836 research outputs found
Exploiting road traffic data for very short term load forecasting in smart grids
If accurate short term prediction of electricity consumption is available, the Smart Grid infrastructure can rapidly and reliably react to changing conditions. The economic importance of accurate predictions justifies research for more complex forecasting algorithms. This paper proposes road traffic data as a new input dimension that can help improve very short term load forecasting. We explore the dependencies between power demand and road traffic data and evaluate the predictive power of the added dimension compared with other common features, such as historical load and temperature profiles
Stochastic gravitational wave background from supernovae in massive scalar-tensor gravity
In massive scalar-tensor gravity, core-collapse supernovae are strong sources
of scalar-polarized gravitational waves. These can be detectable out to large
distance. The dispersive nature of the propagation of waves in the massive
scalar field mean the gravitational wave signals are long lived and many such
signals can overlap to form a stochastic background. Using different models for
the population of supernova events in the nearby universe, we compute
predictions for the energy-density in the stochastic scalar-polarized
gravitational wave background from core-collapse events in massive
scalar-tensor gravity for theory parameters that facilitate strong
scalarization. The resulting energy density is below the current constraints on
a Gaussian stochastic gravitational wave background but large enough to be
detectable with the current generation of detectors when they reach design
sensitivity, indicating that it will soon be possible to place new constraints
on the parameter space of massive scalar-tensor gravity.Comment: to match published version in Phys.Rev.
Inverse-chirp signals and spontaneous scalarisation with self-interacting potentials in stellar collapse
We study how the gravitational wave signal from stellar collapse in scalar-tensor gravity varies under the influence of scalar self-interaction. To this end, we extract the gravitational radiation from numerical simulations of stellar collapse for a range of potentials with higher-order terms in addition to the quadratic mass term. Our study includes collapse to neutron stars and black holes and we find the strong inverse-chirp signals obtained for the purely quadratic potential to be exceptionally robust under changes in the potential at higher orders; quartic and sextic terms in the potential lead to noticeable differences in the wave signal only if their contribution is amplified, implying a relative fine-tuning to within 5 or more orders of magnitude between the mass and self-interaction parameters.This work was supported by the European Unionās H2020 ERC Consolidator Grant āMatter and strong-field gravity: New frontiers in Einsteinās theoryā grant agreement no. MaGRaThā646597 funding from the European Unionās Horizon 2020 research and innovation programme under the Marie SkÅodowska-Curie grant agreement No 690904, the COST Action Grant No. CA16104, from STFC Consolidator Grant No. ST/P000673/1, the SDSC Comet and TACC Stampede2 clusters through NSFXSEDE Award Nos. PHY-090003, and Cambridgeās CSD3 system system through STFC capital grants ST/P002307/1 and ST/R002452/1, STFC operations grant ST/R00689X/1 and DiRAC Allocation ACTP186. R.R.-M. acknowledges support by a STFC studentship
Geometry of General Hypersurfaces in Spacetime: Junction Conditions
We study imbedded hypersurfaces in spacetime whose causal character is
allowed to change from point to point. Inherited geometrical structures on
these hypersurfaces are defined by two methods: first, the standard rigged
connection induced by a rigging vector (a vector not tangent to the
hypersurface anywhere); and a second, more physically adapted, where each
observer in spacetime induces a new type of connection that we call the rigged
metric connection. The generalisation of the Gauss and Codazzi equations are
also given. With the above machinery, we attack the problem of matching two
spacetimes across a general hypersurface. It is seen that the preliminary
junction conditions allowing for the correct definition of Einstein's equations
in the distributional sense reduce to the requirement that the first
fundamental form of the hypersurface be continuous. The Bianchi identities are
then proven to hold in the distributional sense. Next, we find the proper
junction conditions which forbid the appearance of singular parts in the
curvature. Finally, we derive the physical implications of the junction
conditions: only six independent discontinuities of the Riemann tensor are
allowed. These are six matter discontinuities at non-null points of the
hypersurface. For null points, the existence of two arbitrary discontinuities
of the Weyl tensor (together with four in the matter tensor) are also allowed.Comment: Latex, no figure
An iliac-appendiceal fistula causing gastrointestinal bleeding
Ā© 2019 The Authors Aortoenteric fistulas are an uncommon cause of gastrointestinal bleeding, and iliac-appendiceal fistulas are an even rarer cause. We describe a case of an iliac-appendiceal fistula in a patient who presented several months after aortic reconstruction with gastrointestinal bleeding. An extensive workup revealed that the source of bleeding was localized to the appendiceal orifice. The patient underwent an appendectomy with a two-stage procedure involving the iliac graft for definitive repair and ultimately recovered well. Despite the rarity of aortoenteric and iliac-appendiceal fistulas causing gastrointestinal bleeding, keeping a high index of suspicion in patients with a prior vascular repair can prevent death
Structure of Neutron Stars in Massive Scalar-Tensor Gravity
We compute families of spherically symmetric neutron-star models in two-derivative scalar-tensor theories of gravity with a massive scalar field. The numerical approach we present allows us to compute the resulting spacetimes out to infinite radius using a relaxation algorithm on a compactified grid. We discuss the structure of the weakly and strongly scalarized branches of neutron-star models thus obtained and their dependence on the linear and quadratic coupling parameters Ī±0, Ī²0 between the scalar and tensor sectors of the theory, as well as the scalar mass Ī¼. For highly negative values of Ī²0, we encounter configurations resembling a āgravitational atomā, consisting of a highly compact baryon star surrounded by a scalar cloud. A stability analysis based on binding-energy calculations suggests that these configurations are unstable and we expect them to migrate to models with radially decreasing baryon density and scalar field strength
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