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

"Culture wars" involve the puzzling alignment of partisan identity with disparate policy positions, lifestyle choices, and personal morality. Explanations point to ideological divisions, core values, moral emotions, and cognitive hardwiring. Two "multiple worlds" experiments (n = 4581) tested an alternative explanation based on the sensitivity of opinion cascades to the initial conditions. Consistent with recent studies, partisan divisions in the influence condition were much larger than in the control group (without influence). The surprise is that bigger divisions indicate less predictability. Emergent positions adopted by Republicans and opposed by Democrats in one experimental "world" had the opposite outcome in other parallel worlds. The unpredictability suggests that what appear to be deep-rooted partisan divisions in our own world may have arisen through a tipping process that might just as easily have tipped the other way. Public awareness of this counter-intuitive possibility has the potential to encourage greater tolerance for opposing opinions.

Opinion cascades and the unpredictability of partisan polarization

desired partner. This suggests that an exit option increases cooperation. We tested both hypotheses in laboratory experiments with human subjects, using "Trump," a new cardgame representation of a Prisoner's Dilemma. In the first experiment, the exit option reduced dependence and increased selectivity, relative to a no-exit condition. We found that selectivity and dependence both increased cooperation, but for different reasons and with different players, leaving overall cooperation rates unchanged by an option to exit. In a second experiment, the exit option increased selectivity but not dependence, relative to a forced-exit condition. Here we observed higher cooperation with an option to exit, but only for subjects playing defensive strategies.

Unlocking the doors of the Prisoner's dilemma : Dependence, selectivity, and cooperation

This paper integrates research in network exchange and collective action. Network exchange research typically assumes that structurally disadvantaged actors cannot collude. Meanwhile, collective action research shows that cooperation can be undermined by the temptation to free-ride on others' efforts. In this paper we extend the scope of network exchange theory by allowing low-power actors to form coalitions. We also extend game-theoretic research by embedding collective action in a network of social relations and power processes. A theory of coalitions in exchange networks is presented, which predicts the critical mass below which coalitions fail to affect power inequality and above which coalitions become unstable. We present the results of a preliminary experimental test of the theory. The results demonstrate not only that coalitions form but even that they can reverse power inequality. However larger coalitions were more stable than predicted.

https://www.jstor.org/stable/pdfplus/3090152.pdf

Collective action and power inequality : Coalitions in exchange networks

How does social order emerge among autonomous but interdependent agents? The expectation of future interaction may explain cooperation based on rational foresight, but the "shadow of the future" offers little leverage on the problem of social order in "everyday life" -- the habits of association that generate unthinking compliance with social norms. Everyday cooperation emerges not from the shadow of the future but from the lessons of the past. Rule-based evolutionary models are a promising way to formalize this process. These models may provide new insights into emergent social order -- not only prudent reciprocity, but also expressive and ritual self-sacrifice for the welfare of close cultural relatives.

Social Order in Artificial Worlds.

We are strongly supportive of Fossett's theoretical approach and modeling methodology, which uses computational methods to perform thought experiments that generate compelling insights into the enigma of persistent residential segregation in the U.S. We also agree with his theoretical results, which challenge the prevailing view among demographers that institutional discrimination is the essential cause. However, we think he did not go far enough. Fossett limited his analysis to a narrow region of the parameter space that corresponded to conditions observed in one city at one time. This precludes generalization to other times and places and exploration of theoretically motivated “what if” scenarios that trespass beyond the Detroit city limits. When we extended the parameter space, we noticed two interesting results. First, Fossett's “paradox of weak minority preferences” requires qualification. Disproportionate in-group preferences among minorities are indeed segregation-promoting, not integration-promoti...

Michael W. Macy

Papers

Opinion cascades and the unpredictability of partisan polarization

Unlocking the doors of the Prisoner's dilemma : Dependence, selectivity, and cooperation

Collective action and power inequality : Coalitions in exchange networks

Social Order in Artificial Worlds.

Ethnic Preferences and Residential Segregation: Theoretical Explorations Beyond Detroit