Talks by Fernando de Leon
La experiencia del Observatorio Universitario UAM, como un esfuerzo colectivo por impulsar la plu... more La experiencia del Observatorio Universitario UAM, como un esfuerzo colectivo por impulsar la pluralidad en un Universidad Pública en México
Papers by Fernando de Leon
Revista Fitotecnia Mexicana, 2006
En este trabajo se evaluó el rendimiento de semilla, biomasa aérea, índice de cosecha, acame y re... more En este trabajo se evaluó el rendimiento de semilla, biomasa aérea, índice de cosecha, acame y reverdecimiento de dos cultivares de amaranto (Amaranthus hypochondriacus L.) (‘Tulyehualco’, tardío y alto; ‘Frondosa’, precoz y de altura intermedia) bajo dos densidades de población (62 500 y 375 000 plantas/ha). El trabajo se desarrolló en Tulyehualco, México, D. F., mediante siembra directa. Se aplicó riego de auxilio al inicio del cultivo y fertilización con estiércol de bovino (equivalente a 50 kg de N ha-1). El cultivar ‘Tulyehualco’de porte alto y 199 d a la cosecha, mostró mayor rendimiento de semilla (4 t ha-1 a 375 000 plantas/ha) que el cv. ‘Frondosa’ (2.2 t ha-1). En baja densidad de población, el cv. ‘Frondosa’, con 116 d a la cosecha, produjo 600 kg ha-1, y 1200 kg ha-1 en alta densidad; estos rendimientos son similares a los que se obtienen con transplante en Tulyehualco. El cv. ‘Frondosa’ constituye una alternativa de producción, pues además de tener un buen rendimiento d...
Restoration Ecology, 2010
There is considerable interest in the potential use of soils to sequester carbon for climate chan... more There is considerable interest in the potential use of soils to sequester carbon for climate change mitigation. As such, there is a need to evaluate the potential for carbon accumulation in tropical regions. We compared the effects of three annual additions of nitrogen and/or phosphorus on soil carbon and nitrogen contents and pools (bulk soil, macro-, meso-, and microaggregates) of two regenerating secondary tropical dry forest differing in nutrient status and succession stage (10-year-old early-succession stage and approximately 60-year-old late-succession stage). The selected forest sites were located on a shallow calcareous soil in the Yucatá n Peninsula (Mexico). The primary production is limited by nitrogen and phosphorus in earlysuccession stage and by phosphorus in late-succession stage. In each forest site, four independent plots (12 3 12 m 2) were established, the treatments being: controls and plots fertilized during three consecutive years with nitrogen, phosphorus, or nitrogen plus phosphorus. In both forests, soil carbon and nitrogen contents were consistently high, with soil carbon:nitrogen ratios generally greater than 10. Results indicate that usually there are no significant increases of soil carbon stock associated to late succession but can be increased to 3.7 MgÁha 21 Áyr 21 with adoption of fertilizer practices. The potential soil carbon sequestration in early-succession forest was estimated to be 2.7 MgÁha 21 Áyr 21 , and there is no indication that fertilization improves carbon sequestration. In short, results suggest that the soil potential for carbon sequestration in these ecosystems is high and depends on the specific nutrient status of the site.
World Neurosurgery, 2016
Navigation technology is used for training in various medical specialties, not least image-guided... more Navigation technology is used for training in various medical specialties, not least image-guided spinal interventions. Navigation practice is an important educational component that allows residents to understand how surgical instruments interact with complex anatomy and to learn basic surgical skills such as the tri-dimensional mental interpretation of bi-dimensional data. However, inexpensive surgical simulators for spinal surgery are lacking. We therefore designed a low-cost spinal surgery simulator (Spine MovDigSys 01) to allow 3D navigation using 2D images without altering or limiting the surgeon's natural movement. A training system was developed using an anatomical lumbar model and two webcams to passively digitize surgical instruments under MATLAB software control. A proof-of-concept recognition task (vertebral body cannulation) and a pilot test of the system with 12 neuro- and orthopedic surgeons were performed to obtain feedback on the system. Position, orientation, and kinematic variables were determined and the lateral, posteroanterior, and anteroposterior (AP) views obtained. The system was tested using a proof-of-concept experimental task. Operator metrics including time of execution (t), intracorporeal length (d), insertion angle (α), average speed (v¯), and acceleration (a) were accurately obtained. These metrics were converted into assessment metrics such as smoothness of operation and linearity of insertion. Results from initial testing are shown and the system advantages and disadvantages described. This low-cost spinal surgery training system digitized the position and orientation of the instruments and allowed image-guided navigation, the generation of metrics, and graphic recording of the instrumental route. Spine MovDigSys 01 is useful for development of basic, non-innate skills and allows the novice apprentice to quickly and economically move beyond the basics.
