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BACKGROUND: Our objective is to describe a minimally invasive endoscopic surgical technique for performing lateral lumbar interbody fusion (LLIF). LLIF is a common approach to lumbar fusion in cases of degenerative lumbar disease; however, complications associated with psoas and lumbar plexus injury sometimes arise. The endoscopic modification presented here diminishes the requirement for sustained muscle retraction, minimizing complication risk while allowing for adequate decompression in select cases. METHODS: Endoscopic LLIF (ELLIF) was performed in 3 patients from 2019 to 2021. Surgeries were performed in the lateral position under general anesthesia with neurophysiological monitoring. Discectomy, endplate preparation, and harvesting of iliac crest bone were performed through a working channel endoscope. The introduction of an interbody cage (Joimax EndoLIF) was performed over a nitinol blunt-tip wire (Joimax). No expandable blade retractors were required. RESULTS: At 2-year follow-up of these 3 patients, the mean visual analog scale (VAS) score for leg pain improved from 9.3 to 1.7, and the mean Oswestry Disability Index (ODI) score improved from 40 to 8.3. There were no complications, readmissions, or recurrence of symptoms during the 2-year follow-up period. Patients spent an average of 36 hours in the hospital postoperatively and returned to normal daily activities after an average of 48 days. CONCLUSIONS: A minimally invasive modification to the LLIF procedure is presented that offers several potential advantages due to the application of endoscopic techniques: reduced muscle retraction, smaller incision, and the opportunity to perform both indirect decompression and endoscopically visualized discectomy in the same fusion procedure. CLINICAL RELEVANCE: The proposed endoscopic lateral lumbar interbody fusion and decompression is a minimally invasive technique that may provide patients with minimal complications, quick recovery, and good functional recovery.
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Atmospheric nitrogen dioxide (NO2) and sulfur dioxide (SO2) levels were monitored simultaneously by means of Radiello passive samplers at six sites of Santa Clara city, Cuba, in the cold and the warm seasons in 2010. The dissolved ionic forms of NO2 and SO2 as nitrate and sulfite plus sulfate, respectively, were determined by means of ion chromatography. Analysis of NO2 as nitrite was also performed by UV-Vis spectrophotometry. For NO2, significant t tests show good agreement between the results of IC and UV-Vis methods. The NO2 and SO2 concentrations peaked in the cold season, while their minimum levels were experienced in the warm season. The pollutant levels do not exceed the maximum allowable limit of the Cuban Standard 39:1999, i.e., 40 µg/m(3) and 50 µg/m(3) for NO2 and SO2, respectively. The lowest pollutant concentrations obtained in the warm season can be attributed to an increase in their removal via precipitation (scavenging) while to the decreased traffic density and industrial emission during the summer holidays (e.g., July and August).
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Contaminantes Atmosféricos/análisis , Contaminación del Aire/estadística & datos numéricos , Monitoreo del Ambiente , Dióxido de Nitrógeno/análisis , Dióxido de Azufre/análisis , Atmósfera/química , Cuba , Estaciones del AñoRESUMEN
Patterns of species diversity have been associated with changes in climate across latitude and elevation. However, the ecological and evolutionary mechanisms underlying these relationships are still actively debated. Here, we present a complementary view of the well-known tropical niche conservatism (TNC) hypothesis, termed the multiple zones of origin (MZO) hypothesis, to explore mechanisms underlying latitudinal and elevational gradients of phylogenetic diversity in tree communities. The TNC hypothesis posits that most lineages originate in warmer, wetter, and less seasonal environments in the tropics and rarely colonize colder, drier, and more seasonal environments outside of the tropical lowlands, leading to higher phylogenetic diversity at lower latitudes and elevations. In contrast, the MZO hypothesis posits that lineages also originate in temperate environments and readily colonize similar environments in the tropical highlands, leading to lower phylogenetic diversity at lower latitudes and elevations. We tested these phylogenetic predictions using a combination of computer simulations and empirical analyses of tree communities in 245 forest plots located in six countries across the tropical and subtropical Andes. We estimated the phylogenetic diversity for each plot and regressed it against elevation and latitude. Our simulated and empirical results provide strong support for the MZO hypothesis. Phylogenetic diversity among co-occurring tree species increased with both latitude and elevation, suggesting an important influence on the historical dispersal of lineages with temperate origins into the tropical highlands. The mixing of different floras was likely favored by the formation of climatically suitable corridors for plant migration due to the Andean uplift. Accounting for the evolutionary history of plant communities helps to advance our knowledge of the drivers of tree community assembly along complex climatic gradients, and thus their likely responses to modern anthropogenic climate change.
