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Ordered and disordered semiconductor superlattices represent structures with completely opposed properties. For instance, ordered superlattices exhibit extended Bloch-like states, while disordered superlattices present localized states. These characteristics lead to higher conductance in ordered superlattices compared to disordered ones. Surprisingly, disordered dimer superlattices, which consist of two types of quantum wells with one type always appearing in pairs, exhibit extended states. The percentage of dissimilar wells does not need to be large to have extended states. Furthermore, the conductance is intermediate between ordered and disordered superlattices. In this work, we explore disordered dimer superlattices in graphene. We calculate the transmission and transport properties using the transfer matrix method and the Landauer-Büttiker formalism, respectively. We identify and discuss the main energy regions where the conductance of random dimer superlattices in graphene is intermediate to that of ordered and disordered superlattices. We also analyze the resonant energies of the double quantum well cavity and the electronic structure of the host gated graphene superlattice (GGSL), finding that the coupling between the resonant energies and the superlattice energy minibands gives rise to the extended states in random dimer GGSLs.
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Monomer, dimer and trimer semiconductor superlattices are an alternative for bandgap engineering due to the possibility of duplicate, triplicate, and in general multiply the number of minibands and minigaps in a specific energy region. Here, we show that monomer, dimer, and trimer magnetic silicene superlattices (MSSLs) can be the basis for tunable magnetoresistive devices due to the multiplication of the peaks of the tunneling magnetoresistance (TMR). In addition, these structures can serve as spin-valleytronic devices due to the formation of two well-defined spin-valley polarization states by appropriately adjusting the superlattice structural parameters. We obtain these conclusions by studying the spin-valley polarization and TMR of monomer, dimer, and trimer MSSLs. The magnetic unit cell is structured with one seed A with positive magnetization, and one, two, or three seeds B with variable magnetization. The number of B seeds defines the monomer, dimer, and trimer superlattice, while its magnetic orientation positive or negative the parallel (PM) or antiparallel magnetization (AM) superlattice configuration. The transfer matrix method and the Landauer-Büttiker formalism are employed to obtain the transmission and transport properties, respectively. We find multiplication of TMR peaks in staircase fashion according to the number of B seeds in the superlattice unit cell. This multiplication is related to the multiplication of the minibands which reflects as multiplication of the descending envelopes of the conductance. We also find well-defined polarization states for both PM and AM by adjusting asymmetrically the width and height of the barrier-well in seeds A and B.
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Gaussian and Gaussian-related structures are quite attractive due to its versatility to modulate the electronic transport, including its possibility as electron filters. Here, we show that these non-conventional profiles are not the exception when dealing with Fermi velocity barriers in monolayer graphene. In particular, we show that Gaussian Fermi velocity graphene barriers (G-FVGBs) and Gaussian-pulsed-like Fermi velocity graphene superlattices (GPL-FVGSLs) can serve as electron band-pass filters and oscillating conductance structures. We reach this conclusion by theoretically studying the transmission and transport properties of the mentioned structures. The study is based on the continuum model, the transfer matrix method and the Landauer-Büttiker formalism. We find nearly flat transmission bands or pass bands for G-FVGBs modulable through the system parameters. The pass bands improve as the maximum ratio of Fermi velocities (ξmax) increases, however its omnidirectional range is reduced. These characteristics result in a decaying conductance (integrated transmission) withξmax. The integrated transmission remains practically unaltered with the size of the system due to the saturation of the electron pass band filtering. In the case of GPL-FVGSLs the GPL profile results in regions of high transmission probability that can merge as flat transmission minibands if the pulse fraction and the superlattice parameters are appropriately tuned. The GPL profile also results in conductance (integrated transmission) oscillations that can be multiplied or reduced in number by adjusting the pulse fraction as well as the superlattice parameters.
