A new model for epidemic prediction: COVID-19 in kingdom saudi arabia case study.

Coronavirus disease-2019 (COVID-19) is a viral infection that rose in a city in the Chinese province of Hubei, Wuhan. The world did not wait too long until the virus spread to reach Europe, Africa, and America to be a global pandemic. Due to the lack of information about the behaviour of the virus, several prediction models are in use all over around the world for decision making and taking precautionary actions. Therefor, in this paper, a new model named MSIR based on SIR model is proposed. The model is used to predict the spread of the disease in three cities Riyadh, Hufof and Jeddah in the kingdom of Saudi Arabia. Also the estimation of disease propagation with and without containment measure is carried out. We think that the results could be used to enhance the predictability of the pandemic outbreaks in other cities and to build long term artificial intelligence prediction model.

Synthesis, characterization and optical spectroscopy of GdPO4 :Er3.

A series of Er3+ -doped GdPO4 phosphors was synthesized using a conventional solid-state reaction. The monazite structure (space group P121 /n1 ) of the obtained materials was confirmed using X-ray diffraction and Fourier transform infrared spectroscopy. Their optical spectra (excitation, emission, absorption, decay curves) were measured at room temperature in the visible and near-infrared (NIR) regions. The UV-visible-NIR optical absorption spectrum of GdPO4 :7% Er3+ was analyzed based on Judd-Ofelt (J-O) theory and the J-O intensity parameter (Ω2 , Ω4 , Ω6 ) was calculated. J-O intensity parameters were used to evaluate spontaneous emission properties such as branching ratios, transition probabilities, and radiative lifetime. The calculated quantum efficiency of the 1.5 µm emission (4 I13/2 -4 I15/2 ) was calculated to be 89%. This result proved that GdPO4 :Er3+ is suitable for use in optical amplifiers and is a potential host for laser applications. The most interesting transitions, located at about 540 nm, and 1.0 and 1.5 µm were investigated as a function of doping level and of temperature, to assess the conditions needed for the highest emission performance and to explore the range of application, in particular in the fields of lighting, thermal sensing, and of phosphors for bio-imaging.