# L. VelazquezUniversidad Católica del Norte (Chile) · Department of Physics

L. Velazquez

Ph.D. on Physics

## About

86

Publications

13,797

Reads

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547

Citations

Introduction

L. Velazquez received Ph.D. degree on Physical Sciences from the Higher Institute of Technologies and Applied Sciences of Havana in 2007. Since 2008, he has been working at Department of Physics, Universidad Católica del Norte, Antofagasta, Chile. He has specialized on statistical mechanics and its interrelations with other disciplines, such as astrophysics, condensed matter, computational physics and mathematical physics.

Additional affiliations

Education

September 2003 - July 2007

**Instituto Superior de Tecnología y Ciencias Aplicadas**

Field of study

- Physics

November 2000 - July 2003

**Instituto Superior de Ciencias y Tecnología Nucleares**

Field of study

- Nuclear Physics

September 1996 - July 2000

**Instituto Superior de Ciencias y Tecnología Nucleares**

Field of study

- Nuclear Physics

## Publications

Publications (86)

Recently, Velazquez and Curilef proposed a methodology to extend Monte Carlo algorithms based on a canonical ensemble which aims to overcome slow sampling problems associated with temperature-driven discontinuous phase transitions. We show in this work that Monte Carlo algorithms extended with this methodology also exhibit a remarkable efficiency n...

Quantum mechanics and classical statistical mechanics are two physical
theories that share several analogies in their mathematical apparatus and
physical foundations. In particular, classical statistical mechanics is
hallmarked by the complementarity between two descriptions that are unified in
thermodynamics: (i) the parametrization of the system...

Recently (arXiv:0910.2870), we have derived a fluctuation theorem for systems
in thermodynamic equilibrium compatible with anomalous response functions, e.g.
the existence of states with \textit{negative heat capacities} $C<0$. In this
work, we show that the present approach of the fluctuation theory introduces
new insights in the understanding of...

Starting from an axiomatic perspective, \emph{fluctuation geometry} is
developed as a counterpart approach of inference geometry. This approach is
inspired on the existence of a notable analogy between the general theorems of
\emph{inference theory} and the the \emph{general fluctuation theorems}
associated with a parametric family of distribution...

General aspects about the thermodynamics of astrophysical systems are discussed, overall, those concerning to astrophysical systems in mutual interaction (or the called \emph{open astrophysical systems}). A special interest is devoted along the paper to clarify several misconceptions that are still common in the recent literature, such as the direc...

We explore the existing isomorphisms among physical theories of micro and macrophysics, such as the ones existing between classical mechanics and thermodynamics (contact geometry) or quantum mechanics and statistical mechanics (uncertainty relations and complementarity associated with the statistical framework). These isomorphisms motivate a reform...

We survey the main results emerging in the rapidly developing field that considers the geometry of thermodynamics and statistical mechanics. Our ideas of stability depend on variational principles – Maximum Entropy together with Least Action (and the isomorphic Least Exertion) – and this stability (invariance in time) indicates the centrality of th...

In our previous empirical study using digital platforms, we observed that the student workload follows an inverse relation with the notion of learning rate (an application of the kinematic notion of speed contextualized to the learning process). Motivates by this finding, we attempt to estimate the learning rate using a different source of informat...

We present a quantitative study of an online course developed during COVID19 sanitary emergency in Chile. We rebuild the teaching-learning processes considering the activity logs of digital platforms in order to answer the question How do our students study? The analysis evidences the complex adaptive character of the academic environment, which ex...

We study the influence of evaporation (the escape of constituents) on the thermodynamics of a self-gravitating non-relativistic gas of fermions in the framework of Newtonian gravitation. For this purpose, it is reconsidered the called \emph{fermionic King model} introduced by Ruffini and Stella in the context of dark matter halos problems [Astron....

After reviewing several aspects about the thermodynamics of self-gravitating systems that undergo the evaporation (escape) of their constituents, some recent results obtained in the framework of fermionic King model
are applied here to the analysis of galactic halos considering warm dark matter (WDM) particles. According to the present approach, th...

