An increasing number of different unlicensed wireless technologies have been deployed in the TV white space (TVWS). Because MAC/PHY designs of coexisting networks are incompatible, heterogeneous cognitive radio networks operating in the same TVWS spectrum may cause severe mutual interference, which further leads to performance degradation or even the inability to continue operation. Motivated by the competition relationship between different species in a stable ecosystem, this paper formulates the heterogeneous coexistence problem over TVWS as a nonlinear feedback control system (NFCS) based on the Lotka-Volterra competition model. With the differential mean value theorem, we can obtain a feedback controller to the NFCS via solving a sufficient condition in the form of linear matrix inequalities, based on which a spectrum sharing allocation algorithm (SSAA) is proposed to enable the NFCS to converge to any feasible spectrum share. It is shown that the SSAA is compatible with the IEEE 802.19.1 system. Finally, extensive simulations demonstrate the efficiency of the proposed SSAA.
Background: Coronavirus disease 2019 (COVID-19), a newly emerged respiratory disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has recently become pandemic. Clinical observation indicated that elderly patients had high incidence of severe pneumonia and poor treatment efficacy. Therefore, this study was to clarify the characteristics of elderly patients aged 75 or older with COVID-19 pneumonia in order to guide rational treatment for elderly patients. Methods: we enrolled 331 elderly patients aged 75 or older with confirmed COVID-19 in Huoshenshan hospital of Wuhan from February 3rd to March 31st. The cases were divided into general, serious and critical groups according to severity after hospitalization, and the difference among groups were compared by R package statistics software. Results: Compared with general group, serious and critical groups had more underlying comorbidities and higher incidence of cough, breath shortness and anorexia. Moreover, there existed obviously differences in many of laboratory indexes and CT images among them. serious and critical elderly patients were more likely to receive oxygen, mechanical ventilation, expectorant, corticosteroid, abidor, cephaloprin, imipenem, human serum albumin (HSA), nutrition support, anti SARS-CoV-2 positive plasma and actemra. Multivariate analysis of factors showed that male sex, hypertension, diabetes, renal diseases, breath shortness, neutrophil, platelet, creatinine, lactate dehydrogenase were the risk factor for serious and critical illness. While blood cell (WBC) was the protective factor. Conclusion: elderly patients have high incidence of severe pneumonia and poor treatment efficacy. The reasons might be that many of the elderly patients with COVID-19 pneumonia have certain chronic disease, poor immune function and a meager response to the virus. the pathogenic mechanism of SARS-CoV-2 might be involved in the cell-mediated immunity and cytokine storms by acting on lymphocytes.
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