Diffusion Approximation with Henyey-Greenstein Phase Function Using UN Method

Abstract: U1 and P1 approximations are applied to one-dimensional neutron transport equation and Henyey- Greenstein phase function is used for calculating diffusion length. Numerical results obtained from U1 and P1 approximations are compared with each other for different collision parameters and t parameters. Key words: Diffusion approximation, Henyey-Greenstein phase function, UN method UN Metodu Kullanarak Henyey-Greenstein Faz Fonksiyonu ile Difüzyon Yaklaşımı Özet: U1 ve P1 yaklaşımları tek boyutlu nötron transport denklemine uygulandı ve difüzyon uzunluğu hesabı için Henyey-Greenstein faz fonksiyonu kullanıldı. Farklı çarpışma parametreleri ve t parametresi için U1 ve P1 yaklaşımlarından elde edilen nümerik sonuçlar birbiri arasında kıyaslandı. Anahtar kelimeler: Difüzyon yaklaşımı, Henyey-Greenstein faz fonksiyonu, UN metod

Can Some Viral Respiratory Infections Observed Before the Pandemic Announcement Be Related to SARS-CoV-2?

OBJECTIVE: There have been doubts that SARS-CoV-2 has been circulating before the first case was announced. The aim of this study was to evaluate the possibility of COVID-19 in some cases diagnosed to be viral respiratory tract infection in the pre-pandemic period in our center. MATERIAL AND METHODS: Patients who were admitted to our hospital’s pulmonary diseases, infectious diseases, and intensive care clinics with the diagnosis of viral respiratory system infection within a 6-month period between October 2019 and March 12, 2020, were screened. Around 248 archived respiratory samples from these patients were analyzed for SARS-CoV-2 ribonucleic acid by real-time-quantitative polymerase chain reaction. The clinical, laboratory, and radiological data of the patients were evaluated. RESULTS: The mean age of the study group was 47.5 (18-89 years); 103 (41.5%) were female and 145 (58.4%) were male. The most common presenting symptoms were cough in 51.6% (n = 128), fever in 42.7% (n = 106), and sputum in 27.0% (n = 67). Sixty-nine percent (n = 172) of the patients were pre-diagnosed to have upper respiratory tract infection and 22.0% (n = 55) had pneumonia, one-third of the patients (n = 84, 33.8%) were followed in the service. Respiratory viruses other than SARS-CoV-2 were detected in 123 (49.6%) patients. Influenza virus (31.9%), rhinovirus (10.5%), and human metapneumovirus (6.5%) were the most common pathogens, while none of the samples were positive for SARS-CoV-2 RNA. Findings that could be significant for COVID-19 pneumonia were detected in the thorax computed tomography of 7 cases. CONCLUSION: The negative SARS-CoV-2 real-time-quantitative polymerase chain reaction results in the respiratory samples of the cases followed up in our hospital for viral pneumonia during the pre-pandemic period support that there was no COVID-19 among our cases during the period in question. However, if clinical suspicion arises, both SARS and non-SARS respiratory viral pathogens should be considered for differential diagnosis