The Chi distribution is a continuous probability distribution of a random variable obtained from the positive square root of the sum of k squared variables, each coming from a standard Normal distribution (mean = 0 and variance = 1). The variable k indicates the degrees of freedom. The usual expression for the Chi distribution can be generalised to...

We investigate the Jordan–Brans–Dicke action in the cosmological scenario of FLRW spacetime with zero spatially curvature and with an extra scalar field minimally coupled to gravity as matter source. The field equations are studied in two ways. The method of group invariant transformations, i.e., symmetries of differential equations apply in order...

Motivated by the precedent study of Ordenes-Huanca and Velazquez [JSTAT \textbf{093303} (2016)], we address the study of a simple model of a pure non-neutral plasma: a system of identical non-relativistic charged particles confined under an external harmonic field with frequency $\omega$. We perform the equilibrium thermo-statistical analysis in th...

Motivated by the precedent study of Ordenes-Huanca and Velazquez [JSTAT \textbf{093303} (2016)], we address the study of a simple model of a pure non-neutral plasma: a system of identical non-relativistic charged particles confined under an external harmonic field with frequency $\omega$. We perform the equilibrium thermo-statistical analysis in th...

The γ-exponential models were previously proposed as a phenomenological attempt to characterize the properties of stellar systems with a quasi-stationary evolution under the incidence evaporation: e.g.: globular clusters. They represent a parametric family of distributions that unify profiles with isothermal cores and polytropic haloes, thus provid...

We investigate the Jordan-Brans-Dicke action in the cosmological scenario of FLRW spacetime with zero spatially curvature and with an extra scalar field minimally coupled to gravity as matter source. The field equations are studied with two ways. The method of group invariant transformations, i.e., symmetries of differential equations, applied in o...

Conference at the Conference "Entropy 2018: From Physics to Information Sciences and Geometry", Barcelona, May 14-16 Special section: Fourier 250th Birthday: Geometric Theory of Thermodynamics.

p>El desarrollo de habilidades relacionadas con la modelación es un aspecto esencial en la enseñanza de las ciencias hoy en día. El presente trabajo ilustra una propuesta de cómo desarrollar habilidades de modelación físico-matemáticas desde las ecuaciones más simples de la hidrodinámica, es decir, la ecuación de Bernoulli y la ecuación de continui...

This work is devoted to the thermodynamics of gravitational clustering, a collective phenomenon with a great relevance in the N-body cosmological problem. We study a classical self-gravitating gas of identical non-relativistic particles defined on the sphere S^3 ⊂ R^4 by considering gravitational interaction that corresponds to this geometric space...

Experimental studies of non-neutral plasmas in magnetic traps undergo, in some degree of affectation, the incidence of evaporation. For example, the existence of a finite threshold energy $\varepsilon_{c}$ for the escaping of plasma constituents can be favored by the external electrostatic forces near the grounded conducting walls of a cylindrical...

In this work, the normal modes of a two-dimensional oscillating system have been studied from a theoretical and experimental point of view. The normal frequencies predicted by the Hessian matrix for a coupled two-dimensional particle system are compared to those obtained for a real system consisting of two oscillating smartphones coupled one to the...

We introduce a parametric family of models to characterize the properties of astrophysical systems in a quasi-stationary evolution under the incidence evaporation. We start from an one-particle distribution fγ (q, p|β,s) that considers an appropriate deformation of Maxwell-Boltzmann form with inverse temperature β, in particular, a power-law trunca...

Fluctuation geometry was recently proposed as a counterpart approach of Riemannian geometry of inference theory (information geometry), which describes the geometric features of the statistical manifold M of random events that are described by a family of continuous distributions dpξ(x|θ). This theory states a connection among geometry notions and...

We study effects of evaporation on thermo-statistics of rotating 2D non-screened plasma. This system is imperfectly confined by an external homogeneous magnetic field that is non-vanishing in a finite space region only. We assume that constituting particles can only move in a plane and the magnetic field acts on a circular region in the perpendicul...