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Does the intensification of agriculture reduce cultivated areas and, in so doing, spare some lands by concentrating production on other lands? Such sparing is important for many reasons, among them the enhanced abilities of released lands to sequester carbon and provide other environmental services. Difficulties measuring the extent of spared land make it impossible to investigate fully the hypothesized causal chain from agricultural intensification to declines in cultivated areas and then to increases in spared land. We analyze the historical circumstances in which rising yields have been accompanied by declines in cultivated areas, thereby leading to land-sparing. We use national-level United Nations Food and Agricultural Organization data on trends in cropland from 1970-2005, with particular emphasis on the 1990-2005 period, for 10 major crop types. Cropland has increased more slowly than population during this period, but paired increases in yields and declines in cropland occurred infrequently, both globally and nationally. Agricultural intensification was not generally accompanied by decline or stasis in cropland area at a national scale during this time period, except in countries with grain imports and conservation set-aside programs. Future projections of cropland abandonment and ensuing environmental services cannot be assumed without explicit policy intervention.
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Agricultura , Conservación de los Recursos Naturales , Internacionalidad , Modelos TeóricosRESUMEN
Endoscopic techniques in spine surgery are rapidly evolving, with operations becoming progressively safer and less invasive. Lumbar interbody fusion (LIF) procedures comprise many spine procedures that have benefited from endoscopic assistance and minimally invasive approaches. Though considerable variation exists within endoscopic LIF, similar principles and techniques are common to all types. Nonetheless, innovations continually emerge, requiring trainees and experienced surgeons to maintain familiarity with the domain and its possibilities. We present two illustrative cases of endoscopic transforaminal lumbar interbody fusion with a comprehensive literature review of the different approaches to endoscopic LIF procedures.
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Vértebras Lumbares , Fusión Vertebral , Endoscopía/métodos , Vértebras Lumbares/diagnóstico por imagen , Vértebras Lumbares/cirugía , Región Lumbosacra , Procedimientos Quirúrgicos Mínimamente Invasivos/métodos , Fusión Vertebral/métodosRESUMEN
It is largely unknown how South America's Andean forests affect the global carbon cycle, and thus regulate climate change. Here, we measure aboveground carbon dynamics over the past two decades in 119 monitoring plots spanning a range of >3000 m elevation across the subtropical and tropical Andes. Our results show that Andean forests act as strong sinks for aboveground carbon (0.67 ± 0.08 Mg C ha-1 y-1) and have a high potential to serve as future carbon refuges. Aboveground carbon dynamics of Andean forests are driven by abiotic and biotic factors, such as climate and size-dependent mortality of trees. The increasing aboveground carbon stocks offset the estimated C emissions due to deforestation between 2003 and 2014, resulting in a net total uptake of 0.027 Pg C y-1. Reducing deforestation will increase Andean aboveground carbon stocks, facilitate upward species migrations, and allow for recovery of biomass losses due to climate change.
