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Rapidly evolving transients, or objects that rise and fade in brightness on timescales two to three times shorter than those of typical Type Ia or Type II supernovae (SNe), have uncertain progenitor systems and powering mechanisms. Recent studies have noted similarities between rapidly evolving transients and Type Ibn SNe, which are powered by ejecta interacting with He-rich circumstellar material (CSM). In this work we present multiband photometric and spectroscopic observations from Las Cumbres Observatory and Swift of four fast-evolving Type Ibn SNe. We compare these observations with those of rapidly evolving transients identified in the literature. We discuss several common characteristics between these two samples, including their light curve and color evolution as well as their spectral features. To investigate a common powering mechanism we construct a grid of analytical model light curves with luminosity inputs from CSM interaction as well as 56Ni radioactive decay. We find that models with ejecta masses of ≈1–3 M⊙, CSM masses of ≈0.2–1 M⊙, and CSM radii of ≈20–65 au can explain the diversity of peak luminosities, rise times, and decline rates observed in Type Ibn SNe and rapidly evolving transients. This suggests that a common progenitor system—the core collapse of a high-mass star within a dense CSM shell—can reproduce the light curves of even the most luminous and fast-evolving objects, such as AT 2018cow. This work is one of the first to reproduce the light curves of both SNe Ibn and other rapidly evolving transients with a single model. [ABSTRACT FROM AUTHOR]

Rapidly evolving transients, or objects that rise and fade in brightness on timescales two to three times shorter than those of typical Type Ia or Type II supernovae (SNe), have uncertain progenitor systems and powering mechanisms. Recent studies have noted similarities between rapidly evolving transients and Type Ibn SNe, which are powered by ejecta interacting with He-rich circumstellar material (CSM). In this work we present multiband photometric and spectroscopic observations from Las Cumbres Observatory and Swift of four fast-evolving Type Ibn SNe. We compare these observations with those of rapidly evolving transients identified in the literature. We discuss several common characteristics between these two samples, including their light curve and color evolution as well as their spectral features. To investigate a common powering mechanism we construct a grid of analytical model light curves with luminosity inputs from CSM interaction as well as 56Ni radioactive decay. We find that models with ejecta masses of ≈1â€"3 M ⊙, CSM masses of ≈0.2â€"1 M ⊙, and CSM radii of ≈20â€"65 au can explain the diversity of peak luminosities, rise times, and decline rates observed in Type Ibn SNe and rapidly evolving transients. This suggests that a common progenitor systemâ€"the core collapse of a high-mass star within a dense CSM shellâ€"can reproduce the light curves of even the most luminous and fast-evolving objects, such as AT 2018cow. This work is one of the first to reproduce the light curves of both SNe Ibn and other rapidly evolving transients with a single model. [ABSTRACT FROM AUTHOR]

The aim of this work is to study the relationship between electrical, structure, and potentiometric response to nitrate anions using Ion Selective Electrodes (ISE). These ISE are based on chitosan-montmorillonite nanocomposite membranes with different content of montmorillonite. Membrane properties have been studied using SEM, FTIR, and impedance spectroscopy measurements. With the advent of impedance spectroscopy one is allowed to obtain the DC conductivity dependence on montmorillonite concentration and the percolation threshold. Additionally, the potentiometric response to nitrate anions of ISE based on chitosan-clay nanocomposite has been investigated. It is shown that the properties and performance of these membrane electrodes depend upon the clay wt% and that the best sensitivity to nitrate ions (with detection limit 7 × 10−5 M) is obtained near the percolation concentration ca. 8 ± 2.5 wt% of clay. This observation is traceable to higher clay content (higher agglomeration) that tends to decrease the intercalation and absorption of the number of chitosan chains in the interlayer space of montmorillonite. [ABSTRACT FROM AUTHOR]

Background: Gastric cancer is an aggressive disease with nonspecific early symptoms. Its incidence and prognosis in young patients has shown considerable variability. Purpose of the study: Our objective was to retrospectively study patients from our institution aged <30 years with gastric carcinoma. The study was undertaken to describe the experience of gastric cancer in this population, and to demonstrate its specific clinical and pathological characteristics. Materials and methods: We reviewed the cases of histologically confirmed gastric cancer between 1985 and 2006 at the Instituto Nacional de Cancerología of Mexico (INCan); emphasis in our review was placed on clinical presentation, diagnostic and therapeutic intervention, pathology, and the results. Results: Thirty cases of gastric carcinoma were reviewed. The patients' median age was 27 years (range, 18-30 years) and the male:female ratio was 1:1. Conclusion: Gastric cancer exhibits different behavior in patients aged ,30 years, but delay in diagnosis and the tumor's behavior appear to be the most important factors in prognosis of the disease. [ABSTRACT FROM AUTHOR]

In Zacatecas, agriculture consumes 77% of the underground water; 44% of the aquifers are over extracted. All protected agriculture production systems pump water from the aquifers for irrigation, and 96% of the production units were constructed with government support. They also receive support for inputs and domestic production factors. This paper analyzes the impact of agricultural policy on protected tomato production in the state of Zacatecas, Mexico, by examining competitive and efficient technologies and considering alternative sustainable production practices. The Extended Policy Analysis Matrix was applied. The analysis included four technologies under current conditions and two scenarios: a) adoption of sustainable production practices and b) unsustainable practices, at economic and private prices. The sustainable project paid for itself under both private and economic prices. [ABSTRACT FROM AUTHOR]

Forest cover in the dry zone of southern Honduras has suffered drastic reduction, largely as a result of the marginalisation of small farmers onto formerly wooded hillsides. In four case study communities, the relations between the area’s human population and the remaining tree diversity were investigated through a combination of interviews, focus group meetings and inventories. Inventories on 10 farms in 2 communities found an average of 57.6 standing trees (above 2 m in height) and 9388.3 live stumps and seedlings of tree and shrub species (less than 2 m in height) per hectare in recently cropped fields. Tree management practices were found to include the selective promotion of naturally regenerated trees valued by farmers for their products, the elimination of unwanted trees due to competition with crops for light and space, and pruning to reduce competition. Farmers listed 41 species as being actively protected, although protection was largely concentrated on a subset of 5 (Cordia alliodora, Swietenia humilis, Lysiloma spp., Enterolobium cyclocarpum and Albizia saman, in that order); they also described broadening their species preferences in the face of scarcity of preferred species. The study questions the common perception of dry zone farmers as being responsible for continued elimination of tree diversity, and highlights the potential of the management of natural regeneration for meeting the livelihood needs of small farmers. [ABSTRACT FROM AUTHOR]