Summary Background and aims: Zephyranthes mesochloa, is a bulbous species with white flowers that inhabits the subtropical región of South America and presents different chromosome numbers. The aim of this work is to carry out the chromosome analysis of Z. mesochloa from northern Argentina, to contribute to the cytogenetic knowledge of the genus. M&M: Ploidy levels and somatic chromosome numbers were determined in individuals from 8 populations in northern Argentina using conventional staining. In addition, meiotic preparations with acetic carmine were performed on individuals from one population. Results: Seventy-five percent of the populations were diploid, with 2n = 2x = 12 and presented a karyotypic formula of 4m + 4sm + 4st. In two of the diploid populations, individuals with 2n = 13 were observed, with the presence of an additional metacentric chromosome, possibly a B chromosome. Microsporogenesis analysis, in diakinesis and metaphase I, of aneuploid cytotype (2n = 13), showed six bivalents and one univalent in all pollen mother cells analyzed. The remaining populations (25%) were tetraploids with 2n = 4x = 24 and karyotypic formula 8m + 8sm + 8st. Geographically, the distribution of cytotypes in Z. mesochloa is discontinuous. Conclusions: The duplicate karyotype formula in tetraploids regarding its con-specific diploids may indicate the origin of an autopolyploid cytotype. The available data allows us to consider the group of cytotypes as part of a polyploid complex with a basic number of x = 6.

Resumen Introducción y objetivos: Zephyranthes mesochloa es una especie bulbosa de flores blancas que habita en la región subtropical del sur de Sudamérica y registra distintos números cromosómicos. El objetivo del presente trabajo es analizar cromosómicamente individuos de la especie Z. mesochloa del norte de Argentina, con el objeto de contribuir al conocimiento citogenético del género. M&M: El nivel de ploidía y el número cromosómico somático se determinó en individuos procedentes de 8 poblaciones del norte de Argentina a partir de tinción convencional. Además, se realizaron preparaciones meióticas con carmín acético en individuos de una de las poblaciones. Resultados: El 75% de las poblaciones resultaron diploides, con 2n = 2x = 12 y fórmula cariotípica 4m + 4sm + 4st. En dos de las poblaciones diploides se observaron individuos con 2n = 13, con presencia de un cromosoma metacéntrico adicional, que posiblemente se trate de un cromosoma B. El análisis de la microsporogénesis, en diacinesis y metafase I, del citotipo aneuploide (2n = 13), mostró 6 bivalentes y 1 univalente en todas las células madre del polen analizadas. Las poblaciones restantes (25%), resultaron tetraploides con 2n = 4x = 24 y fórmula cariotípica 8m + 8sm + 8st. Geográficamente, la distribución de los citotipos de Z. mesochloa es discontinua. Conclusiones: La fórmula cariotípica duplicada en los tetraploides con respecto a los diploides conespecíficos indicarían un origen autopoliploide de este citotipo. El conjunto de datos disponibles permite considerar al conjunto de citotipos como un complejo poliploide con número básico x = 6.

Abstract In the present study, the approximate fractal morphometry of spherical-type essential oil microemulsions was performed. The geometric fractal characterization was carried out by a recently published continuous half-fractal model which allowed to model microemulsions as systems in their stable thermodynamic equilibrium phase with high degree of homogeneity. Regarding the characteristic of high homogeneity an equation was developed to roughly describe the volume fractal dimension and the fractal volume of two special cases elaborated from Rosmarinus officinalis and Melaleuca alternifolia previously investigated. In addition, referring to the characteristic of high homogeneity, it was possible to approximate the fractal dimension of area and the fractal area for each microemulsion. Our numerical estimates showed coherence with the principles of Hausdorff-Besicovitch geometry and with the experimental evidence about the physical dimension as a non- integer dimension.

Abstract We present the study of the behavior of the electromagnetic field propagating in the ultra-small core photonic crystal fiber (PCF) beyond its fundamental mode cut-off. We first the use plane waves expansion (PWE) method to find necessary parameters and then involve the finitedifference time-domain (FDTD) method accelerated with a graphic processing unit (GPU) for long-range light propagation simulation. The confinement losses beyond λ =1200 nm achieves tens of dB/cm, which can be lowered significantly by increasing the number of cladding rings.

