928 research outputs found
ASTEC -- the Aarhus STellar Evolution Code
The Aarhus code is the result of a long development, starting in 1974, and
still ongoing. A novel feature is the integration of the computation of
adiabatic oscillations for specified models as part of the code. It offers
substantial flexibility in terms of microphysics and has been carefully tested
for the computation of solar models. However, considerable development is still
required in the treatment of nuclear reactions, diffusion and convective
mixing.Comment: Astrophys. Space Sci, in the pres
Co-evolution of RDF Datasets
Linking Data initiatives have fostered the publication of large number of RDF
datasets in the Linked Open Data (LOD) cloud, as well as the development of
query processing infrastructures to access these data in a federated fashion.
However, different experimental studies have shown that availability of LOD
datasets cannot be always ensured, being RDF data replication required for
envisioning reliable federated query frameworks. Albeit enhancing data
availability, RDF data replication requires synchronization and conflict
resolution when replicas and source datasets are allowed to change data over
time, i.e., co-evolution management needs to be provided to ensure consistency.
In this paper, we tackle the problem of RDF data co-evolution and devise an
approach for conflict resolution during co-evolution of RDF datasets. Our
proposed approach is property-oriented and allows for exploiting semantics
about RDF properties during co-evolution management. The quality of our
approach is empirically evaluated in different scenarios on the DBpedia-live
dataset. Experimental results suggest that proposed proposed techniques have a
positive impact on the quality of data in source datasets and replicas.Comment: 18 pages, 4 figures, Accepted in ICWE, 201
Simulating 0+1 Dimensional Quantum Gravity on Quantum Computers: Mini-Superspace Quantum Cosmology and the World Line Approach in Quantum Field Theory
Quantum computers are a promising candidate to radically expand computational
science through increased computing power and more effective algorithms. In
particular quantum computing could have a tremendous impact in the field of
quantum cosmology. The goal of quantum cosmology is to describe the evolution
of the Universe through the Wheeler-DeWitt equation or path integral methods
without having to first formulate a full theory of quantum gravity. The quantum
computer provides an advantage in this endeavor because it can perform path
integrals in Lorentzian space and does not require constructing contour
integrations in Euclidean gravity. Also quantum computers can provide
advantages in systems with fermions which are difficult to analyze on classical
computers. In this study, we first employed classical computational methods to
analyze a Friedmann-Robertson-Walker mini-superspace with a scalar field and
visualize the calculated wave function of the Universe for a variety of
different values of the spatial curvature and cosmological constant. We them
used IBM's Quantum Information Science Kit Python library and the variational
quantum eigensolver to study the same systems on a quantum computer. The
framework can also be extended to the world line approach to quantum field
theory.Comment: 5 pages, 4 figure
Model atmospheres of chemically peculiar stars: Self-consistent empirical stratified model of HD24712
High-resolution spectra of some chemically peculiar stars clearly demonstrate
the presence of strong abundance gradients in their atmospheres. However, these
inhomogeneities are usually ignored in the standard scheme of model atmosphere
calculations, braking the consistency between model structure and
spectroscopically derived abundance pattern. In this paper we present first
empirical self-consistent stellar atmosphere model of roAp star HD24712, with
stratification of chemical elements included, and which is derived directly
from the observed profiles of spectral lines without time-consuming simulations
of physical mechanisms responsible for these anomalies. We used the LLmodels
stellar model atmosphere code and DDAFIT minimization tool for analysis of
chemical elements stratification and construction of self-consistent
atmospheric model. Empirical determination of Pr and Nd stratification in the
atmosphere of HD24712 is based on NLTE line formation for Prii/iii and Ndii/iii
with the use of the DETAIL code. Based on iterative procedure of stratification
analysis and subsequent re-calculation of model atmosphere structure we
constructed a self-consistent model of HD24712, i.e. the model which
temperature-pressure structure is consistent with results of stratification
analysis. It is shown that stratification of chemical elements leads to the
considerable changes in model structure as to compare with non-stratified
homogeneous case. We find that accumulation of REE elements allows for the
inverse temperature gradient to be present in upper atmosphere of the star with
