Detecting Adversarial Examples through Nonlinear Dimensionality Reduction

Deep neural networks are vulnerable to adversarial examples, i.e., carefully-perturbed inputs aimed to mislead classification. This work proposes a detection method based on combining non-linear dimensionality reduction and density estimation techniques. Our empirical findings show that the proposed approach is able to effectively detect adversarial examples crafted by non-adaptive attackers, i.e., not specifically tuned to bypass the detection method. Given our promising results, we plan to extend our analysis to adaptive attackers in future work.Comment: European Symposium on Artificial Neural Networks, Computational Intelligence and Machine Learning (ESANN) 201

Direct torque control for dual three-phase induction motor drives

A direct torque control (DTC) strategy for dual three-phase induction motor drives is discussed in this paper. The induction machine has two sets of stator three-phase windings spatially shifted by 30 electrical degrees. The DTC strategy is based on a predictive algorithm and is implemented in a synchronous reference frame aligned with the machine stator flux vector. The advantages of the discussed control strategy are constant inverter switching frequency, good transient and steady-state performance, and low distortion of machine currents with respect to direct self-control (DSC) and other DTC schemes with variable switching frequency. Experimental results are presented for a 10-kW DTC dual three-phase induction motor drive prototype

Transport in complex flows: reactive, multiphase and supercritical jets

The present work deals with the dynamics of turbulent jet in different configurations and geometries. In particular two aspect, important both in the engineering applications and in the scientific research, are stressed. The first one deals with the mixing in the turbulent jets at near-critical thermodynamic conditions. The second addresses the dynamics of inertial particle in turbulent premixed Bunsen flames. In order to perform a Direct Numerical Simulation (DNS) of a turbulent jet at supercritical conditions a suitable method was developed to mimic the gas thermodynamic behavior. The Van der Waals equation of state has been chosen and an Low Mach number expansion of Navier Stokes equations has been performed. This approach is completely original in the context of real gas equation, and it is considered as useful as the whole Navier Stokes system in the fully compressible formulation especially at very Low Mach number. The new equations are implemented in a numerical code in order to perform the first, in our knowledge, DNS of a fully turbulent coaxial jet in supercritical thermodynamic conditions. The configuration adopted is similar to the coaxial injectors of the liquid rocket engines and consists in an inner jet with liquid-like density and low velocity and in an outer jet characterized by a gas-like density and high velocity. Aim of the simulation is to observe high-density finger-like structures observed in previous experimental visualizations, the so-called “ligaments”, and to understand the mechanism of their formation. In particular these finger-like structure formation is ascribed to the joint effects of the jet dynamics and the thermodynamics condition. In fact the Kelvin-Helmholtz structures, which generates by the peculiar jet configuration, contributes to the “ligaments” formation while the thermodynamic conditions allow these high-density structures to persist in low-density field. In the real gas jet the interface between the high and low density fluid is observed to be thinner than the perfect gas jet, hence the diffusion occurs at smaller and smaller scales. The obtained data are considered useful for the study of the mixing and combustion processes in the near critical conditions. In the LES/RANS context, in addition, DNS data are necessary for the evaluation of sub-grid terms and for development of new models. The dynamics of the inertial particles in turbulent premixed flame is addressed with the same code. The DNS of a reactive Bunsen jet laden with inertial particle is performed. The simulation reproduces a lean Methane/Air premixed flame in the ”flamelet“ regime. The flow is seeded with four particle population of different inertia with the mass density much larger than the fluid one and diameter much smaller than the Kolmogorov length scale. In these conditions, the particle dynamic equation is forced by only the Stokes drag and the one-way coupling regime can be assumed (no fluid-particle or particle-particle interaction occur). A suitable Stokes number is defined as a function of the particle features and of the laminar flame speed and thickness and burned/unburned gas temperature ratio. It is shown that the so-defined “flamelet” Stokes number is the suitable to describe the particle dynamics in the premixed flames. The DNS data are analyzed to address the effects of particle inertia on Particle Image Velocimetry measurements, in particular is observed that the particle inertia induces a time lag in particle to follow the v fluid acceleration across the flame front. This time lag generate a mismatch in the prediction of fluid velocity through the particle velocity. It is shown that the evaluation of high order velocity statistics needs particle with smaller and smaller flamelet Stokes number. The data are analyzed also to address the effects of the interaction between particle inertia and fluctuating flame front on the particle spatial distribution. Two statistical tools are used to this purpose, the Clustering Index, K, and the radial distribution function, g(r). K measures the departure of the actual distribution from the Poissonian distribution, g(r) is the probability to find a couple of particle at a certain distance r. An important outline consists in the presence of particle clusters in the flame brush. In particular also quasi-Lagrangian particles are characterized by not Poissonian spatial distribution as a consequence of the intermittent fluctuation of the instantaneous thin flame front separating two regions with different particle concentration. With the increasing of the Stokes number the cluster intensity increases experiencing a maximum value for order one flamelet Stokes number. All results concerning the particle dynamics are confirmed by experimental measurement on a Bunsen Methane-Air turbulent reacting jet. The obtained results are considered important both for experimental measurements and for soot dynamics and growth strongly influenced by the interaction of particle with the flame front and by their collision

