341 research outputs found

    Crecimiento y eficiencia de uso del nitrógeno en maíz de regadío en una región semiárida según la fertilización nitrogenada utilizada

    Get PDF
    The main groundwater pollution factor in irrigated maize production areas is leaching of nitrogen below the root zone. During the years 1999-2001, experiments were carried out on irrigated maize in the semiarid region of Castilla- La Mancha to evaluate the effect of nitrogen in the growth and yield of maize. Three rates of nitrogen were tested: No (0 kg N ha-1), Nop (175, 150 and 130 kg N ha-1 in 1999, 2000 and 2001, respectively), and Nc (300 kg N ha-1). A high initial level of residual soil NO-3 was found in the spring of 1999 as a consequence of fertilization carryover from the previous years. Although there was no plant response to N fertilization in 1999, significant responses were obtained during the following two years. Moreover, in 2000, the grain production did not show significant differences between Nop and Nc. However, in 2001, maize yield was slightly decreased due to an attempt to decrease the Nop to 130 kg N ha-1, showing significant differences with regard to Nc. The differences in grain yield among nitrogen levels were mainly due to a significant variation in maximum leaf area index, leaf area duration and crop growth rate. There was a decreasing pattern in nitrogen use efficiency values with increasing fertilizer rates, indicating that crop production could be sustained with lower fertilizer applications. Fertilizer practices must be revised in order to control and prevent insofar as possible water pollution in "La-Mancha Oriental" aquifer.El principal contaminante del agua subterránea en las áreas de regadío cultivadas de maíz es la lixiviación del nitrógeno. Durante los años 1999 a 2001 se han realizado ensayos en maíz regado en la región semiárida de Castilla-La Mancha, con el objetivo de evaluar su producción y crecimiento ante tres dosis de nitrógeno: No (0 kg N ha-1), Nop (175, 150 y 130 kg N ha-1 en 1999, 2000 y 2001, respectivamente), y Nc (300 kg N ha-1). El alto nivel inicial de NO-3 residual en el suelo durante la primavera de 1999, consecuencia de la fertilización anterior, propició la falta de respuesta a la fertilización con N. Sin embargo, se obtuvieron respuestas significativas los dos años siguientes. Además, en el año 2000, la producción de grano no registró diferencias significativas entre Nop y Nc. Sin embargo, disminuyó ligeramente la producción en el año 2001 al tratar de reducir la dosis óptima a 130 kg N ha-1, presentando diferencias significativas respecto a Nc. Este hecho fue debido, principalmente, a una variación significativa en el índice de área foliar máximo, la duración del área foliar y la tasa de crecimiento del cultivo. Las dosis más elevadas de fertilizante originaron una disminución de la eficiencia de uso del nitrógeno, por lo que la producción podría obtenerse con unos aportes menores de nitrógeno. Se debe revisar la fertilización para contribuir a controlar y prevenir, en la medida de lo posible, la contaminación en el acuífero de La Mancha Oriental

    Profilaxis antibiótica en cirugía

    Get PDF
    Existe una abundantísima documentación en la literatura acerca de la eficacia de los antibióticos utilizados profilácticamente en cirugía (1-10). Probablemente lo más útil para el trabajo diario de un hospital sea la adopción de pautas concretas que permitan ser evaluadas periódicamente a través de la colaboración, entre otros, de anestesistas, cirujanos y microbiólogos (11,12). En esta línea hemos revisado, de una manera intencionadamente esquemática, diversas facetas relativas a la profilaxis antibiótica en cirugía. Para ello comentaremos algunos aspectos generales de profilaxis de la infección postquirúrgica, unas breves normas para la utilización profiláctica de antibióticos y resumiremos determinadas indicaciones en función del tipo de intervención

    Chronic exposure to environmentally relevant levels of simvastatin disrupts zebrafish brain gene signaling involved in energy metabolism

