5 papers · 1 filter
The T^1-lifting theorem in positive characteristic
Stefan Schroeer
Replacing symmetric powers by divided powers and working over Witt vectors instead of ground fields, I generalize Kawamatas T^1-lifting theorem to characteristic p>0. Combined with…
There are enough Azumaya algebras on surfaces
Stefan Schroeer
Using Maruyama's theory of elementary transformations, I show that the Brauer group surjects onto the cohomological Brauer group for separated geometrically normal algebraic surfac…
Remarks on the existence of Cartier divisors
Stefan Schroeer
Given an invertible sheaf, does it come from a Cartier divisor? This might fail in presence of embedded components. I give some examples and characterize those invertible sheaves t…
Normal del Pezzo surfaces containing a nonrational singularity
Stefan Schroeer
Working over a perfect field, I classify normal del Pezzo surfaces with base number one that contain a nonrational singularity. They form a huge infinite hierarchy; contractions of…
On non-projective normal surfaces
Stefan Schroeer
We construct examples of non-projective normal proper algebraic surfaces and discuss the pathological behaviour of their Neron-Severi group. Our surfaces are birational to the prod…