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Secuestro de Carbono/fisiología , Carbono/metabolismo , Cambio Climático , Conservación de los Recursos Naturales , Árboles/metabolismo , Biomasa , Bosques , América del Sur , Clima TropicalRESUMEN
Our knowledge about the structure and function of Andean forests at regional scales remains limited. Current initiatives to study forests over continental or global scales still have important geographical gaps, particularly in regions such as the tropical and subtropical Andes. In this study, we assessed patterns of structure and tree species diversity along ~ 4000 km of latitude and ~ 4000 m of elevation range in Andean forests. We used the Andean Forest Network (Red de Bosques Andinos, https://redbosques.condesan.org/) database which, at present, includes 491 forest plots (totaling 156.3 ha, ranging from 0.01 to 6 ha) representing a total of 86,964 identified tree stems ≥ 10 cm diameter at breast height belonging to 2341 identified species, 584 genera and 133 botanical families. Tree stem density and basal area increases with elevation while species richness decreases. Stem density and species richness both decrease with latitude. Subtropical forests have distinct tree species composition compared to those in the tropical region. In addition, floristic similarity of subtropical plots is between 13 to 16% while similarity between tropical forest plots is between 3% to 9%. Overall, plots ~ 0.5-ha or larger may be preferred for describing patterns at regional scales in order to avoid plot size effects. We highlight the need to promote collaboration and capacity building among researchers in the Andean region (i.e., South-South cooperation) in order to generate and synthesize information at regional scale.
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Altitud , Biodiversidad , Bosques , Árboles , Clima , América del SurRESUMEN
Bond-based quadratic indices, new TOMOCOMD-CARDD molecular descriptors, and linear discriminant analysis (LDA) were used to discover novel lead trichomonacidals. The obtained LDA-based quantitative structure-activity relationships (QSAR) models, using nonstochastic and stochastic indices, were able to classify correctly 87.91% (87.50%) and 89.01% (84.38%) of the chemicals in training (test) sets, respectively. They showed large Matthews correlation coefficients of 0.75 (0.71) and 0.78 (0.65) for the training (test) sets, correspondingly. Later, both models were applied to the virtual screening of 21 chemicals to find new lead antitrichomonal agents. Predictions agreed with experimental results to a great extent because a correct classification for both models of 95.24% (20 of 21) of the chemicals was obtained. Of the 21 compounds that were screened and synthesized, 2 molecules (chemicals G-1, UC-245) showed high to moderate cytocidal activity at the concentration of 10 microg/ml, another 2 compounds (G-0 and CRIS-148) showed high cytocidal activity only at the concentration of 100 microg/ml, and the remaining chemicals (from CRIS-105 to CRIS-153, except CRIS-148) were inactive at these assayed concentrations. Finally, the best candidate, G-1 (cytocidal activity of 100% at 10 microg/ml) was in vivo assayed in ovariectomized Wistar rats achieving promising results as a trichomonacidal drug-like compound.
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Antitricomonas/química , Antitricomonas/farmacología , Diseño Asistido por Computadora , Evaluación Preclínica de Medicamentos/métodos , Programas Informáticos , Trichomonas vaginalis/efectos de los fármacos , Adulto , Animales , Antitricomonas/uso terapéutico , Análisis Discriminante , Farmacorresistencia Bacteriana , Femenino , Humanos , Estructura Molecular , Ovariectomía , Ratas , Ratas Wistar , Tricomoniasis/tratamiento farmacológicoRESUMEN
Starting from the four DNA bases order in the Boolean lattice, a novel Lie Algebra of the genetic code is proposed. Here, the main partitions of the genetic code table were obtained as equivalent classes of quotient spaces of the genetic code vector space over the Galois field of the four DNA bases. The new algebraic structure shows strong connections among algebraic relationships, codon assignments and physicochemical properties of amino acids. Moreover, a distance defined between codons expresses a physicochemical meaning. It was also noticed that the distance between wild type and mutant codons tends to be small in mutational variants of four genes: human phenylalanine hydroxylase, human beta-globin, HIV-1 protease and HIV-1 reverse transcriptase. These results strongly suggest that deterministic rules in genetic code origin must be involved.
