2,419 research outputs found
ALMA detection of dark chromospheric holes in the quiet Sun
We present Atacama Large Millimeter/submillimeter Array (ALMA) observations
of a quiet-Sun region at a wavelength of 3 mm, obtained during the first solar
ALMA cycle on April 27, 2017, and compare them with available chromospheric
observations in the UV and visible as well as with photospheric magnetograms.
ALMA images clearly reveal the presence of distinct particularly dark/cool
areas in the millimeter maps having temperatures as low as 60% of the normal
quiet Sun at 3 mm, which are not seen in the other data. We speculate that ALMA
is sensing cool chromospheric gas, whose presence had earlier been inferred
from infrared CO spectra.Comment: 9 pages, 3 figures, accepted for publication in ApJ
The relationship between chromospheric emissions and magnetic field strength
Aims. We analyze observational data from 4 instruments to study the
correlations between chromospheric emission, spanning the heights from the
temperature minimum region to the middle chromosphere, and photospheric
magnetic field. Methods: The data consist of radio images at 3.5 mm from the
Berkeley-Illinois-Maryland Array (BIMA), UV images at 1600 A from TRACE, Ca II
K-line filtergrams from BBSO, and MDI/SOHO longitudinal photospheric
magnetograms. For the first time interferometric millimeter data with the
highest currently available resolution are included in such an analysis. We
determine various parameters of the intensity maps and correlate the
intensities with each other and with the magnetic field. Results: The
chromospheric diagnostics studied here show a pronounced similarity in their
brightness structures and map out the underlying photospheric magnetic field
relatively well. We find a power law to be a good representation of the
relationship between photospheric magnetic field and emission from
chromospheric diagnostics at all wavelengths. The dependence of chromospheric
brightness on magnetic field is found to be different for network and
internetwork regions.Comment: 13 pages, 14 figures, 3 table
The chromosphere above sunspots at millimeter wavelengths
Aims: The aim of this paper is to demonstrate that millimeter wave data can
be used to distinguish between various atmospheric models of sunspots, whose
temperature structure in the upper photosphere and chromosphere has been the
source of some controversy. Methods: We use observations of the temperature
contrast (relative to the quiet Sun) above a sunspot umbra at 3.5 mm obtained
with the Berkeley-Illinois-Maryland Array (BIMA), complemented by submm
observations from Lindsey & Kopp (1995) and 2 cm observations with the Very
Large Array. These are compared with the umbral contrast calculated from
various atmospheric models of sunspots. Results: Current mm and submm
observational data suggest that the brightness observed at these wavelengths is
low compared to the most widely used sunspot models. These data impose strong
constraints on the temperature and density stratifications of the sunspot
umbral atmosphere, in particular on the location and depth of the temperature
minimum and the location of the transition region. Conclusions: A successful
model that is in agreement with millimeter umbral brightness should have an
extended and deep temperature minimum (below 3000 K). Better spatial resolution
as well as better wavelength coverage are needed for a more complete
determination of the chromospheric temperature stratification above sunspot
umbrae.Comment: 9 pages, 11 figures.
http://www.aanda.org/articles/aa/abs/2014/01/aa21321-13/aa21321-13.htm
Measuring Entangled Qutrits and Their Use for Quantum Bit Commitment
We produce and holographically measure entangled qudits encoded in transverse
spatial modes of single photons. With the novel use of a quantum state
tomography method that only requires two-state superpositions, we achieve the
most complete characterisation of entangled qutrits to date. Ideally, entangled
qutrits provide better security than qubits in quantum bit-commitment: we model
the sensitivity of this to mixture and show experimentally and theoretically
that qutrits with even a small amount of decoherence cannot offer increased
security over qubits.Comment: Paper updated to match published version; 5 pages, 4 figures, images
have been included at slightly lower quality for the archiv
ALMA Discovery of Solar Umbral Brightness Enhancement at {\lambda}=3 mm
We report the discovery of a brightness enhancement in the center of a large
sunspot umbra at a wavelength of 3 mm using the Atacama Large
Millimeter/sub-millimeter Array (ALMA). Sunspots are amongst the most prominent
features on the solar surface, but many of their aspects are surprisingly
poorly understood. We analyzed a {\lambda}=3 mm (100 GHz) mosaic image obtained
by ALMA, which includes a large sunspot within the active region AR12470 on
December 16, 2015. The 3 mm map has a field-of-view and spatial resolution,
which is the highest spatial-resolution map of an entire sunspot in this
frequency range. We find a gradient of 3 mm brightness from a high value in the
outer penumbra to a low value in the inner penumbra/outer umbra. Within the
inner umbra, there is a marked increase in 3mm brightness temperature, which we
call an umbral brightness enhancement. This enhanced emission corresponds to a
temperature excess of 800 K relative to the surrounding inner penumbral region
and coincides with excess brightness in the 1330 and 1400 {\AA} slitjaw images
of the Interface Region Imaging Spectrograph (IRIS), adjacent to a partial
lightbridge. This {\lambda}=3 mm brightness enhancement may be an intrinsic
feature of the sunspot umbra at chromospheric heights, such as a manifestation
of umbral flashes, or it could be related to a coronal plume since the
brightness enhancement was coincident with the footpoint of a coronal loop
observed at 171 {\AA}.Comment: 16 pages, 5 figures, accepted for publication in ApJ Lette
CRISPR-Mediated Protein Tagging with Nanoluciferase to Investigate Native Chemokine Receptor Function and Conformational Changes
