University of Puerto Rico at Cayey

Engaging in the practice of modeling is one of the core skills identified in the Next Generation Science Standards for K-12 Science Education. Drawing on the findings of fifty years of chemical education research on students’ comprehension of atomic theory and the nature of matter, we argue that student's capacity to model abstract chemical phenomena is important to acquire a deeper conceptual understanding. In this project, we explored how the knowledge of what counts as a scientific model is structured across six modeling dimensions in undergraduate general chemistry students and how that perception interplays with their interpretation of different atomic models. Analysis of semi-structured interviews shows that students possess relatively unsophisticated and unstable knowledge of the nature of scientific models. However, we observed a temporal improvement when their ideas are situated in a context over the course of the interview. Also, students interestingly invoked different ideas to justify the most accurate way of representing the atom, falling back on their perceptions of what serves as a good scientific model. These results have implications for supporting student engagement in the practice of modeling in general chemistry, specifically, when external feedback would be useful for supporting learners in integrating their content knowledge with their modeling knowledge.

ABSTRACTCompetence to regenerate lost tissues varies widely across species. The rat tapeworm Hymenolepis diminuta undergoes continual cycles of shedding and regenerating thousands of reproductive segments to propagate the species. Despite its prowess, H. diminuta can only regenerate posteriorly from a singular tissue: the neck or germinative region (GR). What cells and signaling pathways restrict regeneration competence to the GR? In this study, we show that the head regulates regeneration competence by promoting maintenance of the GR and inhibiting proglottid formation in a distance-dependent manner. Anterior-posterior patterning within the GR provides local signals that contribute to these responses. βcat1 is necessary for stem cell maintenance, proliferation and proglottidization, and sfrp is necessary for maintaining the GR at its proper length. Our study demonstrates that the head organizes a balance of pro- and anti-regeneration signals that must be integrated together and therefore control competence to regenerate.

Competence to regenerate lost tissues varies widely across species. The rat tapeworm, Hymenolepis diminuta, undergoes continual cycles of shedding and regenerating thousands of reproductive segments to propagate the species. Despite its prowess, H. diminuta can only regenerate posteriorly from a singular tissue: the neck or germinative region (GR). What cells and signaling pathways restrict regeneration competence to the GR? In this study, we show that the head regulates regeneration competence by promoting maintenance of the GR and inhibiting proglottid formation in a distance-dependent manner. Anterior-posterior (A-P) patterning within the GR provide local signals that contribute to these responses. βcat1 is necessary for stem cell maintenance, proliferation and proglottidization. On the other hand, sfrp is necessary for maintaining the GR at its proper length. Our study demonstrates that the head organizes a balance of pro- and anti-regeneration signals that must be integrated together and therefore control competence to regenerate.

Compositional tuning of complex metal oxides in Li-ion battery materials influences their performance as well as their end-of-life behavior, in particular, the tendency to release toxic metal cations in aqueous solution. We modeled ternary variants of a parent LiCoO2 delafossite structure by varying the metal identity and relative amounts. This yielded ten model formulations of Li(A4/6B1/6C1/6)O2, where the material is enriched with the A metal and doped with B and C, with Ni, Mn, Co, Fe, Al, V, and Ti as constituent metals. To assess their stability in aqueous conditions, metal release energetics were calculated using a combination of Density Functional Theory calculations and thermodynamics. Metal release in ternary oxides is dictated by subtle variations in the coordination environment of the leaving group. To identify governing chemical features across diverse compositions with varying local coordination environments, we leverage random forest regression and descriptor importance analysis. A key result is that metal–oxygen orbital hybridization, quantified using a projected density-of-states-derived descriptor, Hd/p, provides a physically grounded measure of interaction strength that governs metal release energetics. This refined perspective goes beyond conventional oxidation state considerations and offers more robust insights for materials science. Finally, we model defect surface-bound O2 dimer formation as a proxy for reactive oxygen species (ROS) generation. The results show that Ni-rich compositions more readily stabilize spin-polarized O2 dimers, corroborating experimental reports of an increased ROS-driven biological response. Our results establish a compositional and electronic basis for metal release and surface oxygen reactivity that form a rationale for complex metal oxide design principles.

The 2020 southern Puerto Rico earthquake sequence highlighted the severe seismic vulnerability of informally constructed two-story reinforced concrete (RC) houses. This study examines the failure mechanisms of these structures and assesses the effectiveness of first-floor RC shear-wall retrofitting. Nonlinear pushover and dynamic time–history analyses were performed using fiber-based distributed plasticity models for RC frames and nonlinear macro-elements for second-floor masonry infills, which introduced a significant inter-story stiffness imbalance. A bi-directional seismic input was applied using spectrally matched, near-fault pulse-like ground motions. The findings for the as-built structures showed that stiffness mismatches between stories, along with substantial strength and stiffness differences between orthogonal axes, resulted in concentrated plastic deformations and displacement-driven failures in the first story—consistent with damage observed during the 2020 earthquakes. Retrofitting the first floor with RC shear walls notably improved the performance, doubling the lateral load capacity and enhancing the overall stiffness. However, the retrofitted structures still exhibited a concentration of inelastic action—albeit with lower demands—shifted to the second floor, indicating potential for further optimization.

