3,000 research outputs found
A model for the formation of the active region corona driven by magnetic flux emergence
We present the first model that couples the formation of the corona of a
solar active region to a model of the emergence of a sunspot pair. This allows
us to study when, where, and why active region loops form, and how they evolve.
We use a 3D radiation MHD simulation of the emergence of an active region
through the upper convection zone and the photosphere as a lower boundary for a
3D MHD coronal model. The latter accounts for the braiding of the magnetic
fieldlines, which induces currents in the corona heating up the plasma. We
synthesize the coronal emission for a direct comparison to observations.
Starting with a basically field-free atmosphere we follow the filling of the
corona with magnetic field and plasma. Numerous individually identifiable hot
coronal loops form, and reach temperatures well above 1 MK with densities
comparable to observations. The footpoints of these loops are found where small
patches of magnetic flux concentrations move into the sunspots. The loop
formation is triggered by an increase of upwards-directed Poynting flux at
their footpoints in the photosphere. In the synthesized EUV emission these
loops develop within a few minutes. The first EUV loop appears as a thin tube,
then rises and expands significantly in the horizontal direction. Later, the
spatially inhomogeneous heat input leads to a fragmented system of multiple
loops or strands in a growing envelope.Comment: 13 pages, 10 figures, accepted to publication in A&
Magnetic Jam in the Corona of the Sun
The outer solar atmosphere, the corona, contains plasma at temperatures of
more than a million K, more than 100 times hotter that solar surface. How this
gas is heated is a fundamental question tightly interwoven with the structure
of the magnetic field in the upper atmosphere. Conducting numerical experiments
based on magnetohydrodynamics we account for both the evolving
three-dimensional structure of the atmosphere and the complex interaction of
magnetic field and plasma. Together this defines the formation and evolution of
coronal loops, the basic building block prominently seen in X-rays and extreme
ultraviolet (EUV) images. The structures seen as coronal loops in the EUV can
evolve quite differently from the magnetic field. While the magnetic field
continuously expands as new magnetic flux emerges through the solar surface,
the plasma gets heated on successively emerging fieldlines creating an EUV loop
that remains roughly at the same place. For each snapshot the EUV images
outline the magnetic field, but in contrast to the traditional view, the
temporal evolution of the magnetic field and the EUV loops can be different.
Through this we show that the thermal and the magnetic evolution in the outer
atmosphere of a cool star has to be treated together, and cannot be simply
separated as done mostly so far.Comment: Final version published online on 27 April 2015, Nature Physics 12
pages and 8 figure
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
Differential Effects of Cyclosporin and Etanercept Treatment on Various Pathologic Parameters in a Murine Model of Irradiation-Induced Mucositis
AbstractBackgroundRadiation therapy is the most prescribed treatment for many oncologic indications. One of its common side effects is mucositis with hallmark apoptosis in the intestinal crypt and diarrhea.ObjectiveWe investigated the potential beneficial effects of etanercept and cyclosporin treatment during radiation exposure. The effects of these drugs on intestinal apoptosis, long-term weight loss, diarrhea severity, and survival were examined.MethodsFor acute observation studies, animals pretreated with phosphate buffer saline (PBS) vehicle, either etanercept, or cyclosporin were challenged with either 1 Gy or 13 Gy irradiation and sacrificed 6 hours later. The animals' small intestines were then harvested for histologic analysis. For chronic survival studies, 14.5 Gy irradiation was applied. Etanercept or cyclosporin treatments were given 15 minutes before the irradiation, followed by daily administration.ResultsAt 6 hours postirradiation the maximum apoptotic index observed in the small intestine was ∼25% for both 1 Gy and 13 Gy