Contributions to the mixed-alkali effect in molecular dynamics simulations of alkali silicate glasses

The mixed-alkali effect on the cation dynamics in silicate glasses is analyzed via molecular dynamics simulations. Observations suggest a description of the dynamics in terms of stable sites mostly specific to one ionic species. As main contributions to the mixed--alkali slowdown longer residence times and an increased probability of correlated backjumps are identified. The slowdown is related to the limited accessibility of foreign sites. The mismatch experienced in a foreign site is stronger and more retarding for the larger ions, the smaller ions can be temporarily accommodated. Also correlations between unlike as well as like cations are demonstrated that support cooperative behavior.Comment: 10 pages, 12 figures, 1 table, revtex4, submitted to Phys. Rev.

The CHIME graduate programme in health informatics

In 1999 University College London inaugurated a programme of graduate part-time Health Informatics courses to support the UK National Health Service?s Information for Health strategy. The programme has attracted students from across the UK and abroad, with a diverse range of backgrounds and skills and has proved a challenging and rewarding experience for students and tutors alike. The modular programme aims to provide a thorough grounding in the theory and practice of Health Informatics and addresses important application areas. The guiding principle is that Health Informatics graduates need to understand computers and programming but that, since the majority are not going to become programmers, programming methods should not dominate the curriculum.In the taught phase of the programme students attend college for 3 days a month and complete an assignment each month, based on home study. Students may graduate with a certificate or diploma, or go on to tackle a dissertation leading to an MSc. Research projects have included a patient record system based on speech input, a mathematical model for illustrating to patients the risks associated with smoking, an analysis of Trust staff's preparedness for Information for Health and a patient information leaflet giving advice about drug related information on the Web. As we move towards our fifth intake of students, we are in the process of evaluating our programme and carrying out a follow up study of our graduates? subsequent career pathways

Primitive divisors on twists of the Fermat cubic

We show that for an elliptic divisibility sequence on a twist of the Fermat cubic, u3+v3=m, with m cube-free, all the terms beyond the first have a primive divisor

Security and confidentiality approach for the Clinical E-Science Framework (CLEF)

Objectives: CLEF is an MRC sponsored project in the E-Science programme that aims to establish methodologies and a technical infrastructure for the next generation of integrated clinical and bioscience research. Methods: The heart of the CLEF approach to this challenge is to design and develop a pseudonymised repository of histories of cancer patients that can be accessed by researchers. Robust mechanisms and policies have been developed to ensure that patient privacy and confidentiality are preserved while delivering a repository of such medically rich information for the purposes of scientific research. Results: This paper summarises the overall approach adopted by CLEF to meet data protection requirements, including the data flows, pseudonymisation measures and additional monitoring policies that are currently being developed. Conclusion: Once evaluated, it is hoped that the CLEF approach can serve as a model for other distributed electronic health record repositories to be accessed for research

Hunting and sale of Pangolins across Sub-Saharan Africa: a preliminary analysis

Pangolins (Pholidota: Manidae) are hunted and traded for their meat and scales. We conducted preliminary analyses on the hunting and sale at markets of four species of pangolin across Sub-Saharan Africa based on data from the OFFTAKE database. Our analyses show that all four species of African pangolin are hunted and sold at markets throughout much of Sub-Saharan Africa. The proportion of pangolins as part of the total vertebrates hunted has increased significantly during the 43 years, from 1972-2014, for which we have data

The colonization of maize seedling roots and rhizosphere by Fusarium spp. in Mississippi in two soil types under conventional tillage and notillage systems

