diff --git a/3-99 Research/MARVEL.md b/3-99 Research/MARVEL.md
index 157b7c89..f31b78c5 100644
--- a/3-99 Research/MARVEL.md	
+++ b/3-99 Research/MARVEL.md	
@@ -12,8 +12,19 @@ is by natural convection. This reactor system uses two coolant loops: the primar
 is sodium-potassium salt, while the secondary coolant is lead. These two fluids
 drive 'Stirling Engines', which are how the system generates power.
 
-- [?] What are Stirling Engines? #MARVEL 
-Stirling engines are heat engines that directly convert heat energy into mechanical energy. How they work is they have a piston that travels back and forth from a hot side to a cold side. When the cylinder travels over the hot side 
+
+>[!info] # What are Stirling Engines?
+>- [x] What are Stirling Engines? #MARVEL ✅ 2025-03-21
+>
+> Stirling engines are heat engines that directly convert heat energy into mechanical energy. 
+> How they work is they have a piston that travels back and forth from a hot side to a cold side. 
+> When the cylinder travels over the hot side the volume of air on that side heats up from the hot 
+> walls and expands, forcing the cylinder in the direction of the cold fluid. At the same time,
+> that fluid is getting colder, decreasing in pressure, and creating a vacuum. Then, once the piston
+> moves to the cold side, the chamber compresses, removing the cooling, and heats up pushing 
+> the piston back towards the hots side. Here's a graphic:
+> ![[Pasted image 20250321163711.png]]
+> 
 
 Anyways, MARVEL also uses an interesting drum based system to do power control.
 They use one big central 'insurance' rod, but also have four drums around the cylindrical 
diff --git a/3-99 Research/TLA/Writing a MARVEL Specification in TLA+.md b/3-99 Research/TLA/Writing a MARVEL Specification in TLA+.md
index 7a409141..d7afb472 100644
--- a/3-99 Research/TLA/Writing a MARVEL Specification in TLA+.md	
+++ b/3-99 Research/TLA/Writing a MARVEL Specification in TLA+.md	
@@ -1,5 +1,5 @@
 # What is the MARVEL reactor?
-- [<] What the fuck is MARVEL? #Reading 🆔 furwbi ⏫ 📅 2025-02-28
+- [x] What the fuck is MARVEL? #Reading 🆔 furwbi ⏫ 📅 2025-02-28 ✅ 2025-03-21
 
 # What are some specs that perhaps can be formalized in TLA+?
 ## What are the specs of interest?
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