2,584 research outputs found
A snapshot of the inner dusty regions of a RCrB-type variable
R Coronae Borealis variable stars are suspected to sporadically eject
optically thick dust clouds causing, when one of them lies on the
line-of-sight, a huge brightness decline in visible light. Mid-infrared
interferometric observations of RYSgr allowed us to explore the circumstellar
regions very close to the central star (~20-40 mas) in order to look for the
signature of any heterogeneities. Using the VLTI/MIDI instrument, five
dispersed visibility curves were recorded with different projected baselines
oriented towards two roughly perpendicular directions. The large spatial
frequencies visibility curves exhibit a sinusoidal shape whereas, at shorter
spatial frequencies visibility curves follow a Gaussian decrease. These
observations are well interpreted with a geometrical model consisting in a
central star surrounded by an extended circumstellar envelope in which one
bright cloud is embedded. Within this simple geometrical scheme, the inner
110AU dusty environment of RYSgr is dominated at the time of observations by a
single dusty cloud which, at 10mic represents ~10% of the total flux of the
whole system. The cloud is located at about 100stellar radii from the centre
toward the East-North-East direction (or the symmetric direction with respect
to centre) within a circumstellar envelope which FWHM is about 120stellar
radii. This first detection of a cloud so close to the central star, supports
the classical scenario of the RCrB brightness variations in the optical
spectral domain
Language learning experiences of postgraduate research students in the UK
This article reports on the findings of a pioneering study of formal, non-formal and informal language learning experiences of postgraduate research students in the UK. The research involved a large-scale survey followed by semi-structured interviews. Quantitative and qualitative data analysis shows that the language needs and interests of postgraduate students are barely met due to limited institutional provision of formal language learning opportunities. The study confirms some known facts, such as the composition of the student body (e.g. mostly young, fully-funded full-time students with a significant proportion of international students), and reveals other possibly less-known realities, from a remarkable interest in language learning among research students to the reasons for their interest and the potential impact greater access to language learning could have on their research and beyond. Half of the respondents reported having funded provision of language tuition but one third were not even aware of the existence of a Language Centre at their institution. Student suggestions for alternative language provision are included as these can inform policy and decision-making at postgraduate level in the UK and serve as a basis for further research in this area
Reactor mixing angle from hybrid neutrino masses
In terms of its eigenvector decomposition, the neutrino mass matrix (in the
basis where the charged lepton mass matrix is diagonal) can be understood as
originating from a tribimaximal dominant structure with small deviations, as
demanded by data. If neutrino masses originate from at least two different
mechanisms, referred to as "hybrid neutrino masses", the experimentally
observed structure naturally emerges provided one mechanism accounts for the
dominant tribimaximal structure while the other is responsible for the
deviations. We demonstrate the feasibility of this picture in a fairly
model-independent way by using lepton-number-violating effective operators,
whose structure we assume becomes dictated by an underlying flavor
symmetry. We show that if a second mechanism is at work, the requirement of
generating a reactor angle within its experimental range always fixes the solar
and atmospheric angles in agreement with data, in contrast to the case where
the deviations are induced by next-to-leading order effective operators. We
prove this idea is viable by constructing an -based ultraviolet
completion, where the dominant tribimaximal structure arises from the type-I
seesaw while the subleading contribution is determined by either type-II or
type-III seesaw driven by a non-trivial singlet (minimal hybrid model).
After finding general criteria, we identify all the symmetries
capable of producing such -based minimal hybrid models.Comment: 18 pages, 5 figures. v3: section including sum rules added, accepted
by JHE
Predição da maturidade de fibras de algodão colorido empregando espectroscopia no infravermelho próximo (NIR) e regressão por mínimos quadrados parciais.
Aquaplanets, climate sensitivity, and low clouds
Cloud effects have repeatedly been pointed out as the leading source of uncertainty in projections of future climate, yet clouds remain poorly understood and simulated in climate models. Aquaplanets provide a simplified framework for comparing and understanding cloud effects, and how they are partitioned as a function of regime, in large-scale models. This work uses two climate models to demonstrate that aquaplanets can successfully predict a climate model’s sensitivity to an idealized climate change. For both models, aquaplanet climate sensitivity is similar to that of the realistic configuration. Tropical low clouds appear to play a leading role in determining the sensitivity. Regions of large-scale subsidence, which cover much of the tropics, are most directly responsible for the differences between the models. Although cloud effects and climate sensitivity are similar for aquaplanets and realistic configurations, the aquaplanets lack persistent stratocumulus in the tropical atmosphere. This, and an additional analysis of the cloud response in the realistically configured simulations, suggests the representation of shallow (trade wind) cumulus convection, which is ubiquitous in the tropics, is largely responsible for differences in the simulated climate sensitivity of these two models
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