Large (d, D, D′, s)-bipartite digraphs

AbstractA (d, D, D′, s)-digraph is a directed graph with diameter D and maximum out-degree d such that after the deletion of any s of its vertices the resulting digraph has diameter at most D′. Our concern is to find large, i.e. with order as large as possible, (d, D, D′, s)-bipartite digraphs. To this end, it is proved that some members of a known family of large bipartite digraphs satisfy a Menger-type condition. Namely, between any pair of non-adjacent vertices they have s + 1 internally disjoint paths of length at most D′. Then, a new family of (d, D, D′, s)-bipartite digraphs with order very close to the upper bound is obtained

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

Smart sensing interoperability platforms in the scope of Atlantos

This paper aims to demonstrate the capabilities of a Smart Cable which aims to convert any commercial non-PUCK-enabled sensor in a Smart PUCK-enabled device. Through this development, it can be easily integrated on a sensor web platform in order to access the data in real time, and so there is no need to rely on each sensor manufacturer to comply with Sensor Web Enablement standards. The results presented in this paper were acquired during some real field experiments performed between the 24th and 28th of September at PLOCAN facilities in Gran Canaria. During these days three Turner Designs Cyclops sensors were successfully integrated and tested in a mission using an observing surface vehicle such as the Wave Glider SV-2.Peer Reviewe

Comprehensive Simultaneous Shipboard and Airborne Characterization of Exhaust from a Modern Container Ship at Sea

We report the first joint shipboard and airborne study focused on the chemical composition and water-uptake behavior of particulate ship emissions. The study focuses on emissions from the main propulsion engine of a Post-Panamax class container ship cruising off the central coast of California and burning heavy fuel oil. Shipboard sampling included micro-orifice uniform deposit impactors (MOUDI) with subsequent off-line analysis, whereas airborne measurements involved a number of real-time analyzers to characterize the plume aerosol, aged from a few seconds to over an hour. The mass ratio of particulate organic carbon to sulfate at the base of the ship stack was 0.23 ± 0.03, and increased to 0.30 ± 0.01 in the airborne exhaust plume, with the additional organic mass in the airborne plume being concentrated largely in particles below 100 nm in diameter. The organic to sulfate mass ratio in the exhaust aerosol remained constant during the first hour of plume dilution into the marine boundary layer. The mass spectrum of the organic fraction of the exhaust aerosol strongly resembles that of emissions from other diesel sources and appears to be predominantly hydrocarbon-like organic (HOA) material. Background aerosol which, based on air mass back trajectories, probably consisted of aged ship emissions and marine aerosol, contained a lower organic mass fraction than the fresh plume and had a much more oxidized organic component. A volume-weighted mixing rule is able to accurately predict hygroscopic growth factors in the background aerosol but measured and calculated growth factors do not agree for aerosols in the ship exhaust plume. Calculated CCN concentrations, at supersaturations ranging from 0.1 to 0.33%, agree well with measurements in the ship-exhaust plume. Using size-resolved chemical composition instead of bulk submicrometer composition has little effect on the predicted CCN concentrations because the cutoff diameter for CCN activation is larger than the diameter where the mass fraction of organic aerosol begins to increase significantly. The particle number emission factor estimated from this study is 1.3 × 10^(16) (kg fuel)^(−1), with less than 1/10 of the particles having diameters above 100 nm; 24% of particles (>10 nm in diameter) activate into cloud droplets at 0.3% supersaturation

Optimal non-perfect uniform secret sharing schemes

A secret sharing scheme is non-perfect if some subsets of participants that cannot recover the secret value have partial information about it. The information ratio of a secret sharing scheme is the ratio between the maximum length of the shares and the length of the secret. This work is dedicated to the search of bounds on the information ratio of non-perfect secret sharing schemes. To this end, we extend the known connections between polymatroids and perfect secret sharing schemes to the non-perfect case. In order to study non-perfect secret sharing schemes in all generality, we describe their structure through their access function, a real function that measures the amount of information that every subset of participants obtains about the secret value. We prove that there exists a secret sharing scheme for every access function. Uniform access functions, that is, the ones whose values depend only on the number of participants, generalize the threshold access structures. Our main result is to determine the optimal information ratio of the uniform access functions. Moreover, we present a construction of linear secret sharing schemes with optimal information ratio for the rational uniform access functions.Peer ReviewedPostprint (author's final draft

Does grazing pressure modify diuron toxicity in a biofilm community?

