Mathematical Programming Models for Influence Maximization on Social Networks

In this dissertation, we apply mathematical programming techniques (i.e., integer programming and polyhedral combinatorics) to develop exact approaches for influence maximization on social networks. We study four combinatorial optimization problems that deal with maximizing influence at minimum cost over a social network. To our knowl- edge, all previous work to date involving influence maximization problems has focused on heuristics and approximation. We start with the following viral marketing problem that has attracted a significant amount of interest from the computer science literature. Given a social network, find a target set of customers to seed with a product. Then, a cascade will be caused by these initial adopters and other people start to adopt this product due to the influence they re- ceive from earlier adopters. The idea is to find the minimum cost that results in the entire network adopting the product. We first study a problem called the Weighted Target Set Selection (WTSS) Prob- lem. In the WTSS problem, the diffusion can take place over as many time periods as needed and a free product is given out to the individuals in the target set. Restricting the number of time periods that the diffusion takes place over to be one, we obtain a problem called the Positive Influence Dominating Set (PIDS) problem. Next, incorporating partial incentives, we consider a problem called the Least Cost Influence Problem (LCIP). The fourth problem studied is the One Time Period Least Cost Influence Problem (1TPLCIP) which is identical to the LCIP except that we restrict the number of time periods that the diffusion takes place over to be one. We apply a common research paradigm to each of these four problems. First, we work on special graphs: trees and cycles. Based on the insights we obtain from special graphs, we develop efficient methods for general graphs. On trees, first, we propose a polynomial time algorithm. More importantly, we present a tight and compact extended formulation. We also project the extended formulation onto the space of the natural vari- ables that gives the polytope on trees. Next, building upon the result for trees---we derive the polytope on cycles for the WTSS problem; as well as a polynomial time algorithm on cycles. This leads to our contribution on general graphs. For the WTSS problem and the LCIP, using the observation that the influence propagation network must be a directed acyclic graph (DAG), the strong formulation for trees can be embedded into a formulation on general graphs. We use this to design and implement a branch-and-cut approach for the WTSS problem and the LCIP. In our computational study, we are able to obtain high quality solutions for random graph instances with up to 10,000 nodes and 20,000 edges (40,000 arcs) within a reasonable amount of time.

Determinants of engagement in virtual social networks in Singapore

The use of virtual social networks (VSNs) has been prevalent among consumers worldwide. Numerous studies have investigated various aspects of VSNs. However, these studies have mainly focused on students and young adults as they were early adopters of these innovative networks. A search of the literature revealed there has been a paucity of research on adult consumers’ use of VSNs. This research study addressed this gap in the literature by examining the determinants of engagement in VSNs among adult consumers in Singapore. The objectives of this study are to empirically investigate the determinants of engagement in VSNs and to offer theoretical insights into consumers’ preference and usage of VSNs. This study tapped upon several theories developed in the discipline of technology and innovation adoption. These were Roger’s Diffusion of Innovation, Theory of Reasoned Action (TRA), Theory of Planned Behavior (TPB), Technology Acceptance Model (TAM), Conceptual Framework of Individual Innovation Adoption by Frambach and Schillewaert (2002), Enhanced Model of Innovation Adoption by Talukder (2011), Extended Unified Theory of Acceptance and Use of Technology (UTAUT2) and the Information Systems (IS) Success Model. The proposed research model, named the Media Usage Model (MUM), is a framework rooted in innovation diffusion and IS theories. The MUM distilled the essence of these established models and thus provides an updated, lucid explanation of engagement in VSNs. A cross-sectional, online social survey was conducted to collect quantitative data to examine the validity of the proposed research model. Multivariate data analysis was carried out on a data set comprising 806 usable responses by utilizing SPSS, and for structural equation modeling AMOS and SmartPLS. The results indicate that consumer attitude towards VSNs is significantly and positively influenced by: three individual factors – hedonic motivation, incentives and experience; two system characteristics – system quality and information quality; and one social factor – social bonding. Consumer demographics were found to influence people’s attitudes towards VSNs. In addition, consumer experience and attitude towards VSNs significantly and positively influence their usage of VSNs. The empirical data supported the proposed research model, explaining 80% of variance in attitude towards VSNs and 45% of variance in usage of VSNs. Therefore, the MUM achieves a definite contribution to theoretical knowledge of consumer engagement in VSNs by deepening and broadening our appreciation of the intricacies related to use of VSNs in Singapore. This study’s findings have implications for customer service management, services marketing and consumer behavior. These findings also have strategic implications for maximizing efficient utilization and effective management of VSNs by businesses and operators. The contributions of this research are: firstly, shifting the boundaries of technology or innovation adoption theories from research on employees to consumers as well as the boundaries of Internet usage or adoption research from students to adults, which is also known as empirical generalization; secondly, highlighting the issues associated with lack of significance of social factors in adoption research; and thirdly, augmenting information systems research by integrating important antecedents for success in information systems.