La felicidad en el trabajo parecía inalcanzable frente a los desafíos del mundo laboral contemporáneo. Sin embargo, su estudio se ha fortalecido en la última década. La construcción de instrumentos con inferencias válidas y confiables para medir la felicidad en el trabajo ha sido clave en esta gestión. El propósito de este estudio fue desarrollar y analizar las propiedades psicométricas de la Escala de Felicidad en el Trabajo en una muestra de 539 personas trabajadoras en Puerto Rico. Para ello, se realizaron distintos análisis relacionados a la validez de constructo, análisis de ítems, análisis de fiabilidad y validez discriminante. Los resultados obtenidos demuestran que la versión final (M2) de la Escala de Felicidad en el Trabajo, de 23 ítems y cinco dimensiones: emociones positivas (α = .93), engagement (α = .88), relaciones positivas (α = .95), sentido (α = .92) y orientación al logro (α = .90), cuenta con las propiedades psicométricas adecuadas para utilizarse en estudios e intervenciones organizacionales en Puerto Rico.

Hysteromorpha Lutz, 1931 is a small but broadly distributed genus of diplostomoidean digeneans parasitic as adults primarily in cormorants, but also reported from some other fish-eating birds. Their metacercariae were found in a variety of freshwater fishes as second intermediate hosts. Prior to this study, the genus included only 3 nominal species, 2 of them distributed in the Old World and 1 in the New World. We obtained sequences of partial mitochondrial cox1 gene and nuclear rDNA operon from new specimens collected in Europe, North and South America and used them for species comparisons and phylogenetic analysis. We also examined morphology of our newly collected specimens as well as museum specimens. Our analysis has demonstrated that at least 2 (likely 3) species of Hysteromorpha are distributed in the Americas. Hysteromorpha sp. previously sequenced from larval stages, clearly represents a new species named herein Hysteromorpha ostrowskiaen. sp. Achatz, Locke et Tkach. Morphology of adults of the new species was earlier described in sufficient detail under the name Hysteromorpha triloba (Rudolphi, 1819). Our analyses also suggest the presence of another unknown Hysteromorpha sp. in North America represented by cox1 sequence from southeastern Canada (GenBank JF769473), but no morphological vouchers are available for this species.

Supramolecular hacky sacks (SHS) are a novel class of self-assembled colloidal particles formed from guanosine (G) derivatives, designed to function as versatile tools for cellular and therapeutic applications. Here, we investigate the structure-dependent cellular uptake, intracellular trafficking, and functional performance of SHS particles. Confocal microscopy and flow cytometry studies reveal that SHS uptake is highly dependent on the composition of the G-derivatives, suggesting selective interactions with cellular pathways. Importantly, we demonstrate that SHS particles serve as a biocompatible platform for drug and gene delivery, effectively encapsulating and releasing doxorubicin for enhanced cytotoxicity, as well as facilitating plasmid transfection with sustained fluorescent protein expression. These results establish SHS particles as a versatile biocompatible platform with tunable bioactivity, offering new opportunities for the application of supramolecular assemblies in drug delivery and gene therapy. The inherent biodegradability, simplicity of synthesis, and versatility of SHS particles underscore their potential as next-generation biomaterials for biomedical applications.

Enhancing the mechanical properties of sandwich core structures is important for crashworthiness applications, including protecting passengers and payloads. Existing structures, such as prismatic cells, present limitations like reduced lateral mechanical properties, among others. Non-prismatic reinforcements (NPRs) are introduced as an alternative to developing core structures tailored for multiple loading scenarios. Several NPR ideas are presented. While additive manufacturing allows for exploring the inner space of core structures with different NPRs, manufacturing such structures may present challenges due to their complexities. One of the NPR ideas was combined with the hexagonal honeycomb, a sandwich core widely used for crashworthiness applications, to create a non-prismatic reinforced honeycomb (NPRH). Utilizing fused filament fabrication, NPRH specimens were manufactured as self-supporting structures at three scales. Quasi-static compression experiments were performed in multiple loading directions. Because comparing structures' mechanical properties in multiple loading directions simultaneously may present difficulties, the multi-direction comparison factor and the angle comparison factor are presented as alternatives that relate mechanical properties in multiple loading directions and that can be adapted to different loading scenarios. These parameters were used to compare the NPRH with structures from the literature. The NPRH showed greater specific energy absorption, positioning it as a possible solution for multi-loading crashworthiness applications.