抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

We will review some of the major results in random graphs and some of the more challenging open problems. We will cover algorithmic and structural questions. We will touch on newer models, including those related to the WWW.

Random graphs

Models for the processes by which ideas and influence propagate through a social network have been studied in a number of domains, including the diffusion of medical and technological innovations, the sudden and widespread adoption of various strategies in game-theoretic settings, and the effects of "word of mouth" in the promotion of new products. Recently, motivated by the design of viral marketing strategies, Domingos and Richardson posed a fundamental algorithmic problem for such social network processes: if we can try to convince a subset of individuals to adopt a new product or innovation, and the goal is to trigger a large cascade of further adoptions, which set of individuals should we target?We consider this problem in several of the most widely studied models in social network analysis. The optimization problem of selecting the most influential nodes is NP-hard here, and we provide the first provable approximation guarantees for efficient algorithms. Using an analysis framework based on submodular functions, we show that a natural greedy strategy obtains a solution that is provably within 63% of optimal for several classes of models; our framework suggests a general approach for reasoning about the performance guarantees of algorithms for these types of influence problems in social networks.We also provide computational experiments on large collaboration networks, showing that in addition to their provable guarantees, our approximation algorithms significantly out-perform node-selection heuristics based on the well-studied notions of degree centrality and distance centrality from the field of social networks.

/pdf/maximizing-the-spread-of-influence-through-a-social-network-3nnj0jic76.pdf

Maximizing the spread of influence through a social network

Prior research has provided valuable insights into how and why employees make a decision about the adoption and use of information technologies (ITs) in the workplace. From an organizational point of view, however, the more important issue is how managers make informed decisions about interventions that can lead to greater acceptance and effective utilization of IT. There is limited research in the IT implementation literature that deals with the role of interventions to aid such managerial decision making. Particularly, there is a need to understand how various interventions can influence the known determinants of IT adoption and use. To address this gap in the literature, we draw from the vast body of research on the technology acceptance model (TAM), particularly the work on the determinants of perceived usefulness and perceived ease of use, and: (i) develop a comprehensive nomological network (integrated model) of the determinants of individual level (IT) adoption and use; (ii) empirically test the proposed integrated model; and (iii) present a research agenda focused on potential pre- and postimplementation interventions that can enhance employees' adoption and use of IT. Our findings and research agenda have important implications for managerial decision making on IT implementation in organizations.

/pdf/technology-acceptance-model-3-and-a-research-agenda-on-3xnjvztlvt.pdf

Technology Acceptance Model 3 and a Research Agenda on Interventions

The Structural Transformation of the Public Sphere: An Inquiry into a Category of Bourgeois Society

Video-sharing social media like YouTube provide access to diverse cultural products from all over the world, making it possible to test theories that the Web facilitates global cultural convergence. Drawing on a daily listing of YouTube's most popular videos across 58 countries, we investigate the consumption of popular videos in countries that differ in cultural values, language, gross domestic product, and Internet penetration rate. Although online social media facilitate global access to cultural products, we find this technological capability does not result in universal cultural convergence. Instead, consumption of popular videos in culturally different countries appears to be constrained by cultural values. Cross-cultural convergence is more advanced in cosmopolitan countries with cultural values that favor individualism and power inequality.

/pdf/cultural-values-and-cross-cultural-video-consumption-on-30p3r41tcr.pdf

Cultural values and cross-cultural video consumption on YouTube.

Following Axelrod's model of cultural dissemination, formal computational studies of cultural influence have suggested that more contact between geographically distant regions may increase overall cultural homogeneity and reduce societal polarization. In the present paper, we show that two plausible modifications of Axelrod's original mechanism turn the effect of range of communication upside-down. We assume a continuous rather than a nominal state space and we add the negative side of social influence, heterophobia and rejection. Computational analyses of the resulting model demonstrate that now a larger range of contact can increase rather than decrease the extent of polarization in the population. Further experiments identify the window of conditions under which the effect obtains.

Why more contact may increase cultural polarization

Statistical Mechanics and Social Sciences I

Noise is widely regarded as a residual category—the unexplained variance in a linear model or the random disturbance of a predictable pattern. Accordingly, formal models often impose the simplifying assumption that the world is noise-free and social dynamics are deterministic. Where noise is assigned causal importance, it is often assumed to be a source of inefficiency, unpredictability, or heterogeneity. We review recent sociological studies that are noteworthy for demonstrating the theoretical importance of noise for understanding the dynamics of a complex system. Contrary to widely held assumptions, these studies identify conditions in which noise can increase efficiency and predictability and reduce diversity. We conclude with a methodological warning that deterministic assumptions are not an innocent simplification.

/pdf/the-signal-importance-of-noise-3i6liy55u5.pdf

The signal importance of noise

Survey research reveals deep partisan divisions in the U.S. that extend beyond politics to include cultural tastes, lifestyle choices, and consumer preferences. We show how co-following on Twitter can be used to measure the extent to which these divisions are also evident in social media. We measure political alignment (location on the red-blue spectrum), relevance (overlap between cultural and political interests), and polarization (internal division) in music, movies, hobbies, sports, vehicles, food and drink, technology, universities, religions, and business. The results provide compelling evidence that "Tesla liberals"{ and "bird hunting conservatives" are stereotypes grounded in empirical reality.

Michael W. Macy

Papers

Cultural values and cross-cultural video consumption on YouTube.

Why more contact may increase cultural polarization

Statistical Mechanics and Social Sciences I

The signal importance of noise

Cultural Fault Lines and Political Polarization