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DIALNET OAI Articles (790.801 recursos)

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Mostrando recursos 1 - 20 de 12.206

  1. Influencia del vertido vibratorio en la matriz y dureza del hierro gris con grafito esferoidal

    Sánchez Figueredo, Rigoberto Pastor; García Domínguez, Asdrúbal; Rodríguez González, Isnel; Pérez Rodríguez, Roberto
    Cast irons constitute a group of most versatile materials with multiple industrial applications from the range of mechanical properties that offer. In this study, an experimental analysis of the effects caused by the use of vibrating pouring into the matrix and hardness of ductile irons is exposed. As a result of applying different vibration frequencies, a direct relationship between the vibration frequency and the hardness obtained is demonstrated further improvement is achieved in the spheroidizing. All this leads to a reduction in rejection rates and a decrease in mass nodulizant.

  2. Revisión de las estrategias de modelamiento y análisis aplicados a sistemas híbridos de energía

    Forero Nuñez, Carlos Andrés; Valencia, Jairo Alberto; Sierra Vargas, Fabio Emiro
    The continuous increase of the world energy demand, the necessity of supplying it in a more sustainable manner and the lack of electricity in rural areas have promoted the development of hybrid systems capable of combining a wide variety of energy technologies. This work makes a review of the strategies followed to analyze the performance, dimensions, modeling and evaluation of such energy systems. After gathering some academic information available in the literature, we conclude that the strategies could be classified into three major groups. First one is based on fundamental equations applied during evaluation of each component independently; second group...

  3. Actualidad y perspectivas de una bomba de calor de expansión directa con energía solar

    Gorozabel Chata, Francis B.; Carbonell Morales, Tania
    La bomba de calor de expansión directa con asistencia de energía solar se utiliza en el modo de calefacción para diversas aplicaciones entre las que podemos citar, calentamiento de agua, calentamiento de aire para climatizar edificios, desalinización de agua, secado solar entre otras. El presente trabajo revisa las principales investigaciones sobre esta tecnología enfocando sus aplicaciones para el calentamiento de agua, para lograr este objetivose describen en detalle la configuración básica y avanzadacon la finalidad de caracterizar el coeficiente de desempeño de cada una de estas configuraciones; también es oportuno analizar esta tecnología de acuerdo a la segunda ley de...

  4. Evaluación por el método de los elementos finitos de la influencia de las tensiones residuales en la fatiga de uniones soldadas

    Michel Almaguer Zaldivar, Pavel; Estrada Cinqualbres, Roberto; Pérez Rodríguez, Roberto
    This paper presents a method using the finite element method to evaluate the influence of residual thermal stresses on the fatigue life of welded joints, applied to AISI 1015 butt weld. The procedure is based on the concatenation of transient and static thermal simulations under the action of thermal loads and mechanical fatigue. To make the geometric model, the SolidWorks 2013 software was used and simulations were performed using the Simulation complement. A coefficient of influence of residual stresses on the fatigue life of welded joints was proposed, which under the conditions studied, was equal to 1.14.

  5. Desarrollo de un modelo matemático para dimensionar un deshidratador solar directo de cacao

    Teixeira Da Silva, Juan Manuel; Malpica Pérez, Freddy Alberto
    A transient analytical model was developed which aims to determine the dimensions of a solar dehydrator of cacao that uses heated air as drying media. The air is heated in a flat solar collector and thermal storage unit. Then, the heated air crosses the drying section where the cacao is protected against open atmosphere and allows transmission of solar irradiation. The model was applied to the yard traditional solar drying of cacao.Local average values of environmental conditions were input data to the model. The results indicate that the air can reach a temperature as 65°C with a relative humidity as...

  6. Optimización de la distribución de la flota de cabotaje en múltiples direcciones de transportación

    Herrera Franklin, Jorge; González Cobas, José R.; Rosete Suárez, Alejandro
    The present paper discusses the fleet distribution side of the Ship Routing and Scheduling problem combining factors of tactical and operative levels for an industrial service of maritime transportation of cargoes. A mathematical model based on the Generalized Bin Packing Problem wasused, which issupportedin the Local Search algorithm with first ascent and restart, to guarantee the solution of big instances that make computationally untreatable the problem. Through experimentation, it was determined that the best results were obtained by modifying 3 bits in the allocation matrix of ships by transport directions. In addition,a restart parameter was set based in the iterations...