Interest in developing novel wound dressings with antibacterial properties elaborated from natural sources continues to grow. In this study, a Tween-80 (T80)-stabilized carvacrol (CAR) emulsion was incorporated into pectin (PEC) membranes at 0 (control), 0.25, 0.50, and 1.00% (v/v). Membranes were obtained by the dry-casting method, characterized by scanning electron microscopy, infrared spectroscopy, and CAR retention (HPLC), and tested for antibacterial activity. The retention percentage of CAR in the membranes ranged from 9.1-13.9%. Infrared spectra analysis indicated changes in the hydrogen bonds of the membranes that suggest an interaction between the polymer matrix and the CAR:T80 emulsion. Microstructural analysis of the membranes showed the presence of hole-like features on the surface (≈ 4-6 µm diameter) that indicate entrapment of the micelles in the matrix (microcapsules). The PEC-CAR membranes exhibited antibacterial activity against Escherichia coli and Staphylococcus aureus, two pathogens commonly associated with wounds and intra-hospital infections.

RESUMO A cirurgia paraendodontica é um procedimento que visa resolver problemas que nao poderiam ser resolvidos, ou quando nao é possível realizar o tratamento endodontico convencional. O objetivo deste estudo experimental foi comparar a microinfiltragao apical de dentes seccionados a 45° ou 90° em relagao ao longo eixo do dente e extremidade radicularpreenchida com agregado de trióxido mineral (MTA) utilizando estereomicroscopia. Neste estudo, 26 incisivos centrais superiores foram utilizados. Limpeza e modelagem foram realizadas com o uso da técnica de Oregon e as amostras foram divididas aleatoriamente em dois grupos. No Grupo A (n = 10) foi realizada segao apical em ángulo de 90°, realizando retrocavidade com ponta ultrassonica e retrobturagao com MTA. No grupo B (n = 10), os mesmos procedimentos foram realizados, mas a segao apical estava em um ángulo de 45°. Em seguida, as amostras foram imersas em um corante (nanquim), colocadas em estufa a 37°Cpor 48 h, antes da aplicagao da técnica de clareamento. Posteriormente, os dentes foram avaliados por estereomicroscópio, com aumento de 20x, para análise do vazamento de corante. Os dados foram submetidos ao teste t de Student, com nivel de significáncia p <0,05. Houve diferenga estatisticamente significante entre os grupos. O grupo B apresentou maiores valores de microinfil-tragao apical em comparagao ao grupo A (P = 0,004), mas ambos os grupos apresentaram vazamento de corante. Os resultados mostraram que a segao apical de 90° promoveu menores valores de microinfiltragao de corante na interface do material retrobturador dentinário do que a segao 45° e pode ser considerada a técnica mais efetiva para preparo apical em cirurgia paraendodontica.

ABSTRACT Paraendodontic surgery is a procedure that aims to solve problems that could not be solved by, or when it is not possible to perform conventional endodontic treatment. The aim of this experimental study was to compare the apical microleakage of teeth sectioned at 45° or 90° to the long axis of the tooth and root-end filled with mineral trioxide aggregate (MTA) using stereomicroscopy. In this study, 26 maxillary central incisors were used. Cleaning and shaping were performed with use of the Oregon technique and the samples were randomly divided into two groups. In Group A (n=10) apical section was performed at an angle of 90°, making a retrocavity with an ultrasonic tip and retrofilling with MTA. In group B (n=10) the same procedures were performed, but the apical section was at a 45° angle. Then the samples were immersed in a dye (India ink), placed in an oven at 37° for 48 h before applying the clearing technique. Afterwards the teeth were assessed by stereomicroscope at 20x magnification to analyze dye leakage. Data were submitted to the Student's-t test with significance level p<0.05. There was statistically significant difference between groups. Group B showed higher apical microleakage values compared with group A (P=0.004), but both groups showed dye leakage. The results showed that the 90° apical section promoted lower dye microleakage values at the dentin-retrofilling material interface than the 45°-section and could be considered the most effective technique for apical preparation in paraendodontic surgery.

