The Entropy of Square-Free Words

Finite alphabets of at least three letters permit the construction of square-free words of infinite length. We show that the entropy density is strictly positive and derive reasonable lower and upper bounds. Finally, we present an approximate formula which is asymptotically exact with rapid convergence in the number of letters.Comment: 18 page

Electron-Induced Vibrational Spectroscopy. A New and Unique Tool To Unravel the Molecular Structure of Polymer Surfaces

Among the surface-sensitive spectroscopies used to characterize clean and surface-modified polymers, one technique has rather recently emerged as a very promising complementary tool. High-resolution electron energy loss spectroscopy, or electron-induced vibrational spectroscopy, has potentially all the attributes of the well-known optical (infrared and Raman) spectroscopies; it clearly adds to X-ray photoelectron spectroscopy the possibility to go beyond surface elemental and chemical analysis and to unravel the molecular structure of an extremely thin surface layer of a polymer. This ultrahigh vacuum spectroscopy is shown here to gather information from the last 25 angstrom or so of the polymer surface, as deduced from the analysis of sandwich layers of normal and perdeuterated PMMA Langmuir-Blodgett films. Four case studies of molecular-type information are presented, illustrating (1) the preferential surface segregation of CH3 chain ends on a crystalline polyethylene, (2) selective surface segregation and dynamics of deuterated material in mixtures of normal and deuterated polystyrenes, (3) tacticity induced molecular orientation of PMMA's and polystyrene, and (4) metalization induced molecular reorientation on the surface of polyimide films.</p

Respite for SMEs: a systematic review of socio-technical cybersecurity metrics

Featured Application The results of this work will be incorporated in an application for SMEs in Europe, which aims to improve cybersecurity awareness and resilience, as part of the EU Horizon 2020 GEIGER project. Cybersecurity threats are on the rise, and small- and medium-sized enterprises (SMEs) struggle to cope with these developments. To combat threats, SMEs must first be willing and able to assess their cybersecurity posture. Cybersecurity risk assessment, generally performed with the help of metrics, provides the basis for an adequate defense. Significant challenges remain, however, especially in the complex socio-technical setting of SMEs. Seemingly basic questions, such as how to aggregate metrics and ensure solution adaptability, are still open to debate. Aggregation and adaptability are vital topics to SMEs, as they require the assimilation of metrics into an actionable advice adapted to their situation and needs. To address these issues, we systematically review socio-technical cybersecurity metric research in this paper. We analyse aggregation and adaptability considerations and investigate how current findings apply to the SME situation. To ensure that we provide valuable insights to researchers and practitioners, we integrate our results in a novel socio-technical cybersecurity framework geared towards the needs of SMEs. Our framework allowed us to determine a glaring need for intuitive, threat-based cybersecurity risk assessment approaches for the least digitally mature SMEs. In the future, we hope our framework will help to offer SMEs some deserved respite by guiding the design of suitable cybersecurity assessment solutions.Prevention, Population and Disease management (PrePoD)Public Health and primary car

VAST: a practical validation framework for e-assessment solutions

The influx of technology in education has made it increasingly difficult to assess the validity of educational assessments. The field of information systems often ignores the social dimension during validation, whereas educational research neglects the technical dimensions of designed instruments. The inseparability of social and technical elements forms the bedrock of socio-technical systems. Therefore, the current lack of validation approaches that address both dimensions is a significant gap. We address this gap by introducing VAST: a validation framework for e-assessment solutions. Examples of such solutions are technology-enhanced learning systems and e-health applications. Using multi-grounded action research as our methodology, we investigate how we can synthesise existing knowledge from information systems and educational measurement to construct our validation framework. We develop an extensive user guideline complementing our framework and find through expert interviews that VAST facilitates a comprehensive, practical approach to validating e-assessment solutions.Horizon 2020 (H2020)883588Prevention, Population and Disease management (PrePoD)Public Health and primary car