Group Mentoring: A Study of Mentoring Groups in Three Programs

In an effort to provide more youth with mentors, mentoring programs are implementing several promising new approaches. This report describes the strengths and challenges of group mentoring-an approach that is gaining popularity. Findings suggest that group mentoring is reaching youth and volunteers who are unlikely to participate in traditional one-on-one mentoring, and that the approach may provide youth with important benefits, especially the development of social skills. On the other hand, mentoring groups vary widely in their size, structure and focus, and in the extent to which they foster strong mentoring relationships and benefits for youth. Implications for the mentoring field and for future research are discussed

Charged Cylindrical Collapse of Anisotropic Fluid

Following the scheme developed by Misner and Sharp, we discuss the dynamics of gravitational collapse. For this purpose, an interior cylindrically symmetric spacetime is matched to an exterior charged static cylindrically symmetric spacetime using the Darmois matching conditions. Dynamical equations are obtained with matter dissipating in the form of shear viscosity. The effect of charge and dissipative quantities over the cylindrical collapse are studied. Finally, we show that homogeneity in energy density and conformal flatness of spacetime are necessary and sufficient for each other.Comment: 19 pages, accepted for publication in Gen. Relativ. Gra

Charging Interacting Rotating Black Holes in Heterotic String Theory

We present a formulation of the stationary bosonic string sector of the whole toroidally compactified effective field theory of the heterotic string as a double Ernst system which, in the framework of General Relativity describes, in particular, a pair of interacting spinning black holes; however, in the framework of low--energy string theory the double Ernst system can be particularly interpreted as the rotating field configuration of two interacting sources of black hole type coupled to dilaton and Kalb--Ramond fields. We clarify the rotating character of the $B_{t\phi}$--component of the antisymmetric tensor field of Kalb--Ramond and discuss on its possible torsion nature. We also recall the fact that the double Ernst system possesses a discrete symmetry which is used to relate physically different string vacua. Therefore we apply the normalized Harrison transformation (a charging symmetry which acts on the target space of the low--energy heterotic string theory preserving the asymptotics of the transformed fields and endowing them with multiple electromagnetic charges) on a generic solution of the double Ernst system and compute the generated field configurations for the 4D effective field theory of the heterotic string. This transformation generates the $U(1)^n$ vector field content of the whole low--energy heterotic string spectrum and gives rise to a pair of interacting rotating black holes endowed with dilaton, Kalb--Ramond and multiple electromagnetic fields where the charge vectors are orthogonal to each other.Comment: 15 pages in latex, revised versio

Cosmological Neutrino Background Revisited

We solve the Boltzmann equation for cosmological neutrinos around the epoch of the electron-positron annihilation in order to verify the freeze-out approximation and to compute accurately the cosmological neutrino distribution function. We find the radiation energy density to be about 0.3% higher than the one predicted by the freeze-out approximation. As a result, the spectrum of the Cosmic Microwave Background anisotropies changes by 0.3-05%, depending on the angular scale, and the amplitude of the mass fluctuations on scales below about 100 h^{-1} Mpc decreases by about 0.2-0.3%.Comment: An error is corrected, figure revised; submitted to Ap

Effects of sudden salinity changes on the oxygen consumption and osmoregulatory parameters in the Senegales sole (Solea senegalensis Kaup, 1858)

Senegalese sole juveniles were held into flow-through respirometers and submitted to a sudden salinity change. Briefly, 40-50 g body weight fish were kept into chambers with initial salinity of 37.5 ppt (the same as in culture tanks) and, after an acclimation of 4 hours, the salinity was changed to 5 or 55 ppt. A control group did not experience any salinity alteration. Oxygen consumption was registered every 14 min and fish were sampled (gill biopsy and plasma) at different times (at t=4.5 h and t=7 h in order to determine gill Na+,K+- ATPase activity and plasma cortisol concentration. At t=4.5 h, oxygen consumption showed an inverse relationship with salinity, while gill Na+,K+- ATPase activity increased. Plasma cortisol levels presented a "U-shaped" relationship with salinity. At 7 h, oxygen consumption was higher in the control group, while cortisol and gill Na+,K+- ATPase activity varied in parallel to salinity. Our results suggest that sudden salinity changes evoked an acute stress situation (cortisol increased up to 15x over the basal level) which was slightly attenuate after 7 h. Fish quickly adapted its respiration rate to the new environmental conditions and this rate returned progressively to its normal values after the shock. Regarding enzyme activity, fish increased (55 ppt) or decreased (5 ppt) the ATPase activity depending on the salinity, as described in other studies.This work was supported by Interreg Project 0251_ECOAQUA_5_E, financed by the EDRF (European Regional Development Fund). www.juntadeandalucia.es/agriculturaypesca/ifapa/ecoaqua. &nbsp;Juveniles de lenguado senegal&eacute;s fueron mantenidos en respir&oacute;metros y sometidos a un cambio brusco de salinidad. Resumidamente, peces de 40-50 g se mantuvieron a una salinidad de 37.5 ppt y, despu&eacute;s de una aclimataci&oacute;n de 4 horas, la salinidad se vari&oacute; a 5 &oacute; 55 ppt. Un grupo control no experiment&oacute; ninguna alteraci&oacute;n. El consumo de ox&iacute;geno fue registrado cada 14 min y los peces fueron muestreados (plasma y branquias) a diferentes tiempos (t=4.5 h y t=7 h para determinar la actividad Na+,K+- ATPasa branquial la concentraci&oacute;n de cortisol en plasma). A t=4.5 h, el consumo de ox&iacute;geno fue inversamente proporcional con la salinidad, mientras que la actividad Na+,K+- ATPasa branquial creci&oacute;. El cortisol plasm&aacute;tico present&oacute; una curva en forma de "U" en funci&oacute;n de la salinidad. A t=7 h, el consumo de ox&iacute;geno fue mayor en el grupo control, mientras que la Na+,K+- ATPasa branquial vari&oacute; en paralelo con la salinidad. Nuestros resultados sugieren que un cambio brusco de salinidad provoca una situaci&oacute;n de estr&eacute;s agudo (cortisol aumenta 15 veces su valor basal), que se aten&uacute;a ligeramente despu&eacute;s de 7 h. Los peces r&aacute;pidamente adaptan su tasa respiratoria a esta nueva condici&oacute;n ambiental y luego var&iacute;a progresivamente a su valor inicial. Respecto a la actividad enzim&aacute;tica, los peces aumentaron (55 ppt) o disminuyeron (5 ppt) la actividad ATPasa en funci&oacute;n de la salinidad, como se ha descrito en previos trabajos.Este trabajo fue apoyado por el proyecto Interreg 0251_ECOAQUA_5_E , financiado por el FEDER (Fondo Europeo de Desarrollo Regional). www.juntadeandalucia.es/agriculturaypesca/ifapa/ecoaqua.</p

