2,514 research outputs found
Dental Treatment under General Anesthesia in Healthy and Medically Compromised/Developmentally Disabled Children: A Comparative Study
Aim: To compare the type, number of procedures and working time of dental treatment provided under dental general anesthesia (DGA) in healthy and medically compromised/developmentally disabled children (MCDD children). Design: This cross-sectional prospective study involved 80 children divided into two groups of 40 children each. Group 1 consisted of healthy and Group 2 consisted of MCDD children. Results: Healthy children needed more working time than MCDD children, the means being 161±7.9 and 84±5.7 minutes, respectively (P= 0.0001). Operative dentistry and endodontic treatments showed a significant statistical difference (P= 0.0001). The means of procedures were 17±5.0 for healthy children and 11±4.8 for MCDD children (P= 0.0001). Conclusions: Healthy children needed more extensive dental treatment than MCDD children under DGA. The information from this sample of Mexican children could be used as reference for determining trends both within a facility as well as in comparing facilities in cross-population studies
Merging of Elliptical Galaxies as Possible Origin of the Intergalactic Stellar Population
We present N-body simulations of elliptical galaxy encounters into dry
mergers to study the resulting unbound intergalactic stellar population, in
particular that of the post-Main Sequence stars. The systems studied are pairs
of spherical galaxies without dark halos. The stellar content of the model
galaxies is distributed into mass-bins representing low- and intermediate-mass
stars (0.85 -- 8 solar masses) according to Salpeter's initial mass function.
Our models follow the dynamical evolution of galaxy encounters colliding
head-on from initial low-energy parabolic or high-energy mildly-hyperbolic
orbits, and for a choice of initial-mass ratios. The merging models with
initial parabolic orbits have M2/M1 =1 and 10, and they leave behind
respectively 5.5 % and 10 % of the total initial mass as unbound stellar mass.
The merging model with initial hyperbolic orbit has M2/M1 =1, and leaves behind
21 % of its initial stellar mass as unbound mass, showing that the efficiency
in producing intergalactic stars through a high-energy hyperbolic encounter is
about four times than through a parabolic encounter of the same initial mass
ratio. By assuming that all progenitor galaxies as well as the merger remnants
are homologous systems we obtained that the intergalactic starlight is 17 % and
28 % of the total starlight respectively for the parabolic and hyperbolic
encounters with M2/M1 =1. In all models, different mass stars have the same
probability of becoming unbound and feeding the intergalactic stellar
population.Comment: The Astrophysical Journal, in pres
Power System Oscillations with Different Prevalence of Grid-Following and Grid-Forming Converters
The oscillatory behaviour of the power system is an aspect that is significantly affected by the increasing integration of converter-based generation sources. Several works address the impact of non-synchronous generation on the operation of the system from different points of view, but only a few studies focus on power-frequency oscillations with a prevalence of generation sources interfaced through power electronics. A lack of research can be found in particular in the comparative analysis of the two main control strategies for power converters, namely grid-following and grid-forming. The article aims to contribute to this direction, starting from a theoretical analysis of the two control structures and then examining the case study of an existing transmission system. The research provides a specific insight into the fundamental aspects related to synchronisation mechanism and inertial capabilities of both grid-following with synthetic inertia and grid-forming controls. The difference in the relationship between synchronisation unit and inertial capability is recognised as the fundamental aspect determining the different impacts on the oscillatory characteristics of the system. The observation derived in the theoretical analysis is then applied to an actual power system with a high predominance of converter-based generation, considering the Colombian interconnected national system as a case study
Evolution along the sequence of S0 Hubble types induced by dry minor mergers. II - Bulge-disk coupling in the photometric relations through merger-induced internal secular evolution
Galaxy mergers are considered as questionable mechanisms for the evolution of
lenticular galaxies (S0's), on the basis that even minor ones induce structural
changes that are difficult to reconcile with the strong bulge-disk coupling
observed in the photometric scaling relations of S0's. We check if the
evolution induced onto S0's by dry intermediate and minor mergers can reproduce
their photometric scaling relations, analysing the bulge-disk decompositions of
the merger simulations presented in Eliche-Moral et al. (2012). The mergers
induce an evolution in the photometric planes compatible with the data of S0's,
even in those ones indicating a strong bulge-disk coupling. The mergers drive
the formation of the observed photometric relation in some cases, whereas they
induce a slight dispersion compatible with data in others. Therefore, this
evolutionary mechanism tends to preserve these scaling relations. In those
photometric planes where the morphological types segregate, the mergers always
induce evolution towards the region populated by S0's. The structural coupling
of the bulge and the disk is preserved or reinforced because the mergers
trigger internal secular processes in the primary disk that induce significant
bulge growth, even although these models do not induce bars. Intermediate and
minor mergers can thus be considered as plausible mechanisms for the evolution
of S0's attending to their photometric scaling relations, as they can preserve
and even strengthen any pre-existing structural bulge-disk coupling, triggering
significant internal secular evolution (even in the absence of bars or
dissipational effects). This means that it may be difficult to isolate the
effects of pure internal secular evolution from those of the merger-driven one
in present-day early-type disks (abridged).Comment: Accepted for publication in Astronomy & Astrophysics, 13 pages, 8
figures. Definitive version after proofs. Added references and corrected
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