  7. Modelación matemática de un colector solar de tubos evacuados todo cristal

    Cisneros Ramírez, César Arnaldo; Recalde, Celso
    El trabajo trata sobre la modelación matemática de un colector solar de tubos evacuados todo cristal. En el desarrollo se obtuvo una ecuación para la evaluación del flujo termosifónico que se estableció en un colector de este tipo bajo la influencia de la radiación solar y como particularidad es que esta ecuación tiene en cuenta la relación de áreas que ocupa tanto el flujo caliente y el flujo frío que se establece en el colector. Como resultado se da el valor del flujo que se establece en función del ángulo de inclinación del colector y de la relación longitud/diámetro del...

  8. Thermal hydraulic performance of a wavy fin having two row of circular tubes

    Borrajo Pérez, Rubén; González Bayón, Juan José; Reyes Fernández de Bulnes, Darían
    This paper is about the thermal and hydraulic characterization of a compact heat exchanger having two row of tubes and rectangular wavy fins. The dimension of the tubes and the fin are similar to the used in the air conditioning and refrigeration area. A numerical approach was used and the computational domain was implemented using symmetry and periodic condition. Were considered extended inlet and outlet section for accuracy. The numerical procedure ant its model were certified against published literature and a good match was found. The impinging flow on the fin surface was found responsible for the differences between the...

  9. A new scheme for innovation. An essay

    Bergeron, Michel; de la Torre, Mayra; Harasic, Oscar
    A new model is proposed for innovation based on science and technology, illustrated by a tetrahedron,. The model includes five key actors: Government, Academia, Industry, the Inventor and the Citizen. It is crucial that all actors develop an open collaboration and multiply the exchanges between themselves to promote a climate for inclusive innovation. One original element of the tetrahedron is the recognition of citizen participation, since he/she is, as a consumer, the first one to experience the fallouts (good and evil) of any innovation. Similarly, because of his role in science dissemination, the science journalist must be recognized as an ideal key citizen in the assessment of the social values...

  10. Capacidade de busca e reprodução de trichospilus diatraeae e palmistichus elaeisis (hymenoptera: Eulophidae) em pupas de diatraea saccharalis (lepidoptera: Crambidae)

    Chichera, Roberto Augusto; Pereira, Fabricio Fagundes; Oliveira Kassab, Samir; Hidalgo Barbosa, Rogério; Luiz Pastori, Patrik; Rossoni, Camila
    Successful pest control depends on the ability of the parasitoid to locate and parasitize the host. Thus, we studied biological aspects and the ability of parasitoids Trichospilus diatraeae and Palmistichus elaeisis (Hymenoptera: Eulophidae) reared on Diatraea saccharalis (Lepidoptera: Crambidae) to locate and parasitize pupae of this insect. Thirty-six pupae of D. saccharalis were isolated in glass tubes with three treatments and 12 repetitions. The treatments were: 1) a female P. elaeisis/pupa, 2) a female T. diatraeae/pupa and 3) (a female P. elaeisis + one T. diatraeae)/pupa. The parasitoids were removed from the tubes after 24h and pupae were kept at 25 ±1ºC, 70 ±10% relative humidity (RH) and 14h photoperiod...

  11. Alterações fisiológicas em sementes e metabolismo antioxidativo de plântulas de alface expostas à ação do extrato das folhas de zantedeschia aethiopica spreng

    Zanatta Aumonde, Tiago; Garbin Martinazzo, Emanuela; Borella, Junior; Pedó, Tiago; Do Amarante, Luciano; Amaral Villela, Francisco; Munt De Moraes, Dario
    This work aimed to evaluate the influence of different concentrations of Zantedeschia aethiopica Spreng. extract on the physiological performance of the seed and on the response of the antioxidant metabolism of lettuce seedlings. The treatments consisted of leaves extracts from Z. aethiopica at concentrations of 0, 6, 12, 25 and 50%. Germination, first germination count, germination speed and index, length of shoot and radicle, seedling total dry mass, chlorophyll content, activity of superoxide dismutase, catalase and ascorbarte peroxidase enzymes, lipid peroxidation, hydrogen peroxide quantification and seedling emergence, length of organs, and total dry mass of seedlings were evaluated. The percentage of germination, the length of the shoot and radicle of seedlings...

