Los parámetros algebraicos en el contexto de la modelación matemática

El trabajo parte de una inquietud que se centra en dos aspectos: el uso indistinto que los estudiantes dan a las letras para resolver ecuaciones, para hallar equivalencias algebraicas y para abordar situaciones de variación. Se involucra la función cuadrática como objeto matemático. Esto, al menos por dos razones: en primera instancia porque fue la temática en la cual venían trabajando los estudiantes al momento de realizar el proyecto, y en segundo lugar porque la función cuadrática puede y ha sido interpretada como modelo matemático de procesos de variación cuadrática (Mesa & Ochoa, 2009; Posada & otros, 2006). Analizan diferentes usos que dan los estudiantes a las letras en determinadas tareas

Comparación morfodinámica de la costa noroeste del estado de Quintana Roo, México

A lo largo de las últimas cuatro décadas, en México se ha construido infraestructura en la zona costera, que ha permitido el desarrollo económico de diversas regiones del país; sin embargo, en muchos de los casos compite con procesos naturales y las experiencias evidencian desastres llamados “naturales”, no obstante el factor antropogénico. En el caso de la costa noreste de Quintana Roo, en particular en las playas de Cancún y la Riviera Maya, se ha provocado que la costa cambie de manera gradual sus estados de equilibrio natural; es por ello que los procesos y fenómenos físicos de las playas responden de manera diferente a lo deseado, lo cual implica una serie de modificaciones que pueden llegar a considerarse como adversas tanto en términos ambientales como sociales y económicos. En el presente trabajo se aplica una metodología para la determinación de los estados morfodinámicos de playas que poseen o carecen de la protección del sistema arrecifal mesoamericano. El análisis que se realizó comienza a partir del estudio de la geología y geomorfología costera; en la siguiente etapa se efectuó un análisis de las características físicas de los sedimentos que se depositan en las playas; después se simuló numéricamente el oleaje en playas con ausencia de protección natural (Cancún) y en playas donde se identificaba un sistema arrecifal (Puerto Morelos); por último se establecieron los principales parámetros morfodinámicos de las playas. Los resultados que se obtuvieron muestran la importancia que ostentan los sistemas arrecifales para el establecimiento del comportamiento de las playas, así como para el cambio de la vulnerabilidad que puede inducir la infraestructura sobre ellos

Video-Assisted Thoracoscopy For Penetrating Cardiac Box Injury in Stable Patients

Introduction: In high-volume trauma centers, especially in developing countries, penetrating cardiac box injuries are frequent. Although many aspects of penetrating chest injuries have been well established, video-assisted thoracoscopy is still finding its place in cardiac box trauma and algorithmic approaches are still lacking. The purpose of this manuscript is to provide a streamlined recommendation for penetrating cardiac box injury in stable patients. Methods: Literature review was carried out using PubMed/ MEDLINE and Google Scholar databases to identify articles describing the characteristics and concepts of penetrating cardiac box trauma, including the characteristics of tamponade, cardiac ultrasound, indications and techniques of pericardial windows and, especially, the role of video-assisted thoracoscopy in stable patients. Results: Penetrating cardiac box injuries, whether by stab or gunshot wounds, require rapid surgical consultation. Unstable patients require immediate open surgery, however, determining which stable patients should be taken to thoracoscopic surgery is still controversial. Here, the classification of penetrating cardiac box injury used in Colombia is detailed, as well as the algorithmic approach to these types of trauma. Conclusion: Although open surgery is mandatory in unstable patients with penetrating cardiac box injuries, a more conservative and minimally invasive approach may be undertaken in stable patients. As rapid decision-making is critical in the trauma bay, surgeons working in high-volume trauma centers should expose themselves to thoracoscopy and always consider this possibility in the setting of penetrating cardiac box injuries in stable patients, always in the context of an experienced trauma team

