محمدجواد شایگان

In recent years, determining the most effective time to post on Instagram for increased engagement has become a central concern for digital marketers. Despite its significance, research on this topic remains limited. This study adopts an exploratory research approach to analyze Instagram posts from selected Western countries (Europe and America) and Iranian businesses. The data were collected during the period from February 21, 2022, to March 21, 2022, employing web scraping tools. Classification algorithms, including XGBoost, K-NN, SVM, and Linear Regression, are employed for modeling, with results favoring the XGBoost method for accuracy. The study reveals optimal posting times between 12 and 3 pm for Western Countries businesses and 9 and 12 am for Iranian businesses. Furthermore, it suggests Sunday as the best day for posting in the West, contrasting with Thursday in Iran. In summary, this research underscores the differing ideal posting times in Iran and the West, emphasizing the challenge of constructing a uniform model for all countries.

The success of e-learning is still a challenging issue. This study presents a model for the evaluation of the success of e-learning in three different faculties. More specifically, the present article answers the question of whether e-learning success variables are different in different faculties. The method of this study was descriptive-survey research. Evaluating research validity was conducted through confirmatory factor analysis, and Cronbach's alpha was used to measure the reliability of the research instrument. The method of the structural equation was used for modeling. The findings reveal that the students’ opinions in the three faculties about the success variables were significantly different. In the Faculty of Engineering, teaching with a coefficient of 0.93, in the Humanities, service quality with a coefficient of 0.9, and in the Arts Faculty, support quality with a coefficient of 0.82 were identified as the highest impact factors. On the other hand, significant commonalities were observed.

Today's world is struggling with the COVID-19 pandemic, as one of the greatest challenges of the 21st century. During the lockdown caused by this disease, many financial losses have been inflicted on people and all industries. One of the fastest ways to save these industries from the COVID-19 or any possible pandemic in the future is to provide a reliable, fast, smart, and secure solution for people's health assessment. In this article, blockchain technology is used to propose a model which provides and validates the health certificates for people who travel or present in society.  For this purpose, we take advantage of blockchain features such as being unchangeable, errorless, distributed, and a single point of failure nonexistence, high security, and proper use in protecting people's privacy. Since a variety of antibody and human health proving tests against the virus are developing, this study tries simultaneously to design an integrated and secure system to meet the authenticity and accuracy of different people's health certificates for the companies requiring these certifications. In this system, on the one hand, there are qualified laboratories that are responsible for performing standard testing and also providing results to the system controller. On the other hand, entities that need to receive health certificates must be members of this system. Finally, people are considered as the end-user of the system. To provide test information for the entities, the mechanism of KYC tokens will be used based on the Stellar private blockchain network. In this mechanism, the user will buy a certain amount of KYC tokens from the system controller. These tokens are charged in the user's wallet, and the user can send these tokens from his wallet to any destination company, to exchange the encrypted health certificate information. Finally, considering the appropriate platform provided by blockchain technology and the requirement of a reliable and accurate solution for issuing health certificates during the Covid-19 pandemic or any other disease, this article offers a solution to meet the requirements.