63 research outputs found
On the global uniqueness for the Einstein-Maxwell-scalar field system with a cosmological constant. Part 3: Mass inflation and extendibility of the solutions
This paper is the third part of a trilogy dedicated to the following problem:
given spherically symmetric characteristic initial data for the
Einstein-Maxwell-scalar field system with a cosmological constant ,
with the data on the outgoing initial null hypersurface given by a subextremal
Reissner-Nordstrom black hole event horizon, study the future extendibility of
the corresponding maximal globally hyperbolic development as a "suitably
regular" Lorentzian manifold.
In the first part of this series we established the well posedness of the
characteristic problem, whereas in the second part we studied the stability of
the radius function at the Cauchy horizon.
In this third and final paper we show that, depending on the decay rate of
the initial data, mass inflation may or may not occur. When the mass is
controlled, it is possible to obtain continuous extensions of the metric across
the Cauchy horizon with square integrable Christoffel symbols. Under slightly
stronger conditions, we can bound the gradient of the scalar field. This allows
the construction of (non-isometric) extensions of the maximal development which
are classical solutions of the Einstein equations. Our results provide evidence
against the validity of the strong cosmic censorship conjecture when
.Comment: 48 pages, 5 figures; v2: some presentation changes, mostly in the
Introduction; v3: substantial changes in Section 5; v4: expanded
Introduction; some presentation changes; matches final published versio
On the global uniqueness for the Einstein-Maxwell-scalar field system with a cosmological constant. Part 2: Structure of the solutions and stability of the Cauchy horizon
This paper is the second part of a trilogy dedicated to the following
problem: given spherically symmetric characteristic initial data for the
Einstein-Maxwell-scalar field system with a cosmological constant ,
with the data on the outgoing initial null hypersurface given by a subextremal
Reissner-Nordstrom black hole event horizon, study the future extendibility of
the corresponding maximal globally hyperbolic development as a "suitably
regular" Lorentzian manifold.
In the first paper of this sequence, we established well posedness of the
characteristic problem with general initial data.
In this second paper, we generalize the results of Dafermos on the stability
of the radius function at the Cauchy horizon by including a cosmological
constant. This requires a considerable deviation from the strategy followed by
Dafermos, focusing on the level sets of the radius function instead of the
red-shift and blue-shift regions. We also present new results on the global
structure of the solution when the free data is not identically zero in a
neighborhood of the origin.
In the third and final paper, we will consider the issue of mass inflation
and extendibility of solutions beyond the Cauchy horizon.Comment: 44 pages, 13 figures; v2: a few small changes; v3: a paragraph was
added in the Introduction, minor clarifications were made thoughout, the list
of references was expanded, matches final published versio
Implementation of Compressed Sensing in Telecardiology Sensor Networks
Mobile solutions for patient cardiac monitoring are viewed with growing interest, and improvements on current implementations are frequently reported, with wireless, and in particular, wearable devices promising to achieve ubiquity. However, due to unavoidable power consumption limitations, the amount of data acquired, processed, and transmitted needs to be diminished, which is counterproductive, regarding the quality of the information produced.
Compressed sensing implementation in wireless sensor networks (WSNs) promises to bring gains not only in power savings to the devices, but also with minor impact in signal quality. Several cardiac signals have a sparse representation in some wavelet transformations. The compressed sensing paradigm states that signals can be recovered from a few projections into another basis, incoherent with the first. This paper evaluates the compressed sensing paradigm impact in a cardiac monitoring WSN, discussing the implications in data reliability, energy management, and the improvements accomplished by in-network processing
Water Quality Monitoring and Associated Distributed Measurement Systems: An Overview
info:eu-repo/semantics/publishedVersio
Underwater Acoustic Source Localization and Sounds Classification in Distributed Measurement Networks
info:eu-repo/semantics/publishedVersio
Wireless sensor network-based solution for environmental monitoring: water quality assessment case study
The challenges of climate change, population growth, demographic change, urbanization and resource depletion mean
that the world’s great cities need to adapt to survive and thrive over the coming decades. Slashing greenhouse gas emissions to
prevent catastrophic climate change, while maintaining or increasing quality of life, can be a costly and dif cult process. Two
factors that directly affect the life quality in the XXI century cities are the water and air quality that can be monitored using
the combination of low cost sensing modules, machine to machine (M2M) and internet of things (IoT) technologies. In this
context, this study presents a wireless sensor network architecture that combines low cost sensing nodes and a low cost multi-
parameters sensing probe for reliable monitoring of water quality parameters of surface waters (lakes, estuaries and rivers) in
urban areas. A particular attention is dedicated to the design of the conductivity, temperature and turbidity signal conditioning
circuits, highlighting important issues related to linearisation, measuring dynamic range and low-cost implementation by
using commercial off-the-shelf components and devices. Several issues related to the wireless sensor network implementation
are included in this study, as well as several simulation and experimental results.info:eu-repo/semantics/publishedVersio
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