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Código Genético , Modelos Genéticos , Codón/genética , ADN/genética , Globinas/genética , Proteasa del VIH/genética , Transcriptasa Inversa del VIH/genética , Humanos , Matemática , Mutación , Fenilalanina Hidroxilasa/genéticaRESUMEN
Research on similarity searching of cheminformatic data sets has been focused on similarity measures using fingerprints. However, nominal scales are the least informative of all metric scales, increasing the tied similarity scores, and decreasing the effectivity of the retrieval engines. Tanimoto's coefficient has been claimed to be the most prominent measure for this task. Nevertheless, this field is far from being exhausted since the computer science no free lunch theorem predicts that "no similarity measure has overall superiority over the population of data sets". We introduce 12 relational agreement (RA) coefficients for seven metric scales, which are integrated within a group fusion-based similarity searching algorithm. These similarity measures are compared to a reference panel of 21 proximity quantifiers over 17 benchmark data sets (MUV), by using informative descriptors, a feature selection stage, a suitable performance metric, and powerful comparison tests. In this stage, RA coefficients perform favourably with repect to the state-of-the-art proximity measures. Afterward, the RA-based method outperform another four nearest neighbor searching algorithms over the same data domains. In a third validation stage, RA measures are successfully applied to the virtual screening of the NCI data set. Finally, we discuss a possible molecular interpretation for these similarity variants.
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Química/métodos , Bases de Datos de Compuestos Químicos , Informática/métodos , Algoritmos , Minería de DatosRESUMEN
General patterns of forest dynamics and productivity in the Andes Mountains are poorly characterized. Here we present the first large-scale study of Andean forest dynamics using a set of 63 permanent forest plots assembled over the past two decades. In the North-Central Andes tree turnover (mortality and recruitment) and tree growth declined with increasing elevation and decreasing temperature. In addition, basal area increased in Lower Montane Moist Forests but did not change in Higher Montane Humid Forests. However, at higher elevations the lack of net basal area change and excess of mortality over recruitment suggests negative environmental impacts. In North-Western Argentina, forest dynamics appear to be influenced by land use history in addition to environmental variation. Taken together, our results indicate that combinations of abiotic and biotic factors that vary across elevation gradients are important determinants of tree turnover and productivity in the Andes. More extensive and longer-term monitoring and analyses of forest dynamics in permanent plots will be necessary to understand how demographic processes and woody biomass are responding to changing environmental conditions along elevation gradients through this century.
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Bosques , Biodiversidad , Modelos Lineales , Análisis de Componente Principal , Árboles/crecimiento & desarrolloRESUMEN
There are several classification problems, which are difficult to solve using a single classifier because of the complexity of the decision boundary. Whereas a wide variety of multiple classifier systems have been built with the purpose of improving the recognition process, there is no universal method performing the best. This paper provides a review of different multi-classifiers and some application of them. Also it is shown a novel model of combining classifiers and its application to predicting human immunodeficiency virus drug resistance from genotype. The proposal is based on the use of different classifier models. It clusters the dataset considering the performance of the base classifiers. The system learns how to decide from the groups, by using a meta-classifier, which are the best classifiers for a given pattern. The proposed model is compared with well-known classifier ensembles and individual classifiers as well resulting the novel model in similar or even better performance.
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Fármacos Anti-VIH/farmacología , Farmacorresistencia Viral/efectos de los fármacos , Infecciones por VIH/tratamiento farmacológico , VIH-1/efectos de los fármacos , Infecciones por VIH/virología , HumanosRESUMEN
Objetivo: Analizar la validez y confiabilidad de un cuestionario para la exploración de factores protectores de la salud mental en estudiantes universitarios cubanos. Método: La muestra quedó conformada por 1377 estudiantes. Se utilizó el análisis categórico de componentes principales, el análisis de conglomerados en dos etapas y los árboles de decisión. Resultados: Se identificaron dos factores. La primera dimensión incluyó ítems que tienen un sentido positivo y expresan un desarrollo de estos factores protectores. Esta dimensión mostró un mayor coeficiente de confiabilidad y fue capaz de explicar una mayor proporción de la varianza en los clúster identificados. La segunda dimensión agrupó aquellos ítems relacionados con un pobre desarrollo de estos factores de protección que pudieran constituir en factores de riesgo. Los ítems que mejor predicen la agrupación de los tres clúster están relacionados con la resiliencia, toma de decisiones, la autoeficacia y la autoestima. Conclusión: El instrumento desarrollado mostró su exactitud y precisión en el proceso de obtención de la información necesaria para evaluar los factores de protección de la salud mental en estudiantes universitarios cubanos.
