Modeling of wave propagation in drill strings using acoustic transfer matrix method
In order to understand critical vibrations of a drill bit such as stick-slip and bit-bounce and their wave propagation characteristics through a drillstring system, it is critical to model the torsional, longitudinal, and flexural waves. The objective is to model these waves propagating through the drillstring in a computationally efficient way. Here, a modeling method based on an acoustic transfer matrix between two sets of wave variables at the ends of a cylindrical pipe is proposed. For a drillstring system with multiple pipe sections, the total acoustic transfer matrix is calculated by multiplying all individual matrices of which each is obtained for an individual pipe section. Since drillstring systems are typically extremely long, conventional numerical analysis methods such as FEM require a large number of meshes, which makes it difficult to analyze these drillstring systems. On the contrary, the analytical acoustic transfer matrix method requires significantly low computational costs. For the validation, experimental and numerical data are obtained from a laboratory measurement and by using a commercial FEM package, ANSYS, respectively. They are compared to the modeling results obtained by using the proposed method. It is shown that the modeling results are well matched with the experimental and numerical results.
The impact of vibration mechanism’ installation place on the process of retrieving stuck drill pipe
The authors express their sincere gratitude to Dr. Ja. Kuntsyak (Joint Stock Company “Scientific Design Bureau for Testing of Drilling Tools”, Kyiv, Ukraine) and Prof. V. Vekeryk (Ivano-Frankivsk National Technical University of Oil and Gas, Ukraine) for consultations on technical issues of borehole drilling. 
Scientific advice was obtained from The National Academy of Sciences of Ukraine, Academic Society of Michal Baludyansky (Bratislava, Slovak Republic), National Lviv Polytechnic University (Lviv, Ukraine). 
We greatly appreciate Prof. B. Kopej (Ivano-Fran-kivsk National Technical University of Oil and Gas, Ukraine) for his valuable improvements to this manuscript.
La participacion de los stakeholders en las iniciativas de branding del hospital en las redes sociales: una propuesta de modelo para construir marcas colectivas
Introduction : All health organizations face many managerial and economic challenges such as the consolidation of private and international hospitals, the increasingly interest of society for health education issues or the development of telemedicine. In this framework, many organizations prioritize social media as the main corporate communication tool for building a reputed brand in a collective way along with stakeholders. Objectives : This paper aims to identify a communication model allowing hospitals to efficiently apply branding initiatives on social media in order to build a brand in a collective way with stakeholders. Methodology : We carried out a literature review about corporate communication, health communication, branding and social media; and, then, we proposed the PET Model for Branding Hospitals on Social Media. Results and Conclusion : We conclude that hospitals should create a multidisciplinar corporate communication department, implement management initiatives for allowing health professionals have more time for using social media and integrate health education and patient’s empowerment in every communication initiative.