Physical parameters in the hot spots and jets of Compact Symmetric Objects

We present a model to determine the physical parameters of jets and hot spots of a sample of CSOs under very basic assumptions like synchrotron emission and minimum energy conditions. Based on this model we propose a simple evolutionary scenario for these sources assuming that they evolve in ram pressure equilibrium with the external medium and constant jet power. The parameters of our model are constrained from fits of observational data (radio luminosity, hot spot radius and hot spot advance speed) versus projected linear size. From these plots we conclude that CSOs evolve self-similarly and that their radio luminosity increases with linear size along the first kiloparsec. Assuming that the jets feeding CSOs are relativistic from both kinematical and thermodynamical points of view, we use the values of the pressure and particle number density within the hot spots to estimate the fluxes of momentum (thrust), energy, and particles of these relativistic jets. The mean jet power obtained in this way is within an order of magnitude that inferred for FRII sources, which is consistent with CSOs being the possible precursors of large doubles. The inferred flux of particles corresponds to, for a barionic jet, about a 10% of the mass accreted by a black hole of $10^8 {\rm M_{\odot}}$ at the Eddington limit, pointing towards a very efficient conversion of accretion flow into ejection, or to a leptonic composition of jets.Comment: 11 pages, 2 figures. Accepted for publication in Astrophysical Journa

Tougher Educational Exam Leading to Worse Selection

This paper shows a somehow counterintuitive result: an increase in the exam diculty may reduce the average quality (productivity) of selected individuals. Since the exam does not verify all skills, when its standard rises, candidates with relatively low skills emphasized in the test and high skills demanded in the job may no longer qualify. Hence, an increase in the testing standard may be counterproductive. One implication is that policies should emphasize alignment between the skills tested and those required in the actual jobs.school standard, signaling model, cognitive skill, noncog- nitive skill

New strategies to fight bacterial adhesion

Initial adhesion of bacteria to biomaterials' surface is assumed to be an important stage in their colonization which may to lead to severe infections and loss of medical devices. Thus, the knowledge of how these microorganisms adhere and which factors affect this phenomenon proves to be of great importance in order to avoid their colonization. Hydrophobicity, charge, roughness and chemical composition of surfaces can rule the adhesion process. A better understanding of all these features is crucial for an effective microorganism’s adhesion control. In this context, it is possible to modify the biomaterials’ surfaces through coatings doped with an antimicrobial agent, in order to prevent biofilm formation. So, this mini-review gives a brief account of aspects involved in bacterial attachment to a surface, highlighting the interactions involved and presenting mechanisms that are being used to fight pathogens adhesion. For this intent, hydrophobicity, morphology and topography of doped silver coatings will be exploited as a new approach for the development of antibacterial surfaces

Transthyretin familial amyloid polyneuropathy impact on health-related quality of life

info:eu-repo/semantics/publishedVersio