No abstract

Objectives: Physical diseases are well-established risk factor for suicide, particularly among older adults. However, little is known about the underlying mechanism of the association. This study aimed to describe the prevalence of physical diseases and their influences on the elderly in rural China and to examine the underlying mechanisms of the relationship between physical diseases and suicide. Methods: This matched case–control psychological autopsy study was conducted from June 2014 to September 2015. Consecutive suicide cases (242) among people aged 60 years or above were identified in three Chinese provinces. The suicide cases were 1:1 matched with living comparisons based on age, gender and residential area. Two informants for each participant were interviewed to collect data on their demographic characteristics, the severity index of physical diseases, depressive symptoms, feelings of hopelessness, mental disorders and social support. Results: A significant difference was found between suicide cases and living comparisons regarding the prevalence of physical diseases (83.5% vs 66.5%, p < 0.001) and their severity (11.3 ± 6.2 vs 6.7 ± 5.3, p < 0.001). Independent risks of suicide included the following: not currently married (OR = 2.81, 95% CI = [1.04, 7.62]), mental disorders (OR = 7.18, 95% CI = [1.83, 28.13]), depressive symptoms (OR = 1.15, 95% CI = [1.05, 1.26]) and feelings of hopelessness (OR = 1.51, 95% CI = [1.20, 1.90]). The structural equation model indicated that the relationship between the severity index of physical diseases and suicide was mediated by depressive symptoms, feelings of hopelessness and mental disorders. Conclusion: The severity and number of physical diseases were found to be correlated with suicide among the elderly in rural China, after controlling for demographic characteristics. Physical diseases elevate one’s suicide risk by increasing depressive symptoms, feelings of hopelessness and mental disorders. Efforts for suicide prevention should be integrated with strategies to treat physical diseases along with psychological interventions.

SUMMARYKey management becomes more difficult in multiprivileged group communications due to the dynamic membership and the complex relations between users and resources. Because centralized key management schemes have the drawbacks of the single point of failure, and performance bottleneck and distributed key management schemes are not scalable and lack of central control, decentralized key management schemes are proposed as a tradeoff between them. In this paper, we propose a decentralized group key management scheme using multilinear forms for dynamic multiprivileged groups. Once users join/leave the group and change their privileges, the related session keys should be updated. The rekeying in the joining operation is relatively simple because the keys are deduced from the previous keys based on a one-way function. When rekeying for one leaving/switching operation, a uniform rekeying material is negotiated between the related service groups (SGs) by using multilinear forms. Compared with other schemes in which several rounds of negotiations are executed for rekeying in each joining/leaving/switching operation, only one round of negotiation is required in each leaving/switching operation of our decentralized group key management scheme. At last, the affected session keys can be deduced by the related SGs. Our proposed scheme also supports the dynamic formation and decomposition of SGs, which provides good scalability. Security analysis is provided to show that the proposed scheme is secure. The performance analysis and the simulation results show that the proposed scheme reduces the communication cost greatly.