7,569 research outputs found
Privacy-Preserving Shortest Path Computation
Navigation is one of the most popular cloud computing services. But in
virtually all cloud-based navigation systems, the client must reveal her
location and destination to the cloud service provider in order to learn the
fastest route. In this work, we present a cryptographic protocol for navigation
on city streets that provides privacy for both the client's location and the
service provider's routing data. Our key ingredient is a novel method for
compressing the next-hop routing matrices in networks such as city street maps.
Applying our compression method to the map of Los Angeles, for example, we
achieve over tenfold reduction in the representation size. In conjunction with
other cryptographic techniques, this compressed representation results in an
efficient protocol suitable for fully-private real-time navigation on city
streets. We demonstrate the practicality of our protocol by benchmarking it on
real street map data for major cities such as San Francisco and Washington,
D.C.Comment: Extended version of NDSS 2016 pape
A Temperature and Abundance Retrieval Method for Exoplanet Atmospheres
We present a new method to retrieve molecular abundances and temperature
profiles from exoplanet atmosphere photometry and spectroscopy. We run millions
of 1D atmosphere models in order to cover the large range of allowed parameter
space, and present error contours in the atmospheric properties, given the
data. In order to run such a large number of models, we have developed a
parametric pressure-temperature (P-T) profile coupled with line-by-line
radiative transfer, hydrostatic equilibrium, and energy balance, along with
prescriptions for non-equilibrium molecular composition and energy
redistribution. We apply our temperature and abundance retrieval method to the
atmospheres of two transiting exoplanets, HD 189733b and HD 209458b, which have
the best available Spitzer and HST observations. For HD 189733b, we find
efficient day-night redistribution of energy in the atmosphere, and molecular
abundance constraints confirming the presence of H2O, CO, CH4, and CO2. For HD
209458b, we confirm and constrain the day-side thermal inversion in an average
1D temperature profile. We also report independent detections of HO, CO,
CH and CO on the dayside of HD 209458b, based on six-channel Spitzer
photometry. We report constraints for HD 189733b due to individual data sets
separately; a few key observations are variable in different data sets at
similar wavelengths. Moreover, a noticeably strong carbon dioxide absorption in
one data set is significantly weaker in another. We must, therefore,
acknowledge the strong possibility that the atmosphere is variable, both in its
energy redistribution state and in the chemical abundances.Comment: 20 pages in emulateapj format, 11 figures. Final version, after proof
correction
Trends in aerosol abundances and distributions
The properties of aerosols that reside in the upper atmosphere are described. Special emphasis is given to the influence these aerosols have on ozone observation systems, mainly through radiative effects, and on ambient ozone concentrations, mainly through chemical effects. It has long been appreciated that stratospheric particles can interfere with the remote sensing of ozone distribution. The mechanism and magnitude of this interference are evaluated. Separate sections deal with the optical properties of upper atmospheric aerosols, long-term trends in stratospheric aerosols, perturbations of the stratospheric aerosol layer by volcanic eruptions, and estimates of the impacts that such particles have on remotely measured ozone concentrations. Another section is devoted to a discussion of the polar stratospheric clouds (PSC's). These unique clouds, recently discovered by satellite observation, are now thought to be intimately connected with the Antarctic ozone hole. Accordingly, interest in PSC's has grown considerably in recent years. This chapter describes what we know about the morphology, physical chemistry, and microphysics of PSC's
Recommender Systems
The ongoing rapid expansion of the Internet greatly increases the necessity
of effective recommender systems for filtering the abundant information.
Extensive research for recommender systems is conducted by a broad range of
communities including social and computer scientists, physicists, and
interdisciplinary researchers. Despite substantial theoretical and practical
achievements, unification and comparison of different approaches are lacking,
which impedes further advances. In this article, we review recent developments
in recommender systems and discuss the major challenges. We compare and
evaluate available algorithms and examine their roles in the future
developments. In addition to algorithms, physical aspects are described to
illustrate macroscopic behavior of recommender systems. Potential impacts and
future directions are discussed. We emphasize that recommendation has a great
scientific depth and combines diverse research fields which makes it of
interests for physicists as well as interdisciplinary researchers.Comment: 97 pages, 20 figures (To appear in Physics Reports
Privacy protection in location based services
This thesis takes a multidisciplinary approach to understanding the characteristics of Location Based Services (LBS) and the protection of location information in these transactions. This thesis reviews the state of the art and theoretical approaches in Regulations, Geographic Information Science, and Computer Science. Motivated by the importance of location privacy in the current age of mobile devices, this thesis argues that failure to ensure privacy protection under this context is a violation to human rights and poses a detriment to the freedom of users as individuals. Since location information has unique characteristics, existing methods for protecting other type of information are not suitable for geographical transactions. This thesis demonstrates methods that safeguard location information in location based services and that enable geospatial analysis. Through a taxonomy, the characteristics of LBS and privacy techniques are examined and contrasted. Moreover, mechanisms for privacy protection in LBS are presented and the resulting data is tested with different geospatial analysis tools to verify the possibility of conducting these analyses even with protected location information. By discussing the results and conclusions of these studies, this thesis provides an agenda for the understanding of obfuscated geospatial data usability and the feasibility to implement the proposed mechanisms in privacy concerning LBS, as well as for releasing crowdsourced geographic information to third-parties
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