181 research outputs found
Internet public relations at educational institutions
This paper is of a theoretical and empirical nature. The theoretical part presents the possibilities of the communication methods in public relations that use the Internet where both non-individualized and individualized communication is applied. The empirical part presents an analysis of the research of the websites of primary, lower-secondary and upper-secondary schools in 19 citie
UVSat: a concept of an ultraviolet/optical photometric satellite
Time-series photometry from space in the ultraviolet can be presently done
with only a few platforms, none of which is able to provide wide-field
long-term high-cadence photometry. We present a concept of UVSat, a twin space
telescope which will be capable to perform this kind of photometry, filling an
observational niche. The satellite will host two telescopes, one for
observations in the ultraviolet, the other for observations in the optical
band. We also briefly show what science can be done with UVSat.Comment: 6 pages, 2 figures, accepted for publication in the Proceedings of
the PAS (Proc. of the 2nd BRITE Science conference, Innsbruck
Seminar Users in the Arabic Twitter Sphere
We introduce the notion of "seminar users", who are social media users
engaged in propaganda in support of a political entity. We develop a framework
that can identify such users with 84.4% precision and 76.1% recall. While our
dataset is from the Arab region, omitting language-specific features has only a
minor impact on classification performance, and thus, our approach could work
for detecting seminar users in other parts of the world and in other languages.
We further explored a controversial political topic to observe the prevalence
and potential potency of such users. In our case study, we found that 25% of
the users engaged in the topic are in fact seminar users and their tweets make
nearly a third of the on-topic tweets. Moreover, they are often successful in
affecting mainstream discourse with coordinated hashtag campaigns.Comment: to appear in SocInfo 201
A cyclic bipolar wind in the interacting binary V393 Scorpii
V393 Scorpii is a Double Periodic Variable characterized by a relatively
stable non-orbital photometric cycle of 253 days. Mennickent et al. argue for
the presence of a massive optically thick disc around the more massive B-type
component and describe the evolutionary stage of the system. In this paper we
analyze the behavior of the main spectroscopic optical lines during the long
non-orbital photometric cycle. We study the radial velocity of the donor
determining their orbital elements and find a small but significant orbital
eccentricity (e = 0.04). The donor spectral features are modeled and removed
from the spectrum at every observing epoch using the light-curve model given by
Mennickent et al. We find that the line emission is larger during eclipses and
mostly comes from a bipolar wind. We find that the long cycle is explained in
terms of a modulation of the wind strength; the wind has a larger line and
continuum emissivity on the high state. We report the discovery of highly
variable chromospheric emission in the donor, as revealed by Doppler maps of
the emission lines MgII 4481 and CI 6588. We discuss notable and some novel
spectroscopic features like discrete absorption components, especially visible
at blue-depressed OI 7773 absorption wings during the second half-cycle, Balmer
double emission with V/R-curves showing "Z-type" and "S-type" excursions around
secondary and main eclipse, respectively, and H_beta emission wings extending
up to +- 2000 km/s. We discuss possible causes for these phenomena and for
their modulations with the long cycle.Comment: 19 pages, 22 figures, accepted for publication in MNRA
On a Theoretical Interpretation of the Period Gap in Binary Millisecond Pulsars
We reexamine evolutionary channels for the formation of binary millisecond
pulsars in order to understand their observed orbital period distribution. The
available paths provide a natural division into systems characterized by long
orbital periods (> 60 d) and short orbital periods (< 30 d). Systems with
initial periods 1 - 2 d ultimately produce low mass He white dwarfs with short
orbital periods ( few days), early massive
Case B evolution produces CO white dwarfs with orbital periods < 20 d. Common
envelope evolution result in short period systems (P < 1 d) from unstable low
mass Case B evolution producing He white dwarfs, and from unstable Case C
evolution leading to CO white dwarfs. On the other hand, the long orbital
period group arises from stable low mass Case B evolution with initial periods
> few days producing low mass He white dwarfs and periods > 30 d, and from
stable Case C evolution producing CO white dwarfs. The lack of observed systems
between 23 and 56 days probably reflects the fact that for comparable initial
orbital periods (< few days) low mass Case B and early massive Case B evolution
lead to very discrepant final periods. We show in particular that the lower
limit (~ 23 d) cannot result from common-envelope evolution.Comment: 20 pages, one encapsulated figure, LaTeX, accepted by Ap
Orbital Evolution of Algol Binaries with a Circumbinary Disk
It is generally thought that conservative mass transfer in Algol binaries
causes their orbits to be wider, in which the less massive star overflows its
Roche-lobe. The observed decrease in the orbital periods of some Algol binaries
suggests orbital angular momentum loss during the binary evolution, and the
magnetic braking mechanism is often invoked to explain the observed orbital
shrinkage. Here we suggest an alternative explanation, assuming that a small
fraction of the transferred mass forms a circumbinary disk, which extracts
orbital angular momentum from the binary through tidal torques. We also perform
numerical calculations of the evolution of Algol binaries with typical initial
masses and orbital periods. The results indicate that, for reasonable input
parameters, the circumbinary disk can significantly influence the orbital
evolution, and cause the orbit to shrink on a sufficiently long timescale.