Enferm Infec Microbiol Clin, 2005
Enfermedades Infecciosas Y Microbiologia Clinica, 2006
Empirical antifungal treatment (EAT) in neutropenia is mainly aimed at improving the poor prognos... more Empirical antifungal treatment (EAT) in neutropenia is mainly aimed at improving the poor prognosis of patients with invasive fungal infection through early treatment. The Infectious Diseases Society of America recommends initiating EAT in patients with persistent fever after 5-7 days of antibacterial treatment, and in those in whom remission of neutropenia is not imminent. Nevertheless, EAT has not been shown to be more effective than a placebo, it does not show better results than directed antifungal treatment, its effectiveness is minimal, it is not innocuous, and it is not very efficient with the use of most antifungal agents. All considered, we believe that the aforementioned recommendation for EAT treatment is unjustified. In its place we propose the application of EAT in patients selected on the basis of clinical criteria and risk factors.
European Journal of Agronomy, Apr 1, 2009
Soil management systems may negatively affect the quality of the soil. Policymakers and farmers n... more Soil management systems may negatively affect the quality of the soil. Policymakers and farmers need scientific information to make appropriate land management decisions. Conventional (CT) and zero tillage (ZT) are two common soil management systems. Comparative field studies under controlled conditions are required to determine the impact of these systems on soil quality and yields. The research presented studied plant and soil physical and chemical characteristics as affected by different agricultural management practices, i.e. ZT and CT, cropped with continuous wheat or maize in monoculture (M) or in a yearly rotation (R) of these two crops, either with residue retention (+r) or without residues retention (−r), in an experimental field in the Transvolcanic Belt of Mexico after 14 years. The dominant factors defining soil quality were organic C, total N, moisture, aggregate stability, mechanical resistance, pH and EC. The principal component combining the variables organic C, total N, aggregate stability and moisture content showed the highest correlations with final yield (R = 0.85 for wheat and 0.87 for maize).
The American journal of tropical medicine and hygiene
There are contradictory data about whether highly active antiretroviral therapy (HAART) prevents ... more There are contradictory data about whether highly active antiretroviral therapy (HAART) prevents visceral leishmaniasis (VL) relapses in human immunodeficiency virus type 1 (HIV-1)−infected patients. The aim of this study was to assess the frequency of VL relapses in individuals receiving HAART. Thirty-one patients who received HAART after developing VL were included in a retrospective cohort study. Ten of them received secondary chemoprophylaxis and the rest did not. Eight (38%) patients without secondary chemoprophylaxis showed a VL relapse. None of the seven subjects with VL relapses and 6 of 11 without recurrence (P ס 0.038), in whom all scheduled data were available, showed an increase of more than 100 CD4+ cells/mm 3 during the follow-up. Patients with relapse showed higher levels of HIV RNA viral load at their last visit (P ס 0.047). The frequency of VL relapses in patients receiving HAART is high. Relapses of VL are observed only in individuals with uncontrolled HIV replication and/or poor immunologic responses. * VL ס visceral leishmaniasis; IDU ס intravenous drug users; CDC ס Centers for Disease Control and Prevention; HAART ס highly active retroviral therapy; HIV ס human immunodeficiency virus.
An experience of student's training from Agricultural and Cattle Mastery at the Metropolitan ... more An experience of student's training from Agricultural and Cattle Mastery at the Metropolitan Autonomous University-Xochimilco (UAM-X) is described.
