7,056 research outputs found
Spectropolarimetry with CRISP at the Swedish 1-m Solar Telescope
CRISP (Crisp Imaging Spectro-polarimeter), the new spectropolarimeter at the
Swedish 1-m Solar Telescope, opens a new perspective in solar polarimetry. With
better spatial resolution (0.13") than Hinode in the Fe I 6302 A line and
similar polarimetric sensitivity reached through postprocessing, CRISP
complements the SP spectropolarimeter onboard Hinode. We present some of the
data which we obtained in our June 2008 campaign and preliminary results from
LTE inversions of a pore containing umbral dots.Comment: To appear in "Magnetic Coupling between the Interior and the
Atmosphere of the Sun", eds. S.S. Hasan and R.J. Rutten, Astrophysics and
Space Science Proceedings, Springer-Verlag, Heidelberg, Berlin, 200
Cosmological Adaptive Mesh Refinement
We describe a grid-based numerical method for 3D hydrodynamic cosmological
simulations which is adaptive in space and time and combines the best features
of higher order--accurate Godunov schemes for Eulerian hydrodynamics with
adaptive particle--mesh methods for collisionless particles. The basis for our
method is the structured adaptive mesh refinement (AMR) algorithm of Berger &
Collela (1989), which we have extended to cosmological hydro + N-body
simulations. The resulting multiscale hybrid method is a powerful alternative
to particle-based methods in current use. The choices we have made in
constructing this algorithm are discussed, and its performance on the Zeldovich
pancake test problem is given. We present a sample application of our method to
the problem of first structure formation. We have achieved a spatial dynamic
range in a 3D multispecies gas + dark matter
calculation, which is sufficient to resolve the formation of primordial
protostellar cloud cores starting from linear matter fluctuations in an
expanding FRW universe.Comment: 14 pages, 3 figures (incl. one large color PS) to appear in
"Numerical Astrophysics 1998", eds. S. Miyama & K. Tomisaka, Tokyo, March
10-13, 199
On the benefits of tasking with OpenMP
Tasking promises a model to program parallel applications that provides intuitive semantics. In the case of tasks with dependences, it also promises better load balancing by removing global synchronizations (barriers), and potential for improved locality. Still, the adoption of tasking in production HPC codes has been slow. Despite OpenMP supporting tasks, most codes rely on worksharing-loop constructs alongside MPI primitives. This paper provides insights on the benefits of tasking over the worksharing-loop model by reporting on the experience of taskifying an adaptive mesh refinement proxy application: miniAMR. The performance evaluation shows the taskified implementation being 15–30% faster than the loop-parallel one for certain thread counts across four systems, three architectures and four compilers thanks to better load balancing and system utilization. Dynamic scheduling of loops narrows the gap but still falls short of tasking due to serial sections between loops. Locality improvements are incidental due to the lack of locality-aware scheduling. Overall, the introduction of asynchrony with tasking lives up to its promises, provided that programmers parallelize beyond individual loops and across application phases.Peer ReviewedPostprint (author's final draft
An open and parallel multiresolution framework using block-based adaptive grids
A numerical approach for solving evolutionary partial differential equations
in two and three space dimensions on block-based adaptive grids is presented.
The numerical discretization is based on high-order, central finite-differences
and explicit time integration. Grid refinement and coarsening are triggered by
multiresolution analysis, i.e. thresholding of wavelet coefficients, which
allow controlling the precision of the adaptive approximation of the solution
with respect to uniform grid computations. The implementation of the scheme is
fully parallel using MPI with a hybrid data structure. Load balancing relies on
space filling curves techniques. Validation tests for 2D advection equations
allow to assess the precision and performance of the developed code.
Computations of the compressible Navier-Stokes equations for a temporally
developing 2D mixing layer illustrate the properties of the code for nonlinear
multi-scale problems. The code is open source
Put a tiger in your tank: the polyclad flatworm Maritigrella crozieri as a proposed model for evo-devo
Polyclad flatworms are an early branching clade within the rhabditophoran Platyhelminthes. They provide an interesting system with which to explore the evolution of development within Platyhelminthes and amongst Spiralia (Lophotrochozoa). Unlike most other flatworms, polyclads undergo spiral cleavage (similar to that seen in some other spiralian taxa), they are the only free-living flatworms where development via a larval stage occurs, and they are the only flatworms in which embryos can be reared outside of their protective egg case, enabling embryonic manipulations. Past work has focused on comparing early cleavage patterns and larval anatomy between polyclads and other spiralians. We have selected Maritigrella crozieri, the tiger flatworm, as a suitable polyclad species for developmental studies, because it is abundant and large in size compared to other species. These characteristics have facilitated the generation of a transcriptome from embryonic and larval material and are enabling us to develop methods for gene expression analysis and immunofluorescence techniques. Here we give an overview of M. crozieri and its development, we highlight the advantages and current limitations of this animal as a potential evo-devo model and discuss current lines of research
Gravitational Collapse and Fragmentation in Molecular Clouds with Adaptive Mesh Refinement
We describe a powerful methodology for numerical solution of 3-D
self-gravitational hydrodynamics problems with extremely high resolution. Our
method utilizes the technique of local adaptive mesh refinement (AMR),
employing multiple grids at multiple levels of resolution. These grids are
automatically and dynamically added and removed as necessary to maintain
adequate resolution. This technology allows for the solution of problems in a
