118 research outputs found
Chemo-Archaeological Downsizing in a Hierarchical Universe: Impact of a Top Heavy IGIMF
We make use of a semi-analytical model of galaxy formation to investigate the
origin of the observed correlation between [a/Fe] abundance ratios and stellar
mass in elliptical galaxies. We implement a new galaxy-wide stellar initial
mass function (Top Heavy Integrated Galaxy Initial Mass Function, TH-IGIMF) in
the semi-analytic model SAG and evaluate its impact on the chemical evolution
of galaxies. The SFR-dependence of the slope of the TH-IGIMF is found to be key
to reproducing the correct [a/Fe]-stellar mass relation. Massive galaxies reach
higher [a/Fe] abundance ratios because they are characterized by more top-heavy
IMFs as a result of their higher SFR. As a consequence of our analysis, the
value of the minimum embedded star cluster mass and of the slope of the
embedded cluster mass function, which are free parameters involved in the
TH-IGIMF theory, are found to be as low as 5 solar masses and 2, respectively.
A mild downsizing trend is present for galaxies generated assuming either a
universal IMF or a variable TH-IGIMF. We find that, regardless of galaxy mass,
older galaxies (with formation redshifts > 2) are formed in shorter time-scales
(< 2 Gyr), thus achieving larger [a/Fe] values. Hence, the time-scale of galaxy
formation alone cannot explain the slope of the [a/Fe]-galaxy mass relation,
but is responsible for the big dispersion of [a/Fe] abundance ratios at fixed
stellar mass.We further test the hyphothesis of a TH-IGIMF in elliptical
galaxies by looking into mass-to-light ratios, and luminosity functions. Models
with a TH-IGIMF are also favoured by these constraints. In particular,
mass-to-light ratios agree with observed values for massive galaxies while
being overpredicted for less massive ones; this overprediction is present
regardless of the IMF considered.Comment: 24 pages, 15 figures, 2 tables. (Comments most welcome). Summited to
MNRA
The use of animals at Roman roadside settlements in Britain : contextualizing some new results from Ware, Hertfordshire
Recent analysis of a large faunal assemblage from a Roman roadside settlement at Ware, Hertfordshire has indicated potentially strong links between the nature of animal exploitation on site and its location on Ermine Street. Animal husbandry was focused on the production of cattle and sheep, both of which had experienced stock ‘improvement’ by the late Roman period. Relatively high proportions of horse, and the presence of young horses, suggest the importance of this animal and the potential for its local breeding; the site could have acted as a station for changing or selling horses. The presence of marine fish and black rat also indicate clear links to the wider trade network. This was not an isolated settlement, outside the sphere of Roman influence, as rural Roman sites are often considered to be, but well‐connected to wider economic networks. This paper places these new results in context, by providing a review of faunal assemblages from Roman roadside settlements across Britain. The review indicates that most of the characteristics of animal exploitation at Ware are shared with other roadside settlement sites, though interesting differences also emerge
Thymoma calcification: Is it clinically meaningful?
Among anterior mediastinal lesions, thymoma is the most common. Thymomas are tumors of thymic epithelial cell origin that are distinguished by inconsistent histological and biologic behavior. Chest imaging studies typically show a round or lobulated tumor in the anterior mediastinum. Calcifications in thymomas are classically punctuate or amorphous, positioned within the lesion. Chest computed tomography (CT) features suggesting higher risk thymoma consist of tumor heterogeneity, vascular involvement, lobulation, pulmonary nodules, lymphadenopathy, and pleural manifestations. Imaging findings have an imperfect ability to predict stage and prognosis for thymoma patients. Our objective is to highlight the clinical implications of thymoma calcifications on the diagnosis, clinical manifestation and prognosis. A pubmed and google search was performed using the following words: thymoma calcification, calcified thymus, mediastinal calcification, anterior mediastinal calcification, and calcified thymoma. After reviewing 370 articles, 32 eligible articles describing thymoma calcifications were found and included in this review. Although the presence of thymus calcifications was more common in patients with invasive thymomas, they were present in significant portion of non-invasive thymomas. The presence of calcifications was not a significant factor in differentiating between benign and malignant thymoma. As a result, the type, location, size or other characteristics of thymus gland calcifications were not relevant features in clinical and radiologic diagnosis of thymoma. The histopathological diagnosis is still the only possible way to confirm the neoplastic nature of thymoma. All types of thymomas should be evaluated and managed independently of the presence of calcifications
Simulating the evolution of disc galaxies in a group environment. I. The influence of the global tidal field
We present the results of a series of numerical simulations aimed to study
the evolution of a disc galaxy within the global tidal field of a group
environment. Both the disc galaxy and the group are modelled as
multi-component, collision-less, N-body systems, composed by both dark matter
and stars. In our simulations, the evolution of disc galaxies is followed as
their orbits sink towards the group centre, under the effect of dynamical
friction. We explore a broad parameter space, covering several aspects of the
galaxy-group interaction that are potentially relevant to galaxy evolution.