Riemann curvature of a boosted spacetime geometry

The ultrarelativistic boosting procedure had been applied in the literature to map the metric of Schwarzschild-de Sitter spacetime into a metric describing de Sitter spacetime plus a shock-wave singularity located on a null hypersurface. This paper evaluates the Riemann curvature tensor of the boosted Schwarzschild-de Sitter metric by means of numerical calculations, which make it possible to reach the ultrarelativistic regime gradually by letting the boost velocity approach the speed of light. Thus, for the first time in the literature, the singular limit of curvature through Dirac's delta distribution and its derivatives is numerically evaluated for this class of spacetimes. Eventually, the analysis of the Kretschmann invariant and the geodesic equation show that the spacetime possesses a scalar curvature singularity within a 3-sphere and it is possible to define what we here call boosted horizon, a sort of elastic wall where all particles are surprisingly pushed away, as numerical analysis demonstrates. This seems to suggest that boosted geometries are ruled by a sort of antigravity effect since all geodesics seem to refuse to enter the boosted horizon, even though their initial conditions are aimed at driving the particles towards the boosted horizon.Comment: 33 pages, 8 figures. In the new version, a section and new references have been added, and the presentation has been amended and improve

Energy fluxes in turbulent separated flows

Turbulent separation in channel flow containing a curved wall is studied using a generalised form of Kolmogorov equation. The equation successfully accounts for inhomogeneous effects in both the physical and separation spaces. We investigate the scale-by-scale energy dynamics in turbulent separated flow induced by a curved wall. The scale and spatial fluxes are highly dependent on the shear layer dynamics and the recirculation bubble forming behind the lower curved wall. The intense energy produced in the shear layer is transferred to the recirculation region, sustaining the turbulent velocity fluctuations. The energy dynamics radically changes depending on the physical position inside the domain, resembling planar turbulent channel dynamics downstream

Probabilistic inversion: a preliminary discussion

We continue the discussion on the possibility of interpreting probability as a logic, that we have started in the previous IMEKO TC1-TC7-TC13 Symposium. We show here how a probabilistic logic can be extended up to including direct and inverse functions. We also discuss the relationship between this framework and the Bayes-Laplace rule, showing how the latter can be formally interpreted as a probabilistic inversion device. We suggest that these findings open a new perspective in the evaluation of measurement uncertainty

Design of the radiation shielding for a microsatellite

This paper aims to provide a detailed description of the problems concerning the radiation environment faced while designing a microsatellite at the University of Rome. Although main features of the microsatellite, as well as the environment characteristics expected in candidate orbits are detailed, emphasis is given to expose a generally appropriate procedure for this class of spacecraft. The sector analysis is carried on. and a simple qualitative way to point out critical areas of shielding is shown. The risk concerning the specific devices is assessed, both for total ionization dose and single event upset. The effect of the spot shielding on the most sensitive devices is considered, in order to mitigate SEE occurrence. (C) 2002 International Astronautical Federation. Published by Elsevier Science Ltd. All rights reserved

Toward a formal theory of the measuring system

Measurement aims at obtaining a numerical description of objects/events/persons in real world by means of a measuring system. Measurement is widely used as a key way for obtaining high quality information from the real world. across disciplines. In the present day. there is growing consensus in holding that measurement is characterized by the use of something that qualifies as a "measuring system". Therefore. we discuss sufficient conditions for an empirical system to qualify as a measuring system