1,721,028 research outputs found
On the determination of Jupiter's satellite-dependent Love numbers from Juno gravity data
Full text linkThe Juno gravity experiment, among the nine instruments onboard the spacecraft, is aimed at studying the interior structure of Jupiter to gain insight into its formation. Doppler data collected during the first two gravity-dedicated orbits completed by Juno around the gas giant have already provided a measurement of Jupiter's gravity field with outstanding accuracy, answering crucial questions about its interior composition. The large dataset that will be collected throughout the remaining phases of the mission until the end in July 2021 might allow to determine Jupiter's response to the satellite-dependent tidal perturbation raised by its moons, and even to separate the static and dynamic effects. We report on numerical simulations performed over the full science mission to assess the sensitivity of Juno gravity measurements to satellite-dependent tides on Jupiter. We assumed a realistic simulation scenario that is coherent with the result of data analysis from the first gravity passes. Furthermore, we implemented a satellite-dependent tidal model within the dynamical model used to fit the simulated Doppler data. The formal uncertainties resulting from the covariance analysis show that Juno is indeed sensitive to satellite-dependent tides on Jupiter raised by the inner Galilean satellites (the static Love numbers of degree and order 2 of Io, Europa and Ganymede can be determined respectively to 0.28%, 4.6% and 5.3% at 1 sigma). This unprecedented determination, that will be carried out towards the end of the mission, could further constrain the interior structure of the planet, allowing to discern among interior models and improving existing theories of planetary tidal response
WATER QUALITY ANALYSIS IN NETWORK AND PRIVATE STORAGE TANKS IN INTERMITTENT DISTRIBUTION SYSTEMS
No full textIn countries suffering from chronic water shortages, water distribution systems are often operated on an intermittent basis. As a consequence, the network is involved by cyclical filling and emptying periods causing water quality degradation. During the emptying period, the distribution system is unpressurised and it may occur that pollutants move into the network. Moreover, the stagnation period can promote microbial growth. For this reason water is usually heavily chlorinated in order to maintain it potable. Due to intermittent water service users acquire private tanks, which are used for collecting water during serviced periods and distributing it when public service is not available. The tanks can greatly affect water quality and safety. The present paper aims to assess the water quality variation in a complex hydraulic system such as an intermittent distribution network with private tanks. The water quality parameters, such as residual chlorine concentration, were evaluated inside the network and at the point-of-use, downstream of the private tank, in order to evaluate the fate of disinfectants in the network and the potential risk for the users. A network simulation model was implemented, taking into account the private tanks filling and emptying process. The model was applied to one district in Palermo distribution network (Italy) where data were available both at the tap and in the network
Reducing Doppler noise with multi-station tracking: The Cassini test case
No full textDoppler tracking of Solar System probes is used for spacecraft navigation, planetary geodesy, and tests of the theory of General Relativity. The spacecraft radial velocity is measured by observing the Doppler shift of a radio signal transmitted from an Earth station to the spacecraft and then re-transmitted back, while preserving phase coherence, to the same station (two-way link) or to a different station (three-way link). Specialized orbit determination software is then used to reconstruct the spacecraft trajectory and estimate planetary gravity field coefficients or relativistic parameters. The measurement noise is a crucial element for the accuracy of the final estimates, thus considerable effort has been devoted to improve the range rate accuracy by adopting higher frequency links to reduce the dispersive noise from interplanetary and ionospheric plasmas, and by calibrating the tropospheric path delays with microwave radiometers. While Ka-band radio links (32–34 GHz) allowed a successful suppression of plasma noise, reducing tropospheric noise and ground antenna mechanical noise has been more challenging. The Time-Delay Mechanical noise Cancellation (TDMC) technique is a promising method to reduce mechanical and tropospheric noises and to improve further the accuracy of Doppler measurements. The TDMC is a linear combination of simultaneous Doppler data from a main antenna providing the two-way link and a three-way antenna (generally smaller and stiffer). If the listen-only, three-way antenna is also located in a particularly dry site, the TDMC can considerably reduce both tropospheric and antenna mechanical noises, which are the leading disturbances in two-way Ka-band radio links. For an operational test of this method, we applied the TDMC to Doppler data at X-band (7.2–8.4 GHz) from the Cassini spacecraft acquired during the Saturn tour phase of the mission. Although X-band links are generally dominated by the highly-variable interplanetary plasma noise and are not suitable for the TDMC, we found that, when local noises are particularly large at the two-way antenna, this technique may still lead to up to a factor-of-three noise reduction (at 60-s integration time) with respect to the two-way link. The TDMC can maximize the data quality during unique events, mainly planetary or satellite flybys (such as those considered in the Europa Clipper and JUICE missions), where the scientific results could be severely hampered by adverse conditions at the tracking station
