Analysis of online social network traffic can identify a cascade as it flows through a community but, often, the reasons for its initiation are tacit. Commercial measures of online influence focus on the consequences of influence not the causes and have been criticized as lacking efficacy. This research uses social capital and personal influence theories to investigate the characteristics and behaviours that allow certain network nodes to be able to cascade ideas (or memes) through networks. The relationships between structural, relational and cognitive sources of social capital and two distinct dimensions of influence are investigated using: interviews with experts in the field, focus groups of social network users and 1,970 respondents from three large-scale online communities. Data has been analysed using Structural Equation Modelling (SEM) and allows the researcher to develop robust conclusions on the antecedents to influence. These help to explain recent contradictory findings by different researchers in studies using Social Network Analysis (SNA). The dimensions of influence measured are: respondents’ intention to propagate the message and; the extent to which the message has affected their perception of the subject. The model of influence that leads to both dimensions is strikingly similar; presenting strong support for the notion that contagion-based cascades through networks are predictors of perception change. The paper proposes a bridge between the theories of social capital and personal influence and this is considered an original contribution to these well-established theories. Techniques are suggested which can help organisations to identify opinion-leaders and, if required, subvert or redirect the nature of their influence. Other applications are considered in the fields of: Innovation (identification of lead users); Virtual Organisations (engaging with informal leaders and influencers in networks); Cyber- Defence (identification and subversion of online radicalisation).

e-Research in the Life Sciences examines the use of online tools in the life sciences and finds that their use has significant impact, namely the formation of a Scientific/Intellectual Movement (SIM) (Frickel & Gross, 2005) complemented by a Computerisation Movement (CM) (Kling & Iacono, 1994) which is mobilising global electronic resources to form visible colleges of life science researchers, who are enrolling others and successfully promoting their open science goals via mainstream scientific literature. Those within this movement are also using these online tools to change their work practices, producing scientific knowledge in a highly networked and distributed group which has less regard for traditional institutional and disciplinary boundaries. This thesis, by combining ideas about SIMs and CMs, fills a gap in research that is typically confined to treating new tools as a part of scientific communication or in specialist areas like distributed collaboration but not in terms of broader changes in science. Case studies have been conducted for three types of online tools: the scientific social networking tool FriendFeed, open laboratory notebooks, and science blogs. Data have been collected from semi-structured interviews, and the online writings of research participants. The case studies of exemplary use by scientists of the web form a baseline for future studies in the area. Boundaries between formal and informal scholarly communication are now blurred. At the formal level, which peer-reviewed print journals continue, many academic publishers now also have online open access, frequently in advance of print publication. At the informal level, what used to be confined to water-cooler chat and the conference circuit is now also discussed on mailing lists, forums and blogs (Borgman, 2007). As these online tools generate new practices they have potential to affect future academic assessment and dissemination practices.