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The transfer matrix method is considered to obtain the fundamental properties of 1D Dirac-like problems. The case of 1D problems in monolayer graphene is addressed. The main characteristics of the transfer matrix are analyzed, contrasting them with the ones corresponding to 1D Schrödinger-like problems. Analytic expressions for the transmission coefficient and bound states are obtained. The continuity between bound states and states of perfect transmission is demonstrated in general, and in particular showed for the case of single electrostatic barriers. These findings in principle can be extended to 2D materials with Hamiltonian similar to monolayer graphene such as silicene and transition metal dichalcogenides.
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Periodic superlattices constitute ideal structures to modulate the transport properties of two-dimensional materials. In this paper, we show that the tunneling magnetoresistance (TMR) in phosphorene can be tuned effectively through periodic magnetic modulation. Deltaic magnetic barriers are arranged periodically along the phosphorene armchair direction in parallel (PM) and anti-parallel magnetization (AM) fashion. The theoretical treatment is based on a low-energy effective Hamiltonian, the transfer matrix method and the Landauer-Büttiker formalism. We find that the periodic modulation gives rise to oscillating transport characteristics for both PM and AM configurations. More importantly, by adjusting the electrostatic potential appropriately we find Fermi energy regions for which the AM conductance is reduced significantly while the PM conductance keeps considerable values, resulting in an effective TMR that increases with the magnetic field strength. These findings could be useful in the design of magnetoresistive devices based on magnetic phosphorene superlattices.
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Magnetic silicene superlattices (MSSLs) are versatile structures with spin-valley polarization and tunneling magnetoresistance (TMR) capabilities. However, the oscillating transport properties related to the superlattice periodicity impede stable spin-valley polarization states reachable by reversing the magnetization direction. Here, we show that aperiodicity can be used to improve the spin-valley polarization and TMR by reducing the characteristic conductance oscillations of periodic MSSLs (P-MSSLs). Using the Landauer-Büttiker formalism and the transfer matrix method, we investigate the spin-valley polarization and the TMR of Fibonacci (F-) and Thue-Morse (TM-) MSSLs as typical aperiodic superlattices. Our findings indicate that aperiodic superlattices with higher disorder provide better spin-valley polarization and TMR values. In particular, TM-MSSLs reduce considerably the conductance oscillations giving rise to two well-defined spin-valley polarization states and a better TMR than F- and P-MSSLs. F-MSSLs also improve the spin-valley polarization and TMR, however they depend strongly on the parity of the superlattice generation.
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BACKGROUND: The Brazilian federal government issued Ministerial Ordinance No. 718 in 2010 to expand the funding of orthodontic treatment provided by Brazilian municipalities via the Unified Health System (SUS in Portuguese). AIM: To identify social and structural factors associated with Brazilian municipalities that provide fixed orthodontic appliance therapy and interceptive orthodontic therapy. METHODS: Official Brazilian government databases were used for data collection. Poisson regression with robust variance was used for statistical analysis. RESULTS: Municipalities hosting Dental Specialty Centers (DSCs) with greater installed capacity (type III DSC with 7 dental chairs or over), which employed dentists specializing in pediatric dentistry and orthodontics, were more likely to offer orthodontic services via SUS. CONCLUSIONS: Federal, state, and municipal managers need to review the funding of orthodontic services via SUS, which can be used for creating DSCs and hiring professionals with expertise in orthodontics.
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Ortodontia , Criança , Humanos , Brasil , Ortodontia Interceptora , Assistência Odontológica , OdontopediatriaRESUMO
The transmission and transport properties of biperiodic graphene superlattices are studied theoretically. Special attention is paid to the so-called transparent states of biperiodic superlattices. A Dirac-like Hamiltonian is used to describe the charge carriers in graphene. The transfer matrix method and the Landauer-Büttiker formalism are implemented to obtain the transmittance and conductance, respectively. Similar results to those reported for Schrödinger electrons are obtained. However, in the case of Dirac electrons the splitted bands and the transparent states associated to the biperiodicity depend strongly on the angle of incidence as well as the character of the charge carriers. In fact, the dynamic of the splitted bands and transparent states is inverted for holes. The origin of transparent states is unveiled by obtaining an analytic expression for the transmittance. It is found that resonant transmission through single and double barriers gives rise to transparent states. Regarding the transport properties, it is possible to identify the fundamental changes caused by the biperiodicity. In particular, it is found a splitting, shifting, and diminishment of the conductance peaks with respect to the case of regular periodicity. This opens the door to corroborate experimentally the fundamental characteristics of biperiodic gated graphene superlattices through transport measurements.