Rapid mass transfer in Algol binaries with low mass ratios can also be
accounted for in this scenario.Comment: 9 pages, 5 figures, accepted for publication in Ap
Hubble Space Telescope Spectroscopy of V471 Tauri: Oversized K Star, Paradoxical White Dwarf
We have used the GHRS onboard the HST to obtain Lyman-alpha spectra of the
hot white-dwarf (WD) component of the short-period eclipsing DA+dK2
pre-cataclysmic binary V471 Tauri, a member of the Hyades star cluster. Radial
velocities of the WD, combined with ground-based measurements of the dK
velocities, eclipse timings, and a determination of the dK star's rotational
velocity, yield dynamical masses for the components of M(WD)=0.84 and
M(dK)=0.93 Msun. Model-atmosphere fitting of the Ly-alpha profile provides the
effective temperature (34,500 K) and surface gravity (log g=8.3) of the WD. The
radius of the dK component is 18% larger than that of a normal Hyades dwarf of
the same mass. This expansion is attributed to the extensive coverage of the
surface by starspots, causing the star to expand in response. The WD radius,
determined from a radiometric analysis and from eclipse ingress timings, is
0.0107 Rsun. The position of the star in the M-R plane is in full accord with
theory for a degenerate CO WD. The high temperature and mass of the WD present
an evolutionary paradox: the WD is the most massive known in the Hyades, but
also the hottest and youngest. We suggest that the explanation is that the WD
is indeed very young, and is descended from a triple consisting of a blue
straggler and a more-distant dK companion. We estimate that the common-envelope
efficiency parameter, alpha_CE, was of order 0.3-1.0, in good agreement with
recent hydrodynamical simulations.Comment: Astrophysical Journal, in press. 34 text pages, 8 figure
Evolutionary and pulsational properties of low-mass white dwarf stars with oxygen cores resulting from close binary evolution
The present work is designed to explore the evolutionary and pulsational
properties of low-mass white dwarfs with carbon/oxygen cores. In particular, we
follow the evolution of a 0.33 Msun white dwarf remnant in a self-consistent
way with the predictions of nuclear burning, element diffusion and the history
of the white dwarf progenitor. Attention is focused on the occurrence of
hydrogen shell flashes induced by diffusion processes during cooling phases.
The evolutionary stages prior to the white dwarf formation are also fully
accounted for by computing the conservative binary evolution of an initially
2.5-Msun Pop. I star with a 1.25 Msun companion, and period P_i= 3 days.
Evolution is followed down to the domain of the ZZ Ceti stars on the white
dwarf cooling branch. We find that chemical diffusion induces the occurrence of
an additional hydrogen thermonuclear flash which leads to stellar models with
thin hydrogen envelopes. As a result, a fast cooling is encountered at advanced
stages of evolution. In addition, we explore the adiabatic pulsational
properties of the resulting white dwarf models. As compared with their
helium-core counterparts, low-mass oxygen-core white dwarfs are characterized
by a pulsational spectrum much more featured, an aspect which could eventually
be used for distinguishing both types of stars if low-mass white dwarfs were in
fact found to pulsate as ZZ Ceti-type variables. Finally, we perform a
non-adiabatic pulsational analysis on the resulting carbon/oxygen low-mass
white dwarf models.Comment: 13 Pages, including 16 Postscript figures. Accepted for publication
in MNRA
Adherence as a Predictor of Sexual Behaviors in People Living with HIV/AIDS during the First Year of Antiretroviral Therapy in Rural Cameroon: Data from Stratall ANRS 12110/ESTHER Trial
Objective: This study aims to investigate the time pattern of inconsistence condom use (ICU) during the first year of antiretroviral therapy (ART) and its relationship with treatment adherence in naive HIV-infected adult patients. ' Methods: Data collection was nested within a longitudinal trial on HIV treatment. ICU was defined as reporting to have "never", "sometimes" or "nearly always" used condoms with one's main or casual partner(s) - either HIV-negative or of unknown HIV status in the three previous months. Adherence was defined as taking 100% of their ART prescribed doses in the 4 days before the visit and "not having interrupted treatment", even once, for more than two consecutive days during the 4 previous weeks. Mixed logistic regression was used to study the relationship between adherence and ICU. Results: Among the 459 patients enrolled, 212 (46%) during 334 visits reported to have had sexual intercourse at least once with their partner(s) - either HIV-negative or of unknown HIV status-during the first 12 months of ART. The proportion of ICU was 76%, 50% and 59% at month 0 (M0), month 6 (M6) and month 12 (M12), while 60% and 66% of patients were ART-adherent at M6 and M12, respectively. After adjustment for the frequency of sexual activity, type of sexual partner(s), perceived social class and desire for a child, patients adherent to ART were less likely to report ICU when compared with baseline (AOR [95% CI]: 0.38 [0.19-0.76]; P = 0.006). Conclusions: Adherence to ART is associated with a lower risk of ICU but this result needs to be interpreted carefully. As adherence behaviors are not only determined by problems with the healthcare systems but also by social barriers encountered by patients in their daily life, counseling should not only be ART adherence-centered but also patient-centered, including sexual risk minimization and psychosocial support
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