7,141 research outputs found
Criticality of the "critical state" of granular media: Dilatancy angle in the tetris model
The dilatancy angle describes the propensity of a granular medium to dilate
under an applied shear. Using a simple spin model (the ``tetris'' model) which
accounts for geometrical ``frustration'' effects, we study such a dilatancy
angle as a function of density. An exact mapping can be drawn with a directed
percolation process which proves that there exists a critical density
above which the system expands and below which it contracts under shear. When
applied to packings constructed by a random deposition under gravity, the
dilatancy angle is shown to be strongly anisotropic, and it constitutes an
efficient tool to characterize the texture of the medium.Comment: 7 pages RevTex, 8eps figure, to appear in Phys. Rev.
Genomic analysis of NAC transcription factors in banana (Musa acuminata) and definition of NAC orthologous groups for monocots and dicots
Identifying the molecular mechanisms underlying tolerance to abiotic stresses is important in crop breeding. A comprehensive understanding of the gene families associated with drought tolerance is therefore highly relevant. NAC transcription factors form a large plant-specific gene family involved in the regulation of tissue development and responses to biotic and abiotic stresses. The main goal of this study was to set up a framework of orthologous groups determined by an expert sequence comparison of NAC genes from both monocots and dicots. In order to clarify the orthologous relationships among NAC genes of different species, we performed an in-depth comparative study of four divergent taxa, in dicots and monocots, whose genomes have already been completely sequenced: Arabidopsis thaliana, Vitis vinifera, Musa acuminata and Oryza sativa. Due to independent evolution, NAC copy number is highly variable in these plant genomes. Based on an expert NAC sequence comparison, we propose forty orthologous groups of NAC sequences that were probably derived from an ancestor gene present in the most recent common ancestor of dicots and monocots. These orthologous groups provide a curated resource for large-scale protein sequence annotation of NAC transcription factors. The established orthology relationships also provide a useful reference for NAC function studies in newly sequenced genomes such as M. acuminata and other plant species
Internal avalanches in models of granular media
We study the phenomenon of internal avalanching within the context of
recently introduced lattice models of granular media. The avalanche is produced
by pulling out a grain at the base of the packing and studying how many grains
have to rearrange before the packing is once more stable. We find that the
avalanches are long-ranged, decaying as a power-law. We study the distriution
of avalanches as a function of the density of the packing and find that the
avalanche distribution is a very sensitive structural probe of the system.Comment: 12 pages including 9 eps figures, LaTeX. To appear in Fractal
A community annotation system for Musa genomes
Poster presented at ISHS/ProMusa Banana Symposium Global Perspectives on Asian Challenges. Guangzhou (China), 14-18 Sep 200
Loneliness, Depression, and Inflammation: Evidence from the Multi-Ethnic Study of Atherosclerosis
Objective
Both objective and subjective aspects of social isolation have been associated with alterations in immune markers relevant to multiple chronic diseases among older adults. However, these associations may be confounded by health status, and it is unclear whether these social factors are associated with immune functioning among relatively healthy adults. The goal of this study was to examine the associations between perceived loneliness and circulating levels of inflammatory markers among a diverse sample of adults.
Methods
Data come from a subset of the Multi-Ethnic Study of Atherosclerosis (n = 441). Loneliness was measured by three items derived from the UCLA Loneliness Scale. The association between loneliness and C-reactive protein (CRP) and fibrinogen was assessed using multivariable linear regression analyses. Models were adjusted for demographic and health characteristics.
Results
Approximately 50% of participants reported that they hardly ever felt lonely and 17.2% felt highly lonely. Individuals who were unmarried/unpartnered or with higher depressive symptoms were more likely to report being highly lonely. There was no relationship between perceived loneliness and ln(CRP) (ÎČ = -0.051, p = 0.239) adjusting for demographic and health characteristics. Loneliness was inversely associated with ln(fibrinogen) (ÎČ = -0.091, p = 0.040), although the absolute magnitude of this relationship was small.