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Surface water samples from the Perdido study area presented Cd and V concentrations similar to those reported internationally for waters with: (1) fossil fuel extraction, processing and burning, and (2) sites polluted by anthropogenic wastewater. Results showed an order of magnitude increase in time for Cd, therefore, no general average value was established. For V, however, results of this study suggest a general average value of 1.4 µg L-1 for the area. The observed spatial variation of concentrations could be the result of: (1) temporal variation of external inputs to the area, and coincide with previously reported hydrodynamic patterns of dispersion related to significant river contributions and accumulation areas indicative of eddy circulation or fronts. The Perdido area showed Cd and V concentrations in surface water reflective of anthropogenic impacts, while its spatial and temporal variation could depend significantly on the hydrodynamics of the area.
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Cádmio , Poluentes Químicos da Água , Cádmio/análise , Monitoramento Ambiental , Golfo do México , Vanádio/análise , Água , Poluentes Químicos da Água/análiseRESUMO
We investigated the spatial and temporal distribution of V and Cd in surface sediments of the Yucatan Shelf to establish current average values for the area. V and Cd concentrations are similar to those reported internationally for limestone rocks and surface marine sediments. The observed variability of V concentrations between cruises may be the result of changes in ocean current direction in summer (SW-S) and strong prevailing winds in autumn (N-NE). In addition to the hydrodynamics described above, Cd variations may also be associated with inputs of particulate material by upwelling events and subsequent transport and distribution to the shelf by the Yucatan Channel current (autumn). Considering that both metals showed significant spatial and temporal differences, a range of values for V (0.4-1.5 µg g-1) and Cd (0.05-0.2 µg g-1) are proposed as baseline reference for sediments of the Yucatan Shelf.
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Metais Pesados , Poluentes Químicos da Água , Monitoramento Ambiental , Sedimentos Geológicos , Golfo do México , Metais Pesados/análise , México , Poluentes Químicos da Água/análiseRESUMO
Surface water samples from the Yucatan shelf presented Cd concentrations similar to those reported internationally for non-polluted coastal and marine waters. V concentrations, on the other hand, fall within the range of anthropogenically polluted waters (25% of the sampling sites). In the study area, the probable sources of V could be: (1) carbonate sediments leaching V into the water column and co-transported with fine sediments resuspending as a result of the complex hydrodynamics in the area or, (2) accidental spills from cargo ships transporting oil between the Atlantic and the Gulf of Mexico. Significant spatial and temporal differences were found for both metals; therefore, a regional interval concentration is suggested for V from 1.28 to 1.84 µg L-1 and Cd from 0.003 to 0.09 µg L-1. These differences could primarily be the result of the observed hydrology and hydrodynamics created by the Yucatan current, submarine groundwater discharges and upwelling.
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Metais Pesados , Poluentes Químicos da Água , Cádmio , Monitoramento Ambiental , Sedimentos Geológicos , Metais Pesados/análise , México , Vanádio , Água , Poluentes Químicos da Água/análiseRESUMO
This study analyzed 27 surface sediment samples from the Tamaulipas Continental shelf to determine the spatial-temporal distribution of V and Cd (spring-summer 2016; summer 2017). Average V concentrations (99 ± 18 mg g-1) were similar to that previously reported values for the area, while average Cd concentrations reflect uncontaminated sediments at surface level of the shelf. Inputs of V and Cd may be related to hydrocarbon and anthropogenic contributions from South and North of the Gulf of Mexico. The variability shown by both elements results from the hydrodynamics and hydrology of the area produced by local currents, eddies of the Loop Current, resuspension of fine sediments and contribution of terrigenous material. Considering that both metals showed significant differences (Shapiro-Wilk, p = 0), baseline concentrations could not be established, instead a reference interval of 79-122 µg g-1 for V and 0.121-0.258 µg g-1 for Cd in sediments from the Tamaulipas platform is suggested.
