8,673 research outputs found
Information filtering via Iterative Refinement
With the explosive growth of accessible information, expecially on the
Internet, evaluation-based filtering has become a crucial task. Various systems
have been devised aiming to sort through large volumes of information and
select what is likely to be more relevant. In this letter we analyse a new
ranking method, where the reputation of information providers is determined
self-consistently.Comment: 10 pages, 3 figures. Accepted for publication on Europhysics Letter
Numerical modeling of dynamic powder compaction using the Kawakita equation of state
Dynamic powder compaction is analyzed using the assumption that the powder behaves, while it is being compacted, like a hydrodynamic fluid in which deviatoric stress and heat conduction effects can be ignored throughout the process. This enables techniques of computational fluid dynamics such the equilibrium flux method to be used as a modeling tool. The equation of state of the powder under compression is assumed to be a modified version of the Kawakita loading curve. Computer simulations using this model are performed for conditions matching as closely as possible with those from experiments by Page and Killen [Powder Metall. 30, 233 (1987)]. The numerical and experimental results are compared and a surprising degree of qualitative agreement is observed
Unifying Parsimonious Tree Reconciliation
Evolution is a process that is influenced by various environmental factors,
e.g. the interactions between different species, genes, and biogeographical
properties. Hence, it is interesting to study the combined evolutionary history
of multiple species, their genes, and the environment they live in. A common
approach to address this research problem is to describe each individual
evolution as a phylogenetic tree and construct a tree reconciliation which is
parsimonious with respect to a given event model. Unfortunately, most of the
previous approaches are designed only either for host-parasite systems, for
gene tree/species tree reconciliation, or biogeography. Hence, a method is
desirable, which addresses the general problem of mapping phylogenetic trees
and covering all varieties of coevolving systems, including e.g., predator-prey
and symbiotic relationships. To overcome this gap, we introduce a generalized
cophylogenetic event model considering the combinatorial complete set of local
coevolutionary events. We give a dynamic programming based heuristic for
solving the maximum parsimony reconciliation problem in time O(n^2), for two
phylogenies each with at most n leaves. Furthermore, we present an exact
branch-and-bound algorithm which uses the results from the dynamic programming
heuristic for discarding partial reconciliations. The approach has been
implemented as a Java application which is freely available from
http://pacosy.informatik.uni-leipzig.de/coresym.Comment: Peer-reviewed and presented as part of the 13th Workshop on
Algorithms in Bioinformatics (WABI2013
Thermalisation time and specific heat of neutron stars crust
We discuss the thermalisation process of the neutron stars crust described by
solving the heat transport equation with a microscopic input for the specific
heat of baryonic matter. The heat equation is solved with initial conditions
specific to a rapid cooling of the core. To calculate the specific heat of
inner crust baryonic matter, i.e., nuclear clusters and unbound neutrons, we
use the quasiparticle spectrum provided by the Hartree-Fock-Bogoliubov approach
at finite temperature. In this framework we analyse the dependence of the crust
thermalisation on pairing properties and on cluster structure of inner crust
matter. It is shown that the pairing correlations reduce the crust
thermalisation time by a very large fraction. The calculations show also that
the nuclear clusters have a non-negligible influence on the time evolution of
the surface temperature of the neutron star.Comment: 7 pages, 5 figures, submitted to Phys. Rev.
Measurement of the elastic tensor of SmScO3 and NdSc03 using resonant ultrasound spectroscopy with ab initio calculations
The complete elastic tensors of SmScO3 and NdScO3 were measured using resonant ultrasound spectroscopy (RUS) in combination with ab-initio calculations. Measurement of the elastic tensor of these recently synthesized single crystal RE scandates is essential for understanding dynamic lattice applications including phonon confinement, strain induced thin film growth and superlattice construction. On average, the experimental elastic constants differed by less than 5% of the theoretical values, further validating the accuracy of modern ab-initio calculations as a means of estimating the initial elastic constants used in RUS measurements
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Structure-Induced Reversible Anionic Redox Activity in Na Layered Oxide Cathode
