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Mobile sensor networks (MSNs) can provide sensing coverage to large areas of interest (AoIs). Area coverage and target tracking capabilities of MSNs are heavily depending on their motion control and coordination mechanisms. Many existing MSN motion control algorithms ignore or poorly utilize available information from their operating environment, thus lead to unsatisfactory monitoring performances. This paper proposes a fully distributed semi-flocking algorithm which enables mobile nodes to self-organize themselves based on mobility and sensing information via information exchanges among nearby nodes. A distributed mechanism is designed to maximize area coverage and target tracking performances of MSNs. Mobile nodes perform evaluations based on received information and switch between searching and tracking modes. Behaviors of MSNs controlled by the proposed algorithm are studied under different levels of information exchanges. Our study shows that the proposed semi-flocking algorithm is capable of delivering desirable area coverage and target tracking performances in MSNs.

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In this letter, a non-orthogonal multiple access (NO-MA) scheme is employed for irregular repetition slotted ALOHA (IRSA). Specifically, packet replicas are transmitted with discrete power levels which are pre-determined by the NOMA scheme. In this case, most packet collisions can be resolved in the power domain, contributing to a much lower packet loss rate. Density evolution (DE) analysis is formulated and the degree distributions are optimized for different number of power levels. Simulation results validate our analysis and show that the proposed scheme can outperform existing IRSA schemes.

BackgroundVery few of the primary care doctors currently working in China’s community health centers have a college degree (issued by 5-year medical schools). How to attract college graduates to community services in the future, therefore, has major policy relevance in the government’s ongoing efforts to reform community health care and fill in the long-absent role of general physicians in China. This paper examined medical school students’ attitudes towards working in communities and the factors that may affect their career choices in primary care to inform policy on this subject.MethodsA cross-sectional survey was designed upon the issuance of community health reform policy in 2006 by the Chinese government. The survey was conducted among 2714 medical students from three medical schools in representative regions in China. Binomial and multinomial regression analyses were carried out using a collection of plausible predictors such as place of rearing, income, etc. to assess their willingness to work in communities.ResultsOf the 2402 valid responses, besides 5.7 % objection to working in communities, 19.1 % expressed definite willingness. However, the majority (41.5 %) of students only consider community job as a temporary transition, in addition to 33.7 % using it as their backup option. The survey analyses found that medical students who are more likely to be willing to work in communities tend to come from rural backgrounds, have more exposure to community health reform, and possess certain personally held value and fit.ConclusionTo attract more graduates from 5-year medical schools to work in communities, a targeted recruiting approach or admission policy stands a better chance of success. The findings on the influencing factors of medical students’ career choice can help inform policymakers, medical educators, and community health managers to improve the willingness of swing students to enter primary care to strengthen basic health services.Electronic supplementary materialThe online version of this article (doi:10.1186/s12875-016-0472-5) contains supplementary material, which is available to authorized users.

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