829 research outputs found
Assessing Intended Employee Behavior in Exit Interviews: Attitudinal and Status Effects
In order to assess the effects that attitudes toward particular aspects of work life and status (management vs . non-management) might have on the intended willingness to discuss issues during exit interviews, managerial and non-managerial workers were asked to evaluate their attitudes toward particular aspects of work life, as well as their willingness to discuss these issues during an exit interview. Results showed that status alone did not affect willingness to discuss issues, but that attitudes and status had an interactive effect on willingness
Movement ecology of the white seabream Diplodus sargus across its life cycle: a review
The white seabream Diplodus sargus (L., 1758) (Osteichthyes, Sparidae) is a littoral species living mainly in rocky habitats and distributed in the eastern Atlantic and the Mediterranean. This species is targeted by artisanal and recreational fisheries and presents a high commercial importance. Although classified by IUCN as a "least concern" species, it has been the object of marine ranching and restocking initiatives to counteract locally intense exploitation. Here, we review the current knowledge on the movement ecology of white seabream given the relevance of animal movement in ecological and behavioral studies and their potential application in management and conservation. The literature on this topic was analyzed in order to summarize the results of past research and to identify the gaps that still exist on the matter. We reviewed a total of 27 papers focusing on the movement ecology of white seabream, where acoustic telemetry (n = 12), underwater visual observation and traditional tagging (n = 6), genetic analysis (n = 6), and otolith microchemistry (n = 3) were used. While the first three methods were applied to juvenile and adult fish, the last one was also used with larvae, which have been the object of experimental trials to ascertain their swimming abilities. The largest amount of information on activity rhythms (diurnal with a few exceptions), movement patterns (short distances), homing (ability to come back to the capture site), site fidelity (high), and home range (< 200 ha on average and highly related with seabed morphology) were obtained through acoustic telemetry, whose main limitation is the minimum body size required for its application. The environmental variables found to affect movement patterns in this species are water temperature (which triggers spawning-based vertical movements), local sea conditions (which affect short-scale movements in juveniles), and the main seabed features (orientation and habitat type). The main gaps identified, which need more extensive research and some technological improvements, include the study of the effects of environmental variables on fish movements and further investigations on the movement patterns of juveniles.info:eu-repo/semantics/publishedVersio
Interpretation of flat energy spectra upstream of fast interplanetary shocks
Interplanetary shocks are large-scale heliospheric structures often caused by
eruptive phenomena at the Sun, and represent one of the main sources of
energetic particles. Several interplanetary shock crossings by spacecraft at
AU have revealed enhanced energetic-ion fluxes that extend far upstream of
the shock. Surprisingly, in some shock events, ion fluxes with energies between
keV and about MeV acquire similar values (which we refer to as
``overlapped'' fluxes), corresponding to flat energy spectra in that range. In
contrast, closer to the shock, the fluxes are observed to depend on energy. In
this work, we analyze three interplanetary shock-related energetic particle
events observed by the Advanced Composition Explorer spacecraft where flat ion
energy spectra were observed upstream of the shock. We interpret these
observations via a velocity filter mechanism for particles in a given energy
range. This reveals that low energy particles tend to be confined to the shock
front and cannot easily propagate upstream, while high energy particles can.
The velocity filter mechanism has been corroborated from observations of
particle flux anisotropy by the Solid-State Telescope of Wind/3DP
Particle acceleration in cooling flow clusters of galaxies: the case of Abell 2626
It has recently been proposed a theoretical model which accounts for the
origin of radio mini-halos observed in some cooling flow clusters as related to
electron re-acceleration by MHD turbulence (Gitti, Brunetti & Setti 2002). The
MHD turbulence is assumed to be frozen into the flow of the thermal ICM and
thus amplified in the cooling flow region. Here we present the application of
this model to a new mini-halo candidate, the cluster A2626, and compare the
results with those obtained for the mini-halo in the Perseus cluster. We
present VLA data at 330 MHz and 1.5 GHz of the diffuse radio emission observed
in A2626, and we show that its main properties can be explained by the model.
