Resolución algebraica de problemas estequiométricos

La resolución de problemas, entendida como la metodología para enfrentar situaciones nuevas que impliquen un reto personal, es una estrategia didáctica eficaz que permite generar, consolidar e integrar conocimientos. La resolución de un problema típico en ciencias parte de la comprensión de su enunciado, constituido por un texto corto escrito en lenguaje natural; la traducción de dicha situación al lenguaje matemático constituye un obstáculo en el proceso de resolución de problemas con estructura matemática subyacente. Para desarrollar en los estudiantes de ingeniería química las habilidades matemática y de traducción de lenguajes coloquial-científico-algebraico, se diseñaron enunciados de problemas basados en la estequiometría de compuestos y reacciones, los cuales involucran el planteamiento y resolución de sistemas de ecuaciones algebraicas lineales

Hypoglycemic Effect of Kalanchoe pinnata (Lam) Pers. Leaf Extract

Introduction: Kalanchoe pinnata (Lam) Pers (Crasulaceae) is a succulent ornamental plant. In Costa Rica, the leaves are used as a coadjuvant treatment for Diabetes Mellitus based on traditional knowledge of natural remedies. Moreover, there are some studies mentioning its use for Diabetes Mellitus as medicinal plant in several countries. This research aimed to demonstrate the antidiabetic properties of hydroalcoholic extracts of K. pinnata leaves through phytochemical screening, alpha amylase inhibition and rodent models. Methods: Crude extracts of K. pinnata leaves were prepared by infusion and decoction using water:ethanol (70:30) as a solvent. The extracts prepared by decoction (LAED, lyophilized-water:ethanol decoction) and by infusion (LAEI, lyophilized-water:ethanol-infusion) were analyzed by Folin Ciocalteu, HPLC and capacity of inhibition of α-amylase activity. To determine hypoglycemic activity in rats, extracts were administered orally at doses of 250, 500 and 750 mg/Kg and blood sugar levels were monitored over a four hours period using a glucometer. Results: A significant reduction (p < 0.05) in blood glucose was observed after one hour in rats treated with 500 mg/Kg of LAED extract. Treatment with 750 mg/Kg LAEI induced a statistically significant reduction in blood sugar at 90, 180 and 240 min, showing that the glucose-lowering effect of this extract was greater at a higher concentration. Conclusions: This study confirmed the hypoglycemic effect of K. pinnata extracts in the acute phase in rats and supports the use of this Crassulaceae as a home remedyInstituto Tecnológico de Costa Rica/[1510035]/TEC/Costa RicaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias de la Salud::Instituto de Investigaciones Farmacéuticas (INIFAR

Improved Performance of an Epoxy Matrix as a Result of Combining Graphene Oxide and Reduced Graphene

We present an easy and effective way to improve the mechanical properties of an epoxy matrix by reinforcing it with a combination of graphene oxide (GO) and reduced graphene oxide (RGO). These nanocomposites were prepared with different load of nanofillers: 0.1, 0.4, 0.7, 1.0 wt% and a neat epoxy. Ratios of graphene oxide and reduced graphene (GO : RGO) employed were: 0 : 1, 0.25 : 0.75, 0.5 : 0.5, 0.75 : 0.25, and 1 : 0. Results show that with only 0.4 wt% and a ratio 0.2 : 0.75 of GO : RGO, tensile strength and tensile toughness are 52% and 152% higher than neat epoxy while modulus of elasticity was improved ~20%. The obtained results suggest that it is possible achieve advantageous properties by combining graphene in oxidized and reduced conditions as it shows a synergic effect by the presence of both nanofillers

Efectos de la radiación no ionizante emitida por dispositivos inalámbricos

The use of portable electronic equipment that emits non-ionizing radiation in the electromagnetic spectrum increases steadily and marks a trend likely to integrate functionality and miniaturization. Particularly, cellular telephony is widely used all around the world by a large number of users, despite little is known about the effects they may have on human health or that provides certainty about the results obtained. Many studies and projects to investigate those have been carried out, some have reached alarming results DNA breaks, genotoxicity, while others found no potential or significant threats and namely the results are not conclusive. The investigation document presents an analysis of previous specialized documentation, developed by recognized organizations in order to promote and enhance the discussion of the topic, considered polemical.El empleo de equipo electrónico portátil que emite radiación no ionizante en el espectro electromagnético se incrementa de manera constante y marca una tendencia proclive a la integración de funcionalidades y la miniaturización. Particularmente, la telefonía celular es usada amplia e intensivamente alrededor del mundo por un extenso número de usuarios, a pesar de que poco se sabe de los efectos que podrían tener en la salud humana o la certeza sobre los resultados obtenidos al investigarlos: algunos han alcanzado resultados alarmantes ruptura del ADN, genotoxicidad–, mientras que otros no han encontrado amenazas potenciales o significativas, es decir, los resultados no son concluyentes. El presente documento de investigación realiza un análisis con enfoque integral de la documentación especializada previa, realizada por organismos reconocidos, para favorecer y enriquecer la discusión de este tema, considerado polémico

