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B. R. Schlei

Publications and source records attributed to B. R. Schlei.

At least 19 recordsLinked to original sources
arXiv2016

STEVE - Space-Time-Enclosing Volume Extraction

The novel STEVE (i.e., Space-Time-Enclosing Volume Extraction) algorithm is described here for the very first time. It generates iso-valued hypersurfaces that may be implicitly contained in four-dimensional (4D) data sets, such as temporal sequences of three-dimensional images from time-varying computed tomography. Any final hypersurface that will be generated by STEVE is guaranteed to be free from accidental rifts, i.e., it always fully encloses a region in the 4D space under consideration. Furthermore, the information of the interior/exterior of the enclosed regions is propagated to each one of the tetrahedrons, which are embedded into 4D and which in their union represent the final, iso-valued hypersurface(s). STEVE is usually executed in a purely data-driven mode, and it uses lesser computational resources than other techniques that also generate simplex-based manifolds of codimension 1.

cs.CG↗
arXiv2015

GPU Programming - Speeding Up the 3D Surface Generator VESTA

The novel "Volume-Enclosing Surface exTraction Algorithm" (VESTA) generates triangular isosurfaces from computed tomography volumetric images and/or three-dimensional (3D) simulation data. Here, we present various benchmarks for GPU-based code implementations of both VESTA and the current state-of-the-art Marching Cubes Algorithm (MCA). One major result of this study is that VESTA runs significantly faster than the MCA.

cs.GR↗
arXiv2012

Volume-Enclosing Surface Extraction

In this paper we present a new method, which allows for the construction of triangular isosurfaces from three-dimensional data sets, such as 3D image data and/or numerical simulation data that are based on regularly shaped, cubic lattices. This novel volume-enclosing surface extraction technique, which has been named VESTA, can produce up to six different results due to the nature of the discretized 3D space under consideration. VESTA is neither template-based nor it is necessarily required to operate on 2x2x2 voxel cell neighborhoods only. The surface tiles are determined with a very fast and robust construction technique while potential ambiguities are detected and resolved. Here, we provide an in-depth comparison between VESTA and various versions of the well-known and very popular Marching Cubes algorithm for the very first time. In an application section, we demonstrate the extraction of VESTA isosurfaces for various data sets ranging from computer tomographic scan data to simulation data of relativistic hydrodynamic fireball expansions.

cs.CG↗
arXiv2011

Speeding Up the 3D Surface Generator VESTA

The very recent volume-enclosing surface extraction algorithm, VESTA, is revisited. VESTA is used to determine implicit surfaces that are potentially contained in 3D data sets, such as 3D image data and/or 3D simulation data. VESTA surfaces are non-degenerate, i.e., they always enclose a volume that is larger than zero and they never self-intersect, prior to a further processing, e.g., towards isosurfaces. In addition to its ability to deal with local cell ambiguities consistently - and thereby avoiding the accidental generation of holes in the final surfaces - the information of the interior and/or exterior of enclosed 3D volumes is propagated correctly to each of the final surface tiles. Particular emphasis is put here on the speed up of the original formulation of VESTA, while applying the algorithm to 2x2x2 voxel neighborhoods.

cs.CG↗
arXiv2010

A New Computational Framework For 2D Shape-Enclosing Contours

In this paper, a new framework for one-dimensional contour extraction from discrete two-dimensional data sets is presented. Contour extraction is important in many scientific fields such as digital image processing, computer vision, pattern recognition, etc. This novel framework includes (but is not limited to) algorithms for dilated contour extraction, contour displacement, shape skeleton extraction, contour continuation, shape feature based contour refinement and contour simplification. Many of the new techniques depend strongly on the application of a Delaunay tessellation. In order to demonstrate the versatility of this novel toolbox approach, the contour extraction techniques presented here are applied to scientific problems in material science, biology and heavy ion physics.

cs.CV↗
arXiv2010

Matching Stages of Heavy Ion Collision Models

Heavy ion reactions and other collective dynamical processes are frequently described by different theoretical approaches for the different stages of the process, like initial equilibration stage, intermediate locally equilibrated fluid dynamical stage and final freeze-out stage. For the last stage the best known is the Cooper-Frye description used to generate the phase space distribution of emitted, non-interacting, particles from a fluid dynamical expansion/explosion, assuming a final ideal gas distribution, or (less frequently) an out of equilibrium distribution. In this work we do not want to replace the Cooper-Frye description, rather clarify the ways how to use it and how to choose the parameters of the distribution, eventually how to choose the form of the phase space distribution used in the Cooper-Frye formula. Moreover, the Cooper-Frye formula is used in connection with the freeze-out problem, while the discussion of transition between different stages of the collision is applicable to other transitions also. More recently hadronization and molecular dynamics models are matched to the end of a fluid dynamical stage to describe hadronization and freeze-out. The stages of the model description can be matched to each other on spacetime hypersurfaces (just like through the frequently used freeze-out hypersurface). This work presents a generalized description of how to match the stages of the description of a reaction to each other, extending the methodology used at freeze-out, in simple covariant form which is easily applicable in its simplest version for most applications.