Conclusion
These results indicate that loneliness is not positively associated with fibrinogen or CRP among relatively healthy middle-aged adults
Crop ontology in support of conservation and use of banana genetic resources
Poster presented at Workshop on Crop Ontology and Phenotyping Data Interoperability. Montpellier (France), 31 Mar-4 Apr 201
Using an agent-based model to simulate childrenâs active travel to school
Abstract
Background
Despite the multiple advantages of active travel to school, only a small percentage of US children and adolescents walk or bicycle to school. Intervention studies are in a relatively early stage and evidence of their effectiveness over long periods is limited. The purpose of this study was to illustrate the utility of agent-based models in exploring how various policies may influence childrenâs active travel to school.
Methods
An agent-based model was developed to simulate childrenâs school travel behavior within a hypothetical city. The model was used to explore the plausible implications of policies targeting two established barriers to active school travel: long distance to school and traffic safety. The percent of children who walk to school was compared for various scenarios.
Results
To maximize the percent of children who walk to school the school locations should be evenly distributed over space and children should be assigned to the closest school. In the case of interventions to improve traffic safety, targeting a smaller area around the school with greater intensity may be more effective than targeting a larger area with less intensity.
Conclusions
Despite the challenges they present, agent based models are a useful complement to other analytical strategies in studying the plausible impact of various policies on active travel to school.http://deepblue.lib.umich.edu/bitstream/2027.42/112566/1/12966_2012_Article_757.pd
Shear band dynamics from a mesoscopic modeling of plasticity
The ubiquitous appearance of regions of localized deformation (shear bands)
in different kinds of disordered materials under shear is studied in the
context of a mesoscopic model of plasticity. The model may or may not include
relaxational (aging) effects. In the absence of relaxational effects the model
displays a monotonously increasing dependence of stress on strain-rate, and
stationary shear bands do not occur. However, in start up experiments transient
(although long lived) shear bands occur, that widen without bound in time. I
investigate this transient effect in detail, reproducing and explaining a t^1/2
law for the thickness increase of the shear band that has been obtained in
atomistic numerical simulations. Relaxation produces a negative sloped region
in the stress vs. strain-rate curve that stabilizes the formation of shear
bands of a well defined width, which is a function of strain-rate. Simulations
at very low strain-rates reveal a non-trivial stick-slip dynamics of very thin
shear bands that has relevance in the study of seismic phenomena. In addition,
other non-stationary processes, such as stop-and-go, or strain-rate inversion
situations display a phenomenology that matches very well the results of recent
experimental studies.Comment: 10 pages, 10 figure
Inorganic Chemistry in the Mountain Critical Zone : Are the mountain water towers of contemporary society under threat by trace contaminants ?
Potentially harmful trace elements (PHTEs) do not accumulate homogeneously over mountainous area. Generally, highland areas receive more wet deposition, aerosols, and ions than surrounding lowlands ones, mainly due to orographic enhancement. Within mountainous areas, however, the accumulation of PHTEs is much more complex. Direct cloud deposition of contaminants could act as an important pathway of deposition either from a regional low-altitude, cloud level, orographic clouds, or haze whose frequency of occurrence is much higher than surrounding lowlands areas. The accumulation legacy of PHTEs from local human activities should also be considered when investigating PHTE distribution in mountainous areas. Combined with other phenomena, the PHTE accumulation patterns could be highly variable depending on local topography, dominant winds, and vegetation cover, as well as present and past local practices. Despite their remoteness, mountain ecosystems are highly sensitive to PHTEs loadings
Stability of Plane-Parallel Vibrational Flow In a Two-Layer System
The stability of the interface separating two immiscible incompressible
fluids of different densities and viscosities is considered in the case of
fluids filling a cavity which performs horizontal harmonic oscillation. There
exists a simple basic state which corresponds to the unperturbed interface and
plane-parallel unsteady counter flows; the properties of this state are
examined. A linear stability problem for the interface is formulated and solved
a) for both inviscid and b) for both viscous fluids. A transformation is found
which reduces the linear stability problem under inviscid approximation to the
Mathieu equation. The parametric resonant regions of instability associated
with the intensification of capillary-gravity waves at the interface are
examined and the results are compared to those found in the viscous case in a
fully numerical investigation.Comment: 15 pages, 6 figures; soon to appear in European Journal of Fluid
Mechanic
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