The Revista Cubana de Física (RCF, Cuban Journal of Physics) is a biannual open access journal (e-ISSN 2224-7939, p-ISSN 0253-9268) published by the Cuban Physical Society (SCF) and the School of Physics of the University of Havana (FF-UH) solely funded by its publishers (without charges to the authors). Three types of articles are considered for publications: Regular Original Articles, Original Short Articles and Review Articles. Likewise, the RCF includes other several sections as: Moments of the Cuban Physics, For Physics and Non-Physics, News and Obituaries. Concerning the language, manuscripts in Spanish as well as in English are welcome in Microsoft Office Word (.doc or .docx) and LaTex (.tex) formats. The peer-review is blind and performed by external reviewers outside the editorial team of the RCF, the SCF or the FF-UH.
Sociedad Cubana de Física & Facultad de Física de la Universidad de La Habana
Physics suggests that Nature is made of matter and the so-called anti-matter, the latter in lesser extent. Antimatter is made up of antiparticles with the same mass, but although their charge and magnetic moment are of the same magnitude, they are opposite to those of the corresponding particle of ordinary matter. The collision of particles and antiparticles generates high-energy photons. This paper presents an introduction to the use of antimatter, specifically antielectrons or positrons, to explore and study, through their annihilation with present electrons, aspects as diverse as the metabolism of tissue in a living being and the characteristics of vacancy defects in various materials.
Copyright (c) 2025 Cuban Physical Society & Faculty of Physics of the University of Havana https://creativecommons.org/licenses/by-nc/4.0
Ivar Giaever: An Unlikely Hero of Quantum Times
Giaever, who passed away in June 2025, transformed quantum physics through his experimental discovery of tunnelling in superconductors, a phenomenon predicted by BCS theory and intimately linked to the superconducting gap. Despite his modest academic beginnings, he achieved groundbreaking results at General Electric by demonstrating quasiparticle tunnelling across superconductor–insulator–superconductor junctions. His curiosity, perseverance, and collaborative environment enabled this achievement. The author, whose own research was shaped by tunnelling effects in ceramic superconductors, reflects on Giaever’s profound influence during a fleeting elevator encounter.
We provide a detailed and accessible introduction to the exact theory of capillary phenomena in a cylindrical tube of finite radius. We demonstrate explicitly that Jurin's law always somewhat underestimates the height of liquid rise. The largest deviations occur for small contact angles. In the limiting case of a very large capillary radius, the true column height becomes independent of the radius and approaches a finite limiting value. The mean curvature of a real meniscus is a monotonically increasing function of the capillary radius. We argue that the force balance method is most appropriate for deriving Jurin’s law, whereas the exact capillary equation requires the use of the pressure balance method or the Helmholtz energy minimization procedure.
The Institute of Materials Science and Technology (IMRE) of The University of Havana: 40th Anniversary
This article presents a short review of the scientific history of the Institute of Materials Science and Technology (IMRE) of the University of Havana, from its creation in 1985 to its 40th anniversary. We analyze the main research results achieved during these 40 years, as well as an study of its historical performance.
national and international laboratory facilities
Effects of Coherence and Domain Walls on Diffraction Profiles in Rare-Earth Doped PbTiO₃
The paper presents a study concerning the coherence and domain wall effects on the profile of selected X-ray diffraction (XRD) peaks from the ferroelectric system Pb0.92Ln0.08TiO3 (Ln3+ = La3+, Dy3+). The analysis focuses on the hkl-dependent broadening and asymmetry of certain diffraction peaks. The study was conducted using a diffraction model evaluated with experimentally determined parameters from XRD and Transmission Electron Microscopy (TEM). The results show that both coherence effects and domain wall scattering contribute significantly to peak asymmetries and diffuse intensity between (h00)/(00h) doublets. The results also show that these effects are sensitive to domain size being more pronounced in lower-order reflections. The choice of dopant directly impacts microstructural parameters. The study highlights the complexity of quantifying ferroelectric microstructures alone from diffraction data alone.
