Papers by Pedro J. Colmenares
In a recent article, the author derived a new generalized Langevin equation (NGLE) and its associ... more In a recent article, the author derived a new generalized Langevin equation (NGLE) and its associated Fokker-Planck equation (FPE) of a Brownian particle in a parabolic potential where the thermal bath, consisting of N harmonic oscillators, interacts bilinearly with the external field. The time needed for the system to reach a steady state is longer than that for the classical version (CGLE). We found a completely different scenario for the entropy than when the interaction of the field with the heat bath is off. The new findings for the entropy and its rate physically improve the thermodynamics description of the system.
Physical review, Jul 12, 2023
This article revisits the fluctuation-dissipation relationship of a generalized Brownian particle... more This article revisits the fluctuation-dissipation relationship of a generalized Brownian particle constrained in a harmonic potential and immersed in a thermal bath whose degrees of freedom also interact with the external field. The generalized Langevin equation put forth herein keeps its original form. The different terms now depend on a compound strength related to those of the field and bath oscillators. The resulting theorem keeps Kubo's original form with the memory kernel depending on the frequency of the field. It has the consequence that friction is not a constant but is a function of the field frequency as predicted by molecular dynamics simulations. The position particle distribution and the Fokker-Planck equation associated with the generalized Langevin equation are also derived.
Physical review, Apr 6, 2022
The Journal of Physical Chemistry, 1986
Journal of Molecular Structure: THEOCHEM, 1997
In this paper we derive analytical expressions for the optical susceptibility of a two-level syst... more In this paper we derive analytical expressions for the optical susceptibility of a two-level system immersed in a thermal bath and interacting with an external electromagnetic field, where both of them are considered as noise sources. The dynamics of the system is described by a set of optical stochastic Bloch equations. The noise sources are modeled as Ornstein-Uhlenbeck processes. The optical stochastic Bloch equations are perturbatively solved up to second order in the external field. We found that each noise affects the dynamics in a different manner. Thus, at first order, the bath modifies the transverse relaxation time, whereas the effect of a random field can only be appreciated if the expansion is calculated up to second order, where correlations begin to be important.
Journal of Molecular Structure: THEOCHEM, 2006
The diffusion dynamics of a Yukawa fluid confined in an attractive planar slit pore was studied b... more The diffusion dynamics of a Yukawa fluid confined in an attractive planar slit pore was studied by solving the Smoluchowski/Hypernnetedchain equation for the mean first passage times. We show how the time it takes for a particle to get adsorbed at the wall surface is modulated by the effective potential barrier originated by the fluid local density profile. The effect of wetting layering on the apparent constant for the transverse diffusion towards an attractive pore wall is evaluated.
Condensed Matter Physics, 2005
The diffusion dynamics of ions inside a planar slit with a high constant surface charge density w... more The diffusion dynamics of ions inside a planar slit with a high constant surface charge density was studied by solving the Smoluchowski/Hypernneted-Chain equation for the mean first passage times. The behavior of local properties, such as the potential of mean force, is correlated with the time it takes for an ion to get adsorbed at the surface, and also with macroscopic properties like the salt rejection coefficient and the apparent diffusion constant in porous media, as a function of pore size. We show that the width of the walls has an important effect on the transverse ion diffusion process.
Physics Letters A, 1995
We present a methodology, based on the use of a theorem due to Novikov, to solve the optical stoc... more We present a methodology, based on the use of a theorem due to Novikov, to solve the optical stochastic Bloch equations for a two-level system up to first order in the external field in the presence of a heat reservoir. Two cases are studied. In the first, a white noise bath is considered, while in the second colored noise (Omstein-Uhlenbeck process) is analysed. Elsevier Science B.v.
Physics Letters A, 1997
We have derived a formalism to study high-order effects of the electromagnetic field on the optic... more We have derived a formalism to study high-order effects of the electromagnetic field on the opticai response of a two-level molecular system immersed in a thermal bath. We report expressions for the absorption coefficient and refraction index in terms of the field amplitude and thermal noise parameters.
Physica A: Statistical Mechanics and its Applications, 2001
ABSTRACT It is shown that diffusion's dynamic on any discrete array, including fracta... more ABSTRACT It is shown that diffusion's dynamic on any discrete array, including fractals, can be described by piecewise linear maps. The proposed method, which is geometric in its nature, allows to construct a system of piecewise linear maps based on the nearest neighbor coupling matrix of Cosenza and Kapral. We propose that the dynamics of the map system describes the diffusion dynamics on the array, which in our case is the Sierpinski gasket, due to the existence of an intrinsic homeomorphism between them. It is found that there is a one-to-one correspondence between the partitions of the map and the cells of the fractal. This fact allows to generate specific diffusion trajectories on the fractal in order to study the particle dwell time distribution. Since the method proposed here is completely deterministic, the diffusion on the map is anomalous: the mean square displacement scales with time to a power very near to 2. It is also shown that, as a consequence of the lattice autosimilarity and the finite precision of the calculations, this parameter remains fixed for several levels of construction of the Sierpinski gasket.