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Metais Pesados , Poluentes Químicos da Água , Cádmio , Monitoramento Ambiental , Sedimentos Geológicos , Golfo do México , Metais Pesados/análise , México , Vanádio , Poluentes Químicos da Água/análiseRESUMO
Fano resonances of bilayer graphene could be attractive for thermoelectric devices. The special profile presented by such resonances could significantly enhance the thermoelectric properties. In this work, we study the thermoelectric properties of bilayer graphene single and double barrier structures. The barrier structures are typically supported by a substrate and encapsulated by protecting layers, reducing considerably the phonon thermal transport. So, we will focus on the electronic contribution to the thermal transport. The charge carriers are described as massive chiral particles through an effective Dirac-like Hamiltonian. The Hybrid matrix method and the Landauer-Büttiker formalism are implemented to obtain the transmission, transport and thermoelectric properties. The temperature dependence of the Seebeck coefficient, the power factor, the figure of merit and the efficiency is analyzed for gapless single and double barriers. We find that the charge neutrality point and the system resonances shape the thermoelectric response. In the case of single barriers, the low-temperature thermoelectric response is dominated by the charge neutrality point, while the high-temperature response is determined by the Fano resonances. In the case of double barriers, Breit-Wigner resonances dominate the thermoelectric properties at low temperatures, while Fano and hybrid resonances become preponderant as the temperature rises. The values for the figure of merit are close to two for single barriers and above three for double barriers. The system resonances also allows us to optimize the output power and the efficiency at low and high temperatures. By computing the density of states, we also corroborate that the improvement of the thermoelectric properties is related to the accumulation of electron states. Our findings indicate that bilayer graphene barrier structures can be used to improve the response of thermoelectric devices.
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High surface water-groundwater connectivity characterizes watersheds underlain by karsts, increasing contaminant transport risks. However, karsts are highly complex, making research necessary to understand the transport of contaminants from the surface, through the aquifer, to discharge areas. In Yucatan, the lack of waste water treatment raises the risk of groundwater contamination. We monitored stable isotopes (δ18 O-NO3 and δ15 N-NO3 ), cadmium, and lead to document waste water contamination and transport during the rainy and dry seasons, using water samples collected along the Ring of Cenotes during each season. Specific conductance and pH showed no consistent seasonality, with conductance ranging from 0.5 to 55 mS/cm and pH ranging from 6.6 to 8.6 for most samples. Nitrate concentrations in the cenotes averaged 205 ± 260 µM and no seasonal pattern was observed. Cd and Pb concentrations were 0.1 to 37.9 µg/L and 0.2 to 243.2 µg/L, respectively. Nitrate stable isotope values were 2.6 to 27.2 for δ18 O and 1.2 to 20.7 for δ15 N. The statistical relationship between δ15 N and δ18 O, in dry season samples, indicated that denitrification was occurring. A scale measure for waste water recognition showed: (1) high variability among sites probably related with dry/rainy seasons and/or diverse anthropogenic activities; and (2) specific water quality variables that contribute to contamination at each site during each season. Importantly, our analyses indicate that in the area surrounding the Ring of Cenotes, waste water exhibits spatial and temporal patterns related to complex transport and dilution processes, as is the case in karsts in general.
