Search results for " Geometria"
showing 10 items of 291 documents
Pensare in maniera inventiva. Saggio introduttivo a Ottica e Pittura di H. von Helmholtz
2023
Il saggio ricostruisce il contesto filosofico e scientifico in cui von Helmholtz perviene all’idea che la ricerca in arte, filosofia e scienza comporti benefici reciproci. Si espone la teoria della percezione che von Helmholtz consolida per fornire una giustificazione epistemologica ai risultati della ricerca scientifica sulla percezione visiva e sonora, in cui ottica, psicologia e fisiologia ne definiscono i livelli di analisi. Si illustrano sistematicamente i problemi di percezione delle forme, della profondità, della luce e del colore rilevanti per la visione e la pittura, rendendo esplicito il collegamento tra la ricerca sperimentale di von Helmholtz, quella di Newton, Wollastone, Wheat…
The nonabelian tensor product of two soluble minimax groups
2010
A generalization of groups with many almost normal subgroups
2010
A subgroup $H$ of a group $G$ is called almost normal in $G$ if it has finitely many conjugates in $G$. A classic result of B. H. Neumann informs us that $|G : Z(G)|$ is finite if and only if each $H$ is almost normal in $G$. Starting from this result, we investigate the structure of a group in which each non- finitely generated subgroup satisfies a property, which is weaker to be almost normal.
THE HILBERT FUNCTION OF BIGRADED ALGEBRAS IN k[P1x P1]
2020
We classify the Hilbert functions of bigraded algebras in k[x1, x2, y1, y2] by introducing a numerical function called a Ferrers function.
A Survey on Just-Non-X Groups
2010
Let be a class of groups. A group which does not belong to but all of whose proper quotient groups belong to is called just-non- group. The present note is a survey of recent results on the topic with a special attention to topological groups.
Anti-$PC$-groups and Anti-$CC$-groups
2007
A groupGhas Černikov classes of conjugate subgroups if the quotient groupG/coreG(NG(H))is a Černikov group for each subgroupHofG. An anti-CCgroupGis a group in which each nonfinitely generated subgroupKhas the quotient groupG/coreG(NG(K))which is a Černikov group. Analogously, a groupGhas polycyclic-by-finite classes of conjugate subgroups if the quotient groupG/coreG(NG(H))is a polycyclic-by-finite group for each subgroupHofG. An anti-PCgroupGis a group in which each nonfinitely generated subgroupKhas the quotient groupG/coreG(NG(K))which is a polycyclic-by-finite group. Anti-CCgroups and anti-PCgroups are the subject of the present article.
On compact Just-Non-Lie groups
2007
A compact group is called a compact Just-Non-Lie group or a compact JNL group if it is not a Lie group but all of its proper Hausdorff quotient groups are Lie groups. We show that a compact JNL group is profinite and a compact nilpotent JNL group is the additive group of p -adic integers for some prime. Examples show that this fails for compact pronilpotent and solvable groups.
A combinatorial algorithm related to the geometry of the moduli space of pointed curves
2002
As pointed out in Arbarello and Cornalba ( J. Alg. Geom. 5 (1996), 705–749), a theorem due to Di Francesco, Itzykson, and Zuber (see Di Francesco, Itzykson, and Zuber, Commun. Math. Phys. 151 (1993), 193–219) should yield new relations among cohomology classes of the moduli space of pointed curves. The coefficients appearing in these new relations can be determined by the algorithm we introduce in this paper.
Probability of mutually commuting n-tuples in some classes of compact groups
2008
In finite groups the probability that two randomly chosen elements commute or randomly ordered n−tuples of elements mutually commute have recently attracted interest by many authors. There are some classical results estimating the bounds for this kind of probability so that the knowledge of the whole structure of the group can be more accurate. The same problematic has been recently extended to certain classes of infinite compact groups in [2], obtaining restrictions on the group of the inner automorphisms. Here such restrictions are improved for a wider class of infinite compact groups.
Isoclinism in probability of commuting n-tuples
2009
Strong restrictions on the structure of a group $G$ can be given, once that it is known the probability that a randomly chosen pair of elements of a finite group $G$ commutes. Introducing the notion of mutually commuting n-tuples for compact groups (not necessary finite), the present paper generalizes the probability that a randomly chosen pair of elements of $G$ commutes. We shall state some results concerning this new concept of probability which has been recently treated in [3]. Furthermore a relation has been found between the notion of mutually commuting n-tuples and that of isoclinism between two arbitrary groups.