51 research outputs found
Scaling properties in the adsorption of ionic polymeric surfactants on generic nanoparticles of metallic oxides by mesoscopic simulation
We study the scaling of adsorption isotherms of polyacrylic dispersants on
generic surfaces of metallic oxides as a function of the number of
monomeric units, using Electrostatic Dissipative Particle Dynamics simulations.
The simulations show how the scaling properties in these systems emerge and how
the isotherms rescale to a universal curve, reproducing reported experimental
results. The critical exponent for these systems is also obtained, in perfect
agreement with the scaling theory of deGennes. Some important applications are
mentioned.Comment: 10 pages, 6 figure
Multiscale Modeling of the effect of Pressure on the Interfacial Tension and other Cohesion Parameters in Binary Mixtures
We study and predict the interfacial tension, solubility parameters and
Flory-Huggins parameters of binary mixtures as functions of pressure and
temperature, using multiscale numerical simulation. A mesoscopic approach is
proposed for simulating the pressure dependence of the interfacial tension for
binary mixtures, at different temperatures, using classical Dissipative
Particle Dynamics (DPD). The thermodynamic properties of real systems are
reproduced via the parametrization of the repulsive interaction parameters as
functions of pressure and temperature via Molecular Dynamics simulations. Using
this methodology, we calculate and analyze the cohesive density energy and the
solubility parameters of different species obtaining excellent agreement with
reported experimental behavior. The pressure- and temperature-dependent
Flory-Huggins and repulsive DPD interaction parameters for binary mixtures are
also obtained and validated against experimental data. This multiscale
methodology offers the benefit of being applicable for any species and under
difficult or non-feasible experimental conditions, at a relatively low
computational cost.Comment: 11 pages, 4figures, 4 table
Study of Interfacial Tension between an Organic Solvent and Aqueous Electrolyte Solutions Using Electrostatic Dissipative Particle Dynamics Simulations
The study of the modification of interfacial properties between an organic
solvent and aqueous electrolyte solutions is presented by using electrostatic
Dissipative Particle Dynamics (DPD) simulations. In this article the
parametrization for the DPD repulsive parameters aij for the electrolyte
components is calculated considering the dependence of the Flory-Huggins \c{hi}
parameter on the concentration and the kind of electrolyte added, by means of
the activity coefficients. In turn, experimental data was used to obtain the
activity coefficients of the electrolytes as a function of their concentration
in order to estimate the \c{hi} parameters and then the aij coefficients. We
validate this parametrization through the study of the interfacial tension in a
mixture of n-dodecane and water, varying the concentration of different
inorganic salts (NaCl, KBr, Na2SO4 and UO2Cl2). The case of HCl in the mixture
n-dodecane/water was also analyzed and the results presented. Our simulations
reproduce the experimental data in good agreement with previous work, showing
that the use of activity coefficients to obtain the repulsive DPD parameters
aij as a function of concentration is a good alternative for these kinds of
systems.Comment: 18 pp., 6 figures, 1 tabl
Parametrisation in electrostatic DPD Dynamics and Applications
A brief overview of mesoscopic modelling via dissipative particle dynamics is
presented, with emphasis on the appropriate parametrisation and how to
calculate the relevant parameters for given realistic systems. The dependence
on concentration and temperature of the interaction parameters is also
considered, as well as some applications.Comment: 28 pages, 12 figures in Selected Topics of Computational and
Experimental Fluid Mechanics, Environmental Science and Engineering, J. Klapp
et al. (eds.), Springer Verlag 201
Quantum phases of a three-level matter-radiation interaction model using coherent states with different cooperation numbers
We use coherent states as trial states for a variational approach to study a
system of a finite number of three-level atoms interacting in a dipolar
approximation with a one-mode electromagnetic field. The atoms are treated as
semi-distinguishable using different cooperation numbers and representations of
SU(3). We focus our analysis on the quantum phases of the system as well as the
behavior of the most relevant observables near the phase transitions. The
results are computed for all three possible configurations (,
and ) of the three-level atoms.Comment: 9 pages, 13 figures. arXiv admin note: text overlap with
arXiv:1712.0188
Mirror symmetry in the energy spectra of -level systems
The energy spectrum of a system of atoms of levels interacting with
a one-mode electromagnetic field is studied in the dipole and rotating wave
approximations. We find that, under the resonant condition, it exhibits a
mirror symmetry with respect to the energy where the total number of
excitations. Thus, for any eigenstate with energy
there exists a related eigenstate with
energy via the unitary parity operator in the number of photons
. This is independent of the dipolar coupling between the levels. We give
explicit examples for -level systems.Comment: 5 pages, 4 figure
A triple point in 3-level systems
The energy spectrum of a 3-level atomic system in the -configuration is
studied. This configuration presents a triple point independently of the number
of atoms, which remains in the thermo- dynamic limit. This means that in a
vicinity of this point any quantum fluctuation will drastically change the
composition of the ground state of the system. We study the expectation values
of the atomic population of each level, the number of photons, and the
probability distribution of photons at the triple point.Comment: 5 pages, 8 figure
Variational Study of - and -Atomic Configurations Interacting with an Electromagnetic Field of Modes
A study of the - and -atomic configurations under dipolar
interaction with modes of electromagnetic radiation is presented. The
corresponding quantum phase diagrams are obtained by means of a variational
procedure. Both configurations exhibit normal and collective (super-radiant)
regimes. While the latter in the -configuration divides itself into
subregions, corresponding to each of the modes, that in the
-configuration may be divided into or subregions depending on
whether the field modes divide the atomic system into separate subsystems
or not.
Our variational procedure compares well with the exact quantum solution. The
properties of the relevant field and matter observables are obtained.Comment: 8 pages, 7 figures, 4 table
A semi-classical versus quantum description of the ground state of three-level atoms interacting with a one-mode electromagnetic field
We consider three-level atoms (or systems) interacting with a one-mode
electromagnetic field in the dipolar and rotating wave approximations. The
order of the quantum phase transitions is determined explicitly for each of the
configurations , and , with and without detuning. The
semi-classical and exact quantum calculations for both the expectation values
of the total number of excitations and photon
number have an excellent correspondence as functions
of the control parameters. We prove that the ground state of the collective
regime obeys sub-Poissonian statistics for the and distribution
functions. Therefore, their corresponding fluctuations are not well described
by the semiclassical approximation. We show that this can be corrected by
projecting the variational state to a definite value of .Comment: 28 page
On the Superradiant Phase in Field-Matter Interactions
We show that semi-classical states adapted to the symmetry of the Hamiltonian
are an excellent approximation to the exact quantum solution of the ground and
first excited states of the Dicke model. Their overlap to the exact quantum
states is very close to 1 except in a close vicinity of the quantum phase
transition. Furthermore, they have analytic forms in terms of the model
parameters and allow us to calculate analytically the expectation values of
field and matter observables. Some of these differ considerably from results
obtained via the standard coherent states, and by means of Holstein-Primakoff
series expansion of the Dicke Hamiltonian. Comparison with exact solutions
obtained numerically support our results. In particular, it is shown that the
expectation values of the number of photons and of the number of excited atoms
have no singularities at the phase transition. We comment on why other authors
have previously found otherwise
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