Abstract: Fleas and sucking lice are important vectors of multiple pathogens causing major epidemics worldwide. However these insects are vectors of a wide range of largely understudied and unattended pathogens, especially several species of bacteria’s of the genera Bartonella and Rickettsia. For this reason the aim of the present work was to identify the presence and diversity of Bartonella and Rickettsia species in endemic murine typhus foci in Hidalgo, México. A cross-sectional study was carried out to collect small mammals and their associated ectoparasites during October, 2014. Samples of liver and ear of hosts, and ectoparasites were fixed in absolute ethanol and examined to identify the presence of Bartonella and Rickettsia DNA by the amplification of specific fragments of the gltA and ompB genes using conventional PCR. The recovered sequences were compared with those deposited in GenBank, and phylogenetic analyzes were carried out to identify the position of the pathogens detected with respect to the valid species previously reported worldwide. A total of 47 fleas and 172 sucking lice, belonging to five families (Ceratophyllidae, Leptopsyllidae, Ctenophtalmidae, Hoplopleuridae, Polyplacidae) and related to six species were collected from 40 rodents of four species and one shrew. Only four hosts (two P. beatae, and two R. norvergicus) were positive to Bartonella elizabethae, Bartonella vinsonii and Rickettsia typhi. In the case of ectoparasites, 23 specimens of two flea species (Peromyscopsylla hesperomys and Plusaetis mathesoni) tested positive for B. vinsonii. No evidence of Bartonella or Rickettsia was detected in any lice. Our findings represent the first record of Bartonella elizabethae a confirmed zoonotic pathogen causing endocarditis in México and several new associations of Bartonella with Mexican flea species, which highlight the importance of the establishment of active entomological surveillance in wildlife.

Resumen: Las pulgas y los piojos son vectores de patógenos causantes de epidemias de importancia histórica. Sin embargo, estos insectos son vectores de una amplia gama de patógenos poco estudiados y no atendidos, especialmente varias especies de bacterias de los géneros Bartonella y Rickettsia. Por este motivo, el objetivo del presente trabajo fue identificar la presencia y diversidad de las especies de Bartonella y Rickettsia en un foco de tifus murino en el estado de Hidalgo, México. Se realizó un estudio transversal para recolectar hospederos y sus ectoparásitos durante octubre de 2014. Las muestras de hígado y oreja de los hospederos y los ectoparásitos se fijaron en etanol absoluto y se examinaron para identificar la presencia de ADN de Bartonella y Rickettsia mediante la extracción de DNA y amplificación de fragmentos específicos de los genes gltA y ompB. Las secuencias obtenidas fueron comparadas con aquellas depositadas en GenBank y se realizaron análisis filogenéticos para identificar la posición de los patógenos detectados respecto a las especies válidas previamente reportadas a nivel mundial. Se recolectaron un total de 47 pulgas y 172 piojos chupadores, pertenecientes a seis especies de cinco familias (Ceratophyllidae, Leptopsyllidae, Ctenophtalmidae, Hoplopleuridae, Polyplacidae) asociados con 40 roedores de cuatro especies y una musaraña. Sólo cuatro hospederos (dos P. beatae, y dos R. norvergicus) resultaron positivos para Bartonella elizabethae, Bartonella vinsonii y Rickettsia typhi. En el caso de los ectoparásitos, 23 ejemplares de dos especies de pulgas (Peromyscopsylla hesperomys y Plusaetis mathesoni) fueron positivos para B. vinsonii. No se detectó evidencia de ninguno de los dos patógenos en los piojos analizados. Nuestros hallazgos representan el primer registro de Bartonella elizabethae, un patógeno zoonótico confirmado que causa endocarditis en México y varias asociaciones nuevas de Bartonella con especies de pulgas mexicanas, lo cual resalta la necesidad de implementar vigilancia entomológica activa para el monitoreo de estos patógenos en animales silvestres.

ABSTRACT Based on mass and energy balance equations and data collected in specialized bibliographies, it was proposed a methodology for modeling of an ice bank for thermal storage of energy at low temperature to be used in milk cooling. The data obtained by the equations arrangement were used in the design and installation of a real system, which was tested to collect data and to compare it with the estimated. The data obtained in terms of prediction of ice formation, temperature of the ice bank, water and capacity of the selected refrigeration system prove the adequacy of the equations arrangement, showing that it can be used as a tool for sizing solid ice bank in smooth pipe coils, with good approximation.