Momento Económico (17-18)

En este número Temas de hoy, 2/ Encuentro sobre la Deuda Externa de America Latina y el Caribe, México, Alonso Aguilar, 3/ Fernando Carmona, 5/ Heberto Castillo. 6/ Gantón Garcia Cantú, 7/ Pablo Gómez, 8/ Sergio Méndez Arceo, 9/ Carlos Tello, 11/ Mario J. Zepeda Martinez, 12/ Argentina, Enrique Garcia Vázquez, 16/ Adolfo Pérez Esquivel, 20/ Brasil, Frei Betto, 22/ Ecuador, Blanca Chancoso, 24/ El Salvador, Guillermo Ungo, 25/ República Dominicana, Juan Bosch, 27/ Venezuela, Miguel Ángel Capriles, 28/ Organismos Económicos Latinoamericanos, Homero L. Hernández, 3

Duration of Sleep, Perception of Hunger and Satiety and Weight Gain during Pregnancy

Objective: To determine whether the duration and interruption of sleep, perception of hunger-satiety influence the excessive weight gain in Mexican pregnant women. Materials and Methods: Cross-sectional design, with 305 pregnant women, recruited in a primary care clinic. The duration of sleep was evaluated by interview and a hunger and satiety perception scale was used. Weight was obtained before and during pregnancy. The linear regression model was used to analyze the data. Results: The average number of hours that pregnant women slept was 9.04 hours per night, 83% interrupted sleep and 16.7% gained excessive gestational weight. The pre-gestational body mass index and sleep interruption explained the gestational weight gain. Conclusion: Intervening in factors that influence the interruption of sleep in pregnant women can contribute to prevent excessive weight gain and prevent maternal and child complications

Nitrogen uptake and internal recycling in Zostera marina exposed to oyster farming: eelgrass potential as a natural biofilter

Oyster farming in estuaries and coastal lagoons frequently overlaps with the distribution of seagrass meadows, yet there are few studies on how this aquaculture practice affects seagrass physiology. We compared in situ nitrogen uptake and the productivity of Zostera marina shoots growing near off-bottom longlines and at a site not affected by oyster farming in San Quintin Bay, a coastal lagoon in Baja California, Mexico. We used benthic chambers to measure leaf NH4 (+) uptake capacities by pulse labeling with (NH4)-N-15 (+) and plant photosynthesis and respiration. The internal N-15 resorption/recycling was measured in shoots 2 weeks after incubations. The natural isotopic composition of eelgrass tissues and vegetative descriptors were also examined. Plants growing at the oyster farming site showed a higher leaf NH4 (+) uptake rate (33.1 mmol NH4 (+) m(-2) day(-1)) relative to those not exposed to oyster cultures (25.6 mmol NH4 (+) m(-2) day(-1)). We calculated that an eelgrass meadow of 15-16 ha (which represents only about 3-4 % of the subtidal eelgrass meadow cover in the western arm of the lagoon) can potentially incorporate the total amount of NH4 (+) excreted by oysters (similar to 5.2 x 10(6) mmol NH4 (+) day(-1)). This highlights the potential of eelgrass to act as a natural biofilter for the NH4 (+) produced by oyster farming. Shoots exposed to oysters were more efficient in re-utilizing the internal N-15 into the growth of new leaf tissues or to translocate it to belowground tissues. Photosynthetic rates were greater in shoots exposed to oysters, which is consistent with higher NH4 (+) uptake and less negative delta C-13 values. Vegetative production (shoot size, leaf growth) was also higher in these shoots. Aboveground/belowground biomass ratio was lower in eelgrass beds not directly influenced by oyster farms, likely related to the higher investment in belowground biomass to incorporate sedimentary nutrients