609 research outputs found
Deceleration and Dispersion of Large-scale Coronal Bright Fronts
One of the most dramatic manifestations of solar activity are large-scale
coronal bright fronts (CBFs) observed in extreme ultraviolet (EUV) images of
the solar atmosphere. To date, the energetics and kinematics of CBFs remain
poorly understood, due to the low image cadence and sensitivity of previous EUV
imagers and the limited methods used to extract the features. In this paper,
the trajectory and morphology of CBFs was determined in order to investigate
the varying properties of a sample of CBFs, including their kinematics and
pulse shape, dispersion, and dissipation. We have developed a semi-automatic
intensity profiling technique to extract the morphology and accurate positions
of CBFs in 2.5-10 min cadence images from STEREO/EUVI. The technique was
applied to sequences of 171A and 195A images from STEREO/EUVI in order to
measure the wave properties of four separate CBF events. Following launch at
velocities of ~240-450kms^{-1} each of the four events studied showed
significant negative acceleration ranging from ~ -290 to -60ms^{-2}. The CBF
spatial and temporal widths were found to increase from ~50 Mm to ~200 Mm and
~100 s to ~1500 s respectively, suggesting that they are dispersive in nature.
The variation in position-angle averaged pulse-integrated intensity with
propagation shows no clear trend across the four events studied. These results
are most consistent with CBFs being dispersive magnetoacoustic waves.Comment: 15 pages, 18 figure
Plasma heating in the very early and decay phases of solar flares
In this paper we analyze the energy budgets of two single-loop solar flares
under the assumption that non-thermal electrons are the only source of plasma
heating during all phases of both events. The flares were observed by the
Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and Geostationary
Operational Environmental Satellite (GOES) on September 20, 2002 and March 17,
2002, respectively. For both investigated flares we derived the energy fluxes
contained in non-thermal electron beams from the RHESSI observational data
constrained by observed GOES light-curves. We showed that energy delivered by
non-thermal electrons was fully sufficient to fulfil the energy budgets of the
plasma during the pre-heating and impulsive phases of both flares as well as
during the decay phase of one of them. We concluded that in the case of the
investigated flares there was no need to use any additional ad-hoc heating
mechanisms other than heating by non-thermal electrons.Comment: 22 pages, 10 figures, The Astrophysical Journal (accepted, March
2011
Precedence-constrained scheduling problems parameterized by partial order width
Negatively answering a question posed by Mnich and Wiese (Math. Program.
154(1-2):533-562), we show that P2|prec,|, the
problem of finding a non-preemptive minimum-makespan schedule for
precedence-constrained jobs of lengths 1 and 2 on two parallel identical
machines, is W[2]-hard parameterized by the width of the partial order giving
the precedence constraints. To this end, we show that Shuffle Product, the
problem of deciding whether a given word can be obtained by interleaving the
letters of other given words, is W[2]-hard parameterized by , thus
additionally answering a question posed by Rizzi and Vialette (CSR 2013).
Finally, refining a geometric algorithm due to Servakh (Diskretn. Anal. Issled.
Oper. 7(1):75-82), we show that the more general Resource-Constrained Project
Scheduling problem is fixed-parameter tractable parameterized by the partial
order width combined with the maximum allowed difference between the earliest
possible and factual starting time of a job.Comment: 14 pages plus appendi
Validation of Global EUV Wave MHD Simulations and Observational Techniques
Global EUV waves remain a controversial phenomenon more than 20 yr after their discovery by SOHO/EIT. Although consensus is growing in the community that they are most likely large-amplitude waves or shocks, the wide variety of observations and techniques used to identify and analyze them have led to disagreements regarding their physical properties and interpretation. Here, we use a 3D magnetohydrodynamic (MHD) model of the solar corona to simulate an EUV wave event on 2009 February 13 to enable a detailed validation of the various commonly used detection and analysis techniques of global EUV waves. The simulated event exhibits comparable behavior to that of a real EUV wave event, with similar kinematic behavior and plasma parameter evolution. The kinematics of the wave are estimated via visual identification and profile analysis, with both approaches providing comparable results. We find that projection effects can affect the derived kinematics of the wave, due to the variation in fast-mode wave speed with height in the corona. Coronal seismology techniques typically used for estimates of the coronal magnetic field are also tested and found to estimate fast-mode speeds comparable to those of the model. Plasma density and temperature variations of the wave front are also derived using a regularized inversion approach and found to be consistent with observed wave events. These results indicate that global waves are best interpreted as large-amplitude waves and that they can be used to probe the coronal medium using well-defined analysis techniques
On the Nature and Genesis of EUV Waves: A Synthesis of Observations from SOHO, STEREO, SDO, and Hinode
A major, albeit serendipitous, discovery of the SOlar and Heliospheric
Observatory mission was the observation by the Extreme Ultraviolet Telescope
(EIT) of large-scale Extreme Ultraviolet (EUV) intensity fronts propagating
over a significant fraction of the Sun's surface. These so-called EIT or EUV
waves are associated with eruptive phenomena and have been studied intensely.
