10,542 research outputs found
The production of proton-rich isotopes beyond iron: The ?-process in stars
© 2016 World Scientific Publishing Company. Beyond iron, a small fraction of the total abundances in the Solar System is made of proton-rich isotopes, the p-nuclei. The clear understanding of their production is a fundamental challenge for nuclear astrophysics. The p-nuclei constrain the nucleosynthesis in core-collapse and thermonuclear supernovae. The γ-process is the most established scenario for the production of the p-nuclei, which are produced via different photodisintegration paths starting on heavier nuclei. A large effort from nuclear physics is needed to access the relevant nuclear reaction rates far from the valley of stability. This review describes the production of the heavy proton-rich isotopes by the γ-process in stars, and explores the state of the art of experimental nuclear physics to provide nuclear data for stellar nucleosynthesis
Topological characterization of antireflective and hydrophobic rough surfaces: are random process theory and fractal modeling applicable?
The random process theory (RPT) has been widely applied to predict the joint
probability distribution functions (PDFs) of asperity heights and curvatures of
rough surfaces. A check of the predictions of RPT against the actual statistics
of numerically generated random fractal surfaces and of real rough surfaces has
been only partially undertaken. The present experimental and numerical study
provides a deep critical comparison on this matter, providing some insight into
the capabilities and limitations in applying RPT and fractal modeling to
antireflective and hydrophobic rough surfaces, two important types of textured
surfaces. A multi-resolution experimental campaign by using a confocal
profilometer with different lenses is carried out and a comprehensive software
for the statistical description of rough surfaces is developed. It is found
that the topology of the analyzed textured surfaces cannot be fully described
according to RPT and fractal modeling. The following complexities emerge: (i)
the presence of cut-offs or bi-fractality in the power-law power-spectral
density (PSD) functions; (ii) a more pronounced shift of the PSD by changing
resolution as compared to what expected from fractal modeling; (iii) inaccuracy
of the RPT in describing the joint PDFs of asperity heights and curvatures of
textured surfaces; (iv) lack of resolution-invariance of joint PDFs of textured
surfaces in case of special surface treatments, not accounted by fractal
modeling.Comment: 21 pages, 13 figure
Sampling Sup-Normalized Spectral Functions for Brown-Resnick Processes
Sup-normalized spectral functions form building blocks of max-stable and
Pareto processes and therefore play an important role in modeling spatial
extremes. For one of the most popular examples, the Brown-Resnick process,
simulation is not straightforward. In this paper, we generalize two approaches
for simulation via Markov Chain Monte Carlo methods and rejection sampling by
introducing new classes of proposal densities. In both cases, we provide an
optimal choice of the proposal density with respect to sampling efficiency. The
performance of the procedures is demonstrated in an example.Comment: 11 pages, 2 figure
Eco-efficient supply chain networks: Development of a design framework and application to a real case study
© 2015 Taylor & Francis. This paper presents a supply chain network design framework that is based on multi-objective mathematical programming and that can identify 'eco-efficient' configuration alternatives that are both efficient and ecologically sound. This work is original in that it encompasses the environmental impact of both transportation and warehousing activities. We apply the proposed framework to a real-life case study (i.e. Lindt & Sprüngli) for the distribution of chocolate products. The results show that cost-driven network optimisation may lead to beneficial effects for the environment and that a minor increase in distribution costs can be offset by a major improvement in environmental performance. This paper contributes to the body of knowledge on eco-efficient supply chain design and closes the missing link between model-based methods and empirical applied research. It also generates insights into the growing debate on the trade-off between the economic and environmental performance of supply chains, supporting organisations in the eco-efficient configuration of their supply chains
A Comparison of Big Data Frameworks on a Layered Dataflow Model
In the world of Big Data analytics, there is a series of tools aiming at
simplifying programming applications to be executed on clusters. Although each
tool claims to provide better programming, data and execution models, for which
only informal (and often confusing) semantics is generally provided, all share
a common underlying model, namely, the Dataflow model. The Dataflow model we
propose shows how various tools share the same expressiveness at different
levels of abstraction. The contribution of this work is twofold: first, we show
that the proposed model is (at least) as general as existing batch and
streaming frameworks (e.g., Spark, Flink, Storm), thus making it easier to
understand high-level data-processing applications written in such frameworks.
Second, we provide a layered model that can represent tools and applications
following the Dataflow paradigm and we show how the analyzed tools fit in each
level.Comment: 19 pages, 6 figures, 2 tables, In Proc. of the 9th Intl Symposium on
High-Level Parallel Programming and Applications (HLPP), July 4-5 2016,
Muenster, German
Affine parameterization of the dark sector: costraints from WMAP5 and SDSS
We study a set of universe models where the dark sector is described by a
perfect fluid with an affine equation of state , focusing
specifically on cosmological perturbations in a flat universe. We perform a
Monte Carlo Markov Chain analysis spanning the full parameter space of the
model using the WMAP 5 years data and the SDSS LRG4 survey. The affine fluid
can either play the role of a unified dark matter (UDM), accounting for both
dark matter and a cosmological constant, or work alongside cold dark matter
(CDM), as a form of dark energy. A key ingredient is the sound speed, that
depends on the nature of the fluid and that, for any given background model,
adds a degree of freedom to the perturbations: in the barotropic case the
square of the sound speed is simply equal to the affine parameter ; if
entropic perturbations are present the effective sound speed has to be
specified as an additional parameter. In addition to the barotropic case, we
consider the two limiting cases of effective sound speed equal to 0 or 1. For
our UDM model is equivalent to the standard CDM with
adiabatic perturbations. Apart of a trivial subcase, all models considered
satisfy the data constraints, with quite standard values for the usual
cosmological parameters. In general our analysis confirms that cosmological
datasets require both a collisionless massive and cold component to form the
potential wells that lead to structure formation, and an effective cosmological
constant that drives the late accelerated expansion.Comment: 10 pages, 9 figure
Custom Dual Transportation Mode Detection by Smartphone Devices Exploiting Sensor Diversity
Making applications aware of the mobility experienced by the user can open
the door to a wide range of novel services in different use-cases, from smart
parking to vehicular traffic monitoring. In the literature, there are many
different studies demonstrating the theoretical possibility of performing
Transportation Mode Detection (TMD) by mining smart-phones embedded sensors
data. However, very few of them provide details on the benchmarking process and
on how to implement the detection process in practice. In this study, we
provide guidelines and fundamental results that can be useful for both
researcher and practitioners aiming at implementing a working TMD system. These
guidelines consist of three main contributions. First, we detail the
construction of a training dataset, gathered by heterogeneous users and
including five different transportation modes; the dataset is made available to
the research community as reference benchmark. Second, we provide an in-depth
analysis of the sensor-relevance for the case of Dual TDM, which is required by
most of mobility-aware applications. Third, we investigate the possibility to
perform TMD of unknown users/instances not present in the training set and we
compare with state-of-the-art Android APIs for activity recognition.Comment: Pre-print of the accepted version for the 14th Workshop on Context
and Activity Modeling and Recognition (IEEE COMOREA 2018), Athens, Greece,
March 19-23, 201
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