Role of Radiofrequency Power on the Crystallographic, Morphological and Optical Properties of Sputtered Aluminium Thin Films
Aluminum (Al) thin films are of great interest for applications in telecommunications, microelectronics, and the automotive industry, among others, due to their high conductivity, excellent optical properties and low weight. Their properties depend on the depositition technique and its parameters. In this work, the crystallographic, morphological, and optical characteristics of Al thin films grown by radio-frequency (RF) magnetron sputtering were analyzed. An aluminum target was used in an argon (Ar) atmosphere, and the effect of sputtering power on film properties was investigated. The samples were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and UV-Vis Spectroscopy. The crystalline quality improved with increasing power. AFM and SEM results revealed an increase in roughness, thickness, and grain size with higher sputtering power. UV-Vis spectroscopy showed lower diffuse reflectance at lower power across the 190-900 nm range. The enhancement of film properties is mostly attributed to the increased kinetic energy of sputtered species, directly related to the applied RF power.
High-power Laser Prototype for Soft Tissue Surgery in Dentistry
The development of a high-power semiconductor laser device for soft tissue surgery in dentistry is presented. The block diagram and the elements that they include, the main technical specifications of the prototype, as well as the results obtained from the measurements carried out for its adjustment and start-up, are shown, guaranteeing its reliable operation.
Mw-ML and MW-Mc Seismic Magnitude Scaling Relationships for Cuba
Earthquake catalogs typically report multiple magnitude types, which makes it difficult to perform comprehensive statistical analysis. Internationally, moment magnitude is the preferred reference scale for unification. This study establishes empirical relationships between MW and two magnitudes used in Cuba: (1) amplitude-based ML and (2) coda-duration-based MC, as computed by the National Seismological Service of Cuba for earthquakes recorded from 1998–2022. We evaluated linear and nonlinear regression models, including those accounting for uncertainties in the independent variable (ML or MC). Model parameters were estimated via standard least squares, orthogonal distance least squares, and higher-order moments regression. Using the Akaike (AIC) and Schwarz (BIC) information criteria, we identified the segmented model using orthogonal distance regression (ODR) as most recommended for both MW–ML and MW–MC relationships. These results provide a robust basis for magnitude conversions in Cuban catalog homogenization and seismicity analysis.
Problem-based Learning with Video Analysis: The Case of the Variable-Mass Atwood Machine
This study applies Problem-Based Learning (PBL) to teaching advanced mechanics in undergraduate physics, focusing on variable mass systems through the Atwood machine with chains. Using the Hmelo-Silver PBL model, a structured sequence guided students in problem analysis, hypothesis generation, self-directed study, experimentation, and reflection. The case study combined Newtonian and Lagrangian modeling with experimental validation via Tracker video analysis, enabling students to connect theoretical derivations with accessible empirical data. Results showed strong consistency between theoretical predictions and experimental measurements, despite minor discrepancies from chain oscillations, link impacts, and video resolution limitations. The approach demonstrated how low-cost tools can effectively support experimental inquiry in physics education. Beyond content knowledge, PBL fostered research-oriented skills such as autonomous planning, problem-solving, and collaborative inquiry. The proposed framework provides a replicable model for integrating abstract theory with experimental practice, strengthening active learning and advancing the role of inquiry-based methodologies in STEM curricula.
Computational Optimization of A Stochastic Model for Simulating Apoptotic Signaling
The development of mathematical models to simulate biological processes is essential for understanding the complexity of living systems, allowing for predictions and virtual experiments that would be difficult to carry out under real conditions. In this work, we present a mathematical model to simulate the process of apoptosis or programmed cell death, using the Gillespie algorithm. Additionally, an optimization of this model is proposed, which reduces computation time and enables the model to simulate apoptosis in the cells of a tumor under topical treatment. Results are also presented demonstrating that both models are equivalent. The optimization reduced the execution time of the simulation by two days.
S-shaped or sigmoid curves can be defined as the solutions of autonomous first-order differential equations that satisfy four conditions. Without solving the equations, we demonstrate that the solutions of the logistic family and the Smith-Birch model satisfy these conditions. We introduce two generalizations of the Smith-Birch, whose solutions are identified as S-shaped for some range of variation of the parameters. The new models introduced here predict the spread of the disease better than traditional logistic family models for time series of the cumulative number of cases for the first 61 days of the COVID-19 pandemic in some countries.
Demonstrative Teaching Experiment to Motivate the Study of Radioactivity with a Research Approach
A demonstrative experiment on radioactivity is proposed, applying a research learning approach. The experiment utilizes a radioactive source (90Sr), Geiger-Müller counters, magnets, and electromagnets. Through heuristic discussion, students are guided to discover, among other things, the presence of electrically charged particles in the studied radioactive emission. The experiment was conducted one month before the students formally began their nuclear physics course, the final topic in the Physics 3 subject (Modern Physics) for engineering students. A survey conducted during the first few minutes of the lecture introducing the topic revealed that a high percentage of students recalled the fundamental characteristics of the radioactive decay process of the isotope under study.
