84 research outputs found
Evaluation of Mammographic Segmentation and Risk Classification Based on Tabár Tissue Modelling
Flame-like Ellerman Bombs and Their Connection to Solar UV Bursts
Ellerman bombs (EBs) are small-scale intense brightenings in H wing
images, which are generally believed to be signatures of magnetic reconnection
events around the temperature minimum region of the solar atmosphere. They have
a flame-like morphology when observed near the solar limb. Recent observations
from the Interface Region Imaging Spectrograph (IRIS) reveal another type of
small-scale reconnection events, termed UV bursts, in the lower atmosphere.
Though previous observations have shown a clear coincidence of some UV bursts
and EBs, the exact relationship between these two phenomena is still under
debate. We investigate the spatial and temporal relationship between flame-like
EBs and UV bursts using joint near-limb observations between the 1.6--meter
Goode Solar Telescope (GST) and IRIS. In total 161 EBs have been identified
from the GST observations, and 20 of them reveal signatures of UV bursts in the
IRIS images. Interestingly, we find that these UV bursts have a tendency to
appear at the upper parts of their associated flame-like EBs. The intensity
variations of most EB-related UV bursts and their corresponding EBs match well.
Our results suggest that these UV bursts and EBs are likely formed at different
heights during a common reconnection process.Comment: 5 figures; accepted by ApJ
Dark structures in sunspot light bridges
We present unprecedented high-resolution TiO images and Fe I 1565 nm
spectropolarimetric data of two light bridges taken by the 1.6-m Goode Solar
Telescope at Big Bear Solar Observatory. In the first light bridge (LB1), we
find striking knot-like dark structures within the central dark lane. Many dark
knots show migration away from the penumbra along the light bridge. The sizes,
intensity depressions and apparent speeds of their proper motion along the
light bridges of 33 dark knots identified from the TiO images are mainly in the
ranges of 80200~km, 30\%50\%, and 0.31.2~km~s,
respectively. In the second light bridge (LB2), a faint central dark lane and
striking transverse intergranular lanes were observed. These intergranular
lanes have sizes and intensity depressions comparable to those of the dark
knots in LB1, and also migrate away from the penumbra at similar speeds. Our
observations reveal that LB2 is made up of a chain of evolving convection
cells, as indicated by patches of blue shift surrounded by narrow lanes of red
shift. The central dark lane generally corresponds to blueshifts, supporting
the previous suggestion of central dark lanes being the top parts of convection
upflows. In contrast, the intergranular lanes are associated with redshifts and
located at two sides of each convection cell. The magnetic fields are stronger
in intergranular lanes than in the central dark lane. These results suggest
that these intergranular lanes are manifestations of convergent convective
downflows in the light bridge. We also provide evidence that the dark knots
observed in LB1 may have a similar origin.Comment: 6 figure
Long-term effects of restoration on the links between above-and belowground biodiversity in degraded Horqin sandy grassland, Northern China
Long-term ecological restoration plays an important role in the sustainable development of degraded grassland ecosystem. In this study, the levels of species diversity, genetic diversity and soil microbial diversity in restored grassland were measured by vegetation survey, DNA barcoding and soil microbial high-throughput sequencing technology, so as to explore the relationship between above- and belowground biodiversity and its driving factors in Horqin sandy grassland. In this study, the results found that herb are dominated in restoration grassland types. Plant species richness (SR) from post-non-grazing restoration plot (NGR) communities was significantly higher than other restoration communities (10 ± 1.1, p = 0.004). Genetic diversity indices of dominant plant species in chloroplast DNA (cpDNA), were remarkable greater than nuclear DNA (nrDNA) in each recovering sandy grassland plots (amplitude of difference was 44.8%–70.5% in allelic richness (AR), 81.9%–128.1% in expected heterozygosity (HE)). The soil bacterial and fungal richness from natural mobile dune grassland (NM) communities was notably lower than that from recovering grassland types (1641.9 ± 100.4, p < 0.001; 533 ± 16.6, p < 0.001). In this study, heterogeneous levels of genetic variability among different recovering sandy grassland types were detected. Correlation analyses revealed that there were positive correlations between species diversity and genetic diversity (SR & AR: r = 0.56, R2 = 0.31, p < 0.001; SR & HE: r = 0.33, R2 = 0.11, p = 0.045) and a negative correlation between soil microbial diversity and genetic diversity (r = -0.44, R2 = 0.19, p = 0.005). The final structural equation model explained 38% of the variance in SR, 57% in AR, 52% in soil microbial diversity (SD), 49% in aboveground biomass (AGB), 87% in soil organic carbon (SOC), 47% in soil alkali-hydrolyzable nitrogen (SAN) and 69% in soil available phosphorus (SOP). Long-term ecological restoration had significant direct positive effects on AGB, SOC, SAN, SOP, AR, SR and SD. There was a negative correlation between above- and belowground biodiversity and biological and abiotic factors. The results of this study have clarified the above- and underground biodiversity levels of sandy grassland and the relationship with driving factors under long-term ecological restoration measures, and will provide effective support for the management and sustainable development of sandy grassland