Physica A: Statistical Mechanics and its Applications, 2006
This paper derives the effective force between particles in the framework of dissipative particle... more This paper derives the effective force between particles in the framework of dissipative particle dynamics (DPD) by using the formalism discussed by Revenga et al. [Int. J. Mod. Phys. C 9 (1998) 1319]. In order to mimic realistic systems, we obtained explicit expressions for the effective dissipative force and stochastic intensity force for a point DPD particle interacting with a
Optics Communications, 2011
ABSTRACT We present in this note the analytical solution of the optical Bloch equations for diffe... more ABSTRACT We present in this note the analytical solution of the optical Bloch equations for different scenarios of the parameter space. Our method partially follows the reported by H-R. Noh and W. Jhe [Opt. Commun. 283, (2010) 2353]. However, it differs substantially with the analytical solution reported by these authors. We use the exact solution provided by numerical standard algorithms as a pattern for comparison purposes. We find out a perfect matching of our solution and the numerical one.
Molecular Simulation, 2003
We investigate the flow of a suspension through a constriction by means of the mesoscopic techniq... more We investigate the flow of a suspension through a constriction by means of the mesoscopic technique known as dissipative particle dynamics (DPD). The dispersed phase was modeled as a set of soft spheres interacting through a conservative force while suspended and continuum phases interact via DPD forces. It is shown that a Poiseuille steady state is achieved in the presence
Molecular Simulation, 2007
... Understanding Molecular Simulation: From Algorithms to Applications , San Diego: Academic Pre... more ... Understanding Molecular Simulation: From Algorithms to Applications , San Diego: Academic Press. ... referred to as paper I, a statistical based RMC (SRMC) method was suggested and applied it with great success to liquid water [44. da Silva, FLB, Degrève, L., Olivares-Rivas, W ...
Journal of Physics B: Atomic, Molecular and Optical Physics, 1995
... (10) Here we have defined the function f(w0, l/?2) by: where 1 / ? ~ + ~ l/?z fnr (n = 0. 1, ... more ... (10) Here we have defined the function f(w0, l/?2) by: where 1 / ? ~ + ~ l/?z fnr (n = 0. 1, 2, 3, . . .) It is worth noticing that this result for the average coherence is formally exact. ... At this poinl, it isworth mentioning that an alternative solution for this limit has been explored by us. ...
The Journal of Chemical Physics, 1988
ABSTRACT We report the numerical solution of two new integral equations for the diffused electric... more ABSTRACT We report the numerical solution of two new integral equations for the diffused electrical double layer referred to as WLMB/MSA and WLMB/HNC. The WLMB/MSA uses the homogeneous bulk MSA approximation for the direct correlation function and predicts surface potentials that fare within 5% of the reported Monte Carlo data. The effect of the ionic diameter on the surface potential is studied and a behavior similar to that reported for the HNC/MSA is found. The use of the HNC approximation for the bulk electrolyte direct correlation function improves the description of the density profile for a high concentraiton but gives poor results for low concentrations.
The Journal of Chemical Physics, 2013
We derive expressions for the transverse diffusion coefficient D(z) and the average persistence t... more We derive expressions for the transverse diffusion coefficient D(z) and the average persistence time τ(z; L) within a layer of width L, for particles of a non-homogeneous fluid enclosed in a planar nanopore. The method allows the direct evaluation of these position-dependent dynamical quantities from the equilibrium local particle density profile. We use results for the density and persistence time profiles from the virtual layer molecular dynamics method to numerically assess the significance of the Smoluchowski approximation.
Journal of Chemical Education, 1997
Thermodynamics and Controversy I suspect that there may be a fourth law of thermodynamics: discou... more Thermodynamics and Controversy I suspect that there may be a fourth law of thermodynamics: discourse on any thermodynamic topic increases spontaneously (and perhaps exponentially). This reflects the importance of thermodynamics, and its success. Albert Einstein called thermodynamics, "…the only physical theory of universal content concerning which I am convinced that, within the framework of the applicability of its basic concepts, it will never be overthrown." Even a hint of an exception to thermodynamic principles generates the closest possible scrutiny and considerable discussion. The letter that begins below and those that follow beginning on page 281 fill 13 pages in all. They consist of criticisms and a reply related to a three-page paper by José Belandria that appeared in February, 1995. The author's reply to his critics is longer than the original paper, as is one of the criticisms. The critics have had their say, the author has responded, and, on behalf of all the critics, Robert Freeman has prepared a reply to that response. At this point we can consider this issue closed, and the Journal will publish no further comments on Belandria's paper, nor on the criticisms of it that appear here. We thank all of the contributors to this discussion for the time and effort they have devoted to clarifying the situation.
Journal of Chemical Education, 1997
Thermodynamics and Controversy I suspect that there may be a fourth law of thermodynamics: discou... more Thermodynamics and Controversy I suspect that there may be a fourth law of thermodynamics: discourse on any thermodynamic topic increases spontaneously (and perhaps exponentially). This reflects the importance of thermodynamics, and its success. Albert Einstein called thermodynamics, "…the only physical theory of universal content concerning which I am convinced that, within the framework of the applicability of its basic concepts, it will never be overthrown." Even a hint of an exception to thermodynamic principles generates the closest possible scrutiny and considerable discussion. The letter that begins below and those that follow beginning on page 281 fill 13 pages in all. They consist of criticisms and a reply related to a three-page paper by José Belandria that appeared in February, 1995. The author's reply to his critics is longer than the original paper, as is one of the criticisms. The critics have had their say, the author has responded, and, on behalf of all the critics, Robert Freeman has prepared a reply to that response. At this point we can consider this issue closed, and the Journal will publish no further comments on Belandria's paper, nor on the criticisms of it that appear here. We thank all of the contributors to this discussion for the time and effort they have devoted to clarifying the situation.
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Papers by Pedro J. Colmenares