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Água Subterrânea , Poluentes Químicos da Água , Monitoramento Ambiental , Isótopos , México , Nitratos/análise , Isótopos de Nitrogênio/análise , Poluentes Químicos da Água/análiseRESUMO
Resumen Introducción: En México, las úlceras por presión (UPP) son un indicador de calidad en el Sistema Nacional de Salud, se otorga relevancia a los conocimientos de los profesionales de la salud en cuanto al abordaje integral de las úlceras para el mejoramiento de la seguridad del paciente. Objetivo: Evaluar la efectividad de una intervención educativa como herramienta para mejorar los conocimientos de enfermería en la prevención y tratamiento de las UPP. Método: Estudio pre-experimental basado en una intervención educativa aplicada a un grupo con medición pre y post. La muestra estuvo constituida por 90 licenciados de enfermería que laboran en hospitales públicos de segundo y tercer nivel de atención, ubicados en el puerto de Veracruz. Se diseñaron doce sesiones de 120 minutos cada una para la intervención; en estas se abordaron tópicos de prevención, cuidado y tratamiento de las úlceras. Resultados: La variable prevención, en el indicador adecuado según tus conocimientos, obtuvo un promedio inicial de 74±15 que incrementó en la segunda medición a 91±9. t (p=.003). En la variable tratamiento, el indicador adecuado según tus conocimientos, obtuvo un promedio inicial de 57±16 y en la segunda medición pasó a 76±9. t (p=.002). Conclusión: La aplicación de la intervención educativa permitió mejorar el conocimiento sobre prevención y tratamiento de las UPP, aunque la utilización en la práctica asistencial fue menor.
Abstract Introduction: In Mexico, pressure ulcers are a quality indicator of the National Health System. In order to improve patient security, health professionals need to demonstrate adequate knowledge regarding the handling and addressing of pressure ulcers. Objective: To assess the effectiveness of an educational intervention aimed at improving the knowledge of nursing professionals regarding the prevention and treatment of pressure ulcers. Method: This is a pre-experimental study based on an educational intervention with pre and post measurements. The sample was constituted by 90 graduate nurses working in public hospitals of second and third level located at the port of Veracruz, Mexico. Twelve 120 minutes educational sessions were designed to address the topics of prevention, care, and treatment of pressure ulcers. Results: The variable prevention had a score of 74±15 at pre measurement and 91±9 at post measurement t (p=.003). The variable treatment had an initial score of 57±16, which then increased to 76±9, t (p=.002) after the intervention. Conclusion: The educational intervention improved the knowledge on prevention and treatment of pressure ulcers, without evidence of improving nursing care practice.
Resumo Introdução: No México, as úlceras por pressão (UPP) são um indicador de qualidade no Sistema Nacional de Saúde, sendo relevantes os conhecimentos dos professionais de saúde quanto à abordagem integral das úlceras para o melhoramento da segurança do paciente. Objetivo: Avaliar a efetividade de uma intervenção educativa como ferramenta para melhorar os conhecimentos de enfermagem na prevenção e tratamento das UPP. Método: Estudo pré-experimental baseado em uma intervenção educativa aplicada a um grupo com pré e post medição. A amostra esteve constituída por 90 graduados de enfermagem que laboram em hospitais públicos de segundo e terceiro nível de atenção, localizados no porto de Veracruz. Desenharam-se doze sessões de 120 minutos cada uma para a intervenção; nestas foram abordados tópicos de prevenção, cuidado e tratamento das úlceras. Resultados: A variável prevenção, no indicador adequado segundo com seus conhecimentos, obteve uma média inicial de 74±15 que incrementou na segunda medição para 91±9. t (p=.003). Na variável tratamento, o indicador adequado conforme seus conhecimentos, obteve uma média inicial de 57±16 e na segunda medição passou a 76±9. t (p=.002). Conclusão: A aplicação da intervenção educativa possibilitou melhorar o conhecimento sobre a prevenção e o tratamento das UPP, embora a utilização na prática assistencial tenha sido menor.