Anionic redox reaction (ARR) in lithium- and sodium-ion batteries is under hot discussion, mainly regarding how oxygen anion participates and to what extent oxygen can be reversibly oxidized and reduced. Here, a P3-type Na0.6[Li0.2Mn0.8]O2 with reversible capacity from pure ARR was studied. The interlayer O-O distance (peroxo-like O-O dimer, 2.506(3) Ă…), associated with oxidization of oxygen anions, was directly detected by using a neutron total scattering technique. Different from Li2RuO3 or Li2IrO3 with strong metal-oxygen (M-O) bonding, for P3-type Na0.6[Li0.2Mn0.8]O2 with relatively weak Mn-O covalent bonding, crystal structure factors might play an even more important role in stabilizing the oxidized species, as both Li and Mn ions are immobile in the structure and thus may inhibit the irreversible transformation of the oxidized species to O2 gas. Utilization of anionic redox reaction (ARR) on oxygen has been considered as an effective way to promote the charge-discharge capacity of the layered oxide cathodes for lithium- or sodium-ion batteries. The detailed mechanism of ARR, in particular how crystal structure affects and coordinates with the ARR, is not yet well understood. In the present work, a combination of X-ray and neutron total scattering measurements has been performed to study the structure of the prototype P3-type layered Na0.6[Li0.2Mn0.8]O2 with pure ARR. Unique structural characteristics, rather than prevailing knowledge of covalency of metal-oxygen, enable the stabilization of the crystal structure of Na0.6[Li0.2Mn0.8]O2 along with the ARR. This work suggests that reversible ARR can be manipulated by proper structure designs, thus to achieve high lithium or sodium storage in layered oxide cathodes. For P3-type Na0.6[Li0.2Mn0.8]O2 with relatively weak Mn-O covalent bonding, crystal structure factors play an important role in stabilizing the oxidized species, inhibiting the irreversible transformation of the oxidized species to O2 gas. The finding is important for better design of layered oxide positive materials with higher reversible capacity via the introduction of a reversible anionic redox reaction
Implications of Hyperon Pairing for Cooling of Neutron Stars
The implications of hyperon pairing for the thermal evolution of neutron
stars containing hyperons are investigated. The outcome of cooling simulations
are compared for neutron star models composed only of nucleons and leptons,
models including hyperons, and models including pairing of hyperons. We show
that lambda and neutron pairing suppresses all possible fast neutrino emission
processes in not too massive neutron stars. The inclusion of lambda pairing
yields better agreement with X-ray observations of pulsars. Particularly, the
surface temperatures deduced from X-ray observations within the hydrogen
atmosphere model are more consistent with the thermal history of neutron stars
containing hyperons, if the critical temperature for the onset of lambda and
nucleon pairing is not too small.Comment: 7 pages, 3 figures. To be published in ApJL. The postscript and
additional tables can be found at
http://www.physik.uni-muenchen.de/sektion/suessmann/astro/cool/schaab.089
Configuration mixing in Pb : band structure and electromagnetic properties
In the present paper, we carry out a detailed analysis of the presence and
mixing of various families of collective bands in Pb. Making use of the
interacting boson model, we construct a particular intermediate basis that can
be associated with the unperturbed bands used in more phenomenological studies.
We use the E2 decay to construct a set of collective bands and discuss in
detail the B(E2)-values. We also perform an analysis of these theoretical
results (Q, B(E2)) to deduce an intrinsic quadrupole moment and the associated
quadrupole deformation parameter, using an axially deformed rotor model.Comment: submitted to pr
Real space tests of the statistical isotropy and Gaussianity of the WMAP CMB data
ABRIDGED: We introduce and analyze a method for testing statistical isotropy
and Gaussianity and apply it to the WMAP CMB foreground reduced, temperature
maps, and cross-channel difference maps. We divide the sky into regions of
varying size and shape and measure the first four moments of the one-point
distribution within these regions, and using their simulated spatial
distributions we test the statistical isotropy and Gaussianity hypotheses. By
randomly varying orientations of these regions, we sample the underlying CMB
field in a new manner, that offers a richer exploration of the data content,
and avoids possible biasing due to a single choice of sky division. The
statistical significance is assessed via comparison with realistic Monte-Carlo
simulations.
We find the three-year WMAP maps to agree well with the isotropic, Gaussian
random field simulations as probed by regions corresponding to the angular
scales ranging from 6 deg to 30 deg at 68% confidence level. We report a
strong, anomalous (99.8% CL) dipole ``excess'' in the V band of the three-year
WMAP data and also in the V band of the WMAP five-year data (99.3% CL). We
notice the large scale hemispherical power asymmetry, and find that it is not
highly statistically significant in the WMAP three-year data (<~ 97%) at scales
l <= 40. The significance is even smaller if multipoles up to l=1024 are
considered (~90% CL). We give constraints on the amplitude of the
previously-proposed CMB dipole modulation field parameter. We easily detect the
residual foregrounds in cross-band difference maps at rms level <~ 7 \mu K (at
scales >~ 6 deg) and limit the systematical uncertainties to <~ 1.7 \mu K (at
scales >~ 30 deg).Comment: 20 pages, 20 figures; more tests added; updated to match the version
to be published in JCA
Passive scalar convection in 2D long-range delta-correlated velocity field: Exact results
The letter presents new field-theoretical approach to 2D passive scalar
problem. The Gaussian form of the distribution for the Lyapunov exponent is
derived and its parameters are found explicitly.Comment: 11 pages, RevTex 3.0, IFUM-94/455/January-F
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