Social network analysis and modeling of cellphone-based syndromic surveillance data for ebola in Sierra Leone

Objective:To explore and visualize the connectivity of suspected Ebola cases and surveillance callers who used cellphone technology in Moyamba District in Sierra Leone for Ebola surveillance,and to examine the demographic differences and characteristics of Ebola surveillance callers who make more calls as well as those callers who are more likely to make at least one positive Ebola call.Methods:Surveillance data for 393 suspected Ebola cases(192 males,201 females) were collected from October 23,2014 to June 28,2015 using cellphone technology.UCINET and Net Draw software were used to explore and visualize the social connectivity between callers and suspected Ebola cases.Poisson and logistic regression analyses were used to do multivariable analysis.Results:The entire social network was comprised of 393 ties and 745 nodes.Women(AOR=0.33,95% CI [0.14,0.81]) were associated with decreased odds of making at least one positive Ebola surveillance call compared to men.Women(IR= 0.63,95% CI [0.49,0.82]) were also associated with making fewer Ebola surveillance calls compared to men.Conclusion:Social network visualization can analyze syndromic surveillance data for Ebola collected by cellphone technology with unique insights.

A bound on judicious bipartitions of directed graphs

Judicious partitioning problems on graphs ask for partitions that bound several quantities simultaneously,which have received much attention lately.Scott(2005)asked the following natural question:What is the maximum constant cdsuch that every directed graph D with m arcs and minimum outdegree d admits a bipartition V(D)=V_1∪V_2 satisfying min{e(V_1,V_2),e(V_2,V_1)}cdm?Here,for i=1,2,e(V_i,V_(3-i))denotes the number of arcs in D from V_i to V_(3-i).Lee et al.(2016)conjectured that every directed graph D with m arcs and minimum outdegree at least d 2 admits a bipartition V(D)=V_1∪V_2 such that min{e(V_1,V_2),e(V_2,V_1)}≥((d-1)/(2(2 d-1))+o(1))m.In this paper,we show that this conjecture holds under the additional natural condition that the minimum indegree is also at least d.

On Imbalances in Oriented Tripartite Graphs

An oriented tripartite graph is the result of assigning a direction to each edge of a simple tripartite graph. For any vertex x in an oriented tripartite graph D（U, V, W）, let dx^＋ and dx^- denote the outdegree and indegree respectively of x. Define aui： dui^＋ - dus^-, bvj = dvj^＋ - dvj^- and cwk = dwk^＋ - dwk^- as the imbalances of the vertices ui in U, vj in V and wk in W respectively. In this paper, we obtain criteria for sequences of integers to be the imbalances of some oriented tripartite graph. Keywords Digraph, imbalance, outdegree, indegree, oriented graph, oriented tripartite graph, arc