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2D materials open the possibility to study Dirac electrons in complex self-similar geometries. The two-dimensional nature of materials like graphene, silicene, phosphorene and transition-metal dichalcogenides allow the nanostructuration of complex geometries through metallic electrodes, interacting substrates, strain, etc. So far, the only 2D material that presents physical properties that directly reflect the characteristics of the complex geometries is monolayer graphene. In the present work, we show that silicene nanostructured in complex fashion also displays self-similar characteristics in physical properties. In particular, we find self-similar patterns in the conductance, spin polarization and thermoelectricity of Cantor-like silicene structures. These complex structures are generated by modulating electrostatically the silicene local bandgap in Cantor-like fashion along the structure. The charge carriers are described quantum relativistically by means of a Dirac-like Hamiltonian. The transfer matrix method, the Landauer-Büttiker formalism and the Cutler-Mott formula are used to obtain the transmission, transport and thermoelectric properties. We numerically derive scaling rules that connect appropriately the self-similar conductance, spin polarization and Seebeck coefficient patterns. The scaling rules are related to the structural parameters that define the Cantor-like structure such as the generation and length of the system as well as the height of the potential barriers. As far as we know this is the first time that a 2D material beyond monolayer graphene shows self-similar quantum transport as well as that transport related properties like spin polarization and thermoelectricity manifest self-similarity.
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INTRODUCCIÓN: El Síndrome de Down (SD) es una de las aneuploidías más frecuentes. En Chile, la incidencia es de 2.2 por 1000 nv. La esclerosis tuberosa (ET) es una enfermedad genética autosómica dominante con una prevalencia de 1:600 a 1:10.000 nacidos vivos (nv) que se sospecha prenatalmente por la presencia de rabdomiomas cardiacos. Los tumores cardiacos fetales tienen una prevalencia de 1:10000 nv, los más prevalentes son los Rabdomiomas. El hallazgo de tumores intracraneanos son infrecuentes, dentro del diagnóstico diferencial es necesario descartar la Hemorragia Intraventricular (HIV). CASO CLÍNICO: Paciente de 29 años, M2, Derivada a nuestro centro a las 27+4 semanas para evaluación ecográfica. Entre los hallazgos se encuentran tumores intracardiacos en ventrículo derecho y marcadores blandos para alto riesgo de aneuploidía, por lo que se realiza cariotipo (amniocentesis genética: 47, XX+21). A las 32+0 semanas en una nueva evaluación presenta imagen hiperecogénica sugerente de tumor intracerebral. Se solicita resonancia magnética fetal que informa hemorragia intraventricular (HIV). El parto ocurre con un recién nacido de término, fenotipo concordante con Trisomía 21, ecocardiograma confirma dos tumores intracardiacos (Rabdomiomas) y ecografía cerebral confirma el diagnóstico de HIV Grado III derecho. Ante el diagnóstico diferencial de ET, se realiza ANGIO-TAC que resulta negativo para ET. DISCUSIÓN: En la evaluación ecográfica antenatal, la presencia de tumores intracardiacos asociados a tumor cerebral hace plantear el diagnóstico de una ET. El diagnóstico antenatal de tumores cerebrales vs HIV por ultrasonido es difícil. La resonancia es un examen complementario de gran ayuda, permitiendo un diagnóstico de certeza. La HIV fetal es un diagnóstico poco frecuente de diagnostico prenatal asociado a feto con trisomia 21.
INTRODUCTION: Down Syndrome (DS) is one of the most frequent aneuploidies. In our country its incidence is 2.2 every 1000 newborns. Tuberous sclerosis (TS) is a dominant autosomal genetic disease with a prevalence of 1:6000 to 1:10.000 newborns, this disease is suspected by the finding of cardiac rhabdomyomas. Rhabdomyomas are the most prevalent fetal heart tumors. Intracranial tumors are a rare prenatal finding in ultrasound the main differential diagnosis is Intraventricular Hemorrhage (IVH). The Objective of this paper is present a case report of a fetus with trisomy 21 plus rhabdomyomas and cranial tumors. CASE REPORT: 29 years old patient, referred for ultrasound at 27+4 week. Cardiac tumors and aneuploidy soft markers are found. Genetic amniocentesis is performed (Result: 47, XX+21). At 32+0 weeks ultrasound finding of intracranial tumor. Fetal MRI was performed which reports suspected IVH. Confirmed postnatally. Baby was delivered at term. Neonatal findings: Trisomy 21 phenotype, Echocardiogram with two cardiac tumors (Rhabdomyomas), neonatal brain ultrasound confirms Grade III - IVH. To rule out TS, an Angio-CT is performed which is negative for the disease. DISCUSSION: Cardiac Tumors associated to brain tumors in antenatal period make TS a possible diagnosis. Differentiate brain tumors and IVH by ultrasound is very difficult. MRI is a very helpful tool for an accurate diagnostic. IVH is a rare antenatal diagnosis. Not reported before in a baby with trisomy 21.