Velazquez and Curilef have proposed a methodology to extend Monte Carlo algorithms that are based on canonical ensemble. According to our previous study, their proposal allows us to overcome slow sampling problems in systems that undergo any type of temperature-driven phase transition. After a comprehensive review about ideas and connections of thi...

Smartphone' acceleration sensors have got useful applications in standard physical situations. We have taken advantage of its capabilities in a number of Physics experiments and perform them in a series of examples within classical mechanical and kinematic situations such as free and damped oscillations due to Earth's gravity. By properly connectin...

"Riemannian geometry of fluctuation theory: A counterpart approach of information geometry" is a contribution presented at the XIX Chilean Physics Symposium (2014). Extended notes of this presentation can be found at https://www.researchgate.net/publication/303980516

Neste trabalho foi utilizado o sensor de aceleração de um smatphone em dois experimentos a fim de estudar o movimento circular uniforme e uniformemente acelerado. Os dados coletados em ambos os experimentos foram usados para obter a velocidade angular e a aceleração angular, respectivamente. Os resultados obtidos com o sensor de aceleração apresent...

We introduce a parametric family of models in order to characterize the properties of astrophysical systems in quasi-stationary evolution under the influence of evaporation. We start from a one-particle distribution fγ q, p∣β, εe that is based on an appropriate deformation of Maxwell─Boltzmann form with inverse temperature β and, in particular, a p...

This work deals with thermo-statistical approaches for describing
phenomenon of gravitational clustering in cosmology. We have introduced
a family of N-body Hamiltonian toy models that describe self-gravitating
gas embedded on a n-sphere Sn within a n+1-dimensional real
space Rn+1. The closed character of these Riemannian
manifolds avoids the incid...

Fluctuation geometry was recently proposed as a counterpart approach of
Riemannian geometry of inference theory. This theory describes the geometric
features of the statistical manifold $\mathcal{M}$ of random events that are
described by a family of continuous distributions $dp(x|\theta)$. A main goal
of this work is to clarify the statistical rel...

Classical molecular dynamics (CMD) simulations were carried out to optimizesilicon oxide interfaces with (100), (111), and (110) silicon surfaces. A three body interatomic potential (modified version of Stillinger-Weber) was used to model the interactions between the species. The resulting overall stress energies and average bond lengths and angles...

In this paper, smartphone acceleration sensors were used to perform a quantitative analysis of mechanical coupled oscillations. Symmetric and asymmetric normal modes were studied separately in the first two experiments. In the third, a coupled oscillation was studied as a combination of the normal modes. Results indicate that acceleration sensors o...

The mobile acceleration sensor has been used to in Physics experiments on
free and damped oscillations. Results for the period, frequency, spring
constant and damping constant match very well to measurements obtained by other
methods. The Accelerometer Monitor application for Android has been used to get
the outputs of the sensor. Perspectives for...

The scattering of particles in fractal superlattices has been analyzed by means of the transfer matrix method. The fractal superlattice consists of alternating layers of semiconductor materials following the rule of a Cantor set. This problem can be represented by a model of quantum particles scattering in piecewise constant potential wells. Fracta...

Previously, an extended approach of equilibrium classical fluctuation theory was developed compatible with the existence of anomalous response functions, e.g. states with negative heat capacities. Now, the geometric aspects associated with this new framework are analyzed. The analysis starts from the so-called reparametrization invariance: a specia...

Usually one can find three subjects in the first year of the syllabus of any technical engineering career, namely, calculus, general physics and programming. Being physics a matter lying on the grounds of technical engineering it becomes naturally appropriate to introduce the use of calculus and programming as useful tools in the context of a physi...

Riemannian statistics geometry is proposed in this work as a counterpart approach of inference geometry. This geometry framework is inspired on the existence of a notable analogy between the general theorems of inference theory and the the general fluctuation theorems associated with a parametric family of distribution functions $dp(I|\theta)$, whi...

It is developed a Riemannian reformulation of classical statistical mechanics for systems in thermodynamic equilibrium, which arises as a natural extension of Ruppeiner geometry of thermodynamics. The present proposal leads to interpret entropy $\mathcal{S}_{g}(I|\theta)$ and all its associated thermo-statistical quantities as purely geometric noti...

