2,858 research outputs found
A systematic review of school-based alcohol and other drug prevention programs
Background: Alcohol use in adolescents constitutes a major public health concern. Europe is the heaviest drinking
region of the world. Several school-based alcohol prevention programs have been developed but it is not clear whether
they are really effective. The present study was aimed at identifying the typology with the best evidence of effectiveness
in European studies. Methods: A systematic search of meta-analyses and/or randomized controlled trials (RCTs) on interventions
school-based prevention programs aimed at preventing alcohol consumption or changing the attitudes to consume
alcohol. Results: A meta-analysis published in 2011 and 12 RCTs more recently published were identified. The
meta-analysis evaluated 53 RCTs but only 11.3% of them were conducted in Europe. Globally, 23 RCTs (43.4%) showed
some evidence of effectiveness, and 30 RCTs (56.6%) did not find significant difference between the groups. According
to the conclusions of the meta-analysis, the Unplugged program should be considered as a practice option in Europe.
Among the other 12 RCTs, 42% were conducted in Europe. Globally, 7 studies (58.3%) achieved positive results, and 5
studies (41.7%) did not find significant differences or produced a mixed pattern of results. Three of the 5 European trials
(60%) used the Unplugged program with positive results. Conclusion: Even if further studies should be conducted to confirm
these results, Unplugged appears to be the prevention project with the best evidence of effectiveness in European
studies
Analysis of a load application point in spline coupling teeth
The objective of this paper is to investigate the position of the resultant force in involute spline coupling teeth due to the contact pressure distribution for both ideal and misaligned conditions.
In general, spline coupling teeth are in contact all along the involute profile and the load is far from uniform along the contact line.
Theoretical models available in publications consider the resultant contact force as it is applied at the pitch diameter, and this study aims to evaluate the error introduced within the confines of a common approximation environment. This analysis is carried out through using finite element method (FEM) models, considering spline couplings in both ideal and misaligned conditions.
Results show that the differences between the load application diameter and pitch diameter are not very obvious in both ideal and misaligned conditions; however, this approximation becomes more important for the calculation of the tooth stiffness
Affine actions on non-archimedean trees
We initiate the study of affine actions of groups on -trees for a
general ordered abelian group ; these are actions by dilations rather
than isometries. This gives a common generalisation of isometric action on a
-tree, and affine action on an -tree as studied by I. Liousse. The
duality between based length functions and actions on -trees is
generalised to this setting. We are led to consider a new class of groups:
those that admit a free affine action on a -tree for some .
Examples of such groups are presented, including soluble Baumslag-Solitar
groups and the discrete Heisenberg group.Comment: 27 pages. Section 1.4 expanded, typos corrected from previous versio
Spectral properties of the narrow-line region in Seyfert galaxies selected from the SDSS-DR7
Although the properties of the narrow-line region (NLR) of active galactic
nuclei(AGN) have been deeply studied by many authors in the past three decades,
many questions are still open. The main goal of this work is to explore the NLR
of Seyfert galaxies by collecting a large statistical spectroscopic sample of
Seyfert 2 and Intermediate-type Seyfert galaxies having a high signal-to-noise
ratio in order to take advantage of a high number of emission-lines to be
accurately measured. 2153 Seyfert 2 and 521 Intermediate-type Seyfert spectra
were selected from Sloan Digital Sky Survey - Data Release 7 (SDSS-DR7) with a
diagnostic diagram based on the oxygen emission-line ratios. All the
emission-lines, broad components included, were measured by means of a
self-developed code, after the subtraction of the stellar component. Physical
parameters, such as internal reddening, ionization parameter, temperature,
density, gas and stellar velocity dispersion were determined for each object.
Furthermore, we estimated mass and radius of the NLR, kinetic energy of the
ionized gas, and black-hole accretion rate. From the emission-line analysis and
the estimated physical properties, it appears that the NLR is similar in
Seyfert 2 and Intermediate-Seyfert galaxies. The only differences, lower
extinction, gas kinematics in general not dominated by the host galaxy
gravitational potential and higher percentage of [O III]5007 blue asymmetries
in Intermediate-Seyfert can be ascribed to an effect of inclination of our line
of sight with respect to the torus axis.Comment: Accepted for publication in MNRA
Identification of contact regimes in mechanical components for the evaluation of fretting damage
In this work the regimes of contact in misaligned crowned splined couplings have been analyzed. Experimental tests have been performed in order to identify if fretting damage on the components appears as fretting wear or fretting fatigue. A significant difference was identified on the surface of specimen by analyzing two different tests; the first test emphasized a fatigue damage and in the second test a wear phenomena has been achieved. Also a good correlation has been obtained by analyzing the fretting map obtained by using the Mindlin's theory and experimental result
Fretting damage parameters in splined couplings
This work focuses on the analysis of the debris found in the lubrication oil produced by the wear abrasion during wear tests conducted on crowned splined couplings. During each test the presence and the dimensions of the debris in the oil have been monitored. Tests have been performed by means of a dedicated splined couplings test rig and they have been performed by imposing an angular misalignment on the axes of the components. Results shows that when these components work in misaligned conditions, the relative motion between engaging teeth brings to the rise of a wear phenomenon called fretting wea
A spectroscopic analysis of a sample of narrow-line Seyfert 1 galaxies selected from the Sloan Digital Sky Survey
We revisited the spectroscopic characteristics of narrow-line Seyfert 1
galaxies (NLS1s) by analysing a homogeneous sample of 296 NLS1s at redshift
between 0.028 and 0.345, extracted from the Sloan Digital Sky Survey (SDSS-DR7)
public archive. We confirm that NLS1s are mostly characterized by Balmer lines
with Lorentzian profiles, lower black hole masses and higher Eddington ratios
than classic broad-line Seyfert 1 (BLS1s), but they also appear to be active
galactic nuclei (AGNs) contiguous with BLS1s and sharing with them common
properties. Strong Fe II emission does not seem to be a distinctive property of
NLS1s, as low values of Fe II/H are equally observed in these AGNs. Our
data indicate that Fe II and Ca II kinematics are consistent with the one of
H. On the contrary, O I 8446 seems to be systematically
narrower and it is likely emitted by gas of the broad-line region more distant
from the ionizing source and showing different physical properties. Finally,
almost all NLS1s of our sample show radial motions of the narrow-line region
highly-ionised gas. The mechanism responsible for this effect is not yet clear,
but there are hints that very fast outflows require high continuum luminosities
(> erg/s) or high Eddington ratios (log(L/L)
> -0.1).Comment: 27 pages, 31 figures, 4 tables, accepted for publication in MNRA
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