Objective: To analyze the validity and reliability of a questionnaire in exploring the protective factors of mental health in Cuban university students. Method: The sample was composed of 1377 students. A categorical principal components analysis, a two-step cluster analysis and decision trees were used. Results: Results revealed two components. The first dimension included items that have a positive meaning and express a development of these protective factors. This dimension showed a higher coefficient of reliability and was able to explain a higher proportion of the variance in the clusters identified. The second dimension grouped those items that were related to poor development of these protection factors, which could constitute to risk factors. Items associated with resilience, decision making ability, self- efficacy and self- esteem were the best predictors in the grouping process. Conclusion: The instrument developed showed its accuracy and precision in the process of obtaining the necessary information to evaluate the factors of protection of mental health in Cuban university students.
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El contexto universitario constituye un escenario complejo que puede potenciar el desarrollo personal de los estudiantes, pero también puede estimular la experimentación de emociones negativas. El estudio presentado en este artículo se orientó a explorar la afectividad negativa en estudiantes universitarios. Se realizó un muestreo probabilístico. La muestra estuvo compuesta por 1.377 estudiantes a los que se les administró el Autorreporte Vivencial. Se utilizó el análisis descriptivo univariante y también el análisis de conglomerados en 2 etapas, el análisis categórico de componentes principales y los árboles de decisión. Los resultados revelaron bajos niveles de afecto negativo. Los estudiantes se dividieron en 2 grupos que se diferencian en la intensidad con la que experimentan las diferentes emociones negativas, con mayor presencia de las mujeres en el conglomerado de peores resultados. Se identificó que la tristeza y la angustia demostraron ser los mejores predictores de la afectividad negativa en los estudiantes universitarios. Los resultados alcanzados constituyen los primeros pasos para el diseño de estrategias preventivas y de promoción de la salud mental en el contexto universitario
The university context is a complex space that can enhance the personal development of students, but it can also stimulate negative emotional experiences. This study was aimed at exploring negative affectivity levels in university students. Probabilistic sampling was used. The sample was composed of 1,377 students who completed the Experiential Self-Report. A univariate descriptive analysis, a two-step cluster analysis, a categorical principal components analysis and decision trees were used. Results revealed low levels of negative affectivity. Students were divided into 2 groups according to the intensity with which they experienced various negative emotions, with a higher presence of women in the cluster with worse results. Sadness and distress proved to be the best predictors of negative affectivity in university students. The results obtained are the first steps towards designing preventive strategies and promoting mental health in the university context
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Humanos , Masculino , Femenino , Adulto Joven , Adulto , Estrés Psicológico/epidemiología , Estrés Psicológico/psicología , Emociones/fisiología , Ajuste Emocional/fisiología , Estudiantes/psicología , Proyectos de Investigación/estadística & datos numéricos , Proyectos de Investigación/normas , Planificación Social/tendencias , Salud Mental/estadística & datos numéricos , Salud Mental/normas , Salud Mental/tendencias , Psicología Social/métodos , Proyectos de Investigación/tendencias , Investigación Conductal/métodos , Investigación Conductal/tendencias , Análisis de Datos/métodosRESUMEN
Resumen El estudio se orientó al desarrollo y análisis de la confiabilidad del Cuestionario para la evaluación de percepción de riesgo sobre el consumo de alcohol en estudiantes universitarios. La muestra quedó compuesta por 1377 estudiantes universitarios cubanos. Se utilizó el análisis categórico de componentes principales, el análisis de conglomerados en dos etapas y los árboles de decisión. Se identificaron dos dimensiones, la primera se relacionó con el componente motivacional-conductual de la percepción de riesgo y la segunda con la información sobre los riesgos del consumo. Ambas dimensiones mostraron elevados índices de confiabilidad y se relacionaron con los tres clúster identificados de acuerdo con la adecuación de la percepción de riesgo respecto al consumo de alcohol. El árbol de clasificación logró un 84.4% de buena clasificación, destacándose como predictores los ítems de la dimensión motivacional-conductual. El instrumento diseñado para la evaluación de la percepción de riesgo sobre el consumo de alcohol en estudiantes universitarios mostró adecuados niveles de confiabilidad que favorece su aplicación en este contexto.
