1,290 research outputs found
Structure of the Wake of a Magnetic Obstacle
We use a combination of numerical simulations and experiments to elucidate
the structure of the flow of an electrically conducting fluid past a localized
magnetic field, called magnetic obstacle. We demonstrate that the stationary
flow pattern is considerably more complex than in the wake behind an ordinary
body. The steady flow is shown to undergo two bifurcations (rather than one)
and to involve up to six (rather than just two) vortices. We find that the
first bifurcation leads to the formation of a pair of vortices within the
region of magnetic field that we call inner magnetic vortices, whereas a second
bifurcation gives rise to a pair of attached vortices that are linked to the
inner vortices by connecting vortices.Comment: 4 pages, 5 figures, corrected two typos, accepted for PR
The use of plasma-based deposition with ion implantation technology to produce superhard molybdenum-based coatings in a mixed (C₂H₂+N₂) atmosphere
The influence of the pressure of a mixed gaseous atmosphere (80%C₂H₂+20%N₂) and the supply of a high-voltage negative potential in a pulsed form on the elemental and phase composition, structure and physico-mechanical characteristics of the vacuum-arc molybdenum-based coating
Confidential Boosting with Random Linear Classifiers for Outsourced User-generated Data
User-generated data is crucial to predictive modeling in many applications.
With a web/mobile/wearable interface, a data owner can continuously record data
generated by distributed users and build various predictive models from the
data to improve their operations, services, and revenue. Due to the large size
and evolving nature of users data, data owners may rely on public cloud service
providers (Cloud) for storage and computation scalability. Exposing sensitive
user-generated data and advanced analytic models to Cloud raises privacy
concerns. We present a confidential learning framework, SecureBoost, for data
owners that want to learn predictive models from aggregated user-generated data
but offload the storage and computational burden to Cloud without having to
worry about protecting the sensitive data. SecureBoost allows users to submit
encrypted or randomly masked data to designated Cloud directly. Our framework
utilizes random linear classifiers (RLCs) as the base classifiers in the
boosting framework to dramatically simplify the design of the proposed
confidential boosting protocols, yet still preserve the model quality. A
Cryptographic Service Provider (CSP) is used to assist the Cloud's processing,
reducing the complexity of the protocol constructions. We present two
constructions of SecureBoost: HE+GC and SecSh+GC, using combinations of
homomorphic encryption, garbled circuits, and random masking to achieve both
security and efficiency. For a boosted model, Cloud learns only the RLCs and
the CSP learns only the weights of the RLCs. Finally, the data owner collects
the two parts to get the complete model. We conduct extensive experiments to
understand the quality of the RLC-based boosting and the cost distribution of
the constructions. Our results show that SecureBoost can efficiently learn
high-quality boosting models from protected user-generated data
N/V-limit for Langevin dynamics in continuum
We construct an infinite particle/infinite volume Langevin dynamics on the
space of configurations in having velocities as marks. The construction
is done via a limiting procedure using -particle dynamics in cubes
with periodic boundary conditions. A main step to this
result is to derive an (improved) Ruelle bound for the canonical correlation
functions of -particle systems in with periodic
boundary conditions. After proving tightness of the laws of finite particle
dynamics, the identification of accumulation points as martingale solutions of
the Langevin equation is based on a general study of properties of measures on
configuration space (and their weak limit) fulfilling a uniform Ruelle bound.
Additionally, we prove that the initial/invariant distribution of the
constructed dynamics is a tempered grand canonical Gibbs measure. All proofs
work for general repulsive interaction potentials of Ruelle type (e.g.
the Lennard-Jones potential) and all temperatures, densities and dimensions
Security and Efficiency Analysis of the Hamming Distance Computation Protocol Based on Oblivious Transfer
open access articleBringer et al. proposed two cryptographic protocols for the computation of Hamming distance. Their first scheme uses Oblivious Transfer and provides security in the semi-honest model. The other scheme uses Committed Oblivious Transfer and is claimed to provide full security in the malicious case. The proposed protocols have direct implications to biometric authentication schemes between a prover and a verifier where the verifier has biometric data of the users in plain form.
In this paper, we show that their protocol is not actually fully secure against malicious adversaries. More precisely, our attack breaks the soundness property of their protocol where a malicious user can compute a Hamming distance which is different from the actual value. For biometric authentication systems, this attack allows a malicious adversary to pass the authentication without knowledge of the honest user's input with at most complexity instead of , where is the input length. We propose an enhanced version of their protocol where this attack is eliminated. The security of our modified protocol is proven using the simulation-based paradigm. Furthermore, as for efficiency concerns, the modified protocol utilizes Verifiable Oblivious Transfer which does not require the commitments to outputs which improves its efficiency significantly
Two-scale localization in disordered wires in a magnetic field
Calculating the density-density correlation function for disordered wires, we
study localization properties of wave functions in a magnetic field. The
supersymmetry technique combined with the transfer matrix method is used. It is
demonstrated that at arbitrarily weak magnetic field the far tail of the wave
functions decays with the length , where and are the localization lengths in the absence of a
magnetic field and in a strong magnetic field, respectively. At shorter
distances, the decay of the wave functions is characterized by the length
. Increasing the magnetic field broadens the region of the decay
with the length , leading finally to the decay with at all distances. In other words, the crossover between the orthogonal
and unitary ensembles in disordered wires is characterized by two localization
lengths. This peculiar behavior must result in two different temperature
regimes in the hopping conductivity with the boundary between them depending on
the magnetic field.Comment: 4 page
Measurement of the Cross Section Asymmetry of the Reaction gp-->pi0p in the Resonance Energy Region Eg = 0.5 - 1.1 GeV
The cross section asymmetry Sigma has been measured for the photoproduction
of pi0-mesons off protons, using polarized photons in the energy range Eg = 0.5
- 1.1 GeV. The CM angular coverage is Theta = 85 - 125 deg with energy and
angle steps of 25 MeV and 5 deg, respectively. The obtained Sigma data, which
cover the second and third resonance regions, are compared with existing
experimental data and recent phenomenological analyses. The influence of these
measurements on such analyses is also considered
Phase-space dependence of particle-ratio fluctuations in Pb+Pb collisions from 20A to 158A GeV beam energy
A novel approach, the identity method, was used for particle identification
and the study of fluctuations of particle yield ratios in Pb+Pb collisions at
the CERN Super Proton Synchrotron (SPS). This procedure allows to unfold the
moments of the unknown multiplicity distributions of protons (p), kaons (K),
pions () and electrons (e). Using these moments the excitation function of
the fluctuation measure [A,B] was measured, with A and
B denoting different particle types. The obtained energy dependence of
agrees with previously published NA49 results on the related
measure . Moreover, was found to depend
on the phase space coverage for [K,p] and [K,] pairs. This feature most
likely explains the reported differences between measurements of NA49 and those
of STAR in central Au+Au collisions
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