nucl-th↗
arXiv2004

Phase Transitions in High Energy Heavy-Ion Collisions

Modelling Quark-Gluon Plasma formation and decay in high energy heavy ion reactions is presented in a framework of a multi-module setup. The collective features, governing the equlibrated fluid dynamical stages of the model are emphasized. Flow effects formed from the initial conditions are discussed. Particular attention is given to the improvement of the final hadronization and freeze-out part of the reaction which has strong effects on the observables.

hep-ph↗
arXiv2000

Geometric Morphology of Granular Materials

We present a new method to transform the spectral pixel information of a micrograph into an affine geometric description, which allows us to analyze the morphology of granular materials. We use spectral and pulse-coupled neural network based segmentation techniques to generate blobs, and a newly developed algorithm to extract dilated contours. A constrained Delaunay tesselation of the contour points results in a triangular mesh. This mesh is the basic ingredient of the Chodal Axis Transform, which provides a morphological decomposition of shapes. Such decomposition allows for grain separation and the efficient computation of the statistical features of granular materials.

cs.CV↗
arXiv1999

The QGP-Stall or Not ?

In 1996, D.H. Rischke and M. Gyulassy proposed to use the time-delay signal in Bose-Einstein correlations (BEC) as a signature for the possible formation of a quark-gluon plasma (QGP) in relativistic heavy-ion collisions. In particular, they suggested to measure the ratio of the transversal interferometry radii, $R_{out}/R_{side}$, which can be obtained by fitting experimental BEC data with a parametrization introduced by G. Bertsch et al. in 1988. The transverse radius parameter $R_{out}$ has compared to the transverse radius parameter $R_{side}$ an additional temporal dependence which should be sensitive to a prolonged lifetime of a fireball, in case a QGP was formed in a relativistic heavy-ion collision. This latter phenomenon is known under the term ``QGP stall''. In the following, I shall explain why I believe that the time-delay signal in Bose-Einstein correlations is not a good signature for the possible formation of a QGP.

nucl-th↗
arXiv1999

Is the Time-Delay Signal in Bose-Einstein Correlations a Signature for the Quark-Gluon Plasma at RHIC ?

In 1996, D.H. Rischke and M. Gyulassy proposed to use the time-delay signal in Bose-Einstein correlations (BEC) as a signature for the possible formation of a quark-gluon plasma (QGP) in relativistic heavy-ion collisions. In particular, they suggested to measure the ratio of the transversal interferometry radii, $R_{out}/R_{side}$, which can be obtained by fitting experimental BEC data with a parametrization introduced by G. Bertsch et al. in 1988. The transverse radius parameter $R_{out}$ has compared to the transverse radius parameter $R_{side}$ an additional temporal dependence which should be sensitive to a prolonged lifetime of a fireball, in case a QGP was formed in a relativistic heavy-ion collision. In my presentation, I am going to revisit the above made considerations by addressing various possible scenarios for hadron spectra (single and double inclusives) for Pb+Pb collisions at CERN/SPS beam energies and for Au+Au collisions at BNL/RHIC beam energies, respectively, within a relativistic {\it true} hydrodynamic framework (i.e., HYLANDER-C). I claim, that the time-delay signal in Bose-Einstein correlations {\it is not} a signature for the possible formation of a QGP, and I am going to explain why this is the case.

nucl-th↗
arXiv1998

Bose-Einstein Correlations and the Equation of State of Nuclear Matter

Within a relativistic hydrodynamic framework, we use four different equations of state of nuclear matter to compare to experimental spectra from CERN/SPS experiments NA44 and NA49. Freeze-out hypersurfaces and Bose-Einstein correlation functions for identical pion pairs are discussed. We find that two-pion Bose-Einstein interferometry measures the relationship between the temperature and the energy density in the equation of state during the late hadronic stage of the fireball expansion. Little sensitivity of the light-hadron data to a quark-gluon plasma phase-transition is seen.

nucl-th↗
arXiv1998

Bose-Einstein Correlations and the Equation of State of Nuclear Matter in Relativistic Heavy-Ion Collisions