Abstract The aim of this study was development and to analyze the reliability of risk perception questionnaire about alcohol consumption in university students. The sample was composed by 1377 university students. In the data analysis the authors used categorical principal components analysis, two step cluster analysis and the decision trees. Two dimensions was found, the first dimension was associated with the motivational-behavioral component of risk perception and the second with information about risk of alcohol consumption. Both dimensions shows high levels of reliability and it related with the three clusters identified according the adequacy of risk perception about alcohol consumption. The decision tree obtained 84.4% of good classifications; it emphasizes like predictors items of motivational-behavioral dimension. The instrument designed to assess risk perception on alcohol consumption in university students showed adequate levels of reliability which favors its application in this context.
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Consumo de Bebidas Alcohólicas , Reproducibilidad de los Resultados , Medición de Riesgo , Análisis de Datos , Percepción , Estudiantes , Árboles de Decisión , Análisis por Conglomerados , Encuestas y Cuestionarios , ClasificaciónRESUMEN
Introducción: el consumo de tabaco constituye un serio problema de salud a nivel mundial y en Cuba, especialmente en la población joven. La percepción de riesgo ha sido identificada como una importante variable que influye en el inicio y mantenimiento del consumo de tabaco en esta etapa. Objetivo: explorar las características de la percepción de riesgo respecto al consumo de tabaco en jóvenes universitarios cubanos. Métodos: investigación con enfoque cuantitativo, diseño descriptivo ex post facto. La muestra quedó conformada por 1 377 estudiantes universitarios. Se aplicó un cuestionario para explorar la percepción de riesgo respecto al consumo de tabaco. Se utilizó el análisis descriptivo univariante, el análisis de conglomerados en dos etapas, el análisis categórico de componentes principales y los árboles de decisión. Resultados: se identificaron niveles adecuados de información sobre las consecuencias de este comportamiento de riesgo. Las variaciones más altas fueron en la dimensión conductual-motivacional y fue el mejor predictor en el proceso de agrupación de acuerdo a los niveles de percepción de riesgo. Hay más mujeres que hombres en el grupo con los mejores resultados. Conclusiones: los resultados permitieron una compresión multidimensional de la percepción del riesgo en estudiantes universitarios cubanos(AU)
Introduction: Tobacco consumption is a serious problem in a worldwide and in Cuba, especially in young people. Risk perception has been identified as an important variable that influences the initiation and maintenance of tobacco consumption in this stage. Objetive: To explore the characteristics of risk perception of the tobacco consumption in Cuban university students. Methods: The research was conceived from a quantitative approach with a descriptive ex post facto design. The sample was composed by 1377 university students. It was used the questionnaire of risk perception of tobacco consumption. In the data analysis the authors used univariate descriptive analysis, two step cluster analysis, categorical principal components analysis and the decision trees. Results: It was identified as tendency, adequate levels of information about consequences of this risk behavior. The higher variations were in the behavioral-motivational dimension and it was the best predictor in the grouping process according to levels of risk perception. There are more females than males in the cluster with the best results Conclusions: The results allowed a multidimensional understanding of risk perception of tobacco consumption in Cuban university students(AU)
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Humanos , Salud del Estudiante , Uso de Tabaco/prevención & control , CubaRESUMEN
