2,351 research outputs found
Numerical comparison of pipe-column-separation models
Results comparing six column-separation numerical models for simulating localized vapor cavities and distributed vaporous cavitation in pipelines are presented. The discrete vapor-cavity model (DVCM) is shown to be quite sensitive to selected input parameters. For short pipeline systems, the maximum pressure rise following column separation can vary markedly for small changes in wave speed, friction factor, diameter, initial velocity, length of pipe, or pipe slope. Of the six numerical models, three perform consistently over a broad number of reaches. One of them, the discrete gas-cavity model, is recommended for general use as it is least sensitive to input parameters or to the selected discretization of the pipeline. Three models provide inconsistent estimates of the maximum pressure rise as the number of reaches is increased; however, these models do give consistent results provided the ratio of maximum cavity size to reach volume is kept below 10%.Angus R. Simpson and Anton Bergan
Phosphorylation of Spinophilin Modulates Its Interaction with Actin Filaments
Spinophilin is a protein phosphatase 1 (PP1)- and actin-binding protein that modulates excitatory synaptic transmission and dendritic spine morphology. We report that spinophilin is phosphorylated in vitro by protein kinase A (PKA). Phosphorylation of spinophilin was stimulated by treatment of neostriatal neurons with a dopamine D1 receptor agonist or with forskolin, consistent with spinophilin being a substrate for PKA in intact cells. Using tryptic phosphopeptide mapping, site-directed mutagenesis, and microsequencing analysis, we identified two major sites of phosphorylation, Ser-94 and Ser-177, that are located within the actin-binding domain of spinophilin. Phosphorylation of spinophilin by PKA modulated the association between spinophilin and the actin cytoskeleton. Following subcellular fractionation, unphosphorylated spinophilin was enriched in the postsynaptic density, whereas a pool of phosphorylated spinophilin was found in the cytosol. F-actin co-sedimentation and overlay analysis revealed that phosphorylation of spinophilin reduced the stoichiometry of the spinophilin-actin interaction. In contrast, the ability of spinophilin to bind to PP1 remained unchanged. Taken together, our studies suggest that phosphorylation of spinophilin by PKA modulates the anchoring of the spinophilin-PP1 complex within dendritic spines, thereby likely contributing to the efficacy and plasticity of synaptic transmission
A lower limit on the dark particle mass from dSphs
We use dwarf spheroidal galaxies as a tool to attempt to put precise lower
limits on the mass of the dark matter particle, assuming it is a sterile
neutrino. We begin by making cored dark halo fits to the line of sight velocity
dispersions as a function of projected radius (taken from Walker et al. 2007)
for six of the Milky Way's dwarf spheroidal galaxies. We test Osipkov-Merritt
velocity anisotropy profiles, but find that no benefit is gained over constant
velocity anisotropy. In contrast to previous attempts, we do not assume any
relation between the stellar velocity dispersions and the dark matter ones, but
instead we solve directly for the sterile neutrino velocity dispersion at all
radii by using the equation of state for a partially degenerate neutrino gas
(which ensures hydrostatic equilibrium of the sterile neutrino halo). This
yields a 1:1 relation between the sterile neutrino density and velocity
dispersion, and therefore gives us an accurate estimate of the Tremaine-Gunn
limit at all radii. By varying the sterile neutrino particle mass, we locate
the minimum mass for all six dwarf spheroidals such that the Tremaine-Gunn
limit is not exceeded at any radius (in particular at the centre). We find
sizeable differences between the ranges of feasible sterile neutrino particle
mass for each dwarf, but interestingly there exists a small range 270-280eV
which is consistent with all dSphs at the 1- level.Comment: 13 pages, 2 figures, 1 tabl
On the Proof of Dark Matter, the Law of Gravity and the Mass of Neutrinos
We develop a new method to predict the density associated with weak lensing
maps of (un)relaxed clusters in a range of theories interpolating between GR
and MOND (General Relativity and Modified Newtonian Dynamics). We apply it to
fit the lensing map of the bullet merging cluster 1E0657-56, in order to
constrain more robustly the nature and amount of collisionless matter in
clusters {\it beyond} the usual assumption of spherical equilibrium
(Pointecouteau & Silk 2005) and the validity of GR on cluster scales (Clowe et
al. 2006). Strengthening the proposal of previous authors we show that the
bullet cluster is dominated by a collisionless -- most probably non-baryonic --
component in GR as well as in MOND, a result consistent with the dynamics of
many X-ray clusters. Our findings add to the number of known pathologies for a
purely baryonic MOND, including its inability to fit the latest data from the
Wilkinson Microwave Anisotropy Probe. A plausible resolution of all these
issues and standard issues of Cold Dark Matter with galaxy rotation curves is
the "marriage" of MOND with ordinary hot neutrinos of 2eV. This prediction is
just within the GR-independent maximum of neutrino mass from current
-decay experiments, and is falsifiable by the Karlsruhe Tritium Neutrino
(KATRIN) experiment by 2009. Issues of consistency with strong lensing arcs and
the large relative velocity of the two clusters comprising the bullet cluster
are also addressed.Comment: 4 pages, 1 figure, accepted for publication in ApJL. Added a simple
model of the bullet cluster's high velocity in TeVeS, and discussions of
sterile neutrinos and of non-uniqueness of the lensing deprojectio
Synthesis of 2-BMIDA 6,5-bicyclic heterocycles by Cu(I)/Pd(0)/Cu(II) cascade catalysis of 2-iodoaniline/phenols
A one-pot cascade reaction for the synthesis of 2-BMIDA 6,5-bicyclic heterocycles has been developed using Cu(I)/Pd(0)/Cu(II) catalysis. 2-Iodoanilines and phenols undergo a Cu(I)/Pd(0)-catalyzed Sonogashira reaction with ethynyl BMIDA followed by in situ Cu(II)-catalyzed 5-endo-dig cyclization to generate heterocyclic scaffolds with a BMIDA functional group in the 2-position. The method provides efficient access to borylated indoles, benzofurans, and aza-derivatives, which can be difficult to access through alternative methods
Spiral Galaxies Rotation Curves with a Logarithmic Corrected Newtonian Gravitational Potential
We analyze the rotation curves of 10 spiral galaxies with a newtonian
potential corrected with an extra logarithmic term, using a disc modelization
for the spiral galaxies. There is a new constant associated with the extra term
in the potential. The rotation curve of the chosen sample of spiral galaxies is
well reproduced for a given range of the new constant. It is argued that this
correction can have its origin from string configurations. The compatibility of
this correction with local physics is discussed.Comment: Latex file, 6 pages, 20 figure
Sleep-deprived new mothers gave their infants a higher priority than themselves
ACKNOWLEDGEMENT Special thanks to all the student researchers who helped with the data collection over the years. FUNDING INFORMATION This study was funded by The Center for Music in the Brain which is funded by the Danish National Research Foundation (DNRF 117, awarded to PV). The project was further funded by a European Research Council Consolidator Grant CAREGIVING (No. 615539) to MLK.Peer reviewedPublisher PD
The spacetime structure of MOND with Tully-Fisher relation and Lorentz invariance violation
It is believed that the modification of Newtonian dynamics (MOND) is possible
alternate for dark matter hypothesis. Although Bekenstein's TeVeS supplies a
relativistic version of MOND, one may still wish a more concise covariant
formulism of MOND. In this paper, within covariant geometrical framwork, we
present another version of MOND. We show the spacetime structure of MOND with
properties of Tully-Fisher relation and Lorentz invariance violation.Comment: 6 pages. arXiv admin note: substantial text overlap with
arXiv:1111.1383 and arXiv:1108.344
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