Herbicides affect the structure and functional parameters of fluvial biofilm. Diuron is toxic to primary producers and disrupts endocrine activity. Here, we studied the interaction between this toxicant and several biological compartments in a simple food chain composed of herbivores (the snail Physella [Costatella] acuta) and biofilm. We used indoor experimental channels to which Diuron was added at a realistic concentration (2 μg/L). Bacterial survival and chlorophyll-a and photosynthetic activity were analyzed in the biofilm. We monitored biomass, mortality, reproduction, and motility as end points in the freshwater snail P. acuta. Our results showed that bacterial survival and photosynthetic activity were sensitive to Diuron. Snails were not affected by the herbicide at the concentration tested. No significant interactions between the toxicant and grazers were observed on the biofilm. Reproductive traits, however, were slightly affected, indicating a possible endocrine disruption

Weeds in Cover Crops: Context and Management Considerations

Cover crops are increasingly being adopted to provide multiple ecosystem services such as improving soil health, managing nutrients, and decreasing soil erosion. It is not uncommon for weeds to emerge in and become a part of a cover crop plant community. Since the role of cover cropping is to supplement ecosystem service provisioning, we were interested in assessing the impacts of weeds on such provisioning. To our knowledge, no research has examined how weeds in cover crops may impact the provision of ecosystem services and disservices. Here, we review services and disservices associated with weeds in annual agroecosystems and present two case studies from the United States to illustrate how weeds growing in fall-planted cover crops can provide ground cover, decrease potential soil losses, and effectively manage nitrogen. We argue that in certain circumstances, weeds in cover crops can enhance ecosystem service provisioning. In other circumstances, such as in the case of herbicide-resistant weeds, cover crops should be managed to limit weed biomass and fecundity. Based on our case studies and review of the current literature, we conclude that the extent to which weeds should be allowed to grow in a cover crop is largely context-dependent.This work was supported by the USDA National Institute of Food and Agriculture, Organic Research and Extension Initiative under Project PENW-2015-07433 (Grant No. 2015-51300-24156, Accession No. 1007156) and the National Science Foundation (Grant No. DGE1255832)

Case Report Unusual Transalveolar and Transmuco-Gingival Root Avulsion of a Fractured Primary Central Incisor: A Case with an 8-Year Follow-Up

The purpose of this unique case report is to describe a very unusual dentoalveolar fracture associated with avulsion of the nearcomplete root. A 3-year-old male patient came for consultation after a dentoalveolar trauma with a "fragment that looks like canine" found in his mouth by his mother. This boy suffered root fracture of the upper primary central right incisor, accompanied by transalveolar and transmuco-gingival avulsion of the tooth root fragment, leaving the crown in its position in the dental arch. Clinical and radiological examinations were performed in order to follow up the case: 15 days, one month, and three months after trauma, the crown had a slight mobility without other clinical or radiological signs. After six months, the upper primary central right incisor's crown was exfoliated. Open bite due to the persistence of the pacifier habit favored the crown retention in the mouth. This case emphasizes the importance of primary diagnosis and follow-up of trauma cases. To the best of our knowledge, this kind of dental injury has not been previously described in the literature nor in the current Dental Trauma guidelines for the management of traumatic dental injuries in the primary dentition

Complete tree subset difference broadcast encryption scheme and its analysis

The subset difference (SD) method proposed by Naor, Naor and Lotspiech is the most popular broadcast encryption (BE) scheme. It is suitable for real-time applications like Pay-TV and has been suggested for use by the AACS standard for digital rights management in Blu-Ray and HD-DVD discs. The SD method assumes the number of users to be a power of two. We propose the complete tree subset difference (CTSD) method that allows the system to support an arbitrary number of users. In particular, it subsumes the SD method and all results proved for the CTSD method also hold for the SD method. Recurrences are obtained for the CTSD scheme to count the number, N(n, r, h), of possible ways r users in the system of n users can be revoked to result in a transmission overhead or header length of h. The recurrences lead to a polynomial time dynamic programming algorithm for computing N(n, r, h). Further, they provide bounds on the maximum possible header length. A probabilistic analysis is performed to obtain an O(r log n) time algorithm to compute the expected header length in the CTSD scheme. Further, for the SD scheme we obtain an explicit limiting upper bound on the expected header length