Docentes y bibliotecarios por una biblioteca instructiva.

Sin resume

The effect of working parameters upon elastohydrodynamic film thickness under periodic load variation

There are a number of widely used machine components, such as rolling element bearings, gears and cams, which operate in the lubrication regime known as Elastohydrodynamics (EHD), where lubricant film thickness is governed by hydrodynamic action of convergent geometry, elastic deformation between non-conformal contacting surfaces, and the increase of lubricant viscosity with pressure. Variable loading conditions occur not only in all the machine components mentioned above, but also in natural joints such as hip or knee joints of humans or many vertebrates. Experimental studies of the behaviour of EHD films under variable loading are scarce and to authors’ knowledge systematic studies of the evolution of lubricant film thickness in EHD contacts subjected to forced harmonic variation of load are even less common. The aim of the present study is to explore the effect of load amplitude on the EHD film behaviour. This is done in alternating cycles with the load varying about a fixed, preset value at various amplitudes. Experimental results are compared with a simple theoretical analysis based on the speed of change of contact’s dimensions, a semi-analytical solution which includes both speed variation and squeeze effect, and finally with a full numerical solution

Medicinal plants used in traditional herbal medicine in the province of Chimborazo, Ecuador

Background: Phyto-therapy studies on Chimborazo province in Ecuador are really limited. This area, located within the Andes, is considered a millenarian and intercultural province, where multiples cultures and ethnic groups coexist.Materials and Methods: The study was conducted through direct interviews with 84 ancestral healers from the Province of Chimborazo, Ecuador.Results: We presented ten most used species by ancestral healers of Chimborazo province to cure different illnesses and their medicinal uses. We also provided the application mode and some features of healing that should be emphasized.Conclusion: The nettle was the medicinal plant employed for more different illness and the chamomile was the one with higher prevalence. We could confirm that the Native Ecuadorians have a vast variety of traditions and popular medicinal practices that have great value and are needed to be researched and studied extensively.Keywords: Medicinal plants, Chimborazo, Ecuador, ancestral us

Young stellar clusters throughout the Galaxy and the interaction with their molecular environment

Stars are born within dense clumps of giant molecular clouds, constituting young stellar agglomerates known as embedded clusters. Once the parental gas is expelled through stellar feedback, they evolve into bound open clusters only under special conditions. In this thesis, we study observationally all embedded clusters (ECs) and open clusters (OCs) known so far in the inner Galaxy, investigating particularly their interaction with the surrounding molecular environment. We first compiled a merged list of 3904 clusters from optical and infrared clusters catalogs in the literature, including 71 new embedded clusters discovered by us in the GLIMPSE mid-infrared data after applying a red-color criterion. From this list, 695 clusters are within the Galactic range |l| We found that our OC and EC samples are roughly complete up to ~1 kpc and ~1.8 kpc from the Sun, respectively, after which the completeness decays exponentially. Using available age estimates for a few ECs, we derived an upper limit of 3 Myr for the duration of the embedded phase. Combined with the OC age distribution within 3 kpc from the Sun, we computed formation rates of 0.54, 1.18, and 6.50 Myr^-1 kpc^-2 for bound open clusters, all observed young exposed clusters, and embedded clusters, respectively, implying an EC dissolution fraction of 88% +- 8%. We carried out follow-up 13CO(2-1) and C18O(2-1) mapping observations towards a subsample of 14 clusters showing evidence of ongoing stellar feedback in our previous analysis, and we indeed found kinematic signatures of enhanced turbulence and expanding motions. A more detailed study towards the IR bubble G10.31-0.14, including a comparison with simple geometrical models of the velocity field, reveals that this source is more likely an expanding molecular ring inclined with respect to the plane of the sky, rather than a 3D shell seen in projection

Open clusters: time-scales, core collapse and blue stragglers

We developed a mathematical model to derive time scales and the presence of BS stars. The model is based on the variation of mass through a circle into the cluster defined by a radius, and at a time; this mass cross is translated into a differential equation that it can be integrated for a given radius (r) and a determined time (t). From this equation we can derive the different time scales that allows us to reach conclusions like: clusters not containing blue strugglers (BS) stars disappear younger than those clusters containing BS. In clusters containing BS stars, the volume which takes up half of the cluster mass is bigger than the one corresponding to clusters without BS stars but the time to catch it up is shorter. We also studied, by means of this equation, the core collapse of stars of the cluster and the region where this concentration is stopped/retained; this region is identified by means of the relation $c/ch$, being $c=\log(rt/rc)$ and $ch=\log(rc/rh)$. Where rt and rc are the tidal and the core radius respectively, and rh is the radius where half of the cluster mass is concentrated. The model also drove us to the conclusion that the number of the blue straggler stars in a cluster follows a distribution function whose components are the ratio between relaxation time and the age, labelled as $\it f$, and a factor, named $\varpi$, which is an indicator of the origin of the BS; $\varpi$ increases as the number of BS increase but it is limited to$\sim$5.0. The mentioned distribution function is expressed as $\it NBS$ $\sim$ $\it f^3$($\frac{1}{e^{\frac{f}{\varpi}}-1}$). The validity of this function was carried out by means of matching the number of observed blue straggler (BS) stars to the number of predicted ones in the available sample of OC