Patterns of incidental perineural invasion and prognosis in cutaneous squamous cell carcinoma: A multicenter, retrospective cohort study

To the Editor: Perineural invasion (PNI) is rare and usually incidental in cutaneous squamous cell carcinoma (SCC), with an incidence of 2.5% to 14%.1 Incidental PNI is associated with poor prognosis in cutaneous SCC,2 and some evidence suggests its outcome differs, depending on the PNI pattern. We evaluated patterns of incidental PNI, using a multicenter retrospective cohort of 140 cutaneous SCCs with incidental PNI to determine the influence of nerve involvement on cutaneous SCC prognosis.Dr Canueto is partially supported ~ by grants PI18/000587 (Instituto de Salud Carlos III, cofinanced by Fondo Europeo de Desarrollo Regional) and GRS 1835/A/18 (Gerencia Regional de Salud de Castilla y Leon)

Phylodynamics of Hepatitis C Virus Subtype 2c in the Province of Córdoba, Argentina

The Hepatitis C Virus Genotype 2 subtype 2c (HCV-2c) is detected as a low prevalence subtype in many countries, except in Southern Europe and Western Africa. The current epidemiology of HCV in Argentina, a low-prevalence country, shows the expected low prevalence for this subtype. However, this subtype is the most prevalent in the central province of Córdoba. Cruz del Eje (CdE), a small rural city of this province, shows a prevalence for HCV infections of 5%, being 90% of the samples classified as HCV-2c. In other locations of Córdoba Province (OLC) with lower prevalence for HCV, HCV-2c was recorded in about 50% of the samples. The phylogenetic analysis of samples from Córdoba Province consistently conformed a monophyletic group with HCV-2c sequences from all the countries where HCV-2c has been sequenced. The phylogeographic analysis showed an overall association between geographical traits and phylogeny, being these associations significant (α = 0.05) for Italy, France, Argentina (places other than Córdoba), Martinique, CdE and OLC. The coalescence analysis for samples from CdE, OLC and France yielded a Time for the Most Common Recent Ancestor of about 140 years, whereas its demographic reconstruction showed a “lag” phase in the viral population until 1880 and then an exponential growth until 1940. These results were also obtained when each geographical area was analyzed separately, suggesting that HCV-2c came into Córdoba province during the migration process, mainly from Europe, which is compatible with the history of Argentina of the early 20th century. This also suggests that the spread of HCV-2c occurred in Europe and South America almost simultaneously, possibly as a result of the advances in medicine technology of the first half of the 20th century

Molecular characterization of hepatitis B virus X gene in chronic hepatitis B patients

BACKGROUND: HBV-X protein is associated with the pathogenesis of HBV related diseases, specially in hepatocellular carcinomas of chronic patients. Genetic variability of the X gene includes genotypic specific variations and mutations emerging during chronic infection. Its coding sequence overlaps important regions for virus replication, including the basal core promoter. Differences in the X gene may have implications in biological functions of the protein and thus, affect the evolution of the disease. There are controversial results about the consequences of mutations in this region and their relationship with pathogenesis. The purpose of this work was to describe the diversity of HBV-X gene in chronic hepatitis patients infected with different genotypes, according to liver disease. METHODS: HBV-X gene was sequenced from chronic hepatitis B patient samples, analyzed by phylogeny and genotyped. Nucleotide and aminoacid diversity was determined calculating intragenetic distances. Mutations at 127, 130 and 131 aminoacids were considered in relation to liver disease. RESULTS: The most prevalent genotype detected in this cohort was F (F1 and F4), followed by D and A. Most of the samples corresponding to genotypes A and F1 were HBeAg(+) and for genotypes D and F4, HBeAg(−) samples were represented in a higher percentage. Intragenetic distance values were higher in HBeAg(−) than in positive samples for all genotypes, and lower in overlapped regions, compared to single codification ones. Nucleotide and aminoacid diversities were higher in HBeAg(−), than in HBeAg(+) samples. CONCLUSIONS: Independently of the infecting genotypes, mutations at any of 127, 130 and/or 131 aminoacid positions and HBeAg(−) status were associated with mild liver disease in this cohort

