208,962 research outputs found
Of course we share! Testing Assumptions about Social Tagging Systems
Social tagging systems have established themselves as an important part in
today's web and have attracted the interest from our research community in a
variety of investigations. The overall vision of our community is that simply
through interactions with the system, i.e., through tagging and sharing of
resources, users would contribute to building useful semantic structures as
well as resource indexes using uncontrolled vocabulary not only due to the
easy-to-use mechanics. Henceforth, a variety of assumptions about social
tagging systems have emerged, yet testing them has been difficult due to the
absence of suitable data. In this work we thoroughly investigate three
available assumptions - e.g., is a tagging system really social? - by examining
live log data gathered from the real-world public social tagging system
BibSonomy. Our empirical results indicate that while some of these assumptions
hold to a certain extent, other assumptions need to be reflected and viewed in
a very critical light. Our observations have implications for the design of
future search and other algorithms to better reflect the actual user behavior
Arithmetic coding revisited
Over the last decade, arithmetic coding has emerged as an important compression tool. It is now the method of choice for adaptive coding on multisymbol alphabets because of its speed,
low storage requirements, and effectiveness of compression. This article describes a new implementation of arithmetic coding that incorporates several improvements over a widely used earlier version by Witten, Neal, and Cleary, which has become a de facto standard. These improvements include fewer multiplicative operations, greatly extended range of alphabet sizes and symbol probabilities, and the use of low-precision arithmetic, permitting implementation by fast shift/add operations. We also describe a modular structure that separates the coding, modeling, and probability estimation components of a compression system. To motivate the improved coder, we consider the needs of a word-based text compression program. We report a range of experimental results using this and other models. Complete source code is available
Movement in cluttered virtual environments
Imagine walking around a cluttered room but then having little idea of where you have traveled. This frequently happens when people move around small virtual environments (VEs), searching for targets. In three experiments, participants searched small-scale VEs using different movement interfaces, collision response algorithms, and fields of view. Participants' searches were most efficient in terms of distance traveled, time taken, and path followed when the simplest form of movement (view direction) was used in conjunction with a response algorithm that guided ("slipped") them around obstacles when collisions occurred. Unexpectedly, and in both immersive and desktop VEs, participants often had great difficulty finding the targets, despite the fact that participants could see the whole VE if they stood in one place and turned around. Thus, the trivial real-world task used in the present study highlights a basic problem with current VE systems
Local Search in Unstructured Networks
We review a number of message-passing algorithms that can be used to search
through power-law networks. Most of these algorithms are meant to be
improvements for peer-to-peer file sharing systems, and some may also shed some
light on how unstructured social networks with certain topologies might
function relatively efficiently with local information. Like the networks that
they are designed for, these algorithms are completely decentralized, and they
exploit the power-law link distribution in the node degree. We demonstrate that
some of these search algorithms can work well on real Gnutella networks, scale
sub-linearly with the number of nodes, and may help reduce the network search
traffic that tends to cripple such networks.Comment: v2 includes minor revisions: corrections to Fig. 8's caption and
references. 23 pages, 10 figures, a review of local search strategies in
unstructured networks, a contribution to `Handbook of Graphs and Networks:
From the Genome to the Internet', eds. S. Bornholdt and H.G. Schuster
(Wiley-VCH, Berlin, 2002), to be publishe
Search in Power-Law Networks
Many communication and social networks have power-law link distributions,
containing a few nodes which have a very high degree and many with low degree.
The high connectivity nodes play the important role of hubs in communication
and networking, a fact which can be exploited when designing efficient search
algorithms. We introduce a number of local search strategies which utilize high
degree nodes in power-law graphs and which have costs which scale sub-linearly
with the size of the graph. We also demonstrate the utility of these strategies
on the Gnutella peer-to-peer network.Comment: 17 pages, 14 figure
Oculomotor examination of the weapon focus effect: does a gun automatically engage visual attention?
A person is less likely to be accurately remembered if they appear in a visual scene with a gun, a result that has been termed the weapon focus effect (WFE). Explanations of the WFE argue that weapons engage attention because they are unusual and/or threatening, which causes encoding deficits for the other items in the visual scene. Previous WFE research has always embedded the weapon and nonweapon objects within a larger context that provides information about an actor's intention to use the object. As such, it is currently unknown whether a gun automatically engages attention to a greater extent than other objects independent of the context in which it is presente
Parameterization of the antiproton inclusive production cross section on nuclei
A new parameterization of the antiproton inclusive production cross section
in proton-proton and proton-nucleus collisions is proposed. A sample of
consistent pA->pbar X$ experimental data sets measured on 1<A<208 nuclei, from
12 GeV up to 400 GeV incident energy, have been used to constrain the
parameters. A broader energy domain is covered for the pp->pbar X reaction with
a simplified functional form used in the fits. The agreement obtained with the
data is good. The results are discussed.Comment: 10 pages, 11 figures, 7 tables, submitted to Phys. Rev.
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