737 research outputs found
A Utility-Theoretic Approach to Privacy in Online Services
Online offerings such as web search, news portals, and e-commerce applications face the challenge of providing high-quality service to a large, heterogeneous user base. Recent efforts have highlighted the potential to improve performance by introducing methods to personalize services based on special knowledge about users and their context. For example, a user's demographics, location, and past search and browsing may be useful in enhancing the results offered in response to web search queries. However, reasonable concerns about privacy by both users, providers, and government agencies acting on behalf of citizens, may limit access by services to such information. We introduce and explore an economics of privacy in personalization, where people can opt to share personal information, in a standing or on-demand manner, in return for expected enhancements in the quality of an online service. We focus on the example of web search and formulate realistic objective functions for search efficacy and privacy. We demonstrate how we can find a provably near-optimal optimization of the utility-privacy tradeoff in an efficient manner. We evaluate our methodology on data drawn from a log of the search activity of volunteer participants. We separately assess usersā preferences about privacy and utility via a large-scale survey, aimed at eliciting preferences about peoplesā willingness to trade the sharing of personal data in returns for gains in search efficiency. We show that a significant level of personalization can be achieved using a relatively small amount of information about users
Information Gathering in Networks via Active Exploration
How should we gather information in a network, where each node's visibility
is limited to its local neighborhood? This problem arises in numerous
real-world applications, such as surveying and task routing in social networks,
team formation in collaborative networks and experimental design with
dependency constraints. Often the informativeness of a set of nodes can be
quantified via a submodular utility function. Existing approaches for
submodular optimization, however, require that the set of all nodes that can be
selected is known ahead of time, which is often unrealistic. In contrast, we
propose a novel model where we start our exploration from an initial node, and
new nodes become visible and available for selection only once one of their
neighbors has been chosen. We then present a general algorithm NetExp for this
problem, and provide theoretical bounds on its performance dependent on
structural properties of the underlying network. We evaluate our methodology on
various simulated problem instances as well as on data collected from social
question answering system deployed within a large enterprise.Comment: Longer version of IJCAI'15 pape
Better safe than sorry: Risky function exploitation through safe optimization
Exploration-exploitation of functions, that is learning and optimizing a
mapping between inputs and expected outputs, is ubiquitous to many real world
situations. These situations sometimes require us to avoid certain outcomes at
all cost, for example because they are poisonous, harmful, or otherwise
dangerous. We test participants' behavior in scenarios in which they have to
find the optimum of a function while at the same time avoid outputs below a
certain threshold. In two experiments, we find that Safe-Optimization, a
Gaussian Process-based exploration-exploitation algorithm, describes
participants' behavior well and that participants seem to care firstly whether
a point is safe and then try to pick the optimal point from all such safe
points. This means that their trade-off between exploration and exploitation
can be seen as an intelligent, approximate, and homeostasis-driven strategy.Comment: 6 pages, submitted to Cognitive Science Conferenc
CHANG-ES V: Nuclear Radio Outflow in a Virgo Cluster Spiral after a Tidal Disruption Event
We have observed the Virgo Cluster spiral galaxy, NGC~4845, at 1.6 and 6 GHz
using the Karl G. Jansky Very Large Array, as part of the `Continuum Halos in
Nearby Galaxies -- an EVLA Survey' (CHANG-ES). The source consists of a bright
unresolved core with a surrounding weak central disk (1.8 kpc diameter). The
core is variable over the 6 month time scale of the CHANG-ES data and has
increased by a factor of 6 since 1995. The wide bandwidths of
CHANG-ES have allowed us to determine the spectral evolution of this core which
peaks {\it between} 1.6 and 6 GHz (it is a GigaHertz-peaked spectrum source).We
show that the spectral turnover is dominated by synchrotron self-absorption and
that the spectral evolution can be explained by adiabatic expansion (outflow),
likely in the form of a jet or cone. The CHANG-ES observations serendipitously
overlap in time with the hard X-ray light curve obtained by Nikolajuk \& Walter
(2013) which they interpret as due to a tidal disruption event (TDE) of a
super-Jupiter mass object around a black hole. We outline a
standard jet model, provide an explanation for the observed circular
polarization, and quantitatively suggest a link between the peak radio and peak
X-ray emission via inverse Compton upscattering of the photons emitted by the
relativistic electrons. We predict that it should be possible to resolve a
young radio jet via VLBI as a result of this nearby TDE.Comment: 45 pages, 10 figures, accepted July 2, 2015 to the Astrophysical
Journa
Profiles of epistemological beliefs, knowledge about explanation norms, and explanation skills: changes after an intervention
In this study, we exploratively investigate the relation between studentsā
epistemological beliefs and their declarative knowledge about scientific
explanations and their practical skills to explain psychological phenomena
drawing on scientific theories before and after a training intervention using a
person-centered approach. We theoretically derive profiles of epistemological
beliefs that should be beneficial for constructing scientific explanations. We those
having higher explanation skills show a profile of epistemological beliefs that is
beneficial for explanations skills. Using a latent profile transition analysis and a
sample with Nā =ā 108 students, we explore which profiles of epistemological beliefs,
declarative knowledge about explanations, and explanation skills empirically
emerge before and after an intervention that aimed and fostering studentsā
skills to construct scientific explanations. Before the intervention, two profiles
emerged that differed in epistemological beliefs and explanation skills, but both
did not in declarative knowledge about explanation. The intervention, in general,
yielded a gain in declarative knowledge about explanations and explanation
skills. After the intervention, again, two profiles emerged. However, these profiles
did not differ in their epistemological beliefs but only in declarative knowledge
about explanations and explanation skills. Thus, the intervention seems to level
out the effects of epistemological beliefs. Additionally, the pattern of change in
epistemological beliefs is consistent with theoretical expectations about which
epistemological beliefs are beneficial for explanations. We discuss the results and
their implications, as well as their limitations. Finally, we provide an outlook of
using the person-oriented approach and this studyās type of intervention in the
research on changing epistemological beliefs
Compact Resolved Ejecta in the Nearest Tidal Disruption Event
Tidal disruption events (TDEs) occur when a star or sub-stellar object passes
close enough to a galaxy's supermassive black hole to be disrupted by tidal
forces. NGC 4845 (d=17 Mpc) was host to a TDE, IGR J12580+0134, detected in
November 2010. Its proximity offers us a unique close-up of the TDE and its
aftermath. We discuss new Very Long Baseline Array (VLBA) and Karl G. Jansky
Very Large Array (JVLA) observations, which show that the radio flux from the
active nucleus created by the TDE has decayed in a manner consistent with
predictions from a jet-circumnuclear medium interaction model. This model
explains the source's broadband spectral evolution, which shows a spectral peak
that has moved from the submm (at the end of 2010) to GHz radio frequencies (in
2011-2013) to <1 GHz in 2015. The milliarcsecond-scale core is circularly
polarized at 1.5 GHz but not at 5 GHz, consistent with the model. The VLBA
images show a complex structure at 1.5 GHz that includes an east west extension
~40 milliarcsec (3 pc) long as well as a resolved component 52 milliarcsec (4.1
pc) northwest of the flat-spectrum core, which is all that can be seen at 5
GHz. If ejected in 2010, the NW component must have had v=0.96 c over five
years. However, this is unlikely, as our model suggests strong deceleration to
speeds < 0.5c within months and a much smaller, sub-parsec size. In this
interpretation, the northwest component could have either a non-nuclear origin
or be from an earlier event.Comment: 12 pages, 8 figures, ApJ, in press; v2 includes error corrections and
slight additions to the analysi
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