31,717 research outputs found
Event-based personal retrieval
People who work in a research, academic or business environment often have personal information collections which are large enough to need retrieval aids. A major difference between personal information retrieval and normal document retrieval is that the items to be retrieved are often associated with events in the searcher's life and can be retrieved by their relationship to other events as well as by content. This paper describes some of the background to event-based retrieval and then describes a prototype graphical event-based retrieval system
Blocking and Persistence in the Zero-Temperature Dynamics of Homogeneous and Disordered Ising Models
A ``persistence'' exponent theta has been extensively used to describe the
nonequilibrium dynamics of spin systems following a deep quench: for
zero-temperature homogeneous Ising models on the d-dimensional cubic lattice,
the fraction p(t) of spins not flipped by time t decays to zero like
t^[-theta(d)] for low d; for high d, p(t) may decay to p(infinity)>0, because
of ``blocking'' (but perhaps still like a power). What are the effects of
disorder or changes of lattice? We show that these can quite generally lead to
blocking (and convergence to a metastable configuration) even for low d, and
then present two examples --- one disordered and one homogeneous --- where p(t)
decays exponentially to p(infinity).Comment: 8 pages (LaTeX); to appear in Physical Review Letter
Linearized Einstein theory via null surfaces
Recently there has been developed a reformulation of General Relativity -
referred to as {\it the null surface version of GR} - where instead of the
metric field as the basic variable of the theory, families of three-surfaces in
a four-manifold become basic. From these surfaces themselves, a conformal
metric, conformal to an Einstein metric, can be constructed. A choice of
conformal factor turns them into Einstein metrics. The surfaces are then
automatically characteristic surfaces of this metric. In the present paper we
explore the linearization of this {\it null surface theory} and compare it with
the standard linear GR. This allows a better understanding of many of the
subtle mathematical issues and sheds light on some of the obscure points of the
null surface theory. It furthermore permits a very simple solution generating
scheme for the linear theory and the beginning of a perturbation scheme for the
full theory.Comment: 22 page
ZIP3D: An elastic and elastic-plastic finite-element analysis program for cracked bodies
ZIP3D is an elastic and an elastic-plastic finite element program to analyze cracks in three dimensional solids. The program may also be used to analyze uncracked bodies or multi-body problems involving contacting surfaces. For crack problems, the program has several unique features including the calculation of mixed-mode strain energy release rates using the three dimensional virtual crack closure technique, the calculation of the J integral using the equivalent domain integral method, the capability to extend the crack front under monotonic or cyclic loading, and the capability to close or open the crack surfaces during cyclic loading. The theories behind the various aspects of the program are explained briefly. Line-by-line data preparation is presented. Input data and results for an elastic analysis of a surface crack in a plate and for an elastic-plastic analysis of a single-edge-crack-tension specimen are also presented
Journalism, media and technology trends and predictions 2019
Our 2019 Trends and Predictions report surveys 200 digital leaders from across the world on what they believe will be the challenges and opportunities facing journalism, media and technology this year. This will be the year when the regulation of platform companies starts to bite following growing concern about misinformation, privacy, and market power. Something once considered unthinkable has become ‘inevitable’, in the words of Apple boss Tim Cook – though the details will be messy, hard-fought, and take time to play out. Meanwhile the spread of false, misleading and extreme content will continue to undermine democracies around the world with polarising elections in India, Indonesia and Europe likely flashpoints. Journalism will continue to be hollowed out by structural shifts that have already led to significant falls in advertising revenue. Publishers are looking to subscriptions to make up the difference but the limits of this are likely to become apparent in 2019. Taken together these trends are likely to lead to the biggest wave of journalistic lay-offs in years – weakening further the ability of publishers to hold populist politicians and powerful business leaders to account
The worldwide air transportation network: Anomalous centrality, community structure, and cities' global roles
We analyze the global structure of the world-wide air transportation network,
a critical infrastructure with an enormous impact on local, national, and
international economies. We find that the world-wide air transportation network
is a scale-free small-world network. In contrast to the prediction of
scale-free network models, however, we find that the most connected cities are
not necessarily the most central, resulting in anomalous values of the
centrality. We demonstrate that these anomalies arise because of the
multi-community structure of the network. We identify the communities in the
air transportation network and show that the community structure cannot be
explained solely based on geographical constraints, and that geo-political
considerations have to be taken into account. We identify each city's global
role based on its pattern of inter- and intra-community connections, which
enables us to obtain scale-specific representations of the network.Comment: Revised versio
Clustering and preferential attachment in growing networks
We study empirically the time evolution of scientific collaboration networks
in physics and biology. In these networks, two scientists are considered
connected if they have coauthored one or more papers together. We show that the
probability of scientists collaborating increases with the number of other
collaborators they have in common, and that the probability of a particular
scientist acquiring new collaborators increases with the number of his or her
past collaborators. These results provide experimental evidence in favor of
previously conjectured mechanisms for clustering and power-law degree
distributions in networks.Comment: 13 pages, 2 figure
Stress analysis of a doubly-curved skin with a flared nozzle port, phase v annual summary report
Computer method for stress and deflection calculation of nozzle flow openings in large pressure vessels
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