Smart Grids (SGs) are expected to be equipped with a number of smart devices able to generate vast amounts of data about the network status, becoming the key components for an efficient State ...Estimation (SE) of complex grids. To exploit their potentials, the ICT infrastructure needs to be scalable to follow the increasing amount of data flows and flexible to give the possibility to assign and re-assign grid functions and data flow control policies at runtime, possibly in a context-aware manner. In this scenario, this paper proposes and validates a Cloud-IoT-based architectural solution for SE in SG that combines cloud-capabilities and edge-computing advantages and uses virtualization technologies to decouple the handling of measurement data from the underlying physical devices. Case studies in the field of distribution networks monitoring are also analyzed, demonstrating that the proposed architecture is capable to accomplish the assigned operational tasks, while satisfying the needed quality level from both the communication and the grid perspectives with a significant degree of flexibility and adaptability with respect to state of the art solutions.
Context. 55 Cnc e is a transiting super-Earth orbiting a solar-like star with an orbital period of ~17.7 h. In 2011, using the Microvariability and Oscillations in Stars (MOST) space telescope, a ...quasi-sinusoidal modulation in flux was detected with the same period as the planetary orbit. The amplitude of this modulation was too large to be explained as the change in light reflected or emitted by the planet. Aims. The MOST telescope continued to observe 55 Cnc e for a few weeks per year over five years (from 2011 to 2015), covering 143 individual transits. This paper presents the analysis of the observed phase modulation throughout these observations and a search for the secondary eclipse of the planet. Methods. The most important source of systematic noise in MOST data is due to stray-light reflected from the Earth, which is modulated with both the orbital period of the satellite (101.4 min) and the Earth’s rotation period. We present a new technique to deal with this source of noise, which we combined with standard detrending procedures for MOST data. We then performed Markov chain Monte Carlo analyses of the detrended light curves, modeling the planetary transit and phase modulation. Results. We find phase modulations similar to those seen in 2011 in most of the subsequent years; however, the amplitude and phase of maximum light are seen to vary, from year to year, from 113 to 28 ppm and from 0.1 to 3.8 rad. The secondary eclipse is not detected, but we constrain the geometric albedo of the planet to less than 0.47 (2σ). Conclusions. While we cannot identify a single origin of the observed optical modulation, we propose a few possible scenarios. Those include star-planet interaction, such as coronal rains and spots rotating with the motion of the planet along its orbit, or the presence of a transiting circumstellar torus of dust. However, a detailed interpretation of these observations is limited by their photometric precision. Additional observations at optical wavelengths could measure the variations at higher precision, contribute to uncovering the underlying physical processes, and measure or improve the upper limit on the albedo of the planet.
This paper proposes an optimization algorithm that is suitable for choosing the optimal number and position of the measurement devices in distribution state estimation (DSE) procedures used in modern ...electric distribution networks. The algorithm is based on the techniques of dynamic programming, and its goal is to guarantee both the minimum cost and the accuracy required for the measured data needed to operate management and control issues, such as energy dispatch and protection coordination. Both the uncertainty introduced by the measurement devices and the tolerance in the knowledge of the network parameters (line impedances) are taken into account in the proposed approach. The aggregation of the quantities to be measured in a few measurement points has been favored to reduce the overall cost of the measurement system. Random changes in the loads are considered to establish adequate reference conditions for the tests. Tests relevant to real distribution networks are presented to show the validity of the proposed approach. The results emphasize how both the influence of the tolerance on the network parameters and the cost of the measurement system can dramatically be minimized by suitably choosing the algorithm to be implemented to solve the DSE problem.
Large-scale distributed measurement systems are the object of several applications and research. The goal of this paper is to develop, by employing global positioning system (GPS) receivers, ...measurement techniques that are suited to the continuous monitoring of the electrical quantities in distribution networks in terms of synchronized phasors. The proposed measurement procedures, differently from commercially available phasor measurement units, are based on general-purpose acquisition hardware and processing software, thus guaranteeing the possibility of being easily reconfigured and reprogrammed according to the specific requirements of different possible fields of application and to their future developments.
•Retrieval of the first hydrogen density profile of Venus on the nightside.•Observation of the absorption of the interplanetary Lyman-α emission by the hydrogen in the venusian upper ...atmosphere.•Observation of a decrease of the hot hydrogen density in few days.•Comparison of hydrogen density derived on the dayside and on the nightside from the same instrument.
Observations of the venusian hydrogen corona on the nightside (8PM local time) have been performed with SPICAV instrument on board Venus Express from 12 to 15 October 2011. These observations were associated with interplanetary observations obtained at apoapsis to subtract the interplanetary contribution. The observed brightness variation with altitude on the disk and above the limb shows that one part of the interplanetary emission is scattered out of the line of sight by the venusian hydrogen atoms above the CO2 absorption limb. The emission of the H corona beyond the cylindrical shadow is also scattered in the same way. Taking into account the geometry of the line of sight and this scattering in a radiative transfer model allows us to retrieve for the first time the vertical profile of the hydrogen density on the nightside of Venus from Lyman-α measurements. The derived cold hydrogen density at the exobase is ∼40 times larger than the dayside hydrogen density derived by the same instrument, showing an evening bulge in agreement with in situ measurements of Pioneer Venus. The hot hydrogen density derived at the nightside is ∼5 times larger than the average dayside hot hydrogen density found previously with SPICAV/Venus Express. A decrease of the hot hydrogen content by a factor ∼2 is observed during these three days of observations. This decrease could be explained by a decrease of the hot hydrogen production rate on the nightside driven by a variation of the dayside ionosphere.
