555 research outputs found
Mechanical properties of pulsed laser deposited nanocrystalline SiC films
The mechanical properties of nanocrystalline SiC thin films grown on (100) Si at a substrate temperature of 1000°C under a CH4 atmosphere using the pulsed laser deposition (PLD) technique were investigated. Nanoindentation results showed that films exhibited hardness values around 36GPa and Young modulus values around 250GPa. Scratch tests found that films were adherent to the substrate, with critical load values similar to those recorded for other hard coatings deposited on significantly softer Si substrates. Wear tests performed at a temperature of 900°C showed that films exhibited friction coefficients and wear rates very similar to those measured at room temperature, due to the presence of C-C bonds as evidenced by X-ray photoelectron spectroscopy investigations. These results recommend such coatings for demanding high temperature applications such as nuclear fuel encapsulation
M-Dwarf Fast Rotators and the Detection of Relatively Young Multiple M-Star Systems
We have searched the Kepler light curves of ~3900 M-star targets for evidence
of periodicities that indicate, by means of the effects of starspots, rapid
stellar rotation. Several analysis techniques, including Fourier transforms,
inspection of folded light curves, 'sonograms', and phase tracking of
individual modulation cycles, were applied in order to distinguish the
periodicities due to rapid rotation from those due to stellar pulsations,
eclipsing binaries, or transiting planets. We find 178 Kepler M-star targets
with rotation periods, P_rot, of < 2 days, and 110 with P_rot < 1 day. Some 30
of the 178 systems exhibit two or more independent short periods within the
same Kepler photometric aperture, while several have three or more short
periods. Adaptive optics imaging and modeling of the Kepler pixel response
function for a subset of our sample support the conclusion that the targets
with multiple periods are highly likely to be relatively young physical binary,
triple, and even quadruple M star systems. We explore in detail the one object
with four incommensurate periods all less than 1.2 days, and show that two of
the periods arise from one of a close pair of stars, while the other two arise
from the second star, which itself is probably a visual binary. If most of
these M-star systems with multiple periods turn out to be bound M stars, this
could prove a valuable way of discovering young hierarchical M-star systems;
the same approach may also be applicable to G and K stars. The ~5% occurrence
rate of rapid rotation among the ~3900 M star targets is consistent with spin
evolution models that include an initial contraction phase followed by magnetic
braking, wherein a typical M star can spend several hundred Myr before spinning
down to periods longer than 2 days.Comment: 17 pages, 12 figures, 2 tables; accepted for publication in The
Astrophysical Journa
The development of the Problematic Online Gaming Questionnaire
Background: Online gaming has become increasingly popular. However, this has led to concerns that these games might
induce serious problems and/or lead to dependence for a minority of players. Aim: The aim of this study was to uncover and
operationalize the components of problematic online gaming.
Methods: A total of 3415 gamers (90% males; mean age 21 years), were recruited through online gaming websites. A
combined method of exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) was applied. Latent profile
analysis was applied to identify persons at-risk.
Results: EFA revealed a six-factor structure in the background of problematic online gaming that was also confirmed by a
CFA. For the assessment of the identified six dimensions – preoccupation, overuse, immersion, social isolation, interpersonal
conflicts, and withdrawal – the 18-item Problematic Online Gaming Questionnaire (POGQ) proved to be exceedingly
suitable. Based on the latent profile analysis, 3.4% of the gamer population was considered to be at high risk, while another
15.2% was moderately problematic.
