Concise report : teenage sexting on the rise? Results of a cohort study using a weighted sample of adolescents

Background: The vast differences in sampling techniques, cultural contexts between international studies, the differences in age groups of the samples and various definitions used to measure sexting make it hard to compare how sexting behaviour has evolved over the past years. This exploratory study aims to address this critical gap in the research by using two datasets of a biennial study on adolescents' media use. The first aim of this study is to compare the sexting prevalence and correlates (i.e. age, gender and smartphone ownership) of youth in 2015 and 2017. The second aim is to investigate the risk mitigation behaviours of youth who engage in sexting and to assess how their behaviours differ between the two time points. Methods: The data for cohort 1 were collected in October and November 2015 and comprise of 2663 students from 11 secondary schools in the Dutch-speaking community of Belgium. For the second cohort, the data were collected in October and November 2017 and comprise of 2681 students from 10 secondary schools. A weighing factor was implemented on the dataset. Results: The results show sexting behaviour has significantly increased between cohorts, with 8.3% of the respondents having sent a sext in the first cohort, compared with 12.1% in the second cohort. The sexting prevalence rates also significantly increased between cohorts when taking into account students who owned a smartphone. Furthermore, engagement in sexting was associated with being older, and no gender differences were found. In the second cohort, 36.8% of youth who had sent a sext were identifiable in those images. There were no differences between cohorts. Conclusion: The results indicate that other factors next to smartphone ownership may be associated with an increase in sexting prevalence. The findings also highlight the need for the development of age-appropriate sexting educational materials

MQ^*-IP: An Identity-based Identification Scheme without Number-theoretic Assumptions

In this article, we propose an identification scheme which is based on the two combinatorial problems Multivariate Quadratic equations (MQ) and Isomorphism of Polynomials (IP). We show that this scheme is statistical zero-knowledge. Using a trapdoor for the MQ-problem, it is possible to make it also identity-based, i.e., there is no need for distributing public keys or for certificates within this scheme. The size of the public keys and the communication complexity\ are within the range of other non-number-theoretic identification schemes. In contrast to MQ^*-IP, these schemes do usually no permit identity-based public keys

Equivalent Keys in Multivariate Quadratic Public Key Systems

Multivariate Quadratic public key schemes have been suggested back in 1985 by Matsumoto and Imai as an alternative for the RSA scheme. Since then, several other schemes have been proposed, for example Hidden Field Equations, Unbalanced Oil and Vinegar schemes, and Stepwise Triangular Schemes. All these schemes have a rather large key space for a secure choice of parameters. Surprisingly, the question of equivalent keys has not been discussed in the open literature until recently. In this article, we show that for all basic classes mentioned above, it is possible to reduce the private --- and hence the public --- key space by several orders of magnitude. For the Matsumoto-Imai scheme, we are even able to show that the reductions we found are the only ones possible, i.e., that these reductions are tight. While the theorems developed in this article are of independent interest themselves as they broaden our understanding of Multivariate Quadratic public key systems, we see applications of our results both in cryptanalysis and in memory efficient implementations of MQ-schemes

Classification of Highly Nonlinear Boolean Power Functions with a Randomised Algorithm for Checking Normality

A Boolean function is called normal if it is constant on flats of certain dimensions. This property is relevant for the construction and analysis of cryptosystems. This paper presents an asymmetric Monte Carlo algorithm to determine whether a given Boolean function is normal. Our algorithm is far faster than the best known (deterministic) algorithm of Daum et al. In a first phase, it checks for flats of low dimension whether the given Boolean function is constant on them and combines such flats to flats of higher dimension in a second phase. This way, the algorithm is much faster than exhaustive search. Moreover, the algorithm benefits from randomising the first phase. In addition, by evaluating several flats implicitly in parallel, the time-complexity of the algorithm decreases further. As an application, we determine the level of normality for several, highly nonlinear Boolean power functions

Reference protocols for assessment of trait and reference genotypes to be used as standards in international research projects

PublishedEduardo Notivol es el Contribuidor a la publicación de Españ

Teacher Literacy and Numeracy Skills: International Evidence from PIAAC and ALL

Using the OECD-studies PIAAC and ALL, this paper shows that teachers on average have better literacy and numeracy skills than other respondents in almost all of the 15 countries in the samples. In most countries, teachers outperform others in the bottom percentiles, while in some countries they perform better than others throughout the skill distribution. These results imply that the scope to improve teachers' skills varies between countries and that policy makers should take the shape of the skills distribution into account when designing interventions in order to most efficiently raise teachers' skills

High-global warming potential F-gas emissions in California: comparison of ambient-based versus inventory-based emission estimates, and implications of refined estimates.