Namely, prograde and retrograde orbits, orbital eccentricities, disc
inclination, role of a central bulge in discs, internal disc kinematics, and
galaxy-to-group mass ratios. We find that significant disc transformations
occur only after the mean density of the group, measured within the orbit of
the galaxy, exceeds ~0.3-1 times the central mean density of the galaxy. The
morphological evolution of discs is found to be strongly dependent on the
initial inclination of the disc with respect to its orbital plane. That is,
discs on face-on and retrograde orbits are shown to retain longer their disc
structures and kinematics, in comparison to prograde discs. This suggests that
after interacting with the global tidal field alone, a significant fraction of
disc galaxies should be found in the central regions of groups. Prominent
central bulges are not produced, and pre-existing bulges are not enhanced in
discs after the interaction with the group. Assuming that most S0 are formed in
group environments, this implies that prominent bulges should be formed mostly
by young stars, created only after a galaxy has been accreted by a group.
Finally, contrary to some current implementations of tidal stripping in
semi-analytical models of galaxy evolution, we find that more massive galaxies
suffer more tidal stripping.Comment: 31 pages, 20 figures, and 3 tables. Accepted for publication in MNRA
Preparation interval and cue utilization in the prevention of distraction
Maintaining a selective attention set allows us to efficiently perform sensory tasks despite the multitude of concurrent sensory stimuli. Unpredictably occurring, rare events nonetheless capture our attention, that is, we get distracted. The present study investigated the efficiency of control over distraction as a function of preparation time available before a forthcoming distracter. A random sequence of short and long tones (100 or 200 ms with 50–50 % probability) was presented. Independently from tone duration, occasionally (13.3 % of the time), the pitch of a tone was changed. Such rare pitch variants (distracters) usually lead to delayed and less precise discrimination responses, and trigger a characteristic series of event-related potentials (ERPs) reflecting the stages of distraction-related processing: starting with negative ERPs signaling the sensory registration of the distracter; a P3a—usually interpreted as a reflection of involuntary attention change and finally the so-called reorienting negativity signaling the restoration of the task-optimal attention set. In separate conditions, 663 or 346 ms before each tone (long or short cue-tone interval), a visual cue was presented, which signaled whether the forthcoming tone was a distracter (rare pitch variant), with 80 % validity. As reflected by reduced reaction time delays and P3a amplitudes, valid cues led to the prevention of distraction, but only in the long cue-tone interval condition. The analyses of the cue-related P3b and contingent negative variation showed that participants made more effort to utilize cue information to prevent distraction in the long cue-tone than in the short cue-tone interval condition
Postural control and contingent negative variation during transient floor translation while standing with the ankle fixed
Assessment of Modeled Indoor Air Concentrations of Particulate Matter, Gaseous Pollutants, and Volatile Organic Compounds Emitted from Candles
Candle burning is regarded as an important source of airborne pollutants in indoor environments. Indoor concentrations of aldehydes, benzo(a)pyrene, sulphur dioxide (SO2), nitrogen oxides (NOx), and particulate matter (PM) produced from the burning of scented candles and raw materials with different melting point/oil content (50/1, 55/9, and 65/6) were predicted using a single compartment mass balance model and compared to regulatory or guideline limits. Scented candles may be responsible for indoor acrolein concentrations that could become relevant to health only in the case of chronic exposure. Indoor concentrations of fine PM and SO2 emitted from 65/6 wax burning under worst-case environmental and behavioral conditions were greater than their respective acute guideline limits. However, other waxes had levels of PM and SO2 well below the recommended values. Indoor concentrations of nitrogen dioxide emitted from raw wax burning should be further investigated. The degree of pureness of raw waxes significantly affected the predicted indoor concentrations of PM and SO2. In particular, 65/6 wax was criticized for its high content of impurities
Outcomes After Laparoscopic Conversion of Failed Adjustable Gastric Banding (LAGB) to Laparoscopic Sleeve Gastrectomy (LSG) or Single Anastomosis Duodenal Switch (SADS)
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