14,337 research outputs found
Cool transition region loops observed by the Interface Region Imaging Spectrograph
We report on the first Interface Region Imaging Spectrograph (IRIS) study of
cool transition region loops. This class of loops has received little attention
in the literature. A cluster of such loops was observed on the solar disk in
active region NOAA11934, in the Si IV 1402.8 \AA\ spectral raster and 1400 \AA\
slit-jaw (SJ) images. We divide the loops into three groups and study their
dynamics and interaction. The first group comprises relatively stable loops,
with 382--626\,km cross-sections. Observed Doppler velocities are suggestive of
siphon flows, gradually changing from -10 km/s at one end to 20 km/s at the
other end of the loops. Nonthermal velocities from 15 to 25 km/s were
determined. These physical properties suggest that these loops are impulsively
heated by magnetic reconnection occurring at the blue-shifted footpoints where
magnetic cancellation with a rate of Mx/s is found. The released
magnetic energy is redistributed by the siphon flows. The second group
corresponds to two footpoints rooted in mixed-magnetic-polarity regions, where
magnetic cancellation occurred at a rate of Mx/s and line profiles
with enhanced wings of up to 200 km/s were observed. These are suggestive of
explosive-like events. The Doppler velocities combined with the SJ images
suggest possible anti-parallel flows in finer loop strands. In the third group,
interaction between two cool loop systems is observed. Evidence for magnetic
reconnection between the two loop systems is reflected in the line profiles of
explosive events, and a magnetic cancellation rate of Mx/s
observed in the corresponding area. The IRIS observations have thus opened a
new window of opportunity for in-depth investigations of cool transition region
loops. Further numerical experiments are crucial for understanding their
physics and their role in the coronal heating processes.Comment: Accepted for publication in Ap
MicroR159 regulation of most conserved targets in Arabidopsis has negligible phenotypic effects
BACKGROUND A current challenge of microRNA (miRNA) research is the identification of biologically relevant miRNA:target gene relationships. In plants, high miRNA:target gene complementarity has enabled accurate target predictions, and slicing of target mRNAs has facilitated target validation through rapid amplification of 5' cDNA ends (5'-RACE) analysis. Together, these approaches have identified more than 20 targets potentially regulated by the deeply conserved miR159 family in Arabidopsis, including eight MYB genes with highly conserved miR159 target sites. However, genetic analysis has revealed the functional specificity of the major family members, miR159a and miR159b is limited to only two targets, MYB33 and MYB65. Here, we examine the functional role of miR159 regulation for the other potential MYB target genes. RESULTS For these target genes, functional analysis failed to identify miR159 regulation that resulted in any major phenotypic impact, either at the morphological or molecular level. This appears to be mainly due to the quiescent nature of the remaining family member, MIR159c. Although its expression overlaps in a temporal and spatial cell-specific manner with a subset of these targets in anthers, the abundance of miR159c is extremely low and concomitantly a mir159c mutant displays no anther defects. Examination of potential miR159c targets with conserved miR159 binding sites found neither their spatial or temporal expression domains appeared miR159 regulated, despite the detection of miR159-guided cleavage products by 5'-RACE. Moreover, expression of a miR159-resistant target (mMYB101) resulted predominantly in plants that are indistinguishable from wild type. Plants that displayed altered morphological phenotypes were found to be ectopically expressing the mMYB101 transgene, and hence were misrepresentative of the in vivo functional role of miR159. CONCLUSIONS This study presents a novel explanation for a paradox common to plant and animal miRNA systems, where among many potential miRNA-target relationships usually only a few appear physiologically relevant. The identification of a quiescent miR159c:target gene regulatory module in anthers provides a likely rationale for the presence of conserved miR159 binding sites in many targets for which miR159 regulation has no obvious functional role. Remnants from the demise of such modules may lead to an overestimation of miRNA regulatory complexity when investigated using bioinformatic, 5'-RACE or transgenic approaches.RSA was funded by an ANU postgraduate scholarship and by a CSIRO Emerging Science Initiative. JL is the recipient of an ANU international student postgraduate scholarship. This research was supported by an Australian Research Council grant DP0773270
Narrow-line-width UV bursts in the transition region above Sunspots observed by IRIS
Various small-scale structures abound in the solar atmosphere above active
regions, playing an important role in the dynamics and evolution therein. We
report on a new class of small-scale transition region structures in active
regions, characterized by strong emissions but extremely narrow Si IV line
profiles as found in observations taken with the Interface Region Imaging
Spectrograph (IRIS). Tentatively named as Narrow-line-width UV bursts (NUBs),
these structures are located above sunspots and comprise of one or multiple
compact bright cores at sub-arcsecond scales. We found six NUBs in two datasets
(a raster and a sit-and-stare dataset). Among these, four events are
short-living with a duration of 10 mins while two last for more than 36
mins. All NUBs have Doppler shifts of 15--18 km/s, while the NUB found in
sit-and-stare data possesses an additional component at 50 km/s found
only in the C II and Mg II lines. Given that these events are found to play a
role in the local dynamics, it is important to further investigate the physical
mechanisms that generate these phenomena and their role in the mass transport
in sunspots.Comment: 8 pages, 4 figures and 1 table, accepted for publication in ApJ
Plasma parameters and geometry of cool and warm active region loops
How the solar corona is heated to high temperatures remains an unsolved
mystery in solar physics. In the present study we analyse observations of 50
whole active-region loops taken with the Extreme-ultraviolet Imaging
Spectrometer (EIS) on board the Hinode satellite. Eleven loops were classified
as cool (<1 MK) and 39 as warm (1-2 MK) loops. We study their plasma parameters
such as densities, temperatures, filling factors, non-thermal velocities and
Doppler velocities. We combine spectroscopic analysis with linear force-free
magnetic-field extrapolation to derive the three-dimensional structure and
positioning of the loops, their lengths and heights as well as the magnetic
field strength along the loops. We use density-sensitive line pairs from Fe
XII, Fe XIII, Si X and Mg VII ions to obtain electron densities by taking
special care of intensity background-subtraction. The emission-measure loci
method is used to obtain the loop temperatures. We find that the loops are
nearly isothermal along the line-of-sight. Their filling factors are between 8%
and 89%. We also compare the observed parameters with the theoretical RTV
scaling law. We find that most of the loops are in an overpressure state
relative to the RTV predictions. In a followup study, we will report a heating
model of a parallel-cascade-based mechanism and will compare the model
parameters with the loop plasma and structural parameters derived here.Comment: ApJ, accepted for publicatio
Disk Heating, Galactoseismology, and the Formation of Stellar Halos
Deep photometric surveys of the Milky Way have revealed diffuse structures
encircling our Galaxy far beyond the "classical" limits of the stellar disk.