irradiation. Etanercept and cyclosporin pretreatment had no effect on the irradiation-induced apoptosis. During chronic observation, the rate of weight loss was similar in all test groups. At 7 days postirradiation, the weight loss in phosphate buffered saline-treated control, etanercept, and cyclosporin groups reached a maximum at 19%, 24%, and 31.8%, respectively. The weight lost in the cyclosporin group was significantly higher than in the control group. Neither treatment reduced the severity of diarrhea, but cyclosporin increased the survival rate. Sixty percent of cyclosporin-treated animals survived compared with 27% in the PBS-treated control group and 47% in the etanercept-treated group. Serum tumor necrosis factor-α levels, a biomarker for both etanercept's mechanism of action and treatment efficacy, was inhibited by etanercept throughout the study, but cyclosporin only showed an inhibitory effect at 48 hours postirradiation.ConclusionsOur study demonstrates that cyclosporin increases the survival rate of irradiated animals without affecting parameters such as intestinal histology, weight loss, and diarrhea severity
Radion Dynamics and Phenomenology in the Linear Dilaton Model
We investigate the properties of the radion in the 5D linear dilaton model
arising from Little String Theory. A Goldberger-Wise type mechanism is used to
stabilise a large interbrane distance, with the dilaton now playing the role of
the stabilising field. We consider the coupled fluctuations of the metric and
dilaton fields and identify the physical scalar modes of the system. The
wavefunctions and masses of the radion and Kaluza-Klein modes are calculated,
giving a radion mass of order the curvature scale. As a result of the direct
coupling between the dilaton and Standard Model fields, the radion couples to
the SM Lagrangian, in addition to the trace of the energy-momentum tensor. The
effect of these additional interaction terms on the radion decay modes is
investigated, with a notable increase in the branching fraction to photons. We
also consider the effects of a non-minimal Higgs coupling to gravity, which
introduces a mixing between the Higgs and radion modes. Finally, we calculate
the production cross section of the radion at the LHC and use the current Higgs
searches to place constraints on the parameter space.Comment: 28 pages, 7 figures; v2: error in radion-gauge boson Feynman rules
corrected, version published in JHE
Silencing of the XAF1 gene by promoter hypermethylation in cancer cells and reactivation to TRAIL-sensitization by IFN-β
BACKGROUND: XIAP-associated factor 1 (XAF1) is a putative tumor suppressor that exerts its proapoptotic effects through both caspase-dependent and – independent means. Loss of XAF1 expression through promoter methylation has been implicated in the process of tumorigenesis in a variety of cancers. In this report, we investigated the role of basal xaf1 promoter methylation in xaf1 expression and assessed the responsiveness of cancer cell lines to XAF1 induction by IFN-β. METHODS: We used the conventional bisulfite DNA modification and sequencing method to determine the methylation status in the CpG sites of xaf1 promoter in glioblastoma (SF539, SF295), neuroblastoma (SK-N-AS) and cervical carcinoma (HeLa) cells. We analysed the status and incidence of basal xaf1 promoter methylation in xaf1 expression in non-treated cells as well as under a short or long exposure to IFN-β. Stable XAF1 glioblastoma knock-down cell lines were established to characterize the direct implication of XAF1 in IFN-β-mediated sensitization to TRAIL-induced cell death. RESULTS: We found a strong variability in xaf1 promoter methylation profile and responsiveness to IFN-β across the four cancer cell lines studied. At the basal level, aberrant promoter methylation was linked to xaf1 gene silencing. After a short exposure, the IFN-β-mediated reactivation of xaf1 gene expression was related to the degree of basal promoter methylation. However, in spite of continued promoter hypermethylation, we find that IFN-β induced a transient xaf1 expression, that in turn, was followed by promoter demethylation upon a prolonged exposure. Importantly, we demonstrated for the first time that IFN-β-mediated reactivation of endogenous XAF1 plays a critical role in TRAIL-induced cell death since XAF1 knock-down cell lines completely lost their IFN-β-mediated TRAIL sensitivity. CONCLUSION: Together, these results suggest that promoter demethylation is not the sole factor determining xaf1 gene induction under IFN-β treatment. Furthermore, our study provides evidence that XAF1 is a crucial interferon-stimulated gene (ISG) mediator of IFN-induced sensitization to TRAIL in cancer