Resumen Los manglares son ecosistemas de importante productividad primaria, donde se establece un flujo de energía (nutrientes) con zonas adyacentes y su ambiente acuático, impulsado principalmente por los procesos de degradación. El objetivo del estudio fue estimar el coeficiente de degradación diario (k) de hoja de mangle por medio de bolsas de degradación, en relación con los factores físico químicos del suelo y el aporte de nutrientes (fósforo y nitrógeno) en sedimento del manglar de la Laguna Mecoacán, Golfo de México. El coeficiente de degradación se estimó por medio de bolsas de degradación de hojarasca en seis sitios de monitoreo mensual. Se identificó una rápida degradación durante el primer mes de hasta 51 % en Avicennia germinans (L.) Stearn asociado a procesos de lixiviación por condiciones de inundación. La degradación (k) de Rhizophora mangle L. (k= 0.0052 ± 0.0002) (F= 12.2 p<0.05 n= 216) y Laguncularia racemosa (L.) Gaertn (k= 0.005 ± 0.0003) (F= 3.7 p= 0.02 n= 108) difieren significativamente de A. germinans (k= 0.009 ± 0.0003) (F= 1.2 p= 0.02 n= 216). En relación al T50 de R. mangle y L. racemosa presentaron mayor tiempo de degradación (133 y 138 días respectivamente) comparado con A. germinans (74 días). Se registró una correlación significativa entre la materia orgánica y la humedad del suelo con la constante de descomposición de A. germinans (r= 0.65 p< 0.05 y r= 0.55 p< 0.05 respectivamente). El más alto contenido de nitrógeno total se dio en Pajaral (2 683 mg.Kg) y presentó alta correlación con el contenido de materia orgánica (r= 0.9 p= 0.03); en relación al fósforo total, el nivel más alto se presentó en Boca (2 031 mg.Kg) correlacionado de forma negativa con el pH (r= -0.61 p< 0.05). En conclusión, las diferencias en la velocidad de degradación de las hojas de mangle dependen de la especie (composición foliar), tiempo de exposición o inmersión en agua (patrón de inundación) y heterogeneidad del sedimento (i.e., textura, pH, contenido de humedad y densidad aparente).

Abstract Mangroves are ecosystems with a high primary productivity that is mainly driven mainly by degradation processes. Energy (nutrients) flows from mangroves toward adjacent zones and the surrounding aquatic environment. The objective of the present study was to estimate the daily degradation coefficient (k) of mangrove leaves in relation to physical-chemical soil factors and in situ nutrient supply (phosphorus and nitrogen) in Mecoacán Lagoon, Gulf of Mexico. Leaf litter degradation bags were placed at six monthly monitoring sites to evaluate degradation and to calculate the corresponding degradation coefficients. A rapid degradation of up to 51 % was observed for Avicennia germinans (L.) Stearn during the first month in association with leaching resulting from flood conditions. The degradation of Rhizophora mangle (L.) (k= 0.0052±0.0002) (F= 12.2 p< 0.05 n= 216) and Laguncularia racemosa (L.) Gaertn (k= 0.005±0.0003) (F= 3.7 p= 0.2 n= 108), differed significantly from that of A. germinans (k= 0.009 ± 0.0003) (F= 1.2 p= 0.2 n= 216) did not present significant differences. To reach T50 degradation, R. mangle and L. racemosa required more time (133 and 138 days, respectively) than A. germinans (74 days). Organic matter and soil humidity were significantly correlated with the decay constant of A. germinans (r= 0.65 p< 0.05 and r= 0.55 p< 0.05, respectively). Total nitrogen content was highest in the Pajaral site (2 683 mg.kg) and was also highly correlated with organic matter content (r= 0.9 p= 0.003). Total phosphorus content was highest in the Boca site (2 031 mg.kg) and was also negatively correlated with pH (r= -0.61 p= 0.004). In conclusion, differences in the rate of mangrove leaf degradation depend on the involved species (leaf composition), time of exposure or immersion in water (flooding patterns) and sediment heterogeneity (i.e., texture, pH, humidity content and bulk density). Rev. Biol. Trop. 66(2): 892-907. Epub 2018 June 01.

Abstract: BACKGROUND: Venous thromboembolic disease VTE is a complication that may occur during or after hospitalization. There are few antecedents in our country that evaluate the medical behavior in this subject. OBJECTIVE: To know the prescription related to type, duration and possible causes for omission of thromboprophylaxis in hospitalized patients. MATERIAL AND METHOD: A descriptive, transversal and non-probabilistic study was done, in which from September to November 2016 physicians of Internal Medicine, General Surgery, Intensive Care and Urgency were evaluated through a data collection by questionnaire and presentation of results through descriptive statistics. We also evaluated duration of prescription and dose administered. RESULTS: A total of 556 seconded physicians, 14 service heads, and 234 residents 804 in total were surveyed in seven hospitals in Mexico City belonging to the health system. Thirty percent reported that their hospital has a thromboprophylaxis program; 97.7% consider it safe and 1.2% risky; 96% responded that they prescribe thromboprophylaxis in their patients; 592 73.6% used some clinical prediction scale for VTE; 71% recommended low molecular weight heparin for thrombo prophylaxis and 0.74% administered new generation oral anticoagulants. CONCLUSIONS: Venous thromboembolic disease is potentially preventable; however, prescription shows opportunities for improvement in aspects of pharmacology.

