11,044 research outputs found
"If You Can't Beat them, Join them": A Usability Approach to Interdependent Privacy in Cloud Apps
Cloud storage services, like Dropbox and Google Drive, have growing
ecosystems of 3rd party apps that are designed to work with users' cloud files.
Such apps often request full access to users' files, including files shared
with collaborators. Hence, whenever a user grants access to a new vendor, she
is inflicting a privacy loss on herself and on her collaborators too. Based on
analyzing a real dataset of 183 Google Drive users and 131 third party apps, we
discover that collaborators inflict a privacy loss which is at least 39% higher
than what users themselves cause. We take a step toward minimizing this loss by
introducing the concept of History-based decisions. Simply put, users are
informed at decision time about the vendors which have been previously granted
access to their data. Thus, they can reduce their privacy loss by not
installing apps from new vendors whenever possible. Next, we realize this
concept by introducing a new privacy indicator, which can be integrated within
the cloud apps' authorization interface. Via a web experiment with 141
participants recruited from CrowdFlower, we show that our privacy indicator can
significantly increase the user's likelihood of choosing the app that minimizes
her privacy loss. Finally, we explore the network effect of History-based
decisions via a simulation on top of large collaboration networks. We
demonstrate that adopting such a decision-making process is capable of reducing
the growth of users' privacy loss by 70% in a Google Drive-based network and by
40% in an author collaboration network. This is despite the fact that we
neither assume that users cooperate nor that they exhibit altruistic behavior.
To our knowledge, our work is the first to provide quantifiable evidence of the
privacy risk that collaborators pose in cloud apps. We are also the first to
mitigate this problem via a usable privacy approach.Comment: Authors' extended version of the paper published at CODASPY 201
Phase Separation in Bose-Fermi-Fermi Mixtures as a Probe of Fermi Superfluidity
We study the phase diagram of a mixture of Bose-Einstein condensate and a
two-component Fermi gas. In particular, we identify the regime where the
homogeneous system becomes unstable against phase separation. We show that,
under proper conditions, the phase separation phenomenon can be exploited as a
robust probe of Fermi superfluid
Spontaneous spin textures in dipolar spinor condensates
We have mapped out a detailed phase diagram that shows the ground state
structure of a spin-1 condensate with magnetic dipole-dipole interactions. We
show that the interplay between the dipolar and the spin-exchange interactions
induces a rich variety of quantum phases that exhibit spontaneous magnetic
ordering in the form of intricate spin textures.Comment: 4.1 pages, 4 figure
Abnormal enhancement of electric field inside a thin permittivity-near-zero object in free space
It is found that the electric field can be enhanced strongly inside a
permittivity-near-zero object in free space, when the transverse cross section
of the object is small and the length along the propagation direction of the
incident wave is large enough as compared with the wavelength. The physical
mechanism is explained in details. The incident electromagnetic energy can only
flow almost normally through the outer surface into or out of the
permittivity-near-zero object, which leads to large energy stream density and
then strong electric field inside the object. Meanwhile, the magnetic field
inside the permittivity-near-zero object may be smaller than that of the
incident wave, which is also helpful for enhancing the electric field. Two
permittivity-near-zero objects of simple shapes, namely, a thin cylindrical
shell and a long thin rectangular bar, are chosen for numerical illustration.
