The Open Flux Problem Linker, J. A.; Caplan, R. M.; Downs, C. ...
The Astrophysical journal,
10/2017, Letnik:
848, Številka:
1
Journal Article
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The heliospheric magnetic field is of pivotal importance in solar and space physics. The field is rooted in the Sun's photosphere, where it has been observed for many years. Global maps of the solar ...magnetic field based on full-disk magnetograms are commonly used as boundary conditions for coronal and solar wind models. Two primary observational constraints on the models are (1) the open field regions in the model should approximately correspond to coronal holes (CHs) observed in emission and (2) the magnitude of the open magnetic flux in the model should match that inferred from in situ spacecraft measurements. In this study, we calculate both magnetohydrodynamic and potential field source surface solutions using 14 different magnetic maps produced from five different types of observatory magnetograms, for the time period surrounding 2010 July. We have found that for all of the model/map combinations, models that have CH areas close to observations underestimate the interplanetary magnetic flux, or, conversely, for models to match the interplanetary flux, the modeled open field regions are larger than CHs observed in EUV emission. In an alternative approach, we estimate the open magnetic flux entirely from solar observations by combining automatically detected CHs for Carrington rotation 2098 with observatory synoptic magnetic maps. This approach also underestimates the interplanetary magnetic flux. Our results imply that either typical observatory maps underestimate the Sun's magnetic flux, or a significant portion of the open magnetic flux is not rooted in regions that are obviously dark in EUV and X-ray emission.
ABSTRACT We describe a method for the automatic mapping of coronal holes (CHs) using simultaneous multi-instrument EUV imaging data. Synchronized EUV images from STEREO/EUVI A and B 195 and SDO/AIA ...193 are preprocessed, including point-spread function deconvolution and the application of data-derived intensity corrections which account for center-to-limb variations (limb brightening) and inter-instrument intensity normalization. We systematically derive a robust limb-brightening correction that takes advantage of unbiased long-term averages of data and respects the physical nature of the problem. The new preprocessing greatly assists in CH detection, allowing for the use of a simplified variable-connectivity, two-threshold region-growing image segmentation algorithm to obtain consistent detection results. We generate synchronic EUV and CH maps, and show a preliminary analysis of CH evolution. Several data and code products are made available to the community (www.predsci.com/chd): for the period of this study (2010 June 10 to 2014 August 18), we provide synchronic EUV and CH map data at 6 hr cadence, data-derived limb-brightening corrections for STEREO/EUVI A and B 195 and SDO/AIA 193 , and inter-instrument correction factors to equate their intensities. We also provide the CH image segmentation code module (ezseg) implemented in both FORTRAN-OpenMP and GPU-accelerated C-CUDA. A complete implementation of our CH detection pipeline in the form of a ready-to-use MATLAB driver script euv2chm utilizing ezseg is also made available.
We present a simple to use, yet powerful code package called NLSEmagic to numerically integrate the nonlinear Schrödinger equation in one, two, and three dimensions. NLSEmagic is a high-order ...finite-difference code package which utilizes graphic processing unit (GPU) parallel architectures. The codes running on the GPU are many times faster than their serial counterparts, and are much cheaper to run than on standard parallel clusters. The codes are developed with usability and portability in mind, and therefore are written to interface with MATLAB utilizing custom GPU-enabled C codes with the MEX-compiler interface. The packages are freely distributed, including user manuals and set-up files.
Program title: NLSEmagic
Catalogue identifier: AEOJ_v1_0
Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEOJ_v1_0.html
Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland
Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html
No. of lines in distributed program, including test data, etc.: 124453
No. of bytes in distributed program, including test data, etc.: 4728604
Distribution format: tar.gz
Programming language: C, CUDA, MATLAB.
Computer: PC, MAC.
Operating system: Windows, MacOS, Linux.
Has the code been vectorized or parallelized?: Yes.
Number of processors used: Single CPU, number of GPU processors dependent on chosen GPU card (max is currently 3072 cores on GeForce GTX 690).
Supplementary material: Setup guide, Installation guide.
RAM: Highly dependent on dimensionality and grid size. For typical medium–large problem size in three dimensions, 4GB is sufficient.
Keywords: Nonlinear Schröodinger Equation, GPU, high-order finite difference, Bose-Einstien condensates.
Classification: 4.3, 7.7.
Nature of problem:
Integrate solutions of the time-dependent one-, two-, and three-dimensional cubic nonlinear Schrödinger equation.
Solution method:
The integrators utilize a fully-explicit fourth-order Runge–Kutta scheme in time and both second- and fourth-order differencing in space. The integrators are written to run on NVIDIA GPUs and are interfaced with MATLAB including built-in visualization and analysis tools.
Restrictions:
The main restriction for the GPU integrators is the amount of RAM on the GPU as the code is currently only designed for running on a single GPU.
Unusual features:
Ability to visualize real-time simulations through the interaction of MATLAB and the compiled GPU integrators.
Additional comments:
Setup guide and Installation guide provided. Program has a dedicated web site at www.nlsemagic.com.
Running time:
A three-dimensional run with a grid dimension of 87×87×203 for 3360 time steps (100 non-dimensional time units) takes about one and a half minutes on a GeForce GTX 580 GPU card.