  12. Relaciones filogenéticas entre especies de Psidium (Myrtaceae) presentes en el occidente de Venezuela a partir de secuencias de ADN nuclear (ITS) y plastidial (trnH-psbA)

    Rivero, Gisela; Salazar, Gerardo; Pacheco, Darisol; Sánchez, Adriana; Quirós, Magally; Sthormes, Guillermo
    Western Venezuela is a region with high diversity of Psidium species and, thus, the goal was established to estimate from the molecular sequences the phylogenetic relations between representatives of said genus. In the Venezuelan states of Mérida, Táchira, Trujillo and Zulia, leaves of P. guineense, P. guajava, P. friedrichsthalianum and Calycolpus moritzianus, as well as herbarium samples of P. acutangulum, were collected. The ITS region (ITS-4 and ITS-5 spacers) of the nuclear genome and the trnH-psbA region of the plastidial genome were amplified. Additionally, P. cattleianum and P. cinereum were also analyzed. As an external group were included Blepharocalix salicifolius, Calyptranthes lanceolata, Campomanesia pubescens, Eugenia sulcata, Luma chequen, Marlierea eugeniopsoides, Myrceugenia planipes...

  13. Stratified cluster sampling under multiplicative model for quantitative sensitive question survey

    Xiangke, Pu; Ge, Gao; Yubo, Fan; Mian, Wang
    Os métodos avançados de amostragem e as correspondentes fórmulas são raramente aplicados em perguntas sensíveis de pesquisas quantitativas. Este trabalho desenvolve uma sé- rie de fórmulas para estimação de parâmetros em amostragem de conglomerados estratificados sob um modelo multiplicativo baseadas em teorias clássicas de amostragem e fórmulas de probabilidade total. Ilustra-se o desempenho dos métodos de amostragem e as fórmulas em uma pesquisa de enganos em exames no Campus Dushu Lake da Universidade de Soochow, China. A confiabilidade dos métodos de pesquisa e as fórmulas para pesquisas de perguntas sensitivas quantitativas resultam ser alta.

  14. Satellite observations of the effect of enso on the Tehuantepec and Papagayo upwellings

    Aguirre Gómez, Raúl; Salmerón García, Olivia; Álvarez, Román
    The effects of El Niño Southern Oscillation 1997-1998 on the Eastern Tropical Pacific Ocean are evaluated for the Tehuantepec (Mexico) and Papagayo (Costa Rica) upwelling regions. The influence of this phenomenon was observed by comparing sea surface temperature anomalies over a 3-year period, from winter 1996-1997 to winter 1999-2000. Satellite observations reveal an increment of 3 and 4ºC during the El Niño year 1997- 1998 compared with previous and subsequent years, and the inhibition of upwelling events. It was also observed that during ‘La Niña’, winter 1998-1999, conditions for upwelling events were re-established.

  15. Disponibilidad de fósforo en un suelo de las sabanas bien drenadas venezolanas, bajo diferentes coberturas y tipos de fertilización

    Lozano, Zenaida; Hernández Hernández, Rosa Mary; Bravo, Carlos; Rivero, Carmen; Toro, Marcia; Delgado, Mavelys
    In order to evaluate the effect of cover crops (grass or legume) and the fertilization type on phosphorus availability in a system no-tillage corn - cattle, a field experiment was conducted on a Typic Plinthustults soil in well drained savannas of Vernezuela. The design was a completely random factorial arrangement 2×4 (cover crop × fertilization), with three replicates. The cover crops were Urochloa dictyoneura (UD), Centrosema macrocarpum (CM), and the natural savannah (SN) as control. The P fertilization types were Control (no fertilizer), BRF + M (low dose, 25% P as rock phosphate + mycorrhizal inoculation), ARF (high dose, 100% P as rock phosphate), and ARF + FD (high dose,...