Mathematical Treatment of the Canonical Finite State Machine for the Ising Model
The complete framework for the minimal deterministic automata construction of the one-dimensional Ising model is presented. The approach follows the known treatment of the Ising model as a Markov random field, where the local characteristic is usually obtained from the stochastic matrix. The problem is the inverse relation or how to get the stochastic matrix from the local characteristics given via the transfer matrix treatment. The obtained expressions allow for performing complexity-entropy analysis of particular instances of the Ising model. Two examples are discussed: the 1/2-spin nearest neighbour and next nearest neighbours Ising model.
The Role of Clay Charge in The Mobility of Compensating Cations
The charge of clays plays an important role in the mobility of compensating cations and in swelling processes. In this work we have developed a method to generate Lithium Fluorhectorite (Li-Fh) clay models with a charge of -1.2e and a non-homogeneous charge distribution. This charge is closer to the experimentally reported value. We used this approach to study their interaction with water using Molecular Dynamics (MD) simulations. The MD simulations showed that the Li+ diffusion coefficient increases by two orders of magnitude with decreasing clay charge. Population analyses and Li+ coordination indicate a greater interaction of the cations with water molecules with decreasing clay charge, leading to a deformation in the stacking of clay layers in the 010 model. These results highlight the important influence of clay charge on cation dynamics and structural behavior, providing insight into delamination and swelling mechanisms.
Metal-Insulator Transition described by NOFT
The metal–insulator transition (MIT) is a fundamental phenomenon in condensed matter physics and a hallmark of strong electronic correlations. Hydrogen-based systems offer a simple yet powerful model for investigating the MIT, as their insulating behavior arises purely from electron–electron interactions. In this work, we study finite hydrogen clusters with cubic geometries using Natural Orbital Functional Theory (NOFT), a method capable of accurately describing correlated systems beyond mean-field approaches. We focus on two key signatures of the MIT: the fundamental energy gap and the harmonic average of the atomic one-particle reduced density matrix. Our results show that NOFT captures the transition from insulating to metallic behavior as the interatomic distance decreases. By extrapolating the energy gap to the thermodynamic limit, we estimate a critical distance rc ~1.2 Å, in excellent agreement with quantum Monte Carlo benchmarks. These findings demonstrate the reliability of NOFT for describing strong correlation effects in large-scale models.
Reduced Density Matrix Functional Theory
Radioactivity Levels and Radiation Hazard in Sands from Cuban Beaches
This study assesses the natural radioactivity levels of 226Ra, 232Th, and 40K in sand samples from six Cuban white-sand beaches to evaluate potential radiological risks. Samples were analyzed using high-resolution gamma spectrometry after a one-month equilibrium period. Activity concentrations were determined via key gamma transitions of daughter nuclides. Results show that all measured values of activity, radium equivalent (Raeq), absorbed dose rate (DR), and gamma index (Iγ) are below internationally recommended safety thresholds. La Coloma beach exhibited the highest 232Th activity, slightly exceeding the global mean, but still within safe radiological limits. The calculated gamma index values (0.04–0.52) and dose rates (3–33 nGy·h⁻¹) confirm minimal radiological risk. This work provides a radiological baseline for Cuban beach sands and supports the need for further studies in other major resort areas across the island
Pyroelectric Response and Figures of Merit of Lead-Free Ferroelectric Ceramics
(Bi0.5Na0.5)1-xBaxTiO3 were synthetized via the conventional solid-state reaction sintering method (considering x = 16 and 18 at%) and polarized under an electric field of 2 kV/mm. The pyroelectric behaviour of the studied samples has been analysed by the static method, from the temperature dependence of the pyroelectric current. The figures of merit FV, FD, Fi and FE were investigated in a wide temperature range. The composition with x = 18 at% showed better results than that of x = 16 at% and other reported ceramic systems, especially for FV and FE parameters. A high thermal stability through the studied temperature range was obtained, which is a relevant behaviour for applications involving high-temperature sensors. The results have suggested that (Bi0.5Na0.5)1-xBaxTiO3 is a suitable candidate for pyroelectric sensors and energy harvesting applications.