We find that the power necessary for the re-acceleration of the relic electron
population is only a factor ~ 0.7% of the maximum power that can be extracted
by the cooling flow (as estimated on the basis of the standard model). We also
discuss the observational properties of known mini-halos in connection with
those of host clusters, showing that the radio power of mini--halos increases
with the maximum power of cooling flows. This trend is expected in the
framework of the model. Possible effects of new Chandra and XMM-Newton
estimates of on this trend are considered: we conclude that even if
earlier derived cooling rates were overestimated, cooling flow powers are still
well above the radio powers emitted by mini-halos.Comment: 12 pages, 11 figures, accepted for publication in Astronomy &
Astrophysic
Iron-Dependent Gene Expression in Actinomyces Oris
Actinomyces oris is a Gram-positive bacterium that has been associated with healthy and diseased sites in the human oral cavity. Most pathogenic bacteria require iron to survive, and in order to acquire iron in the relatively iron-scarce oral cavity A. oris has been shown to produce iron-binding molecules known as siderophores. The genes encoding these siderophores and transporters are thought to be regulated by the amount of iron in the growth medium and by the metal-dependent repressor, AmdR, which we showed previously binds to the promoter of proposed iron-regulated genes
A Closer Look at Exoplanet Occurrence Rates: Considering the Multiplicity of Stars without Detected Planets
One core goal of the Kepler mission was to determine the frequency of Earth-like planets that orbit Sun-like stars. Accurately estimating this planet occurrence rate requires both a well-vetted list of planets and a clear understanding of the stars searched for planets. Previous ground-based follow-up observations have, through a variety of methods, sought to improve our knowledge of stars that are known to host planets. Kepler targets without detected planets, however, have not been subjected to the same intensity of follow-up observations. In this paper, we constrain better the stellar multiplicity for stars around which Kepler could have theoretically detected a transiting Earth-sized planet in the habitable zone. We subsequently aim to improve estimates of the exoplanet search completeness—the fraction of exoplanets that were detected by Kepler—with our analysis. By obtaining adaptive optics observations of 71 Kepler target stars from the Shane 3 m telescope at Lick Observatory, we detected 14 candidate stellar companions within 4'' of 13 target stars. Of these 14 candidate stellar companions, we determine through multiple independent methods that 3 are likely to be bound to their corresponding target star. We then assess the impact of our observations on exoplanet occurrence rate calculations, finding an increase in occurrence of 6% (0.9σ) for various estimates of the frequency of Earth-like planets and an increase of 26% (4.5σ) for super-Earths and sub-Neptunes. These occurrence increases are not entirely commensurate with theoretical predictions, though this discrepancy may be due to differences in the treatment of stellar binarity
TOI-561 b: A Low Density Ultra-Short Period "Rocky" Planet around a Metal-Poor Star
TOI-561 is a galactic thick disk star hosting an ultra-short period (0.45 day
orbit) planet with a radius of 1.37 R, making it one of the most
metal-poor ([Fe/H] = -0.41) and oldest (10 Gyr) sites where an
Earth-sized planet has been found. We present new simultaneous radial velocity
measurements (RVs) from Gemini-N/MAROON-X and Keck/HIRES, which we combined
with literature RVs to derive a mass of M=2.24 0.20 M.
We also used two new Sectors of TESS photometry to improve the radius
determination, finding R=, and confirming that
TOI-561 b is one of the lowest-density super-Earths measured to date (=
4.8 0.5 g/cm). This density is consistent with an iron-poor rocky
composition reflective of the host star's iron and rock-building element
abundances; however, it is also consistent with a low-density planet with a
volatile envelope. The equilibrium temperature of the planet (2300 K)
suggests that this envelope would likely be composed of high mean molecular
weight species, such as water vapor, carbon dioxide, or silicate vapor, and is
likely not primordial. We also demonstrate that the composition determination
is sensitive to the choice of stellar parameters, and that further measurements
are needed to determine if TOI-561 b is a bare rocky planet, a rocky planet
with an optically thin atmosphere, or a rare example of a non-primordial
envelope on a planet with a radius smaller than 1.5 R.Comment: Accepted to AJ on 11/28/202
Overfitting Affects the Reliability of Radial Velocity Mass Estimates of the V1298 Tau Planets
Mass, radius, and age measurements of young (<100 Myr) planets have the power
to shape our understanding of planet formation. However, young stars tend to be
extremely variable in both photometry and radial velocity, which makes
constraining these properties challenging. The V1298 Tau system of four ~0.5
Rjup planets transiting a pre-main sequence star presents an important, if
stress-inducing, opportunity to directly observe and measure the properties of
infant planets. Su\'arez-Mascare\~no et al. (2021) published
radial-velocity-derived masses for two of the V1298 Tau planets using a
state-of-the-art Gaussian Process regression framework. The planetary densities
computed from these masses were surprisingly high, implying extremely rapid
contraction after formation in tension with most existing planet formation
theories. In an effort to further constrain the masses of the V1298 Tau
planets, we obtained 36 RVs using Keck/HIRES, and analyzed them in concert with
published RVs and photometry. Through performing a suite of cross validation
tests, we found evidence that the preferred model of SM21 suffers from
overfitting, defined as the inability to predict unseen data, rendering the
masses unreliable. We detail several potential causes of this overfitting, many
of which may be important for other RV analyses of other active stars, and
recommend that additional time and resources be allocated to understanding and
mitigating activity in active young stars such as V1298 Tau.Comment: 26 pages, 12 figures; published in A
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