2,358 research outputs found
On fibred biset functors with fibres of order prime and four
This note has two purposes: First, to present a counterexample to a
conjecture parametrizing the simple modules over Green biset functors,
appearing in an author's previous article. This parametrization fails for the
monomial Burnside ring over a cyclic group of order four. Second, to classify
the simple modules for the monomial Burnside ring over a group of prime order,
for which the above-mentioned parametrization holds
Hochschild cohomology for functors on linear symmetric monoidal categories
Let be a commutative ring with unit. We develop a Hochschild cohomology
theory in the category of linear functors defined from an
essentially small symmetric monoidal category enriched in -Mod, to -Mod.
The category is known to be symmetric monoidal too, so one can
consider monoids in and modules over these monoids, which allows
for the possibility of a Hochschild cohomology theory. The emphasis of the
article is in considering natural hom constructions appearing in this context.
These homs, together with the abelian structure of lead to nice
definitions and provide effective tools to prove the main properties and
results of the classical Hochschild cohomology theory
The (impossible?) formation of acetaldehyde on the grain surfaces: insights from quantum chemical calculations
Complex Organic Molecules (COMs) have been detected in the interstellar
medium (ISM). However, it is not clear whether their synthesis occurs on the
icy surfaces of interstellar grains or via a series of gas-phase reactions. As
a test case of the COMs synthesis in the ISM, we present new quantum chemical
calculations on the formation of acetaldehyde (CH3CHO) from the coupling of the
HCO and CH3 radicals, both in gas phase and on water ice surfaces. The binding
energies of HCO and CH3 on the amorphous water ice were also computed (2333 and
734 K, respectively). Results indicate that, in gas phase, the products could
be either CH3CHO, CH4 + CO, or CH3OCH, depending on the relative orientation of
the two radicals. However, on the amorphous water ice, only the CH4 + CO
product is possible due to the geometrical constraints imposed by the water ice
surface. Therefore, acetaldehyde cannot be synthesized by the CH3 + HCO
coupling on the icy grains. We discuss the implications of these results and
other cases, such as ethylene glycol and dimethyl ether, in which similar
situations can occur, suggesting that formation of these molecules on the grain
surfaces might be unlikely
Finite metacyclic groups as active sums of cyclic subgroups
The notion of active sum provides an analogue for groups of that of direct
sum for abelian groups. One natural question then is which groups are the
active sum of cyclic subgroups. Many groups have been found to give a positive
answer to this question, while the case of finite metacyclic groups remained
unknown. In this note we show that every finite metacyclic group can be
recovered as the active sum of a discrete family of cyclic subgroups
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