Energy nonconservation and relativistic trajectories: Unimodular gravity and beyond

Energy conservation has the status of a fundamental physical principle. However, measurements in quantum mechanics do not comply with energy conservation. Therefore, it is expected that a more fundamental theory of gravity -- one that is less incompatible with quantum mechanics -- should admit energy nonconservations. This paper begins by identifying the conditions for a theory to have an energy-momentum tensor that is not conserved. Then, the trajectory equation for pointlike particles that lose energy is derived, showing that energy nonconservation produces a particular acceleration. As an example, the unimodular theory of gravity is studied. Interestingly, in spherical symmetry, given that there is a generalized Birkhoff theorem and that the energy-momentum tensor divergence is a closed form, the trajectories of test particles that lose energy can be found using well known methods. Finally, limits on the energy nonconservation parameters are set using Solar system observations.Comment: 13 pages. Accepted in Phys. Rev.

Evaluating the capacity of human gut microorganisms to colonize the zebrafish larvae (Danio rerio)

Indexación: Scopus.In this study we evaluated if zebrafish larvae can be colonized by human gut microorganisms. We tested two strategies: (1) through transplantation of a human fecal microbiota and (2) by successively transplanting aerotolerant anaerobic microorganisms, similar to the colonization in the human intestine during early life. We used conventionally raised zebrafish larvae harboring their own aerobic microbiota to improve the colonization of anaerobic microorganisms. The results showed with the fecal transplant, that some members of the human gut microbiota were transferred to larvae. Bacillus, Roseburia, Prevotella, Oscillospira, one unclassified genus of the family Ruminococcaceae and Enterobacteriaceae were detected in 3 days post fertilization (dpf) larvae; however only Bacillus persisted to 7 dpf. Successive inoculation of Lactobacillus, Bifidobacterium and Clostridioides did not improve their colonization, compared to individual inoculation of each bacterial species. Interestingly, the sporulating bacteria Bacillus clausii and Clostridioides difficile were the most persistent microorganisms. Their endospores persisted at least 5 days after inoculating 3 dpf larvae. However, when 5 dpf larvae were inoculated, the proportion of vegetative cells in larvae increased, revealing proliferation of the inoculated bacteria and better colonization of the host. In conclusion, these results suggest that it is feasible to colonize zebrafish larvae with some human bacteria, such as C. difficile and Bacillus and open an interesting area to study interactions between these microorganisms and the host. © 2018 Valenzuela, Caruffo, Herrera, Medina, Coronado, Feijóo, Muñoz, Garrido, Troncoso, Figueroa, Toro, Reyes-Jara, Magne and Navarrete.https://www.frontiersin.org/articles/10.3389/fmicb.2018.01032/ful

Dynamics of Charged Plane Symmetric Gravitational Collapse

In this paper, we study dynamics of the charged plane symmetric gravitational collapse. For this purpose, we discuss non-adiabatic flow of a viscous fluid and deduce the results for adiabatic case. The Einstein and Maxwell field equations are formulated for general plane symmetric spacetime in the interior. Junction conditions between the interior and exterior regions are derived. For the non-adiabatic case, the exterior is taken as plane symmetric charged Vaidya spacetime while for the adiabatic case, it is described by plane Reissner-Nordstr$\ddot{o}$m spacetime. Using Misner and Sharp formalism, we obtain dynamical equations to investigate the effects of different forces over the rate of collapse. In non-adiabatic case, a dynamical equation is joined with transport equation of heat flux. Finally, a relation between the Weyl tensor and energy density is found.Comment: 21 pages, accepted for publication Gen. Relativ. Gra