Resumen: ANTECEDENTES: la enfermedad tromboembólica venosa es una complicación que puede manifestarse durante o después de la hospitalización. Existen pocos antecedentes en nuestro país que evalúan el comportamiento médico en este tema. OBJETIVO: conocer la prescripción relacionada con el tipo, duración y posibles causas de la omisión de tromboprofilaxis en pacientes hospitalizados. MATERIAL Y MÉTODO: estudio descriptivo, transversal y no probabilístico en el que de septiembre a noviembre de 2016 se evaluaron médicos de Medicina Interna, Cirugía General, Terapia Intensiva y Urgencias. Se recolectaron datos por cuestionario y presentación de resultados a través de estadística descriptiva. También se evaluó la duración de la prescripción y la dosis administrada. RESULTADOS: se encuestaron 556 médicos adscritos, 14 jefes de servicio y 234 residentes total: 804 de siete hospitales de la Ciudad de México pertenecientes al sistema de salud. El 30% refirió que su hospital cuenta con un programa de tromboprofilaxis; 97.7% la considera segura y 1.2%, riesgosa. El 96% respondió que prescribe tromboprofilaxis en sus pacientes; 592 74% utilizan alguna escala de previsión clínica de enfermedad tromboembólica venosa. El 71% recomienda heparina de bajo peso molecular para tromboprofilaxis y 0.74% administra anticoagulantes orales de nueva generación. CONCLUSIONES: la enfermedad tromboembólica venosa es potencialmente prevenible; sin embargo, la prescripción muestra oportunidades de mejoría en aspectos de farmacología.

Resumo Plantas que podem ser uma fonte potencial de recursos alimentares (néctar floral, pólen e tecidos vegetais) para o bicudo do algodoeiro durante a entressafra foram avaliadas, considerando as condições ambientais prevalentes na região de Cerrado do Brasil Central. Primeiro, testamos a adequação nutricional dos recursos (pólen e néctar) fornecidos por oito espécies de plantas (erva-doce, margaridão, mamona, quiabo, hibisco, sorgo, feijão guandu e crotalária) como único recurso alimentar para a sobrevivência do inseto. Posteriormente, nós avaliamos se os recursos fornecidos pelas plantas selecionadas continuaram a serem explorados pelo bicudo na presença do algodoeiro, seu recurso alimentar principal. A longevidade média do bicudo do algodoeiro foi significativamente maior quando eles foram alimentados com flores de hibisco (166,6 ± 74,4) e quiabo (34,7 ± 28,9) do que quando alimentados com flores das outras seis espécies. Em seguida, a preferência do bicudo no uso de recursos foi comparada contrastando o quiabo e o hibisco com o algodão, em experimentos de dupla escolha. Os bicudos preferiram as plantas das três espécies na fase reprodutiva em relação àquelas em estádios vegetativos. Embora a preferência por plantas de algodão na fase reprodutiva tenha sido maior, os bicudos preferiram plantas em floração de quiabo e hibisco quando estas foram contrastadas com o algodão na fase vegetativa.

Abstract Plants that have potential as alternative food source (floral nectar, pollen and plant tissues) to the boll weevil during the intercropping season were evaluated considering the prevalent conditions of Cerrado in the Central Brazil. Initially, we tested the nutritional adequacy for the survival of the insect of flower resource (pollen and nectar) provided by eight plant species (fennel, mexican sunflower, castor bean, okra, hibiscus, sorghum, pigeonpea and sunn hemp). Subsequently, we tested if the resources provided by the selected plants continued to be exploited by the boll weevil in the presence of cotton plant, its main food source average longevity of boll weevil adults was significantly longer when they were fed on hibiscus’ flowers (166.6 ± 74.4) and okra flowers (34.7 ± 28.9) than when they fed on flowers of other six species. Subsequently, the preference of the boll weevil in the use of resources was compared between okra or hibiscus and cotton plants, in dual choice experiments. Boll weevils preferred plants of the three species in the reproductive stages than those in vegetative stages. Although the cotton plant in the reproductive stage was the most preferred plant of all, boll weevils preferred flowering okra and hibiscus than cotton at the vegetative stage.

