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.
The paper presents a study concerning the coherence and domain wall effects on the profile of selected X-ray diffraction (XRD) peaks 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 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.
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.
A demonstrative experiment on radioactivity is proposed, applying a research learning approach. The experiment utilizes a radioactive source (90Sr), Geiger-Muller 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.
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.
Aceptado 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.
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.
The first Cuban prototype of a state-of-the-art surgical semiconductor laser for dentistry is presented. Aimed at soft tissue surgery and mucosal treatments, its performance matches that of analogous equipment in the market. The prototype underwent electrical safety and parametric testing, showing high repeatability and reproducibility of the measured optical power values. The equipment is currently being introduced in Havana's Faculty of Dentistry.
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 M(W )and two magnitudes used in Cuba: (1) amplitude-based M(L )and (2) coda-duration-based M-C , 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 (M-L M-C ). 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 M-W-M(L )and M-W-M-C relationships. These results provide a robust basis for magnitude conversions in Cuban catalog homogenization and seismicity analysis.
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 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.
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 (C-n, 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 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 approximate to 1, 2 & Aring;, in excellent agreement with quantum Monte Carlo benchmarks. These findings demonstrate the reliability of NOFT for describing strong correlation effects in large-scale models.
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.
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.
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.
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.
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 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 (124)Xe(54 )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.
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 behaviour, providing insight into delamination and swelling mechanisms.