  16. Surface sediment survey of the seabed on the Northwestern slope of Cuba, Southern Straits of Florida

    Soto, Luis A.; López Veleroni, Diego G.; López Cánovas, Cecilia; Ruiz Vázquez, Ricardo; Lanza Espino, Guadalupe de la
    The seabed off the northwestern coast of Cuba was explored to study the sedimentary and biological characteristics of surface sediments in three blocks leased to REPSOLYPF-Cuba S.A., at depths between 1600 and 2000m. Subcoring of surficial sediments was conducted for stable isotopic analysis, total organic carbon and nitrogen contents, and infauna description. Spatial heterogeneity in moderately laminated sediments was detected among blocks. Surface sediments consist of silty and clay materials, mainly composed by calcite, were impoverished in organic matter and rich in hemipelagic components. From the northeastern end of this area (Block III, 1640m) large limestone blocks stained with hydrocarbons were recovered. Rock fragments had a coarse appearance and were impregnated with...

  17. El daño por oxidación causado por cobre y la respuesta antioxidante de las plantas

    León Morales, Janet María; Sepúlveda Jiménez, Gabriela
    Industrial and agricultural wastes are the main source of copper accumulation in the soil. Copper is an essential micronutrient for plants, required for their growth, and participates in oxidation-reduction reactions. However, copper becomes a toxic metal when it is in tissues at concentrations higher than those needed for plant growth (>30mg·kg-1 ). Copper promotes the generation of reactive oxygen species (ROS), in enzymatic and non-enzymatic form (through the Fenton reaction), which may cause oxidation of proteins and lipids, alter membrane integrity, photosynthesis and growth, and induce cell death. Among the biochemical mechanisms that are induced in response to the oxidative damage caused by copper is the increase in the activities of antioxidant...

  18. Análisis de grandes incendios forestales en la vegetación nativa de Chile

    Castillo S, Miguel; Garfias S, Roberto; Julio A, Guillermo; González R, Luis
    Chile’s Central Zone has been permanently affected by forest fires on the native vegetation, whose damage and effects have not been sufficiently studied at the regional scale, despite the very serious consequences of this problem for the country. Fires during 35 years (1976-2010) were analyzed with the aim of obtaining useful data for future projects of environmental recovery in areas that have been affected by fire. The analysis included fires on more than 2000ha, localized between 32 and 38ºS, and where the biggest damage was concentrated in 1984 and 1999, mainly attributable to the environmental conditions that favored the spread of fires in those years. However, these results do not correspond...

  19. Evaluación de la Toxicidad en Desechos y Suelos Petrolizados empleando semillas de Lactuca sativa L

    Infante, Carmen; Morales García, Fernando A.
    Toxicity of different samples of heavy oil drilled cuttings (10°API) and contaminated soils with medium (27°API) and light (32°API) crude were estimated with Lactuca sativa L bioassays. The toxicity of contaminated soil was evaluated before and after a bioremediation process carried out at laboratory scale. The results show no toxicity in samples of cuttings impregnated with extra heavy oil, as well as any relationship between toxicity and oil and grease concentration in soils. By contrast, soil samples contaminated with light and medium crude oil showed toxicity, expressed in terms of percentage of hypocotyl elongation with respect to the control (soil without oil), before the bioremediation process. After bioremediation there was a...

  20. Efecto del nivel de agua sobre el tamaño y biomasa foliar de sagittaria macrophylla (alismataceae)

    Sánchez Reyes, Vicente; Zepeda Gómez, Carmen; Manjarrez Silva, Francisco Javier; White Olascoaga, Laura
    Sagittaria macrophylla Zucc. is an endemic aquatic plant of Mexico that shows morphological differences in emergent leaves. To determine the effect of water level on growth and biomass of the leaves of this hydrophyte, batches of 30 plants were grown in concrete tanks under semi-natural conditions and tested four flood levels were tested (5, 15, 3 and 45cm). During five periods of 14 days each, length and biomass of leaves (blades and petioles) were evaluated. The values for plants grown from the four flood levels were compared using discriminant function analysis (DFA). In most of the evaluated periods petiole length and biomass increased as the flood level was raised. Plants...

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