This study was conducted from November 2012 to May 2013 to evaluate the effect of inoculating C. canephora with Rhizophagus intraradices and / or Azospirillum brasilense in two substrates in nursery on some morphological and physiological yield components and to determine the amount of phosphorus in plant tissue and quantify mycorrhizal colonization. Soil used was mollic Andosol and two prepared substrates: one was soil and river sand and the other was soil plus 30% coffee pulp (1:1 v / v) in five-kg capacity plastic bags. Treatments were the control, Rhizophagus intraradices, Azospirillum brasilense and a combination of the two on each substrate, giving a total of eight treatments in a split plot in randomized block design with five replications. Samples were taken every 28 days to assess morphological and physiological variables and mycorrhizal colonization and phosphorus content during 140 days after transplant (dat). The results show that inoculation of C. canephora in nursery with either of the microorganisms individually favored growth and dry matter accumulation in morphological and physiological yield components relative to the control. A. brasilense promoted greater biomass accumulation during the evaluation and R. intraradices at the end of the study. R. intraradices increased phosphorus content in the tissue of plants, and higher mycorrhizal colonization was found in the first third of the root when inoculated with R. intraradices.

Con el objetivo de evaluar el efecto de la inoculación con Rhizophagus intraradices o Azospirillum brasilense a C. canephora en algunos componentes morfológicos y fisiológicos del rendimiento en dos sustratos en vivero e identificar la cantidad de fósforo en el tejido vegetal y la colonización micorrízica, se condujo el presente estudio de noviembre de 2012 a mayo de 2013. Se utilizó un Andosol-mólico y se prepararon dos sustratos: suelo y arena de río (1:1 v/v) y suelo más 30 % de pulpa de café en bolsas de plástico con capacidad de 5 kg. Los tratamientos fueron testigo, Rhizophagus intraradices, Azospirillum brasilense y la combinación de ambos en cada sustrato. Se obtuvieron ocho tratamientos distribuidos en parcelas divididas en bloques al azar con cinco repeticiones. Se realizaron muestreos cada 28 días para medir variables morfológicas, fisiológicas y colonización micorrízica, además de la concentración de fósforo a 140 días después del trasplante (ddt). Los resultados muestran que la inoculación del C. canephora en vivero con alguno de los microorganismos inoculados individualmente favoreció el crecimiento y la acumulación de materia seca de los componentes morfológicos y fisiológicos del rendimiento en comparación con el testigo sin inocular. A. brasilense promovió mayor acumulación de biomasa durante la evaluación mientras que R. intraradices al final del estudio. Con R. intraradices se incrementó la concentración de fósforo en el tejido vegetal de las plantas y la mayor colonización micorrízica se presentó en el primer tercio de la raíz cuando se inoculó R. intraradices.

In this paper we deal with the experimental synchronization of the Colpitts oscillator in a real-time implementation. Our approach is based on observer design theory in a master-slave configuration thus, a chaos synchronization problem can be posed as an observer design procedure, where the coupling signal is viewed as a measurable output and a slave system is regarded as an observer. A polynomial observer is used for synchronizing the Colpitts oscillator employing linear matrix inequalities. Finally, a comparison with a reduced order observer and a high gain observer is given to assess the performance of the proposed observer.

En este artículo se aborda la sincronización experimental del oscilador de Colpitts en tiempo real. Nuestra aproximación se realiza mediante la teoría de diseño de observadores en una configuración maestro-esclavo, por lo que el problema de sincronización caótica puede plantearse como el diseño de un observador. Se utiliza un observador polinomial para la sincronización del oscilador de Colpitts empleando desigualdades matriciales lineales. Se realiza una comparación con el observador de orden reducido y con el observador de alta ganancia con la finalidad de verificar el desempeño del observador propuesto.

