34,450 research outputs found
Fake View Analytics in Online Video Services
Online video-on-demand(VoD) services invariably maintain a view count for
each video they serve, and it has become an important currency for various
stakeholders, from viewers, to content owners, advertizers, and the online
service providers themselves. There is often significant financial incentive to
use a robot (or a botnet) to artificially create fake views. How can we detect
the fake views? Can we detect them (and stop them) using online algorithms as
they occur? What is the extent of fake views with current VoD service
providers? These are the questions we study in the paper. We develop some
algorithms and show that they are quite effective for this problem.Comment: 25 pages, 15 figure
Mean- Field Approximation and Extended Self-Similarity in Turbulence
Recent experimental discovery of extended self-similarity (ESS) was one of
the most interesting developments, enabling precise determination of the
scaling exponents of fully developed turbulence. Here we show that the ESS is
consistent with the Navier-Stokes equations, provided the pressure -gradient
contributions are expressed in terms of velocity differences in the mean field
approximation (Yakhot, Phys.Rev. E{\bf 63}, 026307, (2001)). A sufficient
condition for extended self-similarity in a general dynamical systemComment: 8 pages, no figure
Analysis of the Early-time Optical Spectra of SN 2011fe in M101
The nearby Type Ia supernova (SN Ia) SN 2011fe in M101 (cz = 241 km s^(–1)) provides a unique opportunity to study the early evolution of a "normal" SN Ia, its compositional structure, and its elusive progenitor system. We present 18 high signal-to-noise spectra of SN 2011fe during its first month beginning 1.2 days post-explosion and with an average cadence of 1.8 days. This gives a clear picture of how various line-forming species are distributed within the outer layers of the ejecta, including that of unburned material (C+O). We follow the evolution of C II absorption features until they diminish near maximum light, showing overlapping regions of burned and unburned material between ejection velocities of 10,000 and 16,000 km s^(–1). This supports the notion that incomplete burning, in addition to progenitor scenarios, is a relevant source of spectroscopic diversity among SNe Ia. The observed evolution of the highly Doppler-shifted O I λ7774 absorption features detected within 5 days post-explosion indicates the presence of O I with expansion velocities from 11,500 to 21,000 km s^(–1). The fact that some O I is present above C II suggests that SN 2011fe may have had an appreciable amount of unburned oxygen within the outer layers of the ejecta
An Agent Based Model for the Simulation of Transport Demand and Land Use
Agent based modelling has emerged as a promising tool to provide planners with insights on social behaviour and
the interdependencies characterising urban system, particularly with respect to transport and infrastructure planning.
This paper presents an agent based model for the simulation of land use and transport demand of an urban area
of Sydney, Australia. Each individual in the model has a travel diary which comprises a sequence of trips the person
makes in a representative day as well as trip attributes such as travel mode, trip purpose, and departure time.
Individuals are associated with each other by their household relationship, which helps define the interdependencies
of their travel diary and constrains their mode choice. This allows the model to not only realistically reproduce how
the current population uses existing transport infrastructure but more importantly provide comprehensive insight into
future transport demands. The router of the traffic micro-simulator TRANSIMS is incorporated in the model to inform
the actual travel time of each trip and changes of traffic density on the road network. Simulation results show very
good agreement with survey data in terms of the distribution of trips done by transport modes and by trip purposes,
as well as the traffic density along the main road in the study area
Transverse momentum dependence in the perturbative calculation of pion form factor
By reanalysing transverse momentum dependence in the perturbative calculation
of pion form factor an improved expression of pion form factor which takes into
account the transverse momentum dependenc in hard scattering amplitude and
intrinsic transverse momentum dependence associated with pion wave functions is
given to leading order, which is available for momentum transfers of the order
of a few GeV as well as for . Our scheme can be extended to
evaluate the contributions to the pion form factor beyond leading order.Comment: 13 pages in LaTeX, plus 3 Postscript figure
The relation between star formation rate and accretion rate in LINERs
It is argued that there is a linear correlation between star formation rate
(SFR) and accretion rate for normal bright active galactic nuclei (AGNs).
However, it is still unclear whether this correlation holds for LINERs, of
which the accretion rates are relatively lower than those of normal bright
AGNs. The radiatively inefficient accretion flows (RIAFs) are believed to be
present in these LINERs. In this work, we derive accretion rates for a sample
of LINERs from their hard X-ray luminosities based on spectral calculations for
RIAFs. We find that LINERs follow the same correlation between star formation
rate and accretion rate defined by normal bright AGNs, when reasonable
parameters are adopted for RIAFs. It means that the gases feed the black hole
and star formation in these low-luminosity LINERs may follow the same way as
that in normal bright AGNs, which is roughly consistent with recent numerical
simulations on quasar evolution.Comment: 15 pages, 3 figures, accepted for publication in PASP, in pres
On the efficiency of Hamiltonian-based quantum computation for low-rank matrices
We present an extension of Adiabatic Quantum Computing (AQC) algorithm for
the unstructured search to the case when the number of marked items is unknown.
The algorithm maintains the optimal Grover speedup and includes a small
counting subroutine.
Our other results include a lower bound on the amount of time needed to
perform a general Hamiltonian-based quantum search, a lower bound on the
evolution time needed to perform a search that is valid in the presence of
control error and a generic upper bound on the minimum eigenvalue gap for
evolutions.
In particular, we demonstrate that quantum speedup for the unstructured
search using AQC type algorithms may only be achieved under very rigid control
precision requirements.Comment: 17 pages, no figures, to appear in JM
Evidence for anisotropic motion of the clouds in broad-line regions of BL Lacertae objects
The masses of central massive black holes in BL Lac objects are estimated
from their host galaxy absolute magnitude at R-band by using the empirical
relation between absolute magnitude of host galaxy and black hole mass. Only a
small fraction of BL Lac objects exhibit weak broad-line emission, and we
derive the sizes of the broad-line regions (BLRs) in these BL Lac objects from
the widths of their broad emission lines on the assumption of the clouds being
virilized in BLRs. It is found that the sizes of the BLRs in these sources are
usually 2-3 orders of magnitude larger than that expected by the empirical
correlation between BLR size and optical luminosity defined by a sample of
Seyfert galaxies and quasars. We discuss a variety of possibilities and suggest
it may probably be attributed to anisotropic motion of the BLR clouds in these
BL Lac objects. If the BLR geometry of these sources is disk-like, the viewing
angles between the axis and the line of sight are in the range of 2-12 degrees,
which is consistent with the unification schemes.Comment: 5 pages, accepted for publication in Ap
Lagrange Model for the Chiral Optical Properties of Stereometamaterials
We employ a general Lagrange model to describe the chiral optical properties
of stereometamaterials. We derive the elliptical eigenstates of a twisted
stacked split-ring resonator, taking phase retardation into account. Through
this approach, we obtain a powerful Jones matrix formalism which can be used to
calculate the polarization rotation, ellipticity, and circular dichroism of
transmitted waves through stereometamaterials at any incident polarization. Our
experimental measurements agree well with our model.Comment: 10 pages, 3 figures, Theory and experimen
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