1,689 research outputs found
Spontaneous Stratification in Granular Mixtures
Granular materials size segregate when exposed to external periodic
perturbations such as vibrations. Moreover, mixtures of grains of different
sizes spontaneously segregate in the absence of external perturbations: when a
mixture is simply poured onto a pile, the large grains are more likely to be
found near the base, while the small grains are more likely to be near the top.
Here, we report a spontaneous phenomenon arising when we pour a mixture between
two vertical plates: the mixture spontaneously stratifies into alternating
layers of small and large grains whenever the large grains are rougher than the
small grains. In contrast, we find only spontaneous segregation when the large
grains are more rounded than the small grains. The stratification is related to
the occurrence of avalanches; during each avalanche the grains comprising the
avalanche spontaneously stratify into a pair of layers through a "kink"
mechanism, with the small grains forming a sublayer underneath the layer of
large grains.Comment: 4 pages, 6 figures, http://polymer.bu.edu/~hmakse/Home.htm
On the Thermodynamic Geometry and Critical Phenomena of AdS Black Holes
In this paper, we study various aspects of the equilibrium thermodynamic
state space geometry of AdS black holes. We first examine the
Reissner-Nordstrom-AdS (RN-AdS) and the Kerr-AdS black holes. In this context,
the state space scalar curvature of these black holes is analysed in various
regions of their thermodynamic parameter space. This provides important new
insights into the structure and significance of the scalar curvature. We
further investigate critical phenomena, and the behaviour of the scalar
curvature near criticality, for KN-AdS black holes in two mixed ensembles,
introduced and elucidated in our earlier work arXiv:1002.2538 [hep-th]. The
critical exponents are identical to those in the RN-AdS and Kerr-AdS cases in
the canonical ensemble. This suggests an universality in the scaling behaviour
near critical points of AdS black holes. Our results further highlight
qualitative differences in the thermodynamic state space geometry for electric
charge and angular momentum fluctuations of these.Comment: 1 + 37 Pages, LaTeX, includes 31 figures. A figure and a
clarification added
Sex: A change in our guidelines to authors to ensure that this is no longer an ignored experimental variable.
Risk assessment for the spread of Serratia marcescens within dental-unit waterline systems using Vermamoeba vermiformis
Vermamoeba vermiformis is associated with the biofilm ecology of dental-unit waterlines (DUWLs). This study investigated whether V. vermiformis is able to act as a vector for potentially pathogenic bacteria and so aid their dispersal within DUWL systems. Clinical dental water was initially examined for Legionella species by inoculating it onto Legionella selective-medium plates. The molecular identity/profile of the glassy colonies obtained indicated none of these isolates were Legionella species. During this work bacterial colonies were identified as a non-pigmented Serratia marcescens. As the water was from a clinical DUWL which had been treated with Alpron™ this prompted the question as to whether S. marcescens had developed resistance to the biocide. Exposure to Alpron™ indicated that this dental biocide was effective, under laboratory conditions, against S. marcescens at up to 1x108 colony forming units/millilitre (cfu/ml). V. vermiformis was cultured for eight weeks on cells of S. marcescens and Escherichia coli. Subsequent electron microscopy showed that V. vermiformis grew equally well on S. marcescens and E. coli (p = 0.0001). Failure to detect the presence of S. marcescens within the encysted amoebae suggests that V. vermiformis is unlikely to act as a vector supporting the growth of this newly isolated, nosocomial bacterium
Long-term cycles in the history of life: Periodic biodiversity in the Paleobiology Database
Time series analysis of fossil biodiversity of marine invertebrates in the
Paleobiology Database (PBDB) shows a significant periodicity at approximately
63 My, in agreement with previous analyses based on the Sepkoski database. I
discuss how this result did not appear in a previous analysis of the PBDB. The
existence of the 63 My periodicity, despite very different treatment of
systematic error in both PBDB and Sepkoski databases strongly argues for
consideration of its reality in the fossil record. Cross-spectral analysis of
the two datasets finds that a 62 My periodicity coincides in phase by 1.6 My,
equivalent to better than the errors in either measurement. Consequently, the
two data sets not only contain the same strong periodicity, but its peaks and
valleys closely correspond in time. Two other spectral peaks appear in the PBDB
analysis, but appear to be artifacts associated with detrending and with the
increased interval length. Sampling-standardization procedures implemented by
the PBDB collaboration suggest that the signal is not an artifact of sampling
bias. Further work should focus on finding the cause of the 62 My periodicity.Comment: Published in PLoS ONE. 5 pages, 3 figures. Version with live links,
discussion available at
http://www.plosone.org/article/info:doi/10.1371/journal.pone.0004044#to
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