In this paper, a thermodynamic analysis and an exergoeconomic analysis were applied to vapor compression refrigeration cycle with refrigerant HFC-134a. The thermodynamics properties of the each state of the system were calculated and a parametric; analysis of the coefficient of performance, the exergetic efficiency, the power input to the compressor and the mass flow rate of HFC-134a was performed for a given refrigeration capacity. The productive structure of the equipment of the system was generated; in addition, an exergoeconomics analysis was made. We obtained the resources, products and the irreversibilities of each equipment, the exergetic operation cost and the exergoeconomicr operation cost in function of the environmental temperature and the refrigerated spaced temperature. For the Mexican Republic, the variation of the environmental temperature ranged between 20º C and 35ºC in average. For this interval of temperatures and atmospheric pressure of 1 bar, refrigerated spaced temperature of -5ºC and for a refrigeration capacity of 5 TR, the coefficient; of performance of the refrigeration cycle was 6.5 to 4, the exergetic efficiency was 4-91 to 30%, the exergetic operation cost was 4.5 to 10 kW and the exergoeconomic operation cost was 3.7 to 8.5 $/hr.

Se realizó un análisis termodinámico y exergoeconómico a un sistema de refrigeración por compresor de vapor usando HFC-134a. Se obtuvieron las propiedades de los estados termodinámicos del ciclo y se hizo un análisis paramétrico del coeficiente de operación, de la eficiencia exergética, de la potencia suministrada al compresor y del flujo de refrigerante para una potencia frigorífica dada. Se generó la estructura productiva de los equipos del sistema, y a partir de esta se realizó el análisis exergoeconómico, obteniendose los recursos, los productos y las irreversibilidades de cada equipo, con base a éstos se evaluaron los costos de operaciones exergéticos y exergoeconómicos, variando la temperatura ambiente y la temperatura de refrigeración. Para la República Mexicana, la variación de la temperatura ambiente en promedio fue de 20 ºC a 35 ºC; por ejemplo, para este intervalo de temperaturas y para una presión atmosférica de 1 bar, una temperatura frigorífica de -5 °C y una potencia frigorífica de 5 TR, el coeficiente de operación del ciclo estuvo en un intervalo de 6.5 a 4, la eficiencia exergética de 49 a 30%, el costo de operación exergetico de 4.5 a 10 kW y el costo de operación exergoeconómico de 3.7 a 8.5 $/h.

O objetivo neste trabalho foi obter as curvas de congelamento do feijão, cultivar 'gordo', nas temperaturas de -25, -50, -170 e -196 ºC e determinar sua difusividade térmica efetiva. Com vista à obtenção das curvas de congelamento das sementes nas temperaturas de -25 e -50 ºC utilizou-se um freezer criogênico horizontal; para a temperatura de -170 ºC, o vapor de nitrogênio e, para a temperatura de -196 ºC, as sementes foram submersas no nitrogênio líquido. Afim de expressar o comportamento cinético do congelamento das sementes de feijão, foi usado o modelo de Fourier levando-se em consideração o primeiro termo da série, além dos Modelos I e II de Cavalcanti-Mata & Duarte. Os resultados obtidos indicam que os três modelos representam satisfatoriamente os dados experimentais da cinética de congelamento; apesar disto, com o Modelo II de Cavalcanti-Mata & Duarte se obtém o maior coeficiente de determinação. Constata-se também que, para congelar as sementes de feijão até atingir o equilíbrio térmico na temperatura de -25 ºC, o tempo necessário foi de 1200 min; em temperatura de -50 ºC o equilíbrio foi atingido com 480 min; a -170 ºC o equilíbrio se deu em 180 min e, a -196 ºC, em 30 min.

The objective of this study was to obtain the freezing curves of beans, variety 'gordo' at temperatures of -25, -50, -170 and -196 ºC, and determine their effective thermal diffusivity. For the curves of freezing beans seeds at temperatures of -25 and -50 ºC a cryogenic horizontal freezer was used, for temperature of -170 ºC, nitrogen vapor was used and at temperature of -196 ºC seeds were submerged in liquid nitrogen. To express the kinetic behavior of the freezing of bean seeds, the Fourier model was used taking into account the first term of the series and; Cavalcanti-Mata & Duarte model I and II. The results indicate that the three models satisfactorily represent the experimental data of the kinetics of freezing, though with Model II of Cavalcanti-Mata & Duarte highest coefficient of determination were obtained. It is concluded that time necessary to freeze the seeds of beans at temperature of -25 ºC was of 1200 min; at temperature of -50 ºC the equilibrium was reached with 480 min; at -170 ºC the time was 180 min and at -196 ºC it was 30 min.