782 research outputs found
Aging and Energy Landscapes: Application to Liquids and Glasses
The equation of state for a liquid in equilibrium, written in the potential
energy landscape formalism, is generalized to describe out-of-equilibrium
conditions. The hypothesis that during aging the system explores basins
associated to equilibrium configurations is the key ingredient in the
derivation. Theoretical predictions are successfully compared with data from
molecular dynamics simulations of different aging processes, such as
temperature and pressure jumps.Comment: RevTeX4, 4 pages, 5 eps figure
Liquid stability in a model for ortho-terphenyl
We report an extensive study of the phase diagram of a simple model for
ortho-terphenyl, focusing on the limits of stability of the liquid state.
Reported data extend previous studies of the same model to both lower and
higher densities and to higher temperatures. We estimate the location of the
homogeneous liquid-gas nucleation line and of the spinodal locus. Within the
potential energy landscape formalism, we calculate the distributions of depth,
number, and shape of the potential energy minima and show that the statistical
properties of the landscape are consistent with a Gaussian distribution of
minima over a wide range of volumes. We report the volume dependence of the
parameters entering in the Gaussian distribution (amplitude, average energy,
variance). We finally evaluate the locus where the configurational entropy
vanishes, the so-called Kauzmann line, and discuss the relative location of the
spinodal and Kauzmann loci.Comment: RevTeX 4, 8 pages, 8 eps figure
Non-Gaussian energy landscape of a simple model for strong network-forming liquids: accurate evaluation of the configurational entropy
We present a numerical study of the statistical properties of the potential
energy landscape of a simple model for strong network-forming liquids. The
model is a system of spherical particles interacting through a square well
potential, with an additional constraint that limits the maximum number of
bonds, , per particle. Extensive simulations have been carried out
as a function of temperature, packing fraction, and . The dynamics
of this model are characterized by Arrhenius temperature dependence of the
transport coefficients and by nearly exponential relaxation of dynamic
correlators, i.e. features defining strong glass-forming liquids. This model
has two important features: (i) landscape basins can be associated with bonding
patterns; (ii) the configurational volume of the basin can be evaluated in a
formally exact way, and numerically with arbitrary precision. These features
allow us to evaluate the number of different topologies the bonding pattern can
adopt. We find that the number of fully bonded configurations, i.e.
configurations in which all particles are bonded to neighbors, is
extensive, suggesting that the configurational entropy of the low temperature
fluid is finite. We also evaluate the energy dependence of the configurational
entropy close to the fully bonded state, and show that it follows a logarithmic
functional form, differently from the quadratic dependence characterizing
fragile liquids. We suggest that the presence of a discrete energy scale,
provided by the particle bonds, and the intrinsic degeneracy of fully bonded
disordered networks differentiates strong from fragile behavior.Comment: Final version. Journal of Chemical Physics 124, 204509 (2006
Energy landscape of a simple model for strong liquids
We calculate the statistical properties of the energy landscape of a minimal
model for strong network-forming liquids. Dynamics and thermodynamic properties
of this model can be computed with arbitrary precision even at low
temperatures. A degenerate disordered ground state and logarithmic statistics
for the energy distribution are the landscape signatures of strong liquid
behavior. Differences from fragile liquid properties are attributed to the
presence of a discrete energy scale, provided by the particle bonds, and to the
intrinsic degeneracy of topologically disordered networks.Comment: Revised versio
Looking for the right balance between human and economic costs during COVID-19 outbreak
Since the beginning of Coronavirus 2019 (COVID-19) disease outbreak, there has been a heated debate about public health measures, as they can presumably reduce human costs in the short term but can negatively impact economies and well-being over a longer period. Materials and methods: To study the relationship between health and economic impact of COVID-19, we conducted a secondary research on Italian regions, combining official data (mortality due to COVID-19 and contractions in value added of production for a month of lockdown). Then, we added the tertiles of the number of people tested for COVID-19 and those of health aids to evaluate the correspondence with the outcome measures. Results: Five regions out of 20, the most industrialized northern regions, which were affected both earlier and more severely by the outbreak, registered both mortality and economic value loss above the overall medians. The southern regions, which were affected later and less severely, had low mortality and less economic impact. Conclusions: Our analysis shows that considering health and economic outcomes in the assessment of response to pandemics offers a bigger picture perspective of the outbreak and could allow policymakers and health managers to choose systemic, 'personalized' strategies, in case of a feared second epidemic wave
Equilibrium and out of equilibrium thermodynamics in supercooled liquids and glasses
We review the inherent structure thermodynamical formalism and the
formulation of an equation of state for liquids in equilibrium based on the
(volume) derivatives of the statistical properties of the potential energy
surface. We also show that, under the hypothesis that during aging the system
explores states associated to equilibrium configurations, it is possible to
generalize the proposed equation of state to out-of-equilibrium conditions. The
proposed formulation is based on the introduction of one additional parameter
which, in the chosen thermodynamic formalism, can be chosen as the local minima
where the slowly relaxing out-of-equilibrium liquid is trapped.Comment: 7 pages, 4 eps figure
Diffusivity and configurational entropy maxima in short range attractive colloids
We study tagged particle diffusion at large packing fractions, for a model of
particles interacting with a generalized Lennard-Jones 2n-n potential, with
large n. The resulting short-range potential mimics interactions in colloidal
systems. In agreement with previous calculations for short-range potential, we
observe a diffusivity maximum as a function of temperature. By studying the
temperature dependence of the configurational entropy -- which we evaluate with
two different methods -- we show that a configurational entropy maximum is
observed at a temperature close to that of the diffusivity maximum. Our
findings suggest a relationbetween dynamics and number of distinct states for
short-range potentials.Comment: 4 pages, 3 figures, submited to Physical Review Lette
Physics of the liquid-liquid critical point
Within the inherent structure (IS) thermodynamic formalism introduced by
Stillinger and Weber [F. H. Stillinger and T. A. Weber, Phys. Rev. A {\bf 25},
978 (1982)] we address the basic question of the physics of the liquid-liquid
transition and of density maxima observed in some complex liquids such as water
by identifying, for the first time, the statistical properties of the potential
energy landscape (PEL) responsible for these anomalies.
We also provide evidence of the connection between density anomalies and the
liquid-liquid critical point. Within the simple (and physically transparent)
model discussed, density anomalies do imply the existence of a liquid-liquid
transition.Comment: Physical Review Letters, in publicatio
- …