Introducción: el consumo de tabaco constituye un serio problema de salud a nivel mundial y en Cuba, especialmente en la población joven. La percepción de riesgo ha sido identificada como una importante variable que influye en el inicio y mantenimiento del consumo de tabaco en esta etapa. Objetivo: explorar las características de la percepción de riesgo respecto al consumo de tabaco en jóvenes universitarios cubanos. Métodos: investigación con enfoque cuantitativo, diseño descriptivo ex post facto. La muestra quedó conformada por 1 377 estudiantes universitarios. Se aplicó un cuestionario para explorar la percepción de riesgo respecto al consumo de tabaco. Se utilizó el análisis descriptivo univariante, el análisis de conglomerados en dos etapas, el análisis categórico de componentes principales y los árboles de decisión. Resultados: se identificaron niveles adecuados de información sobre las consecuencias de este comportamiento de riesgo. Las variaciones más altas fueron en la dimensión conductual-motivacional y fue el mejor predictor en el proceso de agrupación de acuerdo a los niveles de percepción de riesgo. Hay más mujeres que hombres en el grupo con los mejores resultados. Conclusiones: los resultados permitieron una compresión multidimensional de la percepción del riesgo en estudiantes universitarios cubanos(AU)
Introduction: Tobacco consumption is a serious problem in a worldwide and in Cuba, especially in young people. Risk perception has been identified as an important variable that influences the initiation and maintenance of tobacco consumption in this stage. Objetive: To explore the characteristics of risk perception of the tobacco consumption in Cuban university students. Methods: The research was conceived from a quantitative approach with a descriptive ex post facto design. The sample was composed by 1377 university students. It was used the questionnaire of risk perception of tobacco consumption. In the data analysis the authors used univariate descriptive analysis, two step cluster analysis, categorical principal components analysis and the decision trees. Results: It was identified as tendency, adequate levels of information about consequences of this risk behavior. The higher variations were in the behavioral-motivational dimension and it was the best predictor in the grouping process according to levels of risk perception. There are more females than males in the cluster with the best results Conclusions: The results allowed a multidimensional understanding of risk perception of tobacco consumption in Cuban university students(AU)
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Humanos , Masculino , Femenino , Adulto Joven , Salud del Estudiante , Uso de Tabaco/prevención & control , CubaRESUMEN
Analytical solutions for the case of controlled dispersed-drug release from planar non-erodible polymeric matrices, based on Refined Integral Method, are presented. A new adjusting equation is used for the dissolved drug concentration profile in the depletion zone. The set of equations match the available exact solution. In order to illustrate the usefulness of this model, comparisons with experimental profiles reported in the literature are presented. The obtained results show that the model can be employed in a broad range of applicability.
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Sistemas de Liberación de Medicamentos/métodos , Modelos Teóricos , Polímeros/química , Química Farmacéutica , Preparaciones de Acción Retardada , Difusión , Cinética , Solubilidad , SolucionesRESUMEN
A plausible architecture of an ancient genetic code is derived from an extended base triplet vector space over the Galois field of the extended base alphabet {D,A,C,G,U}, where symbol D represents one or more hypothetical bases with unspecific pairings. We hypothesized that the high degeneration of a primeval genetic code with five bases and the gradual origin and improvement of a primeval DNA repair system could make possible the transition from ancient to modern genetic codes. Our results suggest that the Watson-Crick base pairing G identical with C and A=U and the non-specific base pairing of the hypothetical ancestral base D used to define the sum and product operations are enough features to determine the coding constraints of the primeval and the modern genetic code, as well as, the transition from the former to the latter. Geometrical and algebraic properties of this vector space reveal that the present codon assignment of the standard genetic code could be induced from a primeval codon assignment. Besides, the Fourier spectrum of the extended DNA genome sequences derived from the multiple sequence alignment suggests that the called period-3 property of the present coding DNA sequences could also exist in the ancient coding DNA sequences. The phylogenetic analyses achieved with metrics defined in the N-dimensional vector space (B(3))(N) of DNA sequences and with the new evolutionary model presented here also suggest that an ancient DNA coding sequence with five or more bases does not contradict the expected evolutionary history.