Revista fitotecnia mexicana publ. por la Sociedad Mexicana de Fitogenética
En este trabajo se evaluó el rendimiento de semilla, biomasa aérea, índice de cosecha, acame y re... more En este trabajo se evaluó el rendimiento de semilla, biomasa aérea, índice de cosecha, acame y reverdecimiento de dos cultivares de amaranto (Amaranthus hypochondriacus L.) (¿Tulyehualco¿, tardío y alto; ¿Frondosa¿, precoz y de altura intermedia) bajo dos densidades de población (62 500 y 375 000 plantas/ha). El trabajo se desarrolló en Tulyehualco, México, D. F., mediante siembra directa. Se aplicó riego de auxilio al inicio del cultivo y fertilización con estiércol de bovino (equivalente a 50 kg de N ha-1). El cultivar ¿Tulyehualco¿de porte alto y 199 d a la cosecha, mostró mayor rendimiento de semilla (4 t ha-1 a 375 000 plantas/ha) que el cv. ¿Frondosa¿ (2.2 t ha-1). En baja densidad de población, el cv. ¿Frondosa¿, con 116 d a la cosecha, produjo 600 kg ha-1, y 1200 kg ha-1 en alta densidad; estos rendimientos son similares a los que se obtienen con transplante en Tulyehualco. El cv. ¿Frondosa¿ constituye una alternativa de producción, pues además de tener un buen rendimiento d...
Acta de Investigación Psicológica, 2015
La capacidad para reconocer las emociones es un factor necesario para la normal adaptación del ni... more La capacidad para reconocer las emociones es un factor necesario para la normal adaptación del niño al medio social y educativo; además de permitir la detección de trastornos como el autismo, la ansiedad y la depresión en etapas tempranas del desarrollo. Con el objetivo de comprender este proceso se realizó un experimento en el que participaron 47 niños distribuidos en tres grupos de edad (6-7, 8-9. 10-11 años), que visualizaron fotografías de expresiones faciales y corporales de alegría, tristeza, ira y miedo. Se les pidió que reconocieran la emoción expresada a partir de etiquetas relativas a estas emociones básicas y representadas con emoticonos. Los resultados mostraron un mejor reconocimiento de las expresiones faciales y corporales de miedo en los niños de 8-11 años respecto a los de 6-7 años (p < .01, r > .50). Por otro lado, se mostraron diferencias significativas (p < .01, r > .50), en el reconocimiento de las expresiones faciales de ira respecto a las corporales de ira, entre los niños de 6-7 años y los de 8-11 años. Mientras los niños de 6-7 años discriminan mejor la expresión facial de ira que la corporal, estas diferencias se invirtieron en los niños de 8-11 años. De los resultados obtenidos se puede concluir que el reconocimiento de las expresiones emocionales de ira y miedo es un importante indicador del adecuado desarrollo del niño. Educar en el reconocimiento de estas emociones a partir de la edad de 7 años, podría facilitar una mejor regulación emocional, con un efecto beneficioso sobre el rendimiento académico del niño.
Amaranth (Amaranthus hypochondriacus L.) is a plant species that tolerates the semiarid condition... more Amaranth (Amaranthus hypochondriacus L.) is a plant species that tolerates the semiarid conditions prevailing in sandy soils in the central Valley Mexico region. In spite of its agronomic relevance, there is a lack of information about the soil-plant-microbe interactions in this plant species. The aim of this research was to study the phenotypic changes of the bacterial community considering physiological and biochemical traits, as well as its contribution to the delivery of available nutrients, in the rhizosheath of amaranth cultivated in a sandy soil in the Valley of Mexico. Rhizosheath soil samples were extracted at four stages of the crop plant (seeding, flowering, harvest and postharvest); 38 bacterial isolates were purified and characterized following 8 physiological and 34 biochemical tests. The results revealed high heterotrophic potential in the bacterial community. A cluster analysis and the index of similarity and Euclidean distance of Ward considering all physiological a...
Journal of Environmental Science and Health, Part B, 2014
Agricultural management affects the movement of atrazine in soil and leaching to groundwater. The... more Agricultural management affects the movement of atrazine in soil and leaching to groundwater. The objective of this study was to determine atrazine adsorption in a soil after 20 years of atrazine application under agronomic management practices differing in tillage practice (conventional and zero tillage), residue management (with and without residue retention) and crop rotation (wheatmaize rotation and maize monoculture). Atrazine sorption was determined using batch and column experiments. In the batch experiment, the highest distribution coefficient K d (1.1 L kg ¡1 ) at 0-10 cm soil depth was observed under zero tillage, crop rotation and residue retention (conservation agriculture). The key factor in adsorption was soil organic matter content and type. This was confirmed in the column experiment, in which the highest K d values were observed in treatments with residue retention, under either zero or conventional tillage (0.81 and 0.68 L kg ¡1 , respectively). Under zero tillage, the fact that there was no soil movement helped to increase the K d . The increased soil organic matter content with conservation agriculture may be more important than preferential flow due to higher pore connectivity in the same system. The soil's capacity to adsorb 2-hydroxyatrazine (HA), an important atrazine metabolite, was more important than its capacity to adsorb atrazine, and was similar under all four management practices (K d ranged from 30 to 40 L kg ¡1 ). The HA adsorption was attributed to the type and amount of clay in the soil, which is unaffected by agronomic management. Soils under conservation agriculture had higher atrazine retention potential than soils under conventional tillage, the system that predominates in the study area.
