I have recently moved to Ljubljana, Slovenia, in the quest to find new scientific challenges and make a shift in my career because EPR Spectroscopy is - dead.
Naturally, I came to the very best Slovenian institute, Institute Jozef Stefan - IJS, where about 800 people are working both hard and smart.
Who was Jozef Stefan?
Jozef Stefan was born in the first half of the XIX century in a small Austro-Hungarian town of St. Peter (nearby Klagenfurt) in a Slovenian family.
In his young age, equivalent to high-school today, he expressed great interesting in poetry, languages (Slovenian, Serbo-Croat that was developing in that time, Slavic languages in general and even classical languages, Greek and Latin), but also for physics and math.
Fortunately, Jozef decided to study mathematics and physics in Vienna. One of his math professors was Joseph Petzval. Yes, photography lovers, that Petzval.
After graduating, Josef focused on thermodynamics and behaviour of gasses, also in Vienna, the city of science in that time and even became the vice president of Vienna Academy of Sciences.
What he discovered?
The most famous discovery of Jozef Stefan is the Stefan-Bolzmann Law that describes the irradiation of black body. It's described by the simple equation: 
Stefan problem (Stefanova naloga)
A Stefan Problem is a specific type of boundary value problem for a partial
differential equation concerning heat distribution in a phase changing medium.
In practice, it can be used to describe the diffusion of heat in the boundary phase where ice becomes melted.
This problem is so complex that even today it's possible to write the whole PhD thesis going into the details (check the link from the Title).
Stefan's formula
Stefan's formula defines a specific surface energy at a given interface, determined by the enthalpy difference
Stefan number
The Stefan number, denoted as St or Ste is defined as the ratio of sensible heat to latent heat.
By definition, sensible heat is:
Sensible heat is heat exchanged by a body or thermodynamic system in which the exchange of heat changes the temperature of the body or system, and some macroscopic variables of the body or system, but leaves unchanged certain other macroscopic variables of the body or system, such as volume or pressure
And the latent heat is defined as:
Latent heat is thermal energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process — usually a first-order phase transition.
I owe you the equation: 
Stefan flow
This phenomenon describes the flow caused by the production or removal of the species at an interface.
On the other hand, Fick's first law was also defined in the XIX centruty and it describes the diffusion in the steady state. Amateur... :)
If you want to sleep well, chek this YT video:
Stefan Tube
This is a device used to determine diffusion coefficient.
The principle of work is simple. Gas is floating through the top tube, while the sample (some volatile liquid) is positioned at the bottom. It evaporates, exceeds the top tube and the lavel of the liquid is changing in time
In summary, Jožef Štefan wrote more than 80 scientific publications and defined the problems that are still capturing the imagination of scientists. Writing about him was relatively difficult because I tried to give some of his most notable achievements and yet to keep it on the level of general public.
Ve gore visoke, ve doline,
k vam me želja zmirom bode gnala,
k vam bo duša zmirom vzdihovala,
kraji polni cvetja in miline.
(J. Stefan, odlomek iz pesmi Sonet)
Ok, you deserved one nice photo from Slovenia after reading all the text...
I made this one, few days ago. It's so bad here... Day has only 24h and there are so many temptations and so many choices what to do and where to go.
If there is someone who is a native English speaker I would like to hear why sometimes it's "Stefan's" and why sometimes it's "Stefan". Why that tube, that certainly was Stefan's, is called "Stefan Tube"?