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Humanos , Feminino , Gravidez , Adulto , Rabdomioma/diagnóstico por imagem , Esclerose Tuberosa/diagnóstico por imagem , Síndrome de Down , Hemorragias Intracranianas/diagnóstico por imagem , Neoplasias Cardíacas/diagnóstico por imagem , Diagnóstico Pré-Natal , Diagnóstico Diferencial , Cariótipo , AmniocenteseRESUMO
Electron transmission through different non-conventional (non-uniform barrier height) gated and gapped graphene superlattices (GSLs) is studied. Linear, Gaussian, Lorentzian and Pöschl-Teller superlattice potential profiles have been assessed. A relativistic description of electrons in graphene as well as the transfer matrix method have been used to obtain the transmission properties. We find that it is not possible to have perfect or nearly perfect pass bands in gated GSLs. Regardless of the potential profile and the number of barriers there are remanent oscillations in the transmission bands. On the contrary, nearly perfect pass bands are obtained for gapped GSLs. The Gaussian profile is the best option when the number of barriers is reduced, and there is practically no difference among the profiles for large number of barriers. We also find that both gated and gapped GSLs can work as omnidirectional band-pass filters. In the case of gated Gaussian GSLs the omnidirectional range goes from -50° to 50° with an energy bandwidth of 55 meV, while for gapped Gaussian GSLs the range goes from -80° to 80° with a bandwidth of 40 meV. Here, it is important that the energy range does not include remanent oscillations. On the light of these results, the hole states inside the barriers of gated GSLs are not beneficial for band-pass filtering. So, the flatness of the pass bands is determined by the superlattice potential profile and the chiral nature of the charge carriers in graphene. Moreover, the width and the number of electron pass bands can be modulated through the superlattice structural parameters. We consider that our findings can be useful to design electron filters based on non-conventional GSLs.
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Introducción Un modelo centrado en la enseñanza-aprendizaje supone un cambio en la docencia universitaria, esto implica el uso de metodologías activas con enfoque en el desarrollo de habilidades como el pensamiento crítico (PC) y sentido ético (SE). Objetivo Evaluar el impacto de la implementación del estudio de caso (EC) en el desarrollo de habilidades de PC y SE en estudiantes de enfermería. Métodos Se realizó una intervención longitudinal en una muestra de 103 estudiantes, se aplicó la prueba estadística ANOVA. Resultados Se evaluó el desarrollo de PC al comparar los resultados obtenidos por los estudiantes en tres evaluaciones, se logró evidenciar un progreso en el desarrollo de las habilidades de PC, y SE. Con el análisis de varianza se estableció que el valor del estadístico F fue mayor al crítico (valor p < 0,05), para un nivel de confianza del 95%, se puede rechazar la hipótesis nula. Discusión La implementación de la metodología contribuyó favorablemente en el desarrollo de las habilidades PC y SE en los estudiantes, lo que les permitió identificar y resolver problemas, al fundamentar sus decisiones. Además, fomentó el aprendizaje colaborativo y el respeto, entre pares. Conclusiones La metodología EC promovió un aprendizaje activo y un cambio en la cultura del aula. Si bien, implementar la metodología de EC favoreció el desarrollo de habilidades de PC y SE en los estudiantes de enfermería, es necesario seguir investigando sobre factores que mejoren el proceso de enseñanza-aprendizaje con un enfoque activo.