1) Universidad Autónoma Metropolitana-Xochimilco (México) (2) Colegio de Postgraduados-Campus Mon... more 1) Universidad Autónoma Metropolitana-Xochimilco (México) (2) Colegio de Postgraduados-Campus Montecillo (México) 1
Plant and Soil, 2011
Background and aims Conservation agriculture, the combination of minimal soil movement (zero or r... more Background and aims Conservation agriculture, the combination of minimal soil movement (zero or reduced tillage), crop residue retention and crop rotation, might have the potential to increase soil organic C content and reduce emissions of CO 2 .
Agro Sur, 1997
Leaf area, root lenght and grain yield of Amaranthus hypocondriacus L. grown on a highly compacte... more Leaf area, root lenght and grain yield of Amaranthus hypocondriacus L. grown on a highly compacted soil A highly compacted soil layer was detected in an amaranth field in Tulyehualco, México. The purpose of the present work was to analyze the effect of soil compaction on the crop of amaranth. Two plots with superficial (S) (1015 cm) and intermediate (I) (2025 cm) levels of compaction were compared. Several crop physiology parameters were studied and soil resistance was measured with a digital penetrometer.
Soil Biology and Biochemistry, 2007
The aggregation process in sandy soils depends on biological activity. We reported here results o... more The aggregation process in sandy soils depends on biological activity. We reported here results obtained from one sample time of: (a) adhesion of sand particles by root hairs and fungal hyphae, examined on root sections of four plant species (amaranth, Amaranthus hypochondriacus L.; Bermuda grass, Cynodon dactylon L.; maize, Zea mays L. and sunflower, Helianthus annuus L.) grown at field for 3 months; (b) root-adhering soil (RAS), root biomass (RB), and dry and water stable-aggregate fractions obtained from root:soil monoliths; and (c) arbuscular mycorrhizal colonization. Microscope observations on fine roots (o1 mm) showed that root hairs and hyphae contributed simultaneously, but not in the same proportion, to enmeshment of sand particles (20-150 mm). Hyphae contribution was considerably fewer than that of root-hairs. Maize and Bermuda grass had a higher root-hair density but a lower amount of external hyphae than those of amaranth and sunflower. Root-hairs of Bermuda grass and maize held approximately three times more sand particles than those of amaranth and sunflower (20 and 7 mm À1 of root section, respectively). These results were consistent with the higher RAS:RB ratio of Bermuda grass and maize (302 and 257, respectively), than that of amaranth and sunflower (89 and 159). Intensity of mycorrhizal colonization in the whole root system was higher in maize, Bermuda grass and sunflower (range of 22.7-25%) as compared to that of amaranth (6.8%). A. hypochondriacus, considered as a non-mycorrhizal plant species, showed typical structures (vesicles, hyphae and arbuscules) in the root system. Results emphasized the preponderant role of root hairs (of grasses and dicotyledon species) in the process of soil adhesion by roots under sandy conditions (pumice and feldspath particles) and semi-arid climate. r
Soil and Tillage Research, 2000
Several studies have shown the importance of organic material in the formation and stability of s... more Several studies have shown the importance of organic material in the formation and stability of soil aggregates. The organic matter of soil (SOM) is affected among other factors by the application of farmyard waste and compost, as well as tillage and crop rotation. This paper examines the aggregation and stability of a sandy soil (Haplic Fluvisol) in the valley of Mexico when treated with either 40 Mg ha À1 of compost or urea (80 kg ha À1 of N) and sown to amaranth (Amaranthus hypochondriacus L.) under dryland conditions. The application of compost resulted in a signi®cantly larger proportion of aggregates in the fractions >1 mm (1.0±2.0, 2.0±2.3, 2.3±4.7 mm) than in the smaller fraction (<1 mm). However the stability of the macroaggregates >1 mm in the compost treatment was not higher than in contrasting treatments which did not include organic matter. Compost, which was applied under drought conditions, did not increase the aggregate stability of the soil probably because of the restricted transformation of the compost and microorganism activity. #
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Talks by Fernando de Leon
Papers by Fernando de Leon