A generalization of the Pontryagin-Hill theorems to projective modules over Pr\"ufer domains

Motivated by the Pontryagin-Hill criteria of freeness for abelian groups, we investigate conditions under which unions of ascending chains of projective modules are again projective. Several extensions of these criteria are proved for modules over arbitrary rings and domains, including a genuine generalization of Hill's theorem for projective modules over Pr\"{u}fer domains with a countable number of maximal ideals. More precisely, we prove that, over such domains, modules which are unions of countable ascending chains of projective, pure submodules are likewise projective

An alternative proof of hill's criterion of freeness for abelian groups

In this note we provide a different proof of Hill's criteria of freeness for abelian groups. Our proof hinges on the construction of suitable $G(\aleph_0)$-families of subgroups of the links in Hill's theorem and, ultimately, on the construction of such a family of pure subgroups of the group itself

Second-Order Semi-Discretized Schemes for Solving Stochastic Quenching Models on Arbitrary Spatial Grids

Reaction-diffusion-advection equations provide precise interpretations for many important phenomena in complex interactions between natural and artificial systems. This paper studies second-order semi-discretizations for the numerical solution of reaction-diffusion-advection equations modeling quenching types of singularities occurring in numerous applications. Our investigations particularly focus at cases where nonuniform spatial grids are utilized. Detailed derivations and analysis are accomplished. Easy-to-use and highly effective second-order schemes are acquired. Computational experiments are presented to illustrate our results as well as to demonstrate the viability and capability of the new methods for solving singular quenching problems on arbitrary grid platforms

Single-Switch Non-Isolated Resonant DC-DC Converter for Single-Input Dual-Output Applications

This paper describes a new configuration of Cuk and SEPIC (Single-Ended Primary Converter) ZVS-QR (zero-voltage switching quasi-resonant) combination DC-DC converter for bipolar output with a single switch. The proposed topology employs a single ground-referenced power switch, which simplifies the gate drive design with a single L-C resonant network and provides a bipolar output voltage with good regulation, acceptable efficiency and a step-down/up conversion ratio. This configuration provides dual-output voltage by switching the power switch to zero voltage, which is an interesting alternative for many applications where small size, light weight and high power density are very important aspects. In order to verify its performance, a SEPIC–Cuk Combination ZVS-QR prototype with a cost-effective commercial resonant controller was designed and tested. The experimental results show that the proposed combined topology is suitable for Single-Input Dual-Output (SIDO) applications

Uropatía obstructiva alta. Aspectos clínicos epidemiológicos y terapéuticos

Introduction: obstructive uropathy is observed frequently and at all ages, and the entities that produce it vary by age and gender of the patient, it is more common in men, especially after 60 years. Objective: to characterize patients with upper obstructive uropathy from the clinical, epidemiological and therapeutic point of view. Method: it was performed a descriptive and retrospective study of patients diagnosed with upper obstructive uropathy at "Celia Sanchez" Clinical Surgical Hospital in Manzanillo in the urology service during the period of January 2011-  December 2012. Results: the age group of 42-51 years prevailed with an average age of 51-61 and SD of 7.12. The municipality with the greatest number of patients was presented with 27 cases in Manzanillo. The main cause of upper obstructive uropathy was the renoureteral lithiasis with 50 patients. The prevailing type of obstructive uropathy was the unilateral chronic with 51 patients, and hydronephrosis was the main complication with 20 cases followed by urinary infection with 15 cases. The main surgical technique applied was the Pyelolithotomy in 18 patients followed by Ureterolithotomy in 13 cases. Conclusions: the main cause of upper obstructive uropathy was renoureteral lithiasis.Introducción: la Uropatía Obstructiva se observa con frecuencia y en todas las edades y las entidades que la producen varían según la edad y el género del paciente, es más común en los hombres, sobre todo luego de los 60 años de edad.Objetivo: caracterizar desde el punto de vista clínico epidemiológico y terapéutico a los pacientes con Uropatías Obstructivas Altas.Método: se realizó un estudio descriptivo retrospectivo de los pacientes con diagnóstico de uropatía obstructiva alta en el Hospital Clínico Quirúrgico “Celia Sánchez Manduley” de Manzanillo en el servicio de urología, durante el periodo comprendido entre enero del 2011 hasta diciembre del 2012.Resultados: el grupo de edad entre 42-51 años fue el que predominó con una media de edad de 51.61 y una DE de 7.12. El municipio que mayor número de pacientes presentó fue Manzanillo con 27 casos. La causa principal de Uropatía Obstructiva Alta fue la Litiasis Renoureteral con 50 pacientes. El tipo  de Uropatía Obstructiva que predominó fue la unilateral crónica con 51 pacientes, y la Hidronefrosis fue la principal complicación con 20 casos seguido de las infecciones urinarias con 15. La principal técnica quirúrgica que se empleó fue la Pielolitotomía a 18 pacientes seguido de la Ureterolitotomía a 13 casos.Conclusiones: la causa principal de la uropatía obstructiva alta fue la litiasis renoureteral