Introduction A teaching-learning centered university model implies an evolution characterized by using active methodologies with a focus on the development of skills such as critical thinking (CT), and ethical sense (ES). Objective To assess the impact from the implementation of the Study Case (SC) in the development of critical thinking and ethical sense among nursing students. Methods A longitudinal intervention was conducted on a sample of 103 nursing students. ANOVA tests were performed. Results Critical thinking was assessed by comparing the corresponding results of the students in three evaluations. A progress is development of critical thinking and ethical sense was evidenced. From the ANOVA, it was shown that the F value was higher than the critical reference (p < 0.05) within a 95% confidence interval, and thus, the nil hypothesis was rejected. Discussion The implementation of this methodology favorably contributed for the development of critical thinking and ethical sense skills among the students, an improvement which allowed them to identify and solve problems based on their decision arguments. Moreover, the methodology fostered collaborative learning and respect among colleagues. Conclusions Although the Case Study methodology promoted active learning and a change in the culture of the classroom, it is necessary to continue studying the factors which could improve the teaching-learning processes under an active approach.
Introdução Um modelo centrado no ensino-aprendizagem supõe um câmbio na docência universitária, isto envolve o uso de metodologias ativas com enfoque no desenvolvimento de habilidades como o pensamento crítico (PC) e sentido ético (SE). Objetivo Avaliar o impacto da implementação do estudo de caso (EC) no desenvolvimento de habilidades de PC e SE em estudantes de enfermagem. Métodos Realizou-se uma intervenção longitudinal em uma mostra de 103 estudantes, aplicou-se a proba estatística ANOVA. Resultados Avaliou-se o desenvolvimento de PC ao comparar os resultados obtidos pelos estudantes em três avaliações, atingiu-se evidenciar um progresso no desenvolvimento das habilidades de PC, e SE. Com a análise de variância estabeleceu-se que o valor do estatístico F foi maior ao crítico (valor p < 0,05), para um nível de confiança do 95%, pode se rejeitar a hipótese nula. Discussão A implementação da metodologia contribuiu favoravelmente no desenvolvimento das habilidades PC e SE nos estudantes, o que lhes permitiu identificar e resolver problemas, ao fundamentar suas decisões. Além disso, fomentou a aprendizagem colaborativa e o respeito entre pares. Conclusões A metodologia EC promoveu uma aprendizagem ativa e um câmbio na cultura de aula. Embora, implementar a metodologia de EC favoreça o desenvolvimento de habilidades de PC e SE nos estudantes de enfermagem, é necessário seguir pesquisando sobre fatores que melhorem o processo de ensino-aprendizagem com um enfoque ativo.
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Humanos , Masculino , Feminino , Estudantes de Enfermagem , Pensamento , Relatos de CasosRESUMO
Merida is the largest urban center in the Mexican State of Yucatan. Here domestic sewage is deposited in poorly built septic tanks and is not adequately treated. Because of contamination from such waste, water from the top 20 m of the aquifer is unsuitable for human consumption. Given this situation and because children are highly vulnerable to environmental pollution, including exposure to toxic trace elements, this study focused on evaluating the exposure of children to arsenic (As), chromium (Cr), and mercury (Hg) in water. It also evaluated the relationship between the levels of these elements in water and their concentrations in urine and blood. Among the 33 children monitored in the study, arsenic surpassed WHO limits for blood in 37% of the cases, which could result from the ingestion of poultry contaminated with organoarsenic compounds. In the case of WHO limits for Mercury, 65% of the water samples analyzed, 28% of urine samples, and 12% of blood samples exceeded them. Mercury exposure was correlated with biological sex, some lifestyle factors, and the zone in Merida in which children live. These data suggest that the levels of some toxic metals in children may be affected by water source, socioeconomic factors, and individual behavior.