103,451 research outputs found
Progettare futuri possibili : Pluralismo dei paradigmi e Tras-formazione
No full textIl volume Progettare futuri possibili: pluralismo dei paradigmi e tras-formazione è il
frutto di un confronto interdisciplinare nato dalla summer school di ricerca organizzata
dalla Società di ricerca Educativa e Formativa (SIREF) nel settembre 2024,
che esplora in profondità le sfide educative, sociali e culturali del nostro tempo. Il
titolo stesso ne anticipa il percorso: progettare il futuro significa confrontarsi con
la complessità del presente, riconoscendo il pluralismo dei saperi e adottando approcci
trasformativi capaci di generare orizzonti di possibilità
A Multiscale Approach to the Elastic Moduli of Biomembrane
No full textWe develop equilibrium fluctuation formulae for the isothermal elastic moduli of discrete biomembrane models at different scales. We account for the coupling of large stretching and bending strains of triangulated network models endowed with harmonic and dihedral angle potentials, on the basis of the discrete-continuum approach presented in Schmidt and Fraternali (J Mech Phys Solids 60:172–180, 2012). We test the proposed equilibrium fluctuation formulae with reference to a coarse-grained molecular dynamics model of the red blood cell (RBC) membrane (Marcelli et al. in Biophys J 89:2473–2480, 2005; Hale et al. in Soft Matter 5:3603–3606, 2009), employing a local maximum-entropy regularization of the fluctuating configurations (Fraternali et al. in J Comput Phys 231:528–540, 2012). We obtain information about membrane stiffening/softening due to stretching, curvature, and microscopic undulations of the RBC model. We detect local dependence of the elastic moduli over the RBC membrane, establishing comparisons between the present theory and different approaches available in the literature
Existence of Bounded Trajectories Via Upper and Lower Solutions
No full textThe paper deals with the boundary value problem (on the whole line) u''-f(u,u')+g(u)=0, u(-∞)=0, u(+∞)=1, where g is a continuous non-negative function with support [0, 1], and f is a continuous function. By means of a new approach, based on a combination of lower and upper-solutions methods and phase-plane techniques, we prove an existence result for the problem when f is superlinear in u'; by a similar technique, we also get a non-existence one. As an application, we investigate the attractivity of the singular point (0,0) in the phase-plane (u, u'). Applications of these results in the field of front-type solutions for reaction diffusion equations can be found in L. Malaguti, C. Marcelli, Math. Nachr. 242 (2002), 148—16
The Role of Three-Body Interactions on the Equilibrium and Non-Equilibrium Properties of Fluids from Molecular Simulation
No full textThe aim of this work is to use molecular simulation to investigate the role of
three-body interatomic potentials in noble gas systems for two distinct
phenomena: phase equilibria and shear flow. In particular we studied the
vapour-liquid coexisting phase for pure systems (argon, krypton and x enon) and
for an argon-krypton mixture, utilizing the technique called Monte Carlo Gibbs
ensemble. We also studied the dependence of the shear viscosity, pressure and
energy with the strain rate in planar Couette flow, using a non-equilibrium
molecular simulation (NEMD) technique.
The results we present in this work demonstrate that three-body interactions
play an important role in the overall interatomic interactions of noble gases. This
is demonstrated by the good agreement between our simulation results and the
experimental data for both equilibrium and non-equilibrium systems.
The good results for vapour-liquid coexisting phases encourage performing
further computer simulations with realistic potentials. This may improve the
prediction of quantities like critical temperature and density, in particular of
substances for which these properties are difficult to obtain from experiment.
We have demonstrated that use of accurate two- and three-body potentials for
shearing liquid argon and xenon displays significant departure from the
expected strain rate dependencies of the pressure, energy and shear viscosity.
For the first time, the pressure is convincingly observed to vary linearly with an
apparent analytic g&2 dependence, in contrast to the predicted g&3/ 2 dependence
of mode -coupling theory. Our best extrapolation of the zero -shear viscosity for
argon gives excellent agreement (within 1%) with the known experimental data.
To the best of our knowledge, this the first time that such accuracy has been
achieved with NEMD simulations. This encourages performing simulations with
accurate potentials for transport properties
Improved energy estimates for a class of time-dependent perturbed Hamiltonians
No full textWe consider time-dependent perturbations which are relatively bounded with
respect to the square root of an unperturbed Hamiltonian operator, and whose
commutator with the latter is controlled by the full perturbed Hamiltonian. The
perturbation is modulated by two auxiliary parameters, one regulates its
intensity as a prefactor and the other one controls its time-scale via a
regular function, whose derivative is compactly supported in a finite interval.
We introduce a natural generalization of energy conservation in the case of
time-dependent Hamiltonians: the boundedness of the two-parameter unitary
propagator for the physical evolution with respect to the -th power energy
norm for all . We provide bounds of the -th power energy
norms, uniformly in time and in the time-scale parameter, for the unitary
propagators, generated by the time-dependent perturbed Hamiltonian and by the
unperturbed Hamiltonian in the interaction picture. The physically interesting
model of Landau-type Hamiltonians with an additional weak and
time-slowly-varying electric potential of unit drop is included in this
framework.Comment: 22 pages; in the Introduction and in Sect. 5 presentation of the
results improved, Remark 2.6 adde
Adolescence et psychopathologie
No full textMarcelli Daniel, Braconnier Alain, Coslin Pierre G. Adolescence et psychopathologie. In: Bulletin de psychologie, tome 49 n°425, 1996. pp. 476-479
Purely linear response of the quantum Hall current to space-adiabatic perturbations
No full textUsing recently developed tools from space-adiabatic perturbation theory, in particular the construction of a non-equilibrium almost-stationary state, we give a new proof that the Kubo formula for the Hall conductivity remains valid beyond the linear response regime. In particular, we prove that, in quantum Hall systems and Chern insulators, the transverse response current is quantized up to any order in the strength of the inducing electric field. The latter is introduced as a perturbation to a periodic, spectrally gapped equilibrium Hamiltonian by means of a linear potential; existing proofs of the exactness of Kubo formula rely instead on a time-dependent magnetic potential. The result applies to both continuum and discrete crystalline systems modelling the quantum (anomalous) Hall effect
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