1,347 research outputs found
Segmentation of Loops from Coronal EUV Images
We present a procedure which extracts bright loop features from solar EUV
images. In terms of image intensities, these features are elongated ridge-like
intensity maxima. To discriminate the maxima, we need information about the
spatial derivatives of the image intensity. Commonly, the derivative estimates
are strongly affected by image noise. We therefore use a regularized estimation
of the derivative which is then used to interpolate a discrete vector field of
ridge points ``ridgels'' which are positioned on the ridge center and have the
intrinsic orientation of the local ridge direction. A scheme is proposed to
connect ridgels to smooth, spline-represented curves which fit the observed
loops. Finally, a half-automated user interface allows one to merge or split,
eliminate or select loop fits obtained form the above procedure. In this paper
we apply our tool to one of the first EUV images observed by the SECCHI
instrument onboard the recently launched STEREO spacecraft. We compare the
extracted loops with projected field lines computed from
almost-simultaneously-taken magnetograms measured by the SOHO/MDI Doppler
imager. The field lines were calculated using a linear force-free field model.
This comparison allows one to verify faint and spurious loop connections
produced by our segmentation tool and it also helps to prove the quality of the
magnetic-field model where well-identified loop structures comply with
field-line projections. We also discuss further potential applications of our
tool such as loop oscillations and stereoscopy.Comment: 13 pages, 9 figures, Solar Physics, online firs
The application of compressive sampling to radio astronomy I: Deconvolution
Compressive sampling is a new paradigm for sampling, based on sparseness of
signals or signal representations. It is much less restrictive than
Nyquist-Shannon sampling theory and thus explains and systematises the
widespread experience that methods such as the H\"ogbom CLEAN can violate the
Nyquist-Shannon sampling requirements. In this paper, a CS-based deconvolution
method for extended sources is introduced. This method can reconstruct both
point sources and extended sources (using the isotropic undecimated wavelet
transform as a basis function for the reconstruction step). We compare this
CS-based deconvolution method with two CLEAN-based deconvolution methods: the
H\"ogbom CLEAN and the multiscale CLEAN. This new method shows the best
performance in deconvolving extended sources for both uniform and natural
weighting of the sampled visibilities. Both visual and numerical results of the
comparison are provided.Comment: Published by A&A, Matlab code can be found:
http://code.google.com/p/csra/download
Compression coil provides increased lead control in extraction procedures
Aims We investigated a new lead extraction tool (Compression Coil; One-Tie, Cook Medical) in an experimental traction force study. Methods and results On 13 pacemaker leads (Setrox JS53, Biotronik) traction force testing was performed under different configurations. The leads were assigned to three groups: (i) traction force testing without central locking stylet support (n = 5), (ii) traction force testing with the use of a locking stylet (Liberator, Cook Medical) and a proximal ligation suture (n = 4), (iii) traction force testing with the use of a locking stylet and a compression coil (n = 4). The following parameters were obtained for all groups: stress-strain curves, maximal forces, elastic modulus, post-testing lead length and lead elongation. In Groups 2 and 3 retraction of the locking stylet within the lead was measured [lead tip-locking stylet distance (LTLSD)]. Maximal forces for the three groups were: (i) 28.3 ± 0.3 N; (ii) 30.6 ± 3.0 N; (iii) 31.6 ± 2.9 N (1 vs. 2, P = 0.13; 1 vs. 3, P = 0.04; 2 vs. 3, P = 0.65). Elastic modulus was (i) 22.8 ± 0.1 MPa; (ii) 2830.8 ± 351.1 MPa; (iii) 2447.0 ± 510.5 MPa (1 vs. 2, P < 0.01; 1 vs. 3, P < 0.01; 2 vs. 3, P = 0.26). Mean LTLSD in Group 2 was 19.8 ± 3.2 cm and was 13.8 ± 1.7 cm in Group 3 (P = 0.02). The ratio of LTLSD/post-testing lead length was 0.37 ± 0.03 for Group 2 and 0.24 ± 0.03 for Group 3 (P < 0.01). Conclusion The application of a compression coil leads to an increased lead control expressed by less retraction of the locking stylet within the lead. This enables improved central support of extraction sheaths in the case of challenging extraction procedure
HumanRF: High-Fidelity Neural Radiance Fields for Humans in Motion
Representing human performance at high-fidelity is an essential building block in diverse applications, such as film production, computer games or videoconferencing. To close the gap to production-level quality, we introduce HumanRF1, a 4D dynamic neural scene representation that captures full-body appearance in motion from multi-view video input, and enables playback from novel, unseen viewpoints. Our novel representation acts as a dynamic video encoding that captures fine details at high compression rates by factorizing space-time into a temporal matrix-vector decomposition. This allows us to obtain temporally coherent reconstructions of human actors for long sequences, while representing high-resolution details even in the context of challenging motion. While most research focuses on synthesizing at resolutions of 4MP or lower, we address the challenge of operating at 12MP. To this end, we introduce ActorsHQ, a novel multi-view dataset that provides 12MP footage from 160 cameras for 16 sequences with high-fidelity, per-frame mesh reconstructions2. We demonstrate challenges that emerge from using such high-resolution data and show that our newly introduced HumanRF effectively leverages this data, making a significant step towards production-level quality novel view synthesis
A Comparative Study of Population-Graph Construction Methods and Graph Neural Networks for Brain Age Regression
The difference between the chronological and biological brain age of a
subject can be an important biomarker for neurodegenerative diseases, thus
brain age estimation can be crucial in clinical settings. One way to
incorporate multimodal information into this estimation is through population
graphs, which combine various types of imaging data and capture the
associations among individuals within a population. In medical imaging,
population graphs have demonstrated promising results, mostly for