To provide information for greenhouse gas reduction policies, the California Air Resources Board (CARB) inventories annual emissions of high-global-warming potential (GWP) fluorinated gases, the fastest growing sector of greenhouse gas (GHG) emissions globally. Baseline 2008 F-gas emissions estimates for selected chlorofluorocarbons (CFC-12), hydrochlorofluorocarbons (HCFC-22), and hydrofluorocarbons (HFC-134a) made with an inventory-based methodology were compared to emissions estimates made by ambient-based measurements. Significant discrepancies were found, with the inventory-based emissions methodology resulting in a systematic 42% under-estimation of CFC-12 emissions from older refrigeration equipment and older vehicles, and a systematic 114% overestimation of emissions for HFC-134a, a refrigerant substitute for phased-out CFCs. Initial, inventory-based estimates for all F-gas emissions had assumed that equipment is no longer in service once it reaches its average lifetime of use. Revised emission estimates using improved models for equipment age at end-of-life, inventories, and leak rates specific to California resulted in F-gas emissions estimates in closer agreement to ambient-based measurements. The discrepancies between inventory-based estimates and ambient-based measurements were reduced from -42% to -6% for CFC-12, and from +114% to +9% for HFC-134a

Ancestral Admixture Is the Main Determinant of Global Biodiversity in Fission Yeast

Mutation and recombination are key evolutionary processes governing phenotypic variation and reproductive isolation. We here demonstrate that biodiversity within all globally known strains of Schizosaccharomyces pombe arose through admixture between two divergent ancestral lineages. Initial hybridization was inferred to have occurred ∼20-60 sexual outcrossing generations ago consistent with recent, human-induced migration at the onset of intensified transcontinental trade. Species-wide heritable phenotypic variation was explained near-exclusively by strain-specific arrangements of alternating ancestry components with evidence for transgressive segregation. Reproductive compatibility between strains was likewise predicted by the degree of shared ancestry. To assess the genetic determinants of ancestry block distribution across the genome, we characterized the type, frequency, and position of structural genomic variation using nanopore and single-molecule real-time sequencing. Despite being associated with double-strand break initiation points, over 800 segregating structural variants exerted overall little influence on the introgression landscape or on reproductive compatibility between strains. In contrast, we found strong ancestry disequilibrium consistent with negative epistatic selection shaping genomic ancestry combinations during the course of hybridization. This study provides a detailed, experimentally tractable example that genomes of natural populations are mosaics reflecting different evolutionary histories. Exploiting genome-wide heterogeneity in the history of ancestral recombination and lineage-specific mutations sheds new light on the population history of S. pombe and highlights the importance of hybridization as a creative force in generating biodiversity

A C-Band, Dual-Polarimetric Radar Analysis of a Tornadic Mesoscale Convective System: The 25 May 2011 Northern Illinois and Indiana Tornado Event

During the morning hours of 25 May 2011, at least six tornadoes struck a narrow corridor of Northeast Illinois and Northwest Indiana. Two tornadoes were rated EF0, three EF1, and one EF2. These tornadoes occurred in conjunction with a mesoscale convective system (MCS) that traveled northeast across the region during the early to mid-morning hours, between 1200 UTC and 1500 UTC. The tornadoes occurred at least 65 km away from the nearest NEXRAD WSR-88D radar site. The confirmed tornadoes from this event occurred without severe thunderstorm or tornado warnings likely due to the fact that (1) the squall-line was oriented parallel to the radar beam, (2) there were minimal real-time spotter reports, (3) embedded circulations were shallow, and (4) the tornado-producing storms did not exhibit classic radar signatures at the nearest NEXRAD locations. The tornadoes occurred anywhere from approximately 50-75 km from the C-band dual-polarimetric radar located on the campus of Valparaiso University in Valparaiso, IN. In this presentation, we examine the data gathered from the C-band, dual-polarimetric radar at Valparaiso University. We review the data in hopes of revealing methods that could have better detected the tornadoes produced during this event