Ricerche di Matematica最新文献

Let G be a finite group. A subgroup H of G is called Hall normally embedded in G if H is a Hall subgroup of the normal closure (H^G). In this paper, we fix a subgroup D of Sylow p-subgroup P of G with (1<|D|<|O_p(G)|) and study the structure of G under the assumption that all subgroups H of P with order (|H|=|D|) are Hall normally embedded in G.

We prove a conjecture on the Chow ring of characteristic classes for the special Clifford groups. This conjecture was the only obstacle for obtaining an algorithm computing the maximal indexes of twisted spin grassmannians.

Let (p) be a fixed prime, (a) and (n) are positive integers such that ((p,n) = 1). It is shown that if (G) is a finite group such that for every prime (q) the set of the conjugacy class sizes of all ({ p,q} -) elements of (G) is (left{ {1,p^{a} {,}n,p^{a} n} right}), and there is a (p -) element in (G) whose conjugacy class has size (p^{a}), then (G) is nilpotent and (n) is a prime power.

The non-equilibrium phenomena that characterize the dynamics of an oscillating bubble in a liquid are generally very complex. In this work we study the effects produced by the presence of a gas mixture in which the temperatures of each species are taken into account. Acceleration waves are used to test the stabilizing effects of the model and verify the possibility of shock formation within the bubble. It is shown that the diffusion associated with the presence of multiple temperatures cannot be neglected when describing what happens inside the bubble, even in the sonoluminescence regime.

Spontaneous behavioural responses of individuals to epidemics are a relevant factor in the understanding of infection dynamics. In this work, we consider a vaccine–preventable infectious disease spreading within a population, where vaccination is on a voluntary basis and individuals can conform to either the pro–vaccine or the anti–vaccine group. A switch of vaccinating attitude may occur following an imitation game dynamics. In particular, we incorporate the role of individuals’ opinion flexibility, that is a measure of the personal propensity to change opinion, in the switch of vaccinating attitude. We consider a disease dynamics of Susceptible–Infected–Removed type. Then, we use the tools of kinetic theory to describe the overall system at microscopic, mesoscopic and macroscopic scale. Finally, the role of flexibility of opinion on the vaccination choice during an epidemic is shown by providing some numerical simulations.

The spectrum of a group is the set of orders of its elements. Finite groups with the same spectra as the direct squares of the finite simple groups with abelian Sylow 2-subgroups are considered. It is proved that the direct square (J_1times J_1) of the sporadic Janko group (J_1) and the direct squares ({^2}G_2(q)times {^2}G_2(q)) of the simple small Ree groups ({^2}G_2(q)) are uniquely characterized by their spectra in the class of finite groups, while for the direct square (PSL_2(q)times PSL_2(q)) of a 2-dimensional simple linear group (PSL_2(q)), there are always infinitely many groups (even solvable groups) with the same spectra.

Due to the formal resemblance of some models for the Cauchy stress tensor of elastic solids and viscous fluids, some classes of exact solutions for the equations governing the flows in Navier–Stokes fluids have been generalized to linear and nonlinear elastodynamics. In this paper, we study the conditions under which two special classes of generalized Beltrami flows, the vortices in lattice form and Kelvin’s cat’s eye solutions, are solutions of the equations governing the motions in a linearly elastic transversely isotropic solid.

Recall that a subgroup H of a finite group G is said to be a CSS-subgroup of G if there is a normal subgroup T of G such that (G=HT), and (Hcap T) is SS-quasinormal in G. Clearly, both the c-normal subgroups and the SS-quasinormal subgroups are the CSS-subgroups, but the converse does not hold. In this paper, based on the research of c-normality and SS-quainormality, with the help of the group formation theory, we investigate the supersolvabilty of G by assuming that the subgroups with order |D| are CSS-subgroups of G, where |D| is a prime power. Some relevant results to the c-normality and the SS-quainormality are generalized.

Let ((K_{n},H^-)) be a complete sigraph whose negative edges induce a subgraph H. Let L(3) be the class of all sigraphs having exactly three non-negative eigenvalues (including their multiplicities). In this paper, we characterize ((K_n,U^-)in L(3)), where U is a non-spanning unicyclic subgraph of ( K_n ).

An autonomous model describing biological aspects of synapses affected by electromagnetic fields, is considered. A quaternary system comparable to the third-order FitzHuh–Rinzel (FHR) model is obtained. Linear stability criteria and conditions for Hopf bifurcations are achieved also by means of a ternary auxiliary spectrum showing that some of the resulting conditions recall those related to critical solutions of the FHR system.