Ideal hierarchical secret sharing schemes

Hierarchical secret sharing is among the most natural generalizations of threshold secret sharing, and it has attracted a lot of attention from the invention of secret sharing until nowadays. Several constructions of ideal hierarchical secret sharing schemes have been proposed, but it was not known what access structures admit such a scheme. We solve this problem by providing a natural definition for the family of the hierarchical access structures and, more importantly, by presenting a complete characterization of the ideal hierarchical access structures, that is, the ones admitting an ideal secret sharing scheme. Our characterization deals with the properties of the hierarchically minimal sets of the access structure, which are the minimal qualified sets whose participants are in the lowest possible levels in the hierarchy. By using our characterization, it can be efficiently checked whether any given hierarchical access structure that is defined by its hierarchically minimal sets is ideal. We use the well known connection between ideal secret sharing and matroids and, in particular, the fact that every ideal access structure is a matroid port. In addition, we use recent results on ideal multipartite access structures and the connection between multipartite matroids and integer polymatroids. We prove that every ideal hierarchical access structure is the port of a representable matroid and, more specifically, we prove that every ideal structure in this family admits ideal linear secret sharing schemes over fields of all characteristics. In addition, methods to construct such ideal schemes can be derived from the results in this paper and the aforementioned ones on ideal multipartite secret sharing. Finally, we use our results to find a new proof for the characterization of the ideal weighted threshold access structures that is simpler than the existing one.Peer ReviewedPostprint (author's final draft

2-(Fluoromethyl)-4,7-dimethoxy-1-methyl-1H -benzimidazole

Selectfluor (1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate)) substitutes the TEMPO free radical with fluorine on 4,7-dimethoxy-1-methyl-2-{[(2,2,6,6-tetramethylpiperidin-1-yl)oxy]methyl}-1H-benzimidazole to give the title compound in a 77% yield. A mechanism is proposed for the formation of this novel methylene fluoride

Progress in development of photocatalytic processes for synthesis of fuels and organic compounds under outdoor solar light

With photovoltaics becoming a mature, commercially feasible technology, society is willing to allocate resources for developing and deploying new technologies based on using solar light. Analysis of projects supported by the European Commission in the past decade indicates exponential growth of funding to photocatalytic (PC) and photoelectrocatalytic (PEC) technologies that aim either at technology readiness levels (TRLs) TRL 1–3 or TRL > 3, with more than 75 Mio€ allocated from the year 2019 onward. This review provides a summary of PC and PEC processes for the synthesis of bulk commodities such as solvents and fuels, as well as chemicals for niche applications. An overview of photoreactors for photocatalysis on a larger scale is provided. The review rounds off with the summary of reactions performed at lab scale under natural outdoor solar light to illustrate conceptual opportunities offered by solar-driven chemistry beyond the reduction of CO2 and water splitting. The authors offer their vision of the impact of this area of research on society and the economy

<i>Gaia</i> Data Release 1. Summary of the astrometric, photometric, and survey properties

Context. At about 1000 days after the launch of Gaia we present the first Gaia data release, Gaia DR1, consisting of astrometry and photometry for over 1 billion sources brighter than magnitude 20.7. Aims. A summary of Gaia DR1 is presented along with illustrations of the scientific quality of the data, followed by a discussion of the limitations due to the preliminary nature of this release. Methods. The raw data collected by Gaia during the first 14 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into an astrometric and photometric catalogue. Results. Gaia DR1 consists of three components: a primary astrometric data set which contains the positions, parallaxes, and mean proper motions for about 2 million of the brightest stars in common with the HIPPARCOS and Tycho-2 catalogues – a realisation of the Tycho-Gaia Astrometric Solution (TGAS) – and a secondary astrometric data set containing the positions for an additional 1.1 billion sources. The second component is the photometric data set, consisting of mean G-band magnitudes for all sources. The G-band light curves and the characteristics of ∼3000 Cepheid and RR-Lyrae stars, observed at high cadence around the south ecliptic pole, form the third component. For the primary astrometric data set the typical uncertainty is about 0.3 mas for the positions and parallaxes, and about 1 mas yr−1 for the proper motions. A systematic component of ∼0.3 mas should be added to the parallax uncertainties. For the subset of ∼94 000 HIPPARCOS stars in the primary data set, the proper motions are much more precise at about 0.06 mas yr−1. For the secondary astrometric data set, the typical uncertainty of the positions is ∼10 mas. The median uncertainties on the mean G-band magnitudes range from the mmag level to ∼0.03 mag over the magnitude range 5 to 20.7. Conclusions. Gaia DR1 is an important milestone ahead of the next Gaia data release, which will feature five-parameter astrometry for all sources. Extensive validation shows that Gaia DR1 represents a major advance in the mapping of the heavens and the availability of basic stellar data that underpin observational astrophysics. Nevertheless, the very preliminary nature of this first Gaia data release does lead to a number of important limitations to the data quality which should be carefully considered before drawing conclusions from the data

