24,070 research outputs found
From Competition to Complementarity: Comparative Influence Diffusion and Maximization
Influence maximization is a well-studied problem that asks for a small set of
influential users from a social network, such that by targeting them as early
adopters, the expected total adoption through influence cascades over the
network is maximized. However, almost all prior work focuses on cascades of a
single propagating entity or purely-competitive entities. In this work, we
propose the Comparative Independent Cascade (Com-IC) model that covers the full
spectrum of entity interactions from competition to complementarity. In Com-IC,
users' adoption decisions depend not only on edge-level information
propagation, but also on a node-level automaton whose behavior is governed by a
set of model parameters, enabling our model to capture not only competition,
but also complementarity, to any possible degree. We study two natural
optimization problems, Self Influence Maximization and Complementary Influence
Maximization, in a novel setting with complementary entities. Both problems are
NP-hard, and we devise efficient and effective approximation algorithms via
non-trivial techniques based on reverse-reachable sets and a novel "sandwich
approximation". The applicability of both techniques extends beyond our model
and problems. Our experiments show that the proposed algorithms consistently
outperform intuitive baselines in four real-world social networks, often by a
significant margin. In addition, we learn model parameters from real user
action logs.Comment: An abridged of this work is to appear in the Proceedings of VLDB
Endowment (PVDLB), Vol 9, No 2. Also, the paper will be presented in the VLDB
2016 conference in New Delhi, India. This update contains new theoretical and
experimental results, and the paper is now in single-column format (44 pages
Quantum criticality in a Mott pn-junction in an armchair carbon nanotube
In an armchair carbon nanotube pn junction the p- and n- regions are
separated by a region of a Mott insulator, which can backscatter electrons only
in pairs. We predict a quantum-critical behavior in such a pn junction.
Depending on the junction's built-in electric field E, its conductance G scales
either to zero or to the ideal value G=4e^2/h as the temperature T is lowered.
The two types of the G(T) dependence indicate the existence, at some special
value of E, of an intermediate quantum critical point with a finite conductance
G<4e^2/h. This makes the pn junction drastically different from a simple
barrier in a Luttinger liquid.Comment: 5 pages, 1 figur
Show Me the Money: Dynamic Recommendations for Revenue Maximization
Recommender Systems (RS) play a vital role in applications such as e-commerce
and on-demand content streaming. Research on RS has mainly focused on the
customer perspective, i.e., accurate prediction of user preferences and
maximization of user utilities. As a result, most existing techniques are not
explicitly built for revenue maximization, the primary business goal of
enterprises. In this work, we explore and exploit a novel connection between RS
and the profitability of a business. As recommendations can be seen as an
information channel between a business and its customers, it is interesting and
important to investigate how to make strategic dynamic recommendations leading
to maximum possible revenue. To this end, we propose a novel \model that takes
into account a variety of factors including prices, valuations, saturation
effects, and competition amongst products. Under this model, we study the
problem of finding revenue-maximizing recommendation strategies over a finite
time horizon. We show that this problem is NP-hard, but approximation
guarantees can be obtained for a slightly relaxed version, by establishing an
elegant connection to matroid theory. Given the prohibitively high complexity
of the approximation algorithm, we also design intelligent heuristics for the
original problem. Finally, we conduct extensive experiments on two real and
synthetic datasets and demonstrate the efficiency, scalability, and
effectiveness our algorithms, and that they significantly outperform several
intuitive baselines.Comment: Conference version published in PVLDB 7(14). To be presented in the
VLDB Conference 2015, in Hawaii. This version gives a detailed submodularity
proo
Conductance of a single-atom carbon chain with graphene leads
We study the conductance of an interconnect between two graphene leads formed
by a single-atom carbon chain. Its dependence on the chemical potential and the
number of atoms in the chain is qualitatively different from that in the case
of normal metal leads. Electron transport proceeds via narrow resonant states
in the wire. The latter arise due to strong reflection at the junctions between
the chain and the leads, which is caused by the small density of states in the
leads at low energy. The energy dependence of the transmission coefficient near
resonance is asymmetric and acquires a universal form at small energies. We
find that in the case of leads with the zigzag edges the dispersion of the edge
states has a significant effect on the device conductance.Comment: 9 pages, 4 figure
Limiting efficiencies of solar energy conversion and photo-detection via internal emission of hot electrons and hot holes in gold
We evaluate the limiting efficiency of full and partial solar spectrum
harvesting via the process of internal photoemission in Au-semiconductor
Schottky junctions. Our results based on the ab initio calculations of the
electron density of states (e-DOS) reveal that the limiting efficiency of the
full-spectrum Au converter based on hot electron injection is below 4%. This
value is even lower than previously established limit based on the parabolic
approximation of the Au electron energy bands. However, we predict limiting
efficiency exceeding 10% for the hot holes collection through the Schottky
junction between Au and p-type semiconductor. Furthermore, we demonstrate that
such converters have more potential if used as a part of the hybrid system for
harvesting high- and low-energy photons of the solar spectrum.Comment: Proc. SPIE 9608, Infrared Remote Sensing and Instrumentation XXIII,
960816 (September 1, 2015) 7 pages, 4 figure
-vacuum and inflationary bispectrum
In this paper, we discuss the non-Guassianity originated from the
-vacuum on the CMB anisotropy. For -vacuum, there exist
correlation between points in the acausal two patches of de Sitter spactime.