Regional adaptation defines sensitivity to future ocean acidification

Physiological responses to temperature are known to be a major determinant of species distributions and can dictate the sensitivity of populations to global warming. In contrast, little is known about how other major global change drivers, such as ocean acidification (OA), will shape species distributions in the future. Here, by integrating population genetics with experimental data for growth and mineralization, physiology and metabolomics, we demonstrate that the sensitivity of populations of the gastropod Littorina littorea to future OA is shaped by regional adaptation. Individuals from populations towards the edges of the natural latitudinal range in the Northeast Atlantic exhibit greater shell dissolution and the inability to upregulate their metabolism when exposed to low pH, thus appearing most sensitive to low seawater pH. Our results suggest that future levels of OA could mediate temperature-driven shifts in species distributions, thereby influencing future biogeography and the functioning of marine ecosystems

Complex evolutionary history of the Mexican stoneroller Campostoma ornatum Girard, 1856 (Actinopterygii: Cyprinidae)

<p>Abstract</p> <p>Background</p> <p>Studies of the phylogeography of Mexican species are steadily revealing genetic patterns shared by different species, which will help to unravel the complex biogeographic history of the region. <it>Campostoma ornatum </it>is a freshwater fish endemic to montane and semiarid regions in northwest Mexico and southern Arizona. Its wide range of distribution and the previously observed morphological differentiation between populations in different watersheds make this species a useful model to investigate the biogeographic role of the Sierra Madre Occidental and to disentangle the actions of Pliocene tecto-volcanic processes <it>vs </it>Quaternary climatic change. Our phylogeographic study was based on DNA sequences from one mitochondrial gene (<it>cytb</it>, 1110 bp, n = 285) and two nuclear gene regions (S7 and RAG1, 1822 bp in total, n = 56 and 43, respectively) obtained from 18 to 29 localities, in addition to a morphological survey covering the entire distribution area. Such a dataset allowed us to assess whether any of the populations/lineages sampled deserve to be categorised as an evolutionarily significant unit.</p> <p>Results</p> <p>We found two morphologically and genetically well-differentiated groups within <it>C. ornatum</it>. One is located in the northern river drainages (Yaqui, Mayo, Fuerte, Sonora, Casas Grandes, Santa Clara and Conchos) and another one is found in the southern drainages (Nazas, Aguanaval and Piaxtla). The split between these two lineages took place about 3.9 Mya (CI = 2.1-5.9). Within the northern lineage, there was strong and significant inter-basin genetic differentiation and also several secondary dispersal episodes whit gene homogenization between drainages. Interestingly, three divergent mitochondrial lineages were found in sympatry in two northern localities from the Yaqui river basin.</p> <p>Conclusions</p> <p>Our results indicate that there was isolation between the northern and southern phylogroups since the Pliocene, which was related to the formation of the ancient Nazas River paleosystem, where the southern group originated. Within groups, a complex reticulate biogeographic history for <it>C. ornatum </it>populations emerges, following the taxon pulse theory and mainly related with Pliocene tecto-volcanic processes. In the northern group, several events of vicariance promoted by river or drainage isolation episodes were found, but within both groups, the phylogeographic patterns suggest the occurrence of several events of river capture and fauna interchange. The Yaqui River supports the most diverse populations of <it>C. ornatum</it>, with several events of dispersal and isolation within the basin. Based on our genetic results, we defined three ESUs within <it>C. ornatum </it>as a first attempt to promote the conservation of the evolutionary processes determining the genetic diversity of this species. They will likely be revealed as a valuable tool for freshwater conservation policies in northwest Mexico, where many environmental problems concerning the use of water have rapidly arisen in recent decades.</p