3,208 research outputs found
Multiple Uncertainties in Time-Variant Cosmological Particle Data
Though the mediums for visualization are limited, the potential dimensions of a dataset are not. In many areas of scientific study, understanding the correlations between those dimensions and their uncertainties is pivotal to mining useful information from a dataset. Obtaining this insight can necessitate visualizing the many relationships among temporal, spatial, and other dimensionalities of data and its uncertainties. We utilize multiple views for interactive dataset exploration and selection of important features, and we apply those techniques to the unique challenges of cosmological particle datasets. We show how interactivity and incorporation of multiple visualization techniques help overcome the problem of limited visualization dimensions and allow many types of uncertainty to be seen in correlation with other variables
Analyzing and Visualizing Cosmological Simulations with ParaView
The advent of large cosmological sky surveys - ushering in the era of
precision cosmology - has been accompanied by ever larger cosmological
simulations. The analysis of these simulations, which currently encompass tens
of billions of particles and up to trillion particles in the near future, is
often as daunting as carrying out the simulations in the first place.
Therefore, the development of very efficient analysis tools combining
qualitative and quantitative capabilities is a matter of some urgency. In this
paper we introduce new analysis features implemented within ParaView, a
parallel, open-source visualization toolkit, to analyze large N-body
simulations. The new features include particle readers and a very efficient
halo finder which identifies friends-of-friends halos and determines common
halo properties. In combination with many other functionalities already
existing within ParaView, such as histogram routines or interfaces to Python,
this enhanced version enables fast, interactive, and convenient analyses of
large cosmological simulations. In addition, development paths are available
for future extensions.Comment: 9 pages, 8 figure
GPU Accelerated Particle Visualization with Splotch
Splotch is a rendering algorithm for exploration and visual discovery in
particle-based datasets coming from astronomical observations or numerical
simulations. The strengths of the approach are production of high quality
imagery and support for very large-scale datasets through an effective mix of
the OpenMP and MPI parallel programming paradigms. This article reports our
experiences in re-designing Splotch for exploiting emerging HPC architectures
nowadays increasingly populated with GPUs. A performance model is introduced
for data transfers, computations and memory access, to guide our re-factoring
of Splotch. A number of parallelization issues are discussed, in particular
relating to race conditions and workload balancing, towards achieving optimal
performances. Our implementation was accomplished by using the CUDA programming
paradigm. Our strategy is founded on novel schemes achieving optimized data
organisation and classification of particles. We deploy a reference simulation
to present performance results on acceleration gains and scalability. We
finally outline our vision for future work developments including possibilities
for further optimisations and exploitation of emerging technologies.Comment: 25 pages, 9 figures. Astronomy and Computing (2014
Generalized De Sitter Space
This paper deals with some two-parameter solutions to the spherically
symmetric, vacuum Einstein equations which, we argue, are more general than de
Sitter solution. The global structure of one such spacetimes and its extension
to the multiply connected case have also been investigated. By using a
six-dimensional Minkowskian embedding as its maximal extension, we check that
the thermal properties of the considered solution in such an embedding space
are the same as those derived by the usual Euclidean method. The stability of
the generalized de Sitter space containing a black hole has been investigated
as well by introducing perturbations of the Ginsparg-Perry type in first order
approximation. It has been obtained that such a space perdures against the
effects of these perturbations.Comment: 10 pages, RevTex, to appear in Phys. Rev.
GRBs as standard candles: There is no "circularity problem" (and there never was)
The 2002 discovery of the "Amati Relation" of GRB spectra created the
possibility that this and other correlations of GRB phenomenology might be used
to make GRBs into standard candles. One recurring apparent difficulty with this
program has been that some of the primary observational quantities to be fit as
"data" - the isotropic-equivalent prompt energy and the
collimation-corrected "total" prompt energy energy - depend for
their construction on the very cosmological models that they are supposed to
help constrain. This is the so-called "circularity problem" of standard candle
GRBs. This paper is intended to point out that the circularity problem is not
in fact a problem at all, except to the extent that it amounts to a
self-inflicted wound. It arises essentially because of an unfortunate choice of
data variables, such as , which are unnecessarily model-dependent. If,
instead, the empirical correlations of GRB phenomenology which are formulated
in source-variables are {\it mapped to the primitive observational variables}
(such as fluence) and compared to the observations in that space, then all
circularity disappears. I also indicate here a set of procedures for encoding
high-dimensional empirical correlations in a "Gaussian Tube" smeared model that
includes both the correlation and its intrinsic scatter, and how that
source-variable model may easily be mapped to the space of primitive
observables and fashioned into a likelihood. I discuss the projections of such
Gaussian tubes into sub-spaces, which may be used to incorporate data from GRB
events that may lack some element of the data (for example, GRBs without
ascertained jet-break times). In this way, a large set of inhomogeneously
observed GRBs may be assimilated into a single analysis, so long as each
possesses at least two correlated data attributes.Comment: 10 pages, to appear in New Astronom
Scenario of inflationary cosmology from the phenomenological models
Choosing the three phenomenological models of the dynamical cosmological term
, viz., , and
where is the cosmic scale factor, it has been shown by
the method of numerical analysis that the three models are equivalent for the
flat Universe . The evolution plots for dynamical cosmological term
vs. time and also the cosmic scale factor vs. are drawn
here for . A qualitative analysis has been made from the plots which
supports the idea of inflation and hence expanding Universe.Comment: 12 latex pages with 12 figures; Replaced with the revised version;
Accepeted for `J. Non-lin. Frac. Phen. Sci. Engg.
- …