Chemical Composition and Cytoprotective Activities of Methanolic Extract of Asplenium adiantum-nigrum L. (Aspleniaceae)

Ferns can be a source of polyphenolic compounds, with the fronds being the main parts described in ethnopharmacological studies. The present study screened polyphenolic phytochemicals and evaluated in vitro activities of a methanolic extract of Asplenium adiantum-nigrum L. fronds (AAM), an Aspleniaceae fern collected from the Prades mountains (Tarragona, Spain). Phytocharacterization by HPLC-MS/MS confirmed that the major flavonoids isolated in AAM are flavanols while the major phytochemicals are phenol acids, with chlorogenic acid being the most representative one. Cytotoxicity, cytoprotection, cellular repair activity, and phototoxicity were determined in vitro in the presence of 0.01, 0.1, and 1 mg/mL of the extract. No cytotoxicity was obtained in any of the cell lines tested: non-tumoral (3T3 and HaCaT) and tumoral (HeLa, HepG2, and A549) cells. Additionally, the polyphenolic extract showed greater protective effect against H2O2 in 3T3 than HaCaT cells. Despite the low total phenolic content of AAM (1405.68 mg phenolic phytochemicals/kg dry extract), the cytoprotective activity of this extract could be associated with the synergistic antioxidant action of their polyphenolic profile. In addition, the extract did not present phototoxicity against the non-cytotoxic 1.8 J/cm2 dose of UVA light in both non-tumoral cell lines

CF₃-Bis-TEMPO-Vis : new visible light active bis-benzimidazolequinone alkoxyamine

Alkoxyamines of TEMPO usually dissociate thermally at >100 °C; however, room temperature homolysis, activated by visible light, occurs with benzimidazolequinone derivatives. 1,1’-Dimethyl-2,2’-bis{[(2,2,6,6-tetramethylpiperidin-1-yl)oxy]methyl}-6-(trifluoromethyl)-1H,1’H-[5,5’-bibenzimidazole]-4,4’,7,7’-tetrone (CF₃-Bis-TEMPO-Vis) is prepared in a 59% yield through NBS/H₂SO₄ oxidative demethylations of the dimethoxybenzimidazole-benzimidazolequinone precursor with aqueous work up. The alternative basic work up in air gave the epoxide derivative of CF₃-Bis-TEMPO-Vis. Unlike the latter CF₃-epoxide, both alkoxyamine residues are labile under green light (470−600 nm), and the rate of TEMPO release is three times slower than Bis-TEMPO-Vis