Towards the STM: The Story Behind The First Atomic Resolution Image in Cuba
Scanning tunneling microscopy is a widely used tool in nanoscience and nanotechnology research. This technique has the advantage of allowing the study of surface layers without damaging or destroying them and of achieving atomic resolution. Its simplicity compared to other scientific instruments has allowed different laboratories to build their own microscopes. Here we present how the STM at the University of Havana was built and how it achieved atomic resolution for the first time in Cuba.
Photodissociation Dynamics of the Collinear Van Der Waals Complex NeBr2(B, ν=14-34)
We perform trajectory-based simulations of the dissociative dynamics of the collinear van der Waals complex NeBr2(B,ν) following photoexcitation to the B electronic state and for varying vibrational excitations of the dihalogen molecule in the range ν=14-34. The quantum dynamics of unimolecular decay is mapped onto a classical-like dynamics in an extended phase space. This methodology allows us to compute the time-dependent dissociation probability, intramolecular energy transfer mechanisms, and transient vibrational state distributions of the linear triatomic system, which are challenging to access experimentally using modern pump-probe spectroscopy techniques. The computed quantities can be used to refine interaction potential models at collinear geometries, which are less well characterized than the T-shaped isomer.
Study of the Rotation Dynamics of a Rigid Body through the accelerometer of a Mobile Device
The introduction of the mobile devices in the teaching of physics has gained importance in recent times due to the ample range of sensors they contain and their ability to accomplish measurements in real time. The study of the dynamics of a rigid body rotation using the accelerometer of a smart phone was tackled. The problem is a modification of the standard laboratory device consisting in a crossbeam that rotates in a horizontal plane around a vertical axis. Through an ad hoc Android application, it was possible to visualize the behavior and to measure the radial and tangential components to a linear acceleration. Moreover, the moment of inertia and the friction torque of the crossbeam was calculated. Finally, we discuss some particular cases of the main problem that shows the potential of these devices for physics teaching.
Quasi-classical Dynamics of Hydrogen Molecules Trapped Inside Fullerene Cages
We perform molecular dynamics simulations of hydrogen molecules inside fullerene cages, incorporating quantum effects via the Feynman-Hibbs effective potential method. The distance between hydrogen atoms in the molecule is kept fixed by using the constraint dynamics algorithm. We evaluate the energetic properties and the influence of quantum effects for hydrogen molecules in fullerene cages of varying size and geometry (Cn, n=24, 28, 60, 70), and within a wide range of thermodynamics conditions (i.e., from T=130 K to T=320 K). We compute the temperature dependence of quantities such as the translational and rotational kinetic energies, the total energy and the contribution of quantum effects. It is found that quantum corrections to the total energy are significant even at room temperature. We discuss the possible influence of these properties on the hydrogen storage capacity of these materials.
The Two-state Diffusion Problem with Resetting
The concept of stochastic resetting emerged in 2011, introducing a simple modification to [15] the one-dimensional Random Walk that leads to a stationary distribution and where the first-passage time can be easily optimized. In this context, we will investigate what happens when modeling these phenomena in a framework where a Brownian particle alternates between different states. We will derive the Fokker-Planck equations of the model and analyze the behavior of the probability density of the particle positions for long times and solve the corresponding first-passage time problem. Contrasting with the two-state Brownian motion, we will observe how resetting ensures a stationary behavior in the long run leading to a finite expectation for the first-passage problem. Finally, we will demonstrate how the existence of this expectation guarantees minimum values by varying the resetting or state-change parameters.
Particle Fluence Estimation for Samples Irradiated at a Long-Term Exposure Station (NICA Complex, Dubna)
The prototype of the Target Station for Long-Term Exposure was assembled after all detectors of BM@N Experiment. During collection of the physical data with the 124Xe54 beam of 3.8 GeV kinetic energy at BM@N, different samples were irradiated. Data was analyzed for precise determination of the intensity, the fluence and the absorbed dose for irradiated materials. The beam intensity and profile distributions were determined for each sample. From the obtained intensity, the fluence was calculated for each irradiated sample. Then, the absorbed dose of irradiated materials was be calculated. The study was performed within the ARIADNA Collaboration.
A Finite Element Method Exploration of Technologically Relevant Geometries in PiezoelectricEnergy-Harvesting PZT-4
In a piezoelectric material, any external action that can generate a mechanical deformation could be a potential source of electrical energy. This phenomenon is studied for the development of microscale devices, using as external agents the hydraulic pressure of a fluid, the movement of the human being and others. Nowadays, the main researches are directed to the optimization of the properties of the developed piezoelectric and also to the simulation of different situations that allow the optimization of the energy harvesting devices. The present paper shows some simulations, which have been made by using the finites elements method to simulate the energy harvesting; the results are presented for a commercial piezoelectric, PZT-4.