In Vivo Effects of Immunomodulators in a Murine Model of Fluorouracil-Induced Mucositis
AbstractBackgroundFluorouracil (5-FU) is a pyrimidine analogue used as a cancer treatment. Its toxic side effects, including mucositis, are reported to occur in 40% of the treated patients. Because of the inflammatory component of mucositis, we explored the possibility of modulating this condition with an immunomodulatory agent and a tumor necrosis factor-α inhibitor.ObjectiveThe aim of this study was to evaluate the effect of 2 immunosuppressive agents, etanercept and cyclosporine, in a murine model of 5-FU–induced mucositis.MethodsTo study the short-term effects of 5-FU on mucositis, cyclosporine and etanercept were administered to mice after an injection of 5-FU. The animals (n = 8) were euthanized at 6 hours post-challenge. Hematoxylin and eosin–stained histologic sections of the small intestine were examined for signs of apoptosis. To further examine the potential of cyclosporine in the treatment of 5-FU–induced mucositis in a longer duration, the animals (N = 15) were given 2 challenges of 5-FU within 6 hours. All mice were dosed daily until day 9 with either cyclosporine (100 mg/kg) or phosphate-buffered saline (PBS).ResultsSix hours after 5-FU challenge, 25 mg/kg etanercept and 50 mg/kg cyclosporine had no effect on 5-FU–induced apoptosis (P > 0.05). However, 100 mg/kg cyclosporine significantly reduced the cumulative level of apoptosis >41.6% of the intestinal crypt surface (P < 0.05). During long-term observation, all mice began to lose weight at a rate of approximately 0.8 g/day after 5-FU exposure. The rates of weight loss and survival were not affected by cyclosporine treatment. The diarrhea onset began on day 4 with 46.7% of the PBS-treated mice showing signs of diarrhea compared with 53.3% in the cyclosporine group. The diarrhea score for both groups plateaued on day 7, with a cumulative score of 41 for the PBS group and 50 for the cyclosporine group. Cyclosporine treatment did not affect the diarrhea onset day or severity compared with the PBS-treated group (P > 0.05).ConclusionsOur data indicated that etanercept is not a suitable treatment for 5-FU–induced mucositis. Despite decreased apoptosis in the gut, cyclosporine did not affect the severity of the diarrhea or survival. Therefore, we concluded that cyclosporine treatment was only effective in mediating the short-term apoptotic events in the intestines but has no long-term effect on the animals' survival and diarrhea
Momentum Distribution in the Decay B-->J/psi+X
We combine the NRQCD formalism for the inclusive color singlet and octet
production of charmonium states with the parton and the ACCMM model,
respectively, and calculate the momentum distribution in the decay B-->J/psi+X.
Neglecting the kinematics of soft gluon radiation, we find that the motion of
the b quark in the bound state can account, to a large extent, for the observed
spectrum. The parton model gives a satisfactory presentation of the data,
provided that the heavy quark momentum distribution is taken to be soft. To be
explicit, we obtain epsilon_p=O(0.008-0.012) for the parameter of the Peterson
et al. distribution function. The ACCMM model can account for the data more
accurately. The preferred Fermi momentum p_F=O(0.57 GeV) is in good agreement
with recent studies of the heavy quark's kinetic energy.Comment: revised version to be published in Phys. Rev. D; 27 pages, LaTeX, 7
eps figures, uses a4wide.sty, epsfig.sty and amssymb.st
A three-arm randomised controlled trial comparing Gonadotrophin Releasing Hormone (GnRH) agonist long regimen versus GnRH agonist short regimen versus GnRH antagonist regimen in women with a history of poor ovarian response undergoing in vitro fertilisation (IVF) treatment: Poor responders intervention trial (PRINT)
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