. content letters reveals how books, naturalia various artefacts circula...

Cooperative relationships, which involve the exchange of altruistic behaviors that are costly to the actor and beneficial to the recipient, are thought to be the product of kin selection or reciprocal altruism. Humans form close, enduring, cooperative relationships with nonrelatives. In these relationships, which we call friendships, both emotional and material support are exchanged. If these r...

BACKGROUND Early adolescent alcohol use is a major public health challenge. Without clear guidance on the causal pathways between peers and alcohol use, adolescent alcohol interventions may be incomplete. The objective of this study is to disentangle selection and influence effects associated with the dynamic interplay of adolescent friendships and alcohol use. METHODS The study analyzes data...

Given a graph F , a graph G is uniquely F -saturated if F is not a subgraph of G and adding any edge of the complement to G completes exactly one copy of F . In this paper we study uniquely Ct-saturated graphs. We prove the following: (1) a graph is uniquely C5-saturated if and only if it is a friendship graph. (2) There are no uniquely C6-saturated graphs or uniquely C7-saturated graphs. (3) F...

The friendship paradox is a sociological phenomenon stating that most people have fewer friends than their friends do. The generalized friendship paradox refers to the same observation for attributes other than degree, and it has been observed in Twitter and scientific collaboration networks. This paper takes an analytical approach to model this phenomenon. We consider a preferential attachment...

Children living in households affected by HIV face numerous challenges as they take on significant household-sustaining and caregiving roles, often in conditions of poverty. To respond to their hardships, we must identify and understand the support systems they are already part of. For this reason, and to emphasise the agentic capabilities of children, this article explores how vulnerable child...

objective: one of the main cultural issues in universities is relationships between male and female students. due to the adverse consequences of this issue, explaining of the beyond the causes of friendship with opposite-sex, is one of the first steps in planning for youth issues. methods: this qualitative research was conducted based on content analysis. nineteen female university students wer...

The friendship paradox is revisited by considering both local and global averages of friends. How the economics of attention affects the recruitment of friends is examined. Statistical implications of varying individual attentions are investigated and it is argued that this is one reason why the mean of friends is higher than the median in social networks. The distribution of friends skews to t...