By Stefan-Tiberiu Kis

It is customary to begin something with an introduction. It can be done in many ways and I am by no means an expert at doing one. However, I believe myself capable of doing some monologuing with regards to myself, what and why.

Myself

I finished both my Bachelor's and my Master's at the West University of Timișoara (Temeschburg), Romania. When choosing a path for undergraduate studies, I went with the physics route because it posed a challenge, which comes in agreement with the following phrase:

"Choosing the difficult road will build your character like nothing else."

My Master's degree was focused on computational physics and particle physics with a hint of astrophysics. At some point during my studies I decided that I wanted to do shockwaves and somewhere along the road I managed to get hired as a research assistant which allowed me to shift my entire focus on my thesis (which was in line with my job contract). The main framework of my project was the finite-difference lattice Boltzmann method built in a C/PETSc dominated code for multiple cases of interest. In essence, I was modelling systems for shockwave propagation.

Nowadays I have a vested interest in cosmic-rays and supernova core-collapse mechanisms.

Oh, and, probably a major reason for choosing physics is due to a certain "Christina".

What and Why

The doctoral programme that I was accepted in focuses on simulation and modelling of various phenomena. My main subject of study is the transport of cosmic-rays in the galaxy. Cosmic-rays are charged particles (typically hydrogen nuclei -a hydrogen that is missing its electron-) that travel from a source somewhere in the galaxy (and outside of it), reaching us at some point in time after suffering through various physical processes on the road.

"Why" can be asked in the sense of "why cosmic-rays". The simple answer is astrophysics. The long answer is that I am already familiar with the hydrodynamic research domain and community. This was an entirely new route that I walked on when I first began my PhD, a "difficult road" as it were.

There are a few codes that aim to solve the transport equation and one of them is PICARD, a code written by my supervisor assoz. prof. Dr. Ralf Kissmann, which is subject to continuous development. I am one such person that is working on the code's development.

My first and major goal is to find and compile analytical and semi-analytical solutions in order to test the code against. The ever growing and improving hydrodynamic community has a vast number of tests that can be employed in order to verify their code. This is not the case for the cosmic-ray transport equation as there are very few people working on it. Having a benchmark to test your code against can tell you if your code provides the data that you want.

"The mathematics do not lie, so the liar has to be the code."

My second and final goal is to take into consideration time evolution when it comes to the transport equations. Time moves forward for us and it is no exception for the cosmic-ray sources. Neglecting time is the same as ignoring what is happening in reality. Cosmic-ray sources appear and disappear, they do not last forever.