Gaia Data Release 1: Testing parallaxes with local Cepheids and RR Lyrae stars

Context. Parallaxes for 331 classical Cepheids, 31 Type II Cepheids, and 364 RR Lyrae stars in common between Gaia and the Hipparcos and Tycho-2 catalogues are published in Gaia Data Release 1 (DR1) as part of the Tycho-Gaia Astrometric Solution (TGAS). Aims. In order to test these first parallax measurements of the primary standard candles of the cosmological distance ladder, which involve astrometry collected by Gaia during the initial 14 months of science operation, we compared them with literature estimates and derived new period-luminosity (PL), period-Wesenheit (PW) relations for classical and Type II Cepheids and infrared PL, PL-metallicity (PLZ), and optical luminosity-metallicity (M V -[Fe/H]) relations for the RR Lyrae stars, with zero points based on TGAS. Methods. Classical Cepheids were carefully selected in order to discard known or suspected binary systems. The final sample comprises 102 fundamental mode pulsators with periods ranging from 1.68 to 51.66 days (of which 33 with σ Ω /Ω < 0.5). The Type II Cepheids include a total of 26 W Virginis and BL Herculis stars spanning the period range from 1.16 to 30.00 days (of which only 7 with σ Ω /Ω < 0.5). The RR Lyrae stars include 200 sources with pulsation period ranging from 0.27 to 0.80 days (of which 112 with σ Ω /Ω < 0.5). The new relations were computed using multi-band (V,I,J,K s ) photometry and spectroscopic metal abundances available in the literature, and by applying three alternative approaches: (i) linear least-squares fitting of the absolute magnitudes inferred from direct transformation of the TGAS parallaxes; (ii) adopting astrometry-based luminosities; and (iii) using a Bayesian fitting approach. The last two methods work in parallax space where parallaxes are used directly, thus maintaining symmetrical errors and allowing negative parallaxes to be used. The TGAS-based PL,PW,PLZ, and M V - [Fe/H] relations are discussed by comparing the distance to the Large Magellanic Cloud provided by different types of pulsating stars and alternative fitting methods. Results. Good agreement is found from direct comparison of the parallaxes of RR Lyrae stars for which both TGAS and HST measurements are available. Similarly, very good agreement is found between the TGAS values and the parallaxes inferred from the absolute magnitudes of Cepheids and RR Lyrae stars analysed with the Baade-Wesselink method. TGAS values also compare favourably with the parallaxes inferred by theoretical model fitting of the multi-band light curves for two of the three classical Cepheids and one RR Lyrae star, which were analysed with this technique in our samples. The K-band PL relations show the significant improvement of the TGAS parallaxes for Cepheids and RR Lyrae stars with respect to the Hipparcos measurements. This is particularly true for the RR Lyrae stars for which improvement in quality and statistics is impressive. Conclusions. TGAS parallaxes bring a significant added value to the previous Hipparcos estimates. The relations presented in this paper represent the first Gaia-calibrated relations and form a work-in-progress milestone report in the wait for Gaia-only parallaxes of which a first solution will become available with Gaia Data Release 2 (DR2) in 2018. © ESO, 2017

Unravelling the atomic structure of a metal-covalent organic framework assembled from ruthenium metalloligands

Covalent and metal-organic frameworks (COFs and MOFs) have shown great promise in light-driven processes mainly due to their ligand-to-metal charge-separation properties, as well as having access to a diverse range of photoactive metalloligands and organic linkers. However, both frameworks present individual drawbacks that can potentially be avoided by combining both systems (metal and covalent) to produce metal-covalent organic frameworks (MCOFs), exhibiting the advantages of both material types. Yet, due to their poor crystallinity, the understanding of the structure-properties relation of MCOFs remains unclear. Herein, we report photoactive linkers in the form of a [Ru(tpy)2]2+ (tpy: 2,2′,6,2″-terpyridine) complex which covalently binds to a luminescent pyrene core to yield a new, photoactive Schiff-base MCOF. The structure, thermal, electronic, and optical properties of this novel material have been exhaustively characterized by a wide range of microscopy, spectroscopic, and computational methods. This combined experimental and computational work represents a significant step toward the fundamental understanding of the photoactive units within the framework, their hierarchical arrangement and interactions with substrates, which is essential for the future design of efficient photocatalytic materials

Comarca del Aranda: inventario comarcal del patrimonio geológico de Aragón, 7. (Zaragoza, Aragón, Sistema Ibérico)

Postprint (published version

Comarca de Valdejalón: inventario comarcal del patrimonio geológico de Aragón, 3. (Zaragoza, Aragón, Sistema Ibérico)

Postprint (published version