10,314 research outputs found
Twitter event networks and the Superstar model
Condensation phenomenon is often observed in social networks such as Twitter
where one "superstar" vertex gains a positive fraction of the edges, while the
remaining empirical degree distribution still exhibits a power law tail. We
formulate a mathematically tractable model for this phenomenon that provides a
better fit to empirical data than the standard preferential attachment model
across an array of networks observed in Twitter. Using embeddings in an
equivalent continuous time version of the process, and adapting techniques from
the stable age-distribution theory of branching processes, we prove limit
results for the proportion of edges that condense around the superstar, the
degree distribution of the remaining vertices, maximal nonsuperstar degree
asymptotics and height of these random trees in the large network limit.Comment: Published at http://dx.doi.org/10.1214/14-AAP1053 in the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
A High-Order Radial Basis Function (RBF) Leray Projection Method for the Solution of the Incompressible Unsteady Stokes Equations
A new projection method based on radial basis functions (RBFs) is presented
for discretizing the incompressible unsteady Stokes equations in irregular
geometries. The novelty of the method comes from the application of a new
technique for computing the Leray-Helmholtz projection of a vector field using
generalized interpolation with divergence-free and curl-free RBFs. Unlike
traditional projection methods, this new method enables matching both
tangential and normal components of divergence-free vector fields on the domain
boundary. This allows incompressibility of the velocity field to be enforced
without any time-splitting or pressure boundary conditions. Spatial derivatives
are approximated using collocation with global RBFs so that the method only
requires samples of the field at (possibly scattered) nodes over the domain.
Numerical results are presented demonstrating high-order convergence in both
space (between 5th and 6th order) and time (up to 4th order) for some model
problems in two dimensional irregular geometries.Comment: 34 pages, 8 figure
Pulsed Ultrasound Does Not Affect Recovery From Delayed Onset Muscle Soreness
Aim: To investigate the effects of pulsed Ultrasound (US) in recovery from Delayed Onset Muscle Soreness (DOMS).
Methods: Twelve healthy male athletes (mean age 23.83±1.697 year) performed an eccentric exercise protocol of non-dominant elbow flexors to induce muscle soreness on 2 occasions separated by 3 weeks. Subjects in experimental group received pulsed US (1 MHz, intensity 0.8 W/cm2, mark space ratio 1:10), whereas control group received sham US after 24 h, 48 h and 72 h. Perception of muscle soreness, active ROM and muscle strength were the parameters measured at 0 h, 24 h, 48 h and 72 h with the help of VAS, manual goniometer and JONEX muscles master instrument respectively.
Results: Post hoc t test analysis revealed significant differences (p <0.05) between 0 h and 72 h in the parameter of ROM (t = 6.18) and muscle power (t = 2.54) as well as between 24 h and 48 h in the parameter of muscle soreness (t = 3.13) in control group. Similar differences were also observed in the experimental group. No significant inter-group differences at α level of 0.05 was observed in any parameter at any level.
Conclusion: The pattern of recovery from DOMS was not influenced by the application of pulsed Ultrasound at the parameters discussed here
Topological Sound and Flocking on Curved Surfaces
Active systems on curved geometries are ubiquitous in the living world. In
the presence of curvature orientationally ordered polar flocks are forced to be
inhomogeneous, often requiring the presence of topological defects even in the
steady state due to the constraints imposed by the topology of the underlying
surface. In the presence of spontaneous flow the system additionally supports
long-wavelength propagating sound modes which get gapped by the curvature of
the underlying substrate. We analytically compute the steady state profile of
an active polar flock on a two-sphere and a catenoid, and show that curvature
and active flow together result in symmetry protected topological modes that
get localized to special geodesics on the surface (the equator or the neck
respectively). These modes are the analogue of edge states in electronic
quantum Hall systems and provide unidirectional channels for information
transport in the flock, robust against disorder and backscattering.Comment: 15 pages, 6 figure
Meson Masses and Mixing Angles in 2+1 Flavor Polyakov Quark Meson Sigma Model and Symmetry Restoration Effects
The meson masses and mixing angles have been calculated for the scalar and
pseudoscalar sector in the framework of the generalized 2+1 flavor Polyakov
loop augmented quark meson linear sigma model. We have given the results for
two different forms of the effective Polyakov loop potential. The comparison of
results with the existing calculations in the bare 2+1 quark meson linear sigma
model, shows that the restoration of chiral symmetry becomes sharper due to the
influence of the Polyakov loop potential. We find that inclusion of the
Polyakov loop in quark meson linear sigma model together with the presence of
axial anomaly, triggers an early and significant melting of the strange
condensate. We have examined how the inclusion of the Polyakov loop
qualitatively and quantitatively affects the convergence in the masses of the
chiral partners in pseudoscalar (, , , ) and scalar
(, , ,) meson nonets as the temperature is varied on
the reduced temperature scale. The role of anomaly in determining the
isoscalar masses and mixing angles for the pseudoscalar ( and )
and scalar ( and )meson complex, has also been investigated in the
Polyakov quark meson linear sigma model. The interplay of chiral symmetry
restoration effects and the setting up of restoration trend has been
discussed and analyzed in the framework of the presented model calculations.Comment: 15 pages, 8 figures, 4 table
A Statistical Semi-Empirical Model: Satellite galaxies in Groups and Clusters
We present STEEL a STatistical sEmi-Empirical modeL designed to probe the
distribution of satellite galaxies in groups and clusters. Our fast statistical
methodology relies on tracing the abundances of central and satellite haloes
via their mass functions at all cosmic epochs with virtually no limitation on
cosmic volume and mass resolution. From mean halo accretion histories and
subhalo mass functions the satellite mass function is progressively built in
time via abundance matching techniques constrained by number densities of
centrals in the local Universe. By enforcing dynamical merging timescales as
predicted by high-resolution N-body simulations, we obtain satellite
distributions as a function of stellar mass and halo mass consistent with
current data. We show that stellar stripping, star formation, and quenching
play all a secondary role in setting the number densities of massive satellites
above . We further show that observed
star formation rates used in our empirical model over predict low-mass
satellites below , whereas, star
formation rates derived from a continuity equation approach yield the correct
abundances similar to previous results for centrals.Comment: 21 pages, 17 Figures. MNRAS, in pres
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