Tamarix minoa (Tamaricaceae), a new species from the island of Crete (Greece) based on morphological and plastid molecular sequence data

Tamarix minoa is described from material collected on the S Aegean island of Crete (Kriti), Greece. A morphological comparison with the species considered to be closest, T. africana and T. hampeana, is provided. An original illustration showing the main morphological characters of the new species is also given, as are photographs of the new species in its habitat. The isolated phylogenetic position of T. minoa is shown to be strongly supported by plastid molecular sequence data (trnS-trnG, trnQ-rps16 and ndhF-rpl32), thus warranting its recognition at specific rank.National Geographic Society, research project “Human recreation versus plant diversity on maritime sands in Crete” (NGS grant no. 8573-08). The FPU programme (Mº de Educación, Spain), the I+D+I project CGL2008-05056 (Mº de Educación y Ciencia, Spanish Government), the project OAPN 354-2011 (Mº de Agricultura, Alimentación y Medio Ambiente, Spanish Government) and complementary supporting funds ACIE10-01, ACIE11-05 and ACIE13-08 (University of Alicante, Spain)

Magnetic fields in cluster cores: Faraday rotation in A400 and A2634

We present Faraday rotation data for radio sources in the centers of the Abell clusters A400 and A2634. These clusters contain large (> 100 kpc), tailed radio sources, each attached to the central cD galaxy. These clusters do not have strong cooling cores. Our data extend previous work on rotation measure in cluster centers to larger scales and non-cooling clusters. The rotation measure, and thus the magnetic field, is ordered on scales 10-20 kpc in both clusters. The geometry of the rotation measure appears to be determined by the distribution of the X-ray emitting gas, rather than by the radio tails themselves. We combine our data with previously published X-ray and radio data in order to analyze the magnetic fields in all 12 clusters whose central radio sources have been imaged in rotation measure. We find that the fields are dynamically significant in most clusters. We argue that the Faraday data measure fields in the intracluster medium, rather than in a skin of the radio source. Finally, we consider the nature and maintenance of the magnetic fields in these clusters, and conclude that either the cluster-wide field exists at similar levels, or that a weaker cluster-wide field is amplified by effects in the core.Comment: Accepted for ApJ. 43 pages including 10 embedded figures. Higher resolution versions of the figures available at http://www.aoc.nrao.edu/~jeilek/pubs/Eilekpub.htm

Resonant Kelvin-Helmholtz modes in sheared relativistic flows

Qualitatively new aspects of the (linear and non-linear) stability of sheared relativistic (slab) jets are analyzed. The linear problem has been solved for a wide range of jet models well inside the ultrarelativistic domain (flow Lorentz factors up to 20; specific internal energies $\approx 60c^2$). As a distinct feature of our work, we have combined the analytical linear approach with high-resolution relativistic hydrodynamical simulations, which has allowed us i) to identify, in the linear regime, resonant modes specific to the relativistic shear layer ii) to confirm the result of the linear analysis with numerical simulations and, iii) more interestingly, to follow the instability development through the non-linear regime. We find that very high-order reflection modes with dominant growth rates can modify the global, long-term stability of the relativistic flow. We discuss the dependence of these resonant modes on the jet flow Lorentz factor and specific internal energy, and on the shear layer thickness. The results could have potential applications in the field of extragalactic relativistic jets.Comment: Accepted for publication in Physical Review E. For better quality images, please check http://www.mpifr-bonn.mpg.de/staff/mperucho/Research.htm

Taxonomy and nomenclature in palaeopalynology: basic principles, current challenges and future perspectives