manner that is both more efficient and more versatile than other fixed and
variable resolution methods. The application of AMR to simulate the collapse
and fragmentation of a molecular cloud, a key step in star formation, is
discussed. Such simulations involve many orders of magnitude of variation in
length scale as fragments form. In this paper we briefly describe the
methodology and present an illustrative application for nonisothermal cloud
collapse. We describe the numerical Jeans condition, a criterion for stability
of self-gravitational hydrodynamics problems. We show the first well-resolved
nonisothermal evolutionary sequence beginning with a perturbed dense molecular
cloud core that leads to the formation of a binary system consisting of
protostellar cores surrounded by distinct protostellar disks. The scale of the
disks, of order 100 AU, is consistent with observations of gaseous disks
surrounding single T-Tauri stars and debris disks surrounding systems such as
Pictoris.Comment: 10 pages, 6 figures (color postscript). To appear in the proceedings
of Numerical Astrophysics 1998, Tokyo, March 10-13, 199
Helicity at Photospheric and Chromospheric Heights
In the solar atmosphere the twist parameter has the same sign as
magnetic helicity. It has been observed using photospheric vector magnetograms
that negative/positive helicity is dominant in the northern/southern hemisphere
of the Sun. Chromospheric features show dextral/sinistral dominance in the
northern/southern hemisphere and sigmoids observed in X-rays also have a
dominant sense of reverse-S/forward-S in the northern/southern hemisphere. It
is of interest whether individual features have one-to-one correspondence in
terms of helicity at different atmospheric heights. We use UBF \Halpha images
from the Dunn Solar Telescope (DST) and other \Halpha data from Udaipur Solar
Observatory and Big Bear Solar Observatory. Near-simultaneous vector
magnetograms from the DST are used to establish one-to-one correspondence of
helicity at photospheric and chromospheric heights. We plan to extend this
investigation with more data including coronal intensities.Comment: 5 pages, 1 figure, 1 table To appear in "Magnetic Coupling between
the Interior and the Atmosphere of the Sun", eds. S.S. Hasan and R.J. Rutten,
Astrophysics and Space Science Proceedings, Springer-Verlag, Heidelberg,
Berlin, 200
Multiple-length-scale elastic instability mimics parametric resonance of nonlinear oscillators
Spatially confined rigid membranes reorganize their morphology in response to
the imposed constraints. A crumpled elastic sheet presents a complex pattern of
random folds focusing the deformation energy while compressing a membrane
resting on a soft foundation creates a regular pattern of sinusoidal wrinkles
with a broad distribution of energy. Here, we study the energy distribution for
highly confined membranes and show the emergence of a new morphological
instability triggered by a period-doubling bifurcation. A periodic
self-organized focalization of the deformation energy is observed provided an
up-down symmetry breaking, induced by the intrinsic nonlinearity of the
elasticity equations, occurs. The physical model, exhibiting an analogy with
parametric resonance in nonlinear oscillator, is a new theoretical toolkit to
understand the morphology of various confined systems, such as coated materials
or living tissues, e.g., wrinkled skin, internal structure of lungs, internal
elastica of an artery, brain convolutions or formation of fingerprints.
Moreover, it opens the way to new kind of microfabrication design of
multiperiodic or chaotic (aperiodic) surface topography via self-organization.Comment: Submitted for publicatio
Penile metastasis from primary transitional cell carcinoma of the renal pelvis: first manifestation of systemic spread
BACKGROUND: Almost one-third of all penile metastases are detected at the same time as a primary tumor, whereas the remaining two-thirds are detected a mean of 18 months after the discovery of the primary tumor. Cutaneous metastasis of transitional cell carcinoma (TCC) is extremely rare and generally accepted as the late manifestation of a systemic spread. CASE PRESENTATION: We report the first case of simultaneous penile and lung metastases from a primary TCC of the renal pelvis in a 76-year-old man, that occurred 8 years after a left nephroureterectomy. CONCLUSIONS: This case report underscores the importance of physical examinations of the skin of patients who undergo surgical procedures for TCC from bladder as well as from the upper urinary tract, including those seemingly without metastatic disease, because of the possibility of skin and penile metastatic spread
The course of mental health problems in children presenting with abdominal pain in general practice
Objective. To investigate the course of mental health problems in children presenting to general practice with abdominal pain and to evaluate the extent to which abdominal pain characteristics during follow-up predict the presence of mental health problems at 12 months' follow-up. Design. A prospective cohort study with one-year follow-up. Setting. 53 general practices in the Netherlands, between May 2004 and March 2006. Subjects. 281 children aged 4-17 years. Main outcome measures. The presence of a depressive problem, an anxiety problem, and multiple non-specific somatic symptoms at follow-up and odds ratios of duration, frequency, and severity of abdominal pain with these mental health problems at follow-up. Results. A depressive problem persisted in 24/74 children (32.9%; 95% CI 22.3-44.9%), an anxiety problem in 13/43 (30.2%; 95% CI 17.2-46.1%) and the presence of multiple non-specific somatic symptoms in 75/170 children (44.1%; 95% CI 36.7-51.6%). None of the abdominal pain characteristics predicted a depressive or an anxiety problem at 12 months' follow-up. More moments of moderate to severe abdominal pain predicted the presence of multiple nonspecific somatic symptoms at follow-up. Conclusions. In one-third of the children presenting to general practice for abdominal pain, anxiety and depressive problems persist during one year of follow-up. Characteristics of the abdominal pain during the follow-up period do not predict anxiety or depressive problems after one-year follow-up. We recommend following over time children seen in primary care with abdominal pain
- …