Abstract
The so-called regularized Biot–Savart laws (
R
BS
L
s) provide an efficient and flexible method for modeling pre-eruptive magnetic configurations of coronal mass ejections (CMEs) whose ...characteristics are constrained by observational images and magnetic field data. This method allows one to calculate the field of magnetic flux ropes (MFRs) with small circular cross sections and an arbitrary axis shape. The field of the whole configuration is constructed as a superposition of (1) such a flux-rope field and (2) an ambient potential field derived, for example, from an observed magnetogram. The
R
BS
L
kernels are determined from the requirement that the MFR field for a straight cylinder must be exactly force free. For a curved MFR, however, the magnetic forces are generally unbalanced over the whole path of the MFR. To minimize these forces, we apply a modified Gauss–Newton method to find optimal MFR parameters. This is done by iteratively adjusting the MFR axis path and axial current. We then try to relax the resulting optimized configuration in a subsequent line-tied zero-beta magnetohydrodynamic simulation toward a force-free equilibrium. By considering two models of the sigmoidal pre-eruption configuration for the 2009 February 13 CME, we demonstrate how this approach works and what it is capable of. We show, in particular, that the building blocks of the core magnetic structure described by these models match morphological features typically observed in such types of configurations. Our method will be useful for both the modeling of particular eruptive events and theoretical studies of idealized pre-eruptive MFR configurations.
We explore the performance and advantages/disadvantages of using unconditionally stable explicit super time-stepping (STS) algorithms versus implicit schemes with Krylov solvers for integrating ...parabolic operators in thermodynamic MHD models of the solar corona. Specifically, we compare the second-order Runge-Kutta Legendre (RKL2) STS method with the implicit backward Euler scheme computed using the preconditioned conjugate gradient (PCG) solver with both a point-Jacobi and a non-overlapping domain decomposition ILU0 preconditioner. The algorithms are used to integrate anisotropic Spitzer thermal conduction and artificial kinematic viscosity at time-steps much larger than classic explicit stability criteria allow. A key component of the comparison is the use of an established MHD model (MAS) to compute a real-world simulation on a large HPC cluster. Special attention is placed on the parallel scaling of the algorithms. It is shown that, for a specific problem and model, the RKL2 method is comparable or surpasses the implicit method with PCG solvers in performance and scaling, but suffers from some accuracy limitations. These limitations, and the applicability of RKL methods are briefly discussed.
GPU accelerators have had a notable impact on high-performance computing across many disciplines. They provide high performance with low cost/power, and therefore have become a primary compute ...resource on many of the largest supercomputers. Here, we implement multi-GPU acceleration into our Solar MHD code (MAS) using OpenACC in a fully portable, single-source manner. Our preliminary implementation is focused on MAS running in a reduced physics "zero-beta" mode. While valuable on its own, our main goal is to pave the way for a full physics, thermodynamic MHD implementation. We describe the OpenACC implementation methodology and challenges. "Time-to-solution" performance results of a production-level flux rope eruption simulation on multi-CPU and multi-GPU systems are shown. We find that the GPU-accelerated MAS code has the ability to run "zero-beta" simulations on a single multi-GPU server at speeds previously requiring multiple CPU server-nodes of a supercomputer.
In order to elucidate design principles for biocompatible materials that can be created by in situ transformation from self-assembling oligopeptides, we investigate a class of oligopeptides that can ...self-assemble in salt solutions to form three-dimensional matrices. This class of peptides possesses a repeated sequence of amino acid residues with the type: hydrophobic/negatively-charged/hydrophobic/positively-charged. We systematically vary three chief aspects of this sequence type: (1) the hydrophobic side chains; (2) the charged side-chains; and (3) the number of repeats. Employing a rheometric assay to judge matrix formation, we determine the critical concentration of NaCl salt solution required to drive transformation from viscous state to gel state. We find that increasing side-chain hydrophobicity decreases the critical salt concentration in accord with our previous validation of DLVO theory for explaining this self-assembly phenomenon Caplan et al. (Biomacromolecules 1 (2000) 627). Further, we find that increasing the number of repeats yields a biphasic dependence—first decreasing, then increasing, the critical salt concentration. We believe that this result is likely due to an unequal competition between a greater hydrophobic (favorable) effect and a greater entropic (unfavorable) effect as the peptide length is increased. Finally, we find that we can use this understanding to rationally alter the charged side-chains to create a self-assembling oligopeptide sequence that at pH 7 remains viscous in the absence of salt but gels in the presence of physiological salt concentrations, a highly useful property for technological applications.
Medical complications after stroke Kumar, Sandeep, MD; Selim, Magdy H, MD; Caplan, Louis R, MD
Lancet neurology,
2010, 2010-Jan, 2010-01-00, 20100101, Letnik:
9, Številka:
1
Journal Article
Recenzirano
Summary Patients who have had a stroke are susceptible to many complications. These individuals commonly have comorbidities such as hypertension, diabetes, heart disease, or other ailments that ...increase the risks of systemic medical complications during stroke recovery. However, several complications can arise as a direct consequence of the brain injury itself, from the ensuing disabilities or immobility, or from stroke-related treatments. These events have a substantial effect on the final outcome of patients with stroke and often impede neurological recovery. Cardiac complications, pneumonias, venous thromboembolism, fever, pain, dysphagia, incontinence, and depression are particularly common after a stroke and usually require specific interventions for their prevention and treatment. However, there are few data to guide the management of these complications. Systematic investigations are therefore needed to further study the effects of medical complications on stroke recovery and to improve interventions for the prevention and treatment of these events.
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