Effective communication of taxonomic concepts is crucial to meaningful application in all biological sciences, and thus the development and following of best practices in taxonomy and the formulation of clear and practical rules of nomenclature underpin a wide range of scientific studies. The International Code of Nomenclature for algae, fungi and plants (the Code), currently the Shenzhen Code of 2018, provides these rules. Although early versions of the Code were designed mainly with extant plants in mind, the Code has been increasingly used for fossil plants and, in recent decades, for organic-walled microfossils, the study of which is called palaeopalynology, or simply palynology. However, rules embodied in the Code do not fully reflect the needs and practices of this discipline; and taxonomic practices between fossil applications, especially in palynology, have tended to diverge from practices for extant plants. Differences in these rules and practices present specific challenges. We therefore review the Shenzhen Code as it applies to palynology, clarifying procedures and recommending approaches based on best practices, for example, in the designation and use of nomenclatural types. The application of nomenclatural types leads to taxonomic stability and precise communication, and lost or degraded types are therefore problematic because they remove the basis for understanding a taxon. Such problems are addressed using examples from the older European literature in which type specimens are missing or degraded. A review of the three most important conventions for presenting palynological taxonomic information, synonymies, diagnoses/descriptions and illustrations, concludes with recommendations of best practices. Palynology continues to play an important role in biostratigraphy, palaeoenvironmental analyses, and evolutionary studies, and is contributing increasingly to our understanding of past climates and ocean systems. To contribute with full potential to such applied studies, consistent communication of taxonomic concepts, founded upon clear rules of nomenclature, is essential

Observational Effects of Anomalous Boundary Layers in Relativistic Jets

Recent theoretical work has pointed out that the transition layer between a jet an the medium surrounding it may be more complex than previously thought. Under physically realizable conditions, the transverse profile of the Lorentz factor in the boundary layer can be non-monotonic, displaying the absolute maximum where the flow is faster than at the jet spine, followed by an steep fall off. Likewise, the rest-mass density, reaches an absolute minimum (coincident with the maximum in Lorentz factor) and then grows until it reaches the external medium value. Such a behavior is in contrast to the standard monotonic decline of the Lorentz factor (from a maximum value at the jet central spine) and the corresponding increase of the rest-mass density (from the minimum reached at the jet core). We study the emission properties of the aforementioned anomalous shear layer structures in kiloparsec-scale jets aiming to show observable differences with respect to conventional monotonic and smooth boundary layers.Comment: 32 pages, 9 figures (1 in color), accepted in Ap

Simple Nudges for Better Password Creation

Recent security breaches have highlighted the consequences of reusing passwords across online accounts. Recent guidance on password policies by the UK government recommend an emphasis on password length over an extended character set for generating secure but memorable passwords without cognitive overload. This paper explores the role of three nudges in creating website-specific passwords: financial incentive (present vs absent), length instruction (long password vs no instruction) and stimulus (picture present vs not present). Mechanical Turk workers were asked to create a password in one of these conditions and the resulting passwords were evaluated based on character length, resistance to automated guessing attacks, and time taken to create the password. We found that users created longer passwords when asked to do so or when given a financial incentive and these longer passwords were harder to guess than passwords created with no instruction. Using a picture nudge to support password creation did not lead to passwords that were either longer or more resistant to attacks but did lead to account-specific passwords

Quantification of the probability of containment failure caused by an in-vessel steam explosion for the Sizewell B PWR

AEA Technology has provided an assessment of the probability of α-mode containment failure for the Sizewell B PWR. After a preliminary review of the methodologies available it was decided to use the probabilistic approach described in the paper, based on an extension of the methodology developed by Theofanous et al. (Nucl. Sci. Eng. 97 (1987) 259–325). The input to the assessment is 12 probability distributions; the bases for the quantification of these distributions are discussed. The α-mode assessment performed for the Sizewell B PWR has demonstrated the practicality of the event-tree method with input data represented by probability distributions. The assessment itself has drawn attention to a number of topics, which may be plant and sequence dependent, and has indicated the importance of melt relocation scenarios. The α-mode failure probability following an accident that leads to core melt relocation to the lower head for the Sizewell B PWR has been assessed as a few parts in 10 000, on the basis of current information. This assessment has been the first to consider elevated pressures (6 MPa and 15 MPa) besides atmospheric pressure, but the results suggest only a modest sensitivity to system pressure