Improvements in BepiColombo and JUICE radio science experiments with a multi-station tracking configuration for the reduction of Doppler noise
Full text linkRadio science experiments for planetary geodesy mostly rely on measurements of the Doppler shift of microwave signals sent to a spacecraft by an Earth station, and retransmitted back coherently in phase to the same antenna (two-way link). The retransmitted signal can also be received by a different station in a listen-only configuration (three-way link). In state-of-the-art tracking systems, such as the ones will be used on the future ESA's missions JUICE and BepiColombo, the Doppler error budget is dominated by local noise sources arising at the ground-station, in particular tropospheric scintillation and unmodeled motions of the antenna's structure. In this work, a novel technique aimed at reducing these disturbances is analyzed, with particular emphasis on its benefits to BepiColombo's and JUICE's radio science experiments. The method, referred to as Time-Delay Mechanical-noise Cancellation (TDMC), relies on simultaneous two-way and three-way spacecraft tracking, the latter employing a stiffer listen-only antenna with better mechanical stability and located in a favorable dry region more immune to tropospheric noise. In fact, a proper linear combination of time-shifted observables from the two-way and three-way links can replace local noises of the two-way ground-station with those coming from the listen-only antenna, translating into increased accuracy of the final measurements, while preserving the original Doppler content. We show the results of covariance analyses performed with a multi-arc weighted least square estimator for the entire BepiColombo's Hermean phase and JUICE's flybys of Callisto. We compare the two solutions obtained with and without the application of the TDMC technique. For BepiColombo and JUICE radio science experiments, the two-way links are baselined from the 35-m DSA-3 (Malargüe, Argentina) and the 34-m DSS 25 (Goldstone, California). For the three-way link, we select the 12-m Large Latin American Millimeter Array (LLAMA) antenna for three reasons: 1) its mechanical rigidity with respect to large beam-waveguide antennas, 2) its unique position in the extremely dry Puna de Atacama desert, that assures low tropospheric noise, and 3) its limited longitudinal separation from the two other ground-stations, granting sufficient common visibility time to perform the requested combination of the observables. Besides its noise-reduction effect, enabling unprecedented levels of accuracy on Doppler measurements, TDMC provides also a back-up for unique events: a crucial satellite flyby or a specific passage over a site of particular geophysical interest. Indeed, measurements become virtually independent of unfavorable meteorological conditions at the transmitting station
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Multi Sources Water Supply System Optimal Control: A Case Study
No full textAbstractThe optimal operation of a multi quality network was analysed applying Linear Programming methods. The peculiar service condition of the industrial city of Gela (Italy) was investigated. The network is supplied both from waters derived from a desalination plant and other natural sources. The method aimed to minimise energy cost and find the optimal operation control, while satisfying demand and quality constraints, specifically with regard to water temperature. The method proved to be effective in the selection of the optimal management strategy after the definition of a specific water quality target
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Multivariate Statistical Analysis for Water Demand Modeling
Full text linkAbstractThe actual level of water demand is the driving force behind the hydraulic dynamics in water distribution systems. Consequently, it is crucial to estimate it as accurately as possible in order to result in reliable simulation models. In this paper, a copula-based multivariate analysis has been proposed and used for demand prediction for given return period. The analysis is applied to water consumption data collected in the water distribution network of Palermo (Italy). The approach showed to produce consisted demand patterns and to be a powerful tool to be coupled with water distribution network models for design or analysis problems
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