Clusters and Recurrence in the Two-Dimensional Zero-Temperature Stochastic Ising Model

We analyze clustering and (local) recurrence of a standard Markov process model of spatial domain coarsening. The continuous time process, whose state space consists of assignments of +1 or -1 to each site in ${\bf Z}^2$, is the zero-temperature limit of the stochastic homogeneous Ising ferromagnet (with Glauber dynamics): the initial state is chosen uniformly at random and then each site, at rate one, polls its 4 neighbors and makes sure it agrees with the majority, or tosses a fair coin in case of a tie. Among the main results (almost sure, with respect to both the process and initial state) are: clusters (maximal domains of constant sign) are finite for times $t< \infty$, but the cluster of a fixed site diverges (in diameter) as $t \to \infty$; each of the two constant states is (positive) recurrent. We also present other results and conjectures concerning positive and null recurrence and the role of absorbing states.Comment: 16 pages, 1 figur

Osservazioni Citotassonomiche Su Scilla Barbacaprae, Endemismo Cirenaico, E Sue Affinita' Con Scilla Villosa

RIASSUNTOViene analizzato il cariotipo di Scilla barba caprae, specie endemica di Derna (Cirenaica settentrionale). Il risultato di questa indagine, effettuata su bulbi coltivati nell'Orto Botanico di Catania, e stato il rinvenimento di un corredo cromosomico diploide: z = 2n = 2x = 14 = 2L + 2M1 + 2M2 + 2M3S3 + 2M4 + 2S1 + 2S2.La comparazione fra Scilla barba-caprae e Scilla villosa, che e la specie tassonomicamente piu vicina, ha permesso di evidenziare numerose differenze riguardanti sia il cariotipo che il fenotipo, che consentono di separare le due entita a livello specifico.In particolare il cariotipo di Scilla villosa (2n = 20) differisce da quello fondamentale 2n= 16, relativo alle entita appartenenti al ciclo di Scilla peruviana, per avere in piu quattro cromosomi, mentre quello di Scilla barba-caprae (2n = 14) ne differisce per avere due cromosomi in meno e per la presenza della coppia 2M3S3 formatasi in seguito a fenomeni di traslocazione + delezione

How PI3K-derived lipids control cell division

To succeed in cell division, intense cytoskeletal and membrane remodeling are required to allow accurate chromosome segregation and cytoplasm partitioning. Spatial restriction of the actin dynamics and vesicle trafficking define the cell symmetry and equivalent membrane scission events, respectively. Protein complexes coordinating mitosis are recruited to membrane microdomains characterized by the presence of the phosphatidylinositol lipid members (PtdIns), like PtdIns(3,4,5)P3, PtdIns(4,5)P2 and PtdIns(3)P. These PtdIns represent a minor component of cell membranes, defining membrane domain identity, ultimately controlling cytoskeleton and membrane dynamics during mitosis. The coordinated presence of PtdIns(3,4,5)P3 at the cell poles and PtdIns(4,5)P2 at the cleavage furrow controls the polarity of the actin cytoskeleton leading to symmetrical cell division. In the endosomal compartment, the trafficking of PtdIns(3)P positive vesicles allows the recruitment of the protein machinery required for the abscission

Equivalence of switching linear systems by bisimulation

A general notion of hybrid bisimulation is proposed for the class of switching linear systems. Connections between the notions of bisimulation-based equivalence, state-space equivalence, algebraic and input–output equivalence are investigated. An algebraic characterization of hybrid bisimulation and an algorithmic procedure converging in a finite number of steps to the maximal hybrid bisimulation are derived. Hybrid state space reduction is performed by hybrid bisimulation between the hybrid system and itself. By specializing the results obtained on bisimulation, also characterizations of simulation and abstraction are derived. Connections between observability, bisimulation-based reduction and simulation-based abstraction are studied.\ud \u

Scanning Nanocalorimetry at High Cooling Rate of Isotactic Polypropylene

A wide set of cooling scans and subsequent melting behavior of isotactic polypropylene (i-PP) were investigated using differential scanning calorimetry and nanocalorimetry at very high cooling rate. The latter technique offers, indeed, the distinctive possibility to perform heat capacity measurements at rates of more than 1000 K/s, both in cooling and in heating, to characterize the crystallization. When the i-PP sample was solidified with cooling rate larger than 160 K/s, a novel enthalpic process was observed that was related to the mesomorphic phase formation. Furthermore, at cooling rates higher than 1000 K/s, the i-PP sample did not crystallize neither in the α nor in the mesomorphic form. The subsequent heating scan starting from −15 °C showed an exothermic event, between 0 and 30 °C, ascribed to the mesophase cold crystallization