Team performance according to ball possession characteristics : a social networks approach

Over the last few years, football entered in a period of accelerated access to large amount of match analysis data. Social networks have been adopted to reveal the structure and organization of the web of interactions, such as the players passing distribution tendencies. In this study we investigated the influence of ball possession characteristics in the competitive success of Spanish La Liga teams. The sample was composed by OPTA passing distribution raw data (n=269,055 passes) obtained from 380 matches involving all the 20 teams of the 2012/2013 season. Then, we generated 760 adjacency matrixes and their corresponding social networks using Node XL software. For each network we calculated three team performance measures to evaluate ball possession tendencies: graph density, average clustering and passing intensity. Three levels of competitive success were determined using two-step cluster analysis based on two input variables: the total points scored by each team and the scored per conceded goals ratio. Our analyses revealed significant differences between competitive performances on all the three team performance measures (p < .001). Bottom-ranked teams had less number of connected players (graph density) and triangulations (average clustering) than intermediate and top-ranked teams. However, all the three clusters diverged in terms of passing intensity, with top-ranked teams having higher number of passes per possession time, than intermediate and bottom-ranked teams. Finally, similarities and dissimilarities in team signatures of play between the 20 teams were displayed using Cohen’s effect size. In sum, findings suggest the competitive performance was influenced by the density and connectivity of the teams, mainly due to the way teams use their possession time to give intensity to their game.

Funzioni di Matrici. Proprieta' e applicazione ai social networks

Teoria delle funzioni di matrici. Spiegazione del concetto di network, proprietà rilevanti rilevate attraverso determinate funzioni di matrici. Applicazione della teoria a due esempi di network reali.

Social networks in Argentinian libraries : Tips to formulate a communicational policy

En base a los resultados obtenidos en investigaciones efectuadas por el grupo de investigación del Instituto de Investigaciones en Humanidades y Ciencias Sociales (UNLP-CONICET) sobre redes sociales en distintos tipos de bibliotecas (de investigación, universitarias y populares) en Argentina, se efectúa un balance sobre su uso en este tipo de instituciones y se proponen lineamientos para la formulación de una política comunicacional que las contemple y forme parte del plan de gestión de estas unidades de información. Los mismos apuntan a considerar cabalmente todos los aspectos vinculados a los alcances, limitaciones, usos, riesgos y demás que implica la adopción y la apropiación de diferentes redes sociales (tales como Facebook, Twitter, entre otras), su convivencia, gestión y sustentabilidad a lo largo del tiempo

Essays on social networks, altruism and information diffusion

This dissertation consists of three standalone articles that contribute to the economics literature concerning technology adoption, information diffusion, and network economics in one way or another, using a couple of primary data sources from Ethiopia. The first empirical paper identifies the main behavioral factors affecting the adoption of brand new (radical) and upgraded (incremental) bioenergy innovations in Ethiopia. The results highlight the importance of targeting different instruments to increase the adoption rate of the two types of innovations. The second and the third empirical papers of this thesis, use primary data collected from 3,693 high school students in Ethiopia, and shed light on how we should select informants to effectively and equitably disseminate new information, mainly concerning environmental issues. There are different well-recognized standard centrality measures that are used to select informants. These standard centrality measures, however, are based on the network topology---shaped only by the number of connections---and fail to incorporate the intrinsic motivations of the informants. This thesis introduces an augmented centrality measure (ACM) by modifying the eigenvector centrality measure through weighting the adjacency matrix with the altruism levels of connected nodes. The results from the two papers suggest that targeting informants based on network position and behavioral attributes ensures more effective and equitable (gender perspective) transmission of information in social networks than selecting informants on network centrality measures alone. Notably, when the information is concerned with environmental issues.

