2,507 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
Advanced Television and Signal Processing Program
Contains an introduction and reports on two research projects.Advanced Television Research Progra
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
Genetic Testing and Its Clinical Application in Prostate Cancer Management: Consensus Statements from the Hong Kong Urological Association and Hong Kong Society of Uro-Oncology
BackgroundIn recent years, indications for genetic testing in prostate cancer (PC) have expanded from patients with a family history of prostate and/or related cancers to those with advanced castration-resistant disease, and even to early PC patients for determination of the appropriateness of active surveillance. The current consensus aims to provide guidance to urologists, oncologists and pathologists working with Asian PC patients on who and what to test for in selected populations.MethodsA joint consensus panel from the Hong Kong Urological Association and Hong Kong Society of Uro-Oncology was convened over a series of 5 physical and virtual meetings. A background literature search on genetic testing in PC was performed in PubMed, ClinicalKey, EBSCOHost, Ovid and ProQuest, and three working subgroups were formed to review and present the relevant evidence. Meeting agendas adopted a modified Delphi approach to ensure that discussions proceed in a structured, iterative and balanced manner, which was followed by an anonymous voting on candidate statements. Of 5 available answer options, a consensus statement was accepted if â„ 75% of the panelists chose âAccept Completelyâ (Option A) or âAccept with Some Reservationâ (Option B).ResultsThe consensus was structured into three parts: indications for testing, testing methods, and therapeutic implications. A list of 35 candidate statements were developed, of which 31 were accepted. The statements addressed questions on the application of PC genetic testing data and guidelines to Asian patients, including patient selection for germline testing, selection of gene panel and tissue sample, provision of genetic counseling, and use of novel systemic treatments in metastatic castration-resistant PC patients.ConclusionThis consensus provides guidance to urologists, oncologists and pathologists working with Asian patients on indications for genetic testing, testing methods and technical considerations, and associated therapeutic implications
Integrative analyses identify modulators of response to neoadjuvant aromatase inhibitors in patients with early breast cancer
Introduction
Aromatase inhibitors (AIs) are a vital component of estrogen receptor positive (ER+) breast cancer treatment. De novo and acquired resistance, however, is common. The aims of this study were to relate patterns of copy number aberrations to molecular and proliferative response to AIs, to study differences in the patterns of copy number aberrations between breast cancer samples pre- and post-AI neoadjuvant therapy, and to identify putative biomarkers for resistance to neoadjuvant AI therapy using an integrative analysis approach.
Methods
Samples from 84 patients derived from two neoadjuvant AI therapy trials were subjected to copy number profiling by microarray-based comparative genomic hybridisation (aCGH, nâ=â84), gene expression profiling (nâ=â47), matched pre- and post-AI aCGH (nâ=â19 pairs) and Ki67-based AI-response analysis (nâ=â39).
Results
Integrative analysis of these datasets identified a set of nine genes that, when amplified, were associated with a poor response to AIs, and were significantly overexpressed when amplified, including CHKA, LRP5 and SAPS3. Functional validation in vitro, using cell lines with and without amplification of these genes (SUM44, MDA-MB134-VI, T47D and MCF7) and a model of acquired AI-resistance (MCF7-LTED) identified CHKA as a gene that when amplified modulates estrogen receptor (ER)-driven proliferation, ER/estrogen response element (ERE) transactivation, expression of ER-regulated genes and phosphorylation of V-AKT murine thymoma viral oncogene homolog 1 (AKT1).
Conclusions
These data provide a rationale for investigation of the role of CHKA in further models of de novo and acquired resistance to AIs, and provide proof of concept that integrative genomic analyses can identify biologically relevant modulators of AI response
Advanced Television and Signal Processing Program
Contains an introduction and reports on fifteen research projects.Advanced Television Research ProgramAdams-Russell Electronics, Inc.National Science Foundation Fellowship Grant MIP 87-14969National Science Foundation FellowshipU.S. Navy - Office of Naval Research Grant N00014-89-J-1489U.S. Air Force - Electronic Systems Division Contract F1 9628-89-K-004
Topological Defects and CMB anisotropies : Are the predictions reliable ?
We consider a network of topological defects which can partly decay into
neutrinos, photons, baryons, or Cold Dark Matter. We find that the degree-scale
amplitude of the cosmic microwave background (CMB) anisotropies as well as the
shape of the matter power spectrum can be considerably modified when such a
decay is taken into account. We conclude that present predictions concerning
structure formation by defects might be unreliable.Comment: 14 pages, accepted for publication in PR
Characterizing genomic alterations in cancer by complementary functional associations.
Systematic efforts to sequence the cancer genome have identified large numbers of mutations and copy number alterations in human cancers. However, elucidating the functional consequences of these variants, and their interactions to drive or maintain oncogenic states, remains a challenge in cancer research. We developed REVEALER, a computational method that identifies combinations of mutually exclusive genomic alterations correlated with functional phenotypes, such as the activation or gene dependency of oncogenic pathways or sensitivity to a drug treatment. We used REVEALER to uncover complementary genomic alterations associated with the transcriptional activation of ÎČ-catenin and NRF2, MEK-inhibitor sensitivity, and KRAS dependency. REVEALER successfully identified both known and new associations, demonstrating the power of combining functional profiles with extensive characterization of genomic alterations in cancer genomes
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