On the Midpoint of a Set of XML Documents.

International audienceThe WWW contains a huge amount of documents. Some of them share the subject, but are generated by different people or even organizations. To guarantee the interchange of such documents, we can use XML, which allows to share documents that do not have the same structure. However, it makes difficult to understand the core of such heterogeneous documents (in general, schema is not available). In this paper, we offer a characterization and algorithm to obtain the midpoint (in terms of a resemblance function) of a set of semi-structured, heterogeneous documents without optional elements. The trivial case of midpoint would be the common elements to all documents. Nevertheless, in cases with several heterogeneous documents this may result in an empty set. Thus, we consider that those elements present in a given amount of documents belong to the midpoint. A exact schema could always be found generating optional elements. However, the exact schema of the whole set may result in overspecialization (lots of optional elements), which would make it useless

On the Midpoint of a Set of XML Documents.

International audienceThe WWW contains a huge amount of documents. Some of them share the subject, but are generated by different people or even organizations. To guarantee the interchange of such documents, we can use XML, which allows to share documents that do not have the same structure. However, it makes difficult to understand the core of such heterogeneous documents (in general, schema is not available). In this paper, we offer a characterization and algorithm to obtain the midpoint (in terms of a resemblance function) of a set of semi-structured, heterogeneous documents without optional elements. The trivial case of midpoint would be the common elements to all documents. Nevertheless, in cases with several heterogeneous documents this may result in an empty set. Thus, we consider that those elements present in a given amount of documents belong to the midpoint. A exact schema could always be found generating optional elements. However, the exact schema of the whole set may result in overspecialization (lots of optional elements), which would make it useless

Gonad development of the deep-sea lobster Polycheles typhlops (Decapoda: Polichelidae) from the Central Western Mediterranean

In this paper, we report data related to the reproductive biology of a cosmopolitan mesobathyal lobster, Polycheles typhlops (Decapoda: Polychelidae), caught in the Sardinian waters between 400 and 1400 m of depth. Macroscopic and microscopic analyses were performed on 1104 females and 895 males. The observation on the gonads leads us to conclude that there are seven and four stages of development for the females and for males, respectively. Monthly variations of the percentage distribution related to various stages of development of the ovary and the presence of ovigerous females indicated that the species does not seem to follow a marked seasonal reproductive model, with a long main period for egg hatching that seems to occur between spring and autumn

Improving deep space telecommunications during solar superior conjunctions

We discuss the results achieved so far in the RESCUe (Reliable TT&C During Superior Solar Conjunctions) project, funded by the European Space Agency (ESA), whose goal is improving the reliability and capacity of radio links near superior conjunctions, i.e., in the presence of phase and amplitude scintillation due to solar wind and solar corona. The study focuses on the current architecture’s, as well as new technical solutions’, performances in terms of Bit Error Rate (BER) and Codeword Error Rate (CER), especially in the region of Sun-Earth-Probe (SEP) below 5 degrees.This paper presents the analysis of data from Mars Express, in 2013 and 2015, and Cassini, in 2001 and 2002, acquired during solar superior conjunctions. The data analysis allowed to confirm the Rician model for the amplitude fading, and to compute the power spectrum of the phases introduced by plasma for different frequency bands and SEP angles. Such models have been accommodated into an end-to-end software, named ENd-To-end Radio link Simulator Tool (ENTRuST), replicating the telecommand (TC) and telemetry (TM) reception capabilities of a deep space spacecraft and ground station. Link performance has been characterized for nominal link budget (using baseband models) and contingency scenarios (using ENTRuST) at low SEP angles. In the latter case in particular, solar plasma effects impact severely on the link. Technical solutions, in several domains, to mitigate the impact of plasma scintillation and to improve the radio link performance, are proposed and currently being studied. In particular: a) coding techniques, by using Low-Density Parity-Check (LDPC) codes, both in uplink - namely the LDPC(128, 64) code and the LDPC(512, 256) code, and in downlink – namely the LDPC(32768, 16384) code; b) non-coherent modulation schemes, like Frequency Shift Keying (FSK) and Differentially Encoded Phase Shift Keying (DPSK), as an alternative to coherent modulation schemes, like Phase Shift Keying (PSK); c) diversity techniques (space, time and frequency)

The European ΔDOR Correlator

Over the past decades NASA pioneered the use of VLBI techniques for the determination of the angular position of interplanetary probes. This powerful method, usually called delta-Differential One-way Ranging (ΔDOR), or ΔVLBI, uses a quasar of known celestial coordinates to synchronize clocks at two ground antennas and a phase delay measurement of the spacecraft signal to infer its angular position in the plane containing the baseline vector. By combining observations from multiple baselines (and therefore at least three ground antennas), one could measure the spacecraft celestial coordinates to an accuracy of 10 nanoradians or less . Being almost independent from the dynamical model and a time-localized measurement, ΔDOR is a valuable observable quantity for spacecraft navigation in the interplanetary cruise phase, where gravity gradients are small and single dish Doppler and range measurements are less effective in providing a good determination of the state vector. ESA and the University of Rome "La Sapienza" have undertaken the development of a software correlator for the analysis of ΔDOR data acquired by its 35-m deep space antennas in New Norcia (Australia) and Cebreros (Spain). By using a model of the spacecraft dynamics and earth rotation, the correlator determines the time delay in the arrival of the quasar and spacecraft wavefronts at the two intervening antennas. These quantities are then processed by an orbit determination code to improve the spacecraft ephemerides. The correlator has been validated using observations of the spacecraft Rosetta, Mars Express, Venus Express and SMART-1. By comparing the ΔDOR observations with the known orbit of Mars Express (determined to an accuracy of a few hundred meter from Doppler measurements), the residual delays are less than 0.5 ns, corresponding to a maximum angular error of 15 nanoradians (i.e. 2.25 km at 1 AU). A judicious choice of the reference quasar leads to significantly smaller residual delays. The attained precision is adequate for all foreseen navigational needs of ESA deep space probes