    Get PDF
    Simvastatin (SIM), a hypocholesterolaemic drug belonging to the statins group, is a widely prescribed pharmaceutical for prevention of cardiovascular diseases. Several studies showed that lipophilic statins, as SIM, cross the blood-brain barrier and interfere with the energy metabolism of the central nervous system in humans and mammalian models. In fish and other aquatic organisms, the effects of SIM on the brain energy metabolism are unknown, particularly following exposure to low environmentally relevant concentrations. Therefore, the present study aimed at investigating the influence of SIM on gene signaling pathways involved in brain energy metabolism of adult zebrafish (Danio rerio) following chronic exposure (90 days) to environmentally relevant SIM concentrations ranging from 8 ng/L to 1000 ng/L. Real-time PCR was used to determine the transcript levels of several genes involved in different pathways of the brain energy metabolism (glut1b, gapdh, acadm, accα, fasn, idh3a, cox4i1, and cox5aa). The findings here reported integrated well with ecological and biochemical responses obtained in a parallel study. Data demonstrated that SIM modulates transcription of key genes involved in the mitochondrial electron transport chain, in glucose transport and metabolism, in fatty acid synthesis and β-oxidation. Further, SIM exposure led to a sex-dependent transcription profile for some of the studied genes. Overall, the present study demonstrated, for the first time, that SIM modulates gene regulation of key pathways involved in the energy metabolism in fish brain at environmentally relevant concentrationsThis study was developed under the project Nor-Water -Poluentes emergentes nas águas da Galiza-Norte de Portugal: novas ferramentas para gestão de risco [Reference: 0725_NOR_WATER_1_P], financed by Programa de Cooperação Interreg Portugal/Espanha, (POCTEP) 2014–2020. The study was also supported by the National Funds through Portuguese Foundation for Science and Technology (FCT) under the projects [UID/Multi/04423/2019 and UID/AGR/04033/2013]. S. Barros was supported by the doctoral fellowship [PD/BD/143090/2018] from FCT. J.B. Quintana acknowledges the financial support of Spanish “Agencia Estatal de Investigación” [ref. CTM2017-84763-C3-R-2] and Xunta de Galicia [ref. ED431C2017/36], both co-funded by FEDER/ERDFS

    Operational realization of quantum vacuum ambiguities

    Full text link
    We provide a reinterpretation of the quantum vacuum ambiguities that one encounters when studying particle creation phenomena due to an external and time-dependent agent. We propose a measurement-motivated understanding: Each way of measuring the number of created particles selects a particular vacuum. This point of view gives a clear and physical meaning to the time evolution of the number of particles produced by the agent as the counts in a specific detector and, at the same time relates commonly used quantization prescriptions to particular measurement setups.Comment: 6 pages, 3 figure

    Applicability of mixed-mode chromatography for the simultaneous analysis of C1-C18 perfluoroalkylated substances

    Get PDF
    This is a post-peer-review, pre-copyedit version of an article published in Analytical and Bioanalytical Chemistry. The final authenticated version is available online at: https://doi.org/10.1007/s00216-020-02434-wA new analytical method for the determination of 22 perfluoroalkylated (carboxylic and sulfonic) acids in water samples is presented. The method's objective was to achieve the simultaneous quantification of compounds with different chain lengths (from C1 to C18). To this end, 500 mL of water were extracted with Oasis WAX solid-phase extraction cartridges and eluted with 3 mL of 5% ammonia in methanol. After evaporation to dryness, extracts were reconstituted in methanol:ultrapure water (1:1) and analyzed by mixed-mode liquid chromatography-tandem mass spectrometry (MMLC-MS/MS) using a weak anion exchange/reversed-phase column. The method provided good results, with limits of quantification lower than 1 ng/L in river water for most of compounds, except the two perfluorocarboxylic acids with the longest alkyl chain (>C14) and trifluoroacetic acid, for which a blank contamination problem was observed. The method proved good trueness and precision in both ultrapure and river water (R ≥ 81%, RSD ≤ 15%). After validation, the method was applied to the analysis of nine water samples where nine perfluoroalkylated acids were quantified. Seven of them were ultrashort- (C1-C4) and short-chain (C4-C8) perfluoroalkylated acids, pointing out the importance of developing methods capable to target such substances for further monitoringThis work was supported by the Water Challenges for a Changing World Joint Program Initiative (Water JPI) Pilot Call (ref. WATERJPI2013 – PROMOTE), the Spanish Ministry of Economy and Competitiveness/Spanish Agencia Estatal de Investigación (refs. JPIW2013-117 and CTM2017-84763-C3-2-R), the Galician Council of Culture, Education and Universities (ref. ED431C2017/36) and FEDER/EDRF fundingS
    corecore