Longitude : a privacy-preserving location sharing protocol for mobile applications

Location sharing services are becoming increasingly popular. Although many location sharing services allow users to set up privacy policies to control who can access their location, the use made by service providers remains a source of concern. Ideally, location sharing providers and middleware should not be able to access users’ location data without their consent. In this paper, we propose a new location sharing protocol called Longitude that eases privacy concerns by making it possible to share a user’s location data blindly and allowing the user to control who can access her location, when and to what degree of precision. The underlying cryptographic algorithms are designed for GPS-enabled mobile phones. We describe and evaluate our implementation for the Nexus One Android mobile phone

Land cover analysis in wildland-urban interfaces according to wildfire risk: a case study in the South of France

Each year, forest fires destroy about 500,000 ha of vegetation in Europe, predominantly in the Mediterranean region. Many large fires are linked to the land transformations that have taken place in the Mediterranean region in recent decades that have increased the risk of forest fires. On the one hand, agricultural fallows and orchards are slowly being colonized by vegetation, and on the other hand, the forest is not sufficiently used, both of which result in increased accumulation of fuel. In addition, urbanization combined with forest extension results in new spatial configurations called wildland-urban interfaces (WUI). WUI are commonly defined as areas where urban areas meet and interact with rural lands, wildland vegetation and forests. Spatial analyses were performed using a WUI typology based on two intertwined elements, the spatial organization of homes and the structure of fuel vegetation. The organisation of the land cover in terms of representativeness, complexity or road density was evaluated for each type of WUI. Results showed that there were significant differences between the types of WUI in the study area. Three indicators (i) fire ignition density, derived from the distribution of fire ignition points, (ii) wildfire density, derived from the distribution of wildfire area and (iii) burned area ratio, derived from the proportion of the burned area to the total study area were then compared with each type of WUI. Assuming that the three indicators correspond to important aspects of fire risk, we showed that, at least in the south of France, WUI are at high risk of wildfire, and that of the different types of wildland-urban interfaces, isolated and scattered WUI were the most at risk. Their main land cover characteristics, i.e. low housing and road densities but a high density of country roads, and the availability of burnable vegetation such as forested stands and shrubland (garrigue) explain the high fire risk. Improving our knowledge of relationships between WUI environments and fire risk should increase the efficiency of wildfire prevention: to this end, suitable prevention actions and communication campaigns targeting the types of WUI at the highest risk are recommended

Dzyaloshinskii-Moriya interaction in transport through single molecule transistors

The Dzyaloshinskii-Moriya interaction is shown to result in a canting of spins in a single molecule transistor. We predict non-linear transport signatures of this effect induced by spin-orbit coupling for the generic case of a molecular dimer. The conductance is calculated using a master equation and is found to exhibit a non-trivial dependence on the magnitude and direction of an external magnetic field. We show how three-terminal transport measurements allow for a determination of the coupling-vector characterizing the Dzyaloshinskii-Moriya interaction. In particular, we show how its orientation, defining the intramolecular spin chirality, can be probed with ferromagnetic electrodes

Manufacturing and Installation of the Compound Cryogenic Distribution Line for the Large Hadron Collider

The Large Hadron Collider (LHC) [1] currently under construction at CERN will make use of superconducting magnets operating in superfluid helium below 2 K. A compound cryogenic distribution line (QRL) will feed with helium at different temperatures and pressures the local elementary cooling loops in the cryomagnet strings. Low heat inleak to all temperature levels is essential for the overall LHC cryogenic performance. Following a competitive tendering, CERN adjudicated in 2001 the contract for the series line to Air Liquide (France). This paper recalls the main features of the technical specification and shows the project status. The basic choices and achievements for the industrialization phase of the series production are also presented, as well as the installation issues and status

On the nature of tunable hole g-factors in quantum dots

Electrically tunable g-factors in quantum dots are highly desirable for applications in quantum computing and spintronics. We report giant modulation of the hole g-factor in a SiGe nanocrystal when an electric field is applied to the nanocrystal along its growth direction. We derive a contribution to the g-factor that stems from an orbital effect of the magnetic field, which lifts the Kramers degeneracy in the nanocrystal by altering the mixing between the heavy and the light holes. We show that the relative displacement between the heavy- and light-hole wave functions, occurring upon application of the electric field, has an effect on the mixing strength and leads to a strong non-monotonic modulation of the g-factor. Despite intensive studies of the g-factor since the late 50's, this mechanism of g-factor control has been largely overlooked in the literature.Comment: 9 pages, 6 figure

On the origin of the A1g_{1g} and B1g_{1g} electronic Raman scattering peaks in the superconducting state of YBa2_{2}Cu3_{3}O7−δ_{7-\delta}

The electronic Raman scattering has been investigated in optimally oxygen doped YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ single crystals as well as in crystals with non-magnetic, Zn, and magnetic, Ni, impurities. We found that the intensity of the A$_{1g}$ peak is impurity independent and their energy to $T_{c}$ ratio is almost constant ($2\Delta/k_{B}T_{c}\sim5$). Moreover, the signal at the B$_{1g}$ channel is completely smeared out when non-magnetic Zn impurities are present. These results are qualitatively interpreted in terms of the Zeyher and Greco's theory that relates the electronic Raman scattering in the A$_{1g}$ and B$_{1g}$ channels to \textit{d}-CDW and superconducting order parameters fluctuations, respectively.Comment: Submited to Phys. Rev. Let

Temporally ordered collective creep and dynamic transition in the charge-density-wave conductor NbSe3

We have observed an unusual form of creep at low temperatures in the charge-density-wave (CDW) conductor NbSe$_3$. This creep develops when CDW motion becomes limited by thermally-activated phase advance past individual impurities, demonstrating the importance of local pinning and related short-length-scale dynamics. Unlike in vortex lattices, elastic collective dynamics on longer length scales results in temporally ordered motion and a finite threshold field. A first-order dynamic phase transition from creep to high-velocity sliding produces "switching" in the velocity-field characteristic.Comment: 4 pages, 4 eps figures; minor clarifications To be published in Phys. Rev. Let

Observation of spin-selective tunneling in SiGe nanocrystals

Spin-selective tunneling of holes in SiGe nanocrystals contacted by normal-metal leads is reported. The spin selectivity arises from an interplay of the orbital effect of the magnetic field with the strong spin-orbit interaction present in the valence band of the semiconductor. We demonstrate both experimentally and theoretically that spin-selective tunneling in semiconductor nanostructures can be achieved without the use of ferromagnetic contacts. The reported effect, which relies on mixing the light and heavy holes, should be observable in a broad class of quantum-dot systems formed in semiconductors with a degenerate valence band.Comment: 8 pages, 5 figure