13,522 research outputs found
Wireless sensors and IoT platform for intelligent HVAC control
Energy consumption of buildings (residential and non-residential) represents approximately 40% of total world electricity consumption, with half of this energy consumed by HVAC systems. Model-Based Predictive Control (MBPC) is perhaps the technique most often proposed for HVAC control, since it offers an enormous potential for energy savings. Despite the large number of papers on this topic during the last few years, there are only a few reported applications of the use of MBPC for existing buildings, under normal occupancy conditions and, to the best of our knowledge, no commercial solution yet. A marketable solution has been recently presented by the authors, coined the IMBPC HVAC system. This paper describes the design, prototyping and validation of two components of this integrated system, the Self-Powered Wireless Sensors and the IOT platform developed. Results for the use of IMBPC in a real building under normal occupation demonstrate savings in the electricity bill while maintaining thermal comfort during the whole occupation schedule.QREN SIDT [38798]; Portuguese Foundation for Science & Technology, through IDMEC, under LAETA [ID/EMS/50022/2013
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
Phase transitions and statistical mechanics for BPS Black Holes in AdS/CFT
Using the general framework developed in hep-th/0607056, we study in detail
the phase space of BPS Black Holes in AdS, for the case where all three
electric charges are equal. Although these solitons are supersymmetric with
zero Hawking temperature, it turns out that these Black Holes have rich phase
structure with sharp phase transitions associated to a corresponding critical
generalized temperature. We are able to rewrite the gravity variables in terms
of dual CFT variables and compare the gravity phase diagram with the free dual
CFT phase diagram. In particular, the elusive supergravity constraint
characteristic of these Black Holes is particulary simple and in fact appears
naturally in the dual CFT in the definition of the BPS Index. Armed with this
constraint, we find perfect match between BH and free CFT charges up to
expected constant factors.Comment: 14 pages, 5 figures, corrected typos and references adde
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
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