Such kind of correlation can lead to large local form non-Guassianity in
-vacuum. For the single field slow-roll inflationary scenario, the
spacetime is in a quasi-de Sitter phase during the inflation. We will show that
the -vacuum in this case will lead to non-Gaussianity with
distinguished feature, of a large local form and a very different shape.Comment: 39 pages, 8 figures, references added, minor changes, accepted by
Phys.Rev.
Inequalities for Light Nuclei in the Wigner Symmetry Limit
Using effective field theory we derive inequalities for light nuclei in the
Wigner symmetry limit. This is the limit where isospin and spin degrees of
freedom can be interchanged. We prove that the energy of any three-nucleon
state is bounded below by the average energy of the lowest two-nucleon and
four-nucleon states. We show how this is modified by lowest-order terms
breaking Wigner symmetry and prove general energy convexity results for SU(N).
We also discuss the inclusion of Wigner-symmetric three and four-nucleon force
terms.Comment: 10 page
Geriatrician and Other Physician Disciplines as the Usual Source of Care for Rural and Urban Older Adults: 2004-2010 Medical Expenditure Panel Survey
The purpose of this study is to examine the trend of usual source care (USC) rates and the discipline of choice among rural and urban older adults. Data used in this study were obtained from 2004 to 2010 Medical Expenditure Panel Survey. The yearly percentages of having a specific discipline as the USC were demonstrated from 2004 to 2010. The association of residence with likelihoods of having any of these three physician categories as USCs was assessed holding other individual characteristics constant. The overall sample size is 24,834, of which 20.0% of older adults resided in rural areas. A similar percentage of older adults living in urban areas had USCs than that of rural areas (93.69% vs. 93.46%). Overall, family practitioners were the most common USC noted in this survey while geriatricians are the least. The urban older adults are more likely than the rural ones to have geriatricians as their USC. Geriatrician discipline receives the most intensive education and training to care for older adults. The growing aging population makes it imperative to address the crisis of geriatrician shortage
First-principles method of propagation of tightly bound excitons: exciton band structure of LiF and verification with inelastic x-ray scattering
We propose a simple first-principles method to describe propagation of
tightly bound excitons. By viewing the exciton as a composite object (an
effective Frenkel exciton in Wannier orbitals), we define an exciton kinetic
kernel to encapsulate the exciton propagation and decay for all binding energy.
Applied to prototypical LiF, our approach produces three exciton bands, which
we verified quantitatively via inelastic x-ray scattering. The proposed
real-space picture is computationally inexpensive and thus enables study of the
full exciton dynamics, even in the presence of surfaces and impurity
scattering. It also provides intuitive understanding to facilitate practical
exciton engineering in semiconductors, strongly correlated oxides, and their
nanostructures.Comment: 5 pages, 4 figures. Accepted by PR
Inverse Temperature Dependence of Nuclear Quantum Effects in DNA Base Pairs
Despite the inherently quantum mechanical nature of hydrogen bonding, it is
unclear how nuclear quantum effects (NQEs) alter the strengths of hydrogen
bonds. With this in mind, we use ab initio path integral molecular dynamics to
determine the absolute contribution of NQEs to the binding in DNA base pair
complexes, arguably the most important hydrogen-bonded systems of all. We find
that depending on the temperature, NQEs can either strengthen or weaken the
binding within the hydrogen-bonded complexes. As a somewhat counterintuitive
consequence, NQEs can have a smaller impact on hydrogen bond strengths at
cryogenic temperatures than at room temperature. We rationalize this in terms
of a competition of NQEs between low-frequency and high-frequency vibrational
modes. Extending this idea, we also propose a simple model to predict the
temperature dependence of NQEs on hydrogen bond strengths in general
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