1,250 research outputs found
On extracting sediment transport information from measurements of luminescence in river sediment
Accurately quantifying sediment transport rates in rivers remains an important goal for geomorphologists, hydraulic engineers, and environmental scientists. However, current techniques for measuring long-time scale (102–106 years) transport rates are laborious, and formulae to predict transport are notoriously inaccurate. Here we attempt to estimate sediment transport rates by using luminescence, a property of common sedimentary minerals that is used by the geoscience community for geochronology. This method is advantageous because of the ease of measurement on ubiquitous quartz and feldspar sand. We develop a model from first principles by using conservation of energy and sediment mass to explain the downstream pattern of luminescence in river channel sediment. We show that the model can accurately reproduce the luminescence observed in previously published field measurements from two rivers with very different sediment transport styles. The model demonstrates that the downstream pattern of river sand luminescence should show exponential-like decay in the headwaters which asymptotes to a constant value with further downstream distance. The parameters from the model can then be used to estimate the time-averaged virtual velocity, characteristic transport lengthscale, storage time scale, and floodplain exchange rate of fine sand-sized sediment in a fluvial system. The sediment transport values predicted from the luminescence method show a broader range than those reported in the literature, but the results are nonetheless encouraging and suggest that luminescence demonstrates potential as a sediment transport indicator. However, caution is warranted when applying the model as the complex nature of sediment transport can sometimes invalidate underlying simplifications
Src homology 2 domain containing protein 5 (SH2D5) binds the breakpoint cluster region protein, BCR, and regulates levels of Rac1-GTP
SH2D5 is a mammalian-specific, uncharacterized adaptor-like protein that contains an N-terminal phosphotyrosine binding (PTB) domain and a C-terminal Src Homology 2 (SH2) domain. We show that SH2D5 is highly enriched in adult mouse brain, particularly in purkinjie cells in the cerebellum and the cornu ammonis of the hippocampus. Despite harboring two potential phosphotyrosine (pTyr) recognition domains, SH2D5 binds minimally to pTyr ligands, consistent with the absence of a conserved pTyr-binding arginine residue in the SH2 domain. Immunoprecipitation coupled to mass spectrometry (IP-MS) from cultured cells revealed a prominent association of SH2D5 with Breakpoint Cluster Region protein (BCR), a RacGAP that is also highly expressed in brain. This interaction occurred between the PTB domain of SH2D5 and an NxxF motif located within the N-terminal region of BCR. siRNA-mediated depletion of SH2D5 in a neuroblastoma cell line, B35, induced a cell rounding phenotype correlated with low levels of activated Rac1-GTP, suggesting that SH2D5 affects Rac1-GTP levels. Taken together, our data provide the first characterization of the SH2D5 signaling protein
Dynamics of the Tippe Top via Routhian Reduction
We consider a tippe top modeled as an eccentric sphere, spinning on a
horizontal table and subject to a sliding friction. Ignoring translational
effects, we show that the system is reducible using a Routhian reduction
technique. The reduced system is a two dimensional system of second order
differential equations, that allows an elegant and compact way to retrieve the
classification of tippe tops in six groups as proposed in [1] according to the
existence and stability type of the steady states.Comment: 16 pages, 7 figures, added reference. Typos corrected and a forgotten
term in de linearized system is adde
Chiral extrapolation of lattice data for B-meson decay constant
The B-meson decay constant fB has been calculated from unquenched lattice QCD
in the unphysical region. For extrapolating the lattice data to the physical
region, we propose a phenomenological functional form based on the effective
chiral perturbation theory for heavy mesons, which respects both the heavy
quark symmetry and the chiral symmetry, and the non-relativistic constituent
quark model which is valid at large pion masses. The inclusion of pion loop
corrections leads to nonanalytic contributions to fB when the pion mass is
small. The finite-range regularization technique is employed for the
resummation of higher order terms of the chiral expansion. We also take into
account the finite volume effects in lattice simulations. The dependence on the
parameters and other uncertainties in our model are discussed.Comment: 11 pages, 3 Postscript figures, accepted for publication in EPJ
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