the maximum temperature increase of about 600K.Comment: Comments: Accepted by A&A, 16 pages, 10 figures, 3 table
Two decades of Martini:Better beads, broader scope
The Martini model, a coarse-grained force field for molecular dynamics simulations, has been around for nearly two decades. Originally developed for lipid-based systems by the groups of Marrink and Tieleman, the Martini model has over the years been extended as a community effort to the current level of a general-purpose force field. Apart from the obvious benefit of a reduction in computational cost, the popularity of the model is largely due to the systematic yet intuitive building-block approach that underlies the model, as well as the open nature of the development and its continuous validation. The easy implementation in the widely used Gromacs software suite has also been instrumental. Since its conception in 2002, the Martini model underwent a gradual refinement of the bead interactions and a widening scope of applications. In this review, we look back at this development, culminating with the release of the Martini 3 version in 2021. The power of the model is illustrated with key examples of recent important findings in biological and material sciences enabled with Martini, as well as examples from areas where coarse-grained resolution is essential, namely high-throughput applications, systems with large complexity, and simulations approaching the scale of whole cells. This article is categorized under: Software > Molecular Modeling Molecular and Statistical Mechanics > Molecular Dynamics and Monte-Carlo Methods Structure and Mechanism > Computational Materials Science Structure and Mechanism > Computational Biochemistry and Biophysics
Speed data collection methods: a review
Various studies have been focusing on a wide range of techniques to detect traffic flow characteristics, like speed and travel times. Therefore, a key aspect to obtain statistically significant set of data is to observe and record driver behaviours in real world. To collect traffic data, traditional methods of traffic measurement - such as detection stations, radar guns or video cameras - have been used over the years. Other innovative methods refer to probe vehicles equipped with GPS devices and/or cameras, which allow continuous surveys along the entire road route. While point-based devices provide information of the entire flow, just in the section in which they are installed and only in the time domain, probe vehicles data are referred both to temporal and space domains but ignore traffic conditions. Obviously, it is necessary that the data collected refer to representative samples, by number and composition, of the user population. The paper proposes a review of the most used methods for speed data collection, highlighting the advantages and disadvantages of each experimental approach. Accordingly, the comparison illustrates the best relief method to be adopted depending on the research and investigation that will be performed
A Probabilistic Data Fusion Modeling Approach for Extracting True Values from Uncertain and Conflicting Attributes
Real-world data obtained from integrating heterogeneous data sources are often multi-valued, uncertain, imprecise, error-prone, outdated, and have different degrees of accuracy and correctness. It is critical to resolve data uncertainty and conflicts to present quality data that reflect actual world values. This task is called data fusion. In this paper, we deal with the problem of data fusion based on probabilistic entity linkage and uncertainty management in conflict data. Data fusion has been widely explored in the research community. However, concerns such as explicit uncertainty management and on-demand data fusion, which can cope with dynamic data sources, have not been studied well. This paper proposes a new probabilistic data fusion modeling approach that attempts to find true data values under conditions of uncertain or conflicted multi-valued attributes. These attributes are generated from the probabilistic linkage and merging alternatives of multi-corresponding entities. Consequently, the paper identifies and formulates several data fusion cases and sample spaces that require further conditional computation using our computational fusion method. The identification is established to fit with a real-world data fusion problem. In the real world, there is always the possibility of heterogeneous data sources, the integration of probabilistic entities, single or multiple truth values for certain attributes, and different combinations of attribute values as alternatives for each generated entity. We validate our probabilistic data fusion approach through mathematical representation based on three data sources with different reliability scores. The validity of the approach was assessed via implementation into our probabilistic integration system to show how it can manage and resolve different cases of data conflicts and inconsistencies. The outcome showed improved accuracy in identifying true values due to the association of constructive evidence
- …