This paper reviews results from our own and other observational programs, which
together suggest that, despite their extreme positions, the stars in these
structures were formed in our Galactic disk. Mounting evidence from recent
observations and simulations implies kinematic connections between several of
these distinct structures. This suggests the existence of collective disk
oscillations that can plausibly be traced all the way to asymmetries seen in
the stellar velocity distribution around the Sun. There are multiple
interesting implications of these findings: they promise new perspectives on
the process of disk heating, they provide direct evidence for a stellar halo
formation mechanism in addition to the accretion and disruption of satellite
galaxies, and, they motivate searches of current and near-future surveys to
trace these oscillations across the Galaxy. Such maps could be used as
dynamical diagnostics in the emerging field of "Galactoseismology", which
promises to model the history of interactions between the Milky Way and its
entourage of satellites, as well examine the density of our dark matter halo.
As sensitivity to very low surface brightness features around external galaxies
increases, many more examples of such disk oscillations will likely be
identified. Statistical samples of such features not only encode detailed
information about interaction rates and mergers, but also about long
sought-after dark matter halo densities and shapes. Models for the Milky Way's
own Galactoseismic history will therefore serve as a critical foundation for
studying the weak dynamical interactions of galaxies across the universe.Comment: 20 pages, 5 figures, accepted in for publication in a special edition
of the journal "Galaxies", reporting the proceedings of the conference "On
the Origin (and Evolution) of Baryonic Galaxy Halos", Puerto Ayora, Ecuador,
March 13-17 2017, Eds. Duncan A. Forbes and Ericson D. Lope
Deposition of La2Zr2O7 Film by Chemical Solution Deposition
La2Zr2O7 (LZO) formation of bulk powders and of films by Chemical Solution
Deposition (CSD) process have been studied using propionates. The treatment
involved a one step cycle in the reducing forming gas (Ar-5%H2) to be
compatible with Ni-5at%W RABITS. Large amount of residual carbon was found in
LZO powders formed in these conditions (10 wt %). The volume fraction of the
cube texture in LZO films on Ni-5at%w RABITS was found to be a function of the
speed of the gas flown above sample. This phenomenon is discussed in
considering the C deposited from the carbon-containing gases emitted during the
pyrolysis of the precursor. Using proper conditions (950 ^\circC and the speed
of gas of 6.8\times10^{-2} m/s), LZO films with good surface crystallinity
could be obtained on Ni-5at%W RABITS as demonstrated by X-ray diffraction,
electron backscattered diffraction and RHEED. The existence of residual carbon
in oxide films is a common question to films deposited by CSD processes under
reducing condition
Stress, Motivation and Professional Satisfaction among Health Care Workers in HIV/AIDS Care and Treatment Centers in Urban Tanzania: A Cross-Sectional Study.
Shortages of health care workers (HCWs) represents a serious challenge to ensuring effective HIV care in resource-limited settings (RLS). Stress, motivation, and job satisfaction have been linked with HCW retention and are important in addressing HCW shortages. In this cross-sectional study HCW stress, motivation and perceived ability to meet patient needs were assessed in PEPFAR-supported urban HIV care and treatment clinics (CTCs) in Tanzania. A self-administered questionnaire measuring motivation, stress, and perceived ability to and meet patient needs was given to HCWs at 16 CTCs. Scales measuring HCW satisfaction, motivation, and stress were developed using principle components analysis. Hierarchical linear models were used to explore the association of HCW and site characteristics with reported satisfaction, stress, motivation, and ability to meet patients' needs.\ud
Seventy-three percent (279) of HCWs completed the questionnaire. Most (73%) HCWs reported minimal/no work-related stress, with 48% reporting good/excellent motivation, but 41% also reporting feeling emotionally drained. Almost all (98%) reported feeling able to help their patients, with 68% reporting work as rewarding. Most reported receipt of training and supervision, with good availability of resources. In the multivariate model, direct clinical providers reported lower motivation than management (p < 0.05) and HCWs at medium-sized sites reported higher motivation than HCWs at larger sites (p < 0.05). HCWs at small and medium sites were more likely to feel able to help patients than those from larger sites (p < 0.05 and p < 0.001 respectively). Despite significant patient loads, HCWs in these PEPFAR-supported CTCs reported high levels of motivation, job satisfaction, ability to meet patients' needs, low levels of stress but significant emotional toll. Understanding the relationship between support systems such as strong supervision and training and these outcomes is critical in designing interventions to improve motivation, reduce stress and increase retention of HCWs
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