Yrittäjän sosiaalisten verkostojen muodostuminen, niihin vaikuttavat tekijät, niiden rakenne ja merkitys yrittäjälle

Tämän tutkimuksen tavoitteena oli selvittää kuinka yrittäjän verkostot muodostuvat ja minkälainen niiden rakenne on. Tavoitteena oli myös saada tietoa yrittäjän sosiaalisten verkostojen merkityksestä yrittäjälle. Tutkimus toteutettiin laadullisena tutkimuksena. Tutkimusaineisto kerättiin strukturoidulla haastattelulla ja tutkimusaineiston rinnalla käytettiin yrittäjien havainnollistamia piirroksia sekä tieteellisiä julkaisuja ja kirjallisuutta. Haastateltavina oli sekä nais- että miesyrittäjiä eri paikkakunnilta Etelä-Suomen alueelta. Tutkimustulosten mukaan yrittäjien verkostoissa voidaan havaita eri tasoja, jotka rakentuvat eri tavoilla ja ovat yrittäjälle merkitykseltään erilaisia. Verkoston eri tasoille sijoittuu yrittäjälle tärkeitä ihmisiä sen mukaan mitä hyötyä ja arvoa heillä yrittäjälle on. Tulokset osoittavat, että verkostojen rakentamiseen vaikuttavat sekä liiketoiminnan laatu, motiivit sekä yrittäjän persoona. Tulokset ovat linjassa tämän tutkimuksen perustana olevien teorioiden kanssa. Viitteitä löytyy myös siitä, että yrittäjän sukupuolella on myös merkitystä siihen, millaiseksi sosiaaliset verkostot rakentuvat sekä henkilökohtaisessa elämässä että liike-elämän puolella. Sosiaalisista verkostoista saatavat hyödyt ovat moninaisia. Lisätutkimuksia tulisi tehdä tehokkaiden työkalujen kehittämiseksi henkilöstön ja yrittäjän omien resurssien tunnistamiseksi. Tätä kautta myös yrittäjyyskasvatusta ja yrittäjäneuvontaa voitaisiin tehostaa.

Learning networks and moodle use in online courses: a social network analysis study

Dissertação para obtenção do Grau de Doutor em Ciências da Educação Especialidade em Tecnologias, Redes e Multimédia na Educação e Formação

The double-edged sword of social capital: Three essays on entrepreneurship in developing nations

ABSTRACT My study seeks to answer the main question: "how does entrepreneurs' social capital positively and negatively affect their resource mobilization efforts, and exploitation of entrepreneurial opportunity?" To answer this question, I develop a model for examining positive and negative effects of social capital on resource accumulation by entrepreneurs, and the subsequent effect of resource accumulation on the exploitation of entrepreneurial opportunity, and utilize data from Africa to ëmpirically test the relationships in this model. Developing nations are a suitable context because: a) They require entrepreneurship for economic development, b) They have received less attention in management and entrepreneurship research, c) Because of inadequately-developed institutions, entrepreneurs from developing nations face major resource mobilization challenges hence they often turn to their social ties for resources, and d) The communalistic and collectivistic nature of most developing nations -encouraging support and sharing of resources- may help us better understand how society's values and structures may contribute and also deduct firm resources. My study reveals that social capital contributes resources to entrepreneurs in developing nations at a cost that takes away resources, and that more resources but lower costs facilitate entrepreneurial opportunity exploitation. For entrepreneurs in developing nations, large networks, greater shared identity, and more trust are beneficial. To increase chances of raising more resources, entrepreneurs from communalistic societies should include network members from outside their communities. Besides providing financial support, policy-makers should develop training programs and advisory services on configuration of entrepreneurs' networks so as to achieve more resources at a low cost. My study insights can help improve entrepreneurs' resource accumulation efforts and the subsequent growth of their firms, leading to the overall economic growth of developing nations.

Networks 3: Social Structures

A brief look at the post-industrial, network society, freed from manual labour and liberated from place.

Solidaridad étnica y capital social: el caso de los comerciantes migrantes kichwa-Otavalo en Madrid y La Compañía (Estudios)

En el análisis sobre migrantes, en general, y sobre migrantes descritos como grupos étnicos, en concreto, se tiende a presuponer un tipo de “solidaridad étnica” dentro de sus redes sociales. Esta suposición da por sentado que todos los que se definen como “indígenas” disponen y disfrutan de un capital social basado en la solidaridad. En este artículo se toma el caso de comerciantes migrantes kichwa-otavalo tanto para indagar la suposición de que la etnicidad es la fuente del capital social colectivo y, por tanto, de la solidaridad, como para cuestionar si esta actúa implícita en las cadenas y redes de migrantes, las cuales suelen ser equiparadas a su capital social.

