Geometry of Frictionless and Frictional Sphere Packings

We study static packings of frictionless and frictional spheres in three dimensions, obtained via molecular dynamics simulations, in which we vary particle hardness, friction coefficient, and coefficient of restitution. Although frictionless packings of hard-spheres are always isostatic (with six contacts) regardless of construction history and restitution coefficient, frictional packings achieve a multitude of hyperstatic packings that depend on system parameters and construction history. Instead of immediately dropping to four, the coordination number reduces smoothly from $z=6$ as the friction coefficient $\mu$ between two particles is increased.Comment: 6 pages, 9 figures, submitted to Phys. Rev.

Statistics of the contact network in frictional and frictionless granular packings

Simulated granular packings with different particle friction coefficient mu are examined. The distribution of the particle-particle and particle-wall normal and tangential contact forces P(f) are computed and compared with existing experimental data. Here f equivalent to F/F-bar is the contact force F normalized by the average value F-bar. P(f) exhibits exponential-like decay at large forces, a plateau/peak near f = 1, with additional features at forces smaller than the average that depend on mu. Computations of the force-force spatial distribution function and the contact point radial distribution function indicate that correlations between forces are only weakly dependent on friction and decay rapidly beyond approximately three particle diameters. Distributions of the particle-particle contact angles show that the contact network is not isotropic and only weakly dependent on friction. High force-bearing structures, or force chains, do not play a dominant role in these three dimensional, unloaded packings.Comment: 11 pages, 13 figures, submitted to PR

Thresholds for adding degraded tropical forest to the conservation estate

Logged and disturbed forests are often viewed as degraded and depauperate environments compared with primary forest. However, they are dynamic ecosystems1 that provide refugia for large amounts of biodiversity2,3, so we cannot afford to underestimate their conservation value4. Here we present empirically defined thresholds for categorizing the conservation value of logged forests, using one of the most comprehensive assessments of taxon responses to habitat degradation in any tropical forest environment. We analysed the impact of logging intensity on the individual occurrence patterns of 1,681 taxa belonging to 86 taxonomic orders and 126 functional groups in Sabah, Malaysia. Our results demonstrate the existence of two conservation-relevant thresholds. First, lightly logged forests (68%) of their biomass removed, and these are likely to require more expensive measures to recover their biodiversity value. Overall, our data confirm that primary forests are irreplaceable5, but they also reinforce the message that logged forests retain considerable conservation value that should not be overlooked

Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures

Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo

Determination of artelinic acid in blood plasma by high-performance liquid chromatography

A reversed-phase high-performance liquid chromatographic method is described for the analysis of the new antimalarial drug artelinic acid in blood plasma. The influence of mobile phase composition, pH and type of mobile phase modifier on the retention of artelinic acid on the reversed-phase column is reported. Linear calibration curves were obtained in the range 0-500 ng/ml artelinic acid. Intra-assay and inter-assay variability in the analysis of plasma samples spiked with the drug were ≤ 15%. Plasma samples of the drug were found to be unstable when stored at -20°C, the concentration of the drug decreasing by over 50% within three days. Plasma samples stored at -70°C remained stable for at least two weeks. Initial pharmacokinetic studies in the rat showed that following intravenous administration, plasma concentrations of artelinic acid declined mono-exponentially. The relatively short elimination half-life (17 ± 5 min) of artelinic acid is consistent with what is known for qinghaosu and its derivatives

Influence of bluestain fungi on laboratory rearing of pinewood nematode infested beetles

Au cours de cette étude sont comparés les nombres de #Bursaphelenchus xylophilus transportés par #Monochamus carolinensis lorsque l'insecte se développe dans des bûchettes de pin inoculées avec le champignon #Ophiostoma minus, cause de la coloration du bois et dans des bûchettes non inoculées. Les insectes émergeant des bûchettes inoculées contiennent un plus grand nombre (8198) de "dauer" juvéniles de #B. xylophilus que les insectes émergeant de bûchettes non inoculées (5570). La densité de nématodes est plus élevée dans les bûchettes infectées par le champignon que dans les témoins, mais la différence n'est pas significative. La proportion d'insectes émergeant transportant des nématodes ne dépend pas de l'inoculation du champignon. Cette inoculation n'affecte pas le nombre de jours requis pour le développement de l'insecte, de l'oviposition à l'émergence des stades adultes. La méthode décrite dans cette étude pour l'élevage au laboratoire d'insectes vecteurs de #B. xylophilus$permet d'obtenir des insectes utilisables en vue d'études d'association entre "B. xylophilus$ et ses hôtes vecteurs du genre #Monochamu$. (Résumé d'auteur

Insecticide resistance and implications for future aphid management in Australian grains and pastures: A review

Aphids can cause substantial damage to cereals, oilseeds and legumes through direct feeding and through the transmission of plant pathogenic viruses. Aphid-resistant varieties are only available for a limited number of crops. In Australia, growers often use prophylactic sprays to control aphids, but this strategy can lead to non-target effects and the development of insecticide resistance. Insecticide resistance is a problem in one aphid pest of Australian grains in Australia, the green peach aphid (Myzus persicae). Molecular analyses of field-collected samples demonstrate that amplified E4 esterase resistance to organophosphate insecticides is widespread in Australian grains across Australia. Knockdown resistance to pyrethroids is less abundant, but has an increased frequency in areas with known frequent use of these insecticides. Modified acetylcholinesterase resistance to dimethyl carbamates, such as pirimicarb, has not been found in Australia, nor has resistance to imidacloprid. Australian grain growers should consider control options that are less likely to promote insecticide resistance, and have reduced impacts on natural enemies. Research is ongoing in Australia and overseas to provide new strategies for aphid management in the future