Conclusions: The POGQ seems to be an adequate measurement tool for the differentiated assessment of gaming related
problems on six subscales
The Development of the Problematic Online Gaming Questionnaire (POGQ)
BACKGROUND: Online gaming has become increasingly popular. However, this has led to concerns that these games might induce serious problems and/or lead to dependence for a minority of players. AIM: The aim of this study was to uncover and operationalize the components of problematic online gaming. METHODS: A total of 3415 gamers (90% males; mean age 21 years), were recruited through online gaming websites. A combined method of exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) was applied. Latent profile analysis was applied to identify persons at-risk. RESULTS: EFA revealed a six-factor structure in the background of problematic online gaming that was also confirmed by a CFA. For the assessment of the identified six dimensions--preoccupation, overuse, immersion, social isolation, interpersonal conflicts, and withdrawal--the 18-item Problematic Online Gaming Questionnaire (POGQ) proved to be exceedingly suitable. Based on the latent profile analysis, 3.4% of the gamer population was considered to be at high risk, while another 15.2% was moderately problematic. CONCLUSIONS: The POGQ seems to be an adequate measurement tool for the differentiated assessment of gaming related problems on six subscales
The chromospherically--active binary CF Tuc revisited
New high-resolution spectra, of the chromospherically active binary system CF
Tuc, taken at the Mt. John University Observatory in 2007, were analyzed using
two methods: cross-correlation and Fourier--based disentangling. As a result,
new radial velocity curves of both components were obtained. The resulting
orbital elements of CF Tuc are: = AU,
= AU, =
, and = . The cooler
component of the system shows H and CaII H & K emissions. Our
spectroscopic data and recent light curves were solved simultaneously
using the Wilson-Devinney code. A dark spot on the surface of the cooler
component was assumed to explain large asymmetries observed in the light
curves. The following absolute parameters of the components were determined:
= , = ,
= , = ,
= and = . The
orbital period of the system was studied using the O-C analysis. The O-C
diagram could be interpreted in terms of either two abrupt changes or a
quasi-sinusoidal form superimposed on a downward parabola. These variations are
discussed by reference to the combined effect of mass transfer and mass loss,
the Applegate mechanism and also a light-time effect due to the existence of a
massive third body (possibly a black hole) in the system. The distance to CF
Tuc was calculated to be pc from the dynamic parallax, neglecting
interstellar absorption, in agreement with the Hipparcos value.Comment: 33 pages, 10 figures, accepted for publication by MNRA
Combined Docking and Quantum Chemical Study on CYP-mediated Metabolism of Estrogens in Man
Long-term exposure
to estrogens seriously increases the incidence
of various diseases including breast cancer. Experimental studies
indicate that cytochrome P450 (CYP) enzymes catalyze the bioactivation
of estrogens to catechols, which can exert their harmful effects via
various routes. It has been shown that the 4-hydroxylation pathway
of estrogens is the most malign, while 2-hydroxylation is considered
a benign pathway. It is also known experimentally that with increasing
unsaturation of ring B of estrogens the prevalence of the 4-hydroxylation
pathway significantly increases. In this study, we used a combination
of structural analysis, docking, and quantum chemical calculations
at the B3LYP/6-311+G* level to investigate the factors that influence
the regioselectivity of estrogen metabolism in man. We studied the
structure of human estrogen metabolizing enzymes (CYP1A1, CYP1A2,
CYP1B1, and CYP3A4) in complex with estrone using docking and investigated
the susceptibility of estrone, equilin, and equilenin (which only
differ in the unsaturation of ring B) to undergo 2- and 4-hydroxylation
using several models of CYP enzymes (Compound I, methoxy, and phenoxy
radical). We found that even the simplest models could account for
the experimental difference between the 2- and 4- hydroxylation pathways
and thus might be used for fast screening purposes. We also show that
reactivity indices, specifically in this case the radical and nucleophilic
condensed Fukui functions, also correctly predict the likeliness of
estrogen derivatives to undergo 2- or 4-hydroxylation
Polar branches of stellar activity waves: dynamo models and observations
[Abridged abstract:] Stellar activity data provide evidence of activity wave
branches propagating polewards rather than equatorwards (the solar case).
Stellar dynamo theory allows polewards propagating dynamo waves for certain
governing parameters. We try to unite observations and theory, restricting our
investigation to the simplest mean-field dynamo models. We suggest a crude
preliminary systematization of the reported cases of polar activity branches.
Then we present results of dynamo model simulations which contain magnetic
structures with polar dynamo waves, and identify the models which look most
promising for explaining the latitudinal distribution of spots in dwarf stars.
Those models require specific features of stellar rotation laws, and so
observations of polar activity branches may constrain internal stellar
rotation. Specifically, we find it unlikely that a pronounced poleward branch
can be associated with a solar-like internal rotation profile, while it can be
more readily reproduced in the case of a cylindrical rotation law appropriate
for fast rotators. We stress the case of the subgiant component of the active
close binary HR 1099 which, being best investigated, presents the most severe
problems for a dynamo interpretation. Our best model requires dynamo action in
two layers separated in radius. Observations of polar activity branches provide
valuable information for understanding stellar activity mechanisms and internal
rotation, and thus deserve intensive observational and theoretical
investigation. Current stellar dynamo theory seems sufficiently robust to
accommodate the phenomenology.Comment: 13 pages, 10 figures, 4 tables, accepted by Astronomy and
Astrophysic
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