De 1995 à 1997, le maïs hybride Pioneer 3167 a été semé annuellement à quatre dates dans deux types de sol du Mississippi et échantillonné hebdomadairement de une à quatre semaines après le semis. Les parcelles ont été labourées avec un outil aratoire multi-fonctions et les rangs formés à l'automne, ou n'ont pas été travaillées avant le semis direct du printemps. Avec le labour, les Fusarium spp. ont été isolés plus fréquemment pour les dates de semis les plus précoces et les plus tardives et pour un échantillonnage après 10 et 17 jours. Pour les parcelles sans travail du sol, les fréquences d'isolement étaient globalement plus faibles que pour les parcelles avec travail du sol classique et déclinaient avec l'avancée des dates de semis et l'allongement de la période entre le semis et l'échantillonnage. Les populations de Fusarium les plus élevées ont été trouvées dans la rhizosphère dans des parcelles avec travail du sol classique dont le sol était un limon siliceux et avec l'échantillonnage fait 28 jours après la deuxième plantation de 1997; les populations les plus faibles provenaient d'un sol limono-argileux. Le F. monoliforme, le F. solani et le F. oxysporum ont été les principales espèces de Fusarium isolées des racines de semis de maïs. Dans des essais de pathogénicité, le F. moniliforme et le F. solani ont eu des effets mesurables sur des semis de maïs. Le F. moniliforme a réduit la longueur des racines principales et a réduit le nombre de racines secondaires alors que le F. solani a réduit la masse sèche des racines de semis de maïs.Pioneer 3167 hybrid maize was planted on two soil types in Mississippi on four dates annually from 1995 to 1997 and was sampled at weekly intervals beginning one week and ending 4 weeks after planting. Plots were either tilled with a do-all and rows formed in the fall or were left undisturbed until planting in the spring. Under tillage, Fusarium spp. were isolated most frequently at the earliest and latest planting dates when seedlings were sampled at 10 and 17 days. In no-tillage plots, the overall isolation frequency was lower than in conventional-tillage plots and decreased with later planting dates and sampling times. The highest Fusarium populations were found in the rhizosphere of a silt loam in conventional-tillage plots when seedlings were sampled 28 days after the second planting in 1997, compared to populations from a silty clay soil. Fusarium moniliforme, F. solani and F. oxysporum were the predominant Fusarium spp. isolated from maize seedling roots. In pathogenicity tests, F. moniliforme and F. solani produced measurable effects on maize seedlings. F. moniliforme reduced the length of primary roots and decreased the number of secondary roots, and F. solani reduced root dry weight of maize seedlings

Effective Inner Radius of Tilted Black Hole Accretion Disks

One of the primary means of determining the spin of an astrophysical black hole is by actually measuring the inner radius of a surrounding accretion disk and using that to infer the spin. By comparing a number of different estimates of the inner radius from simulations of tilted accretion disks with differing black-hole spins, we show that such a procedure can give quite wrong answers. Over the range 0 <= a/M <= 0.9, we find that, for moderately thick disks (H/r ~ 0.2) with modest tilt (15 degrees), the inner radius is nearly independent of spin. This result is likely dependent on tilt, such that for larger tilts, it may even be that the inner radius would increase with increasing spin. In the opposite limit, we confirm through numerical simulations of untilted disks that, in the limit of zero tilt, the inner radius recovers approximately the expected dependence on spin.Comment: 5 pages, 4 figures, accepted to ApJ Letter

Probability Models for Degree Distributions of Protein Interaction Networks

The degree distribution of many biological and technological networks has been described as a power-law distribution. While the degree distribution does not capture all aspects of a network, it has often been suggested that its functional form contains important clues as to underlying evolutionary processes that have shaped the network. Generally, the functional form for the degree distribution has been determined in an ad-hoc fashion, with clear power-law like behaviour often only extending over a limited range of connectivities. Here we apply formal model selection techniques to decide which probability distribution best describes the degree distributions of protein interaction networks. Contrary to previous studies this well defined approach suggests that the degree distribution of many molecular networks is often better described by distributions other than the popular power-law distribution. This, in turn, suggests that simple, if elegant, models may not necessarily help in the quantitative understanding of complex biological processes.

Induced encystment improves resistance to preservation and storage of Acanthamoeba castellanii

Several conditions that allow the preservation, storage and rapid, efficient recovery of viable Acanthamoeba castellanii organisms were investigated. The viability of trophozoites (as determined by time to confluence) significantly declined over a period of 12 months when stored at −70°C using dimethyl sulfoxide (DMSO; 5 or 10%) as cryopreservant. As A. castellanii are naturally capable of encystment, studies were undertaken to determine whether induced encystment might improve the viability of organisms under a number of storage conditions. A. castellanii cysts stored in the presence of Mg2+ at 4°C remained viable over the study period, although time to confluence was increased from approximately 8 days to approximately 24 days over the 12-month period. Storage of cysts at −70°C with DMSO (5 or 10%) or 40% glycerol, but not 80% glycerol as cryopreservants increased their viability over the 12-month study period compared with those stored at room temperature. Continued presence of Mg2+ in medium during storage had no adverse effects and generally improved recovery of viable organisms. The present study demonstrates that A. castellanii can be stored as a non-multiplicative form inexpensively, without a need for cryopreservation, for at least 12 months, but viability is increased by storage at −70°C