Sapienza University of Rome

About: Sapienza University of Rome is a education organization based out in Rome, Lazio, Italy. It is known for research contribution in the topics: Population & Medicine. The organization has 62002 authors who have published 155468 publications receiving 4397244 citations. The organization is also known as: La Sapienza & Università La Sapienza di Roma.

The Widom line as the crossover between liquid-like and gas-like behaviour in supercritical fluids

Abstract: According to textbook definitions 1 , there exists no physical observable able to distinguish a liquid from a gas beyond the critical point, and hence only a single fluid phase is defined. There are, however, some thermophysical quantities, having maxima that define a line emanating from the critical point, named ‘the Widom line’ 2 in the case of the constant-pressure specific heat. We determined the velocity of nanometric acoustic waves in supercritical fluid argon at high pressures by inelastic X-ray scattering and molecular dynamics simulations. Our study reveals a sharp transition on crossing the Widom line demonstrating how the supercritical region is actually divided into two regions that, although not connected by a first-order singularity, can be identified by different dynamical regimes: gas-like and liquid-like, reminiscent of the subcritical domains.

Pure Sertoli Cell Cultures: A New Model for the Study of Somatic—Germ Cell Interactions

Abstract: A new technique involving a brief hypotonic treatment was developed for obtaining pure rat Sertoli cell cultures. This method for the selective removal of the germ cells present in Sertoli cell enriched cultures (SCEC) Is based on the differential response of the two cell types to changes in osmolarity. It was found that the optimal conditions for germ cell detachment without Sertoli cell impairment consist of incubation for 2.5 minutes at 20 C in 20 m TRISHCI. When compared with SCEC, the Sertolicell-only cultures (SCOC) thus obtained retain unaltered morphologic features and responsiveness to FSH stimulation (morphologic modifications and 17 β-estradiol secretion). The availability of pure Sertoli cell cultures (Ie, free of contaminating germ cells) provides an advantage in the study of their metabolic activity. Moreover, with this technique it is feasible to compare Sertoli cell function in association with germ cells to function in the absence of germ cells.

Macroscopic Fluctuation Theory for Stationary Non-Equilibrium States

Abstract: We formulate a dynamical fluctuation theory for stationary non-equilibrium states (SNS) which is tested explicitly in stochastic models of interacting particles. In our theory a crucial role is played by the time reversed dynamics. Within this theory we derive the following results: the modification of the Onsager–Machlup theory in the SNS; a general Hamilton–Jacobi equation for the macroscopic entropy; a non-equilibrium, nonlinear fluctuation dissipation relation valid for a wide class of systems; an H theorem for the entropy. We discuss in detail two models of stochastic boundary driven lattice gases: the zero range and the simple exclusion processes. In the first model the invariant measure is explicitly known and we verify the predictions of the general theory. For the one dimensional simple exclusion process, as recently shown by Derrida, Lebowitz, and Speer, it is possible to express the macroscopic entropy in terms of the solution of a nonlinear ordinary differential equation; by using the Hamilton–Jacobi equation, we obtain a logically independent derivation of this result.