However, their wave nature has been challenged by non-wave (or pseudo-wave)
interpretations and the subject remains under debate. A string of recent solar
missions has provided a wealth of detailed EUV observations of these waves
bringing us closer to resolving their nature. With this review, we gather the
current state-of-art knowledge in the field and synthesize it into a picture of
an EUV wave driven by the lateral expansion of the CME. This picture can
account for both wave and pseudo-wave interpretations of the observations, thus
resolving the controversy over the nature of EUV waves to a large degree but
not completely. We close with a discussion of several remaining open questions
in the field of EUV waves research.Comment: Solar Physics, Special Issue "The Sun in 360",2012, accepted for
publicatio
The effect of the dual Src/Abl kinase inhibitor AZD0530 on Philadelphia positive leukaemia cell lines
Background Imatinib mesylate, a selective inhibitor of Abl tyrosine kinase, is efficacious in treating chronic myeloid leukaemia (CML) and Ph+ acute lymphoblastic leukaemia (ALL). However, most advanced-phase CML and Ph+ ALL patients relapse on Imatinib therapy. Several mechanisms of refractoriness have been reported, including the activation of the Src-family kinases (SFK). Here, we investigated the biological effect of the new specific dual Src/Abl kinase inhibitor AZD0530 on Ph+ leukaemic cells. Methods Cell lines used included BV173 (CML in myeloid blast crisis), SEM t(4;11), Ba/F3 (IL-3 dependent murine pro B), p185Bcr-Abl infected Ba/F3 cells, p185Bcr-Abl mutant infected Ba/F3 cells, SupB15 (Ph+ ALL) and Imatinib resistant SupB15 (RTSupB15) (Ph+ ALL) cells. Cells were exposed to AZD0530 and Imatinib. Cell proliferation, apoptosis, survival and signalling pathways were assessed by dye exclusion, flow cytometry and Western blotting respectively. Results AZD0530 specifically inhibited the growth of, and induced apoptosis in CML and Ph+ ALL cells in a dose dependent manner, but showed only marginal effects on Ph- ALL cells. Resistance to Imatinib due to the mutation Y253F in p185Bcr-Abl was overcome by AZD0530. Combination of AZD0530 and Imatinib showed an additive inhibitory effect on the proliferation of CML BV173 cells but not on Ph+ ALL SupB15 cells. An ongoing transphosphorylation was demonstrated between SFKs and Bcr-Abl. AZD0530 significantly down-regulated the activation of survival signalling pathways in Ph+ cells, resistant or sensitive to Imatinib, with the exception of the RTSupB15. Conclusion Our results indicate that AZD0530 targets both Src and Bcr-Abl kinase activity and reduces the leukaemic maintenance by Bcr-Abl
Numerical Simulation of an EUV Coronal Wave Based on the February 13, 2009 CME Event Observed by STEREO
On 13 February 2009, a coronal wave -- CME -- dimming event was observed in
quadrature by the STEREO spacecraft. We analyze this event using a
three-dimensional, global magnetohydrodynamic (MHD) model for the solar corona.
The numerical simulation is driven and constrained by the observations, and
indicates where magnetic reconnection occurs between the expanding CME core and
surrounding environment. We focus primarily on the lower corona, extending out
to ; this range allows simultaneous comparison with both EUVI and
COR1 data. Our simulation produces a diffuse coronal bright front remarkably
similar to that observed by STEREO/EUVI at 195 \AA. It is made up of \emph{two}
components, and is the result of a combination of both wave and non-wave
mechanisms.
The CME becomes large-scale quite low ( 200 Mm) in the corona. It is not,
however, an inherently large-scale event; rather, the expansion is facilitated
by magnetic reconnection between the expanding CME core and the surrounding
magnetic environment. In support of this, we also find numerous secondary
dimmings, many far from the initial CME source region. Relating such dimmings
to reconnecting field lines within the simulation provides further evidence
that CME expansion leads to the "opening" of coronal field lines on a global
scale. Throughout the CME expansion, the coronal wave maps directly to the CME
footprint.
Our results suggest that the ongoing debate over the "true" nature of diffuse
coronal waves may be mischaracterized. It appears that \emph{both} wave and
non-wave models are required to explain the observations and understand the
complex nature of these events
What is the Nature of EUV Waves? First STEREO 3D Observations and Comparison with Theoretical Models
One of the major discoveries of the Extreme ultraviolet Imaging Telescope
(EIT) on SOHO were intensity enhancements propagating over a large fraction of
the solar surface. The physical origin(s) of the so-called `EIT' waves is still
strongly debated. They are considered to be either wave (primarily fast-mode
MHD waves) or non-wave (pseudo-wave) interpretations. The difficulty in
understanding the nature of EUV waves lies with the limitations of the EIT
observations which have been used almost exclusively for their study. Their
limitations are largely overcome by the SECCHI/EUVI observations on-board the
STEREO mission. The EUVI telescopes provide high cadence, simultaneous
multi-temperature coverage, and two well-separated viewpoints. We present here
the first detailed analysis of an EUV wave observed by the EUVI disk imagers on
December 07, 2007 when the STEREO spacecraft separation was .
Both a small flare and a CME were associated with the wave cadence, and single
temperature and viewpoint coverage. These limitations are largely overcome by
the SECCHI/EUVI observations on-board the STEREO mission. The EUVI telescopes
provide high cadence, simultaneous multi-temperature coverage, and two
well-separated viewpoints. Our findings give significant support for a
fast-mode interpretation of EUV waves and indicate that they are probably
triggered by the rapid expansion of the loops associated with the CME.Comment: Solar Physics, 2009, Special STEREO Issue, in pres
Decoherence of molecular wave packets in an anharmonic potential
The time evolution of anharmonic molecular wave packets is investigated under
the influence of the environment consisting of harmonic oscillators. These
oscillators represent photon or phonon modes and assumed to be in thermal
equilibrium. Our model explicitly incorporates the fact that in the case of a
nonequidistant spectrum the rates of the environment induced transitions are
different for each transition. The nonunitary time evolution is visualized by
the aid of the Wigner function related to the vibrational state of the
molecule. The time scale of decoherence is much shorter than that of
dissipation, and gives rise to states which are mixtures of localized states
along the phase space orbit of the corresponding classical particle. This
behavior is to a large extent independent of the coupling strength, the
temperature of the environment and also of the initial state.Comment: 7 pages, 4 figure
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