Throughout the last years, with the liberalization of the energy market, the localization of the sources of power quality disturbances has become a nodal point for operators and customers. In the ...liberalized market, knowledge of the system status, along with the uncertainty affecting the estimated data, is required to operate management and control issues such as energy dispatching and protection coordination. In distribution systems, too many measurement instruments would be needed to obtain a complete observation of the electric quantities. Thus, model-based state-estimation techniques can be implemented to exploit the few real-time measurements from the field and all the other available information to estimate the desired quantities. In this paper, a novel approach to the estimation of the harmonic sources by means of a Bayesian approach is proposed. The procedure also allows the ldquoqualityrdquo of the obtained estimates to be assessed. The theoretical fundamentals of the method are discussed, and results relevant to a simple distribution network are presented.
Context.
Convective motions at the stellar surface generate a stochastic colored noise source in the radial velocity (RV) data. This noise impedes the detection of small exoplanets. Moreover, the ...unknown statistics (amplitude, distribution) related to this noise make it difficult to estimate the false alarm probability (FAP) for exoplanet detection tests.
Aims.
In this paper, we investigate the possibility of using 3D magneto-hydrodynamical (MHD) simulations of stellar convection to design detection methods that can provide both a reliable estimate of the FAP and a high detection power.
Methods.
We tested the realism of 3D simulations in producing solar RV by comparing them with the observed disk integrated velocities taken by the GOLF instrument on board the SOHO spacecraft. We presented a new detection method based on periodograms standardized by these simulated time series, applying several detection tests to these standarized periodograms.
Results.
The power spectral density of the 3D synthetic convective noise is consistent with solar RV observations for short periods. For regularly sampled observations, the analytic expressions of FAP derived for several statistical tests applied to the periodogram standardized by 3D simulation noise are accurate. The adaptive tests considered in this work (Higher-Criticism, Berk-Jones), which are new in the exoplanet field, may offer better detection performance than classical tests (based on the highest periodogram value) in the case of multi-planetary systems and planets with eccentric orbits.
Conclusions.
3D MHD simulations are now mature enough to produce reliable synthetic time series of the convective noise affecting RV data. These series can be used to access to the statistics of this noise and derive accurate FAP of tests that are a critical element in the detection of exoplanets down to the cm s
−1
level.
Our aim is to devise a detection method for exoplanet signatures (multiple sinusoids) that is both powerful and robust to partially unknown statistics under the null hypothesis. In the considered ...application, the noise is mostly created by the stellar atmosphere, with statistics depending on the complicated interplay of several parameters. Recent progresses in hydrodynamic (HD) simulations show however that realistic stellar noise realizations can be numerically produced off-line by astrophysicists. We propose a detection method that is calibrated by HD simulations and analyze its performances. A comparison of the theoretical results with simulations on synthetic and real data shows that the proposed method is powerful and robust.
The problem of locating the sources of harmonic distortion in power networks is still a critical task. Several methods based on multipoint measurement techniques have been recently proposed in the ...literature for harmonic-pollution monitoring. The main goal of this paper is to compare the two most powerful tools designed for this purpose. In this paper, the results of both computer simulations on an IEEE test network and experimental tests performed by means of simultaneous measurements on an ad hoc benchmark power system are presented along with a discussion on the practical usability of such monitoring techniques
Stellar variability strongly impacts the search for low-mass exoplanets with radial velocity techniques. Two types of planet-free time series can be used to quantify this impact: models and direct ...solar observations after a subtraction of the Solar System planetary contribution. Making a comparison among these approaches is necessary to improve the models, which can then be used for blind tests across a broad range of conditions. Our objective is therefore to validate the amplitude of the convective blueshift in plages used in our previous works, particularly in blind tests, with HARPS-N solar data. We applied our model to the structures observed at the time of HARPS-N observations and established a direct comparison between the radial velocity time series. To complete our diagnosis, we also studied the observed radial velocities separately for each diffraction order derived from the individual cross-correlation functions, as well as our line-by-line radial velocities. We find that our previous model had been underestimating the amplitude of the convective blueshift inhibition by a factor of about 2. A direct estimation of the convective blueshift in the spectra, which is shown to be correlated with the plage filling factor, allows us to explain the difference with previous estimations obtained with MDI/SOHO Dopplergrams, based on the specific properties of the Ni line used in this mission. In addition, we identified several instrumental systematics, in particular, the presence of a 2 m/s peak-to-peak signal with a period of about 200 days in radial velocity and bisector. This signal could be due to periodic detector warm-ups, a systematic dependence of the long-term trend on wavelength that is possibly related to the variability of the continuum over time, and/or an offset in radial velocity after the interruption of several months in October 2017. A large amplitude in the convective blueshift inhibition of (360 m/s, namely twice more than in our previous works) must be used when building synthetic times series for blind tests. The presence of instrumental systematics should also be taken into account when using sophisticated methods based on line properties to mitigate stellar activity when searching for very weak signals.
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