4,238 research outputs found
GiRaFFE: An Open-Source General Relativistic Force-Free Electrodynamics Code
We present GiRaFFE, the first open-source general relativistic force-free
electrodynamics (GRFFE) code for dynamical, numerical-relativity generated
spacetimes. GiRaFFE adopts the strategy pioneered by McKinney and modified by
Paschalidis and Shapiro to convert a GR magnetohydrodynamic (GRMHD) code into a
GRFFE code. In short, GiRaFFE exists as a modification of IllinoisGRMHD, a
user-friendly, open-source, dynamical-spacetime GRMHD code. Both GiRaFFE and
IllinoisGRMHD leverage the Einstein Toolkit's highly-scalable infrastructure to
make possible large-scale simulations of magnetized plasmas in strong,
dynamical spacetimes on adaptive-mesh refinement (AMR) grids. We demonstrate
that GiRaFFE passes a large suite of both flat and curved-spacetime code tests
passed by a number of other state-of-the-art GRFFE codes, and is thus ready for
production-scale simulations of GRFFE phenomena of key interest to relativistic
astrophysics.Comment: 23 pages, 4 figures. Consistent with published versio
The genetic basis for adaptation of model-designed syntrophic co-cultures.
Understanding the fundamental characteristics of microbial communities could have far reaching implications for human health and applied biotechnology. Despite this, much is still unknown regarding the genetic basis and evolutionary strategies underlying the formation of viable synthetic communities. By pairing auxotrophic mutants in co-culture, it has been demonstrated that viable nascent E. coli communities can be established where the mutant strains are metabolically coupled. A novel algorithm, OptAux, was constructed to design 61 unique multi-knockout E. coli auxotrophic strains that require significant metabolite uptake to grow. These predicted knockouts included a diverse set of novel non-specific auxotrophs that result from inhibition of major biosynthetic subsystems. Three OptAux predicted non-specific auxotrophic strains-with diverse metabolic deficiencies-were co-cultured with an L-histidine auxotroph and optimized via adaptive laboratory evolution (ALE). Time-course sequencing revealed the genetic changes employed by each strain to achieve higher community growth rates and provided insight into mechanisms for adapting to the syntrophic niche. A community model of metabolism and gene expression was utilized to predict the relative community composition and fundamental characteristics of the evolved communities. This work presents new insight into the genetic strategies underlying viable nascent community formation and a cutting-edge computational method to elucidate metabolic changes that empower the creation of cooperative communities
Review of the Synergies Between Computational Modeling and Experimental Characterization of Materials Across Length Scales
With the increasing interplay between experimental and computational
approaches at multiple length scales, new research directions are emerging in
materials science and computational mechanics. Such cooperative interactions
find many applications in the development, characterization and design of
complex material systems. This manuscript provides a broad and comprehensive
overview of recent trends where predictive modeling capabilities are developed
in conjunction with experiments and advanced characterization to gain a greater
insight into structure-properties relationships and study various physical
phenomena and mechanisms. The focus of this review is on the intersections of
multiscale materials experiments and modeling relevant to the materials
mechanics community. After a general discussion on the perspective from various
communities, the article focuses on the latest experimental and theoretical
opportunities. Emphasis is given to the role of experiments in multiscale
models, including insights into how computations can be used as discovery tools
for materials engineering, rather than to "simply" support experimental work.
This is illustrated by examples from several application areas on structural
materials. This manuscript ends with a discussion on some problems and open
scientific questions that are being explored in order to advance this
relatively new field of research.Comment: 25 pages, 11 figures, review article accepted for publication in J.
Mater. Sc
Segmenting root systems in X-ray computed tomography images using level sets
The segmentation of plant roots from soil and other growing media in X-ray
computed tomography images is needed to effectively study the root system
architecture without excavation. However, segmentation is a challenging problem
in this context because the root and non-root regions share similar features.
In this paper, we describe a method based on level sets and specifically
adapted for this segmentation problem. In particular, we deal with the issues
of using a level sets approach on large image volumes for root segmentation,
and track active regions of the front using an occupancy grid. This method
allows for straightforward modifications to a narrow-band algorithm such that
excessive forward and backward movements of the front can be avoided, distance
map computations in a narrow band context can be done in linear time through
modification of Meijster et al.'s distance transform algorithm, and regions of
the image volume are iteratively used to estimate distributions for root versus
non-root classes. Results are shown of three plant species of different
maturity levels, grown in three different media. Our method compares favorably
to a state-of-the-art method for root segmentation in X-ray CT image volumes.Comment: 11 page
Metal-insulator transition and orbital reconstruction in Mott quantum wells of NdNiO
The metal-insulator transition (MIT) and the underlying electronic and
orbital structure in quantum wells based on NdNiO was
investigated by d.c. transport and resonant soft x-ray absorption spectroscopy.