The enhancement of the electric field becomes stronger when the
permittivity-near-zero object becomes thinner. The physical mechanism of the
field enhancement is completely different from the plasmonic resonance
enhancement at a metal surface
Squeezing electromagnetic energy with a dielectric split ring inside a permeability-near-zero metamaterial
A novel electromagnetic energy squeezing mechanism is proposed based on the
special properties of permeability-near-zero metamaterials. Nearly no energy
stream can enter a conventional dielectric region positioned inside a
permeability-near-zero material. When a source is surrounded by a dielectric
split ring (encloser with a gap opened), the electromagnetic energy generated
by the source is forced to propagate through the gap. When the gap is narrow,
the energy stream density becomes very large and makes the magnetic field
enhanced drastically in the gap. The narrow gap can be long and bended. This
provides us a method to obtain strong magnetic field without using resonance
enhancement.Comment: 17pages, 4 figure
Number-conserving interacting fermion models with exact topological superconducting ground states
We present a method to construct number-conserving Hamiltonians whose ground
states exactly reproduce an arbitrarily chosen BCS-type mean-field state. Such
parent Hamiltonians can be constructed not only for the usual -wave BCS
state, but also for more exotic states of this form, including the ground
states of Kitaev wires and 2D topological superconductors. This method leads to
infinite families of locally-interacting fermion models with exact topological
superconducting ground states. After explaining the general technique, we apply
this method to construct two specific classes of models. The first one is a
one-dimensional double wire lattice model with Majorana-like degenerate ground
states. The second one is a two-dimensional superconducting model,
where we also obtain analytic expressions for topologically degenerate ground
states in the presence of vortices. Our models may provide a deeper conceptual
understanding of how Majorana zero modes could emerge in condensed matter
systems, as well as inspire novel routes to realize them in experiment.Comment: 5 pages, 2 figures; supplement: 4 pages, 1 figur
Finite-Temperature Study of Bose-Fermi Superfluid Mixtures
Ultra-cold atom experiments offer the unique opportunity to study mixing of
different types of superfluid states. Our interest is in superfluid mixtures
comprising particles with different statistics- Bose and Fermi. Such scenarios
occur naturally, for example, in dense QCD matter. Interestingly, cold atomic
experiments are performed in traps with finite spatial extent, thus critically
destabilizing the occurrence of various homogeneous phases. Critical to this
analysis is the understanding that the trapped system can undergo phase
separation, resulting in a unique situation where phase transition in either
species (bosons or fermions) can overlap with the phase separation between
possible phases. In the present work, we illustrate how this intriguing
interplay manifests in an interacting 2-species atomic mixture - one bosonic
and another fermionic with two spin components - within a realistic trap
configuration. We further show that such interplay of transitions can render
the nature of the ground state to be highly sensitive to the experimental
parameters and the dimensionality of the system.Comment: 9 pages, 7 figures; Accepted for publication in Phys. Rev.
Magnetic field configuration and field-aligned acceleration of energetic ions during substorm onsets
International audienceIn this paper, we present an interpretation of the observed field-aligned acceleration events measured by GEOS-2 near the night-side synchronous orbit at substorm onsets (Chen et al., 2000). We show that field-aligned acceleration of ions (with pitch angle asymmetry) is closely related to strong short-lived electric fields in the Ey direction. The acceleration is associated with either rapid dipolarization or further stretching of local magnetic field lines. Theoretical analysis suggests that a centrifugal mechanism is a likely candidate for the parallel energization. Equatorward or anti-equatorward energization occurs when the tail current sheet is thinner tailward or earthward of the spacecraft, respectively. The magnetic field topology leading to anti-equatorward energization corresponds to a situation where the near-Earth tail undergoes further compression and the inner edge of the plasma sheet extends inwards as close as the night-side geosynchronous altitudes
Modulational instability in a layered Kerr medium: Theory and Experiment
We present the first experimental investigation of modulational instability
in a layered Kerr medium. The particularly interesting and appealing feature of
our configuration, consisting of alternating glass-air layers, is the
piecewise-constant nature of the material properties, which allows a
theoretical linear stability analysis leading to a Kronig-Penney equation whose
forbidden bands correspond to the modulationally unstable regimes. We find very
good {\it quantitative} agreement between theoretical, numerical, and
experimental diagnostics of the modulational instability. Because of the
periodicity in the evolution variable arising from the layered medium, there
are multiple instability regions rather than just one as in the uniform medium.Comment: 4 pages, 4 figures, contains experimental + computational +
theoretical results, to appear in Physical Review Letter
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