Modeling the biogeochemical seasonal cycle in the Strait of Gibraltar

A physical-biological coupled model was used to estimate the effect of the physical processes at the Strait of Gibraltar over the biogeochemical features of the Atlantic Inflow (AI) towards the Mediterranean Sea. This work was focused on the seasonal variation of the biogeochemical patterns in the AI and the role of the Strait; including primary production and phytoplankton features. As the physical model is 1D (horizontal) and two-layer, different integration methods for the primary production in the Biogeochemical Fluxes Model (BFM) have been evaluated. An approach based on the integration of a production-irradiance function was the chosen method. Using this Plankton Functional Type model (BFM), a simplified phytoplankton seasonal cycle in the AI was simulated. Main results included a principal bloom in spring dominated by nanoflagellates, whereas minimum biomass (mostly picophytoplankton) was simulated during summer. Physical processes occurring in the Strait could trigger primary production and raise phytoplankton biomass (during spring and autumn), mainly due to two combined effects. First, in the Strait a strong interfacial mixing (causing nutrient supply to the upper layer) is produced, and, second, a shoaling of the surface Atlantic layer occurs eastward. Our results show that these phenomena caused an integrated production of 105 g C m− 2 year− 1 in the eastern side of the Strait, and would also modify the proportion of the different phytoplankton groups. Nanoflagellates were favored during spring/autumn while picophytoplankton is more abundant in summer. Finally, AI could represent a relevant source of nutrients and biomass to Alboran Sea, fertilizing the upper layer of this area with 4.95 megatons nitrate year− 1 (79.83 gigamol year− 1) and 0.44 megatons C year− 1. A main advantage of this coupled model is the capability of solving relevant high-resolution processes as the tidal forcing without expensive computing requirements, allowing to assess the effect of these phenomena on the biogeochemical patterns at longer time scales

On making a graph crossing-critical

A graph is crossing-critical if its crossing number decreases when we remove any of its edges. Recently it was proved that if a non-planar graph G is obtained by adding an edge to a cubic polyhedral (planar 3-connected) graph, then G can be made crossingcritical by a suitable multiplication of its edges. Here we show: (i) a new family of graphs that can be transformed into crossing-critical graphs by a suitable multiplication of its edges, and (ii) a family of graphs that cannot be made crossing-critical by any multiplication of its edges

Walking in Havana, Cuba

Walking pedestrians account for nearly half of all daily trips in Havana. Walking provides many positive and sustainable benefits, including those linked with accessibility, health and energy conservation, but until recently, transport and urban planners have paid relatively little or less attention to the walking environment. Havana is an exceptional case among island cities in many ways and one outstanding feature is the high level of walking with 46 % of all trips carried out by pedestrians. The use of the bicycle accounts for another 1. S % as a sustainable form of mobility. In six other Latin American cities walking and biking taken together account for many less trips resulting in a range of values from 32 % to 40 % ofall trips, in Barranquilla, Curitiba, Guadalajara, Salvador, Recife and Belo Horizante, respectively (Hidalgo Huizenga, 2013, figure 6, p 70). The high values of walking as a share of total trips means that more emphasis should be placed on creating better walking environments. Good walkability depends on factors woven into the urban fabric, such as creating compact built-up areas and preventing city sprawl, increasing spatial accessibility through good street network design, creating public spaces as well as pedestrian and bicycle networks, stimulating walkability, creating mixed functions in the districts preventing social segregation, protecting green urban areas, and improving of public transport infrastructure (Telega et al., 2021, p 3). Both Telega (and CNC 2020) note that the Charter for New Urbanism is aligned "to growing the supply of neighbourhoods that are both walkable and affordable; work to change the codes and regulations blocking walkable urbanism; and advance design strategies that help communities adapt to climate change and mitigate its future impact". The main objective in this study is to explore two methods called movement and place mapping, and walkability surveys (or audits), both of which can highlight issues around walkability and provide different types of data for Havana city. The study concludes with some recommendations for improving walkability