In this work, we discuss the implications of a recently obtained equilibrium
fluctuation-dissipation relation on the extension of the available Monte Carlo
methods based on the consideration of the Gibbs canonical ensemble to account
for the existence of an anomalous regime with negative heat capacities $C<0$.
The resulting framework appears as a s...

Previously, we have presented a methodology to extend canonical Monte Carlo
methods inspired on a suitable extension of the canonical fluctuation relation
$C=\beta^{2}<\delta E^{2}>$ compatible with negative heat capacities $C<0$.
Now, we improve this methodology by introducing a better treatment of finite
size effects affecting the precision of a...

Recently, we have derived a generalization of the known canonical fluctuation relation $k_{B}C=\beta^{2}< \delta U^{2} >$ between heat capacity $C$ and energy fluctuations, which can account for the existence of macrostates with negative heat capacities $C<0$. In this work, we presented a panoramic overview of direct implications and connections of...

Recently, we have presented some simple arguments supporting the existence of
certain complementarity between thermodynamic quantities of temperature and
energy, an idea suggested by Bohr and Heinsenberg in the early days of Quantum
Mechanics. Such a complementarity is expressed as the impossibility of perform
an exact simultaneous determination of...

Previously, we have derived a generalization of the canonical fluctuation
relation between heat capacity and energy fluctuations $C=\beta^{2}<\delta
U^{2}>$, which is able to describe the existence of macrostates with negative
heat capacities $C<0$. In this work, we extend our previous results for an
equilibrium situation with several control param...

In this series of papers we shall carry out a reconsideration of the thermodynamical behavior of the called HMF model, a paradigmatic ferromagnetic toy model exhibiting many features of the real long-range interacting systems. This first work is devoted to perform the microcanonical description of this model system: the calculation of microcanonica...

After a general overview of some features of the relaxation dynamics of the Hamiltonian Mean Field model, its equilibrium thermodynamic properties are used to rephrase the out-of-equilibrium regime for energies below the critical point $u_{c}=0.75$ in terms of an effective dynamical coexistence between a clustered and a gaseous phases, whose existe...

We analyze in this work how the existence of macrostates with negative heat capacities can be accounted for in terms of the thermodynamic stability and the fluctuation-dissipation relation associated with an open system in thermodynamic equilibrium. As a by-product of this reasoning, we also provide new arguments concerning the existence of a compl...

We extend the quasiergodic model proposed as an alternative version of the Antonov isothermal model [L. Velazquez and F. Guzman, Phys. Rev. E 68, 066116 (2003)] by including the incidence of a mass spectrum. We propose an iterative procedure inspired by the Newton-Raphson method to solve the resulting nonlinear structure equations. As an example of...

Molecular dynamics simulations and both normal mode and hyperspherical mode analyses of NO-doped Kr solid are carried out in order to get insights into the structural relaxation of the medium upon electronic excitation of the NO molecule. A combined study is reported on the time evolution of the cage radius and on the density of vibrational states,...

After reviewing some fundamental results derived from the introduction of the generalized Gibbs canonical ensemble, such as the called thermodynamic uncertainty relation, it is described a physical scenario where such a generalized ensemble naturally appears as a consequence of a modification of the energetic interchange mechanism between the inter...

The present work extends the well-known thermodynamic relation $C=\beta ^{2}< \delta {E^{2}}>$ for the canonical ensemble. We start from the general situation of the thermodynamic equilibrium between a large but finite system of interest and a generalized thermostat, which we define in the course of the paper. The resulting identity $< \delta \beta...

According to the recently obtained thermodynamic uncertainty relation, the microcanonical regions with a negative heat capacity can be accessed within a canonical-like description by using a thermostat with a fluctuating inverse temperature. This far-reaching conclusion is used in this Letter for enhancing the potentialities of the well-known Swend...

Magnetically treated water (MTW) was used to stimulate the germination process of Pinus tropicalis M. seeds. This species of Pinus is an endemic of the western part of Cuba and at present is threatened due to a visible decrease that has been detected in its populations. The main cause of this decrease is the low seedling produetion at nurseries, si...

