3,149,843 research outputs found
Data-driven model of the solar corona above an active region
We aim to reproduce the structure of the corona above a solar active region
as seen in the extreme ultraviolet (EUV) using a three-dimensional
magnetohydrodynamic (3D MHD) model. The 3D MHD data-driven model solves the
induction equation and the mass, momentum, and energy balance. To drive the
system, we feed the observed evolution of the magnetic field in the photosphere
of the active region AR 12139 into the bottom boundary. This creates a hot
corona above the cool photosphere in a self-consistent way. We synthesize the
coronal EUV emission from the densities and temperatures in the model and
compare this to the actual coronal observations. We are able to reproduce the
overall appearance and key features of the corona in this active region on a
qualitative level. The model shows long loops, fan loops, compact loops, and
diffuse emission forming at the same locations and at similar times as in the
observation. Furthermore, the low-intensity contrast of the model loops in EUV
matches the observations. In our model the energy input into the corona is
similar as in the scenarios of fieldline-braiding or flux-tube tectonics, that
is, energy is transported to the corona through the driving of the vertical
magnetic field by horizontal photospheric motions. The success of our model
shows the central role that this process plays for the structure, dynamics, and
heating of the corona.Comment: 5 pages, 3 Figures, published in A&A letter
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Active networks: an evolution of the internet
Active Networks can be seen as an evolution of the classical model of packet-switched networks. The traditional and ”passive” network model is based on a static definition of the network node behaviour. Active Networks propose an “active” model where the intermediate nodes (switches and routers) can load and execute user code contained in the data units (packets). Active Networks are a programmable network model, where bandwidth and computation are both considered shared network resources. This approach opens up new interesting research fields. This paper gives a short introduction of Active
Networks, discusses the advantages they introduce and presents the research advances in this field
COMPILATION OF ACTIVE FAULT DATA IN PORTUGAL FOR USE IN SEISMIC HAZARD ANALYSIS
To estimate where future earthquakes are likely to occur, it is essential to combine information about past earthquakes with knowledge about the location and seismogenic properties of active faults. For this reason, robust probabilistic seismic hazard analysis (PSHA) integrates seismicity and active fault data. Existing seismic hazard assessments for Portugal rely exclusively on seismicity data and do not incorporate data on active faults. Project SHARE (Seismic Hazard Harmonization in Europe) is an EC-funded initiative (FP7) that aims to evaluate European seismic hazards using an integrated, standardized approach. In the context of SHARE, we are developing a fully-parameterized active fault database for Portugal that incorporates existing compilations, updated according to the most recent publications. The seismogenic source model derived for SHARE will be the first model for Portugal to include fault data and follow an internationally standardized approach. This model can be used to improve both seismic hazard and risk analyses and will be combined with the Spanish database for use in Iberian- and European-scale assessments
Learning a Policy for Opportunistic Active Learning
Active learning identifies data points to label that are expected to be the
most useful in improving a supervised model. Opportunistic active learning
incorporates active learning into interactive tasks that constrain possible
queries during interactions. Prior work has shown that opportunistic active
learning can be used to improve grounding of natural language descriptions in
an interactive object retrieval task. In this work, we use reinforcement
learning for such an object retrieval task, to learn a policy that effectively
trades off task completion with model improvement that would benefit future
tasks.Comment: EMNLP 2018 Camera Read
Active data structures on GPGPUs
Active data structures support operations that may affect a large number of elements of an aggregate data structure. They are well suited for extremely fine grain parallel systems, including circuit parallelism. General purpose GPUs were designed to support regular graphics algorithms, but their intermediate level of granularity makes them potentially viable also for active data structures. We consider the characteristics of active data structures and discuss the feasibility of implementing them on GPGPUs. We describe the GPU implementations of two such data structures (ESF arrays and index intervals), assess their performance, and discuss the potential of active data structures as an unconventional programming model that can exploit the capabilities of emerging fine grain architectures such as GPUs
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