classification tasks. In most cases, the graph structure is pre-defined and
remains static during training. However, extracting population graphs is a
non-trivial task and can significantly impact the performance of Graph Neural
Networks (GNNs), which are sensitive to the graph structure. In this work, we
highlight the importance of a meaningful graph construction and experiment with
different population-graph construction methods and their effect on GNN
performance on brain age estimation. We use the homophily metric and graph
visualizations to gain valuable quantitative and qualitative insights on the
extracted graph structures. For the experimental evaluation, we leverage the UK
Biobank dataset, which offers many imaging and non-imaging phenotypes. Our
results indicate that architectures highly sensitive to the graph structure,
such as Graph Convolutional Network (GCN) and Graph Attention Network (GAT),
struggle with low homophily graphs, while other architectures, such as
GraphSage and Chebyshev, are more robust across different homophily ratios. We
conclude that static graph construction approaches are potentially insufficient
for the task of brain age estimation and make recommendations for alternative
research directions.Comment: Accepted at GRAIL, MICCAI 202
Treatment with higher dosages of heart failure medication is associated with improved outcome following cardiac resynchronization therapy
Background Cardiac resynchronization therapy (CRT) is associated with improved morbidity and mortality in patients with chronic heart failure (CHF) on optimal medical therapy. The impact of CHF medication optimization following CRT, however, has never been comprehensively evaluated. In the current study, we therefore investigated the effect of CHF medication dosage on morbidity and mortality in CHF patients after CRT implantation. Methods and results Chronic heart failure medication was assessed in 185 patients after CRT implantation. During an overall mean follow-up of 44.6 months, 83 patients experienced a primary endpoint (death, heart transplantation, assist device implantation, or hospitalization for CHF). Treatment with higher dosages of angiotensin-converting enzyme inhibitor (ACE-I) or angiotensin receptor blockers (ARBs) (P = 0.001) and beta-blockers (P < 0.001) as well as with lower dosages of loop diuretics (P < 0.001) was associated with a reduced risk for the primary combined endpoint as well as for all-cause mortality. Echocardiographic super-responders to CRT were treated with higher average dosages of ACE-I/ARBs (68.1 vs. 52.4%, P < 0.01) and beta-blockers (59 vs. 42.2%, P < 0.01). During follow-up, the average dosage of loop diuretics was decreased by 20% in super-responders, but increased by 30% in non-super-responders (P < 0.03). Conclusion The use of higher dosages of neurohormonal blockers and lower dosages of diuretics is associated with reduced morbidity and mortality following CRT implantation. Our data imply a beneficial effect of increasing neurohormonal blockade whenever possible following CRT implantatio
Duchamp: a 3D source finder for spectral-line data
This paper describes the Duchamp source finder, a piece of software designed
to find and describe sources in 3-dimensional, spectral-line data cubes.
Duchamp has been developed with HI (neutral hydrogen) observations in mind, but
is widely applicable to many types of astronomical images. It features
efficient source detection and handling methods, noise suppression via
smoothing or multi-resolution wavelet reconstruction, and a range of graphical
and text-based outputs to allow the user to understand the detections. This
paper details some of the key algorithms used, and illustrates the
effectiveness of the finder on different data sets.Comment: MNRAS, in press. 17 pages, 8 figure
Do maternal environmental conditions during reproductive development induce genotypic selection in Picea abies?
In forest trees, environmental conditions during reproduction can greatly
influence progeny performance. This phenomenon probably results from
adaptive phenotypic plasticity but also may be associated with genotypic
selection. In order to determine whether selective effects during the
reproduction are environment specific, single pair-crosses of Norway spruce
were studied in two contrasted maternal environments (warm and cold
conditions). One family expressed large and the other small phenotypic
differences between these crossing environments. The inheritance of genetic
polymorphism was analysed at the seed stage. Four parental genetic maps
covering 66 to 78% of the genome were constructed using 190 to 200 loci.
After correcting for multiple testing, there is no evidence of locus under
strong and repeatable selection. The maternal environment could thus only
induce limited genotypic-selection effects during reproductive steps, and
performance of progenies may be mainly affected by a long-lasting epigenetic
memory regulated by temperature and photoperiod prevailing during seed
production.L'environnement maternel induit-il une sélection génotypique
durant les différents stades de reproduction chez Picea
abies ?. Chez les arbres forestiers, les conditions environnementales durant la
reproduction peuvent influencer les performances des descendants. Ce
phénomène reflète probablement la plasticité
phénotypique, mais également il pourrait être associé à une
sélection génotypique. Afin de déterminer si des effets
sélectifs durant la reproduction sont spécifiques d'un environnement
donné, deux familles d'épicéa commun non apparentées ont
été obtenues par croisements dirigés dans deux environnements
maternels contrastés (conditions chaude et froide). La première
famille exprimait de larges différences phénotypiques entre les deux
environnements tandis que la seconde ne montrait pas de différence
significative. La transmission des polymorphismes génétiques a
été étudiée au stade de la graine. Quatre cartes
génétiques parentales couvrant 66 à 78 % du génome ont
été construites. Aucun effet de sélection n'a été mis en
évidence aux différents locus étudiés. L'environnement
maternel n'induirait donc que des effets de sélection génotypique
relativement faibles durant les stades de la reproduction. Les performances
des descendants seraient principalement affectées par une mémoire
épigénétique durable régulée par la température et
la photopériode régnant durant la production des graines
- …