The main interest of the present work is the generalization of the Boltzmann-Gibbs distributions and the fluctuation theory based on the consideration of the reparametrization invariance of the microcanonical ensemble. This approach allows a novel interpretation of some anomalous phenomena observed in the non extensive systems like the existence of...

Microcanonical description is characterized by the presence of an internal symmetry closely related with the dynamical origin of this ensemble: the reparametrization invariance. Such symmetry possibilities the development of a non Riemannian geometric formulation within the microcanonical description of an isolated system, which leads to an unexpec...

We introduce a modification of the well-known Metropolis importance sampling algorithm by using a methodology inspired on the consideration of the reparametrization invariance of the microcanonical ensemble. The most important feature of the present proposal is the possibility of performing a suitable description of microcanonical thermodynamic sta...

According to the reparametrization invariance of the microcanonical ensemble, the only microcanonically relevant phase transitions are those involving an ergodicity breaking in the thermodynamic limit: the zero-order phase transitions and the continuous phase transitions. We suggest that the microcanonically relevant phase transitions are not assoc...

In the present paper we continue our reconsideration about the foundations for a thermostatistical description of the called Hamiltonian nonextensive systems (see in cond-mat/0604290). After reviewing the selfsimilarity concept and the necessary conditions for the ensemble equivalence, we introduce the reparametrization invariance of the microcanon...

The foundations for a thermo-statistical description of the called non extensive Hamiltonian systems are reconsidered. The relevance of the parametric resonance as a fundamental mechanism of the Hamiltonian chaoticity in those systems with bound motions in the configurational space is discussed. The universality of this mechanism suggests us the po...

Molecular Dynamics Simulations of the shell dynamics and normal mode analysis (NMA) are carried out to study Rydberg photoexcitation of NO in Xe and Kr solids. In the case of the NO doped Kr system we have completed a previous study on shell dynamics by focusing only on the NMA, however, in the case of the NO doped Xe system we have carried out bot...

(CsI)nCs+ (n = 1,2) cluster ion formation from polycrystalline CsI irradiated by pulsed-UV laser (337 nm) is analyzed by delayed extraction time-of-flight mass spectrometry technique. Measurements were performed for different laser intensities and for several delayed extraction times. Experimental data show that CsI laser ablation produces the emis...

We study the quasi-stationary evolution of systems where an energetic confinement is unable to completely retain their constituents. It is performed an extensive numerical study of a gas whose dynamics is driven by binary encounters and its particles are able to escape from the container when their kinetic energies overcome a given cutou Uc .We use...

Astrophysical systems will never be in a real thermodynamic equilibrium: they undergo an evaporation process due to the fact that the gravity is not able to confine the particles. Ordinarily, this difficulty is overcome by enclosing the system in a rigid container which avoids the evaporation. We propose an energetic prescription which is able to c...

The present effort addresses the question about the existence of a well-defined thermodynamic limit for the astrophysical systems with the following power law form: to tend the number of particles, N, the total energy, E, and the characteristic linear dimension of the system, L, to infinity, keeping constant E/N^{\Lambda_{E}} and L/N^{\Lambda_{L}},...

In the present work we studied the immediate medium response to the excitation to the
A(3ss)A(3s\sigma)
Rydberg state of NO impurity embedded in a solid Kr matrix. The excitation, extended over a large range of the lattice was investigated by classical molecular dynamics simulations. This has been done using Lennard-Jones pair potentials from the...

This Letter deals with the stability of nonlinear Hamiltonian dynamics. The Jacobi–Levi–Civita equation for the geodesic spread is shown to be a powerful tool for the characterization of the so called Hamiltonian chaos. The special case of two degrees of freedom is analyzed and used to study the origin of the instability properties of the Ne⋯I2 mol...

According to self-similarity hypothesis, the thermodynamic limit could be defined from the scaling laws for the system self-similarity by using the microcanonical ensemble. This analysis for selfgravitating systems yields the following thermodynamic limit: send N to infinity, keeping constant E/N^{(7/3)} and LN^{(1/3)}, in which is ensured the exte...