ABSTRACT
The coronavirus disease 2019 (COVID-19) pandemic is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The objective of this study was to determine the clinical course and risk factors for patients showing recurrent SARS-CoV-2 RNA positivity. A total of 1087 COVID-19 patients confirmed by RT-PCR from February 24, 2020 to March 31, 2020 were retrospectively enrolled. Advanced age was significantly associated with mortality. In addition, 81 (7.6%) of the discharged patients tested positive for SARS-CoV-2 RNA during the isolation period. For patients with recurrent RT-PCR positivity, the median duration from illness onset to recurrence was 50 days. Multivariate regression analysis identified elevated serum IL-6, increased lymphocyte counts and CT imaging features of lung consolidation during hospitalization as the independent risk factors of recurrence. We hypothesized that the balance between immune response and virus toxicity may be the underlying mechanism of this phenomenon. For patients with a high risk of recurrence, a prolonged observation and additional preventative measures should be implemented for at least 50 days after illness onset to prevent future outbreaks.
ABSTRACT
Based on coupled-mode theory, the mode transition of the high-order cladding modes in a coated long-period tiber grating (LPFG) has been studied firstly; the mode transition region and non-mode transition region of high-order cladding modes are divided. The response characteristic of cladding mode effective index with increasing the overlay thickness is analyzed; the shift of resonant wavelength in the mode transition region will be larger than that in the non-mode transition region. Further, the changes of the resonant wavelength of some high-order cladding modes with grating period are investigated when the cladding radius are different, the shift between two resonant wavelengths of dual peak in the mode transition region is bigger than that in non-mode transition region when the cladding radius are uniform. And the shift between two resonant wavelengths of dual peak will be increased by the decrease of the cladding radius in both mode transition and non-mode transition regions. Finally, the response characteristics of film refractive index of coated LPFG are investigated for a high-order cladding mode while the cladding radius are different and the overlay thickness is located in mode transition region and non-transition mode region, then the optimized design scheme is come up with. The higher sensitivity dual-peak sensor of coated LPFG than the traditional dual-peak sensor will be obtained when the overlay thickness and refractive index is located in the mode transition region and the grating period close to the phase matching turning points. Further, the resolution power of coated LPFG sensor will further be improved by the appropriate reducing of the cladding radius.