Dynamic Cavity Method in Fully-Asymmetric Models
The physics of disordered systems is a broad and constantly evolving field. In this work, we focus on the study of discrete variable models with asymmetric interactions, in particular the fully-asymmetric ferromagnet and the fully-asymmetric Sherrington-Kirkpatrick. We use the cavity master equation, a well-known technique for the out-of-equilibrium dynamics, to derive average equations describing the time evolution of the magnetization and the energy in these models. In this way, we recovered previous results for the magnetization known from the literature and obtained new equations for the energy. With this work, we contribute to establish the cavity master equation as one of the most relevant techniques in the study of out-of-equilibrium systems and clarify its relationship with previous methods.
Lzcomplexity: Entropy Measurement Library
The library Lzcomplexity is presented, developed for complexity analysis using entropic metrics. The algorithms used to estimate the metrics by means of Lempel–Ziv factorization are described. To face the computational challenges associated with the analysis of large volumes of data, Lzcomplexity implements algorithms that enable parallel processing of the sequences. The experiments carried out and its practical use demonstrate that Lzcomplexity can analyze long sequences in reasonable times and that the included entropic measures are reliable indicators for describing complex systems.
DFT study of BaKN3 and BaRbN3 Perovskites: Revealing their Mechanical, Optoelectronic, and Magnetic Properties
The full-potential linearized augmented plane waves (FP-LAPW) method, which is based entirely on density functional theory (DFT), was used to investigate the structural, electronic, magnetic, optical, and elastic properties of BaXN3(X=K, Rb). This method also employs the Perdew-Burke-Ernzerhof generalized gradient approximation (GGA-PBE) and a modified Beck Johnson TB-mBJ potential in the exchange correlation term. When the resulting structural properties were examined, the findings showed that our compounds are more stable when they are configured as ferromagnetic materials. The total and partial density of state curves were used to assess the contributions of the various bands. Additionally, we discovered that the total magnetic moment is an integer of 6 µB, confirming the half-metallic nature. The mechanical stability of these compounds has been discovered. The elastic parameters are obtained, including the elastic constants, bulk modulus, anisotropy factor, Poisson's ratio, and Pugh's ratio.
Density-functional theory atomic and molecular physics
Correlating Texture and Electromechanical Properties of Activated Carbons
This study presents a simplified experimental method for evaluating the electro-mechanical behavior of activated carbons derived from agro-industrial residues such as sugarcane bagasse, coconut shells, peanut hulls, and rice husks. Using a two-point electrical measurement under controlled uniaxial pressure, we introduce and analyze the parameter ρm/ρ, which shows a strong linear correlation with pressure across all samples. The effective conductivity (σₑ) is modeled using an effective-medium approximation, revealing two competing effects of pressure: improved grain contact at low pressures and grain fracture at high pressures. The derived expression for σₑ(P) incorporates four key parameters that act as a fingerprint for each material. Experimental results confirm the model's predictive capability and highlight the influence of material composition, notably SiO₂ content, on conductivity. This approach provides a reliable, low-cost tool for preliminary assessment of the textural and conductive properties of activated carbons, with potential implications for their optimization in electrical applications.
Historical and Recent Observations of Comets in Cuba
Cuba has a long-standing tradition in comet observation, dating back to the 19th century when figures like José Joaquín de Ferrer recorded comet movements, including the 1807 comet. These efforts continued into the 20th century, with notable events such as the telescopic observation of Halley's Comet in 1910 by Jesuit priest Mariano Gutiérrez-Lanza. His observations contributed to cometary science and alleviated public fears of a collision between the comet and Earth. Today, Cuban amateur astronomers, using digital tools and social media, continue this legacy. Recent observations of comets reflect Cuba's enduring passion for astronomy and highlight its growing interest in this topic.
Instructing Talent Students in Physics: A Challenge
The teaching of Physics in Cuba is in one of its worst moments since the 1960s, at least at the pre-university level. In this article, we highlight the importance of serving students who show talent for this subject at that educational level. In particular, we propose some ideas of very little economic cost that could contribute to the better performance of these students, but also of all young people with a vocational inclination towards Physics and related sciences in Cuba.