3,255 research outputs found
New bounds on the signed total domination number of graphs
In this paper, we study the signed total domination number in graphs and
present new sharp lower and upper bounds for this parameter. For example by
making use of the classic theorem of Turan, we present a sharp lower bound on
this parameter for graphs with no complete graph of order r+1 as a subgraph.
Also, we prove that n-2(s-s') is an upper bound on the signed total domination
number of any tree of order n with s support vertices and s' support vertives
of degree two. Moreover, we characterize all trees attainig this bound.Comment: This paper contains 11 pages and one figur
Inferring Networks of Substitutable and Complementary Products
In a modern recommender system, it is important to understand how products
relate to each other. For example, while a user is looking for mobile phones,
it might make sense to recommend other phones, but once they buy a phone, we
might instead want to recommend batteries, cases, or chargers. These two types
of recommendations are referred to as substitutes and complements: substitutes
are products that can be purchased instead of each other, while complements are
products that can be purchased in addition to each other.
Here we develop a method to infer networks of substitutable and complementary
products. We formulate this as a supervised link prediction task, where we
learn the semantics of substitutes and complements from data associated with
products. The primary source of data we use is the text of product reviews,
though our method also makes use of features such as ratings, specifications,
prices, and brands. Methodologically, we build topic models that are trained to
automatically discover topics from text that are successful at predicting and
explaining such relationships. Experimentally, we evaluate our system on the
Amazon product catalog, a large dataset consisting of 9 million products, 237
million links, and 144 million reviews.Comment: 12 pages, 6 figure
Detecting Singleton Review Spammers Using Semantic Similarity
Online reviews have increasingly become a very important resource for
consumers when making purchases. Though it is becoming more and more difficult
for people to make well-informed buying decisions without being deceived by
fake reviews. Prior works on the opinion spam problem mostly considered
classifying fake reviews using behavioral user patterns. They focused on
prolific users who write more than a couple of reviews, discarding one-time
reviewers. The number of singleton reviewers however is expected to be high for
many review websites. While behavioral patterns are effective when dealing with
elite users, for one-time reviewers, the review text needs to be exploited. In
this paper we tackle the problem of detecting fake reviews written by the same
person using multiple names, posting each review under a different name. We
propose two methods to detect similar reviews and show the results generally
outperform the vectorial similarity measures used in prior works. The first
method extends the semantic similarity between words to the reviews level. The
second method is based on topic modeling and exploits the similarity of the
reviews topic distributions using two models: bag-of-words and
bag-of-opinion-phrases. The experiments were conducted on reviews from three
different datasets: Yelp (57K reviews), Trustpilot (9K reviews) and Ott dataset
(800 reviews).Comment: 6 pages, WWW 201
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A numerical investigation of moment coefficient and flow structure in a rotor-stator cavity with rotor mounted bolts
This paper presents a numerical study of the effect of rotor mounted bolts on the moment coefficient and flow structure within a rotor-stator cavity representative of modern gas turbine engine design. The CFD computations are performed using the commercial code FLUENT. The simulation methodology is first validated using experimental data from plain co-rotating disc and rotor-stator cavities from the open literature. Comparisons are then made with experimental data obtained from a test rig at the Thermo Fluid Mechanics Research Centre (TFMRC), University of Sussex. Computations were performed at Reφ = 6.8 × 106, Cw = 5929 (λT = 0.35) with different numbers of bolts (0 < N < 60), and also a continuous ring, at r/b = 0.9. The study has improved the current understanding of the effect on moment coefficient and flow structure that rotor mounted protrusions have in rotor-stator systems. It is seen that the contribution of skin friction to the moment coefficient reduces as the number of bolts is increased. The size and shape of the wake created by a rotating bolt also means that the pressure loss per bolt reduces with N but the overall effect is to increase the moment coefficient because there are more bolts. Copyright © 2011 by ASME
Fermat's principle in quantum gravitational optics
Interactions incorporating the vacuum polarization effects in curved
backgrounds modify the null cone structure in such a way that the photon
trajectories would not be the space-time geodesics anymore. The gravitational
birefringence introduced as a direct consequence of these effects, will allow
shifts in the photon velocities leading to polarization dependent superluminal
propagation. Taking these effects into account we study Fermat's principle in
the context of the 1+3 (threading) formulation of the space-time decomposition.
We find an expression for the modified spacetime refractive index and show it
is proportional to the light cone correction to the first order. Consequences
of this modification on polarization sum rules and spatial light paths are
considered.Comment: 13 Pages, REVTex format, section on gravitomagnetic monopoles is
removed along with its references, new references adde
A Cost-effective and Emission-aware Power Management System for Ships with Integrated Full Electric Propulsion
Deconfined quantum criticality and generalised exclusion statistics in a non-hermitian BCS model
We present a pairing Hamiltonian of the Bardeen-Cooper-Schrieffer form which
exhibits two quantum critical lines of deconfined excitations. This conclusion
is drawn using the exact Bethe ansatz equations of the model which admit a
class of simple, analytic solutions. The deconfined excitations obey
generalised exclusion statistics. A notable property of the Hamiltonian is that
it is non-hermitian. Although it does not have a real spectrum for all choices
of coupling parameters, we provide a rigorous argument to establish that real
spectra occur on the critical lines. The critical lines are found to be
invariant under a renormalisation group map.Comment: 7 pages, 1 figure. Stylistic changes, results unchange
On the Signed -independence Number of Graphs
In this paper, we study the signed 2-independence number in graphs and give new sharp upper and lower bounds on the signed 2-independence number of a graph by a simple uniform approach. In this way, we can improve and generalize some known results in this area
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