University of Costa Rica

About: University of Costa Rica is a education organization based out in San José, Costa Rica. It is known for research contribution in the topics: Population & Venom. The organization has 9817 authors who have published 16781 publications receiving 238208 citations. The organization is also known as: UCR & Universidad de Costa Rica.

Vegetation as a driver of temporal variations in slope stability: The impact of hydrological processes

Abstract: Although vegetation is increasingly used to mitigate landslide risks, how vegetation affects the temporal variability of slope stability is poorly understood, especially in earthquake-prone regions. We combined 3-year long soil moisture monitoring, measurements of soil physical properties and plant functional traits, and numerical modeling to compare slope stability under paired land uses with and without trees in tropical, subtropical, and temperate landslide- and earthquake-prone regions. Trees improved stability for 5–12 months per year from drawdown of soil moisture and resulted in less interannual variability in the duration of high-stability periods compared to slopes without trees. Our meta-analysis of published data also showed that slopes with woody vegetation were more stable and less sensitive to climate and soil factors than slopes with herbaceous vegetation. However, estimates of earthquake magnitude necessary to destabilize slopes at our sites suggest that large additional stabilization from trees is necessary for meaningful protection against external triggers. (Resume d'auteur)

A study of the production of clarified banana juice using pectinolytic enzymes

Abstract: Summary Pectinolytic enzyme treatments to increase the yield, reduce the viscosity and clarify the juice obtained from ripe banana pulp were studied. Six commercial enzyme preparations were tested on pulps of different ripenesses. Optimal conditions with respect to enzyme concentration, incubation temperature, time and pH levels are reported for the two most effective enzyme preparations. Clear juice yields of between 55 and 60% (based on pulp weight used) are obtained from pulp incubated at 45°C for 1 hr with 0.01% w/w of enzyme by subsequent centrifugation at 2900 maximal relative centrifugal force for 20 min. This corresponds to a yield of total and reducing sugars present in the pulp of over 75%. Untreated control pulps yield less than 5% of juice under these conditions. Hydraulic pressing of the pulps at 16 kg/cm2 gives similar juice yields to those obtained by centrifugation. The juice has an excellent flavour and aroma and provides a possible use for the large quantities of reject bananas available in producer countries.

Remarkable Effects of Axial π* Coordination on the Cr−Cr Quadruple Bond in Dichromium Paddlewheel Complexes

Abstract: It is well-known that donation of electron density into the σ* orbital of a Cr−Cr quadruple bond causes major lengthening of the Cr−Cr distance, and there is some prior evidence that a similar lengthening is caused by dative interaction with the π* orbitals. Some molecules have now been made that allow a definitive assessment of this axial π* effect. A molecule has been designed to ensure that there is axial donation into the π* orbitals but not onto the σ* orbital; ligands have been used in which the donor atoms are tethered to the bridging ligands in such a way that they can reach only the π* orbitals but not the σ* orbital. The ligands used for this purpose are the anions of 2,6-di(phenylimino)piperidine (DPhIP) and 2,2‘-dipyridylamine (dpa). In the compound Cr2(DPhIP)4 four imino nitrogen lone pairs are suitably positioned to donate to the π* orbitals and the Cr−Cr bond length is 2.265(1) A. For direct comparison, the compound Cr2(PhIP)4 (PhIP is the anion of 2-(phenylimino)piperidine) was made and fo...