3,430 research outputs found
Exact Computation of Influence Spread by Binary Decision Diagrams
Evaluating influence spread in social networks is a fundamental procedure to
estimate the word-of-mouth effect in viral marketing. There are enormous
studies about this topic; however, under the standard stochastic cascade
models, the exact computation of influence spread is known to be #P-hard. Thus,
the existing studies have used Monte-Carlo simulation-based approximations to
avoid exact computation.
We propose the first algorithm to compute influence spread exactly under the
independent cascade model. The algorithm first constructs binary decision
diagrams (BDDs) for all possible realizations of influence spread, then
computes influence spread by dynamic programming on the constructed BDDs. To
construct the BDDs efficiently, we designed a new frontier-based search-type
procedure. The constructed BDDs can also be used to solve other
influence-spread related problems, such as random sampling without rejection,
conditional influence spread evaluation, dynamic probability update, and
gradient computation for probability optimization problems.
We conducted computational experiments to evaluate the proposed algorithm.
The algorithm successfully computed influence spread on real-world networks
with a hundred edges in a reasonable time, which is quite impossible by the
naive algorithm. We also conducted an experiment to evaluate the accuracy of
the Monte-Carlo simulation-based approximation by comparing exact influence
spread obtained by the proposed algorithm.Comment: WWW'1
Charge pumping in magnetic tunnel junctions: Scattering theory
We study theoretically the charge transport pumped by magnetization dynamics
through epitaxial FIF and FNIF magnetic tunnel junctions (F: Ferromagnet, I:
Insulator, N: Normal metal). We predict a small but measurable DC pumping
voltage under ferromagnetic resonance conditions for collinear magnetization
configurations, which may change sign as function of barrier parameters. A much
larger AC pumping voltage is expected when the magnetizations are at right
angles. Quantum size effects are predicted for an FNIF structure as a function
of the normal layer thickness.Comment: 4 pages, 3 figures. to be published on Physical Review B Rapid
Communicatio
Smearing Effect in Plane-Wave Matrix Model
Motivated by the usual D2-D0 system, we consider a configuration composed of
flat membrane and fuzzy sphere membrane in plane-wave matrix model, and
investigate the interaction between them. The configuration is shown to lead to
a non-trivial interaction potential, which indicates that the fuzzy sphere
membrane really behaves like a graviton, giant graviton. Interestingly, the
interaction is of r^{-3} type rather than r^{-5} type. We interpret it as the
interaction incorporating the smearing effect due to the fact that the
considered supersymmetric flat membrane should span and spin in four
dimensional subspace of plane-wave geometry.Comment: 26 pages; added referenc
Extracting Multidimensional Phase Space Topology from Periodic Orbits
We establish a hierarchical ordering of periodic orbits in a strongly coupled
multidimensional Hamiltonian system. Phase space structures can be
reconstructed quantitatively from the knowledge of periodic orbits alone. We
illustrate our findings for the hydrogen atom in crossed electric and magnetic
fields.Comment: 4 pages, 5 figures, accepted for publication in Phys. Rev. Let
X-ray study of the double radio relic galaxy cluster CIZA J2242.8+5301
Content: We present the results from observations of the merging
cluster of galaxies CIZA J2242.8+5301 at =0.192. Aims. To study the physics
of gas heating and particle acceleration in cluster mergers, we investigated
the X-ray emission from CIZA J2242.8+5301, which hosts two giant radio relics
in the northern/southern part of the cluster. Methods. We analyzed data from
three-pointed Suzaku observations of CIZA J2242.8+5301 to derive the
temperature distribution in four different directions. Results: The
Intra-Cluster Medium (ICM) temperature shows a remarkable drop from
8.5 keV to 2.7 keV across the northern radio
relic. The temperature drop is consistent with a Mach number and a shock velocity
. We also confirm the
temperature drop across the southern radio relic. However, the ICM temperature
beyond this relic is much higher than beyond the northern one, which gives a
Mach number and shock velocity
. These results agree with
other systems showing a relationship between the radio relics and shock fronts
which are induced by merging activity. We compare the X-ray derived Mach
numbers with the radio derived Mach numbers from the radio spectral index under
the assumption of diffusive shock acceleration in the linear test particle
regime. For the northern radio relic, the Mach numbers derived from X-ray and
radio observations agree with each other. Based on the shock velocities, we
estimate that CIZA J2242.8+5301 is observed approximately 0.6 Gyr after core
passage. The magnetic field pressure at the northern relic is estimated to be
9% of the thermal pressure.Comment: 12 pages, 10 figures, A&A accepte
2-D Simulation of Velocity Distribution in a Doubly Meandering Compound Channel Using CIP-Based Scheme
Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv
Response to Letter to the Editor from Dalan: "Vitamin D Supplementation for Prevention of Type 2 Diabetes Mellitus: To D or Not to D?"
We thank Rinkoo Dalan for the comments on our paper (1, 2). We agree that although the reduction in diabetes risk with vitamin D supplementation among people at high risk for diabetes appears to be moderate (~ 12% relative risk reduction compared to placebo) (3), certain individuals may derive a higher (or lower) benefit based on certain characteristics. For example, in the simplest demonstration of such heterogeneity, vitamin D supplementation reduced diabetes risk by 62% among participants in the Vitamin D and Type 2 Diabetes (D2d) study who had a baseline serum 25-hydroxyvitamin D (25[OH]D) level of less than 12 ng/mL (30 mmol/L) (2).
Consistent with the focus of the scientific community on precision nutrition, we agree that we need to better understand responsiveness to vitamin D supplementation for specific outcomes of interest. The vitamin D response index is an interesting concept that reflects activation of the vitamin D receptor, and it is determined on the basis of measuring vitamin D–triggered changes in the expression of 24 target genes in peripheral blood mononuclear cells and 12 clinical and biochemical parameters (4). There are at least 2 limitations: 1) Although such an index may reflect vitamin D–induced changes in specific response parameters, these changes may not necessarily translate to clinically meaningful outcomes, such as lowering diabetes risk. 2) Low-, mid-, and high-responders are determined with statistical means within a specific cohort but that can be calculated only retrospectively; specific cutoffs to define degree of response need to be established for use in real time in research or in the clinical setting.
The author also suggests that daily, steady exposure to vitamin D is preferred over intermittent exposure for optimal benefit, and we agree. In a secondary analysis from the D2d study, we reported that participants who received the active intervention (100 mcg [4000 units] of vitamin D3 daily) and maintained high 25(OH)D levels that were stable throughout the trial period had the lowest risk of diabetes, whereas participants in the placebo group who maintained similar overall 25(OH)D levels that fluctuated during follow-up did not derive significant benefit (5)
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