2,525 research outputs found
Improved Approximation Algorithms for Stochastic Matching
In this paper we consider the Stochastic Matching problem, which is motivated
by applications in kidney exchange and online dating. We are given an
undirected graph in which every edge is assigned a probability of existence and
a positive profit, and each node is assigned a positive integer called timeout.
We know whether an edge exists or not only after probing it. On this random
graph we are executing a process, which one-by-one probes the edges and
gradually constructs a matching. The process is constrained in two ways: once
an edge is taken it cannot be removed from the matching, and the timeout of
node upper-bounds the number of edges incident to that can be probed.
The goal is to maximize the expected profit of the constructed matching.
For this problem Bansal et al. (Algorithmica 2012) provided a
-approximation algorithm for bipartite graphs, and a -approximation for
general graphs. In this work we improve the approximation factors to
and , respectively.
We also consider an online version of the bipartite case, where one side of
the partition arrives node by node, and each time a node arrives we have to
decide which edges incident to we want to probe, and in which order. Here
we present a -approximation, improving on the -approximation of
Bansal et al.
The main technical ingredient in our result is a novel way of probing edges
according to a random but non-uniform permutation. Patching this method with an
algorithm that works best for large probability edges (plus some additional
ideas) leads to our improved approximation factors
SNO+: predictions from standard solar models and spin flavour precession
Time variability of the solar neutrino flux especially in the low and
intermediate energy sector remains an open question and, if it exists, it is
likely to be originated from the magnetic moment transition from active to
light sterile neutrinos at times of intense solar activity and magnetic field.
We examine the prospects for the SNO+ experiment to address this important
issue and to distinguish between the two classes of solar models which are
currently identified as corresponding to a high (SSM I) and a low (SSM II)
heavy element abundance. We also evaluate the predictions from these two models
for the Chlorine experiment event rate in the standard LMA and LMA+Spin Flavour
Precession (SFP) scenarios. It is found that after three years of SNO+ data
taking, the pep flux measurement will be able to discriminate between the
standard LMA and LMA+SFP scenarios, independently of which is the correct solar
model. If the LMA rate is measured, SFP with for the resonant
can be excluded at more than . A low rate would
signal new physics, excluding all the 90% allowed range of the standard LMA
solution at 3, and a time variability would be a strong signature of
the SFP model. The CNO fluxes are the ones for which the two SSM predictions
exhibit the largest differences, so their measurement at SNO+ will be important
to favour one or the other. The distinction will be clearer after LMA or SFP
are confirmed with pep, but still, a CNO measurement at the level of SSM I/LMA
will disfavour SSM II at about . We conclude that consistency between
future pep and CNO flux measurements at SNO+ and Chlorine would either favour
an LMA+SFP scenario or favour SSM II over SSM I.Comment: 20 pages. Sections 1 and 2 extended, section 4.4 added, references
added and updated. Final version to be published in JHE
Synthetic sequence generator for recommender systems - memory biased random walk on sequence multilayer network
Personalized recommender systems rely on each user's personal usage data in
the system, in order to assist in decision making. However, privacy policies
protecting users' rights prevent these highly personal data from being publicly
available to a wider researcher audience. In this work, we propose a memory
biased random walk model on multilayer sequence network, as a generator of
synthetic sequential data for recommender systems. We demonstrate the
applicability of the synthetic data in training recommender system models for
cases when privacy policies restrict clickstream publishing.Comment: The new updated version of the pape
Contact-induced spin polarization in carbon nanotubes
Motivated by the possibility of combining spintronics with molecular
structures, we investigate the conditions for the appearance of
spin-polarization in low-dimensional tubular systems by contacting them to a
magnetic substrate. We derive a set of general expressions describing the
charge transfer between the tube and the substrate and the relative energy
costs. The mean-field solution of the general expressions provides an
insightful formula for the induced spin-polarization. Using a tight-binding
model for the electronic structure we are able to estimate the magnitude and
the stability of the induced moment. This indicates that a significant magnetic
moment in carbon nanotubes can be observed.Comment: To appear in Phys. Rev. B (2003
Simulating EGFR-ERK signaling control by scaffold proteins KSR and MP1 reveals differential Ligand-Sensitivity Co-Regulated by CBL-CIN85 and Endophilin
10.1371/journal.pone.0022933PLoS ONE68
The Abundance of New Kind of Dark Matter Structures
A new kind of dark matter structures, ultracompact minihalos (UCMHs) was
proposed recently. They would be formed during the radiation dominated epoch if
the large density perturbations are existent. Moreover, if the dark matter is
made up of weakly interacting massive particles, the UCMHs can have effect on
cosmological evolution because of the high density and dark matter annihilation
within them. In this paper, one new parameter is introduced to consider the
contributions of UCMHs due to the dark matter annihilation to the evolution of
cosmology, and we use the current and future CMB observations to obtain the
constraint on the new parameter and then the abundance of UCMHs. The final
results are applicable for a wider range of dark matter parametersComment: 4 pages, 1 tabl
Is the `Finite Bias Anomaly' in planar GaAs-Superconductor junctons caused by point-contact like structures?
We correlate transmission electron microscope (TEM) pictures of
superconducting In contacts to an AlGaAs/GaAs heterojunction with differential
conductance spectroscopy performed on the same heterojunction. Metals deposited
onto a (100) AlGaAs/GaAs heterostructure do not form planar contacts but,
during thermal annealing, grow down into the heterostructure along
crystallographic planes in pyramid-like `point contacts'. Random surface
nucleation and growth gives rise to a different interface transmission for each
superconducting point contact. Samples annealed for different times, and
therefore having different contact geometry, show variations in
characteristic of ballistic transport of Cooper pairs, wave interference
between different point emitters, and different types of weak localization
corrections to Giaever tunneling. We give a possible mechanism whereby the
`finite bias anomaly' of Poirier et al. (Phys. Rev. Lett., {\bf 79}, 2105
(1997)), also observed in these samples, can arise by adding the conductance of
independent superconducting point emitters in parallel
Theory of Current and Shot Noise Spectroscopy in Single-Molecular Quantum Dots with Phonon Mode
Using the Keldysh nonequilibrium Green function technique, we study the
current and shot noise spectroscopy of a single molecular quantum dot coupled
to a local phonon mode. It is found that in the presence of electron-phonon
coupling, in addition to the resonant peak associated with the single level of
the dot, satellite peaks with the separation set by the frequency of phonon
mode appear in the differential conductance. In the ``single level'' resonant
tunneling region, the differential shot noise power exhibit two split peaks.
However, only single peaks show up in the ``phonon assisted''
resonant-tunneling region. An experimental setup to test these predictions is
also proposed.Comment: 5 pages, 3 eps figures embedde
- …