By comparing quantum wells of the same dimension but with two different
confinement structures, we explicitly demonstrate that the quantum well
boundary condition of correlated electrons is critical to selecting the
many-body ground state. In particular, the long-range orderings and the MIT are
found to be strongly enhanced under quantum confinement by sandwiching
NdNiO with the wide-gap dielectric LaAlO, while they are suppressed
when one of the interfaces is replaced by a surface (interface with vacuum).
Resonant spectroscopy reveals that the reduced charge fluctuations in the
sandwich structure are supported by the enhanced propensity to charge ordering
due to the suppressed orbital splitting when interfaced with the
confining LaAlO layer
PLM and design education: a collaborative experiment on a mechanical device
The authors would like to thanks Ms Andia Montes C. and Mr Nelson J. for their helpful suggestions received during this experimentThe shift from sequential to concurrent engineering has initiated changes in the way design projects are managed. In order to assist designers, numerous effective tools have been devised for collaborative engineering, which are also well suited to the business world. Faced with these new challenges, practices in design training must evolve to allow students to be mindful of these evolutions as well as to be able to manage projects in these new work environments. After presenting a state of the art of collaborative tools used in product design, our paper presents an experiment focusing on the codesign of a complex mechanical product. This experiment was carried out between two centers of the Arts et Metiers ParisTech School of Engineering, located in Paris and Angers. We analyze the results obtained in this experiment and discuss some ways to improve future projects for inter-centre training programs in design engineering.The shift from sequential to concurrent engineering has initiated changes in the way design projects are managed. In order to assist designers, numerous effective tools have been devised for collaborative engineering, which are also well suited to the business world. Faced with these new challenges, practices in design training must evolve to allow students to be mindful of these evolutions as well as to be able to manage projects in these new work environments. After presenting a state of the art of collaborative tools used in product design, our paper presents an experiment focusing on the codesign of a complex mechanical product. This experiment was carried out between two centers of the Arts et Metiers ParisTech School of Engineering, located in Paris and Angers. We analyze the results obtained in this experiment and discuss some ways to improve future projects for inter-centre training programs in design engineering
Should We Expect Each Year in the Next Decade (2019–28) to be Ranked Among the Top 10 Warmest Years Globally?
Annual rankings of global temperature are widely cited by media and the general public, not only to place the most recent year in a historical perspective, but also as a first-order metric of recent climate change that is easily digestible by the general public. Moreover, all annual NOAAGlobalTemp anomalies from 1880 (the earliest reading available) through the mid-1970s are well below anomalies of the top 10 warmest years in Table 1, even when considering the uncertainty of the NOAAGlobalTemp time series values. While we expect the algorithm\u27s performance to be largely independent of any changes made to the way that NOAAGlobalTemp (or any other annual global temperature time series) is calculated, we do envision monitoring the algorithm\u27s performance and proposing future fine tuning of the algorithm if warranted. Similarly, the AR with trend extension approach (and the AR without trend extension approach to a lesser extent) appears to slightly outperform the AR+ENSO approach in terms of simulation error and prediction interval width, but again the differences are not statistically significant
Robust Environmental Mapping by Mobile Sensor Networks
Constructing a spatial map of environmental parameters is a crucial step to
preventing hazardous chemical leakages, forest fires, or while estimating a
spatially distributed physical quantities such as terrain elevation. Although
prior methods can do such mapping tasks efficiently via dispatching a group of
autonomous agents, they are unable to ensure satisfactory convergence to the
underlying ground truth distribution in a decentralized manner when any of the
agents fail. Since the types of agents utilized to perform such mapping are
typically inexpensive and prone to failure, this results in poor overall
mapping performance in real-world applications, which can in certain cases
endanger human safety. This paper presents a Bayesian approach for robust
spatial mapping of environmental parameters by deploying a group of mobile
robots capable of ad-hoc communication equipped with short-range sensors in the
presence of hardware failures. Our approach first utilizes a variant of the
Voronoi diagram to partition the region to be mapped into disjoint regions that
are each associated with at least one robot. These robots are then deployed in
a decentralized manner to maximize the likelihood that at least one robot
detects every target in their associated region despite a non-zero probability
of failure. A suite of simulation results is presented to demonstrate the
effectiveness and robustness of the proposed method when compared to existing
techniques.Comment: accepted to icra 201
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