A review on automatic mammographic density and parenchymal segmentation
Breast cancer is the most frequently diagnosed cancer in women. However, the exact cause(s) of breast cancer still remains unknown. Early detection, precise identification of women at risk, and application of appropriate disease prevention measures are by far the most effective way to tackle breast cancer. There are more than 70 common genetic susceptibility factors included in the current non-image-based risk prediction models (e.g., the Gail and the Tyrer-Cuzick models). Image-based risk factors, such as mammographic densities and parenchymal patterns, have been established as biomarkers but have not been fully incorporated in the risk prediction models used for risk stratification in screening and/or measuring responsiveness to preventive approaches. Within computer aided mammography, automatic mammographic tissue segmentation methods have been developed for estimation of breast tissue composition to facilitate mammographic risk assessment. This paper presents a comprehensive review of automatic mammographic tissue segmentation methodologies developed over the past two decades and the evidence for risk assessment/density classification using segmentation. The aim of this review is to analyse how engineering advances have progressed and the impact automatic mammographic tissue segmentation has in a clinical environment, as well as to understand the current research gaps with respect to the incorporation of image-based risk factors in non-image-based risk prediction models
Antenna arrangement and energy-transfer pathways of PSI-LHCI from the moss Physcomitrella patens
Plants harvest light energy utilized for photosynthesis by light-harvesting complex I and II (LHCI and LHCII) surrounding photosystem I and II (PSI and PSII), respectively. During the evolution of green plants, moss is at an evolutionarily intermediate position from aquatic photosynthetic organisms to land plants, being the first photosynthetic organisms that landed. Here, we report the structure of the PSI-LHCI supercomplex from the moss Physcomitrella patens (Pp) at 3.23 angstrom resolution solved by cryo-electron microscopy. Our structure revealed that four Lhca subunits are associated with the PSI core in an order of Lhca1-Lhca5-Lhca2-Lhca3. This number is much decreased from 8 to 10, the number of subunits in most green algal PSI-LHCI, but the same as those of land plants. Although Pp PSI-LHCI has a similar structure as PSI-LHCI of land plants, it has Lhca5, instead of Lhca4, in the second position of Lhca, and several differences were found in the arrangement of chlorophylls among green algal, moss, and land plant PSI-LHCI. One chlorophyll, PsaF-Chl 305, which is found in the moss PSI-LHCI, is located at the gap region between the two middle Lhca subunits and the PSI core, and therefore may make the excitation energy transfer from LHCI to the core more efficient than that of land plants. On the other hand, energy-transfer paths at the two side Lhca subunits are relatively conserved. These results provide a structural basis for unravelling the mechanisms of light-energy harvesting and transfer in the moss PSI-LHCI, as well as important clues on the changes of PSI-LHCI after landing
Frequently Occurring Reconnection Jets from Sunspot Light Bridges
Solid evidence of magnetic reconnection is rarely reported within sunspots,
the darkest regions with the strongest magnetic fields and lowest temperatures
in the solar atmosphere. Using the world's largest solar telescope, the
1.6-meter Goode Solar Telescope, we detect prevalent reconnection through
frequently occurring fine-scale jets in the H line wings at light
bridges, the bright lanes that may divide the dark sunspot core into multiple
parts. Many jets have an inverted Y-shape, shown by models to be typical of
reconnection in a unipolar field environment. Simultaneous spectral imaging
data from the Interface Region Imaging Spectrograph show that the reconnection
drives bidirectional flows up to 200~km~s, and that the weakly ionized
plasma is heated by at least an order of magnitude up to 80,000 K. Such
highly dynamic reconnection jets and efficient heating should be properly
accounted for in future modeling efforts of sunspots. Our observations also
reveal that the surge-like activity previously reported above light bridges in
some chromospheric passbands such as the H core has two components:
the ever-present short surges likely to be related to the upward leakage of
magnetoacoustic waves from the photosphere, and the occasionally occurring long
and fast surges that are obviously caused by the intermittent reconnection
jets.Comment: ApJ, 8 figure
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