Explorando potencialidades para a criação de rede de apoio social a mulheres lusófonas que vivem com câncer de mama em Toronto, Canadá

Introduction: Health indicators tend to be altered due to the participation of people in social networks. Objective: To find out ideas of individuals belonging to Portuguese speaking communities in Toronto, Canada, about the possibility of creating a social support network for women experiencing breast cancer. Method: Nineteen participants of the present ethnographic and critical study answered to questions, providing their opinions regarding to the social support network and its positive and negative aspects. Also, the participants suggested other possible individuals who could participate and help in the creation of such network. Discussions were transcribed, analysed and coded using qualitative software called Atlas ti 6.0. Results: The main components for the creation of the social support network were: the demystification of breast cancer and its prevention, emphasis in health education, dissemination of the need of volunteers and a direct social support to those women. The positive aspects were the participation of oldest women as social leaders and the utilization of schools and religious institutions for publicity. Negative aspects that were perceived as barriers are: the belief that breast cancer is a disease lived by women, the lack of knowledge about its cure and rehabilitation, as well as a collective sensitiveness to it. Also, about the participation of community leaders, the suggestions were: diplomats, priests and pastors, schools directors and communication entrepreneurs. Conclusion: The creation of the social support network should consider the cultural sensitiveness and the inner diversity of the consulted Portuguese speaking communities. Due to the insufficient number of Angolan participants to sustain a major analysis, a special recommendation was that Angolan social leaders and professionals should be invited to design the structure of such network according to their specific cultural traits.

Social Support Networks and Self-Efficacy of Peruvian Women Diagnosed with Cancer: A Biocultural Analysis of Health Behavior Constructs

Thesis (Ph.D.)--University of Washington, 2016-06

Indirect ties in knowledge networks:a social network analysis with ordered weighted averaging operators

This PhD thesis analyses networks of knowledge flows, focusing on the role of indirect ties in the knowledge transfer, knowledge accumulation and knowledge creation process. It extends and improves existing methods for mapping networks of knowledge flows in two different applications and contributes to two stream of research. To support the underlying idea of this thesis, which is finding an alternative method to rank indirect network ties to shed a new light on the dynamics of knowledge transfer, we apply Ordered Weighted Averaging (OWA) to two different network contexts. Knowledge flows in patent citation networks and a company supply chain network are analysed using Social Network Analysis (SNA) and the OWA operator. The OWA is used here for the first time (i) to rank indirect citations in patent networks, providing new insight into their role in transferring knowledge among network nodes; and to analyse a long chain of patent generations along 13 years; (ii) to rank indirect relations in a company supply chain network, to shed light on the role of indirectly connected individuals involved in the knowledge transfer and creation processes and to contribute to the literature on knowledge management in a supply chain. In doing so, indirect ties are measured and their role as means of knowledge transfer is shown. Thus, this thesis represents a first attempt to bridge the OWA and SNA fields and to show that the two methods can be used together to enrich the understanding of the role of indirectly connected nodes in a network. More specifically, the OWA scores enrich our understanding of knowledge evolution over time within complex networks. Future research can show the usefulness of OWA operator in different complex networks, such as the on-line social networks that consists of thousand of nodes.

Joint Optimization for Social Content Delivery in Wireless Networks

Over the last decade, success of social networks has significantly reshaped how people consume information. Recommendation of contents based on user profiles is well-received. However, as users become dominantly mobile, little is done to consider the impacts of the wireless environment, especially the capacity constraints and changing channel. In this dissertation, we investigate a centralized wireless content delivery system, aiming to optimize overall user experience given the capacity constraints of the wireless networks, by deciding what contents to deliver, when and how. We propose a scheduling framework that incorporates content-based reward and deliverability. Our approach utilizes the broadcast nature of wireless communication and social nature of content, by multicasting and precaching. Results indicate this novel joint optimization approach outperforms existing layered systems that separate recommendation and delivery, especially when the wireless network is operating at maximum capacity. Utilizing limited number of transmission modes, we significantly reduce the complexity of the optimization. We also introduce the design of a hybrid system to handle transmissions for both system recommended contents ('push') and active user requests ('pull'). Further, we extend the joint optimization framework to the wireless infrastructure with multiple base stations. The problem becomes much harder in that there are many more system configurations, including but not limited to power allocation and how resources are shared among the base stations ('out-of-band' in which base stations transmit with dedicated spectrum resources, thus no interference; and 'in-band' in which they share the spectrum and need to mitigate interference). We propose a scalable two-phase scheduling framework: 1) each base station obtains delivery decisions and resource allocation individually; 2) the system consolidates the decisions and allocations, reducing redundant transmissions. Additionally, if the social network applications could provide the predictions of how the social contents disseminate, the wireless networks could schedule the transmissions accordingly and significantly improve the dissemination performance by reducing the delivery delay. We propose a novel method utilizing: 1) hybrid systems to handle active disseminating requests; and 2) predictions of dissemination dynamics from the social network applications. This method could mitigate the performance degradation for content dissemination due to wireless delivery delay. Results indicate that our proposed system design is both efficient and easy to implement.