7,118 research outputs found
Bright hot impacts by erupted fragments falling back on the Sun: UV redshifts in stellar accretion
A solar eruption after a flare on 7 Jun 2011 produced EUV-bright impacts of
fallbacks far from the eruption site, observed with the Solar Dynamics
Observatory. These impacts can be taken as a template for the impact of stellar
accretion flows. Broad red-shifted UV lines have been commonly observed in
young accreting stars. Here we study the emission from the impacts in the
Atmospheric Imaging Assembly's UV channels and compare the inferred velocity
distribution to stellar observations. We model the impacts with 2D hydrodynamic
simulations. We find that the localised UV 1600A emission and its timing with
respect to the EUV emission can be explained by the impact of a cloud of
fragments. The first impacts produce strong initial upflows. The following
fragments are hit and shocked by these upflows. The UV emission comes mostly
from the shocked front shell of the fragments while they are still falling, and
is therefore redshifted when observed from above. The EUV emission instead
continues from the hot surface layer that is fed by the impacts. Fragmented
accretion can therefore explain broad redshifted UV lines (e.g. C IV 1550A) to
speeds around 400 km/s observed in accreting young stellar objects.Comment: 12 pages, 4 figures (movies available upon request), accepted for
publicatio
Thermal Diagnostics with the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory: A Validated Method for Differential Emission Measure Inversions
We present a new method for performing differential emission measure (DEM)
inversions on narrow-band EUV images from the Atmospheric Imaging Assembly
(AIA) onboard the Solar Dynamics Observatory (SDO). The method yields positive
definite DEM solutions by solving a linear program. This method has been
validated against a diverse set of thermal models of varying complexity and
realism. These include (1) idealized gaussian DEM distributions, (2) 3D models
of NOAA Active Region 11158 comprising quasi-steady loop atmospheres in a
non-linear force-free field, and (3) thermodynamic models from a
fully-compressible, 3D MHD simulation of AR corona formation following magnetic
flux emergence. We then present results from the application of the method to
AIA observations of Active Region 11158, comparing the region's thermal
structure on two successive solar rotations. Additionally, we show how the DEM
inversion method can be adapted to simultaneously invert AIA and XRT data, and
how supplementing AIA data with the latter improves the inversion result. The
speed of the method allows for routine production of DEM maps, thus
facilitating science studies that require tracking of the thermal structure of
the solar corona in time and space.Comment: 21 pages, 18 figures, accepted for publication in Ap
Gemini optical observations of binary millisecond-pulsars
Milli-second pulsars (MSPs) are rapidly spinning neutron stars, with spin
periods P_s <= 10 ms, which have been most likely spun up after a phase of
matter accretion from a companion star. In this work we present the results of
the search for the companion stars of four binary milli-second pulsars, carried
out with archival data from the Gemini South telescope. Based upon a very good
positional coincidence with the pulsar radio coordinates, we likely identified
the companion stars to three MSPs, namely PSRJ0614-3329 (g=21.95 +- 0.05),
J1231-1411 (g=25.40 +-0.23), and J2017+0603 (g=24.72 +- 0.28). For the last
pulsar (PSRJ0613-0200) the identification was hampered by the presence of a
bright star (g=16 +- 0.03) at \sim 2" from the pulsar radio coordinates and we
could only set 3-sigma upper limits of g=25.0, r= 24.3, and i= 24.2 on the
magnitudes of its companion star. The candidate companion stars to
PSRJ0614-3329, J1231-1411, and J2017+0603 can be tentatively identified as He
white dwarfs (WDs) on the basis of their optical colours and brightness and the
comparison with stellar model tracks. From the comparison of our multi-band
photometry with stellar model tracks we also obtained possible ranges on the
mass, temperature, and gravity of the candidate WD companions to these three
MSPs. Optical spectroscopy observations are needed to confirm their possible
classification as He WDs and accurately measure their stellar parameters.Comment: 17 pages, 7 figures, 6 tables, accepted for publication in MNRA
Tecniche di analisi statica non lineare multimodale per strutture intelaiate
Viene presentata una panoramica delle pi\uf9 efficienti tecniche di analisi statica non lineare, evidenziando i progressi
fatti nella formulazione di procedure con profili di carico adattivi multimodali, finalizzati alla valutazione della
risposta di strutture a comportamento fortemente non lineare. Vengono poi presentate le diverse procedure che
consentono di analizzare il comportamento di strutture irregolari in altezza o con grandi periodi di vibrare, nella
quale la risposta \ue8 fortemente influenzata dai modi superiori. In quest\u2019ambito viene evidenziato il ruolo della
procedura Modal Pushover Analysis, che risulta fra le pi\uf9 efficienti nel riprodurre il comportamento di strutture
fortemente irregolari in pianta e in elevazione a comportamento debolmente non lineare. Viene ripresa una tecnica
di combinazione dei contributi modali mediante la CQC, implementata attraverso l\u2019impiego di coefficienti di
correlazione non lineari per sistemi isteretici. Un esempio numerico nel quale la tecnica viene applicata per la
prima volta a sistemi spaziali irregolari in pianta ne mostra l\u2019efficacia in questo campo
A Non-Negative Matrix Tri-Factorization Based Method for Predicting Antitumor Drug Sensitivity
Large annotated cell line collections have been proven to enable the prediction of drug response in the pre-clinical setting. We present an enhancement of Non-Negative Matrix Tri-Factorization method, which allows the integration of different data types for the prediction of missing associations. To test our method we retrieved a dataset from the Cancer Cell Line Encyclopedia (CCLE), containing the connections among cell lines and drugs by means of their IC50 values, and we integrated it by linking cell lines to their respective tissue of origin and genomic profile. We performed two different kind of experiments: a) prediction of missing values in the matrix, b) prediction of the complete drug profile of a new cell line, demonstrating the validity of the method in both scenarios
Is the CERN recommended SCADA useable for the ST division?
Supervisory Control and Data Acquisition (SCADA) systems are widely used at CERN and in industrial control environments. In order to limit the costs of purchase, maintenance and support, a recommendation for one SCADA system is in preparation by the SCADA working group. This SCADA system should be used for all CERN in-house developed applications as they exist today e.g. in the Technical Control Room (TCR). This presentation will show the actual environment for the control and monitoring of the technical infrastructure at CERN and the needs for the future LHC infrastructure monitoring. The presentation will cover the control activities of all ST groups represented in the ST Control System WG. A possible solution for the integration of the technical infrastructure data into a SCADA system and a solution for the data exchange with the accelerators and the experiments will be presented. This includes a short term planning for the evaluation period as well as the long-term strategy on how to implement the chosen solution
On the Geometry of Surface Stress
We present a fully general derivation of the Laplace--Young formula and
discuss the interplay between the intrinsic surface geometry and the extrinsic
one ensuing from the immersion of the surface in the ordinary euclidean
three-dimensional space. We prove that the (reversible) work done in a general
surface deformation can be expressed in terms of the surface stress tensor and
the variation of the intrinsic surface metric
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