Experimental spectra of the CERN/SPS experiments NA44 and NA49 are fitted while using four different equations of state of nuclear matter within a relativistic hydrodynamic framework. For the freeze-out temperatures, $T_f = 139$ MeV and $T_f = 116$ MeV, respectively, the corresponding freeze-out hypersurfaces and Bose-Einstein correlation functions for identical pion pairs are discussed. It is concluded, that the Bose-Einstein interferometry measures the relationship between the temperature and the energy density in the equation of state of nuclear matter at the late hadronic stage of the fireball expansion. It is necessary, to use the detailed detector acceptances in the calculations for the Bose-Einstein correlations.

nucl-th↗
arXiv1998

Various Models for Pion Probability Distributions from Heavy-Ion Collisions

Various models for pion multiplicity distributions produced in relativistic heavy ion collisions are discussed. The models include a relativistic hydrodynamic model, a thermodynamic description, an emitting source pion laser model, and a description which generates a negative binomial description. The approach developed can be used to discuss other cases which will be mentioned. The pion probability distributions for these various cases are compared. Comparison of the pion laser model and Bose-Einstein condensation in a laser trap and with the thermal model are made. The thermal model and hydrodynamic model are also used to illustrate why the number of pions never diverges and why the Bose-Einstein correction effects are relatively small. The pion emission strength $η$ of a Poisson emitter and a critical density $η_c$ are connected in a thermal model by $η/n_c = e^{-m/T} < 1$, and this fact reduces any Bose-Einstein correction effects in the number and number fluctuation of pions. Fluctuations can be much larger than Poisson in the pion laser model and for a negative binomial description. The clan representation of the negative binomial distribution due to Van Hove and Giovannini is discussed using the present description. Applications to CERN/NA44 and CERN/NA49 data are discussed in terms of the relativistic hydrodynamic model.

nucl-th↗
arXiv1998

Predictions for sqrt{s} = 200 A*GeV Au+Au Collisions from Relativistic Hydrodynamics

The relativistic hydrodynamical model HYLANDER-C is used to give estimates for single inclusive particle momentum spectra in $\sqrt{s}$ = 200 $GeV/nucleon$ Au+Au collisions that will be investigated experimentally in the near future. The predictions are based on initial conditions that the initial fireball has a longitudinal extension of 1.6 $fm$ and an initial energy density of 30.8 $GeV/fm^3$ as obtained from a cascade model. For the collision energy considered here, different stopping scenarios are explored for the first time. Our calculations give particle yields of the order of 10,000 to 20,000 charged particles per event.

nucl-th↗
arXiv1997

Relativistic flows on a spacetime lattice

The relativistic extension of non-relativistic hydrodynamics suffers from notorious difficulties. In non-relativistic hydrodynamics where difficulties also abound, it has proved a useful supplement to study lattice models which can imitate viscous fluid flow. In this paper we construct a relativistic spacetime lattice and construct a dynamics of points, thus a relativistic cellular automaton over it, to model relativistic fluid flow. A simple example is also explicitly studied, and some numerical results with figures are shown in the last section.

physics.flu-dyn↗
arXiv1997

The Equation of State of Nuclear Matter in Heavy Ion Collisions at CERN-SPS Energies from the Viewpoint of Relativistic Hydrodynamics

We present refits of single inclusive cross section data of mesons and baryons for central 158 $AGeV$ Pb+Pb collisions measured by the NA44 and NA49 Collaborations. In the theoretical approach we use the relativistic hydrodynamical code HYLANDER-C. We investigate several equations of state in their capability to describe the measured single inclusive momentum distributions. Based on the obtained fits we present results of the calculated Bose-Einstein correlation functions of identical pion pairs and discuss their features in comparison to measurements.

nucl-th↗
arXiv1997

On the Equation of State of Nuclear Matter in 158A GeV Pb+Pb Collisions

Within a hydrodynamical approach we investigate the sensitivity of single inclusive momentum spectra of hadrons in 158A GeV Pb+Pb collisions to three different equations of state of nuclear matter. Two of the equations of state are based on lattice QCD results and include a phase transition to a quark-gluon plasma. The third equation of state has been extracted from the microscopic transport code RQMD under the assumption of complete local thermalization. All three equations of state provide reasonable fits to data taken by the NA44 and NA49 Collaborations. The initial conditions before the evolution of the fireballs and the space-time evolution pictures differ dramatically for the three equations of state when the same freeze-out temperature is used in all calculations. However, the softest of the equations of state results in transverse mass spectra that are too steep in the central rapidity region. We conclude that the transverse particle momenta are determined by the effective softness of the equation of state during the fireball expansion.

nucl-th↗