© 2020 The Authors G protein-coupled receptors are a major class of membrane receptors that mediate physiological and pathophysiological cellular signaling. Many aspects of receptor activation and signaling can be investigated using genetically encoded luminescent fusion proteins. However, the use of these biosensors in live cell systems requires the exogenous expression of the tagged protein of interest. To maintain the normal cellular context here we use CRISPR/Cas9-mediated homology-directed repair to insert luminescent tags into the endogenous genome. Using NanoLuc and bioluminescence resonance energy transfer we demonstrate fluorescent ligand binding at genome-edited chemokine receptors. We also demonstrate that split-NanoLuc complementation can be used to investigate conformational changes and internalization of CXCR4 and that recruitment of β-arrestin2 to CXCR4 can be monitored when both proteins are natively expressed. These results show that genetically encoded luminescent biosensors can be used to investigate numerous aspects of receptor function at native expression levels
Assessing wellbeing at school entry using the strengths and difficulties questionnaire: professional perspectives
<p>Background: Emotional and behavioural disorders in early childhood are related to poorer academic attainment and school engagement, and difficulties already evident at the point of starting school can affect a child’s later social and academic development. Successful transfer from pre-school settings to primary education is helped by communication between pre-school staff and primary school teachers. Typically, in Scotland, pre-school establishments prepare individual profiles of children before they start school around the age of five years, highlighting their strengths and development needs, for transfer to primary schools. There is, however, no consistent approach to the identification of potential social, emotional and behavioural problems. In 2010, in one local authority area in Scotland, the Strengths and Difficulties Questionnaire (SDQ) was introduced for children about to start school as a routine, structured, component of the transition process to help teachers plan support arrangements for classes and individual children. The SDQ assesses emotional, conduct, hyperactivity/ inattention and peer-relationship problems as well as pro-social behaviour. In order to be an effective means of communicating social and emotional functioning, the use of instruments such as the SDQ needs to be practicable. Finding out the views of pre-school education staff with experience of assessing children using the SDQ was, therefore, essential to establish its future utility.</p>
<p>Aim: The purpose of this study was to explore the views of pre-school education staff about assessing social and emotional wellbeing of children at school entry using the SDQ. The objectives were to examine the opinions of pre-school workers about completing the SDQ and to elicit their thoughts on the value of doing this and their perceptions of the usefulness of the information collected.</p>
<p>Method: Pre-school establishments were approached using a purposive sampling strategy in order to achieve a mix of local authority (n=14) and ‘partnership’ establishments (n=8) as well as different socio-economic areas. Semi-structured interviews (n=25) were conducted with pre-school head teachers (n=14) and child development officers (n=11) in order to explore the process of completing the SDQ along with perceptions of its value. The interviews were transcribed verbatim and analysed thematically.</p>
<p>Results: In general, staff in pre-school establishments viewed the use of the SDQ positively. It was seen as a chance to highlight the social and emotional development of children rather than just their academic or educational ability. Most felt that the SDQ had not identified anything they did not already know about a child. A minority, nevertheless, suggested that a previously unrecognised potential difficulty was brought to light, most commonly emotional problems. Completing the SDQ was felt to be relatively straightforward even though the staff felt under pressure from competing priorities. Concerns were, however, raised about the potential of labelling a child at an early stage of formal education.</p>
<p>Conclusion: The findings from this small scale study suggest that, from the point of view of pre-school education staff, it is feasible to assess children systematically for social and behavioural problems as part of the routine transition process at school entry.</p>
Dynamics of a semiconductor laser with optical feedback
We investigate both experimentally and theoretically the dynamics of a semiconductor laser with optical feedback in the low-frequency fluctuation regime. First we demonstrate that low-frequency fluctuations can be observed for both single and multimode operation of a semiconductor laser with optical feedback. The analysis of the fast dynamics associated with this low-frequency instability is well described by single-mode rate equations. In the multimode regime, fast pulsation is observed in every laser mode. In this case the fluctuations in total intensity are much smaller than those in the intensity of each individual mode, This indicates the presence of anticorrelations dynamics at high frequency between the different laser modes. (S1050-2947(99)08307-9)
Automated Gaze-Based Mind Wandering Detection during Computerized Learning in Classrooms
We investigate the use of commercial off-the-shelf (COTS) eye-trackers to automatically detect mind wandering—a phenomenon involving a shift in attention from task-related to task-unrelated thoughts—during computerized learning. Study 1 (N = 135 high-school students) tested the feasibility of COTS eye tracking while students learn biology with an intelligent tutoring system called GuruTutor in their classroom. We could successfully track eye gaze in 75% (both eyes tracked) and 95% (one eye tracked) of the cases for 85% of the sessions where gaze was successfully recorded. In Study 2, we used this data to build automated student-independent detectors of mind wandering, obtaining accuracies (mind wandering F1 = 0.59) substantially better than chance (F1 = 0.24). Study 3 investigated context-generalizability of mind wandering detectors, finding that models trained on data collected in a controlled laboratory more successfully generalized to the classroom than the reverse. Study 4 investigated gaze- and video- based mind wandering detection, finding that gaze-based detection was superior and multimodal detection yielded an improvement in limited circumstances. We tested live mind wandering detection on a new sample of 39 students in Study 5 and found that detection accuracy (mind wandering F1 = 0.40) was considerably above chance (F1 = 0.24), albeit lower than offline detection accuracy from Study 1 (F1 = 0.59), a finding attributable to handling of missing data. We discuss our next steps towards developing gaze-based attention-aware learning technologies to increase engagement and learning by combating mind wandering in classroom contexts
- …